FR2890264A1 - Binary error rate probability calculating method for server base station, involves calculating probability of collision between bursts, and calculating binary error rate probability so that number of bits of current frame are deleted - Google Patents

Abstract

The method involves calculating probability of collision between bursts so that a concurrent scrambling carrier wave of preset frequency is scrambled by interference of a current carrier wave of a server base station for a number of times over a course of N successive current communication frames with respect to a considered burst. A binary error rate probability is calculated so that a number of bits of the current frame are deleted by interference with a concurrent scrambling carrier wave during a number of FTDMA communication frames as a function of the probability of collision. Independent claims are also included for the following: (1) a system for calculation of a binary error rate probability of an FTDMA frame transmitted with frequency hopping (2) a computer program product executable by a computer or a central processing unit of a dedicated system, for calculation of the probability of collision between bursts (3) a computer program product executable by a computer or a central processing unit of a dedicated system, for calculation of a binary error rate probability.

Description

METHOD AND SYSTEM FOR CALCULATING RATE PROBABILITY

  BINARY ERROR OF FTDMA FRAME TRANSMITTED WITH FREQUENCY HOPPING AND CORRESPONDING PROGRAM PRODUCT.

  The invention relates to a method for calculating, at a given point in space, the probability of the bit error rate of a current communication frame transmitted in FTDMA with frequency hopping by a server base station, in the presence of a plurality of interfering base stations.

  The frequency hopping spread spectrum technique essentially consists of cutting a wide band of frequencies into a fixed number of channels of a given width. The transmission is then performed using a combination of channels emitting successively by jump, on one channel and then on another, for a short time. This operating mode makes it possible at a given moment to transmit a signal that is more easily recognizable on a given frequency, by reducing the risk of interference between the carrier waves emitted by each of the base stations serving a cellular telephone network, for example . It is understood, in fact, that in this situation any server base station, other than a specific base station waitress, is likely to constitute an interfering base station vis-à-vis the latter.

  More specifically, with reference to FIG. 1a, in the case of the transmission of a speech signal by a GSM or FTDMA network for Frequency Time Division Multiple Access in English, for multiple access by frequency distribution and in the time, a server base station is equipped with a plurality, up to eight, TRX transmitting equipment, operating in parallel with the transmission and to ensure the allocation of physical channels to the transmission of the speech signal .

  FIG. 1a shows, in order not to overload the drawing, two transmitting equipments TRX1 and TRX2.

  A speech signal VS is divided into successive voice frames of rank s-1, s, s + 1 of 20 ms, each voice frame being sampled, coded in a succession of binary values to constitute a complete codec of duration 40 ms, ie two speech frame lengths, a full codec including error correction code and redundancy information.

  Referring to Figure 1a, for each TRX transmitter equipment of a base station, server or scrambler, the FTDMA communication frame is subdivided into successive time slots TS, during which the transmission of bursts or "bursts" in English, consisting of parts of each complete codec is performed.

  During a frequency jump in baseband illustrated in FIG. 1a, each transmitter equipment is associated with a determined frequency, chosen from the available frequencies, the frequencies f 1 and f 5 respectively for the devices TRX 1 and TRX 2 shown in FIG. . At each time slot TS is assigned a communication, the communication Ci assigned to the time slot TS number 3 in Figure la. The switching of the transmitting equipment by a pseudo-random or cyclic sequence makes it possible to ensure the frequency jump to each FTDMA communication frame, the CI communication being transmitted on the same rank 3 time slot on each transmitter.

  Burst transmission over a time interval is performed interleaved. A complete codec is subdivided into four bursts and eight half-bursts. The first four half-bursts of the voice frame s are transmitted with the last four half-bursts of the previous voice frame s-1, a half-burst being transmitted over a time interval. Thus, the transmission of a complete codec, and therefore of a voice frame, requires the transmission of eight FTDMA communication frames. The physical transmission channel of the call, Ci in FIG. 1 a, is represented by the time interval TS, of rank 3 in the above-mentioned figure, at the frequency associated with the transmitting equipment which controls the transmission of each frame. FTDMA. Thus, the duration of each time slot TS and of each communication frame depends, on the one hand, on the number of bits of the complete codec, and, on the other hand, on the bit rate of the transmission.

  Figure 1b shows a frequency jump in baseband.

  During a synthesized frequency jump, as illustrated in FIG. 1c, a given call is always attached to a time interval of determined rank, but a transmitting device is no longer associated with a fixed frequency value.

  Thus, with reference to FIG. 1c, for a given jump frequency value, f5 for example in the above-mentioned figure, on each FTDMA communication frame, the occupation of the associated time slots depends on the transmitting equipment associated with the frequency considered. Of course, no TRX transmitter equipment of the same base station is associated with the same jump frequency at a given instant of FTDMA communication frame and each transmitter equipment of a base station has the same charge rate on the same base station. the frequencies, the charge rate corresponding to the percentage of time slots TS occupied on the TRX transmitters of the considered base station.

  To evaluate the risk of interference between a server station and several interfering stations, current known techniques use approaches taking into account the value of the ratio between the carrier wave field of the server station and the sum of the fields of the stations. interfering signals. This designated C / I ratio represents a relative field strength of the gate station to the fields of the interfering stations at a given point in the transmission space.

