Clear-Com Antenna System RF Guide

Radio System RF Guide
RF Guide
Overview
Reliable Wireless Communication is absolutely essential in today’s fast-paced broadcast and live production
markets, but licensing requirements, radio spectrum reallocation and the wide variety of technologies
competing for clear spectrum have created an array of problems for system administrators and end users
throughout the world. Areas of the spectrum that have traditionally been used for wireless intercoms are
becoming increasingly crowded and more difficult to use.
Tempest is a full duplex, 2.4GHz Frequency Hopping Spread Spectrum (FHSS) wireless intercom system.
Tempest operates in 80MHz of the spectrum sometimes referred to as the 2.4GHz ISM band. This band allows
users the ability to operate with no license requirements and no frequency coordination virtually anywhere,
world-wide. Tempest’s RF system, while advanced and sophisticated, has been designed to be very easy
to set up and use. This makes Tempest ideal for traveling shows, rental houses and permanent installations
everywhere.
Keys
• No frequency coordination necessary
• Very easy to setup and use
• Unlicensed spectrum available for use virtually everywhere, world-wide
The 2.4GHz Frequency Band:
The 2.4GHz ISM frequency band is a globally accepted portion of the RF spectrum that is available for
unlicensed use virtually anywhere, world-wide. In the US the 2.4GHz ISM band is 2400MHz to 2483.5MHz.
Elsewhere in the world the band can vary slightly and can go as high as 2495MHz in certain countries.
Tempest utilizes up to 80MHz of this spectrum from 2400 to 2480MHz.
Regulations governing the use of this band throughout the world require that all devices that operate within the
2.4GHz ISM band use technologies that minimize interference and promote cooperative use of the available
spectrum. This allows multiple devices to operate within the band with minimal interference or reduction of
range and performance. This stands in stark contrast to older analog VHF and UHF radio technologies that
have traditionally been used for wireless intercom systems in the past. This means you can pack a whole lot
more users into a much smaller RF band while still maintaining a high quality RF link. There is also the added
benefit that all of this comes without any complicated, time consuming frequency coordination.
Keys
• 2400 – 2480MHz Operational frequency band
• Advanced technology allows multiple devices to operate at once while minimizing interference
• The 2.4GHz ISM band can vary from country to country
RF Guide
FHSS, TDMA, FSK, 2xTX, LPC RF Technology
What do all these letters mean? The good news is that while the Frequency Hopping Spread Spectrum
(FHSS), Time Domain Multiple Access (TDMA), Frequency Shift Keying (FSK), Redundant Data Transmit
(2xTX) and Lost Packet Concealment (LPC) technology that makes Tempest work is very sophisticated and
complex, you don’t have to know all of the ins and outs to use it! We have done all of the hard work for you.
For those that are interested, basically, it works like this.
Frequency Hopping Spread Spectrum – Over time Tempest uses as much of the spectrum as possible, but it
only uses about 1.5MHz of the 80MHz at one time. Tempest uses a narrow band signal, approximately 1.5MHz
wide and changes frequencies, or hops, 200 times a second or every 5ms. Using a narrow band signal allows
Tempest to concentrate RF power into a smaller area of the spectrum. This allows Tempest to “burn through”
RF noise and interference that could otherwise be a significant problem. Additionally, changing frequencies
very rapidly helps make Tempest less susceptible to single point external interference sources, intermodulation
and multipath fading.
Time Domain Multiple Access – In older analog intercom systems each belt as well as the base had their
own individual frequencies. This was easy to engineer, but very spectrally inefficient and very susceptible to
interference and multipath fading. By using TDMA, the Tempest basestation and all of its associated belt packs
operate on the same frequency at any given moment in time. This is called multiple remote access. All of the
devices on the RF link share, or multiplex the frequency. First the basestation “says” what it has to say to each
belt pack while all of the belt packs listen. Then each belt pack in turn “talks” back to the basestation with its
own information. Once all of this occurs the whole system changes frequencies and it happens all over again.
This all takes place so fast that it seems to the intercom user that his talk and listen paths are open all of the
time. The intercom user can talk and listen continuously without any interruption in either direction. We call that
full duplex.
Frequency Shift Keying – FSK is a simple, but robust method of modulation that allows Tempest to send all of
the data necessary for voice communication in the limited amount of time available. FSK is extremely effective
even in very high RF interference environments.
