WO2002001837A2

WO2002001837A2 - Scan wait mode based on received signal strength

Info

Publication number: WO2002001837A2
Application number: PCT/US2001/020429
Authority: WO
Inventors: Alan Varghese
Original assignee: Matsushita Mobile Communication Development Corporation Of U.S.A.
Priority date: 2000-06-27
Filing date: 2001-06-27
Publication date: 2002-01-03
Also published as: AU2001271519A1; WO2002001837A3

Abstract

A method for implementing a user configurable scan wait mode based on RSSI levels. A RF signal from a cellular control channel is detected using a scan algorithm and inputed into a terminal of the RF detector. The received signal strength of the control channel signal is measured. The received signal strength of the control channel is compared to a minimum value. When the received signal strength is below the minimum value, a scan wait timer is activated to discontinue control channel scans for a period of time. After the period of time, the scan algorithm searches for control channel signals. The received signal strength of the control channels is compared to a minimum value. When the measured RF is below the minimum value after this second scan, the user may be prompted to configure the cellular telephone to discontinue scans. The user can configure the scan wait timer to disable continuous control channel scans.

Description

SCAN WAIT MODE BASED ON RECEIVED SIGNAL STRENGTH

FIELD OF INVENTION

This invention relates generally to cellular telephone power save modes and, more specifically, to cellular telephones that are capable of scan wait operation. This invention also relates to user configurable control of base station control channel scans.

BACKGROUND OF THE INVENTION

As cellular telephones have grown in popularity, there has been public demand for mobile units that are smaller and lighter and last longer on a single battery charge. A key to the design of smaller and lighter cellular telephones is the miniaturization of the rechargeable batteries these devices typically use. One design goal for cellular telephones is minimization of power consumption necessary for standby operation. A reason for this is to permit the use of physically smaller and lighter batteries. Cellular telephones must always be powered on to make or receive calls. In order to receive a call, a cellular telephone must be locked on to a control channel with sufficient signal strength to allow the cellular telephone to either receive a page or place a call. To accomplish this, cellular telephones are required to periodically scan for base station control channels. During this scanning process, the cellular telephone is in an idle or standby mode. Also, as a cellular telephone is transported from one location to another, the cellular telephone needs to scan the available control channels within its current region to ensure that it locks on to a strong channel. In addition, within the coverage area of a cellular system, some areas may have limited coverage. As a result, cellular telephones drain power when they are not in use to actually make or receive calls. Building interiors, stores, parking garages and airports may have limited or no coverage making it difficult to make or receive cellular transmissions from these places. Therefore, a cellular telephone within such areas may have to constantly scan for control channels. In performing a control channel scan, the receiver of the cellular telephone must be powered on. If the cellular telephone cannot lock on to a control channel, this may result in a drain on the battery power. Thus, there is demand for a more efficient way to utilize battery power during times when a cellular telephone cannot lock onto a control channel.

In most cases, cellular telephones are designed to scan continuously for suitable control channels. Users keep track of the received signal strength by reading a digital RSSI representation on the cellular telephone liquid crystal display (LCD). RSSI readings inform the user of the received signal strength at a given location. Users are able to decide, given this information, whether a call can be completed. Various methods have been utilized to limit the consumption of battery power for cellular telephones in idle or standby modes. One method employs an extended standby (XSTBY) or discontinuous receiving mode which conserves battery power by shutting down radio frequency, baseband signaling or controller units used for the reception of paging channels based on comparisons between reception related criteria and preset minimum acceptable values. The message error rate (MER) or a combination of MER and RSSI can be used as reception related criteria. An example of this method is described in U.S. Pat. No. 5,471,655 to Kivari et al. One disadvantage of this method is that it is only useful for saving battery power when the cellular telephone is configured only to receive pages or network information rather than when the telephone is configured to scan for access channels. Another disadvantage is that control channel scanning will continue to make demands on battery power.

A second method utilizes call location and time history to extrapolate when and where a user is likely to make or receive calls. This method enables cellular telephones to save battery power by going into a standby mode when users are not likely to make or receive calls. This method also reduces scanning on power up by matching call locations to previously used control channels. An example of this method is described in U.S. Pat. No. 5,799,256 to Pombo at al. A disadvantage of this method is that the cellular telephone will continue to scan for control channels in locations where making or receiving a call is impossible.

