KR101040255B1 - Method for LPI/LPD of DS-CDMA modem - Google Patents

Abstract

The present invention relates to a low-pitched design method of a direct sequence code division multiple access modem. More specifically, in the link budget analysis of DS-CDMA modems, DS-SS design, and control channel design, power control and processing gain control control the ratio of received power to noise power density, thereby concealing the transmission signal by noise. The present invention relates to a low-pitched design method of a direct sequence code division multiple access modem that can implement a low-pitched antenna while facilitating a multi-user connection.

To this end, the present invention controls the transmission power and the reception power so that the reception power density and the noise power density are the same level, so that the transmission signal is concealed by noise. Provide design methods.

Low pittam, spread spectrum, low pittam, LPI, LDI, direct sequence, DS

Description

Low-detection design method of direct sequence code division multiple access modem {Method for LPI / LPD of DS-CDMA modem}

The present invention relates to a low-pitched design method of a direct sequence code division multiple access modem. More specifically, in the link budget analysis of DS-CDMA modems, DS-SS design, and control channel design, power control and processing gain control control the ratio of received power to noise power density, thereby concealing the transmission signal by noise. The present invention relates to a low-pitched design method of a direct sequence code division multiple access modem that can implement a low-pitched antenna while facilitating a multi-user connection.

Unlike a communication method that transmits a signal through a predetermined frequency, a spread spectrum signal is divided into finely divided signals to be spread over a wide frequency band and called spread spectrum (SS). In the spread spectrum, a direct sequence (DS) method in which one signal symbol is spread in a predetermined sequence for communication, and a frequency hopping (FH) method in which a frequency is changed and transmitted over time without fixing a frequency, the above two methods And a hybrid method combining these.

Among them, the frequency hopping method has the advantage that the spectrum is exposed but it is difficult to disturb or catch up. In particular, because military communication is the most important factor in terms of characteristics, the frequency hopping method occupies a very important position in the security technology of military communication. However, the frequency hopping method is difficult to implement a multi-user connection, and thus, it is difficult to implement a communication network having a high system throughput using multiple channels at the same time using the multi-user connection.

Although direct sequencing reduces the power spectral density (PSD) due to the spread band, intentional detection has a weak structure that is inevitable, and thus it is not widely used for military use compared to the frequency hopping method. However, the direct sequence method has the advantage that it is technically easy to implement a multi-user connection, and if the security function is enhanced, it can be fully used for military purposes.

As communication technology and electronic warfare technology has advanced rapidly, the possibility of interference from external threats increases, and low probability of intercept (LPD) techniques are used to establish secure communication. It is becoming a fundamental component of communication equipment. Accordingly, there is a need for research on low-detection technology that is robust from external interference while fully utilizing multi-user access by supplementing the security of the direct sequence spread spectrum method.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a low-pitched design method of a direct sequence code division multiple access modem that can implement low-pitched, while facilitating the connection of multiple users. .

In order to achieve the above object, the low-detect design method of the direct sequence code division multiple access modem according to the present invention controls the transmission power and the reception power so that the reception power density and the noise power density are the same level, so that the transmission signal is It is characterized in that it is concealed by noise.

In addition, the received power may be represented by the following equation.

Where EIRP = P _t × G _t

In addition, the ratio of energy per bit and noise power spectral density required for data modulation and demodulation of the modem from the received power may be expressed by the following equation.

here,

In addition, the processing gain obtained by the direct sequence spread spectrum in the modem can be represented by the following equation.

In addition, when a plurality of terminals are controlled by an operating station in the design of a control channel for power control and processing gain control in the modem, each terminal determines the ratio of the received power density and the noise power density to determine a ratio below the threshold. Control may be requested for coordination of operating stations.

In addition, in the design of a control channel for power control and processing gain control in the modem, when a plurality of terminals are connected without an operating station, the transmission signal power of the counterpart terminal may be controlled between the terminals.

According to the present invention, in the link budget analysis of DS-CDMA modem, DS-SS design and control channel design, the transmission signal is controlled by noise by controlling the ratio of received power density and noise power density through power control and processing gain control. By being concealed, there is an effect that can implement a low-pitham while facilitating the connection of multiple users.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. First, in adding reference numerals to the components of each drawing, it should be noted that the same reference numerals are assigned to the same components as much as possible, even if shown on different drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. In addition, the following will describe a preferred embodiment of the present invention, but the technical idea of the present invention is not limited thereto and may be variously modified and modified by those skilled in the art.

1 is a block diagram illustrating elements of a low-detection design of a direct sequence code division multiple access modem according to the present invention.

