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Claims  |
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What is claimed is:
1. A multi-mode mobile radio telephone station for communicating over
analog or digital traffic channels and control communications over an
analog or a digital control channel and for interacting with a plurality
of base stations where at least some of said base stations conduct control
communications with said mobile station over said analog control channel
and at least some of said base stations conduct control communications
with said mobile station over said digital control channel, said mobile
station comprising:
(a) a mode selection switch for switching said mobile station between an
analog mode and a digital mode, said switch being initially set to its
digital mode for receiving digital control communications over said
digital control channel from one of said base stations.;
(b) means for scanning a set of digital control channels, received from
said digital control communications when said mobile station is switched
to a digital mode;
(c) first overhead message receiving means for determining if one of said
digital control channels is available;
(d) means for conducting control communications with one of said base
stations over a digital control channel associated with this base station
if said one of the digital control channels is available;
(e) means for scanning a first set of analog control channels if none of
said digital control channels is available;
(f) second overhead message receiving means for determining if one of said
analog control channels is available; and
(g) means for conducting control communications with one of said base
stations over an analog control channel associated with this base station
if said one of the analog control channels is available.
2. A multi-mode mobile radio telephone station for interacting with a
plurality of base stations where at least some of said base stations
conduct control communications with said mobile station over analog
control channels and at least some of said base stations conduct control
communications with said mobile station over digital control channels,
said mobile station comprising:
a mode selection switch for switching said mobile station between an analog
mode and a digital mode;
means for conducting control communications with one of said base stations
over an analog control channel associated with this base station when said
mobile station is switched to an analog mode;
means for conducting control communications with one of said base stations
over a digital control channel associated with this base station when said
mobile station is switched to a digital mode;
means for scanning a set of digital control channels,
overhead message receiving means for determining if one of said digital
control channels is available;
means for scanning a first set of analog control channels if none of said
digital control channels is available;
detecting means, connected to said first set of analog control channel
scanning means, for detecting at least one indicating bit which indicates
whether or not a first preferred transmission system has digital traffic
channel capabilities;
means for scanning a set of primary analog paging channels in response to
said indicating bit indicating that said first preferred transmission
system has digital traffic channel capabilities; and
means for scanning a second set of analog control channels in response to
said indicating bit indicating that said first preferred transmission
system does not have digital traffic channel capabilities.
3. A system according to claim 2, said mobile station further comprising:
means for receiving overhead messages over said first or second set of
analog control channels, and
means for scanning control channels associated with a non-preferred
transmission system in the event that an overhead message is not received
from either said first or said second set of analog control channels.
4. In a cellular communications system for communicating over analog and
digital traffic channels and having at least one multi-mode mobile radio
telephone station and a plurality of base stations wherein control
communications may be conducted over analog control channels and digital
control channels, a method comprising:
(a) switching said mobile station to a digital mode;
(b) initiating control communications with a base station over one of said
digital control channels, by scanning a set of digital control channels to
determine if one of said digital control channels is available;
(c) conducting control communications over a digital control channel
associated with this base station if said one of the digital control
channels of said base station is available;
(d) initiating control communications with said base station over one of
said analog control channels by scanning a first set of analog control
channels when none of said digital control channels is available, after
switching said mobile station to an analog mode; and
(e) conducting control communications with one of said base stations over
an analog control channel associated with this base station if said one of
the analog control channels is available;
wherein an available analog or digital control channel is used to assign
the analog and digital traffic channels.
5. A cellular radio telephone communications system, comprising:
a mobile switching center;
plural base stations connected to said mobile switching center, for
receiving and transmitting speech information and control information; and
plural mobile radio telephone stations, including at least one multi-mode
mobile station including:
means for receiving speech and data information from a first base station
over a voice channel;
means for transmitting speech and data information to said first base
station over said voice channel;
means for receiving and decoding control information in an analog format
from said first base station over a first control channel; and
means for receiving and decoding control information in a digital format
from said first base station over a second control channel;
wherein said first base station transmits said control information in a
digital format over said second control channel through a series of time
frames, and each mobile station only monitors said control information
over said second control channel during one of said time frames associated
with said mobile station,
wherein each mobile station is assigned a mobile identification number and
a portion of said number defines its associated time frame.
