Synchronous selective signalling system

A selective call receiver (111) has a first mask (134A) stored within the selective call receiver (111) indicative of a first period of reception for receiving a transmitted communication signal (99) having a plurality of packets (100). Each of the transmitted packet (100) has message information (110). An identifier (106) identifies the packet (100). The control signal (108) is representative of a second mask (134B) indicative of a second period of reception. The second mask is compared with the first mask for determining the second period of reception of the selective call receiver (111). A correspondence between the first and second masks determines whether to change the first period of reception of the selective call receiver (111) for receiving at least one additional packet.

FIELD OF THE INVENTION 
This invention relates in general to signalling systems, and more 
specifically to a signalling system for use in a selective call receiver 
system. 
BACKGROUND OF THE INVENTION 
Prior art selective call receiver systems (paging systems) have endeavored 
to efficiently communicate information to selective call receivers 
(pagers) while providing for effective battery saving operation of the 
selective call receivers. The widely accepted Golay Sequential Code (GSC) 
provides an asynchronous method for communicating message information to 
selective call receivers and has been described in U.S. Pat. Nos. 
4,424,514 and 4,427,980 both issued to inventors Fennell, et al. The GSC 
protocol provides a preamble signal which initially synchronizes the 
selective call receivers to a paging signal. One of the several well known 
preamble signals may be used, each identifying a different group of 
selective call receivers which are used to decode following message 
information. Additionally, U.S. Pat. No. 4,860,003 issued to DeLuca, et 
al. describes power conservation during the reception of a signal, such as 
the GSC signal, in response to a signal indicating the occurrence of 
address information. 
An asynchronous/synchronous signalling system has been defined by the Post 
Office Standardization Code Advisory Group (POCSAG). The operation 
according to the POCSAG signalling system requires selective call 
receivers to synchronously decode the received signal subsequent to being 
synchronized to the POCSAG signal. The POCSAG signal and a method for 
decoding the signal is described in U.S. Pat. No. 4,663,623 issued to Lax, 
et al. Like GSC, a POCSAG transmission may begin asynchronously with 
respect to a prior POCSAG transmission, and once the transmission begins, 
the signal is synchronously decoded until the transmission ends. The 
POCSAG transmission has at least one batch, each batch beginning with a 
synchronization signal followed by eight frames, each frame occurring at a 
predetermined time after the synchronization signal. A selective call 
receiver synchronized to the signal needs to search for its address in 
only a predetermined one of the eight frames. In the remaining seven 
frames, the selective call receiver conserves power by one of the well 
known techniques of battery saving. However, subsequent transmissions, for 
example, the POCSAG signals, need not be either bit or frame synchronized 
to the previous POCSAG transmission. By permitting a subsequent 
transmission signal to be synchronized only with each transmission, and 
not by bit or frame synchronization, the subsequent transmission is 
asynchronously synchronized to the POCSAG signal. 
Most paging protocol signals are designed to co-exist with other paging 
protocol signals. For example, a GSC transmission may be followed by a 
POCSAG transmission which may be followed by a 5-tone sequential 
transmission, etc. It is desirable to provide battery saving features for 
the selective call receiver during the absence of a signal being directed 
to the selective call receiver. This has typically been accomplished with 
a preamble signal preceding the message transmission. Both the GSC and 
POCSAG signals begin with a long preamble signal providing for selective 
call receiver synchronization before the message transmission and 
providing for battery saving in the absence thereof. The preamble signal 
although providing for battery saving and synchronization, decreases the 
overall system message throughput. During the time taken for a preamble 
transmission, no message information is being communicated to the 
selective call receivers, thereby decreasing throughput of the system. 
Synchronous selective call receiver protocols eliminate any preamble 
signal, thereby enabling a more efficient battery savings. A synchronous 
paging signal is shown in U.S. Pat. No. 4,642,632 issued to Ohyagi, et al. 
This synchronous signal has selective call receivers divided into one of a 
plurality of group fields, each group field occurring at a predetermined 
period and having a predetermined maximum message information capacity. 
Since the synchronous signal is always being transmitted, no preamble 
signals are required, and a selective call receiver needs only decode 
paging information while its preassigned group is being transmitted. 
However, varying traffic demands (the amount of message information for a 
group of selective call receivers) may cause the amount of message 
information for one group of selective call receivers to exceed the 
maximum capacity of the group field while another group field has 
available capacity. This causes transmission of idle signals during one 
group field, while in another group field, numerous messages are being 
queued because its capacity is exceeded. The throughput of the overall 
system is decreased because selective overload patterns are generated from 
the varying traffic levels within different group fields. 
Thus, what is needed is a selective call receiver system which selectively 
sacrifices battery saving improvements afforded by a synchronous paging 
signal to prevent or to reduce overload occurring within the selective 
call receiver system. 
SUMMARY OF THE INVENTION 
A selective call receiver has a first mask stored within the selective call 
receiver indicative of a first period of reception for receiving a 
transmitted communication signal having a plurality of packets. Each of 
the transmitted packets has a message information, and a control signal. 
An identifier means identifies the packet. The control signal is 
representative of a second mask indicative of a second period of 
reception. The second mask is compared with the first mask for determining 
the second period of reception of the selective call receiver. A 
correspondence between the first and second masks determines whether to 
change the first period of reception of the selective call receiver for 
receiving the at least one additional packet.

DESCRIPTION OF A PREFERRED EMBODIMENT 
FIG. 1 shows a synchronous signal in accordance with the preferred 
embodiment of the present invention. The signal comprises of a number of 
message packets or frames 100. Each frame is preferably four seconds in 
duration and has a preferred base data rate of 1200 bits per second. 
Although, it will be appreciated that other data rates can be utilized as 
will be described below. Additionally, each frame comprises of a bit sync 
signal 102, preferably 32 bits of alternating 1,0 patterns, followed by a 
frame sync signal 104 preferably one of several predetermined thirty-two 
bit words, and a frame ID signal 106, preferably one thirty-two bit word 
having twenty-one variable information bits containing information such as 
a frame identification number. The bit sync signal 102 provides for 
selective call receiver bit synchronization while the frame sync signal 
104 provides for frame synchronization and may include a signal indicative 
of the data rate of the message information following the frame ID signal 
106. The frame ID signal 106 indicates the number of the frame. Each frame 
is numbered in a preferred sequence from 0 to 63 in a signalling system 
having sixty four frames. Alternately, any number of frames may be used in 
the system, however 2.sup.N frames (where N is an integer) is preferred. 
Following frame ID 106 is a word 108 having a cycle value and a plurality 
of message words 110 follow thereafter. Words 108-110 are, preferably, 
31,21 BCH code words having twenty-one information bits and ten parity 
bits generated according to the well known BCH algorithm. An additional 
even parity bit extends the word to a 32,21 code word. Messages within 
words 110 comprise at least one message having an address signal and 
optional information signals associated with the address signal. 
