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LAMOR: Lifetime-Aware Multipath Optimized Routing Algorithm for Video Transmission over Ad Hoc Networks Liansheng Tan, Ling Xie, King-Tim Ko, Ming Lei and Moshe Zukerman
Abstract—Multipath routing is a key technique to support video transmission over wireless ad hoc networks (WANETs). In WANETs, the lifetime of a node is related to its residual energy, current traffic conditions and the required energy consumed for sending a packet to its next hop in the path. In this paper, we propose a new adaptive routing scheme termed Lifetime-Aware Multipath Optimal Routing (LAMOR) for supporting high-speed real time video transmission in WANETs, which is optimized in terms of lifetime and analyze its characteristics. Both theoretical analysis and simulation results demonstrate that LAMOR indeed extends network lifetime and improves the transmission quality of video streams. Index Terms— Ad Hoc Networks, Routing, Lifetime, Multipath.
I. INTRODUCTION
W
IRELESS ad-hoc network (WANET) consists of a collection of wireless nodes that self-organize into
This research has been partially supported by the Key Project of Chinese Ministry of Education under Grant No. 03114, the National Natural Science Foundation of China under Grant Number 60573188, 60473085 and the Australian Research Council. Liansheng Tan and Ling Xie are with the Computer Science Department of Central China Normal University, Wuhan 430079, PR. China (e-mail:
[email protected],
[email protected]). King-Tim Ko is with Department of Electronic Engineering, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong SAR, PR China (e-mail:
[email protected]) Ming Lei is with School of Electronic Information of Wuhan University, Wuhan 430079, PR. China (e-mail:
[email protected]). Moshe Zukerman is with the Australian Research Council Special Research Center for Ultra-Broadband Information Networks (CUBIN) an affiliated program of National ICT Australia, EEE Dept., The University of Melbourne, Victoria 3010, Australia (e-mail:
[email protected]).
a network without the help of an existing infrastructure. There are many challenges in supporting video communication over WANETs. One of them is routing. There is no fixed infrastructure and the topology is frequently changing due to node mobility or environmental changes. Therefore, it is very hard to maintain a stable and efficient end-to-end route in an ad hoc network. A technique, which recently received research interests, is to partition flows optimally over multiple paths [1]. Multipath routing can aggregate many link rates for a single video stream and hence sustain higher video bit-rates while simultaneously avoiding congestion by load balancing. It is shown in [2] that path diversity is an effective tool for combating correlated packet losses over the Internet. The benefit of a congestion-optimized multipath routing algorithm is studied in [3]. In [4] and [16], the authors further propose a method to optimize rate allocation among a group of video frames and over multiple paths subject to minimum expected video distortion at a receiver. Multipath routing in WANETs has also been investigated from a source coding perspective, particularly with respect to multiple description (MD) codes. Specifically, in [5], multipath routing is used to send multiple descriptions of images and video data over a network with given link throughputs. In a recent report [6], the authors analyze the throughput delay tradeoff curve and show that there is a dramatic increase in throughput for asymptotically large networks, when multipath routing is used in comparison to direct communication in a WANET. Due to power constraints and wireless channel conditions, multipath routing can also introduce significant delay, congestion, and unreliability. Thus, supporting multimedia data with multipath routing is still challenging. In this paper, we focus on an important issue in multipath routing in ad hoc networks, i.e., extending lifetime of nodes and paths. We propose an optimal rate allocation algorithm based on the lifetime of multiple paths. Routing protocols that do not consider lifetime of nodes may result in using the same paths for given traffic demands. This causes a quick exhaustion of energy of the
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nodes, corruption of the links and unreliable data transmission. This problem can become much more serious in video stream because video transfers are long and concentrated. In addition, the energy exhaustion of some nodes may have an effect on the performance of mesh networks. We consider a network that is shared by a set of sources, each of which communicates with its corresponding destination using multiple paths. We develop a new technique for joint optimization called Lifetime-Aware Multipath Optimal Routing (LAMOR), which includes two key techniques: (1) lifetime-optimized multipath routing; and (2) optimal rate allocation among multiple paths.
node by (2) is not sufficient for selecting a long lifetime route. This can be seen from the following analyses. Let variable pik denote the energy consumption required by node i for sending data to its next hop k in a route. Without loss of generality, we assume pik = d2, where d is the distance between two nodes. In some cases, for node i and node j, if C i > C j , but pik >> pjl, then choosing a route including node i will deplete much energy of node i, which may exhaust the node’s energy quickly, and the route including node i will not have longer lifetime than the route including node j. So in the case that the node’s transmitting range is adjustable, in order to avoid using a longer hop, we modify (2) as
~ Ci =
II. LAMOR FOR VIDEO STREAMS A. Lifetime-aware multiple routes discovery In order to ensure reliability in real-time video transmission sessions, we set a node lifetime threshold λ 0 and a path lifetime thresholdλaccording to empirical evaluation in practice to limit the choice of an active node and an active path. The main idea of our algorithm is not to overwork certain nodes on a heavily used path and distribute load among several active paths more evenly, so to extend the lifetime of the nodes. In the whole procedure, we decrease the values of λ0 and λ gradually until some nodes are dead. That means we minimize these two values to the extreme case of that the network is broken down. The Min-Max Battery Cost Routing (MMBCR) and the Conditional Max-Min Battery Capacity Routing (CMMBCR) [14-15] consider the residual energy of each host. The drain rate is a metric that measures the energy consumption speed in a given node. The Minimum Drain Rate (MDR) [7] proposes a method of calculating the drain rate DRi on the basis of the traffic load characteristics. The drain rate DRi of a node i is estimated by averaging the amount of energy consumption and equals to the energy dissipation per second during the past T seconds. ECt denotes the total energy consumption during the past T seconds. We have the following quantity relationship DR i = EC t / T , (1) C i = RBPi / DRi , (2) where the ratio C i = RBPi / DRi signifies how long node i can keep up with routing operations with current traffic conditions, i.e. the lifetime of node i, where RBPi denotes the residual battery. In the circumstance that the node’s transmitting range is adjustable, the estimation for selecting a long lifetime
RBPi EC i
T
+ rct p ik
(3)
rct
denotes the rate at which packets pass through where node i at time t for source C. In a given path rp, we let
~ L p = min Ci . ∀n ∈r i
(4)
p
L p is defined as the lifetime of the path rp . If
Lp > λ
(5)
the path will be chosen as one of the active paths in the multiple path routing. To increase the robustness of multipath routing, we construct maximally disjoint multiple paths in which no more than one path includes the same node to prevent it from being congested, and to utilize the available network resources more efficiently. Another advantage is that in the case where one of the paths is corrupted, the others will not be affected. Under the limiting conditions imposed by the lifetime of nodes and paths, the maximally disjoint multiple routes discovery procedure is described as follows. 1) A host, which starts a route discovery, broadcasts a route request packet. Each route request packet contains . 2) Any host computes its own lifetime periodically by (2). If its lifetime C i
