Papers by Katsutoshi Kusume
2008 IEEE 19th International Symposium on Personal, Indoor and Mobile Radio Communications, 2008
We propose a new differential recursive update algorithm, which significantly reduces the complex... more We propose a new differential recursive update algorithm, which significantly reduces the complexity of iterative minimum mean square error (MMSE) detection and decoding techniques for spread spectrum communication systems. Although the MMSE detector is a less complex suboptimum solution comparing to the optimum one, it is still complex for iterative systems because a large number of matrix inversions need to be computed over different users, symbols, and iterations. The new algorithm enables a smooth transition from the MMSE detection with full complexity to the simple matched filter solution over iterations, thereby achieving complexity reduction. We show by means of computer simulations that the complexity is drastically reduced by the newly proposed algorithm at the expense of increased memory requirements.
International Journal of Wireless Information Networks, 2005
scheme for OFDM systems based on channel state information at the transmitter. The filter is deri... more scheme for OFDM systems based on channel state information at the transmitter. The filter is derived for frequency-selective MISO as well as for SlSO channels using a minimum mean square error criterion with a constraint on transmit power. The guard interval of the resulting transmitted signal is no longer cyclic extension. Drawbacks of OFDM systems such as severe performance degradation for long channel delays exceeding the guard interval and vulnerability to possible nulls of the channel frequency response are addressed. Unlike existing equalizer variants at the receiver, our proposal combats these drawbacks by introducing computational complexity only at the transmitter while the receiver is kept simple as it is an advantage of OFDM systems against single carrier systems. Performance improvement has been confirmed by computer simulations.
The 13th IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, 2000
We present space-time transmit filters for FDD DS-CDMA systems based on partial channel state inf... more We present space-time transmit filters for FDD DS-CDMA systems based on partial channel state information, i. e. we do not take into account the channel coefficients. Although the FDD transmit zero-forcing filter seems to be the most intuitive approach, we focus on the FDD transmit matched filter and the FDD transmit Wiener filter. Similarly to the respective receive filters and TDD transmit filters, the FDD matched filter maximizes the desired signal portion at the receiver and is optimum for low signal-to-noise-ratio scenarios, whereas the FDD transmit Wiener filter takes into account the noise power at the receiver and is therefore able to find an optimum trade-off between signal maximization and interference suppression. Additionally, we show that the FDD transmit matched filter is a type of Eigenbeamforming. The simulation results reveal the excellent performance of the two FDD transmit filters. The FDD transmit Wiener filter even outperforms the TDD transmit matched filter for high signalto-noise-ratio which is based on the instantaneous channel properties.
We consider some aspects of interleave division multiple access (IDMA) in ad hoc networks. IDMA i... more We consider some aspects of interleave division multiple access (IDMA) in ad hoc networks. IDMA is a multiple access technique which relies on an iterative multiuser detection and it has a close relation to CDMA. Traditionally, the medium access control protocol sees the physical layer as a collision model, while in literature the potential of multiuser detection techniques in ad hoc networks has been discussed. Higher efficiency can be achieved if a certain amount of interference is allowed due to the multiuser detection. In this paper we propose a simple complexity reduction technique for IDMA and a design of multiple user-distinct interleavers. The complexity reduction technique is aimed to support a variety of receivers with different capabilities of handling interference. It allows to reduce the complexity significantly while graceful performance degradation can be realized. The proposed multiple interleavers are designed so as to minimize memory requirements and signaling overhead by deriving multiple interleavers from one common interleaver.
EURASIP Journal on Wireless Communications and Networking, 2011
In order to allow for dense spatial reuse in wireless ad hoc networks, multiple access interferen... more In order to allow for dense spatial reuse in wireless ad hoc networks, multiple access interference must be dealt with. This calls for advanced physical layer techniques, such as multiuser detection (MUD) or power control. However, these techniques can only be efficiently applied to ad hoc networks when they are part of a joint physical layer (PHY) and Medium Access Control (MAC) cross-layer design (CLD). In order to better understand both, the potential but also the limits of handling interference by means of MUD and power control, respectively, in this article we provide a comprehensive comparison between MUD-based and power control-based CLDs. We study the behavior of both approaches in terms of throughput, delay, as well as fairness in scenarios with high and low user densities, respectively. To provide more detailed insight in the interaction between MAC and PHY, we separate for each approach the throughput results into gains achieved solely by the MAC layer and by the PHY layer, respectively. These results highlight, among other aspects, some fundamental disadvantage of power control in distributed environments. We conclude that multiuser-based approaches are significantly more beneficial in ad hoc scenarios than power control-based schemes.
Lecture Notes in Computer Science, 2010
In wireless ad hoc networks, cross-layer design aims at reducing multiple access interference and... more In wireless ad hoc networks, cross-layer design aims at reducing multiple access interference and thus obtaining a higher spatial reuse. In order to identify the most suitable solution for future wireless systems, we compared the aggregate throughput achieved by two types of cross-layer designs. While the first approach suppresses the interference by power control at the transmitter side, the second
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Papers by Katsutoshi Kusume