Benefits of LED-based Backlight Solutions

Posted on April 15, 2012 by SSS

Compared with conventional cold cathode fluorescent lamps (CCFLs), LED backlight solutions offer LCD manufacturers a wide range of performance benefits. Above all, LEDs produce a far superior image in terms of color gamut and saturation. LEDs also offer greater contrast and brilliance (they can be switched in less than 100 ns), and unlike CCFL light sources, contain no mercury – making them more environmentally friendly. LEDs are also vibration and shock-proof, and have exceptionally long service lives. Con­tingent on the application, environment, driving considerations and other factors, they operate for 50 000 hours or longer, over a temperature range of -40 °C to85 °C.

Generally speaking, LED backlight solutions possess great flexibility, and as such they can be extended to any diagonal size. Further, if a consistent LED packing density (LEDs per unit area) is maintained, then the luminance remains constant for all backlight unit (BLU) sizes. As a consequence, adapt­ing the luminance to specific requirements necessitates alterations to either the LED packing density or the drive current.

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LED Device Principle

Posted on April 15, 2012 by SSS

While discussing the future of LED technology and specifications, it is instructive to understand their basic construction. As illustrated in Figure 14.1, an LED consists of several layers of semiconducting material. When an LED is subjected to a DC voltage, light is generated in the active layer; the generated light is radiated directly, or by reflection.

In contrast to conventional lamps, which emit a continuous spectrum, an LED emits light of a specific color, depending on the material that is used. There are in fact two systems of materials – AlGalnP and InGaN – that are used to produce LEDs with high luminance in all colors ranging from blue to red, as well as white (by luminescence conversion). Depending on the system type, different voltages are required in order to operate the diode in the conducting direction.

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Symbian: the critical point of the Nokia in 2012?

Posted on January 4, 2012 by SSS

In 2011, soon to be over, the global mobile phone leader Nokia can be described as bad-mouthing the sound constantly, even as once was bad-mouthing to apply for bankruptcy protection, of course, this is ultimately a rumor. But it is undeniable that Apple and Google under the weight, Nokia had a tough year, but a time when the end of the year, Nokia announced that Symbian to give up the name, it is attracted to the industry a guess. What it means This Nokia 2011 for about the past? What indicates of the arrival in 2012?

 

As we all know, in just the past Christmas, based on Apple iOS and Google Android mobile device sales jumped 353%, which proved once again in 2011, Apple and Google is the mobile Internet (mainly smartphones) the protagonist. In contrast, earlier this year announced a strategic cooperation with Microsoft (the future Nokia will give up their smart phones Symbian OS, turn to Microsoft’s Windows Phone system-based) Nokia is losing ground. So far the industry generally believe that Nokia is already the twilight. However, recent statistics from Pingdom has forced the industry by surprise.

 

According to Pingdom compiled statistics from StatCounter, although Apple iOS and Google’s Android growing rapidly, but the 2011 global mobile systems market share point of view, 33.59% of Nokia’s Symbian still topped the list, but when compared with January 2011 30.25% also increased about 3 percentage points. Apple’s market share of iOS 22.56%, 21.74% for the Google Android. Symbian’s lead, especially in market share does not increase due not only with the industry’s expectations and perceptions of people differ on the market, but with Nokia’s strategic restructuring announced earlier this year are quite different.

 

In pay revenues, profits and the enormous costs fell after Nokia with Symbian to keep market share, but also for the Windows Phone to win a year’s time

This is not the author’s question Pingdom statistics, but by the statistics, so why the author for the Nokia 2011 for Symbian strategy insincere and development strategy in 2012 with the reproduction of knowledge and thinking.

 

It stands to reason, in early 2011 entered into a strategic partnership with Microsoft, Symbian and Nokia claims it should have to give up efforts to transform Windows Phone son. However, subsequent development, Nokia’s Symbian’s this insincere seem to give up, but in fact adhere to the strategy is right.

 

You know the first based on Microsoft Windows Phone7 (Mango Edition) Nokia Lumia series (800 and 710) is only the end of October 2011 release, this time has entered the fourth quarter of 2011, and in the air before schedule, Nokia has released its own updated version of Symbian OS Belle and transitional system based on MeeGo N9. It can be said, though Nokia and Microsoft reached a strategic cooperation early on, but look at the year 2011, basically in the Symbian Nokia is still struggling as a main force in the market, both feature phones continue to make up the smart phone market share of the losses on that end, Nokia, Symbian pay out fiercely competitive U.S. market and other revenues, profits and share price decline such a heavy price, the ultimate goal is to wait for an upgraded version of Microsoft’s Windows Phone7 Mango.

 

The so-called thin dead camel than Martha, perhaps too powerful before Nokia’s Symbian, Nokia may adhere tenaciously Symbian, as of the end of 2011, Nokia Symbian’s market share did not fall by, but also keep in the first place . I mean not to say that this is Nokia’s Symbian also has many strong competitiveness, especially in the highly competitive smartphone market, but to stick to Nokia tragic year for Microsoft’s Windows Phone7 has won a valuable time. In this sense, Nokia’s strategy in 2011 was a success, although contrary to the original strategy, and even the taste of some tragic.

