IMT2000TC

In Chapter 1 we identified that some operators were being allocated 2 × 10 MHz paired
channel allocations for IMT2000 and 1 × 5 MHz nonpaired channel (see Table 3.5).
There are two nonpaired bands:
 TDD1 covers 4 × 5 MHz channels between 1900 and 1920 MHz.
 TDD2 covers 3 × 5MHz channels between 2010 and 2025 MHz.

Because the channel is not duplex spaced (the same RF channel is used for downlink
and uplink), the channel is reciprocal. It is therefore theoretically possible to use the
RAKE filter in the handset as a predistortion device. The benefit is that this allows the
implementation of a relatively simple (i.e., RAKE-less) picocell base station.
The frame and code structure are slightly different to IMT2000DS. The 15-slot 10-ms
frame is retained, but each of slots can support a separate user or channel. Each user or
channel slot can then be subdivided into 16 OVSF spreading codes. The spreading factors
are from 1 to 16. (Spreading factor 1 does not spread!)
The combination of time-division duplexing, time-division multiplexing, and a code
multiplex provides additional flexibility in terms of bandwidth on demand, including
the ability to support highly asymmetric channels. The duty cycle can also be actively
reduced (a 1/15 duty cycle represents a 12 dB reduction in power). A mid-amble
replaces the pilot tone and provides the basis for coherent detection. We revisit
IMT2000TC access protocols in Part III of this book, “3G Network Hardware.”