Tony Ottosson

Tony Ottosson
Chalmers University of Technology · Department of Signals and Systems

Professor

About

126
Publications
22,185
Reads
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2,741
Citations
Additional affiliations
January 1999 - July 1999
Ericsson
Position
  • Researcher
August 1993 - December 2008
Chalmers University of Technology

Publications

Publications (126)
Article
Full-text available
The underlying physical link is transparent in most IP-based networks. Contrary to this commonly accepted design rule, we propose that the applications should be made aware of the channel conditions. This is especially fruitful for wireless links where the performance is many orders of magnitudes lower than in fixed networks. Instead of wasting res...
Conference Paper
Full-text available
In this paper the downlink of a multi-user MIMO (MUMIMO) system with multi-mode transmission is considered. We propose a low-complexity algorithm for selecting users and the corresponding number of data streams to each user, denoted as user transmission mode (UTM). The selection is only based on the average received signal-to-noise ratio (SNR) from...
Conference Paper
In this paper we investigate the use of infrastructure half-duplex amplify-and-forward (AF) relays in the downlink of a multi-user (MU) multiple-input multiple-output (MIMO) system, which uses linear precoding based on block-diagonalization. Owing to the half-duplex mode of the relay, the communication is divided into two time-slots. During the fir...
Conference Paper
Recent academic studies of distributed antenna system (DAS) using a frequency-flat fading channel model show that DAS outperforms standard systems, where the base-station (BS) antenna elements are centralized at one location. In this paper the performance of a DAS under time-varying frequency-selective fading based on a realistic channel model is i...
Article
Full-text available
In this paper, several algorithms for compressing the feedback of channel quality information are presented and analyzed. These algorithms are developed for a proposed adaptive modulation scheme for future multi-carrier 4G mobile systems. These strategies compress the feedback data and, used together with opportunistic scheduling, drastically reduc...
Article
Full-text available
In this paper multirate DS/CDMA systems for multimedia applications are dis- cussed. Several modulation schemes for handling multiple bit rates in DS/CDMA are described. An overview of multiuser detectors in general and successive interference cancella- tion (IC) schemes for multirate schemes in particular is given. Numerical bit error probability...
Article
Full-text available
For wireless systems with adaptive modulation and/or scheduling, feedback of channel quality information is often necessary. It has been questioned whether the increased system performance is worth the additional feedback rate and the increased algorithm complexity. In this paper, we study how the feedback rate can be minimized, without losing the...
Article
Full-text available
High data rates, high spectral efficiency, flexibility, and low delays over the air interface will be important features in next-generation wireless systems. The overall challenge will be packet scheduling and adaptive radio transmission for multiple users, via multiple antennas and over frequency-selective wideband channels. This problem needs to...
Article
In wireless communication, adaptive modulation and scheduling are promising techniques for a substantially increased spectral efficiency. To achieve the throughput gain, it is necessary to feedback channel quality information. The required feedback rate may be prohibitively high in many applications, and compression of the feedback information is n...
Article
Full-text available
We focus on wireless multimedia communication and investigate how cross-layer information can be used to improve performance at the application layer, using JPEG2000 as an example. The cross-layer information is in the form of soft information from the physical layer. The soft information, which is supplied by a soft decision demodulator, yields re...
Article
Full-text available
The problem of finding the optimal labeling (bit-to-symbol mapping) of multilevel coherent phase shift keying (PSK), pulse amplitude modulation (PAM), and quadrature amplitude modulation (QAM) constellations with respect to minimizing the bit-error probability (BEP) over a Gaussian channel is addressed. We show that using the binary reflected Gray...
Article
This paper presents an extension for adaptive transmission of a multi-user scheduling algorithm to a cellular environment. In an effort to manage inter-cell interference, scheduling between neighboring base stations is coordinated. To this end, the amount of buffered data at each base station is exchanged within a small group of base stations. More...
