Contention Free Period Research Articles

A Hybrid Channel Access Scheme for Coexistence Mitigation in IEEE 802.15.4-Based WBAN

Wireless body area network (WBAN) is a communication technology, which aims providing both medical and consumer electronics services through sensor devices in, on, or around a human body. Due to the absence of the IEEE 802.15.6-based RF modules, the IEEE 802.15.4, a typical low-power communication technology of which requirements are similar, is considered to implement WBANs. In the case where a lot of WBANs coexist, meanwhile, collisions and signal attenuations may lead to their communication performance degradation. However, the IEEE 802.15.4 does not provide any solutions to solve coexistence problems, and thus, coexistence mitigation schemes for the IEEE 802.15.4-based WBANs are necessary. In this paper, we perform preliminary experiments to identify aspects of coexistence problem among the coexisting IEEE 802.15.4-based WBANs. Based on the results of preliminary experiments, we also propose a hybrid channel access scheme to mitigate coexistence problems in WBANs. The proposed scheme can be classified into two phases. In the first phase, the proposed scheme provides probabilistic collision avoidance on the contention-free period. When the pre-defined requirements of reliability cannot be satisfied with performing the first phase, the proposed scheme performs the second phase, which helps to mitigate collision or interference through changing channel access method. To evaluate the performance of the proposed scheme, we implement our scheme and perform experiments by comparing with an IEEE 802.15.4-based WBAN.

Distributed and Adaptive Medium Access Control for Internet-of-Things-Enabled Mobile Networks

In this paper, we propose a distributed and adaptive hybrid medium access control (DAH-MAC) scheme for a single-hop Internet of Things (IoT)-enabled mobile ad hoc network supporting voice and data services. A hybrid superframe structure is designed to accommodate packet transmissions from a varying number of mobile nodes generating either delay-sensitive voice traffic or best-effort data traffic. Within each superframe, voice nodes with packets to transmit access the channel in a contention-free period (CFP) using distributed time division multiple access, while data nodes contend for channel access in a contention period (CP) using truncated carrier sense multiple access with collision avoidance. In the CFP, by adaptively allocating time slots according to instantaneous voice traffic load, the MAC exploits voice traffic multiplexing to increase the voice capacity. In the CP, a throughput optimization framework is proposed for the DAH-MAC, which maximizes the aggregate data throughput by adjusting the optimal contention window size according to voice and data traffic load variations. Numerical results show that the proposed MAC scheme outperforms existing quality-of-service-aware MAC schemes for voice and data traffic in the presence of heterogeneous traffic load dynamics.

Optimizing Unlicensed Spectrum Sharing for LTE-U and WiFi Network Coexistence

Long-term evolution in unlicensed spectrum (LTE-U) is an emerging technology for expanding cellular network capacity without additional spectrum cost. This paper investigates effective spectrum sharing for coexisting Wi-Fi and LTE-U services. Based on a novel hyper access point (HAP) we introduced for effectively embedding LTE-U in unlicensed Wi-Fi band, LTE-U can directly take advantage of the Wi-Fi point coordination function protocol. To facilitate the coexistence, our HAP dedicates a contention-free period to LTE-U users and allows a contention period (CP) for traditional Wi-Fi users. We investigate the optimization of joint user association and resource allocation to further improve system throughput and user fairness. We formulate a network utility maximization problem based on the Nash bargaining solution (NBS), for which we derive a closed-form expression for the optimal CP length under a given user association. We analyze this NBS-based utility maximization and the performance of the proposed algorithm under log-normal fading, Rayleigh fading, and Rician fading channel models, respectively. Our numerical results corroborate our analysis and demonstrate effective improvement of the system performance by the proposed HAP algorithm against traditional LTE-U deployment.

Voice performance analysis using voice codec by packet fragmentation and contention free periods in wireless networks

The admission control is required to maintain the established route between the source and the destination in the wireless network. To maintain the stability of the route, the wireless channel parameters has to be adopted appropriately. Thus, this study analyzes the wireless access medium parameter through direct coordination (DCF) and point-to-point coordination method. The packets are fragmented in DCF and contention free period interval are adjusted to study the QoS parameters for various VOIP codec using OPNET simulation tool. The result shows that packet fragmentation to 256 bytes and contention free period for 20 ms improves QoS for G.729 for Voice traffic.

