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  • 1.
    Isaksson, Mikael
    et al.
    Telia Research.
    Mestdagh, Denis
    Sjöberg, Frank
    Luleå tekniska universitet.
    Nilsson, Rickard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Ödling, Per
    Bengtsson, Daniel
    Pulse shaping with zipper: spectral compatibility and asynchrony1998Rapport (Övrigt vetenskapligt)
    Abstract [en]

    We have investigated what the effects of adding pulse shaping and windowing to a Zipper-VDSL system would be. By adding short, pulse-shaped wings to the DMT symbol and accepting the, say, 3 % efficiency loss, the spectral sidelobes of the DMT-symbol are reduced. This provides several attractive features including the following: · The pulse shaping in the transmitter reduces the out of band power of the DMT-signal. · The spectral compatibility with other systems such as ADSL and CAP-VDSL is enhanced. · It becomes feasible to use Zipper-VDSL in a time-asynchronous mode, where a VTU-R only synchronizes itself to its VTU-O, while the VTU-R / VTU-O pair may be asynchronous to all other transceiver pairs. · The pulse shaping gives some increase in the depth of spectral notches, for HAM-bands etc. The windowing is a part of a powerful RFI-ingress suppressing method as proposed by John Bingham, Amati.

  • 2. Jakovljevic, Milos
    et al.
    Statovci, Driton
    Nordström, Tomas
    Nilsson, Rickard
    Zazo, Santiago
    VDSL power back-off parameter optimization for a cable bundle2007Ingår i: Proceedings: EUSIPCO 2007, 15th European Signal Processing Conference : September 3 - 7, 2007, Pozna´n, Poland / [ed] Marek Domański; Ryszard Stasiński; Maciej Bartkowiak, Poznan: Poznań University of Technology , 2007, s. 550-554Konferensbidrag (Refereegranskat)
    Abstract [en]

    To better utilize the capacity of the twisted-pair access networks, operators deploying very high-speed digital subscriber line (VDSL) systems need accurate parameters for power back-off (PBO). However, VDSL standards give almost no guidance on how these parameters should be established for a particular network. In this paper we present a new technique for optimizing PBO parameters for a cable bundle, which is based on the Nelder–Mead simplex search algorithm. In this way each operator can easily calculate PBO parameters that match its actual access network down to the individual cable bundle. Using the properties of the PBO, as defined in the VDSL standard, we show how a normalized FEXT coupling can replace the knowledge of the individual couplings during the optimization of the PBO parameters. By simulations based on measured cable data we show that our approach using cable bundle unique PBO (CUPBO) achieves a significant improvements compared to the performance achieved with the ordinary PBO. 1.

  • 3.
    Mohamad, Medhat
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nilsson, Rickard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Beek, Jaap van de
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    A Novel Transmitter Architecture for Spectrally-Precoded OFDM2018Ingår i: IEEE Transactions on Circuits and Systems Part 1: Regular Papers, ISSN 1549-8328, E-ISSN 1558-0806, Vol. 65, nr 8, s. 2592-2605Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Frequency nulling spectral precoding is an approachthat suppresses the out-of-band emission in OFDM systems.In this paper, we discuss the transmitter architecture of thespectrally precoded OFDM systems. We design a novel precoderthat matches the practical implementation of the OFDM modulator.We show that spectral precoding can relax the analog lowpass filtering requirements of the OFDM system transmitter. Weexamine the effect of spectral precoding on the PAPR as wellas the effect of the PA on the spectral precoding suppressionperformance. We also study the compliance of the spectrallyprecoded OFDM transmitter with the 3GPP standardizationmeasures and analyze its computation complexity. At the receiverside, we analyze the in-band interference and BER performanceof the suggested precoding approach.

  • 4.
    Mohamad, Medhat
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nilsson, Rickard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Beek, Jaap van de
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    An analysis of out-of-band emission and in-band interference for precoded and classical OFDM systems2015Ingår i: European Wireless 2015: 21th European Wireless Conference, 20-22 May 2015, Budapest, Hungary, Piscataway, NJ: IEEE Communications Society, 2015, artikel-id 7147703Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper we present analytical expressions for the out-of-band (OOB) emission and in-band interference of two different OOB suppressed OFDM-systems; classical low-pass filtered and precoded. Then, we analytically compare their performance in terms of OOB emission suppression and introduced level of in-band interference. We analyse the fact that the in-band interference introduced by the filter depends on the length of the cyclic prefix as well as the behavior of the channel while that of the precoded OFDM does not. The analysis confirms that edged subcarriers suffer higher in-band interference than central subcarriers. Moreover, frequency precoders, for a specific choice of notching frequencies, can outperform time precoders.

  • 5.
    Mohamad, Medhat
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nilsson, Rickard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Beek, Jaap van de
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Minimum-EVM N-continuous OFDM2016Ingår i: 2016 IEEE International Conference on Communications (ICC): Kuala Lumpur, 22-27 May 2016, Piscataway, NJ: IEEE Communications Society, 2016, artikel-id 7511164Konferensbidrag (Refereegranskat)
    Abstract [en]

    The N-continuous precoder for the suppression ofOOB emission in OFDM systems that minimizes the EVM isintroduced. We show that the minimum in-band interference dueto the introduced precoding approach is 3 dB less than the inbandinterference of existing N-continuous precoders. Moreover,we introduce a novel practical block precoder that approachesthe performance of the suggested optimal precoder. We analyzethe spectrum of the OFDM signal after block precoding, the inbandinterference due to block precoding and the effect of blockprecoding on the BER. The price to pay for block precoding isthe computational complexity that grows linearly with the blocksize.

