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Author: Sandeep Panthula
Publisher:
ISBN:
Category : Code division multiple access
Languages : en
Pages : 224
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Book Description
Code division multiple access (CDMA) implemented with direct-sequence spread spectrum signaling is among the most promising multiplexing technologies for cellular services. The advantages of these include superior operation in multipath environments, flexibility in the allocation of channels and share bandwidth with narrowband communication systems without undue degradation of either performance. The discrepancy in the predictability of narrowband interference and CDMA signal is exploited in this work to propose techniques for narrowband interference cancellation. Linear predictive techniques employed here estimates the interference by processing the past samples and then subtracting it from the received signal to form a signal free of interference. The first proposed method uses this linear prediction model for interference estimation. This method is also used to evaluate the case of multiple received signals at the receiver. The performance of first method degrades with the presence of CDMA signal. So, to account this problem a second method is proposed such that the CDMA signal estimate from the traditional wiener filter is subtracted from the received signal and then it is linearly processed. Linear prediction coefficients are designed using the MMSE criterion to minimize the prediction error.
Author: Sandeep Panthula
Publisher:
ISBN:
Category : Code division multiple access
Languages : en
Pages : 224
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Book Description
Code division multiple access (CDMA) implemented with direct-sequence spread spectrum signaling is among the most promising multiplexing technologies for cellular services. The advantages of these include superior operation in multipath environments, flexibility in the allocation of channels and share bandwidth with narrowband communication systems without undue degradation of either performance. The discrepancy in the predictability of narrowband interference and CDMA signal is exploited in this work to propose techniques for narrowband interference cancellation. Linear predictive techniques employed here estimates the interference by processing the past samples and then subtracting it from the received signal to form a signal free of interference. The first proposed method uses this linear prediction model for interference estimation. This method is also used to evaluate the case of multiple received signals at the receiver. The performance of first method degrades with the presence of CDMA signal. So, to account this problem a second method is proposed such that the CDMA signal estimate from the traditional wiener filter is subtracted from the received signal and then it is linearly processed. Linear prediction coefficients are designed using the MMSE criterion to minimize the prediction error.
Author: Ahmed Masmoudi
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
"Full-duplex operation for wireless communications can potentially double the spectral efficiency, compared to half-duplex operation, by using the same wireless resource to transmit and receive at the cost of a large power difference between the high-power self-interference (SI) from its own transmitted signal and the low-power intended signal received from the other distant transceiver. The SI can be gradually reduced by a combination of radiofrequency (RF) and baseband cancellation stages. Each stage requires the estimation of the different distortions that the SI endures such as the SI channel and the transceiver nonlinearities. This thesis deals with the development of SI-cancellation techniques that are well-adapted to the full-duplex operation.First, we recognize the sparseness of the SI channel and exploit it to develop a compressedsensing (CS) based SI channel estimator. The obtained estimate is used to reduce the SI at the RF prior to the receiver low-noise amplifier and analog-to- digital converter to avoid overloading them. To further reduce the SI, a subspace-based algorithm is developed to jointly estimate the residual SI channel, the intended channel between the two transceivers and the transmitter nonlinearities for the baseband cancellation stage. Including the unknown received intended signal in the estimation process represents the main advantage of the proposed algorithm compared to previous data-aided estimators that assume the intended signal as additive noise. By using the second-order statistics of the received signal, it is possible to obtain the noise subspace and then to estimate the different coefficients without knowing the intended signal. Depending on the number of transmit and receive antennas, we propose to use either the received signal or a combination of the received signal and its complex conjugate. Also, we develop a semi-blind maximum likelihood (ML) estimator that combines the known pilot and unknown data symbols from the intended transceiver to formulate the likelihood function. A closed-form expression of the ML solution is first derived, and an iterative procedure is developed to further improve the estimation performance at moderate to high signal-to-noise ratio. Simulations show significant improvement in SI-cancellation gain compared to the data-aided estimators. Moreover, we present two new SI-cancellation methods using active signal injection (ASI) for full-duplex MIMO-OFDM systems. The ASI approach adds an appropriate cancelling signal to each transmitted signal such that the combined signals from transmit antennas attenuate the SI at the receive antennas. In the first method, the SI-pre-cancelling signal uses some reserved subcarriers which do not carry data. In the second method, the constellation points are dynamically extended within the constellation boundary in order to minimize the received SI. Thus, the SI-pre-cancelling signal does not affect the data-bearing signal. Simulation results show that the proposed methods considerably reduce the SI at a modest computational complexity." --
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Author: Gregory E. Bottomley
Publisher: John Wiley & Sons
ISBN: 1118105273
Category : Technology & Engineering
Languages : en
Pages : 192
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Book Description
The most thorough, up-to-date reference on channel equalization—from basic concepts to complex modeling techniques In today's instant-access society, a high premium is placed on information that can be stored and communicated effectively. As a result, storage densities and communications rates are being pushed to capacity, causing information symbols to interfere with one another. To help unclog pathways for the clearer conveyance of information, this book offers in-depth discussion of the significant contributions and future adaptability of channel equalization and a set of approaches for solving the problem of intersymbol interference (ISI). Chapter explorations in Channel Equalization include: Channel equalization topics presented with incremental learning methodology—from the very fundamental concept to more advanced mathematical knowledge Coverage of technology used in second-, third- and fourth-generation cellular communication systems A set of homework problems that reinforce concepts discussed in the book Tutorial explanations of recent developments currently captured in IEEE technical journals Unlike existing digital communications books that devote cursory attention to channel equalization, this invaluable guide addresses a crucial need by focusing solely on the background, current state, and future direction of this increasingly important technology. A unique mix of basic concepts and complex frameworks for delivering digitized data make Channel Equalization a valuable reference for all practicing wireless communication engineers and students dealing with the pressing demands of the information age.
