Methodical scanning method and apparatus for portable radiotelephones

• US 5,754,956 A
• Filed: 09/20/1995
• Issued: 05/19/1998
• Est. Priority Date: 09/20/1995
• Status: Expired due to Fees

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Marko, Paul D., Brown, David L.., Abreu, Victor M., Pombo, Raul A.
• Primary Examiner(s): Faile, Andrew
• Assistant Examiner(s): Boccio, Vincent F.
• Application Number:
  US08/531,257
• Time in Patent Office: 972 Days
• Field of Search: 379/58, 379/62, 379/63, 379/61, 455/38.3, 455/343, 455/33.1, 455/34.1, 455/54.1, 455/54.2, 455/56.1, 455/62, 455/89, 455/33.4, 455/434, 455/436, 455/437, 455/450-452, 455/515, 455/524-52 5, 370/329, 370/333, 370/337
• US Class Current: 455/434
• CPC Class Codes: H04W 48/16 Discovering, processing access restriction or access information

Abstract

A radiotelephone handset (120) includes an antenna (122) and receiver (124) for receiving a control channel from a plurality of base stations (102, 104, 106). A time division multiple access controller circuit (126) coupled to the receiver stores all received control channel information in a captured data buffer (134). Under control of a processor (128), the handset identifies as candidate suitable base stations those base stations having acceptable received signal strength, acceptable identity or system capability. From the candidates, the handset (120) chooses a suitable base station having acceptable signal quality, access rights and system capability and synchronizes communication with the suitable base station.

Claims

1. A method for initializing communication between a handset and a base station in a telecommunication system, the telecommunication system including a plurality of base stations and the handset, the method comprising the steps of:

repetitively receiving at the handset a plurality of control channel signals, each control channel signal of the plurality of control channel signals being broadcast by a respective base station, each control channel signal including a respective system information field for the respective base station;

storing the respective system information field including an associated location parameter at the handset each time a control channel signal is received;

identifying as candidate suitable base stations one or more base stations corresponding to stored system information fields which satisfy a predetermined criterion;

selecting a suitable base station from the candidate suitable base stations, including

incrementing a missing count for each candidate suitable base station when the associated location parameter does not match a predetermined anticipated location for the suitable base station, and

eliminating the candidate suitable base station as a suitable base station when the missing count exceeds a predetermined missing count threshold; and

synchronizing communication between the handset and the suitable base station,

wherein the receiving step includes

repetitively receiving the plurality of control channel signals at the handset, and

wherein the storing step includes

storing the respective system information fields including an associated location parameter each time a control channel signal is received, and

wherein the selecting step comprises the steps of

incrementing a missing count for each candidate suitable base station when the associated location parameter does not match a predetermined anticipated location for the suitable base station, and

eliminating the candidate suitable base station as a suitable base station when the missing count exceeds a predetermined missing count threshold.

2. A method as defined in claim 1 wherein the associated location parameter comprises a bit count and a slot count.

3. A method for initializing communication between a handset and a base station in a telecommunication system, the telecommunication system including a plurality of base stations and the handset, the method comprising the steps of:

receiving at the handset a plurality of control channel signals, each control channel signal of the plurality of control channel signals being broadcast by a respective base station, each control channel signal including a respective system information field for the respective base station;

identifying each base station corresponding to a received control channel;

storing the respective system information field at the handset, including

storing an identity for each identified base station,

inhibiting the storing of system information fields for a predetermined inhibit time when a predetermined error criterion is satisfied and,

following the predetermined inhibit time, storing a subsequent system information field and determining if the subsequent information field was received from a previously unidentified base station;

identifying as candidate suitable base stations one or more base stations corresponding to stored system information fields which satisfy a predetermined criterion;

identifying the previously unidentified base station as a candidate base station if the subsequent information field satisfies a predetermined error criterion;

selecting a suitable base station from the candidate suitable base stations; and

synchronizing communication between the handset and the suitable base station,

further comprising the steps of

identifying each base station corresponding to a received control channel and wherein the storing step includes storing an identity for each identified base station, and

inhibiting the storing of system information fields for a predetermined inhibit time when a predetermined error criterion is satisfied and,

following the predetermined inhibit time, storing a subsequent system information field,

determining if the subsequent information field was received from a previously unidentified base station, and

identifying the previously unidentified base station as a candidate base station if the subsequent information field satisfies a predetermined error criterion.

