Objectives And Scope
This chapter deals with the design of radiolinks that operate beyond line-of-sight (BLOS). Two transmission modes achieving over-the-horizon communications are examined diffraction and scattering. Diffraction over one or more obstacles can be the predominant transmission mode on most shorter paths (i.e., less than 100 mi, 160 km) displaying long-term median transmission loss (path loss) on the order of 170-190 dB. On longer paths (i.e., from 100 to about 500 mi (160-800 km) or more) scattering...
What Are Paging Systems
Paging is a one-way radio alerting system. The direction of transmission is from a fixed paging transmitter to an individual. It is a simple extension of the PSTN. Certainly paging can be classified as one of the first PCS (personal communication system) operations. The paging receiver is a small box, usually carried on a person's belt. As a minimum, a pager alerts the user that someone wishes to reach him her by telephone. The person so alerted goes to the nearest telephone and calls a...
Frequency Management
In the context of this chapter, frequency management is the art technology of selecting an optimum frequency for HF communication at a certain time of day between any two points on the earth. One important factor is omitted in the process, that is, the interference that may be present in the path, affecting one or both ends of the path. We will be using the terms MUF, LUF, and FOT (OWF). The MUF and LUF are the upper and lower limiting frequencies for skywave communication...
Example CI Calculations Based on
The following minimum input information is necessary for C I (and T I ) calculations 1. Latitudes and Longitudes of Stations A, B, D and E (Including Datum). With this information all of the necessary path lengths, azimuths, and discrimination angles can be calculated. 2. Size, Types, and Polarizations of Antennas. This information is for both systems, preferably with identification of the manufacturers and model numbers. This will allow determination of...
Obstructed Interfering Paths
Unless a microwave path strictly meets the line-of-site criterion provided in Chapter 2, then an obstruction penalty must be imposed. There are other microwave interferers that because of their geography and geometry would appear not to be interference sources. Such facts should be verified regarding spill by diffraction or troposcatter mechanisms into a victim receiver. Diffraction and troposcatter mechanisms are discussed in Chapter 5. The allowable interference levels discussed so far are...
Composition of Basic HF Equipment
A HF installation for two-way communication consists of one or more transmitters and one or more receivers. The most common type of modulation waveform is single-sideband suppressed carrier (SSBSC). The operation of this equipment may be half- or full-duplex. We define half-duplex as the operation of a link in one direction at a time. In this case, the near-end transmitter transmits and the far-end receiver receives then the far-end transmitter transmits and the near-end receiver receives....
Rationale
Interference is an onerous problem that must be dealt with. It is a fact of life and we can do something about it. There are interference issues with all radio systems. In essence, our concern is electromagnetic compatibility (EMC). We turn to the IEEE for help from their standard dictionary (Ref. 1) to define EMC. We think the IEEE definition number 2 is appropriate EMC is the ability of a device, equipment or system to function satisfactorily in its electromagnetic environment without...
Path Profiles
A path profile is a graphical representation of a path between two adjacent radiolink sites in two dimensions. From the profile, tower heights are derived, and, subsequently, these heights can be adjusted (on paper) so that the ray beam reflection point will avoid reflective surfaces. The profile essentially ensures that the proper clearances of path obstructions are achieved. There are three recognized methods to draw a path profile 1. Fully Linear Method. Common linear graph paper is used...
Calculation of Excess Attenuation Due to Rainfall for LOS Microwave Paths
When designing LOS microwave links (or satellite links) where the operating frequency is above 10 GHz, a major problem in link design is to determine the excess path attenuation due to rainfall. The adjective excess is used to denote path attenuation in excess of free-space loss i.e., the terms a, b, c, d, and e in equation (9.1) are losses in excess of free-space loss . Before treating the methodology of calculation of excess rain attenuation, we will review some general link engineering...
Trellis Coded Modulation TCM
TCM is a generalized convolutional coding scheme with nonbinary signals optimized to achieve large free Euclidean distance,'' dE, among sequences of transmitted symbols. This results in a lower Eb N0 value or a smaller bandwidth to transmit binary digital signals at a given rate and BER. TCM uses a redundant alphabet to achieve this advantage. It is obtained by convolutionally encoding k out of n information bits to be transmitted at a certain time. One redundant bit is added where the...
Definitions Of Vsat
A very small aperture terminal (VSAT) is a digital satellite terminal where economy is the key word. The term very small aperture, of course, refers to the size of the terminal antenna. The diameters of VSAT parabolic antennas vary from 0.6 m (2 ft) to 2.4 m (7.8 ft), depending a great deal on the capabilities desired from the terminal. These can vary from a data connectivity (inbound) of 1200 bps up to a full DS1 or E-1. In most cases, the definition denotes a family of modest ''out...
Problems And Exercises
1 Compare spectrum occupancy for one voice channel (or equivalent) for LOS microwave analog SSB, analog FM (conventional), and digital. Assume 1 bit Hz. 2 Calculate N0 for a low-noise receiver with a 1-dB noise figure. 3 Calculate Eb for a RSL of - 85 dBW and a bit rate of 45 Mbps. 4 Calculate Eb N0 given 155 Mbps, a RSL of -82.5 dBW, and a receiver noise figure of 2.7 dB. 5 Describe bit packing. Why is it important in digital transmission, particularly when U.S. FCC licensing is required 6...
