Subject: [NEXTEL-1] Dispatch call origination and set up in a CDMA mobile communication system

From: Marcel <[email-masked]>
Date: Wed, 22 Jan 2003 04:19:27 -0500

> Presently commercially available dispatch service is done with time division multiple
access (TDMA) air interfaces.
TDMA schemes assign each radio to a frequency and a specific time slot in a repeating time
frame. While TDMA achieves
higher capacity of traffic in a given frequency spectrum over systems that are merely
frequency division multiple access
(FDMA), code division multiple access (CDMA) systems permit even greater capacity.
However, CDMA systems present a substantial problem in implementing dispatch calling.
=====================================================================================

Harris, John M. ;   et al.
                                                                               December
26, 2002

Dispatch call origination and set up in a CDMA mobile communication system

                                             Abstract

In a CDMA wireless communication system (200) a dispatch call can be established between
two CDMA mobile stations
(202, 226), or between other mobile stations and the CDMA mobile station, or between a
CDMA mobile station and a
computer (236) located outside of the wireless system. To reduce the delay normally
association with call set up in a CDMA
system, a dispatch processing network (128, 144) is provided in addition to a telephony
switch (118). Dispatch calls and call
set up requests are routed to the dispatch processing network from the radio access
network (110) which includes base
stations (204, 206). Once a dispatch call request is made, while the dispatch processing
network begins setting up a traffic
channel for the originating mobile communication device, the target is also paged, and
upon responding, set up on a traffic
channel. The concurrence of establishing radio links with the target and originating
communication devices substantially reduces
dispatch call set up time.

 Inventors:
              Harris, John M.; (Chicago, IL) ; Crocker, Ronald T.; (St. Charles, IL) ;
Proctor, Lee M.; (Cary, IL)

 Name

                  Motorola, Inc.

       Claims

What is claimed is:

1. A method of originating a dispatch call over a code division multiple access (CDMA) air
interface from a mobile
communication device, comprising: transmitting a dispatch call origination message from
the mobile communication device to a
fixed equipment network over a CDMA channel, the dispatch call origination message
containing a target identifier; in response
to the transmitting, setting up a traffic channel between the mobile communication device
and the fixed equipment network;
setting up a call path between the target and the fixed equipment network; and wherein
setting up the traffic channel and setting
up the call path between the target and the fixed equipment network are performed
concurrently.

2. A method of originating a dispatch call as defined in claim 1, wherein setting up the
traffic channel between the mobile
communication device and the fixed equipment network comprises setting up a communication
link according to a
retransmission protocol to allow retransmission of data packets over the traffic channel.

3. A method of originating a dispatch call as defined in claim 1, wherein setting up the
call path between the target and the fixed
equipment network comprises setting up the call path between a second mobile communication
device and the fixed equipment
network.

4. A method of originating a dispatch call as defined in claim 3, wherein setting up the
call path between the second mobile
communication device and the fixed equipment network comprises setting up the call path
between a mobile communication
device and the fixed equipment network over a CDMA air interface.

5. A method of originating a dispatch call as defined in claim 3, wherein setting up the
call path between the second mobile
communication device and the fixed equipment network comprises setting up the call path
between a mobile communication
device and the fixed equipment network over a time division multiple access (TDMA) air
interface.

6. A method of originating a dispatch call as defined in claim 1, wherein setting up the
call path between the target and the fixed
equipment network comprises setting up the call path between a personal computer and the
fixed equipment network over a
packet network.

7. A method of originating a dispatch call as defined in claim 1, wherein setting up the
call path between the target and the fixed
equipment network comprise: routing the dispatch call origination message from a base site
to a dispatch agent component of
the fixed equipment network; determining a network location of the target at the dispatch
agent; paging the target at the
network location with an incoming dispatch call message; and responding to the incoming
dispatch call message, performed by
the target.

