Browsing by Author "Chang, PR"

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A self-correction Hopfield neural network for computing the bit-level transform image coding
(1997-08-01)
Chang, PR
;
電信工程研究所
;
Institute of Communications Engineering
A Hopfield-type neural network approach is presented, which leads to an analogue circuit for implementing the bit-level transform image. Unlike the conventional digital approach to image coding, the analogue coding system would operate at a much higher speed and it requires less hardware than a digital system. To utilize the concept of neural net, the computation of a two-dimensional DCT-based transform coding should be reformulated as minimizing a quadratic nonlinear programming problem subject to the corresponding 2s complement binary variables of two-dimensional DCT coefficients. A Hopfield-type neural net with a number of graded-response neurons designed to perform the quadractic nonlinear programming would lead to such a solution, in a time determined by RC time constants, not by algorithmic time complexity. Nevertheless, the existance of local minima in the energy function of the original Hopfield model implies that in general the correct globally optimal solution is not guaranteed. To tackle this difficulty, a network with an additional self-correction circuitry is developed to eliminate these local minima and yields the correct digital representations of 2-D DCT coefficients. A fourth-order Runge-Kutta simulation is conducted to verify the performance of the proposed analogue circuit. Experiments show that the circuit is quite robust and independent of parameter variations, and the computation time of an 8 x 8 DCT is estimated as 128 ns for RC = 10(-9).
A self-correction Hopfield neural network for computing the bit-level transform image coding
(1997-08-01)
Chang, PR
;
交大名義發表
;
電信工程研究所
;
National Chiao Tung University
;
Institute of Communications Engineering
A Hopfield-type neural network approach is presented, which leads to an analogue circuit for implementing the bit-level transform image. Unlike the conventional digital approach to image coding, the analogue coding system would operate at a much higher speed and it requires less hardware than a digital system. To utilize the concept of neural net, the computation of a two-dimensional DCT-based transform coding should be reformulated as minimizing a quadratic nonlinear programming problem subject to the corresponding 2s complement binary variables of two-dimensional DCT coefficients. A Hopfield-type neural net with a number of graded-response neurons designed to perform the quadractic nonlinear programming would lead to such a solution, in a time determined by RC time constants, not by algorithmic time complexity. Nevertheless, the existance of local minima in the energy function of the original Hopfield model implies that in general the correct globally optimal solution is not guaranteed. To tackle this difficulty, a network with an additional self-correction circuitry is developed to eliminate these local minima and yields the correct digital representations of 2-D DCT coefficients. A fourth-order Runge-Kutta simulation is conducted to verify the performance of the proposed analogue circuit. Experiments show that the circuit is quite robust and independent of parameter variations, and the computation time of an 8 x 8 DCT is estimated as 128 ns for RC = 10(-9).
A wavelet multiresolution compression technique for 3D stereoscopic image sequence based on mixed-resolution psychophysical experiments
(2000-07-01)
Chang, PR
;
Wu, MJ
;
電信工程研究所
;
Institute of Communications Engineering
Three-dimensional visual communications, made through the use of stereoscopic images, are able to achieve total display realism. In order to create a 3D system with two images (left and right) that should be transmitted simultaneously, the large amount of information contained in the images should be reduced, and an efficient coding appropriate for stereoscopic images is developed. Stereoscopic image sequence compression involves the exploitation of the spatial redundancy between the left and right image frames to achieve the compression ratio higher than that are by the independent compression of the two frames. In order to further achieve the higher compression ratio, in this paper, we employ the mixed-resolution psychophysical experiments to the stereo image compression. The experiments have shown that a stereo image pair with one high-resolution image and one lower-resolution image is sufficient to provide good stereoscopic depth perception. Thus, one image sequence is compressed independent of the other sequence using the motion compensation, while the other sequence is estimated at a lower resolution from this stream using the low-resolution disparity compensation. To implement the mixed-resolution coding, a wavelet multiresolution framework has been adopted to facilitate such an estimation of motion and disparity vectors at different resolutions. Experimental results indicate that the compression ratio for a typical stereoscopic image sequence is about 90, without any significant loss in the perceived 3D stereoscopid image quality. (C) 2000 Elsevier Science B.V. All rights reserved.
