JP2600110B2 - Digital mobile radio communication method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication technique for performing radio communication using digital signals between a mobile station and a base station or between mobile stations, and more particularly, to a technique for reducing the influence of interference waves. And a digital mobile radio communication method capable of improving transmission quality.

[0002]

2. Description of the Related Art As a method for improving the deterioration of transmission quality due to an interference wave, a method similar to maximum likelihood sequence estimation is known. As an example, a method of generating a replica of an interference wave and performing maximum likelihood sequence estimation using a difference between the replica and a received signal (Jin Yoshino, Kazuhiko Fukawa, Hiroshi Suzuki: "Adaptive Interference Canceller by RLS-MLSE", Electronic Information Communication) Journal of the Society, BI
I, J77-B-II, No. 2, February 1994).

[0003]

The method using the maximum likelihood sequence estimation requires a long sequence length in order to identify a desired wave from a received signal on which an interference wave is superimposed. As a result, a large amount of calculation is required in the process of estimating the maximum likelihood sequence. In addition, the method related to the generation of the replica of the interference wave requires more processing operations for generating the replica for the number of interference waves, and thus requires a larger amount of calculation. Generally, since the number of interference waves cannot be specified, a redundant design is required for the processing for replica generation, and the hardware requirements are strict.

[0004]

In order to solve the above-mentioned problems, the present invention focuses on the fact that the interference wave level generally fluctuates slowly. That is, the digital mobile radio communication method according to the present invention, on the transmission side, encodes an information sequence to be provided for transmission, configures a slot for transmission, outputs a transmission signal, and on the reception side receiving the transmission signal, The Euclidean distance minimum decoding weighted using the interference wave level value estimated one unit time ago held in the memory is performed, the interference signal level is obtained by subtracting the decoded signal from the received signal, and the signal is smoothed. Then, this is set as an estimated interference wave level and stored in a memory. Here, the unit time refers to the time required to perform one calculation of the estimated interference wave level.

[0005]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of a digital mobile radio method according to the present invention. First,
FIG. 1 shows an outline of signal processing steps on the transmission side and the reception side.
This will be described below.

On the transmitting side, an information sequence to be transmitted is encoded. This is referred to as an encoded information sequence a.

[0007] Further, the encoded information sequence a is interleaved. This is called a transmission signal sequence b.

On the receiving side, the sum of the transmission signal sequence b and the interference wave signal c is received as a reception signal sequence d.

The received signal sequence d is deinterleaved to obtain a deinterleaved received signal sequence e. The received signal sequence e after deinterleaving is obtained by performing weighted Euclidean distance minimum decoding using the interference wave signal calculated one unit time ago and held in the memory, over all of the predetermined candidate code sequences. The Euclidean distance is calculated and the most likely code sequence is selected. This becomes the decoded sequence f.

For the decoded sequence f thus decoded,
By performing the same operation as the interleaving performed on the transmitting side, an interleaved decoded sequence g is obtained. Assuming that decoding is performed without error, a sequence h composed of a value obtained by subtracting the interleaved decoded sequence g from the received signal sequence d becomes the interference wave signal c itself. However, as the interference wave signal increases, the probability of error during decoding increases, making it difficult to accurately detect the interference wave.

However, in actual digital mobile radio communication, a signal sequence observed as an interference wave signal often has a temporally slow amplitude fluctuation over a plurality of sequences. By utilizing this property, a smoothing operation is performed on the detected sequence h to obtain an estimated interference wave level having a high probability as an interference wave level during the communication. In this way, the reliability of the interference wave level detected on the receiving side is increased, and the transmission quality can be improved.

The estimated interference wave level obtained as described above is temporarily stored and used so as to be used when performing a weighted decoding process in the next processing step.

Next, an embodiment of a transmitting station and a receiving station which embody the digital mobile radio communication method according to the present invention will be described in detail with reference to FIGS.

