4G: The Future Mobile Technology
Mohsin Jamil l , Shahan Parwaiz Shaikh 2, Mohsin Shahzad 3, Qasim Awais4 lNational University of Science & Technology,Pakistan, 2Nanyang Technological University, Singapore. 3University of Sheffield, United KingdomAWah Engineering College, Pakistan.
[email protected],
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[email protected] Abstract: With the rapid growth of user demands, and the limitations of third generation (3G) mobile communication systems, it is expected that fourth generation (4G) mobile systems are likely to reach the consumer market in another 4-5 years. 4G systems are expected to become a platform capable of providing increased bandwidth, higher data rates, and greater interoperability across communication protocols, and user friendly, innovative, and secure applications. This system will primarily focus on seamlessly integrating the existing systems like GSM, wireless LAN, and Bluetooth. This paper describes modulation scheme, different technologies, and network architectures that support 4G mobile systems. Challenges and some applications will also be presented. At last recommendations will be followed by conclusion. I.
INTRODUCTION
First generation (1 G) mobile systems, introduce in early 1980's, initiated commercial mobile voice services. 1G mobile system offered voice and low speed data transmission and was operated in circuit switched mode. These 1G network systems use Frequency Division Multiple Access (FDMA) schemes and operate in the 450 and 800MHz frequency bands. The major problems of 1G mobile system were internetworking between different networks and the quality was far from the standard offered by wire line telephony. These shortcomings were overcome with the advent of the Second Generation (2G) mobile systems. By using digital technology instead of analog one, 2G systems such as Global System for Mobile Communications (GSM) increased the number of supported users within a cell and enhanced voice quality significantly. In its original form, the GSM in the 900, 1800 and 1900MHz frequency bands uses a Time Division Code Multiple Access (TDMA) schemes for circuit mode transmission of digitized speech and digital data at up to 9.6kb/s. Since its commercialization in 1990's, GSM has been currently upgraded, by the introduction of High Speech Circuit Switched Data (HSCSD), General Packet Radio Services (GPRS), and Enhanced Data rates for GSM Evolution (EDGE), Enhanced Circuit Switched Data (ECSD) and Enhanced GPRS (EGPRS). 20's success story prompted the development of 2.50 and (30) mobile systems. Universal Mobile Telecommunications System (UMTS) standards were also developed to yield higher voice capacity and higher-speed data using a wideband carrier (5.2 MHz). The introduction of UMTS, based on Wideband Code Division Multiple Access (WCOMA) technology is a further step towards the increasing demand of high data rates.
In the 30, circuit mode speech and data as well as packet mode data transmission are possible with UMTS. Furthermore, higher data rates were designed to provide new innovative services, like mobile videophone, video streaming, and voice over IP. Moreover, wider coverage was promised with the help of macro, micro, and pico cells. 30 technology supports 144 Kbps data rate, with high speed movement (vehicles), 384 Kbps (on campus) & 2 Mbps for stationary (in building). Even before 30 networks are fully launched and utilized, various study groups are considering the shape of the next generation of cellular technology, so called 40. There is no single global vision for 40 as yet, but the next generation of network is likely to be all IP-based. In 40 the radio interfaces will support up to approximately 100 Mbps for high mobility and up to approximately 1 Obps for low mobility such as nomadic/local wireless access. 40 networks will also feature IP interoperability for seamless mobile Internet access. 30 is based on a wide-area concept applying circuit and packet switching for transmission with limited access technology, such as WCOMA, CDMA and TD-SOMA. However, the 40 standard will base on broadband IP-based, entirely applying packet switching method of transmission with seamlessly access convergence. 4G mobile system will include all systems from various networks~ from public to private~ from operatordriven broadband networks to personal areas: and from cell ular to ad hoc networks. Table 1 presents a short history of mobile technologies.
II.
LIMITATIONS OF 30/NEED FOR 4G
It has been observed that after every 10 years a new mobile generation comes up with new capabilities and functionalities. As the roll out took around 10 years for 2G, a similar period will apply to 30 which has started deploying since 2001 and by the year 2010 it will be the time to deploy 40 [1] networks and with this assumption the work on 40 has been started since year 2000. However 3G systems have some limitations which are stated as: • 30 can support multimedia internet type services at high data rates up to 384kb/s for moving up to 2Mb/s in limited coverage area. [1] • In 30, extension to higher data rate is difficult with COMA due to excessive interference between the services and users. • To ensure connection ubiquity together with high bandwidth and mobility, the network architecture must be heterogeneous rather than homogeneous.