8. A method of originating a dispatch call as defined in claim 7, wherein the step of
routing the dispatch call origination message
from a base site to a dispatch agent component comprises the steps of routing the dispatch
call origination message from a base
site to a first dispatch agent or a second dispatch agent.

9. A method of originating a dispatch call as defined in claim 8 wherein the first
dispatch agent is located within a mobile
switching center.

10. A method of originating a dispatch call as defined in claim 9 wherein the second
dispatch agent is not located within a
mobile switching center.

11. A method of originating a dispatch call as defined in claim 1, further comprising,
upon completion of setting up the traffic
channel between the mobile communication device and the fixed equipment network and
setting up the call path between the
target and the fixed equipment network, sending a talk permission message to the mobile
communication device from the fixed
equipment network.

12. A method of setting up a dispatch call to a target mobile communication device over a
code division multiple access
(CDMA) air interface, comprising: receiving a page notification from a fixed equipment
network at the target mobile
communication device, the page notification including a dispatch notification;
transmitting a page response, including a pilot
power measurement; and if the pilot power measurement indicates a power level above a
preselected threshold, setting up a
traffic channel between the target mobile communication device and the fixed equipment
network.

13. A method of setting up a dispatch call to a target mobile communication device as
defined in claim 12, further comprising:
prior to receiving the page notification at the target mobile communication device:
scanning the pilot signal of at least one serving
cell in the vicinity of the target mobile communication device; determining a strongest
pilot signal and a serving cell
corresponding to the strongest pilot signal; and scanning a paging channel of the serving
cell corresponding to the strongest pilot
signal.

14. A method of setting up a dispatch call to a target mobile communication device as
defined in claim 12, wherein the method
is performed concurrently with fixed equipment network setting up a call path between an
originating device and the fixed
equipment network.

15. A method of setting up a dispatch call to a target mobile communication device as
defined in claim 14, wherein the setting
up the call path between an originating device and the fixed equipment network comprises
setting up the call path between an
originating mobile communication device and the fixed equipment network.

16. A method of setting up a dispatch call to a target mobile communication device as
defined in claim 14, wherein the setting
up the call path between an originating device and the fixed equipment network comprises
setting up the call path between an
originating CDMA mobile communication device and the fixed equipment network.

17. A method of setting up a dispatch call to a target mobile communication device as
defined in claim 14, wherein the setting
up the call path between an originating device and the fixed equipment network comprises
setting up the call path between a
computer and the fixed equipment network.

18. A method of setting up a dispatch call between an originating code division multiple
access (CDMA) mobile communication
device and a target CDMA mobile communication device, comprising: transmitting a dispatch
call origination message from the
originating CDMA mobile communication device to a fixed equipment network over a CDMA
channel, the dispatch call
origination message containing a target identifier corresponding to the target CDMA mobile
communication device; in response
to the transmitting, initiating the set up of a traffic channel between the originating
CDMA mobile communication device and the
fixed equipment network; paging the target CDMA mobile communication device and the fixed
equipment network; and
wherein initiating the set up of a traffic channel and paging the target CDMA mobile
communication device are performed
concurrently.

19. A method of setting up a dispatch call as defined by claim 18, in response to the
paging, the method further comprising:
transmitting a page response, including a pilot power measurement; and in response to
transmitting the page response,
transmitting a talk permission message to the originating CDMA mobile communication device
from the fixed equipment
network.

20. A method of setting up a dispatch call as defined by claim 19, wherein the talk
permission message is transmitted to the
originating CDMA mobile communication device before the traffic channel between the
originating CDMA mobile
communication device and the fixed equipment network is set up, the method further
comprising: alerting a user of the
originating CDMA mobile communication device to begin speaking; and buffering the speech
in the originating CDMA mobile
communication device until the traffic channel between the originating CDMA mobile
communication device and the fixed
equipment network is established; and transmitting the buffered speech to the target CDMA
mobile communication device over
the fixed equipment network.

                                           Description

TECHNICAL FIELD

[0001] This invention relates in general to mobile communication systems, and more
particular to mobile communication
systems using a code division multiple access (CDMA) air interface for dispatch calls.

