EXACT PERFORMANCE MEASURES FOR DIRECT-SEQUENCE CODE SYNCHRONIZATION IN FADING CHANNELS

We investigate the interuser interference in cellular code—division multiple access (CDMA) and timedivision multiple access (TDMA) systems and compare the two multiple access techniques at different levels of user density per cell. The study includes the interference both on the downstream channel (from base station to users) and on the upstream channel (from users to base station). The purpose is to compare the two multiple access techniques when the total bandwidth occupancy and the maximum number of users per cell are the same. The results indicate that on a nondispersive radio channel with a path loss that is proportional to the fourth power of the distance, the interuser interference is approximately 10 dB higher in CDMA. The implication of this result, which holds for both the downstream and the upstream channels, is that for the same total bandwidth and number of users per cell, TDMA gives substantially superior bit error rate (BER) performance. This is confirmed by our numerical results evaluated for both additive white Gaussian noise (AWGN) channels and memoryless flat Rayleigh fading channels. Alternatively, CDMA needs approximately 10 times more bandwidth to achieve the same signal—to—interference (S/I) ratio, a result which may seem surprising, because the fact that CDMA employs a frequency reuse factor of 1 is often given as an evidence that this technique can support a higher number of users than TDMA in a given geographic area and frequency bandwidth.

We investigate the multiuser interference on the downlink channel (from base station to users) in cellular code-division multiple access (CDMA) and time-division multiple access (TDMA) systems. The results indicate that for the same total bandwidth occupancy and maximum number of users per cell, multiuser interference is approximately 10 dB higher in CDMA in fully-loaded cells. The implication of these results is that for the same total bandwidth and number of users per cell, TDMA gives significantly superior bit error rate (BER) performance, as confirmed by our numerical results on additive white Gaussian noise (AWGN) channels as well as on flat Rayleigh fading channels. Alternatively, CDMA needs approximately 10 times more bandwidth than TDMA to achieve the same signal-to-interference ratio (SIR) and bit error rate (BER) performance in fully loaded cells.

Statistical Evaluation of Adaptive Threshold Alignment for a Multi-Carrier CDMA Code Synchronization

An accurate approximation is obtained for the average probability of error in an asynchronous binary direct-sequence spreadspectrum multiple-access communications system operating over nonselective and frequency-selective Rician fading channels. The approximation is based on the integration of the characteristic function of the multiple-access interference which now consists of specular and scatter components. For nonselective fading, the amount of computation required to evaluate this approximation grows linearly with the product KN , where K is the number of simultaneous transmitters and N is the number of chips per bit. For frequency-selective fading, the computational effort grows linearly with the product KN2. The resulting probability of error is also compared with an approximation based on the signal-to-noise ratio. Numerical results are presented for specific chip waveforms and signature sequences.

In this paper, we analyze the Bit Error Rate (BER) performance of Golden coded Multiple-Input Multiple-Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) system over Rician multipath fading channel. We also compare the performance of the MIMO-OFDM system using Golden code in Rayleigh and Rician multipath fading channels. We discuss the effects of the presence of line-of-sight (LoS) component in the multipath fading environment which renders the improvement in the overall performance of the Golden coded MIMO-OFDM. This paper discusses the performance of Golden codes in a frequency selective Rician fading channel. To deal with the frequency selective fading channel, we use the OFDM (Orthogonal Frequency Division Multiplexing) modulation. The BER performance of the Golden coded MIMO-OFDM system under several propagation conditions has been evaluated. Keywords—MIMO, OFDM, Golden STBC, Rayleigh fading, Rician fading.

This paper presents the results of a capacity evaluation for a cellular code-division multiple access (CDMA) system over a wideband fading channel. The study compares the performance of a system based on a conventional matched filter with that based on an adaptive receiver. Trellis codes and various rate convolutional codes are investigated in an attempt to improve the system performance. The performance is measured in terms of the maximum number of simultaneous users per cell for a given bit error rate (BER). The channel model is developed from measured propagation data at 2.6 GHz in heavily built-up urban areas and includes the effect of both intra-cell and inter-cell interferers.

