The Construction Of Structured IS-LDPC Code And Its Application In OFDM Systems

Orthogonal frequency-division multiplexing(OFDM), which is the most common multicarrier transmission technique, has been widely used in wireless communication standards, due to its immunity to the frequency selective fading and multipath fading. However, one major drawback of the OFDM system is high peak-to-average power ratio(PAPR). High PAPR results in the high power amplifier(HPA) with a wide linear range, which leads to the complicated implementation of the radio frequency front-end. Otherwise, the nonlinear HPA would bring about the distortion of the in-band signal and radiation of the out-of-band. Invertible subset low density parity-check(IS-LDPC) code has good error-correcting performance and can significantly reduce the PAPR of the OFDM systems. Since IS-LDPC codes belong to random-like codes, the hardware implementation of IS-LDPC codes is complicated, which is not conducive to the application of IS-LDPC codes to actual communication systems.Firstly, we extend the idea of invertible subset to quasi-cyclic LDPC(QC-LDPC) codes and propose the construction of structured IS-LDPC codes, i.e., invertible subset QC-LDPC(IS-QC-LDPC) codes. The IS-QC-LDPC codes inherit the superiorities of IS-LDPC codes such as significant PAPR reduction performance with low searching complexity. In addition, the IS-QC-LDPC code, which is a kind of QC-LDPC codes, has linear encoding complexity, can be encoded with simple shift registers and significantly reduces the memory utilization. Therefore, IS-QC-LDPC codes greatly enhance the practicability of IS-LDPC codes with all advantages mentioned above and accelerate the further application of IS-LDPC codes to real communication systems.Furthermore, to extend the scenario where IS-LDPC codes apply, we utilize IS-LDPC codes to reduce the PAPR of orthogonal frequency division multiple access(OFDMA) systems. To ensure significant PAPR reduction performance, we design mapping scheme between resource blocks and invertible subsets for uplink and downlink, respectively, due to the difference between uplink and downlink. The simulation results show that the error-correcting performance of IS-LDPC codes is near Shannon limit and IS-LDPC codes can significant reduce PAPR of OFDMA systems, for both uplink and downlink.Finally, we design parameters of IS-LDPC codes to apply IS-LDPC codes to OFDM-wireless local area networks(OFDM-WLAN) systems appropriately. Moreover, to enhance the rubustness against frenquency selective fading, we propose an interleaved invertible subset mapping scheme. The simulation results show that the IS-LDPC code is suitable for the IEEE 802.11 OFDM-WLAN systems due to its good error-correcting and remarkable PAPR reduction performance. By extending application scenarios, we further strengthen the practicability of IS-LDPC codes.