In this study, a full-factorial experimental evaluation of a sensor fusion system based on a real vehicle was performed. The experimental results for different driving scenarios and parameters are discussed and the factors that make the most impact are identified. The performance of sensor fusion depends on many factors such as the sensors used, kinematic model used in the Extended Kalman Filter(EKF) motion of the vehicles, type of road, density of vehicles, and gating methods. The interactions between parameters and the extent to which individual parameters contribute to the overall accuracy of a sensor fusion system can be difficult to assess. This study identified that the distance between the vehicles has the largest impact on the estimation error because the vision sensor performs poorly with increased distance. In addition, it was identified that the kinematic models had no significant impact on the estimation. Last but not least, the ellipsoid gates performed better than rectangular gates.

User cooperation, whereby multiple users share their antennas and transmit to a common destination in a collaborative manner, has been shown to be an effective way to achieve spatial diversity. We propose in this paper, a strategy to minimize the total transmit power in a decode-and-forward (DF) multi-user, multi-relay cooperative uplink, such that each user satisfies its quality-of-service (QoS) data rate. Each user in the proposed system transmits its own data towards the base station and also serves as a relay for other users. The base station assigns one or more relays to each user in order to minimize total power in the uplink. The relay selection is based upon the instantaneous user to base station channels, inter-user channels and also the target rates of the users. The simulation results indicate significant power savings over a non-cooperative uplink, under proposed joint relay selection and power minimization algorithm in a DF cooperative uplink when using a space-time coded cooperative diversity.

Cooperative diversity is a form of distributed space- time macrodiversity capable of mitigating the detrimental effects of multipath fading in a wireless network. Prior work on cooperative diversity has focused on the case that all terminals have a single antenna. However, in many practical situations, it is feasible for one or more terminals to be equipped with an array of multiple antennas. This paper investigates the impact of the presence of a single antenna array in a three terminal orthogonal relaying network. The array may be at the source, relay, or destination. The information outage probability under diversity combining is derived, and closed form expressions given wherever possible. The numerical results suggest that it is best to place the array at the destination, and that it is better to place the array at the relay than at the source.

In this paper, we study concatenated coding for MIMO-OFDM systems. The proposed concatenated system achieves full spatial and frequency diversity at much lower complexity in terms of number of states without any bandwidth expansion. In general, coding for MIMO-OFDM systems is known as space frequency time (SFT) coding. This paper focuses on applying a powerful class of trellis codes known as IQ-TCM. We illustrate the benefits of IQ-TCM in concatenated SFT codes. The results of this study show the performance improvements of IQ-TCM over conventional TCM at the same number of states and spectral efficiency. The reason for that is the larger effective length of IQ-TCM. Also, the simulation results emphasize the importance of an appropriate interleaver design since there is a great loss in performance and diversity if the block interleaver is not designed carefully.

The propagation of ultra wideband (UWB) signals in indoor environments is an important issue with significant impacts on the future direction and scope of the UWB technology and its applications. The objective of this work is to obtain a better assessment of the potentials of UWB indoor communications by characterizing the UWB indoor communication channels. Channel characterization refers to extracting the channel parameters from measured data. An indoor UWB measurement campaign is undertaken. Time-domain indoor propagation measurements using pulses with less than 100 ps width are carried out. Typical indoor scenarios, including line-of-sight (LOS), non-line-of-sight (NLOS), room-to-room, within-the-room, and hallways, are considered. Results for indoor propagation measurements are presented for local power delay profiles (local PDP) and small-scale averaged power delay profiles (SSA-PDP). Site-specific trends and general observations are discussed. The results for path-loss exponent and time dispersion parameters are presented.

In this letter, we present a comparison between the bit error rate (BER) performance of a uniform circular array (UCA) and a uniform linear array (ULA) assuming quadrature phase-shift keying (QPSK) and maximal-ratio-combining (MRC) in a mobile radio communication environment. The results are based on analysis, assuming a flat Rayleigh fading channel with omni-directional antennnas and considering the azimuthal plane only. The analytical BER is derived as a function of the spatial fading correlation for both types of antenna arrays. Results show that for similar aperture sizes the UCA outperforms the ULA when considering all angles-of-arrival. However, there is considerable variability over central angle-of-arrival (AOA) for low-to-moderate angle spreads. For angles-of-arrival concentrated near the broadside of the linear array, the ULA typically performs as well as or better than the UCA. A truncated Gaussian AOA (AOA) distribution is assumed to model spatial correlation and the numerical results focus on four element arrays.