  In a frequency hopping situation, the abovementioned techniques recommend calculating the C / I ratios by hop frequency of the server station and more or less complexly weight the interference generated by the interfering stations on these frequencies, in particular by the load. , the number of transmitting equipment TRX, the number of jump frequencies of the stations considered. The aforementioned techniques have the disadvantage that the average of the C / I ratios is calculated without taking into account that the transmission, at a given jump frequency, is performed over a single time interval of the FTDMA communication frame, while In fact, whatever the value of the C / I ratio for the frequency considered, one can not lose more information than that which is contained in the interfered time interval.

  Under these conditions, considering, for example, a server station having three jumping frequencies, an extremely low C / I level on a frequency of the server station, preventing the valid transmission of the corresponding time interval, and two levels of the C / I ratio raised on the two other frequencies allowing the valid transmission of the time interval, but assuming a level of the average C / I ratio on these three frequencies as intervening on each of these frequencies and preventing the valid transmission of the intervals the transmission is considered to be scrambled, whereas in reality only one third of the information transmitted has actually been lost.

  The foregoing situation is illustrated with reference to Figures I d and 1 e.

  FIG. 1d represents, with reference to FIGS. 1a and 1c, the constitution of a physical channel in FTDMA, from a frequency band FB allocated to the setting up of a mobile telephony service, such as GSM for example and a frequency channel Sh allowing the transmission of the service for a user. The frequency channel Sh enables the constitution of the physical channel PSh on several FTDMA GSM frames comprising eight time slots TS.

  FIG. 1a shows the process of collision between bursts or time intervals of a server base station S and an interfering base station B. The base station server S comprises a transmitter equipment TRX, a channel of frequency f2 and a communication transmitted on the index 3 of the FTDMA frame.

  The interfering base station B has two transmitting equipment, three jump frequency channels f1, f2, f3 and a traffic load rate p = 3/8.

  The point 1) of FIG. 1c represents the successive transmission time intervals of the interfering base station B according to a pseudo-random frequency hopping sequence in gray and the point 2) of FIG. 1e represents the successive time intervals. of the server base station S. The phenomenon of collision between the server base station S and the interfering base station B results from the synchronization of the concomitant time intervals represented in gray, and thus superimposed, of the base station waitresses. The object of the present invention is to overcome the disadvantages and limitations of the techniques of the prior art.

  In particular, an object of the present invention is the implementation of a method for calculating, at a given point in space, the probability of the bit error rate of an FTDMA communication frame transmitted by a server base station in the presence of a plurality of interfering base stations, this bit error rate probability being expressed as a binary error probability distribution from a collision probability distribution between bursts or time intervals waitress base station and interfering base station.

  Another object of the present invention is, in addition, from descriptive data of equipment of an analyzed network, such as load in traffic, reception quality tables, field prediction data and description of frequency plans. , to allow to establish a predictive evaluation of the interference experienced by a receiver at any point of the network, in terms of bit error rate.

  Another object of the present invention is finally the implementation of the aforementioned method for use in the planning and optimization of cellular radio-mobile networks implementing the FTDMA transmission, cellular network as diverse as GSM, GPRS, EDGE, IS-136 for example.

  The method for calculating, at a given point in space, the probability of the bit error rate of a current communication frame transmitted in FTDMA with frequency hopping, which is the subject of the invention, is implemented for all server base station in the presence of a plurality of interfering base stations. Each current communication frame is transmitted by the base station in bursts during a time slot of N FTDMA frames on a physical channel formed by a set of frequency channels each constituting a current carrier wave, subject to a frequency hopping, and allocated at a time interval. Each communication frame is subjected by its carrier wave to the potential interference of concurrent communication frames transmitted during a time slot of N FTDMA frames on a physical channel formed by a set of frequency channels constituting a competing interfering carrier wave, subject to frequency hopping and allocated at this time interval.

  It is remarkable in that it consists, at least, in calculating the probability of collision between bursts such as a competing interference carrier wave of determined frequency that is interfering by interference of said current carrier wave a number K of times during the duration N of a given number of successive common communication frames on this burst, and calculating the probability of the bit error rate K / N such that the same determined number of K bits of the current frame are erased by interference of the current carrier wave with at least one concurrent interference carrier wave for a duration of the same number N of FTDMA communication frames transmitted by this server station, according to this probability of collision between bursts.

  The system for calculating, at a given point in space, the probability of the bit error rate of a current communication frame transmitted in FTDMA with frequency hopping, object of the invention, operates for any base station. waitress in the presence of a plurality of interfering base stations. Each current communication frame is transmitted by the burst server base station during an interval of N FTDMA frames on a physical channel formed by a set of frequency channels each constituting a current carrier wave, subject to frequency hopping, and allocated to a time interval. Each communication frame is subjected by its carrier wave to the potential interference of concurrent communication frames transmitted during a time slot of N FTDMA frames on a physical channel formed by a set of frequency channels constituting a competing interfering carrier wave, subject to frequency hopping and allocated at a time interval.

