Wireless Video System Design

(1)

Wireless Video System Design

A Comprehensive Reference for the System Integrator

November 2009

(2)

Unauthorized use, duplication, or modification of this document in whole or in part without the written consent of Verint Systems Inc. is strictly prohibited.

By providing this document, Verint Systems Inc. is not making any representations regarding the correctness or completeness of its contents and reserves the right to alter this document at any time without notice.

Features listed in this document are subject to change. Please contact Verint for current product features and specifications.

All marks referenced herein with the ® or TM symbol are registered trademarks or trademarks of Verint Systems Inc. or its subsidiaries. All rights reserved. All other marks are trademarks of their respective owners.

About Verint Video Intelligence Solutions

Verint® Video Intelligence Solutions™ is the leading global provider of networked video solutions that enhance the security of people, property and assets. Verint’s award-winning Nextiva® portfolio includes video management software, integrated analytics, encoders and IP cameras, and intelligent DVRs for use in a variety of vertical market environments. Open, standards based and IT friendly, Verint solutions help organizations leverage their existing video investments and place IP video within the reach of virtually every organization.

About Verint Systems

Verint Systems Inc. is a leading provider of Actionable Intelligence®_{solutions for an optimized enterprise}

and a safer world. More than 10,000 organizations in over 150 countries rely on Verint solutions to perform more effectively, build competitive advantage, and enhance the security of people, facilities, and infrastructure.

(6)

₂

About This Guide

When it comes to securing people, property, and essential services, organizations from municipalities and transit authorities to power plants, airports, and all manner of critical infrastructure increasingly recognize the value that wireless video provides.

Wireless technology offers more than just the ability to protect hard-to-wire locations. It reduces reliance on telephone carriers and the expense of telephone charges for significant cost reductions. By decreasing the need to trench and lay cable, it also pares down infrastructure costs and speeds deployment, making it especially useful for temporary installations, as well as for long-term deployments. 1

Wireless video is an excellent choice for historical sites and other settings where cabling is not permitted. It can readily secure remote locations where landline services are not available. And it is appropriate for areas that are prone to downed lines from strong winds, construction, and other environmental hazards. However, the complexity of wireless video technology and the difficulty of keeping pace with emerging

standards and new vendor solutions make system design challenging for both the system integrator and the customer.2

This reference guide is designed to provide system integrators and those organizations that market video solutions with a more complete understanding of wireless video system design and deployment. The guide begins with a thorough exploration of the fundamentals of

wireless communication, including an examination of how radio signals and RF communications work, a review of current and pending wireless standards, an in-depth look at available license-free and US public safety bands, and a detailed description of design factors.

The next section of this guide takes a close look at system design, from the various types of wireless video systems and the circumstances in which each is most appropriately used, to essential design tools and the complexities of building systems that meet customer needs.

Several appendices follow, offering detailed information about use of Verint Nextiva solutions in wireless video systems.

1_{muniwireless.com, August 2007.}

2_{Crossing the Chasm, Mike Perkowski, MuniWireless, March 2007.}

Today, over 400 US municipalities and counties have either deployed wireless networks or are planning to do so.1

Over the next three years, US municipalities are projected to spend over $3 billion to build and operate public wireless networks. And by the year 2009, the municipal wireless market will tally $1 billion in annual sales.2

(7)

For More Information

See the Glossary at the end of this reference guide for a comprehensive list of pertinent terms and their meanings. Finally, a glossary provides an extensive list of pertinent terms and their definitions, and an index helps readers quickly locate topics of interest.

Fundamentals of Wireless Communication

Before designing a wireless video system, it is important to understand the fundamental elements of system design, from such basic concepts as frequency and wavelength to the wireless standards, equipment, and operational considerations that must be part of every design plan. This section of Wireless Video System

Design is devoted to examining these elements and helping the system integrator gain a more complete understanding of the fundamentals of wireless communication.

General Physics of Radio Signals: Frequency and Wavelength

RF (radio frequency) communications work by creating electromagnetic waves at a source and then receiving those electromagnetic waves at a particular destination. The electromagnetic waves travel through the air at almost the speed of light. The wavelength of an electromagnetic signal is inversely proportional to the frequency: that is, the higher the frequency, the shorter the wavelength.

Frequency is measured in hertz (cycles per second), and radio frequencies are measured in kilohertz (KHz or thousands of cycles per second), megahertz (MHz or millions of cycles per second) and gigahertz (GHz or billions of cycles per second). Since higher frequencies result in shorter wavelengths, the

wavelength of a 900 MHz device is longer than that of a 2.4 GHz device.

In general, signals with longer wavelengths travel a greater distance and go through and around objects better than signals with shorter wavelengths, as illustrated below.

(8)

How R

Imagine a location. T dropping a (EM) wav electrons detect this The RF co wiggling e informatio available In designi significant over a cer of informa the cost o must be c all approv

Mainta

Signal Sc A significa solid obje the walls a scattering stronger t Signal sca because o interferen compared yells in a c sound com different s different p they arrive arrive suc out of syn other out.

F Commu

an RF transm This wiggling a pebble in a e that travels wiggling in re s remote elec ommunication electrons in a on. The receiv at a remote lo ng most wire t consideratio rtain distance ation within a of the system compliant with vals and licens

ining Sign

catter ant problem w cts very well. and ceilings. g. The better a he reception. attering reduc of multi-path f ce (ISI). Mult d to an echo c cavern or a v mes back from sound levels. paths to return e at different ch that their pe nc (out of phas

unication S

itter wiggling electron caus pond. The ef from the initi emote location ctron wiggling

n system utiliz specific patte ver can make

ocation, comm less systems ons. First, the e (range) and given time fra must be with h government sing must be

nal Quality

with 2.4 GHz a In order to ge This is called a signal scatte

ces signal qua fading and int i-path fading created when alley. The ori m different dir

Since the ech n to the same

times. If the w eaks and vall se), they canc

Systems W

an electron in ses a ripple e ffect is an ele al location an ns. An RF rec .

zes this phen ern to represe

this same inf municating wi , designers fa system must transfer a ce ame (data rat in budget, the t agency regu attained.

y

and 5 GHz w et around obj d ers, the ality tersymbol can be someone ginal rections at hoes take e location, waves eys are cel each

Work

n one effect, like ctromagnetic nd results in ceiver can omenon by ent formation ithout wires. ace two t operate rtain amount te). Second, e system ulations, and ireless system ects and thro

When m c ms is that rad ough doors, th multipath fadi and c io signals do hese signals m ng occurs, sig cancel each ot not go throug must reflect o gnals arrive ou ther out. 4 gh off of ut of phase

(9)

The same can be said for a radio signal that is scattered by objects it encounters on the way to the receiver. The RF reflections

received by the radio from multiple, indirect paths, though attenuated from the main path, are delayed in time.

