The unconscious mind (or the unconscious) consists of the processes in the mind which occur automatically and are not available to introspection and include thought processes, memories, interests and motivations.
Empirical evidence suggests that unconscious phenomena include repressed feelings, automatic skills, subliminal perceptions, and automatic reactions, and possibly also complexes, hidden phobias and desires.
Thus the unconscious mind can be seen as the source of dreams and
automatic thoughts (those that appear without any apparent cause), the
repository of forgotten memories (that may still be accessible to
consciousness at some later time), and the locus of implicit knowledge
(the things that we have learned so well that we do them without
thinking).
The term "unconscious" (German: Unbewusste) was coined by the 18th-century German Romantic philosopher Friedrich Schelling (in his System of Transcendental Idealism, ch. 6, § 3) and later introduced into English by the poet and essayist Samuel Taylor Coleridge (in his Biographia Literaria). Some rare earlier instances of the term "unconsciousness" (Unbewußtseyn) can be found in the work of the 18th-century German physician and philosopher Ernst Platner.
Influences on thinking that originate from outside of an
individual's consciousness were reflected in the ancient ideas of
temptation, divine inspiration, and the predominant role of the gods in
affecting motives and actions. The idea of internalised unconscious
processes in the mind was also instigated in antiquity and has been
explored across a wide variety of cultures. Unconscious aspects of
mentality were referred to between 2,500 and 600 BC in the Hindu texts
known as the Vedas, found today in Ayurvedic medicine.
In 1880, Edmond Colsenet supports at the Sorbonne, a philosophy thesis on the unconscious. Elie Rabier and Alfred Fouillee perform syntheses of the unconscious "at a time when Freud was not interested in the concept".
Psychology
Psychologist
Jacques Van Rillaer points out that, "the unconscious was not
discovered by Freud. In 1890, when psychoanalysis was still unheard of, William James, in his monumental treatise on psychology (The Principles of Psychology), examined the way Schopenhauer, von Hartmann, Janet, Binet and others had used the term 'unconscious' and 'subconscious'".
Historian of psychology Mark Altschule observes that, "It is
difficult—or perhaps impossible—to find a nineteenth-century
psychologist or psychiatrist who did not recognize unconscious
cerebration as not only real but of the highest importance."
Furthermore, 19th century German psychologists, Gustav Fechner and Wilhelm Wundt, had begun to use the term in their experimental psychology, in the context of manifold, jumbled sense data that the mind organizes at an unconscious level before revealing it as a cogent totality in conscious form."[24]
Freud's view
An iceberg is often (though misleadingly) used to provide a visual representation of Freud's theory that most of the human mind operates unconsciously.
Sigmund Freud and his followers developed an account of the unconscious mind. It plays an important role in psychoanalysis.
Freud divided the mind into the conscious mind (or the ego) and the unconscious mind. The latter was then further divided into the id (or instincts and drive) and the superego (or conscience). In this theory, the unconscious refers to the mental processes of which individuals make themselves unaware. Freud proposed a vertical and hierarchical architecture of human consciousness: the conscious mind, the preconscious, and the unconscious mind—each
lying beneath the other. He believed that significant psychic events
take place "below the surface" in the unconscious mind, like hidden messages from the unconscious. He interpreted such events as having both symbolic and actual significance.
In psychoanalytic terms, the unconscious does not include all
that is not conscious, but rather what is actively repressed from
conscious thought or what a person is averse to knowing consciously.
Freud viewed the unconscious as a repository for socially unacceptable
ideas, wishes or desires, traumatic memories, and painful emotions put
out of mind by the mechanism of psychological repression.
However, the contents did not necessarily have to be solely negative.
In the psychoanalytic view, the unconscious is a force that can only be
recognized by its effects—it expresses itself in the symptom.
In a sense, this view places the conscious self as an adversary to its
unconscious, warring to keep the unconscious hidden. Unconscious
thoughts are not directly accessible to ordinary introspection, but are supposed to be capable of being "tapped" and "interpreted" by special methods and techniques such as meditation, free association (a method largely introduced by Freud), dream analysis, and verbal slips (commonly known as a Freudian slip), examined and conducted during psychoanalysis.
Seeing as these unconscious thoughts are normally cryptic,
psychoanalysts are considered experts in interpreting their messages.
Freud based his concept of the unconscious on a variety of
observations. For example, he considered "slips of the tongue" to be
related to the unconscious in that they often appeared to show a
person's true feelings on a subject. For example, "I decided to take a
summer curse". This example shows a slip of the word "course" where the
speaker accidentally used the word curse which would show that they have
negative feelings about having to do this. Freud noticed that also his
patient's dreams expressed important feelings they were unaware of.
After these observations, he came to the conclusion that psychological
disturbances are largely caused by personal conflicts existing at the
unconscious level. His psychoanalytic theory acts to explain
personality, motivation and mental disorders by focusing on unconscious determinants of behavior.
Freud later used his notion of the unconscious in order to explain certain kinds of neurotic behavior. The theory of the unconscious was substantially transformed by later psychiatrists, among them Carl Jung and Jacques Lacan.
In his 1932/1933 conferences, Freud "proposes to abandon the notion of the unconscious that ambiguous judge".
Jung's view
Carl Gustav Jung, a Swiss psychiatrist,
developed the concept further. He agreed with Freud that the
unconscious is a determinant of personality, but he proposed that the
unconscious be divided into two layers: the personal unconscious and the collective unconscious.
The personal unconscious is a reservoir of material that was once
conscious but has been forgotten or suppressed, much like Freud's
notion. The collective unconscious, however, is the deepest level of the
psyche, containing the accumulation of inherited psychic structures and
archetypal
experiences. Archetypes are not memories but energy centers or
psychological functions that are apparent in the culture's use of
symbols. The collective unconscious is therefore said to be inherited
and contain material of an entire species rather than of an individual.
Every person shares the collective unconscious with the entire human
species, as Jung puts it: "[the] whole spiritual heritage of mankind's
evolution, born anew in the brain structure of every individual".
In addition to the structure of the unconscious, Jung differed from Freud in that he did not believe that sexuality was at the base of all unconscious thoughts.
Controversy
The notion that the unconscious mind exists at all has been disputed.
Jean-Paul Sartre offers a critique of Freud's theory of the unconscious in Being and Nothingness,
based on the claim that consciousness is essentially self-conscious.
Sartre also argues that Freud's theory of repression is internally
flawed. Philosopher Thomas Baldwin argues that Sartre's argument is based on a misunderstanding of Freud.
Erich Fromm
contends that, "The term 'the unconscious' is actually a mystification
(even though one might use it for reasons of convenience, as I am guilty
of doing in these pages). There is no such thing as the unconscious; there are only experiences of which we are aware, and others of which we are not aware, that is, of which we are unconscious.
If I hate a man because I am afraid of him, and if I am aware of my
hate but not of my fear, we may say that my hate is conscious and that
my fear is unconscious; still my fear does not lie in that mysterious
place: 'the' unconscious."
John Searle
has offered a critique of the Freudian unconscious. He argues that the
Freudian cases of shallow, consciously held mental states would be best
characterized as 'repressed consciousness,' while the idea of more
deeply unconscious mental states is more problematic. He contends that
the very notion of a collection of "thoughts" that exist in a privileged
region of the mind such that they are in principle never accessible
to conscious awareness, is incoherent. This is not to imply that there
are not "nonconscious" processes that form the basis of much of
conscious life. Rather, Searle simply claims that to posit the existence
of something that is like a "thought" in every way except for the fact
that no one can ever be aware of it (can never, indeed, "think" it) is
an incoherent concept. To speak of "something" as a "thought" either
implies that it is being thought by a thinker or that it could be
thought by a thinker. Processes that are not causally related to the
phenomenon called thinking are more appropriately called the
nonconscious processes of the brain.
David Holmes
examined sixty years of research about the Freudian concept of
"repression", and concluded that there is no positive evidence for this
concept. Given the lack of evidence for many Freudian hypotheses, some
scientific researchers proposed the existence of unconscious mechanisms
that are very different from the Freudian ones. They speak of a
"cognitive unconscious" (John Kihlstrom), an "adaptive unconscious" (Timothy Wilson), or a "dumb unconscious" (Loftus and Klinger), which executes automatic processes but lacks the complex mechanisms of repression and symbolic return of the repressed, and Robert Langs deep unconscious wisdom system.
