Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1998-09-30
2001-06-26
Hunter, Daniel (Department: 2749)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S422100, C455S432300, C455S435100, C455S445000, C455S453000
Reexamination Certificate
active
06253087
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to wireless telecommunication networks. More specifically, the invention relates to a technique for traffic management in spread spectrum systems.
BACKGROUND OF THE INVENTION
In wireless telecommunication networks, service providers are intensely interested in providing high quality, reliable services for their customers in today's high competitive marketplace. A significant aspect affecting the service quality is the consistency of radio coverage within cell coverage areas of the network. Moreover, an additional aim from the provider's perspective is to be able to increase capacity while maintaining quality and reliability. As known by those skilled in the art, telecommunication networks operating in accordance with code division multiple access (CDMA), which are also referred to as spread spectrum systems, the cell coverage is particularly affected by the traffic load in the cell. For example, as more traffic is carried by the cell, its coverage area tends to contract, on the other hand as less traffic is present, the coverage area of the cell tends to expand.
The tendency for cells to shrink and expand in relation to number of users in the cell is known in the art as “cell breathing” and occurs, for example, since each user in a CDMA system cumulatively contributes to the interference in the cell since they simultaneously share a common frequency band. It should be noted that there are typically multiple frequency layers upon which the users may operate on. The multiple layers permit service providers to add capacity while conforming to predefined frequency bands specified by the operating standard. The inherent nature of spread spectrum systems permits all users to transmit and receive on the same frequency thus each of the transmissions necessarily “interfere” with each other. As more traffic appears in the cell, the more interference is introduced thereby increasing the power threshold that a mobile must transmit to overcome the interference in order to sufficiently communicate with the base station. This effect tends to be more prominent on uplink transmissions from mobiles since their power levels tend to be more limited in comparison to that of the base station.
An undesirable consequence of cell breathing is the development of coverage holes (or gaps) that may occur between cells during periods of high traffic load. Consequently, a mobile straying into a coverage hole may not have a sufficient connection to continue the call, thus the call may be dropped. In the context of the present invention, the term “call” is used interchangeably to include either voice or data traffic. The extent to which coverage holes develop in generally related to the cell planning performed by the service provider. By way of example, the provider typically uses cell planning tools, network measurements, field and drive tests among other things in order to determine a suitable base station deployment for sufficient network coverage. Thus, one known way of minimizing the undesirable occurrence of holes is to simply increase the number of base stations for a given network coverage area. Increasing the density of base stations permits sufficient coverage overlap in order to compensate for cell contraction due to cell breathing. However, a major disadvantage of adding more base stations is that it is an extremely expensive solution to implement in order to counter the effects of cell breathing.
Another technique that has been used in the prior art for reducing the likelihood of coverage holes is to carefully limit the amount of interference in the cell before it reaches precarious levels. Typically this is performed by admission control whereby a strict limit for traffic capacity is imposed within the cell. A theoretical load limit for ideal conditions may be calculated which thereby represents the capacity on the cell at 100% load. However, the practical load limit, which is the capacity level at which the development of coverage problems become unacceptable, is determined by using various theoretical and experimental methods including cell planning tools, network measurements, and field and drive tests. For example, a practical load limit of 65% on the cell may be found to be the point at which coverage holes start to become unacceptable. This may be reflected in a dropped call rate that is approaches unacceptable levels. Therefore, in most cases admission control algorithms are programmed to maintain the capacity levels of cells to stay within the practical load limit. It should be noted that the admission control level can be represented in other ways such as a specific number of users in a cell, for example.
The specific load limit levels may vary from network to network depending on the particular network configuration, for example, number of base stations, traffic volume, type of traffic i.e. voice or data etc. Hence a network operating with a strict form of admissions control may at times, and perhaps unnecessarily, limit the capacity in cells below a higher level that it may otherwise be able to handle, thereby depriving service providers of additional revenue. In view of the foregoing, it would be desirable to implement an improved traffic management technique that minimizes the development of coverage problems without unnecessarily limiting the overall network capacity.
SUMMARY OF THE INVENTION
Briefly described, and in accordance with an embodiment thereof, the invention discloses a technique for improved traffic management in a spread spectrum wireless telecommunication network using admission control. In an embodiment of the invention, a first admission control limit is set for the first frequency based on an acceptable tolerance level for which coverage holes associated with cell breathing may develop. A second admission control limit that is stricter i.e. lower than the first admission control limit is set for a designated frequency. The second admission control limit is set low enough that it is virtually free of coverage problems. As coverage problems develop on the first frequency, mobiles on the first frequency that stray into a coverage hole are diverted to the designated frequency via a hard handoff. Moreover, access attempts made from within a coverage hole on the first frequency are likewise diverted the designated frequency.
In a second aspect of the invention, if the load on the designated frequency exceeds its admission control limit due to a large number of diverted calls, for example, the first frequency loading is checked to determine if it has room to handoff back from the designated frequency. This enables the designated frequency to remain under its admission control limit thus maintaining its ability to continue to receive diverted calls while assuring that there are no coverage problems.
The invention provides improved call traffic management within the wireless network by diverting traffic afflicted by coverage problems on one frequency to an alternative (designated) frequency that is free of such problems. The method thereby improves overall capacity and call quality in the network by utilizing frequency resources in a more efficient manner. These and other advantages of the present invention will become apparent upon reading the following detailed description and studying the various figures of the drawings.
REFERENCES:
patent: 4670899 (1987-06-01), Brody et al.
patent: 5437054 (1995-07-01), Rappaport et al.
patent: 5649293 (1997-07-01), Reed
patent: 5666356 (1997-09-01), Fleming et al.
patent: 5697055 (1997-12-01), Gilhousen et al.
patent: 5809423 (1998-09-01), Benveniste
patent: 5839074 (1998-11-01), Plehn
patent: 5852778 (1998-12-01), Labedz
patent: 5898681 (1999-04-01), Dutta
patent: 781066 (1997-06-01), None
patent: WO97/14260 (1997-04-01), None
European Search Report re RS 101812 Date of mailing of search: Mar. 26, 1999.
Burns Doane Swecker & Mathis L.L.P.
Hunter Daniel
Telefonaktiebolaget LM Ericsson
Woldetatios Yemane
LandOfFree
Method and system for improved traffic management in... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and system for improved traffic management in..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and system for improved traffic management in... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2522105