Radar has become a key sensor in many advanced driver assistance systems (ADAS). Due to its excellent range and Doppler resolution, low cost, and robustness against environmental conditions, it is considered an attractive sensor for detecting and tracking vulnerable road users (VRUs). In this paper, we provide a theoretical analysis of the accuracy of radar based VRU detection and tracking systems, thereby focusing on a number of specific scenarios such as early detection and tracking of VRUs, a VRU crossing the road at constant speed in front of a vehicle, a VRU moving parallel to a vehicle, etc. More specifically, we derive the Cramer-Rao lower bound (CRLB) for position and velocity estimation of a moving target based on a sequence of noisy range, azimuth, and Doppler measurements taken from a moving ego-vehicle equipped with one or multiple radars. Not only does the CRLB serve as a benchmark to evaluate the performance of any practical tracking algorithm, it also allows to gain practical insights regarding the impact of the radar setup and configuration on the tracking accuracy in different realistic scenarios. Furthermore, we show that the generalized least-squares estimator (GLSE) achieves excellent performance when few measurements are available, and propose a novel active sensing (AS) application based on the CRLB where the radar configuration is optimized on the fly to improve either tracking accuracy or computational efficiency.

Due to the continuous demand for higher bit rates, the management of the spatio-temporal intersymbol interference in frequency-selective multiple-input multiple-output (MIMO) channels becomes increasingly important. For single-input single-output channels, equalized precoded partial-response signaling is capable of handling a large amount of intersymbol interference, but, to date, no equalization scheme with general partial-response signaling has been presented for the frequency-selective MIMO channel. Not only does this contribution extend partial-response signaling to the MIMO channel by proposing a general spatio-temporal partial-response precoder, but it also develops a minimum mean-squared-error optimization framework in which the equalization coefficients and the spatio-temporal target response are jointly optimized. Three iterative optimization algorithms are discussed, which update (part of) a row of the target impulse response matrix in each iteration. In particular, the third algorithm reformulates this row optimization as a lattice decoding problem. Numerical simulations confirm that the general partial-response signaling clearly outperforms the traditional full-response signaling in terms of the mean squared error and the bit error rate. The third optimization algorithm has a better performance but a higher complexity, compared to the first and the second algorithm.

Partial-response signaling is known to facilitate the equalizer design because a controlled amount of residual interference is permitted. The design of the target impulse response of the partial-response precoder often assumes perfect channel state information, which is unfortunately not available at the transmitter in most practical applications. Consequently, this contribution focuses instead on the robust and joint design of a spatio-temporal target impulse response and the equalization coefficients for a frequency-selective fading multiple-input multiple-output communication channel based on current and/or previous noisy channel estimates. More precisely, the error in the channel estimates is statistically modeled, and robustness is achieved by minimizing the mean-squared estimation error averaged over the joint distribution of the actual channel and the available channel estimates. Numerical results of the bit error rate confirm that the proposed robust partial-response signaling not only provides a significant performance gain compared to traditional full-response signaling, but also outperforms the naive approach, which ignores channel estimation errors.

High-speed communication over mutually coupled channels can be severely affected by intersymbol interference (ISI) and crosstalk (XT). Multiple-input multiple-output (MIMO) equalization is known to mitigate both ISI and XT, but requires accurate channel information at the receiver (RX) and/or transmitter (TX), when the channel is stochastic. However, since adjusting the equalization filters to the specific channel realization involves a considerable implementational and computational complexity, it is desirable to keep the equalization filters fixed irrespective of the specific channel realization, especially when the channel variability is relatively small. Therefore, we propose a general MIMO transceiver scheme where the equalization filters depend on the channel statistics rather than the actual channel. More specifically, by considering the time-domain equalization with the fixed linear MIMO pre-equalization and adjustable MIMO decision feedback equalization, the complexity associated with passing channel information from the RX to the TX is avoided, and the computationally intensive and iterative calculations of the fixed pre-equalizer can be performed offline rather than on-chip. The proposed equalization scheme is shown to yield only a small performance degradation compared to fully adjustable equalization schemes, thereby enabling multi-Gbit/s chip-to-chip communication over low-cost electrical interconnects which are prone to manufacturing tolerances.

While the requirements for delivering high throughputs increase exponentially with every generation of access node hardware, the device cost is of primary concern. As a result, multiple- input multiple-output (MIMO) equalization, which has been shown to facilitate multi-Gbit/s communication over low-cost parallel electrical interconnects, is emerging as an attractive high- speed interconnect solution for next-generation access nodes. Because of the high operating frequencies, however, the transfer functions of the on- and off-chip interconnects become highly susceptible to manufacturing tolerances (MTs); hence, the equalization filters must be adjusted to the specific channel realization to achieve optimal performance, which involves a high implementation and computational complexity. Considering that the MTs are usually limited, we propose a robust low-complexity transceiver consisting of a fixed MIMO linear pre-equalizer (which avoids the need for feeding back the channel state information to the transmitter), with either a fixed or adjustable MIMO decision- feedback equalizer (DFE). For a specific chip-to- chip interconnect operating at 75 Gbit/s per line and a 26 dB signal-to-noise ratio, we show that the resulting bit error rate does not exceed 10^(-12) for MTs up to 10.5% (fixed DFE) and 17.7% (adjustable DFE) of the nominal line width.

