Fourth Generation of Mobile Communication (4G)
We are experiencing exponential growth rates in mobile communication systems, increasing mobility awareness in society, and deregulation of former monopolized markets while traditional communication paradigms with fixed networks, mobility raises a new set of questions, techniques and solutions. For many countries, mobile communication is the only solution due to the lack of an appropriate fixed communication infrastructure. The trends mentioned above create an ever- increasing demand for well-ended communication engineers who understand the developments and possibilities of mobile communication. What we see today is only the beginning. There are many new and exciting systems currently being developed in research labs. The future will see more and more mobile devices, the merging of classical voice and data transmission technologies, and the extension of today’s internet applications (e.g., the World Wide Web) onto mobile and wireless devices. New applications and new mobile networks will bring ubiquitous multimedia computing to the mass market; radios, personal digital assistants, laptops and mobile phones will converge and many different functions will be available on one device.
This REPORT is an introduction to the field of fourth generation of mobile communications and focuses on digital data transfer. The paper is intended for use by students of EE or communication classes, engineers working with fixed networks who want to see the future trends in networking, as well as managers who need a comprehensible overview in mobile communication. The reader requires a basic understanding of communication and a rough knowledge of the Internet or networking in general.
This work addresses people who want to know how 4G mobile phone systems work, what technology will be next in satellite communication, and how mobility will influence applications, security, or networks.
The job follows a tall and thin’ approach. it covers a whole course in 4G mobile communications, from signals, access protocols, up to application requirements and security. Topics in the higher layers of communication, like the wireless applications are also mentioned here briefly.
1.2 Standards of mobile communication
The main standards and the main markets in which they are used are summarized in the following table.
|Year||Standard||Mobile telephone system||Technology||Primary Markets|
|1981||NMT-450||Nordic Mobile Telephone||Analogus||Europs Middle East|
|1983||AMPS||Advance Mobile Phone System||Analogue||North and South America|
|1985||TACS||Total Access Communication System||Analogue||Europe and Chana|
|1986||NMT 900||Nordic Mobile Telephone||Analogue||Europe, Middle East|
|1991||GSM||Global System for Mobile Communication||Digital||World-wide|
|1991||TDMA D-AMPS||Tune Division Multiple Access||Digital||North and South America|
|1992||CDMA||Code Division Multiple||Digital||N. America, Korsa|
|1993||GSM 1800||Global System for Mobile Communication||Digital||Europe|
|1994||PDC||Personal Digital Cellular||Digital||Japan|
|1995||PCS 1900||Personal Communication Services||Digital||North America|
|2000||CDMA, GPRS||Coded Division Multiple Access||Digital||USA|
|2002||4G, WCDMA||WCDMA/UMTS CDMA 4G||Digital||Japan USA|
Table: Brief History of Mobile Standards.
1.3 Scope of 4G
4G is designed to deliver:
- A wide range of market-focused applications.
- Long-term market-driven creativity, an innovative value chain and real user benefits, driving genuine market demand.
- Advanced, lightweight, easy-to-use terminals with intuitive interfaces Instant, real-time multimedia communications.
- Global mobility and roaming.
- A wide range of vendors and operators, offering choice, competition and affordability.
- High-speed e-mail and Internet access.
1.4 What’s new in 4G
- All network elements are digital.
- Entirely packet-switched networks.
- Higher bandwidths to provide multimedia services at lower cost (up to 100Mbps)
- Tight network security.
1.5 Comparison of 3G and 4G
|Back compatible to 2G.||Extend 3G capacity by one order of magnitude:|
|Circuit and packet switched networks.||Entirely packet switched networks.|
|Combination of existing & evolved equipment.||All network elements are digital.|
|Data rate (up to 2Mbps).||Higher bandwidth (up to 100 Mbps).|
1.6 Rolling out of 4G
NTT DoCoMo already launched the worlds’ first commercialized fourth-generation “FOMA” mobile communication service on October l, 2003. FOMA is the name used in Japan for NTT DoCoMo’s 4G services.
The question of 4G deployments is not a technical issue, but a regulatory and economic one- Subscriber demand is the key factor: user expectations for mobile services are being raised, and for any successful 4G license bidder time to market will be critical. The way 4G is rolled out in a particular market-will depend entirely on the business plans of the mobile operators, and the license requirements imposed by the regulatory authorities.
Today’s mobile network operators can gain the vital business and market experience of providing high-speed mobile data services by introducing packet switching networks such as GPRS (General Packer Radio Service). By the time the new WCDMA, EDGE and cdma2000 wideband radio interfaces are standardized and commercially available, the market will already be attuned to the possibilities of 4G. Japan was the first market to announce specific plans to introduce wideband radio networks based on WCDMA technology. As a result, it is expected that 4G will go into service first in Japan. Currently, WCDMA networks are scheduled to be in operation there in 2001. The 4G licensing process has completed in many countries in Europe, and the first wideband radio networks are expected to enter commercial operation in 2005. Before then, GPRS will be introduced into GSM networks, to increase user bandwidth. The first GPRS systems was introduced early in 2000 in France but due to handset shortest and technical problems of the advance overall network architecture, it was not a success.
