HK1050981B - A method and mobile station for acquiring service in a wireless network - Google Patents

Description

Method and mobile station for acquiring service in wireless network

Technical Field

The present invention relates to a system and method for acquiring service in a wireless network, and more particularly to periodic re-examination of a digital control channel while occupying an analog control channel.

Background

A cellular mobile telecommunications system includes a mobile station that can communicate with any one of a number of geographically distributed base stations in a wireless network. Wireless networks provide communication over analog control and voice channels as well as digital control and voice channels. The use of channels depends on the type of service subscribed by the user and therefore not all of these channels are used. Older cellular systems include only one analog control and voice channel (ACC and AVC, respectively). The Digital Voice Channel (DVCH) was added later. Only newer digital telephones can communicate over a digital voice channel. Recently, wireless network systems have added Digital Control Channels (DCCH), which may provide additional control features. In addition, only telephones configured to communicate over a digital control channel can be used as such. All of these phones are downward compatible, however, which allows even digital types of phones to communicate over analog voice and control channels.

An analog control channel is easier to acquire than a digital control channel due to network system design. Even mobile stations equipped to communicate with digital control channels often initially acquire service on analog control channels. However, the digital control channel IS the preferred service provider for such mobile stations known as IS-136. A digital control channel is preferred since more features and longer standby time, etc. can be provided. The IS-136 TDMA cellular system provides the ACC with the ability to include a control channel information message in its Overhead Message Training (OMT) as a pointer to the DCCH for IS-136 compliant mobile stations. These mobile stations can use the DCCH pointer information to help search for digital services because the ACC IS standardly defined as a subset of the frequencies defined in IS-136, while the DCCH can be located on any IS-136 defined frequency.

A mobile station that may use a DCCH pointer typically acquires synchronization on the DCCH and then reads overhead information to determine whether to remain on the DCCH. The DCCH must be suitable from both signal strength and traffic aspects. The broadcast information provides the minimum Received Signal Strength (RSS) necessary for the mobile station to occupy the DCCH. If the strength of the RSS for a given DCCH mobile station is insufficient to meet the broadcast criteria, the mobile station leaves the channel to attempt to acquire service on another channel. This channel is typically an analog control channel from which the mobile station can obtain the DCCH pointer. Once the mobile station returns to ACC it will continue to receive DCCH pointers at a maximum period of 5 seconds.

If the mobile station cannot seize the DCCH simply because of the received signal strength, it is desirable for the mobile station to re-check the DCCH for suitability for seizure at some later time because the signal conditions are dynamic. The existing solution is to recheck the occupancy suitability of the DCCH each time the OMT is received on the ACC. In this way, the mobile station will only be able to stay on one ACC for up to 5 seconds. The mobile station may not be able to receive incoming pages and may have difficulty initiating calls. Another proposed solution is to start a timer after a DCCH acquisition failure and recheck the occupancy suitability of the DCCH after the timer expires. This requires running a dedicated timer inside the operating system of the mobile station and employing a fixed recheck time, which may not be optimal for all service providers. Specifically, the service provider will not be able to control the frequency with which the mobile station leaves the serving ACC to look for service on the DCCH. Yet another proposed solution is to not recheck the suitability of the occupancy of the DCCH channel as long as the mobile station remains on the same ACC. But this will result in the mobile station not being able to acquire service on the DCCH at some later point, even when the expectation for DCCH service exceeds ACC service.

Yet another proposed solution is disclosed in WO9734438, which teaches the transmission of a registration access message via the ACC. The message is identified by the network, which then selects an appropriate DCCH and sends information about the selected DCCH to the mobile station via the ACC. However, this would require additional processing of the network part.

The present invention is directed to solving one or more of the problems set forth above in a novel and simple manner.

Disclosure of Invention

In accordance with the present invention, disclosed herein is a system and method that periodically attempts to acquire service on a DCCH only when the DCCH is rejected due to unacceptable received signal strength.

Broadly, disclosed herein is a method for use in a wireless network that provides communication services on an Analog Control Channel (ACC) and a Digital Control Channel (DCCH), the method controlling access to the wireless services by a mobile station. The method comprises the following steps: acquiring wireless service on a selected ACC; periodically receiving a pointer to a preferred DCCH as part of a message received from the wireless network via the ACC; initially attempting to acquire wireless service on the preferred DCCH, including determining whether the received signal strength is acceptable and the available service features are acceptable, and if not, indicating that the preferred DCCH is rejected; storing information about the rejected DCCH; and subsequently attempt to acquire wireless service on the rejected DCCH only if the DCCH is rejected due to unacceptable received signal strength.

