GLOBAL NAVIGATION SATELLITE SYSTEM GLONASS INTERFACE CONTROL DOCUMENT

Transcription

1 GLOBAL NAVIGATION SATELLITE SYSTEM GLONASS INTERFACE CONTROL DOCUMENT Code Division Multiple Access Open Service Navigation Signal in L1 frequency and Edition 1.0 MOSCOW 2016

2 Tale of contents List of figures... 3 List of tales... 4 Definitions and acronyms Scope L1OC signal structure L1OC generation Structure of L1OC PRN generator Convolution encoder structure General overview of L1OCd navigation message structure Service field structure of L1OCd data General structure of L1OCd string Service fields of L1OCd string Anomalous strings of L1OCd signal CRC (250,234) CRC (125,109) of string Type CRC (375,351) of string Type Data field structure of L1OCd Data fields and types of L1OCd strings L1OCd strings Type 10, 11 and L1OCd string Type L1OCd string Type L1OCd string Type L1OCd strings Type 31 and L1OCd string Type L1OCd string Type L1OCd string Type Anomalous strings Type 1 and

3 List of figures Figure 2.1 L1OC signal structure... 9 Figure 2.2 L1OC signal generation scheme Figure 2.3 Timing relationship etween components of L1OC modulation sequence Figure 2.4 L1OCd PRN generator structure Figure 2.5 L1OCp PRN generator structure Figure 2.6 Convolution encoder structure Figure 4.1 General structure of L1OCd data string Figure 4.2 Anomalous L1OCd data string Type Figure 4.3 Anomalous L1OCd data string Type Figure 4.4 CRC (250,234) encoding scheme Figure 4.5 CRC (250,234) syndrome calculation scheme Figure 4.6 CRC (375,351) encoding scheme Figure 4.7 CRC (375,351) syndrome calculation scheme Figure 5.1 String Type 10 of L1OCd data Figure 5.2 String Type 11 of L1OCd data Figure 5.3 String Type 12 of L1OCd data Figure 5.4 String Type 20 of L1OCd data Figure 5.5 String Type 25 of L1OCd data Figure 5.6 String Type 16 of L1OCd data Figure 5.7 String Type 31 of L1OCd data Figure 5.8 String Type 32 of L1OCd data Figure 5.9 String Type 50 of L1OCd data Figure 5.10 String Type 60 of L1OCd data Figure 5.11 String Type 0 of L1OCd data

4 List of tales Tale 2.1 First and last 32 chips of L1OCd PRNs Tale 2.2 First and last 32 chips of L1OCp PRNs Tale 4.1 Parameters of L1OCd service fields Tale 4.2 CRC (250,234) in a 2-second string structure of L1OCd signal Tale 4.3 CRC (375,351) in the structure of L1OCd string Type Tale 5.1 Types of string and their content for L1OCd Tale 5.2 Parameters of data fields for strings Type 10, 11 and Tale 5.3 Ephemeris and time accuracy factors Tale 5.4 Parameters of data fields for string Type Tale 5.5 Parameters of data fields for string Type Tale 5.6 Parameters of data fields for string Type Tale 5.7 Parameters of data fields for strings Type 31 and Tale 5.8 The structure of Cospas-Sarsat notice of receipt Tale 5.9 Parameters of data fields for string Type Tale 5.10 Parameters of data fields for string Type

5 Definitions and acronyms CE Convolution Encoder CDMA Code Division Multiple Access CRC Cyclic Redundancy Check d symol in signal name, indicating attriution to a data component DC Digital Circuit f Base frequency (1.023 MHz) FDMA Frequency Division Multiple Access GLONASS Gloal Navigation Satellite System ICD Interface Control Document IS Initial State L1OC CDMA Open Service Navigation Signal in L1 frequency and L1OCd time time scale determined y phase of L1OCd signal at the phase center of an SV antenna L1OCp time time scale determined y phase of L1OCp signal at the phase center of an SV antenna L1SC CDMA Secured Service Navigation Signal in L1 frequency and L2OCp CDMA Open Service Navigation Signal in L2 frequency and (pilot signal) L2OCp time time scale determined y phase of L2OCp signal at the phase center of an SV antenna MS Meander Sequence MSD Mean Solar day MT Moscow Time OC Overlay Code p symol in signal name, indicating attriution to a pilot component PRN Pseudorandom Noise sequence (ranging code) S Sequence SC Synchronous Counter SV Space Vehicle TAI Temps Atomique International International Atomic Time TDM chip y chip Time-Division Multiplexing TS Time Stamp 5

6 UT1 Universal Time is mean solar time at 0 longitude accounted for the effect of polar motion on position of meridians UTC Coordinated Universal Time UTC(SU) Coordinated Universal Time of Russia 6

7 1 Scope 1.1 This Interface Control Document (ICD) defines the parameters etween the space segment, represented y Glonass-K2 space vehicles (SV), and the navigation user equipment (UE) of GLONASS for L1 Code Division Multiple Access (CDMA) navigation. Information common to all GLONASS CDMA signals is given in the document GLONASS. Interface Control Document. General Description of Code Division Multiple Access Signal System (hereinafter General Description ICD) which consists of the following sections: - purpose, composition and concept of GLONASS-ased positioning; - time scales used in GLONASS; - GLONASS geodetic reference; - general characteristics of GLONASS signals; - monitoring GLONASS signal-in-space; - recommendations and algorithms for processing of data transmitted in GLONASS signals. 1.2 Russian Rocket and Space Engineering and Information Systems Corporation, Joint Stock Company () the designer of the GLONASS mission payload is assigned as the developer of ICD and is responsile for its drafting, coordination, revision and maintenance. The current Document comes into force provided that it is signed y the following persons/entities: - GLONASS Chief Designer; - Russian Rocket and Space Engineering and Information Systems Corporation, Joint Stock Company () of ROSCOSMOS State Space Corporation which is the leading organization on the GLONASS payload, service radiofrequency and telemetry systems, ground control and command facilities, and a set of user equipment for different user groups; - Academician M.F. Reshetnev Information Satellite Systems (ISS, JSC) of ROSCOSMOS State Space Corporation prime for development and integration of GLONASS satellites, including system integration of space, launch, and ground control complexes, on-oard mission software used to generate navigation message and SV control data; 7