 

But over the past year, and the development of Microsoft Windows Phone7 fourth quarter of Lumia series of smart phones and caused mixed in different regions and countries, considerable differences in market performance, the Nokia next year is not yet fully embrace Microsoft’s Windows Phone, do not want to, but Microsoft may also need about a year to improve and strengthen the competitiveness of their system.

 

Exposed in the Windows Phone from Microsoft’s road map to see, in the second quarter of 2012 will be released version of Windows Phone7 the Tango, which is the second quarter of 2011, after Microsoft released Mango, Microsoft’s first Windows 2012 Phone7 upgrade version, but the Mango system using the smart phone market, Nokia Lumia reflect the view, the situation is not very optimistic. So this next year, have still to stick to Nokia Symbian, not for anything else, one for insurance (dual system) strategy, the second is to continue to wait for Microsoft’s Windows Phone7 to have a strong competitive edge. Perhaps the fourth quarter 2012 release of Windows Phone7 the Apollo version (may be the legendary Windows Phone8) to let Microsoft have really compete with Apple and Google’s strength, at least in Nokia appears to be so.

 

But so difficult is that Nokia announced cooperation with Microsoft and Symbian have been quick to give up a year’s time, say the transition is necessary, but should always be diluted we go, at least not like this, not only do not give up one kind to the industry but to strengthen the feeling, so to Nokia Symbian Belle before Belle instead of this “medication” or “old wine in new bottle” method corporations are helpless, they would be expedient.

 

Given Nokia’s Symbian in 2011 near the bottom in performance and tenacious rival Apple and Google with less than 10% of the market share gap between Nokia 2012 anyway to force on the Windows Phone. To this end, Nokia launched the so-called return to the U.S. market, “Rolling Thunder” program, as the first step in the plan, it is the fourth largest U.S. carrier T-Mobile officially in January 2012 sales Lumia710, two-year contract price only $ 49.99. Later on will be in mid-2012 with two other operators, AT & T and Verizon contract, which Nokia Ace will support AT & T’s high-speed LTE network, Verizon is selling Lumia710. From product and price point, Nokia’s first raid targeted the United States nearly 150 million in entry-level smartphone users, to avoid the high-end Apple iPhone and Google Android in direct confrontation, the first to grab market share based, With the mid-2012 and the end of Microsoft Windows Phone7 Tango and Apollo versions available, it will be gradually extended to the war, the high-end market.

 

But still I said earlier, because Lumia listed in the early differences in the larger European market performance, or that the Nokia in the U.S. market, “Rolling Thunder” program there is uncertainty, so Symbian is still quite important, is not even or missing. 2011 development has fully proved this point. Therefore, the roadmap to see Nokia Symbian, will release first quarter of 2012 Belle of the upgraded version of Nokia will be followed after the launch of the Nokia version of Carla and Donna, and Donna is the Symbian system will reportedly last update, the time may be is the end of 2012 or early 2013, it will herald the release of Nokia Symbian end of an era. The reason for this Nokia roadmap, is because they know that a camel is bigger, eventually to be eaten, exhausted, when the bullet similar to 2011 with Symbian, a repeat period to keep market share at best is a years, is 2012.

 

From this, the Nokia 2012 will be Windows Phone from Symbian shift the critical point. If in the past, Nokia (including Microsoft) in the mobile Internet will usher in a new period of development, if the trip, everything possible will be to zero. However, the strategies, I believe that Nokia and Microsoft should be no problem, no matter what the outcome, I can only say, Man proposes, God disposes, Nokia 2012 Good luck.

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Frequencies and Channels

Posted on January 3, 2012 by SSS

For a device to determine the difference between RF noise and intentional RF signals, you must configure the device so it knows which signal to monitor. You do this using frequencies and channels. Thc frequency is what distinguishes one RF signal from another, and a channel is generally a portion of the entire frequency assigned to a specific technology such as 802.11b or 802.11a.

Most modem devices hide the frequency information from you in two ways. First, 802.11b devices can communicate with other 802.11b devices because they all use the same total frequency range, which is discussed shortly in this chapter in the “Frequencies” section. You don’t have to know the frequencies used—necessarily—as long as you know you’re using all 802.lib devices.

The second method of hiding the frequency information is through the use of simple channel assignments. Most access points, for example, provide an easy-to-use drop-down box that lists the available channels. Often, these access points make no reference to the actual frequencies used by these channels. Of course, enterprise-class wireless devices from Cisco and other venders reveal this information frequently though it is seldom needed for effective operation.

The concept is similar to the way the domain name system (DNS) works on the Internet. DNS provides a simple naming system for Internet locations, so you don’t have to memorize the IP address. For example, the IP address for SYSEDCO.com is 204.14.106.29. Would you rather remember hundreds of numbers like this or domain names that actually have meaning? If you’re like me, you opted for the second choice. This is what frequency hiding does for you. It’s easier to remember that all your devices should be communicating on channel 11 and using 802.11b than to remember that all devices should use the frequency of 2.462 GHz within the total 2.4 GHz frequency spectrum.

Frequencies

Two major frequencies are used in Wi-Fi networks at this time: the 2.4 GHz ISM (Industrial, Scientific, and Medical) band and the 5 GHz UNII (Unlicensed National Information Infrastructure, pronounced you-nee) band. The ISM band includes a 900 MHz band (starting at 902 MHz and going to 928 MHz), a 2.4 GHz band (starting at 2.4000 GHz and going to 2.5000 GHz), and a 5.8 GHz band (starting at 5.725 GHz and going to 5.875 GHz).

