OFDM in emerging wireless networks: synchronization algorithms and physical layer security

摘要: In the last decade, OFDM has been chosen as physical layer solution for a large variety of wireless, high data rates communication standards. The reasons this success are found in possibility coping with frequency selective channels simple and efficiently implemented transceivers, achieving spectral efficiency. order to push performance these systems close their limit, emerging wireless networks need efficient methods time synchronization, since an erroneous choice symbol timing residual offsets clock carrier frequencies at transmitter receiver can highly impair transmissions due effects ISI ICI. In first part thesis we focus on synchronization algorithms UWB MB systems. First, consider problem analyze case when channel delay spread is larger than cyclic prefix length determined by standard, that ICI not be completely avoided proper timing. case, identify appropriate target maximization ratio total useful received power over all subcarriers given realization. We also present practical low-complexity scheme show its tops results obtained best existing correlation-based estimators. Moreover, very transmission rate MB-OFDM architectures asks offset estimators moderate complexity fast acquisition times. Then, formulate based upon domain symbols, where both observed, jointly estimate them either linear least squares or maximum likelihood approach. assessed through simulation realistic scenario compared previous literature results. In parallel request rates, use sensitive communications raised increasing demand confidentiality (and security general) transmitted information. Physical valuable tool future secure information directly exploiting diversity legitimate nodes attacker. In second thesis, how information-theoretic adapted applied adopt modulation format. multicarrier architecture modeled particular instance MIMO channel. way, able evaluate capabilities system transmitting confidential messages leveraging presented Gaussian wiretap secrecy achievable transmitter/receiver pair presence eavesdropper might structure choose more complex architecture. The features used only transmit secret but share keys. general secret-key agreement (of which seen case) establish closed-form expressions capacity low-power high-power regimes. regime, optimal signaling strategy independent eavesdropper's fading By combining reconciliation privacy amplification, one obtains semi-blind key-distillation knowledge required amplification alone. A similar approach study jamming game environment. scenario, attacker active objective disrupt between users signal. setup zero-sum payoff function represented mutual receiver. Optimal strategies jammer, Nash equilibrium DMT FMT architectures.