RF Related Question - Answer

What do you Mean by EIRP?

EIRP - Equivalent Isotropic ally Radiated Power

The unit of measurement of the strength of a radiated field. Typically that from a radio antenna.

What is Polarization ? What are the types of Polarization?

The polarization of an antenna is the polarization of the wave radiated by the antenna. At a given position, the polarization describes the orientation of the electric field.

Vertical and horizontal are the simplest forms of polarization and they both fall into a category known as linear polarization. However it is also possible to use circular polarization. This has a number of benefits for areas such as satellite applications where it helps overcome the effects of propagation anomalies, ground reflections and the effects of the spin that occur on many satellites. Circular polarization is a little more difficult to visualize than linear polarization. However it can be imagined by visualizing a signal propagating from an antenna that is rotating. The tip of the electric field vector will then be seen to trace out a helix or corkscrew as it travels away from the antenna. Circular polarization can be seen to be either right or left handed dependent upon the direction of rotation as seen from the transmitter.

Another form of polarization is known as elliptical polarization. It occurs when there is a mix of linear and circular polarization. This can be visualized as before by the tip of the electric field vector tracing out an elliptically shaped corkscrew.

What is fading ? What are its different types: a) Based on Multipath time delay spread  b) Based on Doppler spread

Fading is the distortion that a carrier-modulated telecommunication signal experiences over certain propagation media. A fading channel is a communication channel that experiences fading. In wireless systems, fading is due to multipath propagation and is sometimes referred to as multipath induced fading.

What is Rayleigh Fading?

Rayleigh fading is caused by multi path reception. The mobile antenna receives a large number, say N, reflected and scattered waves. Because of wave cancellation effects, the instantaneous received power seen by a moving antenna becomes a random variable, dependent on the location of the antenna

What is multipath Fading?

A form of radio fading caused by the existence of two or more paths between the transmitter and receiver. Delays on the reflected path may add to (strengthen) or subtract from (fade) the main path. Multi path may be overcome by using multiple receive antennas or frequency hopping

How can we minimise multipath fading?

OTD - Orthogonal Transmit Diversity

An optional method of transmission of the Forward CDMA Channel that utilizes two antennas, each transmitting a fraction of the code symbols. It is used to enhance the performance in the presence of fades due to multipath propagation.

What are the different types of diversity?

Space diversity

A method of TX (Transmission) or RX(Reception), or both, in which the effects of fading are reduced by the simultaneous use of two or more antennas. Antennas should ideally be separated by one or more wavelengths.

Time diversity

Transmission in which signals representing the same information are sent over the same channel at different times. 

Explain various types of Antenna Diversity?

OTD - Orthogonal Transmit Diversity

An optional method of transmission of the Forward CDMA Channel that utilizes two antennas, each transmitting a fraction of the code symbols. It is used to enhance the performance in the presence of fades due to multipath propagation - Auxiliary Transmit Diversity Pilot Channel

The Auxiliary Transmit Diversity Pilot Channel is associated with the APCH (Auxiliary Pilot Channel), that is transmitted by a CDMA (Code Division Multiple Access) BS (Base Station) from the non-primary antenna when orthogonal transmit diversity is employed.

FTFPCH - Forward Transmit Diversity Pilot Channel

A pilot channel transmitted by a CDMA (Code Division Multiple Access) BS (Base Station) from the non primary antenna when orthogonal transmit diversity is employed

Explain frequency Diversity?

The signal is transferred using several frequency channels or spread over a wide spectrum that is affected by frequency-selective fading. Middle-late 20th century microwave radio relay lines often used several regular wideband radio channels, and one protection channel for automatic use by any faded channel.

Explain the Time Diversity?

Multiple versions of the same signal are transmitted at different time instants. Alternatively, a redundant forward error correction code is added and the message is spread in time by means of bit-interleaving before it is transmitted. Thus, error bursts are avoided, which simplifies the error correction.