In this thesis a distributed, dynamic, load aware, joint power and frequency allocation protocol for 4G networks along with system-level simulated results are presented. In all cellular networks, a key limiting factor for throughput is inter-cell interference, especially at the cell edges. Several methods have been proposed and adopted in each mobile network generation to cancel or suppress its effects, whereas each method has its drawbacks in terms of receiver complexity or additional control nodes. However, the proposed protocol presented here does not impose any architectural changes.  In 4G networks such as LTE, the choice of OFDMA for the air interface has paved the way for selective frequency and power allocation in the available spectrum. Taking advantage of this opportunity, fractional frequency reuse (FFR) has been proposed in OFDMA based mobile networks in order to reduce the throughput loss at the cell edges due to inter-cell interference. In FFR, center users lose part of available spectrum that is dedicated to the edge users.  Our protocol aims to minimize this loss of center users incurred by FFR, at the cost of minimal degradation at the edges. An eNodeB, only when overloaded, requests its neighbours’ edge band to be used for its center users at a reduced power level. This is done via small message exchange between the eNodeBs. The neighbors of the overloaded eNodeBs solve a small local knapsack problem to decide whether band lending is feasible or not. A distinguishing feature of this protocol is the power level adjustment for the borrowed band, which is mutually decided by the borrower and lender. The band is released when it is not needed or it is causing unacceptable loss to the lender. The implementation is done in a Matlab based LTE system level simulator. For the implementation of our protocol in the simulator, starting point was implementation of FFR-3 functionality, a prerequisite and a baseline for comparison with our protocol. Results are compared among three different setups of re-use1, FFR-3 and our protocol by varying number of overloaded eNodeBs for various numbers of scenarios and the comparison is made based on the center users’ throughput, edge users’ throughput. An estimation of time and protocol overhead is also presented. We have observed center users’ throughput gain up to 46%, at the cost of 9% edge users’ throughput loss, when compared to the classic FFR-3 scheme. The overall system throughput goes up to 26 % in heavily loaded scenario.   The utility of the protocol for an LTE system is evident from the results, which is supported by the dynamic and decentralized nature of the protocol. This ensures better utilization of spectrum, by temporarily allocating more bandwidth where it is needed more.

A successive interference cancellation (SIC) structure is proposed for multiuser interference cancellation (MUI) due to carrier frequency offsets (CFOs) in the uplink of orthogonal frequency division multiple access (OFDMA) systems. The proposed architecture adopts a circular convolution to suppress the impacts caused by CFOs. This paper demonstrates that, with 2 iterations, the SIC has better performance than that of the parallel interference cancellation (PIC), but system complexity is only 1/2K, where K is the number of users in the uplink of OFDMA system. This study also shows that system complexity can be significantly reduced if proper approximation is made.

none

No description available.

Regarding the problems of resource allocation in OFDMA-based wireless communication systems, much of the research effort mainly focuses on finding efficient power control and subcarrier assignment policies. With systems employing multicast transmission, the available schemes in literature are not always applicable. Moreover, the existing approaches are particularly inaccessible in practical systems in which there are a large number of OFDM subcarriers being utilized, as the required computational burden is prohibitively high. The ultimate goal of this research is therefore to propose affordable mechanisms to flexibly and effectively share out the available resources in multicast wireless systems deploying OFDMA technology. Specifically, we study the resource distribution problems in both conventional and cognitive radio network settings, formulating the design problems as mathematical optimization programs, and then offering the solution methods. Suboptimal and optimal schemes with high performance and yet of acceptable complexity are devised through the application of various mathematical optimization tools such as genetic algorithm and Lagrangian dual optimization. The novelties of the proposed approaches are confirmed, and their performances are verified by computer simulation with the presentation of numerical examples to support the findings. / Communications

