1 
Design and performance evaluation of RAKE finger management schemes in the soft handover regionChoi, Seyeong 15 May 2009 (has links)
We propose and analyze new finger assignment/management techniques that
are applicable for RAKE receivers when they operate in the soft handover region.
Two main criteria are considered: minimum use of additional network resources and
minimum call drops. For the schemes minimizing the use of network resources, basic
principles are to use the network resources only if necessary while minimum call drop
schemes rely on balancing or distributing the signal strength/paths among as many
base stations as possible. The analyses of these schemes require us to consider joint
microscopic/macroscopic diversity techniques which have seldom been considered before
and as such, we tackle the statistics of several correlated generalized selection
combining output signaltonoise ratios in order to obtain closedform expressions for
the statistics of interest. To provide a general comprehensive framework for the assessment
of the proposed schemes, we investigate not only the complexity in terms of
the average number of required path estimations/comparisons, the average number
of combined paths, and the soft handover overhead but also the error performance of
the proposed schemes over independent and identically distributed fading channels.
We also examine via computer simulations the effect of path unbalance/correlation as
well as outdated/imperfect channel estimations. We show through numerical exam ples that the proposed schemes which are designed for the minimum use of network
resources can save a certain amount of complexity load and soft handover overhead
with a very slight performance loss compared to the conventional generalized selection
combiningbased diversity systems. For the minimum call drop schemes, by
accurately quantifying the average error rate, we show that in comparison to the
conventional schemes, the proposed distributed schemes offer the better error performance
when there is a considerable chance of loosing the signals from one of the
active base stations.

2 
Adapitve Multiuser Receiver with RAKE Structure and Decision Feedback in Multiuser and Multipath Fading EnvironmentChang, JrWen 30 June 2000 (has links)
A review of adaptive decorrelating detector techniques for directsequence code division multiple access (CDMA) signals is given. The goal is to improve CDMA system performance and capacity by reducing interference between users. The techniques considered are implementations of multiuser receivers, for which background material is given. Adaptive algorithms improve the feasibility of such receivers. An adaptive multiuser receiver for CDMA system has been proposed to increase system capacity. The adaptive decorrelator can be used to eliminate interference from known interferers, though it is prone to noise enhancement. However the receiver is basically designed for synchronous CDMA over AWGN channels. In order to confirm the robustness of the receiver for the asynchronous cases, experimental evaluations are displayed when the relative user delays are small compared to the symbol duration and when the channel is Rayleigh multipath fading as in microcellular scenarios. In addition to the efficient implementation of the decorrelating detector of [1], the receiver also can be adapted to incorporate decision feedback. Successive interference cancellation techniques reduce interference by cancellation of one detected signal from another. And an efficient incorporation of decorrelator with RAKE and (DF) decision feedback receiver for frequencyselective Rayleigh fading multipath channels is also proposed. Performance evaluation of the detector via computer simulation scenarios is conducted to substantiate it's potential for realtime operation.

3 
Multiple Symbol Differential Detection of BPSK in CDMA SystemChung, YiPing 11 July 2001 (has links)
In this thesis, we take an application of multiple symbol differential detection (MSDD)
technique in directsequence code division multiple access (CDMA) system. It is well
known that MSDD is an effective noncoherent demodulator which outperform the
conventional Mary differential phase shift keying (MDPSK) in additive white Gaussian
noise (AWGN) channel. Take MPSK demodulator into consideration, the performance
of MSDD based on noncoherent demodulation approaches the performance of coherent
demodulation. However, there is little research about MSDD in frequencyselective
fading channel. We are now combining the MSDD and Rake receiver to be the signal
demodulator. In conventional, there are two kinds of Rake receivers. One is coherent
demodulator. Another is noncoherent demodulator. For coherent demodulation, it needs
to have channel estimation at each path. The advantage is that the performance will be
improved. On the other hand, the disadvantage is complexity and operation will increase.
On the contrast, for noncoherent demodulation, it is the performance degradation and
complexity simplification. In this thesis, We suggest a multiple symbol differential detection
on Rake receiver for CDMA system. From our computer simulation, only for hard decision,
the performance is improved and the improvement is proportional to the number of multipath
and the number of the length of multiple symbol. This will not happen in conventional MDPSK.
However, from our observation, the improvement of performance is degrading as the number
of multipath increase. Thus, we employee the technique of Viterbi decoding differential
detection (VDDD) to demodulate the differential sequence. By the property of decision
interval, the VDDD can obtain additional improvement.