The 2.4 GHz band is used for 802.11, 802.11b, and 802.llg devices. While the full range from 2.4000 GHz to 2.5000 GHz is included in the designated band, wireless networks use only the range from 2.4000 to 2.4835 GHz because the FCC has provided power output specifications for this range of frequencies only.

The 5 GHz band is used for 802.11a devices and is divided into three bands known as the lower, middle, and upper bands. These bands use a frequency range 100 MHz wide and each contain four nonoverlapping channels. Where the 2.4 GHz devices use FHSS or DSSS, the 5 GHz 802.11a devices use OFDM.

The lower UNII band goes from 5.15 GHz to 5.25 GHz (this is sometimes referenced as 5.150 to 5.250 or as 5150 to 5250, though you will not need to know this for the Wireless# certification exam) and has an FCC-imposed limit of 50 mW of maximum output power. The middle UNII band goes from 5.25 GHz to 5.35 GHz and is limited to 250 mW of output power. The final band, known as the upper band, goes from 5.725 GHz to 5.825 GHz with a total allowed output power of 1 watt.

Channels

The frequency ranges used in the various 802.11 standards and assigned by the FCC are further divided into smaller frequency ranges by the IEEE. These frequency ranges form channels that are used for actual communications. You do not generally use all channels, or the entire frequency range, for a single link between two devices; instead, you choose a single channel to use for communications.

The channels available differ depending on the technology used. These technologies include OFDM, DSSS, and FHSS.

OFDM Channels

Each of the three UNII bands (lower, upper, and middle) provides four channels for communications in an 802.11a network. In most cases, the lower and middle bands are used indoors and the upper band is used outdoors. For this reason, indoor coverage is usually provided by a maximum of eight different channels. Because these channels are separated with no overlapping, they should not interfere with each other.

To better understand channel interference, think back to the early days of 900 MHz cordless phones. Remember turning on the phone only to hear your neighbor’s conversation? You would press the channel button on the phone to change to a different channel and then you’d be listening to the other neighbor’s conversation. Well, maybe it wasn’t that bad, but you understand the point. In much the same way, you cannot operate two wireless networks in the same general area using the same channel— remember, a channel is nothing more than a range of frequencies.

Table 3.1 provides a quick reference of the channels used by 802.11a and OFDM in wireless networks in the Americas on the lower and middle UNO bands. These bands are used by consumer-grade and indoor wireless technologies. Each channel is 20 MHz wide surrounding the center frequency.

DSSS Channels

The DSSS-based technologies, such as 802.11b, provide 11 channels in the U.S. and up to 14 channels in other countries, as listed in Table 3.2. Unlike 802.1 la OFDM channels, 802.11 b/g channels do overlap. This overlap can cause what is sometimes called channel fading or cochannel interference. For example, you would not want to use in the same general area two access points on channels 1 and 2; however, using channels 1 and 11 would be fine.

As you can see from Table 3.2, different locations have different rules. In the U.S., you can use only channels 1-11, while Japan allows the use of all 14 channels. These rules are important to consider when creating and implementing wireless networks.

It is also important to remember that the frequencies listed in Table 3.2 are center frequencies. This means the channel uses the center frequency +/—11 MHz. In the end, each channel uses a 22 MHz wide frequency range. For example, channel 1 uses the range from 2.401 to 2.423 and is centered on 2.412.

FHSS Hopping Sequences

A frequency hopping spread spectrum system does not use channels in the same way as DSSS and OFDM. Instead, FHSS systems hop from frequency-to-frequency using a pseudorandom hopping sequence. This hopping sequence—or pattern—is defined as the channel. During communications, the radios in each device change from one frequency to another in a pseudorandomly generated pattern and then they loop back

through that pattern continually. The amount of time spent on a particular frequency is known as dwell time, and the amount of time it takes to move from one frequency to the next is known as hop time.

The FCC regulates FHSS systems in areas of dwell time, frequencies used, and output power. These regulations restrict the available bandwidth because of dwell time limits and the number of channels because of frequency limits. However, 79 total channels (frequency hop patterns) are available and provide for many colocated systems. However, FHSS equipment is becoming more and more difficult to find and, therefore, is not covered in extensive detail on the exam. You are unlikely to encounter it frequently as you support and implement wireless networks.

There is, of course, one major exception to the ever-decreasing use of FHSS and that is Bluetooth. Bluetooth devices are extremely popular today in PDAs, cell phones, and laptop computers. These devices use FHSS.

Facility Coverage

By this time, you may be wondering why you need to know all this information about frequencies and channels. The answer is simple: By using channels effectively, you can provide the needed coverage in most facilities. The concept of colocation allows for the strategic placement of wireless access points, bridges, and routers based on channels within frequencies, different standards (802.llg vs. 802.11a), or both. In order to implement colocated systems effectively, you must also understand channel interference and the potential problems created by personal area network devices.

