ППРЧ radio

[step-elena]

Пожалуйста, помогите перевести. ППРЧ (псевдослучайная перестройка рабочей частоты) словари дают такой перевод: Frequency hopping. Но встретила и такой перевод: programmed radio frequency tuning. и как переводить правильно СИЧ (скачкообразное изменение частоты), тоже frequency hopping? Заранее спасибо.

[Rengo]

ППРЧ - pseudorandom frequency hopping - PRFH

[step-elena]

Спасибо! Первоначально я тоже так перевела, но потом засомневалась и полезла искать соответствия. Кстати, вот еще какой вариант нашла FHSS frequency hopping spread spectrum. Так что же все-таки правильно?

[Rengo]

http://www.qsl.net/n9zia/wireless/fhss_vs_dsss.html

[step-elena]

Rengo, не могу посмотреть ссылку, Яндекс предупреждает о наличии вируса. :(

[Rengo]

Technical Comparison of Frequency Hopping and Direct Sequence Spread Spectrum
A service of Green Bay Professional Packet Radio ®

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Some terms used:
DSSS - Direct Sequence Spread Spectrum. A RF carrier and pseudo-random pulse train are mixed to make a noise like wide-band signa l.
FHSS - Frequency Hopping Spread Spectrum. Transmitting on one frequency for a certain time, then randomly jumping to another, and transmitting again.
FEC - Forward Error Correction. Common mean of error detection and correction in data networks.
multipath - When the RF signal arrives at the receiving antenna after bouncing through several paths. Degrades received sign al significantly.
DSP - Digital Signal Processor. See Texas Instruments DSP web site.
narrowband - A radio frequency signal that occupies a small amount of space
IQ - The two channels used in quadrature modulation, one in-phase (I), and one shifted 90 degrees from the I channel. (Q)
MAC - Medium Access Control. Part of the radio device managing the protocol and the usage of the link. Decides when to transmit and when to receive, creates the packets headers and filters the received packets.

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FHSS radios are more susceptible to narrowband noise and interference than DSSS systems, so they will need to retransmit the same packet often. FHSS system will ignore most leaky microwave oven radiation, but with a DSSS system, a interfering signal could overload the receiver and bring the entire link down.
FHSS will still overcome some narrowband interference, to a certain level, by just retransmitting the packet again on the next frequency hop. The DSSS system will have to use its FEC to handle the corrupted data, if it's even correctable.

Packet size on average in FHSS systems is only one fifth that of a DSSS packet. 400 bytes typically for a FHSS packet versus 1500 or 2400 bytes for a DSSS one, so large FHSS packets will need to be fragmented. FHSS also suffers from higher MAC latencies. All of this adds up to almost a ten times advantage in raw data throughput for a DSSS system as compared to that in a FHSS one.
That being said, FHSS systems are the cheapest, and easiest to implement. Their RF circuits can use efficient non-linear, class C amplification, all with a nominal bandwidth of 1 MHz. This is especially useful in portable operations where these circuits tend to draw less current.

DSSS systems, on the other hand, require a DSP, linear IQ modulation, IQ spin control, and linear (class A or AB RF power amplification. Along with precise linear amplification of all up/down converters and low noise amplifiers. All these circuits also need to have 22 MHz of bandwidth. Ouch.

FHSS radio systems also appear to do better indoors and in severe multipath environments. This is because the frequency hopping scheme can defeat multipath by just hopping to a new frequency. The wavelength of that new frequency changes just enough to alter the signal path, and therefor change any multipath interference that might occur.
DSSS are much more useful in outdoor and non-cluttered environments. Their processing gain makes them preferable in that situation, where they will have better receiver sensitivity.
A wireless network's data rate is limited by the Ethernet data rate. The more protocol converters and overhead you add to the system, the worse your throughput gets.

[step-elena]

Спасибо, буду разбираться!