References: Kennedy Kennedy and Davis Tomasi Several Review Materials from: Blake Excel Review Center Frenzel PERCDC Miller CERTI Roddy and Coolen EDGE / MITRC Microwave Communications Ferdinand M. Gabriel Rose Ellen N. Macabiog Microwave Radio IF repeaters - Also called heterodyne repeaters. - Received RF carrier is down-converted to an IF frequency, amplified, reshaped, up-converted to an RF frequency, and then retransmitted. IF amplifier Equalizer and shaper RF power amplifier BPF BPF Microwave generator Mixer Mixer IF IF IF From antenna To antenna Receiver Transmitter IF Repeater RF RF Microwave Radio Baseband repeaters - The received RF carrier is down-converted to an IF frequency, amplified, filtered, and then further demodulated to baseband. - The baseband signal, which is typically frequency-division-multiplexed voice-band channels, is further modulated to a mastergroup, supergroup, group, or even channel level. Microwave Radio FM receiver FM Transmitter RF power amplifier BPF BPF Microwave generator Mixer Mixer Multiplexing and demultiplexing equipment IF IF From antenna To antenna Receiver Transmitter Baseband Repeater RF RF To other multiplexers and demultiplexers Microwave Radio FM receiver FM Transmitter RF power amplifier BPF BPF Microwave generator Mixer Mixer Baseband amplifier and equalizer IF IF From antenna To antenna Receiver Transmitter Another Baseband Repeater configuration RF RF Baseband Baseband Microwave Radio RF repeater - The received microwave signal is not down-converted to IF or baseband. - The signal is simply mixed (heterodyned) with a local oscillator frequency in a nonlinear mixer. Microwave Radio RF power amplifier BPF BPF Local Oscillator Mixer LO From antenna To antenna Receiver Transmitter RF Repeater (RFin ± LO) RF out RF in RF out Microwave Radio Diversity - Microwave systems use line-of-sight transmission. This means that the transmitting and receiving antennas must see “eye-to-eye”. Diversity suggests that: -There is more than one transmission path -There is more than one method of transmission available between a transmitter and a receiver. Purpose of Diversity: -The purpose of using diversity is to increase the reliability of the system by increasing its availability. Microwave Radio Frequency Diversity -Modulating two different RF carrier frequencies with the same IF intelligence, then transmitting both RF signals to a given destination. Power Splitter BPF A BPF B C h a n n el c o m bi n er Microwave transmitter frequency A Microwave transmitter frequency B A B IF in RF out Frequency Diversity Transmitter Microwave Radio Quality detector BPF A BPF B C h a n n e l s e p a r a t o r Microwave receiver frequency A Microwave receiver frequency B A B IF out RF in Frequency Diversity Receiver IF switch Microwave Radio Space Diversity - The output of a transmitter is fed to two or more antennas that are physically separated by an appreciable number of wavelengths. - Similarly, at the receiving end, there may be more than one antenna providing the input signal to the receiver. - If multiple receiving antennas are used, they must also be separated by an appreciable number of wavelengths. Microwave Radio BPF C h a n n e l c o m b i n e r Microwave transmitter FM – IF in RF out Single - channel space diversity transmitter RF out Microwave Radio Space-diversity arrangements provide for path redundancy but not equipment redundancy. Space diversity is more expensive than frequency diversity because of the additional antennas and waveguides. Space diversity, however, provides efficient frequency usage and a substantially greater protection than frequency diversity. Microwave Radio BPF C h a n n e l s e p a r a t o r Microwave receiver IF out RF in Single - channel space diversity receiver RF in Microwave Radio Polarization Diversity - A single RF carrier is propagated with two different electromagnetic polarizations (vertical and horizontal). - Electromagnetic waves of different polarizations do not necessarily experience the same transmission impairments. Microwave Radio Hybrid Diversity - A somewhat specialized form of diversity, which consists of a standard frequency-diversity path where the two transmitter/receiver pairs at one end of the path are separated from each other and connected to different antennas that are vertically separated as in space diversity. Microwave Radio Quad Diversity - Another form of hybrid diversity. - Undoubtedly provides the most reliable transmission. - It is also the most expensive. Microwave Radio Two types of