Airspan and Freedom4 demo WiMAX roaming on a laptop
Roaming between WiMAX networks just got a boost after Airspan, an equipment maker, and FREEDOM4, a UK WiMAX operator, showed a laptop with a WiMAX USB dongle that allows the user to roam on WiMAX networks that use different spectrum bands. This is significant because it allows WiMAX operators to enter into roaming agreements with one another, across different countries, so that people who buy WiMAX service from one operator can simply use another operator’s network without additional fees or sign-up hassles. It is particularly interesting for users who want to roam between license-exempt networks or to licensed ones. Operators who own a very small slice of spectrum (say in the 2.6 GHz) can combine it with bigger slice (e.g. 3.6 GHz spectrum) to give users more capacity, and compete with 3G operators.
FREEDOM4 is a joint venture between the FREEDOM4 Group and Intel Capital. It is deploying WiMAX in the 3.6 GHz band in the UK. FREEDOM4’s service is available in Manchester, Milton Keynes and Warwick.
Download the technical specifications of the Airspan USB dongle.
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Here are my comments to the technical specifications of the Airspan USB dongle they are using in the Freedom4 network:
(1) The card does 17 dBm at (4/5) GHz. This means it does 50 mW. At (2/3) GHz it does 22 dBm, which is 160 mW. This is the problem with the base station architecture of WiMAX. The base station can put out a lot of power to reach the laptop, but the laptop has a small power budget and can't put out very much. You're not going to go very far with those power levels on those bands, especially with the types of antennas that they're using. This power level deficit is the main reason that Wi-Fi's architecture wins at delivering bits to an end user. You don't need much power to go a few feet which is just about all you need to do to reach a Wi-Fi access point.
(2) The 33 Mbps "throughput" is nice and beats what you get with a 3G cellco, but I doubt that you'll see anything close to that on a shared channel. This is the same issue you have with 3G service. It goes to hell fast when you get folks really pushing bits.
(3) Wi-Fi 802.11g or 802.11n beats both WiMAX and 3G cellco in pushing bits, hands down. Given this, I'd still rather be accessing a Wi-Fi access point somewhere than sipping bits from either of the other two offerings.
(4) A very disappointing aspect about this dongle: no support for unlicensed bands!
(5) I notice that they're planning on 700 MHz support. Uh huh, that will be the day to wait for!
(6) One last thing:
Remember under the current unlicensed rules, Wi-Fi devices can use power levels up to 30 dBm or 1W or 4W EIRP (in the US at least). This gives Wi-Fi a lot more wiggle room than WiMAX devices, given the way that community has decided to play the game.
To be fair, since WiMAX mostly operates in licensed spectrum, the operators can set power levels in their end user devices to whatever they wish them to be. However, they have to deal with the realities of the power budget of the end user device. Again, with Wi-Fi, you don't have to go very far, but with WiMAX you may have to go a bridge too far….
A limitation of WiMAX remains access to spectrum, particularly lower frequency bands that provide longer range and better foliage and building penetration.
As a technology, WiMAX is designed as a managed, wide area network that can be scaled to femtocell, picocell coverage areas. Licensed spectrum has the advantage of less restricted power and less interference and ad hoc sharing, but, of course, comes at the cost of spectrum licenses.
WiMAX has been looked at for use in unlicensed spectrum but runs up against the same requirements for use of contention based protocols and power/range limitations found in 802.11 Wi-Fi. Because Wi-Fi has already proliferated, use of WiMAX in unlicensed spectrum is commercially redundant and, therefore, unfeasible at this time.
Wi-Fi and WiFi MESH have shown their limitations in being used as wide area networks: for the most part Wi-Fi has proven to be unsuitable for metro area deployments because 2-5 times the number of MESH nodes have been required to achieve planned network coverage. In addition, Philadelphia and other cities where large deployments have been attempted have found it necessary to equip many users with higher power, higher gain antenna units, this blowing out the ‘everybody already has WiFi’ and, therefore, the low cost of Wi-Fi deployment to mass markets.
Neither Wi-Fi, WiMAX, or LTE change the laws of physics the determine how signals propagate at each frequency band.
The obvious solution to providing metro area broadband is to develop a system that uses multiple frequency bands: sub 1 GHz to achieve wide area services and rural broadband combined with higher frequency band operation to achieve higher granularity and higher per user bandwidth. Obviously back haul is a major issue. WiMAX and LTE are being developed to enable ’self back haul’ using an adaptive portion of the available bandwidth or alternative bands including 3.65, 5 and other semi-unlicensed or unlicensed bands. We will see much more on this over the next 2-4 years.. and probably major deployments.