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104-408: Being the first Wi-Fi standard to introduce MIMO support, devices and systems which supported the 802.11n standard (or draft versions thereof) were sometimes referred to as MIMO Wi-Fi products, especially prior to the introduction of the next generation standard. The use of MIMO- OFDM (orthogonal frequency division multiplexing) to increase the data rate while maintaining the same spectrum as 802.11a

208-543: A BPSK , QPSK , 16- QAM or 64- QAM . The total bandwidth is 20 MHz with an occupied bandwidth of 17.8 MHz. Total symbol duration is 3.6 or 4 microseconds , which includes a guard interval of 0.4 (also known as short guard interval (SGI)) or 0.8 microseconds. PHY level data rate does not match user level throughput because of 802.11 protocol overheads, like the contention process, interframe spacing, PHY level headers (Preamble + PLCP) and acknowledgment frames. The main media access control (MAC) feature that provides

312-450: 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. Routers often incorporate a digital subscriber line modem or a cable modem and a Wi-Fi access point, are frequently set up in homes and other buildings, to provide Internet access for

416-527: A 2.0. Furthermore, it has affirmed that all draft-n certified products remain compatible with the products conforming to the final standards. After the first draft of the IEEE 802.11n standard was published in 2006, many manufacturers began producing so-called " draft-n " products that claimed to comply with the standard draft, even before standard finalization which mean they might not be inter-operational with products produced according to IEEE 802.11 standard after

520-637: A block have been received, and so a longer block-length, T {\displaystyle T} , results in a longer decoding delay. One particular example, for 16 transmit antennas, has rate-9/16 and a block length of 22 880 time-slots! It has been proven that the highest rate any n T {\displaystyle n_{T}} -antenna code can achieve is where n T = 2 n 0 {\displaystyle n_{T}=2n_{0}} or n T = 2 n 0 − 1 {\displaystyle n_{T}=2n_{0}-1} , if no linear processing

624-456: A channel at a time. Wi-Fi's radio bands 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. The range of an access point is about 20 m (66 ft) indoors, while some access points claim up to a 150 m (490 ft) range outdoors. Hotspot coverage can be as small as

728-447: A city-wide campaign to convert old phone booths into digital kiosks in 2014. The project, titled LinkNYC , has created a network of kiosks that serve as public Wi-Fi hotspots, high-definition screens and landlines . Installation of the screens began in late 2015. The city government plans to implement more than seven thousand kiosks over time, eventually making LinkNYC the largest and fastest public, government-operated Wi-Fi network in

832-602: A codeword and call an erroneously decoded received codeword Then the matrix has to be full- rank for any pair of distinct codewords c {\displaystyle \mathbf {c} } and e {\displaystyle \mathbf {e} } to give the maximum possible diversity order of n T n R {\displaystyle n_{T}n_{R}} . If instead, B ( c , e ) {\displaystyle \mathbf {B} (\mathbf {c} ,\mathbf {e} )} has minimum rank b {\displaystyle b} over

936-409: 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, the equipment listed the versions of Wi-Fi supported using the name of the IEEE standards. In 2018,

1040-407: 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 in which all communications go through a base station. Ad hoc mode refers to devices communicating directly with each other, without communicating with an access point. A service set is the set of all the devices associated with

1144-401: A data stream across a number of antennas and to exploit the various received versions of the data to improve the reliability of data transfer. The fact that the transmitted signal must traverse a potentially difficult environment with scattering , reflection , refraction and so on and may then be further corrupted by thermal noise in the receiver means that some of the received copies of

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1248-641: A greater degree by common building materials than the 2.4 GHz bands and usually give a shorter range. As 802.11 specifications evolved to support higher throughput, the protocols have become much more efficient in their bandwidth use. Additionally, they have gained the ability to aggregate channels together to gain still more throughput where the bandwidth for additional channels is available. 802.11n allows for double radio spectrum bandwidth (40 MHz) per channel compared to 802.11a or 802.11g (20 MHz). 802.11n can be set to limit itself to 20 MHz bandwidth to prevent interference in dense communities. In

1352-574: A link. An alternative approach to utilizing multiple antennas relies on having multiple transmit antennas and only optionally multiple receive antennas. Proposed by Vahid Tarokh , Nambi Seshadri and Robert Calderbank , these space–time codes (STCs) achieve significant error rate improvements over single-antenna systems. Their original scheme was based on trellis codes but the simpler block codes were utilised by Siavash Alamouti , and later Vahid Tarokh , Hamid Jafarkhani and Robert Calderbank to develop space–time block-codes (STBCs). STC involves

