JP2006339918A - Radio communication terminal and communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a communication system with improved data communication efficiency in a communication area, and a radio communication terminal therefor. <P>SOLUTION: A control unit 18 grasps the reception performance of each of cellular phones in the area, and serially switches a parameter (FEC parameter) in error correction of data to be transmitted to each of the cellular phones in the area in accordance with the reception performance thereof. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a communication system that processes broadcast / multicast data, and a wireless communication terminal that can receive and view such data.

2. Description of the Related Art In recent years, wireless communication terminals represented by mobile phones are not only voice systems that perform wireless communication of voice data for calls, but also packet systems that perform wireless communication using a large amount of multimedia data such as moving image data as packet data. Can be used. In this packet system, a large-capacity frame with high transmission efficiency is used for the transmission frame, and a coding method with high error correction capability is used in the physical layer, so that transmission delays that are important in voice systems are not guaranteed. As a result, a high-speed and low-cost wireless system is realized.
Patent Document 1 below discloses a packet system capable of transmitting high-quality and large-capacity multimedia data while improving the transmission efficiency of wireless communication by sharing one wireless channel with a plurality of terminals. A system for performing a multicast / broadcast service (multicast / broadcast system) has been proposed.

  In the multicast / broadcast system described above, one wireless channel is shared by a plurality of terminals, thereby improving the wireless usage efficiency. Therefore, as an error correction method for a multicast / broadcast system, an encoding method according to the reception state of each terminal as in the conventional packet system and an ARQ (Automatic Repeat Request) method for performing retransmission control when a reception error occurs. It cannot be used. Therefore, in the multicast / broadcast system, an FEC (forward error correction) method is used in which error correction is performed without making a retransmission request to the transmission source for a reception error of data received on the wireless communication terminal side.

JP-T-2004-531937

  By the way, in a multicast / broadcast system, data transmitted from an access point to an access terminal (AT) depending on the setting of a service area (hereinafter referred to as area) for each access point (AP) and the radio wave condition in the area. The required FEC setting (error tolerance) is different. This point will be described with reference to FIGS.

FIG. 1 and FIG. 2 are diagrams for explaining the relationship between the reception state of the wireless communication terminal (AT) in the access point (AP) and the setting of the FEC set in the transmission data.
In FIG. 1A, assuming that the wireless communication terminals AT1 and AT2 in the area have the same reception performance, the reception state of the radio waves transmitted from the access point at the wireless communication terminals AT1 and AT2 is the center of the area. The nearby wireless communication terminal AT1 is better than the wireless communication terminal AT2 at the boundary of the area. That is, if the reception levels of the radio communication terminals AT1 and AT2 are C1 and C2, C1> C2. In such a case, the FEC setting of the transmission data from the access point guarantees error-free for all wireless communication terminals in the area, so that even the wireless communication terminal AT2 in a poor reception state can be surely corrected for errors. To be done. For example, as shown in FIG. 1B, in the case of using FEC with a parity symbol added, the unit data (data length: N) in the unit data (data length: N) can be surely corrected even by the radio communication terminal AT2. A parity symbol length (R) is set.

However, in recent years, there has been an increase in diversity reception-compatible wireless communication terminals that can improve reception performance due to reception diversity or the like, and the reception performance of wireless communication terminals at the boundary of an area is higher than that of the wireless communication terminals in that area. The situation is not the lowest. For example, in FIG. 2, if the radio communication terminal AT3 at the area boundary is a diversity compatible terminal and the radio communication terminal AT2 shown in FIG. 1 is a non-diversity terminal, the reception level C3 of the radio communication terminal AT3 is assumed. May be higher than the reception level of the wireless communication terminal AT2 (C3> C2). In some cases, the reception level of the radio communication terminal AT3 may be higher than that of the radio communication terminal AT1 that does not support diversity near the center of the area.
In such a case, the fact that the FEC setting of the data transmitted from the access point remains based on the wireless communication terminal AT2 having the lowest reception performance means that efficient data transmission is performed as the number of terminals having high reception performance increases. It is no longer a method. That is, as the number of terminals having high reception performance increases, the FEC setting gradually becomes excessive quality, and as a result, the transmission efficiency of data to be transmitted (payload in FIG. 1B) decreases.

  The present invention has been made in view of the above points, and an object thereof is to provide a communication system with improved data communication efficiency in a communication area and a wireless communication terminal therefor.

