Rasmus Krigslund

Physical layer network coding for FSK systems

In this work we extend the existing concept of De- Noise and Forward (DNF) for bidirectional relaying to utilise non-coherent modulation schemes. This is done in order to avoid the requirement of phase tracking in coherent detection. As an example BFSK is considered, and through analysis the decision regions for the denoise operation in DNF are identified. The throughput performance of BFSK in DNF is compared to BPSK.

A Novel Technology for Motion Capture Using Passive UHF RFID Tags

Although there are several existing methods for human motion capture, they all have important limitations and hence there is the need to explore fundamentally new approaches. Here, we present a method based on a radio frequency identification (RFID) system with passive ultra high frequency (UHF) tags placed on the body segments whose kinematics is to be captured. Dual polarized antennas are used to estimate the inclination of each tag based on the polarization of the tag responses. The method has been validated experimentally for the shank and thigh in the sagittal plane during treadmill walking. The reference segment angles for the validation were obtained by an optoelectronic system. Although the method is in its initial phase of development, the results of the validation are promising and show that the movement information can be extracted from the RFID response signals.

Scalable DeNoise-and-Forward in bidirectional relay networks

In this paper a scalable relaying scheme is proposed based on an existing concept called DeNoise-and-Forward, DNF. We call it Scalable DNF, S-DNF, and it targets the scenario with multiple communication flows through a single common relay. The idea of the scheme is to combine packets at the relay in order to save transmissions. To ensure decodability at the end-nodes, a priori information about the content of the combined packets must be available. This is gathered during the initial transmissions to the relay. The trade-off between decodability and number of necessary transmissions is analysed and simulations show, that S-DNF is able to provide a better trade-off than traditional schemes at high SNR.

Interference Helps to Equalize the Read Range and Reduce False Positives of Passive RFID Tags

In various applications of radio frequency identification (RFID) systems, a reader should reliably get the ID of the tags that are within a bounded proximity region, termed the interrogation zone. This gives rise to two types of errors: 1) false negative detections (FNDs), when tags within the intended interrogation zone cannot be read, and 2) false positive detections (FPDs), when tags outside the zone can be read. The detuning effect experienced from the object a tag is attached to exacerbates the occurrence of FND. Solving FNDs by increasing the reader power increases the probability of FPDs for tags outside the zone. Hence, the design of an interrogation zone poses a tradeoff between readability inside versus outside the desired zone. We present a novel method to reduce the probability of FNDs and FPDs and practically equalize the achievable range for tags experiencing detuning. We propose to impose intentional interference on the communication between reader and tag. The expected effects of the proposed method are evaluated using experimental measurements. The results are positive, showing a sharp edge of the interrogation zone and a strong equalization of the range of tuned and detuned tags. Hence, it is concluded that by imposing interference enables the design of well-defined interrogation zones for passive RFID systems.

Potential of RFID Systems to Detect Object Orientation

In this paper we present a novel method for estimating the inclination of passive UHF RFID tags, for use in supply chains to monitor the handling of tagged items. Based on observations of the polarization, a Bayesian estimator of the tag inclination is constructed. The Bayesian estimator has been analyzed and evaluated in a experimental setup. The results shows great potential as the estimator is very robust when determining the inclination.

Orientation Sensing Using Multiple Passive RFID Tags

Knowing the inclination of an object can be valuable information in a supply chain application, e.g., when handling orientation-sensitive objects. In this letter, we present a method for sensing the inclination using radio frequency identification (RFID) technology. The method requires standard RFID equipment and assumes that each object is tagged with a passive UHF tag. We use a simple statistical estimator based on the received signal strength (RSS) of the tag reply. The performance is evaluated via experimental measurements, and the results are positive with a good precision within distances of 2 m.

Cooperative media streaming using adaptive network compression

Media content distribution constitutes a growing share of the services on the Internet. Two distinct distribution approaches used today are layered coding (LC) and multiple description coding (MDC). Current wireless connection technologies, e.g. Wimax, have properties which make them unsuitable for media distribution using traditional approaches. In particular, the asymmetric relationship between the uplink and the downlink bandwidth makes the cooperative distribution difficult. A promising concept, termed MDC with Conditional Compression (MDC-CC), has been proposed [11], which essentially acts as an adaptive hybrid between LC and MDC. In order to facilitate the use of MDC-CC, a new overlay network approach is proposed, using tree of meshes. A control system for managing description distribution and compression in a small mesh is implemented in the discrete event simulator NS-2. The two traditional approaches, MDC and LC, are used as references for the performance evaluation of the proposed scheme. The system is simulated in a heterogeneous network environment, where packet errors are introduced. Moreover, a test is performed at different network loads. Performance gain is shown over both LC and MDC.

3D gesture recognition using passive RFID tags

This paper investigates the application of passive UHF Radio Frequency IDentification (RFID) tags for recognizing gestures in three dimensions. We experimentally assess the possibility to differentiate among predefined motions with a tag or object.We propose a novel method estimating and tracking the tag orientation in 3D based solely on the physical characteristic of the tag reply, using multiple reader antennas distributed around the interrogation zone. The results demonstrate a good potential, as even with simple data processing differentiation of simple gestures is possible. Our investigation therefore shows that the orientation information is available, and can be extracted using suitable data and signal processing techniques.

Measuring the interference at an RFID tag: Where does it have an impact?

In this paper we consider reader collisions in an Radio Frequency IDentification (RFID) system, especially how interference impacts the ability of a passive UHF tag to respond. We propose two innovative applications for using interference: 1) Blocking a tag response, and 2) cooperative reading of a tag. In order to investigate their applicability we focus on the experimental evaluation, where we impose interference on the download and uplink, respectively, and on both links simultaneously. The results are positive with respect to blocking the tag, where modulated Co-Channel Interference (CCI) shows most effective. Based on the measurements it is however not possible to read a tag cooperatively, i.e. the tag is unable to utilize the interference as an additional energy source.

Communication beyond (N)acks: wireless transmission with informative feedback

This paper introduces a scheme for improved data transmission in wireless links. The idea of the proposed scheme is to limit the amount of retransmitted data in case of errors, by using informative feedback instead of the traditionally used binary (ACK or NACK) feedback. The performance of the proposed scheme is assessed and compared to a protocol stack incorporating regular retransmission, in order to determine whether the idea of informative feedback has a potential. The estimation shows a significant improvement in goodput, when the error rate of the communication channel varies from 10-6 to 10-3. Software that implements the proposed scheme is made, and tests are performed in order to verify the estimations. The tests show a significant performance increase, and based on the results it is concluded, that informative feedback in communication protocols has a noticeable potential.