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

learn more… | top users | synonyms

0
votes
0answers
2 views

Repeater based pathing

I'm having trouble finding information on the topic i'm interested in, and maybe my problem is just how i'm wording things. So, let's so i have a repeater-based communication system, where one Node ...
0
votes
1answer
43 views

What benefits can we get from the use of GFDM?

Existing literatures say that the generalized frequency division multiplexing (GFDM) has lower out-of-band emission (OOBE) levels compared to orthogonal frequency division multiplexing (OFDM). ...
0
votes
0answers
15 views

Level crossing rate, Rayleigh

So I'm solving an exercise and I'm wondering if I'm being tricked or not. The problem is to calculate the level crossing rate for a Rayleigh fading channel with threshold $15$ dB below the average ...
1
vote
1answer
43 views

Why is CDMA so complicated, wouldn't this simpler solution work?

I am now reading about Code Division Multiple Access method (CDMA), which is used for multiple hosts to send data at the same time. The main idea behind it is to use orthogonal vector basis to ...
1
vote
3answers
72 views

Two signals with the same frequency in the same area can interfere?

If one signal is transmitting form transmitter $TX_1$ with some frequency $X$ and some other transmitter $TX_2$ is sending some other signal with same frequency $X$ will there be any clash or ...
1
vote
1answer
30 views

FWGN model implementation vs explaination (textbook pages attached)

I came across the FWGN model for multipath channel simulation in the book: "MIMO-OFDM Wireless Comuunications with MATLAB" Here is an explanation about Clarke/Gans model: Some code to generate a ...
0
votes
0answers
10 views

Wireless Resource Allocation Problem: How to acquire channel state information for different frequencies?

I am trying to understand frequency allocation in Dual Hop Relaying S-->R-->D. I have questions about Channel State Information. I am assuming the whole transmission occurs in two time slots and ...
1
vote
0answers
13 views

How can I Map demodulated symbols using GRAY code [closed]

Could anyone help me by giving example how to do mapping of bits/ symbols using Gray code. your help will be much appreciated :)
4
votes
0answers
27 views

DSSS/CDMA: Number of distinguishable users with gold codes [duplicate]

From wikipedia, I know that Gold codes have length $2^n-1$, where $n$ is number of LFSR elements and that there are $2^n-1$ different Gold sequences for this case. E.g. assuming that $n=6$, I have a ...
0
votes
1answer
27 views

How to do base-band simulation of coherent detection of M-ary orthogonal signals?

I currently have a complex base-band simulator for non-coherent detection of M-ary orthogonal waveforms (such as M-FSK). I run the noisy signal through M correlators at lag=0, compute the magnitude ...
1
vote
1answer
56 views

What are the fundamental reasons that suggest us to minimise transmission power for energy-efficient radio link design?

My question in short: Under which scenarios minimising transmission power is beneficial in terms of transmitter energy-efficiency? is there any fundamental reason to keep a low-power oriented design ...
0
votes
0answers
50 views

Minimum Bandwidth condition in FSK

I know that FSK occupies a larger bandwidth compared other keying schemes, BW= f1 -f2 +2Rb where f1 and f2 are carrier frequencies and Rb is the bit rate. For achieving a particular bit rate say 8 ...
1
vote
1answer
89 views

OFDM channel estimation

As we know, if we want to get the time domain response of the channel $h[n]$, we can first get the frequency domain response of the channel $H[k]=Y[k]/X[k]$. And then we do IFFT. But now one OFDM ...
0
votes
0answers
17 views

What is the capacity or spectral efficiency of MIMO frequency selective wideband system?

Assume we have a frequency selective channel with Multiple Input Multiple Output (MIMO) antenna system with $M$ antennas at transmitter and $N$ antennas at receiver. Lets assume we have $K$ ...
1
vote
1answer
65 views

Exact definition of soft bits in digital receiver

At which stage of digital receiver, the bits are considered as soft bits? I am unable to find the exact definition. I have rough idea how soft bits are different from hard bits but in terms of signal ...
0
votes
0answers
12 views

How is each user's channel estimated in FH-CDMA under high Doppler?

Consider a CDMA system operating at high frequency band where the relative velocity between the transmitters and the receiver is high, which means that there is a non-negligible Doppler effect (e.g. a ...
1
vote
1answer
46 views

Mutual information of $ \infty $-PAM

I'm trying to compute using matlab the mutual information for an $ \infty $-PAM input (the limit of a very dense PAM constellation) for a range of snr and I got stuck. I'm working with a real-valued ...
1
vote
0answers
14 views

How do we find the capacity of MIMO wideband point to point system?

This question is in the context of digital communication . In many text books (wireless communication), when people derive the capacity of point to point communication system (one transmit one ...
0
votes
2answers
32 views

Friis law and the power delay profile

Assume we have communication system between transmit and receive over wireless channel. The Friis path loss model is given by the following equation $$P_r = P_t G_t G_r (\frac{\lambda}{4\pi D})^2$$ ...
0
votes
0answers
11 views

iterative decoding of serially concatenated convolutional code

Can SOVA (soft output Viterbi algorithm) be used for iterative decoding of serially concatenated convolutional code. i.e for decoding both inner and outer codes?
0
votes
1answer
30 views

Optimized resource allocation problem

I am from ECE background and trying to solve channel allocation problem. Let's assume I have three users and three available channels. I would like to allocate channel among them in such a way that ...
0
votes
0answers
18 views

Understanding SNR in fading channels and MIMO systems

Signal to Noise ratio plays an important role in understanding the performance of any communication system. I understand the basic concepts of SNR but I am having trouble when trying to bring in a ...
0
votes
1answer
43 views

