Field of the Invention

This invention relates in general to communication systems and more particularly to selective call communication systems.

Background of the Invention

Communication systems utilizing selective call addressing typically employ a receiver that has at least one unique selective call address associated therewith. This receiver is commonly referred to as a selective call receiver or pager. Paging systems for the transmission and reception of radio frequency information are well known to those skilled in the art. When a pager receives and decodes its address, the pager alerts the user to the presence of incoming information and operates to present this information.

The majority of selective call communication systems currently in use do not have the same frequency allocated in multiple metropolitan areas. Typically, this is a disadvantage because if a user wants to travel to another metropolitan area that is serviced by their paging service provider, they must have a pager that receives the channel in that new area.

At this time, there are no selective call communication systems that can operate to determine the validity of a signalling scheme present on a channel that was been acquired while "scanning." Scanning, as it is used here, means the orderly search for information on multiple frequency channels by a synthesized or crystal controlled receiver. Contemporary scanning receivers sequentially scan channels in a predetermined order that is programmed in the hardware or software of the selective call receiver. This method wastes time if there are channels on the scanning list that are inactive or do not contain information that is directed to the user's selective call receiver.

Thus, what is needed is a method for scanning a plurality of frequency channels and dynamically optimizing the scanning list in a hierarchical order to provide optimum scan sequencing for the reception of information by the selective call receiver.

Summary of the Invention

Accordingly, it is an object of the present invention to provide an improved frequency scanning communications system that dynamically optimizes the sequence and time ordering of available signalling frequencies.

In carrying out the above and other objects of the invention in one form, there is provided a selective call communications receiver comprising means for scanning a list of predetermined channels to classify said channels in a priority order and means for receiving information from said channels in accordance with said priority order.

Brief Description of the Drawings

FIG. 1A is a block diagram of the selective call receiver system in accordance with the preferred embodiment.

FIG IB. is a system diagram in accordance with the preferred embodiment. FIG. 2 is a protocol diagram of the system protocol in accordance with the preferred embodiment.

FIG. 3A is a flow diagram of the scanning procedure in accordance with the preferred embodiment.

FIG. 3B is a flow diagram of the scanning procedure in accordance with the preferred embodiment.

FIG. 3C is a flow diagram of the scanning procedure in accordance with the preferred embodiment.

FIG. 3D is a flow diagram of the scanning procedure in accordance with the preferred embodiment. FIG. 3E is a flow diagram of the scanning procedure in accordance with the preferred embodiment.

FIG. 3F is a flow diagram of the scanning procedure in accordance with the preferred embodiment.

Description ^' of a Preferred Embodiment

75

Referring to FIG. 1A, a battery 101 powered selective call receiver operates to receive a signal via an antenna 102. The receiver 103 demodulates the received signals using conventional techniques and forwards the demodulated signal to 80 the control circuitry 104, which decodes and recovers information contained within the received signal. In accordance with the recovered information and user controls 105, the selective call receiver presents at least a portion of the information, such as by a display 106, and signals the 85 user via a sensible alert 107 that a message has been received.

Referring to FIG. IB, the multiple channel paging system comprises a paging terminal 108 that encodes information received from users for transmission by at least one of the 90 plurality of transmitters shown. A radio frequency signal is broadcast from the plurality of transmitters that includes transmitter A, 109, transmitter B, 110, and transmitter N, 111 which typically are located in different metropolitan areas. The signal from each transmitter is transmitted on a frequency 95 unique to that transmitter. The selective call receiver 112 will scan to receive signals broadcast in that respective metropolitan area.

Referring to FIG. 2, an example of the preferred signalling protocol is shown. The duration of the individual

100 packets is not shown to scale, but the overall timing of the frame and its internal packets are representative of the actual implementation. In this figure, four information channels are shown of which 1, 2, and 4 contain information that can be received and decoded to deliver a selective call

105 message. Channel 3 209 is operating with a protocol such as GSC (Motorola's Golay Sequential Code) or POCSAG (Great Britain's Post Office Code Standardisation Advisory Group) that is not recognized by the scanning selective call receiver. The protocol that is running on channels 1, 2, and

110 4 uses an interleaved structure that contains a sync

(synchronization) signal 201, selective call addresses A0, B0, 202, CO, DO, E0, and a network identification (I.D.) code NO,

203. The addresses A0, BO, 202 have corresponding information messages MESSAGE A0, 204, and MESSAGE B0, 205, that are used

115 to convey information to an addressed selective call receiver. The data frame 207 for channel 1 extends from the first sync 201 to the last message MESSAGE Z0 206. This frame structure is continuously repeated on any given channel while updating the address, network I.D., and message fields with pertinent

120 data. Frames are numbered in a rotating manner to allow the pager to receive only the frames that may contain information directed to that pager.