6. A cellular radio telephone communications system, comprising:
a mobile switching center;
plural base stations connected to said mobile switching center, for
receiving and transmitting speech information and control information; and
plural mobile radio telephone stations, including at least one multi-mode
mobile station including:
means for receiving speech and data information from a first base station
over a voice channel;
means for transmitting speech and data information to said first base
station over said voice channel;
means for receiving and decoding control information in an analog format
from said first base station over a first control channel; and
means for receiving and decoding control information in a digital format
from said first base station over a control channel;
wherein said first base station transmits said control information in a
digital format over said control channel through a series of time frames,
and each mobile station only monitors said control information over said
control channel during one of said time frames associated with said mobile
station,
wherein during time frames other than said associated time frame, said
mobile station deactivates to conserve power.
7. A cellular communications system for accommodating radio communication
between multi-mode mobile stations on analog or digital traffic channels
and using digital and analog control channels and a plurality of base
stations, where at least some of said base stations conduct control
communications over analog control channels and at least some of said base
stations conduct control communications over digital control channels,
each of said mobile stations comprising:
means for scanning a set of digital control channels to detect if any such
digital control channel is being transmitted from an associated base
station;
means for determining if a recognizable overhead message is received by
said mobile station on said digital control channel;
means for scanning a set of digital paging channels if said overhead
message is received; and
means for scanning a set of primary analog control channels if said
recognizable overhead message is not received,
wherein said base stations may transmit control information over analog
control channels or digital control channels, and wherein an available
analog or digital control channel is used to assign the analog and digital
traffic channels.
8. The system according to claim 7, wherein said multi-mode mobile stations
switched to an analog mode monitor analog control channel communications
from said base stations and said multi-mode mobile stations switched to a
digital mode monitor digital control channel communications from said base
stations.
9. The system according to claim 7, wherein downlink multi-mode mobile
stations have means for receiving control information on said digital
control channel.
10. The system according to claim 7, wherein bi-directional multi-mode
mobile stations have means for receiving and transmitting control
information on said digital control channel.
11. The system according to claim 7, wherein said digital control and
paging channels are assigned time slots on the same frequency.
12. The system according to claim 7, each of said multi-mode mobile
stations conducting control communications over said digital control
channels further comprising:
means for periodically scanning paging information on said digital paging
channels for a predetermined number of digits, said predetermined number
being substantially less than a total number of digits in said paging
information;
means for comparing said predetermined number of digits to corresponding
digits of an identification code associated with each mobile station;
means for deactivating mobile station power if an output signal from said
comparing means indicates that there was no match between the
predetermined number of digits and the corresponding identification code
digits; and
means for periodically reactivating mobile station power and scanning said
set of digital control channels.
13. A cellular communications system for accommodating radio communication
between multi-mode mobile stations using digital and analog control
channels and a plurality of base stations, where at least some of said
base stations conduct control communications over analog control channels
and at least some of said base stations conduct control communications
over digital control channels, each of said mobile stations comprising:
means for scanning a set of digital control channels to detect if any such
digital control channel is being transmitted from an associated base
station;
means for determining if a recognizable overhead message is received by
said mobile station on said digital control channel;
means for scanning a set of digital paging channels if said overhead
message is received; and
means for scanning a set of primary analog control channels if said
recognizable overhead message is not received;
wherein said digital control and paging channels are assigned time slots on
the same frequency, and wherein said frequency includes a plurality of
frames, each frame including three time slots with a first time slot being
reserved for said digital control channel and a second and third time slot
being reserved for said digital paging channels organized in multiple
frames.
14. The system according to claim 13, wherein said multiple frame includes
sixty-four frames and said synchronization signal indicates the beginning
of each multiple frame.
15. The system according to claim 13, wherein said second and third time
slots contain paging information for a plurality of different mobile
stations.
16. The system according to claim 13, wherein paging information is
distributed over said second and third time slots in each frame of said
multiple frame and excess paging information that can not be communicated
in a particular multiple frame is queued at said base station.
