Contention-based Mechanism Research Articles

HERA: High-Efficiency Resource Allocation Scheme for Newly Joined Mobile Terminal in Heterogeneous Wireless Network

Objectives:To design an efficient resource allocation design for provisioning service of varied traffic classes to Multi-Mode Mobile Terminals (MMTs) in Heterogeneous Wireless Networks (HWNs). In HWNs, users prerequisite certain Quality of Service (QoS); thus, for meeting QoS, theMMTs are handoff to the new network. However, handoff MMTs might induce interference with the ongoing communication of existing MMTs. As resources are shared, resource allocation becomes a challenging task. Methods:This study presents a High-Efficiency Resource Allocation optimization model for HWNs. The HERA scheme first employs Channel State Information (CSI) estimation for mitigating interference and establishing channel availability. Second, using game theory optimal resource is allocated to MMTs and proves the existence of Nash equilibrium (NE) for spectrum resource allocation to MMTs in HWNs. Finally, a hybrid resource allocation algorithm combining contentionless and contention-based is designed to provide an improved resource allocation mechanism. Findings:The experiment outcome shows the HERA scheme allocates resources more efficiently in comparison with Access Fairness Resource Allocation (AFRA)(1), Joint Resource Allocation with Power Optimization (JRA-PO)(2), Resource Allocation and Node Placement (RANP)(3), and Existing Resource Allocation (ERA)(4). The HERA improves throughput by 19.07% and reduces collision by 42.96% in comparison with ERA(4) . Novelty: existing model predominantly focused on either addressing interference or maximizing throughput by leveraging either contention or contention-less resource allocation mechanism. However, in this study both contention-less and contention-based mechanisms are merged to maximize throughput and reduce collision. Keywords: Interference; Quality of service; Resource allocation; Softcomputing; Spectrum utilization; Heterogeneous communication network

Improving the IEEE 802.11 power-saving mechanism in the presence of hidden terminals

Due to its low cost and popularity, the IEEE 802.11 WLAN (wireless local area network) is considered as one of the most promising wireless technologies for IoT (Internet of Things). 802.11 WLAN also provides a PSM (power saving mechanism), by which the devices that have no data to transmit are enabled to turn into doze mode where much less power is consumed. However, the 802.11 PSM is known to be inefficient because of its contention-based mechanism, i.e., it suffers from the performance degradation due to hidden terminals, especially in a network with a large number of devices. In this paper, in order to improve the performance of the 802.11 PSM, we propose a BC (backoff counter) reservation scheme that is combined with a neighbor polling solution. By building analytic models and performing extensive simulations, we show that our proposed scheme provides a much improved performance.

Evaluation of MAC contention techniques for efficient geo-routing in vehicular networks

In this paper we provide a novel performance evaluation methodology and fair comparison of the most relevant MAC-network cross-layer proposals for efficient geo-routing in the context of vehicular networks. In particular, GeoNetworking, the standard European network layer protocol for vehicle-to-vehicle (V2V) communications, proposes Contention-Based Forwarding (CBF) as basic forwarding mechanism, which can be also implemented at MAC layer in order to optimize its operation. A categorization and unified formal description of different proposals for such contention-based mechanisms is provided. We not only qualitatively discuss them, but also derive a more precise mathematical description of the operation of the proposals. Then we put forward a common framework for the analysis of their performance in the critical scenario of emergency warning delivery. Interestingly, with this model the performance metrics can be computed even when each vehicle selects its contention slot in a different way, unlike other models. This approach is validated by a thorough evaluation of the selected proposals in single-hop and multi-hop scenarios under ideal propagation conditions with both the proposed model and simulations. Finally, these techniques are also evaluated under more realistic fading conditions and compared with the purely network-layer implementation of CBF.

Peak avoidance and collision control for contention-based bandwidth requests in WiMAX systems

There are two fundamental bandwidth-request mechanisms specified in the IEEE 802.16 standard: contention-based random access and contention-free polling. For example, non-real-time polling and best-effort services mainly rely on the contention-based mechanism to submit bandwidth requests to the base station (BS). However, the performance degrades considerably when the number of requests is high and they collide with each other. To avoid collision, the standard supports a truncated binary exponential backoff resolution. Nevertheless this resolution is inefficient in dispersing the requests when the network traffic is overloaded. In order to improve the efficiency of the random-access mechanism in the standard, the authors propose a new mechanism that aids mobile stations (MSs) in sending bandwidth requests more efficiently and also avoiding peak traffic. By using the mechanism, MSs send bandwidth requests under low loads, thus avoiding collisions.