Preferably, all of the address signals within the frame are located in a 
first portion and the information signals are located in a subsequent 
portion of the frame. It is well known to those skilled in the art how the 
locate addresses in a first portion and message information in a second 
portion of a frame. Additionally, U.S. patent application Ser. No. 
07/396,189 to DeLuca et al., assigned to the assignee of the present 
invention shows an improved method of locating addresses as in a first 
portion and message information in a subsequent portion of a signal. 
DeLuca is hereby incorporated by reference herein. Word 108 includes the 
cycle value which forms the indicating frames in which a selective call 
receiver is to decode message information as will be discussed below. In a 
paging system having 2.sup.N frames, the cycle value occupies an N bit 
word 108. The remaining bits may contain a boundary signal indicating a 
boundary between the address and information signals in words 110. Words 
108-110 are shown in a vertical orientation to indicate that these words 
may be interleaved in order to improve the immunity of the transmission to 
burst errors. Preferably words 108-110 comprise 18 blocks of words wherein 
each block contains 8 interleaved words. In an alternate embodiment the 
interleaving may be modified or eliminated. 
FIG. 2 shows a battery operated selective call receiver operating in 
accordance with the preferred embodiment of the present invention. The 
radio frequency modulated signal of FIG. 1 is received by antenna 120, 
demodulated by receiver 122 and processed by decoder 124. Decoder 124 may 
be comprised within a microcomputer executing a program causing the 
selective call receiver to process the demodulated signal. A preferred 
microcomputer is the MC68HC05C8 microcomputer manufactured by Motorola, 
and a selective call receiver having a microcomputer decoder is described 
in the aforementioned U.S. Pat. No. 4,860,003 to DeLuca et al. which is 
hereby incorporated by reference herein. The decoder comprises a bit 
synchronizer 126 and a frame synchronizer 128 for synchronizing to signals 
102 and 104, and respectively providing bit and word boundary signals for 
use by the remaining elements of the decoder 124. The decoder 124 
preferably includes an identifier means for identifying the received 
frames or packets. Frame ID decoder 130 and cycle decoder 132 decode 
signals 106 and 108, respectively. The decoded signal 106 and 108 are 
masked by masking function 134B and compared by comparator 136 with 
information contained within a code plug 140. Code plug 140 has a 
predetermined frame ID 142, a predetermined cycle value 144, and a 
predetermined address assigned to the selective call receiver, as well as 
other signals which configure the selective call receiver for desired 
operating characteristics. As will be shown, the predetermined cycle value 
144 allows one selective call receiver to be assigned to a plurality of 
frames. The predetermined frame ID 142 is masked with the predetermined 
cycle value 144 to generate a first mask value (at mask function 134A) 
indicative of a first period of reception of the selective call receiver 
and is used by comparator 136 to enable battery saver 150 to produce a 
first period of reception. Battery saver 150 deactivates receiver 122 for 
certain frames thereby conserving battery power. When the selective call 
receiver receives the information in words 108-110 message decoder 152 
searches for an address signal matching a predetermined address signal 
assigned to the selective call receiver and further decodes information 
signals associated with the address. The message information may then be 
displayed on display 154. 
In an alternate embodiment, the cycle value 108 may contain a signal 
indicative of the cycle to be used. The selective call receiver may 
include a plurality of predetermined cycle values, one of which is 
selected in response to the signal indicative of the cycle to be used. The 
table below shows a relationship between the received signal and the cycle 
value. 
______________________________________ 
SIGNAL CYCLE 
______________________________________ 
000 unused 
001 00 0000 
010 10 0000 
011 11 0000 
100 11 1000 
101 11 1100 
110 11 1110 
111 11 1111 
______________________________________ 
In the table above, the system provides, for example, 6 bits for defining a 
cycle value, thereby providing for 2.sup.6 or, 64 frame IDs. Transmitting 
a signal indicative of the cycle to be used provides for communication of 
the cycle value with less information bits, thereby increasing the amount 
of information bits available for other information which may be included 
in word 108. 
FIG. 3 shows a flow diagram illustrating the operation of the selective 
call receiver decoding a synchronous signal in accordance with the present 
invention. It is assumed the flow diagram begins with the selective call 
receiver in an unsynchronized state. In step 170, the receiver is 
activated. Step 172 attempts bit synchronization (bit sync) for a 
predetermined time, preferably a time greater than the time of one frame. 
If synchronization is unsuccessful, step 174 conserves power for a time 
less than the time of one frame. In other embodiments, the times of steps 
172 and 174 may be varied. Thereafter step 170 is again executed. If in 
step 172, bit sync is found, step 176 searches for frame sync 104. If 
frame sync 104 is not found within a predetermined time, preferably a time 
greater than the time of one frame, step 174 is executed. However, if 
frame synchronization is found, step 178 decodes the frame ID signal 106 
and cycle signal 108 and masks the signals together to generate a second 
mask value as will be described below. Then step 180 determines if the 
frame ID and mask were decoded OK. If not, a frame ID not recognized by 
this embodiment of the invention may be present, or the signal may have 
been corrupted by noise. In response thereof, step 174 is executed. If 
decoded OK, step 182 stores the decoded cycle value in a temporary 
register and reads from the code plug. The predetermined ID and cycle 
value are masked together (at mask function 134A) to obtain the first mask 
indicative of the first period of reception. For example, if the code plug 
contains a predetermined frame ID of 111 and a predetermined cycle value 
of 000, the resulting first mask value is 111. Similarly, if the decoded 
frame ID and cycle value were 001 and 100 respectively, the resulting 
second mask value (at mask function 134B) of X01 (the X indicating a 
"don't care"). Step 184 then compares the first and second masked values, 
111 and X01 and finds them to be not equal. If however the decoded frame 
ID and cycle values were 011 and 100 respectively the resulting second 
mask would be X11, and step 178 would then compare the first and second 
masked values of 111 and X11 and find them to be equal. If the compared 
masks are equal, step 186 synchronously decodes the signal as indicated by 
FIG. 4. In response to step 184 determining the inequality, step 188 
determines the next frame where the first and second masked values will be 
equal. In the preceding example, the decoded frame ID and cycle were 001 
and 100 respectively and the resulting second masked value was X01, it can 
be determined that after two frames the resulting masked value would be 
X11 thereby providing an equality for step 184. This determination may be 
made because the frames are consecutively numbered. Thus step 184 would 
conserve power for two frames. Similar determinations may be made for 
systems having more frame numbers occurring in any predetermined sequence. 
