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Page 1: UMTS and WCDMA Overview

Cellular Mobile Systems and Services (TCOM1010) 2009-April

Day-12_UMTS and WCDMA Overview.doc � Monzur Kabir, Ph.D., P.Eng Page 1 of 19

UMTS and CDMA Overview

1 BACKGROUND INFORMATION .................................................................................................................................2 2 UMTS OVERVIEW ..........................................................................................................................................................2

2.1 UMTS Releases.............................................................................................................................................................3 2.2 UMTS Services .............................................................................................................................................................4 2.3 UMTS Core Network (CN) Overview ..........................................................................................................................4 2.4 UMTS Terrestrial Radio Access Network (UTRAN) ...................................................................................................4 2.5 Frequency Bands ...........................................................................................................................................................5 2.6 UMTS Technology Overview .......................................................................................................................................6

3 2G GSM TO 3G UMTS – NETWORK ARCHITECTURE ..........................................................................................8 3.1 UMTS Network Architecture - Evolution: from 2G-GSM to 3G-UMTS R5................................................................8 3.2 UMTS Network Architecture -- Evolution: from 2G-GSM to 3G-UMTS R7 ............................................................13

4 CDMA AND W-CDMA – AN OVERVIEW .................................................................................................................16 4.1 Multiple Access Technologies ....................................................................................................................................16 4.2 Channelization Multiple Access Techniques ..............................................................................................................17 4.3 CDMA Principle .........................................................................................................................................................17 4.4 Why CDMA ................................................................................................................................................................18 4.5 W-CDMA Overview ...................................................................................................................................................19

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Cellular Mobile Systems and Services (TCOM1010) 2009-April

Day-12_UMTS and WCDMA Overview.doc � Monzur Kabir, Ph.D., P.Eng Page 2 of 19

1 Background Information Pre-reading: See the ‘3G Cellular Mobile Overview’ document. Three major cellular mobile systems under the hood of IMT-2000 are UMTS (by 3GPP), CDMA2000 (by 3GPP2) and EDGE (also called as EGPRS) (by UWCCC or newly named 3G America). The following figure depicts how the 2G systems are heading towards 3G systems (her UMTS is represented by W-CDMA, which is one but the most prominent system of UMTS). This document gives an overview of W-CDMA and CDMA2000 (UWC-136 or EDGE is covered under GSM/GPRS).

http://www.comsec.uwaterloo.ca/~flchiu/CDMA/IMT2000%20standard.pdf

2 UMTS Overview UMTS was formed in 1996 and then joined with few other organizations to form a bigger 3GPP body to carry on the ‘GSM-driven CDMA’ system (see ‘3G Cellular Mobile Overview’ document for a further detail) where it adopts CDMA for the radio interface but keeps GSM technologies as much as it can. The UMTS has three major systems: W-CDMA TD-CDMA and TD-SCDMA. Among them the W-CDMA is the most prominent system.

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2.1 UMTS Releases So far UMTS issued the following Releases (http://www.telecomabc.com/u/umts-releases.html).

• UMTS Release 3 (also called Release 99)

o Based on GSM,

� Backward compatible with GSM,

� Interoperation between UMTS and GSM;

o Definition of the UTRAN

o UTRA

� UMTS FDD (W-CDMA)

o GSM EDGE Radio Access Network (GERAN)

• UMTS Release 4

o Separation of user data flows and control mechanisms,

o UMTS TDD Time Division CDMA (TD-CDMA),

� High data rate UMTS TDD with 3.84 Mchips/s,

� Narrowband TDD with 1.28 Mchips/s;

o Position location functionality;

• UMTS Release 5

o End-to-end packet switching based on IP (IMS),

o Downlink data rate of over 10 Mbit/s (HSDPA),

• UMTS Release 6

o IMS "Phase 2" (IMS Messaging, conferencing and Group Management),

o High Speed Uplink (HSUPA)

o Multimedia Broadcast/Multicast Service (MBMS)

o WLAN interworking

• UMTS Release 7

o Enhanced uplink, other spectrum,

o Multiple Input Multiple Output antennas (MIMO),

o IMS Emergency call handling.

o DSL Access

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Cellular Mobile Systems and Services (TCOM1010) 2009-April

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2.2 UMTS Services http://www.telecomabc.com/u/umts.html In addition to traditional speech and data communication services, UMTS offers the user full interactive multimedia communications, information and entertainment services with speeds of up to 2 Mbit/s, comparable with the current fixed networks. Further evolutions of UMTS will make even higher transmission speeds possible. � In UMTS there are four different kinds of services defined. Each with its own quality of service:

