Research On The Application Of MIMO Technology In Wireless Ad Hoc Networks

Wireless Ad hoc networks have found wide application in wireless communication systems, especially in military communication and broadband wireless communication systems. On the other hand, Multi input Multi output (MIMO) is one of core technologies in future wireless communication system. Its main features can greatly improve the performance of wireless Ad hoc networks, such as network throughput, delay, fairness, coverage, reliability and so on. Especially the capabilities of parallel transmission and multi-packet reception,MIMO can increase the number of communication links by the PHY way. Therefore, it is significant to the tactical communication. Even it may change the communication modes of communication equipments in active service. In this thesis, we firstly make a summary of the main ways to obtain the performance improvement of Ad hoc network by MIMO and show the primary questions needed to be answered and the key technologies applying MIMO to Ad hoc networks. We investigate the problems of utilizing spatial diversity, spatial multiplexing and interference suppression of MIMO in Ad hoc networks. Through in-depth study and a mass of simulations, we achieved the following contributions and innovations:1. Proposes and verifies an improved capacity model of MIMO Ad hoc network with parallel communiatingMIMO can increase the number of communication links by interference suppression in a neighbor of wireless Ad hoc networks. It makes the parallel transmission of MIMO a promising candidate for wide use in tactical Ad hoc networks. Up to now there is only one model analyzing the network capacity operating on parallel transmission mode equipped with MIMO allover the network. But its network model is ambiguous. It is lack of the necessary propagation model and constraints of actual networks. This thesis proposes an improved mathematic model of network capacity, in which we introduce a classical propagation model to analysis the effect of the distance between transmitter and receiver and the distance between excepted receive node and interference node on the network capacity. This is the first model which considers the effect of the total area of the network, average density of nodes, distance between nodes and power threshold of receiving successive packet. These considered factors enable the new model to reflect the changes of channels and networks. By the way, the veracity of capacity model is improved significantly.2. Evaluates the effects of diversity gain on hidden terminal and exposed terminal problem in Ad hoc network for the first time and achieves the optimal application modes for different performance choices At present, most of the researches on spatial diversity are focused on the physical layer without taking into consideration the intricacies of a network-wide deployment. The thesis analyzes the improvement of main performance index of mobile Ad hoc networks (MANET) by diversity gain including transmission bit rates, delay, coverage, routing efficiency and throughput. The effects of diversity gain on hidden terminal and exposed terminal problem in Ad hoc network are evaluated for the first time. We discuss the trade-offs between coverage and bit rates improved by the diversity gain of MIMO. Simulation of the total network is performed with employing traditional MAC and route protocols. The optimal application modes for different performance choices are achieved from the simulation results employing different network parameters. These conclusions can provide helpful guidance in designing operation scheduler of network and adaptive transmission strategy.3. Proposes a novel MAC protocol employing the multi-packet reception (MPR) of MIMOTraditional MAC protocols allow only one pair of communicating nodes in a neighborhood of single-channel Ad hoc networks. Now the SM of MIMO provides a new way for MAC design. We propose a novel MAC protocol employing the multi-packet reception (MPR) of MIMO. In this protocol, exchanges of RTS/SCTS control packets are used to reserve the physical channel. The channel reserve, finite state machine and operation of this protocol are introduced in detail. Furthermore, we present the theory models of normalized saturation throughput for the new protocol. Multipoint-to-point communication is realized in a neighborhood of Ad hoc networks. This is a new communication mode which can speed up the collection and transfer of battlefield information in tactical Ad hoc networks.4. Proposes a novel method to slove the variance problem of coarse timing synchronization for OFDM systemsDuring the implementation of protocols utilizing the parallel communication and MPR of MIMO, the timing synchronization is a prerequisite for successfully detecting. For the study on timing synchronization of MIMO-OFDM used in the distributed Ad hoc networks, this thesis begins with the timing synchronization of OFDM system. With consideration of the timing variance problem, we propose a new method to reduce the variance based on geometry character of synchronization metric. Because of the introducing of an infinitesimal, this method significantly improves the performance of timing synchronization in multi-path channel.5. Proposes a timing synchronization algorithm based on orthogonal variable- period sequences for MIMO-OFDM system in distributed Ad hoc networks For the application of MIMO-OFDM transceiver in distributed Ad hoc networks, we propose a timing synchronization algorithm which presents a novel design method of timing synchronization training sequences, so called"orthogonal variable-period sequences". The training sequence structure of every transmitting antenna is formed with several variable-period modulatable sequences which are taken from different orthogonal sequences. This method can effectively eliminate multi-path fading and Multiple Antennas Interference (MAI) and greatly improves the performance of timing synchronization in multi-path channel. The proposed algorithm solves the problem of very low probability of correct fine timing in traditional synchronization algorithm under multi-path channel.