JP6467992B2 - Wireless communication system - Google Patents

Description

  The present invention relates to a wireless communication system using an erasure correction code.

  In wired and wireless communication systems, it is known that packet loss occurs due to the influence of congestion and reception errors. For this reason, erasure correction codes are often applied for the purpose of providing packet loss tolerance in data communication.

  The erasure correction code adds P parity packets to K information packets, thereby enabling decoding to the original information without retransmission for a certain amount of packet loss. . Note that the erasure correction code can improve the correction capability by adding more parity packets, but the transmission efficiency decreases as the total amount of transmission data increases. For this reason, the number of information packets K and the coding rate R (= K / (K + P)), which are coding parameters of the erasure correction code, can be obtained with the required quality in consideration of the reception error rate in the communication environment. Set to However, assuming the use of a wireless communication system such as LTE (Long Term Evolution) or IEEE 802.16m, the wireless environment changes from moment to moment, so appropriate settings are made according to the change in the communication environment. There is a need.

  As a technique for estimating a communication environment, for example, a technique that uses fluctuations in the reception interval of data packets is known. In other words, fluctuations in the reception interval increase as retransmission processing increases due to deterioration in communication quality, so if the fluctuation in the observed reception interval is large, the packet length is shortened to enhance error tolerance, and if the fluctuation is small, the packet length Is set so as to emphasize communication efficiency (see Patent Document 1).

JP 2013-225761 A

  However, for example, when low-delay communication is required, the number of retransmission processes in the wireless communication unit is generally limited. In this case, since fluctuation of the reception interval is suppressed, it is expected that it is difficult to estimate the communication environment from the reception interval.

  In addition, when considering a system in which a mobile body such as a car communicates using LTE, the communication environment significantly varies as the mobile body moves. Along with this, the modulation and coding scheme and bandwidth allocated for communication with individual users dynamically change, and the amount of data that can be transmitted per transmission frame varies depending on the modulation and coding scheme and bandwidth. Then, as shown in FIG. 13, a plurality of packets are transmitted in one transmission frame, or conversely, as shown in FIG. 14, one packet is transmitted in a plurality of transmission frames. As a result, it is expected that it is difficult to estimate the communication environment from the reception interval.

That is, the conventional technique has a problem that it can be practically functioned only in a very limited communication environment and cannot be applied to various communication environments.
The present invention has been made in view of these problems, and an object of the present invention is to provide a technique for realizing wireless communication that satisfies a desired required reception error rate in various communication environments.

In the wireless communication system of the present invention, a base station configuring a communication network determines a modulation and coding scheme and a bandwidth used for wireless communication with a terminal device in response to a request from the terminal device.
The terminal device includes parameter determination means, resource allocation request means, division coding means, and transmission means. The parameter determination means assumes that the reception error rate in wireless communication with the base station is a preset target error rate, and satisfies the required error rate according to the application that is the source of transmission information so that the erasure correction code is satisfied. The number of encoding target packets and the encoding rate, which are the encoding parameters, are determined, and the packet length of the encoding target packet is obtained from the data length of the transmission information and the number of encoding target packets. The resource allocation request unit transmits a resource allocation request including at least information corresponding to the packet length obtained by the parameter determination unit to the base station. The division coding unit performs division of transmission information and coding into an erasure correction code using the coding parameter determined by the parameter determination unit. The transmission means transmits the transmission packet output from the division coding means with the modulation and coding scheme and bandwidth allocated by the base station.

  On the other hand, the base station includes resource allocation means. Upon receiving the resource allocation request from the terminal device, the resource allocation means determines a modulation and coding scheme that satisfies the target error rate, and in accordance with the information notified by the resource allocation request, transmits the transmission packet in one transmission frame. The bandwidth necessary for transmission is allocated for communication with the requesting terminal device.

According to such a configuration, a minimum bandwidth necessary for transmitting one transmission packet in one transmission frame is allocated to wireless communication between the terminal device and the base station.
As a result, the ability of the erasure correction code can be maximized, and the proportion of dummy data in the transmission frame can be reduced, so that transmission efficiency of the transmission frame can be improved.

  That is, for example, when one transmission packet is divided into m and transmitted in m transmission frames, reception of the transmission packet fails unless all the m transmission frames are successfully received. That is, even if the transmission frame loss probability is the same, the larger the value of m, the higher the transmission packet loss probability. Further, when n transmission packets are combined and transmitted in one transmission frame, if reception of the transmission frame fails, reception of n transmission packets fails. The erasure correction code needs to be generated so that it can be decoded with respect to n packet losses. In either case, the probability of being indecipherable is higher than when one transmission packet is transmitted in one transmission frame, and it is necessary to provide greater redundancy to compensate for this. Therefore, the transmission efficiency is also deteriorated.

  In addition, the code | symbol in the parenthesis described in the claim shows the correspondence with the specific means as described in embodiment mentioned later as one aspect, Comprising: The technical scope of this invention is limited is not.

