An intelligent transportation system is proposed to integrate information and communication technologies into vehicles and transport infrastructure to improve vehicular safety. To accelerate the commercialization of intelligent transportation system, a series of wireless access schemes for vehicular environments are proposed. These schemes, however, still suffer from multiple collisions of emergent messages in control channels (CCH), resulting in a driver may not receiving emergent messages in time. This work develops group reservation medium access control (GRMAC) to minimize the collisions of emergent messages in vehicular environments and thereby increase the availability of emergent messages. GRMAC also allows vehicles to reserve CCH bandwidth when they stay in service channels (SCH) in order to reduce collisions of emergent messages in CCH. GRMAC also migrates the CCH bandwidth scheduling mechanism from CCH to SCHs to reduce the burden on CCH. The theoretical analysis and simulation results under heavy loads shows that GRMAC achieves two time the goodput of conventional IEEE 802.11p/1609 mechanism and six time that of dedicated multi-channel MAC.

Tag anticollision has long been an important issue in RFID systems. To accelerate tag identification, some researchers have recently adopted bit tracking technology that allows the reader to detect the locations of collided bits in a collision slot. However, these methods still encounter the problem of too many collisions occurring at the beginning of identification. This paper proposes an optimal query tracking tree protocol (OQTT) that tries to separate all of the tags into smaller sets to reduce collisions at the beginning of identification. Using bit tracking technology, OQTT mainly adopts three proposed approaches, bit estimation, optimal partition, and query tracking tree. Bit estimation first estimates the number of tags based on the locations of collided bits. Optimal partition then determines the optimal number of the initial sets based on this estimation. Query tracking tree splits a set of collided tags into two subsets using the first collided bit in the tag IDs. This paper analyzes the efficiency of OQTT, which represents how many tags can be identified in a slot. Results show that its efficiency is close to 0.614, the highest efficiency published to date. The simulation results further show that OQTT outperforms other existing algorithms.

Many burst construction algorithms for Orthogonal Frequency Division Multiple Access (OFDMA) were proposed. However, these algorithms do not meet the uplink burst characteristics specified in the IEEE 802.16 standard. This paper therefore proposes the Best Sub channel Oriented algorithm (BSO). BSO not only complies with uplink burst characteristics, but also obtains high throughput by considering the issues of internal fragmentation, external fragmentation, and good-sub channels exploring. BSO shrinks the burst area to avoid internal fragmentation, if the requested bandwidth has been satisfied. BSO minimizes the external fragmentation by evaluating all divided bandwidth areas and shrinking the burst area to fit into a proper available bandwidth area if no available area can accommodate it. To explore the good sub channels, BSO analyzes the channel quality of sub channels and constructs the burst on the sub channels which provide largest throughput. The simulation results under a heavy load indicate that BSO achieves 2 times the throughput achieved by Raster, a conventional algorithm.

This paper addresses how to provide the proportional delay differentiation (PDD) in a wireless LAN (WLAN) and proposes a cross-layer fine-tuning scheduling (CFS) scheme with the goal to maintain PDD among all wireless stations while improving performance in a WLAN. CFS additionally considers the time-varying channel capacity to schedule packets, finely tunes the contention window, and properly arbitrates the backoff time. Also, it operates in a fully distributed manner among all stations and in a cross- layer approach in each station. The simulation results demonstrate that the CFS scheme can provide more satisfactory PDD and higher performance in a WLAN, compared with 802.11e.