OFDMA - Orthogonal Frequency Division Multiple Access PPT by PREM KAMAL
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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.
OFDMA - Orthogonal Frequency Division Multiple Access PPT by PREM KAMAL
- 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.
- 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