  • 6.
    Mohamad, Medhat
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nilsson, Rickard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Beek, Jaap van de
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    N-smooth OFDMIngår i: Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper introduces a new multicarrier system - a practical alternative for N-continuous OFDM: N-smooth OFDM. N-smooth OFDM improves the spectral compactness of practical OFDM systems by suppressing OOB emission. The higher spectral compactness of N-smooth OFDM allows the system to relax requirements of the digital to analog converter (DAC) construction filter. Moreover, it decreases the signal's self interference that results from spectral precoding as well as precoder's computational complexity. 

  • 7.
    Mohamad, Medhat
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nilsson, Rickard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    van de Beek, Jaap
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    An SDR-based prototype of spectrally-precoded OFDM2017Ingår i: EuCNC 2017: European Conference on Networks and Communications, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2017, artikel-id 7980758Konferensbidrag (Refereegranskat)
    Abstract [en]

    Spectrally precoded OFDM is a recent approach that aims for the suppression of the OOB, as well as the in-band gap, emissions in OFDM systems. Theoretically, the technique shows High suppression of the OOB and the in-band gap emissions. Although, practically hardware impairments may limit the precoder's performance. Yet, this demonstration shows that despite the hardware impairments, implemented spectrally precoded OFDM generates emissions tens of decibels less than that of plain OFDM. Therefore, the demonstration proves that communications links are less vulnerable to interference coming from spectrally precoded OFDM signals than to interference coming from plain OFDM signals

  • 8.
    Mohamad, Medhat
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nilsson, Rickard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    van de Beek, Jaap
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Spectrally-Precoded OFDM for 5G Wideband Operation in Fragmented sub-6GHz SpectrumArtikel i tidskrift (Refereegranskat)
    Abstract [en]

    We consider spectrally-precoded OFDM waveforms for 5G wideband transmission in sub-6GHz band. In this densely

    packed spectrum, a low out-of-band (OOB) waveform is a critical 5G component to achieve the promised high spectral

    efficiency. By precoding data symbols before OFDM modulation, it is possible to achieve extremely low out-of-band

    emission with very sharp spectrum transition enabling an efficient and flexible usage of frequency resources. Spectrallyprecoded

    OFDM shows promising results for reaching 5G targets in high-data rate enhanced mobile broadband and ultrareliable

    low-latency communications use cases. Spectral precoding is particularly efficient for wideband transmission

    enabling short-time transmission, which will often require flexible fragmented spectrum usage.

  • 9.
    Mohamad, Medhat
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Taheri, Tayebeh
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nilsson, Rickard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Beek, Jaap van de
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Subspace-precoded OFDM with low Out-of-Band Emissions:it will workManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    Today’s multicarrier transmitters, deployed in essentially all communications radio equipment we use(phones, TV’s, computers, etc.), contain means to avoid undesired out-of-band power emissions. Standards and regulations typically restrict the levels of these emissions in order to allow for an efficient use of the radio spectrum. Radio vendors deploy well-established algorithms such as low-pass filtering or windowing to satisfy these regulations. A new approach, specifically applicable to OFDM systems, known as spectralprecoding, has been studied during the last decade. In particular, subspace precoding has attracted theinterest of academia, for its elegance, and despite a few adamant disadvantages. Recent advances now provide a breakthrough: subspace precoding is now a viable alternative to today’s algorithms.

  • 10.
    Nilsson, Rickard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Activity: An SDR-based prototype of spectrally precoded OFDM2016Konferensbidrag (Övrig (populärvetenskap, debatt, mm))
    Abstract [en]

    OFDM scheme possesses high OOB emission which degrades the spectral efficiency of OFDM systems. Poor spectral efficiency limits the validity of OFDM as a candidate for 5G. Spectrally precoded OFDM is a recent approach that treats the OFDM signal to suppress the out of band (OOB) emission. Although the theoretical results of spectral precoding show very efficient OOB emission suppression (more than 50 dB reduction compared to plain OFDM), practically, hardware impairments limit its performance.We, at Luleå University of Technology, examine the practicality of the suggested approach and show for the first time through this demonstration that despite the hardware impairments, implemented spectral precoded OFDM has OOB emission tens of decibels less than that of plain OFDM. We set up and examine a communication link through which we approve that communication systems are less vulnerable to interference coming from spectrally precoded OFDM signals than to interference coming from plain OFDM signals.

  • 11.
    Nilsson, Rickard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Digital communication in wireline and wireless environments1999Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    This thesis consists of an introduction and five parts dealing with digital communication. Three parts address Discrete Multi-Tone modulation (DMT), a wireline form of Orthogonal Frequency Division Multiplexing (OFDM). One part addresses channel estimation in wireless OFDM and one addresses multiuser detection in wireless Direct Sequence-Code Division Multiple Access (DS- CDMA).The first part presents a new duplex method, called Zipper, for Very High bit rate Digital Subscriber Lines (VDSL). It is a duplex method that offer high flexibility and compatibility with existing services in the access network. The second part presents a digital Radio Frequency Interference (RFI) suppression method. It is located in the frequency domain and it can be used by any DMT-based VDSL system. The third part presents a method to run Zipper in an asynchronous mode with only a small performance loss. This can be of interest for telecom operators when constructing a VDSL system. The fourth part examines the trade-off between pilot symbol spacing and symbol error rate in a wireless OFDM system using Pilot Symbol Assisted Modulation (PSAM). The last part presents a low complexity multiuser detector for wireless DS-CDMA. It consists of a pipelined detector structure that produces Maximum Likelihood Secence Detector (MLSD) decisions on some of the received bits in the sequence. The remaining, previously undetected bits, are fed to a secondary post-processor.

