In this study, an integrated scheme is proposed to stream real‐time scalable videos from a base station to multiple secondary users over cognitive radio networks. The objective of the proposed scheme is to maintain continuous video playback with acceptable perceptual quality at the secondary users end. The proposed scheme is a channel allocation algorithm integrated with a rate control and scheduling algorithms. The channel allocation algorithm is introduced to optimally assign the available channels among the secondary users while taking into considerations their buffer occupancies as well as the channel qualities as seen by the secondary users to meet the requirements of the real‐time streamed videos. While the rate control algorithm adapts the source rate to meet the streaming requirements, the scheduling algorithm splits the transmitted video information based on its importance to guarantee the continuity of video playback. The simulation results do not only demonstrate the efficient utilisation of available resources of the cognitive network by the proposed scheme but highlights a desirable need‐based fairness when allocating the available channels between the secondary users. The simulation results also indicate that scheduling the transmitted video information on a window basis outperforms frame‐based streaming.

This paper presents a simplified automatic modulation classification system based on stepwise regression and Hierarchical Polynomial Classifier. The proposed system applies High Order Cumulants of the received signal to a polynomial network in order to calculate their second order polynomial expansion. Then, stepwise regression model is used as a feature selection system; whereas important features are identified and used for the classification problem and the insignificant features are discarded. With this optimization step, the complexity of the classifier is reduced significantly while maintaining the same classification accuracy as the original Hierarchical Polynomial Classifier with all the expanded features.

In this paper, a new automatic modulation classification system using a polynomial classifier is proposed. The feature set used in the proposed system is comprised of second, fourth and sixth higher order cumulants of the received signal. The polynomial classifier expands the feature vector into a higher dimensional space in which the different modulation types are linearly separable. The performance of the proposed system is tested against BPSK, QPSK, 8-PSK, 16-QAM and 64-QAM constellations. Results showed a relatively higher classification rate for all types of modulations compared to previously published results using fourth and sixth order cumulants with other classification schemes. Moreover, the proposed classification scheme has low computational complexity and is more suited for real time applications.

Hierarchical quadrature amplitude modulation (HQAM) enables unequal priority transmission through the use of non-uniformly spaced constellations. In this paper, we propose an adaptive HQAM (A-HQAM) scheme where the ratios between the constellation distances are regularly adjusted based on the channel condition with the objective of maximizing the transmission efficiency. The source bit stream is divided into multiple sub-streams which are simultaneously transmitted, each on a different priority level. When using A-HQAM, the high priority sub-stream maintains an acceptable bit error rate performance over all channel conditions. As the channel condition improves, the required protection for the high priority sub-stream is reduced allowing for increasing the protection level of lower priority sub-streams. Hence, the number of sub-streams with acceptable BER performances is incrementally increased as the channel condition improves. Analysis and simulation results show that the proposed A-HQAM not only enhances the transmission efficiency but also provides reduced peak to average power ratio (PAPR). The proposed scheme offers reduced complexity by using one constellation size, unlike conventional adaptive schemes which require the use of several constellation sizes. Moreover, a practical A-HQAM implementation is presented which enables the receiver to successfully demodulate the received signal without knowing the varying transmission parameters.

In this paper, we implement an adaptive modulation and channel coding scheme for image transmission over Rayleigh fading channels. We propose a new approach where the modulation level and coding rate are selected based on the importance of the compressed bit stream and channel conditions. The proposed scheme attempts to meet a predefined target bit error rate (BER) and yet avoid over protection, hence it improves the bandwidth efficiency which consequently increases the effective transmission rate. Simulation results show that the proposed scheme significantly improved the spectral efficiency while keeping high peak signal-to-noise ratio (PSNR) performance and excellent perceptual quality.

