JP4571103B2 - Wireless communication device - Google Patents

Description

  The present invention relates to a radio communication apparatus mounted on a marine mobile body that reduces the influence of fading, particularly two-wave interference caused by sea surface reflection.

  In general, multipath fading is a factor that affects the stability of wireless communication. Multipath fading refers to the presence of diffracted waves and reflected waves from obstacles existing on the transmission path in addition to direct waves before radio waves reach from the transmission side to the reception side in wireless communication. The incoming radio waves from the path interfere with each other, and the signal level changes every moment depending on the position of the moving body. Due to this multipath fading, frequency selective fading becomes a problem in digital wireless communication. There are time delays in multiple incoming radio waves. When this time delay is about 0.1 times or more of the clock period of the digital signal to be transmitted, the code of the digital signal causes interference with the adjacent code, code errors occur frequently, and the quality of the communication line is remarkably deteriorated.

  Among multipath fading, especially in maritime mobile communications, there is a two-wave interference caused by a direct wave and a sea surface reflected wave that greatly affects the stability of the communications. As shown in FIG. 5, when the radio wave transmitted from the mobile station 1 reaches the mobile station 2 at a distance, a direct wave and a sea surface reflected wave are generated. In general, multipath fading should also consider reflected waves and diffracted waves from obstacles. However, in maritime mobile communication, there is nothing called an obstacle between the mobile station 1 and the mobile station 2, and it can be said that the interference of the sea surface reflected wave is dominant as a cause affecting reception. FIG. 6 shows a schematic example of the reception level when the mobile station 2 receives a radio wave transmitted at a certain frequency from the mobile station 1, assuming that the mobile stations 1 and 2 are moving at the same altitude. . In general, the reception level is simply attenuated according to the distance. However, especially at sea, there is a valley that abruptly attenuates when the frequency is fixed. This valley is generated by two-wave interference caused by direct waves and sea surface reflected waves. Therefore, when the mobile station 2 is in a position where this valley exists, the reception quality is lowered.

It is widely known that the diversity method is effective as a countermeasure against the multipath fading as described above. In a radio communication system that applies the space diversity method of the receiving antenna, a clock frequency component detector etc. is provided on the receiving side, and among the radio waves received by multiple antennas, the receiving system is switched to the one with the strongest received radio wave intensity, Thereafter, a technique of performing reception processing using a single reception system has been proposed (see, for example, Patent Document 1).
In addition, a network is composed of a plurality of communication devices that perform maritime mobile communication, and the communication device calculates a drop in received radio wave strength due to two-wave interference using what is called a self-localization device, and the radio wave strength is the communication partner. There is a technique of securing an information transmission path to a communication partner by passing through another communication device that joins the network when the level required by is not reached (see, for example, Patent Document 2).
In addition, there is a technique for imparting directivity to radio waves from an antenna by separately controlling the phase amount of the same transmission signal transmitted from each of a plurality of antenna elements constituting the antenna (see, for example, Patent Document 3). .

JP-A-6-31146 JP-A-9-307494 JP 2001-237768 A

  In the technology described in Patent Document 1 of the prior art, on the receiving side, the radio wave that is less affected by the two-wave interference due to the direct wave and the sea surface reflected wave is sequentially switched, and the optimal radio wave intensity is selected from the received radio waves. Since the method of selecting a thing is taken, when all the radio waves which arrived are weak, it cannot respond to multipath fading reduction. Further, in the case of the technique described in Patent Document 2, two-wave interference is calculated using the self-position and the communication partner's position information on the transmission side, but this method transmits information to the communication partner by relay. Therefore, it is assumed that a relay station exists, and the intended effect cannot be obtained by communication between two parties. Furthermore, in the case of the technique described in Patent Document 3, as a method for avoiding two-wave interference between a direct wave and a sea surface reflected wave, directivity is given to a transmission radio wave by electronically operating a fixed antenna. However, many antennas must be used for this purpose. In addition, the phase amount of the transmission signal must be individually controlled according to the number of antennas, and a device that performs complicated calculations is required.