  It is remarkable in that it includes at least one unit for calculating the probability of the bit error rate of a current communication frame transmitted in FTDMA with frequency hopping by this server base station in the presence of a plurality interfering base stations comprising at least, in addition to a central processing unit and input / output devices, a module for calculating the probability of collision between bursts, such as a competing interfering carrier wave of determined frequency being interfering with interference a number K of times during the duration of a given number of successive common communication frames on this burst, and, a module for calculating the probability of the bit error rate K / N such that the same determined number of K bits of the current frame are erased by interference of the current carrier wave with at least one concurrent interfering carrier wave for a duration of the same number N of frames of communication transmitted by this server station, depending on the probability of collision between bursts.

  The method and system objects of the invention are applicable to the calculation of topography, implementation and maintenance or technical management of mobile radio networks operating on the principle of FTDMA transmission with frequency hopping.

  They will be better understood on reading the description and on the observation of the following drawings in which, in addition to FIGS. 1a, 1b, 1c, 1d and the relative to the prior art, FIG. illustrative title, a flowchart of the essential steps to implement the method object of the present invention; FIG. 3a represents, by way of illustration, a flow diagram of the recursive accumulation stages of two interfering base stations, to generate a resultant interfering base station, then the resulting interfering base station and another interfering base station for a calculation of the bit error rate in generalized frequency jump, successively; FIG. 3b represents, by way of illustration, a flowchart of the steps for calculating the probability of bit error rate, in the case of a specific frequency hopping; FIG. 4 represents, by way of illustration, a block diagram of a complete system for calculating, at a point in space, the probability of the bit error rate of a current frame transmitted in FTDMA with frequency hopping by a server base station in the presence of interfering base stations, in accordance with the object of the present invention.

  A description of the method for calculating the bit error rate probability of an FTDMA frame transmitted with frequency hopping by a server base station in the presence of a plurality of interfering base stations of a network or a network. part of mobile radio network, will now be given below in connection with Figure 2.

  In general, and prior to the actual description of the method which is the subject of the present invention, the nonlimiting assumptions of the operating mode of such a network or part of such a network are indicated below: The distribution of time slots, or time slots, designated TS occupied by communications on the TRX transmitters as a function of the load is purely random; the sending of the current communication frames transmitted in FTDMA of all the serving and interfering base stations is synchronized in time for the same network or part of the network; the number of communications carried by an interfering base station is invariant during an FTDMA communication frame, no new communication occurring or ending during an FTDMA communication frame duration.

  In view of the above assumptions, the method which is the subject of the invention applies for any server base station in the presence of a plurality of interfering base stations, each current communication frame being transmitted by the server base station in bursts during a time slot of N FTDMA frames on a physical channel, as previously described in the description with FIGS. 1a or 1b. Each physical channel is formed by a set of frequency channels each constituting a current carrier wave and subject to frequency hopping and thus allocated to a time interval.

  Consequently, each FTDMA communication frame is subjected by its carrier wave to the potential interference of concurrent communication frames transmitted during this time slot of N FTDMA frames on a physical channel formed by the set of frequency channels constituting the interfering carrier wave competing and also subject to a frequency jump and thus allocated to a corresponding TS time slot.

  As represented in FIG. 2, the method according to the invention consists of a step A to calculate the probability of collision between bursts such as a competing carrier wave having a determined frequency that is interfering with interference of the current carrier wave of the server base station a number K of times during the duration of the determined number N of successive current communication frames, on the considered burst.

  Such a calculation operation is justified under the conditions below.

  For the transmission of an FTDMA communication frame, at any instant t and for an interfering base station B having a number a of TRX transmitting equipment, this interfering base station B being the seat of a charge rate p, p corresponding to the percentage of time slots TS occupied on the transmitters of this base station B and having a number of jump frequencies y, the probability that a time interval TS of the interfering base station B is -even jammer is equal to PB = ap / y.

  The assumption of invariance of the communications carried by the interfering station B implies that a temporal interval TS of a transmitting equipment TRX of the interfering base station B occupied by a communication at a given instant t, t denoting the date of transmission of an FTDMA communication frame, is occupied by the same communication during the same number of FTDMA> nVoco frames. Remember that nVoco designates the number of FTDMA frames on which a voice frame is transmitted, this number being equal to eight for the GSM for example.

  Consequently, the probability for a transmitter equipment TRX to be interfering with the transmission time t + 1 of the next TDMA communication frame, knowing that this transmitter equipment TRX was interfering at the time t above, is 1.

  According to a remarkable aspect of the method which is the subject of the invention, the operation consisting in calculating the probability of collision between bursts consists, for any state of interference after n consecutive FTDMA communication frames and for a number N of the following FTDMA communication frames, calculating the probability of collision between bursts from a plurality of bursts between bursts, taking into account the probability of a plurality of jamming events and the occurrence of an interfering station, knowing that a predetermined number i interfering stations have already appeared.

