0
What else can I help you with?
What is the main difference between fdm and ofdm?
FDM and OFDM both have the same overlap!. In FDM the overlap is in the time domain. In OFDM the overlap is in the frequency domain. First (you may already know this) the relationship between the rectangular pulse and the sin(x)/x (sinc) function: A rectangular pulse in the time domain transforms to and from the sinc function in the frequency domain. A sinc function in the time domain transforms to and from a rectangular "brickwall" function in the frequency domain. In other words these two functions transform to each other by either FFT or IFFT. In both FDM and OFDM we are taking multiple carrier frequencies, modulating them, then combining them for transmission. For simplicity lets assume each carrier is on/off modulated. In idealized FDM, we modulate each carrier then send each though a brickwall filter before combining to the antenna. Say the carriers are separated by 500KHz, (say at 1GHz + 500KHz, 1GHz + 1MHz ...) Each carrier's 500KHz brickwall filter in the frequency domain cause a time domain spreading of its on/off pulses into time domain sinc function with zero crossings every 1us. Now, if we make the baud rate 1Mbps, each bit's ideal sampling point (center if eye) occurs at the zero crossing point of all of the potentially interfering sinc functions from previously received bits. In other words there is lots of ISI, but none at the critical moment when the bits are sampled. This is called "signalling at the Nyquist rate" and is related to but not the same as Nyquist sampling which you hear a lot about. (see en.wikipedia.org/wiki/Nyquist_ISI_criterion, apparently I am not allowed to include link because I am new to physicsforums). Of course brick wall filters are hard to make, so we use things like raised cosine filters that create the same beneficial sinc zero crossings. OFDM is analogous to FDM but with time and frequency domain reversed. We on/off modulate our carriers, but they are combined as unfiltered rectangular pulses and sent straight to the antenna (simplification of course). These time domain rectangular pulses become spread in the *frequency* domain as sinc functions. If we on/off modulate each carrier at 1Mbps (1us symbol time), and simultaneously maintain 1MHz carrier spacing ("orthogonal"), then the zero crossings of the sinc functions occur every 1MHz. Their positions are such that at each carrier frequency, all other carrier's smearing sinc functions have zero crossings. Thus each carrier frequency is free from interference. Again there is plenty of interference between these signals, but none at the critical frequencies where the carriers are located. Note the factor of 2 difference between the OFDM bandwidth and the FDM bandwith in my example. This is due to the convention of including negative frequency in the bandwidth in the OFDM case. Naturally, there is much more to it than this, but this is the basics. Hopefully you can figure out from this where the 50% comes from (look at the superimposed sinc functions).
What is the principle of limiting factor in decision making?
The limiting factor is the biggest thing that stands in the way of you solving a problem or accomplishing an objective. Locate the limiting factor as part of your decision-making process to avoid making mistakes. Failure to follow the principle of the limiting factor leads to many poor decisions.
What news channel does the O'reilly factor' air on?
Fox News Channel
How do you calculate burst factor of corrugated box?
=(Bursting Strength*1000)/GSM
What is fedex critical success factor?
I would say: Time reliability Add forecasting crisis
What is SISO-OFDM?
SISO-OFDM is an OFDM system with one transmit and one receive antenna.
What is crest factor of online ups?
Crest factor is the ratio between the instantaneous peak current required by the load and the RMS current (RMS stands for Root Mean Square, which is a type of average). Most common electrical appliances exhibit a crest factor of 1.4 (1.4 is the ratio of the peak value of a sine wave to its RMS value). Computers and IT equipment with Power Factor Corrected power supplies exhibit a crest factor of 1.4. Personal computers and stackable hubs exhibit a crest factor of 2 to 3.
What is crest factor of sin wave?
sqrt(2)
How many sub channels does OFDM use for carrying data?
OFDM uses 48 subchannels for data and 4 are used as Pilot Carriers.
What is 'ofdm'?
Orthogonal frequency-division multiplexing
What is loss of orthogonality means in OFDM technology?
In OFDM, sub-carrier spacing is maintained in such a way that the maximum of one sub-carrier occurs at the minimum of the successive sub-carrier, a loss of orthogonality results if this pattern is not achieved in the sub-carriers of OFDM transmission. Loss of orthogonality is due to ISI, ICS, Frequency offset amongst the sub-carriers of OFDM.
How you eliminate inter symbol interference in ofdm?
Inter symbol interference (ISI) in OFDM systems can be minimized by using a cyclic prefix. This involves adding a copy of the end of each OFDM symbol to the beginning before transmission. The cyclic prefix helps to mitigate the effects of multipath fading and reduces ISI by allowing the receiver to separate the OFDM symbols with a guard interval.
What encoding or modulation technology does 802.11 a use?
OFDM
What encoding or modulation technology does 802.11a use?
OFDM
Can you do successive interference cancellation SIC in OFDM?
yes
What is important factor to be considered in design of summit curves?
The vertical curves at crest is an important factor to be considered in design of summit curves.
What is meant by the term OFDM?
OFDM means Orthogonal frequency-division multiplexing. This is a method on encoding data which in digital television and radio. It is also used on 4G networks.
