JPH10285229A - Transmitter adopting pi/4 shift qpsk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the capacity of a memory of the transmitter that adopts the π/4 shift QPSK, calculates a waveform of data after passing through a Nyquist filter in advance and stores it in the memory. SOLUTION: Assignment of data with respect to a symbol is conducted similarly to the case with a symbol of the 4-phase QPSK, and a mapping circuit 32 provides an output of position information of any of four symbols. The position information of transited symbols is latched in shift registers 6A, 6B and waveform data (I and Q components) in response to the information are read from ROMs 7A, 7B. The communication by the π/4 QPSK is conducted by increasing/decreasing the frequency of a carrier modulated by the I and Q components by fs/8 (fs is a symbol rate) with respect to a frequency fc of the carrier at demodulation. Since number of symbols used by the transmitter is 4, no many addresses of the ROMs are required and the required memory capacity is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a π / 4 shift QP
In the SK transmitting apparatus, waveform data when a symbol transitions, for example, after passing through a Nyquist characteristic filter, is calculated in advance and stored in a memory, and waveform data corresponding to an arrangement of the symbol transition is stored in a memory. The present invention relates to a technical field in which data is read from and transmitted.

[0002]

2. Description of the Related Art One of modulation techniques in digital mobile communication is QPSK (Quadrature Phase).
e Shift Keying). This is located equidistant from the coordinate center on the complex plane as shown in FIG.
It is possible to take four symbols (signal points) in which adjacent ones have a phase difference of π / 2, and 2-bit data is assigned to each symbol. As a technology that takes QPSK one step further, there is a method called π / 4 shift QPSK. In this method, as shown in FIG. 5, every time one symbol corresponding to data is selected, each symbol is converted to π / 4 and rotate the phase difference between symbols ± 45.
゜, ± 135 °. In FIG. 5, the circles and crosses indicate the symbols before and after rotation, respectively, and show how the symbol (11) is moved to the symbol to which the next data is allocated.

In this type of communication system, it is necessary to use a Nyquist characteristic filter in order to eliminate intersymbol interference, secure an occupied bandwidth, and limit adjacent (or next adjacent) leakage power. And especially PDC (Personal Digital C)
cellular, PHS (Personal Han)
When low power consumption is required as in the case of dy Phone System, or in order to handle high-speed data such as PHS, a DSP (Digital Signal) is used.
In the case where the calculation cannot be performed in time, the waveform after passing through the Nyquist filter is calculated in advance without using the DSP, and the digital value of the result is stored in the RO.
M (Read Only Memory), and outputs the output of the ROM sequentially to D / A (Digital / Memory).
(Analog) converter.

The data stored in the ROM, the response waveform of the Nyquist filter, and the configuration of the transmission circuit will be described below. FIG. 6 shows the response waveform of the Nyquist filter, and shows how the symbols do not change (there is no intersymbol interference) even if the waveforms are combined for only two symbols for easy understanding. However, the Nyquist filter has an infinitely long response characteristic in theory, so that it is necessary to abort the calculation by applying a window function in order to limit the response time. If the length of the window is too short, the adjacent leakage power and the symbol point are adversely affected. For example, the calculation is terminated at a total of 11 symbols of the past 5 symbols of interest and the following 5 symbols.

Here, a case is considered where 2-bit data to be transmitted moves from symbol D to point E on the complex plane shown in FIG. The data to be stored in ROM is
7 is a movement locus of data from point D to point E in FIG.
Specifically, it is eight data (interpolated data) corresponding to waveforms at minute intervals separated by a mark between points D and E. This movement trajectory is not determined only by the points D and E, but changes depending on which symbol has passed in the past before passing the point D and which symbol passes after the point E. In the example shown in the figure, the case of moving from point A to point D to point E to point H is shown. For example, if the symbol immediately before point D is other than point A, the movement locus changes.

