In the cloud computing era, the analyses of various types of big data gathered from the Internet of Vehicles, the Internet of Things, and smart sensors/devices achieve convenient services. Some famous applications include vehicle traffic loading on roads (from Google MAP), video sharing for fans group (from Facebook or Youtube), and so on. However, to achieve real-time active safe driving (RT-ASD) under unstable driving in high-threat areas on roads becomes an open issue in cloud computing-based intelligent transportation system. This paper proposes a predictive backward shockwave analysis approach (PSA) to achieve the RT-ASD based on the analyses of macroscopic traffic shockwave (PSA_MA) and microscopic car-following (PSA_mi). The PSA contributes in several aspects to active safe driving: 1) predicting and analyzing high threat of backward shockwaves from the gathered big data of the driving state information vehicles; 2) informing the analyzed threat messages to the vehicles in high-threat areas via the 3-Tier hierarchical cloud computing mechanism; 3) reducing the driving threat certainly; and 4) PSA_MA and PSA_mi can be applied for achieving active safe driving in autonomous self-driving vehicles and human-driving vehicles. The numerical results show that the PSA outperforms in approaches to relative error rate prediction, the accuracy of the backward shockwave determination, average vehicle velocity, average travel time, number of goodput vehicles, time-to-collision, and distance-to-collision.

In 4G cellular networks: LTE/LTE-Advanced and the mobile WiMax network, some key impact factors degrade signal transmission quality and reduce wireless service coverage significantly. The specifications of LTE-Advanced and IEEE 802.16j thus propose a relay-based scheme, namely Mobile Multihop Relay (MMR) networks, to cooperate with the existing cellular network and to guarantee QoS for requests while not obviously increasing the Relay Station (RS) deployment cost. To efficiently deploy different types of RSs becomes a critical issue. Thus, this paper first analyzes the impact factors: transmission quality, deployment price, service coverage and RS overlap index, and then models the cost-effective issue of the RS deployment as an optimization problem. The paper proposes an Adaptive Cost-based RS Deployment (ACRD) approach to form a cost function in terms of all impact factors, and then solves the optimization problem by determining the RS deployment with the least network cost as the solution. Numerical results demonstrate that ACRD outperforms the compared approaches in network cost, transmission quality, RS deployment price, service coverage, and RS overlap index. ACRD deploys more RSs on the areas with high-density populations and thus increases transmission quality and guarantees the quality of service (QoS).

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 © 2013 John Wiley & Sons, Ltd.

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.

Several reliable packet routing approaches have been studied to achieve a high reliable VANET by using the Car-to-car communications and Inter-Vehicle Communications. VANET suffers from high mobility, diverse road topologies, and wireless interference, and thus significantly degrades the connectivity of packet transmissions and network performance. The mathematical analysis can help the approach efficiency, but most works neglect the vehicular accidents happened on roads and then reduces the functionality of the mathematical analysis. This paper thus proposes a two-phase reliable packet routing approach, and then propose a mathematical model to analyze the packet connectivity probability for a multiple-lane road with accidents. Numerical results demonstrate that the proposed approach outperforms the compared works in packet connectivity probability and packet transmission delay under diverse affect factors: number of lanes on a road, vehicle accident probability, number of vehicles, vehicle density, etc. Importantly, the analytical packet connectivity probability and packet delay are close to that of simulations. The good features justify the correctness of the analytical model.

ABSTRACT 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 © 2011 John Wiley & Sons, Ltd.

In wireless networks, the multicast QoS routing is a key technique to increase bandwidth utilization, but the multicast routing is typically complicated and difficult because it belongs to the NP-complete problem. The main goal of a delay-bounded wireless multicast algorithm is to determine the optimal multicast tree that has the least cost while satisfying the delay-bounded requirement. However, previous studies suffer from the Tree setup-break and dangling node problems, and yield a large number of control messages. This paper thus proposes the adaptive distributed multicast routing (ADMR) algorithm to guarantee cycle-free, and to overcome these two problems while yielding the least-cost delay-bounded multicast tree for high-density member multicast networks. Numerical results indicate that ADMR significantly outperforms the Jia-based algorithms in number of control messages and setup convergent time.

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.