TABLE I SHORT HISTORY OF MOBILE TECHNOLOGIES
Technology
IG
2G
3G
4G
Design Began Implementation Services
1970 1981 Analog voice
1980 1991 Digital voice. short message
1990 2001 Higher capacity, data rates up to 2Mbps
2000 2010 Higher capacity, Completely IP- oriented. multimedia. data to hundreds of megabits
Standards
AMPS, TACS. NMT. etc.
TDMA, COMA, GSM
WCDMA. CDMA2000
Single standard
Data Rate
NA
2 Mbps
>200 Mbps
Multiplexing
FDMA
COMA
OFDM
Core Network
PSTN
14.4 kbps TDMA. COMA PSTN
Packet network
Internet
Legend: AMPS CDMA FDMA GSM NMT OFDM PSTN TACS TDMA WCDMA
Advanced mobile phone service Code division multiple access Frequency division multiple access Global system for mobile communication Nordic mobile telephone Orthogonal frequency division multiplexing = Pubic switched telephone network = Total access communications = Time division multiple = Wideband CDMA
= = = = = =
• It is difficult to provide full range of multi-rate services with different QoS and performance requirements due to the constraints imposed on the core network by the air interface standard, e.g. 3G is not a fully integrated system. • The bandwidth available in the 3G mobile systems will be saturated and there are limitations on the combination of frequency and time division duplex modes. • Multi-modes appliances have to implement software configurable hardware architectures. • Limitation of spectrum and its allocation. • Difficult to roam across distinct service environment in different frequency bands. When the 3G was launched, it was assumed that it would become popular among the users but this didn't happen. Network operators were forced to reduce their expectations. Despite the work is going on the higher-speed 3G mobile networks, the main reasons for the leap towards 4G are: • As compare to 3G, 4G will provide rich multimedia contents. The downloading speed of 4G system will exceeds 100 Mbps, which is about 260 times greater than 3G wireless networks.
• Because of single global standard, the roaming between the different networks will be possible. Many services can be access by the users from the same mobile terminal • The 3G mobile network is based on primarily a wide-area concept. In 4G system, utilizing both wireless LAN and cellular design the users will be connected to a high-speed network anywhere, anytime. • In near future, there will be a great demand for high data rates and bandwidth. The 4G technology, would offer high-bandwidth services with the transmission speeds of more than 20 Mbps within the reach of LAN "hotspots", which are installed everywhere in offices, homes, malls and airport lounges. The 2G networks for voice and low speed coverage can be used by the users if they are away from these hotspots. • The 4G mobile networks systems will be cheaper than 3G. This is because they can be built on the existing networks and there will be no need for the operators to completely change their equipments nor will they be required extra spectrum. • The problem of handling increasing numbers of users and diversity of services can be solved by the 4G system as it was based on IP layer technology. III.
FEATURES OF 4G
A.
User Friendliness and User Personalization The combination of user friendliness and user personalization appears to be the winning concept when we try to encourage people to move towards a new technology, which is a time taking process and involves a great deal of effort from the operator's side. In user friendliness the interaction between the applications and users can be minimized and simplifies. In user personalization, the users can configure the mobile terminal and chose services according to their preferences.
B.
Terminal Heterogeneity and Network Heterogeneity 4G provides not only higher data rates but also a clear and valuable advantage in people's everyday life, with the combination of terminal heterogeneity and network heterogeneity. Terminal heterogeneity refers to the different types of terminals in terms of display size, energy consumption, portability/weight, complexity, etc. Network heterogeneity is related to the increasing heterogeneity of wireless networks due to the large number of access technologies available (e.g., UMTS, WiMAX, Wi-Fi, and Bluetooth). C.
Other possible features ofthe 4G systems are • Support interactive multimedia, voice, video, wireless internet and other broadband services. • High speed, high capacity and low cost per bit. • Global roaming and inter-working between different access technologies; both horizontal (intra-system) and vertical (intersystem) handover. • Better scheduling and call admission control techniques.
