Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Basic questions for interview ?? please answer it in short??

Status
Not open for further replies.

ekant

Newbie level 2
Joined
Jan 14, 2010
Messages
2
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Location
kanpur
Activity points
1,295
1) Do negative frequency exist in real life ?
2) define ISI (inter symbol interference)?
3) define ICI (interchannel interference) ?


and many more questions are yet to come !!!


cheers !!
ekant
 

ekant

Newbie level 2
Joined
Jan 14, 2010
Messages
2
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Location
kanpur
Activity points
1,295
Re: Basic questions for interview ?? please answer it in sho

4) Define Interleaver ?
5) Define Crosstalk ?
6) what do you mean by Equalizer ?


This are some questions on which i generally get confused , so do please help me out !!
waiting for your response !!
 

Communications_Engineer

Advanced Member level 3
Joined
Oct 10, 2008
Messages
895
Helped
179
Reputation
358
Reaction score
105
Trophy points
1,323
Location
Sindh, Pakistan
Activity points
5,542
try wikipedia if you don't get any response, which you might not, as they are very simple questions.

During my time as a member, I've observed that members are more interested to answer technical queries rather than answer basic questions whose answers are easily available on google.

Added after 16 seconds:

Just a suggestion
 

Tamas888

Junior Member level 3
Joined
Jun 28, 2010
Messages
25
Helped
1
Reputation
2
Reaction score
1
Trophy points
1,283
Activity points
1,445
The channel ISI free if: H(z)=1 on every frequency.. Interference can be because of multipath because each symbol can be faster than the before symbol... Am I right?
crosstalk can be for example in case of UTP cable. it means you can hear in each cable what you sent on another cable.. therefore you have to “furl” the cables...
Equalizer need when you have multipath channel, it is important for example if your channel isn’t ISI free.. your algorithm must use learning sets and you can for example to minimize the error function which is the difference between the input and the got signal...
and so on....
 

Ahmed Alaa

Full Member level 5
Joined
Jul 22, 2009
Messages
317
Helped
61
Reputation
136
Reaction score
44
Trophy points
1,318
Location
Egypt
Activity points
2,964
Re: Basic questions for interview ?? please answer it in sho

1) No, negative frequencies are just a mathematical artifact. Because a complex exponential is a phasor that rotates in a certain direction with a certain velocity has real and imaginary projections, we eliminate the imaginary projections by adding another phasor rotating in the OPPOSITE direction with the same velocity. This opposite direction is the negative frequency.
Because no imaginary projections in real life, then no negative frequencies as well !!
---------------------------------------

2) ISI is the presence of contributions of all other symbols in a certain symbol. That is because all channels have low pass nature and won't carry sharp pulses that start and end strictly instantaneously. A dispersive channel is either dispersive because of its nature (the material of a cable) which treats every frequency with a diff wave velocity, or because we are obligated to use LPF at the transmitter because the medium is shared (like the case of wireless communications).

----------------------------------------

3) ICI is a problem that is specific for multi-carrier systems, which results from the loss of Orthogonality between the sub carriers.This happens when the FFT is considered over duration where the subcarrier is non integer number of cycles. We mitigate this using cyclic prefix.

-----------------------------------------

4) Interleaving is the scattering of contiguous elements in a data packet into different packet, so that if we lost a whole packet, the loss is in smaller elements that belong to different packets, when we apply de-interleaving, we recover packets that are partially corrupted but not totally lost.

-----------------------------------------

5) Cross talk is the undesired coupling between two neighboring systems, each systems creates an undesired interference on the system in its neighborhood (ex. two cables).

-----------------------------------------

6) An Equalizer is a filter that mitigates ISI, it simulates the inverse transfer function of the channel in order to retrieve a better version of the signal. Digital equalizer are usually tapped-line filters the taps' gain may be adapted through estimating the channel and recognize the varying channel's transfer function.

Hope this helps !
 

vegetablevn

Newbie level 4
Joined
Aug 10, 2010
Messages
6
Helped
2
Reputation
4
Reaction score
1
Trophy points
1,283
Activity points
1,306
Re: Basic questions for interview ?? please answer it in sho

Ahmed Alaa said:
1) No, negative frequencies are just a mathematical artifact. Because a complex exponential is a phasor that rotates in a certain direction with a certain velocity has real and imaginary projections, we eliminate the imaginary projections by adding another phasor rotating in the OPPOSITE direction with the same velocity. This opposite direction is the negative frequency.
Because no imaginary projections in real life, then no negative frequencies as well !!
---------------------------------------

2) ISI is the presence of contributions of all other symbols in a certain symbol. That is because all channels have low pass nature and won't carry sharp pulses that start and end strictly instantaneously. A dispersive channel is either dispersive because of its nature (the material of a cable) which treats every frequency with a diff wave velocity, or because we are obligated to use LPF at the transmitter because the medium is shared (like the case of wireless communications).

----------------------------------------

3) ICI is a problem that is specific for multi-carrier systems, which results from the loss of Orthogonality between the sub carriers.This happens when the FFT is considered over duration where the subcarrier is non integer number of cycles. We mitigate this using cyclic prefix.

-----------------------------------------

4) Interleaving is the scattering of contiguous elements in a data packet into different packet, so that if we lost a whole packet, the loss is in smaller elements that belong to different packets, when we apply de-interleaving, we recover packets that are partially corrupted but not totally lost.

-----------------------------------------

5) Cross talk is the undesired coupling between two neighboring systems, each systems creates an undesired interference on the system in its neighborhood (ex. two cables).

-----------------------------------------

6) An Equalizer is a filter that mitigates ISI, it simulates the inverse transfer function of the channel in order to retrieve a better version of the signal. Digital equalizer are usually tapped-line filters the taps' gain may be adapted through estimating the channel and recognize the varying channel's transfer function.

Hope this helps !

Hi

You can see same topic at the side bar of this site. You can find out some thing same your questions.

Rgs
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top