038-039-040-041-042-043_EETE-VF

EETE NOVEMBER 2012

DESIGN & PRODUCTS WIRELESS COMMUNICATIONS Optimising mobile networks with MIMO and DAS By John Spindler With the groWth in wireless usage due to smart phones, high signal-to-noise ratio (SNr) are needed. rather than being a tablet computers and a growing applications developer base, detriment to network performance, a multi-path environment is mobile operators are constantly looking for ways to deliver more actually exploited by MiMo processing to increase the capacity capacity in their networks without using precious spectrum or the coverage of the network. the key is that each path must resources. Multiple input/ multiple output (MiMo) technology be independent and look different to the receiver. The differ- is now gaining substantial momentum in wide area mobile ences in the multipath are used to create orthogonal communi- wireless network architectures with the launch of Lte services. cation channels analogous to the orthogonal spreading codes MiMo is a key technology that substantially improves network in CDMA-based systems. in addition to being required for the capacity and data throughput in Lte networks while conserving higher orders of modulation, such as 16-QAM and 64-QAM, a spectrum resources. high signal-to-noise ratio MiMo stands for is also required to prop- “multi-input, multi- erly exploit the MiMo output.” it made its wireless channel, and to first broad commercial allow MiMo systems to appearance in 802.11n algorithmically separate systems. input refers to the multiple spatial trans- the number of transmit- mission paths, which ter antennas and output overlap one another in refers to the number of frequency and time. receiver antennas – see figure 1. SISO mode (sin- An in-building Distrib- gle input, single output) uted Antenna System is the classical mode of (DAS) is ideal for MiMo communication architec- because it provides very ture, where there is one good SNr, and in-build- antenna transmitting and ing environments provide one antenna receiving. a rich scattering environ- ment. MiMo uses multiple transmit antennas and MIMO Types multiple receive anten- there are two major cat- nas. Multi-antenna egories of MiMo – spatial configurations have been diversity, in which the around for years, but same data is transmitted with advances in signal over each of the multiple processing and silicon, paths, and spatial multi- MiMo is now economi- plexing, in which each of cally possible in many Fig. 1: SISO and MIMO modes. the paths carries different small form factor devices data. in 2x2 MiMo with such as handsets and data cards. All practical Lte devices sup- spatial diversity, for example, each of the two antennas is es- port MiMo, as required by the 3gPP standard. While initial Lte sentially transmitting and receiving the same data although the networks use downlink 2x2 MiMo (where there are two transmit data is coded differently and each channel is separable. This antennas and two receive antennas), future Lte systems will use mode is primarily used to improve signal quality or to increase downlink 4x2 or even 4x4 MiMo and even higher dimensions the coverage area. in 2x2 MiMo with spatial multiplexing, a of antenna configurations. LTE Advanced systems will have different stream of data is transmitted over each of the two sub- the nominal ability to use up to 8x8 MiMo downlink antenna channels, and this can increase throughput by a factor of up to configurations and up to 4x4 MIMO in the uplink, although ac- 2x over the single sub-channel throughput as shown in figure 2, tual device implementations supporting these modes may take depending on the SNr of each sub-stream, and the base sta- some years to come to market. tion rate adaptation procedure. For MiMo to work, a rich scattering environment (with many Spatial multiplexing is the mode that really takes advantage different paths between transmitter and receiver) as well as a of the capacity improvement capabilities of MiMo. Provided the MiMo channel quality (i.e. SNr and sub-stream separation) John Spindler is director of product management is sufficiently good, the system throughput can be increased at te Connectivity – www.te.com linearly with the number of transmit antennas without using any 38 Electronic Engineering Times Europe November 2012 www.electronics-eetimes.com


EETE NOVEMBER 2012
To see the actual publication please follow the link above