Patent Application
20080037665
The present invention can be appreciated by the description which follows in conjunction with the following figures, wherein:
The embodiments of this invention will be described below with reference to drawings. It should be noted, however, that the embodiments described below are merely examples of embodying this invention. The methods of embodying this invention are not limited to the contents disclosed in the present specification.
As shown in
The wireless communication apparatus described in the First Embodiment includes a receiving antenna 50, a transmitting antenna 60, a detecting unit (DET) 100, a judging unit (JUDG) 110, a transmitting unit (UWB-TX) 120 and a receiving unit (UWB-RX) 130. Incidentally, the transmitting antenna 50 and the receiving antenna 60 may share a single antenna as described further below (refer to
In response to any request for transmission, the detecting unit 100 detects the signals of the wireless communication system in the desired transmission band to avoid any interference with other wireless communication systems. The judging unit 110 compares the level of received signals detected by the detecting unit 100 and the threshold value set in advance to judge whether the signals whose transmission has been requested should be transmitted. The transmitting unit 120 generates radio signals limited to the desired radio band. The transmitting unit 130 receives the UWB signals transmitted from other wireless communication apparatuses to demodulate the data. The demodulation system that depends on the modulation system is realized with a similar configuration as that of ordinary receiver.
In response to any request for transmission, the detecting unit 100 detects any signals detectable in the desired transmission band (for example band 15) to avoid any interference with other wireless communication systems. The level of the detected radio signals is inputted into the judging unit 110 as a function of frequency. Based on the criteria of judgment described further below, the judging unit 110 compares the inputted signal level information with the threshold value set in advance to judge whether the signal should be transmitted or not. In other words, the judgment of the judging unit 110 determines whether the signal should be transmitted or not.
If the signal is not to be transmitted, the transmission process is terminated, and the system prepares for the subsequent request for transmission. For example, if the signal that has been transmitted from another system and received is greater than the level set by the legal regulation and the like and the band of the detected signal is avoided, and as a result if this system cannot transmit the signal, the signal is not transmitted.
On the other hand, if the signal is to be transmitted, the judging unit 110 sets the transmission method (center frequency, bandwidth, pulse waveform, modulation, pulse repetition frequency (PRF) and the like) and transmits the transmission method information to the transmitting unit 120. Based on the information received from the judging unit 110, the transmitting unit 120 generates transmission signals 30, outputs the signals into the space through the antenna 130 and ends the transmission process.
What is important here is the judgment criteria of the judging unit 110 and the transmission method, which will be described below respectively.
An example of detailed configuration of the wireless communication apparatus according to the first embodiment will be described below with reference to the block diagram shown in
The wireless communication apparatus described in the first embodiment comprises a detecting unit 100, a judging unit 110, a transmitting unit 120, a receiving unit 130, an antenna 1050, a band pass filter (BPF) 1055 and an antenna switch 1060.
The detecting unit 100 includes a low pass filter (LPF) 203, a variable gain amplifier 204 and a received signal strength indicator (RSSI) 205. Incidentally, the configuration of the detecting unit 100 is not limited to the one shown in the figure. As described above, in response to any request for transmission, the detecting unit 100 detects the signals of wireless communication systems in the desired transmission band (in the bandwidth 15 of the UWB signals 10 that can be transmitted by wireless communication apparatuses) to avoid any interference with other wireless communication systems.
The signals inputted into the detecting unit 100 are filtered by the low pass filter 203 and signals in the band of approximately 10 MHz are extracted. And the filtered signals are amplified to a desired level by the variable gain amplifier 204.
The amplified signals are inputted into the received signal strength indicator 205. The received signal strength indicator 205 includes half wave rectification circuits wherein diodes are used and outputs DC signals of a level corresponding to the strength of the received field. As for the configuration of the received signal strength indicator 205, various known technologies can be applied.
Another example of configuration of the received signal strength indicator 205 is shown in the second embodiment (
For the signal detection algorithm of this detecting unit 100, the following algorithm may be applied.
(2) Detect all the interference avoiding waves in the band in which the wireless communication apparatus can output. This will enable to expand the transmission band to the maximum.
(3) Detect signals based on the band of the interference avoiding system and the power calculated in the band. This will enable to simplify the frequency and procedure of detection and to detect signals. This method is effective if the interference avoiding system is known.
The judging unit 110 includes a microcomputer and controls the operation of each operating unit of the wireless communication apparatus. The microcomputer includes a processor, a ROM and a RAM.
The ROM stores programs executed by the processor. According to the present embodiment, the ROM stores the program that provides a judging algorithm of transmission methods and the parameters required by the judging algorithm. The processor executes the programs stored in the ROM. The RAM provides a work area for the execution of programs by the processor.
The criteria of judgment of the transmission method in the judging unit 110 include (1) legal regulation, (2) standardization requirement, (3) system performance, (4) performance of transmitter and receiver, (5) necessity of communication and the like.
With regard to (1) the legal regulation, as described above, when it is judged that the output of wireless communication apparatuses must be regulated by legal provisions, the output of radio signals will be regulated in accordance with legal regulations.
