No abstract

In this paper, a balanced space-time block coding method for cooperative relay networks is proposed which guarantees full diversity for any number of mobile relays with minimal delay, provided that few bits of feedback from the destination to the source and the relays are available. As in the case of orthogonal space-time block codes, all transmitted symbols are separately decoded both in the relays and the destination. Therefore, decoding complexity is linear. Many of the proposed solutions in the literature are distributed space-time codes which are designed for limited number of relays. In the proposed scheme, as many number of relays as necessary can be included to increase diversity. Moreover, the proposed scheme has better signal-to-noise ratio improvement compared to relay selection schemes. Lastly, the new method satisfies power consumption fairness among relay terminals and requires no knowledge of topology information.

Abstract. Diversity techniques for communications among sensors are very effective tool to increase reception quality and battery lifetimes. A well-known method to increase diversity in cooperative communications is sensor (relay) selection. However, sensor selection method may lead to the selection of the same (near) sensor for transmission over a long period. One of the alternative techniques to sensor selection is cooperative balanced space-time block coding which utilizes every sensor in sight, thus, distributes the energy consumption among many sensors. Furthermore, it guarantees full diversity for any number of relay sensors. In this work, we consider dual-hop amplify-and-forward wireless sensor network and extend the cooperative balanced space-time block code family to improve its performance. In the proposed scheme, a larger number of codes can be generated for improved coding gain, and better signal-to-noise ratio improvement can be obtained compared to sensor selection schemes.

The statistical cooperative diversity, based on space-time block codes (statistical STBC cooperative diversity) is proposed for binary sensors by several authors. Since Alamouti's code is the only orthogonal code which achieves full diversity and full rate for two sensors, it is used in their works, and their achievable diversity order is 2. Instead of using Alamouti's code, we use extended cooperative space-time block coding (ECBSTBC) which achieves full diversity which is shown analytically and full rate for an arbitrary number of sensors if a limited feedback is available at the active sensors. Another method to increase diversity in cooperative communications is sensor (relay) selection. However, the sensor selection method may lead to the selection of the same (near) sensor for transmission over a long period causing the energy hole problem in sensor networks. The ECBSTBC which utilizes every sensor in sight thus distributes the energy consumption among active sensors and alleviates the energy hole problem. In addition, it can be shown with detailed simulations that the ECBSTBC outperforms both the statistical STBC cooperative diversity and the sensor selection schemes.

The original proposal of the extended balanced space–time block coding (EBSTBC) and its special subsets like balanced space–time block coding utilize all available transmit antennas to guarantee full diversity and to maximize the coding gain when few bits of feedback from the destination to the source are available. Because of the construction technique of EBSTBC, an antenna out of N transmit antennas does not contribute coding gain. To prevent this, a novel EBSTBC design and transmit scheme is proposed. This scheme transmits only N − 1 antennas out of N antennas and an antenna that maximizes the received signal‐to‐noise ratio at the destination doubles its transmit power. The proposed scheme improves performance of the EBSTBC and its subsets and outperforms closed‐loop extended orthogonal space–time block codes, phase feedback based extended space–time block codes, partial phase combining and transmit antenna selection schemes. The difference in performance becomes more prevalent in the presence of feedback errors. The proposed technique can be applied for orthogonal space–time block codes and quasi‐orthogonal space–time block codes if the destination informs the source which antenna has the highest gain. Copyright © 2011 John Wiley & Sons, Ltd.