Keep in touch with your Friends

Keep in touch with your Friends

 When friends move away, it's hard to keep in touch with them. You both get busy with your separate lives and don't have the time to catch up with each other. Nonetheless, it's important to keep in touch with friends.Here are some ideas for keeping in touch with your buds. 

     Phone Call                
 
 Simply pick up the phone and call whenever you can - it doesn't have to be a long phone call. Just a quick 5 minute call can get you caught up with your pal, and he or she will know you were thinking of them. Let her know that you want to know what's going on with her. They're probably interested to hear about what your up to, too!
Make a commitment to call each of your friends at least once a month. If it's helpful, mark your calendar. After you've spoken with a friend, note on your calendar the day you spoke to them. Next month, when you feel like it's been forever since you spoke to that person, you'll know immediately how long ago it actually was.

     Remember birthdays 
 
 Keep track of your close friends' birthdays, and commit to at least sending them a birthday card, if not an actual birthday phone call. Even better: send flowers or a surprise through the mail.

     Update your address book 

  Update your address book with current addresses and phone numbers regularly. When it comes time to make calls or send out holiday cards, you'll be able to immediately reach your friends.
 
     Email or chat online 

  Take advantage of e-mail. Quick and accessible, e-mail is a great way to send a quick note to a friend. In addition, it's a wonderful way to make lunch plans or get the details of an upcoming weekend trip.
  Make sure you both have e-mail addresses, and you're all set! Homemade letters can easily get lost on the way, get torn, or just get boring. E-mailing your pals is a great and helpful way to stay in touch with each other. Use instant messengers such as MSN or AIM to your advantage, by talking to all your pals at once! Whenever you switch on the computer, be sure to check your in-box of updates!

     Mark the moments you wish you could be there 

  Mark the moments you wish you could be there for friends, even when you physically cannot. If you miss a wedding or a friend is a new parent, send a note or thoughtful gift to wish them the best.

Write letters. It's fun to get mail, and sometimes letters can be a great way to let your pal know what's going on with you. Not sure where to start? It's easy! Tell them how much you miss them, and then tell them all about what's going on in your life. Don't be afraid of being boring...if they know exactly what's up, they'll feel closer to you. Some people find it hard to write letters - it's a lot different than talking! Just write as though you're talking to your friend. Use phrases that you say a lot. Do you say "like" pretty much like, every second word? Then use that when you're writing! It's easy once you get going. Finish your letter off with smiley faces, drawings, x's and o's...whatever seems suitable.

Send cards. Hallmark cards are easily accessible, and it's a non-time-consuming way to let your bud know your thinking about them. Pick something that you think will make them laugh, or one with heartfelt sentiments that describe your friendship. Hallmark's line of musical cards - they sing when you open them! - are sure to bring a smile. Then just sign your name, add a quick message, and send it off!

Send gifts in the mail! Baking, books, magnets, bookmarks, jewelry, games, pictures and videos of you and your family and friends...anything goes! Sometimes the littlest things can show that you care the most - just inexpensive trinkets that show that you're thinking of your friend!

     Plan annual get together 

  Whether it's yourself and a best friends or a circle of friends who are now scattered across the country, make it a point to make regular plans for time that you can spend together. You can make it for spouses and children, if they exist, or simply have a weekend together.

References:
                        ehow
                        wikihow


" Keep in touch with your Friends " !

What is a Satellite?

What is a Satellite

In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon.

The world's first artificial satellite, the Sputnik 1, was launched by the Soviet Union in 1957. Since then, thousands of satellites have been launched into orbit around the Earth; also some satellites, notably space stations, have been launched in parts and assembled in orbit. Artificial satellites originate from more than 50 countries and have used the satellite launching capabilities of ten nations. A few hundred satellites are currently operational, whereas thousands of unused satellites and satellite fragments orbit the Earth as space debris. A few space probes have been placed into orbit around other bodies and become artificial satellites to the Moon, Mercury, Venus, Mars, Jupiter, Saturn, and the Sun.


