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 subscriber premises to the cable head-end in cable TV (CATV) networks. The carrier and timing synchronizations needed to ensure orthogonality between different subscriber signals are achieved by sending common pilot signals from the head-end. Whereas N demodulators are required to accommodate N simultaneous users in conventional FDMA systems, OFDMA only requires a single demodulator followed by an N-point discrete Fourier transform (DFT). We analyze the performance of this technique and compare it to time-division multiple access (TDMA) which appears in several international standards. Our results indicate that OFDMA is an attractive multiple access technique which offers increased robustness to narrowband interference, impulse noise, and other signal impairments which characterize typical CATV networks.