![4.42
Bluetooth
History
1994: Ericsson “MC-link” project
Renaming of the project: Bluetooth according to Harald “Blåtand” Gormsen [son of Gorm], King of Denmark in
the 10th
century
1998: foundation of Bluetooth SIG, www.bluetooth.org
1999: erection of a rune stone at Ercisson/Lund ;-)
2001: first consumer products for mass market, spec. version 1.1 released
2005: 5 million chips/week
Special Interest Group
Original founding members: Ericsson, Intel, IBM, Nokia, Toshiba
Added promoters: 3Com, Agere (was: Lucent), Microsoft, Motorola
> 2500 members
Common specification and certification of products
(was: )](https://image.slidesharecdn.com/wirelessfundamental-250526080357-8c5c7680/85/Wireless-Networking-Fundamentals-for-beginnners-pptx-42-320.jpg)
![5.53
Satellite period and orbits
10 20 30 40 x106
m
24
20
16
12
8
4
radius
satellite
period [h]
velocity [ x1000 km/h]
synchronous distance
35,786 km](https://image.slidesharecdn.com/wirelessfundamental-250526080357-8c5c7680/85/Wireless-Networking-Fundamentals-for-beginnners-pptx-53-320.jpg)
![5.67
Overview of LEO/MEO systems
Iridium Globalstar ICO Teledesic
# satellites 66 + 6 48 + 4 10 + 2 288
altitude
(km)
780 1414 10390 ca. 700
coverage global
70° latitude global global
min.
elevation
8° 20° 20° 40°
frequencies
[GHz
(circa)]
1.6 MS
29.2
19.5
23.3 ISL
1.6 MS
2.5 MS
5.1
6.9
2 MS
2.2 MS
5.2
7
19
28.8
62 ISL
access
method
FDMA/TDMA CDMA FDMA/TDMA FDMA/TDMA
ISL yes no no yes
bit rate 2.4 kbit/s 9.6 kbit/s 4.8 kbit/s 64 Mbit/s
2/64 Mbit/s
# channels 4000 2700 4500 2500
Lifetime
[years]
5-8 7.5 12 10
cost
estimation
4.4 B$ 2.9 B$ 4.5 B$ 9 B$](https://image.slidesharecdn.com/wirelessfundamental-250526080357-8c5c7680/85/Wireless-Networking-Fundamentals-for-beginnners-pptx-67-320.jpg)
Wireless Networking Fundamentals for beginnners.pptx
- 1. Wireless Fundamental Eric Kwok Technical Manager, GC+JP Networking Academy
- 2. 1. Why is Wireless More and More important? 2. Wireless Technologies 3. Wireless Standards – 802.11 a/b/g/n 4. The new kid on the block – 802.11ac 5. NetAcad Courses Cisco Confidential 2 © 2015 Cisco and/or its affiliates. All rights reserved.
- 3. • In 1970, the University of Hawaii developed the first wireless network, called ALOHAnet • 400 MHz frequency range • IEEE ratified the original 802.11 standard (1997) - 2Mbps Cisco Confidential 3 © 2015 Cisco and/or its affiliates. All rights reserved.
- 4. Cisco Confidential 4 © 2015 Cisco and/or its affiliates. All rights reserved.
- 5. • PAN/WPAN (Personal Area Network) Bluetooth, IEEE 802.15.4 • LAN (Local Area Network) IEEE 802.11 • MAN (Metropolitan Area Network) IEEE 802.11, IEEE 802.16, IEEE 802.20 • WAN (Wide Area Network) GSM, CDMA, Satelite • http://www.ieee.org/index.html Cisco Confidential 5 © 2015 Cisco and/or its affiliates. All rights reserved.
- 6. © 2015 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 21 • Wireless technologies use electromagnetic waves • What types of communication mediums do we have in wired networks? Coper, Fiber • What communication medium do we have in wireless? The Earth’s Atmosphere 21
- 7. • Frequency (f - Hz) Frequency is the number of occurrences of a repeating event per unit time. • Higher frequency: Greater speed Shorter range High reflection rate Higher absorption in the Earth’s atmosphere Higher costs Cisco Confidential 7 © 2015 Cisco and/or its affiliates. All rights reserved.
