 |
Different categories of antenna are as follows :
1. Wire Antennas - Short Dipole Antenna
2. Microstrip Antennas - Rectangular Microstrip (Patch) Antennas
3. Reflector Antennas - Corner Reflector
4. Travelling Wave Antennas - Helical Antennas
5. Aperture Antennas - Slot Antenna
6. Other Antennas - NFC Antennas
2. What is handover and what are its types?
Handover in mobile communication refers to the process of transferring a call from one network cell to another without breaking the call.
There are two types of handover which are as follows :
Hard Handoff : hard handoff is the process in which the cell connection is disconnected from the
previous cell before it is made with the new one.
Soft Handoff : It is the process in which a new connection is established first before disconnecting the
old one. It is thus more efficient and smart.
3. What is ionospheric bending?
When a radio wave travels into the ionospheric layer it experiences refraction due to difference in
density. The density of ionospheric layer is rarer than the layer below which causes the radio wave to be bent away from the normal. Also the radio wave experiences a force from the ions in the ionospheric layer. If incident at the correct angle the radio wave is completely reflected back to the inner atmosphere due to total internal reflection. This phenomenon is called ionospheric reflection and is used in mobile communication for radio wave propagation also known as ionospheric bending of radiowaves.
4.What is CDMA?
CDMA stands for Code Division Multiple Access which uses digital format. In CDMA systems several transmissions via the radio interface take place simultaneously on the same frequency bandwidth. User data is combined at the transmitter’s side with a code, then transmitted. On air, all transmission get mixed. At the receiver's side the same code is used as in the transmitter’s side. The code helps the receiver to filter the user information of the transmitter from incoming mixture of all transmissions on the same frequency band and same time.
5.Explain the concept of frequency re-use.
The whole of the geographical area is divided into hexagonal shape geometrical area called cell and each cell having its own transceiver. Each BTS (cell site) allocated different band of frequency or different channel. Each BTS antenna is designed in such a way that i cover cell area in which it is placed with frequency allotted without interfering other cell signals. The design process of selecting and allocating channel groups for all of the cellular base station within system is called frequency reuse.
6.Explain Bluetooth.
Bluetooth is designed to be a personal area network, where participating entities are mobile and require sporadic communication with others. It is omni directional i.e. it does not have line of sight limitation like infra red does. Ericsson started the work on Bluetooth and named it after the Danish king Harold Biuetooth. Bluetooth operates in the 2.4 GHz area of spectrum and provides a range of 10 metres. It offers transfer speeds of around 720 Kbps.
7. What are GPRS services?
GPRS services are defined to fall in one of the two categories :
- PTP ( Point to point)
- PTM ( Point to Multipoint)
Some of the GPRS services are not likely to be provided by network operators during early deployment of GPRS due in part to the phased development of standard. Market demand is another factor affecting the decision of operators regarding which services to offer first.
8. What are the advantages of CDMA?
Advantages of CDMa are as follows :
1. Frequency diversity : Transmission is spread out over a large bandwidth due to that less affected by
noise. If bandwidth is increased S/N ratio increases, which means noise will be reduced.
2. Multiplication Resistance : Chipping codes used for CDMA not only exhibit low correlation but also low autocorrelation. Hence a version of the signal that is delayed by more than one chip interval does not interfere with dominant signal as in other multipath environments.
3. Privacy : Due to spread spectrum is obtained by the use of noise like signals, where each user has a
unique code, so privacy is inherent.
4. Graceful Degradation. In CDMA, more users access the system simultaneously as compared to FDMa, TDMA.
9. What are the advantages of spread spectrum?
SPread spectrum has the following advantages :
1. No crosstalk interference.
2. Better voice quality/data integrity and less static noise.
3. Lowered susceptibility to multipath fading.
4. Inherent security.
5. Co-existence.
6. Longer operating distances.
7. Hard to detect.
8. Hard to intercept or demodulate.
9. Harder to jam than narrow bands.
10. Use of ranging and radar.
10. Explain the steps involved in demodulating a signal.
Once the signal is coded, modulated and then sent, the receiver must demodulate the signal. This is
usually done in two steps :
1. Spectrum spreading (e.g., direct sequence or frequency hopping) modulation is removed.
2. The remaining information bearing signal is demodulated by multiplying with a local reference
identical in structure and synchronised with received signal.
#IPECElectronics#InterviewQuestions#SolvedPapers#CoreElectronics#AKTU
0 comments:
Post a Comment