1. MULTICARRIER MODULATION FOR DATA TRANSMISSION

2. INTRODUCTION Modulation techniques: improve the efficiency of transmitted power. Linear equalization of a single carrier signal causes noise or interference. A multi-carrier modulated (MCM )signal can be processed in the receiver without the enhancement of noise.

3. SECTIONS TO BE DISCUSSED  The general technique of parallel transmission on many carriers  The performance that can be achieved on an undistorted channel  Channel impairments  Methods of implementation

4. MULTIPLEXING  BASIC PRINCIPLE  MCM is a form of FDM  Mfs bits/symbol blocks of M bits at a block rate of fs  M bits are used to modulate Nc carriers which are spaced ∆f apart across any usable frequency band  That is m n bits for the carrier at f c,n  The modulated carriers are then summed for transmission

5. BASIC BLOCK DIAGRAM

6. DEMULTIPLEXING In the receiver before demodulation Three methods; 1.Using MCM modems based on FDM technology 2.Using Staggered Quadrature Amplitude Modulation(SQAM) 3.Using Quadrature Amplitude Shift Keying(QASK)

7. POWER SPECTRA FOR 3 METHODS * Sharp filters are needed * Efficiency of band usage is 100% *Amount of filtering is less *Total no. of carriers must be small *Frequency division by baseband processing *Txr and Rxr can be implemented by efficient FFT techniques

8. MAXIMUM ACHIEVABLE BIT RATE Performance of the system is measured in terms of attainable bit rate at a given error rate and Signal To Noise Ratio & The aggregate bit rate for MCM ≥bit rate for SCQAM

9. PROOF FOR HIGH BIT RATE The probability of bit error in symbol-by –symbol detection of QAM signal in sub-band n is, (((1) ; K - error-rate multiplier P - total transmitted power γ n - proportion of power allotted to ea each sub-band

10. Continued.. Now the equation can be inverted and The total no. of bits that can be transmitted in one symbol with error probability P using Nc sub-bands can be written as,

11. Continued.. Now summation can be approximated by integration and maximum bit rate Thus the bit rate = that for a Single Carrier System(SCQAM).

12. ADAPTIVE LOADING  Fixed loading : high error rate in heavily- loaded- sub-bands resulting in greater overall error rate.  The sub-band error rates can be made equal by varying m n.

13. CORRECTING CHANNEL IMPAIRMENTS Linear distortion: ICI & ISI Phase jitter : Reduce random distortion & Tracking is easier Non-linear distortion

14. IMPLEMENTATION Modulation by Inverse Fast Fourier Transform(IFFT) Demodulation by FFT

15. ADVANTAGES Duplex Operation Echo Cancellation Highest Possible Speeds Immunity To Impulse Noise And Fast Fades Tolerable Average SNR And Resultant Error Rate Less Phase Jitter Effects

16. APPLICATIONS  Modems for data transmission and fax on: GSTN 60-108 kHz FDM group band Cellular radio HDSL

17. REFERENCES Base paper; John A.C. Bingham “Multicarrier Modulation for Data Transmission: An Idea Whose Time Has Come ”, IEEE Communications Magazine. Herbert Taub,Donald L. Schilling, GoutamSaha “Principles of Communication Systems”. Bernard Sklar “Digital communications” http://www.educypedia.be/electronics/rfdigmod. htm http://www.educypedia.be/electronics/rfdigmod. htm http://en.wikipedia.org/wiki/phase-shiftkeying http://acronyms.thefreedictionary.com/QASK

18. “THANK YOU”

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