Patent Publication Number: US-10313143-B1

Title: Wireless communication system to provide buffering in a single frequency network

Description:
TECHNICAL BACKGROUND 
     Wireless communications have become increasingly prominent for sending and receiving information. For example, individuals may utilize a wireless communication device for voice communications, video calls, text messaging, email, research, entertainment, and/or for conducting critical business transactions. Wireless communication devices may use wireless protocols, such as Long Term Evolution (LTE), Evolution Data Optimized (EVDO), Code Division Multiple Access (CDMA), Global System for Mobile communications (GSM), High Speed Packet Access (HSPA), and the like to communicate over wireless communication networks. 
     Wireless communication networks comprise a collection of wireless access nodes connected together with communication links. A wireless communication network may also be connected to other communication networks. Wireless communication systems, such as cellular voice and data networks, typically include multiple wireless access nodes spread over a geographic area through which wireless communication devices can register and receive wireless access to wireless communication services. 
     A Single Frequency Network (SFN) is a broadcast network where several access points simultaneously transmit the same signal over the same frequency channel. In an SFN the signal may be amplified and the SFN may maintain overall coverage even in the event of the outage of one or more access points. The wireless access nodes in a wireless communication network may be used to implement an SFN. SFNs are useful to simultaneously transmit the same content to multiple users located in a geographic area. For example, an SFN may stream an audio or video broadcast, like a sporting event. It is important to synchronize the access points, as unsynchronized frames will cause interference in the SFN. Synchronization is also necessary to ensure that as users move around within the coverage area of the SFN, the content is synchronized no matter which access point the user is connected to. 
     OVERVIEW 
     Examples disclosed herein provide a system, method, hardware, and software to provide buffering in a Single Frequency Network (SFN). In one instance, the method includes a multicast server system that transmits multimedia content to wireless access points. The wireless access points determine and transmit SFN transmit time information to the multicast server system. The method further includes the multicast server system using the SFN transmit time information to determine individual buffering information for each of the wireless access points. The method includes the multicast server system adjusting a buffer delay for each individual wireless access point using the individual buffering information and transmitting the multimedia content to the wireless access points. 
     In another example, a wireless communication system provides buffering in a Single Frequency Network (SFN). The wireless communication system includes a multicast server system that transmits multimedia content to wireless access points. The wireless access points determine and transmit SFN transmit time information to the multicast server system. The multicast server system uses the SFN transmit time information to determine individual buffering information for each of the wireless access points. The method includes the multicast server system adjusting a buffer delay for each individual wireless access point using the individual buffering information and transmitting the multimedia content to the wireless access points. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following description and associated figures teach the best mode of the invention. For the purpose of teaching inventive principles, some conventional aspects of the best mode may be simplified or omitted. The following claims specify the scope of the invention. Note that some aspects of the best mode may not fall within the scope of the invention as specified by the claims. Thus, those skilled in the art will appreciate variations from the best mode that fall within the scope of the invention. Those skilled in the art will appreciate that the features described below can be combined in various ways to form multiple variations of the invention. As a result, the invention is not limited to the specific examples described below, but only by the claims and their equivalents. 
         FIG. 1  illustrates a wireless communication system to provide buffering in a Single Frequency Network (SFN). 
         FIG. 2  illustrates the operation of the wireless communication system to provide buffering in the SFN. 
         FIG. 3  illustrates the operation of the wireless communication system to provide buffering in the SFN. 
         FIG. 4  illustrates a wireless communication system to provide buffering in an SFN. 
         FIG. 5  illustrates the operation of the wireless communication system to provide buffering in the SFN. 
         FIG. 6  illustrates an example of a multicast server system to provide buffering in an SFN. 
     
