Wireless terminals and methods including power efficient intelligent roaming and scanning for a communication service provider

ABSTRACT

Power-up systems and methods are provided for a wireless terminal which uses multiple stages of decreasing search complexity in scanning radio channels for service when no service is available. Complexity may be reduced by scanning radio channels for service according to a variable sequence whose composition reflects a higher occurrence of higher priority radio frequency bands than lower priority radio frequency bands, so that higher priority radio frequency bands will be scanned more often than lower priority radio frequency bands. In addition, by turning wireless terminal off for increasing time intervals after each scan, the power-up scan techniques may provide reduced power consumption. By reducing the search complexity during successive stages of scanning, the power-up scan techniques may ensure that the wireless terminal responds quickly and finds a service provider when service does become available.
 [0001] The written description provided herein contains acronyms which refer to, for example, various telecommunication services, components and techniques, as well as features relating to the present invention. Although some of these acronyms are known, use of these acronyms may not be standardized in the art. For purposes of the written description herein, acronyms will be defined as follows:

[0002] Advanced Mobile Phone Service (AMPS)

[0003] Application Specific Integrated Circuit (ASIC)

[0004] Analog Control Channel (ACC)

[0005] Code Division Multiple Access (CDMA)

[0006] Digital Control Channel (DCCH)

[0007] Digital Control Channel History Table (DHT)

[0008] Dynamic Random Access Memory (DRAM)

[0009] Digital Signal Processor (DSP)

[0010] Electronically Erasable Programmable Read Only Memory (EEPROM)

[0011] Federal Communications Commission (FCC)

[0012] Global System for Mobile Communications (GSM)

[0013] Intelligent Roaming Data Base (IRDB)

[0014] Intelligent Roaming Mode (IR Mode)

[0015] Interim Standard (IS)

[0016] Last Acceptable Band (LAB)

[0017] Liquid Crystal Display (LCD)

[0018] Mobile Identification Number (MIN)

[0019] Mobile Switching Center (MSC)

[0020] Number Assignment Module (NAM)

[0021] Personal Communications Network (PCN)

[0022] Personal Communications Services (PCS)

[0023] Private Operating Frequency (POF)

[0024] Random Access Memory (RAM)

[0025] Received Signal Strength (RSS)

[0026] Service Provider (SP)

[0027] System Access List (SAL)

[0028] System Identification Code (SID)

[0029] System Operator Code (SOC)

[0030] Time Division Multiple Access (TDMA)

