Science topic

# Radio Communication - Science topic

Question
Any new and innovative topics in this field will be appreciated; Radio Communication, Antennas and Propagation, Satellite Communication, Microwave Communication, Radio Propagation
Research in electronic approaches that address rural connectivity deficits in cost-efficient ways would be of interest to countries that host rural populations in remote locations. (E-health is one such approach.)
Question
Could any one please help me in suggesting some resources where I could find a comparison curve between signal strength after Multi Path propagation effect with respect to obstacle positions between transmitter and receiver.
After conduction some experiment I found that the effect was greater near Rx or Near Tx but lesser when the obstacle is in same distance from Rx and Tx. Why such phenomena happens?
I suppose this depends on what kind of obstacles you are considering and how they are affecting the signals. If you consider an object that is scattering the signal, then the pathloss will be proportional to (d_1*d_2)^2 where d_1 is the distance from the transmitter to the obstacle and d_2 is the distance from the obstacle to receiver. For a given total propagation distance d_1+d_2, it follows that the pathloss is at its smallest when the scattering object is close to the transmitter or the receiver.
Question
Please guide me about the difference between SINR threshold and Minimum discernable signal.
From my search I have come across the following.
1) A signal can be decoded if the SINR of the received signal is higher than the SINR threshold. Does it mean that we should not be concerned about the minimum required power, and that if the received signal satisfies the SINR threshold, it will be successfully decoded?
2) I also have come across the idea of minimum discernable level. For instance -70 db is considered acceptable for some types of communication.
Which of the two I should follow. As in the first case, I get very low transmit powers and still satisfy the SINR threshold, while the transmit powers in the 2nd case are way too high compared to the first case.
Dear Gul Lakhta ,
There is something basic which you you would like to consider. From the point view of the signals, the interference signal acts in a similar way to noise. When it is added to the symbol signal it will cause that it may be falsely detected if its value is increases such that the combined signal will be located in the neighboring decision regions of the adjacent symbols in the constellation diagram. So the interference and noise have the same effect in the symbol error.
Therefore one speaks not only from S/N ratio but also from the S/(N+I).
The noise has Gaussian amplitude distribution while the interference may not have such distribution because of the nature of the interference.
The interference signal sources are normally known and then they can be subtracted from the composite signal. If after interference cancellation there will be residual interference it will be treated as a noise concerning its effect on the symbol error. In the sense that it will set the S/I +N minimum level to achieve specific bit error rate. You see if N=0 then S/I will set this minimum.
Hope I could answer satisfactorily you question.
Best wishes
Question
This Project continues as an examination of ALL-PASS Band-Pass circuits.
Project Paper : updated Feb 01, 2022
"Analog Phase-Filtering
in Active-Band-Pass Circuits"
emphasizing the use of All-Pass filters.
- - - Here, we continue our earlier "AFX" Project, which was presented in RGN at :
.......
Introduction for the "AFC" project :
...
We examine the "ALL-PASS-FILTER" and develop an Analog Narrow-Band-Pass Audio Filter, which has immediate application in receiving Morse Code signals in a Amateur Radio Station.
...
Our resulting model is an experiment to gather this data.
A Proper Analysis of this design may aid in understanding the nature of All-Pass Filtering. Once an adequate system equation is achieved, then resulting models may be useful in designing Band-Pass Filters for Audio applications which can be based on Non-Resonant Phase-Filtered circuits, similar to our "AFX" design.
...
Theory:
All-Pass (phase-shifting) filters have frequency responses which must be " zero at w=0 and at w=pi ". From the research, This means that AllPass Filters cannot be used for (1) Low-Pass nor (2) High-Pass nor (3) Band-Pass designs. This is because the resulting combination of waveforms are homogeneous ; ie, the combinations are always simple phase shifts,
producing no frequency & amplitude changes. ... *** The authors have developed working Dual-Notch Band-Pass circuits which (1) perform a BAND-PASS function which is f(0) peaked at 700Hz. (2) generates DUAL-NOTCHES around f(0) at plus/minus aprox. 200 Hz . The current All-Pass project is titled : "AFC"
...
*** First Experimental Target : (1) Utilize All-Pass stages to replace resonance tuned Active-BandPass stages.
(2) Reduce Number of MFB active filter stages required to Align Signal Phases (a) in order to support Dual-Notch Generation around f(0) ; (b) in support of our previous project "AFX" "AFV-3RL-v4F-D-vQ-Man".
... Continued Project now uses the Schematic in the groups:
AFC_1R-1A-12A-2F-Sum-S-451 and AFC-3R-2F-8A-Dif-S-451 .
The Bode plot and Magnitude plot are in the pre-paper.
...
The Problem to be resolved is why this design (1) using one All-Pass Lo-Pass paralleled with twelve All-Pass Hi-Pass Filters (2) will produce an Wave-Form Output in the Bode plot. ...The Problem to be resolved is " Why Do One APF Lo-Pass paralleled with Twelve APF Hi-Pass interact in an unfamiliar manner.
...
This "AFC" project is derived from our previous "AFX" project
...
Our long series of projects in Analog Narrow Band-Pass Filters has been presented on our website at : http://www.geocities.ws/glene77is/
...
2021 Oct 12 ...This Project continues as an examination of ALL-PASS Band-Pass circuits. ...This "AFC" project is derived from our previous "AFX" project https://www.researchgate.net/post/Are-there-any-Analog-Active-Audio-Filters-that-match-any-Digital-Signal-Processing-filters. ...
We have a paper attached : "AFC_All-Pass_Phase-Filter_Paper.pdf"
...
"AFC_All-Pass_Phase-Filter_Proj-211129-0502"
...
