I am working on Veins framework, inside OMNET++. I set the property of RSU inside .ned file as follow:
#display("p=150,140;b=10,10,oval;r=90");
The tkenv shows a circle around RSU, but the vehicles received beacons outside the range (circle).
How can I adjust the transmission range of RSU to the Circle?
Adding a display string tag of r is just adding a circle to the graphical output; it does not influence the simulation.
If you define the "transmission range" as the point where the probability of reception is zero, you can calculate this point based on the transmission power at the antenna and the sensitivity of the radio (both set in omnetpp.ini), as well as the used path loss and fading models (set in config.xml). If you change these parameters and models, you are changing this "transmission range".
Note, however, that this range has only little relevance to frame reception probability.
Veins employs the MiXiM suite and approach to model transmissions as two-dimensional (time and frequency) functions of signal power that are modified by path loss and fading effects (both stochastic and deterministic, e.g., due to buildings).
If a frame's receive power is above the sensitivity threshold, its reception probability is computed based on dividing these functions for signal, interference, and noise to derive the SINR and, from that, the bit error rate.
Even at moderate interference levels, this means that most frames cannot be decoded even though they are well above the sensitivity threshold (simply because their SINR was too low).
Just to repeat: I am warning against calculating a "transmission range" for anything other than purely informational purposes. How far you can send in theory has absolutely no relation to how far you can send on a moderately busy channel. This effect is modeled in Veins!
Related
I started (since about one week) using veins (4.4) under omnet++ (5.0).
My current task is to let vehicles adjust their transmission range according to a specific context. I did read a lot of asked questions like these ones (and in other topics/forums):
Dynamical transmission range in the ieee802.11p module
Vehicles Receive Beacon Messages outside RSU Range
How coverage distance and interference distance are affected by each other
Maximum transmission range vs maximum interference distance
Reduce the coverage area between vehicles
how to set the transmission range of a node under Veins 2.0?
My Question:
How to -really- change the transmission range of just some nodes?
From the links above, I knew that the term "transmission range", technically, is related to the received power, noise,sensitivity threshold, etc. which defines the probability of reception.
Since I am new to veins (and omnet++ as well), I did few tests and I concluded the following:
"TraCIMobility" module can adjust the nodes' parameters (for each vehicle, there is an instance) such as the ID, speed, etc.
I could, also, instantiate the "Mac1609_4" (for each vehicle) and changed some of its parameters like the "txPower" during simulation run-time but it had no effect on the real communication range.
I could not instantiate (because it was global) the "connection manager" module which was the only responsible of (and does override) the effective communication range. this module can be configured in the ".ini" file but I want different transmission powers and most importantly "can be changed during run-time".
The formula to calculate the transmission range is in the attached links, I got it, but it must be a way to define or change these parameters in one of the layers (even if it is in the phy layer, i.e., something like the attached signal strength...)
Again, maybe there is some wrong ideas in what I have said, I just want to know what/how to change this transmission range.
Best regards,
You were right to increase the mac1609_4.txPower parameter to have a node send with more power (hence, the signal being decodable further away). Note, however, that (for Veins 4.4) you will also need to increase connectionManager.pMax then, as this value is used to determine the maximum distance (away from a transmitting simulation module) that a receiving simulation module will be informed about an ongoing transmission. Any receiving simulation module further away will not be influenced by the transmission (in the sense of it being a candidate for decoding, but also in the sense of it contributing to interference).
Also note that transmissions on an (otherwise) perfectly idle channel will reach much further than transmissions on a typically-loaded channel. If you want to obtain a good measurement of how far a transmission reaches, have some nodes create interference (by transmitting broadcasts of their own), then look at how the Frame Delivery Rate (FDR) drops as distance between sender and receiver increases.
Finally, note that both 1) the noise floor and 2) the minimum power level necessary for the simulation module of a receiver to attempt decoding a frame need to be calibrated to the WLAN card you want to simulate. The values chosen in the Veins 4.4 tutorial example are very useful for demonstrating the concepts of Veins, whereas the values of more recent versions of Veins come closer to what you would expect from a "typical" WLAN card used in some of the more recent field tests. See the paper Bastian Bloessl and Aisling O'Driscoll, "A Case for Good Defaults: Pitfalls in VANET Physical Layer Simulations," Proceedings of IFIP Wireless Days Conference 2019, Manchester, UK, April 2019 for a more detailed discussion of these parameters.
I am just giving my opinion in case someone was already in my situation:
In veins (the old version that I am using is 4.4), the "connection manager" is the responsible for evaluating a "potential" exchange of packets, thus, its transmission power is almost always set to the upper-bound.
I was been confused after I changed the vehicles "Mac1609_4" transmission power and "graphically", the connection manager was still showing me that the packets are received by some far nodes which in fact was not the case, it was just evaluating whether it is properly received or not (via the formula discussed in the links above).
Thus: changing the "TxPower" of each vehicle had really an effect beside graphically (the messages were not mounted to the upper layers).
In sum, to make a transmission range aware scheme, this is what must be done:
In the sender node (vehicle), and similarly to the pointer "traci" which deals with the mobility features, a pointer to the "mac1609" must be created and pointed to it as follows:
In "tracidemo11p.h" add ->
#include "veins/modules/mac/ieee80211p/Mac1609_4.h"//added
#include "veins/base/utils/FindModule.h"//added
and as a protected variable in the class of "tracidemo11p" in the same ".h" file ->
Mac1609_4* mac;//added
In "tracidemo11p.cc" add ->
mac = FindModule<Mac1609_4*>::findSubModule(getParentModule());
now you can manipulate "mac" as in "traci", the appropriate methods are in the "modules/mac/ieee80211p/Mac1609_4.cc & .h"
for our work, the method will be:
mac->setTxPower(10);//for example
This will have an impact on the simulation in real-time for each node instance.
