The change to the new modality was in late 1998. The system remained in force until then, was established in the forties and fifties by the National Television Systems (NTSC). The change has followed a slow and often controversial.

Officials from the Federal Communications Commission (FCC), television broadcasting channel, manufacturers and academics trying to create a digital standard that does not immediately cease existing televisions obsolete.

The new system operates mostly in the range from 470 to 890 MHz (channels 14 to 83) and UHF frequencies). The old and the new system will coexist until 2006, when emissions should cease NTSC signals, both in the band from 54 to 216 MHz (channels 2 to 13), as in UHF and VHF frequencies.

The FCC then reallocates those channels to digital television

The FCC established in 1987 an advisory committee on advanced television services, the ACATS, which was to advise the FCC on advanced television service in the U.S., including the preparation of a technical standard.

In 1988, the ACATS requested by industry, academia and laboratories to propose standards for advanced television.

In March 1990 the FCC took a major step. Decided that the advanced television service would be given under simulcasting (simulcast) with the conventional service and not regime compatible receivers (the latter was the approach adopted to introduce color television, in which the signal should be possible to see both in color television sets and black and white). In the regime of compatibility of receivers, the signal of high definition television (HDTV) could be captured and displayed in conventional current receivers. But the HDTV signal requires much more information than a color signal, so the receiver would require an additional channel to enter additional information (another 6 MHz channel).

This poses several problems:

1. The HDTV signal transmitted by NTSC channel will have a very efficient system, some modern and unprofitable.
2. You have to assign a new channel for each existing NTSC channel.

 

For these reasons, is why I opted for the simulcast approach. The HDTV signal is transmitted by a 6 MHz channel itself regardless of the NTSC signal (instead of using compatible receivers, where the HDTV signal is obtained from the NTSC signal and the information that goes into the supplemental channel). That could be equipped modern transmission system for full HDTV signal.

However there is still a drawback that existing televisions can not receive an HDTV signal. To prevent these TVs are suddenly useless, the FCC assigned a new channel for service to each of the 1,500 U.S. stations, upon their request. During a transition period, the FCC would require the same program was broadcast simultaneously (or with little delay) both for HDTV, for NTSC (later abolished this requirement). When a large part of the country already use the new TV, NTSC service would be deleted, and the portion of spectrum occupied by new channels would be used for HDTV or other services.

This decision had a decisive impact on the development of a standard for HDTV.

Shortly afterwards they began to receive proposals for HDTV systems, and the ACATS and the FCC decided to submit five proposals evaluation techniques: one analog and four digital. These technical proposals were discussed at the Center for Advanced Television Testing Alexandria, while the image quality was assessed at the Laboratory for Advanced Television Evaluation Ottawa.

In February 1993, after reviewing the ACATS results concluded that the four digital systems to analog exceeded in performance. In turn, each of the four excelled in various aspects. So the ACATS encouraged the promoters to organize into one system the best of the four elements and evaluated.

In May 1993, formed the Grand Alliance, a consortium of AT & T, Zenith, the research center David Sarnoff, General Instrument Corporation, Massachusetts Institute of Technology (MIT), Philips Electronics North America, and France's Thomson Consumer Electronics .

Between 1993 and 1994, the Grand Alliance introduced improvements on the best technical elements of the four systems and created a prototype. Based on this prototype HDTV, the commission of Advanced Television Systems (industry consortium) created a technical standard.

To be transported in a 6 MHz channel (about 20 Mbps) all information of a high definition image data to be compressed (if required to compress the order of Gbps). The Grand Alliance proposal was based on the MPEG2 system.

The key system according to the MPEG compression is not to send larger images (as in NTSC) but only the changes between these images. The result is that much less data are needed to update an image. The compressed video data, audio and other are multiplexed to form a single string of bits. This sequence of bits modulates a signal that is transmitted by terrestrial broadcasting.

On receiving the signal is captured by an antenna and sent to a receiver, which demodulate the signal to obtain the original bit sequence. These bits are demultiplex and recover the compressed data to pass to decompress below.

In November 1995 the FCC ACATS recommended that the standard developed by the Committee on Advanced Television Systems, and this was accepted in 1996 except for one thing. Eased restrictions on the rule that is limited to 18 formats of video resolution approved.

In early 1997, the FCC added other provisions to support the new technical standard, such as allocating canales.El digital television system based on this standard is very flexible, allowing for example a 6MHz channel can provide images high resolution multichannel surround sound, or transmit several television programs of comparable quality to the current programs. This flexibility has made to replace the acronym for High Definition Television (HDTV) for Digital Television (DTV). Besides the standard is open so that you can incorporate future technical improvements.

Historical Evolution in Europe

Digital TV services by satellite began in 1996, with uneven development as the implementation strategy followed, with the most dramatic results in France, with three platforms and more than a million subscribers as a whole.

