KR101771639B1 - Time synchronizing method for various data rate supporting Zigbee and apparatus thereof - Google Patents

Abstract

The present invention relates to a time synchronization method and device for Zigbee supporting a variable transmission rate. The present invention applies a new preamble structure to support a multiple transmission rate and reduces hardware complexity while having a synchronization unit to support the new preamble structure. The present invention does not apply an additional PN code or a new correlation block for the PN code by suggesting the new preamble structure which utilizes already existing data symbols for demodulation in a preamble configuration increased for supporting a variable transmission rate. Even if a synchronization error occurs at a low transmission rate at which the length of a preamble becomes longer due to the minimization of the correlation block while extremely reducing the number of correlation blocks used for synchronization, it is possible to detect a precise synchronization point through correlation information obtained by using synchronization information and correlators of a demodulation unit, which are not used in a synchronization process, thereby providing various variable transmission rates and minimizing hardware complexity.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a time synchronization method for a Zigbee supporting variable rate,

The present invention relates to a Zigbee supporting a variable transmission rate, and more particularly, to a Zigbee that supports a variable transmission rate, a new preamble structure is applied to support a multiple transmission rate, a variable transmission rate Time synchronization method and apparatus for supporting Zigbee.

Recently, as a system capable of providing high quality application services at low cost, there is a growing interest in the Internet of Things (IoT), which provides information and utilizes information and retrieves information through the Internet anytime and anywhere. This kind of internet service is an infrastructure technology that can provide various services by linking objects of physical space and virtual space as a method of connecting virtual objects existing in real objects and cyber environment through the Internet . In order to achieve this, all objects must be connected to the network. There are various kinds of network connection standards such as Bluetooth, UWB (Ultra Wide Band), Zigbee, and wireless LAN (WLAN), but miniaturization and low power consumption There is a high interest in the IEEE 802.15.4 Zigbee specification, which is a possible wireless local area network (WPAN) transmission technology. The IEEE 802.15.4 Zigbee specification is based on a low-speed wireless personal area network (PHY) and a MAC sublayer that defines wireless PHY and MAC sub-layers to support wireless communication of simple low-power devices operating on less than 10 meters of wireless range and low power consumption. It is a standard for. Thus, IEEE 802.15.4 Zigbee is designed as a simple, low-cost network that can provide wireless connectivity for applications that require relatively low data throughput while consuming limited power, Can be provided. However, since the IEEE 802.15.4 Zigbee standard only specifies a single transmission rate of 250 Kbps for the 2.45 GHz band and corresponds to a wireless distance range of about 10 m, application of a sensor network system requiring information acquisition of a wider communication distance There is a limit.

Therefore, it is necessary to change the transmission rate in order to support a wider communication distance. If the transmission rate is lower than the prescribed 250 Kbps, it is expected to increase the communication distance.

However, if the low rate is supported, time synchronization must be obtained in a noisy environment, that is, in an environment with low signal to noise (SNR). To this end, the length of the preamble symbol must be increased to improve correlation characteristics.

In order to increase the preamble symbol length, it is possible to repeat the same preamble symbol or use a new pseudo random noise (PN) code having a long length. However, if the preamble symbol is repeated, it is difficult to distinguish the correct symbol period. A problem arises in which a new additional block for generating such a code and performing correlation operation is required.

Therefore, a new preamble transmission method is needed to improve the acquisition performance of time synchronization and to avoid the need for additional blocks in order to support a low-speed data rate. A new time synchronization method that can reduce the complexity as much as possible while supporting a low- Devices are required.

Korean Patent No. 10-1004101 [Non-air Detection Apparatus and Method for IEEE 802.15.4 Zigbee BPSK Receiver]

D. Park, et al., "Simple Design of Detector in the Presence of Frequency Offset for IEEE 802.15.4 Zigbees," IEEE Trans. Circuit and systems II, vol. 56, no. 4, pp. 330-334, 2009.

It is an object of embodiments of the present invention to solve the above problems and to provide an apparatus and a method for transmitting a new type of correlation < RTI ID = 0.0 > In order to solve the problem of inaccurate correlation calculation of the synchronization process which occurs when only the two symbols are used, the correlation unit configured in the demodulation unit which is not used in the synchronization process is shared, And to provide a time synchronization method and apparatus for a Zigbee that supports a variable rate so as to provide a high time synchronization performance even in a low SNR environment while minimizing a hardware configuration.

Another object of embodiments of the present invention is to provide a method and apparatus for correcting a maximum of 16 Correlators used for demodulation using only one symbol except for symbol & 4, it is possible to maintain the correlation property of preamble that requires up to 8 symbols for 125Kbps, 62.5Kbps, and 31.25Kbps to support Zigbee that supports variable transmission rate with high performance while minimizing synchronous hardware configuration Time synchronization method and apparatus.

It is another object of embodiments of the present invention to provide a new structure capable of configuring a preamble requiring a maximum of 8 symbols with two types of symbols, and to provide a new frequency offset environment of ± 80 ppm defined in the IEEE 802.15.4 Zigbee system standard The complexity is reduced by using only the real part of the values of the real part and the imaginary part generated in the double correlation operation and the multiplier used for constructing the correlator is used as a multiplication result And to provide a time synchronization method and apparatus for a Zigbee that supports a variable rate so that the complexity can be further reduced by replacing it with an adder through analysis.

According to an aspect of the present invention, there is provided a time synchronization method for a Zigbee supporting a variable rate according to an embodiment of the present invention includes generating a complex conjugate signal for a received signal, ; Multiplying the complex conjugate of the received signal by a received signal delayed by the number of chip period samples; And outputs the multiplied signal to the correlation blocks for the two different symbols. The output sum of the selected correlation block according to the transmission rate and the output sum of the correlation block are accumulated in accordance with the transmission rate and output. Providing a result; And the reference signal of the demodulator's correlators is set to a value of a start of frame delimiter (SFD) for frame start identification and is sequentially operated at an offset of two symbol lengths according to the correlation result. Providing a fine correlation result based on the correlation results; And completing the synchronization through the correlation result and the precision correlation result.

As an example of the present invention, the step of providing the correlation correlation result may be performed by selecting two correlation blocks according to a selection signal for selecting one of four transmission rates of 250 Kbps, 125 Kbps, 62.5 Kbps, and 31.25 Kbps, And providing the sum of the outputs of the selected correlation block and the cumulative block among the cumulative blocks that selectively output the first or the third repeated value as a correlation result.

As an example of the present invention, the two correlation blocks are a correlation block for symbol '0' and symbol 'p', and symbol 'p' can be selected for data symbols 1 to 15.

As an example of the present invention, the step of providing the fine correlation result is selected only for the two transmission rates of 62.5 Kbps and 31.25 Kbps among the four transmission rates of 250 Kbps, 125 Kbps, 62.5 Kbps, and 31.25 Kbps.

As an example of the present invention, when 250 kbps is selected as the transmission rate, the result of the correlation block for the first symbol '0' is provided as a coarse correlation result, the step of providing the fine correlation result is omitted, .

As an example of the present invention, when 125 kbps is selected as the transmission rate, the result sum of the correlation blocks for the first symbol '0' and the second symbol 'p' is provided as a coarse correlation result, And the synchronization is completed by the result of the correlation of the relevant curse.

As an example of the present invention, when 62.5 Kbps is selected as the transmission rate, the result sum of the correlation blocks for the first symbol '0' and the second symbol 'p' And adding the result value to the result sum, that is, twice the result sum of the correlation blocks, as a result of the correlation result.

As an example of the present invention, when 31.25 Kbps is selected as the transmission rate, the sum of the correlation blocks for the first symbol '0' and the second symbol 'p' And summing the resultant values, i.e., providing four times the result sum of the correlation blocks as a result of the correlation result.

As an example of the present invention, providing the fine correlation result utilizes two of the demodulator's correlators at a 62.5 Kbps transmission rate and uses four of the demodulator's correlators at a 31.25 Kbps transmission rate.

As an example of the present invention, providing a fine correlation result may be achieved by operating two of the demodulator correlators differently at two symbol intervals at a 62.5 Kbps transmission rate that repeats two symbols twice, The precise synchronization point is determined by the correlation point of the correlation unit.

As an example of the present invention, providing a fine correlation result may be achieved by operating four of the demodulator correlators differently at two symbol intervals at a 31.25 Kbps transmission rate, in which two symbols are repeated four times, The precise synchronization point is determined by the correlation point of the demodulator correlator.

