JP2000041073A - Offset qpsk modem and communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an offset QPSK communication system capable of providing a satisfactory bit error rate(BER) by enabling satisfactory communication even under phasing. SOLUTION: A pilot symbol(PS) inserted in a frame by a modulator is guided through a switch 116 to a phasing distortion estimating part 117 after frame synchronization is detected by a synchronizing detecting part 115 of a receiver. At the distortion estimating part, a distortion vector is estimated based on a received vector and a PS vector, and based on this estimated distortion vector, at a phasing distortion compensating part 118, the influence of phasing upon a data symbol is compensated. The data symbol, for which the influence of phasing is compensated, is decoded by a decoder 119.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an offset QPSK.
The present invention relates to a modem and a communication system, and more particularly to an offset QPSK modem and a communication system capable of compensating fading distortion.

[0002]

2. Description of the Related Art In recent years, demand for mobile communication on land has increased and frequency resources have become scarce. Therefore, various technologies have been developed for effective use of frequency resources. That is, for a point-to-point communication system having a large number of mobile terminals per unit area such as a mobile phone system, the coverage zone of the base station may be small,
Practical use of an efficient multiplex communication system such as CDMA is in progress.

However, in a business radio system such as a fire radio or a taxi radio, the number of mobile terminals per unit area is small and point-to-multipoint communication is performed.
In addition, it is necessary to increase the cover zone of the base station. Also, in a commercial communication system, an FDMA (Frequequent) is required in order to ensure a high communication quality even when a received signal level is low because it is necessary to secure a wide service area.
Multiplexing by ncy Division Multiple Access) is used. In FDMA, band narrowing is being promoted in order to increase the density in the frequency axis direction.

On the other hand, since communication information has become multimedia, communication signals have been unified from conventional analog signals to digital signals, and digital modulation and demodulation systems have become mainstream in conjunction with the aforementioned demand for narrower bandwidths. It is becoming. At present, π / 4 shift QPSK is the mainstream in land mobile communication systems in Japan.

[0005] The π / 4 shift QPSK has the same transmission efficiency as QPSK, and also has a feature that the linear amplification range of the power amplifier can be narrow because the fluctuation of the envelope is small and the instantaneous power does not become zero. FIG. 1 shows a vector locus of π / 4 shift QPSK, and (1) shows a PDC (Pe
rsonal Digital Cellular) method 50% transmission and reception used in mobile phones or wireless communication systems for public business
This is a vector trajectory of the transmission signal when the roll-off rate, which is a parameter indicating the distribution and low-pass filter cutoff characteristics, is 0.5, and the instantaneous minimum power (represented by the radius of the center hole) is about 12 It is only a decibel lower.

However, if the cutoff characteristic of the low-pass filter is made sharp (for example, the roll-off ratio is set to 0.2) to narrow the band, the instantaneous minimum power becomes almost zero as shown in (2). Become. That is, π / 4 shift Q
In a PSK system, if the roll-off ratio is reduced to narrow the band, the instantaneous minimum power becomes almost zero level. Therefore, it is necessary to extend the linear amplification range of the power amplifier, and take advantage of the π / 4 shift QPSK. Can not. When a power amplifier with a narrow linear amplification range is used, distortion generated in the power amplification stage increases, and unnecessary radiation that adversely affects adjacent channels increases.

FIG. 2 shows the vector locus of the offset QPSK. The instantaneous minimum power is the average power even when the cutoff characteristic of the low-pass filter is sharpened (roll-off rate is set to 0.2) to narrow the band. Only about 15 decibels below. Therefore, even when the band is narrowed, the linear amplification range of the power amplifier may be narrow.

[0008]

However, in land mobile communication, the transmitted wave is reflected, diffracted, and scattered by buildings, mountains, and the like, so that the received wave is composed of many radio waves whose phases do not match. This causes a so-called fading in which at least one of the amplitude and the phase of the received signal fluctuates.

In the receiver of the offset QPSK system, it is necessary to synchronize for each symbol and also to synchronize for each frame in order to detect the start of a data symbol. Is difficult and a practical bit error rate (BE
It was difficult to communicate in R). The present invention has been made in view of the above problems, and has as its object to provide an offset QPSK modulation / demodulation apparatus and a communication system capable of performing stable communication even under fading and obtaining a good BER.

[0010]

An offset QPSK modulator according to the present invention converts a data bit sequence into a signal value sequence consisting of IQ2 components, and converts one set of signal value sequences consisting of IQ2 components into one. An encoding unit that outputs a symbol sequence as a symbol, a synchronization symbol insertion unit that inserts a synchronization symbol according to a predetermined rule into a symbol sequence output from the encoding unit, and a symbol in which the synchronization symbol is inserted by the synchronization symbol insertion unit. A pilot symbol insertion unit that inserts a pilot symbol in accordance with a predetermined rule into a sequence and a pilot symbol insertion unit that compares one component of the symbol sequence with the pilot symbol inserted therein at the time of transmission of the other component by 1 / 2 symbol delay, and one component of the symbol sequence delayed by the delay Comprising a quadrature modulator for quadrature modulation using a carrier wave of a predetermined frequency and the other components of the symbol columns pilot symbols are inserted in the bolt insertion portion.

In the offset QPSK modulator according to the present invention, not only a synchronization symbol is inserted into a frame, but also a pilot symbol is inserted into a data symbol according to a predetermined rule. Other offset QPSK modulators use 1
Insert one pilot symbol.

Another offset QPSK modulator is
The pilot symbol insertion unit inserts two or more consecutive pilot symbols. Still other offset QPS
The K modulation apparatus includes a pilot symbol insertion unit that includes two signal values to be inserted into one component of a signal value sequence of a symbol in which a synchronization symbol is inserted by the synchronization symbol insertion unit in accordance with a predetermined rule, and another one of the two signal values. A 1.5 pilot symbol composed of a component and one signal value inserted according to a predetermined rule is inserted.

Still another offset QPSK modulator includes a pilot symbol insertion unit, which includes two or more pilot QPSK modulators according to a predetermined rule for one component of a signal value sequence of a symbol into which a synchronization symbol is inserted by a synchronization symbol insertion unit. Insert a symbol. Offset QP according to the present invention
The SK demodulator includes: a quadrature demodulator for extracting a symbol from a modulated wave; a synchronization detector for identifying a synchronization symbol included in the symbol extracted from the quadrature demodulator; and a synchronization detector after the synchronization symbol is identified by the synchronization detector. An estimating unit that identifies pilot symbols included in the symbols extracted from the orthogonal demodulation unit and estimates the degree of influence of fading, and includes the symbols extracted from the orthogonal demodulation unit based on the fading degree estimated in the estimating unit. A compensator for compensating for the effect of fading on the data symbols to be decoded, and a decoder for reproducing a data bit string from the data symbols compensated by the compensator.

