MXPA01003813A - Combined searching and page monitoring using offline sample storage - Google Patents

Abstract

A novel and improved method for performing paging is described. In one embodiment of the invention a searcher is used to detect spread spectrum signals. Samples received RF signals are stored in a sample buffer. During standby mode, the samples are gathered during paging slots assigned to the mobile. A set of searches are performed on the samples, and if pilot signals are detected additional demodulation is performed to detect paging messages. The resulting set of demodulation data may be combined to increase detection. After a page message has been detected, additional demodulation resources may be activated to processes more complete page messages, or other information channels. In one embodiment of the invention, the searcher includes a demodulator to perform quick page detection without the use of finger elements to reduce idle mode power consumption.

Description

SEARCH AND VERIFICATION OF COMBINED PAGES USING STORAGE OF OUT OF LINE SAMPLES BACKGROUND OF THE INVENTION I. Field of the Invention The present invention relates to wireless communications. More particularly, the present invention relates to a novel and improved search engine for detecting page messages in communication with the extended spectrum. 10 II. Description of the Related Art In the United States patent application no. series 08 / 316,177 entitled "Search Processor Multiple trajectory for a communication system Extended Spectrum Multiple Access "(The request 177) describes a search to detect signals from I extended spectrum. The search engine is particularly suitable for use in a CDMA-based digital cellular telephone system to identify channels pilot transmitted within the CDMA system. Once the pilot channel is identified, the telephone, or "subscriber unit", uses the associated timing information to perform functions such as page message verification and driving communications.

The search engine of the? 177 typically works in communication with a set of digital elements and the decoder placed in a single integrated circuit. Together, the components perform the necessary processing for CDMA communications and page verification. For example, to receive a CDMA signal, the search engine looks for a pilot channel with several deviations in time. Once the pilot is detected, the digital elements are activated to process an associated data channel, such as a paging channel or a traffic channel. To perform the search and signal processing, the searcher and the digital elements receive samples generated in response to RF signals received by the subscriber unit. The samples are typically generated by an RF / IF unit within the mobile telephone or subscriber unit. In general, it is desirable to reduce the power consumption of a subscriber unit to reduce the size and weight of the battery. Additionally, it is desirable to increase the reliability with which the page and other messages are received and processed by the subscriber unit. Up to this point, as well as other objectives, that the present invention is directed.

BRIEF DESCRIPTION OF THE INVENTION The present invention is a novel method and • improved for paging. In one embodiment of the invention, a search engine is used to detect extended spectrum signals. The samples of received RF signals are stored in a sample buffer. During the standby mode, samples are collected during paging intervals assigned to the mobile. A set of searches is carried out on the samples, and if pilot signals are detected, an additional demodulation is performed to detect paging messages. The resulting set of demodulation data can be combined to increase detection. After a page message has been detected, additional demodulation resources can be activated to process more completely the • page messages, or other information channels. In one embodiment of the invention, the search engine includes a demodulator to effect a rapid detection of the page without the use of digital elements to reduce energy consumption in free mode.

