Abstract
A point-to-point (PTP) wireless link is studied that carries long-lived TCP flows and is controlled with active queue management (AQM). A cross-layer queue-aware adaptive modulation and coding (AMC)-based link adaptation (LA) mechanism is proposed for this wireless link to improve the TCP-level throughput relative to the case where AMC decisions are made based solely on the physical layer (PHY) parameters. The proposed simple-to-implement LA mechanism involves the use of an aggressive modulation and coding scheme (MCS) with high spectral efficiency and high block error rates when the queue occupancy exceeds a certain threshold, but otherwise a relatively conservative MCS with lower spectral efficiency and lower block error rates. A fixed-point analytical model is proposed to obtain the aggregate TCP throughput attained at this wireless link and the model is validated by ns-3 simulations. Numerical experimentation with the proposed analytical model applied to an IEEE 802.16-based wireless link demonstrates the effectiveness of the proposed queue-aware LA (QAWLA) mechanism in a wide variety of scenarios including cases where the channel information is imperfect. The impact of the choice of the queue occupancy threshold of QAWLA is extensively studied with respect to the choice of AQM parameters in order to provide engineering guidelines for the provisioning of the wireless link.
Highlights
Along with the User Datagram Protocol (UDP) whose use has gained momentum with emerging multimedia and P2P applications, the Transmission Control Protocol (TCP) has been one of the most widely used transport protocols for most Internet services such as Web browsing, file transfer, remote login, and recently for video streaming [1,2,3]
We study a wireless bottleneck link for a number of long-lived TCP traffic flows with active queue management (AQM) buffer management and AMC-based link adaptation, the interplay between these two components being the main topic of study of this paper, with the goal of potentially increasing the total TCP throughput
Making use of the well-established PFTK formula, we propose in this paper a fixed-point model of a single AQM-controlled wireless link with AMC decisions being based on the dual-regime wireless link (DRWL) framework
Summary
Along with the User Datagram Protocol (UDP) whose use has gained momentum with emerging multimedia and P2P applications, the Transmission Control Protocol (TCP) has been one of the most widely used transport protocols for most Internet services such as Web browsing, file transfer, remote login, and recently for video streaming [1,2,3]. Making use of the well-established PFTK formula, we propose in this paper a fixed-point model of a single AQM-controlled wireless link with AMC decisions being based on the DRWL framework. Such discontinuities lead to scenarios where the boundary point may become the steady-state fluid limit and the conventional fixedpoint model of [43] falls short of modeling discontinuous queue service rates and wireless packet loss rates For such scenarios, we propose an extended fixed-point analytical model to model TCP throughput in AQMcontrolled wireless links in the current study. I=0 where λi(x, α) is the packet sending rate of flow i when the queue takes the value x and we propose to use the PFTK TCP formula (3) to write λi(x, α) with RTT and p being replaced with RTTi(x, α) and p(x, α), respectively.
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