Conference Paper
Full-text available
This paper presents an extension for adaptive transmission of a multi-user scheduling algorithm to a cellular environment. In an effort to manage inter-cell interference, scheduling between neighboring base stations is coordinated. To this end, the amount of buffered data at each base station is exchanged within a small group of base stations. More...
Conference Paper
Using an OFDM based uplink for future cellular networks has been a controversial issue due to difficulties in carrier frequency synchronization. In this paper, a model is provided to quantify the effects of Gaussian distributed carrier frequency offsets in a multiuser OFDM uplink. Both theoretical evaluations and simulations on spectral efficiency...
Article
Full-text available
Systems using coherent multilevel PSK to communicate over flat Rayleigh fading channels are considered. Presented is a closed-form expression for the exact bit error probability when the binary reflected Gray code is used to map bits to symbols. The result is a general, simple, and correct expression, which has not been previously available in the...
Conference Paper
Full-text available
Recent research has shown that a single-carrier system with frequency domain equalization can be a potential alternative to an OFDM-based system in a single user case. In this paper we propose and evaluate an adaptive single-carrier TDMA uplink with scheduling for broadband cellular packet data systems. Frequency division duplex (FDD) is assumed....
Conference Paper
Full-text available
This paper presents two new layer 4 fairness measures, the worst case TCP fairness index and the TCP fairness index. The purpose of the two indices is to measure the performance of algorithms scheduling elastic traffic in wireless networks. Numerical evaluation of round-robin, proportional-fair and max-rate scheduling shows that the new measures ca...
Article
This paper presents a novel unified analysis for the bit-error rate in the downlink of convolutionally coded and single-user detected multicarrier code-division multiple access (CDMA), multicarrier direct-sequence CDMA, time and frequency-domain spreading CDMA, and orthogonal frequency-division multiple access. Performance is analyzed under the ass...
Technical Report
Full-text available
This document contains a first assessment of adaptive transmission schemes and how these fit to the different WINNER scenarios. It focuses on an adaptation due to the channel properties that may vary both in time and frequency or, with respect to the selected antennas, in an OFDM-based air interface. Besides the evaluation by analysis, link si...
Article
Full-text available
This paper concerns the problem of selecting a binary labeling for the signal constellation in M-PSK, M-PAM, and M-QAM communication systems. Gray labelings are discussed and the original work by Frank Gray is analyzed. As is noted, the number of distinct Gray labelings that result in different bit-error probability grows rapidly with increasing co...
Conference Paper
Full-text available
In this paper we study the problem of implementing a successive interference canceller (SIC) for a WCDMA system in fixed-point electronics. Typically, fixed-point implementation is based on an iterative design of simulations and experience, resulting in a time-consuming and inefficient process. From the experience of a conventional design with simu...
Conference Paper
This paper proposes that fairness in wireless networks should be measured using one of the following new measures: the deterministic unfairness bound called the wireless absolute fairness bound (WAFB) or the statistical unfairness bound called the 99-percentile wireless absolute fairness bound (WAFB<sub>99</sub>). Compared with previous fairness de...
Conference Paper
Full-text available
This paper is concerned with the problem of selecting a binary labeling for the signal constellation in an M-PSK communication system. A good starting point is labelings having the Gray property, but this is not altogether enough, since the number of distinct Gray labelings that result in different bit error probability grows rapidly with increasin...
Article
This paper presents a unified analysis for the downlink BER performance of convolutionally coded and single-user detected MC-CDMA, MCDS-CDMA and TFL-CDMA. As a special case, an analysis is obtained also for OFDMA. The intra-cell interference is analyzed under the assumption of Hadamard spreading codes and a correlated frequency-selective Rayleigh-f...
Article
Multiuser detectors (MUD) can significantly increase the spectral efficiency of Code Division Multiple Access (CDMA) systems. In this paper, we present a symbol-level fixed-point Successive Interference Canceller (SIC) that is feasible to implement in Rapid Single Flux Quantum (RSFQ) superconducting electronics. A design procedure for finding the p...
