Note: Descriptions are shown in the official language in which they were submitted.
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INTEGRATED CELLULAR VOICE
AND DIGITAL PACKET DATA TELECOMMUNICATIONS SYSTEMS AND
METHODS FOR THEIR OPERATION
Field of Invention
This invention relates to cellular voice and
Cellular Digital Packet Data (CDPD) telecommunications
systems, and to methods for their operation.
Backaround of Invention
In conventional cellular telephone networks, a
base station is provided for each cell of the area served
by the cellular network. Each base station comprises a
plurality of radio transceivers which provide radio
channels for voice communications between the base
stations and mobile telephones in the cells served by the
base stations. The base stations are connected to mobile
switching centers which provide telecommunications
switching between base stations. A gateway mobile
switching center is connected between the mobile
switching centers and a Public Switched Telephone Network
(PSTN) so that mobile telephones served by the cellular
telephone networks can be connected to telephones served
by the PSTN.
In addition to voice telephony services
provided to mobile telephone users by cellular telephone
networks, there is a demand for packet data services
provided to mobile data terminals. In April 1992 an
industry consortium was formed to develop standards for
providing Cellular Digital Packet Data (CDPD) services.
In July 1993 this consortium released Version 1.0 of a
CDPD Specification which defines standard interfaces and
functionality for CDPD networks.
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A CDPD network may be implemented as an overlay
on an existing cellular telephone network. The CDPD
Specification calls for Mobile Data Base Stations (MDBSs) .
to serve mobile data terminals called Mobile End Stations
(MESS). The MDBSs are connected to Mobile Data
Intermediate Systems (MDISs) which are connected to
external public or private Packet Data Networks (PDNs) so
that the MESS can exchange packet data with Fixed End
Stations (FESs) connected to the PDNs.
The MDBSs use the same radio frequency channels
to exchange packet data with the MESS as do voice base
stations serving mobile telephones in the same serving
area. To avoid radio interference between packet data
transmissions and voice transmissions, the MDBSs must use
radio frequency scanners to scan the voice channels to
determine which voice channels are currently in use by the
voice base stations serving the same area, and tune their
transceivers to only those channels which are not currently
in use for voice communications. Consequently, the MDBSs
"hop" among the voice channels to avoid voice calls which
are currently in progress.
The frequency scanning and retuning operations of
the MDBSs require considerable processing. Moreover, each
frequency hop executed in order to "dodge" a voice call
interrupts packet data transmission, reducing the data
throughput of the CDPD network. Furthermore, because
expensive MDBS hardware, MDIS hardware and transmission
facilities linking the MDBS hardware to the MDIS hardware
are needed to provide CDPD service, the cost of introducing
CDPD service is higher than desired, particularly where the
initial demand for CDPD service is limited. If the CDPD
service providers price the service high enough to pay back
their equipment investment quickly or limit deployment of
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CDPD service to high traffic areas, they risk limiting CDPD
market growth.
Moreover, the boundaries of cells served by MDBSs
do not coincide exactly with the boundaries of cells served
by voice base stations even when the MDBSs and the voice
base stations are co-located. The cell boundaries do not
coincide exactly because the intercell hand off criteria
are different for voice and packet data transmission. The
mismatch of cell boundaries can lead to excessive
interference between channels used for voice communications
and channels used for packet data communications.
Summary of Invention
An object of this invention is to reduce or avoid
some or all of the disadvantages of CDPD networks as
outlined above by integrating CDPD equipment with equipment
providing voice services.
One aspect of this invention provides an
integrated voice and data packet telecommunications system
having a plurality of dual mode channels, the system
comprising:
a plurality of transceivers, at least some of the
transceivers being operable to transmit and receive voice
traffic on at least one of the dual mode channels, and at
least some of the transceivers being operable to transmit
and receive packet data traffic on at least one of the dual
mode channels; and
a controller for controlling the plurality of
transceivers so as to allocate the dual mode channels to
voice communications and packet data communications, the
controller being operable:
to maintain a dual mode queue of dual mode
channels not allocated to voice communications;
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to select a dual mode channel according to its
position in the dual mode queue in response to a demand for
a voice channel; and
to allocate to packet data communications any
dual mode channel not selected for allocation to voice
communications .
