JP6087256B2 - Baseband signal transmitter and receiver - Google Patents

Description

  The present disclosure relates to a communication technique between a base station that transmits / receives a radio signal and a baseband processing device that transmits / receives a baseband signal to / from the base station in a wireless communication network.

  Currently, for flexible deployment of wireless communication networks, baseband signals are not generated in base stations and converted into wireless signals in base stations, but in baseband processing devices installed in different locations from base stations. A configuration for generating is proposed. In this configuration, the baseband processing device generates a baseband signal by performing modulation based on transmission data, transmits the generated baseband signal to the base station using a transmission line such as an optical fiber, and the base station The baseband signal to be received is subjected to frequency conversion (up-conversion) and amplification processing and transmitted as a radio signal to the mobile terminal. On the other hand, the base station performs amplification and frequency conversion (down-conversion) of the radio signal received from the mobile terminal to convert it into a baseband signal, and this baseband signal is subjected to baseband processing using a transmission line such as an optical fiber. The baseband processing device demodulates the received baseband signal.

  Patent Document 1 proposes to compress a baseband signal transmitted and received between a base station and a baseband processing device. Note that the baseband signal is compressed and decompressed by the baseband processor in the transmission from the base station to the baseband processor, and the baseband processor in the transmission from the baseband processor to the base station. Since the compression of the band signal and the decompression at the base station are the same, in the following, the device that compresses the baseband signal is called a transmitting device, and the device that decompresses the compressed baseband signal is called a receiving device. That is, the base station and the baseband processing device each have a transmission device and a reception device.

Special table 2011-526095 gazette

  In Patent Document 1, compression of two in-phase (I) and quadrature (Q) baseband signals is performed separately. Therefore, the transmission device requires respective in-phase and quadrature compression units, and the reception device also has the in-phase and Requires each orthogonal decompression section. Further, in Patent Document 1, since compression is performed by Huffman coding or the like of the difference of each sample of the baseband signal, the data compression rate fluctuates. Therefore, the data rate of the compressed baseband signal sent from the transmission device to the reception device Is variable. However, since transmission between the transmission device and the reception device is generally performed at a fixed data rate, the baseband signal compressed by the method described in Patent Document 1 is used for transmission between the transmission device and the reception device. It is difficult to apply.

  The present invention provides a transmitting apparatus and a receiving apparatus that solve at least one of the above problems.

  According to an aspect of the present invention, the transmission apparatus determines, for each predetermined period, a determination unit that determines a distribution of each sample value of the baseband signal, a determination unit that determines a quantization step based on the distribution, and the determination Encoding means for encoding each sample value of the baseband signal in the quantization step.

  The baseband signal can be effectively compressed at a fixed data rate.

The schematic block diagram of the transmitter by one Embodiment. The schematic block diagram of the compression part by one Embodiment. Explanatory drawing of requantization step determination. Explanatory drawing of the encoding by a requantization step. The schematic block diagram of the receiver by one Embodiment. The schematic block diagram of the decompression | decompression part by one Embodiment.

  Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. In the following drawings, components that are not necessary for describing the embodiment are omitted from the drawings. Moreover, the following embodiment is an illustration and does not limit this invention to the content of embodiment.

  FIG. 1 is a schematic configuration diagram of a transmission apparatus according to an embodiment. The two in-phase (I) and quadrature (Q) baseband signals are digitally converted in analog-to-digital converters (ADC) 11 and 12, respectively. In this example, the ADCs 11 and 12 encode (quantize) each sample value with N bits. The multiplexing unit 13 time-division multiplexes the digitized in-phase and quadrature baseband signals for each sample value, and outputs the result to the compression unit 14 as one sample string. The compression unit 14 performs compression processing of the time-division multiplexed baseband signal from the multiplexing unit 13, and transmits the compressed baseband signal (denoted as a signal in the drawing) and quantization information to the transmission unit 15. To do. Details of the compression processing and quantization information transmitted to the transmission unit 15 will be described later. The transmission unit 15 generates a frame having a predetermined configuration from the compressed baseband signal data and the quantization information, and transmits the frame to the transmission path.

