Alarm method and apparatus for a mobile communication repeating system

An alarm method and apparatus in a mobile communication repeating system having a plurality of repeating modules for informing a base station that a repeating module is out of order. The repeating modules respectively check whether a self repeating module is out of order. A repeating interface unit informs the base station of an alarm state according to a failure of a particular repeating module.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a mobile communication system and, more 
particularly, to an alarm method and apparatus for informing a base 
station that a repeating module is out of order in a mobile communication 
repeating system having a plurality of repeating modules. 
2. Description of the Related Art 
A cellular system, which is a typical mobile communication system, provides 
communication services for a plurality of mobile stations from base 
stations that are positioned at regular intervals. The base stations are 
situated at fixed locations, whereas the mobile station travels according 
to the position of a user. The mobile station may sometimes be located in 
radio wave shadow areas, such as in the interior of a building, subway 
station or arcade or in the closed space of an elevator. When a radio wave 
from the base station is transmitted to such an area, there is a great 
path loss. For instance, the radio wave at the interior of a building is 
characterized by multipath fading having a very short delay. Consequently, 
the signal performance diminishes when the radio wave is transmitted from 
the base station to the interior of a building. Moreover, if the radio 
wave is transmitted from the base station to the rear of a wall or an 
elevator, the signal performance diminishes due to a shadow phenomenon 
which makes it difficult to provide communication services to a mobile 
station located in such radio wave shadow areas as a result of the signal 
degradation. 
Therefore, certain techniques have been proposed for enlarging a 
communication service area irrespective of the position of the mobile 
station. For example, the techniques disclosed in U.S. Pat. No. 5,280,472 
to Gilhousen, et al., entitled "CDMA MICROCELLULAR TELEPHONE SYSTEM AND 
DISTRIBUTED ANTENNA SYSTEM THEREFOR", and Korean Patent Application No. 
96-15231 filed by Chang-hyun Oh, on May 9, 1996, for repeating a code 
division multiple access (CDMA) communication signal (in a CDMA system) 
between a plurality of distributed antennas and base station transceivers 
and in a CDMA system having a plurality of "delay elements" or 
"distributed elements" which are repeating modules that communicate with 
the mobile station through each antenna. This distributed antenna system 
provides multipath signals for facilitating signal diversity. 
Consequently, the communication services can be supplied to mobile 
stations located in radio wave shadow areas, thereby improving the 
performance of the system. 
In the above disclosed mobile communication systems, however, the repeating 
modules are remotely located from the base station and are operated by 
unmanned control. Therefore, the base station can not determine if any of 
the repeating modules are out of order. For example, each repeating module 
displays only a power ON/OFF state via a light emitting diode (LED) which 
is installed at its front surface. Indeed, these systems do not provide 
methods for either checking whether the repeating module is out of order, 
displaying a failure indication or informing the base station that the 
repeating module is out of order. Therefore, the base station cannot 
monitor an alarm state of the repeating module. Consequently, both the 
management efficiency and the reliability of the system is diminished and 
degraded. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a method and 
apparatus for monitoring alarm states of repeating modules from a base 
station. 
In an alarm method of a mobile communication repeating system embodying the 
present invention, repeating modules respectively check whether a 
self-repeating module is out of order. A repeating interface unit informs 
a base station transceiver of an alarm state in accordance with the 
failure of a repeating module. 
An alarm apparatus of a mobile communication repeating system embodying the 
present invention includes: an alarm monitor installed at a repeating 
interface unit, for transmitting a state inquiry message for inquiring 
whether repeating modules are out of order by sequentially designating the 
repeating modules, and informing a base station transceiver of an alarm 
state according to state information of an acknowledge message received 
from a corresponding repeating module; and a failure detector installed at 
the repeating modules one by one, for checking whether a self repeating 
module is out of order in response to the state inquiry message 
designating the self repeating module, and transmitting state information 
to the alarm monitor. 
