Elsevier

Computer Communications

Volume 29, Issue 9, 31 May 2006, Pages 1316-1329
Computer Communications

Dynamic bandwidth allocation for QoS routing on TDMA-based mobile ad hoc networks

https://doi.org/10.1016/j.comcom.2005.10.009Get rights and content

Abstract

The paper proposes several dynamic bandwidth allocation strategies for QoS routing on TDMA-based mobile ad hoc networks. Comprehensively, these strategies are called a distributed slots reservation protocol (DSRP). In DSRP, QoS routing only depends on one-hop neighboring information of each mobile host (MH). In addition, slot inhibited policies (SIPs) and slot decision policies (SDPs) are proposed to determine which slots are valid to use and which slots in the valid slots can be used actually, respectively. In SDPs, three heuristic policies, 3BDP, LCFP, and MRFP, are proposed to increase the success rate of a QoS route and alleviate the slot shortage problems. Moreover, a slot adjustment protocol (SAP) is proposed for a conflicting MH to coordinate the slot usage of its neighbors during the route reservation phase in order to accommodate more routes in the network. The slot adjustment algorithm (SAA) invoked in SAP is a branch-and-bound algorithm, which is an optimum algorithm in terms of the number of slots to be adjusted, on the premise that not to break down any existing route. QoS route maintenance and improvement are also provided. By the simulation results, the proposed protocol cannot only increase the success rate in search of a route with bandwidth requirement guaranteed but also raise the throughput and efficiency of the network.

Introduction

A mobile ad hoc network (MANET) is an infrastructure-less network consisting of numbers of mobile hosts (MHs) communicating with one another via relaying messages among MHs through multihop wireless links. The major challenges of a MANET are its fast changing of topology and the lack of global information. An MH has only its neighboring information due to its transmission capability, such as transmission range, battery power, and so on. These result in the difficulty of developing an efficient routing protocol for MANETs. A routing protocol for MANETs should be capable of not only finding a route for the communicating MHs but also tolerating highly dynamic changing of topology. A large number of researches on routing for MANETs could be found in the literature such as AODV, DSR, TORA, and so on Refs. [1], [2], [3], [4], [5], [6], [7]. Most of them try to find a shortest route between the source and the destination.

Recently, the need to support real-time applications, such as audio or video transmissions, is getting more and more. QoS-support routing protocol is thus, becoming important as well. In addition to finding a route from a source to a destination, a QoS routing for MANETs should also guarantee the end-to-end QoS requirement of the route, such as bandwidth needs, delay constraints, and so on. Recently, QoS routing protocols on MANETs have been studied extensively Refs. [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23]. However, in Refs. [8], [9], [10], [11], [12], [13], [14], QoS routing protocols are designed for layer 3 (network layer). The QoS requirements in these protocols are assumed to be known in advance. Nevertheless, the QoS requirement much depends on the real situation from lower layers. Therefore, it would be more practical if a cross-layer protocol can be devised for QoS routing on MANETs. Thus, some researches take both the MAC and network layers into consideration to design QoS routing protocols for MANETs Refs. [15], [16], [17], [18], [19], [20], [21], [22], [23].

QoS routing protocols on CDMA over TDMA channel model are proposed in Refs. [15], [16], [17], [18], [19], [20]. The multi-path schemes, Refs. [15], [16], [17], are adopted to discover QoS routes in a bandwidth-limited network. A ticket-based algorithm is proposed in Ref. [15] to search for a satisfactory multi-path route. The global link-state information from source to destination is needed in Ref. [16] to search a QoS multi-path route. In Ref. [17], a spiral-multi-path QoS routing protocol is proposed not only to search QoS routes but also to enhance route-robustness and route-stability. Note that if the network bandwidth is sufficient, the protocols, Refs. [15], [16], [17], will just search a single route to satisfy the QoS bandwidth requirements. In Refs. [18], [19], [20], the protocols construct a single QoS routing path depending on one-hop neighbors information. The hidden terminal problem is covered by assigning different codes for the concurrent transmissions within two-hop distance. In Ref. [20], the QoS routing protocol adopts the algorithm in Ref. [18] to resolve slot-scheduling problem. The protocol in Ref. [20] takes not only the bandwidth but also battery life into consideration to search a QoS route.

The protocols, Refs. [15], [16], [17], [18], [19], [20], are designed for CDMA over TDMA channel model. The cost of the code assignment should be counted into the protocol as well. However, the code assignment is not discussed in Refs. [15], [16], [17], [18], [19], [20]. Due to the high cost of using CDMA model, some researches investigate to find the QoS route only on the TDMA channel model Refs. [21], [22].

