Tài liệu Điện thoại di động băng thông rộng không dây P8 docx

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.. According to the WG-Visio

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

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

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 2000 and systems beyond 2000; considering

IMT-2000 spectrum implementation issues and any necessary sharing, compatibility and inter-ference criteria between IMT-2000 and other radio services

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

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

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

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

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

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 (hm) 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 hm¼ 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

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 hm¼ 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 breakbreak-point based on path loss character-istics measured during the day and at night for hm¼ 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, Lc), and the section of road after that where constant attenuation coefficient a is observed Based on measurement for this work, we found that the Lc interval, where the signal level drops precipitously, is approximately 20 m

For purposes of calculating the attenuation coefficient a, we used the entire distance

Figure 5.8 Propagation loss characteristics (h ¼ 2.7 m)

including the LOS portion At three different frequencies, we obtained the following Lcand a values for the 64-m/429-m corners, see Table 5.1

The Lc and attenuation coefficient do not reveal any dependence on frequency It is not certain what effect the LOS distance has on Lc, but it is clear that the farther the intersection is away from the base station, the greater the attenuation coefficient Compared to the NLOS

Table 5.1 Estimated corner loss (Lc) and attenuation coefficient (a)

64-m corner/429-m corner 64-m corner/429-m corner

Figure 5.9 Propagation loss characteristics (hm¼ 1.6 m)

Figure 5.10 Propagation loss characteristics (hb¼ 4.0m, hm¼ 1.6 m, f ¼ 3.35 GHz)