Walsh code

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Walsh code

Also known as "Walsh-Hadamard code," it is an algorithm that generates statistically unique sets of numbers for use in encryption and cellular communications. Known as "pseudo-random noise codes," Walsh codes are used in direct sequence spread spectrum (DSSS) systems such as Qualcomm's CDMA. They are also used in frequency hopping spread spectrum (FHSS) systems to select the target frequency for the next hop. See CDMA.

Walsh Code Algorithm

          (a', b') = (a+b, a-b)
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The spatially uncorrelated feature of the transmission signals is produced using Walsh-Hadamard code sets; then multipath delayed waves are produced for each signal, and finally a different Doppler shift is added for each probe antenna.
where [W.sub.TX] is a TX-side connection matrix with L x M dimensions consisting of a set of Walsh-Hadamard code vectors, with the matrix producing independent Rayleigh fluctuations against M input signals, and [A.sub.RX] is the N x L channel matrix connecting the probe antenna array with the reception antenna array.
The vector [w.sup.(k).sub.delay] is the kth element of the weight matrix [W.sub.delay] (K x K matrix) composed of K Walsh-Hadamard code vectors.
An orthogonal code such as Walsh-Hadamard code is used to achieve minimum multiple access interference (MAI) in the fading channel.