1、STD-ITU-R RECMN F.751-2-ENGL 1997 Y855212 0531082 975 279 Rec. ITU-R F.751-2 RECOMMENDATION ITU-R F.75 1-2 TRANSMISSION CHARACTERISTICS AND PERFORMANCE REQUIREMENTS OF RADIO-RELAY SYSTEMS FOR SYNCHONOUS DIGITAL HIERARCHY-BASED NETWORKS (Question ITU-R 160/9) (1992-1994-1997) The ITU Radiocommunicati
2、on Assembly, considering a) detailed mappings associated with the synchronous digital hierarchy (SDH); that ITU-T Recommendations G.707, G.708 and G.709 specify the bit rates, the multiplexing structure and the b) that ITU-T Recommendations G.781, G.782 and G.783 specify the general characteristics
3、and functions of synchronous multiplexing equipment and ITU-T Recommendation G.784 specifies the management of SDH equipment and networks; c) interfaces of SDH equipment; that ITU-T Recommendations G.703 and G.957 specify the physical parameters of the electrical and optical d) systems (DRRSs); that
4、 Recommendation ITU-R F.750 specifies architectures and functional aspects of SDH digital radio-relay e) meeting the performance requirements and efficient spectrum utilization; f) channelling schemes, that specific transmission features of the radio-relay systems may be required for the transport o
5、f SDH bit rates that the coexistence of SDH-DRRSs with the existing radio systems is required in the present radio recommends 1 that SDH-DRRSs comply with the requirements described in Annex 1. ANNEX 1 1 Introduction 1.1 Scope Annex 1 defines the transmission characteristics and performance requirem
6、ents for the SDH-DRRSs. 2 Applications of SDH digital radio-relay systems (SDH-DRRSs) 2.1 Network interfaces The connection between radio and SDH networks shall be at standardized interface points. The preferred connection is to make the TT points (Recommendation ITU-R F.596) coincide with the netwo
7、rk node interface (“NI) points identified in ITU-T Recommendation G.708. COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Services STD-ITU-R RECMN F.753-2-ENGL 3337 = 4855232 0533083 803 20 28,29, 29.65,30 28,29, 29.65,30 40 40 55, 56,60 280 Re
8、c. ITU-R F.751-2 1 x STM-1 1 X STM-1 2 x STM-1 1 x STM-1 2 x STM-1 1 X STM-1 16-QAM, 32-QAM 256-QAM, 5 12-QAM 64QAM, 128-QAM, 256-QAM 128-QAM (CC), 256-QAM (CC) 32-QAM, 64-QAM 32-QAM (CC), 64-QAM (CC), 512-QAM 2.2 Transport capacity 80 2 x STM-I 2.2.1 High capacity SDH-DRRSs 64-OAM SDH-DRRSs in the
9、long-haul or core network typically operate at STM-1, n x STM-1 or STM-n transmission rates. They are typically deployed in the lower (2-12 GHz) frequency bands. 80 I 4 X STM-1,1 x STM-4 High capacity SDH-DRRSs in short-haul or access networks typically operate at the STM-1 or n x STM-1 transmission
10、 rates. They are usually deployed in frequency bands higher than 12 GHz. 64-QAM (CC) 2.2.2 Medium capacity SDH-DRRSs 110,112 110,112 220 In circumstances when traffic requirements are below those of an STM-1 signal, and to most effectively utilize the available radio bandwidth, radio-relay systems t
11、ypically operate at the STM-RR transmission rate with a VC-3 traffic payload (see 4 6 of Annex 1 to Recommendation ITU-R F.750). 2 X STM-1 16-QAM, 32-QAM 4 x STM-1,1 x STM-4 4 x STM-1.1 x STM-4 16-QAM (CC), 32-QAM (CC) 16-OAM. 32-OAM 2.2.3 Low capacity SDH-DRRSs SDH-DRRSs with payload transport capa
12、city below VC-3, e.g. n x VC-12, are under study. 3 Radio-frequency channel arrangements and compatibility with existing systems 3.1 High capacity SDH-DRRSs SDH-DRRSs shall be compatible with the existing radio-frequency channelling arrangements (see Recommen- dation ITU-R F.746). This will allow ad
13、ministrations to introduce new synchronous digital radio systems without major disruption of existing radio networks employing analogue radio systems and/or plesiochronous digital radio systems. These have generally been based on analogue radio systems and digital systems operating at bit rates up t
14、o 140 Mbit/s. The transmission of 155 Mbit/s signals within these channelling arrangements requires an increase in the bits/Hz spectrum efficiency of radio equipment which may have a consequential impact on the choice of modulation method and on the design of filter circuits. Examples of possible ar
15、rangements which allow transmission of the basic STM-1 rate and multiple STM-1 rates within existing radio-frequency channel plans are given in Table 1. TABLE 1 Examples of possible arrangements which allow transmission of the basic STM-1 rate and multiple STM-1 rates within existing radio-frequency
