Receiver Window Research Articles

Low Complex Inter-Doppler Interference Mitigation for OTFS Systems via Global Receiver Windowing

Orthogonal time frequency space (OTFS) waveform has been considered as a potential candidate for affording a wide range of emerging communications and sensing applications in beyond 5G wireless technologies. OTFS takes advantage of both time and frequency selectivity of the doubly dispersive wireless environment, which has been considered as one of the limiting factors in classical wireless communication technologies. However, the performance of OTFS-based wireless systems is severely affected by fractional Doppler that arises due to inevitable and inherent characteristics of the wireless channel taps of not being always integer Doppler values in the delay-Doppler plane. Thus, this results in severe inter-Doppler interference (IDI) and a low channel sparsity in delay-Doppler (DD) domain. To this end, this work introduces a novel receiver (Rx) windowing technique to combat the impact of fractional Doppler on error performance of the OTFS-based transmission with practical pulse shaping filters at the transceiver. Specifically, we introduce a global cyclic prefix (CP) based raised cosine (RC) windowing at Rx in order to alleviate the effect of IDI on the received signal. To do so, the proposed scheme changes the pulse shape of the OTFS signal in DD domain that defines the IDI level and sparsity of the effective channel. Furthermore, we assess the performance of the proposed Rx windowed OTFS (RW-OTFS) scheme under various practical communication scenarios. The obtained numerical and simulation results validate the accuracy of the proposed IDI mitigator for OTFS systems in practical high-mobility scenarios.

Disk hopper feeding device for active orientation of cylindrical parts with a pointed end

The design of a disk hopper feeding device with gripping organs in the form of radial through profi le sockets and an orienting receiver window for automatic loading of cylindrical parts with a pointed end into automatic rotor machines and lines, including when assembling multi-element products, is considered. The proposed technical solutions make it possible to ensure suffi ciently high reliability and productivity of the hopper feeding device at low circumferential speeds of the disk with gripping organs, which is especially important when loading easily deformable parts or parts with easily damaged coatings.

Numerical evaluation of one-dimensional transparent photonic crystal heat mirror coatings for parabolic dish concentrator receivers

High temperature solar receivers can convert concentrated solar power to heat to drive chemical production or mechanical cycles to produce electricity. Transparent windows with selective coatings that reflect thermal radiation can be used to cover receivers to improve their efficiency. However, in parabolic dish concentrators (PDC) these windows can reflect or absorb incoming solar radiation, and may actually reduce the efficiency and power output from PDC receivers. In this work numerical analysis shows that one-dimensional transparent photonic crystal heat mirrors (TPCHMs), which have the form of a modified dielectric mirror, can be designed to be highly transmissive to solar radiation but highly reflective towards thermal radiation. Results show that TPCHMs can be designed to provide significant enhancements to PDC receiver efficiencies operating at lower solar concentration ratios. Specifically, numerical analysis shows efficiency improvements of at least 62%, and 193% compared to either open-face receivers or the case when the receiver window is coated with a transparent conducting oxide film at operating temperatures of 1000 K and 1500 K, respectively. These results suggest that TPCHM covers have potential for enhancing the performance of smaller PDC systems operating at relatively low solar concentration ratios.

Transmitter and Receiver Window Designs for Orthogonal Time-Frequency Space Modulation

In this paper, we investigate the impacts of transmitter and receiver windows on the performance of orthogonal time-frequency space (OTFS) modulation and propose window designs to improve the OTFS channel estimation and data detection performance. In particular, assuming ideal pulse shaping filters at the transceiver, we derive the impacts of windowing on the effective channel and its estimation performance in the delay-Doppler (DD) domain, the total average transmit power, and the effective noise covariance matrix. When the channel state information (CSI) is available at the transceiver, we analyze the minimum squared error (MSE) of data detection and propose an optimal transmitter window to minimize the detection MSE. The proposed optimal transmitter window can be interpreted as a mercury/water-filling power allocation scheme, where the mercury is firstly filled before pouring water to pre-equalize the time-frequency (TF) domain channels. When the CSI is not available at the transmitter but can be estimated at the receiver, we propose to apply a Dolph-Chebyshev (DC) window at either the transmitter or the receiver, which can effectively enhance the sparsity of the effective channel in the DD domain. Thanks to the enhanced DD domain channel sparsity, the channel spread due to the fractional Doppler is significantly reduced, which leads to a lower error floor in both channel estimation and data detection compared with that of rectangular window. Simulation results verify the accuracy of the obtained analytical results and confirm the superiority of the proposed window designs in improving the channel estimation and data detection performance over the conventional rectangular window design.

