Co-channel interference results when another RF link is using the same channel frequency. Adjacent-channel interference results when another RF link is using an adjacent channel frequency. In selecting a site, a spectrum analyzer can be used to determine if any strong signals are present at the site and, if they are, to determine how close they are to the desired frequency. The further away from the proposed frequency, the less likely they are to cause a problem. Antenna placement and polarization, as well as the use of high-gain, low-side lobe antennas, are the most effective method of reducing this type of interference.
An important part of planning for broadband fixed wireless system is the avoidance of interference. Interference can be caused by effects within the system or outside the system. Good planning for frequencies and antennas can overcome most interference challenges.
When the entire control cable, from the building entrance to the transverter, is encased in steel conduit, no surge arrestors are required. Otherwise, each control cable requires one surge arrestor within two feet of the building entrance, and another surge arrestor within 10 feet of the transverter .
Because the coaxial line carries a DC current to supply power to the transverter, gas-discharge surge arrestors are required. Do not use quarter-wave stub or solid-state type surge arrestors.
When the entire coaxial cable, from the building entrance to the transverter, is encased in steel conduit, no surge arrestors are required. However, local electrical codes require that the conduit be grounded where it enters the building.
When steel conduit is notused to encase the cable, each cable requires one surge arrestor within 2 feet of the building entrance, and another surge arrestor within 10 feet of the transverter .
To provide effective lightning protection, install antennas in locations that are unlikely to receive direct lightning strikes, or install lightning rods to protect antennas from direct strikes . Make sure that cables and equipment are properly grounded to provide low-impedance paths for lightning currents. Install surge suppressors on telephone lines and power lines.
Cisco recommends lightning protection for both coaxial and control cables leading to the wireless transverter . The lightning protection should be placed at points close to where the cable passes through the bulkhead into the building, as well as near the transverter.
The potential for lightning damage to radio equipment should always be considered when planning a wireless link .A variety of lightning protection and grounding devices are available for use on buildings, towers, antennas, cables, and equipment, whether located inside or outside the site that could be damaged by a lightning strike.
Lightning protection requirements are based on the exposure at the site, the cost of link down-time, and local building and electrical codes. If the link is critical, and the site is in an active lightning area, attention to thorough lightning protection and grounding is critical.
Any system components mounted outdoors will be subject to the effect of wind. It is important to know the direction and velocity of the wind common to the site. Antennas and their supporting structures must be able to prevent these forces from affecting the antenna or causing damage to the building or tower on which the components are mounted.
Antenna designs react differently to wind forces, depending on the area presented to the wind. This is known as wind loading. Most antenna manufacturers will specify wind loading for each type of antenna manufactured.
A relatively small effect on the link is from oxygen and water vapor. It is usually significant only on longer paths and particular frequencies. Attenuation in the 2 to 14 GHz frequency range is approximately 0.01 dB/mile, which is not significant .
Microwave RF communication is estimated for rain and frequency. Each maps the world into “rain climate regions”. Based on the region, microwave links can be engineered to support any desired availability. The intersection of the radio margin line and the rain zone line is the distance that can be achieved with 99.999% availability . Except in extreme conditions, attenuation (weakening of the signal) due to rain does not require serious consideration for frequencies up to the range of 6 or 8 GHz. When microwave frequencies are at 11 or 12 GHz or above, attenuation due to rain becomes much more of a concern, especially in areas where rainfall is of high density and long duration. If this is the case, shorter paths may be required .
The systems discussed in this guide operate at frequencies below 6 GHz, so rain is not a concern.
In most cases, the effects of fog are considered to be much the same as rain. However, fog can adversely affect the radio link when it is accompanied by atmospheric conditions such as temperature inversion, or very still air accompanied by stratification. Temperature inversion can negate clearances, and still air along with stratification can cause severe refractive or reflective conditions, with unpredictable results. Temperature inversions and stratification can also cause ducting, which may increase the potential for interference between systems that do not normally interfere with each other. Where these conditions exist, Cisco recommends shorter paths and adequate clearances .
It is important to research any unusual weather conditions that are common to the site location. These conditions can include excessive amounts of rain or fog, wind velocity, or extreme temperature ranges. If extreme conditions exist that may affect the integrity of the radio link, Cisco recommend that these conditions be taken into consideration early in the planning process.
