Science topic

# Wireless Communications - Science topic

This group has been created to bring together those interested in wireless communication research.

Questions related to Wireless Communications

What is the Relation between Absolute Propagation Time (ns) with respect to the Received Power (dBm) at the UE end? I would appreciate if anyone can explain the two graphs and the parameters associated with these graphs. Thanks.

(Two files are attached for reference)

Hi everyone,

I am trying to simulate an M-QAM MIMO system, and I want to decode the received signal using QR decomposition and sphere decoding.

However, I am struggling to understand how to implement the simple tree sphere decoding algorithm.

Here's my understanding so far:

Given a receive signal as follows:

1. Y = HX + N;

where X is a K x 1 vector consisting of K MQAM data symbols, H is a K x K fading matrix, N is a

K x 1 AWGN vector, and Y is the K x 1 received vector.

We perform QR detection as follows:

2. H = QR;

where Q is a K x K Unitary matrix, and R is a upper-triangular matrix with entry R(i, j),

with i and j being the row and column indices respectively.

Then we equalise the receive signal in 1. as:

3. Z = (Q^H)*Y = RX + (Q^H)*N , where Q^H is the Hermitian transpose of Q.

I now want to perform Sphere decoding based on 3. This is where I am struggling.

My best attempt at coding this algorithm in Matlab is shown below (Assuming K = 8, and assuming an arbitrary radius d):

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% ## Inputs:

% # R, upper triangular matrix

% # Z,vector receive signal

% # d, radius of sphere

%

% ## Output

% # X_hat, vector of estimated symbols

n = 8; % n => K

d_vector = zeros(1, n);

d_vector(n) = d;

Upp_bound = zeros(1, n);

Low_bound = zeros(1, n);

minR = d_vector(n);

intersum = zeros(1, n);

intersum(n) = Z(n);

Upp_bound(n) = (d_vector(n) + Z(n))/R(n, n);

Low_bound(n) = (-d_vector(n) + Z(n))/R(n, n);

X_hat = zeros(1, n);

% ## begin algorithm

if Low_bound(n) > Upp_bound(n)

return null;

else

X_hat(n) = Low_bound(n);

end

k = n;

while X_hat(n) <= Upp_bound(n)

if X_hat(k) > Upp_bound(k)

k = k + 1;

X_hat(k) = X_hat(k) + 1;

else

if k > 1

k = k - 1;

d_vector(k) = sqrt(d_vector(k)^2 - (intersum(k + 1) - R(k + 1, k + 1)*X_hat(k + 1))^2);

intersum(k) = Z(k) - R(k, (k + 1):n)*X_hat((k + 1):n);

Upp_bound(k) = (d_vector(k) + intersum(k))/R(k, k);

Low_bound(k) = (-d_vector(k) + intersum(k))/R(k, k);

if Low_bound(k) > Upp_bound(k)

k = k + 1;

X_hat(k) = X_hat(k + 1);

else

X_hat(k) = Low_bound(k);

end

else

while X_hat(k) <= Upp_bound(k)

if minR > norm(Z - R*X_hat, 'fro')^2

X_est_vector = X_hat; %found X_hat

minR = norm(Z - R*X_hat, 'fro')^2;

end

X_hat(k) = X_hat(k) + 1;

end

k = k + 1;

X_hat(k) = X_hat(k) + 1;

end

end

end

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Please could you tell me where I might be going wrong.

Thank you.

Hi everyone,

I am trying to derive the error performance of a wireless communications system, and I run into a series of Independent and Identically Distributed (i.i.d.) random variables (RVs) as follows:

Z = X_1 + X_2 + ... + X_N,

where N denotes the number of RVs being summed together. The distribution of each X_1, .., X_N may be Rayleigh, Rice, etc.

Now, I know that the Central Limit Theorem (CLT) can be applied assuming high N, such that the mean of Z becomes:

E[Z] = N*E[X_N],

and the variance of Z becomes:

Var[Z] = N*Var[X_N].

However, in my case, N is not high enough to use CLT. In fact, I am working with N values in the set N = {2, 3, 4, 5, 6, 7, 8, 9, 10}.

