Instant WirelessTM Series
What is Spread Spectrum?
Spread Spectrum technology is a wideband radio frequency technique devel- oped by the military for use in reliable, secure, mission-critical communica- tions systems. It is designed to trade off bandwidth efficiency for reliability, integrity, and security. In other words, more bandwidth is consumed than in the case of narrowband transmission, but the trade-off produces a signal that is, in effect, louder and thus easier to detect, provided that the receiver knows the parameters of the spread-spectrum signal being broadcast. If a receiver is not tuned to the right frequency, a spread-spectrum signal looks like background noise. There are two main alternatives, Direct Sequence Spread Spectrum (DSSS) and Frequency Hopping Spread Spectrum (FHSS).
What is DSSS? What is FHSS? And what are their differences?
Frequency-Hopping Spread-Spectrum (FHSS) uses a narrowband carrier that changes frequency in a pattern that is known to both transmitter and receiver. Properly synchronized, the net effect is to maintain a single logical channel. To an unintended receiver, FHSS appears to be short-duration impulse noise. Direct-Sequence Spread-Spectrum (DSSS) generates a redundant bit pattern for each bit to be transmitted. This bit pattern is called a chip (or chipping code). The longer the chip, the greater the probability that the original data can be recovered. Even if one or more bits in the chip are damaged during trans- mission, statistical techniques embedded in the radio can recover the original data without the need for retransmission. To an unintended receiver, DSSS appears as low power wideband noise and is rejected (ignored) by most nar- rowband receivers.
Would the information be intercepted while transmitting on air?
WLAN features two-fold protection in security. On the hardware side, as with Direct Sequence Spread Spectrum technology, it has the inherent security fea- ture of scrambling. On the software side, WLAN offers the encryption function (WEP) to enhance security and Access Control.
What is WEP?
WEP is Wired Equivalent Privacy, a data privacy mechanism based on a 40 bit shared key algorithm, as described in the IEEE 802.11a.
Wireless PC Card
Appendix B: Glossary
Ad-hoc Network - An ad-hoc network is a wireless network or other small net- work in which some of the network devices are part of the network only for the duration of a communications session while in some close proximity to the rest of the network.
Architecture - The total design and implementation of the network. It includes the network's topology, transmission technologies and communications proto- cols, management and security systems, and any other attributes that give a net- work a particular set of capabilities and functionalities.
Backbone - The part of a network that connects most of the systems and net- works together and handles the most data.
Bandwidth - The transmission capacity of a given facility, in terms of how much data the facility can transmit in a fixed amount of time; expressed in bits per sec- ond (bps).
Bit - A binary digit. The value - 0 or 1-used in the binary numbering system. Also, the smallest form of data.
BSS (Basic Service Set) - A group of Instant Wireless Network PC Card users and an Access Point.
Buffer - A buffer is a shared or assigned memory area used by hardware devices or program processes that operate at different speeds or with different sets of pri- orities. The buffer allows each device or process to operate without being held up by the other. In order for a buffer to be effective, the size of the buffer and the algorithms for moving data into and out of the buffer need to be considered by the buffer designer. Like a cache, a buffer is a "midpoint holding place" but exists not so much to accelerate the speed of an activity as to support the coordination of separate activities.