17. A mobile station for use in a cellular radio telephone communication
system having analog or digital traffic channels and analog and digital
control channels, comprising:
means for transmitting and receiving speech and data information over said
analog and digital traffic channels;
means for receiving and decoding control information transmitted over an
analog control channel in an analog format; and
means for receiving and decoding control information that is transmitted
over a digital control channel in a digital format;
a mode selection switch for switching a mobile station between an analog
mode and a digital mode, said switch being initially set to its digital
mode for receiving digital control communications over said digital
control channel from a base station;
means for scanning a set of digital control channels, received from said
digital control communications when said mobile station is switched to a
digital mode;
first overhead message receiving means for determining if one of said
digital control channels is available;
means for conducting control communications with one of said base stations
over a digital control channel associated with this base station if said
one of the digital control channels is available;
means for scanning a set of analog control channels if none of said digital
control channels is available;
second overhead message receiving means for determining if one of said
analog control channels is available; and
means for conducting control communications with one of said base stations
over an analog control channel associated with this base station if said
one of the analog control channels is available.
18. The mobile station of claim 17, further including means for selectively
activating said receiving means during predetermined timeslots in a
multiframe and deactivating said receiving means during other times to
thereby reduce power consumption.
19. The mobile station of claim 18, wherein said mobile station has a
binary identification number and said timeslots in a multiframe are
determined by a predetermined number of bits in said identification
number.
20. The mobile station of claim 17, wherein said speech information is
transmitted and received over said analog traffic channels in an analog
format.
21. The mobile station of claim 17, further comprising:
means for transmitting control information over said analog control
channel.
22. The mobile station according to claim 21, further comprising:
means for transmitting control information over said digital control
channel.
23. A cellular radio telephone communications system for communicating over
analog or digital traffic channels, comprising:
a mobile switching center;
plural base stations connected to said mobile switching center, for
receiving and transmitting speech information and control information; and
plural mobile radio telephone stations, including at least one multi-mode
mobile station including:
means for receiving speech and data information from a first base station
over the analog and digital traffic channels;
means for transmitting speech and data information to said first base
station over the analog and digital traffic channels;
means for receiving and decoding control information in an analog format
from said first base station over an analog control channel; and
means for receiving and decoding control information in a digital format
from said first base station over a digital control channel;
a mode selection switch for switching the mobile station between an analog
mode and a digital mode, said switch being initially set to its digital
mode for receiving digital control communications over said digital
control channel from one of the base stations;
means for scanning a set of digital control channels, received from said
digital control communications when said mobile station is switched to a
digital mode;
first overhead message receiving means for determining if one of said
digital control channels is available;
means for conducting control communications with one of said base stations
over a digital control channel associated with this base station if said
one of the digital control channels is available;
means for scanning a set of analog control channels if none of said digital
control channels is available;
second overhead message receiving means for determining if one of said
analog control channels is available; and
means for conducting control communications with one of said base stations
over an analog control channel associated with this base station if said
one of the analog control channels is available.
24. The system according to claim 23, wherein each multi-mode mobile
station further includes:
means for transmitting control information over said analog control
channel.
25. The system according to claim 24, wherein at least some of said
multi-mode mobile stations also include:
means for transmitting control information over said digital control
channel.
26. The system according to claim 23, each multi-mode mobile station
further comprising:
means for periodically scanning said digital control channel;
means for deactivating power to said mobile in the absence of paging
information for said mobile station; and
means for reactivating said scanning means after a preset time period. |
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Claims |
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Description |
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FIELD OF THE INVENTION
The present invention is directed to cellular mobile radio telephone
systems utilizing both analog and digital control channels for
transmitting analog or digital control information between land or base
stations and mobile stations which have analog only, digital only, or
dual-mode traffic channel capabilities. In addition, the present invention
is directed to a cellular telephone system where modified analog and
dual-mode mobile radio telephones may select and communicate over either
analog or digital control channels.
BACKGROUND OF THE INVENTION
Many of the existing cellular systems in the United States are analog-based
systems. Because of significant increases in traffic capacity over the
same frequency spectrum currently used in analog systems, lower cost
operation, and additional mobile telephone features, such as
battery-saving capabilities, a transition is being made from analog to
digital communication in cellular telephone systems. That transition from
analog to digital communication within the same frequency band is often
achieved in a first step by replacing each of the fixed analog traffic
channels with three digital traffic channels and in a second step by
introducing a digital control channel, while maintaining as much as
possible the same base station sites, cell sizes, and frequency plans
designed for analog systems.
