CN107070451B - Equipment ADC precision configuration method in large-scale MIMO system - Google Patents

Abstract

The invention discloses a method for configuring the precision of an ADC (analog to digital converter) of equipment in a large-scale MIMO (multiple input multiple output) system. In a large-scale MIMO system, due to the large number of antennas, configuring a DAC and an ADC with low accuracy for each antenna unit can effectively control the overall power consumption of the transmission system. The invention considers the down link, the large-scale antenna base station as the transmitting terminal configures a low-power consumption 1-bit quantification DAC for each antenna, and the invention can calculate and determine the optimal precision of the receiving terminal ADC meeting the target speed requirement according to the fixed system parameters such as the number of the base station antennas and the terminal equipment. The method is simple in calculation, can realize the target performance of the system with the minimum power consumption cost, and has guiding significance on large-scale MIMO system configuration and hardware design.

Description

A method for configuring ADC precision of equipment in massive MIMO system

technical field

The invention relates to a method for configuring the precision of a device ADC (analog-to-digital conversion unit) in a massive MIMO (multiple input multiple output) system, which belongs to wireless communication technology.

Background technique

In recent years, in order to meet the rapidly increasing demands of mobile data transmission, wireless communication systems urgently need to improve spectrum transmission efficiency. MIMO, that is, using multiple transmit and receive antennas at the transmitter and receiver respectively, can make full use of space resources to suppress channel fading, and significantly improve the channel capacity of the system without increasing spectrum resources and overall transmit power. The advantages. The massive MIMO technology proposed on this basis has become a key component of the next-generation wireless communication system (5G). This technology greatly improves the spatial freedom of wireless signal transmission by configuring hundreds or even thousands of antennas for the base station, thereby improving the spectral efficiency and channel capacity of the system through space division multiplexing. In the multi-user MIMO scheme, one base station serves multiple single-antenna users at the same time, and multiple data streams can be simultaneously transmitted between the base station and the users. As long as the number of base station antennas exceeds the number of users, each user can still obtain considerable spatial degrees of freedom.

However, the increase in the number of antennas also increases the complexity of hardware implementation. In the downlink, each base station transmit antenna needs to be configured with a DAC (digital-to-analog conversion unit), and each terminal receive antenna needs to be configured with an ADC. Therefore, hardware cost and power consumption cost increase rapidly as the number of antennas increases. This greatly limits the application of massive MIMO. There are currently two main solutions to this problem. One is to reduce the number of DACs and ADCs, and use hybrid transceivers to reduce RF links. For example, digital precoding is performed at the transmitter, followed by digital-to-analog conversion, and then analog precoding. Digital precoding still uses traditional zero-breaking (ZF), maximum ratio transmission (MRT) precoding and other methods, while analog precoding requires additional design. When performing beamforming, the lower limit of the number of RF links is the actual number of transmitted data streams, while the upper limit of the beamforming gain is determined by the number of antennas; the second is to reduce the accuracy of the DAC and ADC, and even only use a 1-bit DAC in extreme cases and ADC, because the power consumption of the DAC and ADC increases exponentially with the number of bits of quantization precision. Most of the current solutions consider low-precision DACs or ADCs alone. Therefore, the joint consideration of the precision configuration of the two, especially the trade-off between the two precisions, is of great significance to the design of the actual system. If the above two schemes are combined, the power consumption of the massive MIMO system can be reduced from two aspects at the same time.

When the transmitter is configured with a 1-bit DAC, it is not necessary to configure an infinite-precision ADC at the receiver. Because a low-precision ADC can also achieve close to the maximum data transfer rate, the power consumption will be much lower than that of an infinite-precision ADC. In other words, the accuracy of the ADC requires a trade-off between system transmission performance and hardware and power costs. Designing the accuracy of the receiver ADC according to the specific data rate requirements has very important guiding significance for the system implementation.

SUMMARY OF THE INVENTION

Purpose of the invention: In order to overcome the deficiencies in the prior art, the present invention provides a method for calculating the precision configuration of a device ADC in a massive MIMO system. The method calculates the precision configuration value of the ADC, which can minimize the signal quantization module in the transmission system. It can greatly reduce the overall power consumption of large-scale antenna array systems.

