The marine Internet technology has been proposed to exploit abundant communication and network resources available in the ocean in order to provide more cost‐effective and handy network services therein. Basically, the marine Internet architecture is based on heterogeneous large‐scale dynamic wireless, which consists of different types of networks such as satellite networks, coastline networks, and ship ad‐hoc networks etc. These networks are different in terms of networking cost, capacity, and performance as well as availability and reliability. This imposes challenges for network selection, especially when there is no guarantee on the availability and reliability of network resources in oceans, which is different from network selection in terrestrial environments. Thus, this paper studies a network selection scheme by jointly considering the above uncertainty of network resources based on the analytic hierarchy process (AHP) for marine Internet. The proposed scheme is evaluated through a simulation study on the EXata platform, in comparison with the Simple Additive Weighting and the Multiplicative Exponent Weighting schemes. The simulation results show that the proposed scheme yield better performance.

Resource control is a branch of congestion control in wireless sensor networks (WSNs). The congestion-oriented resource control schemes in WSNs often re-route traffic loads to avoid the congested areas. The re-routing overhead for congestion avoidance is particularly large in large networks. Thus, this kind of congestion control lacks of strong scalability. In this paper, a congestion control based on a geographic routing algorithm (CcbGr) for WSNs is proposed. It determines the congestion status of a node using thresholds of the queue length and the changing rate of the queue length. We adopt a geographic forwarding scheme in avoiding congestion. A new algorithm of distance update is also proposed to by-pass routing holes which are common for geographic routing. When a node is on the edge of a hole, it will increase the distance between itself and the sink according to specific rules. Simulation results show that CcbGr can effectively address network congestion with high scalability.

Interference channel (IC) can achieve significant spectrum benefit due to interference alignment (IA). In this paper, we consider the application of IC to underwater acoustic networks (UANs), which have narrow bandwidth and low channel capacity. Based on the underwater acoustic propagation model, a new IA-based distance-alignment structure (DAS) is studied for UANs with the following contributions. Firstly, the feasibility of proposed DAS in a three-dimension water space has been validated and demonstrated up to 4 pairs of transmit-receive nodes. Then a delay-aware adaptive multiple access (MAC) protocol, which can automatically switches between two basic modes according to interference distance, is investigated, and the performance study shows that the proposed protocol along with the DAS can asymptotically achieve the theoretic result of IC.

The redundant design and dynamic nature of traffic raise an energy inefficiency issue in communication networks. We exploit the selfishness of both users and the network to schedule cooperatively the idle links and nodes into sleep to save energy. We first formulate the sleep scheduling problem from a perspective of routing, and then propose a greedy algorithm to solve the problem. To reduce the complexity of centralized computation, we further propose a user-network cooperation-based mechanism, where the network publishes a proportionally weighted cost-sharing rule related to energy consumption, while the users selfishly choose their routes with the least cost accordingly. The proposed cooperation mechanism attracts users to aggregate their traffic on fewer links and nodes. The network then simply puts the idle links and nodes into sleep. Selfish routing behaviors are modeled by an α-approximate routing game, where the α factor is adopted to consider the energy consumption, packet losses, and delay during re-routing. We prove the equilibrium existence, convergence, and convergence speed of the best responses, and evaluate the lower bound performance in terms of price of anarchy with further improvement by an advertisement method. Distributed algorithms based on the best responses are also developed to implement the cooperative mechanism. Simulation results over network instants from SNDlib show that our game-based algorithms outperform the greedy and heuristic centralized algorithms in saving energy.

This paper investigates the scheduling problem for K-hop frequency-division-duplex cascaded wireless relay networks, where the source, the relays, and the destination form a chain. Two scenarios are considered: 1) directed transmission, in which each relay node only transmits its radio wave to its neighboring downstream node; 2) undirected transmission, in which the radio wave can be received by the two neighboring upstream and downstream nodes, which causes hidden-terminal (HT) problem. The problem of frequency band allocation is formulated, which can be solved to maximize the network rate with decode-and-forward relay strategy. Optimal solution is derived based on a naive scheme, whose achievable rate shows a similar expression as that of time-division-duplex. We further show that the effect of half duplex and HT can be alleviated by increasing the spectrum efficiency of all relay hops when K > 3.

