January 2011 - Telecommunications Blog

A blog for mobile communications systems GSM , UMTS and LTE

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Saturday, January 22, 2011

PE license and exams

1/22/2011 05:50:00 AM 0
PE  license and exams
The PE exam tests your ability to practice competently in a particular engineering discipline. It is designed for engineers who have gained at least four years’ post-college work experience in their chosen engineering discipline. The PE exam is typically the last step in the process of becoming a licensed P.E.

PE exam specifications and design standards

Agricultural
Architectural
Chemical (updated for April 2011 exam)
Civil: Construction
Civil: Geotechnical
Civil: Structural
Civil: Transportation
Civil: Water Resources and Environmental
Control Systems (updated for October 2011 exam)
Electrical and Computer: Computer Engineering

Fundamental WiMAX Concepts

1/22/2011 02:16:00 AM 1
Fundamental WiMAX Concepts
  WiMAX has four fundamental architectural components:


Base Station (BS) : 

      The BS is the node that logically connects wireless subscriber devices to operator networks. The BS maintains communications with subscriber devices and governs access to the operator networks. A BS consists of the infrastructure elements necessary to enable wireless communications, i.e., antennas, transceivers, and other electromagnetic wave transmitting equipment.

      BSs are typically fixed nodes, but they may also be used as part of mobile solutions , for example, a BS may be affixed to a vehicle to provide communications for nearby WiMAX devices. A BS also serves as a Master Relay-Base Station in the multi-hop relay topology .


Wednesday, January 19, 2011

Turbo Code Applications 2

1/19/2011 01:16:00 PM 0
Turbo Code Applications 2
Terrestrial telephony: 
 
    Turbo codes are suited for down-to-earth applications such as terrestrial telephony. Satellite technology provides global coverage and service. UMTS is being standardized to ensure an efficient and effective interaction between satellite and terrestrial networks. 

    An important third generation cellular standard is cdma2000, which is standardized by the third generation partnership project (3GPP). As in UMTS (Universal Mobile Telephone Service), cdma2000 systems use turbo codes for forward error correction (FEC). While the turbo codes used by these two systems are very similar, the differences lie in the interleaving algorithm, the range of allowable input size and the rate of constituent RSC encoders. 

Turbo Code Applications 1

1/19/2011 01:14:00 PM 0
Turbo Code Applications 1

Mobile radio: 
 
     Few environments require more immunity to fading than those found in mobile communications. For applications where delay vs performance is crucial, turbo codes Offer a wide trade-off space at decoder complexities equal to or better than conventional concatenated code performance. The major benefit is that such systems can work with smaller constraint-length convolutional encoders. The major drawback is decoder latency. Turbo codes with short delay are being heavily researched. Turbo codes generally outperform convolutional and block codes when interleavers exceed 200 bits in length. 

Digital video: 
 

Motorola i886

1/19/2011 12:11:00 PM 0
Motorola i886
    The Motorola i886 is a very solid candybar phone coated in soft touch paint for a quality feel. It has a 2.2” QVGA display with 262K colors with an ambient light sensor. The display is good enough; smaller text sometimes looks a bit choppy but is readable and the screen can be used in most lighting conditions with little issue. Below it is a traditional 12 key dialpad with navigation cluster. The 5-way directional pad has three buttons to either side. To the left is menu, send and notifications while to the right you’ll find home, end and back. Like most of the phone the keys are painted with soft touch and they have a good feel to them. They are prominently raised and offer good feedback and travel.


 

Samsung C3530

1/19/2011 12:07:00 PM 0
Samsung C3530
     Smartphones and big screen sizes are all the rage nowadays and even though they offer great functionality, there is still the casual user, who does not need the big screen and just wants to make a call or send a text. But hey, this does not mean that looks don't matter at all.

     The box of the Samsung C3530 contains a micro USB wall charger, standard 3.5 mm ear buds and the user manual. Nothing surprising save for the lack of a USB cable, which is rather annoying.




Nokia C3 Touch

1/19/2011 12:02:00 PM 0
Nokia C3 Touch
    This is a global GSM phone. It can be used with T-Mobile USA and AT&T.


    The design of the Nokia C3 Touch and Type borrows heavily from the higher-end C-series devices as has already been mentioned, especially the Nokia C6-01. Unlike the C6-01 however, the C3 Touch and Type feels extremely well-weighted, solid and reassuringly sturdy in the hand. With a stainless steel finish across the whole unit, it also looks much higher-end than the X3 T&T alternative. The keys are large and visually complement the rest of the phone's aesthetic which is great.


