WO2018143855A1

WO2018143855A1 - Signaling of dmrs and spatial multiplexing configuration for uplink short tti transmissions

Info

Publication number: WO2018143855A1
Application number: PCT/SE2017/051352
Authority: WO
Inventors: Florent Munier; Henrik Sahlin; Jingya Li
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2017-02-03
Filing date: 2017-12-27
Publication date: 2018-08-09

Abstract

According to one aspect of the disclosure, a wireless device for Interleaved Frequency Division Multiplexing (IFDMA) based reference signal (RS) multiplexing for short Physical Uplink Shared Channel (sPUSCH) transmissions is provided. The 5 wireless device is configured to use a frequency allocation that partially overlaps with a frequency allocation of another entity. The wireless device further configured to: receive a plurality of reference signal (RS) configuration bits, process the plurality of RS configuration bits based on a number of spatial layers assigned to the wireless device, determine an RS configuration for sPUSCH transmission based on the 10 processing of the plurality of RS configuration bits, and transmit an RS on the sPUSCH based on the determined RS configuration.

Description

SIGNALING OF DMRS AND SPATIAL MULTIPLEXING

CONFIGURATION FOR UPLINK SHORT TTI TRANSMISSIONS

TECHNICAL FIELD

The disclosure relates to wireless communications, and in particular, to signaling of reference signal (RS) and/or spatial multiplexing configuration for uplink short transmission time interval (sTTI) transmissions.

BACKGROUND

In third generation partnership project (3 GPP) long term evolution (LTE) systems, data transmissions in both the downlink, i.e., from a network node or eNB to a user equipment or wireless device, and the uplink, i.e., from a wireless device or user equipment to a network node or eNB) are organized into radio frames of 10 ms, each radio frame consisting of ten equally-sized subframes of length T_subframe ⁼ 1 ms. LTE uses Orthogonal Frequency Division Multiplexing (OFDM) in the downlink and Single Carrier OFDM (SC-OFDM) in the uplink. The basic LTE downlink physical resource can thus be seen as a time-frequency grid, where each resource element corresponds to one OFDM subcarrier during one OFDM symbol interval.

Furthermore, the resource allocation in LTE is typically described in terms of resource blocks (RBs), where a resource block corresponds to one slot (0.5 ms) in the time domain and 12 contiguous subcarriers in the frequency domain. Resource blocks are numbered in the frequency domain, starting with 0 from one end of the system bandwidth. Similarly, the LTE uplink resource grid is illustrated in FIG. 1, where N¾ is the number resource blocks (RBs) contained in the uplink system bandwidth, N^_C ^B is the number subcarriers in each RB, typically N^_C ^B = 12, N^_y ^L _mb is the number of SC-OFDM symbols in each slot. N^_y ^L _mb = 7 for normal cyclic prefix (CP) and N^ m_b ⁼ 6 for extended CP. A subcarrier and a SC-OFDM symbol forms an uplink resource element (RE).

Downlink data transmissions from a network node to a wireless device are dynamically scheduled, i.e., in each subframe the base station transmits control information about to which terminals data is transmitted and upon which resource blocks the data is transmitted, in the current downlink subframe. This control signaling is typically transmitted in the first 1, 2, 3 or 4 OFDM symbols in each subframe. A downlink system with 3 OFDM symbols as control is illustrated in FIG. 2.

Similar to downlink, uplink transmissions from a wireless device to a network node are also dynamically scheduled through the downlink control channel. When a wireless device receives an uplink grant in subframe n, the wireless device transmits data in the uplink at subframe n+k, where k=4 for FDD system and k varies for time division duplex (TDD) systems.

In LTE, a number of physical channels are supported for data transmissions. A downlink or an uplink physical channel corresponds to a set of resource elements carrying information originating from higher layers while a downlink or an uplink physical signal is used by the physical layer, but does not carry information originating from higher layers. Some of the downlink physical channels and signals supported in LTE are:

· Physical Downlink Shared Channel (PDSCH)

• Physical Downlink Control Channel (PDCCH)

• Enhanced Physical Downlink Control Channel (EPDCCH)

• Reference signals:

• Cell Specific Reference Signals (CRS)

· DeModulation Reference Signal (DMRS) for PDSCH

• Channel State Information Reference Signals (CSI-RS)

PDSCH is used mainly for carrying user traffic data and higher layer messages in the downlink and is transmitted in a DL subframe outside of the control region as shown in FIG. 2. Both PDCCH and EPDCCH are used to cany Downlink Control Information (DO) such as PRB allocation, modulation level and coding scheme

(MCS), precoder used at the transmitter, and etc. PDCCH is transmitted in the first one to four OFDM symbols in a DL subframe, i.e. the control region, while EPDCCH is transmitted in the same region as PDSCH.

Some of the uplink physical channels and signals supported in LTE are:

· Physical Uplink Shared Channel, PUSCH

• Physical Uplink Control Channel, PUCCH

• Physical Random Access Channel (PRACH) • DeModulation Reference Signal (DMRS) for PUSCH

• DeModulation Reference Signal (DMRS) for PUCCH

• Sounding Reference Signal (SRS)

• DeModulation Sounding Reference Signal

The PUSCH is used to carry uplink data or/and uplink control information from the wireless device to the network node. The PUCCH is used to carry uplink control information from the wireless device to the network node.

DMRS for PUSCH

DMRS for PUSCH is used for PUSCH demodulations. More specifically, the DMRS is used by the network node or eNB for uplink channel estimation in the RBs scheduled for the associated PUSCH. DMSR is time multiplexed with associated PUSCH and occupies the same RBs as the PUSCH. The DMRS is transmitted on the REs of the 3^rd SC-OFDM symbol of each slot of a subframe as shown in FIG. 3, where only one RB is shown. It can be seen that DMRS occupies all the subcarriers in the 3^rd symbols of each slot. FIG. 3 is a block diagram of DMRS allocation in a RB of a subframe.

The following are the design goals for uplink DMRS:

• Constant amplitude over transmitted subcarriers for uniform channel excitation and estimation;

• Low peak to average power ratio (PAPR) or cubic metric (CM) in time domain for efficient Power Amplifier (PA) utilization;

• Low cross correlation between different DMRS sequences for low inter-cell interference where different sequences are used in different cells;

The above goals were achieved in LTE by using a combination of computer generated (CG) highly optimized base sequences for lRB and 2RBs and cyclically extended Zadoff-Chu sequences for 3RBs or larger. Let ^_PUSCHO be the DMRS sequence associated with an uplink MIMO layer λ, then the DMRS sequence in LTE is defined as

where m_s = 0,1 corresponding to, respectively, slot 0 and slot 1 as shown in FIG. 3, n =

is the number of subcarriers of the RBs scheduled for the associated PUSCH. In legacy LTE, can be configured with [wffl(0) wW(l)] = [1 1], or [1 - 1] according to Table 5.5.2.1.1-1 of 3GPP Technical Specification (TS) 36.211 which is copied in Table 1. α^λ is a cyclic shift configured for a MIMO layer λ. The cyclic shift a_x in a slot «_s is given as

¾^{=2 12} with

where the values of ¾MRI is configured by higher layers, "DMRS^I is given by the cyclic shift for DMRS field in most recent uplink-related DCI for the transport block associated with the corresponding PUSCH transmission where the value of "DMRS^I is given in Table 5.5.2.1.1-1 of 3GPP technical specification (TS) 36.211, which is copied in Table 1, below. «_PN («_S) is a cell specific number generated pseudo- randomly in a slot by slot basis. n_s E {0,1, ... ,9} is the slot index within a subframe. is a reference signal sequence and is defined by a cyclic shift _a of a base sequence according to

where

number of RBs scheduled for PUSCH. Multiple reference signal sequences are defined from a single base sequence F_{U v}(«) through different values of _a .

Base sequences F_{U v}(«) are divided into groups, where u e {o,i,...,29} is the group number and _v is the base sequence number within the group. So, there are 30 groups of base sequences for each sequence length. For sc ^{= m}N^^B, l<m<5, each group contains one base sequence (v=0). For

m > 6, there are two base sequences (v = 0,l) in each group. The definition of the base sequence r_{M V}(0),... _{M V}(A^^s-l) depends on the sequence length _s · For base sequences of length 3N^_C ^B or larger, r_{u v} (n) is generated through cyclic extension of a Zadoff-Chu (ZC) sequence x_q( ri) as follows v (n ) = x_q (n mod N ¾ ), 0 < n < where the ^ root Zadoff-Chu sequence is defined by

with q given by

= +l/2j + v- (-l)^

The length Nzc of the Zadoff-Chu sequence is given by the largest prime number

By using cyclic extension of the Zadoff-Chu sequences, the base sequences have a constant amplitude over frequency and also maintain the zero auto-correlation cyclic shift orthogonality property of the Zadoff-Chu sequences, which allows generating multiple orthogonal sequences by using different cyclic shifts on a single base sequence. Using extension, not truncation, in general provides better CM for 3 and more RBs. In addition, at least 30 base sequences can be generated this way.

For one and two RBs, however, only a small number of low CM extended Zadoff-Chu sequences is available. To achieve similar inter-cell interference randomization as in the case of 3 or more PRBs, 30 base sequences are desirable. Thus, base sequences for one and two RBs were obtained by computer searches.

Only quadrature phase shift keying (QPSK) based sequences were selected to reduce memory size for storage and computational complexity. The base sequences for one and two RBs (i.e. £? = N_S ^R _C ^B and £? = 2N_S ^R _C ^B) are defined as

RS RB

where the value of φ(η) is given by Table 1 for M_sc = N_SC and by Table 2 for u φ(0),.. , φ(η)

0 -1 1 3 -3 3 3 1 1 3 1 -3 3

1 1 1 3 3 3 -1 1 -3 -3 1 -3 3

2 1 1 -3 -3 -3 -1 -3 -3 1 -3 1 -1

3 -1 1 1 1 1 -1 -3 -3 1 -3 3 -1

4 -1 3 1 -1 1 -1 -3 -1 1 -1 1 3

5 1 -3 3 -1 -1 1 1 -1 -1 3 -3 1

6 -1 3 -3 -3 -3 3 1 -1 3 3 -3 1

7 -3 -1 -1 -1 1 -3 3 -1 1 -3 3 1

8 1 -3 3 1 -1 -1 -1 1 1 3 -1 1

9 1 -3 -1 3 3 -1 -3 1 1 1 1 1

10 -1 3 -1 1 1 -3 -3 -1 -3 -3 3 -1

11 3 1 -1 -1 3 3 -3 1 3 1 3 3

12 1 -3 1 1 -3 1 1 1 -3 -3 -3 1

13 3 3 -3 3 -3 1 1 3 -1 -3 3 3

14 -3 1 -1 -3 -1 3 1 3 3 3 -1 1

15 3 -1 1 -3 -1 -1 1 1 3 1 -1 -3

16 1 3 1 -1 1 3 3 3 -1 -1 3 -1

17 -3 1 1 3 -3 3 -3 -3 3 1 3 -1

18 -3 3 1 1 -3 1 -3 -3 -1 -1 1 -3

19 -1 3 1 3 1 -1 -1 3 -3 -1 -3 -1

20 -1 -3 1 1 1 1 3 1 -1 1 -3 -1

21 -1 3 -1 1 -3 -3 -3 -3 -3 1 -1 -3

22 1 1 -3 -3 -3 -3 -1 3 -3 1 -3 3

23 1 1 -1 -3 -1 -3 1 -1 1 3 -1 1

24 1 1 3 1 3 3 -1 1 -1 -3 -3 1

25 1 -3 3 3 1 3 3 1 -3 -1 -1 3

26 1 3 -3 -3 3 -3 1 -1 -1 3 -1 -3

27 -3 -1 -3 -1 -3 3 1 -1 1 3 -3 -3

28 -1 3 -3 3 -1 3 3 -3 3 3 -1 -1

29 3 -3 -3 -1 -1 -3 -1 3 -3 3 1 -1

Table 1- Definition of φ{η) for M_sc = N_SC in LTE

Χ- ,φ(23)