  • 12.
    Nilsson, Rickard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Multicarrier modulation: duplexing design and interference/distortion mitigation2001Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Aspects of modern communication systems is the overall theme of this thesis with emphasis placed on multicarrier modulation. The work considers four facets of such systems; namely duplexing design, interference mitigation, channel estimation and multiuser detection. The first area deals with duplexing design for very high bit rate digital subscriber lines (VDSL) using discrete multitone modulation (DMT). We present a novel method based on DMT - the Zipper duplex method. Zipper is proposed for VDSL in different standardization bodies worldwide - International (ITU), North America (ANSI) and in Europe (ETSI) where it also has been accepted as a part of the VDSL standard. Zipper has superior flexibility and spectrum efficiency. This is obtained by freely assigning different subcarriers for the up- and downstream direction. In one design Zipper operates fully network synchronized by using a masterclock. In an asynchronous design Zipper operates without any reference to a masterclock which is a requirement for unbundled networks but reduces some of the flexibility. To obtain highest flexibility in unbundled networks, without using a masterclock, an algorithm is derived that self-synchronizes all Zipper modems. Another area deals with interference- and distortion mitigation. Narrowband interference (NBI) in orthogonal frequency division multiplexing- (OFDM) and DMT-based systems is considered. NBI can be very harmful for both radio- and wireline systems. We introduce two efficient NBI cancellers for OFDM and DMT. One canceller is based on a deterministic polynomial model of the NBI. The other canceller models it as a narrowband stochastic process and use the linear minimum mean square error (LMMSE) criterion for the cancellation. We lower its complexity by using the theory of optimal rank reduction. Impulse noise is a different type of harmful interference that can be encountered in VDSL. In this thesis we study the effects of impulse noise in DMT-based VDSL systems and present a robust generalized likelihood ratio test for detecting impulse noise. It is used for obtaining reliable erasures in a Reed-Solomon decoding scheme which reduces the probability of symbol errors significantly. Pilot symbol assisted modulation (PSAM) can be used in OFDM for tracking the distortion variations in a fading radio channel. We analyze the pilot symbol spacing in PSAM as a trade-off between high effective SNR and good channel tracking capabilities for two channel estimators with different complexities. Code division multiple access (CDMA) is part of the standard for the third generation of mobile phones. In this thesis we present a low complexity multiuser detector for a wireless DS-CDMA system. With a pipelined structure it can produce maximum likelihood sequence detector (MLSD) decisions on many of the received bits by only performing additions after the front end matched filters.

  • 13. Nilsson, Rickard
    On the estimation of improper noise in multicarrier DSL systems2005Ingår i: 2005 IEEE International Conference on Communications, 2005, s. 1142-1146Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper we consider the estimation of improper noise in multicarrier DSL systems. We show that the improperness of baseband noise relates to the mirrored frequency components in the positive and negative frequency halves. Spectral leakage in the receiver requires in general widely linear estimation (WLE) techniques of the noise instead of less complex linear estimation (LE) techniques. We describe how to take into account for the improperness in the estimation and how it is possible to neglect it by using smooth receiver windowing. This is demonstrated by using two similar but conceptually different noise estimators, which are based on deterministic and stochastic noise models, combined with LE or WLE. We also describe some practical properties of improper noise estimation in multicarrier DSL systems by showing intuition pleasing connections to spectral leakage, receiver windowing, dimensionality and model parameters, residual noise interference, and complexity.

  • 14.
    Nilsson, Rickard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Radiokanalmätningar i Aitik-gruvans öppna dagbrott: “Know your channel!”2014Rapport (Övrigt vetenskapligt)
    Abstract [sv]

    Vi har utfört bredbandiga radiokanalmätningar i Aitik-gruvans öppna dagbrott i 2.4 GHz bandet med hjälp av mjukvaruradio (SDR). Mätningarna visar att radioekoutbredningen inte sällan uppgår till ca 10-12 us (mikrosekunder) och ofta mer än ca 5 us, p.g.a. de mycket starka signalreflektioner som oundvikligen sker nere i gruvgropen. Radioekoutbredningen är mycket större än vad t.ex. kommersiellt tillgänglig WiFi (baserat på IEEE 802.11 standarden) är konstruerad för (dvs max 0.8 us ekoutbredning), men även modern mobiltelefoni (4G-LTE). En av konsekvenserna är att dessa system kraftigt begränsas av radioekona i Aitik-gruvan vilket väsentligt begränsar och försvårar tillförlitlig radiokommunikation även om den mottagna signalstyrkan är mer än tillräckligt hög.

