Harald Witschnig

A different look on cyclic prefix for SC/FDE

We investigate the use of a known symbol sequence - a so-called unique word (UW) - instead of the well-known cyclic prefix (as it is used in OFDM, orthogonal frequency division multiplexing, systems) for a single carrier system with frequency domain equalization (SC/FDE). The considered SC/FDE system is similar to the one proposed in the IEEE 802.16.3c target group. It is shown that the UW fulfils the theorem of cyclic convolution required for efficient implementation of the SC/FDE structure. We elaborate on the advantages that result for equalization, channel estimation, and synchronisation. Compared to the advantages, the disadvantages in terms of BER behaviour and bandwidth efficiency are rather modest.

Unique word based phase tracking algorithms for SC/FDE-systems

In this paper we consider phase tracking algorithms for single carrier systems with frequency domain equalizers (SC/FDE), which make use of the concept of unique word (UW) blockwise extension instead of the classical concept of cyclic prefix (CP) like it is used for example in OFDM (orthogonal frequency division multiplexing). Very similar to IEEE 802.11a like OFDM systems the overall baseband processing performance of SC/FDE systems largely depends on the design of channel estimation and synchronization algorithms. Some of the synchronization tasks are very straight forward, but the algorithm developer has a lot of freedom for the design of the channel estimator, and for the design of the residual carrier frequency offset tracking procedure (which we call phase tracking). In this paper we focus on the design and performance of unique word based phase tracking algorithms, which are being compared with pilot carrier based phase tracking algorithms for IEEE 802.11a like OFDM systems.

The advantages of a known sequence versus cyclic prefix in a SC/FDE system

In this work we investigate the advantages of a known symbol sequence - a so-called unique word (UW) - instead of the well-known cyclic prefix (as is used in OFDM systems) for a single carrier system with frequency domain equalization (SC/FDE). The concept of UW fulfills the theorem of cyclic convolution - required to implement an efficient equalization for the SC/FDE structure. We elaborate on the advantages that result for decision feedback equalization (DFE) in detail. It is shown that a DFE based on the concept of UW shows significant advantages in comparison to a traditional time domain DFE or a DFE based on cyclic prefix. Simulation results confirm the theoretical advantages.

Automatic impedance matching for 13.56 MHz NFC antennas

This paper deals with the concept, the implementation and the verification of an automatic impedance matching circuit for NFC antennas with a frequency of 13.56 MHz. Besides an introduction to manual tuning and its issues, the fundamental components of an automatic tuning system are outlined. A lab-scaled prototype is built and demonstrated. In the end, the successful operation of this system is tested with several different antennas.

Parameter analysis and reader architectures for broadband 13.56 MHz RFID systems

The underlying paper deals with HF RFID systems and the influences of different parameters on the entire system and the effects for “very high data rates” (VHD) up to 6.7 Mbit/s. After a short introduction to 13.56 MHz RFID systems, characteristic parameters such as Signal to Carrier Ratio, quality factor, bandwidth and energy are pointed out in the context of VHD. Based on that different reader concepts will be evaluated and the implementation of a testplatform will be shown. Finally dynamic effects of the system will be explained, which have to be taken into account for VHD transmissions.

Eigenvalue Analysis of Close Coupled 13.56 MHz RFID-Labels

The technology of RFID (radio frequency identification) is on the way to change industrial processes but also our daily life significantly, as a variety of applications based on this technology are on the way to be implemented. While typical applications in the past had to handle only one tag/label in the field, future applications will have to face many labels in the field. In particular if they show a high coupling factor between them a severe detuning will occur, leading to a loss of functionality in the worst case. Examples for such scenarios may be smart shelfs were goods are equipped with RFID tags or identification cards, passports etc. carried close together. It is topic of this work to characterize the physical behavior of such close coupled systems in terms of effected resonance frequency and others. The influence will be characterized based on mathematical analysis - in particular an eigenvalue analysis. It will be pointed out that a solid mathematical understanding and modeling is absolutely necessary to handle future applications and to guarantee their functionality

High speed RFID lab-scaled prototype at the frequency of 13.56 MHz

SummaryData-intensive applications based on NFC (Near Field Communication) or applications for healthcare/e-government will need an increase of the actual defined and standardized transmission rates of 848 kbit/s. It is topic of this work to point out physical layer parameters, limitations and concepts, allowing to enhance the transmission rate of passive 13.56 MHz RFID systems. Additionally, ongoing standardization activities at ISO 14443 are pointed out, having the aim to standardize significantly enhanced datarates. Finally, an implementation of a lab-scaled prototype with a transmission rate of 6.78 Mbit/s is demonstrated and discussed.ZusammenfassungDatenintensive Anwendungen wie NFC (Nahfeld-Kommunikation) oder Applikationen im Gesundheitsbereich und im Bereich des E-Government erfordern es, die aktuell standardisierte Datenrate von 848 kbit/s zu erhöhen und zu erweitern. Es ist Gegenstand der aktuellen Untersuchungen, physikalische Parameter, Limitierungen und mögliche Konzepte aufzuzeigen, die es erlauben, die aktuellen gültigen Datenraten von 13,56 MHz bei RFID-Systemen zu erhöhen. Im Speziellen werden aktuelle Standardisierungsaktivitäten in Richtung höherer Datenraten im Rahmen von ISO 14443 diskutiert. Abschließend wird ein diskreter Prototyp vorgestellt, der eine Übertragungsrate von 6,7 Mbit/s erreicht.

Broadband NFC - A system analysis for the uplink

Near field communication (NFC) is a new, short-range wireless connectivity technology that evolved from a combination of existing contactless identification and interconnection technologies. Products with built-in NFC will have the aim to simplify the way consumer devices interact with one another. Data-intensive applications based on NFC or applications for health care/e-government need an increase from the actual defined and standardised transmission rates of 424 kbit/s to a higher rate. The topic of this paper is to point out physical layer parameters, limitations and concepts, allowing to enhance the transmission rate of the 13.56 MHz NFC-systems. Finally one implementation of a lab scaled prototype with a transmission rate of 6.78 Mbit/s from card to reader is demonstrated and discussed.

A bandwidth efficiency optimized frequency domain equalization concept for single carrier transmission

The concept of Single Carrier Transmission with Frequency Domain Equalization (SC/FDE) represents one of the most powerful strategies for next generation wireless communication systems. One of the main advantages of this concept, which makes use of a so called cyclic prefix (CP), is its powerful and low complexity equalization procedure in frequency domain. In this paper we investigate frequency domain equalization schemes based on the more bandwidth efficient concepts of Overlap and Add (OA) and Overlap and Save (OS). We explore the main problem of these approaches, namely the difficult predefinition of a maximum equalizer length, and we present a solution which results in a bit error performance absolutely comparable to the CP based equalizer.

Noise Reduction for SC/FDE Systems by Pre- and Post Processing

Noise represents a major performance limiting factor for wireless communication systems. Pre-and post processing of the transmitted information enables to reduce the influence of noise significantly, leading to a severe performance gain. We apply the derivation of an optimal pre-and post processing to a single carrier system with frequency domain equalization (SC/FDE). Comparisons between the standard SC/FDE system with a zero-forcing equalizer and the enhanced system show a performance gain of up to 8 dB at a bit error rate of 10-5.