Clear-Com TEMPEST 2400 - Tech Menu for BaseStation Configuration; BaseStation Configuration Options; BaseStation Information Display

8 Tempest®2400 2-Channel Wireless Intercom System
Theory of Operaon
The above illustraons show the theory of operaon for both the 4-channel (dual antenna) and 2-channel (single antenna) models of
Tempest. The 2-channel model lacks some of the diversity characteriscs found in the 4-channel model. Tempest uses Frequency Hopping
Spread Spectrum (FHSS), Time Division Mulple Access (TDMA), and 2xTX® technology. For example, on Frequency 1 the BaseStaon and
each BeltStaon take turns broadcasng, each with its own me slot to send audio data (TDMA). The total me for one cycle is 5 milliseconds
(1/200 second). The BaseStaon and all BeltStaons hop (FHSS) to a dierent predetermined frequency and the same audio data is sent
again, but on a new frequency and on a dierent BaseStaon antenna (2xTX). Therefore, each receiver has two opportunies to receive the
audio data. Duplicate data is discarded by the receiver and the process starts over with the next packet of audio data.
Tempest is a DSP (Digital Signal Processor) based, full duplex, wireless intercom system. It is a digital, point-to-point
communicaons system, operang in 80MHz of spectrum in the 2.4GHz ISM frequency band. This band allows users to
operate with no license requirements in most locaons. The world-wide acceptance of the 2.4GHz band makes Tempest
ideal for traveling users.
The 2.4GHz band oers many benets. There are, however, a wide variety of technologies and users compeng for clear
spectrum in this limited band. Tempest ulizes patented and proprietary technologies to ensure a robust and reliable RF
link under a wide variety of physical and RF environments. This level of reliability is the most important aribute of any
wireless system.
Tempest ulizes proprietary, Frequency Hopping Spread Spectrum (FHSS) technology that has seven U.S. patents. Mulple
BeltStaon access is achieved by implemenng Time Domain Mulple Access (TDMA) with Frequency Shi Keying (FSK)
modulaon. Tempest uses an Algebraic Code - Excited Linear Predicon (A-CELP) voice compression algorithm to reduce the
bandwidth necessary for transmission and yet maintain the highest possible voice intelligibility. In addion, this algorithm
ulizes advanced lost packet masking technology, which greatly reduces the aect of packet loss, possible in all Digital RF
transmission schemes. The loss of audio packets is managed by the algorithm to reduce the possibility of detecng a loss
of audio.
In the 2.4GHz RF band mul path interference occurs frequently. The Tempest RF scheme is dramacally enhanced with the
addion of proprietary 2xTX technology that transmits each data packet twice. This technique reduces spectral eciency
by half, but greatly increases audio intelligibility by reducing the Eecve Packet Error Rate (EPER) by orders of magnitude.
The system transmits packet data every 5ms and then “hops” or changes frequency. The sequence of frequency changes
is controlled by a predetermined hopping paern. Each hopping paern is opmized such that any new frequency has
a quasi-orthogonal relaonship to the last operang frequency. This quasi-orthogonal frequency relaonship ensures
maximum frequency separaon between any two consecuve hops. Because of this, if an interfering source is present in
one area of the operaonal band, and interferes on a parcular hop, the next hop will be in a clear area of the spectrum
with the best possible chance of transmission success.