This paper presents a novel analytical derivation of the false alarm probability (FAP) and detection probability (DP) for non-line-of-sight (NLOS) detection based on LTE signals. Position estimation in indoor or urban area with cellular wireless communication systems is getting more and more important. However, especially in these environments NLOS propagation causes positioning errors in the order of hundreds of meters. Thus, detection and mitigation of NLOS signals is a critical task. In this paper, we derive the FAP and DP on power-scaled detectors based on LTE multipath signals. The derivation considers frequency-selective fading channels taking sub-sample multipath interference, channel dynamics and initial frequency offsets into account. The results show a simple way to calculate the DP versus FAP. Simulation results verify the analytical probabilities for the WINNER II C2 channel model. Additionally, the simulations show the improved FAP of an antenna array at the receiver.

This paper investigates a reconfigurable intelligent surface (RIS)-aided wideband massive multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) system with low-resolution analog-to-digital converters (ADCs). Frequency-selective Rician fading channels are considered, and the OFDM data transmission process is presented in time domain. This paper derives the closed-form approximate expression of the uplink achievable rate, based on which the asymptotic system performance is analyzed when the number of the antennas at the base station and the number of reflecting elements at the RIS grow to infinity. Besides, the power scaling laws of the considered system are revealed to provide energy-saving insights. Furthermore, this paper proposes a gradient ascent-based algorithm to design the phase shifts of the RIS for maximizing the minimum user rate. Finally, numerical results are presented to verify the correctness of analytical conclusions and draw insights.

In this paper, a pilot-assisted minimum mean square error (MMSE) multiuser channel estimation algorithm is proposed for quasi-synchronous code-division multiple-access (CDMA) systems that undergo frequency-selective channel fading. The frequency-selective multiuser fading channel is represented as a symbol-wise time-varying chip-spaced tapped delay line filter with correlated filter taps. The multiuser channel tap coefficients at pilot symbol positions are estimated under the MMSE criterion with the help of the channel intertap correlation matrix, which is determined by the combined effects of the physical fading channel, transmit filter, and receive filter. In the development of the estimation algorithm, the channel intertap correlation matrix is deemed as an essential factor, and a novel iterative method is proposed for the joint estimation of the channel intertap correlation and filter tap timing based on the received pilot samples. Simulations show that the information of the channel intertap correlation is critical to the performance of the channel estimation, and the channel taps at different delays cannot be assumed uncorrelated for CDMA systems experiencing frequency-selective fading.

This study proposed a method to evaluate proper experimental conditions of eddy current tests under a low signal-to-noise ratio. This method was applied to quantify the detection reliability of the eddy current test to detect corrosion pits on the surface of austenitic stainless-steel weld cladding from the perspectives of probability of detection and probability of false alarm. The fluctuations of flaw signal and noise were described using truncated bivariate normal distributions of a two-dimensional vector composed of the real and imaginary components of a signal. The probabilities of detection and false alarms were formalized as cumulative distributions of the estimated distributions of the maximum flaw signal and the noise exceeding a decision threshold. The receiver operating characteristic curves were created by coupling the probabilities of detection and false alarms at various thresholds. The area under the curve was used to quantify the detection reliability, simultaneously considering the probabilities of detection and false alarms. The results obtained in this study support the applicability of this method in quantitatively evaluating the detection reliability of a non-destructive inspection under a low signal-to-noise ratio.

