OBSAI, which stands for "Open Base Station Architecture Initiative", is an initiative created by Hyundai, LGE, Nokia, Samsung and ZTE in September 2002 with the aim of creating an open market for cellular base stations. The idea behind this initiative was that an open market would substantially reduce the development effort and costs traditionally associated with creating new base station product ranges.
The OBSAI family of specifications provides the architecture, function descriptions and minimum requirements for integration of a set of common modules into a base transceiver station. It:
This approach to writing the set of compatibility specifications is intended to provide the BTS integrator with sufficient flexibility to respond to differences in access technologies, configurations, reliability, capacity, etc.
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A Base Transceiver Station (BTS) has four main blocks or logical entities: radio frequency (RF) block, baseband block, control and clocking block, and transport block. The radio frequency module (RFM) receives signals from portable devices (via the air interface) and converts them to digital data. The baseband block processes the encoded signal and brings it back to baseband before relaying it to the terrestrial network via the transport block. Coordination between these three functions is maintained by a control block.
The OBSAI specification seeks to meet its goal for an open market for BTS components by defining interfaces between the four blocks and external interfaces between the "whole base station" and neighboring devices. The architecture elements thus consist of the following:
Most of the industry focus today revolves around achieving lower cost RF modules and power amplifiers (PA), as these two components usually account for nearly 50 percent of the BTS cost. Consequently, OBSAI works to define reference point 3 (RP3) prior to the other reference points to promote more competitive sources in the RF module and PA market.
A SerDes device is a Serialiser/Deserialiser IC. They are usually used in pair to provide PISO/SIPO functionality at high speed link endpoints. These high speed links can be optical, or electrical interfaces (LVDS, fiber).
This is the radio interface between the Base Station and the User Equipment. In WIMAX for instance, this is achieved using an AIR interface based on the Orthogonal Frequency Division Multiple Access technology as specified in the IEEE 802.16-2004 standard.
Common Public Radio Interface (CPRI), an alternative, competing, standard.