Author: Weiping XuPublisher:
ISBN:
Category :
Languages : en
Pages : 254
Book Description
Interference Suppression Techniques for Multicarrier DS-CDMA.
Author: Weiping XuInterference Suppression for DS/CDMA Systems in Non-Gaussian Impulsive Channels
Author: Seoyoung LeePublisher:
ISBN:
Category :
Languages : en
Pages : 238
Book Description
Simulation results show that the proposed detector provides remarkable performance improvements over the adaptive MD detector in a wide range of near-far situations. The proposed detector has much better near-far resistance than the adaptive MD detector. Finally, fuzzy hybrid detector combines the adaptive MD detector and the hard-limiting matched filter (HLMF) detector. The HLMF detector performs well when the additive impulsive noise significantly dominates over MAI. Simulation results indicate significant performance improvements over the adaptive MD detector alone in impulsive noise-limited environments. When MAI dominates, the fuzzy hybrid detector nearly has the same performance as the adaptive MD detector.
Semi-blind Strategies for Interference Suppression in DS-CDMA Systems
Author: Ryan A. PachecoPublisher:
ISBN:
Category :
Languages : en
Pages : 0
Book Description
QAM modulation of OFDM signals (OFDM-QAM) is a popular modulation scheme for linear communication systems because it achieves good spectral efficiency while simplifying the equalization process. This comes at the cost of requiring accurate synchronization methods in the receiver, highly stable oscillators (low phase-noise); and power inefficient transmission. This work addresses issues in these three areas. First, a new frame synchronization method is developed based on Bayesian changepoint principles. It has higher accuracy then current popular methods, can be implemented recursively, and has been tested with success on experimental data collected in a WLAN testbed. Second, phase-noise resistant communication is investigated by performing an accurate statistical analysis of self-heterodyne communication systems. The analysis can be used to accurately predict the bit error probability of such systems. Third, power efficient transmission using phase-modulation (OFDM-PM) is analyzed. The bandwidth, equivalent baseband model, and symbol error probability are investigated. We can now predict the performance of OFDM-PM systems; for a given spectral efficiency, when operating well into the threshold region of angle-demodulators., The semi-blind algorithms presented in this work attempt to improve interference suppression for a given number of training and information symbols by combining training-based and blind estimation techniques. We first derive the minimum number of training symbols the training-based least squares (LS) estimator requires for complete suppression of interference (in the noiseless case). This provides a benchmark which the semi-blind algorithms are compared against. Next, a framework for semi-blind iterative interference suppression is developed which is then used to enhance the LS estimator by adding the constant modulus and cyclostationary properties used in blind algorithms. Finally, a decision-aided (multistage) semi-blind algorithm that jointly processes the signals from all intra-cell users is presented. Simulation results indicate a significant improvement over training-based and blind estimation techniques. Application of this work is in the reverse-link of third generation short-burst asynchronous DS-CDMA systems subject to both ISI and MAI.
Successive Interference Cancellation in Multicarrier DS/CDMA
Author: Lin FangInterference Suppression Techniques for Multi-rate CDMA Communication Systems
Author: Tao LuoPublisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
This thesis is concerned with interference suppression in multi-rate Code-division multiple-access (CDMA) communication systems. Specifically, the following problems within the area of CDMA communication systems have been addressed: interference suppression through chip waveform design, interference reduction through new diversity techniques for users having low mobility by exploiting inherent channel diversity and joint spatial-temporal interference suppression; all with the ultimate goal to increase the system capacity. First, we examine interference issues in the multi-rate CDMA communication systems. We minimize the interference by designing different chip waveforms for different data rate users. A general chip waveform design framework is formulated. It is shown that it is better to separate different data rate users in spectrum if their quality of service requirements are quite different. Next, we propose a new receiver structure targeting those users having low mobility but whose channels have small dispersion in frequency. We show that even a very small delay spread can be exploited to achieve significant gain in terms of the signal-to-noise ratio. Then we consider joint spatial and temporal interference suppression through an adaptive antenna array. We show that adaptive spatial and temporal correlation control between different users can give us higher system capacity. Sub-optimal algorithms with low complexity are proposed and analyzed. We show that the proposed algorithms reduce the transmit power significantly, therefore, greatly increase the system capacity. Finally, we examine the role of the adaptive antenna array in the multi-rate CDMA communication systems. We show that if we perform beamforming for different data rate users, most of the achieved gain is due to the high data rate users if the total power of the high data rate users is much higher than that of the low rate users. Thus, significant computational savings can be achieved but with near optimum transmit power.
