JP2002512486A - Method and structure for modulating a signal - Google Patents

Abstract

SUMMARY OF THE INVENTION The present invention uses M-level continuous phase modulation where M is the value (2, 4, 8,...) And the symbol to be transmitted consists of two or more bits. Method and arrangement for modulating a signal to be transmitted. The structure comprises a coder (104) and a frequency modulator (120). To allow for flexible transmission of high data rates in a narrow frequency band, the coder (104) encodes each symbol to be transmitted into a separate binary sequence to provide an M-level PSK constellation. Is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

【Technical field】

The present invention relates to a signal modulation method that uses continuous phase modulation and includes coding and frequency modulation of the signal to be transmitted.

[0002]

[Background Art]

The modulation method used for the transmission path becomes an important parameter when a new data transmission system is developed. Due to the loss of the transmission path and the limited capacity of the transmission path, the data symbols to be transferred cannot be transmitted via the transmission path, and in order to obtain good transmission path capacity and transmission quality, The symbols must be modulated using an appropriate method.

[0003] The bandwidth required for transmission is an important factor, especially in wireless systems. The goal is to obtain the maximum transmission capacity while using a narrow bandwidth. On the other hand, it is also an object to make the transmitter and the receiver as easy and effective as possible. In wireless systems, the goal is to use a modulation method with a constant envelope, since C-class amplification solutions can generally be used. C-class amplifiers are simple in structure and efficient. This is especially true as far as the power consumption of the terminal is concerned.

[0004] There are a number of known modulation methods with a constant envelope, with a minimum shift keying M
Includes SK, Gaussian Minimum Shift Keying GMSK, Tamed Frequency Modulation TFM and Continuous Phase Modulation CPM. The GMSK method is used for GSM cellular radio systems. It has a narrow frequency spectrum and high performance, but the data transmission rate is not very high. Coded CPM methods typically have a narrow frequency spectrum and high performance, allowing for high data rates. However, these methods have not been used in known systems because of the complexity of the required device structure.

[0005]

DISCLOSURE OF THE INVENTION

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for transmitting high data rates in a narrow frequency band without the need for complicated devices, and an apparatus for implementing the method. This uses M-level continuous phase modulation where M is the value (2, 4, 8,...), The symbol to be transmitted consists of two or more bits, and the code of the signal to be transmitted This is achieved by signal modulation methods, including modulation and frequency modulation. The method of the invention is characterized in that each symbol to be transmitted is coded into a separate binary sequence and these sequences are transmitted in a binary modulated state, forming an M-level PSK constellation.

Further, the present invention provides that M is a value (2, 4, 8,...) And the symbol to be transmitted is transmitted by M-level continuous phase modulation consisting of two or more bits A structure for modulating a signal, the structure comprising a coder and a frequency modulator. The arrangement of the invention is characterized in that the coder is arranged to code each symbol to be transmitted into a separate binary sequence to form an M-level PSK constellation. Preferred embodiments of the invention are set out in the dependent claims.

Therefore, the basic idea of the present invention is to provide a PSK constellation or state diagram by means of binary modulation. The M level symbols to be transmitted are:
The sequences are coded into binary symbol sequences, which are binary modulated. The methods and arrangements of the present invention provide a number of advantages. In the present invention, continuous phase modulation can be implemented, which makes it possible to use the frequency spectrum efficiently and to make the structure of the receiver relatively simple, for example, as compared to the coded CPM method. it can. The capacity of the modulation method according to the invention is good, especially when the signal-to-noise ratio is not very good.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. First, a preferred embodiment of the structure according to the present invention will be described with reference to the block diagram shown in FIG. This figure shows the structure of the terminal of the wireless system according to the present invention. Of course, to function, the device to be implemented must include elements other than those shown in FIG. 1, as will be apparent to those skilled in the art. However, for simplicity, illustration and description of these elements has been omitted.

For the sake of simplicity, an example will be described here in which a symbol to be transmitted includes two bits and is represented by the following equation: Thus, the desired state diagram consists of four points.

