1、 Rep. ITU-R M.2073 1 REPORT ITU-R M.2073 Feasibility and practicality of prioritization and real-time pre-emptive access between different networks of mobile-satellite service in the bands 1 525-1 559 MHz and 1 626.5-1 660.5 MHz(2005) 1 Introduction and background At WRC-97 the mobile-satellite serv
2、ice (MSS) allocations in the 1 525.0-1 559.0 MHz and 1 626.5-1 660.5 MHz bands were made generic, and Resolution 218 (WRC-97) was adopted. At WRC-2000, this Resolution was replaced with Resolution 222 (WRC-2000). Resolution 222 (WRC-2000) resolves 2 states: “that administrations shall ensure the use
3、 of the latest technical advances, which may include prioritization and real-time pre-emptive access between MSS systems, when necessary and where feasible, in order to achieve the most flexible and practical use of the generic allocations;” Resolution 222 (WRC-2000) also invites ITU-R “to complete
4、studies to determine the feasibility and practicality of prioritization and real-time pre-emptive access between different networks of mobile-satellite systems as referred to in resolves 2 above, while taking into account the latest technical advances in order to maximize spectral efficiency,”. Appl
5、ication of prioritization and intersystem real-time pre-emption is one method by which the spectrum requirements of priority aeronautical mobile-satellite (R) service (AMS(R)S) traffic could be ensured. It was intended to improve spectrum efficiency in the case that distress communication occurs wit
6、h very low probability by shared use of the same spectrum by other communications with low priority. A work plan responding to the request of Resolution 222 (WRC-2000) was established in 2001. Several contributions have been submitted to the meetings of Radiocommnication Working Party 8D for the stu
7、dy. The work plan indicates steps for determining feasibility and practicality of prioritization and real-time pre-emptive access between different MSS networks (hereafter indicated as “prioritization and intersystem real-time pre-emption”) as below. Completion of revision of Recommendation ITU-R M.
8、1089. Definition of the terms “immediate availability” and “real-time pre-emptive access”. Identification of scenarios where real-time pre-emption would be applied. Investigation of potential methodologies and mechanisms to accommodate prioritization and call pre-emption processes (e.g. spectrum res
9、erve pool). Determination of feasibility and further development of technical and operational factors relating to the interface architecture between MSS systems operating in the frequency band of interest. The studies under this Report have addressed aeronautical mobile-satellite (R) service (AMS(R)
10、S), since the contributions were focused on AMS(R)S. 2 Rep. ITU-R M.2073 A revision of Recommendation ITU-R M.1089 was adopted in 2002. This Report addresses the remaining items in the work plan. It is noted that, in resolves 2.3 of Resolution 803 (WRC-03), WRC-03 adopted the following preliminary a
11、genda item for WRC-10: “2.3 to consider results of ITU-R studies in accordance with Resolution 222 (WRC-2000) to ensure spectrum availability and protection for the aeronautical mobile-satellite (R) service, and to take appropriate action on this subject, while retaining the generic allocation for t
12、he mobile-satellite service;” 2 Definitions 2.1 Immediate and real-time Nos. 5.353A, 5.357A and 5.362A of the Radio Regulations (RR) use the term “immediate availability”. Resolution 222 (WRC-2000) also addresses the term “real-time pre-emptive access”. Some have questioned what “immediate” and “rea
13、l-time” mean in terms of time (in s, min, etc.) to accomplish the actions intended. The term “immediate” means a very short period of time (such as a few seconds) as perceived by an individual. An engineer trying to implement this would look at what is possible from a technology point of view and la
14、ws of physics. There is also the operational aspect, where an action is not needed in an instant but depends on the operational environment. Therefore, “immediate” could be a range of values. From a regulatory point of view it may be difficult to define the term “immediate”, as it would have differe
15、nt values dependent on the operating environment. The term “immediate” can be defined as a period of time “less than X s”, where “X” is to be determined and might vary depending on the operating environment. The value “X” should account for various factors such as propagation delays, computer proces
16、sing time, authentication, etc. The term “real-time” also means that spectrum is made available to the requesting system within a specified delay. 2.2 Prioritization and pre-emptive access The terms of “prioritization” and “pre-emptive access” or “pre-emption” are used in this Report. In the context
17、 of this Report, the term “priority” means that if multiple messages are competing for access to a communications resource, then AMS(R)S messages with priority categories (1-6) will be granted access first and followed by other messages. The term “prioritization” is the treatment of different messag
