Multiplex communications – Communication over free space – Combining or distributing information via time channels
Reexamination Certificate
1999-12-03
2002-12-17
Trost, William (Department: 2683)
Multiplex communications
Communication over free space
Combining or distributing information via time channels
C455S561000
Reexamination Certificate
active
06496499
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to media access control and a method for handling transmission of data from a plurality of isochronous devices in networks, and more particularly to distributed media access control and a method that prevents data collisions during transmission over a network.
2. Statement of the Problem
In any network, whether wired or wireless, a need exists to prevent data collisions during transmission over the network. This is particularly true with respect to data transmitted in wireless networks such as cellular telephone systems.
Conventional wireless data networks typically contain a number of spatially distributed cells. Each cell has an access point that is, essentially, a radio transmitter and receiver. Each access point can transmit over a predetermined frequency range, and each access point has a distinct transmission area which defines the cell boundary. A number of devices are provided that can travel from cell to cell. When a device is within a specific cell, the device can transmit data to the access point of that specific cell.
When a number of devices are within a specific cell, each device can desire to transmit data to the access point of the specific cell. In order to handle these transmissions without losing data, the transmission times of each device in the cell must be properly timed so that the devices do not transmit at the same time, thereby, causing a collision of data.
Recently, conventional wireless data networks have been used for local area telephone networks. These local area telephone networks include mobile devices that travel from cell to cell. Due to the nature of the telephonic data, these mobile devices transmit isochronous data. The proper timing of data transmissions becomes even more important when the data is isochronous. Isochronous data signals have the time characteristic of recurring at known, periodic time intervals (see, The New IEEE Standard Dictionary of Electrical and Electronic Terms, Fifth Edition, at page 686 (IEEE Publishing 1993)).
Conventional networks have used a variety of transmission schemes to handle collision of data, especially isochronous data. This is even more important in wireless networks, where detection of collisions is difficult and untimely. In these networks, avoidance of collisions becomes paramount. The IEEE 802.11 standard for wireless networks has adopted a data collision avoidance mechanism that is similar to the mechanisms used in wired data networks. This data collision avoidance mechanism involves listening to other mobile devices that are transmitting to the access point and attempting collision avoidance through the use of random back-off timeouts. Collision avoidance is accomplished by requiring each device desiring to transmit to first choose a random value from within a range specified in the IEEE 802.11 standard. Each such device must then wait this random period of time following the previous transmission before commencing. Although this technique does help avoid collisions, due to the randomness of the algorithm collision avoidance is only achieved probabilistically, collisions still occur often enough to degrade system performance noticeably.
Another failing of this technique is that it is only usable when all the mobile devices within a cell are capable of receiving the previous transmission, so that all devices can time the random back-off timeout from the same point. When mobile devices are widely dispersed within the cell boundary this is often not the case. Also, since IEEE 802.11's basic collision avoidance technique requires periods of non-use of the medium, it wastes useful bandwidth.
Based on the difficulties involved with data collision avoidance, the IEEE 802.11 standard recognizes an alternate collision avoidance technique that can be used in conjunction with the collision avoidance technique previously mentioned. In this alternate technique, the access point controls the transmission of the data from the mobile devices. In this technique, the access point creates a list of devices that are present in the cell. The access point then prompts each mobile device to transmit data at an appropriate time according to the device list. In this manner, the access point has full control of all mobile devices in its specific cell. In addition, the access point keeps track of the mobile units that enter and leave the cell boundary and revises the device list, accordingly. Also, when using the alternate technique, the access point allocates transmission time periods for other devices not participating in the alternate technique to access the wireless network using the collision avoidance with random back-off technique described herein above.
Several problems are also associated with this collision avoidance technique. This technique requires specific protocols and programming at the access point to compile the device list and to direct the mobile devices to transmit data according to the list. In addition, this technique uses valuable bandwidth because the access point must send a signal to the mobile device before data is transmitted. The bandwidth is further limited when the access point reserves transmission time periods for other devices that are not placed on the device list.
In another technique for avoiding collision of data, specifically isochronous data, each device transmits a “jamming” signal that follows an intricate timing algorithm. Each device is required to listen to all the other devices that transmit the “jamming” signal. Based on information gathered from listening to the other devices, each device individually determines a time to transmit data, preferably, when no other device is transmitting. This technique also has associated problems. First, it wastes valuable bandwidth during the times when the mobile devices transmit the “jamming” signal. Second, the technique requires each individual mobile device to “hear” all other devices that are in the cell. It can become impossible for the mobile devices to “hear” all transmissions in the cell when the mobile devices are located at polar ends of the cell or when obstacles create interference.
Therefore, a need exists to control media access to a wireless network that prevents collisions between the transmission of isochronous data by the mobile devices in a cell. Also, a need exists for a technique and an apparatus to control media access that does not require the access point to use additional protocols and programs to determine device transmission times. In addition, a need exists for a technique and apparatus to control media access that does not require the use of additional bandwidth in the wireless network. A need also exists for a technique and apparatus for controlling media access to a wireless network that allows non-participating devices to access the network without reducing the available bandwidth by allocating transmission time periods solely for the non-participating devices. Further, a need exists for a technique and apparatus for controlling media access to a wireless network that does not require each mobile device to “hear” all other mobile devices that are transmitting to the access point of a cell.
SUMMARY OF THE INVENTION
1. Solution to the Problem
These and other problems are solved by the present invention. The present invention contains an apparatus and method for controlling media access that prevents collision of data transmitted by the mobile devices in the cell. In this regard, the apparatus and method of the present invention do not require the access point to use additional protocols or programs to determine transmission times of the mobile devices. Further, the present invention has media access control that is distributed to each mobile device rather than being centralized at the access point of the cell, and allows access by non-participating devices.
Additionally, the apparatus and method of the present invention controls media access to a wireless network that does not require extra bandwidth to be used for deter
Amann Keith Richard
Hamilton Mark Alan
Dorr, Carson , Sloan & Birney, P.C.
Rampuria Sharad
SpectraLink Corporation
Trost William
LandOfFree
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