title: Freediving

text: Most divers rely on increasing fitness by increasing lung capacity. Simple breath-holding practice is highly effective for increasing lung capacity. In an interview on the radio talk show Fresh Air, journalist James Nestor, author of the book "", stated: "Some divers have a lung capacity of 14 liters, which is about double the size for a typical adult male. They weren't born this way. ... They trained themselves to breathe in ways to profoundly affect their physical bodies."


title: Freediving

text: Training for freediving can take many forms, some of which can be performed on land. The University of Miami presents a scientific freediving class that was developed by Claire Paris, a professor and freediver, the class is the first of its kind at the university.


title: Freediving

text: One example is the apnea walk. This consists of a preparation "breathe-up", followed by a short (typically 1 minute) breath hold taken at rest. Without breaking the hold, participants then begin walking as far as possible until it becomes necessary to breathe again. Athletes can do close to 400 meters in training this way.


title: Freediving

text: This form of training is good for accustoming muscles to work under anaerobic conditions, and for tolerance to CO build-up in the circulation. It is also easy to gauge progress, as increasing distance can be measured.


title: Freediving

text: Before competition attempts, freedivers perform a preparation sequence, which usually consists of physical stretching, mental exercise and breath exercise. It may include a succession of variable length static apnea and special purging deep breaths. Results of the preparation sequence are slower metabolism, lower heart rate and breath rate, and lower levels of carbon dioxide in the bloodstream and overall mental equilibrium.


title: Freediving

text: The most obvious hazard is lack of access to air for breathing – a necessity for human life. This can result in asphyxia from drowning if the diver does not reach the surface while still capable of holding their breath and resuming breathing. The risk depends on several factors, including the depth, duration and shape of the dive profile.


title: Freediving

text: Latent hypoxia is a specific hazard of deeper freedives. This effect can cause hypoxic blackout during surfacing.


title: Freediving

text: There are also a wide range of environmental hazards possible specific to the site and water and weather conditions at the time of diving, and there may be other hazards specific to the freediving activity.


title: Freediving

text: Failing to respond to physiological warning signals, or crossing the mental barrier by strong will, may lead to blackout underwater or on reaching the surface. Trained freedivers are well aware of this and competitions must be held under strict supervision and with competent first-aiders on standby. However, this does not eliminate the risk of blackout. Freedivers are encouraged by certification and sporting organisations to dive only with a 'buddy' who accompanies them, observing from in the water at the surface, and ready to dive to the rescue if the diver loses consciousness during the ascent. This is only reasonably practicable if the water clarity allows observation, and the buddy is capable of safely reaching the diver. Due to the nature of the sport, the risks of freediving can be reduced by strict adherence to safety measures as an integral part of the activity, but cannot be eliminated entirely. Competition rules may require all participants to be adept in rescue and resuscitation.


title: Freediving

text: Nicholas Mevoli, a diver from New York died on 17 November 2013 after losing consciousness on surfacing from a 3-minute 38 second dive to a depth of during an official record attempt in the "constant weight without fins" event. He had previously reached greater depths and longer times in other disciplines.


title: Rationale for the Iraq War

text: The rationale for the Iraq War, both the 2003 invasion of Iraq and the subsequent hostilities, was controversial. The George W. Bush administration began actively pressing for military intervention in Iraq in late 2001. The primary rationalization for the Iraq War was articulated by a joint resolution of the United States Congress known as the Iraq Resolution. The US claimed the intent was to "disarm Iraq of weapons of mass destruction, to end Saddam Hussein's support for terrorism, and to free the Iraqi people".


title: Rationale for the Iraq War

text: In the lead-up to the invasion, the United States and the United Kingdom claimed that Saddam Hussein was developing weapons of mass destruction and that he thus presented a threat to his neighbors and to the world community. The US stated, "on November 8, 2002; the UN Security Council unanimously adopted Resolution 1441. All 15 members of the Security Council agreed to give Iraq a final opportunity to comply with its obligations and disarm or face the serious consequences of failing to disarm. The resolution strengthened the mandate of the UN Monitoring and Verification Commission (UNMOVIC) and the International Atomic Energy Agency (IAEA), giving them the authority to go anywhere, at any time, and talk to anyone in order to verify Iraq's disarmament." Throughout late 2001, 2002, and early 2003, the Bush administration worked to build a case for invading Iraq, culminating in then-Secretary of State Colin Powell's February 2003 address to the Security Council. Shortly after the invasion, the Central Intelligence Agency, Defense Intelligence Agency, and other intelligence agencies largely discredited evidence related to Iraqi weapons as well as alleged links to al-Qaeda, and at this point, the Bush and Blair administrations began to shift to secondary rationales for the war, such as the Saddam Hussein government's human rights record and promoting democracy in Iraq. Opinion polls showed that people of nearly all countries opposed a war without a UN mandate and that the perception of the United States as a danger to world peace had significantly increased. UN Secretary-General Kofi Annan described the war as illegal, saying in a September 2004 interview that it was "not in conformity with the Security Council".


title: Rationale for the Iraq War

text: Accusations of faulty evidence and alleged shifting rationales became the focal point for critics of the war, who charge that the Bush administration purposely fabricated evidence to justify an invasion that it had long planned to launch. The US led the effort for "the redirection of former Iraqi weapons of mass destruction (WMD) scientists, technicians, and engineers to civilian employment and discourage emigration of this community from Iraq".


title: Rationale for the Iraq War

text: The United States officially declared its combat role in Iraq over on 31 August 2010, although several thousand troops remained in the country until all American troops were withdrawn from Iraq by December 2011; meanwhile, American troops also engaged in combat with Iraqi insurgents. In June 2014, however, US forces returned to Iraq due to an escalation of instability in the region, and in June 2015, the number of American ground troops totaled 3,550. Between December 2011 and June 2014, Department of Defense officials estimated that there were 200 to 300 personnel based at the US embassy in Baghdad.


title: Rationale for the Iraq War

text: The 1991 Gulf War never fully ended because no armistice formally ended it. As a result, relations between the United States, the United Nations, and Iraq remained strained, although Saddam Hussein issued formal statements renouncing his invasion of Kuwait and made reparations payments. The US and the United Nations maintained a policy of "containment" towards Iraq, which involved economic sanctions, Iraqi no-fly zones enforced by the United States, United Kingdom, and France (until it ended its no-fly zone operations in 1998) and ongoing inspections of Iraqi weapons programs. In 2002, the UN Security Council unanimously passed Resolution 1441 demanding that Iraq "comply with its disarmament obligations" and allow weapons inspections. Iraq war critics such as former weapons inspector Scott Ritter claimed that these sanctions and weapons inspections policies, supported by both the Bush and Clinton administrations, were actually intended to foster regime change in Iraq.


title: Rationale for the Iraq War

text: US policy shifted in 1998 when the United States Congress passed and President Bill Clinton signed the Iraq Liberation Act after Iraq terminated its cooperation with UN weapons inspectors the preceding August. The act made it official US policy to "support efforts to remove the regime headed by Saddam Hussein from power", although it also made clear that "nothing in this Act shall be construed to authorize or otherwise speak to the use of United States Armed Forces". This legislation contrasted with the terms set out in United Nations Security Council Resolution 687, which made no mention of regime change.


title: Rationale for the Iraq War

text: One month after the passage of the "Iraq Liberation Act", the US and UK launched a bombardment of Iraq named Operation Desert Fox. The campaign's expressed rationale was to hamper the Saddam Hussein government's ability to produce chemical, biological, and nuclear weapons, but US national security personnel also reportedly hoped it would help weaken Saddam Hussein's grip on power.


title: Rationale for the Iraq War

text: The Republican Party's campaign platform in the 2000 election called for "full implementation" of the Iraq Liberation Act and removal of Saddam Hussein; and key Bush advisers, including Vice President Dick Cheney, Defense Secretary Donald Rumsfeld, and Rumsfeld's Deputy Paul Wolfowitz, were longstanding advocates of invading Iraq, and contributed to a September 2000 report from the Project for the New American Century that argued for using an invasion of Iraq as a means for the US to "play a more permanent role in Gulf regional security". After leaving the administration, former Bush treasury secretary Paul O'Neill said that "contingency planning" for an attack on Iraq had been planned since the inauguration and that the first National Security Council meeting discussed of an invasion. Retired Army General Hugh Shelton, former chairman of the Joint Chiefs of Staff, said he saw nothing to indicate the United States was close to attacking Iraq early in Bush's term.


title: Rationale for the Iraq War

text: Despite key Bush advisers' stated interest in invading Iraq, little formal movement towards an invasion occurred until the 11 September 2001 attacks. According to aides who were with Defense Secretary Donald Rumsfeld in the National Military Command Center on 11 September, Rumsfeld asked for: "best info fast. Judge whether good enough hit Saddam Hussein at same time. Not only Osama bin Laden." The notes also quote him as saying, "Go massive", and "Sweep it all up. Things related and not."


title: Rationale for the Iraq War

text: After failing to gain UN support for an additional UN authorization, the US, together with the UK and small contingents from Australia, Poland, and Denmark, launched an invasion on 20 March 2003 under the authority of UN Security Council Resolution 660 and United Nations Security Council Resolution 678.


title: Rationale for the Iraq War

text: The October 2002, US congress Iraq War Resolution cited many factors to justify the use of military force against Iraq:


title: Rationale for the Iraq War

text: The Resolution required President Bush's diplomatic efforts at the UN Security Council to "obtain prompt and decisive action by the Security Council to ensure that Iraq abandons its strategy of delay, evasion, and noncompliance and promptly and strictly complies with all relevant Security Council resolutions". It authorized the United States to use military force to "defend the national security of the United States against the continuing threat posed by Iraq; and enforce all relevant United Nations Security Council Resolutions regarding Iraq".


title: Rationale for the Iraq War

text: The US government's belief that Iraq was developing weapons of mass destruction (WMDs), was based upon documents which the CIA argued could not be trusted.


