Not as simple as that!
If you were simply to use a "repeater" to boost the ASDL signal (essentially an amplifier) then the noise would be amplified as well as the ADSL signal as ADSL, as has already been stated, is a collection of tones produced by the modem.
In practice what would be required is a modem to recover the digital data and a DSLAM to generate ADSL again.
This would require a power source at the repeater point (which could be supplied down the line) and somewhere to put it.
Not a particularly scalable solution and expensive for a single line.
Ex <n>ildram , been to SKY MAX - 15,225 Download
BE Unlimited - 21,000 Download 1,200 Upload ON THE LINE THAT SKY COULD ONLY PROVIDE 15,255 DOWN AND 800 UP ON!!!,
Moved house, now BE Unlimited 6,500 Down, 1Mb/s up - gutted!
FTTC Cab installation commenced 12th April - expect full 80 / 20 - bye bye BE, hello BT Infinity soon!