Satellites are used for a large number of purposes. Common types include military and civilian Earth observation satellites, communications satellites, navigation satellites, weather satellites, and research satellites. Space stations and human spacecraft in orbit are also satellites. Satellite orbits vary greatly, depending on the purpose of the satellite, and are classified in a number of ways. Well-known (overlapping) classes include low Earth orbit, polar orbit, and geostationary orbit.

Satellites are usually semi-independent computer-controlled systems. Satellite subsystems attend many tasks, such as power generation, thermal control, telemetry, attitude control and orbit control.

    Satellites Applications                       

Not so long ago, satellites were exotic, top-secret devices. They were used primarily in a military capacity, for activities such as navigation and espionage. Now they are an essential part of our daily lives. We see and recognize their use in weather reports, television transmission by DIRECTV and the DISH Network, and everyday telephone calls. In many other instances, satellites play a background role that escapes our notice:

•     Some newspapers and magazines are more timely because they transmit their text and images to multiple printing sites via satellite to speed local distribution.
•     Before sending signals down the wire into our houses, cable television depends on satellites to distribute its transmissions.
•     The most reliable taxi and limousine drivers are sometimes using the satellite-based Global Positioning System (GPS) to take us to the proper destination.
•     The goods we buy often reach distributors and retailers more efficiently and safely because trucking firms track the progress of their vehicles with the same GPS. Sometimes firms will even tell their drivers that they are driving too fast.
•     Emergency radio beacons from downed aircraft and distressed ships may reach search-and-rescue teams when satellites relay the signal.

References:
                       Wikipedia
                        How Stuff Works

" What is a Satellite? " !

FM Demodulation

    THE PHASE LOCKED LOOP (PLL)  
     
In the last section, the PLL was mentioned as a way to demodulate an FM signal. In addition to FM demodulation, PLLs are used in a wide variety of communications applications, which include TV receivers, tone decoders, telemetry receivers, modems and data synchronizers, to name a few. Many of these applications are covered in electronic communications courses. In fact, entire books have been written on the finer points of PLL operation, analysis, and applications. The approach in this section is intended only to present the basic concept and give you an intuitive idea of how PLLs work and how they are used in FM demodulation. A specific PLL integrated circuit is also introduced.


    The Basic PLL Concept                     
    
The phase locked loop (PLL) is a feedback circuit consisting of a phase detector, a low-pas filter, and a voltage-controlled oscillator (VCO) Some PLLs also includes an amplifier in the loop. A basic block diagram is shown in figure 5.16.

Basic PLL block diagram

The general operation of a PLL is as follows. The phase detector compares the phase difference between the incoming signal, Vi, and the VCO signal, Vo.

When the frequency of the incoming signal, fi, is the difference from that of the VCO frequency, fo, the phase angle between the two signals is also different. The output of the phase detector and the filter is proportional to the phase difference of the two signals. This proportional voltage is fed to the VCO, forcing its frequency to move toward the frequency of the incoming signal until the two frequencies are equal. At this point, the PLL is locked onto the incoming frequency. If fi change, the phase difference also changes, forcing the VCO to track the incoming frequency.
===================================
References
 
" FM Demodulation " !

Mobile Tracking using the Cell ID

Cell ID location tracking system is a great way to know where someone is within an accuracy of about 1km but it is not a substitute for GPS tracking systems. The Cell ID system is only accurate enough to answer the question "Which part of town are you in" and not " Which street are you in". For the majority of users this is sufficient to prove if someone was lying about their location.  

Mobile Tracking using the Cell ID

    What is Cell ID?     

A GSM Cell ID (CID) is a generally unique number used to identify each Base transceiver station (BTS) or sector of a BTS within a Location area code (LAC) if not within a GSM network.

    How Cell ID technique works?      

