WO2017171789A1

WO2017171789A1 - Open loop transmission scheme supporting arbitrary number of antenna ports

Info

Publication number: WO2017171789A1
Application number: PCT/US2016/025227
Authority: WO
Inventors: Xiaoyi Wang; Frederick Vook; Eugene Visotsky
Original assignee: Nokia Solutions And Networks Oy
Priority date: 2016-03-31
Filing date: 2016-03-31
Publication date: 2017-10-05

Abstract

A technique may include determining a number of antenna ports to be used for data transmission, generating a pseudo-random precoder vector including 2^M precoder vector elements, where M is an integer, 2^M is greater than the number of antenna ports to be used for data transmission and 2^M-1 is less than the number of antenna ports to be used for data transmission, pseudo-randomly puncturing one or more of the 2^Mprecoder vector elements such that a number of non-punctured precoder vector elements of the pseudo-random precoder vector matches the number of antenna ports to be used for data transmission, applying each of the non- punctured precoder vector elements of the pseudo-random precoder vector to one of the antenna ports, and transmitting data via the antenna ports and the applied non-punctured precoder vector elements.

Description

Open Loop Transmission Scheme Supporting Arbitrary Number of Antenna Ports

Inventors:

Xiaoyi Wang

Frederick Vook

Eugene Visotsky

TECHNICAL FIELD

[0001 ] This description relates to communications.

BACKGROUND

[0002] A communication system may be a facility that enables communication between two or more nodes or devices, such as fixed or mobile communication devices. Signals can be carried on wired or wireless carriers.

[0003] An example of a cellular communication system is an architecture that is being standardized by the 3^rd Generation Partnership Project (3GPP). A recent development in this field is often referred to as the long-term evolution (LTE) of the Universal Mobile

Telecommunications System (UMTS) radio-access technology. E-UTRA (evolved UMTS Terrestrial Radio Access) is the air interface of 3GPP's Long Term Evolution (LTE) upgrade path for mobile networks. In LTE, base stations or access points (APs), which are referred to as enhanced Node AP (eNBs), provide wireless access within a coverage area or cell. In LTE, mobile devices, or mobile stations are referred to as user equipments (UE). LTE has included a number of improvements or developments.

[0004] A global bandwidth shortage facing wireless carriers has motivated the consideration of the underutilized millimeter wave (mmWave) frequency spectrum for future broadband cellular communication networks, for example. mmWave (or extremely high frequency) may, for example, include the frequency range between 30 and 300 gigahertz (GHz). Radio waves in this band may, for example, have wavelengths from ten to one millimeters, giving it the name millimeter band or millimeter wave. The amount of wireless data will likely significantly increase in the coming years. Various techniques have been used in attempt to address this challenge including obtaining more spectrum, having smaller cell sizes, and using improved technologies enabling more bits/s/Hz. One element that may be used to obtain more spectrum is to move to higher frequencies, above 6 GHz. For fifth generation wireless systems (5G), an access architecture for deployment of cellular radio equipment employing mmWave radio spectrum has been proposed. Other example spectrums may also be used, such as cmWave radio spectrum (3-30 GHz).

SUMMARY

[0005] According to an example implementation, a method is provided for determining a pseudo-random precoder vector for an arbitrary number of antenna ports, the method including: determining a number of antenna ports to be used for data transmission; generating a pseudorandom precoder vector including 2^M precoder vector elements, where M is an integer, 2^M is greater than the number of antenna ports to be used for data transmission and 2^M_1 is less than the number of antenna ports to be used for data transmission; pseudo-randomly puncturing one or more of the 2^M precoder vector elements such that a number of non-punctured precoder vector elements of the pseudo-random precoder vector matches the number of antenna ports to be used for data transmission; applying each of the non-punctured precoder vector elements of the pseudo-random precoder vector to one of the antenna ports; and transmitting data via the antenna ports and the applied non-punctured precoder vector elements.

[0006] According to another example implementation, an apparatus may include at least one processor and at least one memory including computer instructions, when executed by the at least one processor, cause the apparatus to: determine a number of antenna ports to be used for data transmission; generate a pseudo-random precoder vector including 2^M precoder vector elements, where M is an integer, 2^M is greater than the number of antenna ports to be used for data transmission and 2^M_1 is less than the number of antenna ports to be used for data transmission; pseudo-randomly puncture one or more of the 2^M precoder vector elements such that a number of non-punctured precoder vector elements of the pseudo-random precoder vector matches the number of antenna ports to be used for data transmission; apply each of the non- punctured precoder vector elements of the pseudo-random precoder vector to one of the antenna ports; and transmit data via the antenna ports and the applied non-punctured precoder vector elements.

[0007] According to another example implementation, a computer program product may include a computer-readable storage medium and storing executable code that, when executed by at least one data processing apparatus, is configured to cause the at least one data processing apparatus to perform a method including: determining a number of antenna ports to be used for data transmission; generating a pseudo-random precoder vector including 2^M precoder vector elements, where M is an integer, 2^M is greater than the number of antenna ports to be used for data transmission and 2^M_1 is less than the number of antenna ports to be used for data transmission; pseudo-randomly puncturing one or more of the 2^M precoder vector elements such that a number of non-punctured precoder vector elements of the pseudo-random precoder vector matches the number of antenna ports to be used for data transmission; applying each of the non- punctured precoder vector elements of the pseudo-random precoder vector to one of the antenna ports; and transmitting data via the antenna ports and the applied non-punctured precoder vector elements.

[0008] According to another example implementation, an apparatus may include means for determining a number of antenna ports to be used for data transmission; means for generating a pseudo-random precoder vector including 2^M precoder vector elements, where M is an integer, 2^M is greater than the number of antenna ports to be used for data transmission and 2^M_1 is less than the number of antenna ports to be used for data transmission; means for pseudo-randomly puncturing one or more of the 2^M precoder vector elements such that a number of non-punctured precoder vector elements of the pseudo-random precoder vector matches the number of antenna ports to be used for data transmission; means for applying each of the non-punctured precoder vector elements of the pseudo-random precoder vector to one of the antenna ports; and means for transmitting data via the antenna ports and the applied non-punctured precoder vector elements.

[0009] The details of one or more examples of implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 is a block diagram of a wireless network according to an example implementation.

[0011 ] FIG. 2 is a diagram of a wireless transceiver according to an example

implementation.

[0012] FIG. 3 is a diagram illustrating a radio system architecture according to an illustrative example implementation.

[0013] FIG. 4 a flow chart illustrating operation of a base station according to an example implementation.

[0014] FIG. 5 is a block diagram of a wireless station (e.g., base station/access point or mobile station/user device) according to an example implementation.

