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Re: Team 548 Einstein Statement
Everyone should check out the Cisco site for actual tech specifications and in situ performance for the field AP. This unit is designed to cover the entire floor in large buildings with typical coverage of up to 375 ft and with well over 100 users connected. First engineering, DEKA engineers and the wireless consultants all have extensive experience with the units used.
If anything, there should be a caveat to teams to mount the radio away from large metal objects, near the outside of the robot, with a secured power connector and without having robot appendages move against the case while operating. Just this year alone, I have found teams with the radio mounted on the bottom of the robot, or behind the bumper supports, or underneath or behind 2"x4" box tube that is part of an appendage, or with the radio sandwiched between two pieces of metal plate. I even found one team that had constructed an aluminum box out of perf stock to "protect" the radio. |
Re: Team 548 Einstein Statement
Now there's an idea Al... can we just surround the field + field AP with a giant Faraday cage? That should resolve any and all concerns stemming from interference from outside sources!
Note: I'm not really being serious here :) |
Re: Team 548 Einstein Statement
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In an infrastructure environment (by far the most common usage of this technology) usually the transmitter power being set as high as possible without it causing other issues is a good thing. Even in an ad hoc network the number of devices actually moving is usually small. In this environment that may not be the case considering the devices being designed to move around. I can easily see that there's a balancing act where the power level one wants is just enough to do the job while keeping the side effects minimized and that power level will change moment to moment (it may be more power than is being used now, but I suspect it's actually less power than is used now a great deal of the time). Logging of the relevant factors seems critical as otherwise I can't see how anyone can have the data to determine the fit of the solution. |
Re: Team 548 Einstein Statement
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Brian, You are implying that FIRST and/or it's vendors have not made these measurements or know the RF levels on the field. I have to ask, no demand, that you cease making statements based solely on your own experience without any knowledge of what is taking place on FIRST fields. All you are doing is seeding doubt in the minds of those who have no experience in the field. No matter how long your posts, in my mind you are simply throwing rocks at FIRST. The engineering staff has made these measurements, they know what the coverage contour is on fields, and they know the fade margins caused by objects, robots and people on or near the field. While the RF output level of the Cisco router is adjustable, as you know. Setting devices to maximum is rarely the best solution depending on the environment. There is no doubt that the RF level is sufficient to reach 50 ft. However, with outside interference, it is not the transmit power but the receiver sensitivity that needs to be considered. In normal environments, high RF levels are likely to saturate the receivers causing front end overload and intermod products in the demod process. The Cisco device is capable of making more than one watt ERP with the antennas currently used. I have worked the world on less than that, often achieving distances of greater than 800 miles on about 0.5 watt ERP, not calculating for losses in antenna lobes, ground, transmission cable or atmospherics. |
Re: Team 548 Einstein Statement
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Also, you failed to consider that the fade margins are entirely dependent on robot AP placement or it would be impossible for a team to find a placement of the AP that would interfere with communications. There is no way for FIRST to predict all robot designs sufficiently to test on that level. Quote:
2. The robot APs have been positioned in such a way that they don't communicate clearly despite the Cisco 1252's radio output power. It's not a question of could be...there are sufficient examples. 3. All of the APs both field and robot are capable of interfering with each other. Not just when they are on the same radio channel, but when they are on radio channels adjacent to one another. So the radio interference concerns are not just from outside sources. 4. Logging for the relevant issues should be simple enough to do. If one doubts the validity of their position, or values the correctness of their own that's a great way to mitigate both ends of the concerns. 5. I'm not saying that the field AP can't go a further distance, I'm saying that it does not need to. In fact should not unless it's absolutely necessary based on measurements. This goes for the robot APs as well. Right now all evidence supports that the radio power levels are fixed. 6. You are absolutely correct about the radio receiver sensitivity being important. The entire clear channel assessment (CCA) process that allows the robots to be on the same radio channel depends on that sensitivity. In fact it's adjustable for that reason. It's also impacted by the robot AP placement. Regardless of diversity, MIMO, or RTS/CTS. If the receiver can't receive the transmissions on it's radio channels a robot may as well be a rolling jamming device. A robot that can't receive other transmissions it might interfere with, and with a demand to send, will just send on the same radio channels that are probably busy with other robots causing a collision. |
Re: Team 548 Einstein Statement
First of all I would like to say that the previous FMS discussions are extremely interesting. I kind’a like the “SUPER SIMPLE VERSION” the best. This is a very impressive analysis and the more I read the more confused I get. That is probably because my experience is not with electronics and code and “stuff”. Secondly they seem to have moved from the original purpose of the apology from team 548. This is all important information and maybe a new thread needs to be started and let the Team 548 Einstein Statement pass into history.