We demonstrate the performance of a beamformer-RAKE receiver at the uplink of a wideband code division multiple access (WCDMA) system. The receiver employs maximum signal to interference and noise ratio (MSINR) criterion to form its beams in the spatial domain. We propose a new iterative algorithm to solve the generalized eigenvalue problem (GE) resulting from the MSINR beamforming criterion. This algorithm, termed adaptive matrix inversion (AMI), has linear computational complexity with the number of antenna elements. We show the performance gain compared to that of another proposed method.

We investigate eigen-beamforming resulting from the maximum signal to noise ratio (MSNR) criterion. MSNR beamforming criterion leads to a simple eigenvalue problem (SE) so that the weight vector is the principal eigenvector of the covariance matrix of the desired signal. We employ a beamformer-RAKE receiver at the uplink of a wideband code division multiple access (WCDMA) system. The receiver exploits the MSNR based beamforming for spatial processing. There are different algorithms like the power method, the Lagrange multiplier method and the conjugate gradient method to solve the SE. We compare these three algorithms in terms of computational complexity and bit error rate (BER) performance in multipath propagation environment.

The performance of space-time trellis codes paired with iterative equalization/decoding has been reported by Bauch and Naguib (see Wireless Communications and Networking Conference - WCNC', p.261-265, 1999), by Liu, Fitz and Takeshita (see International Conference on Communications - ICC', p.2800-2804, 2001), and by Gozali and Woerner (see PIMRC', Feb. 2002) for MIMO frequency selective fading channels. Assuming perfect knowledge of channel state information at the receiver, the scheme has been shown to exploit multipath diversity in addition to spatial diversity and coding gain. We remove the assumption of ideal channel estimation and investigate the performance of the scheme in the presence of magnitude or phase error estimates. We show that the diversity advantage of the scheme relies heavily on accurate channel estimation and quantify the degradation associated with imperfect channel estimates. Results indicate that a phase error of up to 10 degrees or an amplitude error below 15% are tolerable, such that the diversity advantage of the scheme is maintained. Within these limits, the iterative process provides significant performance gains in the first and second iterations, while diminishing returns are observed for more than two iterations. Finally, we compare our simulation results with outage probability analysis bounds.

We generalize the analysis presented originally by Rensburg and Friedlander (see Thirty-Fourth Asilomar Conference on Signals, Systems and Computers, p.301-305, 2000) to study the robustness of space-time block codes (STBC), paired with linear or circular antenna arrays, to spatial fading correlation. A tight upper bound on the error probability of the scheme is derived based on the distribution of Hermitian quadratic form of complex correlated Gaussian variates. This analytic framework supports various complex orthogonal designs with arbitrary signal cardinalities and arbitrary number of antenna elements. Results indicate that the effective diversity order is retained even when high cross correlation exists and is mainly determined by the geometric mean of the covariance matrix eigenvalues.

This paper considers the application of minimum mean squared error linear space-time processing in tandem with successive interference cancellation (MMSE-SIC) to the extraction of symbol-asynchronous /spl pi//4-DQPSK signals with RRCOS pulse shaping (35%-75% rolloff) in overloaded environments. The performance is analyzed through simulation in terms of the symbol error rate ranked by cancellation order. The effect of signal excess-bandwidth, adjacent channel interference, the number of users, SNR, and array type are considered. The channel statistics of all users are assumed known.

In this paper, we present the comparative spatial fading correlation function of a uniform linear array (ULA) for various angle-of-arrival (AOA) distributions in a mobile radio environment. The spatial fading correlation for ULA is a function of the angle spread and distance between elements. Angle spread is a measure of the energy distribution in AOA and is defined to be the variance in this work. Three AOA distributions are considered in this work: uniform, truncated Gaussian, and Laplacian. Results show that the three AOA distributions give similar spatial fading correlation for the same angle spread suggesting that the variance of the distribution is more important than the actual distribution. Computer simulations are carried out to verify the analytical results.

