Questions tagged [digital-communications]

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

Filter by
Sorted by
Tagged with
0
votes
1answer
75 views

What does it mean that the normalized power of a received equals one?

I have read in that lecture, page 2, here that, the symbols are independent, and normalized to have power 1, which means $E(x x^H) = I$ .. what does that mean? could you please explain that for me?
2
votes
0answers
183 views

Dynamic loop bandwidth for a Costas loop

I'm using a Costas loop for carrier recovery. The BER vs SNR (from GNU Radio Simulation) curve for different loop bandwidths (0.03,0.05 and 0.07) is shown in the graph below. It can be seen that the ...
1
vote
2answers
258 views

Carrier Frequency Offset, Rotating Constellation and Correlator

I have been further reading up on carrier recovery methods and something is not clear to me: It's written that a carrier frequency offset results in a rotating constellation diagram but if you are ...
0
votes
1answer
18 views

What does SDMA's space actually mean?

What does SDMA's space mean? I mean,T for TDMA is time,and unity of time is second. F for FDMA is frequency,and unity of frequency is Hz.Now i know the S for SDMA is space or spatial,but i don't ...
0
votes
1answer
66 views

Phase versus time graph of QPSK

In wikipedia, there was an example on QPSK modulation where the main signal was 11000110 and I contained 1001 and Q contained <...
1
vote
1answer
2k views

What is the difference between Antenna port and Physical Antenna in LTE?

I have just started working on the 5G NR physical layer and I have difficulty understanding the concept of Antenna Port at the downlink. In release 10 there supposedly 15-22 antenna ports for CSIRS (...
1
vote
1answer
63 views

Frame acquisition vs symbol timing synchronization

For a known length of frames and using a known sequence in a preamble that is also of known length can auto correlation at the receiver be enough to acquire timing or is timing synchronization at ...
1
vote
1answer
1k views

Generate Complex White Gaussian Noise in MATLAB

n_3=sqrt(0.1)*randn(1,K); n_4=sqrt(0.1)*randn(1,K); beta_NLoS=(n_3+1i*n_4); % CN(0,0.1) I want to create a $CN(0,0.1)$,does my code have any problem?
5
votes
2answers
195 views

Timing error detector used for symbol timing synchronization

The Gardner timing error detector is independent of carrier phase and frequency error, and is also quite immune to self noise (to my understanding, I may wrong about that). Can one assume that it is a ...
1
vote
2answers
88 views

BPSK signal that has not been pulse shaped by any filter

Can one consider that a BPSK signal that has not gone through any pulse shaping filter to be equivalent to a signal that has gone through a rectangular filter of which the pass BW is equal to the ...
5
votes
2answers
401 views

Intersymbol interference due to limited channel bandwidth

What is the difference between limited-bandwidth induced intersymbol interference (ISI) and ISI due to multipath propagation. I noticed that the delay spread in indoor environment is in the range of ...
0
votes
1answer
1k views

Maximum Likelihood Detection of Signal Vectors in Gaussian Noise

Consider a binary-input additive white Gaussian noise channel. Let $\mathbf{x}_0 = (\sqrt{Es},\sqrt{E_s},⋯,\sqrt{E_s})$ and $\mathbf{x}_1 = (-\sqrt{E_s},-\sqrt{E_s},⋯,-\sqrt{E_s})$, be two codewords ...
1
vote
2answers
120 views

Signal bandwidth of an 802.15.4 signal at 2.4 GHz

This signal uses Offset QPSK with a half sine pulse shaping filter for the purpose of getting a constant signal envelop. Does anyone know the exact bandwidth of this signal after being pulse shaped, ...
2
votes
4answers
78 views

Bandlimiting and OFDM spectrum - what is considered “bandlimited”?

I have been reading about OFDM modulation, it's not clear to me how you can have band-limited OFDM but given its prevalence in wireless communication there must be some designation of approximately ...
1
vote
2answers
1k views

What is a constant envelope modulation?

The Book "Digital Modulation Techniques" by Fuqin Xiong groups digital modulation schemes into two classes: "constant envelope" and "nonconstant envelope." However, I was surprised by the inclusion ...
0
votes
1answer
224 views

Recursive Least Square Adaptive Linear Equalizer

For the adaptive filter to work properly, a desired signal d(n) needs to be provided. The output from the equalizer y(n) is subtracted from d(n) to produce an error signal, which is used to adjust the ...
1
vote
2answers
280 views

Software PLL tracking of carrier frequency in bandlimited transmission

My understanding is that a PLL(either in hardware or software) can recover the carrier frequency(or be used to correct the frequency offset) of a system. My question is how does this work when the ...
0
votes
1answer
36 views

Is there just a carrier in each frequency band in FDMA?

