Yeqing Qian

Neural Network Predistortion Technique for Nonlinear Power Amplifiers with Memory

Digital predistortion is the most promising technique to overcome the nonlinearity of power amplifier (PA). The early work on the field of predistortion is mostly limited to memoryless nonlinear. However, memory effects are typically observed in PA for wideband applications. In this paper, a double-input double-output (DIDO) forward neural network predistorter combined a tapped delay line is proposed to compensate the nonlinear and memory effects of PA simultaneously. The proposed predistortion scheme based on in-phase and quadrature components of transmitted signal can reduce the additional computations of rectangular-to-polar conversion or avoid the complex signal operation as in previous publications, and even can correct any nonlinearity in the conversion process. The adaptive predistorter is realized using indirect learning architecture associated with the backpropagation algorithm. Simulation results using 16-QAM modulated signals demonstrate an outstanding linearization performance.

Performance Analysis of Multi-Hop MIMO Relay Network

Without any doubt MIMO techniques count to the few emerging key technologies for wireless communications. It is obviously that MIMO techniques can improve the system capacity and performance. On the other hand, there has been an upsurge of interest in multi-hop infrastructure-based networks in both industry and academia. In this article, multi-hop MIMO relay network is studied and different channel models are analyzed. At first, 2-hop relay network is worked on within both SISO and MIMO systems. Three channel models are applied into the system and different value of signal-to-noise ratio (SNR) of direct link between BS and MS are observed. Results show that when meeting 100% system efficiency, the required relay SNR gain of 2-antenna system can be reduced to half of that with only one transceiver antenna. After that, multi-hop network is researched. Statistics figures out that when passing through ideal channel, 4-hop relays is possible with given SNR of more than 10 dB whereas, 5-hop communication can be realized in 4times4 MIMO under the assumption of 0 dB of SNR of direct link between BS and MS and 100% system efficiency. With respect to Rayleigh frequency-selective fading channel, SISO system can only ensure 2-hop relays whereas one more hop is supported in 4times4 MIMO network. Furthermore, in 4times4 MIMO, with the increase of hop, extra 3 dB is needed.