A Wireless Surveillance Camera - Realistic Benefits in Business and Residence

A wireless surveillance camera is one of the most sophisticated and practical types of surveillance camera to record and monitor occurrence in its area coverage and immediate surroundings. Residential and business establishments are secured by installing this advanced surveillance camera system to monitor any activities within the coverage of the camera. Installation of wireless camera system is convenient and applicable in different situations even during nigh time. It provides more flexibility to users because it can be easily accessed in remote locations to observe both indoor and outdoor environment.

This kind of digital video camera features radio transmitters to send images to its monitor and receive commands from its control system in remote sites. It is supplied with power from batteries rather than wired electricity making it more portable and handy. Camera users benefit a lot of ways from wireless camera for surveillance and security. It is imperative for homeowners and businessmen to employ the most practical and cheap measures in securing properties using advanced digital technology in camera surveillance.

The wireless surveillance camera has many functions and features that users can take advantage and benefit from it. It can be hidden from any places depending on the objective of the system owner. It can be placed in dome shaped installation which will look like room fixture. In homes, it can monitor possible intrusion of thieves and burglars. In the office, it can give reliable real-time images of employee activities. The wireless CCTV can be camouflage to hide its existence from the prying eyes of people. This will give a major advantage to users of this sophisticated camera system. Some systems have internal memory card for a compliant monitoring system.

The wireless camera has many advanced features that include night vision and motion detection capabilities for a more robust surveillance system. In low-light environment, images can be detected with a reliable technology in night time detection. This gives the best alternative for people especially business to monitor their areas during nighttime to complement its security personnel in guarding their premises. There are video cameras with motion detectors that trigger the system to automatically record the events in digital form.

Image monitoring can be done on live streaming or through a digital video recorder to capture images from remote wireless camera. Wireless camera systems are handy and practical to operate since most of these utilize computer software to operate the movement of camera as well as its other features like zoom lense, illumination, video clarity, and many more.

Another advantage of this surveillance is its wireless characteristics. Technical people as well as owners will be free from rewiring and unhooking cluttered wires. The system is powered by batteries to support the camera's other advanced features. Employing a wireless surveillance camera is the best alternative for businessmen and homeowners to deter criminality and unfortunate events using the best cost-effective and practical security system.

Home Security - Voice Alert System for Peace of Mind

For most people their home is their biggest investment. In 2006 the median price for a home is expected to be $231,000. And of course everyone has insurance on their house. Everyone has insurance on their car as well. But more people have alarms for their car than their home. How does that make any sense?

In the time it takes you to read the next four small paragraphs two more burglaries will occur in the United States. Remember this: property crime occurs every 3 seconds, a home burglary every 15 seconds.

Alarms can act as a successful deterrent. 90 % of police believe alarms deter burglary attempts. There are all kinds of alarms including expensive home security alarm systems monitored by ex-police officers. Silent, noisy, wired, wireless, door, window, motion, monitored, unmonitored-you name it and there is an alarm for it. Signage again is the key. Let burglars know they are in for a hard time ahead of time. The thing is alarms work.

A voice Alarm is a home-security system that is in any intruder in his own voice. This unique safety device can be used as a car alarm or used for any room in your home or office where you would any intruder in no fewer than six points would have been delivered.

The best systems have a wireless PIR sensors transmitters and a remote receiver / speaker base station. This system can be very beneficial for the user to record their own alertnotified in case of an emergency. The key applications in such systems include wireless drive away alarm, Residential and small business security, child monitoring, pool safety and home automation.

These alarm systems are efficient enough to send a signal 300 feet through walls and up to 1000 feet in open space. Voice alert alarm systems help users in case of an emergency and will notify them in any of the following examples:

a) When cars are coming up the drive away.

b) When children go inside your tool shed.

c) When intruders approach the front or back of your house or apartment.

d) As soon as someone enters your garage.

e) People are approaching to the front door.

f) As soon as you parked boat or vehicle is boarded.

g) Security in small business applications.

h) A child gets to close to a swimming pool.

The systems are wireless, waterproof, dependable, affordable, and easy to to install.

The odds are very good that you have read this, because in some way crime has touched your life or you want to be proactive and protect yourself, family, home, shop or from the ravages of crime. This is the first step.

Wireless Camera Security Systems

Every homeowner knows how important it is to protect your home and the belongings. To go to sleep in a home without a security system in place or to leave a home unattended that has no form of security is sending a clear invitation to the criminal mind. Criminals have become more than just calculating; they have become opportunistic and just by presenting the opportunity for something to be stolen is incentive enough for some.

This increasing need for home security has created an abundance of reasonably priced products. The home security business has gone from something only a wealthy rock-star could consider to something every home needs to remain safe. That is one reason why security systems previously only available at great cost to corporations and businesses have been made affordable and accessible to the average homeowner.

Wireless Home Security
Wireless security systems offer the average homeowner savings on costs, the option to install the system by themselves and the option to relocate the system easily if need be. With hard-wired security systems the wires need to be run through the walls and this often requires the handiwork of a professional at an large increase in price. Wireless systems are much cheaper on the other hand, because they can be installed by the average do it yourselfer as there are no wires to install.

