Or Limitations of Point-to-point and Point-to-multipoint Systems for Real-time Video
This is continuation of the discussion on “Why wireless mesh” that got started when I tweeted out my article for SMD last week: Wireless Mesh for Video Surveillance: Why and How. We do get these comments: wireless mesh is expensive, why wouldn’t you use a much simpler and cheaper point-to-point links for video surveillance? Our competitors in the point-to-multipoint space, including fixed WiMAX or ‘WiMAX-like’ systems, echo that by saying that mesh is very complex, multi-hop creates ‘unpredictable environment,’ while point-to-multipoint is deterministic, and therefore better for video.
Disclaimer, before I get underway: low-cost Wi-Fi based point-to-point links have their time and place in video surveillance. If you need to connect a couple of outlying cameras across your parking lot, you can successfully use point-to-point links. We have our own point-to-point product line for exactly these scenarios. However, for the purpose of this article, I’ll focus on deployments with 15 camera locations or greater – a campus, downtown, or industrial site type of environment. The number 15 is somewhat arbitrary, but this is approximately when a lot of wireless providers start having challenges supporting real-time high-resolution video.
PtP and PtMP networks quickly run out of usable spectrum
Compared to point-to-point and point-to-multipoint systems, mesh differentiator is and always has been the ability to “repeat” the signal, and therefore extend the reach of the network beyond the first hop. Eventually PtP and PtMP wireless systems run out of usable spectrum: in order to achieve a clear line-of-site (required at 2.4/4.9/5 GHz), they are forced to radiate from at least one high point (tower or tall building). This fills the airwaves with a chosen band of frequencies, which are limited in number.
Mesh avoids this issue by being able to isolate the RF signal. Radios are typically mounted on street poles where the RF can be directed between buildings and trees in a given pathway back to a final destination, through a series of repeater nodes in a multi-hop configuration. Because the frequencies can be reused along the path, the same limitations of PtP and PtMP solutions do not apply. However, Firetide is the only mesh product that also maintains the low latency, high capacity and distributed architecture required for real-time video, which is why we excel in this space.
Transition to MIMO creates more challenges for PtP and PtMP
It’s also important to note that as the wireless manufacturers move from 802.11a/b/g to 802.11n-based systems, channel size increases from 20 MHz to 40 MHz. That equates to 2 channels in the 2.4GHz range, 1 channel in the 4.9 GHz range, and 11 channels in the 5 GHz range. In other words, 802.11n cuts down the available number of channels by half which will limit the scalability of P2P and P2MP systems even more.
Rigid architecture of PtP and PtMP not the best at handling challenging environments
RF considerations aside, PtP and PtMP system also face other challenges. As I already mentioned, PtP and PtMP systems require tall assets to place the base station in every sector of coverage. We’ve won deals over these providers just because these tall assets (rooftops of privately owned buildings) could not be secured in sufficient quantities. The same challenge applies to industrial facilities, where deploying mesh can be the alternative to constructing towers.
In dense urban environments, even if you do get access to rooftops, the topology of “urban canyons” is such that you cannot achieve LOS from the rooftops to all the camera locations, which requires you to go street level. So that takes us back to street-level coverage with multi-hop, which can only be delivered by a mesh topology. In one city-center deployment – because of dense foliage – we had to shoot under the tree canopy; no point-to-multipoint system can do that.
Of course, you could string point-to-point links and achieve the same mesh-like topology, but then you’ll run into issues of latency and jitter, as you are switching between one PtP link to another. This is most evident in bandwidth intensive applications, such as video, which is why products like Ubiquity or Tranzeo, along with other Wi-Fi products out there, will never be good for more than a handful of cameras in a given geography. The cost advantage is also reduced: you need 4 PtP radios for two links, vs 3 mesh nodes for the same 2 connections. So no dice with PtP either.
Capacity limitations in PtMP lead to high costs of deployments
There are virtually no capacity limitations in PtP space; you can get up to 1 Gig links, from providers such as BridgeWave. So I’ll address the capacity limitations of PtMP systems that we compete with for video surveillance deployments. WiMAX, which is being touted by WiMAX providers as the solution for real-time video surveillance, today delivers only about 30 Mbps of capacity per base station, divided by the number of subscribers. (Theoretical data rate for a fixed WiMAX system is 70 Mbps, so real-world 30 Mbps is generous). A typical standard resolution video camera outputs a 2-3 Mbps video stream, a 1080p HD cameras requires 5-7 Mbps of bandwidth (using H.264), and a 12 megapixel camera can hit as high as 30 Mbps. So you do the math.
According to IMS Research, by 2013 revenue from HD and megapixel cameras will equal that from standard definition cameras (see Day 1 ISC West 2010 Impressions). These systems will be challenged even more as user adoption of HD and megapixel grows.
Mesh is expensive, but vastly less so compared to fiber
To the final argument: “mesh is expensive.” Our solution is not cheap, especially compared to low-cost PtP. But for these types of deployments that I was talking about, low-cost PtP is not the true competitor. The alternative (or the starting point) in the customer’s mind is often fiber – and fiber is vastly more expensive than any type of wireless. In fact, 90% saving off fiber infrastructure is the number I heard just recently at ISC West from our integrator who priced out fiber vs Firetide’s MIMO mesh infrastructure.
In summary, yes, point-to-point links are sufficient for small scale deployments, and you may not need mesh in this case. However, as you move beyond a few links, multiple point-to-point links become very complex to manage, and you’ll ‘gain’ in network management headaches and poor performance what you saved on cost.
For additional discussion on the topic of wireless mesh for video surveillance, see:
- The Many Interpretations of ‘Wireless Mesh’
- Why Flexibility of Mesh Topology is Important for Video Surveillance
- Defining Mobile Video – Notes From IWCE Wireless Killer Apps Panel
- Is Wireless Video Surveillance ‘Easy‘?
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