2021 Oct 04 ...
This Project continues as an examination of All-Pass Band-Pass circuits.
.....We have a Pre-Print attached :
AFC_All-Pass-Phase-Filter-project-211004-1558.pdf
Question
While designing any general optical CDMA network these two terms are often used interchangeably. I want to know the analytical relation between these two. Kindly help
Q=sqrt(2) erfc^-1 (2 BER)
Question
Russian project to explore the moons of Jupiter after 2030 will be based on the nuclear propulsion spacecraft "Nuklon" with an electrical energy power of 0.5 MW. Such energy power gives the opportunity to significantly increase a data transfer performance to Earth. In my opinion, the speed of data transfer can be increase to 100 Mbit/sec. This value will be enough to use 4K Video for the investigation of dynamic processes in the atmosphere of Jupiter and moons. What is your opinion about this?
I did confuse confuse bandwidth with delay a bit, but not in recent comments, I think, because I realised I was doing it.
Unless the entangled pairs are prepared on earth and then half are sent to Jupiter on the satellite, which would require coherence lifetimes of years (many orders of magnitude above present lifetimes), a signal has to be sent from Jupiter at lightspeed (for instance a photon entangled with the state on Jupiter) to convey the entanglement information between the two sites before the quantum measurement, so that the half of the entangled state can be set up on earth. This means that the actual data rate is still limited by the bandwidth of the lightspeed signals, even if data can be sent with no delay,
I guess if zero delay was possible, it would still be useful, for things like steering a remote vehicle, or conversation.
I expect that each entangled state will carry 1 bit, one Q-bit.
I am not sure instantaneous communication will ever happen. It may. I don't understand it enough to be sure it can't work. I hope it may be possible. It would also raise lots of interesting problems with relativity. I wouldn't invest my pension on it, but I might invest fun money.
Question
what is the mean doppler shift for fixed wireless transmitter and receiver?
is it 0 or not?
V = 0m/s
Therefore, Doppler shift = 0
Question
In the attached figure A and B are transmitting to some destination X and Y (not shown in the figure) using transmit power TxA and TxB respectively. Where node C wants to transmit to node D.
Assuming that the distance between all the nodes is known, I want to find the following.
1. The total received power at node D due to the transmissions from node A and node B
combined i.e. total interference.
2. We assume that SINR threshold for successful decoding is Th. What should be the transmit
power of C i.e. TxC , so that its signal can be successfully decoded at node D in the presence
of interference from node A and B
3. How to calculate SINR and BER at node D for the signal transmitted by node C.
Thanks
Assuming that the transmission coefficients of the channels from the A and B to node C are ha and hb and assume that the transmit signal of A is Sa and that of B is Sb then the received signal at node C rC= ha Sa + hb SB
This power can be considered an interference which is added to the white noise to determine the threshold of the useful received signal.
So the total noise at the node C= rC^2 +N
The required signal to noise ratio is then given by
C= B log2 (1 + S/( rC^2 +N))
where S is the useful recieved signal power at node C received from the intended node. Bis the bandwidth and C is the maximum bit rate.
Best wishes
Question
When creating a scenario in order to analyze a link budget in the case of ISL, what would be the given criteria to stablish Tx gain, Rx gain, Power transmitted and the rest of the system parameters for a given link between two satellites in different orbit planes?
It is better to use any text book related to the satellite communication.Go in detail and the after all ,it would be easy to consider some additional parameter( attenuation due to weather/ foliage etc) apart from basics as your have considered previously such power, frequency,polarisation,height,gain etc.
Question
Hi,
I have to simulate the performance of a multi-cell massive MIMO system for both the conventional and Pilot reuse 3. Does someone have some GitHub link, I will be really thankful!
Kind regards,
hi...i am able to write a code for single cell massive mimo system for MRC.ZF and MMSE receivers. Did u get the matlab code for multicell massive mimo, please send me..kiranec121@gmail.com
Question
I have gone through 3GPP TS-38.211, 212, & 213 of the Downlink part I couldn't able to gather the info of the Number of NR-PDCCH blind decoding calculation. If anyone has understood that kindly explain the calculation.
Hi.,
The UE finds the PDCCH specific to it by monitoring a set of PDCCH candidates (a set of consecutive CCEs on which a PDCCH could be mapped) in every subframe. The UE uses its Radio Network Temporary Identifier (RNTI) to try and decode candidates. The RNTI is used to demask a PDCCH candidate's CRC.
Question
Fading degrades the communication system performance due to a loss of signal power without decreasing the noise power over some or all the signal bandwidth, the received signal fluctuates, varies in intensity at each instant, increases and decreases through nulls and zeros of voltage. The probability of experiencing fading with the concomitant bit errors as the Signal-to-Noise Ratio (SNR) drops on the channel limits the link performance. Multipath fading (MF) affects most forms of radio communications links in one way or another. MF occurs in an environment where there is multipath propagation, and the paths change for some reason, resulting of propagating multiple versions of signals transmitted across different paths before they reach the receiver.
Paper:
Sharda B, Bury JSA (2008). Discrete Event Simulation Model For Reliability Modeling Of A Chemical Plant. Winter Simulation Conference.
Hu W, Sarjoughian HS (2005) Discrete-event simulation of network systems using distributed object computing. SPECTS'05.
Digital Modulation in Communications Systems. An Introduction, Agilent Technologies (2001)
Padilha R, Martins B I, Moschim E (2016). Discrete Event Simulation and Dynamical Systems: A study of art. BTSym'16, Campinas, SP – Brasil, December (2016).
it's little complicate
Question
1. Does LTE NB require a seperate antenna for NB-IoT traffic or just works with the same LTE based antenna ?
2. In LTE NB, assuming standalone mode, is it possible to enable multiple carriers (200KHz) for NB-IoT traffic within a cell site or only one carrier (200KHz) per cell ?