BACKGROUND OF THE INVENTION

[0002] Dispatch calling originally was used in fleet radio systems where a central
dispatcher would communicate with remotely
located mobile radios, such as in trucking operations, and public safety radio systems.
Today this concept has evolved into a
type of call between two or mote parties, and where the communication is essentially
simplex or half-duplex in nature, and
where the call is carried in part over a fixed equipment network. This type of calling has
become very popular with small
businesses and even between family members. An example of a present-day state of the art
dispatch system is that operated by
Nextel Communications, Inc. and which uses iDEN mobile phones and infrastructure equipment
manufactured by Motorola,
Inc. Indeed, the so-called "private call" feature of these systems have become a key
marketing factor.

[0003] In general, the private call is a dispatch call between two parties. A first party
knows the private identifier of the second
party, and uses that to make a dispatch call to the second party. The advantage of a
dispatch call is the speed with which the
other party can be contacted, and the "caller speaks first" aspect of a dispatch call.
That is, when the first party initiates a
dispatch call to the second party, the communication system rapidly sets up the call, and
sends a message to the first party's
radio or mobile communication device. Upon receiving the message, the first party's radio
generates an audible alert to let the
first party know when to begin speaking. The second party's radio receives the voice
signal and plays it for the second party to
hear, with the second party having to take any action. The speed with which one party can
communicate information to another
party is significantly less compared to setting up a mobile telephone call between the tow
radios.

[0004] Presently commercially available dispatch service is done with time division
multiple access (TDMA) air interfaces.
TDMA schemes assign each radio to a frequency and a specific time slot in a repeating time
frame. While TDMA achieves
higher capacity of traffic in a given frequency spectrum over systems that are merely
frequency division multiple access
(FDMA), code division multiple access (CDMA) systems permit even greater capacity.
However, CDMA systems present a
substantial problem in implementing dispatch calling.

[0005] In a CDMA system several mobile communication devices communicate on the same
frequency at the same time, but
use different pseudorandom codes to define different channels. CDMA systems achieve higher
capacity through extensive
management of each channel, and in particular managing the power at which the mobile
communication device transmits so that
other mobile communication devices will not have their signal overwhelmed or otherwise
corrupted. However, power
management in a CDMA air interface contributes significantly to the delay in setting up a
call, and has been a prohibiting factor
in designing a CDMA system that can set up calls rapidly, as is necessary to implement
dispatch calling. Another source of
delay in presently available CDMA systems is that standard telephony switching is used
which requires a call to first be set up
between the mobile communication device and the fixed equipment network, which then
switches the call to the party being
called who must answer the call before the calling party can speak. If the calling party
is calling another CDMA service
subscriber, then a link must be set up between the target party, and this is typically
done after the link between the calling party
has set up a link to the fixed equipment network. This delay results in an unacceptable
amount of time being required for
dispatch calling. Therefore there is a need for a method and a system which facilitates
rapid call set up in a system using a
CDMA air interface so that dispatch calling may be implemented.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FIG. 1 shows a system diagram of a communication system in accordance with the
invention;

[0007] FIG. 2 shows a system diagram of a communication system in accordance with the
invention, and illustrating the
distributed aspect of the fixed equipment network;

[0008] FIG. 3 shows a flow chart diagram of a method for establishing a dispatch call in a
CDMA system, in accordance with
the invention; and

[0009] FIG. 4 shows a flow chart diagram of a method for starting a dispatch call to a
CDMA mobile communication device;

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0010] While the specification concludes with claims defining the features of the
invention that are regarded as novel, it is
believed that the invention will be better understood from a consideration of the
following description in conjunction with the
drawing figures, in which like reference numerals ate carried forward. A brief description
of the prior art is also thought to be
useful.

