Universal Mobile Telecommunications System

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Introduction• IMT-2000 (International Mobile Telecommunications ) a global

standard for (3G) wireless communication defined by ITU (International Telecommunication Union )

• UMTS is being developed by Third Generation Partnership project (3GPP), a joint venture of several organizations. – ETSI (European Telecommunication Standard Institute, Europe)

– Association of Radio Industries and Business/Telecommunication Technology Committee (ARIB/TTC) (Japan)

– American National Standards Institute (ANSI) T-1 (USA)

– Telecommunications technology association (TTA) (South Korea)

– Chinese Wireless Telecommunication Standard (CWTS) (China)

• To reach global acceptance, 3GPP is introducing UMTS in phases and annual releases.

UTRAN (UMTS Terrestrial Radio access)

• The most significant change in Release. ’99 by3GPP.

•  UTRAN is subdivided into individual radio network systems (RNSs), where each RNS is controlled by an RNC

• UMTS defines four new open interfaces

– Uu: UE to Node B (UTRA, the UMTS W–CDMA air interface)

– Iu: RNC to GSM Phase 2+ CN interface (MSC/VLR or SGSN) • Iu-CS for circuit-switched data

• Iu-PS for packet-switched data

– Iub: RNC to Node B interface

– Iur: RNC to RNC interface, not comparable to any interface in GSM

UMTS Architecture

• The network of UMTS can be split into 3 main constituents.– Mobile Station called the User equipment UE– Base station subsystem known as Radio

Network Subsystem (RNS) – Core network.

UE (User Equipment)

• equivalent to the mobile equipment (ME) used on GSM networks.

• The Circuit used in UE broadly split

– RF circuitry Handles all elements of the signal, both for the receiver and the transmitter .Uses liner RF power amplifier.

– Base band processing areas. Base band signal processing mainly consists of digital circuitry. This is considerably more complicated than that used in phones for previous generations.

USIM (Universal SIM)• Universal Subscribers Identity Module, advanced version of SIM card

used in GSM

• contains the International Mobile Subscriber Identity Number (IMSI) as well as the Mobile Station International ISDN number (MSISD

• USIM also contains a short message storage area, phone book numbers and call information of the numbers of incoming and outgoing calls can also be stored.

• UMTS mobile station can operate in one of three modes of operation: – PS/CS mode of operation

– PS mode of operation

– CS mode of operation

Radio Network Subsytem

• Interfaces to both the UE and the core network

• Radio transceiver is known as Node B, communicates with various UEs, radio Network controller (RNC )

• The RNC enables autonomous radio resource management (RRM) by UTRAN.

• Node B is the physical unit for radio transmission/reception with cells

RNC Functions• Performs the same functions as the GSM BSC, providing central

control for the RNS elements (RNC and Node Bs) .

• The RNC handles protocol exchanges between Iu, Iur, and Iub.

• Congestion and handover/macro diversity are managed entirely by a single serving RNC (SRNC).

• The term controlling RNC (CRNC) is used to define the RNC that controls the logical resources of its UTRAN access points.

Node-B • Connects with the UE via the W–CDMA Uu radio interface and

with the RNC via the Iub asynchronous transfer mode (ATM)–based interface

• Node B is the ATM termination point

• Node B is the conversion of data to and from the Uu radio interface, including forward error correction (FEC), rate adaptation, W–CDMA spreading/dispreading, and quadrature phase shift keying (QPSK) modulation on the air interface

• The Node B also participates in power control via the inner-loop power control

Frequencies• Currently six bands that are specified for the use for

UMTS/WCDMA.

• Much of the focus on UMTS is currently on frequency allocations around 2GHz.

• Uplink Frequency: 1885- 2025 MHZ

• Downlink Frequency: 2110- 2200 MHz

• The channels are spaced by 5MHz.

• The downlink uses quadrature phase-shift keying (QPSK) for all transport channels.

• Uplink used two separate channels so that the cycling of the transmitter on or off does not cause interference to the audio lines.

