A Novel Cooperative Communication System Based on Multilevel Convolutional Codes

The authors propose a system where single antenna mobile users share antennas to transmit their information cooperatively to the common base station. Each mobile user overhears the coded information transmitted by other users, detects it and further encodes it along with its own information. The encoding is done using multilevel coding scheme with convolutional codes as component codes. The proposed system considers the self-information of user u at level u to reduce complexity while decoding. The coded symbols are mapped to M-ary quadrature amplitude modulation constellation using multi-resolution modulation partitioning. This enables the component codes to be designed for lower order constellation. Each cooperative user transmits multilevel coded symbols to the common base station, thus creating transmit diversity. The base station receives noisy superposition of independent Rayleigh faded signals transmitted by cooperative users and pass it through a multistage decoder. The multistage decoder employs maximum likelihood based Viterbi decoder at each stage to detect the information of each user. The Viterbi decoder applies max-log approximation to reduce the branch metric complexity. The proposed cooperative multilevel coding system outperforms non-cooperative multilevel coding system and is less complex than the existing cooperative multilevel coding system.