Η έρευνα στις ασύρματες τηλεπικοινωνίες κινείται προς την κατεύθυνση της επίτευξης υψηλής κινητικότητας και ταυτόχρονα προς τη μεγιστοποίηση των δυνατοτήτων του ραδιοδιαύλου, όσον αφορά τη χωρητικότητα της γραμμής και την ταυτόχρονη εξυπηρέτηση μεγάλου αριθμού χρηστών. Στόχος είναι η υποστήριξη IMT-Advanced (4G) ταχυτήτων της τάξης των 100 Μbps στην κάτω ζεύξη και 50 Μbps στη άνω με τη μέση φασματική απόδοση να είναι 3 με 4 φορές καλύτερη από την αντίστοιχη του HSPA. Για να επιτευχθούν τόσο οι υψηλές ταχύτητες όσο και η φασματική αποδοτικότητα σε συνδυασμό με την καλή κινητικότητα, πρέπει όπως δείχνει η έρευνα σήμερα, στο φυσικό στρώμα μετάδοσης να εφαρμοστούν τεχνικές OFDMA (Orthogonal Frequency Division Multiple Access - Πολλαπλή Πρόσβαση με Ορθογωνική Διαίρεση Συχνότητας) σε MIMO ή MISO συστήματα, όπως αντίστοιχα συμβαίνει στο WiMAX. Για αυτόν το λόγο στην παρούσα διπλωματική προτείνονται 3 αλγόριθμοι κατανομής των ραδιοπόρων για την κάτερχόμενη ζεύξη των MISO OFDMA. Οι δυο πρώτοι αλγόριθμοι σκοπεύουν τη μεγιστοποίηση του συνολικού ρυθμού μετάδοσης δεδομένων των χρηστών κάτω από τους περιορισμούς στη συνολική διαθέσιμη ισχύ του σταθμού βάσης και την αναλογική δικαιοσύνη μεταξύ των ρυθμών μεταδόσεως δεδομένων των χρηστών. Ο τρίτος αλγόριθμος αντί για τον περιορισμό της αναλογικής δικαιοσύνης εφαρμόζει τον περιορισμό στον ελάχιστο ρυθμό μετάδοσης των δεδομένων κάθε χρήστη. Οι προτεινόμενοι αλγόριθμοι βασίζονται στο σχηματισμό δέσμης ZF ενώ στο δεύτερο αλγόριθμο χρησιμοποιείται και η χωρική συσχέτιση. Παρ’όλο που και οι τρεις αλγόριθμοι είναι υποβέλτιστοι, η απώλεια σε συνολικό ρυθμό μετάδοσης δεδομένων είναι λογική εφόσον πρωταρχικός σκοπός αποτελεί η εξασφάλιση της δικαιοσύνης. Και οι τρεις προτεινόμενοι αλγόριθμοι εν τέλει παρουσιάζουν ικανοποιητική πολυπλοκότητα ώστε η υλοποίηση να είναι δυνατή με χαμηλό κόστος επεξεργασίας. Μπορούν λοιπόν κάλλιστα οι αλγόριθμοι που μελετήθηκαν να χρησιμοποιηθούν στα σύγχρονα ασύρματα συστήματα όπως το πρότυπο WiMAX. Οι προτεινόμενοι αλγόριθμοι εξομοιώθηκαν χρησιμοποιώντας το λογισμικό MATLAB®. Πιο συγκεκριμένα το κεφάλαιο ένα αποτελεί την εισαγωγή της διπλωματικής εργασίας. Αναφέρεται στο σκοπό της όσο και στις μεθόδους που χρησιμοποιήθηκαν για την επίτευξή του. Στο κεφάλαιο δύο γίνεται αναφορά στα ασύρματα συστήματα πολλαπλής πρόσβασης, τα οποία διαχωρίζονται σε σταθερά και κινητά συστήματα επικοινωνιών. Περιγράφονται συστήματα όπως τa 3G και Wi-Fi ενώ στη συνέχεια γίνεται ιστορική αναφορά στην εξέλιξη του WiMAX και μια μικρή παρουσίασή του. Τέλος, γίνεται μια μικρή αναφορά στον ασύρματο ευρυζωνικό δίαυλο. Στο κεφάλαιο τρία παρουσιάζονται θεωρητικά στοιχεία για τα OFDM και OFDMA και παρουσιάζονται οι μαθηματικές εκφράσεις του προβλήματος διαχείρισης των ραδιοπόρων σε αυτά. Επιπλέον, γίνεται αναφορά στους αλγόριθμους διαχείρισης ραδιοπόρων και μια εισαγωγή στο μαθηματικό μοντέλο που χρησιμοποιήθηκε. Το κεφάλαιο τέσσερα περιέχει εκτενή αναφορά στα ασύρματα κανάλια και ιδιαίτερα στα MIMO και στη χωρητικότητά τους. Το κεφάλαιο πέντε περιλαμβάνει τους αλγόριθμους που προτάθηκαν και μελετήθηκαν και ολοκληρώνεται με τα συμπεράσματα από τη διαδικασία εξομοίωσης. Στο κεφάλαιο έξι περιλαμβάνονται τα επιμέρους συμπεράσματα που έχουν εξαχθεί από κάθε κεφάλαιο. / Present research in wireless telecommunications is targeted on achieving high mobility and maximizing the potentials of the radio bus in the same time, concerning line’s capacity and simultaneusly serving a major number of users. The aim is supporting IMT-Advanced (4G) speeds; 100 Μbps download and 50 Μbps upload, with an average spectrum performance three to four times better than HSPA’s. In order to achieve such high speeds, as well as spectrum efficiency, in combination with a fair mobility, it is almost essential as shown in present global research, to apply OFDMA (Orthogonal Frequency Division Multiple Access) technics in the physical layer of MIMO or MISO systems, as applied in WiMAX. Thus, in this dissertation, three algorithms for the radio resource allocation problem of the downlink of MISO-OFDMA are proposed. The first two algorithms are aiming at maximizing the sum user’s data rate under restrictions in total available base station’s power and proportional fairness data rate constraints among users. The third algorithm applies constraints of the minimum data rate of each user instead of proportional rate constraints. The proposed algorithms are based on forming a ZF beam, while in the second algorithm space correlation is used. Although all three algorithms are suboptimal, the loss in total data rate is reasonable, since the primary target is maintaining fair justice among users. All three proposed algorithms have fairly low complexity so they could be applied easily with low calculation cost. Therefore, the investigated algorithms could be applied in modern wireless systems such as WiMAX. These algorithms are assessed by simulation using MATLAB® software. Specifically, chapter one includes the introduction of this dissertation. It is referred to its purpose as well as to the methods applied in. In chapter two there is a brief description in modern wireless telecommunication systems. Systems like 3G and Wi-Fi are presented along with a brief history of WiMAX and its characteristics. In the end of this chapter problems concerning wireless broadband bus are presented. In chapter three theoretical elements on OFDM and OFDMA are analysed along with the mathematical expression of the radio resource allocation problem in OFDMA. Moreover an introduction of a mathematical model is included. Chapter four focuses on detail on the mathematical description of the MIMO-MISO line capacity. In chapter five the three proposed algorithms on the downlink of MISO - OFDMA are presented. It concludes with the simulation results accompanied with some comments and conclusions. In chapter six all the conclusions of this dissertation, chapter by chapter are included in brief.