BRIEF DESCRIPTION OF THE DRAWINGS The features, objects and advantages of the present invention will become more apparent from the detailed description set forth below, when taken in conjunction with the drawings in which the similar reference characters are identified in a manner corresponding to it and where: FIGURE 1 is a cellular telephone system configured in accordance with one embodiment of the invention; FIGURE 2 is a block diagram of a subscriber unit configured in accordance with an embodiment of the invention; FIGURE 3 is a flow diagram illustrating the processing performed within a subscriber unit when performed in accordance with an embodiment of the invention; FIGURE 4 is a block diagram of a search when configured in accordance with one embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES A novel and improved method and apparatus for detecting paging messages is described. The exemplary embodiment described herein is set forth in the context of the digital cellular telephone system. Although use within this context is advantageous, different embodiments of the invention may be incorporated in different environments or configurations. In general, the different systems described herein can be formed using processors controlled by programs and programming systems, integrated circuits or discrete logic, however, implementation in an integrated circuit is preferred. The data, instructions, commands, information, signals, symbols and integrated chips that can be referenced through the application are advantageously represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or a combination of them. In addition, the blocks shown in each block diagram can represent steps of the physical components of computation or of the method. 'Figure 1 is a highly simplified block diagram of a cellular telephone system configured in accordance with the use of the present invention. The mobile telephones and other communication systems (subscriber units 10) are located between the base stations 12, which are coupled to the base station controller (BSC) 14. The mobile switching center MSC 16 connects the BSC 14 to the public switched telephone network (PSTN) 18. During the operation, some mobile telephones conduct telephone calls interconnecting with base stations 12 while others are free, or on mobile waiting, where they verify page messages. According to the use of some CDMA communication protocols, a subscriber unit 10 can be simultaneously interconnected with two base stations 12 in soft or imperceptible transfer. A system and method for operating a cell phone using CDMA techniques is described in U.S. Patent 5,103,459 entitled "System and Method for Generating Signal Waveforms in a CDMA Cell Phone System" granted to the beneficiary of the present invention and incorporated herein. as reference (patent 59). The system of the patent 59 is configured substantially in accordance with the use of the IS-95 over the interface standard or aerial interconnection. Additionally, in one embodiment of the invention, the paging of a subscriber unit 10 is effected substantially in accordance with the substantial method described in the US patent applications serial numbers 08/865, 650, and 08 / 890,355 both titled "Split Double Channel Paging" granted to the beneficiary of the present invention and incorporated herein as a reference (the applications of dual channel pages). In those patent applications, the use of a fast paging message (quick page) transmitted over a reduced coding channel is described. One or more quick pages are transmitted before the full page message (full page) to allow a subscriber unit to reduce the verification time of the page, and therefore reduce the standby power consumption. If the subscriber unit does not receive a positive fast page, then it does not verify the entire page thereby reducing the power consumption in the free mode. Figure 2 is a block diagram of a demodulator used to process CDMA signals according to one embodiment of the invention. The received samples (Rx) are generated by the RF / IF system 190 and the system of the antenna 192, which receives RF signals, filters, down-converts and digitizes the RF signals to the baseband. The samples are supplied to the mux 202 and the sample RAM 204. The mux output 202 is supplied to the searching unit 206 and the digital elements 208, which are coupled to the control unit 210. The combiner 212 couples the decoder 214 to digital elements 208. Typically, control unit 210 is a microprocessor controlled by programs and programming systems and can be located in the same integrated circuit or in a separate integrated circuit.

During the operation, the samples received (samples) are stored in the sample RAM 200 and applied to the mux 202. The mux 202 supplies real-time samples or samples stored to the searching unit 206 and the digital elements 208. The control unit 210 configures the digital elements 208 to effect the demodulation at different time deviations based on the results of the searching unit 208. The demodulation results are combined and passed to the decoder 214, which produces the data. In general, the search carried out by the search engine 208 uses a non-coherent modulation of the pilot channel to test the hypothesis of timing corresponding to several sectors, base stations and multiple paths, while the demodulation carried out by the digital elements 208 is carried out via the coherent demodulation of the data channel. The non-coherent demodulation does not require information from the carrier phase, but detects signal energy more than the data contained in the signal (for a certain type of waveform). The coherent demodulation requires phase information, and therefore more information of the signal, but the data transmitted on the signal can be determined. Through this request, the term demodulation only refers to coherent demodulation, while the search refers to non-coherent demodulation. In one embodiment of the invention, the concentration is carried out by multiplying the samples received with the complex conjugate of the PN sequence and the Walsh function assigned in a single timing hypothesis and digitally filtering the resulting samples, often with an integrated circuit and accumulator of download. In one embodiment of the invention, an improved searcher is provided that performs both the search of the pilot channel and the demodulation of a paging channel on the samples stored in the sample RAM. The demodulation and search can be performed at several time deviations, and the demodulation results are combined to determine if a page message was received. Preferably, the page channel demodulated by the search engine is similar to the fast paging channel described in the dual channel paging applications referenced above. When the message duration is small for quick paging (128 or 256 integrated microcircuits PN to 1.2288 Mcps is 104 or 208 microseconds) and the necessary deviation is small, (approximately 100-400 microseconds) the required samples received can be easily placed in the buffer and processed "offline" to save energy. Figure 3 is a flow chart illustrating the operation of the demodulator of Figure 2 during free mode according to an embodiment of the invention. Free mode is the state where the subscriber unit is on but not making a call. During free mode the subscriber unit verifies by paging messages addressed to it. The paging message can indicate a communication or incoming telephone call. As noted above, the invention is described in the context of a two-size communication system as described in two-channel paging applications. In step 300, the subscriber unit collects and stores the samples received in step 302 during the rapid paging interval assigned to it. In one embodiment, collection is effected by activating the RF / IF unit 190, storing the samples in the sample RAM, and then deactivating the RF / IF system 190. Typically the subscriber unit collects samples for a longer duration than the a single rapid paging interval so that multiple time deviation signals are stored within the set of received samples.