    
    
     DETAILED DESCRIPTION 
     The following description and associated figures teach the best mode of the invention. For the purpose of teaching inventive principles, some conventional aspects of the best mode may be simplified or omitted. The following claims specify the scope of the invention. Note that some aspects of the best mode may not fall within the scope of the invention as specified by the claims. Thus, those skilled in the art will appreciate variations from the best mode that fall within the scope of the invention. Those skilled in the art will appreciate that the features described below can be combined in various ways to form multiple variations of the invention. As a result, the invention is not limited to the specific examples described below, but only by the claims and their equivalents. 
       FIG. 1  illustrates wireless communication system  100  to provide buffering in a Single Frequency Network (SFN). Wireless communication system  100  includes multicast server system  101  and wireless access points  121 - 124 . Multicast server system  101  communicates with wireless access points  121 - 124  over communication links  111 - 114 , respectively. Communication links  111 - 114  may use protocols like Time Division Multiplex (TDM), Internet Protocol (IP), Ethernet, Long Term Evolution (LTE), Data over Cable Service Interface Specification (DOCSIS), or some other communication protocol—including combinations thereof. Wireless communication system  100  may include other components not shown for clarity. 
     In some examples, the SFN comprises a Multimedia Broadcast Multicast Service (MBMS). Examples of multicast server system  101  include a Multicast Coordination Entity (MCE) and a MBMS Gateway (M-GW). Examples of wireless access points  121 - 124  include base stations, base transceiver stations, femtocell base stations, eNodeBs, WIFI hotspots, WIFI access points, and/or other wireless access nodes—including combinations thereof. 
     In operation, multicast server system  101  transmits multimedia content to wireless access points  121 - 124 . Wireless access points  121 - 124  broadcast the multimedia content at the same time over the same frequency channel. For example, multimedia content could comprise live video or audio streaming (news, weather, sports, concerts, etc.). In other examples, the multimedia content could be a software update. In yet another example, the multimedia content may be an alert, such as a weather or amber alert. 
     Wireless access points  121 - 124  determine and transmit SFN transmit time information to multicast server system  101 . In some examples, SFN transmit time information includes buffer status information, a buffer status report (BSR), propagation delay information, backhaul delay information, frame transmission information, error rates, and/or other timing information—including combinations thereof. In an SFN, the transmission needs to be synchronized, however transmission delay may cause the wireless access points to become unsynchronized. In some examples, transmission delay is in the core network, for instance, from the content provider to the wireless communication network. In other examples, the transmission delay may be in the backhaul connection between the wireless access points and the communication network. In yet other examples, the transmission delay may be the wireless access points themselves. In another example, the transmission delay may be caused by the distance between the wireless access point and the multicast server system. 
     Multicast server system  101  uses the SFN transmit time information to determine individual buffering information for each of the wireless access points. The multicast server system adjusts a buffer delay for each individual wireless access point  121 - 124  using the individual buffering information determined for each wireless access point  121 - 124 . Multicast server system  101  transmits the multimedia content to wireless access points  121 - 124 . In some examples adjusting the buffer delay speeds up transmission (i.e. decreasing the buffer). In other examples, adjusting the buffer delay slows down transmission (i.e. increasing the buffer). 
       FIG. 2  illustrates the operation of wireless communication system  100  to provide buffering in an SFN. Multicast server system  101  transmits multimedia content to wireless access points  121 - 124  ( 201 ). For example, the multimedia content may be transmitted in data packets or data blocks. Although not required, each data packet may be time stamped by multicast server system  101  with a packet transmission time. 
     Wireless access points  121 - 124  determine and transmit SFN transmit time information to multicast server system  101  ( 202 ). In some examples, wireless access points  121 - 124  may track the time of receipt for each data packet received. Although not required, multicast server system  101  may determine SFN transit time information. 
     The wireless access points  121 - 124  may previously have synchronized their clocks, so that the timing information would be synchronized. Although not required, wireless access points  121 - 124  may also periodically synchronized their clocks. In some examples, SFN transmit time information may include the timestamp of when a data packet was received by the wireless access point. In other examples, the SFN transmit time information may be the timestamp of when a data packet was transmitted from the wireless access point. 
     Multicast server system  101  uses the SFN transmit time information to determine individual buffering information for wireless access points  121 - 124  ( 203 ). Multicast server system  101  adjusts a buffer delay for each individual wireless access point  121 - 124  using the individual buffering information for each wireless access point  121 - 124  ( 204 ). In some examples, each wireless access point  121  may have a different buffer delay. In some cases, wireless access points  121 - 124  are all synchronized and there is no need to adjust the individual buffer delays. 
