Ying-Hsin Liang

Analytical Model of QoS-Based Fast Seamless Handoff in IEEE 802.16j WiMAX Networks

The IEEE 802.16 standard adopts a centralized resource-allocation mechanism to poll nodes with three polling modes, i.e., the unicast, multicast, and broadcast polling modes, depending on the residual bandwidth of the base station (BS). In the multicast and broadcast polling modes, the BS uses the truncated binary exponential backoff (TBEB) algorithm as the contention-resolution process (CRP) for mobile nodes to access the wireless network while the traffic load increases up to saturation. The random contention-based TBEB used in the initial ranging and bandwidth request suffers from high collision probability under a high traffic load. TBEB thus significantly degrades the grade of service (GoS), particularly while performing handoff in the mobile (IEEE 802.16e) or multihop relay WiMAX (IEEE 802.16j) networks. Additionally, WiMAXs TBEB exhibits two critical problems. First, TBEB neglects the node priority (i.e., the new or handoff node) and the service flow class (i.e., the real-time or nonreal-time service class); thus, it cannot achieve the optimal network revenue. Second, all different-priority connections immediately transit to the same minimum contention windows (CWs) after winning contentions and then easily lead to high collision probability at succeeding contentions. Therefore, this paper first proposes an efficient contention-resolution algorithm that consists of three key contributions: 1) providing the adaptive minimum-maximum backoff-value algorithm (AM^2) to partition collision domains; 2) supporting a dynamic waiting-penalty algorithm (DWP) for successful contentions; and 3) differentiating the decrements of CWs (DDW) to avoid collisions, even though the contentions randomly choose the same CW value. Second, we model the proposed approach as a discrete-time Markov chain model and then mathematically analyze several important metrics, i.e., the collision probability, access delay, GoS, and throughput. Numerical results indicate that the analytical results are very close to the simulation results, which justify the accuracy of the analytical model. Additionally, the proposed approach outperforms IEEE 802.16 and all compared approaches in collision probability, delay, GoS, and network throughput.

Distributed route repair for increasing reliability and reducing control overhead for multicasting in wireless MANET

The Multicast Ad hoc On-Demand Distance Vector (MAODV) routing protocol is proposed for achieving multicast in a Mobile Ad hoc Network (MANET) while reducing bandwidth waste and energy power consumption. In MANET, packets transmission through a multicast tree may always have unreliable links caused by node mobility or lack of energy, and thus significantly degrades the performance. MAODV uses a broadcast-type local repair mechanism to find an alternative route to the multicast tree when some breaks happen on the tree. Although the local repair mechanism provides a specified time-to-live (TTL) to limit the repair range and the hop-count to the group leader, a large number of broadcast-type Route Request (RREQ) messages extensively yields control overhead and requires a large amount of power consumption to send control messages. Thus, this paper proposes a unicast-type multihop local repair protocol for multicast MANETs to recover lost links efficiently while achieving several advantages: increasing network reliability, increasing packet delivery rate, minimizing the number of control messages and reducing repair delay. Moreover, the optimal number of hops used in the multihop neighbor table is analyzed mathematically. Numerical results indicate that the proposed approach outperforms other repair approaches in terms of successful repair rate, control message overhead and packet delivery rate.

Adaptive Cost-Based with Max---Min AMC Routing Algorithm for Increasing Utilization and Reducing Blocking in IEEE 802.16j WiMAX Networks

Based on the IEEE 802.16e standard, WiMAX has proposed a relay-based mechanism, namely IEEE 802.16j, to extend the service area of the Multihop Relay Base Stations (MR-BSs) and to improve the Received Signal Strength quality. IEEE 802.16j thus can achieve two significant advantages: extending the WiMAX service area with a low-cost solution and compatible with the existing WiMAX specifications. The Relay Station (RS) can be classified into three types: Fixed RS, Nomadic RS and Mobile RS according to diverse features of mobility and relaying range. A multihop-relay WiMAX network including various types of RSs exhibits a critical routing issue, i.e., how to determine an efficient relay-based routing path between a Mobile Station (MS) and a MR-BS. This paper thus proposes an IEEE 802.16j-conformed relay-based adaptive competitive on-line routing approach that focuses on the Non-Transparent Relay-Station (NT-RS) mode, where the path with the least cost and the highest AMC coding rate will be selected in terms of the link bandwidth, path length and channel conditions. Numerical results indicate that the proposed routing approach significantly outperforms other approaches in Fractional Reward Loss, network utilization and average end-to-end path delay.

