Algorithms - Signal Scrambling

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Modulated signals are often scrambled when they are modulated. There are many reasons for scrambling the signal, including : spreading the spectrum and reducing the correlation between separate channels. Most scramblers utilise a Maximum Length Pseudo-Random Binary Sequence (MLPRBS or MLS), this uses a shift register an exclusive-or gates to randomise the data, as shown in the following diagrams. There are two general arrangements for implementing a scrambler, the non-synchronising and the self-synchronising types, each has its own benefits and draw backs, the non-synchronising type requires that the transmitter and receiver are synchronised before data transmission starts however once synchronised an input bit error to the receive scrambler will cause a single bit error in the output. The self-synchronising scrambler(shown below), as the name suggests will automatically synchronise to the received bit stream but a single receive bit error will cause N+1 bit errors in the output stream, where N is the length of the shift register.

These algorithms are included for information and are by no means definitive descriptions. If you would like to add anything to these pages then please feel free to email me and I will add your information, with my thanks.

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