Future Trends- Fourth Generation (4G) Systems and Beyond

6 Future Trends: Fourth Generation (4G) Systems and Beyond 6.1 Introduction By looking back to the history of wireless systems, one can reach the conclusion that the industry follows a ten-year cycle. First generation systems were introduced in 1981 followed by the deployment of second generation systems in 1991, ten years later. Moreover, third generation systems are due for deployment in 2001–2002. From the point of view of services, 1G systems offered only voice services, 2G systems also offered support for a primitive type of low-speed data services and 3G systems will enable a vast number of advanced voice and high-speed data services. The trend is towards support for even advanced data services. 3G networks, although having the advantage of support for IP and enhanced mobility, will suffer from a divergence between several standards. This divergence will limit easy roaming between 3G networks based on different standards, thus limiting user mobility. Furthermore, 3G networks will have, in the best case, an upper capacity limit of 2 Mbps. Although more than enough for the application demands of the years to come, 3G networks will most likely need to evolve in order to meet the mobile application demands of the next decades. As in all areas of technology, the quest for better and more efficient systems never ends and as soon as the time for deployment of a system comes, research on the next generation is usually under way. Consequently, the imminent deployment of 3G systems is accompanied by initiation of research on the next generation of systems. If the ten-year cycle continues, it is logical to expect that the next generation of wireless systems, known as Fourth Generation (4G), will reach deployment stage somewhere around 2010. As seen later in the chapter, the vision for 4G and future systems is towards unification of various mobile and wireless networks. However, there is a fundamental difference between wireless cellular and wireless data networks, such as WLANs. The difference is that cellular systems are commonly circuit-switched, meaning that for a certain call, a connection estab- lishment has to take place prior to the call. On the contrary, wireless data networks are packet- switched. It is expected that the evolution of wireless networks towards an integrated system will produce a common packet-switched (possibly IP-based) platform for wireless systems, thus enabling the ‘wireless Internet’. However, in order for such an integration to take place research is needed in order to provide interoperability between wireless cellular networks and wireless data networks. The envisioned unified platform for the next generations of wireless networks will provide transparent integration with the wired networks and enable users to seamlessly access multimedia contents such as voice, data and video, irrespective of the access methods of the various wireless networks involved. The next generations of wireless networks target the market of 2010 and beyond, aiming to offer increased data rates with reports mentioning from 50 Mbps to 155 Mbps. In the course of their development many different types of issues (technical, economical, etc.) must be studied and resolved. Some of them, such as the development of even more efficient modulation techniques, identification of new spectrum, and developments in battery technology/power consumption, are quite straightforward and have been identified during 2G and 3G research and development stages. Other issues are not so clear and are heavily dependent on the evolution of the telecommunications market and society in general. These issues need to be identified and resolved at the earliest possible stage in order to unsure market success for 4G and beyond wireless systems. 6.1.2 Scope of the Chapter This chapter provides a vision of some of the characteristics of 4G and future systems. Section 6.2 describes the design goals and corresponding research issues for 4G systems. Section 6.3 presents a preliminary set of possible 4G service classes. Section 6.4 identifies the challenge of predicting the future of wireless communications and provides three possible scenarios for the future. Finally, the chapter ends with a brief summary in Section 6.5. 6.2 Design Goals for 4G and Beyond and Related Research Issues Since 4G systems target the market of 2010 and beyond, there is time for 4G research and standards development. So far, no 4G standard has been defined and only speculations have been made regarding the structure and operation of 4G systems. The question to ask here is what will be the desired advantages and new features of 4G systems over their predecessors. Due to the fact that related research is under way, 4G is still an acronym without a generally accepted meaning. However, research efforts [1–3] agree more or less on the following targets: † System interoperability. 