3 G Mobile communication

Introduction

• Wireless Generations
• What is IMT-2000
• What IMT-2000 offers
• Key features and objectives
• Spectrum for IMT-2000
• Technologies for IMT-2000
• Migration paths
• Future Trends

1946- 1960s 1980s 1990s 2000s

Appeared 1G 2G 3G

Analog Digital Digital

Multi Multi Unified

Standard Standard Standard

Terrestrial Terrestrial Terr. & Sat

WIRELESS GENERATIONS

1 G -analog (cellular revolution) only mobile voice services

2 G - digital (breaking digital barrier) -mostly for voice services & data delivery possible

3 G - Voice & data (breaking data barrier) Mainly for data services where voice services will also be possible

Beyond 3G Wide band OFDM ?But surely higher data rates

LIMITATIONS OF 2nd GENERATION SYSTEMS

• No Global standards
• No common frequency band
• Low information bit rates
• Low voice quality
• No support of Video
• Various categories of systems to meet specific requirements

THIRD GENERATION (3 G ) STANDARD

• International mobile telecom 2000. imt-2000
• ITU’s vision for third generation mobile system
• a future standard in which a single inexpensive mobile terminal can truly provide communications any time and any where

• Provisioning of these services over wide range of user densities and coverage areas.(in-building , urban , sub-urban, global)
• Efficient use of radio spectrum consistent with providing service at acceptable costly.
• IMT-2000 shall cover application areas presently provided by seperately systems i.e cellular, cordless and paging etc.
• A high degree of commonality of design worldwide.
• A modular structure which will allow the system to grow in size and complexity.
• Single unified standard (data & multimedia services)
• Anywhere, anytime communication
• Across networks, across technologies, seamless operation using a small pocket terminal worldwide.
• High speed access 144kb/s, 384 kb/s & 2mb/s fast wireless access to internet
• Full motion videophone

• Terrestrial & satellite components
• Enhanced voice quality, ubiquitous coverage and enable operators to provide service at reasonable cost
• Increased network efficiency and capacity
• New voice and data services and capabilities
• An orderly evolution path from 2G to 3G systems to protect investments.

IMT TECHNOLOGIES

ITU has finally narrowed down technology options to the following five:

1. IMT -DS (Direct Spread) : W-CDMA UTRA FDD
2. IMT -MC (Multi Carrier) : CDMA 2000
3. IMT-TC ( Time Code) : TD -SCDMA UTRA TDD
4. IMT -SC ( Single Carrier ) : UWC - 136
5. IMT-FT (Frequency Time) : DECT

IMT-2000 HARMONIZATION IS ON-GOING

I

MT standards development involves extensive collaboration between many different organizations

• Today’s operators need seamless 2G 3G
• Many Focus groups have been established by industry
• 2 G operators GSM ; CDG ,UWCC, DECT forum
• 3 G Groups UMTS Forum , OHG
• Focus group for IP-based 3G architecture (3G. IP)
• SDOs created 3G PP (Partnership Projects)SDO Standards Development Organizations

Migration Path

• While a multiplicity of 2G standards have been developed and deployed, the ITU wanted to avoid a similar situation to develop for 3G.
• Hence, the ITU Radio communication Sector (ITU-R) has elaborated on a framework for a global set of 3G standards, which will facilitate global roaming by operating in a common core spectrum and providing migration path from all the major existing 2G technologies. 
• The major 2G Radio access networks are based on either CDMA One or GSM technologies and different migration path is proposed for each of these technologies.

Evolution from GSM to 3G

GSM Evolution

EDGE (Enhanced Data for GSM Evolution)

• Next step towards 3G for GSM/GPRS Networks
• Increased data rated up to 384 Kbps by bundling up to 8 channels of 48 Kbps/channel
• GPRS is based on modulation technique known as GMSK
• EDGE is based on a new modulation scheme that allows a much higher bit rate across the air-interface called 8PSK modulation.
• Since 8PSK will be used for UMTS, network operators will be required to introduce this at some stage before migration to 3G.

