11-01-2013, 03:24 PM
Satellite-Based Internet
Satellite-Based Internet.ppt (Size: 1.03 MB / Downloads: 211)
Internet Services
Defined as any service in which data traffic originates from, travels over, or is destined for the public Internet -- growing from approximately 5.4 Gbps by year-end 1999 to an estimated 21 Gbps by 2003.”
Scope of Discussion
Mobile Applications: Broadband Internet access over mobile (3G). GSO or NGSO options.
Currently supported with limitations: low data rate.
Future support by: Teledesic, Inmarsat
(Extension of mobile voice systems discussed in previous classes)
Frequency Bands
Most commonly used:
C Band (4-8 GHz): very congested already.
Ku Band (10-18 GHz): Majority of DBS systems, as well as current Internet DTH systems (DirectPC and Starband).
Ka band (18-31 GHz): Offers higher bandwidth with smaller antennas, but suffers more environmental impairments and is less massively produced as of today (more expensive) when compared to C and Ka.
Multiple Access Control
To support QoS provisioning for data traffic, a requires priorities. Real-time traffic has the highest priority.
Three implementation groups:
Fixed Assignment: Pre-assigned channels based on FDMA, TDMA or CDMA implementation options.
Random access: Contention based (Aloha and its variations). Each station transmits when needed. Collisions occur for simultaneous transmissions.
Demand Assignment (DAMA): Resource negotiation phase prior to data transmission. Bandwidth allocated on demand using FDMA, TDMA or CDMA schemes.