Redundant Data Transmit (2xTX) – 2xTX technology allows Tempest to send all of the voice communication
data twice, once each on consecutive hops. While this has the effect of halving spectral efficiency, it increases
performance significantly by dramatically reducing Effective Packet Error Rate (EPER). The loss of one packet
transmission in a harsh RF environment is common. However, because of the pseudo random frequency
relationship of the consecutive redundant packet transmission, the potential for loss of any single audio packet
(2 consecutive data packet transmissions) is dramatically reduced. In addition, each packet transmission is
sent out from one of two different antennas. This unique approach enables Tempest to utilize spatial diversity,
frequency diversity, time diversity and polarization diversity.
RF Guide
Lost Packet Concealment – Tempest’s advanced LPC technologies allows some of the audio packets to be
damaged or missing while still preserving the integrity of the audio that the user hears. Tempest utilizes an
A-CELP, Algebraic – Code Excited Linear Prediction voice compression and lost packet concealment scheme.
The result is that it requires more than one audio packet loss (at least four consecutive data packet losses)
before any interruption in audio quality occurs.
Keys
• Advanced technology is applied to create an extremely robust RF link
• FHSS concentrates power at any given moment in time to “burn through” interference
• 2xTX technology greatly improves system performance in virtually all environments
Tempest and 802.11b/g (Wi-Fi)
Wireless LAN technology comes in various forms or standards. The most common wireless network
technology is 802.11b/g or Wi-Fi. These wireless devices also operate in the 2.4GHz ISM band. 802.11b
devices utilize Direct Sequence Spread Spectrum (DSSS) and 802.11g adds Orthogonal Frequency Division
Multiplexing (OFDM) for greater speed. This DSSS technology is very different from the FHSS technology used
in Tempest wireless systems. DSSS spreads out the available RF power over a much wider area so that, at
any given point in the spectrum, the total power at that frequency appears to be much less than if FHSS were
being used.
There are a total of 14 Wi-Fi channels that may be used throughout the world. Only 13 of these are used in
most countries. Many countries, including the United States use only 1 through 11. Each channel is 22MHz
wide (versus 1.5MHz wide for Tempest’s FHSS technology) and most of the channels overlap each other which
prevents their being used in close proximity to other Wi-Fi devices. Channels 1, 6, and 11 are non-overlapping
channels and are the most commonly used Wi-Fi channels for that reason. When channels 1, 6 and 11 are
being used together in the same location they occupy much of the entire 2.4GHz ISM band.
RF Guide
The specific RF characteristics of a Wi-Fi channel vary depending on network data throughput at any given
moment. When the network has very little data moving through it the RF signal appears to be lower in power
and less dispersed. As data throughput approaches the maximum capability of the network the RF signal
appears to be higher in power and more dispersed. The worst case scenario, as pictured on previous page,
for interference from a Wi-Fi device is when the data throughput is very close to maximum. The good news is
that by nature of the way networks work, this doesn’t happen very often. Typically this type of extremely high
data throughput only happens when extremely large files are being downloaded or there is some other high
level, constant draw demand on the Wi-Fi device. Lot’s of users doing normal web surfing activities on a Wi-Fi
network do not produce maximum data throughput conditions.
Tempest’s patented FHSS/TDMA RF design allows it to work well even in the face of very extensive Wi-Fi
networks. The difference in perceived power on any given frequency, at any given moment in time allows
Tempest to “burn through” a Wi-Fi signal and be received on the other end. Just as importantly, it works the
other way too. Because of the greater spreading of the RF signal in Wi-Fi networks, Wi-Fi devices typically will
not see Tempest as a significant interference source and will maintain over 90% of their throughput even with
multiple Tempest systems present.
As with all RF systems, the most important factor to ensuring that both wireless systems work at peak
performance is to get enough physical distance between the two devices. If a typically powered Wi-Fi device
can be kept at least 50 feet (15 meters) away from Tempest components there is an excellent chance that
neither system will see any noticeable interference from the other. Of course, the more separation the better off
both systems will be.
Keys
• Tempest works well even in the presence of extensive Wi-Fi networks
• Differences in FHSS and DHSS help let both RF devices work along side each other
• Getting as much distance as possible between Tempest and Wi-Fi is best
Operational Frequency Band:
Tempest offers seven operational bands inside the 2.4GHz ISM band so that the user can select the frequency
band that is appropriate for the regulations and operational considerations of the location. It is the user’s
responsibility to select a frequency band that is legal for the country of operation. Legal 2.4GHz operation may
vary from country to country. Many countries allow full use of the 2400 – 2480MHz spectrum, but many do not.
Please check with your local RF specialist to ensure that you pick an operational frequency band that is legal
for your country.
