A Protocol to Recover the Unused Time Slot Assignments in Transmission Scheduling Protocols for Channel Access in Ad Hoc Networks

In mobile ad hoc networks without centralized control distributed transmission scheduling protocols for channel access are of interest. Many scheduling-based MAC protocols have been proposed to provide contention-free transmissions and to guarantee certain levels of performance. However, one of the major drawbacks of these protocols is that once a slot is assigned to a particular node if the node does not have a packet to transmit, then the slot is not utilized. This leads to a poor network performance. In our proposed protocol these assigned but un-utilized slots are recovered by other nodes. We use custom computer simulations to compare our new protocol against two ap-proaches that do not recover wasted slots. The simulation models the performance of the physical and link layers and includes a limited network layer that supports end-to-end for-warding of traffic. Through investigations of random networks with varying densities we conclude that our new approach results in an increase in the capacity of the network

A Channel-Access Framework for Scheduling Transmission Assignments in Ad Hoc Networks with Rate Adaptive Radios

In mobile ad hoc networks transmission-scheduling channel-access protocols are of interest because they can ensure collision free transmissions and provide fair access to the channel. The time taken to gain access to the channel is deterministic and hence these types of protocols can also guarantee a certain quality of service. However, these protocols suffer from two major drawbacks. The first issue is poor utilization of the channel due to fixed slot assignments. Once the slot assignments are decided they are held constant for a period of time. As a result the node to which a slot is assigned may not always have a packet to transmit in its assigned slot. This results in wasted slots and leads to poor utilization of the channel. The second issue is that there is no support for networks with rate adaptive radios. In this work a combined solution to both of these shortcomings is presented. In order to make transmission-scheduling channel-access protocols support networks with rate adaptive radios, a process called slot-packing is developed. The design of slot-packing ensures that it works with any transmission-scheduling channel-access protocol. Using slot-packing, we design and investigate a new protocol called adaptive recovering mini-slot transmission scheduling (RMTS-a) that tackles both the shortcomings and improves the performance of the network significantly. A key feature of our RMTS-a protocol is that if a radio assigned to a transmission opportunity is unable to utilize all of the time slot, other radios in the local neighborhood are given the opportunity to transmit in the remaining time. Additionally, because multiple radios within communication range of a transmitter are likely to be able to decode the payload, packets to multiple neighbors can be packed within a single transmission

RMTS: A Novel Approach to Transmission Scheduling in Ad Hoc Networks by Salvaging Unused Slot Transmission Assignments

In mobile ad hoc networks (MANETs) there is no centralized supervision over the network operations. In such networks, it is imperative to have protocols that are implemented locally in a distributed manner. To achieve high network performance utilizing only the wireless channels a distributed transmission-scheduling medium-access control (MAC) protocol is desirable. This type of protocol can guarantee a certain level of quality of service (QOS) and works well in congested networks. However, the transmission schedules are often decided in advance and if a node does not have a packet to transmit in its assigned slot then the slot is unused. We propose a protocol called recovering minislots transmission scheduling (RMTS) that salvages these unused transmission slots that would have otherwise been wasted. We show that the proposed protocol produces significant improvements in network performance over traditional transmission-scheduling approaches