In step 304 the search unit 206 (of Figure 2) performs the search of the pilot on the samples stored at various time deviations. Additionally, the search of the pilot can be done for different signals. For example, the search may be performed for signals from different base stations that use different, or differently deviated pilot codes. When a local maximum is detected above a certain threshold, and the combined function is allowed for the particular search window, the resulting hypothesis is demodulated and combined. Once all the hypotheses in the search list have been completed, the step is performed. In one embodiment of the invention, it is preferable to have a sample RAM 302 large enough to cover the time deviation of a set of multi-path signals. In this way, by simply looking for the same set of samples at different deviations, different pilots are detected. Similarly, the same set of samples can be demodulated at different deviations to process fast pages. Although a fast page channel designated for coherent signaling provides better performance and is therefore preferred in many cases. A rapid paging system can be designed for non-coherent signaling as well. • In step 306 the search engine 206 is changed to the demodulation mode, and the associated paging channel 5 with each signal detected during the search mode is demodulated to determine whether a fast page has been received. The fast pages are processed by performing the coherent demodulation on the set of paging channels that correspond to the set of • 10 pilot channels detected during the search. Thus, in one embodiment of the invention, the fast page channel is demodulated with the search engine after the search has been carried out. Each demodulation is made to a particular deviation within the samples, and the resulting set of flexible decision data of demodulation is combined in a diverse way using • an accumulator within the searcher 206. In step 308 the combined demodulation data is examined to determine if it has been received a positive fast page (ie an indication that the next full page message may be directed to this subscriber unit 10). If not, the subscriber unit returns to step 300. If so, the digital elements 208, the decoder 214 and the unit RF / IF 190 are activated in step 310, and the entire page is processed in step 312. In an alternative embodiment of the invention, the subscriber unit continues to search • samples by other pilots to find new signals to process when the next 5 paging interval occurs. Additionally, if the fast paging channel was not received with sufficient quality, then step 310 is performed in some way to ensure that the full page message is not lost. fc Carrying out both the search and the Fast page processing within searcher unit 206, the fast paging channel can be verified without having to activate the digital elements until a positive fast page is received. In general, most of the page messages will be negative, indicating that there are no pending calls or messages. In this way, the time in which the digital elements 208 and other circuits are activated is significantly reduced. Therefore, the reduction of the circuits used to carry out the verification of the fast page channel increases the waiting time of the subscriber unit 10. This reduction in the circuits is achieved by taking advantage of the reduced coding level of the quick verification channel and the page message fast and storing the samples received for processing. This reduced coding allows the demodulation of the fast paging channel to be effected • with a limited amount of demodulation functionality, and therefore with additional complexity 5 limited in the search engine. Also, the use of the sample RAM 204 allows multiple time demodulation to be performed using a single demodulation machine within the search engine 206, which also reduces the circuits necessary to verify messages of paging. Additional energy savings are obtained by searching and checking the page channel using stored samples. In one mode, the fast paging channel is a bit of BSPK or OOK not encoded sent once or twice. In particular, the time in which the RF / IF unit 190 operates during each ^ page c is reduced by storing the samples when they are generated. Once the samples are stored, the subscriber unit deactivates the unit RF / IF to conserve energy, and searches for samples repeatedly at different deviations or different pilot signals, or both, using only the digital circuit. As noted earlier, effect different searches on the same samples allows the RF unit to turn off once the initial set of samples has been collected. The interruption of the RF unit reduces the power consumption of the mobile during free mode. In contrast, if the samples were not stored, additional samples would have to be collected for longer than necessary to search for the different pilot signals and time deviations. This continuous repair of pilot data would require that the RF unit remain on, and therefore consume energy, for a longer period of time, which would reduce the waiting time of the subscriber unit 10. The embodiment of the invention described provides operational improvements as well as an energy consumption in the improved free mode. In particular, by performing the demodulation and searching on the same set of samples, the demodulation operation improves. This is because the best signals measured by the search of the pilot channel are the best signals for the demodulation of the paging channel because the set of samples is the same. In alternative systems, the search is performed in a first set of samples and the results of that search are used to determine how to demodulate paging channels in a second set of samples.

