Dissertations / Theses on the topic 'QAM-OFDM'

The theme of this thesis is simulation of DVB-C2 transmission. The first part of this thesis is focused mainly on theory, where it describes differences between digital and analog television transmission. The project also explains principle of operation DVB-C and DVB-C2 systems with focus on channel coding a modulation. Application for simulation of DVB-C2 transmission, which is developed in the MATLAB environment is described in the second part. The last part of this thesis includes results of simulations of DVB-C2 transmission and their comparison with measured values of DVB-C transmission.

The main aim of this master's thesis was the create function models of wireless network technologies using the modern multitones modulation like is PFDM and FMT. This work is realised in Matlab – Simulink enviroment and models are tested in development kit. Development kit is universal software defined radio developer by Ettus.

<p>DVB (Digital Video Broadcasting) is the television digital system. It's however much more than a simple replacement for existing analogue television transmission, this system has many advantages such as picture quality and allows you a range of new features and services including subtitling, multiple audio tracks, interactive content, multimedia content. </p><p>The system is based in the OFDM technology, which allows DVB system to exploit the spectrum frequencies in a better way, saving spectrum, but OFDM has an important drawback that is the peak to average power ratio problem. OFDM is based on the FFT algorithms generating orthogonal subcarriers. </p><p>This thesis talks about the improvement of the PAPR problem using the soft compression method. </p><p>The simulation has been developed in Simulink® and Matlab®. With all the information presented in this thesis, any user can simulate the system. Thus, this thesis can be improved using other techniques to solve the PAPR problem.</p>

In order to meet the ever-growing demand for mobile data, a number of different technologies have been adopted by the fourth generation standardization bodies. These include multiple access schemes such as spatial division multiple access (SDMA), and efficient modulation techniques such as orthogonal frequency division multiplexing (OFDM)-based modulation. The specific objectives of this theses are to develop an effective feedback method for interference management in smart antenna SDMA systems and to design an efficient OFDM-based modulation technique, where an additional dimension is added to the conventional two-dimensional modulation techniques such as quadrature amplitude modulation (QAM). In SDMA time division duplex (TDD) systems, where channel reciprocity is maintained, uplink (UL) channel sounding method is considered as one of the most promising feedback methods due to its bandwidth and delay efficiency. Conventional channel sounding (CCS) only conveys the channel state information (CSI) of each active user to the base station (BS). Due to the limitation in system performance because of co-channel interference (CCI) from adjacent cells in interference-limited scenarios, CSI is only a suboptimal metric for multiuser spatial multiplexing optimization. The first major contribution of this theses is a novel interference feedback method proposed to provide the BS with implicit knowledge about the interference level received by each mobile station (MS). More specifically, it is proposed to weight the conventional channel sounding pilots by the level of the experienced interference at the user’s side. Interference-weighted channel sounding (IWCS) acts as a spectrally efficient feedback technique that provides the BS with implicit knowledge about CCI experienced by each MS, and significantly improves the downlink (DL) sum capacity for both greedy and fair scheduling policies. For the sake of completeness, a novel procedure is developed to make the IWCS pilots usable for UL optimization. It is proposed to divide the optimization metric obtained from the IWCS pilots by the interference experienced at the BS’s antennas. The resultant new metric, the channel gain divided by the multiplication of DL and UL interference, provides link-protection awareness and is used to optimize both UL and DL. Using maximum capacity scheduling criterion, the link-protection aware metric results in a gain in the median system sum capacity of 26.7% and 12.5% in DL and UL respectively compared to the case when conventional channel sounding techniques are used. Moreover, heuristic algorithm has been proposed in order to facilitate a practical optimization and to reduce the computational complexity. The second major contribution of this theses is an innovative transmission approach, referred to as subcarrier-index modulation (SIM), which is proposed to be integrated with OFDM. The key idea of SIM is to employ the subcarrier-index to convey information to the receiver. Furthermore, a closed-form analytical bit error ratio (BER) of SIM OFDM in Rayleigh channel is derived. Simulation results show BER performance gain of 4 dB over 4-QAM OFDM for both coded and uncoded data without power saving policy. Alternatively, power saving policy maintains an average gain of 1 dB while only using half OFDM symbol transmit power.

