Chris

Clearwire and LTE-Advanced

Chris — Thu, 04 Aug 2011 21:19:00 GMT

Well it is official. Clearwire announced this week that it will deploy LTE and maintain the existing WiMAX network. For a good article on their announcement, see http://www.fiercewireless.com/story/clearwire-deploy-lte-if-it-can-get-additional-funding/2011-08-03.

Not only is Clearwire deploying LTE, they are deploying LTE-Advanced. LTE-Advanced, or just LTE-A, is the next iteration of LTE that has been defined in Release 10 of the 3GPP specifications. There are a number of advancements that they have incorporated into LTE-A. One of the most interesting, in my opinion, is Carrier Aggregation. It is one of the technologies that Clearwire is intending to use. With Carrier Aggregation, an LTE-A base station (or eNB) and a mobile device (of UE) can talk to each other using multiple frequency blocks spread, or as we would say in broadcast radio, "up and down the dial". So a single UE could send and receive data on 850 MHz, 1900 MHz, and 2.5 GHz simultaneously. This will allow an operator the ability to increase data rates by aggregating the different spectrums that they have.

Another technology that Clearwire is planning on using, as they did with WiMAX, is a Time Division Duplex, or TDD, version of LTE. This will allow them to have a single frequency (or set of frequencies in the case of carrier aggregation) for both the uplink and downlink. The other type of LTE is Frequency Division Duplex or FDD. FDD requires dedicated uplink frequencies and dedicated downlink frequencies. What we have seen so far has been our traditional cellular operators that have gone to LTE, Verizon Wireless and AT&T, will use FDD because the spectrum they have is specifically designed for FDD. Clearwire, on the other hand, will use a single band and TDD.

If you are interested in more information on LTE-A, a colleague of mine, Dr. Nishith Tripathi, has written an overview of LTE-A. For more information, see his blog at http://lteuniversity.com/expert_opinion1/b/nishithtripathi/archive/2010/05/04/lte-advanced-in-5-minutes.aspx.

I wish the best to Clearwire, as well as the other LTE operators, and I look forward to seeing the types of data rates, devices, and services that they have to offer.

What is your opinion? I would love to hear from you and your thoughts on LTE-A or anything on LTE in general.

Thanks,

Chris

Spectrum and LTE

Chris — Fri, 22 Jul 2011 22:41:00 GMT

I was reading my telecom news blogs this week and stumbled across an article about LightSquared and the spectrum they are planning on using for LTE (http://www.fiercewireless.com/story/lightsquared-ceo-ahuja-confident-fcc-will-approve-network-plan/2011-07-19?utm_medium=rss&utm_source=rss). LightSquared's spectrum is part of the L-band satellite spectrum. What dawned me while reading the article was that I didn't really have a good feel for the spectrum breakdown in the U.S. I know about the standard cellular frequencies, i.e. 800 MHz, 1900 MHz, AWS, and 700 MHz, but not some of the others parts of the spectrum. I did a bit of poking around and found this radio spectrum map: www.ntia.doc.gov/osmhome/allochrt.pdf. It was produced by the U.S. Department of Commerce, and shows how we are using the spectrum here in the U.S. It is amazing how many things we have allocated. LightSquared wants to use a satellite band for terrestrial LTE, which is on the lower portion of the map.

Another thing that this map helped me see is how much space is "wasted" by broadcast television. This is the reason for the big push over the last few years to move to a digital television standard in order to free up space for other things. That is what happened a few years ago when some television frequencies were taken back and then sold as the 700 MHz spectrum.

Spectrum will always be an issue in cellular telecommunications. I can see from this map how full things are now. There's no doubt in my mind that in the future we will be playing the same game as now: optimizing some service (like TV) and then reusing that for something else (like cellular data). This map also helps to show why there is so much interest in technologies like Multiple Input Multiple Output (MIMO) and Smart Antennas. It's not just about increasing the data rate; it's about increasing the spectral efficiency (more bits/second/Hz) so that we can continue to increase the data available for subscribers, even if the spectrum itself cannot grow.

I look forward to hearing your thoughts.

Chris

So how many LTE Operators are there?

