Protocol Data Unit Research Articles

Revisiting the IEEE 802.11n A-MPDU Retransmission Scheme

The aggregate MAC protocol data unit (A-MPDU) and Block Acknowledgment (Block Ack) techniques are among the pivotal MAC layer enhancements introduced by the IEEE 802.11n amendment. Although they have been studied extensively in the literature, recent research studies have proven that the existing analytical models proposed for those techniques are not conform to 802.11n standard specifications, since they do not capture the effect of the Block Ack window limit on the aggregation size which provokes critical errors in the estimation of 802.11n MAC layer performance. In this letter, we elaborate a new analytical model compliant with the conventional A-MPDU retransmission scheme to conduct an accurate analysis of the performance of A-MPDU and Block Ack techniques under different network conditions. To validate the accuracy of our model, we compared the numerical results to those obtained using ns-3 simulator and with two other analytical models investigating the performance of 802.11n MAC layer.

An Enhanced ARQ Scheme for A-MPDU Transmission Under Error-Prone WLANs

A protocol-friendly enhanced automatic repeat request (ARQ) scheme is proposed in this letter to improve the probability of successful retransmission by combining lost medium access control protocol data units (MPDUs) and their duplicates into an aggregate MPDU (A-MPDU) when the number of lost MPDUs is small. To study the performance of the proposed scheme, we provide a mathematical model that analyzes the saturation throughput and selects the optimized parameters to obtain the best performance. The simulation results show that the proposed analytical model is accurate and its performance is superior to that of the conventional aggregated selective-repeat ARQ scheme in 802.11ac error-prone wireless local area networks when the channel is worse and the physical layer rate is higher.

A-MPDU aggregation with optimal number of MPDUs for delay requirements in IEEE 802.11ac.

In this paper, we propose a method that estimates an average delay of frames for each queue and finds an optimal number of aggregated Medium Access Control (MAC) Protocol Data Units (MPDUs) to maximize the system throughput with satisfying the delay requirement of each queue when using the Aggregate MPDU (A-MPDU) aggregation in IEEE 802.11ac. The delay is defined as the sum of the queuing delay and the service delay. If few frames in a queue are aggregated, the frames which remain in the queue for next transmissions may violate the target delay because of the overhead for the next transmissions such as the backoff time, Physical Layer Convergence Procedure (PLCP) preamble, and PLCP header. If many of the frames in the queue are aggregated, the frames of the queue and the other queues may violate their target delays because of a long transmission duration and a long channel occupancy. In this paper, we obtain the average delay for each queue and the optimal number of aggregated MPDUs for the delay requirement of each queue in IEEE 802.11ac. At the last, we evaluate and show the performance of our proposed method through simulations. The simulation results show that the proposed method can estimate the average delay for each queue accurately. The simulation results also show that the proposed method can obtain the violation rates on the target delays less than 0.1. Furthermore, the simulation results show that the proposed method can yield higher system throughput than other conventional methods.

Analytical modeling of RLC protocol of LTE using stochastic reward nets

SummaryRLC (radio link control) is a layer 2 protocol of LTE used for reliable transmission of data packets in communication networks. This protocol operates in three modes, namely, transparent mode (TM), unacknowledged mode (UM), and acknowledged mode (AM). In this paper, analytical models are developed to study the flow of data streams in all the three modes of the RLC protocol. Stochastic reward net (SRN) is adopted as a modeling technique as it easily captures various aspects of this protocol such as protocol data unit (PDU) transmission, assigning header with each PDU, requesting for status report, retransmission of PDU(s), management of PDU losses due to expiration of various timers (quick repeat timer, poll timer, status timer). Throughput, average delay and probability of PDU loss are evaluated as the performance measures using the SRN models. Based on these performance measures, a comparative study between the UM and AM is presented which depicts that the modes are performing their key functions decently. Analytical results are also validated via simulation.

