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Everyone used to say Proakis is the best....well...i guess.. you can get almost everything down-to-earth book...
Digital communication book by Bernard Sklar
Adding a few comments to "m_pourfathi"
In (W)CDMA the smallest signal resolution is wellknow "chip" and it's duration is approximately the inverse of bandwidth. Hence, higer the bandwidth the better the resolution for signal samples at receiver. When chip duration (Tc) is smallerm we have...
MIMO-OFDM
MIMO it self is a good technique to achieve diversity gain at receiver, which basically increase the reliability of system as well SNR margin.
Addition to the above comments, OFDM also has a good flexibility over the multipath fading channels. It uses frequency very efficiently...
How CDMA System ??
In Uplink(user to basestation): increase of users will have different offsets to eachother as well as propagate via different channels. These will greatly reduce the orthogonality between codes allocated for each user so the interference.
In Downlink (basestation to user)...
this is a causal system as y(n) only relies on it's past values y(n-1) and x's present and past values...transfer function is
y(n) = y(n-1) +2*x(n) + x(n-1)
Y(z) = Y(z)*z^-1 + 2*X(z) + X(z)*z^-1
H(z) = Y(z)/X(z) = (2+z^-1)/(1-z^-1)
=> 1st order low-pass filter..
IFFT In OFDM?
well it is just a traditional reason...nothing else..In OFDM consider FFT and IFFT as filtering..
The real channel effect is appeared in time domain(such as multipath channel delay spread)..So "assuming" transmit data are in frequency domain, perform the IFFT to get "time domain"...
This is basically an encoder which maps n-bits of symbol to a N=2^n length of Walsh Hadamard sequence. Since Walsh sequences are orthogonal, they can be recovered by taking correlation with the particular Walsh sequene.
Walsh-Hadamard sequence generation:
| H_n -H_n |
H_2n = |...
pn sequence with correlator
Ideally, random sequences should have a infinite length. But Pseudo-Random (PN) sequences are finite length sequences with semi-randomness in the elements in sequences. Some examples are M (or maximal length)-sequence, Gold sequence. They show good but not ideal...
Thanks pals. Actually, I happened to know how much the grouding and shielding is important after starting real works.
What do you guys think, starting a new category and pile all these info. there..?
All,
Is there any guidelines for basic common senses and good practices of making circuits, such as
1. impedence matching
2. termination methods and where they should be used
3. why/when you should need a dumping resistor
4. how to reduce the nosie at Vcc input of ICs
4. the usage and methods...
different of cdma,gsm,wcdma,
CDMA and GSM are basically different as GSM uses TDMA where each user is allocated with a time certain time slot out of 8-time slots. So the time axis is sub-divided and allocated to users. When one user's slot is on, other user signals are off.
However, in CDMA...
ISI symply occur due to non-ideal pulse shaping in transmitter and delay spread of the channel result overlapping other pulses. The way of reducing this is called equalization and there are many types of equalizers, i.e. linear equalizers (ZF, MMSE) and non-linear equalizers(DFE).
To get an...
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