In the offset QPSK demodulator according to the present invention, the degree of fading is estimated based on pilot symbols having a known pattern, and the effect of fading on data symbols is compensated. In another offset QPSK demodulation device, the estimating unit calculates the average value of the individual fading influence degree, which is the fading influence degree for each pilot symbol, calculated based on each of two or more consecutive pilot symbols, as the fading influence degree. I do.

The other offset QPSK demodulator may be configured such that an estimating unit converts an arbitrary one signal value constituting one component of two or more continuous pilot symbols and an arbitrary one signal value constituting the other component into two or more consecutive pilot symbols. The average value of the individual fading influence degrees calculated based on the above is defined as the fading influence degree. Another offset QPSK demodulation apparatus includes, in an estimation unit, one of two signal values having a predetermined pattern included in one component of a symbol extracted from the quadrature demodulation unit and the other signal component included in the other component. The average value of the degree of influence of individual fading calculated based on one signal value having a predetermined pattern is set as the degree of fading influence.

In another offset QPSK demodulator, the estimator calculates the amplitude and phase angle of the degree of fading influence based on the pilot symbol vector and the reception vector of the pilot symbol transmission timing. In another offset QPSK demodulator, the estimating unit calculates the phase angle of the degree of fading influence based on the pilot symbol vector and the reception vector of the transmission timing of the pilot symbol.

In still another offset QPSK demodulator, the estimating unit sets the average value of the individual fading influence degrees calculated based on one component of two or more consecutive pilot symbols as the fading influence degree. The offset QPSK communication system according to the present invention comprises:
An encoding unit that converts the data bit sequence into a signal value sequence composed of IQ2 components, and outputs a symbol sequence in which one set of the signal value sequence composed of IQ2 components constitutes one symbol; and a symbol output from the encoding unit. In the column, a synchronization symbol insertion unit that inserts a synchronization symbol according to a predetermined rule, and a pilot symbol insertion unit that inserts a pilot symbol according to a predetermined rule into the symbol sequence in which the synchronization symbol is inserted in the synchronization symbol insertion unit. A delay unit that delays the transmission time of one component of the symbol sequence in which the pilot symbol is inserted by the pilot symbol insertion unit by one-half of the transmission time of the other component, and delays the symbol sequence delayed by the delay unit. One component and the other component of the symbol sequence in which the pilot symbol is An offset QPSK modulator including a quadrature modulation unit that performs quadrature modulation using a carrier of a predetermined frequency; a quadrature demodulation unit that extracts a symbol from a carrier to be transmitted; and a synchronization symbol included in a symbol extracted from the quadrature demodulation unit. An estimating unit that identifies a pilot symbol included in a symbol extracted from the quadrature demodulation unit after the synchronization symbol is identified by the synchronization detecting unit and estimates a degree of influence of fading; A compensating unit that compensates for the effect of fading on the data symbols included in the symbols extracted from the orthogonal demodulation unit based on the fading degree,
And a decoding unit for reproducing a data bit string from the data symbols compensated by the compensation unit.
And a demodulator.

In the offset QPSK communication system according to the present invention, the degree of fading is estimated by the demodulator based on the known pilot symbols inserted by the modulator, and the effect of fading on the data symbols is compensated. . In another offset QPSK communication system, a pilot symbol different from a pilot symbol used in a pilot symbol insertion unit of another offset QPSK communication system is inserted in a pilot symbol insertion unit.

[0019]

FIG. 3 is a basic functional diagram of an offset QPSK transmitter, in which a data bit sequence is converted into a signal value sequence having IQ2 components by an encoder 31, but one set of signal value sequences. Is called one symbol. The synchronization symbol insertion unit 32 generates a frame by dividing the data symbol into a predetermined number, and inserts a predetermined pattern and a predetermined number of synchronization symbols into the front part of each frame.

Then, the I-component signal is introduced into a quadrature modulator 34 via a first low-pass filter 33, and the Q-component signal is delayed by a 1/2 symbol The signal is introduced to the quadrature modulator 34 via the filter 36. In the quadrature modulator 34, a carrier having a predetermined frequency is quadrature-modulated with a baseband signal composed of an I component signal and a Q component signal, and the modulated carrier is amplified by a power amplifier 37 and then radiated from an antenna.

FIG. 4 is a basic function diagram of the offset QPSK receiver. A received signal received by an antenna is amplified by an amplifier 41, and then a baseband signal is formed from a modulated wave by a quadrature demodulator 42. The first LPF 43 and the second LPF 44 are separated into an I component signal and a Q component signal.
Through the decoder 45. The demodulation of the digital modulation signal requires symbol synchronization and frame synchronization for determining the start position of the data symbol. The synchronization detection unit 46 detects the frame synchronization after the symbol synchronization is achieved. Thereafter, reproduction of the output data from the data symbol is started by the decoder 45.

FIG. 5 is a signal space diagram and a vector locus diagram of the offset QPSK. Under fading, the amplitude and phase of the received signal change with time (a) →
(B) → (c). Therefore, it is difficult to maintain not only synchronization but also to secure stable communication even if synchronization is successfully acquired. However, since the shape in the signal space is preserved even under fading, if the position of a certain point (for example, point A) is known, it is possible to estimate the position at another point.

Therefore, in the present invention, the degree of influence of fading is evaluated by inserting a pilot symbol P of a predetermined pattern for each predetermined bit of a frame, and a data symbol transmitted between two pilot symbols is evaluated. Compensate for the effects of fading.
FIG. 6 is a relationship diagram of the transmission vector T, the fading vector F, and the reception vector R. The reception vector R is expressed as a product of the transmission vector T and the fading vector F.

Therefore, since the receiving side can detect the receiving vector, if the transmitting vector T is known, the fading vector F can be calculated by [Equation 7].

[0025]

(Equation 7)

Therefore, the pilot symbol P (=
By inserting P _i + jP _q ), the transmission vector T (= T _i)
+ JT _q ) becomes P. For example, assuming that the pilot symbol in FIG. 5B is P (k) and the pilot symbol in FIG. 5C is P (k + N), time k and k +
The fading vector in N is represented by [Equation 8].