The use of a common controller for voice and
packet data services avoids the need to scan the voice
channels to determine which voice channels are currently in
use because that information is already available in the
controller. This avoids the cost of radio frequency
scanners and the processing resources needed to drive the
radio frequency scanner. In addition, the common
controller can be designed so as to assign channels to
voice and packet data traffic in a more orderly manner to
reduce the number of channel hops needed for packet data
traffic, as will be explained in greater detail below.
This increases the packet data throughput without
increasing voice call blocking.
The controller may further be operable, in
response to release of the dual mode channel allocated to
voice communications, to return the dual mode channel to
the dual mode queue and to reallocate the dual mode channel
to packet data communications. The controller may operate
the dual mode queue as a Last In, First Out (LIFO) queue so
as to provide as many interruption-free packet data
channels as the voice traffic conditions will permit.
The system may further comprise a plurality of
voice channels in addition to the plurality of dual mode
channels, the voice channels being dedicated to voice
communications. In this case, the controller may also be
operable to maintain a voice queue of idle voice channels.
The controller may be operable, in response to a request
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for a voice channel when at least one voice channel is
present in the voice queue, to select a channel from the
voice queue, and may be operable, in response to a request
for a voice channel when no voice channel is present in the
5 voice queue, to demand a channel from the dual mode queue.
In this manner, the controller only allocates dual mode
channels to voice calls when no voice channels are
available, thereby minimizing interruptions to packet data
transmission for maximum packet data throughput.
Alternatively, because the number of
interruptions to packet data transmission is reduced, the
duration of the switching operations performed at each
interruption has a smaller impact on the data throughput.
Consequently, the design constraints on this switching
duration may be relaxed, reducing the cost of the hardware
and software implementation.
To further improve packet data throughput, the
controller may be operable, in response to release of a
voice channel when at least one dual mode channel is
allocated voice communications, to select a dual mode
transceiver, to hand off a voice call served by the
selected dual mode channel to the released voice channel,
to return the selected dual mode channel to the dual mode
queue, and to reallocate the selected dual mode channel to
packet data communications. The hand off can be triggered
only when the dual mode queue is empty to minimize voice
call hand offs. Alternatively, the hand off can be
triggered if any dual mode channels are allocated to voice
communications to maximize packet data throughput. The
controller can be made operator configurable with respect
to these hand off options.
The integrated voice and packet data
telecommunications system may be a cellular system having a
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plurality of cells, a respective subset of the plurality of
voice channels being assigned to each cell and a respective
subset of the plurality of dual mode channels being
assigned to each cell. In particular, the frequency plan
for the dual mode channels may be distinct from the
frequency plan for the voice channels.
The use of distinct frequency plans for the dual
mode and voice channels reduces the interference between
voice transmissions and packet data transmissions that can
result from the different intercell hand off algorithms
used for voice and packet data communications.
The system may also comprise one or more packet
data channels which are dedicated to packet data operation
to ensure a minimum level of packet data throughput
regardless of the voice traffic. In this case the above
hand off options may be disabled as long as one or more of
the packet data channels is in operation.
One or more of the plurality of transceivers may
be a dual mode transceiver which is operable in a voice
mode to transmit and receive voice traffic, and operable in
a packet data mode to transmit and receive packet data
traffic. In this case, the controller may be operable to
switch the dual mode transceiver between the voice mode of
operation and the packet data mode of operation.
Thus, another aspect of the invention provides an
integrated voice and packet data telecommunications system
comprising at least one dual mode radio transceiver and a
controller. The dual mode radio transceiver is operable in
a voice mode to transmit and receive voice traffic and
operable in a packet data mode to transmit and receive
packet data traffic. The controller is operable to switch
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the dual mode transceiver between the voice mode of
operation and the packet data mode of operation.
Each dual mode transceiver may be implemented as
a processor combined with at least one radio transmitter
and at least one radio receiver. The processor may be
operable in a voice mode for voice communications and in a
packet data mode for packet date communications.