protection switching arrangements: 1. Hot standby 2. Diversity Microwave Radio Hot standby protection. - Each working radio channel has a dedicated backup or spare channel. - Hot standby systems offer 100% protection for each working radio channel. Diversity protection. - A single backup channel is made available to as many as 11 working channels. - A diversity system offers 100% protection only to the first working channel to fail. If two radio channels fail at the same time, a service interruption will occur. Microwave Radio FM Microwave Radio Stations Two types of FM microwave stations: 1. Terminals 2. Repeaters Terminal stations - Points in the system where baseband signals either originate or terminate. Repeater stations - Points in a system where baseband signals may be reconfigured. - Points in a system where RF carriers are simply "repeated" or amplified. Microwave Radio Terminal Station - A terminal station consists of four major sections: 1. The baseband 2. Wire line entrance link (WLEL) 3. FM-IF 4. RF sections Microwave Radio Wireline entrance link (WLEL) - It serves as the interface between the multiplex - terminal equipment and the FM-IF equipment. - It generally consists of an amplifier and an equalizer (which together compensate for cable transmission losses) and level-shaping devices commonly called pre- and deemphasis networks. Microwave Radio IF section - The FM terminal equipment generates a frequency-modulated IF carrier. RF section. - The IF signal enters the transmitter through a protection switch. - The IF and compression amplifiers help keep the IF signal power constant and at approximately the required input level to the transmit modulator (transmod). Microwave Radio Mixer FDM mux Equalizers Preemphasis network Amp Deviator f1 Deviator f2 IF out to microwave transmitter FDM mux Equalizers Deemphasis network Amp FM discriminator Limiter IF in from microwave receiver (f1 ± At/2) (f2 ± At/2) (f1- f2) ± At (a) (b) Baseband Wireline entrance link FM-IF section Microwave terminal station, baseband, WLEL, and FM-IF: (a) transmitter; (b) receiver Microwave Radio Transmod - A balanced modulator that, when used in conjunction with a microwave generator, power amplifier, and Bandpass filter, up-converts the IF carrier to an RF carrier and amplifies the RF to the desired output power. Microwave Radio Microwave generator - Provides the RF carrier input to the up-converter. - It is called a microwave generator rather than an oscillator because it is difficult to construct a stable circuit that will oscillate in the gigahertz range. Microwave Radio Isolator - A unidirectional device often made from a ferrite material. - Used in conjunction with a channel-combining network to prevent the output of one transmitter from interfering with the output of another transmitter. Microwave Radio Microwave terminal station: (a) transmitter; (b) receiver Isolator Protection switch IF amp Compression amp Power amp and BPF RF out (a) IF in Transmod Microwave generator Channel combining network From other channels VF lines to auxiliary channel To protection channel Up-converter RF IF (b) BPF Protection switch IF amp and AGC RF in IF out Receive mod Microwave generator Channel separation network To other channels VF lines from auxiliary channel From protection channel Down-converter RF IF Microwave Radio Channel combining network Microwave IF repeater station BPF and power amp Channel separation network BPF Receive mod Transmod 6000 MHz 5930 MHz IF IF amp/AGC and equalizer Shift mod 6180 MHz 70 MHz Down-converter RF RF Isolator From other repeaters 6110 MHz Microwave generator 5930 MHz To other repeaters Up-converter BPF Shift oscillator 180 MHz Microwave Radio A Rx Tx B Rx Tx C Rx Tx f1 f1 f1 f1 f1 (a) A Rx Tx B Rx Tx C Rx Tx F2 F1 F2 F1 f1 (b) (a) Multihop interference and (b) high/low microwave system Microwave Radio Path Characteristics a.The free-space path is the line-of-sight path directly between the transmitting and receiving antennas (this is also called the direct wave). b. The ground-reflected wave is the portion of the transmit signal that is reflected off Earth's surface and captured by the receive antenna. c. The surface wave consists of the electric and magnetic fields associated with the currents induced in Earth's surface. Microwave Radio d. The sum of these three paths (taking into account their amplitude and phase) is called the ground wave. e. The sky wave is the portion of the transmit signal that is returned (reflected) back to Earth's surface by the ionized layers