Name: Shaun Pola
Student Number: 01067192
The work contained in this assignment for this assignment for Communication Networks, other than that specifically attributed to another source, is that of the author. It is recognised that, should this declaration be found to be false, disciplinary action could be taken and the assignments of all students involved will be given zero marks.
Table of Contents
1. What is UMTS?
2. Standards on
which UMTS is based?
3. Key rivals of
UMTS and some of the advantages it has over them?
4. How is UMTS
architecture set up?
4.1. Hierarchy of
Cellular Design
4.2. Components
of / and Physical Layout of Infrastructure
5. Technical
Characteristics/ Specifications?
6.1. Radio
communication techniques
6.2. Protocols used?
7. Some new
features when compared to current 2G technologies?
7.1. Authentication
7.2. Soft Handoff
9. Companies
involved in its development?
10. Current
deployment/ results of field trials in the world and Australia?
11. What major
problems does the technology face?
13. Review Questions
1. What is UMTS?
The rapid penetration of mobile communications technologies into the marketplace in the mid to late 1990s has seen the demand for services outstrip the ability of telecommunications manufacturers, engineers, and industry organizations to provide solutions that are considered an effective long-term answer. The success of 2G services such as GSM also saw the need to integrate any extended services that were developed, into the existing infrastructure. This led to developments such as GPRS and EDGE which served to extend 2G features without a great deal of expense to mobile operators. However, the underlying issue with these technologies is that they could not solve problems at the very centre 2G systems design. Second generation systems weren’t designed with the idea of high bandwidth, high speed data transfer capabilities. The need for services which could support high data transfer saw the introduction of the third generation standards. UMTS or Universal Mobile Telecommunication System is one of these standards. It is a European standard for 3G services and was developed by the 3rd generation partnership project (3GPP), and has been designed in such a way that it can be easily integrated in with existing 2G infrastructures.
2. Standards on which UMTS is based?
UMTS is based on a standard developed by the International Telecommunications Union (ITU) called the IMT-2000. UMTS itself is a standard developed initially for European markets in mind but is rapidly becoming a globally adopted standard (amongst others). The main organisation behind its development is the 3rd generation partnership project (3GPP). The 3GPP is a collective effort of a larger group of telecommunications industry bodies that’s aim is “to produce globally applicable technical specifications and technical reports for a 3rd generation mobile system based on evolved GSM core networks and the radio access technologies that they support”
Site related to this topic: http://www.3gpp.org/About/about.htm
3. Key rivals of UMTS and some of the advantages it has over them?
There are 3 main standards being developed around the world
under the umbrella of the IMT-2000 standard for 3G networks. In
One of the main advantages UMTS has over the other 2 proposed 3G standards is the capability of infrastructure to be integrated in with existing GSM networks. This is a key point as it is estimated that 71% of current mobile telecommunications subscribers in the world are part of networks using GSM. This suggests that if and when the majority of current operators are to upgrade their networks to a 3G capacity, then financially it would make more sense to go for a UMTS functionality rather than the other two.
Having said this, building a UMTS network is still an expensive option, and there are also a number of technologies which aim to extend existing 2G infrastructure and in the process reduce the overall cost of implementing a service that will provide data transfer rates that are competitive with the full standards. A couple of the more prominent ones are GPRS (General Packet Radio Service) and EDGE (Enhanced Data for GSM Evolution). The problem with these extended GSM technologies is that GSM uses circuit switched technology which tends to waste transmission resources. Full 3G standards uses packet switching principles which tend to better share the transmission medium available.
Site related to this topic:
http://www.3gnewsroom.com/html/whitepapers/year_2001.shtml
(Ericsson white paper on WCDMA)