GSM to UMTS

GSM to GPRS to EDGE to 3G

• GSM can be upgraded for higher data rate upto 115 Kbps through deploying GPRS (General Packet Radio Service) network.This requires addition of two core modules
• SGSN (Serving GPRS Service Node)
• GGSN (Gateway GPRS Service Node)
• GSM radio access network is connected to SGSN through suitable interfaces.
• GPRS phase-II will support higher data rates up to 384 Kbps through incorporating EDGE
• ( Enhanced Data Rate for GSM Evolution).

GSM to 3G

• Further, to support data rates up to 2 Mbps, Third Generation radio access network (3G RAN)
• W-CDMA is deployed. 3G RAN is connected to GSM MSC for circuit oriented services and to SGSN for packet oriented services (internet access). Therefore the migration path can be represented as : 

GSM GPRS W-CDMA.

Migration Summarized

• In terms of migration of major 2G system to 3G capabilities, there would finally be 3 modes of CDMA-based radio interfaces (MC-CDMA, W-CDMA and CDMA-TDD) and two `TDMA based radio interfaces (UWC-136 and DECT).
• Considerable work is being carried out in respect of W-CDMA and CDMA 2000 worldwide. All European countries are expected to deploy W-CDMA as they have GSM based networks. While other countries such as Japan, Korea, USA etc. are likely to use CDMA-2000 or W-CDMA.

FUTURE TRENDS (3 G to 4G ONWARDS)

New data services, interactive TV and evolving Internet behavior will influence mobile data usage. Long sessions in always-on mode will force a re-think of radio access technology to achieve the required but not easy to attain capacity (Gbit/s/km) at low cost. The ideas presented in this article can increase capacity by a factor of 500 with regard to expected cellular deployments. Coverage will be based on large umbrella cells (3G, WiMAX) and numerous Pico cells interconnected to provide the user with seamless high data rate (several Mbs) sessions. Scalable and progressive deployments are possible while protecting the operator’s long-term investment. The 4G infrastructure operator will mix several technologies, each of which has its optimal usage. The connection to one of them will result in a real-time trade-off which will offer the user the best possible service. Some tools that genuinely improve the user’s multimedia quality of experience (availability, response time, definition, etc) are also presented in this article.

4G Mobile

4G will deliver low cost multi-megabit/s sessions any time, any place, using any terminal.

Operational Excellence

Voice was the driver for second generation mobile and has been a considerable success. Today, video and TV services are driving forward third generation (3G) deployment and in the future, low cost, high speed data will drive forward the fourth generation (4G) as short-range communication emerges. Service and application ubiquity, with a high degree of personalization and synchronization between various user appliances, will be another driver. At the same time, it is probable that the radio

access network will evolve from a central-ized architecture to a distributed one.

Service Evolution

The evolution from 3G to 4G will be driven by services that offer better quality (e.g. video and sound) thanks to greater bandwidth, more sophistication in the association of a large quantity of information, and improved personalization. Convergence with other network (enterprise,fixed) services will come about through the high session data rate. It will require an always-on connection and a revenue model based on a fixed monthly fee. The impact on network capacity is expected to be significant. Machine-to-machine transmission will involve two basic equipment types: sensors (which measure parameters) and tags (which are generally read/write equipment). It is expected that users will require high data rates, similar to those on fixed networks, for data and streaming applications. Mobile terminal usage (laptops, Personal digital assistants, hand-helds) is expected to grow rapidly as they become more user friendly. Fluid high quality video and network reactivity are important user requirements. Key infrastructure design requirements include: fast response, high session rate, high capacity, low user charges, rapid return on investment for operators, investment that is in line with the growth in demand, and simple autonomous terminals. The infrastructure will be much more distributed than in current deployments, facilitating the introduction of a new source of local traffic: machine-to-machine. Figure 1 shows one vision of how services are likely to evolve; most such visions are similar. Dimensioning targets A simple calculation illustrates the order of magnitude. The design target in terms of radio performance is to achieve a scalable capacity from 50 to 500 bit/s/Hz/km 2 (including capacity for indoor use), as shown in Figure 2. As a comparison, the expected best performance of 3G is around 10 bit/s/Hz/km2 using High Speed Down link Packet Access (HSDPA), Multiple-Input Multiple-Output (MIMO), etc. No current technology is capable of such performance. Dimensioning objectives Based on various traffic analyses, the Wireless World Initiative (WWI) has issued target air interface performance figures. A consensus has been reached around peak rates of 100 Mbit/s in mobile situations and 1 Gbit/s in nomadic and pedestrian situations, at least as targets. So far, in a 10 MHz spec-trum, a carrier rate of 20 Mbit/s has been achieved when the user is moving at high speed, and 40 Mbit/s in nomadic use. These values will double when MIMO is introduced. Clearly, the bit rate should be associated with an amount of spectrum. For mobile use, a good target is a network performance of 5 bit/s/Hz, rising to 8 bit/s/Hz in nomadic use.

