Current Satellite Internet Access Satellite Capacity
As the demand for satellite capacity has steadily increased, traditional broadcast satellite technology using Ku-band (11-14 GHz ) frequencies becomes limiting. Because they are built to cover a very large downlink area, traditional broadcast satellites have difficulty supporting the flexible distribution of bandwidth needed for broadband internet.
New multiple-beam antennas (MBA) have become a key component in modern Broadband Satellite communication systems because they enable frequency reuse. MBA technology maximizes bandwidth capacity while minimizing required frequency allocation. To use the MBA technology efficiently Broadband satellites use the Ka-band frequencies, multiple pencil-like Spot Beams and Bent-Pipe network architecture.
Satellite Frequency Bands
There are several frequency bands available for the satellite-based broadband marketplace. While each of these frequencies has a place in the market, only the Ka-band frequencies support the robust frequency reuse to efficiently support Broadband Internet access. Listed below are the three most common frequencies and their frequency characteristics and usage:
• Ka-band: While the Ka-band extends from 27 GHz to 40 GHz, it also includes the upper part of the Super-high Frequency (SHF) band and the lower part of the Extremely High Frequency (EHF) range, which extends from 30 to 300 GHz. Broadband satellites systems typically employ the 27.5-30.0 GHz SHF frequency range for uplink transmissions (earth-to-space) and the 17.7-20.2 GHz range for downlink transmissions (space-to-earth). Note that the Broadband application actually overlaps a part of the Ku-band in its downlink frequency band. Because the Ka-band frequency is highly concentrated it provides high gain and a narrow beam-width along with the ability to deploy multiple beams that can be optimized for the area that they cover.
Because Direct Broadcast Satellites use the Ku-band frequencies, DBS installers are most familiar with aligning antenna to the Ku-band frequencies. The graphic below shows a comparison between the Ku-band and the Ka-band frequency. Note that the degree of azimuth is considerably smaller in the Ka-band. This translates to a need for more precise customer transmitter/receiver placement.
Broadband Satellite Spot Beams
While a conventional satellite, using Ku-band, will use a single downlink beam to cover a single area on the Earth, a Broadband satellite, using Ka-band, will use multiple Spot Beams to provide the same coverage. Each of the circles in the graphic below is equivalent to a "cell" in a cellular telephone network and allows multiple reuse of the frequency spectrum.
On average, a Broadband satellite will provide 35 to 45 Subscriber spot beams and about 6 Gateway Earth Station spot beams; about one Gateway spot beam for every 7 or 8 Subscriber spot beams. Transmissions in a Subscriber spot beam are to/from the Subscriber Side Terminal. Transmissions in a gateway spot beam are to/from a Service Provider Ground Station.
The graphic below shows a typical spot beam layout for the United States from a Broadband satellite. Note that other satellite-based Internet service providers such as as StarBand and HughesNet rely upon Ku-band satellites and therefore have only one beam to serve the entire United States.
WildBlue Bent-Pipe Architecture
The WildBlue broadband architecture combines spot beam technology with links that operate on a point-to-point basis. The satellite uses on-board switching to provide two-way data paths between different spot beams. The bent-pipe architecture allows the satellite processor to concentrate on building the data-paths, because the satellite acts as a repeater. In the satellite, the data-path signal is Received, Retuned, Amplified, and Retransmitted but there is no demodulation, decoding or any other type of signal processing.
The satellite divides uplinks and downlinks to user-links, the up/down links between the Subscriber Terminal and the satellite, and feeder-links, the up/down links between the satellite and Gateway. Bent-pipe technology in the satellite switches a user-uplink and a feeder-downlink together to form the upstream data-path between the customer and the service provider. The same technology switches the downstream user-downlink and the upstream feeder-link together to form the downstream datapath between the customer and the service provider.
The combination of the upstream and downstream data-paths connected to a single Gateway form a sub-network. These sub-networks are a part of the larger Service Provider network, inter-connected with fiber rings, providing access to the internet.
The graphic below shows a portion of a Broadband Satellite network. Note that User-links and Gateway-links actually consist of one uplink and one downlink. A single line in the graphic displays an upstream and downstream data-path.
have the following characteristics:
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Located at 22,300 mi. above the equator
• Operating in Ka-band (20-30 GHz) mode