Questions tagged [digital-communications]

Related to all communication systems that use a given digital sequence as an interface between the source and the channel input.

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1 answer
357 views

Determining the bit rate on a real-time USRP implementation

I'm transmitting a 16-QAM signal using an NI 2920 USRP. Here is a snapshot of the front panel that is seen (on LabVIEW) - I'm trying to figure out the bit rate from the given details. The symbol rate ...
1 vote
0 answers
51 views

Is this silk layer for isolation or is there any other use of this type of design?

In one of the bsttery management systems, I found this arrangement on PCB. I am confused by this arrangement. Is it for isolation or is there any other use?
2 votes
1 answer
432 views

Daisy-chaining two ADC with SPI protocol

I'm trying to configure and read two ADCs (MAX11156) with a RaspberryPi. The ADCs are daisy-chained together. For the communication, I'm using python code with the spidev library. The driver is ...
2 votes
1 answer
53 views

Is it acceptable to gate an SPI clock (sck) to disable it when ss is high? (in an FPGA)

As far as I know, gating a clock in an FPGA is a very bad design practice because it can lead to clock skew and higher power consumption. This is specially true for the system's main clock, but what ...
0 votes
2 answers
266 views

Efficiency of FIR filter in verilog language

Implementing a 4-tap FIR unity coefficients, is this code efficient in power and area ? ...
2 votes
1 answer
82 views

Can you identify this digital signal? It looks like a UART signal and can't figure out the baud rate

I'm trying to read the signal between my quadcopter's camera board that is controlled by an android app, and the rotor control board in the drone. There are two boards in the drone: the camera board, ...
4 votes
7 answers
3k views

Is Ethernet synchronous or asynchronous serial?

I already tried googling but I cannot find an exact answer. Some say it is synchronous, some say asynchronous. For example, see these links: https://www.quora.com/Is-Ethernet-synchronous-or-...
1 vote
1 answer
99 views

Is there a digital to analog converter module in network cards?

Network cards convert digital bit streams to an analog signal for transmission. Do they have a DAC module? If so, how fast is it?
1 vote
1 answer
74 views

SPI level translator

I'm planning to connect an IT8951 to an ESP32 through SPI. The issue is that the ESP32 module that I'm using has an output of 1.8V and the IT8951 works with 3.3V SPI. What kind of circuit should I use ...
1 vote
1 answer
51 views

How to compute data rate I can reach with my design?

I implemented a modulator for a transmitter, which sends baseband modulated signal. The transmitter has the following parameters: datarate : 520 Ksps (min), 64,44 Msps (max) Bandwidth: BW = 56 MHz (...
0 votes
1 answer
248 views

What is the bandwidth formula for pulse code modulation (PCM)?

The image below shows the formula for the bandwidth of pulse code modulation (PCM.) There are two questions I want to ask: Bandwidth of the PCM signal waveform is bounded by \$ B_{PCM} = \frac{1}{2}(...
0 votes
1 answer
32 views

Why is channel DC gain sufficient to model optical wireless communications?

I came across the following question at ResearchGate, but I fail to comprehend the answer to it. The question states: Why do we only study the DC gain in VLC channel modeling? In all the papers and ...
0 votes
1 answer
404 views

Can someone help me explain I2S timings when it comes to master and multiple slaves

I am just getting stuck as to what's happening. Below explains the functionality of each of the hardware and how they interact with each other to give you a better idea of the situation. HARDWARE USED:...
0 votes
0 answers
22 views

Why does a UART message appear on sender XBee's input instead of output?

I have a XBee3 Mesh Kit (SMT) that comes with three XBee3 SMT. I upgraded each Xbee3 SMT to the latest firmware (Zigbee-100D) in XCTU, and configured one module to be the coordinator and the other two ...
0 votes
1 answer
82 views

Hamming code question

Suppose we have m data bits and n parity bits. In order for the Hamming code to function: $$m+n<2^n-1$$ If we have 3 parity bits we can have up to 4 data bits. But lets say we don't have 4 data ...
1 vote
1 answer
167 views

In asynchronous communication how is the frequency same but clocks of both devices different?

Am currently studying 8051 microcontroller and in the course the lecturer told that in communication the frequencies of sender and receiver should be same else they will get different bits of data at ...
2 votes
1 answer
1k views

What is difference between resonant and non resonant antennas?

