WO2001033888A1

WO2001033888A1 - Method and apparatus for providing improved control channel selection

Info

Publication number: WO2001033888A1
Application number: PCT/IB2000/001501
Authority: WO
Inventors: Ari Uistola
Original assignee: Nokia Corporation; Nokia Inc.
Priority date: 1999-11-03
Filing date: 2000-10-18
Publication date: 2001-05-10
Also published as: BR0013508A; AU7680600A; MXPA02004400A

Abstract

A method for use in a wireless telecommunications system for performing a control channel selection procedure. The method includes steps of (a) invoking the control channel selection procedure; if the mobile station has left a packet data mode to set up a circuit call, (b) executing a digital control channel service determination procedure; and if the digital control channel service determination procedure returns a first failure indication, indicating that it was unable to select either a digital control channel or a packet control channel, (c) exiting the control channel selection procedure with a second failure indication set. The digital control channel service determination procedure sets the first failure condition if a candidate digital control channel is determined to be barred, and no other candidate digital control channels are indicated as being potentially available, and the mobile station is unable to receive a message (Beacon PCCH Parameters) that provides information regarding a packet control channel.

Description

METHOD AND APPARATUS FOR PROVIDING IMPROVED CONTROL CHANNEL SELECTION

FIELD OF THE INVENTION:

This invention relates generally to wireless communications systems employing digital control and traffic channels and, more particularly, to digital wireless communications systems capable of transmitting and receiving packet data.

BACKGROUND OF THE INVENTION:

Modern wireless mobile stations, such as radiotelephones and personal communicators that operate with a time division multiple access (TDMA) air interface protocol, are capable of transmitting packet data to and receiving packet data from a wireless network infrastructure. These modern systems employ both Digital Control Channels (DCCHs) and Digital Traffic Channels (DTCs) for voice (circuit switched) communications, as well as Packet Control Channels (PCCHs) and Packet Traffic Channels (PTCHs) for packet data, such as Internet data.

One exemplary air interface standard that specifies packet data services is known as TIA/EIA-136. In a recent publication TIA/EIA-136-123-B (13 September 1999) a method was proposed for a mobile station to select a control channel after the mobile station leaves a Packet Control Channel/Packet Traffic Channel (PCCH/PTCH) to set up a circuit call (e.g., a voice call). Section 4.2 (Control Channel Selection) and related sub-sections of TIA/EIA-136- 123-B describes this procedure. A sub-section of most interest herein is Section 4.2.2 (Basic DCCH Service Determination) .

Fig. 2 depicts the presently proposed procedures that are specified in Section 4.2 (Control Channel Selection) for execution by the mobile station, while Fig. 3 depicts the presently proposed procedures that are specified in Section 4.2.2 (Basic DCCH Service Determination) for execution by the mobile station.

Referring to Fig. 3, as presently proposed in Section 4.2.2 (Basic DCCH Service Determination) of the TIA/EIA-136-126-B publication, while in the Basic DCCH Service Determination state the mobile station is required to check or test several conditions or cases. One test that is made (designated as Step A in Fig. 3) is to determine whether a candidate DCCH is identified as being Barred according to a Cell Barred information element sent in an Access Parameters message. If the candidate DCCH is not barred, then control passes to Step H where a DCCH indication is set, and the mobile station exits the procedure. However, if the candidate DCCH is determined to barred at Step A, then the mobile station is expected to proceed as follows: mark the candidate DCCH as ineligible (Step B) and, if the candidate DCCH is not the original DCCH Pointer that was used by the mobile station when it left a PCCH/PTCH to setup a circuit call, the mobile station also marks the original DCCH Pointer as ineligible. If a time is specified in the Cell Barred information element, then the candidate DCCH and the original DCCH Pointer remain ineligible (barred) for the duration of the time specified.

