Re: [WISPA] modulation question
Bryan Scott brought up an important point: You can put QAM subcarriers on OFDM. But you can put almost any other type of subcarrier on OFDM too. That may be a confusing thing. OFDM is method of putting multiple FM modulated carriers on the air. Almost like sending multiple channels containing their own info and then combining all the channels at the far end. Those channels can have QAM subcarriers, but the RF is still FM modulated, not QAM modulated. That may be confusing to some. The FM modulation of OFDM gives it the inherent advantage of angle only modulation methods. Then there are systems that use QAM to modulate the RF. Those systems are less resistant to link problems but are one of the best ways to cram a bunch of data on the link. (V.90 dial up modems are a good example). When they added color to the BW TV signal, they used a QAM method. The original stereo AM radio signal was QAM. Cable modems use QAM. - Original Message - From: Chuck McCown - 2 [EMAIL PROTECTED] To: WISPA General List wireless@wispa.org Sent: Monday, June 16, 2008 11:15 PM Subject: Re: [WISPA] modulation question I think some disambiguation may be in order. QAM is a vector modulation method:. http://en.wikipedia.org/wiki/Constellation_diagram It shares almost nothing with OFDM methods. Irrespective, all receivers (CW, AM, FM, SSB, VSB, angle modulation, OFDM, QAM, TCM, etc) can have an RSSI output from the AGC, limiter or demodulator. Strictly speaking it only means Received Signal Strength Indicator. It is modulation agnostic. It is not related to the modulation. - Original Message - From: Tom DeReggi [EMAIL PROTECTED] To: [EMAIL PROTECTED]; WISPA General List wireless@wispa.org Sent: Monday, June 16, 2008 10:10 PM Subject: Re: [WISPA] modulation question I'm not sure exactly your question? I'm also not sure there is a purpose, as much as reporting what occurs. I'm also not sure if you are looking for an answer at the waveform level versus the Link budget level? RSSI is a factor related to Modulation. More specifically with OFDM. Often in manufacturer spec sheets, it will list the minimum rssi level in order to use a specific modulation. This is not just a random number picked. Someone else will probably explain it better, and I welcome them to, but for now I'll try :-) It has something to do with how OFDM takes the signal and breaks it up into lower powered sub carriers. As modulations are higher, they get broken down into more sub carriers, hence QAM 32,64,256, etc. I believe it has something to do with how the math works with Watts versus DB, when the signal gets split and added back togeather again at a later process. There are two side effects that come... As higher modulations are used, it more work for the card and Transmit power becomes less, and receive sensitivity becomes higher (worse). I guess what I'm saying is that its possible to use a specific modulation at many different power levels/ receive levels (RSSI). It depends on the power rating of the card. However, the point I'm making is, at a given set power level or sensitivity rating of a card running a low modulation, if the modulation type is raised, it will have a calculatable/predictable effect on the signal strength received and sent. Tom DeReggi RapidDSL Wireless, Inc IntAirNet- Fixed Wireless Broadband - Original Message - From: Rogelio [EMAIL PROTECTED] To: WISPA General List wireless@wispa.org Sent: Monday, June 16, 2008 10:06 PM Subject: [WISPA] modulation question I've got a question, which I'm afraid might be a little stupid to some, particularly those with RF backgrounds... I've always thought that modulation rate was directly tied to RSSI (for some law of physics reason or something), but someone else told me that it's not like that (in theory) and what I'm seeing is just certain vendors do that for a particular purpose. What is this purpose? WISPA Wants You! Join today! http://signup.wispa.org/ WISPA Wireless List: wireless@wispa.org Subscribe/Unsubscribe: http://lists.wispa.org/mailman/listinfo/wireless Archives: http://lists.wispa.org/pipermail/wireless/ WISPA Wants You! Join today! http://signup.wispa.org/ WISPA Wireless List: wireless@wispa.org Subscribe/Unsubscribe: http://lists.wispa.org/mailman/listinfo/wireless Archives: http://lists.wispa.org/pipermail/wireless/ WISPA Wants You! Join today! http://signup.wispa.org