The distribution of echoes (reflections) over time (delay spread) can also create ISI, a condition in which the delayed energy from one transmission begins to corrupt the symbol arriving next along the (more) direct path.

Orthogonal Frequency Division Multiplexing (OFDM)

Orthogonal Frequency Division Multiplexing (OFDM) modulation has been growing in usage because of its ability to overcome the problems associated with signal scattering and is especially useful outdoors. OFDM is meant to create a wide-band signal composed of a number of independent (orthogonal) sub-carriers, each carrying a low bit rate data stream.

In 802.11a 5 GHz systems, there are a total of 9 non-overlapping,

20 MHz wide channels, each with 52 sub-carriers that are themselves each approximately 300 KHz wide. The 2.4 GHz 802.11b/g systems have only 3 non-overlapping channels. The sub-carriers are sent in parallel, meaning they are sent and received simultaneously.

The receiver processes these individual signals, each one representing a fraction of the total data being sent. With so many sub-carriers combined in each channel, an enormous amount of data can be transmitted at the same time. The low bit rate data stream allows for a sizeable guard band at the beginning of each symbol, effectively isolating

the symbols from each other and neutralizing the effect of delay spread. In addition, sub-channelized operation in conjunction with the proper error correction system proves to be very tolerant of narrowband multi-path fades.

The error correction used by OFDM is called Forward Error Correction (FEC). FEC sends two copies of the data to the receiver. If part of the primary data is lost, algorithms are used to recover the data from the secondary set of data, thus eliminating the need to resend the data again. In most cases, only a limited number of sub-carriers may be affected by a fade, causing the loss of symbols. With the remainder of the wideband signal unaffected, the error correction system takes over and is able to reconstruct the small percentage of missing data bytes.

Intersymbol interference occurs when the information in the signal cannot be properly read because of signal pulses that overlap when they arrive at the receiver.

(10)

₆

For More Information

See Appendix B: Range and Nextiva Wireless Edge Devices.

The 802.11 Wireless Standard

Originally released in 1997, the IEEE 802.11 standard today comprises three released standards and one draft standard.

802.11a

This standard uses the 5 GHz band and provides a physical data rate of 54 Mbps and actual data throughput up to approximately 24 Mbps. Using standard equipment with omni-directional antennae, the range is up to 30m/100 feet in outdoor environments at the maximum physical data rate. Greater distance can be reached by scaling the data rate down from 54 to 36, 24, 18, 12, 9, or 6 Mbps.

802.11b

This standard uses the 2.4 GHz band and provides a physical data rate of 11 Mbps and actual data throughput up to approximately 6 Mbps. Using standard equipment with omni-directional antennae, the range is up to 100m/300 feet in outdoor environments at the maximum physical data rate. Greater distance can be reached by scaling down the data rate from 11 to 5.5, 2, or 1 Mbps.

802.11g

This is the most commonly used standard and provides better performance than the 802.11b standard. This standard uses the 2.4 GHz band and provides a physical data rate of 54 Mbps and actual data throughput up to approximately 24 Mbps. Using standard equipment with omni-directional antennae, the range is up to 100m/300 feet in outdoor environments at the maximum physical data rate. Greater

distance can be reached by scaling down the data rate from 54 to 36, 24, 18, 12, 9, or 6 Mbps. 802.11g is backwards compliant with 802.11b.

802.11n

This is the next generation of the 802.11 Wireless LAN (WLAN) standard currently being defined by the IEEE. This standard is expected to be ratified in 2008. 802.11n will operate in the same

frequency band as 802.11b/g, but promises to offer significant bandwidth increases, with a potential physical

data rate of 540 Mbps and a potential IP payload data rate of 200 Mbps. Note that the measured IP payload data rate on pre-802.11n products is currently 80 Mbps.

802.11n builds upon previous 802.11 standards by adding Multiple-Input Multiple-Output (MIMO)

technology. MIMO uses multiple transmitter and receiver antennae to allow for increased data throughput via spatial multiplexing and increased range by exploiting spatial diversity. 802.11n promises greater range than 802.11b/g.

(11)

Frequency Channels

The 2.4 GHz Band (License Free)

The 2.4 GHz band has 14 frequency channels, but only 11 are permitted for unlicensed use by the FCC in the US. Each channel extends 11 MHz on each side of the center frequency. Most importantly, the channels overlap. See the table below and the diagram on the following page.

Available Frequency Channels – 2.4 GHz Band

Channel Frequency (MHz) Location

1 2412 US, Europe, Japan

12 2467 Europe, Japan

13 2472 Europe, Japan

(12)

(13)

To the extent that channels overlap, they interfere with each other and reduce available bandwidth. For installations that require multiple access points, three access points using channels 1, 6, and 11 have no overlap. Larger installations must be properly deployed to minimize interference, or a frequency band with more available channels must be used.

Consider This

The 2.4 GHz frequency band is limited by the number of non-interfering channels available, and most wireless office telephones and networking equipment use the same frequency band. This increases the risk of potential interference and can reduce available throughput for transmitting video. Consequently, 2.4 GHz equipment should be used only when there is little risk of interference from other 2.4 GHz equipment being used in the area.

(14)

₁₀

The 5 GHz Bands (License Free)

The 5 GHz band is actually four frequency bands: 5.1 GHz, 5.3 GHz, 5.4 GHz, and 5.8 GHz. The 5 GHz band has a total of 24 channels with 20 MHz bandwidth available. Five of these can be used outdoors without requiring DFS and TPC. Unlike the 2.4 GHz band, the five channels are non-overlapping, so all five channels have the potential to be used in a single wireless system.

