Note: Descriptions are shown in the official language in which they were submitted.
CA 02281959 1999-09-14
-1-
AUTOMATIC RETRANSh~SSION REQUEST
BACKGROUi\'D
The present invention relates to a method for transmitting messages between
mobile stations and a central switching system, and more particularly to
transmitting
these messages using a more efficient communications link protocol over the
air-
interface of a cellular telephone system.
In a typical cellular radio system, a geographical area, e.g., a metropolitan
area, is divided into several smaller, contiguous radio coverage areas called
"cells."
The cells are served by a series of fixed radio stations called "base
stations." The
base stations are connected to and controlled by a mobile services switching
center
(MSC). The MSC, in turn, is connected to the landline (wireline) public
switched
telephone network (PSTI~. The telephone users (mobile subscribers) in the
cellular
radio system are provided with portable (hand-held), transportable (hand-
carried) or
mobile (car-mounted) telephone units (mobile stations) which communicate voice
and/or data with the MSC through a nearby base station. The MSC switches calls
between and among wireline and mobile subscribers, controls signalling to the
mobile stations, compiles billing statistics, and provides for the operation,
maintenance and testing of the system.
FIG. 1 illustrates the architecture of a conventional cellular radio system
built according to the Advanced Mobile Phone Service (AMPS) standard. In FIG.
I, an arbitrary geographic area may be seen divided into a plurality of
contiguous
radio coverage areas, or cells, C 1-C 10. While the system of FIG. 1 is, for
illustration purposes, shown to include only ten cells, the number of cells
may be
much larger in practice. Associated with and located in each of the cells CI-
C10
is a base station designated as a corresponding one of a plurality of base
stations B1-
B10. Each of the base stations B1-B10 includes a plurality of channel units,
each
J
CA 02281959 1999-09-14
-2-
comprising a transmitter, a receiver and a controller, as is well known in the
art.
In FIG. 1, the base stations B 1-B 10 are located at the center of the cells
C1-
C10, respectively, and are equipped with omni-directional antennas
transmitting
equally in all directions. In this case, all the channel units in each of the
base
stations B1-B10 are connected to one antenna. However, in other configurations
of
the cellular radio system, the base stations B1-B10 may be located near the
periphery, or otherwise away from the centers of the cells C1-C10 and may
illuminate the cells C1-C10 with radio signals directionally. For example, the
base
station may be equipped with three directional antennas, each one covering a
120
degrees sector cell as shown in FIG. 2. In this case, some channel units will
be
connected to one antenna covering one sector cell, other channel units will be
connected to another antenna covering another sector cell, and the remaining
channel units will be connected to the remaining antenna covering the
remaining
sector cell. In FIG. 2, therefore, the base station serves three sector cells.
However, it is not always necessary for three sector cells to exist and only
one
sector cell needs to be used to cover, for example, a road or a highway.
Returning to FIG. l, each of the base stations B1-B10 is connected by voice
and data links to a mobile switching center (MSC) 20 which is, in turn,
connected
to a central office (not shown) in the public switching telephone network
(PSTN),
or a similar facility, e.g., an integrated system digital network (ISDN). The
relevant connections and transmission modes between the mobile switching
center
MSC 20 and the base stations B1-B10, or between the mobile switching center
MSC
20 and the PSTN or ISDN, are well known to those of ordinary skill in the art
and
may include twisted wire pairs, coaxial cables, fiber optic cables or
microwave
radio channels operating in either analog or digital mode. Further, the voice
and
data links may either be provided by the operator or leased from a telephone
company (telco).
With continuing reference to FIG. 1, a plurality of mobile stations M1-MIO
may be found within the cells C1-C10. Again, while only ten mobile stations
are
shown in FIG. 1, the actual number of mobile stations may be much larger in
CA 02281959 1999-09-14
-3-
practice and will generally exceed the number of base stations. Moreover,
while none of the
mobile stations Ml-M10 may be found in some of the cells C1-C10, the presence
or absence of
the mobile stations M 1-M 10 in any particular one of the cells C 1-C 10
depends on the individual
desires of each of the mobile subscribers who may travel from one location in
a cell to another or
from one cell to an adjacent or neighboring cell.
Each of the mobile stations M1-M10 includes a transmitter, a receiver, a
controller and a
user interface, e.g., a telephone handset, as is well known in the art. Each
of the mobile stations
Ml-M 10 is assigned a mobile identification number (MIN) which is a digital
representation of the
telephone directory number of the mobile subscriber. The MIN defines the
subscription of the
mobile subscriber on the radio path and is sent from the mobile station to the
MSC 20 at call
origination and from the MSC 20 to the mobile station at call termination.
Each of the mobile
stations M1-M10 is also identified by an electronic serial number (ESN) which
is a factory-set,
"unchangeable" number designed to protect against the unauthorized use of the
mobile station. At
call origination, for example, the mobile station will send the ESN to the MSC
20. The MSC 20
will compare the received ESN to a "blacklist" of the ESNs of mobile stations
which have been
reported to be stolen. If a match is found, the stolen mobile station will be
denied access..
