he VoIP air interface capacity. © 2009 by Taylor & Francis Group, LLC Long Term Evolution: 3GPP LTE Radio and Cellular Technology 10.4.2 Multiuser Channel Sharing Due to the characteristics of the VoIP traffic (strict delay constraints, regular arrival of small size packets), multiuser channel sharing plays an important role when opti- mizing the radio channel interface for VoIP traffic. With multiuser channel shar- ing, multiple users can be multiplexed within the same TTI, and this will lead to significant improvements in VoIP capacity. To stress the importance of multiuser channel sharing as a building block to optimize radio interface for VoIP traffic, it is concluded that VoIP capacity is directly proportional to the average number of scheduled users per TTI. In HSPA, multiuser channel sharing is done by separating users multiplexed into the same TTI in the Orthogonal Variable Spreading Factor (OVSF) code domain, whereas in LTE user separation on PDSCH is done in the frequency domain. An important issue related to multiuser channel sharing is how the transmis- sion resources are divided between simultaneously scheduled users. Conventional methods use an even-share method, where each multiplexed user is given the same amount of resources. The main shortcoming of this method with VoIP traffic is that it wastes resources: The size of the resource allocation has to be done according to the needs of the weak users to guarantee sufficient QoS at the cell border as well. If users in good channel conditions are assigned too many transmission resources, part of the resources are wasted, as the delay requirements do not allow to buffer- ing of enough packets to take full benefit of the allocated transmission resources. At the same time, users in unfavorable channel conditions might not have enough transmission resources to transmit even one VoIP packet at the target block error rate (BLER). A more sophisticated method to assign transmission resources for the sched- uled users is to determine the size of the resource a