JP2012249131A - Receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a receiver for enabling signal separation by suppressing interference at each reception antenna without using equalization processing by a MMSE method.SOLUTION: A receiver comprises: timing indication means for indicating a non-signal period in which no signal of a radio communication system owning the receiver is transmitted; noise estimation means for measuring reception power of a reception signal in the non-signal period for each reception antenna, and outputting the reception power as an interference power value; weighting processing means for calculating a weighting coefficient, for each reception antenna, which decreases with increasing in the interference power value and increases with decreasing in the interference power value, from the interference power value of each reception antenna output by the noise estimation means, multiplying the reception signal of each reception antenna by a corresponding weight coefficient, and outputting signals corresponding to the number of transmission antennas; and demodulation/decoding means for demodulating/decoding each output of the weighting processing means, separating/recovering signals differing from each other transmitted from the plurality of transmission antennas, and outputting the signals.

Description

  The present invention relates to a receiver that receives different signals transmitted from a plurality of transmission antennas by a plurality of reception antennas, and separates and restores each signal.

  In MIMO (Multiple Input Multiple Output) transmission, a transmitter having a plurality of transmitting antennas transmits different signals from the respective antennas, and a plurality of signals received by being combined with a plurality of receiving antennas of the receiver are transmitted. This is a transmission method that separates and restores using the difference in radio channel. In MIMO transmission, it is necessary to accurately separate a plurality of signals that are combined and received at a receiver, and therefore, it is a technical problem to realize a high-accuracy signal separation method with an operation processing amount at a practical level. . As one of the signal separation methods, there is a minimum mean square error (MMSE) method.

  FIG. 4 shows a configuration example of a receiver that performs signal separation using the MMSE method (Non-Patent Document 1). Here, an example corresponding to four transmission antennas and four reception antennas is shown.

  In FIG. 4, the receiver includes receiving antennas 21-j (j = 1, 2, 3, 4), channel estimation means 22, MMSE equalization means 23, square Euclidean distance calculation means 24 corresponding to the number of transmission antenna branches, A log likelihood ratio (LLR) calculating unit 25 and a soft decision channel decoding unit 26 are included.

  The signals respectively received by the receiving antennas 21-j are input to the channel estimation means 22 and the MMSE equalization means 23. The channel estimation means 22 compares the pilot signal included in the received signal with the pilot signal recorded in the receiver, so that a channel between each transmitting antenna provided in the transmitter and each receiving antenna provided in the receiver is obtained. Information (amplitude and phase fluctuation amount in the channel) is calculated. Using the channel matrix H constituted by this channel information, the received signal Y is expressed by the following equation (1).

  Here, yj (j = 1, 2, 3, 4) represents the received signal Y received by the receiving antenna 11-j. di (i = 1, 2, 3, 4) represents a transmission signal X transmitted from the transmission antenna i, and nj represents Gaussian noise N generated at the reception antenna 11-j. hij represents a channel matrix H between the transmitting antenna i and the receiving antenna 11-j.

Based on the channel matrix input from the channel estimation unit 22, the MMSE equalization unit 23 performs equalization processing for suppressing the interference between the antennas on the reception signal input from each reception antenna 21-j. That is, the channel matrix H is used to calculate the MMSE weight W expressed by the equation (2), and the received signal Y is multiplied to perform equalization processing.
W = H ^H (HH ^H + NI) ⁻¹ (2)
Here, I represents a unit matrix, and H ^H represents Hermitian transpose.

  The squared Euclidean distance calculation unit 24, the LLR calculation unit 25, and the soft decision channel decoding unit 26 calculate an LLR for each bit from the equalized signal and perform soft decision channel decoding (demodulation / decoding processing).

Kenichi Higuchi, Hidekazu Taoka, "Multi-antenna Wireless Transmission Technology" NTT DoCoMo Technical Journal Vol.14 No.1 Fusao Nuno et al., "Experimental Prototype Device for Wide Area Ubiquitous Network-MAC Section", 2007 IEICE General Conference B-5-138

  In the equalization processing by the MMSE method, it is necessary to calculate the MMSE weight W represented by the equation (2) after the calculation of the channel matrix H represented by the equation (1). As the calculation amount increases, there is a problem.