-1 3 1 -3 3 -1 1 3 -3 3 1 3 -3 3 1 1 -1 1 3 -3 3 -3 -1 -3

-3 3 -3 -3 -3 1 -3 -3 3 -1 1 1 1 3 1 -1 3 -3 -3 1 3 1 1 -3

3 -1 3 3 1 1 -3 3 3 3 3 1 -1 3 -1 1 1 -1 -3 -1 -1 1 3 3

-1 -3 1 1 3 -3 1 1 -3 -1 -1 1 3 1 3 1 -1 3 1 1 -3 -1 -3 -1

-1 -1 -1 -3 -3 -1 1 1 3 3 -1 3 -1 1 -1 -3 1 -1 -3 -3 1 -3 -1 -1

-3 1 1 3 -1 1 3 1 -3 1 -3 1 1 -1 -1 3 -1 -3 3 -3 -3 -3 1 1

1 1 -1 -1 3 -3 -3 3 -3 1 -1 -1 1 -1 1 1 -1 -3 -1 1 -1 3 -1 -3

-3 3 3 -1 -1 -3 -1 3 1 3 1 3 1 1 -1 3 1 -1 1 3 -3 -1 -1 1

-3 1 3 -3 1 -1 -3 3 -3 3 -1 -1 -1 -1 1 -3 -3 -3 1 -3 -3 -3 1 -3

1 1 -3 3 3 -1 -3 -1 3 -3 3 3 3 -1 1 1 -3 1 -1 1 1 -3 1 1

-1 1 -3 -3 3 -1 3 -1 -1 -3 -3 -3 -1 -3 -3 1 -1 1 3 3 -1 1 -1 3

1 3 3 -3 -3 1 3 1 -1 -3 -3 -3 3 3 -3 3 3 -1 -3 3 -1 1 -3 1

1 3 3 1 1 1 -1 -1 1 -3 3 -1 1 1 -3 3 3 -1 -3 3 -3 -1 -3 -1

3 -1 -1 -1 -1 -3 -1 3 3 1 -1 1 3 3 3 -1 1 1 -3 1 3 -1 -3 3

-3 -3 3 1 3 1 -3 3 1 3 1 1 3 3 -1 -1 -3 1 -3 -1 3 1 1 3

-1 -1 1 -3 1 3 -3 1 -1 -3 -1 3 1 3 1 -1 -3 -3 -1 -1 -3 -3 -3 -1

-1 -3 3 -1 -1 -1 -1 1 1 -3 3 1 3 3 1 -1 1 -3 1 -3 1 1 -3 -1

1 3 -1 3 3 -1 -3 1 -1 -3 3 3 3 -1 1 1 3 -1 -3 -1 3 -1 -1 -1

1 1 1 1 1 -1 3 -1 -3 1 1 3 -3 1 -3 -1 1 1 -3 -3 3 1 1 -3

1 3 3 1 -1 -3 3 -1 3 3 3 -3 1 -1 1 -1 -3 -1 1 3 -1 3 -3 -3

-1 -3 3 -3 -3 -3 -1 -1 -3 -1 -3 3 1 3 -3 -1 3 -1 1 -1 3 -3 1 -1

-3 -3 1 1 -1 1 -1 1 -1 3 1 -3 -1 1 -1 1 -1 -1 3 3 -3 -1 1 -3

-3 -1 -3 3 1 -1 -3 -1 -3 -3 3 -3 3 -3 -1 1 3 1 -3 1 3 3 -1 -3 23 -1 -1 -1 -1 3 3 3 1 3 3 -3 1 3 -1 3 -1 3 3 -3 3 1 -1 3 3

24 1 -1 3 3 -1 -3 3 -3 -1 -1 3 -1 3 -1 -1 1 1 1 1 -1 -1 -3 -1 3

25 1 -1 1 -1 3 -1 3 1 1 -1 -1 -3 1 1 -3 1 3 -3 1 1 -3 -3 -1 -1

26 -3 -1 1 3 1 1 -3 -1 -1 -3 3 -3 3 1 -3 3 -3 1 -1 1 -3 1 1 1

27 -1 -3 3 3 1 1 3 -1 -3 -1 -1 -1 3 1 -3 -3 -1 3 -3 -1 -3 -1 -3 -1

28 -1 -3 -1 -1 1 -3 -1 -1 1 -1 -3 1 1 -3 1 -3 -3 3 1 1 -1 3 -1 -1

29 1 1 -1 -1 -3 -1 3 -1 3 -1 1 3 1 -1 3 1 3 -3 -3 1 -1 -1 1 3

Table 2: Definition of φ(η) for ^j^^^S=2A^^B in LTE

It should be noted that a phase shift of a reference signal sequence does not change its PAPR or CM. Also, the magnitude of a reference signal sequence's autocorrelation or cross correlation with other reference signal sequences does not change if the reference signal is phase shifted. Therefore, a reference signal

where ζ is a real number.

A given reference sequence ¾_;V(w) with sequence number ¾(for example, corresponding to a row in Tables 1 and 2) will have a given value of PAPR or CM. Also, a sequence ¾ _v(w) with sequence number _x and a sequence , _v(n) with sequence number ^will have some cross-correlation c (/_l5/₂), where and ₂ are correlation lags. Good reference signal sequences should have low PAPR or CM and low cross-correlation.

Cubic metric (CM) definition: The CM for a signal, v t), with 3.84MHz nominal bandwidth is defined as

r_ 201og₁₀ m vL_m( ]}- l-52

CM= - dB

1.56 where 20 log₁₀{rms[i^_orrn(t)]} is called raw cubic metric (in dB) of the signal, and

This definition is used in the CM

calculations below.

Cross Correlation definition:

For a set of DMRS base sequences { r_{u v} ( ), n = 0,1, ... , M_sc-l }, the cross correlation between two sequences r_uliVl n) and r_U2,v2 (ⁿ) is defined as

Pi2 = ir |∑^=o^_1 rui,_vi (") ^■ conj(r_u2 ,_v2 (n)) |

Control Signaling for UL-DMRS

An uplink grant can be sent using either DCI format 0 or DCI format 4, depending on the uplink transmission mode configured. For UEs supporting uplink MIMO transmission, DCI format 4 is used. Otherwise, DCI format 0 is used. When MFMO is supported in the uplink, a separate DMRS sequence is needed for each MFMO layer. Up to 4 layers are supported in uplink MIMO in LTE, thus up to four DMRS sequences are needed. The cyclic shifts and Orthogonal Cover Codes (OCC) codes are dynamically signaled in DCI format 0 or DCI format 4 through a Cyclic

n⁽²⁾

Shift Field of 3 bits. This field is used to indicate a cyclic shift parameter, and a length 2 OCC code, \ν^λ, where λ = 0,1, ... , v— 1 and v is the number of layers to be transmitted in the PUSCH scheduled by the DCI. The exact mapping is shown in Table 5.5.2.1.1-1 of 3 GPP TS 36.211 release 13 vl3.0.0, which is reproduced in Table 1 below.

Cyclic Shift n^{1) IRS<1

Field in

=\ λ = 2 λ=3 uplink-related 1 = 0 λ = \ λ = 2 λ=3 λ = 0 λ

DCI format 000 0 6 3 9 1 1 1 1 1 -1 1 -1

001 6 0 9 3 1 -1 1 -1 1 1 1 1

010 3 9 6 0 1 -1 1 -1 1 1 1 1 on 4 10 7 1 1 1 1 1 1 1 1 1

100 2 8 5 11 1 1 1 1 1 1 1 1

101 8 2 11 5 1 -1 1 -1 1 -1 1 -1

110 10 4 1 7 1 -1 1 -1 1 -1 1 -1

111 9 3 0 6 1 1 1 1 1 -1 1 -1

Table 1 : Mapping of Cyclic Shift Field in uplink-related DCI format to ^DMR¾l and

Latency reduction with short TTI transmissions

Packet data latency is one of the performance metrics that vendors, operators and also end-users (via speed test applications) regularly measures. Latency measurements are done in all phases of a radio access network system lifetime, when verifying a new software release or system component, when deploying a system and when the system is in commercial operation.

Shorter latency than previous generations of 3GPP radio access technologies (RATs) was one performance metric that guided the design of Long Term Evolution (LTE). LTE is also now recognized by the end-users to be a system that provides faster access to internet and lower data latencies than previous generations of mobile radio technologies.

Packet data latency is important not only for the perceived responsiveness of the system; it is also a parameter that indirectly influences the throughput of the system. HTTP/TCP is the dominating application and transport layer protocol suite used on the internet today. The typical size of HTTP based transactions over the internet are in the range of a few 10's of Kbyte up to 1 Mbyte. In this size range, the TCP slow start period is a significant part of the total transport period of the packet stream. During TCP slow start, the performance is latency limited. Hence, improved latency can rather easily be showed to improve the average throughput, for this type of TCP based data transactions. Radio resource efficiency could be positively impacted by latency reductions. Lower packet data latency could increase the number of transmissions possible within a certain delay bound; hence higher Block Error Rate (BLER) targets could be used for the data transmissions freeing up radio resources potentially improving the capacity of the system.

One approach to latency reduction is the reduction of transport time of data and control signaling, by addressing the length of a transmission time interval (TTI). By reducing the length of a TTI and maintaining the bandwidth, the processing time at the transmitter and the receiver nodes is also expected to be reduced, due to less data to process within the TTI. As described above, in LTE release 8, a TTI corresponds to one subframe (SF) of length 1 millisecond. One such 1 ms TTI is constructed by using 14 OFDM or SC-FDMA symbols in the case of normal cyclic prefix and 12 OFDM or SC-FDMA symbols in the case of extended cyclic prefix. In LTE release 14, latency reduction is being studied and conducted, with the goal of specifying transmissions with shorter TTIs, such as a slot or a few symbols.

An sTTI can be established with any duration in time and may include resources on a number of OFDM or SC-FDMA symbols within a 1 ms SF. As one example shown in FIG. 4, the duration of the uplink short TTI is 0.5 ms, i.e., seven SC-FDMA symbols for the case with normal cyclic prefix. In particular, FIG. 4 is an example of a 7-symbol sTTI configuration within an uplink subframe. As another example shown in FIG. 5, the durations of the uplink short TTIs within a subframe are of 2 or 3 symbols. Here, the "R" in the Figures indicates the DMRS symbols, and "S" indicates the SRS symbols. In particular, FIG. 5 is an example of a 2/3-symbol sTTI configuration within an uplink subframe. As used herein, short PDSCH (sPDSCH) and short PUSCH (sPUSCH) are used to denote the downlink and uplink physical shared channels with sTTIs, respectively.

DMRS for sPUSCH

UL DMRS with IFDMA

For a given sPUSCH scheduling bandwidth in an uplink subframe, legacy specification will allow up to 8 orthogonal DMRS sequences, each with a unique cyclic shift. These sequences can be used to support uplink MFMO transmission with 4 layers (which is the maximum number layers that are supported in uplink in LTE), each assigned with one cyclic shift, or uplink multi-user MIMO (MU-MIMO) for up to 8 wireless devices, each with one MEVIO layer.

However, since DMRS sequences with different lengths (i.e., bandwidths) are generally not orthogonal, wireless devices with different PUSCH bandwidths cannot generally be scheduled together for MU-MIMO transmission. In LTE Release 10, OCC2 was introduced between two DMRS symbols in two slots of an uplink subframe, i.e. [w^(0) w^(l)] = [1 1] or [1— 1], so that two wireless devices with partially overlapped PUSCH bandwidths can be paired for MU-MIMO.

