Shuttle Communications and Tracking Systems Modeling and TDRSS Link Simulations Studies

An analytical simulation package (LinCsim) which allows the analytical verification of data transmission performance through TDRSS satellites was modified. The work involved the modeling of the user transponder, TDRS, TDRS ground terminal, and link dynamics for forward and return links based on the TDRSS performance specifications (4) and the critical design reviews. The scope of this effort has recently been expanded to include the effects of radio frequency interference (RFI) on the bit error rate (BER) performance of the S-band return links. The RFI environment and the modified TDRSS satellite and ground station hardware are being modeled in accordance with their description in the applicable documents

Digital communications over fading channels

In this report, the probabilities of bit error for the most commonly used digital modulation techniques are analyzed. Analytic solutions are developed for the probability of bit error when the signal is affected by the most commonly encountered impairment to system performance for a wireless channel, the transmission of the signal over a fading channel. In this report, the effect of a slow, flat Ricean fading channel on communications systems performance is examined. Since channel fading significantly degrades the performance of a communication system, the performance of digital communication systems that also use forward error correction channel coding is analyzed for hard decision decoding and, where appropriate, for soft decision decoding. Diversity, another technique to mitigate the effect of fading channels on digital communication systems performance, is also discussed. Also included is a discussion of the effect of narrowband noise interference, both continuous and pulsed, on digital communication systems. We then discuss the analysis of the probability of bit error for the combination of error correction coding and diversity. Following this, we briefly discuss spread spectrum systems. Next, we examine the link budget analysis and various models for channel loss. Finally, we examine in detail the second generation digital wireless standard Global System for Mobile (GSM).Approved for public release; distribution is unlimited

Iterative receiver in multiuser relaying systems with fast frequency-hopping modulation

In this thesis, a novel iterative receiver and its improved version are proposed for relay-assisted multiuser communications, in which multiple users transmit to a destination with the help of a relay and using fast frequency-hopping modulation. Each user employs a channel encoder to protect its information and facilitate interference cancellation at the receiver. The signal received at the relay is either amplified, or partially decoded with a simple energy detector, before being forwarded to the destination. Under flat Rayleigh fading channels, the receiver at the destination can be implemented non-coherently, i.e., it does not require the instantaneous channel information to demodulate the users’ transmitted signals. The proposed iterative algorithm at the destination exploits the soft outputs of the channel decoders to successively extract the maximum likelihood symbols of the users and perform interference cancellation. The iterative method is successfully applied for both cases of amplify-and-forward and partial decode-and-forward relaying. The error performance of the proposed iterative receiver is investigated by computer simulation. Under the same spectral efficiency, simulation results demonstrate the excellent performance of the proposed receiver when compared to the performance of decoding without interference cancellation as well as the performance of the maximum likelihood multiuser detection previously developed for uncoded transmission. Simulation results also suggest that a proper selection of channel coding schemes can help to support significant more users without consuming extra system resources. In addition, to further enhance the receiver’s performance in terms of the bit error rate, an improved version of the iterative receiver is presented. Such an improved receiver invokes inner-loop iterations between the channel decoders and the demappers in such a way that the soft outputs of the channel decoders are also used to refine the outputs of the demappers for every outer-loop iteration. Simulation results indicate a performance gain of about 2.5dB by using the two-loop receiver when compared to the performance of the first proposed receiver

A Study on Covert Underwater Communication System Using the LPI Based on Spread Spectrum

