KR102017823B1 - Method and apparatus for estimating channel in terminal for narrow band Internet of things - Google Patents

Abstract

Provided are a method and apparatus for channel estimation of a narrowband IoT terminal. A reference signal is generated and a sample string for the reference signal symbols is obtained by dividing the received signal by the reference signal. The channel reference value for the current subframe is obtained by combining adjacent reference signal symbols, and a channel average value in the current transmission time interval (TTI) is obtained by performing a moving average of the channel estimate value in subframe units.

Description

Method and apparatus for estimating channel in narrowband IoT terminal

The present invention relates to channel estimation, and more particularly, to a method and apparatus for channel estimation of a narrowband IoT terminal.

The Internet has evolved from a human-centered connection network where humans create and consume information, and an Internet of Things (IoT) network that exchanges and processes information among distributed components such as things. In order to implement IoT, technical elements such as sensing technology, wired / wireless communication and network infrastructure, service interface technology, and security technology are required, and recently, a sensor network and a machine to machine connection for connecting things , M2M), Machine Type Communication (MTC), etc. are being studied.

IoT can appear in various forms of services, such as Smart Metering, Tracking & Tracing, Remote Maintenance & Control, and eHealth. IoT provides an environment for sharing information by connecting things in everyday life through wired and wireless networks, and for this purpose, 3GPP supports the low power wide area (LPWA) communication through the mobile communication network. Narrow Band Internet of Things) standard. It uses a narrow band in a Global System for Mobile Communication (GSM) or Long Term Evolution (LTE) network to support data transmission rates of several hundred kbps or less and wide area services of more than 10 km. It is therefore suitable for communication between remote and low power consumption objects such as water meter reading and location tracking devices.

As data is transmitted using a small resource of a narrow band, the channel estimation reference signal for demodulation is small, so that performance degradation at a low signal to noise ratio (SNR) is inevitable.

An object of the present invention is to provide a method and apparatus for estimating a channel of a terminal for a narrow band internet of things (NB IoT).

According to an embodiment of the present invention, a channel estimation method is provided. The channel estimation method includes generating a reference signal; Obtaining a sample sequence for reference signal symbols from the received signal; Combining the adjacent reference signal symbols to obtain a channel estimate for the current subframe; And performing a moving average of the channel estimate in subframe units to obtain a channel estimate in a current transmission time interval (TTI).

According to an embodiment of the present invention, a signal-to-noise ratio (SNR) gain is obtained using an accumulation technique by using a NB-IoT that does not assume a time-selective fading channel of a low mobility terminal. In addition, in the resource block which is the NB-IoT transmission unit, the SNR gain may be obtained by performing channel estimation by combining reference signals of different symbols for the same frequency.

In addition, since the complexity of channel estimation is low, a channel estimation method suitable for an NB-IoT terminal with low power consumption may be provided.

1 is an exemplary diagram illustrating a narrowband reference signal (NRS) according to an embodiment of the present invention.
2 is a flowchart of a channel estimation method according to an exemplary embodiment of the present invention.
3 is a diagram illustrating soft combining of NRS OFDM symbols according to an embodiment of the present invention.
4 illustrates frequency interpolation according to an embodiment of the present invention.
5 is a structural diagram of a channel estimating apparatus according to an embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification.

Throughout the specification and claims, when a portion is said to include a certain component, it means that it can further include other components, except to exclude other components unless specifically stated otherwise.

Throughout the specification, a terminal may include a user equipment (UE), a mobile station (MS), a mobile terminal (MT), an advanced mobile station (AMS), a high reliability mobile station. (high reliability mobile station, HR-MS), subscriber station (SS), portable subscriber station (PSS), access terminal (AT), machine type communication device, MTC device) and the like, and may include all or a part of functions of the UE, MS, MT, AMS, HR-MS, SS, PSS, AT, and the like.

In addition, the base station (BS) is a node B (evolved node B, eNB), gNB, advanced base station (ABS), high reliability base station (high reliability base station, HR-BS), access point (AP), radio access station (RAS), base transceiver station (base transceiver station (BTS), mobile multihop relay (BSR) -BS, relay that performs the role of a base station (relay station, RS), relay node (RN) serving as base station, advanced relay station (ARS) serving as base station, high reliability relay station serving as base station , HR-RS), small base station (femto BS, home node B (HNB), home eNodeB (HeNB), pico base station (pico BS), macro base station (macro BS), micro base station ( micro BS), etc.], and all or one of NB, eNB, gNB, ABS, AP, RAS, BTS, MMR-BS, RS, RN, ARS, HR-RS, small base station, and the like. There's also an included feature.

The expressions used in the singular herein may be interpreted in the singular or the plural, unless an explicit expression such as “one” or “single” is used.

Hereinafter, a channel estimation method and apparatus according to an exemplary embodiment of the present invention will be described.

