OA19330A - Configurable Codebook For Advanced CSI Feedback Overhead Reduction - Google Patents

Abstract

Network nodes, wireless devices and methods of reducing signaling overhead are provided. In one embodiment, a method includes transmitting to the wireless device at least one power threshold parameter to be used by the wireless device to determine a number of beams to be included in a multi-beam precoder codebook and transmitting to the wireless device a signal to interference plus noise ratio (SINR) to be used by the wireless device to determine to use one of a single beam precoder and a multiple beam precoder.

Description

Note that although terminology from the third génération partnership project, (3GPP) long term évolution (LTE) has been used in this disclosure to exemplify embodiments of the disclosure, this should not be seen as limiting the scope of the disclosure to only the aforementioned system. Other wireless Systems, including NR (i.e., 5G), wideband code division multiple access (WCDMA), WiMax, ultra mobile broadband (UMB) and global system for mobile communications (GSM), may also benefit from exploiting the ideas covered within this disclosure.

Also note that terminology such as eNodeB (base station) and wireless device should be considered non-limiting and does in particular not imply a certain hierarchical relation between the two; in general “eNodeB” could be considered as device 1 and “wireless device” device 2, and these two devices communicate with each other over some radio channel. Herein, we also focus on wireless transmissions in the downlink, but principles disclosed herein the may be equally applicable in the uplink.

The term wireless device used herein may refer to any type of wireless device communicating with a network node and/or with another wireless device in a cellular or mobile communication system. Examples of a wireless device are user device (UE), target device, device to device (D2D) wireless device, machine type wireless device or wireless device capable of machine to machine (M2M) communication, PDA, iPAD, Tablet, mobile terminais, smart phone, laptop embedded equipped (LEE), laptop mounted equipment (LME), USB dongles etc.

The term “network node” used herein may refer to a radio network node or another network node, e.g., a core network node, MSC, MME, O&M, OSS, SON, positioning node (e.g. E-SMLC), MDT node, etc.

The term “radio network node” used herein can be any kind of network node comprised in a radio network which may further comprise any of base station (BS), radio base station, base transceiver station (BTS), base station controller (BSC), radio network controller (RNC), evolved Node B (eNB or eNodeB), Node B, multi-standard radio (MSR) radio node such as MSR BS, relay node, donor node controlling relay, radio access point (AP), transmission points, transmission nodes, Remote Radio Unit (RRU) Remote Radio Head (RRH), nodes in distributed antenna System (DAS), etc.

Note further that functions described herein as being performed by a wireless device or a network node may be distributed over a plurality of wireless devices and/or network nodes.

Before describing in detail exemplary embodiments, it is noted that the embodiments résidé primarily in combinations of apparatus components and processing steps related to configurable codebooks for advanced channel state information (CSI) feedback overhead réduction. Accordingly, components hâve been represented where appropriate by conventional symbols in the drawings, showing only those spécifie details that are pertinent to understanding the embodiments so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

As used herein, relational tenus, such as “first” and “second,” “top” and “bottom,” and the like, may be used solely to distinguish one entity or element from another entity or element without necessarily requiring or implying any physical or logical relationship or order between such entities or éléments.

The concepts presented in this disclosure may be used with two dimensional antenna arrays and some of the presented embodiments use such antennas. Such antenna arrays may be (partly) described by the number of antenna columns corresponding to the horizontal dimension N_h, the number of antenna rows corresponding to the vertical dimension N_v and the number of dimensions corresponding to different polarizations N_p. The total number of antennas is thus N = N_hN_vN_p. It should be pointed out that the concept of an antenna is non-limiting in the sense that it can refer to any virtualization (e.g., linear mapping) of the physical antenna éléments. For example, pairs of physical sub-elements could be fed the same signal, and hence share the same virtualized antenna port. An example of a 4x4 array with cross-polarized antenna éléments is shown in FIG.8, which illustrâtes a two-dimensional antenna array of cross-polarized antenna éléments (N_P = 2), with N_h = 4 horizontal antenna éléments, and N_v = 4 vertical antenna éléments.

Precoding may be interpreted as multiplying the signal with different beamforming weights for each antenna prior to transmission. A typical approach is to tailor the precoder to the antenna form factor, i.e. taking into account N_h, N_v and N_p when designing the precoder codebook.

In closed loop ΜΙΜΟ transmission schemes such as TM9 and TM10, a wireless device estimâtes and feeds back the downlink CSI to the base station. The base station uses the feedback CSI to transmit downlink data to the wireless device. The CSI consists of a transmission rank indicator (RI), a precoding matrix indicator (PMI) and a channel quality indicator(s) (CQI). A codebook of precoding matrices is used by the wireless device to find out the best match between the estimated downlink channel H_n and a precoding matrix in the codebook based on certain criteria, for example, the wireless device throughput. The channel H_n is estimated based on a Non-Zero Power CSI reference signal (NZP CSI-RS) transmitted in the downlink for TM9 and TM 10.

The CQI/RI/PMI together provide the downlink channel State to the wireless device. This is also referred to as implicit CSI feedback since the estimation of H_n is not fed back directly. The CQI/RI/PMI can be wideband or subband depending on which reporting mode is configured.

The RI corresponds to a recommended number of streams that are to be spatially multiplexed and thus transmitted in parallel over the downlink channel. The PMI identifies a recommended precoding matrix codeword (in a codebook which contains precoders with the same number of rows as the number of CSI-RS ports) for the transmission, which relates to the spatial characteristics of the channel. The CQI represents a recommended transport block size (i.e., code rate) and LTE supports transmission of one or two simultaneous (on different layers) transmissions of transport blocks (i.e. separately encoded blocks of information) to a wireless device in a subframe. There is thus a relation between a CQI and an SINR of the spatial stream(s) over which the transport block or blocks are transmitted.

Codebooks of up to 16 antenna ports hâve been defined in LTE Up to Release 13. Both one dimension (ID) and two-dimension (2D) antenna array are supported. For LTE Release 12 wireless device and earlier, only a codebook feedback for a ID port layout is supported, with 2, 4 or 8 antenna ports. Hence, the codebook is designed assuming these ports are arranged on a straight line in one dimension. In LTE Rel-13, codebooks for 2D port layouts were specified for the case of 8, 12, or 16 antenna ports. In addition, a codebook for ID port layout for the case of 16 antenna ports was also specified in LTE Rel13.

In LTE Rel-13, two types of CSI reporting were introduced, i.e. Class A and Class B. In Class A CSI reporting, a wireless device measures and reports CSI based on a new codebook for the configured 2D antenna array with 8, 12 or 16 antenna ports. The Class A codebook is defined by five parameters, i.e. (N₁,N₂,0₁,0₂,codebookConfîg), where (N1,N2) are the number of antenna ports in a first and a second dimension, respectively. 0₂), also referred to as Q_i and Q₂ herein, are the DFT oversampling factor for the first and the second dimension, respectively. codebookConfig ranges from 1 to 4 and defines four different ways the codebook is formed. For codebookConfig=\, a PMI corresponding to a single 2D beam is fed back for the whole system bandwidth while for codebookConfig={2,3,4}, PMIs corresponding to four 2D beams are fed back and each subband may be associated with a different 2D beam. The CSI consists of a RI, a PMI and a CQI or CQIs, similar to the CSI reporting in pre Rel-13.

In Class B CSI reporting, in one scénario (also refers to as “Kcsi-rs > 1”)> the eNB may pre-form multiple beams in one antenna dimension. There can be multiple ports (1, 2, 4, or 8 ports) within each beam on the other antenna dimension, “beamformed” CSI-RS are transmitted along each beam. A wireless device first selects the best beam from a group of beams configured and then measures CSI within the selected beam based on the legacy codebook for 2, 4, or 8 ports. The wireless device then reports back the selected beam index and the CSI corresponding to the selected beam. In another scénario (also refers to as “Kcsi-rs ⁼ 1”), the eNB may form up to 4 (2D) beams on each polarization and “beamformed” CSI-RS is transmitted along each beam. A wireless device measures CSI on the “beamformed” CSI-RS and feedback CSI based on a new Class B codebook for 2, 4, or 8 ports.

A common type of precoding is to use a DFT-precoder, where the precoder vector used to precode a single-layer transmission using a single-polarized uniform linear array (ULA) with N_r antennas is defined as _ε ^ί2π'^οοΓΐρ /2711^ Equation jNi : 4 where l = 0,1,... — 1 is the precoder index and is an integer oversampling factor. A precoder for a dual-polarized uniform linear array (ULA) with antennas for each polarization (and so 2Ah antennas in total) can be similarly defined as ^W1D,DpÇ_I> ^1,Ql) ^— w_1D(0 _ rw_1D(0 .e^w_1D(0\ 0 ⁰ 1Γ¹1

W_1D(0JM

Equation where e⁷^ is a cophasing factor between the two polarizations that may for instance be selected from a QPSK alphabet φ G {0, p tt,

A corresponding precoder vector for a two-dimensional uniform planar arrays (UPA) with N_± x N₂ antennas can be created by taking the Kronecker product of two precoder vectors as w_2D (1, m) = w_1D (l, N^, Qf)®w_w (m, N₂, Q₂), where Q₂ is an integer oversampling factor in the N₂ dimension. Each precoder iv_2D (l, m) forms a DFT beam or a signal radiation pattern having its maximum power gain at a certain direction. Ail the precoders {w_2D(l,m),l = 0, ...,N₁Q₁ -l;m = 0,...,N₂Q₂ - 1} form a grid of DFT beams. An example is shown in FIG. 9, where (N_ltN₂) = (4,2) and (Qi, Q₂) = (4,4). Throughout the following sections, the tenns ‘DFT beams’ and ‘DFT precoders’ are used interchangeably.

More generally, a beam with an index pair (l, m) can be identified by the direction in which the greatest energy is transmitted when precoding weights w_2D(l, m) are used in the transmission. Also, a magnitude taper can be used with DFT beams to lower the beam’s sidelobes. A ID DFT precoder along N_± and N₂ dimensions with magnitude tapering can be expressed as w_îd(1,N₁,Q₁^)=^ β₀β^]2π'°'^ 1 β^^ΟΡΕ and w_1D(m,N₂,0₂,y) =

-J 1^2 j2n-0· ^m _N y_oe ¢2 ⁿ2 y₁e^J Q₂n₂ j2n(N₂-ï)·™, \.Υν₂-16 ^QzN2.

Where 0 < βρ y_k < 1 (i = 0,1,..., — 1; k = 0,1,..., N₂ — 1) are amplitude sealing factors, βι = 1, y_k = 1 (i = 0,1, — 1; k = 0,1, ...,N₂ — 1) correspond to no tapering.

DFT beams (with or without a magnitude taper) hâve a linear phase shift between éléments along each of the two dimensions. Without loss of generality, it can be assumed that the éléments of w(l,m) are ordered according to w(l, m) = w_w (l, N_lt Q_lt β)®\/ν_ίΰ (m, N₂, Q₂, y) such that adjacent éléments correspond to adjacent antenna éléments along dimension N₂, and éléments of w(l, m) spaced N₂ apart correspond to adjacent antenna éléments along dimension If. Then the phase shift between two éléments (l, ni) and w_Sz (l, m) of w(l, ni) can be expressed as:

w_S2(fm) = w_S1(Z,m) (^) · \^as₁j where • Sj = fN₂ + i₂ and s₂ = fN₂ + k₂ (with 0 < î₂ < N₂, 0 < f < If, 0 < k₂ < N₂, and 0 < f < If) are integers identifying two entries of the beam w(l,m) so that (i_1; i₂) indicates to a first entry of beam w(l,m) that is mapped to a first antenna element (or port) and (k_lt k₂) indicates to a second entry of beam w(l, m) that is mapped to a second antenna element (or port).

• a_Si = βί_ίΥί₂ and ot_Sz = Pk₁Yk₂ are real numbers. a, φ 1 (i = Si,s₂) if magnitude tapering is used; otherwise a, = 1.

• Δγ = is a phase shift corresponding to a direction along an axis, e.g. the horizontal axis (‘azimuth’) TTt • Δ₂ =----is a phase shift corresponding to direction along an axis, e.g. the vertical Q2N2 axis (‘élévation’).

Therefore, a k^th beam d(k) formed with precoder w(lk,can also be referred to by the corresponding precoder w(lk, mk), i.e. d(k) = w(lk, mk). Thus a beam d(k) can be described as a set of complex numbers, each element of the set being characterized by at least one complex phase shift such that an element of the beam is related to any other element of the beam where dn (fc) = di(k)ai;ne-’^27r^^pA1-^k+qA2·¹^ = dj(Æ)ain(e^727rAlk)^P Çe^²^²·^ , where di(k) is the z^th element of a beam d(k), ain is a real number corresponding to the z^th and n éléments of the beam d(/c); p and q are integers; and Al k and Zl_{2 k} are real numbers corresponding to a beam with index pair (l_k, m_k) that détermine the complex phase shifts _ej^A_{lik anc}j _ej2nA_2k, respectively. Index pair ((_k,m_k) corresponds to a direction of arrivai or departure of a plane wave when beam d(k) is used for transmission or réception in a UPA or ULA. A beam d(k) can be identified with a single index k' where ' = l_k + 7ViÇim_k , i.e, along vertical or N₂ dimension first, or altematively k' = N₂Q₂l_k + m_k , i.e. along horizontal or If dimension first.

An example of precoder éléments of a beam w(l, m) to antenna ports mapping is shown in FIG. 10, where a single polarization 2D antenna with (/ν₁₅Ν₂ )=(4,2) is illustrated.

is applied on the transmit (Tx) signal to port i (i=el, e2,..., e8). There is a constant phase shift between any two precoder éléments associated with two adjacent antenna ports along each dimension. For example, with Δ₂ defined as above, the phase shift between w^km) and w₂(l,m) is e⁷²^², which is the same as the phase shift between w7(l,m) and w8(l,m). Similarly, with Ai defined as above, the phase shift between w2(l,m) and w4(l,m) is ε^72πΔ1, which is the same as the phase shift between vv5(/,m) and w₇(l, nï).