BACKGROUND OF THE INVENTION

[0031] The present invention relates generally to the field of wireless communications methods and apparatus, and, more particularly, to the acquisition of a communication service provider upon power-up of a wireless terminal.
 [0032] Wireless communications systems are commonly employed to provide voice and/or data communications to subscribers. It will be understood by those having skill in the art that the term “wireless terminal” is used herein to include analog and digital radiotelephones, multiple mode radiotelephones, high function Personal Communications Systems (PCS) devices that may include large displays, scanners, full size keyboards and the like, and laptop, palmtop and pervasive computing devices that include wireless communications capabilities.
[0033] Analog cellular wireless communications systems, such as those designated AMPS (Advanced Mobile Phone System), NMT (Nordic Mobile Telephone)-450 and NMT-900, have long been deployed successfully throughout the world. By contrast, digital cellular wireless communications systems such as those conforming to the North American standard TIA/EIA-136 and the European standard GSM (Global Systems for Mobile Communications) have been in service since the early 1990s. More recently, a wide variety of wireless digital services broadly labeled as PCS (Personal Communications Services) have been introduced. PCS can be implemented via high function wireless terminals that provide functions in addition to those of a cellular telephone, such as facsimile, data communications, data processing, word processing, and other personal communications systems functions. Multiple mode wireless communication terminals that embody two or more of these functions also are included. Other wireless communication terminals that may omit a display and/or a microphone also are included.
 [0034] A current trend is to utilize digital transmission for speech and/or data traffic. Modern digital wireless systems typically utilize different multiple access techniques such as Time Division Multiple Access (TDMA) and/or Code Division Multiple Access (CDMA) to provide increased spectral efficiency. A number of digital cellular standards are in use that are based on Time Division Multiple Access (TDMA). TDMA systems include the TIA/EIA-136 (D-AMPS) system and the GSM system, also known as DCS1800 when used in the 1800 MHz band and as PCS1900 when used in the U.S. 1900 MHz PCS bands. In TDMA systems, such as those conforming to the GSM or TIA/EIA-136 standards, carriers are divided into sequential time slots that are assigned to multiple channels such that a plurality of channels may be multiplexed on a single carrier. Ongoing development of TDMA standards continues to make improvements in service and product utility, such as longer battery life.
 [0035] One feature introduced into the D-AMPS system, for example, is the Digital Control Channel (DCCH) which can reduce the standby battery consumption of wireless terminals that are camped on the DCCH to await calls. Unlike the AMPS broadcast control channel, the DCCH need not be a continuous carrier signal, but occupies only one slot of the 3-slot TDMA frame. The other two slots can contain traffic, but may be empty during periods of low demand. On the other hand, CDMA systems, such as those conforming to the TIA/EIA-95 standard, achieve increased channel capacity by using “spread spectrum” techniques wherein a channel is defined by modulating a data-modulated carrier signal by a unique spreading code, i.e., a code that spreads an original data-modulated carrier over a wide portion of the frequency spectrum in which the communications system operates. For more information on air-interface standards please refer to http://www.tiaonline.org.
[0036] PCS are implemented in systems, such as, advanced digital cellular systems conforming to standards such as TIA/EIA-136, lower-power systems such as DECT (Digital Enhanced Cordless Telephone), and data communications services such as CDPD (Cellular Digital Packet Data). These and other systems are described in The Mobile Communications Handbook, edited by Gibson and published by CRC Press (1996).
 [0037] A major concern with such wireless communication systems is the continued reduction in the time that is needed to scan the wireless communication channels to identify a channel. In searching for a service provider, it is also known to equip multi-mode terminals which may support communication services with a variety of communication service providers with different protocols and implementations such as those described above. For example, it is known to provide dual mode terminals supporting both AMPS and TDMA. In addition, it is known to provide multi-mode terminals supporting multiple frequency band operation. An example is the Digital Advanced Mobile Phone System (D-AMPS) terminal discussed above, for use in the United States, where one of two alternate 800 megahertz (MHz) bands may be utilized to provide both analog and digital services in a particular geographic region. The utilized 800 MHz band may vary in different geographic regions. In addition, digital communication services may be supported by one of a number of different 1900 MHz bands.
 [0038] As shown in FIG. 1, pursuant to regulations of the Federal Communications Commission (FCC) in the United States, for example, the two 800 MHz bands 14, 16 are typically designated “a” and “b”. In particular, the two frequency bands designated “a” 30, 32 and “b” 34, 36 can be 12.5 MHz each allocated in the 800 MHz region for the uplink 14 and the downlink 16, respectively. Thus, the total spectrum allocation is 25 MHz per band. On the other hand, the bands allocated in the 1900 MHz region can be each be designated “A” through “F”. The first three bands A to C 50-60 may have an allocation of 15 MHz each, while the bands D to F 62-72 can have allocations of 5 MHz each. Each of these bands may have, for instance, channels with 30 kHz carrier frequency spacing. Each of the bands may also be further divided into sub-bands (also called probability blocks) in the 800 MHz bands. A purpose of dividing the bands into sub-bands is to allow the system to specify the scanning procedure for the mobile terminal more precisely. The a and the b bands can be sub-divided into sixteen sub-bands each, the bands from A to C can be sub-divided into seven sub-bands each, and the bands from D to F can be sub-divided into three sub-bands each. In the future this band configuration will likely change. Presently, schemes such as these are used for TIA/EIA-136, GSM, CDMA and other systems.
 [0039] Power consumption is an important consideration for mobile phones since lower power consumption can enable mobile phones to have longer standby times thus increasing their operability. Mobile phones operating in cellular systems such as TIA/EIA-136 are required to scan for acceptable service providers according to specific Intelligent Roaming (IR) procedures that are specified in TIA/EIA-136. These procedures define the order in which the mobile phone scans different channels and the priorities assigned to various service providers. The IR procedures typically use a pre-programmed database stored in the wireless terminal called the Intelligent Roaming Data Base (IRDB). The IRDB prioritizes the frequency bands and sub-bands to be scanned based on the probability of finding a preferred service provider within a band. It also stores other parameters such as the number of sub-bands to scan within a frequency band where the sub-band ordering in decreasing order of priority is pre-defined.
[0040] The respective priority of each frequency band typically depends on the status of the service provider that is licensed to use that band. The status of Service Providers (SP) is generally classified into five categories: home, partner, preferred, neutral and forbidden. These multiple service provider categories may be identified by matching the System Identification Code (SID) or System Operator Code (SOC) broadcast on a control channel with the entries in the IRDB. Each of these five categories may de defined as follows:

[0041] (1) home—service provider of choice and normally the service provider with whom the user has a service agreement. If a mobile communication device is registered on or finds a control channel for a home service provider, the device does not attempt to find service on any other frequency band.
 [0042] (2) partner—a partner with the home service provider. If a mobile communication device is registered on or finds a control channel for a partner service provider, the device does not attempt to find service on any other frequency band.
[0043] (3) favored—a service provider with whom the home service provider has a preferential rate and/or service agreement. The mobile communication device will register with a favored service provider only if a home or partner service provider is not found. On the occurrence of certain events, such as a control channel change and/or periodically, the mobile communication device will search other frequency bands for a home or partner service provider.
[0044] (4) neutral—a service provider not identified by a SID or SOC entry in the IRDB. The mobile communication device will register on a neutral service provider if none of home, partner, or preferred service providers are found. On certain events such as a control channel change and/or periodically, the mobile communication device will search other frequency bands for a home, partner, or preferred service provider.
[0045] (5) forbidden—a service provider which is never used under normal circumstances.
[0046] Home and partner SPs may be grouped into one category as acceptable SPs depending on the state of a bit in the IRDB. On the other hand, favored and neutral SPs usually are grouped together as unacceptable SPs.
[0047] During operation of a wireless terminal, RF coverage may be unavailable for a wide variety of reasons. For example, RF coverage could be unavailable in elevators, tunnels, or other structures. On the other hand, RF coverage may also be unavailable when cellular service is not present in a given area. Moreover, lack of acceptable service providers in a particular area may be yet another reason coverage would be unavailable.
 [0048] In the event RF coverage is unavailable, the wireless terminal must execute a power-up scan to find acceptance service providers. When a wireless terminal is powered on, it performs an initialization procedure with the wireless communications system. In general, the wireless terminal scans a plurality of channels and/or time slots in order to locate an appropriate control channel. Wireless terminals that operate in the U.S. AMPS system may only need to scan a limited number of channels at power-up in order to locate a broadcast control channel. For example, broadcast control channels can be confined to a small portion of the available spectrum about 1 MHz wide in order to reduce scan time. Moreover, since in AMPS the broadcast control channel transmissions generally are continuous transmissions, the receiver could alight on a scanned channel at any time and make a measurement. In analog cellular telephones it is known to scan channels in direct sequential order to minimize the frequency changing time from one channel to the next.
[0049] Currently, wireless terminals operating in a wireless communication system such as the TIA/EIA-136 cellular system search for acceptable service on all channels on which the terminal is designed to operate. As noted above, in a TDMA system the channel is typically defined by a frequency and a time slot, and in a CDMA system it is defined by a carrier frequency and a spreading code. Thus, a channel may be defined by a carrier frequency and/or a time slot and/or a spreading code.
 [0050] Shown in FIG. 2 is a block diagram of a conventional power-up scan procedure 200 for a wireless terminal connected to an external power supply. By contrast, FIG. 3 is a block diagram showing a conventional power-up scan procedure 300 for a wireless terminal when not connected to an external power supply, for example when using battery power. These procedures are used by a wireless terminal to scan for service upon power-up or upon losing a channel. When a wireless terminal is unable to find any service using the power-up scan procedure, the power-up scan procedure must be repeated periodically in an attempt to find service.
 [0051] As shown in FIG. 2, the power-up scan is started at Block 201 and is composed of at least three components. These are the Private Operating Frequency (POF) scan 202, the DCCH History Table (DHT) scan 204 and the wideband scan 206. In the POF scan 202, channels are scanned for private systems. A DCCH (Digital Control Channel) history table stores control channels recently camped on by the wireless terminal, and the DHT scan 204 searches those channels for service. In a wideband scan 206, an ordered search through all the channels in every frequency band as specified in an IRDB is made for a control channel with an acceptable SP. Between each scan operation, a determination is made at Blocks 203, 205 and 207, whether a communications channel is found. If so, the power-up scan ends at Block 210. On the other hand, if the communications channel is not found, then the power-up scan simply proceeds to the next scan Block 202, 204, 206 specified by the procedure. The procedures for scanning each band during a wideband scan are specified in Section 4.1.6.6. of TIA/EIA-136-123-B. As described in Section 4.1.6.6., particular techniques used in performing the wideband scan depend on whether scanning is being performed in a 800 or 1900 MHz band. Thus, when the wireless terminal is connected to an external power supply, as shown in FIG. 2, the power-up scan procedure continuously repeats itself until an SP is found.
