KR20160138646A

KR20160138646A - Advanced Hybrid Receiver System based on Soft Decision for Interference Suppression and Cancellation in Sidehaul System

Info

Publication number: KR20160138646A
Application number: KR1020150072734A
Authority: KR
Inventors: 김지형; 황인태; 권태수; 문상미; 박옥선; 말리크 사란쉬; 이문식; 최훈
Original assignee: 한국전자통신연구원; 전남대학교산학협력단
Priority date: 2015-05-26
Filing date: 2015-05-26
Publication date: 2016-12-06

Abstract

The present invention relates to an improved hybrid receiver system based on a soft decision (SD) of a sidehaul system for a next generation cellular system. The improved hybrid receiver system enables mobile small cells to suppress and cancel an influence of interference from surrounding small cells, thereby improving performance compared to mobile communication receiver performance of a successive interference cancellation (SIC) method, a full suppression and cancellation (FSC) method, and the like.

Description

[0001] The present invention relates to a soft-decision-based hybrid receiver system for interference suppression and elimination in a side-

The present invention relates to a receiver for a side-hall system, and more particularly to a receiver for a side-hall system for a next-generation cellular system capable of improving mobile communication performance by suppressing and eliminating the influence of interference from small, To a soft-decision-based hybrid receiver system.

Recently, a number of major research institutes, including the 3rd Generation Partnership Project (3GPP) standard group, have been focusing on the placement of a number of small cells in macrocells to accommodate the growing mobile traffic. However, such a scheme has a problem in that the installation and operation cost of a small cell increases proportionally to the number of small cells to be disposed. Especially, in the environment where the maximum amount of traffic varies by region due to the increase of the floating population, the fixed small cell installation plan is inefficient in terms of installation and operation cost. To solve these problems, it is necessary to develop mobile small cell technology that can be connected to a macro base station with a Gbps wireless backhaul and can be moved by users. However, since the capacity of the wireless backhaul is limited by the capacity of the wireless backhaul of the macro base station, there is a limit to increase the network capacity only by the Gbps wireless backhaul technology. For this reason, sidehaul systems are being developed in which mobile small cells can communicate with peripheral small cells.

However, in a sidehaul system, a mobile small cell has a higher probability of being affected by intercell interference from a peripheral small cell. Particularly, the research to solve the interference problem for the cell boundary area terminal can be classified into the transmission method of reducing the interference in the base station transmitter and the method of handling the interference in the receiver by applying the high performance reception algorithm like the inter-cell cooperative processing technique . However, in the former case, each terminal must feed back channel information for interference processing. Considering the feedback overhead and the inaccuracy of the feedback information as the number of antennas increases, there are restrictions on the method of processing the transmitter interference that requires feedback. On the other hand, the method of handling interference at the receiver does not require feedback, and has recently been receiving attention in 3GPP.

High-performance reception algorithms that can reduce interference effects can be classified into interference suppression receivers and interference cancellation receivers. The NAICS (Network Assisted Interference Cancellation and Suppression) research can be classified into high performance receiver algorithms and related network support methods . In the multi-cell environment, receiver algorithms based on Minimum Mean Square Error (MMSE) are actively proposed from the perspective of interference cancellation and capacity improvement. In 3GPP Release-12, NAICS is approved as SI (Study Item) Improvements, types of support information, and overheads are being discussed.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a mobile small- (SD) soft decision system for a next generation cellular system, which can improve the performance of a mobile communication receiver such as a mobile station, a mobile station, and a mobile station.

The technical problems of the present invention are not limited to the above-mentioned technical problems, and other technical problems which are not mentioned can be understood by those skilled in the art from the following description.

In order to achieve the above object, a soft-decision-based hybrid receiver system for a side-hall system according to an aspect of the present invention includes a mobile subscriber base station And estimates a magnetic signal of the serving cell by eliminating the interference signal using the channel characteristic values and the pre-information for the small cell base stations, thereby eliminating the interference signal of the serving cell ; A demodulator for demapping an output symbol of the receiver according to a modulation scheme; An interleaver interleaving the output of the demodulator to output the interleaver; A channel decoder for decoding a symbol input from the interleaver; And a deinterleaver for deinterleaving the output of the channel decoder and feeding back the deinterleaved signal to the modulation demapper, wherein the advance information includes at least one of a priori LLR (log-likelihood ratio), a posteriori LLR, or extrinsic (additional) LLR.

