Wireless and mobile communication

1. Radio and Satellite Communication Wireless and mobile communication Lecture-5 Instructor : Mazhar Hussain

2. Types of wireless communication celullar wireless computer network radio service

3. Radio Communication • Radio or radio communication means any transmission, emission, or reception of signs, signals, writing, images, sounds or intelligence of any nature by means of electromagnetic waves of frequencies lower than three thousand gigacycles per second (3000 GHz) propagated in space without artificial guide. • Examples of radio communication systems: • Radio broadcasting. • TV broadcasting. • Satellite communication. • Mobile Cellular Telephony. • Wireless LAN. • Multimedia communication & Mobile Internet [Slimane]

4. History • 1864: Maxwell describes radio wave mathematically • 1888: Hertz generates radio waves • 1890: Detection of radio waves • 1896: Marconi makes the first radio transmission • 1915: Radio tubes are invented • 1948: Shannon’s law • 1948: Transistor • 1960: Communication Satellites • 1981: Cellular technology

5. Classification of radio spectrum

6. Evolution of Wireless Systems [Stallings., 2005]

7. Radio Communication • Three main problems: • The path loss • Noise • Sharing the radio spectrum

8. Types of electromagnetic carriers • when the distance between the sender and receiver is short (e.g. TV box and a remote control) infrared waves are used • for long range distances between sender and receiver (e.g. TV broadcasting and cellular service) both microwaves and radio waves are used • radio waves are ideal when large areas need to be coverd and obstacles exist in the transmission path • microwaves are good when large areas need to be coverd and no obstacles exist in the transmission path

9. Wireless applications (services)

10. Advantages and disadvantages of wireless communication • advantages: • mobility • a wireless communication network is a solution in areas where cables are impossible to install (e.g. hazardous areas, long distances etc.) • easier to maintain • disadvantages: • has security vulnerabilities • high costs for setting the infrastructure • unlike wired comm., wireless comm. is influenced by physical obstructions, climatic conditions, interference from other wireless devices

11. Frequency Carries/Channels • The information from sender to receiver is carrier over a well defined frequency band. • This is called a channel • Each channel has a fixed frequency bandwidth (in KHz) and Capacity (bit-rate) • Different frequency bands (channels) can be used to transmit information in parallel and independently.

12. Basics of Radio Communication

13. Radio waves generation • when a high-frequency alternating current (AC) passes through a copper conductor it generates radio waves which are propagated into the air using an antena • radio waves have frequencies between: • 3 Hz – 300 KHz - low frequency • 300 KHz – 30 MHz – high frequency • 30 MHz – 300 MHz – very high frequency • 300 MHz – 300 GHz – ultra high frequency

14. Basics: How do Satellites Work • Two Stations on Earth want to communicate through radio broadcast but are too far away to use conventional means. • The two stations can use a satellite as a relay station for their communication • One Earth Station sends a transmission to the satellite. This is called a Uplink. • The satellite Transponder converts the signal and sends it down to the second earth station. This is called a Downlink.

15. Basics: Advantages of Satellites • The advantages of satellite communication over terrestrial communication are: • The coverage area of a satellite greatly exceeds that of a terrestrial system. • Transmission cost of a satellite is independent of the distance from the center of the coverage area. • Satellite to Satellite communication is very precise. • Higher Bandwidths are available for use.

16. Basics: Disadvantages of Satellites • The disadvantages of satellite communication: • Launching satellites into orbit is costly. • Satellite bandwidth is gradually becoming used up. • There is a larger propagation delay in satellite communication than in terrestrial communication.

17. Basics: How Satellites are used • Service Types • Fixed Service Satellites (FSS) • Example: Point to Point Communication • Broadcast Service Satellites (BSS) • Example: Satellite Television/Radio • Also called Direct Broadcast Service (DBS). • Mobile Service Satellites (MSS) • Example: Satellite Phones

18. Types of Satellite based Networks • Based on the Satellite Altitude • GEO – Geostationary Orbits • 36000 Km = 22300 Miles, equatorial, High latency • MEO – Medium Earth Orbits • High bandwidth, High power, High latency • LEO – Low Earth Orbits • Low power, Low latency, More Satellites, Small Footprint • VSAT • Very Small Aperture Satellites • Private WANs

19. Satellite Orbits Source: Federation of American Scientists [www.fas.org] • Geosynchronous Orbit (GEO): 36,000 km above Earth, includes commercial and military communications satellites, satellites providing early warning of ballistic missile launch. • Medium Earth Orbit (MEO): from 5000 to 15000 km, they include navigation satellites (GPS, Galileo, Glonass). • Low Earth Orbit (LEO): from 500 to 1000 km above Earth, includes military intelligence satellites, weather satellites.

