Wireless Access

Hi Ryan,

Some of that terminology is new to me, but it seems to correlate with different but related terms I know.

CCA is the clear channel assessment.  It's how a Wi-Fi radio either determines if there's a transmission on its channel to receive, or that the channel is clear before transmitting.  It's the carrier sense in carrier cense multiple access.

The noise floor is the RF background noise on the channel.  While it varies somewhat over time, but at any given time it's pretty uniform across the channel.  The higher the noise floor, the stronger a signal must be to be useful.  The there's a direct analog in sound.  In most rooms, the background noise from air movement establishes the noise floor.  If you're in a library, the noise floor is low and a whisper is easily heard.  When you're on the datacenter floor, the noise from all the fans creates a high noise floor, and you have to shout to be understood.  RF works the same way.

I think the packet threshold detector is what I know as the Signal detect threshold.  It's how a Wi-Fi radio detects Wi-Fi contention on the channel.  Wi-Fi radios listen for an 802.11 frame preamble to determine if there's a Wi-Fi transmission on the channel.  That listening generally occurs about 4dB above the noise floor.  Anything weaker than that is unlikely to be successfully decoded and can be talked over.

The energy detect threshold is looking for non-Wi-Fi contention for the channel.  It's looking for a signal about 20dB or more above the noise floor.  If it finds one, it won't attempt to talk over it.

Hope that helps.

Chuck

Hi Ryan,

Some of that terminology is new to me, but it seems to correlate with different but related terms I know.

CCA is the clear channel assessment.  It's how a Wi-Fi radio either determines if there's a transmission on its channel to receive, or that the channel is clear before transmitting.  It's the carrier sense in carrier cense multiple access.

The noise floor is the RF background noise on the channel.  While it varies somewhat over time, but at any given time it's pretty uniform across the channel.  The higher the noise floor, the stronger a signal must be to be useful.  The there's a direct analog in sound.  In most rooms, the background noise from air movement establishes the noise floor.  If you're in a library, the noise floor is low and a whisper is easily heard.  When you're on the datacenter floor, the noise from all the fans creates a high noise floor, and you have to shout to be understood.  RF works the same way.

I think the packet threshold detector is what I know as the Signal detect threshold.  It's how a Wi-Fi radio detects Wi-Fi contention on the channel.  Wi-Fi radios listen for an 802.11 frame preamble to determine if there's a Wi-Fi transmission on the channel.  That listening generally occurs about 4dB above the noise floor.  Anything weaker than that is unlikely to be successfully decoded and can be talked over.

The energy detect threshold is looking for non-Wi-Fi contention for the channel.  It's looking for a signal about 20dB or more above the noise floor.  If it finds one, it won't attempt to talk over it.

Hope that helps.

Chuck

The higher the noise floor, the stronger a signal must be to be useful. Noise is not a signal, it's just random RF energy that a signal must overcome in order to be successfully decoded by a receiver.

Unless you're writing device drivers, I'm not aware of these thresholds being configurable.  Normally, the device manufacturer sets these for an AP or client radio, and you're stuck with it.  That said, it's worth understanding how they work because it can influence AP layout, antenna selection, etc. when designing your Wi-Fi network.  For the most part, I don't consider CCA much in routine Wi-Fi designs anymore.  I considered them carefully prior to 2010, when AP hardware was expensive, Wi-Fi clients were scarce, and radio resource management algorithms were horrific. (Today RRM is just sucky, so it's much better than it used to be.) But if you ever have a capacity problem and you're wondering if adding another AP in the area will help performance, understanding the CCA is important.  Another AP is useless if there's no time for it to talk, so it if will be within the signal detect threshold of another busy AP or within the energy detect threshold of a high-duty-cycle interference source, there's no point adding it.

Hi Ryan,

Some of that terminology is new to me, but it seems to correlate with different but related terms I know.

CCA is the clear channel assessment.  It's how a Wi-Fi radio either determines if there's a transmission on its channel to receive, or that the channel is clear before transmitting.  It's the carrier sense in carrier cense multiple access.