  An object of the present invention is to obtain a wireless communication apparatus that enables two-way communication with stable communication quality by reducing the influence of two-wave interference in maritime mobile communication. To do.

The wireless communication device according to the present invention is a wireless communication device that performs maritime mobile communication, a self-position calculation unit that receives a GPS signal and acquires position information of the own device, and position information of the counterpart device from the received information, The information separation unit that separates the frequency information of the partner device and the switching timing information of the partner device, and receives the received wave at a frequency according to the frequency information of the separated partner device, and the position of the own device obtained by the self-position calculation unit Based on the information, the frequency of the transmission wave currently in use, and the position information of the partner aircraft separated by the information separator , the difference between the path length of the direct wave and the sea surface reflected wave between the partner aircraft is calculated and calculated. Obtain the difference between the path length difference and the half wavelength of the current transmission wave, and if the absolute value of the difference is less than or equal to a predetermined value, the frequency at which the absolute value of the difference is greater than or equal to the predetermined value To the calculated frequency An interference calculation section issues an instruction to replace Ri, in accordance with the instruction for switching the frequency from the interference calculation unit generates the switching timing information of its own, in synchronism with the switching timing information of the separated destination via information separator The frequency switching unit that switches the frequency of the transmission wave to the frequency instructed by the interference calculation unit, the position information of the own device acquired by the self-position calculation unit , and the frequency of the currently used transmission wave switched by the frequency switching unit the switching timing information of the information and its own device is obtained and an information multiplexing section for multiplexing the transmission information.

  According to the present invention, the use frequency of the transmission wave is switched in consideration of the two-wave interference between the direct wave and the sea surface reflected wave, so that the influence of the two-wave interference is suppressed as much as possible, and stable two-way communication is achieved. enable.

Embodiment 1 FIG.
1 is a block diagram showing a configuration of a wireless communication apparatus according to Embodiment 1 of the present invention. This wireless communication apparatus assumes digital data communication using, for example, a TDMA (Time Division Multiple Access) system, and can perform simultaneous communication because the apparatuses form a data link. In addition, it is assumed that the devices are synchronized by a GPS (Global Positioning System) signal.
In FIG. 1, a self-position calculation unit 102 acquires the position information of its own device from a GPS (Global Positioning System) signal and outputs it to the information multiplexing unit 101. In the information multiplexing unit 101, input transmission data to be originally transmitted (including voice data), position information of the own device, frequency information used for current communication selected by the frequency switching unit 104 described later, and switching Timing information is multiplexed and output to the transmission unit 103 as transmission information. The transmission unit 103 converts the frequency of transmission information from the information multiplexing unit 101 using a voltage controlled oscillator (VOC) that oscillates at a frequency selected by the frequency switching unit 104, and converts an RF signal (transmission wave). Generated and supplied to the antenna 105. The antenna 105 transmits the RF signal supplied from the transmission unit 103 as a radio wave. Also, when the antenna 105 receives radio waves from the same type wireless communication device of the other party, the antenna 105 outputs the received RF signal to the receiving unit 106.

  The receiving unit 106 converts the received RF signal into an intermediate frequency, and then performs analog / digital conversion to obtain a baseband signal. This baseband signal is transmission information of the counterpart device, and includes reception data (transmission data of the counterpart device), position information, frequency information, and switching timing information, and the information separation unit 108 separates them. The separated position information of the partner machine is output to the interference calculation unit 107, and transmission data of the partner machine (received data in this machine) is output to a utilization circuit (not shown). The separated frequency information is given to the receiving unit 106 and used for switching the frequency of the local oscillator. Further, the switching timing information is given to the frequency switching unit 104 and used for setting the frequency switching timing.