- 8. • Physical layer is radio frequency (RF) communications. • Wired vs Wireless travel across the bounded medium contains or confines the signal. travel across the unbounded medium. • Absorption • Reflection • Scattering • Refraction • Diffraction • Loss (attenuation) • Free space path loss • Multipath Cisco Confidential 8 © 2015 Cisco and/or its affiliates. All rights reserved.
- 9. Absorption Scattering Reflection Refraction Diffraction Multipath Cisco Confidential 9 © 2015 Cisco and/or its affiliates. All rights reserved.
- 10. • ISM – Industrial Scientific Medical Free to transmit http://en.wikipedia.org/wiki/ISM_band • 2.4GHz and 5 GHz bands • Disadvantage: They are very occupied The frequencies are high 3 KHz 902-928 MHz 2.401-2.483 GHz 3 GHz 3 THz 5.470-5.725 GHz Radiowaves Microwaves 5.725- 5.850 GHz Cisco Confidential 10 © 2015 Cisco and/or its affiliates. All rights reserved.
- 11. • Analog modulation: AM, FM, PM etc • Digital modulation: ASK, APSK, QAM-64 etc • Encoding digital data into wireless signals (OFDM) • Higher bandwidth requires higher modulation techniques • Spread Spectrum: DSSS, FHSS, OFDM Cisco Confidential 11 © 2015 Cisco and/or its affiliates. All rights reserved.
- 12. FHSS DSSS OFDM channel channel Cisco Confidential 12 © 2015 Cisco and/or its affiliates. All rights reserved.
- 13. © 2015 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 28 Amplitude, Frequency, Phase BPSK (1bit) QPSK (2 bits) QAM-16 (4 bits) QAM-64 (6 bits)
- 14. Cisco Confidential 14 © 2015 Cisco and/or its affiliates. All rights reserved.
- 15. • The wireless transmition medium is shared • It is not possible to transmit in the exact same frequency without collisions • How many Hz do we need to transmit 54 Mbps in 802.11g? Answer: 22 Mhz • Solution: we could split the ISM band into channels and map each WLAN/SSID on a single channel, thus having multiple networks in the same band Cisco Confidential 15 © 2015 Cisco and/or its affiliates. All rights reserved.
- 16. 1 6 11 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 2.4 GHz 5 GHz Cisco Confidential 16 © 2015 Cisco and/or its affiliates. All rights reserved.
- 17. It is possible to cover any surface using just 3 channels Channel 1 Channel 1 Channel 6 Channel 11 Channel 11 Channel 11 Channel 1 Channel 6 Channel 6 Channel 6 Cisco Confidential 17 © 2015 Cisco and/or its affiliates. All rights reserved.
- 18. © 2015 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 33 33
- 19. Cisco Confidential 19 © 2015 Cisco and/or its affiliates. All rights reserved.
- 20. • Legacy – released in 1997 • Specified in infrared and wireless • Spread Spectrum – FHSS/DSSS • Speed: 1-2 Mbps • Frequency: 2.4 Ghz and 900 Mhz Cisco Confidential 20 © 2015 Cisco and/or its affiliates. All rights reserved.
- 21. • Both standards appeared about the same time - 1999 • 802.11a Introduces OFDM and takes speed up to 54 Mbps Frequency band: 5 GHz Distance to transmit signal: 25m • 802.11b Bandwidth: 11 Mbps Frequency band: 2.4 GHz Became very popular – called WiFi Cisco Confidential 21 © 2015 Cisco and/or its affiliates. All rights reserved.
- 22. • Standardized in 2003 • Best of both worlds (a & b) • Frequency band: 2.4 GHz • Bandwidth: 54 Mbps • Modulation: OFDM • Used for a long time and can still be found in networks Cisco Confidential 22 © 2015 Cisco and/or its affiliates. All rights reserved.
- 23. • 802.11n – standardized 29 October 2009 • Far greater speeds: theoretical maximum 600 Mbps • Better coverage and density of the signal • Backwards compatible with 802.11 a/b/g • Uses multiple antenaes and MIMO technology • Increased channel width to 40 Mhz • Improved imunity to noise using complex modulation techniques • Support packet aggregation (one header for multiple data packets) 23 Cisco Confidential 23 © 2015 Cisco and/or its affiliates. All rights reserved.
- 24. • MIMO uses DSP processors to multiplex and demultiplex the signal radio radio radio DSP radio radio radio DSP 24 Cisco Confidential 24 © 2015 Cisco and/or its affiliates. All rights reserved.