Figure 1

Figure 2:Dimensioning examples

Multi-Technology Approach

Many technologies are competing on the road to 4G, as can be seen in Figure 3. Three paths are possible, even if they are more or less specialized. The first is the 3G-centric path, in which Code Division Multiple Access (CDMA) will be progressively pushed to the point at which terminal manufacturers will give up. When this point is reached, another technology will be needed to realize the requi-red increases in capacity and data rates. The second path is the radio LAN one. Wide-spread deployment of WiFi is expected to start in 2005 for PCs, laptops and PDAs. In enterprises, voice may start to be car-ried by Voice over Wireless LAN (VoWLAN). However, it is not clear what the next successful technology will be. Reaching a consensus on a 200 Mbit/s (and more) technology will be a lengthy task, with too many proprietary solutions on offer. A third path is IEEE 802.16e and 802.20, which are simpler than 3G for the equivalent performance. A core network evolution towards a broadband Next Generation Network (NGN) will facilitate the introduction of new access network technologies through standard access gateways, based on ETSI-TISPAN, ITU-T, 3GPP, China Communication Standards Association (CCSA) and other standards. How can an operator provide a large number of users with high session data rates using its existing infrastructure? At least two technologies are needed. The first (called “parent coverage”) is dedicated to large coverage and real-time services. Legacy technologies, such as 2G/3G and their evolutions will be complemented by WiFi and WiMAX. A second set of technologies is needed to increase capacity, and can be designed without any constraints on coverage continuity. This is known as picocell coverage. Only the use of both technologies can achieve both targets (Figure 4). Handover between parent coverage and pico cell coverage is different from a classical roaming process, but similar to classical handover. Parent coverage can also be used as a back-up when service delivery in the pico cell becomes too difficult.

Key 4G Technologies

Some of the key technologies required for 4G are briefly described below:

OFDMA

Orthogonal Frequency Division Multiplexing (OFDM) not only provides clear advantages for physical layer performance, but also a framework for improving layer 2 performance by proposing an additional degree of freedom (Pico cell). A good example of a pico cell is a WiFi coverage. By extension, a pico cell has a radius around 50 m and the associated base station is similar to a WiFi access point. It can be deployed indoors or outdoors.

Figure 4:Coverage performance trends

Using ODFM, it is possible to exploit the time domain, the space domain, the frequency domain and even the code domain to optimize radio channel usage. It ensures very robust transmission in multi-path environments with reduced receiver com-plexity. As shown in Figure 5, the signal is split into orthogonal sub carriers, on each of which the signal is “narrow band” (a few kHz) and therefore immune to multi-path effects, provided a guard interval is inserted between each OFDM symbol. OFDM also provides a frequency diversity gain, improving the physical layer performance. It is also compatible with other enhancement technologies, such as smart antennas and MIMO. OFDM modulation can also be employed as a multiple access technology (Orthogonal Frequency Division Multiple Access; OFDMA). In this case, each OFDM symbol can transmit information to/from several users using a different set of subcarriers (subchannels). This not only provides additional flexibility for resource allocation (increasing the capacity), but also enables cross-layer optimization of radio link usage.