4G and future systems should bring something that is missing from their predecessors: flexible interoperability of the various kinds of existing wireless networks, such as satellite, cellular wireless, WLAN, PAN and systems for wireless access to the fixed network. Alternatively, this can be thought of as an ability to roam between multiple wireless and mobile standards (e.g. moving from a cellular network to a WLAN while maintaining connections). If the target of system interoperability is met, the whole worldwide communications infrastructure will be turned into a transparent network allow- ing users to use it independent of a specific access method. Due to the requirement for interoperability of different mobile and wireless networks, a big challenge will be how to access several different mobile and wireless networks through the same terminal. We can identify the three possible configurations described below [3]: Wireless Networks190 – Multimode terminals. This option provides for further development of older generation systems and has also been applied in the past (e.g. dual AMPS-CDMA cellular phones). It calls for a single terminal which is capable of accessing several different wireless networks. This is obviously achieved by incorporating multiple interfaces to the term- inal, one for the access method of every different kind of wireless network. The ability to use many access methods will enable users to use a single device to access the 4G network irrespective of the particular access method used. The option of multimode terminals will offer increased coverage and reliable wireless access in the case of failure of one or more networks in an area. Furthermore, the multimode terminal option lowers the complexity of the fixed part of the network due to the fact that the additional complexity is incorporated into the device [3]. – Overlay network. In this architecture users will access the 4G network through the Access Points (APs) of an overlay network. Upon connection with a terminal, an AP will select the wireless network to which the terminal will be connected. This choice will be made based on user-defined choices, resource availability, QoS requirements, etc. The AP will perform protocol translation and QoS negotiation for the connections. Since APs can monitor the resources used by a user, this architecture supports single billing and subscription. – Common access protocol. This choice calls for use of one or two standard access protocols by the wireless networks. A possible option is for the wireless networks to use either ATM cells with additional headers or WATM cells. † Terminal bandwidth and battery life. Terminals of next generation networks will be characterized by a wide range of supported bandwidths, ranging from several kbps to about 100 Mbps or beyond. The battery life of these devices is expected to be around one week. This advance will be accompanied by reduction in the weight and volume of batteries. † Packet-switched fixed network. According to studies, the 4G architecture will use a connectionless packet switching (possibly IP-based) fixed network to interconnect the several different mobile and wireless networks. † Varying quality of bandwidth for wireless access. The mixing and internetworking of different networks on a common platform will provide a set of, possibly overlapping, layers with different access technologies complementing each other. Depending on their geographical location, users will be served by different layers and enjoy different qualities of wireless access in terms of bandwidth. Possible layers will be [1]: – Distribution layer. This will support digital video and broadcasting services at moder- ate speeds over relatively large cells. This layer will support full coverage and mobility and will cover sparsely populated rural areas. – Cellular layer. This layer will comprise 2G and 3G systems. It will provide high capacities in terms of users and data rates inside densely populated areas such as cities. This layer will offer support for rates up to 2 Mbps. The cell size will obviously be smaller than that used in the distribution layer. This layer will also support full coverage and mobility. – Hot-spot layer. This layer will support high-rate services over short ranges, like offices or buildings. It will comprise WLAN systems, such as IEEE 802.11 and HIPERLAN. Future Trends: Fourth Generation (4G) Systems and Beyond 191 This layer is not expected to provide full coverage, due to its short range, however, roaming should be provided. – Personal network layer. This layer will comprise very short-range wireless connec- tions, such as Bluetooth. Due to the very short range, mobility will be limited, however, roaming should also be provided in this layer. – Fixed layer. This will comprise the fixed access systems, which will also be part of the 4G network of the future. † Advanced base stations. Base stations of future generation networks will utilize smart antennas to increase system capacity. Furthermore, base stations will employ self-config- uring functionality in an effort to reduce operating costs. Finally, these devices will obviously support a multitude of air interfaces in order to accommodate a wide range of terminals. † Higher data rates. 3G systems will have, in the best case, an upper capacity limit of 2 Mbps. Although more than enough for the application demands of the years to come, 3G systems will most likely need to evolve in order to meet the mobile application demands of the next decades. 4G systems aim to provide support for such applications. Although there exists some vagueness regarding the maximum number for data rates of 4G systems, with reports mentioning from 50 Mbps [3,4] to 155 Mbps [2], 4G systems will surely offer significantly higher speeds than 3G systems. In order to support the higher data rates new air interfaces will obviously be introduced. An ideal air interface should be spectrum efficient and provide the flexibility to offer different bit rates. Furthermore, such an interface should be resistant to frequency-selective fading and require little equalization; Orthogonal Frequency Division Multiplexing (OFDM) is an air interface that can meet such requirements and is expected to be greatly used in the wireless systems of tomorrow. It is described in the next subsection. 