- 25. • The multipath effect = the process in which many waves carrying the same information are reflected differently from surfaces and with varying clarity • In 802.11g, the DSP chose the wave with the best signal to noise ratio Although I receive multiple waves, I am going to chose the one with the best quality and interpret it Cisco Confidential 25 © 2015 Cisco and/or its affiliates. All rights reserved.
- 26. • Problem description: some weaker SNR waves are ignored even if there is the possibility that they contain relevant information • In 802.11n, MRC is implemented in the NIC’s DSP so that it takes all the waves and composes just one high-quality wave, thus increasing throughput • Concluding: MRC is a client-side technology If you have an 802.11n board in a 802.11g network, you will have higher-than-ordinary through It’s like having a cat with multiple ears Cisco Confidential 26 © 2015 Cisco and/or its affiliates. All rights reserved.
- 27. Cisco Confidential 43 © 2015 Cisco and/or its affiliates. All rights reserved.
- 28. • How to Increase Speed Without Making it Impossibly Difficult? Increase channel width… beyond 40 MHz Increase number of spatial streams… more than 4 Improve the modulation? Is 64-QAM the best we can do? Better manage the cell 5 Ghz band – in 2015 it’s the perfect thing to have Cost does not vary with freq anymore It’s not as populated as 2.4 It’s a bigger space Why would only one device send at a time? If we can have one device send 3 streams at the same time on the same frequency, why not have 3 devices send 1 stream at the same time on the same frequency instead? Cisco Confidential 44 © 2015 Cisco and/or its affiliates. All rights reserved.
- 29. • MU-MIMO 45 2 clients can receive signals at the same time, on the same frequency Each client has a dedicated spatial stream No collisions anymore “Full-duplex” becomes possible “1 2 3” “a b c” MIMO AP Cisco Confidential 45 © 2015 Cisco and/or its affiliates. All rights reserved.
- 30. • Beyond the 1 Gbps Bar 160 MHz-wide channel width… Up to 160 MHz for APs 80 MHz for stations, 160 MHz optional More spatial streams Up to 8 spatial streams 8 radio circuits sending or receiving Better modulation QAM-256 (8 bits per symbol vs. 6 bits for QAM-64) Up to 4 times faster Cisco Confidential 46 © 2015 Cisco and/or its affiliates. All rights reserved.
- 31. Motivation Can we apply media access methods from fixed networks? Example CSMA/CD Carrier Sense Multiple Access with Collision Detection send as soon as the medium is free, listen into the medium if a collision occurs (original method in IEEE 802.3) Problems in wireless networks signal strength decreases proportional to the square of the distance the sender would apply CS and CD, but the collisions happen at the receiver it might be the case that a sender cannot “hear” the collision, i.e., CD does not work furthermore, CS might not work if, e.g., a terminal is “hidden”
- 32. Hidden terminals A sends to B, C cannot receive A C wants to send to B, C senses a “free” medium (CS fails) collision at B, A cannot receive the collision (CD fails) A is “hidden” for C Exposed terminals B sends to A, C wants to send to another terminal (not A or B) C has to wait, CS signals a medium in use but A is outside the radio range of C, therefore waiting is not necessary C is “exposed” to B Motivation - hidden and exposed terminals B A C
- 33. Terminals A and B send, C receives signal strength decreases proportional to the square of the distance the signal of terminal B therefore drowns out A’s signal C cannot receive A If C for example was an arbiter for sending rights, terminal B would drown out terminal A already on the physical layer Also severe problem for CDMA-networks - precise power control needed! Motivation - near and far terminals A B C
- 34. MACA - collision avoidance MACA (Multiple Access with Collision Avoidance) uses short signaling packets for collision avoidance RTS (request to send): a sender request the right to send from a receiver with a short RTS packet before it sends a data packet CTS (clear to send): the receiver grants the right to send as soon as it is ready to receive Signaling packets contain sender address receiver address packet size Variants of this method can be found in IEEE802.11 as DFWMAC (Distributed Foundation Wireless MAC)
- 35. MACA avoids the problem of hidden terminals A and C want to send to B A sends RTS first C waits after receiving CTS from B MACA avoids the problem of exposed terminals B wants to send to A, C to another terminal now C does not have to wait for it cannot receive CTS from A MACA examples A B C RTS CTS CTS A B C RTS CTS RTS
- 36. Access methods SDMA/FDMA/TDMA SDMA (Space Division Multiple Access) segment space into sectors, use directed antennas cell structure FDMA (Frequency Division Multiple Access) assign a certain frequency to a transmission channel between a sender and a receiver permanent (e.g., radio broadcast), slow hopping (e.g., GSM), fast hopping (FHSS, Frequency Hopping Spread Spectrum) TDMA (Time Division Multiple Access) assign the fixed sending frequency to a transmission channel between a sender and a receiver for a certain amount of time The multiplexing schemes presented in chapter 2 are now used to control medium access!