title: Rationale for the Iraq War

text: George Bush, speaking in October 2002, said that "The stated policy of the United States is regime change... However, if [Saddam Hussein] were to meet all the conditions of the United Nations, the conditions that I have described very clearly in terms that everybody can understand, that in itself will signal the regime has changed." Similarly, in September 2002, Tony Blair stated, in an answer to a parliamentary question, that "Regime change in Iraq would be a wonderful thing. That is not the purpose of our action; our purpose is to disarm Iraq of weapons of mass destruction". In November of that year, Tony Blair further stated that "So far as our objective, it is disarmament, not regime changethat is our objective. Now I happen to believe the regime of Saddam is a very brutal and repressive regime; I think it does enormous damage to the Iraqi people... so I have got no doubt Saddam is very bad for Iraq, but on the other hand I have got no doubt either that the purpose of our challenge from the United Nations is disarmament of weapons of mass destruction; it is not regime change." At a press conference on January 31, 2003, George Bush stated: "Saddam Hussein must understand that if he does not disarm, for the sake of peace, we, along with others, will go disarm Saddam Hussein." As late as 25 February 2003, Tony Blair said in the House of Commons: "I detest his regime. But even now he can save it by complying with the UN's demand. Even now, we are prepared to go the extra step to achieve disarmament peacefully."


title: Rationale for the Iraq War

text: Secretary of State Powell said in his 5 February 2003 presentation to the UN Security Council: On 11 February 2003, FBI Director Robert Mueller testified to Congress that "Iraq has moved to the top of my list. As we previously briefed this Committee, Iraq's weapons of mass destruction program poses a clear threat to our national security, a threat that will certainly increase in the event of future military action against Iraq. Baghdad has the capability and, we presume, the will to use biological, chemical, or radiological weapons against US domestic targets in the event of a US invasion." On 10 April 2003, White House press secretary Ari Fleischer reiterated that, "But make no mistakeas I said earlierwe have high confidence that they have weapons of mass destruction. That is what this war was about and it is about. And we have high confidence it will be found." Despite the Bush administration's consistent assertion that Iraqi weapons programs justified an invasion, former Deputy Secretary of Defense Paul Wolfowitz later cast doubt on the administration's conviction behind this rationale by saying in a May 2003 interview: "For bureaucratic reasons, we settled on one issueweapons of mass destructionbecause it was the one reason everyone could agree on."


title: Rationale for the Iraq War

text: After the invasion, despite an exhaustive search led by the Iraq Survey Group involving a more than 1,400 member team, no evidence of Iraqi weapons programs was found. On the contrary, the investigation concluded that Iraq had destroyed all major stockpiles of weapons of mass destruction and ceased production in 1991 when sanctions were imposed. The failure to find evidence of Iraqi weapons programs following the invasion led to considerable controversy in the United States and worldwide, including claims by critics of the war that the Bush and Blair administrations deliberately manipulated and misused intelligence to push for an invasion.


title: Rationale for the Iraq War

text: Between 1991 and 1998, the United Nations Security Council tasked the United Nations Special Commission on Disarmament (UNSCOM) with finding and destroying Iraq's weapons of mass destruction. In 1996, UNSCOM discovered evidence of continued biological weapons research and supervised destruction of the Al Hakum biological weapons production siteallegedly converted to a chicken feed plant, but retaining its barbed wire fences and antiaircraft defenses. In 1998, Scott Ritter, leader of a UNSCOM inspection team, found gaps in the prisoner records of Abu Ghraib when investigating allegations that prisoners had been used to test anthrax weapons. Asked to explain the missing documents, the Iraqi government charged that Ritter was working for the CIA and refused to cooperate further with UNSCOM.


title: Rationale for the Iraq War

text: On August 26, 1998, approximately two months before the US ordered United Nations inspectors withdrawn from Iraq, Scott Ritter resigned from his position rather than participate in what he called the "illusion of arms control". In his resignation letter to Ambassador Richard Butler, Ritter wrote: On September 7, 1998, Ritter testified before the Senate Armed Services and Foreign Relations Committee, and John McCain (R, AZ) asked him whether UNSCOM had intelligence suggesting that Iraq had assembled the components for three nuclear weapons and all that it lacked was the fissile material. Ritter replied: "The Special Commission has intelligence information, which suggests that components necessary for three nuclear weapons exists, lacking the fissile material. Yes, sir."


title: Rationale for the Iraq War

text: On 8 November 2002, the UN Security Council passed Resolution 1441, giving Iraq "a final opportunity to comply with its disarmament obligations" including unrestricted inspections by the United Nations Monitoring, Verification and Inspection Commission (UNMOVIC) and the International Atomic Energy Agency (IAEA). Saddam Hussein accepted the resolution on November 13 and inspectors returned to Iraq under the direction of UNMOVIC chairman Hans Blix and IAEA Director General Mohamed ElBaradei. Between that time and the time of the invasion, the IAEA "found no evidence or plausible indication of the revival of a nuclear weapons programme in Iraq"; the IAEA concluded that certain items which could have been used in nuclear enrichment -centrifuges, such as aluminum tubes, were in fact intended for other uses. UNMOVIC "did not find evidence of the continuation or resumption of programmes of weapons of mass destruction" or significant quantities of proscribed items. UNMOVIC did supervise the destruction of a small number of empty chemical rocket warheads, 50 liters of mustard gas that had been declared by Iraq and sealed by UNSCOM in 1998, and laboratory quantities of a mustard gas precursor, along with about 50 Al-Samoud missiles of a design that Iraq claimed did not exceed the permitted 150 km range, but which had travelled up to 183 km in tests. Shortly before the invasion, UNMOVIC stated that it would take "months" to verify Iraqi compliance with resolution 1441.


title: Rationale for the Iraq War

text: After the invasion, the Iraq Survey Group (ISG), headed by American David Kay, was tasked with searching for weapons of mass destruction. The survey ultimately concluded that Iraqi production of weapons of mass destruction ceased and all major stockpiles were destroyed in 1991 when economic sanctions were imposed, but that the expertise to restart production once sanctions were lifted was preserved. The group also concluded that Iraq continued developing long-range missiles proscribed by the UN until just before the 2003 invasion.


title: Rationale for the Iraq War

text: In an interim report on 3 October 2003, Kay reported that the group had "not yet found stocks of weapons", but had discovered "dozens of weapons of mass destruction-related program activities" including clandestine laboratories "suitable for continuing CBW [chemical and biological warfare] research", a prison laboratory complex "possibly used in human testing of BW agents", a vial of live C. botulinum Okra B bacteria kept in one scientist's home, small parts and twelve-year-old documents "that would have been useful in resuming uranium enrichment", partially-declared UAVs and undeclared fuel for Scud missiles with ranges beyond the 150 km UN limits, "[p]lans and advanced design work for new long-range missiles with ranges up to at least 1000 km", attempts to acquire long-range missile technology from North Korea, and document destruction in headquarters buildings in Baghdad. None of the weapons of mass destruction programs involved active production; they instead appeared to be targeted at retaining the expertise needed to resume work once sanctions were dropped. Iraqi personnel involved with much of this work indicated they had orders to conceal it from UN weapons inspectors.


title: Rationale for the Iraq War

text: After Charles Duelfer took over from Kay in January 2004, Kay said at a Senate hearing that "we were almost all wrong" about Iraq having stockpiles of weapons of mass destruction, but that the other ISG findings made Iraq potentially "more dangerous" than was thought before the war. In an interview, Kay said that "a lot" of the former Iraqi government's weapons of mass destruction program had been moved to Syria shortly before the 2003 invasion, albeit not including large stockpiles of weapons.


title: Rationale for the Iraq War

text: On 30 September 2004, the ISG, under Charles Duelfer, issued a comprehensive report. The report stated that "Iraq's weapons of mass destruction capability ... was essentially destroyed in 1991" and that Saddam Hussein subsequently focused on ending the sanctions and "preserving the capability to reconstitute his weapons of mass destruction (WMD) when sanctions were lifted". No evidence was found for continued active production of weapons of mass destruction subsequent to the imposition of sanctions in 1991, though "[b]y 2000–2001, Saddam had managed to mitigate many of the effects of sanctions".


title: Rationale for the Iraq War

text: The report concluded in its "Key Findings" that: "Saddam [Saddam Hussein] so dominated the Iraqi Regime that its strategic intent was his alone... The former Regime had no formal written strategy or plan for the revival of weapons of mass destruction after sanctions. Neither was there an identifiable group of weapons of mass destruction policy makers or planners separate from Saddam. Instead, his lieutenants understood weapons of mass destruction revival was his goal from their long association with Saddam and his infrequent, but firm, verbal comments and directions to them." The report also noted that "Iran was the pre-eminent motivator of [Iraq's weapons of mass destruction revival] policy... The wish to balance Israel and acquire status and influence in the Arab world were also considerations, but secondary." A March 2005 addendum to the report stated that "based on the evidence available at present, ISG judged that it was unlikely that an official transfer of weapons of mass destruction material from Iraq to Syria took place. However, ISG was unable to rule out unofficial movement of limited weapons of mass destruction-related materials".


title: Rationale for the Iraq War

text: On 12 January 2005, US military forces abandoned the formal search. Transcripts from high level meetings within Saddam Hussein's government before the invasion are consistent with the ISG conclusion that he destroyed his stockpiles of weapons of mass destruction but maintained the expertise to restart production.


title: Rationale for the Iraq War

text: In the post-invasion search for weapons of mass destruction, US and Polish forces found decayed chemical weapons from the Iran–Iraq War. These chemical weapons led former senator Rick Santorum (R-PA) and representative Peter Hoekstra (R-MI) to say that the US had indeed found weapons of mass destruction in Iraq.


title: Rationale for the Iraq War

text: These assertions were directly contradicted by weapons experts David Kay, the original director of the Iraq Survey Group, and his successor Charles Duelfer. Both Kay and Duelfer stated that the chemical weapons found were not the "weapons of mass destruction" that the US was looking for. Kay added that experts on Iraq's chemical weapons are in "almost 100 percent agreement" that sarin nerve agent produced in the 1980s would no longer be dangerous and that the chemical weapons found were "less toxic than most things that Americans have under their kitchen sink at this point". In reply, Hoekstra said "I am 100 percent sure if David Kay had the opportunity to look at the reports... he would agree... these things are lethal and deadly". Discussing the findings on NPR's "Talk of the Nation", Charles Duelfer described such residual chemical munitions as hazardous but not deadly.


