Showing papers on "Multipath propagation published in 2013"

Broadband Millimeter-Wave Propagation Measurements and Models Using Adaptive-Beam Antennas for Outdoor Urban Cellular Communications

Abstract: The spectrum crunch currently experienced by mobile cellular carriers makes the underutilized millimeter-wave frequency spectrum a sensible choice for next-generation cellular communications, particularly when considering the recent advances in low cost sub-terahertz/millimeter-wave complementary metal–oxide semiconductor circuitry. To date, however, little is known on how to design or deploy practical millimeter-wave cellular systems. In this paper, measurements for outdoor cellular channels at 38 GHz were made in an urban environment with a broadband (800-MHz RF passband bandwidth) sliding correlator channel sounder. Extensive angle of arrival, path loss, and multipath time delay spread measurements were conducted for steerable beam antennas of differing gains and beamwidths for a wide variety of transmitter and receiver locations. Coverage outages and the likelihood of outage with steerable antennas were also measured to determine how random receiver locations with differing antenna gains and link budgets could perform in future cellular systems. This paper provides measurements and models that may be used to design future fifth-generation millimeter-wave cellular networks and gives insight into antenna beam steering algorithms for these systems.

From RSSI to CSI: Indoor localization via channel response

Abstract: The spatial features of emitted wireless signals are the basis of location distinction and determination for wireless indoor localization. Available in mainstream wireless signal measurements, the Received Signal Strength Indicator (RSSI) has been adopted in vast indoor localization systems. However, it suffers from dramatic performance degradation in complex situations due to multipath fading and temporal dynamics.Break-through techniques resort to finer-grained wireless channel measurement than RSSI. Different from RSSI, the PHY layer power feature, channel response, is able to discriminate multipath characteristics, and thus holds the potential for the convergence of accurate and pervasive indoor localization. Channel State Information (CSI, reflecting channel response in 802.11 a/g/n) has attracted many research efforts and some pioneer works have demonstrated submeter or even centimeter-level accuracy. In this article, we survey this new trend of channel response in localization. The differences between CSI and RSSI are highlighted with respect to network layering, time resolution, frequency resolution, stability, and accessibility. Furthermore, we investigate a large body of recent works and classify them overall into three categories according to how to use CSI. For each category, we emphasize the basic principles and address future directions of research in this new and largely open area.

Dude, where's my card?: RFID positioning that works with multipath and non-line of sight

Abstract: RFIDs are emerging as a vital component of the Internet of Things. In 2012, billions of RFIDs have been deployed to locate equipment, track drugs, tag retail goods, etc. Current RFID systems, however, can only identify whether a tagged object is within radio range (which could be up to tens of meters), but cannot pinpoint its exact location. Past proposals for addressing this limitation rely on a line-of-sight model and hence perform poorly when faced with multipath effects or non-line-of-sight, which are typical in real-world deployments. This paper introduces the first fine-grained RFID positioning system that is robust to multipath and non-line-of-sight scenarios. Unlike past work, which considers multipath as detrimental, our design exploits multipath to accurately locate RFIDs. The intuition underlying our design is that nearby RFIDs experience a similar multipath environment (e.g., reflectors in the environment) and thus exhibit similar multipath profiles. We capture and extract these multipath profiles by using a synthetic aperture radar (SAR) created via antenna motion. We then adapt dynamic time warping (DTW) techniques to pinpoint a tag's location. We built a prototype of our design using USRP software radios. Results from a deployment of 200 commercial RFIDs in our university library demonstrate that the new design can locate misplaced books with a median accuracy of 11~cm.

28 GHz propagation measurements for outdoor cellular communications using steerable beam antennas in New York city

Abstract: The millimeter wave frequency spectrum offers unprecedented bandwidths for future broadband cellular networks. This paper presents the world's first empirical measurements for 28 GHz outdoor cellular propagation in New York City. Measurements were made in Manhattan for three different base station locations and 75 receiver locations over distances up to 500 meters. A 400 megachip-per-second channel sounder and directional horn antennas were used to measure propagation characteristics for future mm-wave cellular systems in urban environments. This paper presents measured path loss as a function of the transmitter - receiver separation distance, the angular distribution of received power using directional 24.5 dBi antennas, and power delay profiles observed in New York City. The measured data show that a large number of resolvable multipath components exist in both non line of sight and line of sight environments, with observed multipath excess delay spreads (20 dB) as great as 1388.4 ns and 753.5 ns, respectively. The widely diverse spatial channels observed at any particular location suggest that millimeter wave mobile communication systems with electrically steerable antennas could exploit resolvable multipath components to create viable links for cell sizes on the order of 200 m.