  Thus, the probabilities of jamming events and the appearance of a jamming station advantageously comprise: a first probability, relative to an event denoted T, of no occurrence of a transmitting equipment of a station, interfering or not, on the frequency of the stationary base station, designated station S; a second probability, relative to an event noted T ++ 1 this second probability being the probability of appearance of a TRX transmitter equipment of an interfering station, knowing that this transmitting equipment had not intervened during n communication frames FTDMA consecutive previous; a third probability, relative to an event noted Ti + 1 probability of occurrence of a TRX transmitter equipment of a non-interfering station, knowing that this transmitting equipment had not intervened during the n consecutive preceding FTDMA communication frames; a fourth probability, relating to an event noted Tb, probability of occurrence of a TRX transmitter equipment of an interfering station B, knowing that this transmitting equipment had already intervened in the n consecutive n consecutive FTDMA communication frames; a fifth probability, relative to an event noted probability of occurrence of a TRX transmitter equipment of a non-interfering station, knowing that this transmitting equipment had already intervened in the n consecutive n consecutive FTDMA communication frames.

  By designating P (T) the probability of occurrence of an event T and for an interfering base station B having a number a of transmitting equipment TRX, a number y of jump frequencies and a charging rate p, 13 designating the difference between the number of hop frequencies of the interfering station B and the number a of transmitting equipment of the latter, [3 = y- a, the probability of the transitions or possible events when a new frame appears FTDMA mentioned above is written according to the five possible transitions or events previously mentioned in the TI table description:

Table Ti

A = P (T) =

Y

  A + 1 = P (T1) = p and A + 1 = Osii? Ai + 1 P (Ti + 1) = (ai) (1p) p and Ai + 1 = 0sii>> a Taking into account the following events: BN where interfering station B interferes K times on the same frequency during N consecutive FTDMA communication frames; S2 denotes the certain event, {BN / K E [O, N]} constitutes a complete system of events describing it; BN'l'j designating the event according to which the interfering station B is scrambling K times on the same frequency during N consecutive FTDMA communication frames, with a number i of TRX transmitting equipments having already intervened, of which j of these were Therefore, 1BKN'i'i / i E [0, Min {N, a} DE [0,4 4} is a complete system of events describing BN.

  Taking into account the previous system of events, the value of the probability of collision between bursts satisfies the relation (1): -12- Relation (1) Min {N, a} Min {i, k} K k, i, j PN = PN i = 0 j = 0

NOT

EPK = 1

  The value of the collision probability between the aforementioned bursts can then be computed recurrently from the events or transitions defined previously when a new FTDMA communication frame appears according to relation (2): Relation (2) PN1 0.0 = 0.05.0.0.0.0.0.0.0.0.0.0.0.0.0.0. x Ai + PO j, 0 x (A0 + R ') i + 0 j = 0 N N-1 N 1 and for 1 <k <N, Min {N, a} i

PN -

  i = 0 j = 0 PNk, O, j = Pki xAi + PkN-l1, i-1, j-1xA + i + Pkijx (AO + R 'J) N-1 N-1 PNk, O, j = 0 vi Pk, O, j = 0 dj N - 13 - In the previous relation, the initialization value of the collision probability values between bursts is obtained for k = 0 and the successive values for 1 <k <N with 1 <k <N are recursively explained with respect to the previous probability value for k = k-1.

  Thus, the probability distribution of collision between bursts or time intervals of a server base station and an interfering base station over the duration of an FTDMA communication frame still designated service frame is thus available.

  Step A of FIG. 2 is then followed by a step B of calculating the probability of the bit error rate K / N such that the same determined number of K bits of the current frame is erased by interference of the current carrier wave with at least one concurrent interference carrier wave, for a duration of the same number N of FTDMA communication frames transmitted by the server station S, as a function of the probability of collision between bursts previously calculated in step A In general, it is indicated that the bit error rate for a given interfering station on a frequency fi is calculated in step B shown in FIG. 2 as the product of the probability of collision of bursts and the probability bit erase knowing that there is a collision of frames.

  More specifically, it is indicated that the bit error rate, for a plurality of at least p scrambling base stations B, denoted {le} x = 1 ... x = p, the error rate binary being generated by the interfering base stations, is calculated as the aggregate of the interfering base station equivalent to the p-1 interfering base stations and the interfering base station. of an equivalent interfering base station and an interfering base station, respectively, defines another equivalent or resulting interference base station, erasing K bits during N consecutive FTDMA communication frames.

  The aforesaid operating mode will now be described in conjunction with FIG. 3a in the case of generalized frequency hopping.

  - 14 - Generalized frequency hopping is a special case favorable to the evaluation model.

  In this situation, all interfering base stations jump on all frequencies and the interference levels are the same on each frequency. This property makes it possible to take into account the behavior of the superfluous server base station.

  Accordingly, on each FTDMA communication frame, regardless of the frequency on which the server base station transmits, the probability of interference is then the same.

  For each jump sequence, the probability of interference is therefore substantially the same. Since all the jump sequences are equally likely, the interference probability is the same as if the server base station remains on the same frequency during the N FTDMA communication frames transmitted.

  A corresponding procedure for generalized frequency hopping is now described in connection with Figure 3a.

  An event A is considered. For a communication, the number of bitsequences of N is k.

  HN is the probability associated with this event. The evaluation of this probability can then be carried out particularly advantageously recursively, by accumulating the probabilities of erasure by each interfering base station and assuming the independence of their impact on the erasure of the bits.