As an example of the present invention, completing the synchronization may further include the step of resetting the reference signal of the demodulator's correlators to symbols for correlation with the used symbols for the demodulator operation.

As an example of the present invention, some of the correlators of the demodulator may be set to SFD values to provide fine correlation results, and may be reset to corresponding symbol values for demodulation procedures after the synchronization completion phase, respectively.

As an example of the present invention, the step of providing the correlation correlation result may provide only the result of the real part after the correlation calculation as a correlation result.

As an example of the present invention, in the step of providing the correlation result, the correlation operation for the real part may be performed by a multiplier instead of the multiplier, A sign reversal, a shifter, and an adder.

According to another aspect of the present invention, there is provided a time synchronization method for a Zigbee supporting variable rate, comprising the steps of: determining a number of chip period samples by oversampling a processing speed of a receiver by a multiple of a chip period used for transmission signal spreading; Generating a complex conjugate signal for the received signal and delaying the received signal by a number of chip period samples; Multiplying the complex conjugate of the received signal by a received signal delayed by the number of chip period samples; The multiplied signal is provided to the correlation blocks for two different symbols and the output sum of the correlation block selected according to the selected transmission rate among the four transmission rates of 250 Kbps, 125 Kbps, 62.5 Kbps, and 31.25 Kbps, Providing a correlation result according to an output of an accumulation block which accumulates and outputs a sum in accordance with a data rate; And the reference signal of the demodulator's correlators is set to the value of the SFD for frame start identification and is sequentially operated at the offset of two symbol lengths according to the correlation result, Providing a correlation result; Completing the synchronization through the correlation result and the fine correlation result; And resetting the reference signals of the demodulator's correlators to a symbol for correlation with the used symbols for the demodulator operation according to the completion of the synchronization, the two correlation blocks including a symbol '0' and a symbol 'p' Wherein the symbol 'p' may be selected from data symbols 1 through 15, and the step of providing the fine correlation result may comprise selecting one of four transmission rates of 250 Kbps, 125 Kbps, 62.5 Kbps, and 31.25 Kbps, Lt; RTI ID = 0.0 > 2 < / RTI >

According to an embodiment of the present invention, the step of providing the correlation result includes two correlation blocks according to a selection signal for selecting one of the four transmission rates of 250 Kbps, 125 Kbps, 62.5 Kbps, and 31.25 Kbps, Or providing an output sum of the selected correlation block and the cumulative block among the cumulative blocks that select and output the value repeated three times as a correlation result.

As an example of the present invention, providing a fine correlation result may be achieved by operating two of the demodulator correlators differently at two symbol intervals at a 62.5 Kbps transmission rate that repeats two symbols twice, The precise synchronization point can be determined by the correlation point of the super correlator.

As an example of the present invention, providing a fine correlation result may be achieved by operating four of the demodulator correlators differently at two symbol intervals at a 31.25 Kbps transmission rate, in which two symbols are repeated four times, The precise synchronization point is determined by the correlation point of the demodulator correlator.

According to another aspect of the present invention, there is provided a time synchronization method for a Zigbee supporting variable rate, comprising: providing a phase estimate value of a received signal to correlation blocks for two different symbols; Providing a correlation result according to an output of an accumulation block accumulating and outputting one or two correlation block output sums selected according to a selected transmission rate and an output sum of the correlation blocks in accordance with a transmission rate; The correlator reference signal of the demodulation unit is set to the value of the SFD for frame start identification according to the correlation result and sequentially operated at the offset of two symbol lengths. Based on the correlation results, And a step of providing the image data.

As an example of the present invention, the correlator of the correlation block that provides the coarse correlation result and the demodulator that provides the fine correlation result use the sample unit double correlation algorithm.

According to an embodiment of the present invention, there is provided a method of generating synchronization information, the method comprising: And reconfiguring the reference signals of the demodulator's correlators to symbols for correlation with the used symbols for the demodulator operation according to the completion of the synchronization.

As an example of the present invention, the two correlation blocks are a correlation block for symbol '0' and symbol 'p', and symbol 'p' can be selected for data symbols 1 to 15.

As an example of the present invention, the transmission rate is selected from among four types of 250 Kbps, 125 Kbps, 62.5 Kbps and 31.25 Kbps, and the step of providing the fine correlation result is selected only for the two transmission rates of 62.5 Kbps and 31.25 Kbps among the four transmission rates .

As an example of the present invention, a correlation block in which a step of providing a correlation correlation result is performed, a correlation is calculated using the following equation for synchronization through a preamble of a received signal,

S _l and S _m is one of the preamble symbol that corresponds to the data rate and Ns and Nc is the number of the number of accumulated samples delayed sample, Rs is the n-th sample number, r _x (n) of the two symbols to accumulate _Sx (n) denotes a symbol of the modulated reception data, index x denotes one of predefined symbols, omega ₀ denotes a frequency error between the transmitter and the receiver, and? Denotes an initial phase error.

As an example of the present invention, a correlator of a demodulator in which a step of providing a fine correlation result is performed, a correlation is calculated by using the following equation for synchronization using a symbol '7' defined as SFD value of a received signal as a reference signal,

x and 7 are indexes of the received signal and the reference signal, Ns, Nc, and No are the number of cumulative samples, the number of delay samples, and the number of samples of two symbols used as a synchronization reference signal, offset, r _x (n) is the n-th received signals, S _x (n) of the samples of the modulated symbols received data, ω ₀ is the frequency error between the transmitter and the receiver, θ means and, at this time, the initial phase error

.

According to another aspect of the present invention, there is provided a time synchronization apparatus for a Zigbee supporting variable rate, comprising: a complex conjugate signal generating unit for generating a complex conjugate signal for a received signal; A delay unit for delaying the received signal by the number of chip period samples; A complex multiplier for multiplying the output of the complex conjugate signal generator and the output of the delay unit; And provides the multiplied signal to the correlation blocks for two different symbols and outputs the sum of the output of the selected correlation block and the sum of the outputs of the correlation block according to the transmission rate, And the reference signal of the demodulator's correlators is set to the value of the SFD for the start of the frame according to the correlation result and sequentially operated at the offset of two symbol lengths. Based on the correlation results, And a synchronization unit for confirming and performing synchronization.

As an example of the present invention, the synchronizer includes a correlation block for the symbol '0' and a correlation block for the symbol 'p' selected in the data symbols 1 to 15, a correlation block for the symbols '0' and 'p' A multiplexer for selecting an output or an output sum of the correlation blocks and accumulation blocks according to the transmission rate, a demodulator correlator for confirming the precision correlation result with the multiplexer according to the transmission rate, And a time synchronization control unit for temporarily controlling the operation of the timer.

As one example of the present invention, the transmission rate is selected from four transmission rates of 250 Kbps, 125 Kbps, 62.5 Kbps, and 31.25 Kbps, and for the two transmission rates of 250 Kbps and 125 Kbps, .

As an example of the present invention, the time synchronization control unit may include two correlation blocks according to a selection signal for selecting one of the four transmission rates, and an accumulation block for selectively outputting a value obtained by repeating the sum of the two correlation block outputs once or three times The correlation result is determined through the sum of the output of the selected correlation block and the cumulative block.

As an example of the present invention, the time synchronization control unit may set two or four of the correlators of the demodulating unit to receive the output of the complex multiplier at the time of the coarse synchronization according to the result of the coarse correlation when the transmission rate is 62.5 Kbps or 31.25 Kbps, And the fine correlation result is determined based on the demodulation correlator correlation time point having the largest correlation value.

As an example of the present invention, a correlation block of a synchronization unit calculates a correlation degree using the following equation for synchronization through a preamble of a received signal,

S _l and S _m is one of the preamble symbol that corresponds to the data rate and Ns and Nc is the number of the number of accumulated samples delayed sample, Rs is the n-th sample number, r _x (n) of the two symbols to accumulate _Sx (n) denotes a symbol of the modulated reception data, index x denotes one of predefined symbols, omega ₀ denotes a frequency error between the transmitter and the receiver, and? Denotes an initial phase error.

As an example of the present invention, a correlator of a demodulator shared by a synchronization unit calculates correlation using the symbol '7' defined as the SFD value of the received signal as a reference signal,

x and 7 are indexes of the received signal and the reference signal, Ns, Nc, and No are the number of cumulative samples, the number of delay samples, and the number of samples of two symbols used as a synchronization reference signal, offset, r _x (n) is the n-th received signals, S _x (n) of the samples of the modulated symbols received data, ω ₀ is the frequency error between the transmitter and the receiver, θ means and, at this time, the initial phase error

.

