Quorum-based power-saving (QPS)
protocols have been proposed for ad hoc networks (e.g., IEEE 802.11 ad hoc
mode) to increase energy efficiency and prolong the operational time of mobile
stations. These protocols assign to each station a cycle pattern that specifies
when the station should wake up (to transmit/receive data) and sleep (to save
battery power). In all existing QPS protocols, the cycle length is either
identical for all stations or is restricted to certain numbers (e.g., squares
or primes). These restrictions on cycle length severely limit the practical use
of QPS protocols as each individual station may want to select a cycle length
that is best suited for its own need (in terms of remaining battery power,
tolerable packet delay, and drop ratio). In this paper, we propose the notion
of hyper quorum system (HQS)-a generalization of QPS that allows for arbitrary
cycle lengths. We describe algorithms to generate two different classes of HQS
given any set of arbitrary cycle lengths as input. We also describe how to find
the optimal cycle length for a station to maximize energy efficiency, subject
to certain performance constraints. We then present analytical and simulation
results that show the benefits of HQS-based power-saving protocols over the
existing QPS protocols. The HQS protocols yield up to 41% improvement in energy
efficiency under heavy traffic loads while eliminating more than 90% delay
drops under light traffic loads.
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