Weiliang Zhao

Enhancing the performance of LEACH protocol in wireless sensor networks

LEACH protocol is one of the clustering routing protocols in wireless sensor networks. The advantage of LEACH is that each node has the equal probability to be a cluster head, which makes the energy dissipation of each node be relatively balanced. In LEACH protocol, time is divided into many rounds, in each round, all the nodes contend to be cluster head according to a predefined criterion. This paper focuses on how to set the time length of each round, to prolong the lifetime of the network and increase throughput, which is denoted as the amount of data packs sent to the sink node. The functions of lifetime and throughput related to the time length of each round are deduced. These functions can be used to enhance the performance of cluster-based wireless sensor networks in terms of lifetime and throughput.

Energy-efficient femtocell networks: challenges and opportunities

As a promising technique for next-generation wireless networks, femtocells expand the coverage of cellular networks, provide high data rate for users, decrease the transmission power of user equipments, and increase the spectrum efficiency. In a few years, the number of deployed femtocell base stations (FBSs) will reach hundreds of millions. This huge deployment will bring a lot of challenges in terms of interference management, resource scheduling, and energy consumption. In recent years, more and more attention has been paid to energy-efficient communications. The huge number of deployed FBSs will aggravate energy consumption. In this article, we comprehensively survey the related work on energy efficiency issues in femtocell networks, including energy efficiency metrics, energy consumption models, deployments of femtocells, and energy-efficient schemes. Then a simple sleeping scheme, fixed time sleeping, is presented as a case study for saving the energy of FBSs. Some interesting results are also presented to show that fixed time sleeping makes a good trade-off among energy efficiency, actual waiting time, and call loss.

Modeling Channel Access Delay and Jitter of IEEE 802.11 DCF

With the ever-increasing requirement of WLAN to support real-time services, it is becoming important to study the delay properties of WLAN protocols. This paper constructs a new model to analyze the channel access delay and delay jitter of IEEE 802.11 DCF in saturation traffic condition. Based on this analytical model, average channel access delay and delay jitter are derived for both basic access and RTS/CTS-based access scheme. The accuracy of the analytical model is validated by simulations and furthermore we discuss the impact of initial contention window, maximal backoff stage, and packet size on channel access delay and delay jitter of 802.11 DCF using the proposed model.

An adaptive coordinated MAC protocol based on dynamic power management for wireless sensor networks

To be adaptive to the traffic variations in some real-time sensor applications, AC-MAC is proposed by Jin Ai et al. Based on Sensor Medium Access Control (S-MAC), AC-MAC introduces an adaptive duty cycle scheme within the framework of S-MAC. However, frequent transceiver state switches can lead to the increasing consumption of energy. In order to solve this problem, we focus our research on how to reduce the number of transceiver state switch. By combining AC-MAC with the Dynamic Power Management, it brings in a new protocol, an Adaptive Coordinated MAC Protocol based on Dynamic Power Management for Wireless Sensor Networks, AC-MAC/DPM, which not only guarantees low delay or high throughput, but also reduces the potential energy consumption when the traffic load is high.

MPTC --- A Minimum-Energy Path-Preserving Topology Control Algorithm for Wireless Sensor Networks

The topology control strategies of wireless sensor networks are very important to reduce the energy consumptions of sensor nodes and prolong the life-span of networks. In this paper, we put forward a minimum-energy path-preserving topology control (MPTC) algorithm. MPTC not only resolves the problem of exceeding energy consumption because of the unclosed region in SMECN[2], but also preserves at least one minimum-energy path between every pair of nodes in a communication network. At last, we demonstrate the performance improvements of our algorithm through simulation.

A new backoff algorithm to improve the performance of IEEE 802.11 DCF

For IEEE 802.11 DCF, Backoff Timers of all stations in the wireless LAN are decreased by the same step if the state of channel is idle, and are paused and resumed at the same time. In this paper, we defined this as the “synchronization” feature of 802.11 DCF. The synchronization feature makes the packet collision probability of 802.11 DCF high. To break up the synchronization, this paper proposes a novel asynchronous backoff algorithm for 802.11 DCF, named asyn-DCF. A Markov model is built to analyze the performance of asyn-DCF. The simulation results indicate that asyn-DCF can decrease the packet collision probability significantly and utilize the channel more efficiently comparing to 802.11 DCF.

R-MAC: A New MAC Protocol for Wireless Networks with Asymmetric Links

Most of routing protocols for wireless Ad hoc networks are based on the hypothesis of symmetric link. However, because of the influence from radio power, battery outrage, and environment and so on, asymmetric link is prevalent. At present, projects to solve this problem are mostly set tables of immediate neighbors and indirect neighbors, and use the corporate neighbors to inform the node whose region is larger. In this paper, we solve the problem of asymmetric link in the way to change the frame structure and transmit mechanism of the IEEE802.11 protocol. And get the same effect without building the table of neighbors.

A new backoff algorithm to support service differentiation in ad hoc networks

It is essential to design QoS supported MAC mechanism for supporting QoS in WLAN. In [1], we have proposed a new backkoff algorithm, named RWBO+BEB, to decrease the packet collision probability significantly. In this paper, we explore how to make RWBO+BEB support service differentiation in WLAN, and propose a novel proportional service differentiation algorithm, named p-RWBO, to allocate the wireless bandwidth according to the bandwidth ratio of each station. The basic idea of p-RWBO is that different priority stations use different walking probability, pw, which is a key parameter in RWBO+BEB. An analytical model is proposed to analyze how to choose pw according to the bandwidth ratios of stations. The simulation results indicate that p-RWBO can allocate the wireless bandwidth according to the bandwidth ratio of each station.

A new performance parameter for IEEE 802.11 DCF

In this paper, we define a new performance parameter, named PPT, for 802.11 DCF, which binds successful transmission probability and saturation throughput together. An expression of optimal minimum contention windows (CWmin) is obtained analytically for maximizing PPT. For simplicity, we give a name DCF-PPT to the 802.11 DCF that sets its CWmin according this expression. The simulation results indicate that, compared to 802.11 DCF, DCF-PPT can significantly increase the PPT and successful transmission probability (about 0.95) in condition that the saturation throughput is not decreased.