Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR TRANSMITTING DATA RATE
CONTROL INFORMATION IN MOBILE TELECOMMUNICATION SYSTEM
FOR PACKET DATA TRANSMISSION
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a mobile telecommunication system
for transmission of packet data, and in particular, to a method and apparatus
for
transmitting data rate control (DRC) information.
2. Description of the Related Art
Research has actively been made on high data rate transmission (or packet
data transmission) in the CDMA (Code Division Multiple Access) mobile
communication system. A major mobile communication system having a channel
structure suitable for high rate transmission is a so-called HDR (High Date
Rate)
system standardized by the 3GPP2 (3rd Generation Partnership project 2)
organization
to reinforce data communication in the IS-2000 system.
The HDR system employs a linlc adaptation scheme in which a data rate is
controlled by adapting a code rate and modulation to channel conditions. A
pilot
channel, a MAC (Media Access Control) channel, a traffic channel, and a
control
channel on the forward link are subject to time division multiplexing (TDM)
prior to
transmission in the HDR system. The forward traffic channel utilizing link
adaptation
can be transmitted at 13 data rates by combining three modulations, QPSK
(Quadrature
Phase Shift Keying), 8PSK (8-ary Phase Shift Keying), and 16QAM (16-ary
Quadrature Amplitude Modulation), three code rates, 1/4, 3/8 and 1/2, and the
number
of slots in which a paclcet is transmitted.
An access terminal (AT) measures the carrier to interference ratio (C/I) of
forward pilot channels received from eight effective sectors (active set
sectors),
estimates channels conditions, and then requests a data rate for a forward
traffic
channel and a sector from which it will receive data to an access network (AID
on a
DRC channel. The DRC information is composed of data rate information in a 4-
bit
DRC symbol and cell selection information in a 3-bit index ,by which an 8-bit
orthogonal (Walsh) code is determined.
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FIG. 1 illustrates the relationship between reverse channels in a typical HDR
system. The puncturing patterns of a pilot channel, a DRC channel, and an RRI
(Reverse Rate Indicator) channel on the reverse linlc are shown here.
In FIG. 1, the RRI channel indicates the data rate of a reverse traffic
channel
and the DRC channel transmits DRC information to an AN as stated before. Each
bit
of the DRC information transmitted on the DRC channel is repeated once and
spread
with an 8-bit Walsh code indicating a sector. The result is then spread with a
4-bit
Walsh code. Consequently the DRC symbol has a total of 512 chips and repeats
itself
once so that 1024 chips are filled on the DRC channel. The DRC chips are
divided into
16 64-chip TDM slots and TDM-transmitted with the pilot channel and the RRI
channel after puncturing in the pattern shown in FIG. 1. Upon receipt of data
rates
from ATs within the sector on the DRC channels, the AN schedules user data
according
to the amount of packet data and requested data rate of each user and selects
an AT that
will receive a data packet in the next slot. The AN transmits the data packet
at the
requested data rate to the selected AT for one packet period starting from the
next slot.
FIG. 2 illustrates the lengths of data packets according to data rates on the
forward link in the typical HDR system.
Referring to FIG. 2, the forward traffic channel transmits packets of
different
lengths according to data rates requested by ATs. After one packet is
transmitted, the
AN selects an AT to be serviced on the forward traffic channel in the next
slot and
determines a data rate at which to transmit data to the AT based on DRC
information
received from the ATs within the sector. The AN transmits a preamble at the
start of
each paclcet to inform the destination AT to receive the paclcet and the
length of the
packet. The preamble is multiplied by a Walsh code corresponding to a MAC
index
assigned to the AT and the repeating times of the preamble is determined
according to
the data rate of the packet. Table 1 shoran below lists preamble repetition
and the
number of preamble chips versus data rate. The AT searches for the preamble by
use of
the Walsh code corresponding to its MAC index and checks the data rate.
(Table 1)
Data rate Preamble repetition Chip number
38.4 lcbps 32 1024
76.81cbps ' 16 512
102.4 kbps 12 384
153.6 kbps 8 256
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204.8 kbps 6 192
307.2 kbps 4 128
614.4 lcbps 2 64
921.6 kbps 2 64
1228.8 kbps 2 64
1843.2 lcbps 2 64
2457.6 kbps 2 64
As stated above, after transmission of one packet on the forward link in the
HDR system, the AN schedules user packet data referring to DRC information
received
from the ATs just before the packet transmission. It is to be noted here that
the DRC
information is transmitted in each slot on the reverse link. Although the DRC
information is mmecessary when no schedule is made out, the DRC information is
continuously transmitted on DRC channels. This implies that reverse link
resources are
continuously occupied, thereby decreasing the system capacity of the reverse
link. The
problem becomes worse when data is transmitted at a low data rate (e.g., 38.4
kbps and
76.8 lcbps in FIG. 2) on the forward link. Since DRC information is used only
at the
time for scheduling before complete transmission of a packet, untimely DRC
information for scheduling is useless. Therefore, when data is transmitted at
a low data
rate, which implies that a long packet is transmitted, that is, more slots are
used, the
number of slots used for transmission of unnecessary DRC information is
increased.
