We describe the protocols implemented in the Ricochet MCDN system to provide continuous connectivity to mobile users traveling up to 70 mph. These protocols are general in nature for any frequency-hopping microcell-based system, particularly those that follow the FCC part 15.247 rules [9] and operate in unlicensed spectrum. We also present throughput measurements as a function of velocity and describe a model to predict those numbers based upon the protocols implemented. The MCDN system is a mesh-based system of microcells that are connected wirelessly to an interspersed mesh of wired access points (WAPs) that cover approximately 12 square miles on average [7]. The average microcell density is approximately 5-6 per square mile, with 3-8 overlapping cells at each point. Since the system is entirely packet-based, we have instantaneous hand-off between microcells as there are no complicated cellular-type negotiations for circuits required as all of the information needed to route the packet through the system is included in the header; however, when traveling through the mesh of microcells at a high rate of speed, the mobile unit must acquire new microcells fast enough to ensure continuous connectivity. The system must also know how to route packets to the mobile unit as it drops old cells and acquires new ones, as well as being able to contact a moving mobile unit. This paper discusses the acquisition, registration, and routing protocols that make this possible and reviews performance data of typical mobile users.

We introduce and analyze CARMA-MC (for collision avoidance and resolution multiple access for multiple channels), a new stable channel access protocol for multihop wireless networks with multiple channels. CARMA-MC relies on the assignment of a unique channel and a unique identifier to each node to support correct deterministic collision resolution in the presence of hidden terminals. CARMA-MC dynamically divides the channel of each node into cycles of variable length; each cycle consists of one or more receiving periods and a transmission period. During the receiving period, stations with one or more packets to send compete for the right to acquire the floor of a particular receiver's channel using a deterministic tree-splitting algorithm. Each receiving period consists of collision resolution steps. A single round of collision resolution (i.e., a success, and idle or a collision of control packets) is allowed in each contention step. The receiving period is initiated by the receiver and takes place in the channel assigned to the receiver station. The channel utilization and packet delays are studied analytically and by simulation.

We propose and analyze a specific set of access rules, or "spectrum etiquette", for the 59-64 GHz unlicensed band to allow systems from different manufacturers with different physical and medium-access control protocols to co-exist, sharing the large available bandwidth without interference. The proposed etiquette is unique in that heterogeneous systems are able to co-exist with one another without monitoring the entire band by means of transmissions over a common, narrow band control channel used to establish collision-free transmission schedules over the channels allocated for data transmission within the 59-64 GHz band. Because no common physical layer can be assumed among different systems, the control channel is needed for the systems to schedule transmissions in the rest of the band, and the only means by which systems can communicate with one another over the control channel is the duration of each others' transmissions, which are perceived only as noise. A transmission encoding is defined based on this basic feedback to allow systems to ascertain which system can use which data channel at which time without interference. Analytical and simulation results are presented showing that the proposed etiquette is fair to all the co-existing systems, fully utilizes the spectrum, provides bounded delays for data-channel acquisition time by any given system, and provides minimum channel-use guarantees.

We introduce a new stable multiple access protocol for broadcast channels shared by multiple stations, which we call the incremental collision resolution multiple access (ICRMA) protocol. ICRMA dynamically divides the channel into cycles of variable length; each cycle consists of a contention period and a queue-transmission period. The queue-transmission period is a variable-length train of packets, which are transmitted by stations that have been added to the distributed transmission queue by successfully completing a collision-resolution round in a previous contention period. During the contention period, stations with one or more packets to send compete for the right to be added to the data-transmission queue using a deterministic tree-splitting algorithm. A single round of collision resolution is allowed in each contention period. Analytical results show that collision resolution in ICRMA is much more efficient than DQRAP's. Simulation and analytical results show that ICRMA's throughput is within 5% of the throughput achieved by the ideal channel access protocol based on a distributed transmission queue and incremental collision resolution.

Collision avoidance and resolution multiple access (CARMA) protocols establish a three-way handshake between sender and receiver to attempt to avoid collisions, and resolve those collisions that occur. This paper describes and analyzes CARMA protocols that resolve collisions up to the first success obtained by running a tree-splitting algorithm for collision resolution. An upper bound is derived for the average costs of resolving collisions of floor requests using the tree-splitting algorithm is obtained and applied to the computation of the average channel utilization in a fully connected network with a large number of stations. Our analysis indicates that, because CARMA protocols guarantee a successful transmission for every busy period of the channel, it achieves higher throughput than other contention-based MAC protocols based on collision-avoidance handshakes.

The CARMA-NTG protocol is presented and analyzed. CARMA-NTG dynamically divides the channel into cycles of variable length; each cycle consists of a contention period and a group-transmission period. During the contention period, a station with one or more packets to send competes for the right to be added to the group of stations allowed to transmit data without collisions; this is done using a collision resolution splitting algorithm based on a request-to-send/clear-to-send (RTS/CTS) message exchange with non-persistent carrier sensing. CARMA-NTG ensures that one station is added to the group transmission period if one or more stations send requests to be added in the previous contention period. The group-transmission period is a variable-length train of packets, which are transmitted by stations that have been added to the group by successfully completing an RTS/CTS message exchange in previous contention periods. As long as a station maintains its position in the group, it is able to transmit data packets without collision, An upper bound is derived for the average costs of obtaining the first success in the splitting algorithm. This bound is then applied to the computation of the average channel utilization in a fully connected network with a large number of stations. These results indicate that collision resolution is a powerful mechanism in combination with floor acquisition and group allocation multiple access.

Collision avoidance and resolution multiple access (CARMA) protocols are presented and analyzed.These protocols use a floor acquisition multiple access strategy based on carrier sensing, together with collision resolution of floor requests (RTS) based on a treesplitting algorithm.For analytical purposes, an upper bound is derived for the average costs of resolving collisions of floor requests using the tree-splitting algorithm.This bound is then applied to the computation of the average channel utilization in a fully connected network with a large number of stations.Under light-load conditions, CARMA protocols achieve the same average throughput as floor acquisition multiple access (FAMA) protocols.It is also shown that, as the arrival rate of RTSs increases, the throughput achieved by CARMA protocols is close to the maximum throughput that any FAMA protocol can achieve if propagation delays and the control packets used to acquire the floor are much smaller than the data packet trains sent by stations.Simulation results validate the simplifying approximations made in the analytical model.Our analysis results indicate that collision resolution makes floor acquisition multiple access much more effective.