Cubic interpolation based channel estimator for rectangular M-QAM

This paper propose a Pilot Symbol Assisted Modulation (PSAM) channel estimation and compensation technique for rectangular M-QAM based on Cubic interpolation in order to determine the channel state information (CSI) over flat Rayleigh fading channels. The proposed Cubic channel estimator technique is based on sliding window approach and pilot symbol estimates adjustment in order to reduce its computational time complexity. The Cubic estimator is combined with the Koetter and Vardy (KV) Reed-Solomon (RS) decoder to test its performance. The simulation results show that the Cubic interpolation gives the same performance as the Linear, and Sinc interpolators over slow flat Rayleigh fading channel; however, it achieves significant performance improvement of +1.0dB in symbol error rate (SER) over fast flat Rayleigh fading channel.Keywords: CSI, cubic estimator, fading channel, M-QAM, PSA

Uplink Channel Estimation in WiMAX

WiMAX is an emerging and powerful technology in broadband wireless communications in that it can provide high-speed broadband voice and data ser- vices over distances much greater than Wi-Fi. However, like in any wireless communication system, signal distortion due to channel fading, noise, and Doppler can limit the overall transmission data rate and coverage. To minimize this effect, the receiver must perform channel estimation to remove the effects of the channel. To aid the channel estimation process, known pilot subcarriers are embedded into each OFDM symbol. In this thesis, we will develop and evaluate pilot-assisted channel estimation algorithms for 3 WiMAX modes and features: PUSC (Partial Usage of Subcarriers), AMC (Adaptive Modulation and Coding), and Channel Sounding. Our results show that channel delay spread and signal-to-noise ratio influence the performance of each algorithm and that knowledge of these properties can enhance the system's overall performance

Pilot patterns and power loading in NC-OFDM cognitive radios

Includes abstract.Includes bibliographical references.The implementation of cognitive radios is widely proposed through the use of Orthogonal Frequency Division Multiplexing (OFDM) modulation. In the special case of cognitive radios however, the OFDM modulation scheme cannot simply be implemented without modification due to the huge change in the basic laws of the transmission paradigm. The main reason behind this is that the modulation scheme can no longer assume the contiguousness of its band as well as the interference that may be caused by the cognitive radio users operating in such close proximity to the licensed users. The research presented in this thesis namely identified two areas of cognitive radio which addressed these issues. These were the power loading and channel estimation areas

Channel and frequency offset estimation schemes for multicarrier systems

Doutoramento em Engenharia ElectrotécnicaO presente trabalho aborda o problema da estimação de canal e da estimação de desvio de frequência em sistemas OFDM com múltiplas configurações de antenas no transmissor e no receptor. Nesta tese é apresentado o estudo teórico sobre o impacto da densidade de pilotos no desempenho da estimação de canal em sistemas OFDM e são propostos diversos algoritmos para estimação de canal e estimação de desvio de frequência em sistemas OFDM com antenas únicas no transmissor e receptor, com diversidade de transmissão e MIMO. O estudo teórico culmina com a formulação analítica do erro quadrático médio de um estimador de canal genérico num sistema OFDM que utilize pilotos dedicados, distribuidos no quadro transmitido em padrões bi-dimensionais. A formulação genérica é concretizada para o estimador bi-dimensional LS-DFT, permitindo aferir da exactidão da formulação analítica quando comparada com os valores obtidos por simulação do sistema abordado. Os algoritmos de estimação investigados tiram partido da presença de pilotos dedicados presentes nos quadros transmitidos para estimar com precisão os parâmetros pretendidos. Pela sua baixa complexidade, estes algoritmos revelam-se especialmente adequados para implementação em terminais móveis com capacidade computacional e consumo limitados. O desempenho dos algoritmos propostos foi avaliado por meio de simulação do sistema utilizado, recorrendo a modelos aceites de caracterização do canal móvel multipercurso. A comparação do seu desempenho com algoritmos de referência permitir aferir da sua validade. ABSTRACT: The present work focus on the problem of channel estimation and frequency offset estimation in OFDM systems, with different antenna configurations at both the transmitter and the receiver. This thesis presents the theoretical study of the impact of the pilot density in the performance of the channel estimation in OFDM systems and proposes several channel and frequency offset algorithms for OFDM systems with single antenna at both transmitter and receiver, with transmitter diversity and MIMO. The theoretical study results in the analytical formulation of the mean square error of a generic channel estimator for an OFDM system using dedicated pilots, distributed in the transmitted frame in two-dimensional patterns. The generic formulation is implemented for the two-dimensional LS-DFT estimator to verify the accuracy of the analytical formulation when compared with the values obtained by simulation of the discussed system. The investigated estimation algorithms take advantage of the presence of dedicated pilots present in the transmitted frames to accurately estimate the required parameters. Due to its low complexity, these algorithms are especially suited for implementation in mobile terminals with limited processing power and consumption. The performance of the proposed algorithms was evaluated by simulation of the used system, using accepted multipath mobile channel models. The comparison of its performance with the one of reference algorithms measures its validity

