Patent Application
20100128174
1. Field of the Invention
This invention relates generally to a method for providing an advanced television standards committee (ATSC) data frame and, more particularly, to a method for positioning mobile data in an ATSC data frame.
2. Description of the Related Art
Conventional broadcasting of data, such as television transmission signals, typically uses analog signals. In North America television stations will be transitioning to a digital format where the television transmission signals will be typically produced and transmitted using an advanced television standards committee (ATSC) data frame protocol, well known to those skilled in the art. With the advent of digital data broadcasting techniques, the same amount of information to be broadcast requires less bandwidth as compared to broadcasting analog signals. Therefore, broadcasting of data using digital signals allows additional data to be broadcast in a given bandwidth while still delivering high quality programs. The additional data can be used for many applications, including alternative television programming and other data related services, including the transmission of weather information and traffic information and audio and video files. Further, the transition to digital television transmission enables new receiver technology. While this new receiver technology has been developed to deliver high quality service to stationary receivers, the present invention reveals how modifications can be made to the transmission system to enable reliable reception to mobile devices including consumer portable electronic devices and motor vehicles.
Data is generally transmitted in the form of multiple data frames. Each data frame transmitted to a non-moving receiver typically includes a frame sync portion and a data portion. The frame sync allows the receiver to lock onto the received signal so that the transmitted signal can be received and deciphered by the receiver. In one technique, the frame sync locks the receiver with the received signal by setting equalization coefficients in the receiver.
After a certain period of time, a non-moving receiver goes out of synchronization with the incoming signals. This happens as a result of data dispersion caused by multipath fading during signal propagation. Multipath fading causes errors that affect the quality of reception. The errors are due to intersymbol interference (ISI). ISI is a form of distortion of a signal in which one symbol interferes with subsequent symbols. This is an unwanted phenomenon as the previous symbols have a similar effect to noise, thus making the communication less reliable. Equalizers can be used to correct ISI. Hence, in the case of non-moving receivers, the receiver is locked with the received signals using the frame sync after every predefined interval of time for continuous reception of the data without any significant loss.
For a moving receiver, the data frame suffers additional dispersion caused by the doppler shift along with the distortion caused by ISI due to the multipath fading. Therefore, a receiver in a moving vehicle needs to resynchronize with the incoming data frames more frequently as compared to a stationary or non-moving receiver for successful reception of the data without any significant loss. However, due to the time interval between the transmission of the sync data, receivers in a moving vehicle are not able to adjust the equalizer coefficients as fast as desired, which causes loss of synchronization and loss of a significant portion of the data.
One existing method for overcoming this issue is to incorporate additional encoding into the television data stream including transmitting sync pulses more often. The ATSC standard committee is investigating these types of methods. A significant limitation of these techniques is that the additional encoding required consumes bandwidth that would otherwise be used for transmitting useful data. Some of these techniques reduce the available data throughput to be over 20%. Thus, the owner of the transmitter must remove data that was to be delivered in order to enable mobile reception.
A method proposed in this invention does not require additional encoding schemes to enable the delivery of data to mobile devices. Hence, all of the existing data services can be provided, including stationary and mobile devices.
In accordance with the teachings of the present invention, a method for producing data frames is disclosed including the optimal placement of mobile sensitive data packets in the data frame that has particular application for transmitting mobile data to be received by portable consumer electronics devices and/or moving vehicles. The method includes forming the data frame by inserting the mobile data in the data frame just after a frame sync and before the broadcast data.
Additional features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.
The following discussion of the embodiments of the invention directed to a system and method for providing optimal placement of mobile sensitive data packets in an ATCS data frame is merely exemplary in nature, and is in no way intended to limit the invention or its applications or uses.
The mobile data 18 is inserted into the ATSC data frame 10 just after the frame sync 12 as opposed to randomly dispersing the mobile data 18 in the data segment 14. By inserting the mobile data 18 just after the frame sync 12, the mobile data 18 is received within a coherence time of the receiver in the portable consumer electronics device and/or moving vehicle, thereby minimizing the dispersion losses in the received mobile data 18. Coherence time is defined as the time during which a receiver remains in synchronization with the incoming data as provided by the frame sync 12. In one non-limiting embodiment, the coherence time can be about 1.5 milliseconds for a moving receiver traveling at high speed, where the mobile data 18 is provided in the data frame 10 to be transmitted after the frame sync 12 within 1.5 milliseconds.
To aid in the understanding of the present invention, an exemplary scenario is provided. When an incoming data signal is received by a vehicle moving at a speed of 100 miles per hour (MPH), the doppler shift corresponding to the received data signal is 119 Hertz. A typical coherence time corresponding to the doppler shift of 119 Hz is 3.5 milliseconds. When updating the receiver at twice the data rate, the receiver needs to be synchronized every 1.7 milliseconds, which is every 19,000 symbols. The current ATSC technology standard cannot achieve synchronization beyond 300 symbols. Therefore, in order to effectively transmit the mobile data 18 to the vehicle moving at 100 MPH, the mobile data 18 is inserted just after the frame sync 12 and before the broadcast data 16, so that it is in the coherence time provided by the frame sync 12 to ensure quality reception of the mobile data 18 without any significant losses due to the movement of the vehicle.
The output signal from the data interleaver 26, the frame sync 12 and the mobile data 18 are provided to a data multiplexer 28. The mobile data 18 is directly fed to the data multiplexer 28 to prevent spreading of the mobile data 18 across the entire bandwidth of the data segment 14, which otherwise can cause loss of data due to dispersion when the ATSC data frame 10 is transmitted to the portable consumer electronics device and/or moving vehicle, as discussed above. The data multiplexer 28 multiplexes the output signal from the data interleaver 26, the frame sync 12 and the mobile data 18 for transmission of the ATSC data frame 10.
The ATSC data frame 10 from the data multiplexer 28 is processed by a signal modulator 30. The signal modulator 30 modulates the ATSC data frame 10 onto a carrier signal. An antenna 32 transmits the modulated signal to be received by a receiver 34 of a moving vehicle 36 or a portable consumer electronics device.
Various embodiments of the present invention offer one or more advantages. The present invention provides a method for effectively transmitting ATSC data frames to a portable consumer electronics device and/or moving vehicles. The method of the present invention comprises the insertion of mobile data just after the frame sync in an ATSC data frame so that when the ATSC data frame is received by the portable consumer electronics device and/or moving vehicle there is no loss of mobile data due to dispersion caused by the doppler shift. Further, the method provides an adequate and effective way of transmitting the data to the portable consumer electronics device and/or moving vehicle without any substantial loss of the data.
The foregoing discussion discloses and describes merely exemplary embodiments of the present invention. One skilled in the art will readily recognize from such discussion and from the accompanying drawings and claims that various changes, modifications and variations can be made therein without departing from the spirit and scope of the invention as defined in the following claims.
