[Show abstract][Hide abstract] ABSTRACT: This article proposes an integrated framework for adaptive QoS provision in IEEE 802.16e broadband wireless access networks based on cross-layer design. On one hand, an efficient admission control (AC) algorithm is proposed along with a semi-reservation scheme to guarantee the connection-level QoS. First, to guarantee the service continuity for handoff connections and resource efficiency, our semi-reservation scheme considers both users' handoff probability and average resource consumption together, which effectively avoids resource over-reservation and insufficient reservation. For AC, a new/handoff connection is accepted only when the target cell has enough resource to afford both instantaneous and average resource consumption to meet the average source rate request. On the other hand, a joint resource allocation and packet scheduling scheme is designed to provide packet-level QoS guarantee in term of "QoS rate", which can ensure fairness for the services with identical priority level in case of bandwidth shortage. Particularly, an enhanced bandwidth request scheme is designed to reduce unnecessary BR delay and redundant signaling overhead caused by the existing one in IEEE 802.16e, which further improves the packet-level QoS performance and resource efficiency for uplink transmission. Simulation results show that the proposed approach not only balances the tradeoff among connection blocking rate, connection dropping rate, and connection failure rate, but also achieves low mean packet dropping rate (PDR), small deviation of PDR, and low QoS outage rate. Moreover, high resource efficiency is ensured.
Full-text · Article · Jan 2011 · EURASIP Journal on Wireless Communications and Networking
[Show abstract][Hide abstract] ABSTRACT: Cognitive radio arises as a hot research issue in wireless communications recently, attributed to its capability of enhancing spectral efficiency and catering for the growing demand for bandwidth. As a good embodiment of cognitive radio’s unique feature, i.e. making use of every bit spectral resource, spectrum sensing plays a vital role in the implementation of cognitive radio. To alleviate negative effect on cooperative spectrum sensing brought by bit errors, we introduce a novel concept, i.e. Optimum Detection Location (ODL) and present two algorithms of different computational complexity for locating ODL, together with an ODL-Based cooperative spectrum sensing scheme, with the motivation to exploit the gain derived from geographic advantages and multiuser diversity. Numerical and simulation results both demonstrate that our proposed spectrum sensing scheme can significantly improve the sensing performance in the case of reporting channel with bit errors.
[Show abstract][Hide abstract] ABSTRACT: The IEEE 802.16e network faces the challenge of bandwidth shortage due to the growing demand for high-bandwidth applications. One promising approach is to obtain bandwidth by using cognitive radio (CR) technology, which provides an effective way to achieve incremental bandwidth from unlicensed spectrum. However, the appearance of primary users (PUs) does harm to the performance of secondary users (SUs). In this paper, we propose a QoS-enhanced scheme to prevent real-time services in 802.16e networks from corruption when switching between licensed and unlicensed bands. Adaptive bandwidth reservation mechanism and simplified switch mechanism are proposed to improve QoS performance for 802.16e services. Finally, simulation results show that our scheme has lower connection dropping probability (CDP) at a reasonable cost of connection blocking probability (CBP) than conventional scheme.
[Show abstract][Hide abstract] ABSTRACT: A unique challenge for routing in cognitive radio networks is the collaboration between the route selection and spectrum decision. To solve this problem, in this paper a Spectrum-Tree base On-Demand routing protocol (STOD-RP) is proposed where a spectrum-tree is built in each spectrum band. The formation of the spectrum-tree addresses the cooperation between spectrum decision and route selection in an efficient way. In addition, a new route metric is proposed as well as a fast and efficient spectrum-adaptive route recovery method. Simulation results show that our proposed STOD-RP reduces the control overhead and shortens the average end-to-end delay significantly.
[Show abstract][Hide abstract] ABSTRACT: In the existing literatures on cooperative relay system, the coding scheme adopts the conventional fixed-rate code (traditional code). This paper first studies the rateless code, Raptor code, to cooperative wireless cellular system. In particular, we study the efficiency, reliability, and robustness of cooperative communication in a wireless cellular downlink environment by employing a new scheme based on combining a Raptor code with distributed space-time block code (DSTBC), when channel state information is not available at the transmitter. Considering the flexible code rate characteristic, we find a new measurement, total time slice, to evaluate the performance. Therefore, the number of total time slices at transmitting exactly and the average bit error rate (BER) of cooperation are presented by applying various encoding schemes. The time division multiple access scheme is proposed with half duplex mode. Based on theoretical analyses and simulation results, we show that without channel state information at the transmitter, the cooperative wireless cellular system using Raptor code and DSTBC yields significant performance gain, i.e., reducing the total transmission time and energy consumption, even in a low signal-to-noise ratio (SNR) environment.
