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Right choice is (d) TREES outside the building

To ELABORATE: It has been OBSERVED that propagation within buildings is strongly influenced by specific features. These features are LAYOUT of the building, the construction materials, and the building type.

Correct CHOICE is (d) Urban factor

For EXPLANATION: The urban factor (UF) is DERIVED by COMPARING the predictions by the original Longley –Rice model with those obtained by Okumura. It deals with RADIO propagation in urban areas and is relevant to mobile radio.

Right option is (d) Hata model

Explanation: Log normal shadowing, log DISTANCE PATH LOSS model and determination of percentage of coverage area are practical pat loss estimation techniques. Hata model is only VALID for exterior environment.

Right choice is (d) Huygen’s PRINCIPLE

Easy explanation: The phenomenon of diffraction can be explained by Huygen’s principle. It STATES that all points on a wavefront can be considered as point sources for the production of SECONDARY WAVELETS. And these wavelets combine to produce a new wavefront in direction of PROPAGATION.

The correct answer is (C) Curved surface of Earth

The explanation is: Diffraction allows radio signals to propagate around the curved surface of the Earth. Signals can propagate BEYOND the HORIZON and to propagate behind obstruction. It is the slight bending of light as it passes around the EDGE of an OBJECT.

Correct answer is (b) T-R separation

Easiest EXPLANATION: As with most large scale radio wave PROPAGATION models, the free space model predicts that received signal decays as a function of the T-R separation DISTANCE raised to some power. Often it is given as a function of negative SQUARE root of the distance.

Right option is (b) LARGE CELL mobile radio SYSTEM

Easiest explanation: Hata model is well SUITED for large cell mobile radio systems. But it is not well suited for personal communication system (PCS) which have cells on the ORDER of 1 km radius. Hata model does not have any path specific corrections which are available in Okumura model.

The correct option is (B) Obstruction

Easy explanation: Diffraction loss occurs from the blockage of SECONDARY WAVES such that only a portion of the energy is diffracted around an OBSTACLE. An obstruction causes a blockage of energy from source some of the Fresnel zones, allowing only some of the transmitted energy to REACH the receiver.

Right answer is (c) Brewster angle

The best EXPLANATION: The Brewster angle is the angle at which no REFLECTION OCCURS in the MEDIUM of origin. It occurs when the incident angle is such that the reflection coefficient is equal to zero. The critical Brewster’s angles for diamond, glass and WATER are 67.5°, 57° and 53° respectively.

Right answer is (a) Soft partitions

Easy explanation: Partitions that may be moved are called soft partitions. They do not span to the ceiling. OFFICE BUILDINGS OFTEN have large open areas which are constructed by using moveable office partitions. THUS, space can be reconfigured easily.

Right OPTION is (a) True

To elaborate: The empirical approach is BASED on FITTING curves or analytical expressions that recreate a set of MEASURED DATA. This has the advantage of implicitly taking into account all propagation factors, both known and unknown through actual field measurements.

Correct ANSWER is (a) 1/√(μ∈)

Explanation: For a medium with permittivity, ∈ and PERMEABILITY, μ the velocity of electromagnetic WAVE is given by 1/√(μ∈). It is ALSO known as PHASE velocity. The velocity of light is given by 3*10^8 m/s.

Right option is (C) WALFISCH and Bertoni model

The best EXPLANATION: The impact of rooftops and building height is considered by Walfisch and Bertoni model. It uses diffraction to predict AVERAGE signal strength at street level. It considers path loss to be a product of three FACTORS.

Right answer is (a) Gain and losses from the transmitter

The best I can explain: A link budget is accounting of all of the gains and losses from the transmitter, through the medium (free space, cable, waveguide, ETC.) to the receiver in a TELECOMMUNICATION system. It accounts for the attenuation of the TRANSMITTED signal due to propagation, as well as the antenna gains and MISCELLANEOUS losses.

Right option is (a) Epstein and PETERSON method

Explanation: The Edwards and Durkin algorithm USES Epstein and Peterson method to calculate the loss associated with two DIFFRACTION edges. It is the sum of two attenuations. First is loss at SECOND diffraction EDGE caused by first diffraction edge. And second is the loss at receiver caused by second diffraction edge.