In the present invention, link budget analysis and direct sequence-spread spectrum (DS-SS) design for low-detect design of a direct sequence code division multiple access (hereinafter, "DS-CDMA") modem using power control and Modem control channel design is used as an element of low-pitham design. Hereinafter, each element of the low pit design will be described in detail.

(1) Link Budget Analysis

Link budget analysis is to determine the power characteristics of the transmit and receive channel which is the basis of modem power control. Link budget refers to a task or a calculation result of a specification or adjustment for perfect transmission and reception in a link design of a wireless communication system. That is, all the tasks of designing a scheme for predicting and calculating various elements of a transmitting end, a transmission medium, and a receiving end sensitivity, gain, noise figure, margin, and the like to obtain a stable line quality within an overall target value are included. .

The link budget of a modem can be broadly classified into a satellite modem and a wireless modem according to the environment in which the modem is used. Satellite modems and wireless modems have differences in transmission / reception distances between users and frequencies, equipment configurations and sizes, and channel environments. In this case, the satellite modem may be regarded as the same signal distance in the transmission and reception distance, while the wireless modem may appear in a variety of signal transmission distance depending on the position of the transceiver.

① satellite modem

In the case of satellite modem, various factors such as antenna transmit / receive gain and internal gain, noise figure, pointing loss of satellite transponder can be considered, and factors that do not change are regarded as part of loss and fluctuate. Can be considered a margin on the budget. The power in the satellite modem transceiver can be expressed by the following equation.

In Equation 1, EIRP denotes an output of a transmit antenna, P _t denotes a transmit power, G _t denotes a transmit antenna gain, G _r denotes a receive antenna gain, G _antenna denotes a gain of a transmit / receive antenna, and L _s denotes a path loss. (pass loss) a, L _etc are the other losses, the reception power P _r is a, a _e is the effective area, and a _er of Isotropic antennas represents the effective area of the receiving antenna.

Here, the path loss is calculated according to the transmission and reception frequency and the distance. In the case of the satellite modem, the distance between each terminal operating on the ground and the satellite can be seen as fixed. Therefore, the path loss is determined only by the frequency, and when the operating frequency is fixed, the received power can be seen as a specific gain for the transmit power. This received power is represented as a spectrum that can be compared with the noise level in terms of power density, which makes it possible to detect the channel currently being received.

Through this, it is possible to calculate the energy per bit required for data modulation and demodulation from the received power, which can be determined by the following equation.

In Equation 2, E _b is energy per bit, N ₀ is noise power spectral density, R _d is Data Rate, N is power of noise, k is Boltzmann constant, T is absolute temperature, P _r0 is received power density, and W represents the bandwidth of the transmission signal.

Assuming that the received waveform has a bandwidth efficiency of 1, Equation 2 can be regarded as the ratio P _r0 / N ₀ of the received power density and the noise power density by canceling R _d and W. . Here, P _r0 / N ₀ being 0 dB means that the reception power density and the noise power density are at the same level, and that the transmission signal is concealed by noise.

For example, in the case of QPSK Uncoded Waveform, 10 ^-5 the E _b / N ₀ of about 10 dB is required BER satisfy (Bit Error Ratio). This received signal is 10 dB greater than the noise power density, resulting in a signal floor of 10 dB higher in the spectrum.

On the other hand, there is displayed a different result, if E _b / N ₀ can be is determined from the received power P _r, since the received power P _r is determined by the gain G _r of receiving antenna, G _r is changed. When the gain G _r of the receiving antenna is changed, for example, an antenna having a diameter of d1 and an antenna of d2 may have a relative gain difference by the G _antenna as shown in the following equation (however, the efficiency of the antenna is assumed to be the same).

In this case, the use of a large antenna can increase the reception power density by increasing the reception gain, and relatively increase the ability to detect the transmission channel. For example, when a 2m diameter antenna is used to detect a signal transmitted and received by a terminal using a 1m diameter antenna, a 6 dB reception gain occurs, resulting in a 6 dB higher signal floor on the spectrum.

② wireless modem

Wireless modems are similar in almost all respects to satellite modems, but include the assumption that there may be a device that can detect the signal band between the transmitter and receiver. Thus, in the case of satellite modems, the fact that the signal reach of all terminals assumed to be the same is no longer valid, and the spectrum of all signals sent and received between the transmitter and the receiver is better than that of the receiver by the hostile signal sensing / monitoring device. It can be seen that it can be detected.

(2) DS-SS analysis and design

The DS-SS spreads an input signal into a band signal corresponding to twice the chip rate, and a processing gain obtained by spreading is expressed by the following equation.

