# US 9,438,320 B2 · Iterative nonlinear precoding and feedback for multi-user multiple-input multiple-output (MU-MIMO) with channel state information (CSI) impairments

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- Number: US 9,438,320 B2
- Document ID: US9438320B2
- Status: Granted
- Kind: B2
- Application number: 13/820,335
- Filed: 2011-09-01
- Published: 2013-08-29
- Granted: 2016-09-06
- Earliest claimed: 2010-09-01
- Assignees: InterDigital Patent Holdings, Inc.
- Applicants: Hongsan Sheng; Yingxue K. Li
- Inventors: Hongsan Sheng; Yingxue K. Li
- Web page: https://patentgrep.com/patent/US9438320B2

## CPC

- H04B 7/0417: Feedback systems
- H04B 7/0452: Multi-user MIMO systems
- H04B 7/0626: {Channel coefficients, e.g. channel state information [CSI]}
- H04B 7/063: {Parameters other than those covered in groups H04B7/0623 - H04B7/0634, e.g. channel matrix rank or transmit mode selection}
- H04B 7/0632: {Channel quality parameters, e.g. channel quality indicator [CQI]}
- H04B 7/0654: {at the receiver, e.g. antenna verification at mobile station}
- H04B 7/0663: {using vector or matrix manipulations}
- H04L 1/0026: {Transmission of channel quality indication}
- H04L 25/03343: {Arrangements at the transmitter end}
- H04L 25/4975: {Correlative coding using Tomlinson precoding, Harashima precoding, Trellis precoding or GPRS}
- H04B 7/0465: {taking power constraints at power amplifier or emission constraints, e.g. constant modulus, into account}
- H04L 5/0007: {the frequencies being orthogonal, e.g. OFDM(A) or DMT}
- H04L 25/0202: {Channel estimation}
- H04L 2025/03802: {Signalling on the reverse channel}
- H04B: TRANSMISSION
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)

## Abstract

An iterative nonlinear preceding method based on, for example. Tomlinson-Harashima Preceding (THP) may be implemented in a MU-MIMO system to alleviate the performance degradation due to mismatches between actual Channel State Information (CSI) and impaired CSI available at a transmitter. In such a method, the effective channel may be fed back rather than a nonprecoded channel for a relay backhaul channel such that the iterative precoding and effective channel feedback may reduce the sensitivity to quantization errors and improve spectrum usage efficiency. Additionally, a Channel Quality Indicator (CQI) may be used to estimate a signal-to-interference-plus-noise (SINK) ratio based on quantization errors to accurately derive the effective channel quality of the receiver.

## Claims

### Claim 1

A method for implementing iterative nonlinear precoding (NLP) and feedback in a Multi-User Multiple-Input Multiple-Output (MU-MIMO) system, the method comprising:
estimating an effective precoded channel;
quantizing the effective precoded channel;
suppressing quantization errors associated with the quantized effective precoded channel to obtain quantized estimates for the effective precoded channel by scaling up elements at a right interference part or triangular of an effective precoded channel matrix associated with the effected precoded channel to a power level of elements or at a left interference part or triangular of the effective precoded channel matrix before quantization using at least one of the following: a scalar, booster, or a fixed value or number and scaling back the power level of the elements at the right interference part of the effective precoded channel matrix after quantization; and
feeding back at least one of the following: the quantized estimates of the effective precoded channel; the quantization errors; a square amplitude of the quantization errors; and a Channel Quality Indicator (CQI) generated based on the quantization error to implement an NLP scheme in the MU-MIMO system to improve spectrum usage efficiencies.

### Claim 2 (depends on 1)

The method of claim 1, wherein at least the quantized estimates of the effective precoded channel and the square amplitude of the quantization errors are fed back in a first iteration.

### Claim 3 (depends on 2)

The method of claim 2, wherein the CQI is fed back for each iteration after the first iteration.

### Claim 4 (depends on 1)

The method of claim 1, wherein the scalar or booster are generated based on feedback in the MU-MIMO system.

### Claim 5 (depends on 1)

The method of claim 1, further comprising:
receiving a signal transmitted through a channel matrix, wherein the signal comprises symbols and data generated in response to at least one of: the quantized estimates; the quantization errors; the square amplitude; and the CQI being fed back;
applying a filter to the received signal;
performing a modulo operation on the filtered signal to remap the symbols or data included therein to an original constellation for a subframe; and
detecting the symbols associated with the signal based on a quantizer of the original constellation.