Interference control is crucial in cognitive radio networks and the existing related works focus on quasi-static channels. The expansion of wireless services and applications in everyday life has necessitated support of higher mobility, as evident from the emerging wireless standards. This results in time-varying fading channels within a transmission frame for which the interference power control schemes and power allocation strategies have not been developed yet. This paper proposes several interference control and power allocation strategies with different criteria for underlay cognitive radios in time-varying frequency-selective fading channels and extend the transmission schemes to multiple secondary systems. The transmission schemes are evaluated in terms of interference statistics at the primary receiver and the ergodic capacity of the secondary user link. Simulation results over the wide Doppler range show how the proposed schemes with different criteria shape the interference at the primary receiver and the capacity of the secondary user. The results also illustrate better interference control capability of the proposed approaches over the existing scheme.

LTE-Advanced systems have adopted the concept of Carrier Aggregation (CA) to meet the data rate requirements of IMT-Advanced systems. The CA approach opens up several new implementation challenges as well as opportunities for further performance improvement. Existing works on CA focus on implementation issues, but exploitation of CA-specific features for performance improvement has not been addressed yet. In this paper, we fill this gap and investigate the enhanced frequency diversity exploitation in CA based systems. New interleaving schemes for both downlink OFDMA and uplink SC-FDMA of LTE-Advanced systems are proposed to capture CA-specific enhanced frequency diversity with simple implementation. The proposed schemes also provide full backward compatibility with the LTE system. Performance evaluation via simulation in a simplified LTE system environment corroborates that the proposed approach provides performance advantages in both downlink and uplink.

One of the key technologies introduced in LTE-Advanced in order to increase the capacity is carrier aggregation (CA). Based on this scheme, continuous and non-continuous sub-bands are aggregated in order to achieve larger bandwidth. Such a new technique introduces various challenges in both system aspect and the modeling of the wireless channel. In particular, the traditional channel models that was proposed for current LTE networks may not be appropriate for the LTE-Advanced systems that adopt CA scheme. This is mainly due to the fact that small-scale variations of the channel may change depending on the channel bandwidth. In this paper, we studied and analyzed the bandwidth dependency of the wireless channel based on indoor channel measurements performed at Stanford University. The measurement were conducted at 2.45 GHz center frequency and covered a bandwidth of up to 70 MHz. Here, both large-scale and small-scale channel properties are investigated. In particular, the bandwidth-dependent fading parameters such as K-factor, fade depth, number of paths and delay spread are extracted for both fixed and nomadic receivers. Based on this, we proposed interpolated models for these fading parameters, which can be used to improve the accuracy of simulation for carrier aggregated systems.

Next generation wireless systems require much higher data rate supports and hence larger bandwidths than the existing systems. Due to the compatibility requirement with the existing legacy systems and the constraints on the availability of contiguous spectrum, bandwidth (or carrier) aggregation has recently emerged as a practical means for supporting high data rate requirement of next-generation systems. A practical issue associated with the bandwidth or carrier aggregation is the significant increase of the peak-to-average power ratio (PAPR) of the time-domain signal. This paper proposes a low-complexity PAPR reduction method for bandwidth aggregated systems with orthogonal frequency division multiplexing / multiple-access (OFDM/OFDMA) or single-carrier frequency division multiple access (SC-FDMA). The proposed approach adopts the existing selective mapping concept, but with some modifications for substantially reducing complexity and signaling overhead, while adapting to carrier-aggregated systems. Performance evaluation under 3GPP LTE-Advanced environment shows PAPR reduction advantage of the proposed method while not requiring any signaling overhead.

We propose multiple antenna transmission methods for fast fading channel conditions. Proposed methods allocate alternative multiple antenna transmission modes depending on the SNR, modulation order and Doppler frequency to increase reliability, i.e., decrease bit-error-rate (BER). A major difference of our approach from previous works is to allow different transmission modes during a single frame by considering the channel variations within the frame for high mobility scenarios. First method effectively makes use of available channel knowledge by allocating beamforming (BF) as long as channel knowledge is not outdated and switches to space frequency block coding (SFBC) afterwards. Approximate BER expressions for BF and SFBC that are functions of SNR, modulation order, Doppler frequency and initial channel knowledge are derived to be used as a decision metric for mode allocation throughout the frame. Second method adapts rate and transmission mode across symbols in a frame by considering that average channel power is monotonically decreasing as a function of time within the frame when multiuser diversity is exploited. First method performs as good as the better of BF and SFBC over all SNR values. Second method provides additional performance gain over the first method due to more efficient use of better channel conditions.