8 - Research and Development Center (Korolev) of the Central Research Institute of the Russian Federation Space Forces leading research and development organization of the Russian Ministry of Defense on the GLONASS system; - Russian Institute of Radionavigation and Time (RIRT, OJSC) of Ministry of Industry and Trade of Russian Federation responsile for developing timing facilities of special and dual use, facilities for generating space segment system time; synchronization of GLONASS timing facilities and developing user equipment for different user groups; - Central Research Institute of Machine Building, Federal State Unitary Enterprise (TSNIIMASH, FSUE) the head research institute of the ROSCOSMOS State Space Corporation. ICD is approved y authorized representatives of ROSCOMOS State Space Corporation and Space Forces. ICD comes into force on approval y the Commanding General of the Space Forces and the Director General of the ROSCOSMOS State Space Corporation. In the course of GLONASS system evolution, its individual parameters may change. The developer of ICD ears responsiility for coordination of the suggested modifications with all responsile parties and, if necessary, for drafting new edition of the Document containing such modifications. Modifications and new editions of ICD come into force on approval y the Commanding General of the Space Forces and the Director General of the ROSCOSMOS State Space Corporation. The is responsile for official distriution of GLONASS ICD. 8

9 2 L1OC signal structure 2.1 L1OC generation General scheme of L1OC signal generation L1OC signal is transmitted on carrier frequency (nominal value) f L f MHz MHz and consists of two components of the same power: L1OCd (data component) and L1OCp (pilot component). These components are otained y chip y chip time-division multiplexing (TDM) of two pseudorandom noise sequences (PRNs). L1OC signal is in phase quadrature with L1SC signal, which is delayed y 90º (Figure 2.1). Q L1OCd L1OCp Сhip y chip time-division multiplexing (TDM) L1SC I Figure 2.1 L1OC signal structure Figure 2.2 shows L1OC signal generation scheme. 9

10 f T2 = MHz f T1 = MHz MHz 1 s Data L1OCd SC 125 ps L1OC modulation sequence generator СE 2 ms 4 ms 8 ms 250 sps f T2 4 ms 8 ms 1 s L1SC modulation sequence generator OC1 2 ms 1 s Quadrature modulator I L1SC Σ +90º Q L1OC cos(2π f L1 t) L1 2 ms PRN L1OCd PRN L1OCd S L1OCd f T1 /2 generator f T1 /2 8 ms f T1 /2 PRN L1OCp generator PRN L1OCp f T1 /2 S L1OCp TDM S L1OC 1 s MS 2 f T1 Figure 2.2 L1OC signal generation scheme L1OCd signal generation Modulation sequence of symols of L1OCd signal (S L1OCd ) is the modulo-2 sum of PRN L1OCd chip stream clocked at f T1 /2 = MHz (see 2.2.1), overlay code (OC1) symol stream clocked at 500 sps, and convolution encoder (CE) symol stream clocked at 250 sps (see 2.3) as shown in Figure 2.2. OC1 is a periodic 2-symol code 01 synchronized with CE symols (Т CE = 8 ms) and transmitted with the most significant its first (the first symol of OC1 for a CE symol duration is 0) L1OCp signal generation Modulation sequence of symols for L1OCp signal (S L1OCp ) is the modulo-2 sum of PRN L1OCp chip stream clocked at f T1 /2 = MHz (see 2.2.2) and meander sequence (MS) clocked at 2 f T1 = MHz as shown in Figure

11 MS is a 0101 periodic sequence, synchronized with PRN L1OCp chips and transmitted with most significant its ahead (the first symol of MS for a PRN L1OCp chip duration is 0). MS is intended to form BOC(1,1) spectrum for L1OCp component L1OCd and L1OCp multiplexing The modulation sequence of symols for L1OC signal (S L1OC ) is formed at the TDM output. Figure 2.3 shows the TDM principle of operation. It also shows the second mark position corresponding to PRN chips end/start. The second mark also corresponds to PRN periods end/start. Second mark S L1OCd PRN L1OCp d1 2/f T1 2 μs d2 t p1 p2 S L1OCp 1/(2 f T1 ) 0.5 μs t p1 p1 p1 p1 p2 p2 p2 p2 t S L1OC 1/f T1 1 μs d1 p1 p1 d2 p2 p2 t Figure 2.3 Timing relationship etween components of L1OC modulation sequence 180. Sequence S L1OC is used to phase-shift key Q-component of carrier frequency in L1 y 11

12 2.2 Structure of L1OC PRN generator L1OCd PRN generator Figure 2.4 shows the structure of L1OCd PRN generator DC1 f T1 /2 = = MHz IS1 = PRN L1OCd DC2 2 ms IS2 = * * = SV ID numer IS2 = Figure 2.4 L1OCd PRN generator structure Zero SV ID numer is the reserved one, which can only e enaled upon termination of GLONASS CDMA and FDMA signals comined use. L1OCd PRNs are Gold sequences of length N = 1023 and period T = 2 ms. These sequences are generated y the modulo-2 addition of inary digits (1 and 0) incoming at clock rate f T1 / MHz from digital circuits DC1 and DC2 shown in Figure 2.4. The shift register of DC1 has 10 triggers and feedack from triggers numer 7 and 10. The shift register of DC2 has 10 triggers and feedack from triggers numer 3, 7, 9, and 10. The shift direction in all registers is from lower to higher trigger numer. The following initial state (IS) codes are set into DC registers at 2 ms intervals: - IS1 = into DC1; - IS2 = = , into DC2, where is an SV ID numer. 12