DETAILED DESCRIPTION

[0015] FIG. 1 is a block diagram of a wireless network 130 according to an example implementation. In the wireless network 130 of FIG. 1, user devices 131, 132, 133 and 135, which may also be referred to as mobile stations (MSs) or user equipment (UEs), may be connected (and in communication) with a base station (BS), , which may also be referred to as an access point (AP) or an enhanced Node B (eNB). At least part of the functionalities of an access point (AP), base station (BS) or (e)Node B (eNB) may be also be carried out by any node, server or host which may be operably coupled to a transceiver, such as a remote radio head. BS 134 provides wireless coverage within a cell 136, including to user devices 131, 132, 133 and 135. Although only four user devices are shown as being connected or attached to BS 134, any number of user devices may be provided. BS 134 is also connected to a core network 150 via a SI interface 151. This is merely one simple example of a wireless network, and others may be used.

[0016] A user device (user terminal, user equipment (UE)) may refer to a portable computing device that includes wireless mobile communication devices operating with or without a subscriber identification module (SIM), including, but not limited to, the following types of devices: a mobile station (MS), a mobile phone, a cell phone, a smartphone, a personal digital assistant (PDA), a handset, a device using a wireless modem (alarm or measurement device, etc.), a laptop and/or touch screen computer, a tablet, a phablet, a game console, a notebook, and a multimedia device, as examples. It should be appreciated that a user device may also be a nearly exclusive uplink only device, of which an example is a camera or video camera loading images or video clips to a network.

[0017] In LTE (as an example), core network 150 may be referred to as Evolved Packet Core (EPC), which may include a mobility management entity (MME) which may handle or assist with mobility /handover of user devices between BSs, one or more gateways that may forward data and control signals between the BSs and packet data networks or the Internet, and other control functions or blocks.

[0018] The various example implementations may be applied to a wide variety of wireless technologies or wireless networks, such as LTE, LTE-A, 5G, cmWave, and/or mmWave band networks, or any other wireless network. LTE, 5G, cmWave and mmWave band networks are provided only as illustrative examples, and the various example implementations may be applied to any wireless technology/wireless network.

[001 9] FIG. 2 is a diagram of a wireless transceiver according to an example

implementation. The wireless transceiver shown in FIG. 2 may perform multiple input, multiple output (MIMO) beam forming. Wireless transceiver 200 may be used, for example, at a base station (BS), e.g., Access Point (AP) or eNB, or other wireless device. Wireless transceiver 200 may include a transmit path 210 and a receive path 212.

[0020] In transmit path 210, a digital-to-analog converter (D-A) 220 may receive a digital signal from one or more applications and convert the digital signal to an analog signal. Upmixing block 222 may up-convert the analog signal to an RF (e.g., radio frequency) signal. Power amplifier (PA) 224 then amplifies the up-converted signal. The amplified signal is then passed through a transmit/receive (T/R) switch (or Diplexer 226 for frequency division duplexing, to change frequencies for transmitting). The signal output from T/R switch 226 is then output to one or more antennas in an array of antennas 228, such as to antenna 228A, 228B and/or 228C. Prior to being transmitted by one or more of the antennas in the array of antennas 228, a set of beam weights V_1; V₂, ... or VQ is mixed with the signal to apply a gain and phase to the signal for transmission. For example, a gain and phase, V_1; V₂, ... or V_Q, may be applied to the signal output from the T/R switch 226 to scale the signal transmitted by each antenna (e.g., the signal is multiplied by Vi before being transmitted by antenna 1 228A, the signal is multiplied by V₂ before being transmitted by antenna 2 228B, and so on), where the phase may be used to steer or point a beam transmitted by the overall antenna array, e.g., for directional beam steering. Thus, the beam weights V_1; V₂, ... or V_Q (e.g., each beam weight including a gain and/or phase) may be a set of transmit beamforming beam weights when applied at or during transmission of a signal to transmit the signal on a specific beam, and may be a set of receive beamforming beam weights when applied to receive a signal on a specific beam.

[0021 ] In receive path 212 of wireless transceiver 200, a signal is received via an array of antennas 228, and is input to T/R switch 226, and then to low noise amplifier (LNA) 230 to amplify the received signal. The amplified signal output by LNA 230 is then input to a RF-to- baseband conversion block 232 where the amplified RF signal is down-converted to baseband. An analog-to-digital (A-D) converter 234 then converts the analog baseband signal output by conversion block 232 to a digital signal for processing by one or more upper layers/application layers. [0022] Various example implementations may relate, for example, to 5G radio access systems (or other systems) with support for Massive MIMO (multiple input, multiple output) and optimized for operating in high carrier frequencies such as cmWave frequencies (e.g. from 3 GHz onwards) or mmWave frequencies, as examples, according to an illustrative example implementation. Those illustrative systems are typically characterized by the need for high antenna gain to compensate for increased pathloss and by the need for high capacity and high spectral efficiency to respond to ever increasing wireless traffic. According to an example implementation, the increased attenuation at higher carrier frequencies may, for example, be compensated by introducing massive (multi-element) antenna arrays and correspondingly antenna gain via beamforming at the access point (AP) / base station (BS). The spectral efficiency may typically improve with the number spatial streams the system can support and thus with the number of antenna ports at the BS.

[0023] FIG. 3 is a diagram illustrating a radio system architecture according to an illustrative example implementation. The radio system illustrated in FIG. 3 is merely provided as an illustrative example, and the various example implementations described herein are not limited thereto. Both transmit and receive directions are shown in FIG. 3. In the transmit direction, radio system architecture 300 receives/generates multiple symbols (e.g.,

OFDM/orthogonal frequency division multiplex symbols) 310 which are mapped/provided to M antenna ports 312. Antenna ports 312 in this illustrative example does not refer to physical antenna ports. Rather, antenna ports 312, e.g., as defined by LTE as an illustrative example and as generally used herein, refer to logical antenna ports (logical entities), which may be distinguished by their reference signal sequence. Multiple (logical) antenna port signals can be transmitted over a single antenna/single antenna array, for example. A transceiver unit array 316 includes K transceiver (wireless/radio transmitter/receiver) units (TXRUs). Antenna port virtualization block 314 performs mapping between M antenna ports and K digital inputs of transceiver unit array 316 (e.g., performs mapping between M antenna ports and K TXRUs). On the RF side of transceiver unit array 316, a radio distribution network 318 performs TXRU virtualization, e.g., by mapping or connecting each TXRU to one or more antenna elements of antenna array 320. One TXRU can be connected to {1...L} antenna elements depending on the TXRU virtualization, i.e., mapping between TXRUs and Antenna Elements. Mapping can be either sub-array or full connection. In the sub-array model, one TXRU is connected to subset of antenna elements where different subsets may be disjoint while in the full connection model each TXRU is connected to each antenna element or all antenna elements of the antenna array 320. Radio distribution network (RDN) 318 performs antenna virtualization in the RF domain. In the transmitting direction, M antenna ports feed K TXRUs, and K TXRUs feed L antenna elements where M<K<L, in this illustrative example implementation.

