TDMA Slot Assignment Research Articles

An AdaptiveTDMA Slot Assignment Strategy in Vehicular Ad Hoc Networks

Improving road safety is among the main objectives of Vehicular Ad-hoc NETworks (VANETs) design. This objective would be achieved essentially by the use of efficient safety applications which should be able to wirelessly broadcast warning messages between neighbouring vehicles in order to inform drivers about a dangerous situation in a timely manner. To insure their efficiency, safety applications require reliable periodic data dissemination with low latency. Medium Access Control (MAC) protocols play a primary role to provide efficient delivery and avoid as much as possible data packet loss. In fact, in distributed MAC approaches, packet loss is a consequence of collisions resulted from well known situations of the exposed and hidden node situations. This paper introduces an Adaptive TDMA Slot Assignment Strategy (ASAS) for VANET based on clustering of vehicles. The main aim of this work is to provide a MAC layer protocol that can reduce inter-cluster interference under different traffic loading conditions without having to use expensive spectrum and complex mechanisms such as CDMA or OFDMA. An analysis and simulation results are presented to evaluate the performance of ASAS. Moreover, we compare its performance with two TDMA MAC protocols DMMAC and VeMAC

FrogSim: distributed graph coloring in wireless ad hoc networks

Graph coloring, which is at the heart of several problems arising in wireless ad hoc networks, concerns the problem of assigning colors to the nodes of a graph such that adjacent nodes do not share the same color. This paper deals with the problem of generating valid colorings in a distributed way, while minimizing the number of colors used. Examples of related problems in wireless ad hoc networks are TDMA slot assignment, wakeup scheduling, and data collection. The presented algorithm is inspired by the desynchronization observed in the context of the calling behaviour of male Japanese tree frogs. Experimental results indicate that the proposed algorithm is very competitive with current state-of-the-art approaches.

Adaptive TDMA Slot Assignment Using Request Aggregation in Wireless Sensor Networks

TDMA-based MAC protocols are considered an energy effcient solution to prolong wireless sensor network lifetime. However, their drawbacks such as complexity of slot assignment and schedule maintenance and adaptivity to varying traffc conditions are yet to be handled in an effcient way. In this paper we present On-demand Convergecast Scheduling based (OCS) MAC protocol. It is a centralized and adaptive multihop scheduling-based TDMA protocol which supports convergecast applications. OCS adopts a novel requests aggregation mechanism for adaptive slot assignment such that time slots are assigned on-demand to currently active sources as well as relays. The performance of OCS is compared to existing protocols based on simulations in ns-2. Results show that OCS outperforms protocols such as Z-MAC, S-MAC, and others in terms of delay, throughput and energy effciency.

Cross-Layer Energy and Delay Optimization in Small-Scale Sensor Networks

The general joint design of the physical, MAC, and routing layers to minimize network energy consumption is complex and hard to solve. Heuristics to compute approximate solutions and high-complexity algorithms to compute exact solutions have been previously proposed. In this paper, we focus on synchronous small-scale networks with interference-free link scheduling and practical MQAM link transmission schemes. We show that the cross-layer optimization problems can be closely approximated by convex optimization problems that can be efficiently solved. There are two main contributions of this paper. First of all, we minimize the total network energy that includes both transmission and circuit energy consumptions, where we explore the tradeoff between the two energy elements. Specifically, we use interference-free TDMA as the medium access control scheme. We optimize the routing flow, TDMA slot assignment, and MQAM modulation rate and power on each link. The results demonstrate that the minimum energy transmission scheme is a combination of multihop and single-hop transmissions for general networks; including circuit energy favors transmission schemes with fewer hops. Secondly, based on the solved optimal transmission scheme, we quantify the best trade-off curve between delay and energy consumption, where we derive a scheduling algorithm to minimize the worst-case packet delay.