The concept of mobile telephony was originated in the 1920’s, but it was only in 1947 that the cellular network structure was devised. Up to then, no solution enabled a mobile station to roam far from the antenna system. The concept of cellular communication was born in the Bell laboratories of the USA in the late 1960’s. In the mid 1970’s, AT&T’s Bell labs demonstrated, what came to be known as Cellular Mobile Telephone (CMPT). Cellular technology provides communication to and from the user located anywhere on the glob or within a territory, through a portable lightweight handheld mobile telephone. It is a two way communication process. An area is divided into a number of cells, each with a Radio Base Station (RBS), having a transmitting and receiving tower. In cellular mobile telephone system, the subscriber carries small sized transceiver (transmitter cum receiver) with an assigned radio frequency channel through which the Public Service Telephone Network (PSTN) subscriber can call the mobile, the mobile can call the PSTN subscriber and the mobiles themselves can talk to one another. Based on the concept of efficient spectrum utilization, the cellular mobile radio system design can be analyzed and related to the others. `1 major elements are the concept of frequency reuse channels, the co channel interference reduction factor, handoff mechanism, cell splitting etc. The common problems are path loss, shadowing, multi-path fading, time dispersion, time alignment etc. There are several solutions to solve these problems. To solve these problems several techniques such as channel coding, interleaving, adaptive equalization, frequency hopping etc are used.
2.2 Cellular fundamentals
A cell may be defined an area of radio coverage from one Base Transceiver Station (BTS) antenna system. It is the smallest building block in a mobile network and is the reason why mobile networks are often referred to as cellular networks. The power level of a transmitter within a single cell must be limited in order to reduce the interference with the transmitters of neighboring cells. The interference will not produce any damage to the system if a distance of about 2.5 to 3 times the diameter of a cell is reserved between transmitters.
In order to work properly, a cellular system must verify the following two main conditions.
· Neighboring cells cannot share the same channels. In order to reduce the interference, the frequencies must he reused only within a certain pattern.
· It is two-way communication process. An area is decided into a number of cells, each with a radio base station (RBS), having a transmitting and a receiving tower. Each RDS has a set of channels assigned. The mobile in a given cell send its signals to RBS.A number of RBSs are connected to and controlled by ‘a base station controller (BSC). All the BSCs in the service Qreace connected to the mobile switching center (MSC) which handles major technical like switching, assigning radio channels to every mobile, locating the cell a mobile is in as soon as it is switched on, as it moves From cell, measuring the calls, recording the charges etc The MSC is the switches that interconnect the PSTN (public switched telephone network) and the mobile system.
2.3 A basic cellular system
A basic cellular system consists of three parts: a mobile unit, a cell site, and a Mobile Telephone Switching Office (MTSO).
· Mobile unit: A mobile telephone unit contains a control unit, a transceiver and antenna system.
· Cell site: The cell site provides interface between the MTSO and the mobile units, it has a control unit, radio cabinets, antennas, a power plant, and data terminals.
· MTSO: The switching off-ice, the central coordinating element for all cell sites, contains the cellular processor and cellular switch. It interfaces with Telephone Company Lone offices, controls call processing, and handles billing activities. The radio and high-speed data links connect the three substations. Each mobile unit can only use one channel at a time for its communication link. The MTSO is the heart of cellular mobile system. Their processor provides central coordination and cellular administration.
The cells are grouped into clusters. The number of cells in a cluster must be determined so that the cluster can be repeated continuously within the covering area of an operator. The typical clusters contain 4,7,12 or 21 cells. A balance must be found in order to avoid the interference that could occur between neighboring clusters.
2.5 Cell type
Cells can be of different types based on the antenna direction, size and nature of the area they cover, etc. Some of the cell types are described below:
A. Depending on the antenna direction:
· Omni cells are the cells served by antenna, which transmits, equally in all horizontal direction.
· Sector cell – a cell with uni-directional BTS antenna system.
Three sectored cells from one tower system can also form a circular coverage area. Sectors will be 120 degree apart from each other. In Grameen Phone we use three sectored cells to obtain more or less a circular coverage area.
B. Depending on the size of the cell:
- Macro cell
- Micro cell
- Pico cell
C. Depending on the area
· Urban cell
· Suburban cell
· Rural cells ‘
D. Depending on the cell relationship
- Overlaid cell
- Under laid cell
- Umbrella cell
E. Depending on thee usage
v Indoor cells
v Outdoor cell
v Road cell to give coverage to a particular road, etc.
2.6 Performance criteria
The cellular system provides some important performances which give the subscribers better services. There are four categories for specifying performance criteria.