20. Satellite Orbits

21. Types of Satellites • Satellite Orbits • GEO • LEO • MEO • Molniya Orbit • HAPs • Frequency Bands

22. Geostationary Earth Orbit (GEO) • These satellites are in orbit 35,863 km above the earth’s surface along the equator. • Objects in Geostationary orbit revolve around the earth at the same speed as the earth rotates. This means GEO satellites remain in the same position relative to the surface of earth.

23. GEO (cont.) • Advantages • A GEO satellite’s distance from earth gives it a large coverage area, almost a fourth of the earth’s surface. • GEO satellites have a 24 hour view of a particular area. • These factors make it ideal for satellite broadcast and other multipoint applications.

24. GEO (cont.) • Disadvantages • A GEO satellite’s distance also cause it to have both a comparatively weak signal and a time delay in the signal, which is bad for point to point communication. • GEO satellites, centered above the equator, have difficulty broadcasting signals to near polar regions

25. Low Earth Orbit (LEO) • LEO satellites are much closer to the earth than GEO satellites, ranging from 500 to 1,500 km above the surface. • LEO satellites don’t stay in fixed position relative to the surface, and are only visible for 15 to 20 minutes each pass. • A network of LEO satellites is necessary for LEO satellites to be useful

26. LEO (cont.) • Advantages • A LEO satellite’s proximity to earth compared to a GEO satellite gives it a better signal strength and less of a time delay, which makes it better for point to point communication. • A LEO satellite’s smaller area of coverage is less of a waste of bandwidth.

27. LEO (cont.) • Disadvantages • A network of LEO satellites is needed, which can be costly • LEO satellites have to compensate for Doppler shifts cause by their relative movement. • Atmospheric drag effects LEO satellites, causing gradual orbital deterioration.

28. Medium Earth Orbit (MEO) • A MEO satellite is in orbit somewhere between 8,000 km and 18,000 km above the earth’s surface. • MEO satellites are similar to LEO satellites in functionality. • MEO satellites are visible for much longer periods of time than LEO satellites, usually between 2 to 8 hours. • MEO satellites have a larger coverage area than LEO satellites.

29. MEO (cont.) • Advantage • A MEO satellite’s longer duration of visibility and wider footprint means fewer satellites are needed in a MEO network than a LEO network. • Disadvantage • A MEO satellite’s distance gives it a longer time delay and weaker signal than a LEO satellite, though not as bad as a GEO satellite.

30. Other Orbits • Molniya Orbit Satellites • Used by Russia for decades. • Molniya Orbit is an elliptical orbit. The satellite remains in a nearly fixed position relative to earth for eight hours. • A series of three Molniya satellites can act like a GEO satellite. • Useful in near polar regions.

31. Other Orbits (cont.) • High Altitude Platform (HAP) • One of the newest ideas in satellite communication. • A blimp or plane around 20 km above the earth’s surface is used as a satellite. • HAPs would have very small coverage area, but would have a comparatively strong signal. • Cheaper to put in position, but would require a lot of them in a network.

32. Frequency Bands • Different kinds of satellites use different frequency bands. • L–Band: 1 to 2 GHz, used by MSS • S-Band: 2 to 4 GHz, used by MSS, NASA, deep space research • C-Band: 4 to 8 GHz, used by FSS • X-Band: 8 to 12.5 GHz, used by FSS and in terrestrial imaging, ex: military and meteorological satellites • Ku-Band: 12.5 to 18 GHz: used by FSS and BSS (DBS) • K-Band: 18 to 26.5 GHz: used by FSS and BSS • Ka-Band: 26.5 to 40 GHz: used by FSS

33. Capacity Allocation • FDMA • FAMA-FDMA • DAMA-FDMA • TDMA • Advantages over FDMA

34. FDMA • Satellite frequency is already broken into bands, and is broken in to smaller channels in Frequency Division Multiple Access (FDMA). • Overall bandwidth within a frequency band is increased due to frequency reuse (a frequency is used by two carriers with orthogonal polarization).

