Chapter 11 CIS 325 data communications

CIS-325 Data Communications Dr L G Williams, Instructor CIS-325 Data Communications Chapter Eleven Wireless Networks CIS-325 Data Communications Advanced Mobile Phone Service First generation of cell phones basic devices mobile base transceiver mobile telephone switching office (MTSO) Voice and Control Channels CIS-325 Data Commu Operations Outgoing from mobile input phone number and press send mobile links to base xcvr via control channel base to MTSO to POTS MTSO routes connection back to mobile via voice channel mobile shifts from control to voice CIS-325 Data Commu Operations Incoming to mobile call goes from POTS to MTSO on control channel, MTSO searches for mobile by PAGING every active mobile if found, MTSO rings it and establishes voice channel connection uses xcvr with strongest signal from mobile CIS-325 Data Commu Cells In a city, there might be one MTSO There will be many xcvrs, each in its own area or CELL Cell is hexagonal, with dia of miles or less See fig 11.1, page 318 CIS-325 Data Commu Channels Every mobile in a cell who is talking must have its own channel Otherwise, there will be interference More channels = more users Rule of thumb - one channel can support 20 users CIS-325 Data Commu Spectral Allocation In U.S., we use two 25mHz bands one band from mobile to xcvr one band from xcvr to mobile Each channel uses 30 kHz So - about 832 channels for a city But - channels split between two companies 21 for control, 395 for voice So - can support about 7900 users CIS-325 Data Commu Frequency Reuse Also called Spatial Allocation Cells are small, so signals can be low power Can use same freq in a cell that is far away, but not one nearby at least cells must intervene So - each cell can use about 57 channels So - each cell can support 1140 users CIS-325 Data Commu Hand-offs Mobile phones move from cell to cell As signal fades, mobile asks MTSO for a new base xcvr MTSO polls all base xcvrs to see which has strongest signal with mobile Mobile shifts to new channel coming from new base CIS-325 Data Commu 10 Roaming Mobile has moved to a different city or subscriber area MTSO will check with your provider, via land-line Then will allow you access Keeps track of billing data CIS-325 Data Commu 11 Global System for Mobile Communications (GMS) Second-generation system Widely used in Europe Most of the same concepts as AMPS System is digital, not analog Uses fewer channels, but they are multiplexed CIS-325 Data Commu 12 Subscriber Identity Card Plug this into any mobile and it becomes ‘yours’ Allows very flexible use of system and components CIS-325 Data Commu 13 Mobile Services Switching Center (MSSC) Replaces MTSO, but has same functions Controls many Base Station Controllers Each Controller may control one or more base transceivers MSSC connects system to POTS CIS-325 Data Commu 14 Multiple Access Use spectrum more efficiently by multiplexing channels Frequency-division multiplexing Time-division multiplexing Space-division multiplexing essentially frequency re-use CIS-325 Data Commu 15 Code-division Multiplexing Move message to higher bandwidth more room Encode each signal one bit may now have a 6-bit code Combine several of these channels into same signal, then un-mix at destination can put up to 100 signals on one channel CIS-325 Data Commu 16 Third Generation Wireless Communications Universal Personal Communications Identify yourself to any system, anywhere PCS - Personal Communications Services Global standards for terminals, cell phones Smaller or micro-cells Much greater bandwidth (150 mHz) CIS-325 Data Commu 17 Satellite Communications Geosynchronous 22,300 miles above Simple to track and find Needs strong signal to cover distance Slight delay in signal due to distance CIS-325 Data Commu 18 Satellite Communications Highly Elliptic Orbiting Satellites (HEOS) GEO can’t reach poles very well due to oblique angles Russian’s use HEOS 65 degrees off equater Elliptic orbit • close at South, far/high in North Need satellites for coverage CIS-325 Data Commu 19 Satellite Communications Low Earth Orbiting Satellites (LEOS) Constellation of small, “inexpensive” satellites 200-700 miles high Need >60 for 24 hour coverage Sophisticated hand-off between satellites Tables 11-1 and 11-2, pg 333 lists proposed systems CIS-325 Data Commu 20 Iridium A proposed LEOS system Motorola Voice, data, fax, paging 15-20 ground stations Will not replace cellular system Satellites at 420 nm Phone call at $3/minute CIS-325 Data Commu 21 [...]... billing data CIS- 325 Data Commu 11 Global System for Mobile Communications (GMS) Second-generation system Widely used in Europe Most of the same concepts as AMPS System is digital, not analog Uses fewer channels, but they are multiplexed CIS- 325 Data Commu 12 Subscriber Identity Card Plug this into any mobile and it becomes ‘yours’ Allows very flexible use of system and components CIS- 325 Data Commu... destination can put up to 100 signals on one channel CIS- 325 Data Commu 16 Third Generation Wireless Communications Universal Personal Communications Identify yourself to any system, anywhere PCS - Personal Communications Services Global standards for terminals, cell phones Smaller or micro-cells Much greater bandwidth (150 mHz) CIS- 325 Data Commu 17 Satellite Communications Geosynchronous 22,300 miles above... high Need >60 for 24 hour coverage Sophisticated hand-off between satellites Tables 11- 1 and 11- 2, pg 333 lists proposed systems CIS- 325 Data Commu 20 Iridium A proposed LEOS system Motorola Voice, data, fax, paging 15-20 ground stations Will not replace cellular system Satellites at 420 nm Phone call at $3/minute CIS- 325 Data Commu 21 ... cover distance Slight delay in signal due to distance CIS- 325 Data Commu 18 Satellite Communications Highly Elliptic Orbiting Satellites (HEOS) GEO can’t reach poles very well due to oblique angles Russian’s use HEOS 65 degrees off equater Elliptic orbit • close at South, far/high in North Need 3 satellites for coverage CIS- 325 Data Commu 19 Satellite Communications Low Earth Orbiting Satellites (LEOS)... Controllers Each Controller may control one or more base transceivers MSSC connects system to POTS CIS- 325 Data Commu 14 Multiple Access Use spectrum more efficiently by multiplexing channels Frequency-division multiplexing Time-division multiplexing Space-division multiplexing essentially frequency re-use CIS- 325 Data Commu 15 Code-division Multiplexing Move message to higher bandwidth more room Encode each ... mobile CIS- 325 Data Commu Cells In a city, there might be one MTSO There will be many xcvrs, each in its own area or CELL Cell is hexagonal, with dia of miles or less See fig 11. 1, page 318 CIS- 325. .. they are multiplexed CIS- 325 Data Commu 12 Subscriber Identity Card Plug this into any mobile and it becomes ‘yours’ Allows very flexible use of system and components CIS- 325 Data Commu 13 Mobile... signals on one channel CIS- 325 Data Commu 16 Third Generation Wireless Communications Universal Personal Communications Identify yourself to any system, anywhere PCS - Personal Communications Services