1456-413: A method of encoding which enables full diversity with linear processing at the receiver. Earlier proposals for transmit diversity required processing schemes which scaled exponentially with the number of transmit antennas. Furthermore, it was the first open-loop transmit diversity technique which had this capability. Subsequent generalizations of Alamouti's concept have led to a tremendous impact on

1560-426: 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, mesh, or a combination. Each service set has an associated identifier, a 32-byte service set identifier (SSID), which identifies the network. The SSID is configured within the devices that are part of the network. A basic service set (BSS) is a group of stations that share

1664-424: A performance improvement is aggregation. Two types of aggregation are defined: Frame aggregation is a process of packing multiple MSDUs or MPDUs together to reduce the overheads and average them over multiple frames, thereby increasing the user level data rate. A-MPDU aggregation requires the use of block acknowledgement or BlockAck, which was introduced in 802.11e and has been optimized in 802.11n. When 802.11g

1768-566: A sample of additive white Gaussian noise ( AWGN ). The maximum-likelihood detection rule is to form the decision variables where δ k ( i ) {\displaystyle \delta _{k}(i)} is the sign of s i {\displaystyle s_{i}} in the k {\displaystyle k} row of the coding matrix, ϵ k ( p ) = q {\displaystyle \epsilon _{k}(p)=q} denotes that s p {\displaystyle s_{p}}

1872-489: A single 20 MHz channel with one antenna and 400 ns guard interval ); 802.11n's speed may go up to 150 megabits per second if there are not other Bluetooth, microwave or Wi-Fi emissions in the neighborhood by using two 20 MHz channels in 40 MHz mode. If more antennas are used, then 802.11n can go up to 288 megabits per second in 20 MHz mode with four antennas, or 600 megabits per second in 40 MHz mode with four antennas and 400 ns guard interval. Because

1976-413: A single antenna. One way it provides this is through spatial division multiplexing (SDM), which spatially multiplexes multiple independent data streams, transferred simultaneously within one spectral channel of bandwidth. MIMO SDM can significantly increase data throughput as the number of resolved spatial data streams is increased. Each spatial stream requires a discrete antenna at both the transmitter and

2080-410: A single carrier, whereas 802.11a, Wi-Fi 4, 5 and 6 use orthogonal frequency-division multiplexing . Channels are used half duplex and can be time-shared by multiple networks. Any packet sent by one computer is locally received by stations tuned to that channel, even if that information is intended for just one destination. Stations typically ignore information not addressed to them. The use of

2184-458: A single room with walls that block radio waves or as large as many square kilometers using many overlapping access points with roaming permitted between them. Over time, the speed and spectral efficiency of Wi-Fi have increased. As of 2019, some versions of Wi-Fi, running on suitable hardware at close range, can achieve speeds of 9.6 Gbit/s ( gigabit per second). A 1985 ruling by the U.S. Federal Communications Commission released parts of

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2288-678: A wider channel for higher throughput. Countries apply their own regulations to the allowable channels, allowed users and maximum power levels within these frequency ranges. 802.11b/g/n can use the 2.4 GHz band, operating in the United States under FCC Part 15 rules and regulations. In this frequency band, equipment may occasionally suffer interference from microwave ovens, cordless telephones , USB 3.0 hubs, Bluetooth and other devices. Spectrum assignments and operational limitations are not consistent worldwide: Australia and Europe allow for an additional two channels (12, 13) beyond

2392-449: Is (up to a sign difference), the ( k , q ) {\displaystyle (k,q)} element of the coding matrix, for i = 1 , 2 , … , n T {\displaystyle i=1,2,\ldots ,n_{T}} and then decide on constellation symbol s i {\displaystyle s_{i}} that satisfies with A {\displaystyle {\mathcal {A}}}

2496-568: Is allowed in the code matrix (the above maximal rate proved in only applies to the original definition of orthogonal designs, i.e., any entry in the matrix is 0 , c i , − c i , c i ∗ , {\displaystyle 0,c_{i},-c_{i},c_{i}^{*},} , or − c i ∗ {\displaystyle -c_{i}^{*}} , which forces that any variable c i {\displaystyle c_{i}} can not be repeated in any column of

2600-432: Is divided into a multitude of channels . In the standards, channels are numbered at 5 MHz spacing within a band (except in the 60 GHz band, where they are 2.16 GHz apart), and the number refers to the centre frequency of the channel. Although channels are numbered at 5 MHz spacing, transmitters generally occupy at least 20 MHz, and standards allow for neighbouring channels to be bonded together to form