In the case of sTTI, a single DMRS symbol is available and thus no OCC can be configured. To support more wireless devices with partially overlapped sPUSCH bandwidth in the uplink, it has been agreed that Interleaved Frequency Division Multiplexing (IFDMA) with repetition factor (RPF) 2 for uplink DMRS for sPUSCH will be introduced in LTE 3GPP Release 14, in which uplink DMRS is transmitted on only half of the subcarriers, either even numbered or odd numbered subcarriers. An example with 2RBs is shown in FIG. 6, where a DMRS for one wireless device can be assigned on the DMRS REs at even numbered subcarriers while a DMRS for another wireless device can be assigned on the other half of subcarriers, i.e., DMRS REs at odd numbered subcarriers. Since the two DMRS sequences are transmitted on different subcarriers, they are orthogonal to each other. In this example, the length of each of the two DMRS sequence is 12 and thus the existing length 12 (i.e. = 12) base sequence F_{u v} { n ) can be used.

If only the existing base sequences F_{u v} { n ) are used for IFDMA with RPF=2, then the wireless devices need to be scheduled with a granularity of 2RBs, which restricts resource allocation options in the network, and may lead to reduced data throughput when MU-MIMO wireless devices are scheduled. New sequences will be introduced in Release 14 in order to support scheduling of also odd number of RBs greater than 3RBs. The new sequences will be generated from cyclic extension of Zadoff-Chu sequences, as is done previously.

UL DMRS sequence lengths for IFDMA

However, it is still to be determined whether new sequences with length 6, 18 and 30 are supported in LTE Release 14 in order to support scheduling with lRB, 3RBs and 5RBs for IFDMA with RPF=2, respectively. The main reason is that for these sequence lengths, it is not possible to generate 30 base sequences with cyclic extension of Zadoff-Chu sequences.

Using truncated Zadoff-Chu sequences was proposed for generating the length 30 base sequences for uplink DMRS, in which a length 31 Zadoff-Chu sequence is truncated by dropping either the first or the last entry of the sequence. A set of 30 base sequences were proposed for length 18 sequences through computer search.

For length 6 sequences (i.e., φ(0)-φ(5)), it was proposed to reuse a set of 14 length-6 sequences that was to be introduced for Narrow Band Internet of Things (NB-IOT) in LTE Release 14. The set of 14 length-6 sequences is a subset of the 16 sequences and is shown in Table 4 below.

□ cp(0), cp(l), φ(2), φ(3), φ(4), φ(5)

0 1 1 1 3 -3

¹

1 1 3 1 -3 3

¹

2 -1 -1 -1 1 -3

¹

3 -1 3 -3 -1 -1

¹

4 3 1 -1 -1 3

¹

5 -3 -3 1 3 1

¹

6 -1 1 -3 -3 -1

-¹

7 -1 -1 3 -3 -1

-¹

8 3 -1 1 -3 -3 3

9 3 -1 3 -3 -1 1

10 3 -3 3 -1 3 3

11 -3 1 3 1 -3 -1

12 -3 1 -3 3 -3 -1

13 -3 3 -3 1 1 -3 Table 4: Length-6 DMRS base sequences to be introduced in B-IOT:

ϊ_{α ν} (_η) = _βΜ"⁾ ^ o≤«≤5

DMRS sharing

When the same wireless device is scheduled on consecutive sTTIs, an effective way to reduce the overhead of reference signals for UL data transmission is DMRS sharing. This means that the DMRS is not transmitted in each sTTI. Instead, a certain periodicity in terms of the number of sTTIs is assumed for transmitting DMRS. FIG. 7 illustrates an example of DMRS sharing for the case of a 2/3 -symbol sTTI configuration in an uplink subframe. In this example, DMRS transmitted in sTTI 0 and sTTI 3 are used for the channel estimation for sTTI 1 and sTTI 4, respectively.

DMRS multiplexing

In cases where different wireless devices are scheduled in consecutive short TTIs, DMRS sharing cannot be used. Instead, to reduce the DMRS overhead for UL data transmissions, DMRS multiplexing can be considered. DMRS multiplexing means multiple wireless devices share the same SC-FMDA symbol but have separate SC-FMDA symbols for the data. FIG. 8 illustrates examples of DMRS multiplexing for two different 2/3 -symbol sTTI configurations within an uplink subframe. The DMRS from different wireless devices are multiplexed in the same SC-FDMA symbol marked with "R". The orthogonality between the multiplexed DMRS from different wireless devices should be ensured in order to guarantee good channel estimation and successful data decoding.

For uplink sTTI transmissions, DMRS multiplexing/sharing can be used to reduce the DMRS overhead. With the same frequency allocation, the DMRS of different wireless devices can be multiplexed on the same SC-FDMA symbol by using different cyclic shifts.

In order to keep the scheduling flexibility, different wireless devices can be allocated with different frequency resources, where part of their frequency allocation is overlapped, as shown in FIG. 9. In particular, FIG. 9 illustrates a block diagram of two sPUSCH transmissions with partially overlapped frequency allocation. Here, DMRS multiplexing should also be supported in this partially overlapped frequency allocation case to reduce the DMRS overhead, and at the same time, keep the scheduling flexibility.

The IFDMA-based DMRS multiplexing method discussed above for MU- MIMO transmission on PUSCH can also be used for supporting DMRS multiplexing on sPUSCH with partially overlapped frequency allocations.

Different from DMRS multiplexing for MU-MIMO transmissions on PUSCH, in most cases, there is at most one DMRS symbol per sPUSCH transmission. This implies that OCC cannot be used for DMRS multiplexing when considering sPUSCH transmissions.

SUMMARY

Some embodiments advantageously provide a method, network node and wireless device for signaling of reference signal (RS) and/or spatial multiplexing configuration for uplink short transmission time interval (sTTI) transmissions.

According to one embodiment of the disclosure, a wireless device for reference signal, RS, multiplexing is provided. The wireless device includes processing circuitry configured to: receive at least one RS configuration bit signaled in a downlink control indicator, DCI, field; determine an RS configuration for a short Transmission Time Interval, sTTI, based on a number of spatial layers assigned to the wireless device for transmission and the at least one RS configuration bit; and transmit an RS on the sTTI based on the determined RS configuration.

According to one embodiment of this aspect, the RS configuration includes a transmission comb offset. According to one embodiment of this aspect, the at least one RS configuration bit corresponds to a value, the value being based on the number of spatial layers assigned to the wireless device. According to one embodiment of this aspect, the at least one RS configuration bit is signaled in a cyclic shift, CS, field of the DCI field. According to one embodiment of this aspect, the RS configuration includes a cyclic shift, CS, value and a comb offset. According to one embodiment of this aspect, the determining of the RS configuration for the sTTI based on the number of spatial layers assigned to the wireless device (14) for transmission includes using at least one table defined by at least one of equations: ^ηΟ 85,_λ (^comb ^ 3!<cs + ⁽> )rz > ^max 2,J ^::: 0, ^,.. _max ···^■ 1

nDMRSA = (* bG i3₂ (11 - [ j + 2 [™j + (6)k _;; -f 2Xj + [ ]) _ , - 4, i - 0, ...A_raax - 1 where _max is a maximum number of received spatial layers, λί is a number of spatial layers, NDMRS, λ is a cyclic shift value for a spatial layer.

According to one embodiment of this aspect, the determining of the RS

configuration for the sTTI based on the number of spatial layers assigned to the wireless device for transmission includes using at least one table defined by equation:

where NAP is a number of antenna ports, N_max_cs (N™^ax) is a maximum number of cycle shifts, n is a cyclic shift value, and λ is a spatial layer. According to one

embodiment of this aspect, different CS values associated with the at least one

configuration bit are assigned to different spatial layers.

According to one embodiment of this aspect, the at least one RS configuration bit is at least one demodulation RS, DMRS configuration bit. According to one embodiment of this aspect, the at least one configuration bit is two RS configuration bits. According to one embodiment of this aspect, the number of spatial layers

assigned to the wireless device is 1, 2, 3 or 4 spatial layers.

According to one embodiment of this aspect, the at least one RS configuration bit is configured to be multiplexed with at least one other RS configuration bit from at least one other wireless device on a first symbol in the sTTI. According to one

embodiment of this aspect, a frequency allocation for use by the wireless device is configured to at least partially overlap with another frequency allocation for use by another wireless device.

According to one aspect of the disclosure, a method for a wireless device for reference signal, RS, multiplexing is provided. At least one RS configuration bit signaled in a downlink control indicator, DCI, field is received. An RS configuration for a short Transmission Time Interval, sTTI, is determined based on a number of spatial layers assigned to the wireless device for transmission and the at least one RS configuration bit. An RS is transmitted on the sTTI based on the determined RS configuration. According to one embodiment of this aspect, the RS configuration includes a transmission comb offset. According to one embodiment of this aspect, the at least one RS configuration bit corresponds to a value, the value being based on the number of spatial layers assigned to the wireless device (14).

According to one embodiment of this aspect, the at least one RS configuration bit are signaled in a cyclic shift, CS, field of the DCI field. According to one

embodiment of this aspect, the RS configuration includes a cyclic shift, CS, value and a comb offset. According to one embodiment of this aspect, the determining of the RS configuration for the sTTI based on the number of spatial layers assigned to the wireless device for transmission includes using at least one table defined by at least one of equations:

¾¾_RS,A ^~ (3kcomb + 6k_tSJ ) ^~ _n , A_max ^~ 1 ND R_SA ~

~ 0, ...A_max— 1 ¾_MRSA ^:::: (^k«_>mb(!<cs+i)2 (11^■" |jj + 2 + (6)k _s -t- 2Aj ^ , A_miiX ^::: 4, i === 0, ... A_ma;< - I where _max is a maximum number of received spatial layers, λι is a number of spatial layers, NDMRS, λ is a cyclic shift value for a spatial layer.

According to one embodiment of this aspect, the determining of the RS

configuration for the sTTI based on the number of spatial layers assigned to the wireless device (14) for transmission includes using at least one table defined by equation: ¾ras._¾ 0 _AP - 1

where NAP is a number of antenna ports, N max cs is a maximum number of cycle shifts, n is a cyclic shift value, and λ is a spatial layer. According to one embodiment of this aspect, different CS values associated with the at least one configuration bit are assigned to different spatial layers. According to one embodiment of this aspect, the at least one RS configuration bit is at least one demodulation RS, DMRS

configuration bit. According to one embodiment of this aspect, the at least one RS configuration bit is two RS configuration bits. According to one embodiment of this aspect, the number of spatial layers assigned to the wireless device is 1, 2, 3 or 4 spatial layers.

According to one embodiment of this aspect, the at least one RS configuration bit is configured to be multiplexed with at least one other RS configuration bit from at least one other wireless device on a first symbol in the sTTI.

According to one embodiment of this aspect, a frequency allocation for use by the wireless device is configured to at least partially overlap with another frequency allocation for use by another wireless device. According to another aspect of the disclosure, a network node for reference signal, RS, multiplexing is provided. The network node includes processing circuitry configured to: transmit at least one RS configuration bit signaled in a downlink control indicator, DCI, field, the at least one RS configuration bit corresponding to a RS configuration for a short Transmission

Time Interval, sTTI, based on a number of spatial layers assigned to a wireless device; and receive a RS in the sTTI based on the RS configuration.

According to one embodiment of this aspect, the RS configuration includes a transmission comb offset. According to one embodiment of this aspect, the at least one RS configuration bit corresponds to a value, the value being based on the number of spatial layers assigned to the wireless device. According to one embodiment of this aspect, the at least one RS configuration bit is signaled in a cyclic shift, CS, field of the DCI field.

