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Apple finally unveiled its new products, in the first presentation in a while that introduced more than one new product. I could spend lines and lines talking about the new iPhone 6 and iPhone 6 Plus and about the new Apple Watch, but other people has already done that. You might want to check out these:

Every time Apple releases new products I post the links to some live blogs in my blog. It used to be because I was very active on my blog, talking about new products and stuff and whatnot. Then I realized that it would bring a ton of visits to my blog. In 2012, with the release of the iPhone 5, I got 25k visits in one day. So now I always post links to the live blogs to see if I get the same result… even though I am way less active on my blog now. It worked very well until Apple started broadcasting the events over streaming. Or maybe that was not the reason. Anyhow, posting links to the live blogs gets me now about 100 hits, which is not much more than the daily average. Why am I explaining this? No idea.

As a result of the decline in hits when posting links to live blogs of Apple events, and in an effort to investigate how Google’s crawling and indexing works, I am going to include in this post the following sentences just for fun and experimentation: Instructions to root the iPhone 6. How to root an iPhone 6. iPhone 6 for free. iPhone 7 design leaked. Where to buy an iPhone 8. Water proof iPad.

You never know, maybe now I get tons of hits from people trying to root the iPhone 6 or people who want to find out where to buy an iPhone 8. For the latter I would ask Marty McFly. By the way, this reminds me of that Chaplin movie where you can see a lady using what looks like a cellphone in some footage from early last century. I had a post about it a long time ago.

Anyhow, the main reason why I started writing this post was to highlight the fact that Barcelona was, once again (recall the special mention, with video included, of the launch of Barcelona’s Apple store during the presentation of the iPhone 5), featured in an Apple presentation. In yesterday’s case, with a “mention” of the cool W Hotel in Barcelona.

iwatch_BCN

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I recently was contacted by someone with questions regarding a document I wrote (LTE PHY fundamentals) a few years ago as part of a class at Columbia University and that is hosted on my website. The confusion was regarding Doppler shift and the time separation of the reference signals in LTE.

Quoting the message:

I was trying to tell you that 500 km/h does not mean a Doppler shift that you wrote in your document. If the carrier frequency is low and the receiver is moving through the transmitter Doppler shift will be zero cos(90).

Please read the LTE documentation carefully: Universal Mobile Telecommunications System (UMTS); LTE; Requirements for Evolved UTRA (E-UTRA) and Evolved UTRAN (E-UTRAN). In chapter 7.3, it is clearly written that this speed can be from 15 to 120 in the best case with a Doppler shift, not 500 as you wrote and even calculated the Doppler shift.

After responding to the question, I thought that it would be a good idea to write a quick post here and reference it from my website to clarify this topic if other people had the same questions.

The 3GPP standards do account mobility of up to 500km/h. Checking ETSI TR 125 913 V9.0.0 (Universal Mobile Telecommunications System (UMTS); LTE; Requirements for Evolved UTRA (E-UTRA) and Evolved UTRAN) one can read:

The E-UTRAN shall support mobility across the cellular network and should be optimized for low mobile speed from 0 to 15 km/h. Higher mobile speed between 15 and 120 km/h should be supported with high performance. Mobility across the cellular network shall be maintained at speeds from 120 km/h to 350 km/h (or even up to 500 km/h depending on the frequency band). Voice and other real-time services supported in the CS domain in R6 shall be supported by EUTRAN via the PS domain with at least equal quality as supported by UTRAN (e.g. in terms of guaranteed bit rate) over the whole of the speed range. The impact of intra E-UTRA handovers on quality (e.g. interruption time) shall be less than or equal to that provided by CS domain handovers in GERAN.

The mobile speed above 250 km/h represents special case, such as high speed train environment. In such case a special scenario applies for issues such as mobility solutions and channel models. For the physical layer parametrization EUTRAN should be able to maintain the connection up to 350 km/h, or even up to 500 km/h depending on the frequency band.

Regarding this topic, Samsung did some very interesting experiments on the high speed case inside a plane flying at 750km/h. Also, a recent paper was presented in a Sigcomm workshop that I was part of the TPC committee. It presented high speed measurements of LTE (check the paper titled “Performance of LTE in a High-velocity Environment: A Measurement Study”).

As for the Doppler shift, the Doppler equation does contain a cos(alfa), but alfa will only be 90 degrees when a mobile is under the cell tower, In general, in mobile communications, one does not consider the special case of alfa=0 (see below for more details). Anyhow, the way system specifications are designed is for the worst case scenario. In the case of LTE, the maximum possible doppler shift is for the highest carrier frequency (~2GHz at the time I wrote the document), V=500km/h and alfa=0 (cos(0)=1). That’s why the separation of the pilot tones in the LTE/OFDMA lattice is 0.5ms (the derivation of the value 0.5ms is in my document). Essentially, the Doppler shift defines the coherence time, which is the duration of time for which the channel does not change “substantially” or, more mathematically defined, the delay for which its autocorrelation is “higher” than a certain value (there is different ways to define coherence time depending on how “strict” one wants to be). Pilot tones or reference signals are used to sample the channel to perform equalization and other tricks. The Doppler shift defines the maximum sampling period that will allow to sample the channel correctly. If the channel can change as fast as every 0.5ms, one needs to have one sample at least ever 0.5ms. Therefore, the reference signals are separated every 0.5ms, tackling this way the worst case scenario for the coherence time.