2704-454: Is not necessary to have multiple receive antennas, although to do so improves performance. This process of receiving diverse copies of the data is known as diversity reception and is what was largely studied until Foschini's 1998 paper. An STBC is usually represented by a matrix . Each row represents a time slot and each column represents one antenna's transmissions over time. Here, s i j {\displaystyle s_{ij}}

2808-423: Is not usually significant as it lies at the edges of the bands, and so two 40 MHz bands typically work unless the transmitters are physically very closely spaced. The specification calls for requiring one primary 20 MHz channel as well as a secondary adjacent channel spaced ±20 MHz away. The primary channel is used for communications with clients incapable of 40 MHz mode. When in 40 MHz mode,

2912-418: Is now Clause 20 of the published IEEE 802.11-2012 standard and subsequently renamed to clause 19 of the published IEEE 802.11-2020 standard. IEEE 802.11n is an amendment to IEEE 802.11-2007 as amended by IEEE 802.11k-2008 , IEEE 802.11r-2008 , IEEE 802.11y-2008 , and IEEE 802.11w-2009 , and builds on previous 802.11 standards by adding a multiple-input multiple-output (MIMO) system and 40 MHz channels to

3016-404: Is only true for complex modulation symbols. Since almost all constellation diagrams rely on complex numbers however, this property usually gives Alamouti's code a significant advantage over the higher-order STBCs even though they achieve a better error-rate performance. See ' Rate limits ' for more detail. The significance of Alamouti's proposal in 1998 is that it was the first demonstration of

3120-399: Is recommended. The 5 GHz band has substantial capacity due to many non-overlapping radio channels and less radio interference as compared to the 2.4 GHz band. An 802.11n-only network may be impractical for many users because they need to support legacy equipment that still is 802.11b/g only. In a mixed-mode system, an optimal solution would be to use a dual-radio access point and place

3224-635: Is simply referred to as WLAN , and it may or may not work with " Wi-Fi Certified " devices. As of 2017, the Wi-Fi Alliance consisted of more than 800 companies from around the world. As of 2019, over 3.05 billion Wi-Fi-enabled devices are shipped globally each year. Wi-Fi uses multiple parts of the IEEE 802 protocol family and is designed to work seamlessly with its wired sibling, Ethernet . Compatible devices can network through wireless access points with each other as well as with wired devices and

IEEE 802.11n-2009 - Misplaced Pages Continue

3328-641: 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. Equipment frequently supports multiple versions of Wi-Fi. To communicate, devices must use

3432-548: Is that it has uneven power among the symbols it transmits. This means that the signal does not have a constant envelope and that the power each antenna must transmit has to vary, both of which are undesirable. Modified versions of this code that overcome this problem have since been designed. Two straightforward codes for 4 transmit antennas are: These codes achieve rate-1/2 and rate-3/4 respectively, as for their 3-antenna counterparts. C 4 , 3 / 4 {\displaystyle C_{4,3/4}} exhibits

3536-433: Is the modulation and coding scheme index , or MCS index . The table below shows the relationships between the variables that allow for the maximum data rate. GI (Guard Interval): Timing between symbols. 20 MHz channel uses an FFT of 64, of which: 56 OFDM subcarriers, 52 are for data and 4 are pilot tones with a carrier separation of 0.3125 MHz (20 MHz/64) (3.2 μs). Each of these subcarriers can be

3640-423: Is the modulated symbol to be transmitted in time slot i {\displaystyle i} from antenna j {\displaystyle j} . There are to be T {\displaystyle T} time slots and n T {\displaystyle n_{T}} transmit antennas as well as n R {\displaystyle n_{R}} receive antennas. This block

3744-514: Is the maximum number of receive antennas or receiving RF chains that can be used by the radio. The third number ( c ) is the maximum number of data spatial streams the radio can use. For example, a radio that can transmit on two antennas and receive on three, but can only send or receive two data streams, would be 2 × 3 : 2. The 802.11n draft allows up to 4 × 4 : 4. Common configurations of 11n devices are 2 × 2 : 2 , 2 × 3 : 2 , and 3 × 2 : 2 . All three configurations have

3848-401: Is the path gain from transmit antenna i {\displaystyle i} to receive antenna j {\displaystyle j} , s t i {\displaystyle s_{t}^{i}} is the signal transmitted by transmit antenna i {\displaystyle i} and n t j {\displaystyle n_{t}^{j}} is

