This document discusses Orthogonal Frequency Division Multiple Access (OFDMA), a multiple access technique used in wireless communication. OFDMA is a specialized version of Frequency Division Multiple Access (FDMA) where all subcarriers within a channel are orthogonal to each other, allowing them to overlap without interference. This allows for more efficient spectrum usage than traditional FDMA. OFDMA was introduced in the 1960s-70s and has since been used in technologies like Wi-Fi, WiMAX, LTE, and is being researched for future 5G networks due to its ability to support high-speed data transmission.

1. J.PREM KAMAL DAS
16W91A0423

2. We look into…

3. • OFDMA – Orthogonal Frequency Division Multiple
Access
• One of the multiple access techniques
• Recent Technology in Wireless Communication
• It is related to FDMA

4. •Introduced by Chang, Bell labs in 1966
•Weinstein & Ebert proposed use of FFT and
Guard interval in 1971
•Cimini described the use of OFDMA in mobile
communication
•IEEE 802.11a wireless LAN standards (Wi-Fi) in
1999
•IEEE 802.16 standards for wireless MAN
(WiMAX) in 2004
•First LTE air interface implementation was
demonstrated in 2007

5. • Vector space
A, B and C vectors in space
are orthogonal to each other
A.B=B.C=C.A=0
(A+B+C).A=(mod A)^2
(A+B+C).B=(mod B)^2
(A+B+C).C=(mod C)^2
A
B
C

6. •OFDMA is a specialized frequency division multiple
access (FDMA) method.
•All subcarrier signals within a communication channel are
orthogonal to one another.
•The spacing between carriers are such that they are
orthogonal to one another
•Therefore no need of guard band between carriers.

7. OFDMA TECHNIQUE contd.

8. •The cyclic prefix provides a guard interval to eliminate
intersymbol interference from the previous symbol.
•It repeats the end of the symbol so the linear convolution
of a frequency-selective multipath channel can be modeled
as circular convolution.
•This approach accommodates simple frequency domain
processing, such as channel estimation and equalization.
OFDMA TECHNIQUE contd.

9. •Division of the frequency band allocated for wireless
cellular telephone
•Guard band is placed between the frequency bands.
FDMA vs. OFDMA

10. •Subcarriers overlap with each other.
•Passband bandwidth will be B ≈ N·Δf (Hz).
•By Orthogonality Principle, the signals are
transmitted.
•Receiver identifies the signals with orthogonal
principle.
FDMA vs. OFDMA
OFDMA

12. •Makes efficient use of the spectrum by allowing
overlap.
•Eliminates ISI through use of a cyclic prefix.
•High speed data transmission.
•It is possible to use maximum likelihood decoding
with reasonable complexity.
•OFDM is computationally efficient by using FFT
techniques to implement the modulation and
demodulation functions.

13. •High Peak to Average Power Ratio (PAPR)
•It has higher carrier frequency offset due to different
LOs (Local Oscillators) and DFT leakage.
•It is prone to ISI (Inter Symbol Interference) and ICI
(Inter Carrier Interference). This requires time offset
and frequency offset correction algorithms.
DISADVANTAGES

14. •DAB
•HDTV
•Wireless LAN Networks
•Broadband Wireless Access System
•LTE
APPLICATIONS

15. •5G mobile communication
•Reduction of PAPR
FUTURE SCOPE

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