Abstract:
In one aspect, a method of determining a geographical location of a base station is provided. The base station is within a coverage area of a master base station and requests geographical location information from the master base station through a first Precision Time Protocol (PTP) management message. The base station receives the geographical location information from the master base station through a second PTP management message. In addition, the base station determines the geographical location of the base station from the geographical location information included in the second PTP management message.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. provisional application having Ser. No. 61/768,122, filed on Feb. 22, 2013, which is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    Embodiments of the present invention relate generally to time and frequency alignment systems operating over packet-switched communications networks and, more specifically, to methods and apparatus for distributing location information in addition to precision time transfer. 
         [0004]    2. Description of Related Prior Art 
         [0005]    It has been recognized that by establishing the geographic location of a mobile telephone user, location-based services can be provided, thereby increasing the potential average revenue per user. It is also a federal mandate (in the USA) that, for emergency services, the geographic location of the origin of an emergency (i.e. E911) call be established with a prescribed level of accuracy. GPS-equipped mobile devices can establish their own geographic location if there is a good and unobstructed view of the sky. In other cases the location of the mobile station is established relative to the location of the serving base-station. That is, it is advantageous to establish the geographic location of the base-stations. 
         [0006]    Outdoor base-stations can be equipped with GPS antenna/receiver functionality and thereby establish their location autonomously. In the case of smaller, typically indoor-mounted, base-stations, the option of self-positioning via GPS is not a viable option for reasons of cost and/or visibility of the sky. Determining the location of a base-station that does not have GPS functionality is done by manually surveying the location where the base-station is installed prior to deployment. 
         [0007]    Such pre-deployment surveying does not satisfactorily address the case where the base-station itself can be moved. Pre-deployment surveying is also not appropriate in the case where the base-station device is purchased and installed by the end-user. 
         [0008]    The provider of mobile communication services requires knowledge of the location of the base-station for variety of reasons such as billing and often the service contract pre-supposes a deployment location. Consequently it will be advantageous to ascertain the location of a deployed base-station, albeit approximately, in order to deliver mobile communication services. 
         [0009]    The conventional methodology for distributing timing to base-stations is depicted in  FIG. 1 . The various base-stations (BS-x)  120  are connected back into the service provider network via communication links  160 . The provider has at least one location that can operate as a master clock (MCLK)  110  that represents the timing reference for the base-stations in the (sub)network that home in to the master clock. The master clock is usually associated with a Radio Network Controller (RNC) or a Base-Station Controller (BSC) or even the Mobile Switching Office (MSO). Legacy mobile telephony networks often used TDM links to implement the backhaul from the base-stations and these TDM links (e.g. T1/E1 or SONET/SDH) were suitable for carrying a (frequency synchronization reference signal. 
         [0010]    It is increasingly common for the backhaul network to be replaced with a packet-switched network wherein the physical layer could be implemented by a wide variety of technologies including Ethernet (typically over optical fiber), microwave, ADSL/VDSL, and coax (cable-TV derivative). The timing information  270  in this case is delivered in the form of a packet flow  260 . The technologies used for delivering timing in this situation are packet-based including precision time protocol (PTP) and/or network time protocol (NTP). Whereas legacy mobile telephony required simply a frequency reference, more recent advances require a time/phase reference (as well as frequency). Two-way methods such as PTP and NTP are required to support this requirement. As depicted in  FIG. 2 , timing information is delivered from the master base station  110  clock  215  to the slave clock  225  in the base station  120  over a packet network  250  wherein the processing elements  216  and  226  exchange packets via a flow  260 . 
