Diary 42

The World of 5.8 GHZ Unlicensed

During the 3 years of this NSF project, many changes have been occurring in unlicensed radio technology. In fact, there has been a virtual explosion in 2.4Ghz technology, the next step up in the ISM Bands from the useful 915Mhz radios which, because of the their relative tree and vegetation-penetration qualities are ideal for most low-bandwidth field data collection.

The arena of 2.4Ghz has rapidly evolved into what is popularly known as the 'Wi-Fi' radio bands and services, though more accurately known as the 802.11b standard radios. While their vegetation-penetrating capabilities - as a function of both operating in higher frequencies than 915Mhz and much lower power in most products (100mw instead of 1 Watt as in Freewave radios) - make them far less suitable for field data collection through woods, or rain forests, they are useful for full motion audio-video tasks - such as our installations now on Hog Island.

The explosion in development and marketing of such higher frequency, higher bandwidth (10mbps and up) radios, has now, most recently spawned a growing number of digital radios which operate in the 5.2 to 5.8 Ghz ranges.

There are two sets of FCC rules for unlicensed digital radios operating in the 5Ghz area - Spread Spectrum Part 15 Rules, and UNII rules which do NOT require spread spectrum technologies. As a consequence there are many variations of radios using both technologies - and concomitant rules - now on the market.

The industry is moving so fast that even now there are further standards for radios, such as 802.11a - which is in the 5.8Ghz zone, but pushes data at 56mbps. And right around the corner is 802.11g which will be in the 2.4Ghz zone, at 56mbps, but will be 'downward compatible' with the slower (10mbps) 802.11b Wi-Fi Radios.

We shall examine the utility of such radios for the support of field science.

But below is a lucid explanation of the complex relationships, rules, and product lines by Patrick Leary, a very knowledgeable employee of Alvarion - which started out as 'Breezecom' radio company. It was first posted on the Wireless ISP maillist. And is here reproduced with permission.

-------------------------------

1. FCC Rules

The regulatory rules governing 5GHz are more complicated than 2.4GHz. The complexity guarantees market confusion since most view it within the context of their understanding of 2.4GHz. For WISP purposes, 2.4GHz is fairly simple to understand; there is just one range of band within 2.4GHz (2.4000GHz-2.4835GHz) and only 1 set of rules (the ISM rules).

Things get messier in 5GHz. The FCC has 2 sets of rules that govern 5GHz: the ISM (Industrial, Scientific and Medical) rules and the U-NII (Unlicensed National Information Infrastructure) rules. To further complicate things, U-NII rules breakdown 5GHz into 3 different ranges of 5GHz band and each range has different power rules. The FCC has allocated the U-NII specifically for high-speed digital communications.

The ISM rules -- the same rules that govern 2.4GHz - apply to the 5GHz range of 5.725GHz-5.850GHz for a total of 125MHz. That is a good bit more than the 83.5MHz we can use in 2.4GHz. The ISM rules basically require spread spectrum type technologies such as DSSS and FHSS. Like the other ISM bands of 902MHz-928MHz and 2.4GHz-2.4835GHz, the FCC permits a wide range of devices to operate in this range, not just communication devices.

Table 1 below details the band ranges and their basic rules. You will note that ISM and U-NII actually overlap at the upper end of 5GHz. This creates even more confusion for some. However, notice how the low and mid U-NII band can't be used by ISM devices; these ranges can only be used by digital radio devices.

Table 1.

5GHz bands and basic rules	Band Range	Maximum Power Usage Area
ISM 2.4-2.4835	1 watt max	indoor and outdoor
UNII 5.15-5.25	50mW or 4dBm+10LogB	indoor ONLY
UNII 5.25-5.35	250mW or 11dBm+10LogB	indoor and outdoor
UNII 5.725-7.825	1 watt max or 17dBm+10LogB	indoor or outdoor
ISM 5.725-5.850	1 watt	indoor or outdoor

 

In the view of makers of WLAN products, ISM 5GHz represents a major negative. Why, because 2.4GHz is home to everything from microwave ovens to WLAN. The WLAN crowd wants virgin, dedicated band, free from the bad stigma 2.4GHz gets (deserved or not). Indeed, the promise of a pristine band is the source of much of the hype surrounding 5GHz. This is the primary reason the commodity WLAN builders will likely stay out of the range of 5GHz band where ISM rules can apply and other devices can play.