Software Defined Radio

Software Defined Radio (SDR) benefits from today’s high processing power to develop multi-band, multi-standard base stations and terminals. Although in future the terminals will adapt the air interface to the available radio access technology, at present this is done by the infra-structure. Several infrastructure gains are expected from SDR. For example, to increase network capacity at a specific time (e.g. during

a sports event), an operator will reconfigure its net-work adding several modems at a given Base Transceiver Station (BTS). SDR makes this reconfiguration easy. In the context of 4G systems, SDR will become an enabler for the aggregation of multi-standard pico/micro cells. For a manufacturer, this can be a powerful aid to providing multi-standard, multi-band equipment with reduced development effort and costs through simultaneous multi-channel processing.

Multiple-Input Multiple-Output

MIMO uses signal multiplexing between multiple transmitting antennas (space multiplex) and time or frequency. It is well suited to OFDM, as it is possible to process independent time symbols as soon as the OFDM waveform is correctly designed for the channel. This aspect of OFDM greatly simplifies processing. The signal transmitted by m antennas is received by n antennas. Processing of the received signals may deliver several performance improvements: range, quality of received signal and spectrum efficiency. In principle, MIMO is more efficient when many multiple path signals are received. The performance in cellular deployments is still subject to research and simulations. However, it is generally admitted that the gain in spectrum efficiency is directly related to the minimum number of antennas in the link.

Software Defined Radio

Software Defined Radio (SDR) benefits from today’s high processing power to develop multi-band, multi-standard base stations and terminals. Although in future the terminals will adapt the air interface to the available radio access technology, at present this is done by the infra-structure. Several infrastructure gains are expected from SDR. For example, to increase network capacity at a specific time (e.g. during

a sports event), an operator will reconfigure its net-work adding several modems at a given Base Transceiver Station (BTS). SDR makes this reconfiguration easy. In the context of 4G systems, SDR will become an enabler for the aggregation of multi-standard pico/micro cells. For a manufacturer, this can be a powerful aid to providing multi-standard, multi-band equipment with reduced development effort and costs through simultaneous multi-channel processing.

Multiple-Input Multiple-Output

MIMO uses signal multiplexing between multiple transmitting antennas (space multiplex) and time or frequency. It is well suited to OFDM, as it is possible to process independent time symbols as soon as the OFDM waveform is correctly designed for the channel. This aspect of OFDM greatly simplifies processing. The signal transmitted by m antennas is received by n antennas. Processing of the received signals may deliver several performance improvements: range, quality of received signal and spectrum efficiency. In principle, MIMO is more efficient when many multiple path signals are received. The performance in cellular deployments is still subject to research and simulations . However, it is generally admitted that the gain in spectrum efficiency is directly related to the minimum number of antennas in the link.

Interlayer Optimization

The most obvious interaction is the one between MIMO and the MAC layer. Other interactions have been identified

Handover and Mobility

Handover technologies based on mobile IP technology have been considered for data and voice. Mobile IP techniques are slow but can be accelerated with classical methods (hierarchical, fast mobile IP). These methods are applicable to data and probably also voice. In single-frequency networks, it is necessary to reconsider the handover methods. Several techniques can be used when the carrier to interference ratio is negative (e.g. VSF-OFDM, bit repetition), but the drawback of these techniques is capacity. In OFDM, the same alternative exists as in CDMA, which is to use macro-diversity. In the case of OFDM, MIMO allows macro-diversity processing with performance gains. However, the implementation of macro-diversity implies that MIMO processing is centralized and transmissions are synchronous. This is not as complex as in CDMA, but such a technique should only be used in situations where spectrum is very scarce.