of Earth's atmosphere. Microwave Radio For frequencies above about 30 MHz to 50 MHz, the free-space and ground-reflected paths are generally the only paths of importance. The surface wave can also be neglected at these frequencies, provided that the antenna heights are not too low. Microwave Radio The sky wave is only a source of occasional long-distance interference and not a reliable signal for microwave communications purposes. Microwave Radio In microwave systems, the surface and sky-wave propagations are neglected, and attention is focused on those phenomena that affect the direct and reflected waves. Microwave Radio Sky wave Free-space path (line of sight) Direct space wave Ground reflected wave Surface wave Earth’s surface Propagation path Microwave Radio Fading - A general term applied to the reduction in signal strength at the input to a receiver. - Applies to propagation variables in the physical radio path which affect changes in the path loss between the transmitter at one station and its normal receiver at the other station. - Can occur under conditions of heavy ground fog or when extremely cold air moves over a warm earth. Microwave Radio System Gain - The difference between the nominal output of a transmitter and the minimum input power required by a receiver. - must be greater than or equal to the sum of all the gains and losses incurred by a signal as it propagates from a transmitter to a receiver. - Represents the net loss of a radio system. Microwave Radio System gain min C P G t S ÷ = Gs = system gain (dB) Pt = transmitter output power (dBm) Cmin = minimum receiver input power for a given quality objective (dBm) Microwave Radio gains losses C P t ÷ > ÷ min Gains: At = transmit antenna gain (dB) relative to an isotropic radiator Ar = receive antenna gain (dB) relative to an isotropic radiator Losses: Lp = free-space path loss between antennas (dB) Lf = waveguide feeder loss (dB) between the distribution network (channeI-combining network or channel-separation network) and its respective antenna Lb = total coupling or branching loss (dB) in the circulators, filters, and distribution network between the output of a transmitter or the input to a receiver and its respective waveguide feed Fm = fade margin for a given reliability objective Microwave Radio Microwave power amp P t C h a n n el c o m bi n e r L b From other microwave transmitters C h a n n el s e p ar at or L b Microwave receiver C min To other microwave receivers Lf Lf A t A r Lp, FM System gains and losses Microwave Radio r t b f p m t S A A L L L F C P G ÷ ÷ + + + > ÷ = min • where all values are expressed in dB or dBm. Because system gain is indicative of a net loss, the losses are represented with positive dB values and the gains are represented with negative dB values. Microwave Radio Free-Space Path Loss - Sometimes called spreading loss. - the loss incurred by an electromagnetic wave as it propagates in a straight line through a vacuum with no absorption or reflection of energy from nearby objects. - Frequency dependent and increases with distance. Microwave Radio Free-space path loss 2 2 4 4 | . | \ | = | . | \ | = c fD D L P t ì t Lp = free space path loss (unitless) D = distance (meters) f = frequency (hertz) ì = wavelength (meters) c = velocity of light in free space (3x108 m/s) Microwave Radio Fade Margin - This is the “fudge factor” included in the system gain equation that considers the non-ideal and less predictable characteristics of radio wave propagation such as multi path propagation (multipath loss) and terrain sensitivity. Microwave Radio Non diversity system 70 ) 1 log( 10 ) 6 log( 10 log 30 ÷ ÷ ÷ + = R ABf D Fm 30logD = multipath effect 10log(6ABf) = terrain sensitivity 10log(1-R) = reliability objectives Fm = fade margin (dB) D = distance (kilometers) f = frequency (gigahertz) R = reliability expressed as decimal 1 – R = reliability objective for a one-way 40-km route A = roughness factor: = 4 over a very smooth terrain = 1 over an average terrain = 0.25 over a very rough, mountainous terrain Microwave Radio B = factor to convert the worst-month probability to an annual probability = 1 to convert an annual availability to a worst-month basis = 0.5 for humid areas = 0.25 for average inland areas = 0.125 for very dry or mountainous areas Microwave Radio Receiver Threshold - The minimum wideband carrier power (Cmin) at the input to a receiver that will provide a usable baseband output. - Sometimes called the receiver sensitivity Carrier-to-noise (C/N) ratio - Probably the most important parameter considered when evaluating the performance of a microwave communications system. Microwave Radio Input noise power KTB N = N = noise power (watts) K = Boltzmann's constant (1.38 X 10 -23 J/K) T = equivalent noise temperature of the receiver (kelvin) (room temperature = 290 kelvin) B = noise bandwidth (hertz) Microwave Radio B KT KTB N dBm log 10 001 . 