In an Orthogonal Frequency Division Multiple Access (OFDM) communication system, a downlink bandwidth is composed of a plurality of resource blocks (RBs), and each physical resource block (PRB) is arranged along a frequency axis. It may consist of 12 subcarriers and 14 or 12 OFDM symbols arranged along the time axis. Here, the PRB becomes a basic unit of resource allocation.

A subframe on the time axis consists of two slots of 0.5 msec length. A physical dedicated control channel (PDCCH) region, which is a control channel region, and an enhanced PDCCH (ePDCCH) region, which is a data channel region, are divided and transmitted on a time axis. This is for quickly receiving and demodulating control channel signals. In addition, the PDCCH region is located over the entire downlink band, in which one control channel is divided into control channels of a small unit and distributed in the entire downlink band.

The uplink is divided into a control channel (PUCCH) and a data channel (PUSCH), and the response channel and other feedback information for the downlink data channel are transmitted through the control channel when there is no data channel, and when there is a data channel. Is sent. According to various examples, the channels may be designed differently from the channels transmitted to existing LTE or LTE-A terminals for narrowband transmission for low-cost terminals, and may be transmitted completely from the base station. .

The narrowband for communication of the low cost terminal within the downlink system transmission bandwidth of the LTE system may be defined continuously from any one end of the system transmission bandwidth, or may be defined continuously from both ends. Alternatively, the narrowband may be defined continuously from the middle of the system transmission bandwidth to both ends. Among a plurality of narrow bands in the system transmission bandwidth, the terminal may receive a downlink signal from the base station in all or some RBs of a specific narrow band according to the configuration of the base station or according to a predetermined rule.

Narrow Band Internet of Things (NB IoT) terminal must acquire system information of a cell in order to access a network. To this end, synchronization with a cell should be obtained through a cell search process, and for this purpose, a synchronization signal is transmitted in downlink. The terminal acquires frequency, symbol and frame synchronization using the synchronization signal, and searches for about 504 physical cell IDs (PCIDs). The LTE synchronization signal is designed to be transmitted through 6 PRB resources, and it is impossible to reuse the NB-IoT using 1 PRB. Therefore, a new NB-IoT synchronization signal has been designed and applied equally to the three operating modes of NB-IoT.

A narrowband reference signal (NRS) of the NB IoT is provided as a reference signal for channel estimation required for downlink physical channel demodulation and may be generated in the same manner as in LTE. However, NB-Narrowband-Physical Cell ID (PCID) is used as the initial value for initialization. NRS is transmitted to one or two antenna ports, and up to two base station transmit antennas of NB-IoT are supported.

1 is an exemplary view showing an NRS according to an embodiment of the present invention.

The NRS occupies different resource blocks in a subframe, and as shown in FIG. 1, two NRS symbols are transmitted for each transmit antenna. The NRS may be allocated in three subcarrier intervals so as not to overlap.

According to an embodiment of the present invention, soft combining of adjacent NRS symbols and frequency interpolation are performed to estimate a channel of subcarriers located between NRSs within a symbol, and a channel average value is calculated in subframe units. Is performed to obtain a channel estimate value within the current transmission time interval (TTI). Then, the final channel estimate is obtained by adding the channel estimate in the previous TTI and the channel estimate in the current TTI.

2 is a flowchart of a channel estimation method according to an exemplary embodiment of the present invention.

Channel estimation is performed through the following process.

The terminal receives a signal to the base station (S100), first, for channel estimation, generates a reference signal, that is, an NRS (S110). NRS is generated using a sequence. Here, NRS is a random complex quadrature phase-shift keying (QPSK) sequence, and a random complex sequence may be generated using a 31st-order gold sequence.

The terminal estimates the temporary frequency response of the channel by dividing the received signal by the generated NRS (S120). This process may be referred to as depatterning, and depatterned NRS sample sequences are obtained. The temporary frequency response obtained according to the depatterning process is a channel estimate of the subcarrier where the NRS is located, and is referred to as a first estimate for convenience of description.

Since one PRB is used in NB-IoT, only two NRS samples exist for each transmit antenna in an OFDM symbol including NRS. NB-IoT soft combines adjacent NRS OFDM symbols using a characteristic that does not assume a Time Selective Fading channel, and then takes frequency interpolation, between NRSs in symbols. The channel of the located subcarrier, that is, the subcarrier to which the NRS is not allocated is estimated (S130).

3 is a diagram illustrating soft combining of NRS OFDM symbols according to an embodiment of the present invention, and FIG. 4 is a diagram illustrating frequency interpolation according to an embodiment of the present invention.

As shown in FIG. 3, soft combining of adjacent NRS OFDM symbols (R _0s ) for each subcarrier to which the NRS is allocated is performed on the depatterned NRS sample sequences.

Then, frequency interpolation is performed to estimate a channel of the subcarrier to which the NRS is not assigned. In detail, as shown in FIG. 4, frequency linear interpolation is performed to estimate a channel of a subcarrier located between NRSs in a symbol. Linear interpolation is performed on the subcarriers to which the NRS has been assigned based on the channel estimates of the first estimated values, so as to obtain channel estimates, that is, second estimates for subcarriers located between NRSs in the symbol. In this case, the channel estimation value of the subcarrier located in the PRB edge region may be obtained through edge processing.