•
A common platform to complement other services connection through a common, flexible, seamless, IPbased core network. • Enabling person to person, person to machine, and machine to machine communications. • Can handle pre-existing 30 systems along with other wireless technologies. Following table 2 shows some physical parameters of 40 technology.
transform (FFT) [3] to prevent interference between the closely spaced sub-carriers, allowing an improved spectral efficiency. OFDM achieves multiple access capability usually by using CDMA or TDMA. Since each carrier in an OFDM signal has a very narrow bandwidth (i.e. few kHz), the resulting symbol rate is low. Due to the orthogonal nature of the modulation, these multiple sub-carriers overlap in the frequency domain, but do not cause Inter-Carrier Interference (ICI). In OFDM, the guard band is reduced by the orthogonal packing of the subcarriers, improving the spectral efficiency (figure 1).
TABLE 2 POSSIBLE 4G PARAMETERS
Parameters Key Requirement
Data and voice converged over IP
Network Architecture
Wireless LAN and WAN
IP
All IP (lPv6)
Frequency Band
Higher frequency bands 2 - 8 GHz 5 - 20 MHz (might even go to 100
Bandwidth
MHz or higher) Up to 20 Mbps (might even reach 100
Data Rate
Mbps or more)
Access Technology Forward Error Correction (FEC)
Multi-carrier CDMA (MC-CDMA)or
Concatenated codes
Switching Design Basis
Packet 200 km/hr
Deployment
2007-2010
Component Design
Smarter Antennas, software multiband and wideband radios Multimedia Machine to Machine
IV. TECHNOLOGIES FOR 4G A mix of concepts and technologies involves in the making of 40 mobile communications. Some originate from 30, and are called evolutionary (e.g., evolutions of WCDMA and cdma2000). Other is revolutionary which involves new approaches to wireless mobile. Following are some of the technologies considered for 40.
A.
Fn: Fost fourier transform
OFDM(TDMA)
Mobile Top Speeds
Service type
8andw~
4G
Orthogonalfrequency division multiplexing (OFDM)[J-2)
When a high speed mobile is transmitting its signals in high frequency band, it is affected severely from frequency selective fading. OFDM is being developed to reduce this frequency selective fading. OFDM is a combination of modulation and multiplexing. OFDM is a multi-carrier transmission technique, which uses the similar technique as that of Frequency Division Multiplexing (FDM). Multiple messages can be sent in moving a single radio channel in OFDM using principles of FDM. OFDM uses the spectrum more efficiently by making all the sub-carriers orthogonal to one another, using fast fourier
Following are the parameters ofOFDM in 40 [5] TABLE 3 OFDM PARAMETERS IN 4G User data rate
2.56 - 8.96 Mbps
Modulation
QPSK,16QAM
Coding rate
1/2 - 7/8
Data subcarriers
512 (average) (128, 256,384 optional)
Pilot subcarriers
128 (average) (32, 64, 96 optional)
Symbol duration
200/ls
Guard interval
40/ls
Subcarrier spacing
6.25 kHz
3 dB bandwidth
4 MHz ( 1, 2, 3 MHz optional)
Channel Spacing
5 MHz (1.25 MHz optional)
Carrier frequency
--2GHz
FFT size
1024
B.
Multiple-input multiple-output (MIMO)
SmartlMultiple antennas [1][4] can significantly increase systems capacity and have intelligent functions as suppressions of interference signals, auto-tracking of desired signals, and digital beam-forming with adaptive space-time processing algorithms. One smart-antenna system which shows promise in 40 systems is MIMO (Multi-Input Multi-Output) [1][6], as shown in figure 2, particularly since the antenna systems at both transmitter and receiver are usually a limiting factor when attempting to support increased data rates.
The idea behind MIMO is that the signals at transmit (TX) antennas end and at receive (RX) antennas end are "combined" so that both the quality (Bit Error Rate or BER) and the data rate (bits/sec) of the communication can be improved. From this the both the network's quality of service and the operator's revenues can be increased.
frequency (RF) signal from the antenna. The conversion from analog to digital (on receiving path) and from digital to analog (on the transmitting path) is performed by using the ADCIDAC at the IF section. The base-band operations such as connection setup, equalization, frequency hopping, timing recovery, and correlation are performed at the base-band section.
---H--Antenna
Fig. 2. MIMO wireless system. The transmitter and receiver are equipped with
Rx
multiple antenna elements.