The noise floor is the RF background noise on the channel.  While it varies somewhat over time, but at any given time it's pretty uniform across the channel.  The higher the noise floor, the stronger a signal must be to be useful.  The there's a direct analog in sound.  In most rooms, the background noise from air movement establishes the noise floor.  If you're in a library, the noise floor is low and a whisper is easily heard.  When you're on the datacenter floor, the noise from all the fans creates a high noise floor, and you have to shout to be understood.  RF works the same way.

I think the packet threshold detector is what I know as the Signal detect threshold.  It's how a Wi-Fi radio detects Wi-Fi contention on the channel.  Wi-Fi radios listen for an 802.11 frame preamble to determine if there's a Wi-Fi transmission on the channel.  That listening generally occurs about 4dB above the noise floor.  Anything weaker than that is unlikely to be successfully decoded and can be talked over.

The energy detect threshold is looking for non-Wi-Fi contention for the channel.  It's looking for a signal about 20dB or more above the noise floor.  If it finds one, it won't attempt to talk over it.

Hope that helps.

Chuck

The higher the noise floor, the stronger a signal must be to be useful. Noise is not a signal, it's just random RF energy that a signal must overcome in order to be successfully decoded by a receiver.

Unless you're writing device drivers, I'm not aware of these thresholds being configurable.  Normally, the device manufacturer sets these for an AP or client radio, and you're stuck with it.  That said, it's worth understanding how they work because it can influence AP layout, antenna selection, etc. when designing your Wi-Fi network.  For the most part, I don't consider CCA much in routine Wi-Fi designs anymore.  I considered them carefully prior to 2010, when AP hardware was expensive, Wi-Fi clients were scarce, and radio resource management algorithms were horrific. (Today RRM is just sucky, so it's much better than it used to be.) But if you ever have a capacity problem and you're wondering if adding another AP in the area will help performance, understanding the CCA is important.  Another AP is useless if there's no time for it to talk, so it if will be within the signal detect threshold of another busy AP or within the energy detect threshold of a high-duty-cycle interference source, there's no point adding it.

Hi Ryan,

Some of that terminology is new to me, but it seems to correlate with different but related terms I know.

CCA is the clear channel assessment.  It's how a Wi-Fi radio either determines if there's a transmission on its channel to receive, or that the channel is clear before transmitting.  It's the carrier sense in carrier cense multiple access.

The noise floor is the RF background noise on the channel.  While it varies somewhat over time, but at any given time it's pretty uniform across the channel.  The higher the noise floor, the stronger a signal must be to be useful.  The there's a direct analog in sound.  In most rooms, the background noise from air movement establishes the noise floor.  If you're in a library, the noise floor is low and a whisper is easily heard.  When you're on the datacenter floor, the noise from all the fans creates a high noise floor, and you have to shout to be understood.  RF works the same way.

I think the packet threshold detector is what I know as the Signal detect threshold.  It's how a Wi-Fi radio detects Wi-Fi contention on the channel.  Wi-Fi radios listen for an 802.11 frame preamble to determine if there's a Wi-Fi transmission on the channel.  That listening generally occurs about 4dB above the noise floor.  Anything weaker than that is unlikely to be successfully decoded and can be talked over.

The energy detect threshold is looking for non-Wi-Fi contention for the channel.  It's looking for a signal about 20dB or more above the noise floor.  If it finds one, it won't attempt to talk over it.

Hope that helps.

Chuck

I'm trying to keep this simple.  In a book on Wi-Fi, you could write a chapter on the CCA.  Nobody would read it, but you could write it. 😊

1. All kinds of things emit RF, either intentionally or naturally, and both inside and outside of their intended band.  The combined energy of all those sources that are not distinguishable as signal make up the noise floor.  In Wi-Fi bands, the noise floor varies.  -100 is usually the lower limit, but I rarely find it that low in practice.  I'd call a good noise floor around -95dBm, and it can get much higher in congested Wi-Fi environments.  If your noise floor routinely exceeds -90, it's worth investigating whether there's a way you can reduce it. (reducing radio transmit power, turning off 2.4GHz radios, etc.)  Also note, that it's hard to measure the noise floor.  Most Wi-Fi client adapters just estimate it – some of them quite badly.  Enterprise APs and dedicated test equipment do a better job.

