LTE will bring changes to base station design, giving operators challenges as they start their network planning
"More than any other wireless technology, LTE has the capability to change the face of communications as we know it. That's why our research and development teams have expended considerable effort in the last few years preparing for this point in LTE's development, when the first carriers are preparing for technology trials later this year," said David Kiesling, global product manager for RFS Wireless Infrastructure Solutions.
According to Kiesling, the key question that carriers are asking leading suppliers like RFS is: `Will the technology that we install at the top of the cell tower today need to be changed in the next 12 to 18 months? And what is the lifespan of the LTE hardware and associated systems?'
Forwards and backwards compatibility
One of the major issues facing today's carriers says Kiesling, is how to support the introduction of LTE at the cell site with a minimum of extra real estate and yet ensure that support for legacy wireless technologies – as GSM is rapidly becoming – together with 3G services, is constantly available.
"Then, of course, there is the requirement to future-proof the antenna, diplexers and other base station systems, as end-users change the role that LTE technology plays in their lives," he explained.
These changes, says RFS' global product manager, are likely to involve the displacement of fixed-line broadband with mobile broadband, the possibility of home/office LTE-delivered ADSL solutions and – just to make life interesting – the arrival of femtocells into the transmission equation.
The LTE solutions that carriers install today, says Kiesling, must ensure the highest possible forwards and backwards-wireless capabilities, at the optimum cost, and so ensure that carriers are able to secure a reasonable return on their investment in as short a timeframe as possible.
One of the biggest problems facing carriers as they prepare for trials of LTE technology later this year, or in 2010, will be how to support frequencies at the antenna ranging all the way from 1700 MHz to 2600 MHz.
This is achieved by using broad-band antenna technology and an LTE diplexer at the bottom supporting GSM 1800 and LTE 2600, with the signals combined onto the feeder and sent up into the broad-band antenna. On the receive side of the technology, the antenna can handle the complete wireless spectrum and then the relevant frequencies can be divided out at the base of the antenna.
From a real-estate perspective, says Kiesling, carriers can have the same antenna form factor and cable runs, but have two services operational. This is, he observes, the best solution from an equipment simplicity perspective.
This multi-band approach, he adds, also works for carriers that need support for quad-band operations at the cell tower.
"Traditionally, this would be achieved using separate antennas under a single radome (cover), however each antenna within the radome would still have its own Tx and Rx feeder connectors – meaning that either individual feeders would still be required or that diplexers and combiners would be needed at the bottom and top of the tower to share feeders.
"To support say 900, 1800, 2100 and now 2600 MHz using multiple arrays would lead to eight RF-connectors at the tower top. No carrier can realistically afford eight feeder cable runs per sector," explained Kiesling. Nor is there physically room for eight feeders times the number of sectors to run up most towers. "Using RFS multi-band antennas and our diplexer and triplexer technology, carriers can significantly reduce the number of feeders required," he explained.
RFS' discussions with carriers suggest that the biggest technical hurdles to be faced with effective LTE deployments are in metropolitan (city) areas, specifically the interworking with legacy 2G (GSM) and 3G networks.
In the first phase of metropolitan deployment of LTE, Kiesling predicts that cell reselection (handoff) with a legacy 2G network will almost certainly be required, but real-time handover of a VoIP service between an LTE and a 2G network may not be supported or required at this time.
"Interworking with W-CDMA (2100/900MHz) networks, however, is going to be a high priority. This is especially true in situations where the legacy network is providing a high degree of service continuity in a metropolitan environment, or in areas at the edge of coverage," he said.
Radiocomp, a leading provider of state-of-the-art LTE and WiMAX infrastructure solutions and components, has developed the world's first protocol-agnostic remote radio head (RRH) for mass deployment of LTE infrastructure.
Radiocomp is using PMC-Sierra's PM7832 BRICTM 2 interface controller to implement a unique multi-mode RRH platform that supports both CPRI (v2.1, V3.0, & V4.0) and OBSAI RP3-01 v.4.0 protocols.
"PMC-Sierra's technology enables our LTE and WiMAX remote radio heads, as well as our Local Converter platform for base stations, to support both CPRI and OBSAI RRH protocols. Our Local Converter card seamlessly interconnects to any DSP vendor's solution, making it a key enabler for quick deployment of RRH solutions with new and legacy base stations," says Christian Lanzani, Senior Product Manager for Radiocomp.
"PMC-Sierra's BRIC 2 and BRIC 6 chipsets enable implementation of protocol-agnostic, multi-mode remote radio heads," says Babak Samimi, director of strategic marketing of PMC-Sierra's Communication Products Division. "Multi-mode architectures are the most efficient way to deploy 3G and 4G networks, and we're pleased to be working with Radiocomp to bring this capability to the market."
The benefits of protocol-agnostic RRHs include simplified logistics and greater production volumes, leading to lower cost of ownership for Carriers. "At Radiocomp, our strategy is to simplify radio infrastructure deployment by providing the lightest RRH solution on the market, weighing only 9.7 Kg, and greatly reducing costs," says CEO of Radiocomp, Thomas Noergaard.
"PMC-Sierra is focused on developing industry-leading component solutions for wireless infrastructure, and we share much of the same vision," Noergaard says.