Abstract:
A UE side Broadcast/Multicast Control (BMC) protocol layer determines those Cell Broadcast Service (CBS) messages (and their repetitions) which the UE shall read or ignore in a succeeding CBS schedule period, based on the CBS Schedule Message contents (Message Description Type and New Message Bitmap) received in a current CBS schedule period, the CBS messages already stored in the BMC, and the CBS messages to be received. In this manner, the UE may ignore CBS messages it has already received, without knowledge of the CBS message serial numbers, and thus conserve resources such as battery power.

Description:
FIELD OF INVENTION 
     The present invention relates generally to wireless communication networks, and in particular to a power-efficient method of receiving Broadcast/Multicast Control protocol message by User Equipment. 
     BACKGROUND 
     Modern wireless communication networks are ubiquitous in many parts of the world. With advances in technology, and sophisticated protocols and standards (e.g., 3GPP technical standards), wireless networks deliver far more services than the paging and mobile telephony for which they were originally designed. One such advanced service is the ability of a network to transmit the same information to all User Equipment (UE) within one or more cells (broadcast), or to a select group of UE (multicast). To facilitate this service, the Broadcast/Multicast Control (BMC) protocol is defined as part of the Group Radio Access Network (GRAN) in 3GPP Technical Specification 25.324, “Broadcast/Multicast Control BMC,” the disclosure of which is incorporated herein by reference in its entirety. 
     3GPP TS 25.324 defines BMC as a sublayer in the user plane of Layer  2  of the network layer protocol stack. To place the BMC in context,  FIG. 1  depicts a diagram of the relevant parts of the UTRA FDD radio interface protocol architecture  10 . The BMC  12  resides in Layer  2  above the Radio Link Control (RLC) layer  14 , which maps logical channels. The RLC  14  itself resides above the Media Access Control (MAC) layer  16 , which maps traffic channels. Layer  1  includes the Physical (PHY) layer  18 , which implements transmission and reception. Layer  3  includes the Radio Resource Control (RRC) layer  20 , which provides control for the BMC  14 , RLC  16 , MAC  18 , and PHY  20 . The BMC  12  is transparent for all services other than broadcast/multicast. Note that the BMC exists only in the user plane. 
     On the network side, the BMC implements the Cell Broadcast Service (CBS). CBS is described herein in the context of UTMS; however it is also implemented in other air interface protocols, such as GSM. Accordingly, the description herein is illustrative only and is not limiting. Cell broadcast messages are Short Message System (SMS) text messages, although they are not encumbered by the length restriction of SMS text messages. A CBS message consists of one or more CBS pages, each comprising 82 octets. A CBS message may include up to 15 CBS pages. CBS messages are normally repeated, to increase the probability of successful reception by many UE. 
     All UE capable of receiving CBS messages (that are in idle, CELL_PCH, or URA_PCH RRC-states of Connected mode) may receive each CBS message. The CBS message includes a message ID that identifies the source and type of the CBS message. By inspection of the type in the message ID, individual UEs receiving a CBS message may forward the message to higher layers or discard it, depending on whether the UE is subscribed to a CBS service for that type. In this manner the BMC implements multicast, wherein only groups of subscribers receive certain message types (e.g., news, sports, weather, stock prices, and the like). 
     Each CBS message is delivered in a Physical Data Unit (PDU), and includes various Information Elements (IE). Each CBS message includes a Message Type IE (distinct from the type of CBS service described above). There are three types of CBS message PDUs: CBS message, CBS41 message, and schedule message. A BMS CBS message carries cell broadcast/multicast data and address information for GSM based CBS. A CBS41 message carries cell broadcast/multicast data and address information for ANSI-41. A scheduling message defines the schedule of CBS messages, including the next schedule message, in a succeeding CBS schedule period, which is defined in terms of a number of Common Traffic Channel (CTCH) block sets. Scheduling messages allow for support for UE discontinuous reception (DRX) to preserve battery life. 
     The CBS schedule message defines a succeeding CBS schedule period by defining an Offset to Begin CTCH BS index IE (defining the beginning of the next period) and a Length of CBS Scheduling Period IE (defining the duration of the next period). The CBS schedule message also includes a New Message Bitmap IE that identifies every CTCH BS in the next period during which a complete or partial CBS PDU will be transmitted. The CBS schedule message further includes a Message Description IE for each CBS PDU identified in the New Message Bitmap. The Message Description IE include a Message ID and Message Description Type for each CBS PDU. The encoding of the Message Description Type (MDT) field is presented in  FIG. 2  (Table 11.9-3 of 3GPP TS 25.324). Note that MDT 1 and 0 identify new (and repetitions of new) CBS messages, and MDT 5 and 4 identify old (and repetitions of old) CBS messages. MDT 6 identifies the CBS schedule message of the next period. 