- 37. FDD/FDMA - general scheme, example GSM f t 124 1 124 1 20 MHz 200 kHz 890.2 MHz 935.2 MHz 915 MHz 960 MHz
- 38. TDD/TDMA - general scheme, example DECT 1 2 3 11 12 1 2 3 11 12 t downlink uplink 417 µs
- 39. Access method CDMA CDMA (Code Division Multiple Access) all terminals send on the same frequency probably at the same time and can use the whole bandwidth of the transmission channel each sender has a unique random number, the sender XORs the signal with this random number the receiver can “tune” into this signal if it knows the pseudo random number, tuning is done via a correlation function Disadvantages: higher complexity of a receiver (receiver cannot just listen into the medium and start receiving if there is a signal) all signals should have the same strength at a receiver Advantages: all terminals can use the same frequency, no planning needed huge code space (e.g. 232 ) compared to frequency space interferences (e.g. white noise) is not coded forward error correction and encryption can be easily integrated
- 40. 4.40 History and hi-tech… 1999: Ericsson mobile communications
- 41. 4.41 …and the real rune stone Located in Jelling, Denmark, erected by King Harald “Blåtand” in memory of his parents. The stone has three sides – one side showing a picture of Christ. This could be the “original” colors of the stone. Inscription: “auk tani karthi kristna” (and made the Danes Christians) Inscription: "Harald king executes these sepulchral monuments after Gorm, his father and Thyra, his mother. The Harald who won the whole of Denmark and Norway and turned the Danes to Christianity." Btw: Blåtand means “of dark complexion” (not having a blue tooth…)
- 42. 4.42 Bluetooth History 1994: Ericsson “MC-link” project Renaming of the project: Bluetooth according to Harald “Blåtand” Gormsen [son of Gorm], King of Denmark in the 10th century 1998: foundation of Bluetooth SIG, www.bluetooth.org 1999: erection of a rune stone at Ercisson/Lund ;-) 2001: first consumer products for mass market, spec. version 1.1 released 2005: 5 million chips/week Special Interest Group Original founding members: Ericsson, Intel, IBM, Nokia, Toshiba Added promoters: 3Com, Agere (was: Lucent), Microsoft, Motorola > 2500 members Common specification and certification of products (was: )
- 43. 4.43 Characteristics 2.4 GHz ISM band, 79 (23) RF channels, 1 MHz carrier spacing Channel 0: 2402 MHz … channel 78: 2480 MHz G-FSK modulation, 1-100 mW transmit power FHSS and TDD Frequency hopping with 1600 hops/s Hopping sequence in a pseudo random fashion, determined by a master Time division duplex for send/receive separation Voice link – SCO (Synchronous Connection Oriented) FEC (forward error correction), no retransmission, 64 kbit/s duplex, point-to-point, circuit switched Data link – ACL (Asynchronous Connection Less) Asynchronous, fast acknowledge, point-to-multipoint, up to 433.9 kbit/s symmetric or 723.2/57.6 kbit/s asymmetric, packet switched Topology Overlapping piconets (stars) forming a scatternet
- 44. 4.44 Piconet Collection of devices connected in an ad hoc fashion One unit acts as master and the others as slaves for the lifetime of the piconet Master determines hopping pattern, slaves have to synchronize Each piconet has a unique hopping pattern Participation in a piconet = synchronization to hopping sequence Each piconet has one master and up to 7 simultaneous slaves (> 200 could be parked) M=Master S=Slave P=Parked SB=Standby M S P SB S S P P SB
- 45. 4.45 Forming a piconet All devices in a piconet hop together Master gives slaves its clock and device ID Hopping pattern: determined by device ID (48 bit, unique worldwide) Phase in hopping pattern determined by clock Addressing Active Member Address (AMA, 3 bit) Parked Member Address (PMA, 8 bit) SB SB SB SB SB SB SB SB SB M S P SB S S P P SB
- 46. 4.46 Baseband states of a Bluetooth device standby inquiry page connected AMA transmit AMA park PMA hold AMA sniff AMA unconnected connecting active low power Standby: do nothing Inquire: search for other devices Page: connect to a specific device Connected: participate in a piconet detach Park: release AMA, get PMA Sniff: listen periodically, not each slot Hold: stop ACL, SCO still possible, possibly participate in another piconet