Re: [WISPA] modulation question
what is a sub carrier? For IP guys, think of VLANs. You can cram a bunch of VLANs on an Ethernet link. Each VLAN appears to be its own Ethernet link. But to the trunk, all the VLANs appear just to be payload data. Same thing with RF. The on-the-air signal is modulated. OFDM or FM (or morse code or AM or whatever) method. That is the Ethernet. Inside that modulation, if you pick it apart, you may find the raw data (like Canopy does) or you may find other modulated signals (like the VLAN) that have to be further demodulated (QAM on OFDM like Orthogon). QAM methods are used to cram a ton of information on a link. Whether it is on the raw RF signal on in a subcarrier. But they are not as robust as simple direct modulation. But there is always a tradeoff. The following is not really accurate but it may give a data guy another way of thinking about it. Level 12.4 GHz RF using antennas Level 2OFDM modulation on the RF Level 2 VLANsQAM Sub Carriers Level 3Ethernet data - Original Message - From: Chuck McCown - 2 [EMAIL PROTECTED] To: WISPA General List wireless@wispa.org Sent: Tuesday, June 17, 2008 7:47 AM Subject: Re: [WISPA] modulation question Bryan Scott brought up an important point: You can put QAM subcarriers on OFDM. But you can put almost any other type of subcarrier on OFDM too. That may be a confusing thing. OFDM is method of putting multiple FM modulated carriers on the air. Almost like sending multiple channels containing their own info and then combining all the channels at the far end. Those channels can have QAM subcarriers, but the RF is still FM modulated, not QAM modulated. That may be confusing to some. The FM modulation of OFDM gives it the inherent advantage of angle only modulation methods. Then there are systems that use QAM to modulate the RF. Those systems are less resistant to link problems but are one of the best ways to cram a bunch of data on the link. (V.90 dial up modems are a good example). When they added color to the BW TV signal, they used a QAM method. The original stereo AM radio signal was QAM. Cable modems use QAM. - Original Message - From: Chuck McCown - 2 [EMAIL PROTECTED] To: WISPA General List wireless@wispa.org Sent: Monday, June 16, 2008 11:15 PM Subject: Re: [WISPA] modulation question I think some disambiguation may be in order. QAM is a vector modulation method:. http://en.wikipedia.org/wiki/Constellation_diagram It shares almost nothing with OFDM methods. Irrespective, all receivers (CW, AM, FM, SSB, VSB, angle modulation, OFDM, QAM, TCM, etc) can have an RSSI output from the AGC, limiter or demodulator. Strictly speaking it only means Received Signal Strength Indicator. It is modulation agnostic. It is not related to the modulation. - Original Message - From: Tom DeReggi [EMAIL PROTECTED] To: [EMAIL PROTECTED]; WISPA General List wireless@wispa.org Sent: Monday, June 16, 2008 10:10 PM Subject: Re: [WISPA] modulation question I'm not sure exactly your question? I'm also not sure there is a purpose, as much as reporting what occurs. I'm also not sure if you are looking for an answer at the waveform level versus the Link budget level? RSSI is a factor related to Modulation. More specifically with OFDM. Often in manufacturer spec sheets, it will list the minimum rssi level in order to use a specific modulation. This is not just a random number picked. Someone else will probably explain it better, and I welcome them to, but for now I'll try :-) It has something to do with how OFDM takes the signal and breaks it up into lower powered sub carriers. As modulations are higher, they get broken down into more sub carriers, hence QAM 32,64,256, etc. I believe it has something to do with how the math works with Watts versus DB, when the signal gets split and added back togeather again at a later process. There are two side effects that come... As higher modulations are used, it more work for the card and Transmit power becomes less, and receive sensitivity