18、e types in order of their established priority. The terms of “intersystem pre-emption” or “intersystem pre-emptive access” means accommodating AMS(R)S safety communication messages by transferring spectrum for a limited period of time despite the current usage of the spectrum within a specified dela
19、y that is determined via analysis of the operational requirements and characteristics of the MSS networks involved. Rep. ITU-R M.2073 3 2.3 Other definitions Taking into account above and discussions in 3.2, the following definitions are also used for the purpose of this Report: immediate availabili
20、ty: assignment by the network of required channels for safety communication within a specified period; capacity yielding: action of providing required spectrum for AMS(R)S communications by releasing spectrums for non-safety communications in other MSS networks. 3 Identification of scenarios where r
21、eal-time pre-emptive access would be applied 3.1 Characteristics and requirements of AMS(R)S communications Requirements of AMS(R)S communications and safety communications are well defined by the International Civil Aviation Organization (ICAO) and ITU publications as follows; Annex 10 to the Conve
22、ntion on ICAO Volume III, Part I, Chapter 4: Aeronautical mobile-satellite service ITU Constitution Article 40: Priority of Telecommunications Concerning Safety of Life Radio Regulations RR No. 4.10: Protection of safety services RR No. 5.357A and Resolution 222 (WRC-2000): Priority and protection o
23、f AMS(R)S communications ITU-R Recommendations Recommendation ITU-R M.1037 Bit error performance objectives for aeronautical mobile-satellite (R) service (AMS(R)S) radio link. Recommendation ITU-R M.1089 Technical considerations for the coordination of mobile-satellite systems supporting the aeronau
24、tical mobile-satellite (R) service (AMS(R)S) in the bands 1545 to 1555 MHz and 1646.5 to 1656.5 MHz. Recommendation ITU-R M.1180 Availability of communication circuits in the aeronautical mobile-satellite (R) services (AMS(R)S). Recommendation ITU-R M.1233 Technical considerations for sharing satell
25、ite network resources between the mobile-satellite service (MSS) (other than the aeronautical mobile-satellite (R) service (AMS(R)S) and AMS(R)S. Recommendation ITU-R M.1234 Permissible level of interference in a digital channel of a geostationary satellite network in the aeronautical mobile-satelli
26、te (R) service (AMS(R)S) in the bands 1 545 to 1 555 MHz and 1 646.5 to 1 656.5 MHz and its associated feeder links caused by other networks of this service and the fixed-satellite service. It is noted that some requirements relating to communication delay time, which would significantly affect the
27、applicability of prioritization and intersystem real-time pre-emption, have not clearly been defined yet. However, acceptable call set-up delay time for the air traffic control communications is generally considered as about 500 ms. Other characteristics and requirements of AMS(R)S communications ar
28、e summarized in Annex 1. 4 Rep. ITU-R M.2073 3.2 Conditions in which pre-emptive access would be applied 3.2.1 Characteristics of aeronautical traffic For identifying scenarios where prioritization and intersystem real-time pre-emption would be required, it may be useful to estimate characteristics
29、of peak instantaneous aircraft count (PIAC) using satellite communications as shown in Annex 2. These characteristics, and historical data on AMS(R)S traffic, show that the AMS(R)S traffic and spectrum requirements display predictable diurnal variations and slow long-term growth. It is noted that pr
30、ioritization and intersystem real-time pre-emption would be beneficial only in situations where there are occasional requirements for large amounts of additional AMS(R)S spectrum. Moderately varying AMS(R)S spectrum requirements can be satisfied through the coordination process. There is no evidence
31、 that AMS(R)S traffic exhibits the highly specialized kind of traffic demand, which would be conducive to pre-emption. 3.2.2 Conditions of MSS networks to apply real-time pre-emptive access Real-time pre-emptive access would require the following conditions. 1 Application of capacity yielding is to
32、be agreed among administrations concerned in the frequency coordination. 2 Following conditions are to be agreed among MSS operators concerned: frequency range for yielding and unit of yielding; category and priority of the communication concerned; order of application of capacity yielding among MSS
33、 networks. 3 A sufficient capacity of data link is to be implemented among network control centres (NCCs) of each MSS network. 4 Process of capacity yielding is to be defined and agreed. 3.2.3 Satellite network capacity design The ability of an AMS(R)S network to meet quality objectives is dependent
