Interference Aware Cognitive Femtocell Networks

Femtocells Access Points (FAP) are low power, plug and play home base stations which are designed to extend the cellular radio range in indoor environments where macrocell coverage is generally poor. They offer significant increases in data rates over a short range, enabling high speed wireless and mobile broadband services, with the femtocell network overlaid onto the macrocell in a dual-tier arrangement. In contrast to conventional cellular systems which are well planned, FAP are arbitrarily installed by the end users and this can create harmful interference to both collocated femtocell and macrocell users. The interference becomes particularly serious in high FAP density scenarios and compromises the ensuing data rate. Consequently, effective management of both cross and co-tier interference is a major design challenge in dual-tier networks. Since traditional radio resource management techniques and architectures for single-tier systems are either not applicable or operate inefficiently, innovative dual-tier approaches to intelligently manage interference are required. This thesis presents a number of original contributions to fulfill this objective including, a new hybrid cross-tier spectrum sharing model which builds upon an existing fractional frequency reuse technique to ensure minimal impact on the macro-tier resource allocation. A new flexible and adaptive virtual clustering framework is then formulated to alleviate co-tier interference in high FAP densities situations and finally, an intelligent coverage extension algorithm is developed to mitigate excessive femto-macrocell handovers, while upholding the required quality of service provision. This thesis contends that to exploit the undoubted potential of dual-tier, macro-femtocell architectures an interference awareness solution is necessary. Rigorous evidence confirms that noteworthy performance improvements can be achieved in the quality of the received signal and throughput by applying cognitive methods to manage interference

Radio network management in cognitive LTE-Femtocell Systems

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University London.There is a strong uptake of femtocell deployment as small cell application platforms in the upcoming LTE networks. In such two-tier networks of LTEfemtocell base stations, a large portion of the assigned spectrum is used sporadically leading to underutilisation of valuable frequency resources. Novel spectrum access techniques are necessary to solve these current spectrum inefficiency problems. Therefore, spectrum management solutions should have the features to improve spectrum access in both temporal and spatial manner. Cognitive Radio (CR) with the Dynamic Spectrum Access (DSA) is considered to be the key technology in this research in order to increase the spectrum efficiency. This is an effective solution to allow a group of Secondary Users (SUs) to share the radio spectrum initially allocated to the Primary User (PUs) at no interference. The core aim of this thesis is to develop new cognitive LTE-femtocell systems that offer a 4G vision, to facilitate the radio network management in order to increase the network capacity and further improve spectrum access probabilities. In this thesis, a new spectrum management model for cognitive radio networks is considered to enable a seamless integration of multi-access technology with existing networks. This involves the design of efficient resource allocation algorithms that are able to respond to the rapid changes in the dynamic wireless environment and primary users activities. Throughout this thesis a variety of network upgraded functions are developed using application simulation scenarios. Therefore, the proposed algorithms, mechanisms, methods, and system models are not restricted in the considered networks, but rather have a wider applicability to be used in other technologies. This thesis mainly investigates three aspects of research issues relating to the efficient management of cognitive networks: First, novel spectrum resource management modules are proposed to maximise the spectrum access by rapidly detecting the available transmission opportunities. Secondly, a developed pilot power controlling algorithm is introduced to minimise the power consumption by considering mobile position and application requirements. Also, there is investigation on the impact of deploying different numbers of femtocell base stations in LTE domain to identify the optimum cell size for future networks. Finally, a novel call admission control mechanism for mobility management is proposed to support seamless handover between LTE and femtocell domains. This is performed by assigning high speed mobile users to the LTE system to avoid unnecessary handovers. The proposed solutions were examined by simulation and numerical analysis to show the strength of cognitive femtocell deployment for the required applications. The results show that the new system design based on cognitive radio configuration enable an efficient resource management in terms of spectrum allocation, adaptive pilot power control, and mobile handover. The proposed framework and algorithms offer a novel spectrum management for self organised LTE-femtocell architecture. Eventually, this research shows that certain architectures fulfilling spectrum management requirements are implementable in practice and display good performance in dynamic wireless environments which recommends the consideration of CR systems in LTE and femtocell networks

