Scheduling strategies and throughput optimization for the Downlink for IEEE 802.11ax and IEEE 802.11ac based networks

The new IEEE 802.11 standard, IEEE 802.11ax, has the challenging goal of serving more users compared to its predecessor IEEE 802.11ac, enabling consistent and reliable streams of data (average throughput) per station. In this paper we explore some of the IEEE 802.11ax new mechanisms and compare between the upper bounds on the throughputs of the Downlink unidirectional UDP Multi Users (MU) triadic based on Multiple-Input-Multiple-Output (MU-MIMO) and Orthogonal Frequency Division Multiple Access (OFDMA) transmission multiplexing format in IEEE 802.11ax vs. IEEE 802.11ac in the Single User (SU) and MU modes for 1, 4, 8, 16, 32 and 64 stations scenario in reliable and unreliable channels. The comparison is made as a function of the Modulation and Coding Schemes (MCS) in use. In IEEE 802.11ax we consider two flavors of acknowledgment operation settings where the maximum acknowledgment windows are 64 or 256 respectively. In SU scenario IEEE 802.11ax upper bounds on the throughputs outperform IEEE 802.11ac by about 52% and 74% in reliable and unreliable channels respectively. In MU-MIMO scenario IEEE 802.11ax upper bounds on the throughputs outperform IEEE 802.11ac by about 59% and 103% in reliable and unreliable channels respectively. Also, as the number of stations increases, the advantage of IEEE 802.11ax in terms of the access delay also increases.


