# US 2018/0026765 A1 · Enhanced srs for massive mimo channel estimation

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- Number: US 2018/0026765 A1
- Document ID: US20180026765A1
- Status: Published application
- Kind: A1
- Application number: 15/537,877
- Filed: 2016-01-16
- Published: 2018-01-25
- Earliest claimed: 2015-01-16
- Assignees: RF DSP Inc.
- Inventors: Jason Brent; Dengkui Zhu; Ping Liang
- Web page: https://patentgrep.com/patent/US20180026765A1

## CPC

- H04L 5/0048: {Allocation of pilot signals, i.e. of signals known to the receiver (allocation of control signalling H04L5/0053; use of control signalling H04L5/0091)}
- H04B 7/0452: Multi-user MIMO systems
- H04B 7/0456: Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting
- H04B 7/0617: {for beam forming}
- H04B 7/0626: {Channel coefficients, e.g. channel state information [CSI]}
- H04L 5/0007: {the frequencies being orthogonal, e.g. OFDM(A) or DMT}
- H04W 72/23: in the downlink direction of a wireless link, i.e. towards a terminal
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)
- H04B: TRANSMISSION
- H04W: WIRELESS COMMUNICATION NETWORKS (broadcast communication H04H; communication systems using wireless links for non-selective communication, e.g. wireless extensions H04M1/72)

## Abstract

This invention provides SRS transmission methods to meet the Massive MIMO systems requirements. These methods are described in two separate categories. Firstly, enhancements to multiplex more channels in the same resources for a given SRS transmission and to provide Massive MIMO throughput performance improvements. Secondly, scheduling enhancements to provide adaptive UE-specific scheduling based on channel conditions for each UE. These methods can be combined in different ways in each BS to optimize the channel estimation system capacity for a given level of system performance.

## Claims

### Claim 1

A method for multiplexing a plural of UEs on the same resource element, comprising using SRS transmission to estimate the uplink channel coefficients of each UE; and implementing TO and FO compensation in a MU-MIMO wireless communication system.

### Claim 2 (depends on 1)

The method in claim 1 further comprising NSRS (NSRS≧1) symbols (SRS symbols) are reserved specially for SRS transmission in an uplink subframe.

### Claim 3 (depends on 2)

The method in claim 2 further comprising that the NSRS symbols are preferably continuous when NSRS≧1.

### Claim 4 (depends on 2)

The method in claim 2 further comprising dividing the Nuse useable subcarriers of a SRS symbol into MComb (MComb≧1) non-overlap sets or combs, where KUE1 (KUE1≧1) are multiplexed on a comb through code division multiplexing (CDM), frequency division multiplexing (FDM), or a combination of these two multiplexing methods.

### Claim 5 (depends on 4)

The method in claim 4 further comprising the same KUE1 UEs are scheduled on the same comb of the NSRS SRS symbols with the same multiplexing method in each symbol.

### Claim 6 (depends on 4)

The method in claim 4 further comprising that the numbers MComb and KUE1 is adaptively configured by the BS according to the application scenario such as cell size, the maximum channel delay spread, the system bandwidth, the number of UEs to be served.

### Claim 7 (depends on 2)

The method in claim 2 further comprising dividing the useable subcarriers of a SRS symbol can into MComb (MComb≧1) non-overlap sets or combs, where KUE2 (KUE2≧1) are multiplexed on a comb across the NSRS SRS symbols through code division multiplexing (CDM), frequency division multiplexing (FDM), time division multiplexing (TDM), or a combination of the three multiplexing methods.

### Claim 8 (depends on 7)

The method in claim 7 further comprising that multiplexing KUE2 UEs through CDM is implemented by KUE2 orthogonal sequences with a length of
L
=
N
use

N
SRS
M
Comb
,
where each sequence is constructed by multiplying a sequence sF of length
N
use
M
Comb
in the frequency domain with a cover sequence sT of length NSRS in the time domain or is formulated as s=sFsT or s=sTsF.

### Claim 9 (depends on 7)

The method in claim 7 further comprising that the numbers MComb and KUE2 is adaptively configured by the BS according to the application scenario such as the cell size, the maximum channel delay spread, the system bandwidth, the number of UEs to be served.

### Claim 10 (depends on 1)

The method in claim 1 further comprising that using the estimates of UE speed of motion in the BS PHY to adjust SRS periodicity per UE.

### Claim 11 (depends on 1)

The method in claim 1 further comprising that extra SRS scheduling opportunities is allocated in time periods where no uplink data transmissions are scheduled besides the specially reserved SRS symbols.

### Claim 12 (depends on 1)

The method in claim 1 further comprising that extra SRS scheduling opportunities is allocated in the data symbols of downlink TDD subframes where no data is scheduled besides the specially reserved SRS symbols.

### Claim 13 (depends on 1)

The method in claim 1 further comprising that a BS with TDD echo canceling capability allocates uplink SRS transmissions in downlink subframes while it is concurrently sending downlink data.

### Claim 14 (depends on 1)

The method in claim 1 further comprising that the frequency offset of a UE is estimated by comparing the currently estimated CSI with previous stored CSI when single SRS is transmitted by a UE.

### Claim 15 (depends on 1)

The method in claim 1 further comprising that the methods of multiplexing UEs, comb and orthogonal sequence are combined in different ways to give each BS the flexibility to optimize based on the number of multiplexed SRS users, rate of update of CSI, system throughput performance etc. for a given system configuration and channel conditions.