16、 channel spacing I Channel spacing I MW Capacity Examples of modulation method (1). (2) (1 The term QAM is intended to also encompass forward error correction or coded modulation techniques (like TCM). (2) In this table CC is used as the abbreviation for “band re-use in the Co-channel mode”. COPYRIG
17、HT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling ServicesSTD-ITU-R RECMN F.75L-Z-ENGL 1997 4855232 O533084 748 10 Rec. ITU-R F.751-2 281 1 X STM-RR 3.2 Medium capacity SDH-DRRSs Examples of possible arrangements which allow STM-RR transmission rates w
18、ithin existing radio-frequency channel plans are given in Table 2. 27.5,28 30 TABLE 2 Examples of possible arrangements which allow transmission of STM-RR rates within existing radio-frequency channel spacing 1 x STM-RR CQAM, 16-QAM 1 x STM-RR 9 QPR, 16-QAM I Channel spacing (MHz) I 40 Capacity 1 x
19、STM-RR QPSK Examples of modulation method (1) I 14 I 1 X STM-RR I 16-QAM, 32-QAM 20 2 X STM-RR 64-QAM, 128-QAM 4 Media-specific functions Radio-relay systems may require transmission capacity between “Is to allow for the implementation of a range of radio specific functions (media specific functions
20、). The following functions have currently been identified: a) In order to activate “early warning switching” of radio protection switching equipment during adverse propagation events, an effective method can be derived from the fast detection of error activity (if present) on each separate hop. This
21、 is essential in order to achieve “error free” switching operation. b) ATPC may be advantageous in reducing nodal interference between radio-relay systems. In addition, it can be used to improve linearity or increase the dynamic range of multi-level modulation radio equipment. It is anticipated that
22、 when ATPC is implemented, it will be on a hop-by-hop basis. c) The control signal may need to be accessed at equipment sites providing functions for either multiplex section overhead (MSOH) or regenerator section overhead (RSOH) depending on the physical implementation of radio protection switching
23、 (see 0 3.4 of Annex 1 to Recommendation ITU-R F.750). d) Propagation monitoring This control signal may be needed to collect data on propagation conditions prevalent on the radio route. e) In many applications radio-relay systems offer a variety of auxiliary functions. Examples of such functions ar
24、e as follows: - - - propagation data collection, EarZy warning radio protection switch activation Automatic transmitter power control (ATPC) Radio protection switching information and control Wayside trafic, auxiliary maintenance and monitoring functions wayside traffic, up to n x 1.5 MbiVs or n x 2
25、 Mbit/s, forward error detection and correction, COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Services- auxiliary 64 kbitls data channels, - auxiliary maintenance functions, e.g. station alarms, - temporary datdvoice channels for maintenanc
26、e purposes. f) End-to-end performance monitoring for radio connections composed of multiple SDH regenerative repeaters (RS) without MS termination In this application it may be useful to forward the far-end radio terminai errored blocks information (evaluated on the incoming B2 parity) entering into
27、 the radio system from outside, using dedicated bytes. This will allow the far-end terminai to provide the TMN with the correct end-to-end error performance monitoring without additional processing. 4.1 Techniques for transport of media specific functions Several techniques are available to provide
28、the functions outlined above. The choice of technique may depend on the method of implementation. Two examples are given below. 4.1.1 Radio frame complementary overhead (RFCOH) Radio-relay systems may in some applications require a RFCOH in order to implement the functions outlined above. The RFCOH
29、is added to the STIv-1 signal and is accessible at both radio terminal and repeater equipments. 4.1.2 Section overhead (SOH) Radio-relay systems may in some applications make use of bytes within the SOH in order to implement the functions outlined above using the media specific bytes referred to in
30、0 4.2 of Annex 1 to Recommendation ITU-R F.750, bytes reserved for national usage and the bytes reserved for future international standardization. In this case a way-side traffic up to 2 Mbitls can be transported. However, in the event that IT-T defines the function of those bytes reserved for futur