Colocation

To provide proper coverage in any facility, you need to strike a balance between bandwidth and range. While an access point might be able to provide service to a client that is 100 feet away, it might not provide sufficient speeds for the needs of the user. Table 3.3 provides a listing of the various wireless LAN standards and advertised ranges. Remember, these are advertised ranges and will seldom be seen in production environments. For example, it is not uncommon to lose 20 feet (or more) of distance for every internal wall the signal has to pass through.

Imagine you are installing a wireless network in a facility with the dimensions. In this scenario, we’ll assume you are using 802.llg devices. While the advertised range is 300 feet, the real range will probably be closer to 120-200 feet indoors with walls, filing cabinets, and other objects in the RF space. Let’s also assume you have tested the signal ranges within the building and determined that you can achieve an average range of between 100-150 feet.

Based on this information, you could provide adequate coverage in the facility using six access points located. Note the channels used by the different access points. Using these channels, you can accomplish the needed coverage through colocation without much

channel interference. However, channel interference is an important concept to understand with 802.11b/g networks and this topic will be discussed next.

You should also remember that the farther you get from the access point, the slower your connection becomes. This is a general rule and is applied through dynamic rate shifting or dynamic rate selection, which you will learn about later in the “Bandwidth” section of this chapter. For now, just remember to consider not only if you have coverage in all necessary areas, but also if you have needed coverage (bandwidth) in all of those areas.

Range estimates vary greatly by vendor. Some will tell you to use the figure of 100 feet for your estimates with 802.11 b, while others will tell you to use 75 feet or less in your estimates. For example, Cisco suggests a range of 20-75 feet for 802.11a and 100-150 feet for 802.11b/g. In the real world, you can use these estimates for preliminary planning, but you must test range and coverage in the live environment to ensure accurate results.

Channel Interference

The fact that DSSS channels are centered on frequencies separated by 5 MHz, while the channel is 22 MHz wide, results in overlapping channels. This overlap means that adjacent channels actually use some of the same frequency space for communications. Throughput can suffer greatly and possibly disappear altogether if you attempt to build a wireless network using adjacent channels in the same space.

While not an exact representation of signal overlap because of energy spreading beyond frequencies, illustrates this problem. As you can see, channels 1, 6, and 11 provide the best chance of having no overlap in an installation. While some have suggested using channels 1,4, 8, and 11, tests by various organizations show a loss in throughput of as much as 50 percent when using this latter configuration. For this reason, using channels 1, 6, and 11 is considered a best practice.

This best practice assumes you need three channels. If you are installing a wireless network that will be serviced exceptionally well with two access points, consider using channels 1 and 11. The main thing is to separate the channels by a total of 5 channels or more, which means a channel arrangement of 3 and 8 or 5 and 10 would also be acceptable. Using these channels is helpful if another network is using Wi-Fi technology on channels 1 or 11 at some distance away so the interference is minimal on these close channels. Instances such as these are about the only time you would want to break the “5 channels of separation” rule.

If client devices are not in need of roaming capabilities (the ability to move around and transfer from one access point to another automatically), another colocation solution is to use both 802.11b/g and 802.11a devices in the same space. Because they communicate on different frequencies, they do not interfere with each other.

Here is a great analogy to help you understand this. Imagine you are sitting in a room talking with a friend. Two other friends are sitting behind you as well, but you are not interrupted by them at all. In fact, it seems as if they are not talking as you do not hear a conversation. When you turn and look at them, you discover they are using sign language to converse. Think of your verbal conversation like 802.11b/g and their sign language conversation like 802.11a. While these two wireless standard do not differ as much as verbal and sign language, this analogy illustrates the fact that 802.11a networks cause no interference to 802.11b/g networks, and they are not interfered upon by the 802.1 lb/g networks either.

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Microsoft’s save WP7 ten plan: acquisition of mobile phone makers

Posted on January 2, 2012 by SSS

Windows Phone 7 at risk. According to the latest data, the platform’s global market share of only 1.5%, while its main competitor Android has won more than 50% of the share. At the same time, major mobile phone manufacturers launch of Windows Phone 7 also failed to challenge Apple’s mobile phone. Microsoft is waiting patiently throughout the situation changes.

But there is still no change. Perhaps Microsoft to greatly enhance its position in the mobile market before, this situation does not occur any change. To achieve this may not be easy. Windows Phone 7 is widely regarded as the laughing stock of the consumer, but a very reluctant platform. I feel like the operating system Microsoft to throw in the corner, its own fate.

Fortunately, however, 2012 will be a new beginning, Microsoft has some new initiatives can be better to promote the success of Windows Phone 7. The following is the details:

1, to create a similar strategy with the Nexus

Google made a wise decision: Nexus brand launched by a group of high-quality Android smartphone. Although the company has not developed the smart phone, but still play a key role, which is very important. Google is a big brand, access to consumer and business users. Perhaps Microsoft should also follow this initiative, with hardware partners to develop similar products with the Nexus.

2, close to the operator

Microsoft in the past year with the operators do not establish a good relationship. The company has been trying to sell hardware manufacturers Windows Phone 7 platform, but the promotion is by the operator to take. When Microsoft to understand: the sooner help for operators, sales increase, the faster?

3, to meet the needs of developers

Windows Phone 7 developer is an essential part. If Microsoft is able to find ways to attract developers to Android Windows Phone 7 platform, this system will greatly enhance the probability of success. To attract developers, we need to provide a more attractive profit sharing model. Microsoft has a large amount of cash, it is time to upgrade its position in the applications market.