This paper presents a new technique for multipath detection in wideband mobile radio systems. An intelligent search algorithm using Boolean Satisfiability (SAT) techniques is used to search for the multipath delays. The proposed algorithm finds the multipath components with high probability and hence allows the system to utilize the inherent diversity in these components to mitigate channel fading. Simulation results indicate that the system can achieve 90% detection or higher of all paths at low signal-to-noise ratio under frequency-selective Rayleigh fading conditions.

Cognitive radio (CR) is a promising technology for improving the utilization of the scarce radio spectrum by allowing secondary users to regularly sense the spectrum and opportunistically access the under-utilized frequency bands. However, spectrum sensing in CR environment is a challenging task due to varying radio channel conditions and might lead to interference with licensed users. In this paper, we propose a new framework for CR spectrum sensing based on linear and polynomial classifiers. A cooperative CR network is considered in this paper with CR nodes collaborating in making the decision about spectrum availability. Simulation results indicate that both polynomial and linear classifiers provide high detection rate of primary users with a constant false alarm rate at very small signal to noise ratio conditions. For instance, the proposed techniques can achieve above 90% detection probability at Eb/N0= -7dB with observation window of 50 bits and 10% false alarm rate. It is also shown that the performance improves as we increase the sensing time for both schemes.

In mobile radio communication systems using spread spectrum technology, an accurate estimate of the signal propagation delay is needed in order to recover the transmitted data. This process is usually done using a pseudo noise (PN) code acquisition algorithm to search for the correct propagation delay within a window of possible delays. In this paper, we propose a new approach to solving the PN code acquisition problem using advanced Boolean satisfiability (SAT) techniques. SAT solvers use intelligent search algorithms that can traverse the search space and efficiently prune parts that contain no solutions. These solvers have recently been used to solve many challenging problems in Engineering and Computer Science. In this paper, we show how to formulate the PN code acquisition problem as a SAT instance and evaluate the use of advanced SAT techniques in solving the problem. Our approach is verified by simulation and presented results indicate that the proposed system achieves a detection probability for the correct delay of almost 100% for all practical cases.

In this paper we propose a fair-scheduling algorithm for the transmission of video frames over wireless links. The scheme is based on the occupancy of the video decoder buffer. When the occupancy of the decoder buffer of a given video client becomes increasingly small and approaches a starvation threshold, it gets treated with a higher priority and gets serviced more frequently than other clients who may not be approaching the starvation point. When compared to other commonly-used scheduling algorithms, ours shows a better performance in terms of the end-to-end delay experienced by the video frames.

Multipath detection is very important for the proper operation of wideband communication systems. Conventional detectors using constant threshold result in suboptimal performance since they either fail to detect a multipath component or provide a wrong path to the receiver. In this paper, two adaptive constant false alarm rate (CFAR) multipath detectors are proposed: cell-averaging CA-CFAR and order-statistics OS-CFAR. An experimental indoor wideband communication system operating at the 5 GHz range has been implemented to collect real data for use by the proposed CFAR detectors. Details of the implemented system and experimental results are presented in this paper. It is observed that the OS-CFAR detector outperforms the CA-CFAR in terms of detection capability.

Efficient image transmission over wireless networks is challenged with the limited bandwidth and time-varying nature of the underlying channels. In this paper, we propose a joint variable modulation and power allocation scheme for transmission of compressed images. In our scheme, the modulation level and allocated power are jointly optimized to minimize the mean square error (MSE) of the reconstructed image. We investigate fixed level 16-QAM modulations as well as variable M-QAM with adaptive power allocation. We also introduce an off-line iterative algorithm that finds the optimum combination of modulation and power allocation. Simulation results show that significant improvements in the MSE (in the order of 2~4 dB) and bandwidth efficiency have been achieved when compared to fixed power and modulation level schemes.