Extending the precoder for a dual-polarized ULA may then be done as w_2D._DP(l,m^) = [JJ = [^^y rw_2DG,m) 0 lr 1 Ί

L 0 iv_2D(Xm)J J

Equation

A precoder matrix Wzd.dp for multi-layer transmission may be created by appending columns of DFT precoder vectors as

W⁽ ₂%_Dp = [Μζο,ορί^ΜίΜ w_2DiDP(l_R,m_R,(l)_R)] where R is the number of transmission layers, i.e. the transmission rank. In a spécial case for a rank-2 DFT precoder, m-t = m₂ = m and l₄ = l₂ = l, one has:

^W2D,DP (1,™,Φι,Φ₂) = [™2Ο.Ορ(1,™,Φ1) W_2D.DpG,m,0₂)]

Equation ₌ Iw_2DG,m) 0 1Γ 1 1 1 γ

[ 0 w_2D(l, m)J te⁷^¹ e⁷$²J

For each rank, ail the precoder candidates form a ‘precoder codebook’ or a ‘codebook’. A wireless device can first détermine the rank of the estimated downlink wideband channel based CSI-RS. After the rank is identified, for each subband the wireless device then searches through ail the precoder candidates in a codebook for the determined rank to find the best precoder for the subband. For example, in case of rank =1, the wireless device would search through w_{2D DP}(k, l, φ) for ail the possible (k, l, φ) values. In case of (2Ί rank=2, the wireless device would search through _DP (k, l, φ^ φ₂) for ail the possible (k, l, φ_τ, φ₂) values.

With multi-user ΜΙΜΟ, two or more wireless devices in the same cell are coscheduled on the same time-frequency resource. That is, two or more independent data streams are transmitted to different wireless devices at the same time, and the spatial domain is used to separate the respective streams. By transmitting several streams simultaneously, the capacity of the system can be increased. This however, cornes at the cost of reducing the SINR per stream, as the power has to be shared between streams and the streams will cause interférence to each-other.

When increasing the antenna array size, the increased beamforming gain will lead to higher SINR, however, as the user throughput dépends only logarithmically on the SINR (for large SINRs), it is instead bénéficiai to trade the gains in SINR for a multiplexing gain, which increases linearly with the number of multiplexed users.

Accurate CSI is required in order to perform appropriate nullforming between coscheduled users. In the current LTE Rel.13 standard, no spécial CSI mode for MU-MIMO exists and thus, MU-MIMO scheduling and precoder construction has to be based on the existing CSI reporting designed for single-user ΜΙΜΟ (that is, a PMI indicating a DFT-based precoder, a RI and a CQI). This may prove quite challenging for MU-MIMO, as the reported precoder only contains information about the strongest channel direction for a user and may thus not contain enough information to do proper nullforming, which may lead to a large amount of interférence between co-scheduled users, reducing the benefit of MU-MIMO.

Advanced codebooks comprising precoders with multiple beams hâve shown to improve MU-MIMO performance due to enhanced nullforming capabilities. Codebooks and CSI feedback for multi-beam precoding hâve been disclosed in the literature. One such codebook is described herein.

Let D_n be a size N x N DFT matrix, i.e. the éléments of D_N are defined as [Dyv]/c,z ⁼ 1 j2nkl e n . Each column of D_N can be used as a precoder for a ULA with N antennas to form a DFT beam. So the N columns of D_N are associated with N orthogonal DFT beams.

These TV beams can be rotated to form N new orthogonal beams pointing to slightly different directions. This can be mathematically done by multiplying D_N with a rotation matrix R_N(q) from the left as — R(<i)Dn — RG, d₂, — > d_N], Equation 8 where R_N(q) = diag([_eU7ro_efa-i'n with 0 < q < 1. The amount of rotation is determined by q. In Equation 8, the Ath rotated DFT beam is given by d_k (k=l,2...,N).

The beam rotation above can also be used in the more general case of 2D UPAs with 5 (N_lf N₂) antenna ports to rotate a set of 2D DFT beams as follows:

D_N1,_N2 (Qi<Q2) ⁼ = [d_r d₂ d_N1N2 ] Equation 9

In Equation 9, are rotated 2D DFT beams and constitute an orthonormal basis of the vector space C^N1N2.

When dual polarizations are used in a 2D UPA, the 2D UPA can be considered as two antenna panels on top of each other, each with a different polarization. The same rotated

DFT beams can be applied to both panels. A dual-polarized beam forming matrix can be defined as ^n₁,n₂ Gh, Ç2) ^—

Ον_1:ν₂ ÎQn Q2) 0 ^n₁,n₂ (Qi> ^2) d_x d₂ ... d_NiNz 0 0 ... 0

0 ... 0 d_r d₂ ... d_NiNz = [bi b₂ ... b_2N1N₂ ].

Equation 10

The columns of B_{N1 N}2 (q_lf q₂) constitutes an orthonormal basis of the vector space €^2N1N2. Such a column bi is denoted a single-polarized beam (SP-beam) as it is constructed by a beam d transmitted on a single polarization (i.e. b = or b = [θ]). The optimal rank 1 precoder for a wireless device can be expressed as

2N_±N₂ k=l

Equation 11 where C; is the complex coefficient associated to the i^h beam. Under the assumption that the channel is somewhat sparse, most of the channel energy is contained in a few of the beams. So it is sufficient to describe the precoder by a few of the beams, which keeps down the feedback overhead. Assuming K SP-beams { b_S1, b_S2l ... >b_SK) are selected, where s_k G {1,2,..., 2N_±N₂], then

W = [b_S1 b_S2 ^bs_K

Equation 12

Generally, for the case of rank = r, we hâve

W = [b_S1 b_S2

bSK ]	fcW S2	c«] ·· Ls1 %

Equation 13 where is the coefficient corresponding to beam b_s. and layer r.

The precoder PF in the équation above can be described for a given layer r as a linear combination of beams constructed by cophasing a k^th beam b_Sk with a cophasing coefficient . Such a beam cophasing coefficient is a complex scalar that adjusts at least the phase of a beam relative to other beams. When a beam cophasing coefficient only adjusts relative phase, it is a unit magnitude complex number.

A more refined multi-beam precoder structure is achieved by separating the complex coefficients into a power (or amplitude) and a phase part. Letting and respectively dénoté the power and phase component of , the coefficient corresponding to beam b_s. and layer r can be given as . Equation 14

Using Equation 14 in Equation 13, the rank r multi-beam precoder can be expressed as w = [b_S1 b_S2

. (1) . (Γ)_{Ί e}7«i e^jai . (1)· . (r) _e7«2 _e ^Ja2 . (1) . (r)q _e7«i _β7«1 (l)’ · (D _e7«2 _e7«2

PkI ia^ L^J^aK e^jaK J

Equation 15 = B_s

LeJ^aK wherein

B s — [^S1 ^s_K ]

Equation 16 and

Equation 17

Note that B_s in Equation 16contains the K SP-beams chosen from the matrix

B_N1iN2 (q₃, q₂) in Equation 10. Now, letting and further letting

W₂

W	i = Bs	dP
	Γ jaW eJ 1	(Όί eJH
=	eJ 2	. (r) g7«2
	iaW	• (r) eJaK J

Equation 18

Equation 19 the multi-beam precoder of Equation 15 can be altematively expressed as

W = W] W2 - Equation 20

The sélection of W ₃ may then be made on a wideband basis while the sélection of IV₂ may be made on a subband basis. The precoder vector for l^tfl subband may be expressed as

IV, = Equation 21

That is, only IV₂ is a function of the subband index l and the same applies to ail subbands (i.e., IV _x is selected on a wideband basis).

As multiplying the precoder vector W with a complex constant C does not change its beamforming properties (as only the phase and amplitude relative to the other singlepolarized beams is of importance), one may without loss of generality assume that the coefficients corresponding to e.g. SP-beam 1 is fixed to p_± = 1 and = 1, so that parameters for one less beam needs to be signaled from the wireless device to the base station. Furthermore, the precoder may be further assumed to be multiplied with a normalization factor, so that e.g. a sum power constraint is fulfilled, i.e. that ||w||² = 1.

In some cases, the possible choices of columns οΐ B_NiNz qf) in Equation 10 are restricted so that if column î = i₀ is chosen, so is column i — i₀ + N_rN₂. That is, if an SPbeam corresponding to a certain beam mapped to the first polarization is chosen, e.g.

^bi₀ ^l° , this would imply that the SP-beam b_io+N1N2 j is chosen as well. That tois, the SP-beam corresponding to the said certain beam mapped to the second polarization is chosen as well. This would reduce the feedback overhead as only K_DP = K/2 columns of

B_{N Nz} (q_lt q₂) would hâve to be selected and signaled back to the base station. In other words, the column sélection is donc on a dual-polarized beam (or DP-beam) level rather than an SP-beam level. If a certain beam is strong on one of the polarizations it would typically imply that the beam would be strong on the other polarization as well, at least in a wideband sense, so the loss of restricting the column sélection in this way would not significantly decrease the performance.

What needs to be fed back by the wireless device to the base station is thus:

• The chosen columns of B_s o if K single polarized (SP) beams {b_S1, b_S2> ... , b_SKf are chosen from B_N1N2 (Qi, Qz) t° form the columns of B_s, then this requires at most K \og₂(2N₁N₂) bits.

o If K_DP dual polarized (DP) beams are chosen from B_N1N2 (q_lt q₂) to form the columns of B_s, then this requires at most K_DP log₂(A₁iV₂) bits.

• The DFT basis rotation factors q_r and q₂ in the first and second dimensions, respectively.

o For instance, the qj(C) = i = 0,1,..., Q — l,j G {1,2}, for some value of Q. The corresponding overhead would then be 2 · log₂ Q bits.

• The (relative) power levels associated with the chosen beams o If K SP-beams are chosen from B_N1in₂ Q2) ^to form columns of B_s, the wireless device needs to feed back the relative power levels {p₂, p₃, , p_K} corresponding to the SP-beams. If L is the number of possible discrète power levels, (K — 1) · log₂ L bits are needed to feed back the SP-beam power levels.

o If K_DP DP-beams are chosen, the wireless device needs to feed back the relative power levels {p₂, p₃,..., Pk_dp} corresponding to the DP-beams. If L is the number of possible discrète power levels, (K_DP — 1) · log₂ L bits are needed to feed back the DP-beam power levels.

• The cophasing factors o If K SP beams are chosen from B_N1iN2 (q_r, q·^ to form columns of B_s, the cophasing factors (e^²·, e^^a3,..., e^jaK] of the SP-beams need to be fed back by the wireless device to the base station. For instance, a_k(m) = -^-,m = 0,1,... M — 1, k G {2, 3,...., K], for some value of M. The corresponding overhead would be (K — 1) · log₂ M bits per rank.

o If K_DP DP beams are chosen from B_N1iN2 (q_lt q^ to form columns of B_s, the cophasing factors {e⁷“², e⁷^³,..., e^]a2KDpj need to be fed back by the wireless device to the base station. For instance, a_k(m) = m = 0,1,... M — 1, k G {2, 3,...., 2K_dp], for some value of M. The corresponding overhead would be (2K_DP — 1) · log₂ M bits per rank.

Consider an example codebook with K_DP = 3 dual polarized beams, /^ = 4 antenna ports in the first dimension and N₂ = 4 antenna ports in the second dimension, and an oversampling factor of Q = 4 in both dimensions. Furthermore, the number of possible beam power levels is assumed to be L = 4, the number of levels associated with cophasing factors is M = 8, and a system with 10 MHz carrier bandwidth and N_sub = 9 subbands is assumed. The beam identification, rotation, and relative powers are assumed to be reported once, when they identify W_r. On the other hand, the cophasing factors identify fV₂(0 and are reported once per subband. This means that a total of N_sub(2K_DP — 1) · log₂ M bits are needed to feedback the cophasing factors.

Then, the number of bits to report the following components of the CSI are given as follows:

For Wy a total of 20 bits is needed:

• beam identification: 3 · log₂(4 4) = 12 bits • beam rotation: 2 · log₂(4) = 4 bits • beam relative power: (3 — 1) log₂(4) = 4 bits

For IV₂: cophasing: 9-(2-3-1)- log₂(8) = 135 bits are needed

It can be observed that the vast majority of CSI feedback (87% in this example) is for cophasing information. Furthermore, a total of 155 bits is needed for a single cell. If the wireless device is configured for downlink carrier aggregation with, for example, 5 cells, then 5*155=775 bits are needed.

In some embodiments, the uplink feedback overhead associated with the multi-beam precoder codebook is reduced. Such embodiments include:

• The configuration of one or more power threshold parameters to the wireless device by the base station that the wireless device uses in determining the number of beams to be included in the multi-beam precoder codebook.

• The détermination of the number of beams included in the multi-beam precoder codebook by the wireless device and the subséquent reporting of this information to the base station to aid the base station in determining the UL control information payload size on the UL shared channel.

• Various methods where the détermination of the number of beams included in the multi-beam precoder codebook is performed by the base station.

• A method for further reducing uplink feedback overhead for wireless device selected subband feedback mode where the number of subbands to be fed back is a function of both System bandwidth and the number of beams included in the multi-beam precoder codebook.

Since different wireless devices may expérience different channels with the channel energy contained in different number of beams, using the embodiments disclosed herein, the UCI overhead can be controlled to suit the needs of different wireless devices.