4, the acquisition of a mobile phone manufacturers

In addition to the application, Microsoft should also use cash to acquire a mobile phone manufacturer. Either RIM or Nokia, or other vendors, Microsoft should spend much. This may alienate others, but since Google can buy Motorola Mobile, Microsoft, why not follow it?

5, be patient

Former Microsoft executive Charlie Kindel author said, Android platform next few years, the division will be more serious. If so, Microsoft would have to be patient. This differentiation will eventually annoy the consumer, they will choose other mobile platforms. With security as the starting point for Android collapse from within, may be a viable strategy.

6, and remain closed

Microsoft also guaranteed not panic. Microsoft must not open the source code of Windows Phone 7. The system is just part of the appeal from the closed, which makes Microsoft can like apples firmly in control systems. Closed to maintain the status quo of Windows Phone 7 is a wise move.

7, simplify the upgrade process

Google Android system every year to upgrade, but not in time for vendors to deploy the latest upgrade. Although mango initially made some mistakes, but now has released a timely update. 2012, Microsoft introduced the system should continue to update and simplify the upgrade process.

8, the use of the Windows brand

Microsoft renamed Windows Mobile Windows Phone 7 very strange decision. Windows is a household name, so should be used. 2012, Microsoft should be focused first part of the system name, ie Windows, while Windows 8 platform to demonstrate its links with. If you can achieve this, there may enhance the overall sales of Windows Phone 7.

9, consider the Tablet PC

Indeed, Microsoft has said, Windows 8 will become the company’s Tablet PC operating system. However, the Windows Phone 7 for smaller equipment is completely feasible. This product seems to be 5-7 inches ideal platform for handheld devices. Through a number of improvements, they could become a good choice for business users. Tablet PC is a mobile operating system vendor’s next battlefield, around the market is certainly a big mistake.

10, Apple completely ignored

Microsoft, Apple should be completely ignored. iPhone sales really high, but the iOS overall market share was declining. In addition, Apple also controls the software and hardware. Google is Microsoft should be worried about opponents, Android and Windows Phone 7 the same basic development ideas, goals are the same partners. Apple will only distract attention over

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Microsoft Former executive: WP7 failed because no manufacturer and operators support

Posted on January 1, 2012 by SSS

Gindle left Microsoft at this year and founded his own company. He recently wrote an article entitled “Windows Phone so good, why not develop?” Blog, a detailed description of WP7 phone sales “bland”, and Android phone hot sales of reasons. He said that this has nothing to do with technology, because from a technical point of view better than Android WP7.

His core argument is simple: Microsoft did not win the equipment manufacturers and wireless carriers to support, so they will not give WP7 phone into advertising and marketing costs, and no training their sales team to sell this phone. Instead, they will vote for the marketing costs of the Android platform, which brings Android phone hot.

“WP7 for device manufacturers and mobile operators dismissive. WP7 for equipment manufacturers, said, ‘This is you must use the hardware specifications.’, Then on the wireless carrier said it, ‘This is it for granted is updated , ‘”he wrote. He said that because of this, device manufacturers and wireless carriers before their time and money are all used to sell Android devices, rather than the WP7 phone.

Gindl that consumers know little about technology, they do not want to know what kind of mobile devices, others let them buy what they buy. “They only know to buy mobile phones from wireless carriers and related services and they are usually based on television advertising and retail sales representative to purchase the recommendations.” He said.

Gindl that, WP7 reason for failure, because Microsoft and wireless carriers against each other, resulting in the latter did not do their utmost to promote and sell WP7 phone. “Microsoft and wireless operators against each other, this is the real reason for the failure of WP7, although WP7 much better than Android, but WP7 phone Android phone sales is not as good as in the case of hostility, wireless carriers will make this easy decision: promotional marketing costs into Android devices, and retail sales representatives to sell Android devices out. “he said. In fact, when you turn on the TV, you will see much more than advertising Android phone WP7 phone. But you walk into the store and talk with a sales representative, you will understand that they are more biased in favor of promoting Android devices, rather than the WP7 phone.

Gindl concluded that Microsoft allow WP7 to be successful, you need to persuade wireless carriers more publicity WP7 phone, and better training of its sales team to sell this phone. In addition, Android phones selection of brands and models more than the WP7 phone. Moreover, WP7 phone and did not like the Android and iPhone, so, using familiar application-centric interface, which means that Microsoft needs to provide training to consumers so that they know how to use this phone.

In summary, in order to promote WP7 phone, wireless carriers need to convince Microsoft to invest more advertising, better training of sales team. In addition, Microsoft also needs to market more different brands and models of WP7 phone, and provide quality training, so that consumers understand the charm of this platform

Social alliance to isolate areas of Microsoft, Google + Facebook

Google is difficult to tolerate the oligarchs who dominate the Internet world, in social networks that are able to communicate on behalf of the spirit of the area lost to the Internet Facebook. Therefore, it is the end of June 2011, launched a Google + service, Facebook is to address a huge market.

It is noteworthy that, Google + Although the difficulties encountered, but the overall momentum is still very good. The U.S. genealogy Web site Ancestry.com, founder Paul Allen  to the latest statistics are 62 million users, and in the future is more promising, Allen estimated the actual number of users Google + will break in February 2012 100 million, 200 million in August, and in the end of 2012 will reach 400 million.

