Kien Nguyen

Asynchronous MAC protocol with QoS awareness in wireless sensor networks

In wireless sensor networks (WSNs), MAC protocols utilize duty cycling to extend the network lifetime. Receiver-Initiated MAC (RI-MAC) is an asynchronous duty cycling protocol, which schedules transmissions based on receivers. By letting a receiver initiate the rendezvous for the transmissions between senders and the receiver, the protocol achieves good latency performance at the cost of high energy consumption at the senders. On the other hand, different types of traffic are very popular in WSNs. The MAC protocols are necessarily to be equipped QoS (quality of service) mechanisms to handle with the variation of traffic. In this paper, we propose AQ-MAC; a new asynchronous MAC protocol with QoS awareness. AQ-MAC adopts the receiver-initiated manner and provides QoS service per packet following the priority imposed. When a node has an incoming packet with a high priority, it immediately turns on the radio in order to wait for a transmission initiated by a receiver. Otherwise, the node keeps a low priority packet in a queue and sends out in a burst until a high priority packet comes or after a timeout value. In addition, AQ-MAC utilizes a packet concatenation scheme to improve the energy efficiency by reducing control overhead. We have evaluated AQ-MAC in multiple scenarios using ns-2. The results show that AQ-MAC adapts well with different types of traffic as well as achieves good performance in terms of energy efficiency and latency.

AM-MAC: an energy efficient, Adaptive Multi-hop MAC protocol for sensor networks

Sensor network MAC protocols use a duty cycling mechanism and a multi-hop transmission to create a good trade-off between their energy efficiency and latency. The nodes in duty cycling multi-hop MAC protocols such as RMAC periodically sleep/listen during the operational cycle to reduce their energy consumption by idle listening; and the listening period is usually long in order to support packets in reaching a multi-hop destination in a single cycle (multi-hop transmission). The traffic network in the wireless sensor network is otherwise very scarce, and keeping the radio on during such long listening periods when there is no data transmission in the network wastes energy. In addition, these protocols incur a large amount of control overhead, which is one of the main energy wasted sources. This paper proposes an adaptive low overhead MAC protocol we call AM-MAC (Adaptive Multi-hop MAC). It can reduce the wastage caused by long listening period and minimizes the control overhead. The nodes in AM-MAC use an adaptive method, and thus they can adjust the duration of the listening period according to the traffic load. To reduce the control overhead, a single packet has more than one role. During a multi-hop transmission, the new control packet replaces the RTS/CTS pair, and one DATA packet can play both DATA/ACK roles. An extended evaluation of AM-MAC has been conducted through simulation, against RMAC. The results illustrate that AM-MAC significantly reduces the energy consumption and notably lessens the end-to-end latency.

Low Overhead MAC Protocol for Low Data Rate Wireless Sensor Networks

We propose the low overhead media access control protocol (LO-MAC), a new low latency, energy efficient MAC protocol for low data rate wireless sensor networks. LO-MAC uses both duty cycling and multihop forwarding from the routing-enhanced MAC protocol (RMAC) to reduce idle listening and sleep latency, respectively. Besides that, LO-MAC introduces a traffic-adaptive mechanism, which is based on the fact that a node can sense a busy channel within its carrier sensing range. This mechanism uses carrier sensing as a binary signal, and effectively notifies nodes of the existence of a data packet. The nodes then either keep their radios on to take part in multihop data forwarding or turn them off to save energy. Moreover, LO-MAC takes full advantage of the broadcast nature of wireless communication and lets a packet have different meanings when it is in transmission range of different nodes. In LO-MAC, not only is a request-to-send/clear-to-send pair replaced with a Pioneer (PION) packet, as in RMAC, but also a data packet can play both data and acknowledgement functions. Therefore, control overhead and overhearing energy are significantly reduced. Our simulation results show that LO-MAC outperforms RMAC in terms of energy efficiency while achieving comparable end-to-end latency.

