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5 Initiatives in 4Gmobile Design 5.1 Introduction – Who Needs 4G? What is 4G? 5.1.1 Social Background and Future Trends There has been an evolutionary change in mobile communication systems every decade. The increase in the number of subscribers and transmission data rates leads to a shift to higher frequency bands where wider bandwidth is available. There are two directions for future trends in mobile communications. One is Direction A, which aims to increase transmission data rates where the same mobility as IMT-2000 from indoor to high speed vehicles is maintained. The other is Direction B, which aims to expand mobility from indoor to outdoor where the transmission data rates in the wireless access systems are maintained. Direction B will be suitable for spot area services in order to satisfy the demand for higher data rates, while Direction A will accommodate continuous area services. We focus on Direction A here. The number of subscribers using PDC and PHS in Japan was 62.2 million in October 2000 and has increased by 10 million for 5 successive years. One in 2.6 mobile phone users connected to the Internet in October 2000. This pattern of use has increased significantly, and Internet use is expected to comprise 90 percent of all mobile communication traffic in 2005. The US and Europe are expected to follow a similar trend. Figure 5.1 shows a traffic forecast for Region 3 [97]. From 1999 through 2010, subscribers to voice-oriented services are expected to grow by 1.5 times, and the ratio between voice and multimedia traffic will be nearly 1:2 for total up- and downlinks. Assuming that multimedia traffic grows by 40 percent a year after 2010, it will be 23 times that of 1999, and the ratio between voice and multimedia traffic will be about 1:10. Therefore, to accommodate the considerable multimedia traffic after 2010, we must conduct R&D on key technologies to achieve not only high speed mobility but also high transmission data rates. 5.1.2 Trends in ITU-R At the 18th TG-8/1 in November 1999, the standardisation activities on IMT-2000 were finished and the new working party (WP8F) was established to co-ordinate on systems beyond IMT-2000 as well as to enhance IMT-2000 itself. At the first WP8F meeting in Broadband Wireless Mobile: 3G and Beyond. Edited by Willie W. Lu Copyright  2002 John Wiley & Sons, Ltd. ISBN: 0-471-48661-2 March 2000, 6 working groups were set up (see Figure 5.2) and their terms of reference are as follows [22]. WG-Vision: † Provision of the roadmap to the future in relation to the time perspectives for IMT-2000 and systems beyond IMT-2000. † Co-ordinate and complement the near term aspects of the Radio Technology Working Group and co-ordinate with the other groups in WP 8F. † Conceptualisation of the longer term future (5 to 10 years) and migrate it through a middle defining stage (3 to 7 years) to ultimately deliver a near term work product of specifica- tions as defined in related working groups. † Maintenance and update of other IMT-2000 recommendations (such as concepts, princi- ples, framework requirements and the like). WG-Circulation: † Address to issues that may facilitate the ability of IMT-2000 to achieve global deployment including access, circulation, and common emission requirements. WG-Developing IMT: † Consideration of issues relevant to the needs of the developing countries. † Assurance of the work on IMT-2000 adequately reflects these needs. Conduct of studies in response to Question ITU-R 77/8 and strengthening the liaison with ITU-D as necessary. † Maintenance and update of relevant IMT-2000 recommendations as appropriate may occur within this working group. Broadband Wireless Mobile: 3G and Beyond272 Figure 5.1 Traffic Forecast for Region 3 in 2010 and after. WG-Radio technology: † Maintenance and update of IMT-2000 RSPC terrestrial component in conjunction with external organisations. † Maintenance and update of IMT-2000 RSPC satellite component in conjunction with WP 8D. † Maintenance and update of other IMT-2000 recommendations as appropriate may occur within this working group; address aspects of adaptive antennas for IMT-2000 including technical characteristics, advantages, performance implications and applications. † Consideration of other aspects of technology related to IMT-2000; reception of the work products of the ‘mid-term’ perspective of the WG-Vision and in the ‘near-future’ updates existing specification recommendations or develops new recommendations as appropriate to support implementations of these concepts. † Co-ordination with external organisations in this task will be required. WG-Spectrum: † Spectrum matters related to IMT-2000 and systems beyond IMT-2000; considering IMT- 2000 spectrum implementation issues and any necessary sharing, compatibility and inter- ference criteria