Diversity Combiner in Adaptive Modulation over Fast and Frequency Selective Environment

Signal over fast and frequency selective channel suffers from Doppler and delay effects due to propagation mechanism such as reflection, refraction and diffraction resulting in poor quality reception. Maximal Ratio Combining (MRC) and Adaptive Modulation are some of the techniques previously used to address this problem, but each of these techniques suffers from signal fading and interference distortion as result of weak signal and delay spread respectively. Therefore, an Adaptive modulation technique which incorporates MRC is developed over fast and frequency selective Rayleigh fading channel. The system model in this study employed 10,000 bits randomly generated, gray encoded and modulated with M-ary Phase Shift Keying (M-PSK). The signals were filtered using square root raised cosine filter and then transmitted over fast and frequency selective Rayleigh fading channel. At the receiver, two paths at 100km/hr and 200km/hr were combined using MRC, the channel was estimated using Received Signal Strength Indicator (RSSI) to change the constellation size of the modulation in accordance with the severity of fading. The process was simulated using MATLAB software package. The performance of the proposed system was evaluated using Bit Error Rate (BER) at mobile speeds of 100km/hr and 200km/hr. At Signal to Noise Ratio (SNR) of 10dB, the BER values of 0.0003, 0.0013, 0.0686, and 0.3009 were obtained for conventional MRC with BPSK, QPSK, 8PSK, and 16PSK signaling scheme respectively as against 0.0011 for adaptive MPSK at a mobile speed of 100km/hr while at 200km/hr, the BER values of 0.0134, 0.0161, 0.1947, 0.4116 were obtained using MRC with BPSK, QPSK, 8PSK and 16PSK respectively as against 0.0134 for adaptive MPSK. In conclusion, adaptive modulation incorporating MRC gave the best result due to lower BER values obtained at all SNR considered. The effect of fast and frequency selective Rayleigh channel has been reduced at high speed. Keywords: Adaptive Modulation, Maximal Ratio Combining , M-PSK, Rayleigh Environment, Bit Error           Rate (BER), Signal to Noise Ratio (SNR)

A General Framework for Analyzing, Characterizing, and Implementing Spectrally Modulated, Spectrally Encoded Signals

Fourth generation (4G) communications will support many capabilities while providing universal, high speed access. One potential enabler for these capabilities is software defined radio (SDR). When controlled by cognitive radio (CR) principles, the required waveform diversity is achieved via a synergistic union called CR-based SDR. Research is rapidly progressing in SDR hardware and software venues, but current CR-based SDR research lacks the theoretical foundation and analytic framework to permit efficient implementation. This limitation is addressed here by introducing a general framework for analyzing, characterizing, and implementing spectrally modulated, spectrally encoded (SMSE) signals within CR-based SDR architectures. Given orthogonal frequency division multiplexing (OFDM) is a 4G candidate signal, OFDM-based signals are collectively classified as SMSE since modulation and encoding are spectrally applied. The proposed framework provides analytic commonality and unification of SMSE signals. Applicability is first shown for candidate 4G signals, and resultant analytic expressions agree with published results. Implementability is then demonstrated in multiple coexistence scenarios via modeling and simulation to reinforce practical utility