[0024] According to an example implementation, the number of antenna ports may be an arbitrary (or variable or selectable) number of antenna points. By arbitrary, this means that the number of antenna ports is not limited to just a binary number (2ⁿ) of antenna ports, where n is an integer (e.g., not limited to 2, 4, 8, 16, 32, 64, ... antenna ports), but may be any number of antenna ports (e.g., within an attainable range). A number of different situations may arise where an arbitrary or selectable number of antenna ports may be used.

[0025] According to an example implementation, future LTE and/or 5G networks may configure user devices to measure and report channel state information (CSI) on a certain number of antenna ports N, such that N does not (necessarily) equal 2ⁿ, where n is an integer. Thus, according to an example implementation, the number of (logical) antenna ports used for data transmitting/receiving may not be a binary number of 2n (e.g., 2, 4, 8, 16, 32, ... ), but may be any number. An example case may be to use the enhanced CRI (CSI resource indicator) bits to report CSI for one or more selected beams or CSI-RSs, in the example case where a user device may select multiple CSI-RS resources (MIMO beams) for CSI feedback. In this case, the user device may select 3 resources (or 3 beams or 3 channel state information-reference signals/CSI-RSs) each with, e.g., 8 antenna ports, thus requiring the user device to measure 24 antenna ports in total for the CSI feedback (e.g., where the BS would then use the 24 antenna ports for transmission to the user device). In another example implementation, the user device may measure and report 10 ports for each of 3 resources/beams, for a total of 30 antenna ports to be used for transmission by the BS to the user device. Another case is that the network has 24 antenna ports in each cell, and it configures a user device to measure all 24 ports for the CSI feedback. These are merely some illustrative examples, and any number of antenna ports may be used. Thus, the number of 3 MIMO beams and 8 antenna ports per beam are provided by way of example, any number of total antenna ports may be used, e.g., 20, 22, 24, 26, 28, 30, ... (as some illustrative examples). As noted above, as used herein, the phrase "antenna ports" may typically refer to logical antenna ports.

[0026] In addition, random precoding is a robust open-loop (OL) MIMO transmission scheme where pseudo-randomly selected precoders (or precoder vectors) are applied to the PSDCH (physical shared downlink channel/data channel) transmission. In an example implementation, a different precoder (or precoder vector) may be applied per-subcarrier (or per group of subcarriers) in order to maximize the diversity gain across the transmission bandwidth. For example, the CQI (the channel quality indication, e.g., which may be based on a measured signal-to-interference plus noise ratio/SINR) computation at the user device may be based on a foreknowledge (knowledge in advance by the user device) of the selected set of

precoders/precoder vectors used on the subcarriers, and thus no PMI (precoding matrix indicator) feedback is required. Open loop MIMO may provide low overhead (due to no feedback required), and may be used, for example, in cases of a moderate or fast-changing channel, such as a moderate or high velocity case, as an example.

[0027] Full dimension (FD) MIMO may be used, e.g., in which systems may

simultaneously support or provide both azimuth and elevation MIMO beams. In an example implementation, a user device located in the overlap of 3 FD (full dimension)-MIMO beams may select, for example, 3 CSI-RS resources (3 MIMO beams) each with 8 (for example) ports per beam. In such case, the user device will measure a total of 24 antenna ports and report the CQI (channel quality indication) for the open loop MIMO transmission hypothesis spanning all 24 ports. The BS may then transmit data to the user device via all 24 antenna ports. As a result, the user device may achieve a greater diversity gain across the 3 selected beams. The ability of an open loop transmission scheme to span all 24 antenna ports may assist a moderate to high velocity situation (e.g., moderate/high velocity user device) where optimally co-phasing the multiple ports (e.g., through PMI feedback) may be impractical due to the rapidly time-varying channel. However, while 24 antenna ports (by way of example) are used in this example, it may be the easiest or simplest to generate a binary number (2ⁿ) of precoders (or precoder vector elements), this binary number (e.g., 2, 4, 8, 16, 32, ... ) may not generally match the selected number of antenna ports used for transmission.

[0028] Therefore, according to an example implementation, techniques are provided to support an arbitrary (or selectable) number of antenna ports (e.g., which may be any number of antenna ports, not just a binary number of antenna ports). This technique to support an arbitrary number of antenna ports may be used to support open loop MIMO. For example, a user device located in the overlap of 3 FD (full dimension)-MIMO beams may select 3 CSI-RS resources (3 MIMO beams) each with 10 (for example) ports per beam. In such case, the user device will measure a total of 30 antenna ports and report the CQI (channel quality indication) for the open loop MIMO transmission hypothesis spanning all 30 ports, with the BS transmitting signals to the user device on all 30 antenna ports.

[0029] According to an example implementation, a binary-based multi-level aggregation of precoder vectors may be used to generate or determine an aggregated pseudo-random precoder vector for an arbitrary number of antenna ports. According to an example

implementation, one or more precoder vector elements of the aggregated pseudo-random precoder vector are punctured (e.g., discarded, not applied to antenna ports, or applied at zero power) so that the remaining (non-punctured) precoder vector elements match a number of antenna ports to be used for transmission. Each of the non-punctured precoder vector elements of the aggregated pseudo-random precoder vector are applied to one of the antenna ports. Data may be transmitted via the antenna ports and the applied non-punctured precoder vector elements.

[0030] FIG. 4 is a flow chart illustrating operation of a base station according to an example implementation. In an example implementation, the flow chart of FIG. 4 may describe a method of determining pseudo-random precoder vector (e.g., an aggregated pseudo-random precoder vector) for an arbitrary number of antenna ports. Operation 410 includes determining a number of antenna ports (logical antenna ports) to be used for data transmission. For example, it may be determined that 30 (logical) antenna ports will be used to transmit data from a BS to a user device.

[0031 ] Operation 420 includes generating a (e.g., aggregated) pseudo-random precoder vector (w) including 2^M precoder vector elements, where M is an integer, 2^M is greater than the number of antenna ports to be used for data transmission and 2^M_1 is less than the number of antenna ports to be used for data transmission. For example, if there are 30 antenna ports, then 2^M precoder vector elements may include, for example, 2⁵ = 32 precoder vector elements. For example, the (e.g., aggregated) pseudo-random precoder vector (w) may be generated by aggregating a plurality of smaller-size pseudo-random precoder vectors (vi_k). Each of the smaller-size pseudo-random precoder vectors (vik) includes one or more precoder vector elements. Each precoder vector element includes an amplitude and a phase. Each of the smaller-size pseudo-random precoder vectors (vi_k) may have fewer precoder vector elements than the pseudo-random precoder vector (w). For example, the smaller-size pseudo-random precoder vectors (vi_k) may each be a two-element pseudo-random precoder vector (with each two-element pseudo-random precoder vector including two precoder vector elements).

