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15.6.2 Frequency-Selective Fading D
15.6.2 Frequency-Selective Fading Distortion: Case 2
Consider the frequency-selective case in which the coherence bandwidth is less than the symbol rate, while the symbol rate is greater than the Doppler spread. That is.
fo < W > fa (15.48)
Since the transmission symbol rate exceeds the channel fading rate, there is no fast-fading distortion. However, mitigation of frequency-selective effects is necessary. One or more of the following techniques may be considered (see Figure 15.18):
• Adaptive equalization, spread spectrum (DS or FH), OFDM, pilot signal. The European GMS system uses a midamble training sequence in each trans¬mission time slot, so that the receiver can estimate the impulse response of the channel. A Viterbi equalizer (explained later) is implemented for mitigat¬ing the frequency-selective distortion.
• Once the distortion effects have been reduced, diversity techniques (as well as error-correction coding and interleaving) should be introduced in order to approach AWGN performance. For direct-sequence spread-spectrum (DS/SS) signaling, the use of a Rake receiver (explained later) can be used for providing diversity by coherently combining multipath components that would otherwise be lost.
15.6.3 Fast-Fading and Frequency-Selective Fading Distortion: Case 3
Consider the case in which the channel coherence bandwidth is less than the signal-ing rate. which in turn is less than the fading rate. This condition is mathematically described by
Consider the frequency-selective case in which the coherence bandwidth is less than the symbol rate, while the symbol rate is greater than the Doppler spread. That is.
fo < W > fa (15.48)
Since the transmission symbol rate exceeds the channel fading rate, there is no fast-fading distortion. However, mitigation of frequency-selective effects is necessary. One or more of the following techniques may be considered (see Figure 15.18):
• Adaptive equalization, spread spectrum (DS or FH), OFDM, pilot signal. The European GMS system uses a midamble training sequence in each trans¬mission time slot, so that the receiver can estimate the impulse response of the channel. A Viterbi equalizer (explained later) is implemented for mitigat¬ing the frequency-selective distortion.
• Once the distortion effects have been reduced, diversity techniques (as well as error-correction coding and interleaving) should be introduced in order to approach AWGN performance. For direct-sequence spread-spectrum (DS/SS) signaling, the use of a Rake receiver (explained later) can be used for providing diversity by coherently combining multipath components that would otherwise be lost.
15.6.3 Fast-Fading and Frequency-Selective Fading Distortion: Case 3
Consider the case in which the channel coherence bandwidth is less than the signal-ing rate. which in turn is less than the fading rate. This condition is mathematically described by
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15.6.2 frekuensi-selektif memudar distorsi: Kasus 2Pertimbangkan kasus selektif frekuensi di mana bandwidth koherensi adalah kurang dari nilai simbol, sedangkan tingkat simbol lebih besar daripada penyebaran Doppler. Yaitu.Fo < W > fa (15.48)Karena tingkat simbol transmisi melebihi tingkat memudar channel, ada ada distorsi cepat-memudar. Namun, mitigasi frekuensi-selektif efek diperlukan. Satu atau lebih dari teknik berikut dapat dianggap (Lihat gambar 15.18):• Pemerataan adaptif, penyebaran spektrum (DS atau FH), OFDM, sinyal pilot. Sistem RUPS Eropa menggunakan urutan midamble pelatihan dalam setiap slot waktu trans¬mission, sehingga Penerima dapat memperkirakan respon impulse saluran. Equalizer Viterbi (dijelaskan nanti) dilaksanakan untuk mitigat¬ing frekuensi-selektif distorsi.• Setelah efek distorsi telah berkurang, keragaman teknik (serta koreksi kesalahan coding dan interleaving) harus diperkenalkan dalam rangka untuk pendekatan AWGN kinerja. Untuk langsung-urutan dihamparkan-spektrum (DS/SS) signaling, menggunakan Rake receiver (dijelaskan nanti) dapat digunakan untuk menyediakan keragaman dengan koheren menggabungkan multipath komponen yang lain akan hilang.15.6.3 cepat-memudar dan frekuensi-selektif memudar distorsi: kasus 3Pertimbangkan kasus di mana saluran koherensi bandwidth adalah kurang dari tingkat sinyal-ing. yang pada gilirannya berjarak kurang dari tingkat memudar. Kondisi ini secara matematis digambarkan oleh
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15.6.2 Frequency-Selective Fading Distortion: Case 2
Consider the frequency-selective case in which the coherence bandwidth is less than the symbol rate, while the symbol rate is greater than the Doppler spread. That is.
fo < W > fa (15.48)
Since the transmission symbol rate exceeds the channel fading rate, there is no fast-fading distortion. However, mitigation of frequency-selective effects is necessary. One or more of the following techniques may be considered (see Figure 15.18):
• Adaptive equalization, spread spectrum (DS or FH), OFDM, pilot signal. The European GMS system uses a midamble training sequence in each trans¬mission time slot, so that the receiver can estimate the impulse response of the channel. A Viterbi equalizer (explained later) is implemented for mitigat¬ing the frequency-selective distortion.
• Once the distortion effects have been reduced, diversity techniques (as well as error-correction coding and interleaving) should be introduced in order to approach AWGN performance. For direct-sequence spread-spectrum (DS/SS) signaling, the use of a Rake receiver (explained later) can be used for providing diversity by coherently combining multipath components that would otherwise be lost.
15.6.3 Fast-Fading and Frequency-Selective Fading Distortion: Case 3
Consider the case in which the channel coherence bandwidth is less than the signal-ing rate. which in turn is less than the fading rate. This condition is mathematically described by
Consider the frequency-selective case in which the coherence bandwidth is less than the symbol rate, while the symbol rate is greater than the Doppler spread. That is.
fo < W > fa (15.48)
Since the transmission symbol rate exceeds the channel fading rate, there is no fast-fading distortion. However, mitigation of frequency-selective effects is necessary. One or more of the following techniques may be considered (see Figure 15.18):
• Adaptive equalization, spread spectrum (DS or FH), OFDM, pilot signal. The European GMS system uses a midamble training sequence in each trans¬mission time slot, so that the receiver can estimate the impulse response of the channel. A Viterbi equalizer (explained later) is implemented for mitigat¬ing the frequency-selective distortion.
• Once the distortion effects have been reduced, diversity techniques (as well as error-correction coding and interleaving) should be introduced in order to approach AWGN performance. For direct-sequence spread-spectrum (DS/SS) signaling, the use of a Rake receiver (explained later) can be used for providing diversity by coherently combining multipath components that would otherwise be lost.
15.6.3 Fast-Fading and Frequency-Selective Fading Distortion: Case 3
Consider the case in which the channel coherence bandwidth is less than the signal-ing rate. which in turn is less than the fading rate. This condition is mathematically described by
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- Spread Specirum Systems are systems that
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- Spread Specirum Systems are systems that
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- A.6 FIREWALL PROJECTSThe implementation