These and other objects, features and advantages of the present invention 
will become apparent from the following detailed description of 
illustrative embodiments, which is to be read in connection with the 
accompanying drawings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
In the following description and drawings, specific details such as circuit 
configurations, processing flows and message formats, are set forth to 
provide a more thorough understanding of the present invention. It will be 
apparent to one of ordinary skill in the art, however, that the present 
invention may be practiced without these specific details. In other 
instances, descriptions of well-known functions and constructions have 
been omitted so as not to obscure the present invention. 
Referring to FIG. 1, a radio wave repeating apparatus of a CDMA 
communication system which is disclosed in the above-mentioned Korean 
Patent application No. 96-15231 is shown. The radio wave repeating 
apparatus of FIG. 1 generally includes a base station 100 and a 
distributed antenna element (DAE) 200. The base station 100 includes a 
digital signal processor 110, a transceiver 120 and a distributed antenna 
interface (DAI) 130. The digital signal processor 110 processes a 
transmitting digital signal to generate an intermediate frequency (IF) 
signal and processes a received IF signal to restore the digital signal. 
The transceiver 120 converts the IF signal generated from the digital 
signal processor 110 into a CDMA high frequency signal and converts a 
received CDMA high frequency signal into an IF signal. The DAI 130 is 
electrically connected between the transceiver 120 and the DAE 200. 
Through terminal Tx.sub.-- IN, the DAI 130 receives a high frequency 
signal S11 (in the frequency range of 869-894 MHz) from the transceiver 
120, wherein the S11 signal is attenuated and amplified and then 
transmitted through terminal Tx.sub.-- OUT A as signal S14. Further, the 
DAI 130 delays the signal S11 for a prescribed time, and then generates 
the delayed S11 signal (i.e., signal S15) through terminal Tx.sub.-- OUT 
B. The signal S15 generated from the DAI 130 allows a mobile station to 
operate as a RAKE receiver. The signal S15 is delayed by 1.25 .mu.s as 
compared with the signal S14. 
The DAI 130 also receives a signal S16 (in the frequency range of 824-849 
MHz) and a signal S17 (in the frequency range of 824-849 MHz) through 
terminals Rx.sub.-- IN A and Rx.sub.-- IN B, respectively, wherein such 
signals are attenuated and amplified to generate respective signals S12 
and S13. The signals S12 and S13 are transmitted to the transceiver 120 
through DAI 130 terminals Rx.sub.-- OUT A and Rx.sub.-- OUT B, 
respectively. 
The DAE 200 has distributed elements 300A1, 300A2, 300B1 and 300B2 for 
providing time diversity and space diversity in order to support services 
even in radio wave shadow areas such as described above. The DAE 200 
includes a first DAE string (String A) and a second DAE string (String B). 
The first DAE string (String A) consists of a series of antennas ANT A1 
and ANT A2, which are distributively connected to each other in space, as 
well as distributed elements 300A1 and 300A2, which are connected to 
antennas ANT A1 and ANT A2, respectively. The second DAE string (string B) 
consists of a series of antennas ANT B1 and ANT B2, which are 
distributively connected to each other in different space from the first 
DAE string, as well as distributed elements 300B1 and 300B2, which are 
connected to the antennas ANT B1 and ANT B2, respectively. The distributed 
elements 300A1 and 300B1 are identically positioned in any one space to 
form a first node Node #1, and the distributed elements 300A2 and 300B2 
are identically positioned in another space to form a second node Node #2, 
so as to provide space diversity. The number of distributed elements and 
corresponding antennas may be increased notwithstanding that the system of 
FIG. 1 illustrates each DAE string having only two distributed elements 
and two antennas. 
The DAI 130 and the DAE 200 constitute a distributed antenna apparatus. One 
distributed element transmits a signal received from either the DAI 130 or 
another distributed element to the mobile station through an antenna, and 
transmits a signal received from the mobile station to either another 
distributed element or the DAI 130. Each distributed element delays and 
then transmits the CDMA signal which is transmitted from the transceiver 
120 and processed by the DAI 130. The two distributed elements 300A1 and 
300B1 of the first node Node #1 receive signals S14 and S15 that (as 
described above) are delayed by 0 .mu.s and 1.25 .mu.s, respectively, and 
then transmit signals that are further delayed by 2.5 .mu.s to the second 
node Node #2, as well as the mobile station through the antennas ANT A1 
and ANT B1, respectively. Since the mobile station receives signals 
transmitted from the two nodes, it can operate as the RAKE receiver. For 
example, if the mobile station moves to the second node from the first 
node, the signal strength of the 0 .mu.s and 1.25.mu. is delayed signals 
increase whereas the signal strength of the 2.5 .mu.s and 3.75 .mu.s 
delayed signals decrease. Therefore, since the mobile station receives the 
signals transmitted from the second node, the mobile station operates as 
the RAKE receiver. 
