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Abstract

A system and method for generating and repetitively transmitting a single modulated symbol during idle periods in user data in a digital subscriber line (DSL) communication system. The modulated symbol to be transmitted is selected such that its spectral properties match those of user data modulated symbols. For an asynchronous DSL system, and variants thereof, a preferred idle symbol is the 'superframe' synchronization symbol. A separate modulated symbol would indicate the end of the idle state. In the preferred embodiment, the end-of-idle symbol is the idle symbol shifted by a 180.degree. phase shift. In a preferred embodiment, the transmitter in a DSL modem would calculate the idle state modulated symbol once at the start of the idle period and then simply repeat this symbol until the end of the idle period, in which case the transmitter would invert the final idle symbol. At the receiver, an idle state modulated symbol detector and phase detector are implemented. Symbol detection can be performed in the time-domain for faster and easier detection, requiring little processing power. Upon detection of a 180.degree. phase shift of the idle symbol, the receiver would exit the idle mode. The invention includes method, apparatus, and computer program implementations.

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First Claim