It is a feature of the invention that the storing step includes storing the channel number, the super band and the digital check color code associated with the rejected DCCH. An indicator of the reason for the DCCH acquisition being discarded, specifically, whether due to signal strength or traffic or unknown reasons, is also stored. The minimum signal strength necessary to occupy the rejected DCCH is also stored.

Another feature of the present invention is that the mobile station obtains signal strength measurements when subsequently attempting to acquire wireless service on the rejected DCCH. The mobile station averages the signal measurements. The DCCH is reset to preferred if the subsequently received signal strength is acceptable.

It is still another feature of the present invention that the storing step includes storing information indicating whether the acquired ACC wireless service provider is acceptable or unacceptable. If it is an unacceptable service provider or if an acceptable service provider but the rejected DCCH is rejected because the received signal strength is unacceptable, a triggered scan timer is started. The DCCH is reset to preferred when the triggered timer expires.

In accordance with another aspect of the present invention, a mobile station for use in a wireless network that provides communication services on an Analog Control Channel (ACC) and a Digital Control Channel (DCCH) is disclosed. The mobile station includes a receiver and transmitter that communicate with the wireless network via the ACC and DCCH. A programmed controller is operable to control the receiver and the transmitter and operates in accordance with programs stored in memory to acquire services. The program further includes acquiring wireless service on the selected ACC, periodically receiving a pointer to a preferred DCCH as part of a message received from the wireless network via the ACC, initially attempting to acquire wireless service on the preferred DCCH, including determining whether the received signal strength is acceptable and available service features are acceptable and indicating the preferred DCCH as rejected if not acceptable, storing information about the rejected DCCH in a memory, and subsequently attempting to acquire wireless service on the rejected DCCH only if the DCCH is rejected because the received signal strength is unacceptable.

Further features and advantages of the invention will be apparent from the description and the accompanying drawings.

Drawings

Fig. 1 is a schematic diagram of a cellular mobile telecommunications system using a mobile station according to the present invention;

FIG. 2 is a general block diagram of a mobile station according to the present invention;

figures 3-1 and 3-2 are flowcharts illustrating procedures implemented in the mobile station of figure 2 illustrating the use of DCCH broadcast information and the determination performed by the DCCB pointer; and

fig. 4-1, 4-2, 4-3, and 4-4 are flowcharts illustrating a procedure implemented in the mobile station of fig. 2 as part of intelligent roaming that periodically rechecks the DCCH pointer channel while occupying the ACC.

Detailed Description

Referring initially to fig. 1, a cellular mobile telecommunications system 10 of conventional configuration is illustrated. As is well known, the cellular system 10 is defined by a plurality of cells, which include representative cell locations A, B, C and D. Each cell location a-D includes a respective base station 12, 13, 14 and 15. Each base station 12-15 communicates with a mobile switching center 16 via an inter-cell trunk 17. The mobile station, indicated at 18, may be constituted by a cellular telephone held by the user, for example, in an automobile. It will be apparent that the mobile station 18 may comprise any known form of mobile station capable of communicating with the cellular mobile telecommunications system 10.

The telecommunications system 10 is operable to select one of the base stations 12-15 to communicate with the mobile station 18. As shown, the mobile station 18 is located at cell location D. Thus, communications with the mobile station 18 will be handled by the base station 15. If the mobile station 18 is stationary, it may remain in communication with the base station 15. But if the mobile station 18 is moving it may enter a different cell. For example, as shown, the mobile station 18 may move in the direction shown by dashed line 20 and through cell location B and then to cell location a. Thus, when the mobile station moves from cell location D to respective cell locations B and a, the mobile station 18 hands over communications from base station 15 to base station 13, and subsequently to base station 12.

As IS known, IS-136 TDMA cellular systems have an Analog Voice Channel (AVC) and an Analog Control Channel (ACC). These systems also include a Digital Voice Channel (DVCH) and a Digital Control Channel (DCCH). The present invention will be directed to how the mobile station 18 acquires traffic on these channels and more advantageously on the DCCH.

