ATIS 0700023-2015 Feasibility Study for LTE WEA Message Length.pdf

1、 ATIS-0700023 FEASIBILITY STUDY FOR LTE WEA MESSAGE LENGTH As a leading technology and solutions development organization, the Alliance for Telecommunications Industry Solutions (ATIS) brings together the top global ICT companies to advance the industrys most pressing business priorities. ATIS nearl

2、y 200 member companies are currently working to address the All-IP transition, network functions virtualization, big data analytics, cloud services, device solutions, emergency services, M2M, cyber security, network evolution, quality of service, billing support, operations, and much more. These pri

3、orities follow a fast-track development lifecycle from design and innovation through standards, specifications, requirements, business use cases, software toolkits, open source solutions, and interoperability testing. ATIS is accredited by the American National Standards Institute (ANSI). The organi

4、zation is the North American Organizational Partner for the 3rd Generation Partnership Project (3GPP), a founding Partner of the oneM2M global initiative, a member of and major U.S. contributor to the International Telecommunication Union (ITU), as well as a member of the Inter-American Telecommunic

5、ation Commission (CITEL). For more information, visit www.atis.org. Notice of Disclaimer Technical Specification Group Core Network and Terminals; Technical realization of Cell Broadcast Service (CBS).3Ref 3 3GPP TS 36.331, 3rd Generation Partnership Project; Technical Specification Group Radio Acce

6、ss Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification.3Ref 4 3GPP TS 36.413, 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 Applic

7、ation Protocol (S1AP).3Ref 5 FCC 07-214; Federal Communications Commission Notice of Proposed Rulemaking in the Matter of the Commercial Mobile Alert System; December 14th, 2007.43 Definitions, Acronyms, however, the similar emergency alerts broadcast in Canada may use UCS-2 format. For that reason,

8、 both types of character sets are considered in the analysis. 4.1 Data Format This clause illustrates the role of the data format used to carry the display characters in determining the LTE WEA message length. The 3GPP specifications TS 23.041 Ref 2, TS 36.331 Ref 3, and TS 36.413 Ref 4 describe the

9、 data format used to transmit the WEA message octets within the CMSP infrastructure and then to the mobile devices over the air. For the purpose of this analysis, the focus is on the format used to transmit the data over the air, even though, at times, the other aspects may be referenced (as needed)

10、 as well. 4.1.1 Background Within the LTE, the display characters (also known as warning message contents) are sent over the air using the Cell Broadcast Data (CB Data) format. The encoding of the display characters into this format is done at the Cell Broadcast Center (CBC) and as such the format a

11、nd the contents are transparent to other network nodes (i.e., MME and eNB) within the CMSP infrastructure. The Figure 4.1 illustrates this point. TWIctirbc3AoinboroAtohe method RITE-REPLnformation Bharacters (i.ransmits all trespective ofits). The eNharacters is aGPP TS 23.0s shown in tf CB Data. As

12、tance. Eace sent using ctets. For eaequired to idef octets that s quoted belhe CBC shalf display cha“5 - Fiused to tranACE-WARNIlock (SIB) be., CB Data he octets of whether thoB does not lbusiness be41 Ref 2 dehe Table 4.1,s shown, thh instance isthe CB Data ch CB Datantify the totacan be preseow, 3

13、GPP TSl always incluracters. CBC FunctInitiating brprovided by” gure 4.1 CBsmit the dispNG-REQUESetween the eformat) remCB Data ovese octets carook at the cotween the Cfines the CBOctets 1 82 1 82 1 82 1 the display cere can be areferred to aformat shall Page, therel number of nt within the C23.041

14、Refde all 82 octionality: oadcast by sethe cell, and wATData Formlay characteT between NB and theains the samr the air to ry the actual ntents of CBBC and the mData format Table 4.1haracters armaximum os a CB Databe accommois 1 octet uCB Data PagB Data is 122 clause 5 fets in the Pagnding fixed lehe

15、re necessaTIS-07000234 at is Transprs from one CBC and Mmobile devie end-to-enthe mobile ddisplay charaData. Withobile devicesas shown be CB Data Fe included in f 15 instancePage. So, thdated within sed to carry es present w46 (= 1 + 15urther specife Informationgth CBS mery padding theparent to MMno

16、de to anoME, and betces), but thed from CBCevices as a cters or somthis approac. low: ormat DescriptioNumber of PPage InformaPage LengtPage InformaPage Lengt Page InformatPage LengthPage Informs of Page Ine maximum 15 CB Data Pthe Page Leithin the CB *82 + 15). ies that for a n part of the ssages to

17、 a pages to a lenE and eNB ther node mween MME format useto the mobpart of warnie filler bits (ah, the forman Pages tion 1 h 1 tion 2 h 2 ion 15 15 ation n (wherformation wnumber displages or withngth, and ovData. Thus,given CB DaCB data irresBSC/RNC/eNogth of 82 octeay be differand eNB and to carry