However, when the second masked value indicates the second period of 
response which is more frequent than the first period of response 
indicated by the first masked value, the period of power conservation will 
be reduced (less battery saving). In this way, a ubiquitous signal having 
a second mask indicative of the second period of response may be sent to 
all selective call receivers which have a first mask indicative of a first 
period of reception. Upon receipt, the selective call receivers determine 
whether to change their first period of reception to the second period of 
reception. Thus a selective call receiver terminal can instruct the 
selective call receivers to temporarily change their period of reception 
to ease traffic demand without knowing the period of receptions of 
different selective call receivers. Accordingly, the selective call 
receivers compare the generated second masked value with the generated 
first masked value to determine if the second period of reception is more 
frequent than the first period of reception, and if so, the period of 
reception will be changed. 
FIG. 4 is a flow diagram illustrating synchronously decoding of the 
selective call receiver in accordance with the preferred embodiment of the 
present invention. The flow diagram is entered at step 200 from step 186 
(as shown in FIG. 3). Step 204 decodes message signals from words 110 and 
any boundary signal from word 108. Those skilled in the art will 
appreciated that power conservation may be performed in this step by only 
activating the receiver in coincidence with the occurrence of address 
signals as indicated by a boundary signal. In the event of an address 
matching a predetermined address assigned to the selective call receiver, 
an alert is generated, and the message information signals associated with 
the address decoded. The message signal is then displayed to the user of 
the selective call receiver. In step 206, which is similar to the 
operation of step 188, the next frame having equal first and second masked 
values is determined. Power is then conserved until then. Then in step 208 
the receiver is again activated. In step 210, bit and frame 
synchronization, and the frame ID and cycle values are searched for in 
substantial coincidence with their expected occurrence. 
Step 212 checks if synchronization is maintained. Specifically, step 212 
checks if frame synchronization has been missed for a predetermined number 
"N" consecutive times. In one embodiment, the number "N" is selected so 
that the selective call receiver synchronously operates in a noisy 
environment for several hours. If synchronization is not maintained, the 
flow exits through step 213 to step 174 of FIG. 3 to attempt to regain 
synchronization. By making the value for "N" large, the selective call 
receiver can efficiently conserve power in a noise environment. 
Additionally, the long synchronization lock time provided for by a large 
"N" provides for the interruption of the signal by other paging protocols 
communicating message information while maintaining bit and frame 
synchronization for the selective call receiver. 
If synchronization is maintained, as is the expected typical case (step 
212), step 214 checks if the frame ID and cycle values were correctly 
decoded. If not, the flow through step 216 returns to step 204 to decode 
messages, thereby maintaining the cycle value from a previous decoding of 
the cycle. Furthermore, in the event bit or frame synchronization were 
missed in step 210, bit and frame synchronization can be maintained from a 
previous successful synchronization. This path may be taken in the event a 
frame ID is not recognized by the selective call receiver or if the 
selective call receiver is in a noisy environment when an alternate paging 
protocol is being transmitted. In an alternate embodiment, if either the 
bit or frame synchronization, or frame ID or cycle values were missed, 
step 216 could proceed directly to step 206 thereby conserving power 
through the expected message words of the frame. 
If the frame ID and cycle values are decoded OK in step 216, step 218 
stores the new decoded cycle value in temporary memory and reads the frame 
ID and cycle from the code plug and masks them together as described 
above. Step 220 then checks if the result is substantially the same. If 
so, the flow returns to step 204. If no, the flow proceeds to step 222 to 
determine the number of frames until the masked values are again equal. 
The execution of step 222 is typically in response to a change in the 
received cycle value. 
FIG. 5 shows an example of a synchronous paging signal and the battery 
saver operation of the selective call receiver of FIG. 2. For the sake of 
simplicity, the example shows a signal 230 having only 2.sup.3 (eight) 
repeating frames numbered 0-7. The frame numbers 0-7 are indicated with 
the binary equivalent values 000-111. Lines 240-290 show battery saving 
and signal processing operation of a selective call receiver having a 
predetermined frame ID of 111 and a predetermined cycle value of 000 
(thereby indicating the selective call receiver at the minimum decodes 
only in frame 111). A logic high on line 240-290 indicates the selective 
call receiver is receiving and processing information and a logic low 
indicates the selective call receiver is conserving power. Line 240 shows 
the selective call receiver operation when cycle signal 108 comprises a 
000. This cycle signal indicates that only the frame assigned to the pager 
is to be decoded. This is evidenced by high logic states 242 and 244 which 
are in coincidence with frame 111. 
Line 250 shows the selective call receiver operation with a cycle value of 
100. In this case the resulting masked values of the received frame ID and 
cycle value is X11 during intervals 252, 254, and 256. A mask value of X11 
equals the predetermined frame ID of 111 during frames 011 and 111 of line 
230. Similarly line 260 shows the operation of the selective call receiver 
receiving a cycle value of 110 which causes the receiver to receive and 
process in frames 001, 011, 101, and 111. Similarly line 270 shows the 
operation of a pager receiving a cycle value of 001. 
Line 280 shows the pager receiving a cycle value of 111 for four frames and 
a cycle value of 000 thereafter. When the cycle value is 111, the 
selective call receiver decodes in every frame, and when the cycle value 
is changed to 000, the selective call receiver decodes only in a frame 
having a frame ID equal to the predetermined ID assigned to the pager. 
Also, upon receiving a cycle value wherein the masked values are not 
equal, receiving and processing of the frame is terminated. However, 
because the frames are numbered in a predetermined sequence, the pager is 
capable of reactivating precisely in time to decode the correct frame. In 
this way, the selective call receiver by comparing a second received 
masked value with the corresponding first masked value can increase the 
period of reception for receiving relocated frames to reduce traffic 
build-up or message queuing within the selective call receiver system. 
Line 290 shows the selective call receiver synchronizing to the system. 
During interval 292 no signal is received, possibly because the selective 
call receiver was switched off during this interval. During interval 294 
the signal is received and bit and frame synchronization are accomplished. 
Then a frame ID of 001 and a cycle value of 100 is detected. The selective 
call receiver then determines that frame 011 results in matching masked 
value, and conserves power for the duration of frame 001 and receives and 
processes information during frame 011 as shown by interval 296. The 
selective call receiver is synchronized to the system and conserves power 
after frame 011 until frame 111 wherein the masked values are again equal. 
Thus FIG. 5 shows that a selective call receiver may be reassigned to a 
number of frames using the received cycle value and its internal masked 
value. The selective call receiver may additionally quickly determine the 
proper frame for decoding in the event the cycle value is changed, or when 
synchronization is initially acquired. In systems having more than eight 
frames, such as sixty four frame system, the advantages to battery saving 
and traffic management are even more evident. However, when the selective 
call receivers are directed to a second period of reception through the 
received second masked value, the battery saving features of the selective 
call receiver are inhibited in the interest of reducing traffic build-up 
or message queuing. That is, selective call receivers are directed to 
access frames at a more frequent rates than is indicated by the internal 
generated first masked value. Therefore, using the transmitted second 
masked value, a selective call receiver system can temporarily change the 
period of reception of the selective call receivers without knowing the 
period of receptions of the selective call receivers to reduce traffic 
build-up, etc. 