2.6.1 Voice quality
Voice quality is very hard to judge without subjective tests from users opinions. In this technical area engineers cannot decide how to build a system without knowing the voice quality that will satisfy the users. For any given commercial communications, the voice will be based upon the following criterion: a set value X at which Y percent of customers rate the system voice quality as good or excellent, the top to circuits merits of the five listed bellow:
· CMS- excellent (speech perfectly understandable)
· CM4- good (speech easily understandable, some noise)
· CM3- fair (speech understandable with a slight effort, occasional repetition)
· CM2- fair (speech understandable only with considerable effort, frequent repetition needed )
· CM 1- unusable (speech not understandable)
2.6.2 Service quality
· Coverage: The system should serve an area as large as possible. It is usually not practical to cover 100 percent of the area for two reasons:
a. The transmitted power would have to be very high to illuminate weak spots with sufficient reception, a significant added cost factor.
b. The higher the transmitted power, the harder it becomes to control interference.
· Required grade of service: For a normal start-up system the grade of service is specified for a blocking probability of 0.02 for initiating calls at the busy hour. This is an average value.
· Number of dropped calls: During Q calls in an hour, if a call is dropped and Q-1 calls are completed, then the call drop rate is l/q, this drop rate must be kept low.
2.6.3 Low terminal and service cost
In cellular system the mobile terminal (hand set) and the rate per minute of the call is low than other system.
2.6.4 Support of international roaming
In cellular system one can get the service of call even during moving from one site to another by the process of hand over As the tits roams through the area, it continuous t scan the control channels to ensure that It is tuned to the strongest possible channel If the MS finds one, which is stronger, then the MS retunes to this new control channels If the new control channel belongs to a new Local Area (LA), the MS will also inform the network of its new location.
2.7 Operation of cellular System
For the call set up in the cellular mobile communication system among the subscribers throughout the cellular network the following operations are to be performed.
2.7.1 Mobile unit initialization
When a receiver of a mobile unit is activated, its scans 21 set up channels, which are designed among the 333 channels. It then selects the strongest and locks on for a certain time. This means selecting nearest cell site. This function is done in idle stage and is used independent. After 60 see, this self-location procedure is repeated.
2.7.2 Mobile Originating call
The user places the called number into an originated register, checks to see that the number is correct and pushes the “send” button. A request for service is sent on a selected set-up channel obtained from a self-location scheme. The cell receives it, and in directional cell sites, selects the best directive antenna for the voice channel to us.
At the same time the cell site sends a request to the mobile telephone switching office. (MTSO) via a high-speed data link, The MTSO selects an appropriate voice channel for the call; it also connects the wire-line party through the telephone company zone off-ice.
2.7.3 Network originated call
A land-wire party dials a mobile unit number. The telephone company zone office recognizes that the number is mobile & forwards the call to the MTSO sends a paging message to certain cell site based on the mobile unit number and the search algorithm. Each cell site transmits the page on its own set-up channel. The mobile unit recognizes its own identification on strong set-up channel, lucks on to the cell site.
2.7.4 Call termination
When the mobile user turns off the transmitter, a particular signal (signaling tone) transmit to the cell site, and both sides free the voice channel.
2.8 Handoff procedure
During the call, two parties are on a voice channel. When the mobile unit moves out of the coverage area of a particular cell site, the reception becomes weak. The present cell site requests a handoff. The system switches the call to a new frequency channel in a new cell site without either interrupting the call or altering the user. The call continues as long as the user is talking. The user does not notice the handoff occurrences.
2.9 Hand Over
Hand over is defined as the passing, I taking over a live call between two neighboring cells or frequencies. When a user reaches the edge of a cell, the signal strength (between the serving base station and himself) gets weaker. If his call is not taken over by another cell, his call might be dropped (discontinued). The signal strength criterion is the basic behind a hand over. However, there are many other special reasons why a call could be handed over (bad quality, congestion, etc).
As the cell sizes are getting smaller, the probability of a subscriber to move to a nearby cell while talking is increasing also. Thus the challenge of this cellular concept is to transfer a “live” call to a nearby cell when the user is on the move. The characteristic of such a hand over is the delay time – i.e., how faster the call can be handed over. Now a clays the systems are so intelligent and faster that the user is totally unaware of when they are actually handing over to other cells.
Fig : car crossing a cell
As we are reducing the cell size, the shorter would be “sate distance” and the more would be the number of such hand over and more resources (measurements, calculation, decision making) would be needed from the network element to handle these great number of hand over.
Following figure shows a road, this passes through many cells. A car taking this road will be served by all these cells one after another thus generating a number of handover in one single call.
2.10 Coverage range of a cell
Coverage is defined as the area of the geographical region where a good communication is possible via the mobile station.
By coverage is usually meant that an area is covered if in 90% of that area the signal received by the mobile station is larger than some value. This value is defined by the radio planner on the basis of the area and the equipment specifications. According to the strength of the signals, the coverage may be classified into three types:
2.10.1 Outdoor coverage
This is designed for open area. This may be useful for the rural area coverage. High gain antenna with wide opening angle is possible in this kind of coverage.
