Rising data rates force basestation standards evolution

The growing use of cellular data communications has forced an industry body that defines basestation interfaces to change its specifications to double the datarate between the baseband and RF modules.

The Open Base Station Architecture Initiative (OBSAI) has defined a standard partitioning of a basestation, and the interfaces between those blocks. OBSAI has now adopted the serial form of the RapidIO specification (SRIO) to accommodate data rates of up to 6144Mbit/s on what it calls its RP3 interface, which links the digital baseband to the RF module.

According to Peter Kennington, technical chair of OBSAI, this is important because data rates are rising and basestation manufacturers are trying to keep RF amplifiers close to their antennas to minimise losses. The RP3 interface enables the baseband RF sections to be separated, which in turn enables the RF section to be close to the antenna.

The SRIO standard also enables remote radio heads to be daisychained together, rather than each needing a direct connection back to the baseband equipment, saving on cabling costs. This could be used, for example, to run a number of antennas alongside a stretch of motorway without having to cable each one back to the hut for the baseband equipment.

“This gives a lot more flexibility in terms of deployment,” Kennington said.

He argues that the OBSAI standard has helped innovation in the basestation industry, by creating defined interfaces that create larger markets and more certainty for companies trying to serve sections of the basestation business.

Kennington co-founded Wireless Systems International, which developed digital pre-distortion filters and amplifiers for use in basestations and which was sold on to Andrew Corp in 2002. He said: “If OBSAI had existed at the time it would have made getting the product accepted much easier.”

Work on the OBSAI definition began around the year 2000, when EDGE, CDMA, CDMA 2000 and 3G were the dominant standards. It has already evolved to accommodate WiMax and the next-generation LTE proposals.

Kennington reckons the architecture could be good through until 2020: “Everything takes longer than you think to change.”

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