becomes higher (worse). I guess what I'm saying is that its possible to use a specific modulation at many different power levels/ receive levels (RSSI). It depends on the power rating of the card. However, the point I'm making is, at a given set power level or sensitivity rating of a card running a low modulation, if the modulation type is raised, it will have a calculatable/predictable effect on the signal strength received and sent. Tom DeReggi RapidDSL Wireless, Inc IntAirNet- Fixed Wireless Broadband - Original Message - From: Rogelio [EMAIL PROTECTED] To: WISPA General List wireless@wispa.org Sent: Monday, June 16, 2008 10:06 PM Subject: [WISPA] modulation question I've got a question, which I'm afraid might be a little stupid to some, particularly those with RF backgrounds... I've always thought that modulation
Re: [WISPA] modulation question
Chuck, Nice posts! Thanks for the clarification.(PS. I clearly had some misunderstanding/FUD in my last post, regarding QAM.) While you are at it Can you comment a bit on OFDM, regarding the math, of what occurs to power levels as it divides into subcarriers and recombines on the receive end. There was a good post on the STAROS forums about it a year or so ago, but I couldn't find it again to repost to this list. It brought forth some relevent info on how to correctly do link budget calculations and what RSSI should be expected considering OFDM versus DSSS style gear. Tom DeReggi RapidDSL Wireless, Inc IntAirNet- Fixed Wireless Broadband - Original Message - From: Chuck McCown - 2 [EMAIL PROTECTED] To: WISPA General List wireless@wispa.org Sent: Tuesday, June 17, 2008 9:04 AM Subject: Re: [WISPA] modulation question what is a sub carrier? For IP guys, think of VLANs. You can cram a bunch of VLANs on an Ethernet link. Each VLAN appears to be its own Ethernet link. But to the trunk, all the VLANs appear just to be payload data. Same thing with RF. The on-the-air signal is modulated. OFDM or FM (or morse code or AM or whatever) method. That is the Ethernet. Inside that modulation, if you pick it apart, you may find the raw data (like Canopy does) or you may find other modulated signals (like the VLAN) that have to be further demodulated (QAM on OFDM like Orthogon). QAM methods are used to cram a ton of information on a link. Whether it is on the raw RF signal on in a subcarrier. But they are not as robust as simple direct modulation. But there is always a tradeoff. The following is not really accurate but it may give a data guy another way of thinking about it. Level 12.4 GHz RF using antennas Level 2OFDM modulation on the RF Level 2 VLANsQAM Sub Carriers Level 3Ethernet data - Original Message - From: Chuck McCown - 2 [EMAIL PROTECTED] To: WISPA General List wireless@wispa.org Sent: Tuesday, June 17, 2008 7:47 AM Subject: Re: [WISPA] modulation question Bryan Scott brought up an important point: You can put QAM subcarriers on OFDM. But you can put almost any other type of subcarrier on OFDM too. That may be a confusing thing. OFDM is method of putting multiple FM modulated carriers on the air. Almost like sending multiple channels containing their own info and then combining all the channels at the far end. Those channels can have QAM subcarriers, but the RF is still FM modulated, not QAM modulated. That may be confusing to some. The FM modulation of OFDM gives it the inherent advantage of angle only modulation methods. Then there are systems that use QAM to modulate the RF. Those systems are less resistant to link problems but are one of the best ways to cram a bunch of data on the link. (V.90 dial up modems are a good example). When they added color to the BW TV signal, they used a QAM method. The original stereo AM radio signal was QAM. Cable modems use QAM. - Original Message - From: Chuck McCown - 2 [EMAIL PROTECTED] To: WISPA General List wireless@wispa.org Sent: Monday, June 16, 2008 11:15 PM Subject: Re: [WISPA] modulation question I think some disambiguation may be in order. QAM is a vector modulation method:. http://en.wikipedia.org/wiki/Constellation_diagram It shares almost nothing with OFDM methods. Irrespective, all receivers (CW, AM, FM, SSB, VSB, angle