DOCSIS 3.1 cable modem and upstream channel simulation in MATLAB

The cable television (CATV) industry has grown significantly since its inception in the late 1940’s. Originally, a CATV network was comprised of several homes that were connected to community antennae via a network of coaxial cables. The only signal processing done was by an analogue amplifier, and transmission only occurred in one direction (i.e. from the antennae/head-end to the subscribers). However, as CATV grew in popularity, demand for services such as pay-per-view television increased, which lead to supporting transmission in the upstream direction (i.e. from subscriber to the head-end). This greatly increased the signal processing to include frequency diplexers. CATV service providers began to expand the bandwidth of their networks in the late 90’s by switching from analogue to digital technology. In an effort to regulate the manufacturing of new digital equipment and ensure interoperability of products from different manufacturers, several cable service providers formed a non-for-profit consortium to develop a data-over-cable service interface specification (DOCSIS). The consortium, which is named CableLabs, released the first DOCSIS standard in 1997. The DOCSIS standard has been upgraded over the years to keep up with increased consumer demand for large bandwidths and faster transmission speeds, particularly in the upstream direction. The latest version of the DOCSIS standard, DOCSIS 3.1, utilizes orthogonal frequency-division multiple access (OFDMA) technology to provide upstream transmission speeds of up to 1 Gbps. As cable service providers begin the process of upgrading their upstream receivers to comply with the new DOCSIS 3.1 standard, they require a means of testing the various functions that an upstream receiver may employ. It is convenient for service providers to employ cable modem (CM) plus channel emulator to perform these tests in-house during the product development stage. Constructing the emulator in digital technology is an attractive option for testing. This thesis approaches digital emulation by developing a digital model of the CMs and upstream channel in a DOCSIS 3.1 network. The first step in building the emulator is to simulate its operations in MATLAB, specifically upstream transmission over the network. The MATLAB model is capable of simulating transmission from multiple CMs, each of which transmits using a specific “transmission mode.” The three transmission modes described in the DOCSIS 3.1 standard are included in the model. These modes are “traffic mode,” which is used during regular data transmission; “fine ranging mode,” which is used to perform fine timing and power offset corrections; and “probing” mode, which is presumably used for estimating the frequency response of the channel, but also is used to further correct the timing and power offsets. The MATLAB model is also capable of simulating the channel impairments a signal may encounter when traversing the upstream channel. Impairments that are specific to individual CMs include integer and fractional timing offsets, micro-reflections, carrier phase offset (CPO), fractional carrier frequency offset (CFO), and network gain/attenuation. Impairments common to all CMs include carrier hum modulation, AM/FM ingress noise, and additive white Gaussian noise (AWGN). It is the hope that the MATLAB scripts that make up the simulation be translated to Verilog HDL to implement the emulator on a field-programmable gate array (FPGA) in the near future. In the event that an FPGA implementation is pursued, research was conducted into designing efficient fractional delay filters (FDFs), which are essential in the simulation of micro-reflections. After performing an FPGA implementation cost analysis between various FDF designs, it was determined that a Kaiser-windowed sinc function FDF with roll-off parameter β = 3.88 was the most cost-efficient choice, requiring at total of 24 multipliers when implemented using an optimized structure

An Investigation into the Implementation and Performance of Spectrally Shaped Orthogonal Frequency Division Multiplex

Orthogonal Frequency Division Multiplex (OFDM) is a flexible, robust multi-carrier modulation scheme. The orthogonal spectral shaping and spacing of OFDM sub-carriers ensure that their spectra can be over-lapped without leading to undesirable inter-carrier interference. Conventional OFDM systems have non-band limited Sinc(x) shaped subcarrier spectra. An alternative form of OFDM, referred to hereafter as Spectrally Shaped OFDM, employs band limited Nyquist shaped sub-carrier spectra. The research described in this thesis investigates the strengths and weaknesses of Spectrally Shaped OFDM as a potential modulation scheme for future mobile radio applications. From this research a novel Digital Signal Processing architecture for modulating and demodulating Spectrally Shaped OFDM sub-carriers has been derived which exploits the combination of a complex Discrete Fourier Transform (DFT) and PolyPhase Network (PPN) filter. This architecture is shown to significantly reduce the minimum number of computations required per symbol compared to previous designs. Using a custom coded computer simulation, the effects of varying the key parameters of the novel architecture's PolyPhase Filter (PPN) filter an the overall system complexity, spectral performance and system signal-to-distortion have been extensively studied. From these studies it is shown that compared to similar conventional OFDM systems, Spectrally Shaped OFDM systems possess superior out-of-band spectral qualities but significantly worse Peak-to-Average-Power-Ratio (PAPR) envelope performance. lt is also shown that the absolute value of the end PPN filter coefficients (dependent on the roll-off factor of the sub-carrier spectral shaping) dictate the system signal-to-distortion ratio when no time-domain windowing of the PPN filter coefficients is applied. Finally the effects of a both time and frequency selective fast fading channels on the modulation scheme's uncoded Bit Error Rate (BER) versus Signal-to-Noise (SNR) performance are simulated. The results obtained indicate that Spectrally Shaped OFDM is more robust (lower BER) to frequency-selective fading than time-selective fading