 [0052] By contrast, as shown in FIG. 3, when the wireless terminal is not connected to an external power supply, the power-up scan includes an Intelligent Roaming (IR) restart procedure 312. Thus, after examining all the bands, if no acceptable SP is found, then the wireless terminal must periodically restart the power-up scan procedure to find a service provider. However, while Section 4.1.6.2 specifies that a rescan process 8 must be repeated, Section 4.1.6.2 does not provide specific requirements as to how this should be done.
[0053] The specification of TIA/EIA-136-123-B specifies Intelligent Roaming methods that define wireless terminal search procedures associated with a variety of situations, such as: call release; intelligent roaming restart procedure; power-up scan; wideband scan; triggered scan, including triggered partial scan and triggered wideband scan; band scanning procedures for 800 MHz and 1900 MHz bands; emergency call procedure; analog fax; and data service. In particular, Section 4.1.6.3 of TIA/EIA-136-123-B provides a detailed description of a power-up scan procedure. The power-up scan will result in the wireless terminal station entering a DCCH camping state or settling on the highest priority SP available.
 [0054]FIG. 4 is a flowchart of a power-up scan procedure reproduced from the TIA/EIA-136-123-B specification. This power-up scan procedure will now be explained as per the description given in the specification of TIA/EIA-136-123-B. Once the power-up scan is initiated, at Block A1, the signal strength of all the POFs stored in the wireless terminal station (i. e., that are identified as Acceptable SPs by the SID and/or SOC) is determined. If the Non-Public Priority Enable bit is set to 1, then the signal strength of all POFs may be measured, regardless of the SP category. At Block 403, the strongest two channels then are listed in order of signal strength, and the stronger signal of the two is selected. Next at Block A2/B3, if it is determined that the signal strength is below HISTORY_THRESHOLD, then the power-up scan procedure proceeds to Block 405, which is discussed below.
 [0055] On the other hand, if it is determined at Block A2/B3 that the signal strength is above HISTORY_THRESHOLD, then the power-up scan procedure proceeds to Block A3/B4 where an attempt is made to synchronize to the channel. At Block A3/B4, if it is determined that the channel is not a DCCH, then the power-up scan procedure proceeds directly to Block A5/B6. By contrast, if the channel is a DCCH, then the power-up scan procedure proceeds to Block A4/B5. At Block A4/B5, if there is a POF match and the channel is suitable for camping based on the requirements of Section 4.2, the power-up scan procedure enters the DCCH camping state. If the wireless terminal station has not entered the DCCH camping state, then the power-up scan procedure proceeds to Block A5/B6. At Block A5/B6, the second strongest channel in the POF list is selected if it has not already been examined. If at Block 405 it is determined that the second strongest channel has already been examined, then the power-up scan procedure proceeds to Block B1. On the other hand, if at Block A5/B6 the channel is not the second strongest POF channel, then at Block 409, the power-up scan procedure selects the next strongest RSS channel on the list, and the power-up scan procedure proceeds to Block A2.
 [0056] At Block B1, the status of the DHT Enable is examined. If the DHT Enable bit is set to one, then the power-up scan procedure proceeds to Block B2. On the other hand, if the DHT Enable bit is set to zero, then the power-up scan procedure proceeds to Block C1. At Block B2, the power-up scan procedure determines whether this is the first check of the DHT. If so, then the power-up scan procedure proceeds to select DHT channels in the Last Acceptable Band (LAB).
[0057] By contrast, if this is not the first check of the DHT, then the power-up scan procedure proceeds to select the next unchecked band in the IRBD band order. Also, at Block B2, the signal strengths of all the channels in the DHT are determined for the current band, and at Block 403, the strongest two channels are listed in order of signal strength with the maximum first. If it is determined at Block A2/B3 that the signal strength is below HISTORY_THRESHOLD, and at Block 405 it is determined that all DHT channels have been checked, then the power-up scan procedure proceeds to Block C1. By contrast, if it is determined at Block A2/B3. that the signal strength is above HISTORY_THRESHOLD, then the power-up scan procedure proceeds to Block A3/B4, where another attempt is made to synchronize to the channel. If the channel is not a DCCH, then the power-up scan procedure proceeds to Block A5/B6. Otherwise, the power-up scan procedure proceeds to Block A4/B5, where the wireless terminal station executes the Control Channel Selection procedure (see Section 4.2).
 [0058] Still referring to FIG. 4, if, at Block A4/B5, the wireless terminal station has not entered the DCCH camping state, then the power-up scan procedure proceeds to Block A5/B6, where the second strongest channel in the DHT list is selected for the band under consideration. If this channel has not already been examined, then the power-up scan procedure proceeds through Block 409 to select the next strongest RSS channel on the list, and then proceeds to Block A2/B3. On the other hand, if at Block 405 it is determined that this channel has already been examined and there are remaining bands and channels in the DHT to be checked, then the power-up scan procedure proceeds to Block B1. If at Block 405 it is determined that there are no remaining channels to be checked in the DHT, then the power-up scan procedure proceeds to Block C1.
