Code-division multiple access
Code-division multiple access is a channel access method used by various radio communication technologies. CDMA is an example of multiple access, where several transmitters can send information over a single communication channel; this allows several users to share a band of frequencies. To permit this without undue interference between the users, CDMA employs spread spectrum technology and a special coding scheme. CDMA is used as the access method in many mobile phone standards. IS-95 called "cdmaOne", its 3G evolution CDMA2000, are simply referred to as "CDMA", but UMTS, the 3G standard used by GSM carriers uses "wideband CDMA", or W-CDMA, as well as TD-CDMA and TD-SCDMA, as its radio technologies; the technology of code-division multiple access channels has long been known. In the Soviet Union, the first work devoted to this subject was published in 1935 by Dmitry Ageev, it was shown that through the use of linear methods, there are three types of signal separation: frequency and compensatory.
The technology of CDMA was used in 1957, when the young military radio engineer Leonid Kupriyanovich in Moscow made an experimental model of a wearable automatic mobile phone, called LK-1 by him, with a base station. LK-1 has a weight of 3 kg, 20–30 km operating distance, 20–30 hours of battery life; the base station, as described by the author, could serve several customers. In 1958, Kupriyanovich made the new experimental "pocket" model of mobile phone; this phone weighed 0.5 kg. To serve more customers, Kupriyanovich proposed the device, which he called "correlator." In 1958, the USSR started the development of the "Altai" national civil mobile phone service for cars, based on the Soviet MRT-1327 standard. The phone system weighed 11 kg, it was placed in the trunk of the vehicles of high-ranking officials and used a standard handset in the passenger compartment. The main developers of the Altai system were VNIIS and GSPI. In 1963 this service started in Moscow, in 1970 Altai service was used in 30 USSR cities.
One of the early applications for code-division multiplexing is in the Global Positioning System. This is distinct from its use in mobile phones; the Qualcomm standard IS-95, marketed as cdmaOne. The Qualcomm standard IS-2000, known as CDMA2000, is used by several mobile phone companies, including the Globalstar network; the UMTS 3G mobile phone standard, which uses W-CDMA. CDMA has been used in the OmniTRACS satellite system for transportation logistics. CDMA is a spread-spectrum multiple-access technique. A spread-spectrum technique spreads the bandwidth of the data uniformly for the same transmitted power. A spreading code is a pseudo-random code that has a narrow ambiguity function, unlike other narrow pulse codes. In CDMA a locally generated code runs at a much higher rate than the data to be transmitted. Data for transmission is combined by bitwise XOR with the faster code; the figure shows. The data signal with pulse duration of T b is XORed with the code signal with pulse duration of T c. Therefore, the bandwidth of the data signal is 1 / T b and the bandwidth of the spread spectrum signal is 1 / T c.
Since T c is much smaller than T b, the bandwidth of the spread-spectrum signal is much larger than the bandwidth of the original signal. The ratio T b / T c is called the spreading factor or processing gain and determines to a certain extent the upper limit of the total number of users supported by a base station; each user in a CDMA system uses a different code to modulate their signal. Choosing the codes used to modulate the signal is important in the performance of CDMA systems; the best performance occurs when there is good separation between the signal of a desired user and the signals of other users. The separation of the signals is made by correlating the received signal with the locally generated code of the desired user. If the signal matches the desired user's code the correlation function will be high and the system can extract that signal. If the desired user's code has nothing in common with the signal, the correlation should be as close to zero as possible. If the code is correlated with the signal at any time offset other than zero, the correlation should be as close to zero as possible.
This is used to reject multi-path interference. An analogy to the problem of multiple access is a room in which people wish to talk to each other simultaneously. To avoid confusion, people could take turns speaking, speak at different pitches, or speak in different languages. CDMA is analogous to the last example where people speaking the same language can understand each other, but other languages are perceived as noise and rejected. In radio CDMA, each group of users is given a shared code. Many codes occupy the same channel, but only users associated
The World Factbook
The World Factbook known as the CIA World Factbook, is a reference resource produced by the Central Intelligence Agency with almanac-style information about the countries of the world. The official print version is available from the Government Printing Office. Other companies—such as Skyhorse Publishing—also print a paper edition; the Factbook is available in the form of a website, updated every week. It is available for download for use off-line, it provides a two- to three-page summary of the demographics, communications, government and military of each of 267 international entities including U. S.-recognized countries and other areas in the world. The World Factbook is prepared by the CIA for the use of U. S. government officials, its style, format and content are designed to meet their requirements. However, it is used as a resource for academic research papers and news articles; as a work of the U. S. government, it is in the public domain in the United States. In researching the Factbook, the CIA uses the sources listed below.