1. According to 3GPP, LTE Cat NB1 (NB-IoT) specifies 1 antenna. From the hardware perspective, it should be the same design as regular LTE bands.
2. It seems to be able to support multi-carrier operation
Question
I have been developing models of the ionosphere for some time, but recently, I've been asked "What constitutes sufficiently accurate foF2?" The URSI standard for foF2 scaling from an ionogram is 5d, where d is the frequency resolution of the ionosonde in the vicinity of foF2. Others have mentioned accuracy standards ranging between 0.5 MHz and 1.0MHz. My question is, is there a consensus within the field on the generally required accuracy of foF2? If it is application-specific, what are the necessary accuracy levels for these various applications?
In any responses, please provide references to support your point of view.
I look forward to an interesting and productive discussion.
Dear David, imho maybe accuracy in terms of "MHz" is not sufficient, since there's a significant daily and seasonal foF2 variation (i.e. any MHz specification will be much less sufficient let's say for night- than daytime). I will try to check any valid accuracy standard and turn back to you.
Question
some researcher define Tc = 1/4fd, also Tc = 1/Bd (doppler spread), also Tc = 1/fd (doppler frekuency, Tc = 9/16fd, also Tc = 0,423/fd
Dear Wahyu,
welcome,
There is a good references covering the variations among the the coherence time as a consequence of Doppler shift. The different formulas are a consequence of the definition of the coherence time.  Strictly speaking if there is Doppler shift, the wireless channel will vary with time.Since the coherence time is the time interval at which the correlation between the channel responses at the starting of time and end of the time interval must not get smaller than certain threshold, one gets different Tc for different threshold values.
You can your self set the appropriate threshold value for the correlation and get your own empirical formula.
Best wishes
Question
Please recommend differential amplifier with sensitivity (as low as -40dBm) and Gain above 20dB. Gain bandwidth from Dc to 1MHz?
Thanks
Naveed.
You can estimate sensitivity as equal to = 10×log10(kTB)+NF+C⁄N
C/N is the desired carrier to noise ratio. NF is the noise figure of the amplifier.
plug into your numbers and choose a suitable amp.
we have developed a LNA using discrete components with  a NF of 1.0 dB.
Question
As far as I know SMA has one core while TWBNC has two cores and works on the principle of differential signaling.I wonder if I could find SMA  to TWBNC adapter or converter in the market.I already have search on the internet but couldn't an appropriate one.Kindly suggest...
Thanks
Texas Instruments has a device that is interesting.
The DRV134 and DRV135 are differential output
amplifiers that convert a single-ended input to a
balanced output pair.
I have built discrete 3 OpAmp systems like this,
but without attention to exact impedance matching.
HTH, Glen
Question
As I investigated, some works using SIR/CIR. I wonder that what's a good value of SIR/CIR?
As the Shannon theory shows, capacity and SINR are trade-able.  In fact there is no nonzero SINR low enough to completely prevent communication!
This property manifests itself in standards such as Wi-Fi (IEEE802.11) with protocols that respond to degraded channel conditions by adaptively lowering the data rate.  In addition, if the system tries to communicate the same information repeatedly (ARQ) it becomes more reliable at low SNIRs.  The trade-off is increased latency..
So, I'm afraid, as in so much engineering, the answer to your question is "it depends".  To answer your question you first need to know or decide:
• The desired data rate and tolerance for latency. The lower the data rate and/or the higher the tolerance for latency, the lower your SNIR requirement will be.  Much depends on the application of the wireless sensor network.  Sensors reporting non-urgent parameters such as weather conditions, for example, may have very flexible requirements.  Sensors reporting intrusion or other exigencies would need to be much faster.  And of course, sensors reporting large amounts of data (think a video signal versus a door opening alarm) greatly increases the SNIR requirement.
• The standard you are using.  If your equipment is proprietary, only you can answer the question; if you are using a standard, the standard documents will themselves provide the answer given your constraints.
• Range and interference sources.  If this is from similar devices (as in 802.11 on 2.4GHz) the calculation is a function of the number of devices and their geographic distribution.  If the interference sources are closer to the receiver than the sensor, the interference would be more severe.
• Presence or absence of multipath due to environmental clutter.  The resulting fading and intersymbol interference can drastically affect the required SNIR.  The best world is one with  no obstructions and no sources of reflection, but these are seldom found in the real world.
It's a complicated field with no "one correct" answer!
Question
Multi-gigabit Data Radio Transmission: When will we get to 5G?
The answer to the question is, supposedly by 2020.
There are multiple different trials ongoing or planned for 5G, in different parts of the world. I doubt anyone has pinned down exactly what techniques will become the standard(s), although some candidates often mentioned are massive MIMO and FBMC, as well as channels up in the multiple GHz and multiple 10s of GHz.
On the other hand, you also seem to have answered your own question?
Question
hai every one, i have one doubt, with FM broadcast signals i started modeling the passive bistatic radar, where i received one signal from target(echo signal,moving target with constant velocity), another signal from direct path(called reference signal) these two signals were correlated and got some peak(s), now my problem is how can i prepare threshold and how can i detect the target,
One good way of verifying the proper functioning of your detector is through Monte Carlo simulations. They allow estimating the exact threshold value for guaranteeing a given false alarm probability. I have used this method for the Weibull distribution in the following paper.
Good Luck!
Question
HI I am working on monopole antenna. But I experience one thing that when I increase the ground size to 3*lmbda or more i get total efficiency of the antenna greater than 100% which is not possible. When I decrease the ground plane size the efficiency is less than 100%. Can you please suggest me why this is giving efficiency greater than 100%?