Tuesday, January 18, 2011

Introduction to 802.11 Standard

1/18/2011 02:56:00 PM 0
Introduction to 802.11 Standard
     IEEE 802.11 standard specifies a 2.4 GHz operating frequency with data rates of 1 and 2 Mbps using either Direct Sequence Spread Spectrum (DSSS) or Frequency Hopping Spread Spectrum (FHSS). The IEEE 802.11a standard specifies an OFDM physical layer (PHY) that splits an information signal across 52 separate subcarriers to provide transmission of data at a rate of 6, 9,12, 18, 24, 36, 48, or 54 Mbps. In the 802.11a IEEE standard the 6, 12, and 24 Mbps data rates are mandatory. Four of the subcarriers are pilot subcarriers that the system uses as a reference to disregard frequency or phase shifts of the signal during transmission.
 

Sunday, January 16, 2011

Basic commands and syntax in MATLAB

1/16/2011 12:46:00 PM 0
Basic commands and syntax in MATLAB
    We will speak about Basic commands and syntax in MATLAB to show how we can write code in it .

    If you type in a valid expression and press Enter, MATLAB will immediately execute it and return the result.

>> 2+2
ans =
           4

>> 4ˆ2

ans =
           16

>> sin(pi/2)

ans =
           1

>> 1/0


Intro to MATLAB

1/16/2011 12:30:00 PM 1
Intro to MATLAB
     MATLAB is a software package for computation in engineering, science, and applied mathematics. It offers a powerful programming language, excellent graphics, and a wide range of expertknowledge. MATLAB is published by and a trademark of The MathWorks, Inc.






     The focus in MATLAB is on computation, not mathematics. Hence symbolic expressions and manipulations are not possible (except through a clever interface to Maple). All results are not only numerical but inexact, thanks to the rounding errors inherent in computer arithmetic. The limitation to numerical computation can be seen as a drawback, but it is a source of strength too: MATLAB generally runs circles around Maple, Mathematica, and the like when it comes to numerics.

Thursday, January 13, 2011

Intro to UMTS

1/13/2011 09:56:00 AM 0
Intro to UMTS
     UMTS (Universal Mobile Telecommunications Service) is a third-generation (3G) broadband, packet-based transmission of text, digitized voice, video, and multimedia at data rates up to 2 megabits per second (Mbps). UMTS offers a consistent set of services to mobile computer and phone users, no matter where they are located in the world. 



   

Wednesday, January 12, 2011

What's OFDM-MIMO ?

1/12/2011 11:11:00 AM 1
What's OFDM-MIMO ?
 Multiple Input Multiple Output (MIMO)

     One building block for next-generation wireless access, MIMO (multiple-input, multiple-output), is an advanced antenna technology that can carry 4 to 5 times more data traffic than today’s most advanced UMTS-HSDPA-ready (3G) networks. A network design incorporating MIMO technology provides the scalability needed to quickly deliver multimedia content to the mass market. With MIMO, for example, a ½ megabit picture can be downloaded in a half second or a 30-megabit video in half a minute. 

We know that there are 4 types : SISo , SIMO , MISO and MIMO  


SISo : Single i/p , Single O/p
SIMO : Single i/p , Multi o/p
MISO : Multi i/p , Single o/p

         

OFDM Advantages and Disadvantages

1/12/2011 11:01:00 AM 1
OFDM Advantages and Disadvantages
    The major advantage of OFDM is its robustness against multi path propagation. Thus, it is suitable to be implemented in wireless environments. The introduction of cyclic prefix made OFDM system resistance to time dispersion. OFDM symbol rate is low since a data stream is divided into several parallel streams before transmission. This make the fading is slow enough for the channel to be considered as constant during one OFDM symbol interval.



   

Orthogonal Frequency Division Multiplexing (OFDM)

1/12/2011 10:46:00 AM 1
Orthogonal Frequency Division Multiplexing (OFDM)
      Orthogonal Frequency Division Multiplexing (OFDM) is a multicarrier modulation technique. OFDM provides high bandwidth efficiency because the carriers are orthogonal to each other and multiple carriers share the data among themselves. The main advantage of this transmission technique is their robustness to channel fading in wireless communication environment.

     OFDM is an attractive modulation scheme used in broadband wireless systems that encounter large delay spreads. OFDM avoids temporal equalization altogether, using a cyclic prefix technique with a small penalty in channel capacity.
  