Diversity exploitation is a proven efficient means for addressing detrimental effects of wireless channel fadings. User channelization, where the frequency and time resources are structured into several user channels, can substantially help to capture the diversity, but it has not been well investigated. In this paper, we develop theoretical formulation of optimal resource structures under different performance metrics and then analyze them in frequency-selective time-varying channels. We propose a simplified system model which maintains the main features, and based on which, we develop a new practical approach of user channelization or user resource structuring which captures better diversity for OFDMA systems in multiuser time-varying frequency-selective fading channels. In contrast to the existing user resource structures where relative locations of the resources in the time-frequency grid remain the same throughout the transmission frame, the proposed resource structures evolve within the frame to enjoy better diversity gain. Example designs of the proposed evolving structures are presented from the 3GPP LTE perspective. Simulations done under LTE system environments validate that the proposed practical approach can obtain a near-optimal structure design, and provide significant performance advantage over the existing structures at the mobile speeds ranging from 3 km/h to 350 km/h.

Gaussian frequency shift keying (GFSK) is a promising digital modulation scheme. The design of simple and high-performance receivers for GFSK systems is a challenging task. In this letter, we develop an optimized differential GFSK demodulator and investigate the phase wrapping issue in its implementation. Simulation results show bit-error-rate (BER) performance improvement in comparison with conventional differential demodulators in both AWGN and flat fading channels. We also compare our proposed demodulator with other existing alternatives in terms of BER performance.

The concept of wellness mobile by incorporating continuous monitoring of biometrics on wireless handheld devices has been attracting a lot of attention from both industrialists and academia. In this paper, we propose a probabilistic inference algorithm for the wellness mobile applications by monitoring fluctuations in biometric(s) in order to provide effective inference about human wellness in an efficient and timely manner. Wellness state recognition can be achieved through dynamic probabilistic inference from the sensory data using multiple-modality sensors. Since the overriding goal is to embed this feature into a cellular phone, the proposed algorithm cannot be computationally complex and rely on too many biometrics. Here, the proposed algorithm relies on a single biometric, in which the dynamic probabilistic inference depends on a temporal window of observations of the biometric. Specifically, we monitor skin temperature variations during different activities in order to track the variations in human stress. The algorithm can be generalized by a temporal Bayesian network (TBN) framework. The simplicity of the technique makes it a favorable candidate for implementation on cellular phones with existing biometric sensors that are available in most smart phones today.

The concept of wellness mobile is a novel mobile service wherein wireless handheld devices such as cell phones are equipped with a wellness monitoring application, thereby enabling real-time self-wellness monitoring by the cell phone user. The wellness mobile will provide a safe and protective environment for an increasing cell phone user-population to help combat anti-wellness factors such as stress, fatigue, and illness. However, this emerging technology is still in its infancy, and developing quantifiable measures of wellness and designing intelligent monitoring systems is quite challenging. This paper reviews the recent trends and challenges facing this maturing revolutionary mobile application.

As an alternative to the transmitted reference (TR-) ultra-wideband (UWB), the dual-carrier frequency shifted reference (FSR-) UWB and its high-rate multi-carrier counterparts have been recently studied. In this paper, we consider a lowrate multi-carrier differential modulation and its low-complexity receiver designs. We prove that such a multi-carrier system actually results in a pulse position modulation, where the peak of the transmitted waveform changes location according to the value of the data symbol. Based on this discovery, we develop a simple energy detector by detecting the pulse position in time domain. In addition, the multi-carrier nature of this modulation also enables a differential demodulator in frequency domain. We derived the analytical performance for this receiver. Simulations are carried out to evaluate the performance of these time- and frequency-domain low-complexity receivers.