0 log 10 001 . 0 log 10 ) ( + = = For a 1-KHz bandwidth at room temperature ( ) B N dBm x N dBm log 10 174 174 001 . 0 290 ) 10 38 . 1 ( log 10 ) ( 23 + ÷ = ÷ = = ÷ Microwave Radio Minimum receive carrier power dBm dBm dB N N C C 80 ) 104 ( 24 min ÷ = ÷ + = + = Minimum transmit carrier power (Pt) dBm dBm dB C G P S t 35 . 33 ) 80 ( 35 . 113 min = ÷ + = + = Microwave Radio Carrier-to-Noise Versus Signal-to-Noise Ratio Carrier-to-noise ratio (C/N) - The ratio of the wideband "carrier" to the wideband noise power (the bandwidth of the receiver). Signal-to-noise ratio (S/N) - A postdetection (after the FM demodulator) ratio. Microwave Radio Noise Factor and Noise Figure Noise factor (F) and Noise figure (NF) - These are figures of merit used to indicate how much the signal-to-noise ratio deteriorates as a signal passes through a circuit or series of circuits. Noise factor - a ratio of input signal-to-noise ratio to output signal-to-noise ratio. Microwave Radio Noise factor ) (unitless ratio noise to signal output ratio noise to signal input F ÷ ÷ ÷ ÷ ÷ = Noise figure F NF dB ratio noise to signal output ratio noise to signal input NF log 10 ) ( log 10 = ÷ ÷ ÷ ÷ ÷ = Microwave Radio - Noise figure indicates how much the signal-to-noise ratio deteriorates as a waveform propagates from the input to the output of a circuit. Microwave Radio Thermal noise - Most predominant noise. - Generated in all electrical components Microwave Radio Total noise factor of several cascaded amplifiers 3 2 1 2 1 3 1 2 1 1 1 1 A A A F A A F A F F F n T ÷ + ÷ + ÷ + = FT = total noise factor for n cascaded amplifiers F1 = noise factor, amplifier 1 F2 = noise factor, amplifier 2 F3 = noise factor, amplifier 3 Fn = noise factor, amplifier n A1 = power gain, amplifier 1 A2 = power gain, amplifier 2 A3 = power gain, amplifier 3 Microwave Radio T dB T F NF log 10 ) ( = In Out A1 F1 A2 F2 A3 F3 An Fn Total noise figure Microwave Radio B KT N e d = Te = equivalent noise temperature. No = total output noise power of an amplifier (watts) Ni = total input noise power of an amplifier (watts) A = power gain of an amplifier (unitless) Microwave Radio ) ( e o e o d i o T T AKB N B AKT AKTB N and AN AN N + = + = + = ( ) ( ) T T T T T AKTB T T AKB AN N N S A N S N S N S F e e e i o out i out in T + = + = + = = | . | \ | = = 1 ) ( Signal in Signal out N O N i T N d T e A Noise figure as a function of temperature Microwave Radio Microwave Engineering Procedures: 1. Selection of sites that are line-of-sight to each other (includes tower location). 2. Selection of an operating frequency band. 3. Selection of radio equipment, transmission media and tower. 4. Development of path profiles to determine tower heights. 5. Link budget calculations. 6. Making path surveys. Microwave Radio 9. Installation. 10. Testing of the link (includes equipment lineup, beam alignment, equipment inspection). 11. Acceptance by the customer. 7. Establishment of a frequency plan and necessary operational parameters. 8. Equipment configuration to achieve the most economical fade margin set in step 5. Microwave Radio The K-factor: - This is a numerical figure that considers the non-ideal condition of the atmosphere resulting to atmospheric refraction that causes the ray beam to be bent toward the earth or away from the earth. o e r r radius earth True radius earth Effective k = = Microwave Radio k=1 k>1 K<1 Path length The K-curve Microwave Radio Effective Earth Radius (re) ) 005577 . 0 ( ) ( 04665 . 0 1 S N o km e e r r ÷ = NS = Surface refractivity r o = true earth radius (6370 km) ) ( 1057 . 