Optimum resource allocation (RA) in space division multiple access (SDMA)/orthogonal frequency division multiple access (OFDMA) systems is a prohibitively complex task for which efficient sub-optimal strategies are preferable. In this work, a new space-frequency/time resource allocation (S-FT RA) is proposed, which divides RA in two tasks: the SDMA grouping, for which a new SDMA grouping algorithm is proposed, and the joint frequency/time RA, which is solved using Munkres' algorithm. It is shown that the proposed strategy is flexible and that it achieves a considerable fraction of the maximum achievable average system capacity.
In this paper, a cross-layer scheduler for wireless LAN access points is introduced which includes a MAC and a PHY layer stage. For the MAC scheduler, both a simple round-robin scheme and an adaptive scheme which considers both the queue length and the packet lifetimes of each flow are considered. The MAC scheduler hands over a list with the most important packets to the PHY scheduler, which selects one or more packets according to the channel capacity available for the respective destination stations. It is shown that the combination of the MAC and the PHY layer scheduler increases the throughput while the delay is reduced. Fairness is supported in the way that the performance is enhanced not only for the entire system, but also for the individual flows.
This paper investigates the design and performance of an echo canceller for on-channel repeaters in DVB-T/H network within the framework of the PLUTO project. The possible approaches for echo cancellation are briefly reviewed and the main guidelines for the design of such systems are presented. The main system parameters are discussed. The performance of a FIR echo canceller based on an open loop approach for channel estimation is tested for different radio channel conditions and for different number of taps of the FIR filter. It is shown that a minimum number of taps is recommended to achieve a certain mean rejection ratio or isolation depending on the type of channel. Channel estimation based on training sequences is then investigated. The performance of maximum length sequences and constant amplitude zero autocorrelation (CAZAC) sequences is compared for different channels. Recommendations are given for training sequence type, length and level for DVB-T/H on-channel repeater deployment in single frequency networks.
This paper analyses options for the strategic positioning of next-generation mobile service platforms in terms of the value proposition made to users, including service developers as well as end users. A cross-case comparison of the main value elements of existing and emerging platforms is performed, and the potential synergetic effects between these elements are taken into account and leveraged.
As the IMS represents an overlaying architecture, it is not limited to a single type of access network. However, the switching logic between different access networks is not provided by the IMS on its own. In fact this logic has to be integrated into a dedicated application server. Such an application server manages the transmission of multimedia streaming sessions over different access networks (UMTS, DVB-H, WiFi etc.) via different transmission schemes (unicast, multicast, broadcast). These multimedia streaming sessions are to be controlled within a stateful session management. This component has to be aware of both the content provider's delivery and the user's receiving behavior. Additionally the session management needs to be aware of the access network and the transmission scheme regarding the current user, network or content context to guarantee QoS and ensure the efficiency in providing this service delivery from network side. As a result, the session manager covers mobility aspects like session mobility and bearer mobility. This paper proposes and describes a session management enabler for a real time multimedia streaming architecture in the scope of quadruple play on top of the IP multimedia subsystem (IMS).
This paper proposes an interference suppression technique using edge-removal filter, nulling filter and turbo equalizer for carrier interferometry (CI) based one-cell reuse single-carrier time division multiple access (TDMA) systems. In the proposed scheme, CI technique is employed to generate CI signal which is equivalent to single-carrier signal with its roll-off factor of zero. At the receiver, received CI signal is transformed into frequency-domain signal via fast Fourier transform (FFT). Adjacent-channel interference (ACI) from the same cell is first suppressed by the edge-removal filter and then co-channel interference (CCI) from adjacent cell is suppressed by applying frequency-domain nulling filter. After that, a soft canceller with minimum mean square error (SC/MMSE) based turbo equalizer is utilized to compensate for channel induced intersymbol interference (ISI) as well as extra ISI produced by the edge-removal filter and nulling filter. Computer simulation confirms that interference can be suppressed with the proposed scheme.