modulation, OFDM, QAM, TCM, etc) can have an RSSI output from the AGC, limiter or demodulator. Strictly speaking it only means Received Signal Strength Indicator. It is modulation agnostic. It is not related to the modulation. - Original Message - From: Tom DeReggi [EMAIL PROTECTED] To: [EMAIL PROTECTED]; WISPA General List wireless@wispa.org Sent: Monday, June 16, 2008 10:10 PM Subject: Re: [WISPA] modulation question I'm not sure exactly your question? I'm also not sure there is a purpose, as much as reporting what occurs. I'm also not sure if you are looking for an answer at the waveform level versus the Link budget level? RSSI is a factor related to Modulation. More specifically with OFDM. Often in manufacturer spec sheets, it will list the minimum rssi level in order to use a specific modulation. This is not just a random number picked. Someone else will probably explain it better, and I welcome them to, but for now I'll try :-) It has something to do with how OFDM takes the signal and breaks it up into lower powered sub carriers. As modulations are higher, they get broken down into more sub carriers, hence QAM 32,64,256, etc. I believe it has something to do with how the math works with Watts versus DB, when the signal gets split and added back togeather again at a later process. There are two side effects that come... As higher modulations are used, it more work for the card and Transmit power becomes less, and receive
Re: [WISPA] modulation question
Each system is different as to the number of carriers and a different number of modulation levels on the carriers. Basically it is Shannon's law which defines the maximum rate of data that can be transmitted over a channel. But no real system can hit the Shannon limit. The imperfections in the demodulators vary from manufacturer. The simple answer is the more you try to pump through, the more signal you need. Shannon's law contains a signal to noise ratio as one of the components. If you want to have more throughput, you have to have more signal or less noise. The short answer is, read the manual. I would hope they are all conservative on the published signal levels needed for the different bit rates. As far as DSSS goes, I really don't know if the Shannon formula applies or not. Hmmm... - Original Message - From: Tom DeReggi [EMAIL PROTECTED] To: WISPA General List wireless@wispa.org Sent: Tuesday, June 17, 2008 6:24 PM Subject: Re: [WISPA] modulation question Chuck, Nice posts! Thanks for the clarification.(PS. I clearly had some misunderstanding/FUD in my last post, regarding QAM.) While you are at it Can you comment a bit on OFDM, regarding the math, of what occurs to power levels as it divides into subcarriers and recombines on the receive end. There was a good post on the STAROS forums about it a year or so ago, but I couldn't find it again to repost to this list. It brought forth some relevent info on how to correctly do link budget calculations and what RSSI should be expected considering OFDM versus DSSS style gear. Tom DeReggi RapidDSL Wireless, Inc IntAirNet- Fixed Wireless Broadband - Original Message - From: Chuck McCown - 2 [EMAIL PROTECTED] To: WISPA General List wireless@wispa.org Sent: Tuesday, June 17, 2008 9:04 AM Subject: Re: [WISPA] modulation question what is a sub carrier? For IP guys, think of VLANs. You can cram a bunch of VLANs on an Ethernet link. Each VLAN appears to be its own Ethernet link. But to the trunk, all the VLANs appear just to be payload data. Same thing with RF. The on-the-air signal is modulated. OFDM or FM (or morse code or AM or whatever) method. That is the Ethernet. Inside that modulation, if you pick it apart, you may find the raw data (like Canopy does) or you may find other modulated signals (like the VLAN) that have to be further demodulated (QAM on OFDM like Orthogon). QAM methods are used to cram a ton of information on a link. Whether it is on the raw RF signal on in a subcarrier. But they are not as robust as simple direct modulation. But there is always a tradeoff. The following is not really accurate but it may give a data guy another way of thinking about it. Level 12.4 GHz RF using antennas Level 2OFDM modulation