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Ruder M.A.,University of Mobile | Meyer R.,Com Research GmbH | Kalveram H.,Com Research GmbH | Gerstacker W.H.,University of Mobile
2012 1st IEEE International Conference on Communications in China Workshops, ICCC 2012 | Year: 2012

In Voice services over Adaptive Multi-user channels on One Slot (VAMOS), which has been standardized as an extension to the Global System for Mobile Communications (GSM), the concept of Orthogonal Sub-channels (OSC) is employed. Two overlaid Gaussian minimum-shift keying (GMSK) signals are transmitted in the same time slot and on the same frequency. The aim of VAMOS is to approximately double the cell capacity compared to the legacy GSM system. This work studies the downlink radio resource allocation problem. The base station (BS) can decide which users should share the same time and frequency resource within a cell. Additionally, the power allocation for each user must be considered along with a limitation of the subchannel power imbalance ratio (SCPIR) of the users in each pair. Due to frequency hopping (FH) an estimation of the co-channel interference level is not possible. Therefore, this paper proposes a radio resource allocation scheme that allocates resources without the exact knowledge of the actual interference situation. To reduce the energy consumption of the BS, the resources are allocated for a minimum sum transmit power taking into account a prescribed target frame error rate (FER) at the receiver. Simulation results show that with the proposed resource allocation scheme a significant reduction of the required transmit power is possible. Furthermore, the influence of the equalizers on the FER performance, and therefore also the energy savings are evaluated, considering different VAMOS receiver algorithms. © 2012 IEEE.

Gerstacker W.,Com Research GmbH | Gerstacker W.,University of Mobile | Schober R.,Com Research GmbH | Schober R.,University of British Columbia | And 4 more authors.
AEU - International Journal of Electronics and Communications | Year: 2011

The Global System for Mobile Communications (GSM) is still the most successful mobile communications system worldwide. During the last decade, major steps have been taken towards an improvement of GSM with respect to performance and spectral efficiency. To serve the increasing demands of more and more users for higher data rates, significant efforts are made towards a further evolution of GSM. The standard extension Voice Services over Adaptive Multi-User Channels (VAMOS) has been specified in 3GPP Release 9. In VAMOS mode, two overlaid Gaussian minimum-shift keying (GMSK) signals are transmitted in the same time slot and frequency channel, potentially doubling the capacity of existing GSM networks in many cases. In this paper, we address channel estimation and detection techniques for the VAMOS downlink. In a new 3GPP work item called TIGHTER, it is also foreseen to tighten all downlink receiver performance requirements for all data and voice services by at least 2 dB through the application of more sophisticated processing techniques at the receiver. Furthermore, a 3GPP study on Signal Precoding Enhancements for EGPRS2 (SPEED) to further modify the modulation and coding for data services by introducing OFDM has been started recently. We present ideas for improved receivers to enable tighter performance requirements and for SPEED transmission concepts, which might merit further investigation. © 2011 Elsevier GmbH. All rights reserved.

Ruder M.A.,Friedrich - Alexander - University, Erlangen - Nuremberg | Meyer R.,Com Research GmbH | Obernosterer F.,Com Research GmbH | Kalveram H.,Com Research GmbH | And 2 more authors.
IEEE Transactions on Wireless Communications | Year: 2014

Voice services over Adaptive Multi-user channels on One Slot (VAMOS) has been standardized as an extension to the Global System for Mobile Communications (GSM). The aim of VAMOS is to increase the capacity of GSM, while maintaining backward compatibility with the legacy system. To this end, the Orthogonal Sub-channels (OSC) concept is employed, where two Gaussian minimum-shift keying (GMSK) signals are transmitted in the same time slot and with the same carrier frequency. To fully exploit the possible capacity gain of OSC, new receiver concepts are necessary. In contrast to the base station, where multiple antennas can be employed, the mobile station is typically equipped with only one receive antenna. Therefore, the downlink receiver design is a very challenging task. Different concepts for channel estimation, user separation, and equalization at the receiver of an OSC downlink transmission are introduced in this paper. Furthermore, the system capacity must be improved by suitable downlink power and resource allocation algorithms. Making realistic assumptions on the information available at the base station, an algorithm for joint power and radio resource allocation is proposed. Simulation results show the excellent performance of the proposed channel estimation algorithms, equalization schemes, and joint radio resource and power allocation algorithms in realistic VAMOS environments. © 2014 IEEE.

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