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Thursday, March 26, 2009

MIT Open Course Ware ..enjoy :-)

Today I came across MIT Open Course Ware:

MIT: The Massachusetts Institute of Technology (MIT) is a private research university located in Cambridge, Massachusetts, United States. MIT has five schools and one college, containing a total of 32 academic departments, with a strong emphasis on scientific and technological research. MIT is one of two private land-grant universities[b] and is also a sea-grant and space-grant university.

MIT OpenCourseWare (OCW) is a web-based publication of virtually all MIT course content. OCW is open and available to the world and is a permanent MIT activity.

It's amazing for self learner...

You can know more about OCW @

Here, You can see course details from their website: There is audio-vedio courses as well....
Aeronautics and Astronautics
Athletics, Physical Education and Recreation
Biological Engineering
Brain and Cognitive Sciences
Chemical Engineering
Civil and Environmental Engineering
Comparative Media Studies
Earth, Atmospheric, and Planetary Sciences
Electrical Engineering and Computer Science
Engineering Systems Division
Experimental Study Group
Foreign Languages and Literatures
Health Sciences and Technology
Linguistics and Philosophy
Materials Science and Engineering
Mechanical Engineering
Media Arts and Sciences
Music and Theater Arts
Nuclear Science and Engineering
Political Science
Science, Technology, and Society
Sloan School of Management
Special Programs
Urban Studies and Planning
Women's and Gender Studies
Writing and Humanistic Studies

If we can't study masters , still we can learn more using these courses in our field of interest.

Wednesday, March 11, 2009

GPRS (General Packet Radio Services)

Here, after GSM, before I go to 3G world, thought to spare some time to get clear idea about GPRS. Here, you can find few things about GPRS.

GPRS is a data service for GSM. GPRS is a packet switched mobile data service, it is wireless packet based networks to carry data,

In GPRS, data transferred is encapsulated into short packets with a header containing the origin and destination address.
The packets are then sent individually over transmission network. Packet originate from one user can take different route through the network to the receiver. Packet originate from the many users can be interleaved. So, that transmission capacity is shared. No pre-set time slots are used. Instead network capacity is allocated when needed and released when not needed. This is called statistical multiplexing. In contrast to GSM voice or circuit switched data.

GPRS upgrades GSM data service to be more compatible with LANs, WANs and Internet. GPRS uses radio resources only when the data is to be sent or received.

While the current GSM system was originally designed for voice sessions, the main objective of GPRS is to offer access to standard data networks such as TCP/IP. These networks consider GPRS to be normal sub-network.

In terms of architecture point of view, there are two new important entities in GPRS. GGSN (Gateway GPRS support Node), and SGSN (Serving GPRS Support Node). It also has few additional functionality in BSS.

The SGSN provides subscriber management, mobility management, as well as session management for any mobile GPRS user that has been associated with this SGSN. In order to achieve this task, the SGSN holds interfaces to the GSM subscriber databases: HLR, VLR, AUC and EIR. The SGSNs also hold the interfaces to the BSSs, and provides the authentication and encryption services for secure transmission of user data.

The GGSN provides connectivity to external Packet Data Networks (PDNs).
The GGSN also provides address translation services. Rate adaptation services between the GBS and external networks may also be included in the GGSN. The Border Gateway
provides connectivity to another Operator’s GPRS network.

New interfaces will be required to connect the new entities to the existing GSM network elements. These interfaces will be pre-fixed with the character ’G’ and will support both traffic and signal connections.

The Benefits that GPRS provides compared to Circuit switched data:
The data transferred is encapsulated into short packets with a header containing the origin and destination address. The packets are then sent individually over the transmission network. Packets originating from one user may take different routes through the network to the receiver.

Packets originating from many users can be interleaved, so that the transmission capacity is shared. No pre-set time-slots are used. Instead, network capacity is allocated when needed and released when not needed. This is called statistical multiplexing, in contrast to static time division multiplexing. In static time division multiplexing, time-slots are reserved for one user for the length of the connection regardless of whether it is used or not, as with PCM lines and GSM voice and circuit switched data.

GPRS upgrades GSM data services to be more compatible with LANs, WANs and the Internet.

GPRS uses radio resources only when there is data to be sent or received, and so is well adapted to the very bursty nature of data applications.

Furthermore, it provides fast connectivity and high throughput. While the current GSM system was originally designed for voice sessions, the main objective of GPRS is to offer access to standard data networks such as TCP/IP.