on the RF Level 2 VLANsQAM Sub Carriers Level 3Ethernet data - Original Message - From: Chuck McCown - 2 [EMAIL PROTECTED] To: WISPA General List wireless@wispa.org Sent: Tuesday, June 17, 2008 7:47 AM Subject: Re: [WISPA] modulation question Bryan Scott brought up an important point: You can put QAM subcarriers on OFDM. But you can put almost any other type of subcarrier on OFDM too. That may be a confusing thing. OFDM is method of putting multiple FM modulated carriers on the air. Almost like sending multiple channels containing their own info and then combining all the channels at the far end. Those channels can have QAM subcarriers, but the RF is still FM modulated, not QAM modulated. That may be confusing to some. The FM modulation of OFDM gives it the inherent advantage of angle only modulation methods. Then there are systems that use QAM to modulate the RF. Those systems are less resistant to link problems but are one of the best ways to cram a bunch of data on the link. (V.90 dial up modems are a good example). When they added color to the BW TV signal, they used a QAM method. The original stereo AM radio signal was QAM. Cable modems use QAM. - Original Message - From: Chuck McCown - 2 [EMAIL PROTECTED] To: WISPA General List wireless@wispa.org Sent: Monday, June 16, 2008 11:15 PM Subject: Re: [WISPA] modulation question I think some disambiguation may be in order. QAM is a vector modulation method:. http://en.wikipedia.org/wiki/Constellation_diagram It shares almost nothing with OFDM methods. Irrespective, all receivers (CW, AM, FM, SSB, VSB, angle modulation, OFDM, QAM, TCM, etc) can have an RSSI output from the AGC, limiter or demodulator. Strictly speaking it only means Received Signal Strength Indicator. It is modulation agnostic. It is not related to the modulation. - Original Message - From: Tom DeReggi [EMAIL PROTECTED] To: [EMAIL PROTECTED]; WISPA General List wireless@wispa.org Sent: Monday, June 16, 2008 10:10 PM Subject: Re: [WISPA] modulation question I'm not sure exactly your question? I'm
[WISPA] modulation question
I've got a question, which I'm afraid might be a little stupid to some, particularly those with RF backgrounds... I've always thought that modulation rate was directly tied to RSSI (for some law of physics reason or something), but someone else told me that it's not like that (in theory) and what I'm seeing is just certain vendors do that for a particular purpose. What is this purpose? WISPA Wants You! Join today! http://signup.wispa.org/ WISPA Wireless List: wireless@wispa.org Subscribe/Unsubscribe: http://lists.wispa.org/mailman/listinfo/wireless Archives: http://lists.wispa.org/pipermail/wireless/
Re: [WISPA] modulation question
RSSI, strictly speaking, is the received signal strength. (Received Signal Strength Indicator) The signal can be totally unmodulated or modulated in a very complex method with the same RSSI. I am wondering if what you are asking is about the minimum RSSI needed. Generally speaking, the more complex the modulation, the more received signal you need for a given error rate. - Original Message - From: Rogelio [EMAIL PROTECTED] To: WISPA General List wireless@wispa.org Sent: Monday, June 16, 2008 9:06 PM Subject: [WISPA] modulation question I've got a question, which I'm afraid might be a little stupid to some, particularly those with RF backgrounds... I've always thought that modulation rate was directly tied to RSSI (for some law of physics reason or something), but someone else told me that it's not like that (in theory) and what I'm seeing is just certain vendors do that for a particular purpose. What is this purpose? WISPA Wants You! Join today! http://signup.wispa.org/ WISPA Wireless List: wireless@wispa.org Subscribe/Unsubscribe: http://lists.wispa.org/mailman/listinfo/wireless Archives: http://lists.wispa.org/pipermail/wireless/ WISPA Wants You! Join today! http://signup.wispa.org/ WISPA Wireless List: wireless@wispa.org Subscribe/Unsubscribe: http://lists.wispa.org/mailman/listinfo/wireless Archives: http://lists.wispa.org/pipermail/wireless/
Re: [WISPA] modulation question
