Abstract-A physical-layer network coded two-way relay system applying Low-Density Parity-Check (LDPC) codes for error correction is considered in this paper, where two sources A and B desire to exchange information with each other by the help of a relay R. The critical process in such a system is the calculation of the network-coded transmit word at the relay on basis of the superimposed channel-coded QPSK words of the two sources. For this joint channel-decoding and network-encoding task a generalized Sum-Product Algorithm (SPA) over F16 is developed. This novel iterative decoding approach outperforms other recently proposed schemes as demonstrated by simulations.

Abstract-In adaptive time division duplex (TDD) broadcast multi-antenna orthogonal frequency division multiplexing (OFDM) systems, non-reciprocal transceiver chains at the base station (BS) cause multi-user interference. This is due to the inappropriate spatial filter design at the BS based on the reverse link estimate. Hence, BS transceiver calibration is required. Provided that an estimate of the forward link channel is available at the BS, e.g., in a calibration phase, the transceiver parameters can be estimated by solving a total least squares (TLS) problem. In addition, if mutual coupling between the antennas exists the number of unknown front-end parameters to be estimated increases. Consequently, large matrices need to be decomposed via singular value decomposition (SVD) to attain a calibrated system. To deal with these large matrices a conjugate gradient (CG) method for solving the TLS problem iteratively is proposed in this paper. Simulation results show that the calibration based on the CG method achieves almost the same performance compared to the TLS solution but with significantly reduced complexity.