In this paper, we extend our previous work (2001) to design orthogonal transmit waveforms (OTW) for CDMA systems in MIMO (multiple transmit/receive antennas) mobile radio channels. We evaluate the performance of orthogonal transmit waveforms for uplink communications systems through the use of bit-error-rate (BER) simulation. We investigate the MIMO mobile radio uplink channels for both time-varying flat and frequency selective Rayleigh fading channels. The proposed OTW systems exploit both the spatial and temporal diversity of MIMO mobile radio channels. The effects of angle spread, Doppler frequency, and delay spread of MIMO mobile channels on the BER performance of the OTW system are considered.

In this paper, we derive a closed-form expression for the fading correlation function of a uniform circular array (UCA). The fading correlation for a UCA is a function of antenna spacing, array geometry, as well as the distribution of angle of arrival (AOA). Comparative results on the fading correlation function for both the uniform linear array (ULA) and the UCA are given. Computer simulations are carried out to verify the analytical results.

A beamformer-RAKE receiver (see Naguib, A.F., "Adaptive Antennas for CDMA Wireless Networks", Ph.D. dissertation, Stanford University, 1996) takes advantage of both the spatial and temporal processing associated with a beamformer and a RAKE receiver respectively. We investigate the performance of a beamformer-RAKE receiver at the uplink of the wideband code division multiple access (WCDMA) system. The receiver exploits the maximum signal-to-interference-plus-noise ratio (MSINR) criterion (see Litva, J. and Lo, T.K., "Digital Beamforming in Wireless Communications", Artech House, Boston, 1996) to form the beams in the spatial domain. The blind code gated algorithm (CGA) (see Vasavada, Y.M. et al., Proc. 34th Asilomar Conf. on Signals, Systems and Computers, 2000) is employed to realize the MSINR criterion. We compare the CGA with the modified code filtering approach (CFA) (see Kwon, S. et al., Proc. IEEE Vehicular Tech. Conf., p.1890-4, 1999 ). The performance gain of a beamformer-RAKE compared to a conventional RAKE receiver is demonstrated.

A beamformer-RAKE receiver allows processing of the signal in both the spatial and temporal domain by combining an adaptive antenna array with a RAKE. This can significantly improve the system performance along the reverse link of a wideband code division multiple access (WCDMA) system by providing multiple access interference (MAI) suppression and multipath diversity. We compare the performance of two different beamformer-RAKE receivers that employ the minimum mean square error (MUSE) and the maximum signal to interference and noise ratio (MSINR) criteria to form the beams in the spatial domain. The pilot symbol assisted (PSA) technique and the blind code gated algorithm (CGA) were selected to exploit the aforementioned criteria.

We present the bit-error-rate (BER) performance for a proposed hybrid antenna system that combines a uniform circular phased array and diversity array using maximal-ratio-combining (MRC) in wireless communications. By phased array and diversity array we mean the circle of radius of the uniform circular array (UCA) is one-half wavelength and greater than half wavelength, respectively. The phased array is used in non-fading wireless channels, while the diversity array is used for wireless channels with multipath fading. The BER performance for the proposed antenna system is evaluated through the use of computer simulation. For channels without fading, the BER performance of the phased array with MRC is evaluated as a function of the number of antenna elements. For the fading channel, the BER performance of the diversity array with MRC is function of the spatial antenna correlation. Comparative results on the BER performance for a uniform linear array (ULA) and UCA are given.

This paper examines the performance achieved in AWGN channels and flat Rayleigh fading channels by combining non-coherent multistage parallel interference cancellation with multiple symbol differential detection algorithms for DS/SS CDMA systems using DBPSK and DQPSK modulation. We compare the performance of this multiuser receiver conjugated with traditional differential detection, multiple symbol detection, Viterbi differential decoding, and multiple phase shift differential detection.

