Subject: [NEXTEL-1] Method and apparatus for providing dispatch scan in a CDMA communication system

From: Marcel <[email-masked]>
Date: Wed, 22 Jan 2003 03:42:28 -0500

January 16, 2003

 Rozenstrauch, Alexander ;   et al.

Assignee Name
MOTOROLA, INC.

Method and apparatus for providing dispatch scan in a CDMA communication system

                                             Abstract

A CDMA base site provides dispatch group call service to members of a dispatch group by
using a first long-code mask. The
base site also repeatedly transmits the group call's channel assignment so that a scanning
communication unit can detect that the
call is active. In order for the scanning communication unit to decode the dispatch
communication once the call is detected, it
requests a long-code mask transition from the base site. The base site then transmits a
new long-code mask and begins
encoding the dispatch communication using the new mask. Thus, the scanning communication
unit is able decode the
communication and thereby join the active CDMA dispatch group call.

                                             Claims
What is claimed is:

1. A method for a base site to provide a dispatch scan service to a communication unit in
a CDMA communication system, the
method comprising the steps of: transmitting, by the base site, a channel assignment for a
dispatch call via a paging resource;
encoding, by the base site, dispatch communication for the dispatch call using a first
CDMA long-code mask; receiving, by the
base site, a request for a CDMA long-code mask transition for the dispatch call;
transmitting, by the base site, a second
CDMA long-code mask for the dispatch call in response to the request; and encoding, by the
base site, dispatch
communication for the dispatch call using the second CDMA long-code mask after
transmitting the second CDMA long-code
mask.

2. The method of claim 1 wherein the dispatch call is a group dispatch call.

3. The method of claim 1 wherein the step of transmitting the channel assignment further
comprises the step of repeatedly
transmitting the channel assignment for the duration of the dispatch call.

4. The method of claim 1 wherein the second CDMA long-code mask is transmitted to a
communication unit from which the
request was received.

5. The method of claim 4 further comprising the step of verifying that the communication
unit is authorized to join the dispatch
call before transmitting the second CDMA long-code mask.

6. The method of claim 4 wherein the second CDMA long-code mask is transmitted via a
traffic channel of the dispatch call,
thereby transmitting the second CDMA long-code mask to participants of the dispatch call
in addition to the communication
unit from which the request was received.

7. The method of claim 4 wherein the second CDMA long-code mask is transmitted via an
access channel.

8. A method for a communication unit to obtain dispatch scan service from a base site in a
CDMA communication system, the
method comprising the steps of: scanning, by the communication unit, a paging resource for
a channel assignment for a dispatch
call; transmitting, by the communication unit, a request for a CDMA long-code mask
transition for the dispatch call; receiving,
by the communication unit, a CDMA long-code mask for the dispatch call; and decoding, by
the communication unit, dispatch
communication using the CDMA long-code mask for the dispatch call.

9. The method of claim 8 wherein the dispatch call is a group dispatch call.

10. The method of claim 8 wherein dispatch communication for the dispatch call is encoded
using an initial CDMA long-code
mask at least before the step of transmitting the request for a CDMA long-code mask
transition.

11. The method of claim 8 wherein the request for a CDMA long-code mask transition is
transmitted via a traffic channel of the
dispatch call.

12. The method of claim 8 wherein the request for a CDMA long-code mask transition is
transmitted via an access channel.

13. The method of claim 8 further comprising the step of completing a call in-progress
before transmitting the request for a
CDMA long-code mask transition.

14. A base site comprising: a transmitter capable of transmitting a channel assignment for
a dispatch call via a paging resource
and of transmitting a second CDMA long-code mask for the dispatch call in response to a
request for a CDMA long-code
mask transition for the dispatch call; a receiver capable of receiving the request; and a
processor capable of instructing the
transmitter to transmit the channel assignment, of encoding dispatch communication for the
dispatch call using a first CDMA
long-code mask, of instructing the transmitter to transmit the second CDMA long-code mask,
and of encoding dispatch
communication for the dispatch call using the second CDMA long-code mask after the
transmitter transmits the second CDMA
long-code mask.

15. The base site of claim 14 wherein the processor is capable of instructing the
transmitter to transmit the channel assignment
repeatedly for the duration of the dispatch call.

