W-CDMA radio interface

A two-way radio communication system must transmit signals in the mobile-to-network direction, known as the uplink direction, and in the network-to-mobile direction, known as the downlink direction. Professional radio systems have long tolerated the use of a single radio frequency common to both directions, with speakers taking it in turns to speak: this is the alternating access mode. Since cellular systems are open to a wide audience, it was necessary from the outset to provide a system enabling both communicating users to speak simultaneously, as is the case in fixed telephony: this is the duplex access mode (figure 3 ).

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