Correct ANSWER is (c) GAUSSIAN

To explain: Log normal shadowing implies that measured SIGNAL levels at a specific T-R separation have Gaussian (Normal) DISTRIBUTION. It is about the distance dependent mean of 4.68 where the signal levels have VALUES in dB units.

Right choice is (a) Rayleigh criterion

The BEST explanation: Rough surface is often tested using a Rayleigh criterion. It defines the CRITICAL height of surface protuberances for a GIVEN angle of incidence. The Rayleigh criterion is the criterion for the minimum resolvable detail. The IMAGING process is said to be diffraction-limited when the first diffraction minimum of the image of one source point coincides with the MAXIMUM of another.

Right option is (c) Excess path LENGTH

Best explanation: Excess path length DENOTED by ∆, is the difference between the direct path and the DIFFRACTED path. It is calculated with the help of Fresnel ZONE geometry.

The correct choice is (a) 2D2/λ

Easiest EXPLANATION: Fraunhofer DISTANCE, also KNOWN as far field distance is inversely proportional to wavelength. It DEPENDS on the largest physical dimension of the antennal (D). This distance basically denotes the boundary between far field and near field region.

Right option is (a) Large

For explanation: Reflection occurs when a propagating electromagnetic WAVE impinges upon an object which has very large dimensions when compared to the wavelength of the PROPAGATION wave. Reflection occurs from the surface of the Earth and from BUILDINGS and WALLS.

The correct answer is (b) PRIMARY RAY tracing

Easy explanation: PAF (path attenuation FACTOR) represents a specific obstruction encountered by a ray drawn between the transmitter and receiver in 3-D. This TECHNIQUE of drawing a single ray between transmitter and receiver is called primary ray tracing.

Correct answer is (c) ITS IRREGULAR terrain model

For explanation I would say: The Longley Rice prediction model is also referred to as ITS irregular terrain model. The model is based on electromagnetic theory and on STATISTICAL ANALYSES of both terrain features and radio measurements. It predicts the median attenuation of a radio SIGNAL as a function of DISTANCE and the variability of the signal in time and in space.

The correct choice is (c) Encryption

The explanation is: Encryption is the most effective way to ACHIEVE data security. It is the PROCESS of encoding a message in such a way that only AUTHORIZED parties can access it. Encryption does not itself prevent interference but denies the INTELLIGIBLE CONTENT to a would-be interceptor.

Correct choice is (d) Slow response to rapid change in terrain

Explanation: The major disadvantage with the model is its slow response to rapid changes in terrain. THEREFORE the model is FAIRLY good in urban and suburban AREAS, but not as good in rural areas. Common STANDARD deviations between PREDICTED and measured path loss values are 10 dB to 14 dB.

Correct answer is (d) Effective aperture to physical aperture

To elaborate: The larger the antenna aperture the larger is the resulting signal power DENSITY in the desired DIRECTION. The ratio of effective aperture to the physical aperture is the antenna’s EFFICIENCY.

Correct option is (C) No loss of energy in ABSORPTION

Easy explanation: If the plane wave is INCIDENT on a perfect dielectric, part of the energy is TRANSMITTED into the SECOND medium and part of the energy is reflected back into the first medium. There is no loss of energy in absorption.

The correct option is (b) Microcell approach

Explanation: The microcell zone concept is used in cellular SYSTEMS to specifically increase the CAPACITY and coverage in cellular systems. A HANDOFF is not required at MSC when the mobile travels between zones WITHIN a cell or when a mobile travels from one zone to another within the cell.

The CORRECT choice is (b) False

To ELABORATE: Log normal shadowing OCCURS over a large number of measurement LOCATIONS which have the same T-R separation, but have different levels of clutter on the propagation path. It FOLLOWS log normal distribution.

The correct answer is (c) RADIATED

The BEST I can explain: Power density is the amount of power (time rate of energy transfer) per unit VOLUME. It is also termed as radiated power per unit AREA. In energy transformers including batteries, fuel cells, motors, etc., power density refers to a volume. It is then also called volume power density.