Avoiding multipath to revive inbuilding WiFi localization

Abstract: Despite of several years of innovative research, indoor localization is still not mainstream. Existing techniques either employ cumbersome fingerprinting, or rely upon the deployment of additional infrastructure. Towards a solution that is easier to adopt, we propose CUPID, which is free from these restrictions, yet is comparable in accuracy. While existing WiFi based solutions are highly susceptible to indoor multipath, CUPID utilizes physical layer (PHY) information to extract the signal strength and the angle of only the direct path, successfully avoiding the effect of multipath reflections. Our main observation is that natural human mobility, when combined with PHY layer information, can help in accurately estimating the angle and distance of a mobile device from an wireless access point (AP). Real-world indoor experiments using off-the-shelf wireless chipsets confirm the feasibility of CUPID. In addition, while previous approaches rely on multiple APs, CUPID is able to localize a device when only a single AP is present. When a few more APs are available, CUPID can improve the median localization error to 2.7m, which is comparable to schemes that rely on expensive fingerprinting or additional infrastructure.

28 GHz Angle of Arrival and Angle of Departure Analysis for Outdoor Cellular Communications Using Steerable Beam Antennas in New York City

Abstract: Propagation measurements at 28 GHz were conducted in outdoor urban environments in New York City using four different transmitter locations and 83 receiver locations with distances of up to 500 m. A 400 mega- chip per second channel sounder with steerable 24.5 dBi horn antennas at the transmitter and receiver was used to measure the angular distributions of received multipath power over a wide range of propagation distances and urban settings. Measurements were also made to study the small-scale fading of closely-spaced power delay profiles recorded at half-wavelength (5.35 mm) increments along a small-scale linear track (10 wavelengths, or 107 mm) at two different receiver locations. Our measurements indicate that power levels for small- scale fading do not significantly fluctuate from the mean power level at a fixed angle of arrival. We propose here a new lobe modeling technique that can be used to create a statistical channel model for lobe path loss and shadow fading, and we provide many model statistics as a function of transmitter- receiver separation distance. Our work shows that New York City is a multipath-rich environment when using highly directional steerable horn antennas, and that an average of 2.5 signal lobes exists at any receiver location, where each lobe has an average total angle spread of 40.3° and an RMS angle spread of 7.8°. This work aims to create a 28 GHz statistical spatial channel model for future 5G cellular networks.

Design and Analysis of a Multi-Carrier Differential Chaos Shift Keying Communication System

Abstract: A new Multi-Carrier Differential Chaos Shift Keying (MC-DCSK) modulation is presented in this paper. The system endeavors to provide a good trade-off between robustness, energy efficiency and high data rate, while still being simple compared to conventional multi-carrier spread spectrum systems. This system can be seen as a parallel extension of the DCSK modulation where one chaotic reference sequence is transmitted over a predefined subcarrier frequency. Multiple modulated data streams are transmitted over the remaining subcarriers. This transmitter structure increases the spectral efficiency of the conventional DCSK system and uses less energy. The receiver design makes this system easy to implement where no radio frequency (RF) delay circuit is needed to demodulate received data. Various system design parameters are discussed throughout the paper, including the number of subcarriers, the spreading factor, and the transmitted energy. Once the design is explained, the bit error rate performance of the MC-DCSK system is computed and compared to the conventional DCSK system under multipath Rayleigh fading and an additive white Gaussian noise (AWGN) channels. Simulation results confirm the advantages of this new hybrid design.