Penalty For Not Meeting Obstacle Clearance Criteria
If a radiolink path does not meet the obstacle clearance criteria established in Section 1.4, there is a penalty of excess attenuation due to diffraction loss. Diffraction loss depends on the type of terrain and vegetation. For a given path ray clearance, the diffraction loss will vary from a minimum value for a single knife-edge obstruction to a maximum value for a spherical smooth earth. Methods of calculating diffraction loss are given in Chapter 4. The upper and lower limits of diffraction...
Basic Long Term Median Tropospheric Scatter Loss Lbsr
Lbsr(dB) 30log F - 20log d + F(0d) - F0 + H0 + Aa (5.2) where f the operating frequency in megahertz d greater circle path length in kilometers F(dd) attenuation function F0 scattering efficiency correction factor H0 frequency gain function Aa atmospheric absorption 0d product of the angular distance and path distance (angular distance in radians, path distance distance in kilometers) We disregard the F0 and H0 terms. It should be pointed out that the CCIR method (Ref. 4) is similar to the NBS...
Info
B B 2 B 3 8 4 8 4 8 5 8 6 8 7 8 8 8 9 8 2 8 3 8 4 8 4 X 1 r 8 5 X 1 r 8 6 X 1 r 8 7 X 1 r 8 8 X 1 r 8 9 X 1 r theoretical W and S N values at 106 BER calculated values may differ slightly due to different assumptions. cAs an example, BCH error correction with a redundancy of 6.7 r 6.7 is used for calculations in this table. Source Table 1a, p. 241, ITU-R Rec. F.1101, 1994 Ref.1 . The actual signal-to-noise parameter is related to the average RSL receive signal level , for the relevant BER,...
Lenkurt Navy.mil
Noise in the Radio Portion of Circuits to be Established over Real Radio-Relay Links for FDM Telephony, ITU-R F.395-2, 1990. 2. Permissible Noise in the Hypothetical Reference Circuit of Radio-Relay Systems for Television, ITU-R F.555-1, 1997. 3. B. R. Bean et al., A World Atlas of Atmospheric Radio Refractivity, U.S. Department of Commerce, ESSA, Boulder, CO, 1966. 4. Naval Shore Electronics Criteria, Line-of-Sight Microwave and Tropospheric Scatter Communication Systems, Navelex 0101, 112,...
Model Earth Station
Transmits at 6 GHz, receives at 4 GHz exactly Antenna diameter 3 m D A at 6 GHz 196.8 gain 44 dB Noise figure 1 dB. N0 -203 Hz dBW equation 3.2 Transmitter output power 100 W 20 dBW Transmission line loss 1 dB for both uplink and downlink Modulation on downlink QPSK occupying 7.44 MHz. Coding R f. Eb N0 10 dB producing a BER of 3 X 10- 6 see Figure 4.12 Transmit and or receive on 4 or 6 GHz exactly Antenna diameter 1m D X at 6 GHz 65.6 gain 33 dB 1m D X at 4 GHz 43.7 gain 30 dB Noise figure 8...
Hypothetical Reference Digital Path HRDP for Radio Relay Systems with a Capacity Above the Second Hierarchical Level1
To define error performance, a hypothetical reference digital path is often used to apportion error accumulation. The path is 2500 km long and From ITU-R Rec. F.592-3, 2002. f Section 3.6.3 is based on ITU-R Rec. F.634-3 Ref. 14 . 64 kbit s 64 kbit s 64 kbit s 64 kbit s First order digital multiplex equipment 64 kbit s 64 kbit s 64 kbit s 64 kbit s First order digital multiplex equipment Other multiplex equipment at the CCITT recommended hierarchical levels Figure 3.13. Hypothetical reference...
P
Spherical surface concentric about Si Spherical surface concentric about Si from the antennas to P is constant. Such a point will generate an ellipsoid with 5j and S2 as its foci. We now can define a set of concentric ellipsoidal shells so that the sum of the distances r1 and r2 differs by multiples of a half-wavelength A 2 . The intersection of these ellipsoids defines Fresnel zones on the surface as shown in Figure 1.9. Thus, on the surface of the wavefront, a first Fresnel zone F1 is...
The MTSO or MSC
The mobile telephone switching office MTSO , which is also called mobile switching center MSC , provides the brains for cellular operations in a given Figure 15.47. A cell site controller. Figure 15.47. A cell site controller. Figure 15.48. Cell site, eight-channel power amplifiers with power combiner. Transmitter output at combiner input port is typically 50 dBm. Figure 15.48. Cell site, eight-channel power amplifiers with power combiner. Transmitter output at combiner input port is typically...
Intelsat Standard F Earth Stations
The INTELSAT Standard F earth station operates in INTELSAT's IBS and is similar in most respects to the Standard E earth stations, except that it operates in the 6 4-GHz frequency pair. These earth stations may also be used for the IDR digital services. F-type earth stations may also provide companded frequency division multiplex frequency modulation CFDM FM telephony service. The specified G T values for INTELSAT Standard F earth stations are as follows F-1 G T 22.7 20 log10 f 4 dB K F-2 G T...
Calculation of IF Bandwidth and Peak Frequency Deviation
The IF of a FM receiver must accommodate the RF bandwidth, which consists of the total peak deviation spread and a number of generated sidebands. The IF bandwidth can be estimated from Carson's rule, where A Fp is the peak frequency deviation and Fm is the highest modulating frequency given in the middle column of Table 2.5. 2.6.4.2 Frequency Deviation. The value of AFp in equations 2.17 and 2.18 below is peak deviation. The peak deviation for a particular link should be...