Electromagnetic waves at the frequency range of about 2 to 40 GHz are referredto as microwave. Microwave radio operates in unlicensed bands are 2.4 GHz and 5.7 GHz and are licensed band it could operate like 6GHz, 7 GHz, 8GHz, 10GHz, 11GHz and 13GHz, 15GHz, 18GHz and 23GHz, 38GHz frequency bands. At these frequencies, highly directional beams are possible and microwave is quite suitable for point-to-point transmission. Concentrating all the energy into a small beam using a parabolic antenna (like the familiar satellite TV dish) gives a much higher signal to noise ratio, but the transmitting and receiving antennas must be accurately aligned with each other. It’s a type of unbounded network transmission medium. Microwave is mainly used for satellite communications.A microwave system includes an antenna, radio, multiplexes, waveguide (hollow metal conductor connecting the RF equipment to the antenna) and feed cables . Based on capacity and radio equipment, antenna size, tower heights and terrain elevation will play a major role in how it will plannedand construct the system. These four factors also will dictate system reliability, multi-path fading, fade margin calculations, freshnel zone clearance, interference analysis, system diversity and long-distance specifications
Electromagnetic waves at the frequency range of about 2 to 40 GHz are referredto as microwave. Microwave radio operates in unlicensed bands are 2.4 GHz and 5.7 GHz and are licensed band it could operate like 6GHz, 7 GHz, 8GHz, 10GHz, 11GHz and 13GHz, 15GHz, 18GHz and 23GHz, 38GHz frequency bands. At these frequencies, highly directional beams are possible and microwave is quite suitable for point-to-point transmission. Concentrating all the energy into a small beam using a parabolic antenna (like the familiar satellite TV dish) gives a much higher signal to noise ratio, but the transmitting and receiving antennas must be accurately aligned with each other. It’s a type of unbounded network transmission medium. Microwave is mainly used for satellite communications.A microwave system includes an antenna, radio, multiplexes, waveguide (hollow metal conductor connecting the RF equipment to the antenna) and feed cables . Based on capacity and radio equipment, antenna size, tower heights and terrain elevation will play a major role in how it will plannedand construct the system. These four factors also will dictate system reliability, multi-path fading, fade margin calculations, freshnel zone clearance, interference analysis, system diversity and long-distance specifications
The installation of a wireless network requires much the same basic planning as any wired network. The main difference is that the wireless signal requires some additional planning . Compared to landline solutions, RF has significant advantages in speed, ease and cost of deployment. An RF segment between two sides can be installed in a few days. A typical installation consists with indoor cabinet, power and signal cables between the indoor location and the outdoor location,installation of outdoor components such as outdoor units,RF path planning, site preparation, antennas, lightning protection devices, and cabling suitable for outdoor conditions . Usually, also need to investigate the zoning laws as well as Federal Communications Commission (FCC) and Federal Aviation Administration (FAA) regulations. The installation cost is minimal compared to laying cable and the radio equipment cost is comparable to equipment used with landlines .
The technique of transmitting more than one information signal through a single channel is called multiplexing. There are two types of multiplexing
(a) Frequency Division Multiplexing (FDM) and
(b) Time Division Multiplexing (TDM)
When the information signal is digital and the carrier signal is Sinusoidal, modulation is called shift keying [Book03]. According to the change of the parameter of the carrier (sinusoidal) by the digital signal we have,
(a) Amplitude Shift Keying (ASK)
(b) Frequency Shift Keying (FSK) and
(c) Phase Shift Keying (PSK)
In addition, a combination of ASK and PSK is employed at high bit rates. This method is called Quadrature Amplitude Modulation (QAM) .
The basic idea here is to superimpose the message signal in analog form on a carrier which is a sinusoid of the form
A cos (ωct + )
There are three quantities that can be varied in proportion to the modulating signal: the amplitude, the phase, and frequency. The first scheme is called Amplitude Modulation and the second two are called Angle Modulation schemes.
Fig.1.2 Types of Analog Modulation
There are two types of analog modulation.
1.Amplitude Modulation
2.Angle Modulation.
Angle modulation are also have two different types.
1. Frequency Modulation(FM)
2. Phase Modulation(PM)
In amplitude modulation, the message signal will be present in the amplitude of the transmitted signal.