16. A communication unit comprising: a receiver capable of scanning a paging resource for
a channel assignment for a dispatch
call and of receiving a CDMA long-code mask for the dispatch call; a transmitter capable
of transmitting a request for a
CDMA long-code mask transition for the dispatch call; a processor capable of instructing
the transmitter to transmit the request
and of decoding dispatch communication using the CDMA long-code mask for the dispatch
call.

                                           Description

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is related to a co-pending application, "METHOD AND APPARATUS FOR
PROVIDING
DISPATCH SERVICE IN A CDMA COMMUNICATION SYSTEM", Ser. No. 09/443,538, filed on Nov., 19,
1999,
assigned to the assignee of the present application, which prior application is hereby
incorporated by reference verbatim, with
the same effect as though the prior application were fully and completely set forth
herein.

FIELD OF THE INVENTION

[0002] The present invention relates generally to the field of wireless communications
and, more particularly, to dispatch scan
on code division multiple access (CDMA) communication systems.

BACKGROUND OF THE INVENTION

[0003] Communication systems today, such as Motorola's "iDEN" system, provide users with
so-called dispatch services.
Unlike the interconnect services provided by today's cellular systems, dispatch services
have been traditionally provided by
two-way radio systems. Such services allow a user to communicate in ways that are
difficult or costly using today's cellular
systems. The dispatch group call service, for example, enables a user to communicate with
a group of people simultaneously
and instantaneously, usually just by depressing a push-to-talk (PTT) button. Using a
cellular system, such a call could not occur
instantaneously since either telephone numbers would need to be dialed for a three-way
call or arrangements would need to be
made to setup a conference call.

[0004] Likewise, the dispatch individual call service enables a user to communicate with
another user quickly and
spontaneously. This feature is ideal for two people who are working together but are
unable to speak with one another directly
such as two people working in concert but in different parts of a building. Where a
wireless telephone call is more appropriate
for a conversation, short messages between two people as they work are better facilitated
by the dispatch individual call
service.

[0005] Both of these dispatch services are made more flexible by a so-called dispatch scan
service that allows a user to scan
for call activity across multiple dispatch groups. For example, a user involved in a
dispatch group or individual call can
simultaneously scan for any call activity occurring among members of a different dispatch
group and join such a call while
in-progress. Thus, a user, such as a supervisor, can effectively monitor a number of
different dispatch groups and take part in
their calls as required.

[0006] Although these dispatch services are available to users of Motorola's "iDEN"
system, they are not available on today's
CDMA systems. The co-pending application "METHOD AND APPARATUS FOR PROVIDING DISPATCH
SERVICE
IN A CDMA COMMUNICATION SYSTEM" discloses modifications to the IS-95 CDMA standard to
allow the members
of a dispatch group to decode the group communication. For example, the CDMA long-code
mask used to encode the
communication is generated using a dispatch identifier instead of the Electronic Serial
Number (ESN). Also, a dispatch identifier
is used to determine the appropriate paging resource for transmitting and receiving
dispatch call pages. However, this
co-pending application does not disclose a CDMA embodiment that enables the dispatch scan
service. Therefore, a need
exists for an apparatus and method for providing a dispatch scan service on a CDMA
communication system.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIG. 1 is a block diagram depiction of a CDMA communication system in accordance
with a preferred embodiment of
the present invention.

[0008] FIG. 2 is a logic flow diagram of steps executed by a base site in accordance with
a preferred embodiment of the
present invention.

[0009] FIG. 3 is a logic flow diagram of steps executed by a communication unit in
accordance with a preferred embodiment
of the present invention.

DESCRIPTION OF A PREFERRED EMBODIMENT

[0010] In general, the present invention discloses a method and an apparatus that provide
dispatch scan in a CDMA
communication system. A communication unit that joins a dispatch call already in-progress
is unable to decode the group
communication because it does not have the long code mask required to decode it. The
present invention provides the use of a
long code transition for the dispatch call in order that the joining unit uses the same
long code mask as the other units already
participating in the call.

