ATRAS: adaptive MAC protocol for efficient and fair coexistence between radio over fiber-based and CSMA/CA-based WLANs

Funabiki et al. EURASIP Journal on Wireless Communications and Networking (2017) 2017:129 DOI 10.1186/s13638-017-0907-2 RESEARCH Open Access ATRAS: adaptive MAC protocol for efficient and fair coexistence between radio over fiber-based and CSMA/CA-based WLANs Kaito Funabiki1* , Takayuki Nishio1 , Masahiro Morikura1 , Koji Yamamoto1 , Daisuke Murayama2 and Katsuya Nakahira2 Abstract In this paper, we propose a medium access control (MAC) protocol to allow a radio over fiber-based wireless local area network (RoF-based WLAN) to coexist with legacy carrier sense multiple access with collision avoidance (CSMA/CA)-based WLANs. In RoF-based WLANs, there are long propagation delays between access points (APs) and stations (STAs). When an RoF-based WLAN uses the conventional CSMA/CA protocol and coexists with legacy WLANs, the propagation delay causes unexpected frame collisions and unfairness between the RoF-based WLAN and legacy WLANs. The proposed protocol reduces unexpected frame collisions and improves fairness between the RoF-based WLAN and legacy WLANs in environments where they coexist. It is only necessary to apply the proposed protocol to the AP in the RoF-based WLAN (RoF AP); there is no need to modify STAs, which is an advantage of the protocol. In the proposed scheme, the RoF AP transmits frames during the transmission and reception of frames in the legacy WLAN, such that the frame transmitted by the AP arrives at a destination STA one short interframe space (SIFS) period after the channel became idle, and thus the RoF AP’s frames do not collide with other frames. As a result, the proposed method decreases the likelihood of frame collisions and increases the throughput of the RoF-based WLAN. In addition, the proposed method provides adaptive adjustment of the transmission probability, which enables the RoF-based WLAN and the legacy WLANs to fairly share wireless channels. The proposed protocol has been investigated for IEEE 802.11a/b/g WLANs. Numerical analysis and simulation evaluations show that the proposed scheme increases the TCP throughput of the RoF-based WLAN up to the same level as that in legacy WLANs. Keywords: Radio over fiber, Long distance WLAN, Coexistence, MAC protocol, Propagation delay 1 Introduction Wireless communication is becoming increasingly common, and many wireless standards are now available for wireless local area networks (WLANs). Accordingly, network operators must prepare dedicated wireless access points (APs) for each system, every time a new wireless standard emerges. Existing WLAN standards, such as IEEE 802.11b/g/a/n/ac, are utilized in the 2.4 and 5 GHz bands. Moreover, owing to increasing demand for more capacity, WLAN standards using the millimeterwave (mmWave) band, such as IEEE 802.11ad and IEEE 802.11ay using 60 GHz, are actively being discussed for *Correspondence: Graduate School of Informatics, Kyoto University, Kyoto, Japan Full list of author information is available at the end of the article 1 the provision of broadband wireless access [1]. In addition, the demand for Internet of Things (IoT) applications has drawn attention to sub-1 GHz wireless standards, such as IEEE 802.15.4 [2]. The upcoming IEEE 802.11ah standard has the potential to serve wide-area and low-cost wireless networks for IoT devices [3]. Access networks are required to support various communication standards with different physical (PHY) and medium access control (MAC) layer parameters by a single AP. Network function virtualization (NFV) is a promising method with which to economically realize such flexible wireless access networks [4]. One of the key enablers of NFV for wireless access networks is radio over fiber (RoF) technology. In wireless systems with RoF technology, only radio frequency (RF) units connected to a central office are located in remote © The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Funabiki et al. EURASIP Journal on Wireless Communications and Networking (2017) 2017:129 areas and the central office operates the PHY signal processing and MAC functionality [5–9]. The RF units, which are connected to the central office via an optical fiber, convert the optical signals to electrical signals before transmitting them over the radio channel, and vice versa. Using RoF for wireless systems enables the centralization of the wireless signal processing functions that are currently performed by each AP. The benefit of this approach is that WLANs or wireless personal area networks (WPANs) are able to support any wireless standard by only changing the processing functions at the central office. An RoF-based access architecture for integrating multiple wireless systems was discussed in [8, 9]. However, the integration of the conventional carrier sense multiple access with collision avoidance (CSMA/CA)-based wireless standard with an RoF-based architecture requires research because the long propagation delays in the optical fiber links may cause the CSMA/CA protocol to behave unexpectedly, resulting in a decrease in the system throughput. When designing a MAC protocol for RoFbased WLANs, it is important to take into account backward compatibility with IEEE 802.11 standard to cover existing devices. Moreover, it is also important to take into account how best to support coexistence with legacy CSMA/CA-based systems. WLANs are used widely and many APs are densely deployed. The dense environment is typical for apartment buildings and offices. Because of the limited number of orthogonal frequency channels in 2.4 and 5 GHz band, situations where the neighboring WLANs utilizing the same channel can occur. This paper focuses on a MAC layer solution for IEEE 802.11 WLANs that employ an RoF architecture (RoF-based WLAN) and addresses the coexistence problems between the RoF-based and legacy WLANs. In WLANs that have an RoF-based architecture, delays longer than one half of a slot time cause unexpected frame collision patterns and increase the probability of frame collisions when the WLAN operates using a conventional MAC protocol. In order to solve the severe frame collision problems caused by large propagation delays, several alternative MAC protocols have been proposed [10–12]. For example, Deronne et al. proposed a method for optimizing the slot time value so that unexpected collisions do not occur [10]. However, the use of large slot times increases the overhead, which decreases the system throughput. Moreover, if an RoF-based WLAN coexists with legacy WLANs, the RoF-based WLAN stations that use a large slot time are only able to transmit a few DATA frames because t (...truncated)