Adaptive fuzzy power control for CDMA mobile radio systems
(1996-05-01)
Chang, PR
;
Wang, BC
;
交大名義發表
;
電信工程研究所
;
National Chiao Tung University
This paper introduces a new application of fuzzy-logic control (FLC) theory to the power control in a direct-sequence, code-division multiple-access (DS/CDMA) cellular system over the mobile fading radio channels. Power control is essential in DS/CDMA to compensate for the differing received powers due to both the slowly varying long-term and fast varying short-term fading processes and co-channel interference. The conventional feedback power control algorithms allow the base station to send a power command to either raise or lower each user transmitting signal power level by a fixed power step and then keep the received powers almost equal. The fixed-step approach is actually an integral control whose power increment is determined according to the bang-bang-like control policy. However, this control scheme suffers from poor system stability, large overshoot, and long rise time. To tackle this difficulty, a fuzzy proportional-plus-integral (PI) control, whose input variables are the received power error and error change, is introduced to determine each user's transmitting power in order to maintain simultaneously all users' signal power received at the base station nearly equal and to achieve better system stability and control performance. The derivation of the fuzzy PI control has been carried out by analyzing both the closed-loop steady state behavior and transient response of the system with a priori knowledge of the dynamics of the CDMA mobile fading channels. In fuzzy control, linguistic descriptions of actions in controlling a process are represented as fuzzy rules. This fuzzy-rule base is used by an inference mechanism in conjunction with some knowledge of the states of process in order to determine control actions. These control actions would lead to the fast rise time, minimum overshoot, and small root-mean-squared (rms) tracking error. Furthermore, the additional advantages of fuzzy PI control over conventional control theories are increased robustness despite interference and the ability to handle the time-delay process without system degradation since there is usually a latency between each user and base station. Simulation results show that the fuzzy PI power control provides much smaller rms tracking error and better traffic capacity performance compared with the fixed-step control, especially in poor co-channel interference conditions.
Adaptive fuzzy proportional integral power control for a cellular CDMA system with time delay
(1996-12-01)
Chang, PR
;
Wang, BC
;
交大名義發表
;
電信工程研究所
;
National Chiao Tung University
In this article, we investigate the use of fuzzy logic control techniques for adaptive power control in a direct-sequence code-division multiple-access (DS/CDMA) cellular system over the mobile fading radio channels with propagation time delay, A fuzzy PI (proportional-plus-integral) control whose input variables are the received power error and error change is introduced to determine each user transmitting power in order to simultaneously equalize all users' signal powers received at the base station and achieve better System stability and control performance, This control strategy can ensure long loop transmission delays without causing the system to become unstable, According to the well-known phase-plane method, the derivation of the fuzzy PI control has been carried out by analyzing the response areas, cross-over, and extreme points of the system step response with apriori knowledge of the dynamics of the CDMA mobile fading channels, For a long time-delay fading process, a methodology is developed to modify the rule base to contain the delay information for reducing the deadtime effects of the process, Moreover, the additional advantages of fuzzy PI control over conventional control theories are: increased robustness in spite of interference and the ability to handle the time-delay process whose parameters are not accurately known, Simulation results show that a good performance can he achieved both in rms tracking error and traffic capacity by use of fuzzy PI power control, especially in poor interuser interference and long time delay conditions.
Blind adaptive energy estimation for decorrelating decision-feedback CDMA multiuser detection using learning-type stochastic approximations
(1999-03-01)
Chang, PR
;
Lee, CC
;
Lin, CF
;
電信工程研究所
;
Institute of Communications Engineering
This paper investigates the application of linear reinforcement learning stochastic approximation to the blind adaptive energy estimation for a decorrelating decision-feedback (DDF) multiuser detector over synchronous code-division multiple-access (CDMA) radio channels in the presence of multiple-access interference (MAI) and additive Gaussian noise. The decision feedback incorporated into the structure of a linear decorrelating detector is able to significantly improve the weaker users' performance by canceling the MAI from the stronger users. However, the DDF receiver requires the knowledge of the received energies, In this paper, a new novel blind estimation mechanism is proposed to estimate all the users' energies using a stochastic approximation algorithm without training data. In order to increase the convergence speed of the energy estimation, a linear reinforcement learning technique is conducted to accelerate the stochastic approximation algorithms. Results show that our blind adaptation mechanism is able to accurately estimate an the users' energies even if the users of the DDF detector are not ranked properly. After performing the blind energy estimation and then reordering the users in a nonincreasing order, numerical simulations show that the DDP detector for the weakest user performs closely to the maximum likelihood detector, whose complexity grows exponentially with the number of users.