If the mobile station has knowledge of additional candidate DCCHs it may reinvoke the Control Channel Selection procedure (Fig. 2) using one of these DCCHs as the candidate DCCH (Steps C, D and E) . Otherwise, the mobile station is expected to read a Beacon PCCH Parameters message (Step F) and return from this procedure with a PCCH indication set (Step G) . The Beacon PCCH Parameters message is specified to be one of a number of different types of messages that are sent to the mobile station in a Broadcast Control Channel (BCCH) . The Beacon PCCH Parameters message (see Fig. 6) gives information concerning PCCHs, thereby enabling the mobile station to locate one or more PCCHs.

The inventor has realized that the presently specified mobile station operation is flawed, and has the potential to create a problem that can adversely impact mobile station operation. That is, the presently specified procedure in Section 4.2.2 (Basic DCCH Service Determination) assumes that the mobile station will successfully read a Beacon PCCH Parameters message at Step F. However, in a situation where for some reason there is no Beacon PCCH Parameters message to read at Step F, the presently specified procedure still requires the mobile station to return with the PCCH indication set (Step G) . This error state of the mobile station (no Beacon PCCH Parameters message was read, yet the PCCH indication is set) can then result in an error condition occurring in Section 4.2 (Control Channel Section), where the PCCH indication is tested.

OBJECTS AND ADVANTAGES OF THE INVENTION:

It is a first object and advantage of this invention to provide a technique for improving a control channel selection procedure in a wireless telecommunications system.

It is a further object and advantage of this invention to provide an improved Control Channel Selection method and an improved Basic DCCH Service Determination method for execution by a mobile station.

SUMMARY OF THE INVENTION

The foregoing and other problems are overcome and the objects of the invention are realized by methods and apparatus in accordance with embodiments of this invention. A method is disclosed for use in a wireless telecommunications system for performing a control channel selection procedure. The method includes steps of (a) invoking the control channel selection procedure; for a case where the mobile station has left a packet data mode to set up a circuit call, (b) executing a digital control channel service determination procedure; and for a case where the digital control channel service determination procedure returns a first failure indication, indicating that it was unable to select either a digital control channel or a packet control channel, (c) exiting the control channel selection procedure with a second failure indication set.

The step of executing a digital control channel service determination procedure includes a step, responsive to a case wherein a candidate digital control channel is determined to be barred, and no other candidate digital control channels are indicated as being potentially available, of setting the first failure condition if the mobile station is unable to receive a message that provides information regarding a packet control channel. In a presently preferred embodiment this message is a Beacon

PCCH Parameters (or equivalent) message. The mobile station instead set sets a success indication (and generates a Go_PCCH event), if the mobile station is able to receive the

Beacon PCCH Parameters message.

BRIEF DESCRIPTION OF THE DRAWINGS

The above set forth and other features of the invention are made more apparent in the ensuing Detailed Description of the Invention when read m conjunction with the attached Drawings, wherein:

Fig. 1 is a block diagram of a wireless telecommunications network that operates m accordance with the teachings of this invention;

Fig. 2 is a logic flow diagram showing a conventional procedure that is specified in Section 4.2 (Control Channel Selection) of TIA/EIA-136-123-B (13 September 1999) for execution by the mobile station of Fig. 1;

Fig. 3 is a logic flow diagram showing a conventional procedure that is specified in Section 4.2.2 (Basic DCCH Service Determination) of TIA/EIA-136-123-B (13 September 1999) for execution by the mobile station of Fig. 1;

Fig. 4 is a portion of the logic flow diagram of Fig. 2, and depicts an improved Control Channel Selection procedure in accordance with an aspect of the teaching of this invention;

Fig. 5 is a logic flow diagram that depicts an improved Basic DCCH Service Determination procedure in accordance with a further aspect of the teaching of this invention; and

Fig. 6 shows the general format of a Beacon PCCH Parameters message .