Interference management and system optimisation for Femtocells technology in LTE and future 4G/5G networks

Femtocells are seen to be the future of Long Term Evaluation (LTE) networks to improve the performance of indoor, outdoor and cell edge User Equipments (UEs). These small cells work efficiently in areas that suffer from high penetration loss and path-loss to improve the coverage area. It is said that 30% of total served UEs in LTE networks are vehicular, which poses challenges in LTE networks due to their high mobility, high vehicular penetration loss (VPL), high path loss and high interference. Therefore, self-optimising and dynamic solutions are required to incorporate more intelligence into the current standard of LTE system. This makes the network more adaptive, able to handle peak data demands and cope with the increasing capacity for vehicular UEs. This research has drawn a performance comparison between vehicular UEs who are served by Mobile-Femto, Fixed-Femto and eNB under different VPL scales that range between highs and lows e.g. 0dB, 25dB and 40dB. Deploying Mobile-Femto under high VPLs has improved the vehicular UE Ergodic capacity by 1% and 5% under 25dB and 40dB VPL respectively as compared to other eNB technologies. A noticeable improvement is also seen in signal strength, throughput and spectral efficiency. Furthermore, this research discusses the co-channel interference between the eNB and the Mobile-Femto as both share the same resources and bandwidth. This has created an interference issue from the downlink signals of each other to their UEs. There were no previous solutions that worked efficiently in cases where UEs and base stations are mobile. Therefore, this research has adapted an efficient frequency reuse scheme that worked dynamically over distance and achieved improved results in the signal strength and throughput of Macro and Mobile-Femto UE as compared to previous interference management schemes e.g. Fractional Frequency Reuse factor1 (NoFFR-3) and Fractional Frequency Reuse factor3 (FFR-3). Also, the achieved results show that implementing the proposed handover scheme together with the Mobile-Femto deployment has reduced the dropped calls probability by 7% and the blocked calls probability by 14% compared to the direct transmission from the eNB. Furthermore, the outage signal probabilities under different VPLs have been reduced by 1.8% and 2% when the VPLs are 25dB and 40dB respectively compared to other eNB technologies

Hybrid Access Control Mechanism in Two-Tier Femtocell Networks

The cellular industry is undergoing a major paradigm shift from voice-centric, structured homogeneous networks to a more data-driven, distributed and heterogeneous architecture. One of the more promising trends emerging from this cellular revolution is femtocells. Femtocells are primarily viewed as a cost-effective way to improve both capacity and indoor coverage, and they enable offloading data-traffic from macrocell network. However, efficient interference management in co-channel deployment of femtocells remains a challenge. Decentralized strategies such as femtocell access control have been identified as an effective means to mitigate cross-tier interference in two-tier networks. Femtocells can be configured to be either open access or closed access. Prior work on access control schemes show that, in the absence of any coordination between the two tiers in terms of power control and user scheduling, closed access is the preferred approach at high user densities. Present methods suggest that in the case of orthogonal multiple access schemes like TDMA/OFDMA, femtocell access control should be adaptive according to the estimated cellular user density. The approach we follow, in this work, is to adopt an open access policy at the femtocell access points with a cap on the maximum number of users allowed on a femtocell. This ensures the femto owner retains a significant portion of the femtocell resources. We design an iterative algorithm for hybrid access control for femtocells that integrates the problems of uplink power control and base station assignment. This algorithm implicitly adapts the femtocell access method to the current user density. The distributed power control algorithm, which is based on Yates' work on standard interference functions, enables users to overcome the interference in the system and satisfy their minimum QoS requirements. The optimal allocation of femtocell resources is incorporated into the access control algorithm through a constrained sum-rate maximization to protect the femto owner from starvation at high user densities. The performance of a two-tier OFDMA femtocell network is then evaluated under the proposed access scheme from a home owner viewpoint, and network operator perspective. System-level simulations show that the proposed access control method can provide a rate gain of nearly 52% for cellular users, compared to closed access, at high user densities and under moderate-to-dense deployment of femtocells. At the same time, the femto owner is prevented from going into outage and only experiences a negligible rate loss. The results obtained establish the quantitative performance advantage of using hybrid access at femtocells with power control at high user densities. The convergence properties of the proposed iterative hybrid access control algorithm are also investigated by varying the user density and the mean number of femto access points in the network. It is shown that for a given system model, the algorithm converges quickly within thirty iterations, provided a feasible solution exists