Are you using software or measurements?
Question
I am a PhD student. And my research topic is cellular localisation by using fingerprinting method (database  correlation  method ). I implement some methods and I want to prove the results by using real RSS (radiomap).
THANKS AT ALL
I don't know of a publicly available database, although apps like OpenSIgnal will implicitly have such a database. In terms of actual use of a database, there is a US company, Polaris Wireless, that will integrate its (RSS, path loss -based) location based services solution with operators. These solutions typically work better in radio cluttered areas (urban, indoor) than the TDOA solutions do. You may be able to collaborate with them. Note that such a national map for an operator will change as the network evolves.
Question
Since we can send electromagnetic pulses from Earth to Spacecrafts out of the solar system and induce an electric current in their communication circuitry. Why can't we send more powerful pulses to induce more power to enable the  working of the spacecraft besides communication.
How feasible is my proposal?
Max,
Beamed power is an old old idea.
Do you not remember the SPSS of the 70s? (I guess not...)
The plan to harvest solar power in high orbit, convert it to microwaves, and then beam those microwaves back to the Earth, was interesting.
And the idea was revived by Bob Forward's Starwisp proposal in the 80s.
There's nothing wrong with it except for:
a) The need for large emitters to reduce diffraction spread
b) The need for low-mass and efficient absorbers/converters (optical? microwave?)
It's an old trope to install laser arrays on Mercury and power solar sails to the nearby stars.
Perfectly doable - but to justify it you need deep solar missions - and I suggest that you look at the problem of providing even 1kW of power at Jupiter orbit from the Earth.
(calculate the beam spread for a plausible transmitter, and see how large your 'telescope/laser' needs to be)
Question
I am using Xbee S2 module.
I am working on a project where I need to convert RSSI value in corresponding meter value.
Me and my partner read many documents, and followed those things, but we are not getting expected results.
The received signal strength depends on the transmitter power, the sensitivity of the receiver  the distance between the transmitter and the receiver and the channel condition. That is if if it is line of sight, Rice or Rayleigh.
So, the most straight forward method is to calibrate the signal strength for a given set of prevailing conditions and devices. That is you determine this relation empirically.
You can also build a system model using matlab to work out such relationship.
You may also solve the problem analytically under simplified propagation conditions.
Question
You know, it is difficult to realize phase shift reciprocity of RX link and TX link. therefore, the TDD channel reciprocity of massive mimo systems maybe impossible. However, only consistency is necessary for beamforming, which is easy to be implemented. Could we use the RF frontend of phased array systems as that of massive mimo systems?
Phased array are indeed complicated to deploy. A key benefit of Massive MIMO is that a phased array is not needed! The antennas in the array does not have to be jointlu phase calibrated. The user sends an uplink pilot signal and then the base station array measures the combined effect of the channel and the phase rotation in the hardware. When transmitting in the downlink, the base station then "inverts" the phase (= complex conjugation) and thereby cancels out the phase rotation that occurred in the hardware.
The remaining challenge is to make the uplink and downlink reciprocal at a given antenna, since the hardware chains are different although the physical channel is the same. Fortunately, the conversion factor from the uplink to the downlink channel varies slowly and can estimated in practice. This has been done successfully in all the Massive MIMO testbeds that I know about.
The "need" for phased arrays is actually related to one of the "myths" in the following paper:
Emil Björnson, Erik G. Larsson, Thomas L. Marzetta, “Massive MIMO: Ten Myths and One Critical Question,” IEEE Communications Magazine, vol. 54, no. 2, pp. 114-123, February 2016. (http://arxiv.org/pdf/1503.06854)
Question
Dear All,
Is there anyone who can tell me when using precoding at the BS side, what is the system performance between Rician Channel and Rayleigh Channel?
As we know that the channel should be full rank in order to use precoding, what if the channel is poor condition like LOS or Rician channel? Is this going to affect the precoding performance?
Thanks Shanidul Hoque
Question
How to model the spikes and discontinuities of the power spectrum's of the received signals ?
You might add the random sine waves in the time sequence.
Question
how to start the capacity analysis of massive-MIMO systems?
I hope these materials to be helpful.
Best Luck.
Massive MIMO: Fundamentals and System Designs ( http://liu.diva-portal.org/smash/get/diva2:772015/FULLTEXT01.pdf )
capacity analysis of asymptotically large mimo channels ( attached file)
Question
i want to use these RSSI values i measured to simulate a multipath rayleigh fading in matlab.
Dear Zhang,
I think you may be confusing things here. Wireless propagation channels are modeled by three different phenomena:
1. Pathloss, which is due to the power loss of your signal alongs its transmissions (for example, it is a well known result that in free space, received power decreases as a square of the distance)
2. Shadowing, which accounts for the "large scale fading", due to big buildings or other obstacles. In other words, shadowing accounts for the fact that two close receivers are likely to see correlated values of received power.
3. Multipath fading, which accounts for the fact that multiple copies of the same signal are received and therefore that the response varies along the frequency axis. This is where the Rayleigh distribution intervenes : the envelope of a channel arising from multipath propagation, in NLOS cases obeys a Rayleigh distribution.
These different phenomena are depicted in the figure I attached to my answer. As you can see, Rayleigh fading only causes small scale, fast variations of your received power.
That is why I think your approach is wrong : when you use practical RSSI measurements, you average the received power both on the whole bandwidth of the receiver and on a certain period of time. This averaging makes the effects of fading disappear, and you cannot reconstruct the Rayleigh distribution of the envelope of the received signal afterwards.
