Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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MULTIPLE HYPERBAND RADIOCOMMUNICATIONS SYSTEM
This is a divisional application of Canadian Patent Application Serial No.
2,217,650 filed on April 18, 1996.
BACKGROUND
The present invention relates to cellular communications systems and; in
particular, to a multiple hyperband cellular communications system and
multiple
hyperband capable mobile stations for operation therein. It should be
understood
that the expression "the invention" and the like encompasses the subject
matter of
both the parent and the divisional application.
North American cellular communications have historically been
implemented solely in the 800 MHz Cellular hyperband. The most recent
evolution in cellular communications services involves the adoption of three
additional hyperbands for use in handling mobile communications. Of these
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additional hyperfiands, only the Personal Communication Services (PCS)
hyperband in the 1900 MHz frequency range has been completely defined. With
the existence of the new PCS hyperband, different types of subscriptions and
or
scrvices like speech quality, voice privacy, and encryption may exist for one
mobile station from one hyperband to another, or from one frequency band in
the
Cellular hyperband to another frequency band in the PCS hyperband.
The Cellular hyperband is assigned two telephone frequency bands
(commonly referred to as the A frequency band and the B frequency band) for
carrying and controlling communications. The PCS hyperband, on the other
hand, is specified in the United States of America to include six different
frequency bands (A, B, C, D, E and F). Thus, in accordance with EIA/TIA
Interim Standard IS-136 (the "IS-136 specification") as modified by the PN3388-
1 specification version of Sept. 9, 1994 project no. 3011-1, eight frequency
bands are now available in any given service area to facilitate communications
services.
Each one of frequency bands specified for the Cellular and PCS
hyperbands is allocated a plurality of voice or speech channels and at least
one
access or control channel. The control channel is used to control or supervise
the operation of mobile stations by means of information transmitted to and
received from the mobile stations. Such information may include incoming call
signals, outgoing call signals, page signals, page response signals, location
registration signals, voice channel assignments, maintenance instructions,
hand-
off, and cell selection or reselection instructions as a mobile station
travels out of
the radio coverage of one cell and into the radio coverage of another cell.
The
control or voice channels may operate in either an analog mode, a digital
mode,
or a combination mode.
The individual frequency bands are typically assigned to, and provided
within a hyperband for the service area by only one service company. For
cxample, the A frequency band of the Cellular hyperband is usually reserved
for
use by non-wire Line communications service companies, and the B frequency
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band is usually reserved for use by wire line communications service
companies.
In some instances, a frequency band assigned to one service company for a
given
cell or service area may be assigned to a different service company in another
cell or service area. It is also recognized that the same service company may
provide cellular communications service in multiple frequency bands within
either a single hyperband or across multiple hyperbands.
Cellular hyperband mobile stations have historically been configured to
operate in a particular one of the available frequency bands within the
Cellular
hyperband. For example, if the service company providing cellular service to
the subscriber is a wire line company, the Cellular hyperband mobile station
is
configured with the B frequency band as its "home" frequency band. Reciprocal
billing arrangements between service companies allow subscribers to place
calls
over non-home frequency bands in the event the mobile station is roaming.
These non-home calls, however, typically require payment by the subscriber of
some form of a surcharge and are therefore undesirable. Furthermore, in the
absence of an agreement between service companies, roaming subscribers may
not be able to make a call without operator assistance. For the service
provide; ,
use of foreign frequency bands by subscribers results in a potential loss of
revenue that the provider would like to avoid.
The expansion to multiple hyperband communications capabilities as a
result of the IS-136 specification has necessitated the development and
placement
into service of mobile stations that are capable of accessing both the
Cellular artd
PCS hyperbands. Furthermore, the existence of multiple available hyperbands
-for carrying mobile station communications presents an opportunity for
cellular
telephone switches to control overlapping or adjacent cells in different
hyperbands. It would be beneficial if the cellular communications system were
configured from both tine system and terminal point of view to allow multiple
hyperband capable mobile stations to operate seamlessly between the available
hyperbands. At the same time, however, existing mobile units which are capable
of operation only in the Cellular hyperband should enjoy continued support.
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SI 1MMARY
The present invention provides a registration method for a multiple hyperband
radiocommunication system comprising the steps of:
listening, in a mobile station, to a first control channel being transmitted
on a first
hyperband;
switching, in said mobile station, to a second control channel being
transmitted on a
second hyperband; and
transmitting, from said mobile station, a registration message to a fixed part
of said
radiocommunication system which indicates that said mobile station is now
listening
to said second control channel on said second hyperband.
