A study on integration of mobile communication and TV broadcasting systems operating in UHF band by Hata_ M.; Tomisato_ S

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A study on integration of mobile communication and TV broadcasting systems operating in UHF band by Hata_ M.; Tomisato_ S Powered By Docstoc
                                Masaharu HATA and Shigeru TOMISATO

                               Faculty of Engineering, Okayama University
                     3-1-1, Tsushima-Naka, Okayama-shi, Okayama, 700-8530, Japan
                              E-mail: {hata, tomisato}@cne.okayama-u.ac.jp

Abstract - According to the recent introduction of               band. The outline of this paper is as follows. Section
digital-TV broadcasting services and the band                    II presents the frequency allocation for terrestrial TV
expansion for mobile communication services, new                 broadcasting and mobile communication services in
systems by the integration of mobile communication               the VHF/UHF bands and the future plan announced
and terrestrial TV broadcasting systems in the UHF               by the Japanese government. Section III describes
band are expected to realize efficient resource                  system configurations and layered cell structures for
management and new attractive services. In this                  TV broadcasting and mobile communication systems.
paper, the aspects on system configuration and                   In Section IV, basic aspects for the mobile radio link
mobile radio link design are examined to investigate             design are examined from the viewpoint of
the possibility of integration of mobile communi-                propagation characteristics and frequency sharing
cation and TV broadcasting systems operating in the
UHF band.

