Orthogonal frequency-division multiple access and its application to CATV networks

We introduce the concept of orthogonal frequency-division multiple access ( OFDMA) and investigate its application to send upstream information from su bscriber premises to the cable head-end in cable TV (CATV) networks. The ca rrier and timing synchronizations needed to ensure orthogonality between di fferent subscriber signals are achieved by sending common pilot signals fro m the head-end. Whereas N demodulators are required to accommodate N simult aneous users in conventional FDMA systems, OFDMA only requires a single dem odulator followed by an N-point discrete Fourier transform (DFT). We analyz e the performance of this technique and compare it to time-division multipl e access (TDMA) which appears in several international standards. Our resul ts indicate that OFDMA is an attractive multiple access technique which off ers increased robustness to narrowband interference, impulse noise, and oth er signal impairments which characterize typical CATV networks.