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  • 1.
    Pieskä, Marcus
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science (from 2013).
    Kassler, Andreas
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science (from 2013).
    Reducing the Latency of TCP for 5G mmWave Links2017Conference paper (Refereed)
    Abstract [en]

    Abstract: Recently, 5G systems started to explore the usage of mmWave bands both for access and backhaul due to the extremely large portion of bandwidth available. Cellular systems operating at such frequencies would achieve a significantly higher capacity than current systems. Due to the propagation characteristics at those frequency bands, highly directional links may frequently switch between Line-of-sight and outage if the beam is blocked by obstacles. Such intermittent connectivity combined with high throughput however causes TCP to perform very badly. In this paper, we study the performance of several TCP variants in intermittend mmWave links. We focus on latency aspects as 5G systems should be designed for very low latency. We use ns-3 in emulation mode (DCE) and experiment with real Linux TCP implementations. Unfortunately, all TCP variants that we evaluated, increase the latency tremendously when the mmWave link characteristics switch from Line-of-sight to non Line-of-sight. In addition, when applying bufferbloat solutions such as CoDel, the latency can be controlled at the expense of low throughput. Based on our findings, we develop a method which transparently tunes the receive window of the TCP connections both for upload and download to effectively maintain low latency while at the same time achieving high capacity.

  • 2.
    Pieskä, Marcus
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science (from 2013).
    Kassler, Andreas
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science (from 2013).
    TCP Performance over 5G mmWave Links - Tradeoff between Capacity and Latency2017In: 2017 IEEE 13th International Conference on Wireless and Mobile Computing, Networking and Communications (WiMob), IEEE, 2017, p. 385-394Conference paper (Refereed)
    Abstract [en]

    Recently, 5G systems started to explore the usage of mmWave bands both for access and backhaul. Cellular systems operating at such frequencies would achieve a significantly higher capacity than current systems due to the large frequency block available. Due to the propagation characteristics, highly directional mmWave links may frequently switch between Line-of-sight, Non Line-of-sight and outage if the beam is blocked by obstacles. Such intermittent connectivity combined with high throughput causes TCP to perform very badly. In this paper, we study the performance of several TCP variants over intermittent mmWave links. We focus on latency aspects, use ns-3 with extensions for mmWave links and evaluate the TCP performance with real Linux TCP stacks using the Direct Code Execution (DCE) framework. We also investigate the benefit of bufferbloat solutions such as CoDel, with different TCP variants. We investigate the impact of CoDels configuration parameters and different RTTs on TCP throughput, fairness and queueing delay. The problem of slow recovery of TCP after NLOS periods is less pronounced when multiple flows coexist under CoDel only if some of the flows have very short RTTs. However, under presence of NLOS, the fairness between different flows with different RTT values is reduced.

  • 3.
    Pieskä, Marcus
    et al.
    Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science (from 2013).
    Kassler, Andreas
    Karlstad University, Faculty of Economic Sciences, Communication and IT, Centre for HumanIT. Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Mathematics and Computer Science (from 2013).
    Lundqvist, Henrik
    Huawei, Stockholm.
    Cai, Tao
    Huawei, stockholm.
    Improving TCP Fairness over Latency Controlled 5G mmWave Communication Links2018In: WSA 2018; 22nd International ITG Workshop on Smart Antennas, 2018Conference paper (Refereed)
    Abstract [en]

    In order to increase the capacity of 5G networks, using mmWave band communication links both for access and backhaul are an important alternative due to the large spectrum portion available at those frequency bands. However, mmWave bands exhibit special propagation characteristics which require the usage of highly directional and beam-steerable antennas in order to cope with the significantly higher path loss. Using such links in urban scenarios may lead to frequent blocking events due to moving pedestrians or cars, which may result in the links dynamically changing their characteristics from Line-of-Sight (LOS) to Non Line-of- Sight (NLOS) or outage (OUT). Due to the immediate significant variation in available capacity when changing the link states, TCP connections may experience rapid spikes in end-to-end latency and severe bufferbloat may build up. Although bufferbloat solutions such as CoDel can be deployed to control the delay, they significantly impact capacity and fairness between different TCP flows sharing the same mmWave link. In this paper, we study this fairness issue when running multiple TCP connections over fluctuating mmWave links and deploying AQM schemes to control the latency. We study the effect of length and severity of the NLOS episode upon fairness and latency. Finally, we develop an algorithm that tunes the AQM parameters in order to increase fairness across flows having different RTTs while at the same time reduce their latency.

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