Juergen Lindner

A distributed differential space-time coding scheme for two-way wireless relay networks

We propose a distributed differential space-time coding scheme for two-way relaying over unknown block Rayleigh fading channels. The accent is on a two-time slots scheme, where in the first stage both terminals transmit their signals to the relays and in the second stage the relays broadcast to the terminals. Although we do not assume channel knowledge neither at the relays nor at the terminals, we show that it is possible for the terminals to subtract their contribution from the broadcasted signal and decide on the desired signal from the other terminal. The performance analysis reveals that the two-time slots differential scheme offers advantage over the traditional four-time slots differential scheme.

Multiple window-sliding search

A search for a single pattern in random data is a topic that had attracted attention of both mathematicians and engineers. This paper derives the statistical parameters of an extended problem - a search for multiple patterns - introducing an analytical tool for a broad range of applications.

Iterative detection algorithms for extended MC-CDMA

Multicarrier code division multiple access (MC-CDMA) combines the advantages of CDMA and orthogonal frequency division multiplexing techniques. For time-varying channels, it can be further improved by introducing an additional spreading in the time direction (extended MC-CDMA). Two low complexity iterative detection algorithms with soft feedback are described: the iterative soft block decision feedback equalizer and a recurrent neural network based detector. Performance results are given for a typical mobile radio channel and compared to the optimum maximum likelihood detector. Introducing pilot symbol assisted channel estimation, the optimum number of pilot symbols is determined and the bit error rate performance is compared to the case of ideal channel estimation.

Detection method for MC-CDMA based on a recurrent neural network structure

A detection method based on a recurrent neural network structure is derived for a multi carrier code division multiple access communication system with multi path propagation. Contrary to other neural network approaches, the RNN has the advantage, that network size as well as the coefficients of the network can be derived from parameters which characterize the communication system. The energy function of the RNN is identical to the log-likelihood function of the maximum likelihood detector. Different iteration algorithms for the RNN with an emphasis on parallel processing are discussed. Performance results are given for the Rayleigh fading channel and a typical mobile radio channel. Performance and complexity of the RNN detector are compared with other iterative detection algorithms, specifically a block decision feedback equalizer.

Non-coherent two-way relaying: Rate bounds for the high SNR regime

Rate bounds for the non-coherent two-way relaying channel under the high SNR assumption are derived. No channel knowledge is assumed at neither the terminals nor at the relays. An upper and lower bound on the achievable rates are derived and shown that they differ only by a constant in the high SNR regime. As corollary from the analysis, the degrees of freedom of the non-coherent two-way channel are derived. Additionally, it is shown that the degrees of freedom can be achieved by an AF scheme.

A Recursive Construction of High-Dimensional Grassmann Space-Time Codes for Non-Coherent MIMO Systems

This paper presents a method for construction of high-dimensional Grassmann space-time codes for non-coherent block fading MIMO channels, aiming at codes with large block lengths compared to the number of transmit antennas. The construction method is recursive, starting from a low-dimensional coherent or non-coherent code. The performance analysis of the constructed codes supports the theoretical prediction of performance improvement when increasing the code block length. Additionally, the code structure could potentially offer a possibility for complexity reduction of the decoding procedure.

Block turbo equalization for imperfect channel state information

We propose a soft-input soft-output block equalizer based on constrained minimum variance filters. In contrast to other schemes, our receiver is designed for imperfect channel state information and incorporates the statistics of the channel estimation error. Thereby, we distinguish between data independent and data dependent evaluation of the covariance matrix of the estimation error. We show that the performance of our block equalizer is significantly improved when considering the influence of the actual data symbols on the estimation error. The additional complexity compared to the case when ignoring the data dependency of the estimation error increases quadratically with the block length. We assess the performance of our equalizer for block Rayleigh fading channels via Monte Carlo simulation, employing turbo equalization and one-shot training-based channel estimation

MC-CDMA and OFDMA for indoor communications: the influence of multiple receiving antennas

The influence of multiple receiving antennas on the bit error rate is considered for MC-CDMA and OFDMA. It is shown that in a frequency-selective environment reception with a general multiuser/multiantenna receiver the performance of both schemes tend to become similar with an increasing number of antennas. As an example, this is demonstrated for an indoor scenario.

A non-coherent AF scheme for two-way wireless relay networks based on packings in Grassmann manifolds

Motivated from results for the point-to-point block MIMO fading channels without channel knowledge, we propose an AF scheme for the non-coherent two-way relaying channel with the half-duplex constraint. The communication takes place in two phases, multicast and broadcast. In the multicast phase the terminals send the signals simultaneously. In the broadcast phase, the relays resend the signal received in the broadcast phase. The code construction is based on subspace packings in the Grassmann manifolds. We show, that although no channel knowledge is assumed at either the terminals or at the relays, the terminals are able to subtract the self-interference part of the received signal. The performance analysis shows that the noncoherent two-way relaying outperforms non-coherent one-way relaying and delivers the promise of increased spectral efficiency.

Some geometric methods for construction of space-time codes in Grassmann manifolds

Geometric methods for construction of codes in the Grassmann manifolds are presented. The methods follow the geometric approach to space-time coding for the non-coherent MIMO channel where the code design is interpreted as a packing problem on Grassmann manifolds. The differential structure of the Grassmann manifold provides parametrization with the tangent space at the identity element. Grassmann codes for the non-coherent channel are constructed by mapping suitable subsets of lattices from the tangent space to the Grassmann manifold via the exponential map. As examples, constructions from the rotated Gosset, Barnes-Wall and Leech lattice are presented. Due to the specifics of the mapping, some of the structure is preserved after the mapping to the manifold. The method is further improved by modifying the mapping from the tangent space to the manifold. Ideas for other constructions of Grassmann codes are also presented and discussed.