| 摘要 |
In a multi-directional orthogonal frequency division modulation (OFDM) communication system, for example, on a digital subscriber line, an uplink channel is provided by a first group of the OFDM sub-channels (sub-carriers), and a downlink channel is provided by a second group of the OFDM sub-channels (sub-carriers). In one aspect, communication efficiency is improved by controlling the relative number of sub-channels allocated to each group, and hence controlling the capacity of the channels dynamically. Preferably, the relative capacities are controlled in response to demand for channel capacity. In another aspect, the orthogonality of the sub-carriers generated by different transmitters is improved by providing a frequency and/or time synchronising signal for providing reference frequency and timing. In a further aspect, multiplex communication over a network between three or more stations is provided by distributing the OFDM sub-channels (sub-carriers) between the stations to provide three or more channels within the OFDM bandwidth. |