The IEEE 802.16e standard is proposed for mobile nodes to access high data rate and long transmission radius in WiMAX. For supporting contention-free-based initial ranging and early performing the initial ranging during handoff, IEEE 802.16e specifies the association handoff mechanism in the MAC layer. However, an MS is difficult to determine the scan duration in the association handoff mechanism because it may lose 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 for the association handoff, a long duration significantly degrades the QoS parameters of delay and delay jitter of real-time service flows. This paper thus proposes an efficient adaptive load-balancing association handoff approach (namely ALA) that consists 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 to reduce lost synchronizations, and thus improve the grade of service. PDLB adopts a prediction scheme to accurately predict the moving direction of mobile nodes, and thus achieve the reduction of the number of candidate target BSs in order to minimize the handoff delay and to balance traffic loads. Numerical results demonstrate that the proposed ALA approach obviously outperforms the IEEE 802.16e protocol and other approaches in average handoff delay, number of handoffs, dropping probability, grade of service, network utilization, and number of lost synchronizations.

The VSF-OFCDM system has been proposed as the forward link interface for achieving high data rate in 4G mobile communications, which allocates orthogonal channelization codes of an OVSF code tree in two-dimension (2D) spreading in the time and frequency domains. However, it suffers from two disadvantages namely moderate utilization and low transmission quality. Moderate utilization is caused by code blocking, and low transmission quality is due to the multicode interference from high channel loading in the time domain of the 2D spreading. A trade-off thus exists between code blocking and multicode interference. Lower code blocking means higher interference. For achieving high utilization while also providing high transmission quality is a critical issue that should be addressed in 4G VSF-OFCDM. Therefore, this paper proposes a 2D spreading approach based on Adaptive Load-balancing with Markov decision process (denoted by ALM). The ALM approach consists of three phases: 1) the adaptive 2D spreading phase to select the 2D spreading combinations, 2) a dynamic re-combination of a 2D spreading to decrease channel load while supporting transmission quality, and 3) the cost-based Markov decision process (MDP) code selection approach to minimize code blocking and to select the least cost channelization code as the optimal solution. Numerical results indicate that the proposed approach outperforms other approaches in transmission quality ratio and fractional reward loss.

Based on the IEEE 802.16e standard, WiMAX has proposed a relay-based approach, i.e., IEEE 802.16j, to extend the service area of Base Stations (BSs) and to improve the received signal strength (RSS) quality. IEEE 802.16j has the capability to achieve two significant advantages: low-cost of building IEEE 802.16 WiMAX networks and compatible with existing WiMAX standards. According to diverse features on mobility and relay range, the Relay Station (RS) can be classified into three types: Fixed RS (FRS), Nomadic RS (NRS) and Mobile RS (MRS). The relay-based WiMAX network includes different types of RSs. To efficiently construct the relay-based WiMAX and determine an optimal routing path between a Mobile Station (MS) and the MR-BS become two important issues. This paper thus proposes an IEEE 802.16j-conformed relay-based adaptive competitive on-line routing approach, in which a multihop optimal path is selected in terms of link bandwidth, path length and channel condition. Numerical results indicate that the proposed routing approach significantly outperforms other approaches in Fractional Reward Loss (FRL), network utilization and average end-to-end path delay.

In a heterogeneous wireless network (HWN) that consists of various wireless networks (e.g., WiMAX and WiFi) and cellular communications (e.g., B3G and 4G), vertical handoff acts as an important mechanism for achieving continuous seamless transmissions and improving grade of service. This work thus proposes an adaptive vertical handoff algorithm with predictive RSS to reduce unnecessary handoff while increasing utilization and decreasing connection dropping significantly. The proposed approach determines the optimal target network in two phases: polynomial regression RSS prediction and Markov decision process analysis. Numerical results indicate that the proposed adaptive approach outperforms other approaches in the number of vertical handoffs and SWGoS while yielding competitive utilization.

The main goal of vehicle navigation systems is to determine the optimal routing path for achieving the least travel time and exhausted gasoline. Most navigation systems use the static shortest path routing algorithm or use optional traffic information broadcasted by a centralized traffic information center (TIC) to avoid routing to heavy traffic load roads. Since the traffic information may be gathered from few monitoring devices that only covers some specific highways and roads, it results in some disadvantages, including only supporting partial traffic information on some roads, long update period and low reliability of using a centralized TIC. In consequence, the determined route could be the shortest distance route but it may not meet the demands of the optimal routing: the least travel time and exhausted gasoline. Therefore, we propose herein the wireless sensor network-based adaptive navigation approach, which uses the WiMAX multihop relay networks as the inter-vehicle communications (IVC) to increase the reliability and efficiency of inter-vehicle communications. Real-time traffic information could be gathered from various types of sensors equipped on vehicles and exchanged among neighbor vehicles. As a result, the navigation system can obtain three metrics of the road traffic density, road class and road distance to determine the optimal route. Numerical results indicate that the proposed adaptive navigation approach outperforms other approaches in the average travel time and average exhausted gasoline while yielding competitive average travel distance.

