CN103313259B - The relaying emergent radio data communication framework of low latitude balloon load - Google Patents

Abstract

The relay network consists of a single low-altitude relay platform. The relay platform is hung under the balloon tethered by the rope fixed by the car. The application scenario is a terrestrial cellular network where some base stations are damaged but there are still a small number of base stations (remaining base stations) that can be physically connected. The physical layer of the low-altitude relay can use cognitive radio technology to detect the signal spectrum of the remaining base station, so as to manage the wireless resources of emergency data communication. The functions that the relay platform can realize are: 1) Provide ground users with a connection close to the line of sight ; 2) Adjust the position of the relay platform to ensure that the links between the relay platform and multiple ground base stations have good channel quality; 3) Have a certain cognitive radio function; 4) Realize as a gateway for the remaining base stations Communication with external networks.

Description

Relay emergency wireless data communication architecture for low-altitude balloon load

technical field

The invention relates to the field of wireless emergency communication, in particular to a low-altitude relay emergency wireless data communication method.

Background technique

The existing terrestrial cellular communication system is prone to be paralyzed after a large-scale geological disaster, and then the communication service function will be lost. At present, the relay emergency communication researched at home and abroad includes low-altitude relay platform and high-altitude relay platform. The low-altitude relay platform is relatively flexible, and the overhead and delay are smaller than the high-altitude platform, but the disadvantage is that the coverage is small, and it is easily affected by low air flow disturbance; the high-altitude relay platform has a large coverage, and the delay and overhead are smaller than satellite communications. Obviously larger than the low-altitude relay platform, the economic cost is usually relatively large.

At present, high-altitude platforms mainly use airships to carry communication equipment to establish contact with ground base stations and terminals. On long-duration missions, the airship can go 3 to 5 years without landing. For short-term missions, UAVs can be considered to carry communication equipment. However, the existing technology, whether it is a low-altitude relay platform or a high-altitude relay platform, does not have a high spectrum utilization rate, which may cause many communication failures and have a great impact on disaster relief work. The present invention still adopts the low-altitude relay platform, but the emergency wireless communication design has certain characteristics of cognitive radio.

The low-altitude relay platform is usually carried by a hot air balloon, and the working time is determined by the power supply. The low-altitude relay platform can quickly restore the communication in the disaster area.

Acronyms and key term definitions:

Contents of the invention

Purpose of the invention: For wireless cellular network scenarios where some base stations are damaged but there are still a small number of base stations (remaining base stations) that can still achieve physical connection, that is, consider the next generation of cellular base stations (such as EnodeB1 and EnodeB3 based on the LTE air interface are called remaining base stations) Signals can be transmitted to the gateway of the core network, but due to physical damage caused by the disaster, these remaining base stations cannot communicate with the gateway of the core network normally. At this time, these reserved base stations need to perform data communication and Internet connection with the wireless relay platform close to the geographical location.

The technical scheme of the present invention: the low-altitude wireless relay platform is carried by a balloon, and the size of the load determines the size of the balloon. Balloons are usually divided into two types: the first is a balloon with remote control and self-navigation system, but the system is complicated and expensive; the other is a system fixed with a rope, but the height is limited and the communication coverage is also limited. limit. The present invention adopts the second type, that is, the tethered low-altitude relay system. The emergency system can adjust the position of the air relay platform to ensure that the links between the relay platform and multiple ground base stations have relatively good channel quality.

The system architecture is shown in Figure 1.

Figure 1 shows a design scheme of a single low-altitude relay emergency communication architecture. Considering the linear deployment of three ground base stations EnodeB1-3, multiple mobile stations MT are evenly located in the cells served by each base station. The air relay is mainly composed of five parts: including spectrum sensing module, communication module, spectrum and channel management, communication gateway management module and GPS or Beidou positioning module.

Assume that natural disasters have collapsed EnodeB2, although EnodeB1 and EnodeB3 have not collapsed, but the working status is unknown. This necessitates over-the-air relay deployments.

The considered cellular network is an LTE network, ie the terrestrial base station has an LTE interface. Because the LTE network structure is a flat structure, the ground base station NodeB node and the RNC node merge to form an EnodeB. The cellular base station side has the function of independently completing packet switching. If EnodeB1 and EnodeB3 can still complete signal processing and limited packet switching functions, emergency data communication can be realized directly between MT1 and MT2 and between MT5 and MT6 through local base station nodes.

