System for providing high-efficiency push-to-talk communication service to large groups over large areas

A system, various methods, and a specific apparatus are provided for the purpose of supporting push-to-talk (PTT) service for a very large group featuring a significantly higher number of listeners than the number of potential talkers, as well as a constrained vocabulary in normal usage. The invention takes advantage of speech-to-text and text-to-speech conversion in end user devices for maximum utterance compression. The invention uses the Iridium Mobile Satellite Service (MSS) system and its Short Burst Data (SBD) service for unicast transmission of talker utterances to a PTT Server, and the same system's Global Data Broadcast (GDB) service for multicast retransmission of utterances from the PTT Server to an effectively unlimited number of listeners. The PTT Server provides priority ordering and preemption as necessary when multiple talkers provide near-simultaneous utterances, effectively managing the floor without interactive protocols among the talkers.

BACKGROUND OF THE INVENTION

Push-to-talk (PTT) wireless voice communication has a long history, stretching back to the “handy-talky” military radio of World War II and encompassing various forms of “walkie-talkie” military, police/fire, commercial, hobbyist, and even toy radios. Many such systems have relied on peer to peer radio communication, in which each user transmits directly to all other users via a shared radio spectrum. This technique limits range to that of the individual unit and its transmit power. Other systems, particularly including the dedicated trunked-radio systems deployed for commercial users and first responders, employ repeaters with greater transmit power and receive sensitivity than a handheld unit can achieve, thereby multiplying the reach of a network significantly.

Most recently, PTT systems have been built on top of cellular radio network technologies, allowing the specialized group-communication needs of typical PTT users to take advantage of the commercially successful and widely deployed cellular networks. These systems expand upon the repeater topology model of trunked radio, relying on multiple interconnected base stations to extend the reach of the power-limited handsets, rather than the very large repeater stations typical of trunked radio installations. A development of particular note in this area is the application of Mobile Satellite Services (MSS) systems to PTT group communication, embodied in the Distributed Tactical Communication System (DTCS) developed by the US Navy for Marines deployed around the world. As described in http://www.defenseindustrydaily.com/217M-for-Phase-II-of-Netted-Iridium-Program-05483/, this system builds upon the Iridium MSS system to provide voice group communication for up to 2,000 users in an area up to 250 miles wide. Per http://www.iridium.com/DownloadAttachment.aspx?attachmentID=1197, each spot beam of an Iridium satellite is about 250 miles in diameter, suggesting that DTCS service is provided only within the coverage area of a single beam. In addition to the existing capability, according to http://investor.iridium.com/releasedetail.cfm?ReleaseID=556479, enhanced capabilities under development at the time of this writing promise to expand the DTCS user capacity by a factor of 30. Though not stated explicitly in the public information, this would seem to imply an increase in the number of group members to some tens of thousands (2,000×30=60,000), and may also imply an increase in the range of coverage to incorporate multiple beams in the serving area for a particular group. It is possible that techniques taught in U.S. Pat. No. 6,577,848 may be incorporated in both current and future DTCS designs. In any case, a PTT system built on the Iridium MSS system is of special interest due to its global coverage and ability to provide service in areas that do not have trunked radio or cellular coverage.

In all this prior art, the primary goals of each PTT system have been to adjudicate which user is allowed to speak, and to relay that user's speech burst to all the other users. The older systems relied upon the people themselves to resolve channel utilization conflicts using social protocols, also known as “floor control,” and used direct frequency modulation techniques to convey the analog audio over the radio. Current systems employ digital packet protocols to negotiate floor control, digital speech coding with compression to represent the talker's speech burst (also known as an “utterance”), and digital radio modulation techniques to carry both. Even the latest systems with digital speech coding and the deepest available compression techniques require at least 2,400 bits to convey each second of the talker's utterance over the network, and current designs attempt to match the channel resource to that bit rate so as to convey each utterance in real time. An average utterance lasting 5 seconds thus transmits at least 1,500 bytes over 5 seconds of channel time, plus whatever overhead is required for channel management and floor control in the specific system. Regarding floor control as well, the protocols are generally designed based on the assumption that any group member may attempt to speak at any time; this assumption tends to limit the scale of groups. Outside the domain of PTT service, techniques exist in the prior art that allow users to dictate a message into the Short Message Service (SMS) capability ubiquitous in current cellular handsets, as well as to read back a message received via SMS. This technology is normally used to avoid the use of hands for messaging while driving; it is not normally used to carry on a real-time conversation, for which an ordinary phone call is well suited, and more efficient. However, this speech-to-text and text-to-speech technology is available for application in the PTT domain, and offers the opportunity for extreme compression. For example, the 5-second, 1500-byte utterance mentioned above may require only 150 bytes to convey if transcribed as text.