Chris — Fri, 13 May 2011 20:22:08 GMT

Living here in the United States, I don't think about the rest of the world as often as I would like. So when I think about there being a lot of LTE operators, I focus on the fact that three operators in the US have either launched or are going to launch soon (i.e. Verizon Wireless, MetroPCS, and AT&T). But there was a new report from the GSA (the GSM mobile Suppliers Association) that shows all the operators in the world that have either deployed LTE or are committed in some way to LTE. It is a very interesting report that gives an operator by operator break-down of where they are in the process, i.e. deployed, in trial, starting to work on it, etc. The most interesting statistic is that there are 208 operators that are interested in LTE in 80 countries. Of those interested, 154 have firm commitments and plans. Those 154 are in 60 different countries. Those are pretty big numbers.

The report is a very interesting read and it is great to see that the LTE momentum continuing to pick-up. For more information please see the report at http://www.gsacom.com/news/gsa_329.php4.

What are your thoughts about LTE deployment? I would love to hear your thoughts. Also if you live outside the US, I would love to hear from you about the buzz on LTE. Is it being deployed? What is being discussed? I would love to hear from you.

Chris

Who is 4G?

Chris — Wed, 04 May 2011 14:23:00 GMT

I am sure you have seen the commercials. T-Mobile says they have the largest 4G network. Verizon says they are 4G and they have the fastest 4G network. AT&T also claims 4G. But, they don't all use the same technology. So that begs the question, who is 4G?

Before we discuss that, let's take a look at who makes the rules as to who is 4G. They are the International Telecommunication Union or the ITU. They were the group back in the 90's that set the requirements for who could call themselves 3G and they are setting the requirements for 4G. Interestingly, last year they stated that 4G was reserved for technology like LTE-Advanced or WirelessMAN-Advanced. Technology that provided a significant increase in data rates over 3G. But, late last year they changed that. Now they say anything can be called 4G if it is a "forerunner of these technologies" (like LTE and WiMAX) or "evolved 3G technologies providing a substantial level of improvement in performance and capabilities with respect to the initial third generation systems now deployed" (read HSPA+). So based on this statement you can call yourself 4G if you are LTE, WiMAX, or HSPA+.

T-Mobile, AT&T, Verizon, MetroPCS, and Clear all meet these requirements and are free to call themselves 4G. I hope that helps clear up any confusion on who is 4G. I know it did for me when I did some research on this recently.

What do you think?

For more information on the ITU and 4G, check out http://www.intomobile.com/2010/12/18/itu-reverses-its-decision-lte-wimax-and-hspa-are-now-4g/ and http://www.itu.int/net/pressoffice/press_releases/2010/48.aspx.

I look forward to your thoughts.

The Thunderbolt – A Game Changer?

Chris — Fri, 15 Apr 2011 22:13:00 GMT

Over the past month Verizon Wireless has released the HTC Thunderbolt. Normally we do not talk about mobile devices here on LTE University, but this one is quite interesting. It has a couple of claims to fame. The first is that it is a LTE smartphone. It is Android 2.2 based device and it also supports both LTE and 1xEV-DO for data. Being the first Verizon LTE smartphone is a pretty good claim to fame, but there is more. It is also the first smartphone on Verizon's network that is capable of supporting both voice and data. That is something that the iPhone is not capable of on Verizon's network. This allows a subscriber to talk on the phone while simultaneously surfing the web or using apps that interact with the Internet.

The question is "is this really a game changer"? For me personally I would have to say yes. You see, there is really only one big stick that AT&T has over Verizon and that is the fact that they can do simultaneous voice and data, but Verizon cannot. It is one of the technological issues that come from the technology choices of over 10 years ago. But now the game has changed. Now Verizon is capable of a similar feature. Is this the beginning of more of these types of devices? I hope so.

What do you think?

For more information on the HTC Thunderbolt, check out:

http://www.gottabemobile.com/2011/03/14/htc-thunderbolt-first-verizon-phone-to-feature-simultaneous-voice-data/.

I look forward to your thoughts.

