BER Evaluation of Orthogonal Frequency Division Multiplexing (OFDM) under various Modulation Techniques

Orthogonal frequency division multiplexing (OFDM) has recently received a lot of attention as an effective technique to remove all inter-symbol interference (ISI) caused by multipath fading. OFDM is a promising future technology for wired/wireless communications. This paper gives a theoretical overview of OFDM, application and its advantages/disadvantages. The performance of the developed system is investigated in terms of Bit Error Rate. DOI: 10.17762/ijritcc2321-8169.150518

Partial Shift Mapping Decoding Algorithm to PAPR Reduction in OFDM Systems

Orthogonal Frequency Division Multiplexing (OFDM) is a kind of modulation technique which allows the transmission of high data rates over wideband radio channels subject to frequency selective fading by dividing it to several narrow band and flat fading channels. OFDM has high spectral efficiency and Robustness to multipath fading. In contrast high peak to average power ratio (PAPR) of the transmitted signals is a major drawback of multicarrier systems like OFDM. High PAPR causes the nonlinear distortion in the received data and reduces the efficiency of the high power amplifier in transmitter. To solve the problem many techniques such as SLM and PTS algorithms are proposed. Recently a new simple method with low complexity respected to the SLM and PTS as Partial Shift Mapping (PSM) is proposed by Xing et al. He showed that the PSM method can reduce the PAPR parameter respected the other mentioned methods, effectively. In this paper we will design the corresponding decoder to the PSM technique and will evaluate its robustness respected to the high power amplifier distortion and the AWGN channel. Simulation results will show that the PSM method has a better Power spectrum density and is less sensitive to the type of modulation and number of subcarriers

Partial Shift Mapping Decoding Algorithm to PAPR Reduction in OFDM Systems

Orthogonal Frequency Division Multiplexing (OFDM) is a kind of modulation technique which allows the transmission of high data rates over wideband radio channels subject to frequency selective fading by dividing it to several narrow band and flat fading channels. OFDM has high spectral efficiency and Robustness to multipath fading. In contrast high peak to average power ratio (PAPR) of the transmitted signals is a major drawback of multicarrier systems like OFDM. High PAPR causes the nonlinear distortion in the received data and reduces the efficiency of the high power amplifier in transmitter. To solve the problem many techniques such as SLM and PTS algorithms are proposed. Recently a new simple method with low complexity respected to the SLM and PTS as Partial Shift Mapping (PSM) is proposed by Xing et al. He showed that the PSM method can reduce the PAPR parameter respected the other mentioned methods, effectively. In this paper we will design the corresponding decoder to the PSM technique and will evaluate its robustness respected to the high power amplifier distortion and the AWGN channel. Simulation results will show that the PSM method has a better Power spectrum density and is less sensitive to the type of modulation and number of subcarriers

Evaluation of Channel Coding in OFDM Systems

Channel coding plays a very important role in OFDM systems performance. The structure of OFDM systems makes channel coding more effective in confronting fading channels. Sometimes Coded OFDM is known as COFDM. The role of channel coding in conjunction with frequency and time interleaving is to provide a link between bits transmitted on separated carriers of the signal spectrum, in such a way that the information conveyed by faded carriers can be reconstructed in the receiver. Frequency selectivity, currently known to be a disadvantage, is then turned into an advantage that can be called frequency diversity. Using Channel State Information (CSI), channel coding can yield some additional gain. Channel state information is frequency response of the channel or signal to noise ratio in each carrier. This thesis analyzes OFDM system and the effect of channel coding in reducing BER. Along with this soft decoding and decoding with CSI is also studied. Besides, performance of convolutional codes Turbo codes in OFDM systems is compared and compared. Besides, we compare the performance of convolution and turbo codes in OFDM systems. The results have been validated through simulations. This thesis also presents Space-Frequency Coded OFDM system consisting of two transmitters and a single receiver. Simple Alamouti space time code is used. An Mary PSK modulation is used to modulate the symbols across an OFDM channel. We also proposed a variation of the scheme which tries to spread additional symbols across timefrequency attempting to increase the rate of transmission without changing the type of modulation employed or increasing the bandwidth. A Rayleigh frequency selective slow fading channel is assumed through out the analysis. SER performance of the above systems is carried out with emphasis on the modulation scheme and number of carriers