Hereinafter, preferred embodiments of the present invention as they are 
applied to the above disclosed system of the Korean Patent application No. 
96-15231 will be described. The distributed elements 300A1, 300A2, 300B1 
and 300B2 are referred to as the repeating modules, and the DAI 130 is 
referred to as a repeating interface. By way of example, it is assumed 
that the number of distributed elements within the DAE 200 (including the 
elements 300A1, 300A2, 300B1 and 300B2) is 16, with the number of 
distributed elements for each of the first and second DAE strings being 8. 
Referring now to FIG. 2, an alarm monitor in accordance with the present 
invention as applied to the radio wave repeating apparatus of FIG. 1 is 
shown. The alarm monitor includes a microcontroller 202 and a modem 204 
and is connected to the DAI 130 of the base station 100 (shown in FIG. 1). 
The alarm monitor, under the control of the microcontroller 202, transmits 
a state inquiry message by sequentially designating the distributed 
elements and then informs the base station 100 of an alarm state in 
accordance with state information of an acknowledge message that is 
received from a corresponding distributed element. The state inquiry 
message inquires as to whether the distributed elements are out of order. 
As stated above, the microcontroller 202 controls the operations of the 
alarm monitor. In a preferred embodiment of the present invention, the 
microcontroller 202 uses an 8-bit CMOS (Complementary Metal Oxide 
Semiconductor) EEPROM (Electrically Erasable and Programmable Read Only 
Memory) microcontroller. As discussed in detail below, the flow diagram of 
FIG. 4 illustrates the steps that the microcontroller 202 is programmed to 
perform. The microcontroller 202 is connected to the modem 204 and an 
upper level control device of a system (not shown) within the base station 
100. Since the DAE 200 is remote from the base station 100 and the DAI 130 
is located within the base station 100, a data transceiver or buffer is 
used to transmit data from the microcontroller 202 to the base station 
100. The modem 204 is connected to the microcontroller 202 and to 
receiving terminals Rx.sub.-- IN A and Rx.sub.-- IN B of the DAI 130. 
Specifically, the modem 204 is connected to a high frequency coaxial cable 
receiving the high frequency signals S16 and S17 from the distributed 
elements 300A1, 300A2, 300B1 and 300B2. 
Referring to FIG. 3, a failure detector in accordance with the present 
invention as applied to the radio wave repeating apparatus of FIG. 1 is 
shown. The failure detector includes a first level detector 302 and a 
second level detector 306, a directional coupler 304, a microcontroller 
308, a modem 310, and an ID (Identification) setter 312. The failure 
detector of the present invention (shown in FIG. 3) is connected to each 
of the distributed elements 300A1, 300A2, 300B1 and 300B2 of FIG. 1. As 
explained in further detail below, the failure detector, under the control 
of the microcontroller 308, determines whether a particular 
self-distributed element is out of order in response to the state inquiry 
message designating the self-distributed element. The microcontroller 308 
then transmits state information via the acknowledge message to the alarm 
monitor shown in FIG. 2. The self-distributed element refers to a 
distributed element at which the failure detector of FIG. 3 is installed. 
The first level detector 302, operatively connected between the 
microcontroller 308 and a transmitting terminal Tx OUT of a 
self-distributed element, detects a high frequency transmitting signal 
level that is transmitted from the self-distributed element to another 
distributed element. The directional coupler 304, operatively disposed in 
the signal transmission path between the self-distributed element and the 
antenna of the self-distributed element, induces a signal which is 
reflected from the antenna. This directional coupler 304 is installed at 
the front terminal of a duplexer (not shown) which is connected to the 
antenna. Generally, the directional coupler induces a signal corresponding 
to 1/10 to 1/10000 of a level of the high frequency signal. The second 
level detector 306, operatively connected between the microcontroller 308 
and the directional coupler 304, detects the level of the reflection 
signal generated from the directional coupler 304. The first and second 
level detectors 302 and 306 employ a Schottky diode detector to detect a 
DC voltage level by envelope-detecting the high frequency signals. 