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Because the dual mode transceivers and the
controller are shared between voice and packet data
services, packet data services can added to voice services
for the relatively low incremental cost of the software
required to provide the packet data services. Moreover,
packet data services can be added to existing voice
services without coupling additional radio frequency
equipment to existing cell site antennas, and without
interruptions to existing voice services to install such
equipment. Furthermore, because the transceivers required
for voice and packet data services are located at a common
base station site, voice signals and packet data signals
can be multiplexed together for transmission to and from
the base station site on a shared multiplexed transmission
link to minimize transmission facility costs.
Another aspect of this invention provides a
method of operating an integrated voice and packet data
telecommunications system, the system having a plurality of
dual mode channels, each operable in a voice mode for voice
communications and operable in a packet data mode for
packet data communications. The method comprises
maintaining a dual mode queue of dual mode channels
allocated to packet data communications, selecting, in
response to a demand for a voice channel, a dual mode
channel according to its position in the dual mode queue,
and allocating the selected channel to voice
communications .
Brief Description of Drawings
Embodiments of the invention are described below
by way of example only. Reference is made to accompanying
drawings in which:
Figure 1 is a block schematic view of a CDPD
system overlaid on a cellular-voice telephony system
according to the CDPD Specification;
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Figure 2 is a block schematic diagram of an
integrated CDPD and cellular voice telephony system
. according to an embodiment of the invention;
Figure 3 is a block schematic diagram of a dual-
. 5 mode transceiver of the system of Figure 2;
Figure 4 is a flowchart illustrating a first part
of a channel allocation algorithm used to allocate radio
channels in the integrated system of Figure 2
Figure 5A is a flowchart illustrating a second
part of the channel allocation algorithm in a full dual
mode queue hand off configuration;
Figure 5B is a flowchart illustrating a second
part of the channel allocation algorithm in a partial dual
mode queue hand off configuration; and
Figure 6 illustrates dual mode, packet data and
voice frequency plans for the integrated system of Figure
2.
Detailed Description
Figure 1 is a block schematic view of a CDPD
system 200 overlaid on a cellular voice telephony system
100 according to the CDPD Specification.
The cellular voice telephony system 100 comprises
a plurality of voice base stations (VBSs) 110
interconnected by a plurality of mobile switching centers
(MSCs) 120. Each VBS 110 comprises a plurality of voice
radio transceivers (VTs) 112 which provide radio frequency
channels for voice communications between the VBSs 110 and
mobile voice terminals (for example, MVT 300) in cells
served by the VBSs 110.
A
The VBSs 110 are connected to the MSCs 120 via
multiplexed transmission links, for example T1, E1 or other
standard or proprietary format multiplexed transmission
links. The MSCs 120 provide telecommunications switching
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between the VBSs 110. The MSCs 120 comprise a resource
manager (RM) 120 which controls the allocation of radio
channels to voice calls.
5 A gateway MSC (GMSC) 130 is connected between the
MSCs 120 and a Pub is Switched Telephone Network (PSTN) 400
so that MVTs 300 served by the cellular voice telephony
system 100 can be connected to telephones 500 served by the
PSTN 400.
The CDPD system 200 comprises a plurality of
mobile data base stations (MDBSs) 210 interconnected by a
plurality of mobile data intermediate systems (MDISs) 220.
Each MDBS 210 comprises a plurality of packet data radio
transceivers (PDT) 212 which provide packet data radio
channels for packet data communications between the MDBSs
210 and mobile end systems (MESS) 600 in cells served by
the MDBSs 210. The MDBSs 210 further comprise a scanning
transceiver (ST) 214 which scans the radio frequency
channels used by the VBSs 110 to determine which voice
channels are currently in use. The PDTs 212 are tuned to
radio frequency channels which are not currently in use by
the VBSs 110 to provide packet data communications between
the MDBSs 210 and the MESS 600. Consequently, the MDBSs 210
"hop" among the radio frequency channels to avoid voice
calls which are currently in progress. (See part 405 of
the CDPD System Specification, Release 1.1 issued by the
CDPD Forum on January 19, 1995.)
The MDISs 220 are connected to public or private
packet data networks (for example PDN 700) so that MESS 600
served by the CDPD system 200 can be connected to fixed end
stations (for example FES $00) which are served by the PDNs
700.
