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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Practical diversity combining at receivers (Maximal Ratio Combining & Equal Gain Combining)

I am trying to perform practical diversity combining implemented in GNU Radio by using Ettus N210 USRPs, one as a transmitter and two as receivers. To compare Equal Gain Combining (EGC) and Maximal ...
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11 views

What is the difference between multipath channel and fading channel? [duplicate]

what is the formula of channel reponse of multipath fading? is it h = 1/sqrt(2)[randn(1,N) + irandn(1,N)]; % with N: length of signal or 1/sqrt(2)1/sqrt(Ntap)[r andn(1,Ntap) + ...
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1answer
103 views

How to calculate transmission capacity?

My textbook doesn't explain how they got the answer to this question: "If a transmission channel uses an analog carrier wave that is modulated by eight amplitudes and sixteen frequencies per bit ...
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2answers
39 views

M-Array DPSK decoding and encoding

So i'm trying to figure how how to do the encoding and decoding of an M-array Differential Phase Shift Keying (DPSK) signal. I understand how to do it for binary DPSK, but on higher ordered signals ...
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42 views

Resources on Non-Gaussian Channels

I understand why most of the classic textbooks only consider Additive White Gaussian Noise channels in digital data transmission. Unfortunately in my case noise is not Gaussian and it might even be ...
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1answer
25 views

Reasoning Behind Additional Phase Shift in DPSK

In MATLAB's Comm System Toolbox there is an option for 'Phase Rotation', defined as the phase difference between previous and current modulated symbols when the input is zero. This is the first time ...
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18 views

Is adding zeros part of the Hermitian Symmetry process?

I have been reading about DMT/OFDM and every source I find defines their system differently. I simply want to know if zero insertion is part of the Hermitian symmetry process that produces real OFDM ...
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26 views

Help using an example how to calculate the word length for words formed using sliding window

I have a binary sequence of length N as $10110110111...$ I want to segment the above series into equal blocks of a window of length $L$. One way of determining the block length is using the ...
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1answer
29 views

Maximum Likelihood for colored noise

I have the following question about the maximum likelihood (ML) in presence of inter-symbol interference and colored noise. Assume the communication system is as follows. Information source, ...
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1answer
35 views

What is the cost of Hamming coding?

We know that (7,4) hamming code has 4 message bits and 7 code bits and can detect any single bit error. The (12,4) repetition code has 4 message bits and 12 code bits and can detect any single bit ...
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30 views

Maximum Likelihood question

I have a basic question about maximum likelihood (ML) estimator and its implementation. I am trying to simulate a communication system affected by ISI and noise, while using ML at the receiver side ...
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5 views

small HID tag for 50cm range (like glass HID) interference issues

i was looking at different rfid tags , passive ones to be exact and found that there is a very small and very nice injectable rfid tag, i was wondering if those tags can be bunched one next to the ...
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19 views

How to generate Golay sequence?

I am trying to follow the 25.213 3GPP spec point 5.2.3.1 to generate Golay sequence for the P-SCH channel. I was able to do it recursively for Hadamard sequences, but I am unsure of what golay ...
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1answer
40 views

How can I shift this signal to it's midpoint in order to decode it

I'm wondering if there's a simple way to decode this pulse signal as I'm reading it in. I'm thinking the simplest way to decode this is if i can shift the whole signal down so that it's centered ...
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2answers
33 views

Optimal time for sampling symbol in digital receivers

I'm studying various publications about symbol timing recovery algorithms, Early-late, Mueller and Muller & Gardner. All documents I've read tells that, to minimize ISI : The optimal time for ...
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2answers
33 views

systematic way to determine best bit mapping policy

So in class, we've been asked to find the best bit mapping policy for QAM modulation schemes (4-QAM, 8-QAM, 128-QAM, etc). Best meaning the one that will provide the lowest bit error Probability ...
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3answers
57 views

What is bit rate? How is it related to bandwidth? [closed]

I am very confused about when to use bandwidth as bit rate and where not. Are these terms one and the same?
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1answer
79 views

Calculating energy spectral density function of half-cosine function

I have the following function: $$ g(t) = A\cdot \textrm{rect}\left(\frac{t}{T}\right)\cos\left(\frac{\pi t}{T}\right)$$ How do I find the energy spectral density function? I think? it is defined as ...
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1answer
24 views

How to write cyclic codes?

