Radio and Network Bandwidth Transition

This transition however, needs to deliver transparent cost and performance benefits,
and must take into account future changes in the offered traffic mix and offered traffic
properties. These changes include a radio bandwidth transition—a change from
constant-rate, variable-quality channels to variable-rate, constant-quality channels, and
a network bandwidth transition—a change from synchronous to asynchronous traffic,
and a shift from non-isochronous to isochronous traffic. This radio and network bandwidth
transition is happening because the offered traffic mix contains an increasingly
high percentage of rich media components—audio capture, image capture, video capture,
and data capture. This is the basis for bursty bandwidth.
The burstiness of the offered traffic is determined by the application bandwidth and
application dynamic range in the subscriber’s handset. In 3GPP1, the assumption is
that the dynamic range of any single channel stream can vary between 15 kbps and 960
kbps on a frame-by-frame basis, as demonstrated in Table 14.1. This is equivalent to an
18 dB dynamic range or a 64:1 ratio, which is then accommodated over the radio physical
layer by the OVSF code structure (the SF4 to SF256 chip cover).

However, this is the dynamic range excursion limit for a single channel. As we saw
in earlier chapters, multiple channel streams produce much larger envelope variations,
which are exhibited as large peak-to-average ratios that exercise our RF PA stages in
the handset and Node B transceivers. We noted it was hard to deliver the linearity
needed for multiple codes, as well as power efficiency. This issue does not disappear as
the offered traffic moves into the network; in fact, it gets worse.