Introduction
The latest IEEE 802.11 Standard (WiFi) [1], created and maintained by the IEEE LAN/MAN Standards Committee (IEEE 802.11), is currently the most effective solution within the range of Wireless Local Area Networks (WLAN). Since its first release in 1997 the standard provides the basis for Wireless network products using the WiFi brand, and has since been improved upon in many ways. One of the main goals of these improvements is to increase the throughput achieved by users and to improve the standard's Quality-of-Service (QoS) capabilities. To fulfill the promise of increasing IEEE 802.11 performance and QoS capabilities, a new amendment, IEEE 802.11ax ( also known as High Efficiency (HE) ) was recently introduced [2]. IEEE 802.11ax is considered to be the sixth generation of a WLAN in the IEEE 802.11 set of types of WLANs and is a successor to IEEE 802.11ac [3,4]. The scope of the IEEE 802.11ax amendment is to define modifications for both the 802.11 PHY and MAC layers that enable at least four-fold improvement in the average throughput per station in densely deployed networks [5][6][7][8]. Currently IEEE 802.11ax project is in a very early stage of development, due to be publicly released in 2019 .
In order to achieve its goals, one of the main challenges of IEEE 802.11ax is to enable simultaneous transmissions by several stations and to enable Quality-of-Service. Most of the research papers on IEEE 802.11ax thus far deal with these challenges and examine different access methods to enable efficient multi-user access to random sets of stations. For example, in [9] the authors deal with the introduction of Orthogonal Frequency Division Multiple Access (OFDMA) into IEEE 802.11ax to enable multi user access. They introduce an OFDMA based multiple access protocol, denoted Orthogonal MAC for 802.11ax (OMAX), to solve synchronization problems and reduce overhead associated with using OFDMA. In [10] the authors suggest an access protocol over the UL of an IEEE 802.11ax WLAN based on Multi User Multiple-Input-Multiple-Output (MU-MIMO) and OFDMA PHY. In [11] the authors suggest a centralized medium access protocol for the UL of IEEE 802.11ax in order to efficiently use the transmission resources. In this protocol, stations transmit requests for frequency sub-carriers, denoted Resource Units (RU), to the AP over the UL. The AP allocates RUs to the stations which use them later for data transmissions over the UL. In [12] a new method to use OFDMA over the UL is suggested, where MAC Protocol Data Units (MPDU) from the stations are of different lengths. In [13][14][15][16] a new version of the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol, denoted Enhanced CSMA/CA (CSMA/ECA) is suggested, which is suitable for IEEE 802.11ax . A deterministic backoff is used after a successful transmission, and the backoff stage is not reset after service. The backoff stage is reset only when a station does not have any more MPDUs to transmit. CSMA/ECA enables a more efficient use of the channel and enhanced fairness.
In [17] the authors assume a network with legacy and IEEE 802.11ax stations and examine fairness issues between the two sets of the stations.
In this paper we do not suggest any new air access mechanisms as the papers mentioned above do, but assume that the AP is communicating in a regular fashion with a fixed set of stations. The AP and the stations transmit in a Round Robin fashion, without collisions. We explore some of the Downlink (DL) and UL IEEE 802.11ax new mechanisms given that the AP knows with which stations it communicates, and we compare between the upper bounds on the unidirectional UDP throughputs of IEEE 802.11ax and IEEE 802.11ac in Single User (SU) and Multi User (MU) modes for 1,4,8,16,32 and 64 stations scenarios in reliable and unreliable channels. This is one of the aspects to compare between new amendments of the IEEE 802.11 standard [18]. We note that we do not assume that all the time over the channel is devoted to UDP DL traffic. It is possible that time is partitioned into intervals of UDP DL traffic, UDP UL traffic, TCP traffic etc. In this paper we investigate transmissions in the time interval decvoted to UDP DL traffic.
In this paper we are interested in finding the upper bounds on the throughputs that can be achieved by IEEE 802.11ax and IEEE 802.11ac and in comparing between the two. Therefore, we assume the traffic saturation model where all stations always have data to transmit. Second, we neutralize any aspects of the PHY layer as the relation between the Bit Error Rates (BER) and the Modulation/Coding Scheme (MCS) in use, the number of Spatial Streams (SS) in use, the channel correlation when using MU-MIMO, i.e. we assume that there are independent MU-MIMO channels for each station, the use in sounding protocol etc.
The SU scenario implements sequential transmissions in which a single wireless station sends and receives data at every cycle one at a time, once it or the AP has gained access to the medium. The MU scenarios allow for simultaneous transmission and reception to and from multiple stations both in the DL and the UL directions. UL  of RUs in use, which influences the PHY preamble's length. This paper deals with the DL and a companion paper deals with the UL [19]. The difference between the two papers is in the direction in which data is transmitted: in the current paper the AP transmits data to the stations, while in [19] the stations transmit data to the AP. As an outcome, the current paper suggests scheduling strategies for the transmission of data on the DL, while [19] suggests scheduling strategies for the transmission of data on the UL. The strategies in the two papers are different, using different features of the IEEE 802.11ax amendment, e.g. different control frames.
The remainder of the paper is organized as follows: In Section 2 we describe the new mechanisms of IEEE 802.11ax relevant to this paper. In Section 3 we describe the transmission scenario by which we compare IEEE 802.11ax and IEEE 802.11ac in the SU and MU modes. We assume that the reader is familiar with the basics of the PHY and MAC layers of IEEE 802.11 described in previous papers, e.g. [20]. In Section 4 we analytically compute the IEEE 802.11ax and IEEE 802.11ac throughputs. In Section 5 we make some approximations on the amount of frame aggregation used in our transmission model. In Section 6 we present the throughput of the various protocols and compare them. Section 7 summarizes the paper. Lastly, we denote IEEE 802.11ac and IEEE 802.11ax by 11ac and 11ax respectively.

The new features in IEEE 802.11ax
IEEE 802.11ax focuses on implementing mechanisms to efficiently serve more users, enabling consistent and reliable streams of data ( average throughput per user ) in the presence of multiple users. Therefore, there are several new mechanisms in 11ax compared to 11ac both in the PHY and MAC layers. At the PHY layer, 11ax enables larger OFDM FFT sizes-4X larger-therefore every OFDM symbol is extended from 3.2µs in 11ac to 12.8µs in 11ax.
By narrower subcarrier spacing (4X closer) the protocol efficiency is increased, as the same Guard Interval (GI) is used in both 11ax and 11ac .
To increase the average throughput per user in high-density scenarios, 11ax expands the 11ac Modulation Coding Schemes (MCSs) and adds MCS10 (1024 QAM ) and MCS 11 (1024 QAM 5/6), applicable for transmission with bandwidth larger than 20 MHz.
In this paper we focus on optimizing the IEEE 802.11 two-level aggregation scheme working point first introduced in IEEE 802.11n [1,4] In 11ax and 11ac the size of an MPDU is limited to 11454 bytes. In 11ac an A-MPDU is limited to 1,048,575 bytes and this limit is extended to 4,194,304 bytes in 11ax. In both 11ac and 11ax the transmission time of the PPDU (PSDU and its preamble) is limited to 5.484ms (5484µs) due to the L-SIG (one of the legacy preamble's fields) duration limit [1].
The A-MPDU frame structure in two-level aggregation is shown in Figure 1.
11ax also enables extension of the acknowledgment mechanism by using a 256 maximum acknowledgment window vs. maximum window of 64 in 11ac. In this paper we also assume that all MPDUs transmitted in an A-MPDU frame are from the same Traffic Stream (TS).
In this case up to 256 MPDUs are allowed in an A-MPDU frame of 11ax, while in 11ac up to only 64 MPDUs are allowed.
Finally, in 11ac it is possible to transmit simultaneously up to 4 stations only over the DL using MU. In 11ax this number is extended to 74. Also, in 11ax it is possible to transmit by MU-MIMO or OFDMA both over DL and UL, while in 11ac only UL SU mode is supported.

