Timing Recovery for DOCSIS 3.1 Upstream OFDMA Signals

Data-Over-Cable Service Interface Specification (DOCSIS) is a global standard for cable communication systems. Before version 3.1, the standard has always specified single-carrier (SC) quadrature-amplitude modulation (QAM) as the modulation scheme. Given that the multi-carrier orthogonal frequency-division multiplexing (OFDM) technique has been increasingly popular and adopted in many wired/wireless communications systems, the newest cable communication standard, DOCSIS 3.1, also introduces OFDM as a major upgrade to improve transmission efficiency. In any digital communication systems, timing synchronization is required to determine and compensate for the timing offset from the transmitter to the receiver. This task is especially crucial and challenging in an OFDM system due to its very high sensitivity to synchronization errors. Although there have been many studies on the topic of OFDM timing synchronization, none of the existing methods are not directly applicable to DOCSIS 3.1 systems. Therefore, the main objective of this research is to develop effective and affordable timing synchronization algorithms for the DOCSIS 3.1 upstream signal. Specifically, three timing synchronization algorithms are proposed to comply and take advantage of the structure of the ranging signal (i.e., the signal used for synchronization purpose) specified in DOCSIS 3.1 standard. The proposed methods are evaluated under a realistic multipath uplink cable channel using computer simulation. The first algorithm makes use of the repetitive pattern of the symbol pairs in the ranging signal. The locations of the symbol pairs are determined by calculating a correlation metric and identifying its maximum value. The second and third algorithms are developed so that they exploit the mirrored symmetry of the binary phase-shift keying (BPSK)-modulated time-domain samples, corresponding to the first non-zero symbol in the ranging signal, and look for the exact location of the symmetry point. The first algorithm, with very low hardware complexity, provides reasonable performance under normal traffic and channel conditions. However its performance under a severe channel condition and heavy traffic is not satisfactory. The second and third algorithms provide much more accurate timing estimation results, even under the severe channel condition and heavy traffic flow. Since the second algorithm requires an enormous increase in hardware complexity, a few options are proposed to reduce the hardware complexity but it is still much higher than the complexity of the first algorithm. Applying the same complexity reduction techniques it is demonstrated that the third algorithm has similar hardware complexity to the first algorithm, while its timing estimation performance remains excellent

UNINTENTIONAL RF RADIATION AND RECEPTION IN COAXIAL CABLE TRANSMISSION LINES DUE TO SHEATH CONDUCTOR FAULTS

Despite the ever-growing amount of fiber optics deployed in wireline communications networks, coaxial cable is still a significant component. It is present in the radio frequency (RF) portion of hybrid-fiber-coaxial (HFC) communications networks typically employed in cable telecommunications (CATV) systems which service the majority of US households. Sheath faults in coaxial cables are a common problem for the industry and lead to unwanted and costly ingress or egress of signals into or out of the network. Common-mode currents have been previously identified as a source of ingress or egress for a variety of shielded cables in a number of industrial applications. This paper analyzes the electromagnetic properties of coaxial cable sheath faults to demonstrate that common-mode currents are the principal mechanism explaining the observed radiative properties of such faults, particularly in the lower frequency ranges, e.g. the 5-42 MHz upstream band employed by most U.S. cable system operators. Empirical measurements from coaxial test segments of a variety of sheath faults and configurations are shown to be consistent with results from computer simulations and analytical models of the physical samples. These results in turn are found to support conversion between common-mode and differential-mode currents as the primary causative agent. These findings can be used to better understand the causal mechanisms and requisite conditions for ingress and egress to develop in communications networks, and thereby improve methods to detect, remediate, and prevent sources of network impairment arising from compromised coaxial sheath conductors

Customer premise service study for 30/20 GHz satellite system

Satellite systems in which the space segment operates in the 30/20 GHz frequency band are defined and compared as to their potential for providing various types of communications services to customer premises and the economic and technical feasibility of doing so. Technical tasks performed include: market postulation, definition of the ground segment, definition of the space segment, definition of the integrated satellite system, service costs for satellite systems, sensitivity analysis, and critical technology. Based on an analysis of market data, a sufficiently large market for services is projected so as to make the system economically viable. A large market, and hence a high capacity satellite system, is found to be necessary to minimize service costs, i.e., economy of scale is found to hold. The wide bandwidth expected to be available in the 30/20 GHz band, along with frequency reuse which further increases the effective system bandwidth, makes possible the high capacity system. Extensive ground networking is required in most systems to both connect users into the system and to interconnect Earth stations to provide spatial diversity. Earth station spatial diversity is found to be a cost effective means of compensating the large fading encountered in the 30/20 GHz operating band

The radio spectrum requirements of broadband power line telecommunications systems.