  With reference to FIG. 3a, an interfering station B is considered for which the probability of erasure of bit 0 is noted, knowing that there is a collision with the burst. The probability values 0 can be obtained from a database by reading performance tables of C / I interference values as will be described later in the description. In the substep Bi of FIG. 3a, the probability associated with the corresponding event is given by the relation (3): -15-Relation (3):

NOT

  HN (B) _ E pNCkBk (1-8) ik i = k In the following sub-step B2, two independent interfering stations are then accumulated such that the interfering base stations B and B 'belonging to the set interfering stations {le} x = 1 ... x = p. We denote by Br the equivalent or resulting interference to the combination of the two.

  The probability HN (Br) that the set of two interfering base stations B and B 'clears k bits during N consecutive FTDMA communication frames on one of the frequencies is given by relation (4): Relation (4): ## EQU1 ## The sub-step B2 is then followed by a sub-step. step B3 consisting in effecting the cumulative accumulation of M independent interfering base stations.

  The independence of the M interfering base stations between them makes it possible to consider their presence on the same frequency, by successive accumulations of a scrambler with the equivalent or resulting calculated interference.

  In sub-step B3 of FIG. 3a, it is understood, in particular, that the operation consists, from the aforementioned relation (4), of for example replacing the probability HN (B) by the corresponding probability HN ( Br) obtained in the sub-step B2 and, of course, to call the corresponding probability for any interfering base station BX with BX B 'to cumulate the corresponding probabilities in a relation similar to that of the relation (4) and given according to the relation (5) in which finally the probability of the equivalent or resulting interfering base station is updated.

  -16-Relation (5): - Ck i xCj (ki) (B r N 1_ EN 1 c xHN (Br) xHk (Bx) Ci i = 0 j = 0 CN Step B3 is followed by a sub step B4 consisting, for example, in calling the next interfering base station, then in a substep B5 consisting in verifying that the called interfering base station Bx exists.

  The test operation corresponding to substep B5 is represented by the symbolic relation B '= Q.

  On a negative response to the test sub-step B5, a return is made to the substep B3 for updating the accumulation of the new interfering station Bx called to the resulting interfering base station B computed at the previous iteration.

  The recursive loop thus constructed is continued as long as the list of independent interfering stations Bx is not empty.

  On the contrary, on a positive response to the test substep B5, an end stage of the calculation process is reached and the cumulative probability value for independent interfering M given by the notation is then available. : HN (Br).

  The aforementioned recursive calculation makes it possible to obtain the probability of erasure by all the interfering stations.

  A more detailed description of the operation of calculating the probability of bit error for a specific frequency hopping, having jump frequencies and specific fixed frequencies not known a priori forming a frequency hopping pattern for each frequency fi of the server base station B, will now be given in connection with Figure 3b.

  The procedure described in relation to FIG. 3b applies to the case of any given frequency plane, that is to say for a specific specific frequency jump.

  In this situation, it is then necessary to browse all the frequency hopping sequences that can be allocated to the server base station.

  For a given frequency hopping sequence, the information used is then the number of times the waitress jumps on each frequency, that is to say according to its configuration x = (xi, ... xi, xnf), configuration such as that the waitressing base station appears x; once in transmission on the frequency fi, the server base station having nf frequencies. It is therefore possible to process all jump sequences with similar configurations at the same time.

  Consequently, with reference to FIG. 3b, in this situation, the operation of calculating the probability of binary error consists in determining in a substep B'l the number xi of times that the waiter station B appears on the jump frequency fi for a given number nf of jump frequencies.

  In FIG. 3b, in the substep B'l thereof, the probability of occurrence of this configuration designated by the relation (6) has been designated for the above-mentioned configuration x: Relation 6: nf xl P (x ) = CN 1 xi n N f i_1 iCl The probability of occurrence of the above configuration x actually denotes the weight of this configuration x, that is to say its probability of occurrence. This probability of occurrence is calculated conventionally according to the principle of conditional probabilities, knowing that each frequency fi appears x; times according to the above configuration.

  Step B'1 is then followed by a step B'2 of calculating the probability of bit error rate from the probability of a plurality of scrambling events and occurrence of each jump frequency of the server base station for the considered configuration in the presence of all the interfering stations.

  This plurality of event probabilities is defined from the following events: AN (i, S, x, j) denotes the fact that the server base station is scrambled k; times on the frequency fi and j bits of the frequency fi are scrambled, knowing that there appears x; times; A N (i, S, xi) denotes that the server base station is scrambled k; times on frequency fi, knowing that it appears x, times. The aforementioned event is the union of the preceding incompatible events j); A4 (S, x) refers to the fact that the waitress is scrambled k times knowing that her jump sequence takes the x configuration.