[0059] Continuing with the description of FIG. 4, at Block C1, a wideband scan is performed according to Section 4.1.6.4. A wideband scan is an ordered search through the bands resulting in success (i.e., entering the DCCH camping state or Idle task) or failure. Upon exiting a failed wideband scan, the wireless terminal station, if in a coverage area, shall have a list of favored, neutral and forbidden SPs encountered during the wideband scan. At Block C2, if it is determined that the only Home SPs are preferred or IR is disabled, then the power-up scan procedure proceeds to Block C7, discussed in detail below.
[0060] At Block C3, favored and neutral SPs found during a wideband scan are prioritized according to SP category first. Within the same category, multiple SPs shall be prioritized based on the band order specified in the IRDB.
 [0061] Still referring to FIG. 4, at Block C4, the next channel in the priority ordering is examined, and, if none are left, then the power-up scan procedure proceeds to periodically restart the power-up scan at Block C7. At Block C5, if it is determined that the channel is suitable for camping, then the wireless terminal station shall enter the DCCH camping state and update the HSDB. If the wireless terminal station has not entered the DCCH camping state, then the power-up scan procedure proceeds to Block C6. At Block C6, if the channel is found unsuitable for camping, the entire band containing that channel is rescanned. The wireless terminal station shall enter the DCCH camping state or Idle task on any control channel in that band that it finds suitable but not Forbidden, and then update the HSDB. If a channel suitable for camping cannot be found in that band, then the power-up scan procedure proceeds back to Block C4 and examines the next channel in the priority ordering.
[0062] As discussed above, at Block C7, the power-up scan procedure periodically restarts the power-up scan. TIA/EIA-136-123-B specifies a recommended periodic rescan process in Section 4.1.6.2—Intelligent Roaming (IR) Restart Procedure. As illustrated in FIG. 4, Block C7 takes effect, for example, when (1) there is no coverage, (2) no control channels are found suitable for service, (3) the Home Only Enable bit or the IR DISABLE_FLAG is set to 1, or (4) only Forbidden SPs are found. While Block C7 specifies that the wireless terminal station shall periodically restart the power-up scan procedure from Block A1, no details are specified as to precisely how to restart the operation is to be carried out. Rather, these decisions are left to particular manufacturers.
 [0063] According to Section 4.1.6.2, if (1) the wireless terminal station exits the power-up scan with no suitable SP, or (2) if the wireless terminal station enters the control channel scanning and locking state either (a) as a result of executing the suitable CAND_(—)1 not found procedure or (b) as a result of inability to complete the update digital overhead information task, then the wireless terminal station shall proceed by executing the Intelligent Roaming (IR) Restart Procedure.
[0064] According to the recommended Intelligent Roaming (IR) Restart Procedure, if the IR_DISABLE_FLAG is set, then the wireless terminal station shall initiate a power-up scan searching only for a home SP. The wireless terminal station shall continue to periodically scan until a home SP is found or the wireless terminal station is power cycled. If the IR_DISABLE_FLAG is not set, then the wireless terminal station shall initiate a power-up scan searching for the highest priority SP available. If scanning is unsuccessful, the wireless terminal station shall periodically repeat the IR scanning process.
[0065] Significantly, the manner in which the IR scanning process is repeated is determined by the wireless terminal manufacturer based on considerations such as trading off battery life for service acquisition time and vice-versa. For instance, when the wireless terminal station is powered through an external power supply, the manufacturer may choose to leave the wireless terminal station in continuous IR scanning since power consumption is not a consideration. By contrast, when the wireless terminal station is operating on a battery power, it is desirable that the manner in which IR scanning is repeated takes place as efficiently as possible so that battery life may be extended.
 [0066] As discussed above, in the TIA/EIA-136 system, the manner in which the power-up scan is repeated by the wireless terminal is allowed to be chosen by the wireless terminal manufacturer so as to reduce power consumption in situations where no service is available. Accordingly, it is desirable that the power-up scan is repeated in a manner that can satisfy both of the potentially conflicting requirements of allowing power consumption to be low when no service is available, while quickly providing service to users as it becomes available.
[0067] Accordingly, there continues to be a need for wireless terminals and methods that can efficiently acquire a channel after the power-up scan procedure has failed. There is a particular need for IR restart procedures that can reduce scanning and acquisition time while allowing efficient use of battery power. As discussed above, conventional systems operating according to TIA/EIA-136 standard simply require the wireless terminal to repeat the power-up scan without specifying “intelligent” methods for doing so. Conventional wireless terminals operating according to TIA/EIA-136 standard may not efficiently direct the wireless terminal to a particular band or bands where the wireless terminal may obtain service on a preferred service provider when it is roaming.
 SUMMARY OF THE INVENTION