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2.3 UMTS Core Network (CN) Overview It was all GSM in 2G, which has a circuit switched (CS) core network (CN). In 2.5G (GPRS and EDGE) another core was added, which is a packet-switched (PS) core with GSNs (GPRS Service Nodes). While continuing with these two (CS and PS) with some ‘as needed’ enhancements, the UMTS introduced IP Multimedia Sub-system (IMS) for all IP end-to-end multimedia services (including voice-over-IP). UMTS-CN includes network elements:

o Legacy GSM: MSC, VLR, HLR, EIR etc. o GPRS/EDGE: SGSN, GGSN etc. o IMS core: CBC, CSCF, MRCF, MGCF, SLF, HSS, AS etc.

2.4 UMTS Terrestrial Radio Access Network (UTRAN) http://www.telecomabc.com/u/utran.html The UMTS Terrestrial Radio Access Network (UTRAN) is the fixed network infrastructure that contains the facilities for the transmission to and from the mobile users over radio. The components of the UTRAN are the base stations, which are called Node B in UMTS, and control nodes, which are called Radio Network Controller (RNC). The Radio Network Controllers are connected to the Core Network (CN). �

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Cellular Mobile Systems and Services (TCOM1010) 2009-April

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The interface for the transmission to and from the mobile users is called the UTRA (UMTS Terrestrial Radio Access). There are two different modes: an UMTS FDD mode and a UMTS TDD mode. The FDD requires a paired band (up and down link) whereas TDD works with an unpaired band.

2.5 Frequency Bands The following bands are available for UMTS, in Europe.

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• The UTRA makes use of W-CDMA in the paired bands. These bands are used the following bit-rates:

144 kbit/s in suburban and rural areas (high-mobility => up to 500 km/h) up to

384 - 512 kbit/s in urban areas (medium-mobility => up to 120 km/h)

W-CDMA is officially known as IMT-2000 CDMA Direct Spread (CDMA DS). The main characteristics of W-CDMA are:

o Wideband Direct Sequence CDMA; o Frequency Division Duplex;

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o Chip rate: 3.84 Mcps, can be extended to 8.192 or 16.384 Mcps;

o No need to synchronize the base stations; o Variable spreading code,

Spreading factor from 4 to 256; o Bandwidth between 4.4 and 5 MHz.

• The UTRA TDD has two types: TD-CDMA and TD-SCDMA, which use unpaired band. These bands are used for

high bit rates at hotspots (up to 2 Mbit/s) with low-mobility (less then 10 km/h). All bit rates are based on the first generation of UMTS (Release 1999). Further evolutions of UMTS will make even higher transmission speeds possible

2.6 UMTS Technology Overview IP-based Multimedia Services (IMS) http://www.telecomabc.com/i/ims.html IP-based Multimedia Services (IMS) is a part of the UMTS specification (as of Release 5) that provides IP transport in the core network and the radio access network (UTRAN). IMS enables the convergence of data, speech, and mobile network technology over an IP–based infrastructure. �

IMS was designed to fill the gap between the existing traditional telecommunications technology and Internet technology. This will allow operators to offer end-to-end IP services. This increases the potential for new innovative services and service integration with other networks such as the Internet. IMS enriches the way people communicate with each other by combining voice, image, and video into a single session. IMS uses SIP and session description protocol (SDP) underneath architecture to communicate between various IMS components. The architecture of IMS specifically helps enable and enhance real-time multimedia mobile services such as rich voice services, video telephony, messaging, conferencing, and push services. IMS enables these user-to-user communication services via a number of key mechanisms such as session negotiation and management, quality of service (QoS) and mobility management. However, IMS enables much more than just real-time user-to-user services. High Speed Downlink Packet Access (HSDPA) http://www.telecomabc.com/h/hsdpa.html The HSDPA is an enhancement of the UMTS radio-interface to make higher data rates possible. HSDPA introduces a high speed downlink shared channel (HS-DSCH). This high speed channel is shared among the users. The "theoretical" peak data rate is in the order of 14 Mbps. HSDPA provides average data throughput speeds of 550-1100 kbps to the user. The delay within the network (latency) is also lower. �HSDPA can be implemented in the standard 5 MHz channels available for UMTS. HSDPA requires a software and hardware modification of the base stations (Node B) as well as a software upgrade of the Radio Network controller (RNC). The user will require a new terminal. GSM EDGE Radio Access Network (GERAN) http://www.telecomabc.com/g/geran.html The GERAN is a radio access network architecture, based on GSM/EDGE radio access technologies. The GERAN is fully harmonised with the UMTS Terrestrial Radio Access Network (UTRAN) through a common connectivity to the UMTS core network. This makes it possible to build a combined network for GSM/GPRS and UMTS.