Although this is not and Facebook 1 billion over the same period, but also has given the pace of development, “the king of social networking,” worried. The Microsoft plan with a long history of social development to promote Bing, the search wars this year, analysts believe the main reason is that Microsoft prevailed on Facebook, Twitter and other resources integration.

More than that, Microsoft officially launched in mid-students of social networking services So.cl, which is produced for educational users, but also built on the Facebook network basis. The close relationship between the two companies have been quite obvious.

And their objects? It is clear that Google has. As Microsoft do anything they want on the desktop, no one can be the enemy, Google is also difficult to tolerate it on the Internet was a challenge. A weighted combination of threats and interests, Microsoft Facebook finally standing on one side, and Google is the other side, PK posture revealed beyond doubt.

Conclusion:

From the search, patent, TV, more than in terms of social, Google-Microsoft competition is already very evident. Instead the relationship between Apple Google may improve in the future, and overlapping areas with Facebook being too small. So Schmidt The “Google is Microsoft’s core competitors” thesis is very accurate, the two companies is expected in 2012 will go to war in the mobile space, a show of attack and siege will be staged, and very worth seeing Oh!

Buy cell phones: http://www.sssindustry.com/blog/what-you-should-pay-attention-to-buy-cell-phone/

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RF Behavior

Posted on January 1, 2012 by SSS

RF Behavior

After RF waves leave the antenna and begin to travel through the environment in which communications must occur, many behavioral factors influence the results achieved. Understanding the behavior of RF waves is essential to configuring a working wireless network in small or large environments.

Most of these behaviors will be easy for you to understand as they are similar to what you have learned through experience with light. Remembering that light is part of the electromagnetic spectrum and has a similar behavior to RF will help you understand these behaviors.

Remember that light and infrared do not behave exactly like RF in that they are more easily absorbed into objects; however, they do reflect and refract and even scatter in similar ways.

Reflection

Reflection, as the name indicates, occurs when an RF wave strikes an object with large dimensions in comparison to the wavelength of the propagating wave and is represented. Objects that cause reflections include the earth’s surface, large buildings, walls, and other obstacles in the RF wave path. As suggests, reflection usually occurs in a direction related to the pre-reflection direction of the RF signal. In other words, the signal will be reflected or bounced back from the reflecting object much like a beam of light reflects off a mirror.

The amount of reflection, as opposed to absorption, that occurs depends on two basic things: the frequency of the RF signal and the material of the object. As materials go, metal reflects more than concrete and water absorbs more than concrete. If an object is smoother, like metal, more of the RF signal will remain intact as it is reflected.

In a wireless LAN, reflection can cause a problem known as multipath. Multipath occurs when the main signal is reflected off many objects in the area of the transmission. Multipath can degrade or even cancel out a signal, and this can cause gaps in the RF coverage you achieve. Watch out for metal roofs, metal blinds, and metal doors in the environment, as they can cause reflection and multipath to occur.

Refraction

Refraction, depicted, describes what happens when part of the RF signal is reflected and another portion bends through an object. Cold air is an example of an “object” that might cause refraction. Refraction causes problems for long-distance RF links because changes in the weather or atmosphere can cause a significant portion of the RF signal to be redirected away from the intended target and so much energy may be lost that the receiver cannot detect the signal. A pane of glass can also cause refraction.

Diffraction

Diffraction describes a wave bending around an obstacle, as indicated. To understand diffraction, it might be helpful to think of a rock dropping into a pool of water and the ripples created by this action. Think of the ripples as propagating RF waves. Now imagine placing a stick in the water in a perpendicular fashion in the path of the waves. Notice how the waves diffract around the stick. This action is similar to what happens with RF waves that are diffracted around an object.

This analogy also helps you to understand that diffraction cannot occur if the impeding object is too large. Imagine placing a large piece of plywood in front the ripples propagating out from the entry point of the rock into the water. Now the waves are not strong enough to diffract around the object and they are simply blocked by the plywood—the energy of the waves is absorbed. In much the same way, RF waves might not be able to diffract around large obstructions.

One final reality revealed by this analogy is the concept of RF shadow. Imagine placing a 2 x 4 in the water instead of the stick or plywood. When you place the stick in the water, you cannot see the shadow created, but the 2 x 4 is large enough to reveal the shadow, but not too large—as the plywood is—to block the wave. Look closely behind the 2 x 4 (or the building shown) and you will notice a space where no waves exist. This space is the wave shadow, or on wireless networks, the RF shadow. You will not get wireless reception in this space.

Scattering

Scattering is what happens when the medium the RF wave is traveling through contains objects with dimensions that are small in comparison to the wavelength of the RF signal. Scattering is produced by rough surfaces, small objects, or irregularities in the signal path. Scattering is a lot like many little reflections. When referred to as reflection, the vast majority of the signal is reflected in the same direction, and when referred to as scattering, many portions of the signal are reflected (scattered) in different directions.

