Receiving apparatus, correction method and non-transitory storage medium

A reception apparatus of a time division multiple access (TDMA) system for performing intermittent reception by a reception period of a time slot and a non-reception period of a predetermined number of time slots which follow the reception period and in which reception is suspended includes a symbol clock controller configured to perform symbol synchronization at a timing at which a synchronous word included in the reception period after the non-reception period, and correct a symbol clock frequency of a symbol clock based on a number of time slots and a symbol count value during a previous reception period and the non-reception period following the previous reception period; and a reception period controller configured to correct, after detection of the synchronous word, a reception termination timing of the reception period in which the synchronous word is detected based on the symbol clock with the corrected symbol clock frequency.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from Japanese Application No. 2020-049811, filed on Mar. 19, 2020, the contents of which are incorporated by reference herein in its entirety.

FIELD

The present application relates to a receiving apparatus and a correction method.

BACKGROUND

In a wireless communication terminal (hereinafter, also referred to as a mobile station) that performs intermittent reception, a technique of synchronizing a symbol clock of a mobile station with a symbol clock of a base station has been known.

For example, Japanese Laid-open Patent Publication No. 08-307304 discloses a technique of a mobile communication terminal in which power consumption is reduced to a low level in a standby mode and reception performance is improved.

In the technique described in Japanese Laid-open Patent Publication No. 08-307304, a length of a period for detecting a unique word in a next slot is set in accordance with deviation of a timing to detect the unique word. However, since a length of a reception period in a slot in which synchronization deviation is detected and corrected is inappropriate, it may be difficult to demodulate data of the slot in which the synchronization deviation is detected.

SUMMARY

A receiving apparatus and a correction method are disclosed.

According to one aspect, there is provided a reception apparatus of a time division multiple access (TDMA) system for performing intermittent reception by a reception period of a time slot and a non-reception period of a predetermined number of time slots which follow the reception period and in which reception is suspended, the reception apparatus comprising: a symbol clock controller configured to perform symbol synchronization at a timing at which a synchronous word included in the reception period of the time slot after the non-reception period, and correct a symbol clock frequency of a symbol clock based on a number of time slots and a symbol count value that is a number of counted symbols during a previous reception period and the non-reception period which follow the previous reception period; and a reception period controller configured to correct, after detection of the synchronous word, a reception termination timing of the reception period of the time slot in which the synchronous word is detected based on the symbol clock with the corrected symbol clock frequency.

According to one aspect, there is provided a correction method implemented by a reception apparatus of a time division multiple access (TDMA) system for performing intermittent reception by a reception period of a time slot and a non-reception period of a predetermined number of time slots which follow the reception period and in which reception is suspended, the correction method comprising: performing symbol synchronization at a timing at which a synchronous word included in the reception period of the time slot after the non-eception period, correcting a symbol clock frequency of a symbol clock based on a number of time slots and a symbol count value that is a number of counted symbols during a previous reception period and the non-reception period which follow the previous reception period; and correcting, after detection of the synchronous word, a reception termination timing of the reception period of the time slot in which the synchronous word is detected based on the symbol clock with the corrected symbol clock frequency.

According to one aspect, there is provided a non-transitory storage medium that stores a program that causes a computer to execute a correction method implemented by a reception apparatus of a time division multiple access (TDMA) system for performing intermittent reception by a reception period of a time slot and a non-reception period of a predetermined number of time slots which follow the reception period and in which reception is suspended, the correction method comprising: performing symbol synchronization at a timing at which a synchronous word included in the reception period of the time slot after the non-reception period, correcting a symbol clock frequency of a symbol clock based on a number of time slots and a symbol count value that is a number of counted symbols during a previous reception period and the non-reception period which follow the previous reception period; and correcting, after detection of the synchronous word, a reception termination timing of the reception period of the time slot in which the synchronous word is detected based on the symbol clock with the corrected symbol clock frequency.

The above and other objects, features, advantages and technical and industrial significance of this application will be better understood by reading the following detailed description of presently preferred embodiments of the application, when considered in connection with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present application will be described in detail below with reference to the accompanying drawings. The present application is not limited by the embodiments below. Further, if a plurality of embodiments are present, the present application includes a configuration that is obtained by a combination of some embodiments. Furthermore, in the embodiments below, the same components are denoted by the same reference symbols, and repeated explanation will be omitted.