The continuous transmission of the DRC channels significantly increases
interference
load on the reverse link. Accordingly, if transmission of the DRC channels is
discontinued when DRC information is not needed, interference is reduced and
the
system capacity on the reverse link is increased.
SUMMARY OF THE INVENTION
An object of the present invention is, therefore, to provide a method and
apparatus for transmitting DRC information used to determine a data rate for
the
forward link on the reverse link only when scheduling is needed in a mobile
telecommunication system like an HDR system.
Another object of the present invention is to provide a method and apparatus
for reducing interference load on the reverse linlc in a mobile
telecommunication
system lilce an HDR system.
A further object of the present invention is to provide a method and apparatus
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for increasing the system capacity of the reverse link in a mobile
telecommunication
system like an HDR system.
Still another object of the present invention is to provide a method and
apparatus for reducing interference load on the reverse link for a DRC
information non-
transmission period in a mobile telecommunication system like an HDR system.
The foregoing and other objects of the present invention are achieved by
providing a method and apparatus for tr~smittingh~ceiving DRC information in a
mobile telecommunication system for h~nsmitting packet data. To determine a
data
rate on the forward link in a mobile telecommunication system such as. an HDR
syst~n,
DRC information is transmitted on the reverse link only in time for scheduling
user
data. An AN transmits a DRI bit or an AT detects preambles of all users or its
own
preamble in order to control transmission of the DRC infommtion. Along with
the
DRC information transmission control, some ATs are controlled to transnnit
pilot
channels and RRI chaimels at different time points from other ATs. Therefore,
interference load on the reverse link is reduced and the system capacity of
the reverse
link is increased.
According to an aspect of the present invention there is provided
a method of transmitting data rate control (DRC) information to an
access network (AID transmitting packet data for a first transmission period
having a
plurality of slots iu order to request a data rate for packet data to be
hansmitted by the
AN for a second transmission period after the first transmission peaod in an
access
terminal (A1') of a mobile telecommunication system, comprising the steps of:
receiving a DRC request indicator (DRI), bit in a predetermined slot before a
last slot of the first transmission period; and
generating the DRC information in response to the DRI bit and transmitting
the DRC information to the AN.
According to another aspect of the present invention there is provided
. an access terminal (AT) for transmitting data rate control (DRC)
information to ~ access network (AID h~ns~tting packet data for a first
transmission
period having a plurality of slots according to a requested data rate in order
to request a
data rate for packet data to be transmitted by the AN for a second fission
period
after the fast transmission period is a mobile telecommunication system,
comprising:
a receiver for receiving a DRC request indicator (DRn bit in a predetermined
slot before a last slot of the first transmission period; and
a transmitter for selectively transmitting the DRC information according to
the
DRI bit to the AN. -
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According to a further aspect of the present invention there is provided
a method of controlling transmission of data rate control (DRC)
information from an access terminal (AT} that requests a data rate for packet
data in an
access network (AN) that tr~smits the packet data at the requested data rate
in a
mobile telecommunication system, comprising the steps of
checking a last slot of a first transmission period having a plurality of
slots
when the AN transmits the packet data to the AT for the first tiransmission
period; and
transmitting a DRC request indicator (DRI] bit to the AT in a predetermined
slot before the last slot to request DRC information to be used far a second
transmission period after the first transmission period to the AT.
According to a further aspect of the present invention there is provided
a mobile telecommunication system comprising:
an access network (AN) for ttansimitting packet data for a first transmission
period having a plurality of slots according to a requested data rate and
tr2onsmitting a
DRC request indicator (DRI) bit in a predetermined slot before a Iast slot of
the first
transmission period; ~d '
an access terminal (AT) for selectively transmitting data rate control (DRC)
information to the AN according to the DRT bit to request a data rate for
packet data to
be received for a second transnnission period after the first transmission
period.
According to a further aspect of the present invention there is provided
a method of transmitting data rate control (DRC) information to an
access network (AID in an access terminal (AT) of a second group in a mobile
telecommunication system having the AN for transmitting paucket data at a
requested
data rate for a first transmission period having a plurality of slots, ~d a
phuality of .ATs
divided into a first AT group that includes at least one AT for receiving the
packet data
for the first transmission period and the second AT group that does not
receive the packet
data for the fast transmission period ~d is to receive packet data for a
second
transmission period after the first transnnission period, the method
comprising the steps
of
detecting ATs of the first group by multiplying a received preannble by a
plurality of predetermined orthogonal codes assigned to the plurality of ATs;
detecting the length of the packet data transmitted to the first group of ATs
for
the first transmission period from the preamble and checking a last slot of
the first
transmission period; and
generating the DRC information in a predetermined slot before the last slot
and transmitting the DRC information to the AN.