FIG. 6 shows a table of the possible frames in which a selective call 
receiver having a predetermined ID of 111 operating in the eight frame 
system protocol of FIG. 5 to decode signals. The selective call receiver 
has a predetermined cycle value of 000. The top row corresponds to the 
frame numbers of line 230 of FIG. 5. The left column corresponds to the 
decoded cycle signal 108 of FIG. 1, that is, the received second masked 
value indicates a second period of reception. A "YES" entry in the table 
corresponding to the top row and left column indicates the frame in which 
the selective call receiver of the example will receive and process 
information. It can be seen by the column associated with frame 111 that 
the selective call receiver of the example will always be active in its 
own frame. It can be further seen by viewing the bottom row that a cycle 
value of 111 will cause the selective call receiver to be active in every 
frame. In this way, the selective call receiver is instructed to 
temporarily increases the period of reception for reducing traffic 
build-up on the system. 
FIG. 7 shows a table of possible frames of the selective call receiver of 
FIG. 6 wherein the selective call receiver alternately has a predetermined 
cycle value of 100. The resulting masked value is X11. Thus the selective 
call receiver behaves as if the selective call receiver assigned to both 
frames 011 and 111. 
FIG. 8 shows a block diagram of a paging terminal generating a paging 
signal in accordance with FIG. 1. The functions of the paging terminal is 
implemented within software, for example within a MODAX 500 Radio Paging 
Terminal which is manufactured by Motorola Inc. As shown, message receiver 
320 receives messages for selective call receivers typically from the 
public switched telephone network. The appropriate protocol and address is 
determined for the message. If the message is not to be sent via the 
signal format of the present invention, it is sent to one of the other 
protocol generators 322 which may include GSC and POCSAG protocol 
generators. Messages to be transmitted on the protocol of the present 
invention are stored in a frame queue buffer 324 which has queues for the 
corresponding frames of the signal. The predetermined frame ID of the 
pager corresponding to the message is determined and the message is stored 
in the corresponding frame queue. Capacity analyzer and frame ID/cycle 
generator 326 determine the sequence of frame IDs to be transmitted, 
analyze the capacity of each frame and determine the cycle value to be 
used. The capacity analyzer is also responsive to other protocols being 
transmitted. For example, if the expected occurrence of a frame is to be 
replaced by the transmission of one of the other protocols (thereby 
diminishing the capacity of the frame), the capacity analyzer can account 
for this with the determined cycle value. Bit and frame sync generator 328 
synchronously generates bit and frame synchronization signals. Message 
formatter 330 determines in response to the current combination of 
selective call receivers decoding messages in a frame, the frame queues 
from which messages may be included within the current frame. The messages 
are then formatted for transmission. Transmitter 332 accepts signals from 
blocks 328, 330 and 322 and modulates and transmits radio frequency paging 
signals to selective call receivers via antenna 334 in a manner well known 
to those of ordinary skilled in the art. 
FIG. 9 is a flow diagram illustrating the operation of the capacity 
analyzer and cycle generator of FIG. 8. Step 350 examines the frame queues 
of buffer 324. With each frame being approximately 4 seconds long and 
having a base data rate of 1200 bits per second, each frame capacity is 
approximately 4,800 bits of synchronization and information code words. If 
the traffic capacity of any of the buffers is not exceeded, step 352 sets 
the cycle value to 000, thereby causing the selective call receivers to 
operate only in frames corresponding to the information (first masked 
values) within their respective code plugs. If however, the frame capacity 
is exceeded, step 354 determines a frame having a lesser capacity 
utilization (lesser traffic) which is available for combining by the cycle 
value, and the frames are combined. The step 356 determines if the frame 
capacity of the combined frames are still exceeded. If not, step 360 sets 
the cycle value according to the determined value. If however the capacity 
is still exceeded, step 362 combines more frames as provided for by the 
cycle value. Then step 364 determines if all of the frames of the system 
have been combined. If not, the program returns to step 356 and a check 
for exceeded capacity is again made. If in step 364 all frames are 
combined, a cycle of 111 is selected. Process continues in step 350 from 
either step 360 or step 366. This process allows for continuous adjustment 
of the cycle value to accommodate variation in message traffic which cause 
the capacity of frames to be exceeded. It should be appreciated that the 
rate of change of the cycle value may be further governed in order to 
regulate rapid changes in the operation of the paging system. 
Additionally, the changes in the operation can be weighed against the 
extra power consumption and the changes cause in the individual selective 
call receivers with the paging system. Selective call receivers directed 
to decode in extra frame in response to the cycle value also expend 
additional power while decoding in those frames, thus frustrating their 
battery saving features in the interest of reducing the traffic on the 
paging system. 
FIG. 10 shows a table indicating the frames in which selective call 
receivers will decode in response to the cycle signal. The table 
corresponds to the eight frame ID example described above. The top row 
indicates the frame ID number while the left column indicates the cycle 
value. The entries in the table correspond to the decimal equivalent of 
selective call receivers having predetermined frame IDs which decode 
information in that frame. As can be seen, a cycle value of 000 causes 
only selective call receivers having the predetermined frame IDs matching 
that frame ID to decode in that frame, while a cycle value of 111 causes 
all selective call receivers (predetermined frame IDs of 0-7) to decode in 
every frame. 
An example of the use of the table is given below. For example, if the 
traffic capacity of frame 7 (111) is exceeded, and upon examining the 
other frame queues, it is determined that substantial capacity of frame 3 
is not utilized. Frames 7 and 3 may be combined with a cycle value of 100. 
This cycle value may be utilized until the capacity of frame 7 is no 
longer exceeded (in response to which the cycle value would be returned to 
000). If however the capacity of combined frames 3 and 7 are still 
substantially exceeded and it is determined that frames 1 and 5 still have 
remaining capacity, a cycle value of 110 could be used thereby combining 
frames 1, 3, 5, and 7. In this way, the paging terminal transmits 
information to the selective call receivers which is combined with the 
internal first masked value of the selective call receivers to determine 
the change in the period of reception for relieving traffic variations 
with the paging system. 
Thus, a selective call receiver responds to the synchronized signal 
generated from the paging terminal to receive at least one additional 
frame at a second period of reception as described above. Some selective 
call receivers may require additional battery saver performance and may 
not respond to the cycle value, thereby decoding only those frames 
indicated by the code plug. Alternately, the selective call receiver could 
respond only to a portion of the cycle value. In such an embodiment the 
selective call receiver may only respond to the least significant one or 
two bits of the cycle value thereby limiting the number of possible frames 
in which the pager must be active in order to decode message information. 
