| Wireless sensor networks (WSNs, Wireless Sensor Networks) are emerging technology, which blends computer, wireless communication, sensor, and automatic control, information processing, artificial intelligence, MEMS and other disciplines. WSNs have been widely applied to the military, environmental science, smart home, medical, space exploration and other fields due to the advantages such as large-scale, simple to deploy, low power consumption, dynamic topology, self-organization and scalability. WSNs are data-oriented ubiquitous networks. The purpose of deploy and use of that is to gathering information of the monitoring object, and sending the useful data to far end users in real time by multi-hops. In this transmission link with many hops, there are the uplink monitoring data and downlink control, management data, distribution tasks of the system at the same time. WSNs are often deployed in harsh environments, and the reliability of data transmission is greatly affect by the state of communications link and the interference of the transmission data of other nodes, and the impact is more obvious with the increase of the hop. The data of multiple nodes gathering in a node may result in congestion, increasing network delay and reducing system capacity. In addition, the sensor nodes are battery-powered which are difficult to be replaced. Once the power of the sensor nodes is running out, the function of the whole network will be affected. To the above problems, this thesis studies the reliable and efficient two-way multi-hops data transmission technology based on multi-hops clustering transmission model of WSNs, and has the advantages of energy efficiency and small delay. The main works in this thesis are as follows:1) The author studies and analyses the transmission system model based on virtual multiple-input multiple-output (VMIMO) technology in multi-hops clustering in wireless sensor networks, especially the reliability, energy consumption and throughput of the MIMO system. Considering the characteristics of WSNs such as the need to transfer large volumes of data and the limit of energy, the author regards MIMO as suitable for WSNs due to its advantages such as high reliability, low energy consumption and simple decoding.2) Space-Time Block Coding (STBC) technology can fully make use of the independent single-input single-output (SISO) transmission path in the MIMO channel to get the spatial diversity, and thus improves anti-fading capability of the wireless system and significantly expand system capacity. The thesis studies the OSTBC (Orthogonal Space-Time Block Coding) in the STBC. OSTBC quadrate encode the transmitted data at the transmitter, thus the transmitter can achieve diversity without channel information, and the simplicity for the receiver to decode makes it widely used in practice. But OSTBC has a disadvantage:when the number of transmit antennas are more than2, the data can not get the full rate transmission, and the spectral efficiency is low. So this thesis puts forward an improved algorithm of OSTBC, that is, when the number of transmit antennas is four the system can still achieve full rate transmission.3) In multi-hops relay networks, intermediate nodes simply forward and enlarge the data, while Network Coding (NC) allows intermediate nodes to encode and send the received data. The use of NC can significantly reduce network latency, improve the BER performance and expand system capacity. The thesis studies network coding and its principles. With the characteristics of infinite sensor networks, the author integrates network coding and virtual MIMO technology, and forms a new transmission mode. The simulation results shows that the Virtual MIMO transmission technology combined with Network Coding can not only maintain the advantages of MIMO such as diversity, low energy consumption and resistance to multipath fading, but also can achieve the advantages of NC such as low time delay, high reliability and large capacity. |
PDF Full Text Request