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 🙂
Category: LTE and SAE
The 8-10 Year Interval in Mobile Repeats with LTE
I just realized that new cellular network technologies seem to be launched every 8-10 years. Analog cellular networks such as the C-Netz started operation back in 1984, GSM went on air in 1992 and UMTS became operational in 2002. Now it’s 2008 and LTE and mobile WiMAX are at the doorstep. While WiMAX is a bit ahead and will be used by newcomers, most incumbent operators will probably opt for LTE which in my opinion won’t go live before 2010, i.e. 8 years after UMTS was generally available. And from there it will take another year or two before we see LTE devices beyond PC cards and a network coverage beyond a few major cities.
The Packet Call Becomes History with LTE
This week I’ve been taking a closer look at how LTE networks will be used in practice. One of the big differences to current 3G and 3.5G networks is that LTE is fully based on IP, i.e. there is no longer a circuit switched core network for voice telephony. Today, it makes sense for 3G/3.5G devices to attach to the network without requesting an IP address since they are (still) mostly used for voice telephony. In LTE networks, however, a device without an IP address is completely useless. Hence, the LTE network attach procedure already includes the assignment of an IP address. Consequently, an LTE device will always have an IP address. For people coming from the LAN/WLAN world this is nothing new. For people in the cellular industry, however, this is revolutionary. The 3G/3.5G procedure of ‘establishing a packet call’, a term coined with the old thinking of establishing a circuit switched connection for a voice call in mind, will thus become history with 4G. Many people in the industry will have to change their picture of the mobile world to accommodate for this.
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?
Current LTE Mobile Device Form Factor
Last year, LTE mobile devices where still the of the size of a cabinet. At this year’s 3GSM / Mobile World Congress the hardware has now shrunken to the size of a PC motherboard. The picture on the left shows a LTE mobile with 2×2 MIMO from LTE which was used to stream several videos at a speed of 30+ MBit/s via a LTE prototype base station supplied by Nortel. So by next year we should see first PC-card prototypes. Things are moving ahead.
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!
Will Fixed/Wireless Convergence Push IMS?
Despite its multimedia capabilities the IP Multimedia Subsystem (IMS) hasn’t yet gotten a lot of opportunities to show its capabilities in wireless networks. One of the reasons for this is that current circuit switched mobile voice telephony works well and meets user expectations. Things, however, are improving for IMS.
With the introduction of the iPhone, more and more people are getting aware of multimedia and Internet capabilities of mobile devices. Thus, it might well be possible that multimedia enriched voice calls might also soon appear on the radar screen of users. On the network side many operators are upgrading their current 3G networks to 3.5G and with the first WiMAX networks rolled out now and LTE on the horizon there is sufficient bandwidth for such services. Additionally, WiMAX and LTE networks no longer have a circuit switched part and operators need a solution such as the IMS to be able to offer conversational services over their next generation networks. It thus seems inevitable, that the IMS will have a bright future.
In practice, however, things will be a bit more difficult since third party VoIP service providers such as Skype, Vonage and others could try to take a piece of the wireless market in a similar way as in fixed line networks today. After all, the application layer does not care whether IP packets traverse a DSL line or the air interface of a wireless network as long as there is enough bandwidth. From my own experience, SIP and proprietary VoIP services such as Skype work well over 3.5G wireless networks and even Skype video calls have excellent video quality in both directions.
Network operator based IMS systems, however, have a number of advantages over voice services provided by third parties if the play their cards right:
Network operators today sell both a mobile device and voice service. This means that the service works out of the box, no configuration required by the user. With pre-installed and pre-configured IMS applications such as voice, video calling, presence, etc. they have a head start over third party services for which applications have to be installed on mobile devices.
The IMS is also able to request a certain bandwidth for a session from the transport layer. In case there is congestion anywhere in the network, it will be made sure that multimedia sessions are not impacted.
The third advantage, which I think is a major one, is that IMS gives network operators with both fixed line (think DSL, cable) and wireless assets (think HSPA, WiMAX and LTE) the opportunity to converge their voice + multimedia service offerings both in the network and from the users point of view.
In the fixed line world the transition from analog telephony to VoIP over DSL or cable is already in full swing. The incentive for the user to switch to VoIP is usually a lower price for a combined voice service and Internet access over DSL or cable. When combined with mobile voice + Internet access, network operators can offer their clients Internet access + voice (and multimedia) telephony both at home, in the office or while roaming outside with a single device and a single telephone number.
The IMS also allows to have many devices registered to the same telephone number. This is great since at home it might be more convenient to use a dedicated phone, a notebook or even an IMS capable and connected television set to make a voice or video call.
With Voice Call Continuity (VCC) there is even the possibility that a mobile device automatically switches to Wifi when the user returns home or to his office thus reducing the load on the cellular network. Switching to Wifi at home also solves the issue of 3G/4G in-house coverage which in many regions of the world is inferior to 2G coverage due to the use of higher frequency bands.
And finally, the IMS has the capabilities to transfer a voice call from one device to the other. This is quite interesting in scenarios in which the user returns home and then transfers an ongoing voice call from his mobile phone to a television set and adding a live video stream to the call in the process.
It’s clear that getting all of this right is not a trivial task. But if network operators want to retain their role as a service provider they have to go beyond what third party service providers could offer over a bit pipe.
As always, thoughts and comments are welcome!
More Uses For Curbside VDSL cabinets
A couple of days ago I have rumbled a bit on the big street side cabinets that need to be put into place for VDSL every couple of hundred meters. Recently I have received an interesting eMail from one of you saying that they might just be perfect to put Wifi hotspots inside. Hm, what an interesting idea! At the size of those cabinets there should be some space left for a little access point. And backhaul is definitely not a problem with those fiber cables in the ground.
Well, why not put an HSDPA or, later on, an LTE microcell into these cabinets to increase cellular capacity in high traffic areas!? Again, no backhaul and power problem, as both are available in the cabinet. As microcells only use little transmit power and only cover small areas a little omni-directional antenna discretely put on a nearby pole or wall will do. Interesting possibilites for converged fixed/wireless network operators of the future!
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.