[WISPA] Sandbagging the levy
OK, I fill in one hole and another appeared. (Thanks Brian) I honestly don't know if Orthogon puts the QAM directly on each discrete RF carrier of the OFDM scheme or if those carriers are FMed with a subcarrier containing QAM. So, let me retreat to a previous statement that I still believe to be correct: OFDM does not have any relationship with QAM. (I have CODFM on the brain as that was a superior method of doing OTA HDTV but the ATSC selected 8VSB. But that was in another life...) OFDM strictly speaking only means taking a channel, transmitting multiple RF carriers within that channel. The frequencies are calculated such that there is a minimum of interference between them. Those individual RF carriers are (I discover) commonly refered to by some(most) as subcarriers. Strictly speaking, they are not subcarriers in the classical sense but that is a whole other discussion. I will concede that using the term subcarrier is in common use but is not accurate. (It really depends on what they are doing at the baseband level, so I might be wrong about that opinion as well.) The second channel (R-L) of an FM broadcast signal is on a subcarrier. Color of NTSC video is a subcarrier. Musak is on subcarriers of FM broadcast channels. OFDM bearer channels (howz that for mixing technologies) are discrete RF carriers. But since my opinion of the use of the term subcarrier is in an antiquated minority, I will yield that the term is the commonly accepted method of referring to those carriers. Gheeze it is hard to change. Glad I learned something today... - Original Message - From: Chuck McCown - 2 [EMAIL PROTECTED] To: WISPA General List wireless@wispa.org Sent: Tuesday, June 17, 2008 8:04 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
Re: [WISPA] Sandbagging the levy
BTW, the 93 flood in the midwest was called a 500 year flood. I lived in Quincy, Illinois then and lost some good test gear to the water. Doesn't seem like it has been 500 years since that flood but time does fly. In any event, I feel for you guys in the middle of the country. I filled many sandbags myself. Make sure to honk your own horn after you are done with the emergency. I know I am interested in hearing the stories. Our industry needs to make sure the FCC and the rest of the world knows that we keep working when all the DSL and cable modems stop. 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] Sandbagging the levy
I believe the 93 flood was called the 100 year flood. I filled sandbags that year, as well in a town called Sainte Genevieve, MO (70 miles south of St. Louis). The National Guard took me on a photo op and the area was around Kaskaskia Island was totally obliterated. There were cows on roofs and houses floating down the Mississippi. The levee that was just before the island, that was in the middle of the Mississippi, broke and sank the entire island. The area around there has never recovered. My understanding is that there are now 6 levees that have broke in Missouri. My network is on the west side of St. Louis between the Missouri and Mermac Rivers, I doubt we will see any floods there...but you never know... Time to did out the waders and go shovel some sand... Victoria On Tue, Jun 17, 2008 at 9:56 AM, Chuck McCown - 2 [EMAIL PROTECTED] wrote: BTW, the 93 flood in the midwest was called a 500 year flood. I lived in Quincy, Illinois then and lost some good test gear to the water. Doesn't seem like it has been 500 years since that flood but time does fly. In any event, I feel for you guys in the middle of the country. I filled many sandbags myself. Make sure to honk your own horn after you are done with the emergency. I know I am interested in hearing the stories. Our industry needs to make sure the FCC and the rest of the world knows that we keep working when all the DSL and cable modems stop. 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/ -- Victoria Proffer CEO St. Louis Broadband Visit us @ www.StLBroadband.com 314-974-5600 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] Sandbagging the levy
In Quincy, we had one of the few levees that held until a nut went over and pulled some bags off the top and made it fail on purpose. He had recently been released from jail after serving a term for arson of a school. The local TV station interviewed him as the breech was happening and he was acting like the hero and claiming he was trying to fix the problem. However local levy officials had just visited the very area and said it was one of most sturdy parts. As I recall, a news helicopter or someone actually got footage of him pulling the bags off. He was charged with causing a catastrophe. A local entrepreneur floated a barge over to West Quincy for the purpose of turning it into a restaurant after the water receded. I don't know if that happened or not. Not that any of this has anything to do with WISPA... - Original Message - From: Victoria Proffer [EMAIL PROTECTED] To: WISPA General List wireless@wispa.org Sent: Tuesday, June 17, 2008 9:14 AM Subject: Re: [WISPA] Sandbagging the levy I believe the 93 flood was called the 100 year flood. I filled sandbags that year, as well in a town called Sainte Genevieve, MO (70 miles south of St. Louis). The National Guard took me on a photo op and the area was around Kaskaskia Island was totally obliterated. There were cows on roofs and houses floating down the Mississippi. The levee that was just before the island, that was in the middle of the Mississippi, broke and sank the entire island. The area around there has never recovered. My understanding is that there are now 6 levees that have broke in Missouri. My network is on the west side of St. Louis between the Missouri and Mermac Rivers, I doubt we will see any floods there...but you never know... Time to did out the waders and go shovel some sand... Victoria On Tue, Jun 17, 2008 at 9:56 AM, Chuck McCown - 2 [EMAIL PROTECTED] wrote: BTW, the 93 flood in the midwest was called a 500 year flood. I lived in Quincy, Illinois then and lost some good test gear to the water. Doesn't seem like it has been 500 years since that flood but time does fly. In any event, I feel for you guys in the middle of the country. I filled many sandbags myself. Make sure to honk your own horn after you are done with the emergency. I know I am interested in hearing the stories. Our industry needs to make sure the FCC and the rest of the world knows that we keep working when all the DSL and cable modems stop. 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/ -- Victoria Proffer CEO St. Louis Broadband Visit us @ www.StLBroadband.com 314-974-5600 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/