Propagation Effects With A Low Elevation Angle
As the elevation angle of an earth terminal is lowered, the ray beam penetrates an ever increasing amount of atmosphere. Below about 10 , fading on the downlink signal must be considered. Fading or signal fluctuations apply only to the ground terminal downlink because its antenna is in close proximity to a turbulent medium. The companion uplink satellite path will suffer uplink fluctuation gain degradation only due to scattering of energy out of the path Ref. 16 . Because of the large distance...
TDMA System Clocking Timing and Synchronization It was
Previously stressed that an efficient TDMA system must have no burst overlap, on the one hand, and as short a guard time as possible between bursts, on the other hand. We are looking at guard times in the nanosecond regime. The satellites under discussion here are geostationary. For a particular TDMA system, the range to a satellite can vary from 23,000 to 26,000 statute miles. We can express these range values in time equivalents by dividing by the velocity of propagation in free space or...
Vswr
Ambient Temperature 24 C 75 F Atmospheric pressure, dry air Figure 15.9. Loss versus frequency for air dielectric coaxial cable. Courtesy of the Andrew Corporation Ref. 7. There are a number of important parameters to be considered for the application of coaxial cable as a transmission line. Probably the most important for the system engineer is attenuation or loss as shown in Figures 15.8 and 15.9. Loss varies with ambient temperature. The reference value in the figures is 24 C 75 F . Figure...
Uncoded Satellite Communications
Table 4.5 shows the maximum free distance for R 1 2 systematic and nonsystematic codes for K 2 through 5. It should be noted that for large constraint lengths the results are even more widely separated. 4.2.5 Channel Performance of Uncoded and Coded Systems 4.2.5.1 Uncoded Performance. For uncoded systems a number of modulation implementations are reviewed in the presence of additive white Gaussian noise AWGN and with Rayleigh fading. The AWGN performance of BPSK, QPSK, and 8-ary PSK is shown...
Excess Attenuation Due To Rainfall
Of the factors a through e in equation 9.1 , factor e, excess attenuation due to rainfall, is the principal one affecting path loss. For instance, even at 22 GHz for a 10-km path only 1.6 dB must be added to free-space loss to compensate for water vapor loss. This is negligible when compared to free-space loss itself, such as 119.3 dB for the first kilometer at 22 GHz, accumulating thence approximately 6 dB each time the path length is doubled i.e., add 6 dB for 2 km, 12 dB for 4 km, etc. ....
Skywave Transmission
The skywave transmission phenomenon of HF depends on ionospheric refraction. Transmitted radio waves hitting the ionosphere are bent or refracted. When they are bent sufficiently, the waves are returned to earth at a distant location. Often at the distant location they are reflected back to the sky again, only to be returned to earth still again, even further from the transmitter. The ionosphere is the key to HF skywave communication. Look at the ionosphere as a layered region of ionized gas...
Introduction To Tropospheric Scatter Propagation
The picture of the tropospheric scatter mechanism is still pretty speculative. One reasonable explanation is expressed in USAF Technical Order 31Z-10-13 Ref. 1 . It states that the ability of the troposphere to act as a refractive medium is based on the variations of refractivity caused by heating and cooling of the atmosphere's water content. The variation is inversely proportional to altitude, with the greatest variation taking place nearest the earth's surface. The atmosphere is constantly...
Victim Digital Systems
This text emphasizes digital operation. What special considerations must be taken into account for interference into such digital radio systems As we mentioned earlier, interference into a digital receiver causes threshold degradation. Picture this as an increase in the receiver noise level. Interference can eat into an Eb N0 ratio value or wipe it out completely, making the system unworkable. Looking at it another way, interference increases the N0 value. Remember that our outage threshold on...
Path Analysis Worksheet And Example
A path analysis worksheet is a useful tool for carrying out a path analysis or link budget.'' The bottom line, so to speak, of the worksheet for an analog radiolink is the noise in the worst FDM channel, usually the highest or top voice channel in the baseband. The worksheet sets out in tabular form the required calculations starting with transmitter power output, the various losses and gains from the transmitter outward through the medium, receive antenna system to the input port of the far...
Digital Speech Interpolation
DSI is designed for speech operation to increase system capacity. It is based on the fact that there is active speech on a full duplex voice circuit only a fraction of the time. For one thing, there is the talk-listen effect. In normal operation, while one end of a speech circuit talks, the other end listens. For this effect alone, there is only 50 usage. Also, there are many pauses in normal speech. DSI exploits these periods of nonusage and speech pauses. A similar system was implemented on...
Mitigation Techniques for Multipath Fading
In analog radiolink systems, multipath fading results in an increase in thermal noise as the RSL drops. In digital radio systems, however, there is a degradation in BER during periods of fading that is usually caused by intersymbol interference due to multipath. Even rather shallow fades can cause relatively destructive amounts of intersymbol interference. This interference results from frequency-dependent amplitude and group delay changes. The degradation depends on the magnitude of in-band...
Cellular And Pcs Installations Analog And Digital 1561 Introduction
The goal of this section is to describe cellular installations and PCS facilities, which we will consider as an extension of cellular. In Chapter 10, three basic, generic modulation access schemes were described FDMA typified by AMPS and N-AMPS, TDMA typified by the North American IS-54 standard and the European GSM standard, and, finally, CDMA typified by the North American IS-95 standard. In large cellular schemes all three access modulation types require cells or base stations with their...
