A multi-threshold scheme for feedback load reduction in multiuser MIMO broadcast channel (original) (raw)

Opportunistic Feedback for Multiuser MIMO Systems With Linear Receivers

IEEE Transactions on Communications, 2000

A novel multiuser scheduling and feedback strategy for the multiple-input multiple-output (MIMO) downlink is proposed in this paper. It achieves multiuser diversity gain without substantial feedback requirements. The proposed strategy uses per-antenna scheduling at the base station, which maps each transmit antenna at the base station (equivalently, a spatial channel) to a user. Each user has a number of receive antennas that is greater than or equal to the number of transmit antennas at the base station. Zero-forcing receivers are deployed by each user to decode the transmitted data streams. In this system, the base station requires users' channel quality on each spatial channel for scheduling. An opportunistic feedback protocol is proposed to reduce the feedback requirements. The proposed protocol uses a contention channel that consists of a fixed number of feedback minislots to convey channel state information. Feedback control parameters including the channel quality threshold and the random access feedback probability are jointly adjusted to maximize the average throughput performance of this system. Multiple receive antennas at the base station are used on the feedback channel to allow decoding multiple feedback messages sent simultaneously by different users. This further reduces the bandwidth of the feedback channel. Iterative search algorithms are proposed to solve the optimization for selection of these parameters under both scenarios that the cumulative distribution functions of users are known or unknown to the base station. Index Terms-Diversity methods, feedback, multiple-input multiple-output (MIMO) systems, multiuser channels, scheduling. I. INTRODUCTION M ULTIPLE-INPUT multiple-output (MIMO) is an attractive physical layer (PHY) technology that supports high data rate communications through the use of multiple transmit and receive antennas. The MIMO downlink in cellular systems is one instance of the MIMO broadcast channel, where a point with multiple transmit antennas sends data to multiple destinations, each with one or more multiple receive antennas. Research on the MIMO broadcast channel capacity in [1]-[5] Paper approved by Y. (G.

Feedback Reduction for Random Beamforming in Multiuser MIMO Broadcast Channel

For the multiuser multiple-input multiple-output (MIMO) downlink channel, the users feedback their channel state information (CSI) to help the base station (BS) schedule users and improve the system sum rate. However, this incurs a large aggregate feedback bandwidth which grows linearly with the number of users. In this paper, we propose a novel scheme to reduce the feedback load in a downlink orthogonal space division multiple access (SDMA) system with zero-forcing receivers by allowing the users to dynamically determine the number of feedback bits to use according to multiple decision thresholds. Through theoretical analysis, we show that, while keeping the aggregate feedback load of the entire system constant regardless of the number of users, the proposed scheme almost achieves the optimal asymptotic sum rate scaling with respect to the number of users (also known as the multiuser diversity). Specifically, given the number of thresholds, the proposed scheme can achieve a constant portion of the optimal sum rate achievable only by the system where all the users always feedback, and the remaining portion (referred to as the sum rate loss) decreases exponentially to zero as the number of thresholds increases. By deriving a tight upper bound for the sum rate loss, the minimum number of thresholds for a given tolerable sum rate loss is determined. In addition, a fast bit allocation method is discussed for the proposed scheme, and the simulation results show that the sum rate performances with the complex optimal bit allocation method and with the fast algorithm are almost the same. We compare our multi-threshold scheme to some previously proposed feedback schemes. Through simulation, we demonstrate that the proposed scheme can reduce the feedback load and utilize the limited feedback bandwidth more effectively than the existing feedback methods.

Exploiting multiuser diversity in MIMO broadcast channels with limited feedback

We consider a multiple antenna broadcast channel in which a base station equipped with M transmit antennas communicates with K ≥ M single-antenna receivers. Each receiver has perfect channel state information (CSI), whereas the transmitter has partial channel knowledge obtained via a limited rate feedback channel. Built upon multiuser interference bounds, we propose scalar feedback metrics that incorporate information on the channel gain, the channel direction, and the quantization error, with the goal to provide an estimate of the received signal-to-noise plus interference ratio (SINR) at the transmitter. These metrics, combined with efficient user selection algorithms and zero-forcing beamforming on the quantized channel are shown to achieve a significant fraction of the capacity of the full CSIT case by exploiting multiuser diversity. A multi-mode scheme that allows us to switch from multiuser to single-user transmission is also proposed as a means to compensate for the capacity ceiling effect of quantization error and achieve linear sum-rate growth in the interference-limited region.