Other public and private sources are consulted. Antarctic Information Program Armed Forces Medical Intelligence Center Bureau of the Census Bureau of Labor Statistics Council of Managers of National Antarctic Programs Defense Intelligence Agency Department of Energy Department of State Fish and Wildlife Service Maritime Administration National Geospatial-Intelligence Agency Naval Facilities Engineering Command Office of Insular Affairs Office of Naval Intelligence Oil & Gas Journal United States Board on Geographic Names United States Transportation Command Because the Factbook is in the public domain, people are free under United States law to redistribute it or parts of it in any way that they like, without permission of the CIA. However, the CIA requests. Copying the official seal of the CIA without permission is prohibited by U. S. federal law—specifically, the Central Intelligence Agency Act of 1949. Before November 2001 The World Factbook website was updated yearly. Information available as of January 1 of the current year is used in preparing the Factbook.
The first, edition of Factbook was published in August 1962, the first unclassified version in June 1971. The World Factbook was first available to the public in print in 1975. In 2008 the CIA discontinued printing the Factbook themselves, instead turning printing responsibilities over to the Government Printing Office; this happened due to a CIA decision to "focus Factbook resources" on the online edition. The Factbook has been on the World Wide Web since October 1994; the web version receives an average of 6 million visits per month. The official printed version is sold by the Government Printing Office and National Technical Information Service. In past years, the Factbook was available on CD-ROM, magnetic tape, floppy disk. Many Internet sites use information and images from the CIA World Factbook. Several publishers, including Grand River Books, Potomac Books, Skyhorse Publishing have re-published the Factbook in recent years; as of July 2011, The World Factbook comprises 267 entities, which can be divided into the following categories: Independent countries The CIA defines these as people "politically organized into a sovereign state with a definite territory."
In this category, there are 195 entities. Others Places set apart from the list of independent countries. There are two: Taiwan and the European Union. Dependencies and Areas of Special Sovereignty Places affiliated with another country, they may be subcategorized by affiliated country: Australia: six entities China: two entities Denmark: two entities France: eight entities Netherlands: three entities New Zealand: three entities Norway: three entities United Kingdom: seventeen entities United States: fourteen entitiesMiscellaneous Antarctica and places in dispute. There are six such entities. Other entities The World and the oceans. There are the World. Areas not covered Specific regions within a country or areas in dispute among countries, such as Kashmir, are not covered, but other areas of the world whose status is disputed, such as the Spratly Islands, have entries. Subnational areas of countries are not included in the Factbook. Instead, users looking for information about subnational areas are referred to "a comprehensive encyclopedia" for their reference needs.
This criterion was invoked in the 2007 and 2011 editions with the decision to drop the entries for French Guiana, Martinique and Reunion. They were dropped because besides being overseas departments, they were now overseas regions, an integral part of France. Kashmir Maps depicting Kashmir have the Indo-Pakistani border drawn at the Line of Control, but the region of Kashmir administered by China drawn in hash marks. Northern Cyprus Northern Cyprus, which the U. S. considers part of the Republic of Cyprus, is not given a separate entry because "territorial occupations/annexations not recognized by the United States Government are not shown on U. S. Government maps."Taiwan/Republic of China The name
BlackBerry is a line of smartphones and services designed and marketed by Canadian company BlackBerry Limited. These are designed and marketed by TCL Communication, BB Merah Putih, Optiemus Infracom for the global and South Asian markets using the BlackBerry brand under license. BlackBerry was one of the most prominent smartphone vendors in the world, specializing in secure communications and mobile productivity, well-known for the keyboards on most of its devices. At its peak in September 2013, there were 85 million BlackBerry subscribers worldwide. However, BlackBerry has since lost its dominant position in the market due to the success of the Android and iOS platforms; the BlackBerry line traditionally uses a proprietary operating system developed by BlackBerry Limited known as BlackBerry OS. In 2013, BlackBerry introduced BlackBerry 10, a major revamp of the platform based on the QNX operating system. BlackBerry 10 was meant to replace the aging BlackBerry OS platform with a new system, more in line with the user experiences of modern smartphone operating systems.
