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DTH Technology
सुचना तथा संचारको हकमा बेतारे माध्यमले पकड जमाइरहेको अवस्थामा अब तामाको तार मार्फत घरमा च्यानल हेरिने प्रवृतिलाई बिस्तारै Direct To Home (DTH) बेतारे प्रविधिले विस्थापित गर्दै जानेछ । Dec 31, 2009 मा स्याटेलाइट च्यानल प्रा. लि. ले सुचना तथा संचार मन्त्रालयबाट संचालनको अनुमति पाए लगत्तै डिटिएच प्रविधि नेपालमा औपचारिक रुपमा भित्रिएको हो ।
उपभोक्ताको घरमा सानो डिक्स एन्टेना राखेर सिधै स्याटेलाइट मार्फत च्यानल डाउनलिंक गर्न सकिने DTH पूर्णतया डिजिटल प्रविधि हो । डिजिटल प्रणाली भएकै कारण परम्परागत एनालग केवल तार भन्दा यो बेतारे (wireless) डिटिएच बढी सुविधाजनक र इकोनोमिक छ ।
अहिले Cable Company हरुले Channel Signal लाई Copper Co-axial Cable मार्फत घर-घरमा पुर्याइरहेका छन्, जुन Analog Based छ । DTH System मा भने तपाईलाई एउटा सानो Disk Antenna र Set Top Box (STB) Device प्रदान गरिनेछ जसले विना कुनै तारको झन्झट सिधै Satellite सँग सम्पर्क गरी तपाईलाई digitized signal प्रदान गर्नेछ । Data पूर्णतया Digital हुनाले Information लाई Encryption र Compression पनि गर्न सकिन्छ । Unauthorized Signal हरुले Interference गर्न नसकोस भनी Data Encryption गरिने हुँदा Information पूर्णत Noise Free, Distortion Less तथा Safe हुन्छ । Digital Data लाई चाहिएजति Compress गरी धेरै  च्यानलहरुलाई Multiplex गरी एकै चोटी Transmit गर्न सकिन्छ ।

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Complex technology, simple examples

Posted: December 12, 2009 in info itch
mobile phone communication using multiple access technologies
Taking aside other different multiple access technologies, there are three FDMA, TDMA and CDMA highly being used and acclaimed.
FDMA--The available frequency range is divided in to frequency slots and each slot is provided to each user or for purposes. 1G was totally based on this technology.

TDMA--Similar to FDMA, but here available time frame is divided in to a limited time slots and in each slot data of different user are trasmitted. Europe used this technique to develop GSM, 2G standard mobile.

CDMA–Neither frequency nor time are used, rather code to transmit data of different users within a wideband. North America used the technique to develop IS-95, 2G standard mobile.

It may seem tuff to understand these technologies in such above language. These all techniques are being used by us in our life unknowingly.

FDMA--Whatever one needs something, give him a portion of something. In fdma case, something is frequency as a channel. This is the simple and easy process that we are using in our daily life since when fdma term wasn’t in existence.

If there is a dance party, and three boys need to be danced with lady, then ? If each boy is provided each lady then that would be FDMA. But be noticed that 3 girls are needed here. In tdma, however, only one girl is sufficient. How ? I will tell you.

TDMA–If a girl do dance with a boy and after some time she do with another, then ? means she divides the time of dancing in 3 time slots and in each time slot she do dance with each boy. After doing dance with 3rd boy, she repeats it with first boy. This is TDMA means division of time.

Another best and perfect example is distribution of card in card playing(तास). In one round, one sample of card for each is distributed and in another round one more card is added for each. In which way cards are distributed in the same way tdma works.

CDMA–If in a convention hall, people have gathered and doing gossips in different languages(code) then that would be a example of cdma. No one can understand the language(code) instead the listener and spokeperson. There seems noise, though all are doing conversation without any feeling of noise.

Another best and perfect example is the security code based process of Western Union Money Transfer to transfer money from one region to another. Such tranfer company uses 10 digits which is just alike wideband for cdma. Depending on the 10 digit, a unique code for each transaction is made and all processes of money reception now will depend on that code. Cdma code concept exactly matches with such activity.