title: Rationale for the Iraq War

text: The degraded chemical weapons were first discovered in May 2004, when a binary sarin nerve gas shell was used in an improvised explosive device (roadside bomb) in Iraq. The device exploded before it could be disarmed, and two soldiers displayed symptoms of minor sarin exposure. The 155 mm shell was unmarked and rigged as if it were a normal high-explosive shell, indicating that the insurgents who placed the device did not know it contained nerve gas. Earlier in the month, a shell containing mustard gas was found abandoned in the median of a road in Baghdad.


title: Rationale for the Iraq War

text: In July 2004, Polish troops discovered insurgents trying to purchase cyclosarin, an extremely toxic substance which is an organophosphate nerve agent like its predecessor, sarin, in gas warheads produced during the Iran–Iraq War. To thwart these insurgents, Polish troops purchased two rockets on 23 June 2004. The US military later determined that the two rockets had only traces of sarin, small and deteriorated and virtually harmless, with "limited to no impact if used by insurgents against coalition forces".


title: Rationale for the Iraq War

text: The Dodgy Dossier (or Sexed up dossier) was an article written by Ibrahim al-Marashi which was plagiarised by the British government in a 2003 briefing document entitled "Iraq: Its Infrastructure of Concealment, Deception and Intimidation". This document was a follow-up to the earlier September Dossier, both of which concerned Iraq and weapons of mass destruction and were ultimately used by the government to justify its involvement in the 2003 Invasion of Iraq. Large portions of al-Marashi's paper were quoted verbatim by then United States Secretary of State Colin Powell to the UN General Assembly. The most frequently quoted section was the allegation that Saddam had WMDs that could be launched within 45 minutes.


title: Rationale for the Iraq War

text: The material plagiarised from Marashi's work and copied nearly verbatim into the "Dodgy Dossier" was six paragraphs from his article "Iraq's Security & Intelligence Network: A Guide & Analysis", which was published in the September 2002 issue of the "Middle East Review of International Affairs" (or MERIA). Tony Blair's office ultimately apologised to Marashi for its actions, but not to the MERIA journal.


title: Rationale for the Iraq War

text: The failure to find stockpiles of weapons of mass destruction in Iraq caused considerable controversy, particularly in the United States. US President George W. Bush and Prime Minister of the United Kingdom Tony Blair defended their decision to go to war, alleging that many nations, even those opposed to war, believed that the Saddam Hussein government was actively developing weapons of mass destructions.


title: Rationale for the Iraq War

text: Critics such as Democratic National Committee Chairman Howard Dean charged that the Bush and Blair administrations deliberately falsified evidence to build a case for war. These criticisms were strengthened with the 2005 release of the so-called Downing Street memo, written in July 2002, in which the former head of British Military Intelligence wrote that "the intelligence and facts were being fixed around the policy" of removing Saddam Hussein from power.


title: Rationale for the Iraq War

text: While the Downing Street memo and the yellowcake uranium scandal lent credence to claims that intelligence was manipulated, two bipartisan investigations, one by the Senate Intelligence Committee and the other by a specially-appointed Iraq Intelligence Commission chaired by Charles Robb and Laurence Silberman, found no evidence of political pressure applied to intelligence analysts. An independent assessment by the Annenberg Public Policy Center found that Bush administration officials did misuse intelligence in their public communications. For example, Vice President Dick Cheney's September 2002 statement on Meet the Press that "we do know, with absolute certainty, that he (Saddam) is using his procurement system to acquire the equipment he needs in order to enrich uranium to build a nuclear weapon", was inconsistent with the views of the intelligence community at the time.


title: Rationale for the Iraq War

text: A study coauthored by the Center for Public Integrity found that in the two years after September 11, 2001, the president and top administration officials had made 935 false statements, in an orchestrated public relations campaign to galvanize public opinion for the war, and that the press was largely complicit in its uncritical coverage of the reasons adduced for going to war. PBS commentator Bill Moyers had made similar points throughout the run-up to the Iraq War, and prior to a national press conference on the Iraq War Moyers correctly predicted "at least a dozen times during this press conference he [the President] will invoke 9/11 and al-Qaeda to justify a preemptive attack on a country that has not attacked America. But the White House press corps will ask no hard questions tonight about those claims." Moyers later also denounced the complicity of the press in the administration's campaign for the war, saying that the media "surrendered its independence and skepticism to join with [the US] government in marching to war", and that the administration "needed a compliant press, to pass on their propaganda as news and cheer them on".


title: Rationale for the Iraq War

text: Many in the intelligence community expressed sincere regret over the flawed predictions about Iraqi weapons programs. Testifying before Congress in January 2004, David Kay, the original director of the Iraq Survey Group, said unequivocally that "It turns out that we were all wrong, probably in my judgment, and that is most disturbing." He later added in an interview that the intelligence community owed the President an apology.


title: Rationale for the Iraq War

text: In the aftermath of the invasion, much attention was also paid to the role of the press in promoting government claims concerning weapons of mass destruction production in Iraq. Between 1998 and 2003, "The New York Times" and other influential US newspapers published numerous articles about suspected Iraqi rearmament programs with headlines like "Iraqi Work Toward A-Bomb Reported" and "Iraq Suspected of Secret Germ War Effort". It later turned out that many of the sources for these articles were unreliable, and that some were tied to Ahmed Chalabi, an Iraqi exile with close ties to the Bush administration who was a consistent supporter of an invasion.


title: Rationale for the Iraq War

text: Some controversy also exists regarding whether the invasion increased or decreased the potential for nuclear proliferation. For example, hundreds of tons of dual-use high explosives that could be used to detonate fissile material in a nuclear weapon were sealed by the IAEA at the Al Qa'qaa site in January 2003. Immediately before the invasion, UN Inspectors had checked the locked bunker doors, but not the actual contents; the bunkers also had large ventilation shafts that were not sealed. By October, the material was no longer present. The IAEA expressed concerns that the material might have been looted after the invasion, posing a nuclear proliferation threat. The US released satellite photographs from March 17, showing trucks at the site large enough to remove substantial amounts of material before US forces reached the area in April. Ultimately, Major Austin Pearson of Task Force Bullet, a task force charged with securing and destroying Iraqi ammunition after the invasion, stated that the task force had removed about 250 tons of material from the site and had detonated it or used it to detonate other munitions. Similar concerns were raised about other dual use materials, such as high strength aluminum; before the invasion, the US cited them as evidence for an Iraqi nuclear weapons program, while the IAEA was satisfied that they were being used for permitted industrial uses; after the war, the IAEA emphasized the proliferation concern, while the Duelfer report mentioned the material's use as scrap. Possible chemical weapons laboratories have also been found which were built subsequent to the 2003 invasion, apparently by insurgent forces.


title: Rationale for the Iraq War

text: On August 2, 2004, President Bush stated "Knowing what I know today we still would have gone on into Iraq... The decision I made is the right decision. The world is better off without Saddam Hussein in power."


title: Rationale for the Iraq War

text: Bush's Treasury Secretary Paul O'Neill said that Bush's first two National Security Council meetings discussed invading Iraq. He was given briefing materials entitled "Plan for post-Saddam Iraq", which envisioned dividing up Iraq's oil wealth. A Pentagon document dated March 5, 2001, was titled "Foreign Suitors for Iraqi Oilfield contracts", and included a map of potential areas for exploration.


title: Rationale for the Iraq War

text: In July 2003, Polish foreign minister, Wlodzimierz Cimoszewicz, said "We have never hidden our desire for Polish oil companies to finally have access to sources of commodities." This remark came after a group of Polish firms had signed a deal with Kellogg, Brown and Root, a subsidiary of Halliburton. Cimoszewicz stated that access to Iraq's oilfields "is our ultimate objective".


title: Rationale for the Iraq War

text: One report by BBC journalist Gregory Palast citing unnamed "insiders" alleged that the US "called for the sell-off of all of Iraq's oil fields" and planned for a coup d'état in Iraq long before September 11. Palast also wrote that the "new plan was crafted by neo-conservatives intent on using Iraq's oil to destroy the OPEC cartel through massive increases in production above OPEC quotas", but Iraq oil production decreased following the Iraq War.


title: Rationale for the Iraq War

text: General John Abizaid, CENTCOM commander from 2003 to 2007, said of the Iraq war: "first of all I think it's really important to understand the dynamics that are going on in the Middle East, and of course it's about oil, it's very much about oil and we can't really deny that".


title: Rationale for the Iraq War

text: 2008 Republican Presidential Candidate John McCain was forced to clarify his comments suggesting the Iraq war involved US reliance on foreign oil. "My friends, I will have an energy policy that we will be talking about, which will eliminate our dependence on oil from the Middle East that will prevent us from having ever to send our young men and women into conflict again in the Middle East", McCain said. To clarify his comments, McCain explained that "the word 'again' was misconstrued; I want us to remove our dependency on foreign oil for national security reasons, and that's all I mean."


title: Rationale for the Iraq War

text: Many critics have focused upon administration officials' past relationships with energy corporations. Both George W. Bush and Dick Cheney were formerly CEOs of oil and oil-related companies such as Arbusto, Harken Energy, Spectrum 7, and Halliburton. Before the 2003 invasion of Iraq and even before the War on Terror, the administration had prompted anxiety over whether the private sector ties of cabinet members (including National Security Advisor Condoleezza Rice, former director of Chevron, and Commerce Secretary Donald Evans, former head of Tom Brown Inc.) would affect their judgment on energy policy.


title: Rationale for the Iraq War

text: Prior to the war, the CIA saw Iraqi oil production and illicit oil sales as Iraq's key method of financing. The CIA's October 2002 unclassified white paper on "Iraq's Weapons of Mass Destruction Programs" states on page one under the "Key Judgments, Iraq's Weapons of Mass Destruction Programs" heading that "Iraq's growing ability to sell oil illicitly increases Baghdad's capabilities to finance weapons of mass destruction programs".


title: Rationale for the Iraq War

text: Iraq holds the world's fifth-largest proven oil reserves at , with increasing exploration expected to enlarge them beyond . For comparison, Venezuelathe largest proven source of oil in the worldhas of proven oil reserves.