In this paper, we investigate the potential throughput gain brought by cooperative interference alignment (IA) in multi-hop MIMO networks. Unlike the fully-connected K-user interference network where IA is usually considered, IA cooperations in multi-hop MIMO networks are limited by node density, leading to an inevitable coexistence of IA and non-IA links. Though cooperating links within the same IA group can nullify intra-group interference via IA, uncoordinated inter-group interferences as well as the interferences from non-IA links retain with noises. Hence, whether or not IA can brought throughput gain for such networks is still an open question. In allusion to this question, we firstly extend a cross-layer PHY-MAC model for MIMO networks to jointly abstract the IA and non-IA links with a set of transmission patterns. Then we formulate the problem of throughput-optimal topology control for multi-hop MIMO networks with IA and that without IA and prove their NP-hardness. We further propose integer linear mathematical models for the formulated problems and investigate the benefits of IA cooperations via simulations. Simulation results show that regardless of the number of antennas, IA cooperations do not offer noticeable throughput gain in random networks.

In this paper, we revisit the minimum-length link scheduling problem (MLSP) in wireless networks. Unlike previous scheduling solutions that adopt the interference avoidance approach, we embrace interference among neighboring links via a new technique of interference alignment (IA). Specifically, we use IA to cancel the interference among cooperative neighboring links, while controlling uncoordinated interference from non-neighboring links by traditional link scheduling. This novel approach of scheduling is modeled as an integer linear program based on an extended multiple-input and multiple-output (MIMO)-Pipe model, which not only captures the complex interference relationship between links in multi-user MIMO networks with IA, but also provides a realistic understanding of the interaction of achievable rate and suffered interference both for IA links and non-IA links in multi-user MIMO networks. By resolving the formulated programs, we further investigate the effect of node density and antenna number on the performance gain brought by IA cooperations. Simulation results show that the benefits of IA in MLSP problem generally increase with node density, but decrease with the number of antennas.

Quality of Service (QoS) provisioning for wireless multimedia applications has attracted increasing research attentions. Due to limited bandwidth of time-varying wireless links and various QoS requirements of bursty multimedia applications, an effective call admission control (CAC) policy that efficiently utilizes the bandwidth is desired. We have proposed a Differentiated Queueing Service (DQS) to support per-packet differentiated services for admitted traffic, which has been illustrated feasibility for mixed streams with various QoS requirements in multimedia applications. This paper furthers the research by exploring a DQS-based CAC policy to maximize the bandwidth utilization of wireless networks while provisioning call-level as well as packet-level QoSs for multimedia applications. To this end, we novelly use delay bound violation probability as admission control threshold and a basic DQS-based CAC policy, namely Delay Bound violation probability Guard (DBG) policy is proposed. Then we optimize the policy by formulating it as a Semi-Markov Decision Process (SMDP). The optimal DBG policy is found by solving the linear programming formulation problem. Numerical results show that, the DBG policy over SMDP achieves its goals of maximizing the bandwidth utilization while provisioning both call-level and packet-level differentiated QoSs for each class of multimedia calls in comparison with bandwidth guard CAC policies.

When energy efficiency is considered, cooperative communications may not be appealing since it involves multiple nodes in transmissions. To exploit the benefits of distributed user cooperation in cooperative wireless ad hoc networks (WANETs), we propose a distributed energy-efficient selective diversity (EESD) topology control to improve energy efficiency in the network, which jointly considers network capacity and energy consumption in terms of bits per Joule. EESD forms transmission coalitions via cooperative manner (i.e, diversity) selections, by taking into account the cost of channel information exchange. We then formulate EESD as a coalition game and propose an adaptive coalition formation algorithm for EESD with proved convergence property and stable coalition structures. Simulation results show the performance improvement of EESD in energy efficiency compared to the existing topology control schemes.