As described earlier, the majority of the feedback overhead associated with multibeam precoder codebooks is incurred in feeding back the cophasing information. When K_DP dual polarized beams are chosen from B_N1>Nz (q₁, q₂) to form columns of B_s, the overhead incurred in feeding back the cophasing factors is N_sub(2K_DP — 1) · log₂ M bits. Similarly, when K single polarized beams are chosen from B_NliNz (q_lr q₂) to form columns of B_s, the overhead incurred in feeding back the cophasing factors is N_sub (K — 1) · log₂ M bits. Hence, from an UL overhead réduction perspective, it is bénéficiai to control the number of beams included in B_s (That is, to limit the value of K_DP in the case of dual polarized beams or to limit the value of K in the case of single polarized beams).

In one embodiment, the base station, e.g., eNodeB (eNB), may configure a wireless device with a power threshold parameter P_TH. During beam identification, the wireless device only includes the beams that hâve an associated power component exceeding the configured threshold. In the case of single polarized beams, when the wireless device is selecting a finite set of beams {b_Si, b_Sz> ... ,b_SK} from the full set of beams in Bn^Nz (Qi, Qz), the wireless device only selects the beams that satisfy the constraint

Pi > Pth> Equation 22 where pi is the power component corresponding to beam b_s. as per the définition in Equation 14.

In some embodiments, an alternative constraint of

Pi > P_TH, Equation 23 may also be used in place of the constraint in Equation 22. The constraint in Equation 23 means that the wireless device picks beam b_s. if its associated power component is greater than or equal to the power threshold parameter configured to a wireless device. Similarly, in the case of dual polarized beams, when the wireless device is selecting a finite set of beams {h_S1, b_S2> · ’^s_Kdp} from the full set of beams in B_NiNz (q^ q₂), the wireless device may use either Equation 22 or Equation 23 as the criterion for selecting beam b_s.. Hence, only the phase and power components of the beams included in the matrix B_s (as defined in Equation 16 for example) need to be fed back by the wireless device to the base station. The power threshold parameter P_TH may be semi-statically configured to the wireless device by the base station via radio resource control (RRC) signaling. The power threshold parameter P_TH can either be cell, transmission point, or wireless device spécifie. When cell or transmission point spécifie, P_TH may be associated with an identifier of an NZP CSI-RS, such as csi-RS-ConfigNZPId-rl 1 from 3GPP TS 36.331, the identified NZP CSI-RS is used to détermine the multi-beam CSI feedback. When wireless device spécifie, P_TH may not be associated with a single NZP CSI-RS identifier for a given CSI process, it may instead be associated with a plurality of NZP CSI-RSs for one or multiple CSI process(es).

In some embodiments, the semi-statically configured P_TH parameter may represent a power ratio (i.e., 0 < P_TH < 1) with respect to the beam with the maximum received power.

In an alternative embodiment, multiple power threshold parameters

[P^ P^ · · · may be configured by the base station to the wireless device, where Pj_H is the power threshold parameter associated with rank r and R dénotés the maximum transmission rank. In this scénario, for a given transmission rank r, the wireless device may select beam b_s. if its associated power component pi satisfies one of the following constraints

Cf')

Pi > ^th ’ Equation 24

Pt > Ργ^. Equation 25

Equation 24-Equation 25 imply that beam b_s. is only selected for rank r transmission if its associated power component pi exceeds (or in the case of Equation 25 greater than or Cf) equal to) the rank spécifie power threshold parameter Pj_H .

One of the applications for multi-beam precoder is MU-MIMO transmission to two or more wireless devices in a cell. This is generally good for wireless devices with good channel qualifies, i.e. high SINRs. For wireless devices at the cell edge, their SINRs are generally poor and are not good for MU-MIMO transmissions. Therefore, in another embodiment, a SINR threshold may be used by a wireless device to détermine whether a single beam or multiple beams will be used in the multi-beam precoder. A wireless device may compare its wideband SINR with the SINR threshold and if the wideband SINR is below the SINR threshold, a single beam would be used. Otherwise, multiple beams would be used. In case of multiple beams, the exact number of beams can be determined by methods discussed in the previous embodiments. The SINR threshold can be determined by the base station and signaled to the wireless device. One suitable wideband SINR measure is RSRQ, as defined in 3GPP TS 36.214. Altematively, the wireless device may calculate a wideband CQI assuming a single beam is used with the multi-beam codebook. The wideband SINR is then the spectral efficiency corresponding to the calculated CQI.

LTE CSI feedback in Rel-13 has a payload size on PUSCH or PUCCH that is known beforehand to the base station, e.g., eNodeB (eNB). Furthermore, the base station is also aware of which REs are occupied by PUSCH or by UCI on PUSCH (that is, the UCI resource on PUSCH is known to the base station). The payload size is set by parameters signaled in RRC and/or DCI. Therefore, if the UCI payload size varies according to a parameter not known by the base station, the base station may not be able to décodé the UCI or a PUSCH that carries the UCI. In the above embodiment(s), whether or not a beam is included in the advanced codebook with multi-beam precoder is determined by the power threshold parameter(s). As a resuit, the number of beams included in the multi-beam precoder can vary depending on the channel experienced by a given wireless device and the value of the power threshold parameter configured to the wireless device. Hence, the UCI payload size, which is determined by the feedback overhead, will be varying as a function of the number of beams included in the multi-beam precoder.

Therefore, in some embodiments, the wireless device indicates the number of beams in a multi-beam PMI report in higher layer signaling. Because higher layer messages can be variably sized, base station will be able to décodé messages containing multi-beam reports whose size varies. The multi-beam PMI report may be carried in a MAC control element, an RRC message such as a measurement report, or another suitable higher layer message.

In another embodiment, a two-step approach is taken. In the first step, the number of beams included in the multi-beam precoder is first indicated to the base station by the wireless device via a MAC control element. Once the base station receives this MAC control element message, the base station will know the number of beams included and will know the UCI payload. Then, in the second step, the different components of the CSI including rank indicator, PMI associated with the multi-beam precoder codebook (i.e., and iy₂), and CQI will be reported by the wireless device over PUSCH. Since the base station knows the UCI payload from the first step, the base station will know the resource éléments containing UCI in the PUSCH transmission that contains the CSI report.

In another embodiment, the base station may additionally signal semi-statically the maximum number of beams to be included in the multi-beam precoder codebook. The base station may send the maximum number of beams as part of RRC signaling. The maximum number of beams can either be a cell spécifie or a wireless device spécifie parameter. The actual number of beams selected by the wireless device to be included in the multi-beam precoder codebook based on P_TH can be reported periodically over PUCCH. For example, if the maximum number of beams is configured to be 4, then 2 bits may be used by the wireless device to periodically indicate to the base station the actual number of selected beams using PUCCH. For instance, the subframe in which the actual number of beams included in the multi-beam precoder codebook may be periodically indicated in the subframes satisfying the condition (1 θ^{x n}f + \_ⁿ _s / 2J — —N_Opp_SEÎRI^m.o<iN_pd M_beam^ = 0, Equation 26 where M_beams is a periodicity multiple in subframes that is a new higher layer parameter configured to the wireless device by the base station via higher layer signaling. This higher layer parameter is to be used to détermine in which subframes the wireless device should report the actual number of beams included in the multi-beam precoder codebook over PUCCH. The remaining parameters in Equation 26 are defined as before. Furthermore, a new reporting type (as an extension to the ones described above) may be added to support reporting the actual number of beams included in the multi-beam precoder codebook on PUCCH. Once the wireless device feeds back the actual number of beams included in the multi-beam precoder codebook, the base station has knowledge of the UCI payload size for CSI feedback over PUSCH. Hence, the base station can allocate the appropriate amount of resources to the wireless device for CSI feedback over PUSCH.

In yet another embodiment, the base station may firstly request the wireless device to report the actual number of beams included in the multi-beam precoder codebook on PUSCH. Then, after knowing the number of beams included in the multi-beam precoder codebook, the base station sends a CSI request to ask the wireless device to feedback the different components of the CSI including rank indicator, PMI associated with the multi-beam precoder codebook (i.e., W₁ and W₂), and CQI in a PUSCH report.

In a further embodiment, the wireless device reports the number of beams included in the multi-beam precoder codebook on PUSCH in the same report (i.e., in the same subframe) along with other CSI components such as rank indicator, PMI associated with the multi-beam precoder codebook (i.e., and and CQI. The number of feedback bits for the PMI associated with the multi-beam precoder codebook (i.e., 14^ and W₂) are not known to the base station at this point. If the resource location of the number of beams included in the multi-beam precoder codebook within the PUSCH resource is known to the base station, the base station may first décodé the number of beams included in the multi-beam precoder codebook. Once this is decoded, the base station will know the UCI payload of the CSI report and hence will know the UCI rate matching on the PUSCH transmission that contains the CSI report.

In another embodiment, the base station transmits N non-precoded CSI-RS ports with periodicity P, and the wireless device measures the P port CSI-RS and détermines the number of dominant beams and their associated beam powers. In some embodiments, the wireless device only considers the orthogonal beams when determining the number of dominant beams and their associated powers. The wireless device will periodically report the number of dominant beams and/or the powers associated with the beams after quantization. The base station uses this information to détermine the number of beams suitable for each wireless device.

In one embodiment, the wireless device measures multiple beams using discovery reference signais (DRSs) and reports the received power strengths on these beams. Using these measurement reports, the base station détermines an appropriate number of dominant or significant beams that should be included in the multi-beam precoder codebook. In a detailed embodiment, the base station transmits distinct CSI-RSs in a DRS occasion over orthogonal beams, such as where the CSI-RSs are precoded on an N_XN₂ element array using beams dj from Equation 9, and the wireless device measures and reports received power for each of the CSI-RSs. From the reported power values, the base station détermines the number of beams a given wireless device should include in the multi-beam precoder codebook.

In an alternative embodiment, the wireless device transmits reference signais on the uplink for the purposes of channel sounding. The base station can use these sounding reference signais to estimate the channel H on the uplink. The base station can then multiply to estimated channel matrix H by the B_N±N2 (q^, q₂) matrix of Equation 10 for different rotation parameter combinations Çq₁, q₂). The power associated with each column of the matrix HB_{N N} (q₁, q₂) then represents the power associated with the N_rN₂ orthogonal beams. By comparing the power of the orthogonal beams to a predetermined threshold, the base station can détermine the number of beams that should be included in the multi-beam precoder codebook.

Alternatively, to détermine the number of beams to be included in the multi-beam precoder, the base station can configure the wireless device with Kcsi-rs > 1 Class B CSIRS resources and transmit each CSI-RS port of a given CSI-RS resource using one of Kcsi-rs orthogonal beams. The K_CSi__RS orthogonal beams can be beams d_t from Equation 9.

In one embodiment, the wireless device détermines the power of each of the K_CSI__RS CSI-RS resources as the average power over ail CSI-RS ports in the resource. The wireless device then reports the power values for ail K_CSI__RS resources. In an alternative embodiment, the wireless device reports power values for the K' strongest CSI-RS resources where K’ is configured to each wireless device by the base station. The parameter K' may be RRC signaled to the wireless device and can either be wireless device spécifie or cell spécifie. Using the reported power values corresponding to the K_CSI__RS (or K') resources (where each corresponds to an orthogonal beam), the base station détermines the number of beams to be included in the multi-beam precoder codebook.

In one embodiment, the number of beams to be included in the multi-beam precoder codebook is signaled to the wireless device by the eNB. In one case, the number of beams to be included in the multi-beam precoder codebook is signaled to the wireless device by the base station via higher layer signaling such as RRC or a MAC control element. In an altemate case, the base station signais the number of beams to be included in the multi-beam precoder codebook dynamically via DCI to the wireless device. Depending on the number of beams signaled, the base station is aware of the payload size of CSI to be sent by the wireless device on the UL-SCH.

The majority of the feedback overhead associated with multi-beam precoder codebook is incurred in feeding back the cophasing information. When K_DP dual polarized beams are chosen from B_{N N} (q₃, q₂) to form columns of B_s, the overhead incurred in feeding back the cophasing factors is N_sub(2K_DP — 1) · log₂ M bits. Similarly, when K single polarized beams are chosen from B_{N N} (q₁, q₂) to form columns of B_s, the overhead incurred in feeding back the cophasing factors is N_sub(K — 1) log₂ M bits. Hence, the number of subbands N_sub can also significantly affect the UL overhead. As described previously, LTE supports both higher layer configured subband feedback and wireless device selected subband feedback.

In this embodiment, the UL feedback overhead is further reduced for a wireless device selected subband feedback mode by making the number of subbands to be fed back a function of both system bandwidth and the number of beams to be included in the multi-beam precoder codebook. For instance, for a given system bandwidth, the number of subbands can be reduced when the number of beams to be included in the multi-beam precoder codebook is increased. An example for this embodiment is shown in Table 6.

In another embodiment, the subband size is varied as a function of the number of beams to be included in the multi-beam precoder codebook. For instance, with increasing number of beams to be included in the multi-beam precoder codebook, the subband size is increased. Similarly, with smaller number of beams to be included in the multi-beam precoder codebook, the subband size will be lower. In some variants of this embodiment, both the subband size and the number of subbands are functions of the number of the beams to be included in the multi-beam precoder codebook.

TABLE 6

System Bandwidth	Subband Size k (RBs)	Number of Beams in multi-beam precoder codebook	Number of Subbands
6-7	NA	NA	NA
8-10	2	1	1
2	1
3	1
11-26	2	1	3
2	2
3	2
27-63	3	1	5
2	3
3	2
64-110	4	1	6
2	3
3	2

Recall the example discussed above where an example multi-beam precoder codebook was considered with K_DP = 3 dual polarized beams, = 4 antenna ports in the first dimension and N₂ = 4 antenna ports in the second dimension, and an oversampling factor of Q — 4 in both dimensions. Also note that the number of possible beam power levels was assumed to be L = 4, the number of levels associated with cophasing factors was M — 8, and a system with 10 MHz carrier bandwidth and N_sub = 9 subbands was assumed. For this example, a total of 155 bits were needed for a single cell.