In modern cognitive psychology,
many researchers have sought to strip the notion of the unconscious
from its Freudian heritage, and alternative terms such as "implicit" or
"automatic" have been used. These traditions emphasize the degree to
which cognitive processing happens outside the scope of cognitive
awareness, and show that things we are unaware of can nonetheless
influence other cognitive processes as well as behavior. Active research traditions related to the unconscious include implicit memory (see priming, implicit attitudes), and nonconscious acquisition of knowledge (see Lewicki, see also the section on cognitive perspective below).
Dreams
Freud
In
terms of the unconscious, the purpose of dreams, as stated by Freud, is
to fulfill repressed wishes through the process of dreaming, since they
cannot be fulfilled in real life. For example, if someone were to rob a
store and to feel guilty about it, they might dream about a scenario in
which their actions were justified and renders them blameless. Freud
asserted that the wish-fulfilling aspect of the dream may be disguised
due to the difficulty in distinguishing between manifest content and latent content. The manifest content consists of the plot of a dream at the surface level.
The latent content refers to the hidden or disguised meaning of the
events in the plot. The latent content of the dream is what supports the
idea of wish fulfillment. It represents the intimate information in the
dreamer's current issues and childhood conflict.
Opposing theories
In
response to Freud's theory on dreams, other psychologists have come up
with theories to counter his argument. Theorist Rosalind Cartwright
proposed that dreams provide people with the opportunity to act out and
work through everyday problems and emotional issues in a non-real
setting with no consequences. According to her cognitive
problem solving view, a large amount of continuity exists between our
waking thought and the thoughts that exist in dreams. Proponents of this
view believe that dreams allow participation in creative thinking and
alternate ways to handle situations when dealing with personal issues
because dreams are not restrained by logic or realism.
In addition to this, Allan Hobson and colleagues came up with the activation-synthesis hypothesis which proposes that dreams are simply the side effects of the neural activity in the brain that produces beta brain waves during REM sleep
that are associated with wakefulness. According to this hypothesis,
neurons fire periodically during sleep in the lower brain levels and
thus send random signals to the cortex.
The cortex then synthesizes a dream in reaction to these signals in
order to try to make sense of why the brain is sending them. However,
the hypothesis does not state that dreams are meaningless, it just
downplays the role that emotional factors play in determining dreams.
Contemporary cognitive psychology
Research
While,
historically, the psychoanalytic research tradition was the first to
focus on the phenomenon of unconscious mental activity, there is an
extensive body of conclusive research and knowledge in contemporary cognitive psychology devoted to the mental activity that is not mediated by conscious awareness.
Most of that (cognitive) research on unconscious processes has
been done in the mainstream, academic tradition of the information
processing paradigm. As opposed to the psychoanalytic tradition, driven
by the relatively speculative (in the sense of being hard to empirically
verify) theoretical concepts such as the Oedipus complex or Electra complex,
the cognitive tradition of research on unconscious processes is based
on relatively few theoretical assumptions and is very empirically
oriented (i.e., it is mostly data driven). Cognitive research has
revealed that automatically, and clearly outside of conscious awareness,
individuals register and acquire more information than what they can
experience through their conscious thoughts.
Unconscious processing of information about frequency
For example, an extensive line of research conducted by Hasher and Zacks
has demonstrated that individuals register information about the
frequency of events automatically (i.e., outside of conscious awareness
and without engaging conscious information processing resources).
Moreover, perceivers do this unintentionally, truly "automatically,"
regardless of the instructions they receive, and regardless of the
information processing goals they have. The ability to unconsciously and
relatively accurately tally the frequency of events appears to have
little or no relation to the individual's age,
education, intelligence, or personality, thus it may represent one of
the fundamental building blocks of human orientation in the environment
and possibly the acquisition of procedural knowledge and experience, in general.
A defence mechanism is an unconscious psychological mechanism that reduces anxiety arising from unacceptable or potentially harmful stimuli.
Defence mechanisms may result in healthy or unhealthy
consequences depending on the circumstances and frequency with which the
mechanism is used. In psychoanalytic theory, defence mechanisms (German: Abwehrmechanismen) are psychological strategies brought into play by the unconscious mind to manipulate, deny, or distort reality in order to defend against feelings of anxiety and unacceptable impulses and to maintain one's self-schema or other schemas. These processes that manipulate, deny, or distort reality may include the following: repression, or the burying of a painful feeling or thought from one's awareness even though it may resurface in a symbolic form; identification, incorporating an object or thought into oneself; and rationalization, the justification of one's behaviour and motivations by substituting "good" acceptable reasons for the actual motivations. In psychoanalytic theory, repression is considered as the basis for other defence mechanisms.
Healthy persons normally use different defences throughout life. An ego
defence mechanism becomes pathological only when its persistent use
leads to maladaptive behaviour such that the physical or mental health
of the individual is adversely affected. Among the purposes of ego
defence mechanisms is to protect the mind/self/ego from anxiety or social sanctions or to provide a refuge from a situation with which one cannot currently cope.
One resource used to evaluate these mechanisms is the Defense Style Questionnaire (DSQ-40).
Structural model: id, ego, and superego
Sigmund Freud
The concept of id impulses comes from Sigmund Freud's structural model. According to this theory, id impulses are based on the pleasure principle:
instant gratification of one's own desires and needs. Freud believed
that the id represents biological instinctual impulses in humans, such
as aggression (Thanatos or the death instinct) and sexuality (Eros or the life instinct).
For example, when the id impulses (e.g., desire to have sexual relations with a stranger) conflict with the superego
(e.g., belief in societal conventions of not having sex with unknown
persons), unsatisfied feelings of anxiousness or feelings of anxiety
come to the surface. To reduce these unpleasant feelings, the ego might
use defence mechanisms (conscious or unconscious blockage of the id
impulses).
Freud believed that conflicts between these two structures resulted in conflicts associated with psychosexual stages.
Definitions of individual psyche structures
The iceberg metaphor is often used to explain the psyche's parts in relation to one another
Freud proposed three structures of the psyche or personality:
Id:
The id is the unconscious reservoir of the libido, the psychic energy
that fuels instincts and psychic processes. It is a selfish, childish,
pleasure-oriented part of the personality with no ability to delay
gratification.
Superego:
The superego contains internalised societal and parental standards of
"good" and "bad", "right" and "wrong" behaviour. They include conscious
appreciations of rules and regulations as well as those incorporated
unconsciously.
Ego:
The ego acts as a moderator between the pleasure sought by the id and
the morals of the superego, seeking compromises to pacify both. It can
be viewed as the individual's "sense of time and place".
Primary and secondary processes
In
the ego, there are two ongoing processes. First, there is the
unconscious primary process, where the thoughts are not organised in a
coherent way; the feelings can shift, contradictions are not in conflict
or are just not perceived that way, and condensations arise. There is no logic and no time line. Lust is important for this process. By contrast, there is the conscious secondary process, where strong boundaries are set and thoughts must be organised in a coherent way. Most conscious thoughts originate here.
Reality principle
Id impulses are not appropriate in a civilised society, so there is societal pressure to modify the pleasure principle in favour of the reality principle; that is, the requirements of the external world.
Formation of the superego
The superego forms as the child grows and learns parental and social standards. The superego consists of two structures: the conscience, which stores information about what is "bad" and what has been punished, and the ego ideal, which stores information about what is "good" and what one "should" do or be.
The ego's use of defence mechanisms
When anxiety becomes overwhelming, it is the ego's place to protect the person by employing defence mechanisms. Guilt, embarrassment, and shame often accompany anxiety. In the first definitive book on defence mechanisms, The Ego and the Mechanisms of Defence (1936), Anna Freud
introduced the concept of signal anxiety; she stated that it was "not
directly a conflicted instinctual tension but a signal occurring in the
ego of an anticipated instinctual tension".
The signalling function of anxiety is thus seen as crucial, and
biologically adapted to warn the organism of danger or a threat to its
equilibrium. The anxiety is felt as an increase in bodily or mental
tension, and the signal that the organism receives in this way allows
for the possibility of taking defensive action regarding the perceived
danger. Defence mechanisms work by distorting the id impulses into
acceptable forms, or by unconscious or conscious blockage of these
impulses.
Theories and classifications
The list of defence mechanisms, with no theoretical consensus on the exact number.
Classifying defence mechanisms according to some of their properties
(like underlying mechanisms, similarities or connections with
personality) has been attempted. Different theorists have different
categorizations and conceptualizations of defence mechanisms. Large
reviews of theories of defence mechanisms are available from Paulhus,
Fridhandler and Hayes (1997) and Cramer (1991). The Journal of Personality published a special issue on defence mechanisms (1998).