title: Rationale for the Iraq War

text: Organizations such as the Global Policy Forum (GPF) asserted that Iraq's oil is "the central feature of the political landscape" there, and that as a result of the 2003 invasion of Iraq, friendly' companies expect to gain most of the lucrative oil deals that will be worth hundreds of billions of dollars in profits in the coming decades". According to the GPF, US influence over the 2005 Constitution of Iraq has made sure it "contains language that guarantees a major role for foreign companies".


title: Rationale for the Iraq War

text: Oil exerts tremendous economic and political influence worldwide, although the line between political and economic influence is not always distinct. The importance of oil to national security is unlike that of any other commodity:


title: Rationale for the Iraq War

text: Critics of the Iraq War contend that US officials and representatives from the private sector were planning just this kind of mutually supportive relationship as early as 2001, when the James Baker III Institute for Public Policy and the Council on Foreign Relations produced "Strategic Energy Policy: Challenges for the 21st Century", a report describing the long-term threat of energy crises such as blackouts and rising fuel prices then playing havoc with the state of California. The report recommended a comprehensive review of US military, energy, economic, and political policy toward Iraq "with the aim to lowering anti-Americanism in the Middle East and elsewhere, and set the groundwork to eventually ease Iraqi oil-field investment restrictions". The report's urgent tone stood in contrast to the relatively calm speech Chevron CEO Kenneth T. Derr had given the Commonwealth Club of California two years earlier, before the California electricity crisis, where he said, "It might surprise you to learn that even though Iraq possesses huge reserves of oil and gasreserves I'd love Chevron to have access toI fully agree with the sanctions we have imposed on Iraq."


title: Rationale for the Iraq War

text: Post-Iraq invasion opinion polls conducted in Jordan, Morocco, Pakistan, and Turkey showed that the majority of each country's population tended to "doubt the sincerity of the War on Terrorism", which they characterized instead as "an effort to control Middle East oil and to dominate the world".


title: Rationale for the Iraq War

text: Although there has been disagreement about where the alleged will to control and dominate originates, skeptics of the War on Terror have pointed early and often to the Project for a New American Century, a neoconservative think tank established in 1997 by William Kristol and Robert Kagan. The organization made plain its position on oil, territory, and the use of force in series of publications, including:


title: Rationale for the Iraq War

text: Of 18 signatories to the 1998 PNAC letter, 11 would later occupy positions in President Bush's administration:


title: Rationale for the Iraq War

text: Just after US invasion of Afghanistan, the "London Observer" and "The Guardian" reported plans to invade Iraq and seize its oil reserves around Basra and use the proceeds to finance Iraqi oppositions in the south and the north. Later the US intelligence community called these claims as not credible and said that they had no plan to attack Iraq. On October 14, 2001, The Guardian reported:


title: Rationale for the Iraq War

text: The term petrodollar warfare refers to a conspiracy theory that depicts the international use of the United States dollar as the standard means of settling oil transactions as a kind of economic imperialism enforced by violent military interventions against countries like Iraq, Iran, and Venezuela, and a key hidden driver of world politics. The term was coined by William R. Clark, who has written a book with the same title. The phrase "oil currency war" is sometimes used with the same meaning. In reality, the use of dollars in international oil transactions increases overall U.S. dollar demand by only a tiny fraction, and the dollar's overall status as the major international reserve currency has relatively few tangible benefits for the United States economy as well as some drawbacks.


title: Rationale for the Iraq War

text: According to former Iraqi President Saddam Hussein, the United States did not need to invade Iraq to control the oil. "The New York Times" reported that in February 2003, Baghdad had offered to give the US first priority as it related to Iraq oil rights, as part of a deal to avert an impending invasion. The overtures intrigued the Bush administration but were ultimately rebuffed.


title: Rationale for the Iraq War

text: In 2002, responding to a question about coveting oil fields, George W. Bush said "Those are the wrong impressions. I have a deep desire for peace. That's what I have a desire for. And freedom for the Iraqi people. See, I don't like a system where people are repressed through torture and murder in order to keep a dictator in place. That troubles me deeply. And so the Iraqi people must hear this loud and clear, that this country never has any intention to conquer anybody."


title: Rationale for the Iraq War

text: Tony Blair stated that the hypothesis that the Iraq invasion had "some[thing] to do with oil" was a "conspiracy theory": "Let me first deal with the conspiracy theory that this is somehow to do with oil... The very reason why we are taking the action that we are taking is nothing to do with oil or any of the other conspiracy theories put forward."


title: Rationale for the Iraq War

text: Then Australian Prime Minister John Howard has dismissed on multiple occasions the role of oil in the Iraq Invasion: "We didn't go there because of oil and we don't remain there because of oil." In early 2003 John Howard stated, "No criticism is more outrageous than the claim that United States behaviour is driven by a wish to take control of Iraq's oil reserves."


title: Rationale for the Iraq War

text: Economist Gary S. Becker stated in 2003 that "if oil were the driving force behind the Bush Administration’s hard line on Iraq, avoiding war would be the most appropriate policy".


title: Rationale for the Iraq War

text: According to economist Ismael Hossein-Zadeh (2006): "there is no evidence that, at least in the case of the current invasion of Iraq, oil companies pushed for or supported the war. On the contrary, there is strong evidence that, in fact, oil companies did not welcome the war because they prefer stability and predictability to periodic oil spikes that follow war and political convulsion".


title: Rationale for the Iraq War

text: Political scientist John S. Duffield wrote in 2012 that "no compelling evidence, either in the form of declassified documents or participants' memoirs, has yet emerged indicating that oil was a prominent factor or constant consideration in the thinking of decision makers within the Bush administration".


title: Rationale for the Iraq War

text: Political scientist Jeff Colgan wrote in 2013 that "Even years after the 2003 Iraq War, there is still no consensus on the degree to which oil played a role in that war." Colgan said that the fact that oil contracts were awarded to non-American companies, including Russian and Chinese corporations, is evidence against the view that the war was for oil.


title: Rationale for the Iraq War

text: Along with Iraq's alleged development of weapons of mass destructions, another justification for invasion was the purported link between Saddam Hussein's government and terrorist organizations, in particular al-Qaeda. In that sense, the Bush administration cast the Iraq war as part of the broader War on Terrorism. On February 11, 2003, FBI Director Robert Mueller testified to Congress that "seven countries designated as State Sponsors of TerrorismIran, Iraq, Syria, Sudan, Libya, Cuba, and North Korearemain active in the US and continue to support terrorist groups that have targeted Americans".


title: Rationale for the Iraq War

text: As with the argument that Iraq was developing biological and nuclear weapons, evidence linking Saddam Hussein and al-Qaeda was discredited by multiple US intelligence agencies soon after the invasion of Iraq.


title: Rationale for the Iraq War

text: In asserting a link between Saddam Hussein and al-Qaeda, the Bush administration focused special attention on alleged ties between Saddam Hussein and Jordanian terrorist Abu Musab al-Zarqawi, whom Secretary of State Powell called a "collaborator of Osama bin Laden". Soon after the start of the war, however, evidence of such ties was discredited by multiple US intelligence agencies, including the Central Intelligence Agency CIA, the Defense Intelligence Agency, and the Defense Department's Inspector General's Office. A CIA report in early October 2004 "found no clear evidence of Iraq harboring Abu Musab al-Zarqawi". More broadly, the CIA's Kerr Group summarized in 2004 that despite "a 'purposely aggressive approach' in conducting exhaustive and repetitive searches for such links... [the US] Intelligence Community remained firm in its assessment that no operational or collaborative relationship existed". Despite these findings, US Vice President Dick Cheney continued to assert that a link existed between al-Qaeda and Saddam Hussein prior to the 2003 invasion of Iraq, which drew criticism from members of the intelligence community and leading Democrats. As of the invasion, the State Department listed 45 countries, including the United States, where al-Qaeda was active. Iraq was not one of them.


title: Rationale for the Iraq War

text: The eventual lack of evidence linking the Saddam Hussein government and al-Qaeda led many war critics to allege that the Bush administration purposely fabricated such links to strengthen the case for the invasion. These claims were supported by the July 2005 release of the so-called Downing Street memo, in which Richard Dearlove (then head of British foreign intelligence service MI6) wrote that "the intelligence and facts were being fixed [by the US] around the policy" of removing Saddam Hussein from power. In addition, in his April 2007 report Acting Inspector General Thomas F. Gimble found that the Defense Department's Office of Special Plansrun by then-Undersecretary of Defense Douglas J. Feith, a close ally of Vice President Dick Cheney and Secretary of Defense Donald Rumsfeldpurposely manipulated evidence to strengthen the case for war. The Inspector General's report also highlighted the role of members of the Iraqi National Congress, a group headed by Ahmad Chalabi, in providing false intelligence about connections with al-Qaeda to build support for a US invasion.


title: Rationale for the Iraq War

text: In making its case for the invasion of Iraq, the Bush administration also referenced Saddam Hussein's relationships with terrorist organizations other than al-Qaeda. Saddam Hussein provided financial assistance to the families of Palestinians killed in the conflictincluding as much as $25,000 to the families of suicide bombers, some of whom were working with militant organizations in the Middle East such as Hamas. The White House website also cited Saddam sheltering the People's Mujahedin of Iran, which it accused of killing Americans in the 1970s.


title: Rationale for the Iraq War

text: Abdul Rahman Yasin, a suspect detained shortly after the 1993 World Trade Center bombing attacks, fled once released into Iraq. Shortly after, the FBI discovered evidence linking him to the bomb. After the invasion, Iraqi government official documents translated from Arabic to English described how Saddam's regime provided monthly payments to Yasin while he lived in the United States. Yasin is on the FBI's most wanted terrorists list, and is still at large.


title: Rationale for the Iraq War

text: The US cited the United Nations condemnation of Saddam Hussein's human rights abuses as one of several reasons for the Iraq invasion.


title: Rationale for the Iraq War

text: As evidence supporting US and British claims about Iraqi weapons of mass destructions weakened, the Bush administration began to focus more upon the other issues that Congress had articulated within the Iraq Resolution, such as human rights violations of the Saddam Hussein government as justification for military intervention. That the Saddam Hussein government consistently and violently violated the human rights of its people is in little doubt. During his more than twenty-year rule, Saddam Hussein tortured and killed thousands of Iraqi citizens, including gassing and killing thousands of Kurds in northern Iraq during the mid-1980s, brutally repressing Shia and Kurdish uprisings following the 1991 Gulf War, and a fifteen-year campaign of repression and displacement of the Marsh Arabs in Southern Iraq. In the 2003 State of the Union Address, President Bush mentioned Saddam's government practices of obtaining confessions by torturing children while their parents are made to watch, electric shock, burning with hot irons, dripping acid on the skin, mutilation with electric drills, cutting out tongues, and rape.


