Saturation Throughput Research Articles

THCA: Three-Hop Congestion Awareness Routing Mechanism in WiNoC

Wireless on-chip networks suffer from serious congestion problems due to the expansion of their network size and the joining of wireless nodes, and token passing is very inefficient in the case of low network injection. Aiming at the congestion problem and the inefficiency of token passing in wireless on-chip networks, this paper designs a three-hop congestion-aware routing mechanism in WiNoC. In the scheme of this paper, first, the congestion information is written into Head Flit for propagation through the information piggybacking method, in which the information piggybacking method does not introduce congestion information propagation overhead, second, the port with the smallest congestion value is selected for transmission through the three-hop congestion-aware routing algorithm to reduce the congestion within the subnetwork, and then the wireless node congestion is mitigated through the new wired and wireless packet division method, and finally, the power of wireless nodes is reduced through the dynamic MAC mechanism to reduce the power consumption of wireless nodes. The experimental results show that this paper’s scheme can reduce the intra-subnet congestion, balance the inter-subnet load, reduce the power consumption of wireless nodes, and reduce the latency by 44.6% compared with the basic wireless on-chip network using adaptive routing algorithm, and reduce the latency by 21.8% compared with the wireless on-chip network using global congestion-aware routing algorithm; in different traffic patterns, this paper achieves the highest saturation throughput in different traffic patterns, and the additional hardware overhead of the router increases by only 0.04%.

Modeling and Performance Analysis of LBT-Based RF-Powered NR-U Network for IoT.

Energy harvesting combined with spectrum sharing offers a promising solution to the growing demand for spectrum while keeping energy costs low. New Radio Unlicensed (NR-U) technology enables telecom operators to utilize unlicensed spectrum in addition to the licensed spectrum already in use. Along with this, the energy demands for the Internet of Things (IoT) can be met through energy harvesting. In this regard, the ubiquity and ease of implementation make the RF-powered NR-U network a sustainable solution for cellular IoT. Using a Markov chain, we model the NR-U network with nodes powered by the base station (BS). We derive closed-form expressions for the normalized saturated throughput of nodes and the BS, along with the mean packet delay at the node. Additionally, we compute the transmit outage probability of the node. These quality of service (QoS) parameters are analyzed for different values of congestion window size, TXOP parameter, maximum energy level, and energy threshold of the node. Additionally, the effect of network density on collision, transmission, and energy harvesting probabilities is observed. We validate our model through simulations.

A high-performance fully adaptive routing based on software defined network-on-chip

Adaptive routing techniques have been proven to be effective solutions for handling network congestion and enhancing the performance of Network-on-Chip (NoC). Traditional adaptive routing algorithms may degrade flexibility and lead to the issue of high hardware implementation overhead. In this paper, we propose a fully adaptive routing (FAR) based on Software Defined NoC (SDNoC) to address these issues. The proposed FAR decouples path selection from packet forwarding. The routing path is determined by software techniques in the control layer according to the global congestion status and is encapsulated into the packet to control the forwarding of the packet. Evaluation results show that the proposed FAR yields an improvement of performance over the typical routing schemes in average packet latency and saturation throughput up to 8.2% and 6.1% respectively. The layout area and power consumption are at least 6.2% and 3.9% less compared with the typical routing schemes as well.

Performance analysis of distributed coordination function with early collision detection in In-band Full-duplex wireless networks