Very Small Aperture Terminals VSATs
VSAT networks are specialized satellite networks principally used for data traffic. In Chapter 8, Figure 8.1, we saw that a VSAT network most commonly consists of a hub and a series of small outstation satellite terminals, which we call VSATs. Small VSATs have parabolic dish antennas with diameters ranging from 0.5 m for a very modest installation to up to 2.4 m for a much higher capacity installation. Hubs are much larger facilities to compensate somewhat for the small disadvantaged VSATs. One...
Link Budgets For Digital Satellites 771 Commentary
The link budget, of course, is the primary tool for dimensioning both earth station terminals and their companion satellites. It is used for trade-offs of performance versus cost cost because we are dimensioning equipment . The approach we use is almost identical to that described in Section 6.3.9. Rather than S N, we use Eb N0, which was described in Chapter 3. Performance may be enhanced on digital circuits by the use of FEC forward error correction , with or without interleaving. FEC and...
Mba
Isotropic receive level International switching center Integrated services digital network Intersymbol interference Intersatellite link International Standards Organization Iridium subscriber unit International Telecommunications Union ITU Telecommunications Standardization Sector previously CCITT ITU Radiocommunications Sector previously CCIR 28-30-GHz satellite uplink band, microwave LOS band kilobits per second kilometer kilohertz 14 12 11-GHz satellite communication band microwave LOS band...
V
Conventionally, we require 0.6 Fresnel zone clearance of the beam edge 3-dB point due to obstacles in the path. Figure 1.10 shows path attenuation versus path clearance. Providing 0.6 Fresnel zone clearance usually is sufficient to ensure that attenuation due to an obstacle in or near the ray beam path is negligible. Reference 4 gives some practical Fresnel zone clearance guidelines related to -factor Although there are some variations, there are two basic sets of clearance criteria which are...
G
Where G is the receiving system antenna gain and T better expressed as Tsys is the receiving system noise temperature. Now we offer a word of caution. When calculating G T for a particular receiving system, we must stipulate where the reference plane is. In Figure 6.6 it was called the ''reference point.'' It is at the reference plane where the system gain is measured. In other words, we take the gross antenna gain and subtract all losses ohmic and others up to that plane or point. This is the...
Network Access Techniques 1061 Introduction
The objective of a cellular radio operation is to provide a service where mobile subscribers can communicate with any subscriber in the PSTN, where any subscriber in the PSTN can communicate with any mobile subscriber, and where mobile subscribers can communicate among themselves via the cellular radio system. In all cases the service is full duplex. A cellular service company is allotted a radio bandwidth segment to provide this service. Ideally, for full duplex service, a portion of the band...
Personal Communication Services PCS
It is a radio system it is small it can provide multiple services and it often can be considered an extension of cellular radio. Consider that paging, various types of remote control devices, cordless telephones, wireless PBXs, and wire loop replacement and wireless LANs may be considered PCSs. In our brief discussion below, we will consider only wireless telephones, which are operated in a cellular-like manner. Of course, in this case, cells are much...
Access Techniques 641 Introduction
Access refers to the way in which a communication system uses a satellite transponder. There are three basic access techniques 1. FDMA frequency division multiple access 2. TDMA time division multiple access 3. CDMA code division multiple access With FDMA a satellite transponder is divided into frequency band segments, where each segment is assigned to a user. The number of segments can vary from one, where an entire transponder is assigned to a single user, to literally hundreds of segments,...
Multipath Fading
Multipath fading is the most common type of fading encountered, particularly on LOS radiolinks. It is the principal cause of dispersion, which is particularly troublesome on digital troposcatter and high-bit-rate LOS links. For an explanation of atmospheric multipath fading, we must turn to the refractive index gradient Section 1.3.3 . As the gradient varies, multipath fading results owing to 1 the interference between direct rays Figure 1.11 and the specular component of a ground-reflected...
Percentage Of Time That The Ordinate Is Exceeded
Comparison of the time distribution of the three types of combiner using quadruple diversity. path reliability or link time availability propagation and equipment system reliability. Redundancy is one way to achieve equipment reliability to minimize downtime and maximize link availability regarding equipment degradation or failure. One straightforward way to achieve redundancy effectively is to provide a parallel terminal repeater system. Frequency diversity effectively does just...
Noise Power Ratio NPR
Up to this point we have dealt only with thermal noise in a radiolink. In an operational analog radiolink a second type of noise can be equally important. This is intermodulation IM noise. IM noise is caused by nonlinearity when information signals in one or more channels give rise to harmonics or intermodulation products that appear as unintelligible noise in other channels. In a FDM FM radiolink, nonlinear noise in a particular channel varies as the multiplex signal...
Basic Hf Propagation 1241 Introduction Introduction
A HF wave emitted from an antenna is characterized by a groundwave and a skywave component. The groundwave follows the surface of the earth and Figure 12.1. A typical HF radiolink providing teleprinter service. Courtesy of Radio General Company. Figure 12.1. A typical HF radiolink providing teleprinter service. Courtesy of Radio General Company. can provide useful communication over salt water up to about 650 mi 1000 km and over land from some 10 mi 16 km to 100 mi 160 km or more, depending on...