  An object of the present invention is to provide a receiver that enables signal separation by suppressing interference at each receiving antenna with a small amount of calculation without using equalization processing by the MMSE method.

  In the present invention, in a receiver that receives different signals transmitted from a plurality of transmitting antennas by a plurality of receiving antennas and separates and restores each signal, the signal of the wireless communication system to which the receiver belongs is not transmitted. A timing instructing means for instructing a no-signal period, a noise estimating means for measuring a received power in a no-signal period for each received signal for each receiving antenna, and outputting the received power as an interference power value for each receiving antenna; and a noise From the interference power value for each receiving antenna output from the estimation means, calculate a weighting factor for each receiving antenna that increases the interference power value so that the weight value decreases and the interference power value decreases. Weighting that outputs signals for the number of transmission antennas by multiplying the received signal for each reception antenna by the corresponding weighting factor. Comprising a processing unit, respectively demodulating and decoding the output of the weighting processing unit, a demodulation and decoding unit for separating and restoring and outputting different signals from each other are transmitted from a plurality of transmitting antennas.

  The weighting processing means is configured to use the inverse of the interference power value for each reception antenna as a weighting factor.

  The receiver according to the present invention regards received power in a period during which a signal of the wireless communication system to which the receiver belongs is not transmitted as interference power, assigns a small weight to a reception antenna having a large interference power value, and A large weight is given to a receiving antenna having a small value. That is, for each receiving antenna, the received power in the no-signal period is set as interference power.For example, the weighting factor is calculated simply by calculating the reciprocal of the received power. Since the weighting coefficient is calculated based on the above, processing such as signal separation can be performed with high accuracy.

It is a figure which shows the structural example of the receiver of this invention. It is a figure which shows the example of the timing which measures an interference wave with the noise estimation means. It is a figure which shows the structural example of the radio | wireless communications system to which this invention is applied. It is a figure which shows the structural example of the receiver which performs a signal separation using MMSE method.

FIG. 3 shows a configuration example of a wireless communication system to which the present invention is applied.
In FIG. 3, in a configuration in which each receiving antenna is separated from each other and each receiving antenna and the receiver are connected by an optical fiber, each receiving antenna receives different interference waves or causes interference. There may be a receiving antenna that receives and a receiving antenna that does not receive interference. A feature of the present invention is that, in such an environment where the interference received by each receiving antenna is different, the weighting coefficient of the channel equalization processing is calculated using the difference in interference power at each receiving antenna.

  FIG. 1 shows a configuration example of a receiver according to the present invention. Here, an example corresponding to four transmission antennas and four reception antennas is shown.

  In FIG. 1, the receiver includes a reception antenna 21-j (j = 1, 2, 3, 4), a noise estimation unit 11, a timing instruction unit 12, a weighting processing unit 13, and a square Euclidean distance corresponding to the number of transmission antenna branches. The calculation means 24, the log likelihood ratio (LLR) calculation means 25, and the soft decision channel decoding means 26 are comprised.

  The signals respectively received by the receiving antennas 21-j are input to the noise estimation unit 11 and the weighting processing unit 13. In the noise estimation means 11, the interference wave which each receiving antenna 21-j receives is estimated. That is, with respect to an interference wave in a radio band used by the receiver to receive a signal by a wireless communication system other than the wireless communication system including the receiver or a non-wireless communication system, the receiver is a communication partner. The power of the interference wave is measured during a period in which no signal is transmitted to or received from (for example, a transmitter not shown).

FIG. 2 shows an example of timing at which the noise estimation means 11 measures the interference wave.
FIG. 2 (a) shows a guard time (GT) set between the uplink period (UL) and the downlink period (DL) when the receiver is communicating by the TDD (Time Division Duplex) method. The received power is measured, and the obtained measured value is set as the interference power value. Since the signal of the wireless communication system to which the receiver belongs is not transmitted at the guard time, it can be considered that an interference wave from another wireless communication system or a non-wireless communication system is received.