A third method utilizes an algorithm which divides standby time into scanning and sleep modes. This method utilizes different sleep mode levels to allow the cellular telephone to enter scanning mode intermittently. The longer the cellular telephone is in standby mode, the longer the time intervals between scanning modes will become. This function is supposed to enhance power savings by reducing the scan rate when the cellular telephone is not used for a long period of time. A disadvantage of this method is that a cellular telephone may not be in standby mode for a long time when a user first enters an area without service. In such cases, the cellular telephone will continue to scan for control channels at a frequent rate when there is no probability of finding a suitable channel.

Thus, there is a need in the art for an improved method for reducing battery power consumption when a user enters a no service area and there is no possibility of finding a suitable control channel for making or receiving a call. There is also a need in the art for a user configurable method for reducing battery power consumption based on RSSI readings in a particular location.

SUMMARY OF THE INVENTION

The present invention overcomes the above-described problems in the prior art by providing a user interface that displays RSSI measurements and employs a scan wait mode that reduces battery power consumption.

Generally described, the present invention provides a circuit for measuring RSSI values that may be used to activate a scan wait timer. A minimum RSSI value is used as a threshold to determine whether the signal strength of a control channel is sufficient. When the signal strength falls below the minimum, scans can be suspended for a variable amount of time.

The present invention overcomes the problems of the prior art by utilizing a cellular telephone, or mobile station, that is operable on well known and future cellular telephone systems and signaling protocols. Control channel "beacons" from a base station to a cellular telephone are transferred via Radio Frequency (RF) control channels. The cellular telephone receiver can cease control channel scans and enter a scan wait mode based on RSSI readings according to this invention. During the scan wait mode, RSSI scans for control channel strength are switched off until the user reactivates the scan or until the user configurable time interval expires.

One aspect of the present invention includes a circuit for measuring RSSI values received from a base station. The reception of such values is well known in the art by one of ordinary skill. In this case, the circuit scans for base station control channels using a scan algorithm.

Another aspect of the present invention includes a method for using the maximum measured RSSI value to determine whether adequate service quality is available. This method includes the steps of measuring the maximum RSSI value over a preset period of time using the scan algorithm and comparing the maximum RSSI value with a predetermined minimum value necessary for cellular reception and/or transmission.

Another aspect of the present invention is a method for activating a scan wait timer and, if the maximum RSSI levels are below a minimum value, to hold further control channel scans for a preset time interval.

Yet, another aspect of the present invention is a method for determining whether an insufficient RSSI level is obtained from a second scan after holding for a preset time interval after a first scan, and by saving the two strongest control channel numbers into the cellular telephone's memory. In one embodiment of the present invention, an LCD indicator or a voice memo message will inform the user that no service is available and will give the option of holding further scans unless prompted by the user to continue. Thus, when prompted by the user, the RSSI levels of the two strongest control channels will be measured. When the maximum measured RSSI values fail to meet minimum signal requirements, a partial or wide band scan will be initiated.

In another embodiment of the present invention, an LCD indicator or voice memo message will inform the user that no service is available and will give the user an option to go to a low power mode or continue scanning for control channels. When the user selects low power mode, the user will be prompted to enter a scan wait time. The scan wait timer will suspend control channel scans for the scan wait time entered by the user. Objects, features and advantages of the present invention will become apparent upon reading the following detailed description of the preferred embodiments of the invention, when taken in conjunction with the accompanying drawings and appended claims.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 is a system diagram that illustrates an exemplary environment suitable for implementing various embodiments of the present invention.

Fig. 2 is a flow diagram illustrating the operation of an exemplary embodiment of the present invention.

Fig. 3 is a flow diagram illustrating the operation of an alternative exemplary embodiment of the present invention. Fig. 4 is a flow diagram illustrating the operation of an alternative exemplary embodiment of the present invention.

DETAILED DESCRIPTION

Referring now in detail to the drawings in which like numerals refer to like parts throughout the several views, Fig. 1 is a system diagram that illustrates an exemplary environment suitable for implementing various embodiments of the present invention.