Introduction
Meteor burst communication MBC can provide inexpensive, very low data rate connectivity on links up to about 900 sm 1440 km long. In this discussion, very low data rates are in the range of 10 to over 100 bps average throughput. MBC utilizes the phenomenon of scattering of a radio signal from the ionization trails caused by meteors entering the atmosphere. A meteor trail must have some form of common geometry between one end of a link and the other. The usable life of a trail is short from tens...
Effects of Multipath Dispersion on the Performance of Digital Transhorizon Systems
5.7.5.3.1 Introduction to Time Dispersion Due to Multipath. The multipath dispersion over a digital transhorizon link is considerably worse than the corresponding dispersion over a LOS link for a given frequency band. Consequently, the onset of multipath dispersion, rather than signal-to-noise ratio as the limiting factor in communications performance, occurs at a lower transmission rate for transhorizon links than for LOS links. A significant improvement in the performance can be obtained by...
Fef
Examples of possible sky-wave multihop multimode paths. Figure 12.11. Ionogram idealized sketch. Oblique propagation along magnetic field for a fixed distance point-to-point , F region. High ray H and low ray L and splitting into X-ray and O-ray are shown. Figure 12.11. Ionogram idealized sketch. Oblique propagation along magnetic field for a fixed distance point-to-point , F region. High ray H and low ray L and splitting into X-ray and O-ray are shown. In general, we can say that...
Analysis Of Noise On A Fm Radiolink 281 Introduction
In the design of a radiolink or system of radiolinks, a noise requirement will be specified. In the case of a system carrying FDM telephony, noise power in the derived voice channel will be specified. For a system carrying video, the requirement will probably be stated as a weighted signal-to-noise ratio. Because C N at the receiver input varies with time, noise power is specified statistically. Specifications are typically based on Table 2.1 and derive from the following excerpt from ITU-R....
The Sun As A Noise Generator
The sun is a white noise jammer of an earth terminal when the sun is aligned with the downlink terminal beam. This alignment occurs, for a geostationary satellite, twice a year near the equinoxes and, in the period of the equinox, will occur for a short period each day. The sun's radio signal is of sufficient level to nearly saturate the terminal's receiving system, wiping out service for that period. Figure 9.15 gives the power flux density of the sun as a function of frequency. Above about 20...
Link Budget for a Typical VSAT Operation at KuBand
The model VSAT system in question is a two-way operation using Ku-band frequencies. The outbound link is 128 kbps in a TDM format employing QPSK modulation with coherent detection using rate 2 convolutional coding, K 7 and 3-bit quantization, and Viterbi decoder. The inbound traffic link has a transmission rate of 32 kbps using a HDLC -type frame format, QPSK with similar FEC. The 128-kbps link with its rate -j coding has a coded symbol rate of 256 symbols s. This link requires 200-kHz RF...
Applications Of Hf Radio Communication
HF is probably the most economic means of low data rate transmission over long distances e.g., gt 200 mi . It might be argued that meteor burst communication is yet more economic in some circumstances. Performance makes this difference. As we will show in Chapter 13, meteor burst transmission links have the disadvantage of waiting time between short data packets HF does not. Traditionally, since the 1930s, HF has been the mainstay of ship-shore-ship communication. Satellite communication...
Some Basic Concepts Of Cellular Radio
Cellular radio systems connect a mobile terminal to another user, usually through the PSTN. The other user'' most commonly is a telephone subscriber of the PSTN. However, the other user may be another mobile terminal. Most of the connectivity is extending POTS to mobile users. Data and facsimile services are in various stages of implementation. Some of the terms used in this section have a strictly North American flavor. POTS an abbreviation for plain old telephone service. Figure 10.1 shows a...
Primitive Processing Satellite
The most primitive form of satellite processing is the implementation of on-board regenerative repeaters. This only requires that the uplink signal be demodulated and passed through a hard limiter or a decision circuit. The implementation of regenerative repeaters accrues the following advantages Isolation of the uplink and downlink by on-board regeneration prevents the accumulation of thermal noise and interference. Co-channel interference is a predominant factor of signal degradation because...
Brief Overview of Time Division Multiple Access TDMA
TDMA operates in the time domain and is applicable only to digital systems because information storage is required. To make Section 6.4 complete, a brief overview of TDMA is presented. Chapter 7 gives a more rigorous description of TDMA. With TDMA, use of a satellite transponder is on a time-sharing basis. At any given moment in time, only one earth station accesses the satellite. Individual time slots are assigned to earth stations operating with that transponder in a sequential order. Each...
Summary of Vsat Rf Characteristics
VSAT operation commonly uses either 6 4-GHz band C-band or 14 12-GHz band Ku-band . As operational frequencies increase, receiver noise performance degrades. At C-band we can expect a LNA with 50-K noise temperature at Ku-band, 100 K. Antenna noise temperature Tant at C-band 5 elevation angle is 100 K and at Ku-band 10 elevation angle it is 106 K. Thus typical Tsys for C-band VSAT operation is 150 K and for Ku-band it is 206 K. Line losses for both bands are taken at 1.5 dB for this particular...
Diffraction Over Irregular Terrain
Six diffraction modes of propagation. where 0 is the scatter angle as calculated in the previous section, step 11t f is the operating frequency dLt and dLr are from the path profile and d is the great circle distance taken from the path profile. 4k. If lt 2.4, go to step 5k. If gt 2.4, go to step 6k. 5k. Determine A 0 from Figure 5.17 or by step 6k. Figure 5.17. Knife-edge diffraction loss A v, 0 in decibels below free space Ref. 1 . Figure 5.17. Knife-edge diffraction loss A v, 0...