The paging terminal must correspondingly be programmed with a table of 
selective call receivers having limited response to the cycle value in 
order to direct message information to those selective call receivers in 
the proper frames. 
FIG. 11 shows an alternate signal in accordance with a second embodiment of 
the present invention. The signal has substantially the same attributes as 
described in the signal of FIG. 1 with the exception of words 400 and 402. 
Word 400 includes the frame IDs which need not be numbered in sequence and 
is preferably one of any number of frame IDs. This enables addition of 
frame IDs to the paging system as the requirements change. However, each 
frame ID has a predetermined period which need not be the same period as 
other frame IDs on the system. Word 402 comprises interval and/or 
repetition values, and includes, additionally, a boundary signal 
indicative of the boundary between address and data portions of words 110. 
FIG. 12 illustrates the block diagram of the paging receiver for decoding 
the signal of FIG. 11. The majority of the functions of the selective call 
receiver are identical with the selective call receiver of FIG. 2. Antenna 
120, receiver 122, and display 154 are substantially identical in function 
to those of FIG. 2. Code plug 140 includes the predetermined frame ID 142 
and further includes a predetermined period and repetition values 410. The 
period corresponds to the predetermined period of the predetermined frame 
ID 142. Decoder 124 has bit and frame synchronizers 126 and 128 
respectively, and frame ID decoder 130 and message decoder 152 have 
substantially the same operation. Interval and repetition decoder 420 
decodes signal 400. Comparator 422 sends a signal to battery saver 424 
when the decoded frame ID equals the predetermined frame ID 142. In 
response to the comparator 422, the interval and repetition signal 402, 
the predetermined period, and repetition 410, the battery saver 424 causes 
the receiver 122 to either activate or conserve power. 
FIG. 13 is a flow diagram illustrating the operation of the receiver of 
FIG. 12. Steps 170-176 have been described with respect to FIG. 3. 
Accordingly, upon finding frame synchronization in step 176, step 440 
checks if the received frame ID 400 matches the predetermined ID 142. If 
equal, synchronous decoding occurs in step 442 which is described in 
detail in FIG. 14. If the inequality is determined in step 440, step 444 
decodes messages within the frame. The functions of this step are similar 
to those of step 204 of FIG. 4. If an address matching a predetermined 
address assigned to the selective call receiver is found, an alert is 
generated, and information associated with the address may be decoded and 
stored for displaying. Power conservation is performed in this step after 
the address portion of the frame is received. Step 446 again searches for 
bit and frame synchronization. Step 448 checks if frame synchronization 
has been missed for a predetermined number of times. If yes, step 172 is 
again executed and synchronization is again acquired. If no, step 440 is 
again executed. 
The flowchart of FIG. 13 provides for decoding of information within every 
frame until a frame having a frame ID corresponding to the predetermined 
frame ID is found. If the synchronization of step 446 is unsuccessful, 
subsequent executions of step 444 may use the synchronization from prior 
successful attempts. Alternately, step 444 conserves power during the 
remainder of a frame if the synchronization of step 446 was unsuccessful. 
FIG. 14 is a flow diagram illustrating the synchronous operation of the 
receiver of FIG. 12. The flowchart is entered at step 450 via step 442 of 
FIG. 13 when the frame ID 400 matches the predetermined ID 142. Step 452 
then reads default interval and repetition values 410 from the code plug 
and stores the values temporarily in memory. The received interval and 
repetition signal 402 is also decoded. If decoded OK, step 454 causes step 
456 to substitute the decoded values with the corresponding values from 
the code plug by overwriting the temporary memory. If not decoded OK, step 
456 is bypassed, and the code plug values remain in temporary memory. The 
step 458 sets a temporary variable TREP equal to the repetition value 
stored temporarily in memory. Then, similar to the processes described in 
step 444, step 460 decodes the messages in the frame. After decoding the 
frame, step 462 checks if TREP value is zero. If no, step 464 searches for 
bit and frame sync in the next frame, decrements TREP and returns to step 
460. Steps 460-464 provide for a number of frames to be decoded in 
repetition according to a repetition value either received in the signal 
or stored in the selective call receiver code plug. A preferred 
application is to have the transmitted repetition value less than or equal 
to the repetition value of the code plug. 
After the repetition cycle is completed (zero), step 466 determines if the 
number of frames subsequent to decoding of the frame ID is equal to a 
non-zero integer value M multiplied by the ratio of the predetermined 
period P, and the interval I which is stored in the temporary memory. If 
no, power is conserved for one frame in step 468 and step 466 is again 
executed. Steps 466 and 468 provide for variations in the interval in 
which frames are decoded. If for example, the received interval had a 
value of one, executions of step 466 would result in an inequality until 
the number of frames after the frame ID equal the period of the frame ID 
(e.g., M=1). In another example, if the predetermined period of the 
frame=8 and the received interval=1, step 466 would result in an equality 
(M=1) after eight frames have elapsed after the detected frame, which 
would be in coincidence with the next occurrence of the frame. If however, 
the received interval was 2, step 466 would result in an equality (M=1 and 
2) both after four and eight frames have elapsed after the prior detected 
frame, the latter would be in coincidence with the the next occurrence of 
the frame, while in the former, additional message information may be 
included for selective call receivers assigned to the frame. 
When step 466 results in an equality, step 470 activates the receiver and 
searches for bit and frame synchronization. Then step 472 determines if 
the number of frames after the detected the frame ID corresponds to an 
integer K multiplied by the predetermined period of the frame ID. If 
false, step 472 proceeds to step 458 to decode the number of frames 
specified by the repetition value stored in temporary memory. If yes, step 
474 checks if the frame ID is found. If found, step 452 is again executed 
through connector "1", otherwise step 476 checks if the frame ID has been 
consecutive missed for a predetermined number N. If no, synchronization is 
maintained, and step 452 is again executed. If yes, the flow returns 478 
to reacquire synchronization at step 174 of FIG. 13. In a typical 
operation, step 474 is executed in correspondence with the predetermined 
period of the predetermined ID assigned to the selective call receiver. 
The predetermined value N of step 476 may be selected to maintain 
synchronization for long periods of time in the absence of signal. These 
periods can extend to hours or days depending on parameters of the system, 
thereby providing for efficient battery saving in the absence of a signal 
receivable by the selective call receiver. 