Distributed Resource Reservation in Hybrid MAC With Admission Control for Wireless Mesh Networks

Providing guaranteed quality of service (QoS) for multimedia applications is a challenging topic in wireless mesh networks (WMNs). This paper proposes a distributed resource reservation (RR) mechanism with novel admission control to guarantee QoS performance of real-time sessions (RTSNs) while improving bandwidth utilization in WMNs. The proposed RR mechanism establishes logical clusters (LCs) for identifying interference relationships between nodes and avoids simultaneous transmissions from interfering nodes. Following the established LCs, a cooperative contention and collision-free channel access is achieved in hybrid medium access control (MAC) for multihop data forwarding in WMNs. To efficiently utilize the scarce resources in a contention-free period, soft and hard resources are reserved for RTSNs according to their QoS demands. This is achieved by a novel admission control algorithm. Furthermore, an analytical model is derived for investigating the RR parameters of the proposed mechanism. Simulation results show that the proposed mechanism guarantees the QoS for RTSNs while improving bandwidth utilization.

Traffic differentiation and dynamic duty cycle adaptation in IEEE 802.15.4 beacon enabled WSN for real-time applications

The wireless sensor networks (WSNs) based on the IEEE 802.15.4 beacon enabled mode provide a deterministic resource allocation offered by the guaranteed time slot (GTS) mechanism which is ideal for real-time traffic applications that requires high quality of service (QoS). In the beacon enabled mode the active and optional inactive period is governed by superframe order (SO) and beacon order (BO). Adapting the duty cycle using the SO and BO is desirable to accommodate the changing context of the WSNs traffic for network optimisation. However, existing approaches assumed a fixed SO and BO and segregate the evaluation of the contention access period and the contention free period that forms the active segment. To improve the performance of the IEEE 802.15.4 protocol in respect of the trade-off between power consumption and end-to-end delay, within a required QoS, a combination of dynamic priorities for traffic differentiation and dynamic duty cycle adaptation in the GTS allocation process are introduced. This work demonstrates that the proposed solution provides significantly better performance than the standard allocation method by simultaneously satisfying QoS and service differentiation demands with considerable power savings which is essential for WSNs. The specific novel use of this solution is in an application scenario where the deployed network is situated in an assisted living environment with a rich suite of heterogeneous wireless based communications in place.

Modified GTS Allocation Scheme for IEEE 802.15.4

IEEE 802.15.4 standard is widely used in wireless personal area networks (WPANs). The devices transmit data during two periods: contention access period (CAP) by accessing the channel using CSMA/CA and contention free period (CFP), which consists of guaranteed time slots (GTS) allocated to individual devices by the personal area network (PAN). However, the use of GTS slot size may lead to severe bandwidth wastage if the traffic pattern is not fit or only a small portion of GTS slot is used by allocated device. The proposed scheme devides the GTS slot and then optimizes the GTS slot size by exploiting the value of superframe order (SO) information. The proposed scheme was tested through simulations and the results show that the new GTS allocation scheme perform better than the original IEEE 802.15.4 standard in terms of average transmitted packets, throughput, latency and probability of successful packets.

Adaptive GTS Allocation Scheme with Applications for Real-time Wireless Body Area Sensor Networks

The IEEE 802.15.4 standard not only provides a maximum of seven guaranteed time slots (GTSs) for allocation within a superframe to support time-critical traffic, but also achieves ultralow complexity, cost, and power in low-rate and short-distance wireless personal area networks (WPANs). Real-time wireless body area sensor networks (WBASNs), as a special purpose WPAN, can perfectly use the IEEE 802. 15. 4 standard for its wireless connection. In this paper, we propose an adaptive GTS allocation scheme for real-time WBASN data transmissions with different priorities in consideration of low latency, fairness, and bandwidth utilization. The proposed GTS allocation scheme combines a weight-based priority assignment algorithm with an innovative starvation avoidance scheme. Simulation results show that the proposed method significantly outperforms the existing GTS implementation for the traditional IEEE 802.15.4 in terms of average delay, contention free period bandwidth utilization, and fairness.