In conventional CDMA receivers, the detection of multipath components and RAKE finger management is normally based on the received signal energy per path. These schemes essentially overlook the interference component contaminating the total received power. Consequently, they exhibit poor multipath detection capability especially at low signal-to-interference-plus-noise ratio (SINR). In this paper, we present a new scheme for multipath detection that takes into consideration the interference level in each resolved path individually. Specifically, the proposed scheme is devised to estimate and cancel the interference per path before detection. To account for the hardware limitations of the receiver, we propose a low complexity version of the above scheme which can be easily incorporated into the receiver structure. Our results show that the proposed scheme provides significant improvements in the detection probability of multipath components over the energy-based schemes.

In this paper, performance evaluation for the access channel in third generation CDMA 2000 mobile radio systems is presented. Probability of detection, probability of false alarm, and mean acquisition time are presented in a typical frequency selective Rayleigh fading mobile radio channel. The results provide a general guidelines foe selection of the acquisition circuit parameters at the base station receiver along with access channel parameters. Specifically, it is shown that to minimize the access time for the CDMA system, the access probe preamble length should be selected depending on the number of parallel correlators available at base station receiver.

One of the most challenging problems faced by our modern society is the increasing phenomenon of car thefts. Reports from police departments around the world indicate that car theft in some of the countries reaches more than 300,000 cars a year and the percentage of the cars recovered is not very high. Increasing the possibility of finding a stolen car is very important to both police and car owners. In this paper, a vehicle identification system using an embedded wireless communication system is proposed to address the car theft problem. The proposed scheme is based on forming an ad-hoc network between police cars and the cars within their vicinity in a decentralized manner. The police officer will be automatically notified in case of the presence of a stolen car within visual range. Stolen car’s details will then be displayed to allow police officers to locate the stolen car based on a visual search easily. Prototype implementation along with several applications for the system is presented in this paper.

In this paper, joint optimization of power allocation and channel coding is proposed for image transmission over wireless channels. The proposed scheme works iteratively to find the optimum combination of coding and power transmitted for individual bits to minimize the mean square error for better image quality. It is shown that bits of significant importance (most significant bits) should always be coded and allocated most of the power transmitted. However, other bits of less significance may be sent without coding and with less power. This is done while maintaining the average energy per bit at the same level. The combined approach shows a gain of about 3 dB compared to the case of coding alone. It also has better performance compared to the case of power allocation alone while reducing the peak-to-average ratio.

In current and next 3G and beyond mobile wireless systems, sharing the radio access network has become an important issue for 3G mobile operators. Sharing network infrastructure amongst operators offers an alternative solution to reduce the investment in the coverage phase of WCDMA, allows increased coverage, reduces time to market, and allows earlier user acceptance for WCDMA and its related services. In this paper a novel radio resource management strategy known as adaptive partitioning with borrowing (APB) is proposed to cope with the implied new architectural changes. This strategy is devoted to achieve an efficient usage of the available pool of radio resources while satisfying the required quality of service (QoS) in heterogeneous traffic 3G wireless networks. Grade of service (GoS) and resources utilization are considered in this study to evaluate the network performance. Simulation results indicate that the proposed APB resource allocation provides higher resource utilization under all load conditions leading in turn to increased revenue. Moreover it provides the best balance between the system utilization and the required QoS

In this paper, joint optimization of bit energy and coding is considered for improving the quality of compressed image transmission over wireless channels. The proposed scheme works iteratively to find the best combination of energy distribution among the transmitted bits as well as if coding should be used or not. The minimum mean-square error criterion is used in such optimization rather than the probability of bit error. Simulation results show that a significant gain in performance is achieved while reducing the peak-to-average power ratio and required bandwidth compared to the case of power optimization alone and coding alone, respectively

Abstract In this paper, we present a semi‐analytical approach for analyzing the serial concatenation (SCC) of a high rate convolutional code and a precoded intersymbol interference (ISI) channel. The significance of the proposed approach is that it can be used to identify, for a given outer high rate code and fixed ISI channel, the precoder that results in the lowest error rate floor. In estimating the bit error performance in the floor region, we use analytical techniques developed for trellis codes to compute the overall system minimum squared Euclidean distance, and then use a semi‐analytical approach to find the corresponding multiplicity. We also demonstrate via simulations that the proposed technique may be extended to fading ISI channels with favorable results. We give examples that support our analysis. Copyright © 2006 John Wiley & Sons, Ltd.

