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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

We consider one of the latest feature included in the Release 9 of the GSM/EDGE standard: the Orthogonal Sub Channel (OSC) transmission scheme. OSC aims at doubling the cell capacity by multiplexing two co-cell users on the same radio resource. In this work we deal with the challenge of finding the optimum pairing strategy among co-cell OSC users exploiting the Adaptive QPSK (AQPSK) modulation in both up- and down-link scenarios. The aim of the proposed scheduling algorithm is to i) find the best association among the users and the available OSC logical channels, and ii) select the optimum transmitting powers. The criterion for optimization is the minimization of the overall transmitted power constrained to service quality targets. The proposed scheduling algorithm is performed locally at the BS, exploiting channel state information reported by the users. Numerical results show significant power saving provided by the algorithm in heterogeneous scenarios with variable cell load

A multicell WiMax system which supports orthogonal frequency division multiplexing (OFDM) and antenna arrays at the base stations is considered in this paper as conforming to the IEEE 802.16-2004 standard. Focusing on the uplink, we propose an analytical framework to assess the average error probability of the system over time-dispersive (or, equivalently, frequency selective) and space-dispersive (due to the antenna array) Rayleigh fading channels. The proposed method takes into account the effects of the correlation of the channel gains over the space-frequency domain, the power-angle structure of the inter-cell interference, the array processing at the base station and the interleaving scheme. , which prescribes the employment of OFDM modulation and supports antenna array technology. The pushing demand for broadband systems makes WiMax one of the most promising technologies for the near future in wireless communications. The system is expected to operate in heterogeneous propagation environments as applications range from the provisioning of wireless services in rural areas to intensive and real-time applications on notebooks and other mobile devices. Thereby, a thorough analysis of its performance under realistic and different propagation environments is mandatory.Several works have recently focused on the evaluation of the error rate of bit-interleaved coded OFDM systems over frequency selective fading channels [3]- [5]. To simplify the performance evaluation, the concept of effective signal-to-noise ratio (SNR) has been introduced in [3] as the SNR of an equivalent additive white Gaussian noise (AWGN) channel which would yield the same error probability as that of the considered frequency-selective channel. The effective SNR can be used to adapt modulation and coding to the instantaneous channel conditions (and the service requirements) or to assess the average error rate for a given transmission mode [4]. Average and outage system performances have also been derived in [5] for multiantenna combining techniques in Nakagami-fading propagation environments, while the effects of non-stationary intercell interference on the performance of multiantenna WiMax systems have been studied in [6] [7].