Stay tuned for 3G now:-))


Thursday, March 5, 2009

Wireless evolution ...GSM and CDMA

Well, let me take you the tour about wireless technology. Even if you are a non technical person, you can enjoy it.
As of now, we all are use to with cell phone, so, it will not be difficult to understand the
technology behind.
Well, before actually start to go into nore detail with GSM technology, let’s have a look about what and how wireless technology evolved?
Yes, you are right, we can start with a cordless telephone.
It’s a telephone with a wireless handset that communicates via “radio waves” and the base station connected to a fixed telephone line.
The cordless handset is powered by rechargeable battery, which is charged when the handset sits in the cradle.
Same way, wireless services expanded gradually like
Wireless PBX =>will allow you to use wireless handset within that wireless PBX coverage area.
then Paging and Cellular telephones and Mobile satellite service etc.
So, ultimately, what drives to expand wireless services? From one technology to other? From one generation to other?

It’s coverage and mobility. => from cordless to cell phone => what’s the service or attraction?
1) More coverage (from home coverage to worldwide coverage)
2) More mobility (from very low area (walk able) to high speeds even if you are driving a car).

Now let’s talk about GSM...let’s start from it’s background.
In Earlier days large number of analog systems were used. But it was not matching ideal situation from subscriber point of view. Then to accommodate an increasing number of users and to establish compatibility with the evolution of fixed network toward digital, CEPT (Conference Europeenne des Postset Telecommunications) establish a “Group Special Mobile” in 1982. The work of that group became GSM system and now it is a Global System for Mobile communication.

Clear objective of GSM standards are.
1) Common radio spectrum in all countries 2) Integrated European system with international roaming 3) Create large single market 4) Increase available cellular radio capacity 4) Standardization of network components and network interfaces 5) Better security functions 6) Compatibility with evolution of fixed digital networks 7) Accommodate new services.

Now let’s talk about how wireless technology works? How my voice can reach to the destination? How do we use RF spectrum? What is air interface and how do we process it to support multiple users?

Well, when we talk about mobile communication. It is nothing but an air interface.
1) Mobile telephone is nothing more than an FM radio with over 400 pairs of radio channels.
2) These channels are paired . so that one channel is from mobile to base and other is from base to mobile. This makes possible the full duplex communication. In technical term we refereed them as uplink and downlink frequencies.
3) There is set of two way control channels that control voice channel.
4) Air interface need process by which voice channel allocated to multiple users simultaneously.

Early systems now referred as first generation (1G), used analog technology called Frequency division multiplexing (FDMA). Which means each call is carried over a separate frequency channel.
When you dial a number, a channel pair is assigned to a mobile station for duration of one voice call.
You are right, major problem with that was fewer users can support with a single cell. More technically it has poor quality, less coverage as well. So, second generation (2G) was deployed with digital technology. In early 1990, TDMA was used to introduce the GSM into Europe.
In TDMA, each frequency channel is further divided into a set of time slot. Each time slots further carry a set of data. Result, more users can support, better voice quality, more coverage.
To use these time slots, the analog voice had to be converted to digital. A voice coder, known as a vocoder, performs this process. The number of voice channels per radio channel could be increased significantly.
In mid 1990, CDMA became second type of digital 2G system.
In CDMA the approach was different. Instead of time slot, each voice channel has assigned unique code before being added into radio channel. In terms of analogy imagine an international airport. When you enter the air port, there is announcement in different languages.
English men ears will hear English announcement, germen men will hear in German voice and so on through the languages of the world. You can pick the appropriate signals and overall noise signals as well..Compared with TDMA, CDMA offers more capacity at the same or better voice quality level.
But as we move on......and wireless industry evolve,
TDMA, and FDMA will be sent to the dustbin of the history. GSM path ends with the WCDMA (wide band CDMA) where the CDMA ends with the CDMA2000.
.....stay tuned to know more about 3G, 4G. :-))


3 column blog template

Was trying to modify my current template such that I can use the full page for blogging..could able to do some changes, but didn’t get the exact result I wanted. Well, it requires more change somewhere in a code i guess.

Meanwhile, I came across some good template sites for blogging. Saw some existing google’s template modified by people for google Adsense.
It means, you can have a 3 column template with your exist google blog template like “Harbor”, “Scribe”, “Rounders”, "Tekka" etc.

Here you can download,

Few more website I came across, among them I liked the one which has wide variety of templates with different themes on different subjects.

Happy blogging with new/modified blog templates :-))