Ultra-wideband Channel Model Research Articles

Multi-user communication with DS-CDMA based OFDM UWB system under UWB channel model

Here we have considered multiuser communication scenario with ultra wideband (UWB) communication. For effective use of spectrum for multiuser communication we have proposed two schemes for downlink communication. These systems are DS-CDMA based OFDM systems. Performance of proposed schemes is evaluated with AWGN channel and with multipath fading channel. For considering actual UWB scenario, we have evaluated the performance of both the systems with UWB channel model considered proposed by IEEE 802.15.3a working group. This model is based on Saleh-Valenzuela (SV) model. Performance of our proposed schemes is compared with the time hopping based UWB systems. In DS-CDMA part of our system model we have considered the effect of higher spreading factor for WGN channel.

Path-Loss and Time-Dispersion Parameters of UWB Signals in a Military Airplane

This study aims to obtain a comprehensive understanding of the potentials of ultrawideband (UWB) technology by characterizing the UWB propagation channel in a Hercules C-130 military airplane. In particular, we present a method for calculating the frequency-dependent path-loss factor. Moreover, results include the distance-dependent and frequency-dependent path-loss factors and their standard deviation. Finally, we provide empirical values for the time-dispersion parameters such as the mean excess delay, the maximum excess delay, and the root mean square (rms) delay spread. The values of these parameters can be used for UWB channel modelling.

Parallel Time-Domain Full-Wave Analysis and System-Level Modeling of Ultrawideband Indoor Communication Systems

This paper demonstrates the application of a high-order finite-difference time-domain (FDTD) technique to indoor microwave ultrawideband channel modeling with a two-fold purpose. First, the advantages of both serial and parallel versions of the technique compared to the conventional FDTD are pointed out. It is also shown that the results of this full-wave analysis can be translated from the electromagnetic field level to the system level, to produce simplified, physics-based, site-specific channel models. In particular, the parameters of well-established measurement-based models are determined for a specific indoor site, by means of our electromagnetic simulation. Moreover, the proposed technique is coupled with the Monte-Carlo method to characterize the capacity of a time-hopping pulse position modulation multiple access system. Hence, a connection between the field analysis of a channel and its system-level description is made, establishing the usefulness of this work for performance projections, optimization and compatibility studies of ultrawideband communication schemes and network architectures.

Delay-Sum Antenna Array Reception for Transmitted-Reference Impulse Radio (TR-IR) Systems

For transmitted-reference impulse radio (TR-IR), the conventional antenna array reception will provide array gain and thus improve system bit-error-rate (BER) performance. In this paper, we propose a delay-sum antenna array autocorrelation receiver for the TR-IR systems. Simulation results show that by exploiting spatial correlations between antenna array elements, an extra system performance improvement of 1.3 dB and 2.1 dB can be achieved by the proposed receiver at BER=10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> for the antenna array with 2 and 4 elements, respectively, in the proposed ultra-wideband channel model.

Transmitted-Reference Impulse Radio Systems Based on Selective Combining

Transmitted-reference impulse radio with autocorrelation receiver (TR-IR/AcR) generally requires wideband analog delay line (WADL) with length of several tens nanoseconds. To maximally reduce the length, we propose a TR-IR system based on selective combining, which intelligently selects integration regions for symbol detection. It was shown that when the WADL with a total length of 8 ns is employed, the proposed system has a signal-to-noise ratio gain of 0.5 dB, 2.3 dB, 2,.3 dB and 3.7 dB over the TR-IR/AcR at bit-error-rate of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> for ultra-wideband channel models CM 1 ~ 4, respectively.

