Practical Time Domain Processing in a 3G Handset

We have established that a third-generation handset needs to process in the frequency
domain, the code domain (chip level), and the time domain (bit level and symbol level).
These processing mechanisms need to comprehend the ambiguities introduced by the
radio path including time ambiguities (delay spread) and phase and frequency offsets.

Bandwidth quality is a function of how well those processing tasks are undertaken
and how well the processing adapts to changed loading conditions. Let’s examine
some of the measurements used to qualify adaptive radio bandwidth performance.
Figure 3.24 shows a 12.2 kbps uplink voice channel and 2.5 kbps of embedded signaling.
The channels are punctured and rate-matched and multiplexed to give a channel
rate of 60 kbps. Spreading factor 64 is applied to provide the 3.84 Mcps rate. Variable
gain is applied to take into account the spreading gain. The control channel is 15 kbps
and is therefore spread with SF256 and gain-scaled to be -6 dB down from the DPDCH.

The complex scrambling applied to the uplink is a process known as Walsh rotation,
which effectively continuously rotates the modulation constellation to reduce the PAR
of the signal prior to modulation. It is also known as Hybrid Phase Shift Keying
(HPSK) or sometimes orthogonal complex quadrature phase shift keying. HPSK
allows handsets to transmit multiple channels at different amplitude levels while still
maintaining acceptable peak-to-average power ratios.
Unlike the uplink, where the control bits are modulated onto the Q channel, the
downlink multiplexes voice bits, signaling bits, and control bits together across the I
and Q channels with slightly different rates resulting; voice and signaling bits are at 42
kbps, and pilot, power control, and TFCI control bits are at 18 kbps to give the 60 kbps
channel rate. 98