A. Freud considered defense mechanisms as intellectual and motor
automatisms of various degrees of complexity, that arose in the process
of involuntary and voluntary learningRomanov, E.S. (1996). Mechanisms of psychological defense: genesis, functioning, diagnostics.
Both Freuds studied defence mechanisms, but Anna spent more of
her time and research on five main mechanisms: repression, regression,
projection, reaction formation, and sublimation. All defence mechanisms
are responses to anxiety and how the consciousness and unconscious
handle the stress of a social situation.
Repression: when a feeling is hidden and forced from the consciousness to the unconscious because it is seen as socially unacceptable
Regression: falling back into an early state of mental/physical development seen as "less demanding and safer"
Projection: possessing a feeling that is deigned as socially
unacceptable and instead of facing it, that feeling or "unconscious
urge" is seen in the actions of other people
Reaction formation: acting the opposite way that the
unconscious instructs a person to behave, "often exaggerated and
obsessive". For example, if a wife is infatuated with a man who is not
her husband, reaction formation may cause her to – rather than cheat –
become obsessed with showing her husband signs of love and affection.
Sublimation: seen as the most acceptable of the mechanisms, an expression of anxiety in socially acceptable ways
Otto F. Kernberg (1967) developed a theory of borderline personality organization of which one consequence may be borderline personality disorder. His theory is based on ego psychological object relations theory.
Borderline personality organization develops when the child cannot
integrate helpful and harmful mental objects together. Kernberg views
the use of primitive defence mechanisms as central to this personality
organization. Primitive psychological defences are projection, denial,
dissociation or splitting and they are called borderline defence
mechanisms. Also, devaluation and projective identification are seen as
borderline defences.
Robert Plutchik's (1979) theory views defences as derivatives of basic emotions,
which in turn relate to particular diagnostic structures. According to
his theory, reaction formation relates to joy (and manic features),
denial relates to acceptance (and histrionic features), repression to
fear (and passivity), regression to surprise (and borderline traits),
compensation to sadness (and depression), projection to disgust (and
paranoia), displacement to anger (and hostility) and intellectualization
to anticipation (and obsessionality).
The Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) published by the American Psychiatric Association (1994) includes a tentative diagnostic axis for defence mechanisms.
This classification is largely based on Vaillant's hierarchical view of
defences, but has some modifications. Examples include: denial,
fantasy, rationalization, regression, isolation, projection, and
displacement.
Vaillant's categorization
Psychiatrist George Eman Vaillant introduced a four-level classification of defence mechanisms:
Level I – pathological defences (psychotic denial, delusional projection)
Level IV – mature defences (humour, sublimation, suppression, altruism, anticipation)
Level 1: pathological
When predominant, the mechanisms on this level are almost always severely pathological.
These six defences, in conjunction, permit one effectively to
rearrange external experiences to eliminate the need to cope with
reality. Pathological users of these mechanisms frequently appear
irrational or insane to others. These are the "pathological" defences, common in overt psychosis. However, they are normally found in dreams and throughout childhood as well.
They include:
Delusional projection: Delusions about external reality, usually of a persecutory nature
Denial:
Refusal to accept external reality because it is too threatening;
arguing against an anxiety-provoking stimulus by stating it does not
exist; resolution of emotional conflict and reduction of anxiety by
refusing to perceive or consciously acknowledge the more unpleasant
aspects of external reality
Distortion: A gross reshaping of external reality to meet internal needs
Level 2: immature
These
mechanisms are often present in adults. These mechanisms lessen
distress and anxiety produced by threatening people or by an
uncomfortable reality. Excessive use of such defences is seen as
socially undesirable, in that they are immature, difficult to deal with
and seriously out of touch with reality. These are the so-called
"immature" defences and overuse almost always leads to serious problems
in a person's ability to cope effectively. These defences are often
seen in major depression and personality disorders.
They include:
Acting out:
Direct expression of an unconscious wish or impulse in action, without
conscious awareness of the emotion that drives the expressive behavior
Hypochondriasis: An excessive preoccupation or worry about having a serious illness
Projection: A primitive form of paranoia.
Projection reduces anxiety by allowing the expression of the
undesirable impulses or desires without becoming consciously aware of
them; attributing one's own unacknowledged, unacceptable, or unwanted
thoughts and emotions to another; includes severe prejudice and jealousy, hypervigilance
to external danger, and "injustice collecting", all with the aim of
shifting one's unacceptable thoughts, feelings and impulses onto someone
else, such that those same thoughts, feelings, beliefs and motivations
are perceived as being possessed by the other.
Schizoid fantasy: Tendency to retreat into fantasy in order to resolve inner and outer conflicts
Level 3: neurotic
These mechanisms are considered neurotic,
but fairly common in adults. Such defences have short-term advantages
in coping, but can often cause long-term problems in relationships, work
and in enjoying life when used as one's primary style of coping with
the world.
They include:
Displacement:
Defence mechanism that shifts sexual or aggressive impulses to a more
acceptable or less threatening target; redirecting emotion to a safer
outlet; separation of emotion from its real object and redirection of
the intense emotion toward someone or something that is less offensive
or threatening in order to avoid dealing directly with what is
frightening or threatening.
Dissociation:
Temporary drastic modification of one's personal identity or character
to avoid emotional distress; separation or postponement of a feeling
that normally would accompany a situation or thought
Intellectualization:
A form of isolation; concentrating on the intellectual components of a
situation so as to distance oneself from the associated
anxiety-provoking emotions; separation of emotion from ideas; thinking
about wishes in formal, affectively bland terms and not acting on them;
avoiding unacceptable emotions by focusing on the intellectual aspects (isolation, rationalization, ritual, undoing, compensation, and magical thinking)
Reaction formation:
Converting unconscious wishes or impulses that are perceived to be
dangerous or unacceptable into their opposites; behaviour that is
completely the opposite of what one really wants or feels; taking the
opposite belief because the true belief causes anxiety
Repression:
The process of attempting to repel desires towards pleasurable
instincts, caused by a threat of suffering if the desire is satisfied;
the desire is moved to the unconscious in the attempt to prevent it from
entering consciousness;
seemingly unexplainable naivety, memory lapse or lack of awareness of
one's own situation and condition; the emotion is conscious, but the
idea behind it is absent
Level 4: mature
These
are commonly found among emotionally healthy adults and are considered
mature, even though many have their origins in an immature stage of
development. They have been adapted through the years in order to
optimise success in human society and relationships. The use of these
defences enhances pleasure and feelings of control. These defences help
to integrate conflicting emotions and thoughts, whilst still remaining
effective. Those who use these mechanisms are usually considered virtuous.
Mature defences include:
Altruism: Constructive service to others that brings pleasure and personal satisfaction
Anticipation: Realistic planning for future discomfort
Humour:
Overt expression of ideas and feelings (especially those that are
unpleasant to focus on or too terrible to talk about directly) that
gives pleasure to others. The thoughts retain a portion of their innate
distress, but they are "skirted around" by witticism, for example self-deprecation.
Sublimation:
Transformation of unhelpful emotions or instincts into healthy actions,
behaviours, or emotions, for example, playing a heavy contact sport
such as football or rugby can transform aggression into a game[24]
Suppression:
The conscious decision to delay paying attention to a thought, emotion,
or need in order to cope with the present reality; making it possible
later to access uncomfortable or distressing emotions whilst accepting
them
Other defence mechanisms
Diagram of selected ego defence mechanisms
Pathological
Conversion:
The expression of an intrapsychic conflict as a physical symptom; some
examples include blindness, deafness, paralysis, or numbness. This
phenomenon is sometimes called hysteria.
Splitting:
A primitive defence. Both harmful and helpful impulses are split off
and unintegrated, frequently projected onto someone else. The defended
individual segregates experiences into all-good and all-bad categories,
with no room for ambiguity and ambivalence. When "splitting" is combined
with "projecting", the undesirable qualities that one unconsciously
perceives oneself as possessing, one consciously attributes to another.
Immature
Idealization: Tending to perceive another individual as having more desirable qualities than he or she may actually have.
Introjection:
Identifying with some idea or object so deeply that it becomes a part
of that person. For example, introjection occurs when we take on
attributes of other people who seem better able to cope with the
situation than we do.
Somatization:
The transformation of uncomfortable feelings towards others into
uncomfortable feelings toward oneself: pain, illness, and anxiety.
Wishful thinking: Making decisions according to what might be pleasing to imagine instead of by appealing to evidence, rationality, or reality.