Transmission patterns
As mentioned, one of the main goals of 11ax is to enable larger throughputs in the network when transmitting to several stations. In 11ax it is possible to transmit/receive simultaneously to/from 74 stations over the DL/UL while in 11ac the number of stations is limited to 4, and only over the DL. In this paper we compare the throughputs received in 11ac and 11ax when transmitting to S stations, S = 1, 4, 8, 16, 32 and 64 stations. Transmitting to one station only is done by using the SU mode of transmissions. The AP transmits to one station and receives a Block Ack (BAck) frame in return. In this mode the advantage of 11ax over 11ac is in its more efficient PHY layer and its new MCSs. The unscheduled SU traffic pattern in this case is shown in Figure 2(A) for both 11ac and 11ax.
Transmitting to several stations can be done in two ways. The first is by SU mode.
When transmitting to S stations, the transmission cycle in Figure 2  times. Another alternative is to use MU mode in which the AP transmits simultaneously to several stations in the same transmission opportunity over the channel. In Figure 2  other. This is possible by e.g. configuring the stations in a way that prevents collisions.
For example, the stations are configured to choose their BackOff intervals from very large contention interval, other than the defaults ones [1]. Thus, the AP always wins the channel without collisions.

DL service transmissions' scheduling strategies
There are several DL service scheduling strategies to transmit to a group of stations, and we compare between them. We now specify these scheduling strategies for every number S of stations, S = 1, 4, 8, 16, 32, 64. By x · SU AX (1) and x · SU AC (1) we denote a transmission to n stations in 11ax and 11ac respectively, using the transmission pattern in Figure 2(A) x times in sequence, every transmission is to a different station. By x · MU AC (4) we denote transmissions to 4x stations using the traffic pattern of Figure 2 The DL service scheduling strategies are as follows: • S = 1: 11ac : 1 · SU AC (1) .

Channel assignment
We assume the 5GHz band, a 160MHz channel, the AP has 4 antennas and every station has 1 antenna. In SU(1) and in the DL direction the entire channel is devoted to transmissions of the AP in both 11ac and 11ax . In UL SU the BAck frame is transmitted by using the legacy PHY basic rates. Therefore the UL Ack is sent at legacy mode where the station is transmitting in a 20 MHz primary channel and its transmission is duplicated 8 times in order to occupy the entire 160 MHz. The UL PHY rate is set to the largest possible PHY rate in the set that is smaller or equal to the DL Data rate.
When using MU mode the 160MHz channel is divided into In the case of UL OFDMA the 160 MHz channel is divided into S channels of 160 S MHz each, except in the case of S = 64 where each station is allocated a channel of 2 MHz.

PPDU formats
In Figure  there are the HE-LTF fields, the number of which equals again to the number of SS in use. In this paper we assume that each such field is composed of 2X LTF and therefore of duration 7.2µs [2]. Notice that in SU mode and when using the same number X of SS, the preamble in 11ax is longer than that in 11ac by 4µs + X · (7.2 − 4)µs = 4µs + X · 3.2µs.
Notice also that the PSDU frame in 11ax contains a Packet Extension (PE) field. This field is mainly used in Multi-User (MU) mode and we assume it is not present in SU, i.e. it is of length 0µs.
In The MCS used in the HE-SIG-B field is the minimum between MCS4 and the one used for the data transmissions [2]. The length of this field is also a function of the number of  stations to which the AP transmits simultaneously. Therefore, in the case of e.g. 4 stations the HE-SIG-B field duration is 8µs for MCS0 and MCS1, and is 4µs for MCS2-4 following section 29.3.9.8 in [2]. For MCS5-MCS11 it is 4µs as for MCS4.
In Figure 4(D) we show the PPDU format used in UL MU in 11ax which is used in the traffic pattern of Figure 2(C). Notice again that in 11ax the PSDU is followed by a Packet Extension (PE) field which is used to enable the receiver of the PSDU additional time to move from a reception mode to a transmission mode. The largest duration of this field is 16µs which we assume in this paper.

