When mobiles cannot support multiple antennas due to size or other constraints, conventional space-time coding cannot be used to provide uplink transmit diversity. To address this limitation, the concept of cooperation diversity has been introduced, where mobiles achieve uplink transmit diversity by relaying each other's messages. A particularly powerful variation of this principle is coded cooperation. Instead of a simple repetition relay, coded cooperation partitions the codewords of each mobile and transmits portions of each codeword through independent fading channels. This paper presents two extensions to the coded cooperation framework. First, we increase the diversity of coded cooperation in the fast-fading scenario via ideas borrowed from space-time codes. We calculate bounds for the bit- and block-error rates to demonstrate the resulting gains. Second, since cooperative coding contains two code components, it is natural to apply turbo codes to this framework. We investigate the application of turbo codes in coded cooperation and demonstrate the resulting gains via error bounds and simulations.

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Coded cooperation in wireless communications: space-time transmission and iterative decoding

Map-matching algorithms integrate positioning data with spatial road network data (roadway centrelines) to identify the correct link on which a vehicle is travelling and to determine the location of a vehicle on a link. A map-matching algorithm could be used as a key component to improve the performance of systems that support the navigation function of intelligent transport systems (ITS). The required horizontal positioning accuracy of such ITS applications is in the range of 1 m to 40 m (95%) with relatively stringent requirements placed on integrity (quality), continuity and system availability. A number of map-matching algorithms have been developed by researchers around the world using different techniques such as topological analysis of spatial road network data, probabilistic theory, Kalman filter, fuzzy logic, and belief theory. The performances of these algorithms have improved over the years due to the application of advanced techniques in the map matching processes and improvements in the quality of both positioning and spatial road network data. However, these algorithms are not always capable of supporting ITS applications with high required navigation performance, especially in difficult and complex environments such as dense urban areas. This suggests that research should be directed at identifying any constraints and limitations of existing map matching algorithms as a prerequisite for the formulation of algorithm improvements. The objectives of this paper are thus to uncover the constraints and limitations by an in-depth literature review and to recommend ideas to address them. This paper also highlights the potential impacts of the forthcoming European Galileo system and the European Geostationary Overlay Service (EGNOS) on the performance of map matching algorithms. Although not addressed in detail, the paper also presents some ideas for monitoring the integrity of map-matching algorithms. The map-matching algorithms considered in this paper are generic and do not assume knowledge of ‘future’ information (i.e. based on either cost or time). Clearly, such data would result in relatively simple map-matching algorithms.

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Current map-matching algorithms for transport applications: State-of-the art and future research directions

Orthogonal frequency division multiple access (OFDMA) has recently attracted vast research attention from both academia and industry and has become part of new emerging standards for broadband wireless access. Even though the OFDMA concept is simple in its basic principle, the design of a practical OFDMA system is far from being a trivial task. Synchronization represents one of the most challenging issues and plays a major role in the physical layer design. The goal of this paper is to provide a comprehensive survey of the latest results in the field of synchronization for OFDMA systems, with tutorial objectives foremost. After quantifying the effects of synchronization errors on the system performance, we review some common methods to achieve timing and frequency alignment in a downlink transmission. We then consider the uplink case, where synchronization is made particularly difficult by the fact that each user's signal is characterized by different timing and frequency errors, and the base station has thus to estimate a relatively large number of unknown parameters. A second difficulty is related to how the estimated parameters must be employed to correct the uplink timing and frequency errors. The paper concludes with a comparison of the reviewed synchronization schemes in an OFDMA scenario inspired by the IEEE 802.16 standard for wireless metropolitan area networks.

Synchronization Techniques for Orthogonal Frequency Division Multiple Access (OFDMA): A Tutorial Review

The availability of location information has become a key factor in today's communications systems allowing location based services. In outdoor scenarios, the mobile terminal position is obtained with high accuracy thanks to the global positioning system (GPS) or to the standalone cellular systems. However, the main problem of GPS and cellular systems resides in the indoor environment and in scenarios with deep shadowing effects where the satellite or cellular signals are broken. In this paper, we survey different technologies and methodologies for indoor and outdoor localization with an emphasis on indoor methodologies and concepts. Additionally, we discuss in this review different localization-based applications, where the location information is critical to estimate. Finally, a comprehensive discussion of the challenges in terms of accuracy, cost, complexity, security, scalability, etc. is given. The aim of this survey is to provide a comprehensive overview of existing efforts as well as auspicious and anticipated dimensions for future work in indoor localization techniques and applications.

Recent Advances in Indoor Localization: A Survey on Theoretical Approaches and Applications

In this paper, a fair scheme to allocate subcarrier, rate, and power for multiuser orthogonal frequency-division multiple-access systems is proposed. The problem is to maximize the overall system rate, under each user's maximal power and minimal rate constraints, while considering the fairness among users. The approach considers a new fairness criterion, which is a generalized proportional fairness based on Nash bargaining solutions and coalitions. First, a two-user algorithm is developed to bargain subcarrier usage between two users. Then a multiuser bargaining algorithm is developed based on optimal coalition pairs among users. The simulation results show that the proposed algorithms not only provide fair resource allocation among users, but also have a comparable overall system rate with the scheme maximizing the total rate without considering fairness. They also have much higher rates than that of the scheme with max-min fairness. Moreover, the proposed iterative fast implementation has the complexity for each iteration of only O(K/sup 2/Nlog/sub 2/N+K/sup 4/), where N is the number of subcarriers and K is the number of users.