Frequency-Domain Multiuser Detection for CDMA Systems
Author: Paulo SilvaPublisher: CRC Press
ISBN: 1000794156
Category : Science
Languages : en
Pages : 264
Book Description
Future broadband wireless communication systems are expected to be able to offer new and powerful services enabling fast transmission rates of several tens of Mbit/s. This is an ambitious challenge especially for mobile communication systems since these systems should be able to cope with severely time dispersive channels, associated to the signal multipath propagation. Moreover, these systems should have high spectral and power efficiencies, as well as high capacity and flexibility. Spread spectrum techniques, particularly coded division multiple access (CDMA) techniques allow high capacity and flexibility, continuous transmission requiring low-peak power requirements for the amplifiers, as well as some robustness against fading and time-dispersion effects associated with the multipath propagation. When employed in prefix assisted (PA) block transmission schemes combined with frequency-domain receiver implementations they become especially interesting for broadband wireless systems. In Frequency-Domain Multiuser Detection for CDMA Systems the use of PA block transmission is considered in the context of both DS (Direct Sequence) and MC (Multicarrier) CDMA schemes. The main goal is the study of frequency-domain multiuser detection techniques with iterative signal detection/decoding techniques, also in combination with estimation and cancelation of nonlinear distortion effects. The receiver structures are suitable to scenarios with high interference levels and strongly time-dispersive channels.
Signal Processing for DS/CDMA and OFDM-CDMA Systems: Interference Suppression, Timing Recovery and Space-Time Processing
Author: Interference suppression in single- and multi-carrier CDMA systems
Author: Hua WeiInterference Suppression in Spread-spectrum Networks
Author: Haichang SuiPublisher:
ISBN:
Category :
Languages : en
Pages : 188
Book Description
In this dissertation, interference suppression techniques and applications will be presented for cellular networks with direct-sequence (DS) CDMA and mobile ad hoc networks with frequency-hopped (FH) CDMA. The first part of the dissertation focuses on three novel finger placement designs that effectively equalize the DS-CDMA multi- path downlink channel to restore code orthogonality and consequently suppress multiple-access interference. For typical multipath channel models, the proposed schemes may significantly outperform the uniformly spaced tapped-delay-line equalizer with much less fingers/taps. In addition, analytic insight into the effect of the finger number and the smoothness of the chip pulse are obtained. The second part of the dissertation considers mobile ad hoc networks with FH-CDMA, where error-correcting codes are employed with differential unitary space-time modulation. The use of multiple transmit antennas in FH-CDMA systems, to the best knowledge of the author, has not been proposed in previous literature. The proposed receiver performs decision-feedback demodulation, decision-aided adaptive estimation, and erasure-insertion decoding jointly to suppress arbitrary unknown interference without channel state information. The third part of the dissertation presents network performance analysis for FH-CDMA networks with the proposed transceiver. Information efficiency and transmission range optimization is investigated under realistic time-varying channel models, which extends previous studies based on static channels and/or simplistic physical layer models. Impacts of various design parameters and channel properties on the network performance are revealed. The results also provide guidance on optimizing the modulation and coding scheme from a network perspective.
Statistical Modelling and Reduction of Multiple Access Interference Power in Wideband DS-CDMA and MC-CDMA Communications Systems
Author: Daniel Jeffrey CareyPublisher:
ISBN:
Category : Asynchronous transfer mode
Languages : en
Pages : 140
Book Description
Most standardisation bodies have based their 3G cellular systems on DS-CDMA (W-CDMA, UMTS, cdma2000). With 4G systems desiring improved services and quality of service standards, this thesis investigates multicarrier CDMA (MC-CDMA) as a genuine air interface candidate. A statistical model of the total MAI power incurred over the uplink channel is shown to be very accurately characterised by the Nakagami-m distribution for both asynchronous DS-CDMA and MC-CDMA techniques. Two new CDMA schemes, DF/DS-CDMA and DF/MC-CDMA, are proposed based on the dual-frequency (DF) switching technique introduced in this thesis. These proposed DF schemes offer substantial MAI reduction upon asynchronous reception and clearly outperform (MAI & BER) the standard DS-CDMA and MC-CDMA systems, however, additional bandwidth is required.