Link Budget Analysis and Modeling of Short-Range UWB Channels

Ultrawideband (UWB) technology is an attractive alternative for short-range applications, e.g., wireless personal area networks. In these applications, transmit and receive antennas are very close to each other and the far-field condition assumed in most of the link budget models may not be satisfied. Under near-field conditions, variations in the link budget and pulse shape compared to the far-field can be observed. In this work, a novel line-of-sight UWB link budget model for very short distances is proposed and validated with measurements using different types of antennas. The proposed model, which takes into account all main near-field effects (i.e., phase error, antenna mismatch and reradiation between antennas) and includes frequency, antenna size and orientation as parameters, shows a good agreement with the simulations and the measurements. This model has also been applied to dispersive antennas (e.g., notch-antennas), and can be used in the design and analysis of short-range UWB communication systems.

Comments on "A Generic Statistical-Based UWB Channel Model for High-Rise Apartments

This paper discusses a statistical-based model for ultrawideband (UWB) data from various types of high-rise apartments under different propagation scenarios.

Reply to "Comments on 'A Generic Statistical-Based UWB Channel Model for High-Rise Apartments'"

This paper discusses a statistical-based model for ultrawideband (UWB) data from various types of high-rise apartments under different propagation scenarios. It is a reply to the paper by Nadarajah and Kotz (see ibid., p.1831, 2008).

Clear Channel Assessment in Ultra-Wideband Sensor Networks

Impulse ultra-wideband (UWB) is an attractive technology for large ad hoc sensor networks due to its precise ranging capacity, multi-path fading robustness and low radiation power. The transient and carrier-less nature of low radiation pulse and harsh multipath channel condition makes it cumbersome to implement carrier sensing. We proposed clear channel assessment (CCA) based on preamble-assisted modulation (PAM) for UWB sensor networks. Preamble symbols are periodically inserted into the frame payload in the time domain to serve as regular feature for reliable CCA. We simulated the CCA performance in the multipath UWB channel model developed by IEEE 802.15.4a. PAM and CCA configurations were optimized for the distributed carrier sense multiple access protocol. PAM was accepted by 802.15.4a group as an optional feature. Furthermore, the multiplexed preamble symbols can be exploited for channel estimation to improve communication and ranging.

Evaluation of mobile ultra wideband modems in dense multipath-part 2: performance of DSSS/Rake modems

This paper presents a comparative analysis of the performance of three UWB (ultra wideband) DSSS (direct sequence spread spectrum)/Rake modems used to communicate with mobile platforms over new mobile outdoor and indoor dense multipath UWB channel models developed in a companion paper. The Rake modems analyzed differ in the techniques used to estimate the channel and are called decision-directed parallel- probe and serial-probe modems. The performance analysis includes the effects of time-selective distortion and noise on the estimated tap weights wherein the time constant of the tap weight measurements and the number of Rake taps are optimized. Numerical results are presented for 2 GHz bandwidth transmitted signals, a 7.5 GHz carrier frequency, and channel BPSK symbol rates of .15, 1.5, and 15 Megasymbols/sec. The well known rate 1/2, constraint length 7 convolutional code using 3 bit soft decision Viterbi decoding is assumed. One moving and one stationary platform are postulated, with a velocity of 100 ft/sec for the outdoor channel and 5 ft/sec for the indoor channel. Required values of Es/No to achieve 10-6 decoded error rate are computed as a function of multipath spread.

A Simple Asynchronous UWB Position Location Algorithm Based on Single Round-Trip Transmission

We propose a simple asynchronous UWB (Ultra Wide Band) position location algorithm with low complexity, power consumption and processing delay. In the proposed algorithm, only a single RTTX (Round-Trip Transmission) of UWB pulses is utilized based on the ToA (Time of Arrival) principle. Hence, the proposed algorithm decreases power consumption and processing delay as compared to the basic ToA based on triple RTTXs. Moreover, unlike the TDoA (Time Difference of Arrival) algorithm, the proposed algorithm can perform the position location with low complexity since it does not require strict synchronization between multiple beacons. Simulation results using IEEE 802.15.4a UWB channel models reveal that the proposed algorithm achieves closely comparable position location performance of the basic ToA and TDoA algorithms.