According to one embodiment of this aspect, the RS configuration includes a cyclic shift, CS, value and a comb offset. According to one embodiment of this aspect, the RS configuration for the sTTI based on the number of spatial layers

assigned to the wireless device for transmission is based on at least one table defined by at least one of equations:

nOMRSA - (^7ke*rob + ^3fecs + 6λ χ2 > iax ~ ², i = 0, ...X_max - 1 »£> RSA ^:::: (^ka mbO )2 C¹¹ ~ 0, ... X_m<« ^~ 1

where _maK is a maximum number of received spatial layers, λί is a number of spatial layers, NDMRS, λ is a cyclic shift value for a spatial layer.

According to one embodiment of this aspect, the RS configuration for the sTTI based on the number of spatial layers assigned to the wireless device (14) for transmission is based on at least one table defined by equation:

j _j max ^

As > = (» + Ht^~ ¾^ax _' " = ⁰'^}> - ^N-^SX ^ = 0 N _AP - 1

where NAP is a number of antenna ports, N max cs is a maximum number of cycle shifts, n is a cyclic shift value, and λ is a spatial layer.

According to one embodiment of this aspect, different CS values associated with the plurality of configuration bits are assigned to different spatial layers.

According to one embodiment of this aspect, the at least one RS configuration bit is at least one demodulation RS, DMRS configuration bit. According to one embodiment of this aspect, the at least one RS configuration bit is two RS configuration bits.

According to one embodiment of this aspect, the number of spatial layers assigned to the wireless device is 1, 2, 3 or 4 spatial layers.

According to one embodiment of this aspect, the at least one RS configuration bit is configured to be multiplexed with at least one other RS configuration bit from at least one other wireless device on a first symbol in the sTTI. According to one embodiment of this aspect, a frequency allocation for use by the wireless device is configured to at least partially overlap with another frequency allocation for use by another wireless device.

According to another aspect of the disclosure, a method for a network node

(12) for reference signal, RS, multiplexing is provided. At least one RS configuration bit signaled in a downlink control indicator, DCI, field is transmitted. The at least one RS configuration bit corresponds to a RS configuration for a short Transmission Time

Interval, sTTI, based on a number of spatial layers assigned to a wireless device. A

RS in the sTTI is received based on the RS configuration.

n» RS.X ~ (3ko>mb + 6k_f._s, )).¾ < _maiC ~ .1

nDMRS,A ^::: (^7!<corab + 3k _s + 6 j) )₂ , A_max ~ 2, i - 0, ... A_lwax - 1

»_OMRSA = (* ( t)₂ (11 - [ ] + 2 [™j + (6)k_£S + 2¾ + [ D , X_max - 4, i - 0, ... A_msBl - 1 where _max is a maximum number of received spatial layers, λί is a number of spatial layers, NDMRS, λ is a cyclic shift value for a spatial layer.

According to one embodiment of this aspect, the RS configuration for the sTTI based on the number of spatial layers assigned to the wireless device for

transmission is based on at least one table defined by equation:

»_DMRSA = (« + -~¾¾« - « = OX ... * λ = 0, ... , N_AP - 1 where NAP is a number of antenna ports, N_max_cs is a maximum number of cycle shifts, n is a cyclic shift value, and λ is a spatial layer. According to one embodiment of this aspect, different CS values associated with the at least one configuration bit are assigned to different spatial layers.

According to one embodiment of this aspect, the at least one RS configuration bit is at least one demodulation RS, DMRS configuration bit. According to one embodiment of this aspect, the at least one RS configuration bit is two RS

configuration bits. According to one embodiment of this aspect, the number of spatial layers assigned to the wireless device is 1, 2, 3 or 4 spatial layers.

According to another embodiment of the disclosure, a wireless device for reference signal, RS, multiplexing is provided. The wireless device includes a RS configuration module configured to: receive at least one RS configuration bit signaled in a downlink control indicator, DCI, field; determine an RS configuration for a short Transmission Time Interval, sTTI, based on a number of spatial layers assigned to the wireless device for transmission and the at least one RS configuration bit; and transmit an RS on the sTTI based on the determined RS configuration.

According to another aspect of the disclosure, a network node for reference signal, RS, multiplexing is provided. The network node includes a signaling module configured to: transmits at least one RS configuration bit signaled in a downlink control indicator, DCI, field, the at least one RS configuration bit corresponding to a RS configuration for a short Transmission Time Interval, sTTI, based on a number of spatial layers assigned to a wireless device; and receive a RS in the sTTI based on the RS configuration.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present embodiments, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a block diagram of an LTE uplink resource gird;

FIG. 2 is a block diagram of a system with three OFDM symbols as control; FIG. 3 is a block diagram of DMRS allocation in a resource block (RB) of a subframe;

FIG. 4 is a block diagram of an example of a 7-symbol sTTI configuration within an uplink subframe;

FIG. 5 is a block diagram of an example of a 2/3 -symbol sTTI configuration within an uplink subframe;

FIG. 6 is a block diagram of uplink DMRS with IFDMA of RPF=2; FIG. 7 is a block diagram of an example of DMRS sharing for the case of a 2/3 -symbol sTTI configuration in an uplink subframe;

FIG. 8 is a block diagram of examples of DMRS multiplexing for two different 2/3 -symbol sTTI configurations within an uplink subframe;

FIG. 9 is a block diagram of two sPUSCH transmissions with partially overlapped frequency allocation;

FIG. 10 is block diagram of an exemplary system for retransmission handling in accordance with the principles of the disclosure;

FIG. 11 is a block diagram of sPUSCH transmissions for two wireless devices in accordance with the principles of the disclosure;

FIG. 12 is a block diagram of IFDMA-based DMRS multiplexing of two wireless devices with RPF=2 for sPUSCH transmissions in accordance with the principles of the disclosure;

FIG. 13 is one embodiment of a flow chart of an exemplary RS configuration process of RS code in accordance with the principles of the disclosure;

FIG. 14 is one embodiment of flow chart of an exemplary signaling process of signaling code in accordance with the principles of the disclosure; and

FIG. 15 is a block chart of another embodiment of network node in accordance with the principles of the disclosure; and

FIG. 16 is a block chart of another embodiment of wireless device in accordance with the principles of the disclosure.

DETAILED DESCRIPTION

This disclosure, at least in part, provides a solution for efficiently controlling IFDMA-based DMRS under the following considerations:

several spatial layers may be supported for uplink sTTI transmissions; and/or

several users may be able to multiplex their DMRS on the same SC- FDMA symbol.

To do so, one or more methods and supporting hardware implementations for signaling DMRS configurations of uplink short TTI transmissions are described here. In particular, the signaling methods support multiplexing of DMRS of different UEs for uplink short TTI transmissions.

The signaling is interpreted differently depending on how the wireless device is configured for spatial multiplexing. The supported cases are:

- single user, 1 layer;

multiple user, 1 layer;

single user, multiple layers (SU-MIMO); and

multiple users, multiple layers (MU-MIMO)

The signaling can be done semi- statically via RRC or dynamically via DCI.

The methods, wireless devices and networks described herein reduce signaling overhead by taking advantage of being aware of the allocated users and number of layers. This allows multiple wireless devices and wireless device multiplexing at a minimal DCI or RRC resource consumption.

For the sake of simplicity of the wireless device receiver, and reducing the signaling overhead, sTTI wireless devices may only support IFDMA based UL

DMRS. It has been shown that the channel estimation penalty caused for the need to interpolate the gaps in DMRS REs is negligible, when the RPF (Repetition factor) is relatively small. One or more embodiments of the disclosure described herein thus assume that IFDMA is used for UL DMRS in sTTI.

As used herein, relational terms, 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 elements.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

In embodiments described herein, the joining term, "in communication with" and the like, may be used to indicate electrical or data communication, which may be accomplished by physical contact, induction, electromagnetic radiation, radio signaling, infrared signaling or optical signaling, for example. One having ordinary skill in the art will appreciate that multiple components may interoperate and modifications and variations are possible of achieving the electrical and data communication.

Referring now to drawing figures in which like reference designators refer to like elements there is shown in FIG. 10 an exemplary system for retransmission handling. System 10 includes one or more one or more network nodes 12 and one or more wireless devices 14, in communication with each other via one or more communication networks, paths and/or links using one or more communication protocols such as LTE based protocols. Embodiments are not limited to LTE implementations and can be implemented in other systems such as New Radio (NR) based systems.

Network node 12 includes transmitter 16 and receiver 18 for communicating with wireless device 14, other network nodes 14 and/or other entities in system 10. In one or more embodiments, transmitter 16 and receiver 18 includes or is replaced by one or more communication interfaces.

Network node 12 includes processing circuitry 19. Processing circuitry 19 includes processor 20 and memory 22. In addition to a traditional processor and memory, processing circuitry 19 may comprise integrated circuitry for processing and/or control, e.g., one or more processors and/or processor cores and/or FPGAs (Field Programmable Gate Array) and/or ASICs (Application Specific Integrated Circuitry). Processor 20 may be configured to access (e.g., write to and/or reading from) memory 22, which may comprise any kind of volatile and/or nonvolatile 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 22 may be configured to store code executable by processor 20 and/or other data, e.g., data pertaining to

communication, e.g., configuration and/or address data of nodes, etc.

Processing circuitry 19 may be configured to control any of the methods and/or processes described herein and/or to cause such methods, signaling and/or processes to be performed, e.g., by network node 12. Processor 20 corresponds to one or more processors 20 for performing network node 12 functions described herein. Network node 12 includes memory 22 that is configured to store data, programmatic software code and/or other information described herein. In one or more

embodiments, memory 22 is configured to store signaling code 24. For example, signaling code 24 includes instructions that, when executed by processor 20, causes processor 20 to perform the processes describe herein with respect to network node 12.

The term "network node 12" 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 wireless device 14 or network node 12 may be distributed over a plurality of wireless devices 14 and/or network nodes 12. In other words, it is contemplated that the functions of the network node and wireless device described herein are not limited to performance by a single physical device and, in fact, can be distributed among several physical devices locally or across a network cloud such as a backhaul network and/or the Internet.

Wireless device 14 includes transmitter 26 and receiver 28 for communicating with network node 12, other wireless devices 14 and/or other entities in system 10. In one or more embodiments, transmitter 26 and receiver 28 includes or is replaced by one or more communication interfaces.

Wireless device 14 includes processing circuitry 29. Processing circuitry 29 includes processor 30 and memory 32. In addition to a traditional processor and memory, processing circuitry 29 may comprise integrated circuitry for processing and/or control, e.g., one or more processors and/or processor cores and/or FPGAs (Field Programmable Gate Array) and/or ASICs (Application Specific Integrated Circuitry). Processor 30 may be configured to access (e.g., write to and/or reading from) memory 32, which may include any kind of volatile and/or nonvolatile 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 32 may be configured to store code executable by processor 30 and/or other data, e.g., data pertaining to

communication, e.g., configuration and/or address data of nodes, etc.

Processing circuitry 29 may be configured to control any of the methods and/or processes described herein and/or to cause such methods, signaling and/or processes to be performed, e.g., by wireless device 14. Processor 30 corresponds to one or more processors 30 for performing wireless device 14 functions described herein. Wireless device 14 includes memory 32 that is configured to store data, programmatic software code and/or other information described herein. In one or more embodiments, memory 32 is configured to store RS configuration code 34. For example, RS configuration code 34 includes instructions that, when executed by processor 30, causes processor 30 to perform the signaling describe herein with respect to wireless device 14.

Wireless device 14 may be a radio communication device, wireless device endpoint, mobile endpoint, device endpoint, sensor device, target device, device-to- device wireless device, user equipment (UE), machine type wireless device or wireless device capable of machine to machine communication, a sensor equipped with wireless device, tablet, mobile terminal, mobile telephone, laptop, computer, appliance, automobile, smart phone, laptop embedded equipped (LEE), laptop mounted equipment (LME), USB dongle and customer premises equipment (CPE), among other devices that can communicate radio or wireless signals as are known in the art.