This paper proposes a novel frame synchronization methodology for packets with convolutionally encoded data. Rather than by placing sync bits in a separate header, the sync bits are placed in a midamble and encoded as part of the data sequence, using the error correction encoder to resolve time ambiguities. The scheme is based on the principle that an error in trellis termination may result in decoding a wrong information bit sequence, while the starting portion of the sequence can be decoded as error free. This frame synchronization technique is extended to the synchronization of turbo-coded systems using a list-based approach, where the first synchronizer provides a list of potential packet starting positions, and the following synchronizer makes the final decision. The performance improvement over conventional synchronization techniques is quantified via simulation.

A soft-input soft-output (SISO) multiuser detector (MUD) suitable for inclusion in iterative processing architectures is presented and applied to the detection of the coded time division multiple access (TDMA) cellular uplink. A SISO-MUD processor is located at each base station in the network, and adjacent base stations share information concerning the mobiles they serve. Because the MUD outputs are soft, they are suitable for postdetection macrodiversity combining. The combined signals are then passed to a SISO forward error correction (FEC) decoder, and the soft outputs are fed back to the multiuser detectors. Processing continues in an iterative fashion in accordance with the turbo principle. Simulation results are presented that indicate that use of such a scheme enables cellular systems to be overloaded with more than just one cochannel user per cell at the price of a minimal loss in signal-to-noise ratio (SNR). The proposed implementation assumes the availability of both perfect channel state information and a high capacity backhaul.

A method for coherently detecting and decoding turbo-coded binary phase shift keying (BPSK) signals transmitted over frequency-flat fading channels is discussed. Estimates of the complex channel gain and variance of the additive noise are derived first from known pilot symbols and an estimation filter. After each iteration of turbo decoding, the channel estimates are refined using information fed back from the decoder. Both hard-decision and soft-decision feedback are considered and compared with three baseline turbo-coded systems: (1) a BPSK system that has perfect channel estimates; (2) a system that uses differential phase shift keying and hence needs no estimates; and (3) a system that performs channel estimation using pilot symbols but has no feedback path from decoder to estimator. Performance can be further improved by borrowing channel estimates from the previously decoded frame. Simulation results show the influence of pilot symbol spacing, estimation filter size and type, and fade rate. Performance within 0.49 and 1.16 dB of turbo-coded BPSK with perfect coherent detection is observed at a bit-error rate of 10/sup -4/ for normalized fade rates of f/sub d/T/sub s/=0.005 and f/sub d/T/sub s/=0.02, respectively.

This letter studies the numerical properties of log-MAP-based soft-input soft-output decoding. The ranges of the differences between the path metrics, the soft output, and the complete information are derived. Since the log-MAP algorithm is functionally dependent only upon the differences between path metrics, not their magnitudes, a module normalization technique that is automatically implemented in two's complement arithmetic can be used to accommodate overflow of the path metrics. An expression for the minimum internal data width of a soft-input soft-output decoder that employs the module normalization technique is derived. As an application, the minimum internal data width of a decoder for the turbo code used in third-generation mobile communication systems is determined.

This paper examines the performance improvements achieved in AWGN channels by combining non-coherent subtractive interference cancellation with multiple symbol differential detection. The multiuser receivers considered in this study are the successive interference canceller, the parallel interference cancellation receiver, and the decision feedback receiver. Presented in this study is a comparison of the aforementioned differentially coherent multiuser receivers as they employ standard differential detection, multiple symbol detection, and Viterbi differential decoding. It is observed that consequential improvements are obtained by increasing the memory beyond one symbol and performing sequence estimation of the transmitted phases based on the decision statistics after multiuser detection.

This paper proposes a novel frame synchronization scheme for convolutionally encoded data packets. Rather than placing sync bits in a separate header, the sync bits are placed in a mid-amble and encoded as part of the data sequence, using the error correction encoder to resolve time ambiguities. This technique requires fewer bits for frame synchronisation. The performance improvement over conventional synchronization techniques is explored via simulation. The applicability of the scheme for synchronization of turbo codes is also discussed.