  The interference calculation unit 107 receives the position information of the own device and the frequency information currently being transmitted from the information multiplexing unit 101. Based on the information and the position information of the counterpart device, the interference calculation unit 107 uses the method described later. When the influence of two-wave interference due to sea surface reflections on the current frequency of use is calculated, and the partner aircraft is at a point where the influence of two-wave interference is large, it is necessary to select two of the prepared frequencies at the corresponding point. A frequency that can minimize the influence of wave interference is selected, and a frequency switching instruction is issued to the frequency switching unit 104. The frequency switching unit 104 provides the transmission unit 103 with a control signal for switching to a frequency according to the received instruction. This control signal is a control voltage applied to the variable capacitance diode for determining the operating frequency when a VCO is used as the local oscillator of the transmission unit 103. In transmission section 103, the operating frequency is set to a frequency that minimizes the influence of two-wave interference at the point where the counterpart device is present, according to the control signal from frequency switching section 104, and the frequency conversion of transmission information is performed using the set frequency. Do. Since this frequency switching operation is performed in synchronization with the communicating partner, the frequency switching unit 104 multiplexes the switching timing information together with the selected frequency information into the transmission information by the information multiplexing unit 101. To do.

  The wireless communication apparatus operates as described above, but when performing transmission, the following is preferable. The same transmission information is continuously transmitted a plurality of times, and the phase is controlled to be different from the first time in the second and subsequent transmissions of the continuous transmission. By doing so, even if the first transmission radio wave does not have the desired reception radio wave intensity at the receiving-side counterpart device, the second and subsequent transmissions can be received with the desired radio wave intensity.

Next, the theory that is the idea of the present invention will be described.
The multipath fading phenomenon in the maritime mobile communication has been described with reference to FIGS. 5 and 6, but the multipath fading in the sea is generated by the use frequencies f1 and f2 of the transmission waves as illustrated in FIG. The position (distance from the mobile station 1) is different. It can be seen from FIG. 2 that the fluctuation of the received radio wave intensity caused by sea surface reflection depends on the relative positions of the transmission side and reception side radio communication apparatuses and the transmission frequency used. Therefore, it can be understood that it is sufficient to transmit to the wireless communication apparatus located in the valley of the reception level at the use frequency f1 by using the use frequency f2 that gives the reception level filling the valley. This idea is represented by the thick reception level curve in FIG.
Also, the valley of the reception level becomes deepest when the direct wave of the radio wave from the mobile station 1 and the sea surface reflected wave reach the mobile station 2 in opposite phases in FIG. From this, it can be seen that the condition for maximizing the two-wave interference is when the difference in path length between the direct wave and the sea surface reflected wave between the wireless communication devices is λ / 2 (λ is the wavelength of the transmitted wave). . Therefore, it is only necessary to transmit to a partner device in the vicinity of a position where the path length difference is λ / 2 by using a transmission wave having a frequency that does not become the wavelength.

Next, details of the processing of the interference calculation unit 107 will be described with reference to FIG. In FIG. 4, two-dimensionally shown for ease of explanation, but it can be expanded as it is in an actual three-dimensional space.
First, the coordinates of the mobile station 1 on the transmission side are set to (x1, y1), and the coordinates of the mobile station 2 on the reception side are set to (x2, y2). When the path length of the sea surface reflected wave of the radio wave transmitted from the mobile station 1 to the mobile station 2 indicated by the bold line is L ₁ , the relationship of the formula (1) is established.
L ₁ ² = (x2−x1) ² + (y2 + y1) ² (1)
Similarly, when the path length L ₂ of the direct wave is obtained, the relationship of equation (2) is established.
L ₂ ² = (x2-x1) ² + (y2-y1) ² (2)
From these relationships, the difference ΔL = L ₂ −L ₁ between the direct wave and the sea surface reflected wave is obtained.