13 IS1 and IS2 (inary numers) are registered into DC1 and DC2 in such a way that the least significant it enters the last trigger of register. Short pulses at 2 ms intervals, marking moments of IS codes registering to DCs, are formed in synchronous counter (SC) shown on Figure 2.2 ased on MHz signal and 1 s pulses. Tale 2.1 shows first and last 32 chips of L1OCd PRNs in HEX. For example, 13228DB8 means The record of sequences means that the left-most chip is generated first. Tale 2.1 First and last 32 chips of L1OCd PRNs IS2 (Figure 2.4) First 32 chips PRN L1OCd Last 32 chips IS2 (Figure 2.4) First 32 chips PRN L1OCd Last 32 chips DB E D5 D330E DA8E B31D F74E3 F32BBF55 030BED95 832F D43F8 C319884E 2310BAA3 A CE E302DF78 1B363DAE 9B12F618 5B0093C3 DB B2D6A98 BB09A12E 7B1BC4F5 FB3F0F43 0B1F5D83 8B3B9635 4B29F3EE CB0D3858 2B040AB5 AB20C103 6B32A4D8 EB166F6E D51F792C 0E8093A7 634F66E2 B8D08C69 8E3776CB 55A89C E3F8838E A B7EDF 15448B9A CEDB6111 F83C9BB3 23A E6C847D 95F36EF6 EE1A8F B 584A905E 83D57AD5 B EAD6AFC 03629FB9 D8FD E8 438E8863 2E417D26 F5DE97AD C3396D0F 18A C1 AEF6984A D5B3 970C1E05 571E7BDE D73AB B CE8 F721E75E 0701B59E 87257E BF3 C713D AE2A8 A73E291E 672C4CC5 E F3C65A5 9F18AE13 5F0ACBC8 DF2E007E 3F BF03F925 7F119CFE FF F F31CE3E 4F23ABE5 CF F0E52BE AF2A9908 6F38FCD3 EF1C3765 C89D F9 7ECD9DBC A B58D95 482A671E 25E5925B FE7A78D0 BE966F0A C670C4 D3599A4F E5BE60ED 3E218A66 53EE7F A8 F39874CE 28079E45 45C86B00 9E57818B A8B07B29 732F91A2 1EE064E7 C57F8E6C B6 5E0C733D 33C38678 E85C6CF3 DEBB CDA 68EB899F B

14 2.2.2 L1OCp PRN generator Figure 2.5 shows the structure of L1OCp PRN generator DC1 f T1 /2 = = MHz IS1 = PRN L1OCp DC2 8 ms IS2 = * * = SV ID numer IS2 = Figure 2.5 L1OCp PRN generator structure Zero SV ID numer is the reserved one, which can only e enaled upon termination of GLONASS CDMA and FDMA signals comined use. L1OCp PRNs are truncated Kasami sequences. Their length is N = 4092 and the period is T = 8 ms. These sequences are generated y the modulo-2 addition of inary symols (1 and 0) incoming at clock rate f T1 / MHz from DC1 and DC2 in accordance with Figure 2.5. Shift register in DC1 has 12 triggers and feedack from triggers numer 6, 8, 11 and 12. Shift register in DC2 has 6 triggers and feedack from triggers numer 1 and 6. The shift direction in all registers is from lower to higher trigger numer. The following initial state codes are set into DC registers at 8 ms intervals: - IS1 = into DC1; - IS2 = = , into DC2, where is an SV ID numer. IS1 and IS2 (inary numers) are recorded into in DC1 and DC2 in such a way that the least significant it enters the last trigger of register. Short pulses at 8 ms intervals marking moments of IS codes registering to DCs are formed in synchronous counter (SC) shown in Figure 2.2 ased on MHz signal and 1 s pulses. 14

15 Tale 2.2 shows first and last 32 chips of L1OCp PRNs in HEX. For example, A301543B means The record of sequences means that the left-most chip is generated first. Tale 2.2 First and last 32 chips of L1OCp PRNs IS2 (Fig. 2.5) First 32 chips PRN L1OCp Last 32 chips IS2 (Fig. 2.5) First 32 chips PRN L1OCp Last 32 chips A301543B 20F432D6 E2FBE74D 610E81A0 83FC0D B6D C206BEF6 41F3D81B B37FF8E6 308A9E0B F2854B D7D 9382A15D 1077C7B0 D278122B 518D74C6 AB3E CB64B8 EAC4B D7CE 8BC35BEE 08363D03 CA39E898 49CC8E75 BB40AE88 38B5C865 FABA1DFE 794F7B13 9BBDF DE DA B222A8 DA55EDB FE B36D511B 611C285D 6EC9B3E9 BCB8CAAF 07F10F4A D580760C 001BC290 D26ABBD E33 BB B4879CC1 66F6E587 DDBF2062 0FCE FA2C E503836A 5E4A468F 8C3B3FC9 83EEA47D 519FDD3B EAD618DE 38A76198 ED3CD504 3F4DAC A E1 59A08B55 8BD1F F6 E2E94EB A4EB99E1 271EFF0C E5112A97 66E44C7A 8416C05A 07E3A6B7 C5EC732C C1 B495353C D1 F56F864A 769AE0A C87 179D0A6A D592DFF1 5667B91C ACD4CF8F 2F21A962 ED2E7CF9 6EDB1A14 8C FDCF0D9 CDD E2643AF BCAA6352 3F5F05BF FD50D024 7EA5B6C9 9C573AE9 1FA25C04 DDAD899F 5E58EF72 7EB71F34 ACC FA397 C5FEDAD1 CA2B A3823 A313FDC A4F9301C A CDC18CBF 1FB0F5F E4D C214170B 795DD2EE AB2CABA A0 41E171E6 FAA8B403 28D9CD45 270C56F1 F57D2FB7 4E34EA52 9C DE2788 9BAF5ECE 20E69B2B F297E26D FD4279D9 2F33009F 947AC57A 460BBC3C 15

