An improved signal-to-jamming and noise ratio (SJNR) method is proposed for the linear precoding of multiuser MIMO downlink systems. To well balance suppression of co-channel interference and suppression of noise, the proposed method modifies the noise variance term to argument of a piecewise linear function, and then enhances the suppression of noise. A dynamic power allocation scheme is also introduced to further decrease the overall average bit error rate of the system. Simulation results prove the effectiveness of the proposed scheme.

Error-propagation is an important issue and should be carefully coped with in the decision-feedback equalizers (DFE). Ignoring the impact of error-propagation often leads to impractical laboratory results. In this paper, we investigate two novel layered space-frequency equalizers (LSFE) for single-carrier multiple-input multiple-output (MIMO) systems, where the recently proposed frequency-domain equalizer with time domain noise-predictor (FDE-NP) is adopted at each stage of the LSFE. We first derive the partially-connected LSFE with noise predictor (PC-LSFE-NP) which has exactly the same mean square error (MSE) as the conventional LSFE under the assumption of perfect feedback. However, if error-propagation is considered, the proposed PC-LSFE-NP can achieve better performance than the conventional LSFE due to the more reliable feedback output by the decoders. To reduce the interference from the not yet detected layers in the feedback section, we then introduce the fully-connected LSFE with noise predictor (FC-LSFE-NP), in which all layers are implicitly equalized within each stage and their decisions fed back internally. The powerful feedback filter of FC-LSFE-NP brings significant performance superiority over the conventional LSFE and PC-LSFE-NP with either perfect or imperfect feedback. Moreover, we propose a simple soft-demapper for the equalizers to avoid information loss during decoding, and thus, further improve the performance. Finally, we compare the performance of (PC/FC)-LSFE-NP with the existing schemes by computer simulations.

A sub-optimal practical computationally efficient transmit power allocation algorithm is proposed under the constraints of data rate and max bit error rate (BER) in OFDM systems. By exploiting the relation between the water-filling level and the data rate, the proposed algorithm derives an efficient adaptive coarse searching method for water-filling level without need of preset step and other initial parameters, then determines the required water-filling level by the dichotomy method. When the channel state changes, the proposed algorithm works out a small domain of required water-filling level based on the latest allocation and then tracks the channel quickly. Simulation results show that the proposed algorithm converges quickly and is suitable for time-varying channels.

This letter investigates a practical space time block coded (STBC) cooperative system to determine under what conditions a cooperative system outperforms a direct one, and then proposes two criteria for selecting proper relay based on outage probability and capacity, respectively. Performance analysis and numerical results indicate that the STBC cooperative system is superior in practical scenarios.