23 Nov' 2007 DA-IICT 1

FPGA Implementation Of Direct Sequence Spread

Spectrum (DSSS)

Stage 1 Thesis Presentation

Guide: Prof. Rahul Dubey Presentated By:Examiners: Prof. Deepak Ghodgaonkar Vivek Kr. Choudhary

Prof. M. V. Joshi [200611029]

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Outline of the Presentation

IntroductionLiterature survey Complexity of AlgorithmsProblem DefinitionProgress on ProblemsFuture PlansReferences

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Introduction of DSSSDirect Sequence Spread Spectrum (DSSS) CDMA

is the method used in IS-95 commercial systems.A spread spectrum is a technique in which the

bandwidth of a signal is increased by artificially increasing the bit data rate.

This is done by breaking each bit into a number of sub-bits called “chips.”

Narrow band input from a user is coded (“spread”) by a user-unique broadband code, then transmitted.

Broadband signal is received: receiver knows, applies user’s code , recovers users’ data.

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Generation of DS-CDMA

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Direct Sequence CDMA

Fig: The baseband model of a DS-CDMA transceiver

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Advantages over a fixed-frequency transmission

1. Spread-spectrum signals are highly resistant to noise and interference

Secure data communications.Military influenced Anti-jamming capabilities.Multiple access capabilities.Spread spectrum signal are highly resistant to

noise and interference.

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Problem Definition

Linear Feedback Shift Register (LFSR) implementation for long PN-sequence generation.

Synchronization of PN-sequence between transmitter and receiver.

Error correction and detection of data bits .

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Digital-Bit errors caused by

a) Attenuation and attenuation distortion

b) Delay distortion

c) NoiseSingle bit error detection is possible but not

correction, so retransmission will take place .But Hamming Algorithm can detect and correct

both , so no need of retransmission which is necessary for high speed wireless communication.

Problem Definition

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Literature Survey

Din

Dout

4x 1 Synchronous

RAM

4x 1 Synchronous RAM

Control Logic D Q D Q

D Q

D Q

LFSR implementation of synchronous RAM

Error Detection and Correction

Error detection is the ability to detect errors. Error correction has an additional feature that

enables identification and correction of the errors. Error detection always precedes error correction. Both can be achieved by having extra or redundant

or check bits in addition to data deduce that there is an error

Original Data is encoded with the redundant bit(s)New data formed is known as code word

Hamming Algorithm In 1950, R.W. Hamming described a general method for

constructing code with minimum distance of 3 ,now called Hamming Code.

(n,k) Hamming codes. Minimum distance always 3. Thus can detect 2 errors and correct one error. n=2^m-1, k = n - m, m≥3 .

Maximum-length codes. For every k≥3 integer there exists a maximum length code (n,k) with n = 2k – 1, dmin = 2k-1.

d d d r8 d d d r4 d r2 r1

11 10 9 8 7 6 5 4 3 2 1

r bit’s is the parity bit for one combination of data bit’s

r1: bit’s 1 , 3 , 5 , 7 , 9 ,11

r2: bit’s 2 , 3 , 6 , 7 , 10 ,11

r4: bit’s 4 , 5 , 6 , 7

r8: bit’s 8 , 9 , 10 , 11

Position of redundancy bit’s in hamming code

Example of redundancy bit calculation

Error detection using hamming code

Hamming Algorithm

Fig: Technology schematic 15

RTL Schematic for hamming code generation

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Technology Schematic

Test Bench Waveform

Simulation Results (4 Bit-data input)

Number of Slices: 2 out of 3584 0%

Number of 4 input LUTs:

3 out of 7168 0%

Number of IOs: 11

Number of bonded IOBs:

11 out of 141 7%

Delay: 7.850ns (Levels of Logic = 3)

Future PlansImplementation of Hamming code logic in

Wide band CDMA.Implementation by Viterbi Algorithm because it’s

work at receiving end.

References

[1] Predrag Markovic, Milan Markovic, FPGA/VLSI Implementation Analysis of

PN Sequence Generator for Direct Sequence Spread Spectrum Systems. IEEE

conference, Nis, Yugoslavia,13-15 October 1999.

[2] Sunil Shukla, Neil W. Bergmann, SINGLE Bit Error Correction Implementation in

CRC-16 on FPGA. IEEE conference, 6-8 Dec. 2004.

[3] Behrouz A. Forouzan. Data Communications and Networking. McGraw-Hill 3rd edition,

1 Nov. 1994, pp. 257-259.

[4] Bob Zeidman. Verilog Designer’s Library. Prentice Hall Modern Semiconductor

Design Series, pp. 237-259.

[5] K.H. Tsoi, K.H. leung and P.H.W. Leong, Compact FPGA –based True and Pseudo random

Number Generators. . IEEE conference, 9-11 April 2003.

[6] Taub.Schilling . Principles of Communication System. TATA McGRAW-HILL EDITION,

2nd edition, pp 720-751.

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Thank You!

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Frequency Hopping

Frequency Hopping

IS-95 is a standard for CDMA(Code Division Multiple Access) Digital Cellular.

Mobile Frequency Range Rx: 869-894; Tx : 824-849

Multiple Access Method CDMA/FDM

Duplex Method FDD

Number of Channels 20 (798 users per channel)

Channel Spacing 1250kHz

Modulation QPSK/OQPSK

Channel Bit Rate 1.2288Mb