Space–Frequency Convolutional Coding for Frequency-Asynchronous AF Relay Networks

In this paper, we design a space-frequency (SF) convolutional coding scheme for amplify-and-forward (AF) relay networks that contain multiple distributed relay nodes. The frequency-asynchronous nature of the distributed system is considered in our design. Orthogonal frequency-division multiplexing (OFDM) modulation is adopted, which is robust to certain timing errors. We exploit the signal space diversity technique and employ an extended cyclic prefix (CP) at the source node. The relay nodes need to perform only simple operations, e.g., convolution and amplification, and they need no information about the channels and the frequency offsets. Attributed to the extended CP, the multiple frequency offsets can directly be compensated at the destination. We further prove that both spatial and multipath diversity can be achieved by the proposed scheme. Numerical results are provided to corroborate the proposed studies.