  • 15.
    Nilsson, Rickard
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Beek, Jaap van de
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Channel Measurements in an Open-pit Mine using USRPs: 5G – Expect the Unexpected2016Ingår i: 2016 IEEE Wireless Communications and Networking Conference: WCNC 2016, Doha, Qatar, 3-7  April 2016, 2016, s. 212-217, artikel-id 7564672Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, we describe and analyze the results of a radio channel measurement campaign in an extreme industrial environment; a large open-pit copper mine targeted by next generation’s highly voiced device communications. We present a practical and efficient method to perform robust and high-sensitivity impulse response measurements without a common clock reference using the widely spread USRP hardware. With this technique, we performed channel sounding on a large number of locations within the mine. One important observation is that the radio channel’s impulse response in an open-pit mine can often be more than 10 microseconds long, and much unlike the responses normally associated with Wi-Fi and mobile cellular radio systems, which poses serious design challenges for future 5G radio systems.

  • 16.
    Nilsson, Rickard
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Edfors, Ove
    Luleå tekniska universitet.
    Sandell, Magnus
    Luleå tekniska universitet.
    Börjesson, Per Ola
    Luleå tekniska universitet.
    An analysis of two-dimensional pilot-symbol assisted modulation for OFDM1997Ingår i: 1997 IEEE International Conference on Personal Wireless Communications, Mumbai, India, December 17 - 19, 1997: [conference proceedings] / [ed] Quraish Bakir, Piscataway, NJ: IEEE Communications Society, 1997, s. 71-74Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper we analyze two-dimensional (2D) pilot-symbol assisted modulation (PSAM) for wireless orthogonal frequency-division multiplexing (OFDM). 2D-PSAM has been suggested for wireless OFDM by several authors and is included in a preliminary draft of the standard for European digital video broadcast. We generalize the analysis of single-carrier PSAM to the 2D time-frequency lattice of OFDM. We analyze 2D-PSAM for two different channel estimators: one with good performance and high complexity and one suboptimal with low complexity. We verify that a good rule of thumb is to place the pilots at least as twice as close, in time and frequency, as required by the 2D sampling theorem.

  • 17. Nilsson, Rickard
    et al.
    Magesacher, T.
    Trautmann, S.
    Nordström, T.
    Radio frequency interference suppression in DSL2006Ingår i: Fundamentals of DSL technology, Boca Raton, Fl.: Auerbach publ. , 2006, s. 399-450Kapitel i bok, del av antologi (Övrigt vetenskapligt)
  • 18. Nilsson, Rickard
    et al.
    Nordström, Tomas
    Status of G.vectoring2009Rapport (Övrigt vetenskapligt)
  • 19. Nilsson, Rickard
    et al.
    Nordström, Tomas
    Statovci, Driton
    Recent results on downstream channel estimation for vectored DSL2006Rapport (Övrigt vetenskapligt)
  • 20. Nilsson, Rickard
    et al.
    Nordström, Tomas
    Statovci, Driton
    Soft synchronization methods for multiuser DSL systems2006Rapport (Övrigt vetenskapligt)
  • 21. Nilsson, Rickard
    et al.
    Nordström, Tomas
    Statovci, Driton
    Survey of vectoring and MIMO methods in DSL2006Rapport (Övrigt vetenskapligt)
  • 22.
    Nilsson, Rickard
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Sjöberg, F.
    Wilson, S.K.
    Börjesson, P.O.
    Combating impulse noise in DMT-based VDSL systems1999Ingår i: Proceedings of radiovetenskap och kommunikation: Karlskrona 14-17 juni 1999 / RVK 99 / [ed] Jan-Olof Gustafsson, Karlskrona: Högskolan i Karlskrona/Ronneby , 1999, Vol. 1, s. 384-388Konferensbidrag (Refereegranskat)
  • 23.
    Nilsson, Rickard
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Sjöberg, Frank
    Luleå tekniska universitet.
    Edfors, Ove
    Luleå tekniska universitet.
    Ödling, Per
    Luleå tekniska universitet.
    Wilson, Sarah Kate
    Luleå tekniska universitet.
    Börjesson, Per Ola
    Luleå tekniska universitet.
    A low complexity threshold detector making MLSD decisions in a multiuser environment1998Ingår i: Pathway to a global wireless revolution: VTC '98, 48th IEEE Vehicular Technology Conference, Westin Hotel, Ottawa, Canada, 18 - 21 May 1998, Piscataway, NJ: IEEE Communications Society, 1998, s. 333-337Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper we present a pipelined implementation of an iterative threshold detector, which makes the same decisions as a maximum likelihood sequence detector (MLSD) on some, but not necessarily all, bits. We apply this as a first stage detector in a direct sequence code division multiple access (DS-CDMA) interference-limited multiuser system. In combination with the single-user matched filter (MF) detector we obtain improved performance and lower complexity than with the decorrelating receiver for a limited number of simultaneous users, e.g. up to 25 users with a spreading factor of 127.