3952-417: Is used in applications such as motion detection and gesture recognition . Wi-Fi stations communicate by sending each other data packets , blocks of data individually sent and delivered over radio on various channels. As with all radio, this is done by the modulation and demodulation of carrier waves . Different versions of Wi-Fi use different techniques, 802.11b uses direct-sequence spread spectrum on

4056-469: Is usually considered to be of 'length' T {\displaystyle T} The code rate of an STBC measures how many symbols per time slot it transmits on average over the course of one block. If a block encodes k {\displaystyle k} symbols, the code-rate is Only one standard STBC can achieve full-rate (rate 1) — Alamouti's code . STBCs as originally introduced, and as usually studied, are orthogonal . This means that

4160-551: The Eduroam international authentication infrastructure. 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 whole city and a few nearby villages. In 2005, St. Cloud, Florida and Sunnyvale, California , became

4264-652: The ISM bands for unlicensed use for communications. These frequency bands include the same 2.4 GHz bands used by equipment such as microwave ovens , and are thus subject to interference. In 1991 in Nieuwegein , the NCR Corporation and AT&T invented the precursor to 802.11, intended for use in cashier systems, under the name WaveLAN . NCR's Vic Hayes , who held the chair of IEEE 802.11 for ten years, along with Bell Labs engineer Bruce Tuch, approached

IEEE 802.11n-2009 - Misplaced Pages Continue

4368-586: The Institute of Electrical and Electronics Engineers (IEEE) to create a standard and were involved in designing the initial 802.11b and 802.11a specifications within the IEEE. They have both been subsequently inducted into the Wi-Fi NOW Hall of Fame. In 1989 in Australia, a team of scientists began working on wireless LAN technology. A prototype test bed for a wireless local area network (WLAN)

4472-522: The PHY (physical layer) and frame aggregation to the MAC layer . There were older proprietary implementations of MIMO and 40MHz channels such as Xpress , Super G and Nitro which were based upon 802.11g and 802.11a technology, but this was the first time it was standardized across all radio manufacturers. MIMO is a technology that uses multiple antennas to coherently resolve more information than possible using

4576-516: The Wi-Fi Alliance formed as a trade association to hold the Wi-Fi trademark under which most IEEE 802.11 products are sold. The major commercial breakthrough came with Apple Inc. adopting Wi-Fi for their iBook series of laptops in 1999. It was the first mass consumer product to offer Wi-Fi network connectivity, which was then branded by Apple as AirPort . This was in collaboration with

4680-853: The Wi-Fi Alliance introduced simplified Wi-Fi generational numbering to indicate equipment that supports Wi-Fi 4 ( 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 has stated that the generational level 4, 5, or 6 can be indicated in the user interface when connected, along with the signal strength. The most important standards affecting Wi‑Fi are: 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 . 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

4784-524: The constellation alphabet . Despite its appearance, this is a simple, linear decoding scheme that provides maximal diversity. Apart from there being no full-rate, complex, orthogonal STBC for more than 2 antennas, it has been further shown that, for more than two antennas, the maximum possible rate is 3/4. Codes have been designed which achieve a good proportion of this, but they have very long block-length. This makes them unsuitable for practical use, because decoding cannot proceed until all transmissions in

4888-455: The 11 permitted in the United States for the 2.4 GHz band, while Japan has three more (12–14). 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. This is in contrast to the 2.4 GHz frequency band where the channels are only 5 MHz wide. In general, lower frequencies have longer range but have less capacity. The 5 GHz bands are absorbed to

4992-464: The 2.4 GHz band is seriously congested in most urban areas, 802.11n networks usually have more success in increasing data rate by utilizing more antennas in 20 MHz mode rather than by operating in the 40 MHz mode, as the 40 MHz mode requires a relatively free radio spectrum which is only available in rural areas away from cities. Thus, network engineers installing an 802.11n network should strive to select routers and wireless clients with

5096-408: The 5 GHz band, 20 MHz, 40 MHz, 80 MHz, and 160 MHz channels are permitted with some restrictions, giving much faster connections. 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

5200-400: The 5 GHz band, leaving the 2.4 GHz band for legacy clients. Band steering works by responding only to 5 GHz association requests and not the 2.4 GHz requests from dual-band clients. The 2.4 GHz  ISM band is fairly congested. With 802.11n, there is the option to double the bandwidth per channel to 40 MHz (fat channel) which results in slightly more than double