With regard to (2) the standardization regulation, for example, if the wireless communication apparatus is a system based on the IEEE 802.15.4a which is a US wireless PAN (Personal Area Network) standard, radio signals will be transmitted according to the band and the modulation based on the standardization requirement.
With regard to (3) the system performance, for example, if a high precision positioning is required for nodes, the wider the band of the signal is on the frequency axis, the narrower each pulse gets on the time axis. Therefore, when signals cannot be transmitted by a desired bandwidth, the best effort type signals will be transmitted meaning that signals will be transmitted by the widest band possible while avoiding interference. Or, signals will be transmitted in another band in which there is no restriction of transmission (in Japan, 7.25 GHz to 10.25 GHz).
And, if a UWB system is the positioning system, the precision of the positioning result can be improved to a value close to the desired precision by staggering the transmission timing so as to allow the transmitter to send the desired bandwidth, by positioning a number of times and the like.
In addition, as the wider the transmission frequency width expands the stronger the output power gets, the transmission method can be judged from the viewpoint of communication performance. For example, interference can be avoided by using a plurality of channels at the same time. In this case, however, a receiving system must be provided for each channel and this result in a larger circuit scale and increased power consumption.
In particular, since the UWB wireless communication system according to this invention has a bandwidth of 500 MHz or more, interference can be easily avoided by creating a plurality of 10 MHz channels (e.g., 100 channels). However, the provision of transmitting/receiving systems for 100 channels is not realistic.
Moreover, regarding the precision of distance measurement and the precision of positioning, in the case of transmitting signals by a plurality of channels of a narrow bandwidth, the precision of distance measurement and that of positioning based on transmission pulse width fall sharply as compared with the case of transmitting signals by a single wide band channel.
With regard to (4) the characteristics of the transmitter and receiver, when the configuration of the transmitter and the receiver is restricted (e.g., in the case where the transmitter can generate transmission signals only in a band of 4.2 GHz to 4.8 GHz among the available frequency band of UWB (3.4 GHz to 4.8 GHz), if signals transmitted from other wireless communication systems are present in the band, the transmitter cannot transmit UWB signals in the band.
And even if the transmitter can transmit signals of all the frequencies of the available frequency bands, if the receiver can receive only signals in some of the frequency bands (e.g., 3.4 GHz to 4.0 GHz), the signals transmitted in the band of 4.2 GHz to 4.8 GHz cannot be received. In such a case, the performance of the receiver on the receiving side will be the criteria of judgment. It would be advantageous to make an arrangement in advance to provide each wireless communication apparatus (terminal and base station) with the performance information of these transmitters and receivers.
With regard to (5) the necessity of communication, the issue is a case that can be found in the sensor net system and the like. For example, in the temperature monitoring system and the like wherein measurement data are transmitted every five minutes, it is not always necessary to transmit data every five minutes, and in a situation where interference is concerned, the data to be transmitted are stored in the memory of a transmission node, and such data may be transmitted together with the previous data at the time of the subsequent transmission.
As for other methods (6), the transmission method can be judged based on the communication performance required by the wireless communication apparatus on the transmitting side and the communication performance required by the wireless communication apparatus on the receiving side (number of retransmissions, bit error ratio, and the like), type of transmission packet (data or acknowledgement and the like), and the contents of data to be transmitted.
Or, narrow band signals may be transmitted if the amount of transmission data exceeds the storage capacity allowed by the memory by the application of such an algorithm. Or, signals may be transmitted in the band originally set by changing the value set as the threshold value for judgment. At this time, the transmission power is reduced to reduce any interference that may be exerted to other wireless communication systems and the decrease in the transmission power is compensated by powerful error correction in the data.
As described above, in response to the configuration of the transmitter and the receiver and the requirements of application from the viewpoint of system, various algorithms may be implemented. The judging unit 110 can judge by storing the various judging methods and criteria of judgment mentioned above in advance in the storage medium of the wireless communication apparatus.
The transmitting unit 120 includes a base band unit (modulation) 702, a radio frequency pulse generator (PG) 704 and a power amplifier (PA) 706. The configuration of the transmitting unit 120 includes a phase locked loop, a mixer and the like that generates pulses by an analog circuits, a direct digital synthesizer and the like that uses a digital circuit operating at a high speed and the like, and there are a variety of methods for limiting the band of this invention and that of setting the center frequency.
We will now describe the transmitting unit of the wireless communication apparatus according to the first embodiment with reference to the block diagram shown in
The transmitting unit 120 includes a base band pulse generator (BBPG) 500, a local oscillator 201, a mixer 202, a power amplifier (PA) 503, switches 504 and 507, and band pass filters 505 and 506 that allow fixed band signals to pass.
The base band pulse generating unit 500 generates pulse signals in the base band (e.g., Gaussian pulse having a bandwidth of 1.4 GHz). Then, the mixer 202 mixes the pulse signal of the base band with the radio frequency carrier signal outputted by the local oscillator 201 and converts the frequency of the base band signal to a desired radio frequency band. The power amplifier 503, amplifies the pulse signals thus converted to a radio frequency band (radio frequency pulse signal) to a desired level. The amplified radio frequency pulse signal is inputted into the switch 504.