The multicast mobile ad-hoc network (multicast MANET) is proposed for a sender sending packets to several receivers through a multicast session. Since members of a multicast group changes frequently, the issue of supporting secure authentication and authorization in multicast MANET becomes more critical than the network provided a fixed central authentication (CA) server. This work thus proposes a two-step secure authentication approach for the multicast MANET. First, a Markov chain trust model is proposed to determine the trust value (TV) for each one-hop neighbors. A nodepsilas trust value is analyzed from its previous trust manner in this group. The proposed trust model is proven as an ergodic continuous-time Markov chain model. Second, a node with the highest TV of a group will be selected as the CA server. For increasing reliability, the node with the second highest TV will be selected as the backup CA server that will take over CA when CA fails. The procedures of the secure authentication for group management are detailed. The security analysis of each procedure is analyzed to guarantee that the proposed approach achieves a secure reliable authentication in multicast MANET. Numerical results indicate that the analytical trust value of each mobile node is very close to that of simulation under various situations. The speed of the convergence of the analytical trust value shows that the analytical results are independent of initial values and the trust classes.

IEEE 802.16 is proposed to provide middle-range access and high data rate for real-time transmission through wireless channel. The increasing of access range, data rate, and total number of nodes makes the wireless media access more difficult and critical. For overcoming contentions from requests, IEEE 802.16 thus adopts a centralized-based polling MAC instead of random access control. In such a polling mechanism, the number of polls (NPS) within a frame period becomes an important factor. There are two main reasons. First, not all the polled nodes have packets to be sent, which waste bandwidth used for polling these nodes. Second, that the node has packets to be sent may not be polled immediately and thus increases the polling delay. Therefore, in this paper we analyze NPS based on the Markov chain analysis for minimize the average polling delay while increasing network throughput. Numerical results indicate that the analysis results are very close to the simulation results. Moreover, the number of polls and the waste rate are also analyzed under various NDS and offered loads.

IEEE 802.16 standard is proposed for providing high data rate and middle-range access to Internet through wireless access channel. The increasing of data rate, access range, and total number of wireless nodes makes the wireless media access control more difficult and critical. For minimizing collisions due access contention, IEEE 802.16 thus adopted a polling access mechanism for base station (BS) to polling all subscriber stations (SSs) in turn. Although the polling mechanism overcomes the access contention among all SSs, it suffers from long polling delay and inefficient channel allocation in such WiMAX networks while in the worst case that in the worst case of that a BS polls each SS or group at each frame period. Therefore, we proposed an adaptive polling approach with cost-based call admission control (CAC) for increasing utilization of access channel and network reward, and reducing polling delay. Two mechanisms are proposed in this study, including a two-level adaptive scheduling mechanism for scheduling a dynamic polling list for QoS-based SSs and a cost-based call admission control mechanism for determining of accept a new incoming service flow or not. Numerical results indicate that the proposed approach outperforms IEEE 802.16 standard in fractional reward loss and average delay significantly.

Although wireless sensor networks have been studied extensively, several problems should be addressed, including the sensors placement policy, the data aggregation or fusion issue, and realizable applications. However, one of important issues is the placement policy of sensor nodes. Most studies have proposed the probability-based placement policies for monitoring an overall area. In most applications, not entire area is interested to be sensed. Additionally, the fully monitoring of an entire area causes several disadvantages - high cost of deployment, long transmission delay, slow response, and unnecessary data aggregation. Furthermore, previous works lacked of considering the difference between the sensing radius and the transmission radius that might result in inaccurate analysis. Therefore, the authors propose herein an efficient sensor placement approach (ESP) for a sparse interested area with considering of obstructers that block the data transmission among sensors. Meanwhile, the issue of different radiuses of sensing and transmission is analyzed in detail. Numerical results demonstrate that ESP requires the least number of sensor nodes under various network sizes and different number of obstacles. Moreover, simulation results indicate that the number of sensor nodes decreases when the sensing or transmission radius increases. The running time of ESP, O(K2), is also analyzed, which is better than that of the probability-based approaches, O(N2)> where K is the number of interested grids and N is the number of grids.

