Understanding TPC with IEEE802.11h

If transmission power is too strong：

　→ Radio waves spread further than necessary

　→ Interfere with adjacent access point

　→ Increase power consumption in vain

　→ Radio wave end up reaching to outside of building (Security Risk)



If transmission power is too weak：

　→ Radio wave cannot reach to an expected range

　→ Connection is unstable

Automatic adjust depends on the situation is needed

　→Deliver radio waves only where needed 

　→ Decrease interference

　→ Save power consumption

Volume control for microphone in meeting



When you talk to person close to you

　→Small volume is enough（ Decrease electric power）



When you talk to person far from you

　→Big volume is required（ Increase electric power）



TPC automatically adjusts the volume for you

1. Devices connect to an access point

　↓

2. Devices measure the strength of the radio waves they receive

　↓

3. Devices report the strength to the access point

　↓

4. The access point adjust transmission power depends on the information

　↓

5. The access point transmits at only power level required

1. Reduce interference

　→ Do not spread radio wave more than it is needed

　→ Decrease interference with an adjacent access point



2. Save power consumption

　→ Use only electric power is needed

　→ Extend battery life



3. Enhance security

　→ Ensure range radio wave reach 

　→ Prevent radio wave leaking outside a building



4. Improve overall network efficiency

　→ Multiple access points work with adequate electric power

　→ Improve performance

 IEEE 802.11h  is a Wi-Fi standard that formally defines TPC and DFS as standard specifications 

Background：

5GHz band has been originally used in military, weather radar, satellite communication



Problem：

Once Wi-Fi began using the same frequency band, interference with existing radar systems became a concern.



Solution：

Standardize TPC and DFS with 802.11h

　→ Don’t output radio wave more than needed ( TPC )

　→ Avoid frequency interfering with radar ( DFS )

TPC（ Transmit Power Control）

　→ Adjust transmission power

　→ Decrease interference and save power consuming



DFS（ Dynamic Frequency Selection）

　→ Automatically switch to other frequency when it detects radar

　→ Avoid interference with radar systems

TPC    = Mechanism (concept)  for automatically adjusting transmission power

802.11h = Defining TPC and DFS as standard



Although TPC existed as a concept before 802.11h, it was formally defined as an official standard by 802.11h

It is a duty in mainly Europe



EU regulation：

Wi-Fi devices that use the 5GHz band are required to comply with 802.11h（TPC・DFS）



In fact, it is also common in Japan and North America

Layer 7  Application  │

Layer 6  Presentation │

Layer 5  Session      │  The layers TPC is not applicable

Layer 4  Transport    │

Layer 3  Network      │

Layer 2  Data Link    │

─────────────────────────────

Layer 1  Physical     ← The  layer TPC works

─────────────────────────────

TPC ：The method to automatically adjust transmission power of Wi-Fi



How it works： Devices measure the strength of received raido waves and report back to the access points

　→ Access Point automatically adjust transmission power



Pros：

・Reduce interference

・Save power consumption

・Improve security

・Improve efficiency in whole network



Relationship with 802.11h：

TPC = Concept for automatic adjusting transmission power

802.11h = Define TPC and DFS as standard

　→ It is created for prevent interference from radar in 5GHz band



OSI Layer： Physical Layer（ Layer 1）

TPC = The method to automatically adjust the strength of radio wave depending on the situation 802.11h = The definition of TPC as standard