Neurotic
Isolation:
Separation of feelings from ideas and events, for example, describing a
murder with graphic details with no emotional response.
Rationalization (making excuses):
Convincing oneself that no wrong has been done and that all is or was
all right through faulty and false reasoning. An indicator of this
defence mechanism can be seen socially as the formulation of convenient
excuses.
Regression:
Temporary reversion of the ego to an earlier stage of development
rather than handling unacceptable impulses in a more adult way, for
example, using whining as a method of communicating despite already
having acquired the ability to speak with an appropriate level of
maturity.
Undoing:
A person tries to 'undo' an unhealthy, destructive or otherwise
threatening thought by acting out the reverse of the unacceptable.
Involves symbolically nullifying an unacceptable or guilt provoking
thought, idea, or feeling by confession or atonement.
Upward and downward social comparisons:
A defensive tendency that is used as a means of self-evaluation.
Individuals will look to another individual or comparison group who are
considered to be worse off in order to dissociate themselves from
perceived similarities and to make themselves feel better about
themselves or their personal situation.
Withdrawal:
Avoidance is a form of defence. It entails removing oneself from
events, stimuli, and interactions under the threat of being reminded of
painful thoughts and feelings.
Relation with coping
There are many different perspectives on how the construct of defence relates to the construct of coping;
some writers differentiate the constructs in various ways, but "an
important literature exists that does not make any difference between
the two concepts". In at least one of his books, George Eman Vaillant stated that he "will use the terms adaptation, resilience, coping, and defense interchangeably".
Wi-Fi is a family of wireless networking technologies, based on the IEEE 802.11 family of standards, which are commonly used for local area networking of devices and Internet access. Wi‑Fi is a trademark of the non-profit Wi-Fi Alliance, which restricts the use of the term Wi-Fi Certified to products that successfully complete interoperability certification testing. As of 2010, the Wi-Fi Alliance consisted of more than 375 companies from around the world. As of 2009, Wi-Fi-integrated circuit chips shipped approximately 580million units annually. Devices that can use Wi-Fi technologies include desktops and laptops, smartphones and tablets, smart TVs, printers, digital audio players, digital cameras, cars and drones.
Wi-Fi uses multiple parts of the IEEE 802protocol family and is designed to seamlessly interwork with its wired sibling Ethernet. Compatible devices can network through a wireless access point
to each other as well as to wired devices and the Internet. The
different versions of Wi-Fi are specified by various IEEE 802.11
protocol standards, with the different radio technologies determining
radio bands, and the maximum ranges, and speeds that may be achieved.
Wi-Fi most commonly uses the 2.4 gigahertz (120 mm) UHF and 5 gigahertz (60 mm) SHFISM
radio bands; these bands are subdivided into multiple channels.
Channels can be shared between networks but only one transmitter can
locally transmit on a channel at any moment in time.
Wi-Fi's wavebands have relatively high absorption and work best for line-of-sight
use. Many common obstructions such as walls, pillars, home appliances
etc. may greatly reduce range, but this also helps minimize interference
between different networks in crowded environments. An access point (or
hotspot)
often has a range of about 20 metres (66 feet) indoors while some
modern access points claim up to a 150-metre (490-foot) range outdoors.
Hotspot coverage can be as small as a single room with walls that block
radio waves, or as large as many square kilometres using many
overlapping access points with roaming
permitted between them. Over time the speed and spectral efficiency of
Wi-Fi has increased. As of 2019, at close range, some versions of Wi-Fi
running on suitable hardware can achieve speeds of over 1 Gbit/s (gigabit per second).
Wi-Fi is potentially more vulnerable to attack than wired networks because anyone within range of a network with a wireless network interface controller can attempt access. Therefore to connect to a Wi-Fi network, a user typically needs the network name (the SSID) and a password. The password is used to encrypt Wi-Fi packets so as to block eavesdroppers. Wi-Fi Protected Access
(WPA) is a family of technologies created to protect information moving
across Wi-Fi networks and includes solutions for personal and
enterprise networks. As the security landscape has changed over time
security features of WPA have included stronger protections and new
security practices.
History
In 1971, ALOHAnet connected the Great Hawaiian Islands with a UHF wireless packet network. ALOHAnet and the ALOHA protocol were early forerunners to Ethernet, and later the IEEE 802.11 protocols, respectively.
A 1985 ruling by the U.S. Federal Communications Commission released the ISM band for unlicensed use. These frequency bands are the same ones used by equipment such as microwave ovens and are subject to interference.
The Australian radio-astronomer Dr John O'Sullivan with his colleagues Terence Percival, Graham Daniels, Diet Ostry, and John Deane developed a key patent used in Wi-Fi as a by-product of a Commonwealth Scientific and Industrial Research Organisation (CSIRO) research project, "a failed experiment to detect exploding mini black holes the size of an atomic particle". Dr O'Sullivan and his colleagues are credited with inventing Wi-Fi. In 1992 and 1996, CSIRO obtained patents for a method later used in Wi-Fi to "unsmear" the signal.
The first version of the 802.11 protocol was released in 1997,
and provided up to 2 Mbit/s link speeds. This was updated in 1999 with 802.11b to permit 11 Mbit/s link speeds, and this proved popular.
In 1999, the Wi-Fi Alliance formed as a trade association to hold the Wi-Fi trademark under which most products are sold.
Wi-Fi uses a large number of patents held by many different organizations. In April 2009, 14 technology companies agreed to pay CSIRO $1 billion for infringements on CSIRO patents. This led to Australia labeling Wi-Fi as an Australian invention, though this has been the subject of some controversy.
CSIRO won a further $220 million settlement for Wi-Fi
patent-infringements in 2012, with global firms in the United States
required to pay CSIRO licensing rights estimated at an additional $1
billion in royalties. In 2016, the wireless local area network Test Bed was chosen as Australia's contribution to the exhibition A History of the World in 100 Objects held in the National Museum of Australia.
Etymology and terminology
A
Japanese sticker indicating to the public that a location is within
range of a Wi-Fi network. A dot with curved lines radiating from it is a
common symbol for Wi-Fi, representing a point transmitting a signal.
An example of a service set called "WiFi Wikipedia" consisting of two Basic Service Sets. Notebook_My is able to automatically roam between the two BSSs, without the user having to explicitly connect to the second network.
The name Wi-Fi, commercially used at least as early as August 1999, was coined by the brand-consulting firm Interbrand. The Wi-Fi Alliance had hired Interbrand to create a name that was "a little catchier than 'IEEE 802.11b Direct Sequence'."
Phil Belanger, a founding member of the Wi-Fi Alliance who presided
over the selection of the name "Wi-Fi", has stated that Interbrand
invented Wi-Fi as a pun on the word hi-fi (high fidelity), a term for high-quality audio technology.
The name Wi-Fi has no further meaning, and was never officially a shortened form of "Wireless Fidelity". Nevertheless, the Wi-Fi Alliance used the advertising slogan "The Standard for Wireless Fidelity" for a short time after the brand name was created, and the Wi-Fi Alliance was also called the "Wireless Fidelity Alliance Inc" in some publications.
Interbrand also created the Wi-Fi logo. The yin-yang Wi-Fi logo indicates the certification of a product for interoperability.
Non-Wi-Fi technologies intended for fixed points, such as Motorola Canopy, are usually described as fixed wireless. Alternative wireless technologies include mobile phone standards, such as 2G, 3G, 4G, and LTE.
The name is sometimes written as WiFi, Wifi, or wifi,
but these are not approved by the Wi-Fi Alliance. IEEE is a separate,
but related, organization and their website has stated "WiFi is a short
name for Wireless Fidelity".
To connect to a Wi-Fi LAN, a computer must be equipped with a wireless network interface controller. The combination of a computer and an interface controller is called a station. Stations are identified by one or more MAC addresses.
Wi-Fi nodes often operate in infrastructure mode where all communications go through a base station. Ad-hoc mode refers to devices talking directly to each other without the need to first talk to an access point.
A service set
is the set of all the devices associated with a particular Wi-Fi
network. Devices in a service set need not be on the same wavebands or
channels. A service set can be local, independent, extended or mesh or a
combination.
Each service set has an associated identifier, the 32-byte Service Set Identifier (SSID), which identifies the particular network. The SSID is configured within the devices that are considered part of the network.
A Basic Service Set (BSS) is a group of stations
that all share the same wireless channel, SSID, and other wireless
settings that have wirelessly connected (usually to the same access
point). Each BSS is identified by a MAC address which is called the BSSID.