  In order to overcome the above problems, a first aspect of the present invention is a communication system for transmitting broadcast data from a first broadcasting device that manages a first area to a plurality of wireless communication terminals, wherein the wireless communication The terminal sets the reception sensitivity for the first broadcast device on condition that the reception sensitivity for the broadcast data broadcast from the second broadcast device managing the second area adjacent to the first area exceeds a predetermined threshold. Notification means for notifying the first broadcasting device, wherein the first broadcasting device averages reception sensitivities notified from the plurality of wireless communication terminals and calculates average sensitivity; and When transmitting to a plurality of wireless communication terminals, encoding means for encoding for error correction and the calculated average sensitivity are compared with a predetermined reference sensitivity, and the encoding means is sent to the encoding means according to the comparison result. And adjusting means for adjusting the error correction capability takes is a communication system comprising a.

  Preferably, the predetermined reference sensitivity corresponds to a first reference sensitivity corresponding to a reception sensitivity of a wireless communication terminal that performs diversity reception and a reception sensitivity of a wireless communication terminal that does not perform diversity reception, and the first reference sensitivity. A second reference sensitivity larger than the second reference sensitivity, and the adjustment means increases the error correction capability of the encoding means based on a comparison result between the average sensitivity and the first and second reference sensitivity. Increase step by step as you go.

  In order to overcome the above problems, a second aspect of the present invention is a wireless communication terminal that receives broadcast data from a first broadcast device that manages a first area, and is a second area adjacent to the first area. The reception sensitivity for the broadcast data broadcast from the first broadcast device is notified to the first broadcast device on condition that the reception sensitivity for the broadcast data broadcast from the second broadcast device that manages the broadcast data exceeds a predetermined threshold. In the notification means and the first broadcasting device, the reception sensitivities notified from a plurality of wireless communication terminals are averaged, the average sensitivity is compared with a predetermined reference sensitivity, and the error correction capability is adjusted according to the comparison result. And a broadcast receiving means for receiving the broadcast data that has been encoded.

  ADVANTAGE OF THE INVENTION According to this invention, the data communication efficiency in a communication area can be improved.

Hereinafter, an embodiment of a communication system of the present invention will be described with reference to the accompanying drawings.
In the communication system according to the embodiment, an AP (access point 10; the broadcasting apparatus of the present invention) that manages a specific area receives broadcast information (broadcast data of the present invention) such as broadcast data or multicast data in response to a broadcast request. Distribution (broadcast) to a plurality of mobile phones 20 (an example of the wireless communication terminal of the present invention) in the area. In the following description, the mobile phone is abbreviated as a terminal as appropriate. The following description will be made on the assumption that the packet system is a broadcast system in which the distribution destination is not limited. However, the present invention can be applied to a multicast system in which the distribution destination is limited.

Hereinafter, configurations and operations of the access point 10 and the mobile phone 20 will be described.
FIG. 3 is a block diagram showing the configuration of the access point 10.
As shown in FIG. 3, the access point 10 includes an antenna 11, a radio reception unit 12, a radio transmission unit 13, a packet processing unit 14, a broadcast data processing unit 15, a terminal data storage unit 16, an FEC parameter storage unit 17, and a control unit. 18.

  In the access point 10, the radio wave transmitted from the mobile phone in the area managed by the access point 10 is taken into the wireless reception unit 12 via the antenna 11. The radio reception unit 12 performs detection / demodulation processing on the received radio wave and converts it into digital data (reception data). When the received data is data related to packet data, the packet processing unit 14 processes and processes the packet. When the received data is data related to broadcast data, the data is supplied to the broadcast data processing unit 15 and processed. The

The control unit 18 supervises the overall operation of the access point 10 and records reception strength data (reception strength data) in the terminal data storage unit 16 when receiving a reception strength notification described later from a terminal in the area.
The control unit 18 performs statistical processing and determination processing based on the reception intensity data of the terminals in the area recorded in the terminal data storage unit 16.
In the statistical processing, average reception strength is calculated by performing averaging processing on reception strength notification data (pilot signal strength) of a plurality of terminals in the area. Based on this average reception intensity, the reception performance of the entire mobile phone in the area is grasped.
In the determination process, the average reception intensity calculated by the statistical process is compared with the reference reception intensity measured in advance, and the FEC parameter of the data to be transmitted to the mobile phone in the area is compared according to the comparison result. Set. When setting the FEC parameters, if the average reception strength is smaller than the reference reception strength, a parameter setting with high error correction capability is performed. If the average reception strength is larger than the reference reception strength, the error correction capability is low. Set parameters.