In dense deployments of Wireless Body Sensor Networks (WBSNs), inter-user interference significantly degrades network performance when multiple WBSN users stay in a small area such as hospitals. Due to the high dynamics of the environments, it is usually hard to schedule the transmissions of multiple WBSNs without a central controller. In this paper, we propose a robust and lightweight interference mitigation scheme for realistic WBSN systems through adaptive channel hopping. A WBSN testbed is set up to investigate the impact of inter-user interference on various performance metrics when different severity levels of interference are present. Based on the measurement results, we propose a distributed interference detection and mitigation scheme without any central controller. A WBSN prototype system has been set up and shown that our proposed scheme can effectively detect and mitigate the multi-user interference, with tripling the network throughput in severely interfered environments.

With recent advances in parallel cooperative transmissions between multiple source-destination pairs, interference cancellation (IC) can be achieved to improve the capacity performance of wireless networks. However, from energy efficiency perspective, user cooperation may not be always appealing, since the increased data rate of one user comes at the price of the energy consumed by another user. In this paper, we study the potential benefits/drawbacks of cooperative communications on network-level issues, such as the capacity and the energy efficiency. We show that, in terms of network energy efficiency, cooperative communications do not always outperform non-cooperative communications, and cooperative communications should be dynamically applied in topology control to optimize the overall network energy efficiency. Specifically, we propose an energy-efficient topology control scheme by jointly considering the capacity and energy consumption of non-cooperative and cooperative communications. Simulation results are presented to show the effectiveness of the proposed scheme.

Due to the scarce bandwidth and limited power supply in mobile terminals, performance and energy consumption in wireless communications must be continually focused upon. Cooperative transmissions improve the capacity performance of wireless ad hoc networks (WANETs). However, when energy efficiency is considered, the advantage of user cooperation over non-cooperation does not always exist since it involves multiple nodes with more energy consumption in transmissions. To exploit the benefits of user cooperation in cooperative WANETs, we propose a distributed energy-efficient selective diversity (EESD) topology control to improve energy efficiency, which jointly considers network capacity and energy consumption in terms of bits per Joule. EESD forms transmission coalitions via cooperative manner (i.e, diversity) selection, by taking into account the cost of channel information exchange. We then formulate EESD as a coalition game and propose an adaptive coalition formation algorithm for EESD with proved convergence property and stable coalition structures. Simulation results show the performance improvement of EESD in energy efficiency and network lifetime compared to the existing topology control schemes.

Quality of Service (QoS) provisioning especially delay guarantee is particularly important to the increasing popularity of mobile wireless multimedia applications. Traditional QoS schemes include the per-flow Integrated Service (IntServ) and per-class Differentiated Service (DiffServ) as well as their variants. To overcome the scalability problem of IntServ and the coarse QoS granularity of DiffServ, the per-packet Differentiated Queueing Service (DQS) was proposed. This paper focuses on analytically modeling of the QoS provisioning performance of DQS for mobile wireless multimedia applications. In the analysis, arriving packets of a session are classified into different streams according to their delay requirements. Each stream is described by a modified Fractional Brownian Motion (FBM)based traffic model, where both the traffic self-similarity of multimedia streams and heavy-tailed distribution of packet sizes are considered. We develop a stochastic service capability model for mobile wireless links. Then a delay guarantee model for DQS is further developed by deriving the delay bound violation probability and packet loss rate. Computer simulations are conducted to validate the proposed analytical models.

Reduction of energy consumption is becoming a major concern in communication networks, because of its potential economical benefits and environmental impact. In this paper, we propose a prediction-based traffic aggregation scheme to realize energy saving for green networking. By predicting the traffic loads, the scheme aggregates and reroutes the traffic in some nodes to make them idle and then sleep in the next control time interval when the traffic is predicted light. Simulation results demonstrate that the proposed scheme can yield the accuracy of traffic prediction with a small normalized one-step prediction error and significant energy saving corresponding to the traffic loads in a simple network. Meanwhile, the throughput and delay of the network are almost not affected by the scheme.