D13.2 Techniques and performance analysis on energy- and bandwidth-efficient communications and networking

Deliverable D13.2 del projecte europeu NEWCOM#The report presents the status of the research work of the various Joint Research Activities (JRA) in WP1.3 and the results that were developed up to the second year of the project. For each activity there is a description, an illustration of the adherence to and relevance with the identified fundamental open issues, a short presentation of the main results, and a roadmap for the future joint research. In the Annex, for each JRA, the main technical details on specific scientific activities are described in detail.Peer ReviewedPostprint (published version

Adaptive management of cognitive radio networks employing femtocells

Network planning and management are challenging issues in a two-tier network. Tailoring to cognitive radio networks (CRNs), network operations and transmissions become more challenging due to the dynamic spectrum availability. This paper proposes an adaptive network management system that provides switching between different CRN management structures in response to the spectrum availability and changes in the service time required for the radio access. The considered network management system includes conventional macrocell-only structure, and centralized/distributed structures overlaid with femtocells. Furthermore, analytical expressions of per-tier successful connection probability and throughput are provided to characterize the network performance for different network managements. Spectrum access in dynamic radio environments is formulated according to the quality of service (QoS) constraint that is related to the connection probability and outage probability. Results show that the proposed intelligent network management system improves the maximum capacity and reduces the number of blocked connections by adapting between various network managements in response to free spectrum transmission slots. A road map for the deployment and management of cognitive macro/femto networks is also presented

Spatial spectrum reuse in heterogeneous wireless networks: interference management and access control