So my question is, if I am given the CDF (denoted by F_N(t)) and PDF (denoted by f_N(t)) of each X_1, ..., X_N, how do I evaluate the mean and variance of Z? Do you use some sort of convolution property, or something else?

Any help would be appreciated.

Thank you.

What is difference between spin-transfer torque nano oscillators and spin-hall nano oscillators?

In optical wireless communication, there are two main system architectures:

• Intensity modulation and direct detection (IM/DD)

• Coherent modulation/detection

In IM/DD systems, the optical front-end can only detect the optical intensity while coherent receivers can detect both amplitude and phase.

Discuss how we can benefit from Integrated reflective surfaces in IM/DD and coherent optical wireless systems. For each system type, explain your underlying assumptions and any other essential information to support your arguments.

Hi everyone!

I want to have expertise opinion abut these.

Will it be cost effective or not?

What about the signal strength (SNR) and system complexity?

Hi everyone,

I wanted to know how to perform Rician fading in matlab.

I have done Rayleigh fading, which is simply:

h = sqrt(1/2)*(randn(1, 1) + 1i*randn(1, 1));

From what I understand so far about Rician fading, it is computed in terms of a Rician factor K, and a scaling parameter Omega (I will assume Omega = 1). It is also computed in terms of Line-of-Sight components and Non-Line-of-Sight components.

So what i did was:

hLOS = sqrt(1/2)*(randn(1, 1) + 1i*randn(1, 1));

hNLOS = sqrt(1/2)*(randn(1, 1) + 1i*randn(1, 1));

h = sqrt(K/(K + 1))*hLOS + sqrt(1/(K + 1))*hNLOS;

I want to confirm if this is correct or not. If it is not, please could someone offer some guidance on how to correct this.

Thank you.

How to filter input signal through lognormal shadowing model or kappa mu shadowing model by using a code which generates PDF in Matlab?

i have transfer functions from two different papers. are they same.

in H=exp(-alpha(f)*l)

here, do we have to put values of f or f is just an function related to alpha.?

Machine learning, deep learning, wireless, 5G, 6G and communications

For generating antenna pattern multiplexing when we apply dc biased sinusoidal voltage to the variable reactance of the Electronically Steerable Parasitic Array Radiator (ESPAR) antenna, the received signal appear as harmonic due to non linear properties resulting loosing signal components? which method can minimize the issue for making the antenna pattern more efficient?

In many books and papers, they used to use the complex form of the channel effect response. However, in reality, the signal is real values and also the channel.

Is it correct to use the following approximation? (in MATLAB)

% Rayleigh channel fading

eta = 4; %Path loss exponent

d = 200; %Distance from BS to the user

h_var = sqrt(d^-eta); % channel effect variance, mean is zero

h = h_var*randn(1,length(tx))/sqrt(2);

I just want to know the scope and difficulties for physical implementation at THz band. Is there any testbed to implement a simple measurement setup for THz communication system?

In a signal is to be transmismitted, first pilot symbols are added and then through Mach-zehnder modulator it has to be transmitted for optical communication purposes. So, for pilot symbols, they have to be go through Mach-Zehnder modulator. The output of Mach-Zehnder modulator is E_out=cos(phi); Where phi= ((U+U_dc)/U_pi)*pi. and here, U_dc, U_pi and pi are constant. And U is the information after inserting pilots. This signal E_out is sent through the channel h.

Now, my question is that how should I estimate the channel because the pilot are gone through Mach-Zehnder modulator before the channel. and How should I extract the pilots and estimate the channel? Thank you.

Hi everyone,

I am trying to derive the variance of a Random Variable as part of my research.

I wanted to check if I have simplified the expression in the word document attached correctly. In other words, if I take the variance of a sum or difference of linear combinations (series) of random variables, is that equal to the sums of the variances of the random variables, where the different series differ by a constant "alpha" (see the document). Note that the random variable in each series is the same random variable.