Analysis of superframe duration adjustment scheme for IEEE 802.15.4 networks

The challenge of the IEEE 802.15.4 beacon-enabled mode is how to improve throughput and bandwidth utilization in contention access period (CAP) and contention free period (CFP), respectively. This article proposes a scheme to improve IEEE 802.15.4 medium access control, called superframe duration adjustment scheme (SUDAS), which analyzes the overall of the IEEE 802.15.4 not only CAP but also CFP. SUDAS is expected to effectively allocate guaranteed time slot to the requested devices, it adjusts the length of the slot in superframe duration based on the length of the packet data. This article also presents a comprehensive Markov chain analysis for SUDAS, especially for star topology, to predict the probability of successful transmission, network goodput, average bandwidth utilization, as well as total network energy consumption. The validity of the analytical model is proven by closely matching the simulation experiments. SUDAS performs better than other algorithms in terms of the probability of successful packet transmission, network goodput, average bandwidth utilization, and total energy consumption.

Smart guaranteed time‐slot allocation algorithm for industrial wireless sensor networks emergency message transmission

This paper presents investigation on application of wireless sensor networks (WSNs) in wind power generation systems and highlights an important issue associated with the deadline for the delivery of messages among nodes based on the IEEE 802.15.4E standard. Owing to the limits of standard and the power system application requirements, this research proposes a smart guaranteed time slot (S-GTS) allocation algorithm which is based on the urgent/important matrix. This proposed algorithm promotes the utilisation of contention free period in a superframe. Besides, over seven GTSs can be allocated in a superframe, there are only seven GTSs that can be used in the standard. In addition, this study proves the value of BO and SO upper bound is 6 for the WSN application in power systems. Moreover, the network delay of S-GTS performs better than the 16-time-slot mechanism and i-GAME mechanism.

An optimal fuzzy control medium access in wireless body area networks

Wireless body area network (WBAN) collects significant signals of human body or environment information for health monitoring or professional services. But normal medium access protocols can hardly make a balance and ensure enough reliability of a network because there are specific features and service quality in WBAN applications. Contention access or fixed allocation of bandwidth cannot meet all nodes׳ requirements and may cause collisions and delay. Especially in emergency medical situations, some data must be transmitted immediately for accurate diagnosis and decision. The dropping of critical messages could possibly create life threatening results. In order to improve the reliability and efficiency of data transmission in WBAN, this paper proposes a fuzzy control medium access (FCMA) mechanism based on input parameters for performance gains. It controls the contention window in contention access period (CAP) and slots allocation in contention free period (CFP) according to nodes׳ status. Through simulation analysis, the improved performance of throughput, latency, and packets breakdown is demonstrated by efficient usage of bandwidth and avoidance of collision.

An energy-efficient multiconstrained QoS aware MAC protocol for body sensor networks

One of the most challenging jobs in designing a Medium Access Control (MAC) protocol for Body Sensor Networks (BSNs) is to achieve QoS requirements for heterogeneous traffics generated from various sensors. Increasing the energy-efficiency of the network should be kept in mind while doing this. Physiological data monitoring applications generate different types of traffic including multimedia data packets. These heterogeneous traffics should be treated differently by an underlying communication protocol, allowing the transmission schedule of these traffic types based on their priorities. In this paper, we present an energy-efficient multiconstrained QoS aware MAC protocol, namely eMC-MAC, wherein the medium access control is designed based on traffic prioritization. We have redefined the superframe structure in such a way that the critical data packets are transmitted earlier than other packets. In our proposed eMC-MAC protocol, we have introduced minislots during CFP (Contention Free Period), where requests for urgent packets are collected to the coordinator node in an energy-efficient way. We also develop an energy-efficient algorithm for preempting allocated data transmission slots to facilitate transmission of packets with higher priority. Thus, the proposed eMC-MAC protocol delivers emergency data packets to the coordinator with reduced delay. We have evaluated the effectiveness of our eMC-MAC protocol through extensive simulations in ns-3. The simulation results have shown that it outperforms a number of state-of-the-art MAC protocols for BSNs.