  Accordingly, the plurality of event probabilities in a specific frequency hopping situation advantageously comprises: a first designated probability j) which designates the probability of the aforementioned event AN (i, S, xi, j), probability that the Waitress base station is scrambled k; once by the equivalent interfering base station on the frequency fi and that bits transmitted to the carrier frequency fi by the server base station are scrambled, knowing that the carrier frequency fi of the latter appears x; times; a second probability H11 (\ 1 (i, S, xi), the probability of the event AN (i, S, xi), the probability that the server base station is scrambled twice by the equivalent interfering base station on the frequency fi, knowing that it appears x; times; - a third probability HN (S, x), probability of the event AN (S, x), probability that the server base station is scrambled k times, knowing that the the server base station jump sequence is that of the configuration The first, second and third probabilities above are defined from the probability HN (i) designating the probability that k bits will be erased during N FTDMA communication frames on the This probability is obtained in the same way as for the generalized frequency hopping, this probability being in the case of the generalized frequency hopping identical for all the frequencies. probability probes the relation (7): Relation (7): Cki Ci-ki 1-111 (, k xi N-xi Hn 1-111 (, (i, s, xi, j) = (i) Ci N la second probability satisfies the relation (8): Relation (8): N xi + ki k HNk (i, s, xi) HN (i, S, xi, J) j = ki the third probability satisfies the relation (9): Relation (9): ## EQU1 ## probability of the event that the waitress is scrambled ki times and j bits of the frequency fi Cki Cj-ki are scrambled knowing that this frequency fi y appears xi times, the ratio xi N-xi CI

NOT

  in fact denotes the relative rate of occurrence of scrambled ki bits at the frequency fi in N frames and Hi, (i) denotes the probability that j bits out of n bits are scrambled at the frequency f 1.

  Step B'2 is then followed by a step B'3, which consists of calculating the probability that the bit error rate at the value k / N is experienced by the FTDMA or service frame of the communication frame. Waitress base station.

  The bit error rate probability value mentioned above satisfies the relation (10): Relation (10): HN P (x) H (S, x;) In fact, the probability value of the rate of binary error equal to K / N above is established for a probability P (x) of appearance of the configuration x of the jump frequencies of the server base station as the sum over the set of configurations of each of the third probabilities that the Waitress station is scrambled K times weighted by the probability P (x) of occurrence of the corresponding configuration.

  A more detailed description of a computation system at a given point in the probability space of the bit error rate of a current communication frame transmitted in FTDMA with frequency hopping by a server base station in the presence of a plurality of interfering base stations operating according to the method, object of the invention, as described previously in the description, will now be given in connection with FIG. 4.

  As has been shown in the above-mentioned figure, the system which is the subject of the invention includes at least one calculation unit CU of the probability of the bit error rate of a current communication frame transmitted in FTDMA with jump frequency by the server base station S in the presence of a plurality of interfering base stations B, as previously mentioned in the description. The aforementioned CU calculation unit comprises at least, in addition to a central processing unit CPU and I / O input / output members associated with a RAM working memory, an MI module for calculating the probability of the collision between bursts. such that a competing carrier wave of a determined frequency is interfering, by means of the carrier wave, by a number K of times during the duration of a determined number N of successive common communication frames on the burst, as previously described. in the description with reference to Figures 2, 3a and 3b.

  In addition, the calculation unit CU also comprises a module M2 for calculating the probability of the bit error rate K / N such that the same determined number of K bits of the current frame is erased by interference from the current carrier wave with at least one concurrent interfering carrier wave for a duration of the same number of communication frames transmitted by the server base station as a function of the collision probability between bursts, as described previously in the description in FIG. connection with Figure 2 and Figure 3b.

  In addition, as will be observed in FIG. 4, the calculation unit CU may advantageously comprise a non-volatile programmable memory denoted PM making it possible to store, for example, the first, second, third, fourth and fifth probabilities of appearance. a transmitting equipment for determining the probability of collision between bursts as described above in the description.

  The programmable memory PM may also advantageously enable the first, second and third probabilities to be stored that the server station B is scrambled k times in a specific frequency hopping situation.

  It is understood, in particular, that the existence of the aforementioned non-volatile PM programmable memory is not essential, but that, however, the latter thus makes it possible to store specific network configurations or network portions and, consequently, when a variation of the network by extension and / or modification of the radio characteristics of the latter, it is then possible to update the values stored in the nonvolatile programmable memory PM above.

  The system that is the subject of the invention then appears to be particularly well suited either to the calculation of networks or frequency plans, or to the maintenance and technical management of the latter.

  Finally, as shown in FIG. 4, the system, which is the subject of the invention, furthermore advantageously interconnects the calculation unit CU with the bit error rate, a first database denoted DB1 for delivering, for a network or part of a network, the load parameters p per server station S and / or interferer B, a second database making it possible to deliver the number of equipment for the network or the corresponding network part; transmitter and frequency per server station S and / or interferer B and a third database DB3 for delivering propagation data according to a spatial grid representation and reception quality value tables making it possible to establish a probability value d bit erasure, the value 0 in the case of a collision between time intervals of two different base stations.

  Finally, a fourth database DB4 makes it possible to deliver for the network or the part of the network considered, the frequency plan chosen between a generalized frequency jump or a specific frequency jump respectively. The fourth database makes it possible in particular to deliver the parameter y for the network or the part of the network considered. It is recalled that the probability values 0, bit erasure probability knowing that there is collision between bursts are obtained from bit error rate performance tables as a function of the C / I interference values.

  Finally, the present invention covers a computer program product recorded on a storage medium and executable by a computer or the central processing unit of a dedicated system, such as the system object of the invention described in connection with FIG. 4. This computer program product can advantageously be implanted in the IM module represented in FIG. 4, either from a recording medium or by downloading for example.