Article
Full-text available
Error free transmission is not always possible in today's nor future's communication networks without making retransmissions. Retransmissions, however, introduce delay. To delay sensitive applications the concept of soft information, i.e. lower layer knowledge about the channel conditions, could reduce the number of retransmissions. This paper expl...
Article
Full-text available
The problem of calculating the average bit-error probability (BEP) of coherent M-ary phase-shift keying (PSK) over a Gaussian channel has been studied previously in the literature. A solution to the problem for systems using a binary reflected Gray code (BRGC) to map bits to symbols was first presented by P.J. Lee (see ibid., vol.COM-34, p.488-91,...
Conference Paper
This paper addresses the problem of evaluating the bit-error probability of the individual bits of a symbol in a communication system using coherent M-ary phase shift keying. Exact expressions are provided, and these are evaluated for seven different mappings from bits to symbols, including five Gray mappings, for a 32-PSK system. It is shown that...
Conference Paper
Full-text available
A downlink radio interface for cellular packet data systems with wide area coverage and high spectral efficiency is evaluated. A slotted OFDM radio interface is used, in which time-frequency bins are allocated adaptively to different mobile users within a downlink beam, or sector, based on their channel quality. Frequency division duplex (FDD) is...
Conference Paper
Full-text available
A downlink radio interface is proposed for cellular packet data systems with wide area coverage and high spectral efficiency. A slotted OFDM radio interface is used, in which time-frequency bins are allocated adaptively to different users within a downlink beam, based on their channel quality. Fading channels generated by vehicular 100 km/h user...
Conference Paper
A downlink radio interface for cellular packet data systems with wide area coverage and high spectral efficiency is evaluated. A slotted OFDM radio interface is used, in which time-frequency bins are allocated adaptively to different mobile users within a downlink beam, or sector, based on their channel quality. Frequency division duplex (FDD) is a...
Conference Paper
Full-text available
This paper explores the utilization of soft information in image decoding. Error free transmission is not always possible in today's nor future's communication networks without retransmissions. Retransmissions, however, introduce delay. To delay sensitive applications the concept of soft information, i.e. lower layer knowledge about the channel con...
Conference Paper
Full-text available
In this paper we describe an OFDM based 4G downlink for a wide area coverage and high mobility system. User data are multiplexed and OFDM modulated such that the user with the best predicted channel conditions are always using the channel. This user employs the linear modulation scheme that maximizes the spectral efficiency. We show that the syst...
Article
The extraordinary speed of RSFQ circuits is attractive for the implementation of a successive interference canceller, which is one of the most effective types of multiuser detector. We present system design analysis, optimizing the bit error rate performance and targeting a doubling of the uplink capacity. A complete model is considered: a long-cod...
Chapter
Code-division multiple access is a method allowing several users to share a common physical channel. Different users use different signature sequences for their messages. The signature sequences and the channel determine the interference between different users in the receiver and the performance of the synchronization method used, and thus the sig...
Article
The calculation of the exact bit (BER) and symbol error probabilities of coherent M-ary phase-shift keying (M-PSK) in a Gaussian channel is addressed. We present an alternative formulation of the solution using the cumulative distribution function of the noncentral t-distribution, which is a well-studied distribution in the field of statistics and...
Article
Full-text available
Multiuser detectors (MUD) can significantly in-crease the spectral efficiency of Code Division Multiple Access (CDMA) systems. In this paper, we present a symbol-level fixed-point Successive Interference Canceller (SIC) that is feasible to implement in Rapid Single Flux Quantum (RSFQ) superconducting electronics. A design procedure for finding the...
Article
The problem of calculating the average bit-error probability (BER) of coherent M-ary phase shift keying(PSK) over a Gaussian channel has been studied previously in the literature. A solution to the problem forsystems using a binary reflected Gray code (BRGC) to map bits to symbols was first presented by Lee in [1].
Conference Paper
The noncentral t-distribution that is used to evaluate the symbol-error probability of coherent M-ary phase-shift keying (PSK) is showed. We also give a method to obtain the exact bit-error probability for the binary reflected Gray mapping, and we note that the new expression reveals an error in previously published results.