A time synchronization method and apparatus for a Zigbee supporting a variable bit rate according to an embodiment of the present invention proposes a new preamble structure that utilizes data symbols already existing for demodulation in an increased preamble structure to support a variable bit rate, The PN code or a new correlation block for the PN code is not applied and the number of correlation blocks used for synchronization is extremely reduced and even if a synchronization error occurs at a low transmission rate at which the length of the preamble becomes long due to minimization of the correlation block, In the synchronization process, synchronization information can be detected through correlation information obtained by using unused correlators of the demodulation unit, thereby providing various variable transmission rates while minimizing hardware complexity.

The time synchronization method and apparatus for a Zigbee supporting variable rate according to an embodiment of the present invention uses only the real part of a correlation result in a double correlation calculation used for time synchronization acquisition as the preamble length increases, And the complexity of the hardware can be reduced by replacing the multiplier used for the double correlation operation with the combination of the sign reversal, the shifter and the adder through the result analysis of the multiplication.

A time synchronization method and apparatus for a Zigbee supporting variable rate according to an embodiment of the present invention proposes a new structure capable of configuring a preamble requiring a maximum of 8 symbols using only two types of symbols, It is possible to minimize the hardware configuration and to provide high performance corresponding to the large frequency offset environment of ± 80 ppm defined in the IEEE 802.15.4 Zigbee system standard by allowing the correlation performance limit of the base station to be overcome by utilizing the correlator in the synchronization process .

1 is a block diagram showing a packet structure of an IEEE 802.15.4 Zigbee;
FIG. 2 is a block diagram showing a configuration of a transmitter of an IEEE 802.15.4 Zigbee; FIG.
FIG. 3 is a table showing a chip sequence defined for symbol spreading of IEEE 802.15.4 Zigbee; FIG.
4 is a diagram showing a preamble structure of IEEE 802.15.4 Zigbee.
5 is a conceptual diagram showing a preamble correlation characteristic of IEEE 802.15.4 Zigbee;
FIG. 6 is a conceptual diagram showing correlation characteristics when repeated preamble symbols are transmitted. FIG.
FIG. 7 is a conceptual diagram illustrating a preamble structure for supporting a variable transmission rate according to an embodiment of the present invention; FIG.
FIG. 8 is a conceptual diagram showing a correlation characteristic of a preamble according to an embodiment of the present invention; FIG.
9 is a graph showing time synchronization acquisition performance when a preamble structure according to an embodiment of the present invention is used.
FIG. 10 is a block diagram illustrating a configuration of a variable rate compatible time synchronization apparatus according to an embodiment of the present invention; FIG.
11 is a conceptual diagram illustrating a preamble structure for supporting a variable transmission rate according to another embodiment of the present invention for reducing the number of used symbols.
12 and 13 are conceptual diagrams for explaining a correlation characteristic of a preamble according to another embodiment of the present invention and a modulation part sharing method for synchronization.
FIG. 14 is a block diagram illustrating a configuration of a variable rate compatible time synchronization apparatus according to another embodiment of the present invention; FIG.
15 is a configuration diagram showing a configuration of a correlator according to embodiments of the present invention.
16 is a table showing the types of reference signals for correlation calculation according to embodiments of the present invention.
17 is a block diagram illustrating a multiplier replacement structure of a correlator according to embodiments of the present invention.
18 is a graph showing time synchronization acquisition performance when a preamble structure according to embodiments of the present invention is used.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features and advantages of the invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

It is noted that the technical terms used in the present invention are used only to describe specific embodiments and are not intended to limit the present invention. In addition, the technical terms used in the present invention should be construed in a sense generally understood by a person having ordinary skill in the art to which the present invention belongs, unless otherwise defined in the present invention, Should not be construed to mean, or be interpreted in an excessively reduced sense. In addition, when a technical term used in the present invention is an erroneous technical term that does not accurately express the concept of the present invention, it should be understood that technical terms can be understood by those skilled in the art. In addition, the general terms used in the present invention should be interpreted according to a predefined or prior context, and should not be construed as being excessively reduced.

Furthermore, the singular expressions used in the present invention include plural expressions unless the context clearly dictates otherwise. In the present invention, terms such as "comprising" or "comprising" and the like should not be construed as encompassing various elements or various steps of the invention, Or may further include additional components or steps.

Furthermore, terms including ordinals such as first, second, etc. used in the present invention can be used to describe elements, but the elements should not be limited by terms. Terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, wherein like reference numerals refer to like or similar elements throughout the several views, and redundant description thereof will be omitted.

In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. It is to be noted that the accompanying drawings are only for the purpose of facilitating understanding of the present invention, and should not be construed as limiting the scope of the present invention with reference to the accompanying drawings.

FIG. 1 shows a physical layer protocol data unit (PPDU) configuration of 2.45 GHz frequency band defined in the IEEE 802.15.4 Zigbee standard. According to this standard packet structure, as shown in the figure, a preamble, a State of Frame Delimiter (SFD) indicating a correct start of a packet, a PHR (PHY header) having length information of a physical payload, and a PSDU Unit).

On the other hand, FIG. 2 briefly shows a configuration of a transmitter that actually transmits a packet defined as shown in FIG.

As shown in FIG. 2, the transmitter of the IEEE 802.15.4 Zigbee system constructs symbols (symbol conversion) by collecting 4 bits of input data, and one symbol is DSSS (Direct Sequence Spread Spectrum) spread (Diffusion portion). The spread signal is OQPSK (Offset QPSK) modulation which reduces the bandwidth by delaying the Q-phase by one chip period among the QPSK (Quadrature Phase Shift Keying) method of modulating the odd-numbered chip and the even-numbered chip into I- (OQPSK modulating unit), and then transformed into a waveform corresponding to the half period of the sine wave (Half-Sine Filter).

In the IEEE 802.15.4 Zigbee system, one symbol is spread 8 times using a pseudo noise (PN) code having 32 chips (one symbol is spread by 32 chips because one symbol is 4 bits).

FIG. 3 shows 16 chip sequences for spreading data symbols in a DSSS manner. As shown, the symbols (16 types) consisting of 4 bits are spread to one of the chip sequences shown, and the transmitter and receiver already have blocks for this chip sequence for modulation and demodulation.

FIG. 4 shows a preamble structure of an IEEE 802.15.4 Zigbee system. As shown in FIG. 4, a preamble having a total of 4 bits is composed of 8 symbols in accordance with a data rate of 250 Kbps. Each symbol corresponds to a data symbol {0} Is composed of a spread chip sequence. For convenience, each of the preambles # 1 to # 8 is referred to as a unit preamble.

The specific configuration and time synchronization acquisition method will be described with reference to FIG.

FIG. 5 shows correlation characteristics of preambles supporting a 250 Kbps transmission rate. As shown in FIG. 5, eight unit preambles are arranged in eight chip sequences in which symbol '0' is spread.

The correlation window (symbol correlator) is a symbol '0' for detecting a unit preamble of the symbol '0', and a correlation window is used for the correlation window. A correlation peak (a) of the correlation operation is detected when it is positioned coincident with the unit preamble as shown in the moving window of the correlation window.

As a result, in the case of the distortion-free received signal, the maximum correlation value of 8 times is detected.

If the IEEE 802.15.4 Zigbee system is designed to support a variable transmission rate, that is, a rate lower than 250 Kbps, for example, 125 Kbps, 62.5 Kbps, 31.25 Kbps, and so on to increase the signal arrival distance, And the speed of the chip is maintained, the amount of data to be transmitted is increased.

That is, although 8 preamble units constituting the preamble at a transmission rate of 250 Kbps correspond to 1 symbol each, they correspond to 2 symbols at 125 Kbps, 4 symbols at 62.5 Kbps, and 8 symbols at 31.25 Kbps Symbols.

In order to support this, if a new PN code having a longer length is newly defined according to the individual transmission rate, an additional block is required, which causes a problem of increased hardware complexity. If the existing symbol is repeatedly used, Time synchronization error occurs.

FIG. 6 shows a preamble correlation characteristic when the same symbol is repeated, and is an example of a case where symbols are repeated twice at 125 Kbps.