Attenuation Due To Clouds And
Water droplets that constitute clouds and fog are generally less than 0.01 cm in diameter Ref. 16 . This allows a Rayleigh approximation to calculate the attenuation due to clouds and fog for frequencies up to 100 GHz. The specific attenuation ac is, unlike the case of rain, independent of drop-size distribution. It is a function of liquid water content p1 and can be expressed by where p1 is normally expressed in g m3. Kc is the attenuation constant, which is a function of frequency and...
Preemphasis Deemphasis
After demodulation in a FM system, thermal noise power in some texts called ''idle noise'' is minimum for a given signal at the lowest demodulated baseband frequency and increases at about 6 dB per octave as the baseband frequency increases. This effect is shown in Figure 2.12, which compares thermal noise in an AM system with that in a FM system. To equalize the noise across the baseband, a pre-emphasis network is introduced ahead of the transmitter modulator to provide increasing attenuation...
Excess Attenuation Due To Atmospheric Gases On Satellite Links
The zenith one-way attenuations for a moderately humid atmosphere e.g., 7.5 g m3 surface water vapor density at various starting heights above sea level are given in Figure 9.11 and in Table 9.4. These curves were computed by Crane and Blood Ref. 19 for temperate latitudes assuming the U.S. standard atmosphere, July, 45 N latitude. The range of values shown in Figure 9.11 refers to the peaks and valleys of the fine absorption lines. The range of values for starting heights above 16 km is even...
Block Diagram Of
A9-QPR eye diagram showing ambiguity zones. From Figure 8, ITU-R Rec. F.1101 Ref. 7. Figure 4.26. A9-QPR eye diagram showing ambiguity zones. From Figure 8, ITU-R Rec. F.1101 Ref. 7. Figure 4.27. AZD correction block diagram. From Figure 9, ITU-R Rec. F.1101 Ref. 7. Figure 4.27. AZD correction block diagram. From Figure 9, ITU-R Rec. F.1101 Ref. 7. closest to the pinpoints. Their relative ambiguity positions above or below the pinpoints are also marked for later error correction....
Satellite Orbits
Satellites can be categorized in two ways. The first deals with their altitude above the earth's surface. There are LEOs, MEOs, and GEOs. These Figure 6.1. Simplified functional block diagram of a satellite communications transponder. This is the conventional translating RF repeater or ''bent-pipe''satellite configuration. Figure 6.1. Simplified functional block diagram of a satellite communications transponder. This is the conventional translating RF repeater or ''bent-pipe''satellite...
Site Selection Route Selection Path Profile and Field Survey
Site selection, route selection, path profile, and field survey are carried out in a similar manner as outlined and discussed in Sections 2.2, 2.3, and 2.5. Here, then, we will point out the differences and areas of particular emphasis. 5.4.1.2 Site Selection. Consider these important factors. Whereas on LOS systems several decibels of calculation error may impact hop cost by one or several thousand dollars, impact on over-the-horizon hops may be on the order of hundreds...
Vsat Network Applications
VSATs are commonly implemented in private networks. Why they are attractive depends largely on a country's telecommunication infrastructure. In Radio System Design for Telecommunications, Third Edition By Roger L. Freeman Copyright 2007 John Wiley amp Sons, Inc. Figure 8.1. The conventional VSAT star network configuration. Figure 8.2. A VSAT network based on a mesh architecture. the United States and Canada, economy is the driving factor. Such VSAT networks bypass the local and long-distance...
A22 Conversion Of Radiofrequency Rf Field Strength To Power
Many radio engineers are accustomed to working in the power domain e.g., dBm, dBW . For example, we may wish to know the receive signal level RSL at the input to the first active stage of a HF receiver. In the power domain, the characteristic impedance is not a consideration, by definition. HF engineers traditionally work with field strength usually expressed in microvolts per meter V m . When we convert fiV m to dBm, characteristic impedance becomes important. We remember the familiar formula...
Received Power 13561 Underdense Trails
P r ' T T _3P2P 2 3 13-8 Pt g t g r 2 lt ja1 a2 t a2 10 a3 echoing area of the trail m2 a1 loss factor due to finite initial trail radius a2 t loss factor due to trail diffusion a3 loss factor due to ionospheric absorption t time measured from the instant of complete formation of the first Fresnel zone s t0 half the time taken for the meteor to traverse the first Fresnel zone p T transmitter power W p R t power available from the receiving antenna W gT transmit antenna gain relative to an...
Depolarization On Satellite Links
Depolarization is an effect wherein a satellite link's wave polarization is altered after being launched by the antenna. Some texts refer to depolarization as cross-polarization. For the case of a linearly polarized wave passing through the medium, components of the opposite polarization will be developed. For the case of circular polarization, there will be a tendency to develop into an elliptical wave. This is particularly important for the case of frequency reuse systems, where...
Narrowband Microcell Propagation at PCS Distances
The microcells discussed here have a radial range of lt 1 km. One phenomenon to be considered is the Fresnel break point, which is illustrated in Figure 10.22. Signal level varies with distance R as A Rn. For distances greater than 1 km, n is typically between 3.5 and 4. The parameter A describes the effects of environmental features in a highly averaged manner Ref. 21 . Typical PCS radio paths can be of a LOS nature, particularly near the fixed transmitter where n 2. Such paths may be down the...
