Serially Concatenated Coded Continuous Phase Modulation for Aeronautical Telemetry

This thesis treats the development of bandwidth-efficient serially concatenated coded (SCC) continuous phase modulation (CPM) techniques for aeronautical telemetry. The concatenated code consists of an inner and an outer code, separated by an interleaver in most configurations, and is decoded using relatively simple near-optimum iterative decoding algorithms. CPM waveforms such as shaped-offset quadrature phase shift keying (SOQPSK) and pulse code modulation/frequency modulation (PCM/FM), which are currently used in military satellite and aeronautical telemetry standards, can be viewed as inner codes due to their recursive nature. For the outer codes, this thesis applies serially concatenated convolutional codes (SCCC), turbo-product codes (TPC) and repeat-accumulate codes (RAC) because of their large coding gains, high code rates, and because their decoding algorithms are readily implemented. High-rate codes are of special interest in aeronautical telemetry applications due to recent reductions in available spectrum and ever-increasing demands on data rates. This thesis evaluates the proposed coding schemes with a large set of numerical simulation results and makes a number of recommendations based on these results

Simulación de una transmisión adaptativa para enlaces de microondas en la selva peruana

Tradicionalmente los sistemas de comunicación han venido utilizando esquemas de modulación fija por la sencillez en su implementación que estos ofrecen. Sin embargo, los sistemas de comunicación inalámbrica se caracterizan por utilizar un medio de transmisión dinámico, en el que las condiciones de transmisión cambian de forma continua. Este cambio continuo ocasiona que el uso de esquemas de modulación fija no sea óptimo, su uso conlleva a un sobredimensionamiento de los recursos empleados, tal como la potencia de transmisión, ocasionando mayor consumo de energía y por tanto mayores gastos financieros [Fal04]. Frente a lo expuesto, la modulación adaptativa se presenta como una alternativa ya que permite adecuar los parámetros de transmisión a las condiciones del canal. La modulación adaptativa se encuentra íntimamente ligada con la asignación de los recursos radioeléctricos, es decir, solo asigna los recursos que aseguren su correcto funcionamiento sin desperdiciarlos [Mol11]. Los recursos normalmente considerados para las radiocomunicaciones son el ancho de banda y la potencia de transmisión, pero también se pueden establecer como criterio otros recursos tal como los bits por símbolo trasmitido [Fal04]. De otro lado, los sistemas de comunicación inalámbrica han despertado gran interés y se vienen utilizando tanto en las ciudades como en las zonas rurales. Particularmente, su uso en las zonas rurales está permitiendo la disminución de la brecha de acceso a las comunicaciones de muchas comunidades [dTyC10]. Sin embargo, las condiciones geográficas de determinadas zonas no permite el uso eficiente de los recursos de los sistemas de comunicación inalámbricos. Las condiciones geográficas hacen que el canal de comunicación inalámbrico sea más hostil. El objetivo del trabajo es proponer un esquema de modulación adaptativa para sistemas inalámbricos en zonas rurales. Se contribuye por tanto al desarrollo de técnicas de transmisión adaptativas en redes inalámbricas, ubicadas en zonas de difícil acceso para el mantenimiento, y conseguir sistemas eficientes en energía y en tasa de transmisión. El trabajo se centrará en la modulación adaptativa basada en la variación de los parámetros de potencia, nivel de constelación, tasa de transmisión y probabilidad de error. Es así, que la adaptación utilizando codificación de canal, no será objeto de estudio en la investigación y desarrollo. En el presente proyecto se implementa la técnica de modulación adaptativa, utilizando la tecnología arreglo de compuertas de campo programables (FPGA, Field Programmable Gate Array). Se analiza el desempeño del sistema implementado tomando la relación señal a ruido (SNR, Signal toNoise Ratio) del canal en forma conjunta con los parámetros propios de las variaciones climáticas, como son temperatura y humedad, propios de la zona rural de nuestro país. Las modulaciones que intervienen en el proceso de modulación son 256QAM, 128QAM, 64QAM y QPSK. Inicialmente se hace una revisión de los conceptos que son necesarios para la comprensión de un sistema con modulación adaptativa, como tipos de modulación digital, modulación fija, eficiencia y estimación del canal. Luego se indaga en la arquitectura, formas de implementación y las herramientas de programación propias de los FPGAs. Así como también la configuración y características de las etapas de un sistema de transmisión digital.Tesi

