Pilot-based individual forward and backward channel estimation in Amplify-and-Forward OFDM relay networks

Abstract

In this paper, we propose an Amplify-and-Forward (AF) Orthogonal Frequency Division Multiplexing (OFDM) relay scheme that each relay superimposes its own pilot symbol (PS) such that, individual relay channels can be estimated at the destination. We derive optimal PS designs including both Modification Diagonal Matrix (MDM) and superimposed PS at each relay. These designs are based on channel Mean SquareError (MSE) minimization and Inter-Relay Interference (IRI) elimination, equivalently. It is shown that the number of relays should satisfy the condition, M < N 2(2L−1) , where N and L are the OFDM size and channel order, respectively, and a is the maximum integer part of a. Both Least-Square (LS) and linear minimum MSE channel estimators are derived. Furthermore, the estimator according to uncertain data and approximate computations is derived from an efficient convex optimization problem.

Individual Channel Estimation in a Diamond Relay Network Using Relay-Assisted Training

“…The estimation performance of the S−R 푖 link is worse than that of the R 푖 −D link because the former link is affected by both the propagated noise introduced from the relay nodes and the estimation error of the second-hop link. Moreover, the performance of the proposed scheme is superior to that of the pilotbased scheme described in [17]. The pilot-based scheme aims to superimpose the relay-assisted training onto the source training signal with a special orthogonal constraint.…”

“…The pilot-based scheme aims to superimpose the relay-assisted training onto the source training signal with a special orthogonal constraint. With the same average power and different block length, the total energy of the relay-assisted training in the scheme [17] is reduced compared to the proposed scheme. Moreover, the relay-propagated noise has a serious impact on the estimation of the R 푖 − D link in the scheme [17].…”

“…With the same average power and different block length, the total energy of the relay-assisted training in the scheme [17] is reduced compared to the proposed scheme. Moreover, the relay-propagated noise has a serious impact on the estimation of the R 푖 − D link in the scheme [17]. As a result, the proposed estimation scheme is superior to the scheme [17].…”

“…According to (17), the relay-propagated noise introduced from each relay node is removed thoroughly. As both the CDI and MAI are removed, the minimum MSE of the improved LS estimation is given by…”

“…Unfortunately, it is difficult to obtain an instantaneous CSI. The subsequent work in [17] 2 International Journal of Digital Multimedia Broadcasting had expanded the superimposed training scheme presented in [18] to the area of multirelay networks. The authors derived optimal pilot symbol designs including both modification diagonal matrix and relay superimposed pilot symbol.…”