Implementation of decode-and-forward cooperative communication protocol based on usrps and gnu radio.

摘要

In conventional point-to-point wireless communication, wireless channels may suffer from multipath fading, in which signal attenuation can vary significantly over the course of a given transmission, and thus communication between transmitter and receiver is vulnerable. In recent years, a new paradigm of cooperative communication was proposed and had become a heated topic in the design of wireless networks, such as cellular networks and wireless ad hoc networks. The basic idea lies in cooperative communication is that individual mobile users in wireless networks help each other to send signals to the destination cooperatively. The destination jointly detects multiple copies of the received signals from different cooperative users. Due to the cooperative diversity, the joint detection of the combined signals can be more reliable, and system performance as well as robustness can be significantly improved. The user who helps others forward the information is called a relay. According to the functions of the relay, there are two kinds of cooperative protocols: the relay may first decode the received information and then forward it to the destination as called decode-and-forward (DF) cooperative protocol, or the relay may simply amplify the received signal and forward it as called amplify-and-forward (AF) cooperation protocol. The aim of this thesis research is to implement the DF cooperative communication system based on GNU Radio and Universal Software Radio Peripheral (USRP). Specifically, we focus on a two-user cooperation scheme, one serves as the source node, while the other can be the relay node. The experiments of this model are carried out on GNU Radio, an open-source software development toolkit, and USRPs, computer-hosted software radios. To measure the experiments results, the packet-error-rate (PER) performance analysis is provided for cooperative communications in wireless networks with different configurations, such as various relay positioning, power allocation, payload length and experiment environment. From the simulation results, we can see that the location of the relay plays a critical role in the performance of cooperative communication. The closer the relay to the source, the more transmitter power is preserved; while the closer the relay to the destination, the more receiver power is kept. It is observed that laying the relay near around midpoint of the source and destination will achieve the best cooperative performance. Regarding various power allocation, in a certain low power range, the larger the power is, the better the transmission performance is. However, beyond this power range, different as expected, the less the power is, the better result there will be. This could possibly be caused by the limitation of the amplifier in the USRP boards. Furthermore, with regard to different payload length, the longer the packet is, the more possibilities that the packet is decoded wrong. Finally, tests in different environment show that no matter inside a room, in the narrow hall way, or in open space, the above transmission trend turns out to be the same. The main contribution of the thesis lies in: First, the implementation of the channel estimation based on GNU Radio and USRPs; Second, the design of packet format in order to implement the DF cooperation systems; Third, the implementation of the maximum ratio combing (MRC) and joint decode at the destination. In this research project, we achieve the goal of implementing the DF cooperative communication protocols on the platform of GNU Radio and USRPs, verifying the theoretical performance in books, and learning from experiment results under different scenarios and contributing to the design of DF cooperative communication systems.