Enhancing ZF-SIC by Selective Retransmissions: On Algorithms for Determining the Decoding Order

We consider the uplink of a wireless sensor network with single-antenna sensors, an access point (AP) equipped with multiple antennas, and a common radio channel. To reduce the number of outages resulting from the noise amplification by the zero-forcing (ZF) within the successive interference cancellation (SIC) procedure, the AP is given the possibility to request a selected number of sensors to retransmit their signals in a subsequent time slot. If necessary the AP suspends the ZF-SIC until the requested signals have been retransmitted, making the signal recovery a recursive procedure. The number of sensors required to retransmit depends on the order of the processed sensor signals within the ZF-SIC. We propose two algorithms for determining the decoding order: an algorithm which finds a decoding order necessitating a minimal number of retransmissions, and a suboptimal alternative algorithm with significantly lower complexity. By numerical means the performance and complexities of the considered algorithms are analyzed.