CHANNEL EXPLORATION APPARATUS AND METHOD Field of the Invention The present invention relates generally to a radio apparatus and, more particularly, to a channel scanning apparatus and method comprising the radio apparatus. BACKGROUND OF THE INVENTION Many radiotelephones are energized by a battery. Those battery-powered radiotelephones that minimize energy consumption and conserve battery power have a commercial advantage as they help to prolong battery operation time. The radio communication system in which the radiotelephones operate includes a plurality of channels. The radiotelephone employs a receiver to repeatedly scan between the plurality of channels while the radiotelephone is not in service. The receiver scans through the plurality of channels until it finds one that contains quality of service data.
It is known to periodically turn off the receiver during channel scanning to conserve battery power. The known intermittent receiver operating schemes, which save battery power during channel scanning, are shown in the timing diagrams of FIGS. 1 and 2. FIG. 1 shows a receiver that is initially turned on to perform a scan continuous of all channels (23 to 43 and 323 to 343) for a predetermined period of time, such as 60 seconds. If no channel with quality of service data is found for 60 seconds, the receiver enters an intermittent scan mode to save battery power. During the intermittent scan mode the receiver is turned on periodically for a scan period during which the data on the strongest channels is examined. The receiver is turned off for a second predetermined period of time, such as 9 seconds, between each scanning period. The intermittent scan mode is interrupted when the user operates a key on a radiotelephone keypad or when the quality of service data is on a channel during the scan period. However, the scheme of Figure 1 will only save battery power if no quality of service data are found during continuous scanning and then only when the receiver is turned off for the second predetermined period of time during the intermittent scan mode. There is no saving of battery power during continuous scans or during periods of exploration in intermittent scan mode. Additionally, there is no opportunity for the radiotelephone to find the quality of service data when the receiver is turned off during the second predetermined time period. In Figure 2, a receiver scans all channels (1 to 40) for a period T. A channel is scanned during each time period tx. The receiver is turned on for a first portion of t1 (denoted by a solid line) during which the ones on the channel are examined and turned off for a second portion of t (denoted by a dotted line). The receiver oscillates through each channel until all channels are examined for the quality of service data. The scan cycle continues until it is determined that a scanned channel contains quality of service data. However, because the scheme in Figure 2 must determine whether the quality of service data is presented at the time each channel is scanned, the scan period T and the time of partial scan t must be extended. The scheme in figure 2 also does not distinguish between the weakest or strongest channels that have quality of service data, but instead select the first channel with quality of service data.
Accordingly, what is needed is a channel scanning apparatus and method without prolonged continuous scanning periods, without extended periods where the receiver shuts down and without quality of service data checks during the scanning of each channel. Brief Description of the Drawings Figure 1 illustrates a timing diagram of a known intermittent scan scheme; Figure 2 illustrates a synchronization diagram of a known alternating intermittent scan scheme; Figure 3 illustrates a block diagram of a radio communication system that includes a radio apparatus, the reception circuitry of the radio apparatus being shown in limited detail; Figure 4 illustrates a timing diagram of a scanning method employed by the radio apparatus of Figure 3; and Figure 5 illustrates a flow diagram of the scanning method employed by the radio apparatus of Figure 3. Detailed Description of the Preferred Modes A battery powered apparatus for scanning among a plurality of channels in a radio communication system includes reception circuitry and control circuitry. The receiving circuitry is tunable to any of the plurality of channels and measures the reception resistance of the tuned channel. The control circuitry controls the receiving circuitry to scan through all the plurality of channels one at a time. During scanning, the control circuitry stores a first reading of a measured receive resistor of the tuned channel before turning off the receiving circuitry. The control circuitry stores a second reading of a measured receive resistor of the tuned channel after turning the receiving circuitry back on. Unlike known scanning methods, reception resistance readings are taken from each channel before turning off and after turning on the receiving circuitry. Figure 3 illustrates a radio communication system 300. The radio communication system 300 includes a base station 302 and a radio apparatus 304. The base station 302 provides service to the radio apparatus, such as radio sets 