Research On Scheduling Algorithm Based On The Adaptive Packet Length

With the rapid development of internet and wireless communications,all kinds of mobile devices quickly become prevalent,which makes people have higher requirements of the wireless communications,i.e.high bandwidth and low latency.However,the communication quality of mobile communication is susceptible to interference,which may lead to the increase of wireless communication delay,and this may contradict to the requirement of client.Therefore,the 802.11 n protocol came into being.The 802.11 n protocol adopts frame aggregation technology and MIMO technology to improve bandwidth utilization and keep low latency.In this paper,the scheduling algorithm based on adaptive packet length is studied.Here's the main contributions of the paper:Firstly,in order to ensure the latency requirements of high real-time application and reduce the packet header overhead,the paper proposes an adaptive packet length strategy based on number of symbols(the K-PK packetization strategy)by the joint optimization of the network layer and physical layer.The core of K-PK packetization strategy is to bundle k consecutive input symbols according to a Poisson process into a transmit packet with a fixed length packet header.Simulation and analysis show that the K-PK packetization strategy obtains an optimal value of k that can get the lowest latency and balances the packet header overhead for a given channel with certain bit error probability.Compared with the adaptive packet length strategy based on fixed timeslot(the T-PK packetization strategy),the K-PK packetization strategy is more suitable for the situation of channel with poor quality and volatility,and more in line with the needs of the reality.In order to further explain that the K-PK packetization strategy is more suitable than the T-PK packetization strategy for the fast time-varying channel and how to adjust packet length by the K-PK strategy according to the channel quality,an adaptive channel algorithm based on the K-PK packetization strategy is proposed.The simulation results show that K-PK packetization strategy can obtain lower end-to-end delay than T-PK packetization strategy and fixed packet length in fast time-varying channel.Secondly,although the K-PK packetization strategy is suitable for the situation of channel with poor quality and volatility,which can obtain minimum delay,however,the minimum latency under such environment is also high and needs to be improved.In order to further reduce delay and improve transmission rate,the adaptive coded modulation(AMC)is studied,and then an adaptive coded modulation(AMC)scheme is proposed,which can keep the bit error rate in a range by adjusting code and modulation.On the basis,an adaptive packet length scheme based on AMC is proposed,which combines the K-PK packetization strategy with AMC scheme.Thirdly,based on the K-PK packetization strategy and AMC scheme,a scheduling algorithm based on K-PK packetization strategy and AMC scheme is proposed for the communication scene between base station and user.The core of the scheduling algorithm are briefly decribed below: 1)The client's priority is determined through their data type and the transmission rate,and the channel with high signal-to-noise ratio is allocated to the user with the highest priority level until no idle channel exits;2)The AMC scheme and the best number of symbols is obtained according to client's transmission rate and signal-to-noise of channel;3)The client updates transmission rate according to the number of occupied channels and bundles consecutive input symbols according to the best number of symbols into a transmit packet,and transmits packet in channel according to the AMC scheme.The simulation results show that the scheduling algorithm can meet the delay requirements of various clients,improve throughput,reduce retransmission rate and delay...