The first BB10 powered device was the BlackBerry Z10, followed by other all-touch and keyboard-equipped models. In 2015, BlackBerry re-focused its business strategy and began to release Android-based smartphones, beginning with the BlackBerry Priv slider and the BlackBerry DTEK50. On September 28, 2016, BlackBerry announced it would cease designing its own phones in favor of licensing to partners. TCL Communication became the global licensee of the brand, under the name "BlackBerry Mobile." Optiemus Infracom, under the name BlackBerry Mobile India, BB Merah Putih serve as licensees of the brand, serving the Indian and Indonesian markets, respectively. In February 2017, BlackBerry Mobile released the BlackBerry KeyOne, known for having a physical keyboard below the 4.5 inch screen, having a great battery life, the last device to be designed by BlackBerry Limited. BlackBerry Mobile's latest Android smartphone is the BlackBerry Key2, announced on June 7, 2018 and released on July 13th of that year in the US.
These devices, along with BB Merah Purih's BlackBerry Aurora make up BlackBerry's current lineup. In June 2018, the BlackBerry Key2 was launched in international markets, in India by licensee Optiemus Infracom; the KEY2 is the first BlackBerry-branded smartphone to sport a dual camera setup, it incorporates features such as portrait mode and optical zoom. In August 2018, after the launch of the BlackBerry Key2, Optiemus Infracom has announced the launch of Evolve and Evolve X smartphones for the Indian market sold on Amazon India; the smartphones have been conceptualized and manufactured in India. The Evolve Series was announced on August 2, 2018. Research in Motion, founded in Waterloo, first developed the Inter@ctive Pager 900, announced on September 18, 1996; the Inter@ctive Pager 900 was a clamshell-type device. After the success of the 900, the Inter@ctive Pager 800 was created for IBM, which bought US$10 million worth of them on February 4, 1998; the next device to be released was the Inter@ctive Pager 950, on August 26, 1998.
The first device to carry the BlackBerry name was the BlackBerry 850, an email pager, released January 19, 1999. Although identical in appearance to the 950, the 850 was the first device to integrate email and the name Inter@ctive Pager was no longer used to brand the device; the first BlackBerry device, the 850, was introduced in 1999 as a two-way pager in Germany. The name BlackBerry was coined by the marketing company Lexicon Branding; the name was chosen due to the resemblance of the keyboard's buttons to that of the drupelets that compose the blackberry fruit. The original BlackBerry devices, the RIM 850 and 857, used the DataTAC network. In 2002, the more known convergent smartphone BlackBerry was released, which supports push email, mobile telephone, text messaging, Internet faxing, Web browsing and other wireless information services. BlackBerry gained market share in the mobile industry by concentrating on email. BlackBerry began to offer email service on non-BlackBerry devices, such as the Palm Treo, through the proprietary BlackBerry Connect software.
The original BlackBerry device had a monochrome display. All newer models have been optimized for "thumbing", the use of only the thumbs to type on a keyboard; the Storm 1 and Storm 2 include. System navigation was achieved with the use of a scroll wheel mounted on the right side of device models prior to the 8700; the trackwheel was replaced by the trackball with the introduction of the Pearl series, which allowed four-way scrolling. The trackball was replaced by the optical trackpad with the introduction of the Curve 8500 series. Models made to use iDEN networks, such as Nextel, SouthernLINC, NII Holdings, Mike incorporate a push-to-talk feature, similar to a two-way radio. On January 30, 2013, BlackBerry announced the release of the Q10 smartphones. Both models consist of touch screens: the Z10 features an all-touch design and the Q10 combines a QWERTY keyboard with touchscreen features. During the second financial quarter of 2013, BlackBerry sold 6.8 million handsets, but was eclipsed by the sales of competitor Nokia's Lumia model for the first time.
