Chapter 8. The Earth Segment

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1 Chapter 8. The Earth Segment
第八章 地球段 亞洲大學 資訊工程學系碩士班 呂克明教授 二○○六年十一月二十七日 4/8/2019

2 Chapter 8. The Earth Segment (第八章地球段)
Introduction (緒言) Receive-only home TV Systems (家中單收電視系統) Master Antenna TV System (主天線電視系統) Community Antenna TV System (社區天線電視系統) Transmit-Receive Earth Stations (收發地球站系統) Homework Problems (習題) 4/8/2019

3 Introduction (緒言) The earth segment of a satellite communications system consists of the transmit and receive earth stations (發射與接收地球站). The simplest of those are the home TV receive-only (TVRO) system (電視單收系統). The most complex are the terminal stations used for international communication networks. Also, included in the earth segment are: Earth station on ships at sea (船艦地球站, 需求加裝穩定器與追蹤系統) Commercial and military land stations (商用與軍用陸上地球站) Commercial and military aeronautical mobile stations (航空移動地球站, 例如飛機) 4/8/2019

4 Receive-Only Home TV Systems (家中單收電視系統)
Direct Broadcast Satellite (DBS, 衛星直播系統) service: Some variation in the frequency bands and different geographical regions. In Americas, the downlink band is 12.2 to 12.7 GHz. (500mhz) C-band larger receiving antenna (about 3-m diameter) for network relay to commercial TV outlets. It differs from Ku-band receive-only systems lies in the frequency of operation of the outdoor unit, and EIRP (等效全向輻射功率) of Ku-band is higher. 中華電信電視節目衛星中繼業務（INTELSAT-702之轉頻器,Ｃ頻段）年租費價目表, 單位：新台幣元 77dBW＜EIRP≦80dBW 30,240,000 74dBW＜EIRP≦77dBW 24,192,000 71dBW＜EIRP≦74dBW 18,144,000 68dBW＜EIRP≦71dBW 12,096,000 EIRP≦68dBW 6,048,000 4/8/2019

5 Receive-Only Home TV Systems (家中單收電視系統)(continued)
Polarization interleaving: Frequency reuse by using the alternately polarized LHC/RHC and/or vertical/horizontal to reduce interference to acceptable levels. “Interleaving”是交錯或交流的意思，指左旋圓形極化與右旋圓形極化之間頻率的交錯重複使用或是垂直極化與水平極化之間頻率的交錯重複使用, 其目的是在減少干擾到達可以被接受的程度。 The signal fed to the indoor unit is normally a wideband signal covering the range MHz. The 70MHz Intermediate frequency (IF) carrier must be demodulated and the base band information used to generate a vestigial single sideband (VSSB, 殘餘邊帶 ) signal which is fed into one of the VHF/UHF channel of a standard TV set. 4/8/2019

6 Receive-Only Home TV Systems (家中單收電視系統)(continued)
There are many types of communication, however, such as television, video, facsimile and high-speed data signals that have a large bandwidth incorporating significant low-frequency content. Single sideband (SSB) systems have a poor low-frequency response so vestigial-sideband (VSB) modulation is used, which is derived by filtering double-sideband (DSB) so that one sideband is completely passed and just a trace, or vestige, of the other sideband is included. cos(A+B) = cosAcosB - sinAsinB cos(A-B) = cosAcosB + sinAsinB cosAcosB = (cos(A+B) + cos(A-B) )/2 Let A = wt & B = wct cos wt cos wct = (cos(wc + w) t+ cos(wc - w)t )/2 There are two side band frequencies: wc+w and wc-w 4/8/2019

7 Receive-Only Home TV Systems (家中單收電視系統)(continued)
SSB versus AM: (1) Since the carrier is not transmitted, there is a reduction by 50% of the transmitted power (-3dBm). --In modulation: 1/2 of the power is comprised of the carrier; with the remaining (1/2) power in both sidebands. (2) Because in SSB, only one sideband is transmitted, there is a further reduction by 50% in transmitted power (-3dBm (+) -3dBm = -6dBm). (3) Finally, because only one sideband is received, the receiver's needed bandwidth is reduced by one half--thus effectively reducing the required power by the transmitter another 50% (-3dBm (+) -3dBm (+) -3dBm = -9dBm). 4/8/2019

