Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
2000-02-28
2003-08-12
Maung, Nay (Department: 2681)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S512000, C455S450000, C370S332000
Reexamination Certificate
active
06606499
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the dynamic channel allocation (DCA) for a cellular radiocommunication networks such as a GSM-type network.
A distinction is made between interference-adapted DCA schemes and traffic-adapted DCA schemes. The interference-adapted schemes take account of the quality of the radio signals received, and dynamically allocate the channels assumed to have the lowest noise. The traffic-adapted schemes are based on the knowledge of which channels are used in each cell in order to ensure that two identical channels are not allocated in adjacent cells: they do not rely on any radio quality criterion but require information to be exchanged between the different channel-allocating units within the network.
In the field of the interference-adapted DCA algorithms, the algorithms proposed so far are designed to allocate channels on the radio link for packet mode communications (see M. FRULLONE et al: “Dynamic Channel Allocation for ATDMA”, Proc. of the Race Summit, Lisbon, Nov. 1995, pages 299-203). This is not suitable for networks which support communications in circuit mode, such as GSM. As for the traffic-adapted DCA algorithms, the studies that have been conducted are basically theoretical. Due to the fact that these mechanisms require large exchanges of signaling between the different entities allocating radio resources within the network, they are not particularly well suited to current cellular networks, which do not facilitate such exchanges. At present, therefore, they are of little interest.
These days, mobile network operators apply channel planning techniques as a means of distributing the physical channels to be allocated amongst the different cells of the network. The term “planning” means that each cell is allocated its own list of physical channels from which channels are selected as they are allocated. In the majority of systems, the channel planning is simplified to a frequency planning.
The advantage of such a technique is that it is possible to ensure that no channel is allocated to two adjacent cells, which reduces the risk of interference between two channels allocated in adjacent cells. This ensures a certain radio quality on each channel allocated in the network.
However, frequency planning has the following disadvantages:
1) Its implementation is fastidious. The more irregular the topology of the cellular coverage is (different cell sizes, non-symmetrical patterns, . . . ), the more difficult it is to plan. The concept of a multicellular network with microcells and “umbrella” macrocells makes any attempt at frequency planning even more difficult since it introduces several levels of coverage, each requiring a frequency plan. This also has the effect of restricting the number of frequencies allocated to each cell (thereby limiting traffic).
2) Frequency planning does not make it easy to change the network topology. For example, each time base stations are added to or withdrawn from the network, a new frequency plan is needed over a significant part of the network. This aspect is becoming even more complex now that operators are required to modify their cellular engineering on a frequent basis (integrating microcell zones into the existing network).
3) Frequency planning does not allow the system to allocate resources to mobiles in a flexible manner. In view of the fixed (and limited) number of resources allocated by cells, the system is unable to absorb local traffic peaks due to the lack of available resources.
Whilst frequency planning may remain an interesting solution in a macro-cellular environment (simple and regular cell configuration, homogeneous traffic distribution), it is less so when it comes to other types of environment (micro-cellular, “umbrella” cells, traffic peaks, . . . ).
The sharp increase currently seen in mobile communications traffic due to the success of portable telephones has forced operators to increase the density of their networks. They have therefore now been forced to combine any type of cellular configuration (macrocells, microcells, umbrella cells, omnidirectional antenna, directional antenna, . . .) and accordingly need a more flexible mechanism for allocating channels than frequency planning.
WO96/31075 discloses a method of dynamically allocating channels for a cellular radio network in which “statistical preferences”, i.e. priorities, are assigned to different frequency channels within a same cell. The selection of which frequency channel is to be used is based on these “statistical preferences”. The process of determining “statistical preferences” is based on measurements of channel characteristics, taken when these channels are not being used.
The DCA mechanism disclosed in this document WO96/31075 does not use radio measurements taken during a communication. The same applies to the mechanism described in U.S. Pat. No. 5,507,008. According to the latter document, when a call is being established, the base station of a cell checks that the envisaged channel is not subject to too much interference. If the channel-to-interferer ratio (CIR) is too low, the base station moves on to the next channel in a general list common to all the cells.
GB-A-2,266,433 discloses another DCA mechanism in which several frequency lists are held for each cell. The base station determines a transmission loss of a signal returned by a mobile station in order to select a list of frequencies, from which the channel is selected on the basis of a quality criterion. This quality criterion may be based in particular on the channel-to-interferer ratio. The frequency lists are updated depending on the success encountered during previous attempts to select the channels concerned. Here again, no use is made of radio measurements taken during communication.
An object of the invention is to propose an efficient technique for allocating radio resources dedicated to communications, which does not require prior frequency planning and which therefore releases the operator from the above constraints.
The method is also intended to enable the network to absorb traffic peaks under certain conditions.
SUMMARY OF THE INVENTION
The invention thus proposes a method of dynamically allocating channels in a cellular radio network, wherein a set of physical channels is used in said network to form logical channels dedicated to communications in circuit mode between mobile stations and geographically distributed base stations, each logical channel belonging to a physical channel, and wherein, for each communication established on a logical channel between a base station and a mobile station, radio parameters representative of conditions of said communication on said logical channel are periodically measured. According to the invention, the method comprises the following steps, carried out for each base station:
associating a respective priority index to each physical channel of said set;
holding a first list of physical channels which are not being used by said base station to communicate with any mobile station, and at least a second list of busy physical channels, each having at least one active logical channel dedicated to a communication currently taking place between said base station and any mobile station;
updating the priority indices associated with the physical channels of the second list on the basis of the radio parameters measured in relation to communications taking place on the logical channels belonging to said physical channels of the second list; and
when establishing a communication with a mobile station, selecting for said communication an accessible and non-active logical channel belonging to a physical channel whose priority index is maximum.
As a result of this DCA mechanism, it is no longer necessary, before putting the network into service, to plan the allocation of frequencies between the cells in order to distribute between them the radio resources that can be allocated to mobile communications. The fact that an operator no longer needs to undertake any frequency planning means that there will
Plas Patrick
Verrier David
France Telecom
Gardner Carton & Douglas LLC
Maung Nay
Persino Raymond
Rupp Brian C.
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