Technical scheme: in order to achieve the above purpose, the technical scheme adopted in the present invention is: comprising the steps:

(1) According to the Bussang theory, when the base station transmit antenna is configured with a 1-bit DAC, and the terminal receive antenna is configured with an ideal infinite-precision ADC, the received signal-to-noise ratio γ _ideal of each user in the downlink is:

Among them, ρ _DAC = 0.3634, representing the influence parameter of 1-bit quantization DAC on the received signal-to-noise ratio; the number of base station antennas is N, the number of single-antenna users of the terminal is M, the transmit power is P, and the thermal noise power of the receiving end is N ₀ ;

(2) According to the Bussang theory and step (1), when the transmit antenna of the base station is configured with a 1-bit DAC, and the receive antenna of the terminal is configured with a low-precision ADC with k _ADC quantization bits, the received signal-to-noise ratio γ of each user in the downlink is :

Among them, k _ADC ≥ 3, ρ represents the attenuation factor of the low-precision ADC to the received signal-to-noise ratio; the relationship between ρ and k _ADC is:

(3) When the target data rate is n times the ideal rate, according to Shannon's formula, we have

log(1+γ)=ηlog(1+γ _ideal )

By substituting formula (2), the decay factor ρ can be solved:

(4) After obtaining ρ according to step (3), calculate the configuration value k _ADC required by the ADC accuracy of the terminal receiving antenna according to formula (3):

表示向上取整。in,

Indicates rounded up.

Beneficial effects: The method for configuring the precision of the device ADC in the massive MIMO system provided by the present invention has the following advantages compared to the prior art: 1. The present invention starts from the overall situation of the massive MIMO system, and configures a 1-bit DAC at the transmitting end on the premise 2. The present invention approximates the nonlinear influence of DAC and ADC quantization accuracy on the user data rate into linear , simplifies the solution process and reduces the computational complexity; 3. In the present invention, the number of base station antennas N, the number of users M, the transmit power P, and the noise power N ₀ are flexible; therefore, this scheme is suitable for any signal-to-noise ratio. Multi-user massive MIMO system; 4. The present invention has important value for the design of the actual system; under a given data rate requirement, the present invention can quickly determine the accuracy of the ADC, and obtain the required performance with the lowest power consumption cost.

Description of drawings

1 is a block diagram of a transmitter and a receiver of a massive MIMO system in the present invention;

FIG. 2 is a schematic diagram of the low-precision ADC processing the signal at the receiving end in the present invention;

3 is a schematic diagram of the variation of the ADC accuracy calculated according to the present invention with the target data rate under given conditions;

FIG. 4 is a schematic diagram showing the variation of ADC accuracy with signal-to-noise ratio calculated according to the present invention under given conditions.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings.

FIG. 1 shows the block diagram of the transmitter and the receiver of the massive MIMO system in the present invention. At the transmitter, the original data is modulated to generate M symbols, and then pre-coded to generate N complex signals. The real and imaginary parts of each complex signal pass through the DAC to generate an analog signal, and finally pass through the radio frequency link (RF) and then generate an analog signal. N antennas transmit. At the receiving end, M single-antenna users receive signals respectively, and after being processed by the radio frequency link, digital signals are obtained by ADC module processing, and finally the original data is recovered by demodulation.

Figure 2 shows the operation process of the low-precision ADC on the received signal. The ADC's precision k _ADC is 1 bit, the number of transmit antennas N is 32, and the number of users M is 8. The signal y in the figure is the received signal processed by the radio frequency link. It can be seen from the figure that y is continuously distributed between -5 and 10; the signal y _q is the output signal processed by the ADC, as can be seen from the figure y _q has only 2 values. Obviously, after the processing of the low-precision ADC, the received signal is distorted, and the smaller the k _ADC is, the more serious the distortion is. Therefore, in order to reduce the system power consumption, using a low-precision ADC will affect the system transmission performance. Specifically, the transmission rate will be reduced.

