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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Relationship between “received” signal power and “transmitted” energy per bit?

In digital communications textbooks (e.g., Digital Communications by Bernard Sklar), the relationship between the "received" signal power $P_r$ and the "transmitted" energy per bit $E_b$ is given as ...
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2answers
75 views

carrier frequency difference

Papers use wireless device-dependent radio-metrics as fingerprints. A radio-metric is a component of radio signal, amplitude, frequency and bandwidth. Each device creates a unique set of radio-metrics ...
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95 views

Is multirate signal processing involved in ADSL?

Telecom companies offer different data rates for home/office purposes depending on the money they pay. How are the telecom people able to control the flow of data of different cables. Say supposing a ...
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1answer
21 views

Transmit bitstream from USB over radio

I am extremely new to this and I'm learning by building stuff myself so please let me know if this is too vague and Ill elaborate if I can. Im sure this is something very simple, but cant figure out ...
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2answers
124 views

OFDM transmitter bandwidth

Theory Suppose an OFDM transmitter with four subcarriers is implemented using the structure shown below. If the serial data input rate is 40 bps, each parallel stream will run at 10 bps. ...
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2answers
60 views

Simulating noise in OFDM

I'd like to simulate a certain $E_s/N_0$ in a baseband OFDM MATLAB modem to generate SER curves. I randomize 50 QAM symbols with $N$ subcarriers each in frequency domain, add null frequencies (guard ...
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58 views

sampling a signal below nyquist rate

This question is for people working in multi rate signal processing. Using compressive sensing techniques, we can still recover a signal by sampling below nyquist rate(by decimating the signal). How ...
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30 views

“Time To Lock” in Bit Timing Synchronisation

In the context of bit timing synchronisation in digital communications, what is meant by the requirement that says the "Time to lock to a sampling point should be no more than X symbols"? There seems ...
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29 views

Important differences between BCJR and SOVA algorithms?

BCJR algorithm needs noise variance for Gamma (branch metrices) calculation. So I am wondering does SOVA (soft output Viterbi algorithm) needs noise variance?
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47 views

Legal issues when using a paper [closed]

I'm just curious about the copyright issues when publishing a paper on the Internet. Can some simply take the idea I explained in a manuscript and implement it for his own work? (e.g. using some ...
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16 views

calculating average PSD of N radio frames

i've written a matlab code for the basic ofdm with bpsk modulation. there is no channel coding or compression used at this point. i just want to see the PSD of the transmitted packet. i am getting a ...
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33 views

How to simulate two OFDM Users with low complexity FFT/IFFT?

have two User one of them sending over freq (0-B] and the other transmit over (B-2B]. Both of them are using OFDM and each one has Nc subcarriers. I wanted to simulate the received signal using ...
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31 views

Are there any research value in visible light communication?

My advisor wants me to take the area of visible light communication as my MS project, but I don't know whether there are any research value in this area, it seems most of the tenichnical difficulties ...
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32 views

spread spectrum communication in airport

Does anyone know , how the spread spectrum sequences are used in airports. I've attended a presentation this morning regarding spread spectrum in my college, the author mentioned that the sequences ...
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1answer
22 views

digital modulation

Theoretically in BPSK signal generation we will multiply the digital signal with the carrier and this output we will call as BPSK signl which is an analog signal. But in OFDM if the data is ...
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2answers
69 views

Relationship between Carrier Frequency Offset and the Constellation Diagram

As part of a project I am doing, I have to investigate how having a carrier frequency offset would affect the constellation pattern of the received signal.This question has got me baffled because to ...
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2answers
97 views

OFDM violates sampling theorem

The "textbook" OFDM block diagram is as the below figure. But I wonder if it satisfies the sampling theorem. Here, we have N points $X[k]$ before IFFT, and $$x[n]=\frac{1}{\sqrt{N}}\sum_{k=0}^{N-1} ...
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2answers
44 views

What is the maximum data rate a wireless link can support using BPSK for given BER and SNR?

What is maximum data rate a wireless link can support using BPSK for 10^-6 BER, Bandwidth of channel is 200 kHz and SNR ...
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10 views

Hooping in Physical uplink shared channel

in 4G/LTE communications, there are terms such as group hopping and sequence hopping, in the uplink shared channel. what is the need to do hopping? what is the physical significance of these hoppings? ...
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41 views

causal and ROC and which side the system is on

I want to try to summerize some relationships between z transform, ROC and causality. But I am getting confused between left/right sided sequences, the ROC and causal. If you need stability then ...
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1answer
36 views

what is the relation between bandwidth and channel taps

I've studied that when the bandwidth increases, the number of taps we consider for channel modelling increases(example in WLAN or LTE). why is that happening. why signals with lower bandwidth (example ...
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20 views

does scrambling increse the bandwidth

In LTE systems the in the scrambling section, a gold sequence is used. But I've studied that gold sequences are used in spread spectrum communication. This generally increases the bandwidth. So ...
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1answer
48 views

Q and I part in QAM

I have one confusion in QAM about in-phase I and quadrature Q part, i.e. do they transmit identical data or not? For e.g. if i have 11001001 as a byte to be transferred, so will 4-QAM separate it ...
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32 views

what is the significance of pilot carriers in ofdm [duplicate]

in an OFDM system having a radix two FFT (Say N=64) . all of these sub-carriers are not utilized. while some of the carriers are nulls to prevent leakage in to adjacent bands, say a four to five ...
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26 views

PAPR in the SC-FDMA system

in wireless communication,compared to the OFDM system , why does the SC-FDMA (single carrier FDMA) system has a lower PAPR (peak to average power ratio)? regards, phani tej
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92 views

What is the significance of the DFT in SC-FDMA systems? [closed]

Long term evolution (LTE) systems use single-carrier frequency division multiplex (SC-FDMA) in the uplink. In such a system, there is a DFT block and a sub carrier mapping block before the IFFT block. ...
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229 views

Sampling rate in Wifi 802.11 -> 20 MHz enough with a BW of 20 MHz?

