Telecommunications and the Information Age ET108B. Cell Phone Network

Transcription

1 Telecommunications and the Information Age ET108B Cell Phone Network The Cellular Telephone Network Cellular Telephone Features Carrying Data Across the Cellular Network Satellite Telephone Service

2 Cellular Telephone Network Background Developed in the late 1940 s by Bell Labs Wasn t practical - needed at least transistors or ICs Tubes were too bulky First introduced during the early 1980s Mobile radio telephone systems preceded modern cellular mobile telephony technology. Sometimes retroactively referred to as pre cellular (or sometimes zero generation) systems Technologies used in pre cellular systems included the: Push to Talk (PTT or manual) Mobile Telephone System (MTS)

3 Cellular Telephone Network Background Mobile radio telephone systems preceded modern cellular mobile telephony technology. Technologies used in pre cellular systems included the: Improved Mobile Telephone Service (IMTS) Advanced Mobile Telephone System (AMTS) systems First commercial mobile telephone service MTS in the US in 1946, Differences between Mobile and Cellular systems Mobile telephone. One transmitter/receiver pair served an entire metro area and the number of simultaneous calls allowed was limited by the available frequencies

4 Cellular Telephone Network Background Differences between Mobile and Cellular systems Cellular telephone. The metro area is divided into small areas (6-12 miles wide) each cell gets a set of frequencies for simultaneous calls and the frequencies can be reused in at least every other cell Thus drastically increasing the number of simultaneous calls possible in a metro area See Figure 23-1 at the bottom of page 652

5 The Last Mile Cellular Base Stations Location near the center of each cell in the network Usually they try for the highest point near by Commonly called a base transceiver station (BTS) Major BTS Components Antenna (see figure 23-2 at the top of page 653) The antennas are usually camouflaged to look like palm trees, water tanks, farm silos, etc Transceiver Cell Site Controller that reports signal strength info on all used frequencies to the MTSO Multiplexor for connection to PSTN usually on a T-1 circuit

6 The Last Mile Cellular Base Stations Major BTS Components Battery Backups and generators for emergency power Cellular Transmission Schemes Key Types Frequency Division Multiplexing (FDM) Time Division Multiple Access (TDMA) Code Division Multiple Access (CDMA) Frequency Division Multiplexing American Moble Phone System AMPS - Oldest type used in N. America

7 The Last Mile Cellular Transmission Schemes Frequency Division Multiplexing (TDMA) Carriers get an allocation of 10MHz of bandwidth Only 111 simultaneous calls support per 10MHz band in a cell Time Division Multiple Access (TDMA) Codec in the phone converts voice into digital info Codec in the phone converts voice into digital info Data is then compressed into 8kKbps from 64kbps Data is placed into a time slot only if there is a conversation Vastly increases the density of simultaneous calls support per cell Some of the TDMA standards used in N. America Digital-American Mobile Phone System (D-AMPS) Global System for Mobile Communications (GSM) IS-136 (updated D-AMPS)

8 The Last Mile Cellular Transmission Schemes Time Division Multiple Access (TDMA) Some of the TDMA standards used in N. America Personal Digital Cellular (PDC) Integrated Enhanced Network (iden) Code Division Multiple Access (CDMA) The multiple access is achieved by assigning specific codes to each call and using the code with Direct Sequence spread spectrum transmission The individual calls disappear into the background noise and only reappears when all the noise and calls are run against the code for that call. Vastly increases the density of simultaneous calls support per cell over FDM or D-AMPS

9 The Last Mile Cellular Transmission Schemes Best of TDMA and CDMA Currently the services from carriers using each of these types are evenly matched Appears to currently be a marketing war and besides the best technology doesn t always win a marketing war OS2 vs NT Amiga vs PCs Ford/Chrysler/GM vs a Tucker Cellular Telephones Similar to wire-line phones Both use DTMF for dialing Both have a switch hook function to signal their switch

10 The Last Mile Cellular Transmission Schemes Best of TDMA and CDMA Currently the services from carriers using each of these types are evenly matched Appears to currently be a marketing war and besides the best technology doesn t always win a marketing war OS2 vs NT Amiga vs PCs Ford/Chrysler/GM vs a Tucker Cellular Telephones Similar to wire-line phones Both use DTMF for dialing Both have a switch hook function to signal their switch