The present invention also provides a registration method for a multiple
hyperband radiocommunication system comprising the steps of:
receiving, in a base station, a registration message from a mobile station
which has
switched from listening to a first control channel transmitted on a first
hyperband to a
second control channel transmitted on a second hyperband; and
transmitting a paging message to said mobile station only over at least one
second
control channel on said second hyperband.
According to exemplary embodiments of the present invention, multiple
hyperband capable mobile stations and base stations are described. These
mobile and
base stations support multiple hyperband operations including, for example,
mobile
assisted channel allocation (MACA), mobile assisted handover (MAHO), cell
reselection, traffic channel assignment, control channel location and
registration.
By bridging multiple hyperbands, service quality can be enhanced.
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BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing, and other, objects, features and advantages of the present
invention will be more readily understood upon reading the following detailed
description in conjunction with the drawings in which:
Figure 1 is a cell diagram illustrating an exemplary cell configuration for a
multiple hyperband cellular communications system of the present invention;
Figure 2 is a simplified block diagram of a multiple hyperband mobile station
programmable with hyperband and frequency band selection criteria in
accordance
with the present invention;
Figures 3(a)-3(h) depict exemplary probability blocks for multiple hyperband
control channel location according to an exemplary embodiment of the present
invention;
Figures 4(a) and 4(b) illustrate exemplary messages related to cell
reselection
according to an exemplary embodiment of the present invention;
Figures S(a) and 5(b) illustrate exemplary messages related to MACA
techniques according to an exemplary embodiment of the present invention;
Figure 6 is a flowchart illustrating an exemplary multiple hyperband
registration technique according to an exemplary embodiment of the present
invention;
Figure 7 is an exemplary multiple hyperband handover message according to
an exemplary embodiment of the present invention; and
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Figures 8(a) and 8(b) illustrate exemplary messages related to MAHO
techniques according to an exemplary embodiment of the present invention_
DETAILED DESCRIPTION
Reference is now made to Figure 1 wherein there is shown a cell diagram
illustrating an exemplary cell configuration for a multiple hyperband cellular
communications system according to the present invention. An arbitrary
geographic area (hereinafter "the service area") is divided into a plurality
of cell >
10-18 and 20-26 utilizing both the Cellular and PCS hyperbands. The cells 10-
18 are represented by hexagrams and comprise communications cells wherein one
or both of the separate frequency bands (A and B) available in the Cellular
hyperband are provided via multiple channels. Cells 20-26, on the other hand,
are represented by circles and comprise communications cells one or more of
the
six separate frequency bands (A through F) of radio frequency cellular
communications are provided to mobile stations via multiple channels in the
PCS
hyperband.
Each of the Cellular hyperband cells 10-18 includes at least one base
station 28 configured to facilitate communications over cer-ain channels in at
least one of the two available Cellular hyperband frequency bands. Similarly,
each of the PCS hyperband cells 20-26 includes at least one PCS base station
30
configured to facilitate communications over certain channels in at least one
of
the six available PCS hyperband frequency bands. It will, of course, be
understood that each cell 10-18 and each cell 20-26 may include more than one
base station 28 and 30, respectively, if for example, different service
companies
''S are providing cellular communications services on different frequency
bands
within the same cell.
The base stations 28 and 30 are illustrated as being positionally located at
or near the center of each of the cells 10-18 and 20-26, respectively.
However,
depending on geography and other Irnown factors, the base stations 28 and 30
may instead be located at or near the periphery of, or otherwise away from the
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centers of, each of the cells 14-18 and 20-26. In such instances, the base
stations
28 and 30 may broadcast and communicate with mobile stations 32 located within
the cells 10-18 and 20-26 using directional rather than omni-directional
antennas.
Each one of the base stations 28 and 30 includes a transmitter, a receiver,
and a
base station controller connected to the antenna in a manner and with a
configuration well known in the art.
There are a number of mobile stations 32 shown operating within the
service area of the system of the present invention. These mobile stations 32
each pOSSeSS the requisite functionality for operating in both the Cellular
hyperband and the PCS hyperband (i.e., they are multiple hyperband
communications capable). The configuration and operation of the mobile
stations
32 will be dexribed in more detail herein with respect to Figure 2. It will,
of
course, be understood that existing Cellular hyperband only mobile stations
(not
shown) are compatible with the system of the present invention, but will only
be
able to communicate with Cellular hyperband base stations 28.