4 
A Study on Receiver Design in the UltraWide Band ChannelsChiu, Chihhsien 12 September 2008 (has links)
Ultrawideband (UWB) system is an indoor communication system, high data rate transmission within 510m transmitted range. This system suffers from high dense multipath channels impairment. If the spreading code is not orthogonal in dense multipath channels, severe intersymbol interference (ISI) will degrade the system performance. In this thesis, we will discuss the performance of various receivers in ultrawideband channels.
Rake receiver can collect signal energy from different multipath. However, the imperfect orthogonal property of spreading code will cause severe ISI and degrade the performance of Rake receiver. Least mean square (LMS) chip equalizer not only combines the energy from different multipath, but also suppresses ISI. But, the complexity is too high to realize.
In this thesis, we combine Rake receiver with ISI canceller to enhance system performance. If the canceller is before Rake receiver, we define it as ISIC RAKE. If the canceller is behind Rake receiver, we define it as RAKE ISIC. In the ISI canceller, not only ISI caused by preceding bits is cancelled, but also the ISI caused by following bit is cancelled. In multiuser cases, we are also canceling multiaccess interference (MAI). From simulation results, the proposed method outperforms conventional Rake receiver, Rake receiver combined with LMS symbol equalizer, and LMS chip equalizer. The complexity of proposed method is lower than LMS chip equalizer.

5 
Circuit Design of DS Spread Spectrum ReceiverKuo, CheYu 09 September 2009 (has links)
Traditionally in CDMA system, selective rake receiver is the popular method of
detection. When used in DSUWB system, the complex in door environment will
increase the channel paths. As the channel paths increase, the more fingers which are
part of Rake receiver will increase. It will be difficult for hardware implement when
consider the operation of channel estimation and Rake receiver. And it is unfavorable
for hardware design.
In this thesis, we will use partial Rake receiver to replace selective Rake receiver.
Channel estimation is implemented by template the receiver signals within 2 bit time
window length. The performance is acceptable and the hardware complexity is
reduced. When implement the channel estimation, we combine some blocks of
acquisition and channel estimation for reducing hardware complexity.

6 
Multiscale CLEAN Deconvolution for Resolving Multipath Components in SRake ReceiverWang, Chunyu 31 August 2010 (has links)
Ultrawideband systems can be used in indoor wireless personal area network (WPAN) or shortrange wireless local area network (WLAN) transmission. Yet owing to the effects of indoor dense multipath, it will cause more power consumption. We usually use Rake receiver to improve system performance. However, we should do some compromise between system performance and the design complexity. Thus, the concept of Selective Rake can be used to substitute for the conventional Rake receiver. Selective Rake receiver uses fewer but more powerful paths instead of using all the paths to raise system performance. Hence, we have to precisely detect the multipath components for best performance. Earlier we use CLEAN algorithm to estimate the multipath components. The CLEAN algorithm can be used in selecting the paths with relatively high energy. But as the impact of frequency selective fading makes the transmitted signal distorted, the CLEAN algorithm no longer applies to this situation. Thus, we use Multiscale CLEAN algorithm instead. Multiscale CLEAN algorithm calculate the value of crosscorrelation between the received signal and a set of waveforms, and then choose the higher one as the waveform transmitted. Besides, we use Maximal Ratio Combining to weigh the different paths to get the signal with more power. We represent the signal affected by frequency selective fading by using the second derivatives of Gaussian waveform function with different effective widths of pulse. The waveforms corresponding different effective widths have different spectra which represent the different effects of fading. It is seen that that the multiscale CLEAN has better performance than the CLEAN algorithm with more precise estimation of multipath components. In simulation result, we can figure out path searching using Multiscale CLEAN algorithm is more accurate than using CLEAN algorithm. Even the path with smaller energy gain, using multiscale CLEAN algorithm can search successfully, while CLEAN algorithm cannot do.

