BEAR: Bandwidth-Estimation-based Flow Admission Control and Routing in IEEE 802.15.4-based Ad-hoc Sensor Networks

University of Luebeck, Germany. June 2014.

This dissertation is in the context of supporting real-time multimedia flows in ad-hoc Wireless Sensor Networks (WSNs). Real-time multimedia flows require Quality of Service (QoS) provisioning in terms of bounds on delay and packet loss along with a soft bandwidth guarantee. Typically, WSNs use the IEEE 802.15.4 standard at the Medium Access Control (MAC) and Physical (PHY) layers. The IEEE 802.15.4 standard does not support real-time multimedia flows well. Therefore, our work focuses on supporting real-time multimedia flows in IEEE 802.15.4-based ad-hoc WSNs.

The shared nature of the wireless communication medium results in interference. Interference combined with the overheads associated with a MAC protocol, and the implementation of a networking protocol stack limit the available bandwidth in wireless networks, and can result in congestion, even if the transmission rates of nodes are well below the maximum bandwidth supported by an underlying communication technology. Therefore, to satisfy real-time multimedia flows’ QoS requirements inside IEEE 802.15.4-based ad-hoc WSNs, each node inside the network should determine the amount of data that the node can transfer without negatively impacting the performance of real-time multimedia flows. Moreover, a routing protocol should select a forwarding path that can better satisfy the real-time multimedia flows’ end-to-end QoS requirements.

The MAC layer decides the sharing of the communication medium, and in this dissertation our results demonstrate that enabling or disabling the IEEE 802.15.4’s unslotted Carrier Sense Multiple Access Collision Avoidance (CSMA-CA) MAC layer ACKs impacts channel throughput and packet delivery delay. The parameters that affect the choice regarding enabling or disabling the MAC layer ACKs for real-time multimedia flows are: (i) end-to-end delay and packet loss requirements of real-time multimedia flows, (ii) data load within the interference range of transmitters along the data forwarding path, and (iii) length of the data forwarding path.

In this dissertation, we highlight limitations of the state-of-the-art flow admissioncontrol algorithms for ad-hoc wireless networks. Our results demonstrate that the state-of-the-art flow admission control algorithms for wireless ad-hoc networks fail in their task. We identified multiple factors that an effective available-bandwidth-based flow admission control algorithm should consider. First, increased data traffic in a network increases the CSMA-CA MAC layer overhead. Second, the contention count on a node that is not on a flow’s data forwarding path is a function of the number of transmitters (along the flow’s forwarding path) within the interference range of the node. Third, a flow’s intra-flow contention count on a node (along the flow’s forwarding path) depends on the hop-count distance of the node from the source and the destination nodes. Taking these factors into account, we designed and implemented BandEst; combination of a measurement-based available bandwidth estimation technique and a flow admission control algorithm for IEEE 802.15.4-based ad-hoc WSNs. Our results demonstrate that BandEst significantly outperforms the state-of-the-art flow admission control algorithms for ad-hoc wireless networks.

Finally, we designed and implemented an available-bandwidth-based proactive routing protocol for IEEE 802.15.4-based single-sink and multi-sink ad-hoc WSNs. The available-bandwidth-based proactive routing protocol maintains the best forwarding path in terms of the end-to-end available bandwidth towards each sink node present in a network. Moreover, a node can maintain more than one data forwarding path towards the same sink node. We performed extensive experiments, and compared our proactive routing protocol with a state-of-the-art opportunistic routing protocol. Our results demonstrate that the opportunistic routing protocol can distribute data load unevenly (in case of multiple sink nodes), hence results in high end-to-end delay and low Packet Delivery Ratio (PDR). In case of our proactive routing protocol, selecting forwarding paths by only considering the end-to-end available bandwidth frequently results in lengthy data forwarding paths. Lengthy data forwarding paths result in higher intra-flow contention, hence PDR and end-to-end delay are impacted. One of the experimental scenarios, using multiple sink nodes, demonstrates that in case of our proactive routing protocol, carefully selecting the data forwarding path(s) that are not too long compared to the shortest available data forwarding path(s), but have better end-to-end available bandwidth significantly improves the performance of the proactive routing protocol. Moreover, we integrated BandEst with the available-bandwidth-based proactive routing protocol. Our results indicate that, in general, trading off end-to-end available bandwidth and the length of a data forwarding path may improve end-to-end PDR and delay.