EP0507480B1

EP0507480B1 - Wireless communication device with transmitter power control and printing system using the same

Info

Publication number: EP0507480B1
Application number: EP92302469A
Authority: EP
Inventors: Nobuyasu c/o Canon Kabushiki Kaisha Itoh; Shigeru C/O Canon Kabushiki Kaisha Ueda
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 1991-04-04
Filing date: 1992-03-23
Publication date: 2001-06-20
Anticipated expiration: 2012-03-23
Also published as: US5490287A; EP0507480A2; EP0507480A3; DE69231877D1

Description

The present invention relates to a wireless communication device for transmitting and receiving data, for example, by radiowaves, and to a printing system employing such a device.
In a network of conventional wireless communication devices, the transmission power of each device is set strong enough to be received by the farthest device. A network of wireless communication devices is illustrated in Fig. 5, in which a symbol "O" indicates a wireless communication device. The transmission power of a device 10 is set so that a device 1 farthest from the device 10 can receive the data sent by the device 10. The transmission power of a device 4 can be set lower than that of the device 10, since the device 4 is located substantially at the center of the network so that the distance from the device 4 to the farthest device therefrom is shorter than the distance from the device 10 to the device 1.
Thus, in a network, different devices may have different transmission power levels, according to their locations in the network.
Such a network or device, however, has problems as described below.
Devices located in the peripheral area of the network, such as the device 10 in Fig. 5, use significantly more power than devices located in the central area of the network, such as the device 4. For example, the device 10 always uses the same high power to transmit data to any device, whether to the farthest device 1 or to the neighboring devices 4, 7 and 8. Also, the high power radiowaves sent out by the device 10 naturally reach the area outside the network (e.g., the area below the unit 10 in Fig. 5) as well, so that communication between the devices in the network can be received by a device outside the network. This becomes a significant problem when confidential data is communicated in the network. As a result, security protection becomes difficult.
US-A-5003619 discloses a method and apparatus for adjusting the power of a transmitter in which the transmitter initially transmits a signal at full power and the or each receiver measures the received power. The receivers then transmit a code representative of received power in reply to the transmitter. This code is also transmitted at full power. The transmitter receives the codes from the or each receiver and sets the power of transmission to the or each receiver in accordance with the received code. In this way the codes are used to reduce the power of transmission subsequent to the initial transmission. This arrangement suffers from the disadvantage that the initial signal must be transmitted at full power both from the transmitter and in reply from the receiver.
US-A-3925782 discloses an arrangement for adjusting the power of transmission for a network of transceivers. To reduce the power of transmission from a transmitter the receivers measure the power of the received signal and transmit back to the transmitter a code indicating the transmission power reduction possible which would still allow communication. The transmitter then selects the lowest power reduction request received from the receivers and reduces the power of transmission accordingly. In this way the transmission of power to all of the receivers is reduced to the same level to allow communication with the most distant receiver. In this arrangement the signal is transmitted to all of the receivers and not a selected few. Thus, the range of transmission must encompass the most distant receiver and there is no selective transmission for individual receivers.
In accordance with one aspect the present invention provides a wireless communication apparatus for transmitting data to a plurality of devices by wireless communication comprising:
selecting means for selecting one device from the plurality of devices;
sending means for the wireless transmission of data to the selected device;
control means for variably controlling a transmission power of said sending means used to transmit the data; and
receiving means for receiving status data transmitted by the devices;

said control means includes memory means for storing a table including data representative of the transmission power corresponding to each device, and is adapted to set said transmission power used by said sending means to transmit data to the selected device in accordance with the data representative of the transmission power corresponding to the selected device in the table;
said sending means is adapted to send data representative of the transmission power used by said sending means to the selected device when said table in said memory means is to be updated, so that the selected device can determine the transmission power for returning status data to the apparatus on the basis of the data received by the selected device; and
said control means includes judging means for judging whether the status data representative of receipt of the data by the selected device is received or not by said receiving means and for updating the data representative of the transmission power corresponding to the selected device in the table in said memory means on the basis of the result of judgment of said judging means.