A TDMA-based bandwidth reservation protocol for QoS routing in MANETs is proposed in Ref. [21]. This protocol can solve the hidden-terminal and exposed-terminal problems by taking two-hop neighbors' slots usages into consideration. Each MH maintains the two-hop neighbors' slots usages to select the appropriate slots for each link of the route. If there are many slots to select for a link, random policy is adopted. However, it has a high possibility that the protocol cannot find any route satisfying the QoS requirements, even there exists a QoS route. On the other hand, the QoS routing protocol proposed in Ref. [22] is also based on the TDMA channel model. The protocol maintains one-hop neighboring information for the selection of slots in order to find a QoS route. A route maintenance mechanism for reconstructing a route when the route is broken is described as well. Different from the above channel models, Ref. [23] considers the QoS routing in a contention-based MANETs.

In this paper, a distributed slots reservation protocol (DSRP) for QoS routing on TDMA-based mobile ad hoc networks is proposed. The QoS requirement considered in the paper is the bandwidth requirement, in terms of data slots. The hidden-terminal and exposed-terminal problems are taken into consideration. Slots reuse is the main concept of the protocol. The main differences of the DSRP from the Ref. [22] are slots reuse and slots adjustment mechanism. The slots with least conflict to other MHs or have been used by other MHs are used with high priority if they are valid to use. Thus, the successful rate to find a QoS route can be increased correspondingly. A slot adjustment mechanism is to adjust the slots usages of an MH to tolerate more routes passed by when the slots in an MH have been reserved or used by another route. Doing so can increase the successful rate of discovering a QoS route. Route maintenance is to maintain the connectivity of the QoS route and improve the efficiency of the route. Extensive experiments are performed to verify the superiority of the proposed protocol. The proposed protocol does outperform than the existing methods in call success rate and average delay time.

In general, a QoS service means a constant traffic flow lasts for a period of time and no acknowledgement is required. Thus, the paper assumes that the QoS requirement does not change during route discovery and transmission. On the other hand, since the traffic of a QoS service is constant, the slots reserved in a time frame will be automatically reserved for the following time frames until the end of the service. In addition, no route from the destination to the source for ACK transmission is considered as well.

The rest of this paper is organized as follows. Section 2 presents the system model and describes the challenges in designing the QoS routing protocol on TDMA-based mobile ad hoc networks. Some heuristic policies used for slots selection are proposed in Section 3. Section 4 describes the distributed slots reservation protocol (DSRP), including QoS route discovery and reservation, and QoS route maintenance and improvement. Simulation results are presented and analyzed in Section 5. Section 6 concludes the paper.

Section snippets

The system model and terminology

The paper proposes a distributed slots reservation protocol (DSRP) for QoS routing on TDMA-based mobile ad hoc networks. TDMA-based channel model is shown in Fig. 1, where time is divided into TDMA frames. A TDMA frame is composed of a control subframe and a data subframe. Each subframe contains a number of slots. Each slot can be used for one packet transmission. It is worth mentioning that control packets are scheduled to be transmitted in control subframes and data packets are in data

Slot inhibited policies (SIPs)

For a link AB¯, slot inhibited policies (SIPs) are the polices used for A and B to decide the free slots that are valid to use. That is VSAB¯. The similar ideas can be found in Refs. [21], [22]. For completeness, the ideas of SIPs are explained as follows. SIPs take the hidden terminal and exposed terminal problems into consideration. Let A,BN. If a slot t,tT, is valid to use for A to send to B, t should satisfy the following three policies. The first policy, which is termed sip1, requires

The distributed slots reservation protocol (DSRP)

The distributed slots reservation protocol (DSRP) is an on-demand slots reservation protocol for QoS routing on TDMA-based mobile ad hoc networks. When a source S wants to communicate with a destination D, the QoS route discovery phase will be initiated by S for broadcasting a route request (RREQ) packet to search a QoS route to D. During the QoS route discovery phase, slots inhibited policies (SIPs) decide which slots are valid to use for a link, and slot decision policy (SDP) decides which

Simulation results

The performance of the DSRP in comparison with the related work Refs. [21], [22] is evaluated via simulation study from several aspects, such as call success rate, network throughput, control overhead, average delay time, and the storage to perform the protocol. In the simulation, there are 30 MHs in 1000 m×1000 m area. The transmission range is 300 m, the transmission rate is 11 M bit/s, and the QoS bandwidth requirements are 2 slots and 4 slots. Each frame has 16 data slots and each time slot is 5 

Conclusions

As well-known, QoS service is much demanding with the increasing of the real-time multimedia applications nowadays. Multimedia transmission over wireless networks is becoming important as well. Thus, QoS routing on MANETs is deemed a significant research issue.

This paper proposed several dynamical bandwidth allocation strategies for QoS routing on TDMA-based MANETs. Comprehensively speaking, a distributed slots reservation protocol (DSRP) is proposed, which can construct QoS routes only

Acknowledgements

This work was supported by the National Science Council of the Republic of China under Grants NSC 94-2213-E-032-014 and NSC 94-2524-S-032-003.

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