FIG. 2 is a diagram illustrating a schematic configuration of the compression unit 14. In this example, the compression unit 14 performs compression by requantizing each sample value represented by N bits of the sample sequence input from the multiplexing unit 13 with M bits (N> M). First, the sample sequence from the multiplexing unit 13 is stored in the buffer unit 141 and input to the quantization step calculation unit 144. The quantization step calculation unit 141 obtains a distribution (histogram) of amplitude values of each sample for a predetermined period. Here, S is the number of samples in a predetermined period. The quantization step calculation unit 141 determines the quantization step so that the number of samples included in each section is as uniform as possible (S / 2 ^M ).

  For example, N = 6 bits and M = 3 bits. In this case, the amplitude value of each sample is any one of 64 of −32 to +32. Here, as shown in FIG. 3, among the S samples, those having an amplitude value of 15 to 31, those having 5 to 14, those having 2 to 4, those having 0 to 1, It is assumed that the number is 2 to -1, the number is −5 to −3, the number is −15 to −6, and the number −32 to −16 is S / 8. In this case, the quantization step calculation unit 141 has amplitude values of 15 to 31, 5 to 14, 2 to 4, 0 to 1, −2 to −1, −5 to −3, −15 to −6, − Each of 32 to -16 is defined as one quantization step.

  Then, the quantization step calculation unit 144 notifies each quantization step to the encoding unit 142, and the encoding unit 142 reads out from the buffer unit 141 at the quantization step notified from the quantization step calculation unit 144. Encode sample values. For example, FIG. 4 shows an example of encoding when the quantization step is determined as shown in FIG. In the example shown in FIG. 4, sample values with amplitude values of 15 to 31 are encoded as “011”. The codeword corresponding to each quantization step determined by the quantization step calculation unit 144 can be determined in advance in the order of the amplitude. Further, in order to notify the reception device of the boundary values of the respective quantization steps determined by the quantization step calculation unit 144, the quantization step calculation unit 144 transmits the quantization information indicating the boundary values of the quantization steps to the transmission unit 15. Output to. The quantization information can be, for example, a value below or above each boundary. For example, when the lower value of the boundary is notified in the quantization step of FIG. 5, the quantization step calculation unit 144 sets the values 14, 4, 1, −1, −3, −6, −16 to the quantization information. And

In FIG. 3, in order to simplify the description, a case where S samples can be equally divided by (S / 8) is shown, but there are more cases where the actual number cannot be equally divided. Therefore, in general, the quantization step is determined so that the number of samples included in each of the 2 ^M quantization steps is closest to (S / 2 ^M ). For example, the quantization step calculation unit 144 can determine the quantization step so that the difference between the maximum value and the minimum value of the number of samples included in each quantization step section is minimized. Further, the quantization step can be determined so that the maximum value of the difference in the number of samples in each quantization step section is minimized.

  FIG. 5 is a schematic configuration diagram of a receiving device according to an embodiment. The receiving unit 21 receives the frame transmitted by the transmitting device, and transmits each M-bit sample (signal) of the baseband signal and quantization information to the decompressing unit 22. FIG. 6 is a schematic configuration diagram of the decompression unit 22. Each M-bit sample is input to the buffer unit 221, and the quantization step calculation unit 223 obtains a relationship between the M-bit sample value and the N-bit sample value from the quantization information, and notifies the decoding unit 222 of the relationship. The decoding unit 222 converts the M-bit sample value into an N-bit sample value. At this time, the decoding unit 222 converts the N-bit sample value included in the M-bit sample value into an approximately N-bit sample value. Specifically, when the M-bit value is “010” in the relationship of FIG. 4, it is converted into an N-bit sample value indicating the amplitude value of “9” or “10”, and the M-bit value is “001”. In this case, the sample value is converted into an N-bit sample value indicating an amplitude value of “3”. Returning to FIG. 5, the separation unit 23 separates the N-bit sample value output from the decompression unit 22 for each sample, and converts the in-phase and quadrature digitized baseband signals into digital-to-analog converters (DACs), respectively. ) 24 and 25, the digital / analog converters 24 and 25 output analog baseband signals, respectively.

