Intro to xdsl part 1

QAM constellations

• 16 QAM V.29 (4W 9600 bps)
• V.22bis 2400 bps Codex 9600 (V.29)
• 2W
• first non-Bell modem (Carterphone decision)
• Adaptive equalizer
• Reduced PAR constellation
• Today - 9600 fax!
• 8PSK
• V.27
• 4W
• 4800bps

QAM constellations (cont)

DMT - continued

• time

• frequency

xDSL Line Codes

• PAM
• IDSL (2B1Q)
• HDSL2 (with TCM and optionally OPTIS)
• SDSL
• QAM/CAP
• proprietary HDSL/ADSL/VDSL
• DMT
• ADSL
• G.lite
• VDSL line code war is still raging

Duplexing

• How do we send information in BOTH directions?
• Earliest modems used two UTP, one for each direction (4W)
• Next generation used 1/2 bandwidth for each direction (FDD)
• Alternative is to use 1/2 the time (TDD)
• More advanced DSP uses adaptive echo canceling

ADSL FDD Duplexing

• US uses tones 8 - 32 (below 30 KHz reserved)
• DS uses 256 tones (FDM from tone 33, EC from tone 8)

• POTS

• US

• DS

• 8

• 32

• 256