WC Definitions

1. What is the necessity of Link budget?
           A link budget is accounting of all of the gains and losses from the transmitter, through the medium (free space, cable, wave guide, fiber, etc.) to the receiver in a telecommunication system
· The link budget enables factors such as the required antennas gain levels, radio transmitter power levels, and receiver sensitivity figures to be determined.
· By assessing the link budget, it is possible to design the system so that it meets its requirements and performs correctly without being over designed at extra cost.
· Link budgets are often used for satellite systems.
In addition to satellite systems, link budgets are also used in many other radio communications systems.

2. Define coherence bandwidth?
         Coherence bandwidth is a statistical measure of the range of frequencies over which the channel can be considered “flat” (i.e., a channel which passes all spectral components with approximately equal gain and linear phase)

3. Define cell splitting.
         Cell splitting is the process of subdividing congestedcells into smaller cells each with its own base stations and a corresponding reduction in antenna height and transmitter power. It increases the capacity of cellular system.

4.What is meant by frequency reuse?
         Frequency reuse is the process of using the same radio frequencies on radio transmitter sites within a geographic area that are separated by sufficient distance to cause minimal interference with each other. Frequency reuse allows for a dramatic increase in the number of customers that can be served (capacity) within a geographic area on a limited amount of radio spectrum (limited number of radio channels).

5. What is the principle of staggered QPSK?
         Standard QPSK models are used to generate SQPSK by delaying Q signal by half a bit period prior to modulator input. SQPSK stands for Staggered QPSK. It is also known as Offset QPSK or OQPSK. In SQPSK envelope deep nulls are eliminated and moreover envelope is not constant.
If I and Q are offset by half bit period, one input always remains constant while the other input will change its value. Due to this, transition through origin can be eliminated as observed in QPSK modulation constellation.

7.What is use of automatic repeat request (ARQ) for temporal filter?
          Automatic Repeat reQuest (ARQ), also known as Automatic Repeat Query, is an error-control method for data transmission that uses acknowledgements (messages sent by the receiver indicating that it has correctly received a data frame or packet) and timeouts (specified periods of time allowed to elapse before an acknowledgment is to be received) to achieve reliable data transmission over an unreliable service. If the sender does not receive an acknowledgment before the timeout, it usually re-transmits the frame/packet until the sender receives an acknowledgment or exceeds a predefined number of re-transmissions .
The types of ARQ protocols include Stop-and-wait ARQ, Go-Back-N ARQ, and Selective Repeat ARQ / Selective Reject.

8. Define the term one-frequency repeaters.
        In telecommunications, a repeater is an electronic device that receives a signal and re-transmits it. Repeaters are used to extend transmissions so that the signal can cover longer distances or be received on the other side of an obstruction.
Some types of repeaters broadcast an identical signal, but alter its method of transmission, for example, on another frequency or baud rate.
There are several different types of repeaters; a telephone repeater is an amplifier in a telephone line, an optical repeater is an optoelectronic circuit that amplifies the light beam in an optical fiber cable; and a radio repeater is a radio receiver and transmitter that re-transmits a radio signal.

9. Define Pre coding?
        Precoding is a generalization of beam forming to support multi-stream (or multi-layer) transmission in multi-antenna wireless communications. In conventional single-stream beam forming, the same signal is emitted from each of the transmit antennas with appropriate weighting (phase and gain) such that the signal power is maximized at the receiver output. When the receiver has multiple antennas, single-stream beam forming cannot simultaneously maximize the signal level at all of the receive antennas. In order to maximize the throughput in multiple receive antenna systems, multi-stream transmission is generally required.

10. Define Beam forming?
         Beam forming or spatial filtering is a signal processing technique used in sensor arrays for directional signal transmission or reception.This is achieved by combining elements in an antenna array in such a way that signals at particular angles experience constructive interference while others experience destructive interference. Beam forming can be used at both the transmitting and receiving ends in order to achieve spatial selectivity. The improvement compared with Omnidirectional reception/transmission is known as the directivity of the array.
Beam forming can be used for radio or sound waves. It has found numerous applications in radar, sonar, seismology, wireless communications, radio astronomy, acoustics and Bio medicine.