Enhancements of the IEEE 802.11 Medium Access Control ... - PATS

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Chapter 1. Introductiondesigned to improve on the 802.11g in the amount of bandwidth supported byutilizing multiple wireless signals and antennas (called Multiple-Input Multiple-Output - MIMO technology) instead of one. IEEE 802.11n offers high throughputwireless transmission up to 100Mbps - 300 Mbps. There are already many productson the market based on Draft 2.0 of this proposal. 802.11n is expected to befinalized in November 2009.The IEEE 802.11h [25] standard is supplementary to the MAC layer to complywith European regulations for 5GHz WLANs. Approved in September 2004, theIEEE 802.11h standard defines mechanisms (dynamic frequency selection (DFS)and transmit power control (TPC)) that 802.11a WLAN devices can use to complywith the ITU recommendations.The IEEE 802.11y [25], proposed amendment to the IEEE 802.11 standard, will allowfor Wi-Fi like equipment to operate on a secondary basis in licensed frequencybands (a co-primary basis in the 3650 to 3700 MHz band in the United States). Itwas approved for publication by the IEEE on September 26th, 2008.Table 1.2: EEE 802.11 protocols summaryProt. Date Frequ. Thr. Rate Mod. RangeI RangeO802.11 1997 2.4GHz 0.9Mbps 2Mbps FHSS 20m 100mDSSSThis specification has been extended into 802.11b.802.11a 1999 5GHz 23Mbps 54Mbps OFDM 35m 120m802.11a has 8 available channels.This specification is not interoperable with 802.11b.802.11b 1999 2.4GHz 4.3Mbps 11Mbps DSSS 38m 140mThis specification is not interoperable with 802.11a.802.11b has 14 channels available in 2.4GHz bandwith only 3 non-overlapping channels.It requires fewer access points than 802.11a for coverage of large areas.802.11g 2003 2.4GHz 19Mbps 54Mbps OFDM 38m 140mDSSSThis specification may replace 802.11b.OFDM above 20Mbps, DSSS with CCK below 20Mbps802.11n 2006-9 2.4/5GHz 74Mbps 248Mbps 70m 250m802.11y 2006-8 3.7GHz 23Mbps 54Mbps 50m 5000m12In Tab. 1.2 the summary of the 802.11x has been shown., where Prot. is protocol,Date is release date, Frequ. is frequency, Thr. is typical throughput, Rate is maximaldata rate, Mod. is modulation technique, RangeI is range as an indoor radium (inmeters), and RangeO is range as an outdoor radium.Apart from standards described above there also exist others e.g. 802.11e, 802.11i,802.11p etc. The 802.11e [26] is a proposed enhancement to the 802.11a and 802.11bWLAN specifications offering quality of service (QoS) features, including the pri-
1.4. Ad hoc network definition and applicationoritization of data, voice, and video transmissions.The 802.11i [27] is the security standard for Wi-Fi networks that upgrades theformer "official" wireless security standard, the much-maligned wired equivalentprivacy (WEP). The WEP has been found too easy to crack by those with the righttools and enough patience.The 802.11p [28] (as a draft amendment to the IEEE 802.11 standard) adds thewireless access in the vehicular environment (WAVE). The 802.11p defines enhancementsto the 802.11 standard in order to support Intelligent TransportationSystem (ITS) applications including the data exchange between high-speed vehiclesand between the vehicles and the roadside infrastructure in the licensed ITSband of 5.9 GHz (5.85-5.925 GHz).There also exist HiperLAN (HIgh PErformance Radio LAN) standards operatingin the 5GHz band but defined by the European Telecommunications StandardsInstitute (ETSI) instead of the IEEE. The HiperLAN/1 provides data rates up to20Mbps, the HiperLAN/2 up to 54Mbps. The HiperLAN/1 uses the CSMA/CAmodulation scheme (the standard covers the Physical layer and the Media AccessControl part of the Data link layer like 802.11), where HiperLAN/2 utilizes theOFDMA modulation scheme. The HiperLAN/1 requires no configuration andno central control, it is completely ad hoc. It does not provide real isochronousservices and it is expensive to maintain and operate. There also is no guaranteeof bandwidth using this standard. The HiperLAN/2 is designed in order to provideATM cells, IP packets, Firewire packets (IEEE 1394) and digital voice (fromcellular phones). It offers better quality of service than HiperLAN/1 and it alsoguarantees bandwidth.1.4 Ad hoc network definition and applicationWhat is really an ad hoc network? An ad hoc network is an infrastructurelessmulti-hop network without a centralized entity (Access Point), where every nodeacts as a router as illustrated in Fig. 1.4. According to SearchMobileComputing.comDefinitions "an ad-hoc (spontaneous) network is a local area network or other smallnetwork, especially one with wireless or temporary plug-in connections, in whichsome of the network devices are part of the network only for the duration of acommunications session or, in the case of mobile or portable devices, while insome close proximity to the rest of the network. In Latin, ad hoc literally meansfor this, further meaning for this purpose only, and thus usually temporary." In otherwords [29], an ad hoc network is a collection of communication devices (alsocalled nodes) that want to communicate, but there is no fixed infrastructure availableand there is also no pre-determined organization of available links. Since notall nodes can directly communicate with each other, nodes are required to relaypackets on behalf of other nodes in order to deliver data across the ad hoc network.Moreover, devices in ad hoc networks can be mobile and can use differentpower control practices and therefore the rapid changes in connectivity and link13
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CHAPTER9Contention Window resetting
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9.6. MobiNIAMac protocolthe results
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CHAPTER10Enhanced selection Bounds
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CHAPTER13Conclusions and Perspectiv
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Chapter 13. Conclusion and Perspect
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References[11] HSPA Mobile broadban
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References[43] Intelligent Transpor
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References[71] Chane L. Fullmer J.
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References[101] Mort Naraghi-Pour.
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References[130] P.K. Varshney J. De
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References[158] Q. Lindsey D. Lymbe
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Enhancements of the IEEE 802.11 Medium Access Control ... - PATS

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