The receiver can calculate the discomfort estimation value of the interference signal using a Minimum Mean Squared Error (MMSE) or an Interference Rejection Combining (IRC) scheme.

(BER, BLER, FER, and the like) and a transmission rate (Throughput) by improving the decoding performance through iterative decoding in the channel decoder by using the output fed back from the deinterleaver as the extrinsic ) Can be improved.

According to the soft decision based hybrid receiver system of the side-hole system according to the present invention, in a receiver system such as Successive Interference Cancellation (SIC) and Full Suppression and Cancellation (FSC), the mobile small- It is possible to provide a higher performance gain as compared with the receiver used in existing mobile communication systems. This improves the throughput by improving the error rate (BER, BLER, FER, etc.) showing the improvement of QoS (Quality of Servise) of the user terminals.

In addition, successful application of the soft decision based hybrid receiver system of the side-hole system according to the present invention to a 5G system can be a preemptive technology in a cellular environment. With this technology, large-capacity, high-speed data transmission can improve spectrum efficiency, expand service areas and reduce network construction costs. As described above, the main core technologies of the present invention can bring about academic ripple effects and securing prior arts for national research and development.

The next generation mobile communication core technology obtained through the present invention can contribute not only to enhancement of mobile communication performance but also to terminal, component export and network construction. Specifically, it will contribute to securing superiority in standardization competition and leading the next generation mobile communication market. It will also improve technology self-reliance and price competitiveness of domestic mobile communication industry through transfer of intellectual property rights such as patents related to next generation mobile communication, In addition to reducing the cost of mobile communication industry due to cross-licensing, it is anticipated to reduce the royalty payment and import substitution effect by securing core technology of next generation mobile communication.

1 is a view for explaining a transmitter of a general side-hall system.
2 is a view for explaining a receiver of a general side-hall system.
3 is a diagram for explaining a DMRS (Demodulation Reference Signal) mapping structure of an SC-FDMA symbol.
4 is a flowchart for explaining the operation of the SIC receiver.
5 is a flowchart for explaining the operation of the FSC receiver.
6 is a diagram for explaining a soft-decision-based hybrid receiver for interference suppression and cancellation in a side-hole system according to an embodiment of the present invention.
7 to 10 are graphs for comparing performance of conventional receivers.
FIGS. 11 to 14 illustrate a conventional (SIC-SD / FSC-HD) receivers to which the soft decision (SD) based hybrid receiver scheme of the present invention is applied and the conventional SIC-HD and FSC- This is a graph for comparing performance.

Hereinafter, some embodiments of the present invention will be described in detail with reference to exemplary drawings. It should be noted that, in adding reference numerals to the constituent elements of the drawings, the same constituent elements are denoted by the same reference symbols as possible even if they are shown in different drawings. In the following description of the embodiments of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the difference that the embodiments of the present invention are not conclusive.

In describing the components of the embodiment of the present invention, terms such as first, second, A, B, (a), and (b) may be used. These terms are intended to distinguish the constituent elements from other constituent elements, and the terms do not limit the nature, order or order of the constituent elements. Also, unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the relevant art and are to be interpreted in an ideal or overly formal sense unless explicitly defined in the present application Do not.

1 is a view for explaining a transmitter of a general side-hall system.

The structure of the side-to-side system is designed based on 3GPP LTE-Advanced. A baseband signal of a side channel physical channel can be transmitted and processed in the following steps.

First, each codeword transmitted in a physical channel by attaching a cyclic redundancy check (CRC) attaching block and a code block segmentation / code block CRC is subjected to rate matching, rate matching, And is scrambled on a bit-by-block basis through block concatenation processing. To generate complex-valued symbols, scrambled bits are modulated through a modulation mapper and complex-valued modulation symbols are mapped to one or more transmission layers.

