Research On Multicast Resource Allocation Scheme In IMT-Advanced System

With the rapid development of wireless communication technology, the number of mobile users becomes more and more, and the requirement of quality of service is higher and higher. Thus, the radio resource cannot meet the requirement of communications. To utilize the resource better, the wireless broadcast/multicast technology transmits the same service to multiple users with the same resource and becomes a key technology in the next generation mobile cellular networks (IMT-Advanced). To overcome the problems in the existing resource allocation algorithms and improve the performance of multicast system further, in this dissertation, the multicast resource allocation problems are investigated and some subcarrier allocation, power allocation and bit loading schemes to improve the throughput of multicast system are proposed to ensure the fairness among multicast users, to reduce the feedback load and to balance the tradeoff between transmission time and energy consumption. The main contribution of this dissertation can be summarized as follows:1) To improve the system throughput performance of opportunistic multicast scheduling system, an adaptive user selection scheme is proposed. Firstly, the main idea of opportunistic multicast scheduling is introduced. Secondly, a system throughput matrix (STM) is established, which can be used to imitate the opportunistic multicast scheduling process. According to the channel gain distribution, the value of each element in STM is derived, and the optimal solution is obtained by fully searching the elements in STM. To reduce the computational complexity, a suboptimal heuristic searching scheme is also proposed. Simulation results show that the proposed adaptive user selection scheme can significantly improve the system throughput.2) To ensure the fairness among users in multicast system, a resource allocation algorithm with subcarrier cooperation and user grouping is proposed. The objective is to maximize the throughput while ensuring the fairness among users. With the constraint of transmission power and bandwidth, the optimization problem is established. Then, to reduce the computational complexity, a suboptimal algorithm is proposed, which works in two steps. In the first step, the main idea of subcarrier cooperation is detailed and a novel transmission scheme based on the idea is proposed to improve the transmission efficiency. To reduce the computational complexity, a simplified algorithm is also proposed. In the second step, the water-filling algorithm is adopted to reallocate the power among subcarriers, which can improve the system throughput further. Simulation results show that the proposed schemes can ensure the fairness among services and among users while getting fine system throughput performance.3) To reduce the feedback load of multicast system while ensuring comparable throughput performance, the resource allocation problems are investigated.Assuming that the channel gain distribution is unknown to the BS, a resource allocation scheme based on opportunistic feedback is proposed. Firstly, the key channel gains that can significantly affect the system throughput are proved to belong to a channel gain interval with a large probability. Secondly, a statistical method is proposed to estimate the channel gain interval. Thirdly, the opportunistic feedback scheme (OFS) is formulated and the resources are allocated according to OFS. Compared with the existing schemes, OFS can significantly reduce the feedback load.Assuming that the channel gain distribution is known to the BS, a coding based multicast scheduling algorithm is proposed. Firstly, the coding scheme based on erasure-correction coding and layered coding is proposed. Secondly, according to the channel gain distribution, the transmission rate of basement layer and enhanced layer are derived, respectively. Finally, the basement layer algorithm and the enhancement layer algorithm are proposed, respectively. Compared with the existing scheme, the proposed coding based scheme can get better system throughput performance.4) To balance the tradeoff between transmission time and energy consumption, a resource allocation scheme based on adaptive demodulation mapping (ADMS) is proposed. Firstly, to increase the transmission efficiency, ADMS is introduced to multicast sytstem. Secondly, the expressions of transmission time and energy consumption are derived. Thirdly, a distance minimization problem (DMP) with attenuation function is formulated to balance the tradeoff between the two indexes. The proposed scheme has wide application range. For the system regarding transmission time as the most important index, the transmission time can be minimized by adjusting the value of attenuation function. For the system sensitive to energy consumption, the energy consumption can be minimized. For normal system, the tradeoff between the two indexes is balanced.