Patent Publication Number: US-2004049389-A1

Title: Method and apparatus for streaming text to speech in a radio communication system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001] (not applicable)  
       FIELD OF THE INVENTION  
       [0002] The invention relates generally to a method and apparatus for speech transmission, and more particularly to a method and apparatus for delivering and receiving streaming audio via a text to speech conversion in a radio communication system.  
       BACKGROUND OF THE INVENTION  
       [0003] Encoding speech for transmission in a radio communication channel with a typical speech codec requires substantial processing power for converting the speech into a compressed digital bit stream and the resulting bit stream demands substantial bandwidth for transmission. Implementing multiple speech channels using conventional speech codec technology in a communication system with limited bandwidth would severely limit the number of channels available. For example, trying to transmit 100 channels of speech would require an 800 kilobit per second channel using an 8 kilobit per second speech encoder. This would certainly seem like an expensive and inefficient use of bandwidth with respect to spectrum and the associated hardware required to implement such system. Thus, what is needed is an efficient method of providing speech services that is cost effective and bandwidth efficient in its application.  
       [0004] In a system discussed in U.S. Pat. Nos. 5,590,195 and 5,751,806 both by John O. Ryan and both assigned to Command Audio Corporation (and a related parent case, U.S. Pat. No. 5,406,626), alphanumeric data is transmitted on an FM sub-carrier and stored in memory for subsequent processing. It should be noted that the data sent in the Ryan patents is not “real-time” data or necessarily broadcast “live” in the usual sense and thus not processed as real-time data. (See Col. 7, lines 39-57 of &#39;195). In other words, the Ryan patents do not teach the use of a live bit stream transmission intended for real time playback at a receiver.  
       [0005] Competitive broadcast services, such as satellite radio, demand efficient data transmission. Satellite radio operators provide digital quality radio broadcast services covering the entire continental United States. These services offer approximately 100 channels, of which 50 or more channels in a typical configuration will provide music with the remaining stations offering news, sports, talk and data channels.  
       [0006] Satellite radio improves over terrestrial radio&#39;s potential by offering a better audio quality, greater coverage and fewer commercials. Accordingly, in October of 1997, the Federal Communications Commission (FCC) granted two national satellite radio broadcast licenses. The FCC allocated 25 megahertz (MHZ) of the electromagnetic spectrum for satellite digital broadcasting, 12.5 MHz of which are owned by the assignee of the present application “XM Satellite Radio Inc.” 
       [0007] The system plan for XM Satellite Radio includes digital transmission of substantially the same program content from two or more geosynchronous or geostationary satellites to both mobile and fixed receivers on the ground. In urban canyons and other high population density areas with limited line-of-sight (LOS) satellite coverage, terrestrial repeaters rebroadcast the same program content in order to improve coverage reliability. Mobile receivers are capable of simultaneously receiving signals from two satellites and one terrestrial repeater for combined spatial, frequency and time diversity, which provides significant mitigation of multipath interference and addresses reception issues associated with blockage of the satellite signals. In accordance with XM Satellite Radio&#39;s unique scheme, the 12.5 MHZ band will be split into 6 slots. Four slots will be used for satellite transmission. The remaining two slots will be used for terrestrial reinforcement.  
       SUMMARY OF THE INVENTION  
       [0008] In a first aspect of the present invention, a method for text to speech conversion in a radio communication system comprises the steps of receiving a text transmission over the air at a receiver and converting the text transmission to an audible speech signal at the receiver in real time.  
       [0009] In a second aspect of the present invention, a receiver capable of converting a received text transmission to audible speech comprises a decoder for decoding a received signal received over the air and containing the received text transmission and a text to speech converter for converting the received text transmission into an audible speech signal in real time. The receiver may also comprise an amplifier and speaker for playing the audible speech signal.  
       [0010] In a third aspect of the present invention, a radio system deploying streaming text to speech channels comprises a transmission source transmitting a plurality of digitally encoded channel resources, wherein the channel resources contains at least one channel resource containing digitally encoded text. The radio system further comprises a receiver for selectively decoding the plurality of digitally encoded channel resources, wherein the receiver further comprises a text to speech converter which converts the digitally encoded text into an audible speech signal at the receiver in real time.  