An FPGA Implementation of Carrier Phase and Symbol Timing Synchronization for 16-APSK

Proper synchronization between a transmitter and receiver, in terms of carrier phase and symbol timing, is critical for reliable communication. Carrier phase synchronization is related to the frequency translation hardware, where perfect synchronization means that the local oscillators of the transmitter’s upconverter and receiver’s downconverter are aligned in phase and frequency. Timing synchronization is related to the analog-to-digital converter in the receiver, where perfect synchronization means that samples of the received signal are taken at transmitted symbol times. Perfect synchronization is unlikely in practical systems for a number of reasons, including hardware limitations and the independence of the transmitter and receiver. This thesis explores an FPGA implementation of a PLL-based carrier phase and symbol timing synchronization subsystem as part of a 16-APSK aeronautical telemetry receiver. The theory behind this subsystem is presented, and the hardware implementation of each component is described. Results demonstrate successful demodulation of a test signal, and system performance is shown to be comparable to double-precision floating point simulations in terms of error vector magnitude, synchronization lock time, and BER

Reduced-Complexity Joint Frequency, Timing and Phase Recovery for PAM Based CPM Receivers

In this thesis, we present a reduced-complexity decision-directed joint timing and phase recovery method for continuous phase modulation (CPM). Using a simple linear modulation--pulse amplitude modulation (PAM)--representation of CPM, more popularly known as the Laurent representation of CPM, we develop formulations of a PAM based joint timing error detector (TED) and a phase error detector (PED). We consider the general M-ary single-h CPM model in our developments and numerical examples. We show by analysis and computer simulations that the PAM based error detector formulations have characteristics similar to the conventional (i.e., non-PAM) formulations and they render reliable performance when applied to specific CPM examples; in fact, we show the error detectors are able to perform close to the theoretical limit given by the modified Cramer-Rao bound (MCRB) and able to provide a bit error rate (BER) close to the theoretical value. Also, we investigate the false lock problem in M-ary CPMs and are able to obtain much improved performance over conventional CPM detectors with our PAM based method. Furthermore, the PAM based receivers perform well in the presence of a large frequency offset (on the order of the symbol rate) and are, in general, much more resistant to small carrier frequency variations compared to conventional CPM receivers. We use an existing PAM based frequency difference detector (FDD) for a large carrier frequency recovery. As such, the proposed method of combining the error detectors (FDD, TED and PED) provides important synchronization components for jointly recovering the respective signal attribute offsets (i.e, carrier frequency, symbol timing and carrier phase) for reduced-complexity PAM based CPM receivers, which have been missing up to this point

Nouvelle forme d'onde et récepteur avancé pour la télémesure des futurs lanceurs

Les modulations à phase continue (CPMs) sont des méthodes de modulations robuste à la noncohérence du canal de propagation. Dans un contexte spatial, les CPM sont utilisées dans la chaîne de transmission de télémesure de la fusée. Depuis les années 70, la modulation la plus usitée dans les systèmes de télémesures est la modulation CPFSK continuous phase frequency shift keying filtrée. Historiquement, ce type de modulation est concaténée avec un code ReedSolomon (RS) afin d'améliorer le processus de décodage. Côté récepteur, les séquences CPM non-cohérentes sont démodulées par un détecteur Viterbi à sortie dure et un décodeur RS. Néanmoins, le gain du code RS n'est pas aussi satisfaisant que des techniques de codage moderne capables d'atteindre la limite de Shannon. Actualiser la chaîne de communication avec des codes atteignant la limite de Shannon tels que les codes en graphe creux, implique deremanier l’architecture du récepteur usuel pour un détecteur à sortie souple. Ainsi, on propose dans cette étude d' élaborer un détecteur treillis à sortie souple pour démoduler les séquences CPM non-cohérentes. Dans un deuxième temps, on concevra des schémas de pré-codages améliorant le comportement asymptotique du récepteur non-cohérent et dans une dernière étape on élabora des codes de parité à faible densité (LDPC) approchant la limite de Shannon