In accordance with a second aspect, the present invention provides a wireless communication apparatus for receiving data from a transmitter by wireless communication, comprising:
receiving means for receiving data representative of the transmission power used by said transmitter for wireless communication;
sending means for transmitting status data to said transmitter in response to receipt of the data by said receiving means;
control means for variably controlling transmission power of said sending means used for transmitting the status data to said transmitter,
wherein said control means includes memory means for storing a table including data representative of the transmission power of said sending means, and is adapted to update the table in said memory means according to the data representative of transmission power of the received data.
In accordance with a third aspect the present invention provides a method of transmitting data to a plurality of devices by wireless communication, the method comprising the steps of:
selecting one device from the plurality of devices;
transmitting data by wireless communication to the selected device;
variably controlling a transmission power used for the transmission of the data to the selected device; and
receiving status data transmitted by the device;

setting said transmission power to the selected device in accordance with data representative of the transmission power corresponding to the selected device stored in a table which includes data representative of the transmission power corresponding to each device;
when said table is to be updated, transmitting data representative of the transmission power used in the transmitting step, to the selected device, so that the selected device can determine the transmission power for returning status data on the basis of the data received by the selected device;
judging whether the status data representative of receipt of the data by the selected device is received or not; and
updating the data representative of the transmission power corresponding to the selected device in the table on the basis of the result of the judgement.

In accordance with a fourth aspect, the present invention provides a method of receiving data from a transmitter by wireless communication, the method comprising the steps of:
receiving data by wireless communication which is representative of the transmission power used by said transmitter;
transmitting status data to said transmitter in response to receipt of the data;
variably controlling transmission power used for the transmission of said status data using a stored table of data representative of the transmission power to be used for the transmission of status data; and
updating the table according to the received data representative of transmission power of the data.
Embodiments of the present invention will now be described with reference to the accompanying drawings, in which:
Fig. 1 is a block diagram of a communication device according to one embodiment of the present invention.
Figs. 2 and 3 show a flowchart illustrating the operation of the device shown in Fig. 1.
Fig. 4 is a time chart of transfer data.
Fig. 5 illustrates a network of devices according to the present invention.
Fig. 6 is a block diagram of a communication device used in a printer of a printing system according to another embodiment of the present invention.
Fig. 7 is a block diagram of a communication device used in a host computer of the above mentioned printing system.

[Embodiment 1]

Fig. 1 shows a communication device comprising: an antenna 101 for transmitting and receiving radiowaves; a sending unit 102 for sending out data; a receiving unit 103 for receiving data; a control unit 104 having an environment setting unit 107; a memory 105 for storing data; and operation unit 106. Each of such devices in a network (Fig. 5) has an identification code.
Referring to Fig. 2, when a communication device in a network is powered to transmit data in Step S1, a receiver is selected from the other communication devices in the network (Step S2). Then, the sender device determines in Step S3 the minimum transmission power required for the transmission of the data to the receiver device. This operation may be carried out either serially for all the other devices when powered, or specifically for the receiver device when data is to be transmitted.
In detail, the sender device sends the receiver device the command to sense its own state(Step S4), and judges whether the transmission power is proper or not based on the status which the receiver sends to the sender (Steps S5 and S6). When it is judged to be improper, such as when the sender receives a status signal indicating that the reception has been failed or when the sender does not receive a status signal from the receiver, the sender changes the level of transmission power to send the command again in Step S3. Alternatively, the sender may send, together with the command, data regarding the transmission power level to transmit the command, and the receiver changes its transmission power level, according to the received data, for example, to send a status signal to the sender.
When the transmission power level is judged to be proper in Step S6, the control unit 104 of the sender device stores the data regarding the transmission power level (Step S7), in association with the ID code of the receiver device. On the other hand, the control unit 104 of the receiver also stores the data regarding the transmission power level of the sender, in association with the ID code of the sender (Step S8). The transmission power level is stored in the control unit 104 of the receiver, based on, for example, the above-mentioned data regarding the transmission power received, together with the command, from the sender. In such a way, the environment setting unit 107 included in the control unit 104 of each device stores a table containing the transmission power levels corresponding to the other devices.
Referring to Fig. 3, the sender device examines whether the receiver device is ready for receiving or not (Step S10). When the receiver is not ready, the sender waits for the receiver to be ready (Step 11). When the receiver is ready, the sender sends out the start bit to the receiver (Step S12) so that data transmission will start. Then, the sender transmits the data to the receiver (Step S13) and then, sends out the stop bit (Step S14). Data may be sent out by the unit of a character or a block of several characters, as shown in Fig. 4.
Next, the sender device judges whether any reception errors have occurred in Step S15. For this judgement, various methods can be used, such as, a parity check in which a parity bit is added to each of the data, a successive sending check in which data is sent twice for error detection, an inverse check in which data and the inverse of such data (each bit, "1" or "0", of the data is inverted) are used as the check codes, etc.
Only when it is judged that there is no reception error, does the receiver send the ACK signal to the sender (Step S16). When a reception error is found, the receiver requests the resending of the data in Step S17, and the sender sends the data again via Step S12. In such a case, the transmission power level may be changed. If it is changed, the data of the transmission power level stored in the environment setting unit 107 is updated accordingly and the operation illustrated in Fig. 2 may be omitted. The procedure as described above is repeated for data transfer (If the data transfer is performed by the unit of a character, data transfer operation is performed several times according to the amount of data to be transferred).