Despite the advantages purely digital or digital only mobile telephones
have over their counterparts using analog control channels, many
subscribers may be unwilling to discard their mobile telephones using
analog control channels in order to purchase a purely digital mobile
telephone. In addition, in many rural areas of the country, mobile
telephones having only digital capabilities will not be practical because
only analog control and traffic channels may be installed. On the other
hand, while mobile telephones having analog control channels may be used
anywhere in the country, they do not benefit from the new features
intended for the digital only mobile telephones. It is therefore desirable
to have a method of introducing the advantages attendant to purely digital
cellular mobile telephones also to the mobile telephones using analog
control channels.
In cellular systems using analog control channels, generally only one set
of analog control channels is used. However, a second set of analog
control channels, including dedicated control channels (DCC), paging
channels (PC) and access channels (AC), may be used for setting up calls,
informing the land system about the location of mobile stations, and for
informing the mobile stations about the parameters of the land system. All
mobile stations scan and read one of the dedicated control channels under
certain specified conditions, for example, when the mobile stations become
active, after a certain time period has elapsed, when ordered, or when the
mobile station enters a new geographical part of the cellular system. A
description of a cellular telephone system that incorporates a second set
of analog control channels is set forth in U.S. patent application Ser.
No. 514,540, filed Apr. 26, 1990, now U.S. Pat. No. 5,119,397 and assigned
to the same assignee. The text of this patent is incorporated herein by
reference.
While there has been little progress with respect to a completely
integrated cellular telephone system with both analog and digital traffic
and control channels, some paging systems have attempted to combine analog
and digital capabilities. For example, U.S. Pat. No. 4,857,915 to Andros
et al discloses a paging system which is compatible with transmissions
from analog or digital paging transmitters, i.e. short, digital or analog
voice messages may be transmitted. A paging receiver monitors an
appropriate communication channel for its identification code. Starting
with the least significant bits first, the paging receiver compares
incoming digits on the particular communication channel with its own
identification code. As soon as a mismatch occurs, the paging receiver
turns itself off in order to conserve power. If the paging receiver
determines that a match has been made by the received digital code with
the paging receiver identification code, the paging receiver displays the
place of origin of the page to the subscriber.
While Andros describes reception of pages from either analog or digital
transmitters, Andros does not incorporate the features of a digital
cellular telephone system with an existing analog cellular telephone
system. More particularly, Andros does not disclose a cellular telephone
system in which a mobile telephone may select either a digital or an
analog control channel.
SUMMARY OF THE INVENTION
The present invention is directed to a cellular mobile radio telephone
system in which multi-mode mobile stations may select either analog or
digital control channels. Multi-mode mobile stations are dual-mode and
analog mobile stations, as specified in the IS-54 standard, which have
been modified to conduct control communications over both analog control
channels and digital control channels. Initially, multi-mode mobile
stations scan and communicate over digital control channels. If no digital
control channel is available, the multi-mode mobile stations scan primary
and secondary sets of analog control channels depending upon their
capacity to handle communications over digital traffic channels. In this
way, multi-mode mobile stations benefit from the advantages of monitoring
digital control channels such as battery-saving capabilities resulting
from monitoring digital control channels in a sleep mode.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will now be described in more detail with reference
to preferred embodiments of the invention, given only by way of example,
and illustrated in the accompanying drawings, in which:
FIG. 1 is one possible set of frequency bands allocated for digital, analog
primary, and analog secondary control channels in the mobile telephone
frequency band;
FIG. 2 is a diagram of a system parameter overhead message that may be used
in accordance with the present invention;
FIGS. 3(a)-3(c) comprise a block diagram of a dual-mode mobile station
having both analog and digital control channel capabilities that may be
used in accordance with the present invention;
FIG. 4 is a flow chart outlining a control procedure selection of digital,
analog primary, or analog secondary control channels for a multi-mode
mobile station capable of using both digital and analog control and
traffic channels;
FIGS. 5(a)-5(b) illustrate signal transmissions from the land-based system
on a digital paging channel for conserving battery power in mobile
telephones; and
FIG. 6 is a chart showing the types of traffic and control channels used by
various types of mobile stations.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A possible assignment of frequencies for a primary and an optional
secondary set of analog control channels as well as digital control and
paging channels for a cellular telephone system presupposed by the present
invention is illustrated in FIG. 1. The frequency bands in FIG. 1 (A, B,
A', B', A") are those specified for U.S. cellular telephone systems in the
standard EIA/TIA IS-54 for frequency parameters. The space between
adjacent communication frequencies is 30 kHz. For example, in system A,
333 frequencies may be established in the frequency range from 825,030 MHz
to 834,990 MHz. Similarly, 333 land or base station transmitting
frequencies may be established from 870,030 MHz to 879.990 MHz. One pair
of such uplink and downlink frequencies may be assigned either to one
analog channel or subdivided into several (e.g. three) time slots and
assigned to a corresponding number of digital channels. In this exemplary
embodiment, system A is a preferred system and system B is a non-preferred
system.