0 'is repeatedly applied to the unit preamble and the correlation window (symbol correlator) is also repeatedly applying the symbol' 0 ', the maximum value (a) of the correlation operation is normally generated when the correlation window is located in the first unit preamble do. However, considering the characteristic in which the time synchronization acquisition procedure is performed at an arbitrary point after the automatic gain control (AGC) is performed in the receiver, as shown in the case of the correlation window, it is located at the midpoint between the first unit preamble and the second unit preamble In this case, the maximum value (b) of the correlation operation is also generated. That is, since the maximum value (b) of the correlation operation is detected in the middle portion of the symbol, it is regarded as the start point of the packet and accurate time synchronization can not be obtained.

That is, simply using a symbol used for a preamble can not cope with a variable transmission rate.

Therefore, in the embodiment of the present invention, a new preamble transmission structure as shown in FIG. 7 is provided. FIG. 7 shows an example in which the length of a symbol used for a unit preamble is increased, but is not simply repeated, thereby improving time synchronization acquisition performance.

The symbol '0' applied to the unit preamble at the existing 250 Kbps remains unchanged, and the symbol '0' is used in addition to the symbol 'p' at 125 Kbps, and the symbols 'q' and 'r' are used at 62.5 Kbps. And symmetrically uses the symbols used at 62.5 Kbps at 31.25 Kbps. This minimizes the number of symbols used. Here, symbols 'p', 'q', and 'r' may be set to arbitrary symbols other than '0' out of the 16 data symbols shown in FIG.

That is, since the number of symbols used increases according to the supported transmission rate, the number of symbols used for supporting three types of transmission speeds is eight in total except for the basic rate. If two types of additional transmission rates are supported, the total number of symbols used may be four.

Since it is inefficient to use different kinds of symbols as the total number of symbols used in this embodiment, the first half of the total symbols used in the embodiment of the present invention is used so as not to overlap, and the remaining symbols are configured to be symmetrical. In this case, since the number of symbols (r in the illustrated example) existing in the symmetric position is two consecutive but the total number of symbols increases, the correlation value also becomes large, so that no problem arises.

As a result, the preamble structure of the proposed multi-rate supporting preamble is composed of 2n symbols having symmetrically arranged n different symbols. In order to maintain the preamble, the first symbol is set to '0' It is said to be doing.

FIG. 8 is a conceptual diagram illustrating a correlation characteristic of a preamble according to an embodiment of the present invention. As shown in FIG. 8, the problem described in FIG. 6 is solved. As shown, when the symbol {0, p} is used as a preamble for supporting 125 Kbps, the correlation window (symbol correlator) also uses the symbol {0, p} The maximum value of " 0 "

IEEE 802.15.4 Zigbee systems are specified to accommodate frequency errors of up to ± 80 ppm, and this error causes the phase shift of the received signal, so the time synchronization part should be robust to this frequency offset. However, since IEEE 802.15.4 Zigbee system is required to realize low power and low complexity, it is difficult to apply the synchronization method which requires additional complexity to compensate for the phase of the signal. Therefore, the received signal is synchronized independently of the phase information of the signal Asynchronous mode is used. A scheme used for synchronization of a Zigbee system according to an embodiment of the present invention is a symbol-based double correlation scheme (SBDC), which uses a phase difference between a received signal and a received signal delayed by a symbol period to synchronize, Is multiplied by a received signal delayed by a symbol period, multiplied by a complex conjugate signal of a demodulated delayed symbol (demodulated previous period symbol), and a correlation property between the obtained signal and a preamble symbol according to the preamble structure defined above is checked It is a way to synchronize.

In order to confirm the time synchronization acquisition performance when the variable rate is supported using the proposed preamble structure, it is mathematically modeled to obtain a correlation characteristic for the input signal and time synchronization acquisition performance at a low transmission rate Increase.

When receiving a transmission signal according to the IEEE 802.15.4 Zigbee standard, which has been described with reference to FIG. 1, the reception signal of the receiver reflecting the frequency error between the transmitter and the receiver can be modeled as Equation (1). Additive white Gaussian noise (AWGN) is added to the signal in the receiver, which is taken into consideration.

Here, r _x (n) denotes a received signal of the n-th sample, S _x (n) denotes a symbol of the modulated received data, and index x denotes one of predefined symbols (i.e., data symbols 0 to 15 in FIG. to be. ω ₀ is the frequency error of the transmitter and receiver, and θ is the initial phase error. W (n) is the AWGN for the nth sample.

The correlation computation model of the double correlation method for the received signal is summarized as Equation (2). The AWGN component, W (n), is not considered for convenience of formula expansion.

Here, S _l and S _m are one of the preamble symbols corresponding to the respective transmission rates defined in FIG. 7, 250 Kbps is 0, 125 Kbps is 1, 62.5 Kbps is 2, and 31.25 Kbps is 3. Therefore, S _l and S _m are {0}, p, q, r when {0, p, q, r} and 31.25Kbps when { , r, q, p, 0}. Ns and Nc represent the number of accumulated samples and the number of delayed samples.

In consideration of the performance of the demodulation unit, the receiver uses a clock several times faster than the chip period used for spreading the transmission signal, thereby allowing the receiver to oversample the signal according to the transmission signal spreading chip period. In the embodiment of the present invention, the chip period used for actual transmission signal spreading is oversampled 4 times by using a clock four times faster than the chip period.

Ns in Equation 2 is the cumulative number of samples for one unit preamble. When the chip period is oversampled by 4 times, the number of samples for one unit preamble is 128 at 250 Kbps (1 symbol, 32 chips), and 31.25 1024 in Kbps (8 symbols, 256 chips).

이 된다. 결국 심볼의 길이에 무관하게 언제나 칩 주기당 샘플 수(Nc)가 오버샘플링한 배수(4배 오버샘플링의 경우 4)로 고정되므로 다양한 전송률을 지원할 경우 문제가 되었던 잔류 주파수 오프셋의 영향이 전송률에 무관하게 고정된다.In the above equation, to minimize the influence of the frequency error, a conjugate product operation is performed with r _l (n-Nc) in which the received signal r _l (n) is delayed by Nc samples. Here, the number of delay samples Nc is set to the number of samples per chip period (oversampling multiple, for example, 4 when oversampling 4 times), which is independent of the symbol. The effect of the frequency offset, which is substantially remained by canceling the influence of the frequency offset by using the product of the complex conjugate of the received signal and the received signal delayed by the chip period independent of the symbol length,

. As a result, since the number of samples Nc per chip period is always fixed to a multiple of oversampling (4 in case of 4-times oversampling) regardless of the symbol length, the influence of the residual frequency offset, which is a problem in supporting various transmission rates, .

The correlation property can be obtained by multiplying the preamble symbol S _m (n), which is known in advance, by the conjugate multiplication of S _m (n-Nc) delayed by Nc samples. When the symbol index l of the received signal is equal to the reference signal symbol index m, the maximum value of the correlation result can be obtained, so that an accurate packet can be detected.

The time synchronization acquisition performance for four kinds of variable transmission rates is detected using this correlation model, as shown in FIG. The time synchronization performance depends on how accurately the demodulator can acquire the start point of the packet so that the demodulator can recover the correct data. Therefore, when two consecutive maximum peaks are confirmed for the same point in the preamble interval, Success was judged to be a time synchronization acquisition failure when the start point of the erroneous packet was found and the packet was not detected. The performance evaluation of the time synchronization algorithm is performed on 50,000 packets in an environment with AWGN channel, maximum frequency offset ± 80 ppm.

As shown in the figure, when the proposed preamble is used according to the variable rate support, the time synchronization acquisition performance can be improved by a preamble length according to the variable rate support, and a performance gain of 2 dB can be obtained for each lower transmission rate. As a result, it shows superior time-synchronized acquisition performance in low SNR environment.

FIG. 10 shows a configuration of a variable rate compatible time synchronization apparatus 100 according to an embodiment of the present invention.

To Figure 7 above this by multiplying the incoming signal (the real part Re [r _l] and an imaginary part Im [r _l] of the received signal) the complex conjugate signal and the delay signal is received signal chip unit sample channel delay as illustrated And is applied to a correlation block according to the preamble structure described above.

Here, the delay unit 120 uses a delay unit 120 that does not use the demodulated signal of the previous period and delays the demodulated signal by the number of chip period samples so as to be independent of the demodulated signal of the previous period.

That is, the illustrated configuration includes a complex conjugate signal generating unit 110 for generating a complex conjugate signal for the received signal, a delay unit 120 for delaying the received signal by the number of chip period samples, A complex multiplier 130 for multiplying an output of the complex signal generator 110 and an output of the delay unit 120 and a multiplier 110 for multiplying the output of the complex multiplier 130 by the multiplier 110, And outputs the correlation result according to the correlation result.