In this contribution, we present a linear multiple-input multiple-output (MIMO) equalization scheme at the receiver side for high-speed electrical chip-to-chip communication. As opposed to traditional single-input single-output (SISO) equalization per lane, this MIMO approach enables cooperating receivers to treat crosstalk (XT) between neighboring channels as an information-bearing signal instead of a disturbing signal, allowing to mitigate both inter symbol interference and XT. Given a simulated 4 × 4 MIMO electrical chip-to-chip interconnect channel, we point out that, for a given total number of equalizer taps, MIMO equalization can outperform SISO equalization. Moreover, by further increasing the total number of equalizer taps, MIMO equalization allows to obtain performance gains that are substantially larger than for SISO equalization.

In this contribution, we present a simple but efficient importance sampling technique to speed up Monte Carlo simulations for bit error rate estimation of orthogonal space-time block codes on spatially correlated Nakagami-m fading channels. While maintaining the actual distributions for the channel noise and the data symbols, we derive a convenient biased distribution for the fading channel that is shown to result in impressive efficiency gains up to multiple orders of magnitude.

In this contribution, we present a novel closed-form bit error rate (BER) approximation for orthogonal space-time block codes employing rectangular quadrature amplitude modulation. The multiple-input multiple-output channel is assumed to be affected by arbitrarily spatially correlated Rayleigh fading. We consider a mismatched maximum-likelihood receiver that obtains the channel state information through pilot-based linear minimum mean-square error channel estimation. The presented BER approximation is shown to yield very accurate results over a wide range of signal-to-noise ratios.

Indoor off-body wireless MIMO links between a mobile user equipped with wearable textile patch antennas and a fixed base station exhibit specific channel behavior due to the near presence and movements of the human body. Therefore, they require a dedicated channel model that captures the effects of correlated small-scale Rayleigh fading and correlated lognormal shadowing. A methodology is presented to construct such a model, allowing to predict the bit error characteristics and channel capacity curves based on the shadowing and fading correlation matrices that are extracted from channel measurements. It is shown that by separating shadowing, including effects caused by movement and reorientation of the human body, from small-scale fading, the main mechanisms of the off-body communication link are accurately captured by the model. A clear dependence of the shadowing correlation values on the physical layout of the antenna system is found. In our measurements, shadowing is not significantly decorrelated by polarization diversity or front-to-back diversity whereas the small-scale fading is clearly decorrelated. From the model, MIMO channel realizations with identical bit error rate and channel capacity characteristics as the measured channel can be quickly generated for link emulation purposes.

In this contribution, we provide an exact bit error rate (BER) analysis of orthogonal space-time block codes over arbitrarily distributed (possibly correlated) block fading channels with imperfect channel estimation. The transmitted symbols belong to a PAM or QAM signal constellation. With Ntand Nrdenoting the number of transmit and receive antennas, respectively, the resulting average BER can easily be written as an expectation over 4NtNrreal-valued random variables, but the computation time needed for its numerical evaluation increases exponentially with Ntand Nr. We provide a methodology that allows an efficient numerical evaluation of the exact BER with a computation time that is essentially independent of NtNrand the signal-to-noise ratio.

In this contribution, we examine the effect of imperfect channel estimation on the bit error rate (BER) performance of square orthogonal space-time block codes (OSTBCs). The propagation channels from the Nt transmit antennas to each of the Ntreceive antennas are assumed to be affected by (possibly correlated) flat block fading with an arbitrary distribution. The transmitted symbols belong to a PAM or QAM constellation. The resulting average BER can easily be written as an expectation over 4NtNrreal-valued random variables, but the computing time needed for its numerical evaluation increases exponentially with Ntand Nr. However, we point out that expressing the BER in terms of the distribution of the Frobenius norm of the channel matrix, allows to reduce the BER expression for any number of receive antennas to an expectation over only 2Ns+ 2 random variables (with Nsdenoting the number of information symbols in the OSTBC matrix). Due to the high diversity order of OSTBCs, the numerical evaluation of this expectation is much less time-consuming than a straightforward computer simulation. Moreover, the presented BER expression is useful not only when the fading distribution is given in closed form, but also when only experimental data (e.g. a histogram) on the fading are available.

We present a simple closed-form expression for the BER of orthogonal space-time block codes (OSTBCs) with MMSE channel estimation, assuming PAM and QAM constellations and flat Rayleigh block fading. The BER expression is exact for a certain class of OSTBCs, and provides a very accurate approximation for other OSTBCs.

In a recent paper, Garg et al. present an expression for the exact decoding error probability (DEP) of square orthogonal space-time block codes (OSTBCs) with imperfect channel estimation. We show that their DEP expression is only asymptotically correct and point out how to obtain the exact result for arbitrary signal-to-noise ratio.

In this contribution, we investigate the effect of imperfect channel estimation on the bit error rate (BER) performance of uncoded quadrature amplitude modulation (QAM) with maximal-ratio combining (MRC) multichannel reception. The propagation channels from the transmitter to each of the Nr receive antennas are assumed to be affected by (possibly correlated) flat block fading with an arbitrary fading distribution. The MRC receiver makes use of estimated channel coefficients, obtained from known pilot symbols sent among the data. The resulting average BER for QAM can easily be written as an expectation over 4Nr random variables, but the computing time needed for its numerical evaluation increases exponentially with Nr. We point out that the BER can be expressed in terms of the distribution of the norm of the channel vector, rather than the joint distribution of all channel coefficients. This allows to reduce the BER expression to an expectation over only 4 random variables, irrespective of the number of receive antennas. Moreover, we show that for real-valued constellations and/or real-valued channels, the BER expression reduces to an expectation over less than 4 variables. For practical BER levels, the numerical evaluation of the BER is much less time-consuming than a straightforward computer simulation. The presented BER expression is useful not only when the fading distribution is given in closed form, but also when only experimental data (e.g. a histogram) on the fading are available.