Complementary Code Keying with PIC based microcontrollers for The Wireless Radio Communications

Common problems with digital Radio Communications 4 Interference from other radio communication devices Direct Sequence Spread Spectrum (DSSS) solve this problemDirect Sequence Spread Spectrum (DSSS) solve this problem 4 Interference from multipath signals Complementary Code Keying (CCK) solve this problemComplementary Code Keying (CCK) solve this problem

CCK modulator 4 CCK uses one of 64 nearly orthogonal vectors to generate spreading code word  Implementation is based on PIC16F84

Code word generation  “C” is the code word with LSB first to MSB last  CCK codeword has 4 phase terms. One of them modulates all of the chips (  1 ) and this is used for the QPSK rotation of the whole code vector. The 3 others modulate every odd chip (  2 ), every odd pair of chips (  3 ) and every odd quad of chips (  4 ) respectively

QPSK modulator LEGEND:  1 & 2 - balanced mixers  3 - phase splitter  4 - carrier oscillator  5 - coupler  6 - band-pass filter  7 - power amplifier  8 - antenna  QPSK modulator allows transmitting of two independent channels (I and Q) at the same time

Phase splitter 4 Low cost design 4 Constant phase difference among wide working frequency drift 4 Better performance up to few hundred MHz 4 For higher frequency (UHF bands) can be used micro strip lines with length equal to /4

Circuit diagram of the CCK encoder

Block diagram of the program

Conclusions 4 Improve performance for general multipath environments in radio transmission 4 Transmitter’s part of the CCK transceiver is a low cost effective, but the receiver’s part is more complex 4 The CCK waveform has better E b /N 0 performance than DPSK 4 DSSS with use of Barker’s code is more stable according to the long range and distance between transmitter and receiver in comparison with CCK

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