The low-altitude relay platform is equivalent to the aGW in LTE, and communicates with the external network (such as satellite communication network) through the backhaul link.

The relay has multiple radio interfaces, and each interface supports up to 4 frequency bands, so as to provide data communication services for the multi-interface intelligent terminals on the ground. Ground LTE terminal equipment and base stations support up to 4 frequency bands, which is conducive to improving the capacity of the cellular system.

The low-altitude relay emergency wireless communication design has certain characteristics of cognitive radio, that is, the relay platform has efficient information and knowledge processing capabilities. The node architecture is shown in Figure 2.

Its architectural functions include: the hardware abstraction layer is the encapsulation interface of the upper layer functions, shielding the implementation process of specific hardware details;

Spectrum and channel management allocates spectrum and channel-related resources such as links and frequencies;

The spectrum sensing module provides signal detection;

The communication gateway management module is used to organize and manage the communication between the ground cellular base station EnodeB and the external network;

Data management organizes data for high-level applications;

The information/rules database stores prior knowledge and rules.

The specific implementation of low-altitude relay emergency wireless data communication design is described as follows.

The ground cellular base station adopts an ideal linear topology, and each base station has two power supply modes: wired power supply and battery power supply. Cellular base stations in battery powered mode will use a low transmit power mode in the event of a severe disaster that disrupts wired power.

When a disaster occurs, the communication between the base station and the ground gateway aGW is interrupted, and one of the base stations on the ground, such as EnodeB2, has collapsed. If other adjacent base stations (EnodeB1 and EnodeB3) are not damaged, EnodeB1 and EnodeB3 can form an internal network through self-organizing characteristics , but it cannot connect to external networks. At this time, ground terminals can only be routed through the local base station, but cannot communicate with terminals outside the coverage of the local base station.

In this design, the emergency communication car will drive to the location of the damaged base station, and the relay on the tethered hot air balloon platform will act as the access gateway aGW of the undamaged base station. This gateway with the network backhaul link function can connect the external network with the undamaged base station service terminals or users, and can also provide data communication services to users in damaged cells.

The low-altitude relay is deployed over the damaged base station. Due to the lack of information on the working status of adjacent ground cellular base stations, the emergency communication system needs to detect signals first in the network initialization phase. The spectrum sensing module of the relay platform first detects the signals of adjacent base stations to determine whether the base station is damaged and the spectrum used by the base station.

The relay platform uses the method of energy detection in cognitive radio to detect the base station signal.

The energy detection method can calculate the detection probability P _d of the signal when the false alarm probability P _f and the number of signal detection samples are given. According to the detection probability P _d , the relay platform will determine whether the signal exists or not.

Similarly, given the false alarm probability P _f and the signal detection probability P _d , the number of detection samples of the signal can be obtained, and thus the detection duration can be obtained.

Similarly, for mobile terminals within the range of damaged base stations, the emergency system can allocate frequency bands and links to them through the spectrum and channel management functions of relay nodes.

Within the range of the damaged base station, if there is a new terminal added, the previously allocated frequency band is detected through spectrum sensing. Users using the previously allocated frequency band are defined as primary users, while newly added terminals are defined as secondary users. If the primary user exists, other frequency bands are allocated to the secondary user, so as to achieve effective spectrum sharing and improve network capacity under the condition of an imperfect cellular network architecture.

Ground cellular base stations are powered by batteries. Since the remaining power of the batteries may vary, the transmit power of the base stations may also vary.

When EnodeB1 and EnodeB3 are not damaged, it is assumed that the channel model between the relay and the ground cellular base station is a LOS channel, and the signal mainly has large-scale fading in free space.

The relay office obtains the signal power of EnodeB1 and EnodeB3 according to the measurement and adjusts the distance between the relay platform and EnodeB1 and EnodeB3 through the GPS module, so that the relay platform can provide reliable communication gateway services for the two base stations at the same time.

The invention is different from the existing low-altitude platform, and especially proposes a low-altitude relay platform based on cognitive radio technology to restore data communication in disaster-stricken areas.

The low-altitude relay platform proposed by the present invention is carried by a hot-air balloon tethered by ropes, and the size of the load determines the size of the hot-air balloon. Therefore, the weight of the load should not be too large, otherwise the hot air balloon will be difficult to carry. Therefore, the relay platform only has some functions of the original cellular network gateway and is aimed at data communication applications.

