Energy-Efficient Resource Allocation In Multicast OFDM Systems

With the rapid development of mobile Internet, plenty of wireless applications have become an important part of people’s daily life. However, almost all frequency bands are allocated by exclusive licensing and large portions of spectrum remain under-utilized in fact. It makes the scarce spectrum resource more precious. On the other hand, the whole world is facing severe energy problems and the energy cost for most operators is becoming more and more expensive along with the prevalent use of wireless services. As a result, green communications has become an important issue of science research and industry.Orthogonal frequency division multiple (OFDM) has become one of the key technologies for wireless communications as its strong anti-fading ability. Multicast makes the system resource becoming more shareable which not only improves the efficiency of spectrum but also energy efficient. So the multicast has been widely used in OFDM system. In this dissertation, energy efficiency measured using "throughput per Joule" metric. For the purpose of maximizing the energy efficiency, the resource allocation problem is studied in the following two parts.A spectrum sharing protocol is considered firstly in OFDM system. In the protocol, the cognitive base station employees an adaptive relaying technique to forward primary data by acting as a relay for the primary system. The considered problem is modeled as a non-convex optimization problem which aims to maximize the energy efficiency of the secondary system with the constraint on total transmit power and the minimum required data rate of the primary system. The optimal set of subcarriers used for cooperation and power allocation are obtained by using fractional programming and dual theory. Simulation results reveal that the proposed algorithm performance well.Then, the multiple description coding multicast and beamforming technique are employed to OFDM system. The optimize problem aims to maximize the energy efficiency with the consideration of the total transmit power. A two-step scheme is proposed. Firstly, the beamforming vector is acquired by a vector splitting algorithm and then the subcarrier and power allocation are completed with the fractional programing and subgradient method. Simulation results demonstrate that the proposed scheme obtains better energy efficiency.