  The aforesaid computer program product, when executing executable program instructions, i.e. after RAM call and executed by the CPU, executes the probability calculation. collision between bursts, such as a competing interference carrier carrier of a determined frequency being interfering by interference of the current carrier wave by a number K of times during the duration of a predetermined number N of successive common communication frames on the burst, as described previously in the description with reference to FIGS. 2 and 3a.

  The invention furthermore covers a computer program product recorded on a storage medium and executable by a computer or by the central processing unit of a dedicated system, as previously described in the linked description. with Figure 4.

  It is remarkable that, when executing instructions of the aforementioned executable program, the latter having been loaded into working memory and executed by the central processing unit CPU, the aforementioned program performs the calculation of the probability. of the bit error rate K / N such that the same determined number of K bits of the current frame are erased by interference of the current carrier wave with at least one competing interfering carrier wave for a duration of the same number N communication frames transmitted by said server station, depending on the probability of collision between bursts, as described previously in the description in conjunction with Figures 2 and 3a or 3b.

- 24 -

Claims (15)

  A method of calculating, at a given point in space, the probability of the bit error rate of a current communication frame transmitted in FTDMA with frequency hopping by a server base station in the presence of a plurality interfering base stations, wherein each current communication frame is transmitted by said burst server base station during a time slot of N FTDMA frames on a physical channel formed by a set of frequency channels each constituting a current carrier wave, subject to a frequency hopping, and allocated to a time slot, each communication frame being subjected by its carrier wave to the potential interference of concurrent communication frames transmitted during a time slot of N FTDMA frames on a physical channel formed by a set of frequency channels constituting a competing interference-free carrier wave, subject to a frequency hopping, and allocated to an i temporal interval, characterized in that it consists at least in: calculating the probability of collision between bursts, such as a competing interference carrier wave of determined frequency being interfering by interference of said current carrier wave a number K of times during the duration a determined number N of successive current communication frames, on said burst; calculating the probability of the bit error rate K / N such that the same determined number of K bits of the current frame are erased by interference of the current carrier wave with at least one concurrent interfering carrier wave for a period of one same number N of communication frames transmitted by said server station, as a function of said probability of collision between bursts.   2. Method according to claim 1, characterized in that the operation of calculating said probability of collision between bursts consists, for any state of boiling, after n consecutive FTDMA communication frames, for a number N of FTDMA communication frames following , calculating said burst collision probability from the probability of a plurality of burst collisions from the probability of a plurality of boiling events and occurrence of an interfering station, knowing that a fixed number of interfering stations have already appeared, said probabilities of interference events and occurrence of a jamming station including: a first probability of non-occurrence of a transmitting equipment of a station, interfering or no, on the frequency of said server base station; a second probability of occurrence of a transmitting equipment of an interfering station, knowing that this transmitting equipment had not intervened during the preceding n consecutive FTDMA communication frames; a third probability of occurrence of a transmitting equipment of a non-interfering station, knowing that this transmitting equipment had not intervened in the n consecutive n consecutive FTDMA communication frames; a fourth probability of occurrence of a transmitting equipment of an interfering station, knowing that this transmitting equipment had already intervened in n consecutive preceding FTDMA communication frames; a fifth probability of occurrence of a transmitting equipment of a non-interfering station, knowing that this transmitting equipment had already intervened in the n consecutive n consecutive FTDMA communication frames.   3. Method according to claim 2, characterized in that for a number of transmitting equipment of an interfering station, a number y of jump frequencies of this interfering station, a charge rate p of this interfering station and a difference [3 = y-a between the number of jumping frequencies and the number of transmitting equipment of this interfering station, 2890264 -26- - said first probability A = P (T) = where T denotes Y the occurrence event equipment transmitting a station, interfering or not, on the frequency of said server station; said second probability A + '= P (T ++') = ap where T ++ 'Y designates the occurrence event of a transmitting equipment of an interfering station, knowing that this transmitting equipment had not intervened during the n frames previous FTDMA communications; said third probability A '+' = P (T '+') = (ai) (1- p) where T '+' Y denotes the occurrence event of a transmitting equipment of a non-interfering station, knowing that this transmitting equipment had not intervened in the previous n consecutive FTDMA communication frames; said fourth probability Re = P (T,) = b where Te designates the occurrence event of a transmitting equipment of an interfering station, knowing that this transmitting equipment had already intervened during the n consecutive preceding FTDMA communication frames and b denotes the number of transmitting equipment of this interfering station already intervened; said fifth probability R = P (T) = ç where T denotes Y the occurrence event of a transmitting equipment of a non-interfering station, knowing that this transmitting equipment had already intervened during the n consecutive FTDMA communication frames previous and c is the number of transmitting equipment of this non-interfering station already intervened.   4. Method according to one of claims 2 or 3, characterized in that said bursts collision probability is expressed as a distribution of probabilities of collision between time intervals of a server station and an interfering station over the period of time. a service frame.   - 27 - 5. Method according to claim 4, characterized in that the bit error rate for a given interfering station on a frequency fi is calculated as the sum of the probability of collision of bursts and the probability of bit erasure, knowing that there is a frame collision.   6. Method according to one of claims 4 or 5, characterized in that, for a plurality of at least p interfering stations, the bit error rate generated by the p interference stations is calculated as the cumulative interference station equivalent to p-1 interfering stations and interfering station penalty, the aggregate of two interfering stations respectively an equivalent interfering station and an interfering station defining another equivalent interfering station clearing K bits during N consecutive FTDMA communication frames.   