It is a block diagram which shows the structure of a radio | wireless communications system. It is a sequence diagram which shows the whole operation | movement of a radio | wireless communications system. It is a flowchart of the service start availability determination process which a server performs. It is explanatory drawing which shows the state of the data in each part of a terminal device. It is a flowchart of the transmission preparation process which a terminal device performs. It is a flowchart of the parameter determination process performed in a transmission preparation process. It is a flowchart of the resource allocation process which a base station performs. It is explanatory drawing which shows the relationship between radio | wireless quality information and the bandwidth allocated. It is a flowchart of the parameter determination process in 2nd Embodiment. It is a sequence diagram regarding acquisition of coefficient information. It is a flowchart of the resource allocation process in 3rd Embodiment. It is a flowchart of the resource allocation process in 4th Embodiment. It is explanatory drawing which shows that a some transmission packet is couple | bonded and it transmits with one transmission frame. It is explanatory drawing which shows that one transmission packet is divided | segmented and transmitted with a some transmission frame.

Embodiments to which the present invention is applied will be described below with reference to the drawings.
[1. First Embodiment]
[1.1. System configuration]
As shown in FIG. 1, the wireless communication system 1 includes a base station 10, a server 20, and a terminal device 30. The base station 10 and the server 20 communicate via a wired network, and the base station 10 and the terminal device 30 communicate via a wireless network. The base station 10 and the server 20 are collectively referred to as a network side device.

  In the wireless network, communication conforming to the LTE (Long Term Evolution) standard is performed. That is, based on OFDM communication that is transmitted in parallel using a multi-carrier signal at a low symbol rate, the lower layer (physical layer, link layer) dynamically selects a modulation and coding scheme and assigns a radio band (carrier signal). The upper layer (application layer) is configured to perform communication using the erasure correction code. As the modulation and coding scheme, a combination of QPSK, 16QAM, 64QAM or the like is used as the modulation scheme, and a turbo code or the like is used as the coding scheme.

[1.2. System operation]
The outline of the communication performed between each apparatus which comprises the radio | wireless communications system 1 is demonstrated using the sequence diagram of FIG.

  The link layer (wireless communication unit 31 described later) of the terminal device 30 periodically transmits a reference signal. The base station 10 that has received the reference signal is an indicator that measures the communication quality of the wireless communication for each predetermined frequency range from the reception state of the reference signal, and indicates the rank of the communication quality from the measurement result. A CQI (channel quality indicator) is generated, and this CQI is notified to the terminal device 30 as radio quality information. The link layer of the terminal device 30 stores this CQI and updates the stored content every time it receives a CQI notification. The rank of communication quality indicated by CQI is composed of N (for example, N = 6) stages, and the i (i = 1 to N) -th rank is denoted as CQI # i below. In addition, the larger i is, the better the communication quality is.

  The application layer (hereinafter referred to as “application layer”) of the terminal device 30 receives a transmission request from an application operating on the own device, and includes a service including location information of the own device (requesting terminal device) via the link layer. Send a start request. Receiving this, the base station 10 transfers it to the server 20. The server 20 determines whether or not the service can be started based on the communication congestion around the request source terminal device, and sends the determination result to the source terminal device 30 via the base station 10 based on the start permission notification or the start failure notification. Return it.

  When the application layer of the terminal device 30 receives the start permission notification, the application layer determines the encoding parameter of the erasure correction code, performs erasure correction encoding on the transmission information according to the encoding parameter, and encodes the encoded packet. To the link layer.

The link layer supplied with the encoded packet receives a resource allocation request including information on the packet length L _p of the encoding target packet for erasure correction encoding, which is one of the encoding parameters, and the application type F _ap of the request source. Is transmitted to the base station 10. When a resource allocation notification is received from the base station 10, an encoded packet is transmitted using a transmission frame having a modulation and coding scheme and a bandwidth according to the content of the resource allocation notification.

  Upon receiving the resource allocation request, the base station 10 determines the modulation and coding scheme and allocates the bandwidth, and transmits the result to the terminal device 30 by the resource allocation notification and also notifies the server 20 by the allocation status notification. Notice. Thereafter, the base station 10 performs scheduling according to the assigned content, and performs wireless communication with the terminal device 30 according to the scheduled result.

The server 20 that has received the allocation status notification uses the content for determining whether or not the service can be started.
[1.3. Server configuration]
As shown in FIG. 1, the server 20 includes a wired communication unit 21, an erasure correction decoding unit 22, an available bandwidth database 23, and a service start availability determination unit 24.

The wired communication unit 21 performs communication with the base station 10 via a wired communication network.
When the erasure correction decoding unit 22 receives data encoded by the erasure correction code via the base station 10, the erasure correction decoding unit 22 decodes the received data to generate reception information and provides it to a higher-level application.

  The available bandwidth database 23 manages information related to the user (terminal device 30) who is using the application. Information to be managed includes the number of users in use, location information of users in use, bandwidth (consumption bandwidth) allocated to users in use for communication with the base station 10, and communication with the terminal device 30. Includes at least information on the total bandwidth B that can be used.

  The service start availability determination unit 24 includes a well-known microcomputer having a CPU, a ROM, and a RAM, and stores the service start request from the terminal device 30 received via the base station 10 in the available bandwidth database 23. At least a process for determining whether or not the service can be started is executed using the received information.

[1.3.1. Processing on server]
Processing executed by the service start availability determination unit 24 will be described with reference to the flowchart of FIG. This process is repeatedly executed while the server 20 is activated.

