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Difference between OFDM and CDMA

This page describes difference between OFDM and CDMA technical specifications.

OFDM stands for Orthogonal Frequency Division Multiplexing and CDMA stands for Code Division Multiple Access. OFDM is a multiple carrier system where in multiple carriers are packed very densely and all are allocated with data bits based on complex modulation scheme. CDMA on the other end is a single carrier system. There exists techniques which combines benefits of both viz. MC-CDMA (Multi-Carrier Code Division Multiple-Access) and OFCDM (Orthogonal Frequency & Code Division Multiplexing).

OFDM is employed in the WLAN and WiMAX systems as physical layer modulation technique to enhance the data rate. CDMA is the more secured technique employed in cellular systems due to transmission at noise power level. OFDM is more difficult to operate at the cell edge boundaries compare to CDMA technology. CDMA provides protection in cell edge from inter-cell interference due to scrambling code while OFDM do not have such provision.

Specifications OFDM CDMA
Transmission bandwidth variable with max. upto system bandwidth Equal to Full system bandwidth
Symbol period very long and it depends on subcarrier spacing, it is independent of system bandwidth very short and it is inverse of system bandwidth
multipath resistance Free from multipath upto the length of cycli prefix It is very difficult above 5MHz
MIMO Ideal for MIMO because of signal representation in frequency domain Need more computing power bacause of signal defined in the time domain
User separation Frequency and time, scrambling and spreading can also be used. scrambling and orthogonal spreading codes
Frequency domain distortion & interference sensitivity It is vulnerable to narrow band distortion and interference It is averaged across channel due to spreading
Equalization Easy for all the bandwidths because of frequency domain representation It is very difficult above 5MHz
Frequency selective scheduling It is possible and need very accurate real time feedback of channel conditions from receiver to the transmitter Not possible

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