- EETimes, July Edition, Article "Paper-Thin Batteries set to arrive by 2010" by R. Colin Johnson.
- ARS Technica Article "Scientists create paper-thin, flexible, biodegradable battery".
Sunday, July 19, 2009
Never throw a paper away!!! There might be a battery in it.
Monday, June 29, 2009
Blocked Call Vs Dropped Call
A Blocked Call and a Dropped Call are two very common terms used in telecommunications (Cellular Communications) world these days. These two are completely different phenomena, but the impact they create on a customer is the same, annoyance. In this post I am going to discuss what the differences between these two events are, and briefly explain how they can be handled by the mobile service provider.
Blocked Call:
A Blocked Call is an event that can occur only before the call is completed between the called and the calling parties. Completion of the call here implies the connection being complete for either party to exchange talks. Any call you place on a cellular network, the service provider has to find all the resources necessary to connect the call between the two parties. As I mentioned in my previous post about a wireless call, it is not wireless in entirety and it has to access the wire-line network in order to reach the destination cell phone. In case of a long distance call, a service provider should make sure that there is sufficient network capacity all through the intermediate network hops to carry the call from one end to the other.
If there is not sufficient capacity to carry the call through, this results in a blocked call. When you are in a stadium watching a Baseball match or a Cricket match, when you attempt to make a call, you might hear a voice recording saying “the network is currently busy please try after sometime” or the call may just give three beeps and not connect. This is mainly because of insufficient bandwidth availability (Wireless Channels or the Wire-Line Channels) compared to the number of people attempting to access the network. In one of my posts about Why Sprint Nextel has more dropped calls than AT&T and Verizon? I mentioned that Sprint has an advantage of selecting the higher frequency range of (1900 MHz). If Sprint can tackle the dropped calls issue by installing more cell sites to cover the same area as that of its competitors, this automatically provides higher number of wireless channels in the same geographical area thereby reducing the chances of blocked calls. It still has to build the backbone wire-line network to support the calls but for now let us assume that this matter has been taken care. As the customer base keeps increasing in a geographic area, AT&T and Verizon have to eventually invest to tackle the increasing capacity requests from the customers. But Sprint, already has the wireless network to handle increasing capacity which is definitely an advantage but this is not a great situation to be in. Gradual investment as the customer base grows is always a better situation to be in than investing heavily at once expecting the customer base to rise. So this is a catch 22 situation where the decision has to be made by the service provider depending on the traffic analysis and customer growth analysis made over the years.
This is where traffic management comes into picture. A traffic management team makes sure that the network is always ready to handle the calls at any moment of time including the busiest hour of the day. During events like American Idol or on auspicious days like Christmas Day, Mother’s Day, Father’s Day or New Years Day, the network has to be ready to handle the avalanche of calls that can hit the network. Even in events like the baseball matches, the service provider takes necessary actions to provide more wireless channels by process called Cell Sectoring or another process of turning on smaller and more cellular base station towers to cover the same area.
To summarize things, a Blocked Call is something which occurs before the connection is complete between the called party and the calling party. This phenomenon depends on the entire network, the wireless channels on the calling end, the wire-line backbone network, the wireless channels on the destination end.
Dropped Call:
This is an event that can occur only after the call is connected and the exchange of talks has started. This implies that the network has the capacity to handle this call and the resources necessary for the call have already been allocated to the call. In my previous post I mentioned about the various factors that influence and contribute towards dropping of a call. The dropped call is a result of improper R.F. planning or some of the natural phenomena that cellular signals undergo while travelling in the environment surrounding us. Even as the mobile moves from one coverage area to another coverage area, there might be a dead zone resulting in a dropped call. The co-channel interference also can influence a dropped call but this is more evident in GSM network than CDMA network. A blocked call only depends on the wireless part of the network, i.e. the wireless signal power on the calling side and the wireless signal power on the receiving side.
I tried to explain the difference between a Blocked Call and Dropped Call in simple terms and there might be something that you can add to understand the process better. Please add any comments or suggestions on the blog.
Thank you very much for reading the blog.
Sincerely,
Krishna Chaitanya Emani.
Friday, June 5, 2009
Wireless Communications: Is it Entirely Wireless?
The topic of this blog might be slightly confusing for people who are not familiar with the wireless communications and cellular communications. When you call a technology wireless communications, why should there be a question if it is really wireless? With little over and year experience in the wireless industry, I thought of sharing the knowledge that I gained during this experience.