In-band Full-duplex (IB-FD) wireless has the potential to double the spectral efficiency offering its innate capability to resolve conventional problems emerge owing to the imperfect medium access control (MAC) in In-band half-duplex (IB-HD) wireless networks. IEEE 802.11 distributed coordination function (DCF), a binary slotted exponential back-off with carrier sense multiple access scheme, has been used extensively in literature as the fundamental contention resolution technique to devise MAC protocols for IB-FD wireless networks. Unlike IB-HD, an IB-FD network can contain two simultaneously active transmission links within a single collision domain. This phenomenon invalidates the applicability of existing IB-HD models of the DCF to compute its performance (i.e., saturation throughput) accurately in IB-FD wireless networks. We have proposed two MAC protocols for two types of network scenarios taking early collision detection capability of an IB-FD wireless transceiver into consideration. This paper also presents a distinct analytical model to quantify the performance of the DCF in the context of IB-FD wireless assuming finite number of stations and idle channel conditions. We have applied the concept of primary–secondary transmission links and, thoroughly derived the probability that a station transmits either as primary or secondary in a randomly chosen time-slot taking secondary transmitter’s back-off counter into account. We have also investigated the effect of inter-station interference free IB-FD link on the performance of the DCF. Our protocol, when applied to network without hidden stations, has obtained the highest throughput gain of 1.59, 1.61, 1.68 while the DCF is configured with CWmin of 16, 32, 64, respectively than IEEE 802.11 basic access scheme. We have observed increased throughput gain with hidden stations, thanks to inter-station interference free transmission region, and achieved 2.12, 2.14, 2.16 times higher throughput, respectively than that of IEEE rts-cts access scheme.

Performance Analysis of IEEE 802.11p MAC with Considering Capture Effect under Nakagami-m Fading Channel in VANETs

Vehicular ad hoc networks (VANETs) have recently drawn a large amount of attention because of their enormous potential in road safety improvement and traffic management as well as infotainment service support. As the standard of medium access control (MAC) and physical (PHY) layers for VANETs, IEEE 802.11p has been proposed for more than a decade. Though performance analyses of IEEE 802.11p MAC have been performed, the existing analytical methods still need to be improved. In this paper, to assess the saturated throughput and the average packet delay of IEEE 802.11p MAC in VANETs, a two-dimensional (2-D) Markov model is introduced by considering the capture effect under Nakagami-m fading channel. Moreover, the closed-form expressions of successful transmission, collided transmission, saturated throughput, and average packet delay are carefully derived. Finally, the simulation results are demonstrated to verify the accuracy of the proposed analytical model, which also proves that this analytical model is more precise than the existing ones in terms of saturated throughput and average packet delay.

Saturation throughput maximization in full duplex WLANs using game theory

Saturation throughput maximization in full duplex WLANs using game theory

A Semi-Markov Process Model for Performance Evaluation of DSRC Vehicular Safety Communication

In this study, a new semi-Markov process (SMP)-based model is devised to evaluate the IEEE 802.11p enhanced distributed channel access (EDCA) broadcast performance for vehicular safety communication. Differing from the existing SMP analytical models, the proposed model takes the virtual collision among various prioritized access categories (ACs) inside each vehicle into consideration. Moreover, in contrast to the Markov chain-based models, our model is simpler but with approximate accuracy. Concretely, we first capture the behavior of each AC’s backoff entity using SMP. Then, the parameters of interest in the vehicular ad hoc network (VANET) such as packet transmission probability, conditional collision probability, and saturation throughput are derived. Finally, via MATLAB simulations, we demonstrate that the newly developed model achieves comparable accuracy in calculating these output parameters while its complexity and computation time is around one-tenth of that of the Markov chain-based models. Therefore, the proposed model is more suitable for real-time performance analysis of IEEE 802.11p EDCA safety communication in a freeway scenario.

Pitstop++: Enabling stable and fair deadlock freedom on fault-tolerant NoC

It is essential to design a deadlock-free solution with high performance and low overhead, as a deadlock in NoC systems will result in severe performance degradation or even worse. Traditional deadlock recovery solutions ignore the promptness of deadlock detection and the efficiency of recovery, and they lack fairness and stability when the network is overloaded. In addition, they devote an excessive amount of resources to extremely rare protocol-level deadlocks, resulting in an increase in hardware overhead with little performance improvement. In order to address these issues, Pitstop++ designs a dual-deadlock detection mechanism and a buffer alternating mechanism, which fully considers the timeliness of deadlock detection and the efficiency of recovery. At the same time, Pitstop++ provides fast deadlock detection and efficient deadlock recovery mechanisms for the more common route-level deadlocks, as well as a conservative, low-overhead strategy for the extremely rare protocol-level deadlocks. Compared to Pitstop, Pitstop++ provides an average 51.0% increase in oversaturation throughput and a minimum 44.8% increase in network saturation throughput.

