Moray Rumney, Lead Technologist at Agilent Technology is quite outspoken about the negative impact of what he calls "Peak-Rate marketing in telecommunications", i.e. the gap between proclaimed (theoretical) data rates of wireless systems and realistic data rates and capacity achieved in practice. I fully agree with his arguments and will also discuss this topic in my next book. In the latest Agilent Measurement Journal, Moray looks at the topic again, this time from the point of view of how Femto cells could positively influence the data rate and capacity equation in the future. His argument is that the effect of adding a femto layer (Wifi or 3G/4G femto cells) in an overall network architecture increases throughput and overall capacity by orders of magnitude while increasing theoretic peak data rates of macro cells does relatively little in comparison. An article not to be missed, it starts on page 52! Also interesting from a wireless point of view is the article starting on page 25 about resolving design issues in HSPA mobile devices. Earlier issues of the journal can be found here.
Category: WiMAX
WiMAX Frequency Implications
WiMAX world recently published an interesting article by Caroline Gabriel on spectrum and auction issues for Wimax (and other wireless technologies). A very good read!
I find it very funny how time changes opinions. Some years back, BT couldn't get rid of their mobile branch soon enough. Now, they can't wait to buy spectrum and to start from scratch. Total insanity, but it reflects the reality in my opinion that in the future, only operators being able to offer fixed (via Wifi) + cellular wireless access will remain relevant.
So far, I always thought refarming 900 MHz frequencies was a good idea. After this article I understand the political dimension of this a bit better. I guess some operators are hoping that they can use their current spectrum indefinitely and for a very low price if they can escape an auction.
I guess this would be a major disadvantage for potential new entrants. 900 MHz is great for indoor coverage especially in cities, as even 3G coverage at 2.1 GHz fades away very quickly indoors. So if new entrants wouldn't have a chance to get such bands in the future, they would be at a constant disadvantage everywhere, not only in the countryside.
As a user on the other hand I don't want to wait until 2020 before I get 3G and 4G deep indoors without Wifi. Ugh, a tough call for regulators.
Concerning the first mover advantage and the claimed 18 months WiMAX lead over LTE: First, I think this lead is not really a lead, as it is debatable how much faster WiMAX is compared to current HSPA networks. Additionally I wonder if 802.16e is really ready for prime time. One year ago, three companies have bought nationwide licenses in the 3.6 GHz band in Germany. I haven't heard from them since doing anything beyond patchy deployments in a few places!?
In the meantime, 3G price plans have become available that give users several gigabytes of data per month for a couple of pounds. Should there be any first mover advantage, that's pretty much a show stopper in itself.
Sounds all a bit negative for WiMAX but I think there are still opportunities out there. The 3GPP operators are far away from doing everything right. Especially for those occasional users who just want to open their notebook no matter in which country they are and get access for some time without worrying about subscriptions, SIM cards, etc, this camp has not yet the right answer. And then, there are the countries that don't have 3G yet for various reasons such as India and China. In some countries, however, incumbents are starting to wake up. So hurry, WiMax before this one goes to them as well.
A WiMAX 802.16m Primer – Complying with IMT-Advanced
Like LTE, WiMAX is also competing for a place in IMT-Advanced 4G and shares the same fate as the current LTE standard: It is too slow. As a result, the 802.16m working group has been tasked by the IEEE to enhance the system. While only few details were available so far, the working group has published a very early draft version of the 802.16m System Description Document (SSD). Thanks to Robert Syputa of WiMAX Pro for the tip.
While there are still many gaps in the document, the main features are already described. Here's a short overview with some further background information:
Use of Several Carriers
Like other standards bodies, the IEEE has recognized that increasing the bandwidth used for data transmission is one of the best ways to increase overall data transfer rates. A multi-carrier approach, in which two or even more carriers, which are not necessarily in adjacent bands, are used for transferring data, will be used by the future WiMAX air interface. The approach used by WiMAX is backwards compatible, i.e. 802.16e and 802.16m mobile devices can be served by the same base station on the same carrier. The 802.16e device, however, does not see the channel bundling and continues to use only one carrier. To be backwards compatible, high speed zones are introduced in a frame, which are only available for 802.16m devices. If the carriers used for transmission are adjacent, guard bands that are normally in place to separate the carriers can be used for transferring data.