Performance Analysis with Traffic Accident for Cooperative Active Safety Driving in VANET/ITS

Recently, by using vehicle-to-vehicle and vehicle-to-infrastructure communications for VANET/ITS, the cooperative active safety driving (ASD) providing vehicular traffic information sharing among vehicles significantly prevents accidents. Clearly, the performance analysis of ASD becomes difficult because of high vehicle mobility, diverse road topologies, and high wireless interference. An inaccurate analysis of packet connectivity probability significantly affects and degrades the VANET/ITS performance. Especially, most of related studies seldom concern the impact factors of vehicular accidents for the performance analyses of VANET/ITS. Thus, this paper proposes a two-phase approach to model a distributed VANET/ITS network with considering accidents happening on roads and to analyze the connectivity probability. Phase 1 proposes a reliable packet routing and then analyzes an analytical model of packet connectivity. Moreover, the analysis is extended to the cases with and without exhibiting transportation accidents. In phase 2, by applying the analysis results of phase 1 to phase 2, an adaptive vehicle routing, namely adaptive vehicle routing (AVR), is proposed for accomplishing dynamic vehicular navigation, in which the cost of a road link is defined in terms of several critical factors: traffic density, vehicle velocity, road class, etc. Finally, the path with the least path cost is selected as the optimal vehicle routing path. Numerical results demonstrate that the analytical packet connectivity probability and packet delay are close to that of simulations. The yielded supreme features justify the analytical model. In evaluations, the proposed approach outperforms the compared approaches in packet connectivity probability, average travel time, average exhausted gasoline. However, the proposed approach may lead to a longer travel distance because it enables the navigated vehicle to avoid traversing via the roads with a higher traffic density.

Reward-Based Radio Interface Selection of Hybrid 4G UMTS and LTE Communications for Fast Cloud Accesses

For achieving fast accesses the cloud’s big data through mobile smart node, an extreme high data rate for the forwarding link under high-mobility wireless communications is necessary. 3GPP thus specifies LTE/LTE-Advanced specifications as the 4G system to cooperate with the existing UMTS system. To balance loads among different communication interfaces in the hybrid cellular system is one of the most important issues that should be addressed for achieving efficient radio resource allocations. In a shared packet service, the 3GPP UMTS adopts the VSF-OFCDM interface to allocate orthogonal codes of an OVSF code tree in two-dimension spreading of the time and frequency domains. However, UMTS suffers from high packet loss rate and high bandwidth waste rate. In 4G, although the LTE/LTE-Advanced interface offers a high data rate, it suffers from unbalanced loads and moderate reward. This paper thus proposes an adaptive radio interface selection for balancing loads between the UMTS and LTE/LTE-Advanced interfaces according to various interference and mobility environments. Numerical results indicate that the proposed approach outperforms other approaches in fairness, FRL, utilization and call blocking.

Adaptive radio resource management for maximizing reward and balancing loads in 4G hybrid universal mobile telecommunications system and long term evolution communications

The universal mobile telecommunications system UMTS and long term evolution LTE/LTE-advanced specifications have been proposed to offer high data rate for the forwarding link under high-mobility wireless communications. The keys include supporting multi-modes of various coding schemes e.g., VSF-OFCDM, OFDM, OFDMA, multiple-input multiple-output, relay networks, and so on. To balance loads among different communication interfaces is one of the most important issues that should be addressed for achieving efficient radio resource allocations. In a shared packet service, the 3GPP UMTS adopts the VSF-OFCDM interface to allocate orthogonal codes of an OVSF code tree in two-dimension 2D spreading at the time and frequency domains. However, it easily leads to high packet loss rate and high bandwidth waste rate, because it does not consider interference and the adaptive modulation and coding scheme simultaneously. Conversely, although the LTE/LTE-advanced interface offers a high data rate, it suffers from unbalanced loads and moderate reward. This paper thus proposes an adaptive radio resource allocation for balancing loads between the UMTS and LTE/LTE-advanced interfaces according to various interference and mobility environments. In addition, an adaptive multi-code allocation is proposed for the UMTS to minimize the bandwidth waste rate while guaranteeing quality of service. Numerical results indicate that the proposed approach outperforms other approaches in fractional reward loss and system utilization. Copyright

Adaptive load-balancing association handoff approach for increasing utilization and improving GoS in mobile WiMAX networks