Διαχρονικά, η κυρίαρχη σχεδιαστική επιλογή για την βελτίωση της φασματικής απόδοσης των ασύρματων δικτύων κινητών επικοινωνιών είναι η χωρική επαναχρησιμοποίηση φάσματος, η δυνατότητα δηλαδή να επαναχρησιμοποιείται το ίδιο κομμάτι φάσματος πολλές φορές στο χώρο με την προϋπόθεση ότι διατηρούνται χαμηλά τα επίπεδα των παρεμβολών. Στα σύγχρονα δίκτυα κινητών επικοινωνιών μελετώνται δύο νέοι τρόποι χωρικής επαναχρησιμοποίησης φάσματος: α) η ανάπτυξη φεμτοκυψελών (femtocells), η ανάπτυξη δηλαδή μικρών κυψελών για εξυπηρέτηση κυρίως εσωτερικών χώρων στην ευρύτερη περιοχή κάλυψης μία κύριας κυψέλης, και β) η ενεργοποίηση επικοινωνιών συσκευής-σε-συσκευή (Device-to-Device – D2D), απευθείας δηλαδή επικοινωνιών χωρίς την διαμεσολάβηση του σταθμού βάσης της κυψέλης. Σκοπός της παρούσας διατριβής είναι να μελετηθούν και να αντιμετωπιστούν οι προκλήσεις που προκύπτουν από την εισαγωγή φεμτοκυψελών και την υιοθέτηση επικοινωνιών συσκευής-σε-συσκευή σε κυψελωτά δίκτυα προτυποποιημένα από την 3GPP (3rd Generation Partnership Project). Πιο συγκεκριμένα, μελετώνται τα προβλήματα της διαχείρισης του φάσματος και των παρεμβολών, καθώς και θέματα πρόσβασης στο φάσμα για Long Term Evolution (LTE) και LTE-Advanced (LTE-A) δίκτυα με φεμτοκυψέλες και με επικοινωνίες συσκευής-σε- συσκευή. Για το σκοπό αυτό, αρχικά μελετήθηκαν τα LTE/LTE-A κυψελωτά δίκτυα ως προς το φυσικό επίπεδο, την αρχιτεκτονική και τις παρεμβολές, αποτυπώνοντας και την τρέχουσα κατάσταση στο τομέα της προτυποποίησης των φεμτοκυψελών και των επικοινωνιών συσκευής-σε-συσκευή. Ακολούθησε μια συγκριτική μελέτη μηχανισμών διαχείρισης παρεμβολών σε κανάλια ελέγχου ενός LTE/LTE-A δικτύου με φεμτοκυψέλες και ένας καινοτόμος μηχανισμός ελέγχου ισχύος για μεταδόσεις φεμτοκυψελών, βασισμένος στην ποιότητα εμπειρίας στο τελικό χρήστη. Η δουλειά αυτή άνοιξε νέους ερευνητικούς ορίζοντες, όπου το επίπεδο ικανοποίησης του τελικού χρήστη παίζει ενεργό ρόλο στη διαχείριση του δικτύου και την παροχή των υπηρεσιών. Παρόλα αυτά, η περεταίρω μελέτη προς την κατεύθυνση αυτή είναι εκτός του σκοπού της παρούσας διατριβής. Στην συνέχεια, το κύριο βάρος της μελέτης μεταφέρθηκε στο πρόβλημα της διαχείρισης του φάσματος και των παρεμβολών στο πολύ πιο δυναμικό περιβάλλον ενός κυψελωτού δικτύου όπου επιτρέπονται οι επικοινωνίες συσκευής-σε-συσκευή. Σε πρώτη φάση, θεωρήθηκε ένα σύνολο από ζεύγη συσκευών που επικοινωνούν μεταξύ τους με επικοινωνίες συσκευής-σε-συσκευή και προτάθηκε ένας μηχανισμός συλλογής πληροφορίας παρεμβολών και ένα σχήμα ανάθεσης πόρων βασισμένο στη θεωρία γράφων. Το κύριο αποτέλεσμα της μελέτης αυτής ήταν πως αν και υψηλά επίπεδα χωρικής επαναχρησιμοποίησης μπορούν να επιτευχθούν, η συλλογή και η επεξεργασία πληροφορίας παρεμβολών είναι ένα πολύπλοκο πρόβλημα το οποίο απαιτεί και επιπλέον πόρους σηματοδοσίας. Έτσι, προτάθηκε και αναλύθηκε μίας λύση βασισμένη στον ανταγωνισμό. Πρακτικά οι χρήστες των επικοινωνιών συσκευής-σε-συσκευή εφαρμόζουν ένα σχήμα ανταγωνισμού όμοιο με αυτό που χρησιμοποιείται στα δίκτυα WiFi (Wireless Fidelity), προσαρμοσμένο όμως στο φυσικό επίπεδο των LTE/LTE-A δικτύων. Μαθηματική ανάλυση του σχήματος έδειξε ισχυρή εξάρτηση των επιδόσεων από το πλήθος των χρηστών που ανταγωνίζονται για το φάσμα. Σε μια προσπάθεια περιορισμού του πλήθους των ανταγωνιζόμενων χρηστών μόνο σε αυτούς που βρίσκονται σε γειτνίαση, και άρα μονό σε αυτούς που η άμεση επικοινωνία τους είναι εφικτή, μελετήθηκε το πρόβλημα της ανίχνευσης γειτονικής συσκευής. Με βάση τις τρέχουσες προδιαγραφές της 3GPP, για την επίλυση του προβλήματος ανίχνευσης γειτονικής συσκευής, μία συσκευή είτε ανακοινώνει με μετάδοση περιοδικών μηνυμάτων την παρουσία της σε μια συγκεκριμένη περιοχή, είτε αιτείται από κάποια συγκεκριμένη συσκευή πληροφορία ανίχνευσης. Υιοθετώντας τη δεύτερη περίπτωση, προτάθηκαν βελτιώσεις στο LTE/LTE-A δίκτυο πρόσβασης ώστε να επιτρέπεται η ανάθεση φάσματος για μεταδόσεις ανίχνευσης γειτονικών συσκευών. Παράλληλα, δεδομένου ότι και για τις μεταδόσεις αυτές απαιτείται η κατανάλωση φάσματος, σχεδιάστηκε και αξιολογήθηκε μία λύση βασισμένη στη χωρική επαναχρησιμοποίηση φάσματος. Το βασικό συμπέρασμα ήταν