In a Wifi 802.11n context, I'm looking to find the sampling rate to perform some processing on the signal and I've something I cannot understand : in the book Next Generation Wireless LAN's: 802.11n ...
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84 views

Phase noise estimation and compensation schemes

Brief background There is a known problem that high order modulation schemes suffers from phase noise of reference generator. It's very important issue for e.g. line-of-sight (LOS) modems exploiting ...
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54 views

DC offset removal from tetra signal

Hey I want to remove DC offset from tetra signal captured as inphase and quadrature phase samples(I and Q samples). I and and Q samples are 16 bit signed values. I tried averaging 2000 I and Q samples ...
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2answers
147 views

Viterbi equalizer in a GSM system

I'm about to tackle implementing a Viterbi equalizer fo a GSM system in gnuradio. I went through the internet and ieeexplore and I think that this document explains it best: Application of Viterbi ...
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206 views

How to simulate AWGN in communication systems for specific bandwidth

I am trying to generate a AWGN waveform to add it to the signal of my simulated communication system. The operating bandwidth of the communication system is about ...
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76 views

What is wrong with this method of detecting the presence of a signal?

I am trying to decode Morse code from an audio (wav) file. Here is the technique I am using to detect the presence of the signal: I have a window of size (sampling_freq/tone), where tone is the ...
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1answer
28 views

Timing synchronization in limited channel

I need measure timing of an signal that is send through a noise band limited channel (wireless). By measure timing, I mean measure as exactly as possible when the signal has arrived at the receiver. ...
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2answers
67 views

Adding encryption to a ham radio

Suppose I want to encrypt the voice data before sending using a ham radio, for example this unit. Assume the encryption is simply AES encryption/decryption using predefined fixed key. I am thinking ...
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59 views

SINR averaging in communication system

Under the simulation of a communication system suffering from noise (AWGN) and co-channel interference, what is the appropriate way of calculating SINR? Could one calculate it at a packet level as: ...
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1answer
34 views

Difference between delayed down-converted signal and a down-converted delayed signal

I am having trouble understand what I think should be a pretty simple concept. Conceptually I can understand that a signal that has been down-converted, and then delayed in time is different than a ...
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108 views

How to find the frequency response of a communication channel from input and output symbols' functions in MATLAB?

I want to find the channel frequency response of a digital communications system. I have the functions of the input symbol (a triangle) and the output symbol - a distorted triangle: $$\dfrac{1}{1 + ...
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2answers
617 views

Low Pass Filter in AM Demodulation

I am trying to recover my baseband signal that was AM modulated. I am using the filter command in MATLAB to perform the low pass filtering ...the code is given below: ...
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2answers
63 views

Minimum Samples Per Chip?

Is there a 'Nyquist Criteria' for the minimum samples per chip that are needed for a correlator? I've heard 2, but will 1 work? What are the implications of having less than the minimum (in the ...
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1answer
58 views

Image and video processing in matlab

I have been working on Digital signal processing since Feb-2013. I have good command over it. Now I want to expand work in field of IMAGE and Video processing. Please suggest me best practical guide ...
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1answer
172 views

Alamouti code after or before IFFT block in OFDM

We are trying to implement Alamouti STBC on underlying ofdm signal. We were thinking as to where to write alamouti coder block. I thought we could write it after the cyclic prefixer block as we get a ...
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2answers
203 views

What is the advantages of BPSK+OFDM over usual BPSK (with no OFDM Modulation)?

The other days I read a useful article (on BER v.s. Eb/N0 curve of ofdm) whose link is as bellow. While watching the plot inside, a question was arisen in my mind. I wonder if the BER v.s. Eb/N0 curve ...
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32 views

Entropy when having symbols with same probability

I am trying to work out this problem: Assume that we are transmitting data from a dictionary of 15 symbols. Let the probability of sending one symbol be the same as that of sending any other ...
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3answers
979 views

cyclic prefix in ofdm

in ofdm systems after applying IDFT we take the last N/4 samples and place them before these N samples. this is called cyclic prefix.so why to use a cyclic prefix. the cyclic prefix is used to combat ...
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70 views

OFDM Rayleigh Channel 16-QAM

Is there a difference in the BER of a 16-QAM modulated signal that is sent through a rayleigh channel using OFDM versus not using OFDM? I know for BPSK, there is barely any difference in the BER.
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85 views

comparison between frequency offset estimators

I have been working frequency offset estimation in OFDM. The objective was to compare different frequency offset estimation techniques. By using MATLAB, I have simulated three different estimation ...
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39 views

TDE, OFDE and FDE equalizer simplest exmple in matlab

I want to implement the equalizer in matlab. I am just learning this. I want a good kick start code that can help me to learn it further. I searched a lot on Google but do not find a good reference ...
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1answer
41 views

Capacity computation in Costa sheme

I can not understand the following sentences, could you please anyone guide me ? "Comparing with the embedding in audio signals, the usable bandwidth is greatly reduced, from 22.05 kHz to 4 kHz. ...
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234 views

Using Pilot tones to estimate carrier frequency offset in ofdm

I have been studying carrier frequency offset estimation techniques in OFDM systems. I have understood several of them. when using Pilot tones, as stated in paper (1), the process involves two methods ...
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154 views

Is zero forcing Optimization technique or Equalization technique?

I got some problem in the equalization techniques. I am new to communication simulations but I have done some data analysis labs in my college. I read some where on Internet that in a research paper ...