A smart scheme for relay selection in cooperative wireless communication systems

EURASIP Journal on Wireless Communications and Networking, May 2013

The performance of multiple-input multiple-output systems using spatial multiplexing can be degraded when the spatial information channels are correlated. This work proposes a solution to this problem, which is based on a cooperative wireless communication system. Within the cooperative system, the relay is selected either randomly or using the smart selection scheme, a simple and distributed approach proposed herein. These relay selection schemes are evaluated for several situations within a small cell environment, using a simulator that generates frequency-selective channel realizations. The simulation results show that the smart selection scheme yields high capacity gains close to the theoretical maximum gain.

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A smart scheme for relay selection in cooperative wireless communication systems

Ivo Sousa 0 Maria Paula Queluz 0 Antnio Rodrigues 0 0 Instituto de Telecomunicaes / Instituto Superior Tcnico, Technical University of Lisbon , Lisbon 1049-001, Portugal The performance of multiple-input multiple-output systems using spatial multiplexing can be degraded when the spatial information channels are correlated. This work proposes a solution to this problem, which is based on a cooperative wireless communication system. Within the cooperative system, the relay is selected either randomly or using the smart selection scheme, a simple and distributed approach proposed herein. These relay selection schemes are evaluated for several situations within a small cell environment, using a simulator that generates frequency-selective channel realizations. The simulation results show that the smart selection scheme yields high capacity gains close to the theoretical maximum gain. 1 Introduction In wireless communication systems, the wavelength and the distance between transmitter and receiver terminals are not the only factors that characterize the radio wave propagation phenomenon. All the interacting objects present in the surrounding environment where waves bounce, as well as their dimension and composition, also contribute to the propagation phenomenon. These interacting objects are usually grouped into clusters and induce scattering, where one or more non-uniformities in the medium force radio waves to deviate from a straight trajectory. Scattering leads to a propagation phenomenon known as multipath propagation, where the transmitted data reach the receiver multiple times by two or more paths and/or at different time instants. These different copies of the transmitted signal, having each one a different attenuation, delay, and phase shift, create an amplified or attenuated received signal power, depending on whether the interference is constructive or destructive, respectively. This is a random process designated as multipath fading, which may vary according to time, space, and/or frequency. Another type of fading is the shadow fading, also a random process due to shadowing from obstacles affecting the wave propagation. Fading can be very harmful for any wireless communication system as it can cause a strong destructive interference resulting in a deep loss of signal, which in turn can lead to data transmission failure. One way to cope with this issue is to use multiple-input multiple-output (MIMO) systems. These systems can be defined, in a simple way, as wireless communication systems equipped with multiple antenna elements at the transmitter and at the receiver. MIMO systems exploit multipath and fading propagation phenomena so as to achieve high spectral efficiencies without requiring extra frequency spectrum and transmission power [1,2]. However, the real benefit of MIMO systems does not come from multiple antennas by themselves, but from the way these systems process the antennas signals using, e.g., spatial diversity and spatial multiplexing [3]: Spatial diversity is a powerful technique to mitigate fading and increase link reliability; it combines, in the receiver, different signals from the radio channel, originated by multipath propagation, in order to obtain the sources stream in better conditions. With this MIMO technique, receiver antennas can provide power gain and, if space-time codes are used, spatial diversity transmission gain can also be achieved. All of this can be reached without requiring channel knowledge at the transmitter, i.e., without channel state information (CSI) prior to any data transmission. Spatial multiplexing is a technique that exploits differences in the spatial signatures (e.g., caused by rich scattering) of multiplexed data streams onto the wireless channel so as to separate the different signals, i.e., orthogonal information channels are created when there is significant spatial decorrelation. This can be seen as an additional spatial dimension for communication that yields a degree-of-freedom gain without additional power, time, or bandwidth. Hence, the system capacity can be increased linearly by a factor n, where n is the minimum number of transmit and receive antennas. This MIMO technique can be used with or without CSI at the transmitter (a system with full CSI can lead to higher spectral efficiencies than a system where CSI is only available at the receiver). The use of MIMO systems in the spatial multiplexing mode may bring improvements in terms of spectral efficiency. However, since the spectral efficiency gain lies on the fact that the user is in the presence of rich multipath, the MIMO spectral efficiency gain will decrease for spatially correlated channels. One possible way to circumvent this problem is to increase the separation among the antennas at a communication end, resulting in a higher antenna decorrelation. For the base station (BS) side, increasing the antenna array size might not be a problem, but for the mobile station (MS) side, (...truncated)


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Ivo Sousa, Maria Paula Queluz. A smart scheme for relay selection in cooperative wireless communication systems, EURASIP Journal on Wireless Communications and Networking, 2013, pp. 146, Volume 2013, Issue 1, DOI: 10.1186/1687-1499-2013-146