304, contained within a particular geographical area. The base station 302 communicates with these radio apparatus through the radio frequency (RF) signals, such as the RF signals 303 communicated between the base station 302 and the radio apparatus 304. The RF signals 303 communicate over data and voice channels within a frequency band designated for use with the radio communication system 300. In the illustrated embodiment, the radio communication system 300 is an ETACS cellular radio telephone system operating on a radio frequency band. frequency of 872 MHz to 905 MHz and 917 MHz to 950 MHz that has data and voice channels. The data channels could be channels 23 to 43 and 323 to 343. Radio apparatus 304 includes an antenna 308, a duplexer 309, receiving circuitry 310, control circuitry 312, user interface 314, and transmission circuitry 316 The RF signals 303 detected by the antenna 308 are input as electrical RF reception signals through the duplexer 309 to the reception circuitry 310. The reception circuitry 310 demodulates the electrical RF reception signals in data signals and / or voice signals that are coupled to the control circuitry 312. The control circuitry 312 transmits the speech audio signals to a speaker (not shown) of the user interface 314. The speech audio signals input through of a microphone (not shown) of the user interface 314, are coupled via the control circuitry 312 to the transmission circuitry 316 as electrical audio signals. The transmission circuitry 316 modulates the electrical audio signals in electrical RF transmission signals and couples these signals to the antenna 308 through the duplexer 309. The antenna 308 outputs the electrical RF transmission signals as RF 303 signals. radio apparatus 304 is energized by battery 305, which is removably coupled thereto. The battery 305 includes electrochemical cells 306 to provide power. A positive electrochemical cell terminal 306 is coupled to the battery supply terminal (B +) 307 of the radio apparatus 304. The battery supply terminal 307 supplies battery power to the reception circuitry 310, the control circuitry 312, the user interface 314, and the transmission circuitry 316. The battery 305 has a limited electrical life and provides power until it is discharged to a voltage level that is insufficient to operate the radio apparatus 304 The reception circuitry 310 includes a receiver 320, a reception frequency synthesizer 322 and an RSSI generator (received signal resistance indicator) 324. The receiver 320 is of a double superheterodyne type which is well known in the art. and therefore will be briefly described here below. The receiver 320 is tuned by the reception frequency synthesizer 322. The reception frequency synthesizer 322 applies a local oscillation signal to the receiver 320 through the signaling line 326. The local oscillation signal has an oscillation frequency that it is associated with a channel in a radio communication system 300. The application of the local oscillation signal closes the receiver 320 to the channel. In the illustrated embodiment, the time required for the receiving frequency synthesizer to close the receiver 320 is approximately 3 ms. Once "closed", the receiver 320 mixes the electrical RF reception signals input from the duplexer 309 with the local oscillation signal to extract the reception signals belonging to the channel. After mixing, the reception signals are maintained in the receiver 320 and are routed to the RSSI generator 324 coupled through the reading line 328. Those reception signals held in the receiver 320 are demodulated and coupled to the circuitry control 312 as reception data signals on the audio data line 327. Those directed to the RSSI generator 324 through the reading line 328 are measured by conventional circuitry, such as a wrap detector (not shown), the which provides an analogous DC voltage proportional to the resistance of the reception signals to the control circuitry 312 through the line 329. The analog signal resistance voltage indicates the reception resistance of the current channel. The reception circuitry 310 includes a reception switching circuit 330 coupled between the battery supply terminal 307 and all with respect to the receiver 320, the reception frequency synthesizer 322, and the RSSI generator 324. The switching circuit of reception 330 is controllable to connect battery power to, or disconnect battery power from, receiver 320, reception frequency synthesizer 322, and RSSI generator 324. Switching circuit 330 may be comprised of conventional circuitry , such as a transistor. The control circuitry 312 includes a microprocessor 340, the memory 342, the timer 344, the reception audio circuit 348, and the transmission audio circuit 350. The microprocessor 340 can be any suitable microprocessor, such as a commercially available 68HC11 microprocessor. available from Motorola, Inc. The microprocessor 340 operates the radio apparatus 304 by executing the algorithms read from the memory 342. The microprocessor 340 controls the reception frequency synthesizer 322 to tune the receiver 320 to a particular channel by sending a signal of channel selection thereto through a channel selection line 352. The microprocessor 340 controls the receive switch circuit 