Method for enhancing the reliability of a wireless telecommunications system

A method for determining the operational status of base stations deployed in a cellular telecommunications system comprises continually sharing operational status data with adjacent base stations in accordance with a primary diagnostic protocol. Upon non-receipt of an operational status message, a supplemental diagnostic protocol is executed to identify a malfunctioning base station. The failed status of an identified malfunctioning base station is extended to a mobile switching center over an established data interface. In some circumstances, the mobile switching center extends radio allocation information to a functional base station so that the functional base station may perform temporary administrative services for the adjacent failed base station until permanent repairs can be made.

TECHNICAL FIELD 
This invention relates to base stations, and more particularly, to 
providing seamless telecommunications services to mobile subscribers 
served by cellular base stations in a wireless telecommunications system. 
BACKGROUND OF THE INVENTION 
The world-wide proliferation of wireless telecommunications is the 
consequence of substantial cost breakthroughs in wireless 
telecommunications terminals, more commonly known as "mobile telephone 
stations". The "cellular" principle has also contributed to the growth of 
wireless telecommunications by enabling voice, and data, to be carried 
over an allocated radio spectrum to cell sites across wide geographic 
areas. As a result, it is commonplace for modem subscribers of 
telecommunications services to own separate wireless, and wireline, 
telecommunications terminals which are served by distinct wireless and 
wireline systems. 
Although the average subscriber's expectation of wireless network 
reliability is exceeded by the expectation of wireline network 
reliability, wireless telecommunications service providers endeavor to 
offer highly dependable, seamless service. One obstacle to providing this 
type of service is the unpredictable, random malfunctioning of base 
stations. Presently, a non-functional base station is detected by the 
wireless telecommunications service provider only when field testing by 
technical personnel identifies a malfunction, or when a subscriber 
complains. Identification of a non-functional base station results in 
notification of technical personnel so that appropriate repairs can be 
made. 
A substantial period of time often passes from detection of the 
malfunctioning base station to completion of appropriate repairs. During 
this period, mobile subscribers located in the geographic area affected by 
the non-functional base station are unable to make, or receive, telephone 
calls. As telecommunications service providers are well aware, disruption 
of service is the primary cause for subscriber dissatisfaction and 
frustration. Therefore, there is a need in the art for efficiently 
identifying malfunctioning base stations, and restoring service to mobile 
subscribers affected by malfunctioning base stations in a wireless 
telecommunications system. 
SUMMARY OF THE INVENTION 
The above problem is solved, and a technical advance is achieved in the 
art, by proactively determining the operational status of base stations in 
a wireless telecommunications system, and using functional base stations 
to provide temporary administrative services to malfunctioning base 
stations until permanent repairs can be made. 
In accordance with the preferred embodiment of the present invention, 
cellular base stations in a wireless telecommunications system perform a 
primary diagnostic protocol to dynamically relay operational status 
information. To facilitate the diagnostic process, cell sites in a 
cellular telecommunications system are grouped in clusters. The primary 
diagnostic protocol allows each station to send, and receive, operational 
status messages from surrounding base stations. Geometrical 
characteristics of the clusters are exploited to pass operational status 
information to surrounding cell sites, and minimize the number of 
operational status messages relayed. Upon failure to receive a response, 
or receipt of a malfunctioning status response, the primary diagnostic 
protocol is augmented with a supplementary diagnostic protocol. In some 
cases, an operational base station may provide temporary cell site 
administrative services for the malfunctioning base station until 
permanent repairs are made.

DETAILED DESCRIPTION 
In the preferred embodiment of the present invention, a plurality of cell 
sites in a telecommunications system are arranged in a cell site cluster. 
Preferably, all cell sites in the cluster are served by a single mobile 
switching center. Consistent with convention, cell sites are represented 
as hexagonal structures. An optimum number of cell sites per cluster is 
nine but alternative embodiments may have a fewer, or greater, number of 
cell sites per cluster. 
FIG. 1 is a graphical representation of a preferred embodiment of a cell 
site cluster. More particularly, cell site cluster 100 includes individual 
cell sites 102, 104, 106, 108, 110, 112, 114, 116 and 118. In an 
operational cellular telecommunications system, cluster 100 is surrounded 
by other cell sites. 