The implementation of advanced DS-CDMA receivers based on multiuser detection principles is becoming a reality thanks to the combination of an improved understanding of the theoretical basis of multiuser detection and advances in digital, mixed-signal, and RF technologies. Due to their lower complexity, subtractive interference cancellation approaches are attractive for the practical implementation of multiuser detection. In a parallel interference cancellation receiver, it is practical to use the soft outputs of a matched filter bank for amplitude estimation. A bias arises in the decision statistics, however, due to imperfect estimation and interference cancellation. In this paper, the source of the bias is explicitly recognized, and a partial interference cancellation scheme that mitigates the negative effects of biased estimation and significantly improves system performance is proposed. A practical real-time algorithm that significantly reduces the implementation complexity of this scheme without sacrificing performance is then derived. To facilitate a software radio implementation, the signal processing complexity of the approach is characterized. The real-time processing algorithm is tested via implementation in software on a floating-point general-purpose DSP. The prototype includes a flexible software-based architecture which performs IF sampling and uses digital downconversion prior to baseband processing. The hardware test setup is described, and the results are presented and compared with simulation and analytical results. The experimental results confirm the simulation and analytical results which show large performance gains over the conventional matched filter.

This paper presents a baseband real-time DSP implementation of a multiuser receiver built upon an improved strategy for parallel interference cancellation. Significant performance gains are obtained by using a partial parallel interference cancellation scheme that mitigates the negative effects of biased estimation and imperfect MAI cancellation that are intrinsic to the complete interference cancellation approach. An attractive feature of the implementation is that it has a computational complexity that is linear in the number of users. Experimental test results confirm substantial improvements over the conventional receiver.

A soft-input, soft-output multiuser detection algorithm based on the log-MAP algorithm is presented for asynchronous multiple access networks. The algorithm is applied to a convolutionally coded direct sequence code division multiple access (DS-CDMA) system. The proposed receiver architecture consists of a log-MAP multiuser detector followed by a log-MAP channel decoder. Information is fed back from the channel decoder to the multiuser detector, and processing proceeds in an iterative fashion analogous to the decoding of turbo codes. Simulation results show that the performance of a heavily loaded power controlled DS-CDMA system approaches the single-user bound for both additive white Gaussian noise (AWGN) and fully-interleaved Rayleigh flat-fading channels.

We compare throughput bounds for a frequency-hopped multiple-access (FHMA) system employing variable rate as well as fixed rate coding (FRC). Nonfading as well as Rayleigh-fading channels are explored. The throughput bounds for the variable rate coding (VRC) schemes are based on the assumption that the number of active users in the system, m, is known at any time while the bounds for the FRC scheme assumes that the fixed code rate is optimized for the user population mean, /spl lambda/, where the population is assumed to be Poisson distributed. We present bounds for theoretical "perfect" codes which achieve the capacity as well as bounds for Reed-Solomon (RS) codes of practical block lengths. Finally, we show the dependence of a VRC scheme upon the accuracy of the estimates of m and present a general comparison of the gains of using VRC versus a realistic FRC scheme.

In this paper we derive the asymptotic multiuser efficiency (AME) of M-stage interference cancellation receivers and show that as the number of stages increases to infinity, the receiver is equivalent to the well known decorrelator. This fact holds provided certain bounds on the total cross-correlation between users are met. Thus, in such cases the M-stage receiver has an asymptotic multiuser efficiency which is greater than zero as M/spl rarr//spl infin/ for all user energies, i.e. it is near-far resistant. Additionally, while not strictly near-far resistant in the case of M

Parallel multistage interference cancellation is a promising approach for practical implementation of multiuser detection. However, as this paper shows, direct implementation of multistage parallel interference cancellation (i.e. complete cancellation of the estimated interference) results in biased estimates and consequently reduced performance. A simple technique that mitigates the effect of the bias and provides significant performance gains over the direct implementation is presented.

We consider the use of multistage parallel interference cancellation at the base station of a code-division multiple-access (CDMA) wireless system. Previous work in this area has demonstrated the potential for significant improvements in capacity and near-far resistance. However, most previous work has assumed perfect synchronization with the signals of interest. Practical systems will experience phase jitter and timing errors. We undertake an analysis of the effects of phase and timing errors, obtaining a closed form result for bit-error rate (BER) performance after an arbitrary number of stages of cancellation in an additive white Gaussian noise (AWGN) channel. This result is shown to agree well with simulations. Simulation results are also presented for the important case of frequency selective Rayleigh fading. The results from both analysis and simulations demonstrate that interference cancellation is fairly robust to phase and timing errors.