Cooperative communication can significantly enhance transmission reliability and bandwidth efficiency in wireless networks. Most existing works are focused on physical layer issues of cooperative communications. Many upper layer aspects of cooperative communications merit further research. In this paper, we investigate its impacts on network topology and capacity. Specifically, we present a novel Capacity-Optimized COoperative (COCO) topology control scheme for mobile ad hoc networks (MANETs) with cooperative communications. We consider both upper layer network capacity and physical layer relay selections in the proposed scheme. In addition, only the channel estimate, not the perfect channel status, is assumed to be known in our scheme. The topology control problem in MANETs is formulated as a discrete stochastic optimization problem, which can be solved using a stochastic approximation approach. Simulation results are presented to show the effectiveness of the proposed scheme.

Security is an important issue in mobile ad hoc networks (MANETs). However, security schemes have significant impacts on throughput. That is because 1) they need some overhead and consume some network resources, thus decrease throughput consequently, 2) most previous works consider security and throughput separately in designing a MANET, which can not achieve an overall optimization of network performance. In this paper, we propose a topology control scheme to improve throughput by jointly designing upper layer security schemes and physical layer schemes related to channel conditions and relay selections for cooperative communications. Simulation results show that our scheme can substantially improve throughput in MANETs.

The layered protocol architecture lacks of flexibility to support granular QoS requirements for multi-hop mobile wireless networks with limited bandwidth. Meanwhile, research indicates that TCP behaves inefficiently in such networks. Recently Differentiated Queueing Service (DQS) and Semi-TCP schemes have been proposed to provide granular QoS and improve the performance of TCP, respectively. However, the impact of their correlation on the overall network performance has not been investigated when they are implemented in the same protocol stack since their implementations cross transport layer, network layer and data link layer. To this end, this paper integrates DQS and Semi-TCP to investigate the performance in multi-hop mobile wireless networks. The study comes up with some new possible schemes to further improve the overall performance. According to our study, we propose a new algorithm to estimate the latest departure time and a novel handling of overdue packets, as well as an ACK scheme to decrease nodes' contention. Furthermore, we also design the cross-layer architecture for the integrated solution. Simulation results show that the integrated scheme can further improve throughput and reduce delay.

Cooperative communications can significantly enhance transmission reliability and bandwidth efficiency in wireless networks. However, many upper layer aspects of cooperative communications merit further research. In this paper, we investigate its impacts on network topology and network capacity, which is determined by considerable aspects, such as physical layer capacity, interference, path length, etc. Since cooperative communications enhance physical layer capacity and relay selection impacts network topology directly, we present a Capacity-Optimized COoperative (COCO) topology control scheme for mobile ad hoc networks (MANETs) with cooperative communications. We consider both upper layer network capacity and physical layer relay selections in the proposed scheme. In addition, only the channel estimate, not the perfect channel status, is assumed to be known in our scheme. The topology control problem in MANETs is then formulated as a discrete stochastic optimization problem, which can be solved using a stochastic approximation approach. Further, an improved COCO is presented to reconfigure network topology to track the changing mobile environment dynamically. Simulation results are presented to show the effectiveness of the proposed scheme.

Devices in wireless multihop networks should communicate with each other along minimum energy-consuming paths for energy-saving. To this end, any energy-aware topology control scheme should not destroy these paths. The Localized Dijkstra Topology Control (LDTC) algorithm discussed in this paper aims at constructing a network topology to preserve all the minimum energy paths by using only local information subject to network connectivity. It also takes link quality requirements to assign transmission power. Furthermore, LDTC is proven analytically that it can maintain bidirectional wireless links to facilitate handshake mechanisms. Moreover, within the Euclidean graph, no two links intersect in the derived topology, which can mitigate interference. Simulation results indicate that LDTC generates a simple topology with small node degree and short transmission radius. When cooperating with different routing strategies, it performs well in energy and hop count spanners, and can be easily implemented in wireless multihop networks.