Policy-Based Radio Resource Management in Multicast OFDMA Systems

Η ασύρματηφασματική αποδοτικότητα είναι ένας, όλο και περισσότερο, σημαντικός παράγοντας εξαιτίας της ταχείας ανάπτυξης των ασύρματων υπηρεσιών ευρείας ζώνης. Η σχεδίαση ενός συστήματος με πολλά φέροντα, όπως είναι ένα σύστημα OFDMA,επιτρέπει στα συστήματα να έχουν υψηλή χωρητικότητα για να ικανοποιήσουν τις απαιτήσεις των υπηρεσιών ευρείας ζώνης.Αυτή η αυξημένη χωρητικότητα των συστημάτων μπορεί να βελτιστοποιηθεί περαιτέρω εκμεταλλευόμενοι καλύτερα τα χαρακτηριστικά των ασύρματων καναλιών. Ηθεμελιώδηςιδέα ενός σχήματος κατανομής πόρων είναι η αποτελεσματική κατανομή των διαθέσιμων ασύρματων πόρων, όπως είναι οι υποφορείς και η ισχύς εκπομπής, μεταξύ των χρηστών του συστήματος. Σχετικά με τα προβλήματα της κατανομής πόρων σε ασύρματα συστήματα τηλεπικοινωνιών βασισμένα στην τεχνική OFDMA, η περισσότερη έρευνα επικεντρώνεται στην αναζήτηση πολιτικών ανάθεσης υποφορέων και ισχύος. Οι διαθέσιμες τεχνικές της βιβλιογραφίας δεν μπορούν να εφαρμοστούν όπως είναι σε συστήματα πολυεκπομπής. Επιπλέον, οι υπάρχουσες τεχνικές δεν μπορούν να εφαρμοστούν αμετάβλητες σε πραγματικά συστήματα στα οποία υπάρχει μεγάλος αριθμός OFDMυποφορέων, καθώς η υπολογιστική πολυπλοκότητα είναι πολύ μεγάλη. Ο βασικός στόχος της παρούσας διπλωματικής εργασίας είναι η πρόταση ικανών μηχανισμών κατανομής των διαθέσιμων υποφορέων σε ασύρματα συστήματα πολυεκπομπής χρησιμοποιώντας την τεχνολογία OFDMA. Πιο συγκεκριμένα, σχετικά με τα συστήματα πολυεκπομπής, θεωρούμε ότι τόσο ο σταθμός βάσης όσο και κάθε χρήστης είναι εφοδιασμένοι με μοναδική κεραία και η μονάδα κατανομής δεν είναι ο υποφορέας, όπως στα συμβατικά συστήματα OFDMA, αλλά μία ομάδα γειτονικώνυποφορέων, η οποία ονομάζεται τεμάχιο, με σκοπό τη μείωση της μεγάλης υπολογιστικής πολυπλοκότητας. Ένας αποτελεσματικός αλγόριθμος προτείνεται του οποίου ο στόχος είναι η μεγιστοποίηση του συνολικού ρυθμού μετάδοσης δεδομένων με περιορισμούς στη συνολική διαθέσιμη ισχύ, στο BERανά τεμάχιο και στους αναλογικούς περιορισμούς μεταξύ των ρυθμών μετάδοσης δεδομένων των ομάδων χρηστών. Η προσομοίωση και η ανάλυση της πολυπλοκότητας που παρουσιάζονται, υποστηρίζουν τα πλεονεκτήματα της κατανομής πόρων σε συστήματα πολυεκπομπήςOFDMA τα οποία βασίζονται σε κατανομή τεμαχίων και έχουν ως στόχος την εξασφάλιση της αναλογικότητας μεταξύ των ρυθμών μετάδοσης δεδομένων των ομάδων χρηστών.Wireless spectral efficiency is increasingly important due to the rapid growth of demand for high data rate wideband wireless services. The design of a multi-carrier system, such as an OFDMA system, enables high system capacity suited for these wideband wireless services. This system capacity can be further optimized with a resource allocation scheme by exploiting the characteristics of the wireless fading channels. The fundamental idea of a resource allocation scheme is to efficiently distribute the available wireless resources, such as the subcarriers and transmission power, among all admitted users in the system. Regarding the problems of resource allocation in OFDMA-based wireless communicationsystems, much of the research effort mainly focuses on finding efficient power controland subcarrier assignment policies. With systems employing multicast transmission,the available schemes in literature are not always applicable. Moreover, the existing approachesare particularly inaccessible in practical systems in which there are a large numberof OFDM subcarriers being utilized, as the required computational burden is prohibitivelyhigh. The ultimate goal of this Thesis is therefore to propose affordable mechanisms toflexibly and effectively share out the available resources in multicast wireless systems deployingOFDMA technology. Specifically, according to multicast system, it is assumed thatboth the BS and each user are equipped witha single antenna and the allocation unit is not the subcarrier,as in conventional OFDMA systems, but a set of contiguoussubcarriers, which is called chunk, in order to alleviate the heavy computational burden. An efficient algorithmis proposed whose aim is to maximize the total throughput subject to constraints on totalavailable power,BER over a chunk, and proportional data rates constraints among multicast groups. Simulation and complexity analysis are provided to support thebenefits of chunk-based resource allocation to multicast OFDMA systems with targeting proportional data rates among multicast groups