Author: Ruozhu Li
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
"Full-duplex (FD) wireless communications can potentially double the spectral efficiency by transmitting and receiving simultaneously over the same frequency at a cost of a large power difference between the high-power self-interference (SI), and the low-power intended signal received from the remote transmitter. SI can be reduced gradually by a combination of radio-frequency (RF) and baseband SI-cancellation stages. Each stage requires the estimation of various distortions that the SI endures, such as SI-channel and transceiver nonlinearities. This thesis deals with the development of SI-cancellation techniques that are well adapted to FD operations.We address SI-cancellation for FD operations in the presence of imperfect RF components. In particular, we develop a new scheme to jointly estimate the IQ mixer imbalance, power amplifier (PA) nonlinearities, up-/down-conversion phase-noise and SI-channel. First, we study and develop a baseband model that captures the most significant transceiver RF imperfections, for both separate- and common-oscillator structures used in the up- and down-conversions. A basis expansion model (BEM) is then derived to approximate the time-varying phase-noise, and to transform the problem of estimating the time-varying phase-noise into the estimation of a set of static coefficients. Using the method of maximum likelihood (ML) criterion, the likelihood function is derived in the presence of the unknown intended signal, which leads to the joint estimation of the intended channel, the SI-channel, the nonlinear impairments and the phase-noise. When the intended signal is unknown, an iterative procedure is developed to find the ML estimate of the different parameters based on its own known transmitted data, the known pilot symbols, and the statistic of the unknown intended signal received from the intended transmitter. We consider the two pilot-insertion structures used in LTE for the frequency-multiplexed pilots and the time-multiplexed pilots. Compared to training-based techniques, the full use of the received signal significantly reduces the required number of pilot symbols. Simulation results indicate that the proposed algorithms can offer a superior SI-cancellation performance, with the resulting signal-to-SI-and-noise ratio (SINR) being very close to the signal-to-noise ratio (SNR).Moreover, we study the power of SI after each cancellation stage, taking into account the transceiver impairments. One SI-cancellation scheme, which combines antenna cancellation, RF cancellation and digital cancellation, provides results from real world experiments that show the feasibility of an FD design. In general, it is difficult to assess the exact level of the SI reduction that is obtainable due to the interactions among factors such as transceiver impairments, wireless propagation channel and estimation error. We hereby identify the main factors that affect the cancellation performance. This allows for a better understanding of the obtained performance, and leads to the development of new methods that improves the cancellation capability of FD systems. We address the impact of each transceiver impairment in FD systems, and specify the limiting factors of the RF and baseband SI-cancellation stages for a given architecture. In addition, we demonstrate that reducing the SI before the LNA/ADC, via the RF SI-cancellation stage is necessary to avoid high quantization noise from the ADC. The analysis further reveals that the transmitter nonlinearities need to be modeled and canceled in the baseband SI-cancellation stage. Finally, in light of our simulation results, we discuss the trade-off between the amount of SI-cancellation and the number of cancellation stages, and propose the potential case scenarios for operations with one digital cancellation." --
Author: Peter Stavroulakis
Publisher: Artech House
ISBN: 9781580535748
Category : Computers
Languages : en
Pages : 442
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Book Description
This leading-edge resource offers you a new methodology for analyzing and studying the behavior of wireless communication systems in an interference environment. It provides you with modern tools and techniques for use in real-world applications that help you guarantee optimum system performance. The book treats both additive and multiplicative interfering signals, including in-depth descriptions of how these signals behave, regardless of the source.
