This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2006-350008, filed Dec. 26, 2006, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a radio communication system, in particular, a radio communication terminal and a radio communication system in which a plurality of terminals form a network.
2. Description of the Related Art
In conventional ad hoc networks, for example, a master terminal selects a master terminal candidate from a plurality of slave terminals, and notifies them of priorities thereof. Thereby, when a notifying signal is not broadcasted from the master terminal for a predetermined time, the master terminal candidate acts as a new master terminal in accordance with the priorities, and transmits a notifying signal. Thereby, a time period during which no master terminal exists is shortened, and a terminal which is to participate in the network can immediately start communications with a master terminal (for example, refer to JP-A 2005-6327 (KOKAI)).
However, while a master terminal is receiving a signal, it is difficult for the master terminal to transmit a notifying signal for participating in the network to slave terminals. To transmit a signal in a frequency band in which the master terminal is receiving a signal, it is necessary to provide circuits such as a tunable filter and an echo canceller to prevent the signal transmitted by the master terminal from entering a receiver of the master terminal. These circuits are required to achieve very high performance, and thus consume much power and have large sizes. If the master terminal stops transmitting a notifying signal during reception operation, a terminal which is to newly participate in the network cannot receive a notifying signal, and starts operation as a new master terminal. Therefore, when the network operates under heavy load conditions and a receiving operation time of the master terminal is long, there is the possibility that many master terminals undesirably coexist in the network and system throughput of the network badly deteriorates.
In accordance with a first aspect of the invention, there is provided a radio communication system, comprising:
a master radio communication terminal including: a first transmitting unit configured to transmit a beacon; a second transmitting unit configured to transmit a first notifying signal which includes information of a frequency of the beacon and a transmission timing of the beacon; a measuring unit configured to measure a reception power of a signal transmitted by each of a plurality of slave radio communication terminals; a selecting unit configured to select a notifying radio communication terminal, which is to transmit a second notifying signal, from the slave radio communication terminals based on the reception power, the second notifying signal including the same information of the frequency of the beacon and the transmission timing of the beacon as the information included in the first notifying signal; and a third transmitting unit configured to transmit, to the notifying radio communication terminal, notifying instruction information including an instruction to transmit the second notifying signal, and
at least one slave radio communication terminal of the slave radio communication terminals including: a first receiving unit configured to receive the notifying instruction information; a fourth transmitting unit configured to transmit the second notifying signal to the other slave radio communication terminals when the slave radio communication terminal receives the notifying instruction information; a second receiving unit configured to receive at least one of the first notifying signal and the second notifying signal; and a third receiving unit configured to receive the beacon based on the information included in one of the received first notifying signal and the received second notifying signal.
In accordance with a second aspect of the invention, there is provided a radio communication terminal, comprising: a first transmitting unit configured to transmit a beacon; a second transmitting unit configured to transmit a first notifying signal which includes information of a frequency of the beacon and a transmission timing of the beacon; a measuring unit configured to measure a reception power of a signal transmitted by each of a plurality of slave radio communication terminals; a selecting unit configured to select a notifying radio communication terminal, which is to transmit a second notifying signal, from the slave radio communication terminals based on the reception power, the second notifying signal including the same information of the frequency of the beacon and the transmission timing of the beacon as the information included in the first notifying signal; and a third transmitting unit configured to transmit, to the notifying radio communication terminal, notifying instruction information including an instruction to transmit the second notifying signal.
A radio communication terminal and a radio communication system according to an embodiment are explained below with reference to drawings. The radio communication terminal is sometimes referred to as “terminal”.
According to the radio communication terminal and the radio communication system of the embodiment, system throughput of the network is improved.