     In the next period, the UE must receive all new CBS messages; it may ignore old CBS messages that it has already received. However, prior to receiving each old CBS message, the UE knows the Message ID, but does not know the Message Serial Number, which is an IE transmitted only in CBS message PDUs (not the CBS scheduling message PDU). Thus, for old messages, the UE cannot determine whether it has previously received the message or not. Accordingly, the UE must receive the message. Upon reception, the UE may inspect the Message Serial Number IE to determine whether it has previously received the CBS message. If not, it passes the CBS message to higher layers; if the UE has previously received the CBS message, the UE may discard it. The reception, downconversion, demodulation, decoding, and other processing required to receive an old CBS message, which the UE later learns it had previously received and thus discards, severely and unnecessarily drains UE battery power. 
     To address this deficiency, in 3GPP Release 6, a Change Request was introduced to 3GPP TS 25.324: CR 0028, “Introduction of Serial Number in BMC Schedule Message.” While this should provide Serial Number information to the UE regarding all old CBS messages in the upcoming period, discussions with network operators and inspection of extant networks reveals that the CR has not been widely implemented. Accordingly, the Rel. 6 CR is ineffective to resolve the above-described problem in real-world, deployed networks. 
     Accordingly, a need exists in the art for a method of reliable BMC message handling in the UE, which does not unnecessarily deplete UE battery life, in the absence of network side support for Serial Number identification. 
     The Background section of this document is provided to place embodiments of the present invention in technological and operational context, to assist those of skill in the art in understanding their scope and utility. Unless explicitly identified as such, no statement herein is admitted to be prior art merely by its inclusion in the Background section. 
     SUMMARY 
     The following presents a simplified summary of the disclosure in order to provide a basic understanding to those of skill in the art. This summary is not an extensive overview of the disclosure and is not intended to identify key/critical elements of embodiments of the invention or to delineate the scope of the invention. The sole purpose of this summary is to present some concepts disclosed herein in a simplified form as a prelude to the more detailed description that is presented later. 
     According to one or more embodiments described and claimed herein, the UE side BMC layer determines those CBS messages (and their repetitions) which the UE shall read or ignore based on the CBS Schedule Message contents (Message Description Type and New Message Bitmap), the CBS messages already stored in the BMC, and the CBS messages to be received (as indicated in the Schedule Message). 
     One embodiment relates to a method of efficiently receiving BMC protocol messages by a BMC layer in User Equipment operative in a wireless communication network. A first list comprising Message IDs of CBS messages to be received during a succeeding CBS schedule period, and second list comprising Message IDs of received CBS messages, are maintained. A CBS schedule message is received. It is determined, from the CBS schedule message, all CBS messages scheduled to be broadcast in the succeeding CBS schedule period. All scheduled CBS messages indicated in the CBS schedule message as new or repetition of new are added to the first list. All scheduled CBS messages indicated as old or repetition of old that are not included in the second list are added to the first list. All scheduled CBS messages indicated as old or repetition of old that are included in the second list and for which the corresponding CTCH BS Index in the CBS schedule message is indicted as new in the New Message Bitmap IE, are added to the first list. Resources are configured to receive only the CBS messages in the first list, as well as a CBS schedule message, in the succeeding CBS schedule period. 
     Another embodiment relates to a UE operative in a wireless communication network. The UE includes a transceiver operative to selectively receive messages from a network node, memory, and a processor operatively connected to the memory. The processor is operative to maintain a first list comprising Message IDs of CBS messages to be received during a succeeding CBS schedule period; maintain a second list comprising Message IDs of received CBS messages; cause the transceiver to receive a CBS schedule message; determine, from the CBS schedule message, all CBS messages scheduled to be broadcast in the succeeding CBS schedule period; add to the first list, all scheduled CBS messages indicated in the CBS schedule message as new or repetition of new; add to the first list, all scheduled CBS messages indicated as old or repetition of old that are not included in the second list; add to the first list, all scheduled CBS messages indicated as old or repetition of old that are included in the second list and for which the corresponding CTCH BS Index in the CBS schedule message is indicted as new in the New Message Bitmap IE; and configure resources to receive only the CBS messages in the first list, as well as a CBS schedule message, in the succeeding CBS schedule period. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. However, this invention should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. 