16 2.3 Convolution encoder structure The 125 ps data stream of L1OCd signal is encoded y a rate 1/2 convolution encoder (133,171) shown in Figure 2.6. The switch of the encoder is set to position 1 (lower position) for the first half of a 8-millisecond data it period. Data f T3 f T3 = 125 Hz 2 f T3 Figure 2.6 Convolution encoder structure 16

17 3 General overview of L1OCd navigation message structure The following definitions are used to descrie data structure of navigation messages: it inary symol of data; string sequence of inary symol its of specific length; string field aggregate of string its containing a specific parameter or zeros; service fields of a string fields that contain service data. The semantic scope of these fields is the same for all strings of this signal; data fields of a string fields that contain data which semantic scope is different for different strings of this signal; reserved fields of a string fields which semantic scope and value are not descried in ICD. UE shall ignore these fields. Navigation message of L1OCd signal is transmitted as a continuous sequence of strings of non-fixed and non-predetermined structure. Navigation message of L1OCd signal is transmitted at 125 ps. Navigation message consists of 250-it strings of 2-second duration, as well as of 125- and 275-it anomalous strings of 1- and 3-second duration, respectively. 17

18 4 Service field structure of L1OCd data 4.1 General structure of L1OCd string Bit sequence in a string Figure 4.1 shows general structure of a string of L1OCd signal. The string is 250 its long and of 2 seconds duration. The string consists of fields separate its or groups of its containing specific parameters Preamle Type P1 TS H l P2 KP А CRC 16 Figure 4.1 General structure of L1OCd data string 18

19 Figure 4.1 shows string it numeration, field designation and the numer of its in each field. According to this it numeration, transmission of a string starts with it 1 (the first it of Preamle field) and ends with it 250 (last it of a cyclic redundancy check (CRC) field) Types of fields Each string contains two types of fields: service and data. These fields are defined in accordance with Section 3. Figure 4.1 shows service fields, locations of data fields are shaded. Shaded fields in figures depicting strings of specific type (Figure 5.1, for example) are reserved fields, which shall e ignored y UE Rule for recording digits in fields In the words which numerical values may e positive or negative, the most significant it is the sign it. Symol "0" corresponds to "+" and symol "1" corresponds to "-". The most significant it is registered in the it field which is transmitted first. For example, if = (SV ID numer, see ), then it numer 24 of a string (Figure 4.1) is registered as "1" and its numer 19 to 23 are registered as "0". 19

20 4.2 Service fields of L1OCd string List of L1OCd service fields Each L1OCd string contains service fields of permanent set and position, namely repeated in each string. Tale 4.1 shows the list and parameters of service fields (also see Figure 4.1). Tale 4.1 Parameters of L1OCd service fields Field Numer of its Least significant it Value range Preamle Type H 1 1 0, 1 - l 1 1 0, 1 - P1 4 see P2 1 see KP , 01, 10, 11 - A 1 1 0, 1 - TS s CRC 16 1 see Unit Semantic scope of L1OCd service fields Field Preamle contains the constant value: Preamle = When passing through convolution encoder (133,171) descried in Figure 2.3 the first six its of the sequence ensure its specific initial state. This initial state when comined with the last six it generates the constant 12-symol synchronizing sequence at the output of convolution encoder (133,171) Field Type is a type of a current string. It determines the data (set and position of string data fields) transmitted in the string that contains this field. For example, if current string is of Type 1, then Type =

21 Field is the ID numer of the SV that transmits this navigation message. Semantic scope of field is constant for strings of any type except for those containing almanac. In strings containing almanac, field is denoted А and means the ID numer of the SV, to which almanac data elongs. Zero SV ID numer is the reserved one, which can only e enaled upon termination of of GLONASS CDMA and FDMA signals comined use Field the SV ID numer. H is the attriute of healthy ("0") or non-healthy ("1") navigation signal of Field l is the attriute of validity ("0") or non-validity ("1") of data in the current string of the SV ID numer Field P1 denotes SV call to ground control. This field is not used y a user Field P2 denotes regime of SV orientation: P2 = 0 for the duration of a current string in L1OCd time, SV is Sun-pointing; P2 = 1 for the duration of a current string in L1OCd time, SV either performs noon/midnight turn maneuver or transits from Sun-pointing to noon/midnight turn maneuver or vice versa Field KP is the indication of the expected UTC(SU) correction y plus or minus 1 s at the end of current quarter in GMT (at 3:00 in MT). UTC(SU) corrections shall result in the corresponding corrections of L1OCd time: KP = 00 no correction planned; KP = 01 day length is increased y 1 s in L1OCd time; KP = 10 correction decision is pending; KP = 11 day length is reduced y 1 s in L1OCd time Field A is the indication of correction L1OCd time y plus or minus 1 s at the end of the next string: A = 0 no correction is planned; A = 1 correction is planned. Comination of A = 1 and KP = 11 in the current string denotes that the next string will e an anomalous string Type 1 which is 1 s shorter and of 1 s duration. If the current string shows the comination of A = 1 and KP = 01, then the next string will e anomalous string Type 2 which is 1 s longer and of 3 s duration (also see Appendix E in General Description ICD). 21

