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

Design and Implementation of Distributed Space-Frequency to Achieve Cooperative Diversity in Wireless Relay Networks

Recently, there has been much interest in modulation techniques that can help in achieving transmit diversity motivated by the increased capacity of multiple-input multiple- output (MIMO) channel. To achieve transmit diversity the transmitter needs to be equipped with multiple antennas. The antennas should be well separated to have uncorrelated fading among the different antennas. This results in higher diversity orders and higher coding gains. However, achieving transmit diversity for mobile units requires cooperative diversity. In this context, the space-time codes (STC) for spread spectrum CDMA systems have received great interest in recent times. The schemes presented in this paper ensure that the limitations of conventional correlation receivers are overcome. The effect of the space-time code distribution on the space-time code that achieves full diversity with maximum coding gain over MIMO channels is studied in this paper. In most of the analogous works surveyed so far, it is observed, that, there has been very little focus on the study of systems that exhibit diversity of all the three forms namely: source coding diversity, channel coding diversity and user cooperation diversity. However, in this paper, all these three forms of diversity are uniformly considered and the proposed schemes are studied for their robustness and performance. It is shown, that, the proposed space-time coded communication scheme is both bandwidth and power efficient. To analyze the proposed scheme fully, communication over fading channels is considered. The maximum-likelihood decision metric is used to decode the original information in the presence of channel estimation errors. A study of the performance of the proposed STC system in the presence of slowly changing Rayleigh channels is also presented. Keywords: Multipath fading, Communication systems, Distributed Space-time codes, Wireless relay networks, Signal Processing, Multinode Cooperative communication, multiple sensor detection system

Dispensing with Channel Estimation…

In this article, we investigate the feasibility of noncoherent detection schemes in wireless communication systems as a low-complexity alternative to the family of coherent schemes. The noncoherent schemes require no channel knowledge at the receiver for the detection of the received signal, while the coherent schemes require channel inherently complex estimation, which implies that pilot symbols have to be transmitted resulting in a wastage of the available bandwidth as well as the transmission power