Opportunistic transmission scheduling schemes improve system capacity by taking advantage of independent time varying channels in wireless networks. In the design of such scheduling schemes, the fairness criterion plays an important role in the tradeoff of total system capacity and the achievable throughput of individual users. To meet different fairness demands with a unified opportunistic scheduling scheme, in this paper, we have extended the well known opportunistic scheduling scheme PFS into αPFS, which satisfies arbitrary fairness demands, varying from proportional fairness to maxmin fairness, through adjusting the parameter α. To further improve the achievable diversity gains of αPFS, we extend the αPFS scheme into an αPFS-P scheme. Performances of αPFS and αPFS-P are studied and compared. As demonstrated in the simulation results, both αPFS and αPFS-P can achieve adjustable fairness criteria, varying from proportional fairness to max-min fairness. Compared with αPFS, αPFS-P achieves higher diversity gains with degraded short term performance, which is still better than the performance of PFS.

No abstract

In wireless environments, the inherent time-varying characteristics of the channel pose great challenges on medium access control design. In recent years, multiuser diversity and opportunistic medium access control schemes have been proposed to deal with the channel variation in order to efficiently improve the network throughput. In this paper, we propose a novel MAC protocol called Contention-Based Prioritized Opportunistic (CBPO) Medium Access Control Protocol. This protocol takes advantage of multiuser diversity, rate adaptation, which utilizes the multi-rate capability offered by IEEE 802.11, and black-burst (BB) contention to access the shared medium in a distributed manner. In particular, rather than simply measuring the channel condition for a node pair in communications each time, with the help of multicast RTS, the candidate users with qualified channel condition are selected and prioritized. Then the qualified receivers contend to send back prioritized clear-to-send message (CTS) with BB, which is a pulse of energy, the duration of which is proportional to the CTS priority. The user with the best channel quality is always selected to send back CTS and receive packets from the sender. Extensive simulation results show that our protocol achieves much better performance than IEEE 802.11 and other auto rate schemes with minimal additional overhead.

In multi-hop ad hoc networks, receiver busy tone-based Media Access Control (MAC) protocols have been proposed to solve both the hidden terminal problem and the exposed terminal problem of carrier sense-based MAC protocols. However, with only busy tone signals, senders cannot determine the receiving status of their intended receivers. Invitations from intended senders may fail owing to the non-receivable status of their intended receivers rather than owing to collisions. In this paper, we propose a novel Hybrid Busy tone and Carrier sense-based MAC protocol (HBCMA). Simulation results show that HBCMA achieves better performance than a purely busy tone-based protocol. (2007) 'Hybrid Busy tone and Carrier sense-based MAC protocol in multi-hop ad hoc networks', Int.

No abstract