[0027]

(Equation 8)

As shown in FIG. 5D, from time k to time k
+ N, if the locus of the received vector is smooth, that is, if there is no inflection point on the locus, the data symbol transmitted between pilot symbol P (k) and pilot symbol P (k + N) is transmitted. Can be calculated as a function of the fading vector F (k) at time k and the fading vector F (k + N) at time k + N, so that Equation 9 holds.

[0029]

(Equation 9)

Therefore, the data symbol D (k + n) transmitted between time k and time k + N can be estimated by [Equation 10].

[0031]

(Equation 10)

FIG. 7 is a signal space diagram of the pilot symbol P for explaining the principle of estimating the fading vector based on the pilot symbol P in the offset QPSK system. Shall be performed.

[0033]

[Equation 11]

In the offset QPSK system, since the I signal component and the Q signal component are shifted by シ ン ボ ル symbol, the Q signal component is undefined at the symbol timing of the I signal component.
At the symbol timing of the Q signal component, the I signal component is undefined. Here, the indefinite values of the transmission vector are U _i ,
_Assuming that U _q , the transmission vectors PS _i and PS _{q at} the symbol timing of the I signal component and the symbol timing of the Q signal component are represented by [Equation 12].

[0035]

(Equation 12)

Further, the fading vector F is represented by [Equation 1]
3].

[0037]

(Equation 13)

Here, ignoring the change of the fading vector between 1/2 symbols, the received vector is obtained by multiplying the transmitted vector and the fading vector, so that the received vector R _{i at} the symbol timing of the I signal component is It is represented by [Equation 14].

[0039]

[Equation 14]

The reception vector R _{q at} the symbol timing of the Q signal component is represented by [Equation 15].

[0041]

(Equation 15)

Therefore, the I signal components F _i and Q of the fading vector are
The signal component _Fq can be obtained. That is, [Equation 14]
And [Equation 15] can be transformed as [Equation 16].

[0043]

(Equation 16)

Accordingly, the following four equations (Equation 17) are derived.

[0045]

[Equation 17]

[0046] The four equations consider equations and unknowns F _i and F _q, when obtaining the I signal component F _i and Q signal components F _q fading vector, F _i and F
_q is represented by [Equation 18].

[0047]

(Equation 18)

Therefore, when [Equation 18] is applied to [Equation 9], [Equation 19] is obtained.

[0049]

[Equation 19]

FIG. 8 is a functional diagram of the offset QPSK transmitter according to the present invention. In the basic functional diagram shown in FIG. I have. In this transmitter, an encoder 31, a synchronization symbol insertion unit 32, a pilot symbol insertion unit 38, a 1/2 symbol delay unit 35, a first low-pass filter 33 and a second low-pass filter 36
Is advantageously processed by a digital element, for example the DSP 30.

FIG. 9 is a schematic diagram of the processing of the DSP 30, and FIG. 9A shows transmission data. This bit sequence is symbolized by the encoder 31 into IQ2 components. The synchronization symbol insertion unit 32 divides this symbol into frames of a predetermined number ("6" in this embodiment), and inserts a predetermined number ("3" in this embodiment) of synchronization symbols at the beginning of each frame. Is done.

Then, a predetermined number (in this embodiment, "1") of pilot symbols are inserted for each predetermined data symbol (in this embodiment, "2") in the pilot symbol insertion section 38, and one-half symbol is inserted. In the delay unit 35, the bits constituting the Q component are delayed by ３５ symbol, and the symbols are staggered. The staggered symbols are quadrature-modulated by the quadrature modulator 34, and the power amplifier 3
The signal is transmitted after being power-amplified at 7.

In the above example, the pilot symbols are inserted for the same predetermined number of the data symbols of the I and Q components, but the pilot symbols need not always be inserted for the same predetermined number as long as they are based on a predetermined rule. For example, the number of data symbols between the first pilot symbol and the second pilot symbol may be different from the number of data symbols between the second pilot symbol and the third pilot symbol.

FIG. 10 is an explanatory diagram of an example of inserting pilot symbols. In FIG. 10, a first pilot symbol is inserted after one data symbol following three consecutive synchronization symbols, and after three consecutive data symbols. A second pilot symbol is inserted, and the synchronization symbol of the next frame is present after two subsequent data symbols.

Such a frame structure is defined by the rule (3S-1).
D-1P-3D-1P-2D), the quadrature modulation apparatus according to the present invention can apply an arbitrary rule as long as it is determined in advance, as defined as a structure in which pilot symbols are inserted. FIG. 11 is a functional diagram of the offset QPSK receiver according to the present invention. A received signal is amplified by an amplifying section 111, then demodulated by a quadrature demodulating section 112, and output as an I component signal and a Q component signal. .

After passing through the first and second low pass filters 113 and 114, the I component signal and the Q component signal are branched into three. The first branch signal is a synchronization detection unit 1
15, the frame synchronization is detected based on the synchronization symbol, and after detecting the synchronization, the switch 116 is closed.
Since the second branch signal is guided to the fading vector estimating unit 117 via the switch 116, the synchronization detecting unit 11
After the frame synchronization is detected in step 5, the fading distortion estimating unit 117 estimates a fading vector.

The third branch signal is a fading distortion compensator 1
18, fading distortion is compensated based on the fading vector estimated by the fading vector estimating unit 117. Then, the decoder 119 reproduces the data of the data symbol whose fading distortion has been compensated. In this receiver, the first and second low-pass filters 113 and 114 and the synchronization detector 115,
The switch 116, the fading distortion estimating unit 117, and the fading distortion compensating unit 118 are digitally processed by the DSP 110.

FIG. 12 is a flowchart of a reception processing routine executed by the DSP 110. The execution is started after the synchronization detection unit 115 detects frame synchronization. Index m indicating the order of pilot symbols inserted into one frame in step 12a
Is set to the initial value "1", and the fading vector (F _i + jF _q ) is estimated in step 12b, which will be described later in detail.

Then, in step 12c, the tail fading vector is replaced with the head fading vector according to the following equation. F _0i ← F _ni F _0q ← F _nq Next, in step 12d, the data symbols are stored.
Details will be described later.

[0060] Then, perform the estimation of the re-phasing vector (F _i + jF _q) in step 12e, sandwiched between the first fading vector and (F _0i + jF _0q) and end fading vector (F _ni + jF _nq) at step 12f The fading distortion of the data symbol is corrected, which will be described later in detail. In step 12g, the index m is
It is determined that "M" has been reached, and if a negative determination is made, that is, if the index m is less than "M", step 12h
Increments the index m by the step 12c
Return to Conversely, when a positive determination is made in step 12g,
That is, when the index m reaches "M", this routine is ended once, and the receiving process is executed for the next frame.