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High Speed Uplink Packet Access (HSUPA) http://www.telecomabc.com/h/hsupa.html The HSUPA is an enhancement of the UMTS radio-interface to make higher data rates possible in the uplink. To do so, HSUPA introduces an enhanced dedicated channel (E-DCH). In UMTS Release 6, HSUPA is referred to as E-DCH. � The HSUPA improves the coverage, the throughput as well as the delay of the uplink dedicated transport channels. HSUPA is the counterpart of HSDPA, which improves the data rate on the downlink. Multimedia Broadcast/Multicast Service (MBMS) http://www.telecomabc.com/m/mbms.html The MBMS is a feature to provide the capability for Broadcast and Multicast Services in GERAN (GSM/EDGE) or UMTS mobile networks. MBMS can be used to transfer light video and audio clips or other data to a large group of mobile subscribers in an efficient manner. To do so, MBMS is a so-called point-multipoint service. This means that multiple users receive the same information using the same radio resources. �

In MBMS there are two different kinds of services defined. A broadcast service in which every user can receive the information within the service area and a multicast service in which only users that have subscribed to the service can receive the information. Multicast users have a return channel which gives the possibility for interactive services. This return channel can also be used to subscribe to the desired service. Although MBMS can be used for mobile TV, it has some limitations in the capacity that can be used for this kind of services within the network. MBMS can take up to 30% of the capacity of a cell. In the first phase of Multimedia Broadcast and Multicast Service (MBMS) this capacity can be used to deliver streams of 64 - 256 kbps over an UMTS network and 32 to 128 kbps streams over a GSM/EDGE network. Additional improvements in the technology (such as HSDPA) will enhance the throughput and the quality of service. Multiple Input Multiple Output (MIMO) http://www.telecomabc.com/m/mimo.html The MIMO) is a technique that utilizes multiple antennas at both the transmitter and the receiver, i.e. at both the base station and the terminal in a wireless network. Each antenna sends only a part of the total bit stream. �

MIMO is especially useful in an environment with a lot of multipath fading i.e. in an environment where there are more than one transmission paths from the transmitter to the receiver due to reflections. This is especially the case in a mobile environment and in an in-house environment. MIMO technology will be used by both UMTS and Wi-Fi as a technology to increase the data capacity of a link.

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3 2G GSM to 3G UMTS – Network Architecture This section takes help from to different Internet-web resources.

3.1 UMTS Network Architecture - Evolution: from 2G-GSM to 3G-UMTS R5 http://www.tech-invite.com/Ti-ims-releases.html

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3.2 UMTS Network Architecture -- Evolution: from 2G-GSM to 3G-UMTS R7 http://conningtech.blogspot.com/ GSM: the 2G mobile network Global System for Mobile communications (GSM) is the most popular standard for mobile communications in the world. Its network architecture is shown in figure 1.

Figure-1: GSM network architecture

GPRS: the 2.5G mobile network General Packet Radio Service (GPRS) is a packet oriented mobile data service developed on the GSM infrastructure. It provides data transfer rate from 56 to 114 kbits/s. GPRS network architecture is as shown in figure 2.

Figure-2: GPRS network architecture

EDGE (EGPRS): the 2.75G mobile network Enhanced data rates for GSM evolution (EDGE), enhanced GPRS (EGPRS) or IMT Single Carrier (IMT-SC) is a packet mobile technology evolved from the GPRS infrastructure providing enhanced data transfer rate and reliability.

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The network architecture for EDGE is basically the same as that for GPRS, the same network elements, the same interfaces, the same protocols and the same procedures. The only minor differences lie in the air interface improvement for supporting higher data transfer rate and reliability. UMTS: The 3G mobile network – Release 3 (also called Release 99)

o 64kbits/s circuit switched bearer services o 384 kbits/s packet switched bearer services o location services o call services

UMTS: The 3G mobile network – Release 4 o EDGE radio o multimedia messaging o MExE (mobile execution environment) o improved location services o IP multimedia services (IMS)

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UMTS: the 3G mobile network – Release 5 o IP multimedia subsystem (IMS) o IPv6, IP transport in UTRAN o improvements in GERAN, MExE etc, o HSDPA

UMTS: the 3G mobile network – Release 6

o WLAN integration o multimedia broadcast and multicast o improvements in IMS o HSUPA

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UMTS: the 3G mobile network – Release 7

o Fix mobile convergence o DSL access

4 CDMA and W-CDMA – An Overview Code Division Multiple Access (CDMA) is a multiple access (MA) technology. The meaning of MA in simple terms is: accessing to a network using a shared channel (such as open air radio channel) with other users.