I tried deducing this by using a few properties of variance:

1. Var(aX) = a^2 Var(X)

2. Var([series from 1 to n of] X) = n Var(X)

3. Var(aX + bY) = a^2Var(X) + b^2Var(Y), where X and Y are independent RVs.

However, I am not sure if this correct. Please could you check if my understanding of this is correct.

Thank you.

Hi everyone,

I am having a problem deriving the variance of a variable which is expressed in terms of a series expression where the sum term is a random variable.

I have attached a word document which illustrates the types of expressions which need to be evaluated in my derivation of the random variable in question. I hope this is clear enough to explain my problem.

I want to know how to evaluate these types of expressions, where the random variable is part of the series term.

Thank You

Hi, I am working on UAV deployment in a wireless communication scenario to cache. Does anybody know how to simulate/deploy UAVs in Matlab using weighted or simple k-mean clustering? Below I also attached a snapshot.

Thank you

For polarization diversity in wireless communication, often dual orthogonal polarization antenna is considered. I want to study the effect of non-orthogonal polarization antennas on wireless communication channels.

how to analyze the non-orthogonal polarization antenna effect to make a proper study of polarization diversity in MIMO wireless communication.

kindly suggest any relevant theory or research papers.

Thank you.

We know that in the Han-Kobayashi region, the to be transmitted data is divided into two parts, private and common. So, what type of information does these parts contain ?

Hello everyone, I want the solution manual for this book if there anyone have the solutions kindly refer it to me , Best regards.

In the textbook of Tse "Fundamental of wireless communications", the LOS MIMO channel model is characterized by $H = \alpha \times a(\theta) *a(\gamma)^H $ where a(\cdot)$ is the steering vector. The model uses conjugate transpose while there are other papers use transpose. This has puzzled me a lot. I understand if the transmitt antennas and receive antennas are different, both of them seem to be right. But how about the full-duplex antennas, which one should be right?

I'm looking for an advises regarding Machine Learning methods applied in Wireless books to solve some optimization problems.

According to my knowledge, the channel estimation is to analyze the channel realization based on the pilot signal, and the channel prediction is to obtain it based on past channel realizations.

Therefore, the channel prediction can be utilized when the pilot signal is contaminated. In other words, the channel prediction is only deserved in the situation when the pilot signals are crashed so that the channel estimation doesn’t work.

Did I understand right? Thank you for your valuable responses in advance.

In the context of wireless communication, I have heard people asking will the AI/ML model be trained online/offline? I would like to know what is the difference between these two terms and how they can impact the system performance?

Hey guys,

Please suggest the list of scopus list of journals for VLSI, Wireless networks and Wireless communications (Unpaid and paid)

Since the importance of Machine Learning (ML) is significantly increasing, let's share our opinions, publications, or future applications on Optical Wireless Communication.

Thank you,

Ezgi Ertunc

Hello everyone, I need some channel models MATLAB code to simulate my Underwater Visible Light Communication algorithm. If anybody has some models then please provide. thank you.

Most of the authors presented their work on Mach-Zehnder modulator in fiber optic communication. When I saw Mach-Zehnder Modulator on internet for buying it is showing it with fiber optic cable both sides of Mach-Zehnder Modulator(input and oupt side). My question is that can we use Mach-zehnder modulator for intensity modulation in wireless optical communication? Please help.

What are the areas in fading channels like TWDP,Rayleigh fading Channel,Nakagami fading Channels?? ....Is pursuing research in this area are limited?Is there is a chance of publishing many papers in this area?

I am keen to do research in wireless communication. I would like to know research idea in this field.

Both deep learning (DL) and quantum computing (QC) are emerging technologies in the realm of research. Please share your valuable opinion on the following concerns.

- How DL can be merged with QC?
- What are the current challenges in the DL-based QC?
- What are the tentative application areas for DL-based QC?