The IEEE 802.16e standard is thus proposed for supporting high data rate and dynamic mobility in WiMAX. IEEE 802.16e specifies the association handoff mechanism in the MAC layer, i.e., providing contention-free-based initial ranging, and thus mobile stations can perform the initial ranging early during the handoff period. An MS executing the association handoff during a scan duration is disallowed to send/receive any packets to/from the serving BS. IEEE 802.16e suffers from not determining a precision scan duration period because of losing the transmission opportunity or the response status of the received ranging response (RNG-RSP) message. Although the MS can set a longer scan duration to complete the initial ranging procedure, it significantly degrades handoff delay and delay jitter of real-time service flows. In addition, most handoff studies seldom considered balancing traffic load among neighbor base stations (BSs). This paper thus proposes an efficient Adaptive Load-balancing Association handoff approach (ALA) consisting of two phases: (1) the Adaptive Association Handoff phase (AAH) and (2) the Predictive Direction-based Load Balancing phase (PDLB), to overcome above mentioned problems. AAH proposes an adaptive re-association mechanism to reduce lost synchronizations, and thus improve the grade of service. PDLB adopts the Polynomial Regression-based RSS prediction algorithm to accurately predict the moving direction of mobile nodes. Numerical results demonstrate that ALA significantly outperform IEEE 802.16e and others in average handoff delay, number of handoffs, dropping probability, GoS, network utilization, and number of lost synchronizations. Copyright

Cross-layer channel selection and reward-based power allocation for increasing system capacity and reward in multiple-input-multiple-output wireless communications

For increasing network bandwidth and guaranteeing quality of service in WiMAX, IEEE 802.16 m proposes the multiple-input–multiple-output (MIMO) technique that offers compatible specifications with the existing IEEE 802.16 family specifications. However, the performance of the IEEE 802.16 MIMO specification is significantly degraded in the high-mobility environment and high communication interference. As a result, a sender easily uses inaccurate modulation and coding scheme (MCS) and improper power allocation for different-priority users having different received signal-to-noise ratios. The system capacity is thus affected significantly. Additionally, the multiuser MIMO systems seldom consider that different-priority users and different-class traffic bring different rewards to the system. This study thus proposes a cross-layer reward-based approach (namely CLR) that consists of three schemes: adaptive modulation and coding determination, cross-layer dynamic channel selection, and reward-based weighting power allocation. The proposed CLR approach achieves accurate channel state information determination, optimal channel selection, and adaptive reward power allocation. Numerical results demonstrate that the proposed approach significantly outperforms the other approaches in system reward, system capacity, and the accuracy of the MCS determination.

Cross-Layer-based Local Repair for Maximizing Goodput and Minimizing Control Messages in Multicasting MANET

The Multicast Ad hoc On-Demand Distance Vector (MAODV) protocol achieves multicast routing in self-organizing wireless mobile on-demand networks, e.g., Mobile Ad-hoc Networks (MANETs). However, unreliable wireless links degrade network reliability and network goodput, and the unreliable link problem becomes worse in multicasting because a multicast tree consists of more number of wireless links. MAODV adopts a broadcast-type local repair, and thus yields a large number of broadcast-type repair messages, increases extensive control overhead, and involves largely power consumption. Thus, a cross-layer unicast-type multihop local repair approach is proposed to recover broken links in multicasting MANETs. Additionally, the cross-layer mechanism provides mobile nodes to send a cross-layer message to the TCP sender to keep current congestion window (cwnd) and slow start threshold (ssthresh) when downstream links are temporarily broken, and then increases network goodput. Finally, the optimal number of neighbor-tiers is analyzed and the optimal substitute node is identified. Numerical results demonstrate that the proposed approach outperforms other approaches in successful repair rate, control message overhead, packet delivery ratio, and network goodput.

Adaptive ranging algorithm for fast seamless handoff in WiMAX mobile networks

The WiMAX multicast and broadcast polling modes uses the Truncated Binary Exponential Backoff (TBEB) algorithm as the Contention Resolution Process among distributed mobile nodes while the network traffic load is nearly saturation. TBEB suffers from high collision probability under a high traffic load. TBEB thus significantly degrades the grade of service, especially while considering handoff in the mobile WiMAX network. Thus, this work first proposes an efficient contention resolution algorithm that consists of two key contributions: 1) providing the adaptive minimum-maximum backoff values algorithm (AM2) to partition collision domains and 2) supporting a dynamic waiting-penalty algorithm (DWP) for successful contentions to dynamically decrease CWs while contentions randomly selecting the same CW. Second, we model the proposed approach as a discrete-time Markov chain model, and then mathematically analyze important metrics: collision probability and throughput. Numerical results indicate that the analytical results are very close to the simulation results, which justify the accuracy of the analytical model. Additionally, the proposed algorithm outperforms IEEE 802.16 and all compared approaches in collision probability and network throughput.