RF Guide
Even in locations that allow full band operation you may wish to choose one of the limited operational
frequency bands. This may be the case if you would like to keep Tempest from operating in a given portion of
the spectrum to avoid a specific Wi-Fi device or some other interference source. Having said that, Tempest
works well even when collocated with Wi-Fi or other 2.4GHz devices, so using as much of the band as your
country of operation allows is usually the best idea.
The seven operational frequency bands available for Tempest are:
Choosing the lowest number band that is legal in the country for which you are operating, will usually produce
the best results. The lower the band’s number the more channels and spectrum available for Tempest to use.
This helps ensure that Tempest will have plenty of room to hop and avoid interference sources that may be
present in your area.
The first time a Tempest system is powered up you will be asked to choose an operational frequency band. It
is absolutely crucial that you select a band that is legal for your country of operation. If you are unsure of the
RF requirements in you area, please check with your local RF specialist to ensure that you pick an operational
frequency band that is legal for your country.
Keys:
• You must choose a frequency band that is legal for use in your country of operation
• Tempest has seven frequency bands to choose from
• You may choose a more restrictive band that avoids certain Wi-Fi channels if you wish
Network Number
The network number in Tempest is an RF setting that determines what hopping pattern will be used for
that particular system. It is important to note that the network number has nothing to do with the wired LAN
connection. There are 64 total network numbers or hopping patterns available for use. Network numbers
are numbered 0 – 63. Each hopping pattern has 43 frequencies available for Tempest to use. All 64 hopping
patterns use the same 43 frequencies. The only difference is the order in which those frequencies are used.
Selecting an operational frequency band other than band 1 (full band operation) will result in a reduction of the
frequencies used as the frequencies that are outside of the selected band will be ignored. The default, “out of
the box”, network number setting is 0. It is a very good idea to change this setting before getting started with
your Tempest system. Changing this setting is very easy and can help avoid unwanted interaction with other
Tempest systems that may also be operating on the default selection.
RF Guide
Keys:
• The network number sets the hopping pattern the system will use
• All 64 hopping patterns use the same 43 frequencies, just in different orders
• Changing the default network number from 0 to something else is a good idea
Lockout Key
The lockout key in Tempest is a unique identifier that allows multiple systems on the same network number
to operate without the belt packs getting confused as to which system they are on. Think of it as a ticket to a
show. Let’s say you have a ticket to the 9:00 showing. If you arrive at the correct theater and try to use your
9:00 ticket for the 6:00 show, you won’t be able to get in. That is how the lockout key works. You have to show
up at the correct theater (network number) with the correct ticket (lockout key) to be able to get in.
If a belt pack is on a given frequency at a given time and tries to communicate with a basestation that is also
on that frequency, it will only be granted access to the system if the belt pack has the correct lockout key. So,
in other words, a basestation and a belt pack must both have the correct combination of network number and
lockout key to be able to communicate with each other.
There are 256 total lockout keys available for use. They are numbered 0 – 255. There are 16,384 network
number/lockout key combinations. The default lockout key setting is 255. It is a very good idea to change this
setting before getting started with your Tempest system. Changing this setting is very easy and it can help to
avoid unwanted interaction with other Tempest systems that may also be operating on the default selection.
Keys:
• The lockout key helps keep belt packs communicating with the correct basestation
• A belt pack must have the correct network number/lockout key combination to work with a
basestation
• Changing the default lockout key from 255 to something else is a good idea
Basestation – Belt Pack Pairing
In order for a belt pack to communicate with a particular basestation, both the basestation and the belt pack
must have identical settings for Operational Band, Network Number and Lockout Key. These settings are made
in the basestation and can not be adjusted by the end user at the belt pack. Once the basestation has been set
up on a legal Operational Frequency Band with an appropriate Network Number and Lockout Key, each belt
pack must be paired to that basestation so the belt pack knows the correct RF settings.
A belt pack may be paired with multiple basestations and then quickly switched from one basestation to
another using Tempest’s iSelect roaming technology. This allows belt packs to roam across large and diverse
coverage areas without having to be reconfigured regardless of RF conditions.
Keys:
• Frequency band, network number and lockout key must be set at the basestation prior to pairing
• basestations and belt packs must be paired prior to use
• iSelect roaming allows users to move easily from one basestation to another
RF Guide
Antenna Placement
One of the most important factors in a successful RF system is the placement of the antennas relative to
the desired coverage area. Tempest uses a dual antenna diversity system. It is critically important that both
antennas be connected and properly placed at all times for best RF performance. Unlike older analog VHF and
UHF wireless intercom systems that had dedicated transmit and receive antennas, each Tempest antenna is
both a transmit and a receive antenna. This is very important to remember when setting up Tempest antennas
because this means that both antennas are necessary and equally important. Both antennas must be used and
properly placed at all times or RF performance will suffer.
