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FBMC vs FDM vs OFDM: Complete Comparison


FBMC vs FDM vs OFDM: Complete Comparison

A detailed comparison of FBMC, FDM, and OFDM waveforms covering spectral efficiency, orthogonality, multipath handling, and applications in modern wireless systems.

1. Basics and Concepts

Technique Full Form Concept
FDM Frequency Division Multiplexing Divides spectrum into non-overlapping bands; requires guard bands to avoid interference.
OFDM Orthogonal Frequency Division Multiplexing Uses orthogonal subcarriers allowing spectral overlap without interference.
FBMC Filter Bank Multicarrier Uses filtered subcarriers for excellent spectral containment and real-domain orthogonality.

2. Key Characteristics

  • Spectral Efficiency: FDM (low), OFDM (high), FBMC (very high)
  • Filtering: FDM uses bandpass filters, OFDM uses rectangular pulses, FBMC uses prototype filters
  • Orthogonality: FDM via separation, OFDM over symbol duration, FBMC in real domain
  • Multipath: FDM poor, OFDM uses cyclic prefix, FBMC handles ISI without CP
  • Complexity: FDM low, OFDM medium, FBMC high

FDMA vs FBMC Packets: Real Examples and Mathematics

1. FDMA Packets

FDMA assigns each user a separate frequency band. Each packet occupies a fixed frequency slot over time.

Mathematical Representation


x_k(t) = ∑ s_k[n] · rect((t − nT)/T) · e^{j2Ļ€f_k t}
  • rect(·) is a rectangular pulse of duration T
  • sā‚–[n] is the n-th symbol of user k
  • eŹ²²Ļ€fā‚–t is the carrier

Graphical Idea


| User1: 1kHz |      |      |
| User2: 2kHz     |      |
| User3: 3kHz         |  |

2. FBMC Packets

FBMC uses filtered subcarriers allowing frequency overlap while suppressing interference.

Mathematical Representation


x(t) = ∑ ∑ s_m[n] · g(t − nT) · e^{j2Ļ€mĪ”f t}
  • g(t) is a smooth prototype filter
  • Ī”f = 1/T is subcarrier spacing

Conceptual View


| Sub0 |~~~~~~|
| Sub1   |~~~~~~|
| Sub2     |~~~~~~|

Subcarriers overlap in frequency but remain orthogonal due to filtering.

Guard Bands in FDMA

Guard bands are frequency gaps, not zero-padding in time.

User Assigned Band Guard Band
1 0–1 kHz 1–1.2 kHz
2 1.2–2.2 kHz 2.2–2.4 kHz

FBMC reduces or eliminates guard bands using spectral shaping.

Final Summary

  • FDM is simple but spectrally inefficient.
  • OFDM balances efficiency and complexity using cyclic prefix.
  • FBMC offers the best spectral containment for future wireless systems.

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