There has been a growing interest in multiple-input/multiple-output (MIMO) technologies in recent years, as demonstrated by the adoption of MIMO and multi-user MIMO (MU-MIMO) in new wireless standards.
One example is 802.11n, which provides 750 Mbps of throughput over 80 MHz of bandwidth by using two to four transmit antennas. Such small-scale MIMO systems, with their limited number of antennas, do not exploit the potential of large spatial dimensions that MIMO can offer. Hence, they typically achieve a spectral efficiency of only around 10 bps/Hz.
The goal of MIMO and space-time coding is to achieve maximum transmit diversity (full diversity), which can result in significantly higher transmission rates over limited bandwidth. The promise of many-antenna base stations or large MIMO systems is to improve spectral efficiency by a factor of 10 (or more).
Researchers working on multi-Gigabit local area networks in the 5 GHz and 60 GHz bands, in the evolution of WiFi standards (IEEE 802.11ac and 802.11ad), as well as in the LTE-Advanced and WiMAX (IEEE 802.16m) standards, all share a common belief that systems with higher channel counts (12 × 12, 16 × 16, 24 × 24, or 32 × 32) must be considered.
One reason for this is that large MIMO-based approaches score higher on spectral efficiency than traditional approaches focused on just throughput improvements (e.g. increasing QAM order). The need for more spectrum is an industry-wide problem. While large MIMO won’t solve this problem by itself, it will likely be part of the solution for many future technologies that are currently being developed.
Real-world channel measurements, efficiencies of real-time channel estimation for larger numbers of channel coefficients, precoding techniques, antenna design and calibration – these are all topics that are being studied from a large MIMO perspective.
Nutaq provides researchers and engineers with hardware platforms and rapid prototyping tools that enable them to implement and test their algorithms in real-world scenarios with real-world data. In a previous blog post, we looked at Nutaq’s small-scale MIMO platform, the PicoSDR with support for 2×2 and 4×4 MIMO. In other blog posts we covered larger-scale MIMO systems, called massive MIMO, for future applications (e.g. 5G base stations) where the channel count is expected to exceed 100 transmit and receive channels.
This blog series will look at Nutaq’s hardware platform, the MicroSDR-420, for large MIMO systems (12×12, 16×16, and 32×32), enabling scientists to work on large MIMO and the evolution of existing standards. Stay tuned!