  In this embodiment, the distribution of sample values for each predetermined period is examined, and a quantization step for requantization is determined so that the number of samples becomes equal. That is, in the vicinity of sample values with a large distribution, the quantization step for requantization becomes finer, so that it is possible to compress to a fixed rate while suppressing quantization noise due to requantization. In addition, the number of compression units 14 and decompression units 22 can be reduced to one by performing time division multiplexing on sample values of in-phase and quadrature baseband signals. It is known that the average value and the variance value of the amplitude of the in-phase and quadrature analog baseband signals are similar to each other. Therefore, the sample values of the in-phase and quadrature baseband signals are time-division multiplexed. However, the characteristics of the sample value distribution do not change significantly.

<Second embodiment>
Next, the second embodiment will be described focusing on the differences from the first embodiment. In the first embodiment, the requantization step is obtained from the histogram. In the present embodiment, the average value (μ) and standard deviation (σ) of the amplitude values of the samples for a predetermined period are obtained, and the distribution of the amplitude values is assumed to follow the normal distribution (N, σ ² ). The subsequent steps are the same as in the first embodiment. That is, according to the obtained normal distribution, the quantization step is determined so that the number of included samples (interval integrated value) becomes equal. In this embodiment, an average value (μ) and a standard deviation (σ) (or variance) are used as quantization information.

Claims (11)

Determination means for determining the distribution of each sample value of the baseband signal for each predetermined period;
Determining means for determining a quantization step based on the distribution;
Encoding means for encoding each sample value of the baseband signal in the determined quantization step;
A transmission device comprising:   The transmission apparatus according to claim 1, further comprising transmission means for transmitting the data encoded by the encoding means and the quantization step determined by the determination means to the reception apparatus.   The determining means is configured to set a quantization step interval of a section having a larger number of samples out of two sections including one or more consecutive sample values of the distribution to an interval of a quantum step having a smaller number of samples. The transmission device according to claim 1, wherein the transmission device is made smaller.   The transmission apparatus according to claim 1 or 2, wherein the determination unit determines the quantization step so that a difference between a maximum value and a minimum value of the number of samples included in each quantization step is minimized.   3. The transmission apparatus according to claim 1, wherein the determination unit determines each quantization step so that a maximum value of a difference in the number of samples included in each quantization step is minimized.   The determination unit obtains an average value and variance of sample values of the baseband signal for each predetermined period, and determines that the distribution is a normal distribution according to the average value and variance. 2. The transmission device according to 2.   7. The transmission apparatus according to claim 6, wherein the determination unit determines each quantization step from the normal distribution so that the number of samples included in each quantization step is equal.   The transmission apparatus according to any one of claims 1 to 7, wherein the baseband signal input to the determination unit is obtained by time-division multiplexing two in-phase and quadrature baseband signals. . Reception for receiving M-bit (M is an integer equal to or greater than 2) sample value, 2 ^M quantization steps, and quantization information indicating a relationship between N-bit (N is an integer greater than M) amplitude value A device,
A receiving apparatus comprising: conversion means for converting the M-bit sample value into an N-bit sample value based on the quantization information. The quantization information is information indicating a normal distribution,
The normal distribution is further divided into 2 ^M sections so that the integral value of each section becomes equal, and further includes a determination unit that determines a relationship between 2 ^M quantization steps and amplitude values. The receiving device according to claim 9.   11. The apparatus according to claim 9, further comprising separation means for separating N-bit sample values output from the conversion means and outputting sample values of two in-phase and quadrature baseband signals. Receiver.

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