7. Method according to one of claims 1 to 4, characterized in that, the calculation operation of said bit error rate probability consists, for a generalized frequency jump, all the stations waitresses and / or jammers jumping on the same jump frequencies and all jumping frequencies being equiprobable, to assimilate all the jump sequences to equiprobable sequences, and, for each jump sequence, the interference probability of said server station to the interference probability of this server station in the absence of frequency hopping on this server station during the N FTDMA communication frames.   8. Method according to one of claims 1 to 6, characterized in that the operation of calculating said probability of binary error consists, for a specific frequency jump with jump frequencies and specific fixed frequencies not known to priori forming a frequency hopping pattern, for each frequency fi of the server station, to: determine the number x; of times that the server station appears on the jump frequency fi for a given number nf of jump frequencies; and calculating said bit error rate probability from the probability of a plurality of scrambling and occurrence events of each hop rate of said server station, in the presence of all interfering stations, said plurality of event probabilities comprising: a first probability that said server station is boiled k; Once by said interference station equivalent on the frequency fi and j bits transmitted to the carrier frequency fi are scrambled, knowing that said carrier frequency fi appears xi times; a second probability that said server station is scrambled twice by said equivalent interfering station on the frequency fi, knowing that it appears xi times; a third probability that said server station is scrambled k times, knowing that the jump sequence of said server station is that of said configuration.   9. The method according to claim 8, characterized in that said first probability is established as the cumulative probability of the previous n-bit bits being scrambled by the interfering station equivalent to the frequency fi in N FTDMA communication frames.   10. Method according to claim 8, characterized in that for a probability P (x) of appearance of said configuration, x denoting the occurrence event of said configuration, said probability of binary error is established as the sum on the set of configurations of each of said third probabilities that said server station is boiled k times weighted by the probability of occurrence of the corresponding configuration.   11. System for calculating, at a given point in space, the probability of the bit error rate of a current communication frame transmitted in FTDMA with frequency hopping by a server base station in the presence of a plurality interfering base stations, wherein each current communication frame is transmitted by said burst server base station during a time slot of N FTDMA frames on a physical channel formed by a set of frequency channels each constituting a current carrier wave, subject to frequency hopping, and allocated at a time interval, each communication frame being subjected by its carrier wave to the potential interference of concurrent FTDMA communication frames transmitted during a time slot of N FTDMA frames on a channel physical formed by a set of frequency channels constituting a competing carrier wave, subject to frequency hopping and allocated e at a time interval, characterized in that it includes at least one unit for calculating the probability of the bit error rate of a current communication frame transmitted in FTDMA with frequency hopping by said server base station in the presence a plurality of interfering base stations comprising at least, in addition to a central processing unit and input / output devices: a module for calculating the probability of collision between bursts, such as a frequency-competing interfering carrier wave determined by interference from said one carrier a number K of times during the duration of a determined number N of successive common communication frames on said burst; and, a module for calculating the probability of the bit error rate K / N such that the same determined number of K bits of the current frame are erased by interference of the current carrier wave with at least one competing interfering carrier wave. during a period of the same number N of communication frames transmitted by said server base station, according to said probability of collision between bursts.   12. System according to claim 11, characterized in that the calculation unit further comprises a non-volatile program memory for storing at least: a first, a second, a third, a fourth, a fifth probability value related to the occurrence or non-occurrence of a transmitting equipment of a base station for calculating said probability of collision between bursts; a first, a second and a third probability value that a server base station is scrambled a specified number of times to calculate the probability of the bit error rate K / N.   - 30 - 13. System according to claim 11 or 12, characterized in that it further comprises, interconnected to said calculation unit of the bit error rate: a first database for delivering for a network or part of a network the load parameters p in traffic per serving and / or interfering station; a second database for delivering for said network or said network part the number of transmitting equipment and frequencies per station and / or interfering station; a third database for delivering propagation data according to a mesh spatial representation and reception quality value tables, making it possible to establish a bit erasure probability value in the case of a time interval collision two separate base stations; a fourth database for delivering, for said network or said network part, the chosen frequency plan.   14. Computer program product recorded on a storage medium and executable by a computer or by the central processing unit of a dedicated system, according to one of claims 11 to 13, characterized in that, when executing instructions of said executable program, the latter executing the calculation of the probability of collision between bursts, such as a competing interference carrier wave of determined frequency or interfering interference of said current carrier wave K number of times during the duration of a predetermined number N of successive common communication frames on said burst, according to one of claims 1 to 6.   15. Computer program product recorded on a storage medium and executable by a computer or by the central processing unit of a dedicated system, according to one of claims 11 to 13, characterized in that, when executing instructions of said executable program, it executes the calculation of the probability of the bit error rate K / N such that the same determined number of K bits of the current frame are erased by interference of the wave current carrier with at least one concurrent carrier wave competing for a duration of the same number N of communication frames transmitted by said server station, according to the probability of collision between bursts, according to one of claims 7 to 10.