         [0011]    Whereas  FIG. 1  and  FIG. 2  depict terrestrial methods for distributing time/frequency from the central location to the base-stations, they do not teach how the base-station can assess its own geographical location. In  FIG. 3  a third approach is shown wherein all the elements (base-stations and master clock) derive their timing from a common source, namely a Global Navigation Satellite System (GNSS)  310  (the most commonly quoted example of a GNSS is the global positioning system (GPS) operated by the US Government). The satellite signal  330  is received by the terrestrial elements and by synchronizing to GNSS the terrestrial elements are indirectly aligning themselves in time/frequency. One advantage of the GNSS signal is that it provides not just timing but enables the receivers to establish their own geographical location(s). However, due to constraints such as cost and deployment location considerations, base-stations with GPS/GNSS functionality are usually macro-base-stations deployed outdoors; smaller base-stations (such as micro-, pico-, and femto-base-stations) are often deployed indoors and without a clear view of the sky. 
       SUMMARY OF INVENTION 
       [0012]    Embodiments of the invention described here enable base-stations to establish an approximate location for themselves. Although approximate, the location information is adequate for most applications of location-based services and for network operators and mobile telephony service providers to validate the base-station. 
         [0013]    In one aspect, a method of determining a geographical location of a base station that is within a coverage area of a master base station is provided. The method includes requesting geographical location information from the master base station via a first Precision Time Protocol (PTP) management message. The method further includes receiving the geographical location information from the master base station via a second PTP management message. In addition, the method includes determining the geographical location of the base station from the geographical location information included in the second PTP management message. 
         [0014]    In another aspect, a wireless communication base station positioned within a coverage area of a master base station and configured to perform operations for determining a geographical location of the wireless communication base station is provided. The operations include requesting geographical location information from the master base station via a first PTP management message. The operations further include receiving the geographical location information from the master base station via a second PTP management message. In addition, the operations include determining the geographical location of the wireless communication base station from the geographical location information included in the second PTP management message. 
         [0015]    In yet another aspect, a method for a base station to obtain location-proximity specific information from a master base station is provided. The method includes the step of requesting the location-proximity specific information from the master base station via a first PTP management message. Additionally, the method includes receiving the location-proximity specific information from the master base station via a second PTP management message. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
           [0017]      FIG. 1  depicts a conventional arrangement for distributing synchronization in a wireless network. 
           [0018]      FIG. 2  depicts the essential elements of a master clock and a slave clock suitable for distributing synchronization over a packet network that is applicable to the case where a conventional wireless network utilizes a packet-switched network for implementing connectivity between base-stations and the communication network. 
           [0019]      FIG. 3  depicts an arrangement whereby timing alignment between base-stations and the master clock is accomplished using GNSS techniques. 
           [0020]      FIG. 4  depicts an arrangement whereby one base-station serves as the master for a PTP domain that includes several base-stations in the nearby geographical vicinity, according to an embodiment. 
           [0021]      FIG. 5  depicts the essential elements of the clock system in the base-station acting as the base-station-master, also referred to as Edge Master, according to an embodiment. 
           [0022]      FIG. 6  portrays the messages flowing between the master and the slave clocks, composed of synchronization messages and management messages, according to an embodiment. 
           [0023]      FIG. 7  provides the information associated with location, according to an embodiment. 
           [0024]      FIG. 8  is a table that depicts an assignment of fields to information carried in a management message, according to an embodiment. 
           [0025]      FIG. 9  is a table that provides an explanation of the actions taken based on entries in the actionField of a management message, according to an embodiment. 
           [0026]      FIG. 10  is a table that depicts the value of the actionField for an Event-Report, according to an embodiment. 
           [0027]      FIG. 11  is a table that depicts the assignment of fields in a management TLV, according to an embodiment. 
           [0028]      FIG. 12  is a table that depicts an example assignment of values to ManagementId. 
           [0029]      FIG. 13  is a table that depicts the structure of a LOCATION_INFORMATION management TLV, according to an embodiment. 
           [0030]      FIG. 14  is a flow diagram depicting a method for a base station to obtain location-proximity specific information from a master base station, according to an embodiment. 
       
    
    
       [0031]    For clarity, identical reference numbers have been used, where applicable, to designate identical elements that are common between figures. It is contemplated that features of one embodiment may be incorporated in other embodiments without further recitation. 
