Communication device and communication method

There is provided a communication device that determines a wireless resource for a downlink without performing signaling between a base station and a terminal. A communication device includes a communication unit that transmits and receives a wireless signal, and a wireless resource determination unit that determines a wireless resource used for transmission and reception. The wireless resource determination unit determines, in a communication system including a base station and a terminal, on the basis of a common rule between the base station and the terminal, a plurality of candidates for the wireless resource to be used for downlink communication in the slot for each terminal, and then selects the plurality of candidates for each terminal one by one in such a manner that wireless resources do not overlap between the terminals.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Phase of International Patent Application No. PCT/JP2020/018884 filed May 11, 2020, which claims priority benefit of Japanese Patent Application No. JP 2019-119150, filed in the Japan Patent Office on Jun. 26, 2019. Each of the above-referenced applications is hereby incorporated herein by reference in its entirety.

TECHNICAL FIELD

The technology disclosed herein relates to a communication device and a communication method for performing processing related to a wireless resource for downlink frame transmission from a base station to a terminal.

BACKGROUND ART

In a wireless system in which communication is performed with time synchronization between a base station and a terminal (see, for example, Patent Document 1), it is assumed that it is difficult to maintain a long-time reception state due to battery life of the terminal. As an approach to such a problem, power saving by intermittent operation of terminals has been studied. The terminal is expected to be capable of reducing power consumption by an intermittent operation of cyclically switching between a reception state and a sleep state at a predetermined timing.

In the method described above, it is necessary for the base station to transmit, to each terminal in advance, a control frame that stores information regarding the intermittent operation (for example, “intermittent parameters” such as a cycle and a timing of performing the intermittent operation). Thus, it is necessary to allocate wireless resources for signaling related to control information including the intermittent parameter, and resources available for downlink transmission of data frames are reduced.

For example, a system is considered in which the intermittent parameters are stored in advance in an internal storage area of the terminal, and the intermittent parameters corresponding to the ID of each terminal are registered in a database. In such a system, even in a state where no exchange is performed between the base station and the terminal, the base station can transmit the intermittent parameters while grasping the intermittent parameters of the terminal in advance by using the database, and the terminal can receive the downlink frame from the base station while reducing the power consumption by the intermittent operation.

Here, the intermittent parameters include a reference time as a start point of transmission of the downlink frame, an intermittent cycle, and an offset value added to a transmission start time calculated from the reference time and the intermittent cycle, and are fixed values for each terminal. Furthermore, the frequency to be used is also a fixed value for each terminal. However, there is a possibility that there will be many situations where wireless resources to be used overlap between terminals having similar cycles and offset value parameters, and the base station cannot transmit to a specific terminal. In addition, in a case where the frequency used by each terminal is fixed, there is a possibility that the terminal is largely affected by interference from other systems using the same frequency.

CITATION LIST

Patent Document

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

An object of the technology disclosed herein is to provide a communication device and a communication method for determining a wireless resource for downlink without performing signaling between a base station and a terminal.

Furthermore, another object of the technology disclosed herein is to provide a communication device and a communication method that flexibly determine a wireless resource used for transmission.

Solutions to Problems

The technology disclosed herein has been made in view of the problems described above, and a first aspect thereof is a communication device including a communication unit that transmits and receives a wireless signal, and a wireless resource determination unit that determines a wireless resource to be used for transmission and reception,

in which the wireless resource determination unit determines, in a communication system including a base station and a terminal, a wireless resource to be used for downlink communication on the basis of a common rule between the base station and the terminal.

The wireless resource determination unit determines the wireless resource to be used for downlink communication from a random number sequence generated by a pseudo random number generator shared between the base station and the terminal by using information of the terminal as a downlink destination and time information as initial values.

The wireless resource determination unit uses a start time of a slot as the time information as an initial value, and determines the wireless resource to be used for downlink communication, one by each terminal, in the slot as a transmission cycle.

Alternatively, the wireless resource determination unit uses a start time of subslots obtained by dividing the slot into a plurality as the time information as an initial value, determines, one by each terminal, a candidate for the wireless resource to be used for downlink communication in each of the subslots, and then selects a plurality of candidates for each terminal one by one in such a manner that wireless resources do not overlap between the terminals.

Furthermore, a second aspect of the technology disclosed herein is a communication method including:

determining, in a communication system including a base station and a terminal, a wireless resource to be used for downlink communication on the basis of a common rule between the base station and the terminal; and performing processing related to downlink communication using the determined wireless resource.

Effects of the Invention

According to the technology disclosed herein, it is possible to provide a communication device and a communication method for determining a wireless resource for downlink without performing signaling between a base station and a terminal.

According to the technology disclosed herein, it is possible to provide a communication device and a communication method that flexibly determine a wireless resource used for transmission.

Note that the effects described herein are merely examples, and the effects brought by the technology disclosed herein are not limited thereto. Furthermore, the technology disclosed herein may further exhibit additional effects in addition to the effects described above.

Other objects, features, and advantages of the technology disclosed herein will become apparent from a detailed description based on embodiments described below and the accompanying drawings.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the technology disclosed herein will be described in detail with reference to the drawings. However, communication performed from the base station to the terminal is also referred to as downlink (DL), and communication performed from the terminal to the base station is also referred to as uplink (UL).

First Embodiment

FIG.1schematically illustrates a configuration example of a communication system according to a first embodiment. The illustrated communication system includes a terminal100and a base station200. Although it is assumed that a plurality of terminals is connected to the base station200, only one terminal100is illustrated for simplification of the diagram.

The terminal100is mounted with a global positioning system (GPS) receiver that receives a GPS signal from a GPS satellite300, acquires time information on the basis of the GPS signal, and performs synchronization with the base station200. Furthermore, the terminal100retains in advance a cycle of intermittently performing a reception operation and a reference time to be a start point. Then, the terminal100receives a DL frame transmitted by the base station200, performs demodulation processing, and periodically transmits a UL frame to the base station200. The terminal100is, for example, an Internet of Things (IoT) device that transmits sensor information.

The base station200is equipped with a GPS receiver, acquires time information by receiving the GPS signal, and performs synchronization with the terminal100. Furthermore, the base station200retains the ID of each terminal (including the terminal100), and the intermittent cycle and the reference time described above. Then, the base station200receives the UL frame transmitted by the terminal100, performs demodulation processing, and periodically transmits the DL frame to the terminal100.

FIG.2illustrates an internal configuration example of a communication device that operates as the terminal100. The terminal100includes a wireless transmission unit101, a wireless reception unit102, a frame generation unit103, a wireless control unit104, a wireless resource calculation unit105, a frame detection unit106, a frame demodulation unit107, a terminal parameter retention unit108, an internal clock109, a GPS reception unit110, and a sensor111.

The wireless transmission unit101transmits a wireless signal. Specifically, under control of the wireless control unit104, the wireless transmission unit101converts the UL frame generated by the frame generation unit103into a wireless signal and transmits the wireless signal as radio waves.

The wireless reception unit102receives a wireless signal. Specifically, under the control of the wireless control unit104, the wireless reception unit102receives radio waves, converts the radio waves into a wireless signal, and passes the wireless signal to the frame detection unit106.

The frame generation unit103generates the UL frame to be transmitted to the base station200on the basis of a code obtained from the wireless resource calculation unit105. In the frame to be transmitted to the base station200, for example, sensor information acquired by the sensor111is stored.

The wireless control unit104acquires a current time from the internal clock109, and causes the wireless transmission unit101to transmit the UL frame at a transmission time and a transmission frequency obtained from the wireless resource calculation unit105. Furthermore, the wireless control unit104acquires, from the wireless resource calculation unit105, a time and a frequency at which the DL frame from the base station200is to be received, and causes the wireless reception unit102to perform reception processing at the corresponding time and frequency.

The wireless resource calculation unit105determines a time, a frequency, and codes (a SYNC code and a scramble code) at and with which the UL frame is transmitted to base station200on the basis of information obtained from the internal clock109and the terminal parameter retention unit108. Furthermore, the wireless resource calculation unit105determines a time, a frequency, and codes at and with which the DL frame is received from the base station200. The wireless resource calculation unit105supplies information of the determined time, frequency, and codes to the frame generation unit103, the wireless control unit104, the frame detection unit106, and the frame demodulation unit107.

The frame detection unit106detects a frame from a received signal received by the wireless reception unit102. Specifically, the frame detection unit106extracts a signal of a target frequency from a broadband signal, generates a known sequence from the SYNC code and the scramble code determined by the wireless resource calculation unit105, calculates a correlation value between the known sequence and the received signal, and determines that the frame is detected in a case where the correlation value is a certain value or more.

The frame demodulation unit107demodulates the frame from the received signal. Specifically, the frame demodulation unit107descrambles the received signal using the scramble code calculated by the wireless resource calculation unit105on the basis of the time when the frame detection unit106detects the frame. Thereafter, the frame demodulation unit107extracts a payload portion of the frame from the received signal, and performs error correction code decoding processing and error correction using a cyclic redundancy code (CRC).

The internal clock109acquires the time information from the GPS reception unit110, and calculates the current time by measuring the elapsed time from the acquired time point. The internal clock109supplies the current time to the wireless control unit104and the wireless resource calculation unit105.

The GPS reception unit110receives the GPS signal from the GPS satellite300, and acquires position information and time information of the terminal100.

The sensor111includes a sensor element that acquires information of outside or inside of the terminal100. The sensor information acquired by the sensor111is stored in a transmission frame to the base station200. For example, a temperature sensor or an acceleration sensor corresponds to the sensor111. In a case where it is desired to acquire the position information as the sensor information, the GPS reception unit110may also serve as the sensor111.

Note that in a case where the terminal100receives only the DL frame from the base station200and does not transmit the UL frame to the base station200, the frame generation unit103and the wireless transmission unit101are unnecessary (in some cases, the sensor111is also unnecessary.). Furthermore, in a case where the terminal100transmits only the UL frame to the base station200and does not receive the DL frame from the base station200, the wireless reception unit102, the frame detection unit106, and the frame demodulation unit107are unnecessary.

FIG.3illustrates an internal configuration example of a communication device that operates as the base station200. The base station200includes a wireless transmission unit201, a wireless reception unit202, a frame generation unit203, a wireless control unit204, a wireless resource calculation unit205, a frame detection unit206, a frame demodulation unit207, a terminal parameter retention unit208, an internal clock209, and a GPS reception unit210.

The wireless transmission unit201transmits a wireless signal. Specifically, under control of the wireless control unit204, the wireless transmission unit201converts the DL frame generated by the frame generation unit203into a wireless signal and transmits the wireless signal as radio waves.

The wireless reception unit202receives a wireless signal. Specifically, under the control of the wireless control unit204, the wireless reception unit202receives radio waves, converts the radio waves into a wireless signal, and passes the wireless signal to the frame detection unit206.

The frame generation unit203generates the DL frame to be transmitted to the terminal100on the basis of the code obtained from the wireless resource calculation unit205.