Beneficial effects of the invention:

1. LTE terminals and networks can use up to 4 frequency bands. By using cognitive radio, spectrum resources can be detected in real time to achieve efficient spectrum sharing and large-capacity communication;

2. The position of the relay platform can be adjusted dynamically, and the function as the gateway of the EnodeB1 and EnodeB3 base stations can be completed excellently.

Description of drawings

Fig. 1 is a system architecture diagram of emergency wireless data communication proposed by the present invention;

FIG. 2 is a functional architecture diagram of a relay node proposed by the present invention;

Fig. 3 is the simulation diagram of the detection probability _Pd of the energy detection based on the cognitive radio of the present invention;

4 is a simulation diagram of the number of detection samples of the energy detection based on cognitive radio in the present invention;

Fig. 5 is a deployment diagram of relay position adjustment in the present invention;

Fig. 6 is a calculation diagram of received signal strength at the relay platform of the present invention;

Detailed ways

A low-altitude balloon-loaded relay emergency wireless data communication architecture, including a low-altitude wireless relay platform, a base station, and a mobile terminal. The low-altitude relay platform is carried by a balloon on a car, and consists of a spectrum sensing module, a communication module, a spectrum and a channel Management, communication gateway management module and GPS or Beidou positioning module. The low-altitude relay platform communicates with the external network through the backhaul link. The MT is distributed in the base station, and the mobile terminal is located on the car with the gateway function and the receiving node of the backhaul link. , able to communicate with the Internet backbone network; establish mutual communication links between multiple relay platforms.

The relay has a multi-radio interface, and each interface supports up to 4 frequency bands, and the terrestrial LTE terminal equipment and the base station support up to 4 frequency bands.

The relay platform has efficient information and knowledge processing capabilities.

A simple linear topology of three base stations is selected, and the system architecture is shown in Figure 1. Includes three terrestrial cellular base stations in linear topology, a low-altitude relay platform, and many mobile terminals.

After the disaster, the ground emergency communication vehicle drove into the damaged location of the base station. In this example, enter the position of EnodeB2.

The spectrum sensing module of the relay platform uses the method of energy detection to detect the signal of the ground cellular base station.

The energy detection method can calculate the detection probability P _d of the signal when the false alarm probability P _f and the number of signal detection samples are given.

Now we take the number of samples N to be 50, and the false alarm probabilities are P _fa1 =0.005, P _fa2 =0.025, and Pf _a3 =0.1 respectively. The detection probability P _d of the signal can be obtained through simulation, as shown in FIG. 3 .

From Fig. 3 we can see that for the same false alarm probability P _fa , as the SNR increases, the detection probability P _d becomes higher and higher, that is to say, the probability of signal existence becomes larger.

Under the same SNR, the greater the false alarm probability _Pfa , the greater the detection probability _Pd .

Under the condition of given false alarm probability _Pf and signal detection probability _Pd , the energy detection method can obtain the number of signal detection samples and thus the detection time length.

Now we take the false alarm probabilities as P _fa1 =0.1 and P _fa2 =0.025 respectively, and the detection probabilities as P _d1 =0.9 and P _d2 =0.98 respectively. The number of detection samples can be obtained through calculation and simulation, so as to calculate the detection time.

It can be seen from FIG. 4 that, when the false alarm probability P _fa1 =0.1, the number of samples required to achieve the detection probability P _d2 =0.98 is greater than the number of samples required to achieve the detection probability P _d1 =0.9. But as the SNR increases, the number of samples required by the two is nearly the same. The false alarm probability P _fa2 =0.025, the situation is similar to P _fa1 =0.1.

In the case of the same detection probability _Pd , the smaller the false alarm probability _{Pf is} , the more samples are needed to reach the detection probability _Pd , and the required time is the longest.

To sum up, the energy detection can obtain the existence or non-existence of the signal of the ground cellular base station according to the calculation of P _d .

After the spectrum sensing is completed, it is assumed that neither EnodeB1 nor EnodeB3 is damaged. At this time, the relay adjusts the position relationship with EnodeB1 and EnodeB3 through the GPS module according to the received signal strength or the SNR of the signals received by the two base stations at the relay, so that both can be connected to the external network through the relay.

The location adjustment of the relay is shown in Figure 5.