2.10.2 In-car coverage
This is designed for the coverage inside vehicle. Due to the penetration loss of the glass window of the vehicle, the planners need stronger signal to reach the radio coverage inside the vehicle. For road coverage this kind of coverage is important.
2.10.3 Indoor coverage
This is the most challenging coverage to provide. This is the coverage that the city dwellers would demand. Due to the penetration loss of the thick walls of the building (concrete, glasses, etc.), it is needed to provide stronger signal. However, this can not be guaranteed!! This is because different houses are built in different ways, with different materials. Also that there may be a corner where it is very difficult for the radio signal to reach. As a thumb rule if one can read newspaper in any corner of the house in broad daylight, then it may be possible to reach coverage to that corner Because of the stronger signal requirement for indoor coverage, it is always expensive to provide this kind of coverage.
2.11 Cell splitting
The motivation behind implementing a cellular mobile system is to improve the Utilization of spectrum efficiency. The frequency reuse scheme in one concept and cell splitting is another concept. When traffic density starts to build-up & the frequency channels in each cell cannot provide enough mobile calls, the original cell can be split into smaller cells. Usually the new radius is one-half the original radius, i.e. New cell radius=.Old cell radius/2
Hence, new eel l area= Old area/ 4
So, new traffic load/unit area 4x traffic load /Unit area. There are two kinds of cell-splitting technique:
2.11.1 Permanent splitting:
The installation of every new split cell has to be planned ahead of time, the number of channels, the transmitted power, the assigned frequencies the choosing of the Cell-Site selection and the traffic load consideration should all considered.
2.11.2 Dynamic splitting:
This schemes is based on utilizing the allocated spectrum efficiency in real time. The algorithm for dynamically splitting cell sites is a tedious job since we cannot afford to have one single cell unused during cell splitting at heavy traffic hours. The splitting procedure is shown below:
2.12 Efficient phone operation with minimum power consumption
· Hold the phone, as would any other telephone. While speaking directly into the mouthpiece, angle the antenna in a direction up and over the shoulder. If the antenna is extendable, it should be extended during a call.
· Do not hold the antenna when the phone is in use. 1-biding the antenna affects call quality, may cause the phone to operate at a higher power level then needed and shown talk and standby times.
Check the laws and regulations on the use of telephones in the areas where one drive. When one uses phone while driving then
- It is needed give full attention to driving.
- Use off handshake operation, if available.
- Pull off the road and a park before making or answering a call if driving conditions so require.
2.14 Receiving a call
When you receive a call, the phone rings the indicator light on the top of phone blinks rapidly.
2.15 Answering a call
· Press YES to answer the call.
· When the call is finished, press no.
2.16 Rejecting a call
· Press No when the phone rings If the caller’s network supports it, the cagier will hear a busy tone.
2.17 Putting a call on hold
· Press YES to put a call on hold.
· To put the call off hold, press YES again.
2.18 A typical set of specification for mobile unit
Battery voltage ……………………………. 9.0 to 16.0 Vdc
Received current………………………….. 1.1A (Max)
Transmitted current………………………. 3OA (Max)
Frequency range………………………….. 935-960 MHz
Channel spacing…………………………. 30 kHz
Sensitivity………………………………… I micro volt for 12 dB sired.
Adjacent channel…………………….. Better than 50 dB
All other channel……………………. better than 65 dB
Audio response……………………. 30 Hz to 3 kHz+dB
Harmonic distortion…………….. <5%
Inter modulation…………………. 65 dB
Frequency range…………………. 890-915 MHz
Channel spacing…………………. 30 kHz
Carrier stability………………….. + 2.5 ppm
Load impedance………………… 50 ohm
Output power…………………… 3 watt (nominal Max. Level)
Power steps……………………. seven, 1 dB steps
100% deviation……………… + kHz peak
FM hum & noise…………… <-40 dB
Distortion……………………. < 5%
Tx attach/inhibit time………… < 2 ns
Carrier power inhibit………… 60 dBm
2.19 Capacity and frequency re-use:
Figure: Neighboring cells can not have the same frequency
The number of frequencies in a cell determines the cell’s capacity. Each company with a license to operate a mobile network is allocated a limited number of frequencies These frequencies are distributed throughout the cells in their network. Depending on the traffic load and the availability of frequencies, a cell may have one or more frequencies allocated to it.
To cover an entire country, fur example, frequencies must be re used many times at different geographical locations in order to provide a network with sufficient capacity. The same frequencies can not be used in neighboring cells as they would interfere with each other so special patterns oh frequency usage are determined during the planning of network.
