Retrospective interference alignment for two-cell uplink MIMO cellular networks with delayed CSIT

Abstract

Abstract-In this paper, we propose a new retrospective interference alignment for two-cell multiple-input multiple-output (MIMO) interfering multiple access channels (IMAC) with the delayed channel state information at the transmitters (CSIT). It is shown that having delayed CSIT can strictly increase the sum-DoF compared to the case of no CSIT. The key idea is to align multiple interfering signals from adjacent cells onto a small dimensional subspace over time by fully exploiting the previously received signals as side information with outdated CSIT in a distributed manner. Remarkably, we show that the retrospective interference alignment can achieve the optimal sum-DoF in the context of two-cell two-user scenario by providing a new outer bound.

Joint Interference and Phase Alignment among Data Streams in Multicell MIMO Broadcasting

“…The BER of the proposed algorithm is lower than the algorithms of literature [11,17]. Furthermore, the BER of the proposed algorithm when configured as [7,10,4,13,8] has much better performance in both ideal and delay error CSI as compared with its other configuration [3,4,4,13,8] and Literature [11,17]. Both configurations show overall better BER performance than the existing algorithms which makes it an attractive candidate for reducing the interference among user data streams in MIMO systems.…”

“…The literature [11] adopts MMSE and LSE high-order predicting channel, and although it can improve the channel quality under the delay error CSI to a great extent, the improvement is relatively limited and its performance is inferior to the proposed algorithm. Furthermore, it is obvious from Figure 5 that the proposed algorithm with [7,10,4,13,8] configuration has high sum rate as compared to its other configuration [3,4,4,13,8]. Moreover, both configurations of the proposed IA algorithm outperform Literature [11,17] algorithms which clearly indicates its benefits over the existing algorithms.…”

“…The literature [9] pointed out that the delay CSI can obtain better performance than that without CSI. When the number of users changes and the delay is unknown, in [10] the receiver uses the current CSI and delay CSI and previous precoding to update the current precoding step by step, providing a low-complexity adaptive beam design scheme. Under the classical time delay channel model, the literature [11] predicts the channel by the minimum mean square error (MMSE) and least square error (LSE) and gives a robust IA scheme.…”

“…The backtracking IA in [8,9] required the channel to have interlaced block fading characteristics. The systems in [10,11] had a large overhead.…”

“…As shown in Figure 6, in nonideal CSI, the capacity of several typical algorithms is compared when configured as [7,10,4,13,8] and [3,4,4,13,8]. In time delay error CSI, the proposed algorithm has more room for handling interference and delay error, and minimizes the effects of interference and delay errors, further combining power allocation and phase alignment to improve signal quality.…”