A Guard Code Scheme for Handover Traffic Management in WCDMA Systems

A key performance indicator of mobile wireless networks is failure probability of handover calls. In this paper, we propose a Call Admission Control policy which prioritizes handover calls over new calls in WCDMA systems. The OVSF code occupancy of the system is modeled by a Markov chain and the differentiation between handover and new calls is performed at the code level by introducing a “guard code” scheme. The scheme belongs to the well-known family of guard channel schemes and reserves some code capacity to favor the continuation of handover calls over the new calls. As the management of the general case is intractable, we solve certain numerical instances of the problem and manage to calculate several performance metrics like new call blocking and handover failure probabilities and code utilization. We complete our study with simulation results in the case of higher OVSF code tree capacity.

Multi-class Bandwidth Reservation Scheme Based on Mobility Prediction for Handoff in Multimedia Wireless/Mobile Cellular Networks

Next generation of wireless cellular networks aim at supporting a diverse range of multimedia services to Mobile Terminal (MT) with guaranteed Quality of Service (QoS). The challenge is to maintain the playing continuity of multimedia streams during handoff. In this paper, a bandwidth reservation scheme based on mobility prediction is proposed, to enable high accurate prediction of next crossing cell (target cell) which a MT is going to, in order to avoid too early or over reservation resulting in a waste of resources. The amount of bandwidth to be reserved is dynamically adjusted according to (a) the current position (location) and the extrapolated direction of MT and; (b) the sector and zones of the cell. A Call Admission Control scheme (CAC) is also considered to further guarantee the QoS of real time traffic. The performance of the system is evaluated through discrete event simulation of the wireless cellular environment. Simulation results show that the proposed scheme as compared to several existing schemes is able to reduce the Handoff Call Dropping Probability (HCDP) of real time traffic and the number of terminated ongoing calls of non-real time traffic. In addition, it is efficient to reduce the number of cancelled reservation and subsequently increase the system bandwidth utilization.

Integrated power and handoff control for next generation wireless networks

In this paper, joint downlink power control and handoff design is formulated as optimization problems that are amenable to dynamic programming (DP). Based on the DP solutions which are impractical, two new algorithms suitable for next generation wireless networks are proposed. The first one is an integrated hard handoff/power control scheme that endeavors a tradeoff between three performance criteria: transmitted power, number of handoffs, and call quality. The second is a soft handoff/power control algorithm that also takes into account the additional cost of utilizing soft handoff. The proposed algorithms present a paradigm shift in integrated handoff/power control by capturing the tradeoff between user satisfaction and network overhead, therefore enjoy the advantages of joint resource allocation, and provide significant improvement over existing methods. The achievable gains and the tradeoffs in both algorithms are verified through simulations.

A Framework for JRRM with Resource Reservation and Multiservice Provisioning in Heterogeneous Networks

Inter-working and convergence of heterogeneous wireless networks are paving the way to scenarios in which end users will be capable of using simultaneously services through different Radio Access Technologies (RATs), by means of reconfigurable mobile terminals and different network elements. In order to exploit the potential of these heterogeneous networks scenarios, optimal RAT selection and resource utilization mechanisms are required. As a result, the heterogeneous networks are introducing a new dimension to the Radio Resource Management (RRM) problem, so that new algorithms dealing with the dissimilarities and complementarities of the multiple RATs from a joint perspective have to be considered. In this sense, this paper proposes a Joint Radio Resource Management (JRRM) strategy in a multi-RAT, multicellular and multiservice scenario. An approach based on Fuzzy Neural methodology is presented. Firstly, the way how the proposed Fuzzy Neural framework deals with the multiservice allocation in a heterogeneous scenario is presented. A reinforcement learning algorithm based on neural networks allows guaranteeing a multidimensional QoS focusing on those QoS requirements which mainly affect the user perception of the service. In addition to this, the performances obtained by the Fuzzy Neural JRRM for both real-time and non real-time services, are compared to the ones offered by alternative JRRM strategies. Secondly, special attention is paid to real-time services and to mechanisms to improve their performances. An approach based on predicting future JRRM decisions and on accordingly reserving radio resources for handoff calls is presented. Simulation results will show improvements in terms of both new connection blocking and handoff call dropping probabilities. Finally, the full set of results provides the sufficient insight into the problem to allow stating that the present Fuzzy Neural framework can be a firm candidate for JRRM.

