Category: WiMAX

Verizon first to LTE to counter Sprint with WiMAX?

Just a wild speculation on my part but could the U.S. lead with next generation wireless network deployment after having been a bit slow to deply 3G in the past?

With Sprint launching their next generation WiMAX network in 2008 I wonder if this will push Verizon or AT&T to push LTE out the door as soon as possible? On the other hand the Austrians in the past have also been quite quick to introduce new wireless technologies and opening the network for customers. These days 20% of broadband customers in the country use one of the four HSDPA networks. If the trend continues the country could go very quickly to LTE as it would offer lots of additional capacity.

Comments, as always, are welcome!

What next for mobile telephony?

… asks Moray Rumney, Lead Technologist over at Agilent in the latest edition of the Agilent Measurement Journal (3/2007). In his article, Moray takes a look at which factors contribute to the ever increasing wireless transmission speeds and explains where the limits are and why the 300+ MBit/s promised by LTE and other technologies in a 20MHz channel will remain a theoretical promise rather then becoming a practical reality. He then goes on to describe what is possible with the given physical limits and presents his thoughts about how to address capacity issues in the future. An absolute must read!

The journal is available here and the article can be found on page 32.

Light Reading Webinar on Mobile Backhaul Evolution

With mobile networks getting faster and faster a growing pain for network operators is the backhaul connection between the base station sites and the next element in the network. Today, T-1 or E-1 connections are used with a line rate of 1.5 and 2 MBit/s. With HSDPA being put in place today,  backhaul capacity requirements of 3G base stations now reach 10 MBit/s or more. This means putting additional T-1 or E-1 lines in place. While this might still work today for HSDPA speeds despite the associated rising costs it certainly won’t work tomorrow for WiMAX, LTE and other Beyond 3G technologies that require backhaul capacities of 60 MBit/s per base station and more.

So the big question is what comes after T-1/E-1 connections over copper, fiber or microwave!? The common answer these days seems to be:

IP over Ethernet with the capability to carry legacy GSM (TDM) and UMTS/HSDPA (ATM) links in IP pseudo-wires alongside native IP traffic generated by native WiMAX and LTE base stations.

But how do you connect the base station sites to Carrier Ethernet Networks? Can the last mile be done over copper, is fiber required or is next generation microwave an alternative? Questions over Questions 🙂

I found some answers in a recent one hour Light Reading Webinar on the topic which is available for free at this link. If you are interested in the topic take a look.

Verizon and LTE: All Over IP Is Shaking Up The Wireless World

Recent reports (here and here) that Verizon has chosen LTE as a successor technology of its current CDMA 1xEVDO Rev A. instead of UMB is likely to be a big blow for Qualcom and the CDMA industry as a whole. While the other big CDMA network operator Sprint has decided to go for WiMAX and a lot of global CDMA operators have already jumped ship and went to UMTS/HSDPA, Verizon is the latest addition to the list.

UMB, LTE and WiMAX are all ‘IP only’ technologies that strictly separate the wireless network from the applications running above. This is not only beneficial for users (as discussed here) but also allows network operators to jump ship when going to the next technology. Just as in the case of Verizon and Sprint. No UMTS operators have so far shown their interest to do the same, except for the threats of Vodafone that the LTE timeline is too slow for them and that they are looking what WiMAX can do for them. Might the tight integration of LTE into the already existing 2G/3G GSM/UMTS ecosystem keep operators at bay?

So while UMB is not dead yet, the hill they have to climb just got a lot steeper.

More On User Installable Certificates for Wifi (And WiMAX)

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Some days ago I have speculated how a WiMAX world might look like without SIM cards. It’s likely that certificates are going to be used to authenticate terminals and users to the network (and vice versa). The big open question is whether these certificates are pre-installed and can not be changed, i.e. the device is locked to the network, or if they can be installed by the user. This would have the advantage that a device can be used in any network that allows user installable certificates.

Wireless LAN already uses user installable certificates in WPA-enterprise mode and larger organizations are already making use of this. Here’s an example from a university that uses PEAP. To my surprise, my Nokia N93 phone already seems to support a large number of different EAP authentication methods today, see the picture on the left.

What’s worrying me a bit is the many different types of EAP methods. That’s going to create the heck of an issue for non-tech end users. Also, how do you keep a (software) certificate save? With a SIM card that’s much easier since it is a piece of hardware.