6.2.1 Orthogonal Frequency Division Multiplexing (OFDM) Orthogonal Frequency Division Multiplexing (OFDM) is a form of multicarrier modulation, which splits the message to be transmitted into a number of parts. The available spectrum is also split into a large number of low-rate carriers and the parts of the message are simulta- neously transmitted over a large number of low-rate frequency channels. By recalling that (a) the phenomenon that dominates the error behavior of wireless channels is fading; (b) fading is frequency-selective; and (c) delay spread must be very long to cause significant interference to a carrier, one can realize the inherent robustness of OFDM to fading. Thus, by splitting a message into parts and slowly sending (due to low-carrier bandwidths) these parts in parallel over a number of low-rate carriers, signal reflections due to multipath propagation will probably be late at the receiver only by a small amount of a bit time. This, together with the fact that overall message transmission is made over a large number of low-rate carriers in the same time, results in a high-capacity, multipath-resistant link. OFDM resembles FDMA in that they both split the available bandwidth into a number of carriers. The obvious difference of course is that FDMA is a multiple access technique whereas OFDM is a form of multicarrier transmission. Another difference concerns effi- ciency: FDMA is inefficient in terms of spectrum utilization, since it wastes a significant amount of bandwidth as guard interval between neighboring channels in order to ensure that Wireless Networks192 they do not interfere with one another. This bandwidth overhead allows signals from neigh- boring channels to be filtered out correctly at the receiver. TDMA systems which allow a single user to utilize the entire channel capacity for a specific time period are also subject to a bandwidth overhead since TDMA systems need to be synchronized. As a result, guard time periods occur at the beginning of each user’s slot in order to compensate for synchronization problems between stations. Thus, TDMA systems also waste some bandwidth to ensure their proper operation. Such bandwidth overheads are not desirable in future generations of wireless systems. This is because spectrum is expected to be a scarce resource, and given a certain amount of spectrum this will need to be utilized to the highest extent possible in order to accommodate as many users as possible. OFDM tries to solve this problem by significantly reducing the amount of wasted spectrum by dividing the message to be transmitted into a number of frequency carriers and spacing these carriers very close to each other. In order to ensure that OFDM carriers do not interfere, they are made orthogonal to one another. Orthogonality ensures that although carriers are very close in frequency and their spectra overlap, messages in different carriers do not interfere with one another since detection for one carrier is made at the point where all other carriers are null. In an OFDM system, detection is performed in the frequency domain. The actual signal transmission, however, occurs in the time domain. To better understand this, Figure 6.1 illustrates the operation of a simple OFDM system. As can be seen, OFDM transmission/ reception comprises the following states: † Transmitter: serial to parallel conversion. The data stream to be transmitted takes the form of the word size required for transmission. For instance, if QPSK is used, the stream is split into data words of two bits each. Then each data word is assigned to a different carrier. † Transmitter: modulation of each carrier. The data word that forms the input of each carrier is modulated. † Transmitter: Inverse Fourier Transform (IFT). After the actual contents of the various frequency carriers have been defined, the contents of these carriers form the input to an IFT in order to obtain a representation of the OFDM signal in the time domain. The IFT can be performed using the Fast Fourier Transform (FFT), which nowadays can be imple- mented at low cost. † Transmitter: Digital to Analog Conversion (DAC). The output of the IFT is converted into an analog form suitable for radio transmission. † Receiver. In order to receive the message, the receiver performs the reverse operation to Future Trends: Fourth Generation (4G) Systems and Beyond 193 Figure 6.1 A simple OFDM system the transmitter. It digitizes the received signal (the ADC box in Figure 6.1) and performs an FFT on the received signal in order to obtain its representation in the frequency domain. The output of this is the actual content of the carriers, which are then demodulated in order to obtain the data words transmitted in each carrier. The data words are then combined to produce the original message. One can realize from the above discussion that before OFDM modulation the data on each carrier is considered to be in the frequency domain. Figure 6.2 shows the various carriers of an OFDM transmission. The spectrum of each OFDM carrier has a sin(x)/x form and is modulated at a certain symbol rate. For the purposes of this discussion we assume l ¼ 1 kHz symbol rate. Assuming that the main lobe of the signal on the first carrier is at k kHz, this signal will have the first null at k 1 l,with subsequent nulls occurring every lkHz. If we modulate the second carrier at a frequency exactly l kHz (the symbol rate) higher than the first using the same symbol rate, the mail lobe of