A Hybrid and Secure Priority-Guaranteed MAC Protocol for Wireless Body Area Network

This paper introduces a hybrid and secure MAC protocol (PMAC) for WBAN. The PMAC protocol uses two contention access periods (CAPs) for accommodating normal and life-critical traffic and one contention-free period (CFP) for accommodating large amount of data packets. The priority-guaranteed CSMA/CA procedure is used in the CAP period, where different priorities are assigned to WBAN nodes by adjusting the backoff window size. In addition, a set of security keys is used to prevent illegal access to the network. Analytical expressions are derived to analyze the average delay, power consumption, throughput, and packet loss probability of the PMAC protocol. Results derived from these expressions are validated by computer simulations.

Distributed and Centralized Hybrid CSMA/CA-TDMA Schemes for Single-Hop Wireless Networks

The strength of carrier-sense multiple access with collision avoidance (CSMA/CA) can be combined with that of time-division multiple access (TDMA) to enhance the channel access performance in wireless networks such as the IEEE 802.15.4-based wireless personal area networks. In particular, the performance of legacy CSMA/CA-based medium access control scheme in congested networks can be enhanced through a hybrid CSMA/CA-TDMA scheme while preserving the scalability property. In this paper, we present distributed and centralized channel access models that follow the transmission strategies based on Markov decision process (MDP) to access both contention period and contention-free period in an intelligent way. The models consider the buffer status as an indication of congestion provided that the offered traffic does not exceed the channel capacity. We extend the models to consider the hidden node collision problem encountered due to the signal attenuation caused by channel fading. The simulation results show that the MDP-based distributed channel access scheme outperforms the legacy slotted CSMA/CA scheme. The centralized model outperforms the distributed model but requires the global information of the network.

On improving delay performance of IEEE 802.11p vehicular safety communication

In this work, we present the design of an efficient Deterministic medium Access DA for Dedicated Short-Range Communication DSRC vehicular safety communication over IEEE 802.11p, called Vehicular DA VDA. VDA supports two types of safety services emergency and routine safety messages with different priorities and strict requirements on delay, especially for emergency safety messages. VDA processes both types of safety messages to maintain a balance between two conflicting requirements: reducing chances of packets collisions and lowering the transmission delay. VDA allows vehicles to access the wireless medium at selected times with a lower contention than it would otherwise be possible within two-hop neighbourhood with the classical 802.11p EDCA or DCF schemes. Besides, we propose an improvement of VDA called Dynamic VDA opportunities Re-assignment DVR to avoid network performance degradation caused by interference outside the two-hops. Particularly, our scheme provides an efficient adaptive adjustment of the Contention Free Period CFP duration to establish a priority between emergency and routine messages. Simulations show that the VDA scheme, used with 802.11p, clearly outperforms 802.11p alone in high-offered load conditions while bounding the transmission delay of safety messages. Furthermore, beyond two-hops, DVR is able to efficiently tackle the interference phenomenon by reducing losses and delays of safety applications.

IEEE802.15.4 guaranteed time slot performance analysis and allocation optimization under multi-slot

IEEE802.15.4标准的保障时隙（GTS）机制可分配多个时隙,用于保障实时性数据的传输。针对非竞争接入期多时隙下GTS性能分析的不足,利用网络微积分法分析时延和吞吐量服务曲线及其与能耗的关系,改进IEEE802.15.4传感器节点模型,建模仿真研究GTS参数对网络性能（时延、吞吐量及能耗）的影响。仿真结果表明：根据高低突发性数据率的情况,最优化配置下的GTS可以满足实时性数据的传输。

An efficient GTS allocation scheme for IEEE 802.15.4 MAC layer

Based on IEEE 802.15.4, the contention-free period (CFP) adopts a guarantee time slot (GTS) mechanism to ensure each device can access the radio channel. However, it is hard to get the authority to access the radio channel due to more competitor access the radio channel simultaneously. To cope with this issue, we proposed a guarantee time slot mechanism to enhance the performance and utilization by using CFP. Our proposed method ensures each device has the authority to access the radio channel without any additional step. By comparing with the method of IEEE 802.15.4, the experimental results show that data average transmission delay and energy consumption can be reduced dramatically. In addition, the bandwidth and performance of network is improved since the pre-allocation mechanism can reduce the number of control packets. Several experiments have been conducted to demonstrate the performance of our work.