Design of multicode CDMA systems for 3-D stereoscopic video over wireless ATM networks
(2000-03-01)
Chang, PR
;
Lin, CF
;
Wu, MJ
;
電信工程研究所
;
Institute of Communications Engineering
This paper investigates the application of multicode spread-spectrum code-division multiple-access (SS-CDMA) techniques to three-dimensional (3-D) stereoscopic video transmission over wireless asynchronous transfer mode (ATM) networks. Three-dimensional visual communications, made through the use of stereoscopic images, are able to achieve total display realism. Such services allow users to share the virtual reality (VR) world without any geographical restrictions. In order to create a 3-D system with two images (left and right) that should be transmitted over a bandlimited mobile channel simultaneously, a cost-effective Motion Picture Experts Group (MPEG)-based wavelet multiresolution coding with a joint motion and disparity compensation is developed to reduce a large amount of information contained in the images to meet the low-transmission rate limitation of mobile channels. However, the rapidly variable bit rate (VBR) characteristics of the MPEG-based 3-D videos seems a weakness to the transmission of such videos via a constant bit-rate (CBR) mobile channel. The ATM technique is especially well suited for VER MPEG-based 3-D video because of its ability to allocate bandwidth on demand to these services. However, since the mobile radio has a Limited channel capacity, the overall capacity of the traditional ATM-based SS-CDMA system may not be sufficient to accommodate the MPEG-based 3-D video services requested by the multiple mobile users simultaneously. To tackle this difficulty, a multicode CDMA technique is proposed to provide VER MPEG-based 3-D video services by varying the number of spreading codes assigned to the 3-D video to meet its dynamic throughput requirement. Powerful forward error correction (FEC) codes are necessary to protect the video data so that it can be successfully transmitted at an acceptable signal power level. Two separate FEC code schemes are applied to the header and payload of an ATM cell containing 3-D video data, respectively. The ATM cell header is protected by a relatively powerful FEC code to ensure correct delivery and low cell loss rate (CLR). On the other hand, the ATM cell payload is encoded for varying degrees of error protection according to the priority of the payload data in 3-D videos. An adaptive FEC code combining scheme is proposed to provide the good protection for payload data with the maximization of its code rate to minimize the extra bandwidth for FEC overhead.
Design of spread spectrum multicode CDMA transport architecture for multimedia services
(2000-01-01)
Chang, PR
;
Lin, CF
;
電信工程研究所
;
Institute of Communications Engineering
In this paper, we investigate a new application of the well-known spread spectrum code division multiple access (SS-CDMA) techniques to multimedia services related to the development of the next-generation wireless mobile networks interconnecting with a wireline ATM-based broadband network. Such services allow users to share novel multimedia applications without any geographical restrictions. However, since the mobile radio channel has a fixed limited bandwidth, the traditional SS-CDMA system may not be sufficient to accommodate the variable bit rate (VBR) multimedia services requested by multiple mobile users simultaneously. Moreover, the traffic load at the base station can change dynamically due to the time-varying throughput requirement of these requested multimedia services; To tackle this difficulty, a multicode CDMA (MC-CDMA) technique is proposed to provide multirate multimedia services by varying the number of spreading codes assigned to each user in order to meet its throughput requirement. In MC-CDMA, a spreading code can be used to transmit information at a basic bit rate. Users (video or data) who need higher transmission rates can use multiple codes in parallel. Meanwhile, the maximum available number of codes in the MC-CDMA system is still limited. Hence, a cost-effective dynamic code allocation scheme has then been proposed to dynamically assign appropriate number of codes to each user for achieving the maximum resource utilization for multiuser multimedia services via the mobile radio channel, Finally, a number of real multimedia titles generated from the well-known MacroMind Director are conducted to evaluate the performance of the proposed wireless multimedia CDMA system.