330 to turn on and turn off the reception circuitry 310 by sending a switching control signal through the line of reception. switching control 354. The microprocessor 340 is coupled to the RSSI generator 324 through the line 329 and receives the signal resistance voltage thereof. The microprocessor 340 includes an analog-to-digital converter (not shown) that converts the analog DC voltage of the signal resistance voltage into a digital number. The digital number is stored in the memory 342. The memory 342 is coupled to the RSSI generator 324 through the microprocessor 340, which converts the analog signal resistance voltage emitted from the RSSI generator 324 to the appropriate digital numbers to be stored in the memory 342. The memory 342 may be a read-only memory (ROM), a read-only memory programmable erasable (EPROM), a random access memory (RAM), another suitable memory device, or any combination of the aforementioned. Although the memory 342 is displayed separately from the microprocessor 340, it will be recognized that the memory 342 could be internal to the microprocessor 342 and / or that the microprocessor 340 may contain other memory in addition to the memory 342. In the illustrated embodiment, the memory 342 stores the two largest signal strength voltage readings and their corresponding channel numbers at the locations designated as the "strongest" location and the "next strongest" location as determined by the numerical comparisons carried out by the 349 microprocessor on the representation of the digital number of the resistance voltage of all scanned channels. Memory 342 also stores multiple voltage readings of signal resistance of the current channel. The timer 344 is coupled to the microprocessor 340 and includes one or more conventional synchronizing circuits, such as a commercially available integrated timer circuit. Alternatively, timer 344 may be a software timer generated within the microprocessor 340 or a hardware timer placed within the microprocessor 340. The timer 344, under the control of the microprocessor 340, measures the predetermined time periods for the microprocessor 340. The reception audio circuit 348 is coupled to the receiver 320, the microprocessor 340, and the user interface 314. The reception audio circuit 348 includes conventional circuitry for examining the data quality of received reception data signals. from the receiver 320 through the audio data line 327. If the data of the reception data signals is quality of service, the receiving audio circuit 348 points it to the microprocessor 340. As established, the microprocessor 340 operates the radio apparatus 304 by executing the algorithms stored in the memory 342. One such algorithm is an algorithm of channel exploration. Although not in use, the radio apparatus 304 scans through all of the data channels in the radio communication system 300. In order to save battery power during scanning, the energy for the receiving circuitry 310 is interrupts intermittently. Figures 4 and 5 illustrate a battery saving channel scanning method employed by radio apparatus 304. The battery saving channel scanning method is incorporated in the channel scan algorithm stored in memory 342 and executed by the microprocessor 340. During the channel scan, the transmission circuitry 316 is turned off to save battery power. The transmission circuitry 316 includes a transmit switch circuit (not shown), similar to the receive switch circuit 330, which is controllable by the microprocessor 340 to turn off the transmission circuitry 316. The operation of the radio apparatus 304 will now be described with reference to Figures 3 to 5. The scanning method is initiated when the reception circuitry 310 is turned on at t0 (block 500 of the figure
) . The microprocessor 340 starts a quick scan
(block 502 of figure 5) for a period of time Tx. During Tx the channels are scanned one at a time. As used herein, for each channel, scanning generally includes tuning the reception circuitry 310 to a channel; reading the channel receiving resistance a first time; the shutdown of the reception circuitry 310; the ignition of reception circuitry 310; re-tuning the reception circuitry 310 to the same channel; reading the channel receiving resistance a second time; tuning to a second channel, reading the reception resistance of the second channel a first time; the shutdown of the reception circuitry 310; and the continuation of this process until the reception resistance of each channel is read twice. The rapid scanning method employed by the radio apparatus 304 during Tlf which comprises time t0 to t8, is as follows. At t0, the microprocessor 340 controls the switching circuit 330 to turn on the reception circuitry 310. Between t0 and tlf the microprocessor 340 tunes the receiver 320. The microprocessor 340 programs the reception frequency synthesizer 322 by sending the signal of selection of the receiver. channel designating a first channel to the reception frequency synthesizer 322. After the reception frequency synthesizer 322 is programmed for the first channel, the receiver 320 closes the first channel. At t1 (the RSSI generator 324 takes a first signal strength voltage reading of the reception signals on the first channel.) The RSSI generator 324 