SIP vs. GTP/MIP

Chris — Fri, 18 Jun 2010 21:34:00 GMT

Hello All,

I had a question recently about different types of mobility that I thought might be of interest. The question was about using SIP mobility instead of GTP or MIP in LTE. This is a good question. On the surface both are solving mobility issues so why have different solutions. The problem is that SIP mobility and MIP/GTP are really trying to solve different problems. MIP (or Mobile IP) and GTP (or GPRS Tunneling Protocol) are trying to solve geographical mobility. As a mobile moves through the network, we need to direct the packets to its current S-GW and eNodeB. MIP is an option for sending packets from the P-GW to the current S-GW of the mobile. I don't see many people using MIP. Most are looking at using the GTP. SIP Mobility is used to map the current IP address of the UE to a logical name. Since we can use dynamic IP addresses in LTE, we need a way to map the current IP address assigned by the P-GW to the UE to a logical name that is static (i.e. Chris@LTEISCOOL.com). So they are just trying to solve different problems.

I found this an interesting question and I hope you find this helpful.

Take care,

Chris

Compare and contrast of UMTS and LTE Mobility

Chris — Mon, 17 May 2010 14:15:00 GMT

As I think about mobility in LTE, I always go back to making comparisons with UMTS. I thought t might be good to do a comparison chart of the two. Below is a list of the key mobility terms/concepts and their equivalent terms in UMTS and LTE. Let me know what you think of this and if you have any questions/comments.

Thanks,

Chris

Mobility Concept	UMTS Concept	LTE Concept
Paging Zone	Location Area, Routing Area, UTRAN Registration Area	Tracking Area
Types of Handover	Soft, Softer, and Hard	Hard Only
Basic dBm measurement	Received Signal Code Power (RSCP)	Reference Signal Received Power (RSRP)
Basic dB measurement	Energy per Chip over Noise (Ec/No)	Reference Signal Received Quality (RSRQ)
Measurement Configuration sent to UE	In multiple Measurement Control Messages. One message is needed per event configuration.	Included in RRC Connection Reconfiguration. One message can include multiple measurement configurations.
Intra-Frequency Measurement events	e1 event types	A event types
Inter-Frequency Measurement events	e2 event types	A event types
Inter-RAT Measurement events	e3 event types	B event types

Measurement Event Comparison

Chris — Wed, 12 May 2010 22:43:00 GMT

While sitting in a colleague’s class this week we were discussing the UMTS measurement event types. I thought it might be good to do a comparison of UMTS’s measurement events with the measurement events in LTE. There are a couple of key differences between the two. The first is that UMTS supports a soft handover and LTE does not. That is important in looking at this comparison as there is no active set in LTE. The second difference is that LTE does not highlight the differences between intra-frequency measurements and inter-frequency measurements as strongly as UMTS does. The following table gives a comparison and comments on how the LTE measurements compare with UMTS.

I hope it is helpful.

Thanks,

Chris

LTE Measurement Events and Description	UMTS Measurement Events and Description	Comments
Event A1 - Serving becomes better than threshold	e2f - The estimated quality of the currently used frequency is above a certain threshold	In LTE this may be used to stop looking for a cell on a different frequency or technology, as e2f is used in UMTS.
Event A2 - Serving becomes worse than threshold	e2d - The estimated quality of the currently used frequency is below a certain threshold	In LTE this may be used to start looking for a cell on a different frequency or technology, as e2d is used in UMTS.
Event A3 - Neighbor becomes offset better than serving	e1a - A Primary CPICH enters the reporting range	This comparison is a bit of a stretch. The reason I have equated them is because in both cases a neighbor should be considered for a handover, either soft or hard depending on the technology.
Event A4 - Neighbor becomes better than threshold	e1e - A Primary CPICH becomes better than an absolute threshold
Event A5 - Serving becomes worse than threshold1 and neighbor becomes better than threshold2	e2b - The estimated quality of the currently used frequency is below a certain threshold and the estimated quality of a non-used frequency is above a certain threshold	This comparison is good for saying that the current cell is below an absolute threshold and the new cell is above a threshold. This would mean that the current cell is not good enough and the new one is good, which is a good reason to do a hard handover (in either technology).
Event B1 - Inter RAT neighbor becomes better than threshold	e3c - The estimated quality of other system is above a certain threshold
Event B2 - Serving becomes worse than threshold1 and inter RAT neighbor becomes better than threshold2	e3a - The estimated quality of the currently used UTRAN frequency is below a certain threshold and the estimated quality of the other system is above a certain threshold	This comparison is good for saying that the current cell is below an absolute threshold and the new cell on a different technology is above a threshold. This would mean that the current cell is not good enough and the new one is good, which is a good reason to do a hard handover to the new technology.