4. A method as defined in claim 3 wherein the method further comprises the step of determining a cyclical redundancy check (CRC) status for each received control channel signal and wherein the storing step includes storing a CRC indication for the received control channel signal at the handset, and wherein the previously unidentified base station is identified as a candidate base station if the subsequent information field includes an acceptable CRC indication.

5. A method for initializing communication between a handset and a suitable base station in a telecommunication system, the telecommunication system including the handset and a plurality of base stations, each of the base stations transmitting one control channel of a plurality of control channels, each control channel including system information for the transmitting base station, each control channel being transmitted at a predetermined timing location, the method comprising the steps of:

receiving at the handset a control channel transmitted by a transmitting base station;

storing in a captured data buffer at the handset the system information for the received control channel, the stored system information including at least one of an identity of the transmitting base station and system capability of the transmitting base station;

storing in the captured data buffer, with the system information for the control channel, a received signal strength indication corresponding to the received signal strength for the control channel;

storing in the captured data buffer, with the system information for the control channel, a timing location for the control channel;

identifying the transmitting base station as a candidate suitable base station if the stored received signal strength indication corresponds to an acceptable received signal strength indication;

identifying the transmitting base station as a candidate suitable base station if the stored identity corresponds to an acceptable identity of the transmitting base station;

identifying the transmitting base station as a candidate suitable base station if the stored system capability corresponds to an acceptable system capability of the transmitting base station;

storing, in a candidate profile table, system information for all candidate suitable base stations;

reading from the captured data buffer system information from a subsequently transmitted control channel transmitted by a subsequently transmitting base station;

comparing a timing location of the subsequently transmitted control channel with the stored timing location and determining that the subsequently transmitting base station is the transmitting base station if the timing location of the subsequently transmitted control channel matches the stored timing location;

if the timing location of the subsequently transmitted control channel matches the stored timing location, determining if the subsequently transmitted control channel includes identity information for the subsequently transmitting base station;

if the identity information for the subsequently transmitting base station satisfies predetermined base station identity criteria, determining if the subsequently transmitted control channel includes system capability information for the subsequently transmitting base station;

if the system capability information for the subsequently transmitting base station satisfies predetermined capability criteria, identifying the transmitting base station as the suitable base station; and

synchronizing communication with the suitable base station.

6. A method for initializing communication between a handset and a suitable base station as recited in claim 5 wherein the method further comprises the steps of storing in the captured data buffer, with the system information for the control channel, a cyclical redundancy check (CRC) status for the control channel and storing in the captured data buffer a CRC Count representative of the number of times the CRC status for the transmitting base station was unacceptable.

8. A method for initializing communication between a handset and a suitable base station as recited in claim 5 wherein the method further comprises the steps of establishing a first scan frequency for receiving the control channel, incrementing to a second scan frequency if no control channel is received at the first scan frequency., and entering a sleep mode for a predetermined time period if no control channel is received at the second scan frequency.

9. A method for initializing communication between a handset and a suitable base station as recited in claim 8 wherein the method further comprises the steps of varying the predetermined time period in response to reception of control channels at the first and second scan frequencies.

10. A method for initializing communication between a handset and a suitable base station as recited in claim 5 wherein the method further comprises the steps of, after identifying the transmitting base station as the suitable base station, receiving a synchronizing control channel transmitted by the transmitting base station and if the CRC status of the synchronizing control channel corresponds to acceptable CRC status, synchronizing communication with the suitable base station.

11. A method for initializing communication between a handset and a suitable base station as recited in claim 10 wherein the method further comprises the steps of repetitively receiving the synchronizing control channel until bit synchronization, slot synchronization, frame synchronization and multiframe synchronization are established between the handset and the suitable base station.

7. A method for initializing communication between a handset and a suitable base station as recited in claim 25 wherein the method further comprises the steps of, if the CRC count exceeds a predetermined threshold, inhibiting reception of subsequently transmitted control channels for a predetermined time period, then receiving a lagging control channel and replacing the stored system information for the received control channel with system information for the lagging control channel if a cyclical redundancy check status for the lagging control channel corresponds to an acceptable cyclical redundancy check status and if received signal strength indication for the lagging control channel corresponds to an acceptable received signal strength indication.