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lecture24 - EEE455/591 EEE455/591 Basics of C DMA Re ading...

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EEE455/591 EEE455/591 Basics of CDMA Basics of CDMA Reading: Focus on thesenotes. Section 10.3 Reading: Focus on thesenotes. Section 10.3 Review of 1G (FDMA) and 2G (CDMA) Review of 1G (FDMA) and 2G (CDMA) 1. 2.5G and 3G: CDMA 1. 2.5G and 3G: CDMA 2. Basics of CDMA 3. CDMA Example 3. CDMA Example 4. Why is CDMA Taking Over? 4. Why is CDMA Taking Over?
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Review: 1G-FDMA and 2G-TDMA 1G (AMPS) assigns frequency channel to a link continuously 2G (D-AMPS) assigns timeand frequency slot ( TDMA/FDMA) 2G (GSM) uses Slow Frequency Hopping (SFH) for timeslots GSM has morefrequency reuse with smaller cluster size N GSM is a form of CodeDivision Multiple Access (CDMA ) Coding + interleaving to handlerandom and bursty errors Random errors due to thermal noise, ACI, and CCI Bursty errors due to frequency selective fading Burst errors also due to Multi-Access Interference (MAI)
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Review: Slow Frequency Hopping in GSM For GSM, slow frequency hopping over time Distinct hop sequencefor user Hop sequencefor two users may collide in time/frequency Interleaving + coding helps recover collided information Time Frequency packet collision (lost)
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1. Why CDMA? CDMA of Qualcomm revolutionized Cellular Very bandwidth efficient (1.25 MHz David versus 25MHz Goliath) 2.5G Cellular provides good quality telephony and higher speed data 3G Cellular (CDMA2000 in US and WCDMA) useonly DS/CDMA No need to assign different frequency channels for cells All cells usethesame and entire frequency band All calls in a cell useentire frequency band No need to assign timeslots and to synchronizeuser A call transmits continuously when the caller is talking
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