Average Channel Access Delay Research Articles

Performance Modeling of an LTE LAA and WiFi Coexistence System Using the LAA Category-4 LBT Procedure and 802.11e EDCA Mechanism

This paper studies the performance modeling and analysis of an LAA and WiFi coexistence system using the LAA category-4 LBT procedure and 802.11e EDCA mechanism. Unlike existing work, this study takes into account transmission priorities and the GAP period problem in a coexistence system under an unsaturated condition. A 3-D Markov chain is first built to model an LAA category-4 LBT procedure in the coexistence system, taking into account transmission priorities and the GAP period problem, and a 3-D Markov chain is built to model an 802.11e EDCA procedure, taking into account transmission priorities. Based on the Markov models, theoretical models are further derived for analyzing the performance of the coexistence system in terms of normalized throughput and average channel access delay. The derived analytical models are justified through simulation results and the impacts of major system parameters on the performance of the coexistence system are investigated based on the derived performance models.

Stochastic Geometric Analysis of Multiple Unmanned Aerial Vehicle-Assisted Communications Over Internet of Things

Due to the advantages of large area coverage, low capital cost and fast deployment, unmanned aerial vehicles (UAVs) are believed to play a key role in the emerging Internet of Things (IoT). In this paper, we first develop an effective analytical approach to characterize the properties of UAV-assisted communications over a large number of IoT devices by introducing average channel access delay for packets that can be successfully transmitted. Specifically, an IoT device is said to establish a full transmission to a UAV, only if its time duration covered by the UAV is greater than the specified average channel access delay. Then, we present a stochastic geometry based mathematical framework to analyze the coverage probability and average achievable rate for a multi-UAV assisted downlink network. Different from previous works: 1) we consider a flexible multi-UAV deployment strategy connecting IoT devices to the Internet via sky-haul links to the satellite, where the altitudes of the UAVs can be adjusted to fulfill the requirements of various IoT applications and 2) we derive analytical expressions, in particular integral form, for the coverage probability and average achievable rate. Our results indicate that the developed framework is very helpful for network designers to efficiently determine the optimal network parameters at which the optimum IoT system performances can be achieved.

Analysis and Optimization of Multiple Unmanned Aerial Vehicle-Assisted Communications in Post-Disaster Areas

As a vital component of disaster response and relief, a wireless network needs to be rapidly deployed after a disaster strikes. Due to the advantages of large area coverage, low capital cost, and fast deployment, an unmanned aerial vehicle (UAV) is believed to be a potentially promising choice to recover wireless communication in post-disaster environments. In this paper, the performance gains of utilizing two cooperative UAVs for downlink transmission over a large number of emergency response rescue vehicles on the ground in post-disaster areas are explored. Toward this end, the concept of average channel access delay for a generic vehicle to establish a full transmission to an UAV is introduced, i.e., data packets are said to be successfully transmitted from a UAV to a vehicle only if the time duration for the vehicle covered by the UAV is greater than the specified average channel access delay. Based on the proposed concept, a stochastic geometry based mathematical framework to analyze the coverage probability and average achievable rate for a multi-UAV-assisted downlink network, where vehicles connect to the Internet via satellites in a two-hop manner, is presented. According to the derived closed-form solutions for the network performance metrics, extensive numerical results are provided to illustrate the network performance gains brought by UAVs. Additionally, optimal settings are also presented for network designers to efficiently determine the optimal network parameters so as to achieve the optimum network performances in post-disaster areas.

On the Performance of Interference-Aware Cognitive Ad-Hoc Networks

In this paper we analyze the effects of channel availability on channel access delay and service probability of cognitive networks using a modified IEEE 802.11 Media Access Control Protocol (MAC). For the designed cognitive network, cognitive communication is limited by the interference imposed on primary users. We determine the probability of accessing the channel under Rayleigh fading condition for this opportunistic network. We then use this probability to determine the embedded Markov model of the cognitive nodes. We use this Markov model to determine the average channel access delay, and service rate of cognitive nodes. Both simulation and analytical results are presented to access the system performance.

Throughput and delay analysis of a reliable cooperative MAC protocol in ad hoc networks

In this paper, we present the performance evaluation of the reliable cooperative media access control (RCO-MAC) protocol, which has been proposed in [1] by us in order to enhance system throughput in bad wireless channel environments. The performance of this protocol is evaluated with computer simulation as well as mathematical analysis in thispaper. The system throughput, two types of average delays, average channel access delay, and average system delay, which includes the queuing delay in the buffer, are used as performance metrics. In addition, two different traffic models are used for performance evaluation: The saturated traffic model for computing system throughput and average channel access delay, and the exponential data generation model for calculating average system delay. The numerical results show that the RCO-MAC protocol proposed by us provides over 20% more system throughput than the relay distributed coordination function (rDCF) scheme. The numerical results show that the RCO-MAC protocol provides a slightly higher average channel access delay over a greater number of source nodes than the rDCF. This is because a greater number of source nodes provide more opportunities for cooperative request to send (CRTS) frame collisions and because the value of the related retransmission timer is greater in the RCO-MAC protocol than in the rDCF protocol. The numerical results also confirm that the RCO-MAC protocol provides better average system delay over the whole gamut of the number of source nodes than the rDCF protocol.