In Equation 4, G _p is a processing gain, W _sp is a spread band, R _s is a symbol rate, and R _sp is a code rate of a spread code.

DS-SS, in principle, spreads the output signal, thereby lowering the power density, and an application using the same becomes Code Division Multiple Access (DS-CDMA).

However, DS-CDMA is a method for multi-user access in general, which lowers power density and is not used to exclude detection / listening. Therefore, DS-CDMA is referred to in link budget analysis to implement LPI / LPD through spreading. It is desirable to control the power so that P _r0 / N ₀ is maintained at 0 dB.

① satellite modem

Considering the 10 dB E _b / N ₀ , Uncoded BPSK Waveform example mentioned earlier, the signal floor is 10 dB higher in the spectrum because the received signal is 10 dB greater than the noise power density. In this case, when the 10 dB spread through the DS-SS becomes equal to the reception noise level of the terminal and the received signal level, the device that cannot obtain a signal through proper despreading cannot detect the received signal level on the spectrum. .

For example, if the subscriber's data rate is 32 Kbps, spreading at a code rate of 320 Kcps produces an output band of 640 kHz, and in this process, a gain of 10 dB is gained, thereby concealing the transmission signal sufficiently. At this time, it is preferable that the transmission power is maintained at a level capable of concealing the transmission power by G _p between the transceivers.

As in the link budget analysis, when the G / T is improved by using an antenna larger than the antenna of the terminal, a larger processing gain may be required as shown in the following equation.

In Equation 5, A _e1 and A _e2 mean effective areas of different antennas. It can be seen from Equation 5 that the reception gain of the antenna is determined by the difference of the effective area of the receiving antenna.

For example, if the antenna diameter of the terminal is 2 m and the antenna used to detect / listen the transmission signal is 10 m, a reception gain of about 14 dB is added. To conceal this, a total of 24 dB of processing gain is required, so the required code rate is 8 Mcps and the spread band is 16 MHz.

Since it is difficult to determine the state of the sensing / sensing device in the actual operating environment, it is an effective strategy to actively and flexibly operate the processing gains according to the threat mode / operation mode.

② wireless modem

When using power control between transceivers, we can only assume that there is a hostile signal sensing / sensing device between the transmitter and the receiver because a hostile signal sensing / listening device that is outside the transceiver's reach cannot receive the transmitted signal. .

A path loss difference, such as the following equation, can occur from the assumption that there is only a difference in reach between the receiver and the hostile signal sensing / hearing device on the link budget.

In order to conceal the transmission signal from this, a processing gain such as the following equation is required.

In the case of wireless modems, the ideal detection position is half of the reach, given the fact that the reach is usually short (within 10 km) and that hostile signal sensing / sensing devices close to the transmitter or receiver can be exposed. have. In this case, a hostile signal sensing / sensing device can achieve 6 dB of reception gain compared to the receiver, so a processing gain of 6 dB must be added.

Like satellite modems, it is desirable to operate processing gains depending on the mode because it is difficult to know exactly where a hostile signal sensing / sensing device is located between a transmitter and a receiver.

The processing gain considering both the satellite modem and the wireless modem can be expressed as the following equation.

Processing gains considering other losses and amplitude variations that were not considered previously may be expressed as the following equation.

Here, L represents a loss in consideration of other loss and amplitude variation.

(3) control channel design

In the DS-CDMA modem, the control channel is used for various purposes such as network recognition, subscription, and release. However, the following description focuses on power control and processing control.

The channel design will depend on the presence of the operator. The case where the terminal is controlled by the operating station is shown in FIG.

In FIG. 2, a pilot channel is a channel used for power control of a transmitting terminal, and a synchronization channel is a channel for receiving a pilot channel. The synchronization channel internally receives a pilot channel to perform reception gain, frequency synchronization, and phase synchronization.

As in a commercial CDMA network, a paging channel is a channel for connecting a call to a receiving terminal, and an access channel is a channel used by a transmitting terminal to establish a call. A traffic channel (Outbound) is a channel for transmitting data used for an actual call, and a traffic channel (Inbound) corresponds to a channel for receiving data used for an actual call.

In the operating station controlled structure, one operating station and a plurality of terminals communicate with each other. In this case, the signal transmitted from the terminal to the operating station can control the terminal transmission signal power through the pilot channel (pilot channel) of the operating station, but the signal transmitted from the operating station to the terminal so that the reception power density is different according to the state of each terminal Therefore, it is difficult to implement LPI / LDI while the operating station exchanges control information with the terminal.