Another attribute of prior art systems, and particularly the cellular-based digitally-coded systems in common use today, is their use of a power-optimized traffic channel to convey the coded speech of each utterance. These radio channels are typically run at a power level that assumes not quite perfect channel conditions, but that still requires each user in the group to be holding his or her handset in the talking/listening position wherein the antenna is deployed appropriately. In Iridium, for example, it is well known that the traffic channel power level is so low that during a call the handset must either be attached to a separate antenna mounted in an optimal location, or held to the ear with the embedded antenna extended and angled properly above the head. This likely applies in DTCS as well, although no public information is available to confirm it.

The system attributes described in the two foregoing paragraphs support the observation that some conceivable applications of PTT service are not effectively satisfied by existing prior art systems due to scalability constraints linked to the specific efficiency and capacity considerations associated with the usage assumptions cited. In particular, situations in which most users are only listeners and who either do not need to or cannot keep a handset in optimal position are excluded from the groups supportable in the prior art. What is needed, then, is a system that supports such groups, which may number 10,000 to 1,000,000 or more members listening as a background activity but which feature only a handful of potential speakers.

It is thus a principal aim of the present invention to provide a system that supports PTT services for such large and asymmetric groups, optimizing resource utilization differently from the prior art using novel techniques and construction not found in the prior art.

SUMMARY OF THE INVENTION

In accordance with the principles of the present invention, a method of providing a communication to a receiving device comprises conversion of a first audio utterance into a text based message; and transmission, via a text delivery optimized communication network, of the text based message. The text based message is transmitted, via a broadcast optimized communication network, to at least one receiving device to convert the text based message into a second audio utterance.

In further accordance with the principles of the present invention, a communication device to communicate with a receiving device comprises a speech-to-text converter to convert a first audio utterance into a text based message; and a transmitter to transmit, via a text delivery optimized communication network, the text based message. The text based message is transmitted, via a broadcast optimized communication network, to at least one receiving device to convert the text based message into a second audio utterance.

In further accordance with the principles of the present invention, a method of providing a communication to a receiving device comprises reception, via a broadcast optimized communication network, of a text based message; and conversion of the text based message into a second audio utterance. The text based message is transmitted, via a text delivery optimized communication network, from a transmitting device that converts a first audio utterance into the text based message.

In further accordance with the principles of the present invention, a communication device comprises a receiver to receive, via a broadcast optimized communication network, a text based message; and a text-to-speech converter to convert the text based message into a second audio utterance. The text based message is transmitted, via a text delivery optimized communication network, from a transmitting device converting a first audio utterance into the text based message.

In further accordance with the principles of the present invention, a communication server comprises an input handler to receive, via a text delivery optimized communication network, a text based message; and a subroutine, at the communication server, to identify a destination parameter associated with the text based message. An output handler at the communication server transmits, via a broadcast optimized communication network, the text based message to at least one receiving device based on the destination parameter. The at least one receiving device converts the text based message into an audio utterance.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This invention pertains in general to closed-group push-to-talk communication among associated wireless handset device users. The invention pertains in particular to providing such communication to large groups numbering in the hundreds, thousands, or millions of users, who are distributed widely over an area potentially as large as the entire world. The invention further pertains in particular to using a highly efficient communication means to provide such service.

The present invention provides an asymmetric half-duplex communication construct that uses the Iridium MSS system for a highly efficient PTT service supporting a relatively small number of potential talkers, and a very large number of potential listeners whose various radio equipments are not necessarily in optimal positions for low-power radio reception.

For the highest possible efficiency of speech burst transmission, observe that in the groups with the target asymmetry of talkers and listeners, it is usual for communication to be constrained using a specialized and limited vocabulary such as those found in military, search and rescue, civil defense, firefighting, or law enforcement settings. With the amount of processing capability available in handheld and other portable devices using current technology, the use of a constrained vocabulary allows very reliable speech recognition even without specific-speaker training. Thus the present invention incorporates speech-to-text and text-to-speech capabilities at the user devices for maximum compression of utterances.

For the transport of converted utterances from a talker into the network, the present invention uses the Iridium Short Burst Data (SBD) service, on which more information is available via http://www.iridium.com/DownloadAttachment.aspx?attachmentID=890. This capability is designed to carry messages up to 340 bytes in the most efficient manner available on the Iridium network. Using SBD, the permitted talkers in a PTT group don't need any floor control protocol amongst them. Instead, they use the SBD service's native system access protocol to queue their respective messages into the network. A PTT host server receives these talk burst messages and sends them in turn to the listeners via a heretofore undisclosed Iridium broadcast capability.