Article
Full-text available
In this paper, we propose a hybrid type-II Automatic Repeat request (ARQ) scheme based on optimized Rate Compatible Punctured Convolutional (RCPC) codes combined with simple repetition codes. The proposed scheme has the prospect to provide high throughput over Rayleigh fading channels. This scheme starts the transmission with a rate i code which is...
Conference Paper
Full-text available
A packet switched wireless cellular system with wide area coverage, high throughput and high spectral efficiency is proposed. Smart antennas at both base stations and mobiles improve the antenna gain and improve the signal to interference ratio. The small-scale fading is predicted and a slotted OFDM radio interface is used, in which time-frequency...
Article
This paper studies the trade-off between coding and direct-sequence spreading in a code-division multiple-access (CDMA) system, in the presence of errors in the delay estimate. One extreme is when all spreading is done by forward error correcting codes , referred to as code-spread CDMA (CS-CDMA) systems. CS-CDMA systems have been shown to achieve h...
Article
Full-text available
The bit error rate (BER) of a code spread CDMA system, using low rate convolutional codes for spreading, is analyzed. The system is assumed to operate over a Rayleigh flat fading channel, and white Gaussian noise is added at the receiver front-end. Based on a Gaussian approximation, expressions for the pdf of the signal-to-noise ratios are derived...
Article
Full-text available
Delay estimation of a code-spread codedivision multiple-access (CS-CDMA) system using low-rate maximum free distance (MFD) convolutional codes for bandwidth expansion is studied. Using the repetitive structure of the low-rate MFD codes, the codewords are first permuted using a criterion based on the Cramer-Rao bound that results in good delay estim...
Article
Full-text available
An OFDM-CDMA system that utilizes the channel correlation in both time and frequency to reduce multiple access interference is proposed. Orthogonal Walsh-Hadamard codes are used for spreading and in order for the codewords to stay orthogonal at the receiver, the channel response must be flat in both time and frequency. A frequency selective fading...
Article
Full-text available
Delay estimation of a code-spread code-division multiple-access (CS-CDMA) system using low-rate maximum free distance (MFD) convolutional codes for bandwidth expansion is studied. The MFD codes used, have a repetitive structure, which is utilized for non-data-aided synchronization. The repetition pattern of the code is optimized for good delay esti...
Article
this paper. New estimator proposal The output of the intermediate encoder, for one data bit, is regarded as a set of independent nuisance parameters but, it is actually based on one single bit. Thus, if also the memory of the code is taken into account, the estimator performance will improve
Article
This paper compares the bit-error rate (BER) of both CS-CDMA systems and DS-CDMA systems when using the estimators proposed in [4]. The influence of parameters such as code rate, constraint length and observation interval length is studied
Technical Report
Full-text available
A packet switched wireless cellular system with wide area coverage and high throughput is proposed. The system is designed to be cost effective and to provide high spectral efficiency. It makes use of a combination of tools and concepts: - Smart antennas both at base stations and mobiles, provide antenna gain and improve the signal to interferen...
Article
Recently two new classes of low-rate codes have been presented. The first class is the superorthogonal turbo codes (SOTCs) and the second is the maximum free distance (MFD) convolutional codes.
Conference Paper
Full-text available
A packet switched wireless cellular system with wide area coverage and high throughput is proposed. The system is designed to be cost effective and to provide high spectral efficiency. It makes use of a combination of tools and concepts: - Smart antennas both at base stations and mobiles, provide antenna gain and improve the signal to interfer...
Conference Paper
Full-text available
An OFDM-CDMA system that utilizes the channel-correlation in both time and frequency to reduce multiple access interference is proposed. The mutually orthogonal Walsh-Hadamard codes are used for spreading, and in order for the codewords to stay orthogonal at the receiver the channel must be flat in both time and frequency. A frequency-selective fad...
Article
In this paper we discuss the application of rapid single flux quantum (RSFQ) superconducting digital technology for multiuser detection in wideband code division multiple access base stations. The extraordinary speed of the RSFQ circuits allows us to implement one of the most reliable types of multiuser detector, the successive interference cancell...