[0011] The invention substantially and significantly reduces the delay in setting up a
call path normally associated with CDMA
systems by concurrently setting up call links between the originating mobile station and
the fixed equipment network and
between the target and the fixed equipment network. Furthermore, to further reduce delay,
the link established between the
originating mobile station and the fixed equipment network can be implemented according to
a protocol which uses
retransmission such as a packet network session, instead of a tradition telephone circuit
network session.

[0012] Referring to FIG. 1, there is shown a system diagram 100 of a communication system
in accordance with the invention.
A mobile communication device 102 communicates with a fixed equipment network 104 over a
CDMA air interface 106. The
fixed equipment network comprises a plurality of base stations such as base station 108,
which is a CDMA base transceiver
site, or BTS. As is known, a base site establishes a serving area in the vicinity of the
base site, and mobile communication
devices in the serving are can access the fixed equipment network over the air interface
with the base station. The base station
is part of a radio access network (RAN) 110, which further comprises a selection and
distribution unit (SDU) 112, transcoder
(XC) 114, and a mobility manager (MM) 116. The SDU is responsible for managing link-level
diversity known as Soft
Handoff. The SDU routes information to other components of the fixed equipment network as
shown, depending on the nature
of the information, as will be described herein. The transcoder 114 converts voice
information and data from the encoded form
used over the air interface to standard telephony pulse code modulation (PCM) and
vice-versa. The mobility manager 116
controls the access to the air interface 106, as well interpreting the signaling
information received from the mobile
communication device 102 as well as converting signaling from the mobile switching center
(MSC) 118 to the form required by
the mobile communication device. The RAN 110 is operably connected to the MSC 118, as is
known in the art. The MSC
switches telephone calls within the system and also to the public switched telephone
network (PSTN) 120. Signaling is sent to
the MSC by the MM 116, while telephony traffic is sent between the transcoder 114 and the
MSC. The MSC uses a home
location register 122 in a conventional manner. For data connections, such as internet
access, a packet data serving node
(PDSN) 124 is operably coupled to the RAN. The PDSN provides access and
gateway/proxy/firewall functions between the
system and a public data network (PDN) 126, such as the Internet, so that mobile
communication devices can access content
on the PDN and perform other activity such as email.

[0013] The dispatch calling is facilitated by a dispatch application system (DAS) 128. The
DAS comprises a dispatch
application processor (DAP) 130, surveillance gateway (SG) 132, dispatch access controller
(DAC) 134, packet duplicator
(APD) 136, and a router 138. The DAS is much like the presently used dispatch agent
processors presently in use in some
communications systems. The DAP 130 controls all dispatch calls, including the set up of
dispatch calls, paging mobile
communication devices, and so on. The SG provides the control interface to a law
enforcement agency for lawful intercept of
dispatch call voice traffic. The DAC routes dispatch traffic to other dispatch networks or
DASs over a horizontal network or
private network 140 The HLR 142 coupled to the horizontal network 140 provides a single
point of contact for subscription
information for a given subscriber of the service. The DAP communicates with the HLR to
acquire this subscription information
for use during dispatch call processing.

[0014] Between the RAN 110 and the DAS 128 is the dispatch application gateway (DAG) 144.
The DAG comprises a
dispatch visit location register (D-VLR) or dispatch location register 146 operably
coupled to a dispatch agent (DA) 148. The
DAG also comprises a wireless data agent (WDA) 150. The DA 148 acts as a protocol
converter and changes CDMA
messaging to DAP messaging so that the messages sent over the CDMA air interface via the
MM 116 can be passed on to the
DAP 130 during a dispatch call set up and during the dispatch call itself. The DA also
uses the D-VLR to map dispatch paging
requests to the correct CDMA location areas so that such messages can be routed to the
correct location.