Next, transform precoding is performed on the complex-valued symbols through a transform precoder, and precoding is performed on symbols of each layer for transmission through the antenna port. The precoded symbol is mapped to a resource element of each antenna port in comparison with a reference signal through a mapper, thereby generating a complex-valued time domain SC-FDMA (Single Carrier-Frequency Division Multiple Access) signal And can be transmitted through each antenna port.

2 is a view for explaining a receiver of a general side-hall system.

Since the received data is distorted in size and phase by the channel after the demodulation of the SC-FDMA signal at the receiving end, the advanced receiver uses the reference signal to estimate the channel, . That is, as an inverse process of the transmitting end, resource element demapping, deep decoding, transform de-encode, layer demapping, modulation demapping, descrambling, code block segmentation, rate dematching, channel decoding, code block concatenation CRC check, A transport block CRC, and the like.

In the SC-FDMA technique, M-point FFT processing is performed layer by layer before the IFFT input in the transmitter modulation process, and PAPR (FFT) processing that occurs in the transmitter by performing N-point IFFT (Inverse Fast Fourier Transform) SC-FDMA is used as a side-hall wireless access technology because it minimizes the power consumption of the UE by minimizing the Peak to Average Power Ratio. Here, the subcarrier interval of the N-point FFT is 15 kHz.

3 is a diagram for explaining a DMRS (Demodulation Reference Signal) mapping structure of an SC-FDMA symbol. FIG. 3 shows resource blocks of DMRS (demodulation reference signal) and PSSCH (partitioned and structured control channel).

The minimum unit of resource allocation of the side holes is a resource block (RB), which corresponds to 12 subcarriers (180 kHz) in frequency and one slot in time. One subcarrier in one SC-FDMA symbol is called a resource element (RE).

One slot is composed of 7 SC-FDMA symbols, one slot has a time length of 0.5 ms, and two slots constitute a 1-ms-long sub-frame. Then, 10 subframes are gathered to form a 10-ms radio frame.

Also, the DMRS exists over the entire frequency band for the SC-FDMA symbol as shown in the figure, and has a form in which the DMRS signal is arranged at regular intervals in the time domain. The DMRS is located in the fourth SC-FDMA symbol per slot.

Hereinafter, a description will be given of a conventional receiver method such as a Minimum Mean Square Error (MMSE), an Interference Rejection Combining (IRC), a Successive Interference Cancellation (SIC), a Maximum Likelihood (ML), and a Full Successive Cancellation . The received signal x in the resource element RE of the side-hall system is expressed by Equation (1).

[Equation 1]

Here, s and H are the signal of the serving cell and the corresponding propagation channel characteristic (value), respectively. s _i and H _i are the signal of the i th neighbor cell (inter cell) and the corresponding propagation channel characteristic (value) of p neighboring cells from 1 to n, respectively, and n is noise.

1. Minimum Mean Squared Error (MMSE)

The MMSE receiver scheme is a common scheme for interference cancellation, which regards interference as white noise. Therefore, the interference and noise power σ ² _{I + n} is required for the application of the MMSE scheme, and the signal to be detected in the MMSE receiver

Is expressed as " (2) " I is an identity matrix having a diagonal element of 1 and all others of 0.

&Quot; (2) "

2. Interference Rejection Combining (IRC)

The IRC receiver has better performance than the MMSE receiver in strong interference scenarios and the signal to be detected

Is expressed as " (3) "

&Quot; (3) "

In this case, R _I _{+ n} is a covariance matrix value of the interference and noise, which is calculated by Equation (4) and Equation (5), and r represents the DMRS sequence of the serving cell. E () is the mean,

Is the propagation channel characteristic.

&Quot; (4) "

&Quot; (5) "

3. Successive Interference Cancellation (SIC)

When the SIC scheme is applied, information about the channel matrix causing interference order and interference order for the interference signal is required. The signal to be detected in the SIC receiver

Is expressed as " (6) "

&Quot; (6) "

At this time, σ ² _n is the interference and noise power,

Is a quantized estimate of the interference signal s _i . As shown in FIG. 4, in the SIC receiver, ordering and nulling are performed using W for the received signal x, and slicing is performed by applying symbol level SIC based on a hard decision. Through this process, we obtain the estimated value of the interference signal,

(See Equation 6).