  When this process is activated, the CPU functioning as the service start availability determination unit 24 determines whether a service start request is received in S110. If received, the process proceeds to S120, and if not received, the process proceeds to S180. Hereinafter, the terminal device 30 that has transmitted the service start request is referred to as a request source user.

  In S120, the available bandwidth database 23 is searched based on the location information of the requesting user indicated in the service start request, and the service is provided within a predetermined range centered on the location indicated in the user location information. Extract middle users.

In subsequent S130, referring to the available bandwidth database 23, the total value H of the extracted bandwidth consumption of all users is calculated.
In subsequent S140, the usage rate u (= H / B) for the total bandwidth B available for communication with the requesting user is calculated.

In subsequent S150, it is determined whether or not the usage rate u is smaller than a preset threshold value _Uth . If the usage rate u is smaller than the threshold value U _th , a service start notification is transmitted to the requesting user in S160, and this process is terminated. If the usage rate u is equal to or greater than the threshold value U _th , a service start failure notification is transmitted to the requesting user in S170, and this process ends.

  In S180, it is determined whether an allocation status notification has been received. If the allocation content notification has not been received, the process ends. If the allocation content notification has been received, the process proceeds to S180, where the content of the available bandwidth database 23 is updated according to the content of the allocation status notification and the process ends. To do.

[1.4. Configuration of terminal device]
The terminal device 30 is configured as a smartphone or the like, for example, and moves with a moving body (a vehicle or a person) that holds the terminal device 30. As illustrated in FIG. 1, the terminal device 30 includes a wireless communication unit 31, a packetization unit 32, an erasure correction coding unit 33, an intermittent transmission unit 34, a scheduler operation database 35, and a communication control unit 36. Prepare. Note that the wireless communication unit 31 corresponds to the link layer in FIG. 2, and the part other than the wireless communication unit 31 corresponds to the application layer in FIG.

As indicated by an arrow A in FIG. 4, the packetizing unit 32 uses the transmission information (information length L _D ) provided from the application as a packet length that is one of the encoding parameters determined by the communication control unit 36. according L _p, it is divided into a plurality of coded packets length L _p to be erasure correction coding (packetizing).

  As indicated by an arrow B in FIG. 4, the erasure correction encoding unit 33 determines the code determined by the communication control unit 36 for a plurality of encoding target packets (information packets) generated by the packetizing unit 32. The erasure correction coding is performed according to the coding rate R which is one of the coding parameters. Specifically, a parity packet is generated from the information packet, and this parity packet is added after the information packet. If the number of information packets is K and the number of parity packets is P, the coding rate R is represented by R = K / (K + P).

As indicated by an arrow C in FIG. 4, the intermittent transmission unit 34 adds a header to the information packet and the parity packet output from the erasure correction coding unit 33 to generate a transmission packet of the application layer. Further, as shown by the arrow D in FIG. 4, the transmission packet, intermittently transmitted to the wireless communication unit 31 at predetermined time intervals T _IT. Here, the intermittent transmission is performed to prevent different transmission packets from being transmitted in a single transmission frame by the wireless communication unit 31.

  If the coding parameter of the erasure correction code is not determined by the communication control unit 36, the packetizing unit 32 and the erasure correction coding unit 33 send the transmission information to the intermittent transmission unit 34 as it is.

  The wireless communication unit 31 includes a transmission / reception unit 311 and a wireless quality measurement unit 312. When the radio quality measurement unit 312 periodically transmits a reference signal to the base station 10 via the transmission / reception unit 311 and receives the CQI notification from the base station 10, the radio quality measurement unit 312 stores the CQI indicated in the CQI notification, The stored content is updated every time a CQI notification is received.

The transmission / reception unit 311 transmits / receives various commands processed by the communication control unit 36 and the wireless quality measurement unit 312. Further, when a transmission packet encoded with the erasure correction code is received from the intermittent transmission unit 34, information on the packet length L _p of the encoding parameter determined by the parameter determination process described later and the application type F _ap of the request source application is obtained. The included resource allocation request is transmitted to the base station 10. When a resource allocation notification that is a response to the resource allocation request is received from the base station 10, a transmission packet is transmitted by a transmission frame using the modulation and coding scheme and the allocated band indicated in the resource allocation notification. When generating a transmission frame, as indicated by an arrow E in FIG. 4, dummy data is added to each transmission packet sent from the intermittent transmission unit 34 so as to have a preset block length _LTB. Padding is performed to generate a transport block (transmission frame).

However, the transmitting and receiving unit 311, if the transmission packet length less than the predetermined lower limit value, which is fed continuously within a short predetermined time than the time interval T _IT, as shown in FIG. 13, a plurality of transmission packets A function for generating a single transmission frame using a packet and a function for dividing a transmission packet into a plurality of transmission frames when a transmission packet having a length exceeding a predetermined upper limit value is supplied as shown in FIG. .

The scheduler operation database 35 includes a correspondence relationship between each rank of the CQI and the modulation and coding scheme selected at the rank, and blocks of transport blocks that can be taken at the time of each modulation and coding scheme and the modulation and coding scheme. Data indicating a correspondence relationship with the length L _TB is stored. Note that the block length L _TB changes according to the modulation and coding scheme and the allocated bandwidth (number of subcarriers), and therefore there are a plurality of block lengths L _{TB for} each modulation and coding scheme.