M-ary orthogonal coded/balanced ultra-wideband transmitted-reference systems in multipath

A new M-ary orthogonal coded signaling is introduced to avoid the inter-frame interference that is especially detrimental to realizing high rate ultra-wideband (UWB) transmitted-reference (TR) systems. To further increase the information rate, the inter-pulse interference by an overlap of multipath-delayed pulses is controlled by integrating the signaling and a pair of balanced matched Alters in a joint manner, so as to permit a shorter time delay between the reference and data pulses in TR systems. To evaluate an achievable information rate increase relative to conventional TR, the symbol error probability (SEP) is theoretically derived for the proposed M-ary orthogonal coded/balanced TR system, considering the realistic IEEE standard UWB channel models. In addition, we consider the issue of receiver complexity and present two alternative low- complexity receiver implementations for the proposed TR system.

On the Transceiver Types of IR-UWB Systems at Sub-Nyquist Sampling Rates

In this paper, we present a unified performance analysis for different impulse radio (IR) ultra-wideband (UWB) transceiver types employing various modulation options and operating at sub-Nyquist sampling rates. Stored reference (SR), transmitted reference (TR), and energy detector (ED) receivers are considered employing one of the binary phase shift keying (BPSK), pulse position modulation (PPM), and on-off keying (OOK) modulation types. Realistic UWB channel models (the IEEE 802.15.4a channels) and practical pulse shapes (the root-raised cosine pulse) are used to characterize the statistics of the captured energies of different transceiver types at low sampling rates. The bit error rate (BER) expressions for different transceiver/modulation types are provided explicitly in additive white Gaussian noise channels. In multipath channels, the BER expressions are conditioned on the captured energies; then, the captured energy histograms at sub-Nyquist rates are used towards a semi-analytic evaluation of the BER for different transceiver/modulation combinations. The analyses are then verified via simulations using IEEE 802.15.4a channel models. The results show that in addition to their lower implementation complexities, the TR and ED receivers may be more favorable compared to SR receivers at low sampling rates in terms of their BER characteristics as well.

A Markov Model for Indoor Ultra-wideband Channel with People Shadowing

For an indoor ultra-wideband (UWB) communication system, the line-of-sight (LOS) between the transmitter and receiver may be frequently blocked by moving people. Blocking of LOS may significantly affect the quality of service of on-going UWB communications. Based on the Angular Power Spectrum Density and the human blocking models, we build a packet-level UWB channel model considering the shadowing processes based on a Finite-state Markov Chain. The model is simple enough to be incorporated into existing network simulators like NS-2 and it can be used to facilitate protocol design and quality of service analysis for UWB based wireless personal area networks.

Evaluation of mobile ultra wideband modems in dense multipath-part 1: channel model

The WSSUS channel model has provided a useful tool for modeling random time variant linear channels in the four decades since its introduction. However, with the advent of UWB (Ultra Wideband) communications, it is necessary to replace this model which is valid for Narrowband (NB) channels. This paper develops such a replacement. The development is based upon the tapped delay line model of a linear time- variant channel, which is valid for any ratio of bandwidth to carrier frequency. For simplicity, the analysis assumes a dense multipath environment such as may be experienced in outdoor and indoor urban environments. The thrust of this study is to derive an UWB channel model for dense multipath that will allow a meaningful comparative modem performance evaluation rather than to develop a new precise characterization of UWB channels. Such a model should be useful in preparation of UWB communication standards for mobile links.

Signal-to-Interference-Plus-Noise Ratio Analysis for Direct-Sequence Ultra-Wideband Systems in Generalized Saleh–Valenzuela Channels

In this paper, exact signal-to-interference-plus-noise ratio (SINR) analysis of direct-sequence ultra-wideband (UWB) systems with Rake receiving in the presence of inter-symbol interference and multiple-access interference over a generalized Saleh-Valenzuela (GSV) channel with a generic pulse shaping function is provided. The SINR expression, for synchronized multiple-access, is first obtained without assuming random spreading. The GSV channel structure under consideration is a generalization of the Saleh-Valenzuela channel structure with generalized path-gain and path-arrival models, examples of which can include all the IEEE 802.15.3a UWB channel models and some of the IEEE 802.15.4a models. Then, by the novel treatment of renewal processes, the exact average SINR over the GSV channel statistics is obtained. Our analytical results well match computer simulations and can readily be applied to evaluate and improve the performance of UWB systems over realistic channel and interference models.