       DETAILED DESCRIPTION 
       [0032]    The distribution of time over packet networks is now ubiquitous. The dominant method is the use of the Network Timing Protocol (NTP) for support of general timing applications in general computing applications. However, these implementations, based on existing standards and conventions, are suitable for time alignments of the order of (several) milliseconds. Over the last decade, a new protocol, Precision Timing Protocol (PTP) has emerged supported by industry standards (IEEE 1588-2008, ITU-T Recommendations in the G.827x series). The key differentiator between NTP and PTP is that the new levels of precision that can be obtained with PTP support the needs of a variety of new applications and services. Both PTP and NTP are protocols for exchanging time-stamps associated with time-of-arrival and time-of-departure of designated packets and are thus, in principle if not practice, capable of similar performance levels. 
         [0033]    The deployment architecture for implementing the methods and techniques of the invention described herein is depicted in  FIG. 4 . A collection of base-stations  120  (BS- 1  through BS- 6  for example) and a “special” base-station BS-M  400  are all on the same network and constitute a PTP domain. BS-M  400  is different from base-stations  120  in that it is an “Edge Master.” By this is meant that BS-M  400  has GNSS functionality. Since BS-M  400  has the best reference for time/frequency, it becomes the master of the PTP domain and all the other base-stations operate as slaves. That is, BS-M  400  operates as the master clock as represented in  FIG. 2 . The PTP domain thus is composed of the master  400  and a collection of slaves  120 . Since these base-stations represent small cells, they are all located in a relatively small geographical area. 
         [0034]    Delivery of time/frequency over packet-based networks is the subject of other patents/patent applications such as U.S. Pat. No. 8,385,212, entitled Method and Apparatus for Finding Latency Floor in Packet Networks; U.S. Pat. No. 8,427,963, entitled Method and System for Analyzing and Qualifying Routes in Packet Networks; and U.S. Pat. No. 8,644,348, entitled Method for Generating a Robust Timing Correction in Timing Transfer Systems; U.S. Pat. No. 8,064,484, entitled Enhanced Clock Control in Packet Networks, which are incorporated by reference herein in their entireties. Approaches to defeat transmission asymmetry are described in U.S. Pat. No. 8,594,134, entitled Precision Time Transfer over Optical Fiber; and U.S. Provisional Patent Application No. 61/749,565, filed Jan. 7, 2013 and entitled Universal Asymmetry Correction for Packet Timing Protocols, which are incorporated by reference herein in their entireties. It is feasible to have the remote time-stamping functionality described in U.S. Provisional Patent Application No. 61/789,957, filed Mar. 15, 2013 and entitled Distributed Two-Step Clock, which is incorporated by reference herein in its entirety, as an integral part of BS-M  400 . 
         [0035]    Some of the relevant features of BS-M  400  are depicted in  FIG. 5 . The block labeled “PROC.”  516  represent functions that are common to all PTP implementations. The GNSS Receiver  502  provides a suitable timing (time and frequency) reference  506  to the clock  525  which thus can be considered to be aligned with the (common) GNSS timescale. The PTP block operates in a master mode, delivering the packet timing flow  260  to the other base-stations within the PTP domain. The location information  504  provided via the GNSS receiver establishes the location of the master device BS-M  400 . 
         [0036]    The BS-M  400  distributes this location information using PTP based messaging to the slave base stations  120  that are in the master&#39;s PTP domain. The base-stations  120  use this location information as an approximation for their own geographical location. That is, the location information of the master BS-M  400  serves as a proxy for the location of the subtending slaves  120  in the master&#39;s PTP domain. 
         [0037]    The base-stations BS-x  120  derive their timing from the “master” base-station BS-M  400 . As indicated above, BS-M  400  is distinguished from the others by having means to establish its own location, typically using GNSS methods. A block diagram showing the principal components of BS-M, from the viewpoint of timing, synchronization, and location, is shown in  FIG. 5 . 