A channel estimate value for a predetermined subframe is obtained based on the first estimate value and the second estimate value obtained through this step (S140).

Next, a moving average is performed in subframe units on the channel estimate obtained through the above-described steps to obtain a final channel estimate (S150). The moving average may be performed based on Equation 1 below.

은 n-1번째 서브프레임까지 이동 평균된 채널 추정값이며,

는 n번째 서브프레임에서 추정된 채널 추정값이다. G 값은 시뮬레이션을 통하여 결정될 수 있으며, 여기서는 0.7이며, 이에 한정되는 것은 아니다. here,

Is the channel estimate shifted to the n-1th subframe,

Is the channel estimate estimated in the nth subframe. The G value may be determined through simulation, and here is 0.7, but is not limited thereto.

는 수학식 1과 같이 이동 평균된 n번째 서브프레임을 위한 최종 채널 추정값으로 사용된다. By performing a moving average as shown in Equation 1, a channel estimate (also referred to as a channel estimate up to a previous TTI) that has been moved to the n-1th subframe, and a channel estimate estimated in the nth subframe (the channel in the current TTI) Also called an estimate) to obtain a final channel estimate for the nth subframe.

Is used as the final channel estimate for the moving averaged nth subframe as shown in Equation 1.

According to this embodiment of the present invention, a signal-to-noise ratio (SNR) gain is obtained using an accumulation technique by using a NB-IoT that does not assume a time-selective fading channel of a low mobility terminal. In addition, in the resource block which is the NB-IoT transmission unit, the SNR gain may be obtained by performing channel estimation by combining reference signals of different symbols for the same frequency.

5 is a structural diagram of a channel estimating apparatus according to an embodiment of the present invention.

As shown in FIG. 5, the channel estimating apparatus 1 according to an exemplary embodiment of the present invention includes a processor 110, a memory 120, and a transceiver 130. The processor 110 may be configured to implement the methods described with reference to FIGS. 1 through 4 above.

The memory 120 is connected to the processor 110 and stores various information related to the operation of the processor 110. The memory 120 may store instructions for execution in the processor 110 or temporarily load the instructions from a storage device (not shown). The processor 110 may execute instructions stored or loaded in the memory 120. The processor 110 and the memory 120 may be connected to each other through a bus (not shown), and an input / output interface (not shown) may also be connected to the bus.

The transceiver 130 receives an NRS.

An embodiment of the present invention is not implemented only through the above-described apparatus and / or method, but may be implemented through a program for realizing a function corresponding to the configuration of the embodiment of the present invention, a recording medium on which the program is recorded, and the like. Such implementations may be readily implemented by those skilled in the art from the description of the above-described embodiments.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of the operator using the basic concepts of the present invention as defined in the following claims are also provided. It belongs to the scope of rights.

Claims (8)

A channel estimation method of a narrowband IoT terminal,
Generating a reference signal;
Obtaining a sample sequence for symbols from a received signal, the received signal having a first narrowband reference signal (NRS) symbol and a second NRS symbol for each subcarrier corresponding to the antenna;
A first channel estimate for a first subcarrier where the first NRS symbol and the second NRS symbol are located by combining the first NRS symbol and the second NRS symbol from the obtained sample sequence of symbols; Obtaining a;
Obtaining a second channel estimate for a second subcarrier on which the first NRS symbol and the second NRS symbol are not located based on the first channel estimate;
Obtaining a channel estimate for a current subframe based on the first channel estimate and the second channel estimate; And
Obtaining a channel estimate in a current transmission time interval (TTI) by performing a moving average of the channel estimate in subframe units
Channel estimation method comprising a. In claim 1,
Acquiring the channel estimate in the TTI,
Obtaining a final channel estimate for the current subframe by adding a channel estimate for the current subframe and a channel estimate obtained according to a moving average to a previous subframe.
Channel estimation method comprising a. In claim 1,
Acquiring the sample sequence,
Dividing the received signal by the generated reference signal to obtain a sample sequence for depatterned reference signal symbols
Channel estimation method comprising a. delete In claim 1,
The generating of the reference signal may include generating the reference signal by using a random complex quadrature phase-shift keying (QPSK) sequence. In claim 1,
Obtaining the second channel estimate value,
And frequency interpolation based on a first channel estimate for the first subcarrier to obtain the second channel estimate for the second subcarrier. In claim 1,
Acquiring the second channel estimate value
And obtaining a channel estimate of the subcarrier located in the edge region of the resource. In claim 1,
Acquiring the channel estimate in the TTI,

Obtain a current channel estimate within the TTI using

Is the channel estimate shifted to the n-1th subframe,

Is the channel estimate estimated in the nth subframe, G is the value determined through simulation,

Represents a final channel estimate for the moving averaged nth subframe.

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