[0032] Operation 430 includes pseudo-randomly puncturing one or more of the 2^M precoder vector elements of the aggregated pseudo-random precoder vector (w) such that a number of non-punctured precoder vector elements of the (e.g., aggregated) pseudo-random precoder vector (w) matches the number of antenna ports to be used for data transmission. For example, this may include pseudo-randomly (e.g., using a pseudo-random sequence known by both BS and user device) selecting one or more of the 2^M precoder vector elements to be punctured, and then puncturing these selected precoder vector elements. For example, a number of precoder vector elements may be punctured, where the number of elements to be punctured may be the difference between the 2^M precoder vector elements of the aggregated pseudorandom precoder vector (w) and the number of antenna ports to be used for data transmission. For example, if 30 antenna ports will be used for transmission, and the 2^M precoder vector elements includes 2⁵ = 32 precoder vector elements, then 32-30 = 2 precoder vector elements of the aggregated pseudo-random precoder vector (w) will be punctured, according to an illustrative example. Puncturing, for example, may include discarding or deleting the punctured precoder vector, not applying the punctured precoder vector to any antenna element, and/or applying the precoder vector element to another antenna element using zero power (e.g., zero transmission power or zero amplitude). In this manner, the number of the remaining or non-punctured precoder vector elements of the aggregated pseudo-random precoder vector (w) matches the number of antenna ports (e.g., 30 in this illustrative example).

[0033] Operation 440 includes applying each of the non-punctured precoder vector elements of the pseudo-random precoder vector (w) to one of the antenna ports. The precoder vector elements may perform precoding, which may include pre-distorting a signal prior to transmission.

[0034] Operation 450 includes transmitting data via the antenna ports and the applied non-punctured precoder vector elements.

[0035] While the flow chart of FIG. 4 is provided for the operation of a BS, the operations (one or more of the operations) shown in the flow chart of FIG. 4 may also be performed by one or more user devices. For example, while a BS determines the precoder vector for transmission via the plurality of (logical) antenna ports, a user device may determine the precoder vector (including the non-punctured precoder vector elements) for receiving signals from the BS via the plurality of antenna ports and for CQI calculation. Thus, a user device may determine a number of antenna ports to be used for data reception from the BS; generate an aggregated pseudo-random precoder vector including 2^M precoder vector elements, where M is an integer and 2^M is greater than the number of antenna ports to be used for data transmission and 2^M_1 is less than the number of antenna ports to be used for data transmission; pseudo- randomly puncture one or more of the 2^M precoder vector elements such that a number of non- punctured precoder vector elements of the aggregated pseudo-random precoder vector matches the number of antenna ports to be used for data transmission; apply each of the non-punctured precoder vector elements of the aggregated pseudo-random precoder vector to one of the antenna ports; and receive data from the BS via the antenna ports and the applied non-punctured precoder vector elements. Thus, the user device may determine aggregated precoder vector, pseudo- randomly puncture one or more precoder vector elements of the aggregated pseudo-random precoder vector, apply the non-punctured precoder vector elements to the antenna ports to receive data from the BS. The user device may also measure CQI (channel quality indication, which may be based on a measured and quantized SINR) for each of the (logical) antenna ports. The user device may report the CQI for each antenna port back to the BS, for example. The various further example details described below with respect to the flow chart of FIG. 4 may also be performed by a user device.

[0036] According to an example implementation of the method of FIG. 4, the generating may include: determining M, which is an aggregation level that indicates a number of smaller- size pseudo-random precoder vectors (vi_k) to be aggregated, wherein each of the smaller-size pseudo-random precoder vectors has fewer precoder vector elements than the aggregated pseudo-random precoder vector; and aggregating the M smaller-size pseudo-random precoder vectors to obtain the aggregated pseudo-random precoder vector (w).

[0037] For example, for 2⁵ = 32 precoder vector elements to be generated for the aggregated pseudo-random precoder vector, the aggregation level (M) is 5. Thus, in such an example, the aggregating may include aggregating 5 smaller-size precoder vectors, e.g., such as by aggregating 5 two-element precoder vectors to generate the aggregated pseudo-random precoder vector (w) with 32 precoder vector elements. In an example implementation, the aggregating may be performed, for example, by performing a product operation, such as a Kronecker product, of the M smaller-size pseudo-random precoder vectors. In an example implementation, the M smaller-size pseudo-random precoder vectors may each be determined based on a pseudo-random sequence (l(k,n) known by both the BS and the user device. For example, the M smaller-size pseudo-random precoder vectors may each be determined based on a pseudo-random sequence (l(k,n) known by both the base station and user device, that may be based on a random seed. The random seed, for example, may be based on a subcarrier index (k) and a subframe index (n) on which the precoder vector element is applied.

[0038] According to an example implementation of the method of FIG. 4, each of the smaller-size pseudo-random precoder vectors may include a two-element pseudo-random precoder vector. [0039] According to an example implementation of the method of FIG. 4, the aggregating may include: performing a Kronecker product of each of the M smaller-size pseudo-random precoder vectors to obtain the aggregated pseudo-random precoder vector.

[0040] According to an example implementation of the method of FIG. 4, each precoder vector element includes an amplitude and a phase, wherein each of the M smaller-size pseudorandom precoder vectors includes at least one precoder vector element that has a granularity of phase change for at least the precoder vector element provided as a function of an oversampling rate (Ok).

[0041 ] According to an example implementation of the method of FIG. 4, a change in phase between an element of at least two of the M smaller-size pseudo-random precoder vectors is based on an oversampling rate (O_k) and an integer of a pseudo-random sequence, wherein the oversampling rate is configured by a base station.

[0042] According to an example implementation of the method of FIG. 4, the generating may include: generating, for rank indication (RI) = 1, one aggregated pseudo-random precoder vector (wl); and generating, for rank indication (RI) = 2, two aggregated pseudo-random precoder vectors (wl, w2).

[0043] According to an example implementation of the method of FIG. 4, wherein the generating of each aggregated pseudo-random precoder vector may include aggregating M two- element pseudo-random precoder vectors to obtain the aggregated pseudo-random precoder vector; and at least one precoder vector element of a two-element pseudo-random precoder vector used to generate an aggregated pseudo-random precoder vector for rank indication (RI) = 2 has a phase that is a negative value of a phase of a precoder vector element of a two-element pseudo-random precoder vector used to generate an aggregated pseudo-random precoder vector for rank indication (RI) = 1.

[0044] According to an example implementation of the method of FIG. 4, wherein the pseudo-randomly puncturing includes: determining a pseudo-random sequence (b(k, n));

selecting, based on the pseudo-random sequence, one or more of the 2^M precoder vector elements of the aggregated pseudo-random precoder vector to be punctured; and puncturing the selected one or more precoder vector elements of the aggregated pseudo-random precoder vector.

[0045] According to an example implementation of the method of FIG. 4, at least one of the following is performed: one or more of the punctured precoder vector elements is not applied to an antenna element; and one of the punctured precoder vector elements is applied to a virtual antenna port with zero transmission power. . [0046] According to an example implementation of the method of FIG. 4, a phase of each non-punctured precoder vector element is determined based on a random sequence (l(k, n) known by both a user device and a base station, wherein the random sequence is based on a pseudo-random seed determined based on subcarrier and subframe indices (k, n) on which the precoder vector element is applied, the pseudo-random seed known by the user device and the base station.

