Vol. 64, n° 9-10, September-October 2009
Content available on Springerlink
Gérard Lachapelle, University of Calgary, Canada
Nel Samama, Télécom SudParis, France
Masato Takahashi, NICT, Tokyo, Japan
Gérard Lachapelle, Nel Samama, Masato Takahashi
A non-coherent architecture for GNSS digital tracking loops
Daniele Borio · Gérard Lachapelle
University of Calgary, 2500 University Dr NW, Calgary, Alberta T2N 1N4 Canada
Abstract In this paper, a new, noncoherent architecture for global navigation satellite system tracking loops is proposed and analyzed. A noncoherent phase discriminator, able to extend the integration time beyond the bit duration, is derived from the maximum likelihood principle and integrated into a Costas loop. The discriminator is noncoherent in the sense that the bit information is removed by using a nonlinear operation. By jointly using such a discriminator and noncoherent integrations at the delay lock loop level, a fully noncoherent architecture, able to operate at low carrier-power-to-noise density ratio (C/N0), is obtained. The algorithms proposed have been tested by means of live GPS data and compared with existing methodologies, resulting in an effective solution for extending the total integration time.
Keywords Coherent integration · Global navigation satellite system · GNSS · Long integration · Loop discriminators · Noncoherent integration · Tracking loops · Weak signals
Modelling of ionospheric high-order errors for new generation GNSS
Rolland Fleury1 Mercedes Clemente1 Françoise Carvalho2 Patrick Lassudrie-Duchesne1
1 Institut TELECOM, TELECOM Bretagne, France
2 Centre National d’Etudes Spatiales (CNES), Toulouse, France
Abstract In dual frequency Global Positioning System receivers, the ionospheric propagation delays are commonly estimated and corrected using the “ionosphere free” combinations of pseudo-range observables. With this method, the ionospheric delay is estimated at the firstorder proportional to the inverse of the frequency square. However, higher-order terms exist that may be taken into account when precise corrections are required. The secondorder term results from the influence of the geomagnetic field on the ionospheric propagation of the signals. The third-order term includes the refractive effects due to the bending of the ray. Contributions of the second- and thirdorder terms typically amount to values in the centimetre and millimetre ranges, respectively. In a near future, triplefrequency Global Navigation Satellite Systems transmitting high-resolution codes will become available. These systems are expected to provide a noticeable improvement in accuracy. This paper focuses on the Galileo signals as Galileo In-Orbit Validation Element (GIOVE) signals are now available for acquisition. A solution relying on the triple-frequency characteristics of a signal-in-space is investigated with results based on first measurements of GIOVE-A signals. Eventually, a method is described that relies on precise dual-frequency phase measurements to evaluate the second-order ionospheric contribution for Galileo data.
Keywords GNSS . High-order ionospheric correction . GIOVE-A
RFI mitigation of GNSS signals for radio astronomy: problems and current techniques
André Gilloire, Hervé Sizun
Association Observation Radio—Pleumeur Bodou, France
Abstract Mitigation of man-made radio frequency interference (RFI) is a problem of increasing importance for radio astronomy. Indeed, numerous terrestrial and satellite services of all kinds create lots of electromagnetic signals in a large part of the radio spectrum that are likely to disturb radio astronomical observations. Moreover, the advent of large, highly sensitive radio telescopes such as SKA, LOFAR, etc., will permit the observation of extremely faint and distant radio sources which exhibit large amounts of red shift, hence overlapping with unprotected bands in the radio spectrum. Among various possible causes of RFI, GNSSs have specific characteristics which can be handled appropriately to design efficient mitigation techniques. GNSS signals are generally well documented and the ephemerides of satellites are well known. Therefore, various partially or fully informed methods can be used, which exploit knowledge of the characteristics of the modulations. Adaptive cancellation techniques can also be used that use auxiliary observations coming from additional antennas. Besides, knowing the spatial direction of the disturbing source, spatial filtering and related techniques that can be implemented in antenna arrays are likely to mitigate RFI with minimum knowledge of the GNSS. After recalling some radio astronomy basics, the paper presents a few examples of RFI caused by satellite systems on radioastronomical observations. Then, we give a brief overview of state-of-the-art RFI mitigation techniques for radio astronomy and we present in some details the principles and results pertaining to some methods that seem particularly appropriate to mitigate RFI arising from GNSS signals. The importance of cooperation between GNSS designers and astronomers is finally pointed out.
Keywords Radio frequency interference mitigation . Radio astronomy . Global Navigation Satellite Systems . Informed mitigation techniques . Adaptive cancellation . Antenna arrays
A probabilistic approach to determine mobile station location with application in cellular networks
Mirjana I. Simić · Predrag V. Pejović
University of Belgrade, Serbia
Abstract A probabilistic approach to the mobile station location problem is analyzed, and an algorithm that implements such an approach is presented. Information about the mobile station location is collected in the form of two-dimensional probability density functions provided from various sources. Combining the probability density functions into a joined probability density function is addressed. To provide computational efficiency, a method to limit the space of a possible location of the mobile station to a rectangular region of the minimal size is presented. Discretization of space is performed next, reducing the probability density functions to matrices of probabilities. The algorithm for combining the probability density functions is adjusted for an application with the matrices of probabilities. To reduce the computational burden further, probability density functions of the exclusion type, taking only two values, zero and nonzero, are introduced, providing savings in storage space and computational time. Information about the timing advance parameter value and the received signal level are interpreted by probability density functions of the exclusion type. Application of the algorithm is illustrated by two sets of measurements performed in an urban and a suburban region.
