Losing XM signal under trees
#17
05-20-2018, 04:22 PM
Lm
XM provides digital programming directly from two high-powered satellites in geostationary orbit above the equator: XM Rhythm at 115° west longitude and XM Blues at 85° west longitude in addition to a network of ground-based repeaters. The combination of two satellites and a ground-based repeater network is designed to provide gap-free coverage anywhere within the contiguous U.S., the southern tip of Alaska, and in the southern part of Canada. The signal can also be received in the Caribbean Islands and most of Mexico (reports have stated that areas north of Acapulco are able to receive a steady signal[17]), however XM is not yet licensed for reception by paid subscribers living in these areas.
The original satellites, XM-1 ("Rock") and XM-2 ("Roll") suffer from a generic design fault on the Boeing 702 series of satellites (fogging of the solar panels), which means that their lifetimes will be shortened to approximately six years instead of the design goal of 15 years.[18][19] To compensate for this flaw, XM-3 ("Rhythm") was launched ahead of its planned schedule on February 28, 2005 and moved into XM-1's previous location of 85° WL. XM-1 was then moved to be co-located with XM-2 at 115° WL, where each satellite operated only one transponder (thus broadcasting half the bandwidth each) to conserve energy and cut the power consumption in half while XM-4 ("Blues") was readied for launch. Subsequently, XM launched ground-spare XM-4 ("Blues") ahead of schedule on October 30, 2006 into the 115° WL location to complete the satellite replacement program. On December 15, 2006 XM-1 was then powered down and drifted back to its original location at 85° WL, where it will remain as a backup to XM-3. XM-2 as well was powered down and remains as a backup to XM-4. This makes the current active satellites as XM-3 "Rhythm" and XM-4 "Blues" with two in-orbit spares.[6][20]
XM Satellite Radio headquarters in Washington, D.C., near the New York Avenue metro station.
XM Satellite Radio headquarters in Washington, D.C., near the New York Avenue metro station.
On June 7, 2005, Space Systems/Loral announced that it had been awarded a contract for XM-5.[21][22] XM-5 will feature two large unfurlable antennas. Sirius' Radiosat 5, also to be built by Loral, will have a similar single large antenna.
In American and Canadian metropolitan areas, XM and its Canadian Licensee known as Canadian Satellite Radio (CSR), own and operate a network of approximately 900 terrestrial repeater stations, meant to compensate for satellite signal blockage by buildings, tunnels, and bridges. In the United States XM owns and operates approximately 800 repeater sites covering 60 markets; in Canada CSR is installing approximately 80 to 100 repeaters that will be owned and operated by CSR in the 16 largest Canadian cities. The actual number of repeater sites varies as the signal is regularly tested and monitored for optimal performance. The actual number of sites in the United States has dropped from the original 1,000 installed when the service first launched in 2001. The repeaters transmit in the same frequency band as the satellites. A typical city contains 20 or more terrestrial stations. Typically the receiver owner is unaware when a terrestrial station is being used, unless he or she checks antenna information from the receiver being used. Due to a FCC filing in October 2006, the latest list of XM's US terrestrial repeater network was made available to the public.
The XM signal uses 12.5 MHz of the S band: 2332.5 to 2345.0 MHz. XM provides 128 kilobits per second of its bandwidth to OnStar Corporation for use with XM-enabled GM vehicles, regardless of whether their owners are XM subscribers. American Honda also retains the right to some of the company's bandwidth to transmit messages to Acura vehicles via a service known as AcuraLink.
XM NavTraffic, an optional service, transmits coded traffic information directly to vehicle navigation systems using TMC technology.
Audio channels on XM are digitally compressed using the aacPlus (HE-AAC) codec from Coding Technologies for most channels, and the AMBE codec from Digital Voice Systems for some voice channels, including all of the Traffic and Weather channels.
The XM radio signal is broadcast on 6 separate radio carriers within the 12.5 MHz allocation. The entire content of the radio service, including both data and audio content, is represented by only two carriers. The other 4 carriers carry duplicates of the same content to achieve redundancy through signal diversity. The data on each carrier is encoded using time-delayed and error-correction schemes to enhance availability. Effectively the total radio spectrum used for content is a little over 4 MHz.[23]
Each two-carrier group broadcasts 100 8-kilobit-per-second streams in approximately 4 MHz of radio spectrum. These streams are combined using a patented process to form a variable number of channels using a variety of bitrates. Bandwidth is separated into segments of 4-kilobit-per-second virtual "streams" which are combined to form audio and data "channels" of varying bitrates from 4 to 64 kilobits-per-second.[24]
XM preprocesses audio content using Neural Audio processors that are optimized for the AACplus codec, including spectral band replication (SBR). Audio is stored digitally in Dalet audio library systems using an industry-standard MPEG-1 Layer II at 384 kbit/s, sometimes known as Musicam. The audio is further processed by the Neural Audio processors on the way to broadcast.
