The Study On Energy Conservation And Cooperative Relay Schemes For Ultra-wide Band Wireless Sensor Networks

To satify the QoS (Quality of Service) of the traffic transmission and to combat wireless propagation environment's negective effects on wirelss transmission, it is now highly necessary for wireless sensor networks (WSNs) to employ novel methods to realize reliable services, effective coverage and efficient transmissions. Power control is an efficient energy conservation method, which aims to cutting down the power overhead to achieve energy saving and prolonging sensor's lifetime. Wirelss cooperative relay technology has been regarded as a promising way to improve wireless communication systems'perfromances. Due to the adventages of the signal forwarding function at relays, the coverage on the regions with poor signal strength can be improved and blind spots can be covered by using wirelss relay and cooperation technology, which results in the improved systems'throughput, especially for the cell-edge and blind-spot users. Movitated by the the important role and potential commercial value in the future networks, industry and academia have carried out extensive and deep researches on wirelss relay and cooperation technology, the standardli-zation work of which has achieved substantial progresses.First, a comprehensive survey on the development history, network characteristcs of WSN, and the research status of the energy conservation in WSNs is presented. Next, the development history of wirelss cooperative relay technology is reviewed, and then the research status and issues in this field has been analyzed.In this work, two items are mainly focused on: energy conservation scheme and cooperative relay technology. As observed that the characteristic of UWB signal fading obeys Log-normal distribution, all the performance modeling and anlysis of wirelss coopera-tive relay systems are carried on over Log-normal fading channels.A cluster-based power control scheme for UWB WSNs was proposed under the consideration on the unique properities of WSNs and UWB technology. Also, the implement-tation scheme and implementation cost have been introdced.As it is easy to see that the researchers alway asume that the object systems work in normal fading environments, such as Rayleigh fading channels, ingnoring the effect of large-scale fading in outdoor scenarios and the shadowing in both in/outdoor scenarios. As observing there are some insuffieieneies and limitations among the existed works, the performance of various adaptive transmission schemes, time hopping ultra-wideband (TH UWB) two-ways wirelss relay systems, multi-relay TH UWB wireless cooperative relay systems, multi-hop chain relay systems and multi-branch multi-hop relay system over Log-normal fading channels have been studied, respectively. The main contributions of this work are listed as follows:1. Analytical models to estimate the capacity of log-normal channels are presented for three adaptive transmission schemes:(i) optimal simultaneous power and rate adaptation,(ii) optimal rate adaptation with constant transmit power, and (iii) truncated channel inversion with fixed rate. Closed-form approximation expressions for capacity under these adaptive transmission schemes are derived.2. An accurate analytical model is proposed to study the performance of threshold digital relaying schemes in cooperative systems over log-normal fading channels. The analytical expression for the average end-to-end bit error rate has been derived.3. An analytical model was proposed to study the performance of cooperative links for TH UWB systems under two relay models:amplify-and-forward (AF) and decode-and-forward (DF). The effects of multiuser interference are considered when deriving closed-form expressions for outage probability and average bit error probability (ABEP).4. The outage behavior of the relay-based communication channel of TH UWB systems was studied. Specifically, outage probability and ε-outage capacity in single relay network scenarios and outage probability in multiple relays network scenarios have been analyzed, respectively. The simulation and numerical results show that increasing transmission power is not an efficient way to improve outage probability due to the effect of multi-user interference at relays and the destination.5. Analytical models have been proposed for studying the performance of AF relaying multi-branch multi-hop wireless relaying systems (M2WRS) over Log-normal fading channels. The presented analytical models are for estimating the end-to-end performance of the M2WRS with maximal ratio combining (MRC) and selection combining (SC) schemes. In particular, the closed-form expressions for the parameters of the distribution have been derived for the end-to-end SNR of an AF relaying multi-hop chain link. Then, Accurate analytical expressions have been developed for ABEP, outage probability and ergodic capacity under MRC and SC schemes, respectively. Finally, a theoretical model for the end-to-end bit error rate (BER) performance of DF relaying multi-hop chain systems (MCSs) has been proposed. The expression of the end-to-end BER has been derived and can be used to estimate the end-to-end BER of DF relaying MCSs.