ITC/USA 2011 Conference Proceedings / The Forty-Seventh Annual International Telemetering Conference and Technical Exhibition / October 24-27, 2011 / Bally's Las Vegas, Las Vegas, Nevada<br>The Central Test and Evaluation Investment Program (CTEIP) Integrated Network Enhanced Telemetry (iNET) program is currently testing networked telemetry transceivers (IP.TM-Tx/Rx) using the Internet Protocol (IP), for use in telemetry (TM) channels. A unique characteristic of networked telemetry channel is packet drops due to radio frequency (RF) signal dynamics, i.e., terrain, weather, aircraft attitude, manmade objects, etc.. One of the key measures of the IP.TMTx/ Rx is reliability is link availability (LA), and a key element of LA is time to resynchronize after RF link loss.

碩士<br>國立中興大學<br>通訊工程研究所<br>97<br>A modified PTS algorithm by partitioning an OFDM block into non-disjoint OFDM sub-blocks is presented in this paper for PAPR reduction of M-QAM OFDM signals. Since a 16-QAM constellation can be written as sum of two QPSK sets, respectively four BPSK sets, a non-disjoint sub-block partition of the 16-QAM OFDM block is obtained by applying two different disjoint partitions on QPSK OFDM blocks, respectively four different disjoint partitions on BPSK OFDM blocks. Compared to a disjoint sub-block partition in conventional PTS, numerical results show that themodified PTS with a non-disjoint partition achieves an improvement of PAPR reduction and BER performance for interleaved, adjacent, and random partitioning schemes.

碩士<br>國立臺灣大學<br>光電工程學研究所<br>102<br>To build up a high-speed and low-cost optical access network, it is necessary to fuse a multiple carrier data format and a colorless transmitter based universal into the dense wavelength division multiplexing passive optical network (DWDM-PON) in the near future. The directly modulated transmission of optical 16 quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM) data-stream at its total bit rate up to 20 Gbit/s is demonstrated by up-shifting the relaxation oscillation peak and suppressing its relative intensity noise in a weak-resonant-cavity Fabry-Perot laser diode (WRC-FPLD) under injection-locking. With increasing the injection-locking power from -12 to -3 dBm, the effective reduction on threshold current of the WRC-FPLD significantly shifts its relaxation oscillation frequency from 5 to 7.5 GHz. This concurrently induces an up-shift of the peak relative intensity noise (RIN) of the WRC-FPLD, and effectively suppresses the background RIN level within the OFDM band between 3 and 6 GHz. The enhanced signal-to-noise ratio from 16 to 20 dB leads to a significant reduction of bit-error-rate (BER) of transmitted 16-QAM-OFDM data. After pre-leveling the peak amplitude of the OFDM subcarriers to compensate the throughput degradation of the directly modulated WRC-FPLD, the BER under 25-km SMF transmission can be further improved. To further reduce the cost of the injection-locking master source, the partially coherent WRC-FPLD pair under master-to-slave injection-locking operation is demonstrated for optical 16-QAM OFDM transmission at 20 Gbit/s over 25-km SMF in DWDM-PON with 28 affordable channels achieving BER of below FEC-limit. After master-to-slave injection-locking, the BER of the 16-QAM OFDM data stream under back-to-back and 25-km transmissions can be improved from 3.3x10^-3 to 2.1x10^-5 and from 1.4x10^-1 to 1.2x10^-3, respectively. With OFDM subcarrier pre-leveling, the BER of 16-QAM OFDM data transmitted by the master-to-slave injection-locked WRC-FPLD over 25-km transmission is further improved from 1.2x10^-3 to 2.1x10^-4, concurrently enabling the 28 channel transmissions at 20 Gb/s with BER below FEC-limit of 3.8x10^-3. Moreover, the overall frequency bandwidth of the TO-can packaged colorless WRC-FPLD can be extended from 5 to 9 GHz by replacing the package of the colorless WRC-FPLD from a typical 4-GHz TO-56-can to a 10-GHz TO-56-can. By injection-locking the WRC-FPLD based colorless transmitter packaged in a 10-GHz TO-56-can, the premier demonstration on directly modulated of 16 QAM OFDM transmission up to 36 Gbit/s per channel is demonstrated. The compromised optimization on enlarged modulation bandwidth and declined throughput power of the WRC-FPLD under strong injection-locking is considered, and the trade-off between the RIN suppression and the frequency response degradation with detuning the injection level is discussed. By pre-amplifying the directly modulated optical 16-QAM OFDM data stream covering a bandwidth up to 9 GHz with total raw bit rate of 36 Gbit/s, the receiving bit error rate (BER) under back-to-back transmission can be further reduced from 3.4x10^-3 to 2.1x10^-4. This enables the 36-Gbit/s 16-QAM OFDM transmission over 25-km SMF with its BER matching the FEC criterion at a receiving power of -3 dBm.

