With the trend of globalizing of radio communication technology, every nation is now focusing on international standardization of the technology. As an international standard in the world, the recommendations from the International Telecommunication Union (ITU) is widely recognized, which is formulated by the ITU Radio communication sector (ITU-R) and stated by ITU members. Except the recommendations  cited in the Radio Regulation, others are not required to be carried out by the member countries. However, as ITU recommendations are made by administrations, radio communication operators, equipment manufacturers and other relevant organizations’ expert from all over the world, the recommendations have extremely high execution validity and are carried out by countries around the world more and more commonly.
In the ITU-R recommendations, there are 79 valid P-series recommendations, covering the basic elements of non-ionized media radio wave propagation, radio meteorological data, land point to area propagation path prediction method, ionosphere propagation characteristics, useful and useless signal point to point and earth to space path radio waves propagation, which has significant meaning to people working on radio wave propagation and wireless system design. Thus everyone who are engaged in radio communication research and wireless system design should have a total acquaintance with them and choose appropriate ones. While the P-series is systematic and full of classical theories, and only part of it is translated into Chinese, the selection turns out to be difficult.
In order to facilitate better understanding and using of these recommendations for experts, scholars and engineers who are engaged in radio wave propagation research as well as to fully play the P-series’ guidance role, we put 79 valid P-series recommendations into different categories according to their classification of the contents, highly summarize them and extract their core content from the overview of the radio wave propagation research while regarding the design of wireless system and electromagnetic compatibility analysis as the foothold . After the classification process, on the one hand, to the greatest extent it can help users to find the required content from numerous recommendations, on the other hand, it can directly help the users comprehensively understand and master the ITU-R P series recommendations, so as to fully play to the guiding role of the recommendations and promote a widely application in our country.
2. ITU-R SG3
ITU mainly has three sectors, namely the telecommunication standard sector (ITU-T), the radio communication sector (ITU-R) and the telecommunication development sector (ITU-D). ITU-R has six study groups, which are spectrum management (SG1), radio wave propagation (SG3), space services (SG4), terrestrial services (SG5), broadcasting services (SG6) and science services (SG7) respectively. SG3 mainly focus on propagation of radio waves and the characteristics of radio noise in ionized and non-ionized media with the purpose of improving the performance of radio communication systems. SG3 has four Working Parties (WP3J\WP3K\WP3L\WP3M), and the four parties are responsible for all the research work mainly drafting ITU-R P-series recommendations.
The publication of SG3 mainly involves the research of the basic elements of radio propagation, the modelling analysis of the wireless environment, and the methods of the propagation prediction in different environment and frequency. The main participating countries are the United States, China, South Korea, Japan, Australia, Brazil, Germany, Luxemburg, Canada, Spain, France, Italy, etc. -. In June 2013, China submitted the 8 contributions to WP3J, WP3K, WP3L, WP3M, relevant to the wave propagation prediction method for high-speed train’s wireless communication system , rain attenuation prediction model , the results of the propagation prediction of indoor and outdoor mobile communication . Among these contributions, propagation prediction of high-speed railway radio service issues proposed by the China Research Institute of Radio Wave Propagation was accepted by SG 3 expert and was finally put into the 3K chairman report.
3. ITU-R P-Series Recommendation
Without any exception, all the radio communication services or systems have one or more radio wave transmit links, namely the signal transmit links between the transmit and receive antenna ports of the system. In the transmit links, the radio waves simply transmit in natural environment and will be affected and restricted by the environment between the transmit and receive antennas. Without any doubt, the transmission of the radio waves has a great influence on the validity and effectiveness of radio communication. Also the influence varies from different radio communication services or systems.
Given this, SG3 carried out a series of in-depth research on radio wave transmission, and have solved five major fields of problems. First, what’s the natural environment for radio wave transmission, namely the main content of the research on radio atmosphere. Second, how the natural media influence the transmission of radio waves, namely the research on radio wave propagate effect. Third, how to predict the radio wave transmit effect of radio communication services or systems. Fourth, how to overcome or utilize the radio wave propagate effect while designing wireless system or circuit. Fifth, the electromagnetic compatibility problem, namely how to ensure that all kinds of radio communication services or systems work effectively while not interfering each other. The first two points are the fundamental problem of the radio wave propagation research, and the last three points are problems concerning about the application matters of radio wave propagation model. Figure 1 gives the general presentation of radio wave propagate research.
On basis of the contents, the P-series recommendations are classified into six categories: terms’ definition and basic materials, the environment of radio wave propagation, the propagation in ionosphere, the propagation in non-ionization media, propagation measurement and analysis, electromagnetic compatibility. And the propagation in ionosphere can be divided into radio wave propagation effect and radio wave propagation predict method. The portions of the six categories are shown in Figure 2.
Figure 1. The summarization of the radiowave propagation research.
Figure 2. The classification of the P-series recommendations.
3.1. Terms’ Definition and Basic Materials
The P-series recommendations specifically explained the terms concerning about radio wave and influence made by atmosphere, land and its coverings on propagation, and give definitions on maximum and minimum transmit frequency, worst month, etc. In addition, the recommendations provide the basic materials including the theory of probability and statistics, the numerical terrain database. This part is mainly complicated by 3J, as shown in Table 1.
