Note: Descriptions are shown in the official language in which they were submitted.
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W09713~7 PCT~97/00151
Method and system for testing the condition of
a subscriber station in a radio system
The present invention relates to a method of testing the condition of
a subscriber station in a radio system providing a wireless subscriber interface.
The invention further relates to a radio system providing a wireless subscriber
5 interface and comprising a subscriber network element in a data transmission
connection with a local exchange of a public telephone network, a base station
and subscriber stations, the subscriber network element and said base station
comprising means for transfer of telecommunication signals between the local
exchange and the subscriber stations. The invention further relates to a sub-
10 scriber station in a radio system providing a wireless subscriber interface andconsisting of terminal equipment having a radio part, and of a user interface
linked to the terminal equipment by means of a two-wire line.
The invention relates to monitoring the operation of a subscriber
station used in a WLL system (Wireless subscriber interface), that is, a radio
15 system providing a wireless subscriber interface. In the WLL system, a usual
two-wire telephone set is linked by means of special terminal equipment via a
radio connection to a local exchange in a telephone network, the exchange in
turn being linked to the public telephone network via network cabling. In this
connection, a subscriber station refers to the equipment available to a sub-
20 scriber for transmitting and receiving telecommunication signals, that is, in thecase of the WLL system, the subscriber station comprises WLL terminal equip-ment consisting of a radio part and a teleadapter (to which a user interface,
such as a telephone set, is connected), and a user interface, such as a tele-
phone, a telefax terminal, a computer/modem combination or the like, con-
25 nected to the terminal equipment.
For disturbance-free transfer of telecommunication signals, e.g. sig-
nals associated with a call, subscribers stations have to be monitored in the
WLL system in order for possible malfunction to be detected as early as pos-
sible. Monitoring is very difficult in the WLL system as the WLL terminal is
30 situated on subscriber premises where the operator maintenance personnel
- have no entry. This is why the condition of a WLL subscriber station has to be
monitored via the radio path.
A method of monitoring the operation of a subscriber station in the
WLL system is previously known, wherein a call is transmitted to the sub-
35 scriber station, the call being selected so that the subscriber station answers itautomatically. Having answered the call, the subscriber station is diagnosed to
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be operative. Conversely, if the subscriber station does not answer the call,
the call is repeated until the subscriber station has failed to answer a prede-
termined number of calls, and consequently the subscriber station is diag-
nosed to be inoperative.
The most significant weakness of the above known method is that
the only information conveyed on the subscriber station is that the WLI sub-
scriber station answers a call received via the radio path. This information is
not sufficient for the operator to, e.g. by maintenance or the like, prevent dis-
turbance, or alternatively, deal with temporary disturbances before the user of
the subscriber station detects the disturbance.
It is an object of the present invention to solve the above problem
and provide a better and more versatile method of monitoring the operation of
subscriber stations in order to detect possible malfunction as early as possible,
even before the user of the subscriber station detects the disturbance. These
goals are achieved with the method of the invention, characterized in that a
subscriber station is equipped with testing means for execution of tests indica-tive of the condition of the subscriber station, a predetermined testing mes-
sage is transmitted via the radio path to the testing means of the subscriber
station when no connection is active from the subscriber station, the testing
message containing information indicating the test to be carried out, and a
message indicative of the results of the test carried out is received from the
subscriber station via the radio path.
The invention is based on the idea that it is significantly easier to
test the condition of a subscriber station when subscriber stations are
equipped with special test units by means of which the subscriber units can
independently carry out given test measurements, and transmit information
indicative of the results of the test to the operator as a response to a received
testing message. Consequently the operator can, whenever desirable, e.g.
daily at a predetermined time of the day, start a test sequence for testing the
condition of the subscriber stations in the system. The most significant ad-
vantages of the method of the invention are that it offers the operator a chanceto monitor the condition of e.g. a given subscriber station without any partici-pation of the user of said subscriber station or even any awareness that
his/her subscriber station is being tested, the reliability of the system being sig-
nificantly improved, and that the operator can control the testing means so thatthey will carry out a given test on the basis of information included in the test-
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ing message, and hence all tests do not have to be carried out at the same
time, but can be done periodically e.g. so that a single subscriber station willbe completely tested during one week (that is, e.g. one testtday), which will
shorten the time needed for testing a large number of subscriber stations.
The invention further relates to a system to which the method of the
invention can be applied. The system of the invention is characterized in that
the system comprises a subscriber station with testing means for testing the
condition of the subscriber station as a response to a testing message trans-
mitted from the subscriber network element via the radio path, the information
in said testing message indicating to the testing means the test to be carried
out, and means for transmitting a message indicative of the results of the test
to the subscriber network element via the radio path, and that the subscriber
network element comprises means for transmitting said testing message at a
time specified by the operator, and means for receiving a message indicative
of the results of the test from the subscriber station, and for forwarding the in-
formation indicative of said results to the operator. Thus the system of the in-vention provides the operator with a better chance than before to monitor the
operation of separate subscriber stations centralized, e.g. from a network
management centre.
