Low-cost MIMO real-time demonstrator: concept and first results

In our work, we would like to gain experience on real-world problems of MIMO transmission (e.g., antenna coupling, effects of analog/digital filter accuracy, power consumption, timing, DC offset, channel estimation, TX/RX processing requirements) with a hardware demonstrator as simple as possible. In addition to a quick design and implementation, low overall size is a major goal. To achieve both, we use existing small and low-cost GSM/EDGE modules for the MIMO transmitter and receiver. This paper summarizes the system parameters (e.g., channel bandwidth) as well as the hardware implementation details (e.g., a flexible antenna array setup). It presents MIMO performance measures obtained with the demonstrator (when used as channel sounder) in conjunction with offline MIMO RX processing. In a later stage (not part of this first publication), real-time processing will be implemented (on FPGA and/or DSP), both for open-loop (e.g., STBC, LDC, BLAST) and closed-loop MIMO transmission (i.e., for both long-term and instantaneous channel knowledge at the transmitter). Although somewhat limited due to the narrow GSM/EDGE-like channel bandwidth of about 200 kHz, the results obtained and experience gained with this MIMO demonstrator can be largely applied or scaled to B3G/4G and next-generation WLANs of much wider bandwidth, in particular when based on OFDM (with each subcarrier treated as flat fading).