Evaluation of IEEE 802.11 coexistence in WLAN deployments

This is a pre-print of an article published in Wireless Networks. The final authenticated version is available online at: https://doi.org/10.1007/s11276-017-1540-z.Wi-Fi has become a successful technology since the publication of its first WLAN standard due to continuous advances and updates while remaining always backwards compatible. Backwards compatibility among subsequent standards is an important feature in order to take advantage of previous equipment when publishing a new amendment. At present, IEEE 802.11b support is still mandatory to obtain the Wi-Fi certification. However, there are several harmful effects of allowing old legacy IEEE 802.11b transmissions in modern WLAN deployments. Lower throughput per device is obtained at slow rates, but also the effect known as performance anomaly, which nearly leads to starvation of fast stations, has to be taken into account. Finally, backwards compatibility mechanisms pose an important penalty in throughput performance for newer specifications. This paper presents a thorough analysis of the current state of IEEE 802.11, comparing coverage range and throughput performance among subsequent amendments, and focusing on the drawbacks and benefits of including protection mechanisms.Peer ReviewedPostprint (author's final draft

Solving hidden terminal problem in MU-MIMO WLANs with fairness and throughput-aware precoding and a degrees-of-freedom-based MAC design

© 2016, Shrestha et al. We generally emphasize that the zeroforcing (ZF) technique backed by an appropriate medium access control (MAC) protocol can be used to address the inevitable hidden terminal (HT) problem in multi-user multiple input multiple output (MU-MIMO) wireless local area network (WLAN) settings. However, to address the implementation-specific requirements of MU-MIMO WLANs, such as fairness in client access and throughput of the network, we propose a fairness and a throughput-aware ZF precoding in our design at the physical layer (PHY). This precoding scheme not only solves the HT problem but also meets the fairness and the throughput requirements of MU-MIMO WLANs. Besides, we design a MAC layer protocol, supportive to PHY, which decides transmission opportunities (TXOPs) among access points (APs) based on the available degrees of freedom (DoF). We make a mandatory provision in our design that APs should have a sufficient DoF. This can ensure collision-free transmission whenever APs/transmitters transmit in the HT scenario. Additionally, we design an improved channel sounding process for MU-MIMO WLANs with a less signaling overhead than IEEE802.11ac. We demonstrate the feasibility of our PHY in a USRP2/GNU Radio testbed prototype in the lab settings. It is found that our PHY improves the SNR and effective SNR of the received signal from about 5 to 11 dB in the HT scenario. The performance of our MAC design is checked with simulation studies in a typical six-antenna AP and clients scenario. We observe that our MAC protocol has a slightly higher signaling overhead than traditional ready to send/clear to send (RTS/CTS) due to design constraints; however, the signaling time overheads are reduced by 98.67 μs compared to IEEE802.11ac. Another interesting aspect to highlight is the constant Throughput gain of four to five times that of the traditional RTS/CTS. Our MAC protocol obtains this gain as early as 98.67 μs compared to IEEE802.11ac

Wi-Fi QoS improvements for industrial automation

Digitalization caused a considerable increase in the use of industrial automation applications. Industrial automation applications use real-time traffic with strict requirements of connection of tens of devices, high-reliability, determinism, low-latency, and synchronization. The current solutions meeting these requirements are wired technologies. However, there is a need for wireless technologies for mobility,less complexity, and quick deployment. There are many studies on cellular technologies for industrial automation scenarios with strict reliability and latency requirements, but not many developments for wireless communications over unlicensed bands. Wireless Fidelity (Wi-Fi) is a commonly used and preferred technology in factory automation since it is supported by many applications and operates on a license free-band. However, there is still room for improving Wi-Fi systems performance for low-latency and high-reliable communication requirements in industrial automation use cases. There are various limitations in the current Wi-Fi system restraining the deployment for time-critical operations. For meeting the strict timing requirements of low delay and jitter in industrial automation applications, Quality of Service (QoS)in Wi-Fi needs to be improved. In this thesis, a new access category in Medium Access Control (MAC) layer for industrial automation applications is proposed.The performance improvement is analyzed with simulations, and a jitter definition for a Wi-Fi system is studied. Then, a fixed Modulation and Coding (MCS) link adaptation method and bounded delay is implemented for time-critical traffic in the simulation cases to observe performance changes. Finally, it is shown that the new access category with no backoff time can decrease the delay and jitter of time-critical applications. The improvements in Wi-Fi QoS are shown in comparison with the current standard, and additional enhancements about using a fixed modulation and coding scheme and implementation of a bounded delay are also analyzed in this thesi

QoS based Radio Resource Management Techniques for Next Generation MU-MIMO WLANs: A Survey

IEEE 802.11 based Wireless Local Area Networks (WLANs) have emerged as a popular candidate that offers Internet services for wireless users. The demand of data traffic is increasing every day due to the increase in the use of multimedia applications, such as digital audio, video, and online gaming. With the inclusion of Physical Layer (PHY) technologies, such as the OFDM and MIMO, the current 802.11ac WLANs are claiming Gigabit speeds. Hence, the existing Medium Access Control (MAC) must be in a suitable position to convert the offered PHY data rates for efficient throughput. Further, the integration of cellular networks with WLANs requires unique changes at MAC layer. It is highly required to preserve the Quality of Service (QoS) in these scenarios. Fundamentally, many QoS issues arise from the problem of effective Radio Resource Management (RRM). Although IEEE 802.11 has lifted PHY layer aspects, there is a necessity to investigate MAC layer issues, such as resource utilization, scheduling, admission control and congestion control. In this survey, a literature overview of these techniques, namely the resource allocation and scheduling algorithms are briefly discussed in connection with the QoS at MAC layer. Further, some anticipated enhancements proposed for Multi-User Multiple-Input and Multiple-Output (MU-MIMO) WLANs are discussed