Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-09-09
2001-05-08
Trost, William G. (Department: 2683)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S452200, C455S062000, C455S063300
Reexamination Certificate
active
06230016
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to wireless/cellular radiotelephone systems and an apparatus and method for the assignment of radio frequency (RF) spectrum channels to the different cells within a wireless communication system for optimizing utilization of the available overall radio spectrum.
BACKGROUND OF THE INVENTION
The service area of a wireless communications system is partitioned into connected service domains known as cells, where radio telephone users communicate, via radio links, with the base station serving the cell. The base station (BS) is coupled to the land network. Efficient use of the available radio frequency spectrum is achieved through the reuse of the same radio frequencies in designated co-user cells that are sufficiently separated by distance so that the combined interference generated by all cells is below tolerable levels. The assignment of radio frequencies to cells has been based on regularity assumptions (i.e., equal-sized regularly-spaced cells with uniformly distributed traffic loads), which enable the adoption of simple rules for identifying co-user cells, and for partitioning the RF spectrum into channel sets. When the regularity assumptions do not hold—as is frequently the case in real world situations—the rules of regular channel assignment do not lead necessarily to the efficient utilization of the RF spectrum, if they can be applied at all. To optimally utilize the RF spectrum one must solve the non-regular channel assignment problem.
SUMMARY OF THE INVENTION
Therefore a channel assignment system, embodying the principles of the invention, assigns channels to a group of cells of arbitrary shape, size, and/or location, by the optimal partitioning of the available radio frequencies into non-overlapping sets, the optimal grouping of co-user cells, and the best assignment of the former to the latter. The objective is the maximization of traffic handling capacity. Given the multitude of cells, the objective may be expressed as the maximization of the bottleneck capacity ratio that can be sustained at a satisfactory blocking rate, interference level, and other system constraints, which is the lowest capacity ratio across all cells. The bottleneck capacity ratio is known as the capacity factor. A capacity ratio for a cell is defined as the ratio of the number of radio frequencies assigned to the cell over the number of radio frequencies needed to meet blocking probability requirements. The latter is fixed once the traffic loads and desired blocking are specified. The maximization of the capacity factor is used in the discussion below as an example. Other measures of utilization efficiency of the RF spectrum may also be employed.
A channel assignment can adapt to traffic distribution changes over time by recomputation of the optimal channel assignment based on traffic estimates derived from the observed traffic loads, satistical differences may be determined from real time measurements of traffic load and used for rearranging channel assignments. An assignment of channels to cells based on an expected traffic distribution does not imply an exclusive relationship between them, as shown in detailed description below. Available channels not assigned to a particular cell can be borrowed by that cell if it has a present need for added channel capacity and provided that the interference and other system constraints are satisfied.
The solution of the optimal non-regular channel assignment is decomposed, according to the invention, into two mathematical programs designated as a Master Program and a Subprogram. These are solved iteratively. A channel set augmentation technique may be implemented between solutions of the Master and Subprogram in order to speed up the solution procedure.
In an illustrative embodiment, a cell having exhausted its available assigned channels may borrow a channel that is not assigned to the cell to satisfy capacity.
While the illustrative embodiment herein is characterized in terms of frequency assignments, it is to be understood that the same techniques may be applied to code assignments in a CDMA system and time slot assignments in TDMA systems. It is not believed necessary to describe these alternative arrangements herein.
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Lucent Technologies - Inc.
Milord Marceau
Trost William G.
LandOfFree
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