Page 834 - (ISC)² CISSP Certified Information Systems Security Professional Official Study Guide

communication.

Frequency Hopping Spread Spectrum (FHSS) was an early
implementation of the spread spectrum concept. However, instead of

sending data in a parallel fashion, it transmits data in a series while
constantly changing the frequency in use. The entire range of available
frequencies is employed, but only one frequency at a time is used. As
the sender changes from one frequency to the next, the receiver has to
follow the same hopping pattern to pick up the signal. FHSS was

designed to help minimize interference by not using only a single
frequency that could be affected. Instead, by constantly shifting
frequencies, it minimizes interference.

Direct Sequence Spread Spectrum (DSSS) employs all the available
frequencies simultaneously in parallel. This provides a higher rate of
data throughput than FHSS. DSSS also uses a special encoding
mechanism known as chipping code to allow a receiver to reconstruct

data even if parts of the signal were distorted because of interference.
This occurs in much the same way that the parity of RAID-5 allows the
data on a missing drive to be re-created.

Orthogonal Frequency-Division Multiplexing (OFDM) is yet another
variation on frequency use. OFDM employs a digital multicarrier
modulation scheme that allows for a more tightly compacted
transmission. The modulated signals are perpendicular (orthogonal)

and thus do not cause interference with each other. Ultimately, OFDM
requires a smaller frequency set (aka channel bands) but can offer
greater data throughput.

Cell Phones

Cell phone wireless communications consist of using a portable device
over a specific set of radio wave frequencies to interact with the cell
phone carrier’s network and either other cell phone devices or the
internet. The technologies used by cell phone providers are numerous

and are often confusing. One point of confusion is the use of terms like
2G and 3G. These do not refer to technologies specifically but instead
to the generation of cell phone technology. Thus, 1G is the first
generation (mostly analog), 2G is the second (mostly digital, as are 3G