SEMINAR ON

1
SEMINAR ON CODED ORTHOGONAL FREQUENCY DIVISION
MULTIPLEXING
2
SINGLE CARRIER AND MULTICARRIER
single carrier system
Multi carrier approach
3
MULTIPLE ACCESS TECHNIQUES
Time Division Multiple Access
Frequency Division Multiple Access
Code Division Multiple Access
4
Multipath Problem
5
What is COFDM

• FDM Frequency Division multiplexing
• OFDM Orthogonal FDM
• COFDM Coded OFDM
• COFDM is a Multi-carrier modulation/multiplexing
  technique
• Available bandwidth is divided into several sub
  channels
• Data is serial-to-parallel converted
• Symbols are transmitted on different subcarriers

6
COFDM TRANSMITTER
7
Forward Error Correction

• Convolution coding
• Adds redundancy to the information
• Convolutional coding operates on bit streams
• Low implementation cost
• OFDM gtgt COFDM (Coded OFDM)
• Viterbi decoding
• Hard decision-Each bit is treated on its own
• Soft decision-the probability of each stage of
  decoding is influenced by the confidence of the
  previous result

8
INTERLEAVING
Time interleaving
9
Cont.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Burst Error with Interleaving
1 5 9 13 2 6 10 14 3 7 11 15 4 8 12
1 5 9 13 2 6 10 14 3 7 11 15 4 8 12
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
10
MAPPING
11
Inverse Fourier Transform
The IDFT calculates the following equation
x(n) nth output signal complex value
(time domain) X(k) complex symbol value on
the kth subcarrier (frequency domain)

12
Inverse Fourier Transform
13
Symbol to Waveform
14
Orthogonal principle
15
Sub Carrier Spacing

• The sub-carriers are spaced at regular intervals
  called the sub-carrier frequency spacing (?F).
• The sub-carrier frequency relative to the center
  frequency is k ?F where k is the sub-carrier
  number.

16
Single-frequency networks (SFNs)
17
GUARD PERIOD
18
COFDM RECEIVER
19
DVB-T specification

• A signal that contains either 1705 or 6817 active
  carriers, commonly referred to as 2K and 8K
  respectively. (FFT algorithm )
• QPSK, 16-QAM and 64-QAM constellations.
• Guard Intervals 1/4, 1/8, 1/16 and 1/32 of the
  OFDM symbol length.
• Viterbi code rates 1/2, 2/3, 3/4, 5/6 and 7/8.

20
COFDM SYSTEM PROPERTY

• Interference Rejection/Avoidance

• Power Amplifier Efficiency
• Low Timing Sensitivity is needed
• Frequency Sensitivity
• No Equalizers are needed

21
ADVANTAGES

• Robust against narrow-band co-channel
  interference
• Robust against Inter symbol interference (ISI)
  and fading caused by multipath propagation
• High spectral efficiency
• Efficient implementation using FFT
• Low sensitivity to time synchronization errors
• Facilitates Single Frequency Networks

22
DISADVANTAGES

• Circuitry must be very linear
• Sensitive to Doppler shift
• Sensitive to frequency synchronization
• problems
• High peak-to-average-power ratio (PAPR),
• requiring linear transmitter circuitry, which
  
• suffers from poor power efficiency.

23
APPLICATION

• Digital Audio Broadcasting (DAB) in European
  market
• Wireless Local Area Networks development is
  ongoing for wireless point to point and point to
  multipoint configuration using COFDM technology
• ADSL COFDM forms the basis for the global ADSL
  (asymmetric digital subscriber line) standard

24
System Standards using COFDM

• Wireless
• IEEE 802.11a, g, j, n (WiFi) Wireless LANs
• IEEE 802.15.3a Ultra Wideband (UWB) Wireless PAN
• IEEE 802.16d, e (WiMAX), WiBro, and
  HiperMANWireless MANs
• IEEE 802.20 Mobile Broadband Wireless Access
  (MBWA)
• DVB (Digital Video Broadcast) terrestrial TV
  systems DVB-T, DVB-H, T-DMB and ISDB-T
• DAB (Digital Audio Broadcast) systems EUREKA
  147, Digital RadioMondiale, HD Radio, T-DMB and
  ISDB-TSB
• Flash-OFDM cellular systems
• 3GPP UMTS 3GPP_at_ LTE (Long-Term Evolution), and
  4G
• Wireline
• ADSL and VDSL broadband access via POTS copper
  wiring
• MoCA(Multi-media over Coax Alliance) home
  networking
• PLC (Power Line Communication)

25
CONCLUSION

• The current status of the research is that COFDM
  appears to be a suitable technique as a
  modulation technique for high performance
  wireless telecommunications.
• COFDM was found to perform very well compared
  with CDMA

26
REFERENCES

• STOTT, J.H., 1997. Explaining some of the magic
  of COFDM. Proceedings of 20th International
  Television Symposium, Montreux, June.
• VLSI implementation of OFDM modem, AuthorsAseem
  Pandey, Shyam Ratan Agrawalla Shrikant
  Manivannan
• www.digitalradiotech.co.uk
• www.ert.rwth-aachen.de
• www.4g.co.uk
• www.iec.org

27
THANK YOU