5304-445: The 802.11b/g traffic on the 2.4 GHz radio and the 802.11n traffic on the 5 GHz radio. This setup assumes that all the 802.11n clients are 5 GHz capable, which is not a requirement of the standard. 5 GHz is optional on Wi-Fi 4; quite some Wi-Fi 4 capable devices only support 2.4 GHz and there is no practical way to upgrade them to support 5 GHz. Some enterprise-grade APs use band steering to send 802.11n clients to

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5408-596: The Internet. Different versions of Wi-Fi are specified by various IEEE 802.11 protocol standards, with different radio technologies determining radio bands, 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) SHF radio bands, with the 6 gigahertz SHF band used in newer generations of the standard; these bands are subdivided into multiple channels. Channels can be shared between networks, but, within range, only one transmitter can transmit on

5512-615: The Internet. The coverage of one or more interconnected access points 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 services 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

5616-594: 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, 6, 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

5720-581: The Netherlands simultaneously claim the invention of Wi-Fi, and a consensus has not been reached globally. In 2009, the Australian CSIRO was awarded $ 200 million after a patent settlement with 14 technology companies, with a further $ 220 million awarded in 2012 after legal proceedings with 23 companies. In 2016, the CSIRO's WLAN prototype test bed was chosen as Australia's contribution to

5824-589: The PHY data rate available over a single 20 MHz channel. It can be enabled in the 5 GHz mode, or within the 2.4 GHz mode if there is knowledge that it will not interfere with any other 802.11 or non-802.11 (such as Bluetooth) system using the same frequencies. The MIMO architecture, together with the wider channels, offers increased physical transfer rate over standard 802.11a (5 GHz) and 802.11g (2.4 GHz). The transmitter and receiver use precoding and postcoding techniques, respectively, to achieve

5928-497: The STBC is designed such that the vectors representing any pair of columns taken from the coding matrix is orthogonal. The result of this is simple, linear , optimal decoding at the receiver. Its most serious disadvantage is that all but one of the codes that satisfy this criterion must sacrifice some proportion of their data rate (see Alamouti's code ). Moreover, there exist quasi-orthogonal STBCs that achieve higher data rates at

6032-543: The Wi-Fi Alliance did use 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. IEEE is a separate, but related, organization and their website has stated "WiFi is a short name for Wireless Fidelity". The name Wi-Fi was partly chosen because it sounds similar to Hi-Fi , which consumers take to mean high fidelity or high quality . Interbrand hoped consumers would find

6136-413: The Wi-Fi Alliance, the term Wi-Fi was chosen from a list of ten names that Interbrand proposed. Interbrand also created the Wi-Fi logo . The yin-yang Wi-Fi logo indicates the certification of a product for interoperability . The name is often written as WiFi , Wifi , or wifi , but these are not approved by the Wi-Fi Alliance. The name Wi-Fi is not short-form for 'Wireless Fidelity', although

6240-605: The basis for wireless network products using the Wi-Fi brand. While each amendment is officially revoked when 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

6344-481: The capability. 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 existed. Many universities collaborate in providing Wi-Fi access to students and staff through

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6448-404: The capacity of a MIMO link. Precoding includes spatial beamforming and spatial coding, where spatial beamforming improves the received signal quality at the decoding stage. Spatial coding can increase data throughput via spatial multiplexing and increase range by exploiting the spatial diversity, through techniques such as Alamouti coding . The number of simultaneous data streams is limited by

6552-506: The center frequency is actually the mean of the primary and secondary channels. Local regulations may restrict certain channels from operation. For example, Channels 12 and 13 are normally unavailable for use as either a primary or secondary channel in North America. For further information, see List of WLAN channels . The Wi-Fi Alliance has upgraded its suite of compatibility tests for some enhancements that were finalized after

6656-569: The channel to be idle at the same time and thus begin transmission simultaneously. A collision happens when a station receives signals from multiple stations on a channel at the same time. This corrupts the transmitted data and can require stations to re-transmit. The lost data and re-transmission reduces throughput, in some cases severely. The 802.11 standard provides several distinct radio frequency ranges for use in Wi-Fi communications: 900  MHz , 2.4 GHz, 3.6 GHz, 4.9 GHz, 5 GHz, 6 GHz and 60 GHz bands . Each range

6760-440: The code is full-rate and still only requires linear processing at the receiver, although decoding is slightly more complex than for orthogonal STBCs. Results show that this Q-STBC outperforms (in a bit-error rate sense) the fully orthogonal 4-antenna STBC over a good range of signal-to-noise ratios (SNRs). At high SNRs, though (above about 22 dB in this particular case), the increased diversity offered by orthogonal STBCs yields