4. How is UMTS architecture set up?
4.1. Hierarchy of Cellular Design
The initial implementation UMTS has been designed to utilise existing GSM infrastructure based on the classic ‘cellular’ structure. However, where GSM utilises a single network of cells of roughly equivalent size (variation does occur depending on average amount of subscriber use in certain areas), UMTS will eventually implement a hierarchy of cells. Each layer can cope with a different level of user density. The major difference between each layer in the hierarchy from the user’s point of view is the effective data transfer rate and the rate at which the user can be moving while within the cell. There are 3 main types:
|
Type of Cell |
Typical Coverage
Area |
Max. Data Transfer |
Max. User speed |
|
Macro |
Large cell area, lowly populated areas |
Up to 144kb/s |
500km/hr |
|
Micro |
Used in areas of higher populations density |
Up to 384kb/s |
120km/hr |
|
Pico |
Used for offices or ‘hotspots’ (areas such as airports or train stations |
Up to 2Mb/s |
10km/hr |
Animation
developed by S.Pola using referenced sources of Information
All these 3 layers will use infrastructure known as the UMTS terrestrial radio access network or UTRAN.
Also eventually to be included in this hierarchy is the use of Satellites for Global coverage (global roaming), this however has not been implemented in any currently deployed networks.
4.2. Components of / and Physical Layout of Infrastructure
The physical layout of terrestrial infrastructure is similar to the existing GSM architecture. This aids in achieving one of the aims of UMTS of integration with existing 2G network sites. UMTS can be broken up into 4 distinct functional areas: UE (user equipment), UTRAN (UMTS radio terrestrial radio access network), the CN (core network), and the HE (Home Environment).
The user equipment or ‘terminals’ are the end user devices (more detail on these can be found under Applications of UMTS). They consist of the terminal itself with the UICC/ USIM.
The UTRAN provides the link between the end users and the core network. It is basically all the elements that are required for the radio communications part of the UMTS network. The UTRAN can be further broken down into 2 smaller components:
1. Node B (or base station) – Its primary function is to provide a radio connection between the network and the user ‘terminal’.
2. RNC (radio network controller) – The RNC oversees multiple Node B base stations within a given ‘cell’ and one of its functions is to manage the radio resources within that area. In addition to this it also provides 2 connections to the CN, one to the packet switched domain and the other to the circuit switched.
A very important element is the CN or Core Network. This part of the network is responsible for routing information to its correct destination be it voice traffic bound for the PSTN, or packets destined for the Internet. It has six major components:
1. SGSN (Serving GPRS Support Node) – This is the node for access to the packet switched domain (internet traffic, SMS etc.).
2. GGSN (Gateway GPRS Support Node) – This is a gateway node for connections to other networks. All data traffic going to other operator’s networks or the internet goes through this node.
3. BG (Border Gateway) – Acts as a firewall to prevent attacks by intruders outside the network on subscribers within the network realm.
4. VLR (Visitor Location Register) - This is current serving networks ‘copy’ of the subscriber data needed to provide services. This information initially comes from the HLR (see Home Environment)
5. MSC
(
6. GMSC (Gateway MSC) – Takes care of routing functions required to the current location of the subscriber. Receives and administers connection requests from subscribers from external networks.
The final element is the Home Environment. This part of the network holds service profiles for subscribers to the network. It has 3 major components:
1. HLR – Essentially a database which administers mobile subscribers. There may be multiple HLRs depending on the size of the network.
2. AuC – Database for storage of authentication information for subscribers. It is usually co-located with the HLR, however the databases are kept as separate entities for security reasons. AuC stores the secret keys required in authentication for each subscriber as well as session key generating functions. It also produces the Authentication Vectors which are explained in more detail in ‘Authentication’.
3. EIR (Equipment Identity Register) - A register kept for the purposes of blocking access to the network in the case of stolen phones etc. It keeps a record of the IMEI (International Mobile Equipment Identities) that have been blocked.
Figure 1: Generalised UMTS Architecture
(developed by S.Pola using referenced sources of Information)
1. Technical Characteristics/ Specifications?
UMTS utilizes CDMA (code division multiple access)
technology in different forms depending on the situation. For Pico cells TDD (Time Division Duplex) using TD-CDMA is used, it can
provide data transfer rates of up to 2Mb/s. For macro or micro cells FDD
(Frequency Division Duplex) using W-CDMA is utilized which can achieve data
rates of up to 384 kb/s. The reason why W-CDMA is used over TD-CDMA for macro
cell communications is has been found to be much more effective for situations
where the use is traveling at higher speeds (up to 200km/hr). In addition TD-
CDMA is also suited to asymmetric data transfer (i.e. Personal Internet
traffic, one of the main reasons for Pico cells)
Below is a basic description of
how the time slots are organized for TDD using TD-CDMA:
Figure 2: TD – CDMA Protocol
Statistics Source: Cellular Online
website
Site related to this topic:
http://www.cellular.co.za/umts.htm
http://www.siemens.ie/mobile/umts/facts2.htm
2. How it operates?
2.1. Radio communication techniques
The air interface technique that UMTS uses for all but picocell radio links is called W-CDMA (Wideband Code Division Multiple Access). The basic idea is that 2 bands of frequencies are used for uplink (from mobile user to the network) and downlink (from network to the mobile user). In the UMTS standard the frequency bands reserved are 1980-2010MHz (uplink) and 2170-2200MHz (downlink). W-CDMA uses what is called Direct Sequence Code Division Multiple Access, the basic idea is the mathematical coding techniques are used to create orthogonal signals (ones that are don’t interfere with each other) to interleave different signals simultaneously across the same bandwidth. In the case Pico cells the TD-CDMA technique uses the same coding techniques but the system only operates in half duplex with just one side transmitting at any one time. The changeover between transmitting and receiving occurs so often it appears that there is transmission in both directions simultaneously. This overcomes the need for the uplink and downlink frequencies that aren’t available in certain countries.
2.2. Protocols used?
For certain link communications UMTS uses protocols and products currently used by GSM networks. However for there have a number of new products and designs implemented specifically for UMTS. There have been 4 new communication protocols specifically for use in UMTS networks:
1. Uu – For communications between UE and Node B base stations otherwise known as UTRA or the W-CDMA interface
2. Iu – For communications between the RNC and the GSM 2G+ Core Network (MSC/ VLR or SGSN)split into 2 separate sub-protocols
- Iu-CS for circuit switched data
- Iu-PS for packet switched data
1. Iub – for communications between Node B base stations and RNCs
2. Iur – for communications between RNCs
The three protocols Iu, Iub, Iur are based on ATM transmission principles.
In the case of the core network facilities IP has been chosen as the Network layer protocol for the sake of compatibility with other data networks and ATM has been chosen as the data link protocol.
3. Some new features when compared to current 2G technologies?
3.1. Authentication
Authentication in mobile networks is one topic that has become more critical an issue with the increasing significance of the role of mobile or wireless technologies in modern political and corporate environments. It is not enough for networks merely to be fast and reliable but they must become secure and a trusted medium as well. In GSM authentication was a much simpler process than which will be the case in UMTS. 2G networks are basically only concerned with one particular authentication procedure (i.e. Authenticating the user to his/ her own network). Central to the authentication process is the Subscriber Identity Module or SIM card. It is essentially a smart card with the subscriber information embedded into it. The basic authentication process is based on a shared secret between the user and the network which is indirectly exchanged from user to network each time a connection is made. UMTS basically uses the same idea (this occurred mainly for the sake for backwards compatibility) except that it adds extended functionality. Replacing the SIM will be the UMTS IC Card or UICC. The UICC is still a ‘smart’ card but in the case of UMTS it is merely a platform onto which a number of Subscriber applications maybe loaded. These subscriber applications are referred to as USIMs (User Subscriber Identity Modules).
The USIM contains all the relevant information that a particular network requires to identify the user. One big difference to GSM is that more than one USIM may be placed on the UICC thus providing the user access to more than one network from the same terminal without having to change the smart card in the phone. To access a particular network, the user verifies him/ herself to the network they want to use at that particular time using the corresponding USIM. The UICC also allows for storage of additional applications such as digital signatures that could be used for e-commerce transactions.
Another difference in the UMTS authentication process is that both the subscriber and network are authenticated, this is very important as 3G will involve transmission of a lot more data than in the current networks. Authentication in the case of data transfer is very important as the user has no real way of verifying that a user is who he says he is without it. Two-way authentication is a very important technique for prevention of man-in-middle attacks where an intruder poses as a network for example supplying the user with false information a type of attack very common on current fixed line data networks.