                                                                         II. FREQUENCY ALLOCATION IN
                                                                                VHF AND UHF BANDS
                I. INTRODUCTION
                                                                 According to the public announcement of Japanese
Transition from the analog-TV to the digital-TV
                                                                 government [1], the frequency reallocation plan for
broadcasting service has been started last year in
                                                                 mobile communication and TV broadcasting systems
Japan. New services are seeking to make the digital-
                                                                 operating in the VHF/UHF band can be summarized
TV broadcasting more attractive than current analog-
                                                                 in Fig.1. The transition from the VHF/UHF analog-
TV services. Adjusting the start of digital-TV
                                                                 TV to the UHF digital-TV broadcasting services will
broadcasting service, new mobile phones capable
                                                                 be finished at the year 2011. After the year, current
with digital-TV receiving have been proposed for one
                                                                 VHF band, 90-222 MHz, will be assigned for new
of the future services. Regarding mobile communi-
                                                                 services including mobile communication services.
cation systems, the lack of frequency bands becomes
                                                                 The upper part of the UHF-TV band, 710-770 MHz,
the actual problem due to the increase of users and
                                                                 will be assigned for mobile communication services
the demand for high data rates. Therefore, the
                                                                 from the year 2012. This means that digital-TV
frequency band reallocation plan in which an upper
                                                                 broadcasting services and mobile communication
part of current UHF TV broadcasting band are
                                                                 services will use adjacent frequencies in the UHF
assigned for mobile communication services has been
                                                                 band. Although it depends on frequency sharing
announced recently [1].
                                                                 conditions, this allocation plan makes expectations
       Considering such close relation between
                                                                 for new services by the integration of these systems
communication and broadcasting services in the UHF
                                                                 in near future.
band, new systems by the integration of mobile
communication and TV broadcasting systems are
expected to realize efficient resource management                   90      222      470           710 770               (MHz)
and new attractive services. The works of a study on                  VHF                    UHF
the convergence of the terrestrial fixed wireless                    Analog-               Analog-TV             Mobile
access, mobile cellular and broadcasting networks                      TV                                     Communications
and a technical study on the sharing between those
systems have been proposed and started in the ITU-R                 108 170                            722   810
[2], [3]. From the viewpoint of broadband, mobility,              finished analog-    completed
                                                                                                             for mobile
and asymmetric traffic stream, an idea of new                     TV at the year      the transition
information traffic platforms using TV broadcastings              2011, and           from analog
                                                                                                             from the year 2012
for download channels has been proposed with the                  assigned for        to digital at
                                                                                                         review at the year 2006
                                                                  new services        the year 2011
receiving data of UHF TV broadcasting signals in
indoor environments [4].
       In this paper, we consider more detail conditions         Fig.1 Frequency allocation for TV broadcasting and
to realize the integration of mobile communication                     mobile communication services in VHF/UHF
and TV broadcasting systems operating in the UHF                       bands and the future plan
        III. SYSTEM CONFIGURATION                           2) Same frequency raster is used and all frequencies
               CONSIDERATIONS                               in TV broadcasting and mobile communication
From the viewpoint of uplink and downlink service           systems are reused.
category, TV broadcasting system is suitable for                  As the OFDM transmission technology is
downlink services in nature, and mobile communi-            applied in the digital TV broadcasting system, the
cation system is basically aimed for mutual services.       above mentioned single frequency actually means the
Considering the possibility to introduce a new mobile       frequency with subdivided multiple carrier frequency
communication system for the integration, there are         structure. Taking into that the multi-carrier CDMA is
two applications for uplink configuration; one is to        the candidate transmission technology for the next
use new mobile communication systems and the other          generation mobile communication systems, the
is to use current mobile communication systems. The         superimposed layout will be worth from efficient
interactive service in TV broadcasting is offered by        spectrum utilization and sharing viewpoints. However,
using TV broadcasting network for down link and             the overlapped layout will be introduced at first
fixed telecom network for up link between users and         because of the ease of migration to the integrated
service providers. Therefore, the interactive service       system.
through the integrated network is realized by mobile
phones with TV receiving function and mobile
communication network functions. Terminals
offering some integration of TV and mobile phones
are already found on the market. Although major
function of the conventional TV broadcasting
network is the repeater function for TV programs
between key and local stations, the multimedia data
transmission associated with TV broadcasting will                               Overlapped layout
become more important function in the digital-TV era.                 MBS
      Regarding the fixed telecom and mobile
communication networks, these networks are shifting
towards Internet Protocol (IP)-based networks due to
the expansion of the Internet. Since the most traffic
will be based on IP, one of the critical requirements
for the integrated network is to realize the function
transferring IP traffic efficiently. In line with the
penetration of mobile Internet access services,                                Superimposed layout
interactions between network operators and service
providers will become more critical. Especially,              Fig.2 Layered cell structure for TV broadcasting
direct interactions on the mobility and traffic control             and mobile communication systems
between terminals and service providers will become
one of the key aspects to offer attractive multimedia
services.                                                   IV. MOBILE RADIO LINK CONSIDERATIONS
      Considering the service area size of a TVS (TV        A. Propagation Characteristics
broadcasting station) and the frequency allocation,
cell structure of the integrated system can be              In order to consider the radio link design for the
categorized in two types, overlapped and                    overlapped cell layout, the mobile propagation path
superimposed layouts, as shown in Fig.2. The                loss has been measured in the UHF-TV band [5]. TVS
overlapped layout is based on current TVS service           transmission antenna height is 424m and the effective
area structure and SFN (single frequency network)           radiation power of voice channel is 78.4dBm. The
based frequency allocation. Multiple frequencies with       measured frequency of the voice channel is
geographical frequency reuse are used in TDMA               535.75MHz. Monopole antenna height of mobile
cellular system and same frequency for each cell is         station is 1.5m. Antenna pattern of TVS has been
used in CDMA cellular system. In the superimposed           considered at each measurement points. Figure 3
layout, the service area is covered by plural TVS with      shows path loss characteristics in the urban area of
frequency reuse technology, and there will be two           Okayama city, which is one of the typical local cities
types of frequency allocation.                              in Japan. The ground cover factor of the urban area in
 1) In TV broadcasting system, single frequency is          the city is almost same value corresponding to the
used in each TVS, but multiple frequencies are              urban area categorization in the Okumura-Hata
applied for geographical frequency reuse. In mobile         formula [6]. The measurement result shows that the
communication system, multiple frequencies with             attenuation constant is similar to the value derived
geographical frequency reuse are used in TDMA               by the formula. However, the absolute value of the
cellular system and same frequency for each cell is         path loss is approximately 10dB lower than that of
used in CDMA cellular system.                               the formula. This difference is considered to be
     caused by the high TVS antenna height, low average                                        local cities, and the beam tilting of TVS antenna will
     building height, and, therefore, high line of sight                                       be set within a few degrees. As an example of mobile
     probability between TVS and receiving points. This                                        communication system, let assume the WCDMA
     means that the ground cover factor is not enough to                                       system for the consideration [7]-[9]. Although the
     reflect the effect of city structure to the path loss                                     system capacity is determined by the internal system
     formula. The measurements have also done in the                                           interference, the external interference from TVS
     suburban, rural, and hilly areas. Since the urban area                                    becomes the additional interference noise and
     in the local city is concentrated in small area and                                       degrades the WCDMA system capacity. Figure 5
     changes to the rural area within a short distance, the                                    shows the interference attenuation by the TVS TX
     attenuation constant in the suburban area becomes                                         and MBS RX filters and guard band.
     very large, and the path loss in the hilly area
     fluctuates widely due to the visibility.                                                                              Undesired Wave
                                                                                                                                                 Desired Wave
           Therefore, when we design the downlink of the
                                                                                                                                                                Service Areas
     integrated system for the local city with low average
     building height, we can take almost the same way of                                                            TVS
     current cellular systems. However, we have to take
     care the actual path loss lower than that of the
     formula and the city terrains. For example,                                                                                                                       MBS
     introduction of a sub-system like the satellite TVS
     may be effective for the hilly areas in local cities.                                                                                             Cellular System
     Regarding the uplink design, if the assigned
                                                                                                               Fig.4 Interference from TVS to MBS in
     frequency is 710MHz for a new mobile
                                                                                                                     overlapped layout
     communication system and 810 MHz for the current
     cellular system, the path loss difference on the
     frequency dependency term in the formula is only                                                                                 Carrier Separation
     1.5dB. Since the mobile propagation environments of
     these systems are same, the uplink of the new system