On August 12, 2013, BlackBerry announced the intention to
GSM is a standard developed by the European Telecommunications Standards Institute to describe the protocols for second-generation digital cellular networks used by mobile devices such as mobile phones and tablets. It was first deployed in Finland in December 1991; as of 2014, it has become the global standard for mobile communications – with over 90% market share, operating in over 193 countries and territories.2G networks developed as a replacement for first generation analog cellular networks, the GSM standard described a digital, circuit-switched network optimized for full duplex voice telephony. This expanded over time to include data communications, first by circuit-switched transport by packet data transport via GPRS and EDGE. Subsequently, the 3GPP developed third-generation UMTS standards, followed by fourth-generation LTE Advanced standards, which do not form part of the ETSI GSM standard. "GSM" is a trademark owned by the GSM Association. It may refer to the most common voice codec used, Full Rate.
In 1983, work began to develop a European standard for digital cellular voice telecommunications when the European Conference of Postal and Telecommunications Administrations set up the Groupe Spécial Mobile committee and provided a permanent technical-support group based in Paris. Five years in 1987, 15 representatives from 13 European countries signed a memorandum of understanding in Copenhagen to develop and deploy a common cellular telephone system across Europe, EU rules were passed to make GSM a mandatory standard; the decision to develop a continental standard resulted in a unified, standard-based network, larger than that in the United States. In February 1987 Europe produced the first agreed GSM Technical Specification. Ministers from the four big EU countries cemented their political support for GSM with the Bonn Declaration on Global Information Networks in May and the GSM MoU was tabled for signature in September; the MoU drew in mobile operators from across Europe to pledge to invest in new GSM networks to an ambitious common date.
In this short 38-week period the whole of Europe had been brought behind GSM in a rare unity and speed guided by four public officials: Armin Silberhorn, Stephen Temple, Philippe Dupuis, Renzo Failli. In 1989 the Groupe Spécial Mobile committee was transferred from CEPT to the European Telecommunications Standards Institute. In parallel France and Germany signed a joint development agreement in 1984 and were joined by Italy and the UK in 1986. In 1986, the European Commission proposed reserving the 900 MHz spectrum band for GSM; the former Finnish prime minister Harri Holkeri made the world's first GSM call on July 1, 1991, calling Kaarina Suonio using a network built by Telenokia and Siemens and operated by Radiolinja. The following year saw the sending of the first short messaging service message, Vodafone UK and Telecom Finland signed the first international roaming agreement. Work began in 1991 to expand the GSM standard to the 1800 MHz frequency band and the first 1800 MHz network became operational in the UK by 1993, called and DCS 1800.
That year, Telecom Australia became the first network operator to deploy a GSM network outside Europe and the first practical hand-held GSM mobile phone became available. In 1995 fax, data and SMS messaging services were launched commercially, the first 1900 MHz GSM network became operational in the United States and GSM subscribers worldwide exceeded 10 million. In the same year, the GSM Association formed. Pre-paid GSM SIM cards were launched in 1996 and worldwide GSM subscribers passed 100 million in 1998. In 2000 the first commercial GPRS services were launched and the first GPRS-compatible handsets became available for sale. In 2001, the first UMTS network was launched, a 3G technology, not part of GSM. Worldwide GSM subscribers exceeded 500 million. In 2002, the first Multimedia Messaging Service was introduced and the first GSM network in the 800 MHz frequency band became operational. EDGE services first became operational in a network in 2003, the number of worldwide GSM subscribers exceeded 1 billion in 2004.
By 2005 GSM networks accounted for more than 75% of the worldwide cellular network market, serving 1.5 billion subscribers. In 2005, the first HSDPA-capable network became operational; the first HSUPA network launched in 2007. Worldwide GSM subscribers exceeded three billion in 2008; the GSM Association estimated in 2010 that technologies defined in the GSM standard served 80% of the mobile market, encompassing more than 5 billion people across more than 212 countries and territories, making GSM the most ubiquitous of the many standards for cellular networks. GSM is a second-generation standard employing time-division multiple-Access spectrum-sharing, issued by the European Telecommunications Standards Institute; the GSM standard does not include the 3G Universal Mobile Telecommunications System code division multiple access technology nor the 4G LTE orthogonal frequency-division multiple access technology standards issued by the 3GPP. GSM, for the first time, set a common standard for Europe for wireless networks.