         [0038]    The master clock BS-M  400  (also referred to herein as “Edge Master”) serves as the master clock for the PTP domain composed of the master  400  and the slaves  120  that derive timing therefrom. These devices are all in relatively close geographical proximity and therefore the location of the master serves as a proxy for the location of the slaves. The invention described here shows how the slaves  120  can obtain the location information while maintaining the principles of the protocol standards and therefore can interoperate with slaves and masters that conform to the protocol standard. The standard assumed herein is PTP, specifically IEEE-1588-2008 and the master  400  derives its location information using GPS methods. 
         [0039]    GPS-based location offers a very efficient and accurate synchronization and location solutions for outdoor scenarios. In order to be able to properly estimate time and position, the GPS receiver needs to have an unobstructed line of sight to at least four GPS satellites. However, GPS fails to provide an acceptable level of accuracy in indoor and urban environments. Therefore, it cannot be easily used to synchronize base stations in indoor environments and in some urban environments where most satellites are obscured by buildings. IEEE 1588-2008 is typically used to synchronize indoor base-stations (e.g.  120 ) to the Edge Master  400 . The PTP Edge Master  400  can be used to transmit its location information to the base-stations that are being synchronized. Provided that the base-stations are not located too far from the Edge Master, this location information can be used to approximate the position of the base-stations. 
         [0040]    The GPS receiver in the Edge Master  400  provides the location information  504 . The essential components of the location information  504 , according to one embodiment, are shown in  FIG. 7 . 
         [0041]    The preferred embodiment described here sends the GPS location information  504  over the PTP management channel implemented between the PTP slave and the Edge Master acting also as a PTP manager. This management channel is used to query and configure clocks. Since the published standard IEEE 1588-2008 does not provide a notification service, a notification service is implemented as a proprietary extension of the protocol in order to trigger the transmission of the GPS location information of the Edge Master to the PTP. The standard does provide guidelines on permissible extensions based on “TLV” (Type Length Value) constructs. 
         [0042]    As shown in  FIG. 6 , the master and slave exchange PTP synchronization messages  640  at  610 - 635 . Whereas only one set of exchanges is shown, synchronization message exchanges occur on a continual basis. In addition,  FIG. 6  shows one exchange of management messages  660  at  650 - 655 . There is no prescribed rate for such messages, nor does the standard prescribe a particular order or sequence that must be followed. Interspersing management messages between the exchange of synchronization messages is permitted. 
         [0043]    Once the slave  120  is locked to the Edge Master  400 , the slave  120  issues an Event_Report management message to request the GPS location information. The Event_Report is an extension of PTP management messages and is an implementation of a notification service. 1588 PTP-2008 does not define such a mechanism in the standard, but it provides a mechanism to extend the management messages. In one embodiment, the management messages may be extended to include an actionField value for the Event-Report and a management TLV dataField which specifies information to be reported back to the slave upon the occurrence of a certain event, as discussed in greater detail below. The Edge Master  400  keeps track of all active slaves  120  in a list. 
         [0044]    IEEE 1588-2008 provides a network management mechanism to control the PTP slaves  120  using a TLV format. It defines management messages that are used to access attributes and to trigger events. In one embodiment, the TLV managementId field includes a managementId values table that is extended with a proprietary value LOCATION_INFORMATION that is used to hold the location information of the master base station. LOCATION_INFORMATION itself may include a number of parameters such as a timestamp, latitude, longitude, etc., the values of which are stored in a dataField of the TLV of a management message sent from the master base station to the slave base station. 
         [0045]    In one embodiment, the management messages implement the format provided in  FIG. 8 : 
         [0046]    1. Header 
         [0047]    This is the common message for all PTP messages (See IEEE 1588-2008 section 13.3.1) 
         [0048]    2. targetPortIdentity (PortIdentity) 
         [0049]    For a message generated by a manager, it is the portidentity or node associated to the managed entity. In the case of a response to manager, it is set to sourcePortIdentity of the management message to which it is a response. 