Your basic wireless home security system consists of a central device which receives signals from any number of sensors placed in strategic places around the home. The sensory transmitters are placed at doors, windows and other possible entry points. Each monitors whether that entry point has been opened or tampered with. If anything happens to make the sensor go off, it will send a signal to the central device and an alarm will be sounded.

Residential Security Camera
You can also link some of these wireless indoor systems to wireless outdoor systems and wireless cameras. This offers added protection in that your outdoor area is under surveillance as well. Cameras in and out of doors can also have infra red settings so that you can keep an eye on everything at night.

A home security wireless camera can monitor your home continuously. Its view can be seen over a computer or a television. This allows real time viewing of your property from a place of safety or even a remote location like a hotel room. It can be linked up to video recorders, to your home computer, or even over the Internet. This has already proved to be an excellent tool. It has been known on the rare occasion for a witty home owner to call the police while monitoring their house when on vacation abroad, only for the thieves to be caught red-handed!

Remember that no security system can offer you a 100% guarantee that it will stop all intruders from invading your home and making off with cherished possessions. The best thing to do is choose a system that will do the best job. It is important not to be a miser when it comes to picking out your home security system but instead set a realistic budget and stick to it.

MP3 FM Modulator Pitfalls - The 3 Biggest Mistakes People Unknowingly Make and How to Avoid Them

Many people unknowingly make the mistake about MP3 FM Modulators and mix them up with FM Transmitters. Even though they are very similar they can be very different and give you very different results. We will attempt to help clarify the difference between the FM Modulators and FM Transmitters in this article.

FYI, for the sake of simplicity we will assume that you are going to use this in your car and when we talk about FM Transmitters we are referring to a personal FM Transmitter you can buy off the shelf not a big commercial one or a homemade one.

Mistake #1 Installation Complexity

Most people do not realize that if you go with a FM Modulator instead of a FM Transmitter that you will be required to install it next to the FM Radio. This means you will have to pull out your car's FM Radio and hard wire it into your car's electrical system plus mess with your car's audio system.

This is not only time consuming but you can easily ruin your car's electrical and audio setup as well as potentially get yourself hurt. That is why most hire a professional to install a FM Modulator but that will cost money which could end up being more than the cost of the MP3 Player, Modulator and FM Radio combined.

Mistake #2 Transmitting

The second mistake people make about FM Modulators is they do not realize that the reason it needs to be close to the FM Radio is because it is transmitter the signal from your audio source, which in this case is your MP3 Player, to the car's FM Radio.

And since a FM Modulator typically only goes a few inches or a foot or two are best it needs to be very close to the FM Radio which requires the installation process mentioned above.

Mistake #3 Frequency Options

Third mistake most people do not realize when going with a FM Modulator is the number of frequencies you can select from. Since manufacturers know that you will not be able to change the frequency once it is installed they usually only give you one frequency to pick from or a few at best.

What that means for you is you have to either pick a frequency that is not on the public FM Band of 88.0 to 108.0 such as 87.7 or 87.9 FM for example or you will have to hijack a frequency that is on the public band and hope you do not run into a commercial station trying to broadcast on that frequency as well.

So how do you avoid making those 3 big mistakes?

Very simple if you want to broadcast the audio from your MP3 Player to your car's FM Radio (or any radio for that matter) you will want to buy a GOOD FM Transmitter. I say good because there are so many out there that just flat out stink. Either they don't go very far or the audio quality is just not acceptable. FYI, you can click on the links below to see a good FM Transmitter to consider.

So let's just assume for a moment that you picked a quality FM Transmitter. With it, you can use it not only in your car but also in your home, office, etc. if you wanted to. Plus you can easily power it without having to hard wire it to your car's electrical system. And you can plug in your MP3 Player without dealing with the car's audio systems setup. Finally, if you pick the right kind of good FM Transmitter you can also broadcast your other audio sources like your satellite radio, home stereo, computer and even your TV.

This way you can avoid having to deal with the cost and time of installation and hard wiring as well as possibly screwing up your car's electrical and audio systems. Plus you can transmit further than a modulator and on more frequencies so you won't have to compete with commercial radio stations.

The Need for Setting up Nanny Cams

Your child is your most precious asset and you would always wish that your baby receives the utmost care at all times. This is just what you expect the nanny to offer to your child too. The nanny or full time babysitter is the person who is entrusted with the task of taking care of your most loved belonging. Hence, you would perhaps like to make sure that the person is sincere about the responsibilities handed to her. It is for this purpose that you may consider in-home surveillance system (nanny cams) to be set up at your home for monitoring the activities of the nanny (child care provider or home care giver).

Why set up nanny cams?

There may be the suspicion regarding the nanny being neglectful in her duties or even abusing the child under her care. In such case the offence or innocence of the suspected nanny can be established in the best manner with the help of recordings made by the nanny camera or nanny cam. The nanny cams may be available in various forms. A teddy bear used for playing by the child may house it. Even a potted plant may have it concealed within it in a skillful manner. There are generally to be found built in wireless transmitters within nanny cams using which the video pictures taken are transmitted to receivers of recording device kept hidden in some other room.

