Patent Publication Number: US-2007110001-A1

Title: Wireless system, method for reconnection, and computer readable medium thereof

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
      This application claims priority to Taiwan Patent Application No. 094139671 filed on Nov. 11, 2005.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a wireless system, a method for reconnection, and a computer readable medium thereof for reconnection in an interference environment; specifically to a wireless system, a method for reconnection, and a computer readable medium thereof for reconnection in an interference environment by searching in asynchronous channels.  
      2. Descriptions of the Related Art  
      In a wireless network communication, some unexpected external interferences such as a radio frequency signal of a wireless phone or a microwave of a microwave oven may degrade transmission speed or even influence the connection quality of the wireless network heavily. Consequently, both connection stability and transmission speed of wireless networks have become key research topics in the communication field.  
      Prior reconnection methods for wireless systems are mainly used when a network is still connected. When transmitting data, an end device reports the status of available channels to a host. If the connection quality of the current channel in use is not good, the host informs the end device to change to a new channel. Both the host and the end device switch to this new channel simultaneously and reconnection is done.  
       FIG. 1  shows a mechanism of the prior art to reduce interference in a wireless network environment. The wireless network environment comprises a host  11 , a beacon signal generator  13 , and two end devices  17 . The beacon signal generator  13  is arranged near the host  11  and its basic service area (BSA)  19  is the same as the basic service area of the host  11 . The beacon signal generator  13  transmits a beacon signal periodically. When the wireless network environment is interfered, such as that the host  11  is located within the interference area of an interference source  15 , the host  11  switches to some other channel. The beacon signal generator  13  transmits the channel changing information to the end devices  17 . The end devices  17  then change the active channel to a highest or a lowest frequency band. After obtaining the information of the current channel changed by the host  11  from the beacon signal, the end devices  17  then switch to the current channel used by the host  11  and reconnect to the host  11 .  
      Although the above mechanism can achieve reconnection while interference occurs in a wireless network, the wireless system has to operate with a beacon signal generator. Furthermore, only the environment of the host is considered during reconnection. If an external interference makes an end device unable to receive the beacon signal or the end device unable to switch to the selected new channel, the wireless system is incapable of reconnection. Consequently, considering available channels for both the host and the end device for reconnection becomes a key research issue in this field.  
     SUMMARY OF THE INVENTION  
      An object of this invention is to provide a wireless system for communicating selectively through one of a plurality of channels, which comprise a first channel, a second channel and a third channel. The wireless system comprises an end device and a host, wherein the host initially communicates with the end device through the first channel. The host selects the second channel to communicate with the end device if the host determines that communication with the end device through the first channel is abnormal. The host selects the third channel to communicate with the end device if the host determines that a response from the end device is not received through the second channel. The end device selects the second channel to communicate with the host if the end device determines that communication with the host through the first channel is abnormal, and the end device selects the third channel to communicate with the host if the end device determines that a signal from the host is not received through the second channel. In this way, the wireless system can determine an available channel for communication between the host and the end device and reconnect without adding extra hardware components while the communication is broken.  
      Another object of this invention is to provide a reconnection method for a wireless system. The wireless system comprises a host and an end device, wherein the host initially communicates with the end device through a first channel, which is one of a plurality of channels used in the wireless system. The method comprises the steps of: (a) the host determining whether communication through the first channel is normal, if not, going to steps (b) and (c); (b) the host selecting a second channel to communicate with the end device, wherein the second channel is one of the plurality of channels; (c) the host determining whether a response from the end device is received through the second channel, if not, going to step (d); (d) the host selecting a third channel to communicate with the end device, wherein the third channel is one of the plurality of channels; (e) the end device determining whether communication through the first channel is normal, if not, going to steps (f) and (g); (f) the end device selecting the second channel to communicate with the host; (g) the end device determining whether a signal from the host is received through the second channel, if not, going to step (h); and (h) the end device selecting the third channel to communicate with the host. The method can determine an available channel for the connection between the host and the end device and rebuild the connection without adding extra hardware components while the connection is broken.  