I have been trying to think of a simple example. The only one that comes to mind right now is listening to weak FM broadcast signal. If the station was transmitting a pure tone, you could pick out the tone from the static on a very weak station, but if that same weak station switched from transmitting a tone to some classical music, it would be almost totally lost in the noise. In order for you to get the content of the music, the signal would have to be much stronger. The pure tone contains zero information. The music contains lots of information. You need more power to get more information through the noise. Does that make any sense? - Original Message - From: Chuck McCown - 2 [EMAIL PROTECTED] To: [EMAIL PROTECTED]; WISPA General List wireless@wispa.org Sent: Monday, June 16, 2008 9:14 PM Subject: Re: [WISPA] modulation question RSSI, strictly speaking, is the received signal strength. (Received Signal Strength Indicator) The signal can be totally unmodulated or modulated in a very complex method with the same RSSI. I am wondering if what you are asking is about the minimum RSSI needed. Generally speaking, the more complex the modulation, the more received signal you need for a given error rate. - Original Message - From: Rogelio [EMAIL PROTECTED] To: WISPA General List wireless@wispa.org Sent: Monday, June 16, 2008 9:06 PM Subject: [WISPA] modulation question I've got a question, which I'm afraid might be a little stupid to some, particularly those with RF backgrounds... I've always thought that modulation rate was directly tied to RSSI (for some law of physics reason or something), but someone else told me that it's not like that (in theory) and what I'm seeing is just certain vendors do that for a particular purpose. What is this purpose? WISPA Wants You! Join today! http://signup.wispa.org/ WISPA Wireless List: wireless@wispa.org Subscribe/Unsubscribe: http://lists.wispa.org/mailman/listinfo/wireless Archives: http://lists.wispa.org/pipermail/wireless/ WISPA Wants You! Join today! http://signup.wispa.org/ WISPA Wireless List: wireless@wispa.org Subscribe/Unsubscribe: http://lists.wispa.org/mailman/listinfo/wireless Archives: http://lists.wispa.org/pipermail/wireless/ WISPA Wants You! Join today! http://signup.wispa.org/ WISPA Wireless List: wireless@wispa.org Subscribe/Unsubscribe: http://lists.wispa.org/mailman/listinfo/wireless Archives: http://lists.wispa.org/pipermail/wireless/
Re: [WISPA] modulation question
I'm not sure exactly your question? I'm also not sure there is a purpose, as much as reporting what occurs. I'm also not sure if you are looking for an answer at the waveform level versus the Link budget level? RSSI is a factor related to Modulation. More specifically with OFDM. Often in manufacturer spec sheets, it will list the minimum rssi level in order to use a specific modulation. This is not just a random number picked. Someone else will probably explain it better, and I welcome them to, but for now I'll try :-) It has something to do with how OFDM takes the signal and breaks it up into lower powered sub carriers. As modulations are higher, they get broken down into more sub carriers, hence QAM 32,64,256, etc. I believe it has something to do with how the math works with Watts versus DB, when the signal gets split and added back togeather again at a later process. There are two side effects that come... As higher modulations are used, it more work for the card and Transmit power becomes less, and receive sensitivity becomes higher (worse). I guess what I'm saying is that its possible to use a specific modulation at many different power levels/ receive levels (RSSI). It depends on the power rating of the card. However, the point I'm making is, at a given set power level or sensitivity rating of a card running a low modulation, if the modulation type is raised, it will have a calculatable/predictable effect on the signal strength received and sent. Tom DeReggi RapidDSL Wireless, Inc IntAirNet- Fixed Wireless Broadband - Original Message - From: Rogelio [EMAIL PROTECTED] To: WISPA General List wireless@wispa.org Sent: Monday, June 16, 2008 10:06 PM Subject: [WISPA] modulation question I've got a question, which I'm afraid might be a little stupid to some, particularly