1、 Rec. ITU-R S.1062-4 1 RECOMMENDATION ITU-R S.1062-4 Allowable error performance for a satellite hypothetical reference digital path operating below 15 GHz (Question ITU-R 75-3/4) (1994-1995-1999-2005-2007) Scope The fixed-satellite service (FSS) plays an important role in providing reliable interna
2、tional digital communications. Because of the integration with the terrestrial facilities, a satellite link should be designed to fulfil requirements that are compatible with terrestrial systems. ITU-T Recommendation G.826 specifies performance objectives for a satellite hop in the international por
3、tion of a hypothetical reference digital path (HRDP). In response to those objectives, this Recommendation gives guidance on bit error probability (BEP) or bit-error rate (BER) design masks which can fully comply with the requirements of ITU-T Recommendation G.826. The ITU Radiocommunication Assembl
4、y, considering a) that satellites operating in the fixed-satellite service (FSS) play an important role in providing reliable international digital communications; b) that satellite link performance must be sufficient to allow compliance with overall end-to-end performance objectives and end-user qu
5、ality of service objectives; c) that satellite link performance is generally distance independent; d) that Recommendation ITU-R S.614 specifies satellite link performance objectives which comply with the objectives specified in ITU-T Recommendation G.821; e) that the error performance for hypothetic
6、al reference digital paths (HRDPs) and hypothetical reference connections (HRX) have been specified in ITU-T Recommendation G.826; f) that in defining error performance criteria, it is necessary to take into account all foreseeable error-inducing mechanisms, especially time-varying propagation condi
7、tions and interference, noting a) that Recommendation ITU-R S.1429 Error performance objectives due to internetwork interference between GSO and non-GSO FSS systems for hypothetical reference digital paths operating at or above the primary rate carried by systems using frequencies below 15 GHz, spec
8、ifies the error performance allowance due to interference between different satellite systems and that Recommendation ITU-R S.1323 Maximum permissible levels of interference in a satellite network (GSO/FSS; non-GSO/FSS; non-GSO/MSS feeder links) in the fixed-satellite service caused by other codirec
9、tional FSS networks below 30 GHz, specifies how to calculate the operating margins to allow for both fading and interference, 2 Rec. ITU-R S.1062-4 recommends 1 that future and, wherever possible, existing satellite links within the FSS should be designed to at least meet the specifications for a sa
10、tellite hop in the international portion in ITU-T Recommendation G.826. An example set of design masks derived from ITU-T Recommendation G.826 parameters is presented in Note 1; 2 that the methodology explained in Annex 1 can be used to generate the necessary bit-error probability (BEP) (see Note 4)
11、 design masks specified in Note 1. The same methodology can be used at a 155 Mbit/s rate to derive the mask in Note 2; NOTE 1 In order to fully comply with the requirements of ITU-T Recommendation G.826, the BEP divided by the average number of errors per burst (BEP/, see 3 of Annex 1) at the output
12、 (i.e. at either end of a two-way connection) of a satellite HRDP forming part of an international portion of a connection or path should not exceed during the total time (including the worst month) the design masks defined by the values given in Table 1 and also in the BEP masks given in Fig. 4. 3
13、that the following Notes should be regarded as part of the Recommendation: NOTE 2 Although Note 1 assures full compliance with ITU-T Recommendation G.826, a more stringent mask may be desirable or necessary for certain services. TABLE 1 Bit rate (Mbit/s) Percentage of total time (worst month) BEP/ 0
14、.064 0.2 10.0 1.0 1041.0 1081.5 0.2 2.0 10.0 7 107 3 1085 1092.0 0.2 2.0 10.0 7 1062 1082 1096.0 0.2 2.0 10.0 8 1071 1081 10951.0 0.2 2.0 10.0 4 1072 1092 1010155 0.2 2.0 10.0 1 1071 1091 1010In this case the BEP at the output (i.e. at either end of a two-way connection) of a satellite HRDP operatin
15、g up to and including 155 Mbit/s should not exceed during the total time (worst month) the design mask defined by the values given in Table 2: Rec. ITU-R S.1062-4 3 TABLE 2 Percentage of total time (worst month) BEP/ For = 10 (BEP) 0.2 2 10 1 1071 1091 10101 1061 1081 109NOTE 3 The HRDP referred to
16、in this Recommendation is specified in Recommendation ITU-R S.521. NOTE 4 The BEP ratios given in Notes 1 and 2 could be estimated by BER measurement over a sufficiently long period of time. A method for measuring BERs as a function of percentage of time is given in Annex 1 of Recommendation ITU-R S
