Exploiting multiuser diversity for medium access control in wireless networks

Abstract

Abstract-Multiuser diversity refers to a type of diversity present across different users in a fading environment. This diversity can be exploited by scheduling transmissions so that users transmit when their channel conditions are favorable. Using such an approach leads to a system capacity that increases with the number of users. However, such scheduling requires centralized control. In this paper, we consider a decentralized medium access control (MAC) protocol, where each user only has knowledge of its own channel gain. We consider a variation of the ALOHA protocol, channel-aware ALOHA; using this protocol we show that users can still exploit multi-user diversity gains. First we consider a backlogged model, where each user always has packets to send. In this case we show that the total system throughput increases at the same rate as in a system with a centralized scheduler. Asymptotically, the fraction of throughput lost due to the random access protocol is shown to be 1/e. We also consider a splitting algorithm, where the splitting sequence depends on the users' channel gains; this algorithm is shown to approach the throughput of an optimal centralized scheme. Next we consider a system with an infinite user population and random arrivals. In this case, it is proved that a variation of channel-aware ALOHA is stable for any total arrival rate in a memoryless channel, given that users can estimate the backlog. Extensions for channels with memory are also discussed.

Exploiting Time and User Diversity in Distributed Medium Access Control for Mobile Ad-Hoc Networks

“…Over the recent years there has been some work on exploiting multi-user diversity in a distributed manner, in particular [4], [5], and [6]. In [4], the authors deal with channel-aware ALOHA using a decentralized MAC protocol where a source node would access the medium only when the channel gain is larger than a threshold.…”

“…In [4], the authors deal with channel-aware ALOHA using a decentralized MAC protocol where a source node would access the medium only when the channel gain is larger than a threshold. They consider a centralized network model where many nodes communicate with an access point.…”

Distributed Resource Allocation and Scheduling in OFDMA Wireless Networks

“…Here, we instead consider approaches where each transmitter allocates its transmission rate and power based only on knowledge of its own channel conditions. This can be obtained, for example, via a single pilot signal broadcast by the receiver in a time-division duplex system [5]. This requires much less overhead, but since each user has incomplete information, a distributed approach for resource allocation is required.…”

“…In prior work [5], [6], we have considered a distributed scheduling approach based on the Aloha protocol for the This work was supported in part by the Northwestern-Motorola Center for Seamless Communications and by NSF CAREER award CCR-0238382.…”

QoS-Aware Cooperative and Opportunistic Scheduling Exploiting Multi-user Diversity for Rate Adaptive Ad Hoc Networks

“…In contention-based wireless networks, a challenge to the exploitation of multiuser diversity is that no infrastructural node can behave as a central scheduler. A channel-aware ALOHA protocol is proposed in [11] to exploit multiuser diversity in a distributed fashion. In this work, each flow adjusts its transmission probability based on its channel gain, assuming that each flow knows its own channel gain as well as the distribution of other flows' channel gains.…”