Self Organization and Inter Base Station Coordination
Interference from neighboring base stations and mobile devices is undesired in wireless systems, as it reduces the overall system throughput. The new version of the standard introduces methods and procedures to request mobile devices to perform interference measurements at their location and send them back to the base station. The base station can then use information gathered from different devices to adjust its power settings and potentially also to organize themselves with neighboring base stations using the same frequency.
New Frame Structure
In practice, it has been observed that the 802.16e frame structure, with frame lengths of up to 20 milliseconds is too inflexible. The downside of such long frames is a slow network access and a slow repetition of faulty data blocks, as devices only have one transmission opportunity per frame. 802.16m uses a new frame structure which consists of super-frames (20 ms) which are further divided into frames (5 ms) and again divided into eight sub-frames (0.617 ms). Within each frame of 5 milliseconds, the transmission direction can be changed once. Since eight sub-frames fit into a frame, downlink uplink time allocations of 6/2, 5/3, etc. can be achieved. By switching the transmission direction at least every 5 milliseconds, [34] foresees that HARQ retransmission delays are cut by ¾, the idle to active state transmission time is reduced from above 400 milliseconds down to less than 100 milliseconds and the one way access delay is reduced from almost 20 milliseconds down to less than 5 milliseconds.
Summary
What I haven't seen in the SSD so far is to go beyond 2×2 MIMO to further increase data rates. That's a bit strange since LTE is already at this point!? For the moment, I don't see anything that would push the data rates by an order of a magnitude, which I think would be necessary to comply with IMT-Advanced. Unless, however, the ITU is thinking about downgrading their requirements. Thoughts, anyone?
WiMAX Certificate Authorities
Unlike UMTS and LTE, it looks like WiMAX will not make use of SIM cards but instead embedded authentication information directly in the device. In a world where only private keys are used, this would bind the device to an operator, i.e. a nice look-in scheme. WiMAX however, uses X.509 certificates issued by a certificate authority. If I understand things right, operator look-in of a device is then decided by whether the public key of the certificate authority is known in public or not. It looks like Verisign for example issues X.509 certificates for WiMAX. Now my big question now is: Are the public keys of certificate authorities used for generating WiMAX X.509 certificates public knowledge? Anyone?
MIMO Explained
Multiple Input Multiple Output, or MIMO for short, seems to make it into every wireless radio technology today from Wifi to WiMAX, HSPA+ and LTE. Yes, we know that it requires multiple antennas at the transmitter and the receiver and offers to multiply throughput by sending an individual data stream over each antenna in the same frequency band. But just how can the receivers at the other end separate the two data streams again as they have combined in the air to something completely incomprehensible!? National Instruments has a great introduction to MIMO on their web page which describes this in simple terms with just the right amount of maths that it is still understandable for someone out of college for a decade or more and who hasn’t touched maths since 🙂
Intel Announces Centrino 2 With Optional WiMAX Support
According to Teltarif and the Intel website, Intel will soon launch a new version of their Centrino notebook chipset under the name of "Centrino 2". The Centrino 2 platform will be sold with two different wireless chips: "Shirley Peak" will be the default standard 802.11agn Wifi module. Alternatively a combined Wifi / WiMAX chip named "Echo Peak" brings WiMAX connectivity as part of the chipset but will likely be a bit more expensive than the Wifi only module.
I am a bit disappointed that Intel didn’t have the guts to ship WiMAX as a standard feature with their next generation notebook chipset. It would surely have helped to push WiMAX a lot more. So the question is now how much the price difference is between Shirely and Echo. Let’s hope it is small enough to encourage companies to use it as a differentiator.