Evaluating the impact of aggregation and RTS/CTS schemes on IEEE 802.11 based Linear Wireless Ad‐Hoc Networks

AbstractThe Linear Wireless Ad‐Hoc Network (Linear WANET), as a branch of the Ad‐Hoc network, refers to a self‐organizing multi‐hop wireless network in which nodes are arranged linearly. Frame aggregation and RTS/CTS schemes are introduced in IEEE 802.11 aims to improve network transmission performance. However, the traditional mechanisms may not have good adaptability in linear multi‐hop networks. Thus, we defined a Linear WANET simulation model based on the IEEE 802.11 protocol. We established this model on the NS‐3 network simulator to perform A‐MSDU, A‐MPDU, and two‐level frame aggregation simulation and analyzed the aggregation performance under different channel environments. Meanwhile, the RTS/CTS and TXOP mechanisms were also simulated in this article. We analyzed the performance of each mechanism in a Linear WANET under saturated and unsaturated environments. We found that the linear multi‐hop characteristic has a significant impact on the performance of the frame aggregation mechanism. In the Linear WANET, the A‐MSDU mechanism can improve system performance to a limited extent, but at the same time, it will increase the packet loss rate and delay. So, the two‐level aggregation can improve the maximum throughput of the system with better channel conditions. In the case of single A‐MPDU aggregation, there has a lowest data delivery interval that the Linear WANET system can withstand. The A‐MPDU mechanism is a better choice for the poor channel conditions with unsaturated system throughput. Meanwhile, we also found that the native TXOP mechanism cannot effectively improve the system efficiency of Linear WANET. The RTS/CTS mechanism can enhance system throughput performance in most cases, especially in a saturated throughput environment.

Design and analysis of IEEE 802.11 based Full Duplex WLAN MAC protocol

Full-Duplex (FD) communication is a promising technique that can be used in 5G to potentially double the system throughput compared to conventional Half Duplex (HD) transmission. Recent experiments have demonstrated near-perfect self-interference suppression techniques in the PHY layer to aid the possibility of FD communication. This paper presents a Synchronized Mode Full-Duplex (SM-FD) wireless LAN MAC protocol with appropriate modification of the IEEE 802.11 standard. The proposed SM-FD MAC protocol maintains synchronization between nodes and Access Point (AP) to increase efficiency. SM-FD MAC protocol supports WLAN having both FD and HD capable nodes by establishing both symmetrical links (Node1 ↔ AP) and asymmetrical links (Node1 → AP → Node2). To this end, we have utilized the packet-alignment-based capture effect in an efficient way. The proposed SM-FD MAC protocol has been analyzed using a Markov chain model. The analytical results for RTS and data collision probability, saturated throughput, delay, and energy spent per packet transmission have been derived and validated against simulation.

