Feedback reduction for MIMO broadcast channel with heterogeneous fading (original) (raw)

A multi-threshold scheme for feedback load reduction in multiuser MIMO broadcast channel

21st Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, 2010

In a multiuser system, independent time-varying channels among different users can be exploited to provide multiuser diversity (MUD) gain and increase the system throughput. For the downlink channel, this requires the users to feedback their channel state information (CSI) to the base station (BS), which incurs a large aggregate feedback load, especially when the number of users is large. In this paper, we propose a novel scheme to reduce the feedback load in a downlink orthogonal space division multiple access (SDMA) system by allowing the users to dynamically determine the number of feedback bits to use according to multiple thresholds. These thresholds are derived from the statistics of the signal-to-interference-plus-noise ratio (SINR). Through simulation, we demonstrate that the proposed scheme is more efficient than the existing feedback methods, and it achieves the same sum rate growth as the full CSI feedback scheme. Furthermore, a fast bit allocation method is also proposed for the multi-threshold feedback scheme. Simulation results show that this method achieves almost the same sum rate as that achieved by the the optimal bit allocation algorithm.

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.

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.

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.

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.

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.

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.

Analysis of a New MIMO Broadcast Channel Limited Feedback Scheduling Algorithm with User Grouping

Wireless Personal Communications, 2014

In this paper, we present and analyze a new multiuser multiple-input multipleoutput (MU MIMO) broadcast channel scheduling algorithm with limited feedback and user grouping. Here signal-to-noise-plus-interference-ratio (SINR) feedback is used for the scheduling criteria. The algorithm deals with the following three scenarios: (a) All transmit antennas are active. (b) Receive antennas at the mobile station (MS) with maximum SINR values are assigned to the transmit antennas at the base station (BS). (c) A given receive antenna is not scheduled for more than one BS transmit antenna, which ensures user fairness. A detailed comparison of the proposed algorithm with the limited feedback antenna selection algorithms proposed by Zhang et al. and Sharif et al. is presented. Further, we have extended the proposed algorithm to heterogeneous environment, where users having similar signal-to-noise-ratio (SNR) are grouped together. Also, we evaluate the effects of sending the beamforming data (here indices of the receiving antennas) to the BS in terms of complexity of MS and feedback load ratio. A detailed analytical approach for throughput of the system is presented in this paper for the proposed algorithm. We also verify the simulation results with the analytical results. Keywords Sub optimal antenna selection algorithm • MIMO • MU MIMO • SINR feedback • User grouping 1 Introduction Multiple-input multiple-output (MIMO) systems deliver high capacity over wireless channels with high reliability [2,7,18,19]. Multiple antenna systems have an advantage of spatial mul

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.

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.