Combined Fuzzy-based Rate Management and Selective Power Control for Multimedia CDMA Cellular Systems

Power control mechanisms are essential for CDMA wireless communication systems to enhance user capacity. In this paper, we propose a novel power control scheme which combines transmission rate management with power adjustments for multimedia CDMA cellular systems. In the proposed scheme, a fuzzy logic controller (FLC) is first used to dynamically infer a suitable transmission rate for each service. Then a selective power control (SPC) scheme is used to adjust the transmission power for each service in order to maintain an acceptable signal-to-interference ratio (SIR). Numerical results show that the proposed scheme outperforms the original SPC and the Lagrangian relaxation technique and power control (LRPC) methods in outage probability, average transmission rate, probability of unsuccessful transmission, and probability of changes in transmission rates.

Directional Diversity of Smart Antenna in LAS CDMA Systems

The performance of code division multiple access (CDMA) systems can be affected by small scale fading such as Rayleigh fading channel. In this paper, the application of smart antenna and Large Area Synchronous CDMA (LAS CDMA) systems, which introduce directional diversity channel, is presented. A novel interference cancellation scheme through dynamic space code (DSC) algorithm is briefly described. The directional diversity can be realized from the directional gain of smart antenna system. It can be found that when the number of elements in smart antenna is increase the directional gain of antenna system is much higher than single antenna. The system performance analysis in term of error probability is compared between traditional and LAS CDMA systems in both single and smart antenna systems. From the performance analysis it is found that CDMA system is more susceptible to multipath fading channel than interferences from existing users.

Minimum Cross Correlation Spreading Codes

Multiple access interference (MAI) appears in Code Division Multiple Access (CDMA) systems when the communication channel is a multi-path channel and the spreading codes are not orthogonal. Orthogonality between spreading codes cannot be maintained at the CDMA receiver because the codes may be asynchronous due to channel delay and multi-path spread. The receiver cannot perfectly separate the different signals of the multiple access users, and the resultant MAI limits the capacity of CDMA systems. MAI is a function of the cross correlation property between used spreading codes. In this paper we focus on the cross correlation of the spreading codes, we propose a method to find spreading codes with minimum magnitude of cross correlation. Employing these codes will reduce the resultant MAI in the CDMA system; hence it will increase the system capacity. A great enhancement is shown by comparing found minimum cross correlation spreading codes (MCCSC) with Hadamard and Gold codes.

A Rigorous Proof of MIMO Channel Capacity’s Increase with Antenna Number

It is well known that adding more antennas at the transmitter or at the receiver offers larger channel capacity in the multiple-input multiple-output communication systems. In this letter, a simple proof is presented for the fact that the channel capacity increases with an increase in the number of receive antennas. The proof is based on the famous capacity formula of Foschini and Gans and uses matrix theory.

OVSF Code Sharing and Reducing the Code Wastage Capacity in WCDMA

The non quantized nature of user rate wastes the code capacity in Orthogonal Variable Spreading Factor Codes (OVSF) based Code Division Multiple Access (CDMA) systems. The code sharing scheme in multi code CDMA is proposed to minimize the code rate wastage. The scheme combines the unused (wastage) capacity of already occupied codes to reduce the code blocking problem. Simulation results are presented to show the superiority of the proposed code assignment scheme as compared to existing schemes.

Adaptive Multiuser Channel Estimation using Reduced Kalman/LMS Algorithm

This paper presents an adaptive multiuser channel estimator using the reduced-Kalman least-mean-square (RK-LMS) algorithm. The frequency-selective fading channel is modeled as a tapped-delay-line filter with smoothly time-varying Rayleigh distributed tap coefficients. The multiuser channel estimator based on minimum-mean-square-error (MMSE) criterion is used to predict the filter coefficients. We also present its convergence characteristics and tracking performance using the RK-LMS algorithm. Unlike the previously available Kalman filtering algorithm based approach (Chen, Chen IEEE Trans Signal Process 49(7): 1523–1532, 2001) the incorporation of RK-LMS algorithm reduces the computational complexity of multiuser channel estimator used in the code division multiple access wireless systems. The computer simulation results are presented to demonstrate the substantial improvement in its tracking performance under the smoothly time-varying environment.

Capacity-based compressed mode control algorithm for inter-system measurements in UMTS system

The Inter-system handover between UMTS and GSM is one of the key features in the third generation UMTS cellular system. The compressed mode, with variable transmission gaps and power levels, is standardized to support the inter-frequency/system handover. In this article, a capacity-based compressed mode algorithm which considers potential impacts on the capacity and the priority of operating the compressed mode measurement is proposed to reduce the use of system resources while maintaining the UMTS-to-GSM border-cell handover quality. The performance of the proposed algorithm will be studied based on UMTS simulation platform.

