Asimetrik doğrusal olmayan sürekli fazlı frekans kaydırmalı anahtarlama
Başlık çevirisi mevcut değil.
- Tez No: 46281
- Danışmanlar: DOÇ.DR. ÜMİT AYGÖLÜ
- Tez Türü: Yüksek Lisans
- Konular: Elektrik ve Elektronik Mühendisliği, Electrical and Electronics Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1995
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 59
Özet
ÖZET Sayısal iletimde en önemli parametrelerden birisi hata olasılığıdır. Bu parametrenin iyileştirilmesi için her modülasyon tekniğinde bir takım çalışmalar yapılmaktadır. Bu tezde sürekli fazlı frekans kaydırmalı anahtarlamada çeşitli parametreler değiştirilerek daha iyi hata olasılıkları elde edilmiş ve elde edilen sonuçlar incelenerek bu sonuçların kullanılabilirliği için yorumlar yapılmıştır. IV
Özet (Çeviri)
SUMMARY în the digital- transmission, on© of the most important parameters is error performance. Some improvements are being done to make better this for all modulation techniques. Sometimes, different parameters are chanced and sometimes new modulation tehniques are developed. All these are done for getting better results on error performance. One of the developed modulation tehniques is Continuous Phase Modulation CCPMD.This is a succesful study because of its bandwidth and error probability. Narrower bandwidth, lower spektral sidelobes and better error performance can be obtained. Different types of modulations were obtained by improving CPM. These have continious phase modulation structure generaly. Difference is pulse shape of each one. Because of this, they have different names to ditinguish them. A parameter which is used in all CPMs is modulation index h. Changes on h does not chance the name of modulation but there may occour some good or bad changes. în some cases, h is fixed but in some improved modulations h is variable. This parameter chances in a period of time and gets limited different values. Error performance in this code is better then fixed h. Better performance can be get by using two or more h.In the demodulation of CPM signals, the most important parameter to determine error probability is minimum Euclidian distance. This can be get by calculating distances between all the couples of ways at the end of the each step. Minimum of these values found is Minimum Euclidian Distance dmin. Varius algorithms are used to compute distances true and quickly. For an effective dmin to find error probability, the noise must be white gausian noise and for various L and h values, different algorithms are used to find this h value. Modulator of CPM consist of a filter and a frequency modulator. Fil ter charasteristic chances according to pulse shape gCO.Vi terbi algorithm can be used in the receiver or the system. In theory, there is no problem to form receiver but in practice, there are some problems. For example, complexity in vi terbi detechtors increases with ihe memory. Minimum Shifting Keying CMSKD, a special type of Continiosu Phase Frequency Shifting Keying CCPFSO, uses parallel, type receiver. But this is not the optimum way. If we examine the structure of CPM it is seen that, phase of it, takes specific values with a p>eriod. These values are sample points of Euclidian space. Changes of phase on time is bounded with data bits. At the same time, because of the CPM schemes, phase is continious. Phase states can be sown with modulo 2jt. So that, it can be drawn on a cylinder. This type coded signals have a trellis structure and decoding can be done by vi terbi algorthm. For example, distance between codewords in binary coding is measured with Hamming distance. After that, this VIdistance is compared with nearer two neighbor codewords and the nearest one is decided. Soft decision mechanism is used. Nonlinear CPFSK is a kind of continious phase modulation. If L=.l, a kind of CPM, Spectral Raised cosine CLRECD gets a name CPFSK. A difference from the others CPMs is nonlinear t y of it. This is because, trellis of modulation is defined by a matrix. Another characteristic is that, h chances according to incoming data and phase at the begining of the time interval, h is also a function of CL-1D previous data. As a result of this, phase state at the end of any interval may be different from the phase state at the begining Minimum euclidian Distance and signal to noise ratio are effective on computing error probability of CPMs. Signal to noise ratio is fixed for a channel. So that, if the error performance will improve, dmin is effective factor. If constraint length Cm is increased, dmin will get a better value. Constraint length is the minimum step of all joining ways. During the collection of dmin, there is an integration but this calculation can be reduced to a sinus formül a. Accumul ati vity of d distance facilities calculations.lt is controlled if phase difference between start and end of interval changes. According to this, one of two formules is used. After that, all distances found for each interval are added total. CPFSK uses a matrix different from classic CPM do not use. This matrix is state transmission matrixlt shows which state will be the next state according to state at the begining and incoming data. h values can be compated by using this matrix and phase states. this modulation is a multi h modulation. So that, there are more than one hvalues. This kind of signaling technique is a multi-h phase coding technique. Matrix is same for all the signaling intervals. So the multi-H values are same for all intervals for the same data and phase conditions. This modulation can be improved by chancing some parameters. One of these parameters is phase group. Normally, phase states have the same distance with eac hot hers. Some new results can be obtained by chancing these distances. By this method, Euclidian distance reduced for some intervals and increased for the other intervals. At the end of Cm interval, totaly, dmin is increased according to equal distances. Because of assymmetry of phase states, this kind of modulation is called assymmetric nonlinear continuous phase FSK. Spectral characteristics are similar to MSK because of controlling h value. Some conditions must be paid attention during this kind of adjustment. One of these is the logic of founded results, chenges which are made must not produce alogical results. For example, founded new phases must be between O and 2tt and h values must be convinient too. After all the conditions are kept, a dmin value is found for new phase group. Wrlten algorithms are used to find this. Different algorithms are used to calculate values and show these on devices. Results founded are shown on graphics. Good or bad changes can be seen clearly from these graphics. These graphics can also be used to comment results. When drawn graphics are examined» it can be seen that, linear variation phases causes linear variation of dmin values. After this result, the important is to find optimum solution with dmin and h values. VTIIBetter error performances can be succeed in by some other ways besides examined in this study. For example, better dmin values cen be obtained by changing T period. This is a study independently and results of it must be examined careful y. Similarly, used data bits can be changed. Instead of binary, quoternary or eighternary signaling systems can be used. This is a kind of coded modulation. Frequency spectrum and new dmin values must be examined for this condition. This new technique obtained by changing phase states is not a new modulation technique. This is just an improvement on nonlinear continious phase FSK for a better error performance. Obtained results are satisfactory and open to new developments. IX
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