The switches 504 and 507 operate being interlinked with the control signals 510 received from the judging unit 110 and switch the band pass filters 505 and 506 connecting the output of the power amplifier 503 and the transmission antenna 60. For example, the filter 505 is a band pass filter whose center frequency is the same as the output frequency of the oscillator and having a bandwidth of 1.4 GHz and is used mainly for the elimination of spurious. The filter 506 is a band pass filter whose center frequency is the same as the output frequency of the transmitter and allows signals of a bandwidth of 0.5 GHz to pass through. The control signal 510 outputted from the judging unit is a signal to be connected with the filter for realizing the desired bandwidth.
For example, to transmit a signal with a bandwidth of 0.5 GHz, the output of the power amplifier 503 is connected with the filter 506. The filter 506 limits the band of the 1.4 GHz wide bandwidth signals 551 outputted from the power amplifier to that of the 0.5 GHz band signal. The radio frequency pulse signal 553 whose band has been limited (see
Incidentally, the radio frequency pulse signals 552 shown in
By the control described above, the band of the signals can be limited to a desired bandwidth and their interference to other systems can be reduced. And the band limitation method shown in the present embodiment makes it difficult to limit the band of signals to a desired band in data duplication methods for each frequency of the sub-carrier by a multi-carrier such as OFDM and the like because data are lost due to the band restriction. In other words, the present embodiment is a mode that can be carried out by the UWB-IR system.
And although the present embodiment showed a configuration based on two types of filter each having a separate fixed bandwidth, it is possible to change dynamically the characteristics of bandwidth by adopting a single adaptive filter or a plurality of them. In the case where a single adaptive filter is used for its configuration, the switches 504 and 507 are no longer required, and the control signals 510 outputted by the judging unit are directly inputted into the adaptive filter.
Moreover, a desired band limiting system may be implemented by combining a plurality of band pass filters, low pass filters and band elimination filters having different center frequency or bandwidth or combining them with the frequency characteristics of the antenna.
The transmission waveforms 30 outputted from the antenna 60 are selected by the configuration of the above-mentioned transmitting unit or the configuration of the transmitting unit of the embodiment described further below. In other words, predominant signals from the viewpoint of the system are selected from among the signals outputted by the antenna 60 according to the criteria of judgment described above. An example thereof is the selection of signals 30 to be transmitted of the widest possible band among the signals whose interference to other systems may be reduced sufficiently in the band 20 in which interference should be avoided as shown in
The receiving unit 130 includes a low noise amplifier (LNA) 1070, a local oscillator 1071, mixers 1072 and 1073, a switch 1074, low pass filters (LPF) 1075 and 1076, variable gain amplifiers 1077 and 1078, an analog to digital converters (ADC) 1079 and 1080, and a base band unit (demodulation) 1081.
The antenna 1050 receives the UWB signals (desired signals) of this wireless communication system and the radio signals (interference signals) of other wireless communication systems. Then, the radio signals received by the antenna 1050 are subjected to the filtration of unwanted signals by the band pass filter 1055. Then the filtered radio signals are inputted into the receiving unit 130 through an antenna switch 1060. Incidentally, a circulator or a duplexer may be used in the place of the antenna switch.
The receiving unit 130 inputs the signals inputted from the antenna switch 1060 into the low noise amplifier 1070, which amplifies the signals to a desired level. Then, the mixers 1072 and 1073 mix the signals received with the output of the local oscillator, and convert the frequency of the received signals directly into that of the base band signals. The base band unit 1081 proceeds to a quadrature detection of I/Q signals of the base band whose frequency has been converted to demodulate the data.
We will then describe the operation of each of the units described above.
At the time of data transmission, when the detecting unit 100 completes the detection process described above, the judging unit 110 judges the frequency band that the judging unit 110 should transmit and transmits band control signals 1210 to the radio frequency pulse generator 704. By this process, the frequency and the bandwidth of the signals transmitted from a wireless communication apparatus are controlled. For example, sensor data (e.g., temperature and/or humidity) are inputted into the base band unit 702, spread and demodulated in the base band unit 702. Then, the radio frequency generator 704 generates radio frequency pulse signals whose band is limited. The generated pulse signals are amplified to a desired power level by the power amplifier 706 and are irradiated into the space after passing through the antenna switch 1060, the band pass filter 1050 and the antenna 1050.
At this time, depending on the system, the judging unit 110 may change the setting of the receiving unit 130 by the action of the center frequency control signal 1200 and the bandwidth control signal 1210 in order to receive efficiently signals in the transmission frequency band.
After the transmission of sensor data, the wireless communication apparatus of the communication partner (e.g., base station and the like) sends back an acknowledgment signal (ACK signal). It is highly probable that the ACK signals transmitted from other wireless communication apparatuses have the frequency and bandwidth of signals outputted by the transmitting unit 120. Therefore, the transmitting unit 130 can receive efficiently signals by remaining on standby in the frequency and the bandwidth of the transmission signal in advance.
