Interactive and access protocol may help support many simulta- Backward Compatibility:Because WLANs high-definition video neous contenders. implementing IEEE 802.11ax-2019 must also Finally,in an apartment building,we can support devices using any previous IEEE 802.11 applications are find multiple autonomous and heterogeneous PHY/MAC amendments,mechanisms must also predicted to dominate WLANs overlapping,including short-range be implemented to make it backward compatible WLANs that offer high transmission rates in (i.e.,common frame headers and transmission future Internet usage. small spaces [3].In this scenario,each WLAN rates),although it is a clear source of inefficien- Two examples of is primarily configured independent of the oth- cy. applications that require ers,where the channel selection,channel width. and transmission power are randomly set or are NEW FEATURES AND CONCEPTS throughputs of simply the preset values.Therefore,autonomous The IEEE 802.11ax-2019 amendment may several gigabits per sec WLANs must be able to implement smart decen- include some new technical features compared to the IEEE 802.11ac-2013 amendment.We ond are high-definition tralized self-configuration and self-adaptation mechanisms to minimize the interference among introduce them in this section,providing insight multi-party video them. into their potential performance gains and lim- WLANs must also coexist with other wireless conferences in business itations.All numerical results presented in this networks that operate in the industrial,scientific. section are obtained using the analytical model environments,and and medical (ISM)band,such as wireless sensor and parameters from [6],unless otherwise stated. virtual reality networks and personal area networks.In addi- tion,Long Term Evolution(LTE)operators are SPATIAL REUSE enterfainment currently considering deploying LTE networks in In dense scenarios,the combined use of CSMA/ applications af home, the ISM band [4],which is known as LTE-Un- CA,a conservative CCA,and a high transmit which indude culture, licensed,thus opening further coexistence chal- power level may result in scenarios with limit- lenges for WLANs. ed spatial reuse.A conservative configuration films,and games. of both the CCA and transmit power levels FUTURE WLAN USAGES minimizes the interference among the WLANs Interactive and high-definition video applica- which supports higher transmission rates.How- tions are predicted to dominate future Internet ever,the number of concurrent transmissions is usage.Two examples of applications that require reduced,which may decrease the achievable area throughputs of several gigabits per second are throughput.The alternatives that can be used to high-definition multi-party video conferences reach an optimal trade-off between individual in business environments,which can help avoid transmission rates and the number of concurrent unnecessary travel and meetings,and virtu transmissions that maximize the area throughput al reality entertainment applications at home, include dynamically adapting the transmit power which include culture,films,and games.Addi- level,the CCA level,and the use of direction- tionally,web surfing is moving further toward a al transmissions based on the observed network multimedia experience,where rich text,images, performance. audio,and video content interact.Furthermore, Figure 2a shows three neighboring WLANs. file storage,management,and synchronization The channels that each WLAN uses are shown in the cloud are becoming the standard in terms in Fig.2b.Because WLANs A and C.and B and of content management and generation.Those C partially share their channels,they overlap. applications are bandwidth-demanding,and The three APs are inside the carrier sense range require both reliability and limited delay. of the others,as shown in Fig.2a,which pauses their backoff if either of the other two transmits. REQUIREMENTS Although WLAN C uses the widest channel,it Based on the aforementioned scenarios and achieves the lowest throughput because it over- expected use cases,there are four key require- laps with WLANs A and B,which are indepen- ments for the IEEE 802.11ax-2019 amendment. dent of each other(Fig.2c). Coexistence:WLANs operate as unlicensed Dynamic Adaptation of the Transmit Power devices in the ISM bands.Therefore,the IEEE and CCA Levels:Reducing the used transmission 802.11ax-2019 amendment has to include the power in a WLAN reduces its influence area required mechanisms to coexist with both the which benefits the spatial reuse.However,it may other wireless networks that operate there and result in a larger number of packet errors and the licensed devices. lower transmission rates,as well as an increased Higher Throughput:Improving both the sys- number of hidden nodes. tem and user throughput requires the improved Alternatively,to reduce the area of influ- use of channel resources.IEEE 802.11ax-2019 ence of neighboring WLANs and increase each aims for a four-fold throughput increase com- WLAN's chances to transmit,the nodes in a pared to IEEE 802.11ac-2013.To achieve this WLAN may increase their CCA level,hence goal,some new wireless technologies such as requiring a higher energy level in the channel dynamic CCA,OFDMA (orthogonal frequen- to consider it as occupied and pause the backoff cy-division multiple access),and advanced multi- countdown.In [7],significant throughput gains ple-antenna techniques may be used. are achieved by tuning the CCA level in a multi- Energy Efficiency:The target in IEEE cell WLAN scenario.The downside of increasing 802.11ax-2019 is,at least,to not consume more the CCA level is again the higher interference energy than the previous amendments,consid- that a node may suffer,which could be detrimen ering the aforementioned four-fold throughput tal in some cases. increase,which requires both new low-power Beamforming:Omnidirectional transmissions hardware architectures [5]and new low-power homogeneously spread the transmitted energy in PHY/MAC functionalities. all directions,which fills the channel with energy IEEE Wireless Communications.February 201640 IEEE Wireless Communications • February 