Call Admission Control Algorithms in OFDM-based Wireless Multiservice Networks

Orthogonal frequency division multiplexing (OFDM) is becoming a fundamental technology in future generation wireless communications. Call admission control is an effective mechanism to guarantee resilient, efficient, and quality-of-service (QoS) services in wireless mobile networks. In this paper, we present several call admission control algorithms for OFDM-based wireless multiservice networks. Call connection requests are differentiated into narrow-band calls and wide-band calls. For either class of calls, the traffic process is characterized as batch arrival since each call may request multiple subcarriers to satisfy its QoS requirement. The batch size is a random variable following a probability mass function (PMF) with realistically maximum value. In addition, the service times for wide-band and narrow-band calls are different. Following this, we perform a tele-traffic queueing analysis for OFDM-based wireless multiservice networks. The formulae for the significant performance metrics call blocking probability and bandwidth utilization are developed. Numerical investigations are presented to demonstrate the interaction between key parameters and performance metrics. The performance tradeoff among different call admission control algorithms is discussed. Moreover, the analytical model has been validated by simulation. The methodology as well as the result provides an efficient tool for planning next-generation OFDM-based broadband wireless access systems.

HASP Overlay Cell Over Wireless ATM Microcellular Networks: A Proposed Architecture for Priority Subscribers

Wireless ATM (W-ATM) microcellular networks encounter severe problems during handovers. Microcellular solutions in W-ATM networks increase the network traffic control as a result of frequent handover requests. This paper presents a two-layer microcellular ATM architecture which optimizes the handoff blocking probability performance of priority subscribers (PS) in a congested urban area. The lower layer of the proposed architecture is based on a microcellular ATM solution for normal subscribers (NS) while the higher layer is based on a high altitude stratospheric platform (HASP) overlay solution for absorbing the traffic load of the existed handoff calls of PS. Analysis is performed using Markov state diagrams, in order to optimize the performance of W-ATM networks.

Consumer-Oriented Incoming Call Connection Service for a Ubiquitous Consumer Wireless World

This paper proposes an architecture and protocol infrastructure for a novel consumer-oriented incoming call connection (ICC) service. In the ubiquitous consumer wireless world (UCWW) this service is one of the core services requiring new infrastructural solutions for its realisation. The solution proposed here, besides realising the service, will offer mobile users greater flexibility and management control over incoming calls, enable users to receive incoming calls via multiple access networks/providers through a single identity, enable user-driven, seamless, network-transparent hot access network change (HAC), largely end roaming charges and create a new wireless networking business opportunity among other benefits. The main components and interfaces of the ICC service architecture and infrastructure are described, and protocol candidates are suggested. A generic consumer-oriented ICC service scenario is elaborated theoretically, implemented and experimentally verified for voice over IP (VoIP) connections in a testbed environment which includes network-transparent HAC. Two distinct ICC operational modes are identified and compared in respect of relative signaling latency and processing resources for a number of key functions such as session setup and release, and HAC.

Improving Spectral Capacity and Wireless Network Coverage by Cognitive Radio Technology and Relay Nodes in Cellular Systems

Methods to enhance the use of the frequency spectrum by automatical spectrum sensing plus spectrum sharing in a cognitive radio technology context have been presented and discussed in this paper. Ideas to improve the wireless transmission by orthogonal OFDM-based communication and to increase the coverage of cellular systems by future wireless networks, relay channels, relay stations and collaborate radio have been presented as well. A revised hierarchical deployment of the future wireless and wired networks are shortly discussed.

Analysis of Forwarding Mechanisms on Fine-Grain Gradient Sinking Model in WSN

The communication efficiency of large-scale WSNs with high node density is highly related with specific forwarding strategy in complicated wireless environments. Thus, it is the key problem that how to use the characteristic of high-density to select appropriate forwarding nodes to relieve the load imbalance and improve the communication efficiency. In this paper, we first propose a Fine-grain Gradient Sinking (FGS) model and several data forwarding strategies based on this model. Then we give the criteria of communication efficiency and emphatically analyze the communication efficiency of various forwarding strategies. Simulation results show that forwarding strategies under FGS model can achieve higher communication efficiency, and the efficiency can be further elevated by introducing the statistics of packet receive rate during the forwarding process.

Improving performance of TCP over mobile wireless networks

Mobile IP is a network layer protocol for handling mobility of hosts in the Internet. However, mobile IP handoff causes degradation of TCP performance. Hence, there is a need for improving performance of TCP over mobile IP in wireless mobile networks. We propose an approach which handles losses due to both wireless link errors and host mobility. To handle losses due to host mobility, a method for seamless handoff is proposed. Empirical results show that the scheme provides substantial improvement of performance.