ότι λόγω των χαμηλών απαιτήσεων ποιότητας των μηνυμάτων ανίχνευσης, κάτω από ορισμένες συνθήκες πυκνότητας του δικτύου, μπορεί να επιτραπεί η χωρική επαναχρησιμοποίηση του κυψελωτού φάσματος για μεταδόσεις ανίχνευσης συσκευής.Historically, the spatial spectrum reuse has been the most efficient approach for improving cellular system capacity. Based on this observation, the 3rd Generation Partnership Project (3GPP) has proposed new spatial spectrum reuse schemes, towards fulfilling the International Mobile Telecommunications-Advanced (IMT-Advanced) requirements for the 4G networks. In this direction, a major shift is realized from wide-range cells with high transmit power (macrocells) to low-power small-sized cells (femtocells), while a lot of effort is allocated to the spatial spectrum reuse by enabling Device-to-Device (D2D) communications, i.e., direct communications in a cellular network, without the intervention of the base station. The scope of this thesis is to deal with challenges arising from the introduction of femtocells and D2D communications in cellular networks standardized by 3GPP Release 8 and beyond, i.e., Long Term Evolution (LTE) and LTE-Advanced (LTE-A). More specifically, for the case of femtocells, the interference management problem is studied, while for the D2D communications the radio resource management and the spectrum access challenges are addressed. First, a comprehensive description of the physical layer and architecture of the LTE/LTE-A networks is provided, and the current standardization efforts for the introduction of femtocells and D2D communications are described. Subsequently, different control channel interference management schemes for femtocell-overlaid LTE/LTE-A networks are studied, while an innovative power control scheme for the femtocell downlink transmissions is proposed, utilizing the end user’s quality of experience. This work brings to the surface new research challenges, where the end user’s satisfaction level plays an active role in network management and service provisioning. However, the further investigation of these challenges is out of this thesis’ scope. Considering the much more dynamic environment defined by the D2D communications in a cellular network, the major research effort is then shifted to the resource and interference management problem for D2D communications. Assuming a predefined set of D2D pairs in a cellular network, an interference information collection mechanism and a D2D resource allocation scheme, based on the graph-coloring theory, are proposed. Evaluation results showed that even high spatial spectrum reuse levels can be achieved, the interference collection and processing problem is quite complex, while additional signaling is needed. Taking this into account, a contention-based approach is proposed. Under this approach, the D2D devices compete for accessing the spectrum following a procedure similar with that used in WiFi (Wireless Fidelity) networks. Performance analysis shows that the efficiency of the proposed scheme depends on the number of competing devices. Towards restricting the number of competing devices, only to those that are in proximity and, thus, in valid positions for D2D communication, the device discovery problem is studied. According to the 3GPP standardization efforts, the solution of the device discovery problem requires frequent transmission of discovery signals from each device, either announcing its presence in a specific area, or requesting discovery information from a target device. Adopting the second option, enhancements in the 3GPP standardized access network are proposed, enabling a resource request / allocation procedure for device discovery transmissions. In parallel, a spatial spectrum reuse scheme is designed and evaluated, as an effort to reduce the consumption of radio resources for discovery transmissions. Analytical and simulation results show that, under certain conditions for the network density, a number of discovery transmissions can be enabled in a multi-cellular network even if no interference information is available

