The Power Of Parallel Ofdm Relay Network Optimization

Wireless communication is the high developing technology nowadays. Cooperative communication as a kind of wireless communication has been widely used in wireless sensor networks, wireless Ad hoc networks, wireless Mesh networks and wireless cellular networks, and it will be the key technology for convergence of various heterogeneous networks. Besides, relay cooperative communication could provide higher rates and reliability for our future wireless communication networks, so it has been the highlight in the research community. So, in this paper, we do some research on the technology of relay cooperative communication.According to the way of forward, the cooperative communication network is divided to amplify-and-forward (AF) relaying network and decode-and-forward (DF) relaying network. Outage probability and error symbol rate (SER) are two mostly used performance metrics for wireless communication systems. In order to improve the ratio of frequency spectrum, Weinstein and Ebert found a new transmission system with multi-carriers based on DFT and FFT in1970s. We call the technology as OFDM. With the advantages of high transmission rate, large data, and strong anti-interference ability, OFDM has been widely used in communication.In this paper, we will set a dual-hop half-duplex relaying network model with single source, single purpose and K AF relays. The relays employ parallel transmission protocol. The channels are assumed to be frequency-selective fading, in which OFDM is used. The research direction is to minimize the outage probability of this model by solving the optimization problem of relays’ power assign. Because outage probability of the model depends on many factors, and the power constraint contains individual power constraints of each relay, aggregate power constraints of each sub-carrier, and hybrid constraints of both. It makes the work of solving the optimization problem very complex. In order to simplify the optimization problem, firstly, we find the relationship between the previous studies and the outage probability of the multi-carrier model we have defined. Then a new nonlinear optimization problem is found. And the complex optimization problem can be divided into three cases. The first case is solving the problem just with aggregate power constraint, and we can solve it with sub-optimal linear strategy. The second case is solving the problem just with individual power constraint. For this case, we use a gradient search method to solve it, because the concavity of the objective function guarantees that it definitely converges to the optimal PA scheme. The third case is to solve the problem of multiple power constraints. By solving the three cases, we can get the power of each relay on each sub-carrier at last.