Denial-of-Service (DoS) attacks especially distributed DoS (DDoS) attacks have become significant and increasing threats to the Internet. Huge efforts from both academia and industry have been made on detection and defense of DDoS attacks. However, most detection and defense schemes do not directly aim at protecting the victim of attacks itself (e.g., servers) but attack sources or intermediate network units. Although locating and identifying attacking sources are critical to stop attacks and for legal procedure, rapid and efficient predicting DDoS attacks to happen in the server is more important to reduce damage caused by attacks and even prevent attacks from happening. However, this part has not been addressed sufficiently in the literature. In this paper, we first briefly review research efforts on DDoS attacks, and then discuss a method to define and quantify attacks to severs based on available service rates. This is because the server is often the direct victim of DDoS attacks and the one-point failure of the entire service system. No matter whether there are attacks undergoing, if a sever is overloaded even by normal service requests, the effect imposed to a service system is equivalent to that of attacks. A prediction method for the available service rate of the protected server is then proposed, which applies the Auto Regressive Integrated Auto Regressive (ARIMA) model. Finally, we investigate the proposed prediction method to predict DDoS attacks through simulation studies with NS2. The simulation results show that the prediction algorithm is effective to predict most attacks.

Mobility models are often used to evaluate performances of mobile networks through either analysis or simulation. The epoch mobility model is one of important mobility models that can statistically describe mobile behavior in general. Here an epoch is a random length interval during which a node is supposed to move at a constant velocity. However, a border may force a node to change its motion during an epoch. This phenomenon is often called border effect in the literature. In this case, the original mobility model cannot reflect the real mobile behavior, and it is necessary to study border effect in depth. Epoch distribution is the key to epoch mobility models and may be severely impacted by border effect. Therefore, this paper discusses how to use geometric probability to estimate affected epoch distributions by proposing some methods to calculate border hitting probabilities and estimate epoch distributions that are affected by border effect. A simulation study is also conducted to verify the proposed methods and shows that they can provide good estimations.

Provisioning of more granular quality of services (QoS) for different applications in wireless mesh networks (WMNs) is a challenge issue for scheduling algorithms. Most traditional scheduling algorithms try to provide per-flow or per-class QoS almost without consideration of the end-to-end situation for applications such as path lengths. Actually, for the same type of applications, difficulties for a node to provide end-to-end QoS largely depend on path lengths. Differentiated queueing service (DQS) is a new scheduling algorithm providing more granular QoS in wired networks by taking into account the above issue. In this paper, DQS is improved such that it can be used in WMNs. Meanwhile we also discuss a cross layer implementation of DQS. The earliest deadline first (EDF) scheme is used in comparison with our proposed algorithm since EDF is similar to DQS to some extent. The simulation studies show that the performance of DQS is better than EDF in terms of average goodput and end-to-end delay.

Image emotional semantic research is a promising and challenging issue. This paper analyzes the emotional space and builds a novel scheme that can annotate the image emotion semantic automatically and realize emotional image retrieval. Based on psychological experiments evaluating evoked feelings for art paintings, we first identify an orthogonal three-dimension emotional factor space of images through 12 pairs of emotional words. Then, the following three novel image features are designed for each emotional factor to predict it. They are luminance-warm-cool fuzzy histogram, saturation-warm-cool fuzzy histogram integrated with color contrast and luminance contrast integrated with edge sharpness. The values of emotional factors can be predicted from the image features automatically by using support vector machine of regression. Finally, we design and implement an emotion-based image retrieval system, which enables the users to perform retrieval using emotional semantic words. Experimental results show the effectiveness of our model.