Fig. 1 and the following discussion provide a general overview of a platform onto which the invention may be integrated or implemented. Although in the context of the exemplary environment the invention will be described as consisting of instructions within a software program being executed by a processing unit, those skilled in the art will understand that portions of the invention, or the entire invention itself may also be implemented by using hardware components, state machines, or a combination of any of these techniques. In addition, a software program implementing an embodiment of the invention may run as a stand-alone program or as a software module, routine, or function call, operating in conjunction with an operating system, another program, system call, interrupt routine, library routine, or the like. The term "program module" will be used to refer to software programs, routines, functions, macros, data, data structures, or any set of machine readable instructions or object code, or software instructions that can be compiled into such, and executed by a processing unit. Those skilled in the art will appreciate that the system illustrated in Fig. 1 may take on many forms and may be directed towards performing a variety of functions. Examples of such forms and functions include cellular telephones, radio telephones, portable telephones, two-way pagers, personal computers, hand-held devices such a personal data assistants and calculators, consumer electronics, note-book computers, lap-top computers, and a variety of other applications, each of which may serve as an exemplary environment for embodiments of the present invention.

The exemplary system illustrated in Fig. 1 includes a computing device 110 that is made up of various components including, but not limited to a processing unit 112, non-volatile memory 114, volatile memory 116, and a system bus 118 that couples the non- volatile memory 114 and volatile memory 116 to the processing unit 112. The non- volatile memory 114 may include a variety of memory types including, but not limited to, read only memory (ROM), electronically erasable read only memory (EEROM), electronically erasable and programmable read only memory (EEPROM), electronically programmable read only memory

(EPROM), electronically alterable read only memory (EAROM), FLASH memory, bubble memory, and battery backed random access memory (RAM). The non-volatile memory 114 provides storage for power on and reset routines (bootstrap routines) that are invoked upon applying power or resetting the computing device 110. In some configurations the non- volatile memory 114 provides the basic input/output system (BIOS) routines that are utilized to perform the transfer of information between elements within the various components of the computing device 110. The volatile memory 116 may include, but is not limited to, a variety of memory types and devices including, but not limited to, random access memory (RAM), dynamic random access memory (DRAM), FLASH memory, EEPROM, bubble memory, registers, or the like. The volatile memory 116 provides temporary storage for routines, modules, functions, macros, data etc. that are being or may be executed by, or are being accessed or modified by the processing unit 112. In general, the distinction between non- volatile memory 114 and volatile memory 116 is that when power is removed from the computing device 110 and then reapplied, the contents of the nonvolatile memory 114 remain in tact, whereas the contents of the volatile memory 116 are lost, corrupted, or erased.

The computing device 110 may access one or more external display devices 130 such as a CRT monitor, LCD panel, LED panel, electro-luminescent panel, or other display device, for the purpose of providing information or computing results to a user. In some embodiments, the the external display device 130 may actually be incorporated into the product itself. The processing unit 112 interfaces to each display device 130 through a video interface 120 coupled to the processing unit 110 over the system bus 118.

The computing device 110 may send output information, in addition to the display 130, to one or more output devices 132 such as a speaker, modem, printer, plotter, facsimile machine, RF or infrared transmitter, computer or any other of a variety of devices that can be controlled by the computing device 110. The processing unit 112 interfaces to each output device 132 through an output interface 122 coupled to the processing unit 112 over the system bus 118. The output interface may include one or more of a variety of interfaces, including but not limited to, an RS-232 serial port interface or other serial port interface, a parallel port interface, a universal serial bus (USB), an optical interface such as infrared or IRDA, an RF or wireless interface such as Bluetooth, or other interface.

The computing device 110 may receive input or commands from one or more input devices 134 such as a keyboard, pointing device, mouse, modem, RF or infrared receiver, microphone, joystick, track ball, light pen, game pad, scanner, camera, computer or the like. The processing unit 112 interfaces to each input device 134 through an input interface 124 coupled to the processing unit 112 over the system bus 118. The input interface may include one or more of a variety of interfaces, including but not limited to, an RS-232 serial port interface or other serial port interface, a parallel port interface, a universal serial bus (USB), an optical interface such as infrared or IrDA, an RF or wireless interface such as Bluetooth, or other interface.

It will be appreciated that program modules implementing various embodiments of the present invention may be may be stored in the non-volatile memory 114, the volatile memory 116, or in a remote memory storage device accessible through the output interface 122 and the input interface 124. The program modules may include an operating system, application programs, other program modules, and program data. The processing unit 112 may access various portions of the program modules in response to the various instructions contained therein, as well as under the direction of events occurring or being received over the input interface 124. The computing device 110 may transmit signals to, or receive signals from, one or more communications systems 136 such as a cellular network, RF network, computer network, cable network, optical network or the like. The processing unit 112 interfaces to each communications system 136 through a transmitter 126 and a receiver 128, both coupled to the processing unit 112 over the system bus 118. The transmitter 126 and the receiver 128 may include one or more of a variety of transmission techniques such as a radio frequency interface (AM, FM, PSK, QPSK, TDMA, CDMA,

Bluetooth or other technique) or an optical interface such as infrared or IrDA.