IEEE 802.lie proposed a new MAC protocol, hybrid coordination function (HCF), for achieving QoS with multiple classes of traffic for real-time multimedia services in wireless LANs (WLANs). HCF provides two modes of channel access - the contention free-based mode of HCF controlled channel access (HCCA) and the contention-based of enhanced distributed channel access (EDCA). Nevertheless, two issues in EDCA should be addressed for minimizing collision probability and maximizing throughput. First, EDCA supports the same minimum window for different classes traffic, which increases the collision probability from different classes of traffic. Second, the successful transmission traffic will transit to the minimum backoff stage, which causes unnecessary collisions from the same class traffic. Therefore, in this paper, we first propose a simple, efficient classification of traffic classes. Then, a high performance EDCA approach (H-EDCA), i.e., a distributed differentiated control of contention window, is proposed for suppressing unnecessary collisions from the same class traffic and different classes traffic. Moreover, collision probability and throughput are analyzed in detail based on the discrete-time Markov chain model. Numerical results demonstrate that the proposed H-EDCA approach outperforms significantly EDCA of IEEE 802.11e in both metrics.

In this paper, we propose an efficient, distributed, reliable P2P networks for this purpose, which is called hand-in-hand (HIH) P2P network. First, HIH adopts distributed index servers with unique individual ID as logical ring nodes for storing and managing the file sharing information. Second, HIH adopts a consistent hashing to hash the sharing filename as a seed and maps the seed to a corresponding index server. The consistent hashing achieves some advantages including, scalable, providing a fast, unique file hashing, and load balancing among all index servers. Finally, the data synchronization with backup mechanism and a logical ring structure are proposed for increasing node reliability and data integrity when some index servers may fail abnormally or leave suddenly in such a distributed P2P network. Numerical results indicate that the proposed distributed P2P network, HIH, outperforms other approaches in average number of lost seeds under various failure rates of index server and different number of index servers, and routing information overhead. Furthermore, HIH yields very competitive reliability overhead as comparing with other approaches. Finally, the optimal number of preceding nodes for each index server in HIH is also analyzed and induced it to three.

Vertical handoff provides continuous and seamless transfer between various wireless mobile networks, which have different data transmission techniques and standards. In contrast to the horizontal handoff, the vertical handoff should consider not only the strength of signal power but also QoS classes, network bandwidth and service types, etc. Most of the previous works proposed the Received Signal Strength (RSS) based methods to set thresholds for making the decision and yielded serious ping-pong effect when the mobile node moves around the overlay area of two heterogeneous wireless networks. The ping-pong effect causes unnecessary handoff and brings several drawbacks, including low network throughput, long handoff delay, and high dropping probability. Therefore, in this paper, we propose an efficient cost-based vertical handoff algorithm to reduce unnecessary handoffs while increasing network throughput, decreasing handoff delay, and avoiding connection dropping. Two primary motivations of this paper include the prediction of node mobility from RSS and the adaptive cost-based competitive on-line (COL) method to determine the optimal network to handoff to from all available candidates. Furthermore, message flows of vertical handoffs between 3G/UMTS and WLAN as well as horizontal handoff between WLANs with MIPv6 are expressed in detail. Finally, the handoff delays are analyzed for the proposed MIPv6 handoff. Numerical results demonstrate that the proposed cost-based approach outperforms other approaches in the number of vertical handoffs and connection dropping while yielding competitive throughput.

Abstract The demand and amount of data transfer in heterogeneous wireless network increases as the techniques of the third/fourth generation mobile communications (3G/4G) are progressed significantly. Vertical handoff provides continuous and seamless transfer between various wireless mobile networks, which have different data transmission techniques and standards such as GPRS, UMTS, cdma2000 and IEEE 802.11 family WLANs. In contrast to the horizontal handoff, the vertical handoff should consider not only the strength of signal power but also QoS classes, network bandwidth and service types, etc. Most of the previous works proposed the received signal strength (RSS) based methods to set thresholds for making the decision of performing vertical handoff or not. The RSS‐based approach yields serious ping‐pong effect when the mobile node moves around the overlay area of two heterogeneous wireless networks, which causes unnecessary handoff and increases the handoff overhead. Although the RSS‐based approach with the hysteresis technique decreases the number of unnecessary handoffs, it suffers from large overhead of handoff and causes several drawbacks, including low network throughput, long handoff delay, and high dropping probability. Therefore, an efficient cost‐based vertical handoff algorithm is proposed herein to reduce unnecessary handoffs while increasing network throughput, decreasing handoff delay, and avoiding connection dropping. Two primary motivations of this paper include the prediction of node mobility from RSS and the adaptive cost‐based competitive on‐line (COL) method to determine the optimal network to handoff to from all available candidates. Furthermore, message flows of vertical handoffs between 3G/UMTS and WLAN as well as horizontal handoff between WLANs with MIPv6 are expressed in detail. Finally, the handoff delays are analyzed for the proposed MIPv6 handoff. Numerical results demonstrate that the proposed cost‐based approach outperforms other approaches in the number of vertical handoffs and connection dropping while yielding competitive throughput. Copyright © 2006 John Wiley & Sons, Ltd.