When you make a call from your mobile phone to any other mobile phone in the same area, how do you think the call is connected? The simplest answer one can give is to say that the call goes from my mobile to the destination mobile and the call is completed. But what actually happens in between the mobile phones is a mystery to many people. Let me give a description of what actually happens when you call someone from your mobile phone. Before going to the details of the call flow, let me discuss few of the very terms used in mobile communications.
Base Station: A base station is a wireless receiver installed by the wireless service provider, which receives signals from various mobile devices in a pre-defined geographic area and processes them to complete the call.
Base Station Controller (BSC): A Base Station Controller coupled with the base station make a Base Station Subsystem. Number of base stations are connected to a base station controller which connects the calls to the Mobile Switching Center (MSC) which is described next.
Mobile Switching Center (MSC): This is more intelligent than the Base Station Controller and has far more responsibilities than the BSC. This is like the Switch used in the old telephone systems, which connect the calls between originating and destination telephones.
When you make a call from your mobile phone, the call goes to the local Base Station which is responsible for the calls in your geographic area. Then the call is sent to the BSC and then handed over to the MSC through a wire-line connection made between the Base Station and the BSC and then from the BSC to the MSC. A single MSC has many Base Stations Controllers connected to it and each MSC maintains a register of all the mobile users under each and every Base Station. When the call reaches the MSC, it checks for the location of the destination mobile phone number and transfers the call to the destination Base Station again on a wire-line connection. Then the call is handed off to the destination mobile phone over a wireless channel.
This is a simple case where the call is between two mobile phones belonging to the same Mobile Switching Center (MSC). Even in such a simple case, it is pretty clear that a wireless to wireless or a mobile to mobile call is not wireless in entirety. It is wireless only from our mobile phones to the closest Base Station and then goes a really strong wire-line network built by the mobile service providers. In a more complex case where the call has to travel longer distances, or has to jump from one MSC to another, it is still wireless only from the mobile to the base station and then it traverses the wire-line network over longer distances built between MSC. I will discuss about the various call flows later in my blog taking one scenario at a time.
Please let me know if you have any questions about the explanation I have given in the following blog.
Thanks,
Krishna C. Emani
Monday, May 18, 2009
Notebook for $200. First Step towards future computing.
Hello All,
I purchased my HP laptop with nominal configuration for $1400 in April, 2007. I am sure, that configuration is no longer available and even if it is, it would not cost more than $500. The competitive market is definitely helping the consumers to get a lot value for less money. Laptops with 4GB RAM and latest processor would cost someone around $800 these days. But where is the future heading? Are we going to see the laptop prices going down every day? Are we going to see a laptop with everything (Operating System, Hard Disk Data, and Applications) in the cloud (Cloud Computing) and only has a keyboard and display on the piece in our hand?
This was the inspiration for the company Celio Corp to design an external peripheral to the Smartphone without any Operating System or even a CPU. This great innovation is called the Redfly System and it merely has anything but a graphics processor to provide the necessary graphical experience to the user and a Bluetooth link to connect to the Smart Phone. The complete demonstration of this system can be viewed in the video that I provided above. This is not a completely new concept as Palm introduced something similar to this almost a year back. It was called the Palm Foleo. Please check this video about Palm Foleo. This video actually explains the need for an external display and keyboard very clearly.
Considering that Palm has done this already, you might be wondering what’s the importance and difference in this new Redfly system compared to the one that Palm introduced last year. The prize of the new Redfly System ($200) is very low compared to the Palm Foleo ($499) and technically the Redfly system is less complex than the Foleo as the later had a processor, Linux OS and some other basic applications on it. Another major advantage with the Redfly system is that, its platform independent compared to the Palm Foleo which can only be used with the Palm Smart Phones.
This seems to be a very good idea and it certainly caught the eyes of many major vendors in the smart phones industry. Have to wait and see how this external display device would enter the market and create a wave in the market. The company is ready to launch a device compatible with the Blackberry by the end of this year according to the article I read on the Mobile Handset Design Line website.
References:
1. EE Times for the Video.
2. http://www.mobilehandsetdesignline.com/ – for the Article and release news.
3. http://www.youtube.com/ – For the Palm Foleo Video.
If you have any comments or suggestions about the post, or if you have any updates to the current information provided, please feel free to add comments in the comments section.