The communication control unit 36 is constituted by a microcomputer including a CPU, a ROM, and a RAM, and executes a transmission preparation process for performing settings necessary for transmission of transmission information.
[1.4.1. Processing at terminal device]
The transmission preparation process executed by the communication control unit 36 will be described with reference to the flowchart of FIG. This process is activated every time there is a transmission request from an application executed on the terminal device 30.

  When this process is activated, the CPU functioning as the communication control unit 36 acquires position information indicating the position of the own apparatus in S210. The position information is obtained from a GPS device (not shown) provided separately in the device.

In subsequent S220, a service start request including the position information acquired in S210 is transmitted to the server 20.
In continuing S230, it waits until the response from the server 20 with respect to a service start request | requirement is received, and if a response is received, it will progress to S240.

  In S240, if the response is a start permission notification permitting the start of the service, the process proceeds to S250. On the other hand, if the response is a start impossible notification not permitting the start of the service, the process ends.

In S250, parameter determination processing for determining encoding parameters used in the packetizer 32 and the erasure correction encoder 33 is executed.
In subsequent S260, among the coding parameters determined by the parameter determination process, to set the packet length L _p packetizing unit 32, by setting the coding rate R to erasure correction coding section 33, the transmission request The encoding of the transmission information that is the target into the erasure correction code is started, and the present process ends.

As a result, the transmission information is divided into packets to be encoded (= information packets) having a packet length L _{p by} the packetizing unit 32, a parity packet is added by the erasure correction encoding unit 33, and the intermittent transmission unit 34 at, is processed into transmission packets application layer by the header and the like is applied, are intermittently transmitted per time interval T _iT to the radio communication unit 31. The wireless communication unit 31 modulates a transmission packet that is intermittently transmitted using a set modulation and coding scheme, and wirelessly transmits the transmission packet in one transmission frame.

[1.4.2. Parameter determination process]
Here, the details of the parameter determination process executed in the previous S250 will be described with reference to the flowchart of FIG.

In the present process, first, at S310, it acquires the information length L _D of the transmission information to be transmitted request.
In subsequent S320, the request error rate T _req set for the request source application of the transmission request is acquired.

In subsequent S330, the application type F _ap of the request source application is acquired.
In subsequent S340, it is determined whether or not the application type F _ap indicates an application to be subjected to erasure correction encoding. Note that the application to be coded, for example, the average short control applications such as the length of the information length L _D of the target transmission information corresponds. If the application type F _ap is not an encoding target, the process proceeds to S350. If the application type F _ap is an encoding target, the process proceeds to S360.

  In S350, the functions of the packetizer 32 and the erasure correction encoder 33 are set to OFF without determining the encoding parameter, and this process is terminated. In this case, the transmission information is supplied to the intermittent transmission unit 34 as it is.

In S360, assuming that the reception error rate of the transmission frame in a wireless network is less than the target reception error rate P _target, the encoding parameters of the erasure correction code to satisfy the request error rate T _req acquired in S320 (coded All candidates for the target packet number K and coding rate R) are extracted. Further, the packet length L _p (= L _D / K) of the encoding target packet is calculated based on the information length L _D of the transmission information and the encoding target packet count K. Hereinafter, the set of the packet length L _p and the coding rate R is referred to as a coding parameter.

In subsequent S370, for each of the extracted encoding parameter L _p and R candidates, the length (fixed length) of various headers and footers added to the packet is added to the packet length L _p to transmit by the transmission frame. An actual data length L _PDU that is the length of data that needs to be calculated is calculated.

In subsequent S380, the CQI is acquired from the wireless communication unit 31. The obtained CQI value is denoted as CQI # x (x = 1 to N).
In subsequent S390, the block length L _TB of the transport block is selected for each candidate with reference to the information in the scheduler operation database 35. Specifically, the minimum value that can store the transmission data of the actual data length L _PDU is selected as the block length L _TB from the values that can be taken in the modulation and coding scheme specified from CQI # x. In actual transmission, dummy data is padded by the difference between the actual data length L _PDU and the block length L _TB as shown in FIG.

  In subsequent S400, the transmission efficiency η is calculated for each candidate according to the equation (1).

In subsequent S410, the candidate for maximizing η is determined as the encoding parameters L _p and R, and this process is terminated.

[1.5. Base station configuration]
As illustrated in FIG. 1, the base station 10 includes a wired communication unit 11 and a wireless communication unit 12.
The wired communication unit 11 relays the frame received via the wireless communication unit 12 to the server 20 and relays the frame addressed to the terminal device 30 received from the server 20 to the wireless communication unit 12.

The wireless communication unit 12 includes a transmission / reception unit 121, a wireless quality measurement unit 122, and a scheduler 123.
The transmission / reception unit 121 relays the frame addressed to the terminal device 30 received from the wired communication unit 11 to the terminal device 30 and relays the frame addressed to the server 20 received from the terminal device 30 to the wired communication unit 11.

  Upon receiving the reference signal from the terminal device 30 via the wireless communication unit 12, the wireless quality measurement unit 122 identifies the CQI according to the reception state, and returns a CQI notification to the terminal device 30 that is the reference signal transmission source. By doing so, the specified CQI is notified.