Available Frequency Bands – 5 GHz

Channel Frequency (GHz) Location

36 5.180 Indoor Only 40 5.200 Indoor Only 44 5.220 Indoor Only 48 5.240 Indoor Only 52 5.260 DFS required 56 5.280 DFS required 60 5.300 DFS required 64 5.320 DFS required 100 5.500 DFS required 104 5.520 DFS required 108 5.540 DFS required 112 5.560 DFS required 116 5.580 DFS required 120 5.600 DFS required 124 5.620 DFS required 128 5.640 DFS required 132 5.660 DFS required 136 5.680 DFS required 140 5.700 DFS required 149 5.745 North America 153 5.765 North America 157 5.785 North America 161 5.805 North America 165 5.825 North America

This illustration shows the channel allotment and center frequencies for channels in the 5 GHz frequency band. The two- and three-digit numbers are the channels, and the four-digit numbers are the center frequencies for the channels above them.

(15)

For More Information

See Appendix C: Nextiva Support for 802.11.

The 4.9 GHz Public Safety Band (Licensed)

The US Federal Communications Commission (FCC) allotment of 50 MHz of spectrum in the 4.9 GHz band permits public safety agencies to implement on-scene wireless networks for streaming video, rapid Internet, database access, and the transfer of large files, such as maps, building layouts, medical files, and missing person images. It also allows public safety agencies to establish temporary fixed links to support surveillance operations. This allocation gives every jurisdiction in the country access to the spectrum for interoperable broadband communications. Specific FCC rules are covered in Subpart Y in 47CFR part 90 of the FCC regulations.

A 4.9 GHz band license gives the licensee authority to operate on an authorized channel in this band within the applicant’s jurisdiction (city, county, state). A license allows use of base stations and mobile devices, such as laptops and PDAs.

The 4.9 GHz band must be shared by all licensees in an area, with coordinated usage and channel arrangements. Generally, this is not an issue since few 4.9 GHz transmitters exist and few transmit continuously. Licenses are granted for a period of 10 years.

Increasing the Number of

Channels with Channel

Fragmentation

Since the 4.9 GHz band is limited to 50 MHz, only 2 standard, independent channels of 20 MHz are available in this band. Channel fragmentation in the 4.9 GHz band has been added to allow more than two systems to operate in the same area. With channel fragmentation, a licensee can select a channel bandwidth of 20 MHz (standard channel bandwidth currently supported), 10

MHz, or 5 MHz. The 10 MHz channel bandwidth allows for four independent channels, and 5 MHz allows 10 independent channels. The 5 and 10 MHz channel bandwidths are available only in the 4.9 GHz band.

4.9 GHz Band License Eligibility

Who is eligible to apply for a 4.9 GHz license? All US state and local government entities, private companies sponsored by a government entity (such as private ambulance services), and any organization with critical infrastructure (power companies, pipelines, etc.) that provides public safety services for the protection of life, health, or property. They may apply on the FCC website under the ULS section and must pay a $50 filing fee. Those organizations that do not meet the eligibility requirements, but support public safety, may negotiate with the license holder for sharing agreements.

(16)

₁₂ Changing the channel bandwidth has an impact on available

bit rate. If a 10 MHz channel bandwidth is used, the channel data rate is divided in half; if a 5 MHz channel bandwidth is used, the channel data rate is divided by four.

The table to the right shows the available bit rate with respect to the channel bandwidth used.

Antennae and Transmission Lines

Types of Antennae

There are two broad classifications for antennae, depending on their directivity:

• Omni-directional radiates in all directions (360 degrees)

• Uni-directional radiates best in a particular direction

An omni-directional antenna radiates in all directions with approximately the same power and is non-directional, so its gain tends to be quite low. Omnis are normally deployed when a number of transmitters surround a particular area near the receiver.

The following four figures show that as directionality increases, beam width decreases and gain increases. 20 MHz 10 MHz 5 MHz 6 3 1.5 9 4.5 2.25 12 6 3 18 9 4.5 24 12 6 36 18 9 48 24 12 54 27 13.5 Channel Bandwidth (MHz) vs. Channel Data Rate (Mbps)

(17)

Directivity

Directivity is the ability of an antenna to focus energy in a particular direction when transmitting or to receive energy from a particular direction when receiving. If a wireless link uses fixed locations for both ends, it is possible to use antenna directivity to concentrate the radio beam in the direction required. In mobile applications where the transceiver is not fixed, it may be impossible to predict where the

transceiver will be, so the antenna should ideally radiate as well as possible in all directions. In addition, when transmitters surround the receiver and multiple receivers are not a viable option, the ability to receive from all directions is required. An omni-directional antenna is used in these applications.

Gain

Gain is a “dimensionless ratio,” rather than a quantity that can be defined in terms of a physical quantity,

such as watt (power) or ohm (resistance). Gain is referenced with regard to standard antennae, the two most common of which are isotropic antennae and resonant half-wave dipole antennae. This section focuses on isotropic antennae.

Isotropic antennae radiate equally well in all directions. Real isotropic antennae do not exist, but they provide useful and simple theoretical antenna patterns with which to compare actual antennae. An actual antenna radiates more energy in some directions than in others. Since antennae cannot create energy, the total power radiated is the same as an isotropic antenna. Any additional energy radiated in the directions it favors is offset by equally less energy radiated in all other directions.

The gain of an antenna in a given direction is the amount of energy radiated in that direction compared to the energy an isotropic antenna would radiate in the same direction when driven with the same input power. Usually we are interested only in maximum gain, which is the gain in the direction in which the antenna radiates the most power. Antenna gain of 3 dB compared to an isotropic antenna would be written as 3 dBi.

Radiation Pattern

The radiation pattern (or antenna pattern) describes the relative strength of the radiated field in various directions from the antenna at a constant distance. The radiation pattern is a reception pattern, as well, since it also describes the receiving properties of the antenna. The radiation pattern is three dimensional, but the measured radiation patterns are usually a two-dimensional slice of the three-two-dimensional pattern in the horizontal or vertical planes. These pattern measurements are presented in either rectangular or polar format.

This is a rectangular plot presentation of an 18 dBi antenna typically deployed in projects where a

(18)

₁₄ Polar coordinate systems are used almost

universally. In a polar coordinate graph, points are located by projection along a rotating axis (radius) to an intersection with one of several concentric circles.

Polar coordinate systems may be divided generally in two classes: linear and logarithmic.

Linear Polar Coordinate

Systems

In a linear coordinate system, concentric circles are equally spaced and graduated. Such a grid may be used to prepare a linear plot of the power contained in a signal. For ease of comparison, the equally spaced concentric circles may be replaced with appropriately placed circles representing the decibel

response, referenced to 0 dB at the outer edge of the plot. In this kind of plot, the minor lobes are suppressed. This grid enhances plots in which the antenna has high directivity and small minor lobes.

