WO2009148751A2 - Time aligned group audio reproduction in narrowband and broadband networks - Google Patents
Time aligned group audio reproduction in narrowband and broadband networks Download PDFInfo
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- WO2009148751A2 WO2009148751A2 PCT/US2009/042809 US2009042809W WO2009148751A2 WO 2009148751 A2 WO2009148751 A2 WO 2009148751A2 US 2009042809 W US2009042809 W US 2009042809W WO 2009148751 A2 WO2009148751 A2 WO 2009148751A2
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Classifications
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L65/00—Network arrangements, protocols or services for supporting real-time applications in data packet communication
- H04L65/80—Responding to QoS
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L65/00—Network arrangements, protocols or services for supporting real-time applications in data packet communication
- H04L65/40—Support for services or applications
- H04L65/403—Arrangements for multi-party communication, e.g. for conferences
- H04L65/4046—Arrangements for multi-party communication, e.g. for conferences with distributed floor control
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N21/00—Selective content distribution, e.g. interactive television or video on demand [VOD]
- H04N21/40—Client devices specifically adapted for the reception of or interaction with content, e.g. set-top-box [STB]; Operations thereof
- H04N21/41—Structure of client; Structure of client peripherals
- H04N21/414—Specialised client platforms, e.g. receiver in car or embedded in a mobile appliance
- H04N21/41415—Specialised client platforms, e.g. receiver in car or embedded in a mobile appliance involving a public display, viewable by several users in a public space outside their home, e.g. movie theatre, information kiosk
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N21/00—Selective content distribution, e.g. interactive television or video on demand [VOD]
- H04N21/40—Client devices specifically adapted for the reception of or interaction with content, e.g. set-top-box [STB]; Operations thereof
- H04N21/43—Processing of content or additional data, e.g. demultiplexing additional data from a digital video stream; Elementary client operations, e.g. monitoring of home network or synchronising decoder's clock; Client middleware
- H04N21/4302—Content synchronisation processes, e.g. decoder synchronisation
- H04N21/4305—Synchronising client clock from received content stream, e.g. locking decoder clock with encoder clock, extraction of the PCR packets
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N21/00—Selective content distribution, e.g. interactive television or video on demand [VOD]
- H04N21/40—Client devices specifically adapted for the reception of or interaction with content, e.g. set-top-box [STB]; Operations thereof
- H04N21/43—Processing of content or additional data, e.g. demultiplexing additional data from a digital video stream; Elementary client operations, e.g. monitoring of home network or synchronising decoder's clock; Client middleware
- H04N21/4302—Content synchronisation processes, e.g. decoder synchronisation
- H04N21/4307—Synchronising the rendering of multiple content streams or additional data on devices, e.g. synchronisation of audio on a mobile phone with the video output on the TV screen
- H04N21/43076—Synchronising the rendering of multiple content streams or additional data on devices, e.g. synchronisation of audio on a mobile phone with the video output on the TV screen of the same content streams on multiple devices, e.g. when family members are watching the same movie on different devices
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N21/00—Selective content distribution, e.g. interactive television or video on demand [VOD]
- H04N21/40—Client devices specifically adapted for the reception of or interaction with content, e.g. set-top-box [STB]; Operations thereof
- H04N21/43—Processing of content or additional data, e.g. demultiplexing additional data from a digital video stream; Elementary client operations, e.g. monitoring of home network or synchronising decoder's clock; Client middleware
- H04N21/439—Processing of audio elementary streams
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W76/00—Connection management
- H04W76/40—Connection management for selective distribution or broadcast
- H04W76/45—Connection management for selective distribution or broadcast for Push-to-Talk [PTT] or Push-to-Talk over cellular [PoC] services
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L43/00—Arrangements for monitoring or testing data switching networks
- H04L43/08—Monitoring or testing based on specific metrics, e.g. QoS, energy consumption or environmental parameters
- H04L43/0852—Delays
- H04L43/0858—One way delays
Definitions
- the present application relates to heterogeneous networks.
- the application relates to simultaneous reproduction of an audio signal in heterogeneous networks.
- Group-directed communications are commonplace in enterprise and public safety communication systems.
- voice communications one end device directs an audio stream to a given group (i.e. a "talkgroup") of receiving end devices.
- These receiving end devices reproduce the audio stream through an amplified speaker.
- the manner in which the receiving end devices are used usually results in the reproduced sound being audible to people other than merely the intended recipient.
