Design And Implementation Of Non-Real-time MIMO Testbed

MIMO (Multiple Input Multiple Output) technology, collaborated with Orthogonal Frequency Division Multiplexing (OFDM), has become the most promising approach to satisfy the demand of high-speed multimedia access and already been accepted as an option in several next-generation wireless communication standards, such as LTE and WiMAX. Extensive researches on multiple-antenna transmissions, which provide high spectral efficiency as well as signal reliability, have already been undertaken for years. Due to the highly unstable wireless environment and sophisticated transmission conditions, the simulation results might not always be able to illuminate the real performance of the simulated algorithms. As a result, testbeds, which enable signals to be propagated through real environment, are widely developed by several research institutes and universities in recent years.Categorized by the targets of measurements and analysis, MIMO testbeds could be divided into two types. One is called real-time testbed, on which the process speed of the signals are faster than the transmission rate. It guarantees that the signals could be generated and transmitted continuously. These testbeds have been established. Under most circumstances, baseband processes run on Digital Signal Processors (DSPs), while up/down conversion is realized in Field-Programmable Gate Array (FPGA). After successfully verified by FPGA+DSP, the communication system under test could be turned quickly from FPGA to Application Specific Integrated Circuit (ASIC), so real-time testbeds are used to drive the industrial development of new technical trends. On the contrary, the other type, nonreal-time testbeds aim at providing performance evaluation prototype in which baseband algorithms are often realized in the simulation software (e.g. Matlab), and up/down conversion are accomplished by industrial products. The signal processes are easy to modify or update, so the purpose of establishment of nonreal-time testbeds is verification of immature baseband processing methods. The drawback is that the processing speed is unrealistic to satisfy the demand of continuous transmissions. Platforms of this type are considered as a necessary phase of approaching real-time testbeds.However, the interface between hardware and software involves inconvenient parameters exchanges and low-level programming, which makes it difficult to make full use of the platform. In order to use the testbed efficiently and in a straightforward way, it is desirable to design a friendly and flexible user interface for the testbed, so users can concentrate on researches and the testbed can accommodate a variety of baseband algorithms.In this paper, a general-purpose nonreal-time 4x4 testbed is proposed. This testbed is accessible remotely through the Internet and aims at evaluating baseband algorithms. Details of the realization are hidden from users by DLL (Dynamic Link Library) and theories under evaluation are implemented in MATLAB, so accessing the MIMO propagation channels with little knowledge of the testbed becomes possible. What's more, flexible configurations of the interface lead to a thorough exploitation of the hardware, so a large number of techniques could be verified from the testbed, such as the physical layer technique MIMO-OFDMA in standard IEEE 802.16e. The whole procedure of upconversion, transmission through real wireless environment and downconversion is hidden by the interface, so after generation of baseband samples, users can access the testbed in their own computers simply by calling a MATLAB function.