There are two different perspectives for MIMO systems. First, from the pure diversity point of view, one can enhance the fading statistics of the received signal by the virtue of multiple available replicas being affected by the independent fading channels. The reliability of the communication link can be improved, the outage probability can be decreased, and the effects of multi-path fading can be reduced by sending the same signal through parallel and independent fading channels [6]. The second approach is referred as spatial multiplexing [6]. In this approach the spectral efficiency can be increased by transmitting different information streams on parallel spatial channels associated with the transmit antennas. The receiver terminal should be equipped with at least same number of receive antennas as the number of parallel channels generated by the transmitter in order to separate the individual streams. As the mobile terminals are getting smaller and smaller in size it is difficult to incorporate multiple antennas on them. For solving this issue, a new approach called cooperative MIMO relaying (CMIMOR) or virtual antenna array (VAA) technology has been proposed. This approach appears to be valid for implementing a MIMO system in mobile terminals.
c.
Software defined radio (SDR) Due to the constant evolution of mobile communication systems (2G, 3G, and 4G), the wireless industry is facing problems in global roaming to provide different services to the mobile subscribers. SDR technology promises to solve these problems by implementing the radio functionality as software modules running on a generic hardware platform. Further, different standards can be presented in the radio system through the implementation of multiple software modules. Through SDR the user's terminal can be operated in multimode fashion, adapting themselves to various network wireless interfaces [7]. The main purpose of SDR is to make a user terminal operate in different kinds of wireless networks, overcoming power, cost, size, and compatibility limitations. SDR consists of three major functional blocks as shown in the figure 3, namely front end (RF section), the IF section and the base-band section. The RF section (also called RF frontend) is responsible for transmitting and receiving the radio
Baseband Processing
RF Front-end
Fig. 3. Block Diagram ofa Generic Software Defined Radio
The development of multi-band, multi-standard, multi-mode radio systems using SDR technology is fostered by the availability of smart antennas, wideband RF front-end, wideband ADCIDAC technologies and ever increasing processing capacity of DSPs and general-purpose microprocessors. The main advantages of SDR are: • Flexibility and reconfigurability: which allows dynamic configuration of the system by selecting the appropriate software module to run. • Interoperability: Using the SDR system, it is possible to integrate other associated software functions into the system more easily. • Connectivity: by uploading another software module, we can enable the mobile terminals for using different protocols and standards. SDR has some drawbacks like, it is impossible to have just one antenna and one low noise amplifier to serve the wide range of frequency bands. It can be done by using multiple analog parts to work in different frequency bands but by doing this the complexity and physical size of the terminal will be increased. The other problem is that the available ADCs are not fast enough. Finally, we have to use parallel DSP in order to allow real-time execution of software implemented radio interface functions. V.
APPLICATIONS AND SERVICES
Generally, four categories of services or applications are being developed for use in the 4G wireless communications. They are as follows:
A. Localized/Personalized Information Services Information such as general news, location guides, mobile commerce, and travel services will be provided by the Localized/personalized information services and applications. Through this service roaming on other systems can be performed for the user with single profile. ~
Communications Services
Communications services include short messaging service (SMS), e-mail, video conferencing, fax, and bulletin boards. Although some of these services are available in today's wireless systems, these services will be greatly enhanced in future generations. Speed and reliability are the most notable enhancements planned for these services. ~
Organizational Services
Organizational services include personal digital assistant (POA) capabilities, currency exchange based on user location, and other personal management applications (e.g., calendars, call management, and address books). ~
Entertainment Services
Entertainment services may include streaming audio, streaming video, chat, photo trading, and gaming. In the Asian wireless market, where preliminary iterations of 3G are being deployed, entertainment services are generating substantial revenue. Other main application of 4G is Tele-geoprocessing. It is a combination of Geographical Information Systems (GIS) and Global Positioning Systems (GPS), working in concert over a high-capacity wireless mobile system. Tele-geoprocessing over 4G networks will make it possible for the public safety community to have wireless operational functionality and specialized applications for everyday operations, as well as for crisis management. Virtual navigation is also an important application. A remote database contains the graphical representation of streets, buildings, and physical characteristics of a large metropolitan area. Blocks of this database are transmitted in rapid sequence to a vehicle, where a rendering program permits the occupants to visualize the environment ahead. They may also "virtually" see the internal layout of buildings to plan an emergency rescue, or to plan to engage hostile elements hidden in the building. VI.
CHALLENGES FOR THE 4G MOBILE SYSTEMS
4G systems means to integrate different networks, different terminals and different services together seamlessly. The 4G mobile networks are all-IP based network with heterogeneous connectivity. It allows the users to use the wide range of applications provided by the different providers through the integrated terminals, any time and anywhere. To migrate from current systems to the 4G systems, there would be numerous numbers of challenges we have to face. Below are some of the
challenges that researchers and developers of 4G are likely to face. A.