       [0011] In a fourth aspect of the present invention, a method of transmitting a digital audio radio broadcast transmission containing audio content, comprises the step of providing a plurality of digital music channels compressed with a first audio compression algorithm, the plurality of digital music channels containing data intended for text display on a receiving device and the step of providing at least one text channel transmitted at an average bit rate required for real-time playback by a text-to-speech converter in the receiving device, the at least one text channel containing associated data intended for text display on the receiving device.  
       [0012] In a fifth aspect of the present invention, a device for digital audio radio broadcast transmissions comprises a plurality of digital audio channels compressed with a first audio compression algorithm, wherein at least a first portion of plurality of digital audio channels contains associated data intended for text display on a receiving device and wherein at least a second portion of the plurality of digital audio channels contains associated data intended for real-time play back by a text-to-speech converter in the receiving device. The device further comprises a transmitter for transmitting the plurality of digital audio channels.  
       [0013] In a sixth aspect of the present invention, a device for receipt of digital audio radio broadcast transmissions comprises a receiver having a display and a speaker coupled thereto, wherein the receiver receives a plurality of digital audio channels compressed with a first audio compression algorithm, wherein at least a first portion of plurality of digital audio channels contains associated data intended for text display on the device. The device further comprises a text-to-speech converter in the receiver, wherein at least a second portion of the plurality of digital audio channels contains associated data intended for real-time play back by the receiver using the text-to-speech converter. At least one decoder is used for decoding the first portion of the plurality digital audio channels and for decoding the second portion of the plurality of digital audio channels.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0014]FIG. 1 illustrates a satellite digital audio radio service system architecture in accordance with the present invention.  
     [0015]FIG. 2. is a diagram illustrating a representative bit stream in a frame format for distributing data in accordance with the present invention.  
     [0016]FIG. 3 is a diagram illustrating a communication resource providing text in accordance with the present invention.  
     [0017]FIG. 4 is a diagram illustrating the communication resource of FIG. 3 in further detail in accordance with the present invention.  
     [0018]FIG. 5. is a flowchart illustrating a method in accordance with the present invention.  
     [0019]FIG. 6 is a block diagram of a radio transmission source in accordance with the present invention.  
     [0020]FIG. 7 is a block diagram of a radio receiver unit in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS  
     [0021] The present invention uses a broadcast radio service to deliver real-time streaming audio to listeners via text transmissions over-the-air. Correspondingly, a listener in accordance with the present invention preferably plays back the text transmission via a real-time text-to-speech converter at the receiver. Typical efficient applications of such text-to-speech radio channels are local traffic information, local weather information, stock or financial quotes, sports scores, transportation scheduling information, and real-time speech auxiliary information channels associated with music or talk channels as will be explained in further detail with respect to FIG. 4. Normal speech rates of 2.5 words per second and average word lengths of 10 characters at 8 bits per character would seem to indicate that 240 bit per second channels would be adequate for text-to-speech channels. Real-time compression algorithms, which compress the text prior to transmission and decompress the text at the receiver prior to text-to-speech conversion would further reduce the required channel bit rate. Without compression, a 24 kilobit per second channel could be subdivided to simultaneously support 100 channels providing real-time text to speech. This is readily achievable in a Satellite Digital Audio Radio Systems (SDARS) like the one provided by XM Satellite Radio.  
     [0022] Referring to FIG. 1, satellite radio operators now provide digital radio service to the continental United States. Briefly, the service provided by XM Satellite Radio includes a satellite X-band uplink  11  to two satellites ( 12  and  14 ) which provide frequency translation to the S-band for re-transmission to radio receivers ( 20 ,  22 ,  24 , and  26 ) on earth within the coverage area  13 . The satellites provide for interleaving and spatial diversity. Radio frequency carriers from one of the satellites are also received by terrestrial repeaters ( 16  and  18 ). The content received at the repeaters are also “repeated” at a different S-band carrier to the same radios ( 20 ) that are within their respective coverage areas ( 15  and  17 ). These terrestrial repeaters facilitate reliable reception in geographic areas where LOS reception from the satellites is obscured by tall buildings, hills, tunnels and other obstructions. The signals transmitted by the satellites  12  and  14  and the repeaters are received by SDARS receivers  20 - 26 . As depicted in FIG. 1, the receivers  20 - 26  may be located in automobiles, handheld or stationary units for home or office use. The SDARS receivers  20 - 26  are designed to receive one or both of the satellite signals and the signals from the terrestrial repeaters and combine or select one of the signals as the receiver output.  
