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RF Networks

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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RF Networks

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  1. RF Networks

  2. 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.

  3. RF Terminology 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

  4. 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

  5. These values are calculated using the following formula: 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.

  6. Frequency 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. Kilohertz (kHz) Megahertz (MHz) Gigahertz (GHz) Terahertz (THz)

  7. Spectrum

  8. Tx Power 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: • dBm – a relative power level referencing 1 milliwatt • W – a linear power level referencing Watts

  9. dBm = 10 x log[Power in Watts / 0.001W] 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.

  10. Rx Sensitivity 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.

  11. Radiated Power 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: • dBi: relative to an isotropic radiator • dBd: relative to a dipole radiator • 0 dBd = 2.15 dBi

  12. 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: • Effective Isotropic Radiated Power (EIRP) • measured in dBm = power at antenna input [dBm] + relative antenna gain [dBi] • Effective Radiated Power (ERP) • measured in dBm = power at antenna input [dBm] + relative antenna gain [dBd]

  13. Energy Losses 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).

  14. -3 dB = 1/2 power -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

  15. FCC Guidelines • The ISM Bands are defined as follows: • 902 to 928 MHz • 2400 to 2483.5 MHz • 5725 to 5850 MHz • FCC Part 15, Class B • Unlicensed operation from 2400 to 2483.5 MHz • P2P - EIRP : +36 dBm (4 Watts) • : 3:1 i.e. +24 dBm into 24 dBi • P2MP - EIRP : +36 dBm (4 Watts) • : 3:1 at subscriber (considered P2P)

  16. FCC - Installer 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.

  17. FCC - Installation 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.

  18. WaveRider High Speed Wireless Systems 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.

  19. Direct Sequence Spread Spectrum 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.

  20. 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

  21. Frequency Hopping Spread Spectrum 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.

  22. Hopset Each channel 1MHz wide FHSS – an example f5 f4 f3 f2 f1 1 2 3 4 5 6 7 8 9 10 11 12 TIME

  23. Signal Propagation 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.

  24. 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

  25. Line of Sight 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: • Optical LOS - is related to the ability to see one site from the other • Radio LOS – related to the ability of the receiver to ‘see’ the transmitted signal

  26. 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.

  27. 3rd* 2nd* 1st* Fresnel Zones * Fresnel Zones

  28. The First Fresnel Zone l n d d r = 1 2 n + d d Site A 1 2 d1 Site B • Fresnel Zone diameter depends upon Wavelength, and Distances from the sites along axis • For minimum Diffraction Loss, clearance of at least 0.6F1+ 3m is required d2 Radius of nth Fresnel Zone given by:

  29. When obstructions intrude on the first Fresnel Zone many issues can arise which will affect the performance of the system. The main issues are: • 1. Reflection • incident wave propagates away from smooth scattering plane • multipath fading is when secondary waves arrive out-of-phase with the incident wave causing signal degradation

  30. 2. Refraction • incident wave propagates through scattering plane but at an angle • frequencies less than 10 GHz are not affected by heavy rains, snow, “pea-soup” fog • at 2.4 GHz, attenuation is 0.01 dB/Km for 150mm/hr of rain • 3. Diffraction • incident wave passes around obstruction into shadow regions

  31. Antenna - How it Works 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

  32. The type of system you are installing will help determine the type of antenna used. Generally speaking, there are two ‘types’ of antennae: • Directional • - this type of antenna has a narrow beamwidth; with the power being more directional, greater distances are usually achieved but area coverage is sacrificed • - Yagi, Panel, Sector and Parabolic antennae • - an EUM, NCL Station/Master will use this type of antenna in both Point to Point and Point to Multipoint

  33. Omni-Directional • - this type of antenna has a wide beamwidth and radiates 3600; with the power being more spread out, shorter distances are achieved but greater coverage attained • - Omni antenna • - a CCU or an NCL Master will use this type of antenna

  34. Yagi • better suited for shorter links • lower dBi gain; usually between 7 and 15 dBi

  35. Parabolic • used in medium to long links • gains of 18 to 28 dBi • most common

  36. Sectoral • directional in nature, but can be adjusted anywhere from 450 to 1800 • typical gains vary from 10 to 19 dBi

  37. Omni • used at the CCU or Master NCL for wide coverage • typical gains of 3 to 10 dBi

  38. Antenna Radiation Patterns • Common parameters • main lobe (boresight) • half-power beamwidth (HPBW) • front-back ratio (F/B) • pattern nulls Typically measured in two planes: • Vector electric field referred to E-field • Vector magnetic field referred to H-field

  39. Polarization • An antennas polarization is relative to the E-field of antenna. • If the E-field is horizontal, than the antenna is Horizontally Polarized. • If the E-field is vertical, than the antenna is Vertically Polarized. No matter what polarity you choose, all antennas in the same RF network must be polarized identically regardless of the antenna type.

  40. Polarization may deliberately be used to: • Increase isolation from unwanted signal sources (Cross Polarization Discrimination (x-pol) typically 25 dB) • Reduce interference • Help define a specific coverage area Horizontal Vertical

  41. Antenna Impedance 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.

  42. 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.

  43. Environmental Effects • Ice and wind loading, Salt spray • Radomes used to improve performance in icy, windy conditions (more common with larger solid parabolic dishes). Wind loading can be reduced substantially by using a radome. • Wind loading can produce vibration, which in turn can produce azimuth errors. For longer paths, this can be critical. • Installation - pay close attention to proper sealing of all connector junctions.

  44. The 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.

  45. Attenuation Table

  46. Transmission Line Selection • Physical Characteristics: • Bend radius • Diameter - transition considerations (interface ‘jumper cable’ use) • Environmental considerations • Plenum installation (fire retardant) • Special weather-resistant types • UV resistance very important in tropics

  47. 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

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