         FIG. 1  is a functional block diagram of part of the network layer protocol stack in a wireless communication network node. 
         FIG. 2  is a table of Message Description Type encoding. 
         FIG. 3  is a flow chart of an efficient method of selectively receiving CBS messages. 
         FIG. 4  is a diagram of CBS schedule periods. 
         FIG. 5  is a functional block diagram of a UE. 
     
    
    
     DETAILED DESCRIPTION 
     It should be understood at the outset that although illustrative implementations of one or more embodiments of the present disclosure are provided below, the disclosed systems and/or methods may be implemented using any number of techniques, whether currently known or in existence. The disclosure should in no way be limited to the illustrative implementations, drawings, and techniques illustrated below, including the exemplary designs and implementations illustrated and described herein, but may be modified within the scope of the appended claims along with their full scope of equivalents. 
     In the UE, the BMC layer determines which CBS messages it must receive (and hence may avoid receiving those which would be redundant) in a succeeding CBS schedule period by maintaining information on CBS messages already received, and by parsing the contents of the CBS schedule message in the current CBS schedule period. 
     In particular, the BMC layer maintains two lists: a list of previously received CBS messages (e.g., BMC_ReceivedMessageList), and a list of messages to be received in the next CBS schedule period (e.g., BMC_MessagesToBeReceivedList). By reference to these two lists, and the information carried in the conventional CBS schedule message (without Serial Numbers), the UE BMC layer  12  can resolve which CBS messages it should receive in the succeeding schedule period, and which it can safely ignore. 
     Initially, the BMC  12  inspects the CBS schedule message for the current CBS schedule period. For each CBS message to be transmitted in the next schedule period, the CBS Schedule message contains the Message Description IE which specifies a Message Description Type (MDT) and a Message ID.  FIG. 2  depicts the encodings of the MDT field. The New Message Bitmap IE of this CBS schedule message specifies each CTCH BS which contains a CBS Message (partly or completely) which either: was not sent during the previous schedule period; was sent unscheduled during the preceding schedule period; is the first transmission of a given BMC message in the CBS schedule period; or is a repetition of it within the CBS schedule period. The New Message Bitmap IE also specifies each CTCH BS which contains a CBS message that was transmitted in the previous schedule period. 
     For each new CBS message (MDT:1) or repetition of a new message (MDT:0), the BMC  12  adds the corresponding Message ID to the BMC_MessagesToBeReceivedList. 
     For each old CBS message (MDT:5) or repetition of an old message (MDT:4), the BMC  12  adds the corresponding Message ID to the BMC_MessagesToBeReceivedList under any of the following conditions. First, the old or repetition of old CBS message will be added to the BMC_MessagesToBeReceivedList if the Message ID is not stored in the BMC_ReceivedMessageList. Second, the old or repetition of old CBS message will be added to the BMC_MessagesToBeReceivedList if the Message ID is stored in the BMC_ReceivedMessageList, but the New Message Bitmap IE in the CBS schedule message indicates the corresponding CTCH BS Index as “new.” Third, if the Message ID is stored in the BMC_ReceivedMessageList, but also has already been added to the BMC_MessagesToBeReceivedList, it remains in the BMC_MessagesToBeReceivedList and will be received in the succeeding CBS schedule period. 
       FIG. 3  depicts a method  100  of efficiently receiving CBS messages by a BMC layer  12  in a UE. The method is repeated for each CBS schedule period, in preparation for selectively receiving CBS messages in a succeeding CBS schedule period. The CBS schedule message is received and parsed (block  110 ), based on the Message Description (MDT: 6) and New Message Bitmap extracted from a CBS schedule message received during the previous CBS schedule period. The BMC layer  12  then iteratively loops through all CBS messages scheduled for transmission in the succeeding CBS schedule period. Although  FIG. 3  depicts this processing as two separate, parallel, iterative loops to better describe the processing occurring in each, those of skill in the art will readily recognize that separate iterations may be performed sequentially, or that the BMC layer  12  may combine the loops into a single iterative processing loop. 
     As depicted in  FIG. 3 , for all new CBS messages (MDT:1) or repetitions of new CBS messages (MDT:0) (block  112 ), the corresponding Message ID is added to the BMC_MessagesToBeReceivedList (block  114 ). This process repeats until all new or repetition of new CBS messages have been processed (block  116 ). This iterative process ensures that the BMC layer  14  will, during the succeeding CBS schedule period, receive all new CBS messages, or repetitions thereof, for possibly passing to higher layers, depending on the CBS message content and the CBS message types to which the UE is subscribed. 
