Cross-layer Protocol Research On Energy And Spectral Efficiency For HARQ-Based Multihop Wireless Network

Multihop relay technology is effective to improve the system throughput,extend the communication coverage and enhance the anti-fading capability.Hence,increasing attention is raised in academic and industrial field to multihop relay technology.Hybrid Automatic Repeat reQuest(HARQ)protocol is characterized with the combination of ARQ and Forward Error Correction(FEC),which is able to improve the decoding correctness and is widely used in wireless communications.Multihop relay network with HARQ can further improve the transmission efficiency and reliability.Meanwhile the optimization for energy and spectral efficiency can reduce the system energy consumption,extend the terminal life,and increase the spectral utilization rate,which is becoming a popular field in the next-generation communication framework design.The maximization of energy and spectral efficiency is investigated in this paper,the important contributions of the research can be concluded as follows:Based on the log-domain linear threshold model,considering the multihop relay network with Chase combining based HARQ(CC-HARQ)over Rayleigh fading channels,an approximated expression of averge FER(Frame Error Rate)with CC-HARQ was presented.Thereby we can proceed the cross-layer optimization for energy and spectral efficiency.given the practical parameters such as modulation and coding scheme and frame length.Considering a multihop relay network with CC-HARQ in Rayleigh fading channels,the cross-layer optimum schemes of energy efficiency(EE)were proposed.A closed-form expression of EE was derived,and then the optimal frame length scheme and transmission power allocation method were further designed,towards the joint optimization of frame length and transmission power,a low-complexity alternate iterative algorithm was considered.Simulation experiments of comparisons showed that the proposed cross-layer optimization design is able to improve the EE performance of practical multihop networks,the maximum EE in two-hop scenario reached 15.255 bits per Joule with joint optimization,which is far higher than the individual optimization schemes and conventional scheme with fixed frame length and equal power.To improve the system performance of SE,an exact expression of spectral efficiency(SE)for a multihop CC-HARQ protocol was presented.Afterwards,an optimal frame length scheme,an optimal transmission power allocation method and a cross-layer joint optimization metric was further considered.Simulation results showed that the performance of SE in multihop CC-HARQ relay networks is largely improved by adopting the proposed cross-layer optimization design.Considering the trade-off optimization between EE and SE,a normalized EE-SE tradeoff model was established,by adopting one EE-SE tradeoff exponent,the joint optimal frame length scheme and power allocation solution was investigated,the alternate iterative algorithm was proposed for joint optimization,simulational results showed that the proposed algorithm can guarantee the improvement of system performance with low complexity,the tradeoff relation of EE and SE can be utilized to convert EE-SE gain,which is viewed as a guideline for practical communication system design.