Now, consider the case where the number of dual polarized beams can be reduced to K_DP — 2 by utilizing one or more of the embodiments described above. Then, the number of bits to report the following components of the CSI in the case of K_DP = 2 are given as follows:

For W_P a total of 14 bits is needed:

• beam identification: 2 · log₂(4 · 4) = 8 bits • beam rotation: 2 · log₂ (4) = 4 bits • beam relative power: (2 — 1) · log₂(4) = 2 bits

For IV₂: cophasing: 9-(2-2-1)- log₂(8) = 81 bits are needed.

Hence, a total of 95 bits are needed to feedback CSI for the case of K_DP — 2. This yields a signifïcant réduction (i.e., 39% réduction) in feedback overhead when compared to the overhead required for the case of K_DP = 3.

Since different wireless devices may expérience different channels with the channel energy contained in different number of beams, using the above embodiments the UCI overhead can be controlled to suit the needs of different wireless devices. For instance, a wireless device that expériences a channel with channel energy contained in 2 beams can use an appropriate number of feedback bits (95 bits, in the above example) when compared to the case where the wireless device has to assume that a fixed number of beams will be included in the multi-beam precoder codebook.

Thus, embodiments include a first embodiment wherein a network node configures the wireless device with one or multiple power threshold parameters that the wireless device uses in determining the number of beams to be included in the multi-beam precoder codebook. One or more of the following may also be included:

• The wireless device only includes beams that hâve a power component exceeding the threshold in the multi-beam precoder codebook;

• The power threshold parameters(s) are signaled via RRC and can be associated with an NZP CSI-RS identifier;

• The power threshold parameter(s) can also represent a power ratio with respect to the beam with the maximum received power;

• Different power threshold parameters can be applied to different transmission ranks (see Equation 24-Equation 25);

• In addition, the base station may configure a SINR threshold to the wireless device for the wireless device to déterminé whether a single beam precoder or a multiple beam precoder should be used.

In a second embodiment, the wireless device indicates the number of beams included in the multi-beam precoder codebook to the base station to aid the base station in determining the UL control information payload size on the UL shared channel. One or more of the following may also be included:

• The indication involves a two-step approach where the wireless device indicates the number of beams included in an MAC control element in a first step and then sends the other components of CSI on PUSCH in a second step;

• The wireless device sends the number of beams included in a periodic report on PUCCH and the remaining components of CSI in a different report on PUSCH;

• The base station semi-statically configures the wireless device with a higher layer parameter used to détermine in which subframes the wireless device should report the actual number of beams included in the multi-beam precoder codebook over PUCCH (see Equation 26);

• The wireless device sends the number of beams included in an aperiodic report on PUSCH and the remaining components of CSI in a different report on PUSCH;

• The base station will be triggering these reports;

• The indication of such number of beams along with other components of the CSI report is done via higher layer signaling such as MAC control éléments or RRC signaling;

• The wireless device sends the number of beams included in the same PUSCH report as other CSI components;

• The base station first décodés the number of beams included and then détermines the UCI payload size information for the PUSCH report;

• The wireless device measures a non-precoded P-port CSI-RS and détermines the dominant beams and their associated power and reports this information to the base station;

• The base station semi-statically configures the maximum number of beams to be included in the multi-beam precoder codebook.

In a third embodiment, the base station détermines the number of beams to be used by the wireless device when calculating multi-beam CSI using one of the following:

• The base station transmits orthogonal beams over CSI-RSs in a DRS occasion and configures the wireless device to measure and report the received power for each of the CSIRSs. The base station détermines the number of beams to be used by the wireless device when calculating multi-beam CSI from these power reports;

• The base station détermines the number of beams to be used by the wireless device when calculating multi-beam CSI by using measurements on the sounding reference signais transmitted by the wireless device on the uplink;

• The base station configures the wireless device to receive K_CSI__RS CSI-RS resources. The base station then transmits ail CSI-RS ports of each CSI-RS resource using one beam. The beam is one of Kcsi-rs orthogonal beams, and so each CSI-RS resource is beamformed with one of Kcsi-rs orthogonal beams. The wireless device reports the average power across ail antenna ports for a given CSI-RS resource. The wireless device reports the average power for up to K' of the CSI-RS resources. The eNB then détermines the number of beams to be used by the wireless device when calculating multi-beam precoder codebook using the power values;

• The number of beams to be used by the wireless device when calculating multi-beam CSI is signaled by the base station to the wireless device via RRC signaling, a MAC control element, or DCI.

A fourth embodiment is a method for further reducing uplink feedback overhead for wireless device selected subband feedback mode where the number of subbands to be fed back is a function of both system bandwidth and the number of beams included in the multibeam precoder codebook. According to another aspect a method where the subband size is varied as a function of the number of beams to be included in the multi-beam precoder codebook is provided.

FIG. 11 is a block diagram of a wireless communication network configured according to principles set forth herein. The wireless communication network 10 includes a cloud 12 which may include the Internet and/or the public switched téléphoné network (PSTN). Cloud 12 may also serve as a backhaul network of the wireless communication network 10. The wireless communication network 10 includes one or more network nodes 14A and 14B, which may communicate directly via an X2 interface in LTE embodiments, and are referred to collectively as network nodes 14. It is contemplated that other interface types can be used for communication between network nodes 14 for other communication protocols such as New Radio (NR). The network nodes 14 may serve wireless devices 16A and 16B, referred to collectively herein as wireless devices 16. Note that, although only two wireless devices 16 and two network nodes 14 are shown for convenience, the wireless communication network 10 may typically include many more wireless devices (WDs) 16 and network nodes 14. Further, in some embodiments, WDs 16 may communicate directly using what is sometimes referred to as a side link connection.

The term “wireless device” or mobile terminal used herein may refer to any type of wireless device communicating with a network node 14 and/or with another wireless device 16 in a cellular or mobile communication system 10. Examples of a wireless device 16 are user equipment (UE), target device, device to device (D2D) wireless device, machine type wireless device or wireless device capable of machine to machine (M2M) communication, PDA, tablet, smart phone, laptop embedded equipped (LEE), laptop mounted equipment (LME), USB dongle, etc.

The term “network node” used herein may refer to any kind of radio base station in a radio network which may further comprise any base transceiver station (BTS), base station controller (BSC), radio network controller (RNC), evolved Node B (eNB or eNodeB), NR gNodeB, NR gNB, Node B, multi-standard radio (MSR) radio node such as MSR BS, relay node, donor node controlling relay, radio access point (AP), transmission points, transmission nodes, Remote Radio Unit (RRU) Remote Radio Head (RRH), nodes in distributed antenna system (DAS), etc.

Although embodiments are described herein with reference to certain functions being performed by network node 14, it is understood that the functions can be performed in other network nodes and éléments. It is also understood that the functions of the network node 14 can be distributed across network cloud 12 so that other nodes can perform one or more functions or even parts of functions described herein. Also, functions described herein as being performed by a network node 14 may also be performed by a wireless device 16.

The network node 14 has a beam number déterminer 18 configured to détermine a number of beams to be included in a multi-beam precoder codebook. The wireless device 16 includes a beam power value déterminer 20 to détermine a power value for each beam to be included in a precoder codebook based on the received power threshold parameter.

FIG. 12 is a block diagram of a network node 14 configured to configure a wireless device and to détermine a number of beams to include in a multi-beam precoder codebook by a wireless device. The network node 14 has processing circuitry 22. In some embodiments, the processing circuitry may include a memory 24 and processor 26, the memory 24 containing instructions which, when executed by the processor 26, configure processor 26 to perform the one or more functions described herein relating to configuring the wireless device. In addition to a traditional processor and memory, processing circuitry 22 may include integrated circuitry for processing and/or control, e.g., one or more processors and/or processor cores and/or FPGAs (Field Programmable Gâte Array) and/or ASICs (Application Spécifie Integrated Circuitry).

Processing circuitry 22 may include and/or be connected to and/or be configured for accessing (e.g., writing to and/or reading from) memory 24, which may comprise any kind of volatile and/or non-volatile memory, e.g., cache and/or buffer memory and/or RAM (Random Access Memory) and/or ROM (Read-Only Memory) and/or optical memory and/or EPROM (Erasable Programmable Read-Only Memory). Such memory 24 may be configured to store code exécutable by control circuitry and/or other data, e.g., data pertaining to communication, e.g., configuration and/or address data of nodes, etc. Processing circuitry 22 may be configured to control any of the methods described herein and/or to cause such methods to be performed, e.g., by processor 26. Corresponding instructions may be stored in the memory 24, which may be readable and/or readably connected to the processing circuitry 22. In other words, processing circuitry 22 may include a controller, which may comprise a microprocessor and/or microcontroller and/or FPGA (Field-Programmable Gâte Array) device and/or ASIC (Application Spécifie Integrated Circuit) device. It may be considered that processing circuitry 22 includes or may be connected or connectable to memory, which may be configured to be accessible for reading and/or writing by the controller and/or processing circuitry 22.

In some embodiments, the memory 24 is configured to store CSI reports 30, a number of beams, K, 32, power threshold parameters 34 and SINR values 36. The CSI reports 30 include channel state information received from a wireless device. In some embodiments, the processor 26 is configured to détermine a number of beams via a beam number déterminer 18 to be included in a multi-beam precoder codebook. The processor 26 is further configured to détermine power threshold parameters via a power threshold parameter déterminer 40. In some embodiments, the transceiver 28 is configured to transmit to the wireless device, a signal to interférence plus noise ratio, SINR, to be used by the wireless device to détermine to use one of a single beam precoder and a multiple beam precoder. The processor 26 is also configured to implement a CSI report size déterminer 44 configured to détermine a size of a CSI report received by the network node 14. In the alternative, or in addition, the processor 26 may implement a payload size déterminer 45 configured to détermine an uplink, UL, shared channel payload size based on the number of beams on the UL shared channel. The processor 26 is also configured to détermine a configuration of the wireless device 16 to measure and report a received power for each of different reference signais via a configuration déterminer 46.

In some embodiments, the processor 26 is further configured to détermine a configuration of a wireless device to measure and report a received power for each CSI reference signal via a configuration déterminer 42. The number of beams determined by beam number déterminer 38 may be based on the power reports received from the wireless device.

A transceiver 28 is configured to transmit to the wireless device at least one power threshold parameter to be used by the wireless device to détermine a number of beams to be included in a multi-beam precoder codebook and may be configured to transmit an SINR upon which a wireless decision may base a decision whether to use a single beam procoder or a multi-beam precoder. The transceiver 28 may be configured with an orthogonal beam transmitter 48 to transmit a plurality of orthogonal beams on different reference symbols. The transceiver 28 may also include a report receiver 50, configured to receive a power report for each of the different reference signais and configured to receive CSI reports 30.

FIG. 13 is a block diagram of an alternative embodiment of the network node 20 that includes a memory module 25, a beam number déterminer module 19, a power threshold parameter déterminer module 41, a configuration déterminer module 43, an SINR déterminer module 43, a CSI report size déterminer module 45, a payload size déterminer module 49, a configuration déterminer module 49 and a transceiver module 29. The modules 19, 41, 43, 45, 47, 49 and at least a portion of the module 29 may be implemented as software modules exécutable by a computer processor. Thus, in some embodiments, the memory module 25 is configured to store CSI reports 30, a number of beams 32, power threshold parameters 34, and SINR values 36.

The beam number déterminer module 19 is configured to détermine a number of beams to be included in a multi-beam precoder codebook. The power threshold parameter déterminer module 41 is further configured to détermine power threshold parameters. In some embodiments, the SINR déterminer module is configured détermine a signal to interférence plus noise ratio, SINR, to be used by the wireless device to détermine to use one of a single beam precoder and a multiple beam precoder. The CSI report size déterminer module 45 is configured to détermine a size of the CSI report. A payload size déterminer module 47 is configured to déterminé an uplink, UL, shared channel payload size based on the number of beams on the UL shared channel. The configuration déterminer 49 is configured to détermine a configuration of the wireless device 16 to measure and report a received power for each of different reference signais.

In some embodiments, the transceiver module 29 is configured to transmit to the wireless device a power threshold parameter to be used by the wireless device to détermine a number of beams to be included in a multi-beam precoder codebook. The transceiver 29 may also be configured to transmit a signal to interférence plus noise ratio, SINR, to be used by the wireless device to détermine to use one of a single beam precoder and a multiple beam precoder. The transceiver module 29 may be configured with an orthogonal beam transmitter 51 to transmit a plurality of orthogonal beams on different reference symbols. The transceiver 29 may also include a report receiver module 53 configured to receive a power report for each of the different reference signais and configured to receive CSI reports 30.

FIG. 14 is a block diagram of an embodiment of a wireless device 16 configured to déterminé multi-beam channel State information (CSI). The wireless device 16 may include processing circuitry 62 that may include a memory 64 and a processor 66 the memory 64 containing instructions which, when executed by the processor 66, configure processor 66 to perform the one or more fiinctions described herein relating to configuring the wireless device. In addition to a traditional processor and memory, processing circuitry 62 may include integrated circuitry for processing and/or control, e.g., one or more processors and/or processor cores and/or FPGAs (Field Programmable Gâte Array) and/or ASICs (Application Spécifie Integrated Circuitry).