Performance Evaluation of the Enhanced MI-MAC Protocol for Multimedia Integration over Wireless Cellular Networks

In recent work (Koutsakis et al., IEEE Trans Veh Technol 54(5):1863–1874, 2005), we have introduced multimedia integration multiple access control protocol (MI-MAC). The protocol was shown to achieve superior performance in comparison to other protocols of the literature when integrating various types of multimedia traffic over wireless cellular networks. In this work we enhance the scheduling scheme of MI-MAC by adding three important parameters into its study. These are: (a) the handling of handoff traffic, (b) per user varying channel conditions in the uplink and downlink channels and (c) video sources’ contention for channel resources. These parameters are added in order to evaluate the protocol under a significantly more realistic wireless cellular network scenario. New scheduling ideas are proposed in order to efficiently incorporate the new parameters into the scheme. The evaluation, conducted by comparing the enhanced MI-MAC with another efficient protocol of the literature and with an “ideal” MAC protocol, focuses on the efficient transmission of MPEG-4 video traffic and shows that our scheme achieves excellent performance results.

A Cross-layer Approach to Channel Assignment in Wireless Ad Hoc Networks

To improve the capacity of wireless ad hoc networks by exploiting multiple available channels, we propose a distributed channel assignment protocol that is based on a cross-layer approach. By combining channel assignment with routing protocols, the proposed channel assignment protocol is shown to require fewer channels and exhibit lower communication, computation, and storage complexity than existing channel assignment schemes. A multi-channel MAC (MC-MAC) protocol that works with the proposed channel assignment protocol is also presented. We prove the correctness of the proposed channel assignment protocol. In addition, through a performance study, we show that the proposed protocol can substantially increase throughput and reduce delay in wireless ad hoc networks, compared to the IEEE 802.11 MAC protocol and an existing multi-channel scheme.

An Energy Conservation MAC Protocol in Wireless Sensor Networks

Wireless sensor networks use battery-operated computing and sensing devices. Because of the limitation of battery power in the sensor nodes, energy conservation is a crucial issue in wireless sensor networks. Consequently, there is much literature presenting energy-efficient MAC protocols based on active/sleep duty cycle mechanisms to conserve energy. Convergecast is a common communication pattern across many sensor network applications featuring data gathering from many different source nodes to a single sink node. This leads to high data collision rates, high energy consumption, and low throughput near the sink node. This paper proposes an efficient slot reservation MAC protocol to reduce energy consumption and to make transmission more efficient in data gathering wireless sensor networks. The simulation results show that our protocol provides high throughput, low delivery latency and low energy consumption compared to other methods.

Information-based connection algorithm for supporting QoS in nested mobility network

A multihop mobile wireless network can be a collection of wireless mobile nodes forming a temporary network without the aid of any established infrastructure or centralized administration. Mobile nodes communicate with each other using multihop wireless links. Each mobile node in the network also acts as a router, which forwards data packets to other nodes. A main challenge in the design of this mobile network is the development of dynamic routing protocols that can efficiently find routes between two communicating nodes that often change the network topology drastically and unpredictably. All communications between the nodes inside the mobile network and the global Internet must be maintained, although the mobile router (MR) connecting the other mobile network to the global Internet must change their address; and mobile nodes suffer from end-to-end delay and handoff delay. That is to say, hereafter the packets sailing for the mobile node would not be routed directly for the destination, but will always make a detour by way of HA to the target node. In this paper, we suggest Information-based Connection Algorithm that adds keyword management method in order to resolve such a problem, simulations are carried out with NS-2 for performance evaluation. The results of the simulations show an improvement on throughput and handoff delay, and consequently the QoS improvement.

Adaptive Distributed Channel Assignment in Wireless Mesh Networks

From the channel assignment schemes in time division multiple access (TDMA) slot assignment protocols developed in previous studies, we have found that these protocols do not have a convenient frame length reduction scheme after the expansion of the frame length. As the network size grows, the frame length expands rapidly, particularly when we set it as a power of two. A very long frame may result in poor channel utilization when it contains many unused slots. In this paper, we consider a wireless mesh network with a TDMA structure. We divide each code into time slots to form the channels. We propose a dynamic frame length expansion and recovery method termed adaptive distributed channel assignment (ADCA). This strategy is designed to enhance the utilization of the available channels by taking advantage of the spatial reuse concept. In ADCA, an increase in spatial reuse is achieved by adding a certain amount of control overhead. We show that the bandwidth saved due to the channel spatial reuse is larger than the additional bandwidth spent on the control overhead.