A Mobility Question

Chris — Mon, 22 Mar 2010 16:39:00 GMT

Hello All,

Sorry for my lack of blogging lately. Projects can be tough. With the apologies out of the way, I had a colleague ask a couple of questions recently and I thought it would be good to share the answers with LTE-U.

His main question was about mobility. Mobility in LTE can be quite tricky. The main point of his question was about the frequency band size. In LTE there is a scalable OFDM channel. The bandwidth can vary from 1.4 MHz to 20 MHz. There are also a number of frequency bands that are going to be used for LTE (the new 700 MHz as well as the old PCS and Cellular bands).

The question basically was can a mobile move between frequency bands and the answer is absolutely yes. The second part of the question regarded movement between different sizes of bands. The best way to approach this question is to define two terms. The two terms are intra-frequency and inter-frequency mobility. We are use to these terms in other technologies (i.e. GSM and UMTS), but LTE puts a new spin on things. Intra-frequency mobility is when a mobile moves between two cells and both cells have the same frequencies (I know, not the most profound statement). If there is a change in the center frequency this is now called inter-frequency mobility. In LTE both intra-frequency and inter-frequency mobility are supported. (5/4/10 Note - I has come to my attention that if the bandwidth changes, but the center frequency does not change it is still a intra-frequency handover.)

For example, let's say that an operator has in one city a 10 MHz block in the 850 MHz band that they are using for LTE. In a city that is only a few miles away this same operator has only 5 MHz available in the 850 MHz band. When a subscriber drives from city A to city B the size of the frequency band is changing (as will probably the DC carrier) and the mobile will have to do inter-frequency mobility measurements to provide information on the new cells signal strength.

The reason this is an important discussion is that when the mobile does intra-frequency measurements the network does not need to allow any time to do the measurements. The mobile can just do them whenever they want to. For inter-frequency measurements the mobile must be given time to stop listening to its current cell and listen to a new cell to take the measurements. That increases the level of complexity and the amount of work the mobile will need to do.

I hope this helps give some insight into mobility. Please feel free to send questions if you have any.

Take care,

Chris

The Magic 86

Chris — Tue, 04 Aug 2009 13:45:00 GMT

I had a student in one of my classes ask me about the "Magic 86" number (as much as I would love to insert a Harry Potter reference, I will restrain myself). After a little discussion, it became clear that she was talking about the raw physical bandwidth of LTE and how it was 86 Mbps. She was interested in understanding how this "magic" number was calculated. I thought it would be beneficial to go through the steps in calculating the uplink and downlink maximum theoretical data rates.

Before we start, it is important to note that these data rates are not practical data rates. Typically when I say that "maximum theoretical" it essentially means, in the words of my Granddaddy (we called him "Pa"), "You ain't gonna see that." (It's a southern Oklahoma thing.) In this context I mean a bit more. The standard does not allow for a mobile to reach the magic number, as I'm about to illustrate. Practical maximums will be discussed in a later post, so keep in mind that the numbers presented here are achievable data rates for LTE.

Now, with all of our introductions and caveats covered, let's look at the "Magic 86" number. There are two instances in which this value comes into play. The first is the uplink rate and the second is the downlink with only a single transmit antenna.

