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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Difference between these two digital down conversion methods

I can think of two possible methods of digital down conversion. One seems superior to the the other for most cases, but I'd like to get some DSP experts' comments on the practical differences between ...
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1answer
25 views

Why does DPSK constellation shrink when noise is added?

I am generating a DQPSK waveform at complex base band with constellation points on the unit circle and when I add AWG noise the constellation shrinks. The noisy constellation "blob" migrate inside ...
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1answer
20 views

adding phase noise in signal thorugh freuquency

I want to implement a simple signal for phase noise. According to my supervisor, i shoud be adding phase noise in the frquency. This is my signal. ...
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1answer
16 views

Gray code and M-FSK

Does using a gray code mapping with M-FSK improve the BER performance vs no mapping? I know it helps QAM, and it makes intuitive sense. Doesn't seem as clear cut for M-FSK.
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0answers
25 views

Which MIMO scheme is implemented in a modem?

Hope I phrased the title in a sense. I'm trying to get more knowledge on MIMO , so I read a few paper and i've understood that MIMO system can provide 3 types of improvements : array gain, diversity ...
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0answers
15 views

Time and phase estimation in OQPSK using ML criterion

Let me first make an introduction to the problem by stating some intermediate results: An OQPSK signal has the general form: $$\\\tilde{s}(t)=\sum\limits_{i}\tilde{a}_i ...
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0answers
29 views

BFSK modulation what signal the transmitter actually sends?

I am trying to understand how modulation with carriers works(transmission part). I will express my question in terms of BFSK for simplicity. Let us condiser BFSK modulation with symbols {1,2}. Then ...
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0answers
40 views

BOC receiver implementation to combine both spectra

I am working with Binary Offset Carrier (BOC) modulation in a Software Defined Radio (SDR). I multiply the data with sub-carrier frequency that splits the signal spectrum into two, before RF ...
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0answers
29 views

noise in signal

I am trying to add phase noise in signal. However, when i see the graph in frequency domain the spectrum is not broading. Can anyone tell me what mistake i am making? ...
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0answers
25 views

Reversible QIM For watermarking

I have read your paper with title "Nested Quantization IndexModulation for Reversible Watermarking and Its Application to Healthcare Information Management Systems". enter link description here ...
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1answer
48 views

How to compute bit level soft decisions from an M-ary symbol?

When working with a decoder such as LDPC that can take in soft-decision inputs (or channel posterior probabilities as I've seen them called as well), how are these soft-decision values calculated for ...
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0answers
59 views

Hilbert transform of a bandpass signal

I have a bandpass signal x. I am taking hilbert transform of it. I want to reconstruct amplitude and phase of the signal.Therefore, i am using Hilbert transform. ...
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0answers
39 views

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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0answers
25 views

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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0answers
20 views

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 ...
0
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1answer
15 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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0answers
23 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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0answers
32 views

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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0answers
21 views

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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0answers
33 views

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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0answers
17 views

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 ...
0
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1answer
28 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 ...
0
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1answer
42 views

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 ...
2
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1answer
62 views

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 ...
2
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1answer
56 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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0answers
20 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
41 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
26 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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0answers
35 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
23 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 ...
1
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1answer
53 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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0answers
27 views

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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0answers
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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1answer
79 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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1answer
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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1answer
31 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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1answer
32 views

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, ...
0
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1answer
33 views

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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1answer
64 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 ...
2
votes
1answer
51 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 ...
2
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1answer
38 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 ...
2
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1answer
48 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 ...
1
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1answer
72 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 ...
0
votes
1answer
61 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 ...
0
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3answers
65 views

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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1answer
42 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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2answers
53 views

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)= ...
0
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1answer
110 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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0answers
45 views

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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0answers
12 views

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 ...