2. Energy detect serves two purposes:

• If there's a strong non-Wi-Fi transmission on your channel and you try to talk over it, there's a low probability of success, increasing the odds of a retransmission.  Unsuccessful transmissions waste channel capacity, and use battery capacity, so you don't want a lot of them.  They can also affect the data rate you connect at because high retransmit rates will cause most drivers to reduce their data rate.  For this purpose, there's probably a mathematical threshold that maximizes your potential throughput in a given environment, but it's going to be a moving target so it may be impractical to try to calculate it.
• Wi-Fi uses unlicensed spectrum and shares it with other technologies.  It's important to avoid excessive interference with those technologies, and the energy threshold is a good way of handling that.   Sadly, many competing technologies are much less polite and will stomp all over Wi-Fi.

3. You've got the idea right, but energy detect threshold is meant to address signals that are not Wi-Fi.  Wi-Fi signals are usually identified by the signal (or packet) detect threshold.  That said, if your Wi-Fi receiver begins the CCA after the preamble of a Wi-Fi frame, it will use the energy threshold for the CCA because it won't know it's an 802.11 signal.  The durations of the CCA and preamble are designed to minimize that problem.

There are analogs in common conversation.

If a group of you are having a conversation, it's normal not to talk when somebody else is talking.  Even if the other person is talking quietly, and you could easily talk over them in a normal voice, you don't.  That's the packet detect threshold.  If you can hear them well enough to know they're part of your conversation, you wait your turn.

If you're at Thanksgiving dinner and you're talking to your aunt while your dad is talking to your uncle, it's perfectly polite to talk while your dad and uncle are talking.  If you're at opposite ends of the table and the other conversation isn't too loud, you can have a normal conversation with your aunt at the same time.  But if your dad and uncle are seated right next to you and you speak at the same time as one of them, either your aunt will have a difficult time understanding you or you will interfere with the other conversation.  That volume of the competing conversation that you won't try to talk over is the energy detect threshold.

The higher the noise floor, the stronger a signal must be to be useful. Noise is not a signal, it's just random RF energy that a signal must overcome in order to be successfully decoded by a receiver.

Unless you're writing device drivers, I'm not aware of these thresholds being configurable.  Normally, the device manufacturer sets these for an AP or client radio, and you're stuck with it.  That said, it's worth understanding how they work because it can influence AP layout, antenna selection, etc. when designing your Wi-Fi network.  For the most part, I don't consider CCA much in routine Wi-Fi designs anymore.  I considered them carefully prior to 2010, when AP hardware was expensive, Wi-Fi clients were scarce, and radio resource management algorithms were horrific. (Today RRM is just sucky, so it's much better than it used to be.) But if you ever have a capacity problem and you're wondering if adding another AP in the area will help performance, understanding the CCA is important.  Another AP is useless if there's no time for it to talk, so it if will be within the signal detect threshold of another busy AP or within the energy detect threshold of a high-duty-cycle interference source, there's no point adding it.

Hi Ryan,

Some of that terminology is new to me, but it seems to correlate with different but related terms I know.

CCA is the clear channel assessment.  It's how a Wi-Fi radio either determines if there's a transmission on its channel to receive, or that the channel is clear before transmitting.  It's the carrier sense in carrier cense multiple access.

The noise floor is the RF background noise on the channel.  While it varies somewhat over time, but at any given time it's pretty uniform across the channel.  The higher the noise floor, the stronger a signal must be to be useful.  The there's a direct analog in sound.  In most rooms, the background noise from air movement establishes the noise floor.  If you're in a library, the noise floor is low and a whisper is easily heard.  When you're on the datacenter floor, the noise from all the fans creates a high noise floor, and you have to shout to be understood.  RF works the same way.