(Equation 1) This arrangement comprises a data source 1 which generates a digital signal 102 to be transmitted.
00 is provided. This data source is, for example, a microphone connected to a speech coder, so that the signal to be transmitted is a speech in digital form. Other data sources include a computer or a modem. The data bits are conveyed in parallel, i.e., two at a time, to a coder 104, which performs coding in accordance with the present invention such that the two-bit symbols to be transmitted are represented in a binary symbol sequence. . This encoding is described in detail below.

In a preferred embodiment of the present invention, the binary symbols thus obtained are conveyed to a filter 108, which filters the signal based on a desired spectral pattern. Preferably, a transfer function that follows a Gaussian distribution can be selected as the transfer function of the filter. Therefore, the transfer function can be defined by the following equation.

(Equation 2)

When using a Gaussian distribution, the function h (t) can be chosen as follows.

(Equation 3) Where B is the 3 dB bandwidth of the filter with impulse response h (t),
Therefore, T is the length of the data symbol.

The signal thus obtained is further conveyed to a multiplier 110 and multiplied by the coefficient h of the equation, ie, １ ／. The signal thus obtained is further conveyed to a frequency modulator 120, which performs a conventional frequency modulation, for example by means of a voltage-controlled or numerically controlled oscillator. The phase of the modulated signal is represented by the following equation.

(Equation 4) Here, α _i is 1-2 * bs, and a value of −1 or 1 is obtained. The term bs includes binary sequence bits. The formula and form of the binary sequence are described below. The time reference t 'is the starting point of the data to be transmitted.

[0013] The modulated signal is further conveyed to a high frequency section 122, which can be implemented according to known techniques. An advantage of the present invention is that, for example, the high frequency part of a GSM system can be used as the high frequency part. The modulated RF signal can be represented by the following equation:

(Equation 5) Where E _c is the energy of the modulation symbol, f ₀ is the center frequency, and ψ ₀
Is a random phase that is constant during one burst period. Therefore, a C-class amplifier can be used in the high frequency part, which is a significant effect, especially as far as portable terminals are concerned. From the high frequency portion, the signal is carried to antenna 124. As a transfer function of the filter 108, for example, a root raised cosine
ine) A power cosine function that follows the RRC function can also be advantageously selected.

FIG. 2 shows a second embodiment of the present invention. This embodiment has no filter after the coder. In other respects, this solution is the same as the above solution. FIG. 3 shows a third alternative embodiment of the present invention. In this alternative, the voltage controlled oscillator of FIG. 1 is replaced by an integrator 300 and a phase modulator 302, from which the signal is carried to a higher frequency portion. In other respects, this solution is similar to that described for FIG.

Next, the encoding of the present invention executed in the coder 104 will be described in detail. In the solution of the invention, the coding is performed such that the symbol to be transmitted consisting of a number of bits is represented by a binary symbol sequence. In this example, M = 4
The case will be described. Here, the symbol to be transmitted consists of 2 bits, so this symbol can have four possible values, eg {0, 1, 2, 3}, and the corresponding bit pair is eg {00, 01, 10, 11}.
Therefore, these four values should be transmitted by binary symbols. In the solution of the invention, the encoding is performed such that each two-bit symbol is represented by a sequence of three binary symbols. The coder 104 performs this variant, which can also be performed, for example, on a computer.

FIG. 4 a illustrates a possible state diagram of the modulation method of the invention when M = 4. Here, because of the modulation method with a constant amplitude, the transition of the state diagram forms a unit circle. The origin and end point of these transitions are indicated by points on the unit circle. These points are regularly spaced apart from each other by a phase difference of π / 2. There are four points, one for each possible symbol {00, 01, 10, 11}. The receiver is directed to interpreting the transition from one state to another from the received signal. For example, the transition from state 00 to state 01 can be performed by transition 400, and the transition to state 11 can be performed by transition 402. In known modulation methods, these transitions are performed in one step, as shown in FIG. 4a. The sensitivity of the modulation method to errors is described by the Euclidean distance between adjacent points.