A grande popularidade dos dispositivos móveis que provêm acesso ubíquo à Internet de banda larga, através de redes de rádio, e o volume de tráfego gerado por estes dispositivos estão aumentando a cada ano. Além disso, vem ampliando consideravelmente a frequência com que usuários de dispositivos móveis estão usando serviços baseados na Web. Alguns destes usuários podem estar acessando serviços que precisam de transmissão contínua como, por exemplo, vídeos interativos, outros podem estar apenas lendo e-mails, o que não exige um fluxo contínuo de dados. Mais do que isso, usuários com altos níveis de sinal podem atingir melhores taxas de transferência do que os com níveis menores. Portanto, encontrar a melhor relação entre os usuários que estão acessando serviços sensíveis ao atraso e aqueles que maximizam a taxa de transferência, e ainda ser justo na transmissão, é um relevante desafio para o escalonamento dos recursos de uma rede sem fio. Embora as pesquisas de escalonamento de recursos em redes sem fio tenham evoluído neste sentido, o recente aumento do volume de tráfego mencionado pode levar a uma sobrecarga no sistema, comprometendo o escalonamento. A fim de enfrentar estes desafios, o Orthogonal Frequency Division Multiple Access (OFDMA), tecnologia fundamental para o acesso múltiplo em redes de quarta geração, tem sido considerado também para ser utilizado na próxima geração de rádios móveis. Para implementar um serviço efetivo aos usuários, requisitos, tais como, altas taxas de transferência, tolerância baixa ao atraso, minimização da perda de pacotes e maximização da justiça no escalonamento, devem somar-se à característica, de alta densidade de usuários, que surgiu após o advento da popularização dos dispositivos móveis. Portanto, novas estratégias de escalonamento devem ser idealizadas. Nesta dissertação, deu-se um passo além na proposição de um escalonador para as redes móveis de próxima geração, que busca melhorar a relação entre taxa de transferência e atraso, consequentemente, levando a maiores índices de justiça no escalonamento resultante. O escalonador foi especialmente desenvolvido para lidar com altas densidades de usuários, inerentes às redes modernas, e as redes LTE foram utilizadas como caso de estudo. Desta forma, um novo escalonador ótimo que considera provisão dos requisitos acima mencionados, é modelado. Além disso, uma nova heurística parametrizável, baseada na qualidade do canal do usuário, no atraso permitido por cada serviço e na justiça do escalonamento é proposta, a fim de lidar com cenários sobrecarregados. Resultados demonstram que a abordagem de escalonamento proposta leva a uma taxa de transferência apenas 7,5% menor que os valores ótimos, com 25% a menos de perda de pacotes em cenários sobrecarregados. O modelo também garante que o escalonamento resultante seja pelo menos 0,91 na escala do índice de justiça de Jain. Finalmente, os resultados mostram uma melhor relação entre a eficiência espectral e as métricas de QoS. / The huge popularity of mobile devices that provides a ubiquitous Internet broadband access via radio networks and the volume of traffic generated by these devices in the base stations are increasing every year. Furthermore, the frequency which, mobile users are using web-based services, is increasing, requiring high transfer rates such as transmission of interactive videos. These factors have become the main challenges for the scheduling of radio resources. In order to meet these challenges, the Orthogonal Frequency Division Multiple Access (OFDMA), a key technology for multiple access in fourth generation networks, has also been considered for use in next-generation mobile radios. To implement an effective service to users, requirements such as high transfer rates, lower delay tolerance, minimum packet loss and maximum scheduling fairness, should be added to the requirements that emerged after the advent of the popularity of mobile devices. Therefore, new scheduling strategies should be projected. Despite efforts to solve the downlink (DL) scheduling problem on wireless networks, we are not aware of previous attempts that have addressed the above requirements in a single strategy. In this thesis, we took a step further in this direction and still considering the high densities in small cells inherent in modern networks. In additional, we address the radio DL resource scheduling problem for multiple users using LTE networks as a case study. A new optimal scheduler is modeled regarding Quality of Service (QoS) provisioning. In addition, a parameterized heuristic based on user channel quality and service delay is proposed to reach scheduling solutions for overbooked scenarios. Results demonstrate that the proposed scheduling approaches led to a throughput of 7.5% lower than the optimal ones and 25% lower packet losses in overloaded scenarios. Our model also ensures that the resultant scheduling is at least as fair as 0.91 in Jain fairness index. Additionally, the obtained results show a reasonable trade-off between spectral efficiency and QoS metrics.

