| In the wireless communication system,the wireless channel has the characteristic of fading,which is still the decisive factor that can influence the performance of the wireless system.In order to cope with the characteristic,scholars continuously put forward a variety of methods,among which the application of space diversity techniques based on the multi-antenna is the most widely used.However,in a wireless communication system,due to many restrictions,which includes the terminal equipment's volume,size,power consumption and many other aspects,the multiple antennas can not be installed,which lead to the restrictions of the applications of multi-antenna techniques.The techniques of cooperative diversity in essence utilize the wireless communication terminal equipments in a wireless communication system,which owe a single antenna and correlate mutually,to collaborate mutually and share their antennas with each other.In this way,it can achieve the effects of the analog multi-antenna diversity techniques,and thus exploit the advantages of multi-antenna technology to the full.The traditional cooperative diversity techniques mainly take advantages of the technique of channel coding.Thus it enables the system obtain not only the diversity gain,but also the coding gain.The technique of channel coding used by the cooperative diversity includes channel coding of different formats and different performances,such as RCPC codes,LDPC codes and so on.However,these channel coding schemes exist a problem that code rate is fixed,and can not be well adapted to the changing channels.To aim at this problem,this paper proposes that the fountain codes can be applied to the channel coding scheme of cooperative communication.Since the structure of fountain codes is generaly based on the generated matrix,its performance largely depends on the structure of the generated matrix.But the ring of the generated matrix is one of the main factors affecting the structure of the generated matrix.Therefore,this paper proposes a semi-random generation method to remove the small ring of fountain codes,and then verifies the performance of fountain codes after we removing the small ring by simulation.In the part of decoding,the common decoding algorithm of fountain codes is the standard belief propagation decoding algorithm(BP decoding algorithm),but this algorithm can not very efficiently utilize the current codeword to update the latest information.Dynamic Scheduling Algorithm of LDPC codes has the characteristics that the rate of convergence is very fast and use the current newest information for decoding in time.So in this paper,the Dynamic Scheduling Algorithm isapplied to the decoding of fountain codes,and verifies by simulation that the Dynamic Scheduling Algorithm applied to the decoding of fountain codes can achieve a better performance than the belief propagation decoding algorithm.This paper proposes that the fountain code techniques can be applied to encode collaborative schemes and amplify forwarding schemes.The theoretical analysis shows that if the relay node can decode the information of source node correctly,the diversity gain obtained by cooperative communication system is a full diversity gain with a degree of 2.However,if the decoding fails or decoding error occurs,the system will not obtain any cooperative diversity gain.Whereas in the amplify forwarding schemes,the cooperative system can be able to obtain a certain degree of diversity gain,but its effect is not obvious.Based on this,some people proposes a combination of the two schemes,namely hybrid forwarding(HF)scheme.The simulation results show that collaborative schemes based on hybrid forwarding can perform better and have a lower error rate compared with the previous two ones.And the application of dynamic scheduling algorithm,the system performance will be further improved.Finally,thispaper putforward the cooperation scheme is applied to hybrid forward multi relay cooperative system,and verify the performance of the system by simulation. |
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