Analog modulation is non linear modulation and requires high bandwidth and also have good performance in the presence of noise .
In frequency modulation, the message signal will be present in the instantaneous frequency.
In phase modulation, the message signal will be present in the phase.
In quadrature amplitude modulation, the message will be present in both the amplitude and the phase .
Very rarely base band transmission is used for long distance transmission. A technique called modulation is used for the purpose. In modulation there is a carrier signal. The carrier signal may be an analog sinusoidal signal of a fixed frequency or a train of pulses of certain frequency .
The information signal is placed on the carrier. The information signal introduces certain change in the parameter of the carrier. In the case of analog sinusoidal carrier, it is possible to change the amplitude or frequency or phase or two of them or all of them by the information signal.
The point to modulation is to take a message bearing signal and superimpose it upon a carrier signal for transmission. For ease of transmission carrier signals are generally high frequency for several reasons [Book03]:
For easy (low loss, low dispersion) propagation as electromagnetic waves.
So that they may be simultaneously transmitted without interference from other signals.
So as to enable the construction of small antennas (a fraction, usually a quarter of the wavelength).
So as to be able to multiplex that is to combine multiple signals for transmission at the same time.
Modulation is the process of putting an information signal on a carrier signal for some technical advantages.
Demodulation is the opposite of modulation. That is separation of the information signal from the received modulation signal. For data transmission demodulation is the process of recovering the data signal from the received asked sinusoidal signal.
Modulation is the process by which some characteristic of a carrier signal is varied in accordance with a modulating signal. Many ways exist to modulate a message signal m(t) to produce a modulated (transmitted) signal x(t). For amplitude, frequency, and phase modulation, modulated signals can be expressed in the same form as
s(t) = A (t) cos(2 ƒc t+ (t))
where A(t) is a real-valued amplitude function (a.k.a. the envelope), ¦c is the carrier frequency, and θ(t) is the real-valued phase function.
Communication systems are often organized according to the following structure
Very rarely base band transmission is used for long distance transmission. A technique called modulation is used for the purpose. In modulation there is a carrier signal. The carrier signal may be an analog sinusoidal signal of a fixed frequency or a train of pulses of certain frequency .
The information signal is placed on the carrier. The information signal introduces certain change in the parameter of the carrier. In the case of analog sinusoidal carrier, it is possible to change the amplitude or frequency or phase or two of them or all of them by the information signal.
The point to modulation is to take a message bearing signal and superimpose it upon a carrier signal for transmission. For ease of transmission carrier signals are generally high frequency for several reasons:
For easy (low loss, low dispersion) propagation as electromagnetic waves. So that they may be simultaneously transmitted without interference from other signals. So as to enable the construction of small antennas (a fraction, usually a quarter of the wavelength). So as to be able to multiplex that is to combine multiple signals for transmission at the same time. Modulation is the process of putting an information signal on a carrier signal for some technical advantages.
Demodulation is the opposite of modulation. That is separation of the information signal from the received modulation signal. For data transmission demodulation is the process of recovering the data signal from the received asked sinusoidal signal .
Modulation is the process by which some characteristic of a carrier signal is varied in accordance with a modulating signal. Many ways exist to modulate a message signal m(t) to produce a modulated (transmitted) signal x(t). For amplitude, frequency, and phase modulation, modulated signals can be expressed in the same form as
s(t) = A (t) cos(2 piƒc t+ θ(t))
where A(t) is a real-valued amplitude function (a.k.a. the envelope), ¦c is the carrier frequency, and θ(t) is the real-valued phase function.
Communication systems are often organized according to the following structure
What you’ll learn in this class •How to use internet search and internet resources for schoolworkand home use •Lecture, demonstration and hands-on practice •Develop effective search query formation •Learn how to organize your search •What to do when you’re stuck •Learn how to evaluate the trustworthiness of web sites
Search Basics •Some basic terms: –Web site: a collection of web pages on a web server –Browser: the software you use to view web pages such as:Internet Explorer (IE), Firefox, Safari, Opera –Query: the terms you send to Google to ask your question –URL:the string that refers to the web page –Plugin:an extra piece of code that plugs into the browse such as:Quicktime, Flash, SVG, ….
To get started •I need to tell you a few things: .