The “Battle” Between WiMAX and LTE is Overhyped
Lately, analysts and tech news web sites race to publish posts about WiMAX quickly loosing ground to LTE, as vendors seem to increase their efforts to push LTE out the door sooner. I have to admit I am a bit puzzled as I don’t see anything like that happening .
Here’s why:
Time to market advantage: It is claimed that the WiMAX time to market advantage is fading since efforts for LTE are stepped up. That’s a typical Gartner’s hype cycle curve thing. About a year or two ago, WiMAX was the hype and nobody cared that no matter what the marketing people said it’s normal for a system to take several years from hype to actual deployment. When it came to delivering on the promises it happened what always happens, they had to admit they were not ready yet. It has happened with GSM, it has happened with GPRS, it has happened with UMTS and it will happen again with LTE. Now LTE has hit that spot in the curve and everybody is predicting the same thing as for WiMAX: Trials and deployments are imminent. Give it another 6 months and everybody suddenly sees that marketing and reality are, as always, far apart from each other. And if you don’t believe it yet, take a look at current LTE "mobiles" and compare that to available WiMAX PC-cards and existing networks.
Different markets: The markets for LTE and WiMAX are very different. No GSM/UMTS operator has ever seriously considered going to WiMAX, despite ramblings by Arun Sarin and a few others which in my opinion were only made to push LTE vendors a bit to speed up standards work. The only serious competition WiMAX can create for LTE with established network operators is in the CDMA arena were operators,such as Sprint, that haven’t decided to go to HSPA and are thus in need of a 4G system. In my opinion, WiMAX is the choice for new network operators to challenge the incumbents. And there is not much of a chance such new operators would start with LTE, that turf is in the hand of WiMAX.
Market size: I think most analysts have agreed for quite a while now that the market size for LTE is bigger than that for WiMAX. Not much of a surprise here either.
So I really don’t quite understand the fuzz. What do you think?
The Dangers of Going SIM-Less
Dean Bubley over at the Disruptive Analysis Blog has published an interesting post about the advantages of going SIM-less for next generation connected mobile devices. In essence he argues that today, SIM cards lock users to a single operator and complicate using the device in other networks, locally or abroad. He comes to the conclusion that SIM-less mobile devices are better because users then have control which networks they want to use. While I agree with his arguments, I think there are many ways for operators to deal with SIM-less devices today. It is therefore by no means certain that a device without a SIM gives a greater choice to the user.
When I look at the status quo, SIM-less devices give users much less freedom of choice than devices with SIM cards. The best example are CDMA networks, mostly used in the U.S. Here, devices have no SIM cards and are locked by default to a single operator. Using the device with other networks is not possible and when roaming, users can not use a local SIM card to reduce their costs. Switching local operators is also not possible with the device since it can only be used in one network. And finally, mobile phones can only be bought directly from an operator, so there is no competition and hence prices are unlikely to be very competitive. This approach also gives mobile operators a great degree of freedom to lock handsets down by removing VoIP, Bluetooth and Wifi capabilities that have become very popular on devices which are not locked down to the operator. In short, such a SIM-less world is far from desirable.
So while I think Dean makes some important points I am actually quite happy that the GSM standard uses SIM cards. Here are some examples of what is possible if only the SIM card belongs to an operator while the mobile device belongs to the user:
- Voice Competition: Germany, for example, has become a very competitive MVNO (Mobile Virtual Network Operator) market and prices for prepaid communication have come down over the past two years from 60 Euro cents a minute down to 9 cents or even less. MVNOs basically only sell a SIM card and users just put them into the phone they already have. If there is a better offer and the current MVNO does not adapt, his SIM card is quickly replaced. Great for competition!
- Data Competition: The same applies for prepaid mobile data. If the network coverage is bad or if prices are not competitive, the device can be quickly used with another operator or network by simply exchanging the SIM card.