R
Direct and ground reflected rays, showing the Fresnel ellipse about the direct ray. From Figure 18, Ref. 21. Figure 10.24. Fresnel zone for propagation between transmitter and receiver in clear space between building furnishings and ceiling fixtures. From Figure 35, Ref. 21. Figure 10.24. Fresnel zone for propagation between transmitter and receiver in clear space between building furnishings and ceiling fixtures. From Figure 35, Ref. 21. related to the Fresnel ellipse. If the...
Prediction Of Mbc Link Performance
The starting point in the methodology we present for predicting link performance is the calculation of receiver noise threshold and a threshold for the required BER. We next provide a basic set of MBC relationships, taken from CCIR Rep. 251-5, used to calculate MBC link transmission loss. Several generalized shortcuts are also presented. Methods of calculating other prediction parameters, such as meteor rate, burst duration time, and waiting time probability, are also described. We use a...
Ieee 80211 Layers
The IEEE 802.11 standard places specifications on the parameters of both the physical PHY and medium access control MAC layers of the network. The PHY layer actually handles the transmission of data between nodes, and can use either direct sequence spread spectrum DSSS or frequently hopping spread spectrum FHSS or infra-red IR pulse position modulation. IEEE 802.11 makes provision for data rates of either 1 Mbps or 2 Mbps, and specifies operation in the 2.4 to 2.4835 GHz band in the case of...
Reflection Point
As discussed in Chapter 1, ground reflections are a major cause of multipath fading. These reflections can be reduced or eliminated by adjustment of tower heights, effectively moving the reflection point from an area along the path of greater reflectivity such as a body of water to one of lesser reflectivity such as an area of heavy forest . Of course, for those paths that are entirely over water or over desert, the designer will have to resort to other methods such as vertically spaced space...
Objective And Scope
Line-of-sight LOS microwave radiolinks, in the context of this book, provide broadband connectivity for telecommunications using radio equipment with carrier frequencies above 900 MHz. For most applications these radiolinks are considered a subsystem of a telecommunications network. They carry one or a mix of the following Facsimile, now usually in a digital data format Video, especially conference TV Telemetry which is a specialized subset of data The emitted waveform may be analog or digital....
Discussion of LOS Microwave Fading
Up to this point we have been dealing with the calculation of unfaded signal levels at the far end receiver. A fixed FSL was assumed. On most short links, on the order of 3 mi 5 km or less, only FSL need be considered. As link length hop distance increases, fading becomes a major consideration. Fading is defined Ref. 11 as ''the variation with time of the intensity or relative phase, or both, of any of the frequency components of a received radio signal due to changes in the characteristics of...
Receiver Threshold
Receiver threshold can be defined as the receive signal level RSL required to achieve a certain bit error rate BER . It is a function of the type of modulation used, bandwidth, and the receiver noise, which is usually externally limited. Of course, the lower the receiver threshold, the lower the waiting time. Often a receiver is noise limited by man-made noise. Methodology for calculating threshold using man-made noise as the overriding noise contributor is given in Section 12.9.4. Donich Ref....
Burst Guard Communication
Depending on the actual transponder and link conditions, INTELSAT may establish the clear-sky setting of the C-band link at a C N better than or equal to 10.1 dB in order to ensure the margins identified in Table G.7 of Ref. 2 are provided. The C N, C T, and C N0 values for 10 -3 and 10 -6 are 3.5 dB and 1.1 dB, respectively, less than those shown for clear sky lt 10 -8 . In the case of Ku-band operation where the clear-sky C N includes rain margin, the C T, C N0, and C N values shown in the...
Atmospheric Effects On Propagation
If a radio beam is propagated in free space, where there is no atmosphere by definition , the path followed by the beam is a straight line. The transmission loss in free space was derived in Section 1.2. However, a radio ray propagated through the earth's atmosphere encounters variations in the atmospheric refractivity index along its trajectory that causes the ray path to become curved Ref. 6 . Atmospheric gases will absorb and scatter the radio path energy, the amount of absorption and...
Scatter Communications
Livingston, The Physics of Microwave Propagation, GTE Technical Monograph, General Telephone amp Electronics Laboratories, Bayside, NY, May 1967. 2. Military Handbook, Facility Design for Tropospheric Scatter, MIL-HDBK-417, U.S. Department of Defense, Washington, DC, Nov. 1977. 3. H. T. Dougherty, A Survey of Microwave Fading Mechanisms, Remedies and Applications, U.S. Department of Commerce, ESSA Tech. Rept. ERL-WPL 4, Boulder, CO, Mar. 1968. 4. Engineering Considerations for...
Multipath Fading Calculation Based on Tia Tsb 10F
On digital microwave radiolinks, the fade margin consists of four factors that are power added and constitute the composite fade margin CFM . These four factors are defined below TFM. Thermal fade margin dB sometimes called the flat fade margin is the fade margin discussed in Chapter 2, Section 2.7.2. TFM is the algebraic difference between the nominal RSL and the 1 X 10 3 BER outage threshold for flat i.e., nondispersive fades. Since interference affects unfaded baseband noise, TFM is the only...
Underdense Trails
MBC links basically depend on reflections from underdense trails. An under-dense trail does not actually reflect energy instead, radio waves excite individual electrons as they pass through the trail. These excited electrons act as small dipoles, reradiating the signal at an angle equal, but opposite, to the incident angle of the trail. Signals received from an underdense trail rise to a peak value in a few hundred microseconds, then tend to decay exponentially Figure 13.2 . Decay times from a...