[0047] According to an example implementation, the following procedure may be used to determine an aggregated pseudo-random precoder vector (w):

[0048] For each subcarrier, perform the following steps/operations (A and B): (both the BS and the user device may perform these operations).

[0049] A) Aggregation step (to generate aggregated precoder vector for 2ⁿ ports)

[0050] 1) Determine the level of aggregation (M) given an arbitrary number (N) of antenna ports configured for CSI or CQI measurement at the user device. (N is also the number of antenna ports selected for data transmission). Let M denote the aggregation level and N the configured number of antenna ports, then (2^M>N> 2^(M"1) ). Thus, the 2^M should be selected to be greater than the number of antenna ports (N). Also, the BS may configure CSI- RS (channel state information-reference signals) with N antenna ports for the user device to measure CQI for each antenna port, and the user device may report the CQI for each antenna port back to the BS. Finally, the BS may transmit data to the user device via the N antenna ports.

[0051 ] 2) Given the aggregation level M and user device rank (or rank indication at the user device), the open loop precoding (aggregated precoding vector (w)) is generated as follows for rank-1 (to generate the aggregated pseudo-random precoder vector (w), as the Kronecker product of M smaller-size precoder vectors (vi_k):

w = v * v_h ... * v_lM, where v_lk = [₁ β£ where symbol * denotes the Kronecker product operation. In particular, the Kronecker product operation on length-2 vectors is defined as follows, where t indicates transpose operation:

[a b * [c d]* = [ac ad be bd]*

For other vector lengths, the Kronecker product operation is defined similarly. [0052] 3) For rank-2, W = [w₁ w₂], w₁ = ν_1χ * v_l2 ... * v_lft and w₂ = v *

■■■* ¾, where

vh = [l ]^{tand v}h = [i -

[0053] Therefore, it can be seen from the equation for the smaller-size precoder vector vi_k (above), the smaller-size precoder vector vi_k may be, for example, a two-element precoder vector that includes two precoder vector elements, including a 1, and an exponential term (e^x). The exponential term has an amplitude (absolute value) of 1 and a phase determined based on the random sequence l_k and the oversampling rate O_k. The oversampling rate O_k may be configured by a BS. A change in phase between an element of at least two smaller size precoder vectors (vi_k) may be based on the oversampling rate O_k. Also, or in other words, a granularity of phase change (or amount of phase change for each precoder vector) may be based at least in part on the oversampling rate O_k.

[0054] Also, for rank (or rank indication) = 2, for w₂, a complex conjugate (v*n) of the second vector element is used for vn, resulting in a phase for that is a negative of the phase used for vn in wi (wi in both rank=l, and rank = 2). In other words, for rank=2, vn is the first small- size precoder vector used for wi, and v*n is the first small-size precoder vector used for w₂. v*n has a phase term (in its second element) that is a negative of the phase term in the second element of vn, since * indicates complex conjugate operation.

[0055] 4) For higher ranks, e.g. rank-3, then W = [w_x w_{2 3} ] where w₃ = v^* _h * v^* _h * v_h ... * v_lM, and so on.

[0056] 5) In the above, O_k, such as , 0_1; 0₂,■■■ , 0_M indicates an oversampling rate, configured by the serving BS. For co-polarized antennas, the BS may configure any value for O_x 0₂, ... , 0_M. For cross-polarized antenna panel, the BS may typically, for example, configure O_x = 2 where level- 1 aggregation is used for the antennas with orthogonal polarizations.

[0057] 6) Vector b(k, n) = b₂, ... , b_M] is a pseudo-random sequence known by both the BS and the user device. For instance, the generation of this sequence may be based on a random seed decided by the subcarrier and subframe indices (k, n) in which the precoder is applied, as well as high layer configuration signaling.

[0058] B. Pseudo-randomly puncturing to generate precoder vector for arbitrary number of antenna ports:

[0059] 7) As noted, one or more precoder vector elements of the aggregated pseudo-random precoder vector (w) will be pseudo-randomly selected to be punctured based on pseudo-random sequence (b).. The second pseudo-random sequence (b), such as b k, ri) = [b^ b₂, ... , &2^ΛΜ-Ν]_> is generated to locate the index (or indices) of the punctured precoder vector elements within the aggregated pseudo-random precoder vector (w). In an example implementation, this pseudo-random sequence (b) may pseudo-randomly select one or more precoder vector elements of the aggregated pseudo-random precoder vector (w), e.g., as a function of the sub-carrier and symbol indices on which it is applied. For the punctured vector elements/antenna ports, the user device may discard or delete such precoder vector elements, or may assume zero transmission power for the CQI calculation.

[0060] With the above steps, both the BS and the user device will be aware of the overall precoder on each sub-carrier used for the PDSCH transmission through all the aggregation levels. The BS transmits DMRS (demodulation reference signal)-based PDSCH (physical downlink shared data channel) signal on each sub-carrier using the overall aggregated precoder vector (w). The DMRS based PDSCH signal on each subcarrier may allow the user device to perform channel estimation. According to an example implementation an apparatus may include at least one processor and at least one memory including computer instructions, when executed by the at least one processor, cause the apparatus to: determine a number of antenna ports to be used for data transmission; generate a pseudo-random precoder vector including 2^M precoder vector elements, where M is an integer and 2^M is greater than the number of antenna ports to be used for data transmission and 2^M_1 is less than the number of antenna ports to be used for transmission; pseudo-randomly puncture one or more of the 2^M precoder vector elements such that a number of non-punctured precoder vector elements of the pseudo-random precoder vector matches the number of antenna ports to be used for data transmission; apply each of the non-punctured precoder vector elements of the pseudo-random precoder vector to one of the antenna ports; and transmit data via the antenna ports and the applied non-punctured precoder vector elements.

[0061] According to an example implementation of the apparatus, the pseudo-random precoder vector may include an aggregated pseudo-random precoder vector, and wherein causing the apparatus to generate may include causing the apparatus to determine M, which is an aggregation level that indicates a number of smaller-size pseudo-random precoder vectors (vik) to be aggregated, wherein each of the smaller-size pseudo-random precoder vectors has fewer precoder vector elements than the aggregated pseudo-random precoder vector; and aggregate the M smaller-size pseudo-random precoder vectors to obtain the aggregated pseudo-random precoder vector (w).

[0062] According to an example implementation of the apparatus, each of the smaller- size pseudo-random precoder vectors may include a two-element pseudo-random precoder vector.

[0063] According to an example implementation of the apparatus, the causing the apparatus to aggregate may include causing the apparatus to: perform a Kronecker product of each of the M smaller-size pseudo-random precoder vectors to obtain the aggregated pseudorandom precoder vector.

[0064] According to an example implementation of the apparatus, each precoder vector element includes an amplitude and a phase, wherein each of the M smaller-size pseudo-random precoder vectors includes at least one precoder vector element that has a granularity of phase change for at least the precoder vector element provided as a function of an oversampling rate (Ok).