We consider a simple model for adaptive multistage interference cancellation within a CDMA system, and seek to develop an accurate analytical expression for the performance of this system. Previous work on interference cancellation has relied heavily on simulation techniques or a simple Gaussian approximation (GA). The standard GA ran lead to bit-error rate (BER) results which are optimistic for the conventional receiver, and this also occurs when the approximation is applied to the interference cancellation problem. Additionally, this approximation does not allow the second order effects of the multiple access interference (MAI) to be included in the performance estimates. Several improvements on the standard GA have been suggested which result in accurate performance results for a standard CDMA receiver. This paper presents an analytical expression for the probability of bit error for an adaptive multistage interference canceller, using an improved Gaussian approximation (IGA) for MAI. The BER at any stage of interference cancellation can be recursively computed from the signal-to-noise ratio (SNR), the statistics of the random powers of users, and the processing gain of the CDMA system. The performance of the resulting EER expression is compared with simulation results. Since the second order effects of MAI can be included, the analytical framework presented here can also be used to evaluate the performance of multistage interference cancellation in arbitrary fading environments, and we present results for the performance of interference cancellation in lognormal fading environments.

The standard correlation receiver for code-division multiple access (CDMA) systems is susceptible to the near-far problem. Power control techniques attempt to overcome near-far effects by varying transmitted power levels to ensure that all signals are received with equal power levels. Since these algorithms cannot perfectly compensate for power fluctuations in a mobile communications channel, the capacity of the system is reduced for a given bit-error rate (BER). This paper examines the performance of a CDMA system using imperfect power control by extending analytical techniques that account for multiple access interference. Single cell capacity is compared with systems employing perfect power control.

This paper considers the performance of adaptive interference cancellation applied to a CDMA microcellular environment, by employing a circular geometry and a closed form expression for the bit error rate of a CDMA system with interference cancellation to analyze the effect of out-of-cell interference. Results indicate that out-of-cell interference will severely limit the benefits of interference cancellation in a multicellular system. Attempts to cancel all out-of-cell interference will further degrade the performance. However, selective interference cancellation in which only the strongest out-of-cell interferers are cancelled may result in significant performance enhancement.

We consider a direct-sequence spread-spectrum multiple access communication system with convolutional coding and hard decision decoding. We calculate the packet error probability and throughput of this system. Previous bounds on packet error probability have relied on the worst case assumption of phase and chip synchronous interference. We present new bounds on packet error probability and throughput for the case of both slotted and unslotted systems. These new bounding techniques are based on two advances: an improved Chernoff bound on the error event probability of a convolutional code, and the use of moment space techniques. Numerical results indicate that these new bounds on packet error probability improve on previously reported bounds by more than an order of magnitude. We also examine the problem of choosing the optimum code rate which maximizes throughput. We compare the optimum code rate which results from the bounding technique to the optimum code rate derived from an approximation technique. Although the bounding technique and approximation technique yield very different results for throughput, the resulting choice of optimum code rate is similar.

This paper presents a multistage receiver for code division multiple access (CDMA) systems. Previous multistage receivers have lead to improved multiple access (MA) performance, but require knowledge of received signal powers. This paper proposes a "multistage RAKE" receiver which does not require a priori knowledge of the signal powers or the channel. Performance of the multistage RAKE is simulated for Gaussian and multipath channel models, and for the case of imperfect power control.>

This paper considers the application of trellis coding techniques to direct-sequence spread-spectrum multiple-access (DS/SSMA) communication. The unique feature of the trellis codes considered is that they are constructed over the set of possible signature sequences rather than over some standard 2-D signal constellation. The resulting codes have a small number of signals per dimension. We present several examples of these trellis codes, and suggest possible methods of implementation. We also present a detailed error analysis for this system, which employs techniques developed by Lehnert and Pursley (1987, 1989)) to accurately model the multiple access interference. We generate numerical results for several examples and conclude that the proposed trellis coded systems yield significant performance improvements over binary antipodal DS/SSMA systems. In addition, the new trellis codes perform better than standard error control techniques with the same complexity and code rate. Analytic results are verified with simulations.>