Joachim Wehinger, PhD - Profile on Academia.edu (original) (raw)

Papers by Joachim Wehinger, PhD

Iterative Equalizer Using Soft-Decoder Feedback for Mimo Systems in Frequency-Selective Fading

userver.ftw.at

Iterative receiver structures for multiple-input-multiple-output (MIMO) systems, as well as for c... more Iterative receiver structures for multiple-input-multiple-output (MIMO) systems, as well as for code division mul-tiple access (CDMA), are known to achieve significantly better performance than single-step receivers, at the cost of modest increase in complexity ([1, 2, 3, 4]). The main ...

Method for Processing Data

The invention relates to a method for compiling programs on a system consisting of at least one f... more The invention relates to a method for compiling programs on a system consisting of at least one first processor and a reconfigurable unit. It is provided in this method that the code parts suitable for the reconfigurable unit are determined and extracted and the remaining code is extracted in such a manner for processing by the first processor.

Radio receiver and method for channel estimation

Circuit for signal processing and method performed by such circuit

Device and method for distortion-robust decoding

Iterative multi-user receivers for CDMA systems

Novel SINR-to-CQI Mapping Maximizing the Throughput in HSDPA

2007 IEEE Wireless Communications and Networking Conference, 2007

The HSDPA extension of UMTS promises an improved cell capacity and throughput. This enhancement i... more The HSDPA extension of UMTS promises an improved cell capacity and throughput. This enhancement is mainly achieved by three newly introduced techniques, namely adaptive modulation and coding, hybrid automatic repeat request, and fast scheduling. The used coding and modulation scheme depends on the transmitted transport block size, which in turn is signalled via the channel quality indicator (CQI). The CQI values are calculated with the help of SINRs at each User Equipments and fed back to the base station. An appropriate CQI estimation is necessary to transmit data packets with transport block sizes that maximize the throughput. Therefore, in this work we propose a novel SINR-to-CQI mapping which achieves optimum throughput for selected ITU propagation channel models.

Update Rate of Channel Estimation for UMTS-HSDPA in Time-Varying Channels

2006 IEEE 63rd Vehicular Technology Conference, 2006

We investigate the update rate for channel estimation in time-varying channels for UMTS-HSDPA. Ou... more We investigate the update rate for channel estimation in time-varying channels for UMTS-HSDPA. Our channel estimator is based on correlation of the received chip stream and the known pilot stream. This results in an averaging of the estimated channel over a block. First, we investigate the influence of the update rate by averaging over the perfectly known channel at the

2008 IEEE International Conference on Communications, 2008

We investigate link quality metrics (LQMs) based on mutual information (MI) for fast link adaptat... more We investigate link quality metrics (LQMs) based on mutual information (MI) for fast link adaptation (FLA) in IEEE 802.11n wireless local area network (WLAN) with convolutional coding and higher order modulations. The LQMs are scalar quantities that map the receiver's post-decoding behaviour in a frequency-selective channel into an equivalent behaviour in an AWGN channel. From this metric the expected packet error rate (PER) can be predicted. Two LQMs are presented that are derived from the SINRs of all sub-carriers and streams: the effective SNR and the effective mutual information. The effective mutual information is the mean mutual information including a correction factor which improves the PER estimation accuracy in various highly frequency-selective channels. The FLA algorithm dynamically selects a modulation and coding scheme (MCS) that maximizes the throughput (TP), while keeping the average PER over time below a target value. Furthermore, we present methods of searching for the most suitable MCS. Practical performance bounds are obtained by means of simulations. We show that both investigated LQMs yield accurate PER estimates and that the resulting TP of the FLA algorithm used in a 2 × 2 MIMO bit-interleaved coded modulation (BICM) OFDM system that performs channel estimation is only 1.7 dB from the performance bound of the TP.

Proceedings of the 3rd IEEE International Symposium on Signal Processing and Information Technology (IEEE Cat. No.03EX795), 2004

A novel adaptive space-time Rake receiver is proposed for UMTS frequency division duplex mode bas... more A novel adaptive space-time Rake receiver is proposed for UMTS frequency division duplex mode based on the adaptive minimum bit error rate (AMBER) criterion. The design of this space-time Rake receiver builds on previous results reported by Chen et al. for temporal or spatial processing, respectively. The original AMBER approach assumes short spreading sequences, i.e. they need to be invariant from symbol to symbol. Here we extend the approach to joint space-time processing and tailor the receiver specifically for a UMTS FDD system with long scrambling sequences in the uplink. The base station receiver uses a two-or fourelement antenna array.

IEEE 6th Workshop on Signal Processing Advances in Wireless Communications, 2005., 2005

In this paper, we show by simulations that the interference generated by the Synchronization Chan... more In this paper, we show by simulations that the interference generated by the Synchronization Channel (SCH) and Common Pilot Channel (CPICH) has considerable impact on the throughput of the High-Speed Physical Downlink Shared Channel (HS-PDSCH) in UMTS. First, the simulation model for High Speed Downlink Packet Access (HSDPA) in UMTS is described. The downlink physical layer for the user data on the HS-PDSCH is modelled in detail, whereas the associated signalling is idealised as error-free. The interference from signalling and data channels on the HS-PDSCH is modelled adequately. As a general guideline for system settings in the simulations, we use the test cases specified in 3GPP TS 25.101 whenever applicable.