- 47. 4.47 Scatternet Linking of multiple co-located piconets through the sharing of common master or slave devices Devices can be slave in one piconet and master of another Communication between piconets Devices jumping back and forth between the piconets M=Master S=Slave P=Parked SB=Standby M S P SB S S P P SB M S S P SB Piconets (each with a capacity of 720 kbit/s)
- 48. 5.48 Satellite Systems History Basics Localization Handover Routing
- 49. 5.49 History of satellite communication 1945 Arthur C. Clarke publishes an essay about „Extra Terrestrial Relays“ 1957 first satellite SPUTNIK 1960 first reflecting communication satellite ECHO 1963 first geostationary satellite SYNCOM 1965 first commercial geostationary satellite Satellit „Early Bird“ (INTELSAT I): 240 duplex telephone channels or 1 TV channel, 1.5 years lifetime 1976 three MARISAT satellites for maritime communication 1982 first mobile satellite telephone system INMARSAT-A 1988 first satellite system for mobile phones and data communication INMARSAT-C 1993 first digital satellite telephone system 1998 global satellite systems for small mobile phones
- 50. 5.50 Applications Traditionally weather satellites radio and TV broadcast satellites military satellites satellites for navigation and localization (e.g., GPS) Telecommunication global telephone connections connections for communication in remote places or underdeveloped areas global mobile communication satellite systems to extend cellular phone systems (e.g., GSM or AMPS)
- 51. 5.51 base station or gateway Classical satellite systems Inter Satellite Link (ISL) Mobile User Link (MUL) Gateway Link (GWL) footprint small cells (spotbeams) User data PSTN ISDN GSM GWL MUL PSTN: Public Switched Telephone Network
- 52. 5.52 Basics Satellites in circular orbits attractive force Fg = m g (R/r)² centrifugal force Fc = m r ² m: mass of the satellite R: radius of the earth (R = 6370 km) r: distance to the center of the earth g: acceleration of gravity (g = 9.81 m/s²) : angular velocity ( = 2 f, f: rotation frequency) Stable orbit Fg = Fc
- 53. 5.53 Satellite period and orbits 10 20 30 40 x106 m 24 20 16 12 8 4 radius satellite period [h] velocity [ x1000 km/h] synchronous distance 35,786 km
- 54. 5.54 Basics elliptical or circular orbits complete rotation time depends on distance satellite-earth inclination: angle between orbit and equator elevation: angle between satellite and horizon LOS (Line of Sight) to the satellite necessary for connection high elevation needed, less absorption due to e.g. buildings Uplink: connection base station - satellite Downlink: connection satellite - base station typically separated frequencies for uplink and downlink transponder used for sending/receiving and shifting of frequencies transparent transponder: only shift of frequencies regenerative transponder: additionally signal regeneration
- 55. 5.55 Inclination inclination d d satellite orbit perigee plane of satellite orbit equatorial plane
- 56. 5.56 Elevation Elevation: angle e between center of satellite beam and surface e minimal elevation: elevation needed at least to communicate with the satellite footprint
- 57. 5.57 Link budget of satellites Parameters like attenuation or received power determined by four parameters: sending power gain of sending antenna distance between sender and receiver gain of receiving antenna 2 4 c f r L L: Loss f: carrier frequency r: distance c: speed of light
- 58. 5.58 Atmospheric attenuation Example: satellite systems at 4-6 GHz elevation of the satellite 5° 10° 20° 30° 40° 50° Attenuation of the signal in % 10 20 30 40 50 rain absorption fog absorption atmospheric absorption e
- 59. 5.59 Four different types of satellite orbits can be identified depending on the shape and diameter of the orbit: GEO: geostationary orbit, ca. 36000 km above earth surface LEO (Low Earth Orbit): ca. 500 - 1500 km MEO (Medium Earth Orbit) or ICO (Intermediate Circular Orbit): ca. 6000 - 20000 km HEO (Highly Elliptical Orbit) elliptical orbits Orbits I