The wireless control unit204acquires a current time from the internal clock209, and causes the wireless transmission unit201to transmit the DL frame at a transmission time and a transmission frequency obtained from the wireless resource calculation unit205. Furthermore, the wireless control unit204acquires a time and a frequency at which the UL frame from the terminal100is received from the wireless resource calculation unit205, and causes the wireless reception unit202to perform the reception processing at the corresponding time and frequency.

The wireless resource calculation unit205determines a time, a frequency, and codes (a SYNC code and a scramble code) at and with which the DL frame is transmitted to the terminal100one each by each slot on the basis of information obtained from the internal clock209and the terminal parameter retention unit208. Furthermore, the wireless resource calculation unit205determines a time, a frequency, and codes at and with which the UL frame is received from the terminal100. The wireless resource calculation unit205supplies information of the determined time, frequency, and codes to the frame generation unit203, the wireless control unit204, the frame detection unit206, and the frame demodulation unit207.

The frame detection unit206detects a frame from a reception signal from the wireless reception unit202. Specifically, the frame detection unit206extracts a signal of a target frequency from a broadband signal, generates a known sequence from the SYNC code and the scramble code determined by the wireless resource calculation unit205, calculates a correlation value between the known sequence and the received signal, and determines that the frame is detected in a case where the correlation value is a certain value or more.

The frame demodulation unit207demodulates a frame from the received signal. Specifically, the frame demodulation unit207descrambles the received signal using the scramble code calculated by the wireless resource calculation unit205on the basis of the time when the frame detection unit206detects the frame. Thereafter, the frame demodulation unit207extracts the payload portion of the frame from the received signal, and performs error correction code decoding processing and error correction using the CRC.

The terminal parameter retention unit208retains a terminal ID of each terminal (including the terminal100) connected to the base station200and intermittent parameters (a cycle of performing an intermittent operation and a reference time) for each terminal.

The internal clock209acquires the time information from the GPS reception unit210, and calculates the current time by measuring the elapsed time from the acquired time point. The internal clock209supplies the current time to the wireless control unit204and the wireless resource calculation unit205.

The GPS reception unit210receives the GPS signal from the GPS satellite300and acquires the time information.

Note that in a case where the base station200only receives the UL frame from the terminal100and does not transmit the frame to the terminal100, the frame generation unit203and the wireless transmission unit201are unnecessary. In addition, in a case where the base station200transmits only the DL frame to the terminal100and does not receive the frame from the terminal100, the wireless reception unit202, the frame detection unit206, and the frame demodulation unit207are unnecessary.

FIG.4illustrates a configuration example of a frame transmitted and received between the terminal100and the base station200in the communication system illustrated inFIG.1. Here, configurations of the UL frame and the DL frame are identical.

The illustrated frame400includes fields of ID, DATA, and CRC indicated by reference numerals401,402, and403, respectively. The ID field401stores a terminal-specific identifier of the transmission source of the frame400. The DATA field402stores transmission data. In a case where the frame400is a UL frame, the sensor information acquired by the sensor111is stored in the DATA field402. The CRC field403stores a CRC value calculated for data stored in the ID field401and the DATA field402. The reception side of the frame400uses the CRC value for determination of successful reception.

A payload412of a frame is generated by performing processing of foeward error correction (FEC) or processing of order rearrangement (interleaving) on a sequence in which ID, DATA, and CRC are concatenated. The error correction is a process of improving error correction by adding redundant bits to an input bit sequence. An error tolerance capability increases according to a length of the redundant bits. Therefore, by the signal processing described above, the length of the payload412becomes longer than a sum of original data (ID, DATA, CRC).

Thereafter, a SYNC code411used for frame detection on the reception side is concatenated to a head of the payload412, and then an exclusive OR (XOR) is calculated for each bit by a scramble code420to complete the frame400.

The SYCN code and the scramble code used in the frame400are codes calculated by the wireless resource calculation unit105on the terminal100side or the wireless resource calculation unit205on the base station200side.

Next, a method of calculating wireless resources used in DL communication will be described.

FIG.5illustrates an outline of wireless resources in the communication system illustrated inFIG.1. In the drawing, a horizontal axis is a time axis, and a vertical axis is a frequency axis. The minimum unit on the time axis is treated as a time slot, and the minimum unit on the frequency axis is treated as a channel. Hereinafter, the bandwidth of a channel is FCH(MHz), and a time slot length is LTS(microseconds). Then, one time slot×one channel is a “resource block” which is a minimum unit of the wireless resources. Furthermore, a lump of resource blocks including consecutive NTStime slots and consecutive NCHchannels is treated as a “slot”. In the example illustrated inFIG.5, NTS=6 and NCH=4. The communication system operates using slots, that is, NTStime slots, as a transmission cycle.

In the first embodiment, it is assumed that one resource block is allocated and used in each slot as a wireless resource for the DL frame.

Next, respective methods for calculating the time, the frequency, and the codes among the wireless resources to be used for transmission of the DL frame will be sequentially described.

FIG.6illustrates a pseudo random number generator used to determine the transmission time of the DL frame. The illustrated pseudo random number generator600is a gold code generator using two M sequences601and602. A terminal ID and time information are set as initial values of the M sequences601and602, respectively. In the first embodiment, since the resource block is allocated for each slot, a start time of the slot is used as the time information of an initial value. Then, the transmission time is determined according to the following Equation (1) using a random number sequence generated by the pseudo random number generator600.

[Equation⁢1]TR=t+LTS×mod⁢(xNTS)(1)TR: Frame transmission start timet: Start time of slotTTS: lengthx: Random number sequence generated by pseudo random number generatorNTS: Number of time slots in each slot
Frequency:

Similarly to the time, the transmission frequency is also determined using the pseudo random number generator. A combination of M sequence generator polynomials of the pseudo random number generator used to determine the transmission frequency may be the same as or different from that used to determine the transmission time. The terminal ID and the start time of the slot are set as initial values of each M sequence. The transmission frequency (transmission channel) is determined according to the following equation (2) using the random number sequence generated by the pseudo random number generator.

[Equation⁢2]FR=FBASE+FCB×mod⁢(xNCH)(2)FR: Frame transmission frequencyx: Random number sequence generated by pseudo random number generatorNCH: Number of channels in each slotFBASE: Lowest center frequency among channels in each slotFCH: Channel interval
Sign:

The SYNC code and the scramble code are generated using the pseudo random number generator similarly to the time and the frequency. A combination of M sequence generator polynomials of the pseudo random number generator used for generation may be the same as or different from that used for the transmission time and the transmission frequency. The terminal ID and the start time of the slot are set as initial values of each M sequence. It is assumed that a length matching a SYNC length of the frame and a length matching a frame length are obtained for the SYNC code and the scramble code, respectively, by the pseudo random number generator.

FIG.7illustrates a processing flow of the entire communication system at the time of DL communication.

First, after receiving the GPS signal, the terminal100and the base station200synchronize the internal clocks109and209on the basis of the acquired time information (F701, F711). However, it is not always necessary to perform the processing of time synchronization, and the terminal100and the base station200do not need to perform the processing of time synchronization for a certain period of time once the time synchronization is completed.

Next, the terminal100calculates the wireless resources to be used for reception of the DL frame addressed to the terminal100itself using the pseudo random number generator (seeFIG.6) from the terminal ID of itself and a start time of a reception slot (F702). Similarly, the base station200calculates the wireless resources to be used for transmission of the DL frame to each terminal (including the terminal100) from the ID of each terminal connected to the own station and a start time of each reception slot (F712).

Thereafter, the base station200generates a DL frame on the basis of the calculated code, and converts the generated DL frame into a wireless signal. Then, when the time of the wireless resource for DL transmission to the terminal100comes, transmission of the DL frame is performed at the calculated frequency (F713).

On the other hand, when the reception time of the calculated DL frame comes, the terminal100receives the wireless signal of the calculated frequency, and detects and demodulates the DL frame using the calculated code (F703).

FIG.8illustrates a processing procedure for the terminal100to receive the DL frame during DL communication in the form of a flowchart.

The terminal100calculates the wireless resources to be used for transmission of the DL frame from the terminal ID of itself and the start time of the transmission slot by using the pseudo random number generator (seeFIG.6) on the basis of the above-described method (step S801).

Then, the terminal100waits until the reception time of the DL frame calculated in step S801(No in step S802). When the reception time of the DL frame comes (Yes in step S802), the terminal100receives the wireless signal of the reception frequency of the DL frame calculated in step S801(step S803), and performs detection and demodulation processing of the DL frame using the code calculated in step S801(step S804).

FIG.9illustrates a processing procedure for the base station200to transmit the DL frame during the DL communication in the form of a flowchart.

The base station200calculates the wireless resource to be used for transmission of the DL frame addressed to each terminal by using the pseudo random number generator (seeFIG.6) on the basis of the above-described method from the terminal ID of each terminal connected to the own station and the start time of the transmission slot (step S901).

Then, when generating the DL frame addressed to each terminal using the code calculated in step S901(step S902), the base station200waits until the DL transmission time calculated in step S901(No in step S903).

When the DL transmission time comes (Yes in step S903), the base station200converts the DL frame generated in step S902into a wireless signal, and transmits this DL frame to the corresponding terminal using the frequency calculated in step S901(step S904).

According to the first embodiment, the base station200and the terminal100can calculate the wireless resources for transmission of the DL frame in advance without signaling control information between the base station200and the terminal100. Furthermore, it is possible to perform communication in which power consumption is suppressed by the intermittent operation of the terminal100.

FIG.10illustrates an example of calculation results of the wireless resources of the terminals A to F in the first embodiment in a table form. Furthermore,FIG.11illustrates the wireless resources determined for reception of the DL frame by the terminals A to F on a plane in which a horizontal axis is a time axis and a vertical axis is a frequency axis. InFIG.11, the wireless resources are represented in units of resource blocks, and terminal IDs are described in resource blocks determined by the terminals A to F for the DL frame. However, here, NTS=3 and NCH=3 are set for convenience. Furthermore, inFIG.11, resource blocks that can be used by the terminals A to F without interference of other systems are colored in light gray, and resource blocks that are largely affected by interference from other systems are colored in dark gray. In the example illustrated inFIG.11, the frequency channel f1is easily affected by interference from other systems.

In the first embodiment, each of the terminals A to F allocates and uses one resource block for the DL frame in each slot. As described above, the wireless resources are calculated using the terminal ID and the start time of the slot as the initial values of the pseudo random number generator (seeFIG.6). Thus, the resource block calculated by each terminal in each slot differs accompanying a change in the transmission time (start time of the slot). Therefore, the wireless resources for the DL frame can be flexibly allocated. Consequently, the possibility that the wireless resources used between the terminals overlap and the influence of interference from other systems in a specific terminal can be reduced.

In the examples illustrated inFIGS.10and11, it can be seen that the resource block for the DL frame is determined without overlap between the terminals A to F. Furthermore, in the terminal A, the resource block allocated for the DL frame in the slot of a section of T2to T3is affected by interference from other systems, but the resource blocks allocated in other slots are not affected by interference from other systems. Also in the terminal D, the resource block allocated for the DL frame in the slot of a section of T4to T5is affected by interference from other systems, but the resource blocks allocated in other slots are not affected by interference from other systems.

