Research On The Rateless Code Over AWGN Channel

Spectrum sharing wireless communication can satisfy the requirements of the future wireless communication technology. It can make several communication systems with different structures or belong to different operation businesses access a shared spectrum dynamically and opportunistically, thus the licensed users and/or the unlicensed users can coexist reliably and harmoniously in the spectrum sharing wireless communication. Consequently, spectrum sharing wireless communication can markedly improve the current spectrum utilization efficiency to deal with the shortage of wireless spectrum resource.Rateless Code has three important attributes: Automatic Rate Adaption, Rateless attribute and barrel water effect, thus Rateless Code can be used to realize the interference avoidance, interference suppression and interference cancellation in the spectrum sharing wireless transmission and to complete the link establishment and multiple access control effectively. This article based on the Rateless Code over erasure channel and the related technique of LDPC code proposed a new family of Rateless Code called AR Code which is suitable for AWGN channel.Firstly, the LDPC code related technique was studied. The density evolution which is an analysis and optimization tool of LDPC code was investigated firstly, including density evolution of BP decoding algorithm, density evolution of BP decoding algorithm using Gaussian approximation and discretized density evolution, our simulation showed that the discretized density evolution has low complexity and good performance. Then IRA code which is a new kind of LDPC code was introduced and its discretized density evolution was proposed. Next, a method called progressive edge-growth (PEG) algorithm for constructing Tanner graph of LDPC code was investigated, then the PEG algorithm was slightly tailored to construct IRA code Tanner graph and Information Node PEG algorithm and Check Node PEG algorithm of IRA code were proposed. At last, the performance of Information Node PEG algorithm and Check Node PEG algorithm of IRA code were compared and the results showed that the performance of Check Node PEG algorithm is as the same as the performance of Information Node PEG algorithm.Thereafter, a new family of Rateless Code called AR Code was proposed. This code introduces an accumulator into the LT Code encoder to make the degree of parity node no longer be 1, thus this additional accumulator can eliminate the notable error floor of LT Code over AWGN channel. Next, two kinds of AR Code were proposed, one's information node degree distribution is loosely uniform and another's is restricted at a certain rate. Finally, the performance of AR Code and LT Code were compared and the results showed that both the AR Code with loosely uniform information node degree distribution and the AR Code with restricted information node degree distribution at a certain rate can eliminate the error floor of LT Code, moreover, the performance of the AR Code with restricted information node degree distribution at a certain rate is much better than the LT Code's.Finally, the decoding algorithm of AR Code was investigated. A serial schedule of BP decoding algorithm was introduced firstly, the performance of the standard BP algorithm and the BP algorithm using serial schedule were compared and the results showed that the BP algorithm using serial schedule converges faster than the standard BP algorithm, moreover the computation complexity of the BP algorithm using serial schedule is as the same as the standard BP in each iteration, thus the complexity of the BP algorithm using serial schedule is lower than the standard BP algorithm's. Because of the low complexity of the serial schedule and the characteristic of AR Code, the BP algorithm using serial schedule is adopted by AR Code. At last, a progressive decoding algorithm by preserving check node message is proposed for AR Code, our simulation showed that this algorithm can further reduce the complexity of AR Code decoding algorithm.