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According to a further aspect of the present invention there is provided
an access terminal (AT) of a second group for transmitting data rate
control (DRC,~ information to an access network (AID in a mobile
telecommunication
system having the AN for transmitting packet data at a requested data rate for
a first
transmission period having a plurality of slots, and a plurality of ATs
divided into a first
AT group that includes at least one AT for receiving the packet data for the
first
transmission period and the second AT group that does not receive the packet
data far the
first transmission period ana is to receive packet data for a second
transmission period
after the first transmission period, comprising:
a multiplier for detecting ATs of the first group by multiplying a received
preamble by a plurality of predetermined orthogonal codes assigned to the
plurality of
ATs;
a packet length detector for detecting the length of the packet data
bra~mitted
to the first group of ATs for the first transmission period from the preamble;
a controller for checking a last slot of the first transmission period; and
a transmitter for selectively transmitting the DRC information in a
predetermined slot before the last slot to the AN under the control of the
controller.
According to a further aspect of the present invention there is provided
a method of transmitting data Late control (DRC) information to an
access network (Alb in an access terminal (ATE of a first group in a mobile
telecommunication system having the AN for transmitting packet data at a
requested
data rate for a first hnnsmission period having a phu-ality of slots, and a
plurality of ATs
divided into the first AT group that includes at least one AT for receiving
the packet
data for the first transmission period and a second AT group that does not
receive the
packet data for the first transmission period and is to receive packet data
for a second
transmission period after the first trssion period, the method comprising the
steps
of-.
checking a last slot of the first transmission period; and
generating the DRC information in a predetermined slot before the last slot
and transmitting the DRC information to the AN.
According to a further aspect of the present invention there is provided
an access terminal (AT) of a first group for transmitting data rate
control (DRC) information to an access network (AN} in a mobile
telecommunication
system having the AN for transmitting packet data at a requested data rate for
a first
transmission period having a plurality of slots, and a plurality of ATs
divided into the
first AT group that includes at least one AT for receiving the packet data for
the first
transmission period and a second AT group that does not receive the packet
data for the
first transmission period and is to receive packet data for a second
transmission period
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4c
after the first transmission period, comprising:
a preamble detector for detecting a preamble;
a packet length detector for detecting the length of the packet data received
for
the first trm~mission period from the preamble;
a controller for checking a last slot of the first transmission period based
on
the packet length; and
a transmitter for selectively transmitting the DRC information inv' a
predetermined slot before the last slot to the AN under the control of the
controller.
According to a further aspect of the present invention there is provided
. , an access terminal (ATE in a mobile telecommunication system,
Wig:
a multiplier for sequentially multiplying a received pre~ble by a plurality of
acthogonal codes assigned to a phnality of ATs;
a detector for detecting an AT receiving packet data and the length of the
packet data from the multiplication result;
a controller for determining a termination period of packet data transmission
based on the packet length; and
a transmitter for selectively tratLmnitting data rate control (DRC)
information
in a predetermined period to an access network (AN) before the termination
period.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects, feafiues and advantages of the present invention
will become more apparent from the following detailed description when taken
in
conjunction with the accompanying drawings in which:
FTG. 1 illustrates the puncturing patterns of a pilot channel, a DRC channel,
and an ItRI channel on the reverse link in a typical HDR system;
FIG. 2 illustrates the lengths of data packets versus data rates on the
fotavard
link in the typical HDR system;
FIG. 3 illustrates the slot transmission/reception relationship between the
forward link and the reverse link in a DRC channel transnnission control
operation
according to an embodiment of the present invention;
FIG. 4 is a flowchart illustrating the DRC channel transmission control
operation according to the embodiment of the present invention;
FIG. 5 is a block diagram of an AN transmitter according to the embodiment
of the present invention;
FIG. 6 is a block diagram of an AT transmitter according to the embodiment of
the present invention;
FIG. 7 illustrates the slot transmission/reception relationship between the
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forward link and the reverse linlc in a DRC channel transmission control
operation
according to another embodiment of the present invention;
FIG. 8 is a flowchart illustrating the DRC channel transmission control
operation according to the second embodiment of the present invention;
FIG. 9 is a block diagram of an AT transmitter according to the second
embodiment of the present invention;
FIG. 10 is the slot transmission/reception relationship between the forward
link and the reverse linlc in a DRC channel transmission control operation
according to
a third embodiment of the present invention;
FIG. 11 is a flowchart illustrating the DRC channel transmission control
operation according to the third embodiment of the present invention;
FIG. 12 is a block diagram of an AT transmitter according to the third
embodiment of the present invention; and
FIGS. 13A, 13B, and 13C illustrate transmission of pilot channels and RRI
channels for a DRC channel non-transmission period according to a fourth
embodiment
of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of the present invention will be described hereinbelow
with reference to the accompanying drawings. In the following description,
well-known
functions or constructions are not described in detail since they would
obscure the
invention in unnecessary detail.
