International Telemetering Conference Proceedings / October 25-28, 1993 / Riviera Hotel and Convention Center, Las Vegas, Nevada / Subcarrier use in telemetry has decreased in recent years due to emphasis on all-digital systems, but some cases lend themselves more easily to a mixed-service system carrying subcarriers along with a baseband signal. The 'IRIG 106' Telemetry Standards have maintained and expanded several series of FM subcarriers, but some uses are better served with 'non-standard' subcarriers that might be standard in other types of service, making components relatively easily available and inexpensive. This paper examines topics from the RCC study and describes some of the uses of subcarrier systems available to the telemetry designer.

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Orthogonal frequency division multiplexing¡]OFDM¡^systems play an important role in modern wireless communications due to following advantages: bandwidth saving¡Bcombat with frequency selective fading channel and high throughput. The performance of wireless communications is often degraded by fading channel . adaptive modulation and subcarrier allocation are proposed to overcome the degration to meet the quality of servie¡]QoS¡^. Lagrange method and heuristics method, two of the subcarrier allocation technology under multi-user OFDM, can achieve the goal that maximizing bit rate with minimizing transmitted power. However, significantly high complexity of either Lagrange method or heuristics method makes the implementation difficult. Zhang and Letaief proposed a method of making subcarriers detected one by one to reduce the complexity. However, in piratical, an OFDM system accommodates hundred of , or even thousand of subcarriers, so the method can be improved. In this thesis, we propose a subcarrier allocation method. The users that are not satisfied with the QOS requirement are named demander, and the users satisfied with the QOS requirement are named supplier. In the proposed subcarrier allocation method, we evaluate the number of subcarriers that demanders need and remove the subcarriers from supplier to directly compensate demander. Then the system has lower complexity due to less iterations.

Optical coherent techniques are used to eliminate the power fading found in optical subcarrier multiplexed systems. In a double-side band optical subcarrier system the signal experiences a periodic power fading that is dependent on the fiber dispersion and subcarrier frequency. This power fading is manifested during the direct detection of the subcarrier system using a square-law photodetector. Using a modified optical local oscillator to coherently detect the subcarrier channel this power fading can be eliminated. An optical local oscillator is centered at the optical carrier in order to perform homodyne detection. However, the local oscillator is modulated by a term equal the subcarrier frequency of interest. This is then a dual-frequency optical local oscillator. By controlling the phases of the local oscillator and the local subcarrier oscillator independently in the homodyne detection scheme, both the phase error and power fading of the detected subcarrier channel can be eliminated. This technique also allows the subcarrier to be selected optically, before the optical-to-electrical conversion. Analytical and simulation results are given to show the benefits of optical coherent detection in double-sideband subcarrier systems. By eliminating the periodic power loss found in the double-sideband subcarrier system the signal becomes dispersion limited and not power limited. A comparison of double-sideband and single-sideband subcarrier systems is presented. Multiple subcarriers and subcarrier spacing are also investigated for both double sideband and single sideband subcarrier systems. Optical phase and modulator noise are also considered in the analysis and simulation of coherent detection using a dual frequency optical local oscillator. Since the implementation used to eliminate the power fading is a phase correction based process, the phase noise of both the source and local oscillator lasers must be considered and the technique compared to typical direct and coherent detection techniques. Also, the effects of modulator nonlinearity are simulated for multichannel subcarrier multiplexed systems and comparisons made between the performance of using the dual-frequency local oscillator and typical detection techniques. It is shown that the advantages of the dual-frequency LO are retained in the presence of both phase noise and modulator nonlinearity. / Ph. D.

International Telemetering Conference Proceedings / October 25-28, 1993 / Riviera Hotel and Convention Center, Las Vegas, Nevada / A typical PCM/FM system is designed for a peak to peak carrier deviation of 0.7 times the bit rate of the PCM data. This value of PCM data deviation has been shown to be optimum for both PCM/FM [1] and PCM/FM+FM/FM [2] systems. However, the optimum deviation of the carrier by the FM subcarrier for a PCM/FM+FM/FM system is dependent upon the specific subcarrier type and required subcarrier signal to noise ratio at the receiver output. This paper introduces a simple method to calculate the optimum deviation of the carrier by FM subcarriers for a PCM/FM+FM/FM system. The method developed is used to calculate the optimum value of subcarrier deviation for two sample PCM/FM+FM/FM systems when IRIG constant bandwidth channels are used as FM subcarriers. The calculated optimum values of FM subcarrier deviation of the carrier, subcarrier mod index, are utilized in a companion paper to study the performance of PCM/FM+FM/FM systems [3]. The work presented herein can be extended to calculate the optimum deviation of the carrier by FM subcarriers for any PCM/FM+FM/FM system.