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Re: Team 548 Einstein Statement
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Alternately, you may find that they are trying to hide their own confusion in a cloud of vocabulary and acronyms. Don't be impressed, ask questions. |
Re: Team 548 Einstein Statement
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The situation (The Town Hall With Musical Chairs): 1. You have 7 blind people in a room and there are possibly 4 rooms. 2. They tend to speak at the same volume and they hear just as well as each other. 3. One of those people is the person that everyone is talking to (the key person). 4. That person stands with their back against the wall of the room looking into the space of the room. 5. The other 6 people move around the room blindly. 6. Everyone is trying to be polite and only speak to this key person one at a time. 7. There are invisible portions of the room that make it harder to hear each other (not only are the sounds from each other's perspective too quiet but the voices are too hard for some other people to hear). 8. Any moving person not heard from in a short period of time must stop moving till they hear someone. 9. When they talk it's basically one sentence of some random length at a time then they stop. 10. If someone can't talk for a while they experience a pile up of sentences they must communicate later. Knowing this: 1. If they knew they were in one of the quiet invisible portions they could just not talk and hurry out but they can't see that so they might talk when they should not. 2. If they all scream confusion will set in because just before they start screaming they might not hear someone else or they might be hard to understand at that extreme volume or they might disturb nearby rooms. 3. If they all whisper sometimes someone won't be heard when they are talking but at least someone will be heard if they are close enough to the key person. 4. If they all could just find the right volume they could all talk and hear each other but that volume changes as they move and they all move blindly. My solution: Let everyone talk at different volumes and adjust their volumes as they move. To do it requires communication about the perceived volume as each person talks. Sometimes someone will talk over someone else, but if they all start off slowly increasing volume between their movements it'll be less often they talk over each other and at least someone will get a clear word in edgewise. As long as the balance between volume changing, movement and time is set properly no one should be stuck anywhere for long or continuously talk over anyone else. Let's refer to that balance as being fair to one another. A. The key person is the Cisco 1252 field AP. B. The 6 blind people are the robots and robot APs. C. The voice volumes are the radio transmit powers. D. The rooms are the fields. E. The invisible portions are things that make the robot AP occasionally not receive or have other APs receive it's transmit. F. The short period of silence before which the people must stop is the robot enable that times out in 100ms. G. The sentences they speak of different lengths are the data communicated over the radios. H. The pile up of data they must send when they can't is a network congestion problem. I. When more than one person talks by accident at the same time it's a collision. J. A person in a quiet portion of the room talking because they can't hear someone else talking is a hidden node. K. The restriction on each person to listen for another talking before they talk is clear channel assessment. L. If someone screams into that room that would be a jammer but these people talking over each other serve the same function as that jammer would serve. I'm suggesting they are talking over each other too often right now. Further to link this super simple example and the other: The communications in this example dictates the size of that hole from the other example with the half dollars. If the communications was better perhaps that hole would be quarter sized instead of dime sized. Then it would be easier in the first place to send the half dollars. If the hole was a little bigger and the people stuffing the bits of ground up half dollar were more clearly and quickly communicating the whole problem gets easier. The alternate situation (The Moving Study Hall): I also suggested before that we have 12 people in the room. 6 key people and 6 moving people. Each key person talks with one moving person. In fact, we could strategically place some of the key people against the wall to keep them closer to a certain moving person. The concern that people have with 12 people is that the volume in the room would disturb the rooms next door. They can all be in that room and talk at the same time if they control their voice volumes properly. Sure sometimes they might disturb each other but they already disturb each other in the other example anyway. The basic conclusion: I figure some of this is just a question of controlling that 'volume' of the communications either way. If we can't manage to at least control the 'volume' of those 'voices', I think we should at least record the whole mess so we can find better solutions later. If we can't record everything, at least record the 'volumes' of the 'individual people' and how it is perceived by 'everyone' else. At least then we'll know there were 'quiet spots' in the 'room(s)' and 'who' was in those spots at what times. Sorry this is long but I hope despite it's length that it is very easy to relate to. |
Re: Team 548 Einstein Statement
I'm by no means an 802.11 or antennae expert, and I have seen engineers go for hours on trying to critique a single aspect of a lower-level layer of the OSI model for network communications.
