Direct-Sequence Spread Spectrum (For 802.11B) - Asus WL-100G User Manual

Wireless local area network card for 802.11g and 802.11b wireless networks

Hide thumbs Also See for WL-100G:

Table of Contents

Chapter 5 - Glossary

Direct-Sequence Spread Spectrum (for 802.11b)

Spread spectrum (broadband) uses a narrowband signal to spread the

transmission over a segment of the radio frequency band or spectrum. Direct-

sequence is a spread spectrum technique where the transmitted signal is spread

over a particular frequency range. The Space Link Wireless ASUS WLAN

Card uses Direct-Sequence Spread Spectrum (DSSS) for radio communication.

Direct-sequence systems communicate by continuously transmitting a redundant

pattern of bits called a chipping sequence. Each bit of transmitted data is mapped

into chips by the Wireless ASUS WLAN Card and rearranged into a

pseudorandom spreading code to form the chipping sequence. The chipping

sequence is combined with a transmitted data stream to produce the Wireless

ASUS WLAN Card output signal.

Wireless mobile clients receiving a direct-sequence transmission use the

spreading code to map the chips within the chipping sequence back into bits to

recreate the original data transmitted by the Wireless ASUS WLAN Card.

Intercepting and decoding a direct-sequence transmission requires a predefined

algorithm to associate the spreading code used by the transmitting Wireless

ASUS WLAN Card to the receiving wireless mobile client.

This algorithm is established by IEEE 802.11b specifications. The bit

redundancy within the chipping sequence enables the receiving wireless mobile

client to recreate the original data pattern, even if bits in the chipping sequence

are corrupted by interference. The ratio of chips per bit is called the spreading

ratio. A high spreading ratio increases the resistance of the signal to interference.

A low spreading ratio increases the bandwidth available to the user. The Wireless

ASUS WLAN Card uses a constant chip rate of 11Mchips/s for all data rates,

but uses different modulation schemes to encode more bits per chip at the

higher data rates. The Wireless ASUS WLAN Card is capable of an 11 Mbps

data transmission rate, but the coverage area is less than a 1 or 2 Mbps Wireless

ASUS WLAN Card since coverage area decreases as bandwidth increases.

ASUS WLAN Card

Table of Contents