      Yet a further object of this invention is to provide a computer readable medium for storing a computer program, which executes the above-mentioned method to rebuild connection.  
      The detailed technology and preferred embodiments implemented for the subject invention are described in the following paragraphs accompanying the appended drawings for people skilled in this field to well appreciate the features of the claimed invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  shows a mechanism of the prior art to reduce interference in a wireless network environment;  
       FIG. 2  is a diagram of a first embodiment of this invention;  
       FIG. 3  is a diagram of a second embodiment of this invention; and  
       FIG. 4  is a flowchart of a third embodiment of this invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
      The first embodiment of this invention is shown in  FIG. 2 , which is a wireless system to recover communication in a wireless network environment to avoid interference of external signals. The embodiment communicates through one of a plurality of channels selectively. The wireless system comprises a host  201  and an end device  205 . The wireless system is located within a wireless network constructed by an interference source  203 . In this embodiment, the wireless system follows IEEE 802.15.4 standard and the software layer of the end device  205  is a Zigbee mode dividing its frequency domain into ten (915 MHz) or sixteen (2.4 GHz) channels by using a DSSS (Direct-Sequence Spread Spectrum) technique. Consequently, the plurality of channels can be ten or sixteen channels. If the software layer of the interference source  203  follows WiFi mode and IEEE 802.11 standard and divides its frequency domain into eleven channels by using the DSSS technique, the wireless system may be interfered.  
      Since the bandwidths of the WiFi and the IEEE 802.15.4 overlap partially, the end device  205  may be interfered by the interference source  203  so that disconnection from the host  201  occurs if the end device  205  lies within an interference range  207  of the interference source  203  as  FIG. 2  shows. Consequently, the connection between the host  201  and the end device  205  should be rebuilt. Assuming that IEEE 802.15.4 standard of 2.4 GHz is used in the wireless network environment, the host  201  initially communicates with the end device  205  through a first channel. The host  201  selects a next channel (a second channel) to communicate with the end device  205  if it determines that the communication with the end device  205  through the first channel is abnormal by not receiving a confirmation signal from the end device  205 . The host  201  selects a next channel (a third channel) to communicate with the end device  205  if it does not receive a response from the end device  205  through the second channel for a time period. If the host  201  does receive a response through the second channel, the host  201  records the available channels reported by the end device  205 , wherein the available channels may include multiple channels among the sixteen channels. For example, if the end device  205  determines that the available channels under the interference of the interference source  203  include the second channel, the fourth channel, the eighth channel and the twelfth channel, the end device  205  reports the availability of the second channel, the fourth channel, the eighth channel and the twelfth channel when the host  201  switches to the second channel to communicate. The host  201  records the available channels and then selects one of them to rebuild the connection with the end device  205 .  
      If the host  201  still does not receive a response from the end device  205  through the third channel, the host  201  keeps selecting a next channel to communicate with the end device  205  until receiving a response.  
      Similarly, the end device  205  selects a next channel (the second channel) to communicate with the host  201  if the end device  205  determines that the communication with the host  201  through the first channel is abnormal according to the condition of losing contact with the host  201  through the first channel. The end device  205  selects another next channel (the third channel) to communicate with the host  201  if it does not receive a signal from the host  201  through the second channel. If the end device  205  does not receive a signal from the host  201  through the third channel, the end device  205  keeps selecting a next channel to communicate with the host  201  until receiving a signal.  
      Before changing the communication channel to reconnect with the host  201 , the end device  205  verifies the available channels among the sixteen channels, which are so-called clean channels for maintaining communication and will be reported to the host  201 , i.e., the second channel, fourth channel, eighth channel and twelfth channel. It should be clarified that the clean channels are out of the interference or within the interference but not affecting the communication. After recording the available channels, the host  201  informs the end device  205 , for example, to switch to the fourth channel through the second channel if the host  201  confirms that the fourth channel is the most suitable channel for communication. The host  201  then communicates with the end device  205  through the fourth channel.  
