I’ve been hearing about WiMAX since 2003. Where exactly is it? It’s been 5 years yet not as much as a test infrastructure has been put in place. It’s vaporware folks. If anybody can prove otherwise, I’m listening.

Major WiMAX issues

1) horrible interference management
2) Inefficient MAC (very bad)
3) High Latency
4) Uplink budget sucks (due to ofdma (PAPR), 1, and TDD)
5) Exceedingly poor N=1 performance
6) Cannot do mobile VoIP reliably in N=1 config
7) Expensive PA due to PAPR (effects all OFDMA)
8) Dubious handoff quality on WiMAX
9) Very poor handoff mechanism 3G/2.5G to WiMAX
10) Poorly defined core network
11) Spectral efficiency worse than HSPA in loaded network
12) “We evolve quicker than 3GPP” Not really.

Should i go on. Its sub optimal and that is why they are doing two things; 1) pushing 802.16m, 2) Hype, hype, hype until 802.16m arrives.

In the end and you should consider this

Alaric,

Can you give me some background on how you arrived at your observations about WiMAX technology issues? We’ve been testing a WiMAX deployment in the middle of the U.S. for some time now without any of those problems you mention, and I’m curious to know why our experience is so different from yours.

We’re actually fairly impressed with this WiMAX stuff, given the fact it’s still wireless technology at the end of the day. 8Mbps down, 3Mbps up avg., optimal signal fades off about 9 miles out, still usable up to 14 miles away. The largest logistical issue we faced at installation was getting a large enough Internet pipe into the base station to service the rural deployment. In short, don’t tell me it doesn’t work – we’re already doing it!

FWIW, We’re running an Airspan fixed (802.16d) 3.65GHz deployment. I’m told that an upgrade to the mobile standard 802.16e (as soon as the standard is ratified and the product survives testing and certification) will require one additional server component and a software upgrade.

Estepona Apartments, what´s up neighbor, up in the hills here…

Wimax and Mobile Wimax do not exist.
Hey in the middle of the US…why so vague about yourself or where your deployment is….sounds like you don´t want anyone to check on it!!!
Shady

There’s truth to both Alaric’s comments and Anon’s experience with 3.65 GHz 802.16d.

First, consider Alaric. He is correct that mobile WiMAX will not support true 1:1 frequency reuse, in large, multi-cell deployments. Mobile WiMAX does have a “fake” way of doing 1:1 called segmentation where a 5 or 10 MHz channel can be divided into three independent segments (each with 1/3 of the OFDMA sub-carriers), which are then used for 1:3 reuse. It looks like each sector in a cell is using the total bandwidth but it’s not really 1:1 reuse; just a nifty way to get 1:3 reuse from a single channel. Real 1:1 is not possible because there’s just to much interference, even with all the fancy antenna processing concepts. The standard multi-cell deployment for moWiMAX will be 1:3, which means that carriers really need 15 or 30 MHz of spectrum to do anything reasonable.

I think the comment of the MAC being very bad is not fair. I’d characterize it as mediocre but comparable to HSPA and LTE. The latency is also not bad. I’m seeing ping times on best effort data ranging between 50-100 ms (this is on 2.5 GHz mobile WiMAX gear that’s in the certification pipeline). I think the HSPA numbers are much worse right now (remember, in 3GPP, most of the MAC resides in the RNC, not the nodeB). And VoIP that uses the moWiMAX QoS mechanisms (e.g. UGS) will get great latency (one way voice latency should be less than 40 ms).

The UL link budget comment is spot on, particularly the effect of TDD. When you’re constrained by UL coverage (which is ALWAYS the case), turning your transmitter off half the time isn’t helpful. This is where LTE will kill moWiMAX. With SC-FDMA in the UL and FDD, LTE will have an almost 10 dB UL link budget advantage, which is HUGE.

Anon, the reason you’re not seeing these problems are probably:

1) you don’t have a dense, multi-cell deployment where frequency reuse and interference is an issue
2) you may be using outdoor CPEs which give you a much more benign UL link budget
3) you’re rural deployment may be quite flat and you have a nice tall tower, leading to great RF propagation (hence the big coverage area)
4) you’re BS is lightly loaded with subs so MAC inefficiency isn’t as big an issue as in a dense deployment.

There’s a big difference between a dense urban or suburban deployment covering a thousand square km with 100000 CPEs doing mobility indoors vs a lightly loaded rural deployment with external CPEs. As with most technologies, your mileage may vary.

The issues have been explained pretty well by wirelessman.

I’ll add a few things. A lot of those issues are performance compared to HSPA+, EV-DO Rev B, LTE, UMB. So WiMAX does offer better performance in many regards against HSDPA and ev-do Rev A, though not a huge capacity boost unless you employ mimo on wimax and not the others.

Some of the issues become evident in a loaded multi-cell environment, particularly my complaints about interference management and N=1 issues (WiMAX’s get N=1 through fractional frequency reuse).

Others become more apparent in a mobile setting. Latency on the handoffs is apparently pretty high and combination of N=1, mobile handoffs, and loaded cells is apparently a pretty unstable and unreliable one.

Latency is also an issue for one of WiMAX’s advertised apps…mobile backhaul. No one will use it for mobile backhaul because the per hop latency is 10s of milliseconds and that is too high for that app.

If you have a fixed deployment and/or a lot of spectrum, and most fixed carriers do have a lot of spectrum, then you can make it work. You’ll also notice that intel and WiMAX are hot and heavy over MIMO. That’s because they use it as a bandaid to compensate for limitations elsewhere.

But…..certain WiMAX 802.16e weaknesses are an absolute deal killer for major mobile carriers (the ones that don’t have FCC coverage deadlines or who don’t get Intel capital for new spectrum in japan).

Those killers are the uplink budget and the N=1 performance in mobile setting. HSPA+ is really better than WiMAX in most regards. You can argue that Uplink budget is not an issue since mobile cells are small in places like Europe and Japan but that also effects capacity and QoS.