BASIC TELECOMMUNICATIONS

1. BASIC TELECOMMUNICATIONS Cellular communications

2. BASIC TELECOMMUNICATIONS • The world's first commercial automated cellular network was launched in Japan by NTT in 1979 • The first 1G network launched in the USA was Chicago-based Ameritech in 1983 using the Motorola DynaTAC mobile phone

3. BASIC TELECOMMUNICATIONS In 1991, the second generation (2G) cellular technology was launched in Finland by Radiolinjaon the GSM (Global System for Mobile Communications) standard, which sparked competition in the sector as the new operators challenged the incumbent 1G network operators

4. BASIC TELECOMMUNICATIONS Ten years later, in 2001, the third generation (3G) was launched in Japan by NTT DoCoMo on the WCDMA standard, followed by 3.5G, 3G+ or turbo 3G enhancements based on the high-speed packet access (HSPA) family, allowing UMTS (Universal Mobile Telecommunications System) networks to have higher data transfer speeds and capacity

5. BASIC TELECOMMUNICATIONS The recently released 4th generation, also known as Beyond 3G, aims to provide broadband wireless access with nominal data rates of 100 Mbit/s to fast moving devices, and 1 Gbit/s to stationary devices defined by the ITU-R (International Telecommunications Union-Radio communications Sector)

6. BASIC TELECOMMUNICATIONS • A 4G system should be a complete replacement for current network infrastructure and is expected to be able to provide a comprehensive and secure IP solution where voice, data, and streamed multimedia can be given to users on a "Anytime, Anywhere" basis, and at much higher data rates than previous generations

7. BASIC TELECOMMUNICATIONS • By now you hopefully guessed that the 1G, 2G, 3G and 4G designations refer to the different generations of cellular technology • Cell phones are actually sophisticated radios similar to walkie-talkies and CB radios and were historically referred to as radiophones

8. BASIC TELECOMMUNICATIONS • Both walkie-talkies and CB radios are half-duplex devices, two people communicating on a CB radio use the same frequency, so only one person can talk at a time • A cell phone is a full-duplex device, that means that you use one frequency for talking and a second, separate frequency for listening

9. BASIC TELECOMMUNICATIONS • A walkie-talkie typically has one channel, and a CB radio has 40 channels • A typical cell phone can communicate on 1,664 channels or more! • A walkie-talkie can transmit about 1 mile using a 0.25-watt transmitter,a CB radio, because it has much higher power, can transmit about 5 miles using a 5-watt transmitter

10. BASIC TELECOMMUNICATIONS • A cellular networkor mobile networkis a radio network distributed over land areas called cells, each served by at least one fixed-location transceiver, known as a cell site or base station • In a cellular network, each cell uses a different set of frequencies from neighboring cells, to avoid interference and provide guaranteed bandwidth within each cell

11. BASIC TELECOMMUNICATIONS This is an example of a typical cell topology, notice the towers communicate to the MTSO and the MTSO communicates to the PSTN

12. BASIC TELECOMMUNICATIONS • When joined together these cells provide radio coverage over a wide geographic area • This enables a large number of portable transceivers (e.g., mobile phones, pagers, etc.) to communicate with each other and with fixed transceivers and telephones anywhere in the network, via base stations, even if some of the transceivers are moving through more than one cell during transmission

13. BASIC TELECOMMUNICATIONS • Because cell phones and base stations use low-power transmitters, the same frequencies can be reused in non-adjacent cells • Each cell has a base station that consists of a tower and a small building containing the radio equipment

14. BASIC TELECOMMUNICATIONS • A single cell in an analog cell-phone system uses one-seventh of the available duplex voice channels • That is, each cell is using a percentage of the available channels so it has a unique set of frequencies and there are no collisions • A cell-phone carrier typically gets 832 radio frequencies to use in a city

15. BASIC TELECOMMUNICATIONS • Each cell phone uses two frequencies per call -- a duplex channel -- so there are typically 395 voice channels per carrier • Therefore, each cell has about 56 voice channels available. • In other words, in any cell, 56 people can be talking on their cell phone at one time.

16. BASIC TELECOMMUNICATIONS • For example, a TDMA-based digital system can carry three times as many calls as an analog system, so each cell has about 168 channels available. • Cell phones have low-power transmitters in them with two signal strengths: 0.6 watts and 3 watts (for comparison, most CB radios transmit at 4 watts)

17. BASIC TELECOMMUNICATIONS • The base station is also transmitting at low power, this keeps the transmissions of a base station and the phones within its cell and they do not make it very far outside that cell • As a result cells can reuse the same 56 frequencies across the city

18. BASIC TELECOMMUNICATIONS • Each carrier in each city also runs one central office called the Mobile Telephone Switching Office (MTSO) • This office handles and controls all of the base stations in the region and all of the cell phone connections to the PSTN

19. BASIC TELECOMMUNICATIONS • With the introduction of 2G networks and digital technology cell phone providers are able to use different coding techniques to increase efficiency and call volume • One of these coding techniques is FSK (Frequency Shift Key) to send data over AMPS (Advanced Mobile Phone System) that uses a range of frequencies between 824 megahertz (MHz) and 894 MHz for analog cell phones

20. BASIC TELECOMMUNICATIONS • FSK uses two frequencies, one for 1s and the other for 0s, alternating rapidly between the two to send digital information between the cell tower and the phone • The frequencies used in analog/digital voice channels are typically 30 kHz wide -- 30 kHz was chosen as the standard size because it gives you voice quality comparable to a wired telephone

21. BASIC TELECOMMUNICATIONS • The transmit and receive frequencies of each voice channel are separated by 45 MHz to keep them from interfering with each other • Each carrier has 395 voice channels, as well as 21 data channels to use for housekeeping activities like registration and paging

22. BASIC TELECOMMUNICATIONS There are three common technologies used by cellular networks for transmitting information: • Frequency division multiple access (FDMA) • Time division multiple access (TDMA) • Code division multiple access (CDMA)

23. BASIC TELECOMMUNICATIONS • In an earlier lesson we learned about FDM, TDM and CDM which are technologies that access the physical layer of the OSI (Open System Interconnection) model

24. BASIC TELECOMMUNICATIONS • the difference here is that FDMA, TDMA and CDMA allows multiple users (Multiple Access) simultaneous access to a transmission system using the same methods • multiple access method allows several terminals (cell phones) connected to the same multi-point transmission medium to transmit over it and to share its capacity

25. BASIC TELECOMMUNICATIONS • FDMAputs each call on a separate frequency • TDMA assigns each call a certain portion of time on a designated frequency • CDMA gives a unique code to each call and spreads it over the available frequencies

26. BASIC TELECOMMUNICATIONS Here is a comparison of the three multiple access technologies