title: Rationale for the Iraq War

text: Many critics have argued, despite its repeated mention in the Joint Resolution, that human rights was never a principal justification for the war, and that it became prominent only after evidence concerning weapons of mass destructions and Saddam Hussein's links to terrorism became discredited. For example, during a July 29, 2003, hearing of the Senate Foreign Relations Committee, then Deputy Secretary of Defense Paul Wolfowitz spent the majority of his testimony discussing Saddam Hussein's human rights record, causing Senator Lincoln Chafee (R-RI) to complain that "in the months leading up to the war it was a steady drum beat of weapons of mass destruction, weapons of mass destruction, weapons of mass destruction. And, Secretary Wolfowitz, in your almost hour-long testimony here this morning, onceonly once did you mention weapons of mass destruction, and that was an ad lib."


title: Rationale for the Iraq War

text: Leading human rights groups such as Human Rights Watch and Amnesty International further argued that even had human rights concerns been a central rationale for the invasion, military intervention would not have been justifiable on humanitarian grounds. As Human Rights Watch's Ken Roth wrote in 2004, despite Saddam Hussein's horrific human rights record, "the killing in Iraq at the time was not of the exceptional nature that would justify such intervention".


title: Rationale for the Iraq War

text: More broadly, war critics have argued that the US and Europe supported the Saddam Hussein regime during the 1980s, a period of some of his worst human rights abuses, thus casting doubt on the sincerity of claims that military intervention was for humanitarian purposes. The US and Europe provided considerable military and financial support during the Iran–Iraq war with full knowledge that the Saddam Hussein government was regularly using chemical weapons on Iranian soldiers and Kurdish insurgents. US aid was aimed primarily to prevent Iraqi defeat after 1983. Following along this line, critics of the use of human rights as a rationale, such as Columbia University Law Professor Michael Dorf, have pointed out that during his first campaign for president Bush was highly critical of using US military might for humanitarian ends.


title: Rationale for the Iraq War

text: Others questioned why military intervention for humanitarian reasons would supposedly have been justified in Iraq but not in other countries with even worse human rights violations, such as Darfur.


title: Rationale for the Iraq War

text: By article 1 of the UN Charter, the United Nations has the responsibility: "To achieve international co-operation in solving international problems of an economic, social, cultural, or humanitarian character, and in promoting and encouraging respect for human rights and for fundamental freedoms for all without distinction as to race, sex, language, or religion". By UN Charter article 39, the responsibility for this determination lies with the Security Council.


title: Rationale for the Iraq War

text: US Vice President Dick Cheney, who called the sanctions "the most intrusive system of arms control in history", cited the breakdown of the sanctions as one rationale for the Iraq war. Accepting a controversial large estimate of casualties due to sanctions, Walter Russell Mead argued on behalf of such a war as a better alternative than continuing the sanctions regime, since "Each year of containment is a new Gulf War." However, economist Michael Spagat "argue[s] that the contention that sanctions had caused the deaths of more than half a million children is [as were weapons of mass destruction claims] very likely to be wrong".


title: Rationale for the Iraq War

text: In addition to claiming that the Saddam Hussein government had ties to al-Qaeda, the Bush administration and other supporters of the war argued for continued involvement in Iraq as a means to combat terrorism. President Bush consistently referred to the Iraq war as the "central front in the war on terror".


title: Rationale for the Iraq War

text: A few intelligence experts claimed that the Iraq war actually increased terrorism, even though no acts of terrorism occurred in the US. London's conservative International Institute for Strategic Studies concluded in 2004 that the occupation of Iraq had become "a potent global recruitment pretext" for jihadists and that the invasion "galvanized" al-Qaeda and "perversely inspired insurgent violence" there. Counter-terrorism expert Rohan Gunaratna called the invasion of Iraq a "fatal mistake" that greatly increased terrorism in the Middle East. The US National Intelligence Council concluded in a January 2005 report that the war in Iraq had become a breeding ground for a new generation of terrorists; David B. Low, the national intelligence officer for transnational threats, indicated that the report concluded that the war in Iraq provided terrorists with "a training ground, a recruitment ground, the opportunity for enhancing technical skills... here is even, under the best scenario, over time, the likelihood that some of the jihadists who are not killed there will, in a sense, go home, wherever home is, and will therefore disperse to various other countries." The Council's Chairman Robert L. Hutchings said, "At the moment, Iraq is a magnet for international terrorist activity." And the 2006 National Intelligence Estimate outlined the considered judgment of all 16 US intelligence agencies, held that "The Iraq conflict has become the 'cause celebre' for jihadists, breeding a deep resentment of US involvement in the Muslim world and cultivating supporters for the global jihadist movement."


title: Rationale for the Iraq War

text: Al-Qaeda leaders also publicly cited the Iraq war as a boon to their recruiting and operational efforts, providing both evidence to jihadists worldwide that America is at war with Islam, and the training ground for a new generation of jihadists to practice attacks on American forces. In October 2003, Osama bin Laden announced: "Be glad of the good news: America is mired in the swamps of the Tigris and Euphrates. Bush is, through Iraq and its oil, easy prey. Here is he now, thank God, in an embarrassing situation and here is America today being ruined before the eyes of the whole world." Echoing this sentiment, al-Qaeda commander Seif al-Adl gloated about the war in Iraq, indicating, "The Americans took the bait and fell into our trap." A letter thought to be from al-Qaeda leader Atiyah Abd al-Rahman found in Iraq among the rubble where al-Zarqawi was killed and released by the US military in October 2006, indicated that al-Qaeda perceived the war as beneficial to its goals:


title: Rationale for the Iraq War

text: One of the rationales that the Bush administration employed periodically during the run-up to the Iraq war is that deposing Saddam Hussein and installing a democratic government in Iraq would promote democracy in other Middle Eastern countries. The United States also proclaimed that the monarchies in Jordan and Saudi Arabia, and the military government of Pakistan were American allies, despite the human rights abuses and subversion of democracy attributed to them respectively. As Vice President Cheney argued in an August 2002 speech to the annual Veterans of Foreign Wars convention, "When the gravest of threats are eliminated, the freedom-loving peoples of the region will have a chance to promote the values that can bring lasting peace."


title: Rationale for the Iraq War

text: US General Jay Garner, who was in charge of planning and administering post-war reconstruction in Iraq, compared the US occupation of Iraq to the Philippine model in a 2004 interview in "National Journal": "Look back on the Philippines around the turn of the 20th century: they were a coaling station for the navy, and that allowed us to keep a great presence in the Pacific. That's what Iraq is for the next few decades: our coaling station that gives us great presence in the Middle East", "One of the most important things we can do right now is start getting basing rights with (the Iraqi authorities)", "I hope they're there a long time... And I think we'll have basing rights in the north and basing rights in the south... we'd want to keep at least a brigade", Garner added.


title: Rationale for the Iraq War

text: Also, the House report accompanying the emergency spending legislation said the money was "of a magnitude normally associated with permanent bases".


title: Rationale for the Iraq War

text: Nabil Shaath told the BBC that according to minutes of a conference with Palestinian leader Mahmoud Abbas, Bush said, "God inspired me to hit al Qaeda, and so I hit it. And I had the inspiration to hit Saddam, and so I hit him." "Haaretz" provided a similar translation of the minutes. When an Arabist at the "Washington Post" translated the same transcript, Bush was said to have indicated that God inspired him to "end the tyranny in Iraq" instead.


title: Rationale for the Iraq War

text: In a 2003 interview, Jacques Chirac, President of France at that time, affirmed that President George W. Bush asked him to send troops to Iraq to stop Gog and Magog, the "Bible's satanic agents of the Apocalypse". According to Chirac, the American leader appealed to their "common faith" (Christianity) and told him: "Gog and Magog are at work in the Middle East... The biblical prophecies are being fulfilled... This confrontation is willed by God, who wants to use this conflict to erase his people's enemies before a New Age begins."


title: Rationale for the Iraq War

text: David Harrison claimed in the "Telegraph" to have found secret documents that purported to show Russian President Vladimir Putin offering the use of assassins to Saddam's Iraqi regime to kill Western targets on November 27, 2000.


title: Rationale for the Iraq War

text: Jayna Davis had hypothesised on the purported links between the Oklahoma City bombing, Iraq, and al-Qaeda.


title: Rationale for the Iraq War

text: Abdul Rahman Yasin, a suspect detained shortly after the 1993 US World Trade Center Bombing attacks, fled upon release into Iraq. Shortly after release, the FBI had discovered evidence linking him to the development of the bomb. After the invasion, Iraqi government official documents translated from Arabic to English described that Saddam's regime provided monthly payments to Yasin while he was residing in the United States. Yasin is on the FBI's most wanted terrorists list, and is still at large.


title: Rationale for the Iraq War

text: John Lumpkin, Associated Press Writer, consolidates statements made by Vice President Cheney concerning the 1993 WTC bombing and Iraq. Cheney indicated Saddam's Iraqi government claimed to have FBI fugitive Yasin, alleged participant in the mixing of the chemicals making the bomb used in the 1993 WTC attack, in an Iraqi prison. During negotiations in the weeks prior to the invasion of Iraq, Saddam refused to extradite him.


title: Rationale for the Iraq War

text: Fox News claimed that evidence found in Iraq after the invasion was used to stop the attempted assassination of the Pakistani ambassador in New York with a shoulder-fired rocket.


title: Rationale for the Iraq War

text: US government officials claimed that after the invasion, Yemen and Jordan stopped Iraqi terrorist attacks against Western targets in those nations. US intelligence also warned 10 other countries that small groups of Iraqi intelligence agents might be readying similar attacks.