4. Full Successive Cancellation (FSC)

The FSC receiver is a receiver combining IRC and SIC. The operation procedure of the FSC receiver is shown in FIG.

First, a Signal to Interference Ratio (SIR) of a received signal x is calculated in a side-hall system to which an FSC receiver is applied.

If the SIR is smaller than 0, that is, the size of the interference signal is large,

And is expressed as in Equation (7).

&Quot; (7) "

Where R _S _{+ n} is the covariance matrix of the magnetic signal and noise. Finally, through the SIC, a desired magnetic signal

Is calculated and detected. Where R _n is the covariance matrix of the noise.

&Quot; (8) "

Conversely, when the SIR is greater than 0, that is, when the magnitude of the magnetic signal is large, the magnetic signal is detected through two steps. First, through the IRC,

Which is expressed as " (9) "

&Quot; (9) "

The symbol level SIC then provides the interference signal

Which is expressed as " (10) "

&Quot; (10) "

The detected interference signal Lt; RTI ID = 0.0 > SIC < / RTI > to remove the < RTI ID = 0.0 &

Which is represented as in Equation (8) above.

5. Maximum Likelihood (ML)

ML technique is the most ideal performance technique and has the most complicatedness. The signals to be detected at the ML receiver are expressed by Equation (11).

&Quot; (11) "

Where Ω represents the set of constellation points of the modulation scheme used for the desired signal and the interfering signal.

6 is a diagram for explaining a soft decision based hybrid receiver 100 for interference suppression and cancellation in a side-hole system according to an embodiment of the present invention. The soft decision based hybrid receiver 100 according to an embodiment of the present invention can improve the performance of the SIC and the FSC receiver.

6, a soft decision based hybrid receiver system 100 according to an embodiment of the present invention may be applied to a mobile small cell base station and includes a receiver 110, a modulation demapper 120, A deinterleaver 130, an interleaver 140, and a channel decoder 150. [ Although a deprecation block, a layer demapper, a descrambling block, and the like as shown in FIG. 2 are omitted here, they may be further included.

The receiver 110 estimates an unbiased estimate value s _i of the interference signal s _i transmitted from neighboring mobile (or fixed) small cell base stations with i = 1 to p adjacent to the received signal x

Is calculated as shown in Equation (12). The receiver 110 may be an MMSE or IRC-based receiver, and may be a receiver of another of the above schemes, as the case may be.

&Quot; (12) "

The weight matrix of the MMSE and the IRC receiver 110 are expressed by Equation (13) and Equation (14), respectively. Here, s and H are the signal of the serving cell and the corresponding propagation channel characteristic (value), respectively. s _i and H _i are the signal of the i th neighbor cell (inter cell) and the corresponding propagation channel characteristic (value) of p neighboring cells from 1 to n, respectively, and n is noise.

&Quot; (13) "

&Quot; (14) "

Where σ ² _{I + n} is the power of interference and noise, and R _I _{+ n} is the covariance matrix of interference and noise. For the weight matrix ω of the MMSE or IRC scheme,

The receiver 110 determines that the received signal x is < RTI ID = 0.0 >

And the magnetic signal of the desired serving cell as shown in Equation (15)

Can be estimated.

&Quot; (15) "

Where m is the priori information and is expressed as the average of symbol s = m (E) (s). At the start stage, m = 0 because no dictionary information exists. The prior information may be updated at the receiver 110 via the MMSE or IRC equalizer and then via soft information of the subsequent stage estimate signal. Soft information for soft decision is expressed as LLR (log-likelihood ratio), and priori LLR

, posteriori (posterior) LLR

, extrinsic (additional) LLR

Are respectively expressed by [Expression 16], [Expression 17], and [Expression 18].

