We consider the problem of time domain (TD) channel estimation for wideband millimeter wave systems with a hybrid architecture. TD channel estimators can exploit both angular and delay domain sparsity, and can perform better than frequency domain (FD) estimators exploiting only angular domain sparsity; however, the former usually require a heavier computational load than the latter. To overcome this difficulty, we propose an efficient, two-step TD channel estimator: in the first step, an effective channel incorporated with beamforming, array responses, and pulse shaping is estimated by the least squares (LS) method; in the second, the desired channel is estimated via an orthogonal matching pursuit (OMP) algorithm. It is analytically shown that the proposed two-step method can yield the same outputs as the original single-step TD estimator when an identity pulse shaping matrix and a unitary pilot matrix are employed. The proposed algorithm is simpler to implement than the other estimators based on OMP, because its sensing matrix is block-diagonal. The simulation results demonstrate that complexity reduction of the proposed method is achieved without (or with minor) performance degradation.

This paper proposes a wireless ultra-wide area backhaul network consisting of fixed/mobile access points and a wireless backhaul switch with large scale array antenna for 5G mobile communication. We also consider a hybrid beamforming scheme for wireless ultra-wide area backhaul network. We designed an analog beamformer using the genetic algorithm for sum rate maximization, and conducted channel modeling for the proposed backhaul network by deterministic ray-tracing, which gives low path loss exponent of 3 due to the high position of wireless backhaul switch. In simulation results with zero-forcing (ZF) and maximum ratio transmission (MRT) precoding, we obtained the spectral efficiency over 900 bps/Hz with 99 downlink beams on 3 km radius cell, where 4 streams are supported per beam.

We consider extensions of orthogonal matching pursuit (OMP) and oblique matching pursuit (ObMP) detectors for generalized space shift keying (GSSK). In particular, the maximum a posteriori (MAP) principle is incorporated with the OMP/ObMP so that the posteriori ratio can be maximized iteratively. Due to the fact that the posteriori ratio cannot be evaluated at the receiver unless the activated transmit antennas are known, two types of approximated posteriori ratios are derived. One is a simple approximation that ignores the terms in the posteriori ratio which need the information on transmit antenna activity, and the other is a more complex approximation developed by exploiting the transmit antenna activation probabilities. As a result, two types of MAP-OMPs and MAP-ObMPs are proposed based on these approximations. The performances and computational loads of the proposed schemes are examined and compared with existing OMP- based GSSK detectors. The results demonstrate that incorporating the MAP policies can significantly enhance performances of OMP/ObMP detectors and can yield efficient detectors that can outperform existing methods with little increase in complexity.