8 Receive-Only Home TV Systems (家中單收電視系統)(continued)
A vestigial sideband (殘餘邊帶,VSB) in radio communication is a sideband that has been only partly cut off or suppressed. VSB transmission is similar to single-sideband (SSB) transmission, in which one of the sidebands is completely removed. In VSB transmission, however, the second sideband is not completely removed, but is filtered to remove all but the desired range of frequencies. Television broadcasts (regardless of NTSC, PAL, or SECAM analog video format) use this method if the video is transmitted in AM, due to the enormous bandwidth used. It may also be used in digital transmission, such as the ATSC-standardized 8-VSB. The bandwidth of vestigial-sideband systems is therefore only slightly larger than that of SSB systems but with the increased low-frequency performance of DSB systems. 4/8/2019

9 Receive-Only Home TV Systems (家中單收電視系統)(continued)
數位地面電視現有三種制式，即美國的Advanced Television Systems Committee (ATSC)制式，歐洲的Digital Video Broadcasting-Terrestrial (DVB-T)制式及日本的Integrated Services Digital Broadcasting-Terrestrial (ISDB-T)制式。 雖然移動接收並不是必須的服務，但當市場有此需求時，所選用的數位地面電視制式如能提供這種功能必然更為理想。ATSC制式所採用的殘餘邊帶（vestigial sideband）調制有較高的數據速率，在覆蓋相若範圍時所需的發射器功率亦較低，但並不支援移動接收功能。另一方面，由於DVB-T制式及ISDB-T制式所採用“編碼正交頻分多路複用”(Coded Orthogonal Frequency Division Multiplex)調制在動態及高度靜態多路環境中有較佳表現，因而能夠提供移動接收功能。 4/8/2019

10 Master Antenna TV Systems (主天線電視系統)
A master antenna TV (MATV) systems is used to provide reception of DBS TV/FM channels to a small group of users, for example, to the tenants in an apartment building. It consists of a single outdoor unit feeding a number of indoor units. The advantage is that only one outdoor unit is required, but separate LNA/Cs and feeder cables are required . 4/8/2019

11 Community Antenna TV System (社區天線電視系統)
The community antenna TV (CATV) system employs a single outdoor unit, with separate feeds available, like the MATV. Instead of having a separate receiver for each user, all the carrier are demodulated in a common receiver-filter system. In a remote areas where a cable distribution system may not be installed, the signal can be rebroadcast from a low-power VHF TV transmitter. 4/8/2019

12 Transmit-Receive Earth System (收發地球站系統)
A transmit-only station is required in relaying TV signals to the remote TV receive-only stations. Transmit-receive stations provide both functions and are required for telecommunications traffic. A number of different classes of earth stations are available, depending on the service requirements. Traffic can be broadly classified as heavy route, medium, and thin route. In a thin-route circuit, a transponder channel (36 MHz, C-band) may be occupied by a number of single carriers, each associated with its own voice circuit. The mode of operation is known as single carrier per channel (SCPC, 單路單載波). 4/8/2019

13 Transmit-Receive Earth System (收發地球站系統)(continued)
A medium-route circuit also provide multiple access, either on the basis of frequency-division multiple access (FDMA, 頻分多址) or time-division multiple access (TDMA,時分多址), multiplexed base band signals being carried in either case. In 6/4-GHz heavy-route system, each satellite channel (bandwidth 36 MHz) is capable of carrying over 960 one-way voice circuits simultaneously or a single-color analog TV signal with associated audio (in some systems two analog TV signals can be accommodated). 4/8/2019

14 Homework Problems (習題)
8.1 Explain what is meant by direct broadcast satellite service. 8.2 Explain what is meant by polarization interleaving. 8.4 Explain why the low-noise amplifier in a satellite receiving system in placed at the antenna end of the feeder cable. 8.8 Describe and compare the master antenna TV (MATV) and the community antenna TV (CATV) systems. 8.9 Explain what is meant by the term redundant earth system. 4/8/2019