Backoff Entropy: Predicting Presaturation Peak for IEEE 802.11 DCF Networks

In nonsaturated 802.11 distributed coordination function (DCF) networks, existing studies had observed a salient phenomenon: the maximum stable throughput may be far higher than the saturation throughput and last for a long duration (say, months). Such a maximum stable throughput is called the presaturation throughput peak. The long-duration peak suggests that 802.11 DCF networks may provide a far higher stable throughput than what we generally believe, without worrying about a sudden deterioration of quality of service (QoS). This paper is devoted to developing a general theoretical framework to predict the peak. In the framework, we define a backoff entropy to quantify the uncertainty of the inherent random backoff process of 802.11 DCF networks, and then innovatively introduce a BackoffEntropy-Peak linearity property (i.e., the peak is linearly proportional to the backoff entropy) for the peak prediction. This framework is applicable for a general configuration of contention windows (CWs). It enables us to reveal the most essential dependency of the peak on the initial CW size and the number of network nodes. Further, we design peak-based call admission control (CAC) schemes that can be performed quickly and easily, without requiring network performance measurements and complex calculations. We verify our framework and CAC schemes via widely adopted 802.11 DCF ns2 and ns3 simulators (mostly with typical 802.11 standard settings). Extensive simulations show that our framework and CAC schemes trade within 9% peak prediction errors for making 802.11 DCF networks provide high stable throughput with good QoS (such as short delay and low collision probability). This paper is the first to propose applying the information entropy to study the throughput-stability problem. We believe that this study makes a crucial breakthrough in thoroughly investigating nonsaturated performance and network stability of random access wireless networks.

FleX: A Flex Interconnected HPC System With Stochastic Load Balancing Scheme

We propose a new low-diameter interconnection network called FleX, which offers high flexibility when installing interconnections in a HPC system. FleX consists of multiple layers with only connections between neighboring layers and not within each layer. These structural properties make it easy to achieve a low diameter with regardless of the scale. The cross-like connections between the adjacent layers in FleX impart various alternative minimal paths, allowing FleX to have high resiliency and a wide bisection width. We also discuss the minimal routing scheme and a stochastic load balancing scheme (LBR) for the proposed interconnection network. Through cycle-based simulations, the performance of FleX is evaluated, and the cost and power consumption analyses in comparison with other interconnection networks are also conducted. We verify that FleX has high configuration flexibility with regard to cost and performance, and also provides low latency and high saturation throughput with the same cost over the legacy interconnection networks for the HPC system. Moreover, being synergied with the proposing LBR, we also verify that FleX can expand its saturation throughput further while only sacrificing the latency slightly.

Enhanced collision resolution and throughput analysis for the 802.11 distributed coordination function

SummaryThe IEEE 802 standards rely on the distributed coordination function (DCF) as the fundamental medium access control method. DCF uses the binary exponential backoff (BEB) algorithm to regulate channel access. The backoff time determined by BEB depends on a contention window (CW) whose size is doubled if a station suffers a collision and reset to its minimum value after a successful transmission. Doubling the size of CW reduces channel access time, which decreases the throughput. Resetting it to its minimum value harms fairness since the station will have a better chance of accessing the channel compared to stations that suffered a collision. We propose an algorithm that addresses collisions without instantly increasing the CW size. Our algorithm aims to reduce the collision probability without affecting the channel access time and delay. We present extensive simulations for fixed and mobile scenarios. The results show that, on average, our algorithm outperforms BEB in terms of throughput and fairness. Compared to exponential increase exponential decrease (EIED), our algorithm improves, on average, throughput and delay performance. We also propose analytical models for BEB, EIED and our algorithm. Our models extend Bianchi's popular Markov chain‐based model by using a collision probability that is dependent on the station transmission history. Our models provide a better estimation of the probability that a station transmits in a random slot time, which allows a more accurate throughput analysis. Using our models, we show that both the saturation throughput and maximum throughput of our algorithm are higher than those of BEB and EIED.

Will OFDMA Improve the Performance of 802.11 Wifi Networks?

WiFi 6 based on the IEEE 802.11ax amendment is intended to improve spectral efficiency and area throughput operations in high density environments. This is achieved (among other methods) by the introduction of Orthogonal Frequency Division Multiple Access (OFDMA) and enhanced multi-user Multiple Input Multiple Output (MU-MIMO) features. In this work, we explore the performance of downlink and uplink OFDMA in 802.11ax via extensive simulation based evaluation (latency, throughput, range) compared to conventional single user (SU) transmissions. Based on our results, we conclude that OFDMA can reduce the median latency from ~5 ms to less than 1 ms in non-saturation conditions. When used in conjunction with efficient multi-user buffer status report and restricted EDCA mechanisms, OFDMA can increase the saturation throughput by more than 10 percent. Moreover, UL OFDMA also improves aggregate throughput at longer ranges due to the narrower sub-channels (equivalently increased transmit power spectral density); four stations achieve an aggregate throughput 35 percent higher than a station transmitting SU frames and located at a range 1.5 times closer to the access point.