It is to be clarified that the present invention provides an apparatus and
method
for transmitting DRC information on the reverse link only when scheduling is
needed,
for use in determining a data rate for the forward link in a mobile
telecommunication
system lilce an HDR system. ~ That is, when an AN intends to transmit another
packet in
an HDR system, ATs transmit DRC information just before the previous packet is
completely transmitted. According to the present invention, a decision is
first made on
when to transmit DRC information and the DRC information is transmitted only
at the
decided time. Pilot channels and RRI channels are transmitted at different
time points
according to users in order to reduce interference load on the reverse link
while the
DRC information is not transmitted. Decision as to whether DRC information is
to be
transmitted at the current time point and selective transmission of the DRC
information
based on the decision result will be described in Embodiment 1 to Embodiment
3.
Embodiment 4 offers a method of reducing interference load on the reverse link
by
transmitting pilot channels and RRI channels at different time points
according to users,
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incorporating Embodiment 1 to Embodiment 3 therein.
Embodiment 1
FIG. 3 illustrates the relationship in slot transmission/reception between the
forward Iinlc and the reverse linlc in a DRC channel transmission control
operation
according to a first embodiment of the present invention. This embodiment is
characterized by control of DRC channels with the introduction of a DRI (DRC
Request Indicator) bit. While the following description focuses on the data
rate of
76.8kbps, it is a mere exemplary application. Obviously, the first embodiment
is
applicable to any data rate.
Referring to FIG. 3, an AN controls transmission of DRC channels from all
ATs by informing them whether it needs to receive reverse DRC channels. The AN
transmits the information in a DRI bit on a MAC channel. The DRI bit indicates
whether DRC information is needed fox scheduling after a predetermined slot
period.
The DRC information is needed when transmission of the forward packet is
terminated
in the predetermined slot period and the AN must select the next AT and a data
rate.
The DRI bit is set to 1 if the transmission of the forward packet is
terminated in the
predetermined slot and to 0 if the transmission of the current forward packet
continues.
If the AN requests DRC information within the predetermined slot period and
receives
the requested information, it determines a data rate for the next packet to
transmit.
Assuming that the AN is to transmit a new packet in a second transmission
period
while transmitting a packet to an AT in a first transmission period having a
plurality of
slots, the AN makes out a schedule to determine an AT to receive the new
packet in the
second transmission period and a data rate for the packet in the latter half
of the last slot
of the first transmission period. Fox this purpose, the AN transmits a DRI bit
requesting the DRC information to ATs in the predetermined slot of the first
transmission period. The predetermined slot is located at least two slots
before the last
slot. Preferably, the predetermined slot is the second slot from the last
slot. The
predetermined slot may indicate the first two slots from the last slot and the
last slot in
consideration of the case that a packet is completely transmitted in one slot
in the
second transmission period. For example, if the last slot is 16"' slot, the
predetermined
slot is 14"' slot or 14"', 15"' and 16"' slots. When necessary, the
predetermined slot can
be set to a different value.
FIG. 4 is a flowchart illustrating a DRC channel transmission control
operation according to the first embodiment of the present invention. This is
an
algorithm of controlling transmission of DRC channels from the ATs by the DRI
bit.
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Referring to FIG. 4, an AT reads a DRI bit from a forward MAC channel
signal in step 401 and checks whether the DRI bit is 1 or 0 in step 402. If
the DRI bit is
1, the AT measures the pilot CI of each effective sector (active set sector)
in step 403,
determines a sector corresponding to the highest C/I in step 404, converts the
highest
C/I to a corresponding DRC symbol in step 405, and transmits the DRC symbol to
the
AN in step 406. In step 407, the AT receives the next slot and returns to step
401. As
well known, the DRC symbol conversion is performed by mapping the C/I to the
corresponding DRC symbol.
On the other hand, if the DRI bit is 0 in step 402, the AT jumps to step 407.
Returning to FIG. 3, the DRI bit in an nth forward slot controls the DRC
channel in an (n+1)th reverse slot. The DRC channel arrives in an (n+2)th slot
and
determines a data rate for an (n+3)th forward slot. DRC information must be
requested
three slots before the current packet is completely transmitted in the first
transmission
period, that is, in the second slot from the last slot of the first
transmission period, so
that the DRC information can be received in time for scheduling to determine
the data
rate of a new packet to be transmitted in the second transmission period.
Therefore, the
AN transmits the DRI bit set to 1 three slots before termination of packet
transmission
and transmits DRI bit set to Os in the other slots. If a packet is as long as
N slots, the
DRC channel need not be transmitted in (N-3) slots. The ratio of the number of
slots
for non-DRC channel transmission to the total number of slots in a packet is
(N-3)/N.