High-Resolution Time of Arrival Estimation With Small Samples Considering Time-Varying Channel Fading Coefficient Correlation in OFDM

This paper proposes a new method using orthogonal frequency division multiplexing (OFDM) signals for time-of-arrival (TOA) estimation in complex environments, such as electromagnetic interference and short burst received signals. Under that circumstance, sometimes only a short period of signals that were seriously interfered [i.e., low signal-to-noise ratio (SNR) and small samples] can be received for estimation. However, the traditional algorithm would be faced with a decrease in estimation accuracy under that conditions. Due to the fact that the sparse reconstruction method can recover the original signal from a small number of observations with high probability, this paper proposes an OFDM TOA estimation algorithm based on it. The algorithm not only considers the correlation of the channel complex fading coefficients in the samples at adjacent moments but also considers the off-grid effect. Under the Bayesian learning framework, this correlation and off-grid parameter are introduced into the estimation process, which effectively improves the estimation accuracy under small samples and low SNR conditions. The proposed algorithm first constructs a sparse representation model based on the channel frequency response estimated by the OFDM signal physical layer protocol data unit and then introduce the correlation characterization matrix and the off-grid parameter and make probability assumptions for the noise vector, the off-grid parameter, and the sparse coefficient vector in the model. Finally, according to Bayesian inference, the expectation-maximization algorithm is used to solve the hyperparameters to achieve high-resolution estimation of TOA. The simulation results show that the proposed algorithm has a better estimation performance than the traditional algorithms and existing sparse reconstruction algorithms. In addition, its performance curve is closer to the Cramer-Rao bound at low SNR. At the same time, based on the universal software radio peripheral, the effectiveness of the proposed algorithm is verified by the actual OFDM signal.

DESAIN SISTEM ALARM MOBIL BERBASIS SMS

The alarm device is very important in a vehicle, especially on four-wheeled vehicles. Alarm device installed to avoid in case of danger of theft or destruction of the car. So designed car alarm system that can send short message to car owner who use AT89S52 microcontroller. The hardware arrangement of the car alarm system uses the SMS-based AT89S52 microcontroller in this design, consisting of four main parts of the circuit, the minimum system circuit of microcontroller, power supply, serial communication, Input / Output. In SMS text sent from Wavecom M1306B modem and received by mobile (mobile phone) to SMS center or SMS Center flows in form of PDU (Protocol Data Unit). In the sms format is divided into several segments of data that each segment has a specific purpose. The segments are: SMS center number, destination number, bytes for the purpose of setting this SMS and most important is the SMS content that has been changed in the form of a PDU. To be able to send or upload SMS data to the modem and ordered the modem to send SMS data it required AT Command instructions.

Modeling and Performance Analysis of the Main MAC and PHY Features of the 802.11ac Standard: A-MPDU Aggregation vs Spatial Multiplexing

The Very High Throughput (VHT) supplied by the IEEE 802.11ac standard is the outcome of several amendments incorporated at its both Medium Access Control (MAC) and PHYsical (PHY) layers. In particular, the Aggregate-MAC Protocol Data Unit (A-MPDU) frame aggregation allows, at the MAC level, increasing the amount of data to be transmitted and the spatial multiplexing technique serves at the PHY level to accelerate the rate at which such data are forwarded. Therefore, the goals we are seeking to achieve in this paper are, on one hand, to demonstrate that A-MPDU aggregation and spatial multiplexing may, respectively, lead to a decrease in throughput and an increase in overhead, and on the other hand, to highlight that A-MPDU aggregation and spatial multiplexing have mutual needs that could mutually satisfy operational challenges. For this purpose, we model the 802.11ac station enabling A-MPDU aggregation and spatial multiplexing, and we compute the throughput and the overhead of the 802.11ac network. After that, we run Monte Carlo simulations for validating the accuracy of the mathematical model, and we calculate 95% confidence intervals to establish credibility to the simulation results.

AARF-HT: Adaptive Auto Rate Fallback for High-Throughput IEEE 802.11n WLANs

Wireless Local Area Network (WLAN) has been progressing rapidly. The IEEE 802.11n Physical (PHY) layer provides wider channel bandwidth, shorter guard interval, and up to four data streams. Therefore PHY 802.11n has a maximum of 128 data rate options from 6.5 Mbps to 600 Mbps. In addition, Medium Access Control (MAC) has been added Aggregate MAC Protocol Data Unit (AMDPU) scheme. If AMPDU is transmitted with a data rate corresponding to the channel conditions, then the probability AMPDU is received without error becomes increased. MAC determines the data rate used for transmitting AMPDU using a rate adaptation algorithm. Therefore some papers have proposed rate adaptation algorithms based on channel conditions. In this paper we propose a new rate adaptation algorithm that we call Adaptive Auto Rate Fallback for High Throughput (AARF-HT). Our development is done using NS-3 simulator version 3.26. AARF-HT algorithm performance is also tested through a number of simulations extensively. The simulation results show the data rate adaptation function based on the channel width, guard interval and the number of spatial streams in IEEE 802.11n WLAN has functioned well. The test results also show the AARF-HT algorithm resulted in higher throughput compared to the AARF algorithm.

