Section 3.


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Part 3. Handoff Administration : Location and Task. Presentation. Talk about the handoff method in subtle element. This dialog is general, which applies to both high-level cell frameworks and low-level person on foot frameworks , in both indoor and outside situations. Handoff.
Transcripts
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Part 3 Handoff Management : Detection and Assignment

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Introduction Discuss the handoff methodology in subtle element. This dialog is general, which applies to both high-level cell frameworks and low-level person on foot frameworks , in both indoor and open air situations.

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Handoff

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Coverage regions The scope ranges are sporadic in light of the fact that the radiation example of the base station radio wires, structures, trees, mountains, and other landscape highlights. Contiguous scope ranges may cover impressively. Some cover is fancied in light of the fact that handoff is needed in portable interchanges frameworks when a MS moves starting with one BS scope zone then onto the next over the span of a discussion.

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Handoff The handoff methodology ought to be finished while the MS is in the cover area . As the MS moves toward the BS\'s edge scope, the sign quality and quality start to fall apart. The sign from a neighboring BS (the new BS) gets to be more grounded than the sign from the serving BS (the old BS). Moreover, the new BS gets a more grounded sign from the MS than that got by the old BS. The discussion should be given over to the new BS before the connection between the old BS and the MS gets to be unusable. Something else, the call is lost.

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Handoff administration Three issues should be considered for handoff administration: Handoff identification Channel task Radio connection exchange This part looks at handoff location and channel task. Part 4 will research radio connection exchange.

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3.1 Handoff Detection To start a handoff, two issues must be viewed as: Who starts the handoff process? How is the requirement for handoff identified? At the point when to impact the handoff must be founded on estimations of the connections made at the MS, at the two BSs, or both. It is clear that the estimations can be made at either the MS or the BSs, it is not evident that the choice to impact the handoff can be made either by the system or by the MS .

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Multi-way engendering Since the spread environment is dynamic, even near the first BS, the got signal at the MS could incidentally blur because of multi-way proliferation , so that the sign from another BS may seem more grounded for a brief period . Amid such concise "fades," it is not attractive to impact a handoff as doing as such would just be an impermanent fix; without a doubt, the sign may come back to typical much speedier than the handoff could be actualized.

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Handoff Detection Handoff recognition depends on radio connection estimation . decides the requirement for handoff and the objective or new channel for exchange . The spread between the base station and the MS is comprised of the immediate observable pathway way and diffusing ways brought on by reflections from or diffraction around structures and territory. Therefore, the sign got by the MS anytime comprises of a substantial number of for the most part evenly voyaging uniform plane waves.

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Handoff Detection The plane wave amplitudes, stages, and edges of entry in respect to the heading of movement are irregular. These plane waves meddle and produce a differing field quality example with minima and maxima dividing of the request of a quarter-wavelength separated. The MS\'s gotten sign blurs quickly and profoundly as it travels through this impedance design. By correspondence, the BS collector encounters the same wonder as the MS because of the MS movement. The envelope procedure of this quick blurring wonder is Rayleigh-dispersed if there is no solid observable pathway part, and Rician generally.

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Shadow Fading As the MS moves, distinctive scatterers and territory change the plane waves occurrence on the MS recieving wire. In this manner, superimposed on the quick multi-way blurring are moderate varieties in the normal field quality of the obstruction design because of these new reflection and diffraction ways. This slower blurring marvel is called shadow blurring , which has a lognormal conveyance .

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Quality of a channel Three estimations are utilized to focus the nature of a channel: Word lapse pointer (WEI) 字元錯誤指標 . Metric that shows whether the present burst was demodulated appropriately in the MS. Gotten signal quality sign (RSSI) 接受訊號強度指標 . Measure of got sign quality. The RSSI metric has a huge valuable element range, regularly between 80 to 100 dB. Quality marker (QI) 品質指標 . Appraisal of the "eye opening" of a radio sign, which identifies with the sign to impedance and clamor (S/I) proportion , including the impacts of scattering. QI has a limited reach (identifying with the scope of S/I proportion from 5 dB to maybe 25 dB).