- the receiving end devices are often located near each other, causing their associated listeners to hear the same audio stream simultaneously reproduced by multiple end devices. This is particularly true in public safety uses, in which personnel often respond to incidents in a group and this group (or a subset thereof) may be located in the same local area for an extended period of time.
- Such methods of synchronized presentation work well for the specialized homogeneous narrowband circuit-switched wireless radio networks typically used in i the current generation of enterprise and public safety communication systems.
- the next generation of such communication systems is likely to span multiple narrowband circuit-switched and broadband packet-switched Radio Area Network (RAN) technologies with wholly different methods of synchronization.
- Example circuit-switched narrowband RAN technologies include 25 kHz, 12.5 kHz, or 6.25 kHz equivalent FDMA or TDMA air interfaces (e.g. Project 25, TETRA, DMR).
- Example packet-switched broadband RAN technologies include LTE, UMTS, EVDO, WiMAX, and WLAN air interfaces.
- end devices connected to the circuit-switched narrowband RAN and end devices connected to the packet-switched broadband RAN would reproduce the same audio waveform in an autonomous fashion with respect to one another.
- This cacophony of misaligned sound results in unintelligible audio communication where multiple narrowband and broadband end devices are collocated.
- half-duplex group communication systems provide a mechanism to ensure equitable speaking rights on a given shared communication resource such as a channel or "talkgroup.” To provide this, the floor (i.e. the right to broadcast) is typically granted to the first device to make an appropriate request.
- listeners wait for the current audio stream to finish before initiating a new floor request. If the floor is granted to the first requestor, it is desirable that all listeners be given the opportunity to request the floor at the same instant. This can be achieved if the preceding audio stream ends at the same time for all listeners.
- FIG. 1 illustrates one embodiment of a system.
- FIG. 2 illustrates another embodiment of a system.
- FIG. 3 illustrates the calculated time delays in the embodiment of Fig. 1.
- FIG. 4 illustrates the calculated time delays in the embodiment of Fig. 2.
- Coordinated media (e.g. audio) reproduction across different communication networks such as narrowband (hereinafter referred to as NB) simulcast and broadband (hereinafter referred to as BB) networks.
- NB narrowband
- BB broadband
- the presentation time of media to a heterogeneous group of end devices containing, for example, NB End Devices and BB End Devices, is time aligned such that an audio signal, for example, is reproduced at roughly the same time for all of the End Devices.
- This synchronization provides coherent group audio reproduction, which allows multiple listeners to hear the same audio signal from heterogeneous End Devices in the same physical vicinity without the interference caused by misaligned and overlapping audio streams.
- the synchronization ensures fair floor access in half-duplex communication systems as each listener is given the opportunity to attempt floor acquisition at the same time.
- Fig. 1 One embodiment of a group communication system containing multiple heterogeneous RAN technologies is depicted in Fig. 1.
- the embodiment of Fig. 1 includes a NB simulcast RAN (hereinafter referred to as NB RAN 102), which could be, for example, part of a Project 25 compliant PTT system.
- Fig. 1 also includes a BB RAN 103, which could be, for example, part of an OMA PoC (Open Mobile Alliance Push-to-talk over Cellular) compliant PTT system. Integrated together, they form a single communication System 100. Specifically, the System 100 shown in Fig.
- NB RAN 102 NB simulcast RAN
- BB RAN 103 which could be, for example, part of an OMA PoC (Open Mobile Alliance Push-to-talk over Cellular) compliant PTT system.
- OMA PoC Open Mobile Alliance Push-to-talk over Cellular
- the NB/BB Controller 104 has the ability to independently delay a group-directed audio signal to the NB RAN 102 or BB RAN 103, thereby accommodating the NB or BB End Device 132, 133 which exhibits a statistically significant, e.g. worst case, delay of an audio signal measured from the NB/BB Controller 104 to its reproduction in the NB or BB End Device 132, 133.
- the delay of an audio signal from the NB/BB Controller 104 to its reproduction in BB End Devices 133 is typically significantly longer with respect to the same audio signal transmitted to and reproduced by NB End Devices 132.
- Each of the NB and BB End Devices 130, 132, 133 is a user device that has a transmitter and receiver (not shown). Although mobile NB or BB End Devices are described, at least some of the NB or BB End Devices 130, 132, 133 may be geographically fixed.