In other words, the ACK signals received are inputted from the antenna 1050, and after passing through the band pass filter 1055, the antenna switch 1060, the low noise amplifier 107 and the I/Q mixers 1072 and 1073, the low pass filters 1075 and 1076, the variable gain amplifiers 1077 and 1078, and the analog to digital converters 1079 and 1080, are demodulated at the base band unit 1081.
The demodulated data are processed so that the contents of the data may be judged. And after a retransmission process if necessary, the transmitting unit 120, the receiving unit 130 and the like are shifted to the specified state (e.g., standby mode). Incidentally, after the transmission of the signal, the wireless communication apparatus is reset in the receiving mode, and the switch 1074 is connected with the receiving side (low pass filter 1075 side).
If it is necessary to detect the signals transmitted by this system and other systems before the transmission of the signals and the like, the switch 1074 is connected with the detecting unit 100 side to operate the detecting unit 100. And the detecting unit 100 detects the signals receivable within the desired transmission band and sends the level of the detected radio signals to the judging unit 110. It is possible to change the frequency of the signals detected by the detecting unit 100 by sending the center frequency control signal 1200 from the judging unit 110 to the local oscillator 1071.
It is possible to show the distribution of power 1800 inputted from the antenna 1050 by the frequency axis from the output frequency of the transmitter 1071 by the center frequency control signal 1200 and the voltage value outputted from the detecting unit 100. Incidentally, the threshold value indicating the power level serving as the reference for judgment should be set in advance based on the performance of the receiving unit 130 and that of the detecting unit 100.
We will then describe the operation of the wireless communication apparatus according to the first embodiment with reference to the flowchart shown in
To begin with, the judging unit 110, at the outset of its transmission operation, pulls the trigger on various units of the wireless communication apparatus (S101). For example, a signal from a timer set to generate at a certain interval can be the trigger.
Then the detecting unit 100 detects the incoming radio signals in the band in which the wireless communication apparatus can transmit. At this time, it monitors the radio signal by measuring a number of continuous or discrete points in the band in which the wireless communication apparatus can transmit signals (S102).
Then, the judging unit 110[i1] judges the band in which signals can be transmitted without this system causing interference with other systems by comparing the same with the threshold value set in advance. And as a result of comparison between the judged transmittable band and the bandwidth in which the recipient base station can receive the signals, the judging unit 110[i2] determines the band in which both of them overlap as “the band available for communications while avoiding any active interferences” (S103).
Then, the judging unit 110 judges whether it is possible to secure the bandwidth required for communication within the specified “band available for communication while avoiding any active interference” or not (S104). For example, as the UWB system according to the present embodiment requires a bandwidth of 500 MHz or above, the judging unit 110 confirms whether a bandwidth of 500 MHz or above can be secured in “the band available for communication while avoiding any active interference.”
If the necessary band cannot be secured as a result of the determination, the wireless communication apparatus refrains from transmitting the data, and stores the data to be transmitted in the memory (e.g., temperature data obtained by measuring with a sensor) to transmit at the following transmission timing (S105) and completes the processing.
On the other hand, if the necessary band can be secured as a result of judgment in S104, center frequency, bandwidth, modulation method, and pulse repetition frequency (PRF) are set based on the judgment of the judging unit 110 (S106). Then, the transmitting unit 120 generates the desired signal based on the set information, transmits the generated signals from the antenna 60 (S107) and completes the processing.
Let us consider for example the case wherein the frequency band available for transmission by this wireless communication system is 3.4 GHz to 4.8 GHz, and in the step S102 the detecting unit 100 has detected strong signals in the neighborhood of 4.0 GHz.
For example, in a wireless communication apparatus wherein the detecting unit 100 detects signals by a resolution width of 1 MHz, a frequency band in which this system can transmit signals is reconstituted so that signals transmitted by other systems detected in the vicinity of 4.0 GHz may be avoided by securing a resolution margin of 1 MHz in the face of frequencies exceeding the set threshold value (or same as the threshold value). Then, this system sets “a band available for communication while avoiding any active interference” by comparing the band with frequency band in which the recipient receiver can receive data. And the transmitter 120 generates transmission waveforms within the frequency band and transmits the same through the antenna 60.
We will then describe variations of the process shown in
According to the flowchart shown in
This variation can be realized by replacing the step S104 of the flowchart shown in
In this variation, in the step S104, the band required for communication cannot be secured, and the data for transmission are stored in the memory (S105). Then, the number of failures to communicate and the prescribed threshold value (number of times) are compared (S108) by referring the number of data stored in the memory.
If, as a result of such comparison, the number of failures to communicate is below the prescribed threshold value, the process is terminated. On the other hand, if the number of failures to communicate exceeds the prescribed threshold value, the threshold value is changed (S109) and the process returns to the step S104.