As shown in FIG. 2, the channels are ordered such that the next channel's sync signal for the same frame number

125 always occurs at a time that is Δt time units from the last occurrence of sync on the present channel. The parameter Δt is a system constant that is set to allow for proper acquisition, decoding, and recognition of the network I.D., as well as enough time for the selective call receiver's

130 frequency scanner to change channels and stabilize. Any frequency can be assigned to the channels shown because the only binding constraint in the preferred embodiment of the scanning algorithm is that the system must transmit successive frames on differing frequencies spaced by a time of Δt. This

135 feature in conjunction with the ability of the receiver to order and prioritize the channel scan list greatly increases the utility of the selective call receiver. Once the channels are classified and prioritized, the receiver primarily scans the channels having information directed to the user. By

140 prioritizing the available receive channels, the long "on time" used by the receiver during each scan when determining if the received channel has valid data is prevented. This provides the added benefit of extending the useful operating life of the receiver by conserving power. The time offset for

145 all channels is identical when taken from the beginning of the synchronization word (SYNC) on the current channel to the start of the synchronization word on the next scan channel. This offset of Δt is shown be the dotted lines between channel 1 and 2 208, and channels 2 and 4, 210.

150 FIG. 3A, 3B, 3C, 3D, 3E, and 3F show related parts of the flow diagram representing the scanning algorithm implemented

in accordance with the present invention. The flow diagram may be implemented using either hardware or software in the control circuitry 104 of the selective call receiver. 155 Referring to FIG. 3A, when the selective call receiver shown in FIG. 1 is activated (at turn on), the X0 counter is reset 301 and the receiver samples the first channel of a predetermined list 302 programmed in the control circuitry 104 of the selective call receiver. If the presence of an RF 160 carrier is detected, 303, the receiver proceeds to search for a recognizable bit rate, 304. When no RF carrier is present 303, the channel is marked as D(n) 304. In all cases thereafter, the notation " (n) " is used to show the assignment of an internal pointer that is used by the algorithm to 165 reference a channel. After marking the channel as D(n), the process calls the type I characterization routine.

The type I characterization routine acts as the mechanism for "hard" channel characterization during power up or in a transmission fringe area where loss of signal has occurred 170 causing the receiver to lose one or more channels. From the power-up state after turn-on the X0 counter is reset 301. Referring to FIG. 3B, Step 305 tests the value of the X0 counter to see if X type I characterization cycles have been completed. For a false result, the X0 counter is incremented 175 306, the receiver scans to the next channel on the list 307, and control returns to the RF carrier present test 303. When the X0 counter reaches the value X (meaning X number of channels have been scanned). Step 305 returns a true result. With a true result from step 305, the X0 counter is reset to 180 zero 308 and the type I characterization timer is set 309. The count value programmed in the type I characterization timer is selectable from either a code plug option or a dynamic system activity variable derived from historical channel activity by the receiver. After setting the type I 185 characterization timer 309, control is passed to step 310. Step 310 loops until the type I characterization timer has expired. After the type I characterization timer has expired 310, step 311 checks for any tasks in progress in FIG. 3D, 3E, and 3F. This criteria is denoted by "Task beyond 1 in process 190 ?" on the flow diagram. If a task is in progress.

continuation is paused until the task is completed. If no task was in progress, step 311 passes control to step 307 which scans to the next channel on the list. Step 307 then returns control to step 303 the RF carrier present test. This

195 ends the type I characterization.

Again referring to FIG. 3A, after a true result from step 303, step 312 test the channel for a bit rate. If no bit rate is detected, the channel is marked as C(n) 313 and control is passed to the type I characterization routine, upon the

200 detection of a valid bit rate, step 312 passes control to step 314 and the channel is tested for the presence of a synchronization word. If no sync is detected, the channel is marked as C(n) 315 and control is passed to the type I characterization routine. When sync is detected by step 314,

205 control is passed to step 316. Step 316 checks the data stream from the received information for a valid system marker. The system marker may be found in the synchronization word of all channels that are a member of a network in an area. It is used to denote members of a network that are

210 sequenced relative to a master timing signal. These members have their transmitted frames offset by an integer multiple of Δt. If the system marker is not present step 316 passes control to step 317. Step 317 tests the present channel for being previously marked as an A(n) (primary information

215 reception) channel. If the result of step 317 is false, the channel is marked as E(n) 318 and control is passed to the type I characterization routine. If the channel was previously marked as an A(n), control is transferred to step 319 on FIG. 3C. Step 319 is the entry point of the type II or

220 "soft" characterization routine.