[0015] Referring now to FIG. 2, there is shown a system diagram 200 of a communication
system in accordance with the
invention, and illustrating the distributed aspect of the fixed equipment network. The
equipment shown in this figure is
substantially the same as equipment shown and described in reference to FIG. 1 having the
same name. Due to multiple
instances of similarly named equipment, different reference numerals will be used here.
The user of a CDMA mobile
communication device 202 desires to make a dispatch call to a target, which could be
another CDMA mobile communication
device, a TDMA mobile communication device, or a computer running a virtual mobile
communication device software
application for example. The mobile communication device 202 is known as an originating
mobile communication device 202
since it is originating the dispatch call. The originating mobile communication device
begins by transmitting a dispatch call
origination message from the mobile communication device to the fixed equipment network
over a CDMA channel. The
dispatch call origination message contains a target identifier, such as a private call
identifier, for example. The first component of
the fixed equipment network to receive the message is the base transceiver site (BTS) 204.
The BTS sends the message up to
a base site controller (BSC) 206 which detects the presence of the dispatch call request,
and forwards the message over an IP
network 208 to the dispatch agent (DA) 210. The DA here is the same as that shown in FIG.
1, associated with reference
numeral 148. The DA routes the call request over an IP network or networks 208, 212 to the
dispatch application system
(LAS) 214. The DAS is the same as the DAS in FIG. 1 having reference numeral 128, and is
responsible for setting up and
controlling dispatch calls. The DAS then sends a page request to the appropriate dispatch
agent 218 over the IP network 212,
216. It may be a different DA 218 as shown in FIG. 2, or it may be the same DA 210 that
sent the request to the DAS. Upon
receiving the page request, the DA 218 accesses the D-VLR 220 to determine the appropriate
serving sites to which to send
the page. The DA 218 then routes the page to a target BSC 222, which in turn routes it to
the particular set of target BTS, such
as target BTS 224, which broadcasts the page and the target mobile communication device's
identifier over a broadcast control
channel where it is detected by the target mobile communication device 226.

[0016] Thus far the dispatch request described could be fairly routine. However, given
that the dispatch call being set up here is
a CDMA to CDMA call, there are substantial differences. When the BSC initially passes the
dispatch call request on to the DA
210, it immediately begins allocating communication resources for the call. Specifically,
the CDMA mobile communication
device is assigned to a traffic channel and messaging for facilitating that assignment is
sent to the originating mobile
communication device. Similarly, and concurrently, when the target mobile communication
device responds to the page, the
target BSC 222 begins to set up the call on the target end of the call. By using the
dispatch equipment such as the DAS and the
DA, and not a CDMA MSC to set up the dispatch call, the main delay in setting up the
dispatch call is in call set up at the
serving cells. Conventional call set up is done sequentially. According to the present
invention, call set up is done concurrently
at both ends of the call.

[0017] The channel that is set up over the air interface is similar to a packet data
channel in that it follows a retransmission
protocol. Since a dispatch call is a simplex or half-duplex call, any delay created by
retransmitting voice data packets will be
largely unnoticeable since only one person speaks at a time. The BSC can buffer several
frames of speech before forwarding
them. Furthermore, this takes advantage of discontinuous transmission (DT) operation, when
the speaker pauses or has
unvoiced portions in their speech. The principle advantage to using a retransmission
protocol in a radio network is an
improvement in net system capacity at the expense of increased delay. This increased delay
is difficult to detect due to the
nature of half-duplex communication.

[0018] Once the channels are set up, and the target mobile communication device has
indicated it is ready, the DAP 130 in the
DAS 214 sends a message to the originating mobile communication device to start, and the
call commences. The voice
information travels from the originating mobile communication device to the BTS, then to
the BSC. A packet control function
(PCF) associated with the BSC 206 ensures packets are received and forwarded in order,
essentially controlling the
retransmission aspect of the radio link between the originating mobile communication
device 202 and the BTS. The PCF
forwards packets to the PDSN 228 which adds addressing header information so that the
packets can be transmitted over a
network. If the target mobile communication device is in a different region of the fixed
equipment network, such as is shown
with mobile communication device 226, the PDSN forwards the voice packets over the network
to a second PDSN 230. The
second PDSN removes the header addressing information and forwards the voice packets to
the target BSC/PCF 222, where
the packets are ordered, and then transmitted to the target mobile communication device
226.