The concept of "wellness mobile" is one wherein wireless handheld devices such as cell phones are equipped with "wellness monitoring," thereby enabling real-time self-wellness monitoring by the cell phone user. However, this new technology is still in its infancy, and developing quantifiable measures of wellness and designing intelligent monitoring systems is quite challenging. The overriding purpose of this paper is to propose a simple wellness monitoring algorithm. The novel algorithm iteratively computes and tracks the variations in clusters of biometric measurements aiding in effective wellness management. Stress is a key indicator of wellness in human beings, and is widely regarded as a prime contributor to performance degradation and errors during various human activities. The proposed algorithm tracks the deviations in clusters of skin temperatures measurements during different activities to infer the stress states in humans. The advantage is that this simple algorithm can be implemented on handheld devices by deploying existing biometric sensors that are available in most smart phones today. This will provide cellular phones users an application to monitor their stress states easily and consistently in a non-invasive way because a stressed-out lifestyle is rarely a healthy one.

Remote health monitoring by exploiting wireless communications technologies is an emerging area receiving increasing interests from academia, research labs and industry. This issue has also been brought up in the standardization process of IEEE 802.15 Task Group 6 Wireless Body Area Networks (WBAN). The challenge is to find the appropriate combination of medical data processing techniques and the wireless technology in order to meet the particularly stringent error, latency and power consumption requirements of healthcare applications. In this paper, we present the results of a case study on wireless electrocardiogram (ECG) monitoring over Bluetooth. Based on the special considerations of (processing and transmission) power consumption at wireless ECG sensors, we first propose a low complexity ECG compression method. Comparisons with existing approaches confirm the superior performance of our method. We then study the data reconstruction performance at the Bluetooth receiver and find that: i) the uncompressed ECG data transmission is not necessarily better than the compressed transmission; and ii) there exists an optimum ECG data compression ratio for the wireless link.

This paper describes an evolution and standardization trends of the wireless channel modeling activities towards IMT-Advanced. In particular, the new developed and standardized ITU-R IMT-Advanced multiple-input-multiple-output (MIMO) Channel Model (IMT-Adv MCM) is detailed. The IMT-Adv MCM is compared with the well-known the 3GPP/3GPP2 Spatial Channel Model (SCM), and their main similarities and differences are pointed out. The performance of MIMO systems is greatly influenced by the spatial-temporal correlation properties of the underlying MIMO channels. Here, we investigate the spatial-temporal correlation characteristics of the 3GPP/3GPP2 SCM and the IMT-Adv MCM in term of their spatial multiplexing and spatial diversity gains. The main goals of this paper are to summarize the current state of the art, as well as to point out the gaps in the wireless channel modeling works, and thus hopefully to stimulate research in these areas.

For traditional relaying schemes in cellular networks, the relay stations (RSs) are typically designed for helping either out-of-cell mobile stations (MSs) or intra-cell MSs, depending on whether there exists a direct link between the base station (BS) and MS. In this paper, an uplink (UL) cooperative relaying scheme is proposed, which enables the RSs designed for out-of-cell MSs to help UL communications of intra-cell MSs. A message exchange protocol is provided for the relaying scheme to allow practical network implementations. In particular, two important issues are addressed: efficiency and fairness. For the efficiency issue, a practical power allocation algorithm is proposed for power-efficient cooperation. For the fairness issue, a reward scheme is proposed so that the helping RSs will be compensated.

It is a significant challenge to support high data rate services at high mobile speeds. In this paper, an efficient diversity-exploiting user resource structure, namely evolving- type resource structure, for fast time-varying frequency-selective fading channel environments is designed. This newly proposed resource structure enjoys the advantages of both band-type and interleaved-type structures and avoids their disadvantages by exploiting both the multiuser diversity and the frequency diversity under fast time-varying channels. Simulation results corroborate the performance improvement of the new resource structure over the existing ones under various mobility scenarios.

In this paper, we propose new ranging signal designs for time-division duplexing multiple input multiple output (MIMO) orthogonal frequency division multiple access (OFDMA) systems. Exploiting the channel knowledge from the downlink channel together with initial power control, we develop three ranging transmission schemes which provide multiuser and multi-antenna diversity gains and significant power saving for the subscriber stations. The advantages of the proposed approach over existing methods in terms of ranging performance, energy saving, and complexity saving are illustrated by analytical and simulation results.