         [0050]    3. startingBoundaryHops (UInteger8) 
         [0051]    For a response to a management request it is used to calculate the number of retransmissions by boundary clocks the message experienced. 
         [0052]    4. boundaryHops 
         [0053]    It indicates the remaining number of successive retransmissions of the management message by boundary clocks receiving the message. 
         [0054]    5. reserved 
         [0055]    6. actionField (Enumeration4) 
         [0056]    It indicates the management action that should be performed. The relevant actions are enumerated in  FIG. 9 . 
         [0057]    IEEE 1588-2008 does not provide any management notification service. This service is very useful for a slave to send an unsolicited message to the manager. A notification service is convenient for a slave to notify the Edge master  400  in a manager role of its presence after it has locked to it. This is particularly useful for a PTP service in Annex F mode (multicast Ethernet). The Edge Master  400  can then use the SET operation to send its location data. Therefore, the preferred embodiment introduces a proprietary Event-Report notification as an extension of the operations defined in action Field. 
         [0058]    As shown in  FIG. 10 , the Event-Report can, for example, be associated with an actionField value of 5 and indicate that the management message, transmitted from the slave base station to the Edge Master  400 , includes a single management TLV with a dataField (i.e., the information bits of the TLV other than the header of the TLV) specifying information to be reported back to the slave base station upon the occurrence of a certain event. For example, the data may include a dataField value which specifies that, upon receipt of the management message, the Edge Master  400  should send its geographical location to one of the slave base stations  120 . 
         [0059]    7. Management TLV field format 
         [0060]    The Management TLV field format is defined in  FIG. 11 . 
         [0061]    7.1. tivType (Enumeration16) 
         [0062]    The tivType is MANAGEMENT 
         [0063]    7.2. lengthField (Uinteger16) 
         [0064]    It is set to 2+N, where N is an even number. 
         [0065]    7.3. managementId (Enumeration16) 
         [0066]    Examples of values of the managementId field are shown in  FIG. 12 . 
         [0067]    In the preferred embodiment, the managementId values table is extended with a proprietary value LOCATION_INFORMATION that is used to hold the location information of the Edge Master  400 . LOCATION_INFORMATION is sent to the PTP slave using a SET operation. Examples of LOCATION_INFORMATION parameters are shown in  FIG. 13 . The values of such parameters may be stored in the dataField of the management TLV of the management message sent from the Edge Master  400  to one or more of the slave base stations  120 . Persons skilled in the art will recognize that, if a slave base station  120  receives a management message with LOCATION INFORMATION but does not understand it, then the slave base station  120  will ignore this value and the dataField information associated therewith. The particular parameters of LOCATION_INFORMATION depicted in  FIG. 13  are as follows: 
         [0068]    UTC Time Stamp (Octet[6]): UTC Time of position fix in hhmmss format (example: “12”: hh 00-23 hours “34”:mm 00-59 minutes “56”:ss 00-59 seconds). 
         [0069]    Latitude (Octet[9]): Latitude of fix in ddmmmmmml format (example: “34”: degree 00-90 “44”: minute (integer) 00-59 “0000”:minute (fractional) 0000-9999 “N”: North/South N or S). 
         [0070]    Longitude (Octet[10]): Longitude of fix in dddmmmmmml format (example: “135”: degree 000-180 “44”: minute (integer) 00-59 “0000”:minute (fractional) 0000-9999 “E”: East/West E or W). 
         [0071]    GPS Quality Indication (Octet[1]): Quality Indication in q format (example: “0” Fix not available or invalid, “1” Fix is valid. 
         [0072]    No. of satellites used for positioning (Octet[2]): Number of satellites in use in nn format (example: 04 from to 00 to 12). 
         [0073]    Dilution of Precision (Octet[5]): Dilution of Precision in dd.dd format (example: 02.34 Note 00.00 when position is interrupted or suspended). 
         [0074]    Altitude (Octet[9]): Altitude in saaaaa.au format (example: “+” +/− sign relative to geoid 12345.6 00000.0 to 04000.0 “M” unit meters). 