DETAILED DESCRIPTION OF THE INVENTION

Referring to Fig. 1, there is illustrated a simplified block diagram of an embodiment of a wireless telecommunications system that includes a mobile station 10 that is suitable for practicing this invention. The Figure also shows a network operator A that transmits in a forward or downlink direction both physical and logical channels, such as DCCHs, BCCHs, PCCHs, DTCs, Packet Data Channels (PDCHs) , etc., to the mobile station 10 in accordance with a predetermined air interface standard. In the presently preferred, but not limiting, embodiment, the air interface standard conforms to the above-mentioned TIA/EIA-136 TDMA air interface, and/or to various modifications and enhancements thereto. In a typical case one or more other network operators (network operator B) may also be capable of transmitting to the mobile station 10, although at any given time the mobile station 10 will be connected to only one network operator. While not specifically shown in Fig. 1, it is assumed that a reverse or uplink communication path exists from the mobile station 10 to the network operator, and which conveys mobile originated access requests, DTC, PDCH, etc.

The mobile station 10 typically includes a micro-control unit (MCU) 12 having an output coupled to an input of a display 14 and an input coupled to an output of a keyboard or keypad 16. The mobile station 10 may be considered to be a radiotelephone, such as a cellular telephone or a personal communicator having packet data capabilities, or a wireless packet data terminal. The MCU 12 is assumed to include or be coupled to some type of a read-only memory (ROM) 12A for storing an operating program, as well as a random access memory (RAM) 12B for temporarily storing required data, scratchpad memory, etc. A separate removable SIM 15 can be provided as well, the SIM storing, for example, a preferred Public Land Mobile Network (PLMN) list and other subscriber-related information. The ROM 12A is assumed, for the purposes of this invention, to store a program for executing the software routines required to achieve compatibility with the selected air interface standard, including the enhancements thereto in accordance with the teachings of this invention shown in Figs. 4 and 5.

The mobile station 10 also contains a wireless section that includes a digital signal processor (DSP) 18, or equivalent high speed processor, as well as a wireless transceiver comprised of a transmitter 20 and a receiver 22, both of which are coupled to an antenna 24 for communication with the network operator. A local oscillator (LO) 19, which enables the transceiver to tune to different frequency channels, is controlled from the DSP 18.

Referring now to Fig. 4, the Control Channel Selection procedure is executed in order to allow the mobile station 10 to determine whether or not a given candidate control channel is acceptable for camping purposes (Step 30) . If the candidate control channel is marked as ineligible the mobile station 10 returns from this procedure with a failure indication (Step 32). Otherwise, the mobile station 10 proceed as follows. If the mobile station 10 has just left a PCCH/PTCH to set up a circuit call (Step 34) it executes at Step 36 a Signal Strength Aspects Determination procedure (see Section 4.2.1 of TIA/EIA-136-123-B) , otherwise, if the mobile station 10 has packet data service enabled (Step 35) it also executes the Signal Strength Aspects Determination procedure at Step 37 (see Section 4.2.1). The various steps following Steps 35 and 37 (shown in Fig. 2) are not described further herein, as they are not germane to an understanding of the teachings of this invention .

Assuming for the purposes of the description of this invention that the mobile station 10 has just left the PCCH/PTCH to set up a circuit call (Step 34), and that the Signal Strength Aspects Determination procedure (Step 36) returns a success indication, the mobile station 10 executes at Step 38 the Basic DCCH Service Determination procedure (see Section (4.2.2) of TIA/EIA-136-123-B, as well as the logic flow diagram of Fig. 5). Otherwise, the mobile station 10 returns from the Control Channel Selection procedure with a failure indication (Step 32).

In accordance with an aspect of the teachings of this invention, if the Basic DCCH Service Determination procedure 38 (Fig. 5) returns a failure indication, the mobile station 10 also returns from the Control Channel Selection procedure with a failure indication (Step 32). Otherwise, if the mobile station 10 exits the Basic DCCH Service Determination procedure 38 with the PCCH indication set, the mobile station 10 generates a Go_PCCH event and returns from the Control Channel Selection procedure with a success indication (Step 40) . Otherwise, if the mobile station 10 exits the Basic DCCH Service Determination procedure 38 with the DCCH indication set (see Step H of Fig. 3, as well as the corresponding Step H of Fig. 5), the mobile station 10 instead generates a Go_DCCH event and returns from the Control Channel Selection procedure with a success indication (Step 42).

