Wen-Jiunn Liu

Greedy Routing with Anti-Void Traversal for Wireless Sensor Networks

The unreachability problem (i.e., the so-called void problem) that exists in the greedy routing algorithms has been studied for the wireless sensor networks. Some of the current research work cannot fully resolve the void problem, while there exist other schemes that can guarantee the delivery of packets with the excessive consumption of control overheads. In this paper, a greedy anti-void routing (GAR) protocol is proposed to solve the void problem with increased routing efficiency by exploiting the boundary finding technique for the unit disk graph (UDG). The proposed rolling-ball UDG boundary traversal (RUT) is employed to completely guarantee the delivery of packets from the source to the destination node under the UDG network. The boundary map (BM) and the indirect map searching (IMS) scheme are proposed as efficient algorithms for the realization of the RUT technique. Moreover, the hop count reduction (HCR) scheme is utilized as a short-cutting technique to reduce the routing hops by listening to the neighbors traffic, while the intersection navigation (IN) mechanism is proposed to obtain the best rolling direction for boundary traversal with the adoption of shortest path criterion. In order to maintain the network requirement of the proposed RUT scheme under the non-UDG networks, the partial UDG construction (PUC) mechanism is proposed to transform the non-UDG into UDG setting for a portion of nodes that facilitate boundary traversal. These three schemes are incorporated within the GAR protocol to further enhance the routing performance with reduced communication overhead. The proofs of correctness for the GAR scheme are also given in this paper. Comparing with the existing localized routing algorithms, the simulation results show that the proposed GAR-based protocols can provide better routing efficiency.

Frame-aggregated link adaptation protocol for next generation wireless local area networks

The performance of wireless networks is affected by channel conditions. Link Adaptation techniques have been proposed to improve the degraded network performance by adjusting the design parameters, for example, the modulation and coding schemes, in order to adapt to the dynamically changing channel conditions. Furthermore, due to the advancement of the IEEE 802.11n standard, the network goodput can be enhanced with the exploitation of its frame aggregation schemes. However, none of the existing link adaption algorithms are designed to consider the feasible number of aggregated frames that should be utilized for channel-changing environments. In this paper, a frame-aggregated link adaptation (FALA) protocol is proposed to dynamically adjust system parameters in order to improve the network goodput under varying channel conditions. For the purpose of maximizing network goodput, both the optimal frame payload size and the modulation and coding schemes are jointly obtained according to the signal-to-noise ratio under specific channel conditions. The performance evaluation is conducted and compared to the existing link adaption protocols via simulations. The simulation results show that the proposed FALA protocol can effectively increase the goodput performance compared to other baseline schemes, especially under dynamically-changing environments.

Three-dimensional greedy anti-void routing for wireless sensor networks

Due to the low-cost design nature of greedy-based routing algorithms, it is considered feasible to adopt this type of schemes within the three-dimensional (3D) wireless sensor networks. In the existing research work, the unreachability problem (i.e., the so-called void problem) resulting from the greedy routing algorithms has not been fully resolved, especially under the 3D environment. In this letter, a three-dimensional greedy anti-void routing (3D-GAR) protocol is proposed to solve the 3D void problem by exploiting the boundary finding technique for the unit ball graph (UBG). The proposed 3D rolling-ball UBG boundary traversal (3D-RUT) scheme is employed to guarantee the delivery of packets from the source to the destination node. The correctness proofs, protocol implementation, and performance evaluation for the proposed 3D-GAR protocol are also given in this letter.

Greedy Anti-Void Routing Protocol for Wireless Sensor Networks

The unreachability problem (i.e. the so-called void problem) which exists in the greedy routing algorithms has been studied for the wireless sensor networks. However, most of the current research work can not fully resolve the problem (i.e. to ensure the delivery of packets) within their formulation. In this letter, the greedy anti-void routing (GAR) protocol is proposed, which solves the void problem by exploiting the boundary finding technique for the unit disk graph (UDG). The proposed rolling-ball UDG boundary traversal (RUT) is employed to completely guarantee the delivery of packets from the source to the destination node. The proofs of correctness for the proposed GAR protocol are also given at the end of this letter.

Efficient implementation of an energy-conserving multicast routing protocol for wireless multihop networks

How to provide low energy consumption and high packet delivery ratio are considered the major issues in the protocol design for the wireless multihop networks. The main focus of this paper is to reduce the number of data transmissions such that the energy consumption can be decreased. In the wired networks, the Steiner-Tree is regarded as an optimal approach to construct the multicast structure for specific senders and receivers. However, it is considered an NP-Hard problem for achieving the minimum cost multicast tree under the wireless broadcast environment. In this paper, an Energy-Conserving Multicast Routing (ECMR) protocol is proposed as a heuristic scheme to reduce the number of relaying nodes for the construction of the multicast mesh. Moreover, the proposed algorithm is implemented on an ARM-based embedded platform for performance evaluation. Comparing with the existing multicast routing protocol, the experimental results show that the proposed ECMR scheme can provide better energy conservation while the packet delivery ratio is still preserved.