The 3G wideband CDMA systems (WCDMA) adopt the orthogonal variable spreading factor (OVSF) code tree as the channelization codes management for achieving high data rate transmission in mobile communications. It assigns a single channelization code for each accepted connection. Nevertheless, the data rate of traffic classes should be powers of two of the basic rate, which is impractical and wastes the system capacity when the required rate is not powers of two of the basic rate. One good solution to reduce the waste rate is to assign multiple codes for each accepted connection but it causes two inevitable drawbacks: long handoff delay and new call setup delay due to high complexity of processing with multiple channelization codes, and high cost of using more number of rake combiners at both of the base stations and the mobile nodes. Therefore, we propose herein an adaptive efficient partition algorithm with the Markov decision process (MDP) analysis approach to provide fast handoff while reducing the waste rate significantly. Numerical results show that the proposed approach outperforms the single code assignment scheme in GOS and waste rate. Meanwhile, the optimal number of rake combiners is also analyzed in this paper.

The ad hoc on-demand distance vector (AODV) routing protocol is proposed for achieving dynamic, self-organizing and on-demand multihop routing among mobile nodes in mobile ad hoc networks (MANETs). In AODV, wireless links may be lost occasionally due to the nodes on the routing path that are unreachable. For solving the problem, the AODV protocol provides a local repair mechanism that tries to find an alternative route to destination by broadcasting the RREQ message from the upstream node of the broken. Although the local repair mechanism works with a specified TTL to limit the repair range of RREQ, large number of the broadcast RREQ messages result in extensive control messages and obvious power consumption for transmitting these broadcast messages. Therefore, in this paper we propose an unicast-type multihop local repair protocol to recovery the lost links efficiently while increasing network reliability, increasing utilization, minimizing the number of control messages and shortening the repair delay. Meanwhile, the optimal number of hops of neighbor table is also analyzed. Numerical results indicate that the proposed multihop local repair approach outperforms other repair approaches in fixed successful rate, control message overhead and network utilization.

In 3G WCDMA, several multi-code assignment mechanisms have proposed to reduce the waste rate. Nevertheless, these methods bring two inevitable drawbacks including, high complexity of handling multiple codes, and increasing the cost of using more rake combiners at both the base stations and mobile nodes. Therefore, we propose an adaptive grouping code assignment herein to provide a single channelization code for any possible rate of traffic, even though the required rate is not powers of two of the basic rate. Based on the dynamic programming algorithm, the adaptive grouping approach forms several calls into a group. Then it allocates a subtree to the group and adaptively shares the subtree codes for these calls in the concept of time-sharing of slots during a group cycle time. Numerical results indicate that the proposed adaptive grouping approach reduces significantly the waste rate and thus increases the system utilization.

Since the orthogonal characteristic of the orthogonal variable spreading factor (OVSF) code tree in wideband CDMA (WCDMA) systems, code blocking increases as traffle load or required rate increases. This causes inefficient utilization of channelization codes. Hence, how to efficiently manage the resource of channelization codes of OVSF code tree in WCDMA is an important issue and has been studied extensively. Therefore, in this paper we focus on how to assign channelization code efficiently. Additionally, most researches did not consider the analysis of tree state with dynamic traffic load and lack of systematic call admission control (CAC) mechanism. Therefore, in this paper, we first propose the Markov decision process (MDP) based analysis to assign channelization codes efficiently. Next, we extend the MDP-based approach as the call admission control mechanism to maximize system revenue while reducing blocking. Numerical results indicate that the proposed MDP approach yields the best fractional reward loss and code blocking reward loss as compare to that of others, including the random, left most, and crowded first schemes, and the MDP-based CAC outperforms the capacity-based CAC significantly.