Thank you very much for reading my blog.
Sincerely,
Krishna C. Emani.
Thursday, May 14, 2009
Why Sprint Nextel has more dropped calls than its competitors AT&T and Verizon?
Hello all,
Sprint Nextel is a company that has been on a revival for quite some time. The market has been responding positively to the radical steps taken by Sprint to create a niche for itself in the telecom market. The customer service has been improving over the past few months, a positive vibe is being created in the market about the improvements in the customer service and the network reception. Thanks to the new CEO Dan Hesse for re-vamping the company and prioritizing these major issues to be addressed.
One major issue Sprint Customers always faced is the "Higher Dropped Calls Rate".
Why does Sprint have more dropped calls than its competitors AT&T and Verizon?
This is the topic of my blog and I will be explaining the reasons for this higher dropped call percentage.
First of all, let me tell you some facts about these three major wireless carriers.
Verizon uses CDMA (Code Division Multiple Access) technology and operates in the 800 MHzfrequency range.
AT&T uses TDMA (Time Division Multiple Access) technology and operates in the 800 MHzfrequency range.
Sprint uses CDMA technology and operates in the 1900 MHz frequency range.
Verizon and Sprint use the CDMA technology while AT&T uses the TDMA technology. Each of these technologies have their own advantages and disadvantages, and we are not going into the details of these technologies as they are not responsible for the drop calls, which is the topic of this blog. The next major observation you might have made is in the frequency range in which these carriers operate. Both AT&T and Verizon operate at 800 MHz frequency and Sprint operates at 1900 MHz frequency. Why am I discussing this point? Are you thinking this is the reason for the increased dropped calls on the Sprint Network? If you are thinking that way, you are right on target. Yes the frequency of operation is the major reason for the dropped calls.
Let me explain in detail why this is a valid reason.
Any wireless signal propagating in the free space follows something called as free space path loss to determine the power of the signal at the receiver.
Pr = Pt Gt Gr ( λ / 4πd )2
This is the equation which gives the power of the received signal at the receiver, where Pt is the transmitted power. For more detailed explanation please refer to this page.
As you can see the received power at the receiver is directly proportional to the square of the wavelength of the transmitted signal carrier. As frequency is inversely proportional to the wavelength, lower the frequencies => higher the wavelength and therefore, higher received power. You can clearly observe the decrease in the receiving power as the frequency increases in the table given in the following page. So as the frequency of the signal increases the coverage area of the transmitting antenna reduces. This is exactly the problem faced by Sprint. As you can observe the frequency at which Sprint operates (1900 MHz) is higher than the frequency at which both AT&T and Verizon operate (800 MHz) and as the transmission power of a cell tower is restricted by the FCC regulations, the coverage area of Sprint tower would be lesser than the coverage area of AT&T or Verizon tower. So in order to cover the same area, Sprint needs more transmitting antennas at higher operating frequencies than its competitors operating at lower frequencies.
Easiest thing for us to say is, “why doesn’t Sprint install additional antennas to compensate for the higher frequency range and lower coverage area?” Well Sprint did deploy additional towers everywhere throughout the nation and took extra care to make sure the customers have very less to no dropped calls but in spite of the effort, the network is failing to deliver the results as the higher frequencies are more vulnerable to the surroundings than the lower frequencies. Trees around the cell phone might make the signal weak, black paint can make the signal weak, and there are many other factors that can impact the power of the signal. This creates a lot of holes in the network. This is the reason for increased dropped calls when you are travelling from one location to another.
Another phenomenon called diffraction helps the wireless signal to bend around an obstacle’s edge and reach the receiver. Sprint’s higher frequencies fail to impress in this phenomenon too, as the performance of signal undergoing diffraction is better at lower frequencies than at higher frequencies. The signal bends around the edge of the obstacle better at lower frequencies than at higher frequencies.
Penetration is another phenomenon by which the signal reaches the receiver (cell phone) when you are indoors. Even in the phenomenon, Sprint’s higher frequencies perform badly than its competitors. As the signal penetrates through various obstacles it is attenuated (amplitude reduces as it passes through the walls) and as the frequency increases the rate of attenuation increases, thereby making the signal weak indoors. For additional clarification or explanation of the process please refer to the following white paper.
