Digital Communication is the physical transfer of data (a digital bit stream) over a point-to-point or point-to-multipoint communication channel.

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Vienna Simulator Matlab [on hold]

Does anyone know the system level Vienna simulator for Matlab? I don't understand how the UE spectral efficiency is calculated, as well as the UE throughput: when I look the results file, and I look ...
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MATLAB poly2trellis for Extended Hamming (64,57)

Current understanding: Extended Hamming (64,57) is constructed using generator polynomial 1 + x + x^6 followed by a parity bit at the end of the codeword to get even parity. The Extended Hamming ...
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Do we have aliasing with this chip rate and transmission bandwidth

A particular communication system I came across defines chip time to be 0.57 ns and consequently chip rate is 1760 MHz. The transmission bandwidth is 2.16 GHz. I am wondering, do we suspect to have ...
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Lower order modulation are more robust

In some application of Wifi, I read the following remark To have the largest possible range (coverage), the frames are transmitted at the most robust modulation and coding scheme An example of such ...
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1answer
7 views

Interleaving over OFDM symbols in same transmission

In this question I have asked what are the benefits from interleaving between two codewords over ONE OFDM symbol in packet based transmission made up of more than one OFDM symbol Purpose of ...
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15 views

Modulation and Coding Schemes in 802.11

In 802.11 standards (Wireless LAN) there are schemes called Modulation Coding Schemes (MCS) that are used at the transmitter to signal the data rate of payload for example: MCS of a BPSK modulation ...
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Matched filters

Working on my communication class right now, and I'm having a bit of a problem with the matched filters. As I see it the matched filters "eliminate" some of the noise. We project the received signal ...
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Repeating bits and symbols after coding

In an application of coding and transmission over wireless channel, I saw the following example Original 64 bits $c=[c_1.\cdots,c_{64}]$ are encoded using some coder into a codeword $$c= ...
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What is actually transmitted following LPC of a speech frame?

For each frame, what's sent over to the receiver for decoding? The coefficients , pitch in some bits, voiced/unvoiced classification in another bit? Another broad question to develop intuition about ...
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Spreading sequence and processing gain

The following has been mentioned regarding spreading using a 32 chip sequence 32x spreading contributes a theoretical 15 dB gain to the link budget, I have no clue, why so? Are we referring to the ...
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1answer
21 views

OFDM signal spectrum and characterisitics

Is it correct to say that the spectrum of an OFDM signal is rectangular pulse? What about the spectrum of each transmitted signal over subcarriers? If the OFDM signal has a rectangular frequency ...
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Lower peak to average power ratio by phase shifting

A particular sequence of +1 and -1 as follows: $X=[-1 -1 +1 +1 +1 +1 +1 +1 +1 -1 +1 -1 -1 +1 +1 -1 -1 -1 +1 +1 -1 -1 -1 -1 +1 -1 +1 -1 +1 -1 -1 +1]$ is being transmitted over a wireless channel. It ...
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Purpose of interleaving in OFDM systems

Interleaving is often encountered in digital communication systems. I have seen interleaving between codewords in a single OFDM symbols as follows Assume the bits are denoted by ...
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OFDM subcarriers average energy

Below is a statement regarding the energy of symbols in OFDM subcarriers I don't understand. The two statements are The average energy of the OFDM symbols constellations in each of the subcarriers ...
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1answer
52 views

Are pulse shaping and windowing functions the same in concept?

I read a digital communication problem and they interchange terms as windowing function and pulse shaping and refer to it as same entity. For example the following windowing function with Transition ...
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15 views

Finding minimum phase version of 2D impulse response?