It was adopted by many countries outside Europe. This allowed subscribers to use other GSM networks; the common standard reduced research and development costs, since ha
United States Department of State
The United States Department of State referred to as the State Department, is the federal executive department that advises the President and conducts international relations. Equivalent to the foreign ministry of other countries, it was established in 1789 as the nation's first executive department; the current Secretary of State is Mike Pompeo, who ascended to the office in April 2018 after Rex Tillerson resigned. The State Department's duties include implementing the foreign policy of the United States, operating the nation's diplomatic missions abroad, negotiating treaties and agreements with foreign entities, representing the United States at the United Nations, it is led by the Secretary of State, a member of the Cabinet, nominated by the President and confirmed by the Senate. In addition to administering the department, the Secretary of State serves as the nation's chief diplomat and representative abroad; the Secretary of State is the first Cabinet official in the order of precedence and in the presidential line of succession, after the Vice President of the United States, Speaker of the House of Representatives, President pro tempore of the Senate.
The State Department is headquartered in the Harry S Truman Building, a few blocks away from the White House, in the Foggy Bottom neighborhood of Washington, D. C.. The U. S. Constitution, drafted in Philadelphia in September 1787 and ratified by the 13 states the following year, gave the President the responsibility for the conduct of the nation's foreign relations; the House of Representatives and Senate approved legislation to establish a Department of Foreign Affairs on July 21, 1789, President Washington signed it into law on July 27, making the Department of Foreign Affairs the first federal agency to be created under the new Constitution. This legislation remains the basic law of the Department of State. In September 1789, additional legislation changed the name of the agency to the Department of State and assigned to it a variety of domestic duties; these responsibilities grew to include management of the United States Mint, keeper of the Great Seal of the United States, the taking of the census.
President George Washington signed the new legislation on September 15. Most of these domestic duties of the Department of State were turned over to various new federal departments and agencies that were established during the 19th century. However, the Secretary of State still retains a few domestic responsibilities, such as being the keeper of the Great Seal and being the officer to whom a President or Vice President of the United States wishing to resign must deliver an instrument in writing declaring the decision to resign. On September 29, 1789, President Washington appointed Thomas Jefferson of Virginia Minister to France, to be the first United States Secretary of State. John Jay had been serving in as Secretary of Foreign Affairs as a holdover from the Confederation since before Washington had taken office and would continue in that capacity until Jefferson returned from Europe many months later. From 1790 to 1800, the State Department had its headquarters in Philadelphia, the capital of the United States at the time.
It occupied a building at Fifth Streets. In 1800, it moved from Philadelphia to Washington, D. C. where it first occupied the Treasury Building and the Seven Buildings at 19th Street and Pennsylvania Avenue. It moved into the Six Buildings in September 1800, where it remained until May 1801, it moved into the War Office Building due west of the White House in May 1801. It occupied the Treasury Building from September 1819 to November 1866, except for the period from September 1814 to April 1816, it occupied the Washington City Orphan Home from November 1866 to July 1875. It moved to the State and Navy Building in 1875. Since May 1947, it has occupied the Harry S. Truman Building in the Foggy Bottom neighborhood of Washington. Condoleezza Rice became the second female secretary of state in 2005. Hillary Clinton became the third female secretary of state when she was appointed in 2009. In 2014, the State Department began expanding into the Navy Hill Complex across 23rd Street NW from the Truman Building.
