1. CSIS 6251 CSIS 625 Week 14 Wireless Technologies Cell Phones, LMDS, MMDS, etc. Copyright 2001 - Dan Oelke For use by students of CSIS 625 for purposes of this class only.

2. CSIS 6252 Overview Cell Phone –What is a cell –Analog vs. Digital –TDMA, CDMA, etc. Fixed Wireless –LMDS, MMDS Optical Wireless Final Exam

3. CSIS 6253 Cell Phone Technology Based on the idea of offering mobile phone service Reference: –Much of this material taken from: –http://www.ee.washington.edu/class/498/sp98/final/marsha/final.html –http://www.iec.org/online/tutorials/cell_comm/ –http://www.iec.org/online/tutorials/tdma/ There were early radio to telephone type systems, but cellular technology didn’t start until the early 1980’s. –Limited number of channels in a large area –1981the FCC approved the use of a larger number channels.

4. CSIS 6254 Cell phone overview Based on the idea of using radio frequencies in small areas called cells. –806-890 MHz and 1850-1990 MHz Cells are often laid out in a honeycomb type of topology. –Frequencies can then be re-used in non-adjacent cells. –A cell is 1-2 miles in radius in urban areas –up to 20 miles in radius in rural area. –Micro-Cell and Pico-Cell are used in very small very high density areas Such as inside a sports stadium

5. CSIS 6255 Cellular system components PSTN - Public Switched Telephone System –The “normal” phone system MTSO - Mobile Telephone Switch Office –The switch that controls all of the cell sites –This switch coordinates handoffs between cells Mobile Base Station - The cell site –The antenna, radios, interface equipment, etc. MSU - Mobile Subscriber Units –The cell phone you carry around.

6. CSIS 6256 Cell phone - Analog vs. Digital Analog technology uses FDM with FM analog modulation –call uses a fixed frequency in its cell for the duration –Older scheme - more coverage in united states than digital technology –Any scanner can listen in on these conversations Newt Gingrich knows this well Congress made it illegal to listen in on these conversations, but it is very difficult to enforce unless you come out with a tape

7. CSIS 6257 Cell phone - Analog vs. Digital Digital technology –Uses PCM to get a digital stream –Then uses various audio compression techniques to get voice down to rates as low as 8kbps. Compression may reduce the quality of the voice –New technology with good coverage in high population density areas. –Allows many more calls for a given bandwidth –May use “silence suppression” to further increase capacity Silence suppression - not sending data when there is no-one talking Effectively doubles the amount of data that can be sent. Need to have comfort noise added

8. CSIS 6258 Cell - Modulation techniques FDMA - Frequency Division Multiple Access –used for analog phones –The same thing as Frequency Division Multiplexing TDMA - Time Division Multiple Access –Divides a frequency into multiple timeslots –Each call uses one timeslot in one frequency –Increases the number of calls that may be present –Used with digital technology

9. CSIS 6259 Cell - Modulation techniques (cont.) CDMA - Code Division Multiple Access –Use of entire time and frequency –Each call has minimal interference with one another. –Not a hard limit on the number of calls possible Each call just adds a little more interference GSM - Global System for Mobile Communications –TDMA based system used in Europe. –Voice compressed to 13kbps PCS - Personal Communications Services –use of 1900 MHz frequencies

10. CSIS 62510 Cell handoff As a phone moves from one cell to another, the call must be handed off with minimal interruption. –When signal strength decreases sufficiently, base station notifies switch –The switch queries the other base stations to determine which has the strongest signal from the phone. –The switch then notifies the new base station to take over the call –Normally less voice is dropped for only 10-100ms CDMA can use a “soft” handoff with no interruption –The use of the entire frequency spectrum means that there is no other channel to use

11. CSIS 62511 LMDS - Local Multipoint Distribution System A high speed wireless access technology using bands in the 28-31Ghz frequency spectrum. Speeds in the 100’s of Mbps depending on the amount of spectrum given to a given connection. Is a point-to-multipoint technology –One central site –Many subscriber sites Started in 1998 when FCC auctioned off the spectrum for LMDS –Must own a license to use a set of frequencies. Or pay the current license holder for the privilege of using it

12. CSIS 62512 LMDS - continued May use TDMA or FDMA or combination Encoding techniques of PSK, QPSK, 8PSK, 4- QAM, 16-QAM, or 64-QAM Limited Rage –3-5 Mile radius –Caused by extremely high frequencies and need to have strong signal to noise ratio for higher QAM methods. Reference: –http://www.iec.org/online/tutorials/lmds/

13. CSIS 62513 MMDS - Microwave Multipoint Distribution System Also called Multi-channel Multi-point Distribution System Fixed wireless technology Uses 33 channels of 6MHz each (2.5 - 2.7Ghz) Originally set up for poor man’s cable, now used to send digital data Sprint is the major license holder in the US –Have offered Internet access up to 1Mbps using this technology Up to 35mile radius

14. CSIS 62514 Optical Wireless Also called Free Space Optics Use of lasers sent through air instead of fiber optics cable. Can be point to point or point to multipoint systems Speeds from 155Mbps up to (claimed) 10Gbps Issues to deal with –Movement of buildings –Pigeons and other flying objects –Fog and Rain –Perceived Safety issues Limited Range - 2-4km Reference: –http://www.lightreading.com/document.asp?doc_id=1207http://www.lightreading.com/document.asp?doc_id=1207

15. CSIS 62515 Final Exam Similar format to Mid-term Covers material since the mid-term only. Open book and open note Will be limited to a fixed time –Probably about 2 hours. Questions????