Throughput Analysis of Adaptive Modulated STS-based CDMA System Over Multipath Fading Channel

The throughput enhancement of Space-Time Spreading (STS)-based Code Division Multiple Access (CDMA) system is investigated in this paper. Adaptive Modulation is utilized to improve the data throughput of the system in multipath Rayleigh fading channel. In this contribution, an analytical approach is proposed to compute a new expression for the Bit Error Rate (BER) performance and the output Signal-to-Interference-and-Noise Ratio (SINR) of the RAKE receiver-assisted STS-based CDMA system for QAM data, considering multipath and multiuser interferences. The other contribution of the paper is deriving a new closed form expression for computing the throughput enhancement and the BER performance of the adaptive modulated STS-based CDMA system over multipath fading channel. Simulation and analytical results demonstrate that using adaptive modulation method in this system improves the average throughput by keeping the BER performance at a target level. The novel expressions presented in this paper bring out the facility of evaluation of the proposed system with no need to more calculations and simulations.

Error Probability Distribution and Density Functions for Rayleigh and Rician Fading Channels with Diversity

This paper analyzes the distribution and density functions of the probability of error for Rayleigh and Rician fading channels with diversity. An expression for the signal-to-noise ratio is derived for an asynchronous CDMA (A-CDMA) system with diversity. The error probability distribution and density functions are derived and plotted for different mean energy-to-noise ratios.

An OFDMA-Based Subcarrier and Power Allocation Scheme in Wireless Cooperative Cellular Systems

An OFDMA-based subcarrier and power allocation scheme is proposed in this paper in the wireless cooperative cellular system. It is assumed that users in this system have the ability to relay information to each other to improve the overall system performance. The formulation of this scheme is to maximize the uplink system throughput subject to the half-duplex, distributed power and queue state constraints of each user. A two-slot resource allocation structure is constructed to deal with the half-duplex constraint. A low-complexity suboptimal algorithm is developed to solve the problem efficiently. This algorithm first greedily allocates subcarriers and power to users and then decides the relay selection. Numerical examples demonstrate the good throughput performance of our propose scheme and the effectiveness of the low-complexity algorithm.

The Adaptive PSAM Design in Cross-Layer

The purpose is to design the pilot symbols efficiently and adaptively in communication systems to guarantee the minimum channel estimation error and the required quality of service (QoS). The various adaptive schemes about pilot symbols assisted modulation (PSAM) are obtained in terms of the pilot-insertion frequency and the power arrangement. The pilot-insertion frequency is redefined according to the sampling theory and the characteristics of fading channels, such as the level crossing rate (LCR) and the average fading duration (AFD). The power arrangement is optimized by maximizing the average spectral efficiency (ASE) in cross-layer design system. Besides, the ASE function in such a system is modified taking the imperfect channel state information caused by channel estimation into considered. The closed-form expression of modified ASE is present in this paper. From both the theoretical analysis and simulation points of view, a suitable scheme about PSAM design is obtained for cross-layer design.

Joint Carrier-Frequency Offset and Channel Estimation for MIMO-OFDM Transmission

In this paper, we consider a multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) system operating over frequency-selective fading channels. We propose a novel scheme for joint carrier-frequency offset (CFO) and channel estimation based on the expectation–maximization (EM) algorithm. Furthermore, the Cramer-Rao bounds (CRBs) for both CFO and channel estimators are exploited to evaluate the performance of the proposed scheme. Computer simulations show that the proposed algorithm achieves almost ideal performance compared with the CRBs for both channel and frequency offset estimations.

Constrained Power Control to Enhance the Capacity of Slotted DS-CDMA Cellular Systems

We propose and study the constrained power control scheme for direct sequence code division multiple access (DS-CDMA) systems supporting voice and data services. In the proposed scheme, the voice users are subject to the conventional power control, while the data users are subject to distance dependent transmit power constraint. Several power control profiles for data users are suggested to reduce interference within its own and neighboring cells. For given delay and outage probability requirements, we present an analytical framework to analyze the number of users that can be supported by the proposed scheme. The results are compared to the conventional power control scheme, where no such constraint is imposed. We derive new closed form expression for the interference correction factor for the constrained power control scheme. In addition, we show that the total interference power can be approximated by the log-normal distribution, and we evaluate the mean and variance of the log-normal distribution analytically. We also derive the distribution of the signal-to-noise ratios for voice and data users, which is useful in evaluating the user capacity for slotted DS-CDMA cellular systems with both delay and power constraints.

