Where Have All The Sine Waves Gone Digitizing
- Slides: 20
Where Have All The Sine Waves Gone? Digitizing An Analog World David Waitt Kate Disney 2008 April
Digital Television (DTV) u u Starting on 17 February 2009 New type of broadcasting that will allow better quality picture and sound More efficient use of the radio spectrum The same radio spectrum can now be used for other applications • • Public Safety (Police, Fire) Wireless data Other communications GPS enhancements
Digital Television u What do I need to do if I use a TV antenna and have an older television? • Need a “converter box” to convert the received digital signal into analog video and sound u Nothing is required if your television already has a Digital TV Tuner
Digital Television u u Different levels of quality Standard Definition TV (SDTV) - SDTV is the basic level of quality display and resolution for both analog and digital. Transmission of SDTV may be in either the traditional (4: 3) or widescreen (16: 9) format. Enhanced Definition TV (EDTV) - EDTV is a step up from Analog Television. EDTV comes in 480 p widescreen (16: 9) or traditional (4: 3) format and provides better picture quality than SDTV, but not as high as HDTV. High Definition TV (HDTV) - HDTV in widescreen format (16: 9) provides the highest resolution and picture quality of all digital broadcast formats. Combined with digitally enhanced sound technology, HDTV sets new standards for sound and picture quality in television. (Note: HDTV and digital TV are not the same thing — HDTV is one format of digital TV. )
DTV. . . More Info u u www. dtv. gov The National Telecommunications and Information Administration (NTIA) is administering the coupon program. For more information, visit the NTIA website at www. dtv 2009. gov
Is “Going Digital” Enough? u u Simply digitizing information (Music, video, voice, pictures) for transmission is not enough to use the RF spectrum efficiently The information must be transmitted as efficiently as possible
Common Wireless Devices Today u Cell phone • GSM • (850, 900, 1800, 1900 MHz) • CDMA • (900, 1900 MHz) u Wireless (Wi. Fi, 802. 11) u u Bluetooth u u (2400, 5100, 5800 MHz) (2400 MHz) -> How do these devices use the RF spectrum efficiently?
Getting From Here To There
The “Cell” site Cells are actually “Covered” by multiple cell sites. The cell sites operate on different frequencies so they do not interfere with each other within a given cell.
GSM – Global System for Mobile communications u u Time Division Multiplexing Cell site communicates with up to 8 phones on a single frequency for a short amount of time, “Time Slot” Each slot is. 004615 Seconds AT&T (Cingular), TMobile
CDMA – Code Division Multiple Access u u Phones are assigned codes that are embedded into the signal The cell site can distinguish between the different codes The number of phones communicating on a given frequency is determined by the “Bit Error Rate” Verizon, Sprint
IEEE 802. 11 A/B/G (Wi. Fi) Typical wireless home router u Several methods for varying the radio signal (modulation) u BPSK, QAM 816 -32 -64 -128 -256 u
QPSK Quadrature Phase Shift Keying u u u Vary the phase of the radio signal to indicate one of four locations (0, 90, 180, 270 degrees) Each “star” can represent 2 bits. Amplitude is constant
Higher Order Modulations u u 8 PSK 16 QAM (Quadrature Amplitude Keying) • The more stars in the constellation, the closer they will get to each other, and they will be more susceptible to interference, 256 QAM for very short communications links
Bluetooth Most common use is Bluetooth headsets for use with cellular phones u Frequency Hopping Spread Spectrum u
Frequency Hopping u u u 79 hopping channels Used in a random order 0. 000625 seconds per frequency
Why Frequency Hopping? u If a few packets of data is lost due to interference, only a very small portion of the information is lost!
What Else Can Be Done u What else can be done to encourage “Frequency Re-Use? This drawing shows very poor use of the radio spectrum. if this was a GSM cellular system with, 10 different frequencies, this system could accommodate 80 phones for the state of California
Reducing Coverage Area Reducing the coverage area of each cell site increases capacity, but costs more to deploy the network
Pico-Cells u u u Pico-Cells increase capacity and improve frequency re-use Cell site coverage will overlap, but on a different frequency. Sites using the same frequency are spaced further apart Some pico-cells are small enough to be located in office buildings in closets!
- Where have all the young people gone
- Where have all the criminals gone
- Presente simple en ingles
- Heads down digitizing
- Fast digitizing
- Nullum crimen sine lege nulla poena sine lege
- Nullum crimen sine lege nulla poena sine lege
- Chesmore vs richards
- What do all waves have in common
- What do all waves have in common
- Where have you gone charming billy
- 간접의문문 만들기
- Where have you gone charming billy audio
- Shall i say i have gone at dusk through narrow streets
- I have gone marking analysis
- Where have you gone charming billy characters
- Parts of a longitudinal wave
- Sound waves are transverse waves true or false
- Mechanical waves examples
- How are rainbows made
- What type of waves are sound waves? *