Rightfulness of setting up nanny cams

Some feel it rightful and much needed to install the nanny cams as a means of addressing their worries and concerns about their little ones' care. However, others are of the opinion that the installation of nanny cams is some sort of invasion of privacy. The child care givers need be apprised about the installation of nanny cams while the setting up is taking place as it is a question of trust and feeling of deception.

The setting up nanny cams seem justified in the way that they certainly ensure peace of mind and confidence in the entrustment of child care at the hands of nannies. Besides, it is not illegal to capture pictures or images of activities at one's home for monitoring purpose. There can, however, be restriction on recording of speech without a person's consent. So, it is fine to address the need for in house surveillance especially with regard to nannies caring for children with the help of nanny cams being installed.

ITFS, MDS, MMDS, and BTA History

The Channel Assignments

In 1963, the frequency band 2500-2686 MHz was reserved to educational institutions for over-the-air transmission of instructional TV programs. Transmission was point-to-point, for example, campus-to-campus or campus-to-hospital for continuing education needs. Hence the name: Instructional Television, Fixed Service (ITFS). The power authorized (up to 100 watts) allowed transmit/receive separations of up to 30-40 miles.

In 1972, commercial operators were permitted to use the coexisting commercial band 2150-2162 MHz for over-the-air pay-TV transmissions to rooftop antennas on apartment buildings and private homes and for business data transmissions. Transmitters were similar to those for ITFS service, and the range of these installations was also 30-40 miles. The transmitter site was centered in the coverage area, usually a city, on a preexisting tower or atop a tall building.

The antennas were usually omnidirectional to reach all subscribers in the circular coverage area. The signal was intended for distinct subscriber locations rather than for anyone who wanted to pick up the signals (as in the broadcast services). Therefore the new service was named Multipoint Distribution Service (MDS). This service was the beginning of what we now know as "Wireless Cable". MDS was conceived as an alternate or supplement to conventional cable television (CATV). It was more successful in areas not covered by CATV. In areas where both services were available, it was severely challenged: it could offer only one or two TV channels versus the dozens of channels offered by CATV. Hence, after the novelty of MDS wore off, MDS revenues declined. Clearly, one remedy was to use more channels, and the commercial wireless operators eyed with interest the lightly used ITFS channels reserved for educational purposes.

MDS operators and potential MDS operators filed a Petition for Rulemaking to permit commercial use of some of the ITFS channels. As a result, in 1983 the FCC reallocated eight of the ITFS channels (identified as Groups E and F) for use by commercial over-the-air pay-TV operations. The idea was for each market to have two licensees, each of whom would have four channels. Since this allowed simultaneous broadcast of many more channels than existing MDS, the newly allocated channels became Multichannel Multipoint Distribution Service (MMDS). Many MDS operators have acquired MMDS channel licenses and, in some cases, newly licensed MMDS operators have acquired older MDS operations. Existing ITFS licensees using the E and F channels were not displaced at that time, although the rules permit the MMDS licensee to pay all costs and relocate such a licensee to an alternate channel if one is available.

Almost simultaneously, the FCC allocated three ITFS channels (in Group H) to the relatively new Operational Fixed Service (OFS). This was envisioned as a point-to-point transmit/receive service primarily for the transfer of business information. However, at once MDS and MMDS licensees in large numbers began to acquire licenses for the OFS channels in their markets and use them for one-way analog video programming. Since 1998, the FCC has considered these H channels (H1, H2 and H3) MDS channels.

For purposes of describing operations, we should consider the MDS, ITFS and MMDS services technically identical. For those interested in the FCC's channel assignment plan, it is spelled out in Appendix A of LBA Technical Note 115.

The Cable Television-Type Operation

Historically, wireless cable has been a one-way analog video service. "One-way analog video service" means that it has operated much like commercial broadcast stations, sending one "video stream" such as NBC or CNN over each channel. Viewers used downconverters to step down the transmissions from 2500 MHz frequencies to 65 MHz, and then they could watch the programs on traditional television sets.

The MDS operator who had a license for one channel was limited to offering one channel of programming. The MMDS operator who had a license for four channels was only slightly better off, because four channels were available to cable customers. By aggregating all the MDS and MMDS channels in a market, the consortium of licensees could operate a wireless cable system with as many as 13 channels. Although this may have been viable in the early 1980s, by the 1990s the market demanded dozens of channels from a cable service. MMDS operators still desired use of the ITFS channels to meet this need.

ITFS operators tended to use their channels for long-distance education during regular working hours, and the channels lay fallow on nights and weekends when the wireless cable demand for programming was the greatest. The FCC had placed a provision in its rules that permitted an ITFS licensee to lease its "excess channel capacity". This meant that as long as the ITFS licensee used its channels for educational purposes for a minimum of 20 hours per week per channel, it was free to lease the channel for commercial uses the rest of the time. The FCC rules contain restrictions on the Airtime Lease Agreements to prevent a naive educator-licensee from giving away too many of its rights, but the use of these agreements permitted an explosion in growth in ITFS operations.