Coded time of flight cameras: sparse deconvolution to address multipath interference and recover time profiles

Abstract: Time of flight cameras produce real-time range maps at a relatively low cost using continuous wave amplitude modulation and demodulation. However, they are geared to measure range (or phase) for a single reflected bounce of light and suffer from systematic errors due to multipath interference.We re-purpose the conventional time of flight device for a new goal: to recover per-pixel sparse time profiles expressed as a sequence of impulses. With this modification, we show that we can not only address multipath interference but also enable new applications such as recovering depth of near-transparent surfaces, looking through diffusers and creating time-profile movies of sweeping light.Our key idea is to formulate the forward amplitude modulated light propagation as a convolution with custom codes, record samples by introducing a simple sequence of electronic time delays, and perform sparse deconvolution to recover sequences of Diracs that correspond to multipath returns. Applications to computer vision include ranging of near-transparent objects and subsurface imaging through diffusers. Our low cost prototype may lead to new insights regarding forward and inverse problems in light transport.

End-to-end performance of mixed RF/FSO transmission systems

Abstract: In this paper, we consider a heterogenous scenario where free-space optical (FSO) and radio-frequency (RF) technologies are deployed together as a dual-hop communication system, and we investigate the end-to-end outage performance of this so-called mixed RF/FSO system. The RF and FSO links are, respectively, modeled as Rayleigh fading (due to multipath propagation) and M-distributed fading (due to atmospheric turbulence). We derive exact closed-form expressions for the outage probability and demonstrate that the existing outage results in the literature for mixed FSO systems can be obtained as special cases of our results. The effect of pointing errors in the FSO link is further investigated.

Height Aiding, C/N 0 Weighting and Consistency Checking for GNSS NLOS and Multipath Mitigation in Urban Areas

Abstract: Multiple global navigation satellite system (GNSS) constellations can dramatically improve the signal availability in dense urban environments. However, accuracy remains a challenge because buildings block, reflect and diffract the signals. This paper investigates three different techniques for mitigating the impact of non-line-of-sight (NLOS) reception and multipath interference on position accuracy without using additional hardware, testing them using data collected at multiple sites in central London. Aiding the position solution using a terrain height database was found to have the biggest impact, improving the horizontal accuracy by 35% and the vertical accuracy by a factor of 4. An 8% improvement in horizontal accuracy was also obtained from weighting the GNSS measurements in the position solution according to the carrier-power-to-noise-density ratio (C/N0). Consistency checking using a conventional sequential elimination technique was found to degrade horizontal positioning performance by 60% because it often eliminated the wrong measurements in cases when multiple signals were affected by NLOS reception or strong multipath interference. A new consistency checking method that compares subsets of measurements performed better, but was still equally likely to improve or degrade the accuracy. This was partly because removing a poor measurement can result in adverse signal geometry, degrading the position accuracy. Based on this, several ways of improving the reliability of consistency checking are proposed.

Measurements and Analysis of Propagation Channels in High-Speed Railway Viaducts

Abstract: This paper reports (i) a set of measurements of the wireless propagation channel at 930 MHz, conducted along the "Zhengzhou-Xian" high-speed railway of China in various railway viaduct scenarios, and (ii) an analysis and modeling of the small-scale and large-scale channel parameters based on those measurements. The environment can be categorized into four cases, covering viaducts with different heights and in different suburban environments. Small values of fade depth, level crossing rates, and average fade duration are observed. Akaike's Information Criterion (AIC)-based evaluation indicates that the Ricean distribution is the best to describe small-scale amplitude fading. An analysis of the envelope autocovariance function shows that the coherence distance is less than 10 cm. The Ricean K-factor is modeled as a piecewise-linear function of distance. Moreover, a breakpoint path loss model is developed and shadow fading is investigated using the same break point as for the distance-dependent K-factor model. The Suzuki distribution is found to offer a good fit for the composite multipath/shadowing channels. We find that the viaduct height H, together with the number of surrounding scatterers, significantly affects the small- and large-scale channel parameters. These results are applicable to both normal-speed and high-speed railways, and will be useful in the modeling of railway viaduct channels and the design of railway wireless communication systems.