  • 24.
    Nilsson, Rickard
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Sjöberg, Frank
    Luleå tekniska universitet.
    Isaksson, Mikael
    Luleå tekniska universitet.
    Cioffi, J.M.
    Stanford University.
    Wilson, S.K.
    ArrayComm, San Jose.
    Self-synchronizing a DMT-based VDSL system2001Ingår i: Where minds meet: 2001 IEEE International Conference on Communications ; ICC 2001. June 11 - 14, 2001 ; Helsinki ; conference record / IEEE Communications Society / [ed] Yrjö Neuvo, Piscataway, NJ: IEEE Communications Society, 2001, s. 1249-1253Konferensbidrag (Refereegranskat)
    Abstract [en]

    We present an algorithm for self-synchronizing all modems in a discrete multitone (DMT)-based very high-speed digital subscriber line (VDSL) system using the Zipper duplex method. This solves the problem with non-orthogonal near-end crosstalk (NEXT) that appears in systems with unsynchronized modems. The algorithm we present runs autonomously in each VDSL-modem. It uses the auto-correlation of the DMT-signal to determine the frame-offset of other users, and adjusts the own frame-timing to be better aligned with the other users. With our method all modems will be self-synchronized to within a small fraction of the total DMT frame-length. This self-synchronization suppresses the NEXT to a level far below the background noise-floor. This means that our self-synchronized system has the same performance as a system where all modems are perfectly synchronized to a master clock

  • 25.
    Nilsson, Rickard
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Sjöberg, Frank
    Luleå tekniska universitet.
    Isaksson, Mikael
    UpZide Labs AB, Aurorum.
    Cioffi, John
    Electrical Engineering Department, Stanford University.
    Wilson, Sarah Kate
    ArrayComm, San Jose.
    Autonomous synchronization of a DMT-VDSL system in unbundled networks2002Ingår i: IEEE Journal on Selected Areas in Communications, ISSN 0733-8716, E-ISSN 1558-0008, Vol. 20, nr 5, s. 1055-1063Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present an algorithm that autonomously synchronizes all DMT-Zipper based VDSL modems in an unbundled access network, solving the problem with nonorthogonal NEXT that appears in systems with unsynchronized modems. The algorithm we present runs autonomously in each VDSL-modem in the central office or in the street cabinet. We determine the other modems ' relative frame offsets by exploiting their NEXT signal using the inherent cyclic redundancy found in DMT signals. By estimating the relative frame offsets of the other users, we can adjust a given user's own frame-timing relative to the mean of the others. With our method all modems in the network will be synchronized to within a small fraction of the total DMT frame-length, suppressing the nonorthogonal NEXT to a level far below the background noise-floor. This means that we can achieve the same performance in an unbundled access network without any master clock reference as in a system where all modems are perfectly synchronized using a master clock. Index Terms-Discrete multitone, frame synchronization, subscriber loops.

  • 26.
    Nilsson, Rickard
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Sjöberg, Frank
    Luleå tekniska universitet.
    Leblanc, James
    A narrow-band interference canceller for OFDM-based systems2001Ingår i: Proceedings EPMCC 2001, 2001Konferensbidrag (Refereegranskat)
  • 27.
    Nilsson, Rickard
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Sjöberg, Frank
    Luleå tekniska universitet.
    Leblanc, James
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    A rank-reduced LMMSE canceller for narrowband interference suppression in OFDM-based systems2003Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 51, nr 12, s. 2126-2140Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a narrowband interference (NBI) canceller that suppresses spectral leakage in an orthogonal frequency-division multiplexing (OFDM)-based system caused by a narrowband (NB) signal. We assume that the spectrum of the NB signal is within the spectrum of the OFDM signal. This can be the case, e.g., on digital subscriber lines (DSL) and in new unlicensed frequency bands for radio transmission. The canceller makes linear minimum mean-square error estimates of the spectral leakage by measuring the NBI on a few modulated or unmodulated OFDM subcarriers. It uses a model of the NB signal's power spectral density as a priori information. Using a frequency invariant design, it is possible to cancel NBI from signals that are changing their frequency location with significantly reduced complexity overhead. The operational complexity of the canceller can be lowered by using the theory of optimal rank reduction and using the time-bandwidth product of the NB signal. Analytical performance evaluations, as well as Monte Carlo simulations, show that, without perfect a priori information, this canceller can suppress the spectral leakage from a strong NB signal (e.g., with equal power as the OFDM signal) to well below the background noise floor for typical applications where it causes negligible signal-to-noise ratio and symbol error rate degradation.

  • 28. Nordström, Tomas
    et al.
    Statovci, Driton
    Nilsson, Rickard
    Best practice report on active copper resource management in current DSL2006Rapport (Övrigt vetenskapligt)
  • 29. Nordström, Tomas
    et al.
    Statovci, Driton
    Nilsson, Rickard
    M3.2.1 – Survey of advanced xDSL solutions and proposals for BANITS22007Rapport (Övrigt vetenskapligt)
  • 30.
    Pirinen, Pekka
    et al.
    Oulu University.
    Saarnisaari, Harri
    Oulu University.
    Beek, Jaap van de
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Matinmikko-Blue, Marja
    Oulu University.
    Nilsson, Rickard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Latva-aho, Matti
    Oulu University.
    Wireless Connectivity for Remote and Arctic Areas – Food for Thought2019Konferensbidrag (Refereegranskat)
  • 31. Schmid, R.
    et al.
    Nordström, Tomas
    Nilsson, Rickard
    DSL interoperability - problems and solutions2004Rapport (Övrigt vetenskapligt)
  • 32.
    Sjöberg, Frank
    et al.
    Luleå tekniska universitet.
    Isaksson, Mikael
    Telia Research AB.
    Deutgren, Petra
    Telia Research AB.
    Nilsson, Rickard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Ödling, Per
    Luleå tekniska universitet.
    Börjesson, Per Ola
    Luleå tekniska universitet.
    Performance evaluation of the Zipper duplex method1998Ingår i: New century communications: conference record / ICC '98, 1998 IEEE International Conference on Communications, 7 - 11 June 1998, Atlanta, Georgia, USA, Piscataway, NJ, 1998, s. 1035-1039Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper we present performance results for a new duplex scheme, called Zipper, for DMT-based VDSL systems on copper wires. This scheme divides the available bandwidth by assigning di¤erent subcarriers for the upstream and downstream direction. It has high .exibility to divide the capacity between the up- and downstream as well as good coexistence possibilities with other systems such as ADSL. Simulation results show high bitrate performance in different environments such as mixed ADSL and VDSL traffic, under radio frequency interference, and with different background noise sources.

