In-building systems adopt MIMO

3rd October 2012

ES Admin

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An in-building Distributed Antenna System (DAS) is ideal for MIMO because it provides very good signal-to-noise ratio, and in-building environments provide a rich scattering environment. There are two major categories of MIMO – spatial diversity, in which the same data is transmitted over each of the multiple paths, and spatial multiplexing, in which each of the paths carries different data.

In 2x2 MIMO with spatial diversity, for example, each of the two antennas is essentially transmitting and receiving the same data although the data is coded differently and each channel is separable. This mode is primarily used to improve signal quality or to increase the coverage area. In 2x2 MIMO with spatial multiplexing, a different stream of data is transmitted over each of the two sub-channels, and this can increase throughput by a factor of up to 2x the single sub-channel throughput, depending on the SNR of each sub-stream, and the base station rate adaptation procedure.

Spatial multiplexing is the mode that really takes advantage of the capacity improvement capabilities of MIMO. Provided the MIMO channel quality (i.e. SNR and sub-stream separation) is sufficiently good, the system throughput can be increased linearly with the number of transmit antennas without using any additional spectrum resources. Given the scarcity and cost of the wireless operator’s spectrum, improving the spectral efficiency is a critical goal for improving the overall financial operating margins for the wireless operator.

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You can read the rest of this article in the September issue of Electronic Specifier Design by clicking here.