Regarding this change of threshold value, as shown in
For example, in the case where a change is desired from the threshold value (1) to the threshold value (2), it is possible to realize the change by changing the setting specifying the gain of the power amplifier 706 by the control signal 1210 shown in
If there are a number of bands available for transmission of signals by this system while avoiding any interference, the band for transmission in response to the requirement of the system is selected. For example, (1) transmit in the same condition as the previous transmission mode, (2) transmit in the lowest frequency band among the available bands, (3) transmit in the band of the widest bandwidth among the available bands, (4) transmit in the narrowest bandwidth among the bands in which the desired communication performance or positioning performance can be obtained, and the like. As the center frequency, bandwidth, power consumption, communication performance or positioning performance, and ease to use of the system are mutually interrelated for the signal to be transmitted, it is preferable to choose the optimum method according to its application and environment among various transmission modes described above.
We will describe the specific examples of transmission mode with reference to
To begin with, the question of whether high precision positioning is necessary or not is judged (S111). And if the high precision positioning is necessary, the process proceeds to the step S112. On the other hand, if the high precision positioning is not necessary, the process advances to the step S116.
In the step S112, the question of whether a bandwidth satisfying the required positioning precision can be secured or not is judged. If, as a result thereof, it is judged that the desired bandwidth can be secured, the frequency at which the bandwidth can be secured is selected (S113). Then, the transmission method (the center frequency, bandwidth, modulation method and pulse repetition frequency) is set at the selected bandwidth and frequency (S119), and the process advances to the step S107.
More specifically, if a high precision positioning with an error of 60 cm is required upon the demand of the application side of this wireless communication system, the process advances from the step S111 to the step S112. At the step S112, the question of whether the bandwidth (1.0 GHz) necessary to obtain a positioning precision of 60 cm can be secured or not is judged. As positioning precision and frequency band depend on the performance of the receiver and the positioning algorithm, as mentioned above, these relationships should be set in advance.
On the other hand, if it is judged that the necessary bandwidth cannot be secured in the step S112, the system waits for the prescribed time (e.g., one minute) until the necessary bandwidth (e.g., 1.0 GHz) can be secured. If the necessary bandwidth can be secured during that time, the process advances to the step S113. On the other hand, if the necessary bandwidth cannot be secured even after waiting for the prescribed time, the signal with the maximum bandwidth that can be transmitted within the band available for communication is selected (S115). At this time, upon the request from the application, the positioning precision may be improved by transmitting positioning signals several times. The standby time, bandwidth and number of transmissions should be set in advance. And parameters may be optimized by feeding back the results of actual positioning.
Then, the transmission method (the center frequency, bandwidth, modulation method and pulse repetition frequency) is set by the chosen bandwidth and frequency (S119), and the process proceeds to the step S107.
Then, we will describe the step to be taken when it is determined that no high precision positioning is required in the step S111.
In the step S116, the question of whether the current communication can be established by the same conditions as the previous communication band (center frequency and bandwidth) or not is determined (S116). As a result, if the bandwidth can be secured by the same conditions as the previous communication bandwidth, the same communication band as the previous one is chosen (S117), and the transmission method is set by the chosen bandwidth and frequency (S119) and the process proceeds to the step S107.
On the other hand, if the bandwidth cannot be secured by the same conditions as the previous communication band in the step S116, the communication band is chosen according to the demand of the application (S118). For example, the lowest center frequency may be chosen, or the widest bandwidth may be chosen and so forth.
We will then describe by what procedure the transmission modes described in (1) through (4) above are chosen with reference to the flowchart described in
(1) In the case of transmission by the same condition as the previous transmission mode.
When the process proceeds in the order of S111, S116, S117 and S119, signals can be transmitted by the same conditions as the previous transmission mode. As this configuration eliminates the necessity of resetting the transmission conditions in the transmitter, and as the recipient's receiver receives signals by the same configuration as in the previous time, it is possible to receive signals in the optimum condition and to synchronize easily with the received signals. In addition, the power consumption of the wireless communication system is reduced.
(2) In the case of transmission by the lowest frequency band among the available bands.
When the process proceeds in the order of S111, S116, S118, and S119, it is possible to transmit signals by the lowest frequency band among the available bands. It is possible to limit the transmission loss in the space to the minimum and to improve the reliability of communication by communicating in the lowest frequency band. This enables to reduce the number of retransmission and the power consumption of the wireless communication system.
(3) In the case of transmission by the widest bandwidth band among the available bands.
When the process proceeds in the order of S111, S112, S113, or S119 or S111, S116, S118 and S119, it is possible to transmit signals in the widest bandwidth band among the available bands. Bandwidth and positioning precision are inversely proportional to each other, and bandwidth and transmission speed are proportional to each other. Therefore, it is possible to improve positioning precision and communication speed by transmitting signals in the widest bandwidth band.
(4) In the case of transmission in the narrowest bandwidth among the bands wherein the desired communication performance or positioning performance can be obtained.
When the process proceeds in the order of S111, S116, S118, and S119, it is possible to transmit signals in the narrowest bandwidth among the bands in which the desired communication performance or positioning performance can be obtained. Since receiving power can be reduced so much more as bandwidth gets narrower, under the condition wherein the desired communication performance or positioning performance can be obtained, the narrower the bandwidth gets, the more desirable it becomes. And as the bandwidth occupied by this wireless communication system is narrow in this case, it can easily coexist with other wireless communication systems.
