Examen

Private and public key algorithms. are channel coding algorithms. are source coding algorithms. are encryption methods.

In channel coding, if Rb is the throughput at the output of the source coding. the throughput at the output of the channel coding block is equal to Rb. the throughput at the output of the channel coding block is lower or equal to Rb. the throughput at the output of the channel coding block is larger or equal to Rb.

In time division multiplexing. the errors are discarder along time. information from different subsystems of the RPAS are transmitted sequentially in time. information from different subsystems of the RPAS are transmitted sequentially in frequency.

The bandwith of a M-QAM, if Rb is the throughput at its input. Is roughly the inverse of the symbol time T = log2 (M)/Rb. is a fixed constant multiplied by Tb = 1/Rb. does not depend on Rb.

In a OFDM system with 180 subcarriers of 15 kHz, the bandwith is,. 180/15 kHz. 15/180 kHz. 180×15 kHz.

In TDMA. each RPAS access the channel in a different given time slot. each RPAS access the channel in a different given frequency slot. each RPAS access the channel using a different given code.

The radiation pattern. Provides the shape of the antenna. Provides the design of every part of antenna. Provides the way the power is distributed into the air.

An omnidirectional antenna. Radiates mostly up and down. Radiates mostly in a given directions. Radiates equally in all directions of the horizontal plane.

The directive gain. Is a way of providing the resistence of the antenna. Is a way of providing the radiation pattern. Depends on the overall radiated power.

. The directivity is. The maximum of the radiated intensity. The gain of an omnidirectional antenna. The maximum of the directive gain.

The bandwith of an antenna. Is given by the radiation pattern. Is given by the insertion loss at every frequency. Is the width of its main lobe.

Polarization. Is an interesting phenomena with no practical impact. Is to be taken into account to maximize received power. Is always linear.

A VSWR of value 1. Means 1 cm width of the cables feeding the antenna. Means width and height of antenna ratio is 1. Means no reflected power.

The effective area. Is the wind resistence equivalent area. Is the area of a metal plane with radar section of 1. Is the equivalent area that multiplied by the received power flux provides the receiver power.

Friis formula. Relates received E field to transmitted power. Relates received power with transmitted power. Relates received power with received E field.

MIMO antennas. Are antennas with multiple wires. Are array of antennas in the transmitter and receiver. Are antennas located in multiple different locations.

With MIMO. One cannot improve the signal to noise ratio. One can transmit just using linear vertical polarization. One can improve the troughput.

At the output of an amplifier. We may expect frequencies in other frequencies different from the ones at the output. The amplifier provides at its output the signal at the input with a gain G, regardless of the power of the input. Amplifier are devices to amplify the frequencies, moving the input signal to an upper frequency.

Some common specifications of the devices are. The 1 dB compression point and size. Insertion loss and frequency of operation. The drifting of the LO and humidity range of operation.

Antennas,. do not introduce noise, just collect transmitter power. if frequency is above 3 GHz, introduce a noise of value kT0B. do not collect noise from nearby, e.g. from engines.

Sensitivity, in the digital scenario. does not depend on the throughput, Rb. does depend on the noise introduced by the receiver. decreases with the length of the feeders.

A front end,. Is the structure to protect the antenna. Is the fence around a station installation. Is the first part of the receiver, containing the LNA.

In Tx-Rx design in the same circuit or device. The duplexor perfectly isolates the Rx from the Tx. Part of the Tx power ends at the receiver, good duplexor design o non simultaneous Tx-Rx are some solutions. LNA are not needed.

The propagation used in WiFi, Mobiles and satellites is the. Ionospheric wave. Surface wave. Tropospheric wave.

Reflections are. Always good as we add another ray increasing received power. Not to be taken into account, as they greatly attenuate when reflected. May be good or quite bad depending on the lengths of the direct and reflected path.

Refracction. Is the fenomena that explains a fading because of an obstacle. Makes the propagation bend, usually improving LOS distance. Is a reflection when the ground is quite rough.

When an obstacle is the middle of the propagation, blocking the main ray,. The communication is not possible due to heavy loss. Communication is still possible, improving as the frequency drops. Propagation does not suffer any loss as reflections on mesosphere reach the receiver.

Atmospheric gases cause a fading. If frequencies are above 6 GHz. If frequencies are below 6 GHz. Only if we have a heavy fog.

Rain. Does always fade the signal. Fades de signal but only if frequency is above 6 GHz. Only affects if antennas are headed to the sky.

Vegetation. Fades the signal if frequency is low, below 1 GHz. Behaves as an obstacle if frequency is above 10 GHz. It does not fades the signal but bend the propagation above it.

Empirical methods. Do provide better estimations of loss than planning tools. Provide a mean value with a given error. Can include the precise map of building heights in the estimations of loss.

The exponent of loss. Indicates the type of area. Indicates the type of antennas used. Indicates how the loss grow with the distance.

Doppler effect. Is due to obstacles. Is larger as larger is the speed towards or from the transmitter. Is larger as larger is the antenna.

Multipath. Just fades the overall signal strength. It can cause a frequency drift. It can cause some frequencies to fade more than others.

The. C band is in the range 4-6GHz. The Ku band is in the range 88-108 MHz. The UHF band is in the range 30-300 GHz.

The SOS Word in morse is given by. .-. ...---... ---...---.