Reference is now made to Figure 2 wherein there is shown a simplified
block diagram of a multiple hyperband mobile station 32 according to an
exemplary embodiment of the present invention. The mobile station 32 includes
a processor (CPU) 34 connected to a plurality of tranxeivers 36. The
transceivers 36 are each configured to operate in the frequency bands and
channels of a different hyperband. For example, the tranxeiver 36(1) functions
on multiple channels in at least one of the frequency bands of the 800 MHz
frequency range, and is thus utilized by the mobile station 32 for
communicating
over the Cellular hyperband. The tranxeiver 36(2), on the other hand,
functions
on multiple channels in at least one of the frequency bands of the 1900 MHz
frequency range, and is thus utilized by the mobile station 32 for
communicating
over the PCS hyperband. The remaining tranxeivers 36(3) and 36(4), if
included, function in other frequency ranges; for example, comprising those
additional frequency ranges identified by the IS-136 specification for other
soon
to be made available hyperbands. By means of an output signal from the
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processor 34, the frequency band and precise channel therein on which the
transceivers 36 operate for communications may be xlected. An antenna 38 is
connected to the transrcivers 36 for transmitting and rcceiving radio
communications (both voice and data) over the cellular communications network
utilizing, for example, the base stations 28 and 30 of Figure 1. A data
storage
device 40 (preferably in the form of a read only memory - ROM - and a random
access memory - RANI] is also connected to the processor 34. The data storage
device 40 is used for storing programs and data executed by the processor 34
in
controlling operation of the mobile station 32. There are other components 41
included in the mobile station 32 (like a handset, keypad, etc.) and not
specifically shown in Figure 2 whose nature, operation and interconnection
with
the illustrated components are well known to thox skilled in the art.
The primary modes of operation of the mobile station 32 of interest herein
are: an idle operating mode, wherein the mobile station awaits use through
either
the receipt or initiation of a call; and, an on call operating mode, wherein
the
mobile station is being used by the subscriber to engage in a call. Both of
these
modes will now be described in more detail below with an emphasis on functions
performed by the base stations and the mobile stations to provide seamless
operation across different hyperbands.
When in the idle state, a mobile station tunes to and then continuously
monitors the strongest control channel at its known frequency (generally, the
control channel of the cell in which the mobile station is located at that
moment)
and may receive or initiate a telephone call through the corresponding base
station. When moving between cells while in the idle state, the mobile station
will eventually "lose" radio connection on the control channel of the "old"
cell
and tune to the control channel of the "new" cell. The initial tuning to, and
the
change of, control channel are both accomplished automatically by scanning all
the control channels at their known frequencies in operation in the cellular
system to find the 'best" control channel. When a control channel with good
reception quality is found, the mobile station remains tuned to this channel
until
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the quality deteriorates again. In this manner, all mobile stations are nearly
always "in touch" with the system.
As can be seen firom the foregoing, speedy location of control channels is
significant with respect to overall system performance. If the control
channels
are not located on predetermined and fined frequencies, then the mobile
stations
have to search for the control channels. As dexribed in the above-incorporated
U.S. Patent Application Serial No. 08/331,711 entitled "A Method and
Apparatus for Locating a Digital Control Channel in a Radiocommunication
System" and filed on October 31,1994 (hereafter referred to as the "control
channel locator application"), control channel location is expedited by, for
example, prescribing a search pattern based on a relative likelihood of
finding a
control channel on a particular frequency or group of frequencies. According
to
exemplary embodiments of the present invention, this concept can be extended
to
multiple hyperband systems as follows.
For each of the frequency bands in each of the hyperbands available, e.g.,
bands A and B for the Cellular hyperband and bands A-F for the PCS
hyperband, channels are grouped into probability blocks which are ranked in
accordance with the relative Likelihood of finding the digital control channel
in
each block. Exemplary groupings are illustrated in Figures 3(a)-3(h). These
groupings can be stored in the data storage device 40 of each multiple
hyperband
capable mobile station 32. To locate a control channel, a frequency band
within
one of the available tiyperbands in which a control channel is desired is
selected,
as for example described in the above-incorporated patent application entitled
"Mobile Station Preferences in a Multiple Hyperband Capable Communications
System". Then, a mobile unit can look for a digital control channel within a
highest ranked probability block, followed by a second highest ranked
probability
block and so on, until one is located. Each channel can be examined by the
mobile station as described in the control channel locator patent application.
