An analytical consideration of quantised CSI feedback on the performance of a Multi-User OFDM-system

I. EXTENDED ABSTRACT OFDMA is considered to be a suitable candidate for future radio network systems where high data rates are required. In a multicarrier scheme like OFDMA, the overall channel can be divided in several resources. Having channel knowledge at the transmitter side in a multiuser system, the resources can be allocated to the different users in an optimal manner in terms of a certain criterion, e.g. the maximum capacity. For that purpose, channel state information (CSI) of the resources of the different users has to be known at the transmitter. Having perfect channel knowledge at the transmitter, adaptive subchannel allocation schemes achieve very good performances [1] [2] [3]. However, in a realistic scenario only imperfect channel knowledge is available at the transmitter which leads to a performance degradation using adaptive techniques compared to the maximal achievable performance. The use of diversity is an alternative way to achieve performance enhancements without channel knowledge at the transmitter. Applying frequency hopping [4] or applying a DFT-precoding of the data [5] together with interleaved carrier allocation are examples for techniques to exploit frequency diversity in an OFDMA system. However, the achievable performance using diversity is also worse than the maximal achievable performance using adaptive schemes with perfect channel knowledge. Hence, a comparison between adaptivity with imperfect channel knowledge and diversity has to be made. In [6] [7] [8] first comparisons between adaptivity and diversity has been investigated. In [9] we compared adaptive subcarrier allocation with imperfect channel knowledge to diversity techniques in an OFDM-system. As CSI we employed the instantaneous signal-to-noise ratio (SNR) of the different subcarriers, which was assumed to be outdated and estimated. In this paper, the CSI is assumed to be quantised and fed back over a feedback channel, where we consider CSI feedback bit errors which occur during the transmission over the feedback channel. As system model we consider a one cell OFDMA downlink SISO scenario with one base station (BS) and multiple mobile stations (MS) in a FDD system, where is it assumed that each user has the same requirements in terms of data rate. We assume that the channel coefficients of adjacent subcarriers are independent from each other and Rayleigh distributed with the same average SNR. We employ a Max-SNR Scheduler that favours the users with the best SNR conditions to allocated the different subcarriers to the different users, i.e. one subcarrier is allocated to only …