HR-DSSS

  • An updated implementation of DSSS (HR-DSSS) was specified in the 802.11b addendum using the same 2.4 GHz ISM band.
  • Provides 5.5 and 11 Mbps speeds known as High-Rate DSSS (HR-DSSS)
  • 802.11b devices are backward compatible with the legacy 802.11 DSSS devices.
    This means that an 802.11b device can transmit using DSSS at 1 and 2 Mbps and using HR-DSSS at 5.5 and 11 Mbps. However, 802.11b devices are not capable of transmitting using FHSS; therefore, they are not backward compatible with 802.11 FHSS devices.
  • HR-DSSS, uses another more complex code than 802.11 primes barker code, Complementary Code Keying (CCK), is utilized.
    CCK uses an 8-chip PN, along with using different PNs for different bit sequences.
    CCK can encode 4 bits of data with 8 chips (5.5 Mbps) and can encode 8 bits of data with 8 chips (11 Mbps).
  • The 802.11b amendment states that channels need a minimum of 25 MHz (in comparision to 802.11 prime which required >30 MHz) of separation between the center frequencies to be considered nonoverlapping.

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