The terrestrial broadcasting started before the end of 1998 in the United Kingdom and Sweden. The DVB is promoting its system outside Europe DVB-T for terrestrial broadcasting as a flexible system, capable of HDTV, adaptable to different channels of bandwidth and capable of being used in frequency network coverage of an entire country. This promotion is geared mainly to China, Southeast Asia, Australia, Brazil and Argentina.

The UK has taken a leading role in Europe for the development of digital terrestrial TV (DTT). In the United Kingdom have enabled 6 multiplexes which have been distributed among the existing broadcasters and a trading platform. The broadcasters have been given half multiplex capacity equivalent to 2 programs for existing analog channel. Thus, the BBC has obtained a full multiplex, ITV, Channel 4 and Channel 5, half multiplexes each respectively, and S4C, the Welsh regional broadcaster, otherwise multiplex with exclusive coverage of Wales. For its part, the BDB trading platform, consisting of groups Carlton and Granada, has won three national coverage multiplex and, moreover, half multiplex coverage across the UK, except Wales, has been awarded to the consortium SDN, formed by S4C, NTL and United News and Media.

In parallel with the launch of DTT, there is the beginning of the digital services of BSkyB. The situation is extremely interesting, because this simultaneous launch of digital terrestrial TV services and satellite are added some cable operators are proceeding to digitize their networks. This means that the end user will have to choose which channel of distribution prefers that influence not only the intrinsic merits of each form of distribution, but also the attractiveness of content and forms of grant of user or boxes receivers that offer the different platforms.

Sweden also launched DTT services in early 1999, with two multiplexes and a coverage of 50% of the population. The services were implemented on a common network, while providing the content is brought to the competition.

After years of research, NHK of Japan first developed the modern system of HDTV, and wide screen sweep of 1,125 lines 60 Hz image, making even the film quality of 35mm film.

With increasing interest in high definition, in 1987 the Federal Communications Commission FCC in the USA led to the formation of the Advisory Committee on Advanced Television Service (ACATS, for its acronym in English), responsible for selecting a single standard advanced television terrestrial broadcasting for the U.S., a system standard for high definition television can be transmitted simultaneously with the current NTSC signal, and therefore restricted the scheme to use 6 MHz channel bandwidth.

On 1 June 1990, General Instruments Company of San Diego, California, proposed a land-based HDTV digital HDTV, thus marking a watershed in the history of television. The digital era began, marking the end of analog television and imposing huge industrial challenge to completely reinvent television.

In a concerted effort and adherence to national strategies for market dominance, the U.S. government proposed major manufacturers working each in its proposal to pool their efforts in a "Grand Alliance" to propose a single television system digital HD, with "best of the best-in terms of technologies for each of the participants: AT & T (Lucent), MIT, General Instrument, Zenith Electronics Corporation, North American Philips, David Sarnoff Research Center (RCA), and Thompson Consumer Electronics.

The system of HDTV HDTV proposed would have two main modalities: 1,080 active lines with 1,920 pixels per line square, with interlaced scanning of 59.94 and 60 frames per second, and 720 active lines, with 1.280 pixels per line, with progressive scan 59.94 and 60 frames per second. Both formats also operate with progressive scan 30 and 24 frames per second for the transmission of programs filmed.

The Grand Alliance system employs video compression and transport systems MPEG-2, Dolby Digital (AC-3), and modulation 8-VSB vestigial side band. With this, we developed a widescreen system, relative width / height ratio of 16:9, with five times more picture quality than standard definition television than 480 active lines and relation width / height ratio of 4:3. All this squeezed into a narrow channel TV 6 MHz bandwidth.

Despite having achieved this feat of electronic engineering, the FCC bowed to the interests of the computer industry, and asked in 1995 to include digital standard in various formats under standard definition television (SDTV for short in English) of 480 lines with progressive scanning and interlaced (see Table 5).

Available formats for digital television, according to Table III of the ATSC standard.

Finally, on 24 December 1996, the U.S. government adopted as mandatory standard for terrestrial transmission of digital television and HDTV, the SDTV and HDTV standard for the ACATS, documented by the Committee on Advanced Television Systems (ATSC, by its initials in English). This standard, known as the ATSC standard, left out as regards the imposition of the scanning type (only progressive or interlaced only) in order to achieve, once again, the consensus with the group of interest in the industry computing.

Since the adoption of the ATSC standard, the government body responsible for spectrum allocation in the U.S. agreed to start free allocation of digital channels to all dealers of analog TV channels, in order to stimulate the simultaneous digital transmission programming. Also, set the major goal in this transition to digital transmission, which returns the NTSC analog channel at the end of the transition period, a goal that was set the year 2006 reasonable date for completion of transmission service NTSC .