In view of this phenomenon, as the power consumption of the receiver decreases and the use efficiency of frequency improves, an improvement in the overall efficiency of the system can be expected. The relationship between these desired communication performance and positioning performance on one hand and the center frequency and bandwidth on the other hand should be set in advance by verifications based on simulation and actual measurements and the like. Or the relationship between the performances and the communication modes may be renewed by including the number of retransmissions and packet error ratio and other data constituting the indicator of communication performance in the packets during the operation of the system and by referring these data.
As described above, according to the first embodiment, it is possible to reduce the impacts of the UWB system on the other systems. And it is possible to reduce any deterioration in the performance of the UWB system due to the interference of other systems. In addition, it is possible to reduce power consumption and improve communication performance by controlling the receiving unit to the optimum condition.
We will then examine quantitatively the effect of reducing this interference amount. For example, let us assume the next generation portable phone system (the fourth generation mobile communication system) as another system to which the UWB system produces impacts. Although the specification of the fourth generation mobile communication system is uncertain, according to “Report (draft) of the UWB Radio System Committee” (issued by Japan Ministry of Internal Affaires and Communication), if 1000 or more UWB devices per km2 are used, noise level exceeds the allowable reception level of mobile stations at the rate of 30%. Therefore, the application of this invention enables to reduce the interference of the UWB system with the fourth generation mobile communication systems. For example, the reduction of EIRP to −70 dBm/MHz alone results in a decrease in the probability of noise level exceeding the allowable value to 0.5% or less, and in a sharp diminution of the interference amount of UWB devices.
The detecting unit 100 comprises a local oscillator 201, a mixer 202, a low pass filter (LPF) 203, a variable gain amplifier 204 and a received signal strength indicator (RSSI) 205.
The receiving signals from the antenna 1050 are inputted into the mixer 202 through the low noise amplifier 1070. The mixer 202 can convert the received signals into low frequency signals by mixing the oscillation frequency of the oscillator 201 and the received signals. This enables to mitigate the specification of the circuits subsequent to the mixer 202.
The signals outputted from the mixer 202 are inputted into the low pass filter 203. The low pass filter 203 shuts off sharply the signals from the mixer 202 within the band. The signals having passed through the low pass filter 203 are amplified by the variable gain amplifier 204 to a desired level and are inputted the received signal strength indicator 205. The received signal strength indicator 205 is a circuit for outputting the voltage value of signals from the variable gain amplifier 204.
According to the second embodiment, the receiving frequency converted into power value changes by scanning the oscillation frequency of the oscillator 201 with the control signal 210 from the judging unit 110. The judging unit 110 can obtain the distribution of power received by the antenna 1050 as the function of frequency based on the receiving signal strength outputted by the received signal strength indicator 205 and the control signal 210. As the establishment of the oscillator 201 independently from the detecting unit 100 results in the independent specification of the detecting unit 100 from that of the oscillator of the receiving unit 130, the circuit scale expands but the difficulty of designing can be remarkably reduced.
With regard to the oscillator 201 and the mixer 202 according to the second embodiment, as shown in
The transmitting unit 120 according to the third embodiment includes a counter (COUNT) 601, a storage unit (ROM) 602, a digital to analog converter (DAC) 603, a low pass filter (LPF) 604 and a power amplifier (PA) 503.
The direct digital synthesizer generates waveforms by digital discrete values and generates analog waveforms by the digital to analog converter and filtering. Therefore, the direct digital synthesizer can generate highly free waveforms.
We will describe below the operating principle of the direct digital synthesizer. Upon the input of a clock signal 610, the counter 601 counts the inputted clock signal 610 from 0 to N and generates a stepped digital waveform 611. Each of the count values of the counter is inputted into the storage unit 602. The storage unit 602 outputs data corresponding to each count value inputted. The data stored in the storage unit 602 are data showing the output form by discrete values in advance. Therefore, the signals 612 outputted from the storage unit 602 have discrete input waveforms.
The digital/analog converter 603 converts the signals 612 outputted from the storage unit 602 into analog waveforms 613 and input the same into the low pass filter 604. The low pass filter 604 removes unnecessary higher harmonic component from the inputted analog waveforms 613. Then, the analog waveforms 614 from which the higher harmonic component has been removed are amplified to a desired level by the power amplifier 503 and are irradiated from the antenna 60.
As described above, unlike the transmitting unit (
The transmitting unit 120 according to the fourth embodiment includes a switch 701, pulse generators 721 and 722 and a switch 507. The pulse generators 721 and 722 include respectively a base band unit (BB) 702 and 703, a radio frequency pulse generator (PG) 704 and 705 and a power amplifier 706 and 707.
The radio frequency pulse generators 721 and 722 generate the preset frequency, bandwidth and pulse forms.
The transmitting unit 120 selects the pulse to be generated and the UWB signals to be transmitted by selecting the radio frequency pulse generators 721 and 722.