Table 2 illustrates the ratio of the number of slots for non-DRC channel
transmission to
the total number of slots versus data rates. If packet length is three slots
or less, the
DRC channel is transmitted in all slots. Interference load caused by
transmission of the
DRC channel in a slot period can be reduced at a data rate of 153.6kbps or
below and at
307.2kbps (long pacl~et).
(Table 2)
Data rate Slots per paclcet Slots for non-DRC
channel transmission
(%)
38.4 kbps 16 81.25
76.8 lcbps 8 62.5
102.4 kbps 6 50
153.6 kbps Short 4 25
153.6 kbps Long 16 81.25
204.8 lcbps 3 0
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307.2 l~bps Short 2 0
307.2 l~bps Long 8 62.5
614.4 lcbps 1 0
921.6 l~bps 2 0
1228.8 l~bps 1 0
1843.2 lips 1 0
2457.6 lips 1 0
FIG. 5 is a blocl~ diagram of an AN transmitter according to the first
embodiment of the present invention. The transmitter is characterized by the
introduction of the DRI bit.
Referring to FIG. 5, a traffic channel is encoded in an encoder 501, modulated
in QPSK, BPSK, or 16QAM according to a data rate in a modulator 502, and
interleaved in an interleaves 503. The interleaved traffic channel signal is
punctured
and repeated according to the data rate in a punctures & repeater 504. A
demultiplexer
(DEMUX) 505 outputs 16 successive bits of the repeated signal on 16 parallel
channels.
A Walsh cover unit 506 Walsh-covers the 16 channels with 16 Walsh codes and a
Walsh chip level summer 507 sums the Walsh-covered channel data at a chip
level. A
preamble is repeated according to the data rate in a preamble repeater 511 and
spread
with a Walsh code assigned to a reverse power control channel in a Walsh
spreader 512.
A multiplexes (MUX) 513 multiplexes the outputs of the Walsh chip level summer
507
and the spread preamble received from the Walsh spreader 512 in such a way
that the
preamble is located at the start of the traffic channel.
Now there will be given a detailed description of the transmitter structure
associated with the DRI bit to which the present invention pertains. A pilot
channel, an
FA (Forward Activity) bit or an FAB, and an RA (Reverse Activity) bit or an
RAB are
respectively multiplied by Walsh codes #0, #1, and #2 and transmitted on a
forward
MAC channel. The other 29 Walsh codes are multiplied by reverse power control
(RPC) bits for users prior to transmission. One of the 29 Walsh codes assigned
to the
RPC bits can be assigned for transmission of the DRI bit. For example, Walsh
code #3
can be assigned to the DRI bit. According to the structure of the AN
transmitter of the
present invention, an FA bit is repeated 15 times (occurs 16 times) in a
repeater 521 and
multiplied by Walsh code #1 in a multiplier 522. An RA bit occurs as many
times as a
RABLength factor in a repeater 531 and is multiplied by Walsh code #2 in a
multiplier
532. A DRI bit is multiplied by Walsh code #3 in a multiplier 541. An RPC
Walsh
channel gain controller 551 controls the gain of an RPC channel and a
multiplier 552
.,~",.,."~ .
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multiplies the gain=controlled RPC bits by the other Walsh codes, respectively
A
Walsh chip level summer 553 sums the signals received from the multipliers
522, 532,
541, and 552 at a chip level. The sum occurs four times in a MAC chancel
repeater
554 and is transmitted before and after the second pilot burst in each slot by
halves.
The pilot channel signal is multiplied by Walsh code #0 in a multiplier 561. A
second
MUX 562 connects the output of the first MLTX 513, the output of the MAC
chaimel
repeater 554, and the output of the multiplier 561 as shown in FIG. 3. The
output of the
second MLTX 562 is subject to complex spreading in a complex spreader 563 and
5ltering in a baseband filter 564 prior to transmission.
FIG. 6 is a block diag~rann of an AT transmitter according to the first
embodiment of the present invention. This transmitter is also characterized by
the
introduction of the DRLbit A description of an AT receiver for receiving the
DRI bit
related with the present invention from an AN will be omitted and only the
structure of
the AT transmitter associated with detemnn~ng whether a DRC symbol is to be
transmitted based on the DRI bit related with the present invention will be
described
hereinbelow in detail.
Referring to FIG. 6, a pilot channel is multiplied with Walsh code #0 in a
multiplier 601. An RRI channel is modulated to an 8-bit Walsh symbol in an 8-
cry
orthogonal modulator 611, repel 63 times in a Walsh symbol repeater 612, and
multiplied with Walsh code #0 in a multiplier 613. If the DRI bit is 0, a MUX
631
passes a DRC symbol and if the DRI bit is 0, it blocks the DRC symbol. That
is, the
MUX 631 acts as a selector for selecting the DRC symbol according to the DRI
bit.
The DRC symbol is block-encoded in a block encoder 632 and the codeword is
repeated in a repeater 633. The output of the repeater 633 is multiplied with
Walsh
codes in a series of multipliers 634, 635, and 636. A MLTX 637 TDM multiplexes
the
spread signal with the pilot signal and the RRI.