Towards the Saturation Throughput Disparity of Flows in Directional CSMA/CA Networks: An Analytical Model

Using directional antennas in wireless Ad hoc networks has many superiorities, including reducing interference, extending transmission range, and increasing space division multiplexing. However, directional transmission introduces two problems: deafness and directional hidden terminals problems. We observe that these problems result in saturation throughput disparity among the competing flows in directional CSMA/CA based Ad hoc networks and bring challenges for modeling the saturation throughput of the flows. In this article, we concentrate on how to model and analyze the saturation throughput disparity of different flows in directional CSMA/CA based Ad hoc networks. We first divide the collisions occurring in the transmission process into directional instantaneous collisions and directional persistent collisions. Then we propose a four-dimensional Markov chain to analyze the transmission state for a specific node. Our model has three different kinds of processes, namely back-off process, transmission process and freezing process. Each process contains a certain amount of continuous time slots which is defined as the basic time unit of the directional CSMA/CA protocols and the time length of each slot is fixed. We characterize the collision probabilities of the node by the one-step transition probability matrix in our Markov chain model. Accordingly, we can finally deduce the saturation throughput for each directional data stream and evaluate saturation throughput disparity for a given network topology. Finally, we verify the accuracy of our model by comparing the deviation of analytical results and simulation results.

Optimized data transmission scheme based on proper channel coordination used in vehicular ad hoc networks

In recent years, standardization bodies, academia and automobile manufacturers are working together to develop vehicular ad hoc network (VANET) based communication technologies. VANETs apply various channels like service channels (SCHs) and control channel (CCH) for supplying unbarred street safety facilities and the better condolence as well as effectiveness of driving. In this paper, we suggests a VCI known as variable control CH interval (VCI) MAC (multichannel medium access control) scheme which reduces safety message transmission time and helps to minimize collision probability when the vehicle node increases in the road by using k-means and donkey-smuggler optimization algorithm. The donkey-smuggler algorithm used to find the shortest path among the nodes and k-means clustering algorithm is used to group the sensor nodes. The distance ratio connecting with SCHs and CCHs can be effectively modified in MAC scheme. To improve the intermissions based on traffic situation, a model is carried out called Markov model and this process is called as stochastic process. Conceptual analysis and the simulation resulted to the recommended scheme which is capable to assist IEEE 1609.4 and IEEE 802.11p protocol. While retaining the methodized channelling of condemnatory safety data on control CH, the MAC scheme consequentially improves the higher saturated throughput and gives effective channel utilization of service CHs and minimizes transmission interval of service packets.

Service Differentiation in IEEE 802.11ah WLAN under Restricted Access Window based MAC protocol

The restricted access window (RAW) based channel access scheme proposed for IEEE 802.11ah wireless LAN (WLAN) divides the stations (STAs) in the network into groups and allocates RAW slots for each group of STAs. In this way, the STAs belonging to each group can attempt to access the medium during their designated RAW slot by invoking the enhanced distributed channel access (EDCA) protocol. This paper describes an analytical model to evaluate the saturation throughput of IEEE 802.11ah WLAN under the RAW based scheme, when STAs carry traffic of distinct access categories (ACs) and use the EDCA protocol for medium sharing. However, when groups are formed by randomly selecting the STAs, i.e., if random grouping (RG) scheme is employed, each group will contain STAs carrying traffic of distinct ACs. This will lead to starvation and degraded throughput performance for the low priority class STAs, since they have to contend with high priority class STAs within the same group during the RAW slot assigned. To resolve this issue, we propose an algorithm to realize priority class based grouping (PCG), in which the STAs belonging to the same ACs are grouped together. We also describe an analytical model to evaluate the saturation throughput of the network under the proposed PCG scheme. We establish that saturation throughput of the network and the relative service differentiation ratio of the lower priority class STAs can be significantly improved under the proposed PCG scheme compared to the conventional RG scheme.