Wireless Communication Terminal

A configuration of a wireless communication terminal according to one embodiment will be described with reference toFIG.1.FIG.1is a block diagram illustrating an example of a configuration of the wireless communication terminal according to the embodiment.

As illustrated inFIG.1, a wireless communication terminal1includes an antenna10, an antenna switcher20, a demodulation circuit30, an analog-to-digital (A/D) converter40, a digital-to-analog (D/A) converter50, a modulation circuit60, and a controller70.

The wireless communication terminal1is a wireless communication terminal capable of performing intermittent reception operation. At a time of transmitting a signal, the wireless communication terminal1causes the antenna switcher20to connect the antenna10to the modulation circuit60, turns on a power supply of the modulation circuit60, and transmits a signal. At a time of receiving a signal, the wireless communication terminal1causes the antenna switcher20to connect the antenna10to the demodulation circuit30, turns on a power supply of the demodulation circuit30, and receives a signal. Specifically, the wireless communication terminal1has a function as a receiving apparatus of a time division multiple access (TDMA) system for performing intermittent reception by a time slot reception period and a non-reception period in which reception of a predetermined number of consecutive time slots after the reception period is suspended. In this regard, the wireless communication terminal1performs power saving operation by turning off the power supply of the demodulation circuit30during the non-reception period of the intermittent reception operation.

The antenna10transmits a radio frequency (RF) to a base station. The antenna10receives an RF signal transmitted from the base station.

The antenna switcher20is controlled by the controller70. The antenna switcher20connects the antenna10to the demodulation circuit30or the modulation circuit60under the control of the controller70.

The demodulation circuit30generates an analog signal by demodulating the RF signal received by the antenna switcher20. The demodulation circuit30outputs the generated analog signal to the A/D converter40. Meanwhile, in the non-reception period of the intermittent reception operation performed by the wireless communication terminal1, the controller70turns off the power supply of the demodulation circuit30and the demodulation circuit30performs power-saving operation. The demodulation circuit30does not demodulate the RF signal during the power-saving operation.

The A/D converter40converts the analog signal input from the demodulation circuit30to a digital signal. The A/D converter40outputs the converted digital signal to a reception filter71of the controller70.

The D/A converter50converts a digital signal input from a transmission filter79of the controller70to an analog signal. The D/A converter50outputs the converted analog signal to the modulation circuit60.

The modulation circuit60generates an RF signal by modulating the analog signal input from the D/A converter50. The modulation circuit60outputs the generated analog signal to the antenna10.

The controller70is implemented by, for example, causing a central processing unit (CPU), a micro processing unit (MPU), or the like to execute a program stored in a storage (not illustrated) by using a read only memory (RAM) or the like as a work area. In other words, the controller70implements each of the functions of the wireless communication terminal1of the present embodiment by executing a program that is recorded in a non-transitory computer-readable recording medium. The controller70may be implemented by, for example, an integrated circuit, such as an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA). The controller70may be implemented by a combination of hardware and software.

The controller70includes the reception filter71, a symbol detector72, a forward error correction (FEC) decoder73, a synchronous word detector74, a symbol clock controller75, a reception period controller76, an FEC encoder77, a symbol generator78, and the transmission filter79. The controller70has a function to control each of the units of the wireless communication terminal1.

The reception filter71removes signal components in an unnecessary frequency band included in the digital signal input from the A/D converter40. The reception filter71outputs the digital signal, from which the signal components in the unnecessary band is removed, to the symbol detector72and the synchronous word detector74. The frequency band that is removed by the reception filter71can be set arbitrarily.

The symbol detector72determines a symbol value of the digital signal input from the reception filter71under the control of the symbol clock controller75. Specifically, the symbol detector72determines the symbol value at a timing of a symbol clock input from the symbol clock controller75. The symbol detector72outputs, to the FEC decoder73, data related to the symbol value obtained as a result of the determination.

The FEC decoder73performs an FEC decoding process on the data that is related to the symbol value and that is input from the symbol detector72.

The synchronous word detector74detects a synchronous word from the digital signal input from the reception filter71. When a synchronous word is detected, the synchronous word detector74outputs, to the symbol clock controller75, a timing signal related to a timing at which the synchronous word is detected.