22 Field TS is time stamp, i.e. L1OCd time at the start of a current string. TS is expressed in 2-second intervals within a current day (in L1OCd time). TS = 0 for the first 2-second interval within a day Field CRC is cyclic redundancy check its. CRC field is formed as descried in Anomalous strings of L1OCd signal L1OCd anomalous strings are longer or shorter than 2 s. Strings of Types 1 and 2 are anomalous Figure 4.2 shows L1OCd string of Type 1. This string is used for leap second corrections of L1OCd time when a day length is reduced y 1 s. The string has non-standard duration of 1 s and contains 125 its Preamle Type P1 TS H l P2 KP А CRC 16 Figure 4.2 Anomalous L1OCd data string Type 1 Service fields are transmitted in the string (see 4.2), the only difference is that CRC field is generated using CRC encoding scheme, as descried in 4.5 (also see also Appendix E of the General Description ICD). 22

23 4.3.3 Figure 4.3 shows L1OCd string of Type 2. This string is used to denote leap second corrections of L3OC time when a day length is increased y 1 s. The string has a nonstandard duration of 3 s and contains 375 its. Service fields are also transmitted in the string (see 4.2), the only difference is that CRC field contains 24 its and is generated using CRC encoding scheme descried in 4.6 (also see Appendix E in the General Description ICD). 23

24 Preamle Type P1 TS H l P2 KP А CRC 24 Figure 4.3 Anomalous L1OCd data string Type 2 24

25 4.4 CRC (250,234) CRC (250,234) is used in L1OCd signal for filling CRC field in 2-second strings of navigation message. The location of the CRC field in a string is given in Tale 4.2. The string contains 250 its, where 16 its are allocated for check its of CRC code, 12 its for Preamle, and 22 its for data. String transmission starts from Preamle field. Tale 4.2 CRC (250,234) in a 2-second string structure of L1OCd signal Preamle Data CRC Data its Check its CRC (250,234) generator polynomial is as follows: g(x) X X X X X X X X X X. CRC field is filled y using CRC encoding scheme shown on Figure it data lock is delivered to the input of encoder (starting from 1 st it of Preamle and ending with 222 nd it of data). 250-it code lock is generated at the output of encoder y adding 16 check its. 2 logical zero input data lock (234 its) Figure 4.4 CRC (250,234) encoding scheme 2 1 output code lock (250 its) Figure 4.4: The following steps descrie the encoding procedure using the device shown in 1) Initial state of the 16-it shift register is zeros. 25

26 2) During first 234 shifts oth keys are set to position 1, data lock is directly transmitted to the output of the encoder, the register feedack is closed, and the register state is eing updated. 3) After transmitting the last 234 th data it, oth keys are set to position 2, the register feedack is opened, and during next 16 shifts the register state is eing replaced y zeros, check its are eing transmitted to the output of the encoder. Error detection in a string is performed y analyzing the syndrome, which is calculated for each string of data y using the scheme shown in Figure logical zero 1 1 received lock (250 its) syndrome (16 its) Figure 4.5 CRC (250,234) syndrome calculation scheme The following steps descrie the procedure of error detection in a received lock (a string, starting from the 1 st it of Preamle and ending with the 16 th it of CRC field) using the device shown on Figure 4.5: 1) Initial state of the 16-it shift register is some its (ones and zeros). 2) During first 16 shifts oth keys are set to position 2, the received lock (first 16 its) is eing downloaded to the register. 3) After downloading the 16 th it of the received lock, keys are set to position 1, the received lock (the remaining 234 its) keeps eing downloaded to the register. Syndrome is the name of the state of the register at the instant when the last 250 th it of the received lock is downloaded to trigger 1. 4) After downloading the 250 th it of the received lock to the register, oth keys are set to position 2 for the next 16 shifts in order to enale extraction of the syndrome from the register (and simultaneous downloading of first 16 its of the next string to the register). Zeros in all 16 its of the syndrome indicate asence of errors. Otherwise it shall e decided that the received lock (string) contains errors. 26

27 4.5 CRC (125,109) of string Type 1 CRC (125,109) is used in L1OCd signal to fill in CRC field in strings Type 1. It is generated similarly to code (250,234) through the scheme shown in Figure 4.4 except for the numer of its delivered to the input (109 instead of 234). Error detection is realized through the scheme shown in Figure 4.5 except for the numer of its transmitted to the input (250 instead of 125). 4.6 CRC (375,351) of string Type 2 CRC (375,351) is used in L1OCd signal to fill in CRC field in strings Type 2. Tale 4.3 shows the CRC field location. The string contains 375 its, where 24 its are allocated for check its of CRC code; 12 its for Preamle, and 339 its for data. String transfer starts from Preamle field. Tale 4.3 CRC (375,351) in the structure of L1OCd string Type 2 Preamle Data CRC Data its Check its CRC (375,351) generator polynomial has the following form: g(x) 1 X X 3 X 4 X 5 X 6 X 7 X 10 X 11 X 14 X 17 X 18 X 23 X 24 CRC field is filled y using CRC encoding scheme shown on Figure it data lock is delivered to the input of encoder (starting from 1 st it of Preamle and ending with 339 th it of data). 375-it code lock is generated at the output of encoder y adding 16 check its. 27

28 2 logical zero input data lock (351 its) Figure 4.6 CRC (375,351) encoding scheme output code lock (375 its) The following steps descrie the encoding procedure using the device shown in Figure 4.6: 1) Initial state of the 24-it shift register is zeros. 2) During first 351 shifts oth keys are set to position 1, data lock is eing directly transmitted to the output of encoder, the register feedack is closed, and the register state is eing updated. 3) After transmitting the last 251 st data it, oth keys are set to position 2, the register feedack is opened, and during next 24 shifts the register state is eing replaced y zeros, check its are eing transmitted to the output of the encoder. Error detection in a string is performed y analyzing the syndrome, which is calculated for each string of data y using the scheme shown in Figure logical zero received lock (375 its) Figure 4.7 CRC (375,351) syndrome calculation scheme 24 2 syndrome (24 its) The following steps descrie the procedure of error detection in the received lock (a string, starting from the 1 st it of Preamle and ending with the 24 th it of CRC field) using the device shown in Figure 4.7: 1) Initial state of the 24-it shift register is some its (ones and zeros). 28