The mobile communication has come to the present state following a step by step generation. The first generation of mobile communication was started in Chicago, USA. It was analog one-called AMPS. It could transmit voice at a very slow rate. The second generation mobile was digital. It is able to transmit slow rate data & faster voice compared to first generation. The Third Generation Mobile Communication is the most modern mobile communication, which is already launched in Japan & USA. It provides several special features. In a word its functionality is like magic. As part of the landmark project to deliver the first KPI-compliant UNITS network in Africa to Vodacom, South Africa’s leading cellular network, Siemens Communications has partnered with their counterpart in 4G Technology and wireless network performance engineering solutions provider Actix. This chapter describes the step-by-step evaluation of mobile communication.
3.2 Generations of wireless.
-First generation wireless systems used Analog technologies to provide circuit switched access for mobile voice telephony
- AMPS (Advanced Mobile Phone System)
- MTS, IMTS, NMT, TACS, ETACS, JTACS, others.
– Second-generation wireless systems use the earliest digital technologies provide mainly circuit- switched access for mobile voice telephony
· GSM (Global System for Mobile Communications) TDMA
· IS- 54. IS- 136 TDMA
· IS- 95 CDMA.
– Third generation wireless systems use improved digital technologies to provide packet- switched access for advanced voice and data applications
- wider- bandwidth, higher- capacity, more features and applications
- CDMA2000 IxRTT, IxEV DO, DV, 3xRTT – migration path from IS- 95
- GPRS & UNITS – migration path from GSM and IS – 136 TDMA
- EDGE – migration path from TDMA.
– Fourth Generation technologies are erupting into the marketplace, a revolution that could topple (or be absorbed by) the established players.
3.3 Wireless data
– Each wireless technology offers limited data capability today.
One or more circuit- switched traffic channels arc dedicated to fast data instead of voice
- Dial- up modem emulation is provided at the wireless switch
- Packet data access maybe provided by a muter at the switch, but the RF link is circuit- switched
- Data rates are slow; compression may be provided.
– Even 3G CDPD and Mobitex Data- Only technologies are slow!
– 4G technologies are much better!
- Much faster RF traffic channels
- True packet- switched channel management.
Table 1. Short History of Mobile Telephone Technology
|Service||Analog voice, synchronous data to 9.6 kbps||Digital voice||Higher capacity, packetized data||Higher capacity, broadband data up to 2 Mbps||Higher capacity,
completely Ip-oriented, multimedia, data to hundreds of megabits
|Data Bandwidth||1.9 kbps||14.4 kbps||384 kbps||2 Mbps||200 Mbps|
|Multiplexing||FDMA||TDMA, CDMA||TDMA, CDMA||CDMA||CDMA?|
3.4 Interesting features in 4G
· Support interactive multimedia services: teleconferencing, wireless Internet, etc.
· Wider bandwidths, higher bit rates.
· Global mobility and service portability.
· Low cost.
· Scalability of mobile networks.
3.5 Wireless development and the recent history of 4G
The above figure shows the ages of science & Technology according to the name of scientists of different ages.
– The ITU defined objectives for next-generation mobile systems in a 1998 request for proposals.
– Sponsoring organizations submitted details of proposed radio transmission.
3.6.1 The radio perspective
Original commercial CDMA systems in the 800 MHz. Band complied with IS- 95A, and 1900 MHz. Systems complied with the Joint Standard 008. Both had the following common features:
- 12288 MCPS spreading, signal 125 MHz Wide.
- BTS Sectors have short PN offsets, channels are Walsh codes.
- Mobiles have long PN offsets and transmit one channel only
Traffic Channel Capabilities:
· Rate Set 1: 9600- bps traffic channels for 8 kb/s vocoders.
· Rate Set 2: 14400- bps traffic channels for 13 kb/ s vocoders
and other 14400- max data applications.
3.6.2 IS- 95B: CDMA 3G enhancements
IS- 95B is still considered Third Generation, but offers some needed enhancements to the original IS- 95A and J- Std008.
Improved Access Methods
- Mobiles originally could use only one sector during an access attempt Multipath fading causes roughly 2% failed accesses!
- IS- 95B allows mobiles to use alternate sectors as “backup” during access in case the original sector fades.
Improved Handoff Methods
- Original CDMA provided only fixed- threshold handoff triggers
– Inflexible, can skip needed handoffs but waste unneeded ones
- IS- 95B uses slope and intercept- based thresholds to tailor handoff action to what is really needed for call survival.
Faster Data Services
·Original CDMA allowed data only at the rate of a single traffic channel
· Is- 95B/ IS- 707 allows aggregation of traffic channels for faster data, but not at the rates provided by 3G cdma2000.
3.7 The 4G path from GSM: GPRS, WCDMA, UMTS
3.7.1 GSM history
– The GSM network architecture was defined in work of the ETSI during the late I 980s
- Switching and network architecture based on ISDN concepts
- Roaming and location management derived from early intelligent Networks concepts.
– GSM has enjoyed large business success due to its non-proprietary open architecture and competitive vendors
- Approximately 60% of global wireless subscribers use GSM.