If WiMAX Becomes a 3G (IMT-2000) Standard, What’s Left for 4G?

Now that 3G systems such as UMTS are under full deployment, the industry is looking forward to what comes next. While some say that WiMAX is a 4G system, the IEEE and the WiMAX forum think that 802.16e is rather a 3G technology and have asked the ITU (International Telecommunication Union) to include this standard into its IMT-2000 specification (International Mobile Telecommunications 2000). This specification is generally accepted as being the umbrella defining which standards are to be considered 3G.

This is mainly a political move since in many regions of the world, frequencies are reserved for 3G IMT-2000 systems. If WiMAX were included in IMT-2000, and it looks like it will be in the near future, some frequency bands such as the 2.5 GHz IMT-2000 extension band in Europe could be used for WiMAX without changing policies.

So what remains for IMT-Advanced, the ITU umbrella name for future 4G technologies?

Currently there is still no no clear definition by ITU of the characteristics of future 4G IMT-Advanced systems. The ITU-R M.1645 recommendation gives first hints but leaves the door wide open:

It is predicted that potential new radio interface(s) will need to support data rates of up to approximately 100 Mbit/s for high mobility such as mobile access and up to approximately 1 Gbit/s for low mobility such as nomadic/local wireless access, by around the year 2010 […]
These data rate figures and the relationship to the degree of mobility (Fig. 2) should be seen as targets for research and investigation of the basic technologies necessary to implement the framework. Future system specifications and designs will be based on the results of the research and investigations.

When WiMAX is compared to the potential requirements above it’s quite clear that the current 802.16e standard would not qualify as a 4G IMT-Advanced standard since data rates even under ideal conditions are much lower.

3GPP’s Long Term Evolution (LTE) project will also have difficulties fulfilling these requirements. Even with the recently proposed 4×4 MIMO, data rates in a 20 MHz carrier would not exceed 326 MBit/s. And that’s already a long stretch since putting 4 antennas in a small device or on a rooftop will be far from simple in practice. If WiMAX is accepted as a 3G IMT-2000 technology, how can LTE with a similar performance be accepted as a 4G IMT-Advanced technology?

Additionally, one should also not forget that IMT-2000 systems such as UMTS are still evolving. UMTS is a good example. With HSDPA and HSUPA, user speeds now exceed the 2 MBit/s which were initially foreseen for IMT-2000 systems. But development hasn’t stopped here. Recent new developments in 3GPP Release 7 and 8 called HSPA+, which will include MIMO technology and other enhancements, will bring the evolved UMTS technology to the same capacity levels as what is currently predicted for LTE on a 5 MHz carrier. HSPA+ is clearly not a 4G IMT-Advanced system since it enhances a current 3G IMT-2000 radio technology. Thus, HSPA+ categorized as a ‘enhanced IMT-2000 system’.

Maybe that’s the reason why the IEEE 802.16 working group is already looking forward and has started work on 802.16m with the stated goal of reaching top speeds of 1 GBit/s.

When looking at current research it’s clear that the transmission speed requirements described in ITU-R M.1645 can only be achieved in a frequency band of 100+ MHz. This is quite a challenge since such large bands are few. Thus, I have my doubts whether these requirements will remain in place for the final definition of 4G IMT-Advanced.

Does It Really Matter If A Technology Is 3.5G, 3.9G or 4G?

While discussions are ongoing the best one can do is to look at HSPA+, WiMAX, LTE and other future developments as "Beyond 3G" systems. After all, from a user point of view it doesn’t  matter if a technology is IMT-2000, Enhanced IMT-2000 or IMT-Advanced as long as data rate, coverage and other attributes of the network can keep up with the growing data traffic.

A whitepaper produced by 3G Americas has some further thoughts on the topic.

As always, comments are welcome!

A (WiMAX) world without SIM cards

A recent blog entry of mine on WiMAX terminals with and without support of EAP-SIM and thus SIM cards for authentication has provoked a number of interesting responses. What I take away from them is that first devices will probably not have a SIM card.

So the next logical question is how authentication is done in the absence of a SIM card!? I can see two basic approaches:

1. A device comes with a built in certificate. That’s straight forward. The user goes to a shop, buys a device, it gets activated for him and he’s set. While this is all nice and well the trouble starts when the device breaks or the user wants to use the services of another operator. No way with this model.