Most likely, you'll see that your measured pathloss will obey a law in d^(-a) where d is the distance and a a coefficient higher than 2, as some obstacles will certainly limit your received power. But, to conclude, I really do not think that you can recreate a Rayleigh fading distribution from your measurements - as you are not measuring the good metric for that.
Best regards,
Quentin
Question
What is the scientific facts behind that?
Also that how to represent CDMA, 3G, 4G and 5G.
How to represent Satellite radio communication?
Hexagonal cell shape is perfect in cellular architecture because it cover an entire area without overlapping.
Satellite radios are most commonly used by consumers in automobiles as it offers better sound quality and more station programming choices over traditional AM and FM radio.Consumers typically pay for Satellite radio programming on a monthly subscription basis.
Question
Hello,
I'm trying to generate a plot Gain(dB) vs Freq(MHz) with HFSS. I do know that it can be obtained clicking to "Create Far Field Report->Rectangular Plot" then select Phi and Theta, and all frequencies. The adaptive solution of my model is 890 MHz and I would like to analyze the frequency range 800-1000MHz. I have tried to modify the properties of the Sweep in all three options Interpolating, Fast and Discrete. For sure, something I'm doing wrong because after the analysis (8 hours in Discrete), still I cannot select all frequencies from 800 to 1000 MHz in steps of 1 MHz and only appears the resonant one 890 MHz. See figure. What I'm doing wrong? Thank you.
While mentioning frequency sweep you need to enable Save fields, which is below the frequency setup.....
One more valid point is:
The sweep option you will find only in fast and discreet, but not in Interpolation.
Question
It is proved that current harmonic increases as well as exceeds THD limit when PV is added to main grid. On the other hand, voltage harmonics remains under control of limit.
Question
In a paper by Wignall 1985, he considers the product of the de Broglie frequencies of two particles interacting non-linearly.  This produces sum and difference frequencies in the case of real-valued signals.  It is basically just amplitude modulation.  Wignall, in a parenthetical comment as if it were obvious, states that since in this case the signals are complex, the difference frequencies are discarded.
I have spent half an hour searching the web to no avail.  There is too much material on ordinary modulation, or perhaps I do not know the right keywords.  Can someone explain this, give an example, and provide a reference to a textbook or paper treating the matter?  Thanks in advance!
The real signal is expressed as exp{i o t} + exp{-i o t} = 2 Re exp{i o t}.
In the product ( exp{i o1 t} + exp{-i o1 t} )( exp{i o2 t} + exp{-i o2 t} ), the cross terms give the frequency difference term, while for a complex signal there is no cross term.  It's simple algebra, and that is all what Wignall is implying.  In the Schrödinger equation, the wave function is trully complex, it isn't a calculational trick.
If the medium is non linear, there is a term in f^2 and others of higher orders. If two wave functions superpose, it becomes (f1 + f2)^2, in which there is the considered 2f1.f2 term.
Question
The receiver end is single ended with no phase information!!
You didn't provide any information about what type of array you're talking about, but the simplest answer is no, you need phase information AND element location information to be able to determine relative time of arrival and corresponding angle of arrival information.  Now, on the other hand, if you're talking about using a directional antenna and you have the ability to rotate said antenna and measure just magnitude, then you can obtain direction of arrival information from just the magnitude pattern information.   This is of course assuming line of sight (plane wave) illumination.  In all cases, multi-path AoA is more complicated.
Now, the above discussion gives you an interesting case to consider.  Assuming you're asking about the beam forming capabilities of a set of dipole elements (a typical wireless antenna system, for example) , consider the directionality of a typical linear dipole array (Yagi, Log Periodic Dipole Array, etc.).  Such antennas achieve directionality in a given frequency range based on the physical spacing of the elements and the direct summation of the received RF signal on each element along a transmission line that connects them.  The frequency dependence is a combination of the element spacing both at the propagation velocity in free space and along the transmission line.  When those phases sum properly, you obtain a single lobe along the direction of the array.  If instead I were to put a detector on each element and sum the resulting DC voltage, I would just get a higher DC voltage.  There would be no directionality, since each element would respond like a dipole to the same field regardless of direction.  (Actually there would be mutual coupling effects between the elements which DO give some directional behavior even in this case, but I'm ignoring that for now to make a point.  In fact, one directional antenna design consists of two passive resonant elements with a single dipole element in between!)  So you see, without phase information, even a common passive directional antenna wouldn't work.
Question
Suitable for direct sequence spread spectrum
Golay, Gold and Kazami are the popular ones.
Question
Currently, my friend is working with adaptive channel estimation for high mobility, Zero Forcing, MMSE, ML estimation.
Since the channel estimation for high mobility is complicated, we are moving to non linear estimation like, ML estimation. But this estimation is also complicated.
He needs better ideas to improve the estimation with less complexity.
Channel Estimation is based on LS, ML, MAP, MMSE methods but it can be categorized to training-based, semi-blind and blind methods. Nowaday, pilot-aided methods are used for channel estimation of fast-varying channels.
Question
Looking  for  an answer  from  technical  side
Any embedded board with Ethernet port or WiFi should meet the requirement. We find several boards more 25 numbers.
But IoT with CDMA is evolving and we find limited boards.
One such board is available from Microchip at :
Question
I want to implement at local area for secure communication of  military zone .
Its hard to implement it as ZigBee gives only 250 kbps data rate and it is theoretical. In practical it may be less. It might be possible if you compress your voice signal but it will take more time to transmit. Do you know how to configure ZigBee?
