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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Unique codes for each mobile are created on the forward channel by combining the voice data with 1 of 64 user Walsh codes and then combining that with a sector unique offset of the PN (pseudo-noise) short code (see the Figure).
Spreading function using Walsh codes and Quasi Orthogonal
Many of the concepts from that Motorola-backed proposal have been included in the current 1xEV-DV proposal to improve the performance, including: four-channel hybrid ARQ (automatic request for retransmission), concatenation of multiple Walsh codes, adaptive modulation and coding, and fast cell selection.