between IMT-2000 and other radio services Initiatives in 4Gmobile Design 273 Figure 5.2 Working Group relationship diagram. † Maintenance and update of existing IMT-2000 spectrum related recommendations and reports, as appropriate † Identifying areas where joint work and/or liaison is needed on spectrum matters with other relevant groups, as appropriate. WG-Satellite Co-ordination: † Act as internal WP 8F co-ordinating function and focal point for satellite aspects † Function as the WP 8F point of interface for draft liaison statements to WP 8D on satellite issues † Maintenance and update of ITU-R recommendations related to IMT-2000 and systems beyond IMT-2000 and will work closely with WP 8D † Determine which WP 8F documents are relevant to WP 8D. According to the WG-Vision, a target of service beyond IMT-2000 is illustrated with that of each mobile communication and wireless access service in Figure 5.3, and four scenarios for the systems beyond IMT-2000 are proposed, as shown in Figure 5.4 [23]. Scenario 1: All-round-type (Figure 5.4(a)) Covers the whole range of the deployment area and the transmission rate. Broadband Wireless Mobile: 3G and Beyond274 Figure 5.3 Target of Service beyond IMT-2000. Scenario 2: Complement-type (Figure 5.4(b)) Located in the position not covered by the other mobile communication and wireless access systems, both in terms of the deployment area and the transmission rate. Scenario 3: Area-complement-type (Figure 5.4(c)) They cover the whole range of the transmission rate and are located in the position not Initiatives in 4Gmobile Design 275 Figure 5.4 Scenarios of systems beyond IMT-2000: (a) all-round type, (b) complement type, (c) area complement type, and (d) rate complement type. covered by the other mobile communication and wireless access systems in terms of the deployment area. Scenario 4: Rate-complement-type (Figure 5.4(d)) They cover the whole range of the deployment area and are located in the position not covered by the other mobile communication and wireless access systems in terms of the transmission rate. Broadband Wireless Mobile: 3G and Beyond276 Figure 5.4 (continued) 5.1.3 Wireless Access Systems Related to 4G Mobile The following system requirements should be met in 4G mobile: † high data-rate transmission † high mobility † wide coverage area and seamless roaming among different systems † higher capacity and lower bit cost † wireless QoS resource control Because it is especially hard to realise the system having both high data rates and high mobility, four scenarios are discussed in WG-Vision (see section 5.1.2). There is an idea to include new communication systems such as ITS (Intelligent Transport Systems) and HAPS (High Altitude stratospheric Platform Station) systems at a research level (see Figure 5.5). There is also another approach organised in a layered structure similar to hierarchical cell structures in cellular mobile systems (see Figure 5.6), where vertical handover between systems as well as horizontal handover within a system is necessary [83]. 5.1.4 Key Technologies It is very important to develop key technologies realising high data rates transmission under high mobility. Some of them are illustrated in Figure 5.7 [97], and recent research activities are introduced in detail after 5.2. 5.2 Microwave Propagation In recent years there has been a tremendous upsurge in demand for terrestrial mobile wireless Initiatives in 4Gmobile Design 277 Figure 5.5 Mobile communications systems. communications, yet the availability of spectrum for mobile communications has become increasingly scarce as the information-oriented society has continued to evolve. In pursuit of new spectrum for mobile communications, many are casting their eyes to the hopeful prospects of the microwave band [105]. In order to adopt the microwave spectrum for use by mobile communications, it is essential to gain a clear understanding of the propagation Broadband Wireless Mobile: 3G and Beyond278 Figure 5.6 Layered structure of seamless future network [83]. Figure 5.7 Key technologies in wireless access networks. characteristics of the frequency band and bandwidth of the spectrum to be used. While the sub-microwave band (,2 GHz) has already been extensively developed [4,10], the propaga- tion characteristics of microwave (.3 GHz) transmission at 10 Mb/s or more continue to be studied and still have numerous issues to be addressed. Microwave transmission exhibits greater path losses than conventional UHF-band communications, and it is assumed this can be attributed to frequency selective fading associated with broadband transmission and increased shadowing caused by shrinking Fresnal zones. In order to identify potential service areas, it is essential to clarify attenuation caused by multiple rays as a function of distance, attenuation caused by obstructions, time