In each Metropolitan Statistical Area (there are 305 such areas in the
USA), there are two competing cellular service operators. One operator is
always the established telephone company in the area, the "wire-line"
company, and is referred to as System B. The other operator is an
independent company which does not own the telephone network, the "non
wire-line" company, and is referred to as System A. In the preferred
embodiment, system A is defined as the preferred system.
The frequencies for the primary control channels are those set forth in the
published U.S. standard EIA/TIA IS-54. The number of secondary analog
control channels may be equal to the number of primary analog control
channels, e.g., 21 in each extended frequency band A' and B'. There may be
as many as 42 digital control channels with an associated 84 paging
channels in each of the frequency bands A and B. Those digital channels
not needed as control and paging channels may be utilized as traffic
channels. In the preferred embodiment, the digital dedicated control
channels occupy the first time slot of a frequency, whereas the remaining
time slots on that frequency may be used as paging or traffic channels.
The present invention presupposes in each frequency band (at least in bands
A and B) analog control channels as well as an additional set of digital
control channels that may be scanned by mobile stations. The original
control channels in the analog system will be referred to herein as the
primary control channels. The second subset of analog control channels
corresponding to frequency bands A' and B' will be referred to as
secondary analog control channels. The digital control channels bordering
the primary analog control channels will be referred to as digital control
channels and digital paging channels.
All overhead messages are sent in a group called an overhead message train
(OMT). The first message of the train is the system parameter overhead
message (SPOM). FIG. 2 illustrates an example of a system parameter
overhead message (SPOM) that may be utilized in conjunction with the
present invention. The SPOM is transmitted by a base station on its
associated control channel about once a second. The base station transmits
the same SPOM over both an analog and a digital control channel
simultaneously, but the formats are different. Upon receiving the SPOM,
mobile stations adjust to different cellular systems having various
parameter values.
The SPOM as implemented on an analog control channel generally consists of
two word trains, word 1 and word 2. The T.sub.1 T.sub.2 field at the
beginning of each word represents an indication of message type, and a
T.sub.1 T.sub.2 value of "11" indicates an overhead word. Immediately
following the type field is the digital color code (DCC) field which
identifies the cell or group of cells transmitting the SPOM. Word 1
further includes a system identification field (SID1) for identifying
system A or B, an authentication procedure field (AUTH), and a reserve
field (RSVD) of bits for future use. The protocol capability indicator
field (PCI) is set to an active value, e.g., 1, if the designated control
channel can assign digital traffic channels. Should the PCI bit indicate
an inactive value, e.g., 0, the control channel can only assign analog
traffic channels. A number of additional words coming field (NAWC) is set
to a value which is one less than the total number of words in the
overhead message train (OMT). An overhead message type field (OHD) of word
1 is set to a value of "110" indicating the first word of the system
parameter overhead message. The OHD field of word 2 is set to "111"
indicating the second word of the system parameter overhead message. Also
included at the end of word 1 and word 2 is a parity field (P) for error
detection purposes.
Word 2 includes the following fields: the digital color code (DCC), a
serial number field S; an extended address field E; a registration field
for home stations (REGH); a registration field for roaming stations
(REGR); a discontinuous transmission field DTX; a field (N-1) for
indicating the number of paging channels in the system; a read control
filler field (RCF); a combined paging/access field (CPA); a field (CMAX-1)
for indicating the number of access channels in the system; and an end
indication field (END) which is set at "1" to indicate the last word of
the overhead message train or set to "0" if it is not the last word.
