It is well known, for example in cellular mobile networks, that the interference phenomena between the multiple signals emitted by the base stations and received by a mobile terminal greatly limit the QoS (acronym for “Quality of Service”) offered to the users of the network, and also the overall quantity of traffic that the network can manage. The effect of the intercellular interference is particularly noticeable along the cell boundaries, since for a user situated in the center of a cell, the strength of the useful signal greatly exceeds that of the interfering signals; the QoS therefore especially depends on the users situated at the cell boundary; this is why the engineers responsible for the optimization of the network from the operational perspective invest much of their efforts in the optimization of the network at the cell boundary.
It is possible to combat the intercellular interference phenomena by planning accordingly the power of each base station within the band, or each sub-band, of frequencies of the emission spectrum: this is referred to as “power control”.
The article by R. Combes, Z. Altman, and E. Altman entitled “Self-organizing fractional power control for interference coordination in OFDMA networks” (IEEE ICC 2011) provides a dynamic method for power control in mobile networks of the OFDMA type (acronym for “Orthogonal Frequency-Division Multiple Access”). In this method, it is considered that, within a cellular mobile network, a group of A base stations each emitting with a power Ps(b), where s=1, . . . , A and b=1, . . . , B, in B sub-bands of frequencies. Each base station implements, in an iterative manner (for example periodic), the following steps:                a) reception, from mobile terminals served by said base station s, of measurements of radio parameters performed by these mobile terminals,        b) calculation, for b=1, . . . , B and t−1, . . . , A, of predetermined values Vs,t(b) by means of said measurements,        c) transmission to the other base stations of said values Vs,t(b), and reception, from the other base stations, of the analogous values Vs,t(b),        d) calculation, by means of said values Vt,s(b), of the derivatives        
            ∂      U              ∂              P        s                  (          b          )                      ,where U is a predetermined utility function for said network, and                e) update of the transmission powers Ps(b) so as to reduce the value of said utility function U.        
More precisely, according to this method:
      U    =                  ∑                  s          =          1                A            ⁢              U        s              ,where Us is a predetermined function of the data rates delivered by the base station s.
With regard to the step a), if said radio parameters comprise the attenuation (also referred to as “Reference Signal Received Power”, or RSRP), the measurements may for example be in accordance with the standard 3GPP TS 36.214, “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer”, Section 5.1.1 (“Measurements”). The transmission of these measurements to the server base station is, for example, in accordance with the standard 3GPP TS 36.331 “Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol Specification”, Sections 5.5 (“Measurements”) and 6.3.5 (“Measurement information elements”).
With regard to the step c), the communications between neighboring base stations belonging to an OFDMA network of the 3GPP LTE type (acronym for “Long Term Evolution”) can, for example, use the “X2” interface.
This known method has several drawbacks:
it optimizes a metric associated with the instantaneous QoS of the network; however, such metrics cannot be directly linked to the mean quality criteria, which are the true measurements of quality in which the operator is interested, for example the communications blocking rate or the mean time for file transfer;
the optimality (even partial) of this method has not been proven; it is therefore possible for there to be some scenarios in which this known method degrades the state of the network instead of improving it; and
nor has the stability of this method been proven; the question of the stability is essential in the sense that no operator will wish to implement such a method in their network without cast-iron guarantees with regard to the stability and the resistance to noise.
This method converges toward a stable configuration only with the assumption—obviously unrealistic—of a constant number of users over time and of infinite durations of communication. As it does not converge toward a stable configuration under real conditions of use, it is impossible, based on the observation, even over a very long time, of the dynamic behavior of an implementation of the method, to deduce from this a planning for the emission power of the base stations within the band, or the sub-bands, of frequencies.
It is clear that the aforementioned problem of interference affects practically all the types of mobile networks, whether they be cellular (2G, 3G, and so on) or wireless (WiFi, Bluetooth, and so on). The present invention relates to all these types of networks, in which mobile terminals exchange radiofrequency communications with equipment (base stations, access points, relay-stations, and so on) that will all be denoted under the name of “server stations”.
USPTO Backgrounds
USPTO Backgrounds