couples the first reading to the memory 342 via the microprocessor 340. Immediately after t1 (the microprocessor 340 controls the switching circuit 330 to turn off the reception circuitry 310. In the illustrated mode, the time period between t0 and t is 5 ms.As between tx and t2, the reception circuitry 310 remains off. reception circuitry 310 is kept off for a sufficient period of time so that in a multi-path environment, statistically, the two consecutive signal resistance voltage readings are not taken within the same fading. is 20 ms In the illustrated mode, the time period between t and t2 is 30 ms In T2, the microprocessor 340, which responds to one from the attention of the timer 344 controls the switching circuit 330 to turn the receive circuitry 310. t2 and t3, the receive circuitry 310 retunes the first channel. Re-tuning to the first channel can be carried out by re-programming the reception frequency synthesizer 322 with the first channel through the microprocessor 340. Re-tuning can also be carried out by merely allowing the receiver 320 to return to close, assuming that the programming of the reception frequency synthesizer 322 to the first channel is maintained when the reception circuitry 310 is turned off. The re-tuning without re-programming allows the receiver 320 to close faster. By means of t3, the receiver 320 closes to the first channel. At t3, the RSSI generator 324 takes a second signal strength voltage reading of the reception signals on the first channel. The RSSI generator 324 couples the second reading on the first channel to the memory 342 through the microprocessor 340. The microprocessor 340 determines the largest reading of the first and second signal strength voltage readings, and stores it together with the first channel in the "strongest" location of the memory 342. In the illustrated mode, the time period between t2 and t3 is 5 ms and the time period between t0 and t3, period over which the first channel, is 40 ms. Therefore, the reception circuitry 310 is outside the 40 ms period, only for 10 ms, during which the first channel is read during the quick scan. At t3, the microprocessor 340 tunes the receive circuitry 310 to a second channel. Between t3 and t4, the receiver 320 closes the second channel. At t4, the RSSI generator 324 takes a first signal strength voltage reading of the reception signals on the second channel. The RSSI generator 324 couples the first reading to the memory 342 via the microprocessor 340. Immediately after t4, the microprocessor 340 controls the switching circuit 330 to turn off the reception circuitry 310. At t5, the microprocessor 340 turns on the circuitry reception 310. Between t5 and t6, the reception circuitry 310 is re-tuned to the second channel. At t6, the RSSI generator 324 takes a second signal resistance voltage reading of the reception signals on the second channel. The RSSI generator 324 couples the second reading to the memory 342 via the microprocessor 340. The microprocessor 340 determines the largest of the first and second signal resistance voltage readings of the second channel. The microprocessor 340 compares the largest reading of the second channel with the previous readings stored in the memory 342 in the "strongest" location or the "next to the strongest" location and, if necessary, stores the largest reading and the channel number of the second channel in the "strongest" location or the location "next to the strongest". In the illustrated mode, the fast scan continues in this manner until the signal resistance voltage of each channel is read twice, with the receiver off between the two readings of each channel. The rapid scan process concludes at t8, after the RSSI generator 324 takes a second signal strength voltage reading of the signals on the last channel and couples the second reading to the memory 342 via the microprocessor 340. microprocessor 340 determines the largest of the signal resistance voltage readings of the last channel, compares the largest reading with the readings stored in the "strongest" and "next to the strongest" locations of memory 342, and stores the largest reading in the "strongest" or "next to the strongest" location, if necessary. In the illustrated embodiment, T-_ is only about 840 ms. At no time during T the control circuitry 312 determines whether the quality of service data is present on the scanned channels. This minimizes T1. The reception circuitry 310 is off for 30 of the 40 ms during the fast Tx scan or is off for approximately 75% of Tx. This minimizes the battery power consumption. At the end of Tlf the microprocessor 340 examines the channels with the two strongest signal strength voltages for the data (block 504 of Fig. 5) for a period of time T2. The channels with the two strongest signal strength voltages were determined by the microprocessor 340 and stored in the "strongest" and "next to the strongest" locations of the memory 342 during the rapid T scan.; L. During T2, the microprocessor 340 keeps the reception circuitry 310 on. T2 comprises times t8 to t10. At time t8, microprocessor 340 reads the channel from the "strongest" location of memory 342 and tunes reception circuitry 310 thereto. Between t8 and t9, the microprocessor 340 continues to respond to the