Each cell site has unique set of coordinates with respect to X axis 120, 
and Y axis 122 which intersect at the center of cell site 118. More 
particularly, cell site 102 is identified by coordinates (1,-1), cell site 
104 is identified by coordinates (1,0), cell site 106 is identified by 
coordinates (1,1), cell site 108 is identified by coordinates (0,1), cell 
site 110 is identified by coordinates (-1,1), cell site 112 is identified 
by coordinates (-1,0), cell site 114 is identified by coordinates (-1,-1), 
cell site 116 is identified by coordinates (0,-1), and cell site 118 is 
identified by coordinates (0,0). Cell sites 102, 104 . . . 118 include 
base stations (not shown) which transmit radio messages between mobile 
subscriber terminals, and the mobile switching center for interconnection 
to the rest of the public-switched telephone network. 
FIG. 2 is a simplified block diagram of an exemplary base station found in 
each cell site. In this example, base station 200 includes: power supply 
202; radio frequency (RF) sub-system 210; audio channel sub-system 222; 
and control sub-system 230. Power supply 202 provides power to RF 
sub-system 210 via link 203A and 203B. Control sub-system 230 receives 
power from power supply 202 via link 203C, and audio channel sub-system 
222 receives power over link 203D. 
RF sub-system 210 include first antenna 211, second antenna 213, and RF 
distribution module 212. RF distribution module 212 is interconnected to a 
plurality of administrative modules via data links. More particularly, 
voice radio administrative module 214 is interconnected to the RF 
distribution module via data links 217 A-D, set up radio module 216 is 
interconnected to the distribution module by data link 219, locate radio 
module 218 is interconnected to the distribution module via data link 221, 
and test module 220 is interconnected to RF distribution module 212 via 
link 223. Set up radio module 216 receives call set up requests from 
mobile subscribers located in the cell site served by base station 200. 
Locate radio module 218 locates mobile subscribers for incoming call. In 
the preferred embodiment, self, primary and supplemental diagnostic 
protocols and base station-related data are stored in test module 220. 
Alternative embodiments may employ many more data links interconnecting RF 
distribution module 212 to the administrative modules. 
Audio channel sub-system 222 comprises voice trunk interfaces 224 
interconnected to the mobile switching center via a plurality of voice 
trunks 225. During a call, a voice trunk interface extends voice 
transmissions from the mobile switching center to a specified voice radio 
channel in voice radio module 214 over links 205. The voice transmissions 
are subsequently delivered to mobile subscribers via radio antennas 211, 
213, as is known in the art. 
Control sub-system 230 comprises cell site controller 232, data link 
interface 234 and a plurality of data links 227 to the mobile switching 
center. Cell site controller 232 manages all functions associated with 
base station 200. Particularly, the cell site controller receives call 
requests from mobile subscribers located within the cell site via set up 
module 216, and establishes conversations via voice radio module 214. Cell 
site controller 232 also locates mobile subscribers for incoming calls via 
locate radio module 218, and administers system protocols. Cell site 
controller 232 communicates with the mobile switching center via data link 
interface 234, and with other base stations via inter-base station link 
235, as known in the art. Bi-directional data links 207 interconnect 
sub-system 230 to the modules. In accordance with the preferred 
embodiment, cell site controller 232 is capable of providing call set-up, 
locate, and test functions for other base stations, via inter-base station 
link 235, when directed by the mobile switching center. 
FIG. 3 is a flow diagram describing the steps performed by a base station 
in a cellular telecommunications system during the primary diagnostic 
protocol. In the preferred embodiment, the primary diagnostic protocol 
occurs continuously, unless implementation of the supplemental diagnostic 
protocol is warranted. For purposes of example, assume that the primary 
diagnostic protocol described below is executed by base station 200 in 
cell site 118. Base station 200 is identified by coordinates x=0, y=0 (see 
FIG. 1). Base station 200 is hereinafter referred to as the "data 
gathering" base station to distinguish it from other base stations in the 
cell site cluster. Although the diagnostic procedures are described with 
reference to base station 200, all base stations in the preferred 
embodiment of a cellular system perform diagnostic protocols, and store 
operation status data. 