[0068] According to embodiments of the present invention, power-up systems and methods are provided for a wireless terminal which uses multiple stages of decreasing search complexity in scanning radio channels for service when no service is available. Complexity may be reduced by scanning radio channels for service according to a variable sequence whose composition reflects a higher occurrence of higher priority radio frequency bands than lower priority radio frequency bands, so that higher priority radio frequency bands will be scanned more often than lower priority radio frequency bands. Complexity may also be reduced by reducing the number of channels that are processed further during successive stages of scanning. In addition, by turning wireless terminal off for time intervals between each scan, embodiments of the present invention may provide reduced power consumption. This allows power savings while also allowing a channel to be found quickly. When a channel can not be found, by reducing amount of time the receiver is on, power is reduced during periods of scanning. This reduces the amount of time spent scanning which extends battery life during periods when no channels are found.
[0069] By reducing the search complexity during successive stages of scanning, the power-up scanning of embodiments of the present invention can allow the wireless terminal to respond quickly and find a service provider when service does become available.
 [0070] According to first embodiments of the present invention, a first power-up process is performed to attempt to detect a wireless communications channel while consuming a first amount of power. Upon failure of the first power-up process to detect a wireless communications channel for the wireless terminal, a second power-up process is then performed to attempt to detect a wireless communications channel. Significantly, the second power-up process consumes a second amount of power that is less than the first amount. Power consumption of the wireless terminal can also be reduced by switching off at least one component of the wireless terminal prior to performing the second power-up process. Accordingly, battery life of a wireless terminal may be conserved when no service is available, or is intermittently available, in a given area.
[0071] Power savings are achieved both directly and indirectly by the present invention. For example, turning off the receiver between scans of bands of a direct factor that results in power savings. Another example of direct power savings is scanning a decreasing number of channels within a band during successive stages of scanning. By contrast, an indirect factor that results in power savings is the higher occurrence of higher priority bands than lower priority bands in the band scanning sequence BAND_SEQ. While this increases the probability of finding a wireless communications channel and therefore increases the probability of spending less power scanning, it does not directly contribute to saving power.
 [0072] More specifically, according to embodiments of the present invention, during the first power-up process a first plurality of wireless communications channels can be scanned to attempt to detect a wireless communications channel, and during the second power-up process a second plurality of wireless communications channels that is less than the first plurality may be scanned to attempt to detect a wireless communications channel.
[0073] To allow reduced complexity during each successive scan, in other embodiments a decreasing number of the second plurality of communications channels may be repeatedly scanned to attempt to detect at least one pre-specified wireless communications channel. During scanning, selected ones of the second plurality of communications channels are preferably scanned more frequently than selected others of the second plurality of communications channels in each scan. For example, the selected ones of the second plurality of wireless communications channels may have a first priority designation, while the selected others of the second plurality of wireless communications channels may have a second priority designation that is lower than the first priority designation.
[0074] In other embodiments of the present invention, the second plurality of communications channels can be scanned and changes in the second plurality of communications channels can be detected. If changes are detected, the first power-up process may be re-performed.
 [0075] Changes may be detected by measuring a first mean Received Signal Strength (RSS), rescanning each of the wireless communications channels, measuring a second mean Received Signal Strength (RSS), and determining whether the second mean RSS differs from the first mean RSS by more than a predetermined amount. The second power-up process can be stopped if the second mean Received Signal Strength (RSS) differs from the first mean Received Signal Strength (RSS) by more than a predetermined amount. The first power-up process is then re-performed.
[0076] In preferred embodiments, the first power-up process may comprise a power-up scan procedure in which a Private Operating Frequency (POF) scan is performed, a Digital control channel History Table (DHT) scan is performed, and a wideband scan is performed.
[0077] In other embodiments of the present invention, after the first power-up is performed it can be confirmed whether the step of performing the second power-up process should be executed. One way this can be done is by determining that the wireless terminal is not connected to an external power supply.
[0078] In further embodiments of the present invention, prior to repeatedly scanning the second plurality of communications channels, a Digital control channel History Table (DHT) scan may optionally be performed each time selected ones of the second plurality of communications channels are scanned. A private operating frequency scan may also be periodically performed before repeatedly scanning the second plurality of communications channels. Each time the second plurality of communications channels are repeatedly scanned, the number of channels on which RSS is measured can also be reduced.