As will be described more completely below, the Received Signal Strength Indicator (RSSI) generator 140 provides a measurement of the signal strength of the incoming radio frequency signals and is coupled to the processing unit 112 over the system bus 118. A strong RSSI reading is indicative of a desired service quality area. By comparing RSSI readings with a reference signal strength necessary for service, the processing unit 112 can determine whether service is currently available.

Fig. 2 is a flow diagram illustrating the operation of an exemplary embodiment of the present invention. When a cellular telephone is switched on, it begins a radio frequency scan for control channels at step 202. The scan for control channels 202 is conducted by an RF detector (not shown) using a scan algorithm that is well understood by those skilled in the art.

The RSSI generator 140 measures the incoming signals using standard methods known to those skilled in the art. The RSSI measurement of incoming control channel signals over a predetermined scan time are compared 204 to a minimum threshold value needed for cellular service. This value can be, for example, between -110 and -120 dBm. If any of the measured RSSI values are greater than the predetermined minimum threshold RSSI value, then the cellular telephone is locked onto a control channel with service quality data 206. If none of the measured RSSI values are above the minimum threshold RSSI value then it will be determined whether the scan was the first control channel scan 208. This determination can be done inside the processing unit 112 or by using a counter circuit. If the control channel scan was the first conducted, then further scans will be held for a predetermined time 210 (five seconds, for example) before the scanning for control channels begins again.

After the predetermined time has lapsed, a second scan will be performed 202. If the measured RSSI is still below the minimum threshold RSSI value after the second scan, then the two highest RSSI control channel numbers will be saved into memory 212.

Fig. 3 is a flow diagram illustrating the operation of an alternative exemplary embodiment of the present invention. In this embodiment, after two unsuccessful control channel scans, the cellular telephone will alert the user 302 through the display 130, that service is not available in the user's current geographic location. For example, the message could state, "CURRENTLY IN LOW SIGNAL AREA, PHONE CANNOT MAKE OR RECEIVE CALLS. PRESS ANY KEY WHEN LEAVING LOW SIGNAL AREA." As an alternative to displaying this message, the cellular telephone could provide a voice memo informing the user that service is not available in the user's geographic location. The cellular telephone will shut down various predetermined elements and hold in this standby mode 304 until the user provides an input. The received signal strength of the two stored control channel frequencies will be measured as the most likely candidates for a service quality signal. The process of tuning to the control channels and measuring the RSSI can be accomplished about 2 msec for each channel. So for two control channels, it should take about 4 msec. Thus, this can be accomplished without being noticed by the user. If the two most likely candidates don't meet the minimum threshold RSSI value requirements, the cellular telephone will either perform a partial scan or a wide-band scan 308 for service quality control channels. Methods of conducting these types of scans are well known to those of ordinary skill in the art. A partial or wide-band scan should take about the same amount of time as the power-up scan, so the user should not mind or notice.

Fig. 4 is a flow diagram illustrating the operation of an alternative exemplary embodiment of the present invention. In this embodiment, the scan wait mode is a user configurable feature. After two unsuccessful control channel scans, the cellular telephone will display a message 402 through the display 130. The message will alert the user that service is not available in the user's current geographic location. For example, the message could state, "CURRENTLY IN LOW SIGNAL AREA, PHONE CANNOT MAKE OR RECEIVE CALLS. TO SAVE BATTERY POWER, YOU CAN PUT THE PHONE IN LOW POWER MODE. TO DO THIS, PLEASE PRESS 1." As an alternative to displaying this message, the cellular telephone could give a voice memo informing the user that service is not available in the user's geographic location, please press "1" for low power mode. Another way to do this is to use voice recognition instead of key presses. The user would answer "YES" or "NO" instead of pressing keys.

If the user presses "1" 404, the display 130 will prompt the user, either by a LCD message, voice memo or otherwise to "ENTER THE APPROX TIME IN MINUTES THAT YOU WILL BE IN THIS LOW SIGNAL AREA" 406. In an alternate embodiment, a default value or a value pre-selected by the user may be activated without use interaction. The scan wait timer will be initialized with the user entered value of minutes and will disallow further scans until the end of the user configurable period 408. In certain embodiments, additional power savings can be realized when low power mode is activated by switching all possible components of the cellular telephone to sleep or lower power order.