The methods, network nodes 12 and wireless devices 14 described herein provide for signaling DMRS configurations of uplink short TTI transmissions. In particular, the signaling supports multiplexing of DMRS of different wireless devices 14 and spatial layers for uplink short TTI transmissions. In one or more

embodiments, the IFDMA-based DMRS multiplexing method is used for uplink short TTI transmissions. The cyclic shift is signaled by a N bit cyclic shift field in UL DCI. The comb configuration for DMRS transmission is implicitly indicated by the cyclic shift index. Some examples on how to multiplex DMRS from different wireless devices 14 for sPUSCH transmissions are described below in section "DMRS multiplexing for sPUSCH", considering different frequency allocation cases. The examples on signaling of the DMRS multiplexing are given in section "Signaling of DMRS configuration for sPUSCH".

DMRS multiplexing for sPUSCH

DMRS multiplexing with the same frequency allocation

FIG. 11 is a block diagram of sPUSCH transmissions for two wireless devices 14 with the same frequency allocation, where wireless device 14a is with 2 symbol sPUSCH, and wireless device 14b is with 3 symbol sPUSCH. In other words, wireless devices 14 are assigned the same bandwidth where there is not overlap in frequency allocation for the RS. In particular, FIG. 11 illustrates the case where the multiplexed wireless devices 14 are allocated with the same uplink frequency bandwidth. In other words, in one or more embodiments, the subcarriers within the respective frequency allocation for wireless devices 14a- 14b of FIG. 11 do not overlap since they use different subcarriers, while wireless devices 14a- 14b are still assigned the same bandwidth. In this case, two different DMRS multiplexing approaches can be used, namely,

Approach 1 : DMRS from different wireless devices 14 are multiplexed on the same SC-FDMA symbol and subcarriers (same comb index) by using different cyclic shifts.

Approach 2: DMRS from different wireless devices are multiplexed on the same SC-FDMA symbol but different subcarriers, as shown in FIG. 12. In particular, FIG. 12 is a block diagram of IFDMA-based DMRS multiplexing of two wireless devices 14 with RPF=2 for sPUSCH transmissions. Wireless device 14a is with 2 symbol sPUSCH, and wireless device 14b is with 3 symbol sPUSCH.

Summary: comb-based UL-DMRS can be multiplexed in the CS domain or comb domain

DMRS multiplexing with partially overlapped frequency allocation

Approach 2 as described above can be used when different wireless devices 14 that are allocated with partially overlapped frequency bandwidth. This in in contrast to approach 1 is based on cyclic shift separation which cannot be achieve with partially overlapping bandwidth.

FIG. 12 illustrates examples of IFDMA-based DMRS multiplexing of different wireless devices 14, where the sPUSCH transmissions are allocated with partially overlapped frequency bandwidth. In FIG. 12, the vertical axis is the frequency axis and the horizontal axis is the time axis.

DMRS multiplexing over layers with partially overlapped frequency allocation

Each layer is addressed with a specific shift. In legacy systems, the 4 possible layers are each given a specific DMRS cyclic shift for a given DCI.

Signaling of DMRS configuration for sPUSCH

In each of the configurations, the same number of bits N is used. These bits, i.e., RS configuration bits, may either be signaled via RRC or DCI, or partially signaled via RRC and partially signaled via DCI, although DCI gives a larger dynamic flexibility. The interpretation of the bits is dependent of another parameter as described below.

The following description uses the case of 2 bits or N =2. However, this does not preclude the use of more bits in other implementations of the disclosure. The disclosure advantageously utilizes awareness of the configuration of wireless device 14 in the number of assigned spatial layers. It is based on interpreting the DMRS configuration bits differently when wireless device 14 is configured for a single layer transmission or multiple layer transmission. In other words, at least one RS configuration bit corresponds to a RS configuration for a sTTI based on a number of spatial layers assigned to wireless device 14.

Wireless device 14 is not aware of single- or multi-user MIMO configuration. However, wireless device 14 does know the number of configured layers, received from, e.g., DCI as described in 3 GPP TS 36.212 tables such as Table 5.3.3.1.8-1 to Table 5.3.3.1.8-3, or otherwise. The interpretation of the CS field for comb index and cyclic shift value can then depend of the configured number of layers, so that the settings can be optimized for layer separation. Table xl, x2 and x3, below, show the proposed settings for the new DCI bits and corresponding layer configurations. In one example, the table generating functions are as follow (note: ( )_x denotes the modulo x operation). The parameters k_comb=0, l,...K denotes the comb index number and k_cs=0, l,.. ,L denotes the cyclic shift index for this comb

, (2)

— (^kcomb + 6k_cs, )] — 1

n (2)

(^7kcomb + ^3kcs + ^6λί) ΐ2 ^max 2, 1 0, ... X_max 1

^max 4, i 0, ... λ-_fnax 1

In one or more embodiments of the cyclic shifts are shown in Tables 5a-5c where there are two possible choices for each of the odd and even subcarriers that should be "orthogonal" so that two wireless devices 14 with the maximum number of layers can be paired without any conflicting cyclic shift.

Table 5a for CS allocation, two spatial layers

Table 5b for CS allocation, one spatial layer Cyclic » ⁽²⁾

Shift

Field in

uplink- IFDMA

A = 0 λ = \ λ = 2 λ=3

related Configuration

DCI

format

00 0 2 4 7 Comb offset 0

01 6 8 10 1 Comb offset 0

10 11 3 5 9 Comb offset 1

11 6 8 10 1 Comb offset 1

Table 5c for CS allocation, four spatial layers The configuration allows the assignment of different cyclic shifts to layers for a given comb offset. This solution may be done to handle different users over different comb indices if they have different bandwidth (for example field 00 and field 10) or the same comb index for equal bandwidth (for example 00 and 01). This configuration does not preclude that a similar configuration can be devised using the same principle but multiplexing comb values over layers and users over cyclic shifts.

SRS implementation of the CS field for coverage (mix of combs for the same user). In another example, the table generated follows the principle used for SRS parameters configuration. The cyclic shift _a~ of the sounding reference signal is given as

where _w ^» _s = {o_, «_™ - _l) is configured separately for periodic and each

configuration of aperiodic sounding by the higher-layer parameters cyclicShift and cyclicShift-ap, respectively, for each wireless device 14 and N _ap is the number of antenna ports used for sounding reference signal transmission. The parameter «_S¾_S ^MAX = 8 if K_TC = 2 , otherwise «_s¾_s ^max = 12 . The parameter K_TC is given by the higher layer parameter transmissionCombNum if configured, otherwise K_TC = 2 .

Using the same process described above, the cyclic shift generating equation would be:

¾MRS x = (n + )NS» - n = 0,1, ... N™^x λ = 0 N_AP - 1

¹ AP

As can be seen, the cyclic shift is independent of the comb offset. The maximum value of the cyclic shift N™^ax depends on the number of available combs and required layers N™^ax = N_AP K_TC Assume we also limit the DCI size with two bits and two combs as in the previous example. One of these bits must signal the comb offset. For a case of two combs ( K_TC = 2 ), and using the equation based on SRS for generating the cyclic shift table the following Tables 6a-6c are obtained:

Table 6a for CS allocation, one spatial layer

Table 6b for CS allocation, two spatial layers Cyclic » ⁽²⁾

Shift Field

in

uplink- IFDMA

A = 0 λ = \ λ = 2 1=3

related Configuration

DCI

format

00 0 2 4 6 Comb offset 0

01 1 3 5 7 Comb offset 0

10 0 2 4 6 Comb offset 1

11 1 3 5 7 Comb offset 1

Table 6c for CS allocation, four spatial layers

Therefore, in one or more embodiments, given the CS field value and wireless device 14 knowing its configured spatial layers (as described herein), wireless device 14 is able to determination a value in the table, e.g., 0, 6, 7, etc., and the comb offset. In one or more embodiments, the number of spatial layers assigned to the wireless device 14 is 1, 2, 3 or 4 spatial layers, which are described herein such as with respect to Tables 5a-5c. In one or more embodiments, wireless device 14 receives one or more tables, as described above, for use in the RS configuration process. In one or more embodiments, wireless device 14 generates one or more tables, as described above, for use in the RS configuration process. In one or more embodiments, several tables are combined into one tables such that, in one embodiment, wireless device 14 generates a single table corresponding to Tables 5a-5c, for example.

FIG. 13 is a flow chart of one embodiment of an exemplary RS configuration process of RS configuration code 34 in accordance with the principles of the disclosure. In particular, wireless device 14 is configured, in one or more

embodiments, for Interleaved Frequency Division Multiplexing (IFDMA) based reference signal (RS) multiplexing for short Physical Uplink Shared Channel

(sPUSCH) transmissions, and to use a frequency allocation that partially overlaps with a frequency allocation of another entity. Processing circuitry 29 is configured to receive at least one RS configuration bit signaled in a DCI field, as described herein (Block SI 00). In one or more embodiments, processing circuitry 29 is configured to receive a plurality of RS configuration bits. The signaling of RS configuration bits to wireless device 14 is described in this disclosure.

In one or more embodiments, the plurality of RS configuration bits provides a first RS configuration corresponding to a first number of spatial layers. The plurality of RS configuration bits provide a second RS configuration correspond to a second number of spatial layers, and the first RS configuration is different from the second RS configuration. In one or more embodiments, processing circuitry 29 is configured to process the plurality of RS configuration bits based on a number of spatial layers assigned to wireless device 14, as discussed in this disclosure.

In one or more embodiments, the processing of the plurality of RS

configuration bits based on the number of spatial layers assigned to wireless device 14 includes determining a cyclic shift (CS) field based on the number of spatial layers assigned to the wireless device and the plurality of RS configuration bits. In one or more embodiments, the RS is a demodulation RS (DMRS). In one or more embodiments, processing circuitry 29 is further configured to determine a comb index and CS value based on the CS field. In one or more embodiments, the plurality of RS configuration bits are two RS configuration bits.

In one or more embodiments, the determining of the comb index and CS value includes using at least one table defined by at least one of equations:

nDMH5,?. - (7fr_t-«mb * 3kcs + 6λί)_η , _max ~ 2, i— 0, ... A.,_mtx - .1

^ 0 M RS ,λ ^:~ ( ^ comb f.s + 13 ?. ( ^ + (6)k _¾ + 2λ; + |~| ) , X_K(ax = 4, i = 0, ... λ„ where _maK is a maximum number of received spatial layers, λί is a number of spatial layers, NDMRS, λ is a cyclic shift value for a spatial layer.

In one or more embodiments, the determining of the comb index and CS value includes using at least one table defined by equation:

^max ^

- 0» + < » = M' - N¾^ax λ - 0_f ... , N_AP - 1 where NAP is a number of antenna ports, N max cs is a maximum number of cycle shifts, n is a cyclic shift value, and λ is a spatial layer. Processing circuitry 29 is configured to determine a RS configuration for a sTTI based on a number of spatial layers assigned to the wireless device 14 for transmission and the at least one RS configuration bit, as described herein (Block SI 02). In one or more embodiments, processing circuitry 29 is configured to determine an RS configuration for sPUSCH transmission in the sTTI based on the processing of the plurality of RS configuration bits. Processing circuitry 29 is configured to transmit an RS on the sTTI based on the determined RS configuration, as described herein (Block SI 04). In one or more embodiments, processing circuitry 29 is configured to transmit an RS on the sPUSCH based on the determined RS configuration.

In one or more embodiments, the RS is a demodulation Sounding RS (SRS). In one or more embodiments, different CS values are assigned to different spatial layers. In one or more embodiments, the plurality of RS configuration bits for configuring the RS for sPUSCH transmission are received in Radio Resource Control (RRC) signaling. In one or more embodiments, the plurality of RS configuration bits for configuring the RS for sPUSCH transmission are received in downlink control information (DCI) signaling. In one or more embodiments, the plurality of RS configuration bits for configuring the RS for sPUSCH transmission are received in a Radio Resource Control (RRC) signaling and downlink control information (DCI) signaling.

