The Universal Mobile Telecommunications System (UMTS) is one of the new 3G “third generation” cellular communication systems. It was developed by the 3rd Generation Partnership Project (3GPP), with the proposal to define a global 3G system.It is also called W-CDMA) that offers more efficient multimedia capabilities, a speed of Internet access faster and quality voice transmission.
The Outstanding Features Of The UMTS System Are:
– Possibility of connecting to the Internet through a cellular computer at high speed.
– Multimedia capability that allows you to enjoy audio and video in real time
– Excellent voice transmission with quality comparable to that of fixed network.
Once UMTS is fully available, computer and phone users can be constantly attached to the Internet wherever they travel and, as they roam, will have the same set of capabilities. Users will have access through a combination of terrestrial wireless and satellite transmissions. Until UMTS is fully implemented, users can use multi-mode devices that switch to the currently available technology (such as GSM 900 and 1800) where UMTS is not yet available.
This original form of modulation has many advantages:
- High transmission speeds of up to 2 Mbps, when using the entire spectrum.
- High security and confidentiality due to the use of techniques that allow to approach the maximum capacity of the channel (as for example: convolutional encoders)
- Multiple access of maximum efficiency as long as the jump sequences do not coincide.
- High resistance to interference
- Possibility of working with two antennas simultaneously because the whole spectrum is always used and the important thing is the jump sequence, which facilitates the handover (process of transferring the signal from one antenna to another), where GSM fails a lot.
- UMTS offers another series of advantages such as roaming and coverage worldwide either via terrestrial radio link or via satellite, and is highly standardized with a unique interface for any network.
UMTS 3G Structure Of The Network.
There are several versions of UMTS that have emerged during its development. The release 99 uses the same network structure in GPRS , separating voice communications of data so that there is a circuit switched network for voice and packet switching for data. The radio interface changes with respect to GPRS . In UMTS it appearsthe UMTS Terrestial Radio Access Network (UTRAN) that replaces the BTS nodes with B nodes and the BSC with RNC (Radio Network Controller).
The tendency of UMTS is to avoid the separation between voice and data communications, in ways that use the same mechanisms in both types of communications. In release 5 of UMTS , the IP protocol will be the transport mechanism, both for voice and data, even inthe UTRAN, replacing the ATM network . With release 5 , the control mechanisms for data transmission are separated, with the appearance of the IP Multimedia Subsystem (IMS) for the management of multimedia services using SIP signaling on the packet carrier.
Within the IMS system we can find the following entities:
- HSS (Home Subscriber Server). Contains user subscription profiles. It is the evolution of the HLR with the incorporation of multimedia IP control functions.
- CSCF (Call StateControl Function). It is responsible for the control of the session and is divided, in turn, into several entities that communicate with each other and with the user using the SIP protocol. These are:
- I-CSCF (Interrogating CSCF). It is the entry point and selects, with the help of the HSS , the appropriate SCSCF .
- S-CSCF (Serving CSCF). It receives the SIP requests of the user and performs control of the session.
- P-CSCF (Proxy CSCF). In the case of roaming, it would be located in the visited network and would select the I-CSCF of the originating network.
- MRF (Multimedia Resource Function). Manage the call or session functions with several participants and connections