OFDM is the technology behind high data rates in LTE networks. It involves frequency division multiplexing (FDM) and transmitting data over multiple carrier signals. OFDM splits the available bandwidth into orthogonal subcarriers, allowing multiple users to transmit simultaneously on different subcarriers. This parallel transmission of data over multiple subcarriers increases data rates compared to traditional FDM.

1. 4G technology LTE_OFDM

2. Todays data rates becomes higher as
telecommunication technology is evolving.

3. Today in LTE network it can be more
than 100Mbps.

4. Then what is the technology behind ??

5. It’s OFDM

6. OFDM involves FDM and multi carrier
communication.

7. 1.FDM divides the available bandwidth into many subcarriers.
2.It allows multiple users to access the system simultaneously.
3.Each users data transmits on different subcarriers.

8. Between subcarriers there is a guard
band to avoid interference.

9. In multicarrier FDM the data of a single user can be split into
multiple sub-streams and transmit them in parallel through
various bands. Which makes the data rate higher.

10. Well in OFDM too ,data is transmitted in parallel.
Each subcarrier is modulated with a conventional
digital modulation scheme(QPSK,16QAM etc)

11. The subcarriers are designed to be
orthogonal. This allows the subcarriers to
overlap.

12. Thus bandwidth is saved and higher data
rate is achieved.

13. So OFDM differ with FDM in following
ways:
 Multiple carriers carry the information of each user.
 The sub carriers are orthogonal to each other.
 A guard interval is added to each symbol to minimize the channel delay
spread and inter symbol interference.

14. Understanding Orthogonality:
 In the frequency domain each subcarrier results in a SINC function spectrum
with side lobes producing overlapping.
 So interference occurs except at orthogonally spaced frequency points.
 At orthogonal frequency , individual peaks of subcarriers all line up with the
nulls of the other subcarriers.
 This overlap of spectral energy does not interfere.
 The receiver multiplies the incoming signal by the known set of sinusoids to
recover original bite.

15. Orthogonality:

16. Simple analogue OFDM system
implementation

17. OFDM advantages
 Immunity to selective fading.
 Resilience to interference
 Spectrum efficiency
 Resilient to ISI, delay spread
 Resilient to narrow band effects.

18. OFDM disadvantage:
 High peak to average power ratio.
 Sensitive to carrier offset and drift.

19. OFDM variants:
 Coded OFDM
 Flash OFDM
 OFDMA(multiple access)
 Vector OFDM
 Wideband OFDM

20. Thanks to you all
Fouad Hasan Meraj