the second carrier occurs at a null of the first one. Using this approach, the main lobe of each carrier occurs at nulls of the other carriers. Thus, at the point of detection there is no interference from any other carriers. In an effort to increase the robustness of each carrier to inter-symbol interference (ISI) caused by multipath propagation, the transmitted symbols can be prolonged by adding a guard interval between successive symbol transmissions. The existence of a guard interval allows for delayed components of a symbol’s transmission to reach the receiver before the energy of the next symbol is received. The actual content of the guard interval is produced by repeating the ‘tail’ of the symbol and placing that tail before the actual symbol transmission. Provided that delayed echoes of a signal carrying a symbol k are within the guard interval, multipath propagation does not affect detection of the next symbol, k 1 1. However, by preceding the useful part of the symbol’s transmission time by the guard interval, we lose some bandwidth that cannot be used for transmitting information. Figure 6.3 illustrates the transmission of OFDM symbols in the time domain with use of guard intervals. The arrows in cases ‘a’ to ‘c’ represent the energy of symbol 2 at the receiver, in the time domain. In case ‘a’, there is obviously no intersymbol interference, thus decoding of symbol 3 produces the correct symbol. Decoding is also successful in case ‘b’, where delayed echoes of symbol 2 Wireless Networks194 Figure 6.2 Detection of OFDM symbols overlap with the guard interval of symbol 3. However, in case ‘c’, decoding of symbol 3 will be affected by intersymbol interference since echoes of symbol 2 overlap in time with symbol 3. Variants of OFDM also exist. COFDM stands for Coded OFDM. COFDM enables further resistance to errors due to fading. This is due to the fact that a carrier suffering one or more bit errors can be corrected by the error-correcting code which is transmitted on a different carrier, which may be error-free since fading is frequency selective. However, since coding for error correction is used in most of today’s OFDM systems, the ‘C’ is redundant. Wideband OFDM (WOFDM) is a variant of OFDM where the spacing between carriers is wider in an effort to alleviate the problem of frequency errors between a transmitter and a receiver. The larger spacing ensures that such an error falls in the spacing and thus have a negligible effect on the performance of the system. Thus, an offset occurring at a transmitter will be perceived by the receiver only as a sampling error, which can be tolerated. 6.3 4G Services and Applications The applications and service classes that will dominate the 4G-market are not yet known, however, some trends are emerging from ongoing research [5–8]. A nonexhaustive but indicative list of service classes is as follows: † Tele-presence. This class will support applications that use full stimulation of all senses to provide users with the illusion of actually being in a specific place. These will be real-time virtual reality services and will offer virtual meetings, an evolution of today’s teleconfer- encing applications. The conference attendants, although in different places, will have the illusion of participating in a conference in the very same room. Such applications, coupled with efficient compression techniques, will require capacities in the order of 100 Mbps. Furthermore, extremely strict delays and QoS levels will be demanded due to the real-time nature of these applications. The concept of a virtual meeting will be one of the major applications foreseen in 4G and future systems. † Information access. This class will call for the ability of instantaneous access to large volumes of data such as large video and audio files. Compared to tele-presence, such Future Trends: Fourth Generation (4G) Systems and Beyond 195 Figure 6.3 Adding a guard interval to transmitted symbols applications will be less delay sensitive, since real-time delivery of data is not needed here. As far as data rates are concerned, this class will demand the highest rates possible. However, the traffic pattern will probably be asymmetrical, with 50/1 ratios or more characterizing the downlink/uplink data rate ratio. † Inter-machine communication. This service class will offer devices the ability to commu- nicate with one another either for maintenance or for intelligence purposes. An example application of this type is car engine equipment that contains wireless interfaces enabling parts to contact the respective vendors when malfunctions occur. † Intelligent shopping. This will offer users access to information regarding prices and products offered by shops they visit. Upon entering a shop, the user terminals will auto- matically tune to the shop’s service providers and display information regarding the products sold by the shop. † Security. Secure services will be an indispensable feature of the future generations of networks. Integrity of data is bound to be a crucial factor that will enable the proliferation of banking and electronic payment applications. Furthermore, security services will protect the privacy of users’ personal information. † Location-based services. It is envisioned that 4G and future systems will have the ability to determine the location of users with a high level of accuracy. This cannot be made true with today’s systems which can only report the cell servicing the user, thus being accurate to within a few city blocks at best. Emergency applications will greatly benefit from location-based services. For example, if a person with a health problem calls an ambulance from his handset but is unable to report his location to the operator, his position can be determined with high accuracy by querying the user’s handset for its location. 