Therefore, the locus of movement from point D to point E, that is, the response waveform of the Nyquist filter is theoretically the past,
Although it cannot be expressed without considering all future symbols, in practice, as described above, the response time is limited and E
Response waveforms corresponding to a total of 11 symbols 5 symbols before and 5 symbols after the point are stored in the ROM as data. The interpolation data between the points D and E is shown in FIG.
Corresponds to the waveform data of the minute section delimited by the triangle on the composite waveform.

[0007] Passing of RO of data to be transmitted and RO
FIG. 8 shows the relationship with the reading of the data (trace data of the waveform) in M. In this example, the data to be transmitted is B → C
The state of reading the locus data of the waveform from the ROM when moving from G → A → D → E → H → B → E → F → G and moving to D → E located at the center of the transition is shown. ing.
In FIG. 8, reference numeral 1 denotes a shift register, and corresponding symbols (to be precise, symbol position information) are sequentially transmitted as the symbols move. The number of symbols arranged in the shift register 1 is, for example, eleven. In the above-described symbol movement, the address when reading the locus data of the waveform at the time of moving from the point D of interest to the point E from the ROM 2 is set. , Shift register 1.

[0008] In the 1 / 4π shift QPSK, the transmission itself is quaternary, but since the symbol arrangement is apparently eight phases, the number of bits for specifying the symbol position is three.
Therefore, the number of bits of the address is (number of bits arranged in the shift register 1) × (number of bits specifying the position of the symbol) = 11 × 3. The next symbol is taken into the shift register 1 at a predetermined timing, the arrangement of the symbols stored so far moves, and the oldest symbol, that is, the symbol four symbols before the point E, is pushed out and disappears. In this example, the response time of the Nyquist filter is limited. In this example, the locus data of the waveform relating to the movement from point D to point E in the temporal arrangement of the 11 symbols is read from the ROM. Will be read. ROM for moving from point D to point E
The trajectory data of the waveforms in the above is the above-described interpolation data between the points D and E on the response waveform.

FIG. 9 shows how data is stored in the ROM. In accordance with an address which is the content of the shift register,
Data for specifying a movement locus corresponding to the movement of the symbol of interest, for example, eight pieces of interpolation data are stored. That is, in this case, eight times oversampling is performed, and when an address is output from the shift register, eight data corresponding to this address are sequentially read out by the oversampling clock and sent to the D / A converter as described later. After 8 clocks, the position information of the next symbol enters the shift register and the position information of the symbol 5 symbols before the symbol of interest is pushed out and disappears. Actually, the interpolation data in the ROM is an in-phase component (I component) and a quadrature component (Q component) for specifying a waveform.

FIG. 10 shows the overall configuration of a transmission circuit using such a ROM filter. Numeral 3 denotes serial data (a quantized binary signal sequence) corresponding to data to be transmitted, for example, an audio signal. This is a serial / parallel converter for outputting a 2-bit parallel signal divided into bits. Reference numeral 3 denotes a differential mapping circuit for assigning which of the symbols shown in FIG. 5 the 2-bit parallel signal corresponds to. As described above, in the π / 4 shift QPSK, the symbol arrangement is apparently eight-phase, so that the position information for specifying the symbol position is transmitted from the differential mapping circuit 31 to the first and second positions as 3-bit symbol data. The data is sent to the shift registers 1A and 1B.

In the shift registers 1A and 1B, as described above, symbol position information is sequentially taken in at a predetermined timing, and, for example, eleven symbols are arranged, and the corresponding bit signals are the first and second symbols as addresses.
Are output to the ROMs 2A and 2B. These ROMs 2A,
2B outputs the I and Q components of the waveform data corresponding to the transition of the symbol of interest, and the I component is the first D
/ A converter 41A and a first low-pass filter (LP
F) sent to the first amplitude modulator 5A via 42A,
The component is sent to the second amplitude modulator 5B via the second D / A converter 41B and the second low-pass filter 42B.