Spreading• Data to be transmitted is encoded using a spreading code

particular to a given user • Only the desired recipient is able to correlate and decode

the signal, all other signals appearing as noise, this allows Physical RF channel to be used by several users simultaneously.

• The data of a CDMA signal is multiplied with a chip or spreading code to increase the bandwidth of the signal

• Each physical channel is spread with unique and variable spreading sequence. The overall degree of spreading varies to enable the final signal to fill required channel bandwidth Each physical channel is spread with a unique and variable spreading sequence.

Synchronization

• Synchronisation is provided from the Primary Synchronisation Channel (P-SCH) and the Secondary Synchronisation Channel (S-SCH)

• They spread using synchronisation codes, two types are used.– Primary code and is used on the P-SCH primary

code is the same for all cells and is a 256 chip sequence that is transmitted during the first 256 chips of each time slot. This allows the UE to synchronise with the base station for the time slot

– Secondary code and is used on the S-SCH sixteen different secondary synchronisation codes.Scrambling codes in the S-SCH enable UE to identify which scrambling code is being used and hence it can identify the base station

Power Control• Base station receives signals from UEs at same power level

• If not, the UEs further away will be lower in strength than those closer to the node B and will not be heard. This effect is called as the near-far effect.

• Power control is achieved using 2 techniques.

– open loop used during initial access before communication between the UE and node B is established

– closed loop A measurement of the signal strength is taken in each time slot. As a result of this a power control bit is sent requesting the power to be stepped up or down. This process is undertaken on both the up and downlinks

Channels• UMTS uses CDMA techniques (as WCDMA) as its multiple access

technology, but it additionally uses time division techniques with a slot and frame structure to provide the full channel structure.

• A channel is divided into 10 ms frames, each of which has fifteen time slots each of 666 microseconds length.

• The channels carried are categorised into three types: – Logical:

define the way in which the data will be transferred – transport

transport channel along with the logical channel again defines the way in which the data is transferred

– physical channels. Carries the payload data and govern the physical characteristics of the signal.

Packet data• Packet data is an increasingly important element within mobile

phone applications.

• WCDMA is able to carry data in this format in two ways

– short data packets to be appended directly to a random access burst. This method is called common channel packet transmission and it is used for short infrequent packets.Delay in setting up a packet data channel and transferring the operational mode to this format is avoided.

– Larger or more frequent packets have to be transmitted on a dedicated channel. A large single packet is transmitted using a single-packet scheme where the dedicated channel is released immediately after the packet has been transmitted.

Handover • Handover follows many of the similar concepts to those used for other

CDMA systems.• There are three basic types of handover. All three types are used but

under different circumstances.– Hard handover:

When UE moves out of range of one node B, the call has to be handed over to another frequency channel.

– Soft handover : Technique was not available on previous generations of mobile phone systems. Adjacent cell sites are on same frequency, as a result the UE can receive the signals from two adjacent cells at once,

– Softer Handover.• The decisions about handover are generally handled by the RNC

Advantages of UMTS.• UMTS is a successor to 2G based GSM technologies including GPRS

and EDGE. Gaining a 3rd name 3GSM because it is a 3G migration for GSM

• Support 2Mbit/s data rates. Higher Data rates at lower incremental costs.

• Benefits of automatic international roaming plus integral security and billing functions, allowing operators to migrate from 2G to 3G while retaining many of their existing back-office systems

• Gives operators the flexibility to introduce new multimedia services to business users and consumers

• This not only gives user a useful phone but also translates higher revenues for the operator.

UMTS Applications• Conversational Class applications:

Circuit switched voice service and Packet Switched Voiced Service• Streaming Class applications:

– Streaming / Download (Video, Audio)– Videoconferences.

• Interactive Class applications:– Fast Internet / Intranet. – Mobile E-Commerce (M-Commerce)– Remote Login 

• Background Class applications:– Any non –real time applications like – Multimedia-Messaging, E-Mail

• FTP Access• Mobile Entertainment (Games) 

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