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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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 ...
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2answers
30 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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0answers
9 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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1answer
19 views

reduction of memory cycles in DSP board

i'm implementing an ofdm system coded in floating point c language onto a DSP board. does replacing the static arrays with dynamic arrays and working with addresses wherever required reduce the number ...
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1answer
19 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
23 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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19 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
41 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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1answer
24 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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1answer
21 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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40 views

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

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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1answer
71 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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0answers
51 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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0answers
31 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 ...
3
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2answers
91 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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1answer
83 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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2answers
72 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
26 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
57 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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1answer
45 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
33 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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1answer
44 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
123 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
60 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
50 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 ...
2
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1answer
125 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
125 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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1answer
29 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
282 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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0answers
59 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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3answers
68 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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0answers
31 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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1answer
130 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 ...
2
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1answer
146 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 ...
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39 views

Best strategy for sending digital signal over ultrasound

I'm interested in sending digital data over ultrasound. My initial thought is that it should be first converted to BMC: And then phase shift encoded (PSK): I initially thought to use a Goertzel ...
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1answer
100 views

QAM for analog and digital waves [closed]

I tried the following code for modulation of two analog waves. Can anyone point to how to modulate and demodulate for an analog and a digital wave? I tried by replacing the second signal (x2) with a ...
0
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3answers
91 views

How to display the output as the input with a fractional delay? [closed]

I am trying to introduce a fractional delay in my input vector x[n] so the output is something like y[n]=x[n-M/N]. I am not supposed to use the MATLAB fracdelay function.So, I used sampling and delay. ...
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1answer
30 views

Information to be transmitted being a stochastic process?

I am reading Digital Communication, 3rd edition by Barry & Lee, Book's Webpage: enter link description here This is an excerpt taken from this book (mentioned above) from Chapter 3, Page # 57, ...
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1answer
132 views

Carrier frequency offset (CFO) estimation based on Symbols

In (1), it's said that: If two identical training symbols are transmitted consecutively, the corresponding signals with CFO of $\epsilon$ are related with each other as follows: ...
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0answers
32 views

How does µlaw encoding work with 16-bit signals?

I am new to DSP, so I wan't to know a couple of things. How does µlaw encoding function on a log scale such that you can input 16-bit signals and get the 8-bit µlaw signal output, after compression, ...
3
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2answers
180 views

Doppler effect on Baud Rate

I'm having a hard time wrapping my head around doppler and how it affects a digital communications signal's baud rate. The examples that I've seen explain that the center frequency of a signal is ...
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2answers
74 views

On computing the number of independent values from a signal's bandwidth?

Can anyone help me understand where the value of $2$ comes from in the following statement? ...
3
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1answer
2k views

QPSK Modulation/Demodulation in C++

I'm trying to implement a QPSK Mod/DeMod system in C++. So far i have a bit generator that generates N bits and stores it into an array: ...
0
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1answer
50 views

State-of-art of telecommunications? [closed]

There seems to be a number of different ways for telecommunication. What is the most recent (and maybe standard) technique used today? It seems the simple AM/FM modulations are definitely somewhere in ...
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0answers
52 views

Path gain extraction from a channel impulse response?

I use the ultra wideband channel model proposed by J. Foerster, (Channel modeling sub-committee report final. IEEE document P802.15-02/490r1, Intel R&D, Feb. 2003). How i can extract the path ...
3
votes
1answer
194 views

How to compute the free distance in TCM (Trellis-Coded Modulation)?

I would like to be able to compute the so-called "free distance" for a TCM with a rate 2/3 convolutional code (two inputs, three outputs) inside that I plan to use for 8PSK. My previous assumption was ...
2
votes
1answer
90 views

How is GPS used to synchronize oscillators in a distributed system?

I heard that it is important to have all oscillator clocks at different places be synchronized for example in a geographically distributed system such a telecommunication network. Of course to some ...
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1answer
118 views

WIDELY UNKNOWN?? Wireless Channel Transfer Function or freq response - frequency vs attenuation

We know that the signal attenuates out with distance and according to the channel transfer function or frequency response, the signal frequency components attenuate to different values based on ...
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62 views

Line coding for a modulation order that is not power of 2

In case a symbol encodes a non-integer number of bits, how is done the bit-symbol pairing? For example, we have a 3-levels FSK with bit rate of 1Mbps and a sequence 01011001. What is the symbol ...