RAN QoS Research. Cellular Mobile Communication System

Nowadays new mobile multimedia service is coming forth. The challenge of mobile communication technology is how to fulfil the requirement to wideband multimedia on the condition of limited frequency resource. The existent mobile communication system must tend to offer higher rate multimedia service. The QoS of mobile network directly decides the usability and practicability of network. Currently the QoS of Internet has made a big leap, but that of mobile network a small step. For wireless access network the QoS problems are just became noticeable, and there are a lot of issues waited to study.Some key QoS problems about wireless multimedia service in radio access network are focused in this thesis, especially the following problems: the problems of dynamic bandwidth allocation based call admission strategy and soft handoff, the problems of wireless packet schedule and the problems of wireless TCP improve technology.The main contribution of the theies as follows:(1) Proposing a call admission strategy of wireless multimedia service based on dynamic bandwidth allocation for adapting to the QoS requirement of wireless cellular network. Through setup the model and analysis, the simulation results show that the scheme can decrease call block probability and call drop probability by decrease the service bandwidth of variable bandwidth service when there is not free bandwidth in the cell, and increase bandwidth utilization by increase the service bandwidth of variable bandwidth service when there is free bandwidth in the cell. In addition, the scheme also can increase bandwidth utilization by allowing variable bandwidth service to borrow bandwidth from reservation bandwidth for handoff calls.(2) Proposing a call admission strategy of CDMA soft handoff based on the move speed and move direction of mobile stations. The scheme takes into account the special condition of real environment. Through setup the model and analysis, it is show that the scheme not only expands the capacity of system but also improves the soft handoff QoS as a whole, especially, when the arrival rate of soft handoff call is high.(3) We present a time delay limited wireless multimedia flow schedule algorithm. The algorithm decrease the data sending rate while heavy packet loss rate for corruption lasts short time to avoid the waste of resource by unnecessary data lost and repeattransmission. And when the channel get better, the algorithm increase the data sending rate to guarantee the throughput, delay and packet loss rate of the terminal applications. We also propose a fair compensation strategy and a reallocation method in the algorithm by consider the delay index of lagging flows. The schedule algorithm aim to pursue the system throughput under the condition of guaranteed the bandwidth reservation and limited delay. Through simulation and anylisis, the algorithm can distinguish the error sensitive flow and delay sensitive flow, and guarantee the QoS of different flows.(4) A new radio link control Scheme based on fuzzy logic to improve TCP throughput in WCDMA wireless network is proposed. In which the fuzzy controller consider the RLC queue length, TCP packets arrive rate and the change of the RLC queue to increase or decrease the retransmission number of RLC protocol data units and to drop the newly arrived TCP packets or not. This strategy is simple and easy to implement. The simulation results show that the Scheme can improve the throughout of TCP in wireless network and improve the utilization of radio resource.(5) We analyze the throughput of TCP/RLC with RLC backoff scheme on fading links. The analytical results show that error correlations affect the performance of TCP significantly, and RLC backoff algorithms achieve energy efficiency improvement with the compromise of throughput and delay performance of TCP. This method can help to design a clever RLC layer that preserves error correlations and increases energy efficiency of terminals without compromise much delay and throughput to TCP applications.