Figure 5:OFDM principles

Caching and Pico Cells

Memory in the network and terminals facilitates service delivery. In cellular systems, this extends the capabilities of the MAC scheduler, as it facilitates the delivery of real-time services. Resources can be assigned to data only when the radio conditions are favorable. This method can double the capacity of a classical cellular system. In Pico cellular coverage, high data rate (non-real-time) services can be delivered even when reception/transmission is interrupted for a few seconds. Consequently, the coverage zone within which data can be received/transmitted can be designed with no constraints other than limiting interference. Data delivery is preferred in places where the bit rate is a maximum. Between these areas, the coverage is not used most of the time, creating an apparent discontinuity. In these areas, content is sent to the terminal cache at the high data rate and read at the service rate. Coverages are “discontinuous”. The advantage of coverage, especially when designed with caching technology, is high spectrum efficiency, high scalability (from 50 to 500 bit/s/Hz), high capacity and lower cost. A specific architecture is needed to intro-duce cache memory in the net-work. An example is shown in Figure 8. At the entrance of the access network, lines of cache at the destination of a terminal are built and stored. When a terminal enters an area in which a transfer is possible, it simply asks for the line of cache following the last received. Between the terminal and the cache. A simple, robust and reliable protocol is used between the terminal and the cache for every service delivered in this type of coverage.

Multimedia Service Delivery, Service Adaptation and Robust Transmission

Audio and video coding are scalable. For instance, a video flow can be split into three flows which can be transported independently: one base layer (30 kbit/s), which is a robust flow but of limited quality (e.g. 5 images/s), and two enhancement flows (50 kbs and 200 kbs). The first flow provides availability, the other two quality and definition. In a streaming situation, the terminal will have three caches. In Pico cellular coverage, the parent coverage establishes the service dialog and service start-up (with the base layer). As soon as the terminal enters pico cell coverage, the terminal caches are filled, starting with the base cache. Video (and audio) transmissions are cur-rently transmitted without error and without packet loss. However, it is possible to allow error rates of about 10 -5 /10 –6 and a packet loss around 10 –2 /10 -3 . Coded images still contain enough redundancy for error correction. It is possible to gain about 10 dB in transmission with a reasonable increase in complexity. Using the described technologies, multimedia transmission can provide a good quality user experience.

Coverage

Coverage is achieved by adding new technologies (possibly in overlay mode) and progressively enhancing density. Take a WiMAX deployment, for example: first the parent coverage is deployed; it is then made denser by adding discontinuous Pico cells, after which the Pico cell is made denser but still discontinuously. Finally the pico cell cover-age is made continuous either by using MIMO or by deploying another Pico cell coverage in a different frequency band .Parent coverage performance may vary from 1 to 20 bit/s/Hz/km?, while Pico cell technology can achieve from 100 to 500 bit/s/Hz/km?, depending on the complexity of the terminal hardware and software. These performances only refer to outdoor coverage; not all the issues associated with indoor coverage have yet been resolved. However, indoor coverage can be obtained by:

• Direct penetration; this is only possible in low frequency bands (significantly below 1 GHz) and requires an excess of power, which may raise significant interference issues.

• Indoor short range radio connected to the fixed network.

• Connection via a relay to a Pico cellular access point.

Integration in a Broadband NGN

The focus is now on deploying an architecture realizing convergence between the fixed and mobile networks (ITU-T Broad-band NGN and ETSI- TISPAN). This generic architecture integrates all service enablers (e.g. IMS, network selection, middle ware for applications providers), and offers a unique inter-face to application service providers.

Conclusion

The provision of megabit/s data rates to thousands of radio and mobile terminals per square kilometer presents several challenges. Some key technologies permit the progressive introduction of such networks without jeopardizing existing investment. Disruptive technologies are needed to achieve high capacity at low cost, but it can still be done in a progressive manner. The key enablers are:

• Sufficient spectrum, with associated sharing mechanisms.

• Coverage with two technologies: parent (2G, 3G, WiMAX) for real-time delivery,

and discontinuous Pico cell for high data rate delivery.

• Caching technology in the network and terminals.

• OFDM and MIMO.

• IP mobility.

• Multi-technology distributed architecture.

• Fixed-mobile convergence (for indoor service).

• Network selection mechanisms.

Many other features, such as robust transmission and cross-layer optimization, will contribute to optimizing the performance, which can reach between 100 and 500 bit/s/Hz/km The distributed, full IP architecture can be deployed using two main products: base stations and the associated controllers. Terminal complexity depends on the number of technologies they can work with. The minimum number of technologies is two: one for the radio coverage and one for short range use (e.g. PANs). However, the presence of legacy networks will increase this to six or seven.

• Distributed architecture.

Architecture with a large number of decentralized connections to the core network.