The reduced load approximation technique has been extensively applied to flat networks, but the feasibility of applying it to hierarchical network model has seldom been described. Hierarchical routing is essential for large networks such as the Internet inter/intra-domain routing hierarchy and the Private Network to Node Interface (PNNI) standard. Therefore, this paper proposes an efficient and accurate analytical model for evaluating the performance of hierarchical networks with multiple classes of traffic. A performance analysis model with considering multiple classes of traffic, the complexity of analytical and explosion of computation will be extremely increased, and hence, result in inaccurate analytical. The issue of multiple classes of traffic has to be addressed in performance analysis model. In this paper, we first study the reduced load approximation model for loss networks, and then propose a novel performance evaluation model for large networks with multirate hierarchical routing. The hierarchical evaluation model is based on decomposing a hierarchical route into several analytic hierarchical segments. Once the blockings of these hierarchical segments are accurately determined, the blocking of the hierarchical path can be estimated accurately from these segments blocking. Numerical results indicate that the proposed hierarchical reduced load approximation yields quite accurate blocking probabilities as compared to that of simulation results. Furthermore, the accuracy of the proposed hierarchical reduced load approximation heuristic is independent of the blocking or the offered traffic load. Finally, we also draw some remarks on the convergence of the reduced load based approximation analysis model.

Although the reduced load approximation technique has been extensively applied to flat networks, the feasibility of applying it to hierarchical network model has seldom been described. However, hierarchical routing is essential for large networks, such as the Internet inter/intra-domain routing hierarchy and the PNNI standard. Furthermore, most of research focused on the performance evaluation with fixed routing. Hence, this paper proposes an efficient and accurate analytical model for evaluating the performance of adaptive hierarchical networks with multiple classes of traffic. The evaluation model is based on decomposing a hierarchical route into several analytic hierarchical segments, therefore the blocking of the hierarchical path can be computed from these segments blocking. Numerical results indicate that the proposed adaptive hierarchical reduced load approximation yields quite accurate blocking probabilities as compared to that of simulation results. We also investigate the speed of the convergence rate of the reduced load approximation analysis in both of OD pair level and alternative hierarchical path level.

The reduced load approximation technique has been investigated for flat networks successfully. Nevertheless, less attention has been focused on hierarchical network model. However, hierarchical routing is essential for large networks. For example, the ATM PNNI standard and the Internet inter/intra-domain routing hierarchy. Hence, the goal of this paper is to propose an efficient and accurate analytical model for evaluating the performance of hierarchical networks with multiple classes of traffic. We first study the reduced-load approximation model for multirate loss networks, and then propose a new model for networks with hierarchical routing. Our numerical results show that the proposed hierarchical reduced-load approximation yield quite accurate blocking probabilities as compared to that of simulation results.

For reducing routing information to achieve scalability in large ATM networks, ATM private network-to-network interface (PNNI) adopts hierarchical routing. In order to provide efficient routing, a large ATM network is decomposed into subnetworks, called peer groups (PG), and peer groups will advertise aggregated routing information only. Because the aggregated information is not very precise, a call set up message may be rejected on a chosen route. When an ATM node discovers a call set up message cannot proceed due to insufficient resource, it initiates a back-tracking procedure called "crankback" against call blocking. Although crankback reduces blocking probability, it also causes additional overhead, such as longer setup delay. Therefore, in this paper, we propose two approaches to reduce crankback overhead, The first approach adds additional information into the set up message, referred to as CIS (crankback information stack), to reduce crankback overhead. The other approach, referred to as CT (cost threshold), uses aggregated path cost and the cost information of a previously rejected call set up message to determine whether call setup on the next alternate path should be tried. Our simulation results show that both of the proposed approaches reduce crankback overhead significantly. Especially, the combination of CIS and CT approach achieves further improvement.

For achieving scalable and QoS-ware in large ATM networks, the ATM Private Network-to-Network Interface (PNNI) adopts hierarchical routing which reduces nodal and link information. In order to perform hierarchical routing efficiently, the network will consist of subnetworks, called peer groups, and peer groups will advertise the aggregated information periodically which is based on the time-based update interval or on an event driven basis. The time-based update policy is not adequate to cope with dynamic network traffic. Therefore, we propose a dynamic update policy, referred to as the cost-based update (DCU) policy, to enhance the accuracy of aggregated information and the performance of hierarchical routing, while decreasing the frequency of re-aggregation and information distribution and the overhead of communication. In our simulations, we compare the DCU policy with PNNI time-based update (DCU) policy, full update (FU) policy, and logarithm of residual bandwidth update (LRBU) policy. Our simulation results indicate that the proposed DCU policy yields better performance while significantly reduces the frequency of re-aggregation and the amount of distributed aggregation information.