On Receive Window Design for UF-OFDM Signals Over Multipath Channels

We study the impact of receive windowing on the quality of signal reception for the multicarrier waveform “universal filtered orthogonal frequency division multiplexing” (UF-OFDM), which shows a great potential in asynchronous transmissions. Due to the absence of a cyclic prefix (CP), UF-OFDM signals are more vulnerable to multipath channels. We show that the receive window can be designed to suppress the intersymbol interference (ISI) and intercarrier interference (ICI) induced by multipath propagation. The SINR performance of UF-OFDM signals is evaluated, both analytically and by simulations, for various multipath channel models. About 3 dB SINR gain can be achieved by simply extending the length of the receive window for channels with relatively large root mean square delay spreads.

Extensionless Adaptive Transmitter and Receiver Windowing of Beyond 5G Frames

Newer cellular communication generations are planned to allow asynchronous transmission of multiple numerologies (waveforms with different parameters) in adjacent bands, creating unavoidable adjacent channel interference. Most prior work on windowing assume additional extensions reserved for windowing, which does not comply with standards. Whether windowing should be applied at the transmitter or the receiver was not questioned. In this work, we propose two independent algorithms that are implemented at the transmitter and receiver, respectively. These algorithms estimate the transmitter and receiver windowing duration of each resource element (RE) with an aim to improve fair proportional network throughput. While doing so, we solely utilize the available extension that was defined in the standard and present standard-compliant algorithms that also do not require any modifications on the counterparts or control signaling. Furthermore, computationally efficient techniques to apply per-RE transmitter and receiver windowing to signals synthesized and analyzed using conventional cyclic prefix orthogonal frequency division multiplexing are derived and their computational complexities are analyzed. The spectrotemporal relations between optimum window durations at either side, as well as functions of the excess signal to noise ratios, the subcarrier spacings and the throughput gains provided over previous similar techniques are numerically verified.

Numerical investigation of the isothermal flow field and particle deposition behaviour in a rotating fluidized bed solar receiver

A numerical analysis of the isothermal flow field within a directly irradiated Rotating Fluidized Bed Receiver (RFBR), is presented to provide a systematic assessment of the influence of key receiver control parameters, namely fluidized bed rotational speed and radial fluidizing gas velocity, on the flow field inside the receiver and particle deposition onto the receiver window. To achieve these aims, a Computational Fluid Dynamics (CFD) model of the RFBR was developed and coupled with Discrete Phase Model (DPM) to analyse the fluid flow and particle trajectory in the receiver cavity due to systematic variations in the key control parameters. The fluid flow modelling approach was partially verified by comparing the numerical predictions with previously published experimental flow measurements in a rotating vortex flow device that is geometrically similar to the RFBR. Using the reported modelling approach, the sensitivity of the flow field and particle deposition to the variations in the key control parameters was determined. Flow features and physical mechanisms linked to particle deposition onto the receiver window were identified with the view to better understand the operation of the RFBR and determine suitable operating regimes that achieve a low risk of particle deposition.

Adaptive Receiver-Window Adjustment for Delay Reduction in LTE Networks

The cellular network keeps the vast capacity of queue space at eNodeBs (base stations) to reduce the queue overflow during the burst in data traffic. However, this adversely affects the delay sensitive applications and user quality of experience. Recently, few researchers have focused on reducing the packet delay, but it has a negative impact on the utilization of network resource by the users. Further, it fails to maintain fairness among the users, when competing for a shared resource in coexistence with conventional TCP or UDP users. Therefore, in this paper, the adaptive receiver-window adjustment (ARWA) algorithm is proposed to efficiently utilize the network resources and ensure fairness among the users in resource competitive environment, which requires slight modification of TCP at both the sender and receiver. The proposed mechanism dynamically varies the receiver window size based on the data rate and delay information of the packets, to enhance the performance of the system. Based on extensive experiments, the results illustrate that the ARWA algorithm reduces the delay of TCP packet and increases fairness among the users. In addition to that, it enhances the packet delivery fraction (PDF) and maintains the throughput of the system. Moreover, it competes with other conventional TCP users for the shared network resources in a fair manner.