The method of authentication in UMTS is called Authentication and Key Agreement or AKA. AKA procedures involve the USIM, SGSN/ VLR and the HLR AuC parts of the UMTS architecture. The process is managed by the VLR/ SGSN that the subscriber is connected to at that point in time. Below is a basic overview of how AKA authentication works:
Two Way Authentication Procedures (Animation developed by S.Pola using referenced sources of Information)
The Authentication Vectors (AV) consist of several components a random number (RAND(i)), generated by the Home environment, an expected response (XRES), a cipher key CK(i), an integrity key IK(i) and lastly an authentication token (AUTN(i)).
The XRES is used by the VLR as a reference to compare against the RES generated by the USIM. These responses are based on the ‘shared secret’ idea also used in GSM. The XRES is used to authenticate the user by comparing this to the response generated and sent to the VLR from the USIM.
The cipher keys CK are used for encryption purposes and the integrity keys are used to ensure the transmitted data has not been altered by any unknown source.
The last important component used for two way authentication is the Authentication Token (AUTN). The USIM uses this token to authenticate the network, one of the added functions in UMTS.
Some sites related to this topic:
http://www.globecom.net/ietf/draft/draft-arkko-pppext-eap-aka-03.html
http://siving.hia.no/ikt01/ikt6400/jrdohm99/
3.2. Soft Handoff
Handoff is a term used to describe the sequence of procedures that are carried out by the network when a mobile user moves from the coverage of one particular cell into another to ensure there is continuity of that coverage for the user. It is basically the arrangement for transfer of radio communications from the old cell’s Node b base station (or BTS in GSM) to the new cell’s one. One problem that has plagued existing networks when it comes to this particular process is that often it is quite untidy with call drop-outs or disruptions common. Soft Handoff is a concept that doesn’t currently exist in 2nd generation networks but is part of the UMTS standard and was designed to eliminate this particular problem.
In existing 2G networks when signal strength to a user drops to a pre-determined level a process is initiated where adjacent cells are ordered to check signal strength to the user and to send this information back to the MSC (Mobile-service Station Controller) via the BSC, the MSC then based on this information makes a decision about which particular cell shall take over call transmission to the user. Once a decision is made regarding transfer the previous cell ends transmission at effectively the same time as the new begins. This type of changeover is where the problems with the current systems lie, any signal strength fluctuations to the new cell can result in a call drop-out. This particular problem is a much bigger issue in 3G as all the data transmitted is error sensitive (i.e. packet switched) with these sort of drop-outs introducing errors into the system. In Soft -Handoff when a decision is made to Handoff a call to a new cell the system commands both the existing and new cell to transmit to the user simultaneously using 2 separate codes on the same frequency. The mobile telephone once receiving both these signals then decodes and combines them to optimize signal reception. When the signal strength from the mobile phone to the original cell drops below a certain threshold, it then requests disconnection from that cell, thus ending the simultaneous transmission. There is scope for these multiple transmissions to occur with more than 2 cells. One other difference related to Handoff is that the RNC (the UMTS equivalent of the BSC) manages radio resources rather than the MSC which is the case with GSM systems. A downside to Soft Handoff is it tends to take up precious network bandwidth.
Animation developed by S.Pola
using referenced sources of Information
4. Applications of UMTS
For the user the main difference or advantage they will notice with UMTS over existing cellular services is the broad variety of services that will be on offer. The high bandwidth capabilities of the system make downloading things graphics or images far quicker (as much as 120 times faster), making much elaborate services possible.
The added performance also leaves more scope for making many more types of devices compatible with UMTS. Devices such as handheld communicators, palm or laptop computers which previously saw no application with 1st or 2nd generation mobile technologies can be equipped with a USIM card. With the addition of cameras, speakers/microphones, functions such as video conferencing where voice, video, and data are transmitted simultaneously could be conducted over the UMTS network using these devices.
One problem that UMTS faces is the potential take-up of the technology to offset the expense of building the networks. It is estimated that line rentals, UMTS ready handsets will be considerably more expensive than existing technologies and there needs to be good reasons for consumers to convert. This has lead to the race for the so called ‘Killer Applications’, the applications that users see as potentially very useful in their day to day lives. There is still a large degree of uncertainty about what these will be.