     

Using SC-FDMA in LTE

1/12/2011 02:51:00 AM 0
Using SC-FDMA in  LTE

     Single carrier frequency division multiple access (SC-FDMA) has been adopted by the third generation partnership project (3GPP) for uplink transmission in technology standardized for long term evolution (LTE) of cellular systems.SC-FDMA was chosen because it combines the low PAPR techniques of single-carrier transmission systems, such as GSM and CDMA, with the multi-path resistance and flexible frequency allocation of OFDMA. 
 
     Data symbols in the time domain are converted to the frequency domain using a discrete Fourier transform (DFT).Then in the frequency domain they are mapped to the desired location in the overall channel bandwidth before being converted back to the time domain using an inverse FFT (IFFT).

     

Sunday, January 9, 2011

Turbo-Decoder

1/09/2011 12:22:00 PM 0
Turbo-Decoder

      The turbo code decoder is an iterative Maximum A posteriori (MAP) algorithm. MAP algorithms use a Bayesian analysis of the channel transition probabilities and the state diagram of the encoder to estimate the most likely transmitted sequence of data bits based on the received sequence of data and code bits. The decoder sequentially decodes the results from each constituent encoder. 

      The results of each of these steps are fed to the next step as a-priori information called extrinsic data. After processing the results of all constituent codes, the algorithm goes back to the first constituent code and repeats the process see Figure below.

Turbo-Encoder

1/09/2011 12:16:00 PM 0
Turbo-Encoder

     Turbo code encoders are a concatenation of systematic encoders referred to as constituent codes. (Systematic encoders pass both uncoded data and code bits.) The data is grouped into blocks before coding. Many variations of concatenation have been used: e.g., parallel, serial, and product codes.The figure is an example of a two-constituent code, parallel concatenated turbo encoder.


     

What's the Turbo-code ?

1/09/2011 12:10:00 PM 0
What's the Turbo-code ?

       Turbo coding is a forward error correction (FEC) scheme. Iterative decoding is the key feature of turbo codes. Turbo codes consist of concatenation of two convolution codes. Turbo codes give better performance at low signal to noise ratio (SNR). 

       Interestingly, the name Turbo was given to this codes because of the cyclic feedback mechanism (as in Turbo machines) to the decoders in an iterative manner.The turbo encoder transmits the encoded bits which form inputs to the turbo decoder. The turbo decoder decodes the information iteratively. Turbo codes can be concatenated in series, parallel or in a hybrid manner. Concatenated codes can be classified as parallel concatenated convolutional codes (PCCC) or serial concatenated convolutional codes (SCCC). 

       In PCCC two encoders operate on the same information bits. In SCCC, one encoder encodes the output of another encoder. The hybrid concatenation scheme consists of the combination of both parallel and serial concatenated convolutional codes. The turbo decoder has two decoders that perform iterative decoding. 

we will speak about Encoder next post then Decoder

Monday, January 3, 2011

Frequency Concepts in GSM

1/03/2011 07:52:00 PM 0
Frequency Concepts in GSM
      An MS communicates with a BTS by transmitting or receiving radio waves, which consist of electromagnetic energy. The frequency of a radio wave is the number of times that the wave
oscillates per second. Frequency is measured in Hertz (Hz), where 1 Hz indicates one oscillation per second. Radio frequencies are used for many applications in the world today.
Some common uses include :
                           • Television  --------------> 300 MHz approx.
                           •  FM Radio  --------------> 100 MHz approx.
                           •  Police radios  ----------> Country dependent.
                           •  Mobile networks  ------> 300 - 2000 MHz approx

      The frequencies used by mobile networks varies according to the standard being used2. An operator applies for the available frequencies or, as in the United States, the operator bids for frequency bands at an auction.

Messages in CDMA

1/03/2011 11:13:00 AM 1
Messages in CDMA
 I want to speak about messages in CDMA , how it sent and what the call processing

**  In CDMA, most call processing events are driven by messages.
** Some CDMA channels exist for the sole purpose of carrying, they never carry user’s voice traffic.
          • Sync Channel (a forward channel).
          • Paging Channel (a forward channel).
          • Access Channel (a reverse channel).
          • On these channels, there are only messages, continuously all of the time.
** Some CDMA channels exist just to carry user traffic.
          • Forward Traffic Channel.
          • Reverse Traffic Channel.
          • On these channels, most of the time is filled with traffic and messages are sent only when there is something to do.
** All CDMA messages have very similar structure, regardless of the channel on which they are sent.