Processing circuitry 62 may include and/or be connected to and/or be configured for accessing (e.g., writing to and/or reading from) memory 64, which may comprise any kind of volatile and/or non-volatile memory, e.g., cache and/or buffer memory and/or RAM (Random Access Memory) and/or ROM (Read-Only Memory) and/or optical memory and/or EPROM (Erasable Programmable Read-Only Memory). Such memory 64 may be configured to store code exécutable by control circuitry and/or other data, e.g., data pertaining to communication, e.g., configuration and/or address data of nodes, etc. Processing circuitry 62 may be configured to control any of the methods described herein and/or to cause such methods to be performed, e.g., by processor 66. Corresponding instructions may be stored in the memory 64, which may be readable and/or readably connected to the processing circuitry 62. In other words, processing circuitry 62 may include a controller, which may comprise a microprocessor and/or microcontroller and/or FPGA (Field-Programmable Gâte Array) device and/or ASIC (Application Spécifie Integrated Circuit) device. It may be considered that processing circuitry 62 includes or may be connected or connectable to memory, which may be configured to be accessible for reading and/or writing by the controller and/or processing circuitry 62.

In some embodiments, the memory 64 is configured to store CSI reports 70, a number of beams, K, 72, power threshold parameters 74, SINR values 76 and a number of subbands 78. The processor 66 implements a CSI report generator 80 that generates the CSI reports 48. The processor 66 also implements a beam power value déterminer 20 that is configured to détermine a number of beams to be included in a precoder codebook based on the received power threshold parameter 74. The processor 66 also implements a subband déterminer 84 that is configured to détermine a number of subbands to be fed back to a network node based on a system bandwidth and a number of beams to include in a multi-beam precoder codebook. The processor 66 also implements a precoder selector 86 that is configured to select whether to use one of a single beam precoder and a multiple beam precoder based on the received SINR 76. The transceiver 68 is configured to transmit the determined number of beams 72 and subbands 78 and to receive a power threshold parameter 74 and/or an SINR value 76.

FIG. 15 is a block diagram of an alternative embodiment of the wireless device 16 that includes memory module 65, a CSI report generator module 81, a beam power value déterminer module 21, a subband number déterminer module 85 and a precoder selector module 87. These modules may be implemented as software exécutable by a computer processor. The memory module 45, transceiver module 69, CSI report generator module 81, beam number déterminer module 21, subband number déterminer module 85 and precoder selector module 87 may perform the same functions as memory 44, transceiver 68, CSI report generator 80, beam power value déterminer 20, subband number déterminer 84 and precoder selector 86, respectively.

FIG. 16 is a flowchart of an exemplary process of configuring a wireless device, including transmitting to the wireless device at least one of: a power threshold parameter to be used by the wireless device to détermine a number of beams to be included in a multibeam precoder codebook and a signal to interférence plus noise ratio, SINR, to be used by the wireless device to détermine to use one of a single beam precoder and a multiple beam precoder (block S100).

FIG. 17 is a flowchart of an exemplary process to détermine a number of beams to include in a multi-beam precoder codebook by a wireless device. The process includes receiving via the transceiver 28 from the wireless device 16 the number of beams to be included in a multibeam precoder code book (block S102). The process also includes determining via the payload size déterminer 44 an uplink control information payload size based on the number of beams (block S104).

FIG. 18 is a flowchart of an exemplary process to détermine at a network node a number of beams to be used by a wireless device when generating a multi-beam CSI report. The process includes transmitting via the transceiver 28 orthogonal beams on different reference signais (block S106). The process also includes configuring via the configuration déterminer 47 the wireless device to measure and report a received power for each reference signal (block S108), and calculating via the beam number déterminer 18, a number of beams to be used by the wireless device when generating the multi-beam CSI report based on the power reports (block S110).

FIG. 19 is a flowchart of an exemplary process in a wireless device 16 configured to operate in a sélective subband feedback mode. The process includes determining via the subband number déterminer 84, a number of subbands to be fed back to a network node based on a system bandwidth and a number of beams to include in a multi-beam precoder codebook (block SI 12).

FIG. 20 is a flowchart of an exemplary process in a wireless device 16 for reducing uplink signaling overhead. The process includes receiving via the transceiver 68 at least one of a power threshold parameter and a signal to interférence plus noise ratio, SINR, from a network node (block SI 14). The process also includes at least one of determining via the beam number déterminer 20 a number of beams to be included in a precoder codebook based on the received power threshold parameter and determining via the precoder selector 86 whether to use one of a single beam precoder and a multiple beam precoder based on the received SINR (block SI 16).

FIG. 21 is a flowchart of an exemplary process for a wireless device to adjust uplink signaling overhead. The process includes receiving signaling that configures the wireless device with a first number of beams, N, (block SI 18). the process also includes determining N power values, each power value corresponding to one of the N beams (block S120). The process also includes including channel State information, CSI, in a CSI report, the CSI pertaining to one or more beams whose corresponding power value is above a predetermined power value (block S122).

FIG. 22 is a flowchart of an exemplary process for configuring a network node to détermine a size of a channel state information (CSI) report. The process includes configuring a wireless device with a first number of beams, N (block S124). The process also includes receiving signaling from the wireless device indicating at least one of: N power values, each power value corresponding to one of N beams, and a second number of beams, M’, whose corresponding power value is above a predetermined value (block S126). The process also includes receiving the CSI report from the wireless device, the CSI report containing CSI pertaining to one or more beams whose corresponding power value is above the predetermined power value (block S128). The process also includes determining the size of the CSI report (block S130).

FIG. 23 is a flowchart of an exemplary process for determining at a network node a number of beams to be used by a wireless device when generating a multi-beam channel state information, CSI, report. The process includes transmitting a plurality of distinct reference signais (block S132). The process also includes configuring the wireless device to measure and report a received power to the network node for each of the distinct reference signais (block S134). The process further includes determining the number of beams (block S136). The process also includes signaling the number of beams to the wireless device (block S138).

Thus, some embodiments include a method for a wireless device 16 to adjust uplink signaling overhead. The method includes receiving signaling that configures the wireless device with a first number of beams, N SI 18. The method also includes determining N power values, each power value corresponding to one of the N beams S120. The method also includes including channel state information, CSI, in a CSI report, the CSI pertaining to one or more beams whose corresponding power value is above a predetermined power value S122.

In some embodiments, the method further includes determining whether the number of beams, N, is equal to one or greater than one using a signal to interférence plus noise ratio, SINR. In some embodiments, the method further includes transmitting signaling by the wireless device 16 indicating at least one of: N power values, each power value corresponding to one of the N beams, and a second number of beams, M’, whose corresponding power value is above a predetermined value. In some embodiments, the first number of beams is signaled via radio resource control, RRC. In some embodiments, the predetermined power value represents a power ratio with respect to a beam with a maximum received power. In some embodiments, a signal to interférence plus noise ratio, SINR, is additionally used by the wireless device 16 to déterminé whether the number of beams is equal to one or greater than one. In some embodiments, each beam of the first number of beams (128) and a second number of beams is a kth beam, d(k), that has associated a set of complex numbers and has index pair (l_k, m_k), each element of the set of complex numbers being characterized by at least one complex phase shift such that:

• d_n(k) = df^a^²^?^^ • d_n(k), and dfk) are the z^th and n^th éléments ofd(fc), respectively;

• a_in is a real number corresponding to the z^th and zz^th éléments of d(k);

• p and q are integers;

• beam directions Δ_1Κ and Δ_{2 k} are real numbers corresponding to beams with index pair (Ι^πί^) that détermine the complex phase shifts and _ei^A_{Zik reS}p_ectively; and • each of the at least a co-phasing coefficient between the first and second beam (S130) is a complex number c_k for d(k) that is used to adjust the phase of the z^th element of d(k) according to c_kdi(k).

In some embodiments, a wireless device 16 for reducing uplink signaling overhead is provided. The wireless device 16 includes processing circuitry 62, which may include a memory 64 and a processor 66. The processing circuitry 62is configured to store a number of beams, N, to be included in a multiple beam precoder codebook, the number of N beams being received from a network node 14and further configured to perform at least one of: detennine N power values, each power value corresponding to one of the N beams; and include CSI in the CSI report, the CSI pertaining to one or more beams whose corresponding power value is above a predetermined power valued.

In some embodiments, the processing circuitry 62 is further configured to détermine whether the number of beams is equal to one or greater than one using an SINR. In some embodiments, the wireless device 16 includes a transceiver 68 configured to transmit signaling by the wireless device 16 indicating at least one of: N power values, each power value corresponding to one of the N beams; and a second number of beams, M’, whose corresponding power value is above a predetermined value. In some embodiments, the first number of beams is signaled via radio resource control, RRC. In some embodiments, the predetermined power value represents a power ratio with respect to a beam with a maximum received power. In some embodiments, a signal to interférence plus noise ratio, SINR, is additionally used by the wireless device 16 to déterminé whether the number of beams is equal to one or greater than one.

In some embodiments, a wireless device 16 for reducing uplink signaling overhead is provided. The wireless device 16 includes a memory module 65 configured to store a number of beams to be included in a multiple beam precoder codebook, the number of beams, N, being received from a network node 14. The wireless device 16 includes a beam power value déterminer module 21 configured to détermine N power values, each power value corresponding to one of the N beams. The wireless device 16 further includes a CSI report generator module 81 configured to include CSI in the CSI report, the CSI pertaining to one or more beams whose corresponding power value is above a predetermined power value.

In some embodiments, a method in a network node 14 for determining the size of a channel state information (CSI) report produced by a wireless device is provided. The method includes transmitting to the wireless device 16 configuration information with a first number of beams, N, S124. The method further includes receiving signaling from the wireless device 16 indicating at least one of: N power values, each power value corresponding to one of N beams, and a second number of beams, M’, whose corresponding power value is above the predetermined threshold S126. The method further includes receiving the CSI report containing CSI pertaining to one or more beams whose corresponding power value is above the predetermined power value S128. The method further includes determining the size of the CSI report produced by the wireless device S130. In some embodiments, each beam of the first number of beams (128) and second number of beams is a kth beam, d(k), that has associated a set of complex numbers and has index pair (i_k, m_k), each element of the set of complex numbers being characterized by at least one complex phase shift such that:

• d_n(k) = • d_n(k), and dfk) are the z^th and n^th éléments ofd(k), respectively;

• a_in is a real number corresponding to the z^th and z?^lh éléments of d(k);

• p and q are integers;

• beam directions A_lk and A_2k are real numbers corresponding to beams with index pair (i_k,m_k) that détermine the complex phase shifts εϊ^2πΔί·* and respectively; and • each of the at least a co-phasing coefficient between the first and second beam (S 130) is a complex number c_k for d(k) that is used to adjust the phase of the z^th element of d(k) according to c_kdi(k).

In some embodiments, the method further includes receiving the signaling in a first transmission including a medium access control, MAC, control element and receiving additional components of the CSI report in a second transmission on a physical uplink shared channel, PUSCH. In some embodiments, the method further includes receiving the signaling in a periodic report on a physical uplink control channel, PUCCH, and receiving additional components of the CSI report in a second transmission on a physical uplink shared channel, PUSCH. In some embodiments, the method further includes configuring the wireless device 16 with a higher layer parameter to specify in which subframes the signaling from the wireless device 16 is received. In some embodiments, the method further includes receiving the signaling in an aperiodic report on a physical uplink shared channel, PUSCH, and receiving additional components of the CSI report in a different report on the PUSCH. In some embodiments, the method further includes receiving the signaling on a physical uplink shared channel, PUSCH, that carries additional components of the CSI report. In some embodiments, the method further includes decoding the signaling followed by determining the size of the CSI report. In some embodiments, the first number of beams is signaled via radio resource control, RRC.

In some embodiments, a network node 14 configured to déterminé the size of a channel State information (CSI) report produced by a wireless device is provided. The network node 14 includes a memory 24 configured to store a predetermined power value. The network node 14 also includes a transceiver 28 configured to: transmit to the wireless device 16 configuration information with a first number of beams, N. The transceiver 28 is also configured to receive signaling from the wireless device 16 indicating at least one of: N power values, each power value corresponding to one of N beams; and a second number of beams, M’, whose corresponding power value is above the predetermined value. The transceiver 28 is also configured to receive the CSI report containing CSI pertaining to one or more beams whose corresponding power value is above the predetermined power value. The network node 14 also includes a processor 26 configured to détermine the size of the CSI report produced by the wireless device 16.

In some embodiments, the transceiver 28 is fùrther configured to receive the signaling in a first transmission including a medium access control, MAC, control element and receiving additional components of the CSI report in a second transmission on a physical uplink shared channel, PUSCH. In some embodiments, the transceiver 28 is also configured to receive the signaling in a periodic report on a physical uplink control channel, PUCCH, and receiving additional components of the CSI report in a second transmission on a physical uplink shared channel, PUSCH. In some embodiments, the network node 14 is further configured to configure the wireless device 16 with a higher layer parameter to specify in which subframes the signaling from the wireless device 16 is received. In some embodiments, the transceiver 28 is further configured to receive the signaling in an aperiodic report on a physical uplink shared channel, PUSCH, and receiving additional components of the CSI report in a different report on the PUSCH. In some embodiments, the transceiver 28 is further configured to receive the signaling on a physical uplink shared channel, PUSCH, that carries additional components of the CSI report. In some embodiments, the processor 26 is further configured to décodé the signaling followed by determining the size of the CSI report. In some embodiments, the first number of beams is signaled via radio resource control, RRC.

In some embodiments, a network node 14 configured to détermine the size of a channel State information, CSI, report produced by a wireless device 16 is provided. The network node 14 includes a memory module 25 configured to store a predetermined power value. The network node 14 further includes a transceiver module 29 configured to transmit to the wireless device 16 configuration information with a first number of beams, N. The transceiver module 29 is further configured to receive signaling from the wireless device 16 indicating at least one of: N power values, each power value corresponding to one of N beams, and a second number of beams, M’, whose corresponding power value is above the predetermined value. The transceiver module 29 is further configured to receive the CSI report containing CSI pertaining to one or more beams whose corresponding power value is above the predetermined power value. The network node 14 further includes a CSI report size déterminer module 45 configured to détermine the size of the CSI report produced by the wireless device 16.