The microcontroller 308 of the failure detector is used to control the 
operations of the failure detector. The microcontroller 308 is an 8-bit 
CMOS EEPROM microcontroller similar to the microcontroller 202 of the 
alarm monitor of FIG. 2. The operations illustrated in the flow diagram of 
FIG. 5 are programmed in the microcontroller 308. The microcontroller 308 
is operatively connected to the first and second level detectors 302 and 
306, the modem 310 and the ID setter 312. When the state inquiry message 
designating the self-distributed element is received from the alarm 
monitor, the microcontroller 308 of the failure detector checks whether 
the self-distributed element is operating properly by confirming the 
transmitting signal level and reflection signal level generated from the 
first and second level detectors 302 and 306, respectively. The 
microcontroller 308 then transmits an acknowledge message to the alarm 
monitor through the modem 310. The ID setter 312 sends a unique ID of the 
self-distributed element to the microcontroller 308. The ID setter 312 
uses a dual in-line package (DIP) switch to generate the unique ID. For 
each of the distributed elements of the DAE 200, a unique address is set 
as an ID. Since it has been assumed that the number of the distributed 
elements within the DAE 200 is 16 (i.e., 8 distributed elements for String 
A and String B), a 3-bit address may be used to differentiate between the 
distributed elements of each string independently. 
The alarm monitor of FIG. 2 and the failure detector of FIG. 3 can 
discriminate between the different distributed elements by the unique ID 
that is designated to each of the distributed elements upon the 
transmission and the receiving of the state inquiry message and the 
acknowledge message. Specifically, when the alarm monitor transmits the 
state inquiry message, it sequentially designates the distributed elements 
by the ID. After receiving the acknowledge message, the alarm monitor can 
determine which distributed element transmitted that particular message. 
Moreover, when the failure detector receives the state inquiry message, it 
can determine from the ID whether the particular self-distributed element 
is designated. 
On the other hand, the modem 204 of the alarm monitor and the modem 310 of 
the failure detector are connected to each other through the high 
frequency coaxial cable (not shown) that receives the high frequency 
signals S16 and S17 from the distributed elements. Since the modems 204 
and 310 use a low frequency signal in comparison with the high frequency 
signals S16 and S17, an additional transmission path is not required. This 
transmission path transmits only the high frequency signal. However, a 
power source is supplied to the distributed elements through the high 
frequency coaxial cable which transmits the high frequency signals S14 and 
S15. 
A start-stop synchronization system is used between the modems 204 and 310. 
The state inquiry message and the acknowledge message are transmitted and 
received in accordance with the message formats illustrated in FIGS. 6a 
and 6b, respectively. Specifically, FIG. 6a shows the format of the state 
inquiry message which is transmitted to the failure detector from the 
alarm monitor. The state inquiry message consists of a 22 bit 
synchronizing signal, a single start bit, an 8 bit data signal, and a 
single stop bit. The data signal corresponds to the unique ID which is 
designating one of the distributed elements. In a preferred embodiment of 
the present invention, as shown in FIG. 6a, three bits of the 8 bit data 
signal (i.e., b4, b5 and b6 of bits b0-b7) are utilized to designate the 
ID. Namely, three ID bits A0, A1 and A2 are transmitted in bit locations 
b4, b5 and b6, respectively. When the alarm monitor transmits the state 
inquiry message, a synchronizing signal consisting of 20 logic "0" bits 
and 2 logic "1" bits is transmitted to indicate the start of communication 
sequence, with the start bit, data bits and stop bit being sequentially 
transmitted. The data is transmitted in the order of the least significant 
bit (LSB) (i.e., b0) to the most significant bit (MSB) (i.e., b7) at a 128 
baud rate and communication speed of 128 bps. By transmitting the 
synchronizing signal of 20 logic "0" bits and 2 logic "1" bits, the 
failure detector of a particular distributed element can return to a 
receiving standby state from a start bit standby state by detecting a 
signal by the 10-th bit (i.e., the stop bit). 