[Show abstract][Hide abstract] ABSTRACT: In this paper, a novel scheme cooperative MAC for multi-hop multi-radio wireless mesh networks (WMNs) is proposed to improve the performance of the IEEE 802.11s MAC draft protocol. The proposed scheme allows transmitter (cooperative source node) to request multiple intermediate nodes for cooperative transmission to receiver (cooperative target node) when the direct transmission leads to throughput degradation. These intermediate nodes work as virtual nodes (VNs). If the transmission based on two-hop cooperation can not satisfy the transmission request, the cooperative source node requests to establish three-hop or more-hop cooperative transmission. Thus, a slow one-hop transmission can be transformed into a faster two-hop or more-hop transmission and the proposed scheme utilizes multiple channels for parallel transmissions for decreasing the transmission time and increasing the throughput significantly. Both theoretical analyses and simulation experiments show the effectiveness and efficiency of our proposed scheme.
[Show abstract][Hide abstract] ABSTRACT: The emerging IEEE 802.11s standard draft is a key technology of next-generation wireless networks. It can provide end users with broadband access of fast deployment, low cost, large coverage, and robust architecture. Recently, IEEE 802.11s draft has defined hybrid routing as default routing protocol. When tree-based topology is enabled, different mesh points (MPs) and mesh access points (MAPs) will achieve different loads according to their hops to the root, while previous discussions assumed that all the stations in the network have the same load. In this paper, we proposed an analytical model for IEEE 802.11 networks which considers different loads in hybrid routing. In the model, MPs/MAPs are classified into different groups according to their hops from the root and those closer to the root have a heavier load. We calculate their packet arrival rates in reasonable assumptions and derive the throughput and end-to-end delay. At last, numerical results show the factors, such as hops, affect network performance.
[Show abstract][Hide abstract] ABSTRACT: 3GPP has standardized IP multimedia subsystem (IMS) as the solution for multimedia service delivery based on Internet for future next-generation networks (NGNs) and it aims to merge Internet and wireless cellular networks together in order to enable rich multimedia services. The home subscriber server (HSS) is a crucial entity in IMS, which provides the functions such as access authentication and authorization as well as service data management in GPRS and CS domain. However, it still cannot provide the automatic service selection to help the users access application servers according to their demands and contexts. This paper proposes a novel context-aware service selection approach which helps perform service selection according to individual user's contexts such as the preferences and habits. This approach includes two main components which are set in HSS. One is context management and the other is selection engine, which employs the dynamic fuzzy analysis hierarchy model (DFAHM) to conduct service selection according to the contexts. Based on the quantified dynamic and fuzzy evaluation, the DFAHM helps select the most suitable services for the users. And, the model evaluation is presented to verify the feasibility of DFAHM. The results show that the DFAHM helps achieve service selection according to the users' contexts.
[Show abstract][Hide abstract] ABSTRACT: Due to the emergence of high-capacity wavelength-division multiplexing transmission systems, new optical cross-connect (OXC) architectures that make a large number of fiber/wavelength counts to switch the signal in the optical domain are needed. Optical microelectromechanical system (MEMS) switches are regarded as the most promising optical switch technology to achieve such functionalities. In this paper, we propose a novel integrated multistage two-dimensional (2-D) MEMS optical switch design with Spanke-Benes architecture and compare it with the conventional crossbar architecture, the L-switching architecture, and Shuffle-Benes architecture. Our proposed architecture is very suitable for building large-port-count 2-D MEMS switches and achieves much better performance in terms of beam divergence loss, longest optical path, mirror radius, substrate size, port-to-port repeatability, and power consumption than the other three architectures. Furthermore, compared with the 2-D conventional crossbar switch commercially available now, the proposed architecture can save 50% mirrors, shorten 87.5% longest optical path, minify 65% mirror radius, and shrink 90% substrate size.
