David Waitt Kate Disney 2008 April Digitizing An Analog World

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

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?

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

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

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

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

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

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

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