     However, if wireless access points  121 - 124  are not synchronized, it may be necessary to adjust the individual buffer delays. For example, wireless access point  121  may be transmitting earlier than the other wireless access points in the SFN. Transmission of the multimedia content from the wireless access point  121  may need to be delayed. Multicast server system  101  may increase the buffer delay for wireless access point  121  and not change the buffer delay for wireless access points  122 - 124 . In another example, wireless access point  124  may be transmitting later than wireless access points  121 - 123 , multicast server system  101  may decrease the buffer delay for wireless access point  124 . In some examples, an individual buffer delay may be increased and another individual buffer delay may be decreased. Although not required, an unsynchronized wireless access point may be removed from the SFN. 
     Although not required, multicast server system  101  may transfer the individual buffering information for delivery to wireless access points  121 - 124 ; and wireless access points  121 - 124  may use the individual buffering information to synchronize transmission of the multimedia content. Multicast server system  101  transmits the multimedia content to wireless access points  121 - 124  ( 205 ). 
     Periodically during the transmission of the multimedia content, multicast server system  101  may check the synchronization of wireless access points  121 - 124 . Multicast server system  101  transfer an SFN transmit time information request to wireless access points  121 - 124 . Wireless access points  121 - 124  determine updated SFN transmit time information for delivery to multicast server system  101 . Multicast server system  101  uses the updated SFN transmit time information to determine updated buffering information for each wireless access point  121 - 124 . 
     Multicast server system  101  uses the updated buffering information to determine whether the individual buffer delays for each individual wireless access point  121 - 124  needs to updated/changed. In some examples, the SFN transmit time information request is sent after a specified amount of time. Although not required, multicast server system  101  may periodically transmit a SFN transmit time information request to all wireless access points (active and not active) that are part of the SFN. 
       FIG. 3  illustrates the operation of wireless communication system  100  to provide buffering in an SFN. Multicast server system  101  transmits multimedia content to wireless access points  121 - 124 . Wireless access points  121 - 124  determine and transmit SFN transmit time information to multicast server system  101 . Multicast server system  101  uses the SFN transmit time information to determine individual buffering information for each wireless access point  121 - 124 . Multicast server system  101  adjusts an individual buffer delay for each individual wireless access point  121 - 124 , using the individual buffering information determined for each wireless access point  121 - 124 . Multicast server system  101  transmits the multimedia content to wireless access points  121 - 124 . 
     In this example, multicast server system  101  uses the SFN transmit time information transferred from wireless access point  122  to determine buffering information for wireless access point  122 . The buffering information for wireless access point  122  may indicate that wireless access point is transmitting earlier than the other wireless access points. In order to synchronize the transmission, multicast server system  101  increases the buffer delay to wireless access point  122 . Although not required, additional multicast server systems may be added to increase the coverage area or reduce delay caused by distance between the multicast server systems and the wireless access points. 
       FIG. 4  illustrates wireless communication system  400  to provide buffering in a Single Frequency Network (SFN). Wireless communication system  400  includes a Content Delivery Network (CDN), an LTE communication network, and eNodeBs  421 - 424 . The LTE communication network includes a Broadcast Multicast Service Center (BMSC), a MBMS Gateway (M-GW), and Multicast Coordination Entity (MCE)  401 . Although shown as a separate entity, MCE  401  could be integrated into the M-GW or eNodeBs  421 - 424 . Other elements of the LTE communication network such as a Serving Gateway (S-GW) and a Mobility Management Entity (MME) have been omitted for clarity. 
     In operation, a content provider transmits multimedia content to eNodeBs  421 - 424  over the LTE communication network. ENodeBs  421 - 424  determine and transfer SFN transmit time information for delivery to Multicast Coordination Entity (MCE)  401 . Although not required, the data and signaling may be transmitted over different links. In this example, the data link is shown in a solid line and the signaling link is indicated with a dashed line. 
     MCE  401  uses the SFN transmit time information to determine individual buffering information for each eNodeB  421 - 424 . For example, SFN transmit time information may include packet transmission time, packet receipt time, buffer status information, a buffer status report, propagation delay information, backhaul delay information, frame transmission information, error rates, and/or other timing information—including combinations thereof. 
     Although not required, MCE  401  may process the SFN transmit time information transferred from each eNodeB  421 - 424  to determine an average SFN transmit time for all eNodeBs. Although use of an average SFN transmit time is discussed, other calculations or statistically measures, such as standard deviation may be used to determine the synchronicity of the eNodeBs. 
     For instance, if eNodeB  421  transmitted the data packet at time_1, eNodeB  422  transmitted the data packet at time_2, eNodeB  423  transmitted the data packet at time_3, and eNodeB  424  transmitted the data packet at time_4. The average SFN transmit time would be: 
     