Logarithmic Polar Coordinate

Systems

In a logarithmic polar coordinate system, concentric grid lines are spaced periodically according to the logarithm of the voltage in the signal. Different values may be used for the logarithmic constant of periodicity; this choice affects the appearance of the plotted patterns. Generally the 0 dB reference for the outer edge of the chart is used. The spacing between points at 0 dB and -3 dB is greater than the spacing between -20 dB and -23 dB, which is greater than the spacing between -50 dB and -53 dB. The spacing thus corresponds to the relative significance of such changes in antenna performance.

A Directional Antenna A linear polar plot of a 16 dBi, 27 degree beam width

(19)

-3 dB

For More Information

See the Glossary at the end of this reference guide for a comprehensive list of pertinent terms and their meanings.

Beam Width and the Half-Power Point

An antenna's beam width is usually understood to mean the half-power beam width. Peak radiation intensity is found, and then the points on either side of the peak, which represent half the power of the peak intensity, are located. The angular distance between the half power points is defined as the beam

width. Half the power expressed in decibels is -3 dB, so the half power beam width is sometimes referred to as the 3 dB beam

width.

Both horizontal and vertical beam widths are usually considered. Assuming that most of the radiated power is not divided into side lobes, the directive gain is inversely proportional to the beam width: As the beam width decreases, the directive gain increases.

Side Lobes

No antenna is able to radiate all

energy in one preferred direction. Some energy is inevitably radiated in other directions. These smaller peaks are referred to as side lobes, commonly specified in dB down from the main lobe.

Nulls

In an antenna radiation pattern, a null is a zone in which the effective radiated power is at a minimum. A null often has a narrow directivity angle compared to that of the main beam. Thus, the null is useful for several purposes, such as suppressing interfering signals in a given direction.

(20)

₁₆

Cables

RF cables are almost exclusively coaxial cables, or coax for short, derived from the phrase “of common axis.” Coax cables have a core conductor wire surrounded by a non-conductive material called dielectric or insulation. The dielectric is encompassed by a shielding, which is often made of braided wires. The dielectric prevents an electrical connection between the core and the shielding.

The coax is protected by an outer casing, which is generally made from a PVC material. The inner conductor carries the RF signal, and the outer shield prevents the RF signal from radiating to the atmosphere and prevents outside signals from interfering with the signal carried by the core.

Another interesting fact: the electrical signal always travels along the outer layer of the central conductor, and the larger the central conductor, the better the signal flows. The is the result of the skin effect, a phenomenon that sees the RF signal energy flowing more at the outer surface of the wire than through the middle. The higher the frequency, the more the skin effect and the greater the resistance.

Even though the coaxial construction is good at containing the signal on the core wire, there is some resistance to the electrical flow: as the signal travels down the core, it fades away. This fading is known as attenuation, and for

transmission lines, it is measured in decibels per meter (dB/m). The rate of attenuation is a function of the signal frequency and the physical construction of the cable itself. As the signal frequency increases, so does its attenuation. Cable attenuation should be minimized as much as possible by keeping the cable very short and using high-quality cables.

(21)

Selecting Cables for Use with Microwave Devices

• The shorter the better. The first rule when you install a piece of cable is to try to keep it as

short as possible. Power loss is not linear, so doubling the cable length means that you are going to lose much more than twice the power. In the same way, reducing the cable length by half gives you more than twice the power at the antenna. The best solution is to place the transmitter as close as possible to the antenna, even when this means placing it on a tower.

• You get what you pay for. Any money you invest in buying good quality cable is a bargain. Cheap cables are intended to be used at low frequencies, such as VHF. Microwaves require the highest-quality cables available, and all other choices produce inferior results.

• Avoid RG-58. It is intended for thin Ethernet networking or CB or VHF radio and not for

microwave.

• Avoid RG-213. It is intended for CB and HF radio. In this case, cable diameter does not imply a high quality or low attenuation.

• Whenever possible, use Heliax (foam) cables for connecting the transmitter to the antenna. Heliax cables have a solid or tubular center conductor with a corrugated solid outer

conductor to enable them to flex. Heliax can be built in two ways, using either air or foam as a dielectric. Air dielectric Heliax is the most expensive and guarantees the minimum loss, but is very difficult to handle. Foam dielectric Heliax is slightly more prone to loss, but is less expensive and easier to install. A special procedure is required when soldering connectors in order to keep the foam dielectric dry and uncorrupted. When Heliax is unavailable, use the best-rated LMR cable you can find. LMR is a brand of coax cable available in various diameters that works well at microwave frequencies. LMR-400 and LMR-600 are a commonly used alternative to Heliax.

• Whenever possible, use cables that are pre-crimped and tested in a proper lab. Installing connectors to cable is tricky business ― difficult to do properly even with the proper tools. Unless you have access to equipment that can verify a cable you make yourself (such as a spectrum analyzer and signal generator or time domain reflectometer), troubleshooting a network that uses homemade cable can be difficult.

• Do not abuse your transmission line. Never step on a cable, bend it too much, or try to

unplug a connector by pulling the cable directly. All these behaviors may change the mechanical characteristic of the cable and its impedance, short out the inner conductor to the shield, or even break the line. These problems are difficult to track and recognize and can lead to unpredictable behavior on the radio link.

(22)

₁₈

Connectors

Connectors allow a cable to be connected to another cable or to a component of the RF chain. There is a wide variety of fittings and connectors designed to go with various coaxial lines. A few of the more popular connectors are described below.

Connector Introduced Characteristics Ideal Use

BNC Late 1940s Features two bayonet lugs on the female connector. Mating is achieved with only a quarter turn of the coupling nut.

For cable termination for miniature to

subminiature coaxial cable (RG- 58 to RG-179, RG-316, etc.). These have acceptable performance up to a few GHz and are most commonly found on test equipment and 10Base2 coaxial Ethernet cables. Type N World War II Both the plug/cable and

plug/socket joints are waterproof, providing an effective cable clamp.

Usable up to 18 GHz and very commonly used for microwave applications; available for almost all types of cable.

SMA 1960s High performance and compact in size, with outstanding mechanical durability.

Precision, subminiature units that provide excellent electrical performance up to 18 GHz.

(23)

Selecting Connectors

• Check gender. Virtually all connectors have a well-defined gender, consisting of either

a pin (the male end) or a socket (the female end). Usually cables have male connectors on both ends, while RF devices (such as transmitters and antennae) have female connectors. Devices such as directional couplers and line-through measuring devices may have both male and female connectors. Be sure that every male connector in your system is matched to a female connector.

