Radio system to allow for exchanging messages between a set of stations

A radio system allows for exchanging messages between a set of relay stations (R1, R2, R3 . . . ) and mobile access stations (M . . . ) for communications. At least one common semaphore channel is used through which the relay stations simultaneously transmit code signals (M(R1)+M(R2)+M(R3)+. . . ) at first preset instants and separately transmit a code signal at other preset time instants, the access stations tap the said channel at these various preset instants and the recognition in the access station of code signals received in the first preset instants and the quality of code signals received in the other preset instants constitutes a criterion for establishing the connection between the access station and a relay station corresponding to the recognized code.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a radio system for allowing for exchanging 
messages between a set of relay stations and access stations for 
communications, the system using a least one common semaphore channel 
which is specifically provided to establish the connections between relay 
stations and access stations and through which the relay stations can 
transmit a first code signal at first predetermined instants, whereas the 
access stations comprise means for tapping the said channel at these 
predetermined instants. 
2. Description of the Related Art 
Such a system is known from the British Patent Specification 1 591 159. In 
this system the code signals are constituted by tones: a first tone for 
indicating that the relay station transmitting the tone wishes to send a 
message to the access stations which capture the tone and a second tone 
for indicating that the relay station transmitting the tone does not have 
a message to be broadcast. Thus, if one access station receives various 
tones of different relay stations, it will only be sensitive to the first 
tone if its level exceeds the tones received second. 
This known system presents a first disadvantage due to the fact that it is 
ill-adapted to networks using a semaphore channel and transmitting 
messages of the digital type, as is the case with the RAMAGE network. This 
network is described in the article entitled: "RAMAGE - A Private Mobile 
Radio Telephone Network" by G. Banquet, J. P. Pittion, M. Coudreuse and 
published in "Commutation and Transmit No. 1,1986, pp. 19-30". 
SUMMARY OF THE INVENTION 
One of the objects of the invention is to provide a radio system which is 
suitable for a RAMAGE network. Therefore, according to the invention, a 
system of the type mentioned in the preamble is characterized in that this 
code signal is formed by a digital code defining the relay station that 
transmits the signal and in that its recognition at the access stations is 
a criterion for establishing the connection. 
A further object of the invention is to provide a radio system using 
various criteria for establishing the connection between the access 
station and the relay station. Therefore, according to the invention, a 
system of the type mentioned in the preamble, for which a semaphore 
channel is used for transmitting at preset second instants, of which each 
one is associated to a relay station, a second code signal in a digital 
form, is characterized according to a feature of the invention, in that 
for establishing the connection a second criterion is used consisting of 
analysing the transmitted quality of the second code signal.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In FIG. 1 the references R1, and R3 show the location of different relay 
stations. These different relay stations R1, R2 and R3 can be captured 
inside the zones Z1, Z2 and Z3. An access station M installed, for 
example, on board an automobile, travels inside these zones and a 
communication can be set up between this station M and another access 
station (not shown) by making use of relay stations. The problem which 
occurs thus, first of all, consists for the station M of connecting to one 
of the relay stations R1, R2 or R3. For this purpose a semaphore channel 
is used of which the organization is shown in FIG. 2. In this Figure are 
distinguished the instants designated t1, t2, t3 . . . . t8. At the 
instants t2, t3, t4, t5, t6, t7, the different relay stations radiate code 
signals characterizing them. Thus, at the instants t2 and t5 the relay 
station R1 radiates code signal M(R1) comprising its identification code 
accompained by an error detecting code. In the same manner the relay 
station R2 will radiate at instants t3 and t6 a code signal M(R2) whereas 
the relay station R3 will radiate at the instants t4 and t7 a code signal 
M(R3). At instants t1 and t8 all the relay stations transmit their code 
signals, that is to say, that the superposition takes place of these 
different code signals, which is expressed by M(R1)+M(R2)+M(R3). Thus, the 
recognition of a single one of these code signals at the receivers of the 
access stations indicates that this code signal determines the best 
received relay station. The codes of the frames and multiframes required 
for obtaining a proper synchronization of the system are designated as TR 
and MTR. 
FIG. 3 shows, partly, the structure of an access station. The parts not 
shown are not necessary for comprehending the invention. 