Performance analysis of greedy fast-shift block acknowledgement for high-throughput WLANs

The techniques of frame aggregation and block acknowledgement (ACK) are utilized in the IEEE 802.11n standard for achieving high throughput performance from the medium access control perspective. Conventional greedy scheme for block ACK adopts the transmitter-defined starting sequence number (SSN) to construct the ACK window for recognizing the correctness of data packets. However, there exists correctly received packets that lie outside of the ACK window which will unavoidably be retransmitted by adopting the conventional scheme. In this paper, a greedy fast-shift (GFS) block ACK mechanism is proposed to provide the receiver-defined SSN, which can both implicitly acknowledge the correctly received packets before the SSN and explicitly identify the correctness information for the packets after the SSN. In order to evaluate the effectiveness of the GFS scheme, the analytical models for these two mechanisms are proposed based on the window utilization. Compared to the conventional greedy scheme, it is observed from the simulation results that the proposed GFS method can provide better performance owing to its fast-shift behavior on ACK window.

Performance Analysis of Block Acknowledgement Mechanisms for Next Generation Wireless Networks

The IEEE 802.11n standard has been proposed to provide enhanced throughput performance for the wireless local area networks. Most of the existing research work considers packet aggregation techniques for enhancing the network throughput from the medium access control perspective. Consequently, the large amount of small-sized acknowledgement (ACK) packets are aggregated via the block ACK mechanisms in order to improve the system throughput. In this paper, a block ACK classification is proposed to categorize the existing block ACK mechanisms into the greedy and the conservative schemes. Based on the Markovian techniques, the respective analytical models are constructed in order to measure the throughput-related metric of the window utilization under different packet error probabilities. Simulations are conducted to validate and compare the proposed analytical models associated with the two types of block ACK schemes. It can be observed from the numerical results that the greedy scheme outperforms the conservative approach with comparably higher window utilization.

WSNp1-3: Largest Forwarding Region Routing Protocol for Mobile Ad Hoc Networks

The design of routing protocols is crucial for mobile ad-hoc networks due to their fast-changing characteristics. Most of the ad-hoc routing algorithms are designed based on extensive flooding of control packets, which result in excessive overheads within the networks. The greedy routing algorithms employ localized information from the mobile nodes (e.g. relative distance or direction), which induce comparably less control packets in the networks. However, several problems (e.g voids, loops, or dead-ends) are encountered in most of the greedy algorithms due to the localized characteristics. In this paper, a largest forwarding region (LFR) routing protocol is developed. The mobile node with the largest extended forwarding region (EFR) is selected as the next hopping node for packet forwarding. The associated backward constraint (BC) and dead-end recovery (DER) mechanisms further alleviate the problems resulting from voids in the networks. The performance comparison between the proposed LFR algorithm and other existing greedy routing schemes is conducted via simulations. It is observed that the LFR scheme effectively increases the packet arrival rate without creating excessive control overheads.

Multiple receiver transmission strategy for receiver blocking problem in wireless multi-hop networks

Due to the lack of a centralized coordinator for wireless resource allocation, the design of medium access control (MAC) protocols is considered crucial for throughput enhancement in the wireless multi-hop networks. The receiver blocking problem, which has not been studied in most of the MAC protocol design, can lead to severe degradation for the throughput performance. In this paper, the multiple receiver transmission (MRT) mechanism is proposed to alleviate the receiver blocking problem without the adoption of additional control channels. The performance evaluation of the MRT technique is conducted via simulations and is compared with the conventional IEEE 802.11a MAC protocol. Based on the simulation results, it can be observed that the proposed MRT scheme can alleviate the receiver blocking problem, which effectively enhances the system throughput for wireless multi-hop networks.

Optimality of Frame Aggregation-Based Power-Saving Scheduling Algorithm for Broadband Wireless Networks

The limitation on battery lifetime has been a critical issue for the advancement of mobile computing. Different types of power-saving techniques have been proposed in various fields. In order to provide feasible energy-conserving mechanisms for the mobile subscriber stations (MSSs), three power-saving types have been proposed for the IEEE 802.16e broadband wireless networks. However, these power-saving types are primarily targeting for the cases with a single connection between the base station (BS) and the MSS. With the existence of multiple connections, the power efficiency obtained by adopting the conventional scheduling algorithm can be severely degraded. In this paper, with the consideration of multiple connections and their quality-of-service (QoS) constraints, a frame aggregation-based power-saving scheduling (FAPS) algorithm is proposed to enhance the power efficiency by aggregating multiple under-utilized frames into fully-utilized ones. The optimality on the minimum number of listen frames in the proposed FAPS algorithm is also provided, and is further validated via the correctness proofs. Performance evaluation of proposed FAPS scheme is conducted and compared via simulations. Simulation results show that the power efficiency of FAPS algorithm outperforms the other existing protocols with tolerable frame delay.