Question
options for this are
a.IMT-2000 CDMA Direct Spread (by 3GPP)
IMT-2000 CDMA Multi-Carrier (by 3GPP2)
IMT-2000 CDMA TDD (by 3GPP)
IMT-2000 TDMA Single-Carrier (by ATIS/TIA)
IMT-2000 FDMA/TDMA (by ETSI)
IMT-2000 OFDMA TDD WMAN (by IEEE)
b.IMT-2000 CDMA Multi-Carrier (by 3GPP2)
IMT-2000 CDMA TDD (by 3GPP)
IMT-2000 TDMA Single-Carrier (by ATIS/TIA)
IMT-2000 FDMA/TDMA (by ETSI)
IMT-2000 OFDMA TDD WMAN (by IEEE
c.IMT-2000 CDMA Direct Spread (by 3GPP)
IMT-2000 CDMA Multi-Carrier (by 3GPP2)
IMT-2000 FDMA/TDMA (by ETSI)
IMT-2000 OFDMA TDD WMAN (by IEEE)
d.IMT-2000 CDMA Direct Spread (by 3GPP)
IMT-2000 CDMA Multi-Carrier (by 3GPP2)
IMT-2000 TDMA Single-Carrier (by ATIS/TIA)
IMT-2000 FDMA/TDMA (by ETSI)
IMT-2000 OFDMA TDD WMAN (by IEEE)
A whole lot of 3G proposals were classified as IMT-2000 at the time.  Such standards included CDMA DS, CDMA MC, and some TDD technologies.  The ITU-R went through an evaluation process of them all.  You can find the guidelines for evaluation, known as M.1225, dated 1997 on the ITU web site (see link).  The individual standards bodies did the work and submitted the results to the ITU.  Its probably 1998-1999 time frame.
Question
close all;
clear all;
%
% PARAMETERS
%
freq = 200; %operating frequency
Fs = 20*f; %sampling frequency
L=100; % Number of samples per symbol period
Ts = 1/Fs; % Sampling period
T = Ts:Ts:1/f;
alpha=0.5; % Roll-off factor for the (square-root) raised cosine filters
N=8*L; % N+1 is the length of the square-root raised-cosine filter.
sigma_v=0; % Standard deviation of channel noise
h=1; % Channel impulse response
%
%SOURCE: Take input data from user for transmission
%
pt_dt = input('Data you want to send:','s');
R = isempty(pt_dt);
if R == 1
pt_dt = 'Waleed Ejaz';
else
pt_dt = pt_dt;
end
display(pt_dt);
RR = double(pt_dt);
bb = 1;
Rp = dec2bin(RR,7);
[TA TC] = size(Rp);
for ll = 1:1:TA
for lg = 1:1:TC
msg(bb) = Rp(ll,lg);
bb = bb + 1;
end
end
rt = 1; ht = 1;
for ls = 1:1:TA
for ll = 1:2:(TC-1)
Inp_msg(rt,(ht:ht+1)) = Rp(ls,(ll:ll+1));
rt = rt + 1;
end
end
%
% Transmit Filter
%
pT=f_sr_cos_p(N,L,alpha); % Transmit filter:
xT=conv(f_expander(msg,L),pT); % Transmit signal
%
% Modulation
%
display('Select Type of Modulation');
display('1. BPSK');
display('2. QPSK');
Mod_Type = input('Plz Enter the Type of Modulation:','s');
Carrier = [];
%
% BPSK Modulation
%
if (Mod_Type=='1')
display('Binary PSK');
for ii = 1:1:length(T)
car1(ii) = sin((2*pi*freq*T(ii))); %CARRIER TO BE TRANSMITTED
end
for ii = 1:1:length(xT)
if xT(ii) == '0'
car = -1*car1;
else
car = 1*car1;
end
Carrier = [Carrier car];
end
%
% QPSK Modulation
%
else if(Mod_Type=='2')
for ii = 1:1:length(T)
car1(ii) = sin((2*pi*freq*T(ii))+360); %CARRIER TO BE TRANSMITTED
car2(ii) = sin((2*pi*freq*T(ii))+90); %CARRIER TO BE TRANSMITTED
car3(ii) = sin((2*pi*freq*T(ii))+180); %CARRIER TO BE TRANSMITTED
car4(ii) = sin((2*pi*freq*T(ii))+270); %CARRIER TO BE TRANSMITTED
end
for ii = 1:1:length(Inp_msg)
if Inp_msg(ii) == '00'
car = car1;
else if Inp_msg(ii) == '01'
car = car2;
else if Inp_msg(ii) == '10'
car = car3;
else if Inp_msg(ii) == '11'
car = car4;
end
end
end
end
Carrier = [Carrier car];
end
end % end of if
end %end of else if
%
% CHANNEL
%
xR=conv(h,Carrier);
Pxx = periodogram(xR);
Hpsd = dspdata.psd(Pxx,'Fs',Fs);
plot(Hpsd)
fre=[]; o=1;
len=65537*0.5;
n_len= floor(len/2000);
for p=1:n_len:1980*n_len
fre(o)=sum(Pxx(p:p+n_len));
o=o+1;
end
sa=[];
count=0;
for w=1:1:length(fre)
if(fre(1,w)>5000)
count=count+1;
sa= [sa w];
end
end
count_m=0;
if(count>=1)
E(1,1)=1;
else if(count==0)
E(1,2)=1;
end
end
The error you get because there is some functions which are not defined in the code such as "f_sr_cos_p", for that you have to write an adequate functions, and it should work.
best regards
Question
I'm working on cognitive radio and I want to combine between uwb and cognitive radio.
Hi,
I'm not working on cognitive uwb radio right now, but I did in the past.