29 2) During first 24 shifts oth keys are set to position 2, the received lock (first 24 its) is eing downloaded to the register. 3) After downloading the 24 th it of the received lock, keys are set to position 1, the received lock (the remaining 351 its) keeps eing downloaded to the register. Syndrome is the name of the state of the register at the instant when the last 275 th it of the received lock is downloaded to trigger 1. 4) After downloading the 375 th it of the received lock to the register, oth keys are set to position 2 for the next 24 shifts in order to enale extraction of the syndrome from the register (and simultaneous downloading of first 24 its of the next string to the register). Zeros in all 24 its of the syndrome indicate asence of errors. Otherwise it shall e decided that the received lock (string) contains errors. 29

30 5 Data field structure of L1OCd 5.1 Data fields and types of L1OCd strings Content of data fields depends on a string type indicated in service field Type (see ). Data fields are occupied y its numered: in all strings except Type 1 and 2 (see Figure 4.1); in strings Type 1 (see Figure 4.2); in strings Type 2 (see Figure 4.3). Tale 5.1 enlists string Types used in L1OCd signal. Susequently in case of navigation message update necessity, new types of strings with updated data or new types of data will e introduced. Tale 5.1 Types of string and their content for L1OCd String type 10, 11, 12 Immediate data 20 Almanac Content 25 Earth rotation parameters, ionospheric model parameters, UTC(SU) and International atomic time (TAI) offset model parameters. 16 SV attitude parameters during noon/midnight turn maneuver 31, 32 Long-term dynamic model parameters (LDMP) 50 Cospas-Sarsat notices of receipt 60 Text messages 0 For technological tasks. Ignored y a user 1 2 Anomalous string which is used for leap second correction purpose in case a day length is reduced y 1 s Anomalous string which is used for leap second correction purpose in case a day is increased y 1 s Note: Strings Type 10, 11 and 12 compose a data package, so string Type 11 always follows string Type 10, and string Type 12 follows string Type

31 5.2 L1OCd strings Type 10, 11 and Structure of strings Type 10, 11 and 12 Figures show the structure of strings Type 10, 11 and 12. String Type 11 always follows string Type 10, and string Type 12 always follows string Type 11. These strings transmit immediate data N 4 5 Preamle Type P1 TS N T M 3 РS 6 H 11 l P2 t 10 KP А E E E T R E R T F E 2 5 F T 5 ( t ) ( t ) ( t ) τ c (t ) c ( t ) 13 CRC 16 Figure 5.1 String Type 10 of L1OCd data 31

32 Preamle 12 Type x (t ) H 11 l P1 TS P2 KP А y (t 40 ) z (t 40 ) x (t 35 ) x pc 13 у pc 13 3 CRC 16 Figure 5.2 String Type 11 of L1OCd data 32

33 Preamle Type P1 TS z pс H 11 l P2 y (t 35 KP А ) z (t 35 ) x (t 15 ) y (t 15 ) z (t 15 ) L GPS ( t ) 30 Figure 5.3 String Type 12 of L1OCd data 8 CRC 16 Parameter of data fields of strings Type 10, 11 and 12 are given in Tale 5.2. Horizontal doule lines divide the fields that refer to different strings. 33

34 Tale 5.2 Parameters of data fields for strings Type 10, 11 and 12 Field Numer of its Least significant it Value range N year interval Unit N T hours M 3 1 see PS t s E, E hours E E T R, R 2 1 see F E, T F Т 5 1 see t ) ( t ) ( t ) ( s 2 3 0, c ( t ) s t ) c ( 2 11 s x (t ), y (t ), z (t ) km x (t ) km/s x pc, у 10 pc 13 2 ±4 m Reserved 3 z 10 pc 13 2 ±4 m y (t ), z (t ) km/s x (t ), y (t ), z (t ) L2 18 t ) GPS ( s s Reserved 8 2 km / s Note: Field c ( t ) has 256 range in case of future cancellation of GLONASS time correction y 1 s. 34

35 5.2.2 Semantic scope of fields for strings Type 10, 11 and Preamle, Type,, H, l, P1, P2, KP, A, TS, CRC are service fields (see 4.2) Field N 4 is the numer of the four-year interval in Moscow time (MT) that includes MT day containing the instant t (hereinafter ephemeris N 4 ). At the oundary of a four-year interval the value of ephemeris N 4 may differ from the numer cur N 4 of a current fouryear interval in MT (see Appendix F of General Description ICD). The first year of the first current four-year interval corresponds to 1996, namely cur N 4 = 1 on interval (MT) Field N T is the numer of the day in MT within ephemeris N 4 that contains the instant t (hereinafter ephemeris differ from numer N T ). At the day s oundaries the value of ephemeris N T may cur N T of a current day in MT (see Appendix G of General Description ICD). January 1 in MT of each leap year corresponds to cur N T = 1. January 1, 2100 that according to Gregorian calendar is not a leap year also corresponds to cur N 4 and cur N T = 1. Appendix K of General Description ICD descries the algorithm for transformation of cur N T values to Gregorian calendar date and Greenwich Mean Sidereal Time (GMST) Field current navigation message): M denotes a modification of an SV ID numer (which transmits the M = 000 Glonass-M with L3 navigation payload transmit L3 CDMA signals; M = 001 Glonass-K1 transmitting L3 CMDA signals; M = 011 Glonass-K1 transmitting L2 and L3 CDMA signals; M = 010 Glonass-K2 transmitting L1, L2, and L3 CDMA signals. In the course of GLONASS modernization SV with new modifications from 100 to 111 may e introduced in the orital constellation. Introduction of such SVs in the constellation shall not result in disruption of UE manufactured earlier Field PS is pseudoframe size. This field is defined as a numer of strings to e transmitted starting from the current string Type 10 to the next string Type 10. For example, PS=5 means that the current string Type 10 will e first followed y four strings of different types and then y a string Type 10. PS = 0 means that no data on pseudoframe size is transmitted. 35

