This paper is focused on evolved GSM/EDGE systems complying to the new feature Voice services over Adaptive Multi-user channels on One Slot (VAMOS), recently introduced in the 3GPP GSM/EDGE radio access network (GERAN) standard. VAMOS enables the transmission of two GSM voice streams on the same radio resource through the so called Orthogonal Sub Channel (OSC) multiple access technique which aims at doubling the number of users served by a cell. When adopting this feature, the GSM network experiences a mixture of in-cell and out-of-cell interference which has to be handled by advanced receivers with interference rejection capabilities. In this paper, a novel two-stage receiver is proposed and tested for the uplink of GSM VAMOS systems. The new scheme combines a pre-filtering stage for out-of-cell interference mitigation with a multi-user detector (MUD) for joint equalization of the two multiplexed OSC streams. The approach is suited for either single-antenna or multi-antenna base stations and can accommodate multiple filters for each user to cope with complex multipath propagation scenarios. The new solution is compared with other existing interference cancellation techniques here applied to the specific OSC scenario. Numerical results show significant performance gains in realistic multi-cell simulated scenarios.

Joint OSC Receiver for Evolved GSM/EDGE Systems

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.

Receiver Concepts and Resource Allocation for OSC Downlink Transmission

Widely linear (WL) receivers have the capability to perform single antenna interference cancellation (SAIC) of one rectilinear (R) or quasi-rectilinear (QR) co-channel interference (CCI), a function which is operational in global system for mobile communications (GSM) handsets in particular. Moreover, SAIC technology for QR signals is still required for voice services over adaptive multi-user channels on one slot (VAMOS) standard, a recent evolution of GSM/EDGE standard, to mitigate legacy GSM CCI in particular. It is also required for filter bank multi-carrier offset quadrature amplitude modulation (FBMCOQAM) networks, which are candidate for 5G mobile networks, to mitigate inter-carrier interference (ICI) at reception for frequency selective propagation channels in particular. In this context, the purpose of this paper is twofold. The first one is to get more insights into the existing SAIC technology, and its extension to multiple antenna called MAIC, by showing analytically that, contrary to what is accepted as true in the literature, SAIC/MAIC implemented from standard WL filtering may be less efficient for QR signals than for R ones. From this result, the second purpose of the paper is to propose and to analyze, for QR signals and frequency selective fading channels, a SAIC/MAIC enhancement based on a three-input WL frequency shift (FRESH) receiver, making QR signals always almost equivalent to R ones for WL filtering in the presence of CCI. The results of the paper, completely new, may contribute to develop elsewhere new powerful WL receivers for QR signals and for both VAMOS and FBMC-OQAM networks in particular.

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Enhanced Widely Linear Filtering to Make Quasi-Rectilinear Signals Almost Equivalent to Rectilinear Ones for SAIC/MAIC

Widely linear (WL) filters have the capability to perform single antenna interference cancellation (SAIC) of one rectilinear (R) or quasi-rectilinear (QR) co-channel interference (CCI). The SAIC technology for QR signals is operational in GSM handsets but requires enhancements for both VAMOS standard, an evolution of GSM/EDGE standard, and FBMC-OQAM networks, which are candidate for 5G mobile networks. For this reason, we propose and analyze in this paper, for QR signals, a SAIC/MAIC enhancement based on the concept of three inputs WL FRESH filtering, exploiting almost exhaustively both the non-circularity and the cyclostationarity of QR signals, contrary to classical approaches which only exploit very partially these properties.

/pdf/quasi-rectilinear-msk-gmsk-oqam-co-channel-interference-s2o1wtxy2d.pdf

Quasi-rectilinear (MSK, GMSK, OQAM) co-channel interference mitigation by three inputs widely linear fresh filtering

Widely linear (WL) receivers are able to fulfill single antenna interference cancellation (SAIC) of one rectilinear (R) or quasi-rectilinear (QR) co-channel interference (CCI), a function which is operational in GSM handsets in particular. However, SAIC requires enhancements for QR signals, for both VAMOS standard, an evolution of GSM/EDGE standard, and FBMC-OQAM networks, which are candidate for 5G mobile networks. In this context, the purpose of this paper is twofold. The first one is to show that, contrary to what is accepted as true in the literature, QR signals are less efficient than R ones for conventional WL filtering in the presence of CCI. From this result and for QR signals, the second purpose is to propose a SAIC/MAIC enhancement, based on WL frequency shifted (FRESH) filtering, making QR signals almost equivalent to R ones

https://hal.archives-ouvertes.fr/hal-01254988/document

How to Make Quasi-Rectilinear Signals (MSK, GMSK, OQAM) Almost Equivalent to Rectilinear Ones (BPSK, ASK) for Widely Linear Filtering in the Presence

Voice services over Adaptive Multiuser channel in One Slot (VAMOS) performance in the presence of GMSK interferer is presented. Widely-Linear (WL) MMSE filtering is used to cancel the co-channel GMSK interferer while performing α-QPSK detection. In this paper, two ways of estimating the Sub Channel Power Imbalance Ratio (SCPIR) are discussed. Due to the colouration of the resultant impairment after filtering, WL metric is proposed which incorporates error covariance between I/Q components in the metric computation. WL RSSE is used as the equalizer. Simulation results using the proposed receiver architecture show significant performance important over conventional VAMOS receivers.

Mahesh Gupta Vutukuri

Papers

SAIC receiver algorithms for VAMOS downlink transmission