Environment-adaptation mobile radio propagation prediction using radial basis function neural networks
(1997-02-01)
Chang, PR
;
Yang, WH
;
交大名義發表
;
電信工程研究所
;
National Chiao Tung University
This paper investigates the application of a radial basis function (RBF) neural network to the prediction of Field strength based on topographical and morphographical data, The RBF neural network Is a two-layer localized receptive field network whose output nodes from a combination of radial activation functions computed by the hidden layer nodes. Appropriate centers and connection weights in the RBF network lead to a network that is capable of forming the best approximation to any continuous nonlinear mapping up to an arbitrary resolution. Such an approximation introduces best nonlinear approximation capability into the prediction model in order to accurately predict propagation loss over an arbitrary environment based on adaptive learning from measurement data, The adaptive learning employs hybrid competitive and recursive least squares algorithms, The unsupervised competitive algorithm adjusts the centers while the recursive least squares (RLS) algorithm estimates the connection weights. Because these two learning rules are both linear, rapid convergence is guaranteed. This hybrid algorithm significantly enhances the real-time or adaptive capability of the RBF-based prediction model, The applications to Okumura's data are included to demonstrate the effectiveness of the RBF neural network approach.
Fiber-optic subcarrier multiplexed CDMA local-area networks for subband image transmission
(1996-12-01)
Chang, PR
;
Chang, CC
;
電信工程研究所
;
Institute of Communications Engineering
This paper investigates the application of subcarrier multiplexed code-division multiple-access (CDMA) techniques to image transmission over fiber-optic local-area networks (LAN's), In the hybrid scheme, CDMA is used to suppress the interference caused by the laser nonlinearity in the subcarrier multiplexing (SCM) fiber-optic communication systems, Likewise, the SCM scheme is able to increase the channel data rate of CDMA systems, This hybrid system combines the advantages of both schemes and is particularly well suited to subband coding that divides the image information into multiple parallel data streams using an analysis filter bank, each of which is transmitted via a unique subcarrier-code pair, where the spreading code and subcarrier frequency correspond to the image and one of its subbands, respectively, This hybrid scheme also allows more than one image to be transmitted and be accessed simultaneously at the same channel bandwidth, in which each image is assigned a particular spreading code added to its digital data modulating the subcarrier. After transmission, each received signal is independently recovered at a high-Q surface acoustic wave (SAW) receiver with the matching subcarrier-code pair, Other concurrent signals are rejected by the SAW, Then, all the recovered subbands are reassembled by a synthesis filter bank into a close reproduction to the original image, In this paper, the image quality of subband image transmission via CDMA/SCM fiber-optic channels is evaluated and examined.
Fiber-optic subcarrier multiplexed CDMA local-area networks for subband image transmission
(1996-12-01)
Chang, PR
;
Chang, CC
;
交大名義發表
;
電信工程研究所
;
National Chiao Tung University
This paper investigates the application of subcarrier multiplexed code-division multiple-access (CDMA) techniques to image transmission over fiber-optic local-area networks (LAN's), In the hybrid scheme, CDMA is used to suppress the interference caused by the laser nonlinearity in the subcarrier multiplexing (SCM) fiber-optic communication systems, Likewise, the SCM scheme is able to increase the channel data rate of CDMA systems, This hybrid system combines the advantages of both schemes and is particularly well suited to subband coding that divides the image information into multiple parallel data streams using an analysis filter bank, each of which is transmitted via a unique subcarrier-code pair, where the spreading code and subcarrier frequency correspond to the image and one of its subbands, respectively, This hybrid scheme also allows more than one image to be transmitted and be accessed simultaneously at the same channel bandwidth, in which each image is assigned a particular spreading code added to its digital data modulating the subcarrier. After transmission, each received signal is independently recovered at a high-Q surface acoustic wave (SAW) receiver with the matching subcarrier-code pair, Other concurrent signals are rejected by the SAW, Then, all the recovered subbands are reassembled by a synthesis filter bank into a close reproduction to the original image, In this paper, the image quality of subband image transmission via CDMA/SCM fiber-optic channels is evaluated and examined.