The modulation method used in the embodiment is 16QA.
M. Since 16QAM includes information in its amplitude, it is necessary to take measures against fading in a digital mobile radio communication system. Here, as a countermeasure against fading, a transmission line distortion compensation method (Japanese Patent Laid-Open No. 1-196924) is applied. In the transmission line distortion compensation method, a known symbol (called a pilot symbol or a frame symbol) is periodically inserted into a sequence of a signal to be transmitted on a transmission side. Then, on the receiving side, the transmission line distortion is compensated by estimating the reception envelope level from pilot symbols.

First, on the transmitting side in FIG. 2, an information sequence 1 to be transmitted is encoded by an encoding unit 2 and is symbolized by a signal point arrangement unit 3.

Next, the symbolized sequence 4 is interleaved by an interleaving section 5. Next, pilot symbols are periodically inserted by pilot symbol insertion section 6 into the interleaved sequence.

The transmission signal sequence 7 thus configured is band-limited through the transmission-side root Nyquist filter unit 8, then converted into a high-frequency signal by the transmission-side local oscillator unit 9 and quadrature modulation unit 10, and output from the transmission-side antenna 11. Is done.

On the receiving side in FIG. 3, the high frequency signal received from the receiving antenna 12 is quasi-synchronously detected by the local oscillator 13 and the quasi-synchronous detector 14 having the same frequency as the transmitting side. Further, in order to remove unnecessary waves, the signals are filtered by the receiving-side root Nyquist filter unit 15.

A pilot symbol is separated from the filtered received signal sequence 16 by a pilot symbol separation unit 17. A sequence composed of the separated pilot symbols is called a pilot symbol sequence 18.

The received information sequence 19 from which the pilot symbols have been separated is subjected to fading distortion in a fading distortion compensator 20. Here, in the fading distortion compensator,
In order to estimate fading distortion, a reception envelope level sequence 21 is obtained from a pilot symbol sequence to perform compensation. The obtained reception envelope level sequence is also used for the subsequent decoding unit.

The received information sequence 22 from which the distortion has been removed is deinterleaved by a deinterleaver 23, and
Lead to 4.

On the other hand, the reception envelope level sequence is also deinterleaved and guided to the decoding unit.

The decoded sequence 25 is supplied to an interleave unit 26
Are interleaved by By subtracting the signal sequence 22 from this signal sequence by the subtracter 27, an estimated interference signal sequence is obtained. This signal sequence is smoothed by the smoothing unit 29 and deinterleaved. The deinterleaved value is stored in the memory unit 31 and used as an interference wave level at the time of decoding in the next unit time.

The decoding unit performs weighting with the interference wave level sequence 30 obtained from the present invention in addition to weighting with the conventional reception envelope level sequence 21, and performs minimum Euclidean distance decoding.

The minimum weighted Euclidean distance decoding performs the following. n, v, r (k), and ω are defined as follows.

[0026]

(Equation 1)

[0027]

(Equation 2)

[0028]

(Equation 3)

[0029]

(Equation 4)

N, v, and ω are an interfering wave level sequence, a received information sequence, and a received envelope level sequence one unit time ago, which are deinterleaved and stored in the memory, respectively. R (k) is a k-th candidate code sequence, and N is a sequence length.

At this time, in the minimum Euclidean distance decoding weighted at the interference wave level, M _k given by the following equation is executed over all k.

[0032]

(Equation 5)

Here, M _k is a judgment variable, and δ is a positive constant for stabilization. From _k when M _k takes the minimum value, r
(K) is determined as the decoded sequence 30 and output.

The smoothing section 29 smoothes the input signal sequence by passing it through a first-order low-pass filter. The smoothing unit performs the following. n1, n2
Are defined as follows.

[0035]

(Equation 6)

[0036]

(Equation 7)

N1 and n2 are an interference signal sequence input to the smoothing unit and an interference signal sequence output, respectively. N is the sequence length.

At this time, n1, n2 in the smoothing section
Is related by the following equation:

[0039]

(Equation 8)

Here, p is a positive constant that determines the time constant of the low-pass filter, and is selected between 0 <p <1. Further, n _2i (t−1) is a value one unit time before n _2i .