Thanks for your time.

hello, I'm looking for a simple model for a

**Reconfigurable Intelligent Surfaces-assisted wireless network**that provides a vision for channel modeling for these systems.no matter whether deep learning, machine learning, or convex optimization approach is applied to solving the problem and no matter that it is python or Matlab code

very thanks

For Intensity modulation, I am using external modulation. I want to simulate mach-zehnder modulator based intensity modulation. Please suggest simulation in MATLAB

I have an antenna module which is a planar phased array for 5G NR FR2 base station (i.e., BS type 2-O). I need to perform over-the-air (OTA) radiated conformance testing to verify the performance of antenna module to obey specification of 3GPP. Hence, I study the attached file 3GPP TS 38.141-2 V16.10.0.

For transmitter test (chapter 6), the module is connected with a signal generator (SG), which make NR signals generated by SG are emitted through antenna module. And then, a feed antenna is regarded as receiving end and connected with a signal analyzer (SA) and spectrum for analysing received signal. On the other hand, for receiver test (chapter 7), exchange the placements by module and probe antenna to perform conformance testing. The complete transmission and received process run in a CATR or anechoic chamber.

- How to set parameters (ex.
**total output power, modulation, operation band, bandwidth, frame structure, single or multi-carrier, subcarrier spacing, TDD or FDD, and so on**) of measuring equipment (SG and SA) for radiated conformance testing according to TS 38.141-2? Would you mind take an**simple demonstration**for test items in section 6.2 and 7.3?

In my opinion, the section 4.7.2, 4.9.2 and Annex A is strongly relate to the setup. (I am confused about difference between intention of test configurations and test model respectively in section 4.7.2 and 4.9.2. I googled other materials (others attached file) about this issue, there is only description about Test Model

*in test procedure rather than Test Configurations***NR-FR2-TM***)***NRTC**I have some base of communication system but I am short of practical experience of RF measurement, so this problem maybe is not an easy question to answer. If you cannot answer by a few words, please provide clues or direction of search.

Many thanks for your answer.

If so, we're hiring! - come and join our team to help develop the next generation of intelligent, wearable drug delivery devices. Research opportunities now available in microsensor integration, transdermal delivery and microfludics, and system electronics/communications. Further details available from Dr Conor O'Mahony - feel free to discuss with us!

In your opinion, what are the interesting and worthy topics for research in wireless communication systems?

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?

Hello

I am going through some digital communication literature, where some research papers have used the following formula to calculate the sum rate

Sum_rate=Summation (log2(1+SINR(i)) eq.1

My confusion is as follows:

1. Why is bandwidth(B) not included i.e. B.log2(1+SINR)

2. What will be the units (e.g. bps/Kbps/Mbps etc) if eq.1 is used.

Thanks

Hello, i am searching for some new innovation points in 6G about networking slice recently.

I want to know what updates will be made to network slicing in 6G, which cannot do well in 5G.

(Maybe about architectures, methodologies, algorithms, and combination with other 6G new technologies.)

Can you recommend me some good ideas, innovation points or papers( and white papers), thank you.

Recently, I focus on UAV-enabled air-to-air wireless communications, in which the UAVs are flying at an altitude of 60~150 m. In this case, which channel model is more applicable? Intuitively, I think the LoS channel is suitable since there should be no obstacles at this high altitude. Is my idea correct? Could you provide me with some references, thank you very much for your help!

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.

Recently, I have seen in many papers reviewers are asking to provide computation complexities for the proposed algorithms. I was wondering what would be the formal way to do that, especially for the short papers where pages are limited. Please share your expertise regarding the computational complexities of algorithms in short papers.

Thanks in advance.

I need to write code in MATLAB to find the impulse response of infrared optical wireless communication (IROWC) in the diffuse distribution (wide beam transmitter and wide FOV receiver) ...

Game theory is a very promising technique to achieve optimal outcomes and can be applied to almost all concepts. I am trying to explore game theory for future purposes. However, as a beginner, I couldn't get very good resources regarding game theory.

Please share your resources (i.e., video or blog tutorial, research paper) regarding game theory, which covers the following things.

1. How to apply game theory?

2. How to prove optimal gain after applying game theory, (e.g., proving Nash equilibrium).

3. What are the state-of-the-art game theory techniques?

Thanks in advance.

While reading the literature regarding performance analysis of RIS-Assisted Wireless communication Systems I went through the following terms: Achievable Rate, Sum Rate, Ergodic capacity. How do understand them?