Generally, in wireless communications for terrestrial applications, one usually does not even consider alfa because the heights of the towers (10 to 50m or so) are much smaller than the distances between the mobile devices and the towers (up to 35km for the biggest supported cells), so the value of alfa is always very small. However, in radar applications they do consider alfa because planes are flying at high altitudes.

Anyways, the best way to read about this concepts and have them explained much better than what I did here, is to check Rappaport’s book.

ReferenceSignal

I am quite busy lately and neglecting my blog too much, it is time to catch up a bit. Although work is one of the main things keeping me busy, going back to playing soccer regularly, running quite often and a few other things are keeping me busy… plus it is summer and in summer I rather spend my free time away from my computer.

Anyhow, to catch up, just a few thoughts on a few things.

I have been gathering some old stuff from when I was an undergrad. I will try to post more source code and other projects on my personal website soon.

Happy summer everyone! And for those of you in the southern hemisphere, happy winter! Oh, and could you please share a video of the toilette flushing and spinning the other way?

First of all, the reason why I have been missing in action for a couple of months on my blog has been that I have been rather busy (but “good” busy) with work. Lots of exciting things happened recently, including reaching two of my main milestones for this year. I am still busy, but I will try to be back here every now and then to share stuff that I find interesting.

Having said that, if you know me well, you know that these days I am doing crazy schedules and working many hours so I can also watch as many World Cup games as possible. I will not reach my great achievements from the World Cups of 2010 and 2006, when I saw every single game of each tournament (yes, you read it right, every single one), but I am doing a decent job. By the way, if you happen to have a lot of free time (I had just finished my undergrad in 2006 and I was on a lazy + learning German + travel hiatus, and I was a grad student in 2010), I challenge you to watch every single game of a World Cup. It’s an amazing experience. But not easy. As an example, I saw the Portugal-France semifinal in a ferry with poor satellite reception going from Athens to Paros. And I saw the final in some random restaurant in the less populated side of Siros.

Anyhow, I just wanted to share some thoughts about the World Cup so far:

  • Spain: I knew we were in a bad shape and there was 0 chances we would mean. But still, what Spain did was lame. The way they surrendered after the Netherlands’ second goal was very sad. I guess Spain always sucks in World Cups and now we just had the last 6 years as an exception. The exception that confirms the rule. I was back home in Barcelona for the games against the Netherlands and Chile, so it hurt even more.
  • USA: I like this team a lot, and I am not saying it because the US is my second (actually, now officially permanent) home. I like how they play, very talented young players. And I really like this Dempsey guy. Back in my grad student years, me and my Spanish friends we always played in the intramurals against the US kids. Playing futsal 5on5 we always kicked ass… but when it was 11on11, those guys had so much stamina and energy that we always lost! And I see that in the World Cup too. It’s very interesing how over the last few World Cups the US has scored a large number of goals towards the end of the game, when the rival is tired (a game every 3 days ain’t easy!). Having said that, sometimes one sees that the US does not have that much experience in soccer. For example, no team has used a “polo-type neck” for the jersey since the early 90s. They need a jersey redesign asap! Also, they did not win against Portugal for 2 reasons: 1) that guy whose dad is the former national couch had a terrible game and made an awesome pass to CR96 Ronaldo, and 2) the US has to master the ancient skill of wasting time.
  • Argentina: Playing bad, but with a stellar Messi. I hope they win the World Cup just so there are no more counter arguments (i.e. he never won a World Cup, unlike Maradona and Pele). The world needs to finally agree that Messi is, BY FAR, the greatest player of all times.
  • Germany: My favorite team (aside from Spain) for the last few World Cups. Playing very good. Although I really want Messi to win a World Cup, I hope for a Germany-Brazil final.
  • Ghana: Such a good team. The way they play is just amazing, and although I always cheer for Germany, I was quite annoyed when Klose scored the 2-2. However, kudos for Klose, top scorer of a World Cup tied with Ronaldo (the good one).

I want to write more, but I’ll leave it here for now. Back to work now! I have been here since 7 today. It will be a long day. But it’s all good, fun stuff at work. Projects going great. And, in parallel, a really fun World Cup. What else can one wish for?

640px-WC-2014-Brasil.svg

Ever since I moved to America I have experienced massive wildfires in Southern California, a couple of small earthquakes in California too, a medium earthquake in NY (it felt quite strong in the high rise building where I work!), hurricane Irene, hurricane Sandy and now arctic freezing temperatures. I might be happy living here but, as my mom always reminds me, there is no place like Barcelona.