For the transport of converted utterances from the network back to the multitude of listeners, the present invention uses the Iridium Global Data Broadcast (GDB) service. This capability is design to transmit messages up to several thousand bytes to an unlimited number of receivers within a target delivery area. Each message is addressed to a unique group, and any number of devices may be configured to receive messages to that address. GDB is built upon the Iridium Paging channel described in U.S. Pat. No. 5,603,079, but it uses a timing hierarchy that supports low-latency delivery, and a message format that enables group-directed broadcasting capability, instead of the long cycle and individual addressing techniques designed to support individual low-power pagers that are described there and in related U.S. Pat. Nos. 5,613,194, 5,721,534, and 5,905,443.

A significant advantage of GDB over the techniques used in U.S. Pat. No. 6,577,848, and presumably Iridium DTCS, is that the transmit power level from the satellite is significantly higher in GDB than that of the traffic channel used in the PTT prior art. This attribute is inherited from the Paging channel of U.S. Pat. No. 5,603,079 as implemented in the Iridium MSS system. Listen-only group members are therefore able to receive the converted PTT utterances via this high-power channel with a less capable, that is smaller or not optimally deployed, antenna. This attribute of the present invention enables very large PTT groups, with the potential number of listeners practically unlimited. Additional information regarding GDB is available in U.S. patent application Ser. No. 13/657,295, the entirety of which is expressly incorporated herein by reference.

InFIG. 1, each of multiple Satellites110offers wireless connectivity for push-to-talk and other services to zero or more PTT User Terminals120that lie within each respective Coverage Area115. Each Coverage Area115is formed by its respective Satellite110via transmission and reception of radio frequency energy using its respective Antenna Projections112. Satellites110communicate with one another via one or more wireless Crosslinks111, and with each of one or more Satellite Earth Stations130via a corresponding wireless Feederlink113. Detail regarding these fundamental elements of the Iridium Mobile Satellite Services System is readily available to those skilled in the art, and constitute a basis on which the present invention is built.

Satellite Earth Stations130in turn provide access to the constellation of Satellites110on behalf of ground-based network elements, attaching via Network Interface134to Ground Network140for the transport of data among them. Ground Network140is preferably based on the well-known Internet Protocol and related technologies.

Ground-based network elements pertinent to the present invention include the SBD Gateway150and the GDB Gateway170, which connect to Ground Network140via Network Interfaces154and174respectively. These elements are not new for this invention, and so are not detailed further. Information regarding SBD and its architecture can be found at http://www.iridium.com/support/products/IridiumSBD.aspx. Information regarding GDB and its architecture can be found in U.S. patent application Ser. No. 13/657,295.

PTT Server160is the ground-based actor in the present invention. This network element receives SBD messages via SBD Application Interface165, and sends GDB messages via GDB Application Interface167. PTT Server160is described in detail later underFIG. 3.

FIG. 2details the fundamental method of the present invention, whereby a talker with a PTT User Terminal120speaks and the utterance is conveyed to any number of listeners with their own PTT User Terminals120. Method200, Transmit Utterances from Talker to Multiple Listeners, consists of three independent but communicating processes, shown in the diagram as Talker Process225, Server Process260, and Listener Process227.

Talker Process225operates in PTT User Terminal120as a continuous loop once activated. At Step251, the talker's utterance is captured from the analog audio domain using digital techniques well known to those skilled in the art, and then processing by a speech recognition algorithm to determine the actual sequence of words that was spoken. Numerous speech recognition technologies exist in the art, and any may be incorporated into this method according to the needs of a particular deployment environment or application. In a preferred embodiment, a productized speech recognition engine available on the open market will be incorporated in the method for best results. Once the talker's words have been determined, Step252encodes the recognized speech as text and then compresses it for optimal utilization of transmission resources. Step253in turn packages the compressed text into one or more messages for transmission, in a preferred embodiment, using the Iridium SBD service. These messages are sent in Step254using the capabilities provided in the Iridium system, at which point the process returns to the beginning to stand ready for another utterance.

Server Process260, operating in a continuous loop in PTT Server160, receives at Step261the one or more SBD Messages sent by the talker's PTT User Terminal120at Step254, via SBD Gateway150. These messages are then handled by Subroutine262, Prioritize, Order, and Queue GDB Message(s), which is described in detail underFIG. 4. Subroutine262returns a list of GDB Messages and corresponding destination parameters, which are in turn sent via GDB Gateway170in Step263, whereupon the process returns to the beginning to stand ready for more SBD Messages.

