IEEE 802.16 OFDMA systems have gained much attention for their ability to support high transmission rates and broadband access services. For multiuser environments, IEEE 802.16 OFDMA systems require a resource allocation algorithm to use the limited downlink resource efficiently. The IEEE 802.16 standard defines that resource allocation should be performed with a rectangle region of slots, called a burst. However, the standard does not specify how to construct bursts. In this paper, we propose a heuristic burst construction algorithm, called HuB, to improve the downlink capacity in IEEE 802.16 OFDMA systems. To increase the downlink capacity, during burst constructions HuB reduces resource wastage by considering padded slots and unused slots and reduces resource usage by considering the power boosting possibility. For simple burst constructions, HuB makes a HuB-tree, in which a node represents an available downlink resource and edges of a node represent a burst rectangle region. Thus, making child nodes of a parent node is the same as constructing a burst in a given downlink resource. We analyzed the proposed algorithm and performed simulations to compare the performance of the proposed algorithm with existing algorithms. Our simulation study results show that HuB shows improved downlink capacity over existing algorithms.

With the rapid growth of wireless communication technologies, the demands for large-scale wireless networks have been emerged. One promising solution is the hierarchical architecture that consists of global and local wireless networks. The service discovery is a key issue to meet a vast amount of service demands from mobile nodes. However, under dynamic wireless networks, node failures severely affect the performance of service discovery protocols. Therefore, in this paper, we propose the directory hopping (DH) protocol for efficient service discoveries in dynamic large-scale networks. Basically, DH utilizes the directory for low-overhead service discoveries and periodically moves the directory to other operating nodes. In addition, it provides a fast and efficient recovery mechanism for node failures in dynamic network environments. Through extensive simulations, we show that the proposed DH protocol outperforms existing service discovery schemes.

Wireless network coding (WNC) has been considered as a promising solution with its capability of improving the overall performance of wireless mesh networks. A problem caused when WNC is employed in multi-rate wireless networks is that the link status between the relay node and intended receivers of a coded packet is mutually different. Even though there are links that support higher transmission rates, the relay node must transmit the coded packet at the lowest transmission rate among intended links' rates for the successful reception at all intended receivers. In this paper, we propose a WNC scheme that is combined with Forward Error Correction (FEC) to alleviate the problem explained above. The proposed scheme tries to transmit coded packets with a transmission rate higher than the lowest transmission rate so that the time required to transmit coded packets is reduced. However, it may increase the error rate. To compensate for the increased error rate, we use adaptively controlled FEC code. Our simulation study results show that the proposed scheme can increase the network coding gain compared to existing schemes.

Designing scheduling algorithms that are simple to implement along with the process for servicing packets with low computation complexity is necessary to provide Quality- of-Service (QoS) for high-speed wireless networks. The ordinary frame-based scheduling algorithms are well-known for providing fair service with constant time complexity (O(l)), however, they have limitations of not being able to properly handle location-dependent burst errors in wireless networks. To utilize the advantage of frame-based scheduling algorithms, we propose a newCompensationModelwhich is based onLead-lagModel, to provide smooth compensation, so that frame-based scheduling algorithms can guarantee fairness and reduce delay in error-prone wireless channels. Through the analytical model and simulation studies, we show that frame-based scheduling algorithms withCompensationModelcan provide smaller delay bound and better fairness in wireless networks. Our belief is that the proposed frame-based scheduling algorithm (WFRR) based on the gracefulCompensationModelcan be a strong candidate for the scheduling algorithm in high speed wireless networks since the proposed algorithm has low computational complexity, is simple to implement, and has the ability to handle channel errors.

In the next-generation networks, guaranteeing QoS is one of the important factors, which allows QoS supportable networks such as UMTS and 802.16e to be deployed together. Under such networks, a mobile node (MN) with multiple interfaces demands for the QoS service continuity during a handover. The 802.21 framework enables MNs to freely move in multiple networks. However, supporting QoS service continuity remains as a problem to be solved. In this paper, we propose a network-initiated handover based on the 802.21 framework to provide the QoS service continuity in UMTS/802.16e networks. To support the QoS service continuity, we design a detailed handover procedure that consists of three steps; QoS measurement, passive reservation, and activation. Through our performance evaluation, we show that the proposed handover scheme provides the QoS service continuity of MNs during a handover in terms of guaranteed data rates and latency.

In this paper, we define a resource allocation problem focusing on the scheme minimizing energy consumption of subscribers in uplink subframe of the IEEE 802.16 OFDMA systems. In order to clearly formulate the relation between the uplink resource allocation and energy efficiency of subscribers, we use the multiple choice knapsack (MCK) problem, which is proved to be an NP-hard problem. Instead of finding an optimal solution, we seek a suboptimal solution. Based on the problem formulation, we adopt the existing solution of the Multiple Choice Knapsack problem to solve the resource allocation problem. The suboptimal solution adaptively uses the modulation and coding scheme defined in the IEEE 802.16 systems to minimize the required transmission power while guaranteeing QoS. Our simulation results show that the suboptimal algorithm can reduce the energy consumption up to 53% compared to the channel state information (CSI) scheme, which determines the modulation and coding level only considering the channel state information.