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компромат от конкурентов ZigBee http://www.z-wavealliance.org/modules/iaCM-ZW-PR/readMore.php?id=168820736
(Mar 22, 2007) WLAN INTERFERENCE CASTS DOUBTS ON ZIGBEE, 15.4Recent findings from an independent European manufacturing group have confirmed existing doubts about the viability of wireless control products based on IEEE 802.1.5.4, such as those from the ZigBee community, within the framework of typical residential wireless local area networks (WLAN). The findings, which were published in a recent white paper, showed substantial and frequently debilitating levels of signal interference between devices based on so-called "15.4" and typical residential WLAN technologies, such as IEEE 802.11 (Wi-Fi) and all its variants. The measurements clearly demonstrated that control products using 15.4 technology are seriously compromised and often inoperable even within the most basic residential WLAN. Real World Conditions Are Too Much For ZigBeeTriggered in part by earlier reports of interference problems, comprehensive simulations of WLAN interference against ZigBee and other 15.4 based devices were conducted by employees of leading 15.4 and ZigBee chip vendors last year, and published as part of the IEEE802.15.4-2006 version of the specification. Despite clear evidence of harmful interference levels, these findings went largely unnoticed, overshadowed by the marketing efforts of the ZigBee community.By contrast, WLAN interference tests in Europe were conducted by an independent OEM manufacturer under conditions that closely resemble typical European and US residential and commercial environments. None of the measurements and simulations quoted in the new report came from a ZigBee competitor.The results confirmed existing independent industry observations, which had previously concluded that common WLAN environments based on IEEE 802.11 unavoidably cause significant and even debilitating interference with 15.4 devices. Previous test results shown by the ZigBee community had summarized 15.4 as an operable technology within a residential or light commercial environment where WLAN traffic is also present. However, those tests were conducted under overly unrealistic conditions. For example, some tests measured the ZigBee link over a short distance of only 2-3 feet, while placing the interfering WLAN some 20 to 50 feet away; hardly characteristic of a typical home setup. Other tests operated the WLAN only at unrealistically low network loads, not taking into account typical home activities such as web surfing, VoIP and email, nor to mention video and audio streaming. Moreover, the earlier tests did not take other important real-world considerations into account, such as the dramatic degradation of command response time that 15.4 devices would display in a typical WLAN environment, and the effects of battery life shortened from multiple years down to weeks. The Best Products Still FailedIn the study, four market-leading 15.4 products were tested within a typical single-story residence with carpeting and a combination of brick and sheetrock walls. Other available 15.4 devices were pre-emptively rejected as test subjects because even without WLAN interference, their RF performance was judged to be far below the expected performance quality of such devices. The WLAN interferer was operated at varying distances to the victim receiver, so as to reflect typical installation scenarios. These ranged from having both devices in the same audio-video rack all the way to installations of WLAN anywhere in the house, even approaching the maximum range a WLAN can achieve under ideal circumstances.Even under these non-taxing conditions, the observed data was conclusive:• If both WLAN and 15.4 are resident in the same audio-video rack or present in devices that are only 2-3 feet apart from each other, the interference from WLAN blocks 15.4 signals, independent of which channel is used by the 15.4 device.• If the 15.4 device is operated in a channel that is “between” or “besides” the non-overlapping WLAN channels, the level of WLAN interference causes packet error loss rates in the same room, making 15.4 devices unusable and also degrading the response time and reducing battery life for all other 15.4 devices in the home.• Even if the use of RF channels by WLAN and 15.4 is ideally coordinated in one home, WLAN devices used by a nearby neighbor or public Wi-Fi network can easily create harmful interference. In summary, the claim of the ZigBee community of the existence of “safe” 15.4 and ZigBee channels that are immune to WLAN interference is contradicted by the test results. Further, the test results also showed that ZigBee's current attempts to implement an automatic change of the 15.4 channel (a solution planned for release in future products several years away) is futile for many applications that would be critical to the success of ZigBee.More Interference To ComeIronically, the consistent test conclusions were reached under conservative conditions that were designed to show a minimum level of WLAN interference, and deliberately underestimated the level of interference one would experience from a typical residential WLAN. For example, the tests used only a single WLAN device as the "interferer." Actual interference in home environments would almost certainly be higher, considering that many, if not most households have multiple WLAN devices, and often more than one WLAN. Even these conditions don't take into account a neighbor's WLAN, nor situations where many wireless devices would be operated at the same time, as they might be in a typical home. Applications based on ZigBee or 15.4 that are designed to operate over multiple years using battery power face an even higher risk. Any installation of a nearby WLAN, e.g. at a neighbor’s house or apartment, a city network or other public service, could degrade the operation of ZigBee at a later stage. The fact that this high risk of interference from WLAN is well known – from both simulations and tested measurements – would expose corresponding ZigBee vendors to the risk of litigation and tort.With the emergence of new high definition video and audio "streaming" products designed based on 802.11n and other WLAN technologies, the amount of interference in a typical home WLAN will increase exponentially in the near-term future. It is clear that 15.4-based control technologies attempting to co-exist within this framework will face even greater challenges regarding reliable or even achievable operation. Technologies that operate in frequency bands that are impervious to Wi-Fi interference are emerging as the obvious choice for control applications in today's wireless homes. Due to a sub-1-GHz band design, Z-Wave technology has clear advantages that loom definitively in the wireless control space.# # #Read the White Paper: WLAN Interference against IEEE 802.15.4