Parameters' values
In Table 1 we show the PHY rates and the preambles used in 11ac and 11ax in SU mode and in the various MCSs. In Table 2 we show the PHY rates and the preambles used in 11ac  · SlotT ime which equals 67.5µs for a SlotT ime = 9µs. We also assume that the MAC Header is of 28 bytes and the FCS is of 4 bytes. We use the above values for the various parameters since these are the default ones suggested by the WiFi Alliance [21].
Finally, we consider several channel conditions which are expressed by different values of the Bit Error Rate (BER) which is the probability that a bit arrives corrupted at the destination. We assume a model where these probabilities are bitwise independent [22].   In the entire analysis ahead we assume that the Ack frames' transmissions are all successful because Ack frames are short and in most cases are transmitted in legacy mode.

Single User mode
The throughput in both 11ax and 11ac for the traffic pattern in Figure 2(A) is given by Eq. 1 [20] where BER is the Bit Error Rate: where: The term BO(average) refers to the average value of the BackOff interval, as given in Section 3.5. As was explained in Section 3.5 we use an average value for this interval since there are no collisions.
T (DAT A) and T (BAck) are the transmission times of the data A-MPDU frames and BAck frames respectively. T (BAck) is based on the BAck frame's lengths given in Figure 3.
When assuming 30 bytes we consider the acknowledgment of 64 MPDUs in the BAck.
T Sym DL and T Sym U L are the lengths of the OFDM symbols on the DL and the UL respectively, and every transmission must be of an integral number of OFDM symbols. The additional 22 bits in the numerators of T (DAT A) and T (BAck) are due to the SERVICE and TAIL fields added to every transmission by the PHY layer conv. protocol [1]. R DL and R U L are the DL and UL PHY rates respectively and P DL and P U L are the preambles used in the DL and in the UL respectively (see Figure 4).
The term in Eq. 1 is not continuous, so it is difficult to find the optimal X and Y i(s), i.e. the values for X and Y i(s) that maximize the throughput. However, in [20] it is shown If neglecting the rounding of the denominator of Eq. 1, the received throughput for every X and Y (Y is the equal number of MSDUs in MPDUs) is as large as that received in Eq. 1.
The difference depends on denominator size.
We therefore use the result in [20] and look for the maximum throughput as follows: We check for every X, 1 ≤ X ≤ 64 (also 1 ≤ X ≤ 256 for 11ax) and for every Y , 1 ≤ Y ≤ than the others, up to the above upper limit on the transmission time. We found that the smallest denominator of any of the maximum throughputs is around 1000µs. Neglecting the rounding in the denominator reduces its size by at most 2 · 13.6µs in 11ax and 2 · 4µs in 11ac. Thus, the mistake in the received maximum throughputs is at most 2.8%.

Multi User mode
The throughputs of 11ac and 11ax are given in Eq. 3-6 and their derivation can be found in [20].
The throughput of 11ac for the traffic pattern in Figure 2(B) is given in Eq. 3: where: are the transmission times of the data A-MPDU frames, the BAck frames and the BAR frames respectively. The transmission times of the BAck and BAR frames are based on their lengths given in Figure 3. R DL is the DL PHY rate and R U L is the UL PHY rate. We have the multiplier of 4 in the numerator of Eq. 3 since the AP transmits simultaneously to 4 stations. Also, P DL and P U L are the lengths of the preambles in the DL and in the UL respectively and T Sym DL and T Sym U L are the lengths of the OFDM symbols used in the DL and UL respectively.
The throughput of 11ax for the traffic pattern in Figure 2(C) is given in Eq. 5: where: T ′ (BAck) = T Sym U L · (30 · 8) + 22 T Sym U L · R U L P DL and P U L are again the preambles in the DL and UL respectively. Again, the terms in Eqs. 3 and 5 are not continuous and therefore we again use the result in [20], as in the SU mode, and look for the maximum throughput as specified in Section 4.1 .
The analytical results of 11ax have been verified by an 11ax simulation model running on the ns3 simulator [24] and the simulation and analytical results are the same. This outcome is not surprising however, because there is not any stochastic process involved in the scheduled transmissions in 11ax assumed in this paper. Therefore, we do not mention the simulation results any further in this paper.