In this paper, a spectrum sharing scheme that will coordinate among different co-existing cellular operators competing for the same spectrum band is proposed. Based on this scheme, the cell of an operator can be divided into several sub-regions, and mobile stations (MSs) inside each sub-region form one subset. The whole frequency band assigned to a cell is partitioned into slots dedicated to the subsets based on the quality of service (QoS) demand. When interference from other operators is detected, the victim operator can switch the frequency of the interfered MSs with the MSs in the safe region, and/or switch to the reserved band. In this way, the inter-operator interference (IOI) can be reduced. From the simulation results, it is shown that with the proposed protocol, the total power consumption of both operators can be reduced significantly. Furthermore, it has been demonstrated that in order to reduce the IOI in a high-density area, the operator should reserve more bandwidth for potential frequency-switching.

In cellular networks, a mobile station (MS) may be located in the coverage hole or out of the coverage of the base station (BS). In such a scenario, one or more relay stations (RSs) can be used to facilitate the transmission. Here, a threshold- based opportunistic cooperative ARQ transmission scheme is proposed. Based on this scheme, the transmission between the BS and the MS can be separated into two parts: firstly, the transmission between BS and RSs (BS-RSs link) and secondly, the transmission between RSs and MS (RSs-MS link). The proposed scheme is different from the conventional ACK/NACK used for unicast transmission, in which two new types of ARQ messages are introduced for multicast transmission, namely, the relay-associated ACK/NACK (i.e., R-ACK/R-NACK) and the cooperative ACK/NACK (i.e., C-ACK/C-NACK), for BS-RSs link and RSs-MS link, respectively. A pre-defined threshold is applied to evaluate the reliability of the BS-RSs link. If the number of reliable RSs is larger than the threshold value, the reliable RSs will transmit the packet to the MS in a cooperative manner. Since reliable transmission exists in the BS-RSs link, the BS will release the packet and further transmission of this packet occurs only between reliable RSs and the MS. Therefore, the proposed scheme can reduce the latency of cellular networks and the processing burden on the BS as well as achieve higher throughput as shown in the performance analysis and simulation results.

In this paper, we propose a simple model-based time-of-arrival (TOA) estimation technique for multi-band orthogonal frequency division multiplexing (MB-OFDM) signals based on the ECMA-368 standard [1]. The proposed technique does not need oversampling at the receiver. The key idea is to minimize the energy leakage from the first channel path due to mis-sampling. We use realistic channel models and assume that no channel statistical information is known at the receiver. In our approach, the multi-band signals are coherently combined in order to improve the resolution of the TOA estimation. We compare the performance of the proposed scheme with the well-known maximum-likelihood based algorithm, namely, space-alternating generalized expectation-maximization (SAGE). Simulations based on the ECMA-368 standard parameters in both IEEE 802.15.3a and IEEE 802.15.4a standard channel models show that our approach outperforms the SAGE algorithm by avoiding the local maxima. Furthermore, we have also shown that our approach can achieve a root mean square error of TOA estimation much smaller than the receiver sampling interval and it is robust to the narrowband interference.

In this paper, we compare the downlink capacity and throughput between the variable spreading factor-orthogonal frequency and code division multiple access (VSF-OFCDMA) with one-cell frequency reuse, and the orthogonal frequency division multiple access (OFDMA) with conventional three-cell frequency reuse. Since the multiuser diversity gain in OFDMA systems can be achieved by approximately designing its access schemes, while it is non-trivial for the VSF-OFCDMA systems, the effect of both access schemes on the link capacity are investigated. Our simulation results reveal that although the multiuser diversity gain achieved by OFDMA systems can compensate the loss of low frequency reuse at low to mid range of signal-to-interference-plus-noise ratio (SINR) values, the achievable throughput of VSF-OFCDMA systems is much higher than the OFDMA systems. Furthermore, the impact of user’s location on the inter-cell-interference is also reported.