  In the present embodiment, the FEC parameters include the data length N of one unit block of broadcast data to be transmitted, the payload K occupying the data length N, and the parity symbol length R (= N−K).

When data is transmitted to a mobile phone in the area, the broadcast data processing unit 15 uses the protocol processing unit 152 to receive control data, user data, and broadcast data received from a network device located above the access point 10. The FEC processing unit 151 performs encoding for error correction, for example, block encoding such as Reed-Solomon encoding. This block encoding is performed based on the FEC parameters set by the control unit 18.
The wireless transmission unit 13 broadcasts (distributes) the encoded data generated by the broadcast data processing unit 15 to the mobile phone in the area managed by the access point 10 via the antenna 11.

Next, the configuration of the mobile phone 20 will be described.
FIG. 4 is a block diagram showing a configuration of the mobile phone 20. The mobile phone 20 shown in FIG. 4 shows a configuration of a terminal that performs diversity reception as an example.
As shown in FIG. 4, the mobile phone 20 includes an antenna 21, a wireless transmission unit 22, a broadcast processing unit 23, a wireless reception unit 24, a packet processing unit 25, a microphone 26, a speaker 27, a display unit 28, an input unit 29, and a terminal. An information storage unit 30 and a control unit 31 are provided.

In the mobile phone 20, the radio wave received by the antenna 21 is taken into the wireless reception unit 24. The wireless receiver 24 detects the received radio wave and extracts a baseband signal (received signal), and converts the received signal into digital data (received data).
When the received data is packet data, it is supplied to the packet processing unit 25 for processing. When the received data is broadcast data, it is supplied to the broadcast processing unit 23 for processing.

The broadcast processing unit 23 separates received data (multiplexed data), extracts control data, user data, and broadcast data, and performs decoding for error correction for each unit block. The error correction capability by this decoding increases as the parity symbol length included in the unit block increases.
Further, the decoded data is decoded for video reproduction by the control unit 31 and output to the microphone 26, the speaker 27, and the display unit 28.

In addition to controlling the overall operation of the mobile phone 20, the control unit 18 calculates the reception strength of the terminal itself and notifies the access point 10 of the reception strength data (reception strength notification). When the data communication is the CDMA2000 1xEVDO system, the pilot signal strength is calculated as the reception strength.
The conditions for performing the reception strength notification will be described later.

  When the cellular phone 20 performs diversity reception, the diversity processing unit 241 of the wireless reception unit 24 selects a signal having a high reception strength from the reception signals obtained from the two antennas 211 and 212 shown in FIG. Compared with the case of receiving from a single antenna by processing (selection diversity) or combining and processing the reception signals obtained from the two antennas 211 and 212 (combining diversity), Reception performance can be increased. In FIG. 4, the antenna 211 is a reception-only antenna, and the antenna 212 is a reception / transmission shared antenna.

Next, conditions for the mobile phone 20 to notify the reception intensity will be described with reference to FIGS.
In the communication system according to the embodiment, when a terminal moves from an access point that manages a certain area to another access point that manages an adjacent area (handoff), the terminal notifies the access point of reception strength. .

For example, FIG. 5 is a diagram illustrating a case where the mobile phone 20 hands off from the access point 10-1 to the access point 10-2.
At this time, the cellular phone 20 can gradually receive a signal from the access point 10-2 as it approaches the vicinity of the boundary with the access point 10-2 from the center position of the area of the access point 10-1. (FIGS. 5A and 5B). That is, the reception intensity from the access point 10-2 gradually increases. The mobile phone 20 then sets the reception strength from the access points 10-1 and 10-2 at that time on condition that the signal strength from the access point 10-2 has reached a predetermined reception strength suitable for communication. Based on the value, the reception strength is notified to the access point 10-1. FIG. 5C shows an example of reception intensity data transmitted to the access point 10-1 in the reception intensity notification.

FIG. 6 is a diagram illustrating a case where the mobile phone 20 is handed off from the access point 10-1 to the access point 10-2, as in FIG. 5, but shows a case where the reception performance of the mobile phone is high.
When the reception performance of the mobile phone 20 handed off from the access point 10-1 to the access point 10-2 is high, as shown in FIG. 6, even if the location is close to the center of the area of the access point 10-1, The signal strength from the access point 10-2 to be reached reaches a predetermined reception strength suitable for communication. At this time, since the mobile phone 20 is near the center of the area of the access point 10-1, the reception intensity from the access point 10-1 included in the reception intensity data is as illustrated in FIG. This is larger than the case of 5 (c) (“+2.2” in FIG. 5 versus “+5.1” in FIG. 6).