A traffic channel is encoded in an encoder 641, interleaved in an interleaves
642, and multiplied by a data channel power gain in a gain multiplier (gain
controller)
643. The output of the multiplier 643 is multiplied by Walsh code #2 in a
multiplier
644. The outputs of the MIJX 637 and the multiplier 644 are output to the in
phase (I)
ann and the quadrature (~ arm, respectively: The I arm and the Q arm are
spread in a
complex.spreader 645 and filtered in a baseband filter 646 prior to h~nsmi~on.
Embodiment 2
FIG. 7 illustrates the relationship in slot transmission/reception between the
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forward link and the reverse link according to a second embodiment of the
present
invention. In the second embodiment, transmission of DRC channels is
controlled by
allowing an AT to search for preambles of all ATs within the service area of
an AN.
According to the second embodiment, the AT determines an AT that communicates
packet data with the AN by detecting the preambles of all the ATs and
transmits DRC
information in a predetermined slot period before the packet data is
completely
transmitted.
If each AT also searches for the preambles of the other ATs, it can find out
how long the current forward packet is. Thus, the AT does not transmit its DRC
channel until scheduling is needed. That is, each AT checks whether its DRC
channel
is to be transmitted or not and as a result, it transmits the DRC channel only
in time for
scheduling. The DRC channel transmission is controlled in this manner. As
stated
before, a preamble is multiplied with a Walsh code according to a M'AC index
assigned
to an AT and the length of a packet is variable depending on a data rate.
Therefore,
each AT measures energy by decoding a preamble with Walsh codes corresponding
to
MAC indexes assigned to all the ATs and compares the energy measurement with
preamble repetition times shown in Table 1, thereby fording out the length of
the
current paclcet and locating the start and end slots of the packet. After
receipt of the
first pilot burst in an nth slot, a DRC channel transmits DRC information for
an (n+2)th
slot. Therefore, the AT transmits the DRC channel two slots before the end
slot of the
packet. Since one slot is taken to know the length of the paclcet after the
start slot is
located, the AT transmits the DRC channel in the start slot, too. Therefore,
the number
of slots that need not be transmitted is (N-3), and the ratio of the number of
slots for the
non-DRC channel transmission to an N-slot packet is (N-3)/N as in the first
embodiment.
FIG. 8 is a flowchart illustrating a DRC channel transmission control
operation according to the second embodiment of the present invention.
Referring to FIG. 8, the AT searches for the preambles of all ATs and
determines the length of the current packet in step 801. That is, each of ATs
within the
service area of the AN determines an AT which is receiving a packet from the
AN by
multiplying a received preamble with a plurality of predetermined orthogonal
codes,
mainly Walsh codes, assigned to the ATs and detects the length of the packet
from the
preamble. In step 802, the AT determines whether the current packet will be
terminated
within two slots. If the current paclcet is terminated within two slots, the
AT measures
the pilot C/I of effective sectors (active set sectors) in step 803 and
determines the
CA 02382764 2002-02-22
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-11-
highest C/I and a sector corresponding to the highest C/I in step 804. The AT
converts
the determined C/I to a corresponding DRC symbol in step 805 and transmits the
DRC
symbol to the AN in step 806. On the other hand, if the current packet is not
terminated within two slots in step 802, steps 803 to 807 are omitted.
Upon termination of the packet transmission in step 807, the AT returns to
step
801, searches for preambles of all the ATs, and reads the length of the next
packet. If
the paclcet transmission is not completed in step 807, the AT receives the
next slot in
step 808 and returns to step 802. In step 802, the AT checks whether the
current packet
will be terminated within two slots in the received slot.
FIG. 9 is a block diagram of an AT transmitter according to the second
embodiment of the present invention. The AT transmitter is characterized by
searching
for preambles of all ATs for control of the DRC channel. The structure of the
AN
transmitter related with the pilot channel, the RRI channel, and the traffic
channel is the
same as that shown in FIG. 6. Therefore, a description will be made on only
the
transmitter structure related with decision about whether to transmit a DRC
symbol or
not based on the preambles of all the ATs.
Referring to FIG. 9, upon receipt of a preamble, a preamble buffer 901 stores
it. A Walsh code generator 902 generates Walsh codes for all the ATs within
the sector.
A multiplier 903 multiplies the preamble stored in the buffer 901 by the Walsh
codes.
An accumulator 904 accumulates the product received from the multiplier 903
and an
energy detector 905 detects energy from the accumulation. A packet length
detector
906 detects packet length from the output of the energy detector 905. Since a
period
suitable for DRC symbol transmission can be known from the packet length, a
DRC
controller 907 controls a MUX 921 to selectively transmit the DRC symbol as
shown in
FIG. 7. The DRC controller 907 controls the MUX 921 to pass the DRC symbol two
slots before the paclcet transmission is completed and to block the DRC symbol
in the
other slots. That is, if the length of the packet is shorter than three slots,
the DRC
symbol is transmitted all the time.