     As  FIG. 3  also depicts, all old CBS messages (MDT:5) or repetitions of old CBS messages (MDT:4) (block  120 ) are processed. If such a message is not already included in the BMC_ReceivedMessageList (block  122 )—that is, the UE has not previously received the same CBS message—then the corresponding Message ID is added to the BMC_MessagesToBeReceivedList (block  124 ). 
     If the message is included in the BMC_ReceivedMessageList (block  122 )—that is, the UE has previously received the this CBS message—but the New Message Bitmap IE of the CBS schedule message indicates that the corresponding CTCH BS Index is new (block  128 )—then the corresponding Message ID is also added to the BMC_MessagesToBeReceivedList (block  124 ), notwithstanding the fact that the message has been previously received. If, in the New Message Bitmap IE, a bit corresponding to the CTCH Index of an old message is set as new, this means the old message was not transmitted in the CBS schedule period prior to the current one (in which the CBS schedule message is received and processed). There is a chance that the UE could have missed this message in an earlier transmission when the message was marked with MDT:1 (indicating a new message). To ensure that no CBS message is lost, such messages which are marked in the New Message Bitmap IE are also marked for reception in the next CBS schedule period. 
     If the message is included in the BMC_ReceivedMessageList (block  122 ) (that is, the UE has previously received this CBS message), and the New Message Bitmap IE of the CBS schedule message does not indicate that the corresponding CTCH BS Index is new (block  128 )—but the corresponding Message ID is listed in the BMC_MessagesToBeReceivedList (block  128 ), then the message remains in the BMC_MessagesToBeReceivedList (block  124 ), and will be received in the succeeding CBS schedule period. This situation could occur due to multiple updates for the same message ID. For example, assume a CBS message was received in an earlier CBS schedule period (SP1), and stored in the BMC_ReceivedMessageList. Later an updated CBS message—having the same message ID—is scheduled for transmission, and the scheduling information for this transmission is included in a CBS schedule in the CBS schedule period (SP2). The MDT value is 1, indicating a new message, so the message ID is stored in the BMC_MessagesToBeReceivedList (block  114 ). Note that this updated CBS message should be received in the succeeding CBS schedule period (SP3). If, for some reason, the UE missed reception of the CBS message in SP3, then in the next schedule period (SP4), the CBS schedule message will again schedule it, marked with MDT:5 (old). Accordingly, it will be processed as old (block  120 ) and in the BMC_ReceivedMessageList (block  122 ). However, since the message ID appears in the BMC_MessagesToBeReceivedList (block  128 ), as it was never actually received, it remains in that list (block  124 ), and will be received in SP5. 
     This process repeats until all old or repetition of old CBS messages have been processed (block  130 ). This iterative process ensures that the UE will, during the succeeding CBS schedule period, receive only the old CBS messages that are required to ensure full exposure to the BMC broadcasts/multicasts, and further that the UE will not waste limited battery power receiving old or repetition of old CBS messages which it has previously received. Embodiments of the present invention achieve this result without regard to whether the network implements CR 0028 to 3GPP TS 25.324 by broadcasting Serial Numbers in the CBS schedule message. 
     CBS messages may be segmented. That is, a CBS message can be divided into multiple segments, each of which can be received in different CTCH blocks in the same schedule period. A CBS message, either wholly or partly, is received at the RLC layer  14 , which is responsible for concatenating segments of a CBS message into one complete CBS message according to the RLC layer protocol mentioned in 3GPP TS 25.322. The RLC layer  14  then sends one complete CBS message to the BMC layer  12  for further processing. Each CTCH BS index specified in the Schedule Message may correspond to either a complete or part of a CBS message. To correctly handle segmented CBS messages in the BMC_MessagesToBeReceivedList, the BMC layer  12  receives assistance from lower layers—such as the RLC layer  14  and/or PHY layer  16 —to determine the number of segments of the CBS message. For example, the BMC layer  12  may receive System Frame Numbers (SFN) from the RLC layer  14 , or a count of the number RLC PDUs allocated to one CBS message, in order to determine whether a CBS message is segmented, and to handle it properly if so. 