FIG. 15 shows an example of a synchronous paging signal and the battery 
saver operation of the pager of FIG. 12. In this example, the selective 
call receiver has a predetermined frame ID of 89. Line 500 shows that the 
predetermined period of frame 89 is 8 frames, that is, a frame having an 
ID of 89 occurs every eighth frame. The frame IDs of the intervening 
frames are shown as "***" and are not relevant because the selective call 
receiver only recognizes the frame ID of 89. Lines 510-560 show the power 
conservation and receiving and processing strobe of the selective call 
receiver. A logic high indicates frames where the selective call receiver 
is receiving and processing information and a logic low indicates frames 
where the selective call receiver is conserving power. 
Line 510 shows the selective call receiver receives and processes only 
during the occurrence of frames having an ID of 89 (every eighth frame), 
that is, when the interval signal is a 1 and the repetition signal is a 0. 
Line 520 shows that the selective call receiver receives and processes 
every fourth frame when the interval signal is a 2 and the repetition 
signal is a 0. Note that any frame ID, interval, or repetition signal in 
the fourth frame after frame 89 is ignored by the selective call receiver 
since it does not occur in a frame having an ID of 89. Line 530 shows that 
the selective call receiver receives and processes every other frame when 
the interval signal is a 4 and the repetition signal is a 0. Line 540 
shows that the selective call receiver receives and decodes in 2 
consecutive frames in response to the repetition signal being a 1. Line 
550 shows that the selective call receiver receives and decodes in 3 
consecutive frames in response to the repetition signal being a 3 . 
Finally, line 560 shows that the selective call receiver receives and 
decodes in two consecutive frames every fourth frame in response to the 
interval signal being a 2 and the repetition signal being a 1. 
FIG. 15 shows the flexibility of programming frames for a selective call 
receiver using the interval and repetition values. A selective call 
receiver assigned to a particular frame ID may be programmed to decode in 
various frames. Furthermore, a first frame ID may have a period different 
from a second frame ID. In this way, the paging terminal may redirect 
selective call receivers to different frames for reducing the traffic with 
the paging system. Furthermore, the internal mask of the selective call 
receivers enables the paging terminal to reassign selective call receivers 
without knowing their specific period of receptions, because the internal 
mask determines if the particular selective call receiver may be 
reassigned. 
FIG. 16 shows a block diagram of a paging terminal generating a paging 
signal in accordance with FIG. 11. The functions of the paging terminal 
are substantially identical to the functions described with respect to 
FIG. 8 having identification numbers corresponding thereto. The difference 
is the traffic analyzer and frame ID, interval and repetition generator 
function 570. This function generates frame IDs at the predetermined 
period, determines the interval and cycle values to be included within a 
frame in response to the traffic conditions of the frame. As in the 
capacity analyzer 326 of FIG. 8, block 570 is also responsive to other 
protocols being transmitted. 
FIG. 17 shows the operation of the traffic analyzer and interval and 
repetition generator. When a frame ID is being transmitted, step 580 sets 
the repetition value. First the instantaneous change in traffic for the 
frame is determined. If the increase in traffic from a prior period of the 
frame is in the range of 0 to five thousand bits, a repetition value of 
zero is selected. This indicates a steady average traffic for the frame. 
If however, a change in the order of five thousand to ten thousand bits 
per period was detected, the repetition value of one is selected. This 
value would represent a momentary substantial increase in frame traffic 
such as the increase due to one very long information message. This kind 
of increase is compensated for by causing selective call receivers to 
immediately decode in the following frames. The repetition value increases 
as the magnitude of the instantaneous traffic increases. Thereafter, step 
582 determines the average frame traffic. This determination may be made 
by averaging the number of bits per period received for the frame over a 
predetermined number of frame periods. Step 582 shows that the interval is 
set to zero if the average traffic is zero to five thousand bits, and the 
interval value increases with increasing traffic. 
Thus FIG. 17 shows increasing the repetitions of selective call receivers 
assigned to a frame ID in response to instantaneous changes in frame 
traffic and increasing the interval in response to changes in the average 
traffic of a frame ID. Different criterion can be used to adjust 
repetition and interval values in other embodiments. In this way, the 
paging terminal may redirect selective call receivers to different frames 
for reducing the traffic with the paging system. The internal mask of the 
selective call receivers enables the paging terminal to reassign selective 
call receivers without knowing their specific period of receptions, 
because the internal mask determines if the particular selective call 
receiver may be reassigned. 
FIG. 18 shows a synchronous signal in accordance with another embodiment of 
the present invention. Word 600 includes frame IDs which need not be 
sequentially numbered, and may have any number of frames IDs. Furthermore, 
additional frame IDs may be added as the system requirements change, and 
each frame ID may occur at any interval. Thus a frame ID may "skip" 
through the synchronous signal as required. Word 602 comprises a "skip" 
value which indicates the minimum number of frames until the occurrence of 
the frame ID, and may also include an additionally boundary signal 
indicative of the boundary between the address and data portions of words 
110. 
Accordingly, FIG. 19 shows a block diagram of the paging receiver which 
decodes the signal of FIG. 18. The majority of the functions of the 
selective call receivers are identical with the selective call receiver of 
FIG. 2. Antenna 120, receiver 122, and display 154 are substantially 
identical in function to those of FIG. 2. The code plug 140, however, 
includes the predetermined frame ID 142 and a predetermined minimum "skip" 
value 610. Decoder 124 has bit and frame synchronizers 126 and 128, and a 
frame ID decoder 130 and message decoder 152 which operate substantially 
the same as those of FIG. 2. Skip decoder 620 decodes signal 602. 
Comparator 622 sends a signal to battery saver 624 when the decoded frame 
ID equals the predetermined frame ID 142. In response to the comparator 
622 and the skip signal 602, battery saver 624 causes receiver 122 to 
either activate or conserve power. 
Referring to FIG. 20, a flow diagram is shown illustrating the synchronous 
operation of the embodiment of a receiver shown in FIG. 19. Subsequent to 
finding a frame ID matching the predetermined frame ID within the 
selective call receiver code plug, the operation proceeds to enter the 
flow diagram at step 650. Step 652 decodes the messages in the frame and 
additionally, decodes the "skip" value. Step 654 determines if the "skip" 
value was decoded OK in step 652 (this portion of the transmission may 
have been disrupted by noise). If yes, step 656 conserves power for the 
number of frames indicated by the "skip" value. If no, power is conserved 
for the minimum "skip" value stored in the code plug. Responsive to either 
step 656 or 658, step 660 activates the receiver and searches for bit and 
frame synchronization and frame ID. If a frame ID is found matching the 
predetermined frame ID in step 662, the flow returns to step 652 to 
continue to decode messages. However, if the frame ID is not found, step 
664 determines if frame sync has been missed for a predetermined 
consecutive number N of times. If not, the selective call receiver is 
still synchronized and step 666 causes the messages in the frame to be 
decoded (as in step 652) and power is conserved for the minimum "skip" 
value. Thus, the next frame in which decoding is to be performed is 
determined with respect to the last occurrence of a frame having the frame 
ID matching the predetermined frame ID of the decoder. Subsequently, the 
flow returns to step 660. However, if (step 664) frame synchronization has 
been missed for N consecutive times, the flow exits (step 668) to step 174 
of FIG. 13 to reacquire synchronization. Thus, in response to the "skip" 
value, a selective call receiver may conserve power for any number of 
frames. Additionally, if the pager is decoding in a frame wherein the 
frame ID is not found, the selective call receiver may decode at frame 
intervals corresponding to the minimum "skip" value. In practice, the 
"skip" and minimum "skip" values should be related in such way that a 
selective call receiver having found at least a first frame with the frame 
ID of the selective call receiver, the selective call receiver utilizing 
only the minimum "skip" values will always decode in a frame having the 
frame ID of the selective call receiver. 