34、 on the capacity of the network relative to the traffic loads offered to it. If insufficient capacity is available, access delays will increase. Capacity transfers from lower priority traffic may need to be invoked to satisfy delay requirements for AMS(R)S, substantially increasing delays for low-pr
35、iority communications. Three resources that determine network capacity are satellite radio channels, ground earth station (GES) channel units, and terrestrial interconnection ports. A well-designed AMS(R)S network will most likely be provisioned in these three areas to accommodate traffic peaks with
36、 a very high probability. Under these conditions, the amount of coordinated spectrum available will determine the capacity available to the AMS(R)S system and hence the ability of the system to meet traffic demand. 3.2.4 Factors affecting the design of an AMS(R)S resource management process Resource
37、 sharing among different MSS networks would require some scheme to manage capacity transfer among networks an intersystem resource management process. This intersystem resource management process would have to be defined such that its implementation would result in fair and equitable pre-emption pra
38、ctices by the different MSS operators serving AMS(R)S and other users while maintaining the required high level of availability for their priority services. Rep. ITU-R M.2073 5 To be effective and fair, an intersystem resource management process must include the effects of a number of factors. The f
39、ollowing list gives an indication of what would be required: 1 Some MSS systems include both AMS(R)S and non-AMS(R)S components. 2 An AMS(R)S system must have the ability to quickly bring additional channels on-line so that spectrum transferred may be used. 3 An AMS(R)S system will generally have hi
40、gh-priority (1-6) and low-priority traffic. An AMS(R)S system shall not request capacity from the intersystem resource management system unless all of its low-priority channels, including any non-AMS(R)S channels, have been reallocated to channels with priorities 1-6. 4 The resource management schem
41、es need to take account of the fact that MSS operators are planning satellite designs with a large number of spot beams. The high frequency reuse factor and small regions served by spot beams will provide additional flexibility to meet the AMS(R)S needs in a responsive timely manner. 5 MSS systems t
42、hat are designed to use small-spot beams have high frequency reuse factors and may achieve high efficiency. An AMS(R)S system with large beams that requests spectrum from a system with small beams may cause spectrum in a large number of spot beams to be excluded, reducing the overall spectrum use ef
43、ficiency of the band. 6 An AMS(R)S system must only request pre-emption when a real traffic requirement exists and all intrasystem resources are occupied with traffic of equal or higher priority, so as not to unnecessarily deprive other systems of capacity. 7 The definition of “real-time” is importa
44、nt. The important criterion is that an AMS(R)S system obtains its required spectrum when it needs it. If that criterion is met, real-time may be fractions of a second in some circumstances, and perhaps minutes in others, while still ensuring aeronautical safety. The process of evaluating the feasibi
45、lity of an intersystem resource management system should include a determination of the minimum practical time in which transfer can occur, taking into account the design of the different MSS systems. 8 The system that is asked to transfer spectrum is likely to have internal frequency planning const
46、raints that would determine what spectrum segments are most suitable (or least detrimental) to transfer. Therefore, the request from the AMS(R)S system would be for an amount of spectrum, and the response would necessarily include an identification of the frequency ranges being transferred. The AMS(
47、R)S system would need the agility to rapidly incorporate those new blocks, without knowledge in advance of which specific frequencies they would obtain. 9 Spectrum should be returned as soon as it is no longer needed by the AMS(R)S system. A mutually agreeable and fair procedure must be developed to
48、 determine when spectrum can be returned, again serving safety needs while not unnecessarily depriving other systems. 10 AMS(R)S systems operate in areas where there are multiple systems with overlapping coverage areas. Some procedure would need to be mutually agreed such that all operators needs ar
49、e treated fairly in determining which systems would give up spectrum in any particular pre-emption event. In many cases, more than one system would need to be pre-empted to make spectrum available to an AMS(R)S system. 11 The impact of spectrum transfers of hundreds of kilohertz would be far different from spectrum transfers of a few tens of kilohertz, and the management process will be affected as well. 12 All operators would need to mutually agree on the algorithms used by AMS(R)S operators to determine when and how much additional spectrum is required. 6 Re