title: Rationale for the Iraq War

text: After the Beslan school hostage crisis, public school layouts and crisis plans were retrieved on a disk recovered during an Iraqi raid; this caused concerns in the United States. The information on the disks was "all publicly available on the Internet" and US officials "said it was unclear who downloaded the information and stressed there is no evidence of any specific threats involving the schools".


title: Rationale for the Iraq War

text: According to this hypothesis, the operations in Iraq occurred as a result of the US attempting to put pressure on Saudi Arabia. Much of the funding for al-Qaeda came from sources in Saudi Arabia through channels left over from the Afghan War. The US, wanting to staunch such financial support, pressured the Saudi leadership to cooperate with the West. The Saudis in power, fearing an Islamic backlash if they cooperated with the US which could push them from power, refused. In order to put pressure on Saudi Arabia to cooperate, the invasion of Iraq was conceived. Such an action would demonstrate the power of the US military, put US troops near to Saudi Arabia, and demonstrate that the US did not need Saudi allies to project itself in the Middle East.


title: Rationale for the Iraq War

text: Ahsan Butt argues that the invasion of Iraq was partially motivated by a desire of American policymakers to reassert American prestige and status following 9/11. Butt argues that prior to 9/11 the United States was recognised internationally as the undisputed world superpower and hegemon, but the 9/11 attacks called this status into question. Butt argues that invading Iraq was a means of allowing the United States to demonstrate that it was and intended to remain a global hegemon. Since Afghanistan was too weak a nation to demonstrate American power, Iraq was also invaded. Butt argues that Sadam had also damaged American prestige as he remained defiant following the Gulf War. A 2012 poll found that "Assert dominance in a New American Century" was viewed as the most important motivation for Bush, Cheney, Rumsfeld and neoconservatives by international relations experts.


title: Rationale for the Iraq War

text: Despite these efforts to sway public opinion, the invasion of Iraq was seen by some, including Kofi Annan, the United Nations Secretary-General, Lord Goldsmith, the British Attorney General, and Human Rights Watch, as a violation of international law, breaking the UN Charter, especially since the US failed to secure UN support for an invasion of Iraq. In 41 countries the majority of the populace did not support an invasion of Iraq without UN sanction and half said an invasion should not occur under any circumstances. 73 percent of the population of the United States supported an invasion. To build international support the United States formed a "Coalition of the Willing" with the United Kingdom, Italy, Poland, Australia and several other countries despite a majority of citizens in these countries opposing the invasion. Massive protests of the war occurred in the US and elsewhere. At the time of the invasion, UNMOVIC inspectors were ordered out by the United Nations. The inspectors requested more time because "disarmament, and at any rate verification, cannot be instant".


title: Rationale for the Iraq War

text: Following the invasion, no stockpiles of weapons of mass destruction were found, although about 500 abandoned chemical munitions, mostly degraded and left over from Iraq's Iran–Iraq war, were collected from around the country. The Kelly Affair highlighted a possible attempt by the British government to cover-up fabrications in British intelligence, the exposure of which would have undermined Tony Blair original rationale for involvement in the war. The US Senate Select Committee on Intelligence found no substantial evidence of links between Iraq and al-Qaeda. President George W. Bush has since admitted that "much of the intelligence turned out to be wrong". The Iraq Survey Group's final report of September 2004 stated,


title: Rationale for the Iraq War

text: In the March 2005 Addendum to the Report, the Special Advisor furthermore went on to state that "ISG assesses that Iraq and Coalition Forces will continue to discover small numbers of degraded chemical weapons, which the former Regime mislaid or improperly destroyed prior to 1991. ISG believes the bulk of these weapons were likely abandoned, forgotten and lost during the Iran–Iraq war because tens of thousands of CW munitions were forward-deployed along frequently and rapidly shifting battlefronts." (For comparison, the US Department of Defense itself was famously unable in 1998 to report the locations of "56 airplanes, 32 tanks and 36 Javelin command launch units".) ISG also believed that Saddam did not want to verifiably disarm Iraq of weapons of mass destruction, as required by UN resolutions, for fear of looking weak to his enemies.


title: Rationale for the Iraq War

text: Clare Short claims that in July 2002, UK government ministers were warned that Britain was committed to participating in a US invasion of Iraq, and a further allegation was that "the decision by Blair's government to participate in the US invasion of Iraq bypassed proper government procedures and ignored opposition to the war from Britain's intelligence quarters". Tony Blair agreed to back military action to oust Saddam Hussein with an assessment regarding weapons of mass destruction, at a summit at President George W. Bush's Texas ranch. Also present at the meeting were three other British officialsDefence Secretary Geoff Hoon, Foreign Secretary Jack Straw and Secret Intelligence Service (MI6) head Sir Richard Dearlove.


title: Rationale for the Iraq War

text: In Europe the peace movement was very strong, especially in Germany, where three-quarters of the population were opposed to the war. Ten NATO member countries did not join the coalition with the US, and their leaders made public statements in opposition to the invasion of Iraq. These leaders included Gerhard Schroeder of Germany, Jacques Chirac of France, Guy Verhofstadt of Belgium, and Recep Tayyip Erdoğan of Turkey. Public perceptions of the US changed dramatically as a consequence of the invasion. China and Russia also expressed their opposition to the invasion of Iraq.


title: Rationale for the Iraq War

text: Other possible US objectives, denied by the US government but acknowledged by retired US General Jay Garner, included the establishment of permanent US military bases in Iraq as a way of projecting power (creating a credible threat of US military intervention) to the oil-rich Persian Gulf region and the Middle East generally. In February 2004, Jay Garner, who was in charge of planning and administering post-war reconstruction in Iraq, explained that the US occupation of Iraq was comparable to the Philippine model: "Look back on the Philippines around the turn of the 20th century: they were a coaling station for the navy, and that allowed us to keep a great presence in the Pacific. That's what Iraq is for the next few decades: our coaling station that gives us great presence in the Middle East"; (see also Philippine–American War). Garner was replaced by Paul Bremer after reports came out of his position in SY Coleman, a division of defense contractor L-3 Communications, specializing in missile-defense systems. It was believed his role in the company was in contention with his role in Iraq. The House Appropriations Committee said the report accompanying the emergency spending legislation was "of a magnitude normally associated with permanent bases". However, the United States House of Representatives voted in 2006 not to fund any permanent bases in Iraq.


title: Robert Hegyes

text: Robert Bruce Hegyes (pronounced "Hedyesh"; May 7, 1951 – January 26, 2012) was an American actor best known for his portrayal of high school student Juan Epstein on the 1970s American sitcom "Welcome Back, Kotter" and as detective Manny Esposito on the 1980s American crime drama "Cagney & Lacey". He was the cousin of rock musician Jon Bon Jovi.


title: Robert Hegyes

text: Hegyes was born in Perth Amboy, New Jersey, to a Hungarian-American father, Stephen, and an Italian-American mother, Marie Dominica Cocozza. Hegyes was the oldest of four siblings (Mark, Stephanie, and Elizabeth).


title: Robert Hegyes

text: He grew up in Metuchen, New Jersey, and began acting in high school in the mid-1960s under the guidance of Metuchen High School theater teacher, Barton Shepard. Hegyes attended Glassboro State College after graduating from high school. While there, he worked part-time at the Hardee's fast food restaurant in town. Upon graduation from Glassboro State College (now Rowan University) where he completed his student teaching requirement at


title: Robert Hegyes

text: Haddon Township High School, with a Bachelor of Arts in Speech/Theater and Secondary Education, Hegyes ventured to New York City to pursue a career in acting and soon became a member of a Greenwich Village children's theater group called "Theater in a Trunk," performing educational theater at U.S. President Theodore Roosevelt's birthplace, on East 20th Street. Hegyes continued performing in the Village in educational children's theater, this time as a puppeteer with an arm and rod puppet company, playing Mr. Toad in "The Wind in the Willows." Robert managed to work a third performing job in Washington Square Park and at the Provincetown Playhouse as a member of the political improvisational guerrilla troupe, "Jack LaRumpa's Flying Drum & Kazoo Band."


title: Robert Hegyes

text: Within a year of graduating from college, Hegyes was cast to co-star in the highly acclaimed Off Broadway drama "Naomi Court", starring actor Brad Davis (star of "Midnight Express"). After completing the successful Manhattan Theater Club engagement, Hegyes was cast by Tony Award- winning actor Len Cariou (making his directing debut) to co-star in the Broadway drama, "Don't Call Back", starring Arlene Francis and Dorian Harewood. While performing on Broadway, Hegyes auditioned for television producer James Komack and was cast to star in what was to become the award-winning ABC comedy, "Welcome Back, Kotter". Hegyes portrayed the character of Juan Luis Pedro Felipo de Huevos Epstein (typically referred to as simply "Epstein"). The show lasted four seasons, from 1975 to 1979. Hegyes became one of the show's directors at age 25.


title: Robert Hegyes

text: While on the show, he was the key force of the winning tug-of-war team on the 1976 edition of Battle of the Network Stars.


title: Robert Hegyes

text: Hegyes guest starred in more than thirty television shows, including "Saturday Night Live", "NewsRadio", "", "The Drew Carey Show", and "The Streets of San Francisco". He also appeared in the award-winning Volkswagen Passat commercial "The Chase" for director Kinka Usher. Hegyes appeared in "Honeymoon Hotel", "Underground Aces", "Bob Roberts", "The Purpose", and "Bar Hopping".


title: Robert Hegyes

text: Hegyes made his Los Angeles stage debut as "Chico Marx" in the Westwood and national touring company engagements of "An Evening with Groucho". Upon returning from the tour, Hegyes was cast by producer Barney Rosenzweig to star as a series regular portraying undercover detective "Manny Esposito" in "Cagney & Lacey". During this time he also appeared on the game show "Pyramid" from time to time, and on "Match Game".


title: Robert Hegyes

text: Hegyes became "Artist-in-Residence" at his alma mater, Rowan University, teaching screenplay writing, acting for camera and public speaking, and was a guest lecturer in the Radio/Television/Film & Theater Departments. He was an adjunct instructor at Brooks College in Long Beach, California, where he taught essay writing and public speaking. Hegyes was a California Certified Secondary Education teacher, but had worked infrequently in recent years.