FIG. 14 is one embodiment of flow chart of an exemplary signaling process of signaling code 24. Network node 12 configures wireless device 14 using a frequency allocation. In one or more embodiments, the frequency allocation partially overlaps with a frequency allocation of another entity, e.g., another wireless device 14, for Interleaved Frequency Division Multiplexing (IFDMA) based reference signal (RS) multiplexing for short Physical Uplink Shared Channel (sPUSCH) transmissions. In one or more embodiments, the at least one RS configuration bit is configured to be multiplexed with at least one other RS configuration bit from at least one other wireless device 14 on a first symbol in the sTTI. Processing circuitry 19 is configured to transmit at least one RS configuration bit signaled in a DCI field where the at least one RS configuration bit corresponding to a RS configuration for a sTTI based on a number of spatial layers assigned to a wireless device 14, as described herein (Block SI 06). In one or more embodiments, processing circuitry 19 is configured to transmits a plurality of reference signal (RS) configuration bits. The plurality of RS configuration bits provides an RS configuration for sPUSCH transmission for the wireless device based on a number of spatial layers assigned to the wireless device. In one or more embodiments, the RS configuration includes a comb offset. In one or more embodiments, the at least one RS configuration bit corresponds to a value, the value being based on the number of spatial layers assigned to wireless device 14.

Processing circuitry 19 is configured to receive a RS in the sTTI based on the RS configuration (Block SI 08). In one or more embodiments, processing circuitry 19 is configured to receive an RS on the sPUSCH of the sTTI.

In one or more embodiments, the plurality of RS configuration bits provide a first RS configuration corresponding to a first number of spatial layers. The plurality of RS configuration bits provides a second RS configuration corresponding to a second number of spatial layers. The first RS configuration is different from the second RS configuration. In one or more embodiments, the at least one RS configuration bit or the plurality of RS configuration bits are indicated/signaled in a cyclic shift (CS) field of the DCI field, and are based on the number of spatial layers assigned to the wireless device. In one or more embodiments, the CS field is used to determine a comb index and CS value where the RS configuration includes a cyclic shift, CS, value and a comb offset.

In one or more embodiments, different CS values are assigned to different spatial layers. In one or more embodiments, the at least one RS configuration bit is at least one DMRS configuration bit. In one or more embodiments, the RS is a demodulation RS (DMRS). In one or more embodiments, the RS is a demodulation Sounding RS (SRS). In one or more embodiments, the plurality of RS configuration bits for configuring the RS for sPUSCH transmission are transmitted in Radio Resource Control (RRC) signaling.

In one or more embodiments, the plurality of RS configuration bits for configuring the RS for sPUSCH transmission are transmitted in downlink control information (DCI) signaling. In one or more embodiments, the plurality of RS configuration bits for configuring the RS for sPUSCH transmission are transmitted in a Radio Resource Control (RRC) signaling and downlink control information (DCI) signaling.

FIG. 15 is a block diagram of another embodiment of network node 12.

Network node 12 includes signaling module 36 for performing the functions described for signaling code 24. For example, signaling module 36 is configured to transmit at least one RS configuration bit signaled in a DCI field where the at least one RS configuration bit corresponds to a RS configuration for a sTTI based on a number of spatial layers assigned to a wireless device 14, and receive a RS in the sTTI based on the RS configuration, as described herein.

FIG. 16 is a block diagram of another embodiment of wireless device 14.

Wireless device 14 includes RS configuration module 38 for performing the functions described for RS configuration code 34. For example, RS configuration module 38 is configured to receive at least one RS configuration bit signaled in a DCI field, determine an RS configuration for a sTTI based on a number of spatial layers assigned to the wireless device 14 for transmission and the at least one RS

configuration bit, and transmit an RS on the sTTI based on the determined RS configuration, as described herein.

Therefore, one or more embodiments of the disclosure describe signaling reference signal such as DMRS configurations in a sTTI where the signaling of the DMRS configuration is interpreted differently by wireless device 14 based at least in part on how wireless device 14 is configured for spatial multiplexing.

Some Embodiments

According to one aspect of the disclosure, a wireless device 14 for Interleaved Frequency Division Multiplexing (IFDMA) based reference signal (RS) multiplexing for short Physical Uplink Shared Channel (sPUSCH) transmissions is provided. The wireless device 14 is configured to use a frequency allocation that partially overlaps with a frequency allocation of another entity. The wireless device 14 further configured to: receive a plurality of reference signal (RS) configuration bits, process the plurality of RS configuration bits based on a number of spatial layers assigned to the wireless device, determine an RS configuration for sPUSCH transmission based on the processing of the plurality of RS configuration bits, and transmit an RS on the sPUSCH based on the determined RS configuration. According to one embodiment of this aspect, the plurality of RS configuration bits provide a first RS configuration correspond to a first number of spatial layers. The plurality of RS configuration bits provides a second RS configuration

corresponding to a second number of spatial layers. The first RS configuration is different from the second RS configuration. According to one embodiment of this aspect, the processing of the plurality of RS configuration bits based on the number of spatial layers assigned to the wireless device 14 includes determining a cyclic shift (CS) field based on the number of spatial layers assigned to the wireless device 14 and the plurality of RS configuration bits. According to one embodiment of this aspect, the RS is a demodulation RS (DMRS). According to one embodiment of this aspect, the wireless device 14 is further configured to determine a comb index and CS value based on the CS field.

According to one embodiment of this aspect, the plurality of RS configuration bits are two RS configuration bits.

According to one embodiment of this aspect, the determining of the comb index and CS value includes using at least one table defined by at least one of equations:

n0¾RS,A ^::: (^3kcorab + 6k_ts, )₁₂ , X_max ^■■■■ 1

nOMRSA ~ ^camb + 3k_¾ + & i)rt , X_max ~ 2,\ - 0, ...A_max - 1

¾RSA (k« mi>0 i)₂ (11 - |f] 2 -i- (6)k_cs 2¾ | |) , A_raax - 4, i - 0, ... A_ma where _max is a maximum number of received spatial layers, λί is a number of spatial layers, NDMRS, λ is a cyclic shift value for a spatial layer.

According to one embodiment of this aspect, the determining of the comb index and CS value includes using at least one table defined by equation:

"DMRSU ^ ^(« -<- if— 0¾F - ⁿ ° - ^N<"^{X Λ} ^ °' - - ^NAP - ¹

According to one embodiment of this aspect, the RS is a demodulation

Sounding RS (SRS). According to one embodiment of this aspect, different CS values are assigned to different spatial layers. According to one embodiment of this aspect, the plurality of RS configuration bits for configuring the RS for sPUSCH transmission are received in Radio Resource Control (RRC) signaling. According to one embodiment of this aspect, the plurality of RS configuration bits for configuring the RS for sPUSCH transmission are received in downlink control information (DCI) signaling. According to one embodiment of this aspect, the plurality of RS configuration bits for configuring the RS for sPUSCH transmission are received in a Radio Resource Control (RRC) signaling and downlink control information (DCI) signaling.

According to one aspect of the disclosure, a method for a wireless device 14 for Interleaved Frequency Division Multiplexing (IFDMA) based reference signal

(RS) multiplexing for short Physical Uplink Shared Channel (sPUSCH) transmissions is provided. The wireless device 14 is configured to use a frequency allocation that partially overlaps with a frequency allocation of another entity. A plurality of reference signal (RS) configuration bits are received. The plurality of RS

configuration bits is processed based on a number of spatial layers assigned to the wireless device 14. An RS configuration for sPUSCH transmission is determined based on the processing of the plurality of RS configuration bits. An RS on the sPUSCH is transmitted based on the determined RS configuration.

According to one embodiment of this aspect, the plurality of RS configuration bits provide a first RS configuration correspond to a first number of spatial layers. The plurality of RS configuration bits provides a second RS configuration

corresponding to a second number of spatial layers. The first RS configuration is different from the second RS configuration.

According to one embodiment of this aspect, the processing of the plurality of RS configuration bits based on the number of spatial layers assigned to the wireless device 14 includes determining a cyclic shift (CS) field based on the number of spatial layers assigned to the wireless device 14 and the plurality of RS configuration bits. According to one embodiment of this aspect, the RS is a demodulation RS (DMRS). According to one embodiment of this aspect, the wireless device 14 is further configured to determine a comb index and CS value based on the CS field. According to one embodiment of this aspect, the plurality of RS configuration bits are two RS configuration bits. According to one embodiment of this aspect, the determining of the comb index and CS value includes using at least one table defined by at least one of

equations: l0M S.¾

n. OM RS,?- max 2, i ~ (), ... λ„ 1

DMRS λ, _{ - 4, i - Ο, ,.,λ, - 1

where _maK is a maximum number of received spatial layers, λι is a number of spatial layers, NDMRS, λ is a cyclic shift value for a spatial layer.

According to one embodiment of this aspect, the determining of the comb index and CS value includes usin at least one table defined by equation: 0 N_AP - 1

where NAP is a number of antenna ports, N_max_cs is a maximum number of cycle shifts, n is a cyclic shift value, and λ is a spatial layer.

According to one embodiment of this aspect, the RS is a demodulation

Sounding RS (SRS). According to one embodiment of this aspect, different CS

values are assigned to different spatial layers. According to one embodiment of this aspect, the plurality of RS configuration bits for configuring the RS for sPUSCH transmission are received in Radio Resource Control (RRC) signaling.

According to one embodiment of this aspect, the plurality of RS configuration bits for configuring the RS for sPUSCH transmission are received in downlink control information (DCI) signaling. According to one embodiment of this aspect, the

plurality of RS configuration bits for configuring the RS for sPUSCH transmission are received in a Radio Resource Control (RRC) signaling and downlink control

information (DCI) signaling.

According to aspect of the disclosure, a network node 12 for configuring a wireless device 14 using a frequency allocation that partially overlaps with a

frequency allocation of another entity for Interleaved Frequency Division

Multiplexing (IFDMA) based reference signal (RS) multiplexing for short Physical Uplink Shared Channel (sPUSCH) transmissions is provided. The network node 12 including processing circuitry 19 configured to transmits a plurality of reference signal (RS) configuration bits, and receive an RS on the sPUSCH. The plurality of RS configuration bits provides an RS configuration for sPUSCH transmission for the wireless device based on a number of spatial layers assigned to the wireless device 14.

According to one embodiment of this aspect, the plurality of RS configuration bits indicates a cyclic shift (CS) field based on the number of spatial layers assigned to the wireless device 14. According to one embodiment of this aspect, the CS field indicates a comb index and CS value. According to one embodiment of this aspect, different CS values are assigned to different spatial layers. According to one embodiment of this aspect, the plurality of RS configuration bits are two RS configuration bits. According to one embodiment of this aspect, the RS is a demodulation RS (DMRS). According to one embodiment of this aspect, the RS is a demodulation Sounding RS (SRS).

According to one embodiment of this aspect, the plurality of RS configuration bits for configuring the RS for sPUSCH transmission are received in Radio Resource Control (RRC) signaling. According to one embodiment of this aspect, the plurality of RS configuration bits for configuring the RS for sPUSCH transmission are received in downlink control information (DCI) signaling. According to one embodiment of this aspect, the plurality of RS configuration bits for configuring the RS for sPUSCH transmission are received in a Radio Resource Control (RRC) signaling and downlink control information (DCI) signaling.