3.7.2 Air interface
There are three frequency bands defined for GSM: 900, 1800, and 1900. Within the GSM 900 band, there are 174 frequencies with 200kHz spacing. Separate bands are used for uplink (mobile to base) and downlink (base to mobile).
Within each frequency, there arc 8 timeslots supporting up to 8 users. The modulation scheme is gaussian minimum shift keying, GMSK (a variant of binary phase shift keying) with a bit rate of 271 kbit/s.
The speech signal is processed in 20ms intervals, called speech frames. Each speech frame is compressed and coded using 244 bits. These 244 bits are then encoded with a channel code, interleaved, segmented, and transmitted in 8 TDMA time slots. Similar transmission formats are used for data services.
3.7.3 GSM radio network aspects Frequency planning and re-use. Frequency planning is necessary to avoid the same frequency being used in nearby cells, which would cause unwanted interference. The number of cells that use different frequencies is called the reuse factor. Tighter reuse (lower reuse factor) means that more frequencies can be used in each cell, for a given number of total frequencies, but also means a larger interference between the cells.
Handover. When a user moves during a speech call, it may be necessary to perform a handover to another base station to keep the call. To support this, the mobile station periodically measures the quality of all neighbor cells and reports to the network. The decision when to perform the handover is made in the base station controller.
Power control. Depending on attenuation and interference, different transmit power levels may be needed to obtain adequate signal quality. Power control is used to set the smallest possible power that meets the quality target. This reduces interference towards other users and increases the battery life time.
Frequency hopping. A frequency may be bad in a certain location due to multipath fading, or it may be bad due to interference from other cells. Frequency hopping may be used to avoid staying at a bad frequency, instead a number of frequencies are circulated using a pseudo-random hopping sequence. .
GPRS, General Packet Radio Services, is anextension to GSM that allows more efficient packet data transfer compared to traditional GSM data services. The principle is that a user can be constantly connected to the network without occupying any radio resources (frequency, time slots) until a data packet has to be transferred. When a packet is to be transferred, a temporary channel is assigned to the user; after completed transfer, the channel is quickly released again. GPRS allows many users to share the same timeslot, and also allows a single user to use more than one time slot. It uses an error detection and retransmission scheme to ensure that data packets are correctly delivered to the receiver.
EDGE, Enhanced Data rates for GSM Evolution, is another extension to GSM that allows higher bit rates than GSM does. This is accomplished by using higher order modulation, 8-ary phase-shift keying instead of GSM’s binary phase-shift keying.
3.7.6 WCDMA and UMTS
WCDMA, Wideband Code-Division Multiple Access, is a new radio interface standard that supports a set of Universal Mobile Telecommunication Services, UMTS.
The requirements of UMTS are:
· Coverage and capacity for speech services should be better than GSM, under the same conditions
· The system should be able to efficiently and flexibly handle a mix of real time, variable bit rate, and
· A data rate of 384 kbit/s should be possible to provide with full coverage (everywhere).
· It should be possible to provide a data rate of 2 MbiVs in selected areas, e.g. indoors.
The basic principle of CDMA is that all or many users utilize the same frequency band simultaneously. The benefit of this is that each user has access to the entire system bandwidth all the time, potentially allowing higher data rates than a FDMA/TDMA system where each user has access to only a smaller bandwidth. However, the shared frequency means that the receiver of a particular signal has to cope with strong interference from other users. The CDMA principle used in WCDMA is called directsequence code-division multiple access. In the transmitter, the data sequence is spread by multiplying with a spreading sequence of a higher rate, after which it is modulated and transmitted. Spreading means that each data symbol (represented as +/-1) is repeated a number of times, equal to the spreading factor, and each repeated symbol is multiplied with a new symbol from the spreading sequence. The spreading sequence is a pseudorandom sequence that makes the transmitted signal look like noise. The receiver demodulates the signal and multiplies it with the same spreading sequence as was used in the transmitter. The original data sequence is then restored by taking the average over the repeated symbols.
3.7.7 WCDMA air interface
The CDMA principle is the corner stone for the flexibility of the WCDMA air interface. A higher data rate requires a low spreading factor, which means that the averaging in the receiver occurs over fewer symbols, resulting in less noise reduction.
Therefore, a higher data rate requires a higher transmit power, and will cause stronger interference to other users. Conversely, a lower data rate can use a lower transmit power, causing less interference to other users. The transmit power does not only depend on the data rate, but also on the radio conditions. A user in a good location near the base station requires a lower power than a user far away. Furthermore, it is important that users in good locations keep their powers at a minimum, since they may otherwise cause too strong interference for other users. This is called the near-far effect. This is accomplished through closed-loop power control, whereby the receiver constantly monitors the quality of the received signal, and sends power control commands back to the transmitter, instructing it to either increase or reduce the power.
