Wireless Surveillance Maintenance GuidelinesBy John Honovich, Published Aug 05, 2012, 08:00pm EDT
Maintenance for wireless surveillance is critical, far more so than for wired ones. If you install a wireless surveillance system and forget about it, it will soon be completely broken. In this note, we examine the most common problems and best maintenance techniques for dealing with wireless surveillance.
Top 4 Problems
Here are the most common problems in wireless surveillance we see:
- RF Cabling and Connectors
Wireless surveillance systems are typically mounted outdoors where access to power is challenging and exposure to the elements is common. Unlike wired systems where power can often be provided centrally from inside a building, wireless nodes regularly need access to power on rooftops or light poles. Probably the most common wireless problem, then, is power issues such as brown outs or power cutting out intermittently.
When remote wireless links are inaccessible, it can be hard to tell if the cause is power related, signal strength related, etc. However, we recommend first checking to see if power is available and stable. An issue might seem like a bad connection but simply be the result of bad power.
Antenna alignment is critical. Even slight shifts to the antenna can turn a solid system into a problematic one. Antennas can come out of line for numerous reasons - ranging from the obvious, like strong wind to less common but possible things like poles being hit by a vehicle or a birds mounting on the antenna, etc.
Unfortunately, you can have serious system issues even if the antenna only looks like it is slightly misaligned. As such, you may not be able to simply look up at the antenna and ‘know' that it is a problem. Instead, you will need to monitor the signal strength over time as we explain in a later section.
Obstructions - Physical
New obstructions are one of the most common reasons why a system that worked perfectly well at first suddenly suffers from major problems. Unlicensed, low power wireless that is typically used in surveillance deals very poorly with obstructions. Here are some common examples:
- You install the system in the winter and it works fine. A few months later, as Spring comes, leaves start to grow on a tree in the line of sight. Those leaves reduce signal strength and cause problems in video transmission.
- A few years after a system is installed, the system increasingly has problems. A tree that was once only 7 feet high is now over 12 feet and is in the way of the wireless link.
- A site is having construction done and every time a crane or lift is moved, the video quality drops. The security operators may not see the connection between the two. Rather they may just report it as a flaky system.
Typically you need to remove the obstruction or move the system (often higher to be above the instruction). Now, many wireless professionals argue that this is not a problem with the system as it was something newly added that caused this. Unfortunately and regardless of who is right, users will generally expect the system to function the same regardless of the introduced obstruction.
If you have connectivity problems and the power is good, obstruction issues are the next most common issue after antenna alignments. When installing, look for future potential obstructions (primarily vegetation) and consider putting that into writing as a risk / exception.
Obstructions - Other Systems
A nearby facility has added their own wireless system and is operating at the same frequency as your wireless surveillance system. The end user may see this as intermittent video quality problems. Switching to another frequency channel may resolve this.
RF Connectors and Cables
Over time, RF connectors and cables that link antennas to wireless nodes can have problems, caused by exposure to the elements. You can check for these problems by periodically undoing the connections and checking for the pin for moisture. If you find that, replace the connector.
Monitoring Signal and Noise Levels
To proactively maintain and identify problems, the most important step is to monitor signal and noise levels (with the goal of maximizing signal and minimizing noise). However, these levels can change over time. For instance, if an antenna is shifted or a tree grows, signal level can decline. When the signal level goes down, less bandwidth is available and video quality often suffers.
When turning over the system, make sure to document the signal and noise levels for every wireless link (plus any potential obstructions or site specific concerns, e.g., heavy winds in area). This will be your baseline to maintain and troubleshoot in the future. If the system is performing well at the beginning, this reflects a strong signal to noise ratio. Over time, signal strengths typically drop and noise may increase.
Periodically and whenever you have a maintenance call, you should check the current signal and noise levels. For instance, the system may start with a -72dB signal strength and a -98dB noise level for a Signal to Noise (SnR) ratio of 26dB. However, when you return, the signal may have dropped to -81dB. Even if noise remains the same, the SnR has now dropped to 17dB and the wireless link will no longer be capable of delivering the same throughput / bandwidth.
While signal and noise levels will tell you that the wireless connection has worsened, they cannot directly tell you want caused the problem. You will then need to go and check for misalignments, obstructions, RF connector issues, etc.
Establishing a Remote Connection
One major limitation in monitoring signal and noise levels is getting access to the site. The operators can only tell when they see video problems and they may easily miss it if the problems are intermittent.
A powerful tool in proactively maintaining a system is to have a remote connection into the site so you can easily look in and monitor key wireless indicators. Sometimes, VPNs are set up so that an integrator or service provider can do this. However, many large users of wireless surveillance systems have strict restrictions against such connections that might prohibit this approach.
Wireless Software Tools
While all wireless networking vendors offer real time reporting of signal and strength levels, it is uncommon for them to graph these levels over time or to provide alerts if the metrics hit a certain level. Both of these can be very useful - the latter to see trends over times (e.g., does the signal strength drop only at night or during the weekend, etc.) that might give clues and the former can help in quickly responding to emerging problems.
It is important to learn what monitoring tools a particular wireless networking provider offers and then try to make the best use out of them.
Maintaining wireless surveillance systems will never be easy, unless you outsource it to a cellular carrier (though that brings its own challenges). While wireless is often the right choice for large scale outdoor systems, never understimate the challenges that wireless brings.
For more fundamentals, read our training report on RF fundamentals for wireless surveillance.
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