Fotios Gioulekas

Digital baseband challenges for a 60GHz gigabit link

This paper presents the algorithms and corresponding hardware architectures developed in the context of the nexgen miliwave project, that compose the digital baseband processor of a 60GHz point-to-point link. The nexgen baseband processor provides all basic functionality required from a digital transmitter and receiver, including filtering, synchronization, equalization, and error correction. The techniques selected are capable of compensating impairments due to millimeter-wave front-end and yet support a throughput rate of more than one Gbp, with moderate hardware cost. As the nexgen link targets backhauling applications, a particularly low bit error rate specification of 10−12 has been adopted. Meeting the particular specification, as well as performance and complexity constraints, requires the adoption of sophisticated FEC techniques. Furthermore, extensive verification tasks need to be adopted which include hardware prototyping.

Heterogeneous system level co-simulation for the design of telecommunication systems

The advanced complexity and heterogeneity of modern telecommunication systems mostly lead to the incorporation of heterogeneous implementation technologies and design styles. Consequently, the design representation of such systems often requires the mixed use of distinct model of computations at different abstraction layers. Therefore, heterogeneous co-simulation is needed in order to enable the effective communication and interaction among the involved models of computation. This paper resolves this issue by proposing the heterogeneous co-modelling of telecom systems based on the combination of SDL semantics with C language running on an instruction set simulator, coupling in that way the specification and the first refinement steps of the co-design flow. The missing test link between the corresponding tools that support the SDL-C co-model is addressed by proposing a heterogeneous co-simulation scheme through the development of a mediator. Finally, the proposed methodology and the efficiency of the built environment are evaluated through a case study associated with the design of the MAC layer of the DECT telecom system.

Pilot-less time synchronization for OFDM systems: application to power line receivers

Power line networks provide high-speed broadband communications without the need for new wirings. However, these networks present a hostile environment for high-speed data communications. The most common modulation method used in such systems is OFDM, since it copes effectively with noise, multipath, fading selectivity, and attenuation. A potential drawback of OFDM is its sensitivity to receiver synchronization imperfections, such as timing and sampling frequency offsets. Although several approaches have been proposed for estimating the time and frequency offset, they are based on the use of pilot sequences that are not available in power line communication standards. More importantly, they focus on isolated algorithms for compensating either time or frequency offsets without providing a complete, low complexity, OFDM receiver architecture that mitigates jointly time and frequency errors. This paper focuses on providing an OFDM receiver architecture that can be compatible with many power line standards. Extensive simulation studies show under realistic channel and noise conditions that the proposed receiver provides enhanced robustness to synchronization imperfections as compared to conventional approaches.

Precision and power issues in a medical sensor controller

The continuous growing of the percentage of elderly people in total population the last decades has given significant boost to ehealth technology and applications that allow for the remote health monitoring of aging people, thus acting as a remedy to the explosive costs that would be otherwise needed for full medical coverage. In this context, we present in this paper an efficient ehealth platform based on a low-cost medical sensor controller system, the main features of which have been successfully enhanced in terms of flexibility, accuracy and power consumption so as to be able to provide wide coverage of tests/medical scenarios with the best possible reliability and low power consumption. A low-cost sensor controller capable of performing both simple and more advanced tests with increased accuracy forms the core of the system communicating with a Gateway installed in the patients residence and a tablet or smart phone used for giving instructions to the patient by the medical supervisors. Appropriate processing and filtering algorithms are applied where necessary to enhance the accuracy of sensor measurements achieving substantial improvements close to the level of high-cost commercial ones. Furthermore, a combination of hardware and software techniques are employed which exploit at the best possible extent the idle intervals between measurements resulting in considerably lower power requirements and extension of the platforms portability.

A Low Cost Sensor Controller for Health Monitoring

Aging population can benefit from health care systems that allow their health and daily life to be monitored by expert medical staff. Blood pressure, temperature measurements or more advanced tests like Electrocardiograms (ECG) can be ordered through such a healthcare system while urgent situations can be detected and alleviated on time. The results of these tests can be stored with security in a remote cloud or database. Such systems are often used to monitor non-life threatening patient health problems and their advantage in lowering the cost of the healthcare services is obvious. A low cost commercial medical sensor kit has been used in the present work, trying to improve the accuracy and stability of the sensor measurements, the power consumption, etc. This Sensor Controller communicates with a Gateway installed in the patients residence and a tablet or smart phone used for giving instructions to the patient through a comprehensive user interface. A flexible communication protocol has been defined supporting any short or long term sensor sampling scenario. The experimental results show that it is possible to achieve low power consumption by applying apropriate sleep intervals to the Sensor Controller and by deactivating periodically some of its functionality.