I don't know if it's right place to ask it, but I searched google and books the answer I get seems to be like resonant antenna have small bandwidth and have standing wave instead non resonant antennas ...
8 votes
3 answers
1k views

Why is this 75 ohm resistor present in the Ethernet connector? (10/100Base-TX)

In this datasheet (and in other similar) pins J4, J5, J7, J8 are connected to the ground with a resistor and cap. For 10/100Base-TX pinout it seems they are not used (at least for modern of the ...
0 votes
2 answers
84 views

Unintentional Beamforming

Suppose I have two cross polarized transmit antennas sending the same signal in a rather line-of-sight dominated environment to a receive antenna, is there any chance of creating unintentional ...
0 votes
1 answer
32 views

Multipath destructive and constructive fading and the law of conservation of energy

Multipath in a Rayleigh fading environment causes fading, this fading could be destructive or constructive at a certain point or location in the far field, how does that align with the law of ...
1 vote
1 answer
100 views

>1Mbps UART core on Lattice's ICE40UP-5k FPGA?

I need a UART core able to receive in the ~4-5Mbauds range (the transmitter is able to transmit up to 30Mbauds, over RS422 upstream of the FPGA), but Lattice's 16550 IP core only allows me to ...
0 votes
1 answer
64 views

Costas Loop QPSK/4QAM

I can use a Costas Loop, modified for QPSK/4QAM and recover the frequency and phase successfully when using a pattern of all 1s or all 0s or a pattern that is repetitive for each I and Q data rail (in ...
0 votes
2 answers
45 views

Coding and SNR gain

How does coding reduce the amount of SNR required to detect data for a certain modulation and at a certain bit error rate and does that imply that coding reduces noise power?
0 votes
1 answer
68 views

How Nic process packets

As packet arrives Nic detect it on its interface like wire/air and than packet is kept in Rx FIFO the on chip memory for further processing like offloading and determining it belong to it after ...
2 votes
1 answer
129 views

74HC74D initial output value after power up

I use a touch sensor (Active Low) to light up a light bulb. here I've used a 74HC74D D flip flop to turn on an off the bulb with the sensor pulse (sensor output is active low which is then converted ...
0 votes
3 answers
92 views

Is AXI a good interface for outside communications?

Suppose if we want to get some data from some ADCs, which are placed in a separate chip, and process that data in RISC-V processor. I was looking for an interface to define/use inside the RISC-V chip ...
1 vote
1 answer
71 views

How to convert data signal line coding from RZ to NRZ?

I have a user data stream at 10 kbps and line coded as uni-polar, 0-5 Volts, RZ (return to zero). What methods are there to convert this signal to an NRZ (non return to zero) format? The only way I ...
0 votes
2 answers
61 views

Detect pauses in a digital signal on a scope?

I am currently using a USB-SPI converter and I would like to know if there are stutters caused by some buffer starvation or anything else, i.e. pauses in the stream of digital data. Is there a trick ...
0 votes
1 answer
3k views

2D parity code error detection/correction?

If we assume the following: the received bits were encoded using a 2-D even-parity code, what is min #of error is there. I am a little bit confused , it is clear that the third column has an error ...
0 votes
0 answers
29 views

Isolation barrier in digital signal isolator

Could anyone comment on why a capacitor is better than an inductor according to the statement below: "In general, an isolation barrier implemented with capacitors is better for passing signals to ...
1 vote
0 answers
54 views

How should I understand this interpretation?

Studying spatial diversity in telecommunication engineering (Fundamentals of Wireless Communication, D. Tse and P. Viswannath), I read this paragraph. $${\text {In}}\,{\|}{\textbf h}{\|}^{2}{\text {...
0 votes
1 answer
626 views

USB to RS485: Can I connect A to Common Ground?

I bought a very cheap USB to RS485 dongle to connect to an experimental board of my own. Specifications (may differ from the one I used but externally similar): - Any baud rate from 1200 bps to 115 ...
0 votes
1 answer
55 views

How can I read an RFID tag at the back of a phone FROM THE FRONT?

I'm discovering RFID applications and I would like to be able to read an RFID card I strapped to the back of my phone (the most convenient location for me) by just putting the phone face down on the ...
0 votes
1 answer
44 views

Trouble understanding length matching requirements

I am having trouble understanding where manufacturers are coming up with their length matching requirements. For example, I am looking at length matching for RGMII between a MAC and PHY. My ...
0 votes
6 answers
360 views

How are the bits transmitted over the wire?

