62 research outputs found

    Multicarrier CDMA systems with MIMO technology

    Get PDF
    The rapid demand for broadband wireless access with fast multimedia services initiated a vast research on the development of new wireless systems that will provide high spectral efficiencies and data rates. A potential candidate for future generation wireless systems is multi-carrier code division multiple access (MC-CDMA). To achieve higher user capacities and increase the system data rate, various multiple-input multiple-output (MIMO) technologies such as spatial multiplexing and spatial diversity techniques have been proposed recently and combined with MC-CDMA.This research proposes a chip level coded ordered successive spatial and multiuser interference cancellation (OSSMIC) receiver for downlink MIMO MC-CDMA systems. As the conventional chip level OSIC receiver [1] is unable to overcome multiple access interference (MAI) and performs poorly in multiuser scenarios, the proposed receiver cancels both spatial and multiuser interference by requiring only the knowledge of the desired user's spreading sequence. Simulation results show that the proposed receiver not only performs better than the existing linear detectors [2] but also outperforms both the chip and symbol level OSIC receivers. In this work we also compare the error rate performance between our proposed system and MIMO orthogonal frequency division multiple access (MIMO OFDMA) system and we justify the comparisons with a pairwise error probability (PEP) analysis. MIMO MC-CDMA demonstrates a better performance over MIMO OFDMA under low system loads whereas in high system loads, MIMO OFDMA outperforms MIMO MC-CDMA. However if all users' spreading sequences are used at the desired user receiver, MIMO MC-CDMA performs better than MIMO OFDMA at all system loads.In the second part of this work, user grouping algorithms are proposed to provide power minimisation in grouped MC-CDMA and space-time block code (STBC) MC-CDMA systems. When the allocation is performed without a fair data rate requirement, the optimal solution to the minimisation problem is provided. However when some fairness is considered, the optimal solution requires high computational complexity and hence we solve this problem by proposing two suboptimal algorithms. Simulation results illustrate a significantly reduced power consumption in comparison with other techniques.EThOS - Electronic Theses Online ServiceEPSRCGBUnited Kingdo

    Adaptive Techniques for Packet-Oriented Transmissions in Future Multicarrier Wireless Systems

    Get PDF
    I sistemi wireless dei prossimi anni sono tenuti a fornire trasmissioni caratterizzate da data rate e affidabilità sempre maggiori per sostenere la sempre più crescente richiesta di applicazioni e servizi eterogenei. Inoltre, tali requisiti devono essere soddisfatti nel difficile ambiente di propagazione rappresentato dal canale wireless, e devono far fronte alla scarsità dello spettro radio disponibile. Per tali sistemi, la tecnica di modulazione multiportante nota come orthogonal frequency division multiplexing (OFDM) è emersa come tecnologia chiave a livello fisico grazie alla sua elevata efficienza spettrale, struttura di ricetrasmissione piuttosto semplice e robustezza al fenomeno di multipath fading. In tale contesto, questa tesi indaga nuove tecniche adattative in cui le risorse e parametri di trasmissione sono adattati in base alle informazioni sullo stato di canale al fine di fornire una consegna affidabile ed efficiente di pacchetti dati su canali selettivi in frequenza. Queste tecniche, note in letteratura come link resource adaptation (LRA) e resource allocation (RA), sono proposte in combinazione con un numero di funzionalità avanzate come l'efficiente tecnica di codifica di canale chiamata bit interleaved coded modulation (BICM) e meccanismi di hybrid automatic repeat request (HARQ). Diversamente dalla maggior parte dei problemi di LRA e RA considerati nella letteratura, questa tesi si basa sul goodput come figura di merito, definito come il numero di bit di informazione consegnati in pacchetti senza errori per unità di tempo. Quest'ultimo rappresenta, infatti, una metrica adeguata per dare un quadro attendibile delle effettive prestazioni del collegamento caratterizzato da modulazione e codifici pratici, trasmissioni a pacchetto e meccanismi di HARQ. In dettaglio, i contributi principali della tesi sono: la derivazione di una strategia di LRA che assegna modulazione, tasso di codifica e potenza ad un sistema BIC-OFDM cognitivo; un nuovo metodo di predizione delle prestazioni, che sfrutta la metodologia di effective signal-to-noise ratio (SNR), per sistemi BIC-OFDM impieganti protocolli di HARQ con packet combining; un algoritmo di LRA che seleziona la migliore distribuzione dei bit e tasso di codifica per sistemi BIC-OFDM; uno schema equo di RA che assegna potenza, ordine di modulazione, tasso di codifica e sottoportanti agli utenti sul downlink di un sistema BIC orthogonal frequency division multiple access (OFDMA) col fine di ottimizzare le prestazioni dell'utente avente il valore più basso di goodput