Second Embodiment

In the first embodiment described above, the wireless resources are uniquely determined according to the terminal ID and the slot start time of each terminal. Thus, there is a possibility that a deviation occurs in calculation results, and as the number of terminals increases, a possibility that a plurality of terminals is allocated to the same wireless resource increases. Accordingly, in the second embodiment, a method is employed in which a plurality of candidates for the wireless resource is calculated in one slot on the basis of the terminal ID and the subslot start time, and the base station determines one wireless resource to be actually used for DL transmission from the plurality of candidates for the wireless resource. By applying this method, it is possible to perform adjustment so that the wireless resources do not overlap between terminals, and it is possible to avoid a situation in which DL transmission to some terminals becomes impossible, which occurs when the same wireless resources are allocated between a plurality of terminals. Also in the second embodiment, since the wireless resources for the DL frame are flexibly allocated, it is possible to reduce the possibility that the wireless resources used between the terminals overlap.

Also in the second embodiment, a communication system as illustrated inFIG.1is assumed. Furthermore, it is sufficient if the configuration of the terminal100is similar to that inFIG.2, and thus description thereof will be omitted here.

FIG.12illustrates an internal configuration example of a communication device that operates as the base station200in the second embodiment. A wireless transmission unit201, a wireless reception unit202, a frame generation unit203, a wireless control unit204, a wireless resource calculation unit205, a wireless resource determination unit211, a frame detection unit206, a frame demodulation unit207, a terminal parameter retention unit208, an internal clock209, and a GPS reception unit210are provided. Differences from the first embodiment are that the wireless resource calculation unit205calculates a plurality of wireless resources and that a wireless resource determination unit211is added as a component of the base station200.

The wireless resource calculation unit205determines pluralities of times, frequencies, and codes (SYNC codes and scramble codes) at and with which the DL frame is transmitted to the terminal100in each slot on the basis of the information obtained from the internal clock209and the terminal parameter retention unit208. Furthermore, the wireless resource calculation unit205determines a time, a frequency, and codes at and with which the UL frame is received from the terminal100. The wireless resource calculation unit205supplies information of the determined time, frequency, and codes to the wireless resource determination unit211.

The wireless resource determination unit211determines one resource to be used for DL transmission in each slot from the plurality of wireless resources calculated by the wireless resource calculation unit205. Then, the wireless resource determination unit211supplies information of the determined time, frequency, and codes to the frame generation unit203, the wireless control unit204, the frame detection unit206, and the frame demodulation unit207.

It is sufficient if the frame configuration used in the communication system according to the second embodiment is the same as that of the first embodiment (refer toFIG.6), and thus description thereof will be omitted here. Furthermore, configurations of the UL frame and the DL frame are the same.

Next, in the second embodiment, a method of calculating the wireless resources used for DL communication will be described.

FIG.13illustrates an outline of wireless resources in the second embodiment. Similarly to as described above, the horizontal axis is the time axis, and the vertical axis is the frequency axis. The minimum unit on the time axis is treated as a time slot, and the minimum unit on the frequency axis is treated as a channel. Furthermore, a bandwidth of a channel is FCH(MHz), a time slot length is LTS(microseconds), one time slot×one channel is a resource block, and a lump of resource blocks including consecutive NTStime slots and consecutive NCHchannels is a slot.

A difference from the first embodiment (seeFIG.5) is that a concept of “subslots” obtained by dividing one slot into a plurality of slots in the time axis direction is added in the second embodiment. In the second embodiment, it is assumed that one candidate for the wireless resource for DL transmission of each terminal is calculated in each subslot (that is, by the number of subslots in one slot), and the base station determines one wireless resource to be used for actual transmission in one slot for each terminal from among a plurality of candidates. Furthermore, the number of subslots is equal to the number of wireless resource candidates for DL transmission calculated for each terminal. Then, when the number of time slots in one slot is NTS, the number of time slots in one subslot is NSTS, and the number of wireless resources for DL transmission calculated in one slot for each terminal is NR, NTS=NSTS×NRis satisfied. In the example illustrated inFIG.13, one slot is divided into three subslots in the time direction. In the example illustrated inFIG.5, NTS=6, NCH=4, NSTS=2, and NR=3. InFIG.13, shades of the gray filling the resource blocks are changed for each subslot in one slot.

Hereinafter, each calculation method of the time, the frequency, and the codes in the second embodiment will be sequentially described.

The pseudo random number generator used to set the transmission time is the same as that in the first embodiment, and is a gold code generator using two M sequences601and602(seeFIG.6). A terminal ID and time information are set as initial values of each of the M sequences. In the second embodiment, the resource block is allocated in each subslot, and thus the start time of the subslot is used as the time information of the initial value. Then, using the random number sequence generated by the pseudo random number generator, the transmission time in each subslot is determined according to the following Equation (3).

[Equation⁢3]TR=t+LTS×(i-1)×NSTS+LTS×mod⁢(xiNSTS)(3)
(1≤i≤N, N: number of subslots)TR: Frame transmission start timet: Start time of slotLTS: Time slot lengthxi: Random number sequence generated by pseudo random number generatorNSTS: Number of time slots in each subslot
Frequency:

Similarly to the time, the transmission frequency is also determined using the pseudo random number generator. A combination of M sequence generator polynomials of the pseudo random number generator used to determine the transmission frequency may be the same as or different from that used to determine the transmission time. The ID of the terminal and the start time of each subslot are set as initial values of each M sequence. The transmission frequency (transmission channel) is determined according to the following equation (4) using the random number sequence generated by the pseudo random number generator.

[Equation⁢4]FR=FBASE+FCH×mod⁢(xiNCH)(4)
(1≤i≤N, N: number of subslots)FR: Frame transmission frequencyxi: Random number sequence generated by pseudo random number generatorNCH: Number of channels in each slotFBASE: Lowest center frequency among channels in each slotFCH: Channel interval
Sign:

The SYNC code and the scramble code are generated using the pseudo random number generator similarly to the time and the frequency. A combination of M sequence generator polynomials of the pseudo random number generator used for generation may be the same as or different from that used for the transmission time and the transmission frequency. The ID of the terminal and the start time of the slot are set as the initial values of each M sequence. It is assumed that a length matching the SYNC length of the frame and a length matching the frame length are obtained for the SYNC code and the scramble code, respectively, by the pseudo random number generator.

FIG.14illustrates a processing flow of the entire communication system at the time of DL communication in the second embodiment.

First, after receiving the GPS signal, the terminal100and the base station200synchronize the internal clocks109and209on the basis of the acquired time information (F1401, F1411). However, it is not always necessary to perform the processing of time synchronization, and the terminal100and the base station200do not need to perform the processing of time synchronization for a certain period of time once the time synchronization is completed.

Next, the terminal100calculates a plurality of candidates for the wireless resource for DL transmission in each subslot in one slot from the terminal ID of itself and the start time of the reception subslot (F1402). Similarly, the base station200calculates the candidates for the wireless resource for DL transmission related to each terminal for each subslot in one slot from the ID of each terminal connected to the own station and the start time of each transmission subslot, and performs temporary allocation (F1412).

Moreover, the base station200determines one wireless resource to be mainly allocated in one slot for each terminal from the candidates for the wireless resource for DL transmission temporarily allocated in each subslot (F1413).

Thereafter, the base station200generates a frame on the basis of the calculated code and converts the generated frame into a wireless signal. Then, when the time of the wireless resource for DL transmission of the terminal100comes, frame transmission is performed at the calculated frequency (F1414).

On the other hand, when the time of the calculated wireless resource for DL transmission comes, the terminal100receives a wireless signal of the calculated frequency, and detects and demodulates the frame using the calculated code (F1403).

Here, the terminal100is unaware of which wireless resource the base station200has determined as the mainly allocated resource. Thus, the terminal100repeatedly performs the reception processing with each calculated candidate for the wireless resource in each subslot until the frame from the base station200can be correctly demodulated.

FIG.15illustrates a processing procedure for the terminal100to receive a frame during DL communication in the form of a flowchart.

The terminal100calculates a plurality of candidates (in each subslot) for the wireless resource for DL transmission from the terminal ID of itself and the start time of each subslot in one slot on the basis of the method described above (step S1501).

Then, the terminal100waits until each reception time of the plurality for the candidates for the wireless resource calculated (No in step S1502). When any DL reception time comes (Yes in step S1502), the terminal100receives the wireless signal of the frequency calculated for the corresponding candidate (step S1503), and performs frame detection and demodulation processing using the code calculated for the corresponding candidate (step S1504).

Next, the terminal100checks whether the DL frame has been correctly detected and demodulated at the current reception time (step S1505). In a case where the DL frame has been correctly detected and demodulated (Yes in step S1505), the terminal100ends the reception processing.

On the other hand, in a case where the DL frame has not been correctly detected and demodulated (No in step S1505), the terminal100further checks whether there is still a candidate for the wireless resource for the next DL transmission in the slot (step S1506).

In a case where the wireless resource for the next DL transmission still exists (Yes in step S1506), the terminal100returns to step S1502, waits until the next DL reception time, and repeatedly executes the reception processing described above. Furthermore, in a case where there is no candidate for the wireless resource for the next DL transmission (No in step S1506), the terminal100ends the reception processing.

Next, a method of determining a wireless resource for DL transmission in the second embodiment will be described.

FIG.16illustrates a processing procedure for determining wireless resources for DL transmission in the base station200in the form of a flowchart.

The base station200calculates, on the basis of the terminal ID of each terminal connected to the own station and the start time of the reception subslot, a plurality (in each subslot) of candidates for the wireless resource to be used for DL transmission on the basis of the above equations (3) and (4) (step S1601), and performs temporary allocation of the calculated wireless resource of each candidate (step S1602).

The base station200repeatedly performs the processing of steps51601and51602until the temporary allocation of all the candidates for the wireless resource calculated in each subslot in the slot is completed for all the terminals connected to the own station (No in step S1603).

Then, when the temporary allocation is completed for all the terminals in the slot (Yes in step S1603), the base station200determines one wireless resource for DL transmission to be mainly allocated in one slot from among the plurality of candidates for the wireless resource for DL transmission temporarily allocated in each subslot for each terminal (step S1604).

In a case where the candidates for the wireless resource for DL transmission are calculated in each subslot in one slot for each terminal, it is assumed that the candidates for the wireless resource overlap between the terminals. Accordingly, in step S1604, there is performed processing of determining one wireless resource for DL transmission to be mainly allocated in one slot from among the plurality of candidates for the wireless resource for DL transmission of each terminal so that the wireless resources do not overlap between the terminals.

FIG.17illustrates a processing procedure executed in step S1604in the flowchart illustrated inFIG.16for the base station200to determine the wireless resources for DL transmission to be main allocation for each terminal in the form of a flowchart.