There is concern among short wave (HF) radio users that broadband Power Line telecommunications (PLT) systems could cause serious interference to their services. The purpose of my research was to identify the factors that determine the performance of broadband PLT systems and to investigate how to maximise system performance while minimising the effect of PLT on HF radio systems. The study concentrates on the requirements for Access Band systems used to provide local loop service operating on 230/400V three-phase Low Voltage mains distribution networks. The basis of the study is a comprehensive set of measurements made on Low Voltage mains distribution networks in the UK, mainland Europe and Australia. The new approach to PLT band planning taken in this thesis uses Claude Shannon's information theory to predict the data capacity of arbitrary 3MHz sub bands. The results of the measurement programme are used to determine an optimum frequency band plan for PLT systems, taking account of the needs of the systems and the protection of other users of the HF spectrum. An example of how the proposed band plan can be used on a typical LV distribution network is included. The use of the mathematical models with the results of the attenuation, noise and emission measurements show that it is possible to improve on both the frequency band plans proposed in current PLT standards and the nonstandard frequency usage of many PLT trial systems. This will facilitate the achievement of competitive performance without causing undue radio interference, thus potentially making broadband PLT more acceptable to the HF radio community. The choice of modulation and coding systems required to deliver the predicted performance in the presence of transient interference is also discussed

Data transmissions through HFC return channels

Master'sMASTER OF ENGINEERIN

Digital implementation of an upstream DOCSIS QAM modulator and channel emulator

The concept of cable television, originally called community antenna television (CATV), began in the 1940's. The information and services provided by cable operators have changed drastically since the early days. Cable service providers are no longer simply providing their customers with broadcast television but are providing a multi-purpose, two-way link to the digital world. Custom programming, telephone service, radio, and high-speed internet access are just a few of the services offered by cable service providers in the 21st century. At the dawn of the internet the dominant mode of access was through telephone lines. Despite advances in dial-up modem technology, the telephone system was unable to keep pace with the demand for data throughput. In the late 1990's an industry consortium known as Cable Television Laboratories, Inc. developed a standard protocol for providing high-speed internet access through the existing CATV infrastructure. This protocol is known as Data Over Cable Service Interface Specification (DOCSIS) and it helped to usher in the era of the information superhighway. CATV systems use different parts of the radio frequency (RF) spectrum for communication to and from the user. The downstream portion (data destined for the user) consumes the bulk of the spectrum and is located at relatively high frequencies. The upstream portion (data destined to the network from the user) of the spectrum is smaller and located at the low end of the spectrum. This lower frequency region of the RF spectrum is particularly prone to impairments such as micro-reflections, which can be viewed as a type of multipath interference. Upstream data transfer in the presence of these impairments is therefore problematic and requires complex signal correction algorithms to be employed in the receiver. The quality of a receiver is largely determined by how well it mitigates the signal impairments introduced by the channel. For this reason, engineers developing a receiver require a piece of equipment that can emulate the channel impairments in any permutation in order to test their receiver. The conventional test methodology uses a hardware RF channel emulator connected between the transmitter and the receiver under test. This method not only requires an expensive RF channel emulator, but a functioning analog front-end as well. Of these two problems, the expense of the hardware emulator is likely less important than the delay in development caused by waiting for a functional analog front-end. Receiver design is an iterative, time consuming process that requires the receiver's digital signal processing (DSP) algorithms be tested as early as possible to reduce the time-to-market. This thesis presents a digital implementation of a DOCSIS-compliant channel emulator whereby cable micro-reflections and thermal noise at the analog front-end of the receiver are modelled digitally at baseband. The channel emulator and the modulator are integrated into a single hardware structure to produce a compact circuit that, during receiver testing, resides inside the same field programmable gate array (FPGA) as the receiver. This approach removes the dependence on the analog front-end allowing it to be developed concurrently with the receiver's DSP circuits, thus reducing the time-to-market. The approach taken in this thesis produces a fully programmable channel emulator that can be loaded onto FPGAs as needed by engineers working independently on different receiver designs. The channel emulator uses 3 independent data streams to produce a 3-channel signal, whereby a main channel with micro-reflections is flanked on either side by adjacent channels. Thermal noise normally generated by the receiver's analog front-end is emulated and injected into the signal. The resulting structure utilizes 43 dedicated multipliers and 401.125 KB of RAM, and achieves a modulation error ratio (MER) of 55.29 dB