Researches Of Multi-channel Medium Access Control Scheme In Wireless Sensor Networks

With the rapid developments of MEMS (micro-electro-mechanism system), integrated circuits, wireless communication and information networks, wireless sensor networks (WSN), as a new application pattern of sensing&monitoring network and Wireless Personal Area Networks (WPANs), are becoming an academic and industrial research focus in recent years. Integrated with data collecting, processing and communicating, sensor networks are also inexpensive, easy to be placed and environmental adaptive, they have broad prospects in fields of military, environment, medical and family etc. Density and quantity of nodes are high in WSN. How to build a reliable sensor network application on the basis of performances of throughput, latency and energy consumption is a key factor of real sensor network application. The thesis mainly research and design multi-channel Medium Access Control (MAC) schemes in WSN.Firstly, the thesis analyses already existing MAC algorithms and their limitations. Significance of employing multi-channel is indicated. Then it analyses the common problem in existing multi-channel MAC, namely no less than two radios are required for every node, which is difficult to meet, and network cost will increase if so. Based on clustered network topology, this thesis puts forward a Virtual Link based multi-channel MAC scheme named as VL-MAC, which uses TDMA and FDMA. VL-MAC includes channel assignment, intra-cluster communication and inter-cluster communication. TDMA is employed in intra-cluster communication. Intra-cluster nodes exchange data with cluster heads in time-sharing mode. Neighboring clusters own different channels to avoid interference and collision. Several nonoverlapping Virtual Link (VL) are formed in the whole network, and VL is used to transfer inter-cluster data. Virtual MIMO (Multi-Input Multi-Output) mode is employed between Sink and VLs, in this way, severe data collision and interference around Sink can be avoided. Furthermore, this thesis analyses deafness problem and hidden terminal problem in VL-MAC. VL-MAC only requires nodes equipped with single radio, so it is more practical for applications.802.15.4/ZigBee is the most widely used protocol architecture in WSN. The thesis deeply analyses the MAC scheme of 802.15.4/ZigBee, then designs a VL-MAC based multi-channel scheme for it. The scheme is realized by communication primitives and command frames, which are compatible with 802.15.4/ZigBee and easy to code.VL-MAC is simulated at the end of this thesis. Throughput, latency and energy consumption are the main concerns. The results indicates that VL-MAC has high throughput, low latency and low energy consumption. Furthermore, this thesis designs and realizes an 802.15.4 based multi-channel MAC implement experiment for mine environment. Compared with single channel MAC, we can see that multi-channel MAC can increase network throughput when network payload is heavy.