A new strategy in asymmetric two-user two-relay wireless networks with network coding and hierarchical modulation

In this paper, a new strategy was proposed that combining network coding with hierarchical modulation to solve the problem of asymmetry in two-user two-relay wireless networks. Hierarchical modulation was used to improve the performance of the low-priority stream and network coding was aimed at strengthening the reliability of the high-priority stream. Bit error rate (BER) was obtained to prove the correctness of the simulations. Compared with the conventional network coding scheme, it was obvious that the new strategy performed much better under additive white Gaussian noise (AWGN) channel. However under Rayleigh channel, its advantages played a dominant role in relatively lower signal-to-noise ratio (SNR) while its disadvantages leaded in higher SNR. In addition, simulations were performed to find a proper priority parameter of hierarchical modulation in accordance with the circumstances of the channels.