Some important things to remember when placing Tempest antennas:
• Every antenna has a certain pattern of coverage for which it is useful. The patterns of both Tempest
antennas need to overlap in the desired coverage area to ensure best RF results
• Don’t point directional antennas in two different directions
• Don’t separate omni-directional antennas too far away from each other
• Both antennas are necessary and equally important. Redundant Data Transmit 2xTX, transmissions from both antennas must regularly reach the belt packs to have a robust, successful RF link
• Higher is almost always better when placing antennas
• Maintaining a direct line of sight from the basestation antenna to belt pack is the best possible antenna scenario
• The minimum acceptable application of this is to get the basestation antennas above head level
• In many cases, the best execution is to get the basestation antennas well above the desired
coverage area and point antennas directly down at the coverage area
• Centrally position omni-directional antennas in the middle of the desired coverage area
• Position directional antennas on the edge of the desired coverage area and point them across the area to be covered.
• Always make sure the patterns overlap
• Always keep antennas away from:
• Large metal objects. Stay at least two feet away from these
• Large containers of liquid. Most liquids are intense RF absorbers
• Confined spaces. Don’t set up antennas in rooms or areas that are closed in with very few RF
enter/exit points. Wide open spaces are good
Keys:
• Tempest antennas are both transmit and receive
• Both antennas are necessary and equally important
• Place antennas as high as possible with line of sight from basestation to belt pack
RF Guide
Collocated Systems
It is often necessary to locate several wireless systems together in a venue for a large production. Tempest is
designed to make this easy and effective. There are just a few important guidelines that must be followed to
ensure success.
Hopping Patterns – When operating multiple Tempest systems in the same location it is best to separate the
network numbers of each system by at least four numbers. For example you might use a network number of
1 on the first system, 5 on the second, 9 on the third, 13 on the fourth and so on for as many systems as you
have. You may start with any network number and move from there. 2, 6, 10, 14 is as good as 7, 11, 15, 19,
just as long as you have a separation of four numbers between each system.
Lockout Key – Lockout keys for different systems do not have to be unique as long as the network numbers
are different. None the less, it is a good idea to assign each system a different lockout key as a matter of
safety. Lockout keys do not have to be separated by a minimum number value like network numbers. Any
unique value will do.
Accu-Sync – Collocated Tempest systems should be connected via the Accu-Sync port whenever multiple
systems are being used together. This port synchronizes the RF transmit timing of all of the Tempest
basestations to avoid harmful desensing of receivers. Desensing occurs when one or more transmitters are
broadcasting while one or more closely located receivers are trying to “listen”. Desensing happens even
when the transmitter and receiver in question are not on, or even near, the same frequency. This affect is
extraordinarily harmful to wireless systems and must be avoided at all costs. Accu-Sync sends a very precise
timing signal to all basestations that are connected to the Base-Sync bus to control when those basestations
(and consequently their associated belt packs) transmit. This forces all of the basestations to transmit
simultaneously ensuring that there are no closely located transmitters that are active during the receive cycle
of any other basestation effectively eliminating desensing.
Antenna Location – The antennas of each individual Tempest system should be separated from every other
Tempest system’s antennas by at least 10 feet (3 meters) for best collocated system performance. Spacing of
less than this may be used with multiple Tempest systems, but it will not be ideal. All other antenna placement
rules still apply and should always be followed.
Under favorable conditions, including:
•
•
•
•
•
Little or no external interference
Accu-Sync connected between all systems
Appropriate antenna placement and spacing
Correctly set hopping patterns
Favorable physical environment
Up to a maximum of 10 Tempest 2.4GHz systems each with five belt packs, may be collocated with minimal or
no user perceived impact on system range or performance. Fewer systems will be possible with less favorable
conditions. More systems will be possible if the physical distance between Tempest systems is increased.
Keys:
• Up to 10 basestations and 50 full duplex belt packs may be used
• Network numbers should be separated by at least four numbers
• Accu-Sync should always be used when collocating Tempest systems
RF Guide
Putting It All Together
Tempest is designed to offer a wired-intercom feature set with the convenience, flexibility and freedom of
wireless operation. Tempest is fully compatible with all major 2-Wire and Matrix intercom systems and provides
a transparent, reliable RF interface to the wired world.