Reduced complexity rate-matching/de-matching architecture for the LTE turbo code

The task of rate matching is to extract from the blocks of code bits, delivered by the Long Term Evolution (LTE) Turbo Encoding (TE), the exact set of bits to be transmitted within a given transmission time interval, depending on the existing channel conditions. Within this context, we propose algorithmic improvements on the rate matching procedure, which are applied to the TE output streams, and to the corresponding rate de-matching at the receiver side, respectively. The proposed method facilitates an address assigner that on-the-fly controls the memory addressing operations by defining the interleaving/ puncturing of bits to be transmitted. The usage of this controller leads to a significant latency reduction and to the utilization of low memory resources when compared with other conventional approaches deduced by the LTE standard.

On the construction of LDPC convolutional code ensembles based on permuted circulant unit matrices

In this paper, a construction methodology for ensembles of Low-Density Parity-Check Convolutional Codes (LDPC-CCs) based on permuted circulant unit matrices is proposed. The proposed method directly generates the syndrome former matrices according to specified code parameters and constraints i.e. code-rate, degree-distribution, constraint length, period and memory, in contrast to the majority of the available methodologies that produce relevant error-correcting codes based on either block ones, protographs or spatially-coupled type of codes. Simulation results show that the constructed ensembles demonstrate advanced error-correcting capability of up to 0.5 dB in terms of frame-error and bit-error rates at the convergence region, when compared to the performance of Forward Error Correction schemes adopted by various wireless standards, with comparable hardware complexity even at short codeword-lengths.

Localization of a Target with Three Degrees of Freedom Using a Low Cost Wireless Infrared Sensor Network

The estimation of the position of a mobile target on a plane as well as its orientation is an important aspect for many applications. The indoor or outdoor localization of such a target has been widely addressed in the literature but if a third degree of freedom like rotation has to be also taken into consideration the difficulty in estimating the target position and orientation is significantly increased. A network consisting of only a small number of low cost infrared transmitters/receivers is used in this paper to estimate the position of a mobile target on a plane as well as its draft orientation with an angular step of 45o or less. The distance and orientation estimation is based on the success rate that infrared patterns are retrieved at the target. This success rate parameter is calculated by simple ultra low cost microcontrollers. The architectural complexity and cost of the overall localization system is significantly lower than other approaches without sacrificing speed and accuracy. An error correction scheme like Turbo decoding is applied in order to increase the reliability and stability of the results by correcting burst errors introduced by real time noise.

Use of interleaving and error correction to infrared patterns for the improvement of position estimation systems

A system capable of estimating the position of a mobile target based on the error rate of the received infrared patterns has been presented recently in [1]. In the present work, we explore the effect of using different infrared patterns to the estimation accuracy, the instant noise immunity and the system speed. We apply interleaving and forward error correcting techniques to correct the burst errors stemming from instant noise. We achieved a 25%-50% stability improvement, retrieved 20% less failures and the convergence speed is enhanced by a factor of 4-12.

Application of Forward Error Correcting Algorithms to Positioning Systems

The indoor localisation of a mobile target is an important issue in many robotics, automation, virtual reality and pervasive computing environments. The most sophisticated method for indoor localisation is based on processing the images captured by cameras that are placed on the target in order to recognise familiar landmarks and their distance (Jin et al, 2004); (Porta & Krose, 2006); (Clerentin et al, 2005); (Tovar et al, 2006); (Se et al, 2002). Image processing in conjunction with other localisation approaches described below (Borenstein et al., 1996) is very popular in autonomous robotics applications making feasible the familiarisation of a robot with unknown areas. Stochastic processing is often applied in this case in order to evaluate an estimated position. Nevertheless, expensive sensors and processing units are required in order to support the high computational complexity of this approach. More popular lower cost approaches are based either on measuring the round trip time of a reflected wave or the strength of a signal. In the first case, the cost is higher if optical or laser scanning is employed since very short time intervals have to be measured with high precision (Miura et al, 2006); (Clerentin et al, 2005); (Victorino et al, 2003); (Arras et al, 2001). Ultrasonic signals can offer a lower cost alternative to this approach since the sonar waves travel with much lower speed than light but their main drawback is that this type of signal is not directional enough (Smith & Zografos, 2005); (Minami et al, 2004); (Tardos et al, 2002); (Bicho et al, 2000); (Baskent & Barshan, 1999). Moreover, it is more difficult to isolate the sonar transmitter from the receiver in order to reassure that only the reflected signal will be received. Measuring the signal strength of multiple transmitters (Ladd et al, 2005); (Flora et al, 2005) can also provide an indication about the target position. This technique has already been adopted in cellular phone, Wireless Local Access Network (WLAN) or Bluetooth applications. Although wide areas can be covered in these networks, the distance estimation error is usually higher than half a meter. Even magnetic fields have been used for the accurate non-contact control of tools and medical instruments (Schlageter et al, 2001); (Kosel et al, 2005). The distance measured in this approach cannot be longer than some tenths of centimetres although a distance estimation of up to 10m has been reported in (Prigge & How, 2004). O pe n A cc es s D at ab as e w w w .ite ch on lin e. co m