- Roaming: When I go abroad I usually use a local SIM card because data charges when roaming are still ridiculously expensive. Granted, it is sometimes not convenient to get a local SIM card but if you stay abroad for more than just a day there is a quick return on investment.
- Handset prices: Today I have several choices when I want to buy a new phone: I go to the operator to get a bundle, I go to an electronics store and get a bundle, or I go to one of many online stores and just get a phone. Then I go to the next supermarket, buy a SIM card and I am set. This has had a significant effect on handset prices. Let me give you a recent example: In operator shops, an N95 is currently available for 250 Euros if taken with a 24 month subscription with a basic fee between 10 and 20 Euros a month. I can get the same mobile with the same terms and conditions for 1 euro in most electronic stores today which are not related with the network operator. In addition, the phone is usually not locked down to an operator specific software version with crippeld VoIP and other niceties. And if I don’t want it with a SIM card at all I buy it for 450 euros but without a 10-20 euros a month fee and it becomes even cheaper if you calculate the costs over 2 years. There’s no way of doing that with a SIM-less device with the current model.
So in order for users to benefit from SIM-less devices, a number of additional things need to be in place:
- Location of the certificate server: WiMAX devices are unlikely to use SIM cards from what I hear at the moment. Instead they will use built in or user loadable certificates. The important point is who issues those certificates. If they are issued by a mobile operator, then the user is stuck to one network. This is the same as the current CDMA approach. Therefore, I hope that there will also be certificates issued by an independent certificate authority. When establishing a connection the network would then have to verify the user’s credential with an external certificate authority.
- Networks using external certificate servers: The best external certificate server is of no use if networks only use internal servers. Hopefully competition will prevent this scenario as most network operators are probably happy to get additional revenue from national and international roamers.
In practice I can see networks using both internal and external certificate servers. This would allow the operator to sell devices which are locked to his network and to his control while roaming in exchange for a device subsidy. At the same time users would have the freedom to buy a device with an "open" certificate they could use in any network. They would then have the choice to pay per use, similar to the hotspot model today, or to get a subscription with an operator without being locked in.
Summary
Going SIM-less with WiMAX and other systems is a double bladed sword. If authentication is not "open", we will end up in a situation similarly to what we can observe with CDMA operators today: Users and devices are locked to a single network instead of having a greater choice. While some operators would surely prefer a "closed" authentication solution I think it would do great harm not only to users but also to the industry as it reduces competition among network operators, keeps prices up, and reduces attractiveness for users to go wireless.
The 3GSM Gem in Barcelona: Intel and Motorola’s Live WiMAX network
I had to hold back with this blog entry a bit because I wanted to get permission first to write about what I would say was the most interesting demo I’ve been invited to during the 3GSM / Mobile World Congress:
Lots of WiMAX demos where shown at this years congress and it’s good to see that 802.16e mobile devices have now reached PC-card card sizes and are close to general availability. It’s also nice to see that when the antenna is just a couple of meters away you can see data rates beyond 10 MBit/s. However, that tells you only little about how the system performs in practice when the base station antenna is a couple of blocks away on top of a building and there is interference from neighboring base stations. To go the extra step, Intel and Motorola have teamed up to show how their kit works in a real environment during this years show.
Network Setup
In just a few days, Intel has put up four Motorola WiMAX base stations on rooftops in central Barcelona which were connected to the core network via 50 MBit/s microwave backhaul equipment from Dragonwave. Each base station was equipped with 3 sectors, each on its own 10 MHz channel in the 2.5 GHz band. In total they had three channels available for the network so each base station used the same set of frequencies. The distance between the base stations was about 2 kilometers which is a bit more then what you would see in an inner city network deployment. They couldn’t choose the sites themselves and had to be happy with what they got. On the upside, there is less interference from neighboring cells then there would be in a public network since there were only 4 cells and thus there is no interference from cells further away.