Here, Rx(minimum exclusive subslot number) for each terminal is used as an index for determining the mainly allocated resources. Here, the subslot number is a number obtained by dividing a slot into a plurality of subslots and allocating the subslots in ascending order from a head subslot on the time axis. The Rxof a certain terminal is a smallest subslot number until the candidate for the wireless resource for DL transmission that does not overlap (that is, can be exclusive) with other terminals is found. The Rxis an integer satisfying 1≤Rx≤N (N is the number of subslots in the slot). A method of calculating the Rxof each terminal will be described later. In addition, a resource block number as a serial number is attached to each resource block in the slot, and a resource block temporarily allocated or mainly allocated to the terminal can be indicated by the resource block number.

First, the base station200initializes the Rxof each terminal to N+1 (step S1701). Here, N is the number of subslots obtained by dividing one slot (as described above). Then, the base station200initializes a variable m for counting the number of subslots (or the subslot number) being processed to one (step S1702), and then starts a processing loop of the m-th subslot.

In the processing loop of each subslot, a variable i for counting the number of terminals processed in the processing loop is initialized to one (step S1703), and then the processing loop of an i-th terminal is started.

In the processing loop of each terminal, the base station200calculates the Rxof the i-th terminal (step S1704), and checks whether the calculated Rxis the same as the numerical value before calculation (step S1705). A processing procedure for calculating the Rxof the terminal will be described later.

In a case where the calculated Rxis not the same as the numerical value before calculation (No in step S1705), the temporary allocations of the wireless resources of the (Rx+1)-th and subsequent subslots of the i-th terminal are canceled (step S1707), the processing returns to step S1703, and the processing loop of the m-th subslot is started again.

Furthermore, in a case where the calculated Rxis the same as the numerical value before the calculation (Yes in step S1705), the base station200checks whether the variable i is less than the number I of terminals for which wireless resource allocation is scheduled (that is, whether the processing is yet to be completed for all the target terminals) (step S1706). Then, in a case where the variable i is less than the scheduled number I of terminals for wireless resource allocation (No in step S1706), the base station200increments i by one (step S1708), returns to step S1704, and repeatedly performs the processing for each terminal for the next terminal.

In a case where the variable i has reached the scheduled number I of wireless resource allocations (Yes in step S1706), the base station200ends the processing loop of each terminal, initializes the variable j for counting resource blocks in the subslot to one (step S1709), and then starts the processing loop for the j-th resource block in the m-th subslot.

In the processing loop for the resource block, the base station200first checks whether any terminal has performed temporary allocation to the resource block (step S1710). The resource block number of the resource block being processed is j+J×(m−1) (where J is the number of resource blocks in the subslot). In step S1710, it is checked whether there is a terminal that has been temporarily allocated to the calculated resource block number.

Then, in a case where any terminal has performed temporary allocation to the resource block (Yes in step S1710), the base station200subsequently checks whether there is only one terminal that has performed temporary allocation (step S1711).

Then, in a case where there is only one terminal that has been temporarily allocated to the resource block (Yes in step S1711), the base station200performs main allocation of the resource block to the terminal (step S1712).

On the other hand, in a case where there are two or more terminals that have been temporarily allocated to the resource block (No in step S1711), the base station200calculates the Rxof each of these terminals (step S1713). A processing procedure for calculating the Rxof the terminal will be described later. Then, the terminal having the maximum Rxis extracted (step S1714).

Here, the terminal having the maximum Rxis a terminal having a large minimum subslot number until a candidate that does not overlap with other terminals is found, that is, a terminal in which it is difficult to find a subslot that can be exclusive, and the resource block should be preferentially allocated thereto.

The base station200checks whether there is only one terminal having the maximum Rx(step S1715). Then, when there is only one terminal having the maximum Rx(Yes in step S1715), the base station200performs main allocation of the resource block to the terminal (step S1716).

Furthermore, in a case where there are two or more terminals having the maximum Rx(No in step S1715), the base station200randomly selects one terminal from these terminals and performs main allocation of the resource block to the terminal (step S1717).

Next, the base station200cancels the temporary allocation of the resource block in the m-th subslot of terminals other than the terminal to which the main allocation has been performed in this subslot in step S1716or step S1717(step S1718).

Next, the base station200cancels the temporary allocations of the wireless resources of the (Rx+1)-th and subsequent subslots of the terminal to which the main allocation of the resource block is determined in any one of step S1712, step S1716, or step S1717and changes the Rxto m, and sets the temporarily allocated resource block number of the m-th subslot as a mainly allocated resource block number (step S1719).

Then, the base station200checks whether the variable j is less than the number J of resource blocks in the subslot (that is, whether the processing is yet to be completed for all the resource blocks in the m-th subslot) (step S1720). Then, in a case where the variable j is less than the number J of resource blocks in the subslot (No in step S1720), the base station200increments j by one (step S1722), returns to step S1710, and repeatedly performs similar processing on the next resource block in the m-th subslot.

In a case where the variable j has reached the number J of resource blocks in the subslot (Yes in step S1720), the base station200checks whether the variable m is less than the number N of subslots in the slot (that is, whether the processing is yet to be completed for all the subslots in the slot) (step S1721). Then, in a case where the variable m is less than the number N of subslots (No in step S1721), the base station200increments m by one (step S1723), returns to step S1703, and repeatedly performs similar processing for the next subslot.

Furthermore, in a case where the variable m has reached the number N of subslots (Yes in step S1721), the base station200ends this processing.

FIG.18illustrates a processing procedure for calculating the Rx(minimum exclusive subslot number) of the terminal in the base station200in the form of a flowchart. The Rxof the terminal is the smallest subslot number until a candidate that does not overlap with other terminals (that is, can be exclusive) is found. This processing procedure is performed in step S1704in the flowchart illustrated inFIG.17.

First, the base station200checks whether the resource block number of the main allocation of the wireless resources for DL transmission has been determined for the processing target terminal (step S1801). When the resource block number of the main allocation of the wireless resources for DL transmission of the terminal has been determined (Yes in step S1801), the base station200ends this processing.

In a case where the resource block number of the main allocation of the wireless resources for DL transmission of the terminal is yet to be determined (No in step S1801), the base station200substitutes the subslot number m to be processed in the processing loop of each subslot for the variable n (step S1802).

Then, the base station200checks whether n is equal to or less than the number N of subslots in the slot (that is, whether the subslot being processed is not the last subslot in the slot) (step S1803).

In a case where n exceeds the number N of subslots in the slot, that is, in a case where the subslot being processed is the last subslot in the slot (No in step S1803), the base station200substitutes n for the Rx(step S1806) and ends this processing.

On the other hand, if n is equal to or smaller than the number N of subslots in the slot (Yes in step S1803), the base station200checks the resource block number temporarily allocated to the n-th subslot for the terminal to be processed (step S1804). It is assumed that the base station200performs temporary allocation of resource blocks of each subslot of the terminal by using the above equations (3) and (4).

Then, the base station200checks whether there is another terminal to which the same resource block as that of the terminal is temporarily allocated (step S1805).

In a case where there is no other terminal to which the same resource block as that of the terminal is temporarily allocated (No in step S1805), the base station200substitutes n for the Rx(step S1806) and ends this processing.

Furthermore, in a case where there is another terminal to which the same resource block as that of the terminal is temporarily allocated (Yes in step S1805), the base station200increments n by one (step S1807), returns to step S1803, and repeatedly performs similar processing in the next sub-block.

The Rxof a certain terminal is the smallest subslot number that can reliably determine the wireless resource for DL transmission of the main allocation without causing the terminal to overlap with other terminals. In a case where all the resource blocks temporarily allocated to a certain terminal by the base station200overlap the resource blocks temporarily allocated to any other terminal, the Rxof the terminal is N+1, which is the maximum value.

There is a high possibility that the base station200cannot allocate a resource block for DL transmission in the target slot to a terminal whose Rxis N+1, and cannot perform DL transmission. Furthermore, as the Rxincreases, the number of times the terminal enters the reception state increases, and power consumption increases. Thus, in the processing procedure illustrated inFIG.17, the second embodiment employs an algorithm in which the base station200first uses the above equations (3) and (4) to temporarily allocate one resource block in each subslot in the slot for each terminal, and then mainly allocates the resource blocks temporarily allocated to a plurality of terminals preferentially to the terminal having the maximum Rx(see “processing loop of each resource block” inFIG.18). Furthermore, in the processing procedure illustrated inFIG.18, the Rxof each terminal is calculated every time the target subslot changes (see the “processing loop of each terminal” inFIG.18), and thereafter in the “processing loop of each resource block”, the temporary allocation status in each resource block in the subslot is confirmed to determine the resource of the main allocation. Furthermore, in the “processing loop of each resource block”, for the terminal determined by the resource block to be mainly allocated, the temporary allocations of the wireless resources of the (Rx+1)-th and subsequent subslots are canceled and the Rxis changed to the subslot number under processing, and this terminal is excluded from the target of the main allocation in the processing of the subsequent subslots.

FIG.19illustrates a processing procedure for transmitting the DL frame by using the wireless resources for DL transmission for each terminal determined by the base station200according to the processing procedure illustrated inFIG.16in the form of a flowchart.

The base station200checks the DL transmission resource block determined according to the processing procedure illustrated inFIG.16(step S1901).

Next, when the DL frame addressed to each terminal is generated using the code calculated in step S1601in the flowchart illustrated inFIG.16(step S1902), waiting is made until the DL transmission time of the determined DL transmission resource block (No in step S1903).

When the DL transmission time comes (Yes in step S1903), the base station200converts the DL frame generated in step S1902into a wireless signal, and transmits the DL frame to the corresponding terminal using the transmission frequency of the DL transmission resource block determined according to the processing procedure illustrated inFIG.16(step S1604).

A specific example in which the base station200allocates the wireless resources for DL transmission to the terminals A to F according to the processing procedure illustrated inFIG.17will be described with reference toFIGS.20to31. Here, it is assumed that one slot is divided into three subslots of first (1st), second (2nd), and third (3rd) in the time axis direction, and each subslot is divided into three resource blocks in the frequency axis direction. Furthermore, for convenience of description, resource block (RB) numbers of 1 to 9 are allocated to the respective resource blocks in one subslot.

FIG.20illustrates temporary allocation results of the resource blocks of the terminals A to F calculated on the basis of the above equations (3) and (4) by the base station200. InFIG.20, the resource block numbers temporarily allocated to the terminals A to F in each subslot are described. Furthermore, inFIG.21, the ID of the temporarily allocated terminal is written in the box of each resource block. InFIG.21, all the temporarily allocated terminal IDs are written by being separated with slashes in the resource blocks in which the temporary allocations of the plurality of terminals overlap. Since one temporary allocation is performed by each subslot for each of the terminals A to F, if the number of terminals exceeds the number of resource blocks in the subslot, duplication of temporary allocation always occurs. At the stage of temporary allocation, temporary allocations of a plurality of terminals overlap in resource blocks other than the resource block number6.