[0065] According to an example implementation of the apparatus, each of M smaller-size pseudo-random precoder vector is a Discrete Fourier Transform (DFT) vector, where each element corresponds to one element of complex value in DFT vector, e ²⁰k , with a DFT oversampling rate (Ok) to control the phase granularity of the pseudo-random precoder vector.

[0066] According to an example implementation of the apparatus, a change in phase between an element of at least two of the M smaller-size pseudo-random precoder vectors is based on an oversampling rate (Ok) and an integer of a pseudo-random sequence, wherein the oversampling rate is configured by a base station.

[0067] According to an example implementation of the apparatus, the pseudo-random precoder vector includes an aggregated pseudo-random precoder vector, and wherein causing the apparatus to generate may include: generating, for rank indication (RI) = 1, one aggregated pseudo-random precoder vector; and generating, for rank indication (RI) = 2, two aggregated pseudo-random precoder vectors.

[0068] According to an example implementation of the apparatus, wherein causing the apparatus to generate each of the aggregated pseudo-random precoder vectors may include causing the apparatus to aggregate M two-element pseudo-random precoder vectors to obtain the aggregated pseudo-random precoder vector; and wherein at least one precoder vector element of a two-element pseudo-random precoder vector used to generate an aggregated pseudo-random precoder vector for rank indication (RI) = 2 has a phase that is a negative value of a phase of a precoder vector element of a two-element pseudo-random precoder vector used to generate an aggregated pseudo-random precoder vector for rank indication (RI) = 1.

[0069] According to an example implementation of the apparatus, the pseudo-random precoder vector may include an aggregated pseudo-random precoder vector, and wherein causing the apparatus to pseudo-randomly puncture may include causing the apparatus to determine a pseudo-random sequence (b(k, n)); select, based on the pseudo-random sequence, one or more of the 2^M precoder vector elements of the aggregated pseudo-random precoder vector to be punctured; and puncture the selected one or more precoder vector elements of the aggregated pseudo-random precoder vector.

[0070] According to an example implementation of the apparatus, and further causing the apparatus to perform at least one of the following: discard one or more of the punctured precoder vector elements, and thereby, not apply the one or more punctured precoder vector elements to an antenna element; and apply one of the punctured precoder vector elements to a virtual antenna port using zero transmission power.

[0071 ] According to an example implementation of the apparatus, a phase of each non- punctured precoder vector element is determined based on a pseudo-random sequence (l(k, n) known by both a user device and a base station, wherein the pseudo-random sequence is based on a pseudo-random seed determined based on subcarrier and subframe indices (k, n) on which the precoder vector element is applied, the pseudo-random seed known by the user device and the base station.

[0072] According to another example implementation, a computer program product includes a computer-readable storage medium and storing executable code that, when executed by at least one data processing apparatus, is configured to cause the at least one data processing apparatus to perform a method including: determining a number of antenna ports to be used for data transmission; generating a pseudo-random precoder vector including 2^M precoder vector elements, where M is an integer and 2^M is greater than the number of antenna ports to be used for data transmission and 2^M_1 is less than the number of antenna ports to be used for data transmission; pseudo-randomly puncturing one or more of the 2^M precoder vector elements such that a number of non-punctured precoder vector elements of the pseudo-random precoder vector matches the number of antenna ports to be used for data transmission; applying each of the non- punctured precoder vector elements of the pseudo-random precoder vector to one of the antenna ports; and transmitting data via the antenna ports and the applied non-punctured precoder vector elements.

[0073] According to another example implementation, an apparatus may include means for (e.g., 502A/502B and/or 504, FIG. 5) determining a number of antenna ports to be used for data transmission; generating a pseudo-random precoder vector including 2^M precoder vector elements, where M is an integer and 2^M is greater than the number of antenna ports to be used for data transmission and 2^M_1 is less than the number of antenna ports to be used for data transmission; means for (e.g., 502A/502B and/or 504, FIG. 5) pseudo-randomly puncturing one or more of the 2^M precoder vector elements such that a number of non-punctured precoder vector elements of the pseudo-random precoder vector matches the number of antenna ports to be used for data transmission; means for (e.g., 502A/502B and/or 504, FIG. 5) applying each of the non- punctured precoder vector elements of the pseudo-random precoder vector to one of the antenna ports; and means for (e.g., 502A/502B and/or 504, FIG. 5) transmitting data via the antenna ports and the applied non-punctured precoder vector elements.

[0074] FIG. 5 is a block diagram of a wireless station (e.g., AP or user device) 500 according to an example implementation. The wireless station 500 may include, for example, one or two RF (radio frequency) or wireless transceivers 502A, 502B, where each wireless transceiver includes a transmitter to transmit signals and a receiver to receive signals. The wireless station also includes a processor or control unit/entity (controller) 504 to execute instructions or software and control transmission and receptions of signals, and a memory 506 to store data and/or instructions.

[0075] Processor 504 may also make decisions or determinations, generate frames, packets or messages for transmission, decode received frames or messages for further processing, and other tasks or functions described herein. Processor 504, which may be a baseband processor, for example, may generate messages, packets, frames or other signals for transmission via wireless transceiver 502 (502A or 502B). Processor 504 may control transmission of signals or messages over a wireless network, and may control the reception of signals or messages, etc., via a wireless network (e.g., after being down-converted by wireless transceiver 502, for example). Processor 504 may be programmable and capable of executing software or other instructions stored in memory or on other computer media to perform the various tasks and functions described above, such as one or more of the tasks or methods described above. Processor 504 may be (or may include), for example, hardware, programmable logic, a programmable processor that executes software or firmware, and/or any combination of these. Using other terminology, processor 504 and transceiver 502 together may be considered as a wireless transmitter/receiver system, for example.

[0076] In addition, referring to FIG. 5, a controller (or processor) 508 may execute software and instructions, and may provide overall control for the station 500, and may provide control for other systems not shown in FIG. 5, such as controlling input/output devices (e.g., display, keypad), and/or may execute software for one or more applications that may be provided on wireless station 500, such as, for example, an email program, audio/video applications, a word processor, a Voice over IP application, or other application or software.

[0077] In addition, a storage medium may be provided that includes stored instructions, which when executed by a controller or processor may result in the processor 504, or other controller or processor, performing one or more of the functions or tasks described above.

[0078] According to another example implementation, RF or wireless transceiver(s) 502A/502B may receive signals or data and/or transmit or send signals or data. Processor 504 (and possibly transceivers 502A/502B) may control the RF or wireless transceiver 502A or 502B to receive, send, broadcast or transmit signals or data.

[0079] The embodiments are not, however, restricted to the system that is given as an example, but a person skilled in the art may apply the solution to other communication systems. Another example of a suitable communications system is the 5G concept. It is assumed that network architecture in 5G will be quite similar to that of the LTE-advanced. 5G is likely to use multiple input - multiple output (MIMO) antennas, many more base stations or nodes than the LTE (a so-called small cell concept), including macro sites operating in co-operation with smaller stations and perhaps also employing a variety of radio technologies for better coverage and enhanced data rates.

