Since the inception of IEEE 802.11 wireless local area networks (WLANs) in 1997, wireless networking technologies have tremendously grown in the last few decades. The fundamental IEEE 802.11 physical (PHY) and medium access control (MAC) protocols have continuously been enriched with new technologies to provide the last mile wireless broadband connectivity to end users. Consequently, several new amendments of the basic IEEE 802.11 gradually came up in the forms of IEEE 802.11a, IEEE 802.11b, and IEEE 802.11g. More recently, IEEE 802.11n, IEEE 802.11ac, and IEEE 802.11ad are introduced with enhanced PHY and MAC layers that boost up physical data rates to the order of Gigabit per second. So, these amendments are generally known as high throughput WLANs (HT-WLANs). In HT-WLANs, PHY layer is enhanced with multiple-input multiple-output antenna technologies, channel bonding, short guard intervals, enhanced modulation and coding schemes. The MAC sublayer overhead is reduced by introducing frame aggregation and block acknowledgement technologies. However, several existing studies reveal that, many a time, the aforesaid PHY and MAC enhancements yield negative impact on various upper layer protocols, that is end-to-end transport and application layer protocols. As a consequence, a large number of researchers have focused on improving the coordination among PHY/MAC and upper layer protocols. In this survey, we discuss impact of HT-WLAN PHY and MAC layer enhancements on various transport and application layer protocols. This paper also summarizes several research works that use aforesaid enhancements effectively to boost up data rate of end-to-end protocols. We also point out limitations of the existing researches and list down different open challenges that can be meaningfully explored for the development of the next generation HT-WLAN technologies.

Impact of IEEE 802.11n/ac PHY/MAC High Throughput Enhancements on Transport and Application Protocols—A Survey

IEEE 802.11n/ac wireless local area network (WLAN) supports frame aggregation, called aggregate medium access control (MAC) protocol data unit (A-MPDU), to enhance MAC efficiency by reducing protocol overhead. However, the current channel estimation process conducted only once during the preamble reception is known to be insufficient to ensure robust delivery of long A-MPDU frames in mobile environments. To cope with this problem, we first build a model which represents the impact of mobility with a noise vector in the I-Q plane, and then analyze how the mobility affects the A-MPDU reception performance. Based on our analysis, we develop STRALE, a standard-compliant and mobility-aware PHY rate and A-MPDU length adaptation scheme with ease of implementation. Through extensive simulations with 802.11ac using ns-3 and prototype implementation with commercial 802.11n devices, we demonstrate that STRALE achieves up to 2.9x higher throughput, compared to a fixed duration setting according to IEEE 802.11 standard.

STRALE: Mobility-aware PHY rate and frame aggregation length adaptation in WLANs

Since the inception of Wireless Local Area Networks (WLANs) in the year 1997, it has tremendously grown in the last few years. IEEE 802.11 is popularly known as WLAN. To provide the last mile wireless broadband connectivity to users, IEEE 802.11 is enriched with IEEE 802.11a, IEEE 802.11b and IEEE 802.11g. More recently, IEEE 802.11n, IEEE 802.11ac and IEEE 802.11ad are introduced with enhancements to the physical (PHY) layer and medium access control (MAC) sublayer to provide much higher data rates and thus these amendments are called High Throughput WLANs (HT-WLANs). For both standards, PHY is enhanced with multiple-input multiple-output (MIMO) antenna technologies, channel bonding, short guard intervals (SGI), enhanced modulation and coding schemes (MCS). At the same time, MAC layer overhead is reduced by introducing frame aggregation and block acknowledgement technologies. However, existing studies reveal that although PHY and MAC enhancements promise to improve physical data rate significantly, they yield negative impact over upper layer protocols -- mainly for reliable end-to-end transport/application layer protocols. As a consequence, a large number of schools have focused researches on HT-WLANs to improve the coordination among PHY/MAC and upper layer protocols and thus, boost up the performance benefit. In this survey, we discuss the impact of enhancements of PHY/MAC layer in HT-WLANs over transport/application layer protocols. list down different open challenges that can be explored for the development of next generation HT-WLAN technologies.