[Embodiment 2]

To handle a state where a plurality of communication devices simultaneously transmit data to one device in a network, a wireless communication device according to this embodiment is equipped with a function such as interruption or polling; thereby, the receiver device receives data successively from the sender devices according to the priority of each sender device, or the receiver accesses to a sender in order to request a data transfer when the receiver idles. Further, the polling enable devices may be equipped with a function such that a receiver remotely controls (using radiowaves) the transmission power of a sender during the setting of the transmission power.
If a wireless communication device is added to a network of such wireless communication devices, each existing device stores the data of the distance to the added device and the ID code of the added device, and the added device stores the data of the distance to each of the existing devices and the ID code thereof. The ID codes and the distance data are stored in the environment setting unit 107 (e.g. an E²PROM) of the control unit 104 of each device. As an alternative, to transmit data to an uncataloged device (newly added to the network), a sender device and the uncataloged device (the receiver) may carry out the operation shown by the flowcharts in Figs. 2 and 3, starting with the lowest transmission power level, and the sender and/or the receiver automatically catalog each other.
As described above, since a wireless communication device uses a transmission power level specific to a receiver device, such a device requires less total power and makes it difficult for an outside device to receive a communication of the network. Also, since the transmission power is kept relatively low, wireless interference is substantially prevented.
Since the proper transmission power level varies in proportion to the distance to receivers, the initial value for the transmission power can thus be set. Also, since the device adjusts the transmission power to a proper level which varies depending on external noises, location factors, weather conditions, etc., the reliability or quality of communication is upgraded.

[Embodiment 3]

A wireless communication device according to the present invention can be employed in a communication system to transmit print data from a host computer to a printer. According to this embodiment, one host computer (the sender) transmits print data to a plurality of printers (the receivers) using radiowaves. In Fig. 5, the host computer may be the device 10, and the printers may be the other devices 1 to 9.
Referring to Fig. 6, the printer having an interface for wireless communication comprises: an antenna 601; a receiving unit 602; a sending unit 603; a page memory 604; a bit map memory 605; a font memory 606; a main control unit 607; an environment setting unit 608; an operating panel 609; a printer engine interface 610; and a printer engine 611.
Data transmitted from the host computer is received by the antenna 601 and sent through the receiving unit 602 to be temporarily stored in the page memory 604. When data for one page is accumulated in the page memory 604, the main control unit 607 reads from the font memory 606 the bit map data corresponding to the character data stored in the page memory 604 and develops the bit map data as a dot pattern in the bit map memory 605. Then, the main control unit 607 reads the developed dot pattern data from the bit map memory 605 and sends the data to the printer engine interface 610. The printer engine 610 converts the word (16 bits) or byte (8 bits) data to serial data (P-S conversion) and outputs the converted data as a VIDEO signal to printer engine 611. Printing is thus started. Also, the main control unit 607 sends the status of the printer (e.g. READY, PAPER OUT, WARMING UP) through the sending unit 603 to the host computer. Paper size, the attributes of the print characters (typeface, size, etc), the number of copies, etc. can be determined according to the preferences of a user by operating the operating panel 609. The ID code of the printer and data of the distance to the host computer are stored in the environment setting unit 608. Usually, a nonvolatile memory is used to keep data even if the printer is switched off.
Referring to Fig. 7, the host computer having a wireless communication interface comprises: an antenna 701; a receiving unit 702; a sending unit 703; a main control unit 704; a CPU (e.g. a microprocessor) 705; ROM 706 storing a bootstrap program of the host computer; RAM (e.g. DRAM) 707 for the work area (RAM is memory into which data can be written and from which data can be read); an environment setting unit 708 including a memory, e.g. a nonvolatile memory, to store the printer's ID code and the distance data, both of which are required by the wireless communication device ; a hard disk unit 709; a display interface 711; a CRT 710; a keyboard interface 712; and a keyboard 713.
To transmit the print data of a document composed by using document composition application software (e.g. an editor), the main control unit 704, referring to the information stored in the environment setting unit 708, selects a printer in the network, and sends the print data to the sending unit 703. The print data is accordingly transmitted as serial data from the antenna 701 using radiowaves to the selected printer. The receiving unit 702 receives a status signal from the printer and sends the received signal to the main control unit 704.
In the above-described embodiments, radiowaves are used, but infrared rays, ultrasonic waves or light rays may also be used.
It is to be understood that the present invention is not limited to the disclosed embodiments but intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.