This paper addresses the problem of multipath detection in CDMA systems. In conventional CDMA receivers, the detection of multipath components and RAKE finger management is normally based on the received signal energy per path. These energy-based schemes essentially overlook the interference component contaminating the total received power. Consequently, they exhibit poor detection capability especially at low signal-to-interference-plus-noise ratio (SINR). In this paper, we present a new scheme for multipath detection and RAKE finger assignment that takes into consideration the interference level in each resolved path individually. The proposed scheme utilizes information provided by the pseudo random code acquisition circuit to estimate the interference power per path. To account for the hardware limitations of the receiver, a low complexity version of the proposed scheme is designed and incorporated into the receiver structure. Analytical and simulation results show that the proposed scheme provides significant improvements in the detection probability of multipath components over the energy-based schemes. For instance, our results show that the proposed scheme can achieve the same detection probability of all multipath components as that of the energy-based scheme with a saving of at least 2 dB in E/sub b//N/sub 0/. In some cases, it is shown that the improvement can be as high as 3 dB.

In this paper, a new technique for power allocation to transmitted bits according to their significance on the message quality is presented. The proposed scheme is based on optimizing the power allocation to minimize the mean-square error rather than the bit error probability of image and video signals transmitted over fading wireless channels. An analytical framework for the power allocation technique is developed. Two techniques of power allocation; fixed and adaptive, are investigated in the paper. Simulation results show that the proposed scheme provides a gain of about 3 dB in Eb/N0in AWGN channels and about 4 dB in flat fading channels over conventional equal-power allocation system. This gain is achieved without any increase in bandwidth, as opposed to that achieved with channel coding. The gains achieved with this algorithm come at the expense of slight increase in the peak-to-average power ratio of the transmitted signal

In CDMA systems, assignment of the RAKE fingers to the correct multipath components is crucial for the receiver to combat fading and to take advantage of the multipath diversity. This is particularly important since the number of fingers available is normally limited in order to maintain low receiver complexity. In this paper, we introduce a new RAKE receiver finger assignment algorithm (FAA) based on estimates of the signal-to-interference ratio (SIR) per path, as opposed to signal strength in the conventional schemes. We also introduce a simple algorithm to produce these SIR estimates. A performance comparison between the proposed scheme and the already existing schemes is presented. We show that the proposed scheme provides a significant performance improvement relative to that of the conventional schemes. For instance, the proposed scheme provides gains of up to 3.0 dB at bit error rate 10/sup -4/, relative to the conventional scheme.

The Cramer-Rao lower bound (CRLB) and minimum mean-square error (MMSE) lower bound on the variance of phase estimation in CDMA receivers in AWGN and slow and fast Rayleigh fading conditions are presented. The bounds are useful as benchmark information for implementation of channel estimator algorithms needed for coherent combining in CDMA receivers. Analytical results indicate that increasing the signal-to-noise ratio or/and averaging period for phase estimation improves the performance. Hence, the phase error can be reduced to avoid significant degradation in bit error rate of the system. However, for fast fading there is a high error floor on the phase estimation (about 50 degrees of rms phase error) regardless of how high the signal-to-noise ratio is made. This presents a challenge of achieving acceptable bit error rate performance for users who are moving at very fast speeds.

In this letter, we propose a new tracking scheme that is robust against multipath fading for pseudonoise (PN) code tracking in direct-sequence-spread spectrum systems. The proposed scheme employs an adaptive filter whose taps are adapted using a block least-mean square algorithm and it results in minimizing the effect of multipath interference on the tracking performance. We show that the mean-squared tracking error performance of the proposed scheme is not affected by the presence of closely spaced paths (e.g., one to three chips), unlike that of conventional delay locked loops. We also show that the tap-weight distribution of the filter provides accurate estimates of the multipath delays. For example, at E/sub b//N/sub 0/=5 dB, 98% of the time the path estimates lie within one sample (1/5 of a chip) from the actual delays. Furthermore, simulation results suggest that multipath delays over a wide range of terminal speeds can be tracked successfully. The proposed scheme is well suited for wideband code-division multiple-access systems where a large number of closely-spaced multipath components need to be tracked and used in RAKE combining.