  • 33.
    Sjöberg, Frank
    et al.
    Luleå tekniska universitet.
    Isaksson, Mikael
    Telia Research AB.
    Nilsson, Rickard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Ödling, Per
    Lunds universitet.
    Wilson, Sarah Kate
    Luleå tekniska universitet.
    Börjesson, Per-Ola
    Lunds universitet.
    Zipper - a duplex method for VDSL based on DMT1999Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 47, nr 8, s. 1245-1252Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a new duplex scheme, called Zipper, for discrete multitone (DMT)-based very high bit-rate digital subscriber line (VDSL) systems on copper wires. This scheme divides the available bandwidth by assigning different subcarriers for the upstream and downstream directions. It has high flexibility to divide the capacity between the up and downstream, as well as good coexistence possibilities with other systems such as ADSL. Simulation results show the high bit-rate performance in different environments such as mixed ADSL and VDSL traffic under radio frequency interference and with different background noise sources

  • 34. Sjöberg, Frank
    et al.
    Nilsson, Rickard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Börjesson, Per Ola
    Ödling, Per
    Wiese, Brian
    Bingham, John A. C.
    Digital RFI Suppression in DMT-based VDSL Systems2004Ingår i: IEEE Transactions on Circuits and Systems Part 1: Regular Papers, ISSN 1549-8328, E-ISSN 1558-0806, Vol. 51, nr 11, s. 2300-2312Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, we propose a method for suppressing radio frequency interference (RFI) in discrete multitone (DMT) based very high bit rate digital subscriber line (VDSL) systems. The method operates in the frequency domain of a DMT system. First, we derive a model of how an unknown narrow-band RF signal is mapped onto the DMT carriers. Then, by measuring the RFI on a few unused DMT carriers we are able to subtract RFI estimates from every modulated subcarrier. Simulation results show that this method, applied to an RFI signal with the same average power as the VDSL signal, suppresses the RFI with 40-50 dB, which reduces the average SNR loss from about 20 to less than 0.3 dB.

  • 35.
    Sjöberg, Frank
    et al.
    Luleå tekniska universitet.
    Nilsson, Rickard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Grip, Niklas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Börjesson, Per Ola
    Luleå tekniska universitet.
    Wilson, Sarah Kate
    Luleå tekniska universitet.
    Ödling, Per
    Luleå tekniska universitet.
    Digital RFI suppression in DMT-based VDSL systems1998Ingår i: ICT '98: International Conference on Telecommunications : bridging east & west through telecommunications : 21-25 June 1998, Porto Carras, Greece / [ed] F-N. Pavlidou, 1998, Vol. 2, s. 189-193Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper we describe a method for supressing Radio Frequency Interference (RFI) in Discrete Multitone (DMT) based Very High bit rate Digital Subscriber Line systems. The method operates in the frequency domain of a DMT-system. It is based on a Taylor-expanded transfer function which maps the disturbance from the RF-signal onto the DMT-carriers. By measuring the RF-disturbance on a few unmodulated DMT-carriers we are able to subtract estimates of the disturbance from every modulated DMT-carrier. The RF-signal is assumed to be an unknown narrowband signal. Simulation results show that this method, applied to an RFI-signal with the same average power as the VDSL-signal, reduces the SNR-loss from about 20 dB to less than 1 dB.

  • 36.
    Sjöberg, Frank
    et al.
    Luleå tekniska universitet.
    Nilsson, Rickard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Isaksson, Mikael
    Telia Research AB, Aurorum 6.
    Ödling, Per
    Lund Institute of Technology, Department of Applied Electronics.
    Börjesson, Per Ola
    Lund Institute of Technology, Department of Applied Electronics.
    Asynchronous Zipper: [subscriber line duplex method]1999Ingår i: IEEE International Conference on Communications: 6 - 10 June, 1999, Vancouver, British Columbia, Canada, Piscataway, Nj: IEEE Communications Society, 1999, Vol. 1, s. 231-235Konferensbidrag (Refereegranskat)
    Abstract [en]

    Previously the authors presented a novel duplex method for very high bit-rate digital subscriber lines (VDSL) called Zipper. With this method all VDSL-modems on different wires in the same bindergroup have to be time-synchronized to avoid near-end cross-talk (NEXT). We describe a method which enables Zipper to run in a time-asynchronous mode. By introducing pulse-shaping in the transmitter and windowing in the receiver the NEXT is almost completely suppressed even though the synchronization between modems on neighboring lines is skipped. The remaining NEXT and efficiency loss due to pulse-shaping and windowing results in only a small bit-rate performance loss, typically less than 10% compared to the time-synchronized Zipper. However, with the new freedom of optimizing the lengths of the cyclic suffices with asynchronous Zipper, there may even be a small improvement in bit-rate performance for short wires

