2 research outputs found
Comparative study and performance evaluation of MC-CDMA and OFDM over AWGN and fading channels environment
Η απαίτηση για εφαρμογές υψηλής ταχύτητας μετάδοσης δεδομένων έχει αυξηθεί
σημαντικά τα τελευταία χρόνια. Η πίεση των χρηστών σήμερα για ταχύτερες
επικοινωνίες, ανεξαρτήτως κινητής ή σταθερής, χωρίς επιπλέον κόστος είναι μια
πραγματικότητα. Για να πραγματοποιηθούν αυτές οι απαιτήσεις, προτάθηκε ένα νέο
σχήμα που συνδυάζει ψηφιακή διαμόρφωση και πολλαπλές προσβάσεις, για την
ακρίβεια η Πολλαπλή Πρόσβαση με διαίρεση Κώδικα Πολλαπλού Φέροντος
(Multi-Carrier Code Division Multiple Access MC-CDMA).
Η εφαρμογή του Γρήγορου Μετασχηματισμού Φουριέ (Fast Fourier Transform,FFT)
που βασίζεται στο (Orthogonal Frequency Division Multiplexing, OFDM)
χρησιμοποιεί τις περίπλοκες λειτουργίες βάσεως και αντικαθίσταται από
κυματομορφές για να μειώσει το επίπεδο της παρεμβολής. Έχει βρεθεί ότι οι
μετασχηματισμένες κυματομορφές (Wavelet Transform,W.T.) που βασίζονται στον
Haar είναι ικανές να μειώσουν το ISI και το ICI, που προκαλούνται από απώλειες
στην ορθογωνιότητα μεταξύ των φερόντων, κάτι που τις καθιστά απλούστερες για
την εφαρμογή από του FFT. Επιπλέον κέρδος στην απόδοση μπορεί να επιτευχθεί
αναζητώντας μια εναλλακτική λειτουργία ορθογωνικής βάσης και βρίσκοντας ένα
καλύτερο μετασχηματισμό από του Φουριέ (Fourier) και τον μετασχηματισμό
κυματομορφής (Wavelet Transform).
Στην παρούσα εργασία, υπάρχουν τρία προτεινόμενα μοντέλα. Το 1ο, ( A proposed
Model ‘1’ of OFDM based In-Place Wavelet Transform), το 2ο, A proposed Model
‘2’ based In-Place Wavelet Transform Algorithm and Phase Matrix (P.M) και το
3ο, A proposed Model ‘3’ of MC-CDMA Based on Multiwavelet Transform. Οι
αποδόσεις τους συγκρίθηκαν με τα παραδοσιακά μοντέλα μονού χρήστη κάτω από
διαφορετικά κανάλια (Κανάλι AWGN, επίπεδη διάλειψη και επιλεκτική διάλειψη).The demand for high data rate wireless multi-media applications has increased
significantly in the past few years. The wireless user’s pressure towards
faster communications, no matter whether mobile, nomadic, or fixed positioned,
without extra cost is nowadays a reality. To fulfill these demands, a new
scheme which combines wireless digital modulation and multiple accesses was
proposed in the recent years, namely, Multicarrier-Code Division Multiple
Access (MC-CDMA).
The Fourier based OFDM uses the complex exponential bases functions and it is
replaced by wavelets in order to reduce the level of interference. It is found
that the Haar-based wavelets are capable of reducing the ISI and ICI, which are
caused by the loss in orthogonality between the carriers. Further performance
gains can be made by looking at alternative orthogonal basis functions and
finding a better transform rather than Fourier and wavelet transform.
In this thesis, there are three proposed models [Model ‘1’ (OFDM based on
In-Place Wavelet Transform, Model ‘2’ (MC-CDMA based on IP-WT and Phase Matrix)
and Model ‘3’ (MC-CDMA based on Multiwavelet Transform)] were created and then
comparison their performances with the traditional models for single user
system were compared under different channel characteristics (AWGN channel,
flat fading and selective fading).
The conclusion of my study as follows, the models (1) was achieved much lower
bit error rates than traditional models based FFT. Therefore these models can
be considered as an alternative to the conventional MC-CDMA based FFT. The main
advantage of using In-Place wavelet transform in the proposed models that it
does not require an additional array at each sweep such as in ordered Fast Haar
wavelet transform, which makes it simpler for implementation than FFT. The
model (2) gave a new algorithm based on In-Place wavelet transform with first
level processing multiple by PM was proposed. The model (3) gave much lower bit
error than other two models in additional to traditional models
An Investigation of Orthogonal Wavelet Division Multiplexing Techniques as an Alternative to Orthogonal Frequency Division Multiplex Transmissions and Comparison of Wavelet Families and Their Children
Recently, issues surrounding wireless communications have risen to prominence because of the increase in the popularity of wireless applications. Bandwidth problems, and the difficulty of modulating signals across carriers, represent significant challenges. Every modulation scheme used to date has had limitations, and the use of the Discrete Fourier Transform in OFDM (Orthogonal Frequency Division Multiplex) is no exception. The restriction on further development of OFDM lies primarily within the type of transform it uses in the heart of its system, Fourier transform. OFDM suffers from sensitivity to Peak to Average Power Ratio, carrier frequency offset and wasting some bandwidth to guard successive OFDM symbols. The discovery of the wavelet transform has opened up a number of potential applications from image compression to watermarking and encryption. Very recently, work has been done to investigate the potential of using wavelet transforms within the communication space. This research will further investigate a recently proposed, innovative, modulation technique, Orthogonal Wavelet Division Multiplex, which utilises the wavelet transform opening a new avenue for an alternative modulation scheme with some interesting potential characteristics. Wavelet transform has many families and each of those families has children which each differ in filter length. This research consider comprehensively investigates the new modulation scheme, and proposes multi-level dynamic sub-banding as a tool to adapt variable signal bandwidths. Furthermore, all compactly supported wavelet families and their associated children of those families are investigated and evaluated against each other and compared with OFDM. The linear computational complexity of wavelet transform is less than the logarithmic complexity of Fourier in OFDM. The more important complexity is the operational complexity which is cost effectiveness, such as the time response of the system, the memory consumption and the number of iterative operations required for data processing. Those
complexities are investigated for all available compactly supported wavelet families and their children and compared with OFDM. The evaluation reveals which wavelet families perform more effectively than OFDM, and for each wavelet family identifies which family children perform the best. Based on these results, it is concluded that the wavelet modulation scheme has some interesting advantages over OFDM, such as lower complexity and bandwidth conservation of up to 25%, due to the elimination of guard intervals and dynamic bandwidth allocation, which result in better cost effectiveness