FIG. 4 shows the bit error rate characteristics of this embodiment by computer simulation. The horizontal axis is the average C / I
(Average ratio of desired wave power to interference wave power), and the vertical axis indicates BER (bit error rate).

The simulation condition is a modulation speed of 16 ks.
ymbols / sec, 8 bits / 1 block for coding, pseudo-cyclic block code with coding rate 1/2, as a transmission line model used for simulation, the maximum fading pitch is 80 Hz for the desired wave, and the delay spread is 2 μs. The equal-amplitude two-wave model Rayleigh fading and the interference wave are given an amplitude fluctuation according to a lognormal distribution with a standard deviation of 6.5 dB in addition to the above-mentioned equal-amplitude two-wave model Rayleigh fading.

According to the present invention, the characteristic of the embodiment in which the Euclidean distance decoding is weighted using the detected interference wave level and the decoding is performed with the minimum Euclidean distance without using the interference wave level is shown in FIG. It can be seen that they are superior to the characteristics of the Example (indicated by a mark in the figure).

[0044]

According to the present invention, in a digital mobile radio communication system, an improvement in transmission quality can be realized by a simple method by detecting an interference wave level and using it for decoding.

[Brief description of the drawings]

FIG. 1 is a diagram showing a series of signal sequences obtained in a process in a digital mobile radio communication method according to the present invention.

FIG. 2 is a diagram illustrating a transmitting side according to an embodiment of the present invention.

FIG. 3 is a diagram showing a receiving side according to an embodiment of the present invention.

FIG. 4 is a diagram showing that bit error rate characteristics are improved according to one embodiment of the present invention.

[Explanation of symbols]

 a ... information sequence after encoding b ... transmission signal sequence c ... interference wave signal d ... reception signal sequence e ... reception signal sequence after deinterleaving f ... decoding sequence g ... interleaved decoded sequence h ... sequence g from sequence d Subtracted sequence 1 Information sequence 2 Encoding unit 3 Signal point arrangement unit 4 Symbolized sequence 5 Interleave unit 6 Pilot symbol insertion unit 7 Transmission signal sequence 8 Transmission root Nyquist filter unit 9 Transmission Side local oscillator unit 10: Quadrature modulation unit 11: Transmitting antenna 12: Receiving antenna 13: Receiving local oscillator unit 14: Quasi-synchronous detection unit 15: Receiving root Nyquist filter unit 16: Received signal sequence 17: Pilot symbol separation Unit 18: pilot symbol sequence 19: received information sequence 20: fading distortion compensation unit 21: received envelope level sequence 2 2 ... Received information sequence after distortion removal 23 ... Deinterleave unit 24 ... Decoding unit 25 ... Decoded sequence 26 ... Interleave unit 27 ... Subtractor 28 ... Estimated interference signal sequence 29 ... Smoothing unit 30 ... Smooth interference signal Series 31 ... Memory

Continuation of the front page (56) References JP-A-6-232769 (JP, A) IEICE Technical Report Vol. 93, no. 464 A.P.93-139 (February 1994) 33-39 IEICE Technical Report Vol. 95, No. 12 RCS95-7 (1995-April) 39-44 IEICE Transactions B-2, VOL. 78 NO. 6 (1995-6-25) p. 445-452

Claims (1)

(57) [Claims] 1. A digital mobile radio communication method for performing radio communication by digital signals between a mobile station and a base station or between mobile stations, wherein a transmitting side encodes an information sequence to be transmitted and transmits the encoded information sequence. , And outputs the transmission signal, the receiving side that has received the transmission signal performs Euclidean distance minimum decoding weighted using the estimated interference wave level one unit time earlier held in the memory, A digital mobile radio communication method comprising: obtaining a temporary interference wave level by subtracting a decoded signal from a received signal; smoothing the signal to obtain an estimated interference wave level; and storing the signal in a memory.