# 10 November 2021 - Daily Report
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## Goals

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Checklists:
- [ ] Summarizing 802.11ax background from aruba white paper
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Reference :
[Aruba White Paper](https://www.arubanetworks.com/assets/wp/WP_802.11AX.pdf)
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## Report
### Aruba White Paper
#### Background
Wi-Fi is by now the established way to access the internet, whether at home or at work, from PCs of Cellphones. The figure below shows Wi-Fi Device Annual Shipments.
We can clearly see the increasing demand of Wi-Fi device shipments each year.

Wi-Fi standards originated from IEEE 802.11 working group meeting 6 times every year. They developed and improved Wi-Fi standard overtime starting from 802.11a until now the 802.11ax. The graph below shows shipment of different wifi technology from few recent years.

The goals of 802.11ax Wi-Fi standards is to improve Wi-Fi beyond the previous release : 802.11ac. The working group (IEEE) and Wi-Fi Alliance surveyed Wi-Fi deployments and usage, to identify impediments to wider use and causes of dissatisfaction among user communities.

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The conclusion stated that they will upgrade the advanced peak data-rates under 'good' field conditions and to focus more on 'actual' field conditions and how to improve not just peak performance but also average & worst-case performance in real world conditions.
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#### key features
Some key features of 802.11ax standard are:
- Coordinating multiple access point to reduce interference in areas with overlapping coverage
- Efficient allocation of low data-rate connection for the growing market of Internet-of-Things (IoT) sensors using Wi-Fi for connectivity

The 802.11ax is scheduled to commercial use in mid-to-late 2018. By 2021, many devices already adapted 802.11ax standard.

Some **major features** in 802.11ax are:
1. Downlink and Uplink OFDMA
2. Downlink and upling MU MIMO
3. Higher order modulation (1024 QAM)
4. Advanced OFDM and coding
5. Outdoor operation
6. Reduced Power consumption
7. Spatial re-use
8. Transmit beamforming
9. Single-user ooperation

##### **Downlink and Uplink OFDMA**
OFDMA is one of the more complex features in 802.11ax which allows a single transmission to be split by frequency within a channel, such that different frames addressed to different client devices use groups of subcarriers. Uplink OFDMA is equivalent to downlink OFDMA, but multiple client devices transmit simultaneously on different groups of subcarriers within the same channel. Uplink OFDMA is more difficult to manage than the downlink variety as many different clients must be coordinated. The access point transmits trigger frames to indicate which sub-channels each client can use.

##### **Downlink and uplink multi-user MIMO**
The downlink version extends and existing 802.11ac feature where an access point determines that multipath conditions allow it to send, in a single time-interval, frames to different client devices. 802.11ax increases the size of downlink MU-MIMO groups, allowing more efficient operation.
Uplink multi-user MIMO is a new addition to 802.11ax, but is deferred to wave 2. Like uplink OFDMA, the access point must coordinate the simulataneous transmissions of multiple clients.

##### **Transmit Beamforming**
Access point uses a number of transmit antennas to land a local maximum signal on a receiver's antennas. It improves data-rates and extends range.

##### **Higher-Order Modulation**
Introducing 1024 QAM. Increasing peak data-rates under good conditions (high SNR). OFDM symbols, subcarrier spacing and FFT size are all changed to allow efficient operation of small OFDMA sub-channels. These changes allow an increase in the length of guard interval.

##### **Outdoor Operation**
A number of features improve outdoor performance. The most important is a new packet format where the most sensitive field is now repeated for robustness. Longer guard interval also allow better performance by reducing error chance.

##### **Reduced Power Consumption**
Existing power-save modes are supplemented with new mechanisms allowing longer sleep intervals and shceduled wake times. For IoT devices, a 20MHz-channel-only mode is introduced, allowing for simpler, less powerful chips that supports only that mode.

#### Technical Features of 802.11ax
##### New subcarrier spacing and symbol duration
In 802.11ax, the subcarrier spacing is reduced by a factor of 4x while the OFDM symbol duration increases by 4x. This allows OFDMA to extend to small sub-channels. Each sub-channel requires at least one pilot subcarriers, and with a 2 MHz minimum sub-channel size, a smaller subcarrier spacing loses a much smaller percentage of the overall bandwidth to pilots.

The number of guard and null subcarriers across a channel can be reduced as a percentage of the number of usable subcarriers. Increasing the effective data rate in a given channel.

Then longer OFDM symbol allows for an increase in the cyclic prefix length without sacrificing spectral efficiency, which in turn enables increased immunity to long delay spreads especially in outdoor conditions. The cyclic prefix can be reduced to a smaller percentage of the symbol time.

The drawback is, the frequency accuracy required to successfully demodulate more closely-spaced subcarriers is more stringent. Also the FFT requires more complex chip.

##### OFDMA Advantage
OFDMA is one of two multi-user modes in 802.11ax. The other being MU-MIMO.
- Has been used in other system like cellular communication
- Dividing a transmission across the frequency dimension.
- Allows access point to bundle several frames together in different sub-channel in a single transmission.

##### Downlink multi-user MIMO transmission
- MU-MIMO extends concepts of spatial diversity and beamforming to support simultaneous transmission from an AP to a number of clients.
- MU-MIMO only possible where propagation characteristics allow the AP to identify that a transmission optimized for one client/group of clients will not be heard at a significant signal strength by another client and vice versa.

To identify candidates for MU-MIMO, the AP performs sounding operations, sending null frames from all its antennas to clients.
- Clients return response with matrices of the measured receive level for each AP-antenna to client-antenna pair.

##### Other Advantages
- High-order modulation
- Packet aggregation
- Power-save mechanism using TwT
- 20MHz-only operation for IoT

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## Comment

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## Further Plan

###### tags: `BMW-Lab` `Daily Report` `November 2021`