Dynamic bandwidth assignment (DBA) in Ethernet Passive Optical Networks (EPONs) is based on a frame structure that is broadcast downstream periodically. In most DBA schemes supporting priorities, frames are divided to allocate bandwidth for different traffic classes according to weights, which, however, are often either determined empirically or supposed to be pre-known. How to determine these weights dynamically according to quality of service (QoS) requirements and traffic loads has not been addressed adequately in the literature. This paper discusses a frame division method for supporting prioritized DBA for three traffic classes based on weights determined according to the traffic load and QoS requirement of each traffic class. This method is based on a frame structure that can efficiently support traffic prioritization by allocating per-frame bandwidth for each traffic class according to its medium access delay bound and traffic load. The method is investigated through computer simulation for voice, video and data applications. The simulation results show that it can properly allocate bandwidth to voice with little over-provisioned bandwidth while video can be efficiently prioritized at the expense of less support for data traffic

In this paper, we develop analytical models for a single persistent TCP flow in the presence of channel error-induced packet loss over IEEE 802.11 based multi-hop networks. Two analytical models are proposed, based on different packet loss models: periodic packet loss model and i.i.d. random packet loss model. For the latter, we develop a stochastic model using the Markov renewal reward approach. The analytical results are validated against results using the ns simulator. The results show that the impact of the channel errors is reduced significantly with packet retransmissions on a per-hop basis and the two models are valid for a packet error rate ranging from 0 to /spl sim/0.05.

A Mobile Ad hoc Network (MANET) is a collection of wireless mobile terminals that are able to dynamically form a temporary network without any aid from fixed infrastructure or centralized administration. One critical issue for routing in MANETs is how to select reliable paths that can last as long as possible since terminal mobility may cause radio links to be broken frequently. To solve this problem, a criterion that can judge path reliability is needed. The reliability of a path depends on the number of links and the reliability of each link constituting the path. Many routing metrics in terms of number of links have been proposed, such as the shortest path routing. However, how to measure link availability or reliability in order to find more reliable paths has not been addressed adequately in the literature. (By a link being available, we mean that the radio quality of the link satisfies the minimum requirement for successful communication. Link availability is used to measure probability or degree that a link is available. The terms availability and reliability are used interchangeable in this paper.) This paper first introduces a prediction-based link availability estimation to quantify the link reliability. This quantity makes use of some instantly available information and also considers the dynamic nature of link status in order to properly reflect the link reliability. Then, this quantity has been further used to develop routing metrics for path selection in terms of path reliability to improve routing performances. The proposed schemes have been investigated through computer simulation.

Frequent changes in network topologies caused by mobility in mobile ad hoc networks (MANETs) impose great challenges to designing routing schemes for such networks. Various routing schemes each aiming at particular type of MANET (e.g., flat or clustered MANETs) with different mobility degrees (e.g., low, medium, and high mobility) have been proposed in the literature. However, since a mobile node should not be limited to operate in a particular MANET assumed by a routing scheme, an important issue is how to enable a mobile node to achieve routing performance as high as possible when it roams across different types of MANETs. To handle this issue, a quantity that can predict the link status for a time period in the future with the consideration of mobility is required. In this paper, we discuss such a quantity and investigate how well this quantity can be used by the link caching scheme in the dynamic source routing protocol to provide the adaptability to variable topologies caused by mobility through computer simulation in NS-2.

In this letter, an enhancement to the prediction-based link availability estimation originally proposed by the author, D. J. He, and J. Q. Rao is discussed. This enhancement consists of the principle for the theoretical calculation of link availability, L(T/sub p/), and a better L(T/sub p/) estimation that averts the intuitive parameter setting used by the original one. Numerical comparisons between results given by the two estimations and simulation are provided.

In this paper, we propose a probabilistic preemptive (PP) scheme for service differentiation in optical burst switching (OBS) networks. By changing the preemptive probability, an OBS node can adjust the ratio of burst blocking probability between different traffic classes, while the overall blocking probability is not affected.

With on-demand routing protocols for mobile ad hoc networks (MANETs), for example, dynamic source routing (DSR), a source node tries to find a route to the destination node only when it has a packet addressed to that destination node. And the source node can find a route either from its own route cache or by initializing a route discovery. To reduce the traffic generated by such route discoveries, caching of routing information is necessary. And in the design of caching schemes, cache timeout (i.e., the time period that a link would stay in the cache) is a critical parameter. However, only a few works have been done on how to set it. In this paper, we propose a new link caching scheme with adaptive timeouts. In this scheme, the cache timeout of a link is decided based on the estimation of the link's lifetime. Simulation results show that the proposed scheme can adapt to scenario changes and hence improve the performance of on-demand routing for MANETs.

