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Radio based collision detection for wireless communication system
| Details |
Inventors: Burns, Lawrence M.; Podell, Allen; Fisher, David A.; Ramachandran, Ravi;
Assignee: 3Com Corporation (Santa Clara, CA)
Primary Examiner: Kizou; Hassan
Assistant Examiner:
Attorney, Agent or Firm:
A collision detection method and apparatus which is suitable for use in a wireless CSMA/CD network, or other wireless networks where collision detection is provided. The apparatus includes a detector which detects intermodulation or other mixing products of colliding data transmissions at a station in the network, and a signal processor which indicates collisions between the data transmissions based upon characteristics of the intermodulation products. The system is capable of detecting collisions, both between transmissions from the station on which the device is located and transmissions from other sources, and between two transmissions being received from other sources. The station includes a transmitter having an input for a data packet. Resources coupled to the input add a header to the data packet, the header having characteristics monitored by the collision detector circuitry including a pseudo-random bit sequence. Data transmission signals are supplied to the transmitter in response to the header and the data packet. Thus, collisions occurring during transmission of the header sequence have intervals during which a mismatch occurs between the colliding signal and the data transmission. |
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DETAILED DESCRIPTION A detailed description of a preferred embodiment of the present invention is provided with respect to the figures.
FIG.
1 shows a local area network including a wireless link according to the present invention.
The system includes a CSMA/CD wired LAN 10, such as a standard Ethernet system.
Coupled to the wired LAN are a plurality of end stations 11, 12 as is standard in the art.
Also, coupled to the wired LAN 10, is an access point 13 for communication with wireless stations, including wireless station WSTA 1 and wireless station WSTA 2.
The access point has a typical range having a boundary as illustrated by the dotted line 13, which is defined by the receiver and transmitter technology used to define a basic service area.
Although a variety of communication channel technologies could be used, the preferred system according to the present invention is implemented using a relatively narrow band frequency modulated NRZ channel in the 2.
4 GHz ISM band.
The channel bandwidth in the preferred system is between 7 and 14 MHz.
This channel allocation system allows for allocating a plurality of channels within the ISM band for adjacent basic service areas.
According to the CSMA/CD protocol, in order to gain control of the communication channel, each wireless station must establish that no other stations are currently transmitting.
Thus, the status of the receivers is checked to determine whether the carrier is free.
If the carrier is free, then it begins transmitting.
It is possible that two stations within the BSA will attempt to transmit at or near the same time under this protocol.
Thus, a mechanism to detect collisions between simultaneous or near simultaneous transmissions is needed, such as is well known in the wired Ethernet LAN environment.
However, this presents unique difficulties in the wireless environment.
FIG.
2 provides a block diagram of a wireless station according to the present invention.
The wireless station includes an antenna 20 coupled to an analog receiver 21
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Multiplexer-related 
