Qualcomm Incorporated (QCOM) Message Board

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Technology Stocks : Qualcomm Incorporated (QCOM)

QCOM 173.67

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To: Clarksterh who wrote (123644)	8/29/2002 11:33:43 PM
From: Dexter Lives On	Read Replies (3) of 152472

Advantages of OFDM versus CDMA * Multipath: CDMA can tolerate long delay spreads but it captures only a fraction of the energy of the multipath signal because of the limited number of rake fingers. In OFDM, as long as guard interval is long enough, all inter-symbol-interference is absorbed. Moreover, multipath self-interference affects CDMA but not OFDM. * Narrowband Interference: only a few tones are affected or lost in OFDM, whereas in CDMA the interference affects all symbols. * Impulse Noise: OFDM spreads the impulse noise over a burst reducing its effect, whereas in CDMA several symbols may be lost. * Timing Acquisition: CDMA is very sensitive to timing and requires fast acquisition. This results in complex algorithms and overhead unlike OFDM. * Complexity: the CDMA rake receiver is more complex than OFDM digital front end (FFT). Implementation of equalization, interference cancellation, and adaptive antenna array algorithms is simpler in OFDM. * Power Control: CDMA requires fast and precise power control as it is very sensitive to received power fluctuations which is not the case for OFDM. * Smart antennas: CDMA technology is less sensitive to capacity enhancement by using smart antenna techniques than OFDM technology because of CDMA intra-cell interference behaviour.

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