The up-front cost to the educator to construct a four-channel transmission system and install receive equipment in the schools to be served could run into six figures. Most school systems did not have this kind of money available for an untried technology. So, under the leasing rules, it worked like this: the commercial wireless cable operator in the market paid all the up-front application costs for legal and engineering work to prepare an application to the FCC for a license to be held by the school. The wireless cable operator purchased the equipment, built the transmitter tower, installed the receive sites at the schools and built a studio. The operator worked with several educators in its market, so that most available channels were used, and all shared the transmission facility. Each educator was a licensee in its own right but had a contractual agreement to lease its excess channel capacity back to the wireless cable operator. The educator got the license without having to spend money, had the use of the studio and equipment built by the wireless cable operator and had use of the service for many hours each week. In addition, it received monthly lease payments from the wireless cable operator for use of the channels on nights and weekends. This arrangement is a classic example of business and educational entities cooperating to the good of both. This new, untried technology became a moneymaker for the school in addition to allowing long-distance education to become a reality. And, the wireless cable operator now had access to as many as 33 channels through the use of the ITFS, MMDS and MDS bands. Thirty-one of these channels are immediately adjacent to each other in the 2500 MHz band, and two are at 2100 MHz. The channels designated as the A group, the B group, the C group, the D group and the G group are the reserved educational channels. The channels designated as channel 1, channel 2, the E group, the F group and channels H1, H2 and H3 are available for commercial operators.

Commercial Use Of ITFS Channels

In 1991, the FCC decided to permit wireless cable operators to use ITFS channels for their commercial operations under certain rather strict conditions. A wireless cable operator is defined as one who holds a conditional license, a license or a lease on at least four MDS channels or has an unopposed application pending for at least four MDS channels. The wireless cable operator may request permission to operate on ITFS channels if there are no additional MDS channels available in the market and there are at least eight remaining unused ITFS channels available for future ITFS use in the community. Entities eligible for ITFS licenses may request from the FCC that they be given access to the commercially used ITFS channels for up to 40 hours per week per channel. These conditions are spelled out in 47 CFR §74.990 through §74.992.

BTA Auctions

In the early 1990s, the U.S. economy was down and Congress had discovered the dollar value of the spectrum licenses the FCC granted. It mandated that licenses in most services be granted to the highest bidder. This decision greatly changed the wireless cable market.

In 1995 the FCC rules were changed to specify that all remaining MDS licenses would be auctioned. The decision was made to divide the country into geographic areas, each of which could then be auctioned off. The Rand McNally Basic Trading Area (BTA) divisions were selected, with the addition of a few BTA-like areas to complete coverage of the United States and its territories. Each BTA or BTA-like area is a collection of counties. The physical size varies greatly although they tend to be smaller in the more densely populated east and on the west coast and they tend to be larger in the more sparsely populated areas of the western United States.

What the FCC was granting in its BTA license was the right to use any of the 13 commercial channels (see above for a list) anywhere in its BTA if it could do so without causing interference to any pre-existing licensee or to any adjacent BTA. These pre-existing licensees are called "grandfathered" licensees and their licenses remain in effect and are eligible for renewal at the end of their license term. The grandfathered licenses have a protected service area, which is a 35-mile circle, centered on the transmitter site in use in 1991 when the protected service area rules were finalized. This area may overlap more than one BTA and requires protection from all nearby BTA licensees. The interference protections required for these grandfathered stations is more generous than that provided to BTA licensees, as well. The BTA licensees are protected from interference at the boundary of the BTA, but the irregular shapes of the BTA boundaries are not reflective of real-world propagation conditions and make service to areas at the edge of the service area more difficult.

The MDS auction occurred from November 1995 to March 1996 and yielded $216.3 million. The auction funds were not allocated to the FCC; they went directly into the U.S. Treasury. A total of 493 licenses, one per BTA, were awarded to a total of 67 licensees.

Two-Way Digital Operations

Recently the wireless cable technical standards have been relaxed to permit a one- or two-way digital service. This broadens the potential use of the spectrum. A wireless cable operator may use digital compression to place additional "video streams" in the same number of channels, in effect increasing its channel capacity without using more bandwidth. It may use the response channels for pay-per-view ordering. Or, it may use the two-way service for high-speed wireless Internet or other data transfer applications.

This change in the rules was the result of efforts by a consortium of wireless cable operators, consultants, attorneys, ITFS licensees and equipment manufacturers. This group got together and created a plan to permit two-way use of the wireless cable frequencies. They determined minimum operating standards the equipment could tolerate, interference standards with which operators could live, an expedited processing method and frequency sharing rules the educators and wireless cable operators both found fair. Then the entire package was turned into a proposal at the Commission. The FCC granted substantial portions of the package without change. The initial filing window for two-way applications was in August 2000. Many of these applications have been granted and are being constructed.