FIGS.22and23illustrate results of calculation of the Rxof the terminals A to F by the base station200according to the processing procedure illustrated inFIG.18.

An initial value of the Rxof each of the terminals A to F is N (number of subslots)+1=4. Here, in the examples illustrated inFIGS.20and21, the resource block number6in the second subslot is exclusive for the terminal D, and thus Rx=2 as illustrated inFIG.22. Furthermore, the temporary allocations of the third and subsequent subslots of the terminal D are canceled (as illustrated inFIG.22, the resource block number temporarily allocated to the terminal D in the third subslot is rewritten to zero. Consequently, the resource block number8can be exclusive for the terminal F in the third subslot as illustrated inFIG.23, and thus Rx=3 as illustrated inFIG.22.

FIGS.24and25illustrate results of attempts by the base station200to perform main allocation to the terminals A to F in the order of the resource block number in the processing loop of each resource block in the subslot in the flowchart illustrated inFIG.17.

Referring toFIG.23, in the resource block number1of the first subslot, temporary allocations to the terminal A and the terminal C overlap. Further, referring toFIG.22, both the terminal A and the terminal C have the Rxof four, and thus the base station200randomly selects the terminal A as illustrated inFIG.25, and performs main allocation of the resource block to the terminal A as illustrated inFIG.24. Consequently, as illustrated inFIG.24, the Rxof the terminal A is changed to one, and all the temporary allocations of the second and subsequent subslots of the terminal A are canceled (the resource block number temporarily allocated to the terminal A in the second and subsequent subslots is rewritten to zero). Furthermore, the base station200cancels the temporary allocation of the first subslot to the terminal C (as illustrated inFIG.24, the resource block number temporarily allocated to the terminal C in the first subslot is set to zero).

FIGS.26and27illustrate results of subsequent attempts by the base station200to perform main allocation of the resource block number2.

Referring toFIG.25, in the resource block number2, temporary allocations to the terminal B and the terminal D overlap. Furthermore, referring toFIG.24, because the Rxof the terminal B is four and the Rxof the terminal D is two, and the Rxof the terminal B is the maximum, the terminal B is selected as illustrated inFIG.27, and the resource block is mainly allocated to the terminal B as illustrated inFIG.26. Consequently, as illustrated inFIG.26, the Rxof the terminal B is changed to one, and all the temporary allocations of the second and subsequent subslots of the terminal B are canceled (the resource block number temporarily allocated to the terminal B in the second and subsequent subslots is rewritten to zero). Furthermore, the temporary allocation of the first subslot to the terminal D is canceled (as illustrated inFIG.26, the resource block number temporarily allocated to the terminal D in the first subslot is set to 0).

FIGS.28and29illustrate results of subsequent attempts by the base station200to perform main allocation of the resource block number3.

Referring toFIG.27, in the resource block number3, temporary allocations to the terminal E and the terminal F overlap. Furthermore, referring toFIG.26, because the Rxof the terminal E is four and the Rxof the terminal F is three, and the Rxof the terminal E is maximum, the base station200selects the terminal E as illustrated inFIG.29, and performs main allocation of the resource block to the terminal E as illustrated inFIG.28. Consequently, as illustrated inFIG.28, the Rxof the terminal E is changed to one, and all the temporary allocations of the second and subsequent subslots of the terminal E are canceled (the resource block number temporarily allocated to the terminal B in the second and subsequent subslots is rewritten to zero). Furthermore, the temporary allocation of the first subslot to the terminal F is canceled (as illustrated inFIG.28, the resource block number temporarily allocated to the terminal F in the first subslot is set to zero). Furthermore, the Rxof the terminal F is recalculated according to the processing procedure illustrated inFIG.18, and the Rxof the terminal F is rewritten to two as illustrated inFIG.28.

FIGS.30and31illustrate results of subsequent attempts by the base station200to perform main allocation of each resource block of the second subslot.

Referring toFIG.29, the resource block number4of the second subslot is exclusive for the terminal F, and thus, as illustrated inFIG.30, the base station200performs main allocation of the resource block to the terminal F and cancels all temporary allocations of the third and subsequent subslots of the terminal F (the resource block number temporarily allocated to the terminal F in the third and subsequent subslots is rewritten to zero). Further, the resource block number5is temporarily allocated only to the terminal C, and thus the base station200performs main allocation. Furthermore, as illustrated inFIG.30, the Rxof the terminal C is rewritten to two, and all the temporary allocations of the third and subsequent subslots of the terminal C are canceled (the resource block number temporarily allocated to the terminal C in the third and subsequent subslots is rewritten to zero). Further, the resource block number6is temporarily allocated only to the terminal D as illustrated inFIG.31, and thus the base station200performs main allocation of the resource block to the terminal D as illustrated inFIG.30.

As can also be seen fromFIGS.20to31, after calculating a plurality of candidates for the wireless resource for each terminal in one slot, the base station200can determine the wireless resources so that DL transmission can be performed to all the terminals in the slot by adjusting the candidates for the wireless resource so as not to overlap between the terminals. Furthermore, by determining the wireless resources for DL transmission so as to suppress the number of times that the terminal enters the reception state, reduction of redundant power consumption can be expected.

Third Embodiment

In the second embodiment, the minimum exclusive subslot number Rxis used as an index indicating priority in a case where the temporarily allocated resource block is overlapped among a plurality of terminals. However, in a case where the Rxof the plurality of terminals is the same value, there is no choice but to perform random selection, and the priority cannot be determined in consideration of the mainly allocated resource determination processing situation in the subslot.

Here, the main allocation in a case where temporary allocation results as illustrated inFIG.32are obtained for the terminals A to F will be considered. When the terminal A is selected by the resource block number1, the terminal E is always selected by the resource block number6. Furthermore, when the terminal F is selected by the resource block number2, the terminal B is always selected by the resource block number6. Consequently, as illustrated inFIG.33, this allocation cannot be performed to either the terminal B or the terminal E, and transmission cannot be performed.

In the example illustrated inFIG.33, while the temporary allocations of the terminal B and the terminal E conflict with each other in the resource block number6, the resource block number5remains unused. In the second embodiment, the wireless resource to be mainly allocated is searched only in the range of the candidates for the wireless resource temporarily allocated to each terminal, and it can also be said that the unused wireless resource cannot be sufficiently used.

Accordingly, in the third embodiment, a method is employed in which an index is added that is related to the number of terminals for which the mainly allocated resource determination processing has been completed in the previous subslot among the terminals temporarily allocated to each resource block, and the base station determines the wireless resource actually used for DL transmission from among the plurality of candidates for the wireless resource.

FIGS.34and35illustrate a processing procedure for the base station200to determine the wireless resources for DL transmission to be main allocation for each terminal in the third embodiment in the form of a flowchart. The processing procedure illustrated inFIGS.34and35is performed in step S1604in the flowchart illustrated inFIG.16instead of the processing procedure illustrated inFIG.17.

Here, as an index for determining the wireless resource for DL transmission, in addition to the minimum exclusive subslot number Rxfor each terminal, NSTAthat counts the number of terminals for which the mainly allocated resource block has been determined in the previous subslot for each resource block is newly defined. The NSTAis synonymous with the number of terminals (the number of times a terminal to which a resource block is temporarily allocated misses the main allocation up to the previous subslot) that are always selected for the mainly allocated resource determination processing in the resource block, and it is considered that the possibility that the mainly allocated resource can be determined even in processing of the next subslot is lower as the NSTAis larger. In the processing procedure illustrated inFIG.17, in a case where the Rxof the terminal whose temporary allocation overlaps is the same value, main allocation is selected randomly. On the other hand, the third embodiment has an algorithm in which, in a case where the Rxof the terminal whose temporary allocation overlaps is the same value, comparison of the NSTAis further performed to determine priority, and the mainly allocated resource is determined with priority for the terminal having the largest NSTA.

First, the base station200initializes the NSTAof each resource block to zero (step S3401) and initializes the Rxof each terminal to N+1 (step S3402). Then, the base station200initializes a variable m for counting the number of subslots being processed (or the subslot number) to one (step S3403), and then starts the processing loop of the m-th subslot.

In the processing loop of each subslot, the variable i for counting the number of terminals processed in the processing loop is initialized to one (step S3404), and then the processing loop of the i-th terminal is started.

In the processing loop of each terminal, the base station200calculates the Rxof the i-th terminal according to the processing procedure illustrated inFIG.18(step S3405), and checks whether the calculated Rxis the same as the numerical value before calculation (step S3406).

In a case where the calculated Rxis not the same as the numerical value before calculation (No in step S3406), the temporary allocations of the wireless resources of the (Rx+1)-th and subsequent subslots of the i-th terminal are canceled (step S3408), the processing returns to step S3404, and the processing loop of the m-th subslot is started again.

Furthermore, in a case where the calculated Rxis the same as the numerical value before the calculation (Yes in step S3406), the base station200checks whether the variable i is less than the number I of terminals for which wireless resource allocation is scheduled (that is, whether the processing is yet to be completed for all the target terminals) (step S3407). Then, in a case where the variable i is less than the scheduled number I of terminals for wireless resource allocation (No in step S3407), the base station200increments i by one (step S3409), returns to step S3405, and repeatedly performs the processing for each terminal for the next terminal.

In a case where the variable i has reached the scheduled number I of wireless resource allocations (Yes in step S3407), the base station200ends the processing loop of each terminal, initializes the variable j for counting resource blocks in the subslot to one (step S3410), and then starts the processing loop for the j-th resource block in the m-th subslot.

Details of the processing loop for the resource block are illustrated inFIG.35. In the processing loop for the resource block, the base station200first checks whether any terminal has performed temporary allocation to the resource block (step S3411). The resource block number of the resource block being processed is j+J×(m−1) (where J is the number of resource blocks in the subslot). In step S3411, it is checked whether there is a terminal that has been temporarily allocated to the calculated resource block number.

In a case where any terminal has performed temporary allocation to the resource block (Yes in step S3411), the base station200subsequently checks whether there is only one terminal that has performed temporary allocation (step S3412).

Then, in a case where there is only one terminal that has been temporarily allocated to the resource block (Yes in step S3412), the base station200performs main allocation of the resource block to the terminal (step S3413).

On the other hand, in a case where there are two or more terminals that have been temporarily allocated to the resource block (No in step S3412), the base station200calculates the Rxof each of these terminals according to the processing procedure illustrated inFIG.18(step S3414). Then, the terminal having the maximum Rxis extracted (step S3415).

The base station200checks whether there is only one terminal having the maximum Rx(step S3416). Then, when there is only one terminal having the maximum Rx(Yes in step S3416), the base station200performs main allocation of the resource block to the terminal (step S3417).

Furthermore, on the other hand, in a case where there are two or more terminals having the maximum Rx(No in step S3416), the base station200checks whether the variable m is less than the number N of subslots in the slot (that is, whether the processing is yet to be completed for all the subslots in the slot) (step S3418).