  • 37.
    Sjöberg, Frank
    et al.
    Luleå tekniska universitet.
    Nilsson, Rickard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Wilson, Sarah Kate
    Luleå tekniska universitet.
    Bengtsson, Daniel
    Telia Research.
    Isaksson, Minkael
    Telia Research.
    Power back-off for multiple target bit rates1998Rapport (Övrigt vetenskapligt)
    Abstract [en]

    This contribution describes a new efficient method to perform power back-off in the upstream of a VDSL-system. The method gives higher data rates than the earlier proposals, i.e., the constant back-off method and the reference length method. One conceptual difference with this new method is that we are not using just one design parameter as with the reference frequency and reference length methods. With this new method all users are assigned a certain service class, a target bit rate. The method then performs the power back-off such that it tries to maximize the bit rate (the system margin) for all the other users. The method tries to create FEXT, at each NT, that has the same spectral shape as the background noise. Between 5% and 20% improvement in bit rates is achieved with this new method when using the FSAN models for cable, crosstalk and background noise. The larger improvements over the other methods appear when non-flat background is present. This is because the PSD of the background noise is included in the model used by method. For thinner wires, like the TP1 wire, the method can give more than 20% higher data rate for almost all users.

  • 38. Statovci, Driton
    et al.
    Nordström, Tomas
    Nilsson, Rickard
    Dynamic Spectrum Management for Standardized VDSL2007Ingår i: IEEE International Conference on Acoustics, Speech and Signal Processing: proceedings : April 16-20, 2007, Hawaii Convention Center, Honolulu, Hawaii, U.S.A., Piscataway, NJ: IEEE Signal Processing Society, 2007, s. III-73Konferensbidrag (Refereegranskat)
    Abstract [en]

    Dynamic spectrum management (DSM) improves the capacity utilization of twisted-pair cables by adapting the transmit power spectral density (PSD) of modems to the actual noise environment and channel conditions. Earlier proposed DSM algorithms do not take into account the standardized very high speed digital subscriber line (VDSL) constraints on the allowable transmit PSDs. However, VDSL modems support only restricted transmit PSD shapes resulting from the standardized power back-off (PBO) method, which is controlled by a small set of parameters. Furthermore, since all modems are currently using the same PBO parameters their bit rate performance is severely limited. In this paper, we show how to effectively exploit the standardized PBO concept for DSM to significantly boost bit rates. We also present a low complex DSM algorithm, the user unique PBO (UUPBO) algorithm, for calculating PBO parameters that are uniquely optimized for each modem

  • 39. Statovci, Driton
    et al.
    Nordström, Tomas
    Nilsson, Rickard
    Short overview of spectrum balancing schemes for multiuser DSL2006Rapport (Övrigt vetenskapligt)
  • 40. Statovci, Driton
    et al.
    Nordström, Tomas
    Nilsson, Rickard
    Spectrum balancing for DSL with restrictions on maximum transmit PSD2007Ingår i: Proceedings of the AccessNets 2007: second International Conference on Access Networks, Piscataway, N.J.: IEEE Signal Processing Society, 2007, s. 1-5Konferensbidrag (Refereegranskat)
    Abstract [en]

    To better utilize the capacity of the twisted-pair access networks, operators deploying very high-speed digital subscriber line (VDSL) systems need accurate parameters for power back-off (PBO). However, VDSL standards give almost no guidance on how these parameters should be established for a particular network. In this paper we present a new technique for optimizing PBO parameters for a cable bundle, which is based on the Nelder–Mead simplex search algorithm. In this way each operator can easily calculate PBO parameters that match its actual access network down to the individual cable bundle. Using the properties of the PBO, as defined in the VDSL standard, we show how a normalized FEXT coupling can replace the knowledge of the individual couplings during the optimization of the PBO parameters. By simulations based on measured cable data we show that our approach using cable bundle unique PBO (CUPBO) achieves a significant improvements compared to the performance achieved with the ordinary PBO. 1.

  • 41. Statovci, Driton
    et al.
    Nordström, Tomas
    Nilsson, Rickard
    The constrained normalized-rate iterative algorithm2005Ingår i: 2005 1st International Conference on Computers, Communications and Signal Processing w/Special Track on Biomedical Engineering, Piscataway, NJ: IEEE Communications Society, 2005, s. 50-54Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Dynamic spectrum management (DSM) aims to increase the utilization of cable capacity by adapting the spectra of digital subscriber line (DSL) systems to the real network environment. In this paper we present a new DSM algorithm: the constrained normalized-rate iterative algorithm (C-NRIA). The C-NRIA extends the existing NRIA by ensuring predefined fixed bitrates to some of the users in the cable bundle while offering bitrates to the remaining users on a best effort basis. This reflects many business scenarios where a number of users must be guaranteed a specific service. We show that this type of the optimization problem can be solved efficiently with the C-NRIA by introducing only one balancing parameter that splits the cable capacity among the two user groups.

