Research On Channel Estimation Technology In Relay System

In this paper, we study the pilot power allocation and channel estimation scheme in the amplify-and-forward (AF) relay system based on orthogonal frequency division multiplexing (OFDM) modulation, and propose a channel estimation scheme for AF-based two-path relay cooperative networks.In the second chapter, we study the pilot power allocation in the AF relay system based on OFDM modulation. In the wireless communication system, the pilot power allocation strongly impacts the performance of the system. Because the transmission power of the wireless communication is always limited, and more power allocated to pilot means that there is less power allocated to data, while less power allocated to pilot means that the performance of channel estimation is poor. Thus, there is optimum pilot power allocation. We first give the closed-form expression of the outage probability by analyzing the math model of the system and the process of its channel estimation, then theoretically derive the optimized pilot power allocation (pilot-to-data, pdr). At last, we verify our results through simulation, and it shows that the the numerical results match the analytical results well and the optimized pilot power allocation brings considerable improvement on BER performance.In the third chapter, we propose a channel estimation scheme for the AF relay system based on OFDM modulation. Compared to the traditional point-to-point communication system, there are more links in the relay system, thus the channel estimation for the relay system is a bit challenge. For obtaining the channel state information (CSI) of link between relay and sink, the special pilot for relay should be needed, which may change the original communication resource allocation. For solving this problem, we propose a channel estimation scheme based on superimposed pilot. In the scheme, the pilot is directly superimposed on the data, which means no additional spectrum resource is needed for carrying the pilot. However, suffering from interference from the data, the performance of channel estimation based on superimposed pilot would be poor. Thus, in this chapter a low-complexity recursive interference cancellation algorithm is employed to improve the performance of channel estimation. At last, through simulation we find the performance of our scheme is well enough to meet the requirements of system.In the fourth chapter, a channel estimation scheme for AF-based two-path relay cooperative networks is proposed. In the two-path relay cooperative networks, two half-duplex relays form a virtual full-duplex relay by working alternately. It requires more CSI to cancel the inter-relay interference (IRI). In this chapter, we propose an effective channel estimation scheme and analyze the impact of the amplifying factors in relays. At last, the simulation results are given to verify our scheme.At last, we conclude the study and give some possible future work of the channel estimation for the relay system.