 [0079] In other embodiments, during the first power-up process a first plurality of frequency bands, each of which includes at least one communications channel, are scanned. During scanning of the first plurality of frequency bands, a highest priority frequency band can be scanned for a wireless communications channel. If no wireless communications channel is detected by scanning the highest priority frequency band, at least one lower priority frequency band can be scanned according to a sequence wherein higher priority bands are scanned more often than the lower priority bands. Preferably, more than one lower priority frequency band is scanned. For example, in certain embodiments every frequency band may be scanned at least once.
[0080] According to other embodiments of the present invention, power-up scan systems and methods are provided for attempting to detect a wireless communications channel for a wireless terminal. In response to failure of a preceding power-up process to detect a wireless communications channel, a power-up process is repeatedly performed while consuming decreasing amounts of power in each succeeding power-up process. Each succeeding power-up process is preferably performed after a delay time that increases with each succeeding power-up process. Search complexity may be further reduced by scanning selected ones of wireless communications channels more frequently than selected others of wireless communications channels in each successive scan. Accordingly, efficient scanning of frequency bands for a suitable service provider may be obtained.
[0081] In other embodiments, each succeeding power-up process may repeatedly scan a decreasing number of wireless communications channels to attempt to detect at least one pre-specified wireless communications channel.
 [0082] According to other embodiments of the present invention, a power-up scan method is provided for a wireless terminal that accesses a wireless communications system. The power-up scan method uses a plurality of first communications channels having a first priority designation and a plurality of second communications channels having a second priority designation that is lower than the first priority designation. Preferably, the first communications channels are scanned more frequently than second communications channels in each scan. In response to failure of a preceding scan to detect a wireless communications channel for the wireless terminal, search complexity can be reduced. For example, a decreasing number of the first and second communications channels can be scanned in an attempt to detect at least one pre-specified wireless communications channel. Alternatively, an increasing number of the first communications channels relative to the second communications channels can be scanned during each scan.
[0083] In another embodiment, each successive scan may consume a lesser amount of power than the preceding scan. One way of accomplishing this is by performing each successive scan after a delay time that increases with each successive scan. Typically scanning of the communications channels takes place according to a fixed sequence, BAND_SEQ. However, in further embodiments of the present invention, search complexity may be reduced by repeatedly scanning the first and second communications channels according to a variable sequence. For instance, in one variable sequence the occurrence of the first communications channels may increase in proportion to the total number of communications channels scanned during each repeating scan.
 [0084] In yet other embodiments of the present invention, a first and a second plurality of frequency bands, each of which includes at least one communications channel, are repeatedly scanned. Preferably, the repeated scanning of the first plurality of frequency bands comprises scanning a highest priority frequency band for a wireless communications channel, and if no wireless communications channel is detected by scanning the highest priority frequency band, at least one lower priority frequency band is scanned according to a sequence wherein higher priority bands are scanned with greater frequency than the lower priority bands. The number of first and second plurality of frequency bands may decrease during each successive scan.
[0085] According to other embodiments of the present invention, power-up scan systems and methods are provided for a wireless terminal that accesses a wireless communications system using a plurality of communications channels each of the channels having a predetermined priority. The plurality of communications channels include a group of higher priority communications channels and multiple groups of lower priority communications channels.
 [0086] Although the plurality of communications channels are generally scanned according to a fixed sequence, the plurality of communications channels may be repeatedly scanned according to a variable sequence. For example, in one embodiment of a variable sequence, the occurrence of higher priority communications channels may increase in proportion to the total number of communications channels with each successive scan. Moreover, in another embodiment of a variable sequence, the number of the plurality of communications channels that is scanned is decreased during each successive scan. Thus, the terminal can find a service provider quickly by scanning the higher priority channels in the band more often. The power-up scan method of the present invention can also ensure that the wireless terminal finds a service provider quickly when service does become available. In further embodiments, each successive scan preferably consumes a lesser amount of power than the preceding scan, thereby conserving battery life of the wireless terminal.
[0087] According to other embodiments of the present invention, restart systems and methods are provided for a wireless terminal that accesses a wireless communications system using a plurality of groups of frequency bands. Each group of frequency bands has a relative priority designation. The plurality of groups of frequency bands are sequentially scanned such that groups of frequency bands having a high relative priority designation are scanned more frequently than groups of frequency bands having a lower relative priority designation. In addition, the number of bands in each group may decrease as the relative priority designation of that group increases.
 [0088] As will be understood by those of skill in the art, the above-described embodiments of the invention may be used in combination. As will further be appreciated by those of skill in the art, the present invention may also be embodied as systems and methods and in all types of wireless communication terminals.
BRIEF DESCRIPTION OF THE DRAWINGS