A grande popularidade dos dispositivos móveis que provêm acesso ubíquo à Internet de banda larga, através de redes de rádio, e o volume de tráfego gerado por estes dispositivos estão aumentando a cada ano. Além disso, vem ampliando consideravelmente a frequência com que usuários de dispositivos móveis estão usando serviços baseados na Web. Alguns destes usuários podem estar acessando serviços que precisam de transmissão contínua como, por exemplo, vídeos interativos, outros podem estar apenas lendo e-mails, o que não exige um fluxo contínuo de dados. Mais do que isso, usuários com altos níveis de sinal podem atingir melhores taxas de transferência do que os com níveis menores. Portanto, encontrar a melhor relação entre os usuários que estão acessando serviços sensíveis ao atraso e aqueles que maximizam a taxa de transferência, e ainda ser justo na transmissão, é um relevante desafio para o escalonamento dos recursos de uma rede sem fio. Embora as pesquisas de escalonamento de recursos em redes sem fio tenham evoluído neste sentido, o recente aumento do volume de tráfego mencionado pode levar a uma sobrecarga no sistema, comprometendo o escalonamento. A fim de enfrentar estes desafios, o Orthogonal Frequency Division Multiple Access (OFDMA), tecnologia fundamental para o acesso múltiplo em redes de quarta geração, tem sido considerado também para ser utilizado na próxima geração de rádios móveis. Para implementar um serviço efetivo aos usuários, requisitos, tais como, altas taxas de transferência, tolerância baixa ao atraso, minimização da perda de pacotes e maximização da justiça no escalonamento, devem somar-se à característica, de alta densidade de usuários, que surgiu após o advento da popularização dos dispositivos móveis. Portanto, novas estratégias de escalonamento devem ser idealizadas. Nesta dissertação, deu-se um passo além na proposição de um escalonador para as redes móveis de próxima geração, que busca melhorar a relação entre taxa de transferência e atraso, consequentemente, levando a maiores índices de justiça no escalonamento resultante. O escalonador foi especialmente desenvolvido para lidar com altas densidades de usuários, inerentes às redes modernas, e as redes LTE foram utilizadas como caso de estudo. Desta forma, um novo escalonador ótimo que considera provisão dos requisitos acima mencionados, é modelado. Além disso, uma nova heurística parametrizável, baseada na qualidade do canal do usuário, no atraso permitido por cada serviço e na justiça do escalonamento é proposta, a fim de lidar com cenários sobrecarregados. Resultados demonstram que a abordagem de escalonamento proposta leva a uma taxa de transferência apenas 7,5% menor que os valores ótimos, com 25% a menos de perda de pacotes em cenários sobrecarregados. O modelo também garante que o escalonamento resultante seja pelo menos 0,91 na escala do índice de justiça de Jain. Finalmente, os resultados mostram uma melhor relação entre a eficiência espectral e as métricas de QoS. / The huge popularity of mobile devices that provides a ubiquitous Internet broadband access via radio networks and the volume of traffic generated by these devices in the base stations are increasing every year. Furthermore, the frequency which, mobile users are using web-based services, is increasing, requiring high transfer rates such as transmission of interactive videos. These factors have become the main challenges for the scheduling of radio resources. In order to meet these challenges, the Orthogonal Frequency Division Multiple Access (OFDMA), a key technology for multiple access in fourth generation networks, has also been considered for use in next-generation mobile radios. To implement an effective service to users, requirements such as high transfer rates, lower delay tolerance, minimum packet loss and maximum scheduling fairness, should be added to the requirements that emerged after the advent of the popularity of mobile devices. Therefore, new scheduling strategies should be projected. Despite efforts to solve the downlink (DL) scheduling problem on wireless networks, we are not aware of previous attempts that have addressed the above requirements in a single strategy. In this thesis, we took a step further in this direction and still considering the high densities in small cells inherent in modern networks. In additional, we address the radio DL resource scheduling problem for multiple users using LTE networks as a case study. A new optimal scheduler is modeled regarding Quality of Service (QoS) provisioning. In addition, a parameterized heuristic based on user channel quality and service delay is proposed to reach scheduling solutions for overbooked scenarios. Results demonstrate that the proposed scheduling approaches led to a throughput of 7.5% lower than the optimal ones and 25% lower packet losses in overloaded scenarios. Our model also ensures that the resultant scheduling is at least as fair as 0.91 in Jain fairness index. Additionally, the obtained results show a reasonable trade-off between spectral efficiency and QoS metrics.

