Torleiv Maseng

Pilot assisted channel estimation for OFDM in mobile cellular systems

The use of pilot symbols for channel estimation introduces overhead and it is thus desirable to keep the number of pilot symbols to a minimum. The number of needed pilot symbols for a desired bit error rate and Doppler frequency is highly dependent on the pilot pattern used in orthogonal frequency division multiplexed, OFDM, systems. Five different pilot patterns are analysed by means of resulting bit error rate, which is derived from channel statistics. Rearrangement of the pilot pattern enables a reduction in the number of needed pilot symbols up to a factor 10, still retaining the same performance. The analysis is general and can be used for performance analysis and design of pilot patterns for any OFDM system.

A turbo code interleaver design criterion based on the performance of iterative decoding

The performance of a turbo code is dependent on two code properties: its distance spectrum and its suitability to be iteratively decoded. Both these properties are influenced by the choice of interleaver used in the turbo encoder. This paper presents an interleaver design criterion that focuses on the performance of iterative decoding, based on the correlation properties of the extrinsic inputs. Interleavers designed with the proposed criterion achieve very competitive performances, both in terms of convergence rates and error correcting capabilities.

On the theory and performance of trellis termination methods for turbo codes

The performance of a turbo code can be severely degraded if no trellis termination is employed. This paper investigates the implications of the choice of trellis termination method for turbo codes, and explains the origin of the performance degradation often experienced without trellis termination. An efficient method to derive the distance spectrum of turbo codes for different trellis termination methods is presented. Further, we present interleaver design rules that are tailored to each termination method. Using interleavers designed with these restrictions, we demonstrate that the performance difference between various termination methods is very small, including no trellis termination at all. For example, we demonstrate a turbo code with a 500-bit interleaver that exhibits no sign of an error floor for frame error rates as low as 10/sup -8/, even though no trellis termination is employed.

Turbo codes: correlated extrinsic information and its impact on iterative decoding performance

The performance of a turbo code is dependent on two properties of the code: its distance spectrum and its suitability to be iteratively decoded. The performance of iterative decoding depends on the quality of the extrinsic inputs; badly correlated extrinsic inputs can deteriorate the performance. While most turbo coding literature assumes that the extrinsic information is uncorrelated, we investigate these correlation properties. An iterative decoding suitability measure is presented, intended to serve as an indication on the degree of correlation between extrinsic inputs. The suitability measure can be used as a complement to the weight distribution when ranking interleavers.

A survey on trellis termination alternatives for turbo codes

Numerous strategies and methods for trellis termination of turbo codes have been presented and proposed in the literature. In this paper the most common trellis termination methods are compared and their relative performances are investigated. An important observation is that the performance of a termination method is highly dependent on the particular interleaver choice. Conclusions should thus be drawn for the combination of interleaver and termination method, and not for the termination method alone. Another important conclusion is that the particular choice of termination method is not crucial for the error correcting performance, as long as certain precautions are taken regarding the choice of interleaver.

Adaptive data rate using ARQ and nonuniform constellations

We introduce an automatic repeat request (ARQ) scheme that uses nonuniform signal constellations in order to adapt the data rate to the received signal-to-noise ratio (SNR) in a fading channel without using channel state feedback or incremental redundancy. We have defined nonuniform phase shift key (PSK) and quadrature amplitude modulation (QAM) constellations with an arbitrary number of classes of bits. These constellations may also be of interest for further research into unequal error protection. We present simulations of the throughput in Rayleigh fading and lognormal shadowing, and discuss the cases where our proposed scheme may improve the throughput compared to standard ARQ using uniform signal constellations.

Mist: A Reliable and Delay-Tolerant Publish/Subscribe Solution for Dynamic Networks

In this paper, we present Mist: a reliable and delay-tolerant middleware for information dissemination between highly mobile devices. Mist provides publish/subscribe with guaranteed message delivery in fully connected networks. Through emulation we show how the middleware is effective in static networks, as well as in dynamic topologies with high mobility. We describe how Mist is able to scale using a topic routing mechanism, allowing groups of mobile units to cooperate with infrastructure-based P2P-networks. Finally, we describe recent experiments where Mist has been employed successfully in real-life deployments. The implementation of the middleware, written in Java, is released as open source.

Identity and Privacy in the Internet Age

Session 1: Anonymity and Privacy.- On the Effectiveness of Privacy Breach Disclosure Legislation in Europe: Empirical Evidence from the US Stock Market.- Facilitating the Adoption of Tor by Focusing on a Promising Target Group.- A Parallelism-Based Approach to Network Anonymization.- Security Usability of Petname Systems.- Session 2: Modelling and Design.- An Analysis of Widget Security.- Trade-Offs in Cryptographic Implementations of Temporal Access Control.- Blunting Differential Attacks on PIN Processing APIs.- Session 3: Network Layer Security.- Characterising Anomalous Events Using Change - Point Correlation on Unsolicited Network Traffic.- An Improved Attack on TKIP.- Session 4: Security for Mobile Users.- ContikiSec: A Secure Network Layer for Wireless Sensor Networks under the Contiki Operating System.- A Mechanism for Identity Delegation at Authentication Level.- Introducing Sim-Based Security Tokens as Enabling Technology for Mobile Real-Time Services.- Towards True Random Number Generation in Mobile Environments.- Session 5: Embedded Systems and Mechanisms.- Towards Modelling Information Security with Key-Challenge Petri Nets.- Security and Trust for the Norwegian E-Voting Pilot Project E-valg 2011.- Advanced SIM Capabilities Supporting Trust-Based Applications.- Towards Practical Enforcement Theories.- Session 6: Protocols and Protocol Analysis.- Security Analysis of AN.ONs Payment Scheme.- Formal Analysis of the Estonian Mobile-ID Protocol.- Generating In-Line Monitors for Rabin Automata.

On the design of low rate turbo codes

Low rate codes can be used to achieve coding gain in spread spectrum applications such as direct-sequence code division multiple access. Super-orthogonal- and maximum free distance convolutional codes as well as super-orthogonal turbo codes have previously been reported to be suitable for such systems. We focus on the design of component codes for low rate turbo coding schemes targeting the frame-error rate at low signal-to-noise ratios. We present code search criteria which yield high performing turbo codes on the additive white Gaussian noise channel. Simulation results show that these codes perform better than other low rate turbo codes previously reported in the literature.

Proactive Handover in Heterogeneous Networks Using SIPs

In some areas, overlapping networks provide alternative wireless links like WLAN, GSM, 3G etc. Ideally, the user should be connected to the most attractive network any time according to predefined priorities. This is accomplished with automatic handover. The most likely commercial application of this type is designed for speech, and is using SIP to set up VoIP calls through WLAN networks or mobile networks. To make the handover time as short as possible is essential to make it attractive. This is best done by preparing the alternative networks before the handover is needed. This is called proactive handover. This paper suggests changes to some of the basic SIP messages that open for proactive handover in SIP and help reduce the delays when roaming.