通信工程專業(yè)畢業(yè)論文外文資料翻譯--正交頻分復(fù)用技術(shù)簡(jiǎn)介-其他專業(yè)-資料下載頁
2025-01-19 01:39本頁面
【導(dǎo)讀】正交頻分復(fù)用是一種多載波調(diào)制技術(shù)。將高速數(shù)據(jù)信號(hào)轉(zhuǎn)換成并行的低速子數(shù)據(jù)流，調(diào)制到在每個(gè)子信道上進(jìn)行傳輸。號(hào)可以通過在接收端采用相關(guān)技術(shù)來分開，這樣可以減少子信道之間的相互干擾。從而可以消除碼間串?dāng)_。而且由于每個(gè)子信道的帶寬僅僅是原信道帶寬的一小部分，信。道均衡變得相對(duì)容易。由于這種技術(shù)具有在雜波干擾下傳送信號(hào)的能力，因此常常會(huì)被。利用在容易受外界干擾或者抵抗外界干擾能力較差的傳輸介質(zhì)中。目前正交頻分復(fù)用技。了一個(gè)完整的多載波傳輸系統(tǒng)，叫做正交頻分復(fù)用系統(tǒng)。正交的子載波以及從子載波中恢復(fù)原信號(hào)的問題。但是應(yīng)用正交頻分復(fù)用系統(tǒng)仍然需要大。因此正交頻分復(fù)用技術(shù)遲遲沒有得到迅速發(fā)展。自此正交頻分復(fù)用走上了通信的舞臺(tái)，逐步邁向高速數(shù)字移動(dòng)通信的領(lǐng)域。用為物理層標(biāo)準(zhǔn)，使得傳輸速率可以達(dá)54Mbps。將信號(hào)散播的地區(qū)。部分載波會(huì)受到干擾。
【正文】 requency selective fading or narrowband interference. In single carrier systems, a single fading or interference can cause the entire munication link failure, but in a multi carrier system, only a very small part of carrier interference. The sub channel can also use error correcting codes for error correction. (6) Can effectively resist the interference between the signal waveform, high speed data transmission in multipath environment and fading channels. When the channel because of multipath transmission frequency selective fading, only fell on the band depression sub carrier and carry information affected, subcarrier other unimpaired, therefore better BER performance than the general. (7) Through the joint coding of each sub carrier, has a strong ability of anti fading. 通信工程專業(yè)畢業(yè)設(shè)計(jì)外文資料翻譯 第 9 頁 Orthogonal frequency division multiplexing technology itself has taken advantage of frequency diversity channel fading, if not serious, there is no need to add the time domain equalizer. Through the various channel coding, it can improve the performance of system. (8) Orthogonal frequency division multiplexing technology of narrowband interference is very strong, because these disturbances affect only a small fraction of the sub channel. (9) The channel utilization rate is high, this is an important point in the spectrum is a limited resource in wireless environment。 when the subcarrier number is large, the system spectrum utilization tends to 2Baud/Hz. Although orthogonal frequency division multiplexing has these advantages, but also its modulation mechanism also makes the signal in the transmission process exist some disadvantages. (1) Is very sensitive to the phase noise and carrier frequency. This is orthogonal frequency division multiplexing technology is a very fatal flaw, the orthogonal frequency division multiplexing system is strictly on the orthogonality between sub carrier requirements, any small carrier frequency offset will destroy the orthogonality between subcarriers, causes inter symbol interference, similarly, phase noise can also cause rotation diffusion, symbol constellation points, thus forming the inter channel interference. The single carrier systems do not have this problem, phase noise and carrier frequency offset is only reduced the received signaltonoise ratio, without causing interference to each other. (2) Peak to average ratio is too large. Orthogonal frequency division multiplexing signal is posed of a plurality of sub carrier signal, the carrier signal modulated by different independent modulation symbols. Compared with the traditional method of constant envelope modulation, OFDM has a very high peak factor. Because the signal is the sum of many small signal, the phase of these small signal is determined by the data sequence to be transmitted. Some of the data, these small signal may be same, and amplitude superimposed together to produce the instantaneous peak magnitude. While the peak to average ratio is too large, will increase the plexity of ADC and DAC, and will reduce the efficiency of RF power amplifier. At the same time, in the transmitter, the maximum output power of the amplifier has limited the signal peak, it will produce interference between division multiplexing frequency band and the adjacent bands in orthogonal frequency. (3) The wide linear range. The orthogonal frequency division multiplexing system peak to average power ratio, the nonlinear amplification is more sensitive, so OFDM system than the linear range of amplifier of single carrier systems demand higher. 通信工程專業(yè)畢業(yè)設(shè)計(jì)外文資料翻譯 第 10 頁
高考資料相關(guān)推薦
鄂ICP備17016276號(hào)-1