35. FDMA (cont.) • The number of sub-channels is limited by three factors: • Thermal noise (too weak a signal will be effected by background noise). • Intermodulation noise (too strong a signal will cause noise). • Crosstalk (cause by excessive frequency reusing).

36. FDMA (cont.) • FDMA can be performed in two ways: • Fixed-assignment multiple access (FAMA): The sub-channel assignments are of a fixed allotment. Ideal for broadcast satellite communication. • Demand-assignment multiple access (DAMA): The sub-channel allotment changes based on demand. Ideal for point to point communication.

37. TDMA • TDMA (Time Division Multiple Access) breaks a transmission into multiple time slots, each one dedicated to a different transmitter. • TDMA is increasingly becoming more widespread in satellite communication. • TDMA uses the same techniques (FAMA and DAMA) as FDMA does.

38. TDMA (cont.) • Advantages of TDMA over FDMA. • Digital equipment used in time division multiplexing is increasingly becoming cheaper. • There are advantages in digital transmission techniques. Ex: error correction. • Lack of intermodulation noise means increased efficiency.

39. Frequency Band Trade-Offs • The use of letters probably dates back to World War II as a form of shorthand and simple code for developers of early microwave hardware. • Two band designation systems are in use: adjectival (meaning the bands are identified by the following adjectives) and letter (which are codes to distinguish bands commonly used in space communications and radar).

40. Frequency Band Trade-Offs • Adjectival band designations, frequency in Gigahertz: • Very high frequency (VHF): 0.03–0.3; • Ultra high frequency (UHF): 0.3–3; • Super high frequency (SHF): 3–30; • Extremely high frequency (EHF): 30–300.

41. Frequency Band Trade-Offs • Letter band designations, frequency in Gigahertz: • L: 1.0–2.0; • S: 2.0–4.0; • C: 4.0–8.0; • X: 8–12; • Ku: 12–18; • Ka: 18–40; • Q: 40–60; • V: 60–75; • W: 75–110.

42. Frequency Band Trade-Offs • Today, the letter designations continue to be the popular buzzwords that identify band segments that have commercial application in satellite communications. • The international regulatory process, maintained by the ITU, does not consider these letters but rather uses band allocations and service descriptors listed next and in the right-hand column of Figure 2.9.

43. Frequency Band Trade-Offs • Fixed Satellite Service (FSS): between Earth stations at given positions, when one or more satellites are used; the given position may be a specified fixed point or any fixed point within specified areas; in some cases this service includes satellite-to-satellite links, which may also be operated in the inter-satellite service; the FSS may also include feeder links for other services. • Mobile Satellite Service (MSS): between mobile Earth stations and one or more space stations (including multiple satellites using inter-satellite links). This service may also include feeder links necessary for its operation. • Broadcasting Satellite Service (BSS): A service in which signals transmitted or retransmitted by space stations are intended for direct reception by the general public. In the BSS, the term “direct reception” shall encompass both individual reception and community reception. • Inter-satellite Link (ISL): A service providing links between satellites.

44. Frequency Band Trade-Offs • The lower the band in frequency, the better the propagation characteristics. This is countered by the second general principle, which is that the higher the band, the more bandwidth that is available. The MSS is allocated to the L- and S-bands, where propagation is most forgiving. • Yet, the bandwidth available between 1 and 2.5 GHz, where MSS applications are authorized, must be shared not only among GEO and non-GEO applications, but with all kinds of mobile radio, fixed wireless, broadcast, and point-to-point services as well. • The competition is keen for this spectrum due to its excellent space and terrestrial propagation characteristics. The rollout of wireless services like cellular radiotelephone, PCS, wireless LANs, and 3G may conflict with advancing GEO and non-GEO MSS systems. • Generally, government users in North America and Europe, particularly in the military services, have employed selected bands such as S, X, and Ka to isolate themselves from commercial applications. • However, this segregation has disappeared as government users discover the features and attractive prices that commercial systems may offer.