In a two-way digital wireless cable system, each subscriber has not only a receiver but also a transmitter. These transmitters have low power and send a response back to the response station hub. The response transmission is called the upstream transmission, and the signal from the main transmitter is called the downstream transmission. Originally the system required a directional response transmit antenna oriented directly at the response station hub. However, that meant only trained service personnel could do installation. In an effort to reduce operational costs, some wireless cable operators petitioned the FCC to permit low-gain omnidirectional response antennas to be used so users could install the equipment themselves. This request was granted.

Booster stations

In addition, the FCC rules permitting booster stations have been relaxed, so an operator may more easily add supplemental transmitter locations to serve areas that were previously out of reach. Boosters might be used on the downstream component of the two-way system, or the transmitter frequency of the one-way system. This permits more "cellularization" of the market to improve coverage with multiple transmitters.

Line-of-sight operation

Traditionally, the antennas used for wireless cable have required a line-of-sight (LOS) path between transmit and receive antennas. This limits service providers to putting the hub antenna at a very high central location, often 500 feet above the surrounding area. They must also use a high transmit power to reach the 35-mile limit of the coverage area. In addition, the customer's antennas must often be mounted at the highest point on the rooftop, which is unsightly from the consumer's point of view and may also be in violation of restrictive covenants.

Even with these restrictions, the usable service area is limited to portions of the authorized service area. Any building behind, or "in the shadow of", a larger structure cannot receive service. This larger structure can be a hill or a building or even a water tank. On a nationwide average, LOS service is available only between 30% and 80% of an authorized service area.

In addition, using a very tall high-powered transmitter creates interference problems in adjoining areas. Cooperation between operators in neighboring areas is necessary to resolve the interference issue. Often the same company will have operations in adjacent markets, so it is creating interference problems for itself. Use of a tall, high-powered hub antenna limits the operator's ability to re-use the same frequencies in its market, as well.

Non-line-of-sight operation

To overcome these problems, several manufacturers are working on technology to permit non-line-of-sight operation. This is defined as reliable operation in the absence of a clear LOS path. Although the signal is not expected to penetrate large terrain obstructions, it can be expected to penetrate walls and foliage and bend around buildings. The signal should be robust enough to operate in an environment of multipath fading and in spite of some obstruction and interference. The goal is to achieve coverage of 90% of the authorized service area. Non-LOS (NLOS) paths are not as efficient as LOS paths, but they permit use of shorter, lower-powered transmitters. This allows more re-use of the frequencies.

The areas that have obstructed paths still receive a signal, but it is a weak signal. The NLOS areas receive signal that has traveled along paths that reflect (bounce off an obstruction) or refract (bend as they pass over an obstruction). There are any number of such paths that start at the hub site and end at the customer site. The signal received along any such path is weak, or attenuated. In addition, the paths have different lengths, which means the time delay along them varies. Intelligent customer premises equipment can use error-checking routines to combine the signals from the various paths and correct the flaws in the data sufficiently to have a usable signal. There are ways to predict the attenuation and the multi-path effects, and these calculations indicate the path loss to be expected from a NLOS path. The wireless cable operator can include this loss in its planning, and thereby permit NLOS operation.

Self-Installation of Customer Premises Equipment

One of the larger expenses in a wireless cable operation is providing and installing equipment on the customer premises. As long as the requirement exists to "fine-tune" each installation to optimize the LOS, trained installers must be dispatched for each new subscriber. As wireless cable systems are designed to permit higher loss budgets, customers can install equipment themselves. The goal is to have universally compatible equipment that is available at consumer electronics stores, which consumers can purchase and install themselves. The DirecTV model is the one desired by the wireless cable industry. Consumers buy the DirecTV equipment themselves and most install it themselves. Professional installation is available for a fee if the customer wishes. If this could be accomplished in the wireless cable service, an operator's costs would be greatly reduced.

Glossary

Airtime Lease Agreement. The agreement between the educator and the commercial wireless cable operator to permit the wireless cable operator to use the educator's frequencies during certain times of the week. These agreements are discussed in 47 CFR §74.931.

Booster Station. An additional transmitter used by the wireless cable operator to repeat the signals of the MDS station or originate MDS signals. Booster stations are intended to augment service in areas that are poorly served by the main transmitter.

BTA. Basic Trading Area. A Rand-McNally designation for a geographical unit made up of one or more counties, which Rand McNally has determined have some characteristics in common.

BTA License. A license issued to a wireless cable commercial operator. The BTA licenses were auctioned in 1995 and 1996. A BTA license authorizes an operator to use all of the commercially available channels within a BTA as long as no interference is created to any authorized station existing at the time of the auction.

Cable Television (CATV). A subscription offering of multiple television channels available from a single entity, but CATV usually indicates traditional wired cable.

Customer Premises Equipment (CPE). The system of antenna, transmission line and downconverter or modem installed at the customer's site to permit use of wireless cable broadband technology.

Excess Channel Capacity. Any time during the week that the ITFS licensee's channels are not needed for educational activities. The spectrum used to lie fallow during these hours; now FCC rules permit leasing the use of the channels during this time to commercial operators, creating revenue for the schools and increasing spectrum efficiency. See Airtime Lease Agreement.

Federal Communications Commission (FCC). The federal agency mandated by congress to regulate use of the radio spectrum.