- the NB or BB End Devices 130, 132, 133 communicate with other NB or BB End Devices 130, 132, 133 via an associated NB Base Station 120 or BB Base Station 121, respectively, as well as other not depicted interconnections of the System 100 and associated functions including the NB/BB Controller 104.
- each of the NB and BB End Devices 130, 132, 133 and the NB/BB Controller 104 is shown between each of the NB and BB End Devices 130, 132, 133 and the NB/BB Controller 104 for convenience, one or more intermediaries of different types may be inserted depending on the specific RAN technology deployed. Although NB Base Stations 120 or BB Base Stations 121 and other intermediaries may be mobile (handsets or vehicle mounted), such elements alternatively may be geographically fixed. Each of the NB and BB End Devices 130, 132, 133 also has a speaker (not shown) through which the End Device provides acoustic reproduction of audio to the user, in addition to other circuitry and input/output mechanisms.
- a speaker not shown
- the NB End Devices 130, 132 communicate through the NB RAN 102.
- Examples of such NB End Devices 130, 132 include portable and mobile NB radios or any other End Device which connects, in a wireless fashion, to the NB RAN 102.
- These NB End Devices 130, 132 are connected to the NB/BB Controller 104 via NB Base Stations 120. Referring to Fig. 1, one of the NB End Devices 130 requests and is granted the floor (i.e. the right to speak on a given communication resource) from a floor controller (not shown) of System 100.
- This NB End Device 130 transmits an audio stream (hereinafter referred to as NB Uplink Audio Stream 140) to the NB/BB Controller 104 via the NB Base Station 120.
- the other NB End Devices 132 receive the repeated audio stream (hereinafter referred to as NB Downlink Audio Stream 144) from the NB/BB Controller 104 via one or more NB Base Stations 120.
- the BB End Devices 133 communicate through the BB RAN 103. Examples of such BB End Devices 133 include cell phones, PDAs, laptop computers, or any other End Device which connects, in a wired or wireless fashion, to the BB RAN.
- the BB End Devices 133 are connected to the NB/BB Controller 104 through BB Base Stations 121.
- BB End Devices 133 receive the audio stream (hereinafter referred to as BB Downlink Audio Packets 145) from the NB/BB Controller 104 via BB Base Stations 121.
- BB End Devices 133 along with other components of System 100 not shown in Fig. 1 (e.g. a wired voice dispatch console) are equally capable of requesting the floor and transmitting an audio stream to the NB/BB Controller 104.
- the NB/BB Controller 104 is a combined NB simulcast and BB controller that is responsible for duplicating and routing audio streams to all NB and BB End Devices 130, 132, 133 affiliated to the same logical group.
- the NB and BB End Devices 130, 132, 133 join a group, for example, by turning a physical knob on the device to select a particular logical "talkgroup" or "channel.”
- the NB/BB Controller 104 synchronizes a simulcast transmission of the NB Downlink Audio Stream 144 at the appropriate NB Base Stations 120 by specifying a transmission timestamp (hereinafter referred to as NB TransmisslonTimestam pN) for each audio frame (hereinafter referred to as AudioprameN) contained in the NB Downlink Audio Stream 144.
- NB TransmisslonTimestam pN a transmission timestamp
- AudioprameN audio frame
- NB Transmisslon ⁇ ime stampN is expressed in values relative to a common clock reference (hereinafter referred to as NB Time Source 110) known to the NB/BB Controller 104 and the NB Base Stations 120.
- the NB/BB Controller 104 and the NB Base Stations 120 contain very high precision, nanosecond-accurate, internal clocks (hereinafter referred to as NB Clocks 114) synchronized to a common NB Time Source 110, e.g. the Global Positioning Satellite (GPS) system 1 PPS (Pulse Per Second), via NB Clock Signal 112.
- GPS Global Positioning Satellite
- PPS Pulse Per Second
- the NB/BB Controller 104 When the NB/BB Controller 104 receives the NB Uplink Audio Stream 140 from one of the NB End Devices 130 via a NB Base Station 120, the NB/BB Controller 104 repeats the series of received Audio F rameNS, along with an associated series of NB Transmisslon ⁇ ime stampNS, in NB Downlink Audio Stream 144 to the appropriate NB Base Stations 120.