&Quot; (16) "

&Quot; (17) "

&Quot; (18) "

Where j / j '= 1, 2 and j? J'. The priori LLR may be calculated before the estimation of the interference signal or the like of the MMSE or IRC receiver 110 and the posteriori LLR may be calculated after the estimation of the interference signal or the like in the receiver 110. [ The extrinsic LLR can be calculated differently depending on the modulation method. In addition, p (x) is a PDF (Probability Distribution Function), and Gaussian approximation is used as in Equation (19).

,

Is a variable representing a probability value.

&Quot; (19) "

Here, the average

And the dispersion is

And is calculated by the following equations (20) and (21).

&Quot; (20) "

&Quot; (21) "

Using Equation (18), Equation (18) can be simplified to Equation (22) and Equation (23).

&Quot; (22) "

&Quot; (23) "

Here,? Is a variable depending on a modulation method, and is 8 for QPSK, 10 for 16 QAM, and 42 constant for 64 QAM.

The modulation demapper 120 demaps the output symbols of the receiver 110 according to the modulation scheme and the interleaver 140 performs interleaving on the output of the modulation demapper 120, The channel decoder 150 can recover the original transmission signal by decoding the input symbol.

Channel outputs of decoder 150 is fed back to the modulation demapper (Modulation Demapper) (120) through a deinterleaver 130 for performing the re-interleaving, new extrinsic LLR L _e ^d to update the dictionary information (m) ( s _j ), decoding performance can be improved by an iterative decoding process.

The performance of the receivers in an interference scenario in which adjacent cells exist in addition to the serving cell is analyzed. Here, it is assumed that the number of adjacent cells influencing the interference is one, and the number of adjacent cells is similarly applicable even if the number of the adjacent cells is expanded to a larger number.

[Table 1] shows the simulation parameters and is based on the 20MHz band of the 3GPP LTE-Advanced system. In the case of the serving cell signal, the modulation is 64QAM using the modulation and coding set (MCS) index 27 as shown in Table 2, the code rate is 5/6, the number of code words is 2, The transmission method was applied. In case of interfering signals, channel coding is not performed considering system complexity. 64QAM is used as modulation, and the number of code words is 2 and the spatial multiplexing transmission method is applied to 4 layers.

The channel environment is a time-varying frequency-selective channel with a maximum linear Doppler frequency (f _d ) of 300 Hz and an NLoS (None Line of Sight) of UMi (Urban Micro), a WINNER channel model. In addition, the signal to noise ratio (SNR) ranges from 15dB to 40dB and the SIR is 24dB.

[Table 1]

[Table 2]

7 to 10 are graphs for comparing performance of conventional receivers.

First, FIG. 7 shows the bit error rate (BER) performance of conventional receivers. Coded BER 10 ^-2 , the required SNR for the receiver is shown in Table 3. Since MMSE and IRC are influenced by interference signal, we can see that bit error occurs much and IRC performance is superior to MMSE. In the case of SIC-HD, FSC-HD and ML, we can see that performance is better than MMSE and IRC by eliminating interference signal, and SIC-HD, FSC-HD and ML show improved performance in that order. Hereinafter, HD indicates hard decision, and SD indicates soft decision.

[Table 3]

8 shows the BLER (BLock Error Rate) performance of conventional receivers. The SNR required according to the receiver is shown in [Table 4] in order to satisfy it based on BLER 10 ^-1 . Compared with BER, the overall error rate is increased, but not significantly different from the BER analysis.

[Table 4]

Figure 9 shows the Frame Error Rate (FER) performance of conventional receivers. The SNR required by the receiver to satisfy this criterion, based on FER 10 ^-1 , is shown in [Table 5]. When compared with the BLER, it can be seen that a high SNR of about 1 to 2 dB is required to satisfy the error rate of 10 ^-1 .

[Table 5]

FIG. 10 shows throughput performance of conventional receivers. The throughput according to receiver SNR is shown in [Table 6]. When MCS index 27 is used, the theoretical maximum data rate considering the reference signal and control channel is 142.50 Mbps. The average throughput is improved in order of MMSE, IRC, SIC-HD, FSC-HD, and ML.