Referring now to FIG. 6b, a format of the acknowledge message which is 
transmitted to the alarm monitor from the failure detector is illustrated. 
The acknowledge message consists of a single start bit, an 8 bit data 
signal, and a single stop bit. The data signal includes an ID of the 
self-distributed element and the state 294 information. Specifically, the 
ID is the three bits b4, b5 and b6 (from bit string b0-b7) corresponding 
to A0, A1 and A2, respectively. The state information data, Er0 and Er1, 
is transmitted in the LSBs b0 and b1. 
The data bit Er0 designates that portion of the state information which 
indicates a transmitting failure state. The microcontroller 308 compares 
the transmitting signal level detected by the first level detector 302 
with a first reference level. If the transmitting signal level is lower 
than the first reference level, the microcontroller 308 determines that 
self-distributed element as the transmitting failure state and encodes 
data bit Er0 accordingly. Specifically, a state information Er0 of logic 
"1" indicates the transmitting failure state whereas an Er0 of logic "0" 
represents a normal state. 
Next, the data bit Er1 designates that portion of the state information 
which indicates a voltage standing wave ratio (VSWR) failure state. The 
microcontroller 308 compares the reflection signal level detected by the 
second level detector 306 with a second reference level. If the detected 
reflection signal level is higher than the second reference level, the 
microcontroller 308 determines the self-distributed element as the VSWR 
failure state and encodes data bit Er1 accordingly. Specifically, the 
state information Er1 of logic "1" represents the VSWR failure state 
whereas an Er1 of logic "0" indicates the normal state. 
Referring now to FIG. 4, a flow diagram of the operation of microcontroller 
202 of the alarm monitor (FIG. 2) is shown. Initially, the microcontroller 
202 clears an address ADDR to 0 and sets a flag FLG to logic "0" during an 
initialization operation such as power-on (step 400). The address ADDR is 
a value for sequentially designating the distributed elements and, as 
explained above, corresponds to the ID of the distributed element. The 
address ADDR is sequentially increased from 0 to 7 in increments of 1. 
When the address ADDR is increased up to 7, it is initialized to 0. The 
flag FLG is used to differentiate between the first and second DAE strings 
because they have different transmission paths as shown in FIG. 1. It is 
assumed that a FLG of logic "0" designates the first DAE string, and that 
a FLG of logic "1" designates the second DAE string. 
Next, it is determined whether a confirming period has elapsed (step 402). 
By way of example, assume that the confirming period is set to 0.5 
seconds. If it is determined that the confirming period has elapsed, the 
next step is to check the flag FLG (step 404). If FLG is determined to be 
logic "0" , a state inquiry message with the address ADDR of 0 as the ID 
is transmitted to the first DAE string through the modem 204 (step 406). 
After initialization, since the first address ADDR is 0, the ID will be an 
ID of the first distributed element, e.g., the distributed element 300A1 
of the first DAE string shown in FIG. 1. On the other hand, if FLG is 
determined to be logic "1", the state inquiry message with the address 
ADDR of 0 as the ID is transmitted to the second DAE string through the 
modem 204 (step 408). Next, a determination is made as to whether an 
acknowledge message has been received in response to the transmitted state 
inquiry message (step 410). 
Referring now to FIG. 5, a flow diagram of the operation of the 
microcontroller 308 of the failure detector after receiving the 
transmitted state inquiry message (steps 406 or 408 in FIG. 4) is shown. 
The microcontroller 308 waits for the synchronizing signal during a 
receiving standby state (step 500). When a synchronizing signal is 
received by the modem 310, the microcontroller 308 receives the state 
inquiry message following the synchronizing signal (step 502). 