The figure is the FDMA,and i know that FDMA is that dividing the bandwidth into many blocks(frequency band),i want to ask Is there just a carrier in each frequency band in FDMA?i mean one carrier for ...
0
votes
2answers
281 views

Inter Symbol Interference (ISI) / Equalization in Digital Signal Processing

I am studying the OFDM system and before to start I have decided to study the main concepts of modulation. And I have spent yet a lot of time to understand the concept of an equalization to reduce ISI....
1
vote
0answers
197 views

Blind equalization with constant modulus algorithm in GNU Radio

I'm currently simulating the effect of multitap channel on BPSK as well as its remedy i.e. equalization. The modem is expected to work with satellite TT&C transponder. The communication channel ...
0
votes
1answer
86 views

IQ generation separation

To generate I & Q samples from data samples S I = S(1:2:length(S)-1) * cos(2*pi*f*t) ; Q = S(2:2:length(S) ) * sin(2*pi*f*t) ; I & Q to integer ...
2
votes
2answers
838 views

Preamble Detection and Frequency Offset Estimation in radio packets

I have generated a radio packet of data with a preamble header of 0x55555555 and crc32 for the data only. The entire packet was separated in even and odd streams for I and Q. The I and Q were ...
-1
votes
1answer
65 views

Doppler compensation method for cdma

Do you know of effective and simple methods to compensate for Doppler due to movement for the CDMA protocol?
0
votes
2answers
77 views

The relation of sub-carrier and FDMA

In Mengyu Liu, Yuan Liu, "Charge-then-Forward: Wireless Powered Communication for Multiuser Relay Networks", it is said that while information signals are conveyed by using FDMA over $N$ sub-...
2
votes
0answers
111 views

Why is channel estimation done after synchronization and why does it work?

I am interested in Software Defined Radio communications where almost all processing is pushed to the digital domain. I'm wondering why is channel estimation done after frequency and phase ...
0
votes
5answers
113 views

How can telecommunication system know which part is signal and which is noise? [closed]

When signal is received how can receiver know which part of received signal is signal and which part is noise??
1
vote
0answers
28 views

Question about direct spread spectrum in 802.15.4 at 2.4 GHz

I read the 802.15.4 standard and something is really confusing me: How is spreading achieved in 802.15.4? is it by multiplying, encoding or modulating each data symbol (4 bits) with a certain code ...
1
vote
1answer
459 views

What is the noise whitening process?

I came across this process when working on OFDM in wireless communication. It's mentioned if we have two copies of a signal resulted from SIMO system (Single Rx Multiple Tx), we can process the noise ...
1
vote
1answer
243 views

Digital Downconversion of Signal

DSP-Newbie here... Why are we using the ratio of the center frequency of the signal to the sampling frequency of the signal spectrum when we downconvert the signal? I have an Spectrum with Carriers ...
0
votes
1answer
131 views

PN code generation

Can we generate PN codes (maximal length sequence) using this technique in Matlab where L is the PN length? pn=2*(rand(1,L)>0.5)-1 If yes, why?
0
votes
1answer
72 views

Phase tracking in communication receivers [duplicate]

Why does Costa's loop PLL bandwidth need to be narrow? Text books mention that and yet give no explanation
0
votes
1answer
62 views

Why Isn't the ML Estimator (MLE) in MIMO Spatial Multiplexing Obtained by the Least Squares Solution?

In the simplest scenario of MIMO spatial multiplexing: $$\mathbf{y} = H\mathbf{s} + \mathbf{n}$$ where: $\mathbf{s}=[s_0,s_1,...s_{M-1}] \\\mathbf{y}=[y_0,y_1,...y_{N-1}]$ $\mathbf{n}=[n_0,n_1,......
0
votes
1answer
220 views

What's the relation between the sampling rate and FFT size in OFDM

In OFDM system, Is there relationship between Sampling rate and FFT size? For example, if we downsample or oversample the received signal, Should we decrease or increase the FFT size accordingly? ...
1
vote
0answers
333 views

DPCM Encoder and Decoder Simulation in MATLAB

I am trying to simulate DPCM in order to understand how it works. I am trying to implement the simplest version of DPCM which has a system scheme like in figure 1. Sorry for the quality of the ...
0
votes
1answer
162 views

Get I and Q components from a signal (multple frequency signal)?