17、.614. NOTE 5 For ease of application of this Recommendation the values for the objectives given in Notes 1 and 2 are given in terms of total time and represent the limits of a BEP performance model utilizing the method outlined in Annex 1. In arriving at the objectives given in Notes 1 and 2 the err
18、ors occurring during the unavailable time have been excluded from the calculation of the objectives. An explanation of the relationship between available time and total time is given in Note 7. The objectives for BEPs given in Note 1 are not unique in meeting the requirements of ITU-T Recommendation
19、 G.826. Other BEP masks may be used by the designer where appropriate as long as these masks satisfy ITU-T Recommendation G.826. NOTE 6 This Recommendation will find its primary application in satellite systems operating below 15 GHz. The extension of the performance requirements given in this Recom
20、mendation to systems operating at higher frequencies is the subject of further study. NOTE 7 A period of unavailable time begins at the onset of ten consecutive severely errored seconds (SES) events. These 10 s are considered to be part of unavailable time. A new period of available time begins at t
21、he onset of ten consecutive non-SES events. These 10 s are considered to be part of available time. Unavailability threshold values for BEP can be determined such that the unavailable state is reached with a probability = 0.5 as illustrated in Fig. 3. NOTE 8 The objectives given in Notes 1 and 2 are
22、 given in terms of percentage of the worst month. These monthly percentages correspond to the following yearly percentages: 10% of worst month 4.0% of year; 2% of worst month 0.6% of year; 0.2% of worst month 0.04% of year. NOTE 9 In order to comply with Notes 1 and 2 at frequencies greater than 10
23、GHz, it may be advantageous to make use of fade countermeasures including adaptive forward error-correction (FEC) coding, power control or site diversity. Information on site diversity operation is given in Annex 1, Recommendation ITU-R S.522. NOTE 10 The preferred method of verifying digital satell
24、ite performance is on the basis of in-service measurements. These measurements would utilize the block error detection schemes, which are related to the inherent block size and structure of the transmission system. FEC, scrambling and differential encoding have an impact on the interpretation of the
25、 measurements (see Annex 1, 3). 4 Rec. ITU-R S.1062-4 NOTE 11 The error performance described in Notes 1 and 2 was developed based on the use of an HRDP in the international portion of the link (e.g. switched international gateway-to-switched international gateway). Other applications of the HRDP wi
26、thin the connection are possible (e.g. end office-to-end office) and the error performance objectives can be adjusted accordingly. NOTE 12 The methods described in this Recommendation can be applied to the design of satellite links in private networks. The performance objectives will usually be agre
27、ed between the network operator and the network user via a service level agreement (SLA) as specified in ITU-T Recommendation E.800. NOTE 13 The performance objectives shall be met for the required transmission rate not necessarily for any higher rate created to support multiplexing or error correct
28、ion. For instance, if the transmission rate over a satellite link is 6 Mbit/s and the contracted transmission rate specified in the SLA is 2 Mbit/s, then the objectives for 2 Mbit/s transmission shall apply. Annex 1 1 General, history, definitions, parameters and objectives relating to ITU-T Recomme
29、ndation G.826 The requirements of ITU-T Recommendation G.826 are given in terms of errored blocks as opposed to individual bit errors. The purpose of this specification is to allow the verification of adherence to the performance requirements of ITU-T Recommendation G.826 on an in-service basis. The
30、 specification of performance in terms of block errors instead of bit errors has important consequences for systems where the errors tend to occur in groups, such as systems employing scrambling and FEC. The block used in ITU-T Recommendation G.826 is that group of contiguous bits that normally make
31、s up the inherent monitoring block or frame of the transmission system being employed. ITU-T Recommendation G.826 End-to-end error performance parameters and objectives for international, constant bit-rate digital paths and connections, covers two types of transport system in detail and may be exten
32、ded to other types where necessary. The two types are: the plesiochronous digital hierarchy (PDH) from 64 kbit/s to the primary rate; and the synchronous digital hierarchy (SDH) from the primary rate up to 3 500 Mbit/s. The addition of the sub-primary speeds was made in the year 2002 to facilitate d
33、evelopment at these speeds. However, to maintain stability for the very large installed base of PDH systems it was agreed not to change the long-standing ITU-T Recommendation G.821 which applies to these systems. In SDH terminology an end-to-end circuit is referred to as a PATH. In PDH terminology a