     is also designed by the same way of current cellular                                                                                   Guard          MBS
                                                                                                                X0 dB     TVS
     systems.                                                                                                             TX Filter         Band           RX Filter

                                                                                                                           6 MHz                            5 MHz
Propagation Path Loss (dB)

                             130                                                                                                                                 Frequency
                                          Okumura-Hata Formula
                                                = 2.8
                                                                                                              Fig.5 Attenuation by the TVS TX and MBS RX
                             120                                                                                    filters and guard band
                                                                  Least Square
                                          Free                        Method
                                                                      ( = 3.1 )
                                                                             k                       Assuming that this interference attenuation is X0
                             110              = 2.0
                                                                                               (dB), the free space loss corresponding to the
                                                                                               coordination distance is L (dB), the interference
                             100          Frequency: 535.75MHz        Urban Area
                                                                      in Okayama
                                                                                               reduction by improvement technologies is M (dB),
                                           (TV Voice Channel)
                                                                                               and the radiation power of TVS is T (dBm/MHz),
                             90                                                                then, the external interference level Ix (dBm/MHz) is
                                   7         8        9    10    11   12   13   14 15 16       given by
                                                          Distance (km)
                                                                                                                    Ix    (T    (X 0      L M )).
                                       Fig.3 Path loss characteristics in urban mobile              Let the required overall noise level be Ireq
                                             propagation environment
                                                                                               (dBm/MHz), the thermal noise level be N0
                                                                                               (dBm/MHz), the system capacity with and without
     B. Frequency Sharing Issues                                                               external interference be C and C0, the relative system
                                                                                               capacity C /C0 is given by [9]
     Since the integrated system with overlapped layout
     structure will use adjacent frequencies in the UHF                                                            C       1    ( Ireq /( N 0       Ix ))   1

     band, it is necessary to clarify the sharing conditions.                                                                                          1
                                                                                                                   C0          1      ( Ireq / N 0 )
     Figure 4 shows the worst case interference model for
     the consideration. The undesired wave from TVS to                                               When we apply the system parameters of
     MBS arrives with free space loss. On the other hand,                                      WCDMA used in the reference [7], the relative
     the desired wave from mobile station reaches MBS                                          system capacity becomes as shown in Fig.6. The
     according to the mobile propagation path loss.                                            result shows that the system capacity is sensitive to
     Distance between TVS and MBS may be a few km in                                           the external interference level. And the allowable
external interference level of the WCDMA system                                                   in the UHF band will be feasible by improving the
becomes approximately -120dBm/MHz to keep less                                                    TVS TX filer characteristics. The expansion of the
than 8% capacity reduction without improvement                                                    integrated system will depend on the creation of
technologies, i.e. M = 0dB condition. This means that                                             specific services offered by the system. It will be
if T is 75dBm/MHz and L is 95dB, X0 should be more                                                required that those services should be not only
than 100dB to realize this allowable external                                                     attractive for the system users but beneficial for
interference level. Considering the beam tilting of                                               service providers, mobile communication and TV
MBS receiving antenna, roughly 30dB reduction to                                                  broadcasting operators.
the external interference level can be expected as the                                                 This study has been funded by Grant-in-Aid for
antenna pattern effect. In this case, therefore, the TVS                                          Scientific Research of Japan, under contract number
TX filter has to have at least 70dB down floor                                                    KAKENHI-14550361.
characteristic in the out of occupied frequency band
and 12.5dB/MHz down slope characteristic for the
6MHz guard band. These requirements for the filter                                                                     REFERENCES
are considered to be feasible by current                                                          [1]    “Public announcement on the radio frequency re-
manufacturing technologies.                                                                             allocation policy”, Home page of the Ministry of
                                                                                                        Public Management, Home Affairs, Post and
                               100                                                                      Telecommunications, News Release, Oct. 10,
                               90                                                                       2003, (in Japanese), http://www.soumu.go.jp/
Relative System Capacity (%)

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mobile communication and TV broadcasting systems                                                        (in Japanese)

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