tailieunhanh - Advanced Transmission Techniques in WiMAX Part 13

Tham khảo tài liệu 'advanced transmission techniques in wimax part 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Performance Evaluation of WiMAX System Using Different Coding Techniques 291 From Figure 42 and Figure 43 it is shown that the results obtained from LDPC code and turbo code is better than puncture modified CPC but LDPC and turbo code is more complicated than the proposed method. Fig. 43. BER Comparison between Turbo code CPC punctured CPC at 64 QAM N 512. 292 Advanced Transmission Techniques in WiMAX 10. Delay diversity scheme In this section both puncture and Delay Diversity Scheme DDS are together used to increase the efficiency of CPC system. To further improve the diversity of the channels a transmit diversity technique may be utilized. Many transmit diversity techniques have been explored. One such technique is the transmit delay diversity Figure . In transmit delay diversity a transmitter utilizes two antennas that transmit the same signal with the second antenna transmitting a delayed replica of that transmitted by the first antenna. By so doing the second antenna creates diversity by establishing a second set of independent multipath elements that may be collected at the receiver. Fig. 44. Transmit Delay Diversity Scheme If the multipath generated by the first transmitter fades the multipath generated by the second transmitter may not in which case an acceptable SNR will be maintained at the receiver. This technique is easy to implement because only the composite TX0 TX1 channel is estimated at the receiver. The biggest drawback to transmit delay diversity is that it increases the effective delay spread of the channel and can perform poorly when the multipath introduced by the second antenna falls upon and interacts destructively with the multipath of the first antenna thereby reducing the overall level of diversity. Our simulator for delay diversity technique is based on passing the same signal through the same path during two time intervals by using only one transmitted antenna Figure not two transmitted antennas as in delay diversity technique.