As I recall the 60 GHz band has the problem of major attenuation because the oxygen molecules resonate at 60 GHz which means normal free space loss linear calculations have an anomaly at that range (which is why there is so much spectrum for unlicensed use). You make an excellent point about all the other spectrum available. The problem is we also have to look at the business case of these networks on these frequencies. Since you do not have any chipsets being produced in the millions for these bands there will never be an affordable solution here. Unfortunately (or fortunately) the only reason our industry has been one that could remotely be profitable has been because of the consumer devices that have been adapted due to the cost factor. Traditionally microwave radio equipment has been expensive and mostly due to the almost hand made process for each radio since demand is so low. It's the whole job without experience argument...........
Thank You, Brian Webster www.wirelessmapping.com <http://www.wirelessmapping.com> -----Original Message----- From: Jeromie Reeves [mailto:[EMAIL PROTECTED] Sent: Monday, February 27, 2006 3:04 PM To: WISPA General List Subject: Re: [WISPA] Basic Mesh Theory So how much spectum is needed? 24ghz is fairly clean, 60 ~ 70 is very clean. The problem is NOT the lack of spectrum. It is the lack of gear for the spectrum that would do well for mesh. Low range (oh noes low range!) high bandwidth and low noise. The short range will help with self interferance a lot. The 7ghz (yes, seven ghz of band space) is enough for 56 100mhz channels that are non over lapping channels with a 12.5mhz upper/lower gard band, then toss in cross pol. Ive seen some gear for this band but it is to costly right now for what it does. We need a SoC with 2 or 4 radios, 50~100mhz per radiowith a 2nd seup with 2 ~4 radios ad 200~400mhz per radio. Jeromie Jack Unger wrote: > Brian, > > Exactly. You hit the nail on the head. The high noise levels combined > with not enough license-free frequency space combined with > unrealistically high traffic-handling expectations is going to doom > most public Wi-Fi-based municipal networks to extinction while at the > same time, polluting the license-free spectrum that a responsible, > RF-smart, wireless ISP could have used to deliver reliable service to > some subset (limited by the available license-free frequency space) of > that city's citizens. > > Maybe the RF-smart WISPs will decide to reach out to their cities and > make a case for working together to improve public wireless broadband > access. If WISPs don't work with their city, then the city usually > turns to a mesh vendor who will, in most cases, promise more than the > technology (for the reasons you pointed out) can deliver. Even worse, > large cities are turning to the Earthlinks and Googles of the world, > as if the Earthlink or Google name is somehow going to bend physics > and make these networks work. A big corporate name, as we all should > know by now, does not change the way that RF propagates, or the way > that interference and spectrum pollution slows down network performance. > > Thank you for sharing your thoughts, > jack > > Brian Webster wrote: > >> Jack, >> Let me jump in with some more thoughts on wireless mesh: >> >> I agree with you that RF engineering and RF limitations are not >> being fully >> considered in most mesh deployments. Most mesh designs I have seen are >> theory based and assume the full use of the unlicensed spectrum at hand. >> This will never be the case and therefore limits the overall >> capacity. I saw >> an RFP from the city of Miami Beach and they had done a pre-survey of >> the >> city and found the noise floor at 2.4 GHz at -70 db in most areas. >> Now how >> is one going to deploy a mesh network with the ability to overcome that? >> Typical answer is build more nodes closer to each other so these PDAs >> and >> laptops get enough signal. This ignores the fact that all of these close >> spaced nodes then create more noise for each other because they are >> mounted >> at a height where they hear each other. In high density nodes even >> having 2 >> hops will bring these networks to their knees. There is not enough >> spectrum >> to make it work and be able to load the network up. An 802.11b based >> system >> can not deal with the hidden node problem effectively enough. Even if >> you do >> have all the internode traffic on other frequencies at the high density >> placement required in most cities, the spectrum limits are still a >> big issue >> to have the channels to link all the nodes. I would still like to >> hear of a >> mesh network from any manufacturer that has been deployed and has a high >> density of users that are the kids of today. I want to see what bit >> torrent, >> VOIP and audio streaming do to a mesh in multiple hops. While we can >> make >> the argument that those services can be limited, that is only a band-aid >> approach as today's society is going to expect to be able to use these >> services in one form or another, it may take a while but it will be >> necessary. The cellular companies are already creating the >> expectation for >> this kids to