The process begins in step 300 in which cell site controller 232 determines 
the cluster index (CL) for this particular iteration of the primary 
diagnostic protocol. The cluster index defines the geographic parameters 
of the diagnostic process. For example, a cluster index of "0" indicates 
that the geographic parameter is defined by the eight (8) cell sites 
immediately adjacent to the data gathering base station. In other words, 
CL=0 for cell site 118 implies a geographic parameter defined by cell 
sites 102, 104, 106, 108, 110, 112, 114 and 116. A CL=1 for cell site 118 
indicates that the geographic parameter is defined by the surrounding 
seventy-two (72) cell sites (that is, all adjacent cell site clusters 
which include each one of the eight above-mentioned cell sites in cluster 
100). In this example, assume the cluster index is "0". 
The process continues to decision step 302 in which the cell site 
controller determines whether the CL is greater than its initialized 
coverage area. Prior to operation, each cell site controller is 
initialized with a maximum CL value so that diagnostic protocols are 
performed for only those cell sites for which the data gathering base 
station can ultimately perform administrative services. If the outcome of 
determination step 302 is a "YES" determination, the process ends in step 
303. If, as in this case, the outcome of decision step 302 is a "NO" 
determination, the process continues to steps 304, and 308 which occur 
simultaneously. 
In step 304, base station 200 (identified by coordinates x=0, y=0) sends 
its operational status to the cell site base station associated with 
coordinates x, y-3.sup.C1 (that is, coordinates (0,-1) identifying cell 
site 116). In the preferred embodiment, each base station is equipped with 
a module, such as test module 220, for performing a self-diagnostic test, 
and for issuing its operational status upon receipt of operational status 
from another base station. The self diagnostic test evaluates the 
operational status of each base station component, including antennas, 
voice radio module, set-up radio module, and locate radio module. The 
process continues to step 305 in which base station 200 receives, and 
stores, the operational status from the base station to which its status 
was sent. In this case, base station 200 receives the operational status 
from the base station of cell site 116. In step 306, base station 200 
sends its operational status to the cell site base station associated with 
coordinates x-3.sup.C1, y. In this case, coordinates (-1,0) identify cell 
site 112. In step 307, base station 200 receives the operational status 
from the base station of cell site 112. In the preferred embodiment, the 
operational status from cell site 112 also includes the operational status 
of cell sites 110, 112 and 114. In other words, there was a previous 
exchange of operational data among base stations in cell sites 110, 112, 
and 114. The geometric characteristics of cell site cluster 100, however, 
allows base station 200 to retrieve information about the equipment in 
cell sites 110 and 114 by retrieving the operational status data stored in 
the base station of cell site 112. If even one of the base stations in 
cell sites 110, 112 or 114 is malfunctioning, cell site 112 will not send 
an operational status message, or will send a failure message as the 
operational status. Lack of a response, or receipt of a failure message in 
the data gathering base station, initiates the supplemental diagnostic 
protocol described in FIGS. 4A and 4B. 
In a process occurring simultaneously with process steps 304-307, base 
station 200 sends its operational status to the cell site corresponding to 
coordinates x, y+3.sup.C1 (that is, coordinates (0,1) which identify cell 
site 108) in step 308. The process continues to step 309 in which base 
station 200 receives an operational message from cell site 108. In step 
310, base station 200 sends its operational status to the cell site 
corresponding to coordinates x+3.sup.C1, y (that is, coordinates (1,0) or 
cell site 104). In accordance with the preferred embodiment, the base 
station in cell site 104 has exchanged operational status data with the 
base stations in cell sites 102 and 106. Therefore, operational status 
data associated with cell sites 102, 104 and 106 is stored in the base 
station of cell site 104. In step 311, base station 200 receives, and 
stores, the operational status from cell sites 102, 104 and 106 in the 
response from cell site 104. The operational status messages may be 
relayed via base station antennas, such as radio antennas 211and 213, or 
via inter-base station links, such as link 235. Subsequent to steps 307 
and 311, the cluster index is increased at step 312, and the process 
returns to decision step 302. Alternatively, if an adjacent base station 
was non-responsive, or if a failure message was received, the data 
gathering station initiates the supplemental diagnostic protocol in step 
313. 
The process described above is used to dynamically detect base station 
functionality. FIGS. 4A and 4B describe the steps performed when data 
gathering base station 200 does not receive an operational status message, 
or receives a base station failure message from cell sites 104, 108, 112 
or 116. In other words, FIGS. 4A and 4B describe the supplemental 
diagnostic protocol. 
