Dispensing with channel estimation: differentially modulated cooperative wireless communications

As a benefit of bypassing the potentially excessive complexity and yet inaccurate channel estimation, differentially encoded modulation in conjunction with low-complexity noncoherent detection constitutes a viable candidate for user-cooperative systems, where estimating all the links by the relays is unrealistic. In order to stimulate further research on differentially modulated cooperative systems, a number of fundamental challenges encountered in their practical implementations are addressed, including the time-variant-channel-induced performance erosion, flexible cooperative protocol designs, resource allocation as well as its high-spectral-efficiency transceiver design. Our investigations demonstrate the quantitative benefits of cooperative wireless networks both from a pure capacity perspective as well as from a practical system design perspective

Space-Time-Frequency Shift Keying for Dispersive Channels

Inspired by the concept of the Space-Time Shift Keying (STSK) modulation, in this paper we proposed the Space-Frequency Shift Keying (SFSK) modulation as well as the Space-Time-Frequency Shift Keying (STFSK) concept which spreads the transmit signal not only across the space and time domains, but also the frequency domain. The performance of STSK modulation is degraded by about 2 dB, when the channel changes from uncorrelated frequency-flat fading to the frequency-selective environment of the 6-tap COST207 model. By contrast, as a benefit of Frequency Shift keying, the SFSK and STFSK schemes are capable of maintaining their performance also in frequency-selective fading environments. Finally, we demonstrate that the STSK and SFSK schemes constitute special cases of the STFSK modulatio

Differential Distributed Space-Time Coding with Imperfect Synchronization

Differential distributed space-time coding (D-DSTC) has been considered to improve both diversity and data-rate in cooperative communications in the absence of channel information. However, conventionally, it is assumed that relays are perfectly synchronized in the symbol level. In practice, this assumption is easily violated due to the distributed nature of the relay networks. This paper proposes a new differential encoding and decoding process for D-DSTC systems with two relays. The proposed method is robust against synchronization errors and does not require any channel information at the destination. Moreover, the maximum possible diversity and symbol-by-symbol decoding are attained. Simulation results are provided to show the performance of the proposed method for various synchronization errors and the fact that our algorithm is not sensitive to synchronization error.Comment: to appear in IEEE Globecom, 201