A Design Framework for Scalar Feedback in MIMO Broadcast Channels

EURASIP Journal on Advances in Signal Processing, 2008

Joint linear beamforming and scheduling are performed in a system where limited feedback is present at the transmitter side. The feedback conveyed by each user to the base station consists of channel direction information (CDI) based on a predetermined codebook and a scalar metric with channel quality information (CQI) used to perform user scheduling. In this paper, we present a design framework for scalar feedback in MIMO broadcast channels with limited feedback. An approximation on the sum rate is provided for the proposed family of metrics, which is validated through simulations. For a given number of active users and average SNR conditions, the base station is able to update certain transmission parameters in order to maximize the sum-rate function. On the other hand, the proposed sum-rate function provides a means of simple comparison between transmission schemes and scalar feedback techniques. Particularly, the sum rate of SDMA and time division multiple access (TDMA) is compared in the following extreme regimes: large number of users, high SNR, and low SNR. Simulations are provided to illustrate the performance of various scalar feedback techniques based on the proposed design framework.

Feedback reduction for MIMO broadcast channel with heterogeneous fading

2011 IEEE Symposium on Computers and Communications (ISCC), 2011

This paper considers feedback load reduction for multiuser multiple input multiple output (MIMO) broadcast channel where the users' channel distributions are not homogeneous. A cluster-based feedback scheme is proposed such that the range of possible signal-to-noise ratio (SNR) of the users are divided into several clusters according to the order statistics of the users' SNRs. Each cluster has a corresponding threshold, and the users compare their measured instantaneous SNRs with the thresholds to determine whether and how many bits they should use to feed back their instantaneous SNRs. If a user's instantaneous SNR is lower than a certain threshold, the user does not feed back. Feedback load reduction is thus achieved. For a given number of clusters, the sum rate loss using the cluster-based feedback scheme is investigated. Then the minimum number of clusters given a maximum tolerable sum rate loss is derived. Through simulations, it is shown that, when the number of users is large, full multiuser diversity can be achieved by the proposed feedback scheme, which is more efficient than the conventional schemes.

Multiuser Diversity - Multiplexing Tradeoff in MIMO Broadcast Channels with Limited Feedback

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

We consider joint scheduling and beamforming in a broadcast channel with multiple antennas at the transmitter and a single antenna at the mobile receiver. Perfect channel knowledge is assumed to be available at the receiver while the transmitter is provided with partial channel state information (CSIT) through a limited rate feedback channel. Each user feeds back quantized information regarding the channel vector direction (from a codebook) and a quantized (scalar) channel quality indicator. We identify the tradeoff between multiuser diversity and spatial multiplexing gain given a limited amount of feedback bits. Scaling laws of the above parameters are derived in order to achieve a target rate performance. Our results reveal useful design guidelines for the split of feedback bits for channel quantization and channel quality.

Finite-Rate Feedback MIMO Broadcast Channels with a Large Number of Users

2006 IEEE International Symposium on Information Theory, 2006

We analyze the sum-rate performance of a multiantenna downlink system carrying more users than transmit antennas, with partial channel knowledge at the transmitter due to finite rate feedback. In order to exploit multiuser diversity, we show that the transmitter must have, in addition to directional information, information regarding the quality of each channel. Such information should reflect both the channel magnitude and the quantization error. Expressions for the SINR distribution and the sum-rate are derived, and tradeoffs between the number of feedback bits, the number of users, and the SNR are observed. In particular, for a target performance, having more users reduces feedback load.

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.

Comparison of Practical Feedback Algorithms for Multiuser MIMO

IEEE Transactions on Communications, 2010

We consider the problem of channel state information (CSI) transmission on a fast feedback link for a multiuser MIMO system.We examine the relative merits of channel feedback schemes based on Shannon's source-channel separation theorem and non-separation based schemes and show that the latter are preferable in this application. For the non-separation based schemes, we first consider a simple analog transmission and then develop a hybrid digital-analog transmission scheme which quantizes the CSI using a few bits and sends these bits and also the quantization error using analog transmission. We show that the hybrid scheme achieves a higher throughput compared to both analog and digital transmissions and has a much lower computational complexity compared to a digital scheme.

Feedback schemes for multiuser MIMO-OFDM downlink

2008

Abstract We consider a MIMO-OFDM broadcast channel and compare achievable ergodic rates under three channel state feedback schemes: analog feedback, direction quantized feedback and ldquotime-domainrdquo channel quantized feedback. The third scheme is new, and it is inspired by rate-distortion theory of Gaussian correlated sources. For each scheme we derive the conditions under which the system achieves full multiplexing gain.