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OFDM vs CDMA: Key Differences Explained

wireless communication modulation technique orthogonal frequency division multiplexing code division multiple access cellular system

This article explains the technical differences between OFDM (Orthogonal Frequency Division Multiplexing) and CDMA (Code Division Multiple Access).

OFDM is a multi-carrier system where numerous carriers are packed very densely. Each carrier is allocated data bits based on a complex modulation scheme. CDMA, on the other hand, is a single-carrier system.

Techniques exist that combine the benefits of both OFDM and CDMA, such as MC-CDMA (Multi-Carrier Code Division Multiple-Access) and OFCDM (Orthogonal Frequency & Code Division Multiplexing). OFDM is used in WLAN and WiMAX systems as a physical layer modulation technique to increase data rates.

CDMA is considered a more secure technique, particularly in cellular systems, due to its transmission at noise power levels.

OFDM is generally more challenging to operate at cell edge boundaries compared to CDMA. CDMA provides protection from inter-cell interference at cell edges through the use of scrambling codes, while OFDM lacks a similar built-in mechanism.

OFDM vs. CDMA Specifications

Specification	OFDM	CDMA
Transmission bandwidth	Variable, up to the system bandwidth maximum.	Equal to the full system bandwidth.
Symbol period	Very long, dependent on subcarrier spacing, independent of system bandwidth.	Very short, the inverse of the system bandwidth.
Multipath resistance	Resistant to multipath up to the length of the cyclic prefix.	Very difficult above 5MHz.
MIMO	Ideal for MIMO due to signal representation in the frequency domain.	Requires more computing power because the signal is 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	Vulnerable to narrowband distortion and interference.	Averaged across the channel due to spreading.
Equalization	Easy for all bandwidths because of frequency domain representation.	Very difficult above 5MHz.
Frequency selective scheduling	Possible, requiring accurate real-time feedback of channel conditions from receiver to the transmitter.	Not possible.