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Driven by new subscriptions, extended coverage, and lower tariffs, conventional voice traffic is expected to grow nearly threefold by 2012. However, revenues per delivered minute are declining; compelling mobile operators to cut costs by improving GSM networks efficiency. This paper presents a pioneering feature from Nokia Siemens Networks called Orthogonal Sub Channel. The OSC aims to improve cost efficiency for GSM voice services and support the vision of connecting five billion people by 2015. Efforts are underway to standardize properties associated with this feature in 3GPP Release 9 and in a related work item called VAMOS. The technical method of doubling voice channel capacity entails adopting the quaternary modulation scheme in the downlink and spatially orthogonal sub channels in the uplink, also called multi-user MIMO.
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