Telecommunications – Carrier wave repeater or relay system – Portable or mobile repeater
Reexamination Certificate
1998-10-30
2001-06-05
Hunter, Daniel (Department: 2684)
Telecommunications
Carrier wave repeater or relay system
Portable or mobile repeater
C455S020000, C455S021000, C455S003010, C455S445000
Reexamination Certificate
active
06243560
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to satellite communications. In particular, the present invention relates to reduction of latency in a satellite communications network.
Communication satellites routinely relay staggering amounts of information between multiple earth terminals every day. Uplink signals and downlink signals transmitted through a communication satellite, however, are subject to delays corresponding to the signal time-of-flight through space and the atmosphere between the earth terminals and the satellite. In other words, electromagnetic propagation (the signal) travels at the speed of light (as modified by whatever medium it travels through, including the atmosphere). The time-of-flight introduces a time delay or latency in the signal corresponding to the amount of time it takes the signal to reach its destination. Furthermore, other significant contributors to overall latency typically exist within a system, including, for example, data processing time delay.
Geostationary orbit satellites are often used for communications because of their unique orbital property of staying fixed at a given longitude, zero degrees latitude, and a constant range. That is, a geostationary satellite remains at a fixed (earth-centered) location in the sky (i.e., the satellite has a non-varying azimuth and elevation). However, geostationary satellites must fly in a singular, circular orbit having a zero inclination and an altitude of approximately 22,000 miles. At this relatively great distance, the latency for one “leg” (from the Earth to the satellite, or vice versa) of signal transfer is approximately ⅛ of a second. While this may not appear to be a significant delay, it can become a serious or compromising aspect for real-time applications when (as is typically the case) several legs of travel are needed. One “hop” (i.e., two legs, one up, one down) takes about ¼ second.
Thus two hops, a typical scenario for earth terminals to transmit a signal to another earth terminal (e.g., another individual user or to a central communications facility) and receive a response, can take more than ½ second. If individual earth terminals must pass information through a central communications station, a complete communications loop (round trip query/response) may take more than one second.
In real-time applications (including action video games, for example) a one second latency is unacceptable. Furthermore, many business applications, such as video-conferencing and work sharing (e.g., spreadsheet or whiteboard applications) are very sluggish given these latencies. Given the trend to increasing satellite communications with decreasing cost, such applications, were it not for the latencies involved, would be poised to introduce a new level of worldwide interactivity.
In the past, however, no techniques have been proposed to reduce latencies to acceptable levels. One reason is that satellite designs fall into a few general categories, none of which is particularly suited to reducing latency. A satellilte that demodulates an uplink signal and remodulates data for a downlink is referred to as “regenerative”. A satellite that demodulates an uplink signal, decodes the signals, and recodes the signals is typically referred to as a “regenerative decode/recode” system or just, “decode/recode”. On the other hand, a satellite which simply forwards the received uplink signals unaltered to a ground station is typically referred to as a “bent pipe” system. These past satellite designs, while useful in many situations, do not provide the satellite with anything more than the ability to relay information. Thus, data that needs to be processed in some fashion must make several hops between specialized processing earth terminals, each hop increasing the latency from original transmission to final reception.
A need exists in the industry for a method for reducing latency in satellite communication systems.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to reduce latency in a satellite communication system.
It is another object of the present invention to allow a satellite to process time critical data.
Another object of the present invention is to allow earth terminals located in diverse locations to interact in real-time.
One or more of the foregoing objects are met in whole or in part by a method for reducing latency in signals transmitted between ground stations through a satellite. The method includes the steps of applying, at a first earth terminal, a discriminator to user data. The discriminator delineates action data and forward data, thereby forming delineated user data. The action data represents data to be processed on board a satellite, while the forward data represents data to be forwarded through the satellite without processing.
Subsequently, the earth terminal transmits the delineated user data to a satellite. At the satellite, the delineated user data is partitioned into the action data and the forward data. The satellite then processes the action data to form processed action data and transmits, if necessary, the processed action data from the satellite.
During processing of the user data, the satellite may generate result data in response to the action data and may transmit the result data alone or appended to the processed action data. Thus the satellite, during processing, may prepare additional data as necessary to supplement the processed data. Furthermore, the satellite may store a world model in a memory onboard the satellite. The satellite, in processing the action data, may then apply the world model to the action data.
As an example, the world model may represent a rule set for a video game. The rule set may include, for example, the boundaries (e.g., a race course) within which a player may move, the maximum velocity and acceleration the player may achieve, and effects of environmental effects (e.g., rain, snow, and the like) on the players. The rule set may also include scoring rules (e.g., 100 points for finishing first), collision rules (e.g., collisions occur when two players positions overlap), and the like.
Other world models are also possible. As another example, the world model may represent a conflict scenario. The conflict scenario may include the starting positions of friendly and enemy tanks and planes, and the rules governing their movement, acceleration, identification, and interaction. Thus, rather than incurring extra hops of signal travel to ground based processing centers and associated latency, the satellite may reduce latency by processing action data at the satellite itself.
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patent: 5966412 (1999-10-01), Ramaswamy
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Hunter Daniel
Keller Robert W.
TRW Inc.
Woldetatios Yemane
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