ericssonhistory.com

Figure 6Backward hardware compatibility.tion. Figure 6 shows the backward hardwarecompatibility concept. The baseband unit,C, is added to the existing RBS to improvefunctionality and capacity.Downlink processingboard—TX boardDownlink processing functionsFigure 7 shows the main function blocks forprocessing the downlink. Each of theseblocks also contains other baseband functions(not pictured). The first process is frameprotocol (FP) handling (pictured left). Afterconfirming when the data frames on the commonchannels (paging channel, PCH, andforward access channel, FACH) and the dedicatedchannels (DCH) arrived from the lubinterface, the frame protocol handler alignsthe frames and extracts the payload part ofthe data frame. The payload part contains thedata of the uncoded transport channels.For the dedicated channels, the encodingfunction block• generates the cyclic redundancy check(CRC);• concatenates the transport blocks;• segments the coding blocks;• performs convolutional coding or turbocoding;• inserts the first discontinuous transmission.(DTX);• matches rates; and• performs the first interleaving.To fit the 10 ms radio frame, the transportblocks from different transport channels aremultiplexed in the multiplexing unit(MUX) function block. This activity is followedby insertion of the second DTX, thesecond interleaving, and multicode splitting.Data and control information are thensent to the cell-split function block. Thecontrol information contains transport formatcombination indicator (TFCI) bits andcorresponding transmission power control(TPC) commands which have been mappedwith pilot bits onto the dedicated physicalcontrol channel (DPCCH).After the frame protocols have been handled,the broadcast channel (BCH, which ismapped to the primary common controlphysical channel, P-CCPCH, and to PCHand FACH) and PCH and FACH (which aremapped to the secondary common controlphysical dedicated channel, S-CCPCH) areprocessed in a manner similar to that describedfor the dedicated channels. The cellsplitfunction identifies the common anddedicated physical channels that belong toone cell carrier. These processes are followedby modulation, spreading and weighting,36 Ericsson Review No. 1, 2003