variation of multiple rays, and so on. In addition, there are other issues that must be addressed if we are to implement high-speed, high-quality microwave transmission including: delay time difference characteristic of multiple ray propagation paths and the problem of multiple rays separating and combining. Note too that demand and environments of interest are no longer confined, as they once predominately were, to cities. As the number of SOHO (small office, home office) workers and home-based telecommuters continues to grow, the service demand area is being rapidly pushed out into suburban residential areas, so careful thought must be given to the impact that this kind of environment has on microwave propagation. The only way to resolve these issues is to gather the relevant data through well-designed experimental studies, and to develop accurate models based on the data. 5.2.1 Microwave Mobile Propagation Characteristics in Urban Environments 5.2.1.1 Propagation loss characteristics LOS propagation losses and breakpoint characteristics Microcellular systems featuring transmitting base station antennas installed at a height of 4 m show excellent promise for transmitting in the microwave band. The attenuation coeffi- cient of line-of-sight (LOS) path loss characteristics for these systems can be divided into a 2nd power domain and a 4th power domain, and results for propagation characteristics along roads is in agreement with existing reports for lower frequency transmissions. This point of transformation is referred to as the breakpoint. It has been reported that the point at which the breakpoint appears in urban environments depends on the height of the receiving antenna [79]. When the receiving antenna height (h m ) is set to 2.7 m in urban districts, it is found that the actual measured breakpoint tends to be somewhat shorter than the theoretical value derived taking the reflected waves off the road surface into considera- tion. If one assumes for the theoretical calculation that the road surface is uniformly elevated by a certain degree, then the discrepancy between measured and theoretical values disap- pears. Indeed, we can interpret the presence of vehicles passing back and forth on the road as effectively raising the surface of the road. When we move the receiving antenna down to a height of h m ¼ 1.6 m, the measured results detect no breakpoint at all. This is attributed to the fact that passing vehicles frequently interrupt the propagation path, thus causing non-line-of- sight (NLOS) characteristics to appear. We obtained an average attenuation coefficient of 3.2, thus revealing a rather different property than has been obtained for propagation along road at lower frequencies. Measurements performed in the urban environment were separated into those conducted during the day and those done at night [77]. During the night there were less the one-tenth the Initiatives in 4Gmobile Design 279 number of vehicles on the road as during the day and virtually no pedestrians. Using a quantitative method, we obtained distinctive breakpoint results of 320 m when measurements were done at night for h m ¼ 2.7 m and a frequency f ¼ 3.35 GHz. Comparing this measured value with the theoretical value (first Fresnel zone theory), we obtain an approximate effec- tive road surface height h of 0.6 m. For daytime measurements under heavy traffic conditions at f ¼ 3.35 GHz it was confirmed that h ¼ 1.3 m (with a breakpoint of 170 m), and 1.4 m for the three-frequency average. It is apparent that when traffic volume is light, the effective road height is reduced and the break- point becomes more distant. We also obtained the breakpoint based on path loss character- istics measured during the day and at night for h m ¼ 1.6 m. At three frequencies, effective road heights ranging from 0.2 m to 0.7 m were obtained, for an average of 0.5 m. The fact that h never reached 0, even for sidewalks during periods when there were virtually no people walking about, can be attributed to the presence of trees, street lights, and cars passing on cross streets (Figures 5.8 and 5.9). NLOS path loss characteristics In this section we consider the NLOS path loss characteristics. Figure 5.10 shows typical measured path loss results as a function of distance [78], and reveals sharp jumps in losses at corners where the LOS path changes to a NLOS path. For these measurements, the transmit- ting base station was set up on a straight street (11 m wide) while the mobile receiver travelled down the same straight street then turned off onto two side streets, one (35 m wide) that was 64 m from the base station and the other (44 m wide) 429 m from the base station. The path loss characteristics for the NLOS portion can divided into losses that occur right at the short interval where the straight road turns the corner onto the side road (i.e., corner losses, L c ), and the section of road after that where constant attenuation coefficient a is observed. Based on measurement for this work, we found that the L c interval, where the signal level drops precipitously, is approximately 20 m. For purposes of calculating the attenuation coefficient a, we used the entire distance Broadband Wireless Mobile: 3G and Beyond280 Figure 5.8 Propagation loss characteristics (h m ¼ 2.7 m). [...]