     When all CBS messages for the succeeding period, as determined from the Message Description IE and New Message Bitmap IE of a current-period CBS schedule message, have been processed and the BMC_MessagesToBeReceivedList is populated, the BMC layer  12  configures the PHY layer  16  to receive the CBS message in the BMC_MessagesToBeReceivedList, as well as the CBS schedule message, for the succeeding period. 
     In the succeeding CBS schedule period, upon receiving a (complete or partial) CBS message, the BMC layer  14  removes the corresponding entry, and any repetitions thereof, from the BMC_MessagesToBeReceivedList, and adds the message ID of the CBS message to the BMC_ReceivedMessageList, If the reception of the Schedule message in one or more succeeding CBS schedule periods is missed, then the BMC layer  14  ensures that all the CBS messages received previously are received once again, since BMC layer  14  does not know how many CBS messages have changed during the missed CBS schedule periods. This is ensured by copying the contents of the BMC_ReceivedMessageList to the BMC_MessagesToBeReceivedList, while processing the next Schedule Message received at the BMC layer  14 . 
     A CBS schedule message may be transmitted in any position (CTCH BS) in a CBS schedule period—at or toward the beginning, in the middle, or at or toward the end. According to one embodiment, in lieu of, or in addition to, configuring the PHY layer  16  as soon as the CBS schedule message is parsed and analysed and the BMC_MessagesToBeReceivedList is populated, the BMC layer  12  configures the PHY layer  16  for CBS message reception for the succeeding CBS schedule period at the end of, or after, the current CBS schedule period. In this embodiment, the BMC layer  12  has the updated status of all CBS messages received in the current CBS schedule period, and hence is assured of the most accurate information. This timing is depicted in  FIG. 4 .  FIG. 4  also depicts various equations used to calculate the relevant timing offsets and timing of the PHY layer configuration(s). 
       FIG. 5  depicts a UE  30  operative in embodiments of the present invention. The UE  30  includes a user interface  32  (display, touchscreen, keyboard or keypad, microphone, speaker, and the like); a processor  34 ; memory  36 ; and a radio circuitry, such as one or more transceivers  38 , antennas  40 , and the like, to effect wireless communication across an air interface to one or more base stations in a wireless communication network. The UE  30  may additionally include features such as a camera, removable memory interface, short-range communication interface (Wi-Fi, Bluetooth, and the like), wired interface (USB), and the like (not shown in  FIG. 7 ). According to embodiments of the present invention, the memory  36  is operative to store, and the processor  34  operative to execute, software  42  which when executed is operative to implement a BMC layer  12  operative to implement the methods and functions described herein 
     The processor  34  may comprise any sequential state machine operative to execute machine instructions stored as machine-readable computer programs in the memory, such as one or more hardware-implemented state machines (e.g., in discrete logic, FPGA, ASIC, etc.); programmable logic together with appropriate firmware; one or more stored-program, general-purpose processors, such as a microprocessor or Digital Signal Processor (DSP), together with appropriate software; or any combination of the above. 
     The memory  36  may comprise any non-transient machine-readable media known in the art or that may be developed, including but not limited to magnetic media (e.g., floppy disc, hard disc drive, etc.), optical media (e.g., CD-ROM, DVD-ROM, etc.), solid state media (e.g., SRAM, DRAM, DDRAM, ROM, PROM, EPROM, Flash memory, solid state disc, etc.), or the like. 
     The radio circuitry may comprise one or more transceivers  38  used to communicate with one or more network nodes via a Radio Access Network according to one or more communication protocols known in the art or that may be developed, such as IEEE 802.xx, CDMA, WCDMA, GSM, LTE, UTRAN, WiMax, or the like. The transceiver  38  implements transmitter and receiver functionality appropriate to the Radio Access Network links (e.g., frequency allocations and the like). The transmitter and receiver functions may share circuit components and/or software, or alternatively may be implemented separately. 
     Embodiments of the present invention present numerous advantages over the prior art. In particular, a UE receives all necessary and relevant CBS messages, while avoiding wasting battery power to receive unnecessary CBS messages, in networks that do not transmit CBS message Serial Number information in the CBS message. This power efficient solution is advantageous in existing uses of the BMC protocol, such as commercial services; however, it may find particular utility as the use of CBS expands for emergency services, such as the Commercial Mobile Alert System (CMAS) and Earthquake and Tsunami Warning Service (ETWS). 
     The present invention may, of course, be carried out in other ways than those specifically set forth herein without departing from essential characteristics of the invention. The present embodiments are to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.