31、e intemational standardization, SDH radio-relay systems will comply with ITU-T Recommendation G.708. 5 Transmission techniques SDH-DRRSs will require tighter filtering or a higher number of modulation levels to accommodate the former capacity within the same radio channel. A number of proven techniq
32、ues like error correction, coded modulation, multi-carrier systems, ATPC, adaptive equalization, hit-less or error-less protection switching, space and frequency diversity and cross-polarization cancellation are available to combat various impairments such as multipath dispersive fading, radio inter
33、ference, thermal noise, timing errors, etc. Specific items of SDH-DRRSs on transmission techniques are mentioned below. 5.1 Error correction SOH capacity is not sufficient to accommodate error correction schemes currently in use. The implementation of error correction may further increase the gross
34、bit rate of the radio system. 5.2 Scrambling ITU-T Recommendation G.709 specifies that a 7-stage frame synchronous scrambler shall be used at the STM-n signal level. For radio systems employing certain modulation methods (e.g. 64-QAM) which are envisaged especially for long- haul high capacity radio
35、 systems, such a scrambler is not sufficient for the purposes of demodulation and timing extraction and may not be adequate to ensure a uniform spectral distribution in order to allow compatibility with analogue systems. In addition, short scramblers can lead to data-dependent performance. The radio
36、 design should ensure that adequate scrambling is provided in the radio system. COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling ServicesRec. ITU-R F.751-2 283 6 Performance requirements SDH-DRRSs will be integrated in managed SDH networks. Rad
37、io performance requirements which should be met by SDH-DRRSs are given in the relevant ITU-T and ITU-R Recommendations. Achieving this performance involves providing both high quality equipment and adhering to appropriate route engineering guidelines. This section identifies ITU-T and ITU-R texts ap
38、plicable to successful integration of SDH digital radio systems into the SDH network. 6.1 Error performance ITU-T Recommendation G.821 provides error performance requirements which should be met at the 64 kbit/s level. Recommendation ITU-R F.594 gives performance objectives for high grade digital ra
39、dio links. For medium and local grade circuits, Recommendations ITU-R F.696 and ITU-R F.697, respectively, apply. The requirements for transport networks at or above the primary level are contained in ITU-T Recommendation G.826. The error performance objectives of SDH-DRRSs shall comply with ITU-T R
40、ecommendation G.826. This will also ensure that the SDH-DRRSs meet the ITU-T Recommendation G.821 requirements. 6.2 Timing and synchronization SDH-DRRSs shall be designed to operate in a synchronized network. The general principles and applications guidelines for synchronization of SDH multiplexing
41、equipment are given in ITU-T Recommendation G.782. Derived timing and synchronization specifications are given in ITU-T Recommendation G.783. SDH-DRRSs may derive the timing reference from three types of inputs: - ITU-T Recommendation G.703, external synchronization interface; - ITU-T Recommendation
42、 G.703, plesiochronous digital hierarchy (PDH) signal interface (carrying reference synchronization); - STM-n interface. Depending on the types of SDH-DRRS, one or more timing reference inputs may be available. SDH-DRRSs should have the capability to switch automatically to another timing reference
43、if the selected timing reference is lost (see ITU-T Recommendation G.782). 6.3 Jitter and wander SDH jitter and wander are specified at both STM-n and ITU-T Recommendation G.703 interfaces, in order to control the accumulation of jitter within SDH systems. The jitter and wander characteristics of SD
44、H-based multiplex equipment are given in ITU-T Recommendation G.783 and those of SDH-based line systems are given in ITU-T Recommendation G.958. 6.4 Availabiliy Availability objectives for digital radio systems are given in Recommendation ITU-R F.557. For medium and local grade circuits, Recommendations ITU-R F.696 and ITU-R F.697, respectively, apply. COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Services