Right answer is (a) Power DENSITY of signal scattered to power density of radio wave INCIDENT

The best I can EXPLAIN: The RADAR cross section of a scattering object is defined as the ratio of the power density of the signal scattered in the direction of the receiver to the power density of the radio wave incident upon the scattering object. It has unit of square meters.

Right OPTION is (b) Small

Easiest explanation: Scattering occurs when the medium through which the WAVE travels consists of objects with dimensions that are small compared to the wavelength. But the number of obstacles per unit volume is LARGE.

Right option is (c) Two spatially orthogonal components

The best I can explain: A POLARIZED wave may be MATHEMATICALLY REPRESENTED as SUM of two spatially orthogonal components. For an arbitrary polarization, super position may be used to compute the reflected FIELDS from a reflecting surface.

Correct OPTION is (b) Shadowed region

Easiest EXPLANATION: Diffraction is CAUSED due to PROPAGATION of secondary wavelets into a shadowed region. The field strength in the shadowed region is the vector sum of the electric field components of all the secondary wavelets in the space around the obstacle.

The correct choice is (d) Refraction

The best explanation: Reflection, DIFFRACTION and scattering are the three basic PROPAGATION mechanism which impact propagation in mobile communication system. Large scale propagation model and small scale FADING and multipath propagation are DESCRIBED by the PHYSICS of reflection, diffraction and scattering.

The correct answer is (a) Received signal strength

To explain I would say: Free space PROPAGATION MODEL predicts the received signal strength when there is an unobstructed line of sight path between transmitter and RECEIVER. It assumes the ideal propagation CONDITION that the environment is EMPTY between the transmitter and receiver.

Right CHOICE is (d) Wired TELEPHONE systems

Explanation: EM signals when traveling through wireless channels experience fading EFFECTS due to various effects. But in some cases the transmission is with no OBSTRUCTION and direct LINE of sight such as in satellite communication, microwave and wireless line of sight radio links.

The CORRECT choice is (c) External dimension

To ELABORATE: The losses between floors of a building are determined by external DIMENSIONS as well as MATERIALS of the building. It is also determined using type of construction used to create the floors and external surroundings.

Correct choice is (b) False

To explain: OKUMURA’s model is considered to be among the simplest and best in terms of ACCURACY in path loss PREDICTION for MATURE cellular and land mobile radio system. It is very practical and has BECOME a standard for system planning in modern land mobile system in Japan.

The CORRECT ANSWER is (b) False

The best I can explain: It is important to select a free SPACE reference distance that is appropriate for the propagation environment. The reference distance should always be in the far field of the antenna so that near field EFFECTS do not alter the reference path loss.

Correct CHOICE is (a) Rough surface

Explanation: Scattered waves are produced by rough surfaces, small OBJECTS or by other IRREGULARITIES in the channel. In practice, foliage, street SIGNS, and lamp posts induce scattering in a mobile COMMUNICATION system.

Right OPTION is (d) Signal attenuation

Best explanation: Estimating the signal attenuation caused by diffraction of radio waves over hills and buildings is ESSENTIAL in predicting the field STRENGTH in a given service area. In PRACTICE, prediction is a process of theoretical approximation modified by necessary empirical CORRECTIONS.

Correct answer is (b) TOTAL energy reflected BACK to FIRST medium

Easiest explanation: If the SECOND medium is perfect conductor, then all incident energy is reflected back into the second medium. There is no loss of energy during absorption.

Right choice is (b) Fading model

For explanation I would say: Fading MODELS characterize the rapid fluctuations of the received signal strength over very short travel distance (a few WAVELENGTHS) or SHOT time DURATIONS (on the order of seconds).

Correct choice is (a) Scattering

The explanation: Scattering is a general PHYSICAL process where some forms of radiation, such as LIGHT, sound, or moving particles, are forced to deviate from a straight TRAJECTORY by ONE or more PATHS. It is due to localized non-uniformities in the medium through which they pass.