Referring now to FIGS. 3(a), 3(b) and 3(c), one embodiment of a multi-mode
mobile station for use in a cellular telephone system that operates in
accordance with the present invention is illustrated. With respect to
digital traffic communications, i.e., where digitized voice information is
transmitted between base and mobile stations, the operation of the system
is explained in the context of full-rate transmissions, in which each
packet of digital information is interleaved between two spaced time slots
in a frame of data. It will be readily appreciated, however, that the
invention is equally applicable to other types of cellular radio systems,
such as those in which information is transmitted digitally at half rate.
In the digital part of the multi-mode mobile station depicted in FIG. 3(a),
speech signals from a microphone 100 are received at an analog-digital
mode switch 90 which is controlled by an output signal from a
microprocessor controller 130. Depending upon the mode of the mobile
station, the microprocessor controller 130 directs the mode switch 90 to
connect the microphone output signals to a speech coder 101 for a mobile
station operating in a digital mode (digital traffic channel) or to a
voice processing unit 101A for a mobile station operating in an analog
mode (analog traffic channel).
In the digital mode, the speech coder 101 converts the analog signal from
the microphone 100 into a binary data stream. The data stream is divided
into data packages, according to the time division, multiple access (TDMA)
principle. A fast associated control channel (FACCH) generator 102
generates control and supervision signalling messages that are transmitted
from the mobile station to the land-based station. The FACCH message
replaces a user frame of speech or data whenever it is to be transmitted.
A slow associated control channel (SACCH) generator 103 provides
signalling messages that are transmitted over a continuous channel for
exchange of information between the base station and the mobile station
and vice versa. A fixed number of bits, e.g., twelve, is allocated to the
SACCH for each time slot of a message stream. The channel coders 104 are
connected to the speech coder 101, FACCH generator 102 and SACCH generator
103 for manipulating the incoming data in order to carry out error
detection and correction. The techniques used by the channel coders are
preferably convolutional encoding, which protects important data bits in
the speech code, and cyclic redundancy check (CRC), wherein the
significant bits in the speech coder frame, e.g., twelve bits, are used
for computing a 7-bit check.
A two-burst interleaver 106 is coupled to the channel coders 104. The
two-burst interleaver 106 is controlled by the microprocessor controller
130 so that, at appropriate times, user information over a particular
speech channel is replaced with system supervision messages over the
FACCH. Data to be transmitted by the mobile station is interleaved over
two distinct time slots. A packet of 260 data bits that constitute one
transmitting word, are divided into two equal parts and are allotted to
two different time slots. The effects of Rayleigh fading will be reduced
in this manner. The output of the two-burst interleaver 106 is provided to
the input of a modulo-two-adder 107 so that the transmitted data is
ciphered bit-by-bit by logical modulo-two-addition of a pseudo-random bit
stream.
The output of the channel coder 104 associated with the SACCH generator 103
is connected to a 22-burst interleaver 108. The 22-burst interleaver 108
interleaves data transmitted over the SACCH over 22 time slots, each burst
of SACCH data consisting of 12 bits of information.
The mobile station further includes a Sync Word--DVCC generator 109 for
providing the appropriate synchronization word (Sync Word) and DVCC
(digital verification color code) which are to be associated with a
particular connection. The Sync Word is a 28 bit word used for time slot
synchronization and identification. The DVCC is an 8-bit code sent by the
base station to the mobile station and vice-versa for assuring that the
proper channel is being decoded.
A burst generator 110 generates message bursts for transmission by the
mobile station. The burst generator 110 is connected to the outputs of the
modulo-two-adder 107, the 22-burst interleaver 108, the Sync Word/DVCC
generator 109, an equalizer 114, and a control channel message generator
132, to integrate the various pieces of information from these respective
units into a single bit stream. For example, according to the published
U.S. standard EIA/TIA IS-54, a message burst comprises data (260 bits),
SACCH (12 bits), Sync Word (28 bits), coded DVCC (12 bits), and 12
delimiter bits, combined for a total of 324 bits. Under the control of the
microprocessor 130, two different types of message bursts are generated by
the burst generator 110: control channel message bursts from the control
channel message generator 132 and voice/traffic message bursts.
The control channel message generator 132 generates digital control
messages | | |