Although the correspondence between the search results and the paging channel quality is • Typically reasonable if the time interval between the two events is small, any difference of the channel between the search and the demodulation is virtually eliminated when compared to the de-correlation time of the fading channel leading the search and demodulation on the same samples. Figure 4 is a block diagram of the • 10 searcher 206 when configured according to one embodiment of the invention. The phase samples and the quadrature phase are read from a RAM of samples 302 (Figure 2) and concentrated by the QPSK 402 concentrator using a PN code of the PN 404 code generator where the PN code is compared from a portion in phase (PNI) and a portion in quadrature phase (PNQ). The in-phase and quadrature-phase components resulting from the QPSK 402 concentrator are applied to the multipliers 406 a-d. Processing after the RAM of samples can occur at arbitrary clock frequencies, such as 19 MHz unrelated to the original microcircuit rate. During the search mode, the Walsh code generators 408 and 410 generate the Walsh code of the pilot channel which is applied to multipliers 406a-406d. The multipliers 406a-406d and the ^ * 408a-408d accumulators operate together to discover the concentrated samples as Walsh code pilot pilot Walsh code generator 408. The 5 QPSK concentrator and the Walsh multiplication can occur in order, or be integrated as a single operation for results equivalents The uncovered pilot samples of the 408a and 408d accumulators are applied to the multipliers 420 and 422 twice: once directly, once via the multiplexers 422. The result is that the discovered pilot samples are square, and the square outputs are summed by the adder 412. In this way, the search mode, he product point of the discovered pilot data is calculated, and therefore the correlation energy of the pilot channel to the current deviation. Similarly, the discovered pilot samples of the accumulators 408c and 408d are applied to square circuits 410 the outputs of which are summed by the adder 412. Thus, the square circuits 410 and 412 act to calculate the product point of the pilot data discovered with themselves, and therefore the correlation energy of the pilot channel in the current deviation. l The point products of the adders 412 and 422 are received by the local maximum calculator 414. The local maximum calculator 414 determines the deviation or most probable deviations, from a set of deviations (or hypotheses) attempted by the search engine based on the energy of correlation. For example, the local maximum calculator 414 can save more local energy in a set of oversampled correlation energies to isolate the sample closest to the true deviation. The multipliers 406a and 406b and the accumulators 408a and 408b operate together to discover the samples with the Walsh code of fast paging of the fast page Walsh generator. The set of deviations is generated when the timing of the PN and Walsh codes are adjusted in relation to the samples. In an exemplary search, the PN and Walsh codes are adjusted in small increments around particular search regions. Typically, the code generators are configured by a control system which also defines the search regions with an initial deviation and a final deviation. The control system may be a microprocessor or a digital signal processor controlled by programs and programming systems stored in memory.

The N-max 416 follower collects the set of N largest correlation energies for the different search regions. N is a whole number, preferably in the range of 4 to 16. The use of other criteria for collecting search results, such as the diversity of signal sources, is consistent with the use of the invention. The resulting set of correlation energies and associated deviations (search results) is reported to the control system. In the exemplary embodiment of the invention, once the search operation has been carried out, the control system configures the search engine to effect the demodulation on the paging channel by a set of signals and deviations based on the search results. . To effect the demodulation of the page channel (preferably the fast page channel), the Walsh generator 410 is configured to generate the Walsh code of the paging channel, and the multiplexers 423 are configured to apply the output of the accumulators. 408c and 408d to the multipliers 420. Additionally, the accumulators 408a and 408b are configured to integrate exactly over the bit duration.