In its turn Listener Process227, operating as a continuous loop when activated in one to many PTT User Terminals120, will at Step271receive the GDB Messages addressed to it by Step263. Each received message will be processed at Step272to extract and decode the compressed text carried within it. Then at Step273that text will be put through a speech synthesis algorithm to generate corresponding analog audio and play it to the listener, whereupon the process will return to the beginning to stand ready for more GDB Messages. As with the speech recognition algorithm, numerous speech synthesis technologies exist in the art, and for the purposes of the present invention any suitable product may be incorporated in an implementation embodying Method200.

FIG. 3depicts the detailed architecture of PTT Server160, accompanied by the SBD Gateway150and GDB Gateway170with which it interacts directly via their respective Application Interfaces165and167. In a preferred embodiment, PTT Server160is implemented as a set of Function Modules310that operate as software processes executing on a Programmable Computing Platform300. Programmable Computing Platform300may be any commonly available product that provides the necessary components, which are well known by those skilled in the art and comprise Processing Resources303, Information Storage capacity302, and Communication Interfaces301.

The infrastructure aspect of the present invention is primarily embodied as the specific Function Modules310that are implemented within PTT Server160, Management Functions320, Knowledge Functions330, and Service Functions360.

Within Management Functions320reside typical components that are commonly used in network elements like this one. Platform Manager321provides the operating system that connects the software to the hardware, as well as the common management capabilities that are used for enabling and disabling components and functions. Reporting Agent322provides the capability to report faults and other events, as well as performance statistics and service records, to an operator or network management entity. Provisioning Agent323provides the capability to configure PTT Server160for its network environment, as well as to record in the components of Knowledge Functions330the identities and other characteristics of the users and groups that are permitted to use the services implemented in the components of Service Functions360.

Knowledge Functions330provide storage and retrieval capabilities for the data required to provide PTT service. User Database331holds information about each system user, and Group Database332holds information about each established group including which users are its members.

Service Functions360comprise three components that embody the steps of Server Process260. An SBD Input Handler365takes in the messages containing recognized speech encoded as compressed text that have been sent by a talker's PTT User Terminal120via the SBD service through SBD Gateway150and SBD Application Interface165. Each such message is handed off to Prioritization Engine364, which executes the method ofFIG. 4to order and queue each message for transmission via GDB to the appropriate region or regions where corresponding listeners and their PTT User Terminals120are located. GDB Output Handler367implements the details of sending these messages out via GDB Application Interface167and GDB Gateway170.

FIG. 4details Subroutine262, Prioritize, Order, and Queue GDB Message(s). This method is a part of Server Process260in Method200, Transmit Utterances from Talker to Multiple Listeners, and is implemented in PTT Server160, specifically Prioritization Engine364. The method begins at Step401, in which an incoming SBD Message containing recognized speech encoded as compressed text is selected, its sending user is identified, and the destination group is determined. These determinations are made using identifying data in the message coupled with information in User Database331. In Step402, the message is prioritized by finding the higher of the sending user's priority and the receiving group's priority. These may be the same or different, depending on the user's role both within the group and as a member of other groups with other roles. In a preferred embodiment, these priorities are loaded into User Database331and Group Database332using Provisioning Agent323.

At Step402, the message is then placed in an output queue corresponding to the priority selected at Step401. If there are other messages in the queue at the same priority, this message will go behind them. If there are more message that have been received in this cycle, determined at Step404, the method returns to the top and repeats Steps401,402, and403for each one. Once Step404determines that there are no more incoming messages available in this cycle, the method proceeds to Step405, at which point the multiple priority queues are merged into a single list. This merge places the highest priority messages at the front, followed by the contents of each priority queue in order or precedence. This allows more important messages to go out before less important messages, thereby implementing preemption as well. Finally, at Step406the merged list is returned to Process260for use as an output queue by Step263inFIG. 2.

FIG. 5details the architecture of a PTT User Terminal120. In a preferred embodiment, this will typically be a handset or similar device, but other form factors may also be implemented; this description is generic to any form factor. PTT User Terminal120consists primarily of two major hardware subsystems, Terminal Platform Hardware500and Programmable Application Processor510, and a group of Application Modules520that are implemented as software components executing in Programmable Application Processor510.