You can check the following:
Granelli, Fabrizio, and Honggang Zhang. "Cognitive ultra wide band radio: a research vision and its open challenges." 2nd International Workshop on Networking with Ultra Wide band and Workshop on Ultra Wide Band for Sensor Networks. 2005.
Granelli, Fabrizo, et al. "Research advances in cognitive ultra wide band radio and their application to sensor networks." Mobile Networks and Applications 11.4 (2006): 487-499.
Best,
Fabrizio
Question
Hi all, I'm looking for a WSN development platform with classical sensors interfacing capabilities such as humidity, temperature, gps, movement, but mostly important is the possibility to interface a UHF RFID reader with mid range reading distance capability above a meter of passive tags .
If you know or have any experience of such WSN platform solution don't hesitate to send me back your experience
I don't have any experience in commercial base but we (my team) did it as experimental base. We connected RFID kit with Zigbee module in real test bed. We also expand WSN with Zigbee module with 4 to 5 nodes.
Question
They wont perform sensing  they operate under the condition of interference threshold. so can they use any channel in PU band?
thank you for sharing your intelligence
Question
In massive mimo large number of low power antennas at the base station. Is it possible for signal from the base station antennas to reach the user because of its low power?
Massive MIMO uses multiuser beamforming to focus each signal on its intended user. By adding up the contributions from M antennas coherently, an array gain of M is achieved. This allows to decrease the total transmit power at the base station by M without decreasing the coverage. Please note that the total transmit power of the base station can be pretty large even if the power per antenna is low.
Question
I need to deploy a set of sensors in radio communication frequencies (it can be in 2.4 GHz, 915 MHz or whatever else you consider suitable) that attaches onto a metal barrier like a big shovel. The question is what type of antennas is suitable in that kind of situation?, because we do some small test and there are a lot of communication problems that we want to avoid. The nodes communicates with a base station in infrastructure mode. We planned to put a patch antenna in the base station for directional pattern pointing to sensors node. The sensors  have omnidirectional antennas because the shovel moves at a times. The distance between sensors nodes and base is no more than 5 meters.
Are the sensors autonomous or are they powered by the vehicle? Is this shovel attached to a vehicle. In Dutch we call the whole machine (see picture a shovel). Normally you could benefit from the reflections from the environment. Could this be an option in your case? An other possibility is to place the antennas on the back of the shovel. What also could happen, because the shovel is in the near field of the antenna, that it will be detuned. Did you investigate that? Furthermore the antenna will introduce some current into the metal and thus diffraction on the edges of the shovel, this could be in you advance.
Question
Why Radio Frame in LTE which consists of 10ms time span defined?
Where Radio frame contains 10 subframes each time span of 1ms is defined
LTE FDD Radio Frame structure :-
In time domain :
1) 10 ms long with 10 subframes each of 1 ms.
2) Each subframe has two slots of 0.5 ms each & each slot has 7 orthogonal symbols.
In freq domain :
1) 72 subcarriers each of 15khz bandwidth & grouped into 6 RBs (PRBs).
Collectively :
1) An entity consisting of a subframe (1ms) of time domain & 12 subcarriers is known as Scheduling Block (SB).
2) An entity consisting of a slot (0.5ms) of time domain & 12 subcarriers is known as Resource Block (RB).
3) An entity consisting of a orthogonal symbol (0.071428 ms) & one subcarrier (15khz) is known as Resource Element (RE).
So a LTE radio frame consists of 10 subframes (i.e. total 1 ms) in time domain & 72 subcarriers (i.e. total 1080 Khz) in freq domain.
Why 15kHz? It is because UMTS and LTE have the same clock timing!
I’ll explain it with an example.
In LTE for BW=5MHz, there is 300 subcarrier. (with 10% guard band, 4.5MHz/15KHz=300)
But we know that in IFFT/FFT transformation, Nfft should be a power of 2 (to speed-up the FFT operation). 300 is not a power of 2 and the next power of two is 512.
Fs = Nfft x Δf (because Fs=1/Ts , Ts=Tsym/Nfft and Δf=1/Tsym=15kHz)
For BW=5MHz, Fs=512*15kHz=7.68MHz => Fs=2*3.84MHz
(3.84MHz is chip rate in UMTS).
We could reach to our timing goals by sub-carrier spacing equal to 7.5KHz or 30KHz also, but 15KHz is an agreement base on multicarrier transmission challenges (ISI , Doppler effect, …).
Why 12 sub-carriers is there in a RB? I think if we notice to total subcarrier in different LTE Bandwidth we can guess the answer. 20MHz->1200subcarrier, 15MHz->900, 10MHZ->600, 5MHz->300, 3MHz->180, 1.4MHZ->84 (with 10% guard band for all), 12 is the greatest common divisor of them.
Why 7 Time slots for a RB?
We know that RB is the smallest block that is allocated to an UE in LTE. I think RB Time slots number’s value is an agreement base on latency (.5mSec for a RB) and traffic efficiency (84symbol/.5msec). (84 is equal to 12 subcarrier*7 Recourse Elements). In wimax (IEEE 802.16d), block size is not fixed.
Question
Salt water is a medium that has a high relative dielectric permittivity (around 80) and is also able (rather poorly) to behave as electrical conductor. Conductivity (around 4 siemens/m) involves losses when a wave propagates in such a medium. Penetration depth of radiowaves are however strongly dependant of the wavelength/ frequency spectrum of the transmitted wave. Submarine electromagnetic transmissions are possible only at a few Hertz or a few tens of Hertz (depending on numerous factors including the distance of course). The right figure of merit is the skin depth (defined in many standard textbooks)
Question
What is the best software to simulate Cognitive radio Networks?
I agree with Kishore and think that NetSim is one of the best tools for 802.22 simulation.