45. Frequency Band Trade-Offs • On the other hand, wideband services like DTH and broadband data services can be accommodated at frequencies above 3 GHz, where there is more than 10 times the bandwidth available. • Add to this the benefit of using directional ground antennas that effectively multiply the unusable number of orbit positions. Some wideband services have begun their migration from the well-established world of C-band to Ku- and Ka-bands. • Higher satellite EIRP used at Ku-band allows the use of relatively small Earth station antennas. On the other hand, C-band should maintain its strength for video distribution to cable systems and TV stations, particularly because of the favorable propagation environment, extensive global coverage, and legacy investment in C-band antennas and electronic equipment.

46. Ultra High Frequency • While the standard definition of UHF is the range of 300 to 3,000 MHz (0.3 to 3 GHz), the custom is to relate this band to any effective satellite communication below 1 GHz. • Frequencies above 1 GHz are considered later on. The fact that the ionosphere provides a high degree of attenuation below 100 MHz makes this at the low end of acceptability (the blockage by the ionosphere at 10 MHz goes along with its ability to reflect radio waves, a benefit for ground-to-ground and air-to-ground communications using what is termed sky wave or “skip”). • UHF satellites employ circular polarization (CP) to avoid Faraday effect, wherein the ionosphere rotates any linear-polarized wave. • The UHF spectrum between 300 MHz and 1 GHz is exceedingly crowded on the ground and in the air because of numerous commercial, government, and other civil applications. • Principal among them is television broadcasting in the VHF and UHF bands, FM radio, and cellular radio telephone. • However, we cannot forget less obvious uses like vehicular and handheld radios used by police officers, firefighters, amateurs, the military, taxis and other commercial users, and a variety of unlicensed applications in the home.

47. Ultra High Frequency • From a space perspective, the dominant space users are military and space research (e.g., NASA in the United States and ESA in Europe). • These are all narrow bandwidth services for voice and low-speed data transfer in the range of a few thousand hertz or, equivalently, a few kilobytes per second. • From a military perspective, the first satellite to provide narrowband voice services was Tacsat. • This experimental bird proved that a GEO satellite provides an effective communications service to a mobile radio set that could be transported on a person’s back, installed in a vehicle, or operated from an aircraft. • Subsequently, the U.S. Navy procured the Fleetsat series of satellites from TRW, a very successful program in operational terms. • This was followed by Leasat from Hughes, and currently the UHF Follow-On Satellites from the same maker (now Boeing Satellite Systems).

48. Ultra High Frequency • From a commercial perspective, the only VHF project that one can identify is OrbComm, a low data rate LEO satellite constellation developed by Orbital Sciences Corporation. • OrbComm provides a near-real-time messaging service to inexpensive handheld devices about the size of a small transistor radio. • On the other hand, its more successful use is to provide occasional data transmissions to and from moving vehicles and aircraft. • Due to the limited power of the OrbComm satellites (done to minimize complexity and investment cost), voice service is not supported. • Like other LEO systems, OrbComm as a business went into bankruptcy; it may continue in another form as the satellites are expected to keep operating for some time.

49. Satellite Transmission Bands The C band is the most frequently used. The Ka and Ku bands are reserved exclusively for satellite communication but are subject to rain attenuation

50. L-Band • Frequencies between 1 and 2 GHz are usually referred to as L-band, a segment not applied to commercial satellite communication until the late 1970s. • Within this 1 GHz of total spectrum, only 30 MHz of uplink and downlink, each, was initially allocated by the ITU to the MSS. • The first to apply L-band was COMSAT with their Marisat satellites. • Constructed primarily to solve a vital need for UHF communications by the U.S. Navy, Marisat also carried an L-band transponder for early adoption by the commercial maritime industry. • COMSAT took a gamble that MSS would be accepted by commercial vessels, which at that time relied on high frequency radio and the Morse code. Over the ensuing years, Marisat and its successors from Inmarsat proved that satellite communications, in general, and MSS, in particular, are reliable and effective. • By 1993, the last commercial HF station was closed down. With the reorganization and privatization of Inmarsat, the critical safety aspects of the original MSS network are being transferred to a different operating group.