2016 access protocol may help support many simulta￾neous contenders. Finally, in an apartment building, we can find multiple autonomous and heterogeneous WLANs overlapping, including short-range WLANs that offer high transmission rates in small spaces [3]. In this scenario, each WLAN is primarily configured independent of the oth￾ers, where the channel selection, channel width, and transmission power are randomly set or are simply the preset values. Therefore, autonomous WLANs must be able to implement smart decen￾tralized self-configuration and self-adaptation mechanisms to minimize the interference among them. WLANs must also coexist with other wireless networks that operate in the industrial, scientific, and medical (ISM) band, such as wireless sensor networks and personal area networks. In addi￾tion, Long Term Evolution (LTE) operators are currently considering deploying LTE networks in the ISM band [4], which is known as LTE-Un￾licensed, thus opening further coexistence chal￾lenges for WLANs. Future WLAN Usages Interactive and high-definition video applica￾tions are predicted to dominate future Internet usage. Two examples of applications that require throughputs of several gigabits per second are high-definition multi-party video conferences in business environments, which can help avoid unnecessary travel and meetings, and virtu￾al reality entertainment applications at home, which include culture, films, and games. Addi￾tionally, web surfing is moving further toward a multimedia experience, where rich text, images, audio, and video content interact. Furthermore, file storage, management, and synchronization in the cloud are becoming the standard in terms of content management and generation. Those applications are bandwidth-demanding, and require both reliability and limited delay. Requirements Based on the aforementioned scenarios and expected use cases, there are four key require￾ments for the IEEE 802.11ax-2019 amendment. Coexistence: WLANs operate as unlicensed devices in the ISM bands. Therefore, the IEEE 802.11ax-2019 amendment has to include the required mechanisms to coexist with both the other wireless networks that operate there and the licensed devices. Higher Throughput: Improving both the sys￾tem and user throughput requires the improved use of channel resources. IEEE 802.11ax-2019 aims for a four-fold throughput increase com￾pared to IEEE 802.11ac-2013. To achieve this goal, some new wireless technologies such as dynamic CCA, OFDMA (orthogonal frequen￾cy-division multiple access), and advanced multi￾ple-antenna techniques may be used. Energy Efficiency: The target in IEEE 802.11ax-2019 is, at least, to not consume more energy than the previous amendments, consid￾ering the aforementioned four-fold throughput increase, which requires both new low-power hardware architectures [5] and new low-power PHY/MAC functionalities. Backward Compatibility: Because WLANs implementing IEEE 802.11ax-2019 must also support devices using any previous IEEE 802.11 PHY/MAC amendments, mechanisms must also be implemented to make it backward compatible (i.e., common frame headers and transmission rates), although it is a clear source of inefficien￾cy. New Features and Concepts The IEEE 802.11ax-2019 amendment may include some new technical features compared to the IEEE 802.11ac-2013 amendment. We introduce them in this section, providing insight into their potential performance gains and lim￾itations. All numerical results presented in this section are obtained using the analytical model and parameters from [6], unless otherwise stated. Spatial Reuse In dense scenarios, the combined use of CSMA/ CA, a conservative CCA, and a high transmit power level may result in scenarios with limit￾ed spatial reuse. A conservative configuration of both the CCA and transmit power levels minimizes the interference among the WLANs, which supports higher transmission rates. How￾ever, the number of concurrent transmissions is reduced, which may decrease the achievable area throughput. The alternatives that can be used to reach an optimal trade-off between individual transmission rates and the number of concurrent transmissions that maximize the area throughput include dynamically adapting the transmit power level, the CCA level, and the use of direction￾al transmissions based on the observed network performance. Figure 2a shows three neighboring WLANs. The channels that each WLAN uses are shown in Fig. 2b. Because WLANs A and C, and B and C partially share their channels, they overlap. The three APs are inside the carrier sense range of the others, as shown in Fig. 2a, which pauses their backoff if either of the other two transmits. Although WLAN C uses the widest channel, it achieves the lowest throughput because it over￾laps with WLANs A and B, which are indepen￾dent of each other (Fig. 2c). Dynamic Adaptation of the Transmit Power and CCA Levels: Reducing the used transmission power in a WLAN reduces its influence area, which benefits the spatial reuse. However, it may result in a larger number of packet errors and lower transmission rates, as well as an increased number of hidden nodes. Alternatively, to reduce the area of influ￾ence of neighboring WLANs and increase each WLAN’s chances to transmit, the nodes in a WLAN may increase their CCA level, hence requiring a higher energy level in the channel to consider it as occupied and pause the backoff countdown. In [7], significant throughput gains are achieved by tuning the CCA level in a multi￾cell WLAN scenario. The downside of increasing the CCA level is again the higher interference that a node may suffer, which could be detrimen￾tal in some cases. Beamforming: Omnidirectional transmissions homogeneously spread the transmitted energy in all directions, which fills the channel with energy Interactive and high-definition video applications are predicted to dominate future Internet usage. Two examples of applications that require throughputs of several gigabits per sec￾ond are high-definition multi-party video conferences in business environments, and virtual reality entertainment applications at home, which include culture, films, and games