FIG. WCDMA air interface example
Some key parameters of the WCDMA air interface are:
- Chip rate (rate of the spreading sequences) 3.84 MHz
- Bandwidth 5 MHz
- Modulation QPSK (quaternary phase-shift keying)
- Spreading factor 4, 8, 16, 32, 64, 128, or 256
- Power control rate 1500 Hz
3.7.8 Frequency re-use 1
Because of the CDMA principle, all base stations in a WCDMA system occupy the same frequency, i.e. the frequency reuse factor is 1. This means that the entire spectrum owned by an operator can be used in each cell.
3.7.9 Soft handover
Because of the varying radio conditions, the signal attenuation between the user and the base stations may change very quickly. If the user is connected to only one base station, it may be impossible to move the connection fast enough to always use the base station with the lowest attenuation (the “best” base station).
FIG. Soft handover
In a system with reuse factor 1, it may be disastrous for the system if a user is not connected to the best base station. The reason is that the transmit power in the mobile will by set such that the received signal is strong enough in the connected base station. If another connection is “better”, the transmit power of the mobile may cause too much interference in that base station, degrading the quality for other users. Soft handover means that the user is connected to more than one base station. The goal is to ensure that the best base station is always connected, even when the conditions are quickly varying. In soft handover, the transmit power of the mobile is controlled by the “best” base station, i.e. the base station to which the attenuation is lowest. Thereby, the power can be kept down and excessive interference can be avoided.
3.8 FDMA/TDMA vs. CDMA Here are some technology comparisons between FDMA/TDMA and CDMA.
3.8.1 Fading resistance
Because CDMA systems use a higher bandwidth compared to systems that use FTMA, the systems are less vulnerable to frequency-selective fading. On the other hand, the neartar effect means that fast power control is needed in CDMA systems to ensure that interference is not too large.
A FDMA/TDMA system is limited by its choice of channel bandwidth and time slot structure, which typically can not be changed after standardization. In a CDMA system, on the other hand, the resource sharing is accomplished by control the amount of power transmitted for each user, which can be changed in real-time.
3.8.3 Frequency planning
Systems based on FDMA require frequency planning, which is difficult and time consuming. This is not necessary with CDMA systems.
Mobile stations based on TDMA transmit in short pulses, causing strong power peaks and potentially interfering with other devices. CDMA-based mobile stations, on the other hand-transmit continuously, only changing the power in steps according to varying radio conditions and desired bit rates.
The high bandwidth and chip rates of CDMA makes the transmitters and receivers more complex to design and manufactured compared to FDMA-based devices.
New mobile connections now exceed new fixed connections and, it is expected, will continue so to do. A successful vision for 4th generation systems will be set in a mobile/wire free environment with fixed as a subset. An Operator who wishes to launch 4G mobile, have to have a perfect plan for the total system. In this chapter there are some discussion about that Planning.
4.2 The mobile challenge
The first mobile challenge that of providing mass market voice communication, is largely satisfied by the existing digital cellular systems. The next challenge is to do the same for the Information Society services including graphics, video and mufti media.
4.3 The 4th generation marketplace
The 4th Generation Marketplace in the UK and Europe will be characterized in several ways; Personalization of services with the use of Universal Personal Pocket Terminals that are adaptive to support customer and network specific needs; Customers using wire free products and services with high performance and capabilities (including graphics, video and multi-media) that change how they work and live, with new consumer and business products which incorporate embedded radios to support services such as maintenance, customer care and fraud/theft prevention; a Market rapidly growing in penetration to 40% by 2005 (and continuing to grow), from which the majority of the population will derive benefit, involving significantly increased usage promoted by low costs and an extensive range of services, a highly competitive marketplace at al levels, and the concept of universal availability; and Service which will include advanced wire free services for business and consumers integrated with the information superhighway and its future developments including the European Information Infrastructure; with Vast Growth in value added opportunities based on capabilities within and external to networks and terminals, and new and innovative services stimulated by broadband networks.
New industrial growth from the Collisions and Convergences across industry will be enabled by 4th generation mobile systems with the future role of service providers, and possible restrictions on ownership, key issues for the industry requiring further study.
4.4 UMTS platform
The concept of the GSM platform has become a proven success and UMTS should be implemented so as to benefit from this experience. The merits of building on GSM are evident. Several mobile satellite operators have decided to base their infrastructure on GSM, providing dual operation with common security, authentication and billing mechanisms. Also, the European railway community UIC is to use a slightly modified version oh the GSM air interface for railway applications. Roaming with DECT using the GSM core platform is now in development, and a form of UPT based on the GSM SIM is being considered to provide roaming between fixed networks.
QSM has become a platform for a wide range of services with different terminal standards while using the SIM and MAP (and often the A interface) to provide roaming and billing with security. The GSM MoU Association has recently opened its membership to public operators of telecommunications systems based on the GSM platform irrespective of the terminal interface adopted, conditional on providing roaming services.
