Differential Modulation for Bidirectional Relaying With Analog Network Coding

Sch. of Electron. & Comput. Sci., Peking Univ., Beijing, China
IEEE Transactions on Signal Processing (Impact Factor: 2.81). 08/2010; DOI:10.1109/TSP.2010.2046441
Source: IEEE Xplore

ABSTRACT In this correspondence, we propose an analog network coding scheme with differential modulation (ANC-DM) using amplify-and-forward protocol for bidirectional relay networks when neither the source nodes nor the relay knows the channel state information (CSI). The performance of the proposed ANC-DM scheme is analyzed and a simple asymptotic bit error rate (BER) expression is derived. The analytical results are verified through simulations. It is shown that the BER performance of the proposed differential scheme is about 3 dB away from that of the coherent detection scheme. To improve the system performance, the optimum power allocation between the sources and the relay is determined based on the simplified BER. Simulation results indicate that the proposed differential scheme with optimum power allocation yields 1-2 dB performance improvement over an equal power allocation scheme.

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    ABSTRACT: We Consider a multihop relay network in which two terminals are communicating with each other via a number of cluster of relays. Performance of such networks depends on the routing protocols employed. In this paper, we find the expressions for the average symbol error probability (ASEP) performance of amplify-and-forward (AF) multihop transmission for the simplest routing protocol in which the relay transmits using the channel having the best symbol to noise ratio (SNR). The ASEP performance of a better protocol proposed in [1] known as the adhoc protocol is also analyzed. The derived expressions for the performance are a convenient tool to analyze the performance of AF multihop transmission over relay clusters. Monte-Carlo simulations verify the correctness of the proposed formulation and are in agreement with analytical results. Furthermore, we propose new generalized protocols termed as last-n-hop selection protocol, the dual path protocol, the forward- backward last-n-hop selection protocol, and the forward-backward dual path protocol, to get improved ASEP performances. The ASEP performance of these proposed schemes is analysed by computer simulations. It is shown that close to optimal performance can be achieved by using the last-n-hop selection protocol and its forward-backward variant. The complexity of the protocols is also studied.
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    ABSTRACT: In this paper, we derive a maximum likelihood (ML) decoder of the differential data in a decode-and-forward (DF) based cooperative communication system utilizing uncoded transmissions. This decoder is applicable to complex-valued unitary and non-unitary constellations suitable for differential modulation. The ML decoder helps in improving the diversity of the DF based differential cooperative system using an erroneous relaying node. We also derive a piecewise linear (PL) decoder of the differential data transmitted in the DF based cooperative system. The proposed PL decoder significantly reduces the decoding complexity as compared to the proposed ML decoder without any significant degradation in the receiver performance. Existing ML and PL decoders of the differentially modulated uncoded data in the DF based cooperative communication system are only applicable to binary modulated signals like binary phase shift keying (BPSK) and binary frequency shift keying (BFSK), whereas, the proposed decoders are applicable to complex-valued unitary and non-unitary constellations suitable for differential modulation under uncoded transmissions. We derive a closedform expression of the uncoded average symbol error rate (SER) of the proposed PL decoder with M-PSK constellation in a cooperative communication system with a single relay and one source-destination pair. An approximate average SER by ignoring higher order noise terms is also derived for this set-up. It is analytically shown on the basis of the derived approximate SER that the proposed PL decoder provides full diversity of second order. In addition, we also derive approximate SER of the differential DF system with multiple relays at asymptotically high signal-to-noise ratio of the source-relay links.
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