In the solution of the invention, the symbol to be transmitted consisting of two or more bits is represented by a binary symbol sequence. When M = 4, the number of bits is 2,
The length of the binary symbol sequence representing one symbol is 3 bits. In the state diagram, this means that each state-to-state transition, for example, the 00 → 01 transition, is performed using three transitions, as shown in FIG. The transition to is made by three transitions 404, 406 and 408.

From each of the four points in the state diagram, a transition from one point to another can be made by three transitions, a 3-bit long binary symbol sequence corresponding to these transition forms. Of course, there are many combinations of transitions, for example, shown in FIG. 4c. In FIG. 4c, the transition from state 00 to state 01 is effected by three different transitions 410, 412, 414. Despite the same origin and end point, the path resulting from the transition is different from that shown in FIG. 4b. A different binary symbol sequence corresponds to the transition in FIG. 4c, not the transition in FIG. 4b. To clarify the encoding, a specific binary symbol sequence must be selected for each state-to-state transition.

Here, when a signal modulated according to the present invention is received, the receiver multiplies the received signal between symbols by one of the following values.

(Equation 6) Here, k = 0, 1, 2,.... This rotates the state diagram by half a symbol interval (π / 4). This rotation is performed in either a counterclockwise or clockwise direction based on the sign of the exponent. In the above example, bit "1" is coded to the value "-1", causing a counterclockwise transition. When considering the above rotation by the next multiplier, the rotation in the state diagram is always clockwise.

(Equation 7) The binary combination "000" keeps the constellation stationary, and correspondingly "111" causes 3/4 rotation on the circle. Thus, the exponent multiplier makes the constellation stationary or moving in one direction, but not in both directions during one state transition.

The transition of the state diagram of the modulation method according to the invention can be represented as a three-dimensional path based on FIG. Two examples of three transition paths are shown when a transition from one state diagram point to another occurs. The first path 508 is shown in dashed lines and corresponds to the path shown in FIG. 4b. Second
The path 510 shows the transition from the point 00 to the point 11 and is indicated by a chain line. In the initial state 500, the path diverges and steps 502 and 50
After four, the process ends at a different point in step 506. Four different paths originate from each point (state) and end at four different points. Thus, the sensitivity of the modulation method of the present invention to transmission errors is:
It is not indicated by the Euclidean distance between points, but is indicated by the Euclidean distance between routes.

In the method of the present invention, the encoding can be performed by a computer. FIG.
Block diagram illustrates a possible embodiment of the coder of the present invention. The parallel mode bits 102 of the M-level symbol to be coded are provided as inputs to the coder. Each bit is sent directly to the coder and a delay portion 600-604
Is delayed. In general, the number of symbol bits is an M-logarithm with a base of 2, ie log ₂ (M). Usually, M is 4, 8, 16,. Coder 606
Comprises a state machine having a sequence of M binary symbols, each of which has a length
M-1 and one is selected for output based on the bits at the input. The output can be implemented in parallel mode, so the output has M-1 lines 608, which are converted to serial mode by reading them sequentially with switch 601. Of course, conversion to serial mode can also be implemented in other known ways. In the above example, M = 4, where the number of lines 102 is two and the number of output lines 608 is three. Correspondingly, if M = 8, the number of lines 102 is three and the number of output lines 608 is seven.

Preferably, the coder of the present invention can be implemented in software by using a signal processor or a general-purpose processor. An example of a possible binary symbol sequence for different state-to-state transitions is described. The example shown here shows the case where M = 4. As a result, the symbol to be transmitted is
It consists of two bits, so this symbol has four possible values, for example, $ 0,
1, 2, 3}, and the corresponding bit pair is, for example, {0
0, 01, 10, 11}. The following table shows the binary symbol sequence corresponding to each transition. There are a total of four different sequences, and the transition from one point to another can be made in any one of the four sequences. In the example shown here, the sequence is S ₁ = {000, 010, 101, 111}. The right column of the table shows the sequence index.