Fuzzy neural systems for controlling sound localisation in stereophonic reproduction
(1998-07-01)
Chang, PR
;
Tan, TH
;
電信工程研究所
;
Institute of Communications Engineering
The paper presents a new fuzzy logic control (FLC) approach which leads to a stereophonic reproduction controller for localising an auditory image in the desired direction and at the expected distance. Since an auditory event is usually less precisely resolved than the physical sound space, the auditory event need not coincide with a physical sound source, and can occur at a position where nothing is visible to a listener. It turns out that controlling the auditory image is more difficult than the localisation of a sound image. Unlike the conventional sound image localisation approach, our fuzzy logic controller can take account of knowledge in human auditory perception. The ambiguous human auditory perception in conjunction with the spatial reverberation from the surrounding environment can be represented by a number of fuzzy-set values. From these fuzzy representations, the auditory image localisation controller characterises the function of how control outputs depend on control inputs as fuzzy implications or associations. Furthermore, the overall stereophonic reproduction controller can be realised by a 45-rule fuzzy associative memory (FAM) system. The performance of FLC-based auditory image localisation is verified in a number of experiments.
Narrow-band interference suppression in spread-spectrum CDMA communications using pipelined recurrent neural networks
(1999-03-01)
Chang, PR
;
Hu, JT
;
電信工程研究所
;
Institute of Communications Engineering
This paper investigates the application of pipelined recurrent neural networks (PRNN's) to the narrow-band interference (NBI) suppression over spread-spectrum (SS) code-division multiple-access (CDMA) channels in the presence of additive white Gaussian noise (AWGN) plus non-Gaussian observation noise. Optimal detectors and receivers for such channels are no longer linear. A PRNN that consists of a number of simpler small-scale recurrent neural network (RNN) modules,vith less computational complexity is conducted to introduce best nonlinear approximation capability into the minimum mean-squared error nonlinear predictor model in order to accurately predict the NBI signal based on adaptive learning for each module from previous non-Gaussian observations, Once the prediction of the NBI signal is obtained, a resulting signal is computed by subtracting the estimate from the received signal, Thus, the effect of the NBI can be reduced. Moreover, since those modules of a PRNN can be performed simultaneously in a pipelined parallelism fashion, this would lead to a significant improvement in its total computational efficiency. Simulation results show that PRNN-based NBI rejection provides a superior signal-to-noise ratio (SNR) improvement relative to the conventional adaptive nonlinear approximate conditional mean (ACM) filters, especially when the channel statistics and exact number of CDMA users are not known to those receivers.
Narrowband interference suppression in spread spectrum CDMA communications using pipelined recurrent neural networks
(1998)
Chang, PR
;
電信工程研究所
;
Institute of Communications Engineering
This paper investigates the application of pipelined recurrent neural networks (PRNN) to the narrowband interference (NBI) suppression over spread spectrum CDMA channels in the presence of AWGN plus non-Gaussian observation noise. Optimal detectors and receivers for such channels are no longer linear. A PRNN that consists of a number of simpler small-scale recurrent neural network (RNN) modules with less computational complexity is conducted to introduce best nonlinear approximation capability into the minimum mean squared error nonlinear predictor model in order to accurately predict the NBI signal based on adaptive learning for each module from previous non-Gaussian observations. Once the prediction of the NBI signal is obtained, a resulting signal is computed by subtracting the estimate from the received signal. Thus, the effect of the NBI can be reduced. Moreover, since those modules of a PRNN can be performed simultaneously in a pipelined parallelism fashion, this would lead to a significant improvement in its total computational efficiency. Simulation results show that PRNN-based NBI rejection provides a superior SNR improvement relative to the conventional adaptive nonlinear ACM filters, especially when the channel statistics and the exact number of CDMA users are not known to those receivers.
