Fredrik Lindqvist

Line Topology Identification Using Multiobjective Evolutionary Computation

The broadband capacity of the twisted-pair lines strongly varies within the copper access network. It is therefore important to assess the ability of a digital subscriber line (DSL) to support the DSL services prior to deployment. This task is handled by the line qualification procedures, where the identification of the line topology is an important part. This paper presents a new method, denoted topology identification via model-based evolutionary computation (TIMEC), for line topology identification, where either one-port measurements or both one- and two-port measurements are utilized. The measurements are input to a model-based multiobjective criterion that is minimized by a genetic algorithm to provide an estimate of the line topology. The inherent flexibility of TIMEC enables the incorporation of a priori information, e.g., the total line length. The performance of TIMEC is evaluated by computer simulations with varying degrees of information. Comparison with a state-of-art method indicates that TIMEC achieves better results for all the tested lines when only one-port measurements are used. The results are improved when employing both one- and two-port measurements. If a rough estimate of the total length is also used, near-perfect estimation is obtained for all the tested lines.

Crosstalk channel estimation via standardized two-port measurements

The emerging multiuser transmission techniques for enabling higher data rates in the copper-access network relies upon accurate knowledge of the twisted-pair cables. In particular, the square-magnitude of the crosstalk channels between the transmission lines are of interest for crosstalk-mitigation techniques. Acquiring such information normally requires dedicated apparatus since crosstalk-channel measurement is not included in the current digital subscriber line (DSL) standards. We address this problem by presenting a standard-compliant estimator for the square-magnitude of the frequency-dependent crosstalk channels that uses only functionality existing in todays standards. The proposed estimator is evaluated by laboratory experiments with standard-compliant DSL modems and real copper access network cables. The estimation results are compared with both reference measurements and with a widely used crosstalk model. The results indicate that the proposed estimator obtains an estimate of the square-magnitude of the crosstalk channels with a mean deviation from the reference measurement less than 3 dB for most frequencies.

CSIT sharing over finite capacity backhaul for spatial interference alignment

Cellular systems that employ time division duplexing (TDD) transmission are good candidates for implementation of interference alignment (IA) in the downlink since channel reciprocity enables the estimation of the channel state by the base stations (BS) in the uplink phase. However, the interfering BSs need to share their channel estimates via backhaul links of finite capacity. A quantization scheme is proposed which reduces the amount of information exchange (compared to conventional methods) required to achieve IA in such a system. The scaling (with the transmit power) of the number of bits to be exchanged between the BSs that is sufficient to preserve the multiplexing gain of IA is derived1.

Control Channel Design Trade-Offs for Ultra-Reliable and Low-Latency Communication System

Future generation of wireless networks, i.e. 5G, is envisioned to support several new use-cases demanding transmission reliability and latency that cannot be achieved by the current cellular networks such as long-term evolution (LTE). This paper looks at different design aspects of the control channel(s) to support ultra-reliable low-latency communication considering factory automation as an example scenario. In particular, we show that a fairly balanced design for both the uplink and the downlink control channels can be made given an appropriate selection of modulation, coding, diversity scheme, and time/frequency resources. By means of link-level simulations, we also show that the proposed control channel design supports a block-error rate of 10-9 under Rayleigh fading conditions at a signal-to-interference-plus-noise ratio comparable to that supported by current 4G systems (e.g. LTE). Furthermore, a radio frame structure is proposed to support the user plane end-to-end latency of 1 ms.

Low‐Order and Causal Twisted‐Pair Cable Modeling by Means of the Hilbert Transform

A new low-order and causal twisted-pair cable model for the copper access network is derived. From the serial resistance of the widely used, but non-causal, BT0 model, the serial inductance is computed via the Hilbert transform. By doing so, a causal cable model is obtained containing fewer parameters compared to the BT0 model. The deviation between the two models is evaluated for the standardized ETSI cables.

Impact of crosstalk channel estimation on the DSM performance for DSL networks

The development and assessment of spectrum management methods for the copper access network are usually conducted under the assumption of accurate channel information. Acquiring such information implies, in practice, estimation of the crosstalk coupling functions between the twisted-pair lines in the access network. This type of estimation is not supported or required by current digital subscriber line (DSL) standards. In this work, we investigate the impact of the inaccuracies in crosstalk estimation on the performance of dynamic spectrum management (DSM) algorithms. A recently proposed crosstalk channel estimator is considered and a statistical sensitivity analysis is conducted to investigate the effects of the crosstalk estimation error on the bitloading and on the achievable data rate for a transmission line. The DSM performance is then evaluated based on the achievable data rates obtained through experiments with DSL setups and computer simulations. Since these experiments assume network scenarios consisting of real twisted-pair cables, both crosstalk channel estimates and measurements (for a reference comparison) are considered. The results indicate that the error introduced by the adopted estimation procedure does not compromise the performance of the DSM techniques, that is, the considered crosstalk channel estimator provides enough means for a practical implementation of DSM.

Impact of Crosstalk Estimation on the Dynamic Spectrum Management Performance

The development and assessment of spectrum management methods for the copper access network are usually conducted under the assumption of accurate channel information. Acquiring such information implies, in practice, estimation of the crosstalk coupling functions between the twisted-pair lines in the access network. However, this estimation is not supported or required by current digital subscriber line (DSL) standards. In this work, we investigate the impact of non-ideal crosstalk estimation on the dynamic spectrum management (DSM) performance. Two different crosstalk estimators are considered: a conventional model-based estimator and a novel estimation procedure. The DSM performance is evaluated based on the obtained crosstalk estimates for two different network scenarios consisting of real twisted-pair cables. For a reference comparison, the crosstalk channels are measured with a network analyzer. The simulation results indicate that the novel estimation procedure achieves DSM performance results close to the ones obtained with the network analyzer and that the model-based estimator can lead to an inaccurate rate estimation.

Frequency Domain Echo Canceller for DMT-Based Systems

This letter addresses echo cancellation for digital subscriber line (DSL) communications with discrete multitone (DMT) modulation. The described adaptive echo canceller operates entirely in the frequency domain. The method allows estimation and subtraction of an echo signal impaired by intercarrier and intersymbol interference present when the impulse response of the echo channel is longer than the cyclic prefix. Implementation aspects for symmetric and asymmetric DMT-based systems are described together with ways to lower the computational complexity. Finally, computer simulation results are presented that validates the proposed method.

Characterization of Subscriber Local Loop by Measures and Analysis of Frequency and Impulse Responses

This paper presents methodologies that could be used for characterizing subscriber telephone loops that carry DSL services (ADSL and ADSL2+), by determination and analysis of frequency response, time domain reflectometry, and impulse response of the line. From this analysis, the subscriber loop length, identification and location of impairments such as bridged taps, gauge changes, and open ended termination across the line are carried out. To verify the methodologies presented, results obtained from measurements are drawn and compared to results obtained from computational simulations.

Message Authentication Based on Cryptographically Secure CRC without Polynomial Irreducibility Test

In this paper, we present a message authentication scheme based on cryptographically secure cyclic redundancy check (CRC). Similarly to previously proposed cryptographically secure CRCs, the presented one detects both random and malicious errors without increasing bandwidth. The main difference from previous approaches is that we use random instead of irreducible generator polynomials. This eliminates the need for irreducibility tests. We provide a detailed quantitative analysis of the achieved security as a function of message and CRC sizes. The results show that the presented scheme is particularly suitable for the authentication of short messages.