Here, in a case where the variable m has reached the number N of subslots (No in step S3418), the base station200randomly selects one terminal from among a plurality of terminals having the maximum Rxand performs main allocation of the resource block to the terminal (step S3419).

On the other hand, in a case where the variable m is less than the number N of subslots (Yes in step S3418), the base station200extracts the NSTAof each of the temporarily allocated resource block numbers of the next (that is, the (m+1)-th) subslot of each terminal having the maximum Rx(step S3420).

The base station200checks whether there is only one terminal with the maximum NSTA(step S3421). Then, when there is only one terminal with the maximum NSTA(Yes in step S3421), the base station200performs main allocation of the resource block to the terminal (step S3422).

Furthermore, in a case where there are two or more terminals with the maximum NSTA(No in step S3421), the base station200randomly selects one terminal from among these terminals, and performs main allocation of the resource block to the terminal (step S3423).

Next, the base station200cancels the temporary allocations of the resource blocks in the m-th subslot of the terminal other than the terminal to which the main allocation has been performed in this subslot in any one of steps S3413, S3417, S3419, S3422, or S3423, and adds only one to each NSTAof the temporarily allocated resource blocks of the next (that is, the (m+1)-th) subslot of these terminals (step S3424).

Next, the base station200cancels the temporary allocations of the wireless resources of the (Rx+1)-th and subsequent subslots of the terminal for which the main allocation of the resource blocks is determined in any one of steps S3413, S3417, S3419, S3422, or S3423and changes the Rxto m, and sets the temporarily allocated resource block number of the m-th subslot as the mainly allocated resource block number (step S3425).

Then, the base station200checks whether the variable j is less than the number J of resource blocks in the subslot (that is, whether the processing is yet to be completed for all the resource blocks in the m-th subslot) (step S3426). Then, in a case where the variable j is less than the number J of resource blocks in the subslot (No in step S3426), the base station200increments j by one (step S3428), returns to step S3411, and repeatedly performs similar processing on the next resource block in the m-th subslot.

In a case where the variable j has reached the number J of resource blocks in the subslot (Yes in step S3426), the base station200checks whether the variable m is less than the number N of subslots in the slot (that is, whether the processing is yet to be completed for all the subslots in the slot) (step S3427). Then, in a case where the variable m is less than the number N of subslots (No in step S3427), the base station200increments m by one (step S3429), returns to step S3404, and repeatedly performs similar processing for the next subslot.

Furthermore, in a case where the variable m has reached the number N of subslots (Yes in step S3427), the base station200ends this processing.

A specific example in which the base station200allocates the wireless resources for DL transmission to the terminals A to H according to the processing procedure illustrated inFIGS.34and35will be described with reference toFIGS.36to47. Here, it is assumed that one slot is divided into two first (1st) and second (2nd) subslots in the time axis direction, and each subslot is divided into four resource blocks in the frequency axis direction. In addition, for convenience of description, resource block (RB) numbers of 1 to 8 are allocated to the respective resource blocks in one subslot.

FIG.36illustrates temporary allocation results of the resource blocks of the terminals A to H calculated on the basis of the above equations (3) and (4) and results of calculation of the Rxby the base station200. InFIG.36, the resource block numbers temporarily allocated to the terminals A to F in each subslot are described. An initial value of the Rxof each of the terminals A to H is N (number of subslots)+1=3.FIG.36also illustrates the NSTAof each of the resource blocks, all of which have initial values of zero. Furthermore, inFIG.37, the ID of the temporarily allocated terminal is written in the box of each resource block. InFIG.37, all the temporarily allocated terminal IDs are written by being separated with slashes in the resource blocks in which the temporary allocations of the plurality of terminals overlap. Since one temporary allocation is performed by each subslot for each of the terminals A to H, if the number of terminals exceeds the number of resource blocks in the subslot, duplication of the temporary allocation always occurs. In the examples illustrated inFIGS.36and37, temporary allocations of a plurality of terminals overlap in all resource blocks at the stage of temporary allocation.

FIGS.38and39illustrate results of attempts by the base station200to perform main allocation to the terminals A to H in the order of the resource block number in the processing loop of each resource block in the subslot in the flowcharts illustrated inFIGS.34and35.

Referring toFIG.37, the resource block number1of the first subslot overlaps in temporary allocations to the terminal A and the terminal E. Furthermore, referring toFIG.36, both the terminal A and the terminal E have the Rxof three, and thus the NSTAof resource blocks in which the terminal A and the terminal E are temporarily allocated in the second subslot are subsequently compared. In the second subslot, the terminal A is temporarily allocated with the resource block number5and the terminal E is temporarily allocated with the resource block number6, but since the NSTAof the both is an initial value of zero, the terminal A is randomly selected and is mainly allocated as illustrated inFIG.39. Consequently, as illustrated inFIG.38, the Rxof the terminal A is changed to one, and the temporary allocation of the second subslot of the terminal A is canceled (the resource block number temporarily allocated to the terminal A in the second subslot is rewritten to zero). Furthermore, as illustrated inFIG.38, the temporary allocation of the first subslot to the terminal E is canceled (the resource block number temporarily allocated to the terminal C in the first subslot is set to zero). Moreover, one is added to the NSTAof the resource block number6to which the terminal E whose main allocation has not been determined is temporarily allocated in the second subslot.

FIGS.40and41illustrate results of subsequent attempts by the base station200to perform main allocation of the resource block number2.

Referring toFIG.39, the resource block number2overlaps in temporary allocations to the terminal B and the terminal F. Furthermore, referring toFIG.38, both the terminal B and the terminal F have the Rxof three, and thus comparison of the NSTAof resource blocks in which the terminal B and the terminal F are temporarily allocated in the second subslot is subsequently performed. In the second subslot, the NSTAof the resource block number6temporarily allocated to the terminal B is one, and the NSTAof the resource block number7temporarily allocated to the terminal F is an initial value of zero. Therefore, as illustrated inFIG.41, the terminal B with the maximum NSTAis selected and main allocation is performed. Consequently, as illustrated inFIG.40, the Rxof the terminal B is changed to one, and the temporary allocation of the second subslot of the terminal B is canceled (the resource block number temporarily allocated to the terminal B in the second subslot is rewritten to zero). Furthermore, as illustrated inFIG.40, the temporary allocation of the first subslot to the terminal F is canceled (the resource block number temporarily allocated to the terminal F in the first subslot is set to zero). Moreover, one is added to the NSTAof the resource block number7to which the terminal F whose main allocation has not been determined is temporarily allocated in the second subslot.

FIGS.42and43illustrate results of subsequent attempts by the base station200to perform main allocation of the resource block number3.

Referring toFIG.41, the resource block number3overlaps in temporary allocations to the terminal C and the terminal G. Furthermore, referring toFIG.40, both the terminal C and the terminal G have the Rxof three, and thus comparison of the NSTAof resource blocks in which the terminal C and the terminal G are temporarily allocated in the second subslot is subsequently performed. In the second subslot, the NSTAof the resource block number7temporarily allocated to the terminal C is one, and the NSTAof the resource block number8temporarily allocated to the terminal G is an initial value of zero. Therefore, as illustrated inFIG.43, the terminal C with the maximum NSTAis selected and the main allocation is performed. Consequently, as illustrated inFIG.42, the Rxof the terminal C is changed to one, and the temporary allocation of the second subslot of the terminal C is canceled (the resource block number temporarily allocated to the terminal C in the second subslot is rewritten to zero). Furthermore, as illustrated inFIG.42, the temporary allocation of the first subslot to the terminal G is canceled (the resource block number temporarily allocated to the terminal G in the first subslot is set to zero). Moreover, one is added to the NSTAof the resource block number8to which the terminal G whose main allocation has not been determined is temporarily allocated in the second subslot.

FIGS.44and45illustrate results of subsequent attempts by the base station200to perform main allocation of the resource block number4.

Referring toFIG.43, the resource block number4overlaps in temporary allocations to the terminal D and the terminal H. Furthermore, referring toFIG.42, both the terminal D and the terminal H have the Rxof three, and thus comparison of the NSTAof resource blocks in which the terminal D and the terminal H are temporarily allocated in the second subslot is subsequently performed. In the second subslot, the NSTAof the resource block number8temporarily allocated to the terminal D is one, and the NSTAof the resource block number5temporarily allocated to the terminal H is an initial value of zero. Therefore, as illustrated inFIG.45, the terminal D with the maximum NSTAis selected and main allocation is performed. Consequently, as illustrated inFIG.44, the Rxof the terminal D is changed to one, and the temporary allocation of the second subslot of the terminal D is canceled (the resource block number temporarily allocated to the terminal D in the second subslot is rewritten to zero). Furthermore, as illustrated inFIG.44, the temporary allocation of the first subslot to the terminal H is canceled (the resource block number temporarily allocated to the terminal H in the first subslot is set to zero). Moreover, one is added to the NSTAof the resource block number5to which the terminal H whose main allocation has not been determined is temporarily allocated in the second subslot.

FIGS.46and47illustrate results of subsequent attempts by the base station200to perform main allocation of each resource block of the second subslot.

Referring toFIG.45, the resource block number5is temporarily allocated only to the terminal H, and thus, as illustrated inFIG.46, main allocation is performed and the Rxof the terminal H is rewritten to two. Furthermore, the resource block number6is temporarily allocated only to the terminal E, and thus, as illustrated inFIG.46, the main allocation is performed and the Rxof the terminal E is rewritten to two. Furthermore, the resource block number7is temporarily allocated only to the terminal F, and thus, as illustrated inFIG.46, the main allocation is performed and the Rxof the terminal F is rewritten to two. Furthermore, the resource block number8is temporarily allocated only to the terminal G, and thus, as illustrated inFIG.46, the main allocation is performed and the Rxof the terminal G is rewritten to two.

As can be seen fromFIGS.36to47, a plurality of candidates for the wireless resource is calculated in one slot on the basis of the terminal ID and the subslot start time, and the base station can determine one wireless resource to be actually used for DL transmission while adjusting the plurality of candidates for the wireless resource so as not to overlap with other terminals. Furthermore, when temporary allocations of a plurality of terminals overlap, priority can be determined in consideration of the situation of the resource block temporarily allocated to each terminal in the next subslot.

Fourth Embodiment

In the second and third embodiments, the wireless resources for DL transmission of each terminal are determined only on the basis of information retained by the base station200. In other words, the wireless resources for DL transmission are allocated without considering the request on the terminal side, and thus there is a possibility that the wireless resources that deteriorate communication efficiency of the entire communication system are performed. For example, in a case where the remaining battery level is small and the remaining number of receivable times is small, or in a case where data requiring Ack from the base station is transmitted, requests of the terminal for allocating wireless resources for DL transmission increase.

Accordingly, in the fourth embodiment, the request information regarding the priority of DL transmission is added to the UL frame regularly transmitted by the terminal, and the base station200uses the request information as a new index for determining the wireless resource for DL transmission.