FIG. 13 shows step 12 of the reception processing routine.
12 is a flowchart of a first fading vector estimation routine executed in steps b and 12d, wherein step 1
At 3a, the judgment is made on the index m. When the index m is "1", since the data symbol immediately follows the synchronization symbol, the step 13b
, The pilot symbol for calculating the fading vector is set to the synchronization symbol (S _i + jS _q ), and the process proceeds to step 13e.

If index m is greater than "1"
If it is less than "M", a pilot symbol for calculating the fading vector in step 13c is set to a predetermined "m" th pilot symbol { _Pmi + j
P _mq } and the process proceeds to step 13e. When the index m reaches "M", since it is the last processing of the frame, a pilot symbol for calculating a fading vector is calculated in step 13d in order to use the first synchronization symbol of the next frame as a pilot symbol. The synchronization symbol is set to (S _i + jS _q ) and the process proceeds to step 13e.

In step 13e, a fading vector is calculated, and in step 13f, the ending fading vector is replaced with the leading fading vector, and this routine ends. FIG. 14 is a flowchart of the first fading vector calculation routine executed in step 13e of the fading vector estimation routine. In step 14a, the reception vector (R _ii + jR _iq ) at the I timing and the Q timing at the pilot symbol reception time Request received vector (R _qi + jR _qq). Then, in step 14b, the fading vector (F _i + jF _q ) is calculated using [Equation 18], and this routine ends.

FIG. 15 shows step 12 of the reception processing routine.
14 is a flowchart of a data symbol storage routine executed in step d. In step 15a, an index n representing an order of data symbols existing between pilot symbols is set to an initial value "1". Next, at step 15b, I
The received vector at the timing is represented by ｛R _ii (n) + jR
_iq (n)｝, and the received vector at Q timing is ｛R
_qi (n) + jR _qq (n)}.

In step 15c, the index n is the maximum value
It is determined whether it is equal to "N". If a negative determination is made, it is determined that the storage of all the data symbols existing between the two pilot symbols has not been completed and step 15
The index n is incremented by d and step 15 is performed.
Return to b. Conversely, if the determination in step 15c is affirmative, the routine ends, assuming that the storage of all data symbols has been completed.

FIG. 16 shows step 12 of the reception processing routine.
14 is a flowchart of a fading distortion compensation routine executed in step e, wherein an index n representing an order of data symbols existing between pilot symbols is set to an initial value "1" in step 16a. In step 16b, using the [Equation 19], the I-timing inter-pilot symbol fading vector ΔF _i (k + n) + jF
_q (k + n)} is calculated, and the parameter x is calculated using [Equation 20] in step 16c. Then, in step 16d, one bit ("1" or "0") corresponding to the sign of the parameter x is output.

[0067]

(Equation 20)

Next, in step 16e, [Equation 19]
, Using a Q-timing inter-pilot symbol fading vector {F _i (k + n) + jF _q (k + n)}
Is calculated, and the parameter y is calculated in step 16f using [Equation 21]. Then, in step 16g, one bit ("1" or "0") corresponding to the sign of the parameter y is output.

[0069]

(Equation 21)

In step 16h, it is determined whether or not the index n has reached the maximum value "N". If a negative determination is made, it is determined that the fading distortion has not been compensated for the data symbols between the pilot symbols, and in step 16i the index is determined. n is incremented and the process returns to step 16b. Conversely, if the determination in step 16h is affirmative, this routine is terminated, assuming that fading distortion compensation has been completed for data symbols between pilot symbols.

FIG. 17 is an example of a state assignment diagram in the offset QPSK, in which (0, 0) is set in the first quadrant.
An example is shown in which (1,0) is assigned to the second quadrant, (1,1) is assigned to the third quadrant, and (0,1) is assigned to the fourth quadrant. In this case, at the I timing, if the I component x of the received vector after fading distortion compensation is positive, "1" is output, and if it is negative, "0" is output.

At the Q timing, if the Q component y of the received vector after fading distortion compensation is positive, "0"
Is output, and "1" is output when it is negative. FIG. 18 is a flowchart of an intermediate fading vector calculation process by linear interpolation between the leading fading vector (F _0i + _{jF 0q} ) and the trailing fading vector (F _ni + jF _nq ).
Steps 16b and 1 of the fading distortion compensation routine
6e.

That is, in step 18a, the I component of the intermediate fading vector is calculated using [Equation 22], and in step 18b, the Q component of the intermediate fading vector is calculated using [Equation 23]. To end.

[0074]

(Equation 22)

[0075]

(Equation 23)

In the above embodiment, 1 is used for the data symbol.
Although two pilot symbols are inserted, the denominator of [Equation 18] is close to zero when the situation is close to a specific situation, that is, the situation where [Equation 24] is satisfied, and the fading vector can be accurately estimated. Can not.

[0077]

(Equation 24)

Therefore, it is possible to improve the estimation accuracy of the fading vector by inserting two or more pilot symbols continuously between data symbols. FIG. 19 shows three consecutive pilot symbols ｛P _mi
(1) + jP _mq (1)｝, ΔP _mi (2) + jP
FIG. 9 is an explanatory diagram in the case of inserting _mq (2)} and {P _mi (3) + jP _mq (3)}, in which three pilot symbols are continuously inserted for each predetermined number of data symbols.
The three consecutive pilot symbols may be the same symbol or different symbols.

FIG. 20 is a flowchart of the second fading vector estimation routine, which is executed in place of the fading vector estimation routine shown in FIG. It is assumed that the number of symbols to be continuously inserted is "K". In step 20a, an index k representing the number of pilot symbols to be continuously inserted is set to an initial value "1", and in step 20b, the index m is determined.

If m is “1”, the pilot symbol (P _i + jP _q ) is replaced with the synchronization symbol (S
_i + jS _q ) and the process proceeds to step 20f. m is
If it is greater than "1" and less than "M", the pilot symbol (P _i + jP _q ) is set to a predetermined pilot symbol {P _mi (k) + jP _mq (k)}, and the process proceeds to step 20f. .

