Telecommunications Blog

Telephone networks are known as public telephone networks.

They consist of :

•  Trunk exchange .
•  Local exchange .
•  And lines between them .

The lines can be divided into trunk lines and local lines.

Simplified Trunk Cable Diagram

1- The Trunk Networks

Lines which are used for trunk traffic only are described as trunk lines . These networks can be designed as :

•  Meshed networks
•  Star networks
•  Or mixed networks
• Transmission medium
•  Symmetric copper pair
•  Coaxial copper cable
•  Optical fiber
•  Air (radio )

Trunk /network Configuration

TOOLS USED FOR RF PLANNING :



Network Planning Tool :

• Planning tool is used to assist engineers in designing and optimizing wireless networks by providing an accurate and reliable prediction of coverage,  doing  frequency planning  automatically,  creating neighbor lists etc.







•  With a database that takes into account data such as terrain, clutter, and  antenna radiation patterns,  as  well  as  an intuitive  graphical interface, the Planning tool gives RF engineers a state-of-the-art tool to:

       – Design wireless networks
       – Plan network expansions
       – Optimize network performance
       – Diagnose system problems
• The major tools available in the market are Planet, Pegasos, Cell Cad.
• Also many vendors have developed Planning tools of their  own like Netplan by Motorola, TEMS by Ericsson and so on.

• Designing a cellular system - particularly one that incorporates both  Macrocellular  and Microcellular  networks  is  a delicate  balancing  exercise.

• The goal  is  to  achieve  optimum  use  of  resources and maximum revenue potential whilst maintaining a high level of system quality.

• Full consideration must also be given to cost and spectrum allocation limitations.

• A properly  planned system  should allow  capacity  to  be added economically when traffic demand increases.

• As every urban environment is different, so is every macrocell and microcell network. Hence informed and accurate planning is essential in order to ensure that the system will provide both the increased capacity and  the  improvement  in network  quality where  required,
especially when deploying Microcellular systems.


• RF planning plays a critical role in the Cellular design process.

• By doing a proper RF Planning by keeping the future growth plan in mind we can reduce a lot of problems that we may encounter in the future and also reduce substantially the cost of optimization.

• On the other hand a poorly planned network not only leads to many Network problems , it also increases the optimization costs and still may not ensure the desired quality.

• An antenna is an electrical conductor or system of conductors

             * Transmission - radiates electromagnetic energy into space
             * Reception - collects electromagnetic energy from space

• In two-way communication, the same antenna can be used for transmission and reception

Antenna Definition

   An  antenna  is  a  circuit  element that  provides  a  transition  form  a guided wave on a transmission line to  a  free  space  wave  and  it provides  for  the  collection  of electromagnetic energy.

  In  transmit  systems  the  RF  signal  is generated,  amplified,  modulated  and applied to the antenna.

   In receive systems the antenna collects electromagnetic  waves  that  are “cutting”  through the  antenna  and induce  alternating  currents  that  are used by the receiver.

Polarization


   Polarization  is  the  direction  of  the  electric field and is the same as the physical attitude of the antenna.
 
          - A  vertical  antenna  will  transmit  a  vertically polarized wave.

  The  receive  and  transmit  antennas  need  to possess the same polarization.

  Wireless ad hoc networks have special characteristics related to node mobility, node self-configuration and the lack of centralized access points (APs). However, wireless ad hoc technologies have several disadvantages when compared to traditional wireless
networks, including their limited resources, such as:

       ** Lower processing capacity
       ** Limited memory
       ** Battery dependency

  Because operations are not centralized in a single access point, information is openly distributed among the network nodes. As a result, wireless ad hoc networks are not as secure as typical wireless networks.

  Wireless ad hoc networks are usually associated with wireless mesh networks; however, these two concepts can be dealt separately.

  The essential idea of wireless ad hoc networks is that they are mobile and dynamic. This
concept is not at all new.
Source : IEEE

SS7 Protocol :


     The primary signaling protocol in use today is signaling systems 7(SS7), which interconnects networks such as SSP, SCP .

     The SS7 Protocol stak consist in several individual protocols, including Message Transfer Part (MTP) level1,2 and 3, Integrated services Digital Network User Part, Signaling Connection Control Part (SCCP), and the Transmission Capabilities Application Part (TCAP) working together, these protocols define the format for all SS7 messages, as well as the procedures by which messages are generated and processed.
    

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

     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.
 

    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

     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.

     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

         

    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) 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.
  
     

Hello ,
My name is mahmoud . A communications engineer .I'd like to share all things that i know with you .This blog will discuss all things about Communications engineering and Communications networks as cellular ( GSM , UMTS and LTE ) and networks ( WiFi - WiMAX ).
I wish that i can help each one who needing help or searching for any information .
Thanks ,
Mahmoud