- the participating NB Base Stations 120 Upon receiving NB Downlink Audio Stream 144, the participating NB Base Stations 120 wait until their synchronized NB Clocks 114 are exactly equal to NB TransmisslonTim estampN specified for a given AudioFrameN • At that instant in time, the participating NB Base Stations 120 simultaneously repeat AudioFrameN to all NB End Devices 132 affiliated to the group to which the audio stream is directed. [0019] However, the combined NB/BB Controller 104 does not merely repeat the same NB Downlink Audio Stream 144 provided to NB Base Stations 120 to BB End Devices 133 (by way of BB Base Stations 121).
- timing and synchronization mechanisms used in the NB RAN 102 are typically quite different from those available in the BB RAN 103. Although it is theoretically possible to extend the same time-stamped NB Downlink Audio Stream 144 to BB End Devices 133 if a similar timing mechanism (e.g. a very high precision GPS- locked clock) were disposed in the BB End Devices 133, providing the BB End Devices 133 with such equipment may be impracticable at least due to cost, size, and location concerns.
- a similar timing mechanism e.g. a very high precision GPS- locked clock
- NB Transmisslon ⁇ ime stampN present in NB Downlink Audio Stream 144 specify a transmission time for AudioFrameN • This transmission time is not inclusive of the time needed to process and acoustically reproduce AudioFrameN • Since the amount of time used to perform these functions likely differs amongst NB and BB End Devices, BB End Devices 133 do not possess enough information to synchronize their audio reproduction with that of NB End Devices 132.
- the NB/BB Controller 104 and the BB End Devices 133 shown in Fig. 1 contain moderate precision, millisecond-accurate, internal clocks (hereinafter referred to as BB Clocks 115) locked to a common BB Time Source 111, e.g. a time-of-day clock, via BB Clock Signal 113.
- BB Clocks 115 millisecond-accurate, internal clocks locked to a common BB Time Source 111, e.g. a time-of-day clock, via BB Clock Signal 113.
- simulcast transmission which is achieved using nanosecond-accurate timing mechanisms present in participating NB Base Stations 120
- time aligned reproduction of audio can be achieved using merely the millisecond-accurate timing mechanisms present in participating BB End Devices 133.
- the NB/BB Controller 104 specifies a reproduction timestamp (hereinafter referred to as BB Re productionTimestampN) for one or more Audio F rameN(s) contained in BB Downlink Audio Packets 145 repeated to the appropriate BB End Devices 133 (i.e., the BB End Devices 133 that have selected the channel and joined the group to which the Audi ⁇ FrameN (s) are transmitted).
- BB Downlink Audio Packets 145 are formatted, for example, using the Real-time Transport Protocol (RTP).
- RTP Real-time Transport Protocol
- BBR ep roductionTimestampNS embedded in BB Downlink Audio Packets 145 are relative to the common BB Time Source 111 and inform the BB End Devices 133 as to the exact time the associated AudioprameN is to be acoustically reproduced.
- the participating BB End Device 133 waits until their synchronized BB Clocks 115 are exactly equal to BBR epr oductionTimestampN specified for a given AudioFrameN- At that instant in time, the participating BB End Devices 133 simultaneously reproduce Audio Fr ameN-
- the NB/BB Controller 104 samples the value of NB Clock 114, and sends a time-stamped message containing this value (hereinafter referred to as NB Time Measurement Packets 146) to each NB Base Station 120.
- NB Time Measurement Packets 146 a time-stamped message containing this value
- a NB Base Station 120 subtracts the embedded timestamp from its NB Clock 114 to derive the one-way signal propagation delay (hereinafter referred to as NBpropagationDeiayBaseSiteN) between the NB/BB Controller 104 and the NB Base Station 120.
- NBpropagationDeiayBaseSiteN one-way signal propagation delay
- NBpropagationDeiayBaseSiteN is then sent back to the NB/BB Controller 104 where it is recorded in a memory (not shown). All such NBp rop agationDeiayBaseSiteN measurements to each NB Base Station 120 are then compared and a statistically significant (e.g. worst case, 99% worst case, 95% worst case, 90% worst case) one-way propagation delay (hereinafter referred to as NBp rop agationDeiay) from the NB/BB Controller 104 to all NB Base Stations 120 is recorded in the NB/BB Controller 104.
- the wireless propagation delay between the NB Base Station 120 and the NB End Devices 132 is comparatively negligible.