  The scheduler 123 is a known microcomputer having a CPU, a ROM, and a RAM. When a resource allocation request is received from the terminal device 30, a resource allocation process to be described later is executed, a modulation and coding scheme and a bandwidth to be used for communication with the requesting terminal device 30 are determined, and requested by a resource allocation notification In addition to notifying the original terminal device 30, the allocation content is also notified to the server 20 via the wired communication unit 11. The allocated bandwidth is allocated in units of resource blocks obtained by dividing the entire communication band that can be used in the wireless network into a plurality. Each resource block includes a predetermined number of subcarrier signals. Thereafter, the transmission / reception unit 121 performs communication with the terminal device 30 according to the modulation and coding scheme and bandwidth determined by the scheduler 123.

[1.5.1. Processing at the base station]
The resource allocation process executed by the scheduler 123 will be described with reference to the flowchart of FIG. This process is repeatedly executed while the base station 10 is activated.

  When this process is started, the CPU functioning as the scheduler 123 determines whether or not a resource allocation request is received from the terminal device 30 in S510. If a resource allocation request has not been received, this process ends. If it has been received, the process proceeds to S520.

In S520, the CQI (= CQI # x) of the request source terminal device of the resource allocation request is acquired from the radio quality measurement unit 122.
In subsequent S530, it is determined whether or not the application type F _ap indicated in the resource allocation request is that of an application to be subjected to erasure correction encoding.

If the application type F _ap is the encoding target, the process proceeds to S540. If the application type F _ap is not the encoding target, the process proceeds to S550.
In S540, the modulation and coding scheme and the bandwidth used for communication with the request source terminal apparatus are determined by the first method, and the process proceeds to S560. In the first method, the modulation and coding scheme that satisfies the target reception error rate P _target is determined in the communication quality environment specified from CQI # x acquired in S520. For the bandwidth, the block length L _TB of the transport block is obtained from the determined modulation and coding scheme and the packet length L _p indicated in the resource allocation request, and the data of the block length L _TB is transmitted in one transmission frame. Allocate the minimum bandwidth required for In general, as shown in FIG. 8, the better the communication quality (the larger the CQI # x x), the higher the coding rate with which the coding rate is selected, and the allocated bandwidth becomes narrower.

  In S550, the modulation and coding scheme and bandwidth used for communication with the request source terminal apparatus are determined by the second method, and the process proceeds to S560. In the second method, an existing method in a wireless network, for example, a modulation and coding scheme and a bandwidth that are associated in advance with a CQI # x indicated in a resource allocation request are allocated.

  In S560, the modulation and coding scheme and the bandwidth determined in S540 or S550 are transmitted to the request source terminal device by the resource allocation notification, and the same content is also transmitted to the server 20 by the allocation content notification. Exit.

[1.6. effect]
As described above, in the wireless communication system 1, the terminal device 30 determines the modulation and coding scheme used in the wireless communication between the terminal device 30 and the base station 10 according to CQI # x obtained by observation. Also, the terminal device 30 determines the coding parameters L _p and R of the erasure correction code that maximizes the transmission efficiency η, on the premise of the modulation coding scheme determined from CQI # x. The base station 10 obtains the minimum bandwidth required to transmit each transmission packet subjected to erasure correction coding in one transmission frame according to the coding parameter L _p determined by the terminal device 30. Assign to communication with the device.

  As a result, the ability of the erasure correction code can be maximized, and the proportion of dummy data in the transmission frame can be reduced, so that transmission efficiency of the transmission frame can be improved.

  That is, when a plurality of packets are transmitted in one transmission frame, if one transmission frame is lost due to an error during transmission, the plurality of packets are lost simultaneously. Conversely, when one packet is transmitted in a plurality of transmission frames, if none of the plurality of transmission frames can be received, the packet is lost. In either case, if the probability of frame reception failure is the same, the packet loss rate increases and the probability of non-restoration increases compared to the case where one packet is transmitted in one transmission frame. In addition, if this is to be compensated for, it is necessary to provide greater redundancy, and therefore the transmission efficiency is also degraded.

  In addition, since the wireless communication system 1 includes the intermittent transmission unit 34 that transmits transmission packets to the wireless communication unit 31 at intervals, the plurality of transmission packets are integrated into one frame in the wireless communication unit 31. Can be prevented.

[2. Second Embodiment]
Since the basic configuration of the second embodiment is the same as that of the first embodiment, the description of the common configuration will be omitted, and the description will focus on the differences.

  In the first embodiment described above, the terminal device 30 sets the encoding parameter using CQI # x obtained by observation. On the other hand, the second embodiment is different from the first embodiment in that the encoding parameter is set without using the CQI observation value. Therefore, in this embodiment, the CQI measurement using the reference signal may be omitted.

[2.1. Parameter determination process]
The contents of the parameter determination process, which is the difference from the first embodiment, will be described using the flowchart of FIG. Note that S310 to S370 are the same as the parameter determination process of the first embodiment described with reference to FIG. Below, the process of S420-S460 implemented instead of S380-S410 is demonstrated.