Referring to fig. 2, the mobile station 18 will be described in more detail. The mobile stations 18 comprise IS-136 mobile stations that advantageously communicate in an IS-136 TDMA cellular system. The standard IS-136 forms a compatible standard for cellular mobile telecommunications systems. The standard ensures that a mobile station can obtain service in any cellular system manufactured according to the standard. The IS-136 standard IS incorporated herein by reference.

The mobile station 18, also called a radiotelephone, includes an antenna 22 for transmitting and receiving wireless signals between itself and the wireless network represented by the telecommunications system 10 of fig. 1. The transmitter/receiver 24 is coupled to the antenna 22 for broadcasting and receiving, respectively, wireless signals. The receiver portion demodulates, demultiplexes and decodes the wireless signal into a control channel and a voice channel as discussed above. The voice or data is sent to an input/output device 26 such as a speaker, display, or other output device. The received signal is also sent to the programmable control device 28. Programmable control device 28, in response to messages on the control channel, uses programs and data stored in memory 30 to control and coordinate the functions of mobile station 18 so that mobile station 18 may operate within the wireless network. Programmable control device 28 also controls the operation of mobile station 18 in response to inputs from input/output block 26. The input may include a keyboard. The programmable control device controls the operation of the transmitter/receiver 24 in response to control messages and user inputs.

In accordance with the present invention, a solution is provided to periodically determine the acceptability of the signal strength of rejected DCCH as directed by the loop information in the ACC Overhead Message Training (OMT). Since DCCH is preferred over ACC, periodic measurements of the Received Signal Strength (RSS) of the rejected DCCH pointer channel are obtained. The RSS criteria given in the DCCH broadcast information is used to determine when to retry DCCH acquisition. This can strive to minimize the number of missed ACC pages or incoming calls when using algorithms that currently exist in IS-136 compatible mobile stations. Specifically, the system and method uses existing methods of measuring the RSS of the DCCH pointer channel within the ACC during idle times, but uses the RSS criteria found in the DCCH broadcast information to determine when to retry the DCCH acquisition.

A mobile station (e.g., mobile station 18) that may use a DCCH pointer derived from the ACC will normally acquire synchronization on the DCCH and will then read overhead information to determine whether to remain on the DCCH. The DCCH must be suitable both from the point of view of signal strength and traffic. The broadcast information provides the minimum RSS necessary for the mobile station to occupy the DCCH according to known standards. If the strength of the RSS for a given DCCH mobile station is not sufficient to meet the broadcast criteria, the mobile station must leave the channel in an attempt to acquire service on another channel. This channel is typically the ACC from which the mobile station obtains the DCCH pointer. Once the mobile station returns to the ACC, it will continue to receive DCCH pointer information at a maximum period of 5 seconds. According to the present invention, DCCH broadcast information is used to determine when to attempt to acquire service on the DCCH again.

Referring to fig. 3-1, a flowchart of the operation of the program implemented in programmable control device 28 of fig. 2 to obtain such a service is illustrated. It should be understood that the programming control device 28 performs a variety of different programming functions. The application relates to occupying a certain control channel. Therefore, only the flow chart relating to this feature will be described.

The flow chart identified at node 100 is a routine to obtain an ACC. The programmable control means 28 calls this routine when the mobile station 18 has acquired an ACC. The decision block 102 determines whether or not a DCCH pointer is included on the ACC OMT. If so, decision block 104 determines whether the DCCH has been marked as discarded. If not, the mobile station performs an RSS measurement of the DCCH once during the idle ACC time at block 106. The decision block 108 determines whether the RSS is greater than the minimum RSS of the DCCH pointer channel for the mobile station. If so, the mobile station attempts to acquire the DCCH and determines whether it is suitable for occupation at block 110. The decision block 112 determines whether the mobile station 18 successfully acquired the DCCH. If not, the DCCH discard indicator is set to "unknown" at block 114. If the mobile station can acquire the DCCH at block 112, decision block 116 determines whether the signal strength aspect of the service is acceptable, as described above. If not, the DCCH discard indicator is set to "signal strength" at block 118. If the determination at decision block 116 is that the signal strength is passed, decision block 120 determines whether the traffic aspects of the DCCH are acceptable. If the DCCH provides a service capability subscribed by the user, the service aspect is acceptable. If not, the DCCH discard indicator is set to "traffic" at block 122. If the traffic aspect has passed, control passes to node 124 to cause the mobile station to occupy a DCCH. The control algorithm described here is not used again thereafter until the mobile station occupies the ACC again.

