Packet Access Delay Research Articles

Performance Analysis of Grant-Free Multiple Access for Supporting Sporadic Traffic in Massive IoT Networks

Grant-free multiple access (GFMA) protocol has been regarded as a key element to support sporadic traffic generated from massive internet-of-things (IoT) networks. In GFMA protocol, each IoT device transmits data packets without grant from a base station (BS) via pre-reserved uplink resources. Packet collisions inherently occur when multiple IoT devices transmit packets by using the same radio resource, but the collision effect can be alleviated with multi-packet reception (MPR) capability of the BS. Since a number of studies have focused on improving the physical layer performance such as bit error rate, they may be hard to provide intuitions from the MAC layer perspective when a number of IoT devices sporadically generate uplink packets and attempt the GFMA. In this paper, we thoroughly investigate the GFMA from the MAC layer perspective. We provide an analytical framework based on a Markov chain to capture the performance of the GFMA in terms of packet transmission success probability, ergodic throughput, and access delay. Through simulations, we validate our analytical framework and verify the necessity of adopting MPR technique for supporting a massive number of IoT devices generating sporadic traffic.

Frequency Hopping CR MAC Protocol in Cognitive Radio Ad Hoc Network

To insure the fairness for the Cognitive Radio (CR) nodes with various available channels, a frequency hopping CR MAC protocol based dynamic (named DCR-MAC) is proposed. In the case of uneven distribution of frequency spectrum in cognitive Ad Hoc network, based on the numbers of workable channels of each cognitive node, DCR-MAC protocol adjusts access time dynamically, ensuring the node priority access channel number, in order to improve the overall performance of the network. Meanwhile, against the problem of the multi-channel hidden terminal which appears in cognitive network of single wireless interface configuration, through introducing the segment mechanism, and informing present channels occupied condition of adjacent node via receiving node, DCR-MAC protocol broadcast of channel occupation in transmission channel, and prohibit possible data transmission of adjacent node, in order to solve this problem on this account. Finally, proving that DCR-MAC protocol is obviously excelled other FH CR MAC protocols in through put capacity, packet access delay, accessing fairness which through network simulation.

An Adaptive Channel Scheduling Design for Multi-Hop Handoff Delay Reduction in Internet-Based Wireless Mesh Networks

Seamless handoff support is an essential issue to ensure continuous communications in multi-hop wireless mesh networks (WMNs). Due to the multi-hop transmission of network-layer handoff signaling packets, the handoff performance in WMNs can be largely degraded by the long queueing delay and medium access delay at each mesh router, especially when the backbone traffic volume is high. However, this issue is ignored in existing handoff solutions and multi-channel allocation schemes. In this paper, we address the seamless handoff support from a different perspective and propose a novel channel allocation design in hierarchical WMNs to reduce the queueing delay and medium access delay of handoff signaling packets over multi-hop wireless links and to improve the average channel utilization simultaneously. Both analytical and OPNET simulation results show that the performance of the average channel utilization and total handoff delay can be improved significantly using our proposed channel allocation scheme under various scenarios, as compared to other existing channel allocation and handoff solutions in multi-hop WMNs.

Delay Analysis of OFDMA-Aloha

OFDMA is the basis of future broadband access, due to its many inherent advantages such as scalability and fine granularity for multi-user access. OFDMA-Aloha combines the flexibility of OFDMA with basic Aloha's collision resolution mechanism over sub-carriers, in an attempt to reduce packet collisions and achieve faster retransmission. However, this comes at the expense of a larger slot size, due to lower channel rates per subcarrier. The above gives rise to a fundamental question: whether to use a single wide-band Aloha channel and retransmit via random back-off in next K time slots, or to retransmit immediately in one of K narrow-band sub-channels which are each 1/K slower (OFDMA-Aloha)? We answer this question, by analyzing the two protocols: Aloha and OFDMA-Aloha under the same total bandwidth and load conditions. We first derive the exact distribution of the packet access delay of OFDMA-Aloha in the saturated case. Then, we extend the analysis to the unsaturated case and derive the mean queue length and packet delay by decomposing the system of interfering queues into multiple independent queues utilizing the symmetry in our system. Our results show that if the network is already saturated, channelization does not bring substantial reduction in the collision rate to the point where it outweighs the effect of expanded slot size. In this case the single channel Aloha performs better than OFDMA-Aloha especially when the gap between the number of channels and the number users is large. On other hand, when the network is lightly loaded, OFDMA-Aloha enjoys smaller packet delays, but not for long as it saturates faster than the single channel Aloha.