18、 thile devices. ng message lso known at used for the n = 1 to 15ith 82 octets ay characterin the 1230 (erall, anothethe maximumta Page whenpective of thdeB for eachts (3GPP TS 2ent (e.g., d System e display The eNB contents, s padding e display ) element per each s that can = 82 * 15) r octet is num

19、ber present, e number language 3.038). ATIS-0700023 5 In other words, if the number of octets required to carry the display characters in a CB Data Page is fewer than 82, the CBC would pad remaining bits of a partial octet and the remaining octets of that CB Data Page, thus resulting in always 82 oc

20、tets of Page Information per CB Data Page. The Page Length would tell the mobile devices how many of those 82 octets carry the display characters. This rule of always including 82 octets of Page Information in a CB Data Page is also logical based on the format of the CB Data because the Page Length

21、comes after the Page Information within the CB Data for each CB Data Page. A mobile device can handle the received CB Data if and only if it knows which octet carries the Page Length, accurately. 4.1.2 Analysis The clause 4.1.1 explains that the display characters of WEA message are encoded using CB

22、 Data format. A CB Data contains a certain number of CB Data Pages with 82 octets of Page Information per CB Data Page. The Page Information carries the display characters. The CBC pads the unused bits of an octet and unused octets of a CB Data Page. The number of display characters that can be sent

23、 using the octets of CB Data depends on the character set used. For example, with GSM 7-bit character set, a CB Data Page can include a maximum of 93 display characters with 5 unused bits (and CBC pads those 5 unused bits). With UCS-2, a CBS Page can include a maximum of 41 display characters with n

24、o unused bits. Table 4.2 below illustrates the number of octets in the CB Data required to carry various number of display characters: Table 4.2 Comparison Number of CB Data Octets Vs Number of Display Characters CB Data Length Range of Display Characters (that can be sent) Number of CB Data Pages N

25、umber of Octets GSM 7-bit USC-2 CB Data For Display Minimum Maximum Minimum Maximum 1 84 82 1 93 1 412 167 164 94 186 42 82 3 250 246 187 279 83 1234 333 328 280 372 124 164 5 416 410 373 465 165 2056 499 492 466 558 206 246 7 582 574 559 651 247 2878 665 656 652 744 288 328 9 748 738 745 837 329 36

26、910 831 820 838 930 370 410 11 914 902 931 1023 411 45112 997 984 1024 1116 452 492 13 1080 1066 1117 1209 493 53314 1163 1148 1210 1302 534 574 15 1246 1230 1303 1395 575 615Table 4.2 above shows the number of display characters that can be sent over the air with each CB Data Page. Table 4.2 can al

27、so be used to determine the number of CB Data Pages required to transmit a certain number of display characters, thus allowing to determine the number of CB Data octets required to transmit a certain number of display characters. ATIS-0700023 6 For example, to transmit 280 display characters with GS

28、M 7-bit character set, 4 CB Data Pages will be required and hence, 333 octets of CB Data will be transmitted over the air. On the other hand, to transmit 280 display characters with UCS-2 character set (i.e., 16 bits per character), 7 CB Data Pages will be required and hence, 582 octets of CB Data w

29、ill be transmitted over the air. Table 4.3 and Table 4.4 illustrate how a 280 character WEA message is encoded in the CB Data format using GSM 7-bit and UCS-2 character set. Table 4.3 Number of CB Data Octets for 280 Character GSM-7 bit Display Octet Number Usage Value Padded Bits/Octets Partial Oct

30、ets Complete Octets 1 Number of pages 4 0 0 2 to 83 Page Information 1 Display characters (1 to 93) 5 bits (octet 83) 0 84 Page Length 1 82 0 0 85 to 166 Page Information 2 Display characters (94 to 186) 5 bits (octet 166) 0 167 Page Length 2 82 0 0 168 to 249 Page Information 3 Display characters (

31、187 to 279) 5 bits (octet 249) 0 250 Page Length 3 82 0 0 251 to 332 Page Information 4 Display characters (280) 1 bit (octet 251) 81 octets (252 to 332) 333 Page Length 4 1 0 0 As shown in Table 4.3, the Page Length would be 82 for the first 3 CB Data Pages and 1 for the last CB Data Page. As shown

32、 in Table 4.2, the same octets of CB Data (i.e., 333 octets) will be able to transmit 372 number of GSM 7-bit display characters. ATIS-0700023 7 Table 4.4 Number of CB Data Octets for 280 Character UCS-2 Display Octet Number Usage Value Padded Bits/Octets Partial Octets Complete Octets 1 Number of p

33、ages 4 0 0 2 to 83 Page Information 1 Display characters (1 to 41) 0 0 84 Page Length 1 82 0 0 85 to 166 Page Information 2 Display characters (42 to 82) 0 0 167 Page Length 2 82 0 0 168 to 249 Page Information 3 Display characters (83 to 123) 0 0 250 Page Length 3 82 0 0 251 to 332 Page Information