That is, in S420, the scheduler operation database 35 is referred to, and for each candidate, the block length L _{TB, i} (i = 1 to N) is selected for each CQI rank (CQI # 1 to CQI # N). The details are the same as the processing in S390 described above.

In subsequent S430, the transmission efficiency η _i for each CQI #i is calculated for each candidate according to the equation (2).

In subsequent S440, coefficient information α _{1 to} α _N is acquired. Specifically, as illustrated in FIG. 10A, the coefficient information request including the position information of the own apparatus is transmitted to the server 20, thereby obtaining the server 20. The server 20 sets appropriate coefficient information α _{1 to} α _N for the position specified from the position information indicated in the coefficient information request and returns it by coefficient information notification from the state of the communication environment measured in advance. To do. Note that the service start request / start permission notification may be combined with the coefficient information request / coefficient information notification.

  In subsequent S450, the evaluation value g of each candidate is calculated according to the equation (3).

In subsequent S460, a candidate for maximizing the evaluation value g is selected as the encoding parameters L _p and R, and this process is terminated.

[2.2. effect]
According to the second embodiment described above in detail, the rank of CQI is not specified, and all ranks of CQI are considered from information in scheduler operation database 35 and coefficient information α _{1 to} α _N acquired from server 20. By performing the probabilistic estimation, the coding parameters L _p and R of the erasure correction code that maximizes the transmission efficiency η are determined. The base station 10 obtains the minimum bandwidth required to transmit each transmission packet subjected to erasure correction coding in one transmission frame according to the coding parameter L _p determined by the terminal device 30. Assign to communication with the device.

As a result, even in a situation where it is difficult to obtain an observed value of CQI, it is possible to determine a coding parameter that improves transmission efficiency without impairing the ability of the erasure correction code.
[2.3. Modified example]
The coefficient information α _{1 to} α _N is not necessarily acquired from the server 20, and a preset value may be used. In this case, the coefficient information α _{1 to} α _N may all be the same value. In addition, when the CQI number that can be taken by the telecommunications carrier is limited, the coefficient information corresponding to the rank that cannot be used may be set to zero.

  When setting the coefficient information, if there are a large number of users existing within a certain area based on the user position, the coefficient information corresponding to the low quality rank is set to a large value, and conversely the number of users is When the number is small, the coefficient information corresponding to the high quality rank may be set to a large value. In other words, when communication is newly started, the probability that a band with good characteristics can be used decreases as the number of users increases, so the probability that a modulation coding scheme with a high data rate can be selected decreases. Coefficient information may be set using such characteristics.

In the present embodiment, the coefficient information α _{1 to} α _N is determined according to the information managed by the server 20, but when the base station 10 manages information related to the user distribution status, FIG. As shown, when the weight information request from the terminal device 30 is transferred to the server 20, the user distribution status is transmitted to the server 20, and the server 20 sets the CQI coefficient in consideration of the user distribution status. It may be. In this case, it is assumed that the closer the user is to the base station 10, the higher the possibility of a better communication environment, and the coefficient information α ₁ according to the CQI usage probability calculated from the distance from the base station 10 and the number of existing users. it is conceivable to set the ~α _N.

[3. Third Embodiment]
Since the basic configuration of the third embodiment is the same as that of the first embodiment, the description of the common configuration will be omitted, and the description will focus on the differences.

  In the first embodiment described above, the base station 10 switches the modulation and coding scheme and the bandwidth setting method depending on the application type of the request source. On the other hand, the third embodiment is different from the first embodiment in that the bandwidth setting method is switched according to the spectrum usage state.

[3.1. Resource allocation process]
The contents of the resource allocation process, which is a difference from the first embodiment, will be described using the flowchart of FIG.

  In this process, in S610, it is determined whether a resource allocation request is received from the terminal device 30 or not. If a resource allocation request has not been received, this process ends. If it has been received, the process proceeds to S620.

In S620, the CQI (= CQI # x) of the request source terminal apparatus is acquired from the radio quality measurement unit 122.
In subsequent S630, a modulation and coding scheme to be used for communication with the request source terminal apparatus is determined. Specifically, in the communication environment specified from the CQI acquired in S620, the reception error rate of the transmission frame is determined to be a modulation and coding scheme that satisfies a preset target error rate _Ptarget .

In subsequent S640, an evaluation value e indicating the usage status of the band (spectrum) being used for communication with the request source terminal device is calculated. Here, the spectrum use efficiency calculated from the equation (4) is set as an evaluation value e. However, the number of bits that can be transmitted with one modulation signal encoded by the modulation encoding method determined in S630 is Q _m , the coding rate is r, the number of antennas used for wireless communication is N _tx , and used for one unit time. The number of subcarriers to be performed is N _sc , and the subcarrier interval is W _sc .

In subsequent S650, it is determined whether or not the evaluation value e is greater than or equal to a preset threshold value _Eth . If the evaluation value e is equal to or greater than the threshold value E _th , the process proceeds to S660, and if the evaluation value e is smaller than the threshold value E _th , the process proceeds to S670.

In S660, the block length L _TB of the transport block is obtained according to the packet length L _p indicated in the resource allocation request, and the minimum bandwidth necessary for transmitting the transport block in one transmission frame is allocated. , The process proceeds to S680.