Tempest operates in 80MHz of spectrum in the 2.4GHz ISM frequency band. This band allows users to operate
with no license requirements and world-wide acceptance, making Tempest ideal for traveling shows and
rental houses. The benefits of the 2.4 GHz band are obvious, but there are great technical and operational
challenges created by a wide variety of technologies and users competing for clear spectrum in this band.
Tempest utilizes patented and proprietary technologies to ensure a robust and reliable RF link under a wide
variety of physical and RF environments including areas with heavily populated Wi-Fi networks.
Tempest utilizes a proprietary Frequency Hopping Spread Spectrum (FHSS) technology that has 7 US patents.
Multiple remote access is achieved by implementing Time Domain Multiple Access (TDMA) with Frequency
Shift Keying (FSK) modulation. An Algebraic – Code Excited Linear Prediction (A-CELP) voice compression
algorithm is used to reduce the bandwidth necessary for transmission and yet maintain the highest possible
voice audio quality. Additionally, this algorithm utilizes advanced Lost Packet Concealment (LPC) technology
which greatly reduces the effect of audio data packet loss (common in all RF transmission schemes) on
perceived audio intelligibility. The loss of one audio packet will be covered over by the algorithm so the user will
likely not even realize that there has been an interruption in audio data.
Tempest’s overall RF scheme is then dramatically enhanced with the addition of a proprietary Redundant Data
Transmit 2xTX technology that transmits all audio packet data twice, once each on two consecutive hops.
This technique reduces spectral efficiency by half, but greatly increases audio intelligibility by reducing the
Effective Packet Error Rate (EPER) significantly. The system transmits packet data every 5ms and then “hops”
or changes frequency. The sequence of frequency changes is controlled by a predetermined hopping pattern
which is optimized so that any new frequency has pseudo-random relationship to the last operating frequency.
This frequency relationship ensures maximum frequency separation between any two consecutive hops.
Because of this, if an interfering source is present in one area of the operational band, and interferes on one
hop, the next hop will likely be in a clear area of the spectrum with the best possible chance of transmission
success.
In a harsh RF environment, the loss of one packet transmission is common. However, because of 2xTX
technology the loss of any single audio packet (2 to 3 consecutive data packet transmissions) is reduced
dramatically. In addition Tempest’s 2xTX technology sends each packet transmission from one of two different
antennas. This unique approach enables Tempest to utilize spatial diversity, frequency diversity, time diversity
and polarization diversity.
Older analog wireless intercom systems often have problems covering extremely large areas or multiple
coverage locations. Tempest combats this challenge with iSelect On Command Roaming to allow users to
move from one area of coverage to another quickly and easily. The belt pack remembers the last 64 paired
basestations. The user can then easily select the desired coverage area with the push of a few buttons. This
allows Tempest users to control the operating basestation at any given time, regardless of RF conditions.
Wireless intercom systems are often used in high noise environments that require special design consideration
for proper operation. Tempest operates extremely well even at very high ambient noise levels. Tempest has
an audio dynamic range of greater than 94dB. This is over 40dB greater than other digital wireless intercom
systems in use today. This makes Tempest ideal for sporting events, concerts and other venues that typically
have high levels of unwanted ambient noise.
RF Guide
Patented FHSS/TDMA technology plus transmission redundancy and incorporating various diversity
techniques makes for an RF system that is more robust and reliable under greatly varying operational
conditions than any other RF communication system available today. Accordingly, Tempest displays better
operational range and much higher levels of interference and multipath fade rejection than other digital
wireless intercoms. This is extremely valuable in the demanding world of television and live production.
Tempest offers a host of features and technology to ensure that it performs well in virtually all environments,
virtually anywhere in the world, with virtually no licensing requirements, frequency coordination or fees. Unique
features, unmatched technology, and superior performance truly position Tempest as “wireless for the real
world.”
Tempest®
Tempest is manufactured by CoachComm and distributed by Clear-Com Communication Systems.
Clear-Com Communication Systems®
Americas & Asia Pacific: 850 Marina Village Parkway, Alameda, California 94501 USA. Tel: +1 510 337 6600
Europe, Middle East & Africa: 7400 Beach Drive, IQ Cambridge, Cambridge CB25 9TP UK. Tel: +44 1223 815000
www.clearcom.com
®Clear-Com and the Clear-Com Communication Systems logo are registered trademarks.
CoachComm LLC
www.tempestwireless.com
©2009, CoachComm LLC. All rights reserved.
Tempest® is a registered trademark of CoachComm LLC.
">