The master terminal 101 selects notifying-signal transmitting terminals from the slave terminals in the network. The selecting method is explained later with reference to
In
The notifying signals 401, 405 and 406 notify, during tens of frames, the terminals of the frequency and timing of the beacon 402. During the notification, even when an interference signal 407 occurs and the master terminal 101 has to stop the notifying signal 401, transmission of the notifying signal 406 by the notifying-signal transmitting terminal 104 is continued. Specifically, even when it is hard for slave terminals to receive the notifying signal from the master terminal 101, the slave terminals can receive a notifying signal from the notifying-signal transmitting terminal 104. Therefore, a terminal which is to newly participate in the network can receive the beacon 402, without starting reception of a notifying signal again. When the terminal 101 detects occurrence of the interference signal 407, the terminal 101 stops transmission (transmission of the notifying signal 401) at the frequency band, performs carrier sensing in the main band, and thereafter starts transmission of a notifying signal again in a band where no interference signals exist. Besides signal interference, there are cases where it is difficult for slave terminals to receive a notifying signal from the master terminal due to the position of the master terminal. In consideration of these cases, the notifying-signal transmitting terminal 104 is desirably located in a position distant from the master terminal.
In
The notifying signals 501, 505 and 506 notify, during tens of frames, the terminals of frequency and timing of the beacon 502. Although the notifying signal 501 of the master terminal is transmitted at a frequency different from those of the notifying signals 505 and 506 of the notifying-signal transmitting terminals in
Next, suppose that a demand for participation in the network occurs in the slave terminal 612, and the slave terminal 612 sends a network participation request to the master terminal 610 (Step S604). In this case, the master terminal 610 performs notifying-signal transmitting terminal selection processing, in the same manner as above (Step S605). In the processing, if the master terminal 610 determines to select the slave terminal 612 as the notifying-signal transmitting terminal, the master terminal 610 sends, to the slave terminal 612, a notice of authorization to participate in the network (step S606) together with notifying-signal transmission instruction information (Step S607).
The notifying-signal transmission instruction information may include information such as information to be superposed on the notifying signal, the frequency band of the notifying signal, the spreading code, the beam direction, and the transmission power, as well as the timing information of the notifying signal to be transmitted by the slave terminal 612. The timing when the master terminal 610 performs reception may be designated as the notifying-signal transmitting timing, such that the slave terminal 612 transmits a notifying signal while the master terminal 610 is receiving a signal. Further, the timing may be designated such that the master terminal 610 transmits a notifying signal in a time-division method with other notifying-signal transmitting terminals, in consideration of the cases where the master terminal 610 stops transmission of a notifying signal due to occurrence of an interference signal or the like. In the case of designating the frequency band, it is desirable to designate a band having a frequency which is uncorrelated with the frequency band of the notifying signal transmitted by the master terminals 610. Designating such a frequency band reduces the possibility that the notifying-signal transmitting terminal cannot transmit a notifying signal, either, when an interference signal occurs. In the case of designating the beam direction, directing the beam toward the center of the network or toward the master terminal prevents terminals, which the beacon of the master terminal 610 does not reach, from receiving notifying signals. The notifying-signal transmission instruction information is transmitted from the master terminals 610 with a beacon or a data communication signal.
The terminal 612 which has received notifying-signal transmission instruction information performs notifying-signal transmission start processing (Step S608), in accordance with the contents of the notifying-signal transmission instruction information. If the notifying-signal transmission instruction information does not include a specific instruction as to the frequency band for transmitting a notifying signal, the slave terminal 612 performs a carrier sensing in the main band, and transmits a notifying signal in a band where no interference signals exist. Like the notifying signal transmitted by the master terminal, the notifying signal transmitted by the slave terminal 612 also includes information items necessary for receiving a beacon transmitted by the master terminal.
The master terminal 710 which has received a measuring packet from the slave terminal 711 performs notifying-signal transmitting terminal selection processing (Step S702), and determines whether the slave terminal 711 should be selected as a notifying-signal transmitting terminal. In this example, the master terminal 710 determines not to select the slave terminal 711 as the notifying-signal transmitting terminal, and takes no further actions. The master terminal 710 which has received the measuring packet from the slave terminal 712 performs notifying-signal transmitting terminal selection processing in the same manner (Step S704). Then, suppose that the master terminal 710 determines to select the slave terminal 712 as a notifying signal transmitting terminal. In this case, the master terminal 710 transmits notifying-signal transmission instruction information to the slave terminal 712 (Step S705), and the slave terminal 712 which has received the notifying signal transmission instruction information performs notifying-signal transmission start processing in accordance with the instruction (step S706). The notifying signal transmission instruction information also includes information as to whether notifying signals are simultaneously transmitted at different frequencies as illustrated in
First, sections of the radio communication terminal are explained in accordance with a reception operation. A radio frequency signal received by an antenna 812 is converted into a base band signal having a frequency bandwidth of the main band by an RF/IF processing section 801. The base band signal is converted into a digital signal by an ADC 802.