Seamless handover supported by parallel polling and dynamic multicast group in connected WLAN micro-cells system

WLAN (Wireless Local Area Network) has been seen to be one of the promising access technologies that adapts to 4G cellular network systems in providing very high speed connection with QoS guarantee through the polling function. However, when the handover happens, the contention-based medium access mechanism which is mainly used in WLAN is invoked and introduces unbounded transmission delay due to idle time periods and retransmission because of collision during the handover. If this technique is expanded to use in a microcellular network such as connected WLAN micro-cells, contention-based mechanism, therefore, should not be used to handle the MT’s handover, especially for vehicular users who change access point every few seconds. To overcome these difficulties in handover, we introduce parallel polling scheme in dynamic LMC (Logical Macro Cell) which can reduce delays much and remove packet loss rate. LMC is a virtual single macro cell which is built on a multicast group of adjacent micro-cells. In the same LMC, polling signals are sent from every BS (base station) to give MT (mobile terminal) permission to access one of these BSs. Instead of wasting much time to contend for resources of a new BS during handover, the MT answers the polling as an acknowledgment to connect to that new BS. The polling response is controlled to multicast to all BSs of the same LMC via the core network to synchronize for the next polling cycle. LMC is controlled to dynamically change when the MT comes in a new BS to make polling signals be continuous in a new LMC. Through analytical and simulation results, we show that the parallel polling scheme can achieve no handover latency, no packet loss and maintain mobile users’ throughput stably in the high traffic load condition though it causes overhead on the neighboring cells in both of wired and wireless sections. At speeds of up to70 m/s, the MT can still maintain its stable connection. OMNeT++ simulator with INET project is used to evaluate our proposal.

무선 ATM망에서 rt-VBR 서비스를 위한 동적 슬롯 할당 기법

본 논문에서는 무선 ATM망에서 rt-VBR 서비스를 위한 동적 슬롯 할당 기법을 제안한다. 제안된 방식에서는 슬롯 할당을 요구하기 위한 예약 요청 패킷을 경쟁 기반으로 전송하고, 예약 요청이 성공하면 단말기에서는 비 경쟁 방식으로 동적 매개변수를 전달한다. 기지국 스케줄러는 예약이 성공한 단말기들이 잔여수명과 요청하는 슬롯 수와 같은 동적 매개변수를 전송하기 위한 DPS 미니슬롯을 할당한다. 한편 기지국 스케줄러는 단말기들이 전송한 잔여수명을 기반으로 잔여수명이 가장 짧은 단말기에게 상향 데이터 슬롯을 우선적으로 할당한다. 본 논문에서는 제안한 방식의 성능을 시뮬레이션을 통하여 분석하였다. 시뮬레이션의 결과, 제안한 동적 슬롯 할당 기법은 셀 손실률을 낮게 유지하면서 rt_VBR 서비스가 요구하는 전송 지연을 보장하고 있음을 알 수 있다. This paper proposes the dynamic slot allocation method for real-time VBR (rt-VBR) services in wireless ATM networks. The proposed method is characterized by a contention-based mechanism of the reservation request, a contention-free polling scheme for transferring the dynamic parameters. The base station scheduler allocates a dynamic parameter minislot to the wireless terminal for transferring the residual lifetime and the number of requesting slots as the dynamic parameters. The scheduling algorithm uses a priority scheme based on the maximum cell transfer delay parameter. Based on the received dynamic parameters, the scheduler allocates the uplink slots to the wireless terminal with the most stringent delay requirement. The simulation results show that the proposed method guarantee the delay constraint of rt-VBR services along with its cell loss rate significantly reduced.

A Five-Phase Reservation Protocol (FPRP) for Mobile Ad Hoc Networks

A new single channel, time division multiple access (TDMA)-based broadcast scheduling protocol, termed the Five-Phase Reservation Protocol (FPRP), is presented for mobile ad hoc networks. The protocol jointly and simultaneously performs the tasks of channel access and node broadcast scheduling. The protocol allows nodes to make reservations within TDMA broadcast schedules. It employs a contention-based mechanism with which nodes compete with each other to acquire TDMA slots. The FPRP is free of the "hidden terminal" problem, and is designed such that reservations can be made quickly and efficiently with negligible probability of conflict. It is fully-distributed and parallel (a reservation is made through a localized conversation between nodes in a 2-hop neighborhood), and is thus scalable. A "multihop ALOHA" policy is developed to support the FPRP. This policy uses a multihop, pseudo-Bayesian algorithm to calculate contention probabilities and enable faster convergence of the reservation procedure. The performance of the protocol, measured in terms of scheduling quality, scheduling overhead and robustness in the presence of nodal mobility, has been studied via simulations. The results showed that the protocol works very well in all three aspects. Some future work and applications are also discussed.