IPv6 Convergence for IoT Cyber–Physical Systems

We describe the evolution of the IoT towards a heterogeneous multitopology network subject to dynamic change and volatility yet still capable of secure and dependable operation. As part of this evolution, we outline the key changes in wireless communications technologies and heterogeneous networking that have arisen during the development of the IoT. We briefly outline the emerging area of cyber–physical systems, and associated technical challenges. We then describe how IP convergence can be viewed as the narrow waist connecting endpoint devices and fieldbus devices with applications and services in new Industry 4.0, and cyber–physical system use cases. We outline how a protocol-packing approach can be used for encapsulating LoRaWAN frames with IEEE 802.15.4 and IEEE 802.11 frames. Extending this, we propose a method for ultracompressed IPv6 signaling, and detail how this can be achieved in an example low-power wide-area technology, namely LoRaWAN. To support our proposed approach, we provide real-world analyses where IPv6 commands undergo a process of ultracompression and are then conveyed to a LoRaWAN endpoint. We find that IPv6 command ultracompression can potentially support command packet sizes that are over 20x smaller than the reported worst-case maximum protocol data unit size of 81 bytes.

QoS-Aware A-MPDU Retransmission Scheme for 802.11n/ac/ad WLANS

The aggregate MAC protocol data unit (A-MPDU) is one of the pivotal aggregation schemes, defined by the IEEE 802.11n/ac/ad, to improve the transmission efficiency of MAC layer. However, A-MPDU scheme is not efficient in error-prone conditions due to its decrease in retransmission aggregation levels. To overcome this problem, a novel QoS-aware A-MPDU retransmission scheme is proposed in this letter. The scheme fully exploits the aggregation level while considering the strict end-to-end delay requirements by QoS applications. In the proposed scheme, the aggregation levels of the retransmitted A-MPDU frames are decided based on the aggregation sliding window strategy, and the expected delay of the proposed scheme and the traditional scheme, respectively, which is calculated through theoretical analysis. The effectiveness of the scheme is demonstrated via experimental evaluation using ns-3.

QoS-Aware Adaptive A-MPDU Aggregation Scheduler for Voice Traffic in Aggregation-Enabled High Throughput WLANs

Currently available IEEE 802.11n implementations do not apply aggregate MAC protocol data unit (A-MPDU) aggregation to voice traffic because of its strict end-to-end delay requirements. When multiple nodes contend to send voice and other lower-priority traffic, 802.11n network faces serious performance degradation problems for two major reasons: i) due to the medium access control (MAC) and physical (PHY) layer overheads of individual short voice packet transmissions, the available network throughput for lower-priority traffic significantly decreases, and ii) increased contention results in high voice packet loss rate (PLR). This paper proposes a QoS-aware adaptive A-MPDU aggregation scheduler for voice traffic in 802.11n/ac WLANs that adaptively applies A-MPDU aggregation to voice traffic based on QoS requirements and periodically obtained average medium access delay and end-to-end delay statistics. Performance evaluations on 20 nodes sending uplink 64Kbps voice and saturated best-effort traffic at 150Mbps PHY rate showed that the proposed scheme achieved 160% throughput improvement compared to default implementations in driver. During the simulations with 50 nodes transmitting at 600Mbps PHY rate, the proposed scheme provided up to 275Mbps throughput against 0.13Mbps by default scheme; the proposed scheme delivered all voice packets (PLR = 0 percent) and over 99.9 percent of them had less than 150ms end-to-end delay.