[0089]FIG. 1 illustrates a conventional communications spectrum organization showing channel bands.
[0090]FIG. 2 is a simplified flowchart illustrating operation of a conventional power-up scan when the wireless terminal is connected to an external power supply.
[0091]FIG. 3 is a simplified flowchart illustrating operation of a conventional power-up scan when the wireless terminal is not connected to an external power supply.
[0092]FIG. 4 is a reproduction of a flowchart illustrating operation of a power-up scan as specified by TIA/EIA-136-123-B.
[0093]FIG. 5A is a flowchart illustrating exemplary operations of power-up systems and methods for wireless terminals according to embodiments of the present invention.
[0094]FIG. 5B is a flowchart illustrating exemplary operations of embodiments of power-up systems and methods for wireless terminals according to embodiments of the present invention.
[0095]FIG. 5C is a flowchart illustrating exemplary operations of an aspect of the embodiments shown in FIG. 5B.
[0096]FIG. 5D is a flowchart illustrating exemplary operations of other embodiments of power-up systems and methods for wireless terminals according to embodiments of the present invention.
[0097]FIG. 5E is a flowchart illustrating exemplary operations of other embodiments of power-up systems and methods for wireless terminals according to embodiments of the present invention.
[0098]FIG. 5E is a flowchart illustrating exemplary operations of other embodiments of power-up systems and methods for wireless terminals according to embodiments of the present invention.
 [0099]FIG. 5G is a flowchart illustrating exemplary operations of other embodiments of power-up systems and methods for wireless terminals according to embodiments of the present invention.
[0100]FIG. 6A is a flowchart illustrating exemplary operations of power-up scan systems and methods for wireless terminals according to other embodiments of the present invention.
[0101]FIG. 6B is a flowchart further illustrating the power-up shown in FIG. 6A.
[0102]FIG. 7 is a flowchart illustrating exemplary operations of a power-up for wireless terminals according to other embodiments of the present invention.
[0103]FIG. 8 is a flowchart illustrating exemplary operations of power-up systems and methods according to other embodiments of the present invention.
[0104]FIG. 9 is a flowchart illustrating exemplary operations of stage 1 of the power-up systems and methods shown in FIG. 8.
[0105]FIG. 10 is a flowchart illustrating exemplary operations of stages 2 and 3 of the power-up systems and methods shown in FIG. 8.
[0106]FIG. 11 is a schematic diagram illustrating one possible wireless communication terminal according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION

[0107] The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.