When m reaches “M”, the pilot symbol (P _i + jP _q ) is replaced with the synchronization symbol (S _i + jS
_q ) and proceed to step 20f. Step 20f
Then, the fading vector calculation routine of FIG. 14 is executed, and the following equation is replaced in step 20g. F _ni (k) ← F _i F _nq (k) ← F _{q In} step 20h, it is determined whether or not the index k has reached the maximum value “K”. If a negative determination is made, step 20i is performed.
Increments the index k in step 20b
Return to

When an affirmative determination is made in step 20h, that is, when the index k has reached the maximum value "K", this routine ends the average value of the fading vector calculated in step 20g in step 21j as the tail fading vector. I do. _{F ni ← ΣF ni (k)} / K F nq ← ΣF nq (k) / K The above determines the fading vector in every pilot symbol, but determines the fading vector as an average value, of the one fading vectors I component (Q
It is also possible to estimate the fading vector by associating a plurality of Q components (I components) with the component) and determine the fading vector as the average value.

FIG. 21 is a flowchart of the third fading vector estimation routine, which is executed instead of the fading vector estimation routine shown in FIG. It is assumed that the number of symbols to be continuously inserted is "K". Initial value index k _i and k _q represents the number of pilot symbols to be inserted in succession in step 21a "1"
, And it is determined in step 21b for the index m.

If m is "1", the pilot symbol (P _i + jP _q ) is set to the synchronization symbol (S _i + jS _q ), and the flow advances to step 21f. m is greater than "1"
If it is less than "M", the process proceeds to step 21f to set the pilot symbols (P _i + jP _q) predetermined pilot symbols _{{P mi (k i) +} jP mq (k q)} in step 21e.

When m reaches “M”, the pilot symbol (P _i + jP _q ) is replaced with the synchronization symbol (S _i + jS
_q ) and proceed to step 21f. Step 21f
Then, the fading vector calculation routine of FIG. 14 is executed, and the following equation is replaced in step 21g. F _ni (k _q ) ← F _i F _nq (k _q ) ← F _{q In} step 21 h, it is determined whether or not the index k _q has reached the maximum value “K”.
Increment index k _q by i and step 2
Return to 1b.

When an affirmative determination is made in step 21h, that is, when the index k reaches the maximum value "K", an average value of the fading vector calculated in step 21g is calculated in step 21j. _{F ni (k i) ← ΣF} ni (k q) / K F nq (k i) ← ΣF nq (k q) / K index k _i at step 21k, it is determined whether it has reached the maximum value "K", If a negative determination is made, step 21
increment index k _i by m and step 2
Return to 1b.

When an affirmative determination is made in step 21k, that is, when the index k _q reaches the maximum value “K”,
In step 21n, the average value of the fading vector calculated in step 21j is calculated, and this routine ends. F _ni ← ＫF _ni (k _i ) / K F _nq ← ΣF _nq (k _i ) / K In the above embodiment, K consecutive pilot symbols are inserted into the data symbols, but the frame length is fixed. In this case, if the number of pilot symbols is increased, the number of data symbols is reduced, and the transmission efficiency is reduced.

Therefore, it is possible to insert 1.5 pilot symbols in order to improve the estimation accuracy of fading distortion while preventing a decrease in transmission efficiency. FIG. 22 is an explanatory diagram in the case where 1.5 pilot symbols are inserted, where 2 bits are inserted into the I component and 1 bit is inserted into the Q component. In this case, the rules (3S-2D-1.5P-
2.5D-1.5P-2.5D), pilot symbols are inserted. Note that two bits are used for the Q component,
One bit may be inserted into the I component.

FIG. 23 shows I timing and Q timing.
When the number of pilot symbols to be inserted into
Of the fourth fading vector estimation routine used
A low chart, K_iIs inserted at I timing
Number of pilot symbols, K _qIs inserted at Q timing
Represents the number of pilot symbols to be used. Therefore I timing
Two pilot symbols and one pilot symbol at Q timing
K to enter_i= 2K_q= 1.

When the absolute value of the denominator of [Equation 18] is smaller than a predetermined value (ε ₁ ), the absolute value of the fading vector becomes small, and the estimation accuracy of the fading vector deteriorates. When fading distortion is compensated for using a fading vector having poor estimation accuracy, it is impossible to avoid affecting data symbols. FIG. 24 is a flowchart of a second fading vector calculation routine for solving the above problem, which is executed instead of the first fading vector calculation routine of FIG.

[0091] That Request received vector at I time in step 24a (R _ii + jR _iq) and Q received at the timing vector (R _qi + jR _qq). In step 24b, the value D of the denominator of [Equation 18] is calculated.
In step 24c, it is determined whether the value of D is equal to or smaller than a predetermined value (ε ₁ ). And step 24
When an affirmative determination is made in c, i.e., the value of D of this routine is directly terminated is smaller than the predetermined value epsilon _1. Conversely, when a negative determination is made in step 24c, that is, when the value of D is the predetermined value ε
If it is greater than _one, the fading vector is calculated based on [Equation 18] in step 24d, and this routine ends.

When the second fading vector calculation routine is applied, the fading vector calculated at the next execution of this routine can be used in place of the fading vector not calculated. FIG.
5 is a flowchart of a fifth fading vector estimation routine used in this case, and is a step 1 of the first fading vector estimation routine shown in FIG.
Step 25a between 3e and step 13f is added, the routine ends and bypass step 13f when the value of the denominator D [Equation 18] is smaller than the predetermined value epsilon _1.

However, when pilot symbols having a small denominator D in [Equation 18] are consecutive, a large number of data symbols must be stored, so that the fading vector calculated last time can be used as it is. . In this case, the first fading vector estimation routine in FIG. 13 may be used as it is.

In the above embodiment, the fading vector is estimated using [Equation 18].
8] is complicated and requires a large amount of calculation. However, in the demodulation of the offset QPSK, the absolute value of the fading vector is not necessary, and it is sufficient if the phase angle is known. Thus instead of the fading vector which is determined based on [Equation 18] (F _i + jF _q), fading vector calculated based on [Equation 25] (F _i '+ jF
By using _q '), the amount of calculation can be greatly reduced.

[0095]

(Equation 25)

FIG. 26 is an explanatory diagram of the reason why the declination of the fading vector can be calculated by [Equation 25], and is a diagram assuming that there is no phase difference between the transmitting and receiving apparatuses. FIG.
, The pilot symbol is (P _i + jP _q ) and the indefinite value is (U _i + jU _q ). Also in the received vector I timings (R _ii + jR _iq) Q timing as (R _qi + jR _qq).