7 
Area and Power Conscious Rake Receiver Design for Third Generation WCDMA SystemsKim, Jina 17 January 2003 (has links)
A rake receiver, which resolves multipath signals corrupted by a fading channel, is the most complex and power consuming block of a modem chip. Therefore, it is essential to design a rake receiver be efficient in hardware and power. We investigated a design of a rake receiver for the WCDMA (Wideband Code Division Multiple Access) system, which is a third generation wireless communication system. Our rake receiver design is targeted for mobile units, in which lowpower consumption is highly important. We made judicious judgments throughout our design process to reduce the overall circuit complexity by trading with the performance. The reduction of the circuit complexity results in low power dissipation for our rake receiver. As the first step in the design of a rake receiver, we generated a software prototype in MATLAB. The prototype included a transmitter and a multipath Rayleigh fading channel, as well as a rake receiver with four fingers. Using the software prototype, we verified the functionality of all blocks of our rake receiver, estimated the performance in terms of bit error rate, and investigated tradeoffs between hardware complexity and performance. After the verification and design tradeoffs were completed, we manually developed a rake receiver at the RT (Register Transfer) level in VHDL. We proposed and incorporated several schemes in the RT level design to enhance the performance of our rake receiver. As the final step, the RT level design was synthesized to gate level circuits targeting TSMC 0.18 mm CMOS technology under the supply voltage of 1.8 V. We estimated the performance of our rake receiver in area and power dissipation. Our experimental results indicate that the total power dissipation for our rake receiver is 56 mW and the equivalent NAND2 circuit complexity is 983,482. We believe that the performance of our rake receiver is quite satisfactory. / Master of Science

8 
Adaptive DSCDMA Receivers with Fast Tracking Capability for Wireless CommunicationsSun, Chunhung 25 April 2007 (has links)
The direct sequence (DS) code division multiple access (CDMA) is one of the most promising multiplexing technologies for wireless communications. It is also a core technology used in the wideband CDMA (WCDMA) system for the third generation (3G) wireless communication systems. In practice, in the CDMA systems the incomplete orthogonal of the spreading codes between users may introduce the socalled multiple access interference (MAI). Usually, the nearfar problem exists when the interfering users are assigned powers much higher than the desired user. Such that the system performance might degrade, dramatically, and thus limits the system capacity. To circumvent the abovementioned problems many effective adaptive multiuser detectors, based on the minimum mean square error (MMSE) and the minimum output energy (MOE) criteria subject to certain constraints have been proposed. In addition, to mitigate multipath fading effect, RAKE receiver was adopted due to the advantages of path diversity, thus, enhances the system performance. To implement the blind adaptive multiuser detector the linearly constrained minimum variance (LCMV), which is the constrained version of MOE, has been suggested. Further, the LCMVbased receivers exhibit high sensitivity to the channel mismatch caused by the unreliable estimation. To deal with this problem the constant modulus (CM) criterion was considered. In this dissertation, to deal with diverse phenomena encountered in practical channels, we first propose new blind adaptive multiuser detectors, based on the Min/Max criterion associated with the LCCM approach. For implementation the LC exponential window (EW) recursive leastsquare (RLS) algorithm is derived, and is referred to as the EW LCCMRLS receiver. It can be used to effectively suppress the MAI and ISI, simultaneously, over multipath fading channels and are robust to mismatch problem caused by inaccuracies in the acquisition of timing and spreading code of the desired user. To reduce the complexity of the abovementioned blind adaptive multiuser receiver with the LCCMRLS algorithm, the socalled generalized sidelobecanceller (GSC) structure is adopted, results in obtaining new CMGSCRLS algorithm. Moreover, to further improve the system performance for multipath fading and timevarying channel, the sliding window (SW) LCCMRLS and SW CMGSCRLS algorithms are developed. It can be employed for multipath fading channel with the rapidly changing strong narrowband interference (NBI), which is joined suddenly to the CDMA systems. To look more inside the effect of selecting the initial value of the input signals autocorrelation matrix, some theoretical analyses for the SW LCRLS as well as EW LCRLS are provided. Since, unfortunately, the LCCM criterion is known to highly depend on the exact knowledge of the desired user amplitude that is not known exactly at receiver. In the final of this dissertation, a novel linearly constrained adaptive constant modulus RLS (LCACMRLS) algorithm for blind DSCDMA receiver is proposed. With this new proposed LCACMRLS algorithm, the amplitude variation of the desired user, due to changing characteristics of the channel, can be tracked adaptively. Thus, better performance achievement, in terms of output signaltointerferenceplusnoise ratio (SINR) and bit error rate (BER), over the conventional LCCMLMS and LCCMRLS algorithms can be expected.