For each signal to be demodulated, the control system configures the PN generator and the Walsh generators to the particular deviation, and the samples are demodulated again. The uncovered samples of the fast paging channel of the accumulators 408a and 408b are applied to the multipliers 420. Additionally, the uncovered samples of the pilot channel are applied to the multipliers 420 via the muxes 423. To effect the product point of the pilot and the data of paging, the outputs of the multipliers 420 are summed by the adder 422, and the flexible decision data of the resulting projected fast paging channel are received by the retention circuits 424. Various other methods for adjusting the carrier phase will be evident, including the use of a cross product operation or other methods of phase rotation. The point product recovers the data that are in phase with the pilots and weights for the combination. The output of the holding circuits 424 is then received by the combiner accumulator 426, for each demodulated signal, the accumulator 426 is added to the results of the demodulation. Once the set of signals are demodulated, the combined fast page data is sent to the control system, which estimates the transmitted data by making a rigorous decision based on the flexible decision data • accumulated. Based on the rigorous decision, it is determined if a quick page has been sent. Additionally, in one embodiment of the invention, the energy of the discovered pilot channel data is calculated again by performing a dot product operation, and the resulting pilot energy is accumulated for each signal by the accumulator 426. Cumulative pilot energy is sent to the control system. In one embodiment of the invention, the control system determines whether the fast paging data is reliable based on the accumulated pilot energy. If the cumulative pilot power is above a certain threshold, then the results of the fast paging channel are reliable. Otherwise, then the next fast page interval is processed, or the full page channel is processed. As noted above, the use of the same samples to process the pilot and paging channels ensures that the channel is the same for both processing, which improves the demodulation performance. In this way, a system has been described and a method for performing page verification. The above description of the preferred embodiments is provided to enable any person skilled in the art to make use of the present invention. The various modifications to those modalities will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other modalities without the use of an inventive faculty. In this way, the present invention is not intended to be limited to the modalities shown herein but according to the broadest scope consistent with the principles and novel features described herein. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (11)

1. CLAIMS Having described the invention as above, the content of the following claims is claimed as property. A method for receiving a page, characterized in that it comprises the steps of: (a) storing first received samples; (b) searching for the first samples received from pilot channels to produce the set of pilot channels detected; (c) demodulating the first received samples to detect a fast paging message based on the set of detected pilot channels; (d) generating second samples received when the fast page message is detected; (e) demodulating the second samples received to detect a second paging channel.
2. 2. The method according to claim 1, characterized in that it also comprises searching on a list of pilot channels of potentially neighboring base stations.
3. The method according to claim 1, characterized in that it further comprises the step of activating a demodulation element to demodulate the second samples received.
4. 4. The method according to claim 3, characterized in that it also comprises the step of activating an RF unit to generate the second samples received.
5. The method according to claim 4, characterized in that it further comprises the step of deactivating the RF unit after the first received samples are stored.
6. 6. A method for receiving pages, characterized in that it comprises the steps of: storing first received samples; detecting a correlation energy of a pilot channel and demodulating a first paging channel within the first received samples; and demodulating a second paging channel within other received samples.
7. The method according to claim 6, characterized in that it further comprises the step of decoding flexible decision data to the second paging channel.
8. 8. The method according to claim 6, characterized in that it also comprises the step of generating the received samples.
9. 9. The method according to claim 6, characterized in that it also comprises the steps of: activating the search engine during fast page 5 intervals; activate the demodulation unit during the full paging interval when a quick page message is received. i
10. 10. A search method via the test of the 10 energy of the correlator between the received samples and a set of hypotheses of the pilot PN code.
11. 11. A method for performing page message reception verification, characterized in that it comprises the steps of: concentrating the pilot channel by detected pilots to produce a set of detected signals; concentrating a set of first paging channels that correspond to the set of signals 20 produced in the concentrated data; project the concentrated data on the concentrated pilot data that produce a data set of demodulator paging channel; and combine.