Certification
The IEEE does not test equipment for compliance with their standards. The non-profit Wi-Fi Alliance was formed in 1999 to fill this void—to establish and enforce standards for interoperability and backward compatibility, and to promote wireless local-area-network technology. As of 2010, the Wi-Fi Alliance consists of more than 375 companies and includes 3Com (now owned by HPE/Hewlett-Packard Enterprise), Aironet (now owned by Cisco), Harris Semiconductor (now owned by Intersil), Lucent (now owned by Nokia), Nokia and Symbol Technologies (now owned by Zebra Technologies). The Wi-Fi Alliance enforces the use of the Wi-Fi brand to technologies based on the IEEE 802.11 standards from the IEEE. This includes wireless local area network (WLAN) connections, device to device connectivity (such as Wi-Fi Peer to Peer aka Wi-Fi Direct), Personal area network (PAN), local area network (LAN) and even some limited wide area network
(WAN) connections. Manufacturers with membership in the Wi-Fi Alliance,
whose products pass the certification process, gain the right to mark
those products with the Wi-Fi logo.
Specifically, the certification process requires conformance to the IEEE 802.11 radio standards, the WPA and WPA2 security standards, and the EAP
authentication standard. Certification may optionally include tests of
IEEE 802.11 draft standards, interaction with cellular-phone technology
in converged devices, and features relating to security set-up,
multimedia, and power-saving.
Not every Wi-Fi device is submitted for certification. The lack
of Wi-Fi certification does not necessarily imply that a device is
incompatible with other Wi-Fi devices. The Wi-Fi Alliance may or may not sanction derivative terms, such as Super Wi-Fi, coined by the US Federal Communications Commission (FCC) to describe proposed networking in the UHF TV band in the US.
(Wi-Fi 1, Wi-Fi 2, Wi-Fi 3 are unbranded but have unofficial assignments)
Equipment frequently support multiple versions of Wi-Fi. To
communicate, devices must use a common Wi-Fi version. The versions
differ between the radio wavebands they operate on, the radio bandwidth
they occupy, the maximum data rates they can support and other details.
Some versions permit the use of multiple antennas, which permits greater
speeds as well as reduced interference.
Historically, equipment has simply listed the versions of Wi-Fi using the name of the IEEE standard that it supports. In 2018,
the Wi-Fi alliance standardized generational numbering so that
equipment can indicate that it supports Wi-Fi 4 (if the equipment
supports 802.11n), Wi-Fi 5 (802.11ac) and Wi-Fi 6 (802.11ax). These
generations have a high degree of backward compatibility with previous
versions. The alliance have stated that the generational level 4, 5, or 6
can be indicated in the user interface when connected, along with the
signal strength.
The full list of versions of Wi-Fi is: 802.11a, 802.11b, 802.11g, 802.11n (Wi-Fi 4), 802.11h, 802.11i, 802.11-2007, 802.11-2012, 802.11ac (Wi-Fi 5), 802.11ad, 802.11af, 802.11-2016, 802.11ah, 802.11ai, 802.11aj, 802.11aq, 802.11ax (Wi-Fi 6), 802.11ay.
Uses
Internet access
Wi-Fi technology may be used to provide local network and Internet access
to devices that are within Wi-Fi range of one or more routers that are
connected to the Internet. The coverage of one or more interconnected access points (hotspots)
can extend from an area as small as a few rooms to as large as many
square kilometres. Coverage in the larger area may require a group of
access points with overlapping coverage. For example, public outdoor
Wi-Fi technology has been used successfully in wireless mesh networks in London. An international example is Fon.
Wi-Fi provides service in private homes, businesses, as well as
in public spaces. Wi-Fi hotspots may be set up either free-of-charge or
commercially, often using a captive portal webpage for access. Organizations, enthusiasts, authorities and businesses,
such as airports, hotels, and restaurants, often provide free or
paid-use hotspots to attract customers, to provide services to promote
business in selected areas.
Similarly, battery-powered routers may include a cellular Internet radio modem
and Wi-Fi access point. When subscribed to a cellular data carrier,
they allow nearby Wi-Fi stations to access the Internet over 2G, 3G, or
4G networks using the tethering technique. Many smartphones have a built-in capability of this sort, including those based on Android, BlackBerry, Bada, iOS (iPhone), Windows Phone and Symbian,
though carriers often disable the feature, or charge a separate fee to
enable it, especially for customers with unlimited data plans. "Internet
packs" provide standalone facilities of this type as well, without use
of a smartphone; examples include the MiFi- and WiBro-branded devices. Some laptops that have a cellular modem card can also act as mobile Internet Wi-Fi access points.
Many traditional university campuses in the developed world provide at least partial Wi-Fi coverage. Carnegie Mellon University built the first campus-wide wireless Internet network, called Wireless Andrew, at its Pittsburgh campus in 1993 before Wi-Fi branding originated.
By February 1997, the CMU Wi-Fi zone was fully operational. Many
universities collaborate in providing Wi-Fi access to students and staff
through the Eduroam international authentication infrastructure.
City-wide
An outdoor Wi-Fi access point
In the early 2000s, many cities around the world announced plans to
construct citywide Wi-Fi networks. There are many successful examples;
in 2004, Mysore
(Mysuru) became India's first Wi-Fi-enabled city. A company called
WiFiyNet has set up hotspots in Mysore, covering the complete city and a
few nearby villages.
In May 2010, London mayor Boris Johnson pledged to have London-wide Wi-Fi by 2012. Several boroughs including Westminster and Islington already had extensive outdoor Wi-Fi coverage at that point.
Officials in South Korea's capital Seoul
are moving to provide free Internet access at more than 10,000
locations around the city, including outdoor public spaces, major
streets and densely populated residential areas. Seoul will grant leases
to KT, LG Telecom, and SK Telecom. The companies will invest $44 million in the project, which was to be completed in 2015.
Wi-Fi stations communicate by sending each other data packets: blocks of data individually sent and delivered over radio. As with all radio, this is done by the modulating and demodulation of carrier waves. Different versions of Wi-Fi use different techniques, 802.11b uses DSSS
on a single carrier, whereas 802.11a, Wi-Fi 4, 5 and 6 use multiple
carriers on slightly different frequencies within the channel (OFDM).
As with other IEEE 802 LANs, stations come programmed with a globally unique 48-bit MAC address (often printed on the equipment) so that each Wi-Fi station has a unique address.
The MAC addresses are used to specify both the destination and the
source of each data packet. Wi-Fi establishes link-level connections,
which can be defined using both the destination and source addresses. On
reception of a transmission, the receiver uses the destination address
to determine whether the transmission is relevant to the station or
should be ignored. A network interface normally does not accept packets
addressed to other Wi-Fi stations.
Due to the ubiquity of Wi-Fi and the ever-decreasing cost of the
hardware needed to support it, most manufacturers now build Wi-Fi
interfaces directly into PC motherboards, eliminating the need for installation of a separate network card.
Channels are used half duplex and can be time-shared
by multiple networks. When communication happens on the same channel,
any information sent by one computer is locally received by all, even if
that information is intended for just one destination. The network interface card interrupts the CPU only when applicable packets are received: the card ignores information not addressed to it.
Use of the same channel also means that the data bandwidth is shared,
such that, for example, available data bandwidth to each device is
halved when two stations are actively transmitting.
A collision happens when two stations attempt to transmit at the
same time. They corrupt transmitted data and require stations to
re-transmit. The lost data and re-transmission reduces throughput. In
the worst case, where multiple active hosts connected with maximum
allowed cable length attempt to transmit many short frames, excessive
collisions can reduce throughput dramatically. A scheme known as carrier sense multiple access with collision avoidance (CSMA/CA) governs the way the computers share the channel.
Waveband
In
the 2.5 GHz wavebands as well as others, transmitters straddle multiple
channels. Overlapping channels can suffer from interference unless this
is a small portion of the total received power.
A keychain-size Wi-Fi detector
The 802.11 standard provides several distinct radio frequency ranges for use in Wi-Fi communications: 900 MHz, 2.4 GHz, 5 GHz, 5.9 GHz, and 60 GHz bands. Each range is divided into a multitude of channels.
Countries apply their own regulations to the allowable channels,
allowed users and maximum power levels within these frequency ranges.
The ISM band ranges are also often used.
Spectrum assignments and operational limitations are not
consistent worldwide: Australia and Europe allow for an additional two
channels (12, 13) beyond the 11 permitted in the United States for the
2.4 GHz band, while Japan has three more (12–14). In the US and other
countries, 802.11a and 802.11g devices may be operated without a
license, as allowed in Part 15 of the FCC Rules and Regulations.