Cooperation strategies for inter-cell interference mitigation in OFDMA systems

Recently the use of modern cellular networks has drastically changed with the emerging Long Term Evolution Advanced (LTE-A) technology. Homogeneous networks which were initially designed for voice-centric and low data rates face unprecedented challenges for meeting the increasing traffic demands of high data-driven applications and their important quality of service requirements. Therefore, these networks are moving towards the so called Heterogeneous Networks (HetNets). HetNets represent a new paradigm for cellular networks as their nodes have different characteristics such as transmission power and radio frequency coverage area. Consequently, a HetNet shows completely different interference characteristics compared to homogeneous deployment and attention must be paid to these disparities when different tiers are collocated together. This is mostly due to the potential spectrum frequency reuse by the involved tiers in the HetNets. Hence, efficient inter-cell interference mitigation solutions in co-channel deployments of HetNets remain a challenge for both industry and academic researchers. This thesis focuses on LTE-A HetNet systems which are based on Orthogonal Frequency Division Multiplexing Access (OFDMA) modulation. Our aim is to investigate the aggressive interference issue that appears when different types of base stations are jointly deployed together and especially in two cases, namely Macro-Femtocells and Macro-Picocells co-existence. We propose new practical power adjustment solutions for managing inter-cell interference dynamically for both cases. In the first part dedicated to Femtocells and Macrocell coexistence, we design a MBS-assisted femtocell power adjustment strategy which takes into account femtocells users performance while mitigating the inter-cell interference on victim macrocell users. Further, we propose a new cooperative and context-aware interference mitigation method which is derived for realistic scenarios involving mobility of users and their varying locations. We proved numerically that the Femtocells are able to maintain their interference under a desirable threshold by adjusting their transmission power. Our strategies provide an efficient means for achieving the desired level of macrocell/femtocell throughput trade-off. In the second part of the studies where Picocells are deployed under the umbrella of the Macrocell, we paid a special attention and efforts to the interference management in the situation where Picocells are configured to set up a cell range expansion. We suggest a MBS-assisted collaborative scheme powered by an analytical model to predict the mobility of Macrocell users passing through the cell range expansion area of the picocell. Our goal is to adapt the muting ratio ruling the frequency resource partitioning between both tiers according to the mobility behavior of the range-expanded users, thereby providing an efficient trade-off between Macrocell and Picocell achievable throughputs.Récemment, l'utilisation des réseaux cellulaires a radicalement changé avec l’émergence de la quatrième génération (4G) de systèmes de télécommunications mobiles LTE/LTE-A (Long Term Evolution-Advanced). Les réseaux de générations précédentes (3G), initialement conçus pour le transport de la voix et les données à faible et moyen débits, ont du mal à faire face à l’augmentation accrue du trafic de données multimédia tout en répondant à leurs fortes exigences et contraintes en termes de qualité de service (QdS). Pour mieux répondre à ces besoins, les réseaux 4G ont introduit le paradigme des Réseaux Hétérogènes (HetNet).Les réseaux HetNet introduisent une nouvelle notion d’hétérogénéité pour les réseaux cellulaires en introduisant le concept des smalls cells (petites cellules) qui met en place des antennes à faible puissance d’émission. Ainsi, le réseau est composé de plusieurs couches (tiers) qui se chevauchent incluant la couverture traditionnelle macro-cellulaire, les pico-cellules, les femto-cellules, et les relais. Outre les améliorations des couvertures radio en environnements intérieurs, les smalls cells permettent d’augmenter la capacité du système par une meilleure utilisation du spectre et en rapprochant l’utilisateur de son point d’accès au réseau. Une des conséquences directes de cette densification cellulaire est l’interférence générée entre les différentes cellules des diverses couches quand ces dernières réutilisent les mêmes fréquences. Aussi, la définition de solutions efficaces de gestion des interférences dans ce type de systèmes constitue un de leurs défis majeurs. Cette thèse s’intéresse au problème de gestion des interférences dans les systèmes hétérogènes LTE-A. Notre objectif est d’apporter des solutions efficaces et originales au problème d’interférence dans ce contexte via des mécanismes d’ajustement de puissance des petites cellules. Nous avons pour cela distingués deux cas d’étude à savoir un déploiement à deux couches macro-femtocellules et macro-picocellules. Dans la première partie dédiée à un déploiement femtocellule et macrocellule, nous concevons une stratégie d'ajustement de puissance des femtocellules assisté par la macrocellule et qui prend en compte les performances des utilisateurs des femtocells tout en atténuant l'interférence causée aux utilisateurs des macrocellules sur leurs liens montants. Cette solution offre l’avantage de la prise en compte de paramètres contextuels locaux aux femtocellules (tels que le nombre d’utilisateurs en situation de outage) tout en considérant des scénarios de mobilité réalistes. Nous avons montré par simulation que les interférences sur les utilisateurs des macrocellules sont sensiblement réduites et que les femtocellules sont en mesure de dynamiquement ajuster leur puissance d'émission pour atteindre les objectifs fixés en termes d’équilibre entre performance des utilisateurs des macrocellules et celle de leurs propres utilisateurs. Dans la seconde partie de la thèse, nous considérons le déploiement de picocellules sous l'égide de la macrocellule. Nous nous sommes intéressés ici aux solutions d’extension de l’aire picocellulaire qui permettent une meilleure association utilisateur/cellule permettant de réduire l’interférence mais aussi offrir une meilleure efficacité spectrale. Nous proposons donc une approche basée sur un modèle de prédiction de la mobilité des utilisateurs qui permet de mieux ajuster la proportion de bande passante à partager entre la macrocellule et la picocellule en fonction de la durée de séjour estimée de ces utilisateurs ainsi que de leur demandes en bande passante. Notre solution a permis d’offrir un bon compromis entre les débits réalisables de la Macro et des picocellules