Conference Paper
Full-text available
A packet switched wireless cellular system with wide area coverage and high throughput is proposed. It is designed to be cost effective and to provide high spectral efficiency. The high performance is achieved by the use of long term channel predictions, in both time and frequency, scheduling among users, and smart antennas combined with adaptive...
Conference Paper
Full-text available
A packet switched wireless cellular system with wide area coverage, high throughput and high spectral efficiency is proposed. Smart antennas at both base stations and mobiles improve the antenna gain and improve the signal to interference ratio. The small-scale fading is predicted and a slotted OFDM radio interface is used, in which time-freque...
Article
Full-text available
The performa,- in terms of bit-error proba, ity of low-ra convolutiona codes isa ddressed. The Heller bound on the free dista is revisedai a na,- e formula is given. A discussion of the keypa,- determining the code performa ar how toobta good codes is followed bya compa of codes of va ra fora fixedconstra t length. It is concluded tha simply loweri...
Article
Full-text available
When a convolTcode is used to provide forward error correction for packet data transmission, the standard performance measures of convolTcodes, i.e., bit error rate and first-event error rate, become lme useful Instead we are interested in the averageprobabilT y of bl ck (or packet) error. In this paper a modified transfer function approach is used...
Conference Paper
Full-text available
The Wireless IP project within the PCC program studies problems that are crucial in the evolution of UMTS to-wards high data rates, as well as in future 4G technologies aimed at rapidly mobile terminals. The goal is to attain higher throughput for packet data in particular in downlinks, without bandwidth expansion and while providing acceptabl...
Article
Recent publications on new improved convolutional codes claim different codes to be optimum under the optimum distance spectrum (ODS) criterion. This correspondence presents results from a study independent of the previous works, and seeks to clarify some inconsistencies. In addition, some new improved feed-forward convolutional encoders are presen...
Conference Paper
Full-text available
The bit error rate (BER) of a code spread CDMA system, using low rate convolutional codes for spreading, is analyzed. The system is assumed to operate over a Rayleigh flat fading channel, and white Gaussian noise is added at the receiver front end. Based on a Gaussian approximation, expressions for the pdf of the signal-to-noise ratios are derived...
Conference Paper
Full-text available
To evaluate the performance of a convolutional code it is common to use a union bound on either the bit-error rate or the first-event error rate. Since these bounds are given as infinite sums they must be truncated to be evaluated. However, as the tail of the infinite sum is discarded, the upper bound turns into an approximation. Two methods to eva...
Article
Full-text available
Different modulation schemes supporting multiple data rates in a Direct Sequence Code Division Multiple Access (DS/CDMA) system are studied. Both AWGN and multipath Rayleigh fading channels are considered. It is shown that the multi processing-gain scheme and the multi-channel scheme have almost the same performance. However, the multi-channel sche...
Article
Full-text available
In this paper the performance of different multi-rate schemes in Direct Sequence Code Division Multiple Access (DS/CDMA) systems are evaluated. The assumptions are random code sequences and AWGN channel. We have looked at four different solutions: different spreading factors, mixed modulation, parallel channels and Parallel Combinatory Spread Spect...
Article
Full-text available
The performance of a CDMA system employ-ing very low-rate maximum free distance codes for com-bined coding and spreading is analyzed when successive o r parallel interference cancellation is applied. An analytical approach to the evaluation of the bit error rate is presented and shown to give results close to simulations. Our results show that the...
Article
Full-text available
Flexible and low-complexityvariable rate coding schemes based on rate-compatible
Article
Full-text available
In this work we studied the performance of the hybrid type-II Automatic Repeat reQuest #ARQ# system on Rayleigh fading channels. This system is based on High Rate Optimized Rate Compatible Punctured Convolutional #HRO-RCPC# codes combined with simple repetition codes. The performance is investigated for di#erent packet sizes and constraint lengths...