Multiple 4G definitions
Since the work has just begun on 4G mobile networks, there is no well accepted or unique definition of 4G presented. Despite of huge research and years of discussion, there is no worldwide consensus on the definition of 4G. However some R&D companies, operators, and organizations are starting to identify some common characteristics. There is a need for global 4G standard from users to service providers, to manufactures. B.
Multimode user devices
As there will be wide range of applications provided by multiple wireless networks, a terminal will be needed which can adapt to different wireless networks by reconfiguring itself. This will be done by a multimode terminal which eliminates the need to use multiple terminals (or multiple hardware components in a terminal). Multimode terminals can be implemented using software defined radio approach. Figure 4 illustrates the block diagram of an ideal software radio. It consists of two parts namely analog and digital. Analog part of the receiver have an antenna, a bandpass filter (BPF), and a low noise amplifier (LNA). The signal received in the digital part is first digitized by the analog/digital converter (ADC) after the analog processing. After ADC the DSP will process the digitized signal in accordance with the wireless environment. Analog
Digital Baseband ADC
nsp
Fig. 4. An ideal software defined radio
C.
Wireless System Selection
Using 4G mobile, the user can select any available wireless networks for the required application. Because the using of a suitable network for a specific service as every network has unique features, hence the right selection of network can ensure the QoS required by each session. However, the challenge is to correctly select the network for each communication session since network availability changes from time to time. One of the solutions to this challenge is that while making the network selection, the network resources and minimum QoS requirements should be considered [8]. D.
Terminal Mobility
To get different types of wireless services at any time and anywhere, is known as terminal mobility. Terminal mobility is must in 4G infrastructure because the 4G network will be a
heterogeneous network. In terminal mobility, there are two main issues, location management and handoff management. In location management the mobile terminal is tracked and located by the system for possible connection. While on going communications is maintained by the handoff management when the terminal roams. In the 4G network systems, it is even more difficult to solve the handoff problem because two types of handoff are involved, horizontal handoff and vertical handoff. Figure 5 illustrates the horizontal and vertical handoff. Horizontal handoff is performed when the terminal roaming is in same wireless systems that is from one cell to another cell, while vertical handoff is done when the terminal movement is between two different wireless systems (e.g., from WLAN to GSM).
UMTS
cowrage
I . . . Vertical ~ndoff
GSM cover.
•
•
New access architectures: In future mobile networks there may be a need for the non conventional access architectures to replace conventional ones in many circumstances. More studies need to be conducted on these approaches. Spectrum issues: Designing a real wireless system without the knowledge of frequency bands (spectrum) is very difficult, in particular for multi-antenna based system such as MIMO technology. VIII. CONCLUSION
In this paper the overall vision of the 4G mobile communication systems was presented. Through discussion it has been revealed that the future mobile network will provide very high data rate. We also discussed the technologies that are the main building blocks of 4G which includes OFDM, MIMO, and SDR. It is difficult to predict which technology will emerge in 4G cellular systems. However the multiple access techniques (OFDM) successfully come across channel impairments and present a good complex implementation for supporting the high wireless data rates. Therefore multi-carrier systems are forecast as being most applicable for the 4G mobile networks implementation by many research groups and forums and as such these techniques are continued to mature. Some of the applications and services which are the key factors in the success of 4G are also introduced and in the last some of the challenges of 4G mobile networks are briefly highlighted.
--+ 'Horizontal handoff
Fig. 5. Vertical handoff and horizontal handoff [7] VII. RECOMMENDATIONS
4G can be seen as a common, flexible and scalable converging platform. Equivalently, 4G can be understood as combination of many networks and access technologies. Integrating several networks and access technologies, to realize a pleasant mobile network would be one of the greatest initial challenges of 4G. Some recommendations that are solved are as follows. • 4G definitions: There is no worldwide consensus on the definition of the 4G, regardless of huge efforts and several years of discussions. A global definition of 4G is needed before its standardization starts. • Seamless interconnectivity: 4G mobile network will be the network of networks, then how these heterogeneous networks will work and how they will appear as the single network. • User centric approach: The most logical approach to the 4G development appears to be putting the user in the center of the scene, developing the new technology based on the user demands and expectations. Failing to provide the user needs may leads to the failure of 4G.
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