Influence of CSI Feedback Errors on Capacity of Linear Multi-User MIMO Systems

Abstract

In this paper, we discuss the influence of feedback channel errors on throughput of linear multi-user multiple-input multiple-output (MIMO) systems employing vector quantization (VQ) algorithms for encoding channel state information (CSI).We consider an approach where the receiver estimates the downlink channel and chooses one of the predefined channel characterization codewords whose indices are transmitted back to the transmitter. In practice, the feedback channel will introduce errors in transmission of the indices and we evaluate the resulting channel capacity loss for different system setups.We demonstrate the performance of two types of systems, one using time division multiplexing of individual users and another transmitting to multiple users. We evaluate two basic error mitigation approaches: the first one with user expurgation using error-detection codes and the second one, based on specially designed VQ indexing. We show that the proposed schemes are very robust to even relatively high bit error rates in the feedback link and that proper VQ indexing may suffice for actual system design, even if the feedback channel is not very reliable.Index Terms-Multi-user MIMO systems, channel state information, vector quantization, feedback channel.

Comparison of Partial CSI Encoding Methods in Multi-User MIMO Systems

“…Since the mean received power at all mobile receivers is identical, we can omit power losses from the large-scale effects, assume that the total transmit and receive power at each transmission instant is equal to P and normalize all entries in the channel matrix to unit variance. Finally, it is assumed that there are no delays and transmission errors in the feedback channel (we discuss systems with imperfect feedback links in [11,12]). …”

“…Secondly, based on the individual users' CSI codebooks, codebooksB andŜ (P) are optimized with the throughput maximization criterion. Based on (12), one can see that receiver CSI in form of the vector h k consists of the scalar value of channel singular value d max k and the eigenmode v H k . Since these values are independent, we propose an algorithm, which separately quantizes the information about eigenmodes in codebookv and singular values in codebookd.These two independent receiver codebooks will then be used to design two independent transmit codebooksB andŜ (P), respectively.…”

On the Impact of Precoding Errors on Ultra-Reliable Communications

“…The impact of CSI feedback errors have been evaluated from a system capacity point of view. For example, the work in [5] evaluates the influence of CSI feedback errors on the throughput performance of multi-user MIMO systems, whereas [6] demonstrates the significant performance degradation when a UE intentionally reports the wrong CSI to the eNodeB. Previous reliability analyses [2], [3] have not considered these types of imperfections.…”

Vector Quantized CSI Prediction in Linear Multi-User MIMO Systems

“…Such imperfections can be generally classified as bit errors, bit erasures and transmission delays, which cause the base station to use outdated and/or erroneous CSI information when broadcasting information to the mobile receivers. The problem of feedback channel bit errors was treated by us in [7] and shown to be manageable by proper indexing design. The related problems of feedback channel delay and feedback channel erasures, however, are much more difficult to alleviate.…”