Is there anyway to get the I and Q components from a signal in the time domain? The signal has multiple frequencies. So far I have been doing this in a SIMPLE situation: Fast fourier transform to ...
0
votes
0answers
46 views

Can we sample the signal with any period as long as the Nyquist rate is respected

I have a question regarding the sampling rate. Suppose that we transmitted a signal $m(t)$ then at receiver side, we received the continuous signal $x(t)$, which is time varying and sampled with a ...
0
votes
1answer
113 views

methods of crest factor minimization

i am studying the methodes CF minimization. and have a doubt. in each methods there are steps with DFT and IDFT or like this FFT and IFFT. Everyone provides the fact, that they use DFT and IDFT for ...
0
votes
1answer
74 views

Homodyne concept of receiver

I would like to understand a concept of homodyne architecture of I-Q demodulator and how the wave looks like at each step. It is a bandpass Signal: Step 1: multiplication with cos and sin wave. I ...
0
votes
1answer
65 views

Don't understand the relation about the wireless communication flow chart and TDMA illustration diagram

The first picture is the wireless communication flow chart,and the second is the TDMA illustration diagram,Which part of first picture is TDMA ? or if first picture is the standard process for TDMA,...
1
vote
2answers
767 views

Does a matched filter really improve SNR?

Does the matched filter actually improve SNR or does it maximize it (making sure that it is not less than what it should be) ? improving SNR would not make sense to me as suppose a receiver has a ...
0
votes
1answer
52 views

Relation between Wireless Power Transfer, Wireless Information Transfer and the definition of sum rate

I read this paper Charge-then-Forward: Wireless Powered Communication for Multiuser Relay Networks ,and it said it on the second page ,and I don't really understand why is the theory ,the author said,...
0
votes
1answer
19 views

The difference about WPCN and TDMA or FDMA

I am a little bit confused about the difference WPCN and TDMA or FDMA,i mean the level difference. WPCN is a wireless powered communication network,as the name implies,it can transmit the information ...
0
votes
1answer
339 views

number of subcarriers for an OFDM system

For an OFDM system, it is necessary to know the number of subcarriers. For example for the subcarrier $k^e$, we must have: $B_k <B_c$ with $B_c$ the channel coherence bandwith. And $B_k=\frac{1} {...
0
votes
2answers
35 views

Rate in CDMA setup

I am working on a CDMA system with only 4 chips/symbol. I want to use $R=\frac{1}{2}log_2(1+SNR)$ chips/channel use to calculate what $SNR$ I require to successfully receive a given transmission. In ...
0
votes
0answers
82 views

minimum usable 5G cellphone signal level?

I'm a programmer (not and EE) working on a project to simulate coverage and capacity for 5G cellphone signals at 26 GHz. But I've done enough path loss calculations for terrestrial and satcom radio ...
0
votes
1answer
65 views

IQ modulation principle

I am new in the signal processing. I hope I can get help. I want to ask a question regarding IQ modulation work . Why can’t I simply multiply a complex base-band signal with a cosine to modulate it?
2
votes
0answers
141 views

How can I oversample the received signal by double of sampling time and have two signals

I have a question, how can I make the sampling in Matlab for the received the signal by half of time duration of symbol (Ts), and have two copies of signal (that's the process of fractional sampling ...
2
votes
2answers
109 views

How to solve equations for the MMSE receiver?

Given the following equations for the achievable rate of the Minimum Mean-Squared Error Receiver [1]: $$\mu = \frac{1}{K-1} \sum_{i=1, i \neq k}^{K}{\frac{1}{Mpd_{i}\left(1 - \frac{K-1}{M}+ \frac{K-1}...
0
votes
2answers
233 views

matched filter for doppler

To remove the Doppler shift, we can use a bank of matched filter. But, to use this method, we need an interval $[-f_{max};f_{max}]$. How can we approximate this interval?
1
vote
2answers
199 views

Phase ambiguity in QAM modulation

I'm currently studying a decision directed carrier recovery scheme. Basically a PLL try to estimate the phase error in the current received symbol, the phase detector compensate the incoming symbol's ...