Design And Simulation Of Packet Scheduling Algorithms In The Downlink Of OFDM System

Owing to the capabilities of combating the frequency selective fading and supporting high data rate, Orthogonal Frequency Division Multiplexing (OFDM) has been widely acknowledged as a key technology for next-generation mobile communication system and wireless broadband access system. However, the explosive growth of multimedia applications and the scarcity of radio resource impose new challenges on the design and optimization of OFDM system. As an important element of Radio Resource Management (RRM), the design of Packet Scheduling Algorithm (PSA) plays an important role in allocating radio resource and guaranteeing QoS for OFDM system. Furthermore, since90s, the mobile communication system has been growing towards supporting the coexistence of multiple services such as voice, data and image transmission. More attention has been paid on the design of PSA to support mixed services in OFDM system.In this paper, on the basis of three design goals including throughput maximization, fairness and QoS guarantee, we categorize the existing packet scheduling algorithms into three types, throughput-oriented PSA, fairness-oriented PSA and QoS-oriented PSA. In order to solve the problems in related works, we proposed three algorithms, which are throughput-oriented Maxgain+LWF algorithm, fairness-oriented SPF algorithm and QoS-oriented DTC algorithm. The Maxgain+LWF algorithm aims to maximize system throughput by means of jointly allocating power and subcarriers. The SPF algorithm aims to decrease the implementation complexity of proportional fairness criterion for multicarriers system. The DTC algorithm aims to simultaneously guarantee QoS for real-time and non-real-time services, and increase the number of satisfied users. In view of the conflict between the higher performance requirements of multimedia applications and the scarcity of radio resource, we also propose a compensation strategy called Subcarrier Reallocation Algorithm (SRA) so as to optimize radio resource utilization. With the SRA, the performance of the scheduling algorithms will be greatly improved. In order to demonstrate performance efficiency, we apply SRA to the proposed SPF and DTC algorithms, as a result, another two new algorithms (DTC+SRA algorithm and SPF+SRA algorithm) are created.For the purpose of performance evaluation, we construct the simulation environment by VC++6.0, and make comparisons with other existing algorithms. Simulation results demonstrate that, as expected, the algorithms proposed in this paper outperform other algorithms.