Contrasting the relevant portions of Figs. 2 and 4, it can be seen that the mobile station 10 exits the Control Channel Selection from Steps 38/32 with a failure indication on a condition wherein neither one of the PCCH or the DCCH indications is set when the mobile station 10 returns from the Basic DCCH Service Determination routine

(Step 38), whereas previously (see Fig. 2) it was not possible to exit the Control Channel Selection procedure from the Basic DCCH Service Determination routine with a failure condition indicated. Instead, if the DCCH was barred at Step A of Fig. 2, and if no DCCHs were left in the Pointer list, the execution of Steps F and G would automatically result in the PCCH indication being set, whether or not the mobile station 10 was successful in reading the Beacon PCCH Parameters message at Step F. As such, if the DCCH indication was not set at Step 38, then the PCCH indication was guaranteed to be set, resulting then always in the generation of the Go_PCCH event at Step 40. It can be seen that the improved operation of the Control Channel Selection procedure shown in Fig. 4 has corrected and avoided the occurrence of this problem. Turning now to the improved Basic DCCH Service Determination procedure shown m Fig. 5, the mobile station 10 applies the following criteria to determine whether or not a candidate DCCH is suitable from a basic service perspective. The mobile station 10 first reads the DCCH Structure and Control Selection Parameters messages sent on the candidate DCCH (Steps 50 and 52) . The mobile station 10 tests for (Step 54) and then uses, if present, an Additional DCCH Information information element to determine its assigned DCCH according to a Mobile Station PCH Allocation procedure (see TIA/EIA-136-121) . If the candidate DCCH is not the assigned DCCH (Step 56), the mobile station 10 re-mvokes the Control Channel Selection procedure using the assigned DCCH as the candidate (Step 58) .

If the Additional DCCH Information information element is found not to be present at Step 54, at Step A (see again Fig. 3) a determination is made as to whether the candidate DCCH is identified as Barred according to the Cell Barred information element sent m the Access Parameters message.

If the DCCH is not barred, control passes to Step H as before to set the return value for the DCCH indication

(DCCH_Ind) . That is, the mobile station 10 declares the candidate DCCH as acceptable for camping purposes and returns from the Basic DCCH Service Determination procedure with the DCCH indication set.

If instead at Step A the DCCH is determined to be barred, the mobile station 10 proceeds to mark the candidate DCCH as ineligible (Step B) . If the candidate DCCH is not the original DCCH Pointer (see TIE/EIA-136-336) used by the mobile station 10 when it left the PCCH/PTCH to set-up the circuit call, it also marks the original DCCH Pointer as ineligible and, if the time parameter is specified m the Cell Barred information element, the candidate DCCH and the original DCCH Pointer (if different from the candidate DCCH) remain ineligible for the specified time. If the mobile station 10 has knowledge of additional candidate DCCHs (Step C) as derived from the DCCH Pointer List message sent on a PCCH, it may re-invoke the Control Channel Selection procedure using one of the additional DCCH(s) as a candidate DCCH (Steps D and E) .

If the mobile station 10 does not have knowledge of additional candidate DCCHs at Step C, then in accordance with an aspect of this invention control passes instead to Step F' where the mobile station attempts to read the Beacon PCCH Parameters message. If the Beacon PCCH Parameters message is determined to be found and readable, then the mobile station 10 returns from this procedure with the PCCH indication set (PCCH_Ind) at Step G. However, if the Beacon PCCH Parameters message is not found, then the mobile station 10 instead returns from the Basic DCCH

Service Determination procedure with a failure indication

(Step I) . Referring again as well to Fig. 4, this results in the failure path being taken from Step 38 to Step 32, and avoids the problem that would occur if the PCCH indication were set, without the mobile station 10 actually reading the Beacon PCCH Parameters message during the Basic DCCH Service Determination procedure.

