RFFDM vs. OFDM: Key Differences Explained
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This article compares Frequency Division Multiplexing (FDM) and Orthogonal Frequency Division Multiplexing (OFDM) techniques, highlighting the differences between them.
FDM stands for Frequency Division Multiplexing, while OFDM stands for Orthogonal Frequency Division Multiplexing.
As shown in the figure, in FDM systems, carriers are spaced far apart from each other. In contrast, OFDM systems have densely packed carriers that are orthogonal to each other. Orthogonal means that the peak of one carrier occurs at the null point of the other. This makes OFDM systems more bandwidth-efficient compared to FDM systems, where carriers are not orthogonal.
Key Differences
Here’s a breakdown of the key differences between FDM and OFDM:
- Bandwidth Efficiency: OFDM is more bandwidth-efficient than FDM due to the orthogonal arrangement of carriers.
- Peak to Average Power Ratio (PAPR): OFDM systems usually have a higher PAPR compared to FDM systems. However, PAPR in OFDM can be reduced using techniques like scrambler modules.
- Data Rate: OFDM systems provide higher data rates compared to FDM systems when using the same bandwidth.
- Applications:
- FDM: Used in radio and satellite communications where good guard bands between adjacent frequency bands are required.
- OFDM: Used in WiMAX (802.16d/16e), WLAN (802.11g/11n), and LTE technologies, which require higher data rates and are primarily used for broadband internet services.
- Multipath Interference: OFDM systems are more susceptible to multipath interference compared to FDM systems. However, this can be mitigated using advanced algorithms such as cyclic prefix insertion.
- Bandwidth Allocation: In FDM, the entire bandwidth is typically used by a single user/subscriber. In OFDM, the bandwidth is divided into many narrow-band channels, with each allocated to a user/subscriber. This allows OFDM to support more subscribers/channels compared to FDM.
Summary
| Feature | FDM | OFDM |
|---|---|---|
| Carrier Spacing | Far apart | Densely packed, orthogonal |
| Bandwidth Efficiency | Lower | Higher |
| PAPR | Lower | Higher (can be mitigated) |
| Data Rate | Lower | Higher |
| Multipath Sensitivity | Lower | Higher (can be mitigated) |
| Bandwidth Allocation | Entire bandwidth per user | Divided into narrow channels per user |
| Applications | Radio, Satellite Communications | WiMAX, WLAN, LTE |
Understanding the differences between FDM and OFDM requires extensive knowledge of carrier multiplexing techniques for the optimal use of limited frequency resources.