A network provider has several hundred radio base stations ( cells) that make up its network. Each base station is a "cell" which covers a physical area and these cells connect together to make up the entire network. The size of cells depends on the density of base station installed in a given area. Cell sizes can vary from 100m in cities to 3K in rural areas .A mobile phone connects to the network using the cell in which it is located.. As the mobile moves, it leaves one cell and joins another. The new cell then takes responsibility for connecting the phone to the network.
Every time the cell that "owns" the mobile changes, you can get the cell id and cell name ( if available) . You can tell which cell controls the mobile by the name or by resolving the cell id against a database of cell id to locations.

Cell ID location tracking is based on information that is freely available from the airwaves, and the location information is the form of a CELL ID, and the name of the CELL. The name of the cell is usually the name of a part of town, and so this is good enough to know where someone is. 

Source:       
               FlexiSPY
               Wikipedia   
               GSM Modem

" Mobile Tracking using the Cell ID " !

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Code Division Multiple Access (CDMA)

    CDMA         

Short for Code-Division Multiple Access, a digital cellular technology that uses spread-spectrum techniques. Unlike competing systems, such as GSM, that use TDMA, CDMA does not assign a specific frequency to each user. Instead, every channel uses the full available spectrum. Individual conversations are encoded with a pseudo-random digital sequence. CDMA consistently provides better capacity for voice and data communications than other commercial mobile technologies, allowing more subscribers to connect at any given time, and it is the common platform on which 3G technologies are built.

Code Division Multiple Access (CDMA)

CDMA users share a common frequency channel. All users are on the same frequency at the same time. However, each pair of users is assigned a special code that reduces interference while increasing privacy.

    Advantages of CDMA

Most efficient use of available bandwidth the foremost advantage is the large band width and its equivalent effect utilization for sending and receiving the data.

No separate time Access divisions
In CDMA technology there is no time limitation slot division for using the band width and sending and receiving the data like in TDMA.

Power and bandwidth frequency
Power frequency remains constant in both sending and receiving and uniform bandwidth keeps the transmission faster and in time.

Resource allocation
Another advantage of CDMA is the flexible resource allocation which means that a certain kind of pin code is provide to the active users to communicate with each other. Fixed time and bandwidth keeps the simultaneous exchange of message at both sender and receivers end and specific number of packets with limited length keeps the extra traffic out of the channel.

    Disadvantages of CDMA     

The main disadvantage of CDMA is that it can’t be used for the multi channel or multiple transmission paths. All the communication is performed over a single path. This make it fixed for singular purposes which is main drawback of CDMA technology.

    Space Division Multiple Access (SDMA)  

Space Division Multiple Access (SDMA) - A variation of TDMA and CDMA that potentially will be used in high-bandwidth, third-generation wireless products.

SDMA is a channel access method based on creating parallel spatial pipes next to higher capacity pipes through spatial multiplexing and/or diversity, by which it is able to offer superior performance in radio multiple access communication systems. In traditional mobile cellular network systems, the base station has no information on the position of the mobile units within the cell and radiates the signal in all directions within the cell in order to provide radio coverage. This results in wasting power on transmissions when there are no mobile units to reach, in addition to causing interference for adjacent cells using the same frequency, so called co-channel cells. Likewise, in reception, the antenna receives signals coming from all directions including noise and interference signals. By using smart antenna technology and differing spatial locations of mobile units within the cell, space-division multiple access techniques offer attractive performance enhancements. The radiation pattern of the base station, both in transmission and reception, is adapted to each user to obtain highest gain in the direction of that user. This is often done using phased array techniques.

     Comparison of Multiple Access Systems
 

Comparison of Multiple Access Systems

This table summarizes some of the technical aspects of the multiple access technologies.

The technology used determines the channel's capacity. TDMA triples the capacity of FDMA, but CDMA capacity can be up to seven times that of TDMA.

References:
                   WiFi Notes
                   Wikipedia
                   CDMA University
                   WEBOPEDIA
                   How Stuff Works


" Code Division Multiple Access (CDMA) " !