Terminal Platform Hardware500comprises typical componentry found in handset devices used for other purposes, and will in a preferred embodiment be all or nearly all off-the-shelf items. Iridium Radio Access Module501provides the hardware and firmware required to access the Iridium satellite network and take advantage of its services. Audio Input/Output Components502include the usual microphone and speaker, as well as digital conversion and driver functions necessary to take in speech uttered by the user and play out speech received over the network. Tactile/Visual Components503include the usual keypad and screen, as well as other buttons and indicators, that are used to provide a typical user interface experience. Programmable Application Processor510also comprises typical componentry found in modern handset devices used for other purposes, and will in a preferred embodiment be all or nearly all off-the-shelf items. It may also be embedded in common chipsets with much of the Terminal Platform Hardware500. Peripheral I/O Interfaces511, Information Storage512, and Processing Resources513provide capabilities that are obvious by their names.

Application Module520consists of software components that execute in Programmable Application Processor510and embody the end-user aspects of the present invention. It should be noted that these components are built on top of the usual operating system and hardware drivers, which are not shown but which can be inferred by those skilled in the art. Components are grouped into function sets for convenience of representation and description, but these groupings do not necessarily constrain implementation.

Knowledge Functions530contain representations of and operations on data that is relevant to the PTT capability. User Identity Module531embodies identifiers, authentication keys, and other information that ensures a particular device can access services in the network. It is similar to, and in a preferred embodiment may be implemented as, a standard Subscriber Identity Module (SIM) that is well known to those skilled in the art. Group Membership Info532embodies the specific PTT groups of which the user is a member, including the identity of the group for the purpose of receiving GDB messages. It may also include a list of indices referring to other users that are members of the group, and that appear in Contact Directory533which records those other users that are known to this one. Recognition Dictionary534contains information that aids the speech recognition algorithms of Step252, and may be either general or mission-specific in nature according to the needs of a particular deployment. Similarly, Synthesis Dictionary535contains information that aids the speech synthesis algorithms of Step273, and may also be either general or mission-specific according to deployment needs.

Management Functions560perform housekeeping operations relevant to the overall PTT capability. Authentication Agent561embodies the protocol interactions necessary to ensure that the network is authentic, and to assure the network that the user is authentic and authorized. It uses information in User Identity Module531for this purpose. Specific methods are not pertinent to the present invention, and may consist of either standard or purpose-built protocols, although a preferred embodiment will use commonly available and well known standards. Similarly, Registration Agent562uses Group Membership Info532to establish presence on the network and within one or more groups as appropriate for a particular deployment. Here again, a preferred embodiment will use standard methods and protocols for these functions, although in the present invention the corresponding signaling will be carried in Iridium SBD messages, rather than other transport services that may be more commonly used. Provisioning Agent563provides capabilities for making and managing entries in the various modules under Knowledge Functions530. Both local and over the air mechanisms are available in a preferred embodiment, and in particular in the present invention, secure messaging via Iridium GDB will be available for updating common data in multiple PTT User Terminals120.

The heart of the present invention is found in Talker Functions550and Listener Functions570, which embody Talker Process225and Listener Process227, respectively, fromFIG. 2. On the talker side, Speech Input Driver551takes care of interacting with the input hardware of Audio Input/Output Components502to execute the capture of utterances that occurs in Step251. Recognition Engine552embodies the speech recognition algorithms and coding that occurs in Steps251and252; as previously noted, this is implemented in a preferred embodiment using an off-the-shelf technology, although for particular deployments one or more special-purpose technologies may be incorporated without loss of generality. SBD Output Handler553then handles the packaging and transmission of coded messages via the Iridium SBD service, using the capabilities of the Iridium Radio Access Module501.

On the listener side, GDB Input Handler571uses the capabilities of Iridium Radio Access Module501to receive pertinent GDB broadcast messages according to the groups identified in Group Membership Info component532. Synthesis Engine572in turn handles the decoding of text and embodies the speech synthesis algorithms according to Steps272and273of Method200. Here again, Synthesis Engine572will in a preferred embodiment consist of off-the-shelf technologies, but for particular deployments one or more special-purpose technologies may be incorporated without loss of generality. Audio Output Drive573then handles the interaction with the output hardware of Audio Input/Output Components502to play out the synthesized speech according to Step273ofFIG. 2.

The invention has been described above with reference to preferred embodiments and specific applications. It is not intended that the invention be limited to the specific embodiments and applications shown and described, but that the invention be limited in scope only by the claims appended hereto. It will be evident to those skilled in the art that various substitutions, modifications, and extensions may be made to the embodiments as well as to various technologies which are utilized in the embodiments. It will also be appreciated by those skilled in the art that such substitutions, modifications, and extensions fall within the spirit and scope of the invention, and it is intended that the invention as set forth in the claims appended hereto includes all such substitutions, modifications, and extensions.