Abstract
The quality of two-way links is always asymmetric in practical two-way relay channels (TWRC) and therefore, the capacity of TWRC will be limited by the weaker link. An asymmetric modulation scheme, with physical layer network coding, was presented in order to improve the transmission reliability in TWRC. This makes full use of the stronger link to improve the overall transmission rate and also ensures the reliability of the weaker link. The simulation results show that the proposed asymmetric modulation scheme in the case of strongly asymmetric channels, compared to the symmetric transmission, enhances the system capacity significantly and also guarantees the system reliability.
Highlights
Network coding (NC) was originally proposed to improve the performance of multicast throughput in wired networks by Ahlswede et al in 2000 [1]
Physical layer network coding (PLNC) was proposed to improve the throughput of two-way relay channel (TWRC) [2], which maps the superimposition of the signals received simultaneously to a digital bit stream
The design of modulation suited for TWRC with PLNC can be BPSK or QPSK [6], and an unconventional 5-ary modulation which is optimized according to the channel condition [7]
Summary
Network coding (NC) was originally proposed to improve the performance of multicast throughput in wired networks by Ahlswede et al in 2000 [1]. In the symmetric rate transmission of TWRC, in order to ensure the reliability of the weaker link, the stronger link has to transmit and receive with low-order modulation as same as the weaker link. For this reason, the stronger link does not take advantage of its good channel conditions to improve the overall transmission rate, which lowers the validity. This paper investigates the asymmetric rate transmission both in the multiple access phase and broadcast phase of the two-phase TWRC by designing an asymmetric modulation scheme with PLNC. The performance of the system depends on the design at nR, which is a key point in this paper
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