- the statistically significant delay from the time an audio frame is sent from the NB/BB Controller 104 to the time the audio signal it contains is acoustically reproduced by the speaker in a NB End Device 132 is then calculated as:
- NB Device p rocessmgDe i ay is the known time to process (e.g., demodulate, error-correct, and decode) the audio signal in the NB End Devices 132.
- NBoeviceProcessmgDeiay is measured or estimated prior to the NB End Devices 132 being shipped and device-to-device variation is comparatively negligible.
- NBR epr oductionDeiay may be periodically recalculated by NB/BB Controller 104, which permits modification of NBReproductionDeiay as participating NB Base Stations 120 are added to or removed from the NB RAN 102.
- the NB/BB Controller 104 samples the value of BB Clock 115, and sends a time-stamped message containing this value (hereinafter referred to as BB Time Measurement Packets 147) to a representative set, e.g. all, of the BB End Devices 133.
- the BB End Device 133 Upon receiving BB Time Measurement Packet 147, the BB End Device 133 subtracts the embedded timestamp from its BB Clock 115 to derive the one-way signal propagation delay between the NB/BB Controller 104 and the BB End Device 133 (hereinafter referred to as BBp ropa g a t lon DeiayDeviceN). All such BBpropagatjonDeiayDeviceN measurements are then compared and the statistically significant one-way propagation delay (hereinafter referred to as BBp ropa g a t lon Deiay) from the NB/BB Controller 104 to the representative set of BB End Devices 133 is recorded in the NB/BB Controller 104.
- BBp ropa g a t lon Deiay the statistically significant one-way propagation delay
- BBoeviceProcessingDeiay is the known time to process (e.g., demodulate, error-correct, de-jitter, and decode) audio packets in the BB End Devices 133. Similar to NB Device p rocessmgDe i ay , BB Device p rocessmgDe i ay is measured or estimated prior to BB End Device 133 being shipped and device-to-device variation is again comparatively negligible.
- BBR epr oductionDeiay may be periodically recalculated by NB/BB Controller 104, which permits modification of BB Reproduc t lonD eiay as participating BB End Devices 133 are added to or removed from the BB RAN 103.
- Fig. 3 A diagram of the time delays described above in relation to the embodiment of Fig. 1 is shown in Fig. 3.
- the NB/BB Controller 104 specifies a NB ⁇ ransmisslon ⁇ ime stampN to NB Base Stations 120 and a BB Repro ductionTimestampN to BB End Devices 133 for each Audio Fr a m eN repeated.
- the NB/BB Controller 104 calculates the delay from a starting time 0, in units of the NB Clock 114, at which time the first AudioFrameo is to be simulcast by NB Base Stations 120 (hereinafter referred to as NB Trail smissionTimestampDeiay) and the delay from the same starting time 0, in units of the BB Clock 115, at which time the first AudioFrameo is to be reproduced by BB End Devices 133 (hereinafter referred to as BBR epr oductionTimestampDeiay).
- NB ⁇ ransmisslon ⁇ ime stampDeiay is calculated by the NB/BB Controller 104 to be equal to NBp ropa g atlon Deiay
- NB ⁇ ransmisslon ⁇ imestamp Deiay and NBp ropa g atlon Deiay are calculated via the following algorithm:
- BB Re productionDeiay* is BBReproductionDeiay in units of NB Clock 1 14
- NBReproductionDeiay* is NBR epr oductionDeiay in units of BB Clock 1 15.
- This translation between clock units is possible, since NB/BB Controller 104 knows the respective frequencies (e.g. 1 kHz, 1 MHz, IGHz) and relationship (i.e. at a given instant in time, it can sample both clocks) of both NB Clock 114 and BB Clock 115.
- NB ⁇ ransmlsslonTlm estampDelay and BBR epr oductionTimestampDelay may be Stored On SL ⁇ Q V- group basis in a periodically-updated database in the NB/BB Controller 104. This permits the NB/BB Controller 104 to adjust these values whenever a new NB or BB End Device 130, 132, 133 joins or leaves the group if the particular End Device statistically affects these calculated delay values in a significant way (e.g., greater than 1%, 2%, 5%, 10%, etc.).
- the NB/BB Controller 104 determines its NB Re productionDeiay or BB Re productionDeiay and recalculates NB Transmisslon ⁇ im e S tampDeiay or BBReproductionTimestampDelay if determined appropriate.