[0019] In addition to another CDMA mobile communication device, the target device can be,
for example, a TDMA mobile
communication device, or even a personal computer connected to the internet. TDMA dispatch
systems are presently in
widespread use, and an operator operating a public TDMA dispatch communication system may
wish to add CDMA service,
and have intersystem dispatch communication. This is accomplished, according to the
invention, by providing a network
connection to the TDMA dispatch system 232. The TDMA system uses the same dispatch
components, so it interfaces readily
with the CDMA system.

[0020] In an alternative embodiment of the invention, a dispatch call is made between the
originating CDMA mobile
communication device 202 and a personal computer 236 connected to the internet or other
public data network 234. In setting
up such a call, the computer must have a virtual mobile communication device client
software application running to detect and
receive dispatch calls. Such software applications are presently in use for telephone
calling over the internet, and modification of
such for dispatch applications is a routine change. As the traffic channel for the
originating mobile communication device is being
set up, the DAS utilizes the PDSN 228 to set up the call path to the computer. The most
common way of contacting the
computer is by use of a proxy server the client application logs onto, much the way
instant messaging client applications do.

[0021] Setting the call path over the internet when the target is a computer is also done
concurrently as the traffic channel for
the originating CDMA mobile communication device is being set up. Referring now to FIG. 3,
there is shown a flow chart
diagram 300 of a method for establishing a dispatch call in a CDMA system, in accordance
with the invention. At the start 302
the CDMA mobile communication device is registered for service and ready to make a
dispatch call, meaning the user of the
mobile communication device has selected a party to be called. Generally, once the party
to be called has been selected, the
user pushes and holds a button on the mobile communication device, known as a "push to
talk" button or PTT button.
However, as the call must first be set up, the user must wait for the mobile communication
device to give an indication as to
when to begin talking, which is not done until it receives the talk permission message
from the DAP. Once the button is pushed,
the mobile communication device transmits the dispatch call origination message (304). The
BSC receives the message and
recognizes that it is a dispatch call origination message (306). In response, two things
occur concurrently. The BSC that
received the dispatch call origination message begins the process of allocating and
assigning the mobile communication device
to a traffic channel (308). This process results in setting up a traffic channel between
the mobile communication device and the
fixed equipment network. While that is happening, the dispatch agent passes the message on
to the DAS, and in particular the
DAP component of the DAS. The DAS immediately pages the target (312). The paging can take
several seconds because a
dispatch agent must access a D-VLR, ascertain which cell or cells the target is located,
then forward the message to those cells.
In alternative embodiments, such as making a dispatch call to a computer, the DAS has to
wait for the page to be forwarded
over the internet, or other public data network.

[0022] Assuming the target is operational, it will receive the page and respond (314).
Once the target responds, if the target is
an mobile communication device, the communication resources must be allocated and assigned
so that the target can be placed
on a traffic channel. Once the target call path is set up, the DAP in the DAS sends a talk
permission message to the originating
mobile communication device (316), and the user of the originating mobile communication
device can begin speaking. This
process can take as long as 8-10 seconds.

[0023] To ensure that the user of the originating mobile communication device can commence
speaking and the target is able to
receive and play the voice signal, the originating mobile communication device waits for
an alert, such as a talk permission
message, to generate an event indicating to the user that the user may commence speaking,
thus ensuring that the target is ready
to receive the transmission. Typically the event is an audible alert, often referred to as
a "beep." Upon hearing the beep, the user
begins speaking. Of course, other events may be used in combination or instead of an
audible alert, such as displaying an icon
on a display of the mobile communication device, or flashing a light, and so on.

[0024] Some conflicts may occur in attempting to establish a dispatch call, such as the
target may already be engaged in a
dispatch call, or may not presently be registered for service. In a CDMA system the timing
is especially important because of
the more involved channel set up compared to TDMA systems. In particular power levels must
be controlled so that the mobile
communication device's signal doesn't interfere with any others. The present invention
solves this problem in a number of ways.