On the other hand, the carrier wave from the oscillator 51 operating based on the clock output from the clock generator 50 is directly input to the first amplitude modulator 5A and amplitude-modulated by the I component from the low-pass filter 42A. The carrier is phase-shifted by π / 2 by the π / 2 phase shifter 52 and input to the second amplitude modulator 5B, where
The amplitude is modulated by the Q component from B. Amplitude modulator 5
The outputs of A and 5B are combined by a combining circuit 53, and the combined wave is transmitted from an antenna (not shown).

[0013]

If the length of the window for the response waveform of the Nyquist filter is, for example, 11 symbols as described above, since the symbol position information is 3 bits, 11 × 3 = 33 bits. There is a problem that a ROM corresponding to the address is required, the storage capacity of the ROM becomes enormous, the device becomes large, and the cost is high.

An object of the present invention is to reduce the memory capacity of a transmitting apparatus that calculates a waveform after passing through a Nyquist filter in advance using π / 4 shifted QPSK and stores the result in a memory. .

[0015]

According to the present invention, in a transmitting apparatus of π / 4 shift QPSK, adjacent symbols are located at an equal distance from a coordinate center on a complex plane, and adjacent symbols have a phase difference of π / 2. In addition to determining four symbols, a binary signal sequence, which is data to be transmitted, is divided into two bits, and four types of data determined by these two bits are assigned to the four symbols, respectively. A signal processing unit that outputs the position information of the symbol corresponding to the 2-bit data as a digital signal, and the position information of the symbol from the signal processing unit is sequentially fetched at a predetermined timing, and the symbol of interest and its A shift register in which an array of position information of preceding and succeeding symbols is stored while being shifted, and a pre-calculated waveform data after passing through a filter having a predetermined characteristic when a symbol changes. The in-phase component and the quadrature component are stored in association with the transition of the symbol, and the digital signal corresponding to the array of the positional information of the symbol output from the shift register and stored in the shift register is used as an address. A memory from which in-phase and quadrature components of data are read, and a frequency of a carrier wave for demodulation is represented by f
c, if the symbol rate is fs, the frequency is fc ± f
s / 8, a carrier output unit for outputting the first and second carriers having a phase difference of π / 2 from each other, and the first and second carriers read out from the memory by analog signals corresponding to in-phase and quadrature components. First and second amplitude modulators for amplitude-modulating the first and second carrier waves, respectively,
And a synthesizing unit for synthesizing the modulation output from the amplitude modulation unit and outputting a synthesized wave.

Here, the arrangement of the position information of the symbol of interest and the symbols before and after it, which is stored in the shift register, means that when a waveform corresponding to a certain symbol P is to be output, it is necessary to reach the symbol. This means the sequence of the transition of the positional information of the symbol including the past symbol that has transited and the future symbol after passing through the symbol P.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing the configuration of a transmitting apparatus according to an embodiment of the present invention, an outline of this embodiment will be described with reference to FIG. The eight symbols (signal points) indicated by A1 to A4 and B1 to B4 on the complex plane have a phase difference of 45 degrees between adjacent symbols, and the conventional π /
In the case of 4-shift QPSK, the group of A1 to A4 and B
Groups 1 to B4 are to be subjected to data allocation (mapping) alternately at a timing according to the symbol rate.

This embodiment employs a π / 4 shift QPSK
Required 8 position information because it apparently required 8 symbols, but realized a π / 4 shift QPSK communication method using only the position information of 4 symbols used in 4-phase QPSK. Thus, the number of ROM addresses is reduced, and an increase in memory capacity is suppressed.

When the data changes from (10) to (11), if the carrier is rotating counterclockwise in FIG. 1 in the case of the conventional π / 4 shift QPSK, the symbol corresponding to the data is A4 From A4 to A2, but in this example, it is apparently changed from A4 to A1, that is, the data (11) is mapped as A1, and the position information of A1 is output to the shift register. However, since this is the same as the conventional four-phase QPSK, the carrier is advanced by π / 4. To advance the carrier means to advance the carrier when demodulating in the receiving device,
The frequency of the carrier wave at the time of demodulation is fc, and the symbol rate is fs
Then, the carrier frequency used in the transmission device is f
It becomes a value (fc + fs / 8) obtained by adding s / 8.