4.1 Multiple Access Technologies

Note: The diagram should add CSMA/BA as well

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4.2 Channelization Multiple Access Techniques Let us consider four communications entities: space, frequency, time and code. More than one communication signal can be carried by a single channel if any one of the above entity is different for those signals. That is, the receiver side can separate the desired signal from all other signals.

o Space => Space Division Multiple Access => same time, same frequency, same coding for all signals but different space for each of them

o Time => Time Division Multiple Access

=> same space, same frequency, same coding for all signals but different time for each of them

o Frequency => Frequency Division Multiple Access => same space, same time, same coding for all signals but different frequency for each of them

o Code => Code Division Multiple Access

=> same time, same space, frequency for all signals but different code for each of them

Multiple Access Schemes (http://www.umtsworld.com/technology/cdmabasics.htm)

4.3 CDMA Principle The CDMA technique codes each bit of data into a pattern looks like many tiny bits, called Chips (see the figure below). The chip pattern (chipping sequence) is the ‘Code’. Each transmitting station uses separate code. If the receiving station uses the same code then it can recover this signal from a mix of many signals (at same frequency, time and space)

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Since the coded signal looks like higher bit-rate signal (7 times higher in the above example) the bandwidth of the resultant signal is expected to be higher. In the above example, if the original signal bandwidth is 1 MHz then the coded signal’s bandwidth is 7 MHz. However, this seven bandwidth is not used just this signal. It is shared by many others (bandwidth per user is lower enough). The following figures show how CDMA signal is generated in the transmitter and recovered in the receiver.

CDMA spreading (http://www.umtsworld.com/technology/cdmabasics.htm)

4.4 Why CDMA The CDMA technology is wining over the TDMA (just like how TDMA won over FDMA). Note that, first generation system was analog and could not be TDMA or CDMA. The 2G is digital and by that time TDMA technology was improved and cost of TDMA system decreased enough to beat the FDMA technique. In 3G CDMA was not mandatory (TDMA could be the technology) but found an improved way to provide service. Apart from its comparable bandwidth efficiency with TDMA it has the following two killer advantages:

o Security CDMA is coded. If the code is secret the communication is secured

o No hard limit of capacity TDMA defines a fixed number of time-slot and that’s it - no more, no less – and same quality of service for all slots CDMA can accommodate up to 2N users, where N is code length (number of chips per code). If the code length is, for example, 16 then the number of user is about 64 thousands!! But hang on, this is not that high since it is a requirement to keep the codes different in a signification number of bits (not just one or two); otherwise the receiver may not be able to detect the signal without too many errors. That is, higher code separation is related to better

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signal reception. Question is how much separation is good enough? It is like, what voice quality is good enough for you in a poor coverage area. The fact is there is no hard threshold. This is the key to the flexibility we are talking about. If a network operator reduces its quality it can allocate more codes and hence more users using the same bandwidth (Just imagine a poorer quality at peak hours and better quality at other hours).

4.5 W-CDMA Overview W-CDMA (Wideband Code Division Multiple Access) is the main technology for UMTS radio access scheme (other two well-known technologies are TD-CDMA and TD-SCDMA). The W-CDMA is implemented in UMTS Terrestrial Radio Access (UTRA) network called UTRAN. The access scheme for UTRA is Direct Sequence CDMA (DS-CDMA). The information is spread over a band of approximately 5 MHz. This wide bandwidth has given rise to the name Wideband CDMA. In WCDMA, there are two different modes of operation possible:

o TDD: In this duplex method, uplink and downlink transmissions are carried over the same frequency band by using synchronized time intervals. Thus time slots in a physical channel are divided into transmission and reception part.

o FDD: The uplink and downlink transmissions employ two separated frequency bands for this duplex method. A pair of frequency bands with specified separation is assigned for a connection. Since different regions have different frequency allocation schemes, the capability to operate in either FDD or TDD mode allows for efficient utilization of the available spectrum

WCDMA Technical Specifications (http://www.privateline.com/3G/WCDMA.pdf)

The chip rate may be extended to two or three times the standard 3.84 Mcps to accommodate data rates higher than 2 Mbps. The 200 kHz carrier raster has been chosen to facilitate coexistence and interoperability with GSM.


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