Preliminary Results on 3D Channel Modeling: From Theory to Standardization

Three dimensional beamforming (3D) (also elevation beamforming) is now gaining a growing interest among researchers in wireless communication. The reason can be attributed to its potential to enable a variety of strategies like sector or user specific elevation beamforming and cell-splitting. Since these techniques cannot be directly supported by current LTE releases, the 3GPP is now working on defining the required technical specifications. In particular, a large effort is currently made to get accurate 3D channel models that support the elevation dimension. This step is necessary as it will evaluate the potential of 3D and FD(Full Dimensional) beamforming techniques to benefit from the richness of real channels. This work aims at presenting the on-going 3GPP study item "Study on 3D-channel model for Elevation Beamforming and FD-MIMO studies for LTE", and positioning it with respect to previous standardization works

Semi-orthogonal user selection for MISO systems with quantized feedback

2008 International ITG Workshop on Smart Antennas, WSA 2008; Darmstadt; Germany; 26 February 2008 through 27 February 2008For MISO multi-user downlink wireless communication system with precoding at the transmission, the channel state information at the transmitter can provide tremendous capacity gains. However, the amount of feedback data increases with the number of users in the cell and the number of transmit antennas. In this paper, we study on different algorithms and criteria in order to significantly reduce the amount of feedback data. We associate the classical norm criterion with a criterion based on the orthogonality between the user channels. Without cooperation between the users, we only allow users that are semi-orthogonal to feedback their channel information (CQI and CDI) to the base station. The feedback CDI is quantized using a local grassmanian packing. We show that the proposed combined criterion with a finite feedback rate gives better performance compared to the norm criterion. Furthermore we show that the performance is not affected by CQI quantization

Performance evaluation of multicast MISO-OFDM systems

In this paper, we analyze the performance of multicast orthogonal frequency division multiplexing (OFDM) systems with single and multiple transmit antennas. We show that the resource allocation that includes the subcarrier allocation, bit loading, and the precoding vector selection in the multiple-input single-output (MISO) case is a difficult optimization problem. Consequently, we propose suboptimal algorithms based on the maximization of the sum data rate and the maximization of the minimum user data rate criteria. For practical application, we consider a complete transmission chain by combining powerful erasure codes with the proposed algorithms. Using this scheme, we guarantee that each user receives the same amount of information to decode the same data. Simulation results show that, for both single-input single-output (SISO)-OFDM and MISO-OFDM cases, the proposed multicast OFDM systems achieve gains over the worst user case algorithm.FP6-IYTE wireless project and Euripides European project SMAR

Algorithmes de sélection d'utilisateurs à complexité réduite pour les systèmes MIMO multi-utilisateurs

Pour la voie descendante des systèmes de radiocommunication MISO multi-utilisateurs avec précodage à l'émission, il est important de réduire le débit de la voie de retour. Dans cet article, nous étudions différents algorithmes et critères permettant de réduire significativement le débit de la voie de retour. Pour réduire ce débit, nous utilisons un premier critère sur les normes des canaux et un second sur la séparation spatiale des utilisateurs. Nous proposons, en absence de coopération entre les utilisateurs, une méthode de réduction de débit de la voie de retour opportuniste qui n'autorise que les utilisateurs orthogonaux entre eux à transmettre leurs canaux sur la voie de retour. Nous déterminons les seuils théoriques à appliquer et finalement, nous évaluerons les performances de ces différents critères de sélection par simulation numérique

Performance of semi-orthogonal user selection for multiuser MISO systems

IEEE 9th Workshop on Signal Processing Advances in Wireless Communications, SPAWC 2008; Recife; Brazil; 6 July 2008 through 9 July 2008In MISO multiuser downlink wireless communication systems with precoding at the transmission, the capacity depends on the channel state information at the transmitter. Since the feedback data rate increases with the number of users in the cell it is important to perform a selection of the users at the receiver. In this paper, we evaluate the performance of different user selection algorithms at the receiver side through the noisy uplink channel. We evaluate the effect of the noisy channel on the classical norm criterion and on a criterion based on the orthogonality between the user channels. Without cooperation between the users, we only allow users that are semi-orthogonal to feedback their channel information as analog and quantized information to the base station through the noisy uplink channel. We propose an algorithm to reduce the noise effect on the analog feedback for semi-orthogonal user selection algorithm. We show that the semi-orthogonal criterion with quantized feedback gives better performance compared to the norm criterion for perfect and noisy uplink channels

Etude des performances des systèmes de communication MISO avec voie de retour

Dans cet article nous étudions différentes solutions de voie de retour pour les systèmes de communication point à point à antennes multiples à l'émission (MISO). Nous considérons deux familles de voies de retour : la voie de retour analogique pour laquelle le vecteur des coefficients des canaux avec ou sans normalisation est simplement transmis en analogique et la voie de retour basée sur une quantification vectorielle du canal normalisé. Nous présentons différentes bornes ainsi que des résultats de simulation. Pour un rapport signal à bruit faible à moyen, la voie de retour analogique avec normalisation du canal donne les meilleures performances. L'augmentation du nombre de mots de code dans la version quantifiée permet de réduire la distorsion mais la chaîne devient alors plus sensible au bruit de la voie montante

Performance of multicast MISO-OFDM systems

13th European Wireless Conference: Enabling Technologies for Wireless Multimedia Communications, EW 2007In this paper, we evaluate the performance of multicast OFDM systems with single and multiple transmit antennas. We have shown that it is possible to increase the data rate of multicast OFDM systems by selecting the users with good channel for each subcarrier. For the single transmit antenna case, the resource allocation has been applied using the two-step algorithm where subcarrier allocation and bit loading are performed separately. For the multiple transmit antennas case, we have proposed a suboptimal algorithm using a set of precoding vectors. In this study, we present the simulation results of the complete transmission chain where we have associated the resource allocation algorithms with a powerful erasure code. The results show that the proposed algorithms outperform the classical worst case algorithm for both single and multiple transmit antennas. © EW 2007 - 13th European Wireless Conference: Enabling Technologies for Wireless Multimedia Communications. All rights reserved

Adaptive Resource Allocation for Multicast OFDM Systems with Multiple Transmit Antennas

Abstract — We evaluate the impact of multiple transmit antennas on the performance of multicast OFDM systems. Associated with a powerful erasure code, it is possible to increase the data rate of multicast OFDM systems by selecting for each subcarrier the users with a good channel condition. We show that the resource allocation which includes the precoding vector selection, subcarrier allocation and bit loading is a difficult optimization problem. We propose two suboptimal algorithms to solve this problem. In the first algorithm, we optimize the precoding vector using an interior point method while the second proposed algorithm avoids this optimization. When the users are not symmetrically distributed around the base station, we add a fair scheduler to guarantee that each user receives the same amount of data. We present simulation results where we compare the proposed multicast systems with classical multicast OFDM systems. When the users are symmetrically distributed around the base station, the gain is rather small, whereas when the users are non-symmetrically distributed, the second algorithm outperforms OFDM systems with subcarrier allocation