A Channel Splitting Strategy for Reducing Handoff Delay in Internet-Based Wireless Mesh Networks

Seamless intergateway handoff support is an essential issue to ensure continuous communications in Internet-based wireless mesh networks (WMNs). Due to the existence of multihop wireless links, traditional handoff schemes designed for single-hop wireless access networks can hardly guarantee the low handoff latency requirement in multihop WMNs. Existing solutions on reducing the handoff delay in WMNs ignore one important factor for the long handoff delay: the channel access delay of handoff signaling packets over the multihop wireless mesh backbone network. In this paper, we address the seamless intergateway handoff issue in Internet-based WMNs from a different perspective and propose a channel splitting strategy to reduce the channel access delay of handoff signaling packets over multihop wireless links. The handoff procedures of two scenarios when a mobile node has one or two transceivers are designed, and two transmission strategies for scheduling the delivery of handoff signaling packets are proposed. Simulation results show that by using the proposed channel splitting strategy, the handoff delay requirement in WMNs can be guaranteed, regardless of the background data traffic, and the average channel utilization can also be improved.

Performance analysis and optimization of best-effort service in IEEE 802.16 networks

The IEEE 802.16-based WiMAX technology has great potential for the fourth-generation mobile networks. Some of its service classes use the contention-based broadcast polling mechanism to request resources. In this paper, we investigate the performance experienced by these services when the network is unsaturated. In particular, we model each subscriber station as an M/G/1 queue where the service time is determined by the parameters of the network configuration and the binary exponential backoff contention resolution algorithm. We develop a fixed-point analysis to derive analytical expressions for network throughput and packet access delay. The accuracy of the analytical model is validated by comparing it with simulation over a wide range of operating conditions. The implications of various different parameter configurations on the performance are investigated using the analytical model. Moreover, we show that the model can be degenerated to the saturated condition. The utility of both the unsaturated and saturated models is further demonstrated by finding the optimal set of parameter values that maximize the network throughput. Copyright © 2011 John Wiley & Sons, Ltd.

Cognitive wireless personal area network for monitoring and control

AbstractIn this paper, we propose and evaluate a cognitive personal area network (CPAN) suitable for wireless monitoring and control outside the Industrial, Scientific and Medical (ISM) band. Network is based on frequency hopping but the channels are selected on the basis of spectrum sensing performed by the nodes. Nodes balance their data collecting activity and spectrum sensing such that the duration of spectrum sensing done by a node is proportional to the number of packets previously transmitted by that node. We show that the operation of a node in this setup can be modeled as a gated exhaustive round‐robin system with vacations, and analyze the performance of the system. The impact of the value of the penalty factor, which determines the duration of sensing activity with respect to transmission, on packet access delay and stability limits of the system is discussed in detail. Copyright © 2009 John Wiley & Sons, Ltd.

Cross-Layer Optimization for Multimedia Transport over Multicode CDMA Networks

Most previous work on code division multiple access (CDMA) considers the bit error ratio (BER) at the physical layer and the frame drop ratio (FDR) at the medium access control layer separately. However, a better system performance, e.g., in terms of a lower overall frame loss ratio (FLR), can be achieved if BER and FDR are jointly optimized. In this paper, we propose a cross-layer optimization scheme called traffic-adaptive scheme for multicode CDMA operating over a time division multiple access (TDMA) channel. Based on the traffic condition and buffer status, this scheme employs a Markov Decision Process (MDP) to determine the optimal value of the maximum number of simultaneous data frames that can be transmitted in each time slot of a TDMA frame so as to minimize the overall FLR of the system. To facilitate implementation, we also propose an approximation scheme named the rate-adaptive scheme to reduce the computation cost. Simulation and analytical results show that both the traffic-adaptive scheme and rate-adaptive scheme can significantly reduce FLR, increase the system throughput, and optimize the packet access delay of the system. Furthermore, the rate-adaptive scheme can achieve a performance close to the traffic-adaptive scheme when the traffic load in the system is high.

Modelling and analysis of nonsaturated opportunistic spectrum access networks

An analytic model for an unslotted opportunistic spectrum access network under nonsaturation traffic conditions is proposed and its performance, such as MAC access delay and system delay of secondary packets, is analysed. Numerical examples are given to show the performance of secondary users in cognitive radio networks.

Performance analysis of downlink traffic in WiMAX networks by considering a shadowing radio propagation model

We investigate in this paper the implications of scheduling and adaptive modulation and coding AMC on the performance of downlink traffic in OFDMA-based IEEE 802.16 cells. To this end, we model the downlink traffic as a discrete-time Markov chain by assuming exponential interarrival times of packets at the upstream of the unidirectional unbuffered connection maintained by the base station with each associated subscriber station SS. Various performance metrics are derived by considering two usual scheduling policies: equal-slot sharing ESS and equal-throughput sharing ETS. In particular, the estimated packet access delays provide a lower bound on the achieved delays in case of buffering. Besides, our model considers the adaptivity of the modulation and coding schemes MCSs used by the base station. By assuming uniform distribution of the SSs over the cell and shadowing log-normal radio propagation, we derive the probability density function of the signal-to-noise ratios measured at the level of the SSs. Albeit defined in the context of WiMAX networks, this second contribution can be exploited in more generic wireless settings. Several numerical results are presented and discussed to expose the effects of system parameters and scheduling policies on performance.

