# DSSS encoding/ decoding

**URL:** <https://discourse.julialang.org/t/dsss-encoding-decoding/101857>\
**Category:** Signal and Image Processing\
**Tags:** question\
**Created:** [July 20, 2023, 9:42pm UTC](https://discourse.julialang.org/t/dsss-encoding-decoding/101857 "2023-07-20T21:42:56Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![ufechner7](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/ufechner7/32/51363_2.png) [@ufechner7](https://discourse.julialang.org/u/ufechner7)\
**Post date:** [July 20, 2023, 9:42pm UTC](https://discourse.julialang.org/t/dsss-encoding-decoding/101857/1 "2023-07-20T21:42:56Z")

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Hello,

I am trying to implement DSSS encoding/ decoding in Julia.

Any hints how to start?

Encoding:

- input: low frequent signal
- input: digital secret sequence
- filter: bandwidth filter
- output: analog (sampled) spread spectrum signal

Decoding:

- input: analog (sampled) spread spectrum signal
- input: digital secret sequence
- output: low frequent signal

Questions:

- how can I generate the spreading sequence?
- how can I implement the coding?
- how can I implement the decoding?

See: [Direct-sequence spread spectrum - Wikipedia](https://en.wikipedia.org/wiki/Direct-sequence_spread_spectrum)

Some closed source Matlab code: [Direct Sequence Spread Spectrum(DS SS) - File Exchange - MATLAB Central](https://nl.mathworks.com/matlabcentral/fileexchange/28420-direct-sequence-spread-spectrum-ds-ss)

Some open source Matlab code: [GitHub - mahmut-aksakalli/DirectSequenceSpreadSpectrum: it contains MATLAB simulation of Direct Sequence Spread Spectrum technique.](https://github.com/mahmut-aksakalli/DirectSequenceSpreadSpectrum)

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<div class="post-metadata">

**Author:** ![mbaz](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/mbaz/32/17295_2.png) [@mbaz](https://discourse.julialang.org/u/mbaz)\
**Post date:** [July 20, 2023, 11:47pm UTC](https://discourse.julialang.org/t/dsss-encoding-decoding/101857/2 "2023-07-20T23:47:49Z")

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Here’s a quick approximation, using CommunicationsSequences.jl to generate the spreading sequence.

```julia
using CommunicationsSequences

# 7-bit spreading sequence
l = LFSR(lfsrtaps[3], mapping = (1, -1))
seq = first(l, 7)

# 10 data bits to be transmitted
tx_data = rand((0,1),10)

# generate DSSS sequence
dsss = Int[]
for i in 1:10
    if tx_data[i] == 1
        append!(dsss, seq)
    else
        append!(dsss, -seq)
    end
end

# recover bits from DSSS sequence
rx = reshape(dsss, 7, 10) # one bit per column
rx_data = Int[]
for i in 1:10
    if sum(rx[:,i] .* seq) > 0
        append!(rx_data, 1)
    else
        append!(rx_data, 0)
    end
end

# verify
tx_data .== rx_data

```

You also mentioned generating an analog sampled spread spectrum signal. How to do this depends on the details: are you using pulse shaping? Adding noise? Matched filtering?