When the radio is of Ieee80211DimensionalRadio radio type, why doesn't the INET 4.4 have a communicationRange parameter?
If not, please help how to set this parameter.
The reason is the same, why a WiFi card in a real computer does not have a setting where you can set how far the WiFi card can communicate. You do not set range in a real system. You set the transmission power and the effective range depends on that.
In short, you have to calculate the required power backwards from the range. Obviously, that is extremely complicated assuming that there are error correction, directional antennas, non-freespace propagation, etc..
The best you can do is to manually change the TX power and experiment to set it to a level suitable to you.
(additionally: There is no such thing as communication range in real world. There is always a probability that a packet is received for any distance. The question is, where you set your cutoff probability. This is always subjective).
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 have a table, where each row of the table contains state (registers). There is logic that chooses one particular row. Only one row receives the "selected" signal. State from that chosen row is then accessed. Either a portion of the state is connected as an output to the IO of the module, or else a portion of the IO is used as input to update the state.
If I were implementing this with a circuit, I would use pass-gates. The selected signal would turn on one set of pass-gates, which would connect the row's registers to a bus. The bus would then be wired to the IO bundle. This is fast, small area, and low energy.
There is a straight forward way of implementing this in Chisel. It encodes the selected row as a binary number, and then applies that number to the select input of a traditional mux. Unfortunately, for a table with 20 to 50 rows, and state of hundreds of bits, this implementation can be quite slow, and wasteful in area and energy.
The question has two parts:
1) Is there a way to specify busses in Chisel, such that you have pass-gates or traditional tri-state drivers all hung off the bus?
2) Failing that, is there a fast, small area, low energy way of doing this in Chisel?
Thanks
1) Chisel does not fully support bidirectional wires, but via the experimental Analog type (see example), you can at least stitch a bus through your Chisel code between Verilog Black Boxes.
2) Have you tried Mux1H in chisel3.util? It emits essentially a sum of products of the inputs and their corresponding select bits. I'm not sure how this compares to your proposed implementation. I would love to see a QOR comparison. If this construct is not sufficient and you cannot express precisely what you want in chisel, you can use a parameterized BlackBox to implement your one-hot mux and instantiate it as you please.
Is there an algorithm or some heuristic to decide whether digital audio data is clipping?
The simple answer is that if any sample has the maximum or minimum value (-32768 and +32767 respectively for 16 bit samples), you can consider it clipping. This isn't stricly true, since that value may actually be the correct value, but there is no way to tell whether +32767 really should have been +33000.
For a more complicated answer: There is such a thing as sample counting clipping detectors that require x consecutive samples to be at the max/min value for them to be considered clipping (where x may be as high as 7). The theory here is that clipping in just a few samples is not audible.
That said, there is audio equipment that clips quite audible even at values below the maximum (and above the minimum). Typical advice is to master music to peak at -0.3 dB instead of 0.0 dB for this reason. You might want to consider any sample above that level to be clipping. It all depends on what you need it for.
If you ever receive values at the maximum or minimum, then you are, by definition, clipping. Those values represent their particular value as well as all values beyond, and so they are best used as outside bounds detectors.
-Adam
For digital audio data, the term "clipping" doesn't really carry a lot of meaning other than "max amplitude". In the analog world, audio data comes from some hardware which usually contains a "clipping register", which allows you the possibility of a maximum amplitude that isn't clipped.
What might be better suited to digital audio is to set some threshold based on the limitations of your output D/A. If you're doing VOIP, then choose some threshold typical of handsets or cell phones, and call it "clipping" if your digital audio gets above that. If you're outputting to high-end home theater systems, then you probably won't have any "clipping".
I just noticed that there even are some nice implementations.
For example in Audacity:
Analyze → Find Clipping…
What Adam said. You could also add some logic to detect maximum amplitude values over a period of time and only flag those, but the essence is to determine if/when the signal hits the maximum amplitude.