In this paper we present an analytical approach to evaluate the M-QAM bit error rate (BER) of OFDM direct conversion receivers subject to carrier frequency offset (CFO), channel estimation error, outdated channel state information and flat receiver I/Q imbalance in Rayleigh time and frequency selective fading channels. Based on correct modeling of the correlation between channel estimates and received signals with carrier frequency offset and receiver I/Q imbalance, the bit error rate can be numerically evaluated by averaging bit error rates on different subcarriers using an analytical expression of triple integrals. The results illustrate that the analysis can approximate the simulative performance very accurately if the power delay profile of fading channels, the receiver I/Q imbalance parameters and carrier frequency offset are known.
Adaptive image coding scheme are well adapted to multirate cognitive networks. A Cognitive device will be able to reconfigure itself to adapt its baseband radio transmitter to the required bit rate of the coding scheme. In this paper, a such platform able to adapt the radio access technology (RAT) to the image coding scheme is described. To optimize the RAT bit rate to the image coding bit rate, our system chooses and reconfigures in real time the radio baseband functions. It makes some cross-layer adaptation between PHY and application layers.
In this paper, the application of beamforming in a single frequency network (SFN) is examined. A single frequency network is characterized by the transmission of the same signal from multiple base stations simultaneously. Since a user receives the signal from many base stations, the beamforming weights for many different base stations need to be jointly optimized for the transmission. An optimality criterion is given and three different beamforming strategies with varying computational complexity and performance are investigated. Their performances are compared to the case of SFN transmission without beamforming, showing significant gains for realistic numbers of transmit antennas at the base stations and numbers of users in the SFN.
The deployment of payment systems protective of the customer privacy is an hard challenge. Accountability and payment seem to require a direct link to the customer credentials (e.g. his credit card number or bank account), this exposes the user to be profiled on his habits. Static and uniquely identified mappings to user credentials, hold by a trusted third party, may vanish all the parallel anonymization/pseudonymisation efforts done to avoid disclosure of the user identity to the provider of the service. This paper proposes P-DIBS (pseudonymised distributed billing system), a billing framework devised to protect user privacy. P-DIBS is developed as an extension of a previously proposed pseudonymization mechanism. It relies on an intermediate brokerage entity, referred to as "Accounting Server", operating between the bank and the service provider on behalf of the end user, yet having no knowledge neither about his real identity nor about his real account number. A fundamental novelty of the proposed approach is the possibility, through a distributed procedure involving mutual interaction across the various system components, to guarantee linkability upon improper user behavior (e.g. misuses) without requiring a single trusted third party in the system to possess all the knowledge necessary to disclose the user.
Digital satellite broadcasting, primarily targeted to unidirectional services, soon expanded to the interactive domain, utilising uplink technologies such as DVB-RCS. In this context, due to their wide and uniform coverage, satellites can provide an ideal medium for the provision of triple play services (voice, video and data) to remote areas not covered by terrestrial infrastructures. This paper discusses and demonstrates the delivery of triple play services over a fully functional platform utilising the second-generation satellite broadcasting technology (DVB-S2) for the downlink combined with DVB-RCS for the uplink.
RESOLUTION aims at developing a wireless three-dimensional (3-D) local positioning system with measurement accuracy in the centimetre regime and real-time ability. A novel frequency modulated continuous wave (FMCW) radar principle with pulsed active reflector is employed. This High-Precision-Localisation-System (HPLS) will be implemented together with common WLAN systems that are used for data communication purposes. Due to its high data rate capabilities and large potential bandwidth, the 802.11a/n standard allocated bandwidth around 5.5 GHz is applied. Special emphasis is given to the system's reconfigurability by efficiently using inherent synergies between the WLAN system and the HPLS approach. To allow multifunctional tasks, highly integrated system on chip (SoC) frontends will be designed on advanced CMOS or BiCMOS technology. Smart power and adaptive performance control will be applied to minimise the power consumption according to application needs. In order to enhance performance and coverage range, the transceiver features adaptive antenna combining (AAC) in the radio frequency (RF) receiver. AAC significantly decreases the power consumption, size and costs, since the number of multiple components is reduced to a minimum. Because of the high 3-D resolution and real-time ability, which can be achieved in indoor environments with strong multipath effects and fading, novel local positioning applications, e.g. for smart factories, robotics, interactive guiding, object tracking and augmented reality are presumably leading to a large economic potential.