For a impulse response $\mathbf{h}=[h_0 \space h_1 \space … \space h_n]$, one can find a always find a minimum phase version of $\mathbf{h}$ by using an appropriate All-Pass system. For my problem, ...
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1answer
25 views

Necessity of Cyclic Prefix in OFDM

I have a question on CP-OFDM. In recent years people are talking about filter bank approach where they are trying to filter out the out of band side lobes using filters. Besides they are presuming ...
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1answer
19 views

Modelling transmitter and receiver impairments in communication system

A paper I read studied the effect of transmitter impairments and receiver impairments by modeling both as additive white Gaussian noise. The noise for transmitter impairmenets are added before the ...
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32 views

Chip rate and sample rate

If a sequence of +1 and -1 with chip rate ($\frac{1}{0.57 ns}$) is being used for purpose of estimating channel impulse response with delay spread of 6ns. We decide to have a new rate change to rate ...
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1answer
20 views

Path loss effect on BER

Does including log distance path loss to a communication system cause a drastic difference to the BER of the system? In other words, if I have a simulation for a communication system without path ...
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1answer
32 views

Golay complementary sequences for channel estimation - MATLAB

There are set of complementary sequences known as Golay sequences that are used for channel estimation because of the nice property they have which is that the sum of the autocorrelation function of ...
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State definition in Viterbi Algorithm?

An ISI channel of length 'L+1' $\mathbf{h}=[h_0 \space h_1 \space … \space h_L]$can always be modeled as a finite state machine(FSM) of memory 'L'. For a binary input $x\in\{+1,-1\}$,a state can be ...
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15 views

Parameter selection for log distance path loss model

I am currently referring to the following book MIMO-OFDM Wireless Communications with Matlab in which the log distance path loss model is given by the equation: $P_{LD}(d)[dB] = PL_F(d_0) + ...
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27 views

Carrier frequency offset and carrier leakage

Recently I study frequency Offset estimation due to mismatch in carrier frequency from the oscillator at the receiver. I understand how this cause problem can cause a phase shift. But I also saw that ...
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39 views

How to write time waveform of transmitted sequence with certain chip rate?

I have been studying a book which describes how to write the waveform of sequence that has certain chip rate $T_c$. The sequence with chip rate $T_c$ is for example $$X=[-1 -1 +1 +1 +1 +1 +1 +1 +1 ...
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27 views

Performance of Viterbi detector over non-minimum phase channels

For sequences that are transmitted over channels with memory $\mu=n$ and response H=$[h_0 h_1 … h_n]$,Viterbi algorithm implements Maximum Likelihood (ML) detection and BCJR implements Maximum ...
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A sequence OFDM modulated with normalization factor

The following sequence is used to modulate 52 subcarriers. Twelve out of 52 are non zero. I was wondering $S_{[–26, 26]} = \sqrt{13/6} \{0, 0, 1+j, 0, 0, 0, –1–j, 0, 0, 0, 1+j, 0, 0, 0, –1–j, 0, 0, ...
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Questions regarding OFDM, FFT, IFFT

The questions below are for OFDM, IFFT, FFT operations. Example 1 In OFDM modulation, a stream of parallel symbols are input to an IFFT operation of size $M$ for example and the output is time ...
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54 views

Autocorrelation function between received and training signal used for channel estimation

I have read a paper that performs Channel Estimation of Wireless Channel as follows. A training sequence of length $N$, lets call it $a_N(i)$ for $i\in[0:N-1]$ is repeated twice then sent out over ...
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32 views

Pilot symbols in IEEE 802.11a

In IEEE 802.11a standards, there are many fields. Of which is the Data field which has 52 available sub-carriers used for transmission of coded bits. If the subcarrier locations are numbered from ...
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1answer
34 views

Output signal in digital communication

In digital communications systems we say that the received signal can be expressed as $$y(t)= x(t)+ n(t)\tag1$$ if x(t) is the transmitted signal and $n(t)$ is the noise. I am wondering whether a ...
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45 views

Spreading symbols with sequence before transmission

I have been learning IEEE 802.11ad and the following processing algorithm I was wondering what is the need for spreading with Golay sequence. I am guessing it has to with something like spread ...
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1answer
54 views

Differential BPSK vs BPSK what are the advantages and disadvantages?