A joint venture consisting of the architectural firms of Goody and the Louis Berger Group won a $2.5 million contract in January 2014 to begin planning the renovation of the buildings on the 11.8 acres Navy Hill campus, which housed the World War II headquarters of the Office of Strategic Services and was the first headquarters of the Central Intelligence Agency. The Executive Branch and the U. S. Congress have constitutional responsibilities for U. S. foreign policy. Within the Executive Branch, the Department of State is the lead U. S. foreign affairs agency, its head, the Secretary of State, is the President's principal foreign policy advisor. The Department advances U. S. objectives and interests in the world through its primary role in developing and implementing the President's foreign policy. It provides an array of important services to U. S. citizens and to foreigners seeking to visit or immigrate to the United States. All foreign affairs activities—U. S. Representation abroad, foreign assistance programs, countering internatio
Self-censorship is the act of censoring or classifying one's own discourse. This is done out of fear of, or deference to, the sensibilities or preferences of others and without overt pressure from any specific party or institution of authority. Self-censorship is practiced by film producers, film directors, news anchors, journalists and other kinds of authors including individuals who use social media. In authoritarian countries, creators of artworks may remove material that their government might find controversial for fear of sanction by their governments. In pluralistic capitalist countries, repressive judicial lawmaking can cause widespread "rivercrabbing" of Western media. Self-censorship can occur in order to conform to the expectations of the market. For example, the editor of a periodical may consciously or unconsciously avoid topics that will anger advertisers, customers, or the owners in order to protect her or his livelihood either directly or indirectly; this phenomenon is referred to as soft censorship.
Article 19 of the Universal Declaration of Human Rights guarantees freedom of speech from all forms of censorship. Article 19 explicitly states that "everyone has the right to freedom of expression. People communicate to affirm one's identity and sense of belonging. People may express their opinions or withhold their opinions due to the fear of exclusion or unpopularity. Shared social norms and beliefs create a sense of belonging, but they can create a suppression of expression in order to comply or belong. People may adjust their opinions to go along with the majority attitude. There are different factors that contribute to self-censorship such as gender, education, political interests and media exposure. For some, the reason for their change in beliefs and opinions are rooted in fear of isolation and exclusion; the risk of negative reactions is greater than expressing one's true beliefs. Journalists censor themselves due to threats against them or their interests from another party, editorial instructions from their supervisor, perceived conflicts of interest with a media organization's economic sponsors, advertisers or shareholders, etc.).
Self-censorship occurs when journalists deliberately manipulate their expression out of fear of, or deference to, the sensibilities or preferences of others and without overt pressure from any specific party or institution of authority. Self-censorship of journalists is most pervasive in societies where governments have official media censorship policies and where journalists will be jailed, fined, or lose their job if they do not follow the censorship rules. Organizations such as have raised concerns about news broadcasting stations Fox News, censoring their own content to be less controversial when reporting on certain types of issues such as the War on Terror. In their book Manufacturing Consent, Noam Chomsky and Edward Herman argue that corporate ownership of news media strongly encourages systematic self-censorship owing to market forces. In this argument with liberal media and self-censorship is evident in the selection and omission of news stories, the framing of acceptable discussion, in line with the interests of the corporations owning those media.
The journalists have sought censorship advice from military authorities in order to prevent the inadvertent revelation of military secrets. In 2009, The New York Times succeeded in suppressing news of a reporter's abduction by militants in Afghanistan for seven months until his escape from captivity in order to'reduce danger to the reporter and other hostages'. Journalists have sometimes self-censored publications of news stories out of concern for the safety of people involved. Jean Pelletier, the Washington D. C. correspondent for the Montreal La Presse newspaper, uncovered a covert attempt by the Canadian government to smuggle US diplomats out of Iran during the Iranian Hostage Crisis before the "Canadian Caper" had reached its conclusion. In order to preserve the safety of those involved, he refused to allow the paper to publish the story until the hostages had left Iran, despite the considerable news value to the paper and writer. Self-censorship became a quite frequent practice in Russia after 2000's government take-overs and consolidation of media, further deepened after 2014-2015 laws on'undesirable organisations'.