In the case where an AT among a plurality of ATs receives packet data from an
AN in a first transmission period including a plurality slots, the AT
transmits a DRC
symbol in slots from a predetermined slot before the end of the first
transmission period
(two slots before the last slot) to request a data rate for packet data to be
transmitted in
a second transmission period after the first transmission period. Tlus
operation can be
performed in ATs that are not receiving the packet data from the AN in the
first
CA 02382764 2005-O1-28
12
transmission period as well as the AT receiving the packet data in the first
transmission
period. That is, if terminals receiving packet data from the AN in the first
hansmission
period is a first group and terminals that are not receiving the packet data
fiom the AN
in the first transmission period is a second group, the second group transmits
DRC
symbols to the AN in the predetermined slot before the transmission of the
packet data
to the first group is completed. The first group also transmits DRC symbols bo
the AN
in the predetermined slot before the transmission of the packet data is
completed.
The DRC symbols outputted from the MLJX 921 are blocky in a block encoder 922
by
(8,4,4). And, the block-encoded symbols are inputted to a codeword repeater
(923). The codeword repeater
repeats the block-ernx>ded symbols crnresponding to a siae to be transmitted
and outputs the repeated
symbols to a first multiplier 924. The first multiplier 924 multiplies the
repeated symbols with a
predetermined Welsh code W o and outputs the multiplied symbols to a second
multiplier 925. The second
multiplier 925 Welsh-covers the multiplied symbols with a Welsh cover index of
the DRC and outputs the
Welsh-covered symbols to a third multiplier 926. The symbols multiplied in the
second multiplies 925 are
multiplied with another predetermined Welsh code W o in the third multiplier
926, and the symbols
multiplied in the third multiplier 926 are outputted to a MIJX 944.
In addition, a pilot symbol to be transmitted through a pilot channel is
inputted to a fourth
multiplier 931. And, the fourth multiplier 931 multiplies the pilot symbol
with the predetermined Welsh
code W o and outputs the multiplied symbol to the MilX 944.
And, a reverse rate indicator (RRI) is inputted to 8-ary orthogonal modulator,
and the 8-ary
ord~ogonal modulator odhogor~ally modulates the RRI. And, a Welsh symbol
repeal 942 repeats the
modulated RRI with a proper size to be transmitted and outputs the repeated
RRI to a fifth multiplier 943.
The fifth multiplier 943 multiplies the repeated RRI and outputs the
multiplied RRI to the MUX 944.
And then, the MIJX 944 TDM multiplexes the inputted symbols and outputs it to
a complex
spreader 960.
Meanwhile, information to be transmitted through a trai~c channel are inputted
to an encoder 951,
and the encoder 951 encodes the information wording to an encoding method
required in a mobile
communication system. And, the encoded symbols are modulated in a modulator
952 and outputted to an
interleaver 953. The interleaver 953 interleaves the modulated symbols to
prevent information burst error
and outputs the interleaved symbols to a data charnel gain controller 954. The
data channel gain controller
CA 02382764 2005-O1-28
12a
954 applies a gain of a channel when transmitting the symbols through the
channel to the interleaved
symbols and outputs the symbols to a sixth multiplier 955. The sixth
multiplier 955 multiplies the symbols
received from the data channel gain controller with a predetermined Welsh code
W 2 and outputs the
multiplied symbols to the complex spreader 960.
And then, the complex spreader 960 spreads the TDM multiplexed symbol received
from the
MIJX 944 through I channel, and spreads the symbol received from the sixth
multiplier 955 through Q
channel to thereby output the symbols to a baseband filter 970. And then, the
baseband filter 970
respectively filters the symbols received through the I channel and the Q
channel.
Embodiment 3
FIG. 10 illustrates the relationship in slot transmission/reception between
the
forward link and the reverse link in a DRC channel tra~mission control
operation
according to a third embodiment of the present invention. In this embodiment,
the
DRC chapel of an AT receiving the current forward channel is controlled.
Referring to FIG. 10, since only the DRC charruel of an AT receiving a packet
from the AN is controlled in the third embodiment of the present invention,
there is no
need for a detector for detecting the preambles of the other ATs as compared
to the
second embodiment. The AT assigned to the current forward tragic channel can
detect
packet length and locate the start and end slots of the packet by searching
for the
pxeamble destined for the AT. The AT can also find out a time period in which
DRC
information is not needed until the scheduling time before the packet is
completely
transmitted. As in the second embodiment, the DRC channel is transmitted in
the start
slot and the last two slots of the packet.
FIG. 1I is a flowchart illustrating a DRC channel transmission control
operation in which the DRC channel of the AT receiving the forward traffic
chaimel is
controlled according to the third embodiment of the present invention.
Referring to FIG. 11, the AT searches for a preamble transmitted from the AN
in step 1101 and determines whether it has received a packet in step 1102.