Verification of failover effects from distributed control system communication networks in digitalized nuclear power plants

Abstract Distributed Control System (DCS) communication networks, which use Fast Ethernet with redundant networks for the transmission of information, have been installed in digitalized nuclear power plants. Normally, failover tests are performed to verify the reliability of redundant networks during design and manufacturing phases; however, systematic integrity tests of DCS networks cannot be fully performed during these phases because all relevant equipment is not installed completely during these two phases. In additions, practical verification tests are insufficient, and there is a need to test the actual failover function of DCS redundant networks in the target environment. The purpose of this study is to verify that the failover functions works correctly in certain abnormal conditions during installation and commissioning phase and identify the influence of network failover on the entire DCS. To quantify the effects of network failover in the DCS, the packets (Protocol Data Units) must be collected and resource usage of the system has to be monitored and analyzed. This study introduces the use of a new methodology for verification of DCS network failover during the installation and commissioning phases. This study is expected to provide insight into verification methodology and the failover effects from DCS redundant networks. It also provides test results of network performance from DCS network failover in digitalized domestic nuclear power plants (NPPs).

IEEE 802.15.4 Frame Aggregation Enhancement to Provide High Performance in Life-Critical Patient Monitoring Systems.

In wireless body area sensor networks (WBASNs), Quality of Service (QoS) provision for patient monitoring systems in terms of time-critical deadlines, high throughput and energy efficiency is a challenging task. The periodic data from these systems generates a large number of small packets in a short time period which needs an efficient channel access mechanism. The IEEE 802.15.4 standard is recommended for low power devices and widely used for many wireless sensor networks applications. It provides a hybrid channel access mechanism at the Media Access Control (MAC) layer which plays a key role in overall successful transmission in WBASNs. There are many WBASN’s MAC protocols that use this hybrid channel access mechanism in variety of sensor applications. However, these protocols are less efficient for patient monitoring systems where life critical data requires limited delay, high throughput and energy efficient communication simultaneously. To address these issues, this paper proposes a frame aggregation scheme by using the aggregated-MAC protocol data unit (A-MPDU) which works with the IEEE 802.15.4 MAC layer. To implement the scheme accurately, we develop a traffic patterns analysis mechanism to understand the requirements of the sensor nodes in patient monitoring systems, then model the channel access to find the performance gap on the basis of obtained requirements, finally propose the design based on the needs of patient monitoring systems. The mechanism is initially verified using numerical modelling and then simulation is conducted using NS2.29, Castalia 3.2 and OMNeT++. The proposed scheme provides the optimal performance considering the required QoS.

ETSI SmartBAN System Performance and Coexistence Verification for Healthcare

European Telecommunications Standard Institute (ETSI) Technical Committee (TC) Smart Body Area Network (SmartBAN) defines and specifies low-power physical and medium access control layers for SmartBANs. Several use cases have been defined for SmartBAN, such as sleep monitoring, fall monitoring, and apnea monitoring. The specialist task force 511, working under ETSI TC SmartBAN, studied the performance of the system and evaluated coexistence with other wireless systems. In this paper, the simulator model based on the SmartBAN specification is introduced. Based on the simulation results, the receiver sensitivity for the SmartBAN system is defined. In addition, the interference model extracted from the measurements in the Oulu university hospital is discussed. This paper presents the summary of the simulation results based on the above-mentioned interference models. The simulation results showed that when there is a high interference in a communication channel, the SmartBAN system cannot gain an acceptable frame error level without a physical layer protocol data unit repetition technique and a high signal-to-interference power ratio level (SIR). In a low interference scenario, repetition is also needed when SIR is less than 9 dB.

Adaptive A-MPDU retransmission scheme with two-level frame aggregation compensation for IEEE 802.11n/ac/ad WLANs

The aggregate MAC protocol data unit (A-MPDU) is one of the significant frame aggregation schemes to improve the performance for high-rate IEEE 802.11n/ac/ad wireless local area networks (WLANs). However, the performance of the A-MPDU scheme does not meet the user expectations because the frame length of the retransmitted A-MPDU will be inevitably and sharply reduced due to the effect of the lost subframe on the number of the aggregatable subframes (i.e., the aggregation level). To overcome this problem, an adaptive A-MPDU retransmission scheme with the two-level frame aggregation compensation is proposed. In this scheme, when the aggregation level of the retransmitted A-MPDU frame dramatically decreases, one of the appropriate two-level aggregation strategies is adaptively employed to compensate the length of the retransmitted A-MPDU frames according to the theoretical analysis of the throughput performance for the conventional A-MPDU scheme and two strategies of the two-level aggregate frame respectively. Simulations using ns-3 platform are performed and the results demonstrate that the proposed adaptive A-MPDU retransmission scheme can achieve higher throughput and medium access control (MAC) layer efficiency.