Sunday, January 2, 2011

Adv. & DisAdv. of GSM and IS-95

1/02/2011 05:11:00 PM 0
Adv. & DisAdv. of GSM and IS-95
Advantages of 2G GSM

  • GSM is mature; this maturity means a more stable network with robust features.
  • Less signal deterioration inside buildings.
  • Ability to use repeaters.
  • Talktime is generally higher in GSM phones due to the pulse nature of transmission.
  • The availability of Subscriber Identity Modules allows users to switch networks and handsets at will, aside from a subsidy lock.
  • GSM covers virtually all parts of the world so international roaming is not a problem.
  • The much bigger number of subscribers globally creates a better network effect for GSM handset makers, carriers and end users.
Disadvantages of 2G GSM

  • Pulse nature of TDMA transmission used in 2G interferes with some electronics, especially certain audio amplifiers. 3G uses W-CDMA now.
  • Intellectual property is concentrated among a few industry participants, creating barriers to entry for new entrants and limiting competition among phone manufacturers.[citation needed]
  • GSM has a fixed maximum cell site range of 35 km, which is imposed by technical limitations.[2]

An intro to WiMAX

1/02/2011 12:36:00 AM 0
An intro to WiMAX
WiMAX (Worldwide Interoperability for Microwave Access) ( 802.16 - 802.16e )



     It was defined by the WiMAX Forum is a telecommunication protocol that provided fixed and fully mobile broadband access (IEEE 802.16e ). WIMAX was developed to promote conformance and interoperability of the IEEE 802.16 standard (Wireless MAN). Meanwhile WIMAX Forum is the organization which dedicated to certifying the interoperability of broadband wireless access (BWA). WIMAX Forum will conduct the testing to ensure that different mobile broadband system from many manufactures work properly.

    

Saturday, January 1, 2011

Secret codes for Samsung

1/01/2011 05:30:00 PM 0
Secret codes for Samsung
*#1111#          ------->      S/W Version
*#1234#          ------->      Firmware Version
*#2222#         
------->      H/W Version
*#8999*8376263# 
---->   All Versions Together
*#8999*8378#  
------->    Test Menu
*#4777*8665#  
------->    GPSR Tool
*#8999*523#    
------->    LCD Brightness
*#8999*377#    
------->    Error Menu
*#8999*327#    
------->    EEP Menu
*#8999*3825523# 
---->   Don't Know.
*#8999*667#    
------->    Debug Mode
*#92782#         
------->    Phone Model (Wap)

GSM NETWORK COMPONENTS

1/01/2011 05:00:00 PM 1
GSM NETWORK COMPONENTS
   The GSM network is divided into two systems. Each of these systems are comprised of a number of functional units which are individual components of the mobile network. The two systems are:
              • Switching System (SS)
              • Base Station System (BSS)
    In addition, as with all telecommunications networks, GSM networks are operated, maintained and managed from computerized centers.

AUC     Authentication Center

GSM PHASES

1/01/2011 04:52:00 PM 2
GSM PHASES
    In the late 1980s, the groups involved in developing the GSM standard realized that within the given time-frame they could not complete the specifications for the entire range of GSM
services and features as originally planned. Because of this, it was decided that GSM would be released in phases with phase 1 consisting of a limited set of services and features. Each new
phase builds on the services offered by existing phases.

Phase 1

   Phase 1 contains the most common services including:
          • Voice telephony
          • International roaming
          • Basic fax/data services (up to 9.6 kbits/s)
          • Call forwarding
          • Call barring
          • Short Message Service (SMS)
 

Basics of Optical Fibers

1/01/2011 04:24:00 PM 2
Basics of Optical Fibers
    A fiber-optic system is similar to the copper wire system that fiber-optics is replacing. The difference is that fiber-optics use light pulses to transmit information down fiber lines instead of using electronic pulses to transmit information down copper lines. Looking at the components in a fiber-optic chain will give a better understanding of how the system works in conjunction with wire based systems.


    At one end of the system is a transmitter. This is the place of origin for information coming on to fiber-optic lines. The transmitter accepts coded electronic pulse information coming from copper wire. It then processes and translates that information into equivalently coded light pulses. A light-emitting diode (LED) or an injection-laser diode (ILD) can be used for generating the light pulses. Using a lens, the light pulses are funneled into the fiber-optic medium where they travel down the cable. The light (near infrared) is most often 850nm for shorter distances and 1,300nm for longer distances on Multi-mode fiber and 1300nm for single-mode fiber and 1,500nm is used for for longer distances.