Having located and tuned to a control channel, but while still in the idle
operating mode, the mobile station 32 receives a neighbor list from the
cellular
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system via a communications broadcast from the base stations 28 or 30
identifying call neighbors (i.e., other base stations) that are available for
server
selection. The mobile station can measure on one or more of the channels to
identify a new server when, for example, its current server no longer
satisfies
certain transmission criteria_ For multiple hyperband capable mobile stations
32 ,
the neighbor list can include information pertaining to servers operating on
the
Cellular hyperband, as well as servers operating on the PCS hyperband. For
example, the system can transmit a message having the exemplary format
illustrated in Figure 4(a) to identify, as pan of a neighbor list, one or more
servers in the same hyperband as the conQOl channel to which the mobile
station
32 is currently listening. Similarly, for candidate servers on ocher
hyperbands,
the system can transmit a message having the exemplary format seen in Figure
4(b). Although the exemplary message formats of Figures 4(a) and 4(b) provide:
a two bit length field for identifying a hyperband (e.g., 00 = Cellular
hyperband, O1 = PCS hyperband, others reserved), those stalled in the art will
appreciate that additional bits could be used to identify more than four
different
hyperbands. Alternatively, a single message can be transmitted which
identifies
a particular hyperband associated with each channel to be measured.
Registration is performed in radiocommunication systems to, among
other reasons, inform the system of each mobile's general location, e.g., in
which cell or cells a mobile station is currently located. Registration can be
performed periodically or after certain events occur, such as power up or
power
down, or both periodically and after certain events occur. Once a mobile
station
has registered with the system, the system can then direct pages to the mobile
station on the appropriate control channel(s). However, the advent of multiple
hyperbands adds further complexities to this issue. As described above, an
idle
mobile station 32 can switch between different hyperbands by way of cell
reselection according to exemplary embodiments of the present invention. Thus,
according to an exemplary embodiment of the.prcsent invention illustrated in
Figure 6, a mobile station which switches hyperbands will also register with
the
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system so that the system knows on which hyperband to issue subsequent paging
messages. For example, if mobile station 32 is first listening to a control
channel on the Cellular hyperband transmitted by a base station 28 and
subsequently begins Listening to a control channel on the PCS hyperband
5 transmitted by a base station 30, then that mobile station will issue a
registration
message to the system providing, among other data, an indicator of the new
hyperband within which it is now listening. In this way, the system need not
page the mobile station 32 using base stations 28.
Figure 6 is a flowchart illustrating an example of registration according to
10 the present invention. Therein, the mobile station determines if a period
has
expired for registration at block 60. If so, then the mobile sends a
registration
message to the system at block 62. The mobile station checks to see whether
the
current control channel is within the same hyperband as the control channel to
which the mobile station was listening at the time of the last registration
message
at block 64. If not, then the mobile station will also register at block 62.
Otherwise, no registration occurs during this cycle. Of course those skilled
in
the art will readily appreciate that Figure 6 is only an example since this
exemplary embodiment is readily combinable with other conventional forms of
registration as mentioned above. For example, if a system did not use periodic
registration, then block 60 could be replaced by other event-driven types of
registration.
Another function which can be performed by idle mobile stations 32 is
mobile assisted channel allocation (MACA). Using a MACA technique, idle
mobile stations are instructed to measure either or both of the word error
rate or
received signal strength on channels designated by the serving base station 28
or
30. The base srarion can, for example, instruct these idle mobile stations to
perform such measurements via transmission overhead signalling to all of the
mobile stations, e.g., the broadcast control channel (BCCH). Having made
measurements on the identified frequencies, the mobile stations 32 then report
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this information to the base station so that the information can be used in
allocating channels (traffic andlor control channels) throughout the system.
For example, the system can send a list of up to eight frequencies
on the BCCH which all idle mobile stations shall measure the signal strength
of
and report to the base station. The number of frequencies to be measured can
be
variable, as can the selection of method for determining signal quality. As
with
the foregoing exemplary embodiment related to cell reselection, a message such
as that seen in Figure 5(a) can be transmitted to a mobile station instructing
to
measure on channels within a current, serving hyperband. An analogous
message, an exemplary version thereof depicted in Figure 5(b), can be
transmitted to the mobile for measuring on channels which are in a different
hyperband. Alternatively, a single message identifying the specific hyperband,
whether serving or other, associated with each frequency to be measured can be
issued by the system. The mobile stations can be instructed by the system to
measure each listed frequency a predetermined number of times, e.g., 4 times,
with a predetermined spacing between measurements, e.g., 20ms. A resultant
average of either signal strength or error rate can then be calculated and
returned
to the base station.
As another example, the idle mobile station can be instructed by
the system to measure the quality of the serving digital control channel
(DCC),
i.e., the control channel that the idle mobile station is locked and listening
to, by
performing a running average over a last predetermined number, e.g., 32, of
readings of its associated paging channel (PCH) for both signal quality, e.g.,
word error rate, and signal strength, e.g., RSS. The mobile station can be
instructed to perform either or both of the above described measurements
continuously or just before the idle mobile station accesses the system.
The system can also instruct the idle mobile stations regarding
when reports should be sent informing the system of the measurement results
and
what information these reports should contain. For example, the idle mobile
stations) can be instructed to inform the system of the measurement results
when
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they make a predetermined type of access to the system, e.g., a registration
access and/or an origination access. In such reports, the mobile station can
be:
instructed to include information pertaining to, for example, one or more of:
what type of measurement were made (i.e., the DCC or other channels or both),
whether the report is based on a full measurement interval and the measurement
results themselves.
In the on call operating mode, mobile station 32 may experience a
degradation in connection signal quality due to the changing interference
conditions caused by its own movement andlor other system variations. Once a
connection's quality drops below an acceptable threshold, the mobile station
will
be instructed to changeover to a new frequency to continue the connection. The
techniques for handling this changeover are known as handover or handoff
techniques and describe the interaction between the original serving base
station,
candidate replacement serving base stations and the mobile station being
served.
Many different types of handover techniques are known and used in
radiocommunication systems today, such as so-called soft handover wherein both
an original serving base station and the replacement serving base station
transmit
the same information to the mobile station for a period of ame to create a
seamless transfer of the connection, as welt as transmission diversity.
According to exemplary embodiments of the present invention, a multiple
hyperband capable mobile station can be handed over from a traffic channel in
one hyperband to a traffic channel in another hyperband. For example,
referring
to Figure 1, a mobile station 32 which is in the midst of a connection being
served by PCS hyperband base station 30 in cell 26 moves into cell I8. Since
base station 28 in cell 18 can now provide a better quality connection to this
particular mobile station, it is desirable to handover the connection from the
PCS
hyperband base station 30 in cell 26 to the Cellular hyperoand base station 28
in
cell 18. This can be accomplished, for example, by transmitting a signal from
base station 30 in cell 26 to the mobile station 32 informing the mobile
station of
the new frequency and hyperband to which it should tune to continue the
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connection. As an example, the handover message can have the format shown irt
Figure 7. Note that this exemplary handover message implies the current
hyperband when the field for a target hyperband is omitted. Those skilled in
the
art will appreciate that a hyper~and indicator, regardless of whether the
target
hyperband is the current or a different hyperband, for each handover message
could alternatively be provided.
One way to identify the particular new frequency and hyperband to which
a handover should be made is !mown as mobile assisted handover (MAHO). By
way of MAHO techniques, the mobile station can assist in the selection of an
appropriate handover frequency and hyperband by measuring on candidate traffic
channels and reporting these measurement to the base station. For example, a
connected mobile station can measure on other frequencies during time slots in
which it is idle, i_e., those which are not being used to support the
connection.
According to the present invention, the mobile station receives a MAHO list
1S identifying cell neighbors that the mobile station should scan for and
measure on
for purposes of effecttiating a hand-off when the mobile station moves from
cell
to cell. This list informs the mobile station of both the channel and the
hyperband on which to measure.
Figures 8(a) and 8(b) depict exemplary message formats for instructing a
mobile to measure channels disposed in its current hyperband and for
instructing
a mobile station to measure channels disposed in a hyperband other than that
to
which it is currently listening, respectively. Alternatively, a single message
format could be provided which identifies specific channels and hygerbands
without relying on absence of an indicator as an assumption that the current
2S hyperband is implied.
The above~escribed exemplary embodiments are intended to be
illustrative in all respecu, rather than restrictive, of the present
invention. Thus
the present invention is capable of many variations in detailed implementation
that can be derived from the description contained herein by a person sldlIed
in
the art. For example although the present invention has been described with
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I4
respect to operation in the Cellular and PCS hype~ands, it will be understood
that the disclosed invention may be implemented in and across any of a number
of available hyperbands. All such variations and modifications are considered
to
be within the scope and spirit of the present invention as defined by the
following
claims_