No preview · Article · Apr 2008 · Journal of Lightwave Technology
[Show abstract][Hide abstract] ABSTRACT: This paper proposes an efficient and adaptive cross-layer routing scheme coined path cost-based Routing (PCBR) scheme for multi-channel, multi-hop wireless mesh networks (WMNs). In our scheme, paths are selected based on the path cost determined by the three important metrics: end-to-end delay, available bandwidth, and path packet loss rate. The end-to-end delay and available bandwidth are redefined based on the 802.11s MAC protocol to fit the multi-channel, multi-hop WMNs. Mesh Routers (MRs) process most route discovery work in themselves to reduce the number of retransmissions in flooding the route discovery packets. The route is preferred with less end-to-end delay, more available bandwidth, and less power consumption by adapting the coefficients of the three metrics. The simulation results show that the proposed scheme is very suitable for the multi-channel, multi-hop WMNs.
[Show abstract][Hide abstract] ABSTRACT: In IP Multimedia Subsystem (IMS), Interrogating Call Session Control Function (I-CSCF) assigns the most suitable Serving-CSCF (S-CSCF) to the user performing IMS registration, which is defined by the Third Generation Partnership Project (3GPP) as S-CSCF assignment. Current approaches to implement S-CSCF assignment, however, incur the low utilization of S-CSCF resources. In this paper, we design a hybrid Peer-to-Peer (P2P) based S-CSCF overlay network called Hyson. Based on Hyson, we propose a novel approach to implement S-CSCF assignment called HSA, which can enhance the utilization of S-CSCF resources. HSA is accomplished by collaborative work of S-CSCFs. Simulation results show that HSA enables not only IMS network to have a much greater user capacity but also S-CSCFs to produce much smaller processing delay than current approaches.
[Show abstract][Hide abstract] ABSTRACT: This paper proposes an efficient approach to optimize the performance of uplink transmission in IEEE 802.16e BWA networks. First, an enhanced bandwidth request (BR) scheme is designed, which takes all uplink nrtPS/BE connections in the same subscriber station (SS) or a rtPS/ErtPS connection as a unit to request bandwidth, as well as defines unicast polling index to indicate whether a SS needs to be polled. This approach reduces the BR delay and the signaling overhead caused by the BR scheme in IEEE 802.16e. Meanwhile, through cross-layer optimization, a joint bandwidth allocation (BA) and packet scheduling scheme is proposed to balance the tradeoff between QoS provision and system throughput under effective admission control. The theoretical analyses and the simulation results show that our approach achieves significant improvements in QoS provision, BR signaling overhead, and system throughput.
[Show abstract][Hide abstract] ABSTRACT: We present an admission control (AC) algorithm for the specific case of pre-provisioned IEEE 802.16 d links for VoIP aggregates. The algorithm approaches AC from a new perspective as admission criterion is speech quality, the sole true quality metric for voice services. As we found the E-Model can be used to reliably estimate speech quality and the resulting R-Score as admission criterion. Moreover, we show that speech quality can be evaluated on aggregate level without compromising individual call's speech quality. The algorithm is simple, fast, and precise and its behaviour is consistent over a range of different deployments.
[Show abstract][Hide abstract] ABSTRACT: In the existing papers on cooperative diversity, the fading channels are idealistically assumed to be Rayleigh fading channel. Taking into account the realistic propagation environments in the presence of spatial fading correlation, the performance of cooperative protocols using distributed space-time block code (DSTBC) in the two-ring scattering model is analyzed. The time division multiple access scheme is proposed with half duplex mode. Cooperative scheme is proposed, because cooperative diversity can combat the fading correlation by spatial decorrelation which is produced by independent multipaths and scattering paths between source nodes (SNs) and destination nodes (DNs). Cooperative relaying is shown to increase the link stability (or, alternatively, decrease the link outage probability) significantly. Therefore, the outage capacity and average bit error rate (BER) of cooperation are presented by applying various cooperative schemes in the correlated channel. Based on theoretical analyses and simulation results, the cooperative diversity yields significant performance gain in correlated channel, i.e., reducing the spatial correlation of each path and enhancing the overall performance of virtual MIMO system by high quality of cooperative interuser channel.
[Show abstract][Hide abstract] ABSTRACT: This paper proposes a cross-layer design for resource allocation in IEEE 802.16 OFDMA networks, which aims to provide QoS guarantee and fairness for heterogeneous traffics with different channel conditions and priorities. First, "QoS rate " is defined to characterize the instantaneous rate required for meeting the QoS constraints. Accordingly, the "QoS rate " requirements are processed following strict priority. At each priority level, the target of resource allocation is to minimize the resource consumption for maintaining the "QoS rate" constraints. Then, fairness is provided for the "non-QoS rate" requirements in terms of weight fairness and proportional fairness, respectively. The simulation results show that our approach ensures low QoS outage probabilities, as well as balances the tradeoff between resource efficiency and fairness.