애드혹 네트워크에서 협력통신을 위한 도움노드 선정방법 비교연구

본 논문에서는 애드혹 무선 네트워크에서 채널 전송속도를 높일 수 있는 협력통신 기법에서 도움노드를 선정하는 방법에 대한 연구를 수행하였다. 송수신 노드가 RTS/CTS 제어 프레임을 서로 교환한 이후에 도움노드를 선정하는 사후선정 기법을 채용한 참고문헌 연구결과를 컴퓨터 모의실험을 사용하여 성능비교를 수행하기 위해 시뮬레이터를 구현하였다. 성능평가 척도는 시스템 처리량과 채널 액세스 지연시간을 사용하였으며, 통신노드는 모두 지정된 통신영역 내에서 독립적으로 이동하는 모델을 사용하였다. 성능비교와 장단점 분석을 통해 취합된 결과는 성능이 우수한 새로운 도움노드 선정기법을 설계하는데 귀중한 자료가 될 것으로 판단된다. In this paper, a study on finding an appropriate helper node that can help increase effective frame transmission rate for cooperative communications at ad hoc networks is carried out. Those researches from reference use the reactive helper node selection mechanism which starts its role after exchanging RTS and CTS frames between source and destination nodes, and are implemented into our simulator for performance comparison. System throughput and average channel access delay are used for performance measures and all communicating nodes are assumed to move independently within the communication range. It is anticipated that this research result can be used as basic information for designing a new efficient helper node selection scheme.

Throughput and Delay Analysis of a Network Coding-enabled Cooperative MAC Protocol for Ad Hoc Networks

Cooperative communications and network coding schemes have been proposed to increase system throughput for ad hoc networks. In this paper, we present throughput and delay analysis of the new network coding-enabled cooperative MAC protocol called NC-MAC, which has been proposed by us in order to significantly enhance system performance. This protocol introduces an approach that can accommodate both cooperative communication and network coding for wireless ad hoc networks by slightly increasing overhead and modifying standards. The performance is evaluated using mathematical analysis and computer simulation and two performance measures, system throughput and average channel access delay, are used for a performance comparison with previous schemes. It is assumed that all the frames exchanged over a wireless channel are susceptible to transmission errors, which is a new but more reasonable assumption differentiating this research from previous research. Numerical results show this protocol provides significantly enhanced system performance compared with conventional cooperative MAC protocols used in previous research. For instance, system performance is 47% higher using the NC-MAC protocol than when using the rDCF protocol.

Impact of Different Thresholds on SSB Algorithm

Slow Start Backoff (SSB) Algorithm is a simple, efficient, distributed, and well performed medium access control (MAC) layer protocol designed for wireless adhoc networks to share the medium. SSB is able to alleviate intensive collisions in congested environments and SSB can also minimize the average channel access delay in light load environments. Compare with the traditional binary exponential backoff (BEB) algorithm, SSB provides better performance over a wider range of network condition. In this paper, impact of different threshold values on the performance of SSB algorithm is evaluated, and then we use this result to find out a proper value of threshold that increases the performance of SSB algorithm based on the channel status. Moreover, we provide a simple and accurate analytical model to analysis the system throughput of SSB algorithm in this paper. Simulations are also conducted to evaluate the performance of SSB algorithm. The results confirm that the performance of SSB algorithm can be greatly improved by an appropriate value of threshold. Besides, the results also show the SSB algorithm outperforms the traditional BEB algorithm and other backoff algorithms in both high load and light load environments.

Modeling Channel Access Delay and Jitter of IEEE 802.11 DCF

With the ever-increasing requirement of WLAN to support real-time services, it is becoming important to study the delay properties of WLAN protocols. This paper constructs a new model to analyze the channel access delay and delay jitter of IEEE 802.11 DCF in saturation traffic condition. Based on this analytical model, average channel access delay and delay jitter are derived for both basic access and RTS/CTS-based access scheme. The accuracy of the analytical model is validated by simulations and furthermore we discuss the impact of initial contention window, maximal backoff stage, and packet size on channel access delay and delay jitter of 802.11 DCF using the proposed model.