have you tried using Google ?
a 5sec keying in prompt me with at least 10+ pages on UMTS.

=bob=

Although you should be doing your own homework...

UMTS is the next evolution of the GSM radio interface, "UTRAN - UMTS
Terrestrial Radio Access Network" as opposed to the current GSM radio
interface - "GERAN - GPRS/EDGE Radio Access Network".

Anyway, UMTS is based around a CDMA multiplexing principle. There are two
modes of UMTS - FDD and TDD (Frequency and Time division duplexing),
referring to the way the duplexing is handled. FDD is the most common, and
uses a seperate 5MHz channel (seperated by a significant chunk of spectrum,
190MHz typically) for each direction. The rest of this post will be based
around FDD.

The binary signal is spread onto a carrier with a chipping rate of 3.84
megachips. Spreading factors vary from 4-512, and QPSK modulation is used.
Data to/from a single UE (phone) is spread & multiplexed using different
channelisation codes, and then scrambled using different scrambling codes.
The different scrambling codes are used to distinguish between multiple UEs
(in the uplink) and multiple Node Bs (base stations) (in the downlink).

The basic network-side structure of UMTS is still essentially a GSM core
network. The BSS and BTS are replaced with the RNC (radio network
controller) and Node B respectively. An RNC controls multiple Node Bs. The
RNC then interfaces, like the BSC, with entities like the SGSN and MSC.

CDMA is a fairly complex idea, and so is rake receiving - a way of using
information from other users using a channel to help assist when
demodulating each symbol. It is also used to help combat the multipath
effect, when the time difference arrival of multiple instances of the signal
is larger than a single symbol period. The idea is that there are several
"correlators" in the receiver, each of which correlate each different delay
of the signal using the spreading code. The information from each correlator
can then be "weighted" to assist the demodulation process. Each correlator
can be called a "finger" which works in parallel, hence the reason the name
"rake" is used.

As for links, google brings up quite a few ranging from overviews to more
technical articles. You might also want to check the GSM/3GPP specifications
at http://www.3gpp.org. In particular, the 25 series will be of interest to
you, as they describe the lower levels of the radio link.