1 
Nonlinear Multiple Narrowband Interference Cancellation Filtering with Inverse QRDRLS Algorithm for CDMA SystemChang, Suhua 06 July 2001 (has links)
The technique of directsequence (DS) code division multiple access (CDMA) cellular systems has been the focus of increased attention. In this thesis, the problem of narrowband interference (NBI) cancellation for the DSCDMA communication systems is considered. It has been shown that the performance of single NBI cancellation for CDMA systems by using the nonlinear filtering approach, the socalled DDK filter or the MDK filter, is superior to the one using the linear filtering approach. The main concern of this thesis is to deal with the multiple NBI cancellation. This may occur in some practical application, for instance, in the 2.4GHz CDMA system, the bluetooth and wireless LAN may exist in the same frequency band with different power ratio.
In this thesis, the nonlinear filtering with fast convergence least square (LS) algorithms, viz., the modified inverse QRDRLS (IQRDRLS) and the interior point (IP) LS algorithms, are devised for multiple NBI cancellation in the multiuser CDMA system. In fact, the IQRDRLS and the IP LS algorithms are known to have better numerical stability and convergence property in the RLS family. Since in the nonlinear MDK filter with the IQRDRLS algorithm, the prediction error £`k,k1 used in the conventional IQRDRLS is replaced by the nonlinear function of £l(£`k,k1), and is defined to as the modified IQRDRLS algorithm. The merits of the proposed algorithms are verified via computer simulation. We showed that the performance of our proposed algorithms outperformed the one using the conventional nonlinear filtering approach with LMS algorithm, in terms of convergence property and the signaltonoise ratio improvement (SNRI).

2 
FPGA Software Design of Constrained Adaptive Inverse QRDRLS AlgorithmPan, AiRong 23 June 2004 (has links)
In this thesis, the multicarrier (MC) code division multiple access (CDMA) system in Rayleigh fading channel is considered. The system performance will be degraded due to multiple access interference (MAI) or background noise. It is know that linearly constrained inverse QRdecomposition (LCIQRD) recursive leastsquare algorithm can overcome the problems. The main concern of this thesis is to implement the circuit of LCIQRD algorithm. FPGA components and sets up a high efficient programmable hardware module. In this thesis, we implemented the circuit of LCIQRD algorithm via a chip of Field Programmable Gate Array (FPGA) with Verilog HDL.
The conventional IQRD circuit design employs systolic array architecture. The advantages of systolic array architecture include modularity and hardware simplicity. These properties are extremely desirable for VLSI implementation. In fact, we expect to reduce the execution time of the conventional IQRD algorithm circuit design. Therefore, in this thesis a modified IQRD circuit design is proposed to improve the effect of circuit implementation. It also has advantage of modularity and reduces the execution time. In order to degrade complexity of LCIQRD algorithm circuit design, the area and speed of circuit are the consideration in this thesis. The data source is produced by Matlab software. We verify the performance of the system in terms of BER (bit error rate) and SINR (signal to interference and noise ratio).Finally, LCIQRD algorithm circuit is realized in the Altera EP20k1500EFC33 chip and on the Quartus II of Altera. The algorithm circuit uses 51536 logic elements (LE) for 30 bits fixed point design.

3 
Multiuser Interference Cancellation in Multicarrier CDMA System with Constrained Adaptive Inverse QRDRLS AlgorithmLiao, TaiYin 09 July 2001 (has links)
In this thesis, the multicarrier (MC) code division multiple access (CDMA) system is considered in Rayleigh fading channel. The main concern of this thesis is to devise a new direct linearly constrained constant modulus (LCCM) inverse QRDRLS algorithm for multiple access interference (MAI) cancellation and the problem due to the mismatch of the channel estimator. In the conventional approach, two significant detectors are applied to the system for multiuser interference suppression, one is the blind adaptation algorithm and the other is adaptive linearly constrained PLIC approach. However, the mirror effect may occur when the blind adaptation algorithm is employed. It might affect the performance in terms of bit error rate (BER), although the desired signal to interference (due to other users) improvement is still acceptable. Moreover, in case that the channel coefficients could not be estimated perfectly, the mismatch problem may occur to degrade the performance of the adaptive linearly constrained PLIC approach with the LMS or RLS algorithm.
To overcome the mismatch problem, the conventional approach is to use the LCCM criterion with gradient algorithm. However, the convergence rate of the gradient algorithm is too slow to be implemented in realtime wireless communication system. In this thesis, to have fast convergence rate and to circumvent the mismatch problem, the robust LCCMIQRD algorithm is devised and applied to the MCCDMA system in Rayleigh fading channel. The proposed robust LCCMIQRD algorithm has shown to be more effective in terms of MAI cancellation and the mismatch due to imperfect channel estimator. The performance, in terms of BER, of the proposed algorithm is superior to that of the conventional PLIC based algorithms, the blind adaptation algorithm, and the conventional LCCM gradient algorithm.