Enhanced BlockACK method for A‐MPDU transmission in IEEE 802.11n/ac/ad WLANs

An enhanced block acknowledgement (BlockACK) method for the aggregate MAC protocol data unit (A-MPDU) transmission is proposed. In the proposed method, the position information of each aggregated subframe is carried by the A-MPDU using the reserved bits and a novel position information control is used to acknowledge the A-MPDU. By utilising the enhanced BlockACK method, the aggregation level of the A-MPDU transmission will not be constrained by the effect of lost subframes. Theoretical analysis and simulation results demonstrate that the enhanced BlockACK method can achieve a more stable aggregation level and higher throughput than the conventional one.

A New Aggregation Based Scheduling Method for Rapidly Changing IEEE 802.11ac Wireless Channels

In this paper we suggest a novel idea to improve the Throughput of a rapidly changing WiFi channel by exploiting the standard aggregation schemes in IEEE 802.11ac networks. The idea is based on blindly transmitting several copies of the first 4 MAC Protocol Data Units (MPDU) in the Transmission Window. This increases the probability that the window moves forward, enabling the transmission of new MPDUs and resulting in increased Throughput. It turns out that transmitting 2 copies of each of the first 4 MPDUs yields the best Throughput gain, in the order of 50% - 60% in PHY rates of 1.3 - 3.5 Gbps and few hundreds of bytes MPDUs. The proposed idea has advantage over Link Adaptation since it reduces the actual PHY rate only for the transmission of few MPDUs while Link Adaptation reduces the PHY rate for all the transmissions.

Saturation throughput analysis of IEEE 802.11ac TXOP sharing mode

A mathematical model to analyse the saturation throughput of IEEE 802.11ac medium access control (MAC) is proposed. The main contributions of the proposed model are the integration of the transmission opportunity (TXOP) sharing mode and the consideration of variable-length MAC protocol data units, instead of a fixed-length assumption. By using the model, accurate results (within 2% relative error) for the IEEE 802.11ac TXOP sharing mode are achieved.

Enhanced Two-Level Frame Aggregation with Optimized Aggregation Level for IEEE 802.11n WLANs

IEEE 802.11n defines a significant two-level frame aggregation scheme aimed at improving the transmission efficiency of MAC layer. However, the performance of the two-level frame aggregation scheme does not meet the user expectation due to the inevitable aggregation and retransmission overheads. To overcome this problem, an enhanced two-level frame aggregation with the optimized aggregation level is proposed in this letter for IEEE 802.11n wireless local area networks (WLANs). In the proposed scheme, in order to maximize the throughput of the two-level frame aggregation, the aggregation level (i.e., sub-MPDUs, the number of the aggregated sub-MAC protocol data units) used for the two-level frame aggregation is optimized and adjusted dynamically according to the subframe size, the maximum aggregation level (MAL) allowed by the current two-level frame aggregation and the real-time channel bit-error-rate (BER). Results from the simulation show the superiority of the proposed enhanced two-level aggregation in respect of throughput performance.

IEEE 802.11ac/ad 무선 LAN의 적응형 MCS 구현 연구

This paper analyzes the rate adaptation scheme and suggests applicable strategy of the MCS(Modulation and Coding Scheme) for improving DCF throughput in the IEEE 802.11ad and 802.11ad wireless LAN. IEEE 802.11ac and 802.11ad wireless LAN provide MCS technique that dynamically adjusts modulation level and code rate to the time-varying channel conditions in order to obtain considerably high data rates. But these standards did not provide rate adaptation algorithm, so this paper surveyes rate adaptation algorithm and suggests MCS scheme applied to IEEE 802.11ac and 802.11ad wireless LAN. Specially A MAC(Medium Access Control) layer throughput is evaluated over error-prone channel in the IEEE 802.11ac-based wireless LAN. In this evaluation, DCF (Distributed Coordination Function) protocol and A-MPDU (MAC Protocol Data Unit Aggregation) scheme are used. Using theoretical analysis method, the MAC saturation throughput is evaluated with the PER (Packet Error Rate) on the condition that the number of station, transmission probability, the number of parallel beams and the number of frames in each A-MPDU are variables.