碩士<br>國立臺灣科技大學<br>電機工程系<br>94<br>The orthogonal frequency division multiplex (OFDM) system has advantages of high bandwidth efficiency, and is able to resist the multipath fading interference; its major disadvantage is high peak to average power ratio (PAPR). The signal through power amplifier is clipped due to the operation point of power amplifier. This clipped signal results in distortion. The easiest method of counteracting the distortion is to reduce the intensity of the signal which enters power amplifier. This makes the operation point of power amplifier drop to linear region. It is not a reasonable solution because this method will reduce bandwidth efficiency largely. Digital baseband predistorter can not only maintain the high bandwidth efficiency but also make predistorter cascaded with power amplifier be efficient linearization. Power amplifier which is intrinsic nonlinear characteristic is a important component in communication systems. When a non-constant signal is go through nonlinear power amplifier, its output signal has spectrum regrowth phenomenon, which gives rise to adjacent channel interference. Therefore, the linearization of power amplifier reduces bit error rate; at the same time, it also has to suppress spectrum regrowth. In this thesis, we will analyze the use of predistorter to compensate the nonlinear distortion caused by power amplifier in OFDM and QAM system. We will use amplitude-phase predistorter to compensate the memoryless power amplifier. We also use indirect learning architecture combined with polynomial-based model, which uses least-squares algorithm to obtain polynomial coefficients of predistorter, to achieve linearized power amplifier. Finally, we compare the performance which different predistorters combined with different power amplifier.

The use of coding in telecommunications systems reveals to be a technique with an essential contribution to the improvement of the recovery of transmitted signals. Depending on the circumstances to which a signal is subjected at transmission, by recurring to coding, it is possible to attenuate the unfavorable effects that result from this process, obtaining a signal with superior quality in comparison with a scenario where the presence of coding is absent. This study aims to test the feasibility of a high-rate wireless communications system using TCH codes being applied to an OFDM signal, subjected to noise components introduced by a wireless AWGN channel, considering a free path propagation model. Due to their correlation properties, the use of TCH codes reveals to be adequate since they allow the same codewords to be used to realize both error correction and channel estimation, mitigating the channels effects, leading to the realization of a receiver with lower complexity. With the intent of performing a qualitative analysis to this system, a simple simulation is executed in MATLAB where an OFDM signal is generated, being therefore applied various TCH codes and, through channel estimation, obtain the BER for their respective code lengths and, consequently, coding gains. The results were obtained for the modulation indexes of 16, 64 and 256-QAM. These demonstrate that the implementation of TCH codes is a viable option to reduce the rate of recovered errors, enabling the reception of a signal with better reliability, especially for higher code lengths and modulation indexes.<br>O uso de codificação em sistemas de telecomunicações revela-se uma técnica com um contributo essencial na melhoria da recuperação de sinais transmitidos. Dependendo das circunstâncias às quais um sinal é submetido aquando a sua transmissão, com recurso à codificação, é possível atenuar os efeitos adversos resultantes deste processo, obtendo uma qualidade no sinal recebido superior face a um cenário com ausência da mesma. Este estudo tem como objetivo testar a exequibilidade de um sistema de comunicações sem fios para alto débito usando códigos TCH e aplicando-os a um sinal OFDM, sujeito a componentes de ruído introduzidos por um canal sem fios AWGN, considerando um modelo de propagação em espaço livre. Devido às propriedades de correlação destes códigos, a sua utilização revela-se adequada pois permite que as mesmas palavras de código sejam utilizadas para efetuar correção de erros, minimizando os efeitos do canal, possibilitando o desenvolvimento de um recetor com menor complexidade. Visando efetuar uma análise qualitativa do sistema, é realizada uma simulação simples em MATLAB onde é gerado um sinal OFDM ao qual são aplicados diversos códigos TCH, realizando estimação de canal com a finalidade de obter o BER para os diferentes comprimentos dos códigos e, consequentemente, ganhos de codificação relativos aos mesmos. Os resultados obtidos foram realizados para os índices de modulação 16, 64 e 256-QAM. Estes demonstram que o uso destes códigos é uma opção viável para reduzir os erros detetados, permitindo recuperar o sinal com maior fiabilidade, especialmente para comprimentos de código e índices de modulação elevados.