34、 4 Display characters (124 to 164) 0 0 333 Page Length 4 82 0 0 334 to 415 Page Information 5 Display characters (165 to 205) 0 0 416 Page Length 5 82 0 0 417 to 498 Page Information 6 Display characters (206 to 246) 0 0 499 Page Information 6 82 0 0 500 to 581 Page Information 7 Display characters

35、(247 to 280) 0 14 octets (567 to 581) 582 Page Length 7 68 0 0 As shown in Table 4.4, the Page Length would be 82 for the first 6 CB Data Pages and 68 for the last CB Data Page. As shown in Table 4.2, the same octets of CB Data (582 octets) will be able to transmit 287 number of UCS-2 display charac

36、ters. 4.1.3 Summary of Analysis The analysis shows that the number of CB Data Pages required to carry the display characters, and not the number of octets required to accommodate those display characters, has a role in determining the WEA message length in LTE. The number of CB Data octets transmitt

37、ed over the air can be determined using the following formula: GSM 7-bit: 1 + 83 * (ceiling (character-count/93) Formula 1 UCS-2: 1 + 83 (ceiling (character-count/41) Formula 2 For example, with GSM 7-bit character set an alert text with 280 display characters will require 333 octets of CB Data and

38、the following illustrates how it can be derived from the Formula 1. Number of octets = (1 + 83 * (ceiling (280/93) = (1 + (83 * (4) = (1 + 332) = 333. It has to be noted that same number of CB Data octets can carry 372 display characters with GSM 7-bit character set. That is because ceiling (372/93)

39、 also results in the value 4. On the other hand, an alert text with 279 display characters would require 3 CB Data Pages (because ceiling (279/93) results in the value 3) and hence, 250 octets of CB Data. ATIS-0700023 8 In the same way, Formula 2 can be used to determine CB Data octets required to c

40、arry the 280 display characters with UCS-2 format as shown below: Number of octets = (1 + 83 * (ceiling (280/41) = (1 + (83 * (7) = (1 + 581) = 582. It has to be noted that same number of CB Data octets can carry 287 display characters with UCS-2 format. That is because ceiling (287/41) also results

41、 in the value 7. 4.2 CB Data Transmission Over The Air In LTE, the WEA messages are transmitted over the air using system information block (SIB) type 12. 4.2.1 Background 4.2.1.1 Bits per SIB12 Segment The 3GPP TS 36.331 Ref 3, clause 5.2 states the following on the number of bits that can be carri

42、ed inside one segment of SIB12: “The physical layer imposes a limit to the maximum size a SIB can take. When DCI format 1C is used the maximum allowed by the physical layer is 1736 bits (217 bytes) while for format 1A the limit is 2216 bits (277 bytes), see TS 36.212 22 and TS 36.213 23.” Note that

43、the above are the maximum number of bits that a physical layer allows a SIB to have. In some situations, the physical layer may not have so-many bits available to share with SIB (for example, with the lower carrier bandwidth, the number of bits that are available for the physical layer may be smalle

44、r). In some situations, the physical layer may require more bits for its own processing and may thus be able to share only a smaller number of bits with the SIB (e.g., lower coding rate will result in a fewer number of bits available to SIB). In summary, the number of bits available for a SIB can be

45、 fewer than the above-quoted maximum value and the actual bits available vary based on the carrier bandwidth and coding rate. This analysis does not go into further details of illustrating the mapping between the bandwidth/coding rate to number of SIB bits, but rather just points out that the number

46、 of bits available can be fewer than the maximum quoted. Therefore, one cannot really determine the number of display characters that can be sent over the air based using the above mentioned maximum value. 4.2.1.2 Segmentation The 3GPP 36.331 clause 5.2.15 Ref 3 also has the following: “CMAS notific

47、ation is contained in SystemInformationBlockType12. Segmentation can be applied for the delivery of a CMAS notification. The segmentation is fixed for transmission of a given CMAS notification within a cell (i.e. the same segment size for a given segment with the same messageIdentifier, serialNumber

48、 and warningMessageSegmentNumber). E-UTRAN does not interleave transmissions of CMAS notifications, i.e. all segments of a given CMAS notification transmission are transmitted prior to those of another CMAS notification. A CMAS notification corresponds to a single CB data IE as defined according to

49、TS 23.041 37.” The above paragraph is telling that in the event a CMAS notification has more bits than the number of bits the physical layer allows SIB to have, the bits will be transmitted using segmentation. For each notification, there can be up to 64 segments. The size of a SIB segment (for a given segment, for a given event notification) always remains the same. This means that, as an example, if a WEA message is transmitted using two segments, then when those segments are repeated, they will have the same size as whe