In this series:
Designers face a number of challenges when working with wireless communication technologies. These include the limited availability of radio frequency spectrum and complex time-varying wireless environments. Different innovative techniques are being proposed to meet the increasing demand for higher data rates, better quality of service (QoS), fewer dropped calls, higher network capacity, and improved user coverage. These techniques all involve improving spectral efficiency and link reliability. The use of multiple antennas at the receiver and/or transmitter in a wireless system, popularly known as multiple-input multiple-output (MIMO) communications or smart antennas, is an emerging technology that promises significant improvements in these areas.
The inspiration behind MIMO communications originates from the human body: two eyes, two ears, etc. With multiple eyes, we can improve our vision range and depth perception. Similarly, two ears improve sound quality by providing two correlated sound signals. In the same way, we can increase the throughput of a communication system by using MIMO devices. However, everything comes with a price. In this case it means increased signal processing power requirements and complexity. Luckily, the impressive evolutionary improvements of FPGA and DSP processors mean we are more than happy to pay these prices.
Multiple antennas can be exploited to leverage different advantages. The average increase in the signal-to-noise ratio (SNR) at the receiver that arises from the coherent combining effect of multiple antennas at the receiver or transmitter (or both) is called “array gain”. Array gain is the improvement in the average received SNR over a standard single-input single-out (SISO) link. Diversity can be exploited when multiple copies of the same signal are transmitted and/or received independently. If the multiple channels are statistically independent, then a maximum degree of diversity gain is available. Spatial multiplexing (SM) offers a linear (the number of transmit-receive antenna pairs) increase in the transmission rate (or capacity) for the same bandwidth and with no additional power expenditure.
Physical beamforming and eigen-beamforming exploits multiple antennas to reduce interference. Interference reduction can be implemented at the transmitter where the goal is to minimize the interference energy sent towards the co-channel users while delivering the signal with high quality to the desired user. Interference reduction enables the use of aggressive frequency re-use factors and improves network capacity.
Nutaq provides a wide range of products that support these functionalities. The PicoSDR wireless development platform can be used as a compact MIMO 2×2/4×4 solution, covering a wide frequency range. This solution comes with a QAM64 orthogonal frequency-division multiplexing (OFDM) reference design, giving you a head start in the development of high-efficiency waveforms. To learn more about the PicoSDR platform, visit http://www.nutaq.com/products/picosdr.