[Table 6]

FIGS. 11-14 illustrate a conventional soft and hard decision (HD) based SIC-HD and FSC-HD receivers and a soft decision (SD) based hybrid receiver system 100 scheme of the present invention -HD) receiver according to the present invention.

11 shows the Coded BER performance of the receivers. Coded BER 10 ^-2 , the required SNR according to the receiver's decision (HD / SD) is shown in [Table 7]. SD is about 2dB better than HD, and the performance is improved in the order of SIC-HD, FSC-HD, SIC-SD, FSC-SD and ML.

[Table 7]

12 and 13 show BLER and FER performance according to the decision of receivers. The SNR required according to the decision (HD / SD) of the receiver is shown in Tables 8 and 9 to satisfy the criterion based on BLER and FER 10 ^-1 . The difference between the BLER and the FER performance is about 1dB, and when compared with the BER, the overall error rate is increased, but it is not significantly different from the BER analysis.

[Table 8]

[Table 9]

14 shows throughput performance of receivers. Throughput (HD / SD) according to receiver decision is shown in [Table 10]. When MCS index 27 is used, the theoretical maximum data rate considering the reference signal and control channel is 142.50 Mbps. The average throughput is improved in order of SIC-HD, FSC-HD, SIC-SD, FSC-SD and ML.

[Table 10]

As described above, the receiver system 100 of the present invention provides an unbiased estimate of the interference signal through the MMSE or IRC receiver 110

Is estimated as in Equation (12), and the interference signal is suppressed and removed. The interference signal is updated through soft information expressed as LLR (Log-Likelihood Ratio). In the above simulation, it is confirmed that the proposed receiver improves the error rate and the transmission rate in the 20MHz band of the 3GPP LTE-Advanced system compared to the conventional receiver.

As described above, according to the soft-decision-based hybrid receiver system 100 of the side-hole system according to the present invention, in the case of successive interference cancellation (SIC) and full suppression and cancellation By suppressing and eliminating the influence of interference from the cells, higher performance gains can be provided compared to the receiver used in existing mobile communication systems. This improves the throughput by improving the error rate (BER, BLER, FER, etc.) showing the improvement of QoS (Quality of Servise) of the user terminals. In addition, successful application of the soft-decision-based receiver of the side-hole system according to the present invention to a 5G system can be a preemptive technology in a cellular environment. With this technology, large-capacity, high-speed data transmission can improve spectrum efficiency, expand service areas and reduce network construction costs. As described above, the main core technologies of the present invention can bring about academic ripple effects and securing prior arts for national research and development. The next generation mobile communication core technology obtained through the present invention can contribute not only to enhancement of mobile communication performance but also to terminal, component export and network construction. Specifically, it will contribute to securing superiority in standardization competition and leading the next generation mobile communication market. It will also improve technology self-reliance and price competitiveness of domestic mobile communication industry through transfer of intellectual property rights such as patents related to next generation mobile communication, In addition to reducing the cost of mobile communication industry due to cross-licensing, it is anticipated to reduce the royalty payment and import substitution effect by securing core technology of next generation mobile communication.

The foregoing description is merely illustrative of the technical idea of the present invention, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the present invention.

Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

Receiver 110,
A Modulation Demapper (120)
The deinterleaver 130,
The interleaver 140,
Channel decoder 150,

Claims

A soft-decision-based hybrid receiver system for a side-hall system,
Calculates an unbiased estimate of the interference signal transmitted from the mobile small cell base stations adjacent to the received signal x and removes the interference signal using the channel characteristic values and the preliminary information for the small cell base stations A receiver for removing the interfering signal for estimating the magnetic signal of the serving cell and outputting the interfering signal;
A demodulator for demapping an output symbol of the receiver according to a modulation scheme;
An interleaver interleaving the output of the demodulator to output the interleaver;
A channel decoder for decoding a symbol input from the interleaver; And
And a deinterleaver for deinterleaving the output of the channel decoder and feeding back the output to the demodulator,
Characterized in that the advance information is updated by using a priori priori LLR, a posteriori LLR or an extrinsic LLR as soft information for soft decision. .