Open Base Station Architecture Initiative

The Open Base Station Architecture Initiative (OBSAI) was a trade association created by Hyundai, LG Electronics, Nokia, Samsung and ZTE in September 2002 with the aim of creating an open market for cellular network base stations. The hope was that an open market would reduce the development effort and costs traditionally associated with creating base station products.

Goal

The OBSAI specifications provided the architecture, function descriptions and minimum requirements for integration of a set of common modules into a base transceiver station (BTS). It:

• defined an internal modular structure of wireless base stations.
• defined 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.
• defined internal digital interfaces between BTS modules to assure interoperability and compatibility.
• supported different access technologies such as GSM, Enhanced Data Rates for GSM Evolution (EDGE), CDMA2000, WCDMA or IEEE 802.16 marketed as WiMAX.

This was intended to provide the BTS integrator with flexibility. A version 2.0 system reference document was published in 2006.

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 definined interfaces between the four blocks and external interfaces between the "whole base station" and neighboring devices. Architecture elements included the four functional blocks mentioned above. An external network interface is defined 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 WiMAX systems. An eternal radio interface is between the BTS and subscriber devices. Examples are Uu or Um to the user equipment (UE) for 3GPP systems or R1 for WiMAX. Internal interfaces between the functional blocks are called 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 at the time revolved 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.

Reference point interfaces

R1 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.

See also

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

External links

• OBSAI RP3 Specifications v2.0