APPLICATION OF ORTHOGONAL AND QUASI ORTHOGONAL SPACE TIME BLOCK CODING IN WIRELESS RELAY NETWORK

Abstract

Currently. Reasearch in the 41h generation to extract diversity derived from the concept of capacity enhancement by multiple- input multiple-output(MIMO)channels is mainly focused on different modulation techniques . To garner diversity at the transmitter end, the transmitter needs to be installed with more than one antenna. The spatial separation between between these transmit antennas should be large enough to have independent fading among the different antennas, So by making this kind of system, we can increase the diversity orders and coding gains .Since we have more freedom at the base stations, we can afford to install base stations or transmitter end with more no of antennas, but generally it is not easy to equip the small mobile units with more no of antennas with independent fading channel profiles. In that scenario, diversity can only be acheived through users(i.e mobile subscribers) cooperation resulting something which we call as cooperative diversity. So this diversity achieved cooperatively gives a new dimension over which we can increase diversity orders. Distributed orthogonal and quasi orthogonal Space Time code came into cooperative communication field to achieve cooperative diversity intelligently. Using this scheme or technique in wireless relay networks, the antennas of the distributive relays could successfully work as transmit antennas of a sender and build a space time code at the receiver. In this thesis work, we have given the design criterion for some of practical distributed space time codes. 1-lere we have applied orthogonal and quasi orthogonal designs which at their inception were used in the for multiple antenna systems. it is assertained that orthogonal space time codes(OSTBC) gives full diversity and their decoding complexity increases linearly .But quasi orthogonal space time block codes(QOSTBCs)generally do not have full diversity,so in this thesis work we have picked up symbols -ç from rotated constellation to make our quasi orthogonal design to provide full diversity.The OSTBCs and QOSTBCs are most befited for transmissions in the relay network setting applying distributed space time coding because of 'scale free " property leads to good performance. our simulation results show that Distributed OSTBCs and QOSTBCs gain decrese in error rates than other codes. We also compare the performance of distributed space time codes(DSTBCs) with decode-and-forward and amplify- and-forward,using quasi orthogonal designs.