This paper presents a self-organizing medium access control (MAC) protocol framework for distributed sensor networks with arbitrary mesh topologies. The novelty of the proposed In-band self-organized MAC (ISOMAC) protocol lies in its in-band control mechanism for exchanging time-division multiple access (TDMA) slot information with distributed MAC scheduling. A fixed-length bitmap vector is used in each packet header for exchanging relative slot timing information across immediate and up to two-hop neighbors. It is shown that, by avoiding explicit timing information exchange, ISOMAC can work without networkwide time synchronization, which can be prohibitive for severely cost-constrained sensor nodes in very large networks. A slot-clustering effect, caused by in-band bitmap constraints, enables ISOMAC to offer better spatial channel reuse compared to traditional distributed TDMA protocols. ISOMAC employs a partial node wake-up and header-only transmission strategy to adjust energy expenditure based on the instantaneous nodal data rate. Both analytical and simulation models have been developed for characterizing the proposed protocol. Results demonstrate that, with in-band bitmap vectors of moderate length, ISOMAC converges reasonably quickly, that is, approximately within a four to eight TDMA frame duration. Also, if the bitmap header duration is restricted within 10 percent of packet duration, then the energy penalty of the in-band information is quite negligible. It is also shown that ISOMAC can be implemented in the presence of network time synchronization, although its performance without synchronization is just marginally worse than that with synchronization.

This paper presents an architectural solution to address the problem of scalable routing for data intensive applications in very large sensor networks. Due to large routing overheads, the control complexity of the existing sensor routing protocols, both node-centric and data-centric, do not scale well in very large networks with potentially thousands of sensor devices. In this paper, we develop a hybrid architectural solution off-network control processing (ONCP) that achieves scalable routing in large networks by shifting certain amount of routing functions to an "off-network" routing server. A tiered routing approach is proposed to avoid network-wide control message dissemination. Our experimental results indicate that for large sensor networks with realistic data models, the packet drop, latency, energy performance and bandwidth usage of ONCP can be significantly better than those for completely distributed routing protocols such as directed diffusion.

This paper presents a performance comparison between the DSRC-recommended 802.11 Medium Access Control (MAC) and a novel Vehicular Self-Organizing MAC (VeSOMAC) protocol in the context Intelligent Transportation System applications. VeSOMAC is a distributed TDMA protocol that relies on in-band control exchange for autonomous and self-configurable TDMA slot allocation. Detailed network and vehicular traffic models have been developed for a Cooperative Collision Control (CCA) application operating in urban traffic intersection scenarios. Simulation results demonstrate that unlike the 802.11 style contention based protocols, VeSOMAC can offer better vehicle safety through smaller and bounded packet latency in vehicular ad hoc networks.

This paper presents a novel Medium Access Control protocol for inter-vehicular wireless networking using the emerging Dedicated Short Range Communication (DSRC) standards. The main contribution of the paper is the design of a self- configuring TDMA protocol capable of inter-vehicle message delivery with short and deterministic delay bounds. The proposed Vehicular Self-Organizing MAC (VeSOMAC) is designed to be vehicle location and movement aware so that the MAC slots in a vehicle platoon can be time ordered based on the vehicles' relative locations for minimizing the multi-hop delivery delay. A novel feature of VeSOMAC is its in-band control mechanism for exchanging TDMA slot information during distributed MAC scheduling. It is shown that by avoiding explicit timing information exchange, VeSOMAC can work without inter-vehicle time synchronization. The in-band control mechanism is also used for fast protocol convergence during initial network setup and topology changes due to vehicle movements. A simulation model has been developed for comparing VeSOMAC's performance with that of DSRC-recommended 802.11 MAC protocol for highway traffic safety applications.