The Study For Packet Transmission Over Wireless Fading Channels

The transmitted signals in wireless communication system are heavily deterioratedby channel fading. Hybrid ARQ, cooperative communication and wireless multihopnetworks techniques are some effective measures to combat channel fading. The currentresearches are mostly carried from the information-theoretic or BER views. Howeverfor most practical communication systems, the data is always transmitted in packets,therefore, the impact of the packet length on the system performance must be taken intoaccount. On the other hand, with the idea of cross-layer design being recognized widely,it is necessary to obtain the PER and throughput, to instruct the cross-layer optimization.With the above backgrounds, this dissertation studies some key technologies for thepacket transmission over fading channels, including the PER analysis, hybrid ARQtechnique, cooperative communication, and admission control in wireless multihopnetwork. The main contributions of this dissertation are concluded as follows:Firstly, this dissertation studies the average PER performance for the packettransmissions over fading channels. The existing work for the PER analysis is studiedmainly by computer search, approximating, or loose bounding. With the concept of‘inverse coding gain’, this dissertation derives the close-form upper bounds for PER forthe packet transmission with conventional modulation and coding schemes overRayleigh fading, and the upper bounds become tight in high SNR region or with largepacket length. Then, it is proved that the inverse coding gain generally follows anapproximately linear relationship with the logarithm of the packet length, for theconventional modulation and coding schemes. This dissertation also proposes a noveldefinition for the ‘steep degree’ for the PER curves in AWGN channel frommathematical view. With this novel definition, it is proved that PER curves get steeperwhen the packet length becomes larger, and the PER curves for coding systems aregenerally steeper than those for uncoding systems. These conclusions agree with thesimulation results in the existing works.Secondly, by employing Renewal-Reward theory, this dissertation studies theaverage throughput performance for type-I hybrid-ARQ system over fast fadingchannels. For Rayleigh fading, a simple expression for the optimal packet length tomaximize the average throughput is obtained, and it is found that the optimal packetlength linearly increases with the increase of the protocol overheads and the averageSNR under Rayleigh fast fading channel.Thirdly, the average throughput performance is studied for type-I and type-IIhybrid-ARQ systems over slow fading channels. Assuming that the PER curves inAWGN present strict steep characteristic, an approximate throughput expression is derived. It is also found that the optimal number for maximum retransmissions is one,and the optimal power allocation scheme should put the whole power to the first roundtransmission.Fourthly, this dissertation studies the PER performance in high SNR region for thecooperative packet relay systems over Rayleigh fading and Nakagami-m fadingchannels, and discusses the impact of packet length on the performance differencebetween AF and DF modes. It is found that the performance of DF is always better thanthat of AF, and when packet length increases, the performance difference reduces.Fifthly, this dissertation studies the optimal relay location for cooperative packetrelay systems and the optimal power allocation for cooperative DF systems. It is foundthat the optimal relay will always be located in the middle between the source and thedestination nodes for AF, while for DF, when packet length becomes large, the optimalrelay moves from close to the destination towards the midpoint. For DF mode, theoptimal power allocation scheme will always put more power to the source node, andwhen the packet length becomes larger, more power on the source node should beallocated.Finally, this dissertation proposes a high efficient admission control scheme toguarantee the QoS for real-time multimedia traffic transmission over wireless multihopnetworks. By employing cross-layer design, this scheme mainly includes adestination-originated process on routing layer to admit or deny a coming flow based onthe information sensed in MAC layer. The new flow is admitted only when its QoScould be guaranteed and while the QoS of the existing flows would not be harmed. Withvery low control overheads, the scheme can guarantee the throughput, end-to-end delayand delay violation of the real-time traffic, which is proved by the analysis andsimulation. Compared to the traditional schemes, the proposed scheme also evidentlyimproves the channel utilization.