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The frequency scanning and retuning operations of
the MDBSs 210 combined with overhead data transfer
- operations needed to effect movement of packet data traffic
from one channel to another channel amount to a
considerable processing load on the MDBSs 210. Moreover,
each frequency hop executed in order to "dodge" a voice
call interrupts packet data transmission, reducing the data
throughput of the CDPD system 200. Furthermore, because
expensive MDBS hardware (including the ST 214), MDIS
hardware and transmission facilities linking the MDBS
hardware to the MDIS hardware are needed to provide CDPD
service, the cost of introducing CDPD service is higher
than desired, particularly where the initial demand for
CDPD service is limited. The boundaries of cells served by
the MDBSs 210 do not coincide exactly with the boundaries
of cells served by VBSs 110 even when the MDBSs and the
voice base stations are co-located because the intercell
hand off criteria are different for voice and packet data
transmission. The mismatch of cell boundaries can lead to
excessive interference between channels used for voice
communications and channels used for packet data
communications .
Figure 2 is a block schematic diagram of an
integrated CDPD and cellular voice telephony system 900
according to an embodiment of the invention. The
integrated system 900 comprises a plurality of dual mode
base stations (DBMSs) 910 interconnected by a plurality of
Nortel MTXTM mobile switching centers (MTXs) 920. Each
DMBS 910 comprises a plurality of voice radio transceivers
(VTS) 912 which provide voice radio channels for voice
communications between the DMBSs 910 and mobile voice
terminals (for example, MVT 300) in cells served by the
DMBSs 910.
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The DMBSs 910 are connected to the MTXs 920 via
multiplexed transmission links, for example T1, E2 or other
standard or proprietary format multiplexed transmission
links. The MTxs 920 provide telecommunications switching
between the DMBSs 910. The MTXs 920 comprise a resource ,
manager (RM) 922 which controls the allocation of radio
channels to voice calls.
The MTXs 920 also perform the function of a
gateway MSC, connecting the integrated system 900 to the
Public Switched Telephone Network (PSTN) 400 so that MVTs
300 served by the integrated system 900 can be connected to
telephones 500 served by the PSTN 400.
Each DMBS 910 further comprises a plurality of
dual mode radio transceivers (DMTs) 914. Figure 3 is a
block schematic diagram showing a DMT 914 in more detail.
The DMT 914 comprises a radio transmitter 10, and radio
receiver 20, and a signal processor 30 comprising a
processing unit 32 and a memory 34 for storing instructions
to be executed by the processing unit and data required for
execution of those instructions. The signal processor 30
receives voice and packet data signals from the MTX 920 and
processes those signals for transmission by the radio
transmitter 10. The signal processor 30 also receives
voice and packet data signals from the radio receiver 20
and processes those signals for transmission to the MTX
920. The signal processor 30 receives control signals from
the RM 922 to switch the signal processor 30 between-a
voice mode in which it provides signal processing
appropriate for voice signals and a packet data mode in
which it provides signal processing appropriate for packet
data signals.
J
Consequently, the DMTs 914 are operable in a
voice mode to exchange voice traffic with MVTs 300 in cells
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served by the DMBSs 910, and operable in a packet data mode
to exchange packet data traffic with MESS 600 served by the
DMBSs 910. The RMs 922 of the MTXs 920 operate as
controllers for switching the DMTs 914 between the voice
mode of operation and the packet data mode of operation as
will be explained in greater.detail below.
Each DMBS 910 further comprises a packet data
transceiver (PDT) 916 which operates only in the packet
data mode and is dedicated to exchanging packet data
signals with MESs 600 served by the DBMSs 910.
The MTxs 920 perform MDIS functions for packet
data transmissions and are connected to public or private
packet data networks (for example PDN 700) so that MESS 600
served by the integrated system 900 can be connected to
fixed end stations (for example FES 800) which are served
by the PDNs 700.
The VTs 912, DMTs 914 and PDT 916 are connected
to the RMs 922 of the MTXs 920 via one or more shared
multiplexed transmission links.
The RM 922 of each MTX 920 maintains a VT queue
and a DMT queue for each DMBS 910 served by the MTX 920.
