In this article I wanted to revisit the concept of 802.11b versus Bluetooth and provide an update on coexistence issues, potential solutions and the impact of the technologies on each other in terms of market acceptance.
802.11 and Bluetooth are not meant to be interoperable, so the key issue is that of coexistence, and this relates only to the 802.11 protocols operating in the 2.4 GHz band (i.e., 802.11b and 802.11g). Though the key concern is coexistence in the same frequency band, increasingly many product vendors are also concerned about situations where both technologies are collocated in a single system (e.g., a notebook).
Because Bluetooth is an aggressive frequency hopper it is not subject to much interference from 802.11b, but the opposite is not true. The degree of degradation of 802.11b data rates depends on the operating environment and the distance between the Bluetooth and 802.11b transceivers.
The interference with 802.11b is an important concern for Bluetooth backers for two reasons. First, many of them are also developers of 802.11b solutions and they want to see both technologies thrive. Second, in enterprise settings Bluetooth adoption may be curtailed as network administrators are focused first and foremost on supporting 802.11b.
One simple solution to alleviate interference is the use of Class 2/3 Bluetooth transceivers rather than more robust Class 1 solutions. Class 2/3 solutions provide an effective range of 10-20 meters while Class 1 solutions are closer to 100 meters.
System vendors implementing both technologies in a single system have a number of design solutions that they can rely on. They can interface the respective media access controllers (MACs) to make sure that only one radio is transmitting at a time (along the lines of the Intersil-Silicon Wave Blue802 solution), and they can adjust their antenna placement and use.
The degree of industry concern about Bluetooth and IEEE 802.11b is reflected in the fact that there are already two groups are studying the problem and looking to make recommendations. The Bluetooth Special Interest Group (SIG) has set up a WLAN Working Group and the IEEE 802.15 Working Group has authorized Task Group 2 (TG2). The TG2 is to develop a “coexistence model” to quantify the mutual interference and then develop a “recommended practice” for better coexistence.
In ABI’s view the most promising development has been the FCC’s changes to Part 15 rules to allow for adaptive frequency hopping (AFH). Frequency hopping solutions (like Bluetooth) no longer have to spread their signal over the entire 2.4 GHz band. Instead if they sense other technologies transmitting they can limit their hop sequence to just the unoccupied channels. This should in theory virtually eliminate interference posed by Bluetooth to technologies such as 802.11b that occupy a static channel while transmitting.
Collaborative vs. Non-Collaborative
In general there are two models for 802.11b/Bluetooth coexistence: collaborative and non-collaborative. Collaborative solutions are for those cases where both Bluetooth and 802.11b transceivers are in a single host device. The radios collaborate either at the MAC layer and/or the protocol layer to coordinate and schedule alternate access to the airwaves. Symbol, Mobilian, and Intersil-Silicon Wave are all using somewhat different collaborative schemes, featuring different levels of complexity.
Non-collaborative solutions are for those cases where there are two transceivers in two separate devices. AFH, which has been targeted at being rolled into the Bluetooth 1.2 specification, is the most promising non-collaborative scheme. However, ABI understands that recent delays in Bluetooth SIG work on AFH could mean that AFH will be an optional component of the Bluetooth 1.2 specification, rather than being mandatory. Bluetooth 1.2 is expected to receive final ratification in mid to late 2003. Therefore Bluetooth chipsets incorporating the official version of AFH are unlike to appear until late 2003/early 2004. However, Bluetooth chipset vendors such as Silicon Wave, Motorola and Zeevo have indicated that they plan to implement proprietary interpretations of AFH into their chipsets prior to the ratification of Bluetooth 1.2.
Overlapping Usage Scenarios
Bluetooth is really optimized for temporary connections (especially peer-to-peer), unlike 802.11 where most connections are for a longer duration and the access point is typically the central point of the network.
Bluetooth does not have the data rate, operating range, and handover/roaming features that a robust 802.11 network can provide. Bluetooth will more likely be used for brief bursts of data exchange. Conversely, 802.11 solutions are not designed to match the cost and energy consumption points that Bluetooth delivers.
The applications in which both Bluetooth and 802.11 could both be considered competing alternatives for example could include portable Internet audio players and digital cameras, where both Bluetooth and 802.11 could facilitate file transfer. Product vendors have to decide that if they can only support one technology whether they want the lower cost and better power efficiency of Bluetooth, or the higher data rates of 802.11.
In the long run the technologies should be complementary in most, but not all, applications. However, much depends on the relative cost of the different technologies, and the further innovations with 802.11.
Specifically Bluetooth must maintain a healthy differential to 802.11 in terms of the total cost of implementation. Also, with players such as Microsoft and Intel intensely focused in 802.11, there is potential for 802.11 to also be optimized for peer-to-peer applications and to encroach upon Bluetooth-type networks.
With new 802.11 protocols such as 802.11a and 802.11g and the decision to delay Bluetooth Radio2 (which is targeting data rates up to 12 Mbps), there will be a growing disparity in respective data rates. ABI believes that this will better help crystallize the respective applications that each is optimized for.
Both technologies will be better positioned to thrive if coexistence schemes currently being developed are broadly implemented. In addition, cost-effective combo 802.11/Bluetooth solutions should play an important role, as there are clearly situations where device vendors ideally need to support both technologies in a single host device for different applications.
Allied Business Intelligence Inc is an Oyster Bay, NY-based technology research think tank that offers expert advice and research on wireless, broadband, and emerging technologies. Details can be found at www.alliedworld.com or by calling 516-624-3113.