Chonggang Wang

A survey of transport protocols for wireless sensor networks

In this article we present a survey of transport protocols for wireless sensor networks (WSNs). We first highlight several unique aspects of WSNs, and describe the basic design criteria and challenges of transport protocols, including energy-efficiency, quality of service, reliability, and congestion control. We then provide a summary and comparison of existing transport protocols for WSNs. Finally, we discuss several open research problems.

Upstream congestion control in wireless sensor networks through cross-layer optimization

Congestion in wireless sensor networks not only causes packet loss, but also leads to excessive energy consumption. Therefore congestion in WSNs needs to be controlled in order to prolong system lifetime. In addition, this is also necessary to improve fairness and provide better quality of service (QoS), which is required by multimedia applications in wireless multimedia sensor networks. In this paper, we propose a novel upstream congestion control protocol for WSNs, called priority-based congestion control protocol (PCCP). Unlike existing work, PCCP innovatively measures congestion degree as the ratio of packet inter-arrival time along over packet service time. PCCP still introduced node priority index to reflect the importance of each sensor node. Based on the introduced congestion degree and node priority index, PCCP utilizes a cross-layer optimization and imposes a hop-by-hop approach to control congestion. We have demonstrated that PCCP achieves efficient congestion control and flexible weighted fairness for both single-path and multi-path routing, as a result this leads to higher energy efficiency and better QoS in terms of both packet loss rate and delay.

A new collision resolution mechanism to enhance the performance of IEEE 802.11 DCF

The medium-access control (MAC) protocol is one of the key components in wireless local area networks (WLANs). The main features of a MAC protocol are high throughput, good fairness, energy efficiency, and support priority guarantees, especially under distributed contention-based environment. Based on the current standardized IEEE 802.11 distributed coordination function (DCF) protocol, this paper proposes a new efficient collision resolution mechanism, called GDCF. Our main motivation is based on the observation that 802.11 DCF decreases the contention window to the initial value after each success transmission, which essentially assumes that each successful transmission is an indication that the system is under low traffic loading. GDCF takes a more conservative measure by halving the contention window size after c consecutive successful transmissions. This gentle decrease can reduce the collision probability, especially when the number of competing nodes is large. We compute the optimal value for c and the numerical results from both analysis and simulation demonstrate that GDCF significantly improve the performance of 802.11 DCF, including throughput, fairness, and energy efficiency. In addition, GDCF is flexible for supporting priority access by selecting different values of c for different traffic types and is very easy to implement it, as it does not requires any changes in control message structure and access procedures in DCF.

Priority-based congestion control in wireless sensor networks

In wireless sensor networks (WSNs), congestion occurs, for example, when nodes are densely distributed, and/or the application produces high flow rate near the sink due to the convergent nature of upstream traffic. Congestion may cause packet loss, which in turn lowers throughput and wastes energy. Therefore congestion in WSNs needs to be controlled for high energy-efficiency, to prolong system lifetime, improve fairness, and improve quality of service (QoS) in terms of throughput (or link utilization) and packet loss ratio along with the packet delay. This paper proposes a node priority-based congestion control protocol (PCCP) for wireless sensor networks. In PCCP, node priority index is introduced to reflect the importance of each node. PCCP uses packet inter-arrival time along with packet service time to measure a parameter defined as congestion degree and furthermore imposes hop-by-hop control based on the measured congestion degree as well as the node priority index. PCCP controls congestion faster and more energy-efficiency than other known techniques

Issues of transport control protocols for wireless sensor networks

The paper presents a survey on transport control protocols for wireless sensor networks (WSNs). First, it lists the disadvantages of traditional transport control protocols (TCP and UDP) for the environment of WSNs. Second, several design issues of transport control protocols for WSNs are presented. Third, some existing transport control protocols for WSNs are classified and compared. Finally, several problems needing further studying are outlined.

Voice communications over zigbee networks

This article provides an overview of ZigBee-enabled wireless networks and discusses the feasibility of supporting voice communications over ZigBee networks. We begin by providing an overview of the ZigBee technology followed by an evaluation of voice quality and performance over such an impoverished wireless channel. Two types of voice communications, namely full-duplex voice over IP (VoIP) and half-duplex push-to-talk (PTT) are considered. Voice quality of VoIP is measured using the R-factor [1] (a well known objective speech quality metric). The quality of PTT, however, is evaluated based on packet-loss rate, delay, and jitter. The simulation results demonstrate that a low-power, low-rate wireless sensor network can support a limited range of voice services.

On use of traditional M/G/1 model for IEEE 802.11 DCF in unsaturated traffic conditions

For analysis of the IEEE 802.11 distributed coordination function (DCF), one of the key assumptions commonly accepted is that every node always has at least one frame to transmit. In practice, however, this assumption may or may not be valid, particularly under unsaturated traffic conditions. In this paper, we assess the accuracy in using the traditional M/G/1 queueing model for the DCF as an alternative model at an individual node, and analyze its performance in unsaturated traffic conditions. Analytical and simulation results are compared to demonstrate a reasonable accuracy of the proposed approach for varying traffic loads at an individual node

A New Slot-Count Selection Algorithm for RFID Protocol

EPCglobal RFID generation-2 (Gen-2) protocol [1] has been proposed for ultra-high frequency (UHF) passive tags and is being deployed. Gen-2 .proposes a slotted random anti-collision algorithm, including an adaptive slot-count (Q) selection algorithm. The integer-valued parameter Q in Gen-2 plays a critical role in tag collision resolution. This adaptive algorithm dynamically adjusts value of Q based on the type of replies from tags. However, it modifies the value of Q the same way whether there is a collided reply or no reply. This approach could lead to a slow tag identification speed, since it does not recognize the differences in duration between the collided reply and no reply. This paper proposes a new slot-count selection algorithm which changes the parameter Q with different amounts depending on whether the reader receives a collided reply or there is no reply by a pre-specified waiting time. It is demonstrated, through analysis and simulations, that the new proposed algorithm achieves significantly faster tag identification speed compared to that of the existing Gen-2 adaptive Q algorithm.

A probability-based algorithm to adjust contention window in IEEE 802.11 DCF

The paper proposes a new probability-based algorithm to adjust the contention window in 802.11 DCF (distributed coordination function). Our main motivation is based on the observation that 802.11 DCF decreases the contention window to the initial value after each successful transmission, which essentially assumes that each successful transmission is an indication that the system is under low traffic loading. PDCF (probability-based DCF) takes a more conservative measure by halving the contention window size with a probability f after each successful transmission. This decrease behavior lowers the collision probability, especially when the competing node number is large. We compute the optimal value for f, and the numerical results from both analysis and simulation demonstrate that PDCF significantly improve the performance of 802.11 DCF, including throughput, fairness, and energy efficiency. In addition, PDCF is flexible for supporting priority access by selecting different values of f for different traffic types; it is fully compatible with the original 802.11 DCF, and simple to implement, as it does not require changes in control message structure and access procedures in DCF.

Future internet services and applications

The Internet has been successfully deployed for several decades due to its high flexibility in running over different physical media and supporting different high-layer protocols and applications, including traditional file transfer, email, and client-server-based web applications, among others. The future Internet is expected to be more agile, scalable, secure, and reliable. Meanwhile, we have witnessed the unprecedented development and growth of new applications and services in recent years ranging from location-based services, social networking, cloud computing, and peer-to-peer (P2P)-based applications. Such rapidly emerging applications with different requirements and implications for the future Internet design pose a significant set of problems and challenges.