Low-Earth-Orbit Satellite (LEO)

                      Low Earth Orbit Satellite (LEO) is satellite communication technologies. One technology is called the Iridium. It is a mobile satellite system. Iridium was a concept of launching 66 satellites but it was originally 77 satellites when it was proposed on FCC. Iridium is owned by the Motorola. The application was submitted to FCC in the year 1990. Its original concept was to use 7 polar orbits with 11 satellites in each. The coverage of this is around the world. This concept uses line of sight coverage from point to point virtually any other point on the globe. This uses a spot beam from the radio communications services on board each of the satellites. This technology of the spot beam concept introduced the high frequency reuse capacities that had not been achieved before. The satellite that was used was small compared to the others that had been used. Its electronic circuits inside were very sophisticated.

                        The initial features available on LEO networks are Radio Determination Service (RDSS), Voice communications (VC), Paging (P), Facsimile (Fax) and Data Communications (DC). The RDSS is used at the location of vehicle fleets, aircraft, marine vehicles, etc.  Voice communication is used on dial up digital voice communications anywhere in the world. Paging is used as a one way paging service. It includes alphanumeric display for up to two lines, but will expand to short messaging services (SMS) at 160 characters. Fax is used as a two way facsimile service. Data communication is used in two way transmission of data.

Here is a figure of an arrangement concept of LEO:

                        In this particular arrangement, the satellites are located at the height of 400+ nautical miles above the earth, in a polar orbit. In the polar orbit, the satellite moves around the earth’s poles and passes over any specific point along its path very quickly. The satellites have a speed of 7,400 meters per second in different orbits. Gateway feeder links uses the spectrum in the Ka band. Iridium used approximately 16.5 MHz of bandwidth in the L band. 

Advantages to LEO satellite telemetry:

·         Global applications in developing a remote environmental monitoring communication system.

·         Two-way communications.

·         Easy to setup and low maintenance cost.

·         Low profile, non-directional whip helix antenna.

·         Easy access to data.

·         No FCC or other governmental agency requirements for data transmission.

·         Coverage in very remote areas.

·         Data is proprietary.

·         Stevens is able to quickly detect any problems with transmission of data.

·         Systems verifies that data has been transmitted which minimizes risk of missing data.

·         Event notification on line, by pager, etc.

·         Lower power transceivers compared to GEO transmitter system.

·         LEO transceivers hardware system is lower in cost than a GEO transmitter system.

Disadvantage to LEO satellite telemetry:  

·         Monthly service fee which could be expensive with frequent transmission of data.

·         Power outage at GCC would shut down the communication server, which could delay transmission of data to end user until power is restores. However, no data is lost.

·         LEO satellites have much shorter life span(five to eight years) than GEO satellites.

Sources:

Broadband Telecommunications Handbook by Regis Bates

http://www.stevenswater.com/telemetry_com/leo_info.aspx 

Third Generation (3G) Wireless System

               Today, internet connection is available in mobile phones. This is made possible by using GPRS technology, but now there are modern methods in accessing internet through mobile phones, these are 3G and 4G technologies.

                GPRS uses packet data technology. With packet networks, you can immediately access the mobile internet. This enables you to access the existing applications of the internet such as email and web browsing without dialing into an ISP. Using the medium or the radio link, several users can share the same radio channel very efficiently. With packet data, users will only pay for the amount of data they actually communicate and not the idle time. Packet based communication is compatible with all other types of communication. GPRS can support the Internet Protocol (IP) as well as X.25 protocol.

                   There is a new technology that takes cellular community closer to UMTS or the 3G. It has a new modulation scheme called 8-phase shift keying (PSK). It also provides higher data rates than GPRS. This technology is called Enhanced Data for Global Environment (EDGE). The data rates allocated for EDGE are started at 384 Kbps and above as a second stage to GPRS. EDGE uses a combination of FDMA and TDMA as the multiple access control methods. If we view the OSI stack model, EDGE uses FMDA and TDMA at the MAC layer.

                    EDGE is very special because its bandwidth is efficient than the GMSK modulation scheme used in the GSM standard, it creates a new modulation scheme. This technology provides a new physical layer: 8- PSK modulation, instead of GMSK. EDGE still retains existing GSM parameters. These include frame length, eight time slots per frame, and a 270.833 KHz symbol rate. These techniques help EDGE to promote worldwide or globally into the market.

                         UMTS is part of a global family of 3G mobile communications systems. It takes full advantage of the trend of converging existing and future information networks, devices and services, and the potential synergies that can be derived from such convergence. 

                          Mobile internet has many applications. There are applications for moving to a wireless and a 3G environment. These applications are customized infotainment, multimedia messaging service, mobile intranet/extranet access, mobile internet access, location based services rich voice, wireless advertising, mobile information, business solutions, mobile transactions, mobile entertainment, person-person communications and bearer entrance and periodic.

                            There is an issue that needs to consider whether to simplify provide a wireless IP pipe to a service offering hosted elsewhere on the internet, or to go for an interoperable end-to-end solution. In wireless IP pipe business using tunneling protocols will become a commodity operation, where cost, coverage, and data rate are the only competitive dimensions.

Here are some advantages and disadvantages of 3G:

Advantages:

·         Overcrowding is relieved in existing systems with radio spectrum.

·         3G has more bandwidth, security and reliability.

·         Provides interoperability among service providers.

·         Availability of fixed and variable rates.

·         Support to devices with backward compatibility with existing networks.

·         Always online devices – 3G uses IP connectivity with existing networks.

·         Rich multimedia services are available

Disadvantages:

·         The cost of cellular infrastructure, upgrading base stations is very high.

·         Needs different handsets.

·         Roaming and data/voice work together has not yet been implemented.

·         Power consumption is high.

·         Requires closer base stations and are expensive.

·         Spectrum-license costs, network deployment cost and handset subsidies subscribers are tremendous. 

Sources:

Broadband Telecommunications Handbook by Regis J. Bates

http://www.umtsworld.com/applications/applications.htm

http://www.careerride.com/3g-advantages-and-disadvantages.aspx