I think the packet threshold detector is what I know as the Signal detect threshold.  It's how a Wi-Fi radio detects Wi-Fi contention on the channel.  Wi-Fi radios listen for an 802.11 frame preamble to determine if there's a Wi-Fi transmission on the channel.  That listening generally occurs about 4dB above the noise floor.  Anything weaker than that is unlikely to be successfully decoded and can be talked over.

The energy detect threshold is looking for non-Wi-Fi contention for the channel.  It's looking for a signal about 20dB or more above the noise floor.  If it finds one, it won't attempt to talk over it.

Hope that helps.

Chuck

I'm trying to keep this simple.  In a book on Wi-Fi, you could write a chapter on the CCA.  Nobody would read it, but you could write it. 😊

1. All kinds of things emit RF, either intentionally or naturally, and both inside and outside of their intended band.  The combined energy of all those sources that are not distinguishable as signal make up the noise floor.  In Wi-Fi bands, the noise floor varies.  -100 is usually the lower limit, but I rarely find it that low in practice.  I'd call a good noise floor around -95dBm, and it can get much higher in congested Wi-Fi environments.  If your noise floor routinely exceeds -90, it's worth investigating whether there's a way you can reduce it. (reducing radio transmit power, turning off 2.4GHz radios, etc.)  Also note, that it's hard to measure the noise floor.  Most Wi-Fi client adapters just estimate it – some of them quite badly.  Enterprise APs and dedicated test equipment do a better job.

2. Energy detect serves two purposes:

• If there's a strong non-Wi-Fi transmission on your channel and you try to talk over it, there's a low probability of success, increasing the odds of a retransmission.  Unsuccessful transmissions waste channel capacity, and use battery capacity, so you don't want a lot of them.  They can also affect the data rate you connect at because high retransmit rates will cause most drivers to reduce their data rate.  For this purpose, there's probably a mathematical threshold that maximizes your potential throughput in a given environment, but it's going to be a moving target so it may be impractical to try to calculate it.
• Wi-Fi uses unlicensed spectrum and shares it with other technologies.  It's important to avoid excessive interference with those technologies, and the energy threshold is a good way of handling that.   Sadly, many competing technologies are much less polite and will stomp all over Wi-Fi.

3. You've got the idea right, but energy detect threshold is meant to address signals that are not Wi-Fi.  Wi-Fi signals are usually identified by the signal (or packet) detect threshold.  That said, if your Wi-Fi receiver begins the CCA after the preamble of a Wi-Fi frame, it will use the energy threshold for the CCA because it won't know it's an 802.11 signal.  The durations of the CCA and preamble are designed to minimize that problem.

There are analogs in common conversation.

If a group of you are having a conversation, it's normal not to talk when somebody else is talking.  Even if the other person is talking quietly, and you could easily talk over them in a normal voice, you don't.  That's the packet detect threshold.  If you can hear them well enough to know they're part of your conversation, you wait your turn.

If you're at Thanksgiving dinner and you're talking to your aunt while your dad is talking to your uncle, it's perfectly polite to talk while your dad and uncle are talking.  If you're at opposite ends of the table and the other conversation isn't too loud, you can have a normal conversation with your aunt at the same time.  But if your dad and uncle are seated right next to you and you speak at the same time as one of them, either your aunt will have a difficult time understanding you or you will interfere with the other conversation.  That volume of the competing conversation that you won't try to talk over is the energy detect threshold.

The higher the noise floor, the stronger a signal must be to be useful. Noise is not a signal, it's just random RF energy that a signal must overcome in order to be successfully decoded by a receiver.

Unless you're writing device drivers, I'm not aware of these thresholds being configurable.  Normally, the device manufacturer sets these for an AP or client radio, and you're stuck with it.  That said, it's worth understanding how they work because it can influence AP layout, antenna selection, etc. when designing your Wi-Fi network.  For the most part, I don't consider CCA much in routine Wi-Fi designs anymore.  I considered them carefully prior to 2010, when AP hardware was expensive, Wi-Fi clients were scarce, and radio resource management algorithms were horrific. (Today RRM is just sucky, so it's much better than it used to be.) But if you ever have a capacity problem and you're wondering if adding another AP in the area will help performance, understanding the CCA is important.  Another AP is useless if there's no time for it to talk, so it if will be within the signal detect threshold of another busy AP or within the energy detect threshold of a high-duty-cycle interference source, there's no point adding it.