This should be a basic but fundamental question. Suppose I have a source and destination communicating over a wire. Source wants to send bit stream 01101 to ...
0 votes
0 answers
26 views

Convolution between bit stream sampled by N number of samples per bit with a channel modeled as low pass filter

I generated a bit stream in MATLAB, from the transmitter to be convoluted by the channel I use MATLAB function "randi" between 0 & 1, so it generates random vectors of 0s & 1s and ...
0 votes
0 answers
31 views

Can I reconstruct the channel impulse response from OFDM least square channel estimation?

I'm working on a successive interference cancellation (SIC) project for an OFDM system. I used pilots and least square channel estimation to estimate the channel frequency response (CFR.) It works ...
2 votes
1 answer
2k views

How to tell whether a line coding scheme has DC component or not

I'm new to EE, trying to understand things as a non technical audience. My textbook says one of bipolar encoding schemes called alternate mark inversion (AMI) has no DC component and we can think ...
0 votes
1 answer
168 views

How do I stop signal looping with I/O port in this communication system

I am still a student. When I am designing communication system I am facing this problem: As shown in the figure I need to communicate with Master and Slave. But Master and Slave have single I/O port ...
1 vote
1 answer
95 views

Proof of Shannon capacity theorem

I was looking for a formal proof of the Shannon capacity theorem, which states the condition which is the maximum data rate possible between two wireless channels. I could not find the proof. Does it ...
1 vote
1 answer
278 views

Decision feedback equalizer

I have a question regarding the implementation of MMSE-DFE. Here is the conventional block diagram: The signal y shown in the pic is, for clarification, y(kT) i.e. the signal y(t) coming out from the ...
6 votes
4 answers
1k views

Algorithm for compressing a stream of 12-bit ADC data in a Cortex M0 microcontroller

In my application, a Cortex M0 microcontroller currently samples an ADC signal at 10 kHz and sends the result via a USB serial cable to a computer. I want to now increase the sampling rate to over 100 ...
1 vote
5 answers
589 views

What is the exact difference between synchronous and asynchronous serial transmission?

I'm having a hard time understanding the exact distinction between synchronous and asynchronous serial because different sources have confusing description. For example, some source say a separate ...
1 vote
1 answer
80 views

How is a GPS receiver able to calculate SNR?

I know that there is a certain relation between bit error rate and SNR for every modulation scheme. But i wonder how a GPS receiver can measure bit error rate and how it able to calculate SNR (I could ...
0 votes
1 answer
138 views

Are there any noise cancellation algorithm used in wireless communication? if so in which layer?

I understand that there are 7 layers in the OSI model. I would like to know is there any noise cancellation algorithm used in wireless communication? If so in which layer is it used? I am looking for ...
0 votes
4 answers
110 views

How to name the frequency of digital signal?

Let's imagine that we have some MCU in which each GPIO pin can be set high or low with a single assembler instruction (BSET/BCLR for example). If we divide one by the instruction execution time we get ...
0 votes
1 answer
49 views

Question regarding bandwidth of digitally modulated signals

Assume that there are two carrier frequencies, 20 GHz (RF) and 200 THz (Optical). Both of these carrier waves are modulated by a digital signal using QPSK scheme. Consider the frequency spectrum (or ...
0 votes
0 answers
61 views

Digital up conversion and digital down conversion

Description: I’m trying to use the standard sample rate of 61.44 MSPS on both sides of my digital transceiver(DUC and DDC,) so I’ll upsample my data from baseband data rate 3.84 MSPS to 61.44 MSPS ...
0 votes
2 answers
65 views

Calculate the minimum data rate required for transmission of EEG signals (0.4-64.4Hz)

I'm a little bit confused here. I assumed that the transmission is going to be PCM, so I calculated this way: I assumed number of bits (n) and sampling frequency (64.4 * 2) then I said that the ...
0 votes
1 answer
117 views

Do high-speed asynchronous to synchronous UART converters exist?

I need to send synchronous serial data with control characters and 8b/10b encoding at about 5Mbaud - and I need to send that from a laptop; I do have UART ports which can keep up with these speeds, ...

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