The illustrated synchronization unit 140 supports four types of variable rate, 250 Kbps, 125 Kbps, 62.5 Kbps, and 31.25 Kbps as shown in FIG. 7, and the correlation blocks 141a to 141h are composed of eight , And a multiplexer 142 for selecting one, two, four, or eight result sums according to a variable rate select signal.

That is, the synchronization unit 140 is composed of 2n correlation blocks in which correlation blocks for n different symbols are symmetrically arranged and a multiplexer for selecting a sum of outputs of the correlation blocks, and a configuration supporting four kinds of variable transmission rates The multiplexer 142 outputs the output sum of the correlation blocks selected by different combinations according to the transmission rate among the eight correlation blocks 141a to 141h in which the four correlation blocks 141a, 141b, 141c and 141d are symmetrically arranged.

The illustrated correlation blocks 141a to 141h sequentially receive the symbol '0', the symbol 'p', the symbol 'q', the symbol 'r', the symbol 'r', the symbol 'q', the symbol 'p' ', Where symbol' p ', symbol' q ', symbol' r 'are selected so as not to overlap in data symbols 1 to 15.

On the other hand, when the transmission rate is reduced to half from the reference rate of 250 Kbps, the used symbol is doubled. Therefore, when 250 kbps is selected as the transmission rate, the result of the correlation block 141a for the first symbol '0' When the transmission rate is 125 Kbps, the result sum of the correlation blocks 141a and 141b for the first symbol '0' and the second symbol 'p' is provided as a correlation result, and the transmission rate is 62.5 Kbps The result sum of the first four correlation blocks 141a to 141d is provided as a correlation result. When 31.25 Kbps is selected as the transmission rate, the result sum of the eight correlation blocks 141a to 141h is provided as a correlation result.

Meanwhile, the synchronization unit 140 includes a time synchronization control unit 143 for providing a signal for a data rate to the multiplexer 142, receiving the output, confirming completion of synchronization, and allowing the subsequent demodulation unit to operate.

According to an embodiment of the present invention, a new PN code can be defined and a high time synchronization performance without additional blocks can be provided while increasing the preamble in order to support a low transmission rate.

However, despite this configuration, since there are many correlation blocks to be configured in the synchronous part in order to support the four kinds of transmission speeds, there is a limitation in reducing the complexity, and additional symbols' p 'and' there arises a problem that the area is increased by a circuit for detecting q 'and' r '.

Accordingly, another embodiment of the present invention will be described in which the hardware configuration is further reduced so as to be optimized for an IEEE 802.15.4 Zigbee system aiming at realizing low power and low complexity.

11 is a conceptual diagram illustrating a preamble structure for supporting a variable transmission rate according to another embodiment of the present invention for reducing the number of used symbols. Unlike the structure of the preamble explained with reference to FIG. 7, the preamble includes a symbol '0' . That is, in the method using the existing four symbols, the method using the two symbols is simplified, and when the number of symbols required for the preamble increases, the symbol {0, p} is repeated.

0 ',' p ',' 0 ',' p ', and 31.25 Kbps for symbols of' 0 'and' p 'for a transmission rate of 250 Kbps, symbols' 0' Use the symbols '0', 'p', '0', 'p', '0', 'p', '0', and 'p'

In this case, if the transmission rate is 250 kbps or 125 kbps, accurate time synchronization can be obtained through the synchronous correlation block for the symbol '0' and the symbol 'p' (see FIG. 8). However, in the case of 62.5 Kbps or 31.25 Kbps, ', and' p 'are repeated, the ambiguity problem of time synchronization acquisition described above occurs in FIG.

That is, although the number of sync blocks can be reduced by reducing the number of symbols used, the time synchronization reliability at low speed is lowered.

In another embodiment of the present invention, such a problem is solved by using a demodulation unit which is in a standby state and has a correlator during the operation of the synchronization unit.

To this end, another embodiment of the present invention basically obtains a coarse correlation result through two-symbol correlation blocks constituting a synchronization unit, and obtains a fine correlation result, and then obtains an accurate time synchronization result in which ambiguity of time synchronization acquisition is resolved through these results. That is, another embodiment of the present invention utilizes demodulator correlators that are in idle state with symbols that are already used, without adding additional PN codes or blocks for processing them, so that the hardware configuration can be minimized and the circuit size can be further reduced have.

12 and 13 are conceptual diagrams for explaining the correlation characteristic of a preamble according to another embodiment of the present invention and a method of sharing a modulation part for synchronization. In a synchronization process of 62.5 Kbps in which symbol {0, p} And explains how to resolve the ambiguity of time synchronization acquisition that occurs.

12 is an example of a case where the first symbol set {0, p} of the preamble is precisely synchronized when the symbol {0, p, 0, p} is used and FIG. 13 is an example of using symbols {0, p, 0, p} Is an example of a case where the preamble is not correctly synchronized in the first symbol set {0, p} and is erroneously synchronized with the second symbol set {0, p} as the start position.

12 and 13, although the correlation window calculates the coincidence through the correlation operation on the symbol {0, p, 0, p}, the correlation operation is performed only on the first two symbols {0, p} . The synchronization unit according to another embodiment of the present invention obtains the correlation result (time at which the correlation value for the two symbols becomes maximum) using only one pair of correlation blocks for symbols '0' and 'p' Correlation arithmetic operation is required for the symbols {0, p}, but no correlation operation is required for the following two symbols. That is, through the correlation window of the synchronization unit, the context synchronization is performed using the correlation result of which the correlation value becomes the maximum in the first two symbols {0, p} of the preamble or the following two symbols {0, p}. As a result, the synchronization through the correlation result corresponds to synchronization for finding any two symbol start positions included in the preamble other than the start position of the preamble.

When the curse synchronization is performed, the reference signals of the demodulator's correlators are set to the value of the start of frame delimiter (SFD) (symbol '7') for frame start identification according to the correlation result, } Length offset, and then the precise correlation result can be obtained based on the correlation results, and the synchronization can be completed through the demodulator correlator having the largest precision correlation result.

In the example shown in FIG. 12, context synchronization is performed using the correlation result of the maximum correlation value at the first two symbols (i.e., the start of the preamble) of the preamble through the correlation window of the synchronization unit. That is, it corresponds to the case where the start point of the preamble is accurately detected and synchronized.

When the cursive synchronization is performed, the reference signal of the demodulator's correlators is set to the value of the start of frame delimiter (SFD) (symbol '7' The precision correlation result that maximizes the correlation result can be obtained through the demodulator correlator 1 to which the offset is not applied and the synchronization correlation can be achieved through the correlation result and the precision correlation result .

On the other hand, in the case of FIG. 13, when synchronization is performed in two symbols (i.e., the middle of the preamble) located at the second position rather than the first two symbols of the preamble through the correlation window of the synchronization unit, And becomes in a synchronized state corresponding to the start positions of the two repeated symbols {0, p} constituting the preamble.

Even if the erroneous frame synchronization is performed, the reference signal of the demodulator's correlators at that time is set to the value of the start of frame delimiter (SFD) (symbol '7') for frame start identification, And the correlation value is calculated using the offset of the correlation value, the precision correlation result in which the correlation result becomes the maximum can be obtained through the demodulation part correlator 2 to which the offset is applied once. .

 As a result, even if the synchronization timing of the preamble occurs at an interval of two symbols using the value of the SFD set to the symbol '7', a plurality of demodulator correlators whose offset is set at intervals of two symbols are used for SFD By examining the correlation value, the start position of the actual data can be known through accurate SFD synchronization, so that only two correlation blocks can be used in the synchronization part.

In this manner, in the case of a transmission rate of 31.25 Kbps in which two symbols {0, p} are repeated four times, four demodulator correlators can be sequentially operated by applying two symbols offset 0 to 3. That is, there is a case in which one correct sync and three inaccurate sync occur when {0, p} is repeated four times according to the result of the curse correlation. The precise synchronization point can be known through the SFD correlation results obtained by four demodulator correlators having no two symbol offsets, one, two, or three times based on the respective cus synchronization points.

If {0, p} is repeated eight times to support 15.625 Kbps instead of 31.25 Kbps, 8 demodulator correlators can be used. Theoretically, up to 7.8125 Kbps can be achieved because 16 demodulator correlators are provided.

As a result, synchronization can be performed using the correlation result only through the synchronization unit when the transmission rate is 250 Kbps or 125 Kbps, and synchronization is performed using the precision correlation result using the demodulator correlator when the transmission rate is lower than 250 Kbps or 125 Kbps.