title: Robert Hegyes

text: Having returned to live in his hometown of Metuchen, New Jersey in 2009, Hegyes made his last public appearance in early January 2012, reprising his "An Evening with Groucho" role as Chico Marx, this time in three performances of "The Marx Brothers: Flywheel, Shyster and Flywheel," a staged radio play re-creating several episodes of the early-1930s broadcasts.


title: Robert Hegyes

text: Hegyes was married to Mary Kunes (1973–1977). He then married Kyle Drummer (1979–1984). With his third wife Lynn O'Hare (1987–1993), he had two children, Cassondra (Cassie) (born 1987) and Mack (born 1991). Hegyes was in a long-term relationship with Cynthia Wylie (1994–2007), who brought two children to the relationship, Alex (born 1988) and Sophia (born 1991) He was the cousin of rock singer Jon Bon Jovi and opera singer Mario Lanza.


title: Robert Hegyes

text: On January 26, 2012, after suffering from chest pains at his home in Metuchen, New Jersey, Hegyes died from an apparent heart attack at John F. Kennedy Medical Center in Edison, New Jersey, at age 60.


title: Phase-shift keying

text: Phase-shift keying (PSK) is a digital modulation process which conveys data by changing (modulating) the phase of a constant frequency reference signal (the carrier wave). The modulation is accomplished by varying the sine and cosine inputs at a precise time. It is widely used for wireless LANs, RFID and Bluetooth communication.


title: Phase-shift keying

text: Any digital modulation scheme uses a finite number of distinct signals to represent digital data. PSK uses a finite number of phases, each assigned a unique pattern of binary digits. Usually, each phase encodes an equal number of bits. Each pattern of bits forms the symbol that is represented by the particular phase. The demodulator, which is designed specifically for the symbol-set used by the modulator, determines the phase of the received signal and maps it back to the symbol it represents, thus recovering the original data. This requires the receiver to be able to compare the phase of the received signal to a reference signal such a system is termed coherent (and referred to as CPSK).


title: Phase-shift keying

text: CPSK requires a complicated demodulator, because it must extract the reference wave from the received signal and keep track of it, to compare each sample to. Alternatively, the phase shift of each symbol sent can be measured with respect to the phase of the previous symbol sent. Because the symbols are encoded in the difference in phase between successive samples, this is called differential phase-shift keying (DPSK). DPSK can be significantly simpler to implement than ordinary PSK, as it is a 'non-coherent' scheme, i.e. there is no need for the demodulator to keep track of a reference wave. A trade-off is that it has more demodulation errors.


title: Phase-shift keying

text: There are three major classes of digital modulation techniques used for transmission of digitally represented data:


title: Phase-shift keying

text: All convey data by changing some aspect of a base signal, the carrier wave (usually a sinusoid), in response to a data signal. In the case of PSK, the phase is changed to represent the data signal. There are two fundamental ways of utilizing the phase of a signal in this way:


title: Phase-shift keying

text: A convenient method to represent PSK schemes is on a constellation diagram. This shows the points in the complex plane where, in this context, the real and imaginary axes are termed the in-phase and quadrature axes respectively due to their 90° separation. Such a representation on perpendicular axes lends itself to straightforward implementation. The amplitude of each point along the in-phase axis is used to modulate a cosine (or sine) wave and the amplitude along the quadrature axis to modulate a sine (or cosine) wave. By convention, in-phase modulates cosine and quadrature modulates sine.


title: Phase-shift keying

text: In PSK, the constellation points chosen are usually positioned with uniform angular spacing around a circle. This gives maximum phase-separation between adjacent points and thus the best immunity to corruption. They are positioned on a circle so that they can all be transmitted with the same energy. In this way, the moduli of the complex numbers they represent will be the same and thus so will the amplitudes needed for the cosine and sine waves. Two common examples are "binary phase-shift keying" (BPSK) which uses two phases, and "quadrature phase-shift keying" (QPSK) which uses four phases, although any number of phases may be used. Since the data to be conveyed are usually binary, the PSK scheme is usually designed with the number of constellation points being a power of two.


title: Phase-shift keying

text: BPSK (also sometimes called PRK, phase reversal keying, or 2PSK) is the simplest form of phase shift keying (PSK). It uses two phases which are separated by 180° and so can also be termed 2-PSK. It does not particularly matter exactly where the constellation points are positioned, and in this figure they are shown on the real axis, at 0° and 180°. Therefore, it handles the highest noise level or distortion before the demodulator reaches an incorrect decision. That makes it the most robust of all the PSKs. It is, however, only able to modulate at 1bit/symbol (as seen in the figure) and so is unsuitable for high data-rate applications. Yet there is the possibility of extending this bit/symbol, given the modulators symbol encryption / decryption logic system.


title: Phase-shift keying

text: In the presence of an arbitrary phase-shift introduced by the communications channel, the demodulator (see, e.g. Costas loop) is unable to tell which constellation point is which. As a result, the data is often differentially encoded prior to modulation.


title: Phase-shift keying

text: This use of this basis function is shown at the end of the next section in a signal timing diagram. The topmost signal is a BPSK-modulated cosine wave that the BPSK modulator would produce. The bit-stream that causes this output is shown above the signal (the other parts of this figure are relevant only to QPSK). After modulation, the base band signal will be moved to the high frequency band by multiplying formula_7.


title: Phase-shift keying

text: Sometimes this is known as "quadriphase PSK", 4-PSK, or 4-QAM. (Although the root concepts of QPSK and 4-QAM are different, the resulting modulated radio waves are exactly the same.) QPSK uses four points on the constellation diagram, equispaced around a circle. With four phases, QPSK can encode two bits per symbol, shown in the diagram with Gray coding to minimize the bit error rate (BER) sometimes misperceived as twice the BER of BPSK.


title: Phase-shift keying

text: The mathematical analysis shows that QPSK can be used either to double the data rate compared with a BPSK system while maintaining the "same" bandwidth of the signal, or to "maintain the data-rate of BPSK" but halving the bandwidth needed. In this latter case, the BER of QPSK is "exactly the same" as the BER of BPSK and believing differently is a common confusion when considering or describing QPSK. The transmitted carrier can undergo numbers of phase changes.


title: Phase-shift keying

text: Given that radio communication channels are allocated by agencies such as the Federal Communications Commission giving a prescribed (maximum) bandwidth, the advantage of QPSK over BPSK becomes evident: QPSK transmits twice the data rate in a given bandwidth compared to BPSK - at the same BER. The engineering penalty that is paid is that QPSK transmitters and receivers are more complicated than the ones for BPSK. However, with modern electronics technology, the penalty in cost is very moderate.


title: Phase-shift keying

text: As with BPSK, there are phase ambiguity problems at the receiving end, and differentially encoded QPSK is often used in practice.


title: Phase-shift keying

text: The implementation of QPSK is more general than that of BPSK and also indicates the implementation of higher-order PSK. Writing the symbols in the constellation diagram in terms of the sine and cosine waves used to transmit them:


title: Phase-shift keying

text: The first basis function is used as the in-phase component of the signal and the second as the quadrature component of the signal.


title: Phase-shift keying

text: Comparing these basis functions with that for BPSK shows clearly how QPSK can be viewed as two independent BPSK signals. Note that the signal-space points for BPSK do not need to split the symbol (bit) energy over the two carriers in the scheme shown in the BPSK constellation diagram.


title: Phase-shift keying

text: QPSK systems can be implemented in a number of ways. An illustration of the major components of the transmitter and receiver structure are shown below.


title: Phase-shift keying

text: Although QPSK can be viewed as a quaternary modulation, it is easier to see it as two independently modulated quadrature carriers. With this interpretation, the even (or odd) bits are used to modulate the in-phase component of the carrier, while the odd (or even) bits are used to modulate the quadrature-phase component of the carrier. BPSK is used on both carriers and they can be independently demodulated.


title: Phase-shift keying

text: However, in order to achieve the same bit-error probability as BPSK, QPSK uses twice the power (since two bits are transmitted simultaneously).


title: Phase-shift keying

text: If the signal-to-noise ratio is high (as is necessary for practical QPSK systems) the probability of symbol error may be approximated:


title: Phase-shift keying

text: The modulated signal is shown below for a short segment of a random binary data-stream. The two carrier waves are a cosine wave and a sine wave, as indicated by the signal-space analysis above. Here, the odd-numbered bits have been assigned to the in-phase component and the even-numbered bits to the quadrature component (taking the first bit as number 1). The total signal the sum of the two components is shown at the bottom. Jumps in phase can be seen as the PSK changes the phase on each component at the start of each bit-period. The topmost waveform alone matches the description given for BPSK above.


title: Phase-shift keying

text: "Offset quadrature phase-shift keying" ("OQPSK") is a variant of phase-shift keying modulation using four different values of the phase to transmit. It is sometimes called "staggered quadrature phase-shift keying" ("SQPSK").


title: Phase-shift keying

text: Taking four values of the phase (two bits) at a time to construct a QPSK symbol can allow the phase of the signal to jump by as much as 180° at a time. When the signal is low-pass filtered (as is typical in a transmitter), these phase-shifts result in large amplitude fluctuations, an undesirable quality in communication systems. By offsetting the timing of the odd and even bits by one bit-period, or half a symbol-period, the in-phase and quadrature components will never change at the same time. In the constellation diagram shown on the right, it can be seen that this will limit the phase-shift to no more than 90° at a time. This yields much lower amplitude fluctuations than non-offset QPSK and is sometimes preferred in practice.


title: Phase-shift keying

text: The picture on the right shows the difference in the behavior of the phase between ordinary QPSK and OQPSK. It can be seen that in the first plot the phase can change by 180° at once, while in OQPSK the changes are never greater than 90°.


title: Phase-shift keying

text: The modulated signal is shown below for a short segment of a random binary data-stream. Note the half symbol-period offset between the two component waves. The sudden phase-shifts occur about twice as often as for QPSK (since the signals no longer change together), but they are less severe. In other words, the magnitude of jumps is smaller in OQPSK when compared to QPSK.


title: Phase-shift keying

text: The license-free shaped-offset QPSK (SOQPSK) is interoperable with Feher-patented QPSK (FQPSK), in the sense that an integrate-and-dump offset QPSK detector produces the same output no matter which kind of transmitter is used.


