Browse Prior Art Database

TRANSMISSION OF HIGH STABILITY CLOCKS OVER HDSL

IP.com Disclosure Number: IPCOM000008788D
Original Publication Date: 1998-Sep-01
Included in the Prior Art Database: 2002-Jul-12
Document File: 3 page(s) / 161K

Publishing Venue

Motorola

Related People

Richard Lane: AUTHOR [+6]

Abstract

This document describes the application of the HDSL data transmission standard in a GSM Picocellular application. In this application the use of HDSL is novel in that the communication link not only transmits data but is also used to distribute a high accuracy GSM reference clock.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 45% of the total text.

Page 1 of 3

MOTOROLA Technical Developments

@

TRANSMISSION OF HIGH STABILITY

CLOCKS OVER HDSL

by Richard Lane, Howard Benn, Andrew Gillions, Kevin Hobbis, Naeam Wahid and Terry Dicks ABSTRACT

  This document describes the application of the HDSL data transmission standard in a GSM Picocellular application. In this application the use of HDSL is novel in that the communication link not only transmits data but is also used to distribute a high accuracy GSM reference clock.

ered link clock. The recovered link clock is then used as a reference by frequency synthesizers in the radio transceiver. Similarly, the Motorola I st gener- ation Picocell architecture consists of many remote- ly mounted radio transceiver heads (PCUs) which connect back to a single controller. However, in the case of Picocell, the communication link between PCU and controller can be either optical-fibre or HDSL.


1. HDSL OVERVIEW

   High Data-rate Subscriber Line (HDSL) is an emerging data transmission standard which prom- ises to revolutionize the data transmission industry by allowing relatively high data transmission rates over "unconditioned" copper twisted-pair cables. Current HDSL technology typically allows full- duplex data-rates of 1024Mbps over a single twist- ed-pair and 2048Mbps over two twisted-pairs. HDSL has applications such as El trunk replace- ments, where its key advantages are: the increase in distance between repeaters (from typically <lKm with El to typically 3Km with HDSL) and the abili- ty to use "unconditioned" cables. The term uncondi- tioned refers to cabling with relatively undefined impedance characteristics and which may contain

impedance discontinuities such as those caused by junction-boxes and patch-panels. As its name sug- gests, HDSL is designed for use over standard sub- scriber lines or telephone lines and, therefore, can exploit existing copper-infrastructure which is abundant world-wide.


2.2 CLOCK TRANSMISSION

  The GSM specifications state that the transmit- ted RF carrier signal must have a maximum fre- quency error of 50ppb peak [l] and a maximum phase error of 20" peak [2]. RF signals with this accuracy are synthesized from a 2.048MHz refer- ence source which is passed directly in the optical- fibre case and indirectly in the case of HDSL. This frequency coincides with the 2.048Mbps full-duplex interface provided by HDSL El replacement mo- dem. However, HDSL implementations will always transmit data over the HDSL link at a higher data- rate than 2.048Mbps due to the overheads of HDSL. For example, the ETSI standard for HDSL specifies a data-rate of 2.336Mbps over the HDSL link

although this is transparent to the user who only sees 2.048Mbps. Furthermore, since the El clock accuracy requirement on the 2.048MHz clock is rel- atively relaxed (+50Hz) the HDSL modem must be able to cope with this clock variation. Typically, this is done with bit-stuffing which effectively removes the phase-locked relationship between the master r&/slave tclk and...