In some embodiments, a method in a network node 12 of determining the size of a channel state information (CSI) report produced by a wireless device 16 is provided. The method includes configuring the wireless device 16 with a first number of beams, N, S124. The method further includes receiving signaling from the wireless device 16 indicating at least one of: N power values, each power value corresponding to one of N beams, and a second number of beams, M’, whose corresponding power value is above threshold S126. The method further includes receiving the CSI report from the wireless device, the CSI report containing CSI pertaining to one or more beams whose corresponding power value is above the predetermined threshold S128. The method further includes determining the size of the CSI report S130.

In some embodiments, a network node 14 of determining the size of a channel state information (CSI) report produced by a wireless device 16 is provided. The network node 14 includes processing circuitry 22 which may include a memory 24 and a processor 26. In some embodiments, the memory 24 is configured to store a first number of beams, N, and a second number of beams, M’. A transceiver 28 is configured to receive at least one of: N power values, each power value corresponding to one of N beams, and a second number of beams, M’, whose corresponding power value is above a predetermined value. The transceiver 28 is configured to receive the CSI report from the wireless device 16, the CSI report containing CSI pertaining to one or more beams whose corresponding power value is above the predetermined power value. The processor is configured to déterminé the size of the CSI report.

In some embodiments, a network node 14 configured to détermine the size of a channel state information (CSI) report produced by a wireless device 16 is provided. The network node 14 includes a memory module 25 configured to store a first number of beams N and a second number of beams, M’. The network node 14 further includes a transceiver module 29 configured to receive at least one of: N power values, each power value corresponding to one of N beams, and a second number of beams, M’, whose corresponding power value is above a predetermined value. The transceiver module 29 is also configured to receive the CSI report from the wireless device 16, the CSI report containing CSI pertaining to one or more beams whose corresponding power value is above the predetermined power value. The network node further includes a CSI report size déterminer module 45 configured to détermine the size of the CSI report.

In some embodiments, a method for determining at a network node 14 a number of beams to be used by a wireless device 16 when generating a multi-beam channel state information, CSI, report is provided. The method includes transmitting a plurality of distinct reference signais S132. The method also includes configuring the wireless device 16 to measure and report a received power to the network node for each of the distinct reference signais S134. The method fùrther includes determining the number of beams S136, and signaling the number of beams to the wireless device 16 S138.

In some embodiments, a network node 14 configured to détermine a number of beams to be used by a wireless device when generating a multi-beam channel state information, CSI, report is provided. The network node 14 includes processing circuitry 22 which may include a memory 24 and a processor 26. The memory 24 is configured to store CSI reports 30. The processor 26 is configured to cause transmission of a plurality of distinct reference signais. The processor 26 is also configured to configure the wireless device 16 to measure and report a received power to the network node 14 for each of the distinct reference signal. The processor 26 is also configured to détermine the number of beams. A transceiver 28 is configured to signal the number of beams to the wireless device.

In some embodiments, a network node 14 configured to détermine a number of beams to be used by a wireless device 16 when generating a multi-beam channel state information, CSI, report is provided. The network node 14 includes a memory module 25 configured to store CSI reports. The network node 16 includes a transmitter module 29 configured to transmit a plurality of distinct reference signais. A configuration déterminer module 49 is configured to configure the wireless device 16 to measure and report a received power to the network node 14 for each of the distinct reference signais. A beam number déterminer module 19 is configured to détermine the number of beams. The transceiver module 29 is configured to signal the number of beams to the wireless device.

In some embodiments, a method in a wireless device 16 for reducing uplink feedback overhead for a wireless device 16 operating in a sélective subband feedback mode is provided. The method includes determining a number of subbands to be fed back to a network node based on a system bandwidth and a number of beams to include in a multibeam precoder codebook SI 12. In some embodiments a size of a subband is a function of the number of beams.

In some embodiments, a wireless device 16 for operating in a sélective subband feedback mode is provided. The wireless device includes processing circuitry 62 which may include a memory 64 and a processor 66. The memory 64 is configured to store a number of subbands to be fed back to a network node 14. The processor 66 is configured to détermine the number of subbands to be fed back based on a system bandwidth and a number of beams to be included in a multi-beam precoder codebook. In some embodiments, a size of a subband is a function of the number of beams.

In some embodiments, a wireless device 16 for operating in a sélective subband feedback mode is provided. The wireless device includes a memory module 65 configured to store a number of subbands to be fed back to a network node. The method includes a subband déterminer module 85 configured to déterminé the number of subbands to be fed back based on a system bandwidth and a number of beams to be included in a multi-beam precoder codebook.

Some embodiments include:

Embodiment 1. A method of configuring a wireless device, the method comprising: transmitting to the wireless device at least one of:

a power threshold parameter to be used by the wireless device to détermine a number of beams to be included in a multi-beam precoder codebook; and a signal to interférence plus noise ratio, SINR, to be used by the wireless device to détermine to use one of a single beam precoder and a multiple beam precoder.

Embodiment 2. The method of Embodiment 1, wherein the at least one power threshold parameter is signaled via radio resource control, RRC, and is associated with a nonzero power channel State information reference signal, CSI-RS, identifier.

Embodiment 3. The method of Embodiment 1, wherein different power threshold parameters are applicable to different transmission ranks.

Embodiment 4. The method of Embodiment 1, wherein a power threshold parameter represents a power ratio with respect to a beam with a maximum received power.

Embodiment 5. The method of Embodiment 1, wherein the wireless device is configured by the network node to include only beams having a power component exceeding a threshold in a multi-beam precoder code book.

Embodiment 6. A network node configured to configure a wireless device, the network node comprising:

processing circuitry including a memory and a processor;

the memory configured to store power threshold parameters;

the processor configured to détermine a number of beams to be included in a multi-beam precoder codebook; and a transceiver configured to transmit to the wireless device at least one of: power threshold parameter to be used by the wireless device to détermine a number of beams to be included in a multi-beam precoder codebook; and a signal to interférence plus noise ratio, SINR, to be used by the wireless device to détermine to use one of a single beam precoder and a multiple beam precoder.

Embodiment 7. The network node of Embodiment 6, wherein the at least one power threshold parameter are signaled via radio resource control, RRC, and is associated with a non-zero power channel State information reference signal, CSI-RS, identifier.

Embodiment 8. The network node of Embodiment 6, wherein different power threshold parameters are applicable to different transmission ranks.

Embodiment 9. The network node of Embodiment 6, wherein a power threshold parameter represents a power ratio with respect to a beam with a maximum received power.

Embodiment 10. The network node of Embodiment 6, wherein the wireless device is configured by the network node to include only beams having a power component exceeding a threshold in a multi-beam precoder code book.

Embodiment 11. A method in a network node configured to détermine a number of beams to include in a multi-beam precoder codebook by a wireless device, the method including:

receiving from the wireless device the number of beams to be included in a multibeam precoder codebook; and determining an uplink, UL, control information payload size on the UL shared channel based on the number of beams.

Embodiment 12. The method of Embodiment 11, wherein the network node is configured to receive the number of beams in a first transmission including a medium access control, MAC, control element and to received additional CSI components in a second transmission on a physical uplink shared channel, PUSCH.

Embodiment 13. The method of Embodiment 11, wherein the network node is configured to receive the number of beams in a periodic report on a physical uplink control channel and to receive additional CSI components in a second transmission on a physical uplink shared channel, PUSCH.

Embodiment 14. The method of Embodiment 11, wherein the network node is further configured to semi-statically configure the wireless device with a higher layer parameter to specify in which subframes the wireless device reports the number of beams.

Embodiment 15. The method of Embodiment 11, wherein the network node is configured to receive the number of beams in an aperiodic report on a physical uplink shared channel, PUSCH, and to receive additional CSI components in a different report on the PUSCH.

Embodiment 16. A network node configured to configure a wireless device, the network node comprising:

processing circuitry including a memory and a processor;

the memory configured to store a number of beams to be included in a multibeam precoder codebook; and the processor configured to détermine an uplink, UL, shared channel payload size based on the number of beams on the UL shared channel; and a transceiver configured to receive the number of beams.

Embodiment 17. The network node of Embodiment 16, wherein the network node is configured to receive the number of beams in a first transmission including a medium access control, MAC, element and to received additional CSI components in a second transmission on a physical uplink shared channel, PUSCEL

Embodiment 18. The network node of Embodiment 16, wherein the network node is configured to receive the number of beams in a periodic report on a physical uplink control channel and to receive additional CSI components in a second transmission on a physical uplink shared channel, PUSCH.

Embodiment 19. The network node of Embodiment 16, wherein the network node is further configured to semi-statically configure the wireless device with a higher layer parameter to specify in which subframes the wireless device reports the number of beams.

Embodiment 20. The network node of Embodiment 16, wherein the network node is configured to receive the number of beams in an aperiodic report on a physical uplink shared channel, PUSCH, and to receive additional CSI components in a different report on the PUSCH.

Embodiment 21. A method for determining at a network node a number of beams to be used by a wireless device when generating a multi-beam channel state information, CSI, report, the method comprising:

transmitting a plurality of orthogonal beams on different reference signais;

détermine a configuration of the wireless device to measure and report a received power for each reference signal; and calculating a number of beams to be used by the wireless device when generating the multi-beam CSI report based on the power reports.

Embodiment 22. The method of Embodiment 21, wherein the network node calculâtes the number of beams by using measurements on a sounding reference signal transmitted by the wireless device on the uplink.

Embodiment 23. A network node configured to détermine a number of beams to be used by a wireless device when generating a multi-beam channel State information, CSI, report, the network node comprising:

processing circuitry including a memory and a processor:

the memory configured to store CSI reports;

the processor configured to:

détermine a configuration of the wireless device to measure and report a received power for each CSI reference signal; and calculate a number of beams to be used by the wireless device when generating the multi-beam CSI report based on the power reports.

Embodiment 24. The method of Embodiment 23, wherein the network node calculâtes the number of beams by using measurements on a sounding reference signal transmitted by the wireless device on the uplink.

Embodiment 25. A network node configured to détermine a number of beams to be used by a wireless device when generating a multi-beam channel state information, CSI, report, the network node comprising:

a memory module configured to store CSI reports;

a configuration module configured to détermine a configuration of the wireless device to measure and report a received power for each CSI reference signal;

a beam number déterminer module configured to calculate a number of beams to be used by the wireless devise when generating the multi-beam CSI report based on the power reports.

As will be appreciated by one of skill in the art, the concepts described herein may be embodied as a method, data processing system, and/or computer program product.

Accordingly, the concepts described herein may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects ail generally referred to herein as a “circuit” or “module.” Furthermore, the disclosure may take the form of a computer program product on a tangible computer usable storage medium having computer program code embodied in the medium that can be executed by a computer. Any suitable tangible computer readable medium may be utilized including hard disks, CD-ROMs, electronic storage devices, optical storage devices, or magnetic storage devices.

Abbreviations used in the preceding description include:

• ID	One dimensional
• 2D	Two-Dimensional
• 3GPP	Third Génération Partnership Project
• 5G	Fifth Génération
• ACK	Ackno wl edgement
• ASIC	Application Spécifie Integrated Circuit
• ARQ	Automatic Retransmission Request
• CA	Carrier Aggregation
• CB	Codebook
• CDMA	Code Division Multiple Access
• CFAI	CSI Feedback Accuracy Indicator
• CFI	Control Information Indicator
• CP	Cyclic Prefix
• CPU	Central Processing Unit
• CQI	Channel Quality Indicators
• CRS	Common Reference Symbol/Signal
• CSI	Channel State Information
• CSI-RS	Channel State Information Reference Symbol/Signal
• dB	Decibel

	• DCI	Downlink Control Information
	• DFT	Discrète Fourier Transform
	• DL	Downlink
	• eNB	Enhanced or Evolved Node B
5	• DP	Dual Polarization
	• EPC	Evolved Packet Core
	• EPDCCH	Enhanced Physical Downlink Control Channel
	• EPRE	Energy per Resource Element
	• E-UTRAN	Evolved or Enhanced Universal Terrestrial Radio Access Network
10	• FDD	Frequency Division Duplexing
	• FD-MIMO	Full Dimension ΜΙΜΟ
	• FFT	Fast Fourier Transform
	• FPGA	Field Programmable Gâte Array
	• GSM	Global System for Mobile Communications
15	• HARQ	Hybrid ARQ
	• ID	Identifier
	• IFFT	Inverse FFT
	• LSB	Least Significant Bit
	• LTE	Long Term Evolution
20	• M2M	Machine-to-Machine
	• MCS	Modulation and Coding Scheme (or State)
	• ΜΙΜΟ	Multiple Input Multiple Output
	• MME	Mobility Management Entity
	• MSB	Most Significant Bit
25	• MU-MIMO	Multi-User ΜΙΜΟ

	• NAK	Non-Acknowledgement
	• NZP	Non-Zero Power
	• OCC	Orthogonal Cover Code
	• OFDM	Orthogonal Frequency Division Multiplexing
5	• PCFICH	Physical Control Format Indicator Channel
	• PDA	Personal Data Assistance
	• PDCCH	Physical Downlink Control Channel
	• PDSCH	Physical Downlink Shared Channel
	• PRB	Physical Resource Block
10	• PMI	Precoder Matrix Indicator
	• PUCCH	Physical Uplink Control Channel
	• PUSCH	Physical Uplink Shared Channel
	• QPSK	Quadrature Phase Shift Keying
	• RB	Resource Block
15	• RE	Resource Element
	• Rel	Release
	• RI	Rank Indicator
	• RRC	Radio Resource Control
	• SINR	Signal to Interférence plus Noise Ratio
20	• SNR	Signal to Noise Ratio
	• SP	Single Polarization
	• SR	Scheduling Request
	• SU-MIMO	Single User ΜΙΜΟ
	• TDD	Time Division Duplexing
25	• TFRE	Time/Frequency Resource Element
	• TP	Transmission Point

• TS Technical Spécification • Tx Transmit • UCI Uplink Control Information • UE User Equipment • UL Uplink • ULA Uniform Linear Array • UMB Ultra Mobile Broadband • UPA Uniform Planar Array • WCDMA Wideband Code Division Multiple Access • ZP Zéro Power.

