A wide range of services and applications become possible when accurate position information for a radio terminal is available. These include: location-based services; navigation; safety and security applications. The commercial, industrial and military value of radio-location is such that considerable research effort has been directed towards developing related technologies, using satellite, cellular or local area network infrastructures or stand-alone equipment. This work studies and investigates two location techniques. The first one presents an implementation scheme for a wideband transmission and direction finding system using OFDM multi-carrier communications systems. This approach takes advantage of delay discrimination to improve angle-of-arrival estimation in a multipath channel with high levels of additive white Gaussian noise. A new methodology is interpreted over the multi carrier modulation scheme in which the simulation results of the estimated channel improves the performance of OFDM signal by mitigating the effect of frequency offset synchronization to give error-free data at the receiver, good angle of arrival accuracy and improved SNR performance. The full system simulation to explore optimum values such as channel estimation and AoA including the antenna array model and prove the operational performance of the OFDM system as implemented in MATLAB. The second technique proposes a low cost-effective method of tracking and monitoring objects (examples: patient, device, medicine, document) by employing passive radio frequency identification (RFID) systems. A multi-tag, (totalling fifty-six tags) with known ID values are attached to the whole patient’s body to achieve better tracking and monitoring precision and higher accuracy. Several tests with different positions and movements are implemented on six patients. The aim is to be able to track the patient if he/she is walking or sitting; therefore, the tests considered six possible movements for the patient including walking, standing, sitting, resting, laying on the floor and laying on the bed, these placements are important to monitor the status of the patient like if he collapsed and fall on the ground so that the help will be quick. The collected data from the RFID Reader in terms of Time Stamp, RSS, Tag ID, and a number of channels are processed using the MATLAB code.

Approved for public release, distribution is unlimited / Orthogonal frequency division multiplexing (OFDM) is being successfully used in numerous applications. It was chosen for IEEE 802.11a wireless local area network (WLAN) standard, and it is being considered for the fourthgeneration mobile communication systems. Along with its many attractive features, OFDM has some principal drawbacks. Sensitivity to frequency errors is the most dominant of these drawbacks. In this thesis, the frequency offset and phase noise effects on OFDM based communication systems are investigated under a variety of channel conditions covering both indoor and outdoor environments. The simulation performance results of the OFDM system for these channels are presented. / Lieutenant Junior Grade, Turkish Navy

