Obsai

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Contents 1 INTRODUCTION 2 BTS Structure 3 RP3 interface 4 SERDES 5 R1 Interface 6 REFERENCE

[edit] INTRODUCTION

OBSAI stands for "Open Base Stations Standards Initiative". It is an inititative created by Hyundai, LGE, Nokia, Samsung, and ZTE in September 2002. It aims to "...create 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 that have been 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 (BTS). 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 IEEE802.16/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.

[edit] BTS Structure

A 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 transmitting it to the terrestrial network via the transport block. Coordination between these three functions is maintained by a control block.

OBASAI specification seeks to meet its goal for an open market for Base stations componenets by definning interfaces between the four block and external interfaces between the "whole base station" and neighbouring devices. The architecture elements thus consists of the following:
- Functional Blocks (the four entities seen previously)
- External network interface. This defines the interface between the Base Station 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 802.16/WIMAX systems.
- External radio interface, between the Base Station and the suscriber devices. Examples are Uu or Um to the User Equipment (UE) for 3GPP systems or R1 for IEEE802.16/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. 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 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.

[edit] RP3 interface

The OBSAI Reference Point 3 (RP3) specification defines the interface between the Baseband module and the RF module of a base station. It does specify a maximum of 9 pairs of unidirectional links for every RF and baseband module.
The specification allows for line rates of i*768 Mbps, i=1, 2, 4.
This is achieved by using an Optical link between the BaseBand Module and the RF module.

[edit] SERDES

A SerDes device is comprised in the Baseband Module. This is the device to which the optical link is connected to in order to achieve the high rate between the Baseband Module and the RF unit.

[edit] 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.

[edit] REFERENCE

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