[0080] It should be appreciated that future networks will most probably utilise network functions virtualization (NFV) which is a network architecture concept that proposes virtualizing network node functions into "building blocks" or entities that may be operationally connected or linked together to provide services. A virtualized network function (VNF) may comprise one or more virtual machines running computer program codes using standard or general type servers instead of customized hardware. Cloud computing or data storage may also be utilized. In radio communications this may mean node operations may be carried out, at least partly, in a server, host or node operationally coupled to a remote radio head. It is also possible that node operations will be distributed among a plurality of servers, nodes or hosts. It should also be understood that the distribution of labour between core network operations and base station operations may differ from that of the LTE or even be non-existent.

[0081 ] Implementations of the various techniques described herein may be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. Implementations may implemented as a computer program product, i.e., a computer program tangibly embodied in an information carrier, e.g., in a machine-readable storage device or in a propagated signal, for execution by, or to control the operation of, a data processing apparatus, e.g., a programmable processor, a computer, or multiple computers. Implementations may also be provided on a computer readable medium or computer readable storage medium, which may be a non-transitory medium. Implementations of the various techniques may also include implementations provided via transitory signals or media, and/or programs and/or software implementations that are downloadable via the Internet or other network(s), either wired networks and/or wireless networks. In addition, implementations may be provided via machine type communications (MTC), and also via an Internet of Things (IOT).

[0082] The computer program may be in source code form, object code form, or in some intermediate form, and it may be stored in some sort of carrier, distribution medium, or computer readable medium, which may be any entity or device capable of carrying the program. Such carriers include a record medium, computer memory, read-only memory, photoelectrical and/or electrical carrier signal, telecommunications signal, and software distribution package, for example. Depending on the processing power needed, the computer program may be executed in a single electronic digital computer or it may be distributed amongst a number of computers.

[0083] Furthermore, implementations of the various techniques described herein may use a cyber-physical system (CPS) (a system of collaborating computational elements controlling physical entities). CPS may enable the implementation and exploitation of massive amounts of interconnected ICT devices (sensors, actuators, processors microcontrollers,...) embedded in physical objects at different locations. Mobile cyber physical systems, in which the physical system in question has inherent mobility, are a subcategory of cyber-physical systems. Examples of mobile physical systems include mobile robotics and electronics transported by humans or animals. The rise in popularity of smartphones has increased interest in the area of mobile cyber- physical systems. Therefore, various implementations of techniques described herein may be provided via one or more of these technologies.

[0084] A computer program, such as the computer program(s) described above, can be written in any form of programming language, including compiled or interpreted languages, and can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit or part of it suitable for use in a computing environment. A computer program can be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by a communication network.

[0085] Method steps may be performed by one or more programmable processors executing a computer program or computer program portions to perform functions by operating on input data and generating output. Method steps also may be performed by, and an apparatus may be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application-specific integrated circuit).

[0086] Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer, chip or chipset. Generally, a processor will receive instructions and data from a read-only memory or a random access memory or both. Elements of a computer may include at least one processor for executing instructions and one or more memory devices for storing instructions and data. Generally, a computer also may include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto-optical disks, or optical disks. Information carriers suitable for embodying computer program instructions and data include all forms of non-volatile memory, including by way of example semiconductor memory devices, e.g., EPROM,

EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks. The processor and the memory may be supplemented by, or incorporated in, special purpose logic circuitry.

[0087] To provide for interaction with a user, implementations may be implemented on a computer having a display device, e.g., a cathode ray tube (CRT) or liquid crystal display (LCD) monitor, for displaying information to the user and a user interface, such as a keyboard and a pointing device, e.g., a mouse or a trackball, by which the user can provide input to the computer. Other kinds of devices can be used to provide for interaction with a user as well; for example, feedback provided to the user can be any form of sensory feedback, e.g., visual feedback, auditory feedback, or tactile feedback; and input from the user can be received in any form, including acoustic, speech, or tactile input.

[0088] Implementations may be implemented in a computing system that includes a back-end component, e.g., as a data server, or that includes a middleware component, e.g., an application server, or that includes a front-end component, e.g., a client computer having a graphical user interface or a Web browser through which a user can interact with an

implementation, or any combination of such back-end, middleware, or front-end components. Components may be interconnected by any form or medium of digital data communication, e.g., a communication network. Examples of communication networks include a local area network (LAN) and a wide area network (WAN), e.g., the Internet.

[0089] While certain features of the described implementations have been illustrated as described herein, many modifications, substitutions, changes and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the various

embodiments.

Claims

WHAT IS CLAIMED IS :

1. A method of determining a pseudo-random precoder vector for an arbitrary number of antenna ports, the method comprising:

determining a number of antenna ports to be used for data transmission;

generating a pseudo-random precoder vector including 2^M precoder vector elements, where M is an integer and 2^M is greater than the number of antenna ports to be used for data transmission and 2^M_1 is less than the number of antenna ports to be used for data transmission; pseudo-randomly puncturing one or more of the 2^M precoder vector elements such that a number of non-punctured precoder vector elements of the pseudo-random precoder vector matches the number of antenna ports to be used for data transmission;

applying each of the non-punctured precoder vector elements of the pseudo-random precoder vector to one of the antenna ports; and

transmitting data via the antenna ports and the applied non-punctured precoder vector elements.

2. The method of claim 1 wherein the pseudo-random precoder vector comprises an aggregated pseudo-random precoder vector, wherein the generating comprises:

determining M, which is an aggregation level that indicates a number of smaller-size pseudo-random precoder vectors (vik) to be aggregated, wherein each of the smaller-size pseudorandom precoder vectors has fewer precoder vector elements than the aggregated pseudo-random precoder vector; and

aggregating the M smaller-size pseudo-random precoder vectors to obtain the aggregated pseudo-random precoder vector (w).

3. The method of claim 2 wherein each of the smaller-size pseudo-random precoder vectors comprises a two-element pseudo-random precoder vector.

4. The method of any of claims 2-3 wherein the aggregating comprises:

performing a Kronecker product of each of the M smaller-size pseudo-random precoder vectors to obtain the aggregated pseudo-random precoder vector.

5. The method of any of claims 2-4 wherein each precoder vector element includes an amplitude and a phase, wherein each of the M smaller-size pseudo-random precoder vectors includes at least one precoder vector element that has a granularity of phase change for at least the precoder vector element provided as a function of an oversampling rate (Ok).

6. The method of any claims 2-5 wherein each of M smaller-size pseudo-random precoder vector is a Discrete Fourier Transform (DFT) vector, where each element corresponds to one element of complex value in DFT vector, e ²⁰k , with a DFT oversampling rate (Ok) to control the phase granularity of the pseudo-random precoder vector.