- 60. 5.60 Orbits II earth km 35768 10000 1000 LEO (Globalstar, Irdium) HEO inner and outer Van Allen belts MEO (ICO) GEO (Inmarsat) Van-Allen-Belts: ionized particles 2000 - 6000 km and 15000 - 30000 km above earth surface
- 61. 5.61 Geostationary satellites Orbit 35,786 km distance to earth surface, orbit in equatorial plane (inclination 0°) complete rotation exactly one day, satellite is synchronous to earth rotation fix antenna positions, no adjusting necessary satellites typically have a large footprint (up to 34% of earth surface!), therefore difficult to reuse frequencies bad elevations in areas with latitude above 60° due to fixed position above the equator high transmit power needed high latency due to long distance (ca. 275 ms) not useful for global coverage for small mobile phones and data transmission, typically used for radio and TV transmission
- 62. 5.62 LEO systems Orbit ca. 500 - 1500 km above earth surface visibility of a satellite ca. 10 - 40 minutes global radio coverage possible latency comparable with terrestrial long distance connections, ca. 5 - 10 ms smaller footprints, better frequency reuse but now handover necessary from one satellite to another many satellites necessary for global coverage more complex systems due to moving satellites Examples: Iridium (start 1998, 66 satellites) Globalstar (start 1999, 48 satellites)
- 63. 5.63 MEO systems Orbit ca. 5000 - 12000 km above earth surface comparison with LEO systems: slower moving satellites less satellites needed simpler system design for many connections no hand-over needed higher latency, ca. 70 - 80 ms higher sending power needed special antennas for small footprints needed Example: ICO (Intermediate Circular Orbit, Inmarsat) start ca. 2000
- 64. 5.64 Routing One solution: inter satellite links (ISL) reduced number of gateways needed forward connections or data packets within the satellite network as long as possible only one uplink and one downlink per direction needed for the connection of two mobile phones Problems: more complex focusing of antennas between satellites high system complexity due to moving routers higher fuel consumption thus shorter lifetime Iridium and Teledesic planned with ISL Other systems use gateways and additionally terrestrial networks
- 65. 5.65 Localization of mobile stations Mechanisms similar to GSM Gateways maintain registers with user data HLR (Home Location Register): static user data VLR (Visitor Location Register): (last known) location of the mobile station SUMR (Satellite User Mapping Register): satellite assigned to a mobile station positions of all satellites Registration of mobile stations Localization of the mobile station via the satellite’s position requesting user data from HLR updating VLR and SUMR Calling a mobile station localization using HLR/VLR similar to GSM connection setup using the appropriate satellite
- 66. 5.66 Handover in satellite systems Several additional situations for handover in satellite systems compared to cellular terrestrial mobile phone networks caused by the movement of the satellites Intra satellite handover handover from one spot beam to another mobile station still in the footprint of the satellite, but in another cell Inter satellite handover handover from one satellite to another satellite mobile station leaves the footprint of one satellite Gateway handover Handover from one gateway to another mobile station still in the footprint of a satellite, but gateway leaves the footprint Inter system handover Handover from the satellite network to a terrestrial cellular network mobile station can reach a terrestrial network again which might be cheaper, has a lower latency etc.
- 67. 5.67 Overview of LEO/MEO systems Iridium Globalstar ICO Teledesic # satellites 66 + 6 48 + 4 10 + 2 288 altitude (km) 780 1414 10390 ca. 700 coverage global 70° latitude global global min. elevation 8° 20° 20° 40° frequencies [GHz (circa)] 1.6 MS 29.2 19.5 23.3 ISL 1.6 MS 2.5 MS 5.1 6.9 2 MS 2.2 MS 5.2 7 19 28.8 62 ISL access method FDMA/TDMA CDMA FDMA/TDMA FDMA/TDMA ISL yes no no yes bit rate 2.4 kbit/s 9.6 kbit/s 4.8 kbit/s 64 Mbit/s 2/64 Mbit/s # channels 4000 2700 4500 2500 Lifetime [years] 5-8 7.5 12 10 cost estimation 4.4 B$ 2.9 B$ 4.5 B$ 9 B$