Keywords Global system for mobile communications (GSM) · Localization · Positioning · Universal mobile telecommunications system (UMTS)
Indoor Wi-Fi positioning: techniques and systems
Frédéric Lassabe · Philippe Canalda · Pascal Chatonnay · François Spies
Université de Franche-Comté, Montbéliard , France
Abstract If outdoor positioning is widely treated and quite precise, positioning indoors or, more generally, in heterogeneous environments, as well as mobility prediction, requires important devices. New wireless technologies (e.g., Wi-Fi, Ultra Wide Band) combine the mobility of terminals with large bandwidth. Terminal mobility is one of the major pillars of applications attempting to become context-aware, and a large bandwidth enables new services such as multimedia contents streaming towards mobile terminals. Being context-aware and able to provide services in a mobile environment requires the knowledge of spatial and temporal data about the terminal. The key phase in the achievement of mobility management is the positioning process. We propose a layered positioning system based on a model combining a reference point-based approach with a trilateration-based one. Several layers of refinement are offered based on the knowledge of the topology and devices deployed. The more data are known, the better adapted to its area the positioning system can be.
Keywords Indoor positioning · Wi-Fi network · Friis-based calibrated model · Model by refinement · Media guide · Middleware · Multimedia platform
Positioning in WLAN environment by use of artificial neural networks and space partitioning
Miloš N. Borenović & Aleksandar M. Nešković
1 School of Electrical Engineering, University of Belgrade, 73 Bulevar kralja Aleksandra, 11120 Belgrade, Serbia
2WCRG, School of Informatics, University of Westminster, 115 New Cavendish St, London W1W 6UW, UK
Abstract Short range wireless technologies such as wireless local area network (WLAN), Bluetooth, radio frequency identification, ultrasound and Infrared Data Association can be used to supply position information in indoor environments where their infrastructure is deployed. Due to the ubiquitous presence of WLAN networks, positioning techniques in these environments are the scope of intense research. In this paper, the position determination by the use of artificial neural networks (ANNs) is explored. The single ANN multilayer feedforward structure and a novel positioning technique based on cascade-connected ANNs and space partitioning are presented. The proposed techniques are thoroughly investigated on a real WLAN network. Also, an in-depth comparison with other well-known techniques is shown. Positioning with a single ANN has shown good results. Moreover, when utilising space partitioning with the cascade-connected ANNs, the median error is further reduced for as much as 28%.
Keywords Artificial neural network . Location . Positioning . Radio . Space partitioning .WLAN
Mobility support across hybrid IP-based wireless environment: review of concepts, solutions, and related issues
Mohammad Reza HeidariNezhad1 Zuriati Ahmad Zukarnain1 Nur Izura Udzir2 Mohamed Othman1
1 Department of Communication Technology and Network, Faculty of Computer Science and Information Technology, University Putra Malaysia, 43400 Serdang, Selangor, Malaysia
2 Department of Computer Systems, Faculty of Computer Science and Information Technology, University Putra Malaysia, 43400 Serdang, Selangor, Malaysia
Abstract The 4G or Beyond 3G wireless networks is consist of IP-based heterogeneous access networks from 3G cellular, WiFi, WiMAX to other emerging access technologies such as mesh networks. The key objective of designing the next generation wireless networks is to support of mobile subscribers. To support the mobile host in the hybrid wireless access technologies, many solutions based on network protocol stack have been proposed in the literature. In this article, after review of mobility concepts, a special attention is given to some of the mobility management methods as well as handover techniques across various wireless access networks. We have also compared the major mobility protocols in each layer for their features. Finally, some of the open issues that needed to be addressed in mobility management protocol in the next generation wireless networks are outlined.
Keywords Handover . Next generation wireless network . Mobility management
Analytical evaluation of multicast packet delivery and user-clustering schemes in high-speed cellular networks
Neila El Heni · Xavier Lagrange
Institut TELECOM, TELECOM Bretagne, France
Abstract Transmission on data-oriented radio interfaces of cellular networks has been primarily designed for unicast applications. Nevertheless, unicast may not optimize the resource usage when the same content has to be transmitted to several users in the same cell. In this context, multicast seems to be an efficient means to convey data. In this paper, we develop an analytical model that allows the computation of the mean bitrate for both multicast and multiple-unicast transmission schemes. Furthermore, we propose a multicast transmission scheme called the equal-bitrate (EB) algorithm that allocates bandwidth to mobiles according to their instantaneous channel quality. We compare it to adaptations of the well-known max-signal-to-noise ratio and round robin to multicast. We propose to group users into clusters. The clustering method combines multicast and unicast transmission schemes according to the user’s average channel conditions. We use the analytical model to evaluate the proposed solutions. We compare the resulting performance against pure multicast and multiple-unicast approaches. We show that the EB algorithm offers a good trade-off between throughput and fairness. Also, we show that mixed clustering achieves good performance compared to conventional clustering methods.
Keywords Clustering · Fairness · HSDPA · Multicast transmission · Rayleigh fading