A power measurement processing section 803 is used for measuring the signal powers of signals from slave terminals, when the terminal operates as a master terminal. The powers of signals received from slave terminals are calculated by using, for example, RSSI (received-signal intensity) of the signal band. The timing of measurement is notified by a control processing section 806 when a network participation request is received from a slave terminal or a power measuring packet is received. Suppose that power measuring packets are periodically transmitted from slave terminals, and the control processing section 806 knows the period of transmission. The measured signal power is stored in a terminal category DB (DB: database) 811 through the control processing section 806.
A notifying-signal reception processing section 804 is used for receiving a notifying signal from the master terminal when the terminal operates as a slave terminal. The control section 806 is notified of data of a notifying signal obtained by the notifying-signal reception processing section 804, that is, data necessary for receiving a beacon from the master terminal, such as the frequency and timing of the beacon.
A data signal reception processing section 805 is used for receiving the notifying-signal transmission instruction information, when receiving transmission data from the master terminal or the slave terminals and receiving a beacon from the master terminal. When a beacon is received, the data signal reception processing section 805 receives information necessary for receiving a beacon from the control processing section 806. After receiving a beacon, the data signal reception processing section 805 notifies the control processing section 806 of information necessary for participating in the network and slot assignment information for data communications, which are included in the beacon. When transmission data is received from the master terminal or the slave terminal, the data signal reception processing section 805 receives the slot assignment information from the control processing section 806, and performs reception in accordance with the information.
Next, sections of the radio communication terminal are explained in accordance with a transmission operation.
A notifying-signal transmission processing section 809 prepares a notifying signal and transmits the notifying signal to a DAC 808, when the terminal operates as the master terminal. Beacon information to be superposed on the notifying signal is received from the control processing section 806.
A data signal transmission processing section 810 receives data from the control processing section 806, and performs data transmission to the master terminal or slave terminals, and beacon transmission. Signals output from the notifying-signal transmission processing section 809 and the data signal transmission processing section 810 are converted into analogue signals by the DAC 808, further converted into radio frequency signals by an RF/IF processing section 807, and then output from the antenna 812.
The control processing section 806 performs exchange of data with the high layer, and notifying-signal transmitting terminal determination processing, in addition to the above processing.
The terminal category database 811 stores information of the slave terminals in the network, when the radio communication terminal operates as the master terminal.
A signal input from the ADC 802 is frequency-converted by Δf in a complex multiplication processing section 901. Thereafter, the signal is complex-conjugated in a complex conjugate processing section 902, and a complex multiplication section 903 performs complex multiplication of the input signal from the ADC 802 and the complex-conjugated signal. Thereby, a phase differential vector of the two narrow-band signals 301 and 302 shown in
According to the above structure, slave terminals can receive a notifying signal, without knowing in which frequency band in the main band the notifying signal exists. Further, even when a plurality of terminals transmit notifying signals, the slave terminals can receive them without special processing, as long as the notifying signals have the same contents and the same Δf value. Therefore, the notifying-signal transmitting terminal can transmit a notifying signal at a desired frequency.
The master terminal has a database (terminal category database 811) storing information of slave terminals in the network. The terminal category database 811 stores information of reception power from the slave terminals, priorities of the slave terminals on serving as a notifying-signal transmitting terminal, and the notifying-signal transmitting terminal type.
The reception powers are ranked according to the intensity thereof. In this example, the reception powers are grouped under levels 1 to 5, and the terminals of level 5 have the strongest power. If the system is a system where terminals perform transmission power control, it is necessary to perform normalization using the transmission power of slave terminals.
