Joint low-rate feedback and channel quantization for the MIMO broadcast channel (original) (raw)

Efficient Quantization for Feedback in MIMO Broadcasting Systems

2006 Fortieth Asilomar Conference on Signals, Systems and Computers, 2006

We consider the problem of joint multiplexer-scheduler design for transmitting independent data streams over a Gaussian multiple-antenna broadcast channel in which feedback is used to convey channel state information from receivers to the transmitter. It is known that various low complexity strategies can achieve the optimal rate scaling as a function of receiver population size. In this work we develop a simple and efficient quantization strategy for use on the feedback link of such architectures.

Tree-Structured Random Vector Quantization for Limited-Feedback Wireless Channels

2011

We consider the quantization of a transmit beamforming vector in multiantenna channels and of a signature vector in code division multiple access (CDMA) systems. Assuming perfect channel knowledge, the receiver selects for a transmitter the vector that maximizes the performance from a random vector quantization (RVQ) codebook, which consists of independent isotropically distributed unit-norm vectors. The quantized vector is then relayed to the transmitter via a rate-limited feedback channel. The RVQ codebook requires an exhaustive search to locate the selected entry. To reduce the search complexity, we apply generalized Lloyd or k-dimensional (kd)-tree algorithms to organize RVQ entries into a tree. In examples shown, the search complexity of tree-structured (TS) RVQ can be a few orders of magnitude less than that of the unstructured RVQ for the same performance. We also derive the performance approximation for TS-RVQ in a large system limit, which predicts the performance of a moderate-size system very well.

On channel quantization and feedback strategies for multiuser MIMO-OFDM downlink systems

IEEE Transactions on Communications, 2009

We consider a multiuser MIMO-OFDM downlink system with single antenna mobile terminals (MTs) where channel state information at the base station is provided through limited uplink feedback (FB). In order to reduce the FB rate and signal processing complexity, the available bandwidth is divided into resource blocks (RBs) whose number of subcarriers reflects the coherence bandwidth of the channel. This approach is very common in the standardization of 4th generation wireless communication systems and justifies an independent channel quantization per RB. Within this framework the paper contains two main contributions. Firstly we provide joint conditions on the channel coherence bandwidth and the FB rate per RB that allow for a simpler quantization of the RB channel matrix (spacefrequency) by a space vector, causing negligible performance loss in terms of system achievable throughput. This is accomplished after deriving a new metric for codebook design in RB channel quantization that exploits spatial and frequency correlation. As a second contribution we investigate the trade-off between accurate channel knowledge and frequency/multiuser diversity. It is seen that even for a moderate number of MTs in the network, concentrating all the available FB bits in characterizing only one RB provides a significant gain in system throughput over a more classical distributed approach and this result is validated both analytically and by simulations.

Channel Quantization and Feedback Optimization in Multiuser MIMO-OFDM Downlink Systems

IEEE GLOBECOM 2008 - 2008 IEEE Global Telecommunications Conference, 2008

We consider a multiuser MIMO-OFDM downlink system with single antenna mobile terminals (MTs) where channel state information at the base station is provided through limited uplink feedback (FB). In order to reduce the FB rate and signal processing complexity, the available bandwidth is divided into resource blocks (RBs) whose number of subcarriers reflects the coherence bandwidth of the channel. This approach is very common in the standardization of 4th generation wireless communication systems and justifies an independent channel quantization per RB. The paper has two main contributions: firstly we show conditions on the coherence bandwidth of the channel and the FB rate per RB that allow for a simpler characterization of the RB channel matrix by a space vector, causing negligible performance loss. This is accomplished after deriving a new performance metric for RB channel quantization that exploits spatial and frequency correlation. As a second contribution we investigate the trade-off between accurate channel knowledge and frequency/multiuser diversity. It is seen that even for a moderate number of MTs in the network, concentrating all the available FB bits in characterizing only one RB provides a significant gain in system throughput over a more classical distributed approach and this result is validated both analytically and by simulations.

Codebook-based quantized MIMO feedback for closed-loop transmit precoding

2009 Conference Record of the Forty-Third Asilomar Conference on Signals, Systems and Computers, 2009

Advanced quantization schemes are proposed for closed-loop transmit precoding over correlated multiple-input multiple-output (MIMO) channels in this work. Unlike the conventional schemes that directly quantize the MIMO channel covariance matrix and feed back each quantized matrix element, the proposed schemes quantize the channel covariance matrix by exploiting the common rank-one codebook shared by mobile stations and base stations. Compared to the conventional quantization schemes, the proposed quantization schemes can achieve comparable throughput performance with more than 50% overhead reduction at the cost of affordable increase in computational complexity.