The VT queue contains identifiers of idle VTs 912. The DMT
queue contains identifiers of DMTs 914 which are currently
operating in packet data mode.
Figure 4 is a flowchart illustrating a first part
of a channel allocation algorithm used by the RMs 922 to
allocate radio channels in the integrated system 900. When
a request for a voice channel is received by the RM 922
(either because a MVT 300 is attempting to initiate a voice
call or because another terminal is attempting to initiate
a call to a MVT 300), the RM 922 first examines the voice
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queue to determine whether any VTS 912 are idle. If idle
VTS 912 are found in the voice queue, the RM allocates an
idle VT 912 to the voice call and updates the voice queue. .
If the voice queue is empty, the RM 922 examines
the dual mode queue to determine whether any DMTs 914 are
operating in packet data mode. (The RM 922 automatically
configures any DMTs 914 that are not allocated to a voice
call in packet data mode for transmission of packet data on
demand.) If DMTS 914 are found in the dual mode queue, the
RM 922 allocates a DMT 914 from the dual mode queue on a
last in, first out (LIFO) basis, and updates the dual mode
queue.
If the voice queue and the dual mode queue are
both empty, the RM 922 initiates refusal of the voice
channel request.
The channel allocation algorithm described above
ensures maximum use of all voice channels before packet
data transmission are interrupted to provide voice
communications. Moreover, as many of the DMTs 914 as
possible are used for uninterrupted packet data
transmissions. In addition, the PDT 916 is always used for
uninterrupted packet data communications.
Figure 5A is a flowchart illustrating a second
part of the channel allocation algorithm when the RM 922 is
configured in a full dual mode queue hand off
configuration. Voice channels are released when a voice
call served by a DMBS 910 is handed off to another DMBS
910, when a MVT 300 disconnects or when a release order is
received indicating that the network or another terminal
has disconnected. When a voice channel is released, the RM '
922 determines whether the released voice channel was
provided by a VT 912 or a DMT 914. If the released voice
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channel was provided by a DMT 914, the DMT 914 is returned
to the dual mode queue and switched to packet data mode.
If the released voice channel was provided by a
5 VT 912, the transceiver which provided by the released
voice channel is now available for use by any other voice
call. In particular, the VT 912 which provided the
released voice channel could now provide a voice channel
for any voice call which is currently being handled by a
10 DMT 914 operating in voice mode. This would enable the DMT
914 to switch to packet data mode to provide higher packet
data throughput.
Consequently, if the released voice channel was
15 provided by a VT 912, the RM 922 selects a DMT 914 which is
currently operating in voice mode, hands off a voice call
from the selected DMT 914 to the VT 912 which previously
provided the released voice channel, and returns the
selected DMT 914 to the dual mode queue, switching the
selected DMT 914 to the packet data mode.
Advantageously, the RM 922 may select the DMT 914
which was last allocated from the dual mode queue for the
voice call hand off. The RM 922 may maintain a DMT voice
queue for this purpose, entering the DMTs 924 into the DMT
voice queue when they are switched from the packet data
mode to the voice mode. The RM 922 may then select DMTs
914 from this queue on a LIFO basis when VTs 912 able to
provide voice channels become available.
The full dual mode hand off arrangement described
above may result in a large number of voice call hand offs
in heavy voice traffic and this may be deemed unacceptable
for some applications. To increase packet data throughput
while reducing voice call handoff activity, the steps of
Figure 5A may be replaced by the steps of Figure 5B which
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implement a partial dual mode handoff strategy. According
to the partial dual mode hand off strategy, voice calls are
handed off from DMTS 914 to released VTs 912 only when the
dual mode queue is empty (i.e. when all DMTs 914 are
operating in voice mode, so that none of the DMTs 914are
contributing to packet data throughput).
Full dual mode handoff and partial dual mode hand
off as described above may be implemented in the RM 922 as
options which are configurable by the service provider who
operates the integrated network 900. The hand off options
may be automatically disabled when operational measurements
indicate that the integrated system 900 is in a voice
overload condition. The hand off options may also be
disabled so long as at least one dedicated packet data
channel (provided by the PDT 916) remains in service.