The switches 701 and 507 are switched synchronously by the control signals 510 outputted by the judging unit 110 to select the radio frequency pulse generators 721 or 722 that generate the transmission signals.
The transmission data 710 are inputted into the radio frequency pulse generators 721 or 722 selected by the switch 701. The selected radio frequency pulse generators 721 and 722 output specific pulses respectively set in advance.
The transmitting unit according to the fourth embodiment described above has a specific effect of being easy to implement. For example, when this configuration is designed by a 0.18 mm CMOS process, it is possible to implement the unit with a circuit area of approximately 2 mm×2 mm per radio frequency pulse generator 721. Therefore, the provision of a plurality of radio frequency pulse generators to generate the desired bandwidth and pulse form does not constitute a major obstacle from the viewpoint of implementation.
Then the communication system according to the fifth embodiment of this invention will be described.
To begin with, we will describe the background behind the characteristics of the fifth embodiment. Depending on the pulse width of the transmission signals 801, the optimum configuration of the receiving unit 132 of the wireless communication apparatus on the receiving side differs. In other words, for receiving narrow band signals on the time axis (broad band on the frequency axis) 811, the front-end analog receiving circuit (e.g., low noise amplifier) must be able to receive signals in a broad band. For receiving signals in a broad band, the radio frequency specification is severe and much current must be let to flow in comparison with the case of receiving signals in a narrow band.
Furthermore, the reception of broad band signals involves a demerit in that gain, noise indicators and other elements of amplifier performance deteriorate. And when digital signal processing is taken into account, digital conversion at a high speed sampling speed (e.g., 1 Gsps) will be required for capturing narrow band signals on the time axis. Similarly, high speed signal processing will also be required. As a result, in a broad band system, the power consumption of the receiving unit will be greater than that of a narrow band system.
On the other hand, due to the possibility of increasing the transmission power under the present legal regulation, the use of broad band signals improves the state of communication. In addition, since the pulse is narrow on the time axis, theoretically high precision positioning and measurement of distance are possible. On the contrary, in a narrow band (broad band on the time axis) system, interferences with other systems can be easily avoided, and the specifications relating to the performance of receivers are more mitigated.
The wireless communication apparatus on the transmitting side include a receiving antenna 50, a transmitting antenna 60, a detecting unit 100, a judging unit 110, a transmitting unit 120 and a receiving unit 130. The wireless communication apparatus on the receiving side includes a receiving antenna 52, a transmitting antenna 62, a detecting unit 102, a judging unit 112, a transmitting unit 122 and a receiving unit 132. The wireless communication apparatus on the receiving side has the same configuration of the same name as that of the wireless communication apparatus on the transmitting side.
The wireless communication apparatus on the transmitting side transmits UWB signals 801 from the antenna 60. Regarding the waveform of the UWB signals 801, the pulse width on the time axis changes as shown by 811 and 812 by the bandwidth of the UWB signal 801.
The fifth embodiment is characterized by the configuration of the receiver 132 on the receiving side and its control algorithm.
According to the fifth embodiment, the wireless communication apparatus on the receiving side judges the characteristics of the received signals in order to optimize the characteristics of the receiving unit 132 in response to the received signals. Accordingly, (1) the wireless communication apparatus on the transmitting side includes the data relating to the transmission method of packets (bandwidth, pulse waveform and the like) in the signals to be transmitted[i3]. (2) The wireless communication apparatus on the transmitting side includes the data relating to the communication state of packets (number of retransmissions, bit error rate and the like) in the signals to be transmitted[i4]. (3) The transmission method of the signal (bandwidth and the like) is detected by sampling the preamble of the transmission packet at a high speed. (4) The power of transmission signal is detected in any freely chosen band to judge the band of the transmission signal. (5) If this system uses known channels, the transmission band is judged by detecting the level of signals in the band specified by the standard (e.g., the IEEE standard). By such means, the characteristics of the received signals can be judged. The judgment method of received signals described above is prescribed in advance.
The signals outputted from the transmitting unit 120 to which the fifth embodiment applies are transmitted in a variety of bandwidths due to the requirement of the system and the restriction of bandwidth for the purpose of reducing interferences. Based on the information judged by the judging unit 112, the receiving unit 132 can optimize the characteristics of the receiving unit 132. Therefore, the power consumption of the receiving unit 132 can be reduced and the performance of the wireless communication apparatus can be improved.
We will describe below quantitatively the effect by the fifth embodiment. For example, when it is possible to foresee that signals in the 500 MHz band will be received from a receiving system in the 1.5 GHz band, the 3 bit analog digital converter that operated at a sampling rate of 1.5 GHz can be reduced to a sampling rate of 500 MHz. This reduction of sampling rate can lead to a sharp reduction of power consumption from 200 mW to 20 mW. And the signal processing speed of the base band can also be reduced.
The optimization of the receiving system in response to the input signals is important from the viewpoint of reducing power consumption. In particular, in the case of nodes of a sensor net system and the like driven by a button cell, the effect of reducing power consumption is important.