6864-432: The coding matrix: where * denotes complex conjugate . It is readily apparent that this is a rate-1 code. It takes two time-slots to transmit two symbols. Using the optimal decoding scheme discussed below, the bit-error rate (BER) of this STBC is equivalent to 2 n R {\displaystyle 2n_{R}} -branch maximal ratio combining (MRC). This is a result of the perfect orthogonality between

6968-469: The consumer and enterprise spaces have built products that have achieved this certification. The following are milestones in the development of 802.11n: Wi-Fi Wi-Fi ( / ˈ w aɪ f aɪ / ) is a family of wireless network protocols based on the IEEE 802.11 family of standards, which are commonly used for local area networking of devices and Internet access, allowing nearby digital devices to exchange data by radio waves . These are

7072-438: The cost of inter-symbol interference (ISI). Thus, their error-rate performance is lower bounded by the one of orthogonal rate 1 STBCs, that provide ISI free transmissions due to orthogonality. The design of STBCs is based on the so-called diversity criterion derived by Tarokh et al. in their earlier paper on space–time trellis codes . Orthogonal STBCs can be shown to achieve the maximum diversity allowed by this criterion. Call

7176-401: The data may be closer to the original signal than others. This redundancy results in a higher chance of being able to use one or more of the received copies to correctly decode the received signal. In fact, space–time coding combines all the copies of the received signal in an optimal way to extract as much information from each of them as possible. Most work on wireless communications until

7280-400: The data rate. However, in North America, when in 2.4 GHz, enabling this option takes up to 82% of the unlicensed band. For example, channel 3 SCA (secondary channel above), also known as 3+7, reserves the first 9 out of the 11 channels available. In Europe and other places where channels 1–13 are available, allocating 1+5 uses slightly more than 50% of the channels, but the overlap with 9+13

7384-519: The database. Signal fluctuations can cause errors, which can be reduced with noise-filtering techniques. For low precision, integrating Wi-Fi data with geographical and time information has been proposed. The Wi-Fi RTT capability introduced in IEEE 802.11mc allows for positioning based on round trip time measurement, an improvement over the RSSI method. The IEEE 802.11az standard promises further improvements in geolocation accuracy. Wi-Fi sensing

7488-405: The early 1990s had focused on having an antenna array at only one end of the wireless link — usually at the receiver. Seminal papers by Gerard J. Foschini and Michael J. Gans, Foschini and Emre Telatar enlarged the scope of wireless communication possibilities by showing that for the highly scattering environment, substantial capacity gains are enabled when antenna arrays are used at both ends of

7592-516: The exhibition A History of the World in 100 Objects held in the National Museum of Australia . 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'." According to Phil Belanger, a founding member of

7696-414: The first cities in the United States to offer citywide free Wi-Fi (from MetroFi ). Minneapolis has generated $ 1.2 million in profit annually for its provider . In May 2010, the then 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. New York City announced

7800-496: The matrix). This rate limit is conjectured to hold for any complex orthogonal space–time block codes even when any linear processing is allowed among the complex variables. Closed-form recursive designs have been found. These codes exhibit partial orthogonality and provide only part of the diversity gain mentioned above . An example reported by Hamid Jafarkhani is: The orthogonality criterion only holds for columns (1 and 2), (1 and 3), (2 and 4) and (3 and 4). Crucially, however,

7904-404: The minimum number of antennas in use on both sides of the link. However, the individual radios often further limit the number of spatial streams that may carry unique data. The a × b  : c notation helps identify what a given radio is capable of. The first number ( a ) is the maximum number of transmit antennas or transmitting TF chains that can be used by the radio. The second number ( b )

8008-453: The most antennas possible (one, two, three or four as specified by the 802.11n standard) and try to make sure that the network's bandwidth will be satisfactory even on the 20 MHz mode. Data rates up to 600 Mbit/s are achieved only with the maximum of four spatial streams using one 40 MHz-wide channel. Various modulation schemes and coding rates are defined by the standard, which also assigns an arbitrary number to each; this number

8112-476: The most widely used computer networks, used globally in home and small office networks to link devices and to provide Internet access with wireless routers and wireless access points in public places such as coffee shops, hotels, libraries, and airports. Wi-Fi is a trademark of the Wi-Fi Alliance , which restricts the use of the term " Wi-Fi Certified " to products that successfully complete interoperability certification testing. Non-compliant hardware