Indoor Experience
Sitting comfortably in the lobby of a hotel in Central Barcelona, I first had a chat with the technical project manager responsible for the network setup. Very good to have somebody with a technical background to talk to. During our discussion I got a first impression of the network performance as there were two notebooks connected to the network, one via a WiMAX PC-card adapter and the other via a CPE (Customer Premises Equipment) box the size of a DSL or cable modem. Despite sitting in the ground floor lobby, the base station being a couple of rooftops away on the other side of the hotel, the probably heat insulated and RF absorbing windows and just using the built in antennas of the devices we still got a data rate exceeding 2 MBit/s via both the CPE and the PC-card adapter. Note that both were SISO (Single Input Single Output) devices. As even this speed is far beyond what you can make use of while surfing the web we streamed a couple of video streams being sent live from WiMAX connected vehicles touring the city. The resolution of the stream was around 320×240 pixels and with a frame rate of 30 fps and the video streams were crisp and clear. One of the notebooks also had an engineering monitor software package on it to observe lower layer performance of the PC card and it was interesting to see how the card goes through the different modulation and coding schemes from QPSK to 64-QAM as reception conditions changed.
Outdoor Experience
Later on we went outside and used Segways to speed up and down the streets with a notebook attached to it to see how the network copes with mobility. Again the video stream performance was flawless and we streamed a U.S. TV station over the Internet which is quite bandwidth hungry. But even this does not require a bandwidth beyond 5 MBit/s which was obviously not the limit of the network. When asked what the highest throughput is that can be observed in the network I was told that it is around 13 MBit/s with 64-QAM and about 1.5 MBit/s at the cell edge with QPSK ½ modulation and coding despite the fact that the cells are too far away from each other. Interesting numbers showing the direction in which we are headed once 2×2 MIMO is added and proper cell sizes are used.
Here’s a video taken and produced by Marc Wallis and Michael Ambjorn of Intel/Motorola respectively:
(copyright by M. Wallis / M. Ambjorn of Intel/Motorola)
Conclusion
I came away very impressed from the demo as the speeds were amazing. We didn’t loose the connection to the network even once during the one and a half hours sitting in the hotel and touring the city. That says a lot about the software stability of the PC-card and the network. Thanks a lot to Intel for the VIP tour invitation it was definitely the best demo I have seen during the Congress.
Wireless Now Accounts For A Third Of Austria’s Broadband Connections
Bad news for all of those who keep telling people that wireless broadband can’t compete with DSL and cable because networks couldn’t cope with the traffic: You are wrong! Arthur D. Little consulting published a study last week that last year 57% of new broadband connections were wireless (3.5G + WiMAX a bit I guess) compared to 36% of new connections via DSL and 7% cable.
In total 46% of broadband connections are now via DSL, 26% via cable and 28% wireless. As I am in in Austria from time to time and have a local SIM card for mobile broadband I think the reasons for this outright success are the following:
- Very competitive pricing for wireless broadband
- Prepaid offers. I for example have a prepaid SIM for 3.5G with 3GB worth of data which I can consume over 12 months. 1GB afterwards can be had 20 euros with a validity period of another 12 months. The same 20 euros buy 2 GBs with a validity period of 1 month. Even cheaper offers are available via postpaid.
- So far pricing for DSL was very uncompetitive in Austria
- All four wireless operators are advertising their broadband solutions heavily
I think these number show quite impressively that well designed 3.5G networks can cope with the load of broadband Internet access from a significant percentage of the population. I can confirm this myself as my wireless HSPA connection has always worked nice so far whenever I was in Austria. Therefore fears by some mobile network operators that their networks might be overloaded are unfunded, unless of course they have an under dimensioned network.
Also thoughts can be put at rest that wireless broadband is not profitable. With wireless voice minute prices down to 5 euro cents a minute in Austria and mobile broadband used heavily I haven’t heard anybody complain about losses.