XM channels XM Pops and Fine Tuning are broadcast in 5.1 surround sound audio quality. The technology, titled XM HD Surround, is the result of a partnership between XM and Neural Audio Corporation which provides content with six discrete channels of digital audio. XM Live also broadcasts in this format for certain concerts and studio performances. XM manufacturing partners such as Denon, Onkyo, Pioneer Electronics (USA) Inc., and Yamaha have introduced home audio systems capable of playing XM HD Surround.
The original satellites, XM-1 ("Rock") and XM-2 ("Roll") suffer from a generic design fault on the Boeing 702 series of satellites (fogging of the solar panels), which means that their lifetimes will be shortened to approximately six years instead of the design goal of 15 years.[18][19] To compensate for this flaw, XM-3 ("Rhythm") was launched ahead of its planned schedule on February 28, 2005 and moved into XM-1's previous location of 85° WL. XM-1 was then moved to be co-located with XM-2 at 115° WL, where each satellite operated only one transponder (thus broadcasting half the bandwidth each) to conserve energy and cut the power consumption in half while XM-4 ("Blues") was readied for launch. Subsequently, XM launched ground-spare XM-4 ("Blues") ahead of schedule on October 30, 2006 into the 115° WL location to complete the satellite replacement program. On December 15, 2006 XM-1 was then powered down and drifted back to its original location at 85° WL, where it will remain as a backup to XM-3. XM-2 as well was powered down and remains as a backup to XM-4. This makes the current active satellites as XM-3 "Rhythm" and XM-4 "Blues" with two in-orbit spares.[6][20]
XM Satellite Radio headquarters in Washington, D.C., near the New York Avenue metro station.
XM Satellite Radio headquarters in Washington, D.C., near the New York Avenue metro station.
On June 7, 2005, Space Systems/Loral announced that it had been awarded a contract for XM-5.[21][22] XM-5 will feature two large unfurlable antennas. Sirius' Radiosat 5, also to be built by Loral, will have a similar single large antenna.
In American and Canadian metropolitan areas, XM and its Canadian Licensee known as Canadian Satellite Radio (CSR), own and operate a network of approximately 900 terrestrial repeater stations, meant to compensate for satellite signal blockage by buildings, tunnels, and bridges. In the United States XM owns and operates approximately 800 repeater sites covering 60 markets; in Canada CSR is installing approximately 80 to 100 repeaters that will be owned and operated by CSR in the 16 largest Canadian cities. The actual number of repeater sites varies as the signal is regularly tested and monitored for optimal performance. The actual number of sites in the United States has dropped from the original 1,000 installed when the service first launched in 2001. The repeaters transmit in the same frequency band as the satellites. A typical city contains 20 or more terrestrial stations. Typically the receiver owner is unaware when a terrestrial station is being used, unless he or she checks antenna information from the receiver being used. Due to a FCC filing in October 2006, the latest list of XM's US terrestrial repeater network was made available to the public.
The XM signal uses 12.5 MHz of the S band: 2332.5 to 2345.0 MHz. XM provides 128 kilobits per second of its bandwidth to OnStar Corporation for use with XM-enabled GM vehicles, regardless of whether their owners are XM subscribers. American Honda also retains the right to some of the company's bandwidth to transmit messages to Acura vehicles via a service known as AcuraLink.
XM NavTraffic, an optional service, transmits coded traffic information directly to vehicle navigation systems using TMC technology.
Audio channels on XM are digitally compressed using the aacPlus (HE-AAC) codec from Coding Technologies for most channels, and the AMBE codec from Digital Voice Systems for some voice channels, including all of the Traffic and Weather channels.
The XM radio signal is broadcast on 6 separate radio carriers within the 12.5 MHz allocation. The entire content of the radio service, including both data and audio content, is represented by only two carriers. The other 4 carriers carry duplicates of the same content to achieve redundancy through signal diversity. The data on each carrier is encoded using time-delayed and error-correction schemes to enhance availability. Effectively the total radio spectrum used for content is a little over 4 MHz.[23]
Each two-carrier group broadcasts 100 8-kilobit-per-second streams in approximately 4 MHz of radio spectrum. These streams are combined using a patented process to form a variable number of channels using a variety of bitrates. Bandwidth is separated into segments of 4-kilobit-per-second virtual "streams" which are combined to form audio and data "channels" of varying bitrates from 4 to 64 kilobits-per-second.[24]
XM preprocesses audio content using Neural Audio processors that are optimized for the AACplus codec, including spectral band replication (SBR). Audio is stored digitally in Dalet audio library systems using an industry-standard MPEG-1 Layer II at 384 kbit/s, sometimes known as Musicam. The audio is further processed by the Neural Audio processors on the way to broadcast.
XM channels XM Pops and Fine Tuning are broadcast in 5.1 surround sound audio quality. The technology, titled XM HD Surround, is the result of a partnership between XM and Neural Audio Corporation which provides content with six discrete channels of digital audio. XM Live also broadcasts in this format for certain concerts and studio performances. XM manufacturing partners such as Denon, Onkyo, Pioneer Electronics (USA) Inc., and Yamaha have introduced home audio systems capable of playing XM HD Surround.
#19
05-20-2018, 07:49 PM
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