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In two-tier networks, which consist of macrocells and femtocells, femtocells can offload the traffic from macrocells thereby improving indoor signal coverage. However, the dynamic deployment feature of femtocells may result in signal interference due to limited frequency spectrum. The tradeoff between broad signal coverage and increased signal interference deserves further exploration for practical network operation. In this paper, dynamic frequency resource management is proposed to avoid both co-tier and cross-tier Orthogonal Frequency Division Multiple Access downlink interference and increase frequency channel utilization under co-channel deployment. A graph-based non-conflict group discovery algorithm is proposed to discover the disjoint interference-free groups among femtocells in order to avoid the co-tier interference. A macrocell uses the femtocell gateway for frequency resource allocation among femtocells to avoid cross-tier interference. We formulate the optimized frequency resource assignment as a fractional knapsack problem and solve the problem by using a greedy method. The simulation results show that the average data transfer rate can be increased from 21% to 60%, whereas idle rate and blocking rate are decreased in the range of 15% Ï 22% and 60% Ï 82%, respectively, as compared with conventional graph coloring and graph-based dynamic frequency reuse schemes. Two-tier networks contain femtocells and macrocells. A macrocell deployment is significantly more costly than femtocell deployment. It requires acquiring, leasing, and determining a site for a base station installation, which may not be easy to accomplish. Femtocell technology offers plugand-play for configuration; low deployment cost and traffic offload from the macrocell. It improves the macrocell's capacity and signal coverage in a simple and economical manner [4,5]. A femtocell consists of a small cellular base station, operates on a licensed spectrum, and connects to a service provider's broadband system to offer wireless access service [6]. A sample deployment of a twotier LTE network consisting of several femtocell base stations (FBSs) and a macrocell base station (MBS) is depicted in Figure 1. The FBS provides access service for femto User Equipment (fUE), and the MBS does so for macro User Equipment (mUE). Femtocells provide a smaller radio signal and connect to the core network by a wired backhaul link. The femto gateway (FGW) is an intermediate node that controls and manages FBSs and performs traffic routing for the core network. In addition, the FGW also supports femto-specific functions such as admission control, handover control, and interference management.Because femtocells are usually installed as demanded by people, self-organization, and self-management functions, are very important for the operation of femtocell networks. Selforganization will allow femtocells to detect the installed environment in order to integrate themselves into the core network, where self-management will enable femtocells to tune parameters for netwo...

Among the scheduling services, rtPS (real-time polling service) is designated for real-time applications. Among three packet delay intervals, performance effect on polling interval has been widely studied, but less on the intervals of scheduling and delivery. To evaluate the performance of delay-sensitive rtPS applications, instead of using continuous queueing model, a discrete-time GI-G-1 model, which considers intervals of polling, scheduling, and delivery, is proposed. By taking VoIP as a typical rtPS application, the transmission latency under different QoS settings, polling probability, and traffic load are presented. The latency is also compared among various codec schemes. The results indicate that when the codec rate is either fulfilled or dissatisfied by the promised bandwidth of service levels, the performance is highly dependent upon the polling probability, no matter what the traffic condition is. However, if the codec rate is in between the promised bandwidth of various service levels, the polling probability is a dominant factor in light traffic environment, while the settings on QoS parameters will strongly determine the performance in heavy traffic situation. In addition to the verification using simulation, the bandwidth utilization derived from the GI-G-1 model can be applied to improve the serving capacity of base stations. Copyright (c) 2011 John Wiley & Sons, Ltd

The IEEE 802.16e standard specifies the QoS support at the MAC level for wireless broadband access network. To meet the QoS requirements, an efficient scheduling algorithm at base station (BS), which is not defined in the standard, is necessary for slots allocation. In this paper, a Slot-based BS scheduling algorithm with Maximum Latency Guarantee and Capacity First (SMLG-CF) is proposed. With SMLG-CF, the connection request is satisfied with highest slot capacity first. Together with the use of dynamic sub-frame adjustment, the overall system transmission can be efficiently improved. Through the finer slots calculation and accurate transmission time scheduling, the maximum latency guarantee can be better achieved for urgent requests. In the simulation, we compare the proposed mechanism with the deficit fair priority queue scheduling algorithm and the Highest Urgency First scheduling algorithm. The simulation results reveal that SMLG-CF outperforms both algorithms from the aspect of maximum latency violation rate and average transmission rate. Copyright (C) 2011 John Wiley & Sons, Ltd

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