We introduce the concept of generalized stochastically bounded burstiness (gSBB) for Internet traffic, the tail distribution of whose burstiness can be bounded by a decreasing function in a function class with few restrictions. This new concept extends the concept of stochastically bounded burstiness (SBB) introduced by previous researchers to a much larger extent - while the SBB model can apply to Gaussian self-similar input processes, such as fractional Brownian motion, gSBB traffic contains non-Gaussian self-similar input processes, such as /spl alpha/-stable self-similar processes, which are not SBB in general. We develop a network calculus for gSBB traffic. We characterize gSBB traffic by the distribution of its queue size. We explore the property of sums of gSBB traffic and the relation of input and output processes. We apply this calculus to a work-conserving system shared by a number of gSBB sources, to analyze the behavior of output traffic for each source and to estimate the probabilistic bounds for delays. We expect this new calculus to be of particular interest in the implementation of services with statistical qualitative guarantees.

One critical issue for routing in mobile ad hoc networks (MANET) is how to select a reliable path that can last longer since mobility may cause radio links to break frequently. To answer this question, a criterion that can judge path reliability is needed. The reliability of a path depends on the availability of the links constituting the path. However, how to measure link availability to answer the above question has not been addressed adequately in the literature. In this paper, a prediction-based link availability estimation is introduced and verified through computer simulations. This estimation algorithm can be used to develop a metric for path selection in terms of path reliability, which can improve the network performance as shown by simulation results.

Dynamic channel assignment (DCA) schemes can provide a more efficient solution than fixed channel assignment (FCA) schemes for future mobile cellular networks to meet the requirements of the ever-growing number of mobile users. This is due to due to its better adaptability to unevenly-distributed and changing traffic load. However, it is observed that in DCA with the soft handoff policy, a handoff call will suffer a higher dropping probability than the blocking probability of a new call in the case of no handoff prioritization. This is definitely undesirable from the user's point of view. The channel carrying approach, which allows a mobile station to continue to use its currently occupied channel when it handoffs to a new cell, can easily change the stated situation above. We investigate two channel carrying strategies through simulations, and find that the one called "channel carrying last" performs better.

This paper presents a new dynamic and adaptive bandwidth allocation scheme to prevent handoff failure due to lack of resources in mobile cellular networks, known as the measurement-based preassignment (MPr) technique. This technique is particularly useful in micro/pico cellular networks which offer quality of service (QoS) guarantees against call dropping. The proposed MPr scheme distinguishes itself from the well-known guarded channel based schemes in that it allows the handoff calls to utilize a pre-reserved channel pool before competing for the shared channels with new call arrivals. The key advantage of the proposed MPr scheme is that it can easily derive the number of channels that needs to be reserved for handoff based on a pre-determined call dropping probability, without the need for solving the often complex Markov chain required in guarded channel schemes, thus making the proposed MPr scheme simple and efficient for implementation. In addition, the MPr scheme is dynamical in that it can adjust the number of reserved channels for the handoff according to the traffic changes in the system.

Call admission control (CAC) is one of the key elements to provide quality of service (QoS) guarantee in wireless mobile networks. A good CAC scheme should efficiently support handoffs and maintain a high utilization of the scarce radio resource while it should also be simple for implementation. Since the traditional guard channel policy is not optimal for a hard constrained handoff dropping probability, new CAC algorithms have been studied in the literature. Among them, the distributed call admission control seems to be simpler and more efficient with regards to the above requirements. However, there are some problems in the original scheme which make the implementation complex and lead to performance degradation. In this paper, we will first discuss simplifications to the original scheme, and then further enhance the modified scheme by considering the difference of mobility support requirement between high and low mobility users. The simulation results show that the enhanced scheme gives better performance.