Reference 10 in this FIG. 3 shows the antenna of the station. This antenna 
is used both for tramsmission and reception. An antenna relay 12 having 
two positions R and T allows connecting this antenna 10 into either a 
transmission branch 15, the antenna relay 12 being at position T, or a 
receiving branch 20, the antenna relay 12 then being in position R. A 
modem circuit 25 is used for receiving and transmitting digital data 
specifically transmitted through the semaphore channel. The modulating 
portion MOD of this modem 25 is connected to the input of transmission 
branch 15 just like the telephone circuit (this is represented by the 
broken-line arrow 26). A modulator 30 modulates a carrier with the input 
signals to transmission branch 15; the carrier emanates from a local 
oscillator 35 which is also used by the receiving branch 20. A 
high-frequency amplifier 37 supplies the required level to the 
transmitting antenna 10. The receiving branch 20 comprises a preamplifier 
stage 40 for boosting the signals emanating from the antenna 10, and a 
frequency changing stage 42 being connected to the output of stage 40. 
This frequency changing stage also uses the local oscillator 35. It should 
be observed that the frequency thereof is changed accordingly as 
transmission or reception is effected. This change of frequency is 
symbolized by the switch 44 having two positions R and T actuated 
simultaneously with the antenna relay 12. Furthermore, the frequency of 
the output signal differs not only from the difference in duplex but also 
from the value of the intermediate frequency. At the output of stage 20 
there is thus an intermediate-frequency amplifying stage 46, followed by a 
level limiter 48. A subsequent frequency discriminator 50 supplies, on the 
one hand messages to the demodulator portion DEMOD of the modem 25, and on 
the other hand speech signals to the sound portion. This is shown by a 
dotted-line arrow 52. The messages for establishing the connection between 
the access station and the relay station are managed and processed by a 
microprocessor set 60. In this set a synchronization part Sy is 
distinguished which supplies, as a function of the recognized code signals 
TR and MTR, the signals iSy providing as a function of time the expected 
number of time locations of the code signals emanating from the different 
relay stations. This portion Sy also provides a Sync signal indicating 
that the synchronization with a semaphore channel is maintained. 
The operation of the microprocessor set 60 will now be explained with the 
aid of the flow charts shown in FIGS. 4a and 4b. 
The flow chart of FIG. 4a begins with a box KO indicating the start of the 
sequence of the operating program as will presently be described. The next 
box K1 indicates a verification of the value of the Sync signal. The value 
"1" indicates that the synchronization is obtained and box K2 is proceeded 
to. This verification is also performed when the Sync value is not equal 
to 1. The box K2 represents the initiating phase of the program. Different 
counters m1, m2, . . . mi, . . . mN, are set to zero, each of them being 
assigned to a relay station and N thus representing the number of 
considered relay stations. A counter T is also set to zero. This counter T 
is incremented at the frames during which the receiver M compares the 
receiving quality of the code signals received from different stations R1, 
R2, . . . RN. Different memory locations Q1, Q2, . . . Qi, QN, each of 
them being assinged to one of the N relay stations, is initiated by a 
maximum value O.sub.MAX. The box K3, which follows, consists of an 
analysis of the code signal of a relay station which has just been 
received. This analysis, not forming a part of the invention, will not be 
described and is explained in the aforementioned article entitled "Ramage, 
A Private Mobile Radiotelephone Network" published in 1986. This analysis 
provides a number Ne indicating the number of errors detected in the code 
signal M(Ri) transmitting the identification of one of the relay stations. 
This number Ne is verified in the box K4. A number of errors exceeding 10 
or the erroneous reception of M(Ri) allows of passing on to box K5. As the 
recognition of M(Ri) has not been good, an indicator C is set to "O" and 
the number of the detected relay station "i" is determined by the signal 
iSy and not by the code signal M(Ri), and it is set at 10 in the memory 
location NP. IF Ne falls short of 10, box K6 is proceeded to; here 
indicator C is set at "1" and the number of the relay station "i" is 
determined by the recognition of the code signal M(Ri), the number of 
errors Ne is stored in a memory part NP. From boxes K5 or K6, box K10 is 
proceeded to where the message iSy is examined to know whether something 
happens at the instants (tl, t8 . . . ) when all the code signals of the 
relay stations are transmitted simultaneously; if this is the case, box 
K11 is proceeded to, if not, box K12. 
In box K11, the indicator C is verified, if it indicates that the code 
signal M(Ri) has been received in good condition, the counter mi which is 
assigned thereto is incremented (box K13). If the code signal has been 
poorly received, box K14 is proceeded to. Then box K12 relates to the case 
when a code signal has been recognized outside the instants at which all 
the code signals are transmitted simultaneously. In this box K12 a 
correction is made of the signal quality, that is to say that this quality 
decreases by the number of errors supplied during the process of box K3. 