802.11a/h/j/n/ac/ax can use the 5 GHz U-NII band,
which, for much of the world, offers at least 23 non-overlapping 20 MHz
channels rather than the 2.4 GHz ISM frequency band, where the channels
are only 5 MHz wide. In general, lower frequencies have better range
but have less capacity. The 5 GHz bands are absorbed to a greater degree
by common building materials than the 2.4 GHz bands, and usually give
shorter range.
As 802.11 specifications evolved to support higher throughput,
the protocols have become much more efficient in their use of bandwidth.
Additionally they have gained the ability to 'bond' channels together
to gain still more throughput where the bandwidth is available. 802.11n
allows for double radio spectrum/bandwidth (40 MHz- 8 channels) compared
to 802.11a or 802.11g (20 MHz). 802.11n can also be set to limit itself to 20 MHz bandwidth to prevent interference in dense communities.
In the 5 GHz band, 20, 40, 80 and 160 MHz bandwidth signals are
permitted with some restrictions, giving much faster connections.
Communication stack
Wi-Fi is part of the IEEE 802 protocol family. The data is organized into 802.11 frames that are very similar to Ethernet frames at the data link layer, but with extra address fields. MAC addresses are used as network addresses for routing over the LAN.
Wi-Fi's MAC and physical layer
(PHY) specifications are defined by IEEE 802.11 for modulating and
receiving one or more carrier waves to transmit the data in the
infrared, and 2.4, 3.6, 5, or 60 GHz frequency bands. They are created and maintained by the IEEE LAN/MAN Standards Committee (IEEE 802).
The base version of the standard was released in 1997, and has had many
subsequent amendments. The standard and amendments provide the basis
for wireless network products using the Wi-Fi brand. While each
amendment is officially revoked when it is incorporated in the latest
version of the standard, the corporate world tends to market to the
revisions because they concisely denote capabilities of their products. As a result, in the market place, each revision tends to become its own standard.
In addition to 802.11 the IEEE 802 protocol family has specific
provisions for Wi-Fi. These are required because Ethernet's cable-based
media are not usually shared, whereas with wireless all transmissions
are received by all stations within range that employ that radio
channel. While Ethernet has essentially negligible error rates, wireless
communication media are subject to significant interference. Therefore,
accurate transmission is not guaranteed so delivery is therefore a best-effort delivery mechanism. Because of this, for Wi-Fi, the Logical Link Control (LLC) specified by IEEE 802.2 employs Wi-Fi's media access control (MAC) protocols to manage retries without relying on higher levels of the protocol stack.
For internetworking purposes Wi-Fi is usually layered as a link layer (equivalent to the physical and data link layers of the OSI model) below the internet layer of the Internet Protocol. This means that nodes have an associated internet address and, with suitable connectivity, this allows full Internet access.
Modes
Infrastructure
Depiction
of a Wi-Fi network in infrastructure mode. The device sends information
wirelessly to another device, both connected to the local network, in
order to print a document
In infrastructure mode, which is the most common mode used, all
communications goes through a base station. For communications within
the network, this introduces an extra use of the airwaves, but has the
advantage that any two stations that can communicate with the base
station can also communicate through the base station, which enormously
simplifies the protocols.
Ad hoc and Wi-Fi direct
Wi-Fi also allows communications directly from one computer to another without an access point intermediary. This is called ad hoc Wi-Fi transmission.
Different types of ad hoc network exist. In the simplest case network
nodes must talk directly to each other. In more complex protocols nodes
may forward packets, and nodes keep track of how to reach other nodes,
even if they move around.
Ad-hoc mode was first invented and realized by Chai Keong Toh in his 1996 invention of Wi-Fi ad-hoc routing, implemented on Lucent WaveLAN 802.11a wireless on IBM ThinkPads over a size nodes scenario spanning a region of over a mile. The success was recorded in Mobile Computing magazine (1999) and later published formally in IEEE Transactions on Wireless Communications, 2002 and ACM SIGMETRICS Performance Evaluation Review, 2001.
Similarly, the Wi-Fi Alliance promotes the specification Wi-Fi
Direct for file transfers and media sharing through a new discovery- and
security-methodology. Wi-Fi Direct launched in October 2010.
Another mode of direct communication over Wi-Fi is Tunneled Direct Link Setup (TDLS), which enables two devices on the same Wi-Fi network to communicate directly, instead of via the access point.
Multiple access points
Access points send out beacon frames to announce the presence of networks.
An Extended Service Set
may be formed by deploying multiple access points that are configured
with the same SSID and security settings. Wi-Fi client devices typically
connect to the access point that can provide the strongest signal
within that service set.
Increasing the number of Wi-Fi access points for a network provides redundancy, better range, support for fast roaming and increased overall network-capacity by using more channels or by defining smaller cells.
Except for the smallest implementations (such as home or small office
networks), Wi-Fi implementations have moved toward "thin" access points,
with more of the network intelligence
housed in a centralized network appliance, relegating individual access
points to the role of "dumb" transceivers. Outdoor applications may use
mesh topologies.
Performance
Parabolic
dishes transmit and receive the radio waves only in particular
directions and can give much greater range than omnidirection antennas
Yagi-Uda antennas, widely used for television reception, are relatively compact at Wi-Fi wavelengths
Antenna
of wireless network interface controller Gigabyte GC-WB867D-I. Simple
stick-like antennas like these have unidrectional reception and
relatively low range of 20m or so.
Wi-Fi operational range depends on factors such as the frequency band, radio power output,
receiver sensitivity, antenna gain and antenna type as well as the
modulation technique. In addition, propagation characteristics of the
signals can have a big impact.
At longer distances, and with greater signal absorption, speed is usually reduced.
Transmitter power
Compared
to cell phones and similar technology, Wi-Fi transmitters are low power
devices. In general, the maximum amount of power that a Wi-Fi device
can transmit is limited by local regulations, such as FCC Part 15 in the US. Equivalent isotropically radiated power (EIRP) in the European Union is limited to 20 dBm (100 mW).
To reach requirements for wireless LAN applications, Wi-Fi has
higher power consumption compared to some other standards designed to
support wireless personal area network (PAN) applications. For example,
Bluetooth provides a much shorter propagation range between 1 and 100m and so in general have a lower power consumption. Other low-power technologies such as ZigBee
have fairly long range, but much lower data rate. The high power
consumption of Wi-Fi makes battery life in some mobile devices a
concern.
Antenna
An access point compliant with either 802.11b or 802.11g, using the stock omnidirectional antenna
might have a range of 100 m (0.062 mi). The same radio with an external
semi parabolic antenna (15 dB gain) with a similarly equipped receiver
at the far end might have a range over 20 miles.
Higher gain rating (dBi) indicates further deviation (generally toward the horizontal) from a theoretical, perfect isotropic radiator,
and therefore the antenna can project or accept a usable signal further
in particular directions, as compared to a similar output power on a
more isotropic antenna.
For example, an 8 dBi antenna used with a 100 mW driver has a similar
horizontal range to a 6 dBi antenna being driven at 500 mW. Note that
this assumes that radiation in the vertical is lost; this may not be the
case in some situations, especially in large buildings or within a waveguide.
In the above example, a directional waveguide could cause the low power
6 dBi antenna to project much further in a single direction than the 8
dBi antenna, which is not in a waveguide, even if they are both driven
at 100 mW.
On wireless routers with detachable antennas, it is possible to
improve range by fitting upgraded antennas that provide higher gain in
particular directions. Outdoor ranges can be improved to many kilometres
through the use of high gain directional antennas at the router and remote device(s).
MIMO (multiple-input and multiple-output)
This Netgear Wi-Fi router contains dual bands for transmitting the 802.11 standard across the 2.4 and 5 GHz spectrums and supports MIMO.
IEEE 802.11n (Wi-Fi 4) and IEEE 802.11ac
(Wi-Fi 5) allow devices to have multiple antennas. Multiple antennas
enable the equipment to focus on the far end device, reducing
interference in other directions, and giving a stronger useful signal.
This greatly increases range and network speed without exceeding the
legal power limits.
IEEE 802.11n can more than double the range.
Range also varies with frequency band. Wi-Fi in the 2.4 GHz frequency
block has slightly better range than Wi-Fi in the 5 GHz frequency block
used by 802.11a (and optionally by 802.11n).