- the System 100 may contain many End Devices, the NB/BB Controller 104 is able to adjust the NB Transmissl o n ⁇ ime stampDeiay and BBReproductionTimestampDelay to account for only those End Devices that are to reproduce a given audio signal (e.g. that are present on the channel and joined to a particular group).
- the NB/BB Controller 104 can calculate and store delays on a per-End Device basis, instead of on a per-group basis. Doing so permits the NB/BB Controller 104 to, for example, reduce the delay of the audio signal to the reproducing End Devices if the transmitting End Device is also the End Device which exhibits the longest propagation delay.
- NB ⁇ imes tampStart the synchronized NB Clock 114
- BB ⁇ imes tampStart the synchronized BB Clock 115
- AudioFrameTime is the duration of audio, specified in units of the NB Clock 114, contained in each AudioFrameN of the NB Downlink Audio Stream 144.
- the NB Base Stations 120 receiving NB Downlink Audio Stream 144 follow ordinary simulcast behavior, waiting until their NB Clocks 114 are equal to the specified NB Transmisslon ⁇ ime stampN before transmitting the corresponding Audio F rameNto NB End Devices 132.
- Each Audio FrameN in BB Downlink Audio Packets 145 contains a BBReproductionTimestampN which is calculated per the following algorithm:
- AudioFrameTime is the duration of audio, specified in units of the BB Clock 115, contained in each AudioprameN of the BB Downlink Audio Packets 145.
- the BB End Devices 133 receiving BB Downlink Audio Packets 145 by way of BB Base Stations 121 wait until their BB Clocks 115 are equal to the BBReproductionTimestampN before acoustically reproducing the associated AudioFrameN.
- the BB End Devices 133 perform decryption and decompression to prepare the packet contents such that the audio waveform can be presented to the listener at the time indicated by BBR epr oductionTimestampN.
- the BB End Device 133 may employ techniques such as time compression to align with future BB Reproduc t lon ⁇ im estampS embedded in Downlink BB Audio Packets 145.
- the term "late” may be set by an arbitrary threshold (hereinafter referred to as BBR epr oductionThreshoid) of 180 milliseconds, for example. If BBReproductionThreshoid is exceeded, the packet(s) may be skipped and audio reproduction may be started on time with subsequent packets.
- FIG. 2 Another embodiment of the heterogeneous communication system is shown in Fig. 2.
- This System 200 includes a NB Controller 204, a BB Controller 205, a NB Time Source 210, a BB Time Source 211, NB Base Stations 220, BB Base Stations 221, NB End Devices 230, 232, and BB End Devices 233.
- a common BB Time Source 211 is used to synchronize the BB Clock 215 in BB Controller 205 and BB End Device 233.
- a common NB Time Source 210 is used to synchronize the NB Clock 214 in NB Controller 204, BB Controller 205, and NB Base Stations 220.
- BB End Devices 233 are equally capable of such behavior.
- the audio stream from a BB End Device 233 is first forwarded to NB Controller 204 such that it may be processed in a manner similar to that of NB Uplink Audio Stream 240.
- a single NB/BB Controller 104 repeats NB Uplink Audio Stream 140 to both the NB and BB End Devices 132, 133 through NB and BB RANs 102, 103 respectively.
- a NB Controller 204 repeats NB Uplink Audio Stream 240 to the NB End Devices 232 through NB RAN 202 and a separate BB Controller 205 repeats NB Uplink Audio Stream 240 to the BB End Devices 233 through BB RAN 203.
- the NB Controller 204 treats the BB Controller 205 similar to another NB Base Station 220.
- the NB Controller 204 repeats NB Uplink Audio Stream 240 as NB Downlink Audio Stream 244 to the BB Controller 205. Doing so essentially permits an ordinary NB simulcast controller in NB RAN 202 to be used as the NB Controller 204.
- the BB Controller 205 upon receiving NB Downlink Audio Stream 244 from NB Controller 204, reformats and repeats the audio stream as BB Downlink Audio Packets 245 to the BB End Devices 233 by way of BB Base Stations 221. [0038] Similar to the embodiment of Fig.
- the BB Controller 205 periodically measures BBp ropa g a t lon DeiayDeviceN from the BB Controller 205 to a representative set, e.g. all, of the BB End Devices 233 using the BB Time Measurement Packets 247. As before, all such BBp rO p aga t lon DeiayDeviceN measurements to each BB End Device 233 are then compared and a statistically significant (e.g.
