Gerard J. M. Janssen

Noncoherent ultra-wideband systems

The need for low-complexity devices with low-power consumption motivates the application of suboptimal noncoherent ultra-wideband (UWB) receivers. This article provides an overview of the state of the art of recent research activities in this field. It introduces energy detection and autocorrelation receiver front ends with a focus on architectures that perform the initial signal processing tasks in the analog domain, such that the receiver does not need to sample the UWB received signals at Nyquist rate. Common signaling and multiple access schemes are reviewed for both front ends. An elaborate section illustrates various performance tradeoffs to highlight preferred system choices. Practical issues are discussed, including, for low-data-rate schemes, the allowed power allocation per pulse according to the regulators ruling and the estimated power consumption of a receiver chip. A large part is devoted to signal processing steps needed in a digital receiver. It starts with synchronization and time-of-arrival estimation schemes, introduces studies about the narrowband interference problem, and describes solutions for high-data-rate and multiple access communications. Drastic advantages concerning complexity and robustness justify the application of noncoherent UWB systems, particularly for low-data-rate systems.

Wideband indoor channel measurements and BER analysis of frequency selective multipath channels at 2.4, 4.75, and 11.5 GHz

Results from propagation measurements, conducted in an indoor office environment at 2.4, 4.75, and 11.5 GHz, are presented. The data were obtained in small clusters of six measurements, using a coherent wideband measurement system. The channel characteristics for the three frequencies are compared by evaluating path loss, rms delay spread, and coherence bandwidth. An analytical model for evaluation of the bit-error rate (BER) of the stationary frequency selective indoor channel is developed for a coherent binary phase shift keying (BPSK) receiver, based on the complex impulse response of the channel. Computational BER results are obtained for data rates up to 50 Mb/s, using the measured multipath channel impulse responses. The BER results for a number of clusters are presented and compared for the maximum reliable data rate as inferred by the measured rms delay spread of the channel.

An overview of ultra wide band indoor channel measurements and modeling

In this paper, an overview of reported measurements and modeling of the ultra wide band (UWB) indoor wireless channel is presented. An introduction to UWB technology and UWB channels is provided. Different UWB channel sounding techniques are discussed and approaches for the modeling of the UWB channel are reviewed. The available indoor UWB channel measurement results are consulted and accordingly, the major UWB channel parameters are presented and compared to those of narrowband systems. The novelty of this work is the gathering of different UWB channel parameters, analysis, and comparison. Added with the influence of UWB antenna in channel-modeling as well as the frequency-dependency of the channel parameters, leading to a conclusion on the UWB radio channel modeling.

Multinode Spectrum Sensing Based on Energy Detection for Dynamic Spectrum Access

Sharing of the frequency spectrum between licensed primary users and unlicensed secondary users (SUs) requires reliable detection of spectrum occupancy by the SUs. Due to fading, single terminal detection is unreliable and results in a high probability of missed detection. This problem is solved by applying cooperative detection. In this paper two novel energy-based cooperative detection methods using weighted combining for Dynamic Spectrum Access are presented and analyzed. Weighting is based on the local mean SNR and the optimum log-likelihood ratio. Simulation results show a substantial improvement for the proposed weighting methods compared to equal gain combining and hard decision combining.

Propagation measurements in an indoor radio environment at 2.4 GHz, 4.75 GHz and 11.5 GHz

Propagation measurements were performed in an indoor radio environment at 2.4 GHz, 4.75 GHz, and 11.5 GHz using a coherent measurement system consisting of an HP synthesized sweeper and a network analyzer. The three frequencies are compared by evaluating the RMS time delay spread and path loss characteristics. Such frequency comparisons in an indoor radio environment are reported.<<ETX>>

Analysis of a UWB Indoor Positioning System Based on Received Signal Strength

This paper explores the possibility to design an indoor ultra wideband (UWB) ranging and positioning system using the received signal strength (RSS). Due to the extremely large bandwidths, the effects of small scale fading are reduced to the level where the knowledge of the path loss model (PLM) can be employed for accurate and reliable distance estimation. This approach enables trilateration based position estimation while significantly reducing the synchronization effort. A limited number of measurements is necessary in order to calibrate the PLM parameters but no extensive database of measurements is required, such as in fingerprinting methods. Based on simulated UWB channels, the effects of uncertainties in the PLM parameters on the estimated distance are characterized. Data from a UWB measurement campaign in indoor line-of-sight (LOS) scenarios are used to verify the performance of such a system.

Radio resource allocation for cellular networks based on OFDMA with QoS guarantees

In this paper we address the problem of radio resource allocation for QoS support in the downlink of a cellular OFDMA system. The major impairments considered are cochannel interference (CCI) and frequency selective fading. The allocation problem involves assignment of base stations and subcarriers, bit loading, and power control, for multiple users. We propose a three-stage, low-complexity, heuristic algorithm to distribute radio resources among multiple users according to their individual QoS requirements, while at the same time maintaining the QoS of already established links in all the cochannel cells. The allocation objective is to minimize the total transmit power, which adds to reducing CCI. Simulation results show a superior performance of the proposed method when compared to classical radio resource management techniques. Our scheme allows us to achieve almost 6 times higher capacity (sum data rate) than the method based on FDMA with power control, at a blocking probability of 0.02.

Performance enhancement of differential UWB autocorrelation receivers under ISI

The autocorrelation receiver (AcR) is a suboptimum, low-complexity receiver architecture particularly suited to ultra-wideband (UWB) communication systems. As the bit rate increases, interference among pulses due to multipath propagation causes serious impairments of the AcRs performance. To mitigate this effect, we propose an appropriate design of the chip code and of the delay hopping (DH) code. We provide conditions to be satisfied by the DH code in order to reduce the nonlinear intersymbol interference (ISI) and the bias term, which are peculiar nuisance parameters of autocorrelation receivers. By extending the length of the chip code, we show that N/sub p/ transmitted pulses per symbol can be employed to suppress the average linear ISI of N/sub p/-1 previous symbols. Simulated results confirm the performance improvement in terms of bit-error rate. However, in previous work it has been shown that the noise power linearly increases with N/sub p/. Although a large number of pulses per symbol is favorable for ISI mitigation, we show that the transmission of a single pulse minimizes the probability of error, for bit rates lower than an upper bound depending on the channel root mean-square delay spread and on the noise power.

Analysis and comparison of autocorrelation receivers for IR-UWB signals based on differential detection

In this paper we propose two innovative detection schemes for IR-UWB communication systems based on the autocorrelation receiver and differential detection. The proposed schemes avoid the need for a complex analog multiplier by employing: (i) a limiter in the reference branch only; or (ii) employing also a limiter in the signal branch. Analytical models for the statistics of the decision variables are presented for the receivers, and the analytical and simulated BER exhibit an excellent agreement. We point out the dependence of the performance on some important system parameters, that shows the system design trade-off between receiver complexity and performance.

Review of range-based positioning algorithms

This tutorial reviews algorithms which turn measured ranges into position solutions. From their basic mathematical principles, we relate and compare relevant aspects of these algorithms. Special attention is given to the direct (non-iterative) algorithms, which are frequently applied in indoor positioning. Most of them are shown to be essentially the same, as they can be related through applying different weighting schemes. This tutorial is intended as a useful guide to help researchers and system designers evaluate and select appropriate range-based positioning algorithms for their applications at hand.