The 802.11ac
standard, uses the 5 GHz band exclusively and is capable of
multi-station WLAN throughput of at least 1 gigabit per second, and a
single station throughput of at least 500 Mbit/s. In the first quarter
of 2016, The Wi-Fi Alliance certifies devices compliant with the
802.11ac standard as "Wi-Fi CERTIFIED ac". This standard uses several
signal processing techniques such as multi-user MIMO and 4X4 Spatial
Multiplexing streams, and large channel bandwidth (160 MHz) to achieve
the Gigabit throughput. According to a study by IHS Technology, 70% of
all access point sales revenue In the first quarter of 2016 came from
802.11ac devices.
Radio propagation
With Wi-Fi signals line-of-sight usually works best, but signals can transmit, absorb, reflect, and diffract through and around structures, both man made, and natural.
Due to the complex nature of radio propagation
at typical Wi-Fi frequencies, particularly around trees and buildings,
algorithms can only approximately predict Wi-Fi signal strength for any
given area in relation to a transmitter. This effect does not apply equally to long-range Wi-Fi, since longer links typically operate from towers that transmit above the surrounding foliage.
Mobile use of Wi-Fi over wider ranges is limited, for instance,
to uses such as in an automobile moving from one hotspot to another.
Other wireless technologies are more suitable for communicating with
moving vehicles.
Distance records
Distance records (using non-standard devices) include 382 km (237 mi)
in June 2007, held by Ermanno Pietrosemoli and EsLaRed of Venezuela,
transferring about 3 MB of data between the mountain-tops of El Águila and Platillon. The Swedish Space Agency transferred data 420 km (260 mi), using 6 watt amplifiers to reach an overhead stratospheric balloon.
Interference
Network
planning frequency allocations for North America and Europe. Using
these types of frequency allocations can help minimize co-channel and
adjacent-channel interference.
Wi-Fi connections can be blocked or the Internet speed lowered by
having other devices in the same area. Wi-Fi protocols are designed to
share the wavebands reasonably fairly, and this often works with little
to no disruption. To minimize collisions with Wi-Fi and non Wi-Fi
devices, Wi-Fi employs Carrier-sense multiple access with collision avoidance
(CSMA/CA), where transmitters listen before transmitting, and delay
transmission of packets if they detect that other devices are active on
the channel, or if noise is detected from adjacent channels or from non
Wi-Fi sources. Nevertheless, Wi-Fi networks are still susceptible to the
hidden node and exposed node problem.
A standard speed Wi-Fi signal occupies five channels in the
2.4 GHz band. Interference can be caused by overlapping channels. Any
two channel numbers that differ by five or more, such as 2 and 7, do not
overlap (no adjacent-channel interference). The oft-repeated adage that channels 1, 6, and 11 are the only non-overlapping channels is, therefore, not accurate. Channels 1, 6, and 11 are the only group of three
non-overlapping channels in North America. However, whether the overlap
is significant depends on physical spacing. Channels that are four
apart interfere a negligible amount-much less than reusing channels
(which causes co-channel interference)-if transmitters are at least a few metres apart. In Europe and Japan where channel 13 is available, using Channels 1, 5, 9, and 13 for 802.11g and 802.11n is recommended.
However, many 2.4 GHz 802.11b and 802.11g access-points default
to the same channel on initial startup, contributing to congestion on
certain channels. Wi-Fi pollution, or an excessive number of access
points in the area, can prevent access and interfere with other devices'
use of other access points as well as with decreased signal-to-noise ratio
(SNR) between access points. These issues can become a problem in
high-density areas, such as large apartment complexes or office
buildings with many Wi-Fi access points. Wi-Fi 6 has greatly improved power control, and suffers less from interference in congested areas.
Other devices use the 2.4 GHz band: microwave ovens, ISM band devices, security cameras, ZigBee devices, Bluetooth devices, video senders, cordless phones, baby monitors, and, in some countries, amateur radio, all of which can cause significant additional interference. It is also an issue when municipalities
or other large entities (such as universities) seek to provide large
area coverage. On some 5GHz bands interference from radar systems can
occur in some places. For base stations that support those bands they
employ Dynamic Frequency Selection which listens for radar, and if it is
found, will not permit a network on that band.
These bands are can be used by low power transmitters without a
license, and with few restrictions. However, while unintended
interference is common, users that have been found to cause deliberate
interference (particularly for attempting to locally monopolize these
bands for commercial purposes) have been issued large fines.
Throughput
Graphical representation of Wi-Fi application specific (UDP) performance envelope 2.4 GHz band, with 802.11g
Graphical representation of Wi-Fi application specific (UDP) performance envelope 2.4 GHz band, with 802.11n with 40 MHz
Various layer 2 variants of IEEE 802.11 have different
characteristics. Across all flavours of 802.11, maximum achievable
throughputs are either given based on measurements under ideal
conditions or in the layer 2 data rates. This, however, does not apply
to typical deployments in which data are transferred between two
endpoints of which at least one is typically connected to a wired
infrastructure, and the other is connected to an infrastructure via a
wireless link.
This means that typically data frames pass an 802.11 (WLAN) medium and are being converted to 802.3 (Ethernet) or vice versa.
Due to the difference in the frame (header) lengths of these two
media, the packet size of an application determines the speed of the
data transfer. This means that an application that uses small packets
(e.g., VoIP) creates a data flow with a high overhead traffic (e.g., a
low goodput).
Other factors that contribute to the overall application data
rate are the speed with which the application transmits the packets
(i.e., the data rate) and the energy with which the wireless signal is
received. The latter is determined by distance and by the configured
output power of the communicating devices.
The same references apply to the attached throughput graphs, which show measurements of UDP
throughput measurements. Each represents an average throughput of 25
measurements (the error bars are there, but barely visible due to the
small variation), is with a specific packet size (small or large), and
with a specific data rate (10 kbit/s – 100 Mbit/s). Markers for traffic
profiles of common applications are included as well. This text and
measurements do not cover packet errors but information about this can
be found at the above references. The table below shows the maximum
achievable (application specific) UDP throughput in the same scenarios
(same references again) with various different WLAN (802.11) flavours.
The measurement hosts have been 25 metres apart from each other; loss is
again ignored.
OSBRiDGE 3GN – 802.11n Access Point and UMTS/GSM Gateway in one device
Wi-Fi allows wireless deployment of local area networks (LANs). Also,
spaces where cables cannot be run, such as outdoor areas and historical
buildings, can host wireless LANs. However, building walls of certain
materials, such as stone with high metal content, can block Wi-Fi
signals.
Since the early 2000s, manufacturers are building wireless network adapters into most laptops. The price of chipsets for Wi-Fi continues to drop, making it an economical networking option included in ever more devices.
Different competitive brands of access points and client
network-interfaces can inter-operate at a basic level of service.
Products designated as "Wi-Fi Certified" by the Wi-Fi Alliance are backward compatible. Unlike mobile phones, any standard Wi-Fi device works anywhere in the world.
Access point
An AirPort wireless G Wi-Fi adapter from an Apple MacBook.
A wireless access point (WAP) connects a group of wireless devices to an adjacent wired LAN. An access point resembles a network hub, relaying data
between connected wireless devices in addition to a (usually) single
connected wired device, most often an Ethernet hub or switch, allowing
wireless devices to communicate with other wired devices.
Wireless adapters allow devices to connect to a wireless network.
These adapters connect to devices using various external or internal
interconnects such as PCI, miniPCI, USB, ExpressCard, Cardbus and PC Card. As of 2010, most newer laptop computers come equipped with built in internal adapters.
Router
Wireless routers integrate a Wireless Access Point, Ethernet switch, and internal router firmware application that provides IProuting, NAT, and DNS
forwarding through an integrated WAN-interface. A wireless router
allows wired and wireless Ethernet LAN devices to connect to a (usually)
single WAN device such as a cable modem, DSL modem or optical modem.
A wireless router allows all three devices, mainly the access point and
router, to be configured through one central utility. This utility is
usually an integrated web server
that is accessible to wired and wireless LAN clients and often
optionally to WAN clients. This utility may also be an application that
is run on a computer, as is the case with as Apple's AirPort, which is
managed with the AirPort Utility on macOS and iOS.
Wireless bridging can connect a wired network to a wireless
network. A bridge differs from an access point: an access point
typically connects wireless devices to one wired network. Two wireless
bridge devices may be used to connect two wired networks over a wireless
link, useful in situations where a wired connection may be unavailable,
such as between two separate homes or for devices that have no wireless
networking capability (but have wired networking capability), such as consumer entertainment devices;
alternatively, a wireless bridge can be used to enable a device that
supports a wired connection to operate at a wireless networking standard
that is faster than supported by the wireless network connectivity
feature (external dongle or inbuilt) supported by the device (e.g.,
enabling Wireless-N speeds (up to the maximum supported speed on the
wired Ethernet port on both the bridge and connected devices including
the wireless access point) for a device that only supports Wireless-G).
