Multiple Video Broadcasts Using Several Wi-Fi Bands

Dear Readers.

We would like to present the following scenario and then would like to ask for your expertise advice.

We have a need to install 40+ wireless video cameras in one single building. We would like to be able to view the video of at least 5-10 units all at once on a PC screen. But need to be able to switch to another group of 5-10 units without any kind of delay in rendering the picture or video. The switch should be instantaneous.

1. Will it be possible to have all 40+ cameras transmitting their signal all at once where the receiver is able to switch between a group of 5-10 cameras at a time ? What frequency band(s) would you suggest we use to transmit the video signal in order to achieve our goals ?

We understand that the 2.4GHz band has only 3 non-overlapping channels and the 5GHz band has 23 non-overlapping bands. We are not sure about the 3.6GHz and the 4.9GHZ Wi-Fi bands with respect to their bandwidth and the number of non-overlapping channels.

2. If it is not possible to have all 40+ video cameras all broadcasting their signals all at once then what would be the maximum number of cameras that can transmit their signal at the same time using any one or a combination of the above available legal bands ?

We understand using several different bands utilized by the many video transmitters we will need the appropriate tuner capable of receiving these different bands all at once. If it is still not possible with the parameter we have described above then please feel free to make any "out of the box" suggestions.

Thanking you

Victor

Yes, you can do it with multiple frequencies but your bigger problem for "the switch should be instantaneous" will be video synchronization. Each camera will have it's own sync pulse source and although close to each other in frequency they will not be in phase. This means your monitor equipment may need some time to react to the sync signals as it moves to a different camera. The effect will be a sideways slip or rolling of the picture as the source is changed and if you are digitizing the signal, an additional delay while the capture device re-locks to the new source.

There are ways around the problem, a frame buffer being the obvious choice but you need 40+ of them and that works out very expensive, another option, if the cameras have a sync input "genlock" is to broadcast a synchronizing signal from one source that each camera locks to. That brings them all into line so instantaneous switching is possible.

Brian.

I have already commented to this doubtful idea. There is no room in any Wifi or lower-microwave bands to carry so many video FM channels without interference.

In microwave radio transmission, one needs a free spectrum and good antennas on both link ends to be able to transmit several channels without interference. This holds for free-space, no obstacles, no interferers at close side band and wide angle separation of lines of sight.

Attempting to transmit many FM video channels through a building, with moving people, etc., cannot work.

Use optical fiber cables. They are low-cost and there will be no interference. Digital video to fiber interfaces are available. Such network can and will work.

betwixt said:

Yes, you can do it with multiple frequencies but your bigger problem for "the switch should be instantaneous" will be video synchronization. Each camera will have it's own sync pulse source and although close to each other in frequency they will not be in phase. This means your monitor equipment may need some time to react to the sync signals as it moves to a different camera. The effect will be a sideways slip or rolling of the picture as the source is changed and if you are digitizing the signal, an additional delay while the capture device re-locks to the new source.

There are ways around the problem, a frame buffer being the obvious choice but you need 40+ of them and that works out very expensive, another option, if the cameras have a sync input "genlock" is to broadcast a synchronizing signal from one source that each camera locks to. That brings them all into line so instantaneous switching is possible.

Brian.

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Brian thank you for your reply. We too believe that the deployment of so many canmeras will require the utilization of several different bands. From a similar post on this same forum we discovered that the 2.4 GHz does not have sufficient channels that will allow 40+ cameras to broadcast their signals all at the same time. As for your solution to the syncronization of each cameras signal I will need to study this in some depth in order to wrap my head around the terms and concepts you have explained. But thanks to you it appears that with adjustments to each camera this hurdle can also be overcome.

Thanks again.

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jiripolivka said:

I have already commented to this doubtful idea. There is no room in any Wifi or lower-microwave bands to carry so many video FM channels without interference.

In microwave radio transmission, one needs a free spectrum and good antennas on both link ends to be able to transmit several channels without interference. This holds for free-space, no obstacles, no interferers at close side band and wide angle separation of lines of sight.

Attempting to transmit many FM video channels through a building, with moving people, etc., cannot work.

Use optical fiber cables. They are low-cost and there will be no interference. Digital video to fiber interfaces are available. Such network can and will work.

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Hello jiripolivka thank you again for your reply. I understand your reply but would like to ask what specifically about the Wi-Fi band will prevent the deployment of so many cameras ? By spreading the 40+ signals across several bands would this not reduce if not eliminate the possibility of any adjacent channel interference. Also if there is a possibility of interference then will the idea of say having only 5-10 cameras broadcasting their signals at a time ? We need to be able to monitor a group of 5-10 cameras located in the same locale at a time. We are also unable to use a wired solution because it will add a high price tag to the overal cost. The only solution is a wireless solution at the moment.

Thank you for your reply.

Victor

How about adding 4 wi-fi routers or something like that? Then data from 10 cameras comes to nearest router and use one channel with better antenna to retranslate interleaved data to main Wi-Fi receiver? Think about big places with restaurants, shops, etc. with free wi-fi, where more than 40 peoples use internet and online videos. It all works because mobile devices Wi-Fi area is limited, and all places have their own routers that serve only nearest users. Camera antanna can be made smaller or attenuated, so it does not interfere with other router areas. So for each 10 cameras you have additional Wi-Fi box wich needs to be configured and provided with power, no data cords.

