Multiplex communications – Communication over free space
Reexamination Certificate
1998-08-06
2003-08-05
Vincent, David (Department: 2661)
Multiplex communications
Communication over free space
C370S338000
Reexamination Certificate
active
06603744
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a wireless communication method, and specifically to a method for connecting a device to a wireless USB (Universal Serial Bus).
BACKGROUND OF THE INVENTION
The USB is specified as a standard “Point to Multipoint” interface, which connects a computer to low and medium speed devices, such as a mouse, a keyboard and a printer, as detailed in co-pending Japanese Patent Application No: 09-212784, assigned to the present assignee, the teachings of which are incorporated by reference herein. While conventionally a connection destination has to be selected for each device, such as a keyboard port for a keyboard, a mouse port for a mouse, a printer port for a printer, and a serial port for a modem, when the USB is employed, a USB device need only be connected to a USB port. In addition, since the USB supports the Hot Plug & Unplug function, connections can be easily changed, even when the computer is in use. In the mobile notebook computer and PDA (Personal Digital Assistant) environment, however, even the connection of a USB cable imposes a large load on a user. Damage to a connector on the host side may be caused by inadvertent insertion and removal of a connector on the device side. It is preferable, therefore, that for a mobile environment a wireless connection be made available.
Typical currently-available wireless communication systems employ the wireless LAN IEEE 802.11 standard and the IrDA communication method. The IEEE 802.11 standard was designed mainly for communication between computers, and is not suitable for communication between computers and peripheral devices. IrDa was designed with the assumption that it would be used for point to point connections, not point to multipoint connections, such as the USB connection. The USB is regarded as a main interface for future apparatuses connected to PCs (Personal Computers), and it is assumed that it will be incorporated in many apparatuses. If a wireless USB can be provided, it can constitute means for the very easy connection of peripheral devices.
IBM TDB, Vol. 40, No. 04, (April 1997) pp. 87-88 teaches a wireless USB. This reference, however, does not take into account problems that will arise with the wireless USB. In IBM TDB, Vol. 37, No. 04B, pp 91-93, (April 1994), a system is disclosed for connecting a wireless module to a conventional bus in a computer and for connecting the wireless module to a peripheral device connected to the bus. In this reference, however, problems caused by a wireless USB are not described.
What is desired is a system configuration for a USB that enables a computer to manage all the devices connected to the USB, and performs polling to acquire communicated data and to detect state changes. Solutions for the following four problems must be found to provide a satisfactory wireless system configuration.
(1) Designation of packet destinations—The destination of a USB packet is designated by using a USB address or non-specified bus topology, which changes dynamically depending on the configuration of a current device. When wireless communication is employed, an address in one system might be identical to one in another system, and as it is difficult to suppose a definite bus topology, the unique determination of a destination for a packet is not possible.
(2) Time limitation for a response—According to the USB specification, a device that receives a packet from a host or a function device is required to send a response within a 16-bit time period (1.33 &mgr;s when operating at full speed). However, as the wireless communication speed is in general less than the full speed of the USB, 12 Mbps, and as in many cases a collision avoidance mechanism is required, it is difficult to comply with the time requirement for the above bus turn around time.
(3) Frame synchronization—In order to synchronize with a USB frame of the computer, an SOF packet is issued every Ims. The SOF packet must be transmitted at the start time of the frame precisely, but it is difficult to set a wireless transmission time so exactly due to changes in the environment. Furthermore, when the communication speed is low, the transmission of a synchronous packet every 1 ms imposes a great load on a communication channel.
(4) Control provided by the signal line state—Packets are not employed on the USB for port control functions, such as connection, disconnection, suspension, resumption, and reset, and the execution of port control functions are notified by static changes in signal line states. This method cannot be copied into wireless communication.
It is, therefore, one object of the present invention to provide a method for resolving the above wireless USB problems.
It is another object of the present invention to employ a wireless USB to remove a load imposed by the need to make a cable connection and to facilitate the disconnection and moving of devices.
It is an additional object of the present invention to extend a wireless USB and to provide a mechanism for enabling inter-host communication.
SUMMARY OF THE INVENTION
According to the present invention, a wireless hub connected to the USB bus in a computer side, and a wireless port connected to a USB interface of a peripheral device (generally, this is applicable to any device, and hereinafter such a unit will be referred to simply as a device), are provided and wireless communication is performed between the two. The wireless hub performs communication with the computer, and converts a USB packet routed to a device (a routing direction hereinafter sometimes called downstream) into a wireless signal, and a wireless signal received from a device into a USB packet. The wireless port attached to each device also converts a wireless signal into a USB packet and vice versa. While multiple wireless ports are usually connected to a single wireless hub, an arrangement of one wireless hub and a single wireless port is also possible. A wireless hub and a wireless port each have a device identifier (ID) uniquely assigned to them, and in the USB-wireless conversion, a destination specified by a USB address or bus topology, is converted into a device identifier.
A bidirectional buffer, for example, is provided in a wireless hub that, acting as a substitute, sends a response in accordance with the type of received packet and the state of a buffer. A USB packet received from the computer connected to the wireless hub is stored in the buffer, and is transmitted when the wireless medium can be used. A wireless port again converts the received wireless packet into a USB packet, and transmits it to a connected device. The response from the device is converted into a wireless packet, which is then transmitted to the wireless hub and is stored at the buffer therein. When the wireless hub is polled for the same contents by the computer, the wireless hub reads from the buffer the response that was received from the device, and transmits it to the USB bus. During a period at the wireless hub extending from the receipt of the first USB packet to the receipt of a wireless packet from downstream, all communication request (IN/OUT) transactions directed to the same destination are disregarded, and a NAK signal is returned to the computer indicating the device is not ready to perform processing. It should be noted, however, that SETUP transactions are constantly transmitted to the wireless link and ACK signals are returned to the computer. A time out in the USB can be avoided by using the above processing sequence.
The wireless hub periodically broadcasts a packet indicating the port states, and controls the operation of the wireless ports, while at the same time maintaining the frame synchronization in the wireless system. On the other hand, a wireless port for which there is a change in the device state, such as connect, disconnect, or remote wake-up, transmits to the wireless hub notification of the state change as the response to this packet. The length of a packet period is set long enough not to impose an excessive load on a communication channel and sho
Ishikawa Hiroshi
Mizutani Akihiko
Pant Amrit
Cameron Douglas W.
Dougherty Anne V.
Vincent David
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