In a preferred embodiment of the system of the invention, the test-
ing means of the subscriber station comprise means for measuring the signal
level of a received signal, and for transmitting a message indicative of the
measuring result via the subscriber network element further to the operator.
This embodiment of the invention allows the operator to receive information on
the field strength as seen by the subscriber station and to conclude from this
information if e.g. problems of a malfunctioning subscriber station are due to aweak field strength, i.e. the fact that the subscriber station is e.g. incorrectly
placed. In this case the operator can contact the user of the subscriber stationand tell him/her to transfer the subscriber station to another place where the
field strength is likely to be better, or alternatively, by reconfiguration, to trans-
fer the subscriber station to an adjacent base station. Furthermore, as the
testing message and the message indicative of the results of the test are
transmitted on the control channel of the system, execution of the test speeds
up as no traffic channel has to be assigned to the subscriber station during thetest, but all information relevant to the test can be transmitted on the controlchannel between the subscriber network element and the subscriber station by
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utilizing system call frames.
In another preferred embodiment of the invention, signalling be-
tween a subscriber station and a subscriber network element is essentially
similar to that defined in NMT-900 specifications, the subscriber network ele-
ment being arranged to use frame 1a, 1a', 1a" or 1b defined in NMT-gO0
specifications point 4.3.2.1 as a testing message, and the subscriber station isarranged to transfer the message indicative of the test results to the subscriber
network element by frame 10a or 10d defined in NMT-900 specifications point
~.3.2.2. This embodiment of the invention provides a chance to apply the
method of the invention to the WLL system based on the NMT-900 mobile
communication system, the signalling of the subscriber station and the sub-
scriber network element associated with testing a subscriber station being
formed such that subscriber stations of the NMT-900 system can also be util-
ized in the system. This means that although all aspects of the signalling of the
subscriber network element are not similar to the signalling defined in the
NMT-900 specifications, the differences are, however, insignificant as regards
the operation of a conventional NMT-900 mobile station, and consequently do
not cause disturbance.
The invention further relates to a subscriber station for applying the
method of the invention, and which can be used in the system of the invention.
The subscriber station of the invention is characterized in that the terminal
equipment comprises testing means for testing the condition of the subscriber
station as a response to a testing message transmitted to the testing means,
the information in said testing message indicating to the testing means the testto be performed, and means for transmitting a message indicative of the test
results via the radio path to other parts of the system. Thus the subscriber sta-
tion of the invention allows the operator to monitor its operation via the radiopath without the user of the subscriber station having to participate in or be
aware of the monitoring.
The preferred embodiments of the method, system and subscriber
station of the invention are disclosed in the attached dependent claims 2 to 3,
5 to 7, and 9.
In the following the invention will be described in greater detail by
means of a preferred embodiment of the invention with reference to the ac-
companying drawings, in which
Figure 1 shows a block diagram of a first preferred embodiment of
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the system of the invention, and
Figures 2A and 2B illustrate signalling frames utilized in the method
of the invention.
Figure 1 shows a block diagram of a first preferred embodiment of
5 the radio system of the invention. Figure 1 shows the part of the WLL system
to which the method of the invention can be applied. The WLL system shown
in Figure 1 is based on the NMT-900 system (Nordisk Mobil Telefon), simpli-
fied by irrelevant properties having been omitted. Base stations 5 are similar to
parts of the NMT-900 cellular radio system. This means that signalling be-
10 tween a subscriber station 1 and the base stations is quite similar to the sig-
nalling between a subscriber station and a base station in the NMT-900 mobile
communication system. Consequently, calls to a conventional NMT-900 sys-
tem mobile station 9 can also be forwarded via the base stations 5 and a sub-
scriber network element 6, provided that the operator has programmed the
15 subscriber network element 6 for forwarding calls regarding said telephone.
The subscriber station 1 shown in Figure 1 consists of a user inter-
face, i.e. a telephone set 2, and terminal equipment 3. The telephone set 2
shown in Figure 1 can be a conventional voice-frequency telephone set con-
nectable to a fixed telephone network. A two-wire line 4, via which signals can
20 be transferred between the terminal equipment and the telephone set con-
nects the telephone set 2 and the terminal equipment 3. The terminal equip-
ment 3 comprises signal processing means for adapting a speech path to a
radio channel. Such signal processing means include e.g. a radio part 11
comprising an antenna 8, a radio transmitter and a radio receiver, and a tele-
25 adapter 10 for fitting the radio part to a conventional telephone set 2.