     [0023] Referring to FIG. 2, a plurality of communication resource channels (Channel  1  through  100 ) are shown in accordance with the present invention. In this instance, the over-the-air protocol frame format  100  of the XM Satellite Radio system is shown. This frame format  100  is based on a 432 millisecond frame as shown in FIG. 2 where each frame is subdivided into 8 kilobit per second sub-channels  102 . The first two 8 kilobit per second subchannels of each frame  103  are assigned to a Time Slot Control Channel (TSCC), which contains broadcast information about the remaining subchannels. This broadcast information includes service descriptive data to enable end users to view information pertinent to the services available, such as labels for active services, songs and artists and service categories and also includes format configuration data necessary for receivers to extract a specific service from the frame, such as service-to-sub-channel maps or similar data position indicators, as well as other broadcast data. The remaining subchannels  102  can be dynamically grouped to form higher bit rate payload channels  104 . The payload channel or communication resource  104  provides the necessary bandwidth to transport a high-quality digital audio signal to the listener as well as other data as will become more apparent. When a listener changes channels, a receiver in accordance with the present invention simply extracts a different payload channel from the frame  100 . It should be noted that each receiver in the XM Satellite System has a unique identifier allowing for the capability of individually addressing each receiver over-the-air to enable or disable services or to provide custom applications such as individual data services or group data services.  
     [0024] Referring to FIG. 3, each payload channel or communication resource  104  preferably comprises a preamble  106 , a service control header  200  and a service component  108 , which is 8 kilobits per second in this example. The service component contains the content that will be delivered to the listener, whether it is music, speech, text (which may or may not be converted to speech) or possibly video in future applications. Correspondingly with reference to FIG. 4, each service control header  200  comprises a frame start ID  204 , bit rate index field  208 , and a service component control field  210 . The service component control field (SCCF)  210  would contain information about the service component  108 . For example, a SCCF  210  might contain information indicating that the content in service component  108  is text and should be decoded using a text-to-speech converter. Alternatively, SCCF  210  might indicate that the content in service component is compressed digital audio and that an audio decoder is required.  
     [0025] Referring to FIG. 5, a flow chart illustrating a text-to-speech method  300  in a communication system in accordance with the present invention is shown. At step  302 , text is preferably encoded in a data stream as shown in FIG. 2. Preferably, the text is embedded in a portion of a payload channel or alternatively as part of the TSCC or an auxiliary data field  212  as shown in FIG. 4. At step  304 , the encoded text is transmitted from a transmission source (preferably an SDARS system that delivers real-time streaming audio). Preferably, the transmission source provides a plurality of digital music channels compressed with a first audio compression algorithm, the plurality of digital music channels having associated data, transmitted simultaneous with the music channels and located in the TSCC or in the Payload Channel, intended for text display on a receiving device. The transmission source also provides at least one text channel transmitted at an average bit rate required for real-time (audio) playback by a text-to-speech converter in the receiving device, the at least one text channel also having associated service data intended for text display on the receiving device and having associated configuration data intended to enable the receiving device to extract the text channel from the frame. At step  306 , the encoded text is transmitted over a plurality of communication resources or channels along with music and/or speech or other data. In other words, at least the text transmission on one of a plurality of communication resources, a digitally encoded music signal on another of the plurality, and optionally a digitally encoded speech signal on yet another of the plurality is transmitted. At step  308 , the encoded text is received over the air at the receiving device. The plurality of resource channels containing the text transmission (and optionally the digitally encoded music signal or the digitally encoded speech signal) is preferably selectively decoded. The encoded text is then converted to an audible speech signal at the receiving device in real time at step  310 .  
