Prediction model for the GSM Dual Half Rate gain in a noise-limited environment based on field measurements and simulations

The GSM voice capacity can be enhanced by the OSC (Orthogonal Sub Channel) functionality. It allows the sharing of a Half Rate (HR) channel for two separate HR users. OSC makes the pairing of these HR users by dividing the modulation constellation into two separate parts in downlink, and by utilizing the non-correlating training sequences in uplink. OSC thus doubles the offered capacity in those areas where the network conditions allow the pairing. The pairing can be done if the received power level is high enough. In addition, there are quality triggers for the pairing and un-pairing, according to the applied OSC algorithm. This paper investigates the expected OSC gain by taking into account the typical OSC pairing criteria. The effect is analyzed based on the realistic outdoor field measurement data. Furthermore, a model for the OSC performance is developed. This model is utilized as a basis for the simulations that take into account the relevant parameter behavior of the OSC algorithm. The outcome is an estimate of the achievable OSC capacity gain based on the OSC capable handset penetration and network performance statistics, with an indication of optimal OSC parameter values.