I am studying cyclic codes. From what I understood of it, a cyclic code is a special kind of linear code with the property that any codeword cyclic shift is also a codeword. Generally, we start with ...
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1answer
32 views

Coherence bandwidth/delay spread in OFDM

Say we want to design an OFDM system and we have some parameters given to us, i.e. the coherence time $T_c$ and the max delay spread $T_m$. It's clear to me why we need to ensure $T_s(N+N_{cp}) \ll ...
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How often do a LTE eNodeB scheduler schedule?

Scheduler schedules the resource for each UE. How often do a LTE eNodeB scheduler schedule? Is the time between each scheduling fixed? any idea/reference will be great help on this regard. Thanks.
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1answer
52 views

Derive chernoff bound for $\mathrm{erfc}(x)$

I'm trying to derive the Chernoff bound $\mathrm{erfc}(x) \le \exp(-x^2)$, by first showing: $$\mathrm{erfc}(x) = ...
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1answer
34 views

Fully random PN sequence

Can a CDMA PN sequence be fully random, as in encryption-grade randomness, or must it be deterministic? I have tried the first bytes of SHA-256 hashes as PN sequences, but somehow they don't coexist ...
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2answers
45 views

suppose if we send AM modulated message signal through space how the receiver will be knowing that we applied AM modulation?

suppose if we send AM modulated message signal through space how the receiver will be knowing that we applied AM modulation basically how it will be knowing that which modulation is applied for our ...
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1answer
84 views

Bit Error Probability for 8PSK

I'm trying to understand how to derive the BEP for 8PSK by geometrically looking at the decision regions. Say I have this 8PSK signal set and the corresponding decision boundaries. I assume that ...
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15 views

Inconsistency in LTE UE-Specific Reference Signal for Special Subframe Configurations 9

Refer 3GPP 36.311 (Release 11 or higher) section 6.10.3.2 or Figure 6.10.3.2-3 shown below, Here UE-RS is defined for Special Subframe configuration# 9 as seen in the middle row of sub figures in ...
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How to achieve Shannon's capacity if coding introduces a spectral efficiency loss?

I am a little bit confused concerning different Shannon's notions : Over an AWGN channel Shannon's capacity is in my knowledge : $R_b<C=B.\log(1+SNR)$. Is Shannon's "limit" a different notion than ...
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61 views

Question about ASK, correlation, and frequency domain

So I'm currently studying ASK (amplitude shift keying) and how it is modulated and demodulated. The modulation take out data signal, $M(t)$, and multiplies it with our carrier frequency, lets say ...
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65 views

How to measure/estimate symbol rate of a signal with unknown ( but probably QAM ) modulation?

Is it possible to estimate the symbol rate of a signal whose modulation is not know exactly but it can only be guessed that it is probably some kind of QAM (probably 64 or 256). What is the best way ...
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1answer
68 views

Why do we really split pulse shaping between the transmitter and the receiver?

EDIT: There was a small error in my code when plotting the Squared RC. Below is the correct frequency response, and clearly RC² doesn't fulfill Nyquist's criterion. ...
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10 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 say I have a repeater-based communication system, where one node ...
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1answer
78 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). ...
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19 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 ...
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1answer
50 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 ...
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3answers
104 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 ...
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1answer
51 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 ...
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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 ...
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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 ...
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1answer
32 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 ...
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2answers
71 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 ...
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67 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 ...
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1answer
98 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 ...
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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 $K$ ...
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1answer
99 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 ...
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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 ...
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1answer
50 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 ...
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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 ...
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2answers
52 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 $$P_r = P_t G_t G_r (\frac{\lambda}{4\pi D})^2$$ ...
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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?
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1answer
32 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 ...