Reduced feedback for selective fading MIMO broadcast channels

In this article, we analyze the selective multiple-input multiple-output broadcast channel, where links are assumed to be selective in both time and frequency. The assumption of full channel knowledge at the transmitter side requires a large amount of feedback, and it is therefore not practical to be implemented in real systems. A more feasible solution with finite rate feedback originally proposed by Jindal in IEEE Trans. Inf. Theory is applied here to the selective fading case, where the minimal number of feedback bits required to achieve the full multiplexing is derived. We show that the correlation between time frequency channels can be used in order to minimize the number of feedback bits to the transmitter side while conserving the maximal multiplexing gain. Finally, the practical implementation of a time-frequency channel quantization scheme is addressed, and a low-complexity scheme that also achieves the multiplexing gain is proposed.

Limited feedback signaling for MIMO broadcast channels

IEEE 6th Workshop on Signal Processing Advances in Wireless Communications, 2005.

Recently, a number of techniques have been introduced to exploit multiuser diversity of a wireless multiple input multiple output (MIMO) broadcast channel (BC) that consists of a base station (BS) with t transmit antennas and K mobile stations (MS) with multiple antennas. However, prior works have ignored the rate overhead associated with feedback of MIMO BC channel state information (CSI), which is roughly K times larger than single-user MIMO CSI (i.e., it is O(tr) where r = P K k=1 r k and r k is the number of antennas at the kth MS). Considering the amount of feedback signaling, quantization is a necessity for effective feedback transmission as a form of partial CSI. In this paper, we propose the greedy multi-channel selection diversity (greedy MCSD) scheme based on block MMSE QR decomposition with dirty paper coding (block MMSE-DP), where partial CSI is almost sufficient. The sum-rate performance of our novel scheme approaches extremely close to the sum capacity of MIMO BC as the number of users increases, whereas the feedback overhead is reduced by a factor of 2t 3 /L(t 2 − t), in which L is the number of active channel vectors. Simulation results validate the expectation from the analysis.

Quantized Feedback for Slow Fading Channels

2006

Two topics in fading channels with a strict delay constraint and a resolutionconstrained feedback link are treated in this thesis. First, a multi-layer variable-rate single-antenna communication system with quantized feedback, where the expected rate is chosen as the performance measure, is studied under both short-term and long-term power constraints. Iterative algorithms exploiting results in the literature of parallel broadcast

Channel State Feedback Over the MIMO-MAC

IEEE Transactions on Information Theory, 2011

We consider the problem of designing low latency and low complexity schemes for channel state feedback over the MIMO-MAC (multiple-input multiple-output multiple access channel). We develop a framework for analyzing this problem in terms of minimizing the MSE distortion, and come up with separated source-channel schemes and joint source-channel schemes that perform better than analog feedback. We also develop a strikingly simple code design based on scalar quantization and uncoded QAM modulation that achieves the theoretical asymptotic performance limit of the separated approach with very low complexity and latency, in the case of single-antenna users. Index Terms Multiple-Antenna Multiple-Access Channel, Channel State Feedback, Wireless Communications I. INTRODUCTION C ONSIDER a frequency division duplex (FDD) cellular system with sufficient frequency spacing between the uplink and downlink channels, such that the uplink and downlink fading coefficients are independent. A base station (BS) with M antennas wishes to serve K user terminals (UTs), with N t antennas each, using some MIMO broadcast channel precoding technique, such as linear beamforming, Dirty-Paper Coding or some low-complexity non-linear precoding approximation thereof. Essential to these techniques is the availability of accurate channel state information at the transmitter (CSIT), that is, the BS must know the user downlink channels. We consider the popular block-fading model, according to which the channel coefficients remain constant for time-frequency slots of some finite but large number of channel uses (complex dimensions), and change independently from slot to slot. We assume that the UTs have perfect knowledge of their downlink channels on each block, which can be obtained from downlink training symbols broadcasted by the BS. Then, at each time slot, the downlink channel coefficients must be fed back to the BS on the uplink. We can model this CSIT feedback as signaling over a MIMO multiple-access channel (MAC). It has been shown in [8], [9] that the relevant performance measure that dominates the downlink rate gap 1 is the mean-square error (MSE) distortion at which the BS is able to represent the UTs channel coefficients (this will be made more precise in the sequel). It follows that the CSIT feedback problem consists of lossy transmission under an end-to-end MSE distortion constraint of

Vector Quantization of Channel Information in Linear Multi-User MIMO Systems

2006 IEEE Ninth International Symposium on Spread Spectrum Techniques and Applications, 2006

In this paper, we propose a new vector quantization (VQ) algorithm for encoding channel state information feedback in multiple antenna, multiuser systems operating on flat fading channels with rich scattering. We consider an approach where the receiver chooses an instantaneous throughput maximizing modulation matrix from a finite set of predefined matrices (codewords). The codebook of modulation matrices is constructed based on joint optimization of the dominant channel eigenmodes of users and separate quantization of power levels. The proposed algorithm is very flexible and can be used in a variety of system configurations, including varying number of receiver antennas and frequency selective channels. We implement the proposed algorithm on flat fading MIMO channels and show the influence of the feedback rate on system capacity. We demonstrate that, even with low feedback rate, the ergodic capacity of the proposed system closely approaches the theoretic capacity of the system with perfect channel state information at the transmitter.