Hi Ryan,

Some of that terminology is new to me, but it seems to correlate with different but related terms I know.

CCA is the clear channel assessment.  It's how a Wi-Fi radio either determines if there's a transmission on its channel to receive, or that the channel is clear before transmitting.  It's the carrier sense in carrier cense multiple access.

The noise floor is the RF background noise on the channel.  While it varies somewhat over time, but at any given time it's pretty uniform across the channel.  The higher the noise floor, the stronger a signal must be to be useful.  The there's a direct analog in sound.  In most rooms, the background noise from air movement establishes the noise floor.  If you're in a library, the noise floor is low and a whisper is easily heard.  When you're on the datacenter floor, the noise from all the fans creates a high noise floor, and you have to shout to be understood.  RF works the same way.

I think the packet threshold detector is what I know as the Signal detect threshold.  It's how a Wi-Fi radio detects Wi-Fi contention on the channel.  Wi-Fi radios listen for an 802.11 frame preamble to determine if there's a Wi-Fi transmission on the channel.  That listening generally occurs about 4dB above the noise floor.  Anything weaker than that is unlikely to be successfully decoded and can be talked over.

The energy detect threshold is looking for non-Wi-Fi contention for the channel.  It's looking for a signal about 20dB or more above the noise floor.  If it finds one, it won't attempt to talk over it.

Hope that helps.

Chuck

I'm trying to keep this simple.  In a book on Wi-Fi, you could write a chapter on the CCA.  Nobody would read it, but you could write it. 😊

1. All kinds of things emit RF, either intentionally or naturally, and both inside and outside of their intended band.  The combined energy of all those sources that are not distinguishable as signal make up the noise floor.  In Wi-Fi bands, the noise floor varies.  -100 is usually the lower limit, but I rarely find it that low in practice.  I'd call a good noise floor around -95dBm, and it can get much higher in congested Wi-Fi environments.  If your noise floor routinely exceeds -90, it's worth investigating whether there's a way you can reduce it. (reducing radio transmit power, turning off 2.4GHz radios, etc.)  Also note, that it's hard to measure the noise floor.  Most Wi-Fi client adapters just estimate it – some of them quite badly.  Enterprise APs and dedicated test equipment do a better job.

2. Energy detect serves two purposes:

• If there's a strong non-Wi-Fi transmission on your channel and you try to talk over it, there's a low probability of success, increasing the odds of a retransmission.  Unsuccessful transmissions waste channel capacity, and use battery capacity, so you don't want a lot of them.  They can also affect the data rate you connect at because high retransmit rates will cause most drivers to reduce their data rate.  For this purpose, there's probably a mathematical threshold that maximizes your potential throughput in a given environment, but it's going to be a moving target so it may be impractical to try to calculate it.
• Wi-Fi uses unlicensed spectrum and shares it with other technologies.  It's important to avoid excessive interference with those technologies, and the energy threshold is a good way of handling that.   Sadly, many competing technologies are much less polite and will stomp all over Wi-Fi.

3. You've got the idea right, but energy detect threshold is meant to address signals that are not Wi-Fi.  Wi-Fi signals are usually identified by the signal (or packet) detect threshold.  That said, if your Wi-Fi receiver begins the CCA after the preamble of a Wi-Fi frame, it will use the energy threshold for the CCA because it won't know it's an 802.11 signal.  The durations of the CCA and preamble are designed to minimize that problem.

There are analogs in common conversation.

If a group of you are having a conversation, it's normal not to talk when somebody else is talking.  Even if the other person is talking quietly, and you could easily talk over them in a normal voice, you don't.  That's the packet detect threshold.  If you can hear them well enough to know they're part of your conversation, you wait your turn.

