Design World – Power Transmission Reference Guide June 2019

eeworldonline.com | designworldonline.com 6 • 2019 DESIGN WORLD — EE NETWORK 15

W iFi 6

WHY IS MORE SPECTRUM NEEDED?

The availability of unlicensed spectrum in

the 2.4-GHz and 5-GHz bands has driven

Wi-Fi growth. It has lowered the barrier of

entry for new-comers and enabled low-

cost deployments that have made Wi-Fi

a ubiquitous local network connectivity

technology.

But it has also contributed to its woes,

as unlicensed spectrum is being shared by

a multitude of devices (including non-Wi-Fi

equipment using Bluetooth, Zigbee and

others) and forced the technology to make

compromises as it coexists with many users.

Additional unlicensed spectrum will address

the two main problems that users face:

Congestion – The low number of Wi-Fi

channels available today forces many users

to share available bandwidth and creates

congestion.

Restricted 80-MHz and 160-MHz channel

availability – Today the limited amount of

contiguous spectrum makes it difficult to

enable 80-MHz or 160-MHz channels, yet

high data throughput can only come when

wide channels are available.

CHANNEL CONGESTION

In Wi-Fi networks using Wi-Fi 5 (802.11ac)

or older Wi-Fi versions using OFDM

(orthogonal frequency-division multiplexing)

access technology, all devices connected

on the same channel split its capacity. When

connected on a channel with a high number

of devices, users will experience low data

throughput, as each one of them waits their

turn to transmit (or receive) data. Congestion

is caused by devices connected on the same

access point and sharing the same channel.

Though it may be less intuitive,

congestion is also caused by devices in

neighboring networks, on the same channel,

or on an overlapping channel. All these

devices compete for access to the same

RF channel spectrum. Channel congestion

is particularly problematic in dense urban

areas, airports, or stadiums where there are

Wi-Fi signals from hundreds of access points

and client devices.

The 2.4-GHz and 5-GHz frequency

bands support a limited number of non-

overlapping 20-MHz and 40-MHz channels.

Wi-Fi 5 and Wi-Fi 6 (802.11ax) standards

added support for an 80-MHz and 160-

MHz channel width to allow for higher data

speed. But in practice, the wider channels

are rarely deployed. Only six 80-MHz

and two 160-MHz channels are currently

available in the 5-GHz band.

In dense environments or large

enterprises, it’s hard to find an 80-MHz or

160-MHz channel free from interference

caused by devices on overlapping channels.

In response, network administrators often

choose to disable these capabilities, thereby

restricting the data speed available on their

network.

When considering the case of a two-

antenna (MIMO streams) client station

typically used with phones, laptops, and

tablets, the max achievable speed on a

40-MHz Wi-Fi 5 deployment is only 400

Mbps, while a Wi-Fi 6 deployment can only

hit a maximum of 574 Mbps at the physical

layer. At the TCP layer -- i.e. usable data

throughput -- the results are in the range of

60% to 70% of the above numbers.

It is obvious that spectrum availability

limits will quickly hamper Wi-Fi technology

evolution. Meanwhile, broadband access

speeds (DOCSIS, passive optical network,

fiber to the home) keep rising at a rapid

pace, and applications like video streaming,

VR/AR and gaming require more and more

bandwidth. Additionally, Wi-Fi is a critical

enabler of 5G technology; it likely will be

widely used for mobile-traffic offload and

providing 5G indoor coverage via FWA

(Fixed Wireless Access). In the near future,

with no improvements to the spectrum

availability, the Wi-Fi network may well

become a bottleneck as all services are

ultimately accessed via Wi-Fi.

IP traffic predictions from

the Cisco annual Mobile

Visual Networking Index.

IP traffic by access technology

26% CAGR

2017-

Mobile (46% CAGR)

Fixed/Wi-Fi from mobile devices (53% CAGR)

Fixed/Wi-Fi from Wi-Fi-only devices (18% CAGR)

Fixed/wired (15% CAGR)

48% from

mobile devices

51% is Wi-FI

Exabytes

per month

450

400

350

300

250

200

150

100

50

0

2017 2018 2019 2020 2021 2022

Note: Fixed/Wi-Fi from mobile devices may include a small amount of fixed/wired from mobile devices

Source: Cisco VNI Mobile, 2019

Litepoint — Test and Measurement HB 06-19.indd 15 6/10/19 9:28 AM