The need for accurate positioning has gained significant interest recently, especially in cluttered environments where signals from satellite navigation systems are not reliable. Positioning systems based on ultrawide bandwidth (UWB) technology have been considered for these environments because UWB signals are able to resolve multipath and penetrate obstacles. These systems usually obtain range measurements from time-of-arrival (TOA) estimation of the first path, which can be a challenge in dense multipath environments. In this paper, we analyze and compare the performance of matched filter (MF) and energy detector (ED) TOA estimators based on thresholding in UWB dense multipath channels. The main advantage of threshold-based estimators is that they have the potential for complete analog implementation and hence they are particularly attractive for applications that require low cost battery-powered devices. Closed-form expressions for the estimator bias and mean square error (MSE) are derived as a function of the signal- to-noise ratio. A comparison with results obtained from Monte Carlo simulation confirms the validity of our analytical approach. This analysis enables us to determine the threshold value that minimizes the MSE, a critical parameter for optimal estimator design. A simple criteria to determine the threshold value is also presented. It is shown that the estimation accuracy is mainly affected by the ambiguity in the selection of the correct peak at the output of the MF or ED, caused by the fading characteristics of the first path. We also evaluate the performance loss of ED estimators with respect to MF estimators. Finally, results based on experimental measurements in an indoor residential environment are presented in order to compare the performance of TOA estimators in realistic environments.

In this paper, a novel joint time-of-arrival (TOA) estimation and localization technique for ultra-wideband (UWB) sensor network applications is proposed. To our best knowledge, most works reported in the literature set the threshold for a TOA estimator based on the parameters of the received signal only. In this work, we use the residual localization error as a metric to accurately choose the threshold values. A sub-optimal version of the proposed algorithm with lower computational complexity is also discussed and the improvements are demonstrated using Monte-Carlo simulations based on the IEEE 802.15.4a channel models.

In this paper, we analyze the localization accuracy of a linear least-squares technique both theoretically and via simulations. Closed-form expressions for the mean square localization errors are derived both for line-of-sight (LOS) and non-line-of-sight (NLOS) scenarios and compared with the Cramer-Rao lower bound (CRLB). Analysis reveals that the localization error tends to increase as the mobile terminal moves away from the reference base-station.

In this paper, the authors analyze the effects of system bandwidth, transmitter-receiver (TX-RX) separation distance and line-of-sight (LOS) blockage on the ranging error in realistic ultra-wideband (UWB) channels. Data collected from extensive UWB indoor propagation channel measurements conducted in various types of apartments with bandwidth of 7 GHz are used to study the above effects. Here, a threshold-based time-of-arrival (ToA) estimator is employed to estimate the ToA of the first arriving path. An optimum threshold value is set for each measurement data set according to the channel operating conditions by adapting the thresholding technique proposed in Dardari and Win, 2006, Analysis of the measurement results show that the ranging error is independent of the TX-RX separation distance. However, the presence of LOS blockage increases the ranging error due to the positive bias introduce by different materials that block the LOS path. We then develop a model to quantify the effect of bandwidth on the ranging error due to multipath dispersion, which is found to be well-modeled by an exponential function.

Non-line-of-sight (NLOS) identification and mitigation carries significant importance in wireless positioning systems. In this paper, the authors 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 LOS/NLOS identification. Simulation results show that correct identification can be achieved with over 90% of the realizations for most channel models. A weighted least squares localization algorithm is also developed using the NLOS information, and accuracy gains with respect to a conventional least squares algorithm are demonstrated via Monte-Carlo simulations.

In this paper, the performance of the non-coherent and the differential-coherent ultra-wideband direct chaotic communication (UWB-DCC) systems are evaluated. Both of these systems are proposed for the low-rate wireless personal area applications. Based on these systems, a 2 GHz wide chaotic signal is directly generated into the lower band of the UWB spectrum i.e. 3.1-5.1 GHz. The information component is modulated by the chaotic signal based on either the chaotic-on-off keying or the differential-chaos-shift-keying modulation schemes. At the receiver, for the non-coherent scheme, a simple envelope detector is used as an energy collector. While for the differential-coherent scheme, a delay line and an integrator are required. Various system design parameters and tradeoffs are discussed in the paper in order to meet the low complexity, low power consumption and low cost requirements while still compliant with the FCC UWB regulation. An overview of the IEEE 802.15.4a standardized UWB channel models used for system simulations is given. Additionally, the system performance in both AWGN channel and various types of multipath channels are provided in order to further demonstrate the capability and to compare the two proposed schemes

