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lecture25a - EEE455/ 591 EEE455/ 591 2G Cellular Systems-...

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Unformatted text preview: EEE455/ 591 EEE455/ 591 2G Cellular Systems- CDMA 2G Cellular Systems- CDMA Reading: Focus on PowerPoint. Reading: Focus on PowerPoint. Textbook pp. 730-745,769-774 Textbook pp. 730-745,769-774 Review: Why CDMA? Review: Why CDMA? CDMA Link Budget CDMA Link Budget I S-95 Speech Codec I S-95 Speech Codec Sequence Fundamentals (PN and Walsh) Sequence Fundamentals (PN and Walsh) I S-95 Traffic Channels (Reverse, Forward) I S-95 Traffic Channels (Reverse, Forward) I S-95 Control Channels (Access, Forward) I S-95 Control Channels (Access, Forward) Other Advantages of I S-95 Other Advantages of I S-95 Review: Bandwidth and I nterference Rejection Advantages of CDMA No Adjacent Channel I nterference (ACI ). (No guard bands for FDMA) No need for guard time for TDMA. No need for frequency assignment. No need for time slot assignment. Dont transmit when not speaking. (2.5 times improvement in capacity) Co-channel interference (CCI ) handled by FEC + CDMA. No capacity reduction by cellular reuse factor N. Multiple Access I nterference (MAI ) handled by coding Same FEC code handles AWGN or thermal noise. CDMA Link Budget Consider a DS-CDMA system of bandwidth W for N u users each with power P s . Each user sends data at a rate of R bits/ sec, encoded at rate r<1 with distance d min . Power Budget: Coding Gain (CG): = d min r Processing Gain (PG) = W/ R or (L c = T b / T c ) Multi-Access I nterference (MAI ) = P s / (N u-1)P s = 1/ (N u-1) Resulting SI R:...
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This note was uploaded on 11/01/2009 for the course EEE 455 taught by Professor Hui during the Spring '09 term at ASU.

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lecture25a - EEE455/ 591 EEE455/ 591 2G Cellular Systems-...

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