      When the host  201  tries to connect with the end device  205  through some channel, it stays at the channel for a specific amount of time which is twice as long as the required amount of time for the end device  205  to switch the whole sixteen channels. For example, if the required time to switch a channel is 0.5 second for the end device  205 , the required time for switching the whole sixteen channels is 8 seconds. Consequently, the host  201  stays at a channel for sixteen seconds waiting for a response so that the host  201  will not miss the chance to receive the response from the end device  205 .  
      The host  201  and the end device  205  can transmit a confirmation signal to each other within a specific period of time to determine whether the communication is normal or not. If a response message is not received after transmitting n successive confirmation signals, the communication is regarded as disconnection. For example, the specific period of time may be five seconds and the number n for transmitting the confirmation signals is six times. So if there is no response message received after thirty seconds, the communication between the host  201  and the end device  205  is regarded as disconnection. The host  201  and the end device  205  then perform the aforementioned processes to recover the connection independently.  
      The second embodiment of this invention is shown in  FIG. 3 , which is a wireless system in a wireless network environment able to recover communication in order to avoid or to reduce the influence of interference of external signals. The difference between this embodiment and the first embodiment is that the wireless system comprises several end devices. This embodiment communicates selectively through one of a plurality of channels which comprises a first channel, a second channel and a third channel. It should be clarified that these three channels are used herein only for explanation. The actual number of the plurality of channels in practice is not restricted to three. The wireless system comprises a first end device  301 , a second end device  303 , a third end device  305 , a fourth end device  307  and a host  201 . The wireless network environment is interfered by a first interference source  309  and a second interference source  311 . In this embodiment, the wireless system also follows IEEE 802.15.4 standard of the 2.4 GHz and the software layers of the interference sources  309  and  311  follow WiFi mode.  
      The communications between the host  201  and the first, second and fourth end devices  301 ,  303  and  307  may be abnormal or even totally broken since they are located either within an interference area  313  of the first interference source  309  or within an interference area  315  of the second interference source  311 . Consequently, the host  201  should reconnect with the first, second, and fourth end devices  301 ,  303  and  307 . In this embodiment, the host  201  initially communicates with the first, second, third and fourth end devices  301 ,  303 ,  305  and  307  through the first channel. As shown in  FIG. 3 , both the first end device  301  and the second end device  303  are located within the interference area  313  and the fourth end device  307  is located within the interference area  315 . The host  201  selects a next channel, e.g., the second channel to try communicating with the first, second and fourth end devices  301 ,  303  and  307  if determining that the communications with the first, second and fourth end devices  301 ,  303  and  307  through the first channel are abnormal. The third end device  305 , which is able to communicate with the host  201  through the first channel, keeps using the first channel for communication. The host  201  selects a next channel, e.g., the third channel for communication if determining that no response is received from the first, second and fourth end devices  301 ,  303  and  307  through the second channel. If the host  201  is aware that the communication with the first end device  301  may be rebuilt through the second channel by receiving a response from the first end device  301 , the host  201  communicates with the first end device  301  through the second v channel temporarily. In addition, the response transmitted by the first end device  301  also records the available channels detected by the end device  301 .  
      Similarly, if any end device determines that the communication with the host  201  through the first channel is abnormal, the end device selects a next channel, e.g., the second channel to try communicating with the host  201 . If the end device determines that no signal is received from the host  201  through the second channel, it selects a further next channel, e.g., the third channel to try communicating with the host  201 .  
