Article

Quantization and Bit Allocation for Channel State Feedback in Relay-Assisted Wireless Networks

IEEE Transactions on Signal Processing (Impact Factor: 2.79). 12/2011; 61(2). DOI: 10.1109/TSP.2012.2224344
Source: arXiv

ABSTRACT

This paper investigates quantization of channel state information (CSI) and
bit allocation across wireless links in a multi-source, single-relay
cooperative cellular network. Our goal is to minimize the loss in performance,
measured as the achievable sum rate, due to limited-rate quantization of CSI.
We develop both a channel quantization scheme and allocation of limited
feedback bits to the various wireless links. We assume that the quantized CSI
is reported to a central node responsible for optimal resource allocation. We
first derive tight lower and upper bounds on the difference in rates between
the perfect CSI and quantized CSI scenarios. These bounds are then used to
derive an effective quantizer for arbitrary channel distributions. Next, we use
these bounds to optimize the allocation of bits across the links subject to a
budget on total available quantization bits. In particular, we show that the
optimal bit allocation algorithm allocates more bits to those links in the
network that contribute the most to the sum-rate. Finally, the paper
investigates the choice of the central node; we show that this choice plays a
significant role in CSI bits required to achieve a target performance level.

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    ABSTRACT: This paper investigates quantization of the channel state information (CSI) in a cooperative cellular network. This CSI, delivered to some central node, is to be used to allocate resources in order to maximize the sum-rate in a multi-source network assisted by multiple relays. We start by deriving tight bounds on the performance loss due to quantization and then, through minimizing these bounds, we propose an efficient quantization and bit allocation technique. To this end, we present the bound on the overall performance loss as the sum of individual terms where each term represents the loss caused by the quantization of the CSI for an individual link. Then we show that each of these terms can be written as the product of two important components: the standard quantization error, and the link coefficient which is only a function of the large scale fading parameters. The quantization error is similar for all links and leads to the optimal quantization problem. Then using a simple bound on the quantization error, and also considering the link coefficients, we allocate bits to quantize each link. Further, we discuss the candidates in the network to play the role of the central node. A numerical example shows that the overall sum-rate (overall CSI demand), is significantly increased (decreased) through bit allocation.
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    ABSTRACT: In wireless networks, having channel state information (CSI) at some central node is essential for most resource allocation problems. We turn our attention to the uplink transmission in a cellular network where the cell users are assisted by a single relay; our goal is to maximize sum rate over the users. Understanding that assuming perfect CSI is a purely theoretical construct, we investigate the scenario where only quantized CSI (QCSI) is available at a central node. Here we design quantization levels which minimize the performance loss in terms of loss in sum rate due to quantization in the network. Next, assuming a finite capacity for the CSI feedback link, we argue that the performance loss may be further reduced through proper bit allocation, i.e., quantization of different links with different precision. We further show that for any given network, there is always savings in terms of CSI bits required as long as optimal bit allocation is deployed. Finally, we propose a lower bound on performance loss achieved through optimal bit allocation.
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    ABSTRACT: In this paper the performance of decode-and-forward (DF) opportunistic relaying systems with limited feedback is studied. Firstly an approximate expression of outage probability for limited-feedback opportunistic relaying is derived. Secondly the diversity gain with limited feedback is proved to be only 2 regardless of the number of potential relays or feedback accuracy, which differs from the full-diversity gain achieved by the ideal opportunistic DF relaying. Moreover, further analysis shows that with the increasing accuracy of feedback, the outage probability will approach to that of the ideal opportunistic relaying. Based on the theoretical results, a feedback method is developed to determine the minimum number of feedback bits with the outage loss under control. Simulation results confirm the theoretical analyses.
    No preview · Conference Paper · Aug 2013