From any of blocks 114, 118 or 122, the control program passes to block 126 and operates to store in the memory 30 the channel number, the super band, the DVCC and the minimum RSS necessary for occupancy calculated from the broadcast information. The control program then reacquires an ACC at node 128.

Assuming that the DCCH was discarded in the previous cycle, in the subsequent cycle the control program will pass from decision block 104 to decision block 130 which determines whether the DCCH was discarded due to signal strength. If so, the control program attempts to acquire wireless service on the rejected DCCH by measuring the RSS of the DCCH during ACC idle time at block 132. According to the invention, when the mobile station obtains the minimum number of RSS measurements for the DCCH pointer channel, it averages them and compares the average to the stored DCCH broadcast RSS criteria, and when the RSS average is found to be Z db greater than the stored DCCH broadcast RSS, the mobile station will reset the DCCH pointer discard information. The function is implemented at decision block 134. Specifically, if enough samples have been taken and the average RSS is greater than the DCCH broadcast RSS + Z, the DCCH pointer discard information is reset at block 136. If not, the control program proceeds to the ACC occupancy routine illustrated in FIG. 3-2. The ACC occupation routine may also be implemented from any of blocks 102, 108 or 130 as a negative result, and also after resetting the discard information at block 136.

Fig. 3-2 illustrates an ACC occupancy routine. The routine begins at block 140 where it determines whether a DCCH pointer is available. If so, decision block 142 determines whether the DCCH in question is to be discarded. If so, decision block 144 determines whether the channel was dropped due to signal strength. If not, decision block 146 determines whether the ACC must be left. The mobile station 18 may leave the ACC, for example if the mobile station moves to another cell. If the ACC must be left, all DCCH pointer discard information is reset at block 148. The routine is then ended. If it is not necessary to leave the ACC, the control program remains in the ACC occupancy mode.

If it is determined at decision block 142 that the DCCH pointer has not been discarded or it was discarded due to signal strength at block 144, control passes to block 150 which implements the ACC acquisition routine shown in fig. 3-1.

Thus, in accordance with this aspect of the invention, if the DCCH is discarded due to the signal strength criteria only, the mobile station will attempt to reacquire the discarded DCCH because the signal strength is dynamic and the traffic aspect is relatively more static. This way the method does not require a dedicated timer to re-check the DCCH and does not require continuous measurement of the RSS of the DCCH, since the RSS is only tapped when a control channel information message is received, which will only be spaced by a few seconds. The method saves current and increases standby time by measuring RSS non-continuously. This also minimizes the number of missed ACC pages, i.e., incoming calls.

Referring to fig. 4-1 through 4-4, a flow chart of a process implemented in programmable control device 28 of fig. 2 as part of using Intelligent Roaming (IR) to trigger scanning is illustrated.

Fig. 4-1 illustrates a flow diagram of a routine for acquiring an ACC. The flow chart begins at node 200 and is invoked when the mobile station 18 acquires an ACC. The decision block 202 determines whether or not a DCCH pointer is included on the ACC OMT. If so, decision block 204 determines whether the DCCH has been marked as discarded. If not, the mobile station performs an RSS measurement of the DCCH during the idle ACC time at block 206. The decision block 208 determines whether the RSS is greater than the minimum RSS of the DCCH pointer channel of the mobile station. If so, the mobile station attempts to acquire the DCCH and determines whether it is suitable for occupation at block 210. The decision block 212 determines whether the mobile station 18 has successfully acquired the DCCH. If not, the DCCH discard indicator is set to "unknown" at block 214. If the mobile station can acquire the DCCH at block 212, decision block 216 determines whether it is acceptable in terms of signal strength as described above. If not, the DCCH discard indicator is set to "signal strength" at block 218. If the signal strength aspect has passed at decision block 216, decision block 220 determines whether the traffic aspect of the DCCH is acceptable, as described above. If not, the DCCH discard indicator is set to "traffic" at block 222. If the service aspect is acceptable, control passes to node 224 to cause the mobile station to occupy a DCCH. The control algorithm described here is then not used until the mobile station again occupies an ACC.

