Energy-Efficient Collaborative Communications for Wireless Sensor Networks
In this thesis an energy efficient collaborative communication system for wireless sensor networks is presented in order to reduce the energy consumption of wireless sensor networks in the presence of AWGN and Rayleigh fading without decreasing the quality of service of data transmission. Due to the reduction of energy consumption of wireless sensor networks, the life time of sensor networks is extended. In collaborative communications, a set of transmitter nodes transmits the same data at the same time towards a common receiver, denoted as the base station, where the received signals are combined coherently. A coherently combined signal at the receiver indicates that a large amount of transmitted power is combined; this is referred to as constructive interference. As a result of this constructive interference, collaborative communications produce a substantial power gain, as well as a considerable reduction in bit error rate and a significant gain in capacity. The main focus in this thesis is on theoretical aspects of the development of a collaborative communication system. The key factors that degrade the performance of collaborative communication systems i.e., phase, frequency and time synchronization errors, are identified. A synchronization process is designed to reduce the phase and frequency synchronization errors among the collaborative nodes and the base station. The theoretical model of the collaborative communication system with imperfect phase and frequency synchronization in the presence of AWGN and Rayleigh fading is proposed, modelled, theoretically analyzed and simulated. The performance of collaborative communication system is evaluated by investigating several figures of merit. The considered figures of merit are received power, bit error rate, energy efficiency and channel capacity. The theoretical findings of the collaborative communication system are verified using Monte Carlo simulation by considering the parameters of off-the-shelf products i.e., CC2420 and AT86RF212. Closed form expressions are derived for the received power as a function of number of collaborative nodes, bit error rate (BER) as a function of SNR (Eb/N0) and channel capacity as a function of signal to noise ratio and the number of collaborative nodes. To analyze the energy efficiency of the proposed collaborative communication system, the energy consumption of the collaborative communication system is modelled, simulated and analyzed. The analytical and simulation results showed that the proposed collaborative communication system produces significant power gain, a reduction in BER and significant capacity gain in the presence of phase errors, frequency errors, AWGN and Rayleigh fading. A detailed theoretical analysis and Monte Carlo simulation revealed that the proposed collaborative communication system is an energy efficient communication system that can be implemented in sensor networks, as approximately N (number of collaborative nodes) times less the total transmitted power is required than for the single input single output (SISO) communication for a specifies transmission range.
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