Figure & illustrates distinct dual mode, packet
data and voice frequency plans for the integrated system of
Figure 2. The frequency plans are based on seven groups of
channels dedicated to voice communications (Va, Vb, Vc, Vd,
Ve, Vf, and Vg), seven groups of channels dedicated to
packet data communications (PDa, PDb, PDc, PDd, PDe, PDf
and PDg), seven groups of channels that can be used for
either voice or packet data communications (DMa, DMb, DMc,
DMd, DMe, DMf and DMg), and assume two VTs 912, two DMTs
914 and one PDT 916 per cell. The use of distinct
frequency plans for the dual mode channels, packet data
channels and the voice channels reduces the interference
between voice transmissions and packet data transmissions
that can result from the different intercell hand off
algorithms used for voice and packet data communications.
In the integrated system 900, the RM 922 and the '
DMTs 914 are shared between voice and packet data services,
so that packet data services can be added to voice services
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for the relatively low incremental cost of the software
required to provide the packet data services. Moreover,
the use of a common RM 922 for voice and packet data
services avoids the need to scan the voice channels to
determine which voice channels are currently in use because
that information is already available in the controller.
This avoids the cost of radio frequency scanners 214 of the
CDPD network 200 and the processing resources needed to
drive the radio frequency scanners 214. In addition, the
common RM 922 assigns channels to voice and packet data
traffic in a more orderly manner to reduce the number of
channel hops needed for packet data traffic. This
increases the packet data throughput without increasing
voice call blocking.
Alternatively, because the number of channel hops
is reduced, the duration of the switching operations
performed at each channel hop has a smaller impact on the
data throughput. Consequently, the design constraints on
this switching duration may be relaxed, reducing the cost
of the hardware and software implementation.
The embodiments described above may be modified
without departing from the principles of the invention, the
scope of which is defined by the claims below.
For example, the integrated system 900 could have
more or fewer DMBSs 910 or more or fewer MTXs 920 than
illustrated. Some or all of the MTXs 920 could serve
multiple DMBSs 910.
Each DMBS 910 could have a different number of
the various transceiver types. For example, some or all of
the DMBSs 910 could have no VTs 912 so long as enough DMTs
914 are provided to meet the demands of the voice traffic.
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The VTs 912 may be DMTs 914 that are operator
configured to operate only in voice mode. Similarly, the
PDTs 918 may be DMTs 914 that are operator configured to
operate only in packet data mode.
The VTs 912 could be AMPS, TDMA or dual mode
AMPS/TDMA transceivers and the DMTs 914 could be operate in
AMPS mode or TDMA mode when in voice mode. The DMTS 914
could even be "triple mode transceivers" selectively
operable in AMPS mode, TDMA mode and packet data mode. If
transceivers selectively operable in both AMPS and TDMA
voice modes are used, the channel allocation algorithms
described above will need to be extended accordingly.
where the demand for mobile packet data services
is relatively light, no PDTs 916 may be provided, all
packet data services beingprovided by the DMTs 914. In
this case, the partial or full dual mode hand off
procedures are particularly advantageous as means for -
increasing packet data throughput.
The invention could also be implemented on a
network architecture having separate voice transceivers 112
and packet data transceivers 212 that can operate on the
same radio frequency channels as illustrated in Figure 1,
provided that the radio frequency channels that can be used
for both voice and packet data communications are allocated
from a common queue. This could be implemented, for
example, by connecting the VTs 112 and PDTs 212 in Figure 1
to a common controller which manages the queue.
In the embodiment described above, a separate
processor 30 is provided for each DMT 914. Alternatively,
a processor 30 could be shared by multiple DMTs 914, or
separate processing units 32 could be provided for each DMT
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914 while a single memory 34 could be shared by multiple
processors 32.
The embodiment described in detail above is
particularly suited to applications in which voice traffic
is given priority over packet data traffic. Some
applications may place other relative priorities on voice
traffic. and packet data traffic, and the control algorithm
may be modified to suit the modified priorities.
Similarly, some applications may favour queue management
schemes other than LIFO, for example FIFO or activity-based
queuing schemes.
These and other modifications of the embodiment
described in detail above are within the scope of the
invention as defined by the claims below.