  As described above, the two-wave interference has the most influence when the direct wave and the sea surface reflected wave reach the receiving side in opposite phases, that is, when the path length difference ΔL = λ / 2. is there. Therefore, the interference calculation unit 107 calculates the half wavelength from the current use frequency of the own device. Next, the difference between the path length of the direct wave and the sea surface reflected wave calculated as described above from the distance between the mobile stations and the half wavelength of the current transmission wave is obtained, and the absolute value of the obtained difference is a predetermined value. When the value is equal to or smaller than the value, the frequency of the wavelength at which the absolute value of the difference is equal to or greater than the predetermined value is calculated. Here, the fact that the absolute value of the difference is equal to or smaller than the predetermined value indicates that the reception level is in a valley that makes the communication inappropriate at the current use frequency f1 in FIG. On the other hand, as a method of obtaining the frequency of the wavelength at which the absolute value of the difference is equal to or greater than a predetermined value, a table that associates position information with the used frequency is prepared in advance, and the frequency that enables the most stable communication among them is prepared. You can choose. As an example for this, two operating frequencies are prepared for one position information, and at the point where the influence of two-wave interference becomes large when one frequency is used, the frequency is switched to the other frequency. do it. This makes it possible to keep the reception level stable.

  As described above, according to the first embodiment, in maritime mobile communication, the frequency at which transmission information is frequency-converted to a transmission wave is set to the difference between the path lengths of the direct wave and the sea surface reflected wave with the counterpart device. Is switched to a selected value that does not become half wavelength, and transmission is performed as appropriate, so that a sudden drop in the reception level caused by a change in the distance between moving bodies at sea is suppressed, and reception performance is continuously maintained. Therefore, two-way communication with stable communication quality is enabled in maritime mobile communication greatly affected by two-wave interference. Further, since the use frequency is determined by simple calculation using the positional relationship of the marine mobile body, the processing time can be shortened and the use frequency can be switched in real time. In addition, the use of a VCO for frequency switching does not require a plurality of antenna configurations or complicated calculations, and the complexity and scale of the wireless communication device can be suppressed.

It is a block diagram which shows the function structure of the radio | wireless communication apparatus by Embodiment 1 of this invention. It is explanatory drawing which shows the reception level at the time of using a different transmission frequency. It is explanatory drawing which shows the improved receiving level which concerns on Embodiment 1 of this invention. It is explanatory drawing which shows the processing method of the interference calculation part which concerns on Embodiment 1 of this invention. It is explanatory drawing showing how the electromagnetic wave is transmitted in maritime mobile communication. It is explanatory drawing which shows the example of the reception level which received two-wave interference.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 101 Information multiplexing part, 102 Self-position calculation part, 103 Transmission part, 104 Frequency switching part, 105 Antenna, 106 Reception part, 107 Interference calculation part, 108 Information separation part

Claims (1)

In a wireless communication device that performs maritime mobile communication,
A self-position calculator that receives GPS signals and obtains position information of the own machine;
An information separating unit that separates the position information of the partner machine, the frequency information of the partner machine and the switching timing information of the partner machine from the reception information, and receives a received wave at a frequency according to the frequency information of the separated partner machine;
Based on the position information of the own device acquired by the self-position calculation unit, the frequency of the currently used transmission wave, and the position information of the partner device separated by the information separation unit , When the difference in the path length of the sea surface reflected wave is calculated, the difference between the calculated path length difference and the half wavelength of the current transmission wave is calculated, and the absolute value of the calculated difference is less than the predetermined value An interference calculation unit that calculates a frequency of a wavelength at which the absolute value of the difference is equal to or greater than a predetermined value, and issues an instruction to switch to the calculated frequency;
In response to a frequency switching instruction from the interference calculation unit, the switching timing information of the own device is generated, and the frequency of the transmission wave is set in synchronization with the switching timing information of the partner device separated by the information separation unit. A frequency switching unit for switching to a frequency instructed by the calculation unit ;
Position information of the own device acquired by the self-position calculating unit, and an information multiplexing section for multiplexing the frequency switching section by the switched transmits the switching timing information of the frequency information and the own device in the transmission wave currently in use information A wireless communication apparatus comprising:

Images