As well, since the ISM rules specify spread spectrum, next generation technologies like OFDM can't live there. [There is a temporary exception to this granted on behalf of Wi-LAN and pending a permanent rulemaking.] The U-NII rules allow for more advanced signaling like OFDM. That is why the 802.11a OFDM WLAN standard applies to U-NII bands, not ISM. This promise of virgin bands plus the ability to use newer technologies will drive the mass of the WLAN market to build product mostly for the low and mid U-NII bands. That includes chipmakers since they are interested in the mass of the wireless market, which is WLAN, not wireless broadband. By contrast, those in wireless broadband want the higher power offered by either the 5GHz ISM range and the upper U-NII, but builders of such product will be much more limited than is experienced in 2.4GHz.

2. Applicable standards

IEEE 802.11a

Currently, the only IEEE standard applicable to 5GHz is the 802.11a OFDM standard that defines speeds up to 54Mbps. [Certain realities of communications protocols, like the delay that occurs between packet acknowledgement, will keep the effective throughput probably less than 1/2 that]. Like all 802.11 and extensions, 802.11a is designed specifically and solely for wireless LAN applications.

Confusing to the marketplace, 802.11a does not define just one range of band like 802.11b. The 802.11a standard can be used in any of the U-NII bands. This means not all 802.11a will interoperate. As well, as discussed previously, most 802.11a products will use the low and mid U-NII bands to avoid interference. To prevent low U-NII band products from being used outdoor, WLAN vendors using this band use fixed antennas on their WLAN products. The first chips built for U-NII indeed use this low power band.

Many customers and prospects are hoping vendors will soon ship mid and upper U-NII 802.11a products with external connectors in hopes that this will be the answer to their wireless broadband needs. However, just as 802.11b forces major tradeoffs when deployed for wireless broadband, careful considerations must be made with 802.11a as well. In the words of our Chief Scientist, Naftali Chayat, from his recent article in EE Times, "The parameters of the OFDM need to be carefully matched to the environment. In the 802.11a WLAN standard, for example, the FFT interval is 3.2 microseconds, while the guard interval is 0.8 microseconds - commensurate with the longest indoor multipath. For outdoor systems longer guard intervals are needed and the FFT interval is made longer to maintain efficiency."

IEEE 802.16a Wireless HUMAN

Earlier this year, the IEEE ratified the first wireless standard created specifically for outdoor wireless metropolitan area networks. However, as ratified, 802.16 only covers bands above 10GHz. An extension to 802.16, identified as 802.16a, is in development. This extension defines a version of the standard for unlicensed frequencies, specifically 5GHz. Called wireless HUMAN (High-speed Unlicensed Metropolitan Area Network); 802.16a is expected to be completed some time in fall 2002. 802.16a will implement air protocols optimized for PtMP in large outdoor deployments. Accordingly, it will be far superior than trying to use 802.11a. It will tailor the protocol to deal effectively with the diverse range packet sizes experienced in wireless broadband, such as very small voice packets. The standard will enable the base station to collect information on the traffic demands and allocates time accordingly. "By grouping the uplink transmissions together the waste due to turnaround time is minimized as well. This is the baseline mechanism incorporated into 802.16 MAC," continued Naftali in his article. Many in the market are hoping that the forthcoming 802.16a will do for wireless broadband what 802.11b did for wireless LAN - serve as a catalyst that encourages mass adoption of wireless broadband, thus creating volumes sufficient to drive down CPE prices. Unfortunately, no one can build an 802.16a product until the technical choices for 802.16a are resolved and there are thus, of course, no compliant 802.16a on the market.

Patrick J. Leary, BWA Evangelist, Alvarion

Executive Committee Member, WCA/LEA

office 352.592.5409 cell 770.331.5849

patrick.leary@alvarion.com