These algorithms are summarized more mathematically as follows.

The time synchronization acquisition in the synchronous part can be expressed as the following equation (3).

S _l and S _m are one of preamble symbols corresponding to a transmission rate, Ns and Nc are the number of accumulated samples and the number of delay samples, and Rs is the number of accumulated two symbols, 2 for a transmission rate of 63.5 Kbps and 31.25 Kbps 4 " In addition, r _x (n) is the n-th received signals, S _x (n) of the sample is one of a symbol, the index x of the modulated received data is pre-defined symbol, ω ₀ is the frequency error between the transmitter and the receiver, θ is Initial phase error.

Here, when the received signal symbol index l and the reference signal symbol index m are equal to each other, the maximum value of correlation results can be obtained. However, time synchronization ambiguity exists due to accumulation of correlation values for {0, p} symbols. Therefore, the result according to Equation (3) is used as a correlation result.

Thereafter, when the transmission rate is 63.5 Kbps or 31.25 Kbps, two or four of the 16 correlators of the demodulation unit are used to obtain precision correlation results for precise time synchronization.

In order to explain the acquisition of the fine correlation result using the demodulation unit, the basic demodulation unit's correlation calculation method is expressed by the following equations (4) and (5). The demodulator correlator applied to the embodiment of the present invention uses a sample-based double correlation algorithm for memory reduction.

Here, Nc is 4, and Mx _{, k} (n) is defined by the following equation (5).

x and m are indexes of the received signal and the reference signal, and Ns and Nc represent the number of accumulated samples and the number of delayed samples. Y _m represents the correlation value between the m-th reference signal and the received signal r _{x, k} (n) among the 16 candidate groups (FIG. 3), and represents the largest value when x and m of the received signal are equal. Therefore, the correlation calculation result values Y ₀ to Y ₁₅ are compared with the 16 candidate signals received, and the demodulation is performed with the reference signal having the largest correlation value.

In another embodiment of the present invention, such a demodulator correlator is used for precision correlation result calculation for precise time synchronization, and the algorithm for this can be summarized as Equations (6) and (7) below. However, since the correlation operation with the SFD is performed, the symbol '7' (seventh reference signal) which is the SFD value according to the standard is used as a reference, and it may be replaced with another symbol value if necessary.

는 다음의 수학식 7과 같이 정의된다.Here, Nc is 4,

Is defined by the following Equation (7).

x and 7 are indexes of the received signal and reference signal, Ns, Nc, and No are the number of cumulative samples, the number of delay samples, the number of samples of two symbols {0, p} time offset, r _x (n) of the demodulation correlator is n received signals, S _x (n) are symbols, ω ₀ of the modulated received data frequency offset between the transmitter and the receiver, θ of the second sample indicates the initial phase error do. In particular, h represents the temporal offset of the demodulator correlator used in parallel to calculate the SFD detection time.

의 상관연산 결과값을 나타낸다. 따라서, 동기부의 상관기를 이용하여 대략적인 시간동기를 획득한 후, 복조부 상관기를 {0, p} 심볼을 구성하는 샘플 수의 h배만큼 시간적 오프셋을 두어 병렬적으로 배치하여 수신 신호와 상관연산을 취한다. 이때, 상관연산 최대값은 시간적 오프셋을 두고 병렬적으로 배치된 복조부 상관기와 수신신호의 SFD {7} 심볼이 정확하게 일치할 때 발생한다. 따라서 값이 최대가 되는 상관기의 상관 연산 시점을 검출함으로써, 정확한 SFD 심볼의 위치를 검출하고, 이를 통해 정밀한 시간 동기를 획득할 수 있다.Specifically, h is an offset corresponding to a symbol length of {0, p}, has a value of 0 and 1 in case of 62.5 Kbps, and 0, 1, 2, and 3 in case of 31.25 Kbps. This is because of two cases where the time synchronization acquisition ambiguity occurs at 62.5 Kbps, and at the case of 31.25 Kbps, four cases where the time synchronization acquisition ambiguity occurs. Y _{h, 7} denotes a 7th reference signal corresponding to the SFD symbol with a time offset of h times the number of samples constituting the {0, p} symbol,

Of the correlation calculation result. Therefore, after obtaining approximate time synchronization using a correlator of the synchronization unit, the demodulator correlator is arranged in parallel with a time offset of h times the number of samples constituting the {0, p} symbol, Lt; / RTI > In this case, the correlation maximum value occurs when the demodulator correlator arranged in parallel with the temporal offset and the SFD {7} symbols of the received signal are exactly matched. Therefore, by detecting the correlation calculation time of the correlator having the maximum value, the position of the accurate SFD symbol can be detected, and precise time synchronization can be obtained.

Figure 14 is a real part Re [r _l] and an imaginary part Im [r _l] of the received signal (reception signal, as a schematic view showing a configuration of a variable bit rate supported time synchronizer according to the other embodiment of the present invention, illustrated ) Is multiplied by a delay signal delayed by the number of chip unit samples, and the result is applied to two correlation blocks according to the preamble structure described above with reference to FIG.

Here, the complex conjugate signal generating unit 210, the delay unit 220, and the complex multiplier 230 are the same as those described above with reference to FIG. 10, and thus a detailed description thereof will be omitted.

The result of the multiplication of the real part of the complex multiplier 230 and the result of the imaginary part multiplication are provided to output the correlation result according to the variable rate. The synchronizer 240 receives the four types of variable rate, 250 Kbps, And a correlation block 241 and 242 for symbol '0' and symbol 'p' to support 125 Kbps, 62.5 Kbps and 31.25 Kbps, (243).

The accumulation block 243 accumulates the correlation values of the two correlation blocks 241 and 242 at 62.5 Kbps and 31.25 Kbps, and outputs the sum of two correlation blocks through the accumulation unit and the accumulation control unit 1 or 3 times And outputs the selected value. That is, the correlation value for two symbols repeated in the same way is a multiple of the result sum of two correlation blocks, or all the correlation blocks are necessary or almost the same. Therefore, in order to simplify the configuration, An accumulation block 243 is applied.

In the illustrated implementation, synchronization unit 240 includes a correlation block 241 for symbol '0' and a correlation block 242 for symbol 'p' selected in data symbols 1 to 15, A multiplexer 244 for accumulating the correlated block output sums for '0' and 'p' and outputting the accumulated sum for a plurality of accumulated accumulation times, a multiplexer 244 for selecting the output or sum of the correlation blocks and the accumulated blocks according to the transmission rate, And a time synchronization controller 245 for temporarily controlling the correlator operation of the demodulator 400 for confirming the precision correlation result with the multiplexer according to the transmission rate.

The time synchronization controller 245 utilizes the correlators of the demodulator 400 to obtain precise correlation results in the synchronization process in which the demodulator 400 is not operated. To this end, the time synchronization controller 245 determines that the synchronization is performed in the demodulator 400 The demodulation unit 400 obtains correlation results between SFDs included in the reception signal provided by the complex multiplier 230 and a plurality of correlators to which two symbol offsets are sequentially applied, And obtains precise synchronization information according to the correlation value. Upon receiving the precise synchronization information (FS) obtained from the parallel operation correlators of the demodulation unit 400, the time synchronization control unit 245 completes the synchronization using the information and transmits the synchronization completion signal SD to the demodulation unit 400 ) To use the temporarily used correlators for demodulation.

For this purpose, the time synchronization controller 245 may set the initial reference signal of the correlators to be used for obtaining the precise correlation result among the correlators of the demodulator 400 as the seventh reference signal, which is the value of the SFD, 2450), the corresponding value may be initially set.

Meanwhile, when the synchronization process is completed, the time synchronization controller 245 informs the demodulator 400 to reset the reference signal of the demodulator's correlators to the reference signal symbol for correlation with the used symbols. Of course, the reconfiguration process may be automatically performed in the demodulation unit 400 according to the synchronization completion signal.

When the variable rate is used in accordance with the illustrated configuration, the synchronization unit 240 calculates the result of the correlation block for the first symbol '0' at a transmission rate of 250 kbps as a correlation result, and calculates a precision correlation result Can be omitted and the synchronization can be completed with the result of the correlation of the correlation. When the transmission rate is 125 kbps, the result sum of the correlation blocks for the first symbol '0' and the second symbol 'p' is calculated as a coarse correlation result, the process of calculating the fine correlation result is omitted, Can be completed.