34、n end-to-end circuit is referred to as a CONNECTION. Rec. ITU-R S.1062-4 5 Transport system performance is specified in terms of parameters called errored seconds (ESs) and severely errored seconds (SESs) in both PDH and SDH with SDH having an additional parameter called block errors to give a great
35、er resolution for the higher transmission speeds. These blocks have a duration that is much shorter than a second. An SDH block, whose size depends upon the transmission speed, is a set of consecutive bits that may not be contiguous if the block happens to bridge a container boundary, for example. 1
36、.1 Definitions from ITU-T Recommendation G.826 1.1.1 Error performance events for paths Errored block (EB) A block in which one or more bits are in error. Errored second (ES) A 1 s period with one or more EBs. Severely errored second (SES) A 1 s period which contains 30% EBs or at least one defect (
37、see ITU-T Recommendation G.826 for definition of defects). Note that SESs are a sub-set of ESs. Background block error (BBE) An EB not occurring as part of an SES. 1.1.2 Error performance events for connections Errored second (ES) A 1 s period in which one or more bits are in error or during which l
38、oss of signal or alarm indication signal is detected. Severely errored second (SES) A 1 s period which has a bit-error ratio of 1 in 103. 1.2 Parameters Error performance should only be evaluated while the path or connections is in the available state. For a definition of the entry/exit criteria for
39、 the unavailable state see Note 7 and Annex A of ITU-T Recommendation G.826. Errored second ratio (ESR) The ratio of ES to total seconds in available time during a fixed measurement interval. Severely errored seconds ratio (SESR) The ratio of SES to total seconds in available time during a fixed mea
40、surement interval. Background block error ratio (BBER) The ratio of EBs to total blocks during a fixed measurement interval, excluding all blocks during SES and unavailable time. 1.3 Monitoring blocks Table 3 shows the block size and number of blocks/s for various transmission rates. 6 Rec. ITU-R S.
41、1062-4 TABLE 3 Relationship between bit rate, block size and number of blocks/s Bit rate (Mbit/s) Block size (bits) Number of blocks/s 1.544 4 632 333 2.048 2 048 1 000 6.312 3 156 2 000 44.736 4 760 9 398 51.84 6 480 8 000 155.52 19 440 8 000 1.4 Performance objectives The end-to-end objectives def
42、ined in ITU-T Recommendation G.826 are reproduced for convenience in Table 4. The performance objectives are given as a function of transmission system bit rate. The ranges of block sizes accommodated at these bit rates are also given. As stated above, the block size will be that associated with the
43、 frame structure of the transmission system. These objectives are specified for available time. TABLE 4 End-to-end performance objectives for a 27 500 km international digital HRDP or HRX from ITU-T Recommendation G.826 Rate (Mbit/s) 64 kbit/s to primary rate(1)1.5 to 5 5 to 15 15 to 55 55 to 160 16
44、0 to 3 500 Bits/block Not applicable 800-5 000 2 000-8 000 4 000-20 000 6 000-20 000 15 000-30 000(2)ESR 0.04 0.04 0.05 0.075 0.16 (3) SESR 0.002 0.002 0.002 0.002 0.002 0.002 BBER Not applicable 2 104(4)2 1042 1042 104104(1)It is not required to apply these objectives to equipment that was designed
45、 prior to 2003. Performance objectives for such equipment are given in ITU-T Recommendation G.821. (2)As currently defined, VC-4-4c (ITU-T Recommendation G.707) is a 601 Mbit/s path with a block size of 75 168 bits/block. Since this block size is outside the recommended range for 160-3 500 Mbit/s pa
46、ths, performance on such VC-4-4c paths is outside this Table. The BBER objective for VC-4-4c using the 75 168 bit block size is 4 104. (3)ESR objectives tend to lose their significance at high bit rates and are therefore not specified for paths operating above 160 Mbit/s. However, for maintenance pu
47、rposes, ES monitoring should be implemented. (4)For systems designed prior to 1996, the BBER objective 3 104. Rec. ITU-R S.1062-4 7 Digital paths and connections operating at bit rates covered by this Recommendation may be carried by transmission systems operating at higher bit rates. Such systems m
48、ust be designed and implemented to objectives that will support the end-to-end objectives of their tributaries, current and anticipated. Under the assumption of random error distribution, meeting the allocated objectives in Table 1/G.826 for the higher bit rate systems should ensure that all tributa
49、ries will also be achieving their objectives. 1.5 Apportionment of the end-to-end objectives to portions of the path The end-to-end performance objectives are apportioned between international and national portions of an HRDP using the allocation principles detailed in 6.2 of ITU-T Recommendation G.828 (see Fig. 1). IG: International gatewayPEP: Path end point If a path terminates at the IG, only the international portion alloc
