Multiple Input Multiple Output (MIMO) Systems in Digital Wireless Communications
One of the limiting and most costly resource in current and future communication systems is the bandwidth. Therefore, there is a strong need for techniques that aim at better exploiting the available spectrum. MIMO systems are a promising approach to increase the data rates maintaining the channel bandwidth. In this technology, multiple antennas are employed at the transmitter (Tx) and at the receiver (Rx), resulting in a communication channel with multiple inputs and multiple outputs (MIMO).
One possible realization of a MIMO system employing two antennas at both, the transmitter and the receiver, is illustrated above. A stream of bits is demultiplexed into two substreams (spatial multiplexing), each is sent over a different antenna. The two signals superpose each other at any Rx antenna. The receiver seeks to reconstruct the genuine transmitted sequences. Under the assumption of independent subchannels between all Tx and Rx antennas only half of the spectrum that would be required by a single input single output system will be occupied. The Bell Labs have demonstrated in their BLAST project that enormous capacities are achievable in practice, at least over benign MIMO channels.
As already mentioned, MIMO systems that employ spatial multiplexing aim to increase the data rate. However, MIMO systems that make use of a technique called space time coding can exploit the spatial diversity of the MIMO channel and, thus, increase the link quality. Therefore, MIMO systems can offer an increased data rate, increased reliability, or a trade-off between both.
At ISS the goal of the algorithm group is to contribute to and advance knowledge in this area. Research focuses mainly on the following aspects of MIMO systems:
- Exploiting Multiuser Diversity in a Packet Data Multiantenna Downlink (current project)
- Capacity of MIMO Channels with Channel Estimation/Synchronization (former project)
- Space-Time Processing (Synchronization and Detection in MIMO Systems) (former project)
Martin Senst, Meik Dörpinghaus, Markus Jordan