According to one aspect of the disclosure, a method for configuring a wireless device 14 using a frequency allocation that partially overlaps with a frequency allocation of another entity for Interleaved Frequency Division Multiplexing

(IFDMA) based reference signal (RS) multiplexing for short Physical Uplink Shared Channel (sPUSCH) transmissions is provided. A plurality of reference signal (RS) configuration bits are transmitted. The plurality of RS configuration bits provides an RS configuration for sPUSCH transmission for the wireless device 14 based on a number of spatial layers assigned to the wireless device 14. An RS is received on the sPUSCH.

corresponding to a second number of spatial layers. The first RS configuration is different from the second RS configuration. According to one embodiment of this aspect, the plurality of RS configuration bits indicates a cyclic shift (CS) field based on the number of spatial layers assigned to the wireless device 14.

According to one embodiment of this aspect, the CS field indicates a comb index and CS value. According to one embodiment of this aspect, different CS values are assigned to different spatial layers. According to one embodiment of this aspect, the plurality of RS configuration bits are two RS configuration bits. According to one embodiment of this aspect, the RS is a demodulation RS (DMRS). According to one embodiment of this aspect, the RS is a demodulation Sounding RS (SRS).

According to one embodiment of this aspect, the plurality of RS configuration bits for configuring the RS for sPUSCH transmission are transmitted in Radio Resource Control (RRC) signaling. According to one embodiment of this aspect, the plurality of RS configuration bits for configuring the RS for sPUSCH transmission are transmitted in downlink control information (DCI) signaling. According to one embodiment of this aspect, the plurality of RS configuration bits for configuring the RS for sPUSCH transmission are transmitted in a Radio Resource Control (RRC) signaling and downlink control information (DCI) signaling.

[0001] According to aspect of this disclosure, a wireless device 14 for Interleaved Frequency Division Multiplexing (IFDMA) based reference signal (RS) multiplexing for short Physical Uplink Shared Channel (sPUSCH) transmissions is provided. The wireless device 14 is configured to use a frequency allocation that partially overlaps with a frequency allocation of another entity. The wireless device 14 includes an RS configuration module configured to: receive a plurality of reference signal (RS) configuration bits, process the plurality of RS configuration bits based on a number of spatial layers assigned to the wireless device 14, determine an RS configuration for sPUSCH transmission based on the processing of the plurality of RS configuration bits, and transmit an RS on the sPUSCH based on the determined RS configuration. According to aspect of this disclosure, a network node 12 for configuring a wireless device 14 using a frequency allocation that partially overlaps with a frequency allocation of another entity for Interleaved Frequency Division Multiplexing

(IFDMA) based reference signal (RS) multiplexing for short Physical Uplink Shared Channel (sPUSCH) transmissions is provided. The network nodel2 includes a signaling module configured to transmits a plurality of reference signal (RS) configuration bits, the plurality of RS configuration bits providing an RS

configuration for sPUSCH transmission for the wireless device based on a number of spatial layers assigned to the wireless device, and receive an RS on the sPUSCH.

Some Other Embodiments

According to one embodiment of the disclosure, a wireless device 14 for reference signal, RS, multiplexing is provided. The wireless device 14 includes processing circuitry 29 configured to: receive at least one RS configuration bit signaled in a downlink control indicator, DCI, field; determine an RS configuration for a short Transmission Time Interval, sTTI, based on a number of spatial layers assigned to the wireless device 14 for transmission and the at least one RS configuration bit; and transmit an RS on the sTTI based on the determined RS configuration.

According to one embodiment of this aspect, the RS configuration includes a transmission comb offset. According to one embodiment of this aspect, the at least one RS configuration bit corresponds to a value, the value being based on the number of spatial layers assigned to the wireless device 14. According to one embodiment of this aspect, the at least one RS configuration bit is signaled in a cyclic shift, CS, field of the DCI field.

According to one embodiment of this aspect, the RS configuration includes a cyclic shift, CS, value and a comb offset. According to one embodiment of this aspect, the determining of the RS configuration for the sTTI based on the number of spatial layers assigned to the wireless device 14 for transmission includes using at least one table defined by at least one of equations: ⁿDMRSA = (* bG i3₂ (11 - [ j + 2 [^™j + (6)k _;; -f 2Xj + [ ]) _ , - 4, i - 0, ...A_raa where _max is a maximum number of received spatial layers, λί is a number of spatial layers, NDMRS, λ is a cyclic shift value for a spatial layer. According to one

embodiment of this aspect, the determining of the RS configuration for the sTTI based on the number of spatial layers assigned to the wireless device 14 for transmission includes usin at least one table defined by equation:

According to one embodiment of this aspect, different CS values associated with the at least one configuration bit are assigned to different spatial layers.

According to one embodiment of this aspect, the at least one RS configuration bit is at least one demodulation RS, DMRS configuration bit. According to one embodiment of this aspect, the at least one configuration bit is two RS configuration bits.

According to one embodiment of this aspect, the number of spatial layers assigned to the wireless device 14 is 1, 2, 3 or 4 spatial layers.

According to one embodiment of this aspect, the at least one RS configuration bit is configured to be multiplexed with at least one other RS configuration bit from at least one other wireless device 14 on a first symbol in the sTTI. According to one embodiment of this aspect, a frequency allocation for use by the wireless device 14 is configured to at least partially overlap with another frequency allocation for use by another wireless device 14.

According to one aspect of the disclosure, a method for a wireless device 14 for reference signal, RS, multiplexing is provided. At least one RS configuration bit signaled in a downlink control indicator, DCI, field is received. An RS configuration for a short Transmission Time Interval, sTTI, is determined based on a number of spatial layers assigned to the wireless device 14 for transmission and the at least one RS configuration bit. An RS is transmitted on the sTTI based on the determined RS configuration.

According to one embodiment of this aspect, the RS configuration includes a transmission comb offset. According to one embodiment of this aspect, the at least one RS configuration bit corresponds to a value, the value being based on the number of spatial layers assigned to the wireless device 14. According to one embodiment of this aspect, the at least one RS configuration bit are signaled in a cyclic shift, CS, field of the DCI field.

According to one embodiment of this aspect, the RS configuration includes a cyclic shift, CS, value and a comb offset. According to one embodiment of this aspect, the determining of the RS configuration for the sTTI based on the number of spatial layers assigned to the wireless device 14 for transmission includes using at least one table defined by at least one of equations:

¾¾_RS,A ^~ (3kcomb + 6k_tSJ ) ^~ _n , A_max ^~ 1

ND R_SA ~

~ 0, ...A_max— 1 ¾_MRSA ^:::: (^k«_>mb(!<cs+i)2 (11^■" |jj + 2 + (6)k _s -t- 2Aj ^ , A_miiX ^::: 4, i === 0, ... A_ma;< -- where _max is a maximum number of received spatial layers, λί is a number of spatial layers, NDMRS, λ is a cyclic shift value for a spatial layer. According to one

embodiment of this aspect, the determining of the RS configuration for the sTTI based on the number of spatial layers assigned to the wireless device 14 for transmission includes using at least one table defined by equation:

»¾ = (» + ⁱ -- ¾r - « - o,i, ... n^« λ = 0, ... , N_AP - 1

^NAP

According to one embodiment of this aspect, the at least one RS configuration bit is at least one demodulation RS, DMRS configuration bit. According to one embodiment of this aspect, the at least one RS configuration bit is two RS configuration bits. According to one embodiment of this aspect, the number of spatial layers assigned to the wireless device 14 is 1, 2, 3 or 4 spatial layers. According to one embodiment of this aspect, the at least one RS configuration bit is configured to be multiplexed with at least one other RS configuration bit from at least one other wireless device 14 on a first symbol in the sTTI. According to one embodiment of this aspect, a frequency allocation for use by the wireless device 14 is configured to at least partially overlap with another frequency allocation for use by another wireless device 14.

According to another aspect of the disclosure, a network node 12 for reference signal, RS, multiplexing is provided. The network node 12 includes processing circuitry 19 configured to: transmit at least one RS configuration bit signaled in a downlink control indicator, DCI, field, the at least one RS configuration bit corresponding to a RS configuration for a short Transmission Time Interval, sTTI, based on a number of spatial layers assigned to a wireless device 14; and receive a RS in the sTTI based on the RS configuration.

According to one embodiment of this aspect, the RS configuration includes a transmission comb offset. According to one embodiment of this aspect, the at least one RS configuration bit corresponds to a value, the value being based on the number of spatial layers assigned to the wireless device 14. According to one embodiment of this aspect, the at least one RS configuration bit is signaled in a cyclic shift, CS, field of the DCI field. According to one embodiment of this aspect, the RS configuration includes a cyclic shift, CS, value and a comb offset. According to one embodiment of this aspect, the RS configuration for the sTTI based on the number of spatial layers assigned to the wireless device 14 for transmission is based on at least one table defined by at least one of equations:

nDMRS.X ~ (^^ omb + 6k_cs, )_t2 < A_max ~ .1 nD RS,X ^k_comi, 3k_ts -i- 6Aj) , A_raa;< 2, ϊ 0, ... A_a>ax - 1

where _max is a maximum number of received spatial layers, λί is a number of spatial layers, NDMRS, λ is a cyclic shift value for a spatial layer. According to one embodiment of this aspect, the RS configuration for the sTTI based on the number of spatial layers assigned to the wireless device 14 for transmission is based on at least one table defined by equation: MRSA == (n +^™--)¾ , H - 0,1, ... N™* ... , N_AP - 1 where NAP is a number of antenna ports, N_max_cs is a maximum number of cycle shifts, n is a cyclic shift value, and λ is a spatial layer.

According to one embodiment of this aspect, the at least one RS configuration bit is at least one demodulation RS, DMRS configuration bit.

According to one embodiment of this aspect, the at least one RS configuration bit is two RS configuration bits. According to one embodiment of this aspect, the number of spatial layers assigned to the wireless device 14 is 1, 2, 3 or 4 spatial layers. According to one embodiment of this aspect, the at least one RS configuration bit is configured to be multiplexed with at least one other RS configuration bit from at least one other wireless device 14 on a first symbol in the sTTI. According to one embodiment of this aspect, a frequency allocation for use by the wireless device 14 is configured to at least partially overlap with another frequency allocation for use by another wireless device 14.

According to another embodiment of the disclosure, a method for a network node 12 for reference signal, RS, multiplexing is provided. At least one RS configuration bit signaled in a downlink control indicator, DCI, field is transmitted. The at least one RS configuration bit corresponds to a RS configuration for a short Transmission Time Interval, sTTI, based on a number of spatial layers assigned to a wireless device. A RS in the sTTI is received based on the RS configuration.

nOMRSA ~ (^comb + ³*<cs + 6Aj)_¾2 ^max ^™ 2,1 = 0, ... _max - 1

»™RSA * ( _»m_h( _s+i (Π - |~| + 2 + (6}k _s - 2λ_; + , A._Kias « 4.1 » 0, ...A_roax

where _max is a maximum number of received spatial layers, λί is a number of spatial layers, NDMRS, λ is a cyclic shift value for a spatial layer.

According to one embodiment of this aspect, the RS configuration for the sTTI based on the number of spatial layers assigned to the wireless device 14 for transmission is based on at least one table defined by equation: ¾RSA W NcT^x ... , N_AP - 1

According to one embodiment of this aspect, the at least one RS configuration bit is configured to be multiplexed with at least one other RS configuration bit from at least one other wireless device 14 on a first symbol in the sTTI. According to one embodiment of this aspect, a frequency allocation for use by the wireless device 14 is configured to at least partially overlap with another frequency allocation for use by another wireless device 14. According to another embodiment of the disclosure, a wireless device 14 for reference signal, RS, multiplexing is provided. The wireless device 14 includes a RS configuration module 38 configured to: receive at least one RS configuration bit signaled in a downlink control indicator, DCI, field; determine an RS configuration for a short Transmission Time Interval, sTTI, based on a number of spatial layers assigned to the wireless device 14 for transmission and the at least one RS

configuration bit; and transmit an RS on the sTTI based on the determined RS configuration.