The priority is an indicator indicating whether a slave terminal is suitable as a notifying-signal transmitting terminal. The priority is determined by the master terminal using a certain standard, or the slave terminals notify the master terminal of the priorities thereof. In this example, slave terminals are grouped under six levels, that is, Levels 0 to 5. Level 0 indicates terminals which cannot transmit a notifying signal, and level 5 indicates terminals which are most suitable as a notifying-signal transmitting terminal. An example of a slave terminal which is most suitable as a notifying-signal transmitting terminal is a terminal having a long power-supply duration. The priority depends on the time for which the terminal can continuously supply the power. For example, terminals which are connected to an AC power source and can be used without checking power consumption have a higher priority. Conversely, terminals which operate on batteries and have a little battery remaining amount gain a lower priority. Further, as a result of interference detection in the main band performed by the terminals, terminals suffering frequent interference gain a lower priority, and terminals in which interference is not detected for a long time in a frequency band in the main band gain a higher priority.
The notifying-signal transmission terminal type indicates how the notifying-signal transmitting terminal transmits a notifying signal. For example, terminals registered as “Freq” transmit a notifying signal simultaneously with a notifying signal of the master terminal, by using a frequency different from that of the master terminal as shown in
First, the master terminal measures the signal powers from the slave terminals (Step S1101). The signal power measurement may be performed by using network participation requests from the slave terminals, or using power measuring packets. Next, the master terminal updates the values of the terminal category database 811 in accordance with the measured signal powers (Step S1102). Using the update result, the master terminal selects N terminal(s) (N is an integer not smaller than 1) having a high reception power as notifying terminal 1 from terminals having a priority level 1 or larger level (Step S1103). Specifically, the master terminal selects at least one terminal close to the master terminal. The notifying terminal 1 is a terminal which transmits a notifying signal in a time-division method with a notifying signal of the master terminal, in consideration of the cases where the master terminal cannot transmit a notifying signal during a reception operation. If terminals exceeding N exist in the category of the same reception power, a terminal having a higher priority is selected.
Further, using the update result, the master terminal selects M terminal(s) (M is an integer not smaller than 1) having a lower reception power as notifying terminal 2 from terminals having a priority level 1 or larger level (Step S1104). Specifically, the master terminal selects at least one terminal distant from the master terminal. The notifying terminal 2 is a terminal which transmits a notifying signal simultaneously with a notifying signal of the master terminal by using a frequency different from that of the master terminal, in preparation for the cases where the master terminal cannot transmit a notifying signal due to interference signals. If terminals exceeding M exist in the category of the same reception power, a terminal having a higher priority is selected. Lastly, when there is any change in the section of the notifying terminal in the database, the master terminal notifies the relevant notifying terminals of the notifying-signal transmission instruction information or notifying-signal stop instruction information (Step S1105).
It is specifically explained below how the database and the notifying-signal transmitting terminals are changed in the terminal arrangement illustrated in
Suppose that the master terminal has the terminal category database 811 illustrated in
As illustrated in
First, sections are explained in accordance with reception operation. Although four antennas are illustrated in
Radio frequency signals received by the antenna 812 are converted into base band signals having a frequency bandwidth of the main band by RF/IF processing sections 801. The base band signals are converted into digital signals by the ADCs 802.
An antenna directivity processing section 1401 rotates the phases of the received signals and adds the received signals in accordance with instructions from a control processing section 1402, and thereby outputs a received signal having an antenna directivity in accordance with the instructions. A power measurement processing section 803 is used for measuring signal power from slave terminals when the radio communication terminal operates as the master terminal. The powers of signals received from slave terminals are calculated by using, for example, RSSI of the signal band. The timing of measurement is notified by a control processing section 1402 when a network participation request is received from a slave terminal or a power measuring packet is received. Suppose that power measuring packets are periodically transmitted from slave terminals, and the control processing section 1402 is notified in advance of the period of transmission. The measured signal powers are stored in a terminal category DB 1403 through the control processing section 1402.