From any of blocks 214, 218 or 222, the control routine proceeds to block 226, which is operable to store in the memory 30 the channel number, the super band, the DVCC and the minimum RSS required for occupation calculated from the broadcast information. The control program then reacquires an ACC at node 228 using the routine shown in fig. 4-3.

If it is determined at decision block 202 that a DCCH pointer is not included in the OMT, at decision block 204 that the DCCH is rejected, or at block 208 that the RSS is not greater than the minimum value, control passes to block 230 which implements the ACC occupancy routine shown in fig. 4-2.

Referring to fig. 4-2, an ACC occupancy routine is illustrated. The routine begins at block 232 by determining whether a DCCH pointer is available. If so, decision block 234 determines whether the pointer channel information is equal to the discarded DCCH information. The pointer channel information is the information stored at block 226 of fig. 4-1. If so, control returns to the acquire ACC routine shown in FIG. 4-1 at block 236. If it is determined at decision block 232 that the DCCH pointer is not available or the pointer channel information is equal to the rejected DCCH information, the control program passes to decision block 238 where it is determined whether the ACC must be left. If so, all DCCH pointer discard information is reset at block 240 and the control program returns to normal function at node 242. If it is not necessary to leave the ACC, decision block 241 determines whether the triggered scan timer has expired. If not, the control program remains in the ACC occupancy mode, as indicated at point 243. If the triggered scan timer has expired, the triggered scan timer expiration routine illustrated in FIGS. 4-4 is invoked at block 244.

Referring to fig. 4-3, the reacquisition ACC routine called at block 228 of fig. 4-1 is illustrated. The routine begins at block 246 with a determination of whether the ACC is an acceptable service provider based on intelligent roaming criteria. A service provider is considered acceptable if it is the home service provider or partner provider of the mobile station user. A service provider is considered unacceptable if it is not a home or partner provider and is not a disabled service provider. If the ACC is acceptable, decision block 248 determines whether the DCCH discard indicator is set to signal strength. If not, control returns to the ACC occupancy routine of FIG. 4-2. If so, or if it is determined at decision block 246 that the ACC is not an acceptable service provider, at block 252 a triggered scan timer is started to the value RESCAN _ COUNT of the Intelligent Roaming Database (IRDB). The control program then passes to block 250 to implement the ACC occupancy routine.

Referring to fig. 4-4, a flow diagram of a trigger scan timer expiration routine is illustrated. The routine begins at block 254 by resetting the DCCH pointer discard information. The decision block 256 determines whether the ACC is an acceptable service provider. If not, a triggered partial scan according to the intelligent roaming criteria is implemented at block 258. If the ACC is an acceptable service provider, the control program passes to the ACC occupancy routine of FIG. 4-2 at block 260.

Thus, according to this aspect of the invention, the mobile station 18 will re-check the rejected DCCH only if the DCCH was rejected due to signal strength criteria, since signal strength is dynamic and traffic aspects are relatively more static. No dedicated timer is needed to re-check the DCCH. But instead uses the existing triggered scan timer for intelligent roaming. The mobile station 18 uses the trigger scan timing defined by the parameters downloaded to the mobile station 18 by the home service provider. The home service provider can thus control the frequency with which the mobile station 18 leaves the ACC service in an attempt to acquire service on the DCCH. This control is desirable because when the mobile station checks the DCCH, it no longer has traffic on the ACC. The service provider can determine the trade-off of missed incoming calls and preferred services as it would for any other triggered scan.

More specifically, if the mobile station is on an unacceptable service provider, this is done by starting a trigger scan timer. Also, if the mobile station is on an acceptable service provider according to intelligent roaming, the triggered scan timer is started only if the DCCH is rejected due to signal strength. DCCH pointer discard information is reset when the triggered scan timer expires and the triggered scan process is performed according to IR requirements when on an unacceptable service provider and/or returned to read the ACC OMT when on an acceptable service provider. Whenever the mobile station again reads a control channel information message on the ACC OMT, it can re-attempt to acquire service on the pointed DCCH because it is no longer being dropped.