Claims

A wireless communication apparatus for transmitting data to a plurality of devices by wireless communication comprising:

selecting means for selecting one device from the plurality of devices;

sending means (102) for the wireless transmission of data to the selected device;

control means (104) for variably controlling a transmission power of said sending means (102) used to transmit the data; and

receiving means (103) for receiving status data transmitted by the devices;

characterised in that

said control means (104) includes memory means (107) for storing a table including data representative of the transmission power corresponding to each device, and is adapted to set said transmission power used by said sending means (102) to transmit data to the selected device in accordance with the data representative of the transmission power corresponding to the selected device in the table;

said sending means (102) is adapted to send data representative of the transmission power used by said sending means (102) to the selected device when said table in said memory means (107) is to be updated, so that the selected device can determine the transmission power for returning status data to the apparatus on the basis of the data received by the selected device; and

said control means (104) includes judging means for judging whether the status data representative of receipt of the data by the selected device is received or not by said receiving means (103) and for updating the data representative of the transmission power corresponding to the selected device in the table in said memory means (107) on the basis of the result of judgment of said judging means.
Apparatus according to claim 1, wherein said selecting means is adapted to select sequentially each of the plurality of the devices when the apparatus is turned on, and said control means (104) is adapted to update the data representative of the transmission power corresponding to the sequentially selected device in the table in said memory means (107) in accordance with the result of judgment by said judging means.
Apparatus according to claim 2, wherein when said table in said memory means (107) does not include data representative of the transmission power corresponding to a selected device, said control means (104) is adapted to control said sending means (102) to transmit data at a low transmission power level, and if said judgement means judges that the status data has not been received by said receiving means (103), said control means (104) is adapted to increase the transmission power of said selecting means (102) until said judgement means judges that the status data has been received by said receiving means (103).
Apparatus according to any preceding claim, wherein said memory means (107) comprises a nonvolatile memory.
Apparatus according to any preceding claim, wherein said control means (104) is adapted to update the data representative of the transmission power corresponding to the selected device in said table in said memory means (107) when the transmitted data is not correctly received by the selected device.
Apparatus according to claim 5, wherein when the transmitted data is not correctly received by the selected device, said control means (104) is adapted to update the data in accordance with a resend request from the selected device received by said receiving means (103).
Apparatus according to claim 1 including determining means for determining whether a status of the selected device is ready or not when said judging means judges that the status data representative of receipt of the data is received by said receiving means (103), and for repeating the determination after a predetermined time if the status is determined to be not ready.
Apparatus according to claim 7, wherein said sending means (102) is adapted to send a predetermined amount of data between a start bit and an end bit when the status of the selected device is determined to be ready.
Apparatus according to any preceding claim wherein said sending means (102) is adapted for transmitting print data generated by a host computer and said devices comprise printers.
An apparatus according to claim 9, further comprising the host computer for generating the print data.
A wireless communication apparatus for receiving data from a transmitter by wireless communication, comprising:

receiving means (103) for receiving data representative of the transmission power used by said transmitter for wireless communication;

sending means (102) for transmitting status data to said transmitter in response to receipt of the data by said receiving means (103);

control means (104) for variably controlling transmission power of said sending means (102) used for transmitting the status data to said transmitter,

wherein said control means (104) includes memory means (107) for storing a table including data representative of the transmission power of said sending means (102), and is adapted to update the table in said memory means (107) according to the data representative of transmission power of the received data.
Apparatus according to claim 11 including judgment means for judging whether the receiving means (103) has correctly received the data, wherein said control means (104) is adapted to update the table in said memory means (107) when said judgement means judges that the receiving means (103) has not correctly received the data.
Apparatus according to claim 11 or claim 12, wherein said memory means (107) comprises nonvolatile memory.
Apparatus according to any one of claims 11 to 13 arranged to receive print data from a print transmitter for printing by a printer.
Apparatus according to claim 14, further comprising converting means for converting the print data including a character code into a dot pattern.
Apparatus according to claim 15, further comprising a memory capable of storing the dot pattern converted by said converting means for one page.
Apparatus according to claim 15 or claim 16, further comprising the printer for printing the dot pattern.
A method of transmitting data to a plurality of devices by wireless communication, the method comprising the steps of:

selecting one device from the plurality of devices;

transmitting data by wireless communication to the selected device;

variably controlling a transmission power used for the transmission of the data to the selected device; and

receiving status data transmitted by the device;

characterised by the steps of:

setting said transmission power to the selected device in accordance with data representative of the transmission power corresponding to the selected device stored in a table which includes data representative of the transmission power corresponding to each device;

when said table is to be updated, transmitting data representative of the transmission power used in the transmitting step, to the selected device, so that the selected device can determine the transmission power for returning status data on the basis of the data received by the selected device;

judging whether the status data representative of receipt of the data by the selected device is received or not; and

updating the data representative of the transmission power corresponding to the selected device in the table on the basis of the result of the judgement.
A method according to claim 18, including the initial steps of:
sequentially selecting each of the plurality of devices, sequentially transmitting said data to each selected device, judging whether the status data is received or not, and updating the data representative of the transmission power corresponding to the sequentially selected devices in the table in accordance with the result of the judgement.
A method according to claim 19 wherein when the table does not include data representative of the transmission power corresponding to a selected device, the predetermined data is transmitted at a low transmission power level and if it is judged that the status data has not been received, the transmission power is increased until it is judged that the status data has been received.
A method according to claim 18 including the step of determining whether the transmitted data is correctly received by the selected device and updating the data representative of the transmission power corresponding to the selected device if it is determined that the data has not been correctly received.
A method according to claim 21 wherein the data representative of the transmission power corresponding to the selected device is updated in accordance with a resend request from the selected device.
A method according to claim 18 including the step of determining whether the selected device is ready or not when it is judged that the data has been received by the selected device, and if the selected device is determined not to be ready, repeating the determination after a predetermined time.
A method according to claim 23 including the step of sending a predetermined amount of data between a start bit and an end bit when it is determined that the selected device is ready.
A method according to any preceding claim for transmitting print data generated by a host computer to printers.
A method according to claim 25 including the steps of receiving print data from the host computer.
A method of receiving data from a transmitter by wireless communication, the method comprising the steps of:

receiving data by wireless communication which is representative of the transmission power used by said transmitter;

transmitting status data to said transmitter in response to receipt of the data;

variably controlling transmission power used for the transmission of said status data using a stored table of data representative of the transmission power to be used for the transmission of status data; and

updating the table according to the received data representative of transmission power of the data.
A method according to claim 27 including the steps of judging whether the data has been correctly received; and updating the table if it is judged that the data has not been correctly received.
A method according to claim 27 or claim 28 for receiving print data from a print transmitter for printing.
A method according to claim 29 including the step of converting the print data including a character code into a dot pattern.
A method according to claim 30 including the step of storing the dot pattern for one page.
A method according to claim 30 or claim 31 including the step of printing the dot pattern.