  • 42.
    Statovci, Driton
    et al.
    Telecommunications Research Center Vienna.
    Nordström, Tomas
    Telecommunications Research Center Vienna.
    Nilsson, Rickard
    The normalized-rate iterative algorithm: a practical dynamic spectrum management method for DSL2006Ingår i: EURASTP journal an applied signal processing, ISSN 1110-8657, E-ISSN 1687-0433, Vol. 2006, nr 95175, s. 1-17Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a practical solution for dynamic spectrum management (DSM) in digital subscriber line systems: the normalized-rate iterative algorithm (NRIA). Supported by a novel optimization problem formulation, the NRIA is the only DSM algorithm that jointly addresses spectrum balancing for frequency division duplexing systems and power allocation for the users sharing a common cable bundle. With a focus on being implementable rather than obtaining the highest possible theoretical performance, the NRIA is designed to efficiently solve the DSM optimization problem with the operators' business models in mind. This is achieved with the help of two types of parameters: the desired network asymmetry and the desired user priorities. The NRIA is a centralized DSM algorithm based on the iterative water-filling algorithm (IWFA) for finding efficient power allocations, but extends the IWFA by finding the achievable bitrates and by optimizing the bandplan. It is compared with three other DSM proposals: the IWFA, the optimal spectrum balancing algorithm (OSBA), and the bidirectional IWFA (bi-IWFA). We show that the NRIA achieves better bitrate performance than the IWFA and the bi-IWFA. It can even achieve performance almost as good as the OSBA, but with dramatically lower requirements on complexity. Additionally, the NRIA can achieve bitrate combinations that cannot be supported by any other DSM algorithm.

  • 43. Statovci, Drtiton
    et al.
    Nordström, Tomas
    Nilsson, Rickard
    Oksman, V.
    Revised upstream power back-off for VDSL2006Ingår i: 2006 IEEE International Conference on Acoustics, Speech and Signal Processing: Toulouse, France, 14 - 19 May 2006, Piscataway, N.J.: IEEE Signal Processing Society, 2006, s. IV-633-IV-636Konferensbidrag (Refereegranskat)
    Abstract [en]

    Accurate upstream power back-off (PBO) parameters are needed by operators deploying very high-speed digital subscriber line (VDSL) modems. Although a standardized PBO method for VDSL exist, the standard gives little or no guidance to an operator how to establish these optimized PBO parameters for its particular network and customers. In this paper, we present an efficient algorithm based on the Nelder-Mead simplex search which calculates optimized upstream PBO parameters. To make the PBO parameter calculation independent of the network scenario we present a new method for establishing worst-case far-end crosstalk (FEXT) noise, which is based on virtual modems

  • 44.
    Taheri, Tayebeh
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Mohamad, Medhat
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nilsson, Rickard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Beek, Jaap van de
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Joint spectral-spatial precoders in massive-MIMO OFDM transmittersIngår i: Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper we propose novel joint spectral-spatial precoders for large-antennaOFDM systems that suppress both spatial multi-user interference and spectral out-ofbandpower emissions. We analyse the performance of the proposed precoder in termsof spectral characteristics, system sum-rate and transmitter complexity. We show inparticular that, interestingly, the proposed joint maximum-ratio precoder has a simpletransmitter structure of two separate and consecutive banks of spectral and spatialprecoders.

  • 45.
    Taheri, Tayebeh
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nilsson, Rickard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Beek, Jaap van de
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Asymmetric Transmit-windowing for low-latency and robust OFDM2016Ingår i: Globecom Workshops (GC Wkshps), 2016 IEEE, Piscataway, NJ: IEEE Communications Society, 2016, artikel-id 7848842Konferensbidrag (Refereegranskat)
    Abstract [en]

    In the content of low-latency 5G systems we revisit in this paper the question of shortening the cyclic prefix in windowed OFDM system without sacrificing OOB power emissions or increasing the ISI and ICI. Based on interference power analysis we propose a new asymmetric window which provides 30 percent cyclic prefix length reduction without increasing adjacent-channel interference power or channel-induced ISI/ICI.

  • 46.
    Taheri, Tayebeh
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nilsson, Rickard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Beek, Jaap van de
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Quasi-Cyclic Symbol Extensions for Shaping the OFDM Spectrum2018Ingår i: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248, Vol. 17, nr 10, s. 7054-7066Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    N-continuous orthogonal frequency division multiplexing (OFDM) is a promising solution to the outof- band (OOB) emission issue in OFDM systems where the Nth-order continuity between OFDM symbols leads to lower OOB emission than the plain OFDM, however, high self-interference in such systems is an obstacle. In this paper we propose a new class of quasi-cyclic symbol extensions which makes the OFDM system N- continuous. The new extension leads to low OOB emission while the additive interference is less than other N-continuous OFDM systems. Moreover, we propose a general analysis of the spectrum and interference that occurs in a linear precoded OFDM system. The framework is applicable to many N-continuous OFDM systems including our proposed method.

  • 47.
    Tayebeh, Taheri
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nilsson, Rickard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    van de Beek, Jaap
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Hybrid spectral precoding/windowing for low-latency OFDM2017Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper we present a joint precoded and windowed OFDM system. This new hybrid method provides flexibility to suppress the out-of band (OOB) emission in non-contiguous OFDM systems used in cognitive radio. This method also provides the possibility of shortening the cyclic prefix without sacrificing the OOB emission or increasing the additional interference which is the case in low-latency future systems.

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