With the ATSC standard, you will need to make decisions about the quality of the image to be transmitted to the user, ie, if you send a certain standard definition SDTV program, using the digital channel for simultaneous transmission of multiple programs at all "SDTV multiplex," or whether you will be sent with the highest quality available high-definition HDTV, thus becoming more competitive. The high-definition broadcast HDTV would be the preferred medium for sports events and programming in PrimeTime. In this regard, several U.S. television networks, cable operators and DBS programmers have announced their intention to provide programming services to HDTV HDTV by the end of 1998, and at least in the top ten markets in the country (including DirecTV and HBO).

Today, the limiting factor for achieving high definition at home, is the lack of television screens can handle. Month to month announced improvements, including the recently offered by Fujitsu, have developed around a flat screen 42-inch wide-screen 16:9 ratio with 1.024 pixels per line, only one step of full high definition. However, the full potential of the standard for HDTV HDTV requires more than they can deliver the best television screens today, so this revolution in digital television technology is triggering the start of a technological niche research and industrial development in television display manufacturers.

To see the need for compression formats, I will summarize the process of digitization of analog video. The standard defines the analog video lines per frame and frames per second (not all lines containing active video). To digitize analog video signal to sample all the active video lines. Each color sample is encoded into YUV signal (Y-luminance, U and V chrominance). An example of conversion from analog color television to a digital video signal is:

PAL: 576 active lines, 25 frames per second, for 720 pixels and 8 bit per sample to 13.5 Mhz:

1. Luminance (Y): 720x576x25x8 = 82,944,000 bits per second
2. Chrominance (U): 360x576x25x8 = 41,472,000 bits per second
3. Chrominance (V): 360x576x25x8 = 41,472,000 bits per second

Total number of bits: 165,888,000 bits per second (approx. 166Mbits/sg). None of the common systems of video transmission provide sufficient transfer this wealth of information (the Video CD has a transfer rate of 1.4 Mbps and 6 Mbps cable)

Different Types of Compression

MPEG Compression

It is a standard defined specifically for video compression, used for transmission of digital video images. The algorithm used to compress still images also compares the present with the previous frames and future to save only the parts that change. The signal includes digital-quality sound. The disadvantage of this system is that due to its high complexity needs to rely on specific hardware.

There are different options depending on the application:

Standard MPEG-1 Video-CD chosen: VHS-quality digital sound.

MPEG-2 is used in the DVD (Digital Video Disk). Quality than MPEG-1.

High quality MPEG-3 video: 1920x1080x30 Hz with transfers between 20 and 40 Mbps

MPEG-4 is in development.

MJPEG Compression

It basically consists of treating the video as a sequence of still images and independent compression and decompression using the JPEG algorithm, then, reassemble the video image. This can be done in real time and even with little investment in hardware. The disadvantage of this system is that it can be considered as a video standard for even includes the audio signal. Gold problem is that the dependence of transfers tends storage system, since the compression rate is not very large. In practice it is feasible to achieve the quality SVHS thus may work semi.

The conception of television more efficient (better quality) has brought the need to introduce digital television systems. The insertion of this technology we can see from how to work the TV signal from procurement, through the presentation of a television screen, so you could say that there are two general approaches to digital TV working from treatment Signal:

The analog signal is converted to digital TV to be broadcast and then be brought back to analog at the receiver, thereby increasing the efficiency of transmission and also has the ability to add new features.

A digital system itself, in which the signal is digitized before leaving the chamber for further processing and digital broadcast until presented to the receiver.

In evaluating the benefits of Digital TV among which we can cite: reliability, efficient multiplexing, miniaturization, data processing management, less calibration problems, increased complexity in managing capacity, versatility and have greater capacity channels we would realize that is the way best suited to the present and future changes taking place in humanity.

In addition, digital communications have benefited by the tendency of industry to use solid-state components for the construction of their systems. These components provide greater reliability than any other component used in analog systems. Thanks to these solid state components such as integrated circuits, the size of communications equipment has been tremendously reduced and consequently the data management is more efficient than analog techniques.

Modern trends in communication are aimed at the creation of increasingly complex systems that are managed with great ease due to digitization. This is due largely to the versatility of digital systems.

Currently, digital TV is not widely used in the field of commercial television because of some problems of bandwidth, but, however, these problems are being overcome. Digital television in its infancy has been exploited in the field of aerospace research in studying the moon and other planets in the test which proved successful.

NOKIA N95 8GB


I tested the Nokia N95 to 8GB all black during the last months and I can say that I was very impressed. Not only are all its features like GPS, 3G connectivity, Wi-Fi, Bluetooth stereo and dual slide with dedicated audio buttons, but most of all the camera, it almost was part of my family in recent months, in perfect photos and film-quality DVD.