The symbol clock controller75outputs a symbol clock to the symbol detector72when the wireless communication terminal1receives the RF signal. The symbol clock controller75outputs a symbol clock to the symbol generator78when the wireless communication terminal1transmits the RF signal. The symbol clock controller75includes a built-in symbol counter that performs counting for each of symbol clocks. The symbol clock controller75measures the number of symbols in a period from a time of a previous reset of counting of symbol clocks to a current time, and derives a symbol count value. If a timing signal is input from the synchronous word detector74when the wireless communication terminal1receives the RF signal, the symbol clock controller75resets an output timing of a symbol clock and the symbol counter with reference to the timing signal.

When resetting the output timing of the symbol clock and the symbol counter, the symbol clock controller75refers to the symbol count value at this time, and calculates a difference in the symbol clock between the wireless communication terminal1and the base station. The symbol clock controller75corrects a symbol clock frequency fc of the wireless communication terminal1based on the calculated difference in the symbol clock and the number of time slots after a time slot in which a latest synchronous word is detected. A method for correcting the symbol clock frequency fc will be described later. The symbol clock controller75outputs frequency corrected data related to a correction result of the symbol clock frequency to the reception period controller76.

After the synchronous word detector74has detected the synchronous word, the reception period controller76corrects a reception termination timing in a time slot period in which the synchronous word is detected based on the frequency corrected data that is input from the symbol clock controller75. A method for correcting the reception termination timing in the time slot period in which the synchronous word is detected will be described later. The reception period controller76outputs timing corrected data related to the corrected termination timing to the FEC decoder73.

The FEC encoder77performs an FEC encoding process on transmission data that is to be transmitted to the base station. The FEC encoder77outputs the transmission data subjected to FEC encoding to the symbol generator78.

The symbol generator78converts the transmission data that is subjected to the FEC encoding and input from the FEC encoder77to a symbol value. The symbol generator78outputs a signal related to the symbol value to the transmission filter79at a timing of the symbol clock that is input from the symbol clock controller75.

The transmission filter79removes signal components in an unnecessary frequency band included in the signal that is related to the symbol value and that is input from the symbol generator78. The transmission filter79outputs the signal, from which the signal components in the unnecessary band is removed, to the D/A converter50. The frequency band that is removed by the transmission filter79can be set arbitrarily.

Process of correcting symbol clock frequency A process of correcting the symbol clock frequency fc according to the embodiment will be described with reference toFIG.2.FIG.2is a timing diagram for explaining the method for correcting the symbol clock frequency fc.

In the timing diagram illustrated inFIG.2, a transmission timing of the base station, a reception timing of the wireless communication terminal1, an intermittent reception cycle of the wireless communication terminal1, a symbol clock of the base station, and a symbol clock of the wireless communication terminal1are illustrated.

A period T1indicates a non-reception interval in the intermittent reception operation of the wireless communication terminal1that is located in a range covered by the base station. In the period T1, the wireless communication terminal1turns off the power supply of the demodulation circuit30and performs power-saving operation. In the period T1, the symbol clock of the base station and the symbol clock of the wireless communication terminal1are not synchronized with each other.

A time point t1indicates a timing at which the non-reception interval of the intermittent reception of the wireless communication terminal1is terminated and a reception interval is started. At a timing of the time point t1, the wireless communication terminal1turns on the power supply of the demodulation circuit30and enters a state in which demodulation of a reception signal is available. During a period from the time point t1to a timing at which the reception interval is terminated, the symbol detector72outputs data on a single symbol for each of symbol clocks that are input from the symbol clock controller75. When a predetermined number of symbols are input, the FEC decoder73performs the FEC decoding process on the input data.

A time point t2indicates a timing at which the wireless communication terminal1receives a last symbol of a synchronous word. At the time point t2, a timing of a transmission slot80that is a time slot on the base station side coincides with a timing of a reception slot90that is a time slot on the wireless communication terminal1side. Therefore, at the time point t2, a timing at which the wireless communication terminal1receives a last symbol of a synchronous word81and a timing at which the base station transmits the last symbol of the synchronous word81coincide with each other. Here, the synchronous word detector74outputs a timing signal related to a timing of detection of the synchronous word to the symbol clock controller75. The symbol clock controller75resets the output timing of the symbol clock of the wireless communication terminal1and the symbol counter based on the timing signal that is input from the synchronous word detector74. In the present embodiment, a process of resetting the output timing of the symbol clock and the symbol counter may be referred to as symbol synchronization. At this moment, the symbol clock of the base station and the symbol clock of the wireless communication terminal1coincide with each other.