Note should be made of the fact that the process block (Step F) of the prior art Basic DCCH Service Determination procedure of Fig. 3 has been replaced with the decision block (Step F') of Fig. 5, thereby enabling the failure indication at Step I to be generated upon the inability of the mobile station 10 to receive the Beacon PCCH Parameters message.

Although described above in the context of a specific TDMA air interface known at present as TIA/EIA-136-123-B (13 September 1999), the teachings of this invention can be applied to modifications and variations of this and other air interface standards that are capable of providing data services such as packet data services. Furthermore, the teachings of this invention are not limited for use in a TDMA type of network, but can be applied as well to both wide band and narrow band code division, multiple access (CDMA) networks.

Thus, while the invention has been particularly shown and described with respect to preferred embodiments thereof, it will be understood by those skilled in the art that changes in form and details may be made therein without departing from the scope and spirit of the invention.

Claims

CLAIMSWhat is claimed is:

1. In a wireless telecommunications system, a method for performing a control channel selection procedure, comprising steps of:

invoking the control channel selection procedure;

for a case where the mobile station has left a packet data mode to set up a circuit call;

executing a digital control channel service determination procedure; and

for a case where the digital control channel service determination procedure returns a first failure indication, indicating that it was unable to select either a digital control channel or a packet control channel, exiting the control channel selection procedure with a second failure indication set.

2. A method as in claim 1, wherein the step of executing a digital control channel service determination procedure comprises a step of:

for a case wherein a candidate digital control channel is determined to be barred, and no other candidate digital control channels are indicated as being potentially available, setting the first failure condition if the mobile station is unable to receive a message that provides information regarding a packet control channel.

3. A method as in claim 1, wherein the step of executing a digital control channel service determination procedure comprises a step of:

for a case wherein a candidate digital control channel is determined to be barred, and no other candidate digital control channels are indicated as being potentially available, setting the first failure condition if the mobile station is unable to receive a Beacon PCCH Parameters message.

4. A method as in claim 1, wherein the step of executing a digital control channel service determination procedure comprises steps of:

for a case wherein a candidate digital control channel is determined to be barred, and no other candidate digital control channels are indicated as being potentially available, setting the first failure condition if the mobile station is unable to receive a Beacon PCCH Parameters message, otherwise setting a success indication if the mobile station is able to receive a Beacon PCCH Parameters message.

5. In a wireless telecommunications system, a mobile station comprising a receiver, a data processor coupled to an output of said receiver, and a stored program for controlling the operation of said data processor, said data processor operating under the control of said stored program for performing a control channel selection procedure, said stored program controlling said data processor for invoking the control channel selection procedure and, for a case where said mobile station has left a packet data mode to set up a circuit call, for causing said data processor to execute a digital control channel service determination procedure and, for a case where the digital control channel service determination procedure returns a first failure indication that indicates that the digital control channel service determination procedure was unable to select either a digital control channel or a packet control channel, for directing said data processor to exit the control channel selection procedure with a second failure indication set.

6. A mobile station as in claim 5, wherein the data processor, when executing the digital control channel service determination procedure, is responsive to a case wherein a candidate digital control channel is determined to be barred, and no other candidate digital control channels are indicated as being potentially available, for setting the first failure condition if the receiver is unable to receive a message that provides information regarding a packet control channel.

7. A mobile station as in claim 5, wherein the data processor, when executing the digital control channel service determination procedure, is responsive to a case wherein a candidate digital control channel is determined to be barred, and no other candidate digital control channels are indicated as being potentially available, for setting the first failure condition if the receiver is unable to receive a Beacon PCCH Parameters message, while otherwise setting a success indication and a Go_PCCH event if the receiver is able to successfully receive the Beacon PCCH Parameters message.