• Less is best. Try to minimize the number of connectors and adapters in the RF chain. Each connector introduces some additional loss (up to a few dB for each connection, depending on the connector).

• Buy. Do not build. As mentioned earlier, buy cables that are already terminated with

the connectors you need, whenever possible. Soldering connectors is not easy, and to do this job properly is almost impossible for small connectors, such as U.FL and MMCX. Even terminating foam cables can be difficult.

• Do not use BNC for 2.4GHz or higher. Use SMA type connectors (or N, SMB, TNC, etc.) Microwave connectors are precision-made parts and can be easily damaged by mistreatment. As a general rule, you should rotate the outer sleeve to tighten the connector, leaving the rest of the connector (and cable) stationary. If other parts of the connector are twisted while tightening or loosening, damage can occur.

• Never step on connectors or drop connectors on the floor when disconnecting cables. This happens more often than you may think, especially when working on a

mast over a roof.

• Never use tools such as pliers to tighten connectors. Always use your hands.

• When working outside, remember that metals expand at high temperatures and contract at low temperatures. A highly tightened connector in the summer can bind or

(24)

₂₀

RF Line of Sight (LOS)

The least understood of all topics in long-distance, wireless transmission may be RF Line of Sight (LOS). Most people believe that if you are able to see the other end of the intended link, there is clear RF LOS. This is not true at times because of the way that radio signals behave. All radio signals will generate a conical transmission pattern, with the widest point being the midpoint of the signal path. This pattern is known as the Fresnel Zone and needs to be clear of obstacles to ensure maximum power transfer from the transmitter to the receiver. As the distance of the wireless link increases, the Fresnel Zone becomes a larger fraction to consider; since RF signals travel in straight lines, the curvature of the earth can actually cause the signals to be attenuated.

The Fresnel Zone

The Fresnel Zone is the area around the visual Line of Sight into which radio waves spread after they leave the antenna. Typically, 20% Fresnel Zone blockage introduces little signal loss to the link. Beyond 40% blockage, signal loss becomes significant. This calculation is based on a flat earth and does not take the curvature of the earth into consideration. For long links, have a microwave path analysis performed taking this and the topography of the terrain into account.

(25)

For More Information

For information about Nextiva wireless edge devices, decoders, and antennae, plus third-party switches and power supplies, see Appendix A: An Overview of Verint Nextiva Wireless Systems.

Foliage Attenuation

Foliage Attenuation is the reduction in signal strength or quality as the result of signal absorption by trees or foliage obstructions in the signal's LOS path. Trees account for 10 to 20 dB of loss per tree in the direct path. Loss depends upon the size and type of tree; large trees with dense foliage create greater loss. It is safe to assume that if light cannot penetrate a stand of trees, microwave losses will be unacceptable.

Frequency (MHz) Approximate Attenuation (dB/Meter)

432 0.10 - 0.30 1296 0.15 - 0.40 2304 0.25 - 0.50 3300 0.40 - 0.60 5600 0.50 - 1.50 10000 1.00 - 2.00

The Effect of Weather on Microwave Systems

Rain, fog, and snow have negligible impact on system performance for wireless systems operating below 11 GHz.3 Conversely, systems functioning above 11 GHz need to take weather into consideration. One example is satellite TV systems. The size of the RF signal carrying direct-to-home television is about the size of the average raindrop. When the weather is clear, the RF signal can reach the satellite TV dish with a minimum of degradation. However, when it starts to rain, some of the signal gets absorbed by rain, so less of it reaches the dish on the roof. In fact, very heavy

rain can entirely eliminate the signal.

The effects of weather begin to be felt above 4 GHz, so 2.4 GHz would not be affected by the weather at all. However, the 2.4 GHz band is quite busy, and the effect of weather conditions on the 5 GHz band is negligible in comparison to effect on the 2.4 GHz band over a half-mile link. The number of cameras and the amount of

RF cells needed for the system (and not the weather) are the determining factors when selecting

equipment and frequency band.

Consider This

To illustrate the different impact of weather on signal, assume that rain is falling at 30mm (just over one inch) per hour. The resulting

attenuation at 5 GHz is just 0.07 dB/km, but nearly 7 dB/km at 30 GHz.

(26)

₂₂ 3_{Since Verint products operate at 2.4, 5.3, 5.4, and 5.8 GHz, such environmental factors have an insignificant effect on their} performance.

Designing Wireless Video Systems

Now that we have explored the basics of wireless video, we will proceed with more detailed design considerations, using Nextiva intelligent edge devices to illustrate design constructs.

Types of Systems

Point-to-Point Wireless Systems

Point-to-point is the most straightforward wireless system, usually consisting of a single Nextiva S4100 transmitter/receiver pair, as shown below.

(27)

When to Use Point-to-Point Considerations and Limitations The point-to-point system is used when a single, remotely-located

camera must be connected to equipment that requires a coaxial cable input, such as a DVR, matrix, or analog monitor. Point-to-point can also be used when two or three remote cameras require wireless transmission, but the cameras are physically too far apart to allow for point-to-multipoint implementation.

There are instances when a point-to-point system will incorporate an S4200 and an S4300 access point. This is when the recording and viewing are performed using Nextiva Enterprise or Verint nDVR™.

• No embedded video analytics

• No Nextiva or Verint nDVR support

• MAC modes available: SPCF and SDCF (Default MAC mode is SDCF)

• No standard 802.11 support

• Security: 128-bit AES OCB encryption with key rotation

• For configuration, we recommend using SConfigurator

(28)

₂₄

Point-to-Multipoint Wireless Systems

Point-to-multipoint systems incorporate two or more Nextiva S4200 transmitters and one or more Nextiva S4300 access points, as illustrated below.

When to Use Point-to-Multipoint Considerations and Limitations

Point-to-multipoint systems allow several S4200 transmitters to share the same RF channel, enabling multiple cameras feeds to be received by a single S4300 access point, accommodating locations where there are several remote cameras that require wireless connections to the receiving end.

Since point-to-multipoint systems support channel sharing, many more cameras can be deployed in point-to-multipoint systems than in point-to-point systems, which have a finite number of channels available.

• MAC protocols available: SPCF and SDCF (Default MAC mode is SPCF)

• No frame bursting available

For point-to-multipoint wireless video over 802.11: This infrastructure system is used integrate our wireless video encoder with an existing 802.11 WLAN. Data (such as video, audio, meta-data, etc.) can be sent to Nextiva, nDVR, a Web client, or a standalone video receiver.

