RF Networks. There are two aspects of networking which must be considered when installing either an NCL or LMS product:. 1. Ethernet Networking (IP). 2. Radio Networking (RF). This presentation will focus on the RF side of the NCL and LMS products. RF Terminology.
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There are two aspects of networking which must be considered when installing either an NCL or LMS product:
1. Ethernet Networking (IP)
2. Radio Networking (RF)
This presentation will focus on the RF side of the NCL and LMS products.
Wavelength is the distance between identical points in the adjacent cycles of a waveform. In wireless systems, this length is usually specified in meters, centimeters, or millimeters
The size of the wavelength varies depending on the frequency of the signal. Generally speaking, the higher the frequency the smaller the wavelength.
The WaveRider family of products operate in the 2.4000 - 2.4835 GHz range (NCL and LMS2000) as well as the 905 - 925 MHz range (LMS3000).
At 2.4 GHz the wavelength is 12.5cm
At 905 MHz the wavelength is 33cm
Wavelength = 3 x 102
f (frequency in MHz)
This calculation is important to remember, especially when installing antennas. Ideally, the antenna should be installed no closer than 10 wavelengths to the nearest reflective surface.
Frequency is the number of complete cycles per second in alternating current direction. The standard unit of frequency is the hertz, abbreviated Hz. If a current completes one cycle per second, then the frequency is 1 Hz.
Tx is short for “Transmit”
All radios have a certain level or Tx power that the radio generates at the RF interface. This power is calculated as the amount of energy given across a defined bandwidth and is usually measured in one of two units:
W = 0.001 x 10[Power in dBm / 10 dBm]
The NCL and LMS radios have Tx power of +18dBm, which translates into .064 W or 64 mW.
Rx is short for “Receive”
All radios also have a certain ‘point of no return’, where if they receive a signal less than the stated Rx Sensitivity, the radio will not be able to ‘see’ the data.
This is also stated in dBm or W.
The NCL and LMS radios have a receive sensitivity of –82 dBm. At this level, a Bit Error Rate (BER) of 10-5 (99.999%) is seen.
The actual level received at the radio will vary depending on many factors.
In a wireless system, antennas are used to convert electrical waves into electromagnetic waves. The amount of energy the antenna can ‘boost’ the sent and received signal by is referred to as the antennas Gain.
Antenna gain is measured in:
There are certain guidelines set by the FCC that must be met in terms of the amount of energy radiated out of an antenna. This ‘energy’ is measured in one of two ways:
In all wireless communication systems there are several factors that contribute to the loss of signal strength. Cabling, connectors, lightning arrestors can all impact the performance of your system if not installed properly.
In a ‘low power’ system (such as the NCL and LMS products) every dB you can save is important!! Remember the “3 dB Rule”.
For every 3 dB gain/loss you will either double your power (gain) or lose half your power (loss).
-6 dB = 1/4 power
+3 dB = 2x power
+6 dB = 4x power
Sources of loss in a wireless system: free space, cables, connectors, jumpers, obstructions
System must be installed by a “Professional Installer” as defined in FCC Document 15.247 Part 15;
Complete understanding of FCC emissions regulations for unlicensed operation in the 2.4 GHz ISM Band.
Installer must have a full understanding of the impact of various types of antennae, amplifiers and other active and passive components on the compliance of the equipment under FCC regulations.
An external Power Amp cannot be used in conjunction with WR radio components, in order to comply with FCC regulatory emissions requirements. Use of an external PA device with a WaveRider system is deemed illegal and may result in significant penalty to the manufacturer, seller, and customer.
Unique connectors provide means of compliance.
Standard connectors require professional installation to ensure compliance.
The NCL and LMS systems are designed to support terrestrial fixed links in an outdoor environment. Typical distances achieved while staying within FCC guidelines are:
Point to Multipoint: up to 8km
Point to Point: up to 15km
These distances may vary depending on the installation, antennae chosen, cabling, etc.
Also known as Direct Sequence Code Division Multiple Access (DS-CDMA), DSSS is one of two approaches to spread spectrum modulation for digital signal transmission over the air.
The stream of information to be transmitted is divided into small pieces, each of which is allocated to a frequency channel across the spectrum.
When transmitted, the data is combined with a higher data-rate bit sequence (also known as a chipping code) that divides the data according to a spreading ratio.
The transmitter and the receiver must be synchronized with the same spreading code.
The chipping code helps the signal resist interference and also enables the original data to be recovered if data bits are damaged during transmission.
22 MHz wide
Also known as Frequency Hopping Code Division Multiple Access (FH-CDMA), FHSS radios transmit "hops" between available frequencies according to a specified algorithm which can be either random or preplanned.