It may had described it with basic concepts because I am new to omnet-veins, these was done in less than one week (and will be provided for new users as well).
I hope it will be helpful (and correct)
How can I record statistic of the RSSI value for a communication in veins ?, i'm using 5.1 version. in the previous version it was a function which calculates the rssi in phy802.11 layer but it doesn't exist anymore.
thank you.
This is addressed in an answer to "How does veins calculate RSSI in a Simple Path Loss Model?":
Taking Veins version 5 alpha 1 as an example, your application layer
can access the ControlInfo of a frame and, from there, its RSS, e.g.,
as follows:
check_and_cast<DeciderResult80211*>(check_and_cast<PhyToMacControlInfo*>(wsm->getControlInfo())->getDeciderResult())->getRecvPower_dBm()
The above code returns the absolute receive power (in dBm) measured at the center frequency of the corresponding frame.
Note that, while this gives you "some" indication of received signal strength, it is far from the only way to do that. In fact, vendors are free to implement whatever mechanism they deem fit to derive a number that indicates how strongly a signal was received.
I need to reduce the coverage area of communication between vehicles. Should I reduce values of these parameters in omnetpp.ini?
*.**.nic.phy80211p.sensitivity = -89dBm
*.**.nic.phy80211p.maxTXPower = 10mW
*.**.nic.phy80211p.thermalNoise = -110dBm
If not, which parameters can I modify please?
If by coverage area you mean communication range, the short answer is yes, you can modify these parameters to reduce the communication range (which I'd probably do by lowering the maximum transmission power). Alternatively, you can change the channel properties (in config.xml) by adding a corresponding analog model that has the behavior you're looking for. I recommend having a look at the Two-Ray Interference model and the Obstacle Shadowing model, which are part of VEINS.
In the current Veins version (i.e. 4.5) you can also reduce the maxInterfDist of the ConnectionManager which will result in overall less vehicles getting an AirFrame given to their NICs which they then try to decode. However, this only decreases the distance of the best possible communication (i.e. without buildings in LOS, etc.) and not the average distance which usually is way smaller due to fading effects and buildings.
in my opinion, the maxTXPower and maxInterfDist do not affect the coverage area between vehicles. You should modify the "..nic.mac1609_4.txPower" and "..nic.phy80211p.sensitivity". For a better understanding, you may check the answer from Christoph Sommer in this thread: how to set the transmission range of a node under Veins 2.0?
I want to keep a constant number of cars in my (long) simulation (OMNeT+Veins). I do not care about mobility that much so i could probably use the Veins in-built function *.manager.numVehicles = 100. The thing is that if i do not specify any(enough) vehicle flows (from SUMO) my simulation terminates instantly (because of no events). So i create some flows (that exit the simulation sooner) and Veins fills up for the cars as they dissappear.
Is there a more elegant way to do this? I'd prefer to just use the numVehicles function since it's easier and the cars move minimally so they remain in the simulation for long.
I need steady-state vehicular density (number of vehicles fixed - even if old ones leave and new ones enter to replace them at the same instant).
Thanks,
Andreas
The autoShutdown parameter can be set to false to instruct the coupling interface to keep going even though there are no more cars in the simulation. See https://github.com/sommer/veins/blob/veins-4.5/src/veins/modules/mobility/traci/TraCIScenarioManagerLaunchd.ned#L55
https://stackoverflow.com/a/71071341/7215379 has a solution. It actually is meant to keep the number of vehicles in simulation constant. You can look into the possibility of reusing it.
I am using the FMOD library to apply FFT to an audio stream, providing me with a constantly updating fixed number of frequency bins. Each bin represents an equal frequency range, with a value between 0 and 1 to represent the intensity of this range from the processed audio. FMOD documentation states that these values can be represented in decibels, where val is the value between 0 and 1:
Decibels = 10.0f * (float)log10(val) * 2.0f
I am attempting to make an automated strobe-like beat detecting visualisation. So far, I test at a constant interval to see whether a particular frequency bin's intensity value surpasses a specified boundary - if this is the case, the strobe flashes. Although a pretty crude way of doing this, it works fairly effectively for my requirements.
However, this specified boundary only works effectively when the system/music player's volumes are maximum. When I reduce either volume, the strobe sensitivity is reduced and becomes either very inaccurate or stops flashing completely. I assume that I need to normalise the data in some way so analysis is performed independent of volume, though by scaling the data by 1/value of largest bin the largest value is always maxed out. This surpasses the specified boundary permanently, causing the strobe to flash indefinitely. I can't think how else this can be achieved and have been on a mental block for days - any help or a point in the right direction would be greatly appreciated!
Normalise over a a longer scale. You'll need something like an envelope follower with a long release time.
If you search for 'compressor' source code, or automatic gain control something will definitely turn up.
But broadly in pseudo C++, and working on your incoming audio (the time-domain signal before the FFT):
auto instant_level = std::abs(signal);
peak_level *= 0.99f;
peak_level = peak_level > instant_level ? peak_level : instant_level;
Now peak_level decays slowly over time. And you can use this to calculate a gain factor to normalize your incoming audio. Adjust the 0.99f as required for a sensible decay time and for the correct sample rate.
There's also a Signal Processing stack exchange site where you'll get quicker answers to these kinds of questions (although occasionally with an almost incomprehensible piece of algebra attached :) )