Adaptive Unequal Error Protection Fountain Codes

As a new channel coding technology,unequal error protection fountain codes have the advantages of rate adaption,low encoding and decoding complexity and no feedback retransmission,and are widely used in wireless broadcasting systems.Among them,EWF(Expanding Window Fountain)with intermediate feedback does not focus on the protection of less important packets after the decoding of more important packets,which makes the number of encoded packets needed to complete the decoding more.At the same time,compared with no coding scheme,the scheme needs more encoded packets to complete decoding when the average packet loss rate is smaller.To solve the above problems,this paper proposes an enhanced unequal error protection fountain coding scheme(Enhanced UEP codes).After the decoding of more important packets is completed,the number of transmitted encoded packets needed to complete the decoding is reduced by protecting the less important packets,and the transmission efficiency is improved.On this basis,we further propose an adaptive unequal error protection fountain coding strategy(Adaptive UEP codes),which adaptively selects the coding parameters and coding scheme according to the channel packet loss rate,so as to improve the efficiency of the information transmission.The details are as follows:(1)In order to solve the problem that the traditional EWF need more encoded packets to complete decoding,an enhanced unequal error protection fountain code is proposed.Firstly,after the decoding of more important packets is completed,the scheme reduces the protection of more important packets and increases the protection of less important packets by increasing the proportion of less important packets in the encoded packets with the small degree values,so as to speed up the decoded speed of less important packets and reduce the number of the encoded packets needed to complete the decoding.On this basis,combining the characteristics of the robust soliton distribution function,a new enhanced fixed distribution function is proposed.The degree distribution function can increase the probability of degree one with the decrease of the number of packets involved in coding,which not only ensures that the decoding failure probability is low when K is larger,but also reduces the decoding failure probability when K is smaller,so as to improve the universality of the coding scheme.(2)Furthermore,by comparing the coding scheme with the no coding scheme,we find that the scheme needs more packets to complete decoding when the channel packet loss rate is smaller,and the transmission efficiency is relatively lower.In order to improve the efficiency of the information transmission,the adaptive unequal error protection fountain coding strategy is proposed,which can adaptively adjust the coding parameters and choose whether to adopt the coding scheme according to the channel packet loss rate.Specifically,the adaptive adjustment of coding parameters can adaptively adjust the protection of packets which are different importance by calculating the optimal values of coding parameters under different average packet loss rates,so as to increase the protection of more important packets when the channel packet loss rate is larger,reduce the protection of more important packets when the channel packet loss rate is smaller.Furthermore,by calculating the number of the encoded packets needed to complete the information transmission in the wireless broadcast scenario using the enhanced unequal error protection fountain codes and the no coding scheme respectively,the adaptive selection coding criterion can be obtained,that is,when the average packet loss rate is smaller than a certain threshold,the no coding method is adopted,when the average packet loss rate is larger than the threshold,the enhanced unequal error protection fountain coding scheme is adopted,so as improve the efficiency of information transmission.