Cellular Controlled Short-Range Communication for Cooperative P2P Networking

This article advocates a novel communication architecture and associated collaborative framework for future wireless communication systems. In contrast to the dominating cellular architecture and the upcoming peer-to-peer architecture, the new approach envisions a cellular controlled short-range communication network among cooperating mobile and wireless devices. The role of the mobile device will change, from being an agnostic entity in respect to the surrounding world to a cognitive device. This cognitive device is capable of being aware of the neighboring devices as well as on the possibility to establish cooperation with them. The novel architecture together with several possible cooperative strategies will bring clear benefits for the network and service providers, mobile device manufacturers and also end users.

Analytical models for capacity estimation of IEEE 802.11 WLANs using DCF for internet applications

We provide analytical models for capacity evaluation of an infrastructure IEEE 802.11 based network carrying TCP controlled file downloads or full-duplex packet telephone calls. In each case the analytical models utilize the attempt probabilities from a well known fixed-point based saturation analysis. For TCP controlled file downloads, following Bruno et al. (In Networking ’04, LNCS 2042, pp.␣626–637), we model the number of wireless stations (STAs) with ACKs as a Markov renewal process embedded at packet success instants. In our work, analysis of the evolution between the embedded instants is done by using saturation analysis to provide state dependent attempt probabilities. We show that in spite of its simplicity, our model works well, by comparing various simulated quantities, such as collision probability, with values predicted from our model. Next we consider N constant bit rate VoIP calls terminating at N STAs. We model the number of STAs that have an up-link voice packet as a Markov renewal process embedded at so called channel slot boundaries. Analysis of the evolution over a channel slot is done using saturation analysis as before. We find that again the AP is the bottleneck, and the system can support (in the sense of a bound on the probability of delay exceeding a given value) a number of calls less than that at which the arrival rate into the AP exceeds the average service rate applied to the AP. Finally, we extend the analytical model for VoIP calls to determine the call capacity of an 802.11b WLAN in a situation where VoIP calls originate from two different types of coders. We consider N ₁ calls originating from Type 1 codecs and N ₂ calls originating from Type 2 codecs. For G711 and G729 voice coders, we show that the analytical model again provides accurate results in comparison with simulations.

Robust Detection of Unauthorized Wireless Access Points

Unauthorized 802.11 wireless access points (APs), or rogue APs, such as those brought into a corporate campus by employees, pose a security threat as they may be poorly managed or insufficiently secured. An attacker in the vicinity may easily get onto the internal network through a rogue AP, bypassing all perimeter security measures. Existing detection solutions do not work well for detecting rogue APs configured as routers that are protected by WEP, 802.11 i, or other security measures. In this paper, we describe a new rogue AP detection method to address this problem. Our solution uses a verifier on the internal wired network to send test traffic towards wireless edge, and uses wireless sniffers to identify rouge APs that relay the test packets. To quickly sweep all possible rogue APs, the verifier uses a greedy algorithm to schedule the channels for the sniffers to listen to. To work with the encrypted AP traffic, the sniffers use a probabilistic algorithm that only relies on observed wireless frame size. Using extensive experiments, we show that the proposed approach can robustly detect rogue APs with moderate network overhead. The results also show that our algorithm is resilient to congested wireless channels and has low false positives/negatives in realistic environments.

An Expression for the Average Quantization Error

The quantization error for MIMO (multiple-input multiple-output) downlink channels is known to be the minimum of independent and identically distributed beta random variables. In this note, an exact expression is derived for the average quantization error. Computational issues relating to its correctness, usage and approximations are discussed.

A new proportional differentiation scheme based on batch scheduling for optical burst switching networks

Optical burst switching (OBS) is a promising switching paradigm for building the next generation optical internet. The proportional differentiation model is very convenient for network operators to quantitatively adjust the quality differentiation among service classes. To provide proportional differentiated services for OBS networks, a proportional differentiation scheme based on batch scheduling is proposed in this article. The scheme adopts the batch scheduling idea to reserve data channel resources for a batch of data bursts. It helps to decrease burst dropping probability. When some data bursts are unsuccessfully scheduled, a preemption method is used to keep a proportional burst dropping probability among service classes according to the expected burst dropping probability equations given by the proportional differentiation model. The scheme has low computational complexity. Simulation results show that the scheme can provide proportional differentiated services and efficiently decrease the burst dropping probability.