7. The method of any of claims 2-5 wherein a change in phase between an element of at least two of the M smaller-size pseudo-random precoder vectors is based on an oversampling rate (Ok) and an integer of a pseudo-random sequence, wherein the oversampling rate is configured by a base station.

8. The method of any of claims 1-7 wherein the pseudo-random precoder vector comprises an aggregated pseudo-random precoder vector, and wherein the generating comprises:

generating, for rank indication (RI) = 1, one aggregated pseudo-random precoder vector; and

generating, for rank indication (RI) = 2, two aggregated pseudo-random precoder vectors.

9. The method of claim 8 wherein:

the generating of each aggregated pseudo-random precoder vector comprises aggregating M two-element pseudo-random precoder vectors to obtain the aggregated pseudo-random precoder vector; and

at least one precoder vector element of a two-element pseudo-random precoder vector used to generate an aggregated pseudo-random precoder vector for rank indication (RI) = 2 has a phase that is a negative value of a phase of a precoder vector element of a two-element pseudorandom precoder vector used to generate an aggregated pseudo-random precoder vector for rank indication (RI) = 1.

10. The method of any of claims 1-9 wherein the pseudo-random precoder vector comprises an aggregated pseudo-random precoder vector, and wherein the pseudo- randomly puncturing comprises:

determining a pseudo-random sequence (b(k, n));

selecting, based on the pseudo-random sequence, one or more of the 2^M precoder vector elements of the aggregated pseudo-random precoder vector to be punctured; and

puncturing the selected one or more precoder vector elements of the aggregated pseudorandom precoder vector.

11. The method of any of claims 1-10 wherein at least one of the following is performed: one or more of the punctured precoder vector elements is not applied to an antenna element; and

one of the punctured precoder vector elements is applied to a virtual antenna port, with zero transmission power.

12. The method of any of claims 1-11 wherein a phase of each non-punctured precoder vector element is determined based on a random sequence (l(k, n) known by both a user device and a base station, wherein the random sequence is based on a pseudo-random seed determined based on subcarrier and subframe indices (k, n) on which the precoder vector element is applied, the pseudo-random seed known by the user device and the base station.

13. An apparatus comprising means for performing a method of any of claims 1-12.

14. A computer program product for a computer, comprising software code portions for performing the steps of any of claims 1 -12 when said product is run on the computer.

15. An apparatus comprising at least one processor and at least one memory including computer instructions, when executed by the at least one processor, cause the apparatus to: determine a number of antenna ports to be used for data transmission;

generate a pseudo-random precoder vector including 2^M precoder vector elements, where M is an integer and 2^M is greater than the number of antenna ports to be used for data transmission and 2^M_1 is less than the number of antenna ports to be used for transmission;

pseudo-randomly puncture one or more of the 2^M precoder vector elements such that a number of non-punctured precoder vector elements of the pseudo-random precoder vector matches the number of antenna ports to be used for data transmission;

apply each of the non-punctured precoder vector elements of the pseudo-random precoder vector to one of the antenna ports; and

transmit data via the antenna ports and the applied non-punctured precoder vector elements.

16. The apparatus of claim 15 wherein the pseudo-random precoder vector comprises an aggregated pseudo-random precoder vector, and wherein causing the apparatus to generate comprises causing the apparatus to:

determine M, which is an aggregation level that indicates a number of smaller-size pseudo-random precoder vectors (vik) to be aggregated, wherein each of the smaller-size pseudorandom precoder vectors has fewer precoder vector elements than the aggregated pseudo-random precoder vector; and

aggregate the M smaller-size pseudo-random precoder vectors to obtain the aggregated pseudo-random precoder vector (w).

17. The apparatus of claim 16 wherein each of the smaller-size pseudo-random precoder vectors comprises a two-element pseudo-random precoder vector.

18. The apparatus of any of claims 16-17 wherein causing the apparatus to aggregate comprises causing the apparatus to:

perform a Kronecker product of each of the M smaller-size pseudo-random precoder vectors to obtain the aggregated pseudo-random precoder vector.

19. The apparatus of any of claims 16-18 wherein each precoder vector element includes an amplitude and a phase, wherein each of the M smaller-size pseudo-random precoder vectors includes at least one precoder vector element that has a granularity of phase change for at least the precoder vector element provided as a function of an oversampling rate (Ok).

20. The apparatus of any claims 16-19 wherein each of M smaller-size pseudo-random precoder vector is a Discrete Fourier Transform (DFT) vector, where each element corresponds to one element of complex value in DFT vector, e ²⁰k , with a DFT oversampling rate (Ok) to control the phase granularity of the pseudo-random precoder vector.

21. The apparatus of any of claims 16-20 wherein a change in phase between an element of at least two of the M smaller-size pseudo-random precoder vectors is based on an oversampling rate (Ok) and an integer of a pseudo-random sequence, wherein the oversampling rate is configured by a base station.

22. The apparatus of any of claims 15-21 wherein the pseudo-random precoder vector comprises an aggregated pseudo-random precoder vector, and wherein causing the apparatus to generate comprises:

23. The apparatus of claim 22 wherein:

causing the apparatus to generate each of the aggregated pseudo-random precoder vectors comprises causing the apparatus to aggregate M two-element pseudo-random precoder vectors to obtain the aggregated pseudo-random precoder vector; and

wherein at least one precoder vector element of a two-element pseudo-random precoder vector used to generate an aggregated pseudo-random precoder vector for rank indication (RI) = 2 has a phase that is a negative value of a phase of a precoder vector element of a two-element pseudo-random precoder vector used to generate an aggregated pseudo-random precoder vector for rank indication (RI) = 1.

24. The apparatus of any of claims 15-23 wherein the pseudo-random precoder vector comprises an aggregated pseudo-random precoder vector, and wherein causing the apparatus to pseudo-randomly puncture comprises causing the apparatus to:

determine a pseudo-random sequence (b(k, n));

select, based on the pseudo-random sequence, one or more of the 2^M precoder vector elements of the aggregated pseudo-random precoder vector to be punctured; and

puncture the selected one or more precoder vector elements of the aggregated pseudorandom precoder vector.

25. The apparatus of any of claims 15-24 and further causing the apparatus to:

discard one or more of the punctured precoder vector elements, and thereby, not apply the one or more punctured precoder vector elements to an antenna element; and

apply one of the punctured precoder vector elements to a virtual antenna port, using zero transmission power.

26. The apparatus of any of claims 15-25 wherein a phase of each non-punctured precoder vector element is determined based on a random sequence (l(k, n) known by both a user device and a base station, wherein the random sequence is based on a pseudorandom seed determined based on subcarrier and subframe indices (k, n) on which the precoder vector element is applied, the pseudo-random seed known by the user device and the base station.

27. A computer program product, the computer program product comprising a computer- readable storage medium and storing executable code that, when executed by at least one data processing apparatus, is configured to cause the at least one data processing apparatus to perform a method comprising:

determining a number of antenna ports to be used for data transmission;