In the recent past, increasingly more TV channels are provided and much higher bandwidth is required by each channel in service provider based IPTV systems. Therefore, bandwidth shortage problems may arise, which can induce unsatisfactory provisioning of Quality of Experience (QoE) for IPTV subscribers, in particular, with respect to the call blocking probability (CBP) and the channel availability (CA), two most important QoE metrics.The most straightforward method to solve this issue is to proportionally increase the a priori bandwidth reservation. However, it may not be sustainable. In this dissertation, we focus on solutions with smarter use of the precious bandwidth resources. More specifically, our original contribution lies in the fact that we propose innovative schemes and algorithms to effectively decrease the CBP and consequently to improve the channel availability in bandwidth capacity limited IPTV systems. Moreover, these proposed methods can be easily implemented in a practical IPTV system, and can help the service providers to enhance the QoE of their subscribers.Firstly, we introduce background knowledge related to IPTV systems. Besides, we study and propose two different user behaviour models to be used to depict user behaviour in both stationary and peak-hour scenarios. Next, we elaborate a state-vector-based simulation methodology to evaluate user CBP for a single link, for an entire delivery network with tree topology, as well as for IPTV systems with different channel formats. These evaluations are carried out for both stationary and peak-hour scenarios.After that, a TV channel access control (TCAC) scheme is proposed with the aim to decrease the CBP. The proposed TCAC scheme is applied in both stationary and peak-hour scenarios. Simulation results show considerable QoE improvement introduced by using our TCAC scheme. We also elaborate an intentional switching delay (iSD) channel request admission control method to improve the channel availability in an IPTV system with users zapping channels sequentially. A series of comprehensive case studies have been conducted and show that our iSD method can effectively improve the channel availability, with only slightly degrading the average watching delay.Last but not least, aiming to further improve the IPTV channel availability, we derive a combined algorithm, namely the combination of the TCAC scheme with the iSD method. Simulation results indicate that when the intentional delay introduced by the iSD method is large enough, additional gain can be obtained by applying this combined scheme.