those with RF backgrounds... I've always thought that modulation rate was directly tied to RSSI (for some law of physics reason or something), but someone else told me that it's not like that (in theory) and what I'm seeing is just certain vendors do that for a particular purpose. What is this purpose? WISPA Wants You! Join today! http://signup.wispa.org/ WISPA Wireless List: wireless@wispa.org Subscribe/Unsubscribe: http://lists.wispa.org/mailman/listinfo/wireless Archives: http://lists.wispa.org/pipermail/wireless/ WISPA Wants You! Join today! http://signup.wispa.org/ WISPA Wireless List: wireless@wispa.org Subscribe/Unsubscribe: http://lists.wispa.org/mailman/listinfo/wireless Archives: http://lists.wispa.org/pipermail/wireless/
Re: [WISPA] modulation question
I think some disambiguation may be in order. QAM is a vector modulation method:. http://en.wikipedia.org/wiki/Constellation_diagram It shares almost nothing with OFDM methods. Irrespective, all receivers (CW, AM, FM, SSB, VSB, angle modulation, OFDM, QAM, TCM, etc) can have an RSSI output from the AGC, limiter or demodulator. Strictly speaking it only means Received Signal Strength Indicator. It is modulation agnostic. It is not related to the modulation. - Original Message - From: Tom DeReggi [EMAIL PROTECTED] To: [EMAIL PROTECTED]; WISPA General List wireless@wispa.org Sent: Monday, June 16, 2008 10:10 PM Subject: Re: [WISPA] modulation question I'm not sure exactly your question? I'm also not sure there is a purpose, as much as reporting what occurs. I'm also not sure if you are looking for an answer at the waveform level versus the Link budget level? RSSI is a factor related to Modulation. More specifically with OFDM. Often in manufacturer spec sheets, it will list the minimum rssi level in order to use a specific modulation. This is not just a random number picked. Someone else will probably explain it better, and I welcome them to, but for now I'll try :-) It has something to do with how OFDM takes the signal and breaks it up into lower powered sub carriers. As modulations are higher, they get broken down into more sub carriers, hence QAM 32,64,256, etc. I believe it has something to do with how the math works with Watts versus DB, when the signal gets split and added back togeather again at a later process. There are two side effects that come... As higher modulations are used, it more work for the card and Transmit power becomes less, and receive sensitivity becomes higher (worse). I guess what I'm saying is that its possible to use a specific modulation at many different power levels/ receive levels (RSSI). It depends on the power rating of the card. However, the point I'm making is, at a given set power level or sensitivity rating of a card running a low modulation, if the modulation type is raised, it will have a calculatable/predictable effect on the signal strength received and sent. Tom DeReggi RapidDSL Wireless, Inc IntAirNet- Fixed Wireless Broadband - Original Message - From: Rogelio [EMAIL PROTECTED] To: WISPA General List wireless@wispa.org Sent: Monday, June 16, 2008 10:06 PM Subject: [WISPA] modulation question I've got a question, which I'm afraid might be a little stupid to some, particularly those with RF backgrounds... I've always thought that modulation rate was directly tied to RSSI (for some law of physics reason or something), but someone else told me that it's not like that (in theory) and what I'm seeing is just certain vendors do that for a particular purpose. What is this purpose? WISPA Wants You! Join today! http://signup.wispa.org/ WISPA Wireless List: wireless@wispa.org Subscribe/Unsubscribe: http://lists.wispa.org/mailman/listinfo/wireless Archives: http://lists.wispa.org/pipermail/wireless/ WISPA Wants You! Join today! http://signup.wispa.org/ WISPA Wireless List: wireless@wispa.org Subscribe/Unsubscribe: http://lists.wispa.org/mailman/listinfo/wireless Archives: http://lists.wispa.org/pipermail/wireless/ WISPA Wants You! Join today! http://signup.wispa.org/ WISPA Wireless List: wireless@wispa.org Subscribe/Unsubscribe: http://lists.wispa.org/mailman/listinfo/wireless Archives: http://lists.wispa.org/pipermail/wireless/
