Co-channel interference (CCI) occurs in a wireless receiver when multiple signals are present. The receiver experiences excessive CCI under overload which occurs when there are more signals than receive antennas. This makes separation and estimation of the transmitted data signals difficult. We develop a novel reduced-complexity receiver structure for the separation and symbol detection of multiple co-channel signals in frequencyflat Rayleigh fading channels. Moreover, we show that list-based group-wise processing can achieve better performance at low and moderate signal-to-noise ratios than existing group-wise soft information processing schemes. The receiver is equipped with multiple antennas and developed to work under overload. Its structure consists of a linear preprocessor followed by a nonlinear reduced-complexity symbol detector. The proposed list group-search detection (LGSD) algorithm relies on list feedback and reduces complexity by iteratively searching over groups of transmitted symbols. It outputs a list of likely data symbols which is well suited to further processing using soft input error control decoders. Simulation shows that LGSD can achieve near optimum joint maximum likelihood performance under overload at significantly lower complexity.

Consider a multiuser system where an arbitrary number of users communicate with a distributed receive array over independent Rayleigh fading paths. The receive array performs minimum mean squared error (MMSE) or zero forcing (ZF) combining and perfect channel state information is assumed at the receiver. This scenario is well-known and exact analysis is possible when the receive antennas are located in a single array. However, when the antennas are distributed, the individual links all have different average signal to noise ratio (SNRs) and this is a much more challenging problem. In this paper, we provide approximate distributions for the output SNR of a ZF receiver and the output signal to interference plus noise ratio (SINR) of an MMSE receiver. In addition, simple high SNR approximations are provided for the symbol error rate (SER) of both receivers assuming M -PSK or M -QAM modulations. These high SNR results provide array gain and diversity gain information as well as a remarkably simple functional link between performance and the link powers.

Pilot contamination occurs when cells simultaneously transmit the same pilot sequences, creating interference. Unsynchronizing the pilots can reduce pilot contamination, but it can produce data to pilot interference. In this paper, we investigate the impact of pilot contamination and other interference, namely data to pilot interference, on the performance of finite massive MIMO systems with synchronized and unsynchronized pilots. Two unsynchronized pilot schemes are considered. The first is based on the time-shifted pilot scheme in [1], where pilots overlap with downlink data from nearby cells. The second timeshifted method overlaps pilots with uplink data from nearby cells. Results show that if there are small numbers of users, the first time-shifted method provides the best sum rate performance. However, for higher numbers of users, the second time-shifted method has advantage compared to other methods. We also show that time-synchronized pilot is not necessarily the worst case scenario in term of sum rate performance when shadowing effect are considered.

Abstract-We develop a novel differential spatial modulation (DSM) scheme for amplitude phase shift keying (APSK) modulation, which can either improve throughput or performance over DSM for PSK. Then we investigate the impact of time-varying fading on DSM. We find performance degrades if the fading is too fast due to differential detection. The impact of a long outer error control code (ECC) is also considered. Its performance is limited by the slowly varying channel required for differential detection. We consider using reconfigurable antennas to periodically change the channel conditions and hence significantly improve coded performance for DSM systems.

We propose a Decode-and-Forward (DF) scheme using distributed Turbo code (DTC) for a three-node (source, relay, and destination) wireless cooperative communication system. The relay decodes, then interleaves, and reencodes the decoded data. It then forwards the reencoded packet and its instantaneous receive SNR to the destination. The performances using both ideal and quantized SNR are studied. The destination uses a modified metric within a Turbo decoding algorithm to scale the soft information calculated for the relay code. The proposed scheme is simple to implement and performs well.