A notifying-signal reception processing section 804 is used for receiving a notifying signal from the master terminal when the terminal operates as a slave terminal. The control section 1402 is notified of data of a notifying signal obtained by the notifying-signal reception processing section 804, that is, data necessary for receiving a beacon from the master terminal, such as the frequency and timing of the beacon. When the notifying-signal reception processing section 804 performs notifying-signal reception processing, the antenna directivity processing section 1401 is preferably controlled to be omnidirectional.
A data signal reception processing section 805 is used when receiving transmission data from the master terminal or the slave terminals and receiving a beacon from the master terminal. When a beacon is received, the data signal reception processing section 805 receives information necessary for receiving a beacon from the control processing section 1402. After receiving a beacon, the data signal reception processing section 805 notifies the control processing section 1402 of information necessary for participating in the network and slot assignment information for data communications, which are included in the beacon. When transmission data is received from the master terminal or the slave terminal, the data signal reception processing section 805 receives the slot assignment information from the control processing section 1402, and performs reception in accordance with the information.
Next, sections of the radio communication terminal are explained in accordance with a transmission operation. A notifying-signal transmission processing section 809 prepares a notifying signal and transmits the notifying signal to an antenna directivity processing section 1404, when the terminal operates as the master terminal. Beacon information to be superposed on the notifying signal is received by the notifying-signal transmission processing section 809 from the control processing section 1402. A data signal transmission processing section 810 receives data from the control processing section 1402, and performs data transmission to the master terminal or slave terminals, and beacon transmission. Signals output from the notifying-signal transmission processing section 809 and the data signal transmission processing section 810 are input to the antenna directivity processing section 1404.
The antenna directivity processing section 1404 rotates phases of signals and outputs the signals to DACs 808 corresponding to the respective antennas, in accordance with instructions from the control processing section 1402. For example, in notifying-signal transmission processing, if a notifying signal is transmitted in a time-division method with the notifying signal of the master terminal, it is preferable to perform omnidirectional transmission with no directivity, in consideration of the cases where the master terminal cannot transmit a notifying signal during reception operation. Further, if a notifying signal is transmitted simultaneously with the notifying signal of the master terminal in preparation for the cases where the master terminal cannot transmit a notifying signal due to interference signals, it is preferable to form a beam toward the center of the network or toward the master terminal. Such a structure prevents an unnecessary increase in the size of the network, and improves the throughput of the system. Directivity parameters may be instructed by the master terminal, or determined by the notifying-signal transmitting terminal by estimating the incoming direction of the beacon and recognizing the direction of the master terminal with use of the incoming direction estimate technique. The signals output from the antenna directivity processing section 1404 are converted into analogue signals by the DAC 808, further converted into radio frequency signals by the RF/IF processing sections 807, and then output from the antennas 812.
Although antenna patterns are formed by digital signal processing in the embodiment of
The control processing section 1402 performs exchange of data with the high layer, notifying-signal transmitting terminal determination processing, and determines the antenna directivity, in addition to the above processing. The terminal category database 1403 stores information of the slave terminals in the network, when the radio communication terminal operates as the master terminal.