A time point t3indicates a timing at which the reception interval of the intermittent reception of the wireless communication terminal1is terminated and the non-reception interval is started. At a timing of the time point t3, the wireless communication terminal1turns off the power supply of the demodulation circuit30and starts power-saving operation.

A time point t4indicates a timing at which the non-reception interval of the intermittent reception of the wireless communication terminal1is terminated and the reception interval is started again. At a timing of the time point t4, the wireless communication terminal1turns on the power supply of the demodulation circuit30and enters a state in which demodulation of a reception signal is available. In other words, in the example illustrated inFIG.2, a single cycle is formed of the four reception slots90. During a period from the time point t4to a timing at which the reception interval is terminated, the symbol detector72outputs data of a single symbol for each of symbol clocks that are input from the symbol clock controller75. However, since the wireless communication terminal1starts the reception interval with reference to a symbol clock that is based on an oscillator inside the symbol clock controller75, a timing of the reception slot and a timing of the transmission slot of the base station are deviated from each other. Therefore, the symbol detector72is not able to output a desired result.

A time point t5indicates a timing at which the wireless communication terminal1receives the last symbol of the synchronous word. However, since the timing of the transmission slot80of the base station and the timing of the reception slot90of the wireless communication terminal1are deviated from each other, the timing at which the wireless communication terminal1receives the last symbol of the synchronous word81and a timing at which the base station transmits the last symbol of the synchronous word81are deviated from each other. Therefore, at the time point t5, the synchronous word detector74does not output the timing signal indicating the timing of detection of the synchronous word.

A time point t6indicates a timing at which the base station transmits the last symbol of the synchronous word. At the timing of the time point t6, the synchronous word detector74detects the synchronous word and outputs the timing signal to the symbol clock controller75. Then, similarly to the operation at the time point t2, the symbol clock controller75resets the output timing of the symbol clock of the wireless communication terminal1and the symbol counter.

At the time point t6, the symbol clock controller75corrects the symbol clock frequency of the wireless communication terminal1. Specifically, the symbol clock controller75refers to the count value of the number of symbols at the time point t6, calculates a difference in the number of symbol clocks between the base station and the wireless communication terminal1, and corrects the symbol clock frequency of the wireless communication terminal1based on a result of the calculated difference and the number of time slots that are present after the time slot in which the latest synchronous word is detected. For example, in a communication format illustrated inFIG.2, the number of symbols in a single time slot is set to 10. As in the example illustrated inFIG.2, the symbol counter of the symbol clock controller75normally indicates40at a moment at which the synchronous word is detected in a four-slot cycle.

Here, it is assumed that the symbol detector72detects41as the number of symbols for four slots. This means that the symbol clock in a single cycle of the wireless communication terminal1is earlier than the symbol clock of the base station by a single symbol, that is, the symbol clock frequency fc is increased. The symbol clock controller75corrects the symbol clock frequency based on a value of the difference. In this case, the symbol clock controller75sets the symbol clock frequency such that the number of symbol clocks in a single cycle is delayed by a single symbol. In other words, the symbol clock frequency fc is set such that (a symbol clock frequency before correction×(the number of symbol clocks in a single cycle−a difference in the number of symbol clocks)/the number of symbol clocks in a single cycle). Accordingly, it is possible to synchronize the symbol clock frequency fc of the wireless communication terminal1with the symbol clock frequency of the base station. Meanwhile, in the example illustrated inFIG.2, for simplicity of explanation, it is assumed that the number of symbols included in a single time slot is set to 10, but this is a mere example, and the present application is not limited to this example. The number of symbols included in a single time slot may be set arbitrarily.

A time point t7indicates a timing at which the reception interval of the intermittent reception of the wireless communication terminal1is terminated and a non-reception interval is started. At a timing of the time point t7, the wireless communication terminal1turns off the power supply of the demodulation circuit30and starts power-saving operation. Further, the number of symbol clocks during a period from a timing at which the synchronous word ends to a timing at which the reception slot ends is already known. At a timing of the time point t7, the symbol clock frequency fc of the wireless communication terminal1is synchronized with the symbol clock frequency of the base station. This is because, after detection of the synchronous word, the reception period controller76corrects a reception termination timing of the reception slot90that has detected the synchronous word, based on the symbol clock that is corrected by the symbol clock controller75. Therefore, the timing at which the wireless communication terminal1receives the last symbol of the synchronous word81and the timing at which the base station transmits the last symbol of the synchronous word81coincide with each other. Accordingly, after the time point t7, the symbol clock frequency of the base station and the symbol clock frequency of the wireless communication terminal1are synchronized with each other. In other words, the reception period controller76corrects a reception start timing and a reception termination timing after the reception slot90in which the synchronous word is detected.

