Abstract:
In a network of wireless communication devices, each device has a unit for transmitting information, a unit for variably controlling the transmission power for transmission of information, a unit for receiving information transmitted, and a unit for controlling the other units. Each device shifts the transmission power to a level proper to a current receiver device.

Description:
This application is a continuation of application Ser. No. 07/858,071 filed Mar. 26, 1992, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     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. 
     2. Description of the Related Art 
     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 &#34;0&#34; 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. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to solve the above problems by providing a wireless communication device which changes its transmission power according to a current receiver, for example, to a level just high enough to communicate with the current receiver device. Thus, a device according to the present invention requires less total power and contributes to network security. 
     Another object of the present invention is to provide a printing system which uses such a device and thus does not require high power. 
     Other objects, features and advantages of the present invention will become apparent in the attached drawings, the detailed description of the preferred embodiments and the claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiments of the present invention will be described hereinafter with reference to the drawings. 
     [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 own 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 judgment, 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, &#34;1&#34; or &#39;0&#34;, 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 (on 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 E 2  PROM) 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 according to the present invention 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 a device according to the present invention 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) on 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&#39;s ID code and the distance data, both of which are required by the wireless communication device of the present invention; 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 on 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 spirit and scope of the appended claims.