Reliability of Cooperative Transmission
Cooperation among nodes in wireless networks can significantly improve network throughput and reliability. These potential benefits lead wireless network designers to deploy cooperative schemes in networks to meet the high data rate required for multimedia services offered by modern wireless networks. As relay and cooperative multiple-access (MAC) channels have many applications in cellular networks as shown in Figure 1, this project proposes coding schemes for these channels and studies their outage performance. The proposed schemes are based on coherent decode-forward relaying and joint decoding at the destinations. The project shows the impact of these coding techniques in improving the outage performance and achieving the full diversity order.
Multiple advanced techniques are proposed for next-generation cellular standards, including LTE and LTE-A, to improve network spectral efficiency. These techniques include multi-cell processing, heterogeneous network deployment and device-to-device (D2D) communication. The downlink cooperation is achieved through multi-cell processing technology. In contrast, this project utilizes D2D technology to propose a cooperative coding scheme for the uplink transmission as shown in Figure 2. In D2D technology, two close user equipments (UEs) can cooperate to create a virtual MISO system and send their information to the base station (eNodeB) at higher rates than resource partitioning transmission. The project provides simple transmission scheme that satisfies practical constraints of wireless transmission including half-duplex and short decoding delay constraints. The project studies the throughput and outage performance of the proposed scheme.
In order to meet the half-duplex constraint in wireless communication, we divide the transmission block into 3 phases with variable durations as shown in Figure 3. Each UE splits its information into a cooperative and private part. The two UEs partially exchange their information in the first two phases, then cooperatively transmit to the base station in the third phase. The base station decodes directly without any block delay, at the end of each block using joint decoding of the received signals over the 3 phases.
Achievable rate region:
The results in Figure 4 show that the proposed cooperative MAC scheme is near optimal, as its achievable rate region is close to the outer bound, especially when the cooperative links are much stronger than the direct links. Moreover, cooperation clearly outperforms the resource partitioning transmission (used in LTE-A) and the concurrent transmission with successive interference cancellation.
In addition to the achievable rate region and optimal resource allocation, outage performance is an important criterion in wireless communication, as many services often require a specific rate to be sustained.
We consider a single antenna at both UEs and the BS but the results can be extended to the MIMO case in a future study. We consider a block fading channel where all links remain constant over each transmission block and independently vary in the next block. We also assume full CSI at the receiver side with limited CSI at the transmitter side where each UE knows the phase of its channel to the BS such that the two UEs can employ coherent transmission. Moreover, each UE knows the relative order between each cooperative link and the corresponding direct link so that it can choose to cooperate when its cooperative link is stronger than the direct link.
We study both common and individual outages. An individual outage pertains to incorrect decoding of one user information regardless of the other user information, while a common outage pertains to incorrect decoding of either user information or both. Because of the information exchanging phases, outage analysis must also consider outages at the UEs. The rate splitting and superposition coding structure also complicates outage analysis and requires dependent analysis of the outage for different information parts. Figure 5 shows that as the received SNR increases, the proposed cooperation improves outage performance over both resource partitioning and concurrent non cooperative transmission schemes in spite of additional outages at the UEs.
Outage Rate Region
Some services may require target outage probabilities instead of the target rates. For these services, we can obtain the individual and common outage rate regions as shown in Figure 6 where the target outage probability is 1%. This figure compares the common and individual outage probabilities of the proposed scheme, resource partitioning scheme (current LTE-A) and concurrent transmission with SIC scheme. It can be seen that, compared with non-cooperative schemes, cooperation significantly improves the outage rate region.
Special Case of Half-duplex Relay Channel
Half-duplex partial DF relaying is a special case of the proposed cooperative MAC scheme when one UE has no information to send and works only as a relay to the other UE as shown in Figure 7.
Figure 8 considers the outage for relay channel. It shows the impact of partial DF relaying, coherent relaying and joint decoding at the destination in improving the outage performance compared with full DF and non-coherent relaying, direct and dual-hop transmission schemes.
- “Outage Analysis for Coherent Decode-Forward Relaying over Rayleigh Fading Channels,”
A. Abu Al Haija and M. Vu, IEEE Trans. Commu., vol. 63, no. 4, pp. 1162–1177, Apr. 2015.
- “Spectral Efficiency and Outage Performance for Hybrid D2D-Infrastructure Uplink Cooperation,”
A. Abu Al Haija and M. Vu, IEEE Trans. Wireless Commu., vol. 14, no. 3, pp. 1183–1198, Mar. 2015.
- “Rate Maximization for Half-Duplex Multiple Access with Cooperating Transmitters,”
A. Abu Al Haija and Mai Vu, IEEE Trans. on Comm., vol. 61, no. 9, pp. 3620 – 3634, Sept. 2013.
- “Outage Analysis for Half-Duplex Partial Decode-Forward Relaying over Fading Channel,”
A. Abu Al Haija and M. Vu, IEEE GLOBECOM, Dec. 2014.
- “Uplink Outage Analysis for Mobile-to-Mobile Cooperation,”
A. Abu Al Haija and M. Vu, D2D workshop, IEEE GLOBECOM, Dec. 2013.
- “A Half-Duplex Cooperative Scheme with Partial Decode-Forward Relaying,”
A. Abu Al Haija and M. Vu, IEEE ISIT, July 2011.
- “Joint Typicality Analysis for Half-Duplex Cooperative Communication,”
A. Abu Al Haija and M. Vu, The 12th Canadian Workshop on Information Theory (CWIT), May 2011.