In particular, in the case of a wireless modem, the state of each terminal is significantly different according to a fading channel. On the other hand, in the case of satellite modems, the path loss due to weather conditions between terminals is less than 2 to 3 dB at frequencies below the SHF band, so that a limited LPI / LPD can be realized by using a link margin through processing gain. have.

The operating station and the terminal exchange the P / N code information of the counterpart terminal with the approximate transmit power level, available bandwidth, processing gain setting according to the threat node and operation mode determination through the control channel.

When the terminals are connected by the operating station, since the counterpart transmission signal power can be controlled through the control channel between the terminals, the complete LPI / LPD can be implemented. However, when multiple terminals use the same band in terminal-to-terminal communication, each terminal may have a different power control level according to a communication channel state, so an unexpected power density increase may occur and thus a signal may be detected. In order to prevent this, each terminal may determine a reception E _b / N ₀ and use a method of requesting control for coordination of the operating station when it is below a predetermined level.

In the channel structure without an operating station, a complete LPI / LPD may be implemented in a manner of controlling counterpart transmission signal power between terminals in the same manner as a communication state after connecting between terminals in the operating station controlled structure.

On the other hand, LPI / LPD-capable DS-CDMA modems can communicate under noise power density, so they can be applied in the form of cognitive radio that searches for empty frequencies.

The above description is merely illustrative of the technical idea of the present invention, and various modifications, changes, and substitutions may be made by those skilled in the art without departing from the essential characteristics of the present invention. will be. Accordingly, the embodiments disclosed in the present invention and the accompanying drawings are not intended to limit the technical spirit of the present invention but to describe the present invention, and the scope of the technical idea of the present invention is not limited by the embodiments and the accompanying drawings. . The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the present invention.

The present invention can be widely applied to the communication system using the DS-SS scheme, particularly in the field of low pittam of military communication.

1 is a block diagram showing elements of a low-pitched design of a direct sequence code division multiple access modem according to the present invention;

2 is a configuration diagram when the terminal is controlled by the operating station.

Claims (6)

In the low-detect design method of a direct sequence code division multiple access modem, A method for designing a low-pitched direct-mode code division multiple access modem according to claim 1, wherein the transmission power and the reception power are controlled so that the reception power density and the noise power density are the same. The method of claim 1, The received power (P _r ) is a low-detect design method of a direct sequence code division multiple access modem, characterized by the following equation.

Where EIRP = P _t × G _t , P _t is the transmit power, G _t is the transmit antenna gain, A _er is the effective area of the receive antenna, d is the transmit and receive distance, L _etc other losses, G _r is the gain of the receive antenna is the wavelength of the signal. The method of claim 2, The ratio of the energy per bit (E _b ) and the noise power spectral density (N ₀ ) required for data modulation and demodulation of the modem from the received power is represented by the following equation. Tom design method.

here,

where k is the Boltzmann constant, T is the absolute temperature, N is the power of the noise, W is the bandwidth of the transmitted signal, R _d is the data rate, and P _r0 is the received power density. The method of claim 3, wherein The processing gain (G _p ) obtained by the direct sequence spread spectrum in the modem is represented by the following equation, which controls the processing gain to control the received power density and the noise power density so that the transmission signal is concealed by noise. Low phantom design method of direct sequence code division multiple access modem, characterized in that.

Here, E _b is energy per bit, N ₀ is noise power spectral density, (E _b / N ₀ ) _required is the minimum E _b / N _{0 required} at the receiving terminal, A _e1 is the receiving antenna area of the receiving terminal, A _e2 Is the receiving antenna area of the host, d ₁ is the distance from the transmitting terminal to the receiving terminal, and d ₂ is the distance from the transmitting terminal to the host. 5. The method of claim 4, The modem has a control channel for transmission power control and processing gain control, when a plurality of terminals are controlled by the operating station, Continuously while maintaining the condition that at the time of the design of the control channel, a signal transmitting terminal for receiving at a receiving terminal to perform communication while maintaining the power of the transmitting terminal such that the minimum E _b / N ₀ with E _b / N _If it detects ₀ and determines that the detected E _b / N ₀ is less than the minimum required E _b / N ₀ , the operator requests control for coordination of the operating station, and the receiving station receives a processing request to increase the transmit power while simultaneously processing for low detection. A method of designing a low-pitched antenna for a direct sequence code division multiple access modem characterized by increasing gain (G _p ). The method of claim 1, The modem has a control channel for power control and processing gain control, when a plurality of terminals are connected to each other without an operating station, When the control channel is designed, the low-detect design method of the direct sequence code division multiple access modem, characterized in that to control the transmission signal power of the other terminal between the respective terminals.

Images