       
         
           
             
               SFN 
               ⁢ 
               
                   
               
               ⁢ 
               transmit 
               ⁢ 
               
                   
               
               ⁢ 
               time 
             
             = 
             
               
                 ( 
                 
                   
                     time_ 
                     ⁢ 
                     1 
                   
                   + 
                   
                     time_ 
                     ⁢ 
                     2 
                   
                   + 
                   
                     time_ 
                     ⁢ 
                     3 
                   
                   + 
                   
                     time_ 
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                     4 
                   
                 
                 ) 
               
               4 
             
           
         
       
     
     Using the average SFN transmit time MCE  401  may determine whether each individual eNodeB  421 - 424  is within a threshold time of the average SFN transmit time. In some examples, if the eNodeB is within a threshold time of the average SFN transmit time, the eNodeB will be considered synchronized. If the eNodeB is not within the threshold, the eNodeB may need to be synchronized. In some examples, the unsynchronized eNodeB may be temporarily or permanently removed from the SFN. 
     Multicast server system  401  adjusts an individual buffer delay for each unsynchronized eNodeB using the individual buffering information. For example, the SFN transmit time for eNodeB  424  may be earlier than the other eNodeBs. MCE  401  increases the buffer delay for eNodeB  424  (i.e. slow-down or delay transmission) in order to synchronize eNodeB  424  with the other eNodeBs. 
     In another example, the SFN transmit time for eNodeB  424  may be later than the other eNodeBs. MCE  401  decreases the buffer delay for eNodeB  424  (i.e. speed up transmission) in order to synchronize eNodeB  424  with the other eNodeBs. Note there may be a default buffer to all eNodeBs, in order to allow the buffer delay to be decreased. 
     By adjusting the buffer delay, MCE  401  can synchronize the transmission time for a data packet for all eNodeBs in the SFN. Transmission time may be affected by backhaul delays, base station load, buffer fill, etc. MCE  401  transmits the multimedia content to eNodeBs  421 - 424 . 
       FIG. 5  illustrates the operation of wireless communication system  400  to provide buffering in an SFN. A content provider transmits multimedia content to eNodeB  424  over the LTE communication network. ENodeB  424  determines and transmits SFN transmit time information to MCE  401 . Although not required, MCE  401  may determine the SFN transmit time information rather than receiving it from eNodeB  424 . 
     MCE  401  uses the SFN transmit time information to determine individual buffering information for eNodeB  424 . MCE  401  adjusts a buffer delay for eNodeB  424  using the individual buffering information for eNodeB  424 . MCE  401  transmits the multimedia content to eNodeB  424 . 
       FIG. 6  illustrates multicast server system  600  to provide buffering in an SFN. Multicast server system  600  is an example of multicast server system  101  and multicast coordination entity  401 , although multicast server system  101  and multicast coordination entity  401  may use alternative configurations. Multicast server system  600  could be a discrete system, a distributed system, and/or could be integrated into other systems. 
     Multicast server system  600  comprises communication transceivers  601  and processing system  603 . Processing system  603  comprises processor circuitry  611  and memory  612  that stores operating software  613 . Software  613  includes transmission module  614 , buffering information module  615 , buffer delay module  616 , and request module  617 . Processing system  603  is linked to communication transceivers  601 . Multicast server system  600  may include other well-known components that are not shown for clarity, such as, servers, computer systems, databases, and power systems. 
     Communication transceivers  601  comprise a physical communication port, signal processing circuitry, software, and/or some other communication components. Communication transceivers  601  may use various protocols, such as IP, TDM, Ethernet, wireless, or some other network communication format—including combinations thereof. Communication transceivers  601  exchange signaling and other control data with communication nodes as described herein. 