In this paper, we present an adaptive PN code acquisition scheme using automatic censoring to suppress the multipath replicas in direct-sequence code division multiple access (DS-CDMA) communications. We introduce the problem under consideration and describe the proposed acquisition scheme which employs a serial search strategy and an automatic censored cell averaging CFAR detector based on ordered data variability (ACCA-ODV). The performances are analyzed in frequency-selective Rayleigh fading channels. Expressions for the probability of false alarm (PFA) and the mean acquisition time are derived. The performances of the proposed processor are evaluated and compared with those of the conventional adaptive acquisition scheme based on the fixed censoring point detector.

This paper compares parallel acquisition with hybrid acquisition in terms of mean acquisition time in code acquisition system of forward link and reverse link of direct sequence code division multiple access (DS-CDMA) system. The mean acquisition time of the hybrid and parallel acquisitions is derived from the distribution of the multiple correct code-phase offsets. Especially, the mean acquisition time of the hybrid acquisition scheme is derived by considering both case 1 (the correct code-phase offsets are included in one subset) and case 2 (the correct code-phase offsets exist at the boundary of two subsets), which are caused by the distribution of the correct code-phase offsets in the subset. Results are provided for the performance comparison between hybrid acquisition and parallel acquisition under the same hardware complexity in the forward and reverse links. In our performance evaluation of code acquisition in DS-CDMA system, the hybrid acquisition shows a better performance than the parallel acquisition in terms of mean acquisition time of the both links in the frequency-selective Rayleigh fading channel.

An approximate analytical formulation of the resource allocation problem for handling video services with scene changes in a cellular multirate direct sequence code division multiple access (DS-CDMA) system is presented. The video traffic accounts for slow and fast motions. The novelty in this paper is that all grade of service (GoS) or quality of service (QoS) requirements at the connection level, packet level and link layer are satisfied simultaneously, instead of being satisfied at the connection level or at the link layer only. The analytical formulation shows how the GoS/QoSs in the different layers are intertwined across the layers. A complete sharing (CS) scheme with guard capacity is used for the resource sharing policy at the connection level based on the mean rates of the connections. The CS model is solved using a K-dimensional Markov chain. Numerical results illustrate that significant gain in system utilization is achieved through the joint coupling of connection/packet levels and link layer.

A parallel combinatory (PC)-hybrid pulse interval modulation-optical code division multiple access (hPIM-OCDMA) system is proposed. In the PC-hPIM-OCDMA system, a user chooses e among K code sequences assigned to the user and sends e2b-ary PIM symbols for a given frame, where b is the number of bits per PIM symbol. The PC-hPIM-OCDMA system can offer higher bit rate than hPIM-OCDMA systems, and then it can reduce the effect of MAI, without reducing the bit rate. The bit error rate (BER) of PC-hPIM-OCDMA is derived, by considering that the dominant interference is MAI, which is caused by cross-correlation of strict optical orthogonal codes (SOOCs). Numerical results show that the PC-hPIM-OCDMA system can offer lower BER and accommodate more users than hPIM-OCDMA systems.

A framework for navigation using cellular code division multiple access (CDMA) signals is studied in this paper. Theoretical lower bounds on the navigation performance using pseudorange measurements drawn from the cellular CDMA base transceiver stations (BTSs) are derived. Moreover, the navigation performance for a mapper/navigator framework is studied in the presence of timing discrepancies between the mapper and navigator. In this framework, a mapping receiver (mapper) estimates the stochastic dynamic clock biases of the BTSs and shares these estimates with a navigating receiver (navigator). The optimal navigation performance of the mapper/navigator framework in the presence of timing discrepancies is analyzed, and a practical upper bound on the resulting position error is derived. Experimental results for a ground vehicle and unmanned aerial vehicles (UAVs) are presented. The ground vehicle results show a mean distance difference of 5.51 m between the cellular CDMA-only navigation solution and a GPS navigation solution in the absence of clock bias discrepancies. The UAV results show an improvement of 10.57 m in the root-mean-square error of the cellular CDMA navigation solution, when the sector clock bias discrepancies are accounted for utilizing the statistical model relating observed clock biases from different sectors of the same BTS cell.