3.2. The Environment of Radio Wave Propagation
The study of the environment of radio wave propagation is for the purpose of gathering natural environment information, and laying the foundation for mastering the mechanism of radio wave propagation. The main factors that influence the propagation of radio wave are atmosphere and land with its coverings, and atmosphere can be divided into four layers, namely magnetosphere, ionosphere, stratosphere and troposphere. They are the main media that influence the radio wave, and land with its coverings are the only boundary conditions of radio wave .
Terrestrial electrical parameters and ionosphere have great influence on medium wave and long wavelengths and wave with frequency below them. Ionosphere reflection is the major propagation method for shortwave. And troposphere and land coverings are the main factors that influence the propagation of ultra-short wave and microwave.
Therefore, the 3J and 3L working groups in SG3 conduct some research focusing on radio wave propagation environment, mainly including ionosphere’s reference characteristics, troposphere (especially the lower layers of atmosphere under 1 km altitude)’s refractive index, the variation of space distribution of moisture as well as its ramification (rain, fog, cloud) and sandstorm, land’s electric characteristic and variation of land’s temperature, humidity and atmospheric pressure changing from time to locations . The results are summarized as the P-series recommendations shown in Table 2.
3.3. Ionosphere Propagation
The study of ionosphere propagation is mainly about the interaction of radio waves and ionization media. Ionosphere is the atmosphere between 60 km and about 2000 km to 3000 km. Ionosphere mainly affect the propagation of radio waves with frequencies lower than high frequency. Radio waves with lower frequencies can’t pass through ionosphere but being reflected to the land. The propagation of VHF and waves with higher frequencies can ignore the ionosphere’s influence , especially the microwave which can transmit through the whole atmosphere. So the P-series recommendations specially studied the radio waves with frequencies lower than ultra-short wave propagation problems. This part of recommendations are mainly accomplished by 3 L work group, and shown in Table 3 in detail.
3.4. Propagation in Non-Ionizing Media
Radio wave is mainly influenced by non-ionizing media such as troposphere, land with its coverings, and thus it
Table 1. P-series recommendations about definitions and basic materials.
Table 2. P-series recommendations about the radiowave propagation environment.
Table 3. P-series recommendations about the ionospheric propagation.
produces various propagation effect, such as the scattering and attenuation made by rain and sands, multipath propagation, focusing effect, atmosphere duct propagation, diffraction, scattering and reflection caused by surficial materials, etc. Furthermore, for different radio service and system, the influence from non-ionizing media is different. So how to predict the influence in different radio services and systems appears to be necessary. The 3K and 3M working groups in SG3 have carried out deep research on the prediction method of radio wave propagation effect and model in non-ionizing media, and summarized as the P-series recommendations shown in Tables 4-6. Table 4 summarized various propagation effect that the recommendations involve.
According to difference applied range, propagation in non-ionizing medium prediction methods in P-series Recommendations are divided into two types: terrestrial service and space service. The two methods are listed in Table 5 and Table 6 respectively. Prediction methods mainly contain broadcast service, fixed service, mobile service (including terrestrial, maritime and aerospace mobile service) and so on.
Table 4. P-series recommendations about radiowave propagation effect in non-ionizing medium.
Table 5. P-series recommendations about propagation prediction method of terrestrial service.
Table 6. P-series recommendations about propagation prediction method of space service.
3.5. Propagation Measurement Analysis
In order to build the radio propagation model and verify the analysis to propagation model, SG3 Research Group gives suggestions, which focus on troposphere data collection, ionospheric measurement and spatial wave field strength measurement, about transmission test and analysis. Details are listed in Table 7.
3.6. Radio Electromagnetic Compatibility
Radio wave propagation can not only be applied to the design of wireless system and hardwired, but also be used for the electromagnetic compatibility analyses of the systems and services. In order to ensure various legitimate radio communication systems and stations working effectively, the 3M working group in SG3 take on the obligation to calculate, predict and evaluate the interference effect which includes the interference between radio stations, interference between space station and radio station and the influence factor of frequency sharing. Details are listed in Table 8.
This paper introduces ITU and ITU-R Study Group and briefly summarizes their Recommendations. Furthermore, the operating mode of the third study group and the input documents are interpreted in detail. Lastly, from both wireless system design and electromagnetic compatibility analysis perspective, all of 79 P-series Recommendations are analyzed and classified, and the main contents of each Recommendation summarized. The Recommendations are divided into six categories which are Terms’ Definition and Basic Materials, Radiowave Propagation Environment, Ionospheric Propagation, Propagation in Non-ionizing Medium, Measurement and Analysis of Propagation Characteristics and Electromagnetic Compatibility. The classification of P-series Recommendations has directive significance to ITU-R Recommendations and positive effect on promoting ITU-R Recommendations widely used in China.
This work was partially supported by the National Science and Technology Major Project under Grants No.
Table 7. P-series recommendations about measurement and analysis of propagation characteristics.
Table 8. P-series recommendations about the electromagnetic compatibility.
2013ZX03003016 and No. 2015ZX03002008, National High-tech R&D Program (863 Program) under Grants No.2014AA01A706.
 UK Propagation and Prediction Methods for the Planning of Short-Range Outdoor Radio-Communication Systems and Radio Local Area Networks in the Frequency Range 300 MHz to 100 GHz. ITU-R Document 3K/56-E, Jun 2013.