The Other standards in the family c—f, h—j, n are service enhancement and extensions, or corrections to previous specifications. IEEE Operating in an unregulated frequency band, The original version of the standard IEEE IR channels remains a part of the standard but has no actual implementations.
It is really more of a "meta-specification" than a rigid specification, allowing individual product vendors the flexibility to differentiate their products. Legacy Hence, chipsets and products were easily upgraded to support the The dramatic increase in throughput of Since the lower data rates use less complex and more redundant methods of encoding the data, they are less susceptible to corruption due to interference and signal attenuation.
Extensions have been made to the Many companies call enhanced versions " These extensions have been largely obviated by the development of The first widespread commercial use of the It is common to hear that channels 1, 6 and 11 and where available by the regulator, channel 14 do not overlap and those channels or other sets with similar gaps can be used such that multiple networks can generally operate in close proximity without interfering with each other.
Rather, they specify the center frequency of the channel and a spectral mask for that channel. The spectral mask for Therefore, it is incorrect to say that channels 1, 6, and 11 do not overlap. It is more correct to say that, given the separation between channels 1, 6, and 11, the signal on any channel should be sufficiently attenuated to minimally interfere with a transmitter on any other channel.
But this is not universally true. For example, a powerful transmitter on channel 1 can easily overwhelm a weaker transmitter on e. In one lab test, throughput on a file transfer on channel 11 decreased slightly when a similar transfer began on channel 1, indicating that even channels 1 and 11 can interfere with each other a little bit. The channels that are available for use in a particular country will differ according Regulator in that country.
Channels 10 and 11 are the only channels which are common throughout the world. The simulation results show that the proposed method kept the probability of handover failure and unnecessary handover below 0. Compared with previous studies, the proposed method reduced the number of handover failures and unnecessary handovers up to Using the proposed prediction method, the MT can benefit high bandwidth and low network access cost from the WLAN with minimum interruption regardless of speed.
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Competing interests: The authors have declared that no competing interests exist. Next-generation wireless networks will be driven by an all-IP-based network infrastructure that provides seamless mobility and ubiquitous access to Internet through heterogeneous wireless networks [ 1 ]. In heterogeneous wireless network, wireless local area network WLAN is highly preferred owing to its high capacity and low access cost [ 2 , 3 ].
Wireless Local Area Networks Quality of Service
However, because of limited WLAN coverage, handover from a cellular network to the WLAN may lead to a high number of handover failures and unnecessary handovers when a mobile terminal MT is in a high-speed environment because the MT requires less time to cross the WLAN coverage when the speed increases [ 3 , 4 ]. The MT leaves the WLAN coverage before the handover process is executed causing network connection breakdown and service interruption [ 3 — 5 ].
Unnecessary handover is undesirable because it wastes network resources [ 7 ]. At present, WLAN application is restricted to static or pedestrian navigation environment [ 8 ]. For example, in the patient monitoring system using heterogeneous wireless networks proposed by Niyato et al. In addition, the fuzzy multi-criteria-based vertical handover algorithm presented by Kaleem et al. Yan et al. The L th of handover failure presented by Yan et al. The unnecessary handovers L th presented by Yan et al. The results show that both the probability of handover failure and unnecessary handover are kept within the user acceptable value [ 6 , 15 ].
However, the optimum time to take the second RSS sample point was not considered by the authors. We have found that the larger the time gap between the two RSS sample points is, the lower becomes the accuracy of the prediction result.
Therefore, using the methods presented by Yan et al. In this paper, a novel vertical handover method is proposed to improve the accuracy of the traveling-time estimation and to minimize both handover failure and unnecessary handover to the WLAN when the MT is in a high-speed environment. A low-pass filter can be used to suppress the shadowing part [ 18 ]. Similarly, the r value can be calculated by replacing in 7 with.
In this paper, we assume Doppler shift problem caused by high mobility can be mitigated by using the Doppler diversity. In [ 19 ], Doppler domain multiplexing communication structure is proposed to achieve the maximum Doppler diversity in time varying fading. Furthermore, the Doppler frequency offset estimation and compensation algorithms presented in [ 20 , 21 ] can be used to alleviate the Doppler effects in high-speed environment.
This is to minimize the impact of RSS fluctuation. The median method [shown in 8 ] is used instead of the mean method [ 23 ] because it overcomes a sudden large increase or decrease in the RSS value caused by an unintended factor. Therefore, RSS value is given as 8. The maximum number of RSS samples is limited to 30 to avoid excessive sampling at low traveling speed.
From 11 Substituting 13 into 12 yields Substituting 14 into 10 yields distance l as Instead of using the time threshold similar to what were previously presented in [ 6 , 15 ], we introduce a threshold for distance d known as d th so that the MT can make handover decision by comparing the measured d value with d th directly. We can derive d th from 18 by replacing l with l th and d with d th. It is given as 19 where l th is the traveling distance threshold. From 16 , l th for handover failure l thf and unnecessary handover l thu can be expressed as 20 By substituting 20 into 19 yields d th for handover failure d thf as Similarly, d th for unnecessary handover d thu can be determined by substituting 21 into 19 and it is given as The relationship between d and l is shown in Fig 2A , which shows that d inversely varies with l , indicating that the greater the traveling distance within WLAN coverage l is, the smaller is the d value.
Referring to 22 and 23 , both d thu and d thf are depending on the handover latency, acceleration or deceleration rate and velocity.
The proposed method triggers a handover to the WLAN if and only if measured d value is less than estimated d th value. Relationship between A the d value and traveling distance l and B d th , acceleration and velocity. The WLAN cell is expected within the coverage of cellular network. Otherwise, it remains connected to cellular network.
The simulation parameters listed in Table 1 were selected to observe the performance of the proposed method.
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The radius r is set as 50 m and the total handover latency for the handover into and out of the WLAN was 2 seconds as in [ 6 , 15 ]. At that development criminal words will provide increased aside. ISBN ebook wireless local area networks. ISBN reform.
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