Adaptive Windowing for ICI Mitigation in Vehicular Communications

The performance of orthogonal frequency division multiplexing systems in vehicular environments suffers from intercarrier interference (ICI) and the inherent non stationarity of the channel statistics. Receiver windowing constitutes an effective technique for enhancing the banded structure of the frequency-domain channel matrix, thus improving the effectiveness of a banded equalizer for ICI mitigation. However, its optimality has been verified only for stationary channels with perfectly known statistics. In non stationary channels, the second-order statistics have to be tracked and the optimal performance can be achieved at the expense of cubic complexity over the number of the subcarriers. To overcome this limitation, an adaptive windowing technique is proposed that is able to track directly an optimal receiver window in terms of average signal-to-interference noise ratio, requiring only linear complexity. Extensive simulation results verify both the ability of the proposed approach to track the time varying channel statistics and its increased robustness to channel estimation errors that are common in vehicular environments.

Mitigating TCP Incast Issue in Cloud Data Centres using Software-Defined Networking (SDN): A Survey

Transmission Control Protocol (TCP) is the most widely used protocol in the cloud data centers today. However, cloud data centers using TCP experience many issues as TCP was designed based on the assumption that it would primarily be used in Wide Area Networks (WANs). One of the major issues with TCP in the cloud data centers is the Incast issue. This issue arises because of the many-to-one communication pattern that commonly exists in the modern cloud data centers. In many-to-one communication pattern, multiple senders simultaneously send data to a single receiver. This causes packet loss at the switch buffer which results in TCP throughput collapse that leads to high Flow Completion Time (FCT). Recently, Software-Defined Networking (SDN) has been used by many researchers to mitigate the Incast issue. In this paper, a detailed survey of various SDN based solutions to the Incast issue is carried out. In this survey, various SDN based solutions are classified into four categories i.e. TCP Receive Window based solutions, Tuning TCP Parameters based solutions, Quick Recovery based solutions and Application Layer based solutions. All the solutions are critically evaluated in terms of their principles, advantages, and shortcomings. Another important feature of this survey is to compare various SDN based solutions with respect to different performance metrics e.g. maximum number of concurrent senders supported, calculation of delay at the controller etc. These performance metrics are important for deployment of any SDN based solution in modern cloud data centers. In addition, future research directions are also discussed in this survey that can be explored to design and develop better SDN based solutions to the Incast issue.

Mixed Numerologies Interference Analysis and Inter-Numerology Interference Cancellation for Windowed OFDM Systems

Extremely diverse service requirements are one of the critical challenges for the upcoming fifth-generation (5G) radio access technologies. As a solution, mixed numerologies transmission is proposed as a new radio air interface by assigning different numerologies to different subbands. However, coexistence of multiple numerologies induces the inter-numerology interference (INI), which deteriorates the system performance. In this paper, a theoretical model for INI is established for windowed orthogonal frequency division multiplexing (W-OFDM) systems. The analytical expression of the INI power is derived as a function of the channel frequency response of interfering subcarrier, the spectral distance separating the aggressor and the victim subcarrier, and the overlapping windows generated by the interferer's transmitter windows and the victim's receiver window. Based on the derived INI power expression, a novel INI cancelation scheme is proposed by dividing the INI into a dominant deterministic part and an equivalent noise part. A soft-output ordered successive interference cancelation (OSIC) algorithm is proposed to cancel the dominant interference, and the residual interference power is utilized as effective noise variance for the calculation of log-likelihood ratios for bits. Numerical analysis shows that the INI theoretical model matches the simulated results, and the proposed interference cancelation algorithm effectively mitigates the INI and outperforms the state-of-the-art W-OFDM receiver algorithms.

Time Discriminator for Satellite Radar Altimeter Tracker System

The article considers the design of optimum time discriminator for onboard delay-lock loop of a spacebased radar altimeter. The basic signal model is simplified remaining however adequate enough to the task of keeping echo-signal within the tracking receiver window. Along with the optimal one the quasi-optimal maximum-point and maximal-steepness-point discriminators are proposed. The discriminator curves of all considered structures are calculated. It is shown that the quasi-optimal discrimination yield about 2.5 times to the optimal one in the equivalent time fluctuations. Such a loss can be considered a tolerable cost of achieved hardware simplicity.