[Show abstract][Hide abstract] ABSTRACT: Cooperative diversity is effectively used to combat the correlated fading. In the existing papers on cooperative diversity, the fading channels are idealistically assumed to be Rayleigh fading channel. Taking into account the realistic propagation environments in the presence of spatial fading correlation, i.e., geometry-based stochastic channel model, we study the performance of existing cooperative protocols in the two-ring scattering model. The two source nodes (SNs) and two destination nodes (DNs) form a 2times2 virtual MIMO cooperative system. Therefore, the bit error rate (BER) of cooperation at transmitter is presented in the interference relay channel. The time division multiple access (TDMA) scheme is proposed with half duplex mode. Based on theoretical analyses and simulation results, the cooperative diversity brings performance improvement in correlated channel, even with the keyhole MIMO channel. And, cooperative strategy reduces the spatial correlation of each path, increases the capacity of the correlated channels and enhances the overall performance of virtual MIMO system by high quality of cooperative interuser channel.
[Show abstract][Hide abstract] ABSTRACT: In IEEE 802.16e networks, the mobility of mobile stations (MSs) induces that energy saving becomes an important issue for the battery-powered MSs to extend their operational lifetime. Based on the characteristics of power saving class (PSC) types and data delivery service types defined in IEEE 802.16e standard, we propose an efficient sleep mode management scheme to save energy. Using the quality of service (QoS) parameters associated with transport connections, we not only design the downlink and uplink PSC parameters, but also introduce the PSC anti-expansion mechanism. The analyses and simulation results demonstrate that the proposed scheme can minimize the energy consumption of MSs under the condition that the QoS requirements of each connection are guaranteed.
[Show abstract][Hide abstract] ABSTRACT: The combination of the SIP-based service and peer-to-peer (P2P) can improve the performance of traditional client-server SIP system. However, current P2P SIP systems have many disadvantages. For example, node heterogeneity (e.g., bandwidth, CPU, storage and uptime) has not been considered enough which affects the scalability and service availability of P2P overlay; session setup latency is higher than that of traditional SIP system; and high cost is paid to maintain DHT overlays during a long idle uptime. In order to overcome these disadvantages, this paper proposes a novel hierarchical and breathing P2P SIP system. Its hierarchical overlay is composed of more than two suboverlays with different physical capability and system availability. Based on the hierarchical overlay, we propose a Node Virtualization Model that enables a node to share physical capability of powerful nodes in higher-level suboverlays. Suboverlays adopt breathing overlay model that enables a node to quit P2P overlay temporarily after a long idle uptime and rejoin P2P overlay when new SIP services are initiated on it. Based on the performance analysis and simulation results, our proposed system achieves better scalability and resource availability as well as shorter session setup latency, less bandwidth for DHT maintenance traffic and larger storage capacity than current P2P SIP systems.
[Show abstract][Hide abstract] ABSTRACT: In this paper, we have derived the form of the maximum capacity for MIMO-OFDM system by adaptively allocating power in space, time and frequency domains in the case of perfect channel side information at the receiver (CSIR) and a zero-mean spatially white (ZMSW) channel distribution at the transmitter. Both the effects of Rayleigh fast fading and shadowing on the ergodic capacity are considered. The ergodic capacities achieved by the three different power allocation schemes, filling water in space-time-frequency domain, filling water in space-frequency domain and equally allocating power, are compared. For the ergodic capacity, the optimal power allocation scheme is filling water in space-time-frequency domain, which can obtain the maximal capacity as well as reduce the computation complexity.
[Show abstract][Hide abstract] ABSTRACT: IEEE 802.16e standard did not specify any bandwidth reservation scheme that provides quality of service (QoS) support for real-time services, especially for handover real-time ones. The bandwidth reservation schemes, which were not designed for 802.16e system dedicatedly, could also be applied to it. But their performance is our main concern. In this paper, based on the handover probability and the traffic arrival probability, a dynamic bandwidth quasi-reservation scheme (DBQRS) is proposed to provide QoS guarantee for mobile and fixed wireless real-time multimedia services in 802.16e networks. The corresponding admission control policy is also designed for this scheme. A simulation model is developed to evaluate the performance of the DBQRS using OPNET modeler. The simulation results demonstrate that the DBQRS not only minimizes the new service flow (SF) blocking rate and the handover SF dropping rate, but also reduces the access delay of new real-time SF and enhances the bandwidth utilization.