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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This is a great improvement compared to the system applying Walsh Codes, which need to cancel N-1 users in the worst case.
5 MHz rate Modulation Number of 256 Cyclic prefix Data sub-carriers (FFT length) Maximum Doppler 111Hz Channel model Frequency Spreading Sequences CQS Walsh codes OFDM symbol period PT OFDM DT OFDM symbol number in 7 symbol number in one period one period Signal bit 8-PSK scheme Number of 5.
This relationship holds for both the Hadamard numbering of the Walsh codes in IS-95 and CDMA2000 as well as the bit-reversed Hadamard code numbering used in wideband CDMA (W-CDMA).
OVSF codes are orthogonal codes similar to the Walsh codes used in 2G CDMA (IS-95) BTS.
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
2288 Mbps chip rate, an IS-95 forward link pilot channel and 16 orthogonal channels with 0 to 63 selectable Walsh codes.