Performance Analysis of Punctured Turbo Code under An AWGN Channel

Turbo code is a coding technique that enhances a reliable data transmission. Because of special structure of encoder and iterative decoder, it could obtain 1dB at low EbN0 db that closed the channel capacity limit. However, the redundant bits in coding would decrease the bandwidth efficiency. The puncturing scheme could improve the bandwidth efficiency. Different puncturing pattern could provide a different level of performance. We focus on the analysis of puncturing pattern to compare those performances. In this paper, we discuss the performance of punctured turbo coding on different location of punctured bits and different number of punctured bit. keyword:Turbo code、Punctured Turbo Code、Channel coding, Performance analysis I、 Introduction How to ensure that correct information and transmission efficiency is important in a communication system. Using a digital communication, it economizes on bandwidth and the digital signals could hardly to suffer from noise interference in transmission. Channel coding is used to protect the transmitted data in the digital communication system. The transmitted data are added redundant bits in channel coding. It could function as error correction or error detection. There are many type of channel coding, such that Hamming Code, Linear Block Code, Convolutional Code, Turbo Code..., etc. Each of channel coding has a different performance under different communication environments. Turbo code is proposed as a near to Shannon limit encoding [1]. Because of its structure of encoder and iterative decoding, it could obtain a lower Bit Error Rate (BER) at the receiver. It would provide a largest data transmission in a finite bandwidth [10]. So, turbo code is proposed to the application on wireless communication system, such as asynchronous satellite communication, W-CDMA system..., etc [1-3]. Because of special structure of encoder and iterative decoder, turbo coding could approach a performance of error floor. However, the coding rate of turbo code is not perfect. Some researchers proposed punctured turbo code which could be applied in high code rate in communication system. The performance of punctured turbo code is worse than that of turbo code dose but coding scheme could improve bandwidth efficiency [3]. The puncturing pattern could be used to adjust code rate to meet the communication system requirement [4][7-8]. Although punctured turbo code could increase bandwidth efficiency, different punctured location could affect a different performance at the receiver. Kouse et al. [4] proposed the puncturing scheme with the codeword weight calculation. When the bit in codeword is with a high weight, it had to avoid puncturing that bit. It could not puncture the systematic sequence because the systematic bit is with a high weight. Consequently, the puncturing scheme should alternative the lower weight bits to be punctured. Hence, how to decide a good pattern in high rate system is an important task. In this paper, the block size of the mother code is assumed to be 1024. Performance analysis focuses on the case of 4 bits in the puncturing pattern. Different punctured location and different number of punctured bits is provided in the analysis. The performance analysis on different location of punctured bits and number of punctured bits is presented in the following section. In the third section, the simulation results are given. Finally, a conclusion is given. II、 Analysis of Puncturing pattern In this section, the structure of punctured turbo code is described. The block diagram of punctured turbo code is given in Fig 1. Channel k bits source M n bits Turbo Code X0 X1 X2 Punctured Pattern