8216-452: The name catchy, and that they would assume this wireless protocol has high fidelity because of its name. Other technologies intended for fixed points, including Motorola Canopy , are usually called fixed wireless . Alternative wireless technologies include Zigbee , Z-Wave , Bluetooth and mobile phone standards . To connect to a Wi-Fi LAN, a computer must be equipped with a wireless network interface controller . The combination of

8320-566: The project, which was to be completed in 2015. Wi-Fi positioning systems use known positions of Wi-Fi hotspots to identify a device's location. It is used when GPS isn't suitable due to issues like signal interference or slow satellite acquisition. This includes assisted GPS , urban hotspot databases, and indoor positioning systems. Wi-Fi positioning relies on measuring signal strength ( RSSI ) and fingerprinting. Parameters like SSID and MAC address are crucial for identifying access points. The accuracy depends on nearby access points in

8424-494: The protocol stack. For internetworking purposes, Wi-Fi is usually layered as a link layer 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. Space%E2%80%93time block code Space–time block coding is a technique used in wireless communications to transmit multiple copies of

8528-551: The range that employ that radio channel. While Ethernet has essentially negligible error rates, wireless communication media are subject to significant interference. Therefore, the 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

8632-504: The receiver uses the destination address to determine whether the transmission is relevant to the station or should be ignored. A scheme known as carrier-sense multiple access with collision avoidance (CSMA/CA) governs the way stations share channels. With CSMA/CA stations attempt to avoid collisions by beginning transmission only after the channel is sensed to be idle, but then transmit their packet data in its entirety. CSMA/CA cannot completely prevent collisions, as two stations may sense

8736-437: The receiver with only linear processing. In order to consider a decoding method, a model of the wireless communications system is needed. At time t {\displaystyle t} , the signal r t j {\displaystyle r_{t}^{j}} received at antenna j {\displaystyle j} is: where α i j {\displaystyle \alpha _{ij}}

8840-400: The receiver. In addition, MIMO technology requires a separate radio-frequency chain and analog-to-digital converter for each antenna, making it more expensive to implement than non-MIMO systems. Channels operating with a width of 40 MHz are another feature incorporated into 802.11n; this doubles the channel width from 20 MHz in previous 802.11 PHYs to transmit data, and provides twice

8944-467: The redundancy purely provides diversity in space and time. This is contrast with space–time trellis codes which provide both diversity and coding gain since they spread a conventional trellis code over space and time. Siavash Alamouti invented the simplest of all the STBCs in 1998, although he did not coin the term "space–time block code" himself. It was designed for a two-transmit antenna system and has

9048-400: The same channel also means that the data bandwidth is shared, so for example, available throughput to each device is halved when two stations are actively transmitting. As with other IEEE 802 LANs, stations come programmed with a globally unique 48-bit MAC address. The MAC addresses are used to specify both the destination and the source of each data packet. On the reception of a transmission,

9152-411: The same group that helped create the standard: Vic Hayes , Bruce Tuch, Cees Links , Rich McGinn, and others from Lucent . In the year 2000, Radiata, a group of Australian scientists connected to the CSIRO, were the first to use the 802.11a standard on chips connected to a Wi-Fi network. Wi-Fi uses a large number of patents held by many different organizations. Australia, the United States and

9256-457: The same maximum throughputs and features, and differ only in the amount of diversity the antenna systems provide. In addition, a fourth configuration, 3 × 3 : 3 is becoming common, which has a higher throughput, due to the additional data stream. Assuming equal operating parameters to an 802.11g network achieving 54 megabits per second (on a single 20 MHz channel with one antenna), an 802.11n network can achieve 72 megabits per second (on

9360-419: The same uneven power problems as C 3 , 3 / 4 {\displaystyle C_{3,3/4}} . An improved version of C 4 , 3 / 4 {\displaystyle C_{4,3/4}} is which has equal power from all antennas in all time-slots. One particularly attractive feature of orthogonal STBCs is that maximum likelihood decoding can be achieved at

9464-515: The same wireless channel, SSID, and other settings that have wirelessly connected, usually to the same access point. Each BSS is identified by a MAC address called the BSSID . The IEEE does not test equipment for compliance with their standards. The Wi-Fi Alliance was formed in 1999 to establish and enforce standards for interoperability and backward compatibility , and to promote wireless local-area-network technology. The Wi-Fi Alliance enforces