Victor43 said:

Brian thank you for your reply. We too believe that the deployment of so many canmeras will require the utilization of several different bands. From a similar post on this same forum we discovered that the 2.4 GHz does not have sufficient channels that will allow 40+ cameras to broadcast their signals all at the same time. As for your solution to the syncronization of each cameras signal I will need to study this in some depth in order to wrap my head around the terms and concepts you have explained. But thanks to you it appears that with adjustments to each camera this hurdle can also be overcome.

Thanks again.

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Hello jiripolivka thank you again for your reply. I understand your reply but would like to ask what specifically about the Wi-Fi band will prevent the deployment of so many cameras ? By spreading the 40+ signals across several bands would this not reduce if not eliminate the possibility of any adjacent channel interference. Also if there is a possibility of interference then will the idea of say having only 5-10 cameras broadcasting their signals at a time ? We need to be able to monitor a group of 5-10 cameras located in the same locale at a time. We are also unable to use a wired solution because it will add a high price tag to the overal cost. The only solution is a wireless solution at the moment.

Thank you for your reply.

Victor

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Dear Victor, in my opinion you have never worked with interfering systems. To get some experience, get two or three wireless cameras (one costs ~$20 with a receiver now) and try to run a pair in your environment. You will find what I wrote, that it cannot work.
Time sequencing is used in many camera networks but never by Wifi, only by cables.
Do not waste time and money, your idea will not work. Wifi is not designed for such purpose.

Using all available channels means you have no reserve for other Wifi applications too. One thing you can't do with live video is hold it up while something else is hogging the frequency. I too would not advise you to try such an ambitious aproach, you will run in to problems and it would be a huge investment to abandon. Wired camaras are always best and although you need lots of cable, it will still work out cheaper than the wireless option and it avoids all the RF path problems and interference at the same time.

Perhaps a half-way solution would be to select the cameras using distributed switches. Maybe 8 cameras connect to a selector circuit then connect down a single cable back to base. The selection being made by WiFi or cabled command. It excludes certain combinations of cameras being used simultaneously but if that's acceptable it would be simpler to implement and much cheaper.

Brian.

Terminator3 said:

How about adding 4 wi-fi routers or something like that? Then data from 10 cameras comes to nearest router and use one channel with better antenna to retranslate interleaved data to main Wi-Fi receiver? Think about big places with restaurants, shops, etc. with free wi-fi, where more than 40 peoples use internet and online videos. It all works because mobile devices Wi-Fi area is limited, and all places have their own routers that serve only nearest users. Camera antanna can be made smaller or attenuated, so it does not interfere with other router areas. So for each 10 cameras you have additional Wi-Fi box wich needs to be configured and provided with power, no data cords.

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Dear Terminator thank you for your reply. Your idea sounds very interesting. At the moment we are discussing the means for a feasible solution with a China based supplier. They are looking into using the bands 0.9GHz 1.2GHz 1.5GHz in order to allow 40+ wireless video cameras to operate without interference.

However I will be happy to address your ideas to them.

Very insightful thinking.

Victor

@Terminator3 thank you for your reply. Your idea sounds very interesting. At the moment we are discussing the means for a feasible wireless solution with a China based supplier. They are looking into using the bands 0.9GHz 1.2GHz 1.5GHz in order to allow 40+ wireless video cameras to operate without interference.

However I will be happy to address your ideas to them. Very insightful thinking.

Thank you

@jiripolivka thank you again for your reply. Yes you are right in fact I do not possess the experience with interference systems. No contest there. However as I mentioned to my reply to Terminator3 above we are working with an overseas supplier in implementing a design to ensure that all 40+ cameras are able to operate at the same time. More then likely the use of the Wi-Fi bands will not be used because as betwixt mentioned that this will prevent other Wi-Fi devices from using these same bands. I trust that our supplier will test the design to ensure that the system of 40+ cameras all work as designed prior to them being designated ready for shipping.

Thanks for your comments good job.

Thanks

@betwixt thank you for your post. I understand your reply and your point is well taken. As I stated in my reply to Terminator3 post it will be more then likely that the Wi-Fi bands will not be used because of the same reasons that you have described. I do understand that by using up all available channels in the Wi-Fi bands will prevent other Wi-Fi enabled devices from operating properly.

The only other idea that I have given some thought to is grouping say 10-20. Where this group of cameras will use only non Wi-Fi bands at a time. The grouping could be done in a matter of having say 10-20 cameras grouped by floor all broadcasting their signals at once and then switching to another group located on a different floor and so on. So the picture of only 10-20 will be available at a time. This will prevent us from viewing the video from the other groups though.

With respect to running cables this option at this point is just not feasible. The distances between the cameras and monitors could easily exceed distances of 350 feet not to mention having to pass cables through concrete floors and concrete stairwells. There will be at least two monitoring stations that will be configured to receive all wireless video signals.

Thanks again for this suggestion in the event a wireless solution does not materialize we may need to consider an alternative such as a wired approach.

Good point though.

Victor

Thank you for all three post.Your replies all have been very helpful. Thank you to all of you.

Terminator3 said:

How about adding 4 wi-fi routers or something like that? Then data from 10 cameras comes to nearest router and use one channel with better antenna to retranslate interleaved data to main Wi-Fi receiver? Think about big places with restaurants, shops, etc. with free wi-fi, where more than 40 peoples use internet and online videos. It all works because mobile devices Wi-Fi area is limited, and all places have their own routers that serve only nearest users. Camera antanna can be made smaller or attenuated, so it does not interfere with other router areas. So for each 10 cameras you have additional Wi-Fi box wich needs to be configured and provided with power, no data cords.

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Thanks for your feedback. Your idea is exactly what the maufacturer decided to go with. Thought you might want to you. Victor

thank you for letting me know, i am pretty happy knowing that