Instructional Television Fixed Service (ITFS). The frequencies set aside for use of educational entities in the course of their educational mission. The channels are six MHz wide each. The reserved channels range from 2500 MHz to 2686 MHz. The service is "fixed" in that the transmitter and receive sites are identified to the FCC and specified in the license. The purpose of this service is to permit long-distance learning. For example, a hospital may be a licensed receive site and use the service for continuing education. The FCC rules for ITFS stations may be found in 47 CFR §74, Subpart I (which begins at §74.900).

Line-of-Sight (LOS). A clear, unobstructed microwave path exists between transmit and receive antennas. Microwave LOS propagation requires not only that the direct path between the two antennas be unobstructed, but that an area around the path also be clear. This area is sausage-shaped and surrounds the direct path in all three dimensions. It is larger in diameter (extends farther from the direct path) in the center than at the endpoints, and varies in diameter with frequency and with the length of the total path. It is called Fresnel zone clearance after the French mathematician who developed the formula.

Multipoint Distribution Service (MDS). A domestic public radio service rendered from one or more fixed transmitting sites to multiple receiving locations. These channels are six MHz wide each. An MDS licensee may operate either as a common carrier or as a non-common carrier, but must specify such to the FCC. The frequencies originally assigned for this service are in the 2150-2162 MHz band. The frequency bands 2596-2644 MHz and 2650-2680 MHz were added when the need for more spectrum became apparent. The FCC rules for MDS stations may be found in 47 CFR §21, Subpart K (which begins at §21.900).

Multichannel Multipoint Distribution Service (MMDS). An MDS service utilizing multiple transmitting channels. The FCC rules for MMDS stations may be found in 47 CFR §21, Subpart K (which begins at §21.900).

Response Station. In a two-way digital wireless cable system, the customer site is the response station. It communicates back to the wireless cable system, communicating directly with the response station hub.

Response Station Hub. A fixed facility operated by the licensee or the wireless cable operator, for the reception of information transmitted by one or more response stations. The response station must use digital modulation with uniform power spectral density.

Wireless Cable. Use of microwave frequencies to aggregate multiple channels of video programming, which are then offered to subscribers. The use of microwave frequencies instead of wires makes it much easier to serve homes in less-dense areas. In addition, the cost of wiring is eliminated.

Why Synchronous For Wireless

Why Not Asynchronous?

To understand the benefits of a synchronous protocol, it helps to first look at the disadvantages of an asynchronous protocol. When a node using an asynchronous protocol such as 802.11 wants to transmit a frame, it normally will simply transmit the frame after it senses the channel is idle for a period of time (which is called Carrier Sense Multiple Access, or CSMA). If a collision is determined, due to the lack of an acknowledgment frame, the frame is re-transmitted after waiting an amount of time that increases exponentially for each retransmission. In order to minimize the impact of a collision and to maximize the chance of a successful reception of the data frame, 802.11 includes an optional collision avoidance (CA) function where a short Request-To-Send/Clear-To-Send (RTS/CTS) exchange is first performed, which causes devices overhearing those frames to not access the channel for a period of time. This collision avoidance function may be beneficial in some situations, but it comes with a large overhead and introduces problems of its own, and the impact of these problems is greatly increased in a long-range outdoor system. Some of the problems associated with carrier sensing (CSMA) and collision avoidance (CA) protocols include:

Acknowledgment Overhead: This is compounded over long distance links due to propagation time.

Exponential Back-off: This is compounded in outdoor networks, where re-transmissions are common due to interference, which causes latency to increase exponentially.

"Hidden Nodes": This is a classic problem with 802.11 CSMA, where carrier sensing at the transmitter does not sense interference at the receiver. This is greatly compounded in outdoor networks, where obstructions and long distances between the transmitters normally results in them not being able to hear each other.

"Exposed Nodes": This is a classic problem with 802.11 CA, where the RTS message between a transmitter and receiver causes other potential transmitters to become idle when they could have transmitted successfully to a different receiver. This is greatly compounded in a mesh network, where there are normally many active receivers.

CA Overhead: The collision avoidance overhead due to the RTS-CTS-Data-ACK exchange requires 4 propagation times, which results in large overhead on long-distance links.

CSMA Failures: In a small office or cafe, all stations can normally hear each, which allow them to properly carrier sense and avoid collisions. In an outdoor wireless network, many stations can not normally hear each other, resulting in collisions that cause nodes to experience exponential back-off.

Ad-hoc Architecture: When connecting to an access point in a small office or cafe, all communications occur between stations and the access point (which is called infrastructure mode) and not directly between the stations. This means that most of the transfers do not collide, because all the downlink transmissions from a single device, the access point. In a mesh network using the ad-hoc mode or infrastructure mode, there are many transmitters and receivers simultaneously, and transfers can all collide.

Injustice: Another classic problem with 802.11 MAC layer isunfairness, and the problem greatly increases in outdoor networks. Due to the increasing back-off during retransmissions, nodes with fewer retransmissions are more likely to gain access to the channel than nodes that are retransmitting. Additionally, nodes that sense the channel becoming idle earlier are more likely to get access to the channel, and over long distances this results in unfairness to some nodes due to their location.

