Multiplex communications – Communication techniques for information carried in plural... – Adaptive
Reexamination Certificate
1998-03-05
2001-12-25
Chin, Wellington (Department: 2664)
Multiplex communications
Communication techniques for information carried in plural...
Adaptive
C370S345000
Reexamination Certificate
active
06333937
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention involves improvements to communications systems and methods in a wireless communications system.
2. Description of Related Art
The medium access control (MAC) layer of the ISO/OSI reference model, controls the assignment of a shared transmission medium resource to transmitting stations by using an access method such as time division multiplex, frequency division multiplex, code division multiplex, and the like. In collision oriented multiple access schemes, such as Aloha and Ethernet, if a transmitting station gains access to the shared medium while another station is transmitting on the medium, the transmitted data becomes corrupted. The access method provides an orderly way for the stations to back off from their transmission and retry at a later time. In the Aloha access method, a station broadcasts its packet when ready, the sender listens to see if it collides with other packets, and if so, re-transmits after a random interval. In the Slotted Aloha access method, packets are constrained to start at the beginning of a time slot, the sender listens to see if it collides with other packets, and if so, re-transmits after a random interval, in a later time slot. In Carrier Sense Multiple Access/Collision Detect (CSMA/CD) access methods, such as Ethernet, a transmitting station waits until the medium is quiet before starting to transmit and then continues to listen while transmitting. If two stations transmit during the same interval, both stations detect this and continue to transmit for a certain length of time to ensure that all stations on the medium detect the collision. The transmitting stations then wait for a random interval before attempting to transmit again. Details of the Ethernet access method are provided in the book by Hegering and Lapple, entitled “Ethernet, Building a Communications Infrastructure”, Addison-Wesley, 1993. In all applications of multiple access methods, design engineers try to estimate the maximum number of stations that will attempt to gain access to the shared medium in an average interval and then provide a sufficient number of time domain channels, frequency domain channels, or code domain channels, for example, to accommodate those stations.
In wireless communications, the medium is defined by a cell region occupied by a base station that serves a number of remote stations. At least some classes of messages between the remote stations and the base station, such as channel access requests or transmission control messages, employ collision oriented multiple access schemes to gain access to the shared medium, in order to conserve the radio spectrum. When a remote station wishes to request a session with the base station, it uses a collision oriented multiple access scheme. In a crowded interval when two or more remote stations attempt to access the base station, if the base station detects that a collision has occurred on the shared access channel, it can respond by broadcasting a negative acknowledgement (NACK) signal. Many times, however, the base station does not detect that a collision has occurred among requesting remote stations. Alternately, if the remote stations detect that a collision has occurred, they can back off and retry at a later time. But, in either case, it is difficult for the base station to quantitatively assess the reduced performance that the remote stations suffer during the interval of high usage.
What is needed is some way for the base station to have accurate information about the reduced performance that the remote stations suffer during an interval of high usage, to enable the base station to adaptively provide additional channels to the remote stations.
SUMMARY OF THE INVENTION
In accordance with the invention, each remote station in a wireless network cell that uses a collision oriented multiple access scheme, counts the number of retries attempted to gain access to the base station for a particular message. When a remote station attempts to transmit an access request message over a common access channel, it can determine that its message has failed in several ways. If the base station detects that a collision has occurred on the common access channel, it can respond by broadcasting a negative acknowledgement (NACK) signal. Alternately, the remote station can detect that a collision has occurred. As another alternative, another remote station in the same cell can detect that a collision has occurred, and relays that information back to the first remote station through the base station. The remote, having failed in its attempt to successfully transmit its access request message the base station, will have to retry the access under the collision oriented multiple access scheme. The remote station accumulates the count of its retries for a particular access request message, in a retry count register. The accumulated value of the number of retries in the register is then inserted in a retry count field of the access request message. The retry count field is a medium access control (MAC) layer field of the ISO/OSI reference model.
After one or more retries, the base station successfully receives the access request message. The base station strips off the retry count field as part of the normal MAC layer protocol processing. The base station runs a common access channel allocation manager program that adaptively provides additional channels to the remote station, depending on the number of retries the remote station required to successfully transmit the access request message. The base station maintains an allocation table that relates the retry count value extracted from the retry field, and the corresponding level of service or channel capacity that is required for a given probability that an access request will be successful on the first try. In response to the retry count value extracted from the retry field exceeding a given threshold, the common access channel allocation manager program adaptively provides additional channels to the remote station. In a time division multiplex access method, the common access channel allocation manager program adaptively provides alternate time slots. In a frequency division multiplex access method, the common access channel allocation manager program adaptively provides alternate frequency carriers. In a code division multiplex access method, the common access channel allocation manager program adaptively provides alternate codes. In an orthogonal frequency division multiplex (OFDM) wireless access method where the waveform is composed of many closely spaced frequency carriers, each carrying a single complex (magnitude and phase) symbols, the common access channel allocation manager program adaptively provides an alternate set of closely spaced frequency carriers.
In this manner, the base station has accurate information about the reduced performance that the remote stations suffer during an interval of high usage, to enable the base station to adaptively provide additional channels to the remote stations.
Currently, the invention has advantageous applications in the field of wireless communications, such as cellular communications or personal communications, where bandwidth is scarce compared to the number of the users and their needs. Such applications may be effected in mobile, fixed, or minimally mobile systems. However, the invention may be advantageously applied to other, non-wireless, communications systems as well.
REFERENCES:
patent: 4905302 (1990-02-01), Childress et al.
patent: 5117501 (1992-05-01), Childress et al.
patent: 5212806 (1993-05-01), Natarajan
patent: 5440545 (1995-08-01), Buchholz et al.
patent: 5533025 (1996-07-01), Fleek et al.
patent: 5862488 (1999-01-01), Kotzin et al.
patent: 5940771 (1999-08-01), Gollnick et al.
patent: 5974310 (1999-10-01), Bilgic
patent: 6014374 (2000-01-01), Paneth et al.
patent: 6052594 (2000-04-01), Chuang et al.
patent: 6085114 (2000-07-01), Gibbons et al.
patent: 6088588 (2000-07-01), Osborne
AT&T Wireless Services Inc.
Chin Wellington
Jones Prenell
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