[0025] Referring now to FIG. 4, there is shown a flow chart diagram 400 of a method for
starting a dispatch call to a CDMA
mobile communication device. At the start 402 a user of an originating mobile
communication device has pressed the PTT
button on the originating mobile communication device, or otherwise initiated a dispatch
call. As described above, once the
originating mobile communication device transmits a dispatch call origination message, the
BSC serving that mobile
communication device may immediately begin setting up a channel between the originating
mobile communication device and
the base station. At the same time the BSC is busy allocating and assigning resources, and
signaling the originating mobile
communication device, the DAP pages the target mobile communication device (404). If the
target mobile communication
device is available, it responds to the page with appropriate messaging, and includes a
pilot power measurement. The pilot
power measurement includes a measurement of all the pilot signals the target mobile
communication device can detect from
surrounding serving cells. The target mobile communication device may also alert the
target user that a dispatch call is imminent
by, for example, emitting an audible alert signal. If the pilot power measurement is
higher than a preselected threshold, indicating
sufficient dependability of the radio link, the fixed equipment can do one of several
things to inform the originating mobile
communication device that the target is ready. A first alternative is to queue the beep
until after the traffic channel between the
originating mobile communication device and the fixed equipment network has been built. A
second alternative is to delay the
traffic channel assignments until the beep arrives at the originating mobile communication
device, and allow the user to begin
speaking while the traffic channel is set up, storing the voice information in the
originating mobile communication device until the
traffic channel is set up. Once the traffic channel is set up, the buffeted speech can be
transmitted at a high rate to the target
mobile communication device where it is buffered and played. This second alternative has
the benefit of quickly building up the
buffet at the target mobile communication device. A third alternative is to send the
traffic channel assignment to the originating
mobile communication device in anticipation of getting the page response from the target
mobile communication device. This
involves sending the traffic channel assignment message to the originating mobile
communication device about 150 msecs before
the beep notification is expected to arrive. In the fixed equipment if the page response
comes back from the target and the
target is not already busy, the fixed equipment will then proceed to send null data to the
target mobile communication device.
However, if the page response does not come back or the target mobile communication device
is already busy in a call, the call
set up will be halted.

[0026] The pilot power measurement is used by the fixed equipment to determine whether or
not there is a strong likelihood
that the target mobile communication device will be able to establish a reliable channel.
In some cases the fixed equipment may
assign the target to two different cells, which is a soft handoff state.

[0027] Thus, the invention provides a method of originating a dispatch call over a code
division multiple access (CDMA) air
interface from a mobile communication device, comprising transmitting a dispatch call
origination message from the mobile
communication device to a fixed equipment network over a CDMA channel, the dispatch call
origination message containing a
target identifier; then, in response to the transmitting, setting up a traffic channel
between the mobile communication device and
the fixed equipment network and setting up a call path between the target and the fixed
equipment network. Setting up the
traffic channel and setting up the call path between the target and the fixed equipment
network are performed concurrently. One
aspect of the invention is that the traffic channel between the mobile communication
device and the fixed equipment network
comprises setting up a communication link established according to a retransmission
protocol to allow retransmission of data
packets over the traffic channel.

[0028] Setting up the call path between the target and the fixed equipment network
comprises routing the dispatch call
origination message from a base site to a dispatch agent component of the fixed equipment
network. The fixed equipment
network goes about determining a network location of the target at the dispatch agent, and
pages the target at the network
location with an incoming dispatch call message. The target, whether it be another mobile
communication device or a computer
connected to the fixed equipment network over a public data network, responds to the
incoming dispatch call message,
performed by the target. Routing the dispatch call origination message from the base site
to the dispatch agent component
comprises routing the dispatch call origination message from the base site to a first
dispatch agent or a second dispatch agent
because there can be multiple dispatch agents serving various regions. The dispatch agent
serving the base site of the originating
mobile communication device is typically located within a mobile switching center
affiliated with the base site. The second
dispatch agent, since it serves a different region, is typically not located within a
mobile switching center. In one embodiment,
once the two mobile communication devices are established on their respective traffic
channels, the fixed equipment network,
and in particular the DAP, sends a talk permission message to the mobile communication
devices.

