Cellular

 

The AWS RF challenge
The AWS band is the highest frequency allocated to-date by the FCC for cell-based wireless applications; its total span—from 1710MHz to 2155MHz—is enormous. AWS is provided as paired spectrum, with the uplink allocated to the 1710 to 1755MHz band, and downlink to the 2110 to 2155MHz band. A huge 355MHz gap separates the pair.
This gap makes AWS spectrum unique. “The total AWS uplink and downlink stretches from 1710 to 2155MHz, representing a 25 percent bandwidth. Accommodating this is a huge challenge for a base station antenna,” Kiesling says. “Simple physics imposes slightly different antenna RF behavior at the lower and upper ends of this band. So, for optimum network performance it’s essential that the uplink and downlink are balanced. When the AWS auctions were first announced, there wasn’t a single antenna on the market that met these requirements.”
A focused development program by the RFS team resulted in the Optimizer ‘S-series’ AWS/Personal Communications Service (PCS) broadband base station antenna, specifically designed to provide the closest performance matching of AWS uplink and downlink. The outcome is an azimuth horizontal beamwidth difference of less than seven degrees between uplink and downlink; and a gain difference of less than 1dB.
The new band also presents unique transmission attenuation challenges. “The broadband wireless data applications planned for the AWS band demand maximum signal-to-noise ratios and minimal bit error rate (BER),” says Larry Heisler, RFS Director of Marketing and Product Management. “At the band’s elevated frequencies, transmission line attenuation will be an important factor in ‘link budget’ calculations, impacting on BER and signal-to-noise. Achieving premium attenuation— particularly in the downlink—is critical.”
RFS’s low-attenuation transmission line solution is its CELLFLEX ‘A’ Premium Attenuation transmission line. CELLFLEX ‘A’ offers attenuation improvements of up to eight percent, in cable diameters of 7/8, 1-1/4 and 1-5/8-inch. Most importantly, it retains its mechanical integrity with no concession on crush strength.

Tackling the overlay
The AWS spectrum will mostly be deployed as part of an overlay strategy; meeting the time-to-market objective is the over-riding consideration, Kiesling explains. “Taking advantage of as much existing infrastructure as possible minimizes capex, and reduces roll-out time. But, ensuring minimal interruption, or impact, on the QoS of existing services is also essential.”
A further issue—both from a site zoning/planning permit and vertical real-estate rental opex perspective—is to provide compact tower-top overlay solutions of a size and weight equivalent to existing single-band equipment. RFS’s ‘quad’ polarized Optimizer S-series antenna fits the bill. “Using this antenna [in an AWS/PCS overlay] you are able to retain the same number of antennas on a sector, with PCS on one side and AWS on the other,” says Kiesling. “From a zoning perspective this is a huge benefit!”
RFS offers similar ‘two-in-one’ AWS advantages with its new range of dual-duplex AWS tower-mount amplifiers (TMAs). Complementary to the Optimizer ‘S’ series, these TMAs are available in either dual AWS band,or dual-band AWS/PCS. Compact and high-performance, they provide the essential uplink amplification required in broadband wireless data services. These AWS TMAs show particularly low loss at both mid-band and band-edge, assuring QoS.
Rounding out these offerings are RFS tailored filter solutions to address co-location interference that may occur in AWS band overlays. Similarly, the company is developing diplexer solutions to permit feeder sharing.
Lastly, a nationwide overlay deployment demands streamlined logistics—a tightly coordinated network of delivery centers providing the correct RF solution-sets, to the right locations, at the right time. “Speed of network roll-out is ultimately dependent on supply logistics—an area where RFS excels, both in the US and abroad,” Kiesling says. One solution used successfully by RFS is base station ‘kitting’. The RFS AWS kitting solution will bundle together all RF elements required for a particular base station site—antennas, TMAs, cut-to-length transmission line, connectors, jumpers, and other accessories—for practical