Some sites related to this topic:
http://www.siemens.ie/mobile/applications/index.htm
http://www.umts-forum.org/press/article047.html
5. Companies involved in its development?
Many of the biggest telecommunications companies in the world have substantial investments in UMTS technologies. There are a lot partnerships with different companies responsible for developing different parts of the required infrastructure. Some of these partnerships are listed below:
1. ALCATEL + FUJITSU (Evolium SAS)
2. SIEMENS + NEC (Mobisphere Ltd.,) + CASIO / TOSHIBA
3. MOTOROLA + CISCO + FUJITSU + PIONEER + ALCATEL (Alcatel RNC, MOTOROLA Node B)
4. NOKIA + CISCO (IP Core network)
5. NOKIA + Interdigital (technology development relationship)
6. NORTEL + Matsushita/Panasonic + SAMSUNG
7. LUCENT (alone)
8. ERICSSON (alone)
6. Current
deployment/ results of field trials in the world and Australia
Deployment/ and or field trials of UMTS at this stage has
been fairly limited at this stage limited to
In
In
In Isle of Man, the first successful
voice call was made over the UMTS system in May 2001, at the same time however,
an integrated software fault was found with the handsets, and the initial
roll-out was delayed until December 2001. In June 2001, the first video call
was made, which showed the potential and benefits of a larger colour screen. In August 2001, the first IP packet data call over
UMTS provided fast internet and data application access at a high bandwidth.
The network went live in December
2001, with 24 out of 28 base stations operative, however a limited number of
NEC handsets meant that only a limited trial is possible.
There is currently no deployment of a UMTS network in
7. What major problems does the technology face?
The biggest challenge faced by those designing and building mobile network infrastructure is ensuring that the network constructed can cope with the peak traffic demands that may occur when it is operational, in other words ensuring sufficient bandwidth is available within a given cell. With any of the proposed 3G systems this becomes even more of an issue because of the added bandwidth required for 3G services.
Because bandwidth will be at such a premium, there is a need to keep individual cell sites as small as possible to balance the available bandwidth amongst the users within a given area. This of course has to be offset against the huge cost in constructing networks that are able to meet user demands. The more sites you build to allow a higher level of users, the higher the cost of both building and maintaining the network. A careful balance must be struck between the two.
8. Key Learning Points
- UMTS was a 3G standard developed by a
working group called 3GPP specifically for European markets but is being
adopted worldwide. Comes under the umbrella of much larger standard called
IMT-2000 developed by the ITU.
- The reason behind development of 3G
standards was to address the limited capability of current mobile
technologies to handle high speed data transfer.
- Designed to integrate with existing GSM
infrastructure to reduce costs of building new networks.
- This aims to make implementation
cheaper than other proposed 3G standards
- Claims to have data transfer rates of
up to 2Mb/s.
- Uses the W-CDMA air interface is used
outdoor larger areas as it effective when the user is moving at
considerable speed (up to 200km/hr)
- Uses TD-CDMA air interface in small
area indoor environments to achieve the maximum predicted data rates in
asymmetric data transfer applications (i.e. Internet)
- Has one other major 3G competitor in
Cdma2000 which has attracted large interest in the
- Design of network architecture will
differ considerably from current designs with a hierarchy of cells ranging
in both size and data transfer rates.
- Introduces new concepts such as Mutual
Authentication and Soft Handoff.
- Concept of the SIM card to be extended
in the form of the USIM which has added functionality.
- The USIM runs as an application over a
UICC smart card, this concept allows for access to more than 1 network
from the same terminal.
- Currently being developed by major
telecommunications companies such as Motorola, Alcatel, Nokia etc.
- Uses IP over it’s core network to
increase compatibility with linked data networks, Internet etc.
- Uses ATM transmission to aid in high
data transfer rates.
- User Equipment designed to incorporate
new types of devices such as laptops, personal organisers in addition to
currently used handsets.
- One concern of network operators
currently is whether the technology will be adopted as enthusiastically as
GSM was for example.
- Currently the search is on by operators
for the so called ‘Killer Applications’, the applications which users
can’t live without.
- Another issue is the balance of cost of
building the network with building one with sufficient capacity to be able
to deliver on its promised capabilities.
9. Review Questions
1. Who
is responsible for developing the UMTS standard?
1.