This paper describes a comprehensive statistical model for UWB propagation channels that is valid for a frequency range from 3-10 GHz. It is based on measurements and simulations in the following environments: residential indoor, office indoor, built-up outdoor, industrial indoor, farm environments, and body area networks. The model is independent of the used antennas. It includes the frequency dependence of the pathloss, as well as several generalizations of the Saleh-Valenzuela model, like mixed Poisson times of arrival and delay dependent cluster decay constants. The model can thus be used for realistic performance assessment of UWB systems. It was accepted by the IEEE 802.15.4a working group (WG) as standard model for evaluation of UWB system proposals

In this paper, a statistical-based ultra-wideband (UWB) indoor channel model which incorporates the clustering of multipath components (MPCs) is proposed. The model is derived based on measurement data collected in the frequency band of 3-10 GHz in various types of high-rise apartments under different propagation scenarios. The aim here is to investigate in more detail the clustering of MPCs phenomenon. The description of clustering observed within the channel relies on two classes of parameters, namely, inter-cluster and intra-cluster parameters which characterize the cluster and MPC, respectively. All parameters are described by a set of empirical probability density functions derived from the measured data such as the distribution of clusters and MPCs, clusters and MPCs arrivals. In addition, the measurement procedure and data analysis techniques are also discussed. This model is suitable for performance analysis of WPAN systems that employ UWB technology e.g. IEEE 802.15.3a and IEEE 802.15.4a.

In this paper, a ultra wideband direct chaotic communications technology is proposed for the low-rate wireless personal area network applications. Based on this system, a 2 GHz wide chaotic signal is directly generated into the lower band of the UWB spectrum i.e. 3.1-5.1 GHz. The information component is modulated by the chaotic signal based on the differential chaos shift keying modulation scheme. At the receiver, a correlator based receiver is used to demodulate the received signal. Various system design parameters are discussed in the paper and the tradeoffs between these parameters are highlighted. These issues include band plan, PHY service access point payload bit rates, scalability, power consumptions and link budget for various operating conditions are also addressed. Additionally, the system performance in both AWGN channel and multipath channel are provided in order to further demonstrate the capability of the proposed system.

The paper presents a statistical characterization of an ultra-wideband (UWB) indoor propagation channel based on measurements conducted in various types of high-rise apartments in several cities in Korea. Measurements were carried out in the frequency band of 3-10 GHz. Various communication links were considered including both line-of-sight (LOS) and non-LOS (NLOS) scenarios which cover within-the-room and room-to-room propagation. The measurement procedure allows us to characterize both the small-scale and the large-scale statistics of the channel. The aim is to study in more detail the behavior of the UWB propagation channel and to provide more of the measurement data required for the standardization activities in the IEEE 802.15.4a channel modeling subgroup. Channel characteristics examined include the distance and frequency dependency of path loss, shadowing fading statistics and multipath temporal-domain parameter statistics, such as the mean excess delay, RMS delay spread and the number of dominant paths.

A novel stochastic wideband dynamic spatio-temporal indoor channel model which incorporates both the spatial and temporal domain properties as well as the dynamic evolution of paths when the mobile moves is proposed based on the concept of a Markov process. The derived model is based on dynamic measurement data collected at a carrier frequency of 5.2 GHz in typical indoor environments. Multipath components are estimated using the super-resolution frequency domain space-alternating generalized expectation maximization algorithm prior to identification of path "birth" and "death" using a new data analysis method. Analysis shows that multiple births and deaths are possible at any instant of time. Furthermore, correlation exists between the number of births and deaths. Thus, an M-step 4-state Markov channel model (MCM) is proposed in order to account for these two effects. The spatio-temporal variations of paths within their lifespans are taken into consideration by the spatio-temporal vector which was found to be well modeled by a Gaussian probability density function while the power variation can be modeled by a simple low-pass filter. In addition, the methodology used to extract the MCM parameters from the measurement data is also presented. Due to the distinction in the birth-death statistics, the model is generalized through segmentation of the measurement runs and can be completely parameterized by several sets of Markov parameters associated with the type of environment and scenario under consideration. The implementation of the model is also detailed and, finally, the model is evaluated by comparing key statistics of the simulation results with the measurement results.