Making path selection faster: a routing algorithm for ONoC.

Optical network-on-chip (ONoC) is an effective communication architecture to realize high performance and energy efficiency. Diverse routing algorithms are proposed to avoid the congestion, tolerate the faults, and reduce the insertion loss or energy consumption. However, existing algorithms did not consider the characteristic optical circuit-switching of ONoC, which aggravates the network congestion and degrades the associated performance severely. In this paper, by exploiting congestion prediction technique, we propose a new routing algorithm for ONoC, named loophole-routing, to improve the success rate of path-setup and decrease the latency. We use the congestion prediction technique to analyze the latency and predict the port condition caused by the network congestion. Theoretical analysis and experimental results of different synthetic traffic patterns show that the loophole-routing improves network latency over XY routing and OE-turn routing by 15.56%, 25.71%, 18.92%, 66.67% and 42.86% under uniform, hotspot1, hotspot2, transpose2 and transpose3 traffic patterns while improving the saturation throughput by 31.43%, 34.33%, 35.29%, 67.86% and 99.5% under uniform, hotspot1, hotspot2, transpose2 and transpose3 traffic patterns on average than XY routing. In addition, our proposed loophole-routing has the benefits of high path diversity and adaptive degree and low computing complexity and overhead and the potential to make fault-tolerant path selection.

Modeling and analyzing the performance of high-speed packet I/O

Recently, 10 Gbps or higher speed links are being widely deployed in data centers. Novel high-speed packet I/O frameworks have emerged to keep pace with such high-speed links. These frameworks mainly use techniques, such as memory preallocation, busy polling, zero copy, and batch processing, to replace costly operations (e.g., interrupts, packet copy, and system call) in native OS kernel stack. For high-speed packet I/O frameworks, costs per packet, saturation throughput, and latency are performance metrics that are of utmost concern, and various factors have an effect on these metrics. To acquire a comprehensive understanding of high-speed packet I/O, we propose an analytical model to formulate its packet forwarding (receiving--processing--sending) flow. Our model takes the four main techniques adopted by the frameworks into consideration, and the concerned performance metrics are derived from it. The validity and correctness of our model are verified by real system experiments. Moreover, we explore how each factor impacts the three metrics through a model analysis and then provide several useful insights and suggestions for performance tuning.

Saturation Throughput Analysis of Steganography in the IEEE 802.11p Protocol in the Presence of Non-Ideal Transmission Channel

Vehicular network is a communication technology designed to provide comfort and improve life safety and driving efficiency on the road. In vehicular network, trustworthy communication is very important as fake applications may lead to disastrous road accidents. Several information hiding methods are used to enable vehicles to communicate secretly or to covertly report a misbehaving vehicle. The work in this paper focuses on a performance analysis based on 2-D Markov chain model for the system throughput of steganographic scheme in relation to the IEEE 802.11p standard. This model studies wireless padding (WiPad) that is used to hide data into the padding of packets at the physical layer of wireless local area networks (WLANs). The analytical study is under non-saturated conditions with non-ideal transmission channel. The study also considers the rate of packet arrival with the first order of buffer memory, back-off timer freezing, back-off phases, and short retry limit to satisfy the IEEE 802.11p specifications. It emphasizes that taking these factors into account are significant in modelling the system throughput of the steganographic channel. These factors typically provide a precise channel access estimation, yield more accurate findings of system throughput, use the channel efficiently, prevent overestimation of saturation throughput, and ensure that no packet is served indefinitely. The model is validated by comparing the numerical and simulation results under different network parameters. Analytical and simulation results stated that the values of the system throughput of the steganographic channel based on data and control frames are low as the vehicles number $n$ , traffic arrival rate $\lambda $ , packet size, and the value of Bit Error Rate (BER) increase.