  As described above, in FIGS. 5 and 6, in the access point 10-1, the reception strength data of the access point 10-1 to be notified becomes larger as the mobile phone has higher reception performance. Therefore, in the access point 10-1, the reception strength data of the access point 10-1 notified from the mobile phone in the area can be used as an index of the reception performance of the mobile phone in the own area.

The access point 10-1 acquires and records the reception strength (pilot strength) for the access points 10-1 and 10-2 from the mobile phone 20 in the area by the sequential reception strength notification. FIG. 7 shows an example of recording pilot strength.
Here, as described above, the reception intensity from the adjacent access point 10-2 is merely a condition for performing the reception intensity notification, and has a substantially constant value as shown in FIG. Therefore, what is important in grasping the reception performance of the mobile phone in the area is the reception intensity from the access point 10-1. Hereinafter, the reception intensity from the access point 10-1 will be described as “reception intensity data”.

  Next, a process (mainly a process performed by the control unit 18) performed by the access point 10 that acquired the reception intensity data of the mobile phone in the area by the reception intensity notification will be described.

First, the control unit 18 of the access point 10 records reception intensity data transmitted from the mobile phone in the area in the terminal data storage unit 16 and then performs an averaging process (statistical process) according to the following equation (1). That is, as shown in the equation (1), the average reception intensity Pilot _ave is calculated by taking the average of the reception intensity data in a certain period. Based on this average reception strength Pilot _ave , the overall reception performance of the mobile phone in the area is grasped.

なお、ｋは最新の時間データ（Pilot[n]が受信強度データの最新値となる）、αは時間平均を行うための時間幅、である。

Here, k is the latest time data (Pilot [n] is the latest value of the received intensity data), and α is a time width for performing time averaging.

  Next, the average reception intensity calculated by the statistical processing is compared with the reference reception intensity measured in advance, and the FEC parameter of the data to be transmitted to the mobile phone in the area according to the comparison result Set. When setting the FEC parameters, if the average reception strength is smaller than the reference reception strength, a parameter setting with high error correction capability is performed. If the average reception strength is larger than the reference reception strength, the error correction capability is low. Set parameters.

FIG. 8 is a diagram illustrating an example of FEC parameter settings.
In general, reception performance is improved in the order of non-diversity-equipped terminals, diversity-equipped terminals (selective diversity), and diversity-equipped terminals (combined diversity). Pilot _ref ")" is measured. Then, the FEC parameters are set according to the comparison result between the average reception intensity calculated by the statistical processing and the reference reception intensity. For example, FEC parameters are set so as to satisfy the following formula (2).

ここでPilot_ref[i]は図８の各Pilot信号の基準値（ｉ＝０〜２、ｉは図８における「Ｎｏ」に対応）、βは、０．５〜１までの確率変数である。

Here, Pilot _ref [i] is the reference value of each Pilot signal in FIG. 8 (i = 0 to 2, i corresponds to “No” in FIG. 8), and β is a random variable from 0.5 to 1. .

  Further, the parameter setting process of the access point 10 (the process of the control unit 18) will be described with reference to the flowchart of FIG.

First, the reference reception strength is measured by the reference device to determine the reference reception strength (step ST1). Further, the FEC parameters corresponding to the reference reception intensity are also determined in advance and recorded in the FEC parameter storage unit 17 (step ST1). That is, the data used as the processing reference as illustrated in FIG. 8 is determined and recorded in advance.
Then, when the access point 10 actually starts operating, it receives a reception strength notification from each terminal in the area (step ST2), and sequentially records the received strength data acquired by the received strength in the terminal data storage unit 16, Statistical processing is performed on the recorded data (step ST3). In the statistical processing, for example, the time average is taken according to the above equation (1), and the average received intensity is calculated.