An approximation of the optimal A-MPDU structure
In this section we show an approximation to the value of X OP T , the number of optimal MPDUs in an A-MPDU, i.e. the number of MPDUs that maximizes the throughput, as a function of the BER. We concentrate on 11ax although the computation is valid for 11ac as well.

The case BER>0
We re-write Eq.
Notice that given a number Y of MPDUs in an A-MPDU, the throughput increases as X increases. Therefore, it is worthwhile to transmit as large A-MPDUs as possible, up to the limit on the transmission time of the A-MPDU frame. Let T be this limit, 5484µs in our case. Then, the following approximation on the relation between X and Y can be written: or: In Eqs. 8 and 9 we approximate that the sum of the A-MPDU transmission time plus the DL preamble is T .
We now substitute the term for X in Eq. 7 by the term in Eq. 9 and receive: Notice that the denominator of Eq. 10 is a constant and so to find the maximum throughput as a function of Y one needs to find the maximum of the following function: The optimal Y , Y OP T , is given in Eq. 12: Notice that by Eq. 9 we can now write the optimal X, X OP T , as: Notice that we look for an integer Y OP T and that Y OP T must be at least 1. Therefore, Eq. 13 is only an approximation for X OP T .

The case BER=0
For BER=0 Eq. 7 becomes: and one needs to optimize the function: which reveals that in every MPDU it is worthwhile to contain the maximum number of Therefore: 6 Throughput's models and results

Transmissions' models and scenarios
We compare between all applicable configurations and DL service scheduling flavors of the AP transmissions to up to 64 stations. The service scheduling flavors are as follows: Concerning 11ac : • DL SU, UL SU Back transmission in legacy mode, up to 64 MPDUs in an A-MPDU frame, denoted previously as SU AC (1).

• DL 4 users MU-MIMO, UL 4 times SU BAck transmission in legacy mode, up to 64
MPDUs in an A-MPDU frame, denoted previously as MU AC (4).
In the next section we show three sets of results. In Figure 6

