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METHOD FOR INCREASING DYNAMIC RANGE IN IA 2-WIRE HALF DUPLEX WIRELINE INTERFACE FOR SYSTEMS USING DSP BASED ADAPTIVE SIGNAL CANCELLATION

IP.com Disclosure Number: IPCOM000009070D
Original Publication Date: 1999-Jun-01
Included in the Prior Art Database: 2002-Aug-06
Document File: 3 page(s) / 141K

Publishing Venue

Motorola

Related People

Anthony Gerkis: AUTHOR

Abstract

Products utilizing a DSP based adaptive signal cancellation method for removing the inbound (receive - from station to landline) component from the outbound (transmit - from landline to station) signal path in 2-wire wireline half-duplex mode of operation can experience failure to detect TRC tones or digital signahng control data for large in- bound signals that saturate either the outbound coarse gain adjustment or the A/D CODEC. This would occur when the landline connection has high attenuation and the station must be aligned with high inbound output levels.

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MOTOROLA Technical Developments

METHOD FOR INCREASING DYNAMIC RANGE IN IA 2-WIRE HALF DUPLEX WIRELINE INTERFACE FOR SYSTEMS USING DSP

BASED ADAPTIVE SIGNAL CANCELLATION

by Anthony Gerkis

INTRODUCTION

  Products utilizing a DSP based adaptive signal cancellation method for removing the inbound (receive - from station to landline) component from the outbound (transmit - from landline to station) signal path in 2-wire wireline half-duplex mode of operation can experience failure to detect TRC tones or digital signahng control data for large in- bound signals that saturate either the outbound coarse gain adjustment or the A/D CODEC. This would occur when the landline connection has high attenuation and the station must be aligned with high inbound output levels.

  The invention being disclosed is a system for the detection of Tone Remote Control (TRC) wireline commands in half duplex mode in high loss landline to station wireline connections using adaptive fdter- ing and a timed gain adjustment in the transmit wireline (TX WL) signal path.

INVENTION

  Since the base station will be aligned such that the Low Level Guard Tone (LLGT) TRC command will always be detected in normal operation, the gain of the TX WL signal can be reduced by as much as 20 dB (since the Function Tone (FT) is nor- mally 20 db above LLGT) in the presence of a receive wireline (RX WL) signal. This gain reduc- tion will ensure that the A/D CODEC or subsequent TX WL coarse gain adjustment stages do not satu- rate and cause distortion in the TRC decode spec- bum to mask the TRC detection. If there is a large disparity between aligned TX WL and RX WL lev- els in the station, the Host software will reduce the gain in the TX WL path whenever RX Audio is muted to the WL. Once a HLGT/FT combination is received, the RX Audio to RX WL is muted and the aligned TX WL gain is restored.

APPLICATION EXAMPLE

  The MTR2000 analog base station/repeater uses a 5V supply on the wireline board hardware (opera- tional amplifiers and CODECs included) as a cost saving measure. In the 2-wire mode of operation, the TX WL and RX WL signal paths are summed at the wireline board output. As a result, the outbound signal from the landline contains both TX WL as well as RX WL audio when audio is muted to the wireline. As an additional cost saving measure, the cancellation or removal of the RX WL (inbound) signal from the outbound path is performed by adaptive filtering in the DSP (requiring no addition- al hardware). The problem is that the cancellation is ineffective if the RX WL signal is distotted, or there is spectral impurity in the inbound WL signal. It was found that...