  FIG. 2 (b) shows the measured value obtained by measuring the received power in the unallocated area of the random access slot when the receiver performs communication based on random access (for example, Non-Patent Document 2). Is the interference power value. Similar to the guard time described above, in the unassigned area of the random access slot, the signal of the wireless communication system to which the receiver belongs is not transmitted, so that an interference wave from another wireless communication system or a non-wireless communication system is received. Can be regarded as doing.

The noise estimation unit 11 may output the received power of the measured interference wave to the weighting processing unit 13 as it is, but the interference power received power N _j (obtained by the n-th measurement at the receiving antenna 21-j. The average of n) may be output to the weighting processing means 13 as the interference power value P _j (n). Further, as a result of using the forgetting factor α as in Expression (3), the result of performing the weighted average processing on the received power N _j (n) of the interference wave may be output as the interference power value P _j (n).
P _j (n) = (N _j (n) + αP _j (n−1)) / (1 + α) (3)
By performing the averaging process and the like in this way, the interference power can be accurately estimated even when the dispersion of the interference power is large.

  The timing instruction unit 12 notifies the noise estimation unit 11 of the timing for measuring the interference power. For example, in the case of the TDD system, a control signal is output to the noise estimation means 11 at the timing when the guard time starts and ends. In the case of the random access method, an unallocated area is extracted in a random access slot using a beacon or the like, and a control signal is output to the noise estimation means 11 at the timing when the area starts and ends. The noise estimation unit 11 measures the interference power over the period notified by the timing instruction unit 12 and updates the interference power value.

The weighting processing unit 13 performs weighting processing on the reception signal input from each reception antenna based on the interference power corresponding to each reception antenna input from the noise estimation unit 11. Specifically, as shown in Equation (4), the inverse of the interference power value P _j (n) at the receiving antenna 21-j is set to the weighting factor k (N _j ).
k (N _j ) = 1 / P _j (n) (4)

  In this way, by setting the weighting factor so that the weighting factor decreases as the interference power increases at each receiving antenna, the weight of the received signal with low interference power, that is, high signal quality, increases. Separation becomes possible.

  The squared Euclidean distance calculation unit 24, the LLR calculation unit 25, and the soft decision channel decoding unit 26 calculate the LLR for each bit from the weighted signal and perform soft decision channel decoding (demodulation / decoding processing).

  In the receiver of the present invention, the received power in a period in which the signal of the wireless communication system to which the receiver belongs is not transmitted is regarded as interference power, a weight is given to a receiving antenna having a large interference power value, and the interference power is By assigning a large weight to a receiving antenna having a small value, the amount of calculation can be reduced as compared with the conventional MMSE method involving channel equalization processing.

DESCRIPTION OF SYMBOLS 11 Noise estimation means 12 Timing instruction means 13 Weighting processing means 21 Receiving antenna 22 Channel estimation means 23 MMSE equalization means 24 Square Euclidean distance calculation means 25 LLR (Log Likelihood Ratio) calculation means 26 Soft decision channel decoding means

Claims (2)

In a receiver that receives different signals transmitted from multiple transmitting antennas by multiple receiving antennas and separates and restores each signal,
Timing instruction means for instructing a no-signal period during which a signal of the wireless communication system to which the receiver belongs is not transmitted;
Noise estimation means for measuring the received power in the no-signal period for each received signal for each receiving antenna and outputting the received power as an interference power value for each receiving antenna;
From the interference power value for each of the receiving antennas output from the noise estimation means, a weighting factor that decreases the weight value as the interference power value increases, and increases the weight value as the interference power value decreases. Weighting processing means for calculating for each reception antenna, multiplying the reception signal for each reception antenna by a corresponding weighting factor, and outputting signals for the number of transmission antennas,
A receiver comprising: demodulation and decoding means for demodulating and decoding the outputs of the weighting processing means, and separating and restoring different signals transmitted from the plurality of transmission antennas. The receiver of claim 1,
The receiver is characterized in that the weighting processing means is configured to use a reciprocal of the interference power value as a weighting factor for each of the receiving antennas.

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