The subscriber station 1 uses radio frequency signals to communi-
cate via the antenna 8 with the base station 5 (the Figure shows three base
stations BS) via which calls are forwarded to the subscriber network element 6
and further to an exchange 7 in a PSTN network (Public Switched Telephone
30 N~twork), i.e. a fixed telephone network. In the case of Figure 1, the sub-
scriber network element 6 can be linked to the local exchange of a fixed tele-
phone network via e.g. an open multiplexer interface of type CCITT Q.512 V2
or V5.1 or V5.2 using a 2 MbiVs PCM system (Pulse Code Modulation).
The subscriber network element 6 shown in Figure 1 is quite similar
35 to the MTX exchange in the NMT-900 system except that properties irrelevant
to the WLL system have been omitted, such as operations associated with
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W 0 97/33447 PCTAF~7/00151
handover not needed in the WLL system.
In accordance with the invention, the terminal equipment 3 of the
subscriber station 1 comprises a measuring unit 13 with means for testing the
condition of the subscriber station using a plurality of optional tests. Conse-
quently the measuring unit 13 is able to monitor the condition of the subscriberstation 1 by measuring e.g. the signal level of a signal received via the radio
path. The measuring unit 13 further comprises means for e.g. testing the con-
dition of the user interface 2 by means of current, voltage and insulation re-
sistance measurements performed on the two-wire line 4. By means of these
tests the terminal equipment also finds out if a user interface 2 is at all linked
to it, or if the user has unplugged the telephone from the terminal equipment 3.The measuring unit 13 preferably also comprises a memory for re-
cording data regarding disturbances in the operation of the terminal equip-
ment. The data is stored in the memory until a testing message is forwarded to
the subscriber station from the subscriber network element 6, leading to re-
lease of the data for the use of the operator.
In accordance with the invention, the operator may activate, e.g.
from a network management centre by remote control, a test sequence in
which the subscriber network element 6 goes through every system subscriber
station one at a time, and performs one or more tests on them. Such a test
sequence may start e.g. automatically daily at a given time. The testing time ispreferably chosen so that during the testing the system loading level is low (a
small number of calls in progress).
Figures 2A and 2B illustrate the signalling frames utilized in the
method of the invention and in the system of Figure 1.
To test the condition of the subscriber station 1 of Figure 1, the sub-
scriber network element 6 transmits a testing message S1 via a base station
to the subscriber station 1 on a control channel. A frame 1 a, 1a', 1a" or 1 b de-
fined in the NMT-900 specifications point 4.3.2.1 (NMT Doc 900-1, January
29, 1985) is preferably used as the testing message. Figure 2A illustrates
frame 1a (Calling Channel Indication, General). In accordance with this em-
bodiment, variable Z is always assigned the value 0, whereas the test desired
is denoted by values of the variables A1 to A3.
After performing the desired test, the subscriber station forwards
3~ information on the measuring result to the subscriber network element by us-
ing message S2, preferably frame 10a or 10d defined in the NMT-900 specifi-
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cations point 4.3.2.2. Figure 2B illustrates frame 10a (Call acknowledgement
from MS on calling channel, and access on access channel). In accordance
with this embodiment (and as distinct from the NMT-900 specifications) said
frame is transmitted in full. The information indicative of the test results is for-
5 warded via variables A1 to A4.
When a testing message S1, in which variable A1 has been as-
signed the value 1; is forwarded to the testing means 13, the measuring unit
performs a test to see if a user interface is linked to the terminal equipment
and if malfunction has occurred in the subscriber station. After the tests, infor-
10 mation on the results is forwarded via the subscriber network element to theoperator by message S2, i.e. by transmission of the frame of Figure 2B, vari-
able A1 being assigned the value 1, and the bits (A2=bOb1b2b3b4b5b6b7b8,
A3=bOb1b2b3b4b5b6b7b8 and A4=bOb1b2b3b4b5b6b7b8) of variables A2 to
A4 being coded on the basis of the results e.g. so that in variable A2:
bit bO=1 ~ user interface linked
bit b1=1 ~ error condition 1 in terminal
bit b2=1 ~ error condition 2 in terminal
bit b8=1 ~ error condition 8 in terminal.
Similarly, when a testing message S1, i.e. the frame of Figure 2A, in
which variable A1 has been assigned the vaiue 2, is forwarded to the testing
means 13, the measuring unit 13 measures the signal level of the received
signal. The measuring unit 13 forwards the measurement result to the sub-
scriber network element by message S2, where variable A1=2, and variables
A2 and A3 are assigned values depicting a measured dBm value in hexa-
decimals (negative), that is, e.g. -91 dBm = 5B (in hexadecimals) and -112
dBm = 70 (in hexadecimals).
It will be appreciated that the above description and the accompa-
nying drawings are presented by way of illustration only. It will be understood
by those skilled in the art that various modifications and changes may be
made without departing from the spirit and scope of the invention disclosed in
the appended claims.
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