Welcome to Unlicensed WiMAX!
I started Unlicensed WiMAX because there's a lot of confusion... and not a lot of solid information... about the subject of WiMAX technology used in license-exempt spectrum (unlicensed is a term more widely recognized, hence the title).
There are a number of products that purport to be "WiMAX" that operate in license-exempt spectrum, especially the 5.x GHz bands, and even some that operate in the 4.9 GHz public safety band. But such products are not true WiMAX.
To be true WiMAX products:
- An official "profile" for a particular portion of spectrum and some basic technical characteristics (channel size, FDD/TDD, etc.) must be created by the WiMAX Forum.
- A number of vendors must create products that purport to comply with the profile; there has to be a minimum number of products available for interoperability to "matter".
- A product that conforms to the profile must be submitted for interoperability testing at a testing facility officially sanctioned / certified / blessed by the WiMAX Forum.
- The product must pass the interoperability testing.
- Only then can the product be called, officially, "WiMAX"; the WiMAX Forum is both an interoperability test and a branding campaign.
All current "WiMAX" products that operate in license-exempt spectrum... all of them... fail this checklist at Point 1 - to date, there is no WiMAX Forum profile for using WiMAX in any license-exempt spectrum.
Until and unless a product meets all five points above, any product to date that purports to be WiMAX operating in license-exempt spectrum does not and can not offer any guarantee of interoperability, and thus offers no investment protection. Such products need to be considered proprietary.
Vendors fudge this a great extent and, when pressed, will concede the above points, and offer some (weasel-wording) "assurances" about the lack of real WiMAX compliance:
- Their license-exempt spectrum "WiMAX" product is fully compliant with IEEE 802.16d-2004 and "thus" will interoperate with any other product similarly compliant. This has some validity as 802.16d-2004 includes the 5.8 GHz license-exempt band.
- That they've conducted private interoperability testing "plugfests" with other major vendors.
- "Trust Us" - we're big enough and our systems are "high-end" enough that a firmware upgrade can fix any identified incompatibilities or issues or "Our systems are essentially Software-defined", so fixing problems is "just a firmware upgrade".
Point 1 fails because, as was vividly proven with 802.11 (no suffix - the original IEEE Wireless Local Area Network specification), it's quite possible to be fully compliant with a specification, and utterly unable to interoperate with another product that also claims to be "fully compliant with" said specification. Remember - "compliance" with a specification is purely in the "eye of the creator". While it's possible for an objective third party to certify compliance of a product / system against a specification... in practice, that rarely happens. (802.11 only succeeded, and wildly, when 802.11b was created with one and only one "physical layer" - Direct Sequence Spread Spectrum (DSSS) and the Wi-Fi Alliance began certifying interoperability and granting [and policing the use of] the Wi-Fi brand and logo.
Point 2 fails because private plugests are... private! They don't have to disclose what was tested against what, and even if successful, what was tested was particular products / systems at particular firmware revisions. Once those products and associated firmware is updated, the plugfest results are essentially moot - you have no way of knowing if any two particular License-exempt "WiMAX" systems will in fact interoperate.
Point 3 fails because, while you hope that your particular product will be supported by the vendor in perpetuity, the BWIA industry is rife with abandoned products... and even orphaned products when the vendor went out of business. One vivid example is Wi-LAN who offered a product line that used OFDM in the early days of WiMAX, that they assured buyers would be software-upgradeable to full WiMAX compliance. As I understand it, that never happened, and Wi-LAN soon afterwards ceased manufacturing of actual systems.
Your only real investment protections for License-exempt WiMAX systems, it seems to me, are:
- True, blessed, official WiMAX Forum certification / compliance / branding of a particular product / system.
- A vendor big / stable / "solid" enough, trusted enough that can offer very solid guarantees (like, in writing) of current and future interoperability.
So... there's lots to write about on the rapidly-growing subject of License-exempt / Unlicensed WiMAX. Feel free to write me with comments, suggestions, general feedback - anything - firstname.lastname@example.org.
By Steve Stroh
This article is Copyright © 2008 by Steve Stroh. Excerpts and links are expressly permitted (and encouraged.)