As for Europe, threats to media freedom have shown a significant increase in recent years. Journalists and whistleblowers have experienced threats. Self-censorship is one of the major consequences of such circumstances. A study published in 2017 by the Council of Europe found that in the period 2014-2016 that 40% of journalists involved in the survey experienced some kind of unwarranted interference, in particular psychological violence, including slandering and smear campaigning, cyberbulling. Other forms of unwarranted interference include intimidation by interest groups, threats with force, intimidation by political groups, targeted surveillance, intimidation by the police, etc. In terms of geography, cases of physical assault were more common in the South Caucasus, followed by Turkey, but were present in other regions as well. In China, the media has to go to greater extents to censor mu
Microwave transmission is the transmission of information by microwave radio waves. Although an experimental 40-mile microwave telecommunication link across the English Channel was demonstrated in 1931, the development of radar in World War II provided the technology for practical exploitation of microwave communication. In the 1950s, large transcontinental microwave relay networks, consisting of chains of repeater stations linked by line-of-sight beams of microwaves were built in Europe and America to relay long distance telephone traffic and television programs between cities. Communication satellites which transferred data between ground stations by microwaves took over much long distance traffic in the 1960s. In recent years, there has been an explosive increase in use of the microwave spectrum by new telecommunication technologies such as wireless networks, direct-broadcast satellites which broadcast television and radio directly into consumers' homes. Microwaves are used for point-to-point communications because their small wavelength allows conveniently-sized antennas to direct them in narrow beams, which can be pointed directly at the receiving antenna.
This allows nearby microwave equipment to use the same frequencies without interfering with each other, as lower frequency radio waves do. Another advantage is that the high frequency of microwaves gives the microwave band a large information-carrying capacity. A disadvantage is. Microwave radio transmission is used in point-to-point communication systems on the surface of the Earth, in satellite communications, in deep space radio communications. Other parts of the microwave radio band are used for radars, radio navigation systems, sensor systems, radio astronomy; the next higher part of the radio electromagnetic spectrum, where the frequencies are above 30 GHz and below 100 GHz, are called "millimeter waves" because their wavelengths are conveniently measured in millimeters, their wavelengths range from 10 mm down to 3.0 mm. Radio waves in this band are strongly attenuated by the Earthly atmosphere and particles contained in it during wet weather. In a wide band of frequencies around 60 GHz, the radio waves are attenuated by molecular oxygen in the atmosphere.
The electronic technologies needed in the millimeter wave band are much more difficult to utilize than those of the microwave band. Wireless transmission of informationOne-way and two-way telecommunication using communications satellite Terrestrial microwave relay links in telecommunications networks including backbone or backhaul carriers in cellular networksWireless transmission of powerProposed systems e.g. for connecting solar power collecting satellites to terrestrial power grids Microwave radio relay is a technology used in the 1950s and 1960s for transmitting signals, such as long-distance telephone calls and television programs between two terrestrial points on a narrow beam of microwaves. In microwave radio relay, microwaves are transmitted on a line of sight path between relay stations using directional antennas, forming a fixed radio connection between the two points; the requirement of a line of sight limits the separation between stations to the visual horizon, about 30 to 50 miles.
Before the widespread use of communications satellites, chains of microwave relay stations were used to transmit telecommunication signals over transcontinental distances. Beginning in the 1950s, networks of microwave relay links, such as the AT&T Long Lines system in the U. S. carried long distance telephone calls and television programs between cities. The first system, dubbed TD-2 and built by AT&T, connected New York and Boston in 1947 with a series of eight radio relay stations; these included long daisy-chained series of such links that traversed mountain ranges and spanned continents. Much of the transcontinental traffic is now carried by cheaper optical fibers and communication satellites, but microwave relay remains important for shorter distances; because the radio waves travel in narrow beams confined to a line-of-sight path from one antenna to the other, they don't interfere with other microwave equipment, so nearby microwave links can use the same frequencies. Antennas must be directional.
Typical types of antenna used in radio relay link installations are parabolic antennas, dielectric lens, horn-reflector antennas, which have a diameter of up to 4 meters. Directive antennas permit an economical use of the available frequency spectrum, despite long transmission distances; because of the high frequencies used, a line-of-sight path between the stations is required. Additionally, in order to avoid attenuation of the beam, an area around the beam called the first Fresnel zone must be free from obstacles. Obstacles in the signal field cause unwanted attenuation. High mountain peak or ridge positions are ideal. Obstacles, the curvature of the Earth, the geography of the area and reception issues arising from the use of nearby land are important issues to consider when planning radio links. In the planning process, it is essential that "path profiles" are produced, which provide information about the terrain and Fresnel zones affecting the transmission path; the presence of a water surface, such as a lake or river, along the path must be ta