0 S h O S e N N ÷ = h S = height of potential site in km Microwave Radio K-curve conditions: a.Sub-standard condition 1 < k - the microwave beam is bent away from the earth. It is as if the earth’s curvature is extended or the earth bulge is effectively increased hence, the path is shortened and the tower must be increased. Microwave Radio b. Standard condition 3 4 = k Under this condition, the fictitious earth radius appears to be longer than the true earth’s radius, thus, the earth path is assumed to be smooth (no obstacles besides mid-path earth bulge) such that the microwave beam is neither bent toward the earth or away from the earth. Microwave Radio c. Super-standard condition 3 4 > k This condition results in an effective flattening of the equivalent earth’s curvature and the microwave beam is bent toward the earth, which allows decreasing the tower heights. Microwave Radio d. Infinity condition (Flat earth condition) · = k This condition results to zero curvature (as if the earth is very flat) and the microwave beam follows the earth’s curvature. Microwave Radio Earth Bulge (e b ) - This is the height at which an obstacle along the path is further raised due to the earth’s curvature. 75 . 12 5 . 1 ) ( 2 ) ( 1 ) ( ) ( 2 ) ( 1 ) ( Km Km m b mi mi ft b d d e d d e = = Microwave Radio Fresnel Clearance - Another factor that must be added to the obstacle height to obtain an overall effective obstacle height. - It derives from EM wave theory that a wavefront has expanding properties as it travels through space. Fresnel Zone Radius - The amount of additional clearance that must be allowed to avoid problems with the Fresnel phenomenon. Microwave Radio ) ( ) ( ) ( 2 ) ( 1 ) ( 1 ) ( ) ( ) ( 2 ) ( 1 ) ( 1 3 . 17 1 . 72 km GHz km km m mi GHz mi mi ft D f d d F D f d d F = = 60% of the 1st Fresnel Zone Radius (0.6F1) - This is a situation when there is no net change in attenuation or “no gain, no loss” condition occurs and when 60% of the first Fresnel radius clears a path obstruction in microwave systems. Microwave Radio Higher Fresnel Zone Radius n F F n 1 = n = nth Fresnel zone Microwave Radio Microwave Link Budget Calculations Path Profile - This is a graphical presentation of the path traveled by the radio waves between the two ends of the link. - It determines the location and height of the antenna at each end of the link. - It ensures that the link is free of obstructions, such as hills, trees, buildings, etc. Microwave Radio 1. Transmit Parameters a. Transmit Power (dBw, dBm) b. Transmitter Transmission Line Loss (dB) c. Transmitter Antenna Gain (dB) ft GHZ dB T m GHz dB T T D f G D f G D D G log 20 log 20 5 . 7 log 20 log 20 8 . 17 6 ) ( ) ( 2 2 + + = + + = | . | \ | = | . | \ | = ì ì t q Microwave Radio d. Effective Isotropically Radiated Power (EIRP) - The actual power going into the antenna multiplied by its gain with respect to an isotropic radiator. ) ( ) ( ) ( dB T dBw T dBw t t G P EIRP G P EIRP + = = ) ( ) ( ) ( ) ( dB T dB T dBw T dBw T T T L G P EIRP L G P EIRP ÷ + = = Microwave Radio Effective Radiated Power (ERP) - The power input multiplied by the antenna gain measured with respect to a half-wave dipole. - An ideal half-wave dipole has a gain of 2.14 dBi. Therefore, EIRP is 2.14 dB greater than the ERP for the same antenna-transmitter combination. dB ERP EIRP 14 . 2 + = Microwave Radio 2. Path Parameters a. Free Space Loss b. Fade Margin dBm dBm dBm dBw dBw dB IT RSL FM FMIT RSL FM f ormulas additonal ÷ = ÷ = ) ( ) ( : c. Isotropic Receive Level (IRL) Microwave Radio 3. Receive Parameters a. Receiver Antenna Gain (dB) b. Receiver Transmission Line Loss (dB) c. Carrier-to-Noise Ratio (C/N) dB dBm dB N RSL N C ÷ = | . | \ | ) ( d. Receiver Sensitivity Microwave Radio 4. Miscellaneous Parameters a. Net Path Loss (NPL) b. Receive Signal Level (RSL) c. Noise Threshold dB dBm dB dBm dB dBw dB dBw NF B N or NF mW kTB N NF B N or NF kTB N + + ÷ = + = + + ÷ = + = log 10 174 1 log 10 log 10 204 log 10 ) ( ) ( ) ( ) ( Microwave Radio d. FM Improvement Threshold (FMIT) dB N FMIT dB dB 10 _) ( _) ( + = Microwave Radio Reliability % 100 ) 1 ( x outage R ÷ = For multi-hop link n S xR xR xR R R ... 3 2 1 = Outage = the amount of time that the requirements will not be met R1, R2, …Rn = individual reliability Microwave Radio Availability - the percentage of time a system or link meets performance requirements MTTR MTBF MTBF A + = MTBF = mean time between failures MTTR = mean time to repair Microwave Radio Unavailability - the percentage of time a system or link does not meet requirements % 100 ) 1 ( x A U MTTR MTBF MTTR U ÷ = + = Microwave Radio Passive Repeaters a. Back-to-back Parabolic Antenna Repeater or Back-to-back Horn Antenna Repeater - consists of two parabolic antennas or horn antennas connected back-to-back through a short piece of waveguide - this is relatively inefficient, seldom used except in extremely short paths Microwave Radio b. Billboard Repeater -flat, metal-type reflector, which acts as a microwave mirror that reflects EM waves surfaces of adequate flatness is highly efficient (close to 100%) Microwave Radio Gain of Billboard Repeater Thank you!