     [0026] Referring to FIG. 6, a device  400  for digital audio radio broadcast transmissions is shown. The device  400  generates a plurality of real time digital audio channels, where each audio channel is comprised of either digital audio compressed with a first audio compression algorithm or streamed text intended for playback with a text-to-speech converter, wherein at least a first portion of plurality of real time digital audio channels contains associated data intended for text display on a receiving device and optionally at least a second portion of the plurality of digital audio channels contains associated data intended for real-time play back by a text-to-speech converter in the receiving device. In one particular embodiment as shown in FIG. 6, the plurality of digital audio channels are shown as “data source 1”  402 , “data source 2”  403  and “data source N”  404 . The data in the plurality of digital audio channels containing digital audio data will preferably be routed via an audio router  401  to an encoder  405 . This data is encoded at a different rate than the data received by a text buffer  406  as will be further explained below. The data in the plurality of digital audio channels containing data associated with the audio data will preferably be routed via a data router  407  to the encoder  405 . The data coming from the audio router  401  is preferably digital audio, which may be compressed with a first audio compression algorithm. The data routed via the data router  407  is preferably the first portion of the plurality of digital audio channels that contains associated data intended for text display on the receiving device. The data that is routed ultimately through the text buffer  406  is from digital audio channels configured for text-to-speech playback and optionally from the second portion of the plurality of digital audio channels that contains associated data and intended for real-time play back by a text-to-speech converter in the receiving device. The data routed through the text buffer  406  is preferably encoded at a rate of N bits/second that matches an N bits/second decoder used by the receiving device for live text-to-speech conversion. After encoding, the data is formatted, multiplexed and then routed via an uplink delivery system  410  to a transmitter  412  for transmitting the plurality of digital audio channels.  
     [0027] Referring to FIG. 7, a receiver unit  600  is shown capable of converting a received text transmission to audible speech. The receiver unit  600  preferably has a display  617  and a speaker  616  and the receiver unit further receives a plurality of digital audio channels comprised of either digital audio compressed with a first audio compression algorithm or streamed text encoded for real-time play back by a text-to-speech converter  612 . The text-to-speech converter preferably has an N bit/second decoder matching the N bit/second encoder used by the transmitting device (see  408  of FIG. 6). At least a first portion of the plurality of digital audio channels contains associated data intended for text display on the receiver unit. Optionally, at least a second portion of the plurality of digital audio channels contains associated data intended for real-time play back by the receiver using a text-to-speech converter.  
     [0028] The receiver unit  600  preferably comprises a receiver  602  coupled to a decoder  604  for decoding a received signal received over the air and containing the received text transmission. The receiver  602  may also comprise tuning circuits (not shown) and the decoder  604  may also comprise decryption logic (if the data received is encrypted) as known in the art. The received signal containing the received text transmission is preferably received over the air and transmitted over a 240 bit per second channel. The receiver unit also preferably comprises a controller  605  and a multiplexer  606  for appropriately multiplexing signals between an audio decompressor  608 , a speech decompressor  610 , or the text-to-speech converter  612  for converting the received text transmission into an audible speech signal in real time. The resultant signal from either the audio decompressor  608 , the speech decompressor  610 , or the text-to-speech converter  612  is then amplified at amplifier  614  and outputted through speaker  616  for playing an audible speech signal. The audio decompressor  608  may also comprise digital to analog converters (not shown) as is known in the art. The resultant signal from the audio decompressor  608 , the speech decompressor  610 , or the textto-speech converter  612  may also contain associated data in the form of text that can optionally be displayed via the display  617 . It should be understood that a receiver unit in accordance with the present invention could receive data in the form of text information that is associated with music, news, talk, or even the “text-to-speech” channels and essentially provides programming information such as channel id, artist name, song title, news segment title, talk show guest name, weather location, traffic location, and so on. This text data can optionally be displayed or remain embedded and invisible to the user of the receiver unit. It should also be understood that the text data received in a “text-to-speech” channel is likely to be separate and apart from the associated data that provides text information such as programming information for a given channel. The “text-to-speech” channel data would likely be encoded and decoded at a rate different from the data providing the music, news and talk channels or possibly even the text data associated with such channels. To further the efficiency of the text-to-speech channel, the real time text transmission may be compressed, allowing for reduced bit rates required for transmission. If the text is compressed, it would preferably be decompressed using a text decompressor  611  prior to application to the text-to-speech conversion in the receiver unit  602 .  
     [0029] Thus, the present invention has been described herein with reference to a particular embodiment for a particular application. Those having ordinary skill in the art and access to the present teachings will recognize additional modifications, applications and embodiments within the scope thereof. For example, the present invention is not limited to use in satellite radio applications. It is therefore intended by the appended claims to cover any and all such applications, modifications and embodiments within the scope of the present invention. The description above is intended by way of example only and is not intended to limit the present invention in any way except as set forth in the following claims.