Abstract Radio link adaptation, multiple antenna techniques, relaying methods and dynamic radio resource assignment are among the key methods used to improve the performance of wireless communication networks. Opportunistic resource block (RB) allocation in downlink orthogonal frequency division multiple access (OFDMA) with limited feedback is considered. The spectral efficiency analysis of multiuser OFDMA with imperfect feedback path, multiple antenna methods and relaying methods is a particular focus. The analysis is derived for best-M feedback methods and for a RB-wise signal-to-noise ratio (SNR) quantization based feedback strategy. Practical resource fair round robin (RR) allocation is assumed at the RB assignment, i.e., each user gets the same portion of the available RBs. The fading of each RB is modelled to be independent and identically distributed (IID). This assumption enabled a communication theoretic approach for the performance evaluation of OFDMA systems The event probabilities related to the considered OFDMA systems are presented so that the feedback bit error probability (BEP) is a parameter in the expressions. The performance expressions are derived for the BEP in the case of binary phase-shift keying (BPSK) modulation and single antenna methods. Asymptotic BEP behavior is considered for the best-M feedback methods when the mean SNR tends to infinity. The system outage capacity and the average system spectral efficiency are investigated in the case of multiple antenna schemes. Antenna selection and space-time block coding (STBC) are considered in multiple antenna schemes when each RB is allocated exclusively to a single user. Simple OFDMA-spatial division multiple access (SDMA) schemes are also analyzed when zero forcing (ZF) detection is assumed at the receiver. Relay enhanced dynamic OFDMA with single and multiple antennas at each end is considered for fixed infrastructure amplify-and-forward (AF) relaying methods. The average spectral efficiency has been derived for the best-M and RB-wise one bit feedback schemes, antenna selection and STBC methods. The best choice for a combination of multiple antenna scheme and feedback strategy depends on several system parameters. The proposed analytical tools enable easy evaluation of the performance of the investigated schemes with different system parameters. The fundamental properties of the combinations of feedback and multiple antenna schemes are extensively studied through numerical examples. The results also demonstrate that the analytical results with idealized IID fading assumption are close to those obtained via simulations in a practical frequency selective channel when RBs are selected properly. Dynamic RB allocation is attractive for practical OFDMA systems since significant performance gain over random allocation can be achieved with a practical allocation principle, very low feedback overhead and an imperfect feedback channel.

Aim of thesis was to acquaint with architecture and process of signal in systems using broadband LTE wireless technology. Thesis in detail is described physical layer of system. Next there is described comparison of LTE and WiMAX and table with all present systems. Thesis also is contained information about tested LTE system in real traffic. Next aim was created simulation of LTE system in downlink and uplink. Interface was created for easier configuration of each characteristics of transfer and type of interference of useful signal. This interface is contained control of whole simulation and presentation of measured values. Measured data were processed into graphs, which show dependence of error rate BER on C/N of useful and interference signal.