Analysis and evaluation of the maximum throughput for data streaming over IEEE 802.15.4 wireless networks

Recently, multiple novel applications have been developed using IEEE 802.15.4-based radio modules. In this paper, we focus on the maximum throughput that one can obtain with IEEE 802.15.4-based transceivers that operate in the license-free 2.4 GHz band using the 2450 direct-sequence spread spectrum physical layer. The results of the thorough maximum throughput analysis for single-hop and multi-hop data streaming scenarios in the beacon-enabled with both contention access and contention-free periods and nonbeacon-enabled networks are presented. The results of the analysis are compared with the results of the experiments, which were performed using contemporary IEEE 802.15.4 hardware transducers. Aside from defining the maximum possible throughput for the different scenarios, the presented data disclose the effect of various parameters on communication throughput and latency. The presented results reveal the capabilities of the IEEE 802.15.4 technology and enable one to estimate the feasibility of using the technology for particular applications.

MONET Special Half-Issue “Recent Advances on Communications and Networking in China”

Editorial: This special issue features extended versions of six of the best papers selected from the conference Chinacom 2011, which was held in Harbin, China, on August 17– 19, 2011. The emerging vehicular networks are targeted to provide efficient communications between mobile vehicles and fixed roadside units (RSU), and support mobile multimedia applications and safety services with diverse quality of service (QoS) requirements. In the paper titled “Medium Access Control for QoS Provisioning in Vehicle-to-Infrastructure Communication Networks”, Bi, Cai, Shen and Zhao propose a busy tone based medium access control (MAC) protocol with enhanced QoS provisioning for life critical safety services. By using busy tone signals for efficient channel preemption in both contention period (CP) and contention free period (CFP), emergency users can access the wireless channel with strict priority when they compete with multimedia users, and thus achieve the minimal access delay. Furthermore, through efficient transmission coordination on the busy tone channel, contention level can be effectively reduced, and the overall network resource utilization can be improved accordingly. The authors develop an analytical model to quantify the medium access delay of emergency messages. Extensive simulations with Network Simulator (NS)-2 validate the analysis and demonstrate that the proposed MAC can guarantee reliable and timely emergency message dissemination in a vehicular network. Delay tolerant networks (DTNs) rely on the mobility of nodes and sequences of their contacts to compensate for lack of continuous connectivity and thus enable messages to be delivered from end to end in a “store-carryforward” way, where multiple relay nodes are usually employed in the message delivery process. In the paper “Performance Modeling for Relay Cooperation in Delay Tolerant Networks Layered Fault”, Liu, Jiang, Nishiyama and Kato focus on such relay cooperation and analytically explore its impact on the delivery performance in DTNs. Specifically, the authors first develop a continuous time Markov chain-based theoretical framework to model the complicated message delivery process in delay tolerant networks adopting the two-hop relay algorithm. They then derive closed-form expressions for both the expected V. C. M. Leung (*) Department of Electrical and Computer Engineering, University of British Columbia (UBC), Vancouver, Canada e-mail: vleung@ece.ubc.ca

A New QoS Resource Allocation Scheme Using GTS for WPANs

IEEE 802.15.4 (for low-rate Wireless Personal Area Networks--WPANs) (IEEE 802.15.4 Standard-2003) and IEEE 802.15.7 (for Short-Range Wireless Optical Communication Using Visible Light) (IEEE 802.15.7 Standard--2011) are two typical standards for WPANs that support Quality-of-Service (QoS) through a Guaranteed Time Slot (GTS) mechanism to allocate a specific duration within a superframe structure for a time division multiplexing transmission. The low bandwidth utilization problem may occur in the GTS mechanism when the allocated bandwidth is less than the available bandwidth. However, this problem has not been resolved thoroughly in any of the standard or current research thus far. This paper analyzes GTS performance in QoS-guaranteed transmission and proposes a new GTS allocation scheme named Unbalanced GTS Allocation Scheme (UGAS), which improves the bandwidth resource efficiency. Our scheme tries to solve the bandwidth under-utilization problem by using Network Calculus theory based on the fluid model and greedy algorithm. The UGAS scheme divides the Contention-Free Period into time slots of different durations to support various bandwidth requirements. Time slots are allocated using an approximation QoS model to minimize under-utilization. Compared with the standard GTS allocation scheme, UGAS makes an efficient bandwidth allocation with the QoS-guaranteed model and without breaking the standard protocol. The numerical results show that the average bandwidth utilization using UGAS can be improved by 30 % as compared with the standard scheme.