How to avoid TCP congestion without dropping packets: An effective AQM called PINK

This paper proposes PINK (Passive INverse feedbacK), a queue management algorithm designed to indirectly impose a certain resource allocation policy on defined sets of client hosts. PINK adds intelligence at intermediate nodes that connect client hosts to bottleneck links or to external networks in general, allowing these nodes to dynamically modify the TCP Acknowledgements (ACKs) segments passing through. The modification consists in replacing advertised Receive Window fields (RCV.WNDs) with custom values, in order to enforce a specific bandwidth utilization upper bound. To compute new RCV.WND values, PINK needs only the number of active connections, the flows RTTs and the transmission channel bandwidth. It follows that PINK permits to impose a centralized bandwidth management without the cooperation of clients, which means that no modification or addition to end hosts is needed. Furthermore, as demonstrated in this paper, our proposal does not constrain client hosts performance without purpose; on the contrary, PINK improves efficiency on multiplexed channels by exploiting their capacity and by maintaining a low queuing delay and guarantees optimal flow fairness without forcing any packet drop. We validate PINK performance in multiple scenarios by using the ns-3 network simulator.

DRWA: A Receiver-Centric Solution to Bufferbloat in Cellular Networks

The problem of overbuffering in the current Internet (termed as bufferbloat) has drawn the attention of the research community in recent years. Cellular networks keep large buffers at base stations to smooth out the bursty data traffic over the time-varying channels and are hence apt to bufferbloat. However, despite their growing importance due to the boom of smart phones, we still lack a comprehensive study of bufferbloat in cellular networks and its impact on TCP performance. In this paper, we conducted extensive measurement of the 3G/4G networks of the four major U.S. carriers and the largest carrier in Korea. We revealed the severity of bufferbloat in current cellular networks and discovered some ad-hoc tricks adopted by smart phone vendors, which mitigate the impact of bufferbloat but result in performance degradation under various practical scenarios. To address the problem, we propose dynamic receiver window adjustment (DRWA) that requires slight TCP modification only in smart phones, thus guarantees quick deployment via over-the-air updates. Our extensive real-world tests confirm that DRWA reduces the latency of TCP flows by 25-49 percent and increase TCP throughput by up to 51 percent in certain scenarios. It is further verified that DRWA has significant effect on the latency of Voice-over-IP traffic and on the traffic going through TCP split scenarios with performance enhancing proxy.

Combining traffic-shaping methods with congestion control variants for HTTP\xa0adaptive streaming

HTTP Adaptive Streaming (HAS) is a streaming video technique widely used over the Internet. However, it has many drawbacks that degrade its user Quality of Experience (QoE). Our investigation involves several HAS clients competing for bandwidth inside the same home network. Studies have shown that managing the bandwidth between HAS clients using traffic-shaping methods improves the QoE. Additionally, the TCP congestion control algorithm in the HAS server may also impact the QoE, because every congestion control variant has its own method to control the congestion window size. Based on previous work, we describe two traffic-shaping methods, the Hierarchical Token Bucket shaping Method (HTBM) and the Receive Window Tuning Method (RWTM), as well as four popular congestion control variants: NewReno, Vegas, Illinois, and Cubic. In this paper, our objective is to provide a detailed comparative evaluation of combining these four congestion control variants with these two shaping methods. The main result indicates that Illinois with RWTM offers the best QoE without causing congestion. Results were validated through experimentation and objective QoE analytical criteria.

Low Complexity CFO Compensation in Uplink OFDMA Systems With Receiver Windowing

Orthogonal frequency division multiple access (OFDMA) systems in the uplink suffer from multiple access interference (MAI) due to their high sensitivity to frequency misalignments between different users. In this paper, we propose the application of time domain receiver windowing methods to confine the leakage caused by multiple carrier frequency offsets (CFOs) to a few neighboring subcarriers with almost no additional computational burden. The CFO effects can be translated into a linear system of equations with a coefficient matrix that is called interference matrix. As a result of receiver windowing, we can approximate the interference matrix with a quasi-banded one by neglecting its small elements outside a certain bandwidth. This allows us to propose a class of low complexity CFO compensation techniques. These techniques are applicable to the generalized subcarrier allocation scheme (G-CAS). The complexity reduction in the proposed solutions is substantial when compared to the existing ones in the literature. It is worth mentioning that this substantial complexity reduction is achieved in expense of some bandwidth efficiency loss. Hence, there exists a tradeoff between bandwidth efficiency and complexity. Solutions based on both zero forcing (ZF) and minimum mean squared error (MMSE) criteria are proposed and compared. Simulation results demonstrating the effectiveness of the proposed algorithms in approaching the optimal performance are also presented.