Optimal nonlinear adaptive prediction and modeling of MPEG video in ATM networks using pipelined recurrent neural networks
(1997-08-01)
Chang, PR
;
Hu, JT
;
交大名義發表
;
電信工程研究所
;
National Chiao Tung University
This paper investigates the application of a pipelined recurrent neural network (PRNN) to the adaptive traffic prediction of MPEG video signal via dynamic ATM networks, The traffic signal of each picture type (I, P, and B) of MPEG video is characterized by a general nonlinear autoregressive moving average (NARMA) process, Moreover, a minimum mean-squared error predictor based on the NARMA model is developed to pro,ide the best prediction for the video traffic signal, However, the explicit functional expression of the best mean-squared error predictor is actually unknown, To tackle this difficulty, a PRNN that consists of a number of simpler small-scale recurrent neural network (RNN) modules with less computational complexity is conducted to introduce the best nonlinear approximation capability into the minimun mean-squared error predictor model in order to accurately predict the future behavior of MPEG video traffic in a relatively short time period based on adaptive learning for each module from previous measurement data, in order to provide faster and more accurate control action to avoid the effects of excessive load situation, Since those modules of PRNN can be performed simultaneously in a pipelined parallelism fashion, this would lead to a significant improvement in the total computational efficiency of PRNN, In order to further improve the convergence performance of the adaptive algorithm for PRNN, a learning-rate annealing schedule is proposed to accelerate the adaptive learning process, Another advantage of the PRNN-based predictor is its generalization from learning that is useful for learning a dynamic environment for MPEG video traffic prediction in ATM networks where observations may be incomplete, delayed, or partially available, The PRNN-based predictor presented in this paper is shown to be promising and practically feasible in obtaining the best adaptive prediction of real-time MPEG video traffic.
Optimal nonlinear adaptive prediction and modeling of MPEG video in ATM networks using pipelined recurrent neural networks
(1997-08-01)
Chang, PR
;
Hu, JT
;
電信工程研究所
;
Institute of Communications Engineering
This paper investigates the application of a pipelined recurrent neural network (PRNN) to the adaptive traffic prediction of MPEG video signal via dynamic ATM networks, The traffic signal of each picture type (I, P, and B) of MPEG video is characterized by a general nonlinear autoregressive moving average (NARMA) process, Moreover, a minimum mean-squared error predictor based on the NARMA model is developed to pro,ide the best prediction for the video traffic signal, However, the explicit functional expression of the best mean-squared error predictor is actually unknown, To tackle this difficulty, a PRNN that consists of a number of simpler small-scale recurrent neural network (RNN) modules with less computational complexity is conducted to introduce the best nonlinear approximation capability into the minimun mean-squared error predictor model in order to accurately predict the future behavior of MPEG video traffic in a relatively short time period based on adaptive learning for each module from previous measurement data, in order to provide faster and more accurate control action to avoid the effects of excessive load situation, Since those modules of PRNN can be performed simultaneously in a pipelined parallelism fashion, this would lead to a significant improvement in the total computational efficiency of PRNN, In order to further improve the convergence performance of the adaptive algorithm for PRNN, a learning-rate annealing schedule is proposed to accelerate the adaptive learning process, Another advantage of the PRNN-based predictor is its generalization from learning that is useful for learning a dynamic environment for MPEG video traffic prediction in ATM networks where observations may be incomplete, delayed, or partially available, The PRNN-based predictor presented in this paper is shown to be promising and practically feasible in obtaining the best adaptive prediction of real-time MPEG video traffic.
Programmable switched-capacitor neural network for MVDR beamforming
(1996-01-01)
Yang, WH
;
Chang, PR
;
交大名義發表
;
電信工程研究所
;
National Chiao Tung University
In this paper, a real-time adaptive antenna array based on a neural network approach is presented, Since an array operating in a nonstationary environment requires a programmable synaptic weight matrix for the neural network, the switched-capacitor (SC) circuits with the capability of programmability and reconfigurability is conducted to implement the neural-based adaptive array. Moreover, the SC techniques can directly implement the neural network with less chip area and provide the ratio of SC-equivalent resistors with accuracy of 0.1 percent. Programming of the switched-capacitor values could be made by allocating each synaptic weight to a set of parallel capacitors with values in a digitally programmable capacitor array (PCA), A relatively wide range of values (5 to 10 binary bits resolution) can be realized for each synaptic weight. A simulation tool called SWITCAP is used to verify the validity and performance of the proposed implementation, Experimental results show that the computation time of solving a linear array of 5 elements is about 0.1 ns for 1 ns time constant and is independent of signal power levels.
