Systems and methods for controlling audible speech distortion in a GPS-based CDMA wireless network using ATM transport

Abstract

A Base Station Controller (BSC) that reduces the occurrence of audible noise in a Code Division Multiple Access (CDMA) radio network is provided. The BSC according to one embodiment of the present invention comprises a Media Stream Board (MSB) for compressing groups of 160 PCM speech samples from a Public Switch Telephone Network (PSTN) into vocoded frames, and a Special Purpose Board (SPB) for reformatting the vocoded frames from the MSB into over-the-air CDMA vocoded frames. The MSB and SPB each have a local timer that is slave to 'PSTN time'. The BSC further comprises a Timing Unit Board (TUB) connected to a GPS receiver. The TUB receives 'GPS time' from the GPS receiver. The TUB generates timing cells, each containing time-of-day information according 'GPS time'. The TUB distributes the timing cells to the MSB and SPB over an Asynchronous Transfer Mode (ATM) network. The MSB and SPB use the received timing cells to compare their local timer, which tracks 'PSTN time', to 'GPS time'. The MSB and the SPB realign their local timer with 'GPS time' whenever their local timer drifts from 'GPS time' outside of a predetermined time window.

Description

field of invention [0001] The present invention relates generally to Code Division Multiple Access (CDMA) wireless communication networks, and, more particularly, to systems and methods for reducing the occurrence of audible noise in CDMA wireless networks. Background of the invention [0002] A CDMA wireless network provides a communication link between a caller on the public switched telephone network (PSTN) and a caller on a mobile station (MS). The PSTN supports pulse code modulation (PCM) voice signals, which are digital voice signals sampled at a frequency of 8KHz. The CDMA network consists of a base station controller (BSC) for compressing groups of 160 PCM voice samples from the PSTN into 20 ms vocoded frames, and radio base stations (RBS) for The encoded frame is modulated into a spread spectrum signal and the spread spectrum signal is broadcast to MSs. [0003] The RBS broadcasts the spread spectrum modulated frames to the MSs at a specific frame offset time that...

AI Technical Summary

Problems solved by technology

One disadvantage of this approach is that it frequently introduces audible noise into the speech signal whenever "PSTN time" drifts by 125 microseconds relative to "GPS time"

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