6.4 Challenges: Predicting the Future of Wireless Systems In the course of research on 4G and future systems many issues of different types (technical, economical, etc.) must be studied and resolved. Some, such as the development of even more efficient modulation techniques, identification of new spectrum, and developments in battery technology/power consumption, are quite straightforward and have been identified during 2G and 3G research and development stages. Other issues are not so clear and are dependent on the evolution of the telecommunications market and society in general. Although the aim of 4G research will obviously be towards better performance, certain aspects of the telecom- munications market and society’s perception of communications may significantly influence the market penetration of products for the next generation of mobile and wireless networks. As already mentioned, 4G and future systems target the market of 2010 and beyond. Since we cannot reliably foresee the state of telecommunications and society after such a time period, it is practical to study possible evolution scenarios in order to identify issues that may impact the future market for such systems and thus affect the related research. Three such scenarios have been identified [5–8]. In the remainder of this section, we provide a short overview of the concepts of these scenarios, how these three scenarios were created and finally present the three scenarios. Wireless Networks196 6.4.1 Scenarios: Visions of the Future The concept of scenarios as tools for prediction future situations was first used after World War II to evaluate the significance of development in various technological areas. In order to keep up with the increasing pace of development, the two superpowers needed to set certain priorities. The problem was which priorities to set. A possible solution was to spy on the other side, understand its priorities and act accordingly. The other option was to act independently by predicting the developments and set priorities according to the predictions. Since a single prediction is not accurate, more than one possible prediction for the future was preferable in order to prepare for more than one different alternative situation. Each of these different predictions is called a scenario. Scenarios are basically stories that express assumptions about the future. These assump- tions are the result of different individuals’ and groups’ beliefs about the future. Scenarios are usually produced by posing specific questionnaires to, possibly, specialized groups of people. The individual opinions combine to produce a set of trends for the future. By identifying the trends that are sure to play an important role in the future and varying the relative impact of other trends, several scenarios are produced. Scenarios are useful in cases where limited knowledge on a future situation exists, however, a decision regarding the situation has to be made. There are, of course, inherent vulnerabilities of the scenario-based approach: one cannot predict what will really happen, but only speculate based on present situations. Furthermore, in the process of identifying the trends that make up the scenarios, several factors that influence the situation might be over- looked or misinterpreted. Furthermore, as we approach the time of the situation under study, visions on the situation may change and thus some trends may vanish and new ones may appear. 6.4.2 Trends for Next-generation Wireless Networks In the process of the research mentioned in Ref. [8], several trends regarding next generation wireless networks (2010 and beyond) were identified. These are briefly summarized below: † Globalization of products, services and companies. Globalization has affected peoples’ lives ever since the time ancient civilizations started to come in contact with each other. However, globalization show a surge with the invention of television, Internet and tele- communications in general. According to the survey, the impact of globalization will continue to exist and will surely affect the telecommunications scene of the future. † Communicating appliances. This trend states that future consumer devices, such as TV sets, videos and stereos, will employ ‘intelligence’. Although this is also true for the present, future consumer devices are expected to make certain kinds of decisions on their own and have the necessary equipment to communicate with other devices. † Services become more independent of the underlying infrastructure. This trend states that future services are expected to be more separated from the infrastructure they use. This will enable many different devices to use the same network infrastructure. † Information trading/overflow. Communications in the society of the future will be an integral part of peoples’ lives. Computers will be the primary means for accessing infor- mation, thus diminishing the importance of printed versions of mass communications like newspapers. This trend also identifies the possibility of individuals receiving large Future Trends: Fourth Generation (4G) Systems and Beyond 197 amounts of information, much more than they can handle. This trend identifies the need for refining and controlling information exchanges. † Standardization diversification. This trend identifies the possibility of companies taking over control of the market and forcing their own de facto standards. This could be either due to political issues inside standards development organizations or market success giving power to some companies. The following sections provide three scenarios for the future of telecommunications that were identified by research. Figure 6.4 shows the way social issues and standardization affect the generation of those scenarios. 