Contention-based uplink transmission in unscheduled access

Voice communication has traditionally been carried out on circuit switched networks only. This is not true today since some voice communication is done over IP-networks, such as the Internet. A general term for this type of voice communication transmission is Voice over Internet Protocol, or simply VoIP. The main benefit of VoIP is its cost-efficiency concerning both system maintenance and international calls. VoIP-services will probably have an increased popularity with the switch to Long Term Evolution (LTE), due to its high capacity and bit-rates. Voice communication is highly sensitive to end-to-end delay. Obtaining transmission resources in LTE using the conventional contention-free transmission method contributes to the end-to-end latency. This is due to the scheduling signalling which can only be done in specified intervals on a scheduling channel, so called D-SR intervals. The D-SR interval can be long if the load is high. This work investigates the possible capacity gain for VoIP-users by using an alternative contention-based transmission method. This method uses a pre- set broadcast grant to be used by any user. However, as the load increases, the contention from several users will become more common since the grant is shared by everyone. Hence, restrictions to the alternative transmission method in order to decrease the load are also analysed. Two different grant methods are evaluated: the conventional contention-free and the contention- based. A system simulator is used to investigate the two grant methods. The simulator models a complete LTE system in a multi-cell environment. The simulations show it is necessary to limit the contention-based access to only VoIP packets of a certain size. Unlimited use of contention-based access is clearly shown to be useless: the capacity is zero VoIP-users per cell. Further on, when comparing contention-free access to contention-based limited to VoIP packets for different D-SR intervals, it is found that the two methods have similar VoIP-user capacities for D-SR interval of 10 ms and lower. VoIP packet limited contention-based transmissions have a significantly higher VoIP-user capacity for D-SR intervals over 10 ms.Validerat; 20101217 (root