On the contrary, when it has become possible to use a band of 1.5 GHz from a system of 500 MHz band, improvements in communication performance can be expected as exemplified by an increase of 1.8 times in the communication distance. This is due to the fact that in the UWB system output power is specified as an output power per unit frequency band, and that a three times increase in the bandwidth results simply in a three times increase in the allowable output power. As a result, the power of received signals increases.
Incidentally, even if the receiving unit 132 stands by with any characteristic not corresponding to the receiving waveform, as far as the center frequency is the same, the fact that the bandwidth of the pulse signal received is wide or narrow may result in the deterioration of receiving performance as described above, but it is possible to communicate. However, this may cause some operationally undesirable consequences such as an improvement in error rate of communication due to deteriorations in reception performance, a remarkable deterioration in system efficiency and the like.
As described above, from the viewpoint of system performance, the optimization of the receiving unit corresponding to the pulse waveform is important, and we will show another mode of carrying out among its application plans.
The process shown in
According to the fifth embodiment, the receiving unit 130 includes a means for changing the characteristics so that the signals transmitted may be received more efficiently. After the end of the transmission process (S107 in
As a result, when it is judged that the characteristics of the receiving unit 130 should be changed, the characteristics of the receiving unit 130 are changed based on the transmitted signals (in other words, the information provided by the judging unit 110) (S122). Then, the receiving unit 130 stands by in that state for ACK signals, and when an ACK signal has been received, the received signal is demodulated (S123).
On the other hand, when it is judged that the characteristics of the receiving unit 130 will not be changed, the receiving unit 130 maintains the characteristics of the initial state (S124).
Upon receiving an ACK signal, the wireless communication apparatus on the transmitting side will be in the standby mode. On the other hand, if the wireless communication apparatus on the transmitting side receives no ACK signal within the prescribed time, it retransmits the data transmitted last time and proceeds to other steps. These steps taken after receiving the ACK signals depends on the system specification.
As the ACK signals and other signals to be transmitted (receiving signals) are highly likely to have the same bandwidth as that of the signals transmitted by the wireless communication apparatus on the transmitting side, signals can be received in the optimum manner by adjusting in advance the characteristics of the receiving unit 130 of the wireless communication apparatus on the transmitting side so that the signals transmitted by the wireless communication apparatus on the transmitting side can be received in the optimum manner in the band of transmission signals when the wireless communication apparatus on the transmitting side transmitted the signals.
And the example described above presupposes the system in which the ACK signals are exchanged. However, when the reception of any signal can be expected after the wireless communication apparatus has transmitted signals independently from the ACK signals, the characteristics of the receiving unit 130 can be adjusted optimally by proceeding to a similar process.
We will then describe a variation of the fifth embodiment.
This variation is a process mainly applied to the base station, which we will describe with reference to
The sensor node is a wireless communication terminal provided with sensors (e.g., temperature sensor and/or humidity sensor and the like) and transmits the information on temperature and/or humidity measured by the sensors. The base station, which receives information from a plurality of sensor nodes located at different places, is mainly on the standby to receive data.
The radio signals 801 arriving at the receiving antenna 62 are detected by the detecting unit 102. And when the bands 20 (see
And this variation is effective even if the interference signals of other systems detected by the base station and the sensor net nodes are different. For example, when this wireless communication system is communicating in the 3.4 GHz to 4.8 GHz band (bandwidth 1.4 GHz), if a mobile telephone terminal transmitting a signal with a several hundred milliwatt output is present within the communication bandwidth, the front-end low noise amplifier (LNA) can be saturated, and the communication by this wireless communication system becomes almost impossible. However, according to this variation, as the base station stands by while avoiding the band used by the mobile telephone terminal, the communication quality of this wireless communication system can be secured.
In order to enable this variation function effectively, for example the base station may be provided with a plurality of band pass filters and/or band removing filters. When signals constituting interference waves with this wireless communication system are detected, the base station can reduce the deterioration of communication performance by the interferences given by other system by using these filters.
Incidentally, it is preferable that the algorithm designed to be put to work when the signals that should be avoided have been detected be implemented in advance in the sensor nodes and the base station. For example, when the wireless communication system whose interference should be avoided has been detected in the band in which transmission is planned, signals should be transmitted on the low frequency side. This is because low frequency signals have a small propagation loss. And signals may be transmitted in a frequency band where as many transmission bandwidths as possible can be secured. And signals may be transmitted in the 7.25 GHz to 10.25 GHz band in which no interference mitigation algorithm is required by the regulatory texts. In this way, it is preferable that the band selecting method and/or prioritization and the like corresponding to the system be implemented.
As described above, according to the fifth embodiment, it is possible to reduce the interferences given by other systems and to prevent the deterioration of system performance and the disruption of communication.
This invention can be applied to the UWB wireless communication systems, and in particular profitably to sensor network and other telemetry systems and data radio transmission systems as well as positioning systems.
While the present invention has been described in detail and pictorially in the accompanying drawings, the present invention is not limited to such detail but covers various obvious modifications and equivalent arrangements, which fall within the purview of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-144342 | May 2006 | JP | national |