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Handoff Detection Handoff may depend all the more dependably on WEI of the present channel as opposed to RSSI. In the event that WEI is great, then handoff is not performed. Be that as it may, it is important to collect WEI estimations over a timeframe , while RSSI is known immediately. To settle on the handoff choice precisely and rapidly, it is alluring to utilize both WEI and RSSI.

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Handoff Detection RSSI estimations are influenced by separation ward blurring , lognormal blurring (i.e., shadow blurring), and Rayleigh blurring (i.e., multipath blurring). Separation ward blurring , or way misfortune , happens when the got sign gets to be weaker because of expanding separation in the middle of MS and BS. Shadow blurring happens when there are physical impediments (e.g., slopes, towers, and structures) between the BS and the MS, which can diminish the got signal quality. Multipath blurring happens when two or more transmission ways exist (because of sign being reflected off structures or mountains) between the MS and BS.

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Multipath blurring There are two sorts of multipath blurring: Rayleigh blurring happens when the snags are near the getting radio wire; in time scattering , the reflected sign originates from an article far from the accepting recieving wire. In a perfect world, the handoff choice ought to be founded on separation ward blurring and, to some degree, on shadow blurring. The handoff choice is free of Rayleigh blurring.

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This can be proficient by averaging the got signal quality for an adequate time period. The issue is that other than transmitting and accepting the wanted signs for the correspondence interface, the MS should likewise quantify or test all frequencies in the band of enthusiasm to locate a suitable handoff competitor.

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Handoff and execution Handoffs are costly to execute so superfluous handoffs ought to be dodged . In the event that the handoff criteria are not picked fittingly, then in the covering district between the two BS scope range limits, the get back to may be given and forward a few times between them . In the event that the criteria are excessively traditionalist , then the call may be lost before the handoff can occur. The handoff choice making criteria turn out to be considerably more basic with the advancement to littler cell sizes , which is going on to build the limit of frameworks and to lessen power necessities of MSs. Problematic and wasteful handoff techniques will lessen the quality and dependability of the framework.

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TDMA framework: Depending on the radio framework\'s TDMA casing structure and term, it may take 100 to 500 msec to quantify all conceivable recurrence channels. Keeping up a short rundown of the best applicant channels is a sensible option since the quantity of estimations of the in all likelihood hopeful BSs can be expanded. Consequently, the choice should be founded on a total of momentary force estimations, which can in this manner normal out the Rayleigh blurring.

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Channel correlation Channel examinations for handoff depend on RSSI and QI measurements . Since the multi-way environment tends to make the RSSI and QI measurements shift generally in the short term, and since it is ideal not to perform handoff to moderate brief multipath blurs in light of the fact that these blurs are nonreciprocal, and on the grounds that such handoffs could bring about pointless burden on the system, the MS ought to normal or channel these estimations before utilizing them to decide. TDMA framework : the estimation\'s pace procedure relies on upon the edge structure of the radio framework. This ability can be utilized to visit every recurrence divert thus. The estimations acquired in this procedure are utilized to keep up a requested rundown of channels as contender for handoff.

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PACS radio framework: has a casing span of 2.5 msec. For a PACS framework with 25 recurrence channels, this relates to going by every channel each 62.5 msec. A client moving at 1 msec goes around 33% wavelength at 2 GHz in this time interim. In the event that reception apparatus differences is utilized in the radio framework at the MS, then the more prominent of the two qualities would be chosen and the remaining estimations would be disposed of.

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Filtering ought to be connected to both RSSI and QI estimations. No less than two separating routines are conceivable: window averaging flawed can joining.

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window averaging 視窗平均法 The MS keeps up a number relative to the present\'s normal estimations, and the last w - 1 estimations, where w is the window size . The MS performs the accompanying method for each new estimation: s k = s k-1 + m k – m k-w where s k alludes to the window\'s total at time k, and m k to the estimation made at time period k. Note that the MS must keep up a present\'s record test and the past w tests.

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defective can coordination 漏æ\'žæ•\'合法 The MS actualizes a discrete, computerized one-post low-pass channel: s k = as k-

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