Uniform quantizer for gaussian input signal

I have a gaussian signal $x$ with zero mean and unit variance. I am quantizing it by using a uniform quantizer of step size $q$ calculated by $$q = \frac{x_\mathrm{max} - ...
1
vote
0answers
22 views

Steps to derive Bit Error Rate for a particular equalization technique as a function of SNR

BER for BPSK modulation shows how to derive the bit error rate. The derivation is quite straightforward to follow. But, I do not know if one needs to derive the analytical expression for BER based on ...
2
votes
1answer
34 views

Concepts: Ideal and non-ideal channel resulting in intersymbol interference

I am following the book: Blind equalization and Identification by Zhi Ding and Ye Li. In Chapter 2, the concept of T spaced equalizers is presented. It is mentioned that the output of the channel is ...
0
votes
1answer
57 views

Crest Factor of OFDM signal

I have been given a OFDM signal of crest factor of 12dB. The crest factor is the ratio of peak power to the average power of the signal. Does anyone have any idea how crest factor of 12dB is derived ...
2
votes
0answers
33 views

Practicality of the assumption of i.i.d. for Rayleigh channels

I would like to understand how far the assumption of having i.i.d. is accurate/valid (from the practical point of view) when an OFDM system is working in Rayleigh channels. Is this means the channel ...
5
votes
2answers
368 views

Why not use zero-signal in digital transmission?

This is something that bothers me from time to time and has always been hand-waved away with some plausible but non-rigorous explanation. For clarity, consider the QPSK case where we have the ...
0
votes
0answers
45 views

How to determine the magnitude of the discrete time Fourier transform

I am new and studying the discrete signal processing. I am solving the question related to DSP, and I am having trouble in understanding the breakdown of signal through DTFT. Determine the DTFT ...
0
votes
0answers
20 views

Conceptual questions on MC-CDMA - where to perform equalization?

I have some basic questions on MC-CDMA technology. Below are the steps involved and the Questions. Please correct me if there is any mistake in the steps. An intuitive answer will be very helpful. ...
2
votes
0answers
121 views

Matlab: Help in understanding and applying Rayleigh effect and equalization

I am trying to simulate a flat fading Rayleigh channel for BPSK modulation. Then I want to apply Minimum Means Square Algorithm for channel equalization, assuming full knowledge of the channel ...
0
votes
0answers
26 views

Differences in data rates compared to PCM

I'm trying to find a decent source that compares the efficiency of regular PCM (64kbps) to other methods of signal encoding, but am not having much luck. So far I've found: ADPCM - similar @ 32kbps, ...
0
votes
1answer
40 views

BER Analysis of Dual hop Decode and Forward Relay

I want to perform fair BER analysis between Two-hop Decode and Forward relay communication (S-->R-->D) and Direct Transmission from S-->D. The links have Rayleigh fading. Now for fair analysis 1) ...
0
votes
0answers
14 views

Reference : Blind equalizers for CDMA communication

I would like to know which equalizers are commonly used in practice for Direct sequence CDMA communication. For a project, I need to simulate CDMA communication with a blind equalizer and was ...
1
vote
1answer
58 views

Why does FEC seem to make BER worse at low Eb/N0?

I've been plotting BER curves and am wondering why FEC seems to make a BER curve worse at low Eb/N0 than the un-coded theoretical BER curve? My example plot below is for Differential BPSK using a ...
1
vote
1answer
112 views

How to convert time-domain signal to complex envelope?

Matlab and Simulink Communications Toolbox digital demodulators are defined to only work on the complex envelope representation of a baseband signal. To obtain the time-domain representation of this ...
0
votes
1answer
80 views

Determine minimum distance between two symbols in 16-QAM using the average symbol energy

If the probability of bit error for a square M-ary QAM is $P_M = (1-(1-P_\sqrt{M})^2)$ where $P_\sqrt{M} = 2(1-\frac{1}{\sqrt{M}})Q(\sqrt{\frac{3E_s}{(M-1)N_0}})$ and $E_s$ is the average symbol ...
0
votes
1answer
60 views

Fast fourier transform for an audio file

I need to do FFT on an audio file(to be exact it is a real number array of audio samples). But the output of FFT should be complex numbers. I have a hard time understanding how to convert this. For ...
0
votes
1answer
144 views

Confusion between samples per second and samples per symbol

My understanding of sampling frequency is when we have an analog signal x(t) we convert it to a digital signal. Assume the sampling frequency is denoted by $f_s$ then the sampling time $T_s$. In my ...
1
vote
2answers
82 views

Quadrature modulation

I have a question: What is the difference between $ I \cos(t) - Q \sin(t) $ and $ I \cos(t) + Q \sin(t) $ except that they are phase shifted 90 degrees ? On the internet I can find both ...
0
votes
1answer
76 views

Example exercise - Shannon's law on PCM-digitized signal

I am studying for a Digital Communications course in my university, and I am presented with the following example exercise. You have a sound signal with spectral components in the 300-3000 Hz ...
1
vote
2answers
115 views

Rayleigh BER in Simulink

I'm using the Rayleigh Channel in Simulink but I can't calculate the BER. I always get values near to 0.5 which doesn't make sense (even using high EbNo values). [In this simulink model][1] I found a ...
1
vote
1answer
42 views

Is there an existing feedback elimination algorithm that can be implemented in iOS?

The project I'm working on allows a user to speak through a PA system with their iphone as the microphone. Unfortunately, the existing audio units in iOS don't eliminate the feedback between the PA ...
4
votes
2answers
126 views

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 ...
0
votes
1answer
37 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 ...
0
votes
1answer
22 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. ...
0
votes
1answer
47 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.
0
votes
0answers
32 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 ...
0
votes
0answers
28 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 ...
0
votes
0answers
46 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 ...