Absorption

The final important RF behavior that you must understand is absorption. As noted earlier, absorption is what makes microwaves work and your wireless signal degrade. RF signals can be absorbed by many different objects, including the air through which the signals pass, causing a reduction in signal strength until, eventually, the signal is lost. Water is an excellent signal absorber above the 2 GHz range. This is why the 2.4 GHz range is generally used by microwave ovens. While the RF waves can move through food well, water molecules cannot vibrate fast enough to keep up with the RF waves and so they absorb the energy instead.

It is important to remember that humans are basically moving food (not a pleasant thought, huh?) because we are mostly water. Therefore, the more humans in a space, the more of the RF signal that will be absorbed. Keep this in mind for large convention spaces with low ceilings and large rooms. For this same reason, it is important to remember that most living things have a large saturation of water, including plants and animals, and therefore, heavily forested areas are prime spots for weakened signals in the 2.4 GHz spectrum.

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RF Defined

Posted on December 30, 2011 by SSS

It should be immediately clear that there are at least two important words related to RF that need to be defined; however, there is a third word that also needs to be defined to fully understand RF. These three words are

■           Radio

■           Frequency

■           Signal

The radio is the device that generates and receives the signal known as an RF signal, and this signal is transmitted on a specific frequency. The frequency is what distinguishes one RF signal from another. Technically, the number of times per second the signal cycles or repeats a particular waveform is the source of the frequency identification. This means that a signal operating at the 2.4 GHz frequency is cycling 2,400,000,000 times per second (1 GHz = 1 billion cycles per second and 1 MHz = 1 million cycles per second).

Electric energy can be made to vary over time. This variance in electrical energy is known as a signal. There are two general categories of signals: digital and analog. The sine wave is an example of an analog signal.

Figure 2.1 illustrates a sine wave. As time passes, the sine wave’s intensity increases to some maximum point (point A) and then returns to the baseline (point 0). The wave’s intensity decreases to some minimum point (point B) and then returns to the baseline again. This process continues over time.

By adjusting the number of cycles (going from point 0 to A to 0 to B to 0) in a given window of time, you adjust the frequency. represents two cycles of the wave.

Digital signals differ from analog signals in that the digital signal varies abruptly between two electrical values, and the analog signal varies gradually, as was demonstrated. Digital signals are used to communicate and relay information within computer networks, but are not used as carriers of information in RF networks. Only analog signals are used as carriers of information. The information being carried by the RF waves might be digital or analog, but it is encoded (carried) on analog signals in an RF-based network connection.

An analog carrier signal can carry data represented by analog or digital techniques. This carrying of an information signal on a carrier signal is known as modulation. Modulation has been utilized for decades; one well-known example is the modem. The mod in modem stands for modulator, and the dem stands for demodulator. Much like a modem modulates and demodulates information traveling on a telephone wire, an RF radio modulates data to send through the RF medium and demodulates data received through the medium. The sending of this signal from the radio out through the antenna is known as radiation.

As discussed in Chapter 1, all that is needed to represent digital data is some form of variance between two states. The analog or digital signals carried across the RF signals from device-to-device on a wireless network provide this variance.

RF Range and Speed Factors

To effectively implement an RF-based network, such as Wi-Fi or WiMAX, you need to understand the factors that impact the distance or range RF signals can travel and the bandwidth available for communications. In this case, bandwidth refers to the speed of the communications. Issues such as line-of-sight, Fresnel Zone clearance, interference devices, and standard RF behavior become very important when setting up a wireless network.

Line-of-Sight

Line-of-sight (LOS) is the seemingly straight line from the object in view (the transmitter) to the observer’s eye (the receiver). This is also called the visual line-of-sight. The LOS is a seemingly straight line because, in fact, light waves travel in a similar fashion to RF waves.

Light waves can bounce off objects and be redirected. A mirror demonstrates this well. Stand directly in front of a mirror and note what you can see in the mirror. Now take a step to your right or left and note what you can see. You should be able to see more objects or information opposite to the direction of your move. For example, if you step to your right, you’ll now see more items that are actually located to your left and vice versa.

Why does this phenomenon occur? The light waves are bouncing off the objects and soaring toward the mirror. The mirror is then reflecting the light according to the directionality of the strike against the mirror. If you position your eyes in the path of this reflected light, you can therefore see the objects.

In this same way, RF devices must have LOS with each other in order to communicate. As this example demonstrates, they do not necessarily need to have direct visual LOS as the RF waves can pass through some objects and reflect, refract, and diffract, around others. This is particularly true for indoor communications and is the reason LOS concerns are more relevant to outside connections than they are to inside communications.

When creating building-to-building connections, visual LOS must be in place. While you might not be able to see the receiver you are transmitting to, the space between the transmitter and the receiver (or two transceivers) must be mostly clear. This space is referred to as the Fresnel Zone.

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Important Foundational Networking Concepts

Posted on December 29, 2011 by SSS

To fully understand wireless LAN technologies, you need to have a basic understanding of general networking concepts. Among these concepts, several important items stand out, including networking terminology, networking communications, and networking models. If you are already familiar with basic networking terms and concepts, you may choose to skip ahead to the summary section of this chapter. However, a review might be helpful even for those savvy in basic networking, and if you are new to the networking world, this section will be very beneficial.