Shaped Offset QPSK Capacity

In this work we compute the capacities and the pragmatic capacities of military-standard shaped-offset quadrature phase-shift keying (SOQPSK-MIL) and aeronautical telemetry SOQPSK (SOQPSK-TG). In the pragmatic approach, SOQPSK is treated as a modulation scheme as opposed to an encoder, and no iterations are performed between the SOQPSK demodulator and the outer binary decoder. We also evaluate the capacity of SOQPSK-TG constrained on a reduced complexity detection scheme based on the pulse amplitude modulation (PAM) representation of continuous phase modulation (CPM). The spectral efficiency of the PAM based SOQPSK-TG (SOQPSK-TG-PAM) is computed and shown to be superior to that of SOQPSK-MIL despite having the same detection complexity. We also show that the natural mapping of SOQPSK between input bits and SOQPSK waveforms maximizes the pragmatic capacity. Any other mapping such as differential encoding reduces the pragmatic capacity. We then focus on SOQPSK-TG due to its high spectral efficiency and present the performance results of a serially concatenated convolutional code (SCCC) SOQPSK-TG pragmatic scheme (SCCC-SOQPSK-TG), a low-density parity-check code (LDPC) SOQPSK-TG pragmatic scheme (LDPC-SOQPSK-TG), and a serially concatenated coded SOQPSK-TG scheme (SC-SOQPSK-TG). The LDPC scheme performs within 1.05 dB of the SOQPSK-TG capacity curve for various coding rates

FINITE BLOCKLENGTH SYMMETRIC INFORMATION RATE OF SOQPSK

In this paper we compute a lower bound, namely the dependence testing (DT) bound, on the maximum achievable rates (expressed in bits/channel use) with military standard shaped-offset quadrature phase shift-keying (SOQPSK-MIL) and aeronautical telemetry SOQPSK (SOQPSK-TG) schemes over additive white Gaussian noise (AWGN) channels under finite code blocklength, probability block error and equiprobable input constraints. The DT bound results for SOQPSK-MIL and SOQPSK-TG are used to lower bound their respective spectral efficiencies (expressed in bits/s/Hz). We simulate a serially concatenated convolutional code (SCCC) using SOQPSK-MIL as the inner code, and show that it performs within 1:1 dB of the SOQPSK-MIL DT bound for various coding rates. The numerical results also demonstrate the performance loss compared to the channel capacity due to the finite blocklength constraint.International Foundation for TelemeteringProceedings from the International Telemetering Conference are made available by the International Foundation for Telemetering and the University of Arizona Libraries. Visit http://www.telemetry.org/index.php/contact-us if you have questions about items in this collection

LDPC CODED APSK FOR AERONAUTICAL TELEMETRY

This paper presents the performance of capacity-approaching low-density parity check (LDPC) coded amplitude phase shift keying (APSK) over aeronautical telemetry channels. We show the bit-error rate results for code-rates of 1/2, 2/3, 3/4, and 4/5 with 16 and 32 point constellations. Results are presented and compared between an optimal and sub-optimal reduced-complexity demodulating system. We also compare the results with SOQPSK-TG under similar channel conditions and provide an estimate of backoff needed for implemention with power amplifiers.International Foundation for TelemeteringProceedings from the International Telemetering Conference are made available by the International Foundation for Telemetering and the University of Arizona Libraries. Visit http://www.telemetry.org/index.php/contact-us if you have questions about items in this collection