9568-409: The set of pairs of distinct codewords, then the space–time code offers diversity order b n R {\displaystyle bn_{R}} . An examination of the example STBCs shown below reveals that they all satisfy this criterion for maximum diversity. STBCs offer only diversity gain (compared to single-antenna schemes) and not coding gain. There is no coding scheme included here —

9672-489: The simple, linear decoding scheme that goes with their codes under perfect channel state information assumption. Two straightforward codes for 3 transmit antennas are: These codes achieve rate-1/2 and rate-3/4 respectively. These two matrices give examples of why codes for more than two antennas must sacrifice rate — it is the only way to achieve orthogonality. One particular problem with C 3 , 3 / 4 {\displaystyle C_{3,3/4}}

9776-628: The standard publication, nor even among themselves. The Wi-Fi Alliance began certifying products based on IEEE 802.11n draft 2.0 mid-2007. This certification program established a set of features and a level of interoperability across vendors supporting those features, thus providing one definition of "draft n" to ensure compatibility and interoperability. The baseline certification covers both 20 MHz and 40 MHz wide channels, and up to two spatial streams, for maximum throughputs of 144.4 Mbit/s for 20 MHz and 300 Mbit/s for 40 MHz (with short guard interval ). A number of vendors in both

9880-445: The structure. Similarly, battery-powered routers may include a mobile broadband modem and a Wi-Fi access point. When subscribed to a cellular data carrier, they allow nearby Wi-Fi stations to access the Internet. Many smartphones have a built-in mobile hotspot capability of this sort, though carriers often disable the feature, or charge a separate fee to enable it. Standalone devices such as MiFi - and WiBro -branded devices provide

9984-403: The symbols after receive processing — there are two copies of each symbol transmitted and n R {\displaystyle n_{R}} copies received. This is a very special STBC. It is the only orthogonal STBC that achieves rate-1. That is to say that it is the only STBC that can achieve its full diversity gain without needing to sacrifice its data rate. Strictly, this

10088-403: The transmission of multiple redundant copies of data to compensate for fading and thermal noise in the hope that some of them may arrive at the receiver in a better state than others. In the case of STBC in particular, the data stream to be transmitted is encoded in blocks , which are distributed among spaced antennas and across time. While it is necessary to have multiple transmit antennas, it

10192-514: The use of four spatial streams at a channel width of 40 MHz. IEEE 802.11n-2009 is an amendment to the IEEE 802.11-2007 wireless-networking standard. 802.11 is a set of IEEE standards that govern wireless networking transmission methods. They are commonly used today in their 802.11a , 802.11b , 802.11g , 802.11n, 802.11ac and 802.11ax versions to provide wireless connectivity in homes and businesses. Development of 802.11n began in 2002, seven years before publication. The 802.11n protocol

10296-762: The use of the Wi-Fi brand to technologies based on the IEEE 802.11 standards from the IEEE. 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

10400-494: The wireless communications industry. Tarokh et al. discovered a set of STBCs that are particularly straightforward, and coined the scheme's name. They also proved that no code for more than 2 transmit antennas could achieve full-rate. Their codes have since been improved upon (both by the original authors and by many others). Nevertheless, they serve as clear examples of why the rate cannot reach 1, and what other problems must be solved to produce 'good' STBCs. They also demonstrated

10504-639: The world. The UK has planned a similar project across major cities of the country, with the project's first implementation in the London Borough of Camden . Officials in South Korea's capital Seoul were 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 was planning to grant leases to KT, LG Telecom, and SK Telecom. The companies were supposed to invest $ 44 million in

10608-573: Was developed in 1992 by a team of researchers from the Radiophysics Division of the CSIRO (Commonwealth Scientific and Industrial Research Organisation) in Australia, led by John O'Sullivan . A patent for Wi Fi was lodged by the CSIRO in 1992 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. In 1999,

10712-458: Was first demonstrated by Airgo Networks. The purpose of the standard is to improve network throughput over the two previous standards— 802.11a and 802.11g —with a significant increase in the maximum net data rate from 54 Mbit/s to 72 Mbit/s with a single spatial stream in a 20 MHz channel, and 600 Mbit/s (slightly higher gross bit rate including for example error-correction codes, and slightly lower maximum throughput ) with

10816-426: Was released to share the band with existing 802.11b devices, it provided ways of ensuring backward compatibility between legacy and successor devices. 802.11n extends the coexistence management to protect its transmissions from legacy devices, which include 802.11g , 802.11b and 802.11a . There are MAC and PHY level protection mechanisms as listed below: To achieve maximum output, a pure 802.11n 5 GHz network

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