... the path loss distribution approximates the Rayleigh distribution when the traffic volume is high even for LOS transmissions When traffic is low, on the other hand, there are at least two stable components resulting from the direct wave and the wave reflected off the ground and incoherent components As noted by Durgin et al [25], these additive signals produce a distribution in which deeper fading occurs... will differ depending on the volume of traffic even in LOS terrain [122] Figure 5.11 shows the path loss distribution results on Rayleigh probability paper for high and low traffic volumes measured over a 200-m distance Figure 5.11 Cumulative distributions of the path losses for different traffic conditions (hb ¼ 4 m, hm ¼ 1.3 m, f ¼ 8.45 GHz, High traffic: 1500 units/30 min.; low traffic: 600 units/30 min.)... low base station antenna, the diversity effect from the polarisation tended to be rather small Fading characteristics In mobile communications, fading often occurs even when the mobile station is not moving This is because of the effects of vehicles and other objects present in and around the propagation path It has been reported that these variations will differ depending on the volume of traffic even... transmission, the delay characteristics exhibit different behaviours between before the breakpoint and after the breakpoint The results of an earlier study showing the delay spread cumulative distribution for 3.35 GHz frequency are presented in Figure 5.13 [80] Approximating a straight line, the distribution exhibits a logarithmic normal distribution The slope of the distribution for the domain before the breakpoint... have different frequency response characteristics through which transmitted signals suffer from different delay, amplitude, and phase distortions in each channel When the bandwidth is relatively broader, received signal data at a receiver have frequency-selective faded spectrum The channels are then called frequencyselective fading channels The transmitted signals through the frequency-selective fading... Delay spread/distance distribution (hb ¼ 4.0 m, f ¼ 3.35 GHz) Broadband Wireless Mobile: 3G and Beyond 286 Figure 5.15 Arriving wave site variation The path loss characteristic for LOS paths is equal to an attenuation coefficient of about 2 Yet NLOS links exhibited corner losses somewhat greater than in urban environments of 30 to 40 dB, and did not always exhibit uniform attenuation with distance Typical... arrival angle distribution at the base station is critically important for deciding whether to make the antenna beam more narrow and for understanding the mechanism of propagation Measured and simulated results for spatio-temporal distribution characteristics are also reported Figure 5.20 shows a comparison of the spatio-temporal distribution characteristics done in the same way for a suburban residential... function of distance for various receiving antenna heights in LOS transmission [81] The delay spread increases with distance By applying approximate straight lines to better grasp the change trends, it is apparent that the lower the hm the steeper the gradient This can be attributed to the fact that, when the height of the antenna is approximately the same as that of vehicles and pedestrians, direct waves... of arriving wave increases, and the waves also exhibit substantial site variation The fluctuating number of waves can be attributed to paths disappearing due to interference among multiple rays, paths disappearing as a result of nonuniform reflective surfaces of buildings, and so on It is also clear that many sites exist where a single primary wave dominates Focusing on a 200-meter range between transmitting... that the path losses of the LOS path increased by about an average of 15 dB Under the same conditions, the path losses for the NLOS path increased by about 9 dB These correspond to the cross polarisation discrimination (XPD), the ratio of received power when the transmitted signal and received signal have different polarisations In contrast to a study that obtained an XPD of 6 dB using a high base . over a 200-m distance Broadband Wireless Mobile: 3G and Beyond282 Figure 5.11 Cumulative distributions of the path losses for different traffic conditions (h b ¼. systems beyond IMT-2000. † Co-ordinate and complement the near term aspects of the Radio Technology Working Group and co-ordinate with the other groups in