Stay warm out there guys!

weather

Back in 2006 I made a mistake. I wrote my undergrad thesis in Catalan. It is a very cool study on Common Radio Resource Management Strategies (CRRM) for GERAN+UMTS heterogeneous networks. I found very interesting results and proposed a bunch of techniques for certain CRRM functions. Eventually, some of my results ended up in a paper published in the proceedings of IEEE PIMRC.

My undergrad thesis is 177 pages long double space. There is a whole bunch of indexes, tables of content, references and other stuff, so it must not be more than 140 pages of text at double space.

I have translated myself the introduction and most of chapter 2, but I have no time for the whole thing. At the current rhythm I estimate I would be done in over a year, which is fine. But I am looking for volunteers who would like to help me translate it to English a bit faster. We do not need Shakespeare English, just something that can be understood. If you decide to volunteer, you decide how much you want to translate. One paragraph, one page, two pages… up to you. I will add a section at the end acknowledging everyone who helps me translate it.

Thanks!

This morning, when I opened my Gmail, I got a notification of a newly improved inbox, which can be customized and lists among your emails stuff from your social media and other things. I checked a bit to see what it is and how it works. A minute later, I disabled it.

Then I realized about something. For the last few years, every time Gmail has introduced a new feature, I have disabled it. In today’s case, I do not want my Inbox to look any different than what it looks now and, specially, I don’t want anything else listed in my inbox. No social media. My inbox is where I want to have my incoming emails.

Recently I also disabled the new (and terrible) compose window. And, unlike many people, I did not activate any custom theme on my inbox. It still has the same basic colors it had over 6 years ago when I created my account.

I am curious. What do you guys think? Are you actually using any of these new Gmail features?

I have not had time to write anything here lately because I have been (and still am) very busy with work. The good news is that it is because of a very cool project about which I am very excited. And any free time I have I spend it running in Central Park, hanging out with friends, hanging out with my girlfriend, watching movies (Iron Man 3 – Good, After Earth – Bad, Safe House – Very good, Parker – Good) …

As I have done sometimes before, this post will contain a bunch of things I have found out lately that, as a post, might be useless, but hopefully they will help someone at some point who is searching for answers on Google.

(N.A.: My knowledge of Unix is very basic – I am a Windows user – but I am getting better at a quite decent pace)

  • To do remote desktop from Ubuntu to a Windows machine use rdesktop.
  • To do remote desktop from anywhere to Ubuntu, install xrdp on Ubuntu.
  • When using rdesktop, use the option “-f” to make it full screen. When you wonder how the heck do I minimize a full screen in Ubuntu, do not waste your time like I did. Here is the answer: ctrl+alt+enter. Use the same keyboard shortcut to get back into full screen.
  • If an Ubuntu machine boots up without a screen connected to it, the display will not work if you connect it later). Turn off the machine, connect the display and turn it on again. The same symptom seems to occur when you disconnect the display from an Ubuntu machine for a while.
  • rdesktop on Ubuntu experiences noticeable delay if you machine does not have a decent graphics card. Chances are, you do not have a decent graphics card. It might improve a bit better if you install actual drivers for your graphics card instead of using the “default” ones.
  • A USRP N210 will not work if it does not see a gigabit connection. This is something you should know already (and I should have known), but it made me waste quite some time trying to figure out what was going on.

That’s it for today. I gotta get back to work.

The main reason I am where I am and I have achieved what I have achieved is the Balsells Fellowship. This fellowship program was started in 1996 by Pete Balsells to help Catalan students come to California to pursue graduate studies at the Henry Samueli School of Engineering of UCI. Pete Balsells, the program and his director, Prof. Roger Rangel, gave me the opportunity back in 2006 to come to America and I will forever thank them for giving me the opportunity to live the Catalan-American dream.

I was reading last night a nice article about the Balsells Fellowship that was posted in the news section of the Henry Samueli School of Engineering website:

Building Towers: Fellowship Program Brings Catalan Engineering Students to the Samueli School

The people of Catalonia, Spain, have a centuries-old cultural tradition of building human towers, or castells (castles). Usually seen at festivals or competitions, the castellers climb up each other and stand on their countrymen’s shoulders to construct a tower that can reach 10-human-stories high, often with a child on top. A crowd surrounds them, providing the safety net.

Successful engineer and Catalan native Peter J. Balsells is creating another sort of human tower, one of opportunity, right here at UC Irvine. In 1995, he endowed the Balsells-Generalitat Fellowship program in The Henry Samueli School of Engineering. Since then, nearly 100 of the most talented young engineers and scientists from Catalonia have come to UCI to pursue graduate studies and conduct research in engineering.

[…]

I just added some LTE resources on my website. Some are links that I had already shared here in this blog, but some other stuff is new. I posted some material I prepared when I was back at Columbia University taking a class on LTE and WiMAX networks (all the documents were done by me except for the LTE link budget calculator). Some of the resources are:

More coming soon!

About me:

Born in Barcelona, moved to Los Angeles at age 24, ended in NYC, where I enjoy life, tweet about music and work as a geek in security for wireless networks.
All the opinions expressed in this blog are my own and are not related to my employer.
About me: http://rogerpiquerasjover.net/

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