FM Improvement Threshold
FM is wasteful of bandwidth when compared to AM-SSB, for instance. However, this waste of bandwidth is compensated for by an improvement in thermal noise power when the input signal level RSL reaches FM improvement threshold i.e., when C N , 10 dB . In other words, we are giving up bandwidth for a thermal noise improvement. If we were to draw a curve of signal-to-noise power ratio at the output of the FM demodulator versus the carrier-to-noise ratio at the input Figure 2.26 , we will note three...
Calculating Atmospheric Noise Using ITUR P3728 ITUR
P.372 Ref. 30 is the most widely accepted data source and methodology on atmospheric noise. It has been derived from years of noise-monitoring data taken from monitoring stations around the world. The data are presented graphically as atmospheric noise contours at 1 MHz and then may be scaled graphically or by formula to the desired frequency. CCIR divides a 24-h day into six time blocks of 4 h each starting at 12 midnight. For seasonal variations in atmospheric noise, there are charts for the...
The General Propagation Problem Above 10 GHz
Propagation of radio waves through the atmosphere above 10 GHz involves not only free-space loss but several other important factors. As expressed in Ref. 1, these are as follows 1. The gaseous contribution of the homogeneous atmosphere due to resonant and nonresonant polarization mechanisms. 2. The contribution of inhomogeneities in the atmosphere. 3. The particulate contributions due to rain, fog, mist, and haze includes dust, smoke, and salt particles in the air . Under 1 we are dealing with...
Intelsat Standard B Earth Stations
Standard B earth stations are smaller than their Standard A counterpart. They operate in the 6 4-GHz band and the G T is 31.7 dB K. They transmit receive TV and related aural channels. The latter are in a FDM FM configuration. Standard B also operates with companded FDM FM and SCPC using QPSK. It operates with E1 DS1 bit streams in the International Business Service IBS Ref. 21 and Intermediate Data Rate IDR carriers. Maximum data rates in such cases are E-3 DS3 rates up to the nominal 45 Mbps....
Notes On Mbc Transmission Loss
Some insight is given in Ref. 8 regarding transmission loss at 40 MHz. Table 13.3 shows link distance the two components of MBC transmission loss, MBC scatter loss, and free-space loss and the total transmission loss. We see that the values range around Donich's 180-dB reference model 180 dB Ref. 6 and the 40-MHz values of Figure 13.9. How will a typical link operate with such loss values when a simple link budget technique is applied We use the receiver model described in Section 13.5.2, where...
Improved Lincompex For Hf Radio Telephone Circuits
Lincompex is an acronym for link compression and expansion. It is a technique that provides a uniquely controlled companding compression-expansion function on SSB voice circuits. Performance improvement on links employing Lincompex is reported to be 22 dB minimum across time for typical speech signals under varying propagation conditions with a maximum improvement of 47 dB Refs. 40, 41, and 42 . On systems using Lincompex, speech is compressed to a comparatively constant amplitude and the...
Limitation of Flux Density on Earths Surface
The frequency bands shown in Section 6.3.2 are shared with other services, such as terrestrial point-to-point radiolink microwave. The flux density of satellite signals on the earth's surface must be limited so as not to interfere with terrestrial radio services band-sharing with satellite systems. CCIR recommends the following flux density limits excerpted from ITU-R Rec. SF.358-4 Ref. 7 . Maximum Power Flux Density on Earth Surface 1. that, in frequency bands in the range 2.5 to 27.5 GHz...
Meteor Burst Communication657
13.2.2 Distribution of Meteors, 660 13.3 Typical Meteor Burst Terminals and Their Operation, 663 13.4 System Design Parameters, 665 13.4.2 Operating Frequency, 666 13.5 Prediction of MBC Link Performance, 667 13.5.3 Positions of Regions of Optimum Scatter, 668 13.5.4 Effective Length, Average Height, and Radius of Meteor Trails, 670 13.5.5 Ambipolar Diffusion Constant, 671 13.5.8 Burst Time Duration, 675 13.5.9 Burst Rate Correction Factor, 678 13.5.10 Waiting Time Probability, 679 13.6 Design...
Apertureto Medium Coupling Loss
In Chapter 2 antenna gain was treated as free-space antenna gain or the ratio of the maximum radiated power density at a point in space to the theoretical maximum radiated power density of an isotropic antenna at the same relative point in space. No degradation factors were included. In tropospheric scatter and diffraction links such degradations cannot be neglected. Whereas LOS microwave antennas are seldom mounted near ground and antenna apertures are relatively small,...
Bit Packing
We sometimes estimate the required bandwidth for a binary transmission system by assuming 1 bit Hz. In most practical cases this is somewhat optimistic. Our goal, remember, is to achieve better than 4.5 bits Hz. For digital transmission, phase modulation has a number of excellent attributes. Among these are robustness and improved noise immunity. When we describe ''phase,'' we usually employ a circle to represent 360 of phase. In the case of BPSK binary phase-shift keying , we describe two...
Preface To The Third Edition
This book provides the essential design techniques for radio systems that operate at frequencies of 3 MHz to 100 GHz and which will be employed in the telecommunication service. We may also call these wireless systems, wireless being synonymous with radio, Telecommunications is a vibrant industry, particularly on the ''radio side of the house.'' The major supporter of this upsurge in radio has been the IEEE and its 802 committees. We now devote an entire chapter to wireless LANs WLANs detailed...
