Diversity Transmission and Reception of DAPSK Over Noncoherent Wireless Communication Channels

In a wireless communication link, multiple-input multiple-output (MIMO) techniques have been developed to increase throughput and reliability of data transmission by employing multiple antennas at the transmitter and the receiver sides. Recently, cooperative relaying techniques have been proposed to enlarge the cellular coverage and realize distributed spatial diversity in terms of user cooperation. Other than MIMO and cooperative relaying techniques, orthogonal frequency-division multiplexing (OFDM) is also a promising technique and widely adopted in many recent and future wireless communication standards since it can make very efficient use of available spectrum and be easily combined with other existing communication techniques. Most of past studies on MIMO, OFDM, and cooperative relaying systems focus on coherent detection, which is based on the assumption that perfect channel state information (CSI) of all transmission links including instantaneous channel impulse response, signal-to-noise power ratio (SNR), and average channel statistics is available at the receiver. However, in fast time-varying environment, the sufficiently accurate CSI of all transmission links is very difficult to obtain, and thus performing coherent detection may not be feasible. In order to reduce the requirement for perfect CSI, a differential modulation technique with high power efficiency, namely differential amplitude and phase shift keying (DAPSK), has been proposed and well studied in point-to-point communications. DAPSK employs a star constellation with multiple concentric amplitude rings, each containing the same number of uniformly distributed phasors, and sequentially encodes information onto the amplitude ratio and phase difference between currently and previously transmitted symbols. By operating two consecutively received signals, the differential detection of DAPSK can be achieved without any CSI. In this thesis, we apply DAPSK into the noncoherent MIMO, OFDM, and multiple-relay systems and design the diversity transmission and reception of DAPSK for these noncoherent wireless communication systems to improve the system error performance and simplify the receiver implementation.
In the noncoherent MIMO system, a new differential space-time modulation (DSTM) using diversity-encoded DAPSK is proposed with low and fixed peak-to-average power ratio at each transmit antenna. The maximum-likelihood (ML) and an asymptotic ML (AML) receiver are developed for differentially detecting diversity-encoded DAPSK signals over independent but not identically distributed (inid) time-correlated Rician fading channels. The knowledge of CSI including average channel moments, received SNRs, and average noise power is required for realizing the ML receiver, while the AML receiver is devoid of any CSI except average noise power and thereby much easier to implement. The bit error probability (BEP) upper bound is analyzed for the AML receiver over inid time-correlated Rician fading channels. Particularly, an approximate BEP upper bound of the AML receiver is also derived for inid time-invariant Rayleigh fading channels with large received SNRs. By virtue of this approximate bound, a design criterion is developed to determine the appropriate diversity encoding coefficients for the proposed DAPSK MIMO system. For the noncoherent OFDM system with multiple receive antennas, resort to uniformly interleaved subcarrier grouping can divide all correlated subcarriers of an OFDM system into the nonoverlapping groups containing lightly correlated subcarriers. Thus, the previously developed diversity-encoded DAPSK and the corresponding AML receiver can be directly applied by treating each group as a MIMO system with lightly correlated transmit antennas so that both frequency diversity and spatial antenna diversity can be achieved. Finally, in the noncoherent amplify-and-forward multiple-relay system using DAPSK, an equal gain combining (EGC) receiver and a weighted gain combining (WGC) receiver are developed to noncoherently combine received signals from direct and multiple relay links and thereby achieve cooperative diversity. The EGC receiver operates without any CSI, while the knowledge of average SNRs on source-relay and relay-destination links is required for realizing the WGC receiver. A unified expression of BEP upper bound is analytically derived for both receivers over inid time-invariant Rician and Nakagami-m fading channels with or without link SNR estimation errors. Numerical and simulation results verify the correctness and tightness of the derived BEP bounds and show that the proposed DAPSK systems can provide improved error performance over the existing works on the above-mentioned noncoherent wireless communication systems.