Question
Also is the efficiency a very important parameter for studying MSA?
First you have to eliminate bad matching in input, that means using impedance transformers or BALUN network. But if you have the perfectly matched antenna, still there would not be perfect radiation; because the antenna structure determines how the current would distribute on antenna. And when the current is not distributed to radiate, the radiation efficiency degraded.
One traditional way is to increase dielectric constant but in this way the antenna performance become narrow-band.
The other way is to observe the current distribution on antenna structure and try to reshape its structure so maximum current get closer to its edge. This again might result in bandwidth degradation.
Question
What will be the repercussions if we use horizontally polarized antennas connected with high power sources?
For radio sound broadcasting in the upper HF broadcast bands (6 to 30 MHz) both horizontally and vertically polarized antennas will work, although horizontal polarization is more common. This is logical is, as these frequencies are generally used to reach far away (500-5000 km) areas by means of ionospheric radio wave propagation. This calls for directional antennas to beam the energy towards the coverage area, both in the horizontal and the vertical plane. Using horizontal polarization gives addition antenna gain due to the ground reflection near the antenna.
For radio sound broadcasting in the tropical bands (2 to 3 MHz) or in the lower shortwave bands (3 to 7 MHz) the antennas used may also be horizontally polarized antennas suspended at 0.1 to 0.2 lambda above ground. These antennas radiated straight upwards and that radiation is reflected by the ionosphere to cover a continuous area around the transmitter with a radius of 300-500 km (typically) with excellent signal strength. This propagation mechanism is called Near Vertical Incidence Skywave (NVIS).
In the higher medium wave (1 to 1.5 MHz) ionospheric radio wave propagation is still possible at nighttime and sufficiently high horizontally polarized antennas would work at night to cover longer distances. Vertical polarization may also be used for this. Daytime absorption in the ionosphere, however, is very high.
NVIS would be possible at nighttime, but suspending horizontal antennas much lower than 0.1 lambda above ground requires either an extensive ground screen or the amount of power lost into the ground below the antenna will be very high.
Ionospheric propagation is not possible or not practical at frequencies below 1 MHz. Therefore most broadcast station on long or medium wave (0.1 - 1.5 MHz) are designed for ground wave propagation, for which vertically polarized antennas work best. These antennas also need extensive ground screens, as the ground is part of the antenna itself and ground losses directly cause reduction of the antenna efficiency.
Antenna gain, ground losses and voltages between antenna and earth for horizontal and vertical antennas with `thin´ elements can be modeled quite well with free Method of Moments (MoM) antenna packages such as NEC-2 or NEC-4. Be sure to use Sommerfeld ground, and please compare your results with good antenna books (Kraus, Jasik) to avoid common simulation pitfalls. If your simulation are contradicting common theory, they might be wrong :-)
Question
Is there any method to increase, artificially, the cut-off frequency of ionosphere? Or is it only a solar flare phenomenon.
The critical frequency of the ionosphere is not a fixed value. It roughly varies with time of day, day of the year, and the 11-year long solar cycle. Short term variation is influence by many factors, of which the solar radiation and the earth magnetic field are the main drivers.
Solar flares may disturb the more usual arrangement of the ionosphere, and can be seen as anomalies in ionospheric radio wave propagation, sometimes even totally disrupting all ionospheric propagation.
The critical frequency of the F-layer is measured near real-time by ionosonde stations. Please take a look at them, they are very informative. The following link is from an ionosonde in Belgium, but there are several in your area as well:
Is your interest driven by radio wave propagation issues, or earth science interest?
Question
We are working on designing a small research UAV system. However we are asking ourselves how to deal with the issues of doppler effect on our RF communications due to the motion of the vehicle.
What are the common techniques to deal with doppler in RF communications?
PLL is usually implemented d in analog domain but digital locked loop also exist that do the same in discrete time domain. however the most useful techniques for your case would be frequency recovery technique in addition to clock and phase recovery. the book written by Mengali is great reference in synchronization technique.
Question
I read a little about software defined radio (SDR) and found it quite interesting. Moreover, found that they have been quite frequently used in lab experiments. But, the cost is still about \$740 for an average quality SDR and kind of find it unpopular. What kind of future does it have? Why is it not so popular or am I missing something? Can SDR revolutionize radio? Should it be cheaper and more commercial?
Question
Is it possible to establish high quality data and voice communication in underwater?
Dear Viky,
A communication link consists of a transmitter , a receiver and a communication medium. Every medium has the suitable signal energy form to propagate easily in it.
Good electricity conductors such as metals are conveyor of electricity.Therefore transmission lines are made from metallic conductors like copper and aluminium.It is not practical to connect the transmitters and receivers in underwater by transmission line.
Therefore one uses the suitable wireless system for under ware communication.
Basically there are two basic wave types, the acoustic waves and the electromagnetic waves. Sea water is salty and therefore good conducting as Dr Garry mentioned. Consequently it attenuates the electromagnetic waves and this attenuation increase as the frequency increases. Only low frequency electromagnetic waves are capable to propagate an appreciable distance before it gets undetectable.Therefore the radio wave under sea water communication is restricted to very low frequency waves with very small band width and consequently very low data rates. Newly, short distance under water optical communication links are developed operating in the wavelength range from 0.4 to 0.55 micrometers.They can be considered also wireless electromagnetic wave communication.
As a medium the sea water is suitable as a fluid is suitable for acoustic wave propagation. Therefore, the under water communication systems are normally
based on acoustic wave transmission. Here piezo electric transducers are used to convert the electrical signal into acoustic waves and vice verse. The rest of the system remains the same.For more details please go to the link: www.tr.ietejournals.org/article.asp?issn=0256-4602;year=2012