Recent years, Orthogonal Frequency Division Multiplexing (OFDM) system gets more and more attentions for its great benefit to the optical fiber communication system for improving the transmission performance. Not only better performance in long distance transmission but also high bit-rate is attractive feature of the OFDM system. The OFDM technology has been developed for the wireless communication system, and is now used in Asymmetric Digital Subscriber Line (ADSL), ETSI Digital Audio Broadcasting (DAB), Digital Video Broadcasting (DVB), High Definition Television (HDTV), Wireless Local Area Network (WLAN) and so on. The OFDM is extensively used in broadband wired and wireless communication systems, and it solves the problem of intersymbol interference (ISI) effectively. Actually, the OFDM is a kind of Multi-Carrier Modulation (MCM), and it is not a brand-new technology. The history of the OFDM can be traced back to 1966 when Chang of Bell Labs introduced the concept of the OFDM. In this thesis, I will briefly introduce the background of optical fiber communication system, then, explain my motivation and the structure of this thesis. Next, theoretical study has been conducted. For the simulation, I discuss the performance of the OFDM system related to the number of subcarriers and the erbium-doped fiber amplifier (EDFA) repeater output power. It revealed that small number of subcarriers had better transmission performance. In my study case, repeater output power of 0dBm was the optimum condition. In addition, experimental study has been conducted. For the experiment, the waveform required for the OFDM signal generation was calculated offline, and it was realized by the Arbitrary Waveform Generator (AWG). Finally, this thesis is concluded.

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Although fiber optic communication systems have enjoyed tremendous developments since their inception roughly fifty years ago, there are still improvements to be made. One such area for growth, relating more to long-haul applications of optical fibers, is the mitigation of nonlinear penalties. These nonlinear penalties appear due to the transmitted signal affecting the material properties of the fiber itself, and are more prominent when said signal has more energy in it—a conflicting effect from the traditional stance where more energy is considered beneficial. These penalties come in different forms, although they all have the same degrading effects for the system in question. Therefore, it is imperative to find new techniques that can mitigate these nonlinear penalties to ensure the optimal performance for our systems. One such technique, that we call multi-subcarrier processing, is the interest of the thesis here. The first section proposes a new method to compensate for the receiver side digital signal processing. More specifically, it introduces an algorithm that can remove the intermediate frequency offset that the signal acquires after passing through the system, which is necessary for coherent systems employed today. As some traditional algorithms used in the signal processing no longer work for multi-subcarrier systems, this new algorithm is necessary to compensate effectively for said offset. The second section introduces a new signal processing technique for the multiplexing and demultiplexing of multi-subcarrier signals. By making use of the well-known Fast Fourier Transform algorithm, the computational cost for generating said signals can be drastically reduced as the number of subcarriers grow larger. As systems continue the trend of operating at greater baud rates, the savings introduced here should be of even greater significance for commercial systems of the future. / Thesis / Master of Applied Science (MASc)

Advances in communications technologies entail demands for higher data rates. One of the popular solutions to fulfill this requirement was to allocate additional bandwidth, which unfortunately is not anymore viable due to spectrum scarcity. In addition, spectrum measurements around the globe have revealed the fact that the available spectrum is under-utilized. One of the most remarkable solutions to cope with the under-utilization of radio-frequency (RF) spectrum is the concept of cognitive radio (CR) with spectrum sharing features, also referred to as spectrum sharing systems. In CR systems, the main implementation issue is spectrum sensing because of the uncertainties in propagation channel, hidden primary user (PU) problem, sensing duration and security issues. Hence, the accuracy and reliability of the spectrum sensing information may inherently be suspicious and questionable. Due to the imprecise spectrum sensing information, this dissertation investigates the performance of an orthogonal frequency-division multiplexing (OFDM)-based CR spectrum sharing communication system that assumes random allocation and absence of the PU's channel occupation information, i.e., no spectrum sensing is employed to acquire information about the availability of unused subcarriers or the PU's activity. In addition, no cooperation occurs between the transmitters of the PUs and secondary users (SUs). The main benefit of random subcarrier utilization is to uniformly distribute the amount of SUs' interference among the PUs' subcarriers, which can be termed as interference spreading. The analysis and performance of such a communication set-up provides useful insights and can be utilized as a valid benchmark for performance comparison studies in CR spectrum sharing systems that assume the availability of spectrum sensing information. In the first part this dissertation, due to the lack of information about PUs' activities, the SU randomly allocates the subcarriers of the primary network and collide with the PUs' subcarriers with a certain probability. The average capacity of SU with subcarrier collisions is employed as performance measure to investigate the proposed random allocation scheme for both general and Rayleigh channel fading models. In the presence of multiple SUs, the multiuser diversity gain of SUs is also investigated. To avoid the subcarrier collisions at the SUs due to the random allocation scheme and to obtain the maximum sum rate for SUs based on the available subcarriers, an efficient centralized sequential algorithm based on the opportunistic scheduling and random allocation (utilization) methods is proposed to ensure the orthogonality of assigned subcarriers. In the second part of this dissertation, in addition to the collisions between the SUs and PUs, the inter-cell collisions among the subcarriers of SUs (belonging to different cells) are assumed to occur due to the inherent nature of random access scheme. A stochastic analysis of the number of subcarrier collisions between the SUs' and PU's subcarriers assuming fixed and random number of subcarriers requirements for each user is conducted. The performance of the random scheme in terms of capacity and capacity (rate) loss caused by the subcarrier collisions is investigated by assuming an interference power constraint at PU to protect its operation. Lastly, a theoretical channel fading model, termed hyper fading channel model, that is suitable to the dynamic nature of CR channel is proposed and analyzed. To perform a general analysis, the achievable average capacity of CR spectrum sharing systems over the proposed dynamic fading environments is studied.