be able to audio stream on demand. If someone has >> knowledge of >> a loaded mesh network please let me know. Don't get me wrong, I love the >> idea of mesh and wish it could work and want to see it work. It's >> just that >> I've been in ham radio since 1989 and was in to the packet radio >> technology, >> we as hams built networks where we dealt with all of these issues (I >> know it >> was only 1200 baud but the problems remain). There are two major >> problems >> in mesh from my viewpoint. One, if you have a carrier sense based >> collision >> avoidance system, you always have limited capacity because only one >> radio >> can talk at a time (part of the HDX problem). Two, if you do not have a >> carrier sense based system then you can overcome noise with a stronger >> signal. This causes cell site shrinkage or breathing and changes the >> coverage area. Most people deal with this by building transmitters >> closer to >> each other, problem is that there is limited unlicensed spectrum >> which is >> not enough room for most systems to deal with this. >> I really would like to see mesh work and hope to be proven wrong. >> There is >> a lot of promise in mesh implementations out there but until I have seen >> them under residential internet use loads I remain skeptical. >> >> >> >> Thank You, >> Brian Webster >> www.wirelessmapping.com <http://www.wirelessmapping.com> >> >> >> >> -----Original Message----- >> From: Jack Unger [mailto:[EMAIL PROTECTED] >> Sent: Monday, February 27, 2006 1:46 AM >> To: WISPA General List >> Subject: Re: [WISPA] Basic Mesh Theory >> >> >> Jeromie, >> >> You raise some good points... and here are some more differences between >> Matt's fully-meshed WIRED network example and the real-world conditions >> under which WIRELESS mesh networks are so often deployed today. >> >> 1) REROUTING - Only a node failure or a high peak traffic load would >> normally force a routing path change on a fiber/copper network. On a >> wireless mesh, routing path changes will also result from interference >> caused by other same-network nodes, interference from other networks, >> and interference from other wireless non-network sources. Routing path >> changes will also be caused by the movement of obstructions and other >> rf-reflective objects such as trees and vehicles. >> >> 2. CAPACITY - Fiber/copper networks typically start out with >> high-capacity (compared to wireless) full-duplex links. Wireless mesh >> networks start out with low-capacity half-duplex links. >> >> 3. CONNECTIVITY - Fiber/copper mesh network nodes have two or more paths >> to other nodes. "Real-world" wireless mesh networks may contain nodes >> that, in some cases (the traditional "mesh" definition not withstanding) >> only have a path to one other node. For example, obstructions may block >> paths to all but one (or even no) other nodes. >> >> 4. ENGINEERING - Fiber/copper mesh networks are typically properly >> engineered for traffic-carrying capacity, QoS, latency, etc. >> "Real-world" wireless mesh networks are typically deployed in near-total >> ignorance of the Layer 1 (wireless layer) conditions. That's the great >> attraction (IMHO) of muni-mesh networking today. These networks are >> thrown up in the belief that they don't need any Layer 1 design or >> engineering expertise and that this will allow for quick, widespread >> deployment. Last time I looked however, there was still "no free lunch". >> I predict that the muni >> mesh networks that are "thrown up" today (Philadelphia will be a prime >> example, unless it's re-engineered correctly) will fail and fail >> miserably to meet the high expectations that have been raised like free >> or low-cost broadband for all. In addition, muni mesh networks today >> typically lack adequate traffic engineering and performance testing >> under load. >> >> The way that muni networks are being marketed today will likely lead to >> a black eye for the entire license-free wireless broadband industry >> within 18 to 24 months. >> >> I'm not saying that wireless mesh networks should never be used. There >> are certain (obstructed, short-link, low capacity) environments where >> they will be the best, most economical solution. I'm just saying that >> the false claims and marketing hype surrounding MOST (and let me repeat, >> MOST) of today's mesh networking claims, particularly mesh network nodes >> that contain just a single 2.4 GHz radio are going to come back to bite >> both the vendors and the cities that deploy these networks without >> sufficient wireless knowledge in the false belief that wireless mesh >> networks are just "plug-and-play". >> >> Sorry about my rant, but other than a few responsible >> multiple-radio/multiple-band mesh equipment vendors, the current mesh >> marketing/hype environment is in a word - disgraceful. >> >> jack >> >> > -- WISPA Wireless List: wireless@wispa.org Subscribe/Unsubscribe: http://lists.wispa.org/mailman/listinfo/wireless Archives: http://lists.wispa.org/pipermail/wireless/ -- WISPA Wireless List: wireless@wispa.org Subscribe/Unsubscribe: http://lists.wispa.org/mailman/listinfo/wireless Archives: http://lists.wispa.org/pipermail/wireless/
