Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1998-03-31
2001-05-01
Kizou, Hassan (Department: 2738)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S362000
Reexamination Certificate
active
06226281
ABSTRACT:
The field of the invention is that of transmitting radio signals in code division multiple access (CDMA) type cellular networks. More precisely, the present invention relates to a method of controlling terminal transmitter power in a CDMA type cellular network, and to a base station controller and a base station implementing the method.
BACKGROUND OF THE INVENTION
A CDMA type cellular network is constituted by a plurality of cells each having radio coverage provided by a base station. The base stations are connected to a controller. Within each cell, terminals, e.g. mobile terminals, communicate in CDMA mode with the base station of the cell, i.e. with all of the terminals using transmission in the same frequency band, and with transmitted data being spread by spreading sequences. These sequences are conventionally pseudo-random number (PN) sequences that are statistically orthogonal to one another, so as to limit interference between signals that have been spread by different sequences.
In such a cellular network, when interference within a cell increases, signal-to-noise ratio (S/N) conditions deteriorate and the base station of the cell requests each active terminal to increase the power of the signals it transits by some number of decibels (dB). The interference may come either from terminals transmitted in adjacent cells and parented on other base stations, or else be due to an increase in the number of users in the cell in question. Interference is due to a loss of statistical orthgonality between the spreading sequences because of multiple paths.
That problem is raised in PCT patent application WO 93/09626 which is fully incorporated in the present application by reference.
The drawback of that solution is that a generalized increase in the transmission power of the terminals gives rise not only to interference within the cell under consideration, but also causes increased interference in adjacent cells. The base stations of the adjacent cells will therefore also request the terminals with which they are in communication to increase their transmission powers in order to overcome the interference. Very quickly, this mechanism can therefore lead to escalation until all of the terminals throughout the CDMA network have reached maximum transmission power, thereby completely paralyzing the system.
OBJECTS AND SUMMARY OF THE INVENTION
A particular object of the present invention is to remedy that drawback.
More precisely, one of the objects of the invention is to provide a method of controlling terminal transmission powers in a CDMA type cellular network that does not lead to the communications system becoming paralyzed.
Another object of the invention is to provide a base station and a base station controller that implements the method.
These objects, and others that appear below, are achieved by a method of controlling the transmission power of terminals in a CDMA type cellular network, wherein, when the transmission power of a number n
1
of said terminals is authorized to be increased by a total amount P dB, the method consists in instructing a number n
2
of said terminals, benefiting from better transmission quality in the up direction, to decrease their total transmission power by P dB.
Terms concerning “total” increase in transmission power are used to designate the sum of the power increases of the n
1
terminals. Similarly, terms concerning “total” decrease of transmission power correspond to the sum of the decreases in the transmission powers of the n
2
terminals. In this way, equilibrium is obtained between the power increases and the power decreases from the terminals, thereby making it possible to conserve a constant level of interference in the cell or cells under consideration.
Advantageously, said n
2
terminals are those benefiting from the best transmission quality in said up direction. Thus only those terminals that are already benefitting from best transmission quality are penalized.
The quality criterion making it possible to define up transmission quality is preferably the signal-to-noise ratio S/N, which is proportional to the energy received per information bit divided by the spectrum density of the noise power, Eb/No. This noise power spectrum density is the sum of the contributions of thermal noise plus interference.
The method of the invention is advantageously applied to mobile terminals. It can be implemented in a base station of a CDMA type cellular network or in a base station controller for such a network.
The method of the invention is preferably implemented when the mean level of total received power at the base station exceeds a first threshold value or when the sum of the terminal transmission powers exceeds a second threshold value.
The invention also provides a base station for a CDMA type cellular network in which terminals are to communicate. The base station includes means for allocating to a number n
1
of terminals suffering from insufficient transmission quality in the up direction shares in a total transmission power resource equal to the sum of power decreases requested of a number n
2
of terminals benefiting from transmission of better quality in said up direction.
The invention also provides a controller for base stations in a CDMA type cellular network in which terminals are to communicate. The controller includes means for allocating to a number n
1
of terminals suffering from insufficient transmission quality in the up direction shares in a total transmission power resource equal to the sum of power decreases requested of a number n
2
of terminals benefiting from transmission of better quality in said up direction.
REFERENCES:
patent: 5245629 (1993-09-01), Hall
patent: 5267262 (1993-11-01), Wheatley, III
patent: 5333175 (1994-07-01), Ariyavisitakul et al.
patent: 5475861 (1995-12-01), Hall
patent: 5559790 (1996-09-01), Yano et al.
patent: 5619525 (1997-04-01), Wiedeman et al.
patent: 5689815 (1997-11-01), Yamazaki et al.
patent: WO9307702 (1993-04-01), None
patent: WO9309626 (1993-05-01), None
Cordier Christophe
Fratti Marco
Alcatel
Elallam Ahmed
Kizou Hassan
Sughrue Mion Zinn Macpeak & Seas, PLLC
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