- BBoeviceProcessmgDeiay is the known time to process (e.g., demodulate, error-correct, de-jitter, and decode) audio packets in the BB End Devices 233.
- BBoeviceProcessmgDeiay is measured or estimated prior to BB End Device 233 being shipped and device-to-device variation is again comparatively negligible.
- BBR epr oductionDeiay may be periodically recalculated by BB Controller 205, which permits modification of BB Reproduc t lon Deiay as participating BB End Devices 233 are added to or removed from the BB RAN 203.
- the NB Controller 204 periodically measures NBp ropa g a t lon DeiayBaseSiteN from the NB Controller 204 to each NB Base Station 220 using the NB Time Measurement Packets 246.
- the NB Controller 204 depicted in the embodiment of Fig. 2 considers BB Controller 205 to be another NB Base Station 220.
- the NB Controller samples its NB Clock 214, and sends a time-stamped message containing this value to BB Controller 205.
- BB Controller 205 Upon receiving NB Time Measurement Packet 246, BB Controller 205 subtracts the embedded timestamp from its NB Clock 214 to derive the one-way signal propagation delay (hereinafter referred to as NBp ropa g a t lon DeiayBBControiier) between the NB Controller 204 and the BB Controller 205. Unlike the operation of other NB Base Stations 220, however, the BB Controller 205 does not merely return NBpropagationDeiayBBControiier back to NB Controller 204. Instead, BB Controller 205 calculates a new NBp ropa g a t lon DeiayBBControiierf per the following algorithm:
- NBpropagationDelayBBControllerf NBp rO p aga tionDelayBBController + BBR ep roductionDelay* "
- NB D eviceProcessmgDeiay is the known time, in units of NB Clock 214, to process (e.g., demodulate, error-correct, and decode) the audio signal in NB End Devices 232.
- BB Reproduc , lonDe i ay* is the BB Reproduc , lonDe i ay in units of NB Clock 214.
- BB Controller 205 returns this value to NB Controller 204 in a NB Time Measurement Packet 246.
- All NBp ropa g atlon DeiayBaseSiteN measurements to each NB Base Station 220 along with NBpropagatjonDeiayBBControiierf as calculated above are then compared and a statistically significant (e.g. worst case, 99% worst case, 95% worst case, 90% worst case) one-way propagation delay (hereinafter referred to as NBp ropa g a t lon Deiay) from the NB Controller 204 to all NB Base Stations 220 and BB Controller 205 is recorded in the NB Controller 204.
- the wireless propagation delay between the NB Base Station 220 and the NB End Devices 232 is comparatively negligible.
- the statistically significant delay from the time an audio frame is sent from the NB Controller 204 to the time the audio signal it contains is acoustically reproduced by the speaker in the NB End Device 232 is then calculated as:
- NB D eviceProcessmgDeiay is the known time to process (e.g., demodulate, error-correct, and decode) the audio signal in the NB End Devices 232.
- NBDeviceProcessmgDeiay is measured or estimated prior to the NB End Devices 232 being shipped and device-to-device variation is again comparatively negligible. Unlike the embodiment of Fig.
- NBR ep roductionDeiay is also inclusive of the NBpropagationDeiayBBControiierf as reported by BB Controller 205 (which is itself inclusive of BBReproductionDeiay).
- BB Controller 205 which is itself inclusive of BBReproductionDeiay.
- NBReproductionDeiay may be periodically recalculated by NB Controller 204, which permits modification of NBReproductionDeiay as participating NB Base Stations 220 or BB End Devices 233 are added to or removed from the System 200.
- a diagram of the time delays described above in relation to the embodiment of Fig. 2 is shown in Fig. 4.
- the NB Controller 204 provides a NB TransmisslO nTimestampN to NB Base Stations 220 for each AudioFrameN embedded in NB Downlink Audio Stream 244. To facilitate this, NB Controller 204 calculates NB ⁇ ransmisslon ⁇ im estampDeiay which represents the delay from a starting time 0, in units of the NB Clock 214, at which the first Audio Fr a m eo is to be simulcast to NB Base Stations 220 and BB Controller 205. As in an ordinary NB RAN 202, NB Controller
- NB End Device 230 transmits NB Uplink Audio Stream 240 to NB Controller 204 through a NB Base Station 220.
- the NB Controller 204 immediately samples the synchronized NB Clock 214 (hereinafter referred to as NB Time stampStart).