A time point t8indicates a timing at which the non-reception interval of the intermittent reception of the wireless communication terminal1is terminated and the reception interval is started again. At a timing of the time point t8, the wireless communication terminal1turns on the power supply of the demodulation circuit30and enters a state in which demodulation of the reception signal is available. At a timing of the time point t8, the symbol clock frequency of the wireless communication terminal1is synchronized with the symbol clock frequency of the base station. Therefore, a timing at which the wireless communication terminal1receives a top symbol of the synchronous word81and a timing at which the transmission station transmits a top symbol of the synchronous word81coincide with each other. In other words, a timing at which the non-reception interval is changed to the reception interval of the intermittent reception of the wireless communication terminal1coincides with a timing at which the base station transmits a top symbol of the transmission slot.

Further, in the present embodiment, it is preferable that the symbol clock frequency of the wireless communication terminal1before correction is set to be higher than the symbol clock frequency of the base station. This is because, for example, as indicated at the timing of the time point t4, a top of the reception slot of the wireless communication terminal1is located ahead of a top of the corresponding transmission slot of the base station. Accordingly, the wireless communication terminal1is able to first receive the top symbol of the synchronous word81, and therefore is able to correct the symbol clock frequency more appropriately.

As described above, in the present embodiment, the symbol clock frequency of the base station and the symbol clock frequency of the wireless communication terminal1are synchronized with each other. Accordingly, in the present embodiment, a timing of change from the non-reception interval to the reception interval in the intermittent transmission of the wireless communication terminal1and a timing of the top symbol of the transmission slot of the base station coincide with each other. Therefore, in the present embodiment, it is possible to set the reception period in the intermittent reception appropriately.

In the present embodiment, it is not necessary to turn on the power supply of the wireless communication terminal1at an earlier timing in order to synchronize the symbol clock frequency of the base station with the symbol clock frequency of the wireless communication terminal1. Further, in the present embodiment, reception of the top symbol of the transmission slot that is transmitted from the base station is started at a moment at which the non-reception interval is changed to the reception interval. With this configuration, in the present embodiment, it is possible to increase a time in which the wireless communication terminal1operates in a power-saving mode, so that it is possible to reduce power consumption.

Modification

A modification of the present embodiment will be described below.

In the present embodiment, the symbol clock controller75corrects the symbol clock frequency based on a calculated difference between the number of set symbols and the number of measured symbols in a single reception interval between two points, but the present application is not limited to this example. The symbol clock controller75may set the symbol clock frequency by calculating (the symbol clock frequency before correction×the number of symbol counts/the number of symbol clocks in a single cycle). Further, when a difference in the number of symbols is extremely small after correction of the symbol clock or the like, it may be possible to correct the symbol clock frequency by extending a period till next correction by, for example, doubling the current four-slot reception interval in which the correction is performed to an eight-slot reception interval.

The wireless communication terminal1may correct the symbol clock frequency as described above every time the power supply is turned on, or may store a correction value in an internal memory of the wireless communication terminal1once correction is performed and may perform the correction using the correction value in a second or later correction. Specifically, when the power supply of the wireless communication terminal1is turned on after the correction is performed once, the symbol clock controller75may read the correction value stored in the memory and correct the symbol clock frequency. In other words, the wireless communication terminal1may start to receive a signal from the base station in a state in which the symbol clock frequency is corrected.

In the present embodiment, it is explained that a single base station is used, but the present embodiment is applicable to a wireless communication system that includes a plurality of base stations. For example, in a wireless communication system that includes a plurality of base stations, when symbol clock frequencies among the base stations are not synchronized, and when the wireless communication terminal1moves from a certain base station to another base station, the wireless communication terminal1may correct the symbol clock frequency again by the method according to the present embodiment. Further, once correction is performed, it may be possible to store a correction value in the internal memory of the wireless communication terminal1, and perform the correction by using the correction value in a second or later correction. Furthermore, when the power supply of the wireless communication terminal1is turned on after the correction is performed once, the symbol clock controller75may read the correction value that is stored for each of the base stations in the memory, and correct the symbol clock frequency.

According to the present application, it is possible to set an appropriate reception period in intermittent reception.