MIMO and Smart Antennas for Mobile Broadband ... - 4G Americas

6.7.13 CONFIGURATIONSThe key element in the TMA is the Low Noise Amplifier (LNA). It is always preceded by a preselectorfilter. Today’s TMAs are universally of the dual duplex type, which allows use in duplexed feeders. Thus,two additional filters are included to pass the downlink and isolate the LNA. Most often, the filterbandwidths cover a full license band but other variants occur, including filters with additional out-of-bandrejection to improve BTS interference immunity.A TMA can be a single band device as above. Increasingly, single-band TMAs are provided as integratedpairs in dual, or twin, assemblies in order to reduce cost, weight, and the number of devices on the tower.Dual band TMAs combine two single band TMAs in one device. There may be a separate RF path foreach band or they may be diplexed into a single path at the BTS port and/or ANT port. Diplexers canalso be integrated with single band TMAs creating units with non-amplified RF paths often referred to asbypass or pass-through configurations.Deployment of additional license bands is leading to further consolidation into TMAs supporting morethan two RF paths and frequency bands, again driven by efforts to avoid additional units of towermounted equipment.6.7.14 ENHANCED FEATURES — AISGThe Antenna Interface Standards Group (AISG) is an organization whose membership includes themajority of leading wireless equipment manufacturers and many major wireless operators. Since itsfoundation in 2001, AISG has driven the development of a protocol for communication between basestations and tower top equipment, including antennas, TMAs, and other devices. The universally adoptedAISG protocol facilitates control and monitoring of functions such as antenna down tilt and TMA alarms.Early implementations utilized separate cables for the connection between base and tower. Morerecently, a system is increasingly favored where the signals are borne by a 2 MHz carrier on one or morefeeder cables. The components in the RF path must then be designed for compatibility with AISGcommunication whether they process the signals or simply pass the low frequency carrier. For example,crossband couplers may have DC and control signal bypass or block on one or more of their branches.The AISG protocol provides a platform for implementation of advanced features in tower top equipment,allowing better performance optimization and diagnostics while ensuring interoperability between anydevices supporting the standard. Adding remote connectivity to the AISG system will also reduce thefrequency of site visits, having beneficial impact on the operating budget.4G Americas MIMO and Smart Antennas for Mobile Systems – October 2012 – All Rights Reserved113