Adaptive relaying protocol multiple-input multiple-output orthogonal frequency division multiplexing systems

In wireless broadband communications, orthogonal frequency division multiplexing (OFDM) has been adopted as a promising technique to mitigate multi-path fading and provide high spectral efficiency. In addition, cooperative communication can explore spatial diversity where several users or nodes share their resources and cooperate through distributed transmission. The concatenation of the OFDM technique with relaying systems can enhance the overall performance in terms of spectral efficiency and improve robustness against the detrimental effects of fading. Hybrid relay selection is proposed to overcome the drawbacks of conventional forwarding schemes. However, exciting hybrid relay protocols may suffer some limitations when used for transmission over frequency-selective channels. The combination of cooperative protocols with OFDM systems has been extensively utilized in current wireless networks, and have become a promising solution for future high data rate broadband communication systems including 3D video transmission. This thesis covers two areas of high data rate networks. In the first part, several techniques using cooperative OFDM systems are presented including relay selection, space time block codes, resource allocation and adaptive bit and power allocation to introduce diversity. Four (4) selective OFDM relaying schemes are studied over wireless networks; selective OFDM; selective OFDMA; selective block OFDM and selective unequal block OFDM. The closed-form expression of these schemes is derived. By exploiting the broadcast nature, it is demonstrated that spatial diversity can be improved. The upper bound of outage probability for the protocols is derived. A new strategy for hybrid relay selection is proposed to improve the system performance by removing the sub-carriers that experience deep fading. The per subcarrier basis selection is considered with respect to the predefined threshold signal-to-noise ratio. The closed-form expressions of the proposed protocol in terms of bit error probability and outage probability are derived and compared with conventional hybrid relay selection. Adaptive bit and power allocation is also discussed to improve the system performance. Distributed space frequency coding applied to hybrid relay selection to obtain full spatial and full data rate transmission is explored. Two strategies, single cluster and multiple clusters, are considered for the Alamouti code at the destination by using a hybrid relay protocol. The power allocation with and without sub-carrier pairing is also investigated to mitigate the effect of multipath error propagation in frequency-selective channels. The second part of this thesis investigates the application of cooperative OFDM systems to high data rate transmission. Recently, there has been growing attention paid to 3D video transmission over broadband wireless channels. Two strategies for relay selection hybrid relay selection and first best second best are proposed to implement unequal error protection in the physical layer over error prone channels. The closed-form expressions of bit error probability and outage probability for both strategies are examined. The peak signal-to-noise ratio is presented to show the quality of reconstruction of the left and right views

Distributed space-frequency coding for OFDM-based hybrid relay selection

Cooperative communication in conjunction with orthogonal frequency division multiplexing (OFDM) has recently emerged as a promising technique with the potential to dominate future generations of broadband wireless communications systems. In this paper, we propose an OFDM modulation scheme combined with distributed space-frequency codes (DSFC) based upon a hybrid relay selection protocol. The DSFC process is not required for the amplify-and-forward (AF) relays to reduce the system complexity. Simulation results show that a substantial improvement in bit error rate (BER) performance can be achieved in comparison with conventional relaying protocols. Full rate transmission and diversity order is attainable by this proposed system

Power allocation of distributed space-frequency coding for OFDM-based hybrid relay selection

Cooperative communications in conjunction with orthogonal frequency division multiplexing (OFDM) has recently emerged as a promising technique to mitigate multi-path fading and provides high spectral efficiency in broadband wireless communications systems. In this paper, we investigate resource allocation of an OFDM modulation scheme combined with distributed space-frequency codes (DSFC) based upon a hybrid relay selection protocol. The optimum problem is divided into two suboptimal problems. The first one is to optimize the power allocation between the source and relay nodes under a sum power constraint. Then the relay power is optimized for the selected relay nodes according to the channel power gain of the second time slot. Simulation results show that a substantial improvement in terms of bit error rate (BER) and capacity performance can be achieved in comparison with conventional relaying protocols