     Processor circuitry  611  comprises microprocessor and other circuitry that retrieves and executes operating software  613  from memory  612 . Memory  612  comprises a non-transitory computer-readable storage medium, such as a disk drive, flash drive, data storage circuitry, or some other memory apparatus. Memory system  612  could be a single device or be distributed across multiple devices. Processor circuitry  611  is typically mounted on one or more circuit boards that may also hold memory  612  and portions of communication transceivers  601 . 
     Operating software  613  comprises computer programs, firmware, or some other form of computer-readable processing instructions. Operating software  613  may include an operating system, utilities, drivers, network interfaces, applications, or some other type of software. When executed by processor circuitry  611 , software  613  directs processing system  603  to operate multicast server system  600  as described herein. In particular, transmission module  614  directs processing system  603  to transmit multimedia content for delivery to the wireless access points. Buffering information module  615  directs processing system  603  to use the SFN transmit time information received from each wireless access point to determine individual buffering information for each wireless access point. Buffer delay module  616  directs processing system  603  to use the individual buffering information for each wireless access point to adjust a buffer delay for each individual wireless access point. Request module  617  directs processing system  603  to transfer an SFN transmit time information request for delivery to the wireless access points. The request may be sent periodically to all wireless access point receiving the multimedia content. 
     Referring back to  FIG. 1 , wireless access points  121 - 124  comprise RF communication circuitry and an antenna. The RF communication circuitry typically includes an amplifier, filter, RF modulator, and signal processing circuitry. Wireless access points  121 - 124  may also comprise a router, server, memory device, software, processing circuitry, cabling, power supply, network communication interface, structural support, or some other communication apparatus. Wireless access points  121 - 124  could be a base station, base transceiver station, eNodeB, Internet access node, telephony service node, wireless data access point, or some other wireless communication system—including combinations thereof. Wireless access points  121 - 124  comprise network elements that provide communications services to wireless communication devices. Wireless access points  121 - 124  may comprise switches, wireless access nodes, Internet routers, network gateways, application servers, computer systems, communication links, or some other type of communication equipment—including combinations thereof. 
     Multicast server system  101  comprises a computer system and communication interface. Multicast server system  101  may also include other components such as a router, server, data storage system, and power supply. Multicast server system  101  may reside in a single device or may be distributed across multiple devices. Multicast server system  101  is shown externally to wireless access points  121 - 124 , but multicast server system  101  could be integrated within the components of wireless access points  121 - 124 . Multicast server system  101  could be a mobile switching center, network gateway system, Internet access node, application server, service node, or some other communication system—including combinations thereof. 
     Communication links  111 - 114  use metal, glass, air, space, or some other material as the transport media. Communication links  111 - 114  could use various communication protocols, such as Time Division Multiplex (TDM), Internet Protocol (IP), Ethernet, communication signaling, CDMA, EVDO, WIMAX, GSM, LTE, WIFI, HSPA, or some other communication format—including combinations thereof. Communication links  111 - 114  could be a direct link or may include intermediate networks, systems, or devices. 
     The above description and associated figures teach the best mode of the invention. The following claims specify the scope of the invention. Note that some aspects of the best mode may not fall within the scope of the invention as specified by the claims. Those skilled in the art will appreciate that the features described above can be combined in various ways to form multiple variations of the invention. As a result, the invention is not limited to the specific embodiments described above, but only by the following claims and their equivalents.