    Spectrum Adaptation in Cognitive Radio Systems with Operating Constraints

    Get PDF
    The explosion of high-data-rate-demanding wireless applications such as smart-phones and wireless Internet access devices, together with growth of existing wireless services, are creating a shortage of the scarce Radio Frequency (RF) spectrum. However, several spectrum measurement campaigns revealed that current spectrum usage across time and frequency is inefficient, creating the artificial shortage of the spectrum because of the traditional exclusive command-and-control model of using the spectrum. Therefore, a new concept of Cognitive Radio (CR) has been emerging recently in which unlicensed users temporarily borrow spectrum from the licensed Primary Users (PU) based on the Dynamic Spectrum Access (DSA) technique that is also known as the spectrum sharing concept. A CR is an intelligent radio system based on the Software Defined Radio platform with artificial intelligence capability which can learn, adapt, and reconfigure through interaction with the operating environment. A CR system will revolutionize the way people share the RF spectrum, lowering harmful interference to the licensed PU of the spectrum, fostering innovative DSA technology and giving people more choices when it comes to using the wireless-communication-dependent applications without having any spectrum congestion problems. A key technical challenge for enabling secondary access to the licensed spectrum adaptation is to ensure that the CR does not interfere with the licensed incumbent users. However, incumbent user behavior is dynamic and requires CR systems to adapt this behavior in order to maintain smooth information transmission. In this context, the objective of this dissertation is to explore design issues for CR systems focusing on adaptation of physical layer parameters related to spectrum sensing, spectrum shaping, and rate/power control. Specifically, this dissertation discusses dynamic threshold adaptation for energy detector spectrum sensing, spectrum allocation and power control in Orthogonal Frequency Division Multiplexing-(OFDM-)based CR with operating constraints, and adjacent band interference suppression techniques in turbo-coded OFDM-based CR systems

    Performance Optimization Over Wireless Links With Operating Constraints

    Get PDF
    Wireless communication is one of the most active areas of technological innovations and groundbreaking research ranging from simple cellular phones to highly complex military monitoring devices. The emergence of radios with cognitive capabilities like software defined radios has revolutionized modern communication systems by providing transceivers which can vary their output waveforms as well as their demodulation methods. This adaptability plays a pivotal role in efficient utilization of radio spectrum in an intelligent way while simultaneously not interfering with other radio devices operating on the same frequency band. Thus, it is safe to say that current and future wireless systems and networks depend on their adaptation capability which in turn presents many new technical challenges in hardware and protocol design, power management, interference metrics, distributed algorithms, Quality of Service (QoS) requirements arid security issues. Transmitter adaptation methods have gained importance, and numerous transmitter optimization algorithms have been proposed in recent years. The main idea behind these algorithms is to optimize the transmitted signals according to the patterns of interference in the operating environment such that some specific criterion is optimized. In this context, the objective of this dissertation is to propose transmitter adaptation algorithms in conjunction with power control for wireless systems focusing on performance optimization based on operating constraints. Specifically, this dissertation achieves joint transmitter adaptation and power control in the uplink and downlink of wireless systems with applications to Multiple-Input-Multiple-Output (MIMO) wireless systems and cognitive radio networks. In addition, performance of the proposed algorithms are evaluated in the context of fading channels, taking into consideration the time-varying nature of wireless channels
    • …
    corecore