Bit Allocation Between Per-Cell Codebook and Phase Ambiguity Quantization for Limited Feedback Coordinated Multi-Point Transmission Systems

Abstract

Coordinated multi-point (CoMP) transmission is a promising technique for improving spectral efficiency of full frequency reuse cellular systems. However, its performance will be severely degraded if the feedback strategies are not carefully designed for providing channel information through limited uplink resources to the coherently cooperated base stations. In this paper, we study per-cell codebook based limited feedback scheme, which is highly desirable for CoMP systems due to its scalability and flexibility. Specifically, we investigate the issues related to phase ambiguity (PA), which comes from the per-cell codebook structure. We first analyze how many bits are required for the PA feedback to ensure an allowed performance loss. We then propose an adaptive bit allocation algorithm to divide a given amount of feedback bits between the per-cell codebooks for single-cell channel direction quantization and a codebook for PA quantization, aiming at minimizing the average global channel direction quantization error. Finally we provide a scaling law of the number of feedback bits per-user when the bit allocation algorithm is used. Simulation results show that the proposed bit allocation algorithm significantly improves the throughput of coherent CoMP systems either with equal number or different number of antennas at each base station.

Coordinated Multi-Point Transmission Strategies for TDD Systems with Non-Ideal Channel Reciprocity

“…This leads to severe performance loss for CoMP systems, which will be shown by simulations later. Such a problem resembles the phase ambiguity problem in limited feedback CoMP systems with per-cell codebookbased channel quantization [13], where phase ambiguities exist between the independently quantized channel direction information from each coordinated BS to a user. In limited feedback CoMP systems, feeding back the phase ambiguities to the BSs is an immediate way to solve the problem, which however is not applicable to our problem here.…”

“…Second, CoMP channel is a concatenation of multiple single-cell channels. As a result, the downlink CSI is corrupted by multiplicative noises, which are either caused by non-ideal uplink-downlink channel reciprocity in time division duplex (TDD) systems [12], or by structured codebook in frequency division duplex (FDD) systems [13]. Compared with additive noises such as channel estimation errors, these multiplicative noises are more detrimental because they hinder the co-phasing of coherent CoMP transmission.…”

On an HARQ-based coordinated multi-point network using dynamic point selection

“…As a result, the channel gains can be assumed to be perfectly known by the receivers [18][19][20][21][22][23][24][25][26][27][28][29][30][36][37][38][39][40][41]. On the other hand, there is no CSI available at the BSs (CSIT), except the HARQ feedback bits.…”

“…In these works, the focus is on investigating the effect of training signals, providing imperfect *Correspondence: behrooz.makki@chalmers.se Department of Signals and Systems, Chalmers University of Technology, Gothenburg 412 96, Sweden CSIR, on the network performance. The second group, on the other hand, is the papers in which, while the receivers are assumed to perfectly estimate the channels (perfect CSIR), the BSs have access to imperfect CSIT obtained by quantized CSI feedback [18][19][20][21][22][23][24][25][26][27][28][29][30]. Here, it is concentrated on the effects of the CSIT quantization and the quantized CSIT error is normally modeled as Gaussian noise.…”

“…Here, it is concentrated on the effects of the CSIT quantization and the quantized CSIT error is normally modeled as Gaussian noise. However, some other CSI quantization schemes have been summarized in [21][22][23][24][25][26][27][28] as well. Finally, to study the effect of BS synchronization, [27][28][29][30] have considered the cases where the BSs are provided with quantized CSI of the channel phase, while the amplitudes are perfectly fed back.…”