System and method for testing radio frequency wireless signal transceivers using wireless test signals

Abstract: A method of facilitating wireless testing of multiple radio frequency (RF) signal transceiver devices under test (DUTs). Using multiple antennas within a shielded enclosure containing the DUTs, multiple wireless RF test signals radiated to the DUTs can have their respective signal phases controlled to maximize the direct-coupled signals to their respective intended DUTs while minimizing the cross-coupled signals. Additionally, the wireless RF test signals radiated to the DUTs can have their respective signal magnitudes controlled to normalize the direct-coupled signals to their respective intended DUTs while still sufficiently reducing the cross-coupled signals. As a result, compensation is provided for the multipath signal environment within the shielded enclosure, thereby simulating wired test signal paths during wireless testing of the DUTs.

Semiblind frequency-domain timing synchronization and channel estimation for OFDM systems

Abstract: In this article, we propose unit vectors in the high dimensional Cartesian coordinate system as the preamble, and then propose a semiblind timing synchronization and channel estimation scheme for orthogonal frequency division multiplexing (OFDM) systems. Due to the lack of useful information in the time-domain, a frequency-domain timing synchronization algorithm is proposed. The proposed semiblind approach consists of three stages. In the first stage, a coarse timing offset related to the delayed timing of the path with the maximum gain in multipath fading channels is obtained. Then, a fine time adjustment algorithm is performed to find the actual delayed timing in channels. Finally, the channel response in the frequency-domain is obtained based on the final timing estimate. Although the required number of additions in the proposed algorithm is higher than those in conventional methods, the simulation results show that the proposed approach has excellent performance of timing synchronization in several channel models at signal-to-noise ratio (SNR) smaller than 6 dB. In addition, for a low-density parity-check coded single-input single-output OFDM system, our proposed approach has better bit-error-rate performance than conventional approaches for SNR varying from 3 to 8 dB.

Spectral Efficiency of Distributed MIMO Systems

Abstract: Distributed multi-input multi-output (D-MIMO) system is a promising system to greatly improve the spectral efficiency and power efficiency of the cellular system. The performance analysis of the spectral efficiency of D-MIMO system is a fundamental problem for both theoretical study and technique evaluation. In this paper, the theoretical performances of spectral efficiency for D-MIMO system and traditional collocated MIMO (C-MIMO) system are studied and compared. First, a composite D-MIMO channel including path loss, shadow fading and multipath fading is given. Conditioned on the desired user position, by using the tight bounds and central limit theory, the analytical approximations of the mean and the cumulative distribution function (CDF) of the mutual information (MI) are derived for C-MIMO and D-MIMO channels at both high signal to noise ratio (SNR) and low SNR. Assuming that the users are randomly distributed in the cell, the CDFs of the spectral efficiency are also given for the C-MIMO and D-MIMO cellular system, and the closed-form expressions for the mean spectral efficiency, mean outage spectral efficiency are derived. Finally, the theoretical comparisons between C-MIMO and D-MIMO for large number of antennas are given, and simulation results are presented which validate the analytical results.

Cancellation of power amplifier induced nonlinear self-interference in full-duplex transceivers

Abstract: Recently, full-duplex (FD) communications with simultaneous transmission and reception on the same channel has been proposed. The FD receiver, however, suffers from inevitable self-interference (SI) from the much more powerful transmit signal. Analogue radio-frequency (RF) and baseband, as well as digital baseband, cancellation techniques have been proposed for suppressing the SI, but so far most of the studies have failed to take into account the inherent nonlinearities of the transmitter and receiver front-ends. To fill this gap, this article proposes a novel digital nonlinear interference cancellation technique to mitigate the power amplifier (PA) induced nonlinear SI in a FD transceiver. The technique is based on modeling the nonlinear SI channel, which is comprised of the nonlinear PA, the linear multipath SI channel, and the RF SI canceller, with a parallel Hammerstein nonlinearity. Stemming from the modeling, and appropriate parameter estimation, the known transmit data is then processed with the developed nonlinear parallel Hammerstein structure and suppressed from the receiver path at digital baseband. The results illustrate that with a given IIP3 figure for the PA, the proposed technique enables higher transmit power to be used compared to existing linear SI cancellation methods. Alternatively, for a given maximum transmit power level, a lower-quality PA (i.e., lower IIP3) can be used.