ITG Workshop on Smart Antennas (IEEE Cat. No.04EX802), 2004

In this paper we examine a space-time multiuser receiver with two parallel interference cancellat... more In this paper we examine a space-time multiuser receiver with two parallel interference cancellation (PIC) stages for the uplink in the UMTS-FDD mode. The structure has a performance which is better than the one of the maximum-ratio combiner (MRC) and can reach the single-user performance under the assumption of perfect channel knowledge. Even with channel estimation the propsed receiver achieves a very good performance while maintaining low complexity.

Upper Bounds on the Ergodic and Outage Capacities of Relay Networks Using UWB Links

2006 Fortieth Asilomar Conference on Signals, Systems and Computers, 2006

We derive, evaluate, and discuss upper bounds on ergodic and outage capacities for a three-node r... more We derive, evaluate, and discuss upper bounds on ergodic and outage capacities for a three-node relay network. The considered relay network has ultra-wideband (UWB) radio channels between the source, destination, and relay nodes. The derived bounds indicate that ergodic and outage capacities of the considered UWB-linked network increase up to 300% when a relay between the source and the destination is used. Furthermore, the bounds indicate that there is an optimum position for the relay node between the source and the destination, where ergodic capacity is maximized. Our numerical results shows that for the non-line-of-sight (NLOS) scenario, with the same signal to noise ratio on all links, the optimum position for the relay node is close to the center of source and destination.

Fifth IEE International Conference on 3G Mobile Communication Technologies (3G 2004) The Premier Technical Conference for 3G and Beyond, 2004

We propose an iterative receiver for a multi-carrier (MC) code division multiple access (CDMA) sy... more We propose an iterative receiver for a multi-carrier (MC) code division multiple access (CDMA) system in the uplink for users moving at vehicular speed. MC-CDMA is based on orthogonal frequency division multiplexing (OFDM), thus time-variant channel estimation can be performed for every subcarrier independently. The variation of a subcarrier over the duration of a data block is upper bounded by a maximum Doppler bandwidth which is determined by the maximum velocity of the users and the carrier frequency. We exploit results from the theory of time-concentrated and bandlimited sequences and apply a Slepian basis expansion for timevariant subcarrier estimation. The Slepian basis functions are determined by two parameters; the block length and the maximum Doppler bandwidth. This approach enables timevariant channel estimation without complete knowledge of the second-order statistics of the fading process. The performance of the iterative receiver is validated for a wide range of velocities by simulations.

Iterative receiver with channel estimation for MC-CDMA

Low-complexity joint data detection and channel estimation in time-variant flat-fading channels within the SAGE framework

2004 IEEE International Conference on Communications (IEEE Cat. No.04CH37577), 2004

In this work we compare channel estimation algorithms for use in an iterative CDMA receiver in a ... more In this work we compare channel estimation algorithms for use in an iterative CDMA receiver in a block fading environment. The receiver consists of a soft multiuser data estimator, a bank of single user decoders, and a multiuser channel estimator. The multiuser data estimator is implemented as parallel interference canceler with unconditional post-MMSE filtering (PIC-MMSE) and the decoder is a soft-in soft-out MAP decoder. In the channel estimator we make use of dedicated pilot symbols and fed back soft-code symbols which are exploited as additional soft pilot symbols when the iterations proceed. We show that using extrinsic information increases the receiver performance significantly compared to using a posteriori information in the feedback for channel estimation. We introduce a linear MMSE (LMMSE) estimator which takes into account the variances of fed back code symbols and compare it to approximations of the leastsquares (ALS) estimator and the linear minimum-mean-squareerror (ALMMSE) estimator. Performance results are illustrated in terms of bit error rate (BER) and average normalized square error (ANSE) of the channel estimators. They show that the newly proposed LMMSE algorithm outperforms the ALS and ALMMSE algorithms.

2006 IEEE 7th Workshop on Signal Processing Advances in Wireless Communications, 2006

In this work we analyze the mean-square error (MSE) of two correlative channel estimators in time... more In this work we analyze the mean-square error (MSE) of two correlative channel estimators in time-variant channels. Both estimators make use of orthogonal basis functions that approximate the time-variant channel. The first approximation is based on a set of time shifted rectangular basis (RB) functions. The second approximation makes use of Slepian basis (SB) functions. We calculate the number of basis functions that minimize the MSE for the RBand the SB-approach. Both estimators are designed for the full velocity range using the maximum velocity as design parameter only. Further, we apply the two estimators to the high-speed downlink packet access (HSDPA) mode of UMTS and illustrate the impact of the MSE on the throughput. With the SB-approach we observe a gain of roughly 0.4 dB over the RB-functions in case of an i.i.d. Rayleigh multipath channel with five taps.

IEEE International Conference on Communications, 2003. ICC '03., 2003

Multi-carrier code division multiple access (MC-CDMA) systems are under intense investigation for... more Multi-carrier code division multiple access (MC-CDMA) systems are under intense investigation for high bit rate wireless communication systems. Their equalization is based on the fast Fourier transform, allowing for an efficient implementation. Iterative receivers with joint detection and decoding have been shown to achieve very good performance for direct sequence (DS)-CDMA systems. We apply this concept to MC-CDMA, the multiuser detector is implemented as parallel interference canceller with post-minimum mean squared error filtering. In this contribution a new pilot based channel estimation scheme based on random time domain sequences is developed. The presented simulation results for a multi path scenario show, that in a fully loaded system with 64 users the single user bound can be approached up to 1 dB. A bit error rate (BER) of 10 −3 is reached already at an Eb/N0 of 12 dB with a 4 state, rate 1/2 convolutional code.