Finally, these are the reasons for Sprint’s higher drop call rate and lack of signal indoors. You might be wondering, why Sprint chose these higher frequencies when there are so many disadvantages associated with the frequency range? Well that’s a valid question and there is a substantial reason for this selection. I would be discussing the reasons and advantages of selecting this higher frequency range in my later blogs.
Currently Sprint is making an intriguing effort to fill the holes in the network and provide spotless network to its customers by using various technologies like using a broadcaster at home to pull the signals and re-broadcast them in the house, using these repeaters in places of reported signal lose etc. Will it be successful in changing the image that the customers currently have? We have to wait and see.
Thanks a lot for reading my blog. Feel free to leave comments on this discussion or also feel free to email me any questions you might have on the following discussions.
References:
1. http://www.crouse-hinds.com/wirelessIO/PDF/White%20Paper/white_paper_frequencies.pdf
2. http://www.dsprelated.com/showarticle/62.php
3. http://www.fcc.gov/pshs/techtopics/techtopics17.html
Sincerely,
Krishna Chaitanya Emani.
Tuesday, May 12, 2009
What's the Secret Behind Apple's Success?
Sincerely,
Saturday, May 9, 2009
Making a video using Windows Movie Maker
1. Open Windows Movie Maker. Usually you dont find the icon on the desktop, so you have to search for it or open it from the start menu.
2. Select all the pictures, videos and the audio songs (for Background of the movie) which you want to involve in the movie. You can do this by dragging and dropping the items in the windows movie maker or Click on File -> Import Media Items.
3. Once you select all the pictures that you want to include in your movie, you are at the door step of creating your first movie.
4. The simplest way to create a movie is to click on the option "Auto Movie" on the top of the toolbar. This would arrage all the pictures and videos you imported into a movie and you can see a preview of the movie in the window to the right.
5. But if you want to make a sensible movie, by selecting an audio song matching the situation of the pics and videos you have, you need to spend a little more time. Well, infact quite some time. If you observe the windows movie maker screen, you will find a Video, Audio/Music and the Title Overlay options.
6. From the imported media, select the pictures you want to add to the video and drag them and drop them on the Video Bar.
7. Select the Song or Audio file you want to use as a background into the Audio Bar.
8. You can arrange the timing of each picture by dragging the length of the picture in the video bar. You can see the timing of each picture by looking at the timeline bar above the video bar. If you want to go to minute timing details, you can zoom into the timeline by clicking on the zoom option.
9. To add special effects to the pictures in your video e.g. Zoom In, Fade, Pixelate etc, right click on the picture in the video bar and click on the effects option. Select the effect you would like to use and click add. You will find all the effects in the window to the right and click OK. To get a preview of how your pic looks with the special effects, you can click on the play button on the right and view the pic.
10. Adding titles and credits. You can do this by clicking on Tools -> Titles and Credits. Then you can either add the titles at the beginning of the video on a blank screen or select the picture on which you want to add the titles. By doing this you can make your video more inteactive. You can do this to any picture and add the subtitles to make the video informative.
11. Transitions: You can manage how one picture disappears and the next picture appears in your video by using the transitions. Click on Tools -> Transitions. Select the transition style you would like to use and drag and drop that in the timeline where you want to use this transition.
12. Sometimes you might want to remove the audio of the video you recorded and just use the background music. When you add the video, you find an additional Audio bar added to the video bar. You can right click on that Audio and click the option mute.
13. Once you make all the arrangements of the pictures, transitions, audio, titles and credits, you have to save the movie. Click File -> Publish Movie -> This Computer -> Enter the Name of the Movie and select a place to save the video -> Select the Recommended option and click Publish.
This might take a few minutes but you are all done, and you have a mpg video saved on your computer.
You can play this on any computer now, you can write a CD or a DVD and play it on your TV or projector. You will love to see yourself on a huge screen dont you?
I tried to cover most of the points but of course not every detail. I am sure you will be able to figure out the other trivial parts of this process. If you got any questions, feel free to post them and I will reply to you personally or make a post addressing the issue.
Hope this post helps some of you create some simple videos. This is a sample video that I made picturizing the feelings of my undergrad friends, when we met 2 years after our graduation. Feel free to leave comments on the video too.
http://video.google.com/videoplay?docid=-7102057580557078607&ei=SckFSp2SCZSkrQL2p4nFCw&q=auroreunion
Thanks,
Krishna Chaitanya Emani.