Fig. 3 shows the ADC calculated according to the algorithm of the present invention when the signal-to-noise ratio is P/N ₀ =0dB, N=128, M=8 and the target data rate is 0-100% of the ideal rate respectively precision. As can be seen from the figure, if the data rate is to reach 0 to 39% of the ideal rate, the accuracy of the ADC must reach at least 1 bit; if it is to reach 40% to 76%, it must be at least 2 bits; if it is to reach 77% % to 93%, at least 3 bits; if 94% to 98%, at least 4 bits. The specific steps for calculating k _ADC are as follows:

(1) From N=128, M=8, and the signal-to-noise ratio P/N ₀ =0dB, when a 1-bit DAC and an ideal infinite-precision ADC are configured, the received signal-to-noise ratio γ _ideal of each user in the downlink is calculated. , the formula is:

Among them, ρ _DAC =0.3634, which represents the influence parameter of 1-bit quantization DAC on the received signal-to-noise ratio.

(2) According to the Bussang theory and step (1), when the transmit antenna of the base station is configured with a 1-bit DAC, and the receive antenna of the terminal is configured with a low-precision ADC with k _ADC quantization bits, the received signal-to-noise ratio γ of each user in the downlink is :

Among them, k _ADC ≥ 3, ρ represents the attenuation factor of the low-precision ADC to the received signal-to-noise ratio; the relationship between ρ and k _ADC is:

(3) When the target data rate is n times of the ideal rate, according to the Shannon formula, there is log(1+γ)=ηlog(1+γ _ideal ), and the target data rate η and formula (2) are substituted into the formula to calculate the attenuation factor ρ, the formula is:

(4) Calculate the ADC accuracy k _ADC of the terminal receiving antenna from ρ obtained in step (2) and formula (3). The formula is:

表示向上取整。in,

Indicates rounded up.

Fig. 4 shows that under the condition of N=128 and M=8, when the target data rate η is 50%, 70% and 90% respectively, the ADC accuracy k _ADC calculated by the present invention varies with the signal-to-noise ratio P/N ₀ schematic diagram. The range of P/N ₀ is -15dB to 15dB. As can be seen from the figure, for the same target data rate η, the higher the signal-to-noise ratio, the larger the value of k _ADC . It shows that in the actual system, the higher the signal-to-noise ratio, the higher the requirements for hardware such as ADC.

The present invention starts from the overall situation of the massive MIMO system, and on the premise that the transmitting end is configured with a 1-bit DAC, the ADC accuracy k _ADC obtained according to steps (1)-(4) is the minimum value under the condition that the data rate reaches ηγ _ideal . accuracy. The smaller the precision, the smaller the hardware and power consumption costs. Therefore, the present invention balances the data transmission rate with the cost of system hardware and power consumption, and achieves the target rate with the minimum cost.

The above is only the preferred embodiment of the present invention, it should be pointed out that: for those skilled in the art, without departing from the principle of the present invention, several improvements and modifications can also be made, and these improvements and modifications are also It should be regarded as the protection scope of the present invention.

Claims (1)

1. a method for configuring the accuracy of equipment ADC in a massive MIMO system, is characterized in that: comprising the steps: (1) According to the Bussang theory, when the base station transmit antenna is configured with a 1-bit DAC, and the terminal receive antenna is configured with an ideal infinite-precision ADC, the received signal-to-noise ratio γ _ideal of each user in the downlink is:

Among them, ρ _DAC = 0.3634, representing the influence parameter of 1-bit quantization DAC on the received signal-to-noise ratio; the number of base station antennas is N, the number of single-antenna users of the terminal is M, the transmit power is P, and the thermal noise power of the receiving end is N ₀ ; (2) According to the Bussang theory and step (1), when the transmit antenna of the base station is configured with a 1-bit DAC, and the receive antenna of the terminal is configured with a low-precision ADC with k _ADC quantization bits, the received signal-to-noise ratio γ of each user in the downlink is :

Among them, k _ADC ≥ 3, ρ represents the attenuation factor of the low-precision ADC to the received signal-to-noise ratio; the relationship between ρ and k _ADC is:

(3) When the target data rate is n times of the ideal rate, according to Shannon's formula, we get log(1+γ)=ηlog(1+γ _ideal ) Substitute formula (2) to solve the decay factor ρ:

(4) After obtaining ρ according to step (3), calculate the configuration value k _ADC required by the ADC accuracy of the terminal receiving antenna according to formula (3):

in,

Indicates rounded up.

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