Since the transition from A4 to A1 takes one symbol transition time (1 / fs), fc is advanced as described above in accordance with this time, so that A2 becomes B2.
And the communication is performed. The waveform data stored in the ROM corresponding to this symbol transition is interpolation data between A1 and A4.

In this example, the data is described as moving counterclockwise on the complex plane. In the case of clockwise rotation, A1 is assigned after A4, and the carrier is delayed by π / 4. As a result, it is the same as the case where the communication has been performed from A4 to B1. That is, in this case, the frequency of the carrier used in the transmitting device is fc−fs / 8. As described above, the present invention is characterized in that symbols are assigned in the same manner as in 4-phase QPSK, and the carrier frequency is shifted by fs / 8 with respect to fc.

Next, a circuit configuration for realizing such a method will be described with reference to FIG. The same parts as those in FIG. 10 are denoted by the same reference numerals. The serial signal according to the data to be transmitted is converted into a 2-bit parallel signal by the serial / parallel converter 3, and the mapping circuit 32 outputs the position information of the symbol according to the parallel signal. The mapping performed here (allocating the parallel signal to the symbol and outputting the position information) is the same as the four-phase QPSK, so the differential mapping performed by π / 4 shift QPSK is not performed.

The mapping circuit 32 outputs the position information of the assigned symbol. This position information is a 2-bit signal because there are four symbols,
And the second shift registers 6A and 6B sequentially take in the 2-bit position information. For example, the position information of 11 symbols including five symbols before and after a symbol to be transmitted (symbol of interest). Is stored.

In the first and second ROMs 7A and 7B,
As described in the section of the related art, the response waveform data of the Nyquist filter corresponding to the transition of 11 symbols including five symbols before and after each symbol to be transmitted is stored. This waveform data
For example, to specify the movement trajectory of data connecting the shift register to be transmitted and the symbol immediately before the shift register, for example, 8
Pieces of pre-calculated interpolation data, R shown in FIG.
The same as the data in the OMs 2A and 2B, the first ROM
7A stores data of the I component, and the second ROM 7B stores data of the Q component. However, FIG.
Although the number of address lines from the shift register 1A (1B) at 0 is 3 × 11, in this example, since the position information of the symbol is specified by 2 bits, the shift register 6A
The number of address lines from (6B) is 2 × 11 and RO
The number of bits of the address of the data in M7A (7B) is 2 ×
It becomes 11.

In the shift registers 6A and 6B, the latest symbol position information is fetched by the clock from the clock generator 50, the oldest symbol position information is discarded, and an array of 11 symbol position information is used as an address. The I and Q components of the waveform data are read from the ROMs 7A and 7B, respectively. The clock defines the symbol rate fs, and the pulse interval of the clock is 1 / fs second. When an address is given to the ROM 7A (7B), for example, eight pieces of interpolation data are sequentially read by the oversampling clock, and the D / A converter 4
1A (41B) and low-pass filter 42A (42B)
Is input to the amplitude modulator 5A (5B).

On the other hand, the carrier output from the oscillator 51 is applied to the phase locked loop (PLL) circuit 54 to generate a fs / 4 signal.
Only can be advanced. That is, the frequency is fc + fs / 4. Note that fc is the transmission carrier frequency as described above, and is also the frequency when demodulated by the receiving device. Cos 及 び 2π is applied to the first and second amplitude modulators 5A and 5B.
(Fc + fs / 8) t} and sin {2π (fc + fs
/ 8} is input, and the low-pass filter 42A,
The modulated signals are modulated by the I component and the Q component output from 42B, respectively, and the modulated outputs are combined by the combining unit 53. In this case, the symbol is counterclockwise in FIG. 1, and the correspondence between the position coordinates of the symbol and the data assigned to the symbol is shifted in the memory on the receiving device side so as to be counterclockwise.