Abstract This paper presents a statistical characterization of an ultra wideband (UWB) indoor propagation channel based on measurements conducted in various types of high‐rise apartments in several cities of Korea. Measurements were carried out in the frequency band of 3–10 GHz. Various communication links were considered including both line‐of‐sight (LOS) and non‐LOS (NLOS) scenarios, which covered within‐the‐room and room‐to‐room propagations. The measurement procedure allows us to characterize both the large‐scale and the small‐scale statistics of the channel. The aim here is to study in more detail the statistical characteristics of the UWB propagation channel and to provide insight for future statistical channel modeling work. Channel characteristics examined include the distance and frequency dependency of path loss, shadowing fading statistics, and multipath temporal‐domain parameter statistics such as the mean excess delay, RMS delay spread, and the number of dominant paths. Copyright © 2005 John Wiley & Sons, Ltd.

A novel stochastic wideband dynamic directional indoor channel model which incorporates both the spatial and temporal domain properties as well as the dynamic evolution of paths when the mobile moves is proposed based on the concept of a Markov process. The derived model is based on dynamic measurement data collected at a carrier frequency of 5.2 GHz in several typical indoor environments. Analysis shows that multiple births and deaths are possible at any instant of time. Furthermore, correlation exists between the number of births and deaths. Thus, an M-step, 4-state Markov channel model is proposed in order to account for these two effects. The spatio-temporal variations of paths within their lifespan are taken into consideration by the spatio-temporal vector which was found to be well-modeled by a Gaussian probability density function while the power variation can be modeled by a simple low pass filter. The implementation of the model is detailed and finally, the model validity is evaluated by comparing key statistics of the simulation results with the measurement results.

In this paper, the spatial and temporal dispersion and correlation properties of a wideband dynamic directional indoor channel at 5.2 GHz are presented based on extensive measurement campaigns in four different environments under various propagation scenarios. Channel spatio-temporal dispersions are assessed in terms of the rms delay spread (DS) and rms azimuth spread (AS), respectively, while the correlation properties are determined by the spatio-temporal correlation coefficient. A strong correlation is observed with the presence of the line-of sight (LOS) path but degraded when the LOS is obstructed. The variations of the spatio-temporal dispersions with mobility are also investigated where higher values of spatio-temporal dispersions were found when the transmitter and receiver separation increased particularly in a more cluttered environment. The average values of the rms DS and rms AS for all investigated environments and scenarios are also given. These parameters can be used as empirical values for the 5 GHz band WLAN systems.

In this paper, a new statistical wideband indoor channel model which incorporates both the clustering of multipath components (MPCs) and the correlation between the spatial and temporal domains is proposed. The model is derived based on measurement data collected at a carrier frequency of 5.2 GHz in three different indoor scenarios and is suitable for performance analysis of HIPERLAN/2 and IEEE 802.11a systems that employ smart antenna architectures. MPC parameters are estimated using the super-resolution frequency domain space-alternating generalized expectation maximization (FD-SAGE) algorithm and clusters are identified in the spatio-temporal domain by a nonparametric density estimation procedure. The description of the clustering observed within the channel relies on two classes of parameters, namely, intercluster and intracluster parameters which characterize the cluster and MPC, respectively. All parameters are described by a set of empirical probability density functions (pdfs) derived from the measured data. The correlation properties are incorporated in two joint pdfs for cluster and MPC positions, respectively. The clustering effect also gives rise to two classes of channel power density spectra (PDS)-intercluster and intracluster PDS-which are shown to exhibit exponential and Laplacian functions in the delay and angular domains, respectively. Finally, the model validity is confirmed by comparison with two existing models reported in the literature.

In this paper, the serial interference cancellation (SIC) technique and the frequency domain SAGE (FD-SAGE) algorithm are jointly used to detect and estimate the radio channel parameters of interest. The implementation of the SAGE algorithm in the frequency domain is novel. Furthermore, the parallel interference cancellation (PIC) technique in the standard SAGE algorithm is replaced by the SIC technique. The SIC technique demonstrates more stable performance especially in a multipath rich environment. The two-dimensional (2-D) FD-SAGE algorithm and the SIC technique are introduced and their performance demonstrated by using real indoor channel measurement data to jointly estimate the number of multipath components (MPCs), their time-of-arrivals (TOAs), angle-of-arrivals (AOAs) and complex amplitudes. Their performance is evaluated and compared using synthetic data and results using 2-D unitary ESPRIT (another form of super-resolution algorithm).