Please help me with the following formulation.

I want to calculate transmit power that can satisfy a given SINR threshold on the receiver side.

My formulation is as follows:

SINR=Received_Power/(Interference+Noise) Eq. 1

If SINR Threshold (SINR_th) is known, we can get the Required_Received_Power and thus the "Required_Transmit_Power" power as follows:

SINR_th=Required_Received_Power/(Interference+Noise) Eq. 2

We know that

Received_Power=Transmit_Power/Pathloss; Eq. 3

OR

Required_Received_Power=Required_Transmit_Power/Pathloss; Eq. 4

Substituing "Required_Received_Power" in Eq.2 with the right hand side of Eq.4, we get

SINR_th=(Required_Transmit_Power/Pathloss)/(Interference+Noise) Eq. 5

OR

Required_Transmit_Power=SINR_th x (Interference+Noise) x Pathloss Eq. 6

Please advise whether this formulation is correct or not as I am getting wrong results.

Thank you!!!

In OFDM, First we modulate our message signal and then we take the IFFT of that signal to load the message on subcarrirers. And after that the cyclic prefix is added to combat the frequency selective nature of channel. What should be the length of the cyclic prefix?

I am curious about what happened to the atomizer software by Buckheit J. (http://statweb.stanford.edu/~wavelab/personnel/) and if it is available somewhere.

Sadly I found only 2 dodgy sites that require a login to download the MATLAB code. Does someone have any information on where to get it from?

Alternatively, if there are other toolkits that have implemented this code please let me know, it does not have to be MATLAB, any language is fine for me :).

Thank you.

Hi everyone, hope you are perfect!

today I am going to have a plea of you to lend me a hand if is possible.

as an wireless communication researcher, I come across many phrases that I have no idea about them. one of them is "optical front-hauls" and another one is "grant-free Transmission"!!!

If you can give me an imagination or illustration, what would it be?

Thanks for making time in advance.

**#communication**

**#5gtechnology**

**#6G**

**#wirelesscommunications**

How can I calculate the bit error rate of orbital angular momentum for wireless communication? I found this paper 'Error probability on the detection of orbital angular momentum detection' but in this paper, they are calculating the probability of the detection of the OAM mode like if the information were carried by the mode. While I am interested in the case where OAM modes are used to create orthogonal channels.

How do we represent zero interference on db scale?

I am using the following formula for calculating the Received_Power_TH (TH stands for threshold). Received_Power_TH is the power of the received signal required for successful decoding. I am using the following formulation.

SINR=Received_Power - Interference - Noise Or

The Recieved_Power that satisfies the SINR_TH (or in other words the minimum Received_Power required for successful decoding) is given as follows

SINR_TH=Received_Power_TH - Interference - Noise Or

Received_Power_TH =SINR_TH + Interference + Noise

However, i get the following results which seem counter intuitive.

Assuming SINR=25, Interference=-50, Noise= -95

Received_Power_Th =25-50-95=-120

Now if we do not have any interference e.g. in a case when there is only one node transmitting, we get the following

Received_Power_TH=25-95=-70

This result seems counter intuitive as Received_Power_TH for successful reception in case of no interference should drop below the value we get when we have interference whereas in this case the Received_Power_TH is equal to -120 in case of interference and it increases to -70 when there is no interference.

Many thanks

While going through the Literature I found that the performance analysis of wireless communication System was done by us one of the following three methods:

1. Moment Generating Function-Based performance Analysis

2. PDF Based performance Analysis

3. Characteristic Function-Based performance Analysis

I want to know about ML algorithms that are used to train the data set: e.g. in routing protocols in WSN.

Apart from experiments available for WiFi, IoT, LTE etc., we also want our students to work on experiments on 5G. Does someone have a set of pre-built NetSim experiments which we can quickly adopt for our course? If not, any suggestions on what kind of experiments can be done would be valuable? Thank you.

Is it possible to employ Beamforming for interference mitigation when two smart phones are communicating directly without any relay (such as Access Point, Base Station or some other kind of relay nodes) in between. We assume that many pairs of smart phone pairs are communicating directly and may interfere with each other. Therefore beamforming (if possible) will help reduce interference.