UMTS should adopt a similar approach with the specification of a number of standardized interfaces with specific interfaces to allow the cost effective multi- sourcing of infrastructure. As with GSM, the SIM (or USIM), MAP (or its replacement) and Billing Interfaces will be very important. The UMTS interfaces will perform many similar functions to those of GSM but will differ where necessary to support the more complex service and feature structure of UMTS.
4.5 Critical success factors
Success in a modern telecommunications venture is dependent on an available market and on an investment environment in which a sensible minimal risk business opportunity can be foreseen by financiers. The remainders of the success factors are targeted against meeting these two over-riding criteria. The more stable and more predictable the sector is seen to be, the more funding that will be available at attractive terms. This means that roll out occurs more rapidly, pay- hack is achieved in a shorter timescales, and the tariffs can be set to attract mass market participation from the outset, with the benefits that mobility and access to the information superhighway, fundamental to the success of the UK and Europe, can be achieved as quickly as possible.
The success factors are grouped into market, regulatory environment, industrial sector, standards and technology.
The Group considers that an initial total market opportunity of 8 million users is required to support the necessary investment by manufacturers of UMTS terminals, growing to at least 60 million within 10 years. Growth thereafter is subject to market development.
At the end of 1996, Japan had 18.2 million cellular customers and 4.9 million users of the Personal Handyphone System (PF1S); these markets are predicted to rise to 34 million for cellular and 38 million for PHS by the year 2010; a cordless market of 20 million at the year 2000 is expected to remain static until the year 2010. In financial terms, Japan consider this to be a market growing from a current £10,000 million (equivalent to 40,000 employees) to £32,000 million in 2000, and £93,000 million by 2010, by then supporting 520,000 employees.
Already in Scandinavia the penetration of cellular mobile is approaching 30%, in the UK it is almost 12% and within Europe and developed countries it is anticipated to rise to greater than 50% of the population. (Within the Stockholm district in Sweden the peak period penetration is estimated at up to 60%). The scale of the industry has grown vastly and within the UK there are over 100,000 employees are engaged on cellular domestic end export activities.
GSM MoU Association has given estimates that 150 million GSM terminals will be in use world-wide by the end of the century. GSM global usage will further grow to at least 200 million terminals by 2005, constituting a truly mass market. UMTS will go on to provide two major enhancements. Firstly the addition of broadband multimedia services and secondly the ability to connect via cellular mobile networks, global satellite networks, private cordless networks, and through wireless access to fixed public networks, whichever is the best for the user’s situation at any time.
4.5.2 Regulatory and licensing
Policy announcements setting out a calendar for the adoption of UMTS standards by the UK and Europe, for the release of a designated frequency allocation, and the conditions for licensing are recommended to encourage potential operators and manufacturers to commit resources to the third generation standards-making process and subsequent investment in third generation mobile technology.
It is important that the conditions for licensing the telecommunications business in Europe are not seen to be transient. An unstable historical environment is likely to deter both operators and manufacturers from making the massive investment necessary to implement third generation mobile.
The Group considers that it is essential to have a regulatory regime which will ensure that operators can reasonably expect that the licensing conditions offered will remain in place long enough to ensure that the massive investment in new technology is recovered, and that the market opportunities, identified during conception and licensing, will not be distorted by changes in regulatory policy. This may require a policy statement from the respective member states within Europe to ensure that this is achieved.
4.5.3 Industrial sector
Commercial successes will not he achieved without an announced commitment by strong manufacturers to support the standard and the technology – ideally a minimum of 3 infrastructure manufacturers and 10 volume terminal manufacturers. This will provide operators with both competitive choice for their network and an identifiable source of product so that the network can be exploited.
A stable standard is required, with open interfaces for all external interconnection and key internal network functional blocks. Such a standard will limit development brisk and maximize returns to manufacturers from development expenditure. It will create a competitive environment where users can change between operators and allow both choice and purchase confidence.
Technological solutions must be found which will ensure new services e.g. multi media and broadband services can be provided and migrated to and from fixed networks.
Technological solutions are required for Network, Architectures and Terminals which, when applied to high volume market, will produce very low cost terminals and low tariffs.
Technological solutions should allow migration from the existing second generation mobile systems where appropriate.
Technological solutions must take account of the strong convergence between the Information Technology and telecommunications sectors, in both the network infrastructure and terminal equipment fields.
Technological solutions must offer flexibility of service provision e.g. the capability to mix voice and data in various proportions, support variable rate data, etc.
4.6 Network issues
4.6.1 Service requirements
UNITS is required to support a wide range of services, generally incorporating those familiar within second generation cellular, fixed, cordless, satellite and PMR networks. The UMTS standard will also support a range of more advanced services such as multimedia. However, it is planned that in most cases, UMTS will provide support for these services, rather than itself define the actual services. Multi-media services will require the availability of higher bandwidths at variable rates, on demand (i.e. packet-based services