Research On Buffer Management And Packet Scheduling Algorithms In Wireless Networks

With the development of mobile communications, mobile users and Internet users are increasing dramatically. People expect that next generation mobile communication systems can provide larger capacity and support mobile multimedia services. Besides providing real-time speech service, next generation mobile communication systems are required to support other services such as low/high rate data, pictures etc. Heterogeneous services have different quality of service (QoS) requirements, for example, the requirements of time delay, packet loss rate, and transmitting rate for heterogeneous services are differentiated. There are two main objects for wireless network design, one is to guarantee QoS requirements of heterogeneous services, and the other is to make resource utilization maximized. This recurs to radio resource management (RRM). Radio resource management for the third generation mobile communication systems includes call admission control, handoff control, power control, load control and packet scheduling. This dissertation pays attention to buffer management and packet scheduling in wireless multimedia packet networks.A brief introduction on the evolution of wireless networks is presented in chapter 1, followed with an overview on buffer management and packet scheduling algorithms. We also give some advices and basic thoughts on these problems.As well as packet scheduling algorithms, buffer management algorithms also need to consider channel condition. In chapter 2, a fair packet dropping algorithm is proposed to decide dropping policy in wireless networks when congestion occurs. The algorithm considers both channel condition and fairness so as to achieve tradeoff between throughput and fair services, when slight congestion occurs, algorithm trends to drop packet fairly, so as to grant each flow acquire the resource according their proportion; when moderatecongestion occurs, algorithm trends to drop packet of flows which has worse channel condition, to reduce send rate of these flows, so as to relieve congestion; when severe congestion occurs, algorithm trends to drop packet fairly again, through flow control mechanism of upper layer, sending rate of all flow will be greatly reduced, so as to accelerate congestion relief.In order to improve the fairness and adaptability of RED algorithm, the buffer occupancy of individual flow is replaced by a new introduced variable -Sharing Index to indicate the network resource share among difference flows, so as to overcome the limitation of using buffer occupancy. The definition of Sharing Index in wireless networks is also extended, to make it consider both fairness and system performance (channel condition). Through defining rules of both Sharing Index and queue length, a fuzzy logic based buffer management algorithm named FF-RED is proposed. When calculating packet dropping probability in FF-RED algorithm, the probability will further increase or decrease based on the sharing of network resource (by means of Sharing Index), so it can use the difference between flows to make congestion relief more quickly, and it has better adaptability and fairness.In chapter 4, a random early expiration detection based buffer management algorithm for real-time traffic over wireless networks is propsed. The main idea is to predict whether new arrival packet can reach the receiver under the limit of maximal delay bound, and random discard the packet based on estimate result, so as to prevent invalid transmission wasting wireless resources, and at meanwhile to decrease queue delay and to reduce expiration probability of following packets. Considering the characters of wireless link such as variable channel condition and transmission error, the algorithm is composed of three steps: aimed to guarantee the delay of retransmission packets, using the method which is similar to early congestion detection to detect expiration and discard packets in advance; adaptive adjusting the drop probability based on the trend of channel condition; re-calculating the threshold value when the link rate is changed. The influence on the TCP...