Channel Access Delay and Buffer Distribution of Two-User Opportunistic Scheduling Schemes in Wireless Networks

In our earlier works, we proposed rate adaptive hierarchical modulation-assisted two-best user opportunistic scheduling (TBS) and hybrid two-user scheduling (HTS) schemes. The proposed schemes are innovative in the sense that they include a second user in the transmission opportunistically using hierarchical modulations. As such the frequency of information access of the users increases without any degradation of the system spectral efficiency (SSE) compared to the classical opportunistic scheduling scheme. In this paper, we analyze channel access delay of an incoming packet at the base station (BS) buffer when our proposed TBS and HTS schemes are employed at the BS. Specifically, using a queuing analytic model we derive channel access delay as well as buffer distribution of the packets that wait at BS buffer for down-link (DL) transmission. We compare performance of the TBS and HTS schemes with that of the classical single user opportunistic schemes namely, absolute carrier-to-noise ratio (CNR)-based single user scheduling (ASS) and normalized CNR-based single user scheduling (NSS). For an independent and identically distributed (i.i.d.) fading environment, our proposed scheme can improve packet's access delay performance compared to the ASS. Selected numerical results in an independent but non-identically distributed (i.n.d.) fading environment show that our proposed HTS achieves overall good channel access delay performance.

Performance Analysis of IEEE 802.15.4 Beacon-Enabled Mode

In this paper, a mathematical model for the beacon-enabled mode of the IEEE 802.15.4 medium-access control (MAC) protocol is provided. A personal area network (PAN) composed of multiple nodes, which transmit data to a PAN coordinator through direct links or multiple hops, is considered. The application is query based: Upon reception of the beacon transmitted by the PAN coordinator, each node tries to transmit its packet using the superframe structure defined by the IEEE 802.15.4 protocol. Those nodes that do not succeed in accessing the channel discard the packet; at the next superframe, a new packet is generated. The aim of the paper is to develop a flexible mathematical tool able to study beacon-enabled 802.15.4 networks organized in different topologies. Both the contention access period (CAP) and the contention-free period defined by the standard are considered. The slotted carrier-sense multiple access with collision avoidance (CSMA/CA) algorithm used in the CAP portion of the superframe is analytically modeled. The model describes the probability of packet successful reception and access delay statistics. Moreover, both star and tree-based topologies are dealt with; a suitable comparison between these topologies is provided. The model is a useful tool for the design of MAC parameters and to select the better topology. The mathematical model is validated through simulation results. The model differs from those previously published by other authors in the literature as it precisely follows the MAC procedure defined by the standard in the context of the application scenario described.

A Collision Alleviation Scheme for IEEE 802.11p VANETs

IEEE 802.11p protocol, also known as Wireless Access for the Vehicular Environment provides dedicated short range communication for future Vehicular Ad Hoc Networks (VANETs). According to the IEEE 802.11p standard, the highest priority traffic transmission often suffers from the consecutive collisions in bursty arrival or congested scenarios because of the naive pre-assumption of a low level of congestion in the system, and thus results in emergent messages delayed. In this paper, we propose a simple, but yet well performing collision alleviation scheme to alleviate intensive collisions between highest priority access categories which usually used to schedule emergency message since safety is the most critical and promising issue in VANET. In addition to theoretical analysis, simulations are conducted to evaluate its performance. The simulation results show that the proposed scheme can not only increase the achievable channel throughput of the legacy protocol at most 15%, but also reduce the average packet access delay of the legacy protocol at least 5% and the packet collision probability at most 60% in congested VANET environments.

Performance Analysis of Best-Effort Service in Saturated IEEE 802.16 Networks

The IEEE 802.16 standard is a promising technology for the fourth-generation mobile networks and is being actively promoted by the Worldwide Interoperability for Microwave Access (WiMAX) Forum: an industry-led consortium. Among the various service classes supported in the standard, best-effort service is expected to be the major service class subscribed to by users due to its operational simplicity and lower charging rate compared with other service classes. In this paper, we investigate the throughput and packet-access-delay performance of best-effort service using the contention-based bandwidth request mechanism in a saturated IEEE 802.16 network. In particular, we develop a simple fixed-point analysis to approximate the failure probability of a bandwidth request and derive analytical expressions for network throughput and packet access delay. Furthermore, the uniqueness of the fixed point is established. The accuracy of the analytical model is validated by comparison with simulation over a wide range of operating conditions. The implications of various different parameter configurations on the system performance are investigated using the analytical model. The utility of the model is further demonstrated by finding the maximum achievable throughput and obtaining its corresponding optimal initial contention window.

