Write short note on
Iridium satellite system
Wireless local loop:
Wireless local loop (WLL), is the use of a wireless communications link as the "last mile / first mile" connection for delivering plain old telephone service (POTS) or Internet access (marketed under the term "broadband") to telecommunications customers. Various types of WLL systems and technologies exist. Other terms for this type of access include Broadband Wireless Access (BWA), Radio In The Loop (RITL), Fixed-Radio Access (FRA), Fixed Wireless Access (FWA) and Metro Wireless (MW). In traditional telephone networks, your phone would be connected to the nearest exchange through a pair of copper wires.Wireless local loop (WLL) technology simply means that the subscriber is connected to the nearest exchange through a radio link instead of through these copper wires. In general, WLL is cheaper and quicker than copper wire connectivity. As the cost of copper rises over time and so does the cost of digging, this is likely to become an ever more significant advantage. In a traditional wire-line network, the cost of the 'last mile' would amount to a substantial portion of the total cost of putting up the network.This would be particularly true in remote locations with few subscribers or in difficult terrain. It is this part of the cost that WLL significantly reduces. The economics of WLL thus works in its favour. WLL is also a more suitable technology for a quick rollout of a network as it bypasses digging ditches to lay copper wires.This is a significant factor in crowded urban localities, where permission to dig may be almost impossible to get. Another major advantage of using a radio link for the last mile is that it considerably reduces the number of faults. Close to 90% of all basic telephone faults occur in the last mile part of the network. With a radio link replacing the wires, these faults become almost negligible. There are various technologies like frequency division multiple access (FDMA), time division multiple access (TDMA) and code division multiple access (CDMA) used for WLL. The one that is being used in India is CDMA. This is a full-fledged cellular mobile technology. In fact, it is the most dominant technology for mobile phone services in countries like the US and Korea.
Iridium satellite system
The Iridium satellite constellation is a satellite constellation providing voice and data coverage to satellite phones, pagers and integrated transceivers over Earth's entire surface. Iridium Communications owns and operates the constellation and sells equipment and access to its services. It was originally conceived by Bary Bertiger, Dr. Ray Leopold and Ken Peterson in late 1987 (and protected by patents by Motorola in their names in 1988) and then developed by Motorola on a fixed-price contract from July 29, 1993 to November 1, 1998 when the system became operational and commercially available. The constellation consists of 66 active satellites in orbit, and additional spare satellites to serve in case of failure. Satellites are in low Earth orbit at a height of approximately 485 mi (781 km) and inclination of 86.4°. Orbital velocity of the satellites is approximately 17,000 mph (27,000 km/h). Satellites communicate with neighboring satellites via Kaband inter-satellite links. Each satellite can have four inter-satellite links: two to neighbors fore and aft in the same orbital plane, and two to satellites in neighboring planes to either side. The satellites orbit from pole to pole with an orbit of roughly 100 minutes. The satellites each contain seven Motorola/Freescale PowerPC 603E processors running at roughly 200 MHz, connected by a custom backplane network. One processor is dedicated to each cross-link antenna ("HVARC"), and two processors ("SVARC"s) are dedicated to satellite control, one being a spare. Late in the project an extra processor ("SAC") was added to perform resource management and phone call processing. The original design as envisioned in the 1960s was that of a completely static "dumb satellite" with a set of control messages and time-triggers for an entire orbit that would be uploaded as the satellite passed over the poles. It was found that this design did not have enough bandwidth in the space-based backhaul to upload each satellite quickly and reliably over the poles. Moreover, fixed, static scheduling would have left more than 90% of the satellite links idle at all times.
Briefly describe the congestion control, slow start and fast retransmit mechanism.
Discuss the three different mechanisms to improve the cell capacity and coverage area in a cellular system.
Discuss about SCHEDULING
Briefly Discuss about Requirements Analysis
Discuss about Staffing