Let's look at the uplink first. In the uplink there are two key assumptions: first, that we are using a 20 Mhz spectrum and, second, that we are always able to support 64 QAM. Since we are assuming a 20 MHz spectrum, we have 100 Resource Blocks (RB) per slot (.5 ms). A RB has 84 Resource Elements (RE). In every RB there are 12 REs that are lost due to overhead (specifically the Uplink Reference Signal). That leaves us with 72 REs per RB. Since resources are assigned per ms, a UE will be assigned a minimum of two RBs (one in the first .5 ms and one in the second .5 ms). For simplicity's sake, I am calling this a Resource Block pair. This will give us a total of 144 REs per Resource Block pair. If all of the bandwidth is given to just one UE, then that UE will received a total of 14400 REs (144 REs per RB and 100 RBs). With the maximum modulation scheme of 64QAM, we are able to transmit 6 bits per RE. That gives us 86400 bits per subframe or 86.4 Mbps. The following table provides a summary of these calculations.

Uplink

Total Bandwidth (MHz)	20
Total Resource Blocks	100
Resource Elements per Resource Block	84
Resource Element Overhead	12	Uplink Reference Signals
Available Resource Elements per Resource Block (after overhead)	72
Resource Elements per Resource Block pair (in one ms)	144
Total Resource Elements available per subframe	14400
Bits per Resource Element	6	64 QAM
Total bits per subframe	86400
Raw Channel Bandwidth (Mbps)	86.4

Let's take a look at the downlink maximum theoretical data rates. We are going to examine this in two stages. The first is when we are using a single transmit antenna (also referred to as Single Input Single Output or SISO) or when we are using a 2x2 MIMO or Multiple Input Multiple Output. The second case is when we are using 4x4 MIMO. The difference is that there is more overhead for 4x4 MIMO.

In the first case we will look at the SISO or 2x2 MIMO maximum theoretical data rates. The calculations start the same as they did for the uplink case. We assume a 20 MHz spectrum and a 64 QAM modulation scheme. For every Resource Block pair we will lose 24 REs for overhead, 12 for the Physical Downlink Control Channel and 12 for Downlink Reference Signals. This gives us a total of 144 REs per RB after the overhead is removed. If all of the bandwidth is given to just one UE, then that UE will receive a total of 14400 REs (144 REs per RB and 100 RBs). With the maximum modulation scheme of 64QAM, we are able to transmit 6 bits per RE. That gives us 86400 bits per subframe or 86.4 Mbps. So for SISO in the DL and the UL, they both support the same maximum. All we need to do is double this number for a 2x2 MIMO case. That gives us a maximum of 172.8 Mbps. The following table provides a summary of these calculations.

Downlink SISO or 2x2 MIMO

Total MHz	20
Total Resource Blocks	100
Resource Elements per Resource Block	84
Resource Elements per RB pair	168
Resource Element Overhead - PDCCH	12	Assuming only one OFDM symbol for PDCCH
Resource Element Overhead - Reference Signals	12
Available Resource Elements per Resource Block (after overhead)	144
Total Resource Elements available per subframe	14400
Bits per Resource Element	6	64 QAM
Total bits per subframe	86400
Raw Channel Bandwidth (Mbps) for SISO	86.4
Raw Channel Bandwidth (Mbps) for 2x2 MIMO	172.8

In the last case we will examine the maximum bandwidth for 4x4 MIMO. The calculations are the same as the other DL case with just one change. There are more Reference Signals that are lost due to overhead. When this new overhead number is used, the per antenna data rate drops from 86.4 to 81.6 Mbps. We take this number and multiply it by 4 and we have the maximum of 326.4 Mbps. Se the following table for more details.

Downlink 4x4 MIMO

Total MHz	20
Total Resource Blocks	100
Resource Elements per Resource Block	84
Resource Elements per RB pair	168
Resource Element Overhead - PDCCH	12	Assuming only one OFDM symbol for PDCCH
Resource Element Overhead - Reference Signals	20
Available Resource Elements per Resource Block (after overhead)	136
Total Resource Elements available per subframe	13600
Bits per Resource Element	6	64 QAM
Total bits per subframe	81600
Raw Channel Bandwidth (Mbps)	81.6	per antenna
Raw Channel Bandwidth (Mbps)	326.4	4x4 MIMO

So there you have it. This is where the "magic" numbers come from. I hope that I have not taken too much of the mystique behind LTE away from you. In all seriousness, I hope this helps to provide some understanding of where these capacity numbers come from. If you have any questions, please let me know.