Hop Reservation Multiple Access (HRMA) for Ad-Hoc Networks

A new multichannel MAC protocol called Hop-Reservation Multiple Access (HRMA) for wireless ad-hoc networks (multi-hop packet radio networks) is introduced, specified and analyzed. HRMA is based on simple half-duplex, very-slow frequency-hopping spread spectrum (FHSS) radios and takes advantage of the time synchronization necessary for frequency hopping. HRMA allows a pair of communicating nodes to reserve a frequency hop using a reservation and handshake mechanism that guarantee collision-free data transmission in the presence of hidden terminals. We analyze the throughput achieved in HRMA for the case of a hypercube network topology assuming variable-length packets, and compare it against the multichannel slotted ALOHA protocol, which represents the current practice of MAC protocols in commercial ad-hoc networks based on spread spectrum radios, such as Metricom’s Ricochet system. The numerical results show that HRMA can achieve much higher throughput than multichannel slotted ALOHA within the traffic-load ranges of interest, especially when the average packet length is large compared to the duration of a dwell time in the frequency hopping sequence, in which case the maximum throughput of HRMA is close to the maximum possible value.