         [0075]    EOT (Octet[1]): End of path position in format 0x00—The End Of Text EOT marks the end of the Path Position. 
         [0076]      FIG. 14  is a flow diagram depicting a method  1400  for a base station (e.g., one of the base stations  120 ) to obtain location-proximity specific information from a master base station (e.g., Edge Master  400 ), according to an embodiment. At step  1410 , the base station and the master base station exchange PTP synchronization messages. PTP synchronization messages are well-known to persons skilled in the art. In some cases, synchronization message exchanges may occur on a continual basis. 
         [0077]    At step  1420 , the base station requests location-proximity specific information by transmitting an Event_Report management message to the master base station. As discussed, the Event_Report management message is an implementation of a notification service. In one embodiment, the Event_Report management message may be a PTP management message that includes a predefined actionField value such as that discussed above with respect to  FIG. 10 . Specifically, the predefined actionField value may indicate that the management message includes a single management TLV with a dataField specifying location-proximity specific information to be reported upon the occurrence of a certain event. For example, the location-proximity specific information may be a geographical location of the master base station that the master base station establishes using GNSS techniques, and the event may be the receipt of the Event_Report management message. Alternatively, one or more slave base stations may establish their geographical locations and report this information to the master base station, which then distributes the information. Other types of information that are location-proximity specific include weather information and local alarm information such as fire and burglary alarm information. The base station may request to be notified of such weather information and local alarm information, similar to the request for geographical location information discussed above. In such cases, the event may be a weather update, a local alarm being issued, and the like. 
         [0078]    At step  1430 , upon the occurrence of the event specified in the Event_Report management message, the master base station transmits to the base station a management message with the requested location-proximity specific information. The management message with the requested information may include an actionField value of SET, a management TLV managementld value indicating the location-proximity specific information stored in a dataField of the management TLV, and the location-proximity specific information itself that is stored in the dataField. In the case of geographical location, the dataField may store, e.g., values for the LOCATION_INFORMATION parameters discussed above with respect to  FIG. 13 . As discussed, the base station that receives such geographical location information may use the information to establish its own geographical location. Other types of information such as weather information and local alarm information may be transmitted and used in a similar manner. 
         [0079]    Note, IEEE 1588-2008 does not prescribe any rate for the synchronization and management messages of steps  1410 - 1430 . Nor does there need to be a particular order or sequence that must be followed. For example, the management messages of steps  1410 - 1420  may be interspersed between the exchanges of synchronization messages of step  1410 . Further, multiple synchronization and management messages may be exchanged. 
         [0080]    Advantageously, techniques disclosed herein permit properties to be shared between a collection of base stations. In particular, a master base station may distribute geographical location information via PTP based management messages to slave base stations in geographical proximity to the master base station. Often, the geographical location of the master base station is adequate for the slave base stations to use as their own geographical locations. The master-slave communication may be achieved using allowed features of the timing protocol, such as a management TLV extension of PTP, and consequently will not result in interoperability if any slave base station is not equipped with the feature. 
         [0081]    While the forgoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. For example, aspects of the present invention may be implemented in hardware or software or in a combination of hardware and software. One embodiment of the invention may be implemented as a program product for use with a computer system. The program(s) of the program product define functions of the embodiments (including the methods described herein) and can be contained on a variety of computer-readable storage media. Illustrative computer-readable storage media include, but are not limited to: (i) non-writable storage media (e.g., read-only memory devices within a computer such as CD-ROM disks readable by a CD-ROM drive, flash memory, ROM chips or any type of solid-state non-volatile semiconductor memory) on which information is permanently stored; and (ii) writable storage media (e.g., floppy disks within a diskette drive or hard-disk drive or any type of solid-state random-access semiconductor memory) on which alterable information is stored. Such computer-readable storage media, when carrying computer-readable instructions that direct the functions of the present invention, are embodiments of the present invention.