Abstract
In this paper, a novel scheme is proposed to enhance the spectral efficiency of a two-way cooperative relaying system, where two source terminals exchange information directly and via K intermediate relays using the three-phase two-way decode-and-forward (DF) protocol. Signal space diversity (SSD) is incorporated into the two-way cooperative relaying system in the proposed scheme that exploits the inherent diversity in the modulation signal space by rotating and expanding the ordinary constellation. The proposed SSD-based three-phase two-way DF relaying scheme exchanges four symbols in three time slots and thus doubles the spectral efficiency as compared to the conventional three-phase two-way DF relaying system, where six time slots are required to exchange the same four symbols. This improvement in spectral efficiency is achieved without adding any extra complexity, bandwidth, or transmit power. A comprehensive analysis of the proposed scheme is carried out in this paper, and closed-form expressions for various performance metrics, including error probability, outage probability, and channel capacity, are derived. It is shown that the proposed scheme provides a diversity gain equal to one higher than the number of relays. The paper also studies different schemes for the optimization of relay position and power allocation. Finally, Monte Carlo simulations are performed which confirm the validity and accuracy of the analytical framework.
Highlights
Cooperative relaying has gained a lot of interest from both academic and industrial communities due to its application prospects to facilitate range-rate improvements of future wireless communication systems [1,2,3,4]
The error probability expression of the proposed SSC-2W scheme was derived over the Rayleigh fading channel
It was shown that the proposed SSC-2W scheme enhances the performance and doubles the spectral efficiency of the conventional three-phase two-way DF relaying system
Summary
Cooperative relaying has gained a lot of interest from both academic and industrial communities due to its application prospects to facilitate range-rate improvements of future wireless communication systems [1,2,3,4]. In the proposed SSC-2W scheme, each of the two source terminals broadcasts its first symbol from the expanded constellation to the opposite source terminal and the relays in different time slots, i.e., the first and second time slots. The proposed SSC-2W scheme exchanges four symbols in three time slots and enhances the spectral efficiency by 100 % when compared with the conventional three-phase two-way DF relaying system, without adding any extra complexity, bandwidth, or transmit power. The expanded constellation maintains the same number of bits per signal point as in the ordinary constellation To this end, we explain the use of SSD in the three-phase two-way DF relaying system. In the second time slot, T2 broadcasts only one of the two SSD symbols (i.e., zT2,1), which is received at T1 and the ith relay as yT2T1 = yT2Ri =. The proposed SSC-2W scheme increases the data rate, spectral efficiency, and diversity when compared with the conventional three-phase twoway DF relaying system without any additional bandwidth or transmit power
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