Article
Full-text available
Flexible and low-complexityvariable rate coding schemes based on rate-compatible convolutional
Article
Currently, a global third-generation cellular system based on code-division multiple-access (CDMA) is being developed with a wider bandwidth than existing second-generation systems. The wider bandwidth provides increased multipath resolution in a time-dispersive channel, leading to higher frequency-selectivity. A generalized RAKE receiver for inter...
Article
In a CDMA cellular system, the process of the mobile station searching for a cell and achieving code and time synchronization to its downlink scrambling code is referred to as cell search. Cell search is performed in three scenarios: initial cell search when a mobile station is switched on, idle mode search when inactive, and active mode search dur...
Article
Full-text available
In our previous work, we have proposed a hybrid typeII Automatic Repeat reQuest (ARQ) scheme (Scheme 5) based on the Rate Compatible Punctured Convolutional (RCPC) codes which performs significantly better than all the other ARQ schemes in all the channel conditions. In this work, we study the performance of Scheme 5 based on High Rate Optimized RC...
Article
Full-text available
CDMA is a key technology to be used for 3rd generation personal communication systems. In this paper we first give a brief overview of the ETSI wideband CDMA (WCDMA) system. Research to improve WCDMA and similar systems is however still ongoing and we will describe some of the key aspects that we believe will be important in the near future. In a W...
Article
A multicode direct-sequence code-division multiple-access system experienceslarge envelope variations as a result of a sum of many independently spreadsignals. However, large envelope variations is problematic because it reducesthe spectral efficiency, the efficiency of the power amplifiers and theperformance. All these effects depend on the non-li...
Conference Paper
Changing from orthogonal spreading codes in a direct-sequence CDMA (DS-CDMA) system to more powerful forward error correcting convolutional codes is proven superior in an asynchronous uplink system. This approach is referred to as code-spread CDMA (CS-CDMA). In this paper these two systems are compared in a synchronous downlink scenario. Both syste...
Article
We consider joint source-channel and multiuser decoding for frequency selective Rayleigh fading code-division multiple-access channels. The block source-channel encoder is defined by a vector quantizer. We investigate optimal (minimum mean-square error) decoding and “user-separated” decoding of lower complexity. The studied decoders are soft in the...
Article
Full-text available
In code division multiple-access (CDMA) systems, maximum total throughput assuming a matched filter receiver can be obtained by spreading with low-rate error control codes. Previously, orthogonal, bi-orthogonal and super-orthogonal codes have been proposed for this purpose. We present in this paper a family of rate-compatible low-rate convolutional...
Conference Paper
In this paper, a generalized RAKE receiver for interference suppression and multipath mitigation is proposed. The receiver exploits the fact that time dispersion significantly distorts the interference spectrum from each base station in the downlink of a CDMA system. Compared to the conventional RAKE receiver, this generalized RAKE receiver may hav...
Conference Paper
Full-text available
Different floating-point and fixed-point implementation issues of the log-MAP algorithm for decoding turbo codes are studied. A theoretical framework is proposed to explain why the log-MAP turbo decoders are more tolerant of overestimation of SNR than underestimation. A linear approximation (the Log-Lin algorithm) that allows for efficient ASIC imp...
Conference Paper
In this paper, algorithms for cell search in W-CDMA are presented. Two scenarios of cell search are considered: (i) the initial cell search when a mobile station is switched on; and (ii) the target cell search in idle and active modes. For the initial cell search, large frequency errors (e.g. 20 kHz) are considered. The performance of cell search i...
Conference Paper
Delay estimation of a code-spread code division multiple access (CS-CDMA) system using low-rate maximum free distance (MFD) convolutional codes for bandwidth expansion is studied. Using the repetitive structure of the low-rate MFD codes, the codewords are first permuted using a criterion based on the Cramer-Rao bound that results in good delay esti...
Article
The performance of an asynchronous code division multiple access (CDMA) system (uplink) employing very low-rate maximum free distance codes for combined coding and spreading is analyzed when successive or parallel interference cancellation is applied. An analytical approach to the evaluation of the bit error rate is presented and shown to give resu...