Channel Identification: Secret Sharing Using Reciprocity in Ultrawideband Channels

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> To establish a secure communications link between any two transceivers, the communicating parties require some shared secret, or key, with which to encrypt the message so that it cannot be understood by an enemy observer. Using the theory of reciprocity for antennas and electromagnetic propagation, a key distribution method is proposed that uses the ultrawideband (UWB) channel pulse response between two transceivers as a source of common randomness that is not available to enemy observers in other locations. The maximum size of a key that can be shared in this way is characterized by the mutual information between the observations of two radios, and an approximation and upper bound on mutual information is found for a general multipath channel and examples given for UWB channel models. The exchange of some information between the parties is necessary to achieve these bounds, and various information-sharing strategies are considered and their performance is simulated. A qualitative assessment of the vulnerability of such a secret sharing system to attack from a radio in a nearby location is also given. </para>

NLOS Identification and Weighted Least-Squares Localization for UWB Systems Using Multipath Channel Statistics

Non-line-of-sight (NLOS) identification and mitigation carry significant importance in wireless localization systems. In this paper, we propose a novel NLOS identification technique based on the multipath channel statistics such as the kurtosis, the mean excess delay spread, and the root-mean-square delay spread. In particular, the IEEE 802.15.4a ultrawideband channel models are used as examples and the above statistics are found to be well modeled by log-normal random variables. Subsequently, a joint likelihood ratio test is developed for line-of-sight (LOS) or NLOS identification. Three different weighted least-squares (WLSs) localization techniques that exploit the statistics of multipath components (MPCs) are analyzed. The basic idea behind the proposed WLS approaches is that smaller weights are given to the measurements which are likely to be biased (based on the MPC information), as opposed to variance-based WLS techniques in the literature. Accuracy gains with respect to the conventional least-squares algorithm are demonstrated via Monte-Carlo simulations and verified by theoretical derivations.

Parametric Modeling of Wideband and Ultrawideband Channels in Frequency Domain

This paper investigates parametric modeling of wideband and ultrawideband (UWB) wireless channels in the frequency domain. By uniform sampling of the channel frequency response (CFR), an equivalent discrete channel can be obtained. The channel impulse response (CIR) of the discretized channel can be obtained by applying inverse discrete Fourier transform to the uniformly spaced CFR samples. Both uniformly spaced CFR and CIR samples can be extended to periodic sequences with the same period. It is shown that parametric modeling in the frequency domain is possible, if and only if the uniformly spaced CFR samples satisfy the wide-sense stationary (WSS) condition that is equivalent to the uncorrelated scattering (US) condition for the discrete CIR. This new WSS-US condition is fulfilled if the underlying continuous-time wideband or UWB channel is WSSUS with independent path gains and arrival times. It is also shown that there exists an analytic relation between the power spectral density of the uniformly spaced CFR samples and the power profile of the discrete CIR that satisfies the WSS-US condition. The main goal of this paper is to demonstrate that the wideband and UWB channels can be adequately modeled by low-order autoregressive (AR) and/or AR moving average models in the frequency domain. The results on channel modeling are illustrated by simulation examples.

The Distribution of Sums of Path Gains in the IEEE 802.15.3a UWB Channel Model

When multipath arrival times and gains are specified by the IEEE 802.15.3a ultra-wideband (UWB) channel model, formulas are derived for the characteristic function of the sum of gains arriving in a given time window. These formulas are first used to determine structural properties of the corresponding distributions and densities. The formulas are then used to compute the distribution and density functions by numerically inverting the characteristic function. For small time windows, the densities of the path-gain sums are bimodal and therefore highly non-Gaussian