Some embodiments are described herein with reference to flowchart illustrations and/or block diagrams of methods, Systems and computer program products. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer (to thereby create a spécial purpose computer), spécial purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computer readable memory or storage medium that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer readable memory produce an article of manufacture including instruction means which implement the function/act specified in the flowchart and/or block diagram block or blocks.

The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a sériés of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

It is to be understood that the functions/acts noted in the blocks may occur out of the order noted in the operational illustrations. For example, two blocks shown in succession may in fact be executed substantially concurrently or the blocks may sometimes be executed in the reverse order, depending upon the functionality/acts involved. Although some of the diagrams include arrows on communication paths to show a primary direction of communication, it is to be understood that communication may occur in the opposite direction to the depicted arrows.

Computer program code for carrying out operations of the concepts described herein may be written in an object oriented programming language such as Java® or C++. However, the computer program code for carrying out operations of the disclosure may also be written in conventional procédural programming languages, such as the C programming language. The program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer. In the latter scénario, the remote computer may be connected to the user's computer through a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider).

Many different embodiments hâve been disclosed herein, in connection with the above description and the drawings. It will be understood that it would be unduly repetitious and obfuscating to literally describe and illustrate every combination and subcombination of these embodiments. Accordingly, ail embodiments can be combined in any way and/or combination, and the présent spécification, including the drawings, shall be construed to constitute a complété written description of ail combinations and subcombinations of the embodiments described herein, and of the manner and process of making and using them, and shall support claims to any such combination or subcombination.

It will be appreciated by persons skilled in the art that the embodiments described herein are not limited to what has been particularly shown and described herein above. In addition, unless mention was made above to the contrary, it should be noted that ail of the accompanying drawings are not to scale. A variety of modifications and variations are possible in light of the above teachings without departing from the scope of the following claims.

Claims (79)

1. A method for a wireless device to adjust uplink signaling overhead, the method comprising:

receiving signaling that configures the wireless device with a first number of beams, N;

determining N power values, each power value corresponding to one of the N beams; and including channel state information, CSI, in a CSI report, the CSI pertaining to one or more beams whose corresponding power value is above a predetermined power value Jhe CSI including a relative beam power indication for each one of the N beams and a set of cophasing factors for each beam and for each sub band.

2. The method of Claim 1, further comprising determining whether the number of beams, N, is equal to one or greater than one using a signal to interférence plus noise ratio, SINR.

3. The method of any of Claims 1 and 2, further comprising:

transmitting signaling by the wireless device indicating at least one of:

N power values, each power value corresponding to one of the N beams, and a second number of beams, M’, whose corresponding power value is above a predetermined value.

4. The method of any of Claims 1-3, wherein the first number of beams is signaled via radio resource control, RRC.

5. The method of any of Claims 1-4, wherein the predetermined power value represents a power ratio with respect to a beam with a maximum received power.

6. The method of Claim 3, wherein a signal to interférence plus noise ratio, SINR, is additionally used by the wireless device to détermine whether the second number of beams is equal to one or greater than one.

7. The method of Claims 1-6, wherein each beam of the first number of beams and second number of beams is a kth beam, d(k), that has associated a set of complex numbers and has index pair (l_k, m_k), each element of the set of complex numbers being characterized by at least one complex phase shift such that:

• d_n(k) = άι(^α_ίιη6^^2π^^Δ^^Δ2^· • d_n(kf and dfk) are the z^th and n^th éléments ofd(k), respectively;

• ai _n is a real number corresponding to the z^th and n^th éléments of d(k);

• p and q are integers;

• beam directions A_{l k} and zl_2;k are real numbers corresponding to beams with index pair (l_k,m_k) that détermine the complex phase shifts e^j2n2il'^k and ^²⁷¹^ respectively; and • each of the at least a co-phasing coefficient between the first and second beam (S130) is a complex number c_k for d(k) that is used to adjust the phase of the z^th element of d(k) according to c_kdi(k~).

8. A wireless device configured to adjust uplink signaling overhead, the wireless device comprising:

processing circuitry configured to store a first number of beams, N, to be included in a multiple beam precoder codebook, the first number of beams, N, being received from a network node; and and further configured to perform at least one of:

determining N power values, each power value corresponding to one of the N beams; and including CSI in a CSI report, the CSI pertaining to one or more beams whose corresponding power value is above a predetermined power value, the CSI including a relative beam power indication for each one of the N beams and a set of co-phasing factors for each beam and for each sub band.

9. The wireless device of Claim 8 wherein the processor is further configured to détermine whether the first number of beams is equal to one or greater than one using an SINR.

10. The wireless device of any of Claims 8 and 9, further comprising: transmitting signaling by the wireless device indicating at least one of:

N power values, each power value corresponding to one of the N beams; and a second number of beams, M', whose corresponding power value is above a predetermined value.

11. The wireless device of any of Claims 8-10, wherein the first number of beams is signaled via radio resource control, RRC.

12. The wireless device of any of Claims 8-11, wherein the predetermined power value represents a power ratio with respect to a beam with a maximum received power.

13. The wireless device of Claim 10, wherein a signal to interférence plus noise ratio, SINR, is additionally used by the wireless device to détermine whether the second number of beams, M’, is equal to one or greater than one.

14. The wireless device of Claims 8-13, wherein each beam of the first number of beams and second number of beams is a kth beam, d(k), that has associated a set of complex numbers and has index pair (l_k, m_k), each element of the set of complex numbers being characterized by at least one complex phase shift such that:

• d_n(k) = d^a^ei²⁷¹^^ • d_n(kf and d^k) are the z^th and /7^th éléments ofd(k), respectively;

• a_in is a real number corresponding to the z^th and n^th éléments of d(k);

• p and q are integers;

• beam directions A_lk and d₂,k ^are real numbers corresponding to beams with index pair that détermine the complex phase shifts εί²⁷¹^ and ej²⁷¹^* respectively; and • each of the at least a co-phasing coefficient between the first and second beam is a complex number c_k for d(k~) that is used to adjust the phase of the z^th element of d(k) according to c_kdi(k).

15. A wireless device configured to adjust uplink signaling overhead, the wireless device comprising:

a memory module configured to store a number of beams to be included in a multiple beam precoder codebook, the number of beams, N, being received from a network node ; and a beam power value déterminer module configured to détermine N power values, each power value corresponding to one of the N beams; and a CSI report generator module configured to include CSI in a CSI report, the CSI pertaining to one or more beams whose corresponding power value is above a predetermined power value, the CSI including a relative beam power indication for each one of the N beams and a set of co-phasing factors for each beam and for each sub band.

16. A method for a network node to déterminé a size of a channel state information (CSI) report produced by a wireless device, the method comprising:

transmitting to the wireless device, configuration information with a first number of beams, N;

receiving signaling from the wireless device indicating at least one of:

N power values, each power value corresponding to one of N beams; and a second number of beams, M’, whose corresponding power value is above a predetermined power value, and receiving the CSI report containing CSI pertaining to one or more beams whose corresponding power value is above the predetermined power value, the CSI including a relative beam power indication for each one of the N beams and a set of co-phasing factors for each beam and for each sub band; and determining the size of the CSI report produced by the wireless device.

17. The method of Claim 16, further comprising receiving the signaling in a first transmission including a medium access control, MAC, control element and receiving additional components of the CSI report in a second transmission on a physical uplink shared channel, PUSCH.

18. The method of any of Claims 16 and 17, further comprising receiving the signaling in a periodic report on a physical uplink control channel, PUCCH, and receiving additional components of the CSI report in a second transmission on a physical uplink shared channel, PUSCH.

19. The method of any of Claims 16-18, further comprising configuring the wireless device with a higher layer parameter to specify in which subframes the signaling from the wireless device is received.

20. The method of any of Claims 16-19, further comprising receiving the signaling in an aperiodic report on a physical uplink shared channel, PUSCH, and receiving additional components of the CSI report in a different report on the PUSCH.

21. The method of any of Claims 16-20, further comprising receiving the signaling on a physical uplink shared channel, PUSCH, that carries additional components of the CSI report.

22. The method of any of Claims 16-21, further comprising decoding the signaling followed by determining the size of the CSI report.

23. The method of any of Claims 16-22, wherein the first number of beams is signaled via radio resource control, RRC.

24. A network node configured to détermine a size of a channel state information (CSI) report produced by a wireless device, the network node comprising:

a memory configured to store a predetermined power value;

a transceiver configured to:

transmit to the wireless device configuration information with a first number of beams, N;

receive signaling from the wireless device indicating at least one of:

N power values, each power value corresponding to one of N beams; and a second number of beams, M’, whose corresponding power value is above the predetermined power value; and receive the CSI report containing CSI pertaining to one or more beams whose corresponding power value is above the predetermined power value, the CSI including a relative beam power indication for each one of the N beams and a set of co-phasing factors for each beam and for each sub band; and a processing circuitry configured to détermine the size of the CSI report produced by the wireless device.

25. The network node of Claim 24, wherein the transceiver is further configured to receive the signaling in a first transmission including a medium access control, MAC, control element and receiving additional components ofthe CSI report in a second transmission on a physical uplink shared channel, PUSCH.

26. The network node of any of Claims 24 and 25, wherein the transceiver is further configured to receive the signaling in a periodic report on a physical uplink control channel, PUCCH, and receiving additional components of the CSI report in a second transmission on a physical uplink shared channel, PUSCH.

27. The network node of any of Claims 24-26, wherein the processor is further configured to configure the wireless device with a higher layer parameter to specify in which subframes the signaling from the wireless device is received.

28. The network node of any of Claims 24-27, wherein the transceiver is further configured to receive the signaling in an aperiodic report on a physical uplink shared channel, PUSCH, and receiving additional components of the CSI report in a different report on the PUSCH.

29. The network node of any of Claims 24-28, wherein the transceiver is further configured to receive the signaling on a physical uplink shared channel, PUSCH, that carries additional components of the CSI report.

30. The network node of any of Claims 24-29, wherein the processor is further configured to décodé the signaling foliowed by determining the size of the CSI report.

31. The network node of any of Claims 24-30, wherein the first number of beams is signaled via radio resource control, RRC.

32. A network node configured to détermine a size of a channel State information, CSI, report produced by a wireless device, the network node comprising:

a memory module configured to store a predetermined power value;

a transceiver module configured to:

transmit to the wireless device configuration information with a first number of beams, N;

receive signaling from the wireless device indicating at least one of:

N power values, each power value corresponding to one of N beams; and a second number of beams, M’, whose corresponding power value is above the predetermined value; and receive the CSI report containing CSI pertaining to one or more beams whose corresponding power value is above the predetermined power value, the CSI including a relative beam power indication for each one of the N beams and a set of co-phasing factors for each beam and for each sub band; and a CSI report size detenniner module configured to détermine a size of the CSI report produced by the wireless device.

33. A method for a network node to détermine a size of a channel state information (CSI) report produced by a wireless device, the method comprising: configuring the wireless device with a first number of beams, N;

receiving signaling from the wireless device indicating at least one of:

N power values, each power value corresponding to one of N beams; and a second number of beams, M’, whose corresponding power value is above a predetermined power value; and receiving the CSI report from the wireless device, the CSI report containing CSI pertaining to one or more beams whose corresponding power value is above the predetermined power value, the CSI including a relative beam power indication for each one of the N beams and a set of co-phasing factors for each beam and for each sub band; and determining the size of the CSI report.

34. A network node configured to déterminé a size of a channel state information (CSI) report produced by a wireless device, the network node comprising:

processing circuitry configured to store a first number of beams, N, and a second number of beams, M’·, and a transceiver configured to receive at least one of:

N power values, each power value corresponding to one of N beams; and a second number of beams, M’, whose corresponding power value is above a predetermined power value; and the transceiver configured to receive the CSI report from the wireless device, the CSI report containing CSI pertaining to one or more beams whose corresponding power value is above the predetermined power value, the CSI including a relative beam power indication for each one of the N beams and a set of co-phasing factors for each beam and for each sub band; and the processing circuitry configured to détermine the size of the CSI report.

35. A network node configured to détermine a size of a channel State information (CSI) report produced by a wireless device, the network node comprising:

a memory module configured to store a first number of beams N and a second number of beams, M’; and a transceiver module configured to receive at least one of:

N power values, each power value corresponding to one of N beams; and a second number of beams, M’, whose corresponding power value is above a predetermined power value; and the transceiver module configured to receive the CSI report from the wireless device, the CSI report containing CSI pertaining to one or more beams whose corresponding power value is above the predetermined power value, the CSI including a relative beam power indication for each one of the N beams and a set of co-phasing factors for each beam and for each sub band; and a CSI report size déterminer module configured to détermine a size of the CSI report.

36. A method for determining at a network node a number of beams to be used by a wireless device when generating a multi-beam channel State information, CSI, report, the method comprising:

transmitting a plurality of distinct reference signais;

configuring the wireless device to measure and report a received power to the network node for each of the distinct reference signais;

determining the number of beams N; and signaling the number of beams N to the wireless device; and receiving a CSI report containing CSI, the CSI including a relative beam power for each one ofthe N beams and a set of co-phasing factors for each beam and for each sub band.

