Jungle wrote:
"
<I assume you know that for decades the US military have been using spread
spectrum technology to send digital information. A spread spectrum system is
one in which the transmitted signal is spread
over a wide frequency band, much wider, in fact, than the minimum bandwidth
required to transmit the information being sent. This technology is used in
cordless phones as well as to send control
signals to probes and satelites.>"
I dont think this has anything to do with a digital FM station. If that is
what you are insinuating then the radio receivers would need a far more
sophisticated circuitry to capture the signals being broadcast thus adding
to the cost of what is already deemed very expensive. In fact this was done
in order to facilitate the integrity of the USA Military communication
across their military network ( Although some aspects of the technique are
being exploited by Cellular Networks).
Simply put, spread spectrum is a method by which a normally-narrowband radio
signal is spread out to a much wider bandwidth before transmission takes
place. Upon reception of the signal, the receiver recovers the original
narrowband signal through the reverse process, naturally referred to as
despreading. Spreading and despreading can be accomplished in many ways, but
are usually done using one of two common techniques, direct sequence and
frequency hopping.
In direct sequence, the radio signal is multiplied by a pseudo-random
sequence (PRBS) whose bandwidth is much greater than that of the signal
itself, thereby spreading its bandwidth. In frequency hopping, the
pseudo-random sequence is used to move the radio signal about, in a random
fashion,across a broad frequency band (i.e. the frquency divided into sub-
bands).
Regardless of the spreading technique used, the purpose for doing so is to
exploit one or more of the many benefits of spread spectrum:
Interference rejection, signal hiding, frequency band sharing (code-division
multiplexing)and anti-jam properties, which I hope is not a needed facet for
a commercial Radio station. Why would a Radio Station hides its signals?
In conclusion, the protocols underlying the use of these spread spectrum
techniques requires them to operate under different architectures. One is
ideal for an Infracstructure Network whilst the other is used in AD-Hoc
networks as stipulated by the IEEE 802.11b standard for wireless.
Even though Simulcast transmission was to be used the argument for
justifying it(thus adding to recurring costs)in the present time would not
be a sensible proposition.
I hope this underpin what I surmised as to your understanding in earlier
posting.
Thanks
Mohin
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