A Novel Quantize-and-Forward Cooperative System: Channel Estimation and M-PSK Detection Performance

EURASIP Journal on Wireless Communications and Networking, Jul 2010

A method to improve the reliability of data transmission between two terminals without using multiple antennas is cooperative communication, where spatial diversity is introduced by the presence of a relay terminal. The Quantize and Forward (QF) protocol is suitable to implement in resource constraint relays, because of its low complexity. In prior studies of the QF protocol, all channel parameters are assumed to be perfectly known at the destination, while in reality these need to be estimated. This paper proposes a novel quantization scheme, in which the relay compensates for the rotation caused by the source-relay channel, before quantizing the phase of the received M-PSK data symbols. In doing so, channel estimation at the destination is greatly simplified, without significantly increasing the complexity of the relay terminals. Further, the destination applies the expectation maximization (EM) algorithm to improve the estimates of the source-destination and relay-destination channels. The resulting performance is shown to be close to that of a system with known channel parameters.

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A Novel Quantize-and-Forward Cooperative System: Channel Estimation and M-PSK Detection Performance

EURASIP Journal on Wireless Communications and Networking Hindawi Publishing Corporation A Novel Quantize-and-Forward Cooperative System: Channel Estimation and M-PSK Detection Performance Iancu Avram 0 Nico Aerts 0 Dieter Duyck 0 Marc Moeneclaey 0 Carles Anton-Haro 0 Department of Telecommunications and Information Processing, Faculty of Engineering, Ghent University , 9000 Gent , Belgium A method to improve the reliability of data transmission between two terminals without using multiple antennas is cooperative communication, where spatial diversity is introduced by the presence of a relay terminal. The Quantize and Forward (QF) protocol is suitable to implement in resource constraint relays, because of its low complexity. In prior studies of the QF protocol, all channel parameters are assumed to be perfectly known at the destination, while in reality these need to be estimated. This paper proposes a novel quantization scheme, in which the relay compensates for the rotation caused by the source-relay channel, before quantizing the phase of the received M-PSK data symbols. In doing so, channel estimation at the destination is greatly simplified, without significantly increasing the complexity of the relay terminals. Further, the destination applies the expectation maximization (EM) algorithm to improve the estimates of the source-destination and relay-destination channels. The resulting performance is shown to be close to that of a system with known channel parameters. 1. Introduction As wireless communication networks become more widespread, new methods are being developed to increase the reliability of information transfer. In a multipath propagation environment, the reflected signals can combine both constructively or destructively at the receiving antenna, giving rise to Rayleigh fading. This imposes an upper bound on the reliability of a point-to-point communication system. One way to overcome this problem is by the use of multielement sending or receiving antennas [1]. However, due to size constraints of mobile terminals, this technique cannot always be applied. In a cooperative communication system, this problem is overcome by exploiting the broadcast nature of wireless communication. Information broadcast by the source is also received by terminals other than the destination. These terminals relay to the destination the information sent by the source, creating additional independent channels between source and destination. This technique is analyzed from an information theoretic point of view in [2], where upper and lower bounds are obtained for the capacity of the relay channel. In [3], it is shown that in a fading environment, the spatial diversity introduced by the relay terminals improves the reliability of a communication system, which is now determined by the probability that all channels are simultaneously in fading. By increasing the reliability of the communication system, higher data rates can be achieved without increasing the transmitter power. Alternatively, one can keep the data rate constant and lower the transmission energy, extending the battery life of portable devices. The diversity gain of various cooperative strategies is discussed in [4]. It is shown that the Amplify and Forward (AF) protocol, in which the relay amplifies the received signal, indeed introduces spatial diversity. However, when using half-duplex terminals that cannot transmit and receive data at the same time, the relay needs to store the received information, in order to forward it later on. This situation is depicted in Figure 1. The AF protocol assumes this data can be stored with an infinite precision. In a more realistic system, this data is quantized before storage, yielding the Quantize and Forward (QF) protocol. In [5], upper and lower bounds on the capacity of the relay channel are obtained for a relay that quantizes the received data using a Source h1 Wyner-Ziv coding scheme. Other quantization methods have been analyzed in [6, 7]. The QF protocol described in [6] is attractive for the use in wireless sensor networks, because the complexity of the individual relay terminals is kept low. This is done by moving the more computational intensive tasks to the destination, where typically there is more processing power available. While cooperative communication has been well investigated from an information theoretic point of view, other aspects also need to be studied in the development of a practical implementation. The issue of channel coding is addressed in [8], where low density parity check (LDPC) codes are designed for the Decode and Forward (DF) protocol. Channel parameter estimation is discussed in [9] for the AF protocol, where pilot-based estimates are calculated for the different channel coefficients involved. Because only the received pilot symbols are used in [9], the obtained estimates could be further refined by also using the information about the channels that is embedded in the re (...truncated)


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Avram, Iancu, Aerts, Nico, Duyck, Dieter, Moeneclaey, Marc. A Novel Quantize-and-Forward Cooperative System: Channel Estimation and M-PSK Detection Performance, EURASIP Journal on Wireless Communications and Networking, 2010, pp. 1-11, Volume 2010, Issue 1, DOI: 10.1155/2010/415438