While this invention has been described in detail with particular reference to preferred embodiments thereof, it will be understood that variations and modifications can be effected within the scope of the invention as defined in the appended claims.

Claims

CLAIMSWhat is claimed is:

1. A method for implementing a scan wait mode for discontinuous control channel scans, comprising the steps of: measuring the received signal strength of a plurality of control channels; comparing the received signal strength of each of the plurality of control channels to a minimum threshold RSSI value; if the received signal strength of a threshold number of the plurality of control channels is below the minimum threshold RSSI value, disabling further measuring of the received signal strength of the plurality of control channels for a scan wait time.

2. The method of claim 1, wherein the threshold number includes the number of the plurality of control channels and the disabling further measuring step further comprises the step of reducing power supplied to a receiver circuit used for measuring the received signal strength.

3. The method of claim 1 further comprising the step of providing a low-signal indicator, the low-signal indicator identifying that further measuring has been disabled.

4. A method for implementing a scan wait mode for discontinuous control channel scans, comprising the steps of: measuring the received signal strength of a plurality of control channels; if the received signal strength of a threshold number of the plurality of control channels is below the minimum threshold RSSI value, re-measuring the received signal strength of each of the plurality of control channels; comparing the received signal strength of each of the plurality of control channels to a minimum threshold RSSI value; if the received signal strength of a threshold number of the plurality of control channels is below the minimum threshold RSSI value, disabling further measuring of the received signal strength of the plurality of control channels for a scan wait time.

5. The method of claim 4, wherein the threshold number includes the number of the plurality of control channels and the disabling further measuring step further comprises the step of reducing power supplied to a receiver circuit used for measuring the received signal strength.

6. The method of claim 4 further comprising the step of providing a "low-signal indicator", the low-signal indicator identifying that further measuring has been disabled.

7. A radio telephone comprising: a receiver; a controller; a memory device coupled to the controller and containing a scan program; a received signal strength detector coupled to the receiver and the controller; and a battery for supplying power to the receiver, the controller and the received signal strength detector; the controller, in response to instructions contained in the scan program, being operative to: (a) tune the receiver to a plurality of control channels;

(b) for each of the plurality of control channels, read the received signal strength of the control channel from the received signal strength detector; (c) compare the read received signal strength for each of the plurality of control channels to a minimum threshold RSSI value; and

(d) if the read received signal strength for a threshold number of the plurality of control channels is below the minimum threshold RSSI value, delay from tuning the receiver to any of the plurality of control channels for a scan wait time.

8. The method of claim 7 where the scan wait time is a predetermined time period.

9. The radio telephone of claim 7 further comprising: a keypad that is electrically coupled to the controller, and the controller is further operative to receive an input signal from the keypad, the input signal identifying a period of time for the scan wait time.

10. The radio telephone of claim 7, further comprising a keypad that is electronically coupled to the controller, and wherein the scan wait time can be defined by actuating the keypad independent from the scanning process performed by the controller.

11. A radio telephone comprising: a receiver; a controller; a memory device coupled to the controller and containing a scan program; a received signal strength detector coupled to the receiver and the controller; and a battery for supplying power to the receiver, the controller and the received signal strength detector; the controller, in response to instructions contained in the scan program, being operative to:

(a) tune the receiver to a plurality of control channels;

(b) for each of the plurality of control channels, read the received signal strength of the control channel from the received signal strength detector;

(c) compare the read received signal strength for each of the plurality of control channels to a minimum threshold RSSI value;

(d) if the read received signal strength for a threshold number of the plurality of control channels is below the minimum threshold RSSI value, tune the receiver to a plurality of control channels;

(e) for each of the plurality of control channels, read the received signal strength of the control channel from the received signal strength detector;

(f) compare the read received signal strength for each of the plurality of control channels to a minimum threshold RSSI value; and (g) if the read received signal strength for a threshold number of the plurality of control channels is below the minimum threshold RSSI value, delay from tuning the receiver to any of the plurality of control channels for a scan wait time.

12. The method of claim 11 where the scan wait time is a predetermined time period.

13. The radio telephone of claim 11 further comprising a keypad that is electrically coupled to the controller, and the controller is further operative to receive an input signal from the keypad, the input signal identifying a period of time for the scan wait time.

14. The radio telephone of claim 11, further comprising a keypad that is electronically coupled to the controller, and wherein the scan wait time can be defined by actuating the keypad independent from the scanning process performed by the controller.