
Tony OttossonChalmers University of Technology · Department of Signals and Systems
Tony Ottosson
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126
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January 1999 - July 1999
August 1993 - December 2008
Publications
Publications (126)
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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....
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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,...
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...
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 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...
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...
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...
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...
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...
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...
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...
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...
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].
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.
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...
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...
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...
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...
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...
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...
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...
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
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
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...
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.
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
Flexible and low-complexityvariable rate coding schemes based on rate-compatible
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...
Flexible and low-complexityvariable rate coding schemes based on rate-compatible convolutional
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...