Research On Key Techniques Of Radio Resource Allocation In Relay-enhanced Cellular Networks

The spectrum utilization, energy consumption and cost are the three key factors which make the mobile communication network sustainable growth. Compared with the4 G system, the 5G system has been significantly improved on the spectral efficiency, energy efficiency and cost efficiency to achieve the sustainable growth. Multicast is not only the high spectrum utilization technology, but also the high energy efficiency technology. It is a key of 5G system. To improve the energy efficiency of multicast, relay technology has been introduced into multicast communications, called cooperative multicast. Specifically, the cooperative multicast transmission consists of two phases: in the first phase, a BS broadcasts its data to all users, which leads to a low outage probability on cell-center users while a high outage probability on cell-edge users. In the second phase, some successful users act as relays to assist the failed users. With designing good cooperative multicast mothod, the energy efficiency of multicast system can be improve greatly. Therefore, the main contributions of this paper are providing the methods about relay selection and power control in cooperative mulicast system.We first proposed a probability-based relay selection and power control method for the two-phase cooperative multicast communication. We treated the energy-efficiency as the objective function and the outage probability as the constraint. Then, we obtained the optimal active probability as well as the corresponding relay power. Simulation results indicated that our method can achieve higher energy efficiency.Then we investigated the relationship between the outage probability and the user power consumption in two-phase cooperative multicast communications. We found that the unbalanced outage probability of the cell-center and the cell-edge users was the main reason that caused the large user power consumption. To deal with the issue, we proposed an autonomous relaying scheme, called the probability-based relay selection and power control, to minimize the user power consumption for any given multicast data rate.In particular, we developed the optimal algorithm under the balanced outage reduction efficiency. We also found the sub-optimal algorithm under the balanced outage probability. Since the computational complexities of both optimal and sub-optimal algorithms linearly increased as the growth of the quantized distance between the base station and users, they can be implemented in practical systems. Simulation results demonstrated that our algorithms can reduce the user power consumption up to about 54% and 40%,respectively.Finally, we introduce the contribution of this paper, and analyse the future works.