Author: Stefan Panic
Publisher: CRC Press
ISBN: 1466508426
Category : Computers
Languages : en
Pages : 263
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Book Description
Fading and Interference Mitigation in Wireless Communications will help readers stay up to date with recent developments in the performance analysis of space diversity reception over fading channels in the presence of cochannel interference. It presents a unified method for computing the performance of digital communication systems characterized by a variety of modulation and detection types and channel models. The book includes coverage of multichannel reception in various fading environments, influence of cochannel interference, and macrodiversity reception when channels are simultaneously affected by various types of fading and shadowing.
Author: Mutamed Khatib
Publisher: BoD – Books on Demand
ISBN: 9535117327
Category : Technology & Engineering
Languages : en
Pages : 256
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Book Description
Wireless communications have a strong impact on improving the quality of life in this century. Smart phones industry is now considered one of the most attractive fields, so advanced research is conducted in order to improve the quality of service in wireless communication environments. Many design challenges such as power consumption, quality of service, low cost, high data rate and small size are being treated every day. This book aims to provide highlights of the current research in the field of wireless communications. The subjects discussed are very valuable to communication researchers as well as researchers in the wireless related areas. The book chapters cover a wide range of wireless communication topics that are considered key technologies for future applications.
Author: Xufang Wang
Publisher:
ISBN: 9781361205785
Category :
Languages : en
Pages :
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Book Description
This dissertation, "Interference Cancellation in Impulse Radio" by Xufang, Wang, 王徐芳, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled "Interference Cancellation in Impulse Radio" Submitted by Xufang Wang for the degree of Doctor of Philosophy at The University of Hong Kong in January 2005 Ultra wideband (UWB) technology has recently received much attention as a potential candidate for low-cost short-range ultra high-speed wireless communications. One of the enabling techniques for ultra wideband (UWB) communications is impulse radio. Impulse radio employs short-duration pulses, producing a signal with an ultra wide (several GHz) bandwidth. This radio system has to co-exist with many existing communication systems transmitting on the same frequency band, for example, IEEE 802.11a WLANs operating around 5GHz, so interference poses problems for its use. In this thesis, two schemes are proposed for interference cancellation in impulse radio. In the first scheme, a preprocessor for ultra wideband (UWB) communications using impulse radio is proposed. The received UWB signal is divided into subband signals, which can be individually processed and recombined before demodulation of the signal. Perfect reconstruction of the pulses via analog subband processing is achieved. The division of subbands is flexible and the number depends on the number of frequency bands that require processing. Only the subbands that require processing need to be digitized, so the sampling rate requirement is greatly reduced. The proposed preprocessor can be applied to signal processing in impulse radio. The application of the preprocessor to narrowband or wideband interference cancellation is demonstrated, and found to be effective and robust. In the second scheme, the effect of interference on the performance of the UWB system is analyzed and interference cancellation by template design is proposed. Simulation results show that the scheme can effectively suppress interference and improve system performance. The scheme is applicable to both wideband and narrowband interference cancellation. For high speed ultra wideband communications using impulse radio, intersymbol interference (ISI) is unavoidable. The traditional method of combating ISI is to employ an equalizer. Due to the low duty cycle of UWB pulses and extremely short UWB pulse width, however, the number of the equalizer taps has to be impractically large and equalization is only achievable at an exceptionally high pulse rate. A novel ISI cancellation scheme based on wavelet transformation is also proposed. Knowledge of the channel is not required. The desired signal pulse can be distinguished from the interference pulse and precisely located. Instead of using the traditional received pulse, wavelet transformation is applied to generate a new spike signal for demodulation. A detailed theoretical analysis is presented and close-form expressions are derived. Finally, the ISI cancellation algorithm is modified to handle false alarms in noisy environments. 2 DOI: 10.5353/th_b3145936 Subjects: Radio - Interference Radio frequency Ultra-wideband devices
Author: Tatsuo Itoh
Publisher: John Wiley & Sons
ISBN: 0471463922
Category : Technology & Engineering
Languages : en
Pages : 482
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Book Description
A survey of microwave technology tailored for professionals in wireless communications RF Technologies for Low Power Wireless Communications updates recent developments in wireless communications from a hardware design standpoint and offers specialized coverage of microwave technology with a focus on the low power wireless units required in modern wireless systems. It explores results of recent research that focused on a holistic, integrated approach to the topics of materials, devices, circuits, modulation, and architectures rather than the more traditional approach of research into isolated topical areas. Twelve chapters deal with various fundamental research aspects of low power wireless electronics written by world-class experts in each field. The first chapter offers an overview of wireless architecture and performance, followed by detailed coverage of: Advanced GaAs-based HBT designs InP-based devices and circuits Si/SiGe HBT technology Noise in GaN devices Power amplifier architectures and nonlinearities Planar-oriented components MEMS and micromachined components Resonators, filters, and low-noise oscillators Antennas Transceiver front-end architectures With a clear focus and expert contributors, RF Technologies for Low Power Wireless Communications will be of interest to a wide range of electrical engineering disciplines working in wireless technologies.