3GGP
2.
McDonalds
3.
ITU
4.
2. What
is the major competitor for UMTS in the
1.
GSM
2.
AMPS
3.
Cdma2000
4.
EDGE
3. What
is the air interface technique used by UMTS?
1.
W-CDMA
2.
TDMA
3.
CDMA
4.
FDMA
4. What
is the generic name given to the user equipment in UMTS?
1.
Handsets
2.
Terminals
3.
User Stations
4.
RNCs
5. What
does UMTS stand for?
1.
United
2.
Universal
3.
Uniform Metric Telephony Standard
4.
Unified Major Telecommunications Structure
6. Name
the 4 major elements of the UMTS architecture?
1.
CN, UTRAN, UE, HE
2.
Node B, RNC, SGSN, GGSN
3.
RNC, UE, BG, BTS
4.
BTS, BSC, MSC, SGSN
7. How
many different types of cells are in the UMTS hierarchy?
1. 2
2. 4
3. 1
4. 6
8. What data-link
protocol is used by the Core Network?
1.
ATM
2.
IP
3.
X.25
4.
UDP
9. How
fast is the predicted maximum data transfer rate?
1.
2Mb/s
2.
150kb/s
3.
10Mb/s
4.
100b/s
10. Where
have UMTS currently been deployed in a non trial environment?
1.
2.
3.
4.
11. What
part of the UMTS architecture is responsible for storing subscriber
information?
1. Node
B
2.
HE (HLR)
3.
RNC
4.
BTS
12. Which
of the following is one advantage of UMTS for the user when compared with GSM?
1.
SMS
2.
Mutual Authentication
3.
Encryption over air interface
4.
Itemised billing
13. What
part of the UMTS network is responsible for ‘Handoff’ duties?
1.
Node B
2.
RNC
3.
SGSN
4.
HLR
14. What
type of Handoff is UMTS to implement?
1.
Hard Handoff
2.
Soft Handoff
3.
No Handoff
4.
Super Soft Handoff
15. What type
of network layer protocol is to be used by the core network in UMTS?
1.
IP
2.
UDP
3.
X.25
4.
Ethernet
16. What
is the equivalent of the BTS (GSM) in the UMTS architecture?
1.
Node B
2.
RNC
3.
SGSN
4.
GGSN
17. Which
of the currently implemented mobile network standards is UMTS designed to
integrate with?
1.
GSM
2.
AMPS
3.
CDMA
4.
Cdma2000
18. Which
element of the core network acts as a gateway for voice calls?
1. MSC
2.
GMSC
3.
BG
4.
GGSN
19. Name a company involved with its current development?
1.
Enron
2.
Motorola
3.
BHP
4.
Hustler
20. What is name of the process of data transfer from User to Network?
1.
Uplink
2.
Downlink
3.
UpStream
4.
Downstream
References
1.
Harte L.,
Levine R., Kikta R., 2002, 3G Wireless Demystified, 1st
edn.,McGraw-Hill, New York.(pp51-52,356-358,
2.
Tisal J,1997,
GSM Cellular Radio, 1st edn.
3.
Webb W.,
1998, Understanding Cellular Radio, 1st edn. Artech House.(pp
232-236)
Acronyms
2G – Second generation mobile technology
3G – Third generation mobile technology
3GGP – The third generation partnership
project, association of telecommunications bodies responsible for UMTS Standard
AMPS – First generation mobile technology involving transmission techniques
ATM – Asynchronous Transport Mode
– data-link layer protocol
EDGE – Enhanced Data for GSM evolution, 2+ generation mobile technology
GPRS – General Packet Radio Service, technology developed for 2nd generation GSM networks to handle packet switched data
GSM – Global System for Mobile Communications, one of the 2G technologies currently in use
RNC – Radio Network Controller part of the UMTS architecture
UMTS – Universal Mobile Telecommunications System, one of the 3G standards to be implemented developed by 3GPP
UTRAN – UMTS radio terrestrial radio
access network, part of UMTS architecture that handles all radio based
communications in UMTS
W-CDMA – Wideband Code Division Multiple Access, one of the air interfaces to be used by UMTS
TD-CDMA – Time Division Code Division Multiple Access