The supplemental diagnostic process begins in step 400 in which the data 
gathering base station determines the cluster index of this particular 
iteration of the supplemental diagnostic protocol. For purposes of 
example, assume that the cluster index for this iteration of the 
supplemental diagnostic is "0". Therefore, the geographic parameter is 
still defined by the eight (8) cell sites surrounding base station 200. 
The process continues to decision step 402 in which base station 200 
determines whether the cluster index is greater than its coverage area. If 
the outcome of decision step 402 is a "YES" determination, the process 
ends in step 403. If the outcome of decision step 402 is a "NO" 
determination, the process continues, simultaneously, to a series of 
decision steps in which operational status messages received from adjacent 
base stations during the primary diagnostic protocol are evaluated by the 
data gathering base station to determine which adjacent base stations are 
experiencing failure. The supplemental diagnostic process is required 
because base station 200 does not query each base station in the cell site 
cluster for operational status data. Particularly, in decision step 404, 
base station 200 determines whether the operation status reply received 
from the cell site associated with the coordinates x, y-3.sup.C1 (that is, 
coordinates (0,-1) corresponding to cell site 116) indicates that the cell 
site is active. If the outcome of decision step 404 is a "NO" 
determination, the process continues through connector "A" to FIG. 4B 
described below. If the outcome of decision step 404 is a "YES" 
determination, the process continues to decision step 406 in which base 
station 200 determines whether the operational status message received 
from the cell site associated with the coordinates x-3, y.sup.Cl (that is, 
coordinates (-1, 0) corresponding to cell site 112) indicates that cell 
site 112 is active. If the outcome of decision step 406 is a "NO" 
determination, the process continues to step 410 in which the data 
gathering base station 200 extends the operational status of all base 
stations (as collected during the primary diagnostic protocol) to base 
station 116 identified by coordinates x, y-3.sup.C1 In this manner, base 
stations in cell site cluster 100 are informed of adjacent base station 
failure. If the outcome of decision step 406 is a "YES" determination, the 
process continues to step 408 in which base station 200 determines whether 
the operational status reply received from the cell site associated with 
coordinates x+3.sup.C1, y-3.sup.C1 (that is, cell site 102) indicates that 
the base station is active. If the outcome of decision step 408 is a "NO" 
determination, the process continues to step 410 in which base station 200 
extends the operational status all base stations, as collected during the 
primary diagnostic protocol to the cell site associated with coordinates 
x, y-3.sup.C1 (cell site 116). If the outcome of decision step 408 is a 
"YES" determination, the process continues through connector A to FIG. 4B 
described below. 
In step 412, occurring simultaneously with the process described above, 
base station 200 determines whether the operational status message 
received from the cell site identified by coordinates x, y+3.sup.C1 (that 
is, cell site 108) indicates that the base station in cell site 108 is 
active. If the outcome of decision step 412 is a "NO" determination, the 
process continues through connector "B" to FIG. 4B. If the outcome of 
decision 412 is a "YES" determination, the process continues to step 414 
in which base station 200 determines whether the cell site associated with 
coordinates x+3.sup.C1, y (that is, cell site 104) is active. If the 
outcome of decision step 414 is a "NO" determination, the process 
continues to step 418 in which base station 200 sends operational status 
messages collected during the primary diagnostic protocol to the cell site 
associated with coordinates x, y+3.sup.C1, (cell site 108). If the outcome 
of decision step 414 is a "YES" determination, the process continues to 
step 416 in which base station 200 determines whether the operational 
status received from the cell site corresponding to coordinates 
x-3.sup.C1, y+3.sup.C1 (that is, cell site 110) indicates that the base 
station of cell site 110 is active. If the outcome of decision step 416 is 
a "NO" determination, the process continues to step 418 in which base 
station 200 sends the status messages collected during the primary 
diagnostic protocol to the cell site identified by coordinates x, 
y+3.sup.C1 (cell site 108). If the outcome of decision step 416 is a "YES" 
determination, the process continues through connector B to FIG. 4B. 