      Before selecting the first, second, or third channel to communicate with the host  201 , the first, second, third and fourth end devices  301 ,  303 ,  305  and  307  respectively verify the available channels and then inform the host  201  of the clean channels for maintaining communication. Table 1 shows the temporary connection channel and the available channels for each end device  301 ,  303 ,  305  and  307  to communicate with the host  201  while interference occurs. For example, the temporary connection channel for the second end device  303  to communicate with the host  201  is the twelfth channel and the available channels for the second end device  303  are from the third channel to the thirteenth channel. After receiving these reports, the host  201  determines that one of the most suitable available channel is the fourth channel because the fourth channel is one of the common available channels for all the end devices  301 ,  303 ,  305  and  307 . Then the host  201  informs the first, second, third and fourth end devices  301 ,  303 ,  305  and  307  to switch to the fourth channel for reconnection through the eleventh, the twelfth, the first and the seventh channels, respectively. It should be noted that the host  201  selects either one of the common available channels for all of the end devices  301 ,  303 ,  305  and  307  or one of the channels available for the biggest number of the end devices  301 ,  303 ,  305  and  307 .  
                               TABLE 1                                           Connection           End Device   Available Channels   Channel                                                        First   4-15   11           Second   3-13   12           Third   1-16   1           Fourth   2-13   7                      
 
      Although the wireless system in the second embodiment simply shows four end devices and two interference sources, people skilled in this field can easily deduce an embodiment of a wireless system comprising any number of end devices and any number of interference sources.  
      The third embodiment of the subject invention is a reconnection method for a wireless system which comprises a host and an end device. The host initially communicates with the end device through a first channel. At least one of the host and the end device is influenced by an interference source.  
      The method for reconnection is shown in  FIG. 4 . In step  401 , the host determines whether the communication through the original channel, i.e., the first channel is normal or not. If yes, step  401  is repeated after a specific amount of time. If not, step  403  is executed in which the host selects a next channel, e.g., a second channel to communicate with the end device. Step  405  is then executed wherein the host determines whether a response is received from the end device through the second channel. If not, the method returns to step  403  and the host selects a further next channel, e.g., a third channel to communicate with the end device. If yes, step  407  is executed wherein the host records the available channels reported by the end device. Step  409  is then executed wherein the host informs the end device to switch to one channel, namely a fourth channel, from the available channels. Step  411  is executed wherein the host communicates with the end device through the current switched channel, i.e., the fourth channel and the process of reconnection of the host ends.  
      Similarly, the end device determines whether the communication through the original channel is normal or not in step  413 . If yes, step  413  is repeated after a specific amount of time. If not, step  415  is executed wherein the end device verifies the available channels under the interference. Step  417  is then executed wherein the end device selects a next channel to communicate with the host. Step  419  is then executed wherein the end device determines whether a signal is received from the host through the channel. If not, the method returns to step  417  wherein the end device selects a further next channel to communicate with the host. If yes, step  421  is executed wherein the end device receives a certain channel informed by the host through the channel selected in step  417 . Then step  411  is executed wherein the host communicates with the end device through the certain channel and the process of reconnection of the end device ends.  
      More specifically, if the end device determines that communication through the original channel is abnormal in step  413  and the host does not determine that communication through the original channel is abnormal yet in step  401 , the end device independently executes step  415  to determine the available channels, and then executes step  417  and step  419  to find out one channel for communicating with the host. The host is informed of the available channels. The host then executes step  407 , step  409  and step  411 .  
      The method may be executed by using a computer readable medium which stores a computer program. The computer program comprises code to execute the above-mentioned steps of the method. The computer readable medium can be a floppy disk, a hard disk, an optical disc, a flash disk, a tape, an internet accessible database or any storage medium with a similar functionality of storage which is easily thought by people skilled in the field.  
      The first, the second, the third and the fourth channels herein are only intended to indicate that they are different channels. That means, for example, the second channel selected by the host and the second channel selected by the end device are not restricted to the same channel.  
      According to the above descriptions, the subject invention can achieve reconnection when either the host or the end device loses contact, or both the host and the end device lose contact. The subject invention may be implemented without adding extra hardware components.  
      The above embodiments are used as the examples of the subject invention and used to explain the technical characters of the subject invention and are not used to limit the range of the subject invention. People skilled in this field may proceed with a variety of modifications and replacements based on the disclosures and suggestions of the invention as described without departing from the characteristics thereof. Nevertheless, although such modifications and replacements are not fully disclosed in the above descriptions, they have substantially been covered in the following claims as appended.