According to another aspect of the disclosure, a network node 12 for reference signal, RS, multiplexing is provided. The network node 12 includes a RS

configuration module 38 configured to: transmits at least one RS configuration bit signaled in a downlink control indicator, DCI, field, the at least one RS configuration bit corresponding to a RS configuration for a short Transmission Time Interval, sTTI, based on a number of spatial layers assigned to a wireless device 14; and receive a RS in the sTTI based on the RS configuration.

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 all 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.

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 special purpose computer), special 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 series 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 procedural 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 scenario, 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 have 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, all embodiments can be combined in any way and/or combination, and the present specification, including the drawings, shall be construed to constitute a complete written description of all 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 all 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

What is claimed is:

1. A wireless device (14) for reference signal, RS, multiplexing, the wireless device (14) comprising processing circuitry (29) configured to:

receive at least one RS configuration bit signaled in a downlink control

indicator, DCI, field;

determine an RS configuration for a short Transmission Time Interval, sTTI, based on a number of spatial layers assigned to the wireless device (14) for

transmission and the at least one RS configuration bit; and

transmit an RS on the sTTI based on the determined RS configuration.

2. The wireless device (14) of Claim 1, wherein the RS configuration includes a transmission comb offset.

3. The wireless device (14) of Claim 1, wherein the at least one RS

configuration bit corresponds to a value, the value being based on the number of spatial layers assigned to the wireless device (14).

4. The wireless device (14) of Claim 1, wherein the at least one RS

configuration bit is signaled in a cyclic shift, CS, field of the DCI field.

5. The wireless device (14) of Claim 1, wherein the RS configuration includes a cyclic shift, CS, value and a comb offset.

6. The wireless device (14) of Claim 5, wherein the determining of the RS configuration for the sTTI based on the number of spatial layers assigned to the wireless device (14) for transmission includes using at least one table defined by at least one of equations:

nD 8S,¾. ^:::: (7 omb 3kcs + & )rz > ^_ro3X ^■"■ 2,\ 0, ... A_m3>; -^■ 1

(11 - [|J + + (6)k_t,_; + 2Aj + 0, ..,A_wax - I

7. The wireless device (14) of Claim 5, wherein the determining of the RS configuration for the sTTI based on the number of spatial layers assigned to the wireless device (14) for transmission includes using at least one table defined by equation:

^HMRSA = (» + ⁱ _¾H)¾r . « = 0.1. ... N™^x λ = 0, ... , Ν_ΛΙ> - 1

^ΝΛΡ

8. The wireless device (14) of Claim 5, wherein different CS values associated with the at least one configuration bit are assigned to different spatial layers.

9. The wireless device (14) of Claim 1, wherein the at least one RS configuration bit is at least one demodulation RS, DMRS configuration bit.

10. The wireless device (14) of Claim 1, wherein the at least one

configuration bit is two RS configuration bits.

11. The wireless device (14) of Claim 1, wherein the number of spatial layers assigned to the wireless device (14) is 1, 2, 3 or 4 spatial layers.

12. The wireless device (14) of Claim 1, wherein the at least one RS configuration bit is configured to be multiplexed with at least one other RS configuration bit from at least one other wireless device (14) on a first symbol in the sTTI.

13. The wireless device (14) of Claim 1, wherein a frequency allocation for use by the wireless device (14) is configured to at least partially overlap with another frequency allocation for use by another wireless device (14).

14. A method for a wireless device (14) for reference signal, RS,

multiplexing, the method comprising:

receive at least one RS configuration bit signaled in a downlink control indicator, DCI, field (SI 00);

determine an RS configuration for a short Transmission Time Interval, sTTI, based on a number of spatial layers assigned to the wireless device (14) for transmission and the at least one RS configuration bit (S102); and

transmit an RS on the sTTI based on the determined RS configuration (SI 04).

15. The method of Claim 14, wherein the RS configuration includes a transmission comb offset.

16. The method of Claim 14, wherein the at least one RS configuration bit corresponds to a value, the value being based on the number of spatial layers assigned to the wireless device (14).

17. The method of Claim 14, wherein the at least one RS configuration bit are signaled in a cyclic shift, CS, field of the DCI field.

18. The method of Claim 14, wherein the RS configuration includes a cyclic shift, CS, value and a comb offset.

19. The method of Claim 18, wherein the determining of the RS configuration for the sTTI based on the number of spatial layers assigned to the wireless device (14) for transmission includes using at least one table defined by at least one of equations: ^N _0MRSA (H ~

[~j + 2 + (6)k _;; -f 2λ₍ + [ J) _ , A._{n iX} - 4, i - 0, ...A_mi where _max is a maximum number of received spatial layers, λί is a number of spatial layers, NDMRS, λ is a cyclic shift value for a spatial layer.

20. The method of Claim 18, wherein the determining of the RS configuration for the sTTI based on the number of spatial layers assigned to the wireless device (14) for transmission includes using at least one table defined by equation: ¾RS = + nsf— -)¾r - » - <u. - S^*» λ ^» ο, ... , N_AP - 1

21. The method of Claim 18, wherein different CS values associated with the at least one configuration bit are assigned to different spatial layers.

22. The method of Claim 14, wherein the at least one RS configuration bit is at least one demodulation RS, DMRS configuration bit.

23. The method of Claim 14, wherein the at least one RS configuration bit is two RS configuration bits.

24. The method of Claim 14, wherein the number of spatial layers assigned to the wireless device (14) is 1, 2, 3 or 4 spatial layers.

25. The method of Claim 14, wherein the at least one RS configuration bit is configured to be multiplexed with at least one other RS configuration bit from at least one other wireless device (14) on a first symbol in the sTTI.

26. The method of Claim 14, wherein a frequency allocation for use by the wireless device (14) is configured to at least partially overlap with another frequency allocation for use by another wireless device (14).

27. A network node (12) for reference signal, RS, multiplexing, the network node (12) including processing circuitry (19) configured to:

transmit at least one RS configuration bit signaled in a downlink control indicator, DCI, field, the at least one RS configuration bit corresponding to a RS configuration for a short Transmission Time Interval, sTTI, based on a number of spatial layers assigned to a wireless device (14); and

receive a RS in the sTTI based on the RS configuration.

28. The network node (12) of Claim 27, wherein the RS configuration includes a transmission comb offset.

29. The network node (12) of Claim 27, wherein the at least one RS configuration bit corresponds to a value, the value being based on the number of spatial layers assigned to the wireless device (14).

30. The network node (12) of Claim 27, wherein the at least one RS configuration bit is signaled in a cyclic shift, CS, field of the DCI field.

31. The network node (12) of Claim 27, wherein the RS configuration includes a cyclic shift, CS, value and a comb offset.

32. The network node (12) of Claim 31, wherein the RS configuration for the sTTI based on the number of spatial layers assigned to the wireless device (14) for transmission is based on at least one table defined by at least one of equations: ^N _0MRSA (11

~ [~j + 2 + (6)k _;; -f 2Xj + [ J) _ , A_{n iX} - 4, i - 0, -,.λ„ where _max is a maximum number of received spatial layers, λί is a number of spatial layers, NDMRS, λ is a cyclic shift value for a spatial layer.

33. The network node (12) of Claim 31, wherein the RS configuration for the sTTI based on the number of spatial layers assigned to the wireless device (14) for transmission is based on at least one table defined by equation: ¾RS = + nsf— -)¾r - » * <u. - S^*» λ ^» ο, ... , N_AP - 1 where NAP is a number of antenna ports, N max cs is a maximum number of cycle shifts, n is a cyclic shift value, and λ is a spatial layer.

34. The network node (12) of Claim 31, wherein different CS values associated with the at least one RS configuration bit are assigned to different spatial layers.

35. The network node (12) of Claim 27, wherein the at least one RS configuration bit is at least one demodulation RS, DMRS configuration bit.

36. The network node (12) of Claim 27, wherein the at least one RS configuration bit is two RS configuration bits.

37. The network node (12) of Claim 27, wherein the number of spatial layers assigned to the wireless device (14) is 1, 2, 3 or 4 spatial layers.

38. The network node (12) of Claim 27, wherein the at least one RS configuration bit is configured to be multiplexed with at least one other RS configuration bit from at least one other wireless device (14) on a first symbol in the sTTI.

39. The network node (12) of Claim 27, wherein a frequency allocation for use by the wireless device (14) is configured to at least partially overlap with another frequency allocation for use by another wireless device (14).

40. A method for a network node (12) for reference signal, RS, multiplexing, the method comprising:

transmitting at least one RS configuration bit signaled in a downlink control indicator, DCI, field, the at least one RS configuration bit corresponding to a RS configuration for a short Transmission Time Interval, sTTI, based on a number of spatial layers assigned to a wireless device (SI 06); and

receive a RS in the sTTI based on the RS configuration (SI 08).

41. The method of Claim 40, wherein the RS configuration includes a transmission comb offset.

42. The method of Claim 40, wherein the at least one RS configuration bit corresponds to a value, the value being based on the number of spatial layers assigned to the wireless device (14).

43. The method of Claim 40, wherein the at least one RS configuration bit is signaled in a cyclic shift, CS, field of the DCI field.

44. The method of Claim 40, wherein the RS configuration includes a cyclic shift, CS, value and a comb offset.

45. The method of Claim 44, wherein the RS configuration for the sTTI based on the number of spatial layers assigned to the wireless device (14) for transmission is based on at least one table defined by at least one of equations: ^N _0MRSA (11

~ [~j + 2 + (6)k _;; -f 2Xj + [ J) _ , A._{n iX} - 4, i - 0, ...A_ral where _max is a maximum number of received spatial layers, λί is a number of spatial layers, NDMRS, λ is a cyclic shift value for a spatial layer.

46. The method of Claim 44, wherein the RS configuration for the sTTI based on the number of spatial layers assigned to the wireless device (14) for transmission is based on at least one table defined by equation: ¾RS = + nsf— -)¾r - » * - NS^* λ ^» ο, .^.. , N_AP - 1 where NAP is a number of antenna ports, N max cs is a maximum number of cycle shifts, n is a cyclic shift value, and λ is a spatial layer.

47. The method of Claim 44, wherein different CS values associated with the at least one configuration bit are assigned to different spatial layers.

48. The method of Claim 40, wherein the at least one RS configuration bit is at least one demodulation RS, DMRS configuration bit.

49. The method of Claim 40, wherein the at least one RS configuration bit is two RS configuration bits.

50. The method of Claim 40, wherein the number of spatial layers assigned to the wireless device (14) is 1, 2, 3 or 4 spatial layers.

51. The method of Claim 40, wherein the at least one RS configuration bit is configured to be multiplexed with at least one other RS configuration bit from at least one other wireless device (14) on a first symbol in the sTTI.

52. The method of Claim 40, wherein a frequency allocation for use by the wireless device (14) is configured to at least partially overlap with another frequency allocation for use by another wireless device (14).

53. A wireless device (14) for reference signal, RS, multiplexing, the wireless device (14) comprising a RS configuration module (36) configured to:

receive at least one RS configuration bit signaled in a downlink control indicator, DCI, field;

determine an RS configuration for a short Transmission Time Interval, sTTI, based on a number of spatial layers assigned to the wireless device (14) for transmission and the at least one RS configuration bit; and

transmit an RS on the sTTI based on the determined RS configuration.

54. A network node (12) for reference signal, RS, multiplexing, the network node (12) comprising a signaling module (38) configured to:

transmits at least one RS configuration bit signaled in a downlink control indicator, DCI, field, the at least one RS configuration bit corresponding to a RS configuration for a short Transmission Time Interval, sTTI, based on a number of spatial layers assigned to a wireless device (14); and

receive a RS in the sTTI based on the RS configuration.