4 
WaveletBased Multiuser MCCDMA Receiver with Linearly Constrained Constant Modulus Inverse QRDRLS AlgorithmLiu, HsiaoChen 07 July 2002 (has links)
In this thesis, the problem of multiple access interference (MAI) suppression for the multicarrier (MC) code division multiple access (CDMA) system, based on the waveletbased (WB) multicarrier modulation, associated with the combining process is investigated for Rayleigh fading channel. The main concern of this thesis is to derive a new scheme, based on the linearly constrained constant modulus (LCCM) criterion with the robust inverse QR decomposition (IQRD) recursive least squares (RLS) algorithm to improve the performance of the conventional MCCDMA system with combining process. To verify the merits of the new algorithm, the effect due to imperfect channel parameters estimation and frequency offset are investigated.
We show that the proposed robust LCCM IQRDRLS algorithm outperforms the conventional LCCMgradient algorithm [6], in terms of output SINR, improvement percentage index (IPI), and bit error rate (BER) for MAI suppression under channel mismatch environment. Also, the performance of the WB MCCDMA system is superior to the one with conventional MCCDMA system. It is more robust to the channel mismatch and frequency offset. Moreover, the WB MCCDMA system with robust LCCM IQRDRLS algorithm does have better performance over other conventional approaches, such as the LCCMgradient algorithm, maximum ratio combining (MRC), blind adaptation algorithm and partitioned linear interference canceller (PLIC) approach with LMS algorithm, in terms of the capability of MAI suppression and bit error rate (BER).

5 
Performance of the MCCDMA Receiver with the GSCIQRDRLS AlgorithmTu, JhenJi 04 July 2003 (has links)
Capacity of CDMA system is limited to interference due to other users. System performance is degraded by nearfar problem when undesired users are closer to base station. Beside, the channel parameters could not be estimated perfectly at receiver, refer to as mismatch problem, which would also degrade the system performance.
We would like to consider the MAI and nearfar interference cancellation by adaptive linear constraint algorithms to implement linear constraint minimum variance (LCMV) approach. To exploit the linearly constrained filtering, the structure of the generalized sidelobe canceller (GSC) has been employed, where the constrained problem is converted into an unconstrained form with fewer parameters. GSC structure is an indirect but simpler implementation of LCMV algorithm. Moreover, it is also known that the constant modulus (CM) criteria has advantage to combat the channel mismatch, and the performance of the adaptive constraint algorithm based on CM criteria will be investigate.
In this thesis, we will derive a new GSCIQRDRLS algorithm to combat MAI and nearfar problems by combining LCIQRDRLS algorithm [1][5] and GSC structure [17]; and prove that the GSC and LC structures based IQRDRLS algorithms are equivalent, which means that the good performance of LCIQRDRLS algorithm can be achieved by a simpler GSC structure algorithm. We will also derive a new GSCCMIQRDRLS algorithm to improve the system performance under mismatch problem by combining CM criteria [20] and GSCIQRDRLS algorithm.

6 
Modified Generalized Sidelobe Canceller with Inverse QRDRLS AlgorithmChang, ChunLin 11 July 2003 (has links)
The conventional temporal filtering approach cannot be used to separate signal from interference which occupies the same temporal frequency band as signal. Using a spatial filtering at the receiver can separate signals from interference that originates from different spatial location. Many adaptive array beamforming algorithms, based on linear constraints, have been proposed for suppressing undesired interference and being applied to wireless communication systems for multiuser detection. The adaptive array system can be employed to automatically adjust its directional to achieve the purpose that nulls the interferences or jammers and thus, enhances the reception of the desired signal. Inverse QR Decomposition Recursive Leastsquare (IQRDRLS) algorithm has many advantages such as where the LS weight vector be computed without back substitution, a well known numerical stable algorithm and offering better convergence rate, steadystate meanssquare error, and parameter tracking capability over the adaptive least mean square (LMS) based algorithms. In this thesis, a new application, GSCIQRDRLS combining Generalized Sidelobe Canceller (GSC) and IQRDRLS algorithm, is developed. It preserves the advantages of GSC such as simple structure, less computations, and converts a linearly constrained optimization problem into a standard optimum filtering problem. But the performance is equivalent between GSCIQRDRLS and LCIQRDRLS algorithms.

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