H ELECTRICITY
H04 ELECTRIC COMMUNICATION TECHNIQUE
H04L TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
H04L5/00 Arrangements affording multiple use of the transmission path
H04L5/0001 Arrangements for dividing the transmission path
H04L5/0003 Two-dimensional division
H04L5/0005 Time-frequency
H04L5/0007 the frequencies being orthogonal, e.g. OFDM(A) or DMT