Rather than debate network power, what if I instead just measure the efficiency of communication -- how long does it take for a given amount of data to be communicated. The radio tap header contains the data rate and encoding scheme. If it is low, well it could be for any number of reasons, but if it is high, approaching the theoretical limit, then that must mean that things are clicking along just fine. It isn't that hard to measure or even to log. Unless you have strong evidence that shows signal strength to be a root cause of many robot failures, I don't think this discussion will bear fruit. It can easily eat up many forum pages, but no fruit. Greg McKaskle |
Re: Team 548 Einstein Statement
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1. The necessary signal strength to balance, distance, throughput and interference will always be changing. Creating such a test was already presented in the thesis last page. Anything less than adapting (even if the adaptation is a shell script making the adjustment once a second) will surely have a short coming somewhere. Just the additional consequence of the movement of the robot APs. 2. It's not just the signal strength from the radio output but the antennas, the antenna placements and the competition for the channels (so which way one divides the 9 available radio channels matters as well as the distances between the users of each channel). So the only way I can envision finding the optimum or at least the 'good enough' for FIRST is active data collection and response. I have tried this with a bunch of APs just as a test and it worked fine. However, I'm not sure I consider my experiment to be a great proof of anything other than possibilities. I didn't design it to be comparative against FIRST just as a demonstration. I think Cisco now offers per-packet information headers (PPI headers) for 802.11n instead of radiotap (see also this). Radiotap offers IEEE80211_RADIOTAP_RATE but I'm not sure about the active encoding and PPI headers offers rate, but aren't these in units of 500kbps? I know they are making additions for VHT to accomodate 802.11ac. Also are the D-Link 1522s capable of tagging packets with information with the stock firmware? OpenWRT has some development work for radiotap not so sure about PPI headers. Not saying I'm against doing this just pointing out pros/cons. |
Re: Team 548 Einstein Statement
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I was using radio tap, but I'm sure there are other standards, and it will continue to evolve and improve as it plays a larger role in our everyday lives. Greg McKaskle |
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Re: Team 548 Einstein Statement
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This is not to say they don't have layers of responsive adaptation but as the thesis link demonstrated with Atheros chipset 802.11n development boards the responsive adjustment of transmit power to stike the best balance is not an existing feature. You can control the transmit power and it is effected by various existing settings but not in the manner I'm describing. Relinked as it's now a page back: Adaptive Transmit Power Control Based on Signal Strength and Frame Loss Measurements For WLANs Perhaps someone could find a device that has those features but that's a whole separate issue. Generally what I am describing is closest to: Aruba Adaptive Resource Management (ARM), Dynamic Radio Management (DRM), Radio Resource Management (RRM), and anyone else with their own WiFi architecture generally (my apologies Greg if that was your grander point). Of course if all the devices were from Aruba, Cisco or Extreme we could exploit their infrastructure as they decribe but I figure FIRST is not interested in spending that sort of money considering the robot APs. Also some of these adaptive infrastructures are probably a bit too slow at minute intervals given the duration of a FIRST match. Again they usually make the reasonable assumption your AP isn't bolted to a robot and dancing around. 802.11F does provide a channel for similar communications via inter-acess point protocol. Though it's not clear to me if that is currently extended from the Cisco 1252 in any way to mitigate the specific power concerns I've highlighted with any other vendor. I'm sure Cisco's RRM works just great with other Cisco devices (I'm using it right now). However, so far as I know currently Cisco uses LWAPP not really 802.11F for their RMM feature set. Given I have this feature working as a shell script pulling down the maximum radio power right now on some DD-WRT access points I know that FIRST doesn't need anything very fancy to achieve this basic balance. However, it's certainly not a feature you'll just get with random 802.11n hardware. |
Re: Team 548 Einstein Statement
This sounds like a great conversation to have on the 802.11 board. This thread is the wrong place to have it. This thread is about Team 548's Einstein Statement. This thread is not about your crackpot theories on beamforming or adaptive power control. Please stop hijacking threads.
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Re: Team 548 Einstein Statement
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My crackpot theories as you put it are backed by PhD level work yours are backed by....vapor. I'll write this again, The Einstein reports CLEARLY indicated that insufficient logs were kept. I did not make that mistake I merely pointed out where additional logging should be implemented. If you doubt my points log the data and prove it. Shifting blame like with 548's statement instead of being open and accountable is how this all got started and clearly some of you learned nothing. I've been more than tolerant of some of your blatant and often obvious discrimination. To the rest of you who treated me with some respect thanks for some consideration. |
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