Much appreciated in advance.

I need to know about the appropriate tools for modeling, simulation, and analysis of wireless communication systems other than MATLab.

IRS can create higher beamforming gain with the help of an “intelligent” reflector. But, this brings other practical issues.

How does BS/AP synchronize with the reflector about the amplitude and phase?

where IRS is the intelligent reflective surfaces, BS is the base station and AP is the access point.

In wireless communication channel modeling, capacity is calculated based on computed H matrix and SNR value.

H matrix is calculated through a different models - COST..WINNER..etc.

I am wondering how to calculate SNR at different locations of UE In a cell?

many papers assume a certain SNR before capacity calculation.

How one can calculate SNR in an urban macro environment in presence of scatterers with different BS-UE positions in distance and angle?

I am looking for SNR calculation throughout a cell for MIMO wireless channel using directive antennas.

In 5G, the mixed-numerology is introduced to support diverse QoS requirements. It is also mentioned in the spec that simultaneous transmission and reception with different numerologies in CA is possible.

However, there is few materials mentions how this is achieved. Does a UE requires multiple antennas to transmit with resources of different numerology at the same time? Or it can be done by a single antenna? If the latter is the truth, how does a UE deal with different SINR values generated by resources with different numerologies? (different SINR values lead to different modulation scheme, how can this be done with single antenna?)

p.s.

I have found one paper that is related to my question:

It seems that a UE can deal with resources with different numerology simultaneously, with different modulation scheme. Yet, this paper does not show how this is achieved by the smartphone.

I'm looking for the best tool for UAVs' path planning; also the tool should support wireless communication.

How fast does the traffic load of WiFi network change? What is the average time that the WiFi traffic load remains constant for different traffic types e.g. internet browsing, video streaming, voice call, e.t.c ?

I am trying to obtain closed-form expressions of outage probability for a user in a given cell. Here I am including inter-cell interference (from other adjacent cells) in the expression of SINR. Now I need to obtain the closed-form expressions of outage probability over a fading channel like Nakagami or Rayleigh. Please suggest any information regarding this. thanking you

I want to know how can we implement nakagami fading in MATLAB and get the small scale fading coefficients for this nakagami distribution in MIMO-OFDM channel. Any MATLAB code would be helpful. Are these coefficients time varying and how to get these coefficients for a certain time interval?

I am try to build a system model where intelligent reflecting surface is used to enhance the receiver's SNR depending on the position of the receiver.

Based on what I read, a signal is scattered at the atom level and constructive/ destructive superposition is used to direct the signal to a certain user. My question is: Can the signal be directed to a user behind the IRS?

Dear all,

We all know about the fast and rapid developments in machine learning algorithms. But the question is that if we want to implement them for low latency (less than 1 ms) applications using wireless communications, is it possible?

I am able to generate Rayleigh coefficients as per the following code (function) in python using H=(1/sqrt(2))*(randn(N)+randn(N)*1i)

def RAYLEIGH(d, etaa, num_symbols):

// Input arguments (Distance, pathloss exponent and samples required (depends on data if fast fading)//

c=1/(d**etaa);

h1 = np.sqrt(c); //(Pathloss is multiplied with Rayleigh coefficient)

h = h1*((np.random.randn(num_symbols)+1j*np.random.randn(num_symbols))/np.sqrt(2));

g = (np.absolute(h))**2; // Magnitude

return h.tolist(), g.tolist(); // Return as a list

How to generate the Rician Coefficients given d (distance), etaa (path loss exponent) on the same lines.

In addition to the path made by 5G (small cell coverage, massive mimo, mm-waves, etc ), 6G is going to merge other areas such as bio-medical, artificial intelligence, robotics, etc.

What are the key enabling technologies of the 6G networks?

How can I estimate the propagation loss between an unmanned aerial vehicle (UAV) or drone, and user equipment (UE) on the ground? is it safe to assume a line-of-sight scenario? how about the drone's altitude? is there a specific air-to-ground formula I can use?