Low Complexity GFDM Receiver Based on Sparse Frequency Domain Processing

Abstract: Generalized frequency division multiplexing (GFDM) is a multi-carrier modulation scheme. In contrast to the traditional orthogonal frequency division multiplexing (OFDM), it can benefit from transmitting multiple symbols per sub-carrier. GFDM targets block based transmission which is enabled by circular pulse shaping of the individual sub- carriers. In this paper we propose a low complexity design for demodulating GFDM signals based on a sparse representation of the pulse-shaping filter in frequency domain. The proposed scheme is compared to receiver concepts from previous work and the performance is assessed in terms of bit error rates for AWGN and Rayleigh multipath fading channels. The results show, that for high-order QAM signaling, the error performance can be significantly improved with interference cancellation at reasonable computational cost.

Overlay cognitive radio OFDM system for 4G cellular networks

Abstract: In this study, we integrate overlay cognitive radio technology into 4G cellular networks for the sharing of TV spectrum. On one hand, OFDM is a promising technique for high-speed data transmission over multipath fading channels and has been considered to be the best candidate for 4G mobile networks. On another hand, the overlay cognitive radio model makes it possible to have two concurrent transmissions in a given interference region, where conventionally only one communication takes place at a given time. We investigate different service provision scenarios and propose both time domain and frequency domain overlay cognitive radio OFDM systems for next generation cellular networks. Numerical results show our proposed schemes can achieve satisfying performance in different use cases.

Wireless communication with chaos

Abstract: The modern world fully relies on wireless communication. Because of intrinsic physical constraints of the wireless physical media (multipath, damping, and filtering), signals carrying information are strongly modified, preventing information from being transmitted with a high bit rate. We show that, though a chaotic signal is strongly modified by the wireless physical media, its Lyapunov exponents remain unaltered, suggesting that the information transmitted is not modified by the channel. For some particular chaotic signals, we have indeed proved that the dynamic description of both the transmitted and the received signals is identical and shown that the capacity of the chaos-based wireless channel is unaffected by the multipath propagation of the physical media. These physical properties of chaotic signals warrant an effective chaos-based wireless communication system.

Short-Term Fading Behavior in High-Speed Railway Cutting Scenario: Measurements, Analysis, and Statistical Models

Abstract: Cuttings are widely used in high-speed railway (HSR) transportation to ensure the flatness of rails. The special structure of cuttings results in rich reflection and scattering, and creates dense multipath components. This paper presents a series of measurements of the propagation channel at 930 MHz conducted along the “Zhengzhou-Xi'an” HSR of China, to characterize the small-scale fading behavior of rail-cutting scenarios as a function of the geometry of cuttings, including crown width and bottom width. Raw data are collected in six cuttings (five cuttings are used for developing the model, while the other one is used for validation) in rural and suburban environments. We propose a set of effective methods to statistically model the spatial/temporal variations – including fade depth (FD), level crossing rate (LCR), average fade duration (AFD), and Ricean ${K}$ -factor – as a function of the structural parameters of cuttings. Akaike's Information Criterion (AIC)-based evaluation indicates that the Ricean distribution is the best to describe small-scale fading. In addition, the rich multipath and directionality of the transmitting antennas lead to a non-monotonous dependence of the ${K}$ -factor on the distance between transmitter and receiver. The autocovariance function of the deviation of the extracted ${K}$ -factors from the proposed model is presented and the coherence length is investigated. Our results show that even though a cutting is a scenario with severe fading, a “wide” cutting (i.e., with both wide crown and bottom widths) is conducive to the reduction of the severity of fading.