A method to establish a time synchronization for base stations in a cellular network is derived based on the maximum likelihood estimation principle. Its performance is analyzed and compared to a heuristic technique from the literature. The main feature of these synchronization algorithms is that a time synchronization of the base stations is achieved by measurements from the users in the downlinks that are associated to the base stations. The steady-state is reached after a low number of iterations and a low residual error is obtained. The good accuracy allows the application of this algorithm in the context of single frequency networks (SFN), where a high degree of time-synchronization between participating base stations is required.
A frequency sharing technique is necessary for using the limited frequency resources efficiently. In this paper we study the condition for sharing frequency bands in two cases. One is the case that the frequency band is already allocated to the specific communication. The other is the case of allocating the new frequency bands to communication systems having interference avoiding techniques. For each case we investigate the conditions for sharing frequency bands and the suggestions for that are presented in this paper.
DFT Spread OFDM has been proposed recently to reduce the Peak to Average Power Ratio (PAPR) of conventional OFDM transmission. Besides PAPR reduction, an important implication of DFT Spreading is that the independent parallel sub-channels between the sub-carriers cease to exist. This in turn leads to difference in its performance limits as compared to the conventional OFDM system. This paper analyzes the error probabilities of DFT Spread OFDM systems, and derives their analytical closed form expressions for the AWGN, fading AWGN, multipath and fading multipath channel scenarios. Simulation results presented in last section confirm the validity of the derived analytical expressions.
This paper describes an analysis of the performance overheads caused by the processing and space requirements of IPsec when protecting Mobile IPv6 (MIPv6) signaling. Signaling between the Mobile Nodes and the Home Agent (HA) in a large-scale reference scenario is considered. The analysis is based on queuing theory and focuses on the overall utilization of the HA by the MIPv6 signaling processes as well as the total mean response time for a mobility process in the network. The results can assist network designers in finding the most appropriate security configuration for their specific network and mobility scenario.
Localization and tracking (LT) algorithms for low data rate (LDR) ultra wideband (UWB) systems developed within the Integrated Project PULSERS Phase II are reviewed and compared. In particular, two localization algorithms, designed for static networks with mesh topologies, and one Tracking Algorithm, designed for dynamic network with star topologies are described and/or compared. Each of the localization algorithms adopts a different approach, namely, a centralized non-parametric weighted least squares approach (WLS), and a distributed Bayesian approach that relies on the cooperative maximization of the log-likelihood of range measurements (DMLL). The performance of these two alternatives are compared in a 3D indoor scenario under realistic ranging errors. The tracking algorithm is a fast non-parametric technique based on multidimensional scaling (MDS) and its performance is tested in a dynamic scenario. The proposed algorithms are practical and robust solutions addressing distinct network topologies and/or service requirements related to LDR-LT applications.
Network selection mechanism in 4G mobile networks is a newly introduced mechanism that handles the selection of the best network to satisfy a service request. Network selection needs to take part prior to admission of the service in a particular access network participating in the 4G system. This paper proposes to model this decision using a game theoretic approach; specifically defining a game between the access networks themselves, competing in a non-cooperative manner to maximize their payoff. The outcome of the game is a decision of which subset of the set of service requests made to the 4G converged system should be admitted by each access network.
Our aim is to develop a microwave (X-band) antenna whose radiation pattern is electronically controlled. The radiation pattern of the regular antennas is determinated by the Fourier-transform of the phase and amplitude distribution on the antenna aperture. This radiation pattern is fixed by the mechanics so the alteration of it is impossible. Therefore let us construct an antenna system, which contains several antenna elements. All elements are actuated by separated transmitters, let us control the amplitude and the phase of the supplying current of the antenna elements. In such way, we are able to control the radiation pattern of the antenna system. The controlling is computerized so that there is a possibility to change the radiation pattern several times in a second.
This paper analyzes the performance of direct sequence ultra-wideband (DS-UWB) systems in a very dense and realistic multipath channel scenario with temporal and spatial diversity, considering Monte-Carlo simulation method and semi-analytical development. This work analyzes the impact of antenna elements and the number of rake fingers on the system performance, emphasizing the effects of the pulse shape correlation.