The master terminal has the terminal category database 1403 storing information of slave terminals in the network. The terminal category database 1403 stores information of reception powers from the slave terminals, priorities of the slave terminals on serving as a notifying-signal transmitting terminal, the type of the notifying-signal transmitting terminal, and classified antenna pattern groups. The reception powers are ranked according to the intensity thereof. The reception powers for the respective antenna patterns are stored for each terminal in the database. In this example, the reception powers are grouped under levels 1 to 5, and the terminals of level 5 have the strongest power. If the system is a system where terminals perform transmission power control, it is necessary to perform normalization using transmission powers of slave terminals. The priority is an indicator indicating whether a slave terminal is suitable as a notifying-signal transmitting terminal. The priority is determined by the master terminal using a certain standard, or the slave terminals notify the master terminal of the priorities thereof. In this example, slave terminals are grouped under six levels, that is, Levels 0 to 5. Level 0 indicates terminals which cannot transmit a notifying signal, and level 5 indicates terminals which are most suitable as a notifying-signal transmitting terminal. An example of a slave terminal which is most suitable as a notifying-signal transmitting terminal is a terminal having a long power supply duration. For example, terminals which are connected to an AC power source and can be used without checking power consumption have a higher priority, and terminals which operate on batteries and have a little battery remaining amount gain a lower priority. Further, as a result of interference detection in the main band performed by the terminals, terminals suffering frequent interference gain a lower priority, and terminals in which interference is not detected for a long time in a frequency band in the main band gain a higher priority. The notifying-signal transmission terminal type indicates how the notifying-signal transmitting terminal transmits a notifying signal. For example, terminals registered as “Freq” transmit a notifying signal simultaneously with a notifying signal of the master terminal, by using a frequency different from that of the master terminal as shown in
First, before measuring the signal powers from the slave terminals, the master terminal forms one of the antenna patterns which the master terminal has (Step S1601). If the master terminal measures the signal power from slave terminals by using a network participation request signal, the master terminal forms an antenna pattern when a signal such as a postamble following a network participation request is transmitted, for example. If the master terminal periodically performs measurement, the master terminal forms an antenna pattern when receiving a power-measuring packet transmitted from the slave terminals. After forming an antenna pattern, the master terminal receives signal powers from the slave terminals (Step S1101). The signal power measurement may be performed by using network participation request signals from the slave terminals, or using power-measuring packets. Next, the master terminal updates the terminal category database 1403 by using values of the measured signal powers, in accordance with the antenna pattern (Step S1102). The above steps are performed for all the antenna patterns (Step S1602). For example, in the database of
When measurement of the power is finished for all the antenna patterns (Yes of Step S1602), the master terminal performs grouping of the terminals according to the antenna patterns (Step S1603), by using the database update result. First, the master terminal finds a terminal whose signal power greatly decreases only in a specific antenna pattern. The master terminal determines that the terminal exists in the direction of null in the relevant antenna pattern. In determining whether the signal power greatly decreases, when there is a pattern in which the relevant terminal has a signal power lower by at least 20 dB than an average signal power of the terminal for all the patterns, it is determined that the terminal exists in the direction of the null of the pattern. When a terminal has a similar signal power on average for each of the patterns, the terminal does not belong to any antenna pattern groups. By using the above method, the master terminal classifies all the terminals.
The master terminal selects N terminal(s) having a higher reception power as the notifying terminal 1 from terminals having a priority of level 1 or larger level in all the pattern groups (Step S1604). The notifying terminal 1 is as defined above. Thereafter, the master terminal selects M terminal(s) having a lower reception power as the notifying terminal 2 from terminals having a priority of level 1 or larger level for each of the pattern groups (Step S1605). The notifying terminal 2 is as defined above. Lastly, if there is any change in the notifying terminal section of the database, the master terminal notifies the relevant terminals of notifying-signal transmission instruction information, or notifying-signal stop instruction information (Step S1105). Although the priority levels in the steps S1604 and 1605 are set to level 1 or larger level, they are not limited to level 1, but may be set to desired levels according to necessity.
Suppose that the master terminal has the database with the contents illustrated in
After grouping, the master terminal determines the notifying-signal transmitting terminal. In the conditions illustrated in
In this example, the positions of the terminals are estimated and the terminals are grouped by using the antenna patterns. However, for example, the following structure may be adopted: terminals are provided with GPS, and notify the master terminal of the position information of the terminals, and the master terminal stores the GPS position information in the database in association with the terminal information. In this case, terminals close to each other may be classified as one group, and a synchronizing signal notifying terminal may be selected from the group.
According to the above embodiment, even when the master terminal is in reception operation and cannot transmit a notifying signal, a terminal with a demand for participation in the network can easily participate in the network by using a notifying signal from the notifying-signal transmitting terminal.
Further, since notifying signals are transmitted from a plurality of terminals by using different frequencies, terminals with a demand for participation in the network can easily participate in the network, by virtue of the antenna diversity effect and frequency diversity effect. Since terminals with a demand for participation in the network can easily participate in the network, an undesirable increase of the master terminals is prevented, and the system throughput of the network is increased.
Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.
Number | Date | Country | Kind |
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2006-350008 | Dec 2006 | JP | national |