On the other hand, when 62.5 Kbps is selected as the transmission rate, the sum of the sum of the correlation blocks for the first symbol '0' and the second symbol 'p' The result sum, that is, twice the result sum of the correlation blocks, is calculated as the correlation result. Then, two of the correlators of the demodulator 400 are operated at intervals of two symbols to determine a precise synchronization point at the demodulator correlator correlation point having the largest correlation value.

When 31.25 Kbps is selected as the transmission rate, the sum of the result of the correlation blocks for the first symbol '0' and the second symbol 'p' , I.e., four times the sum of the sum of the correlation blocks, is calculated as the correlation result. Then, four of the correlators of the demodulator 400 are operated at intervals of two symbols to determine the precise synchronization point as the demodulator correlator correlation point having the largest correlation value.

According to another embodiment of the present invention, a new PN code definition, a high time synchronization performance without additional blocks for the same, and a circuit area can be minimized while the preamble is increased to support a low data rate.

On the other hand, the result of the double correlation operation used for time synchronization acquisition is a complex value composed of a real part and an imaginary part, and a square operation is required for the size comparison. In addition, since the correlator window size is increased according to the variable rate support, a large number of multipliers and adders are required, thereby increasing hardware complexity.

However, as described above, the double correlation operation according to the embodiment of the present invention compensates for the influence of the frequency offset by using the product of the complex conjugate of the received signal and the received signal delayed by a chip period independent of the symbol length, Therefore, even if only the real part Re [C _DC (n)] is used by omitting the imaginary part from the correlation calculation result made of the real part and the imaginary part, it provides a relatively satisfactory level of results.

Therefore, the synchronizer 240 of the illustrated variable rate support time synchronizer receives the real number and the imaginary number, but can provide only the real number Re [C _DC (n)] as the output of the correlation calculation result.

FIG. 15 is a block diagram showing a configuration of a correlation block according to an embodiment of the present invention. FIG. 15 shows a correlator 300 when only the real part of the double correlation calculation type time synchronization unit is used. (310, 320) in which a real part and an imaginary part are sequentially inputted, of a delay conjugate product (Z ₁ (n)) of an input signal provided by a complex multiplier, and a multiplier And an accumulator, and the output of the accumulator outputs only the value of the real part.

Here, the reference signal Z _ref (n) of the double correlation operation is a result of operation on a preamble signal which is known in advance, and one of four values {1, -1, i, -i} , Which is equivalent to a simple sign inversion and an exchange operation between the real and imaginary terms, so that a multiplier-free implementation is possible. In this case, it is possible to replace the multiplier with a sign exchange, and an exchange that exchanges the real and imaginary terms.

Meanwhile, in the embodiment of the present invention, 4-times oversampling is applied in consideration of the influence on the demodulation performance due to the occurrence of the time synchronization error. In this case, the reference signal values have five kinds as shown in FIG.

Cases 1 and 2 do not require a separate calculation, and Case 3 can obtain a correlation value in sign reversal. Since cases 4 and 5 are constant values, these operations can be replaced by sign inverters, shifters, and adders.

FIG. 17 is a block diagram illustrating a configuration of a block 351 for case 4 and a block 352 for case 5, which is an alternative configuration of the multiplier of the correlator according to the embodiment of the present invention.

As shown in the figure, the correlation result can be obtained only by the shifter and the adder.

As a result, the synchronization unit 240 described above may use only the real part of the complex correlation results, or use a multiplier substitution configuration reflecting the correlation operation characteristics of FIG. 16 and FIG. 17 to greatly reduce the hardware burden do.

FIG. 18 is a graph showing the performance of a variable rate support time synchronizer according to embodiments of the present invention. FIG. 18 is a graph illustrating the performance of a variable rate support time synchronizer according to an embodiment of the present invention, Performance of another embodiment of the present invention in which two symbols are used and only two correlation blocks may be configured. As can be seen, there is almost no performance difference.

The foregoing and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. However, the present invention is not limited to the above-described embodiments, and various changes and modifications may be made by those skilled in the art without departing from the scope of the present invention. .

100: variable rate support time synchronizer
110: conjugate complex signal generator 120:
130: complex multiplier 140: synchronizer
141a-141h: Correlation block 142: Multiplexer
143: Time synchronization controller
200: variable rate support time synchronizer
210: conjugate complex signal generator 220:
230: Complex number multiplying unit 240: Synchronization unit
241, 242: correlation block 243: accumulation block
244: Multiplexer 245: Time synchronization control unit
400: demodulator

Claims (33)

Generating a complex conjugate signal for the received signal and delaying the received signal by a number of chip period samples;
Multiplying the complex conjugate of the received signal by a received signal delayed by the number of chip period samples;
And outputs the multiplied signal to the correlation blocks for the two different symbols. The output sum of the selected correlation block according to the transmission rate and the output sum of the correlation block are accumulated in accordance with the transmission rate and output. Providing a result;
And the reference signal of the demodulator's correlators is set to a value of a start of frame delimiter (SFD) for frame start identification and is sequentially operated at an offset of two symbol lengths according to the correlation result. Providing a fine correlation result based on the correlation results;
And completing the synchronization through the correlation result and the precision correlation result,
Wherein the step of providing the correlated correlation result comprises the steps of: selecting one of four transmission rates of 250 Kbps, 125 Kbps, 62.5 Kbps, and 31.25 Kbps; And providing an output sum of a selected correlation block and an accumulation block as a correlation result among the accumulation blocks for selecting and outputting the repeated values.
delete The method of claim 1, wherein the two correlation blocks are a correlation block for symbol '0' and symbol 'p', and symbol 'p' is selected for data symbols 1 to 15. A Zigbee Time synchronization method.
2. The method of claim 1, wherein the step of providing the fine correlation result is performed only for two transmission rates of 62.5 Kbps and 31.25 Kbps among the four transmission rates of 250 Kbps, 125 Kbps, 62.5 Kbps, and 31.25 Kbps. Time synchronization method for Zigbee.
4. The method of claim 4, wherein when 250 kbps is selected as the transmission rate, the result of the correlation block for the first symbol '0' is provided as a coarse correlation result, the step of providing the fine correlation result is omitted, Time synchronization method for Zigbee supporting variable rate.
The method of claim 4, wherein when 125 kbps is selected as the transmission rate, the result sum of the correlation blocks for the first symbol '0' and the second symbol 'p' is provided as a coarse correlation result, And the synchronization is completed based on the correlation result. The time synchronization method for a Zigbee supporting variable rate.
[Claim 4] The method of claim 4, wherein when the transmission speed is 62.5 Kbps, the sum of the correlation blocks for the first symbol '0' and the second symbol 'p' Value of the correlation blocks, i.e., twice the result sum of the correlation blocks, as a result of the correlation result.
The method of claim 4, wherein if 31.25 Kbps is selected as the transmission rate, the result sum of the correlation blocks for the first symbol '0' and the second symbol 'p' Value, i.e., four times the sum of the sum of the correlation blocks, as a correlation result.
5. The method of claim 4, wherein providing the fine correlation result utilizes two of the demodulator's correlators at a 62.5 Kbps transmission rate and uses four of the demodulator's correlators at a 31.25 Kbps transmission rate. Time synchronization method for Zigbee.
The method of claim 9, wherein providing the fine correlation result comprises: operating two of the demodulator correlators at two symbol intervals at a 62.5 Kbps transmission rate that repeats two symbols twice, And a precise synchronization point is determined as a correlation point of the juxtaposition correlator. The time synchronization method for a Zigbee supporting variable rate.
The method of claim 9, wherein providing the fine correlation result comprises: operating four of the demodulator correlators differently at two symbol intervals at a 31.25 Kbps transmission rate of repeating two symbols four times, And a precise synchronization point is determined as a correlation point of a demodulator correlator. The time synchronization method for a Zigbee supporting a variable rate.
2. The method of claim 1, wherein completing the synchronization further comprises reconfiguring a reference signal of the demodulator's correlators to a symbol for correlation with use symbols for a demodulator operation. Time Synchronization Method for Zigbee.
2. The apparatus of claim 1, wherein some of the correlators of the demodulator are set to SFD values to provide fine correlation results, and are reset to corresponding symbol values for demodulation procedures after the synchronization completion phase, respectively Time Synchronization Method for Zigbee Supporting Rate.
4. The method of claim 1, wherein providing the correlation result comprises: performing a double correlation operation and providing only a result of the real part as a correlation result.
[14] The method of claim 14, wherein the providing the cost correlation result comprises: performing a correlation operation on the real part using a multiplier, Wherein the step of generating the time-synchronized Zigbee signal comprises the step of performing a code reversal, a shifter, and an adder.
Determining a number of chip period samples by oversampling the processing speed of the receiver by a number of times greater than a chip period used for transmission signal spreading;
Generating a complex conjugate signal for the received signal and delaying the received signal by a number of chip period samples;
Multiplying the complex conjugate of the received signal by a received signal delayed by the number of chip period samples;
The multiplied signal is provided to the correlation blocks for two different symbols and the output sum of the correlation block selected according to the selected transmission rate among the four transmission rates of 250 Kbps, 125 Kbps, 62.5 Kbps, and 31.25 Kbps, Providing a correlation result according to an output of an accumulation block which accumulates and outputs a sum in accordance with a data rate;
And the reference signal of the demodulator's correlators is set to the value of the SFD for frame start identification and is sequentially operated at the offset of two symbol lengths according to the correlation result, Providing a correlation result;
Completing the synchronization through the correlation result and the fine correlation result;
And resetting the reference signals of the demodulator correlators to symbols for correlation with the used symbols for the demodulator operation according to the completion of the synchronization,
Wherein the two correlation blocks are correlation blocks for symbol '0' and symbol 'p', symbol 'p' may be selected for data symbols 1 through 15, 62.5 Kbps, 31.25 Kbps, and 62.5 Kbps and 31.25 Kbps, respectively. The time synchronization method for a Zigbee supporting a variable transmission rate is as follows.
16. The method of claim 16, wherein providing the correlation result comprises: selecting one of four transmission rates of 250 Kbps, 125 Kbps, 62.5 Kbps, and 31.25 Kbps, And providing the sum of the outputs of the selected correlation block and the accumulation block as a correlation result. The method of claim 1, further comprising:
16. The method of claim 16, wherein providing the fine correlation result comprises: operating two of the demodulator correlators differently at two symbol intervals at a 62.5 Kbps transmission rate that repeats two symbols twice, And a precise synchronization point is determined as a correlation point of the juxtaposition correlator. The time synchronization method for a Zigbee supporting variable rate.
16. The method of claim 16, wherein providing the fine correlation result comprises: operating four of the demodulator correlators differently at two symbol intervals at a 31.25 Kbps transmission rate of repeating two symbols four times, And a precise synchronization point is determined as a correlation point of a demodulator correlator. The time synchronization method for a Zigbee supporting a variable rate.
The phase estimation value of the received signal is provided to the correlation blocks for two different symbols and the output sum of one or two correlation blocks selected according to the selected transmission rate and the sum of the outputs of the correlation block are cumulatively accumulated and output Providing a correlation result according to an output of the block;
The correlator reference signal of the demodulation unit is set to the value of the SFD for frame start identification according to the correlation result and sequentially operated at the offset of two symbol lengths. Based on the correlation results, , ≪ / RTI >
Characterized in that the two correlation blocks are correlation blocks for symbol '0' and symbol 'p' and symbol 'p' can be selected for data symbols 1 to 15. Time synchronization for a Zigbee supporting a variable rate Way.
21. The method of claim 20, wherein the correlator of the correlation block providing the correlation result and the correlator of the demodulation block providing the fine correlation result use a sample unit bi-correlation algorithm.
21. The method of claim 20, further comprising: completing synchronization through the correlation result and the fine correlation result; And reconfiguring the reference signals of the demodulator's correlators to symbols for correlation with the used symbols for the demodulator operation according to the completion of the synchronization.
delete The method of claim 20, wherein the transmission rate is selected from among four types of transmission rates of 250 Kbps, 125 Kbps, 62.5 Kbps, and 31.25 Kbps, and the step of providing precision correlation results is selected for only two transmission rates of 62.5 Kbps and 31.25 Kbps among the four transmission rates Time synchronization method for a Zigbee supporting variable rate.
21. The method of claim 20, wherein the correlation block in which the step of providing the correlation correlation result is performed is characterized in that correlation is obtained by the following equation for synchronization through a preamble of a received signal,