36 Field t is the instant in MT to which immediate data (ephemeris and clock data) relates. t is expressed y 90-second intervals during current day that instant is referred to as the instant t (timescale MT is implied). N T in MT. In this document Any change of immediate data is accompanied y a compulsory change of t field. In case data is updated every 30 minutes, the first and the last instant t are 15 minutes apart from the oundary of a day. The data can e updated every 90 seconds upon necessity. In this case t ecomes multiple of 90 s Fields E E, E T denote an age of ephemeris and clock data, respectively, of an SV ID numer (which transmits this navigation message) expressed in the numer of six-hour intervals elapsed either etween ephemeris and clock data receipt and the instant t for the relay regime or etween initial data receipt and the instant (propagation) regime. respectively: Fields R E, R E,Т = 01 relay; R E,Т = 10 prediction (propagation); t for the ephemeris prediction R T denote regime for generation of ephemeris and clock data, R E,Т = 11 use of intersatellite measurements. This data is used y GLONASS Telemetry, Command and Control facilities Fields F E, F Т denote accuracy factors dependent on ephemeris and clock errors, respectively. These fields contain equivalent pseudorange errors (σ) to SV ID numer at the instant t. Tale 5.3 shows values of F E and F Т (in decimals) and their corresponding errors σ. Tale 5.3 Ephemeris and time accuracy factors F, F E Т σ, m F, F E Т σ, m F, F E Т σ, m not defined 36

37 factors. Appendix P of General Description ICD provides recommendations on F E, F Т accuracy Field t ) denotes a correction to L1OCd time of the SV ID numer ( (transmitting current navigation message) for transformation to GLONASS time at the instant t. The relations of field t ) to L1OCd time ( T L1OCd instant t are as follows: ( ) and GLONASS time ( T GL ) at the T GL (t ) T (t ) (t ). L1OCd Field t ) denotes relative deviation of carrier frequency t ( numer from the nominal carrier frequency f c at the instant t : f of SV ID f C (t ). f C t f Field t ) is a half rate of relative deviation ( t )) of carrier frequency ( f t of nominal carrier frequency С t ) shall e defined as follows: ( f of SV ID numer at the instant t. The value in field ( 1 2 d (t) dt (t ). instan t t Appendix D of General Description ICD descries the transformation from time of incoming signal to GLONASS time Field t ) denotes a correction for transformation from GLONASS time to c ( MT at the instant t. Field c ( t ) relates to GLONASS time ( T GL follows: ) and MT at the instant t as T MT (t ) T (t ) (t ). GL с 37

38 Field c ( t ) denotes rate of correction c ( t ) at the instant t. The value in field t ) is defined as follows: c ( d (t) s c (t ). dt instan t t to MT. Appendix D of General Description ICD descries transformation from GLONASS time Fields x (t ), y (t ), z (t ) denote the coordinates of the center of mass of the SV ID numer at the instant t in the orthogonal geocentric Greenwich coordinate system employed in GLONASS. Fields x (t ), y (t ), z (t ) (coordinates) calculated ased on precise dynamic model. contain precise ephemerides Field x (t ), y (t ), z (t ) denote velocity vectors of the SV ID numer center of mass at the instant t in the orthogonal geocentric Greenwich coordinate system employed in GLONASS. Fields x (t ), y (t ), z (t ) contain the coordinated ephemerides (velocities) which are calculated ased on precise ephemerides in the manner which allows minimizing methodological errors of ephemeris prediction using the simplified dynamic model inherent to many receivers Field x (t ), y (t ), z (t ) denote vector components of perturing odies induced accelerations of the SV ID numer center of mass at the instant t in the orthogonal geocentric Greenwich coordinate system accepted for GLONASS. Fields x (t ), y (t ), z (t ) contain the coordinated ephemerides (accelerations) which were calculated ased on precise ephemerides in the manner which allows minimizing methodological errors of ephemeris prediction using the simplified dynamic model inherent to many receivers. Algorithms for calculation of coordinates and velocity vector components for the SV s center of mass ased on ephemeris data is descried in Appendix J of General Description ICD Fields x pc, у pc, z pc denote coordinates of the antenna phase center transmitting L1OC signal in the coordinate system which axes are parallel to an SV-fixed reference system and its origin is referenced to the SV s center of mass. Description of the SVfixed reference system is provided in Appendix R of General Description ICD. This Appendix 38

39 also contains algorithm for transformation SV s center of mass coordinates to coordinates (in PZ-90) of its antenna phase center. ( T L1OCd ): Field L2 denotes offset of L2OCp time ( T L2OCp ) relative to L1OCd time T T. L2 L2OCp L1OCd Parameter L2 is necessary for transformation from L2OCp time to L1OCd time and then to GLONASS time Field t ) is a fractional part of a second in the offset of the GPS time ( N А ) GPS ( relative to GLONASS time ( T GL ) at the instant t : t ) T T T, GPS ( GPS GL where T is an integer offset expressed in integer seconds and calculated y a user ased on the received GPS navigation messages. Transformation from GLONASS time to GPS time is descried in Appendix C of General Description ICD. 39