9 
CostBased CLEAN Algorithm for Selective RAKE Receivers in UWB SystemsKe, Chihchiang 29 July 2008 (has links)
In this thesis, we propose a costbased CLEAN algorithm to accurately find dense multipath parameters and improve the performance of selective RAKE receiver in indoor UWB systems. RAKE receiver can resolve the dense multipath interference problems with the multipath parameters. Because the weak paths are of lower valuable for system performance improvement, selective RAKE receiver combines only the strongest multipath components and reduce the number of fingers to lower the complexity of RAKE receiver. However, selective RAKE receiver needs accurate multipath detection to decide the suitable number and parameters of fingers. In order to improve the performance of selective RAKE receiver, the main issue in this thesis is to detect the best paths of channel with the CLEAN algorithm. CLEAN algorithm uses the correlation of the received signal and the template signal as the basis for searching paths. If there are closely adjacent paths, or if one of signal paths is relatively stronger, the detection error of paths may occur and thus affects the performance of the receiver. EPbased CLEAN algorithm uses the cost function and the evolutionary programming (EP) to search the multipath delay times and gain coefficients for minimizing the cost function. Accurate multipath detection and high resolution of adjacent paths can be obtained. However, EPbased CLEAN algorithm makes a timeconsuming blind search. In the thesis, a CLEAN algorithm based on the cost function is proposed. The proposed costbased CLEAN algorithm searches the delay times near the peaks of the crosscorrelation for local minimum of the cost function, and then uses CLEAN algorithm to extract autocorrelation components and obtain the accurate multipath detection. By testing the IEEE802.15.3a UWB channel models, and comparing with CLEAN algorithm, the costbased CLEAN algorithm in the thesis can achieve better detection accuracy in multipath searching, and improve the performance of selective RAKE receiver.

10 
Effective capacity evaluation of advanced wideband CDMA and UWB radio networksPirinen, P. (Pekka) 24 November 2006 (has links)
Abstract
High radio capacity is one of the main targets in wireless network planning. The characteristics of the broadband radio channel pose serious challenges for achieving this goal. This thesis views the capacity problem from two frameworks. In the first, the effective user capacity in advanced direct sequence wideband codedivision multipleaccess (DSCDMA) radio networks is evaluated. Sensitivity to various imperfections in key system parameters is studied. The analysis is based on a mathematical foundation that presents complex signal models and enables evaluation of the performance losses due to parameter estimation errors and multipath fading. The effective number of users supported in a cell is restricted by the multiple access interference (MAI) in the same cell (intracell interference) and overall background noise. The studied wideband CDMA receiver structures comprise conventional rake receivers with both the maximal ratio combining (MRC) and equal gain combining (EGC) schemes that can be supplemented with either linear decorrelating or nonlinear successive cancellationbased multiuser detectors and Mantenna spatial diversity.
The second framework focuses on direct sequence spread spectrumbased ultra wideband (UWB) indoor communications. Cochannel interference limited capacity is evaluated against the outage probability criterion in exponentially decaying lognormal multipath fading channels. Distancedependence and spatial distribution of users is taken into account at different spatial cell configurations. Only moderate complexity partial rake receivers with noncoherent combining are employed. Total interference is composed of interpath, multipath, intracell, and intercell interference contributions. Lognormal sum approximations and simulations are used to evaluate distributions of the desired and interfering signals. The impact of the timing errors at the receiver monopulse correlation is studied.
The numerical results for the wideband CDMA framework show that effective user capacity and sensitivity depend critically on the joint impact of nonidealities in system parameters (e.g., channel profile, severity of fading, receiver algorithms). User capacities of the studied multiuser enhanced receivers were more prone to these impairments than those of the simpler single user receivers. The results should be used for network planning and optimization.
The numerical results of the UWB framework suggest that, even in the multipath rich channel, the optimal number of rake fingers can be less than half of the significant multipaths. Differences between circular, square, and hexagonal cell models proved to be minor with respect to link distance distributions. The derived link distance statistics are useful tools in the analytic piconet dimensioning and optimization.

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