• MAC protocol available: 802.11 only

• Security: WPA1 & 2 PSK and enterprise

(29)

Point-to-Point and Point-to-Multipoint Wireless Systems with Repeaters

These systems are similar to the standard point-to-point and point-to-multipoint systems, respectively, with the addition of one or more Nextiva S4300-RP repeater units.

When to Use Repeaters Considerations and Limitations

Point-to-Point Point-to-Multipoint

Repeater units are necessary when the transmission path of the receiver is blocked by obstacles or when the transmission distance is too great. Deploying repeaters will further delay data being sent through them.

• No embedded video analytics

• No Nextiva or Verint nDVR support and no SConfigurator support for the S1100

• MAC modes available: SPCF and SDCF (Default MAC mode is SDCF)

• No frame bursting

• For configuration (S4100), we recommend using SConfigurator

• MAC protocols available: SPCF and SDCF (Default MAC mode is SPCF)

(30)

Bridge Ap The follow Bridge ap is required this case, deployed in remote location. I bridges si pplications wing is an illus When to plications are no d in another. Tw

with one on eac when a project locations that m n some of these nce they may re

stration of a b Use a Bridge ormally deploye wo S4300 bridge ch building. At t requires networ must communica e cases, S4300-equire 24 VAC p bridge applica Application ed when data in e units would be times, a bridge s rk equipment to ate with a netwo -RP units are co power. ation. one building e deployed in system is be deployed ork in another onverted into Consid • MAC proto (Default M • No standa • Security: 1 rotation derations and ocols available: MAC mode is SD rd 802.11 supp 128-bit AES OC d Limitations SPCF and SDC DCF) ort B encryption wi 26 CF ith key

(31)

Bridge Applications with Repeaters

A bridge application with repeater functions in the same manner as the bridge application alone, with the same limitations.

(32)

₂₈

RF Cell Considerations

Non-Adjacent Channels

All channels in the 5 GHz bands are non-overlapping, simplifying system design since there is a larger number of channels available for use in a single site. However, there can still be interference issues when using adjacent channels, such as channels 149 and 153 in the 5.8 GHz band.

Using the Nextiva 5 GHz product line allows you to deploy three

separate RF cells in one location without interference from RF signals from other Verint wireless devices installed in the same location. Using non-adjacent channels removes the cross-talk risk between RF cells, and the antennae do not need to be spaced any given distance apart.

Adjacent Channel Interference

Broadband adjacent channel interference generates considerable side band energy that falls into the pass band of the adjacent channel. Under these conditions, the amount of link margin, or the size of the Signal to Interference Ratio (SIR), has a significant effect on the data throughput of the RF channel affected.

(33)

For More Information

See Appendix D: Maximum S4200 Units per S4300 Bridge and Appendix E: Using IP Cameras with the Nextiva S4200. Antenna Separation Requirements

For larger sites where more than three RF cells are needed, adjacent channels must be used. This will not cause interference between channels if the antenna separation rules are correctly applied.

Setup 5 GHz (13-dBi Antenna with 40º

Beam Width)

2.4 GHz (6.5-dBI Antenna with 60º Beam Width)

Side by side 43 feet (13m) 55.8 feet (17m)

On top 13 feet (4m) 6.2 feet (1.9m)

Back to back 7.9 feet (2.4m) 15.7 feet (4.8m)

If antennae with narrower beam widths are used, distances may be reduced.

The installation scenario below uses antenna separation that meets the requirements. This setup uses only 5 GHz units with the antennae located on the same side of a building. The units using adjacent channels 52 and 56 are separated by the prescribed 43 feet (13m). You can intersperse other units in between, as long as they do not use adjacent channels. In this way, you can increase the unit density without worrying about interference problems.

(34)

₃₀

For More Information

See RF Line of Sight (LOS)

earlier in this guide.

Designing for Maximum Range

Determining Range

In order to accurately calculate system range, it is important to first understand the terms below.

dB-Decibels

Decibels are logarithmic units often used to represent power, gain, and loss in an RF system. The Decibel

dB is actually a dimensionless value found by taking the log of the ratio of two like units, such as power in

watts or milliwatts. For example, dB = 10 log P2/P1, where P1 is the reference value, and P2 is the value

to convert to decibels.

There are two common units of measure that can be used when converting power to decibels: dBW (dB watts) and dBm (dB milliwatts). dBW is power in decibels relative to 1 watt, and dBm is power in decibels relative to 1 milliwatt.

• To convert from watts to dBW, use: Power in dBW = 10* (log x/1) where x is the power in watts.

• To convert from milliwatts to dBm, use: Power in dBm = 10* (log x/1) where x is the power in

milliwatts. (Since the reference value is always 1, we do not normally include it in the calculations.)

Both formulas are identical, except that they yield different results. For example, if 1 watt was used, the log of 1 is 0, and the log of 1000 (1 watt equals 1000 milliwatts) is 3; the value for dBW in this case would be 0, and the value for dBm would be 30.

Just make certain the same formula is used for all power values, since using dBm for one power value and dBW for another in the same calculation will yield erroneous results.

Remember: decibels are used in system calculations to allow for simple calculations of gain and loss, since you only need to add and subtract the db values from each other. If the power information available is in watts or milliwatts, simply apply one of the above formulas to convert the power to decibel form.

Line of Sight (LOS)

Line of Sight, when speaking of RF, means more than just

being able to see the receiving antenna from the transmitting antenna. In order to have true RF LOS, no objects (including trees, houses, or the ground) can be in the Fresnel Zone. The Fresnel Zone is the area around the visual LOS into which radio waves spread out after they leave the antenna. This area must be clear, or else signal strength will weaken.

Transmit Power

Transmit power refers to the amount of RF power that comes

out of the antenna port of the radio. Transmit power is usually measured in watts, milliwatts, or dBm.

Receiver Sensitivity

Receiver (or receive) sensitivity refers to the minimum level

signal the radio can demodulate. In other words, the

An Example

S4200 TX power: 20 dBm S4300 RX sensitivity: -89 dBm Total link budget: 109 dBm

(35)

For More Information

See Appendix F: The Verint RF

Margin Calculator.

sensitivity is the lowest level signal from which the receiver can get coherent information. For example, with sound waves, transmit power is how loud someone is yelling and receiver sensitivity is how soft a voice someone can hear.