The transmitter operates in synchronization with a receiver, which remains tuned to the same center frequency as the transmitter.
As the signal leaves the antenna it propagates, or disperses, into space. The antenna selection will determine how much propagation will occur.
At 2.4 GHz it is extremely important to ensure a that a path (or tunnel) between the two antennas is clear of any obstructions. Should the propagating signal encounter any obstructions in the path, signal degradation will occur.
Trees, buildings, hydro poles, and towers are common examples of path obstructions.
The greatest amount of loss in your wireless system will be from Free Space Propagation. The Free Space Loss is predictable and given by the formula:
FSL(dB) = 32.45 + 20Log10F(MHz) + 20Log10D(km)
The Free Space Loss at 1km using a 2.4 GHz system is:
FSL(dB) = 32.45 + 20Log10(2400) + 20Log10(1)
= 32.45 + 67.6 + 0
= 100.05 dB
Attaining good Line of Sight (LOS) between the sending and receiving antenna is essential in both Point to Point and Point to Multipoint installations.
Generally there are two types of LOS that are used discussed during installations:
To quantify Radio Line of Sight, the Fresnel Zone theory is applied. Think of the Fresnel Zone as a football shaped tunnel between the two sites which provides a path for the RF signals.
At WaveRider acceptable Radio Line of Sight means that at least 60% of the first Fresnel Zone plus 3 meters is clear of any obstructions.
Radius of nth Fresnel Zone given by:
When obstructions intrude on the first Fresnel Zone many issues can arise which will affect the performance of the system. The main issues are:
Path Profile characteristics may change over time, due to vegetation, building construction, etc.
Path Profile characteristics may change over time, due to vegetation, building construction, etc.
The antenna converts radio frequency electrical energy fed to it (via the transmission line) to an electromagnetic wave propagated into space.
The physical size of the radiating element is proportional to the wavelength. The higher the frequency, the smaller the antenna size.
Assuming that the operating frequency in both cases is the same, the antenna will perform identically in Transmit or Receive mode
The type of system you are installing will help determine the type of antenna used. Generally speaking, there are two ‘types’ of antennae:
Typically measured in two planes:
No matter what polarity you choose, all antennas in the same RF network must be polarized identically regardless of the antenna type.
A proper Impedance Match is essential for maximum power transfer. The antenna must also function as a matching load for the Transmitter ( 50 ohms).
Voltage Standing Wave Ratio (VSWR), is an indicator of how well an antenna matches the transmission line that feeds it.
It is the ratio of the forward voltage to the reflected voltage. The better the match, the Lower the VSWR. A value of 1.5:1 over the frequency band of interest is a practical maximum limit.
Return Loss is related to VSWR, and is a measure of the signal power reflected by the antenna relative to the forward power delivered to the antenna.
The higher the value (usually expressed in dB), the better. A figure of 13.9dB is equivalent to a VSWR of 1.5:1. A Return Loss of 20dB is considered quite good, and is equivalent to a VSWR of 1.2:1.
Andrew Corporation HeliaxThe Transmission Line
The type of cable selected depends mostly on the length of that cable required. Generally, the longer the cable run the better the cable must be in terms of attenuation.
Attenuation refers to the degradation of the signal as it travels through the cable. This is usually stated as a loss in dB per 100 feet.
Line Loss or Attenuation paramount – refer to your Link Budget Calculations to determine how much loss is acceptable and still have a viable link.
Foam dielectric, Air Dielectric, Pressurized types of Coaxial Cable. Waveguide use also possible but typically not cost-effective
Your connector selection will be determined based on the following:
For the most part the cabling manufacturers also manufacture the connectors that go on the cables. ‘Knock off’ connectors are available, but don’t always fit the cable the way the manufacturers connectors do.
Generally the only decision that needs to be made is what gender of connector to install…Male or Female
Antennas – usually Female
Lightning Arrestors – usually Female
For maximum protection, ground must be connected close to point of entry into building - within 2ft.
Typically structural steel OK for ground connection
Typical Lightning ArrestorThe Lightning Arrestor
Do not use Gas Lines or Water pipes.
Check Electrical Code for grounding restrictions.
Through WaveRiders Professional Services Group (PSG), a Network Feasibility Assessment can be done to establish the viability of a proposed wireless network with either the NCL or LMS products.
To establish the viability of a link prior to installing any equipment, a Link Budget Calculation needs to be made. Performing this calculation will give you an idea as to how much room for path loss you have, and give you an idea as to link quality.
Using the WaveRider Link Path Analysis Tool (LPA Tool), the Fade Margin and other link criteria can be mathematically calculated to determine link quality.
Ie. If you have an RSL of –60dB and a Rx Threshold of –72dB, than your fade Margin would be 12dB