In S670, in accordance with that shown in the resource allocation request packet length L _p, assigning the minimum bandwidth required to transmit the packet in the m transmission frame, the process proceeds to S680.

  In S680, the modulation and coding scheme determined in S630 and the bandwidth determined in S660 or S670 are transmitted to the requesting terminal device 30 by the resource allocation notification, and the same is applied to the server 20 by the allocation content notification. Is transmitted, and this process is terminated.

[3.2. effect]
In this embodiment, if the spectrum utilization efficiency e is equal to or greater than the threshold E _th , one transmission packet is transmitted in one transmission frame. If the spectrum utilization efficiency e is smaller than the threshold E _th , one transmission packet is divided into a plurality of transmission packets. Bandwidth is allocated so as to be divided and transmitted in a plurality of transmission frames. That is, the low spectrum utilization efficiency e means that the size of the transport block length L _TB is limited. In a situation where one packet is transmitted in one transport block, the packet length L _p is limited. Will be. Then, as the packet length L _p is short, the higher the proportion of the header in the transport block, the transmission efficiency is lowered. In such a case, if one packet is allowed to be transmitted in a plurality of transport blocks, one header is always included in one transport block, but one header is included in each transport block. Will be included. That is, the limitation on the packet length L _p is eliminated, and the ratio of the header to the packet is reduced, so that transmission efficiency may be improved.

[3.3. Modified example]
The method for obtaining the spectrum utilization efficiency is not limited to the method shown in the equation (4). For example, when efficiency is defined in advance for each CQI rank CQI # 1 to CQI # N, the information may be used.

The evaluation value e is not limited to the spectrum utilization efficiency, and a packet length L _p or the like may be used.
In the present embodiment, the transmission is selected from one transmission frame or m transmission frames, but the condition may be divided into three or more conditions.

[4. Fourth Embodiment]
Since the basic configuration of the fourth embodiment is the same as that of the third embodiment, the description of the common configuration will be omitted, and differences will be mainly described.

In the third embodiment described above, the resource allocation method is switched in accordance with the spectrum usage status (in the first embodiment, the type of the requesting application). In contrast, in the fourth embodiment, in that the switching in accordance with the state of the coding is determined from the packet length L _p to be notified, and the third embodiment differs. In the present embodiment, information on the application type of the request source may be deleted from the information transmitted in the resource allocation request.

[4.1. Resource allocation process]
The contents of the resource allocation process, which is a difference from the third embodiment, will be described using the flowchart of FIG. However, since the processing of S610 to S630 is the same as that of the third embodiment, description thereof will be omitted, and S690 to S730 executed instead of S640 to S680 will be described.

In other words, in this embodiment, S690 is executed after S630.
In S690, a determination value e for determining the encoding state is calculated from the equation (5). Note that L _th is a constant, and the L _PDU is obtained from the packet length L _p as described in the first embodiment.

In subsequent S700, it is determined whether or not the evaluation value e is greater than or equal to a preset threshold value _Eth . If the evaluation value e is a threshold E _th or more, the process proceeds to S710 as erasure correction coding is applied, as an evaluation value e is smaller than the threshold value E _th, the erasure correction coding is not applied S720 Proceed to That is, if erasure correction coding is applied, it is determined that the packet length L _p and thus the L _PDU are limited to a certain size.

In S710, similar to the processing in S660, the block length L _TB of the transport block is obtained according to the packet length L _p indicated in the resource allocation request, and is necessary for transmitting the transport block in one transmission frame. Allocate a minimum bandwidth and proceed to S730.

In S720, the minimum bandwidth required to determine the block length L _TB of the transport block according to the packet length L _p indicated in the resource allocation request, and to transmit the transport block in m transmission frames or less And proceed to S730.

  In S730, the modulation and coding scheme determined in S630 and the bandwidth determined in S710 or S720 are transmitted to the requesting terminal device 30 by the resource allocation notification, and the same is applied to the server 20 by the allocation content notification. Is transmitted, and this process is terminated.

[4.2. effect]
According to the fourth embodiment described in detail above, the base station 10 determines whether or not erasure correction coding is applied based on the information L _p obtained by the resource allocation request, and allocates the bandwidth. Switching methods. For this reason, even in a situation where it is difficult for the base station 10 to acquire the application type of the request source, bandwidth allocation can be performed accurately according to the application state of the erasure correction code.

[5. Other Embodiments]
As mentioned above, although embodiment of this invention was described, this invention can take a various form, without being limited to the said embodiment.

  (1) In the above embodiment, the scheduler 123, the service start availability determination unit 24, and the communication control unit 36 are configured by a microcomputer, and the functions of these units are realized by software. However, the present invention is not limited thereto. It is not a thing. You may make it implement | achieve the whole or one part of these each part by hardware, such as a logic circuit.

(2) In the above-described embodiment, the wireless network is described as complying with the LTE standard. However, the present invention is not limited to this. For example, the present invention is also applicable to a wireless communication method that may conform to a standard other than LTE, such as IEEE 802.16m. Is possible. In this case, the block length L _TB may be replaced with NDB that is the transmission frame length.

  (3) In the above embodiment, the terminal device 30 includes the intermittent transmission unit 34. However, when the transmission / reception unit 311 does not have a function of transmitting a plurality of packets in one transmission frame, intermittent transmission is performed. The part 34 may be omitted.