Referring to FIG. 3C, the purpose of the type II characterization routine is to allow for quick and positive classification of channels based on the use of the system marker and the timing relationship between network member

225 channels. This routine will allow a number of "misses" on one or more channels without having to re-characterize the complete channel list. This is accomplished using a cycle that by definition scans the complete active channel list once per type II characterization cycle, then testing for the

230 completion of that cycle in the last Y seconds. Because the type II characterization cycle is interrupt driven, an asynchronous parallel timer (not shown) implemented as a detached task is used to provide the timing reference for the test in step 320. This asynchronous timer starts at the 235 instant that step 319 fails for the first time after the completion of a type II characterization cycle. By using this timer and knowing the number of channels on the scan list, the type II characterization routine will prevent the receiver from uncontrollably scanning through the channel list for

240 information when some amount of valid data (eg. system markers) has been detected. As control is passed to the type II characterization routine, step 319 tests for the lack of a valid system marker detection in the last Z minutes. The variable Z is selected from a programmed receiver option. If

245 no system markers have been detected in the last Z minutes, control is passed to the type I characterization routine. If any system markers were detected in the last Z minutes, control is passed to step 320. Step 320 tests for the completion of a type II characterization cycle in the last Y

250 seconds. If this is true, the type II characterization timer 321 is set and control is passed to step 322. If false, control is passed to step 324. The purpose of step 322 is to allow the receiver to "sleep" for a period determined by the count programmed into the type II characterization timer.

255 Advancement to step 323 is made when the type II characterization timer expires. The processing will continue to step 324 if no tasks are in progress in FIG. 3D, 3E, and 3F. This criteria is denoted by "Task beyond 1 in process ?" on the flow diagram. If any tasks are in process, control is

260 not passed to step 324 until they are complete. When control is passed to step 324, the receiver proceeds to another channel having the correct frame number to find the network I.D. and timing to receive the complete or partial (as much as needed) information contained in the new frame on the new

265 channel. The type II characterization routine terminates the test loop comprising all elements shown on FIG. 3C and passes control to step 325. After the complete channel list has been scanned, the type II characterization routine is complete.

Referring back to FIG. 3A, when step 316 is true, control 270 is passed to step 326 and the Z0 timer is reset. After step 326, control is passed to step 327.

Referring to FIG. 3D, step 327 marks the present channel as B(n) then passes control to step 328. Step 328 calculates the next channel having the same frame number, that is, the

275 frame number in which the network I.D. is expected. The receiver then proceeds to that next channel. Upon completion of step 328, control is transferred to step 325. Step 325 tests for presence of a synchronization word. Upon detection of a synchronization word, control is transferred to step 329.

280 Step 329 tests for presence of a system marker. If true, step 330 resets the Z0 timer. Step 331 tests for a network I.D.. If false, step 332 checks the current channel to determine if it was previously marked as an A(n) . If true, step 333 advances the A(n) fail I.D. counter. Step 334 tests the A(n)

285 I.D. fail counter to see if it has reached the predetermined count of K. K determines the number of misses allowed before re-characterization of an A(n) channel. When step 334 is true, the channel is marked as E(n) 335. After marking the channel or when step 334 is false, the receiver returns to a

290 type II characterization. When step 331 is true, the A(n) I.D. fail counter is reset 336.

The channel is then marked as A(n) 337 and the address frame timer is started 338. Step 340 searches for the correct frame address. If false, step 347 waits until the address

295 frame timer expires. Step 347 serves to allow reception of the correct data frame by the receiver. When step 347 is true, step 348 interrupts any characterization which may be in progress, then transfers control to step 341.

Referring to FIG. 3F, step 341 tests for sync. When

300 present, step 342 tests for a system marker, and when found, resets the Z0 timer, step 343. Step 344 resets the A(n) I.D. fail counter. Then step 345 tests for the detection of a correct selective call address. If true, step 346 decodes a message and return to type II characterization.

305 The notation A(n), B(n), C(n), D(n) , and E(n) are used throughout this specification to denote decreasing levels of channel priority. The algorithm begins with a predetermined

list of channels and a scan order associated with pre¬ programmed information, a successful channel history, and the

310 home channel. From this point, the algorithm dynamically reclassifies the channels into a new prioritized list to be used as a basis for scanning operations. For example, a user's primary information channel would be classified as an A(n) and given interrupt priority over the scan list. The

315 receiver continuously updates the channel list to create the beforementioned successful channel history.

When a system network member is found, scanning changes to a method wherein the channels are scanned based on their predetermined time order, each channel being separated from

320 the previous channel by at least one Δt.