A Portfolio Approach to NLOS and Multipath Mitigation in Dense Urban Areas

Abstract: Non-line-of-sight (NLOS) reception and multipath interference are major causes of poor GNSS positioning accuracy in dense urban environments. They are commonly grouped together. However, both the mechanisms by which they cause position errors and many of the techniques for mitigating those errors are quite different [1]. For example, correlation-based multipath mitigation has no effect on the errors caused by NLOS reception. University College London (UCL) has investigated the performance of a number of multipath and/or NLOS mitigation techniques in dense urban areas, including C/N0-based solution weighting [2], advanced consistency checking [3], dual-polarization NLOS detection [4] and vector tracking [5]. In this paper, we present a new multipath detection technique based on comparing the measured C/N0 on multiple frequencies and also new dual-polarization results. Meanwhile, other researchers have demonstrated NLOS detection using a panoramic camera [6, 7] or 3D city model [8, 9] and detection of NLOS and multipath using an antenna array [10]. All of these techniques bring some improvement in positioning performance in urban environments, but none of them eliminate the effects of both NLOS reception and multipath interference completely. As the different techniques are largely complementary, best performance is obtained by using several of them in combination, a portfolio approach. This paper comprises three parts. The first presents a feasibility study on a new multipath detection technique using multi-frequency C/N0 measurements. Constructive multipath interference results in an increase in the measured C/N0, whereas destructive multipath interference results in a decrease. As the phase of a reflected signal with respect to its directly received counterpart depends on the wavelength, the multipath interference may be constructive on one frequency and destructive on another. Thus, by comparing the difference in measured C/N0 between two frequencies with what would normally be expected for that signal at that elevation angle, strong multipath interference may be detected. However, the converse is not true because, depending on the path delay, the phase of the multipath interference may also be consistent across the two frequencies. Consistency across three frequencies in the presence of multipath interference is much less likely than consistency across two. Therefore, by comparing C/N0 measured across three (or more) frequencies, the chance of detection is improved substantially, noting that reliability is less critical as part of a portfolio approach to multipath detection than for a stand-alone technique. Experimental results are presented demonstrating the potential of this approach using GPS and GLONASS data collected in Central London. The second part of the paper presents the results of the first multi-constellation test of the dual-polarization NLOS detection technique pioneered at UCL [4]. This separately correlates the right hand circularly polarized (RHCP) and left hand circularly polarized (LHCP) outputs of a dual-polarization antenna and differences the resulting C/N0 measurements, producing a result that is positive for directly received signals and negative for most NLOS signals. Data was collected at six different sites in Central London and NLOS reception of both GPS and GLONASS signals was detected. Position solutions with the NLOS signals removed are compared with the corresponding all-satellite solutions. The final part of the paper addresses the portfolio approach to NLOS and multipath mitigation. Each technique is assessed qualitatively for its ease of implementation and its efficiency at detecting or directly mitigating both NLOS reception and multipath mitigation. A compatibility matrix is then presented showing which techniques may be combined without conflict. Suitable portfolios are then proposed both for professional-grade and for consumer-grade user equipment. References [1] Groves, P. D., Principles of GNSS, inertial, and multi-sensor integrated navigation systems, Second Edition, Artech House, 2013. [2] Jiang, Z., P. Groves, W. Y. Ochieng, S. Feng, C. D. Milner, and P. G. Mattos, “Multi-Constellation GNSS Multipath Mitigation Using Consistency Checking,” Proc. ION GNSS 2011. [3] Jiang, Z., and P. Groves, “GNSS NLOS and Multipath Error Mitigation using Advanced Multi-Constellation Consistency Checking with Height Aiding,” Proc. ION GNSS 2012. [4] Jiang, Z., and P. D. Groves, “NLOS GPS Signal Detection Using A Dual-Polarisation Antenna,” GPS Solutions, 2012, DOI: 10.1007/s10291-012-0305-5. [5] Hsu, L.-T., P. D. Groves, and S.-S. Jan, “Assessment of the Multipath Mitigation Effect of Vector Tracking in an Urban Environment,” Proc ION Pacific PNT, 2013. [6] Marais, J., M. Berbineau, and M. Heddebaut, “Land Mobile GNSS Availability and Multipath Evaluation Tool,” IEEE Transactions on Vehicular Technology, Vol. 54, No. 5, 2005, pp. 1697-1704. [7] Meguro, J., et al., “GPS Multipath Mitigation for Urban Area Using Omnidirectional Infrared Camera,” IEEE Transactions on Intelligent Transportation Systems, Vol. 10, No. 1, 2009, pp. 22-30. [8] Obst, M., S. Bauer, and G. Wanielik, “Urban Multipath Detection and mitigation with Dynamic 3D Maps for Reliable Land Vehicle Localization,” Proc. IEEE/ION PLANS 2012. [9] Peyraud, S., et al., “About Non-Line-Of-Sight Satellite Detection and Exclusion in a 3D Map-Aided Localization Algorithm,” Sensors, Vol. 13, 2013, pp. 829-847. [10] Keshvadi, M. H., A. Broumandan, and G. Lachapelle, “Analysis of GNSS Beamforming and Angle of Arrival Estimation in Multipath Environments," Proc ION ITM, San Diego, CA, January 2011, pp. 427-435.