Study of continuous-phase four-state modulation for cordless telecommunications. Assessment by simulation of CP-QFSK as an alternative modulation scheme for TDMA digital cordless telecommunications systems operating in indoor applications

One of the major driving elements behind the explosive boom in wireless revolution is the advances in the field of modulation which plays a fundamental role in any communication system, and especially in cellular radio systems. Hence, the elaborate choice of an efficient modulation scheme is of paramount importance in the design and employment of any communications system. Work presented in this thesis is an investigation (study) of the feasibility of whether multilevel FSK modulation scheme would provide a viable alternative modem that can be employed in TDMA cordless communications systems. In the thesis the design and performance analysis of a non-coherent multi-level modem that offers a great deal of bandwidth efficiency and hardware simplicity is studied in detail. Simulation results demonstrate that 2RC pre-modulation filter pulse shaping with a modulation index of 0.3, and pre-detection filter normalized equivalent noise bandwidth of 1.5 are optimum system parameter values. Results reported in chapter 5 signify that an adjacent channel rejection factor of around 40 dB has been achieved at channel spacing of 1.5 times the symbol rate while the DECT system standards stipulated a much lower rejection limit criterion (25-30dB), implying that CP-QFSK modulation out-performs the conventional GMSK as it causes significantly less ACI, thus it is more spectrally efficient in a multi-channel system. However, measured system performance in terms of BER indicates that this system does not coexist well with other interferers as at delay spreads between 100ns to 200ns, which are commonly encountered in such indoor environment, a severe degradation in system performance apparently caused by multi-path fading has been noticed, and there exists a noise floor of about 40 dB, i.e. high irreducible error rate of less than 5.10-3. Implementing MRC diversity combiner and BCH codec has brought in a good gain.Higher Education Ministr