In this paper, we discuss an approach for analyzing the serial concatenation of a high rate convolutional code and a preceded intersymbol interference (ISl) channel. The proposed approach is simple and can be used to identify the preceder that results in the lowest error rate floor analytically without resorting to simulations. Also, the proposed approach can be used to enhance the interleaver design to achieve further performance improvement. We extend the proposed technique to fading ISI channels using statistical models of these channels. Simulation results suggest that the optimal preceder, when selected based on the statistical model of the channel, is optimal or somewhat optimal for the time varying channel. We finally remark that the proposed analytical approach is not limited to high rate convolutional codes, but it also applies to arbitrary high rate linear outer codes.

Multipath propagation is a major source of degradation in the performance of conventional PN code tracking loops. The mean-square tracking error of a conventional delay-locked loop (DLL) exhibits an irreducible floor due to the presence of closely spaced multipath components. We present a new PN code tracking algorithm that does not suffer from the presence of multipath components. This algorithm utilizes a finite impulse response (FIR) adaptive filter to mitigate the effect of multipath on delay estimation. It is shown that the tap-weight vector of the adaptive filter can be used to provide accurate estimation of the multipath delays. It is also shown that the mean-square tracking error of the proposed scheme is not affected by paths that are very close (within 1 to 2 chips apart). The effect of terminal mobility is also investigated by simulating the performance under frequency selective fading channel conditions with different Doppler frequencies. The proposed scheme is well suited for wideband CDMA systems where a large number of closely spaced multipath components need to be tracked and used in RAKE combining.

The acquisition-based capacity of a DS/CDMA system is defined as the maximum number of simultaneous users that can achieve PN code acquisition with certain reliability. This paper introduces a novel PN code acquisition scheme utilizing an LMS adaptive filter structure to estimate the delay offset of the desired user in the presence of multiple access interference. It is shown that the adaptive filter significantly outperforms conventional matched filter acquisition schemes. It improves the acquisition-based capacity because it takes into consideration the presence of the multi-user interference while finding the optimum tap-weight setting as opposed to the matched filter which completely neglects the interference. For a PN code length of 127 chips, the matched filter can support only 6 users while the adaptive filter supports up to 40 users at a probability of acquisition failure of 1%. This is essentially the same as the capacity achieved at 10/sup -3/ bit-error-rate.

This paper investigates tracking of direct-sequence spread-spectrum (DS/SS) signals based on an adaptive filtering technique. It is shown that a previously proposed hardware for code acquisition is also capable of code-tracking, and, hence, by performing both acquisition and tracking with the same circuitry, a significant simplification in the overall DS/SS receiver structure is gained. Analytical results show that the proposed scheme has a good tracking performance, as measured by the hold-in time and the false alarm penalty time, and is less sensitive to variations in the signal-to-noise ratio (SNR) compared to conventional delay-locked loops (DLLs). Moreover, simulation results show that the proposed adaptive filter tracking scheme has a smaller residual tracking error than that produced by a conventional maximum-likelihood estimator (MLE).

This paper investigates the tracking of DS/SS signals based on an adaptive filtering technique. It is shown that a previously proposed system for code acquisition is also capable of code tracking and, by performing both acquisition and tracking with the same circuitry, significant simplification in the overall DS/SS receiver is gained. Analytical results show that the proposed scheme has a good tracking performance, as measured by the hold-in time and the false alarm penalty time, and less sensitivity to variations in the received SNR compared to conventional delay lock loops (DLLs).