Therefore, R _ii = P _i , R _qq = P _q R _iq = U _q , and R _qi = U _i . At this time, the argument of the fading vector is Q
A vector (−R _iq + j) obtained by rotating the reception vector at the timing and the reception vector at the I timing by 90 ° counterclockwise.
R _ii ) and a difference vector (R _iq + R _qi ) + j (R _qq −
R _ii ).

However, the above is a vector (−R _iq + jR _ii ) obtained by rotating the reception vector at the Q timing (R _qi + jR _qq ) by 90 ° counterclockwise with respect to the reception vector at the I timing.
A description when present in more right, when present on the left side - declination of the fading vector is estimated by _{(R iq + R qi) +} j (R ii -R qq). Then, the positional relationship between both can be distinguished by the sign of _{(R ii * R qi + R} iq * R qq).

[0099] in the case of further inserting the 1.5 or more symbols of the pilot symbol _{(R ii * R qi + R} iq * R qq)
The bit error rate (BER) hardly deteriorates even if the sign of is not calculated. That is, when 1.5 or more pilot symbols are inserted, the fading vector can be calculated by [Equation 26].

[0100]

(Equation 26)

Even when the fading vector is estimated using the simplified formula [Equation 25] or [Equation 26], the accuracy of the fading vector estimation is degraded when the absolute value of the fading vector is reduced. As described above, when the fading vector is used to estimate the fading vector, if the absolute value (= D) of the fading vector is smaller than a predetermined value (ε ₁ ), the fading vector may not be estimated. .

Note that the next or previous estimated value may be used instead of the fading vector not estimated at this time, as described above. Further, when the distribution of the Q component of the reception vector at the I timing when the absolute value of the fading vector is small, the distribution near the I axis (that is, R
_iq ≒ 0) or often distributed found in Sutakatsu of previous symbol values near (i.e. R _iq ≒ P _q or -P _q).

Therefore, when the absolute value of the fading vector is small, when a pilot symbol is received, the received vector at I timing can be used as it is as a fading vector. Note that when the I component is on the left half plane, it is necessary to make the reception vector rotated by π a fading vector. Further, when only the reception vector at the I timing is used, the accuracy of the fading vector is not sufficient.
The average vector of the timing reception vector and the vector obtained by rotating the reception vector by −π / 2 may be used as the fading vector.

FIG. 27 shows a third fading vector operation.
FIG. 24 is a flowchart of a routine,
Step 27a is added to the fading vector calculation routine.
And 27b have been added. Affirmative decision in step 24c
When it is determined, that is, the denominator of [Equation 18] is
(Ε ₁If it is less than), then in step 27a,
F 'is the absolute value of the I component of the reception vector at the I timing
Where F ″ is the absolute value of the Q component of the received vector at the Q timing.
Set to a value.

Next, in step 27b, the I component of the fading vector is set to the average value of F 'and F ", and the Q component is set to zero. This routine is terminated. Is used to estimate the fading vector, but it is also possible to estimate the fading vector based on either the received vector at the I timing or the received vector at the Q timing.

It is assumed that two pilot symbols are represented by [Equation 27].

[0107]

[Equation 27]

Here, assuming that the two indefinite values at the I timing are U _1i and U _2i , the two transmission vectors PS _1i and PS _{2i at} the I timing are represented by [ _Equation 28].

[0109]

[Equation 28]

The fading vector is [Equation 13], and the two reception vectors at I timing are [Equation 2].
9].

[0111]

(Equation 29)

When [Equation 27] and [Equation 13] are used, the reception vector is represented by [Equation 30].

[0113]

[Equation 30]

Equation 30 is regarded as an equation in which F _i and F _q are unknown numbers, and equation 31 is satisfied when F _i and F _q are solved.

[0115]

(Equation 31)

Therefore, the I component F of the fading vector
_i 'and the Q component _Fq ' can be easily obtained by [Equation 32].

[0117]

(Equation 32)

In the above, the case where only the I timing is used has been described. However, it is also possible to estimate the fading vector using only the Q timing. in this case,
The estimation of the fading vector is performed by [Equation 33].

[0119]

[Equation 33]

As is apparent from the above description, when 1.5 or more pilot symbols are inserted, it is possible to estimate the fading vector based on the reception vector at the timing when a plurality of symbols are inserted. Become. For example, when inserting two symbols at I timing and one symbol at Q timing, 1.5 symbols are inserted.
It is possible to estimate the fading vector based on the two received vectors at I timing.

FIG. 28 shows a case where a plurality of
Calculate fading vector using received vector
Fourth fading vector operation rule used when
In the flowchart of FIG.
A method for estimating the easing vector is determined. I timing
The fading vector based only on the received vector
When estimating, the process proceeds to step 28b.
The first received vector in (R _1i+ JR_1q), The second
The received vector of (R_2i+ JR_2q). And
In step 28c, the phasing is performed using [Equation 32].
After that, this routine is terminated.

Only based on the reception vector at Q timing
Step 28 when estimating the fading vector
Proceeding to d, the first received vector at Q timing is
(R _1i+ JR_1q), The second received vector is (R_2i+ J
R_2q). And at 28e,
Use this routine to calculate the fading vector
To end.

When estimating the fading vector based on the received vector at the IQ timing, step 28
f, the received vector at the I timing is calculated as (R _ii
+ JR _iq ) and the reception vector at the Q timing is set to (R _qi + jR _qq ). Then, in step 28g, the fading vector is calculated by using [Equation 25], and this routine ends.

According to the above, it is possible to improve the estimation accuracy of the fading vector by using the average value of the reception vector at the I timing, the reception vector at the Q timing, and the reception vector at the IQ timing as the fading vector. However, since it is necessary to properly use three sets of mathematical expressions, the fading vector calculation routine becomes complicated.

Therefore, an offset QPSK modulator is used in FIG.
As shown in FIG. 9, the demodulation device can be simplified by inserting a plurality of pilot symbols only at one of the I timing and the Q timing. In a digital mobile communication system, when a mobile station is located in a place where radio wave propagation conditions are good, such as a hill or a mountain, the distance between the mobile station and the base station is several times the design value due to an overreach phenomenon. Communication may be possible even at a distance, and interference occurs between a plurality of mobile communication systems.

In order to prevent such interference, it is general to add a function of inserting a unique color code for each mobile communication system and prohibiting communication between systems having different color codes. . However, when a color code is inserted into a frame when the frame length is fixed, the number of data that can be inserted decreases, and the transmission efficiency decreases.