[0011] The present invention can be more fully understood with reference to FIGS. 1-3.
FIG. 1 is a block diagram depiction of
a CDMA communication system 100 in accordance with a preferred embodiment of the present
invention. Preferably, the
CDMA communication system 100 is a system in accordance with the well-known
Telecommunications Industry
Association/Electronic Industries Association Standard 95 (TIA/EIA IS-95-B) modified as
described below to implement the
present invention and modified as described in co-pending application "METHOD AND
APPARATUS FOR PROVIDING
DISPATCH SERVICE IN A CDMA COMMUNICATION SYSTEM" to provide dispatch group and individual
service.
CDMA communication system 100 could alternatively be based upon the TIA/EIA IS-2000 (CDMA
2000) standard rather
than IS-95.

[0012] CDMA communication system 100 comprises fixed network equipment and mobile
communication units. The fixed
network equipment includes a base site 101 that is preferably networked to other base
sites, controllers, and switches, all part
of the fixed network equipment of system 100 and all well known to those skilled in the
art. For simplicity, only base site 101 of
the fixed network equipment is shown in FIG. 1. Again for simplicity, only three of what
could be thousands of mobile
communication units are shown in FIG. 1. Communication units 103-105 each preferably
comprise CDMA-capable wireless
phones. They communicate with base site 101 via a CDMA air interface that comprises
coded-channel communication
resources 115 and 116. In an alternative embodiment, however, the communication units
could comprise any communication
device capable of communicating via a CDMA air interface.

[0013] Each of the communication units 103-105 comprises a common set of elements, a
transmitter, a receiver, and a
processor. In particular, processor 110, which typically comprises one or more processing
devices (e.g., microprocessors,
digital signal processors, etc.) and memory devices, is coupled to a transmitter 109 and a
receiver 111. Each of these elements
is well-known in the art. In the preferred embodiment, under the control of software
algorithms stored in the memory devices of
processor 110 and in cooperation with the other elements shown, the processor 110 performs
those tasks required for
operation of the communication unit, including the method described relative to FIG. 3.

[0014] Similarly, base site 101 comprises elements well-known in the art, a transmitter
106, a receiver 108, and a processor
107. Coupled to transmitter 106 and receiver 108, processor 107 preferably comprises
memory devices and processing
devices such as a microprocessor and digital signal processor. In the preferred
embodiment, under the control of software
algorithms stored in the memory devices of processor 107 and in cooperation with the other
elements shown, the processor
107 performs those tasks required for operation of the base site, including the method
described relative to FIG. 2.

[0015] Operation of the preferred CDMA communication system 100, in accordance with the
present invention, occurs
substantially as follows. Communication units 103 and 104 are, for the purpose of
illustration, logically arranged into a dispatch
group (or talkgroup) 113 that is involved in a dispatch group call supported by base site
101. Preferably, processor 107
instructs base site transmitter 106 to repeatedly transmit an IS-95 (or CDMA 2000)
CHANNEL_ASSIGNMENT for the
dispatch call via CDMA paging resource 115. Also, processor 107 encodes the dispatch
communication for the dispatch call
using a first CDMA long-code mask.

[0016] The dispatch scan service allows the user of communication unit 105 to monitor for
and join the dispatch call
in-progress. Communication unit receiver 111 scans paging resource 115 for a channel
assignment for the dispatch call. Since
the dispatch call is in progress, the communication unit 111 will receive the channel
assignment. However, communication unit
111 will not be able to decode the dispatch communication of the dispatch call on CDMA
traffic channel 116 since base site
101 and communication units 103 and 104 are using the first CDMA long-code mask to
encode/decode the communication.
Preferably, communication units 103 and 104 received the long-code mask at the beginning
of the call, i.e., before
communication unit 105 was attempting to join. Therefore, communication unit processor 110
instructs transmitter 109 to
transmit a request for a CDMA long-code mask transition for the dispatch call. Preferably,
communication unit 105 transmits
this request using an IS-95 (or CDMA 2000) ORDER message via CDMA traffic channel 116.
Alternatively however, this
request may be transmitted via a CDMA access channel.

[0017] Base site receiver 108 receives the request for a CDMA long-code mask transition
and in response processor 107
instructs the transmitter 106 to transmit a second CDMA long-code mask. Preferably, the
second CDMA long-code mask is
transmitted within an IS-95 (or CDMA 2000) ORDER message via traffic channel 116. The
communication unit receiver 111
receives the second CDMA long-code mask as do communication units 103 and 104. Base site
processor 107 switches from
using the first CDMA long-code mask to using the second to encode dispatch communication
for the dispatch group call. Thus,
processor 110 can now decode the dispatch communication and effectively join the dispatch
call while in-progress.

