Deptt. of Electronics & Comm. Engg.

In this paper, a general Alamouti space time block code structure is proposed for multiple-input multiple-output-orthogonal frequencydivision multiplexing (MIMO-OFDM) in WiMAX systems for 2 X NR antenna configurations. The signal detection technology used in this paper for MIMO-OFDM system is Zero-Forcing Equalization (linear detection technique). The analysis of Signal to Noise Ratio (SNR) vs Bit Error Rate (BER) for MIMO in WiMAX system has been done. For this purpose modulation technique QPSK has been considered for different convolution-codes (CC)-rates. Also Reed-Solomon (RS) codes have been implemented along with CC codes. Comparisons between ideal channel, Additive White Gaussian Noise (AWGN) and practical fading channel, Rayleigh channel has been done. Also the comparison is provided on the basis of SNR vs BER graph for different antenna configurations.

MIMO-OFDM system has been currently recognized as one of the most competitive technology for 4G mobile wireless systems. MIMO-OFDM system can compensate for the lacks of MIMO systems and give play to the advantages of OFDM system. In this paper, a general Quasi orthogonal space time block code (QOSTBC) structure is proposed for multiple-input multiple-outputorthogonal frequency-division multiplexing (MIMO-OFDM) systems for 8X8 antenna configuration. The signal detection technology used in this paper for MIMO-OFDM system is Zero-Forcing Equalization (linear detection technique). In this paper the analysis of high level of modulations ( i.e M-QAM for different values of M) on MIMO-OFDM system is presented. Here AWGN, Rayleigh and Rician channels have been used for analysis purpose and their effect on BER for high data rates have been presented. The proposed MIMO-OFDM system with QOSTBC using 8X8 antenna configuration has better performance in terms of BER vs SNR than the other systems.

In an OFDM system, typical sub-carrier modulation schemes include Binary Phase Shift Keying (BPSK), Quadrate Phase Shift Keying (QPSK), and Quadrature Amplitude Modulation (QAM). High level of modulation is used in order to increase the data rate of the OFDM system. In this paper the analysis of high level of modulations (16-PSK, 32-PSK,64-PSK,128-PSK,16-QAM, 64-QAM) on OFDM system is presented. Here AWGN and Rayleigh channels have been used for analysis purpose and their effect on BER for high data rates have been presented.

MIMO-OFDM system has been currently recognized as one of the most competitive technology for 4G mobile wireless systems. MIMO-OFDM system can compensate for the lacks of MIMO systems and give play to the advantages of OFDM system. In this paper, a general Quasi orthogonal space time block code (QOSTBC) structure is proposed for multiple-input multipleoutput-orthogonal frequency-division multiplexing (MIMO-OFDM) systems for 4X4 antenna configuration. The signal detection technology used in this paper for MIMO-OFDM system is Zero-Forcing Equalization (linear detection technique).

With the advance of wireless communications, the problem of bandwidth scarcity has become more prominent. Cognitive radio technology has come out as a way to solve this problem by allowing the unlicensed users to use the licensed bands opportunistically. To sense the existence of licensed users, many spectrum sensing techniques have been devised. This paper presents the energy detection based spectrum sensing technique. In the present work, the comparison of ROC curves has been done for various wireless fading channels using squaring and cubing operation. The cubing operation shows an improvement of up to 0.6 times as compared to the squaring operation for AWGN channel. For Rayleigh channel, the improvement achieved is up to 0.4 times as we move from squaring to cubing operation in an energy detector.

In this paper a fiber communication system is employed using Giga Ethernet Passive Optical Network (GE-PON) architecture. In this architecture an optical fiber is employed directly from a Central Office to the home. A 1:8 splitter is used as a PON element which establishes communication between a Central Office to different users. In this paper GE-PON architecture has investigated for different lengths from a Central Office to the PON in the terms of BER. For 10 Gbit/s system the plots between the BER and transmission distance is plotted and it is seen that as the distance increases beyond the 15 km the BER is increased very sharply. Results in the form of Voice and Data spectrum for different users of FTTH with GE-PON architecture are shown.