2 0 Each of the cells Cl-C 10 is allocated a subset of the radio frequency
(RF) channels
assigned to the entire cellular system by the concerned government authority,
e.g., the Federal
Communications Commission (FCC) in the United States or the CRTC in Canada.
Each subset of
RF channels is divided into several voice or speech channels which are used to
carry voice
conversations, and at least one paging/access or control channel which is used
to carry
2 5 supervisory data messages, between each of the base stations B 1-B 10 and
the mobile stations
Ml-M10 in its coverage area. Each RF channel comprises a duplex channel
(bidirectional radio
transmission path) between the base station and the mobile station. The RF
channel consists of a
pair of separate frequencies, one for transmission by the base station
(reception by the mobile
station) and one for transmission by the mobile station (reception by the base
35
' CA 02281959 1999-09-14
-4-
station). Each channel unit in the base stations B1-B10 normally operates on a
preselected one of the radio channels allocated to the corresponding cell,
i.e., the
transmitter (TX) and receiver (RX) of the channel unit are tuned to a pair of
transmit and receive frequencies, respectively, which does not change. The
transceiver (TX/RX) of each mobile station Ml-M10, however, may tune to any of
the radio channels specified in the system.
In typical land line systems, remote stations and control centers are
connected by copper or fiber optic circuits which have a data throughput
capacity
and performance integrity that is generally significantly better than the data
throughput capacity and performance integrity provided by an air interface in
a
cellular telephone system. As a result, the conciseness of overhead required
to
manage any selected communication link protocol for land line systems is of
secondary importance. In cellular telephone systems, an air interface
communications link protocol is required in order to allow a mobile station to
communicate with a cellular switching system. A communications link protocol
is
used to initiate and to receive cellular telephone calls.
The electromagnetic spectrum available for use by cellular telephone systems
is limited and is divided into units called channels. Individual channels are
used as
communication links either on a shared basis or on a dedicated or reserved
basis.
When individual channels are used as communication links on a shared basis,
multiple mobile stations may either listen to or contend for the same
channels. In
the contending situation, each shared channel can be used by a plurality of
mobile
stations which compete to obtain exclusive use of the channel for a limited
period
of time. On the other hand, when individual channels are used as communication
links on a dedicated basis, a single mobile station is assigned the exclusive
use of
the channel for as long as it needs it.
In light of the generally reduced data throughput capacity and performance
integrity afforded by an individual channel in a channel sharing situation in
a
cellular telephone environment, the selection of an efficient air interface
protocol to
serve as the basis of the communication link becomes paramount.
CA 02281959 1999-09-14
-5-
The communication link protocol is commonly referred to as a layer 2 protocol
within the
communications industry and its functionality includes the delimiting or
framing of higher level
messages. Traditional layer 2 protocol framing mechanisms of bit stuffing and
flag characters are
commonly used in land line networks today to frame higher layer messages,
which are referred to
as layer 3 messages. These layer 3 messages may be sent between communicating
layer 3 peer
entities residing within mobile stations and cellular switching systems.
In cellular systems, the likelihood of successfully sending a message over a
radio channel
is inversely proportional to the length of the message since the entire
message will be considered
to be in error even if only a single bit of the transmitted message is
received in error. In order to
address this problem, messages are first divided into small packets or frames.
Thus, it becomes
important for the cellular system to know if all of the transmitted packets
are correctly received by
a mobile station.
SUMMARY
In accordance with a first aspect of the invention there is provided a method
for obtaining
a report on the status of frames comprising a message transmitted from a
cellular communication system to a remote station comprising the steps of:
sending a status
2 0 request to the remote station; and transmitting a bit map from the mobile
station to the base
station, wherein the bit map indicates which of a plurality of frames have
been correctly received
by the remote station.
In accordance with a second aspect of the invention there is provided a base
station for
use in a cellular communication system comprising: means for transmitting a
status request to a
2 5 mobile station; means for receiving a bit map from the mobile station in
response to the polling
request; means for interpreting the bit map to determine which of a plurality
of frames have been
correctly received by the mobile station when the status request was received.
Finally, there is provided a mobile station for use in a cellular
communication system
comprising: means for receiving a status request from the cellular system;
means for forming a bit
3 0 map which indicates which of a plurality of frames have been correctly
received by the mobile station when the status request was received; means for
transmitting the
bit map to the cellular system.
CA 02281959 1999-09-14
-6-
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:
Figure 1 illustrates the architecture of a conventional cellular radio system;
Figure 2 illustrates a three sector cell which may be used in the system shown
in Figure 1;
Figure 3 illustrates a block diagram of an exemplary cellular mobile radio
telephone
system;
Figure 4 illustrates the logical channels which make up the digital control
channel
according to one embodiment of the present invention;
Figures Sa-b illustrate SPACH Header sections A and B, respectively, according
to one
embodiment of the present invention;
Figures 6a-b illustrate the Random Access Procedures for a base station and a
mobile
station according to one embodiment of the present invention;
Figures 7a-b illustrate a SPACH ARQ Mode Procedure for a mobile station and a
base
station according to one embodiment of the present invention;
Figure 8 illustrates an ARQ Mode Begin frame according to one embodiment of
the
2 0 present invention; and
Figure 9 illustrates an ARQ Mode Continue frame according to one embodiment of
the
present invention.
CA 02281959 1999-09-14
_'7_
DETAILED DESCRIPTION
Although the description hereinafter focuses on systems which comply with IS-
54B and
its successors, the principles of the present invention are equally applicable
to a variety of
wireless communication systems, e.g., cellular and satellite radio systems,
irrespective of the
particular mode of operation (analog, digital, dual mode, etc.), the access
technique (FDMA,
TDMA, CDMA, hybrid FDMA/TDMA/CDMA, etc.), or the architecture (macrocells,
microcells,
picocells, etc.). As will be appreciated by one skilled in the art, the
logical channel which carries
speech and/or data may be implemented in different ways at the physical layer
level. The physical
channel may be, for example, a relatively narrow RF band (FDMA), a time slot
on a radio
frequency (TDMA), a unique
code sequence (CDMA), or a combination of the foregoing. For purposes of the
present invention,
1 S the term "channel" means any physical channel which can carry speech
and/or data, and is not
limited to any particular mode of operation, access technique or system
architecture.
This application contains subject matter which is related to U.S. Patent
5,353,332 entitled
"Method and Apparatus for Communication Control in a Radiotelephone System,"
issued
October 4, 1994, U.S. Patent 5,404,355 entitled "Digital Control Channel",
issued April 4,
2 0 1995, U.S. Patent 5,610,917 entitled "Layer 2 Protocol for the Random
Access Channel and the
Access Response Channel", issued March 11, 1997, U.S. Patent 5,603,081
entitled "A Method for
Communicating in a Wireless Communication System," issued February 11, 1997,
U.S. Patent
5,745,523 entitled "Multi-Mode Signal Processing," issued April 28, 1998 and
U.S. Patent
5,420,864 entitled "A Method of Effecting Random Access in a Mobile Radio
System," issued
2 5 May 30, 1995.
Figure 3 represents a block diagram of an exemplary cellular mobile
radiotelephone
system according to one embodiment of the present invention. The system shows
an exemplary
base station 110 and a mobile station 120. The base station includes a control
and processing unit
130 which is connected to the mobile
CA 02281959 1999-09-14
_8_
switching center MSC 140 which in turn is connected to the public switched
telephone network (not illustrated).
The base station 110 for a cell includes a plurality of voice channels handled
by voice channel receiver 150 which is controlled by the control and
processing unit
130. Also, each base station includes a control channel transceiver 160 which
may
be capable of handling more than one control channel. The control channel
transceiver 160 is controlled by the control and processing unit 130. The
control
channel transceiver 160 broadcasts control information over the control
channel of
the base station or cell to mobiles locked to that control channel.
When the mobile 120 is in an idle mode, the mobile periodically scans the
control channels of base stations like base station 110 to determine which
cell to
lock on or camp to. The mobile 120 receives the absolute and relative
information
broadcast on a control channel at its voice and control channel transceiver
170.
Then, the processing unit 180 evaluates the received control channel
information
which includes the characteristics of the candidate cells and determines which
cell
the mobile should lock onto. The received control channel information not only
includes absolute information concerning the cell with which it is associated,
but
also contains relative information concerning other cells proximate to the
cell which
the control channel is associated.
For a better understanding of the structure and operation of the present
invention, the digital control channel (DCC) may be divided into three layers:
layer
1 (the physical layer), layer 2 and layer 3. The physical layer defines the
parameters of the physical communications channel, e.g., RF spacing,
modulation
characteristics, etc. Layer 2 (L2) defines the techniques necessary for the
accurate
transmission of information within the constraints of the physical channel;
e.g.,
error correction and detection, etc. Layer 3 (L3) defines the procedures for
reception and processing of information transmitted over the physical channel.
According to the present invention, the DCC is comprised of the logical
channels shown in Figure 4. The DCC logical channels include: the broadcast
control channel (BCCH) (which is further comprised of the fast broadcast
control
CA 02281959 1999-09-14
-9-
channel F-BCCH, the extended broadcast control channel E-BCCH, and the short
message service broadcast control channel S-BCCH); the SPACH which includes
a short message service point to point channel (SMSCH), a paging channel (PCH)
and an access response channel (ARCH); and a random access control channel
(R.ACH).
The BCCH acronym is used to refer collectively to the F-BCCH, E-BCCH,
and S-BCCH logical channels. These three logical channels are used, in
general,
to carry generic, system-related information. Some attributes of these three
channels are: unidirectional (i.e., downlink), shared, point-to-multipoint
(i.e.,
broadcast), and unacknowledged. The fast BCCH is a logical channel used to
broadcast, for example, time critical system information. The extended BCCH is
a logical channel used to broadcast, for example, system information that is
less
time critical than the information sent on the F-BCCH. The short message
service
BCCH is a logical channel that is used to broadcast, for example, short
messages
used for the SMS broadcast service.
The SPACH channel is a logical channel that includes the SMSCH, PCH and
ARCH and is used to send information to specific mobile stations for SMS point-
to-
point, paging and access response purposes. The paging channel PCH is a subset
of the SPACH used to deliver pages and orders. The access response channel
ARCH is a subset of the SPACH to which the mobile station may autonomously
move upon successful completion of an access on a random access channel. The
ARCH may be used to convey analog voice channel or digital traffic channel
assignments or 'other responses to a mobile access attempt. Layer 2 automatic
retransmission requests are possible for the ARCH and SMSCH using
acknowledgement frames sent on the RACH. The SMS point-to-point channel
SMSCH is used to deliver short messages to a specific mobile station receiving
SMS
services. The attributes of the SPACH are: unidirectional (downlink) and
shared.
The PCH is point-to-multipoint and unacknowledged. The ARCH and SMSCH are
point-to-point and may be acknowledged or unacknowledged.
The random access channel RACH is used to request access to the system.
CA 02281959 1999-09-14
-10-
The attributes of this channel are unidirectional (uplink), shared, point-to-
point, and
acknowledged. Contention resolution and/or collision avoidance information is
provided on the forward subchannel corresponding to any given frame sent on
the
RACH.
S The SPACH layer 2 protocol can be used whenever a TDMA burst is used
to carry point-to-point SMS, Paging, or ARCH information. A single SPACH layer
2 protocol frame can be constructed so as to fit, for example, within a 125
bit
envelope. Additional bits (e.g., five) are reserved for use as tail bits
resulting in
a total of 130 bits of information carried within each slot assigned for SPACH
purposes. A summary of the possible SPACH formats is provided in the first
table
below. A summary of the fields comprising layer 2 protocol frames for SPACH
operation is provided in the second table below.
Similar frame formats can be used for the SPACH channels such that the
frames will have a common Header A. The contents of the Header A determine
whether or not additional information, known as Header B, is present in any
given
SPACH frame. The Header A discriminates between hard (dedicated) page frames,
PCH frames, ARCH frames and SMSCH frames. A Hard Triple Page frame
containing three 34-bit mobile station identifications MSIDs can be sent on
the PCH
(Burst Usage BU = Hard Triple Page). A Hard Quadruple Page frame containing
four 20 bit or 24 bit MSIDs can also be sent on the PCH (BU = Hard Quadruple
Page).
One or more L3 messages may be transmitted in one frame, or continued
over many frames. MSIDs are only carried within frames where BU= Hard Triple
Page, Hard Quadruple Page, and ARQ Mode BEGIN in addition to BU = PCH,
ARCH and SMSCH where the Burst Type BT may be set to Single MS1D, Double
MSID, Triple MSID or Quadruple MSID. The mobile station identity type (IDT)
field identifies the format of all MSIDs carried within a given SPACH frame
(i.e.,
no mixing of MSID formats is allowed). Pages carried on the PCH are not
allowed
to continue beyond a single SPACH frame (even though the protocol allows for
it).
All other PCH messages may continue beyond a single SPACH frame.
CA 02281959 1999-09-14
-11-
For non ARQ mode operation, the L2 SPACH protocol supports sending a
single L3 message to multiple MSIDs in addition to the fixed one-to-one
relationship
between MSIDs and L3 messages. The Message Mapping field (MIvl7 is used to
control this aspect of the layer 2 frame operation. A valid SPACH frame
requires
that all L2 header information pertinent to a given L2 frame be included
entirely
within that frame, i.e., L2 header from a given SPACH frame cannot wrap into
another SPACH frame. The Offset Indicator field (OI) is used to allow both the
completion of a previously started layer 3 message and the start of a new
layer 3
message to occur within a single SPACH frame.
The following table summarizes possible SPACH formats:
SMS PCH ARCH CAN BE CONTINUED
Single MSID Y Y Y Y
Double MSID N Y Y Y
Triple MSID N Y Y Y
Quadruple MSID N Y Y Y
1$ Hard Triple Page N Y N N
(MIN)
Hard Quadruple N Y N N
Page
fTMSI)
Continue Y Y Y Y
ARQ Mode BEGIN Y N Y Y
ARQ Mode CONTINUEY N Y Y
Figure Sa illustrates the SPACH Header A according to one embodiment of
the present invention. The SPACH Header A contains burst usage information and
flags for managing mobile stations in a sleep mode. The BU field provides a
high
level indication of burst usage. According to the present invention, the
operation
performed on each SPACH channel is not predetermined. The BU field indicates
whether the burst is being used for paging, access response, or short message
services. The flags indicate changes in sleep mode configuration as well as
CA 02281959 1999-09-14
-12-
broadcast control channel information. This header can be present in all
possible
SPACH frame types. Figure Sb illustrates the SPACH Header B according to one
embodiment of the present invention. The SPACH Header B contains
supplementary header information used to identify the remaining content of the
layer
2 frame. This header is present when Header A indicates a burst usage of type
PCH, ARCH or SMSCH.
The following table summarizes the SPACH Layer 2 Protocol fields:
Field Name Length Values
(bits)
BU = Burst Usage 3 000 = Hard Triple Page
(34 bit
MSID)
001 = Hard Quad Page
(20 or 24
bit MSID)
010 = PCH Burst
011 = ARCH Burst
100 = SMSCH Burst
101 = Reserved
110 = Reserved
111 = Null
1~ PCON = PCH Continuation 1 0 = No PCH Continuation
1 = PCH Continuation,
Activated
BCN = BCCH Change Notification1 Transitions whenever
there is a
change in F-BCCH information.
SMSN = SMS Notification 1 Transitions whenever
there is a
change in S-BCCH information.
PFM = Paging Frame Modifier1 0 = Use assigned PF
1 = Use one higher than
assigned
PF
BT = Burst Type 3 000 = Single MSID Frame
001 = Double MSID Frame
010 = Triple MSID Frame
011 = Quadruple MSID
Frame
100 = Continue Frame
101 = ARQ Mode Begin
110 = ARQ Mode Continue
111 = Reserved
IDT = Identity Type 2 00 = 20 bit TMSI
O1 = 24 bit MINI per
IS-54B
10 = 34 bit MIN per IS-54B
11 = 50 bit IMSI
CA 02281959 1999-09-14
-13-
MSID = Mobile Station 20/24/34/5020 bit TMSI '
Identity
24 bit MINI
34 bit MIN
50 bit IMSI
MM = Message Mapping 1 0 = One instance of L3LI
and
L3DATA per instance of
MSID.
1 = One instance of L3LI
and
L3DATA for multiple MSIDs.
OI = Offset Indicator 1
j
0 = No message offset
included.
1 = Message offset included.
CLI = Continuation Length7 Number of bits remaining
$ Indicator in the
previous L3 message.
L3LI = Layer 3 Length 8 Variable length layer
Indicator 3 messages
supported up to a maximum
of 255
octets.
L3DATA = Layer 3 Data Variable Contains a portion (some
or all) of
the layer 3 message having
an
overall length as indicated
by L3LI.
The portion of this field
not used to
carry layer 3 information
is filled
with zeros.
PE = Partial Echo 7 The 7 least significant
bits of the
mobile station IS-54B
MIN.
TID = Transaction Identity2 Indicates which ARQ mode
transaction is being
transmitted on
the ARCH or SMSCH.
FRNO = Frame Number 5 Uniquely identifies specific
frames
sent in support of as
ARQ mode
transaction.
FILLER = Burst Filler Variable All filler bits are set
zero.
CRC = Cyclic Redundancy 16 Same Generator polynomial
Code as IS-
54B (includes DVCC)
According to the present invention, a mobile station (MS) can be in a
plurality of states. A mobile station shall be in the "start random access"
state
before the first unit of a message that is to be transmitted by a random
access has
been transmitted. The mobile station shall be in the "start reserved access"
state
before the first unit of a message that is to be transmitted by a reservation
based
access has been transmitted. The mobile station shall be in the "more units"
state
if there are more units associated with the current access event yet to be
transmitted.
The mobile station shall be in the "after last burst" state if the last unit
of an access
f
CA 02281959 1999-09-14
-14-
event has been transmitted. Finally, the mobile station shall be in the
"success"
state after a complete message has been sent successfully.
The layer 2 protocol also contains a plurality of flags. Forward shared
control feedback (SCF) flags are used to control transmissions on the RACH. A
busy/reserved/idle (BRI) flag is used to indicate whether its corresponding
uplink
RACH slot is Busy, Reserved or Idle. Six bits are used for these flags and the
different conditions are encoded as shown in the table below:
BRIS BRIO BRI3 BRI2 BRh BRIO
Busy 1 1 1 1 0 0
Reserved 0 0 1 1 1 1
Idle 0 0 0 0 0 0
A received/not received (R/N) flag is used to indicate whether or not the
base station received the last transmitted burst. A five times repetition code
is used
for encoding this flag as shown in the table below:
R/N4 R/N3 R/Nz R/N, R/No
Received . 1 1 1 1 1
Not Received 0 0 0 0 0
According to the present invention, partial echo (PE) information is used to
identify which MS was correctly received after the initial burst of random
access has
been sent or which MS is intended to have access to a reserved RACH slot. For
example, the seven least significant bits L,SBs of an IS-54B MIN can be used
as
partial echo information.
- CA 02281959 1999-09-14
-1$-
The following table shows how a mobile station decodes received flags
according to its Layer 2 state. Note that only the flags relevant to its Layer
2 state
are shown. In the "Start random access" state, the BRI flag is the only
relevant
flag. During a multiburst message transmission both the BRI and RlN flags are
relevant. In the summations in the following table, b; equals the bit value.
Layer 2 StateBusy/Reserved/Idle Received/Not
Received
Busy Reserved Idle ReceivedNot
received
111100001111 000000 11111 00000
Start random N/A NIA
1 6
access Idle
IF
~
bt
<
2
AND
bt
<
2
tI
t3
Start reservedReserved NIA N/A
IF
<
3
bits
difference
to
access Reserved
flag
code
value
More units Busy
IF
<
4
bits
difference
to
Busy
flag
code
value ~btz4 ~bt<4
t-t tt
After last Busy
burst IF
<
4
bits
difference
to
Busy
flag
code s s
value ~6,z4 ~b,<4
The mobile station interprets a received coded partial echo (CPE) value as
having been correctly decoded if it differs by less than 3 bits from the
correctly
coded partial echo. Tfiis is referred to as PE match.
A mobile station is allowed a maximum of Y+1, where Y=(0..7), access
attempts before considering the attempt to transfer a message as a failure.
The
random delay period used by a mobile station after not finding BRI=Idle when
ready to send the first burst of an access attempt or after a transmission
attempt
failure, is uniformly distributed between 0 and 200 ms with a granularity of
6.667
r
CA 02281959 1999-09-14
-16-
ms (the length of a time slot). A mobile station is not allowed to make more
than
Z, where Z=(0..3), consecutive repetitions of an individual burst during an
access
attempt.
When a mobile station is in the start "random access" state, it looks at BRI
information in the first occurrence of a downlink DCC slot, regardless of the
sub
channels of the current DCC. If the mobile station finds BRI=Idle, it sends
the
first burst unit of its message in the corresponding sub channel uplink RACH.
If
BRI=Busy or Reserved, the mobile station generates a random delay time. After
the random delay time has expired the mobile shall repeat the foregoing
procedure.
The search for BRI=Idle is to be repeated a maximum of X+1 times, where
X=(0...9), for each transmission attempt. With the exception of an
origination, the
MS still monitors its PCH during random access procedures.
When a mobile station is in the "start reserved access" state, it looks at BRI
and PE information in all downlink slots of the current DCC, regardless of
subchannels, for a slot where BRI=Reserved and a PE match occurs, which will
be
explained below. The base station (BS) can assign a reserved slot for a given
mobile station MS regardless of which subchannel the MS may have previously
used. If a mobile station finds this slot, it sends the first unit of its
message in the
corresponding uplink RACH subchannel. If the mobile station does not find this
slot within a predetermined time-out period (T), it enters the "start random
access"
state. After the first burst of a random access has been transmitted, the
mobile
reads the partial echo field in the next downlink slot of the current DCC that
corresponds to its RACH subchannel. If a PE match is found and R/N=1, the
mobile assumes that the first burst of its access attempt has been correctly
received
by the BS and then enters either the "after last burst" state or the "more
units" state.
If the mobile does not find a PE match, it generates a random delay time and
enters
the "start random access" state.
If the mobile station has additional bursts to send, it enters the "move
units"
state and then checks R/N after sending each of these bursts. If the mobile
station
finds that R/N=Received after sending a burst, it considers that burst as
correctly
CA 02281959 1999-09-14
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received by the BS; otherwise, it considers the burst as not received by the
BS. If
the mobile station finds that BRI=reserved or idle, it also considers the
burst as not
received by the BS. If more than S+1, where S=(0,1), consecutive Not Busy
readings of BRI are made by the mobile, it aborts the transmission of the
message
and starts another transmission attempt after a random delay. If a given burst
is
considered to be received, the mobile transmits the next burst of the message
in the
next slot of the subchannel. If a burst is found to be not received, the
mobile re-
transmits it.
The mobile reads the SCF flags of the currently used subchannel after it has
~ transmitted the last burst of its current access attempt. If R/N = Received,
the MS
considers the message to have been correctly transmitted. If R/N = Not
Received
and BRI = Reserved or Idle, the MS considers the last burst as not received.
If
more than S+1, where S=(0,1), consecutive combined RJN=Not Received and
BRI=Not Busy readings are made by the mobile station, it aborts the
transmission
of the message and starts another transmission attempt after a random delay.
If
RIN=Not Received and BRI=Busy, the mobile re-transmits the last transmitted
burst.
The foregoing random access procedures are illustrated in Figures 6a-b.
Figure 6a illustrates the random access procedure for a mobile station while
Figure
6b illustrates the random access procedure for a base station. Set forth below
is an
itemized description of the use of the truth table in the flow chart shown in
Figure
6a:
1. The truth .table is examined at start of a contention based access at
block 10. If BRI = "Reserved" or "Busy" the mobile station shall
increment the Busy/Idle counter and then compare it to X. If BRI =
"Idle" the mobile station shall set Unit ctr to 1 and send the first
burst of its access attempt.
2. The truth table is examined after sending any given intermediate
burst of an access attempt with at least one more burst pending at
block 20. If BRI = "Idle" or "Reserved" the mobile station shall
CA 02281959 1999-09-14
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increment Stop ctr and PB ctr and then compare Stop ctr to S. If
BRI = "Busy" and R/N = "Not Received" the mobile station shall
increment PB ctr and then compare it to Z. If BRI = "Busy" and
R/N = "Received" the mobile station shall increment Unit ctr and
S set PB ctr to zero.
3. The truth table is examined after sending the last burst of an access
attempt at block 30. If RlN = "Received" then the mobile station
shall consider the message as successfully sent. If BRI -
"Reserved" and R/N = "Not Received" the mobile station shall
increment Stop ctr and PB ctr and then compare Stop ctr to S. If
BRI = "Busy" and R/N = "Not Received" the mobile station shall
resend the last burst of the access attempt.
4. The truth table is examined at the start of a reservation based access
at block 40. If BRI = "Busy" or "Idle" then the mobile station
examines the reservation timer. If BRI = "Reserved" and the PE
does not match then the mobile station examines the reservation
timer. If BRI = "Reserved" and the PE does match then the mobile
station shall set Unit ctr to 1 and send the first burst of the access
attempt.
According to one embodiment of the present invention, a unique method for
determining the status of frames sent to a mobile station is disclosed and is
illustrated in Figures 7a-b. The BMI (base station, mobile telephone service
center
and internetworking function) starts an Automatic Retransmission Request (ARQ)
mode transaction by sending an ARQ Mode BEGIN frame which is illustrated in
Figure 8. The ARQ Mode BEGIN frame is used to start the delivery of a L3
ARCH or SMSCH message in the ARQ mode. If the L3 message is too long to fit
into a single ARQ Mode BEGIN frame, then the remaining L3 information is
carried using additional ARQ Mode CONTINUE frames as necessary. If the L3
message does fit within a single ARQ Mode BEGIN frame, it is padded with
filler
as necessary. The ARQ Mode Begin frame contains a Header A and a Header B
CA 02281959 1999-09-14
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which in turn contain various layer 2 overhead information. In this example,
the
Header A section has identified this frame as a point-to-point SMS channel,
however
the present invention is not limited thereto. The ARQ Mode BEGIN frame
contains
a Mobile station.identity (MSID) and a Partial Echo (PE) field which is set to
some
value, for example, the 7 least significant bits of the mobile station's IS-
54B mobile
identification number (MIN). A transaction identifier (TID) field is included
and
uniquely identifies which instance of an ARQ mode transaction is being sent to
a
mobile station. The PE field in conjunction with the transaction identifier
T1D
identifies the transaction initiated by the ARQ Mode BEGIN frame and serves to
- associate any subsequent ARQ Mode CONTINUE frames with the same transaction.
A L3 length indicator (L3LI) field is used by the mobile station to calculate
the
number of ARQ Mode CONTINUE frames which will follow the ARQ Mode
BEGIN frame. Finally, the ARQ Mode Begin frame contains a layer 3 data field
(L3DATA).
As a result of sending an ARQ Mode BEGIN frame; the BMI may wait for
an acknowledgment from the mobile station since this frame contains
information
pertaining to the potential success of an ARQ Mode transaction. If the BMI
decides
not to wait for a mobile station acknowledgment, it shall proceed to send an
ARQ
Mode CONTINUE frame which will be described below. However if the BMI
decides to wait for an acknowledgement, the BMI shall proceed as follows. For
the
case of soliciting a reservation based acknowledgement in a given downlink
slot, the
BMI polls the mobile station by setting the BRI flag (part of the SCF) to
"Reserved"
and by setting the PE field (part of the SCF) to the value corresponding to
the target
mobile station. The BMI then waits for an uplink ARQ Status frame on the same
access path on which it polled the mobile station. If an ARQ Status message is
not
received on the reserved access slot or is received but with an incorrect
indication
of outstanding frames, the BMI shall resend the ARQ Mode BEGIN frame up to a
predetermined number of times. If the BMI does not receive a correct ARQ
Status
message after a certain number of attempts, it shall terminate the ARQ Mode
transaction. If the BMI does receive a correct ARQ Status frame after a
certain
CA 02281959 1999-09-14
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number of attempts, it shall proceed to send an ARQ Mode CONTINUE frame.
The BMI sends as many ARQ Mode CONTINUE frames as necessary to
complete the initiated ARQ Mode transaction. The ARQ Mode CONTINUE frame,
which is illustrated in Figure 9, contains the Partial Echo (PE) field and a
transaction identifier (TID) which together uniquely identify which instance
of an
ARQ mode transaction is being sent to the mobile station. The ARQ Mode
CONTINUE frame also includes a Continuation Frame Number (FRNO) field which
identifies individual continuation frames, and a portion of the L3 data
(L3DATA).
An ARQ Mode BEGIN frame has an implicit frame number FRNO value of 0
~ associated with it whereas ARQ Mode CONTINUE frames have explicit FRNO
values which start at 1 and range from 1 to 31. The FRNO value is incremented
for each new ARQ Mode CONTINUE frame sent by the BMI to a MS in support
of a specific ARQ Mode transaction.
The BMI may poll the mobile station while sending any intermediate ARQ
Mode CONTINUE frame. If the BMI decides to issue an intermediate poll it shall
proceed as follows. In a given downlink slot the BMI sets the BRI flag to
"Reserved" and sets the PE field to the value corresponding to the target
mobile
station. The BMI then waits for an uplink ARQ Status message on the same
access
path on which it polled the mobile station. If an ARQ Status message is not
received on the reserved access slot, the BMI resends the current ARQ Mode
CONTINUE frame up to a predetermined number of times. If the BMI does not
receive a correct ARQ Status frame after a certain number of attempts, the BMI
terminates the ARQ Mode transaction. If the BMI does receive a correct ARQ
Status frame after a certain number of attempts, it continues to send ARQ Mode
CONTINUE frames that have not yet been correctly received by the mobile
station.
When the BMI sends the last ARQ Mode CONTINUE frame, the BMI proceeds in
a manner described below.
The BMI polls the mobile station while sending the last ARQ Mode
CONTINUE frame as follows. For the case of soliciting a reservation based
acknowledgement in a given downlink slot, the BMI sets the BRI flag to
"reserved"
CA 02281959 1999-09-14
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and sets the PE field to the value corresponding to the target mobile statioa.
The
BMI then waits for an uplink ARQ Status frame on the same access path on which
it polled the mobile station. If an ARQ Status frame is not received on the
reserved
access slot, the BMI resends the current ARQ Mode CONTINUE frame up to a
predetermined number of times. If the BMI does not receive a correct ARQ
Status
frame after a certain number of attempts, the BMI terminates the ARQ Mode
transaction. If the BMI does receive an ARQ Status frame and the FRNO MAP
indicates "all correct", the ARQ Mode transaction is considered to be
successfully
completed. If the BMI does receive an ARQ Status frame and the FRNO MAP
does not indicate "all correct", the BMI resends those ARQ Mode COrfITNLJE
frames that have not yet been correctly received by the mobile station. The
BMI
resends any given ARQ Mode CONTINUE frame up to a predetermined maximum
number of times before terminating the ARQ Mode transaction.
The operation of the SPACH ARQ mode for the mobile station will now be
described. After a mobile station has successfully completed transmission of a
message on the RACH (as indicated by the SCF flags), it reads up to a
predetermined number of SPACH frames beginning 40ms after successfully
completing the RACH message transmission. When the mobile station receives an
ARQ Mode BEGIN frame with a ~MSID matching its own, it proceeds as follows.
The mobile station stores the TID for ARQ Mode transaction identification
purposes. The number of pending ARQ Mode CONTINUE frames can then be
calculated based on the received L3LI. The FRNO MAP, which is a bit map, is
set
to RECEIVED for FRNO zero (corresponding to the ARQ Mode BEGIN) and NOT
RECEIVED for all pending ARQ Mode CONTINUE frames. According to one
embodiment of the present invention, a 1 can be used to signify that a frame
has
been received and a 0 can be used to signify that a frame has not been
received.
The FRNO MAP supports BMI transmissions up to 32 ARQ Mode frames in length
(1 BEGIN frame and 31 CONTINUE frames). The portion of the L3 message
carried in L3DATA shall be stored. The mobile station then proceeds as
described
in the next section. Of course those skilled in the art will readily
appreciate that the
CA 02281959 1999-09-14
-22-
FRNO bit map could be expanded or reduced so as to support a greater or fewer
number of frames transmitted from the BMI.
The mobile station shall read SPACH frames and respond as follows. If a
poll occurs, i.e., a PE match occurs along with the BRI flag set to
"Reserved", the
mobile station sends an ARQ Status frame to the BMI with a FRNO MAP that
indicates the reception status of all ARQ frames correctly received to that
point of
the current ARQ mode transaction. If the FRNO MAP indicates that an "all
correct" condition exists, the mobile station considers the corresponding ARQ
Mode
transaction to be successfully completed. Otherwise, if an ARQ Mode CONTINUE
~ frame is correctly received for an outstanding ARQ Mode transaction (i.e.,
PE and
TID sent in the ARQ Mode CONTINUE frame match) the mobile station stores the
L3DATA contained therein and sets the corresponding FRNO MAP position to
RECEIVED. If no ARQ Mode CONTINUE frame or poll is received for a
predetermined period, the mobile station can autonomously transmit an ARQ
Status
frame using a contention based random access. A maximum number of such
autonomous ARQ Status frame transmissions may be sent before the corresponding
ARQ Mode transaction is terminated.
While a particular embodiment of the present invention has been described
and illustrated, it should be understood that the invention is not limited
thereto since
modifications may be made by persons skilled in the art. The present
application
contemplates any and all modifications that fall within the spirit and scope
of the
underlying invention disclosed and claimed herein.