Αντικείμενο της παρούσας διδακτορικής διατριβής είναι η μελέτη και ο σχεδιασμός καινοτόμων αλγορίθμων φυσικού επιπέδου σε ασύρματα συστήματα επικοινωνίας που χρησιμοποιούν διαμόρφωση με πολύπλεξη συχνότητας ορθογωνίων φερουσών (Orthogonal Frequency Division Multiplexing - OFDM). Η έρευνα επικεντρώθηκε σε δύο κατηγορίες προβλημάτων, στον σχεδιασμό αλγορίθμων προσαρμοστικής διαμόρφωσης καθώς και αλγορίθμων αντιμετώπισης ισχυρού θορύβου φάσης. Αναπτύχθηκαν αλγόριθμοι εκτίμησης φάσης με γραμμική πολυπλοκότητα, μέσω ενός καινούργιου εναλλακτικού μοντέλου περιγραφής του συστήματος. Το μοντέλο αυτό επιτρέπει την επέκταση των κλασικών αλγορίθμων εκτίμησης της κοινής φάσης με στόχο την εκτίμηση του συνολικού διανύσματος θορύβου φάσης. Επιπλέον, η τεχνική διαγώνιας φόρτωσης (diagonal-loading) προσαρμόστηκε κατάλληλα για τη βελτίωση σύγκλισης της προτεινόμενης λύσης. Τέλος, προτάθηκε και αξιολογήθηκε ένα συνολικό σύστημα OFDM όπου η εκτίμηση του καναλιού, της διαταραχής φάσης και των δεδομένων βασίζονται στο κριτήριο ελαχίστων τετραγώνων, διατηρώντας έτσι τη συνολική πολυπλοκότητα σε χαμηλά επίπεδα. Στο πλαίσιο του σχεδιασμού αλγορίθμων προσαρμοστικής διαμόρφωσης προτείνεται ένα γενικό μοντέλο περιγραφής απόδοσης συστήματος ικανό να περιγράψει τα αναπτυσσόμενα πρωτόκολλα μετάδοσης. Η πρόταση αυτή εντάσσεται στην οικογένεια των τεχνικών ισοδύναμης σηματοθορυβικής απεικόνισης (Εffective SNR Μapping - ESM). Χρησιμοποιώντας τις τεχνικές ESM και κατάλληλους περιορισμούς στην παραμετροποίηση των μεταβλητών μετάδοσης, αναπτύχθηκαν αλγόριθμοι προσαρμοστικής διαμόρφωσης χαμηλής πολυπλοκότητας που ικανοποιούν διαφορετικά κριτήρια βελτιστοποίησης. Επιπρόσθετα, προτείνεται ένα γενικό πλαίσιο για τον σχεδιασμό αλγορίθμων προσαρμοστικής διαμόρφωσης, χρησιμοποιώντας προσεγγιστικά μοντέλα απόδοσης. Ορίστηκαν οι κατάλληλες μετρικές για την ποσοτικοποίηση της σπατάλης ενέργειας που επιφέρει η χρήση προσεγγιστικών μοντέλων. Μελετήθηκε η επίδραση της καθυστέρησης ανατροφοδότησης πληροφορίας καναλιού στους αλγορίθμους και παρήχθησαν κατάλληλα μοντέλα περιγραφής απόδοσης που συμπεριλαμβάνουν το χρόνο καθυστέρησης. Το συνολικό αποτέλεσμα της εργασίας είναι αλγόριθμοι που καταφέρνουν υψηλή απόδοση συστήματος, με χαμηλή πολυπλοκότητα, κάτι το οποίο τους κάνει υλοποιήσιμους σε ρεαλιστικά συστήματα. / The objective of this thesis is to study and develop novel, low complexity physical layer algorithms for Orthogonal Frequency Division Multiplexing (OFDM) based communication systems. The study aims at two algorithmic categories, namely adaptive modulation and coding and compensation of severe phase noise (PHN) errors. A parameterized windowed least-squares (WLS) decision directed phase error estimator is proposed via proper (alternative) system modeling, applied to both channel estimation and data detection stage in OFDM systems. The window is optimized so as to minimize the post-compensation error variance (PCEV) of the residual phase, analytically computed for arbitrary PHN and frequency offset (FO) models. Closed-form expressions for near-optimal windows are derived for zero-mean FO, Wiener and first-order autoregressive PHN models, respectively. Furthermore, the diagonal-loading approach is properly employed, initially proposed for providing robustness to a general class of estimators in the presence of model mismatch, to enhance convergence of the iterative estimation scheme, in those high-SNR regions where the effect of data decision errors dominates performance. In the proposed OFDM scheme, channel, IFO estimation and data equalization are also based on the LS criterion, thus keeping the overall system complexity low. A generic performance description model is proposed and used for AMC algorithmic design, capable of describing most of current and under preparation communication protocols. This model proposition is incorporated to a larger family of performance modelling techniques named Effective SNR Mapping techniques (ESM). Using the ESM techniques and proper parameter adaptation constraints, a number of low-complexity AMC algorithms are developed under a chosen set of optimization scenarios. A framework for the design of AMC algorithms using approximate performance description models is proposed. Specific bounds are derived for quantifying the power loss when using approximate models. The effect of outdated channel state information is also studied by statistically characterizing the effective SNR at the receiver. This description allows parameter adaptation under mobility scenarios. The main value of this collective procedure is the development of low complexity- high performance algorithms, implementable on pragmatic OFDM systems.

Parameter estimation and signal detection are the two key components of a wireless communication system. They directly impact the bit-error-ratio (BER) performance of the system. Several criteria have been successfully applied for parameter estimation and signal detection. They include maximum likelihood (ML), maximum a-posteriori probability (MAP), least square (LS) and minimum mean square error (MMSE) etc. In the linear detection framework, linear MMSE (LMMSE) and LS are the most popular ones. Nevertheless, these criteria do not necessarily minimize the BER, which is one of the key aspect of any communication receiver design. Thus, minimization of BER is tantamount to an important design criterion for a wireless receiver, the minimum bit/symbol error ratio (MBER/MSER). We term this design criterion as the minimum-error-probability (MEP). In this thesis, parameter estimation and signal detection have been extensively studied based on the MEP framework for various unexplored scenar-ios of a wireless communication system. Thus, this thesis has two broad categories of explorations, first parameter estimation and then signal detection. Traditionally, the MEP criterion has been well studied in the context of the discrete signal detection in the last one decade, albeit we explore this framework for the continuous parameter es-timation. We first use this framework for channel estimation in a frequency flat fading single-input single-output (SISO) system and then extend this framework to the carrier frequency offset (CFO) estimation of multi-user MIMO OFDM system. We observe a reasonably good SNR improvement to the tune of 1 to 2.5 dB at a fixed BER (tentatively at 10−3). In this context, it is extended to the scenario of multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) or MIMO-OFDM with pa-rameter estimation error statistics obtained from LMMSE only and checked its effect at the equalizer design using MEP and LMMSE criteria. In the second exploration of the MEP criterion, it is explored for signal detection in the context of MIMO-relay and MIMO systems. Various low complexity solutions are proposed to alleviate the effect of high computational complexity for the MIMO-relay. We also consider various configurations of relay like cognitive, parallel and multi-hop relaying. We also propose a data trans-mission scheme with a rate of 1/Ns (Ns is the number of antennas at the transmitter) with the help of the MEP criterion to design various components. In all these cases, we obtain considerable BER improvement compared to the existing solutions.

科学研究費補助金 研究種目:基盤研究(C)(2) 課題番号:07805037 研究代表者:片山 正昭 研究期間:1995-1996年度