Minimization of Collision in Energy Constrained Wireless Sensor Network

Wireless Sensor Networks (WSNs) are one of the fastest growing and emerging technologies in the field of Wireless Networking today. The applications of WSNs are extensively spread over areas like Military, En-vironment, Health Care, Communication and many more. These networks are powered by batteries and hence energy optimization is a major concern. One of the factors that reduce the energy efficiency of the WSN is collision which occurs due to the high density of data packets in a typical communication channel. This paper aims at minimizing the effects of congestion leading to collision in the network by proposing an effective algorithm. This can be done by optimizing the size of the contention window by introducing pa-rameters like source count and α. If the contention window of a node is low, it results in collision. If the size of the contention window of a node is high then it results in a medium access delay. Thus minimizing colli-sion and medium access delay of data packets conserve energy.

MAC Protocol for Multimedia Traffic in Optical Wireless Communications

Due to the advantages optical wireless (OW) offers over radio, there is currently increasing interest in its performance evaluation. There is a need for MAC protocols specifically designed for OW to accommodate high bandwidth multimedia (voice and video) services. This paper proposes a mathematical model of a MAC protocol in OW environment and its performance evaluation with all audio (Poisson) sources (zero video sources) and, later, by adding a variable bit rate (VBR) video (Poisson/self-similar) source in the system which has been generated after conducting extensive experiments on a real time video stream. The system performance in terms of throughput, packet access delay, packet dropping probability and statistical multiplexing gain is evaluated analytically and then verified through simulation results. The effect of Poisson sources on the system is also compared with self-similar (video) source and novel results are reported.

Split-channel pipelined packet scheduling for wireless networks

To reduce medium access control (MAC) overhead and improve channel utilization, there has been extensive research on dynamically adjusting the channel access behavior of a contending station based on channel feedback information. This paper explores an alternative approach, named pipelined packet scheduling, to reduce the MAC overhead. MAC overheads can be divided into bandwidth-dependent and bandwidth-independent components and these overheads can both be reduced by using split-channel pipelining mechanisms, as demonstrated in this paper. In the past, pipelining mechanisms have not been well studied. This paper introduces two total pipelining schemes that attempt to fully pipeline contention resolution with data transmission. Further, the paper identifies shortcomings of total pipelining in the wireless environment and proposes a partial pipelining approach to overcome these shortcomings. Simulation results show that substantial performance improvement in channel utilization, average packet access delay, and access energy cost can be achieved with a properly designed scheme.

Performance of binary exponential backoff CSMA in WiFi and optimal routing in mobile ad hoc networks

In this paper we show that the CSMA IEEE 802.11 protocol (Wifi) provides packet access delays asymptotics in power law. This very feature allows us to specify optimal routing via polynomial algorithm while the general case is NP-hard.

Performance analysis of low rate wireless technologies for medical applications

In this article, we discuss what wireless technologies can be used for medical applications and how well they perform in a healthcare/hospital environment. We consider the emerging low-rate Wireless Personal Area Network technology as specified in the Institute of Electrical and Electronics Engineers 802.15.4 standard and evaluate its suitability to the medical environment. We focus on scalability issues and the need to support tens of communicating devices in a patient's hospital room. We evaluate the effect of packet segmentation and backoff parameter tuning to improve the overall network performance that is measured in terms of packet loss, goodput, and access delay. We also evaluate the performance of 802.15.4 devices under interference conditions caused by other 802.15.4 devices and by wireless local area networks using IEEE 802.11b.

Access delay for nodes with finite buffers in IEEE 802.15.4 beacon enabled PAN with uplink transmissions

In this work we analyze the performance of a personal area network operating under the IEEE Standard 802.15.4 in the beacon enabled mode, and derive the probability distribution of packet access delay and calculate the throughput. We assume that the network is operating in non-saturation mode and that the nodes have finite buffers. We model the operation of the PAN using the theory of discrete time Markov chains and M/G/1/K queues. The model considers acknowledged uplink transmission and includes the impact of different parameters such as packet arrival rate, number of stations, station's buffer size, packet size, and inactive period between the beacons. The model also captures the problem of congestion at the beginning of the superframe due to multiple transmissions being delayed from the previous superframe, and we propose a correction to the standard in order to avoid this problem. In order to achieve acceptable access delays and small blocking probability at the buffer (which has to be small), PAN must be operated at throughput less than 50%, which can be achieved by restricting the number of the nodes in the PAN, or by reducing the packet arrival rates at the nodes.