In box K14 the counter mi is examined with respect to the code signal 
determined in box K5 or K6; if the contents of the counter mi are no less 
than 3, the contents of the other counters mi containing the other relay 
stations (that is to say that j can ssume all values from 1 to N except 
for the value i), are examined (see box K15). If the tests relating to the 
given "i" and performed in the boxes K14 and K15 turn out to be positive, 
it is examined (see box K16) whether the access station was not already 
connected to the station Ri; this is indicated by the contents of a memory 
LOC. If it is already connected to the station Ri, box K17 is proceeded 
to; if it is not, boxes K18 and K19 are proceeded to where a connecting 
procedure is started. This procedure commences by putting indicator CX 
into position "1" (box K18) and the relay station, to which the access 
station is connected, is requested (box K19) to start the process of 
connecting to station Ri; this having been effected, box K17 is proceeded 
to where the counter T is incremented. The contents of this counter are 
compared to a limited value TMX (box K20, FIG. 4b). If the maximum value 
is not reached, box K21 is proceeded to. Here, the indicator CX is tested. 
If not a single request for a connection has been formulated, box K3 is 
returned to. If a request for a connection has been formulated, box K22 is 
proceeded to, where the indicator RC indicating whether the response has 
arrived is tested; if the test turns out negative box K3 is returned to. 
The box K23 which follows is a decoding procedure of the answer; if this 
is positive, box K30 is proceeded to where the connection to the station 
Ri is effected. When the contents of the counter have reached the maximum 
value TMX, it is there also tested, box K40, whether a request for a 
connection has been made. If this is not the case, in box K41 a search 
loop is triggered of the relay stations Ri received best. Therefore, one 
sets to zero an index p the memory MM1 in which the maximum value will be 
stored of the contents of the memories Mi, the memory MM2 in which will be 
stored the value immediately below the preceding maximum value, the value 
captured in the contents of the memory mi and finally the memory Q in 
which the maximum value is stored of the contents of the memories Qi. The 
search for these three values is effected in the loop including the boxes 
K42 to K49. 
The box K42 corresponds with the incrementation of the index p used in this 
loop. The box K43 leves the loop when the index p exceeds N, N being the 
number of relay stations. The boxes K44 to K47 explain the searching for 
the values MM1 and MM2 explained hereinbefore; in the box K45 also the 
value of the index p, for which the value mp is highest, is stored. In the 
same fashion in boxes K48 and K49 effect the search for the maximum value 
contained in the counters Qi as well as the index p for which this maximum 
value is obtained. 
When the search is ended by the verification of box K43, box K50 is 
proceeded to where it is verified whether the difference between the 
values MM1 and MM2 exceeds or is equal to 3. If this is the case, it is 
verified in box K51 whether the note Qi, having the same index as mi 
contained in MM1, exceeds a minimum value Qmin. If this is the case, in 
box K52 the value of the index is maintained in order to make an attempt 
for a connection with the corresponding relay station. In the opposite 
case it is verified, in box K53, whether the value Q exceeds Qmin. If this 
is not the case, box K54 is proceeded to and the program is stopped and, 
for example, it is left up to the user to make other attempts. If Q 
exceeds Qmin, box K55 is proceeded to. 
In box K55 it is examined whether a connection has already been established 
with the relay station R.sub.j. If this is the case, box K1 is returned 
to. If not, in box K56, the indicator CX is set to 1 and then, in box K57, 
the same procedure as indicated with respect to the box K10 is performed 
for the relay station R.sub.j. Then, one proceeds to box K58 which is, 
finally, a waiting phase. This box K58 comes also after box K40 which as 
already been described, and relates to the case when the verification of 
CX is positive. When the answer returns (box K59) it is verified (box 
K60); if it is positive the connection is made to the relay station thus 
determined, box K62, upon which box K1 is returned to. 
If the answer is negative one proceeds to the choice of another relay 
station; therefore one begins at the elimination of the choice of the 
relay station from which one has just received a negative answer by 
setting to zero, box K61, the values mj and Qj which correspond thereto, 
and box K41 is returned to. 
The Applicants have chosen the following parameters for a convenient 
operation of the system. 
The multiframe comprising a common code signal contains q times the frame 
sequence of the different code signals of each of the N relay stations. 
QMAX=80q 
Qmin=20q 
TMAX=8(Nq+1) 
Although the present invention has been particularly described with a flow 
chart showing as a preference that the first criterion is satisfied in the 
first place, that is to say the criterion based on the recognition of the 
code signals, as the case may be, it should be understood that within the 
scope of the invention, the second criterion can also be satisfied 
initially, that is to say the criterion based on the transmitted quality 
of the code signals. This can be effected by reversing the order of the 
tests K50 and K53.