SCTP performance improvement based on virtual receiver window

This article puts forward one algorithm for stream control transfer protocol (SCTP) improvement with limited receiver buffer (RBUF). As is well known, SCTP is one of the most important transfer control protocol, but most researches focus on the situations without the RBUF limit. In this study, we analyze the impact of the RBUF size on the performance. Computer simulations show that the network utility is low in reliable transfer, when the RBUF size is smaller than bandwidth delay product. By studying the transmission sequence number (TSN) transfer progress, we find that the peer receiver window (PEER_RWND), which lags behind the true receiver window (RWND), leads to the poor network utility. To improve SCTP performance with limited RBUF, the virtual receiver window (VIRTUAL_RWND) is introduced. Based on the VIRTUAL_RWND, one algorithm is proposed to increase the sending rate. Computer simulations have evaluated an excellent performance of the proposed algorithm at both ideal link without lost packet and nonideal link with lost packet.

Easing Congestion in Computer Networks using the Receiver-Window Modification (RWM) Scheme

Random Early Detection (RED), Adaptive RED (ARED), BLUE and other Active Queue Management (AQM) queues have been proposed to replace drop-tail queues for Transmission Control Protocol/Internet Protocol (TCP/IP) networks to ease network congestion. Together with the Exp licit Congestion Notification (ECN) scheme, they had shown some pro mise over the drop tail queues. However, the timeout mechanism or the duration of the reception of three duplicate acknowledgements (ACKs), due to early-dropped packets, delays the response time of TCP in reducing the network congestion. Moreover, using ECN has its downsides: i) its messages may get lost; and ii) TCP implementations at the source, router and the destination have to be ECN-co mpliant (which presents a significant problem in today's implementations). To minimize these problems, this paper presents a novel AQM modification scheme called Receiver-W indow Modification (RWM), wh ich can be used together with any AQM queue for congestion avoidance in packet switched networks, especially at ingress and gateway routers. RWM improves on the average queue sizes, one-way end-to-end packet delays, delay jitter, throughput and number of dropped packets. It also overcomes the dependency of these AQM queues on the queues of downstream routers since ECN messages may get dropped or delayed due to congestion at these routers. We carry out extensive NS2 simulat ions to show our results and to support our claims.

A TCP acceleration algorithm for a wireless link using rate adaptation based on round-trip-time and virtual receiver window information

Fast transmission control protocol (TCP) was previously proposed for high capacity network environments with long delay, and TCP with Snoop performs better than conventional TCP enhancements in mobile wireless network environments. However, FAST TCP has limitations when used over a dynamic mobile wireless link with a high frame error ratio (FER) and frequent delay changes due to the variable rate. We propose an enhanced TCP acceleration algorithm at the TCP sender side which efficiently adapts to the maximum transmission rate of a mobile wireless link using the round trip time (RTT) and virtual receiver window (RWND) information. The proposed algorithm provides superior performance over mobile wireless network environments.

Receiver window designs for radio frequency interference suppression in DMT systems

Windowing is often applied at the DMT (discrete multitone) receiver to suppress radio frequency interference (RFI). The spectral roll-off of the window determines how neighbouring tones are affected by RFI. However, the roll-off of the window is not of equal importance in all frequency range. In particular, the roll-off in high frequency will be inconsequential when the side lobes are so small that RFI is not the dominating noise. The window is designed here to minimise total interference. The frequency response of the proposed window achieves a good trade-off in spectral roll-off between high and low frequencies. As a result, fewer tones will be dominated by RFI than in the cases of commonly used Hanning and Blackman windows, in which the stopband in high frequency are often over designed. We have considered the case for informed receiver (RFI information available to the receiver) and uninformed receiver (RFI information unavailable to the receiver). In either case, the proposed window is channel-independent and can be obtained in a closed form.