An energy efficient, high throughput MAC protocol using packet aggregation

In wireless sensor networks, most MAC protocols switch radios off periodically, employing the so-called duty cycle mechanism, in order to conserve battery power that would otherwise be wasted by energy-costly idle listening. In order to minimize the various negative side-effects of the original scheme, especially on latency and throughput various improvements have been proposed. The novel Aggregation MAC or AG-MAC protocol presented in this paper combines two of the most promising improvements into one protocol. Firstly, the idea to forward packets over multiple hops within one duty cycle as initially introduced in RMAC. Secondly, a packet aggregation scheme that not only increases throughput but also reduces power consumption that would otherwise be incurred by additional control packets. Since data packets in sensor networks are comparatively small significant gains are to be expected. Furthermore, AG-MAC incorporates our previously presented idea of scheduling data transmissions with minimum latency, thereby performing packet aggregation together with the multi-hop transmission mechanism in a most efficient way. We evaluated AG-MAC using the prominent network simulator ns-2 and the results show that our protocol can outperform state of the art protocols both in terms of energy efficiency and throughput.

Using carrier sensing to improve energy efficiency of MAC protocol in sensor networks

Energy efficiency is a requirement when designing a MAC protocol for wireless sensor networks. To reduce needless energy use, most MAC protocols exploit the duty cycling technique, in which the radio frequently turns on and off in each operational cycle. Among those protocols, the multi-hop MAC protocol routing enhanced MAC (RMAC) enables multi-hop transmission to minimize the latency burden, which is the main disadvantage of duty cycling. In each cycle, when nodes are awake, RMAC can exploit the cross-layer information to initialize the multi-hop flow and the data packet transmission is scheduled in the subsequent sleep period. This technique, however, introduces the long listening period problem in which nodes have to keep the radio on even when no flow data is scheduled. We propose a solution to solve that problem by adding a short period after the synchronized process. In this period, we use carrier sensing as a binary signal, which lets the nodes know the traffic status of the network. After the period, nodes go to the sleep state when no data exists in the network; otherwise nodes operate similarly to the RMACs basic scheme. Simulations showed that our solution can improve energy efficiency while only slightly increasing latency.

Impact of QoS operations on an experimental testbed network

Abstract By making the best use of limited bandwidth, quality of service (QoS) provisioning over internet is essential for satisfying various types of internet-application requirements. The traffic classification and scheduling are the key functions to provide various kinds of class of service (CoS) under an overload condition. This paper investigates QoS performance in a network equipment testbed when implementing these main functions. We examine the major CoS functions provided by the Juniper T320 router, and measure their performance. In addition to fundamental analysis of the QoS behavior, we show the impact of QoS operations on a parallel system distributed in multi-domain networks as a practical case study of grid environments.

Impact of contention on performance of flows in multi-hop MAC protocol for sensor networks

The MAC protocol in wireless sensor networks (WSNs) plays an important role in conserving energy and it generally adopts a duty cycling mechanism to eliminate idle listing energy at the cost of high delivery latency. The most effective method of bypassing the latency disadvantage is forwarding a packet over multiple hops in an operational cycle. The combination of duty cycling and multi-hop forwarding creates a new class of MAC protocol called multi-hop MAC, which has been proven to outperform other single-hop duty cycling protocols both in term of energy efficiency and latency. A packet in such a protocol is always relayed via multiple hops toward a sink in a cycle. The flow from a source node to the sink is affected by contention because of the sharing characteristic of wireless channels. We investigated what effect contention had on the flow capacity of Demand Wakeup MAC (DW-MAC), which is a state-of-the-art multi-hop MAC protocol. We also found that instead of using the original large contention window (CW), a DW-MACs flow using a smaller CW could avoid unnecessary contention and use channels more efficiently. The analysis and resulting ns-2 simulation revealed that DW-MAC with the new values for CW achieves higher throughput, lower end-to-end latency, and greater energy efficiency.