2. Another model would be to use a username and password to be supplied by the user. It could work in a similar fashion as with Wireless LAN today. I can also imagine user installable certificates. While both  being a bit more complicated then pre-installed certificates it would preserve the flexibility the SIM card approach offers today.

I like and depend on flexibility since I travel a lot and a device locked to a single network is useless for me. While I am certainly not the average user I am sure the majority would prefer openness over being locked into a single garden.

If you have further information on this topic, please leave a comment.

The Nokia N800, WiMAX And Embedded 802.16e Chips

Speculations are growing that Nokia is working on a version of the N800 Internet tablet with a WiMAX chip in addition to Bluetooth and Wifi. This report on Heise News, a reliable German tech website, links Nokia’s plans with the launch of Sprint’s WiMAX network in 2008.

They also link to an interesting data sheet of a WiMAX Module from SyChip, (which they say may or may not be related to the N800 WiMAX development) which contains quite interesting high level details of first generation embedded WiMAX chips. According to the data sheet the WiMAX module is 21.6 x 23.7 x 1.5mm in size and supports 802.16e. The block diagram shows two antenna connectors for MIMO in downlink direction and single stream transmission in uplink direction. Mobile devices communicate with the embedded module either via SDIO or USB.

One of the mysteries around WiMAX to me, still, is how users and devices will be authenticated since I haven’t seen any kind of SIM card specification for WiMAX yet. The data sheet, however, says that the following security mechanisms are supported: EAP-SIM, EAP-AKA, EAP-TLS. While EAP-TLS works with certificates, EAP-SIM was originally specified by 3GPP (UMTS standards body) for Wifi authentication using  the secret keys and subscriber ID contained on a GSM/UMTS SIM card. For details take a look here. Since EAP-SIM has been specified independently from the underlying network technology, it should integrate nicely into WiMAX as well.

This raises the question though what kind of equipment is used on the network side that supports EAP-SIM authentication!? If you have more information, please let me know!

IEEE Wifi And Ethernet Standards Now Available For Free

Nortel and Cisco have decided to use some of their marketing budget for something really useful for engineers, namely to open up the IEEE standards 802 library for free public access. These include the famous Ethernet (802.1,2,3), Wifi (802.11) and WiMAX (802.16) standards. A great help for all doing research in this area. Little downside: Only approved documents are available which excludes hot documents such as the current 802.11n draft.

WiMax Matrix A and Matrix B MIMO

Ever wondered what the difference is between WiMAX Matrix A and Matrix B MIMO? As a reader of this blog you just might have. In recent certification reports and functionality comparisons between WiMAX kit of different vendors these acronyms have sprung up but, as usual, without further explanations. Don’t fear, help is on the way! This article written by Shamik Mukherjee of Motorola and published on WiMAX.com gives a very good overview including a look at WiMAX beamforming.

So here’s a quick summary of Matrix A and B:

Matrix A: Coverage Gain

In a 2×2 antenna configuration (2 transmitter antennas, 2 receiver antennas), a single data stream is transmitted in parallel over the two paths. A mathematical algorithm known as Space Time Block Codes (STBC) is used to encode the data streams of the two antennas to make them orthogonal to each other. This improves the signal to noise ratio at the receiver side which can be used to:

  • Increase the cell radius
  • To provide better throughput for subscribers that are difficult to reach (e.g. deep indoors or moving at higher speeds).
  • For terminals which already experience good signal conditions Matrix A has the benefit that higher order modulation (e.g. 64QAM) can be used and fewer error correction bits are necessary which in turn increases transmission speeds to that subscriber.

Matrix B: Capacity Increase

This flavor of MIMO, also known as Spacial Multiplexing MIMO (SM-MIMO), sends an independent data stream over each antenna. Thus, in case signal conditions are excellent, the data rate is doubled, tripled or quadrupled depending on the number of antennas used in both the transmitter and receiver. In practice, WiMAX MIMO is defined for two antennas at each side.

Mandatory and Optional Features

For WiMAX Wave 2 certification, both 2×2 Matrix A and Matrix B capabilities are required according to the article. Beamforming capabilities, also known as Adaptive Antenna Systems (AAS), is optional.