Có 40+ tài liệu thuộc chủ đề "Hệ thống không dây"
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Fixed Wireless Access Systems. The goal of this chapter is to review the main techniques used for Wireless Local Loop (WLL) including the Multichannel Multipoint Distribution Service (MMDS), and the Local Multipoint Distribution Service (LMDS). The chapter also deals with the wireless local loop subscriber terminals, Wireless Local Loop Interfaces to the Public Switched Telephone Network (PSTN), and the IEEE...
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The first attempt to define a standard was made in the late 1980s by IEEE Working Group 802.4, which was responsible for the development of the token-passing bus access method.. The first standard, 802.11b, extends the performance of the existing 2.4 GHz physical layer, with potential data rates up to 11 Mbps. Therefore, the use of WLANs helps reduce the...
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It involves the specification of the transmission medium and the signal encoding to be used. AAL1 supports services that demand a constant bit rate, which is agreed during connection establishment and must remain the same for the duration of the connec- tion. and (c) the management plane, which includes plane management for manage- ment of the whole system and coordination...
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11.1.1 Historical Overview. One of the first research concepts for PANs dates back to an IBM research project in 1996 and is known. Figure 11.1 The various kinds of wireless networks. The electrical current used in this approach is approximately 1 nA, which is much lower than the natural electrical current of the human body. The size of the SIG...
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Then, in Section 12.2, we review the types of attacks on wireless networks. Section 12.3 presents the classes of services of any reliable security system including confidentiality, nonrepudiation, authentication, access control, integrity, and availability. Section 12.4 presents the main aspects of the Wired Equivalent Privacy (WEP) Protocol. Section 12.5 introduces the security aspects of mobile IP. Section 12.6 investigates the...
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We then review the main characteristics of the commonly used stochastic distribu- tions used for the simulation of wireless networks. Others defined simulation as the process of experimenting with a model of the system under study using computer program- ming. It measures a model of the system rather than the system itself.. Shannon defined a model as ‘the process of...
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14.1 Introduction. The field of mobile wireless communications is currently one of the fastest growing segments of the telecommunications industry. To gain insight into the momentum of the growth of the wireless industry, it is sufficient to state the tremendous growth in the number of worldwide subscribers of wireless systems. As far as the near future is concerned, it is...
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1.1 Motivation of the Book. The aim of these adaptive transceivers is to provide mobile users with the best possible compromise amongst a number of contradicting design factors, such as the power consumption of the hand-held portable station (PS), robustness against transmission errors, spectral eficiency, teletrafic capacity, audiohideo quality and so forth [ 2. The fundamental limitation of wireless systems...
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Equalizers can also be distinguished on the basis of the criterion used to optimise their coefficients. This is necessary in order to study the performance of the equalizers in multilevel modulation environment, since the choice of the modulation mode will affect the performance of the equalizer.. Gray-coding of the bit sequence gives rise to the formation of a number of...
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Algorithms have been developed in order to automatically adapt the coefficients of the equalizer directly [ l 181 or by utilizing the estimated CIR [124,125]. This was followed by the application of the algorithm for adaptive equalizers . Let us now commence the derivation of the Kalman algorithm.. Figure 3.1: Signal-flow representation of the Kalman system and measurement models, which...
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Let us now commence with a brief overview of the AQAM scheme.. A brief overview of the principles of AQAM in a narrow-band Rayleigh fading channel en- vironment is given here. These characteristics of the AQAM switching regime will be shown more explicitly in Section 4.3.4.. This trade-off is governed by the values of the switching thresholds 1,. In the...
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The schematic of the turbo encoder is shown in Figure 5.1. The iterative decoding structure of the turbo decoder is shown in Figure 5.3. L , Figure 5.3: Schematic of the turbo decoder.. is generated by subtracting the contribution of the channel outputs, as shown in Figure 5.3. Consequently, as the number of iterations increases, the estimation of the decoded...
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(a) SNR versus BEP over AWGN channels (b) PDF f7(y) of the instantaneous SNR y Over Rayleigh channel. Figure 6.2(a) depicts the instantaneous BEP as a function of the instantaneous channel SNR. The exact value of the outage probability is given by:. The average BEP P. Let us describe the detailed operation of the adaptive modem scheme of Figure 6.3....
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However, in stipulating this assump- tion, the delay incurred between channel quality estimation and the actual utilization of the estimate was neglected in the wideband AQAM schemẹ. The incorrect estimate precipitates further errors at the output of the equalizer. The performance of the fixed modulation modes of our AQAM scheme in conjunction 257. with error propagation is depicted in Figure...
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Consequently, as depicted in Figure 8.1, the passage of the input sequence { I k } through the channel results in the channel output sequence {vk} that can be expressed as. 7 , and it produces an estimate Ik-T of the transmitted signal IkPT. 2L+m possible combinations of the binary channel input sequence. Expounding further, we denote each of the...
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These switching thresholds govern the tradeoff between the mean BER and the BPS performance of the system. We will briefly summarise, how the performance of the equalizer and the AQAM scheme can be jointly optimized.. As expected, the AQAM switching criteria of the narrow-band scenario mentioned in Section 9.1 has to be modified for the wideband channel environment. Consequently, the...
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10.1 Introduction to Turbo Codes. Figure 10.1: Turbo encoder schematic.. Figure 10.2: Turbo decoder schematic.. Therefore, the iterative scheme shown in Figure 10.2 is usually used. 10.2 Jacobian Logarithmic RBF Equalizer. Expressing Equation 10.3 in a logarithmic form and substituting in the Jacobian logarithm, we obtain:. Note from Equation 10.5 that vil, is a summation of the delayed components. Figure...
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The soft values of the channel coded bits ck are typically quantified in the form of the log-likelihood ratio defined in Equation 10.6. Before passing the above a posteriori LLRs generated by the SISO equaliser to the SISO decoder of Figure 11.1, the contribution of the decoder - in the form of the a priori information C,". Subsequently, the channel...
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A Framework for Existing and Future Wireless Standards, submitted to the Proceedings of the IEEE OIEEE, 2001. Motivated by these requirements in the context of the CDMA-based third-generation wireless systems the outline of the chapter is as follows. In Section 12.2 we re- view the current state-of-the-art in multi-user detection with reference to the receiver family- tree of Figure 12.4....
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13.1 Introduction. The outline of the chapter is as follows. 13.2 Orthogonal Frequency Division Multiplexing. 13.2.1 Historical Perspective. ing techniques which aim to minimise the peak power of the OFDM signal. 13.2.1.2 Synchronization. 13.2.1.3 OFDM / CDMA. 13.2.1.4 Adaptive Antennas. 13.2.1.5 OFDM Applications. Figure 13.1: Schematic of N-subcarrier OFDM transmission system.. 13.2.2 OFDM Modem Structure. In practice, however, it is...