Do the unboxing of the N95 8GB is a very pleasant experience. I can see the care of Nokia to enhance its product. Of man can see the differences to the N95 original, starting with the packaging. The screen of the N95 8GB has a QVGA resolution (240 x 320 pixels) and is slightly larger, with 2.8 "to 2.5" of the N95 original. Already the navigation keys are slightly smaller, but very easy to use. The battery is 1200 mAh now, which lasts more than the previous model. The camera lost its protective cover, but honestly I think this is not the slightest fault.

Close to 160MB of the original model, the 8GB capacity of the N95 is taking the breath, to save up to 20 hours of movies or up to 6000 songs, not to mention the programs, the N-Gage games and more.

Click below to continue reading this post on the N95 8GB.

Like I commented on a matter for the N95 is perfect, only missing even a touchscreen display. As a user of a wireless touchscreen in the first days of use I was tempted to use your fingers to select the icons on the screen, but then I used to because the navigation with the buttons works well. And I must say that touchscreen displays are great, but nothing is better than a keyboard for real at the time you want a fast connection. You can also write short texts to speed on the keyboard of the N95 and it works with external Bluetooth keyboard, which is very perfect for a blogger who needs to write down any ideas for posts and columns that can arise at any time.

Like I said before, the camera of 5 megapixel with video camera is the high point of the N95, and my favorite feature on your phone. This camera with Xenon LED flash and Carl Zeiss lenses completely replaced my digital camera because it takes great pictures in macro, and good images even in low light conditions. It is good to remember that beyond the 8GB of internal memory, the N95 8GB also has a slot for microSD cards up to 16GB, bringing the capacity to 24GB. Forget the previous sentence, which was pure delusion on my part.

Another very important point for a lover of music is the player with its own keyboard slide. I am always listening to music while walking down the street, and he replaced my iPod with praise in this, thanks to remote control headset, which has dedicated buttons for start, stop, go back and move the songs, in addition to the microphone to answer calls. Unfortunately failed to test the N95 with stereo Bluetooth headsets because I have not bought these headphones, but this is on my list of priorities.

The Nokia N95 8GB is not as fine as my mobile phone, but if you take into account that it replaces a phone, MP3 player, a camcorder and a digital camera at the same time, the size is totally acceptable, and moreover, he went well on the test to be carried in the pocket of blue jeans. The GPS with Nokia Maps and Google Maps is a chapter, but the key is that the N95 also works as a browser by giving instructions to each curve. Included with the phone is 6 months to use the Nokia Maps service. Another tip is to join the OVI, which joins the most diverse services of Nokia.

One of the best things about the N95 is the fact that he has a good integration with Exchange and other services to access their calendars, emails and contacts in your company's network, so if you change a contact on the street, it will be updated automatically in your primary calendar.

You can install different types of programs, such as OfficeSuite, you may open, edit and even create documents in PowerPoint, Word and Excel, which can greatly increase your productivity when you're away from the office.

He comes with some demos of the N-Gage games, like Gameloft's Asphalt 3 and FIFA 07 by Electronic Arts. Access to the web browser of Nokia is difficult in the beginning, but you usually. You should also keep an eye on the latest programs to install, but some are essential, such as YouTube, Fring, Qik and Opera Mini. Check here a list of 50 programs for the N95 8GB Must created by N95 Blog.

I tested the N95 to sync with Windows Vista and found it perfect. When connecting the phone to a computer connected to the web and install the programs, you will have full access to your N95. The Lifeblog is very interesting, but not tested much further. The Sync with Mac also works very well with the Nokia Multimedia Transfer program. Easily send music from iTunes to the N95, nothing could be simpler, and download the pictures through iPhoto.

The Nokia is also sending very well in promoting the product, because besides the great NJornadas campaign, also launched the Nokia Without Limits, a blog written by my friends and Deividas Pazos Alexandre Ottoni Jovem Nerd counting the number of tips and program to install on N95, addition to a promotion that will give a N95 8GB! Another point to highlight is the opening of the Nokia Store SP in Sao Paulo, one of 10 concept stores the brand around the world.

In a next test we will take a look at the Nokia N81 here in DD, and soon we will post on the famous 5800 XpressMusic, the first touchscreen phone from Nokia that rekindled my hope for a future N-Series as a useful to the pleasant , adding a screen with a touchscreen QWERTY keyboard, which could appear in a third slider, who knows.

My final verdict on the N95 8GB is highly positive, as is cell phone or a digital camera. The N95 8GB is a great choice, and is easily among my favorites of Nokia devices. But I think the best compliment I can make the N95 8GB is that this post should have been done in a month but ended up three months with the unit. And I confess that barely returned to the N95 8GB, I am greatly missed, especially the camera and GPS!