Networking Terminology

As you learn about wireless networking technologies, you have to understand some basic networking terms:

■             Packet

■             Bandwidth

■            Throughput

■            Latency

■            Authentication

 

■           Broadcast

■           Node

■            Host

■            Server

■            Client/Workstation

■            Protocol

■            Network

■            LAN

■            WAN

A packet or datagram is the basic unit of information used in modern computer networks. Packets usually include sending and receiving device information, error-control data, and the message being sent from the source to the destination device. When sending large data files across the network, the data is split into multiple packets and then sent.

Bandwidth refers to the information carrying capacity of a network. Bandwidth is usually measured in kilobits per second (KBPS) or megabits per second (MBPS). It is also important to understand throughput and how it differs from bandwidth. Throughput is generally used to reference the actual amount of “real” data that can be sent across the network. All networks consume a certain amount of the available bandwidth because of overhead issues such as error-control, broadcasts, and collisions. Because of this, throughput is generally somewhat lower—and sometimes much lower—than the stated bandwidth of the network. This—the extra overhead—is why an 11 Mbps wireless connection provides only 5-6 Mbps of actual throughput.

Sometimes communications between devices on a network are delayed because of the distance from one device to the other or the speed of the connecting devices, such as routers. This delay is known as latency. Latency can have a significant impact on network communications because the actual speed of communications is dependent on the combine bandwidth and latency.

When a device connects to a secure network, it must be validated. This validation is called authentication. Both people and devices can be authenticated and, in the most secure environments, both are authenticati using a secure mechanism. In wireless networks, the default authenticati type is an open authentication model, and you should use additional seci measures. These might include WPA/WPA2 or VPN tunnels to encrypt

wireless traffic and EAP-type authentication mechanisms. These security measures are covered in more detail in Chapter 11.

A particular type of packet used in network discovery and communications is a broadcast. Broadcasts are used to discover network services such as DHCP servers and devices such as wireless access points. Broadcasts can cause decreased performance on wired networks as each node (device connected or point of connection to the network) must evaluate the packet because no specific node is identified in the broadcast message.

A host is a type of node connected to the network. This node can be a server, client, or any device hosting services, peripherals, or data. The server is a specific kind of host that is intended for data storage, service provision, and various centralized computing purposes. Examples of servers include email servers, telnet servers, file and print servers, and Internet access servers. A client or workstation is a host that utilizes the services of the network. Sometimes the term workstation is used to refer to a powerful desktop computer whether it is connected to a network or not.

For all the hosts on a network to communicate with one another, they must speak a common language. These standard methods of digital communication are known as protocols. In most cases, the term protocol refers to higher-level communications such as TCP/IP (from the Internet world) or IPX/SPX (from the Novell world), however, you could apply the term protocol to Ethernet or token-ring technologies that operate at a much lower level. In its most basic sense, a protocol is a standardized set of instructions for communications between nodes on a network, and the instructions can apply to the physical level or the application level of the communications process.

I have used the term network throughout the previous section many times and through this use have, in effect, defined the term. A computer network is an arrangement of interconnected devices utilizing a shared protocol (or a set of shared protocols) for communications.

There are two other terms you should know that are used frequently in the networking world: LAN and WAN. A LAN is a local area network and a WAN is a wide area network. A LAN is usually defined as a network confined to a single location; this location can be a single building or a campus with multiple buildings. A WAN is usually the combination of two or more LANs separate by some significant distance; a WAN can span a city or the globe. When using wireless networking technology, these terms—LAN and WAN—are usually combined with a W to represent wireless and thus you have a WLAN or WWAN.

 

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Wi-Fi/WMM/WPA/WPA2/ Certification

Posted on December 29, 2011 by SSS

Wi-Fi Certification

Wi-Fi certified hardware or software is certified to meet the specifications set forth by IEEE standards. A device can be Wi-Fi certified for one standard or for many. The Wi-Fi Alliance is responsible for certifying products in this way.

WMM Certification

WMM or Wi-Fi Multimedia is a certification using a subset of the 802.1 le draft standard. If a product has this certification, it means that it provides QoS features in line with the 802.1 le standard for VoIP or multimedia streaming services.

Remember, a draft standard is a proposed standard that has not yet been ratified. To be ratified means to be approved. In the case of IEEE standards, ratification is performed by the standard governing body.

WPA/WPA2 Certification

Another certification managed by the Wi-Fi Alliance is the WPA/WPA2 certification. The WPA certification verifies that a device or software meets the demands of the Wi-Fi Alliance WPA certification, which is based on a subset of the 802.lli standard and provides for encryption on wireless networks. The WPA2 certification is a verification of compliance with

 

the 802.1 li standard. The IEEE does not refer to 802.1 li as WPA2; this is a term trademarked by the Wi-Fi Alliance only.

This difference in terms between the standards and the certifications often leads to confusion in the marketplace. A perfect example of this is the WPA-Personal and WPA-Enterprise technologies. WPA-Personal is a subset of the WPA certification that uses a passphrase or shared key to secure communications. WPA-Enterprise is the subset that requires an authentication server. Many vendors implement this in a way that does not clearly differentiate between the two subsets of the WPA certification, leading to a confused perspective in the marketplace that says all WPA implementations are the same. Nothing could be further from reality. WPA-Personal, in most cases, uses the same passphrase until it is changed manually. WPA-Enterprise can use certificates and other more secure authentication and encryption mechanisms, making it easier to manage centrally and, when implemented properly, more secure.

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