FIG.48illustrates a configuration example of a payload portion of the UL frame in the fourth embodiment. Respective fields of ID, DATA, and CRC indicated by reference numerals4801,4802, and4804are similar to those of the frame400illustrated inFIG.4, and thus description thereof will be omitted here.

The REQUEST field indicated by reference numeral4803includes information regarding a priority, which is one bit of zero or one. Furthermore, the priority between respective pieces of information is set so as to be in descending order from the highest bit, and in a case where the priority is one, the priority is high. Therefore, the base station200preferentially allocates the wireless resources for DL transmission to the terminal having the largest numerical value when a bit string of the REQUEST field4803is set as an unsigned binary number. Examples of the information to be used include information regarding latency tolerance and data priority. In a case of the delay tolerance, the terminal sets one thereto in a case where the remaining number of receivable times calculated from the remaining battery level falls below a predetermined threshold. Furthermore, in a case where the data priority is high, such as transmitting data requiring Ack from the base station, or the like, the terminal sets one thereto.

The CRC value calculated for the data stored in the ID field4801, the DATA field4802, and the REQUEST field4803is stored in the CRC field4804. Then, FEC or interleave processing is performed on a sequence obtained by concatenating ID, DATA, REQUEST, and CRC to generate a payload of a frame. Then, after the SYNC code used for frame detection is concatenated to the head of the payload, an exclusive OR is obtained for each bit by the scramble code to complete the frame.

FIG.49illustrates a processing flow of the entire communication system at the time of DL communication in the fourth embodiment.

First, after receiving the GPS signal, the terminal100and the base station200synchronize the internal clocks109and209on the basis of the acquired time information (F4901, F4911). However, it is not always necessary to perform the processing of time synchronization, and the terminal100and the base station200do not need to perform the processing of time synchronization for a certain period of time once the time synchronization is completed.

Thereafter, when UL communication is performed from the terminal100to the base station200, the base station200acquires request information of the terminal100from the REQUEST field of the UL frame (F4912).

Next, the terminal100calculates a plurality of candidates for the wireless resource for DL transmission in each subslot in one slot from the terminal ID of itself and the start time of the reception subslot (F4902). Similarly, the base station200calculates candidates for the wireless resource for DL transmission related to each terminal in each subslot in one slot from the ID of each terminal connected to the own station and the start time of each transmission subslot, and performs temporary allocation (F4913).

Then, the base station200determines one wireless resource to be mainly allocated in one slot for each terminal, from the temporarily allocated candidates for the wireless resource for DL transmission while considering the acquired request information (F4914).

Thereafter, the base station200generates a frame on the basis of the calculated code and converts the generated frame into a wireless signal. Then, when the time of the wireless resource for DL transmission of the terminal100comes, frame transmission is performed at the calculated frequency (F4915).

On the other hand, when the time of the calculated wireless resource for DL transmission comes, the terminal100receives a wireless signal of the calculated frequency, and detects and demodulates the frame using the calculated code (F4903). The terminal100is unaware of which wireless resource the base station200has determined as the mainly allocated resource. Thus, the terminal100repeatedly performs the reception processing with each calculated candidate for the wireless resource until the frame from the base station200can be correctly demodulated.

FIGS.50and51illustrate a processing procedure for the base station200to determine the wireless resources for DL transmission to be main allocation for each terminal in the fourth embodiment in the form of a flowchart. The processing procedure illustrated inFIGS.50and51is performed in step S1604in the flowchart illustrated inFIG.16instead of the processing procedure illustrated inFIG.17.

Here, as an index for determining the wireless resource for DL transmission, request information acquired from each terminal is added in addition to the minimum exclusive subslot number Rxfor each terminal and the NSTAthat counts the number of terminals for which the mainly allocated resource block has been determined in the previous subslot for each resource block. Specifically, Nreqis a numerical value obtained by converting the bit string of the REQUEST field included in the UL frame from the terminal as an unsigned binary number into a decimal number, and the terminal having the largest Nreqis preferentially selected.

First, the base station200initializes the NSTAof each resource block to zero (step S5001) and initializes the Rxof each terminal to N+1 (step S5002). Then, the base station200initializes a variable m for counting the number of subslots being processed (or the subslot number) to one (step S5003), and then starts the processing loop of the m-th subslot.

In the processing loop of each subslot, the variable i for counting the number of terminals processed in the processing loop is initialized to one (step S5004), and then the processing loop of the i-th terminal is started.

In the processing loop of each terminal, the base station200calculates the numerical value Nreqobtained by converting the bit string of the REQUEST field included in the UL frame from the i-th terminal as an unsigned binary number into a decimal number (step S5005). Next, the base station200calculates the Rxof the i-th terminal according to the processing procedure illustrated inFIG.18(step S5006), and checks whether the calculated Rxis the same as the numerical value before calculation (step S5007).

In a case where the calculated Rxis not the same as the numerical value before calculation (No in step S5007), the temporary allocations of the wireless resources of the (Rx+1)-th and subsequent subslots of the i-th terminal are canceled (step S5009), the processing returns to step S5005, and the processing loop of the m-th subslot is started again.

Furthermore, in a case where the calculated Rxis the same as the numerical value before the calculation (Yes in step S5007), the base station200checks whether the variable i is less than the number I of terminals for which wireless resource allocation is scheduled (that is, whether the processing is yet to be completed for all the target terminals) (step S5008). Then, in a case where the variable i is less than the scheduled number I of terminals for wireless resource allocation (No in step S5008), the base station200increments i by one (step S5010), returns to step S5005, and repeatedly performs the processing for each terminal for the next terminal.

In a case where the variable i has reached the scheduled number I of wireless resource allocations (Yes in step S5008), the base station200ends the processing loop of each terminal, initializes the variable j for counting resource blocks in the subslot to one (step S5011), and then starts the processing loop for the j-th resource block in the m-th subslot.

Details of the processing loop for the resource block are illustrated inFIG.51. In the processing loop for the resource block, the base station200first checks whether any terminal has performed temporary allocation to the resource block (step S5012). The resource block number of the resource block being processed is j+J×(m−1) (where J is the number of resource blocks in the subslot). In step S5012, it is checked whether there is a terminal that has been temporarily allocated to the calculated resource block number.

In a case where any terminal has performed temporary allocation to the resource block (Yes in step S5012), the base station200subsequently checks whether there is only one terminal that has performed temporary allocation (step S5013).

Then, in a case where there is only one terminal that has been temporarily allocated to the resource block (Yes in step S5013), the base station200performs main allocation of the resource block to the terminal (step S5014).

On the other hand, in a case where there are two or more terminals that have been temporarily allocated to the resource block (No in step S5013), the base station200extracts a terminal having the maximum Nreq(step S5015).

The base station200checks whether there is only one terminal having the maximum Nreq(step S5016). Then, in a case where there is only one terminal having the maximum Nreq(Yes in step S5016), the base station200performs main allocation of the resource block to the terminal (step S5017).

In a case where there are two or more terminals having the maximum Nreq(No in step S5016), the base station200calculates the Rxof each of these terminals according to the processing procedure illustrated inFIG.18(step S5018). Then, the terminal having the maximum Rxis extracted (step S5019).

The base station200checks whether there is only one terminal having the maximum Rx(step S5020). Then, when there is only one terminal having the maximum Rx(Yes in step S5020), the base station200performs main allocation of the resource block to the terminal (step S5021).

Furthermore, in a case where there are two or more terminals having the maximum Rx(No in step S5020), the base station200checks whether the variable m is less than the number N of subslots in the slot (that is, whether the processing is yet to be completed for all the subslots in the slot) (step S5022).

Here, in a case where the variable m has reached the number N of subslots (No in step S5022), the base station200randomly selects one terminal from among a plurality of terminals having the maximum Rxand performs main allocation of the resource block to the terminal (step S5023).

On the other hand, in a case where the variable m is less than the number N of subslots (Yes in step S5022), the base station200extracts each NSTAof the temporarily allocated resource block number of the next (that is, the (m+1)-th) subslot of each terminal having the maximum Rx(step S5024).

The base station200checks whether there is only one terminal with the maximum NSTA(step S5025). Then, when there is only one terminal with the maximum NSTA(Yes in step S5025), the base station200performs main allocation of the resource block to the terminal (step S5026).

Furthermore, in a case where there are two or more terminals with the maximum number of NSTA(No in step S5025), the base station200randomly selects one terminal from these terminals, and performs main allocation of the resource block to the terminal (step S5027).

Next, the base station200cancels the temporary allocations of the resource blocks in the m-th subslot of the terminal other than the terminal to which main allocation has been performed in any one of steps S5014, S5017, S5021, S5023, S5026, or S5027, and adds 1 to each NSTAof the temporarily allocated resource block of the next (that is, the (m+1)-th) subslot of these terminals (step S5028).

Next, the base station200cancels the temporary allocations of the wireless resources of the (Rx+1)-th and subsequent subslots of the terminal for which the main allocation of resource blocks is determined in any one of steps S5014, S5017, S5021, S5023, S5026, or S5027and changes the Rxto m, and sets the temporarily allocated resource block number of the m-th subslot as the mainly allocated resource block number (step S5029).

Then, the base station200checks whether the variable j is less than the number J of resource blocks in the subslot (that is, whether the processing is yet to be completed for all the resource blocks in the m-th subslot) (step S5030). Then, in a case where the variable j is less than the number J of resource blocks in the subslot (No in step S5030), the base station200increments j by one (step S5032), returns to step S5012, and repeatedly performs similar processing on the next resource block in the m-th subslot.

In a case where the variable j has reached the number J of resource blocks in the subslot (Yes in step S5030), the base station200checks whether the variable m is less than the number N of subslots in the slot (that is, whether the processing is yet to be completed for all the subslots in the slot) (step S5031). Then, in a case where the variable m is less than the number N of subslots (No in step S5031), the base station200increments m by one (step S5033), returns to step S5004, and repeatedly performs similar processing for the next subslot.

Furthermore, in a case where the variable m has reached the number N of subslots (Yes in step S5031), the base station200ends this processing.

Note that, in the flowcharts illustrated inFIGS.50and51, the Nreqis used as the index with the highest priority, but the determination processing of the wireless resource for DL transmission may be performed with the Nreqbeing lower than the other indexes Rxand NSTA.

A specific example in which the base station200allocates the wireless resources for DL transmission to the terminals A to F according to the processing procedure illustrated inFIGS.50and51will be described with reference toFIGS.52to63. Here, it is assumed that one slot is divided into three subslots of first (1st), second (2nd), and third (3rd) in the time axis direction, and each subslot is divided into three resource blocks in the frequency axis direction. Furthermore, for convenience of description, resource block (RB) numbers of 1 to 9 are allocated to the respective resource blocks in one subslot.