Transmit power and receiver sensitivity together constitute what is known as link budget. The link budget is the total amount of signal attenuation you can have between the transmitter and receiver and still have communication occur. For LOS situations, a mathematical formula can be used to figure out the

approximate range for a given link budget. For non-LOS applications, range calculations are more complex because of the various ways in which the signal can be attenuated.

RF Communications and Data Rate

Data rates are usually dictated by the system: that is, how much data must be transferred and how often does the transfer need to take place. Lower data rates allow the radio module to have better receive sensitivity and thus more range. Note that in a point-to-point Nextiva S4100 system using the integrated 12 dBi antennae (5 GHz), radio sensitivity at the maximum possible data rate of 54 Mbps is -72 dBm, whereas radio sensitivity at the lowest available data rate (6 Mbps) is -90 dBm. This translates to a maximum distance of 200 meters at 54 Mbps and 2.6 KM for 6 Mbps or about 13 times more distance in LOS conditions.

Simplifying the Creation of RF Systems with the Verint RF Margin Calculator

The Verint RF Margin Calculator, an MS Excel spreadsheet-based tool, is designed to simplify the creation of RF systems and can be used without in-depth

knowledge of wireless systems. The Calculator allows you to select the necessary frequency band for the system, the type of system (i.e., point-to-point or point-to-multi-point), and several other parameters to accurately design a system that meets your project requirements. Use of the RF Margin Calculator when designing systems is covered later in this guide.

Before calculating RF margin, it is important to become familiar with the terms that follow.

Term Definition

RF Margin The amount of extra gain available in the wireless system when the path loss is subtracted from the total gain of the system.

System Gain The addition of the power provided by the radio transmitter, the gain of the transmitter’s antenna, the gain of the receiver’s antenna, and the sensitivity of the radio receiver.

Radio Transmission Power

The amount of energy the radio transmitter is able to produce. The amount of power produced by the radio is regulated depending on the frequency band being used. This helps ensure that everyone using the frequency band has equal opportunity to transmit their data across the air.

Antenna Gain The amount that the power from the transmitter is increased by the antenna. The higher the _{gain of the antenna, the farther the signal travels. The maximum gain used in a system is} also regulated, so that the maximum amount of power produced by the transmitter does not

(36)

₃₂

Term Definition exceed the level specified in regulations.

Receiver Sensitivity

The minimum acceptable value of received power needed to achieve acceptable

performance. In other words, the sensitivity value of the receiver is the lowest power level at which the receiver can extract the information from the signal being sent from the

transmitter.

Path Loss May be the result of many factors, such as free space loss, refraction, reflection, connector loss, and cable loss. Path loss is usually expressed in dB.

Free Space Loss (FSL)

The transmission loss between two ideal antennae, assumed to be in a vacuum. FSL is the propagation loss due solely to spreading of the wave front and assumes no blockage of line of sight or the first Fresnel Zone.

Refraction The bending of an electromagnetic wave as it passes between materials of different density. An example of this is a wave going from humid air to drier air.

Reflections

Occur when a wave hits a surface it cannot penetrate. The wave deflects off the surface at an angle that is the same as the angle at which the original wave hit. Since many objects that may be in the path of the wave have irregular surfaces (i.e., are not smooth), the wave can reflect in all directions.

Connector and Cable Loss

Occurs because of the need to connect the antenna to the radio. Since the connection of these two components requires some type of cable, the cable and the connectors that hold them together cause a loss of signal strength prior to the signal being sent out into the air. This is why short cables and a minimum number of connectors should be used in a wireless system.

(37)

Basic Tools for Designing a

Wireless System

Site Layout. The site layout needs to have the camera locations, obstructions (if possible), and the head end clearly marked. A site layout with distances marked is desirable.

Video Resolution and Frame Rates. This provides an estimate of the amount of bandwidth required per camera in the system.

Head End Equipment. This is the video’s final destination. Does the implementation require analog at the head end or will it use nDVR or Nextiva?

RF Margin Calculator. This Verint calculator helps you easily determine the maximum length of RF links and video bandwidth limits and select antennae.

Protractor and Ruler. These simple, but invaluable tools of the trade help you determine the minimum beam width required to capture multiple cameras.

Creating the Proper Design

At the outset, certain information and tools are essential to creating the proper design. At times, when some of this information is unavailable or unknown, you must make assumptions that the customer must qualify. It is important to avoid over-complicating the design during this process.

Getting Started: What You Need to Know

The Number of Cameras

Without information about cameras within the system, there is no way to determine anything else about the system. You may not get all of this information, but the more you have, the easier it will be. The key information required is:

• How many cameras will there be, and what types (analog, IP, fixed, PTZ)?

• What are the distances from the head end?

• Do all cameras have RF Line of Sight (LOS) to the head end? (Will repeaters be required?)

• What video quality and frame rates are expected?

Camera Locations

Another important piece of information is the location of the cameras. Most customers will have a site layout that you can obtain. If this information is unavailable, a verbal description of the site should be requested. If this is not possible, only a generic system design can be created, with a disclaimer stating that no site information was available at the time of the system design and quote and that design and associated quote are thus for budgetary

purposes only.

Transmission Distances

A further requirement for a quality design is the distances of the camera locations to the head end. If all distances are not available, the camera locations farthest away from the head end are sufficient.

Head End Location

Finally, the location of the head end (wired network point of presence) should be determined so that the system can be laid out.

(38)

₃₄

The Preliminary Layout

The example below offers the preliminary information needed to determine how this system can be set up. Although all distances to the head end are not listed, we know that the maximum distance is less than 1 km.

From this information, we can create our basic system as shown below. All camera locations will require an S4200 unit, and the head end will require multiple S4300 access points. As you can see, there are three S4300 access points at the head end. The camera locations naturally divided the cameras into three distinct groups, which are referred to as RF cells. With this all in place, the system design can

be finalized with the required antennae and a determination of expected throughput for the cameras in the different cells.

(39)

Determining Beam Width

Once the RF cells have been determined and distances have been measured, the minimum beam width for the antennae required for each RF cell can be established. This requires a protractor and a ruler. To determine the minimum beam width:

1. Use the ruler to draw a line from the head end location to each of the outer camera positions for each RF cell. (Refer to the following figure.)

