The purpose of filtering a telephone channel so precisely was that AT & T were attempting to use the same wires for many telephone conversations simultaneously using the technique of frequency division multiplexing ( FDM ) and it was important for reasons of privacy, as well as intelligibility, that there was no crosstalk between the channels.
22.
The most commendable achievement of IEEE 802.15.3a was its consolidation of 23 UWB PHY specifications into two proposals using : Multi-Band Orthogonal Frequency Division Multiplexing ( MB-OFDM ) UWB, supported by the WiMedia Alliance, then adopted by the USB-IF for Wireless USB and by the Bluetooth SIG for high speed Bluetooth, while the Direct Sequence-UWB ( DS-UWB ) approach, supported by the UWB Forum, was abandoned.