reception audio circuitry 348, which examines the reception data signal for the quality of service data (block 506 of FIG. 5). If the quality of service data is found, the microprocessor 340 keeps the receiver 320 tuned in this channel, places the radio apparatus 304 in service (block 508 of figure 5) and terminates the scan (block 510 of figure 5) . In the illustrated embodiment, the time period between t8 and t9 is approximately 120 ms. If the quality of service data on the channel stored in the "strongest" location of the memory 342 is not found, the microprocessor 340 reads the channel from the location "next to the strongest" of the memory 342 and tunes the receiver 320 to the same at time t9. Between t9 and t10, the microprocessor 340 continues to respond to the reception audio circuit 348, which examines the reception data signal for the quality of service data (block 506 of FIG. 5). If the quality of service data is found, the microprocessor 340 keeps the receiver 320 tuned in this channel, places the radio apparatus 304 in service (block 508 of figure 5) and terminates the scan (block 510 of figure 5) . In the illustrated embodiment, the period of time between t9 and t10 is approximately 120 ms. If the quality of service data is not found on any of the channels stored in the "strongest" and "next to the strongest" locations of the memory 342, the microprocessor 340 determines whether more than a predetermined number of scans have occurred. consecutive hits (block 512 of figure 5). If more than a predetermined number of consecutive rapid scans have not occurred, another rapid scan is performed (block 502 of FIG. 5). If more than a predetermined number of consecutive rapid scans have occurred, the predetermined number being in the illustrated mode four, the scanning method performs a slow scan (block 514 of FIG. 5) at time t10. The slow scan occurs over a period of time T3. During T3 all control channels are scanned one at a time. The slow scan events are similar to those of the rapid scan of the Tx period. For example, at t10, the microprocessor 340 turns on the reception circuitry 310 and tunes the reception circuitry 310 to the first control channel. Between t10 and t11 # the receiver 320 closes the first channel. In you, the RSSI generator 324 takes a first signal strength voltage reading on the first channel and couples the first reading to the memory 342 via the microprocessor 340. Immediately after tllf the microprocessor 340 turns off the receiving circuitry 310 .
In the illustrated mode, the time period between t10 and t?: L is equal to the time period between t0 and t of the fast scan, 5 ms. However, the slow scan differs from the fast scan in the amount of time that the receiving circuitry 310 remains off. The period between tlx and t12, wherein the reception circuitry 310 is off, is preferably 110 ms. The events in t12 and t13 of the slow scan are similar to those of t2 and t3 in the fast scan. For example, at t12, the microprocessor 340 turns on the reception circuitry 310. Between t12 and t13, the receiver 320 closes the first channel again. At t13, the RSSI generator 324 takes a second signal strength voltage reading on the first channel and couples the second reading to the memory 342 via the microprocessor 340. In the embodiment illustrated, the time period between t12 and t13 is similar to the time period between t2 and t3, which is 5 ms. The period of time between t10 and t13 on which the first channel is slowly scanned is preferably 120 ms. Accordingly, the reception circuitry 310 is only on for 10 ms of the 120 ms period over which the first channel is slowly scanned. The slow scan continues in the aforementioned manner until all remaining data channels are scanned and period T3 expires. Although T3 is substantially longer in duration than T1 (receiving circuitry 310 is off for about 92% of T3, thereby minimizing battery power consumption.) At the end of T3 and at the end of the slow scan, the microprocessor 340 proceeds to examine the channels with the two strongest signal strength voltages as determined during the slow scan
(block 504 of figure 5). The two strongest channels of the slow scan are examined in the same way previously exposed in relation to the fast scan
(blocks 506 to 512 of figure 5). Although the radio apparatus 304 is illustrated as a cellular radiotelephone, the present invention will also find application in radios, televisions, cordless telephones, two-way radios, pagers, personal digital assistants, and the like, and "apparatus" as used in the present must refer to all those electronic devices energized by battery and their equivalents. In this way, it can be seen that a scanning apparatus and a scanning method are exposed which save battery power. Unlike the prior art scanning methods, the conservation of battery power begins immediately after the receiving circuitry is turned on. Prolonged periods when the receiver shuts down are avoided in order to increase the opportunity for the radiotelephone to find the quality of service data. Also, when carrying out data checks on only a limited number of channels (ie, those that are more likely to have quality of service data), the receiver's turn-on time is reduced and greater savings are realized. battery.