[0018] FIG. 2 is a logic flow diagram 200 of steps executed by a base site in accordance
with a preferred embodiment of the
present invention. Preferably, this method is embodied in the software stored in the
memory devices of CDMA base sites and
used to provide dispatch scan service to the communication units of the CDMA communication
system.

[0019] The logic flow begins (202) when the base site transmits (204) a channel assignment
for a dispatch call via a paging
resource. The base site then encodes (206) dispatch communication for the dispatch call
using a first CDMA long-code mask.
Upon receiving (208) a request for a CDMA long-code mask transition for the dispatch call
from a communication unit, the
base site preferably verifies (210) that the communication unit is authorized to join the
dispatch call. Such authorization checking
is well known in the art and typically involves checking a database for the appropriate
stored privileges. Upon verifying
authorization, the base site transmits (212) a second CDMA long-code mask for the dispatch
call. Finally, having transmitted
the second mask to the requesting communication unit and the communication units already
participating in the call, the base site
begins encoding (214) the dispatch communication of the dispatch call using the second
CDMA long-code mask, and the logic
flow for the base site ends (216). Thus, the requesting communication unit is now able to
decode the dispatch communication
using the second CDMA long-code mask.

[0020] FIG. 3 is a logic flow diagram 300 of steps executed by a communication unit in
accordance with a preferred
embodiment of the present invention. Preferably, this method is embodied in the software
stored in the memory devices of the
communication units and used to obtain dispatch scan service from the base sites of a CDMA
communication system.

[0021] The logic flow begins (302) when the communication unit begins (304) a call or
communication service. In addition to
this communication activity, the communication unit user may also desire to monitor the
call activity of a specific dispatch group.
Preferably then either the user or the user's pre-programming triggers the communication
unit to scan (306) a paging resource
for a dispatch call channel assignment for that specific dispatch group. In the preferred
embodiment, when the scanning detects
a dispatch call channel assignment, the user may complete (308) the call in-progress, and
then in order to join the dispatch
group call, transmit (310) a request for a CDMA long-code mask transition. One skilled in
the art will note that the step of
completing a call in-progress may be no more than abruptly ending that call or service. In
response to the request, the
communication unit receives (312) a CDMA long-code mask for the dispatch call. The
communication unit can then begin
decoding (314) the dispatch communication of the dispatch group call using the CDMA
long-code mask, and the logic flow for
the communication unit ends (316).

[0022] Logic flow diagram 300 illustrates a scenario in which a communication unit begins
(304) a call and then completes
(308) the call before attempting to join the dispatch group call. In practice, the
communication unit may be idle with respect to
other communication services and yet monitoring for call activity by scanning for a
channel assignment. In this scenario, steps
304 and 308 would not be part of the method performed.

[0023] The present invention, in the manner described above, provides a dispatch scan
service to communication units in a
CDMA communication system that supports dispatch communication. Specifically, in the
preferred embodiment of the
invention, a CDMA base site provides dispatch group call service to members of a dispatch
group by using a first long-code
mask. The base site also repeatedly transmits the group call's channel assignment so that
a scanning communication unit can
detect that the call is active. In order for the scanning communication unit to decode the
dispatch communication once the call is
detected, it requests a long-code mask transition from the base site. The base site then
transmits a new long-code mask and
begins encoding the dispatch communication using the new mask. Thus, the scanning
communication unit is able to decode the
communication and thereby join the active call.

[0024] The descriptions of the invention, the specific details, and the drawings mentioned
above, are not meant to limit the
scope of the present invention. It is the intent of the inventors that various
modifications can be made to the present invention
without varying from the spirit and scope of the invention, and it is intended that all
such modifications come within the scope of
the following claims and their equivalents.

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From: Rick Parrish <[email-masked]>
Date: Wed, 22 Jan 2003 19:44:13 -0600

Marcel wrote:

>3. The method of claim 1 wherein the step of transmitting the channel assignment further comprises the step of repeatedly transmitting the channel assignment for the duration of the dispatch call.
>  
>
Motorola re-invents the "late-entry" or continuation message.

-rick (sorry, this is funny - don't ask why)