Next, the microcontroller 308 determines whether the ID of the state 
inquiry message is equal to a unique ID set by the ID setter 312 (step 
504). If they are not equal, microcontroller 308 returns to step 500 since 
the ID of the state inquiry message does not designate the 
self-distributed element. On the other hand, if they are equal, the 
transmitting signal level and the reflection signal level generated from 
the first and second level detectors 300 and 304, respectively, are 
confirmed (step 506). Next, an alarm state is determined by checking 
whether the self-distributed element is out of order (step 508). In 
particular, as mentioned above, if the level of the transmitting signal is 
lower than the first reference level, the self-distributed element is 
determined to be in a transmitting failure state. Moreover, if the level 
of the reflection signal is higher than the second reference signal, the 
self-distributed element is determined to be in the VSWR failure state. 
The microcontroller 308 of the failure detector then transmits an 
acknowledge message to the alarm monitor through the modem 310 according 
to the state information of the alarm state (step 510). The acknowledge 
message includes the state information Er0 and Er1 and the ID information 
A0, A1 and A2 of the selfdistributed element. The microcontroller 308 then 
returns to the receiving standby state of step 500. As shown above, the 
failure detector checks whether the self-distributed element is out of 
order in response to the state inquiry message designating the 
self-distributed element and transmits the state information to the alarm 
monitor. 
Referring back to step 410 of FIG. 4, if the acknowledge message is 
received from the failure detector of the distributed element, the 
microcontroller 202 stores the state information of the acknowledge 
message (step 412). If, on the other hand, the acknowledge message is not 
received, it is assumed that the corresponding distributed element is out 
of order and the microcontroller 202 stores the state information 
indicating that the corresponding distributed element is out of order 
(step 414). 
Next, the flag is checked to determine whether FLG is logic "0" (step 416). 
If it is determined that FLG is logic "0", FLG is set to logic "1" (step 
418) and then the address ADDR is increased by 1 (step 420). Thereafter, 
the above operations are repeated with respect to the next distributed 
element designated by the address ADDR (return to step 402). If (at step 
416) FLG is determined to be logic "1", FLG is initialized to logic "0" 
(step 422). Next, the address is checked to determine whether the address 
ADDR is 7 (step 124). If ADDR is 7, it is determined that the above 
operations for all the distributed elements (i.e., the 16 distributed 
elements of the DAE 200 for the two separate strings each having 8 
distributed elements) in the above example are completed. Next, an output 
of the alarm state of the base station 100 is updated (step 426). In 
particular, if the confirmation of the alarm state for the 16 distributed 
elements is ended, the microcontroller 202 informs the base station of a 
confirmation result. Since the above operations are implemented 16 times 
with respect to the first and second DAE strings at intervals of, e.g., 
0.5 seconds, the alarm output is updated once every 8 seconds. The 
microcontroller 202 then initializes the address ADDR to 0 (step 428) and 
the process flow returns to step 402. Moreover, if (at step 424) the 
address ADDR is not 7, ADDR is increased by 1 (step 420) and the process 
returns to step 402. 
As demonstrated above, the alarm monitor inquires whether the distributed 
elements are out of order and informs the base station of the alarm state 
according to the state information of the acknowledge message received 
from the corresponding distributed element. Consequently, the distributed 
elements (i.e., the repeating modules) detect their failure states and the 
DAI (i.e., the repeating interface unit) informs the base station of the 
alarm state according to the failure state of the repeating module. 
Advantageously, since the base station can monitor the alarm state of the 
repeating module by the output of the alarm state, a system may be used 
efficiently used and the reliability improved. 
While the invention has been shown and described with reference to a 
particular preferred embodiment thereof, it is to be understood by those 
skilled in the art that various changes in form and details may be made 
therein without departing from the spirit and scope of the invention. For 
example, the present invention may be applied to a mobile communication 
system such as a personal communication service (PCS) using the repeating 
modules in order to obtain enhanced system performance by repeating a 
communication signal. The order of confirming the alarm state of the 
repeating modules, confirming period, or an output updating period of the 
alarm state may also be varied. Therefore, it is not intended that the 
present invention be limited to the specific embodiment disclosed as the 
best mode contemplated for carrying out the present invention, but that 
the present invention includes all embodiments falling within the scope of 
the appended claims.