Here, when the transition of the symbols of FIG. 7 exemplarily described in the section of the prior art is applied to this example, it becomes as shown in FIG. That is, the data is (10) → (01) →
When the state changes from (11) to (00), the conventional transmitting apparatus maps as A4 → B3 → A2 → B1 as shown by the dotted line. In this example, the symbols assigned by the mapping circuit 32 are as shown by dashed lines. A4 → A2 → A2 → A4
Becomes On the receiving side, by using the conventional π / 4 shift QPSK receiving apparatus as it is, (10) → (01)
→ (11) → (00) data is demodulated.

As described above, according to the present embodiment, π /
If 4-shift QPSK communication can be realized, and data is transmitted using four symbols, the position information of the symbols will be 2 bits, and if the number of symbols stored in the shift register is 11 as described above, ROM7
The address taken into A and 7B is 11 × 2 bits. Therefore, the number of bits of the address is reduced by one as compared with the case where data is transmitted by eight symbols.
The required memory capacity for 7B is halved.

[0029]

According to the present invention, π / 4 shift QPSK
In the transmitting apparatus that calculates the waveform after passing through the Nyquist filter in advance and stores the result in the memory, the memory capacity can be reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram conceptually explaining the operation of an embodiment of the present invention on a complex plane.

FIG. 2 is a configuration diagram illustrating a circuit configuration according to the embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a comparison of mapping between an embodiment of the present invention and a conventional method.

FIG. 4 is an explanatory diagram showing QPSK symbols.

FIG. 5 is an explanatory diagram showing symbols of π / 4 shift QPSK.

FIG. 6 is a waveform diagram showing a response waveform after passing through a Nyquist filter.

FIG. 7 is an explanatory diagram showing an example of mapping performed using conventional π / 4 shift QPSK.

FIG. 8 is an explanatory diagram showing how an address is output from a shift register and data is read from a ROM.

FIG. 9 is an explanatory diagram conceptually showing data stored in a ROM.

FIG. 10 is a configuration diagram showing a circuit configuration of a transmission device used for a conventional π / 4 shift QPSK.

[Explanation of symbols]

 Reference Signs List 3 serial / parallel converter 32 mapping circuit 41A, 41B D / A converter 42A, 42B low-pass filter 5A, 5B amplitude modulator 50 clock generator 51 oscillator 52 phase shifter 53 synthesis circuit 54 PLL circuit 6A, 6B shift register 7A , 7B ROM

Claims (1)

[Claims] 1. A phase difference between adjacent symbols located at an equal distance from a coordinate center on a complex plane and π / 2 between adjacent symbols.
In addition to determining the number of symbols, a binary signal sequence, which is data to be transmitted, is divided into two bits, and four types of data determined by these two bits are assigned to the four symbols, respectively. A signal processing unit for outputting the position information of the symbol corresponding to the bit data as a digital signal; the position information of the symbol from the signal processing unit is sequentially fetched at a predetermined timing; A shift register in which the array of the positional information of the symbol is stored while being shifted; and an in-phase component and a quadrature component of the pre-calculated waveform data after passing through a filter having a predetermined characteristic when the symbol changes. And is stored in association with the transition of the symbol, and corresponds to an array of the positional information of the symbols output from the shift register and stored in the shift register. A digital signal as an address that, the waveform data - a memory for data in-phase component and quadrature component are read, fc the frequency of the carrier wave for demodulation, Shinborure - bets fs
Then, the frequency is fc ± fs / 8 and π
A carrier output unit for outputting the first and second carriers out of phase with each other; and amplitude modulation of the first and second carriers with analog signals corresponding to the in-phase and quadrature components read from the memory, respectively. Π / 4 characterized by comprising: first and second amplitude modulating sections, and a synthesizing section for synthesizing modulation outputs from the first and second amplitude modulating sections and outputting a synthesized wave. Transmission device for shift QPSK.