Spread spectrum CDMA systems for subband image transmission
(1997-02-01)
Chang, PR
;
交大名義發表
;
電信工程研究所
;
National Chiao Tung University
;
Institute of Communications Engineering
This paper investigates the application of spread spectrum code-division multiple access (SS-CDMA) techniques to subband image transmission over a bandlimited radio channel. For the transmission of images over SS-CDMA AWGN channels, a subband coding scheme that divides the image information into a number of independent data streams using an analysis filter bank, each of which Is multiplied by its unique signature PN code, enables the transmission of these data streams via multiple parallel virtual channels created by their corresponding PN codes. With a sufficiently large number of streams, the total signal is able to fit within the narrow radio channel bandwidth even though the total bandwidth of all the signals may exceed the channel bandwidth. At receiver, each received signal is separately recovered at the decoder by multiplying its PN code and integrating over the code length in order to obtain the desired subband. All the recovered subbands are then reassembled by a synthesis filter bank into a close reproduction to the original image. Additionally, for color subband image transmission, color images are first transferred to luminance (Y) and two chrominance components (I, Q). Each component is then decomposed independently into several subbands for SS-CDMA transmission. Therefore, a number of additional PN codes are required to support the transmission of the chrominance signals over the CDMA channels whereas the luminance signal was treated in the same manner as monochrome pictures. Moreover, SS-CDMA allows more than one image to he transmitted and be accessed simultaneously at the same limited channel bandwidth, If all the product signals for different images are transmitted over the SS-CDMA AWGN channel with perfect power control, the performance is the same as if the data were transmitted in a single stream. However, the quality of the farther received images would he degraded when the near-far problem occurs. In this paper, the image quality of both the monochrome and color subband image transmission via SS-CDMA AWGN channels is evaluated For both perfect and imperfect power control cases.
Spread spectrum multiple-access with DPSK modulation and diversity for image transmission over indoor radio multipath fading channels
(1996-04-01)
Wang, BC
;
Chang, PR
;
交大名義發表
;
電信工程研究所
;
National Chiao Tung University
As demand for networked multimedia applications is increasing rapidly, it is important to provide the ubiquitous accessibility for these services in wireless communication environment, Such access allows users to share novel multimedia applications without any geographical restrictions. In this paper, we investigate the application of the well-known antimultipath spread spectrum code-division multiple access (SS-CDMA) techniques to image transmission related to the development of next-generation multimedia wireless local area networks within a building, SS-CDMA is particularly well suited to a subband coding scheme that divides the image information into multiple parallel data streams using an analysis filter bank, each of which is multiplied by its unique spreading code, All the product signals are then transmitted at the same time in the same radio channel, even though the total bandwidth of all the signals may exceed the channel bandwidth. Each received signal is independently recovered at the decoder by multiplying its spreading code and all the recovered subbands are then reassembled by a synthesis filter bank into a close reproduction to the original image, A forward error correction (FEC) scheme based on convolutional codes with interleaving is proposed to minimize the effect of bursty channel errors on the picture duality degradation, Better image quality can be achieved by using the predetection diversity combining in order to combat the indoor multipath distortion, In this paper, the image quality of subband image transmission via SS-CDMA indoor fading channels with differential phase shift keying (DPSK) modulation is evaluated and examined, Simulation results show that the image peak signal-to-noise (PSNR) ratio is inversely related to a logarithmic function of bit error rate when each subband employs equal protection channel coding.
Spread spectrum multiple-access with DPSK modulation and diversity for image transmission over indoor radio multipath fading channels
(1996-01-01)
Wang, BC
;
Chang, PR
;
電信工程研究所
;
Institute of Communications Engineering