- Each Audiop r a m eN in NB Downlink Audio Stream 244 will contain a NB TransmisslO nTimestampN which is calculated per the following algorithm: JN DTransmissionTimestampN JN DTimestampStart " • " IN DTransmissionTimestampDelay " • "
- Audio Fr a m e T i m e is the duration of audio, specified in units of the NB Clock 214, contained in each AudioFrameN of the NB Downlink Audio Stream 244.
- the NB Base Stations 220 receiving NB Downlink Audio Stream 244 follow ordinary simulcast behavior, waiting until their NB Clocks 214 are equal to the NB TransmisslonTim estampN before broadcasting Audio F rameNto NB End Devices 232.
- the BB Controller 205 also receives NB Downlink Audio Stream 244 with embedded NB TransmisslonTimestamp NS for each Audio Fr a m eN- As in the embodiment of Fig.
- BB Controller 205 provides a BBR epr oductionTimestampN to BB End Devices 233 for each Audio Fr a m eN in BB Downlink Audio Packets 245.
- the BB Controller 205 calculates BBR epr oductionTimestampN for each AudioFrameN received in NB Downlink Audio Stream 244 as follows:
- ampN* is the received NB ⁇ ransmisslonTimestampN in units of
- BB Clock 215, and NB D eviceProcessmgDelay* is the NBoeviceProcessingDelay in Units of BB
- BB Controller 205 knows the respective frequencies (e.g. 1 kHz, 1 MHz, IGHz) and relationship (i.e. at a given instant in time, it can sample both clocks) of both NB Clock 214 and BB Clock 215.
- NBDeviceProcessmgDelay is measured or estimated prior to the NB End Devices 232 being shipped and device-to-device variation is again comparatively negligible.
- the BB End Devices 233 receiving BB Downlink Audio Packets 245 by way of BB Base Stations 221 wait until their BB Clocks 215 are equal to the BBReproductionTimestampN before acoustically reproducing Audio F rameN.
- the BB End Devices 233 perform decryption and decompression to prepare the packet contents such that the audio waveform can be presented to the listener at the time indicated by
- DDReproductionTimestampN- [0052]
- certain rare conditions may lead to excessively long measured values of NB PrO p a g a , lonDe i ayB aseSiteN and BBpropagationDeiayDeviceN-
- these values are not representative of the vast majority of similarly measured delays.
- the NB and/or BB Controllers can take this into account by discarding those delays that are in a preset percentile of the longest delays measured (e.g. >95%, >98%, >99%).
- This measurement is calculated by ordering all of the NBp ropagat i onDe i ayBaseS i teN measurement values into an ordered set from minimum to maximum value. If, for example, the worst 90% NBp rop agationDeiayBaseSiteN measurement value is to be selected, the value in that ordered set whose index is 0.9 times the number of values in the set is chosen. If, for example, the worst 95% NBpropagationDeiayBaseSiteN measurement value is to be selected, the value in that ordered set whose index is 0.95 times the number of values in the set is chosen. This same method can be applied to the measured BBp rop agationDeiayDeviceN values. Note any other statistical measure (e.g.
- time delays greater than two or three standard deviations from the mean delay time can alternatively be used. This measure provides a method of filtering out the extreme delay cases from greatly increasing the overall audio reproduction delay experienced by all of the End Devices affiliated to a given group at the possible understood cost of occasional overlapping audio and/or floor acquisition difficulty.
- audio signals have been discussed, media signals other than solely audio signals (e.g. text, device control, video) can also be coordinated using the above technique.
- audio signal is intended to encompass signals communicated between the various components in the network that contain audio information to reproduce the original audio signal sent from the originating End Device to the reproducing End Devices (e.g. compressed or encrypted signals that are based on, but are not exactly, the original audio signal).
- the techniques shown in Figs. 1 and 2 coordinate audio or other media reproduction across heterogeneous communication systems.
- collocated end devices By synchronizing the presentation time of audio to a group, collocated end devices all present audio at roughly the same time, providing coherent reproduction of the original audio. Thus, multiple listeners hear the same audio from multiple end devices simultaneously and fair access to a given floor in half-duplex communication systems is provided as each listener is given the opportunity to attempt floor acquisition at about the same instant in time.
- Either embodiment contains the ability to delay audio to each RAN of the heterogeneous system independently, thereby accommodating End Devices that have significantly longer transmission-to-reproduction delays.
Abstract
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