6.4.3 Scenario 1: Anything Goes This scenario has the following characteristics: † High development rate for telecommunications. † Transparent access to the network. † Manufacturing companies have a strong market power. † Large number of de facto standards. † Generic hardware equipment will run software enabling specialized services. † Self-configuring systems. In this scenario, telecommunications technology is envisioned to achieve a deep market penetration and become an essential part of peoples’ everyday life. This will lead to fierce industrial competition and decreased cost of product manufacturing and service offering. The reduced cost of products and services will enable almost everyone to have the ability to Wireless Networks198 Figure 6.4 The three scenarios’ dependence on standardization and social issues. [...]... of 4G and future mobile and wireless systems Such systems target the market of 2010 and beyond, aiming to offer support to mobile applications demanding data rates of 50 Mbps and beyond Due to the large time window to their deployment, both Future Trends: Fourth Generation (4G) Systems and Beyond 201 the telecommunications scene and the services offered by 4G and future systems are not known yet and. .. yet and as a result aims for these systems may change over time However, as 3G systems move from the research to the implementation stage, 4G and future systems will take their place as an extremely interesting field of research on future generation wireless systems This chapter has covered a number of issues: † 4G design goals and related research issues 4G and future systems aim to provide a common IP-based... inter-machine communication and intelligent shopping will be enabled by 4G and future systems † The challenge of predicting the future of wireless systems The exact state of 4G and future systems cannot be reliably foreseen, due to the large time window until their deployment Many issues of these systems are not so clear and are dependent on the evolution of the telecommunications market and society in general.. .Future Trends: Fourth Generation (4G) Systems and Beyond 199 seamlessly access the services of the next generations of networks regardless of what access system is used The increased acceptance of 4G and future systems will raise research to extreme levels with crucial aims being the identification of techniques... interested in OFDM and its aim is to achieve market acceptance of OFDM through the establishment of a single high-speed OFDM standard References [1] Mohr W Development of Mobile Communications Systems Beyond Third Generation, Wireless Personal Communications, Kluwer, June 2001, pp 191-207 [2] Lilleberg J and Prasad R Research Challenges for 3G and Paving the Way for Emerging New Generations, Wireless... afford the increased cost of advanced services Such services will use the different wireless networks in combination and will be relatively expensive Consequently apart from other research issues, the issue of smooth integration and interoperability of 4G and future systems and 2G/3G legacy systems will have to be efficiently solved Furthermore, despite the fact that the customer base will be divided, telecommunications... Gessler F, Lagergren F, Queseth O, Stridh R, Unbehaun M, Wu J and Zander J Telecom scenarios for the 4 th Generation Wireless Infrastructures, In Proc of the PCC Workshop, Stockholm, Sweden, 1998 [7] Flament M, Gessler F, Lagergren F, Queseth O, Stridh R, Unbehaun M, Wu J and Zander J An Approach to 4 th Generation Wireless Infrastructures-Scenarios and Key Research Issues, In Proc of IEEE VTC 1999 [8] M... future systems aim to provide a common IP-based platform for the multiple mobile and wireless systems and possibly offer higher data rates The desired properties of 4G systems are identified OFDM, a promising technology for providing high data rates, is presented † 4G services and applications Although the applications and service classes that will dominate the 4G market are not yet known, research... will eventually come up with a mandatory security standard and act as Orwell’s Big Brother, by making sure that all companies either follow this standard or are shut down Every company that either manufactures telecommunication products or offers services will be tested to ensure compliance with the security standard This will possibly lower the number of legal operators and product manufacturers since... peoples’ lives will serve a very diverse range of needs Users will demand availability of ready-to-use systems, tailored for their needs Thus, it would be desirable to research towards intelligent ad hoc systems, able to either automatically deploy and configure themselves or demand little such knowledge and intervention by users Furthermore, personal adaptation of services based on user preferences would . 6 Future Trends: Fourth Generation (4G) Systems and Beyond 6.1 Introduction By looking back to the history of wireless systems, one can. Goals for 4G and Beyond and Related Research Issues Since 4G systems target the market of 2010 and beyond, there is time for 4G research and standards development.