2. Using the protractor, determine the angle between the two lines previously drawn.

a. Place the midpoint of the protractor on the point at the head end where the two previously drawn lines intersect.

b. Line up the zero degree line with one of the lines so that the second line is under the protractor.

c. Read the value on the protractor where the second line falls on the graduated dial. This will be the angle between the two lines that are used to determine the beam width required for the antenna. (See the figure on the following page.)

(40)

₃₆ 3. The example below shows an angle of 17 degrees. This means an antenna with a beam width greater than 17

degrees is required to ensure all cameras are in the antennae beam.

• Since there is an 18 degree beam width antenna available, one would assume this would be the logical choice based on the 17 degree angle of separation between the outer camera locations. However, the choice of antenna is based on more than just this criterion.

(41)

Completing the Design Using the Verint RF Margin Calculator

Now that the camera location, distances, minimum beam width requirements, and RF cell creation are complete, the RF Margin Calculator should be used to bring everything together. There are two ways to go about completing the system design, depending on the information you have available.

• Determine the required antennae based on known frame rate and resolution requirements. This method may require reorganization of RF cells if the available bandwidth based on the distances involved does not meet the requirements for the project.

• Determine the maximum amount of bandwidth available per camera based on the throughput available for the distances, cameras, and antennae needed for a functional system.

Adding System Information to the Calculator

1. From the Country drop-down box, select the country where the system is to be installed. If the country is not in the list, select Unregulated.

2. Select the Frequency Band to be used for the system, as agreed upon by the customer. If this has not been determined, select one of the 5 GHz bands available in the country selected.

3. Select the system type: point-to-point or point-to-multipoint.

• Select point-to-point for: o S4100 units

o When S4300 units are used as a bridge

o When using a repeater; the transmit side of the repeater to a single receiver (S4300 or S4100-Rx)

• Select point-to-multipoint for:

o Multiple S4200 units transmitting to one S4300

(42)

₃₈ 4. Enter the longer link distance in the RF cell:

• For point-to-multipoint systems, this would be the camera location in the RF cell farthest from the receiving point.

• Select the Channel Data Rate that will provide the data throughput necessary for the RF link.

5. Select the Units (both Master and Slave) for the system.

6. Select the antenna model that satisfies the distance and beam width requirements for the RF link:

• If the selected antennae do not have the gain needed to satisfy the minimum margin for the length of the link, the box around the margin value will turn yellow and the margin value will turn

red .

• Select an antenna that allows the margin to be at least 15 dB.

• If an antenna is not available with the appropriate gain and bandwidth combination to have all the cameras within the beam width with sufficient margin, the Channel Data Rate must be reduced to allow for greater receiver sensitivity and, thus, longer range.

• If you are unable to find a combination of antenna and data throughput that satisfies the needs of the customer, either a repeater is required or the number of cameras in the RF cell must be reduced, or both.

7. Once the appropriate antennae have been selected, all parts for the system are identified, and a quote can be created.

(43)

Tower Height Calculations

The RF Margin Calculator automatically calculates the height at which the antennae must be mounted to ensure that 60% of the first Fresnel Zone is clear of any obstructions.

Additionally, the Advanced RF Margin Calculator interface calculates the required height of the antennae in both meters and feet.

The RF Margin Calculator also provides a graphical view of the Fresnel Zone on a separate tab.

Fresnel Zone Calculator Results

For More Information

(44)

₄₀

The Pre-Installation Site Survey

This is a basic overview of what should be considered while doing a wireless site survey. A site survey is simply a map of the site at which your customer wants to install his/her wireless products. It is perhaps the most important step you must take before implementing any type of wireless devices.

Questions to Ask

• What type of facility (site) is it? The answer to this simple question can have a significant impact and extend the time required to complete the survey.

• How big is the facility? The size will affect the power output required, as well as security considerations.

• Is it indoor or outdoor (or both)? Different types of construction affect radio transmissions differently.

─ A hospital presents a good example of a site with indoor hazards. It has radiology equipment, fire doors, lead-lined walls in the x-ray department, elevators, and doctors with PDAs. Be aware of dead zones inside.

• If outdoors, does the area experience frequent tornados or hurricanes? Strong winds can disrupt a long-distance, wireless connection by moving one or both of the radio devices. Weatherproof enclosures may need to be added to your installation list.

• Are there any existing wireless or wired networks? Ask the facility’s network administrator the following questions:

─ How many users are on the current network? How many will there be two years from now? (This has an impact on bandwidth considerations.)

─ Are there any firewalls or routers, and, if so, are any ports blocked? ─ What protocols are allowed/blocked on the LAN?

─ If there is a wireless network in place, what DSSS channels does it use? ─ Where are the wired LAN connections located (wiring closets)?

• Is a tower required? If installing a system in a PTMP situation, a 20-foot tower may be needed to clear an obstacle.

─ Do you have access to the roof?

─ Is the roof structurally sound enough to support a tower? ─ Do you need a permit to install a tower?

─ Do you need an engineer?

Consider This

Look at the site from an RF perspective, as well as a wired perspective. The survey should be well documented and include the following:

• IP addressing (including all existing networks)

• Interference sources

• Equipment placement

• Power considerations

(45)

• Are facility blueprints available? Creating drawings from scratch can take time and are likely not to be accurate. Existing blueprints can provide you with dimensions, firewall locations, power outlets, network closets, and other pertinent details.

• Are there building facilities, such as cafeterias, that have microwave ovens (a major source of interference)?

Site Survey Equipment

In most cases you will need:

• At least one access point (S4300) and/or Spectrum Analyzer (see below)

• An Ethernet switch, cables, and connectors

• Plenty of paper; be prepared to walk, sketch, and record your signal strengths

Site survey software is valuable for properly planning a wireless deployment. Many site survey software packages are commercially available.

A Spectrum Analyzer is also invaluable during a site survey since it can easily provide you with the following data:

• Signal strength (in dB)

• Noise floor (in dBm)

• Signal to Noise Ratio (SNR) (in dB)

Additional equipment to consider when surveying an outdoor installation includes:

• Binoculars and two-way radios

• Camera for taking pictures

• Rain suit

• Battery packs

• DC to AC converters

• Measuring wheel

Things to Record During a Survey

• Trees (Fresnel Zone interference)

• Buildings (diffraction)

• Lakes (reflection, major cause of multipath)

• Visual LOS

• Link distance (for distances greater than 7 miles, compensate for the curvature of the earth)

• Roof accessibility

• Weather hazards

• If during the winter, trees that will grow into the Fresnel Zone during the summer months

Wireless Video System Design