These problems are basic issues with asynchronous protocols such as 802.11, and all of these problems are drastically increased in outdoor wireless networks. Most people have experienced performance problems related to these issues in offices or cafes, but in outdoor mesh networks the impact of these problems is greatly increased, sometimes resulting in a complete collapse of the MAC layer.

Why Synchronous?

The most obvious reason to choose a synchronous protocol for an outdoor wireless network is to coordinate communications over large coverage areas. Scheduling transmissions not only enhances the efficiency of spectral utilization but also enhances quality of service (QoS) through latency controls, rate control, and traffic prioritization. There are some crude ways to implement scheduled transmissions without being synchronous, such as by simple polling. In fact, 802.11 includes an optional Point Coordination Function (PCF) that uses polling (and 802.11e extends this functionality in the optional Hybrid Coordination Function). In addition, 802.11 also contains some features synchronous in its basic specification, in particular, its timing (TSF), the unit set up at regular intervals, their watches, which can then be used by functions such as power, allowed , unless a machine of sleep can wake up periodically at the right time to see if there are no data for them. However, there are many reasons not to consider a synchronous protocol 802.11. Some featurestraditionally associated with synchronous protocols, such as WiMAX or SkyPilot's SyncMesh(TM) protocol, include:

Contention-less Data Transmissions: 802.11's base Distributed Coordination Function (DCF) normally puts data in contention, meaning that multiple nodes may transmit simultaneously. WiMAX and SyncMesh schedule data transmissions within time slots, avoiding the contention of data, allowing more bounded latency.

Ranging: DOCSIS (the cable modem standard), WiMAX, and SyncMesh all include a time ranging function, which determines how far apart nodes are in order to compensate for RF propagation at the speed of light. This maximizes efficiency, since inter-frame spaces then do not have to allow for the time of the RF propagation. Synchronous protocols that do not support ranging suffer from this overhead and polling protocols pay the propagation penalty twice. While the speed of light is normally considered fast, on long distance Links of 10s of microseconds start to add up, especially in times of decreasing the transmission to higher bandwidths and modulations.

Time Magazine Scholarship Slots: synchronous nature SyncMesh offers the possibility of granting slots applicants. This means that the nodes may be granted extended rights to communicate in a specific increase time efficiency. asynchronous protocols do not offer this. Periodic time slot grants are useful in providing upper classes ofservice for applications like Voice over IP (VoIP).

Clock Precision: The features of a synchronous protocol benefit from very precise clocks, which means continually adjusting for phase between time sync messages (or signals from an external clock source) or using very frequent sync messages (SyncMesh performs the former since it is more efficient).

These advanced MAC features are just some of the benefits of using a synchronous protocol, but there is another equally important, if not more important, reason to use a synchronous protocol for broadband wireless mesh - to dynamically point antennas. One of the most effective tools an RF engineer uses to improve a wireless link and to minimize a link's impact on others is the use of directional antennas. The benefits of directional antennas include:

Increased link budget (both on transmit and receive), resulting in higher modulation and longer range

Decreased interference susceptibility from external sources

Decreased interference to other systems

Increased power due to point-to-point regulations in many countries

However, the challenge with using directional antennas is just that - they are directional, which requires manual pointing and alignment. In mesh networks, it is advantageous to have 360° omnidirectional coverage. 360° coverage from every node provides easy installation, maximizes redundancy, and avoids expensive and time-consuming system engineering of the mesh. To provide a node with 360° coverage using directional antennas, multiple antennas are needed, and as the gain of the antennas increases the number of antennas needed to provide 360° coverage also increases. This basic relationship applies no matter what antenna technology is used, from fixed sectors to beam-forming arrays - each of these antenna designs focuses RF energy, and as the antenna gain increases, the RF energy is more focused, decreasing the coverage angle. And while some advanced beam-forming techniques do not use fixed antenna sectors, the RF energy is still focused in a particular direction, so the beam direction needs to be varied in order to provide 360° coverage. So, most 802.11 mesh networks with directional antennas use manual pointing, where 360° coverage is not provided, and the network must be engineered link-by-link. There has been some research around dynamically pointing antennas with 802.11, but its asynchronous nature prohibits antenna pointing coordination. One challenge with an asynchronous protocol is that some of the transmissions need to be made with omnidirectional antennas (such as omnidirectional Request-To-Send messages), since transmissions are not naturally pre-coordinated. While such a method may allow for higher modulation transmission of the actual data frames, it suffers from decreased range, increased interference, and increased overhead due to the coordination (the latter can be very significant in an outdoor wireless system due to high modulations and the speed-of-light propagation). Alternatively, an asynchronous system could simply use a directional antenna only for transmissions, and use a separate omnidirectional antenna for receptions. The challenge here is that interference is an issue with the receiver, and an omnidirectional receive antenna neither increases the desired signal nor decreases the interference or noise. So, range and link modulation are limited due to the lack of receive antenna gain. Additionally, when only a single side of a link uses a directional antenna, it is not normally classified as a point-to-point link, and many regions limit the effective output power of the link. By using a fully synchronous protocol, such as SyncMesh, where every communication is coordinated (even bandwidth request opportunities and network entry points), antennas can be pointed on both transmit and receive. This provides all of the benefits of a system consisting entirely of point-to-point links, while still providing the redundancy and simple installation of an omnidirectional system. While these benefits are significant, there are some challenges around creating a fully synchronous mesh protocol. To summarize so far, there are two primary reasons to use a synchronous, scheduled protocol within a mesh network: MAC layer coordination and to point directional antennas. Regarding the latter, to avoid the challenges of dynamically pointing antennas, some multi-antenna systems use a separate radio for each antenna (or subset of antennas). This has several problems, with the most obvious problem being cost. Even though there is now the availability of inexpensive 802.11 radios, these radios have many hidden costs due to:

