MIMO OFDM Spatial Multiplexing Testbed
MIMO Spatial Multiplexing (SM) is widely used to increase the data rate via wireless channels with no extra time and frequency resources. Multiple symbols are transmitted with multiple antennas from a transmitter at the same time and frequency. The same number of antennas are needed to decode the symbols at a receiver. The data rate can be increased with the number of transmitting antennas. Combined with Orthogonal Frequency Division Multiplexing (OFDM), MIMO SM is one of the key technologies of the state-of-the-art cellular networks such as Long Term Evolution (LTE).
In this project, we implemented a Software Defined Radio (SDR) prototype for the 6×6 MIMO SM. The key features are:
- Six transmitting antennas and six receiving antennas
- OFDM with 128 subcarriers (105 subcarriers are used as data subcarriers.)
- QPSK modulation
- 6×6 zero forcing MIMO SM decoder
- 2.4GHz unlicensed frequency band
Detailed Testbed Description
The prototype consists of twelve National Instruments (NI) USRP-2921s. Each USRP works as a transmitting or receiving antenna. A common reference clock and Pulse Per Second (PPS) are provided by a function generator for synchronization of USRPs. The digital signal processing and USRP controlling are implemented with NI LabVIEW, a widely-used GUI-based software toolkit for digital system design. Two PCs are used: one for the transmitter and the other for the receiver, each PC driving six USRPs. With LabVIEW, the prototype can be easily changed to test platforms for various wireless communication techniques such as Interference Alignment (IA).
Download Software for the Testbed
The software for this testbed and setup instructions are available at this National Instruments web page 6×6 MIMO-OFDM System with NI USRP. This paper describes how to set up the 6×6 prototype, including background on MIMO communication and an explanation of the hardware configuration.
Going Beyond Six Antennas
The spatial multiplexing testbed was extended to 8×8 operation by Erik Luther at National Instruments. You can find more information about this prototype including vi downloads on his page Building an Affordable 8×8 MIMO Testbed with NI USRP.