Impact of IEEE 802.11n/ac PHY/MAC High Throughput Enhancements over Transport/Application Layer Protocols - A Survey.

IEEE 802.11 has evolved from 802.11a/b/g/n to 802.11ac in order to meet ever-increasing high throughput demand. The newest standard supports various channel widths up to 160 MHz by bonding multiple 20 MHz channels. In order to efficiently utilize multiple channel widths, 802.11ac defines two operations, namely, dynamic channel access (DCA) and dynamic bandwidth operation (DBO). In this paper, we reveal that the use of DCA improves channel utilization significantly, and DBO not only partly overcomes secondary channel hidden interference problems but also achieves better channel utilization. However, when a transmitter attempts to send an enhanced RTS frame before data transmission as part of DBO, the station has no way to know how much bandwidth will be used, thus leading to malfunction of virtual carrier sensing at neighboring stations. On the other hand, the use of enhanced RTS/CTS without hidden traffic wastes airtime significantly. To address these problems, we first define how to calculate an appropriate value of duration field for enhanced RTS/CTS, and then develop an algorithm which adaptively enables/disables DBO considering the (secondary) hidden interference. Through ns-3 simulations, we demonstrate that the proposed scheme achieves up to 2x higher throughput compared to the baseline of 802.11ac.

Enhancement of wide bandwidth operation in IEEE 802.11ac networks

State-of-the-art IEEE 802.11ac supports wide bandwidth operation, which enables aggregating multiple 20 MHz channels up to 160 MHz bandwidth, as a key feature to achieve high throughput. In this paper, our experiment results reveal various situations where bandwidth adaptation without changing the receiver's baseband bandwidth, called operating channel width (OCW), leads to poor reception performance due surprisingly to time-domain interference not overlapping with the incoming desired signal in frequency domain. To cope with this problem, we develop RECONN, a standard-compliant and receiver-driven OCWadaptation scheme with ease of implementation. Our prototype implementation in commercial 802.11ac devices shows that RECONN achieves up to 1.85× higher throughput by completely eliminating time-domain interference. To our best knowledge, this is the first work to discover the time-domain interference problem, and to develop OCW adaptation scheme in 802.11ac system.

RECONN: Receiver-Driven Operating Channel Width Adaptation in IEEE 802.11ac WLANs

A fundamental problem in 802.11 wireless networks is to accurately determine the cause of packet losses. This becomes increasingly important as wireless data rates scale to Gbps, where lack of loss differentiation leads to higher loss in throughput. Recent and upcoming high-speed WLAN standards, such as 802.11n and 802.11ac, use frame aggregation and block acknowledgements for achieving efficient communication. This paper presents BLMon, a framework for loss differentiation, that uses loss patterns within aggregate frames and aggregate frame retries to achieve accurate and low overhead loss differentiation. Towards this end, we carry out a detailed measurement study on a real testbed to ascertain the differences in loss patterns due to noise, collisions, and hidden nodes. We then devise metrics to quantitatively capture these differences. Finally, we design BLMon, which collectively uses these metrics to infer the cause of loss without requiring any out-of-band communication, protocol changes, or customized hardware support. BLMon can be readily deployed on commodity devices using only driver-level changes at the sender-side. We implement BLMon in the ath9k driver and using real testbed experiments, show that it can provide up to 5!improvement in throughput.

Loss Differentiation: Moving onto High-Speed Wireless LANs

An important problem in 802.11 wireless networks is to accurately differentiate between losses while incurring low overhead. Lack of loss differentiation can result in throughput degradation, which becomes increasingly severe as data rates scale up. This paper presents BLMon, a loss differentiation scheme for 802.11n networks that leverages loss patterns in aggregate frames and frame retries to distinguish between losses. BLMon achieves high accuracy, incurs low overhead and does not require any protocol changes or customized hardware support.

Haseeb Niaz

Papers

Loss Differentiation: Moving onto High-Speed Wireless LANs

BLMon: A Loss Differentiation Scheme for 802.11n