The Research On Scheduling Algorithm In OFDM System

Evolution is the main theme of the development of future communication networks. The future communication networks will evolve into an all-IP network where wired and wireless networks converge. The future wireless communication systems connect wireless access network providing all kinds of different traffic to the cored network based on IP packets, which form a public, flexible, a variety of access methods coexisting and scalable network platform. As a high-performance physical layer solution, OFDM is one of the selected technologies in the future wireless communication systems including B3G/4G systems. OFDM scheduling optimizes the quality of service (QoS) performance of users’packets by means of cross-layer design, and selected adaptively transmission parameters according to wireless channels’ changes in time, frequency and space. It raises average the spectral efficiency, transmission rate and system capacity of system on the basis of maintaining the QoS requirement of different traffic packets, and taking the fairness among users into account. Therefore, OFDM has very broad application prospect in future wireless communication systems. This paper researches mainly the algorithm which relates to OFDM scheduling.Firstly, the article describes the basic knowledge of OFDM dynamic resource allocation and scheduling, which includes the principle of OFDM technology and radio resource management. In the radio resource management, the article analyses particularly the swarm intelligence algorithm and its application in OFDM dynamic resource allocation.Secondly, a new proportional fair scheduling scheme is proposed in multi-user OFDM system for heterogeneous classes of traffic in the article, and the article simulates the performance of the proposed scheme. The scheme determines the proportional constraint among users’rates according to the ratio of users’data to be passed, maximizes the sum of system’s weight capacity under the proportional constraint among users’rates; provides different types of packets in users’queues different weight factor, and calculates users’weights by the packet weight factor; not only defines the channel priority factor, but also allocates users sub-carriers by the factor under the constraint of the proportion among users’rates while allocating sub-carriers; finally derives a linear power allocation pattern.Finally, the article proposes two weighted cross-layer resource allocation schemes, which are suitable for heterogeneous traffic, with proportional fairness for multi-user OFDM system on the basis of researching the swarm intelligence algorithm; and simulates the performance of the two schemes. In the MAC layer, the two schemes not only assume that every user in the system had multiple queues, that every queue carried respectively traffic of different types; but also carry out the weighted proportional fairness scheduling. In the PHY layer, the two schemes, which are firstly based on the weighted proportional fairness scheduling, define the maximum of system’s weighted capacity sum under the proportional constraints among users’rates as optimization target. Then the proposed scenario1leads artificial fish swarm algorithm into its sub-carrier allocation, and derives a new power allocation pattern. The proposed scenario2leads the cloud adaptive particle swarm optimization algorithm into its sub-carrier, and uses population migration algorithm to carry out power allocation.