OFDMA

1
OFDMA

• Orthogonal Frequency Division Multiple Access

2
What is OFDMA?

• Multi-user version of OFDM
• Multiple access is achieved by assigning subsets
  of subcarriers to individual users

3
What is OFDMA? (cont.)

• Quality of Service (QoS) - control the data rate
  and error probability.
• Broadband Wireless Access Systems.
• Combination of Frequency domain and Time domain
  multiple access.

4
How OFDMA Works?

• OFDM Mechanism
• Divides into multiple sub-signals
• Orthogonal Sub-carriers.
• IFFT at TX, FFT at RX.

5
How OFDMA Works? (cont.)

• OFDMA Mechanism
• Time Frequency recourses separate the multiple
  user signal.
• Different groups of sub-carriers and OFDM
  symbols.

6
How OFDMA Works? (cont.)

• Allocation in Frequency domain.
• Formation of the sub-channels from sub-carriers.
• Adjacent sub-carrier method (ASM) Diversity
  sub-carrier method (DSM).
• Time for ASM DSM - Multiple of OFDM symbols.

7
VARIATIONS OF OFDMA AND HOW THEY DIFFER

• Various flavors of OFDMA.
• Concept of Sub-channelization allows four
  variations
• Frequency Division Multiplexing (FDM).
• Figure. Frequency Division Multiplexing
  (FDM)Spacing is put between two adjacent
  sub-carriers

8
VARIATIONS OF OFDMA AND HOW THEY DIFFER (cont.)

• Orthogonal Frequency Division Multiplexing
  (OFDM).
• Figure. Orthogonal Frequency Division
  Multiplexing (OFDM)Sub-carriers are closely
  spaced until overlap

9
VARIATIONS OF OFDMA AND HOW THEY DIFFER (cont.)

• Difference b/w OFDM OFDMA
• Figure. Uplink Subchannelization in WiMAX
• OFDM - only one SC transmits in one time slot.
• OFDMA - several SC's transmitted at the same time
  slot over several sub-channels

10
VARIATIONS OF OFDMA AND HOW THEY DIFFER (cont.)

• Scalable OFDMA (sOFDMA)
• Adds scalability.
• Reduces system complexity of smaller channels
  improves performance of wider channels.
• Flash-OFDM
• 1st commercially deployed OFDMA-based mobile
  broadband wireless communications system.
• Capability to work around interfering signals.

11
Applications

• One of the best solutions for mobile devices.
• Spectral efficiency
• Power
• Shorter delays
• Collision avoidance

12
Applications(cont.)

• WIMAX, IEEE 802.16e
• Wi-Fi connectivity
• Data telecommunication
• Portability and mobility
• Last Mile broadband access

13
Applications(cont.)

• 4G Wireless Systems
• For mobile devices
• Faster than 3G (Downlink 100 Mbps, Uplink 50
  Mbps)

14
Applications(cont.)
15
Thanks for your patient listening!

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