Zhenzhou Tang

An Environment Monitoring System for Precise Agriculture Based on Wireless Sensor Networks

To solve the problems occurring in the traditional precision agriculture such as poor real-time data acquisition, small monitoring coverage area, excessive manpower requirement etc., this paper designs and deploys an environment monitoring system for precise agriculture based on wireless sensor networks in a red bayberry greenhouse located on a hillside. This system can automatically collect the temperature, humidity, illumination, voltage and other parameters of the deployment zone, and transmit the data to the remote server via GPRS in real time. This system also includes a web-based platform integrated with Google Maps to release the greenhouse environmental status and provide real-time voice and SMS alarm service. Since the experimental area is lack of mains supply, the system is powered by solar and storage batteries. The experiment result shows that the low-cost system has strong scalability, and can provide real-time, stable and accurate service for precise agriculture.

An Energy-Efficient Relay Selection Strategy Based on Optimal Relay Location for AF Cooperative Transmission

In this paper, an energy-efficient optimal relay selection strategy which is jointly optimized with the energy-efficient optimal power allocation scheme for AF cooperative transmission is proposed. The relay selection criterion is the distance from the potential relay to the corresponding optimal relay locations where the minimum transmission power of the source, the relay or their total can be achieved. In order to determine the optimal relay locations, a universal algorithm with low computational complexity and easy implementation is also presented. Simulations are conducted to validate our theoretical analysis. The results show that with the relay selected by the proposed strategy, the cooperative transmission can achieve considerably high energy-efficiency.

RP-MAC: A Passive MAC Protocol with Frame Reordering for Wireless Sensor Networks

Idle listening is one of the main factors for energy consumption in wireless sensor networks, and the duty cycle mechanism is widely used to reduce idle listening. In this paper, we present a new receiver-initiated duty cycling MAC protocol for wireless sensor networks, called reordering-passive MAC (RP-MAC), which includes receiver wake-up time estimation scheme and frame reordering scheme. We evaluate the performance of RP-MAC in ns-2 network simulator, and the simulation results shows that RP-MAC achieves higher energy efficiency, higher network throughput and lower end-to-end delay compared to other passive protocols, especially in case of heavy traffic or low duty cycle.

How Network Coding Benefits Converge-Cast in Wireless Sensor Networks

Network coding is one of the most promising techniques to increase the reliability and reduce the energy consumption for wireless sensor networks (WSNs). However, most of the previous works mainly focus on the network coding for multi-cast or uni- cast in WSNs, in spite of the fact that the converge-cast is the most common communication style in WSNs. In this paper, we investigate, for the first time as far as we know, the feasibility of acquiring network coding benefits in converge-cast, and we present that with the ubiquitous convergent structures self-organized during converge-casting in the network, the reliability benefits can be obtained by applying linear network coding. We theoretically derive the network coding benefits obtained in a general convergent structure, and simulations are conducted to validate our theoretical analysis. The results reveal that the network coding can improve the network reliability considerably.

Network coding in convergecast of wireless sensor networks: Friend or foe?

Convergecast is probably the most common communication style in wireless sensor networks (WSNs). And network coding (NC) is a promising concept to improve throughput or reliability of convergecast. Most of the existing works have mainly focused on exploiting these benefits without considering its potential adverse effect. In this paper, we argue that network coding may not always benefit convergecast. This viewpoint is discussed within four scenarios: The network-coding-aided (NC-aided) and the none-network-coding (none-NC) convergecast schemes with or without automatic repeat request (ARQ) mechanisms. The most concerned performance metrics, including packet collection rate, energy consumption and end-to-end delay, are investigated. Theoretical analyses and simulation results show that the way network coding operates, i.e., conscious overhearing and the prerequisite of successfully decoding, could naturally diminish its advantages in convergecast. And NC-aided convergecast schemes may even be inferior to none-NC ones when the wireless link delivery ratio is high enough. The conclusion drawn in this paper casts a new light on how to effectively apply network coding to practical WSNs.

An Improved Power Control Strategy for Cognitive Radio Networks with Imperfect Channel Estimation

Power control of secondary user is an important issue for cognitive radio systems to protect the transmission of primary users. There are several ways to protect the primary user under the accurate estimation of the channels. In this paper, we focus on the protection of primary user under the imperfect channel estimation. We first gives the mathematical expressions of the outage probability of the primary link and the capacity of the secondary user under imperfect channel estimation. In order to alleviate the impact of channel estimation error and to enhance the robustness of the primary link, an improved power control strategy is then proposed. We also study the tradeoff between the primary user protection and the capacity of the secondary user via computer simulations.

ALLEE-MAC: An Adaptive Low Latency and Energy Efficient MAC Protocol for Wireless Sensor Networks

Energy efficiency is one of the most concerned issues in wireless sensor networks, and periodic listen/sleep mechanism is widely used to reduce energy consumption. But fixed listen/sleep scheme also introduces additional latency in packet delivery and waste of energy for unnecessary idle listening. In this paper, we propose a low latency and energy efficient MAC protocol with an adaptive listen/sleep mechanism, named ALLEE-MAC. Two novel schemes are introduced, one is continual data transmission scheme and the other is early-sleep scheme. For achieving these schemes, a cross-layer design approach is adopted in ALLEE-MAC. Simulations have been done to evaluate the performance of the proposed new protocol, by which we can find out that ALLEE-MAC can really reduce packet end-to-end delay and energy consumption compared with S-MAC/AL.

An energy-efficient relay selection strategy based on optimal relay location for AF cooperative transmission

In this paper, an energy-efficient optimal relay selection strategy which is jointly optimized with the energy-efficient optimal power allocation solution for AF cooperative transmission is proposed. The relay selection criterion is the distance to the optimal relay locations where the minimum transmission power of the source, the relay or their total can be achieved. To determine those most energy-efficient relay locations, a universal algorithm with low computational complexity and easy implementation is also presented in this paper. The simulations are conducted to validate our theoretical analysis. The results show that with the relay selected by the proposed strategy, the cooperative transmission can achieve considerably high energy-efficiency.

Performance Analysis of Multi-User Multi-Round Linear Network Coded Cooperation

This letter presents a novel linear network coded cooperation (LNCC) scheme, called multi-user multi-round LNCC (M2-LNCC), for many-to-one communications in wireless networks. The scheme involves multiple users, each of which has an independent message destined to a common base station (BS). The peculiarity of the M2-LNCC is that, not only the native messages, but also the codewords generated via linear network coding (LNC) in the previous time slots participate in the subsequent LNCC operations. Thus, the LNCC operation is performed for multiple rounds and the benefits of LNCC are further exploited. The closed-form expression for the tight approximation of the outage probability is derived in this letter, and the analyses on the asymptotic outage probability and diversity order are also presented. The analysis results show that the M2-LNCC scheme with M(M ≥ 2) users and N + 1(N ≥ 1) time slots is able to achieve the diversity order MN + 1. Monte Carlo simulations are conducted to verify the correctness of our theoretical analyses.

An improved channel order estimation method for OFDM systems based on MDL criterion

Channel estimation plays an important role in wireless OFDM systems. This paper studies the channel order estimation problem, which aims to estimate the number of paths of wireless channels. We first introduce the traditional channel order estimation method based on minimum description length (MDL) criterion. We find that the traditional method do not perform well when the number of channel samples is small. In order to solve this problem, we propose an improved channel order estimation method, which is also based on MDL criterion. Simulation results show that the improved method has a better performance than the traditional method in terms of estimation precision.