Throughput results
Recall that in Figure 6  We see from Figure 6(A) that the largest throughput is received in MU AX (4). Notice that the throughout of MU AX (8) is only slightly smaller than that of MU AX (4). From Table 2 one can see that the PHY rates in MU AX (8) are half of those of MU AX (4). This is balanced by twice the number of stations to which the AP transmits. However, in MU AX (4) 522 MSDUs are transmitted in an A-MPDU frame compared to 520 MSDUs in MU AX (8). Also, the DL preamble in MU AX (8) is slightly larger than in MU AX (4) due to the HE-SIG-B field.
These two factors reduce the throughput of MU AX (8) compared to MU AX (4).
In MU AX (16) the PHY rates are less than half of those in MU AX (8) and together with the larger preamble this explains why MU AX (16) has a smaller throughput than MU AX (8) and MU AX (4). The explanation for the throughputs of MU AX (32) and MU AX (64) is similar to those given above for MU AX (8) and MU AX (16). Notice that the PHY rates in MU AX (64) are less than half of those of MU AX (32) and also that MCS10 and MCS11 are not applicable for MU AX (64), which is a main factor in the sharp decrease in the throughput of MU AX (64) compared to MU AX (32).
Notice also that for all stations 11ax outperforms 11ac due to larger PHY rates and simultaneous transmissions of BAck frames in the UL compared to sequential transmissions in legacy mode in 11ac . For 4,8,16, 32 and 64 stations and using MU-MIMO, 11ax outperforms 11ac by 59%, 4470 vs. 2808 Mbps, the throughputs in MU AX (4) and MU AC (4) respectively. In SU when transmitting to 1 station only, 11ax outperforms 11ac by 52%, 1133 vs. 742 Mbps.
Although the throughput metric is important, so is the access delay metric, defined in this paper as the time elapsed between two consecutive transmissions from the AP to the same station. Notice for example that in the case of MU AX (4) that achieves the largest throughput, the access delay in the case of 64 stations is 16 times the cycle of Figure 2(C) while in MU AX (64) the access delay is only one such cycle. Notice also that we refer here to the access delay and not to the packet delay. Since there are retransmissions in the IEEE 802.11 MAC, the packet delay is defined as the delay since a packet is first transmitted and until it is successfully received.
In Figure 6(B) we show the access delays for the various DL service scheduling transmissions' flavors. Some applications benefit primarily from lower latency, especially real-time streaming applications such as voice, video conferencing or even video chat. The trade-off between latency and throughput becomes more complex as applications are scaled out to run in a distributed fashion. The access delay results are as expected; the access delay is lower when the AP transmits simultaneously to additional stations . It seems that the cycles are about the same in length in all DL service scheduling transmissions' flavors and the relation between access delays is about the same between the number of stations to which the AP transmits simultaneously.
In Figures 6(C) and 6(D) we show the results for BER=10 −6 . There are some trends in this BER that become more prominent in BER=10 −5 so we concentrate now only on BER=10 −5 .
In Figure 6(E) we show the maximum throughput as a function of the number of stations for the case BER=10 −5 . An interesting difference compared to BER=0 is that the best transmission flavor is MU AX (8) compared to MU AX (4) in BER=0. MU AX (8) outperforms MU AX (4) due to the short MPDUs and its smaller PHY rates. The optimal A-MPDU frame structure in both DL service scheduling flavors is 255 MPDUs of one MSDU each.
In MU AX (4) a cycle lasts 2.944ms and in MU AX (8) it is 5.583ms. In MU AX (8) twice the number of MSDUs are transmitted than in MU AX (4), but this is done in less than twice the cycle length of MU AX (4) due to equal overhead in both DL service scheduling flavors.
This leads to a larger throughput in MU AX (8). In BER=0 the cycle length of MU AX (4) is 5.596ms compared to 5.583ms in MU AX (8), i.e. about the same. However, the number of MSDUs in MU AX (4) is slightly larger than twice the number of MSDUs in MU AX (8) (522 vs. 520) and the preamble is slightly shorter. Therefore in BER=0 MU AX (4) has a slightly larger throughput.
When comparing between the throughputs of MU AX (8)  Overall it can be concluded from Figure 6 that there is not any one best flavor. For example, MU AX (8) achieves the maximum throughput but MU AX (16) and MU AX (32) also achieve high throughput but with smaller access delays compared to MU AX (8).
In Figure 7 we show the throughput optimization performance of MU AX (4) and In BER=0 it is efficient to transmit large MPDUs. Therefore, the limit on the A-MPDU frame size is imposed by the limit of 5.484ms on the transmission time of the PPDU. Only in larger PHY rates there is room for more than 64 MPDUs and in these cases 11ax/256 has an advantage over 11ax/64 . In BER=10 −5 it is efficient to transmit short MPDUs.
In this case the significant limit is the number of MPDUs. 11ax/256 outperforms 11ax/64 from MCS2 because it enables transmitting more short MPDUs than 11ax/64 . A detailed analysis of this phenomenon can be found in [23].
Another interesting phenomenon is the relation between UL MU-MIMO and UL OFDMA. When using UL OFDMA the UL PHY rates are much smaller than those in UL MU-MIMO (see Table 2). However

Summary
In this paper we compare between DL service scheduling flavors to optimize throughputs of 11ac and 11ax over the DL when considering UDP like traffic and several DL service scheduling stations are transmitting in the system. We also consider several transmission flavors in 11ac and 11ax using MU-MIMO and OFDMA. We look for upper bounds on the throughput received at the MAC layer after neutralizing any aspects of the PHY layer as the relation between the BER and the MCSs in use, the number of Spatial Streams (SS) in use, channel correlation when using MU-MIMO, the sounding protocol etc.   11ax outperforms 11ac by the order of several tenths of percentage because it enables simultaneous transmissions on both the DL and the UL while 11ac has this capability over the DL only, and for 4 stations only. Also, 11ax has larger PHY rates which also improve its efficiency compared to 11ac.
In 11ax there is not one best DL service scheduling transmission flavor. MU AX (8) achieves good results in terms of throughout, but MU AX (16) and MU AX (32) also achieve good throughput results, but with significantly smaller access delay. 11ax achieves its best throughputs in MCS11 in the case of up to 32 stations, and in MCS9 in the case of 64 stations.