Fair multiuser channel allocation for OFDMA networks using Nash bargaining solutions and coalitions

We present a multiuser synchronization scheme for tracking the mobile's uplink time and frequency offsets. It uses the redundancy introduced by the cyclic prefix and does not need additional pilots. We show performance results of an orthogonal frequency division multiplexing (OFDM)-based radio interface based on the universal mobile telecommunication system (UMTS) parameters. For a UMTS-typical mobile channel environment, the performance of a coherent system employing the scheme is virtually indistinguishable from the performance of a perfectly synchronized system. In a differentially modulated system, synchronization errors decrease the system performance by about 0.7 dB compared to a perfectly synchronized system.

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A time and frequency synchronization scheme for multiuser OFDM

In this paper, we study the Symbol Error Probability (SEP) performance of a hybrid/integrated satellite-terrestrial cooperative network. In particular, we focus on the case of mobile relays that forward the satellite signal to a masked mobile destination node. The Selective Decode-and-Forward (SDF) transmission scheme is implemented and only the relay nodes which can successfully decode the satellite message are selected to retransmit the signal. The destination node exploits the spatial diversity advantages by implementing a typical Maximum Ratio Combining (MRC) technique. The closed-form expressions for the exact average SEP of the arbitrary M-ary phase shift keying and M-ary quadrature amplitude modulation signaling with MRC diversity reception over independent but not necessarily identically distributed fading channels are derived using a Moment Generating Function (MGF) approach. These closed-form expressions are represented in terms of a finite sum of Lauricella hypergeometric functions. The analytical expressions show excellent agreement with the simulation results. Numerical results show that for a system using QPSK under the frequent heavy shadowed fading condition, the diversity gain of approximately 7 dB can be obtained at the SEP of 10-1 with respect to the direct transmission, when only one relay is used. It increases to around 12 dB in the case of 3 relays.

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Exact Symbol Error Probability of Hybrid/Integrated Satellite-Terrestrial Cooperative Network

SUMMARY

This paper proposes new transmission schemes for the delivery of satellite services. In the proposed scenarios, mobile terminals are allowed to forward the signal received from the satellite. This scheme provides spatial diversity just like MIMO transmission schemes. Moreover, the coverage area is extended because masked terminals have an additional opportunity to get the service from neighboring terminals. We use the paradigm of cooperative communications to compare the advantages and limitations of several scenarios in hybrid terrestrial/satellite systems. In particular, we study the following basic transmission scheme: in a first time slot, the satellite sends its signal and, in a second time slot, mobile terrestrial terminals are relaying the satellite signal. An analysis framework is proposed and applied to this cooperation scenario at the destination terminal. The framework is modeling the cooperation process and clearly separates the control part from the data user part. The paper outlines the importance of the control part by evaluating the relay selection policy on a basic hybrid satellite/ad hoc system. Copyright © 2011 John Wiley & Sons, Ltd.

Improving satellite services with cooperative communications

The GPS and GALILEO systems will take advantage of new signal modulations such as Binary Offset Carrier (BOC) that uses a square wave sub-carrier to create separate spectra on each side of the transmitted carrier. That signal could share the existing frequency bands with each other while reserving the spectrum, it provides spectral isolation and leads to significant improvements in terms of tracking, interference and multipath mitigation. As this BOC modulation, along with a modified version called alternate BOC (ALTBOC), is a serious candidate for GALILEO and GPS, it is important to understand all characteristics of this signal, in order to conduct several studies like payload design, receiver implementation, performance and robustness evaluation. One of the aspects of this signal is the power spectrum density that impacts all characteristics presented above. The aim of this paper is, in a first part, to review the currently admitted BOC power spectrum density theoretical expressions, and to discuss a deviation of the assumptions necessary for the derivation of these classical theoretical expressions w.r.t to the reality of these signals. Then, a second objective is to present theoretical expressions of ALTBOC and constant envelope ALTBOC power spectrum densities. First the paper recalls the formal expressions of the different possible offset carrier modulations: BOC, ALTBOC and constant envelop ALTBOC signals in the time domain. Then, the assumptions for the development of the classical power spectrum density calculation are clearly laid down. Next, it is shown that in the case of odd ratio (2*fs/fc) BOC signals, these assumptions, and particularly the fact that the BOC square sub-carrier can be incorporated in the chip waveform, are not met. Then, we show that, for these calculation assumptions to be met in that case of odd ratio BOC, it is equivalent to modify the code sequence. Finally, with this view, the obtained power spectrum density is the same as the one obtained with the classical theory, due to the negligible effect of the code sequence correlation values. Finally, we present the theoretical expressions of the ALTBOC and constant envelope ALTBOC power spectrum densities.

https://hal-enac.archives-ouvertes.fr/hal-01021737/document

BOC Power Spectrum Densities

Filter banks able to demultiplex channels of different sizes are necessary on board the satellite when a single bit-rate channel is assigned to each user. In this paper, the method referred to as the fast convolution filter bank is analyzed for regenerative payloads. The size of the input fast Fourier transform (FFT) depends on the narrowest channel, while the inverse fast Fourier transform (IFFT) number of points is relative to the decimation ratio associated with each channel. In order to reduce the complexity, most of the frequency coefficients are forced to zero, leading to a violation of the overlap-and-save (OS) condition. It is shown that the resulting error can be modeled as a cyclostationary process, and an optimization method based on minimization of the associated mean-square error (MSE) is proposed. Fast convolution is then compared with multistage implementation in terms of flexibility, reconfigurability, and complexity.

Marie-Laure Boucheret

Papers

A time and frequency synchronization scheme for multiuser OFDM

Exact Symbol Error Probability of Hybrid/Integrated Satellite-Terrestrial Cooperative Network

Improving satellite services with cooperative communications

BOC Power Spectrum Densities

Fast convolution filter banks for satellite payloads with on-board processing