CDMA for cellular systems can be described as follows. As with 

FDMA， each cell is allocated a frequency (   ) ，which is split into two parts, half for reverse (mobile unit to base station) and half for (   ) (base station to mobile unit). For full-duplex (   ) . a mobile unit uses both reverse and forwardchannels. Transmission is in the form of direct-sequence spread (本题) , which uses a chipping code to increase the data rate of the transmission, resulting inan increased signal bandwidth. Multiple access is provided by assigning (   ) chipping codes to multiple users, so that the receiver can recover the transmission of an individual unit from multiple transmissions.