Researches for oceans are limited to military purpose such as underwater sound detection and tracking system. Among the various ocean technologies, for the purpose of personal or military security, underwater acoustic communications with low-probability-of-interception covert characteristics were received much attention recently. Covert underwater acoustic communication system is designed for the transmission signal is not intercepted by the unintended another receivers. Covert communication system must operate at low signal-to-noise ratio. Therefore, typical covert communication systems use a spread spectrum communication technology. Spread spectrum signals used to hide the transmitted signal by transmitting it at low power and making it difficult for an unintended listener to detect the signal in the presence of background noise. The problem for spread spectrum communications in an underwater acoustic channel is the multipath arrivals, which create severe interchip and inter symbol interferences. In order to improve performance in multipath underwater channel, this thesis proposed turbo equalization techniques based on RAKE receiver for spread spectrum communications. RAKE receiver was applied threshold comparison and weighted coefficient. In this thesis, the performance of the proposed transceiver model is analyzed. This thesis focused not only single user but also multiuser. Many earlier works focused on the single-user detection problem. They are often inspired by advances made in wireless radio communications and sometimes dedicated to the underwater acoustic communications. In a single user code acquisition algorithm was proposed. However, the growing interest in underwater communications led researchers to consider the multiuser detection and acquisition problem in an underwater communication network system. By expanding single user communication concept, this thesis proposed a multiuser access communication system based on turbo equalized RAKE model. Thesis analyzed the performance of the proposed multiple access communication for covert communication by simulations. Also number of users are fixed on two, underwater experiment was conducted and demonstrate that proposed model is very effective for covert multiuser underwater communications.목 차 List of Tables ii List of Figures iii Abstract iv 제 1 장 서론 1 제 2 장 은밀 수중 통신 기법 3 2.1 대역 확산 기법 4 2.2 은밀 수중 통신에 적합한 채널 부호화 기법 6 2.3 대역확산 기반 수중 음향 통신 모델 8 제 3 장 은밀 수중 통신에서 효율적인 복호 방식 제안 10 3.1 반복기반의 터보 등화 복호 방식 10 3.2 RAKE 기반의 터보 등화 복호 방식 13 3.3 시뮬레이션 성능 비교 분석 17 3.4 실제 수중 실험을 통한 성능 비교 24 제 4 장 은밀 다중 접속을 위한 송수신 구조 32 4.1 은밀 다중 접속 송신 구조 33 4.2 은밀 다중 접속 수신 구조 36 4.3 시뮬레이션 성능 분석 39 4.4 실제 수중 실험을 통한 성능 분석 41 제 5 장 결 론 46 감사의 글 38 참고문헌 40Maste

Mobile multiple access study

Multiple access techniques (FDMA, CDMA, TDMA) for the mobile user and attempts to identify the current best technique are discussed. Traffic loading is considered as well as voice and data modulation and spacecraft and system design. Emphasis is placed on developing mobile terminal cost estimates for the selected design. In addition, design examples are presented for the alternative techniques of multiple access in order to compare with the selected technique

Estudio de la métrica cúbica en sistemas multiportadora

En el estándar LTE, tradicionalmente se ha usado el parámetro PAPR para medir la pérdida de eficiencia en el amplificador de potencia. Actualmente, se recomienda el uso del parámetro denominado métrica cúbica (Cubic Metric, CM) para tal fin. En trabajos previos se han utilizado técnicas de reducción de la CM, pero no se ha tenido en cuenta la distorsión del amplificador ni se ha comprobado mediante un cálculo de tasa de errores. El objetivo de este trabajo es comparar ambos parámetros PAPR y CM dentro de un sistema completo, teniendo en cuenta un amplificador y calculando la tasa de errores.Traditionally, in LTE standard the parameter PAPR has been used to measure the power amplifier efficiency loss. Using the named cubic metric (CM) parameter for this purpose is recommended currently. In previous research it has been used techniques to reduce the CM, but neither amplifier distortion was taken into account nor a bit error rate verification. The aim of this project is to compare both PAPR and CM parameters within a complete system, taking into account an amplifier and the bit error rate.Grado en Ingeniería en Sistemas de Telecomunicació

Estudio de la métrica cúbica en sistemas multiportadora

En el estándar LTE, tradicionalmente se ha usado el parámetro PAPR para medir la pérdida de eficiencia en el amplificador de potencia. Actualmente, se recomienda el uso del parámetro denominado métrica cúbica (Cubic Metric, CM) para tal fin. En trabajos previos se han utilizado técnicas de reducción de la CM, pero no se ha tenido en cuenta la distorsión del amplificador ni se ha comprobado mediante un cálculo de tasa de errores. El objetivo de este trabajo es comparar ambos parámetros PAPR y CM dentro de un sistema completo, teniendo en cuenta un amplificador y calculando la tasa de errores.Traditionally, in LTE standard the parameter PAPR has been used to measure the power amplifier efficiency loss. Using the named cubic metric (CM) parameter for this purpose is recommended currently. In previous research it has been used techniques to reduce the CM, but neither amplifier distortion was taken into account nor a bit error rate verification. The aim of this project is to compare both PAPR and CM parameters within a complete system, taking into account an amplifier and the bit error rate.Grado en Ingeniería en Sistemas de Telecomunicació

Space Shuttle/TDRSS communication and tracking systems analysis

In order to evaluate the technical and operational problem areas and provide a recommendation, the enhancements to the Tracking and Data Delay Satellite System (TDRSS) and Shuttle must be evaluated through simulation and analysis. These enhancement techniques must first be characterized, then modeled mathematically, and finally updated into LinCsim (analytical simulation package). The LinCsim package can then be used as an evaluation tool. Three areas of potential enhancements were identified: shuttle payload accommodations, TDRSS SSA and KSA services, and shuttle tracking system and navigation sensors. Recommendations for each area were discussed