Walsh code


Also found in: Dictionary, Wikipedia.
Related to Walsh code: OVSF

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)
Mentioned in ?
References in periodicals archive ?
Once the Walsh code is assigned, the digital data are first filtered digitally, then quadrature phase-shift keying (QPSK) modulated and analog summed in such a fashion as to combine other channels being downlinked to the mobile.
Specifications for the Zebra source include a 1.2288 Mbps chip rate, an IS-95 forward link pilot channel and 16 orthogonal channels with 0 to 63 selectable Walsh codes. An internal temperature-compensated crystal oscillator (TCXO) is incorporated with a stability of 2.5 ppm from 10 [degrees] to 50 [degrees] C.
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).
Besides all above three receivers with CQS, the result of traditional PIC-MMSE-WMRC (Walsh Codes) receiver is marked as the solid curve with squares.
We also notice that the PIC-MMSE-PMRC (CQS) outperforms over the PIC-MMSE-WMRC (Walsh Codes).
In all the cases of both Figures, the PIC-MMSE-WMRC (Walsh codes) has the worst performance, which shows that the CQS plays a key role to help the system improve the channel tracking ability.
This is a great improvement compared to the system applying Walsh Codes, which need to cancel N-1 users in the worst case.