On the other hand, in a digital communication system, redundant bits generated based on a predetermined rule are added to original data bits on the transmission side, and errors such as bit inversion generated during transmission on the reception side are eliminated. Error control for detection and correction is applied. Offset QPSK according to the present invention
When the modem has an error control function, it is possible to prevent interference between mobile communication systems without adding a color code by using a pilot symbol having a different pattern for each mobile communication system. Becomes possible.

FIG. 30 shows mobile communication systems A and B
Is an example of assigning pilot symbols to
A case where pilot symbols are inserted at five positions in a frame is shown. That is, for the communication system A, the first
To the fifth position from (−1−j1), (−1−j1), respectively.
1), (-1-j1), (1 + j1), and (1 + j1) pilot symbols are inserted.

For the communication system B, (1 + j1), (1 + j1),
The pilot symbols (−1−j1), (1 + j1), and (−1−j1) are inserted. Then, the first pilot symbol (-1-j) is transmitted from the transmitter of the communication system A.
The data transmitted between 1) and the second pilot symbol (-1-j1) is calculated by the receiver of the communication system A based on the first pilot symbol and the second pilot symbol of the communication system A. Since the data is compensated by the fading vector, the error control function does not recognize that an error has occurred, and correct data is reproduced.

However, when the data transmitted from the transmitter of the communication system A is received by the receiver of the communication system B, the first pilot symbol (1 + j
1) and data interposed between the first pilot symbol (-1-j1) and the second pilot symbol (-1-j1) based on the fading vector calculated based on the second pilot symbol (1 + j1). Since the compensation is compensated, the phases of the data symbols are all inverted, so that the error control function recognizes that an error has occurred and the output of the data is blocked.

That is, in the offset QPSK modem according to the present invention, the color code is not used,
That is, it is possible to prevent interference between communication systems without reducing transmission efficiency.

[0132]

According to the offset QPSK modulator according to the present invention, it is possible to insert a pilot symbol into a frame with a simple configuration. ADVANTAGE OF THE INVENTION According to the offset QPSK demodulation apparatus which concerns on this invention, it becomes possible to detect the influence degree of fading by receiving a pilot symbol and to compensate the influence of fading to a data symbol.

According to the offset QPSK communication system of the present invention, the degree of influence of fading is detected by inserting a pilot symbol into a frame by the modulator and receiving the pilot symbol by the demodulator, and the effect of fading on the data symbol is detected. And stable communication can be performed.

[Brief description of the drawings]

FIG. 1 is a vector locus of π / 4 shift QPSK.

FIG. 2 is a vector locus of an offset QPSK.

FIG. 3 is a basic configuration diagram of an offset QPSK transmitter.

FIG. 4 is a basic configuration diagram of an offset QPSK receiver.

FIG. 5 is a signal space diagram and a vector locus of an offset QPSK.

FIG. 6 is a relationship diagram of a transmission vector, a fading vector, and a reception vector.

FIG. 7 is a signal space diagram of pilot symbols.

FIG. 8 is a functional diagram of an offset QPSK transmitter according to the present invention.

FIG. 9 is a schematic diagram of a DSP process.

FIG. 10 is an explanatory diagram of an example of inserting pilot symbols.

FIG. 11 is a functional diagram of an offset QPSK receiver according to the present invention.

FIG. 12 is a flowchart of a reception processing routine.

FIG. 13 is a flowchart of a first fading vector estimation routine.

FIG. 14 is a flowchart of a second fading vector calculation routine.

FIG. 15 is a flowchart of a data symbol storage routine.

FIG. 16 is a flowchart of a fading distortion compensation routine.

FIG. 17 is a state assignment diagram.

FIG. 18 is a flowchart of a process of calculating a fading vector by linear interpolation.

FIG. 19 is an explanatory diagram of a case where continuous pilot symbols are inserted.

FIG. 20 is a flowchart of a second fading vector estimation routine.

FIG. 21 is a flowchart of a third fading vector estimation routine.

FIG. 22 is an explanatory diagram in the case of inserting 1.5 pilot symbols.

FIG. 23 is a flowchart of a fourth fading vector estimation routine.

FIG. 24 is a flowchart of a second fading vector calculation routine.

FIG. 25 is a flowchart of a fifth fading vector estimation routine.

FIG. 26 is an explanatory diagram of the reason why the declination of the fading vector can be calculated.

FIG. 27 is a flowchart of a third fading vector calculation routine.

FIG. 28 is a flowchart of a fourth fading vector calculation routine.

FIG. 29 is an explanatory diagram of a case where a pilot symbol is inserted only at I timing.

FIG. 30 is an example of pilot symbol allocation.

[Explanation of symbols]

 Reference Signs List 30 DSP 31 Encoder 32 Synchronization symbol insertion unit 33 First LPF 34 Quadrature modulation unit 35 1/2 symbol delay unit 36 Second LPF 37 Power amplification unit 38 Pilot symbol insertion unit 41 Amplifying unit 42: Quadrature demodulation unit 43: First LPF 44 ... Second LPF 45 ... Decoder 46 ... Synchronization detection unit 110 ... DSP 111 ... Amplification unit 112 ... Quadrature demodulation unit 113 ... First LPF 114 ... Second LPF 115 ... Synchronization detection unit 116 ... Switch 117 ... Fading distortion estimation unit 118 ... Fading distortion compensation unit 119 ... Decoder

Claims (23)