title: Phase-shift keying

text: These modulations carefully shape the I and Q waveforms such that they change very smoothly, and the signal stays constant-amplitude even during signal transitions. (Rather than traveling instantly from one symbol to another, or even linearly, it travels smoothly around the constant-amplitude circle from one symbol to the next.) SOQPSK modulation can be represented as the hybrid of QPSK and MSK: SOQPSK has the same signal constellation as QPSK, however the phase of SOQPSK is always stationary.


title: Phase-shift keying

text: The standard description of SOQPSK-TG involves ternary symbols. SOQPSK is one of the most spread modulation schemes in application to LEO satellite communications.


title: Phase-shift keying

text: This variant of QPSK uses two identical constellations which are rotated by 45° (formula_16 radians, hence the name) with respect to one another. Usually, either the even or odd symbols are used to select points from one of the constellations and the other symbols select points from the other constellation. This also reduces the phase-shifts from a maximum of 180°, but only to a maximum of 135° and so the amplitude fluctuations of formula_16-QPSK are between OQPSK and non-offset QPSK.


title: Phase-shift keying

text: One property this modulation scheme possesses is that if the modulated signal is represented in the complex domain, transitions between symbols never pass through 0. In other words, the signal does not pass through the origin. This lowers the dynamical range of fluctuations in the signal which is desirable when engineering communications signals.


title: Phase-shift keying

text: On the other hand, formula_16-QPSK lends itself to easy demodulation and has been adopted for use in, for example, TDMA cellular telephone systems.


title: Phase-shift keying

text: The modulated signal is shown below for a short segment of a random binary data-stream. The construction is the same as above for ordinary QPSK. Successive symbols are taken from the two constellations shown in the diagram. Thus, the first symbol (1 1) is taken from the "blue" constellation and the second symbol (0 0) is taken from the "green" constellation. Note that magnitudes of the two component waves change as they switch between constellations, but the total signal's magnitude remains constant (constant envelope). The phase-shifts are between those of the two previous timing-diagrams.


title: Phase-shift keying

text: Dual-polarization quadrature phase shift keying (DPQPSK) or dual-polarization QPSK - involves the polarization multiplexing of two different QPSK signals, thus improving the spectral efficiency by a factor of 2. This is a cost-effective alternative to utilizing 16-PSK, instead of QPSK to double the spectral efficiency.j


title: Phase-shift keying

text: Any number of phases may be used to construct a PSK constellation but 8-PSK is usually the highest order PSK constellation deployed. With more than 8 phases, the error-rate becomes too high and there are better, though more complex, modulations available such as quadrature amplitude modulation (QAM). Although any number of phases may be used, the fact that the constellation must usually deal with binary data means that the number of symbols is usually a power of 2 to allow an integer number of bits per symbol.


title: Phase-shift keying

text: For the general M-PSK there is no simple expression for the symbol-error probability if formula_19. Unfortunately, it can only be obtained from


title: Phase-shift keying

text: The bit-error probability for formula_24-PSK can only be determined exactly once the bit-mapping is known. However, when Gray coding is used, the most probable error from one symbol to the next produces only a single bit-error and


title: Phase-shift keying

text: The graph on the right compares the bit-error rates of BPSK, QPSK (which are the same, as noted above), 8-PSK and 16-PSK. It is seen that higher-order modulations exhibit higher error-rates; in exchange however they deliver a higher raw data-rate.


title: Phase-shift keying

text: Bounds on the error rates of various digital modulation schemes can be computed with application of the union bound to the signal constellation.


title: Phase-shift keying

text: Bandwidth (or spectral) efficiency of M-PSK modulation schemes increases with increasing of modulation order "M" (unlike, for example, M-FSK):


title: Phase-shift keying

text: Differential phase shift keying (DPSK) is a common form of phase modulation that conveys data by changing the phase of the carrier wave. As mentioned for BPSK and QPSK there is an ambiguity of phase if the constellation is rotated by some effect in the communications channel through which the signal passes. This problem can be overcome by using the data to "change" rather than "set" the phase.


title: Phase-shift keying

text: For example, in differentially encoded BPSK a binary "1" may be transmitted by adding 180° to the current phase and a binary "0" by adding 0° to the current phase.


title: Phase-shift keying

text: Another variant of DPSK is Symmetric Differential Phase Shift keying, SDPSK, where encoding would be +90° for a "1" and −90° for a "0".


title: Phase-shift keying

text: In differentially encoded QPSK (DQPSK), the phase-shifts are 0°, 90°, 180°, −90° corresponding to data "00", "01", "11", "10". This kind of encoding may be demodulated in the same way as for non-differential PSK but the phase ambiguities can be ignored. Thus, each received symbol is demodulated to one of the formula_24 points in the constellation and a comparator then computes the difference in phase between this received signal and the preceding one. The difference encodes the data as described above. "Symmetric differential quadrature phase shift keying" (SDQPSK) is like DQPSK, but encoding is symmetric, using phase shift values of −135°, −45°, +45° and +135°.


title: Phase-shift keying

text: The modulated signal is shown below for both DBPSK and DQPSK as described above. In the figure, it is assumed that the "signal starts with zero phase", and so there is a phase shift in both signals at formula_31.


title: Phase-shift keying

text: Analysis shows that differential encoding approximately doubles the error rate compared to ordinary formula_24-PSK but this may be overcome by only a small increase in formula_25. Furthermore, this analysis (and the graphical results below) are based on a system in which the only corruption is additive white Gaussian noise (AWGN). However, there will also be a physical channel between the transmitter and receiver in the communication system. This channel will, in general, introduce an unknown phase-shift to the PSK signal; in these cases the differential schemes can yield a "better" error-rate than the ordinary schemes which rely on precise phase information.


title: Phase-shift keying

text: One of the most popular applications of DPSK is the Bluetooth standard where formula_16-DQPSK and 8-DPSK were implemented.


title: Phase-shift keying

text: For a signal that has been differentially encoded, there is an obvious alternative method of demodulation. Instead of demodulating as usual and ignoring carrier-phase ambiguity, the phase between two successive received symbols is compared and used to determine what the data must have been. When differential encoding is used in this manner, the scheme is known as differential phase-shift keying (DPSK). Note that this is subtly different from just differentially encoded PSK since, upon reception, the received symbols are "not" decoded one-by-one to constellation points but are instead compared directly to one another.


title: Phase-shift keying

text: Call the received symbol in the formula_35 timeslot formula_36 and let it have phase formula_37. Assume without loss of generality that the phase of the carrier wave is zero. Denote the additive white Gaussian noise (AWGN) term as formula_38. Then


title: Phase-shift keying

text: The decision variable for the formula_40 symbol and the formula_35 symbol is the phase difference between formula_36 and formula_43. That is, if formula_36 is projected onto formula_43, the decision is taken on the phase of the resultant complex number:


title: Phase-shift keying

text: where superscript * denotes complex conjugation. In the absence of noise, the phase of this is formula_47, the phase-shift between the two received signals which can be used to determine the data transmitted.


title: Phase-shift keying

text: The probability of error for DPSK is difficult to calculate in general, but, in the case of DBPSK it is:


title: Phase-shift keying

text: which, when numerically evaluated, is only slightly worse than ordinary BPSK, particularly at higher formula_25 values.


title: Phase-shift keying

text: Using DPSK avoids the need for possibly complex carrier-recovery schemes to provide an accurate phase estimate and can be an attractive alternative to ordinary PSK.


title: Phase-shift keying

text: In optical communications, the data can be modulated onto the phase of a laser in a differential way. The modulation is a laser which emits a continuous wave, and a Mach–Zehnder modulator which receives electrical binary data. For the case of BPSK, the laser transmits the field unchanged for binary '1', and with reverse polarity for '0'. The demodulator consists of a delay line interferometer which delays one bit, so two bits can be compared at one time. In further processing, a photodiode is used to transform the optical field into an electric current, so the information is changed back into its original state.


title: Phase-shift keying

text: The bit-error rates of DBPSK and DQPSK are compared to their non-differential counterparts in the graph to the right. The loss for using DBPSK is small enough compared to the complexity reduction that it is often used in communications systems that would otherwise use BPSK. For DQPSK though, the loss in performance compared to ordinary QPSK is larger and the system designer must balance this against the reduction in complexity.


title: Phase-shift keying

text: At the formula_50 time-slot call the bit to be modulated formula_51, the differentially encoded bit formula_52 and the resulting modulated signal formula_53. Assume that the constellation diagram positions the symbols at ±1 (which is BPSK). The differential encoder produces:


title: Phase-shift keying

text: So formula_52 only changes state (from binary "0" to binary "1" or from binary "1" to binary "0") if formula_51 is a binary "1". Otherwise it remains in its previous state. This is the description of differentially encoded BPSK given above.


title: Phase-shift keying

text: The received signal is demodulated to yield formula_58 and then the differential decoder reverses the encoding procedure and produces


title: Phase-shift keying

text: Therefore, formula_60 if formula_52 and formula_62 differ and formula_63 if they are the same. Hence, if both formula_52 and formula_62 are "inverted", formula_51 will still be decoded correctly. Thus, the 180° phase ambiguity does not matter.


title: Phase-shift keying

text: Differential schemes for other PSK modulations may be devised along similar lines. The waveforms for DPSK are the same as for differentially encoded PSK given above since the only change between the two schemes is at the receiver.


title: Phase-shift keying

text: The BER curve for this example is compared to ordinary BPSK on the right. As mentioned above, whilst the error rate is approximately doubled, the increase needed in formula_25 to overcome this is small. The increase in formula_25 required to overcome differential modulation in coded systems, however, is larger typically about 3 dB. The performance degradation is a result of noncoherent transmission in this case it refers to the fact that tracking of the phase is completely ignored.


title: Phase-shift keying

text: formula_76 will give the probability that a single sample taken from a random process with zero-mean and unit-variance Gaussian probability density function will be greater or equal to formula_77. It is a scaled form of the complementary Gaussian error function:


title: Phase-shift keying

text: The error rates quoted here are those in additive white Gaussian noise (AWGN). These error rates are lower than those computed in fading channels, hence, are a good theoretical benchmark to compare with.


title: Phase-shift keying

text: Owing to PSK's simplicity, particularly when compared with its competitor quadrature amplitude modulation, it is widely used in existing technologies.