40 5.3 L1OCd string Type Structure of string Type 20 Figure 5.4 shows the structure of string Type 20. Strings of this type are used for transmission of almanac data for one SV А transmitting one or several CDMA signals Preamle Type P1 TS 12 А H l P2 KP А N S 6 E А 6 N А SR А М А τ А 14 ТО λ А t A Δi А ε А 15 ω А ΔТ А T A 7 23 CRC 16 Figure 5.4 String Type 20 of L1OCd data Tale 5.4 provides parameters of data fields for string Type

41 Tale 5.4 Parameters of data fields for string Type 20 Field Numer of its Least significant it Value range А TO 2 1 see N S Unit E A hours N А hours SR А 5 1 see M А 3 1 see A А s half-cycle t 5 21 A s i 20 A half-cycle 20 A A half-cycle T 9 A s T 14 A s/orit Reserved Semantic scope of fields for String Type 20 transmitted Preamle, Type,, H, l, P1, P2, KP, A, TS, CRC are service fields (see 4.2) Field А is a numer of the SV for which almanac data in the current string is TO field orit type. Content and structure of data fields for string Type 20 depend on the value in the Field TO. TO = 00 corresponds to the circular orit of km (current GLONASS orit). This document summarizes data fields for string Type 20 only for TO = Field N S denotes the numer of SVs in the orital constellation transmitting one or several CDMA signals for which almanac is roadcast. 41

42 Field E A denotes age of SV s almanac from the time almanac parameters (ephemeris and clock data) were uploaded to an SV till the date numered N А (see ) Field N А is a calendar numer of days in MT within a four-year interval to which almanac relates. January 1 of a leap year corresponds to not a leap year in the Gregorian calendar also corresponds to N А = 1. January 1, 2100 which is N А = Field SR A denotes status register of L1, L2 and L3 signals. This field contains 5 its. The first (most significant) it represents L1 status, the second one represents that of L2, the third one that of L3. Bit 1 denotes transmission of the corresponding signal; 0 means asence of the signal. Health of the given navigation signal and its data validity is determined y attriutes H and x p (see и ). 4 th and 5 th its of Field M А denotes a modification of the SV : А SR А field are reserved ones. M А = 000 Glonass-M carrying L3 navigation payload transmitting L3 CDMA; M А = 001 Glonass-K1 transmitting L3 CDMA signals; M А = 011 Glonass-K1 transmitting L2 and L3 CDMA signals; M А = 010 Glonass-K2 transmitting L1, L2, and L3 CDMA signals. In the course of GLONASS modernization SV with new modifications (from 100 to 111) may e introduced in the orital constellation. Introduction of such SVs in the constellation shall not result in disruption of UE manufactured earlier. А Field A denotes rough correction for transformation from L3OCd time of SV to GLONASS time at the eginning of day N 1) in MT. ( А A T GL,NА TGL,N T А 1 L1OCd,N А 1 1 TL1OCd,N А, where TGL,N 1 А is GLONASS time corresponding to the eginning of day N 1 ) in MT; ( А T is L1OCd time of SV L1OCd, NА 1 А corresponding to the eginning of day ( N 1 А ) in MT; Operator denotes the nearest integer. Note: value A in almanac data of each SV is the same and its accuracy is aout 1 ms for all signals of this SV. 42

43 within day within day the instant Field А denotes geodetic longitude of the first ascending node of SV orit А N А, in geocentric coordinate system used in GLONASS Field N А. t denotes the instant in MT when SV А passes the first ascending node A Field i is correction to nominal value (64.8º) of orit inclination of SV at A А t (MT). A Field A is eccentricity of SV А orit at the instant A t (MT) Field A is argument of perigee for SV А orit at the instant A t (MT) Field TA denotes correction to nominal value (40544 s) of mean draconic orital period of SV А at the instant A (MT). t (MT) Field T A is the rate of draconic orital period of SV А at the instant A Appendix M of General Description ICD provides the algorithm for calculating coordinates and velocity vector components for the SV s center of mass ased on almanac. t 43

44 5.4 L1OCd string Type Structure of string Type 25 Figure 5.5 shows the structure of string Type 25. This type of string is used for transmission of Earth rotation parameters (see Appendix L of General Description ICD), ionosphere model parameters (see Appendix Q of General Description ICD), UTC(SU) and TAI offset model parameters (see Appendix H of General Description ICD) and other parameters Preamle Type P1 TS H 11 l P2 KP А x p N B y p x p y p x p y p B B 1 B 2 c_a c_f c_a p UTC TAI 9 26 CRC 16 Figure 5.5 String Type 25 of L1OCd data Tale 5.5 provides parameters of data fields for string Type

45 Tale 5.5 Parameters of data fields for string Type 25 Field Numer of its Least significant it Value range Unit N B hours x p, y 14 p x p, y 14 p 9 x p, y 14 p arc second 8 10 arc second/day 2 10 arc second/day 2 B s B B s / msd c _ A s / msd c _ F SFU c _ A 0 p nt UTC TAI s Reserved 26 Notes: 1 For field B range is selected to allow for possile future cancellation of UTC(SU) correction SFU solar flux unit, 1 SFU = 1 10 W /(m Hz) Semantic scope of fields for string Type Preamle, Type,, H, l, P1, P2, KP, A, TS, CRC are service fields (see 4.2) Field N B is the calendar numer of a day (MT) within a four-year interval to which parameters transmitted in the current string relate. January 1 of a leap year corresponds to N B = 1. January 1, 2100 that according to Gregorian calendar is not a leap year also corresponds to N B = Fields x p, y p, x p, y p, x p, y p are parameters of quadratic polynomial used to determine the position of the instantaneous Earth s pole. These parameters are specified as for the eginning of day N B in MT (T MT ). 45