11 The Last Mile Cellular Telephones Similar to wire-line phones All calls to and from both go through the switch associated with each type of telephone Key parts of a cellular telephone See Figure 23-6 on page 658 Antenna Transmitter and Receiver Frequency synthesizer generates reference frequencies Logic board Diplexer separates the transmit and receive signals Logic Board Brain of the phone

12 The Last Mile Cellular Telephones Logic Board Major tasks Communicate with the BTS on the following» Call Set-up» Call Teardown» Call Teardown» Signal strength Cell phone identification 32 bit identifying code is sent to the BTS and on to the MTSO» These codes have been stolen in the past and used to charge massive international and long distance charges Changing power requirements As newer technologies and better phone designs are implemented the phones got smaller and their power requirements decreased

13 The Last Mile Cellular Telephones Changing power requirements Batteries also have higher power densities and also hold their charges longer.

14 The Mobile Telephone Switching Office Characteristics Cellular provider s digital switch Class 5 switch with line and trunk interfaces Types of connections to the switch BTS Usually T-1 Circuits leased from the ILEC Trunk circuits that connect the MTSO to either a CLEC or ILEC s Class 5 switch Can be fiber or copper Depends upon location and required capacity Trunks to other MTSOs or long distance carriers See Figure 23-7 on page centers

15 The Mobile Telephone Switching Office Major components Multiplexers for wire-line connections Emergency power systems Software for communicating with BTS s Software for passing calls from one servicing cell to another Based upon radio transceiver signal strength Involves managing the set-up and teardown of calls

16 Connecting the BTS to the MTSO The BTS is connected to the MTSO Usually over a T-1 circuit A specific call is only using the T-1 when there is conversation to move Otherwise another cellular phone is using that part of the T-1 When a Cellular phone with a on-going conversation leaves a cell site It quits using the T-1 that connects the first BTS to the MTSO and uses the T-1 connection of the new BTS See Figure 23-8 on page 661

17 Signaling Three types of signaling in cellular phones Cellular telephone to MTSO BTS to MTSO MTSO to rest of the world Cellular telephone to MTSO The MTSO doesn't see the cellular phone go off-hook it receives a message from the phone saying it is offhook The phone receives a dial tone when the switch is ready for a number The phone uses DMTF signaling to dial

18 Signaling BTS to MTSO Signaling is per IS-634 standard Works with all types of transmission schemes AMPS, D-AMPS, TDMA, and CDMA BTS forwards off-hook, on-hook, signal level and dialed numbers to the MTSO along with all the signals required for call setup and teardown MTSO to Outside World Acts like any other local switch Has links to: SS-7 network, ILEC local and Tandem switches, CLEC switches, Long distance switches, etc

19 The Cellular Telephone Network Roaming between Regions Possible when SS-7 messages go between cellular providers National networks like AT&T, T-Mobile, and Sprint also simplify roaming Most of the time the costs aren t passed to the customers Billing Home Location Reregister (HLR) Database that holds information required to identify the provider of the cellular service for each phone IS-41 standard defines how billing info is passed between cellular carriers

20 The Cellular Telephone Network Cellular Telephone Features Most plans provide features that are extra cost items for wired phones Caller ID Voice mail Etc. See the list of features starting on page 663 Data Across the Cellular Network Protocols for modems connected to FDM cellular phones MNP10, MNP10EC, TXCEL and EC2 on FDM cellular To work ISPs must support at least one of the above protocols

21 The Cellular Telephone Network Data Across the Cellular Network Protocols for using modems connected to cellular phones Max rate is 14.4kbps with 9.6kbps and 4.8kbps the most common Can also be used to send FAX s Much higher data rates are possible on the three Much higher data rates are possible on the three different digital schemes

22 Satellite Telephone Service Original three consortiums that developed systems Iridium, Globalstar, and Teledesic Characteristics Uses low-orbit satellites Globalstar need 48 for coverage of most of the earth Iridium was the first to offer service Very pricy $3000 phones $7 a minute usage charges System needs links to the PSTN to route calls