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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]
1
23 Nov' 2007 DA-IICT 2
Outline of the Presentation
IntroductionLiterature survey Complexity of AlgorithmsProblem DefinitionProgress on ProblemsFuture PlansReferences
2
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.
23 Nov' 2007 DA-IICT 4
Generation of DS-CDMA
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23 Nov' 2007 DA-IICT 5
Direct Sequence CDMA
Fig: The baseband model of a DS-CDMA transceiver
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23 Nov' 2007 DA-IICT 6
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 .
23 Nov' 2007 DA-IICT 8
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.
23 Nov' 2007 DA-IICT 22
Thank You!
22
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