Multipath congestion control in content-centric networks

Abstract: Data communication across the Internet has significantly changed under the pressure of massive content delivery. Content-Centric Networking (CCN) rethinks Internet communication paradigm around named data retrieval, in contrast with the host-to-host transport model of TCP/IP. Content retrieval is natively pull-based driven by user requests, point-to-multipoint and intrinsically coupled with the availability of network storage. By leveraging the key features of CCN transport, in this paper we propose for the first time a congestion control mechanism realizing efficient multipath communication over content-centric networks. Our proposal is based on a Remote Adaptive Active Queue Management (RAAQM) at the receiver that performs a per-route control of bottleneck queues along the paths. We analyze the stability of the proposed solution and assess its performance by means of CCN packet-level simulations under random and optimal route selection.

72 GHz millimeter wave indoor measurements for wireless and backhaul communications

Abstract: As the mobile cellular carriers are currently facing a spectrum crunch, researchers are concentrating on higher carrier frequency bands, such as E-band (71-76 GHz and 81-86 GHz) for the next generation wireless communication systems. The E-band is promising due to its large available, continuous bandwidth and robust weather resilience. In this paper, we demonstrate a spread spectrum sliding correlator channel sounder operating at a center frequency of 73.5 GHz with an 800 MHz null-to-null bandwidth. The channel sounder provides a multipath time resolution of 2.33 ns. 72 GHz millimeter wave propagation and penetration characteristics in an indoor office environment are investigated using the sliding correlator channel sounding system. Data collected and processed from the measurements shows that strong received power can be achieved from the multipath-rich indoor environment, in the presence of multiple obstructions. The data obtained from this measurement campaign may be utilized for the design of future fifth generation millimeter wave indoor cellular systems.

Pattern-Reconfigurable Planar Circular Ultra-Wideband Monopole Antenna

Abstract: A novel pattern-reconfigurable compact planar ultra-wideband monopole antenna is presented. By the incorporation of four p-i-n diode switches and two parasitic elements, the antenna's radiation patterns can be shaped to concentrate energy in specific directions while minimising the gain in other unwanted directions without significantly affecting the impedance bandwidth of the antenna. A fully functional prototype has been developed and tested. The measured results of the return loss, radiation patterns, and realised gain verify the effectiveness of the proposed antenna configuration. The antenna switches its radiation patterns between an omni-directional mode and two directional modes with opposite directions in the operating range from 3 to 6 GHz. The proposed antenna could be a suitable candidate for advanced and smart radio applications such as cognitive radio (CR) as it can enhance the radio front-end flexibility and performance by adding the benefits of pattern diversity, specifically in multipath environments.

Distributed Angle Estimation for Localization in Wireless Sensor Networks

Abstract: In this paper, we design a new distributed angle estimation method for localization in wireless sensor networks (WSNs) under multipath propagation environment. We employ a two-antenna anchor that can emit two linear chirp waves simultaneously, and propose to estimate the angle of departure (AOD) of the emitted waves at each receiving node via frequency measurement of the local received signal strength indication (RSSI) signal. An improved estimation method is further proposed where multiple parallel arrays are adopted to provide the space diversity. The proposed methods rely only on radio transceivers and do not require frequency synchronization or precise time synchronization between the transceivers. More importantly, the angle is estimated at each sensor in a completely distributed manner. The performance analysis is derived and simulations are presented to corroborate the proposed studies.

SPUMIC: Simultaneous phase unwrapping and multipath interference cancellation in time-of-flight cameras using spectral methods

Abstract: We propose a framework for simultaneous phase unwrapping and multipath interference cancellation (SPUMIC) in homodyne time-of-flight (ToF) cameras. Our multi-frequency acquisition framework is based on parametric modeling of the multipath interference phenomena. We use robust spectral estimation methods with low computational complexity to detect and estimate multipath parameters. Using simulations and analysis we demonstrate that our proposed solution is implementable in real-time on existing ToF cameras without requiring any hardware modifications.