Hardware Implementation of Skeletonization Algorithm for Parallel Asynchronous Image Processing

This paper presents an FPGA realisation of an application-specific cellular processor array designed for asynchronous skeletonization of binary images. The skeletonization algorithm is based on iterative thinning utilizing a ‘grassfire’ transformation approach. The purpose of this work was to test the performance of a fully parallel asynchronous processor array and to evaluate the inhomogeneity of wave propagation velocity. A proof-of-concept design has been implemented and evaluated, the results are presented and discussed.

Design of 100 μW Wireless Sensor Nodes for Biomedical Monitoring

Wireless sensor nodes span a wide range of applications. This paper focuses on the biomedical area, more specifically on healthcare monitoring applications. Power dissipation is the dominant design constraint in this domain. This paper shows the different steps to develop a digital signal processing architecture for a single channel electrocardiogram application, which is used as an application example. The target power consumption is 100 μW as that is the power energy scavengers can deliver. We follow a bottleneck-driven approach: first the algorithm is tuned to the target processor, then coarse grained clock-gating is applied, next the static as well as the dynamic dissipation of the digital processor is reduced by tuning the core to the target domain. The impact of each step is quantified. A solution of 11 μW is possible for both radio and DSP running the electrocardiogram algorithm.

Improved Fractional Fourier Transform Based Receiver for Spatial Multiplexed MIMO Antenna Systems

In this work the performance of a Fractional Fourier transform (FrFT) based Minimum Mean Squared Error receiver for MIMO systems with space time processing over Rayleigh faded channels is presented. The proposed receiver called Optimum FrFT based MIMO receiver (OFMR) shows improved performance outperforming the simple MMSE receiver in Rayleigh faded channel.

A GMSK Receiver with Beamformer Weight Refinement

We present an adaptive antenna algorithm for Gaussian minimum-shift keying (GMSK)-based cellular systems with beamformer weights that are iteratively computed using re-encoded data to suppress cochannel interference (CCI). Filtered training sequences are proposed in order to compensate for the effects of timing offsets that occur for asynchronous cochannel signals. Also, we extend the receiver to include a linear equalizer that mitigates intersymbol interference (ISI). Various multistage receivers incorporating the proposed beamformer and equalizer algorithms are presented. Their performance is evaluated using simulated and real time-division multiple-access (TDMA) data, demonstrating that the proposed beamforming algorithms suppress CCI and significantly improve the performance compared to a conventional GMSK receiver.

Robust Channel Estimation and Multiuser Detection for MC–CDMA Systems Under Narrowband Interference

In this paper, we present a robust adaptive channel estimator and a robust multiuser detector for wireless multicarrier code-division multiple access (MC–CDMA) systems under narrowband interference (NBI). The conventional least-squares (LS) channel estimator performs poorly when narrowband interfering signals contaminate the multicarrier systems. A new weighted recursive least M-estimate (WRLM) channel estimator is hence developed to estimate multipath fading channels in the presence of NBI. The new robust channel estimator resorts to M-estimate and weighted least-squares (WLS) techniques. Simulations show that the WRLM channel estimator offers substantial performance gain over conventional recursive least-squares (RLS), recursive least M-estimate (RLM) and weighted RLS (WRLS) channel estimators under NBI. With the estimated channel coefficients, a robust multiuser detector is proposed to jointly suppress multiple access interference (MAI) and NBI. The performance of the linear decorrelator will degrade substantially in the presence of NBI. A weighted least M-estimate (WLM) algorithm is therefore developed to combat the NBI. The WLM multiuser detector is also based on the weighted M-estimate concept. Numerical results show that the proposed WLM multiuser detector significantly outperforms over the conventional linear decorrelator, the robust decorrelator with M-estimate and the WLS detector under NBI.

Methods for Compression of Feedback in Adaptive Multi-carrier 4G Schemes

In this paper, several algorithms for compressing the feedback of channel quality information are presented and analyzed. These algorithms are developed for a proposed adaptive modulation scheme for future multi-carrier 4G mobile systems. These strategies compress the feedback data and, used together with opportunistic scheduling, drastically reduce the feedback data rate. Thus the adaptive modulation schemes become more suitable and efficient to be implemented in future mobile systems, increasing data throughput and overall system performance.

Dynamic Sensor Self-Organization for Distributive Moving Target Tracking

To support distributive tracking of moving targets in a wireless sensor network, sensors that receive signal from the same target must collaborate to facilitate collaborative, distributed target tracking. We present an efficient dynamic sensor self-organizing algorithm that clusters sensors into groups without requiring a centralized control. Extensive simulations are conducted to verify the performance improvement as well as the communication reduction for the proposed methods.