37. A network node configured to détermine a number N of beams to be used by a wireless device when generating a multi-beam channel state information, CSI, report, the network node comprising:

processing circuitry configured to:

store CSI reports;

cause transmission of a plurality of distinct reference signais;

configure the wireless device to measure and report a received power to the network node for each of the distinct reference signal;

détermine the number of beams N; and signal the number of beams N to the wireless device; and receiving a CSI report containing CSI, the CSI including a relative beam power for each one of the N beams and a set of co-phasing factors for each beam and for each sub band.

38. A network node configured to détermine a number N of beams to be used by a wireless device when generating a multi-beam channel state information, CSI, report, the network node comprising:

a memory module configured to store CSI reports, the CSI reports containing CSI, the CSI including a relative beam power for each one of the N beams and a set of co-phasing factors for each beam and for each sub band;

a transmitter module configured to transmit a plurality of distinct reference signais;

a configuration déterminer module configured to configure the wireless device to measure and report a received power to the network node for each of the distinct reference signais;

a beam number déterminer module configured to détermine the number of beams N; and the transmitter module configured to signal the number of beams N to the wireless device.

39. A method for a user equipment to adjust uplink signaling overhead, the method comprising:

receiving signaling that configures the user equipment with a first number of beams, N;

determining N power values, each power value corresponding to one of the N beams; and including channel State information, CSI, in a CSI report, the CSI pertaining to one or more beams whose corresponding power value is above a predetermined power value,_the CSI including a relative beam power for each one of the N beams and a set of co-phasing factors for each beam and for each sub b and.

40. The method of Claim 39, further comprising determining whether the number of beams, N, is equal to one or greater than one using a signal to interférence plus noise ratio, SINR.

41. The method of any of Claims 39 and 40, further comprising:

transmitting signaling by the user equipment indicating at least one of:

N power values, each power value corresponding to one of the N beams, and a second number of beams, M’, whose corresponding power value is above a predetermined value.

42. The method of any of Claims 39-41, wherein the first number of beams is signaled via radio resource control, RRC.

43. The method of any of Claims 39-42, wherein the predetermined power value represents a power ratio with respect to a beam with a maximum received power.

44. The method of Claim 41, wherein a signal to interférence plus noise ratio, SINR, is additionally used by the user equipment to détermine whether the second number of beams is equal to one or greater than one.

45. The method of Claim 39-44, wherein each beam of the first number of beams and second number of beams is a kth beam, d(k), that has associated a set of complex numbers and has index pair (l_k, m_k), each element of the set of complex numbers being characterized by at least one complex phase shift such that:

. d_n(k) = • d_n(k), and d^k) are the z^th and n^th éléments ofd{k), respectively;

• a_in is a real number corresponding to the z^th and n^th éléments of d(k);

• p and q are integers;

• beam directions Δ_{1 k} and A_2k are real numbers corresponding to beams with index pair (7_k,m_k) that détermine the complex phase shifts e^j27Tûl'^k and e^j2nA2’^k respectively; and • each of the at least a co-phasing coefficient between the first and second beam is a complex number c_k for d(k) that is used to adjust the phase of the z^th element of d(k) according to c_kdi(ky

46. A user equipment configured to adjust uplink signaling overhead, the user equipment comprising:

processing circuitry configured to store a first number of beams, N, to be included in a multiple beam precoder codebook, the first number of beams, N, being received from a base station; and and further configured to perform at least one of:

determining N power values, each power value corresponding to one of the N beams; and including CSI in a CSI report, the CSI pertaining to one or more beams whose corresponding power value is above a predetermined power value, the CSI including a relative beam power for each one of the N beams and a set of co-phasing factors for each beam and for each sub band.

47. The user equipment of Claim 46, wherein the processor is further configured to détermine whether the first number of beams is equal to one or greater than one using an SINR.

48. The user equipment of any of Claims 46 and 47, further comprising: transmitting signaling by the user equipment indicating at least one of:

N power values, each power value corresponding to one of the N beams; and a second number of beams, M’, whose corresponding power value is above a predetermined value.

49. The user equipment of any of Claims 46-48, wherein the first number of beams is signaled via radio resource control, RRC.

50. The user equipment of any of Claims 46-49, wherein the predetermined power value represents a power ratio with respect to a beam with a maximum received power.

51. The user equipment of Claim 48, wherein a signal to interférence plus noise ratio, SINR, is additionally used by the user equipment to détermine whether the second number of beams, M’, is equal to one or greater than one.

52. The user equipment of Claim 46, wherein each beam of the first number of beams and second number of beams is a kth beam, d(k), that has associated a set of complex numbers and has index pair (l_k, m_k), each element of the set of complex numbers being characterized by at least one complex phase shift such that:

• d_n(k) = dfk^a^e^^MQMk).

• d_n(k), and dfk) are the z^th and n^th éléments ofdÇk), respectively;

• a_in is a real number corresponding to the z^th and «^th éléments of d(k);

• p and q are integers;

• beam directions 4_{l k} and â_2k are real numbers corresponding to beams with index pair (Ιι^,τη^ that détermine the complex phase shifts e^^2lTAi-^k and ei^{2jlA2 k} respectively; and • each of the at least a co-phasing coefficient between the first and second beam is a complex number c_k for d(k) that is used to adjust the phase of the z^th element of d(k) according to c_kdi(k).

53. A user equipment configured to adjust uplink signaling overhead, the user equipment comprising:

a memory module configured to store a number of beams to be included in a multiple beam precoder codebook, the number of beams, N, being received from a base station; and a beam power value déterminer module configured to détermine N power values, each power value corresponding to one of the N beams; and a CSI report generator module configured to include CSI in a CSI report, the CSI pertaining to one or more beams whose corresponding power value is above a predetermined power value, the CSI including a relative beam power for each one of the N beams and a set of co-phasing factors for each beam and for each sub band.

54. A method for a base station to détermine a size of a channel State information (CSI) report produced by a user equipment, the method comprising:

transmitting to the user equipment, configuration information with a first number of beams, N;

receiving signaling from the user equipment indicating at least one of:

N power values, each power value corresponding to one of N beams; and a second number of beams, M’, whose corresponding power value is above a predetermined power value, and receiving the CSI report containing CSI pertaining to one or more beams whose corresponding power value is above the predetermined power value, the CSI including a relative beam power for each one of the N beams and a set of co-phasing factors for each beam and for each sub band; and determining the size of the CSI report produced by the user equipment.

55. The method of Claim 54, further comprising receiving the signaling in a first transmission including a medium access control, MAC, control element and receiving additional components of the CSI report in a second transmission on a physical uplink shared channel, PUSCH.

56. The method of any of Claims 54 and 55, further comprising receiving the signaling in a periodic report on a physical uplink control channel, PUCCH, and receiving additional components of the CSI report in a second transmission on a physical uplink shared channel, PUSCH.

57. The method of any of Claims 54 and 56, further comprising configuring the user equipment with a higher layer parameter to specify in which subframes the signaling from the user equipment is received.

58. The method of any of Claims 54-57, further comprising receiving the signaling in an aperiodic report on a physical uplink shared channel, PUSCH, and receiving additional components of the CSI report in a different report on the PUSCH.

59. The method of any of Claims 54-58, further comprising receiving the signaling on a physical uplink shared channel, PUSCH, that carries additional components of the CSI report.

60. The method of any of Claims 54-59, further comprising decoding the signaling followed by determining the size of the CSI report.

61. The method of any of Claims 54-60, wherein the first number of beams is signaled via radio resource control, RRC.

62. A base station configured to détermine a size of a channel state information (CSI) report produced by a user equipment, the base station comprising:

a memory configured to store a predetermined power value;

a transceiver configured to:

transmit to the user equipment configuration information with a first number of beams, N;

receive signaling from the user equipment indicating at least one of:

N power values, each power value corresponding to one of N beams; and a second number of beams, M’, whose corresponding power value is above the predetermined power value; and receive the CSI report containing CSI pertaining to one or more beams whose corresponding power value is above the predetermined power value, the CSI including a relative beam power for each one of the N beams and a set of co-phasing factors for each beam and for each sub band; and a processing circuitry configured to détermine the size of the CSI report produced by the user equipment.

63. The base station of Claim 63, wherein the transceiver is further configured to receive the signaling in a first transmission including a medium access control, MAC, control element and receiving additional components of the CSI report in a second transmission on a physical uplink shared channel, PUSCH.

64. The base station of any of Claims 62 and 63, wherein the transceiver is further configured to receive the signaling in a periodic report on a physical uplink control channel, PUCCH, and receiving additional components of the CSI report in a second transmission on a physical uplink shared channel, PUSCH.

65. The base station (14) of any of Claims 62-64, wherein the processor is further configured to configure the user equipment with a higher layer parameter to specify in which subframes the signaling from the user equipment is received.

66. The base station of any of Claims 62-65, wherein the transceiver is further configured to receive the signaling in an aperiodic report on a physical uplink shared channel, PUSCH, and receiving additional components of the CSI report in a different report on the PUSCH.

67. The base station of any of Claims 62-66, wherein the transceiver is further configured to receive the signaling on a physical uplink shared channel, PUSCH, that carries additional components of the CSI report.

68. The base station of any of Claims 62-67, wherein the processor is further configured to décodé the signaling followed by determining the size of the CSI report.

69. The base station of any of Claims 62-69, wherein the first number of beams is signaled via radio resource control, RRC.

70. A base station configured to détermine a size of a channel State information, CSI, report produced by a user equipment, the base station comprising:

a memory module configured to store a predetermined power value;

a transceiver module configured to:

transmit to the user equipment configuration information with a first number of beams, N;

receive signaling from the user equipment indicating at least one of:

N power values, each power value corresponding to one of N beams; and a second number of beams, M', whose corresponding power value is above the predetermined value; and receive the CSI report containing CSI pertaining to one or more beams whose corresponding power value is above the predetermined power value, the CSI including a relative beam power for each one of the N beams and a set of co-phasing factors for each beam and for each sub b and; and a CSI report size déterminer module configured to détermine a size of the CSI report produced by the user equipment.

71. A method for a base station to détermine a size of a channel state information (CSI) report produced by a user equipment, the method comprising:

configuring the user equipment with a first number of beams, N;

receiving signaling from the user equipment indicating at least one of:

N power values, each power value corresponding to one of N beams; and a second number of beams, M’, whose corresponding power value is above a predetermined power value; and receiving the CSI report from the user equipment, the CSI report containing CSI pertaining to one or more beams whose corresponding power value is above the predetermined power value, the CSI including a relative beam power for each one of the N beams and a set of co-phasing factors for each beam and for each sub band; and determining the size of the CSI report.

72. A base station configured to détermine a size of a channel state information (CSI) report produced by a user equipment, the base station comprising:

processing circuitry configured to store a first number of beams, N, and a second number of beams, M', and a transceiver configured to receive at least one of:

N power values, each power value corresponding to one of N beams; and a second number of beams, M', whose corresponding power value is above a predetermined power value; and the transceiver configured to receive the CSI report from the user equipment, the CSI report containing CSI pertaining to one or more beams whose corresponding power value is above the predetermined power value, the CSI including a relative beam power for each one ofthe N beams and a set of co-phasing factors for each beam and for each sub band; and the processing circuitry configured to détermine the size of the CSI report.

73. A base station configured to déterminé a size of a channel State information (CSI) report produced by a user equipment, the base station comprising:

a memory module configured to store a first number of beams N and a second number of beams, M’; and a transceiver module configured to receive at least one of:

N power values, each power value corresponding to one of N beams; and a second number of beams, M’, whose corresponding power value is above a predetermined power value; and the transceiver module configured to receive the CSI report from the user equipment, the CSI report containing CSI pertaining to one or more beams whose corresponding power value is above the predetermined power value, the CSI including a relative beam power for each one of the N beams and a set of co-phasing factors for each beam and for each sub band; and a CSI report size déterminer module configured to détermine a size of the CSI report.

74. A method for determining at a base station a number of beams N to be used by a user equipment when generating a multi-beam channel State information, CSI, report, the method comprising:

transmitting a plurality of distinct reference signais;

configuring the user equipment to measure and report a received power to the base station for each of the distinct reference signais;

determining the number of beams N; and signaling the number of beams N to the user equipment: and receiving a CSI report having CSI, the CSI including a relative beam power for each one ofthe N beams and a set of co-phasing factors for each beam and for each sub band.

75. A base station configured to détermine a number of beams N to be used by a user equipment when generating a multi-beam channel state information, CSI, report, the base station comprising:

processing circuitry configured to:

store CSI reports, the CSI reports containing CSI, the CSI including a relative beam power for each one of the N beams and a set of co-phasing factors for each beam and for each sub band;

cause transmission of a plurality of distinct reference signais;

configure the user equipment to measure and report a received power to the base station for each of the distinct reference signal;

détermine the number of beams N; and.

signal the number of beams N to the user equipment.

76. A base station configured to détermine a number of beams N to be used by a user equipment when generating a multi-beam channel state information, CSI, report, the base station comprising:

a memory module configured to store CSI reports, the CSI reports containing CSI, the CSI including a relative beam power for each one of the N beams and a set of co-phasing factors for each beam and for each sub band;

a transmitter module configured to transmit a plurality of distinct reference signais;

a configuration déterminer module configured to configure the user equipment to measure and report a received power to the base station for each of the distinct reference signais;

a beam number déterminer module configured to détermine the number of beams N; and the transmitter module configured to signal the number of beams N to the user equipment.

77. The method of any of Claims 1, wherein a number of sub bands is a function of system bandwidth and a number of beams included in a multi-beam precoder codebook.

78. The method of any of Claims 1 and 77, wherein a number of bits of the CSI

5 for reporting the co-phasing factors is given by N_sub(2K_DP — 1) · log₂ M, where N_sllb is the number of sub bands, Kd_p is a number of beams and Af is a number of bits used to represent a co-phasing factor.

79. The method of any of Claims 1, 77 and 78, wherein the CSI also includes for 10 each beam, a beam identification and a beam rotation.