MPRTP: multipath considerations for real-time media

Abstract: The Internet infrastructure often supports multiple routes between two communicating hosts and, today, especially mobile hosts usually offer multiple network interfaces, so that disjoint paths between the hosts can be constructed. Having a number of (partly or fully) disjoint paths available may allow applications to distribute their traffic, aggregate capacity of different paths, choose the most suitable subset of paths, and support failover if a path fails. Exploiting multipath characteristics has been explored for TCP, but the requirements for real-time traffic differs notably. In this paper, we devise a multipath communication model for Real-time Transport Protocol (RTP); present minimal set of required protocol extensions; develop algorithms for scheduling RTP traffic across multiple paths at the sender and a corresponding de-jittering algorithm at the receiver side; and evaluate our proposal in varying scenarios using media traffic across different emulated mobile access network setups.

Indoor Localization Using FM Signals

Abstract: The major challenge for accurate fingerprint-based indoor localization is the design of robust and discriminative wireless signatures. Even though WiFi received signal strength indicator (RSSI) signatures are widely available indoors, they vary significantly over time and are susceptible to human presence, multipath, and fading due to the high operating frequency. To overcome these limitations, we propose to use FM broadcast radio signals for robust indoor fingerprinting. Because of the lower frequency, FM signals are less susceptible to human presence, multipath, and fading, they exhibit exceptional indoor penetration, and according to our experimental study they vary less over time when compared to WiFi signals. In this paper, we demonstrate through a detailed experimental study in three different buildings across the US, that FM radio signal RSSI values can be used to achieve room-level indoor localization with similar or better accuracy to the one achieved by WiFi signals. Furthermore, we propose to use additional signal quality indicators at the physical layer (i.e., SNR, multipath, etc.) to augment the wireless signature, and show that localization accuracy can be further improved by more than 5 percent. More importantly, we experimentally demonstrate that the localization errors of FM and WiFi signals are independent. When FM and WiFi signals are combined to generate wireless fingerprints, the localization accuracy increases as much as 83 percent (when accounting for wireless signal temporal variations) compared to when WiFi RSSI only is used as a signature.

Maximum-Likelihood Direct Position Estimation in Dense Multipath

Abstract: The problem of localizing a transmitting source by observing the signal at several base stations (BSs) is considered. In this paper, a direct position estimation (DPE) algorithm for a dense multipath channel is formulated and analyzed, based on a Gaussian approximation. The algorithm provides robust and accurate position estimation in a multipath environment, which is a challenging problem, particularly when the signal-to-noise ratio (SNR) is low and when the multipath is dense. It is shown that the DPE is superior to the common indirect approach. In the indirect approach, the time of arrival (TOA) is estimated independently at each BS, whereas in the DPE, all the received signals from all BSs are processed jointly. We show that the proposed algorithm approximates the maximum-likelihood (ML) solution. We treat TOA based on synchronized source and receivers and the differential TOA (DTOA) where only the receivers are synchronized. Analytic results for the performance of the algorithm are provided. Finally, simulations demonstrate the advantage of DPE over the indirect method at low SNR for various multipath channel models and that the analysis closely approximates the simulation results.

Detection of movable objects

Abstract: Systems and methods for sensing targets on an opposite side of a wall are disclosed. In some aspects, the techniques include providing an indication to a user that portions of reflected radar signals were blocked by radiofrequency-blocking material at the wall. In some aspects, the techniques include identifying candidate targets as multipath echoes or motion-induced errors based on a correlation map.

Indoor Localization of Passive UHF RFID Tags Based on Phase-of-Arrival Evaluation

Abstract: This paper introduces a two-dimensional localization system for passive UHF RFID transponders based on phase-of-arrival evaluation of the backscattered tag signal. A multiple-channel system, where alternately one path is configured as a transmitter and the remaining paths work as receivers, is used to permit the position estimation. To improve localization accuracy and reduce disturbances caused by multipath propagation, a frequency-stepped continuous-waveform approach is employed. To achieve proof of concept, a local position measurement system demonstrator comprising an RFID reader, passive EPC Gen 2 RFID tags, several transceivers, baseband hardware, and signal processing was used for measurements. The results show excellent localization accuracy, even in an indoor environment.