Next, an FEC parameter corresponding to the calculated average reception strength is determined based on a predetermined reference reception strength and FEC parameter settings. For example, the FEC parameters are determined according to whether or not the conditional expression shown in the above equation (2) is satisfied (steps ST4 to ST7).
For example, in the example shown in FIG. 8 and Expression (2), it is checked whether or not Expression (2) is satisfied in order with i = 0 (i: corresponding to “No” in FIG. 8). The parameter is changed so that the error correction capability becomes high (step ST5). If i = 0 is not satisfied, whether or not i = 1 is satisfied is checked, and if satisfied, the FEC parameter is checked. Is changed so as to reduce the error correction capability (step ST7). If i = 1 is not satisfied, the FEC parameter setting is set to i = 2.

As described above, according to the communication system according to the embodiment, the reception performance of the mobile phone in the area is grasped, and the parameter for error correction of data transmitted to each mobile phone in the area according to the reception performance Since the (FEC parameter) is sequentially switched, data with high error correction capability is not transmitted even though the reception performance of the mobile phone in the area is improved. Therefore, the data transmission efficiency in the area can always be kept optimal.
As a result, it is possible not only to transmit higher-quality multimedia data, but also to simultaneously distribute a plurality of multimedia data and to transmit packet data at a higher speed.

  As described above, the embodiments of the present invention have been described in detail with reference to the drawings. However, the specific configuration is not limited to these embodiments, and includes design changes and the like without departing from the gist of the present invention. . For example, the wireless communication terminal of the present invention includes a device having a wireless communication function, such as a mobile phone, a wireless communication card, and a wireless communication module.

It is a figure for demonstrating the relationship between the reception state of the radio | wireless communication terminal (AT) in an access point (AP), and the setting of FEC set to transmission data. It is a figure for demonstrating the relationship between the reception state of the radio | wireless communication terminal (AT) in an access point (AP), and the setting of FEC set to transmission data. It is a block diagram which shows the structure of an access point. It is a block diagram which shows the structure of a mobile telephone. It is the figure which illustrated the case where a mobile telephone handed off between access points. It is the figure which illustrated the case where a mobile telephone handed off between access points. An example of recording pilot strength is shown. It is a figure which shows an example of the setting of the parameter of FEC. It is a flowchart which shows the parameter setting process of an access point.

Explanation of symbols

10 ... Access point
11 ... Antenna
12 ... Wireless receiver
13 ... Wireless transmitter
14 ... Packet processor
15 ... broadcast data processing section
16. Terminal data storage unit
17 ... FEC parameter storage
18 ... Control unit 20 ... Mobile phone
21 ... Antenna
22 ... Wireless transmitter
23. Broadcast processing section
24 ... Wireless receiver
25 ... Packet processing unit
26 ... Microphone
27 ... Speaker
28 ... Display section
29 ... Input section
30 ... Terminal information storage unit
31 ... Control unit

Claims (3)

A communication system for transmitting broadcast data from a first broadcasting device that manages a first area to a plurality of wireless communication terminals,
The wireless communication terminal is
Notification means for notifying the first broadcast device of the reception sensitivity for the first broadcast device on condition that the reception sensitivity for the second broadcast device managing the second area adjacent to the first area exceeds a predetermined threshold With
The first broadcasting device is
A calculation means for averaging the reception sensitivities notified from the plurality of wireless communication terminals and calculating an average sensitivity;
Encoding means for performing encoding for error correction when transmitting the broadcast data to the plurality of wireless communication terminals;
A communication system comprising: an adjusting unit that compares the calculated average sensitivity with a predetermined reference sensitivity and adjusts an error correction capability of the encoding unit according to the comparison result. The predetermined reference sensitivity corresponds to a first reference sensitivity corresponding to a reception sensitivity of a wireless communication terminal that performs diversity reception and a reception sensitivity of a wireless communication terminal that does not perform diversity reception, and is larger than the first reference sensitivity. 2 standard sensitivity,
2. The communication according to claim 1, wherein the adjustment unit increases the error correction capability of the encoding unit in a stepwise manner as the average sensitivity increases based on a comparison result between the average sensitivity and the first and second reference sensitivities. system. A wireless communication terminal that receives broadcast data from a first broadcast device that manages a first area,
Notification means for notifying the first broadcast device of the reception sensitivity for the first broadcast device on condition that the reception sensitivity for the second broadcast device managing the second area adjacent to the first area exceeds a predetermined threshold When,
In the first broadcasting apparatus, the reception sensitivity notified from a plurality of wireless communication terminals is averaged, the average sensitivity is compared with a predetermined reference sensitivity, and the error correction capability is adjusted according to the comparison result. Broadcast receiving means for receiving the broadcast data,
Wireless communication terminal equipped with.

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