  (4) The functions of one component in the above embodiment may be distributed to a plurality of components, or the functions of a plurality of components may be integrated into one component. In addition, at least a part of the configuration of the above embodiment may be replaced with a known configuration having a similar function. Moreover, you may abbreviate | omit a part of structure of the said embodiment. Further, at least a part of the configuration of the above embodiment may be added to or replaced with the configuration of the other embodiment. In addition, all the aspects included in the technical idea specified only by the wording described in the claim are embodiment of this invention.

  (5) In addition to the wireless communication system described above, the computer functions as the terminal device 30, the base station 10, the server 20, the communication control unit 36, the scheduler 123, and the service start availability determination unit 24 that are components of the wireless communication system. For example, a medium for recording the program, a resource allocation method, and the like.

  DESCRIPTION OF SYMBOLS 1 ... Wireless communication system 10 ... Base station 11 ... Wired communication part 12 ... Wireless communication part 20 ... Server 21 ... Wired communication part 22 ... Loss correction decoding part 23 ... Available bandwidth database 24 ... Service start availability determination part 30 ... Terminal device DESCRIPTION OF SYMBOLS 31 ... Wireless communication part 32 ... Packetization part 33 ... Erasure correction encoding part 34 ... Intermittent transmission part 35 ... Scheduler operation database 36 ... Communication control part 121,311 ... Transmission / reception part 122,312 ... Radio quality measurement part 123 ... Scheduler

Claims (8)

In a wireless communication system (1) in which a base station (10) constituting a communication network determines a modulation and coding scheme and a bandwidth used for wireless communication with a terminal device in response to a request from the terminal device (30) ,
The terminal device
Assuming that the reception error rate in wireless communication with the base station is a preset target error rate, the encoding parameter of the erasure correction code so as to satisfy the required error rate according to the application that is the source of transmission information Parameter determining means (36: S250) for determining the number of encoding target packets and the encoding rate, and obtaining the packet length of the encoding target packet from the data length of the transmission information and the number of encoding target packets;
Resource allocation requesting means (311) for transmitting to the base station a resource allocation request including at least information corresponding to the packet length determined by the parameter determining means;
Division coding means (32, 33, 34) for performing division of the transmission information and coding into erasure correction codes using the coding parameters determined by the parameter determination means;
A transmission means (311) for transmitting a transmission packet output from the division encoding means with the modulation encoding scheme and bandwidth allocated by the base station;
With
The base station
When receiving the resource allocation request from the terminal apparatus, the modulation and coding scheme satisfying the target error rate is determined, and the transmission packet is transmitted in one transmission frame according to the information notified by the resource allocation request. Resource allocation means for allocating a bandwidth necessary for communication to communication with the terminal device (123: S510 to 560)
A wireless communication system comprising: The parameter determination means includes
Quality information acquisition means (36: S380) for acquiring wireless quality information;
Candidate extraction means (36: S360) for extracting the encoding parameter candidates satisfying the required error rate;
For each candidate extracted by the candidate extraction unit, the modulation coding specified by the radio quality information acquired by the quality information acquisition unit is the transmission efficiency when the erasure correction encoding is performed according to the candidate. Efficiency calculation means (36: S340) for calculation based on the method;
The wireless communication system according to claim 1, further comprising: determining a candidate that maximizes the transmission efficiency as the encoding parameter. The parameter determination means includes
Candidate extraction means (36: S360) for extracting the encoding parameter candidates satisfying the required error rate;
For each candidate extracted by the candidate extraction means, the transmission efficiency when the erasure correction coding is performed according to the candidate is determined for each rank of the radio quality information by a modulation coding scheme specified from the rank. Efficiency calculation means (36: S440) for calculation as a premise;
Evaluation value calculation means (36: S450) for calculating an evaluation value for each candidate using coefficient information representing the transmission efficiency for each rank calculated by the efficiency calculation means and the weight of each rank;
The wireless communication system according to claim 2 , wherein a candidate for maximizing the evaluation value is determined as the encoding parameter.   The wireless communication system according to claim 3, wherein the coefficient information is acquired from one of network side devices constituting the communication network.   The wireless communication system according to claim 4, wherein the network side device sets the coefficient information according to a distribution of users in a predetermined area to which the terminal device belongs. The transmission means has a function of transmitting the packet continuously supplied within a preset time limit on one transmission frame,
The wireless communication system according to any one of claims 1 to 5, wherein the division encoding means intermittently transmits the generated transmission packet at intervals of the time limit or more (34). .   The resource allocation means obtains an evaluation value that becomes a larger value as the transmission efficiency estimated from the information indicated in the resource allocation request is higher, and when the evaluation value is smaller than a preset threshold value, The wireless communication according to any one of claims 1 to 6, wherein a bandwidth necessary for transmitting the transmission packet in a plurality of transmission frames is allocated to communication with the terminal device. system.   When one of the network side devices constituting the communication network receives a request to start communication from the terminal device, the network side device obtains an evaluation value that increases as the current processing load of the network side device increases. 8. A limiting means (24: S110 to S160) for disabling the start of communication of a request source when the evaluation value is larger than a preset threshold value. The wireless communication system according to any one of the above.