FIG.52illustrates temporary allocation results of the resource blocks of the terminals A to F calculated on the basis of the above equations (3) and (4) and results of initializing the NSTAof the resource blocks by the base station200. InFIG.52, the resource block numbers temporarily allocated to the terminals A to F in each subslot are described. Furthermore, inFIG.53, the ID of the temporarily allocated terminal is written in the box of each resource block. InFIG.53, all the temporarily allocated terminal IDs are written by being separated with slashes in the resource blocks in which the temporary allocations of the plurality of terminals overlap. Since one temporary allocation is performed by each subslot for each of the terminals A to F, if the number of terminals exceeds the number of resource blocks in the subslot, duplication of temporary allocation always occurs. In the examples illustrated inFIGS.52and53, in the stage of the temporary allocation, temporary allocations of the plurality of terminals overlap in the resource block other than the resource block number6.

FIGS.54and55illustrate results of calculation of the Rxof the terminals A to F by the base station200according to the processing procedure illustrated inFIG.18and results of calculation of the Nreqof the terminals in the processing loop of each terminal illustrated inFIG.50.

An initial value of the Rxof each of the terminals A to F is N (number of subslots)+1=4. Here, in the examples illustrated inFIGS.52and53, the resource block number6in the second subslot is exclusive for the terminal D. Therefore, as illustrated inFIG.54, the Rx=2 in the terminal D. Furthermore, the temporary allocations of the third and subsequent subslots of the terminal D are canceled (the resource block number temporarily allocated to the terminal D in the third subslot is rewritten to zero). Consequently, as illustrated inFIG.55, in the third subslot, the resource block number8can be exclusive for the terminal F. Therefore, as illustrated inFIG.54, the Rx=3 in the terminal F.

FIGS.56and57illustrate results of attempts by the base station200to perform main allocation to the terminals A to F in the order of the resource block number in the processing loop of each resource block in the subslot illustrated inFIG.51.

Referring toFIG.55, in the resource block number1of the first subslot, temporary allocations to the terminal A and the terminal C overlap. Accordingly, referring toFIG.54, the terminal C is larger when referring to the Nreqof each of the terminal A and the terminal C, and thus the base station200selects the terminal C and performs main allocation of the resource block as illustrated inFIG.57. Consequently, as illustrated inFIG.56, the Rxof the terminal C is changed to one, and all the temporary allocations of the second and subsequent subslots of the terminal C are canceled (the resource block number temporarily allocated to the terminal C in the second and subsequent subslots is rewritten to zero). Furthermore, as illustrated inFIG.56, the base station200cancels the temporary allocation of the first subslot to the terminal A (the resource block number temporarily allocated to the terminal A in the first subslot is set to zero). Moreover, as illustrated inFIG.56, the base station200adds one to the NSTAof the resource block number5to which the terminal A whose main allocation has not been determined is temporarily allocated in the second subslot.

FIGS.58and59illustrate results of subsequent attempts by the base station200to perform main allocation of the resource block number2.

Referring toFIG.57, the resource block number2overlaps in temporary allocations to the terminal B and the terminal D. Accordingly, referring toFIG.56, the terminal B is larger when referring to the Nreqof each of the terminal B and the terminal D, and thus the base station200selects the terminal B and performs main allocation of the resource block as illustrated inFIG.59. Consequently, as illustrated inFIG.58, the base station200changes Rxof the terminal B to one, and cancels all the temporary allocations of the second and subsequent subslots of the terminal B (the resource block number temporarily allocated to the terminal B in the second and subsequent subslots is rewritten to zero). Furthermore, as illustrated inFIG.58, the base station200cancels the temporary allocation of the first subslot to the terminal D (the resource block number temporarily allocated to the terminal D in the first subslot is set to zero). Moreover, as illustrated inFIG.58, the base station200adds one to the NSTAof the resource block number6to which the terminal D whose main allocation has not been determined is temporarily allocated in the second subslot.

FIGS.60and61illustrate results of subsequent attempts by the base station200to perform main allocation of the resource block number3.

Referring toFIG.59, the resource block number3overlaps in temporary allocations to the terminal E and the terminal F. Thus, referring toFIG.58, the Nreqof each of the terminal E and the terminal F has the same value, and thus the base station200further compares the Rxwith each other. Since the Rxof the terminal E is four and the Rxof the terminal F is three, and the Rxof the terminal E is maximum, the base station200selects the terminal E and performs main allocation of the resource block as illustrated inFIG.61. Consequently, as illustrated inFIG.60, the base station200changes the Rxof the terminal E to one, and cancels all the temporary allocations of the second and subsequent subslots of the terminal E (the resource block number temporarily allocated to the terminal E in the second and subsequent subslots is rewritten to zero). Furthermore, as illustrated inFIG.60, the base station200cancels the temporary allocation of the first subslot to the terminal F (the resource block number temporarily allocated to the terminal F in the first subslot is set to zero). Moreover, as illustrated inFIG.60, the base station200adds one to the NSTAof the resource block number4to which the terminal F whose main allocation has not been determined is temporarily allocated in the second subslot. Furthermore, the base station200recalculates the Rxof the terminal F and changes the Rxto two.

FIGS.62and63illustrate results of subsequent attempts by the base station200to perform main allocation of each resource block of the second subslot.

Referring toFIG.61, the resource block number4is temporarily allocated only to the terminal F, and thus the base station200performs main allocation of the resource block. Further, the base station200rewrites the Rxof the terminal F to two as illustrated inFIG.62, and cancels all the temporary allocations of the third and subsequent subslots of the terminal F as illustrated inFIGS.62and63(the resource block number temporarily allocated to the terminal F in the third and subsequent subslots is rewritten to zero). Furthermore, the resource block number5is temporarily allocated only to the terminal A, and thus the base station200performs main allocation of the resource block. Further, the base station200rewrites the Rxof the terminal A to two as illustrated inFIG.62, and cancels all the temporary allocations of the third and subsequent subslots of the terminal A as illustrated inFIGS.62and63(the resource block number temporarily allocated to the terminal A in the third and subsequent subslots is rewritten to zero). Furthermore, since the resource block number6is temporarily allocated only to the terminal D as illustrated inFIG.60, the base station200performs main allocation of the resource block as illustrated inFIG.62.

As can also be seen fromFIGS.52to63, after calculating a plurality of candidates for the wireless resource for each terminal in one slot, the base station200can determine the wireless resources so that DL transmission can be performed on all terminals in the slot by adjusting the candidates for the wireless resource so as not to overlap each other on the basis of the request information from each terminal. Furthermore, by determining the wireless resources for DL transmission so as to suppress the number of times that the terminal enters the reception state, reduction of redundant power consumption can be expected.

While the three embodiments related to the technology disclosed herein have been described, effects brought by the technology disclosed herein will now be described.

According to the technology disclosed herein, it is possible to calculate the wireless resource for DL transmission in advance without signaling the control information between the base station and the terminal, and it is possible to achieve DL transmission with suppressed power consumption of the terminal.

Furthermore, according to the technology disclosed herein, the parameter (initial value to the pseudo random number generator) changes in each transmission, and the wireless resource for DL transmission can be flexibly allocated. Consequently, the possibility that the wireless resources used between the terminals overlap and the influence of interference from other systems in a specific terminal can be reduced.

Furthermore, according to the technology disclosed herein, after calculating a plurality of candidates for the wireless resource for DL transmission for each terminal in the slot, the base station can perform adjustment so that the candidates for the wireless resource do not overlap between the terminals. Furthermore, the base station can allocate wireless resources from a plurality of candidates to each terminal while considering various information such as request information from the terminal.

INDUSTRIAL APPLICABILITY

The technology disclosed herein has been described in detail with reference to the specific embodiments. However, it is obvious that those skilled in the art can modify or substitute the embodiment without departing from the gist of the technology disclosed herein.

The technology disclosed herein can be applied to, for example, the IoT domain to flexibly allocate wireless resources of downlink communication without signaling between the terminal and the base station, and it is possible to reduce the possibility that the wireless resources used between the terminals overlap, and the influence of interference from other systems in a specific terminal. Of course, the technology disclosed herein can be similarly applied to various types of wireless systems including a terminal and a base station.

In short, the technology disclosed herein has been described by way of example, and the contents of the description herein should not be interpreted restrictively. In order to determine the gist of the technology disclosed herein, the claims should be considered.

Note that the technology disclosed herein may have the following configurations.(1) A communication device including a communication unit that transmits and receives a wireless signal, and a wireless resource determination unit that determines a wireless resource to be used for transmission and reception,in which the wireless resource determination unit determines, in a communication system including a base station and a terminal, a wireless resource to be used for downlink communication on the basis of a common rule between the base station and the terminal.(2) The communication device according to (1) above, in whichthe wireless resource determination unit determines the wireless resource to be used for downlink communication from a random number sequence generated by a pseudo random number generator shared between the base station and the terminal by using information of the terminal as a downlink destination and time information as initial values.(3) The communication device according to (2) above, in whichthe wireless resource determination unit determines the wireless resource to be used for downlink communication, one by each terminal, in a slot having a predetermined time length.(4) The communication device according to (3) above, in whichthe wireless resource determination unit uses a start time of a slot as the time information as an initial value, and determines the wireless resource to be used for downlink communication, one by each terminal, in the slot as a transmission cycle.(5) The communication device according to (4) above, in whichthe wireless resource determination unit determines a plurality of candidates for the wireless resource to be used for downlink communication in the slot for each terminal, and then selects the plurality of candidates for each terminal one by one in such a manner that wireless resources do not overlap between the terminals.(6) The communication device according to (3) above, in whichthe wireless resource determination unit uses a start time of subslots obtained by dividing the slot into a plurality as the time information as an initial value, determines, one by each terminal, a candidate for the wireless resource to be used for downlink communication in each of the subslots, and then selects a plurality of candidates for each terminal one by one in such a manner that wireless resources do not overlap between the terminals.(7) The communication device according to (6) above, in whichthe wireless resource determination unit allocates a wireless resource for downlink transmission of each terminal in consideration of a minimum number of subslots (Rx) until a candidate for a wireless resource for downlink transmission that is capable of being exclusive for each terminal is found in a case where a candidate for a wireless resource allocated in a certain subslot overlaps between terminals.(8) The communication device according to (7) above, in whichthe wireless resource determination unit allocates the wireless resource for downlink transmission of each terminal in a case where a candidate for a wireless resource allocated in a certain subslot overlaps between terminals, in further consideration of a number (NSTA) of terminals for which a candidate for a wireless resource of each terminal in a next subslot overlaps.(9) The communication device according to (8) above, in whichthe wireless resource determination unit allocates the wireless resource for downlink transmission of each terminal in consideration of request information from each terminal in a case where a candidate for a wireless resource allocated in a certain subslot overlaps between terminals.(10) The communication device according to any one of (1) to (9) above, in whichthe communication device operates as the base station, and transmits a downlink frame by using the wireless resource determined by the wireless resource determination unit.(11) The communication device according to (1) above, in whichthe communication device operates as the terminal, and waits to receive a downlink frame in each of a plurality of candidates for the wireless resource determined in a slot by the wireless resource determination unit.(12) A communication method including:determining, in a communication system including a base station and a terminal, a wireless resource to be used for downlink communication on the basis of a common rule between the base station and the terminal; andperforming processing related to downlink communication using the determined wireless resource.

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