OBSAI

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:

• defines an open, standardized internal modular structure of wireless base stations.
• defines a set of standard BTS modules with specified form, fit and function such that BTS vendors can acquire and integrate modules from multiple vendors in an OEM fashion.
• defines open, standards-based internal digital interfaces between BTS modules to assure interoperability and compatibility.
• supports different access technologies such as GSM/EDGE, CDMA2000, WCDMA or IEEE 802.16/WIMAX.

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.

BTS structure

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:

• Functional Blocks (the four entities seen previously)
• External network interface. This defines the interface between the BTS and the operator network. Examples are: (lub) to the Radio Network Controller (RNC) for 3GPP systems, R6 to the Access Services Network Gateway (centralized Gateway) or R3 to Connectivity Services Network (CSN) for IEEE 802.16/WIMAX systems.
• External radio interface, between the BTS and the subscriber devices. Examples are Uu or Um to the User Equipment (UE) for 3GPP systems or R1 for IEEE 802.16/WIMAX.
• Internal interfaces between the functional blocks known as Reference Points (RP). RP1 is the interface that allows communication between the control block and the other three blocks (RP1 also specifies UDPCP - UDP based reliable communication protocol). RP2 provides a link between the transport and baseband blocks, while RP3 connects the baseband and RF entities. RP4 provides the DC power interface between the internal modules and DC power sources.

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.

SerDes

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).

R1 interface

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.

References

• OBSAI Systems Specifications v2.0
• OBSAI RP3 Specifications v2.0

See also

Common Public Radio Interface (CPRI), an alternative, competing, standard.