Table 1 transition sequence S ₁ 0 → 0000 S ₁ (1) 0 → 1 111 S ₁ (4) 0 → 2 010 S ₁ (2) 0 → 3 101 S ₁ (3) 1 → 0 010 S ₁ (2) 1 → 1000 S ₁ (1) 1 → 2 101 S ₁ (3) 1 → 3 111 S ₁ (4) 2 → 0 111 S ₁ (4) 2 → 1 101 S ₁ (3) 2 → 2000 S ₁ (1) 2 → 3 010 S ₁ (2) 3 → 0 101 S ₁ (3) 3 → 1 010 S ₁ (2) 3 → 2 111 S ₁ (4) 3 → 3000 S ₁ (1)

Another form for the sequence is S ₂ = {000,100,011,111}
It is. This sequence should preferably be selected such that the number of "1" bits is increased by one when a transition from one sequence to another occurs. Note that the rotation of the state diagram by the following values at the receiver is taken into account in the above sequence:

(Equation 8) Here, k = 0, 1, 2,.... Thus, the coding determines the current state and the state in which the transition is taking place, after which the binary sequence corresponding to the obtained transition is searched in the table, and then the binary sequence is output to the coder output. Is set to be set.

FIG. 7 shows a bit stream after encoding. This bit stream is a binary sequence 70
Consisting of groups from 0 to 704, each binary sequence corresponds to one symbol to be transmitted. These binary sequences are transmitted sequentially in time slots or frames based on the multiple access method used. The solution of the invention is preferably applicable to any digital data transfer system, for example cellular radio systems, subscriber terminal equipment and base stations. Although the present invention has been described in detail with reference to the accompanying drawings, the present invention is not limited thereto, and various changes may be made within the scope of the present invention described in the claims. it is obvious.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of a structure according to the present invention.

FIG. 2 is a block diagram showing a second embodiment of the structure according to the present invention.

FIG. 3 is a block diagram showing a third embodiment of the structure according to the present invention.

FIG. 4a shows an example of a PSK state diagram.

FIG. 4b shows an example of a PSK state diagram.

FIG. 4c is a diagram showing an example of a PSK state diagram.

FIG. 5 shows the state-to-state transition of the state diagram of the method according to the invention.

FIG. 6 shows an embodiment of a coder according to the invention.

FIG. 7 is a diagram showing an example of a coded bit stream.

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Claims (11)

[Claims] 1. A signal using M-level continuous phase modulation, where M is the value (2, 4, 8,...), Wherein the symbol to be transmitted consists of two or more bits, and In the signal modulation method, including the coding and frequency modulation, each symbol to be transmitted is coded into a separate binary sequence, and these sequences are transmitted in binary modulation to form an M level PSK constellation. A method comprising: 2. The method of claim 1, wherein each symbol to be transmitted is represented by a predetermined serial mode binary sequence. 3. The length of each binary sequence representing a symbol to be transmitted is M-
2. The method according to claim 1, wherein one bit is used. 4. The method of claim 2, wherein each transition from one point of the PSK constellation to another is performed by a number of different transitions determined by binary sequence bits. 5. The method of claim 4, wherein the point-to-point transition is performed by a M-1 transition. 6. The method of claim 1, wherein the binary sequence is selected such that the number of “1” bits is increased by one when a transition from one sequence to another occurs. 7. M is a value (2, 4, 8,...) And the symbol to be transmitted modulates the signal to be transmitted by M-level continuous phase modulation consisting of two or more bits. In an arrangement, comprising a coder (104) and a frequency modulator (120), the coder (104) encodes each symbol to be transmitted into a separate binary sequence and generates an M level A signal modulation structure, wherein the signal modulation structure is configured to form a PSK constellation. 8. The coder (104) identifies each symbol to be transmitted with a length of M-
The structure of claim 7, wherein the structure is configured to code into a one bit binary sequence. 9. The arrangement according to claim 7, wherein said frequency modulator is implemented by a voltage controlled oscillator. 10. The arrangement of claim 7, comprising a filter (108) operatively connected to an output of said coder. 11. An arrangement according to claim 7, wherein said coder (104) is implemented by software as processor software.