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David Waitt Kate Disney 2008 April Digitizing An Analog World.

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Presentation on theme: "David Waitt Kate Disney 2008 April Digitizing An Analog World."— Presentation transcript:

1 David Waitt Kate Disney 2008 April Digitizing An Analog World

2 Is “Going Digital” Enough?  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

3 Common Wireless Devices Today  Cellphone GSMGSM (850, 900, 1800, 1900 MHz)(850, 900, 1800, 1900 MHz) CDMACDMA (900, 1900 MHz)(900, 1900 MHz)  Wireless (WiFi, )  (2400, 5100, 5800 MHz)  Bluetooth  (2400 MHz)  How do these devices use the RF spectrum efficiently?

4 GSM – Global System for Mobile communications  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 Seconds  AT&T (Cingular), T- Mobile

5 CDMA – Code Division Multiple Access  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

6 What Else Can Be Done  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

7 Reducing Coverage Area Reducing the coverage area of each cell site increases capacity, but costs more to deploy the network

8 Bluetooth  Most common use is Bluetooth headsets for use with cellular phones  Frequency Hopping Spread Spectrum

9 Frequency Hopping  79 hopping channels  Used in a random order  seconds per frequency

10 Why Frequency Hopping?  If a few packets of data is lost due to interference, only a very small portion of the information is lost!


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