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11.What are the advantages of CDMA?
Advantages of CDMA are as follows:
• 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. • Multiplication Resistance: Chipping codes used for CDMA not only exhibit low correlation but also low auto correlation. Hence a version of the signal that is delayed by more than one chip interval does not interfere with dominant signal as in other multi path environments.
• 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.
• Graceful Degradation. In CDMA, more users access the system simultaneously as compared to FDMa, TDMA.
12.What are the advantages of spread spectrum?
Spread spectrum has the following advantages:
• No cross talk interference.
• Better voice quality/data integrity and less static noise.
• Lowered susceptibility to multi path fading.
• Inherent security.
• Longer operating distances.
• Hard to detect.
• Hard to intercept or demodulate.
• Harder to jam than narrow bands.
• Use of ranging and radar.
13. 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: Spectrum spreading (e.g., direct sequence or frequency hopping) modulation is removed.The remaining information bearing signal is demodulated by multiplying with a local reference identical in structure and synchronized with received signal.
14. How can a Pseudo Random Noise Code be usable?
To be usable for direct sequence spreading, a PN code must meet the following conditions:
• Sequence must be built from 2 leveled numbers.
• The codes must have sharp auto correlation peak to enable code synchronization.
• Codes must have a low cross-correlation value, the lower it is, more are the number of users which can be allowed in the system.
• The codes should be “balanced” i.e. the difference between ones and zeros in code may only be one.
15.What are different categories of antenna and give an example of each?
Different categories of antenna are as follows:
• Wire Antennas – Short Dipole Antenna
• Micro strip Antennas – Rectangular Micro strip (Patch) Antennas
• Reflector Antennas – Corner Reflector
• Travelling Wave Antennas – Helical Antennas
• Aperture Antennas – Slot Antenna
• Other Antennas – NFC Antennas
16.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.
17. 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 radio waves.
18.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.
19.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 sell signal.
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 Bluetooth. Bluetooth operates in the 2.4 GHz area of spectrum and provides a range of 10 meters. It offers transfer speeds of around 720 Kbps. These are the questions and answers for Electronics and communication engineering. I have covered all important topics. you can easily crack the interview. Now be prepared with these question and answer in interview.
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