The circle in Figure 5 represents the relay platform, and the initialization position is above the midpoint of EnodeB1 and EnodeB3. If the strength of the signal from EnodeB1 at the relay is greater than the strength of the signal of EnodeB3, then move the position of the relay to the EnodeB3 side, as shown by the dotted line in Figure 5; otherwise, move to the EnodeB1 side.

Assuming that the coverage of the base station is 500 meters, the distance between EnodeB1 and EnodeB3 is 2000 meters. The transmission power of EnodeB1 is P _t1 =0.1w, the transmission power of EnodeB3 is P _t1 =0.05w, and the relay height and position are adjusted according to the signal strengths of EnodeB1 and EnodeB3 received at the relay. Ground LTE base stations work in the 2.4GHz frequency band, and the signal wavelength can be obtained according to the formula λ=ν/f.

The signal power P _r received by the relay from EnodeB1 and EnodeB3 can be calculated according to the formula Calculate d) to obtain B, where the path loss power can be obtained by Calculated, d represents the distance between the relay and the ground base station.

The calculation result is shown in Figure 6.

It can be drawn from Figure 6 that the received signal power gradually decreases as the distance increases. If we set the minimum threshold of received signal strength at the relay to be -85dBm, then we can see from Figure 6 that the distance between the relay and EnodeB1 is 1800 meters, and the distance from EnodeB3 is 1200 meters.

According to the cosine law, the angle between the line connecting the relay and EnodeB1 and the ground can be obtained, and then the height of the relay from the ground can be calculated to complete the deployment of the relay platform.

The basic principles and main features of the present invention and the advantages of the present invention have been shown and described above. Those skilled in the industry should understand that the present invention is not limited by the above-mentioned embodiments. What are described in the above-mentioned embodiments and the description are only to illustrate the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will also have Various changes and improvements fall within the scope of the claimed invention, which is defined by the appended claims and their equivalents.

Claims (1)

1. A low-altitude balloon-loaded relay emergency wireless data communication architecture, including a low-altitude wireless relay platform, a base station, and a mobile terminal; the low-altitude relay platform is carried by a balloon tied to a car, and consists of a spectrum sensing module, a communication module, and a spectrum sensing module. It consists of channel management, communication gateway management module and GPS or Beidou positioning module; multiple mobile stations are distributed within the coverage of ground base stations, and mobile terminals are carried on ground vehicles; through low-altitude relay platforms, these MTs and mobile terminals on vehicles are Able to communicate with the Internet backbone network; not only a single low-altitude relay platform communicates with the external network through a backhaul link, but also establishes a mutual communication link between multiple relay platforms; under the relay emergency wireless data communication architecture , the relay platform also has a multi-radio interface, so as to communicate with ground LTE terminal equipment and base stations; compared with other wireless data communication architectures based on relays, the communication architecture and the relay platform therein have efficient information and knowledge processing capability; it is characterized in that: the spectrum sensing module of the relay platform first detects the signals of adjacent base stations to determine whether the base station is damaged and the frequency spectrum used by the base station; the relay platform uses the method of energy detection in cognitive radio Detect the base station signal; the energy detection method calculates the detection probability P _d of the signal under the given false alarm probability P _f and the number of signal detection samples, and the relay platform will determine whether the signal exists or not according to the detection probability P _d ; Given the false alarm probability P _f and the signal detection probability P _d , the number of detection samples of the signal is obtained, and thus the detection duration is obtained; the emergency system involves multiple cellular base stations, EnodeB1, EnodeB2 and EnodeB3, among which EnodeB2 is in a damaged state due to the disaster; for For mobile terminals within the range of damaged base stations, the emergency system allocates frequency bands and links to them through the spectrum and channel management functions of relay nodes; The frequency band is detected; the user who uses the previously allocated frequency band is defined as the primary user, and the newly added terminal is defined as the secondary user; if the primary user exists, other frequency bands are allocated to the secondary user, so that in the imperfect cellular network architecture Realize effective spectrum sharing under certain conditions, and improve network capacity; when EnodeB1 and EnodeB3 are not damaged, if the channel model between the relay platform and the ground cellular base station is a LOS channel, the signal mainly has free space large-scale fading; the relay The platform obtains the signal power of EnodeB1 and EnodeB3 according to the measurement and adjusts the distance between the relay platform and EnodeB1 and EnodeB3 through the GPS module, so that the relay platform can provide reliable communication gateway services for the two base stations at the same time.