FIG. 21 shows an example of a synchronous paging signal and the battery 
saver operation of the selective call receiver of FIG. 19. In this 
example, the selective call receiver has a predetermined frame ID of 99. 
Lines 700 and 740 shows that the frame ID 99 may occur at a multitude of 
positions. Line 700 shows the frame ID of 99 occurring eight frames apart, 
while line 740 shows the frame ID of 99 occurring three and five frames 
apart. The frame IDs of the intervening frames of lines 700 and 740 are 
shown as "***" and are not relevant because the selective call receiver 
only recognizes the frame ID of 99. Lines 710-730 and 750-760 show the 
power conservation and receiving and processing strobe of the selective 
call receiver. A logic high indicates frames where the selective call 
receiver is receiving and processing information and a logic low indicates 
frames where the selective call receiver is conserving power. 
Line 710 shows a selective call receiver which, from a previous "skip" 
value, has been directed to decode in coincidence with the occurrence of 
the first frame 99. This frame has a "skip" value of 7 which causes the 
selective call receiver to conserve power for seven frames and begin 
decoding thereafter, which is in coincidence with the second occurrence of 
frame ID 99 of line 700. During the second occurrence of frame ID 99, the 
selective call receiver receives a new skip value of 45, which causes the 
selective call receiver to conserve power for 45 frames subsequent. 
Line 720 shows a selective call receiver which, from a previous "skip" 
value, has been directed to decode in coincidence with the occurrence of 
the first frame 99. The selective call receiver, (line 720) has a 
predetermined minimum "skip" value of "0". A decoded "skip" value of 6 
causes the selective call receiver to conserve power for 6 frames. Upon 
activating, the selective call receiver does not recognize the frame ID of 
the seventh frame but decodes information in that frame. The subsequent 
frame contains the ID of 99 and a "skip" value of 245, and the selective 
call receiver decodes the frame and conserves power for 245 frames. Thus, 
by providing a "skip" value less than the occurrence of the next frame ID 
for the selective call receiver, the selective call receiver can be made 
to decode in additional frames. Upon finding the frame ID of the selective 
call receiver, additional power conservation is performed. 
Line 730 shows the operation of a selective call receiver having a minimum 
skip value of 1. Subsequent to a decoded first frame having an ID of 99, 
the selective call receiver receives a "skip" value of 3 and conserves 
power for 3 frames. The information in the fourth frame is decoded, 
however, if a frame ID of 99 is not found, the selective call receiver 
decodes the fourth frame and conserves power for the minimum skip value of 
1 and then decodes the sixth frame. This frame also does not have a frame 
ID of 99 and power is again conserved for the minimum skip value of 1 
frame. The selective call receiver then decodes the eight frame wherein 
the frame ID of 99 is found and a skip value of 73 is decoded. After 
decoding the frame, the selective call receiver conserves power for the 
subsequent 73 frames. Thus, a selective call receiver with a minimum 
"skip" value of 1 decodes every other frame until a frame having the frame 
ID of the selective call receiver is found. 
Line 750 shows a method for decoding the signal of line 740. Upon decoding 
the first frame of line 740 having an ID of 99 and a "skip" value of 0, 
the selective call receiver decodes in every subsequent frame until a 
frame having an ID of 99 is found. Three frames later, frame ID 99 and a 
"skip" value of 4 is found. Thus, the selective call receiver has decoded 
in four consecutive frames. In response to a "skip" value of 4 the 
selective call receiver conserves power for four frames wherein it 
reactivates, decodes the frame and responds to a new "skip" value of 43. 
Line 760 shows another example of a signal as in 740 wherein every "skip" 
value corresponds to the occurrence of frames having a frame ID of 99. 
FIG. 22 shows a block diagram of a paging terminal generating a paging 
signal in accordance with FIG. 18. The functions of the paging terminal 
are substantially identical to the functions described with respect to 
FIG. 8 having identification numbers corresponding thereto. The difference 
being traffic analyzer and frame ID and skip value generator function 800. 
This function generates frame IDs and determines the "skip" values to be 
included within a frame in response to the traffic conditions of the 
frame. As in the capacity analyzer 326 of FIG. 8, block 800 is also 
responsive to other protocols being transmitted. 
FIG. 23 is a flow diagram illustrating the operation of the traffic 
analyzer and interval and repetition generator. When a frame ID is being 
transmitted, step 810 determines the average frame traffic and the next 
available frame having a vacant frame ID. Then step 812 determines if the 
amount of traffic is greater than the traffic provided for by the next 
vacant frame. If not, step 816 determines the subsequent available frame 
having a vacant frame ID, and returns to step 812. This sequence continues 
until the step 812 is satisfied. Then in step 814, the frame ID is 
assigned to the last determined frame. A "skip" value is set to either 
correspond to or be less than the occurrence of the of the determined 
frame in order that the extra frames may accommodate traffic sufficient to 
change the equality of step 812. 
In alternate embodiments, frames IDs may be assigned additionally in 
response to a minimum and/or maximum number of frames between frame IDs 
associated with each frame ID. Additionally, the assigned frame must 
provide for any minimum predetermined "skip" value associated to the 
selective call receivers having that predetermined frame ID. 
Thus, signals corresponding to three embodiments of the present invention 
have been shown. FIG. 1 shows a signal which has a predetermined number of 
frame IDs numbered in a predetermined sequence. FIG. 11 shows a signal in 
which any number of frame IDs may be used in any sequence, however, the 
period of each frame ID is constant. FIG. 18 shows a signal in which any 
number of frame IDs may be used in any sequence. It should be appreciated 
that the repetition value may be used with any of the signals as described 
if FIG. 11, or be entirely eliminated. Additionally, with some minor 
modifications to the signal of FIG. 1, all three signals may be combined, 
thereby providing an extremely flexible paging system. Since selective 
call receivers receiving signals of FIGS. 1, 11 and 18 need not decode 
frame IDs and cycle, interval, period or "skip" values in every frame in 
which messages are decoded, and since the bit sync 102, frame sync 104 and 
message signals 110 have the same messages, messages within frames having 
frame IDs of one embodiment may be properly decoded by selective call 
receivers operating in accordance with another embodiment of the 
invention. In order to provide for an efficiently operating paging system, 
means for frame assignment of one, two or all three of the embodiments 
should be provided. 
