One thing I've come to notice over the past few years dealing with GSM and now into UMTS is the amount of acronyms for absolutely everything. Maybe you know a few, maybe you just ignore them! Either way I'm going to put a few on here. As I remember them I'll edit and re-post, if there's anything you don't know and want to, post it up and I'll try and find out for you.
Enjoy the reading!!
The first generation of analogue mobile phone technologies including AMPS, TACS and NMT
The second generation of digital mobile phone technologies including GSM, CDMA IS-95 and D-AMPS IS-136
The enhancement of GSM which includes technologies such as GPRS
The third generation of mobile phone technologies covered by the ITU IMT-2000 family
BTS & WBTS
Base Transceiver Station; the network entity which communicates with the mobile station.
The area covered by a cellular base station. A cell site may sectorise its antennas to service several cells from one locationCell site
The facility housing the transmitters/receivers, the antennas and associated equipment
Frequency Division Duplex; a radio technique which uses paired spectrum; UMTS has an FDD element
General Packet Radio Service; standardised as part of GSM Phase 2+, GPRS represents the first implementation of packet switching within GSM, which is a circuit switched technology. GPRS offers theoretical data speeds of up to 115kbit/s using multislot techniques. GPRS is an essential precursor for 3G as it introduces the packet switched core required for UMTS
Handoff/Handover or HO
The transfer of control of a cellular phone call in progress from one cell to another, without any discontinuity
Universal Mobile Telecommunications System; the European entrant for 3G; now subsumed into the IMT-2000 family as the WCDMA technology.
Universal Subscriber Identity Module; the 3G equivalent of the GSM SIM
Time Division Duplex; a radio technology for use in unpaired spectrum. WCDMA/UMTS includes a band for TDD mode usage and both PHS and DECT use this technology
Wideband CDMA; the technology created from a fusion of proposals to act as the European entrant for the ITU IMT-2000 family
Phew... as i say, got something you don't know? Post it on here..
It's not something that is being used currently, however I can give you as simple an explanation as I can into how it'll work.
At the moment on the UMTS networks every cell site is on the same frequency, around the 2100MHz mark.(Each operator has a different frequency but they're all around this point) Previously on GSM each operator had their own frequency, Voda and O2 were on 900MHz, Orange and T-Mob on 1800. Within these bands they were split into smaller frequency channels, these were reused over the networks footprint, each cell or sector having a specific BCCH channel for your handset to synch to. Every time you made a call you're allocated a specific block of time on one of the operators transmitters. What's important to remember is the fact while you're in a call that little slot of time on that particular transmitters frequency (each transmitter being different) belongs to you, no-one else uses it. (not strictly true if you know about baseband hopping but for the sake of this explanation!)
Within the UMTS network it's slightly different. Say Orange for example, but it's the same for all of the networks, each WBTS site is at the same frequency. When you make a call, pass data etc the network allocates you a dedicated channel which is code multiplexed, this uniquely identifies your data to the network, it then allows it to route the data accordingly. Using this method, with a code for each user thats transmitting or receiving each cell site can be on the same frequency.
Now with HSDPA is based along the same lines as before except instead of a dedicated channel each user shares resource. As most data is bursty it allows data to be sent by one user, once the data is sent another user gets access to the resource and so on. All it's doing is, when some users are silent, not sending any data, more resource is spent on those who want it. Thus resulting in "perceived" high speeds, of up to 10Mbps!! (Again this is also dependant on the link that supplies the WBTS) With HSDPA packet throughput is better which results in more users and quicker response times, latency is another term for it I think.