Satellite Communication

Posted: February 21, 2008 in info itch
Satellite and  Earth Station

Satellites are those equipment that revolve our earth ( like moon ) and act as a repeater section. The transponder section of it receives signal from the earth station, amplifies the signal and then transmit(broadcast) it in to required place. Satellite do exactly in the same way as hub do in the star topology of network. So, if transponder fail, then the all system will go down. The uplink and downlink frequencies of it are separated by 45 MHz to avoid interferance.

It is a microwave communication and hence requires Line Of Sight(LOS) to transmit and receive signal. LOS means the earth station in ground and satellite in sky could see each other. The frequencies that it utilizies falls on the category of GigaHertz(GHz). Among the several freq. band separation of microwave, C, Ku and Ka bands are allocated for commercial satellite communication.
To make satellite able to stay in space revolving round the earth, Rocket having the satellite equipment is required to launch to sky with velocity greater than escape velocity. Escape velocity means the velocity required against the earth’s gravitation.
The 1st satellite ,sputnik1, was launched by Soviet Union in october 4, 1957 which again lauched the first living creature(sputnik2), a dog named Laika in to space on November 3, 1957. Explorer 1 was the first satellite of United States, launched in January 31, 1958. The early communication satellites were in relatively low altitude orbits(below 36000 km) and consequently sped around the earth in a few hours. This required the ground antennas to move constantly in order to beam signals to them.
The orbit in range of 36000 km above the earth surface is called geostationary orbit as the satellite in that orbit do round the earth in the same time that the earth takes to round in it’s own axis, means 24 hours. So though both earth and satellite revolve, the satellite appears to be stationary from a particular earch surface. This provides easyness in work eliminating the need of ground antennas to move constantly regarding satellite movement.
The satellites in 36000 km are called geostationary or geosynchrounous satellite while satellites below 36000 km are called low earth satellite satellites. In theoritical concept, 3 satellites in geostationary orbit can cover the whole earth while 64 are required in low earth orbit.
In 1965, Early Bird satellite was launched in to a much higher equatorial orbit of 36000 km.

After the invention of cellular concept in 1960 in mobile technology, the craze over so drastically up that even the latest technologies are becoming the oldest one. The invention of transistor in 1947 converted the bulky instruments, using vacuum tubes, to small one. The accumulation of discrete components in one chip, Integrated Chip(IC), made electronic goods to be benefited. VLSI(Very Large Scale Integration), SLSI(Super Large Scale Integration) etc. are causing goods to reduce their size, shape and cost too.

The recent development in mobile are categorized broadly in terms of generation(G). The mobile in the decade of 60 were used to be 1G, totally analog based. The cellular constumer were used to be registered manually when moving from one cell to another.

2G came in 1990 with knowledge about digital concept. In actual mean mobile captured it’s pace through this generation. Since 2nd Generation, hand off not only became easy and fast but also sophisticated too. Till the journey of 2G, Network Controlled HO(NCHO) has been turned in Mobile Assisted HO(MAHO). SMS (Short Message Service) is the most favourable service provided by it where two user (subscriber) can communicate through text. To reduce the burden of MSC, BSC blocks have been placed in between BS and MSC. 
2.5G came in to existence with internet approach but it’s speed fasten with the emergence of 3G. Broadband Integrated Service Digital Network (B-ISDN) in 3G made it capable of accessing voice, data, video simultaneously and HSPA(High Speed Packet Access) transferring data in fastest manner. Together with advanced modulation technique mobile technology is making itself more sophisticated than mentioned in words and languages. 
The latest upgrades in mobile technology, 3.5G,4G, in highly developed countries are showing the truth that yet there is some more things to be innovated in mobile field.

“‘Xcuse me, sir , Can i come in ?” I.
‘Ya sure and have a sit.’ Watching my all CV, he said
‘Shall we start, then ?’
“It’s my pleasure sir.”

‘Why do mobile phones are called cellular phones?’
“The region on which mobile technology is being used is divided in terms of hexagonal shaped cells. So, due to cellular concept, they are called.”

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