If you're at Thanksgiving dinner and you're talking to your aunt while your dad is talking to your uncle, it's perfectly polite to talk while your dad and uncle are talking.  If you're at opposite ends of the table and the other conversation isn't too loud, you can have a normal conversation with your aunt at the same time.  But if your dad and uncle are seated right next to you and you speak at the same time as one of them, either your aunt will have a difficult time understanding you or you will interfere with the other conversation.  That volume of the competing conversation that you won't try to talk over is the energy detect threshold.

The higher the noise floor, the stronger a signal must be to be useful. Noise is not a signal, it's just random RF energy that a signal must overcome in order to be successfully decoded by a receiver.

Unless you're writing device drivers, I'm not aware of these thresholds being configurable.  Normally, the device manufacturer sets these for an AP or client radio, and you're stuck with it.  That said, it's worth understanding how they work because it can influence AP layout, antenna selection, etc. when designing your Wi-Fi network.  For the most part, I don't consider CCA much in routine Wi-Fi designs anymore.  I considered them carefully prior to 2010, when AP hardware was expensive, Wi-Fi clients were scarce, and radio resource management algorithms were horrific. (Today RRM is just sucky, so it's much better than it used to be.) But if you ever have a capacity problem and you're wondering if adding another AP in the area will help performance, understanding the CCA is important.  Another AP is useless if there's no time for it to talk, so it if will be within the signal detect threshold of another busy AP or within the energy detect threshold of a high-duty-cycle interference source, there's no point adding it.

Hi Ryan,

Some of that terminology is new to me, but it seems to correlate with different but related terms I know.

CCA is the clear channel assessment.  It's how a Wi-Fi radio either determines if there's a transmission on its channel to receive, or that the channel is clear before transmitting.  It's the carrier sense in carrier cense multiple access.

The noise floor is the RF background noise on the channel.  While it varies somewhat over time, but at any given time it's pretty uniform across the channel.  The higher the noise floor, the stronger a signal must be to be useful.  The there's a direct analog in sound.  In most rooms, the background noise from air movement establishes the noise floor.  If you're in a library, the noise floor is low and a whisper is easily heard.  When you're on the datacenter floor, the noise from all the fans creates a high noise floor, and you have to shout to be understood.  RF works the same way.

I think the packet threshold detector is what I know as the Signal detect threshold.  It's how a Wi-Fi radio detects Wi-Fi contention on the channel.  Wi-Fi radios listen for an 802.11 frame preamble to determine if there's a Wi-Fi transmission on the channel.  That listening generally occurs about 4dB above the noise floor.  Anything weaker than that is unlikely to be successfully decoded and can be talked over.

The energy detect threshold is looking for non-Wi-Fi contention for the channel.  It's looking for a signal about 20dB or more above the noise floor.  If it finds one, it won't attempt to talk over it.

Hope that helps.

Chuck

I'm trying to keep this simple.  In a book on Wi-Fi, you could write a chapter on the CCA.  Nobody would read it, but you could write it. 😊

1. All kinds of things emit RF, either intentionally or naturally, and both inside and outside of their intended band.  The combined energy of all those sources that are not distinguishable as signal make up the noise floor.  In Wi-Fi bands, the noise floor varies.  -100 is usually the lower limit, but I rarely find it that low in practice.  I'd call a good noise floor around -95dBm, and it can get much higher in congested Wi-Fi environments.  If your noise floor routinely exceeds -90, it's worth investigating whether there's a way you can reduce it. (reducing radio transmit power, turning off 2.4GHz radios, etc.)  Also note, that it's hard to measure the noise floor.  Most Wi-Fi client adapters just estimate it – some of them quite badly.  Enterprise APs and dedicated test equipment do a better job.