S _l and S _m is one of the preamble symbol that corresponds to the data rate and Ns and Nc is the number of the number of accumulated samples delayed sample, Rs is the n-th sample number, r _x (n) of the two symbols to accumulate , Where S _x (n) is a symbol of modulated received data, index x is one of the predefined symbols, ω ₀ is the frequency error of the transmitter and receiver, and θ is the initial phase error. Time Synchronization Method for Zigbee Supporting Rate.
21. The method of claim 20, wherein the correlator of the demodulator in which the step of providing the fine correlation result is performed calculates correlation using the symbol '7' defined as the SFD value of the received signal as a reference signal,

x and 7 are indexes of the received signal and the reference signal, Ns, Nc, and No are the number of cumulative samples, the number of delay samples, and the number of samples of two symbols used as a synchronization reference signal, offset, r _x (n) is the n-th received signals, S _x (n) of the samples of the modulated symbols received data, ω ₀ is the frequency error between the transmitter and the receiver, θ means and, at this time, the initial phase error

Time synchronization method for a Zigbee supporting variable rate.
A complex conjugate signal generating unit for generating a conjugate complex signal with respect to the received signal; A delay unit for delaying the received signal by the number of chip period samples;
A complex multiplier for multiplying the output of the complex conjugate signal generator and the output of the delay unit;
And provides the multiplied signal to the correlation blocks for two different symbols and outputs the sum of the output of the selected correlation block and the sum of the outputs of the correlation block according to the transmission rate, And the reference signal of the demodulator's correlators is set to the value of the SFD for the start of the frame according to the correlation result and sequentially operated at the offset of two symbol lengths. Based on the correlation results, And a synchronization unit for confirming and performing synchronization,
The synchronization unit accumulates the correlation block output for the symbol '0' and the correlation block for the symbol 'p' selected in the data symbols 1 to 15, and the sum of the correlation block outputs for the symbols '0' and 'p' A multiplexer for selecting an output or an output sum of the correlation blocks and accumulation blocks according to the transmission rate, and a demultiplexer for checking the operation of the demodulator correlator for confirming the precision correlation result with the multiplexer according to the transmission rate And a time synchronization controller for controlling the variable transmission rate of the Zigbee.
delete 27. The method of claim 27, wherein the transmission rates are selected from four transmission rates of 250 Kbps, 125 Kbps, 62.5 Kbps, and 31.25 Kbps, and the synchronization unit performs synchronization using the correlation correlation results for two transmission rates of 250 Kbps and 125 Kbps, The apparatus of claim 1, wherein the ZigBee supports a variable rate.
[Claim 29] The method of claim 29, wherein the time synchronization controller comprises: two correlation blocks according to a selection signal for selecting one of the four transmission rates; and an accumulation block Wherein the coarse correlation result is determined based on the sum of the output of the selected correlation block and the cumulative block.
The time synchronization controller according to claim 30, wherein the time synchronization controller is configured to transmit 2 or 4 of the correlators of the demodulator to receive the output of the complex multiplier at the time of the coarse synchronization according to the result of the coarse correlation when the transmission rate is 62.5 Kbps or 31.25 Kbps, And the fine correlation correlations are determined based on a demodulation correlator correlation point having a greatest correlation value. The time synchronization apparatus for a Zigbee supporting a variable transmission rate.
27. The apparatus of claim 27, wherein the correlation block of the synchronization unit obtains a degree of correlation using the following equation for synchronization through a preamble of a received signal,

S _l and S _m is one of the preamble symbol that corresponds to the data rate and Ns and Nc is the number of the number of accumulated samples delayed sample, Rs is the n-th sample number, r _x (n) of the two symbols to accumulate , Where S _x (n) is a symbol of modulated received data, index x is one of the predefined symbols, ω ₀ is the frequency error of the transmitter and receiver, and θ is the initial phase error. Time Synchronizer for Zigbee with Transfer Rate.
27. The apparatus of claim 27, wherein the correlator of the demodulator shared by the synchronization unit uses correlation symbol '7' defined as the SFD value of the received signal as a reference signal,

x and 7 are indexes of the received signal and the reference signal, Ns, Nc, and No are the number of cumulative samples, the number of delay samples, and the number of samples of two symbols used as a synchronization reference signal, offset, r _x (n) is the n-th received signals, S _x (n) of the samples of the modulated symbols received data, ω ₀ is the frequency error between the transmitter and the receiver, θ means and, at this time, the initial phase error

And a time synchronization unit for the Zigbee supporting the variable rate.

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