Enhanced Relay Selection and Scheduling for Better Load Balancing in Multi-Hop Networks

Enhanced Relay Selection and Scheduling for Better Load Balancing in Multi-Hop Networks

Soumaya Hamouda, Tarek Bejaoui
DOI: 10.4018/jbdcn.2012100102
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Relaying technology is likely to bring real progress to the next generation cellular networks due to its capability of boosting the system capacity and coverage. However, despite recent advances in relay deployment, some challenging problems still remain such as radio resource allocation and relay selection. The authors investigate both relay selection and scheduling strategy in order to improve the system radio capacity as well as the network load balancing. They propose a new path selection scheme based on the radio channel quality and the relay station load criteria. Performance analysis showed that the authors approach outperforms the existing path selection algorithms in terms of outage probability and global throughput in the system, especially in high traffic conditions. It is revealed that most of the cell edge users which would be rejected when applying common selection scheme, can now have access to a selected relay station and achieve a high end-to-end throughput. A new scheduling strategy is proposed in the second part of this paper, on the basis of a dynamic subframe partitioning. Simulation results show that the outage probability is reduced and more balanced resource allocation is provided. Simulation results showed that some relay stations which were not able to offer any service with the fixed subframe partitioning, can achieve a high data rate with the authors proposed dynamic scheduling strategy.
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The path selection problem for mobile stations has been discussed in different documents belonging to the IEEE 802.16’s relay task group and 3GPP LTE-Advanced. Multi-hop routing protocols using different cost metrics have been also proposed in several contributions (e.g., Perkins & Bhaguat, 1994; Perkins & Royer, 1999; Cao et al., 2008; Lee et al., 2009), such as shortest-path routing, load-aware routing, SINR-based selection or throughput-based selection.

Shortest-path routing: This routing algorithm described in Perkins and Bhaguat 91994) and Perkins and Royer (1999) aims at finding the route with the minimum hop count value. It assigns a path with the least number of hop-counts to a Mobile Station (MS); it has been widely used in both wired and wireless networks. The most important feature of the shortest path is that it usually has the minimum communication delay and is easily implemented. However, the use of the minimum hop count for path cost is not always perfect. Many researches show that this kind of protocols degrades network performance due to congestion on these selected relays along the minimum hop path (Bharadwaj et al., 2011).

Load-aware routing: The load-aware routing protocols is presented in Lee and Gerla (2001) and Cao et al. (2008); this protocol aims at discovering routes with the minimum traffic load. It selects the path that cumulates the least consumption. These load-aware routing protocols use different cost metrics to measure traffic load of a route. For example, they used the number of packets buffered at intermediate relays along the route as a route selection metric. Thus, load-aware routing protocols can avoid congestion by denying access to relays with high traffic load. Considering the path selection on the basis of a minimum load, may however not be very efficient. In fact, this selection can add more delays and does not guarantee high data rate, especially when the user is located at an important distance from the selected relays.

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