[Claims] An encoding unit configured to convert a data bit sequence into a signal value sequence including IQ2 components and output a symbol sequence including one set of the signal value sequences including IQ2 components as one symbol; A synchronization symbol insertion unit that inserts a synchronization symbol according to a predetermined rule into a symbol sequence output from the unit, and a pilot symbol according to a predetermined rule in the symbol sequence in which the synchronization symbol is inserted by the synchronization symbol insertion unit. A pilot symbol insertion unit to be inserted; a delay unit that delays a transmission time of one component of the symbol sequence in which the pilot symbol is inserted by the pilot symbol insertion unit by １ ／ symbol compared with a transmission time of the other component; One component of the symbol sequence delayed by the delay unit and the pilot symbol Offset QPSK modulation anda quadrature modulator for quadrature modulation using a carrier wave of the other component and the predetermined frequency of the input symbol string. 2. The offset QPSK modulation apparatus according to claim 1, wherein said pilot symbol insertion section inserts one pilot symbol. 3. The offset QPSK modulation apparatus according to claim 1, wherein said pilot symbol insertion section inserts two or more consecutive pilot symbols. 4. The pilot symbol insertion unit includes two signal values inserted according to a predetermined rule into one component of a symbol sequence into which a synchronization symbol has been inserted by the synchronization symbol insertion unit, and the other component has 2. The offset QPSK modulation apparatus according to claim 1, wherein a 1.5 pilot symbol composed of one signal value inserted according to a predetermined rule is inserted. 5. The pilot symbol insertion unit comprises at least one signal value inserted according to a predetermined rule into only one component of a symbol sequence into which a synchronization symbol has been inserted by the synchronization symbol insertion unit. 2. The offset QPSK modulator according to claim 1, wherein a pilot symbol is inserted. 6. A quadrature demodulation unit for extracting a symbol from a carrier wave, a synchronization detection unit for identifying a synchronization symbol included in the symbol extracted from the quadrature demodulation unit, and a synchronization symbol identified by the synchronization detection unit. Later, an estimator for identifying a pilot symbol included in the symbol extracted from the quadrature demodulator and estimating the degree of fading influence, and is extracted from the quadrature demodulator based on the fading degree estimated in the estimator. A compensating unit for compensating for the effect of fading on data symbols included in the decoded symbols, and a decoding unit for reproducing a data bit string from the data symbols compensated by the compensating unit.
PSK demodulator. 7. The method according to claim 1, wherein the estimating unit sets an average value of individual fading influence degrees, which is a degree of fading influence for each pilot symbol, calculated based on each of two or more consecutive pilot symbols as a fading influence degree. Item 7. An offset QPSK demodulator according to item 6. 8. An estimating unit, which is calculated based on an arbitrary one signal value forming one component of two or more consecutive pilot symbols and an arbitrary one signal value forming the other component. The offset QPSK demodulator according to claim 6, wherein an average value of the individual fading influence degrees is set as the fading influence degree. 9. The signal processing apparatus according to claim 1, wherein the estimating unit includes one of two signal values having a predetermined pattern included in one component of the symbol extracted from the quadrature demodulating unit and the other signal component. 9. The offset QPSK demodulator according to claim 8, wherein an average value of the individual fading influence degrees calculated based on one signal value having a predetermined pattern is set as the fading influence degree. 10. The offset according to claim 6, wherein the estimating unit calculates an amplitude and a phase angle of the degree of fading influence based on a pilot symbol vector and a reception vector of the transmission timing of the pilot symbol. QPSK demodulator. 11. The offset QP according to claim 6, wherein the estimating unit calculates the degree of fading influence using Equation (1).
SK demodulator. (Equation 1) 12. The offset QPSK demodulation according to claim 6, wherein the estimating unit calculates the phase angle of the degree of fading influence based on a pilot symbol vector and a reception vector of the transmission timing of the pilot symbol. apparatus. 13. The offset QPSK demodulator according to claim 6, wherein the fading vector is calculated by using [Equation 2]. (Equation 2) 14. The offset QP according to claim 6, wherein the estimating unit calculates the degree of fading influence using Equation (3).
SK demodulator. (Equation 3) 15. When the absolute value of the fading vector calculated this time is smaller than a predetermined value, that is, when [Equation 4] holds, the estimating unit determines that the pilot symbol used this time is The offset QPSK demodulator according to any one of claims 11 to 13, wherein a fading vector is calculated using a next pilot symbol instead. (Equation 4) 16. When the absolute value of the fading vector calculated this time is smaller than a predetermined value, that is, when [Equation 4] is satisfied, the estimating unit determines that the pilot symbol used this time is The offset QP according to any one of claims 11 to 13, wherein a previously calculated fading vector is used instead.
SK demodulator. 17. When the absolute value of the currently calculated fading vector is smaller than a predetermined value, that is, when [Equation 4] is satisfied, the estimating unit calculates the Q component of the fading vector. The offset QPSK demodulator according to any one of claims 11 to 13, wherein the offset QPSK demodulator is set to zero. 18. When the absolute value of the currently calculated fading vector is smaller than a predetermined value, that is, when [Equation 4] holds, the estimating unit calculates the I component of the fading vector. Setting the Q component to zero in the absolute value of the I component of the reception vector at the I timing when the pilot symbol is received, the absolute value of the Q component of the reception vector at the Q timing when the pilot symbol is received, or the average value of both. Item 14. The offset QPSK demodulator according to any one of Items 11 to 13. 19. The offset QPSK demodulation according to claim 6, wherein the estimating unit sets an average value of the individual fading influence degrees calculated based on one component of two or more consecutive pilot symbols as the fading influence degree. apparatus. 20. The offset QPSK demodulator according to claim 19, wherein the estimating unit calculates an individual fading influence degree based on [Equation 5] using I components of two or more consecutive pilot symbols. (Equation 5) 21. The offset QPSK demodulator according to claim 19, wherein the estimating unit calculates the individual fading influence degree based on [Equation 6] using the Q components of two or more consecutive pilot symbols. (Equation 6) 22. An encoding unit that converts a data bit sequence into a signal value sequence composed of IQ2 components, and outputs a symbol sequence having one set of the signal value sequence composed of IQ2 components as one symbol. A synchronization symbol insertion unit that inserts a synchronization symbol according to a predetermined rule into a symbol sequence output from the unit, and a pilot symbol according to a predetermined rule in the symbol sequence in which the synchronization symbol is inserted by the synchronization symbol insertion unit. A pilot symbol insertion unit to be inserted; a delay unit that delays a transmission time of one component of the symbol sequence in which the pilot symbol is inserted by the pilot symbol insertion unit by １ ／ symbol compared with a transmission time of the other component; One component of the symbol sequence delayed by the delay unit and the pilot symbol An offset QPSK modulator comprising: a quadrature modulator for orthogonally modulating the other component of the inserted symbol sequence using a carrier of a predetermined frequency; a quadrature demodulator for extracting a symbol from a carrier to be transmitted; A synchronization detection unit for identifying a synchronization symbol included in the symbol extracted from the unit, and a pilot symbol included in the symbol extracted from the quadrature demodulation unit after the synchronization symbol is identified by the synchronization detection unit. And an estimating unit for estimating the degree of influence of fading, and a compensating unit for compensating for the effect of fading on data symbols included in the symbols extracted from the orthogonal demodulation unit based on the degree of fading estimated in the estimating unit. A decoupling unit for reproducing a data bit string from the data symbols compensated by the compensating unit. Offset Q comprising a de section, the
An offset QPSK communication system using the PSK demodulator. 23. The offset QPSK communication system according to claim 13, wherein said pilot symbol insertion unit inserts a pilot symbol different from a pilot symbol used in a pilot symbol insertion unit of another offset QPSK communication system.