Thus, according to the invention disclosed herein, if the DCCH is rejected due to unacceptable received signal strength, the mobile station attempts to reacquire wireless service on the rejected DCCH.

Claims (22)

1. A method for use in a wireless network providing communication services on an analog control channel ACC) and a digital control channel DCCH, the method controlling access to the wireless services by a mobile station, the method comprising the steps of:

acquiring wireless service on a selected ACC;

periodically receiving a pointer to a preferred DCCH as part of a message received from the wireless network via the ACC;

initially attempting to acquire wireless service on a preferred DCCH, including determining whether received signal strength is acceptable and available service features are acceptable, and if not, indicating the preferred DCCH as being discarded;

storing information about the rejected DCCH, and

if the DCCH is rejected due to unacceptable received signal strength, then an attempt is made to acquire wireless service on the rejected DCCH.

2. The method of claim 1 wherein the storing step comprises storing the channel number, the super-band, and the digital verification color scale associated with the rejected DCCH.

3. The method of claim 1 wherein the storing step comprises storing an indicator of the reason that DCCH acquisition was rejected.

4. The method of claim 3 wherein the storing step comprises storing the reason that the DCCH was rejected as being due to signal strength or due to traffic or unknown reasons.

5. The method of claim 1 wherein the storing step comprises storing a minimum signal strength necessary to seize the rejected DCCH.

6. The method of claim 1 wherein the mobile station obtains signal strength measurements when subsequent attempts are made to acquire wireless service on the rejected DCCH.

7. The method of claim 6, further comprising the step of averaging the signal strength measurements.

8. The method of claim 6, further comprising the steps of: the DCCH is reset to preferred if the subsequently received signal strength is acceptable.

9. The method of claim 1, wherein the storing step comprises: information is stored indicating whether the wireless service provider of the acquired ACC is acceptable or unacceptable.

10. The method of claim 9, further comprising the step of: if it is an unacceptable service provider or if it is an acceptable service provider but the rejected DCCH is rejected because the received signal strength is unacceptable, a triggered scan timer is started.

11. The method of claim 10, further comprising the step of: the DCCH is reset to preferred when the triggered scan timer expires.

12. A mobile station for use in a wireless network providing communication services on an analog control channel ACC and a digital control channel DCCH, the mobile station comprising:

a receiver and transmitter for communicating with a wireless network via an ACC and a DCCH; and

a programmed controller operable to control the receiver and the transmitter and to operate in accordance with a program stored in a memory to acquire services, comprising: the method includes acquiring wireless service on a selected ACC, periodically receiving a pointer to a preferred DCCH as part of a message received from the wireless network via the ACC, initially attempting to acquire wireless service on the preferred DCCH, including determining whether received signal strength is acceptable and available service features are acceptable, and if not, indicating the preferred DCCH as rejected, storing information about the rejected DCCH in a memory, and subsequently attempting to acquire wireless service on the rejected DCCH if the DCCH was rejected due to unacceptable received signal strength.

13. The mobile station of claim 12 wherein the memory is for storing a channel number, an ultra-band, and a digital verification color code associated with the rejected DCCH.

14. The mobile station of claim 12, wherein the memory is configured to store an indicator of a reason why DCCH acquisition was rejected.

15. The mobile station of claim 14, wherein the memory is configured to: the reason why the DCCH was discarded is stored as being due to signal strength or traffic or unknown reasons.

16. The mobile station of claim 12 wherein the memory is configured to store a minimum signal strength necessary to seize the rejected DCCH.

17. The mobile station of claim 12 wherein the controller is operative to obtain the received signal strength measurement in a subsequent attempt to acquire wireless service on the rejected DCCH.

18. The mobile station of claim 17, wherein the controller is configured to average the signal strength measurements.

19. The mobile station of claim 17, wherein the controller is to: the DCCH is reset to preferred if the subsequently received signal strength is acceptable.

20. The mobile station of claim 12, wherein the memory is for storing information indicating whether a wireless service provider of the acquired ACC is acceptable or unacceptable.

21. The mobile station of claim 20, wherein the controller is to: if it is an unacceptable service provider or if an acceptable service provider but the rejected DCCH is rejected because the received signal strength is unacceptable, a triggered scan timer is started.

22. The mobile station of claim 21, wherein the controller is to: the DCCH is reset to be preferred when the triggered scan timer expires.