In FIG. 4B, decision steps 420 and 428 occur simultaneously. Particularly, 
in decision step 420, data gathering base station 200 once again 
determines whether the operational status message received from the cell 
site identified by coordinates x, y-3.sup.C1 (cell site 116) indicates 
that the cell site is active. If the outcome of decision step 420 is a 
"NO" determination, the process continues to step 436 described below. If 
the outcome of decision step 420 is a "YES" determination, the process 
continues to step 422 in which the base station 200 determines whether the 
base station serving the cell site x-3.sup.C1, y (that is, cell site 112) 
is active. If the outcome of decision step 422 is a "NO" determination, 
the process continues to step 426 described above. If the outcome of 
decision step 422 is a "YES" determination, the process continues to step 
424 in which the polling base station determines whether the base station 
in cell site x+3.sup.C1, y-3.sup.C1 (that is, cell site 102) is active. If 
the outcome of decision step 422 is a "NO" determination, the process 
continues to step 426 in which operational status is received from the 
cell site corresponding to coordinates x, y-3.sup.C1 (cell site 116). If 
the outcome of decision step 424 is a "YES" determination, the process 
continues to step 436. 
In FIG. 4B step 428, base station 200 once again determines whether the 
base station associated with coordinates x, y+3.sup.C1 (cell site 108) is 
active. If the outcome of decision step 428 is a "NO" determination, the 
process continues to step 436. If the outcome of decision step 428 is a 
"YES" determination, the process continues to step 430 in which the data 
gathering base station determines whether the base station associated with 
the coordinates x+3.sup.C1, y (cell site 104) is active. If the outcome of 
decision step 430 is a "NO" determination, the process continues to step 
434 in which base station 200 receives the operational status from, cell 
site 108 associated with coordinates x, y+3.sup.C1. If the outcome of 
decision step 430 is a "YES" determination, the process continues to step 
432 in which base station 200 determines whether the base station 
identified by coordinates x-3.sup.C1, y+3.sup.C1 (cell site 110) is 
operational. If the outcome of decision step 432 is a "NO" determination, 
the process continues to step 434 in which base station 200 receives a 
status message from the cell site identified by coordinates x, y+3.sup.C1 
(cell site 108). If the outcome of decision step 432 is a "YES" 
determination, the process continues to step 436 in which base station 200 
increases the cluster index to reach cell sites in a greater geographic 
area. In step 438, the data gathering base station 200 extends data 
identifying all non-active (failed) base stations to the mobile switching 
center via data interface 234. Subsequent to step 438, the process returns 
to FIG. 4A step 402 via connector "C" until all base stations are active, 
and technical personnel have reset all base stations to perform the 
primary diagnostic protocol. 
FIG. 5 describes, in greater detail, the steps performed by base station 
200 in response to identifying non-functional base stations during the 
supplemental diagnostic protocol. More particularly, in step 500, base 
station 200 identifies the cell sites identified as having non-active (or 
failed) base stations. In step 502, base station 200 extends a failure 
message to its serving mobile switching center via a data link. The 
failure message includes the coordinates of all failed cell sites, the 
time of the failure determination for each cell site, and date of the 
failure determination for each cell site. 
In step 504, base station 200 receives a failure acknowledgment message 
from the mobile switching center. The process continues to step 506 in 
which base station 200 receives information for administering 
telecommunications services to mobile subscribers located in selected 
non-functional cell site. More particularly, the serving mobile switching 
center extends set-up channel, and locate channel information associated 
with at least one failed cell site to cell site controller 232 of base 
station 200. Other base stations in cell site cluster 100 may receive call 
set-up and locate data associated with the same or other failed cell 
sites. In step 508, base station 200 uses the information received from 
the mobile switching center to set up calls for mobile subscribers located 
in the failed cell sites via inter-base station links. In the preferred 
embodiment, a plurality of functional cell sites may serve mobile 
subscribers affected by the malfunctioning of a single base station. 
Advantageously, cell sites are arranged in clusters which allow any given 
base station to gather operational status information of surrounding cell 
sites without querying each base station in those cell sites. A 
supplemental diagnostic protocol is initiated when identification of a 
particular, failed base station is required. Subsequent to verification of 
base station failure, functional base stations may be directed by the 
mobile switching center to perform administrative tasks for a failed base 
station until permanent repairs are made. 
While this invention is described with reference to a preferred embodiment, 
it is understood that those skilled in the art may devise numerous other 
arrangements without departing from the scope of the invention.