Upon
receipt of the packet, the AT determines whether the packet will be terminated
~t~thin
two slots in step 1103. If it is, the AT measures the pilot C/I of effective
sectors in step
1104, determines the highest GI and a sector corresponding to the highest C/I
in step
1105, maps the highest C/I to a corresponding DRC symbol in step 1106, and
hansmits
the DRC symbol to the AN in step 1107. On the other hand, if the packet will
not be
terminated within two slots in step 1103, the AT jumps to step 1108. If the
packet
transmission is completed in step 1108, the AT receives the next slot in step
1109.
Then, the AT determines whether the current packet will be terminated within
two slots
CA 02382764 2005-O1-28
-13-
in the new slot in step 1103 and determines whether to transmit the DRC
channel
according to the determination result.
FIG. 12 is a block diagram of an AT hnnsmitter according to the third block
diagram of the present invention. The AT transmitter is characterized by
control of the
DRC channel of an AT that receives the ceureat forward traffic channel. Since
the
transmitter structure associaded with the pilot channel, the RRI channel, and
the tragic
channel is the same as that shown in FIG. 6, only the transmitter struchue
associated
with determining whether to transnnit the DRC symbol will be described in
detain.
Referring to FIG. 12, a preamble detector 1201 detects a preamble destined for
the AT. A packet length detector 1202 detects packet length from the pre~ble.
Since
a time period in which the DRC symbol must be. transmitted can be known from
the
packet length as shown in FIG. 10, a DRC controller 1203 controls a MITX 1221.
to
pass the DRC symbol two slots before the packet transmission is te<minated and
to
block the DRC symbol in the other slots. That is, if the packet length is
shorter than
three slots, the DRC symbol is passed all the time. _
In addition, referring to Figure I2, elements illustrated therein correspond
to
their Figure 9 counterparts. Specifically, reference numbers 1211, 1222, 1223,
1224,
1225, 1226, 1231, 1241, 1242, 1243, 1244, 1251, 1252, 1253, 1254, 1255, 1260
and
1270 correspond with 91 l, 922, 923, 924. 925, 926, 931, 941, 942, 943, 944,
951, 952,
953, 954, 955, 960 and 970 respectively.
Embodiment 4
In the first and second embodiments, interference load is reduced by
controlling the DRC channels of all ATs. However, since the DRC channels are
transmitted with the pilot channels and the RRI chaimels in time division,
pilot
channels and RRI channels from users are tr~mitted apt the same time- paints
even
though the DRC channels are not transmitted. As a result, the interference
load is not
reduced when the pilot and RRI ch~nels are tran~nitted from the users.
Therefore; if
the pilot channels and the RRI channels are tr~mitted at different time poi's
according to the users for the DRC non transmission period, interference load
can be
equally distnbuted. This is the basic idea of Embodiment 4.
FIGs. 13A, 13B, and 13C illustrate time points at which the pilot channels and
the RRI channels are h~ansmitted for a DRC nontraasmission period.
CA 02382764 2005-O1-28
13a
Referring to FIGS. 13A, 13B, and 13C, all .ATs are grouped into ones assigned
to even numbered MAC indexes and odd-numbered MAC indexes to transmit (heir
pilot and RRI channels at different time points. The ATs can be grouped in a
different
way. The odd-numbered AMC index group transmits pilots and RRI channels in odd-
numbered TDM slots as shown in FIG. 13B, whereas the even-numbered AMC index
group transmits pilots and RRI channels in even-numbered TDM slots as shown in
FIG.
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13C. The resulting equal distribution of interference load contributes to the
increase of
the reverse link system capacity. That is, if a plurality of ATs are divided
into a first
group (e.g., an odd-numbered group) and a second group (e.g., an even-numbered
group), the first group terminals transmit pilot signals and RRI channels in a
first group
of slots (e.g., odd-numbered slots) and the second group terminals transmit
pilot signals
and RRI chamiels in a second group of slots (e.g., even-numbered slots).
The above operation can be performed independently, or in conjunction with
the first to third embodiments, respectively.
In accordance with the present invention as described above, transmission of
DRC channels is controlled so that DRC information is transmitted on the
reverse linlc
only when necessary in an HDR system. Therefore, interference load on the
reverse
link is reduced and the system capacity of the reverse linlc is increased.
Furthermore
pilot chamzels and RRI channels are transmitted at different time points
according to
users for a DRC non-transmission period, thereby further decreasing the
interference
load generated for the DRC non-transmission period.
While the invention has been shown and described with reference to certain
preferred embodiments thereof, they are mere exemplary applications. While the
embodiments have been described in the context with the HDR system, they are
applicable to any telecommunication system where packet data and DRC
information
are transmitted. The embodiments are not limited to Walsh codes either.
Therefore, it
will be understood by those slcilled in the art that various changes in form
and details
may be made therein without departing from the spirit and scope of the
invention as
defined by the appended claims.