2. Energy detect serves two purposes:

• If there's a strong non-Wi-Fi transmission on your channel and you try to talk over it, there's a low probability of success, increasing the odds of a retransmission.  Unsuccessful transmissions waste channel capacity, and use battery capacity, so you don't want a lot of them.  They can also affect the data rate you connect at because high retransmit rates will cause most drivers to reduce their data rate.  For this purpose, there's probably a mathematical threshold that maximizes your potential throughput in a given environment, but it's going to be a moving target so it may be impractical to try to calculate it.
• Wi-Fi uses unlicensed spectrum and shares it with other technologies.  It's important to avoid excessive interference with those technologies, and the energy threshold is a good way of handling that.   Sadly, many competing technologies are much less polite and will stomp all over Wi-Fi.

3. You've got the idea right, but energy detect threshold is meant to address signals that are not Wi-Fi.  Wi-Fi signals are usually identified by the signal (or packet) detect threshold.  That said, if your Wi-Fi receiver begins the CCA after the preamble of a Wi-Fi frame, it will use the energy threshold for the CCA because it won't know it's an 802.11 signal.  The durations of the CCA and preamble are designed to minimize that problem.

There are analogs in common conversation.

If a group of you are having a conversation, it's normal not to talk when somebody else is talking.  Even if the other person is talking quietly, and you could easily talk over them in a normal voice, you don't.  That's the packet detect threshold.  If you can hear them well enough to know they're part of your conversation, you wait your turn.

If you're at Thanksgiving dinner and you're talking to your aunt while your dad is talking to your uncle, it's perfectly polite to talk while your dad and uncle are talking.  If you're at opposite ends of the table and the other conversation isn't too loud, you can have a normal conversation with your aunt at the same time.  But if your dad and uncle are seated right next to you and you speak at the same time as one of them, either your aunt will have a difficult time understanding you or you will interfere with the other conversation.  That volume of the competing conversation that you won't try to talk over is the energy detect threshold.

The higher the noise floor, the stronger a signal must be to be useful. Noise is not a signal, it's just random RF energy that a signal must overcome in order to be successfully decoded by a receiver.

Unless you're writing device drivers, I'm not aware of these thresholds being configurable.  Normally, the device manufacturer sets these for an AP or client radio, and you're stuck with it.  That said, it's worth understanding how they work because it can influence AP layout, antenna selection, etc. when designing your Wi-Fi network.  For the most part, I don't consider CCA much in routine Wi-Fi designs anymore.  I considered them carefully prior to 2010, when AP hardware was expensive, Wi-Fi clients were scarce, and radio resource management algorithms were horrific. (Today RRM is just sucky, so it's much better than it used to be.) But if you ever have a capacity problem and you're wondering if adding another AP in the area will help performance, understanding the CCA is important.  Another AP is useless if there's no time for it to talk, so it if will be within the signal detect threshold of another busy AP or within the energy detect threshold of a high-duty-cycle interference source, there's no point adding it.

Hi Ryan,

Some of that terminology is new to me, but it seems to correlate with different but related terms I know.

CCA is the clear channel assessment.  It's how a Wi-Fi radio either determines if there's a transmission on its channel to receive, or that the channel is clear before transmitting.  It's the carrier sense in carrier cense multiple access.

The noise floor is the RF background noise on the channel.  While it varies somewhat over time, but at any given time it's pretty uniform across the channel.  The higher the noise floor, the stronger a signal must be to be useful.  The there's a direct analog in sound.  In most rooms, the background noise from air movement establishes the noise floor.  If you're in a library, the noise floor is low and a whisper is easily heard.  When you're on the datacenter floor, the noise from all the fans creates a high noise floor, and you have to shout to be understood.  RF works the same way.

I think the packet threshold detector is what I know as the Signal detect threshold.  It's how a Wi-Fi radio detects Wi-Fi contention on the channel.  Wi-Fi radios listen for an 802.11 frame preamble to determine if there's a Wi-Fi transmission on the channel.  That listening generally occurs about 4dB above the noise floor.  Anything weaker than that is unlikely to be successfully decoded and can be talked over.

The energy detect threshold is looking for non-Wi-Fi contention for the channel.  It's looking for a signal about 20dB or more above the noise floor.  If it finds one, it won't attempt to talk over it.

Hope that helps.

Chuck