[0029] The invention also provides a method of setting up a dispatch call to a target
mobile communication device over a code
division multiple access (CDMA) air interface. During dispatch call set up the target CDMA
mobile communication device
receives a page notification from the fixed equipment network, the page notification
including a dispatch notification. The target
CDMA mobile communication device responds by transmitting a page response, including a
pilot power measurement. If the
pilot power measurement indicates a power level above a preselected threshold, the fixed
equipment network, and in particular
the BSC serving the target mobile communication device's cell, commences settings up a
traffic channel with the target CDMA
mobile communication device. Typically the target CDMA mobile communication device is not
engaged in a call, and is in an
idle mode. At periodic intervals the mobile communication device "wakes up" and scans the
pilot signal of at least one serving
cell in the vicinity of the target mobile communication device, and preferably all the
serving cells it can detect. The target mobile
communication device commences determining a strongest pilot signal and a serving cell
corresponding to the strongest pilot
signal. Then the target mobile communication device commences scanning a paging channel of
the serving cell corresponding to
the strongest pilot signal to look for page messages. All of this activity at the target
mobile communication device is performed
concurrently while the fixed equipment network is setting up a call path between the
originating device and the fixed equipment
network. In this case the originating device may be another mobile communication device or
a device from outside the wireless
system, such as a computer.

[0030] Furthermore, the invention provides specifically a method of setting up a dispatch
call between an originating code
division multiple access (CDMA) mobile communication device and a target CDMA mobile
communication device. Wen the
user of an originating CDMA mobile communication device presses a dispatch talk or PTT
button or equivalent, the originating
CDMA mobile communication device transmits a dispatch call origination message to the
fixed equipment network over a
CDMA inbound control channel. The dispatch call origination message contains a target
identifier corresponding to the target
CDMA mobile communication device. In response, the fixed equipment network initiates the
set up of a traffic channel between
the originating CDMA mobile communication device and the fixed equipment network. The
fixed equipment network also
pages the target CDMA mobile communication device. The set up of a traffic channel and
paging the target CDMA mobile
communication device are performed concurrently to reduce dispatch call set up delay. The
page is received by the target
CDMA mobile communication device if it is available, and it transmits a page response,
including a pilot power measurement.
The pilot power measurement is available because the mobile communication device has
already performed the measurement to
determine which serving cell's paging channel to monitor. In response to transmitting the
page response, the fixed equipment
network transmits a talk permission message to the originating CDMA mobile communication
device from the fixed equipment
network. Typically transmitting the talk permission message is done by queuing the talk
permision message, and sending it after
the traffic channle is built, but according to an alternative embodiment the talk
permission message can be sent over a broadcast
control channel or a dedicated control cahnnel to the originating CDAM mobile
communication device before the traffic channel
is built. The originating CDMA mobile communication device then commences alerting the
user of the originating CDMA
mobile communication device to begin speaking, and the mobile communication device buffets
the speech until the traffic
channel between the originating CDMA mobile communication device and the fixed equipment
network is established. Once
the traffic channel is established, the mobile communication device begins transmitting
the buffered speech to the target CDMA
mobile communication device over the fixed equipment network. It can transmit the speech
in digital form at a high rate, so as
to reduce delay, as well as provide the target mobile communication device with a buffet
of speech.

[0031] While the preferred embodiments of the invention have been illustrated and
described, it will be clear that the invention
is not so limited. Numerous modifications, changes, variations, substitutions and
equivalents will occur to those skilled in the art
without departing from the spirit and scope of the present invention as defined by the
appended claims.