Optimal channel equalization for filterbank transceivers in presence of white noise

Filterbank transceivers are widely employed in data communication networks to cope with inter-symbol-interference (ISI) through the use of redundancies. This dissertation studies the design of the optimal channel equalizer for both time-invariant and time-varying channels, and wide-sense stationary (WSS) and possible non-stationary white noise processes. Channel equalization is investigated via the filterbank transceivers approach. All perfect reconstruction (PR) or zero-forcing (ZF) receiver filterbanks are parameterized in an affine form, which eliminate completely the ISI. The optimal channel equalizer is designed through minimization of the mean-squared-error (MSE) between the detected signals and the transmitted signals. Our main results show that the optimal channel equalizer has the form of state estimators, and is a modified Kalman filter. The results in this dissertation are applicable to discrete wavelet multitone (DWMT) systems, multirate transmultiplexers, orthogonal frequency division multiplexing (OFDM), and direct-sequence/spread-spectrum (DS/SS) based code division multiple access (CDMA) networks. Design algorithms for the optimal channel equalizers are developed for different channel models, and white noise processes, and simulation examples are worked out to illustrate the proposed design algorithms

Data transmissions through HFC return channels

Master'sMASTER OF ENGINEERIN

Simulation of wireless communication system using OFDM principle

FDMA, TDMA and CDMA are the well known multiplexing techniques used in wireless communication systems. While working with the wireless systems using these techniques various problems encountered are (1) multi-path fading (2) time dispersion which lead to intersymbol interference (ISI) (3) lower bit rate capacity (4) requirement of larger transmit power for high bit rate and (5) less spectral efficiency. The use of orthogonal frequency division multiplexing (OFDM) technique provides better solution for the above mentioned problems. The benefits of OFDM are high spectral efficiency, resiliency of RF interference, and lower multi-path distortion. OFDM is a powerful modulation technique that is capable of high data rate and is able to eliminate ISI. The use of FFT technique to implement modulation and demodulation functions makes it computationally more efficient

Design of optimal equalizers and precoders for MIMO channels

Channel equalization has been extensively studied as a method of combating ISI and ICI for high speed MIMO data communication systems. This dissertation focuses on optimal channel equalization in the presence of non-white observation noises with unknown PSD but bounded power-norm. A worst-case approach to optimal design of channel equalizers leads to an equivalent optimal H-infinity filtering problem for the MIMO communication systems. An explicit design algorithm is derived which not only achieves the zero-forcing (ZF) condition, but also minimizes the RMS error between the transmitted symbols and the received symbols. The second part of this dissertation investigates the design of optimal precoders which minimize the bit error rate (BER) subject to a fixed transmit-power constraint for the multiple antennas downlink communication channels under the perfect reconstruction (PR) condition. The closed form solutions are derived and an efficient design algorithm is proposed. The performance evaluations indicate that the optimal precoder design for multiple antennas communication systems proposed herein is an attractive/reasonable alternative to the existing precoder design techniques