Recently I have come across different variation of the sane modulation techniques. I am quite confused about the advantages of different constellations. In particular, what are the advantages of using ...
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53 views

Nyquist rate and oversampling

Assuming we have time domain signal $$x(t)\,\,\,\,\,\,\, 0\leq t< T$$ and we decide to upsample the signal by factor $L\geq1$. Then the samples of this oversampled time domain signal are ...
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General questions regarding OFDM modulation

In Orthogonal frequency division multiplexing (OFDM), data symbols are modulated using an N pt-IFFT operation to produce ONE output OFDM Assume we have total of $N$ QAM symbols which are input to ...
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32 views

Use of Equalizers in communication systems for Intersymbol interference

In communication systems with high data rates, Intersymbol Interference (ISI) is a major problem (ISI). I have read in books that one way to combat this problem is to use time domain equalizers (ZF, ...
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MMSE Equalizer in communication system

This question is regarding applying minimum mean square operation at the receiver side of communication system. I have read in paper that Given an output signal from communication system $$R(k)= ...
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1answer
67 views

BPSK vs $\pi/2$ BPSK, what the benefits?

I have come across modulation techniques that have $\pi/2$ phase shifts from the regular constellations. For example $\pi/2 $ BPSK vs constellation the regular BPSK. Other examples include $\pi/2 $ ...
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spectral mask and power spectral density

I have been reading a paper that specifies the spectral mask for certain communication devices attempting transmit over a channel Can someone explain 1) importance if this spectral mask, is it a ...
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Why can CPRI links not be wireless?

I have been studying about CRAN and the CPRI links (fronhaul links) and have observed that CPRI links are always either fiber cable or some electrical interface. Why is this needed? Is it related to ...
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Matlab : Proper estimation of weights and How to calculate MSE for QPSK signal for Constant Modulus Algorithm

I had asked conceptual Question about Constant Modulus Algorithm. I am implementing the simple steps of the algorithm, as I do not have the cma() built in ...
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Modulation GMSK with I/Q

I have a doubt about something. GMSK Modulated signal is equal to I+Q (with I = cos and Q = sin) or I+i.*Q ? Thank you. Best regards.
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64 QAM versus lower order modulation

This question is regarding digital modulation. If 64 QAM always provides rates greater than BPSK or 16 QAM, then why do systems always use higher order modulation of QAM? Thanks
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What is the output of IFFT operations, continuous or discrete time?

Assume we have a sequence of symbols $$S= \{0, 0, 1+j, -1-j, 0 ,0 , 1+j,-1+j\}$$ and that this sequence is a frequency domain sequence and will be input to an IFFT operation. Is the output a ...
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Scrambler generator polynomial with initial state

A length-127 frame scramble uses the following generator polynomial $$G(D)= D^7+D^4+1$$ If the all ones initial state is used, how can one obtain the 127 bit sequence? I am not interested in the ...
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1answer
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Doppler Model, how does it affect the fading impulse response?

I have been reading a paper that mentions Doppler model that may be included in the fading characteristics of impulse response. One example of bell shaped Doppler Spectrum is the following $$S(f) = ...
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1answer
11 views

Carrier sense multiple access, MAC layer

A medium access control MAC mechanism in wireless local area network and Ethernet is called Carrier Sense Multiple Access. There are two different types of this CSMA 1- CSMA/Collision Detection 2- ...
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Analog to digital conversion : Help in understanding how to represent quantized orbit

Problem : How do I use a map - The Bernoulli Shift Map to generate binary output using the following concepts that can find its application in coding ? Concept : The Dyadic map also called as the ...
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How to implement path loss in wireless communications?

I would like to implement path loss propagation model in a cellular network scenario. I know that the path loss can be modeled as follows: ...
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58 views

Transmission capacity in “duobinary coding”

In "duo-binary signalling" how exactly is the transmission capacity increased? Because , when we encode the binary bits, the bit duration remains the same, but the amplitude will change. Then how can ...