A dual-band wireless bridge can also be used to enable 5 GHz wireless
network operation on a device that only supports 2.4 GHz wireless and
has a wired Ethernet port.
Wireless range-extenders or wireless repeaters can extend the
range of an existing wireless network. Strategically placed
range-extenders can elongate a signal area or allow for the signal area
to reach around barriers such as those pertaining in L-shaped corridors.
Wireless devices connected through repeaters suffer from an increased
latency for each hop, and there may be a reduction in the maximum
available data throughput. In addition, the effect of additional users
using a network employing wireless range-extenders is to consume the
available bandwidth faster than would be the case whereby a single user
migrates around a network employing extenders. For this reason, wireless
range-extenders work best in networks supporting low traffic throughput
requirements, such as for cases whereby a single user with a Wi-Fi
equipped tablet migrates around the combined extended and non-extended
portions of the total connected network. Also, a wireless device
connected to any of the repeaters in the chain has data throughput
limited by the "weakest link" in the chain between the connection origin
and connection end. Networks using wireless extenders are more prone to
degradation from interference from neighboring access points that
border portions of the extended network and that happen to occupy the
same channel as the extended network.
Embedded systems
Embedded serial-to-Wi-Fi module
The security standard, Wi-Fi Protected Setup,
allows embedded devices with limited graphical user interface to
connect to the Internet with ease. Wi-Fi Protected Setup has 2
configurations: The Push Button configuration and the PIN configuration.
These embedded devices are also called The Internet of Things
and are low-power, battery-operated embedded systems. A number of Wi-Fi
manufacturers design chips and modules for embedded Wi-Fi, such as
GainSpan.
Increasingly in the last few years (particularly as of 2007),
embedded Wi-Fi modules have become available that incorporate a
real-time operating system and provide a simple means of wirelessly
enabling any device that can communicate via a serial port.
This allows the design of simple monitoring devices. An example is a
portable ECG device monitoring a patient at home. This Wi-Fi-enabled
device can communicate via the Internet.
These Wi-Fi modules are designed by OEMs so that implementers need only minimal Wi-Fi knowledge to provide Wi-Fi connectivity for their products.
In June 2014, Texas Instruments
introduced the first ARM Cortex-M4 microcontroller with an onboard
dedicated Wi-Fi MCU, the SimpleLink CC3200. It makes embedded systems
with Wi-Fi connectivity possible to build as single-chip devices, which
reduces their cost and minimum size, making it more practical to build
wireless-networked controllers into inexpensive ordinary objects.
Network security
The main issue with wireless network security
is its simplified access to the network compared to traditional wired
networks such as Ethernet. With wired networking, one must either gain
access to a building (physically connecting into the internal network),
or break through an external firewall.
To access Wi-Fi, one must merely be within the range of the Wi-Fi
network. Most business networks protect sensitive data and systems by
attempting to disallow external access. Enabling wireless connectivity
reduces security if the network uses inadequate or no encryption.
An attacker who has gained access to a Wi-Fi network router can
initiate a DNS spoofing attack against any other user of the network by
forging a response before the queried DNS server has a chance to reply.
Securing methods
A
common measure to deter unauthorized users involves hiding the access
point's name by disabling the SSID broadcast. While effective against
the casual user, it is ineffective as a security method because the SSID
is broadcast in the clear in response to a client SSID query. Another
method is to only allow computers with known MAC addresses to join the network, but determined eavesdroppers may be able to join the network by spoofing an authorized address.
Wired Equivalent Privacy (WEP) encryption was designed to protect against casual snooping but it is no longer considered secure. Tools such as AirSnort or Aircrack-ng can quickly recover WEP encryption keys. Because of WEP's weakness the Wi-Fi Alliance approved Wi-Fi Protected Access (WPA) which uses TKIP.
WPA was specifically designed to work with older equipment usually
through a firmware upgrade. Though more secure than WEP, WPA has known
vulnerabilities.
The more secure WPA2 using Advanced Encryption Standard was introduced in 2004 and is supported by most new Wi-Fi devices. WPA2 is fully compatible with WPA. In 2017, a flaw in the WPA2 protocol was discovered, allowing a key replay attack, known as KRACK.
A flaw in a feature added to Wi-Fi in 2007, called Wi-Fi
Protected Setup (WPS), let WPA and WPA2 security be bypassed, and
effectively broken in many situations. The only remedy as of late 2011
was to turn off Wi-Fi Protected Setup, which is not always possible.
Virtual Private Networks can be used to improve the confidentiality of data carried through Wi-Fi networks, especially public Wi-Fi networks.
Data security risks
The older wireless encryption-standard, Wired Equivalent Privacy (WEP), has been shown
easily breakable even when correctly configured. Wi-Fi Protected Access
(WPA and WPA2) encryption, which became available in devices in 2003,
aimed to solve this problem. Wi-Fi access points typically default to an
encryption-free (open) mode. Novice users benefit from a zero-configuration device that works out-of-the-box, but this default does not enable any wireless security,
providing open wireless access to a LAN. To turn security on requires
the user to configure the device, usually via a software graphical user interface
(GUI). On unencrypted Wi-Fi networks connecting devices can monitor and
record data (including personal information). Such networks can only be
secured by using other means of protection, such as a VPN or secure Hypertext Transfer Protocol over Transport Layer Security (HTTPS).
Wi-Fi Protected Access encryption (WPA2) is considered secure, provided a strong passphrase is used. In 2018, WPA3 was announced as a replacement for WPA2, increasing security; it rolled out on June 26.
Piggybacking
Piggybacking refers to access to a wireless Internet connection by
bringing one's own computer within the range of another's wireless
connection, and using that service without the subscriber's explicit
permission or knowledge.
During the early popular adoption of 802.11, providing open access points for anyone within range to use was encouraged to cultivate wireless community networks, particularly since people on average use only a fraction of their downstream bandwidth at any given time.
Recreational logging and mapping of other people's access points has become known as wardriving.
Indeed, many access points are intentionally installed without security
turned on so that they can be used as a free service. Providing access
to one's Internet connection in this fashion may breach the Terms of
Service or contract with the ISP. These activities do not result in sanctions in most jurisdictions; however, legislation and case law differ considerably across the world. A proposal to leave graffiti describing available services was called warchalking.
Piggybacking often occurs unintentionally – a technically
unfamiliar user might not change the default "unsecured" settings to
their access point and operating systems can be configured to connect
automatically to any available wireless network. A user who happens to
start up a laptop in the vicinity of an access point may find the
computer has joined the network without any visible indication.
Moreover, a user intending to join one network may instead end up on
another one if the latter has a stronger signal. In combination with
automatic discovery of other network resources (see DHCP and Zeroconf) this could possibly lead wireless users to send sensitive data to the wrong middle-man when seeking a destination (see man-in-the-middle attack). For example, a user could inadvertently use an unsecure network to log into a website, thereby making the login credentials available to anyone listening, if the website uses an unsecure protocol such as plain HTTP without TLS.
An unauthorized user can obtain security information (factory
preset passphrase and/or Wi-Fi Protected Setup PIN) from a label on a
wireless access point can use this information (or connect by the Wi-Fi
Protected Setup pushbutton method) to commit unauthorized and/or
unlawful activities.
Health concerns
The World Health Organization
(WHO) says, "no health effects are expected from exposure to RF fields
from base stations and wireless networks", but notes that they promote
research into effects from other RF sources. Although the WHO's International Agency for Research on Cancer (IARC) later classified radio-frequency electromagnetic fields (EMFs) as "possibly carcinogenic to humans (Group 2B)"
(a category used when "a causal association is considered credible, but
when chance, bias or confounding cannot be ruled out with reasonable
confidence"), this classification was based on risks associated with wireless phone use rather than Wi-Fi networks.
The United Kingdom's Health Protection Agency
reported in 2007 that exposure to Wi-Fi for a year results in the "same
amount of radiation from a 20-minute mobile phone call".
A review of studies involving 725 people who claimed electromagnetic hypersensitivity,
"...suggests that 'electromagnetic hypersensitivity' is unrelated to
the presence of an EMF, although more research into this phenomenon is
required."
Alternatives
A number of other "wireless" technologies provide alternatives to Wi-Fi in some cases:
