Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02309472 2000-OS-25
FIELD OF THE INVENTION
The present invention relates generally to a method and system for
transmitting data from a base
station to subscriber stations. More specifically, the present invention
relates to a method and system
for transmitting data from a base station to subscriber stations, where the
subscriber stations have
different abilities to receive the transmission and the transmission is
packaged correspondingly.
BACKGROUND OF THE INVENTION
Wireless communications has undergone tremendous development and growth.
Current digital
wireless telephone networks based on multiple access techniques such as CDMA,
FDMA or TDMA
can offer high quality voice communications. However, these networks are not
efficient at offering
data communications when a number of users must be serviced, and a sharp
increase in demand for
data communications over wireless networks is expected.
For example, the IS-95 standard for CDMA networks can offer a maximum data
rate of 9.6
kbaud or 14.4 kbaud depending on the selected service. As known to those of
skill in the art, however,
these rates are generally too slow to meaningfully accommodate modern data
applications, such as
web-browsing and/or file transfer. Attempts have been made to increase the
maximum data rate within
IS-95. For example, U.S. Patent Number 5,930,230 to Odenwalder teaches a high
data rate CDMA
wireless communication system that offers certain improvements over IS-95.
However, Odenwalder is
directed to the CDMA environment, and primarily contemplates the transfer of
data from subscriber
stations to base stations, (typically referred to as the "uplink" or "reverse"
channel) and thus does not
address the need for increased transmission of data from base stations to
subscriber stations (typically
referred to as the "downlink" or "forward" channel).
Another difficulty exists with IS-95 type networks in that they assign a
dedicated
communication channel between the base station and a subscriber unit and
therefore the bandwidth of
the dedicated channel is unavailable to other users in the network, even when
no data is being
transmitted between the base station and the subscriber unit. Thus, for
connectionless services such as
packet networks, such a system does not typically provide effective use of
limited and/or bandwidth,
which is a necessity for servicing large numbers of users.
U.S. Patent 5,949,814, also to Odenwalder ("Odenwalder #2") teaches system
which does
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provide a high data rate supplemental channel for CDMA telecommunications
systems. In this scheme,
the transmission system includes an in-phase channel set and a quadrature-
phase channel set. The in-
phase channel set provides a set of orthogonal medium rate control and traffic
channels and the
quadrature-phase channel set provides the high-rate supplemental channel and
an extended set of
medium-rate channels that are orthogonal with respect to each other.
While Odenwalder #2 can increase the downlink data transmission rate, it is
not generally
suitable for transmitting data to multiple subscriber stations, which have
different abilities to receive
the transmission. Further, Odenwalder #2 requires certain overhead control
communication between
the base station and the mobile user in order to commence a high data rate
communication
therebetween. Such a system is not well suited to systems such as packet
communication systems
where small amounts of data may need to be transferred to users as the
necessary overhead may make
the communication inefficient relative to the amount of data transferred.
Similarly, such a system is not
well suited to situations wherein a variety of users need data transmitted to
them.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a novel method, system and
apparatus for
transmitting data from a base station to one or more subscriber stations,
which obviates or mitigates at
least one of the above-identified disadvantages of the prior art.
According to one aspect of the invention, there is provided a system for
transmitting data
comprising a base station having a microprocessor, a modem, a radio and an
antenna, the base station
operable to transmit a radio signal; a plurality of subscriber stations having
a microprocessor, a modem,
a radio and an antenna each operable to a receive the signal at a different
reception-quality than at least
one other the subscriber stations; the signal including a frame having an
identifier recoverable by all of
the subscriber stations regardless of the reception-qualities, and a remaining
portion recoverable by at
least one of the subscriber stations, the identifier indicating whether the
subscriber station need recover
the remaining portion.
According to another aspect of the invention, there is provided a frame for
transmission a
plurality of subscriber stations each having a reception-quality corresponding
to an ability to recover
the transmission, the frame comprising an identifier packaged for recovery
regardless of the reception-
qualities and including information representing whether a receiving
subscriber station is within a range
of reception-qualities; a header packaged for recovery by subscriber stations
within the range and
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including address information; and at least one payload packet packaged for
recovery by subscriber
stations in accordance with the address information.
A data channel for transmitting data from a base station to subscriber
stations is provided. Each
subscriber station has a different service-class which reflects the reception-
quality of the data
transmitted from the base station. The data channel is organized into a
plurality of frames. Each frame
contains service-class information that is packaged in the frame in such a
manner that all subscriber
stations can recover the service-class information. The frame also includes
payload data destined for at
least one of the subscriber stations. The payload data is packaged in the
frame in such a manner that
the subscriber station having payload data destined therefor can recover its
payload data, regardless of
its service class. Subscriber stations that have no payload data destined
therefor, and/or which are in a
poorer service-class than the destined subscriber-stations, can use the
service-class information to
determine that the remainder of the frame can be ignored. An apparatus, system
and method relating to
the data channel are also provided.
BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the present invention will now be described, by way
of example only,
with reference to the attached Figures, in which:
Figure 1 is a schematic representation of a network incorporating a data
channel in accordance
with an embodiment of the invention;
Figure 2 is a schematic representation of the base station shown in Figure 1;
Figure 3 is a schematic representation of one of the subscriber stations shown
in Figure 1;
Figure 4 is a schematic representation of a frame for transmission over the
network shown in
Figure 1;
Figure 5 is a flowchart of a method for assembling and transmitting the frame
of Figure 4 in
accordance with another embodiment of the invention; and
Figure 6 is a flowchart of a method for receiving and recovering the
transmitted frame of Figure
4 in accordance with another embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to Figure 1, a wireless network incorporating a system for
transmitting data is
indicated generally at 20. Network 20 includes a radio base station 24 and a
plurality of subscriber
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CA 02309472 2000-OS-25
stations 28a, 28b . .. 28n. In a presently preferred embodiment, radio base
station 24 is connected to a
data telecommunications network (not shown), such as a land line-based
switched data network, by an
appropriate gateway and one or more backhauls (not shown in Figure 1 ), such
as a T1, T3, E 1, E3, OC3
or other suitable land line link, or can be a satellite or other radio or
microwave channel link or any
other link suitable for operation as a backhaul as will occur to those of
skill in the art.
Base station 24 communicates with subscriber stations 28 which, in a present
embodiment, are
fixed and installed at subscriber premises, as is common in a wireless local
loop (WLL) system. The
number 'n' subscriber stations can vary depending upon the amount of radio
bandwidth available
and/or the configuration and requirements of the subscriber stations 28.
A data channel 32 is established between base station 24 and each subscriber
station 28. Data
channel 32 carries information to be transferred from base station 24 to
respective subscriber stations
28a, 28b ... 28n as needed. Data channel 32 can be implemented with networks
using a variety of
multiple access techniques, including TDMA, FDMA, CDMA or hybrid systems such
as GSM, etc. In
a present embodiment, data transmitted over data channel 32 is transmitted as
packets encapsulated
within frames, the details of which will be discussed in greater detail below.
The ability of a base station 24 to properly receive a signal transmitted to
it, hereinafter referred
to as the "reception-quality" of the signal, is determined in different
manners according to the multiple
access technique employed to transmit the signal. For example, in TDMA or FDMA
systems, the
received signal strength is the determination most often used. In CDMA
systems, the ratio of received
bit power to received interference power (often expressed as ES/No, where ES
is energy per symbol, and
No is the received interference energy) is the relevant determination. In any
event, the reception-
quality of channel 32 at each subscriber station 28 can vary depending on a
variety of factors, including
multipath interference (from the presence of nearby buildings, etc.), radio
noise sources (including
transmissions by other users or radio noise sources), geographical features,
the distance of the
subscriber station 28 from base station 24, the quality of the receiver in the
subscriber station 28, etc.
as is well understood by those of skill in the art. With distance, typically a
signal attenuates as 1/rr',
where r is the distance between the subscriber station 28 and base station 24,
and N> 1. In IS-95
CDMA systems, for example, N typically is 3<N<5.
In Figure 1, groups of reception-qualities experienced at subscriber stations
are organized and
represented as rings 36, where each ring 36a, 36b ... 36n corresponds to a
reception-quality at a
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subscriber station 28a, 28b ... 28n. In the Figure, rings 36a, 36b ... 36n are
shown concentrically
expanding about base station 24 to indicate increasing distance therefrom, but
rings 36 are actually
defined with respect to the reception-quality at subscriber stations 28 and
thus subscriber station 28b
might be physically located closer to base station 24 than subscriber station
28a but is in ring 36b
(which has a lower reception-quality than ring 36a) due to the above-mentioned
other factors affecting
reception-quality, such as nearby noise sources, etc. Thus, as will be
apparent to those of skill in the
art, Figure 1 is a logical representation of reception-quality rings 36.
Furthermore, Figure 1 illustrates that there is one subscriber station 28a,
28b .. . 28n in each ring
36, however it will be understood that in most actual implementations of the
present invention, each
ring 36 will include multiple subscriber stations 28, each having a reception-
quality within a range of
reception-qualities defined for the respective ring 36. For example, ring 36a
may contain subscriber
stations 28 with a reception-quality greater than 20 db, while ring 36b may
contain subscriber stations
28 with a reception-quality between l Odb and 20db and ring 36n may contain
subscriber stations 28
with a reception-quality between -20db and Odb. Accordingly, rings 36
intermediate ring 36b and ring
36n would have reception-qualities between Odb and 10 db. In any event, as
illustrated in Figure 1,
subscriber station 28n will receive channel 32 at a lower reception-quality
than subscriber station 28b,
which in turn will receive will receive channel 32 at a lower reception-
quality than subscriber station
28a, but at a better reception-quality than subscriber station 28n. As will be
described below in more
detail, data to be transmitted to a base station 28 is packaged for
transmission according to the ring 36
the station is presently in.
It is contemplated that, in most actual implementations each subscriber
station 28 may transition
between different rings 36 at different times, depending on such factors as
weather and/or local noise
created by other electrical devices located proximal to the subscriber station
28. Accordingly, at
appropriate intervals or predetermined events, each subscriber station 28 will
report its present
reception-quality to base station 24. Base station 24 operates to maintain a
database of the latest
reported reception-qualities and groups subscriber stations 28 into rings 36
according to a range of
reception-qualities defined for each ring 36.
As used herein, the terms "package", "packaged" and "packaging" refer to the
overall
arrangement of the transmission of the packaged data for its reception at an
intended destination.
Packaging of data can include, without limitation, applying different levels
of forward error correcting
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(FEC) codes (from no coding to high levels of coding and/or different coding
methods), employing
different transmissions rates, employing different modulation schemes (QPSK,
QAM 4, QAM 16,
QAM64, etc.) and any other techniques or methods for arranging data
transmission with a selection of
the amount of radio (or other physical layer) resources required, the data
rate and probability of
transmission errors which are appropriate for the transmission. For example, a
packet of data can be
packaged with 1/4 coding and QAM64 modulation for transmission to a first
intended receiver and
another packet can be packaged with 1/2 coding and QAM256 modulation for
transmission to a second
intended receiver which has a better reception-quality than the first.
Figure 2 shows base station 24 in greater detail. Base station 24 comprises an
antenna 40, or
antennas, for receiving and transmitting radio-communications over
communication channel 32. In
turn, antenna 40 is connected to a radio 44 and a modem 48. Modem 48 is
connected to a
microprocessor-router assembly 52. A suitable microprocessor would be a SPARC
processor system
manufactured by SLJN Microsystems. It will be understood that assembly 52 can
include multiple
microprocessors, as desired. The muter within microprocessor-muter assembly 52
is connected to a
backhaul 56 in any suitable manner, which in turn connects base station 24 to
a packet switched data
network (not shown).
Referring now to Figure 3, subscriber station 28 is shown in greater detail.
Subscriber station
28 comprises an antenna 60, or antennas, for receiving and transmitting radio-
communications over
communication channel 32. In turn, antenna 60 is connected to a radio 64 and a
modem 68, which in
turn is connected to a microprocessor-assembly 72.
Microprocessor-assembly 72 can include, for example, a StrongARM processor
manufactured
by Intel, that performs a variety of functions, including implementing A/D-D/A
conversion, filters,
encoders, decoders, data compressors, de-compressors and/or packet
disassembly. As seen in Figure 3,
microprocessor-assembly 72 interconnects modem 68 and a data port 76, for
connecting subscriber
station 28 to an intelligent device, such as a personal computer, personal
digital assistant or the like
which is operable to process data received over communication channel 32.
Accordingly,
microprocessor-assembly 72 is operable to process data between data port 76
and modem 68.
Referring now to Figure 4, a frame for transmission over channel 32 is
indicated generally at
100. In a presently preferred embodiment, frame 100 is selected to require 10
milliseconds of
transmission time, although longer or shorter transmission times for frame 100
can be selected if
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desired. As understood by those of skill in the art, frame 100 can be measured
in terms of a duration of
time. In turn, that duration can carry a given number of symbols for
transmission. In turn, those
symbols can represent data, the actual amount of data being represented by a
symbol depending on how
the data is packaged into a symbol, typically packaged using a combination of
modulation and
S encoding. Thus, it will be appreciated that, while the duration of frame and
the symbol rate of the
frame may remain constant, the effective data rate transmitted within a frame
will depend on the
packaging of the data. The application of these concepts to the present
invention will be discussed in
greater detail below.
Frame 100 includes a ring (or reception-quality) packet 104, a header packet
108 and a plurality
of payload packets 1121, 1122 . . . 112X. As mentioned above, depending upon
the packaging of payload
packets 112, the quantity 'x' of payload packets 112 in frame 100 can vary,
and the factors affecting
this variation will be discussed in greater detail further below.
Ring packet 104 is composed of a destination-ring identifier field 116 and a
frame-length field
120. It is presently preferred that destination-ring field I 16 is two bits in
length and frame-length field
120 is ten bits in length. Destination-ring field 116 identifies the outermost
ring 36 with the lowest
reception-quality from base station 24 for which a frame 100 contains at least
one payload packet 112
destined for a subscriber station 28 resident in that outermost ring. For
example, a frame 100 with a
destination-ring identifier field 116 corresponding to ring 36b can include
payload packets for
subscriber stations 28a or 28b, but not for 28n. Frame length field 120
contains the value 'x', to
indicate the number of payload packets 1121, 1122 .. . 112X in frame 100.
Unlike payload packets 112, destination ring field 116 and frame-length field
120 are always
packaged into ring packet 104 in a robust manner to ensure recovery by all
subscriber stations 28a, 28b
... 28n when frame 100 is transmitted over channel 32. Such robust packaging
allows every subscriber
station 28 served by base station 24 to recover fields 116 and 120. In the
present embodiment, the
robustness of ring packet 104 is achieved in the following manner: Fields 116
and 120 undergo a
forward error correction (FEC) operation 124 and then undergo a modulation
operation 128 prior to
their insertion into ring packet 104. The type of forward error correction
operation 124 and
modulation operation 128 are selected based on the needs of subscriber station
28n (i.e. -the subscriber
station 28 with the poorest reception-quality) located on ring 36n.
For example, if channel 32 employs CDMA multiple access technology, it is
presently preferred
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that where subscriber station 28n has an ES/Io level of 3db, then a suitable
forward error correction
operation 124 will be rate '/z coding and modulation operation 128 will be 4-
QAM (QPSK). An
appropriate combination of forward error correction operation 124 and
modulation operation 128 will
not only assist and/or assure the recovery of ring packet 104 by subscriber
station 28n, but that that the
remaining subscriber stations can also recover ring packet 104. Suitable
forward error correction
operations 124 and modulation operations 128 for a given subscriber station
28n having a given
reception-quality will occur to those of skill in the art.
Table I in Appendix I shows exemplary packaging for frame 100 in a CDMA system
according
to various SNRs. Column 1, labeled Ec/No, is an SNR measurement that indicates
the Energy per chip
per a given noise level as experienced by a given subscriber station 28.
Column 2, labeled spreading
factor, indicates the number of chips per symbol. Column 3, labeled Modulation
Symbols, indicates
the modulation operation used in the packaging of the data. Column 4, labeled
coded bits/symbol,
indicates the number of bits per symbol after undergoing the modulation
operation of column 3.
Column S, labeled code rate, indicates the coding operation used in the
packaging of the data. Column
6, labeled symbol repetition factor, indicates the factor by which symbols are
repeated, to further
package the data for robust recovery. Column 7, labeled bits/symbol, indicates
the effective bits per
symbol. Column 8, labeled bits/frame, indicates the effective bits per frame
assuming all bits in the
frame are packaged according to the modulation rate, coding rate and using the
symbol repetition factor
shown in the same row. Column 9, labeled Es/No, is an SNR measurement that
indicates the Energy
per symbol per a given noise level as experienced by a given subscriber
station 28. Column 10, labeled
Eb/No, is an SNR measurement that indicates the Energy per bit per a given
noise level. It will be
understood by those of skill in the art that columns 1, 9 and 10 bear a fixed
relationship to each other.
Accordingly, presently preferred encoding operations 124 (see columns 5 and 6)
and
modulation operations 128 (see column 3) are shown in Table I. However, other
suitable means of
packaging destination ring field 116 and frame-length field 120 into ring
packet 104 in a robust
manner, and/or combinations thereof, will now be apparent to those of skill in
the art.
Header packet 108 contains a plurality of identifier-fields 132 which contain
identifying
information about each payload packet 112. In a present embodiment, identifier
fields 132 include an
address field 136, a format field 140 and a length field 144. Address field I
36 indicates which of the
destination subscriber station 28a, 28b ... 28n is intended to receive the
respective payload packet 112.
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Format field 140 indicates the modulation and encoding used to prepare the
respective payload packet
112X, the details of which will be discussed in greater detail below. Length
field 144 indicates the
length of the respective payload packet 112. Header packet 108 also contains a
CRC packet 148, which
can be used by each subscriber station 28a, 28b ... 28n to determine whether
it has correctly received
header packet 108. Flush-bits 152 are added to ensure recognition of the end
of header packet 108
when it is decoded, as understood by those of skill in the art.
It is presently preferred that each address-data field 136 is twelve bits in
length, that each
format-data field 140 is four bits in length, that each length-data field144
is twelve bits in length, that
CRC field 148 is eight bits in length, and that flush-bits 152 are eight bits
in length. However, other
lengths can be employed to suit particular requirements, as will occur to
those of skill in the art.
Identifier-packets 132, CRC packet 148 and flush-bits 152 are packaged into
header packet 108
in a suitably robust manner to ensure recovery by all subscriber stations 28
that are located between
base station 24 and the ring indicated in destination-ring field 116
(inclusive). In other words, if
destination-ring field 116 indicates ring 36b, then the contents of header
packet 108 are packaged for
robust recovery by all subscriber stations 28 in rings 36a and 36b, but
station 28n in ring 36n may not
be able to receive header packet 108.
In the present embodiment, the robust packaging of header packet 108 is
achieved in the
following manner: Packets 132, CRC packet 148 and flush-bits 152 undergo an
encoding operation
158 and then undergo a modulation operation 162 to form header packet 108. The
forward encoding
operation 158 and modulation operation 162 are chosen based on the reception-
quality needed to
recover header packet 108 by the subscriber stations located on the ring
identified by destination-ring
field 116. It is presently preferred that encoding operation 158 is rate 1/3
convolutional encoding, and
that modulation operation 162 is M-ary QAM, where M can be 4, 16, 64 or 256.
An appropriately chosen combination of encoding operation 158 and modulation
operation 162
will not only assist and/or assure the recovery of header packet 108 by a
subscriber station 28 located at
the ring indicated by destination-ring packet 116, but that that subscriber
stations 28 located
therebetween and base station 24 can also recover header packet 108.
Accordingly, presently preferred
encoding operations 124 (see columns 5 and 6) and modulation operations 128
(see column 3) are
shown in Table I. However, other suitable encoding operations 158, modulation
operations 162,
and/or other means of packaging packets 132, CRC packet 148 and flush-bits 152
into header packet
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CA 02309472 2000-OS-25
108 in a robust manner, and/or combinations thereof, will occur to those of
skill in the art.
Each payload packet 112 is composed of one or more data packets 166 and flush
bits 170. Each
payload packet 112 is destined for one or more subscriber stations 28 that lie
between base station 24
and the ring specified in destination-ring packet 116 (inclusive). Data
packets 166 can be any type of
data received at base station 24. For example, data packets 166 can be TCP/IP
packets, where it is
desired to transmit IP packets to a subscriber station 28. Data packets 166
can be specifically
addressed to a particular subscriber stations 28a, 28b .. . 28n each of which
has its own unique address
and/or one or more broadcast addresses can be defined.
Data packets 166 can be of any length (as indicated by length field 144) and
data to be placed
into data packets 166 can be combined or segmented, as needed, to an
appropriate size. Generally, a
data packet 166 can include a portion of one, or one or more packets intended
for a single subscriber
station 28. Flush bits 170, which in a present embodiment are eight bits in
length, are added to the end
of data packets 160 for substantially the same reasons as flush bits 152.
Each data packet 166, and its corresponding set of flush bits 170, is packaged
into a respective
payload packet 112, 1122 ... 112X. This packaging is performed in a robust
manner, according to the
formatting specified in the format field format field 140 respective to its
payload packet 112. This
packaging assists and/or ensures recovery by the destination subscriber
station 28. (Incidentally, other
subscriber stations 28 that are located between base station 24 and the ring
where the destination
subscriber station 28 resides can also recover the payload packet 112, but in
general, such recovery will
not be performed, and appropriate security measures can be employed to prevent
eavesdropping.) For
example, if a frame 100 includes a destination ring field 166 defining a
transmission to ring 36n and
includes a payload packet 112 destined for subscriber station 28b, then the
payload packet 112 will be
packaged such that it is recoverable by subscriber stations 28a and 28b. The
specific forward encoding
operation 174 and modulation operation 178 are selected based on the reception-
quality at subscriber
station 28b located on the ring 36b identified by the address-data field 136
respective to the payload
packet 112. It is presently preferred that encoding operation 174 is rate-N
convolutional encoding
(where N is a real number that is larger than 0) and that modulation operation
178 is "M-ary QAM",
(where M can be 4, 16, 64 or 256), and where N and M are selected
appropriately for the reception-
quality in the ring 36 indicated by format field 140.
It is contemplated that, overall, the encoding operation 174 and/or the
modulation operation 178
CA 02309472 2000-OS-25
and/or other robust packaging can be common or individually selected for each
payload packet 112 in a
single frame 100. For example, where there are a wide range of reception-
qualities for subscriber
stations 28 within a particular ring 36, then a common modulation operation
178 can be used for each
subscriber station 28 within that particular ring 36, but a different encoding
operation 174 can be used
to accommodate the range of reception-qualities within the ring 36.
The selection of encoding operations 174 and/or modulation operations 178
and/or other robust
packaging for each payload packet 112 within frame 100 can depend on the
actual application and/or
type of data being carried over channel 32. (As the application and/or type of
data may have different
requirements to achieve the required probability of packet error.) For
example, a file transfer
transmission (ftp) has a low tolerance to errors compared to a voice over IP
(VOIP) connection. Thus
payload packets 112 transmitted to a first subscriber station 28 in ring 36b
can be encoded with '/4
convolutional coding while payload packets sent to another subscriber station
28 in ring 36b, but for a
VOIP connection, can be coded with %2 convolutional coding.
As will be apparent to those of skill in the art, when an encoding operation
174 and modulation
operation 178 are common for a destination ring 116, for example ring 36b,
payload packets 112
intended for subscriber stations 32 in higher rings, i.e. ring 36a, can also
be included in frame 100 if
desired, although such payload packets 112 intended for higher rings 36 will
be packaged with a
superfluous level of robustness for their intended destination.
Presently preferred encoding operations 124 (see columns 5 and 6) and
modulation operations
128 (see column 3) are shown in Table I. However, other suitable encoding
operations 174,
modulation operations 178, and/or means of robustly packaging data packets 166
and flush bits 170
into each payload packet 112, and/or combinations thereof, will occur to those
of skill in the art.
Referring now to Figure 5, a method for transmitting data that is in
accordance with an
embodiment of the present invention is shown. For purposes of assisting in the
explanation of the
method, reference will be made to network 20 and frame 100. At step 200, data
packets 166 are
received by base station 24 for transmission to one or more subscriber
stations 28 and buffered until a
sufficient amount of data is received to fill a frame 100. In this example,
data packets 166 are received
at base station 24, either via backhaul 56 or from other subscriber stations
28 that have transmitted the
packets to base station 24, and microprocessor-router assembly 52 buffers data
packets 166 for
subsequent assembly into frame 100. As will now be apparent to those of skill
in the art, the amount of
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data which is sufficient to fill a frame 100 is dependent upon the selected
encoding operations 158 and
174 and the selected modulation operations 162 and 178. Thus, the
determination of the receipt of a
sufficient amount of data is made assuming the best (i.e. most data rate
efficient) encoding and
modulation operations or when a preselected time period has expired from the
receipt of the earliest
data packet 166, this latter parameter being employed to ensure that a frame
100 is assembled and
transmitted before a preselected maximum latency period is exceeded. Any
received data which cannot
be placed into the assembled frame 100, due to the encoding and/or modulation
operations being less
data rate efficient, is buffered and assembled in due course into the next
frame 100 to be assembled.
When a sufficient amount of data is received to fill frame 100, a
determination is made at step
204 of the ring 36 with the lowest reception-quality which contains a
subscriber station 28 to which at
least one received data packets is addressed. Step 204 is performed by
microprocessor-muter assembly
52 which examines the destination address of each of the received data packets
166 to determine the
ring 36 with the lowest reception-quality from base station 24 that has a
subscriber station 28 which is
the destination for at least one of the data packets 166.
At step 208 payload packets 112 are assembled and inserted into frame 100. An
appropriate
encoding operation 174 and modulation operation 178 is applied to the received
data packets 166,
appropriate flush-bits 170 are added and the result is inserted into one or
more of payload packets 112.
Data packets 166 that are intended for the same subscriber station 28 can be
grouped for insertion into
one or more common payload packets 112.
The modulation operation 178 can be selected for all processed packets 166,
according to the
ring 36 determined in step 204 (i.e. - if ring 36a is the determined ring,
256QAM is used on all
packets, or if ring 36b is the determined ring, 64QAM is used on all packets),
or, as previously
discussed, it is also contemplated that the modulation operation employed to
process packets can be
changed, from packet-to-packet, if desired. In a similar fashion, the encoding
operation 174 can be
selected for all processed packets 166, according to ring 36 determined in
step 204 (i.e. - if ring 36a is
the determined ring, rate %2 coding is used on all packets, or if ring 36b is
the determined ring, rate'/4
coding is used on all packets), or, also as previously discussed, the encoding
operation employed to
process packets can be changed from packet-to-packet if desired. It is
presently contemplated that a
single modulation operation 178 will be selected for all packets 166 in a
frame 100, but that encoding
operation 174 will be changed according to differences in the reception-
qualities of subscriber stations
12
CA 02309472 2000-OS-25
28 within rings 36 and/or according to desired packet error probability rates.
Once payload packets 112 are assembled, header packet 108 is assembled and
inserted into
frame 100 at step 212. Header packet 108 is assembled as previously discussed,
whereby the
destination subscriber station 28 for each respective payload packet 112 is
inserted into each address
S field 136; the format (i.e. the modulation and/or encoding) of each
respective payload packet 112 is
inserted into format fields 140; and the length of each respective payload
packet 112 is inserted into
each length field 144. Finally, a CRC code is generated, according to these
identifier-packets 132, and
inserted into CRC field 148. Flush bits 152 are then added, and at this point,
fields 132 and 148 and
flush bits 152 are encoded according to encoding operation 158 and modulated
according to modulation
operation 162. Encoding operation 158 and modulation operation 162 are
selected such that header
packet 108 is robustly packaged for the reception-qualities of all subscriber
stations 28 in the ring 36
determined in step 204.
Next, at step 216, ring packet 104 is assembled. The outermost destination
ring 36 determined
at step 204 is inserted into destination ring field 116, and the frame length,
in terms of the number of
payload packets 'x', is inserted into frame length field 120. Fields 116 and
120 are then forward error
corrected using operation 124, modulated using modulation operation 128, and
then inserted into ring
packet 104. Operations 124 and 128 are selected such that ring packet I 04 is
robustly packaged for a
high level of probability of reception by all subscriber stations 28 served by
base station 24.
Next, at step 220, the now-assembled frame 100 is transmitted over channel 32
to subscriber
stations 28a, 28b ... 28n. The transmission can occur in the usual manner,
using known techniques.
It is to be understood by those of skill in the art that modifications can be
made to the above-
described method without departing from the present invention. For example, if
modulation operation
178 and encoding operation 174 are preselected for given destination rings 36
determined at step 204,
then determining the amount of received data which is sufficient to fill a
frame 100 is a simple matter
and can be determined as each data packet 166 is received. In such a case step
204 is performed when
each packet 166 is received and the lowest reception-quality ring 36 is
determined for all packets
received to that time. The received data packets 166 are scaled according to
the defined modulation
and encoding operations and the resulting scaled data size is compared to the
selected maximum size of
frame 100. If the defined maximum frame size, or if the predefined maximum
latency period, is not
exceeded the next received packet 166 is examined, the lowest reception-
quality ring 36 updated, if
13
CA 02309472 2000-OS-25
necessary, the scaling operation re-performed and the size (and/or latency
time) examined again.
Referring now to Figure 6, a method for recovery of the transmitted frame 100
by a subscriber
station 28 is shown, in accordance with an embodiment of the present
invention. At step 300, frame
100 is received by a subscriber station 28. Radio 64 receives frame 100, where
it is transferred to
modem 68.
At step 304, destination ring packet 104 is recovered. In a present
embodiment, this is
accomplished by modem 68 which uses a demodulation operation complementary to
modulation
operation 128, and by microprocessor-assembly 72 which uses a decoding
operation complementary to
forward error correction operation 124. In a present embodiment, the
demodulation operation and
decoding operation are predefined for all subscriber station stations 28 and
are intended to allow the
recovery of ring packet 104 even under the lowest reception-quality within
network 20. When ring
packet 104 is recovered, destination ring field 116 and frame length field 120
are now available to
microprocessor-assembly 72 to assist in the further processing of frame 100,
as described below.
At step 308, a determination is made as to whether the subscriber station 28
is within or on the
destination ring 36 indicated in destination ring field 116 (i.e. - the
subscriber station 28 has a
reception-quality at least equal to that of the ring indicated in destination
ring packet 116). If, at step
308, it is determined that the receiving subscriber station 28 has a lower
reception-quality than that
indicated in destination ring field 116, the method discards the frame at step
312 and returns to step 300
to receive and process the next frame 100.
If, however, at step 308, it is determined that the receiving subscriber
station 28 has a reception-
quality at least equal to that corresponding to the ring 36 indicated in
destination ring field 116, then
one or more of payload packets 112 within frame 100 can be addressed to the
subscriber station 28 and
the method advances to step 316.
At step 316, destination header packet 108 is recovered. In a present
embodiment, this is
accomplished by modem 68 which uses a demodulation operation complementary to
modulation
operation 162, and by microprocessor-assembly 72 which uses a decoding
operation complementary to
encoding operation 158. In a present embodiment, the appropriate demodulation
operation and/or
decoding operation can be determined based on the information contained in
destination ring 116
recovered at step 304 or can be preselected and fixed within network 20. These
operations are intended
to allow the recovery of header packet 108 with a high probability of success
at even the subscriber
14
CA 02309472 2000-OS-25
station 28 with the lowest reception-quality in the ring 36 indicated by
destination ring field 116.
The method then advances to step 320, where it is determined whether the
recovered CRC
packet 148 from header packet 108 is valid for the recovered header packet
108. If CRC packet 148 is
not valid for recovered header packet 108, (i.e. a reception error has
occurred), then the receiving the
subscriber station 28 determines that it has not correctly recovered header
packet 108 and the method
advances to step 324 for exception handling. Any exception handling protocol
can be used, as will
occur to those of skill in the art, including sending a NACK or taking no
explicit exception handling
action.
If, at step 320, the recovered CRC is valid, then the receiving subscriber
station 28 determines
that it has correctly recovered header packet 108, and the method advances to
step 328. At step 328,
payload packets 112 addressed to the receiving subscriber station 28 are
recovered. Microprocessor-
assembly 72 refers to respective identifier-packets 1321... 132X in order to
determine which payload
packets 1121, 1122 . .. 112X are addressed to the receiving subscriber station
28. Those payload packets
112 which are addressed to the receiving subscriber station 28 are recovered
from frame 100, using a
demodulation operation complementary to modulation operation 178, and a
decoding operation
complementary to encoding operation 174 which is indicated in format fields
140 in packets 132 or
which can have been predefined in network 20.
The method then returns to step 300 to process the next received frame 100.
It is contemplated that the present invention can be particularly suitable for
carrying
conferencing data, either voice or video, as one or more payload packets 112
within a frame 100 can be
addressed (by, for example, including addressing information that indicates
all subscriber stations 28
within the call that should recover the payload packet 112) for recovery by a
plurality of subscriber
stations 28 participating in the conference. Such payload packets 112 can
contain conferencing data. It
will be now apparent that the packaging of the data can be robustly-packaged
for guaranteed recovery
by subscriber stations at some intermediate level of reception-quality,
allowing for some acceptable
level of loss of payload data 112 by subscriber stations having a lower level
of reception-quality, but
guaranteed recovery by subscriber stations at a higher level of reception-
quality. Alternatively, a
channel 32 can be set up simply for one conference of a set of subscriber
stations 28 participating in the
conference call.
While the embodiments discussed herein are directed to certain exemplary
implementations of
CA 02309472 2000-OS-25
the invention, it will be understood that combinations, sub-sets and
variations of the embodiments are
within the scope of the invention. For example, data packets 166 received via
backhaul 56 or from
other subscriber stations 28 can be buffered in base station 24 to organize
frames in any desired
fashion, such as grouping frames according to rings 36a, 36b ... 36n.
Buffering of data packets 166 in base station 24 can also allow the selection
of frame size (i.e.
the amount of symbols within a frame of a given predetermined time-length), as
the amount of
modulation and/or encoding and/or forward error correction actually needed to
assemble each packet in
the frame can be chosen as desired.
It is also contemplated that additional channels can be provided in network
20, as desired. For
example, one channel can be dedicated to one group of rings 36a. . . 36c,
while a second channel can be
dedicated to rings 36d . .. 36n. In addition, or in the alternative, an
additional channel can be encrypted
in order to improve the security of transmissions on network 20.
Additional channels can be added to accommodate subscriber stations having
newer and/or
faster radios than other subscriber stations on network 20. In this
embodiment, the newer/faster
subscriber stations 28 can be backward compatible, to include the capability
of receiving the older
channel and the capability of receiving the additional channel.
It is also contemplated that additional channels can be provided simply to
improve latency on
network 20, thereby increasing the overall throughput of data from the base
station to the subscriber
stations. Further, buffering of packets in base station 24 can be performed to
manage latency according
to the type of data, and it's associated quality of service (QoS)
requirements. For example, data
associated with web browser activities can be buffered and transmitted when
possible, with relatively
unlimited latencies, while data associated with a VOIP connection can be
transmitted on a priority basis
to reduce the latency to the required low levels for such connections.
Additional base stations 24 can also be added to network 20, whereby known
soft-handoff or
similar techniques are incorporated into network 20, in order to further
improve throughput and overall
capabilities of network 20.
It is contemplated that the network can be divided into a plurality of service-
classes (or rings)
and one or more subservice-classes (or sub-rings) within each service-class.
In this situation, a given
level of modulation can be used for each service-class, and a given level of
error correction can be used
for each subservice-class.
16
CA 02309472 2000-OS-25
While the embodiments discussed herein use combinations of encoding and
modulation to
robustly package frames and/or portions thereof according to different desired
reception-quality at
different subscriber stations, it is contemplated that any means of robust
packaging can be used, as
desired.
S It is contemplated that various methods can be used to determine the format
of robust packaging
(i.e. modulation and/or encoding) used to package packets within frame 100.
For example, each
subscriber station 28 can report its reception-quality (either as an exact
measurement or by indicating
the ring 36 in which the subscriber 28 is currently resident) to base station
24. In turn, payload packets
112 can be packaged (i.e. encoded and/or modulated) according to a
predetermined format, known to
both base station 24 and subscriber stations 28, according to the reported
reception-quality. In this
manner, base station 28 need not provide format field 140 to each subscriber
station 28, as the
subscriber station 28 can simply decode the relevant payload packet 112
according to the predetermined
format. In the foregoing scenario, it will thus be apparent that format fields
140 can be eliminated.
Alternatively, format fields 140 can be included within frame 100 which
further incorporate a
control-bit to indicate that the payload packet 112 addressed to a given
subscriber station 28 is
packaged according to a predetermined format based on a subscriber station's
28 reception-quality, or
the control-bit can indicate that the payload packet 112 is packaged according
to some other format,
which is indicated in the following bits within the format field 140.
It is also contemplated that format fields 140 can be eliminated, as the
format of robust
packaging can be determined by receiving subscriber stations 28 using "blind
detection", i.e. a
receiving subscriber station 28 can simply attempt to decode a payload packet
112 at various levels of
demodulation and decoding until the data packets 116 are meaningfully
recovered. Other combinations
and variations for choosing and detecting the type of robust packaging will
now be apparent to those of
skill in the art.
While the embodiments discussed herein are directed to multiple-access schemes
conducted
over wireless, it will be understood that the present invention can be applied
to a variety of multiple-
access schemes, such as over twisted-pair or coaxial links, and that various
methods can be used such
as TDMA, FDMA or CDMA.
The present invention provides a novel data channel in a network having at
least one base
station and a plurality of subscriber stations. The data channel can be
composed of a plurality of frames
17
CA 02309472 2000-OS-25
having at least one packet that is readable by all subscriber stations which
indicates whether the
receiving subscriber station is an intended addressee for all or part of the
frame. The frame and/or
portions thereof are robustly packaged in any appropriate manner, to ensure
and/or assist the intended
addressee subscriber stations) is capable of recovering the any data addressed
thereto, and that the
S unintended addressees subscriber stations are capable of determining that
they need not recover all or
part of the data contained in the frame. By only robustly-packaging the frame,
and/or portions thereof,
according to different reception-quality requirements of different subscriber
stations, less complex
robust packaging can be used for stations that have lower reception-quality
requirements, thereby
packaging more data into each frame, yet ensuring that the network is capable
of reaching subscriber
stations having greater reception-quality requirements by packaging the frame
in a more robust manner.
The above-described embodiments of the invention are intended to be examples
of the present
invention and alterations and modifications may be effected thereto, by those
of skill in the art, without
departing from the scope of the invention which is defined solely by the
claims appended hereto.
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CA 02309472 2000-OS-25
Appendix I
Table I
Spreading Symbol EslNo
EclNo Factor ModulationCoded Code RepetitionBitlsymbolBitslframefor EbINo
dB chi s mbolsbitsls rate Factor 10"-3 dB
sls mbol FER
mbol dB
-9.06 2 4 2 0.328 3 0.22 4198.4-6.05 0.55
-8.81 2 4 2 0.357 3 0.24 4569.6-5.8 0.43
-8.31 2 4 2 0.392 3 0.26 5017.6-5.3 0.53
-7.56 2 4 2 0.435 3 0.29 5568 -4.55 0.83
-7.26 2 4 2 0.328 2 0.33 6297.6-4.25 0.59
-7.01 2 4 2 0.357 2 0.36 6854.4-4 0.47
-6.51 2 4 2 0.392 2 0.39 7526.4-3.5 0.57
-5.76 2 4 2 0.435 2 0.44 8352 -2.75 0.87
-5.01 2 4 2 0.486 2 0.49 9369.6-2 1.12
-4.51 2 4 2 0.556 2 0.56 10675.2-1.5 1.05
-4.26 2 4 2 0.328 1 0.66 12595.2-1.25 0.58
-4.01 2 4 2 0.357 1 0.71 13708.8-1 0.46
-3.51 2 4 2 0.392 1 0.78 15052.8-0.5 0.56
-2.76 2 4 2 0.435 1 0.87 16704 0.25 0.85
-2.01 2 4 2 0.488 1 0.98 18739.21 1,11
-1.51 2 4 2 0.556 1 1.11 21350.41.5 1.04
-0.51 2 4 2 0.646 1 1.29 24806.42.5 1.39
1.49 2 4 2 0.770 1 1.54 29568 4.5 2.62
4.49 2 16 4 0.435 1 1.74 33408 7.5 5.09
4.99 2 16 4 0.488 1 1.95 37476.48 5.10
5.74 2 16 4 0.556 1 2.22 42700.88.75 5.28
6.99 2 16 4 0.646 1 2.58 49612.810 5.88
8.74 2 16 4 0.770 1 3.08 59136 11.75 6.86
12.99 2 64 6 0.646 1 3.88 74419.216 10.12
15.24 2 64 6 0.770 1 4.62 88704 18.25 11.60
16.99 2 256 8 0.556 1 4.45 85401.620 13.52
17.99 2 256 8 0.646 1 5.17 99225.621 13.87
20.49 2 256 8 0.770 1 6.16 11827223.5 15.60
I9
