Article

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

IEEE Transactions on Signal Processing (Impact Factor: 3.2). 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.
    Information Sciences and Systems (CISS), 2012 46th Annual Conference on; 01/2012