FIG. 24 shows an example of a frame assignment that combines signals of 
FIGS. 1, 11 and 18 and signals from other paging protocols. Line 900 shows 
frames numbered 1 through 48, each frame having a common bit sync, frame 
sync and message information structure signals. Line 910 shows frames with 
frame IDs assigned according to FIG. 1. This embodiment of the invention 
has been modified such that every other frame is assigned a frame ID in 
accordance with FIG. 1. The frames are preferably numbered in even 
increments between values of 1 and 63, and the cycle values are selected 
such that the selective call receivers only decode in odd numbered frames. 
Thus, the remaining frame IDs are placed in the even numbered frames. It 
should be further appreciated that using this modification, frame IDs 
operation in accordance with FIG. 1 may alternately be used every 4th, 
8th, . . . , 2.sup.N th frames, thereby providing for more frames to be 
used by the other embodiments. Selective call receivers receiving the 
frames of line 910 operate according to the dictates of the cycle value 
received in the frames. 
Lines 920, 922 and 924 show frames with frame IDs operating in accordance 
with the signal of FIG. 11. Line 920 shows a frame ID which has a period 
12 frames, line 922 shows a frame ID which has a period of 6 frames and 
line 924 shows a frame ID having a period of 18. Selective call receivers 
decoding in frames of either lines 920, 922 or 924 operate in accordance 
with the interval and repetition signals contained therein. 
Line 930 shows remaining frames which are available for use with frame IDs 
used in accordance with the signal of FIG. 18. Any number of frame IDs may 
be used on the frames of line 930, each frame ID including a skip value 
causes the selective call receivers to conserve power according with the 
selective call receiver of FIG. 19. The frame IDs of the frames on lines 
920-930 are preferably different from those of line 910 such that they are 
not recognized by the selective call receivers decoding the signal of FIG. 
1. 
For example, the period of the frame ID of line 920 is 12, and if the 
interval in frame 2 of line 900 is 3, the group of selective call 
receivers having the frame ID of line 12 would also decode in frame 
numbers 6 and 10. The frame ID of these frames belong to selective call 
receivers of lines 922 and 924, respectively. If, in another example, the 
interval in frame 2 of line 900 is 4, the group of selective call 
receivers having the frame ID of line 12 would also decode in frame 
numbers 5, 8 and 11, respectively. Thus, frame IDs of frames 5 and 11 are 
assigned to the selective call receivers of line 910, while the frame ID 
of frame 8 is assigned to the selective call receivers of line 930. 
Therefore, in this example, the selective call receivers, of the 
embodiment corresponding to FIG. 11, decode message information in frames 
operating in correspondence with the embodiments of FIGS. 1 and 18. 
Items 940, 950 and 960 illustrate that other signalling protocols may 
coexist with this embodiments of the present invention. Preferably, each 
frame is substantially 4 seconds in duration. Item 940 shows that a GSC 
signal is transmitted in place of frames indicated by 21, 22 and 23 on 
line 900. The GSC signal may be either data messages or voice messages. 
The GSC signal occupying these positions makes decoding of frame IDs and 
information by selective call receivers of the invention impossible. Since 
selective call receivers of the invention have a predetermined response to 
the absence of frame IDs, the subsequent frames in which they decode my be 
predicted. Thus, selective call receivers operating in accordance with 
line 910 having missed a frame ID in frame indicated by 21 will find a 
proper frame ID in the frame indicated by 23. These selective call 
receivers will respond according to the previous cycle value in the other 
frames of line 910. Additionally, selective call receivers operating in 
accordance with line 922, which missed a frame ID in the frame indicated 
by 22, will find a proper frame ID in the frame indicated by 28. 
Accordingly, the response of the group of selective call receivers in the 
intervening frames are predictable based on the predetermined interval and 
repetition values assigned to the group of selective call receivers, 
allowing the messages for the selective call receivers to be placed in the 
intervening frames. 
Furthermore, selective call receivers operating in accordance with line 930 
which are programmed to expect a frame ID in frame 20, will miss the frame 
ID and, will decode in accordance with the minimum skip value assigned to 
that group of selective call receivers. If the minimum skip was 0, these 
selective call receivers will decode in every subsequent frame until a 
frame ID matching their predetermined frame ID is found. Thus, messages 
for these selective call receivers may be placed in any frame after frame 
22. Battery saving operation of these selective call receivers may be 
restored by "forcing" a frame having their frame ID in another frame, for 
example frame identified by number 26, thereby giving these selective call 
receivers a new skip value. Since the frame identified by 26 was apriori 
assigned to selective call receivers of line 920, the selective call 
receivers of line 920 will miss their expected frame ID at frame 26, 
causing these selective call receivers to decoded according to their 
predetermined interval and repetition values until the occurrence of frame 
identified by 38. Thus, the response of the selective call receivers of 
the invention to the GSC message is predictable, and synchronization to 
the signal is maintained. Accordingly, similar example responses to the 
POCSAG signal 950 and the analog voice signal 690 may be made. In this 
way, this invention facilitates the additions of other signalling systems 
by temporarily frustrating the battery saving features of the selective 
call receivers. 
It should be appreciated that since selective call receivers of all three 
embodiments continue to decode in a known manner if an expected frame ID 
and or cycle value is not found. This provides for the transmission of 
another protocol such as the POCSAG or GSC paging protocol, while the 
selective call receivers remain in synchronization. Furthermore, this 
aspect provides for forcing the frame ID of a first frame of selective 
call receivers in the expected frame of another group of selective call 
receivers location to recover the battery save feature of the first group 
of selective call receivers. 
Furthermore, the similarity in the paging terminals of FIGS. 8, 16 and 22 
enable the combination of different functions. A frame queue 324 may hold 
the queues of the frames of all three embodiments to facilitate the 
combination. Accordingly, a frame which may have selective call receivers 
of one, two or all three embodiments may be analyzed by the capacity 
analyzer of each embodiment for total frame capacity. The selective call 
receivers of FIGS. 2, 12 and 19 operate substantially identically with the 
exception of the response to the received frame ID, cycle, interval and 
repetition, or skip value. Thus, a method for decoding any of the three 
embodiments may be incorporated into every selective call receiver, and an 
additional signal stored in the code plug of the selective call receiver 
to indicate the embodiment of the invention the selective call receiver. 
Although several embodiments of the invention have been described by way of 
example, other modifications may be made to the description herein, while 
remaining within the spirit of the present invention.