Implementation of alamouti mimo communication system using usrp/gnu radio transceivers
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With increasing high-data-rate requirements for communication services, multi-antenna MIMO technology has grown as an advanced and effective approach featuring for its high bandwidth-efficiency and high date rate transmission. For example in the 4th Generation cellular standard, networks should support services with transmission rate of 100 mega bit/s for mobile users. In this case MIMO with space-time coding offers a new approach which is robust to channel fading and improves the system capacity. Space-time code is applied to multi-antenna channels for both spatial diversity and time diversity. The data are specifically copied and encoded for multiple transmitting antennas to include more details, while at the receive side, the signals are independently received by each receiving antennas but jointly decoded to overcome transmission errors. In this thesis project, we intend to implement Alamouti Multiple-Input-Multiple-Output (MIMO) system using GNU Radio and Universal Software Radio Peripheral (USRP) hardware. The implementation focuses on the MIMO system with two transmit antennas and two receive antennas, with all the antennas working under same frequency. GNU Radio series software is carried on Linux-based Ubuntu operating system and the hardware in this implementation is USRP2 with RFX 2400 daughter board and VERT 2450 antennas. The performance of the implementation is evaluated by measuring bit error rate and bandwidth of multiple channel impulse response with various configurations such as topology of transceivers, transmitting power and data frame structure. The experiment results show that the performance of the system depends on the distance between transmitter and receiver as signals are fading rapidly during the transmission. When the receiver is moved far away from the transmitter, less power will be received. In a certain power range, the larger the power is, the less errors occur. Besides, the structure of data frame also affects the error-rate performance. We observe that the proportion of data bits and pilot bits should be no less than one to preserve transmission power. In this research project, we have achieved the goal of implementing an Alamouti MIMO system on GNU Radio and USRP test platform and our observations have verified the theoretical expectation. The main contributions of this project lie in several aspects. First, we developed some new signal processing blocks on GNU Radio in order to implement the Alamouti-coded MIMO system. Several new blocks, such as Alamouti source block and Alamouti receiver block, are developed and added into GNU Radio library to realize implement functionality. Second, we designed a customized data frame structure with special pilot signal for the system to acquire channel state information. Third, we developed a maximum likelihood detector and joint decoder at the receiver end for the Alamouti-coded MIMO system. The GNU radio signal processing blocks that we developed through this project also enrich the GNU Radio function library which will be beneficial to some other USRP/GNU Radio implementation.