amplifiers
increased processing power and processor interconnect
increased node size
increased power consumption

However, there is a bigger problem with using multiple radios - self-interference. Even if the radios each use separate frequencies and employ guard bands (which is impractical due to the limited number of channels in many frequency bands), all radios interfere on some level. This can be seen by looking at an 802.11 radio's published adjacent channel rejection values, which is basically the amount of interference from communications on an adjacent non-overlapping channel. The Problems caused by this self-interference characteristics are amplified by the Outdoor Wireless, as a high level of foreign interference and signal reception due to weak links in the long and high levels of obstruction. For matters of cost and limited availability of a limited number of radio channel is sometimes used. To use some systems of 2 or 3 radios per node. However, this means a reduced number of radio, a small number of antennas, which means very low profitantennas are used, or 360° coverage is not provided. Both of these restrictions are a large problem for an outdoor mesh system. To mitigate the interference issues, the most obvious solution is to provide high levels of isolation between the radios and between the antennas. Traditionally, this would mean expensive filters and large amounts of physical shielding which is expensive and increases node size. However, it is impractical to cost effectively provide a sufficient amount of isolation in a mesh node, given typical outdoor wireless scenarios where the received signal may be under -90 dBm while the transmissions might be at +30 dBm. Adjacent, or even alternate, channel rejection along with filters and physical isolation are not enough to provide anywhere near the level of isolation required. So, interference between the radios is not addressed, and results in decreased link modulation and reduction in link range, which are the two main reasons one would use a directional antenna in the first place. Another general technological issue with using a radio per directional antenna is that such a system can't take advantage of steerable (adaptive beam-forming) antennas. Steerable antenna technology allows an antenna's pattern to be electronically adjusted, so a radio per beam cannot be used since there are no fixed beams. All of these issues can be addressed by using a synchronous protocol to coordinate all transmissions so that a single radio can be switched among many antennas (or between beam-steering weights). And even though a single radio architecture may not seem to have the capacity of a multiple radio architecture, a multiple radio system cannot take advantage of additional radio capacity due to self-interference. And, the real bottleneck of a mesh network is almost always at the bandwidth injection point (gateway), which means the use of multiple radios in the majority of nodes in a mesh network is wasted money.

Why Not Synchronous?

We've analyzed the benefits of synchronous protocols and the disadvantages of asynchronous protocols in outdoor wireless networks, but what are the disadvantages of using a synchronous protocol? Here are a few disadvantages, and potential solutions:

Clocks need to be synchronized: Devices participating in a synchronous protocol obviously needed synchronized clocks. This can be provided in several ways, including external clock sources such as GPS or over-the-air clock synchronization. SyncMesh uses a combination of the two, which leverages the accuracy of GPS clocks with the low cost of over-the-air synchronization.

Clocks need to be very accurate: This usually requires expensive clock crystals that are accurate over a wide temperature range. SyncMesh provides an extremely accurate clock source by utilizing an over-the-air calibration protocol along with an internal calibration algorithm that maintains accuracy even with inexpensive crystals.

Inefficiencies: Many synchronous, slotted protocols are inefficient due to their simple Time Division Multiple Access (TDMA) MAC layers, which assigns fixed slots to each user. To overcome this, SyncMesh uses a dynamic slot allocation scheme which assigns all slots in real time.

Lack of interoperability with other systems. Since many outdoor wireless systems leverage unlicensed frequencies, multiple systems may need to share the spectrum. Carrier sensing systems may be able to (in theory) share the spectrum by avoiding simultaneous use, while more complex synchronous systems will not understand each other. However, we've already seen that carrier sensing has issues, and many systems 'tweak' the carrier sensing and back-off protocols to get an unfair advantage over other users of the spectrum. SyncMesh handles multiple users of the spectrum by pointing antennas - the high link budget point-to-point link can avoid interference from other systems, while its directional nature avoids interfering with other systems.

Complexity: WiMAX-like synchronous systems are much more complex that asynchronous 802.11 systems. That is why WiMAX CPEs are more expensive than 802.11 clients, and why WiMAX base stations are significantly more expensive than 802.11 access points. SyncMesh has been developed over a period of 6 years and runs on top of off-the-shelf 802.11 silicon, which lowers cost.