Performance Evaluation and Enhancement of IEEE 802.11 WLAN over Multipath Fading Channels in GNU Radio and USRP Platform

Abstract

This thesis focuses on the evaluation and enhancement of the Frame Error Rate (FER) performance of IEEE 802.11 a/g/p standard 5 GHz frequency band WLAN over Rayleigh and Rician distributed fading channels in the presence of Additive White Gaussian Noise (AWGN). Orthogonal Frequency Division Multiplexing (OFDM) based transceiver is implemented by using real-time signal processing frameworks (IEEE 802.11 Blocks) in GNU Radio Companion (GRC) and Ettus USRP N200 is used to process the symbol over the wireless radio channel. The Frame Error Rate (FER) is calculated for each sub-carrier conventional modulation schemes used by OFDM such as BPSK, QPSK, 16, 64-QAM with different punctuated coding rates. More precise SNR is computed by modifying the SNR calculation process of YANS and NIST error rate model to estimate more accurate FER. Here, real-time signal constellations, OFDM signal spectrums etc. are also observed to find the effect of multipath propagation of signals through flat and frequency selective fading channels. To reduce the error rate due to the multipath fading effect and Doppler shifting, channel estimation (CE) and equalization techniques such as Least Square (LS) and training based adaptive Least Mean Square (LMS) algorithm are applied in the receiver. The simulation work is practically verified at GRC by turning into a pair of Software Define Radio (SDR) as a simultaneous transceiver. The applied Low Pass Interpolation (LPI) technique based LS channel estimator gives better equalization of the transmitted symbols for the ideal static AWGN channel model as per the FER curve response for the SNR range from 5 to 25 dB. On the other hand, the similar estimator in the mobility condition considering the relative speed 𝑣 = 84 𝑚/𝑠 with associated normalized Doppler shift 𝑓𝑑𝑇𝑠 = 0.0133 in fading channel models, the transceiver prototype has no significant improvement in FER curve as this estimator has no adaptability with rapidly changing channel condition for similar values of SNR. It has been observed that after applying the proposed novel adaptive LMS channel estimation technique considering the different values of relative speed 𝑣 𝜖 {84, 120, 150} 𝑚/𝑠, normalized Doppler shift 𝑓𝑑𝑇𝑠𝜖 {0.0133, 0.0188, 0.0235}, chosen modulation scheme 64-QAM (2/3) with 24 Mbps data rate the FER at receiver significantly decreased almost tends to zero while the SNR approached 25 dB for both Rayleigh (NLOS) and Rician (LOS) distributed fast time-varying wireless fading channel models.