U.S. patent application number 13/953070 was filed with the patent office on 2013-11-28 for method and apparatus for fast closed-loop rate adaptation in a high rate packet data transmission.
This patent application is currently assigned to QUALCOMM Incorporated. The applicant listed for this patent is QUALCOMM Incorporated. Invention is credited to Rashid Ahmed Akbar Attar, Naga Bhushan, Eduardo S. Esteves.
Application Number | 20130315143 13/953070 |
Document ID | / |
Family ID | 24278709 |
Filed Date | 2013-11-28 |
United States Patent
Application |
20130315143 |
Kind Code |
A1 |
Esteves; Eduardo S. ; et
al. |
November 28, 2013 |
METHOD AND APPARATUS FOR FAST CLOSED-LOOP RATE ADAPTATION IN A HIGH
RATE PACKET DATA TRANSMISSION
Abstract
In a high data rate communication system capable of variable
rate transmission, an open loop rate control can be adjusted with a
closed loop rate control to maximize throughput. An access point
generates interleaved multi-slot packets that allow an access
terminal to transmit indicator messages to the access point in
accordance with recently received data carried within slots of the
multi-slot packets.
Inventors: |
Esteves; Eduardo S.; (San
Diego, CA) ; Attar; Rashid Ahmed Akbar; (San Diego,
CA) ; Bhushan; Naga; (San Diego, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
QUALCOMM Incorporated |
San Diego |
CA |
US |
|
|
Assignee: |
QUALCOMM Incorporated
San Diego
CA
|
Family ID: |
24278709 |
Appl. No.: |
13/953070 |
Filed: |
July 29, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11592568 |
Nov 3, 2006 |
8498308 |
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13953070 |
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09570210 |
May 12, 2000 |
7245594 |
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11592568 |
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Current U.S.
Class: |
370/328 |
Current CPC
Class: |
H04W 28/18 20130101;
H04W 28/04 20130101; H04W 16/02 20130101 |
Class at
Publication: |
370/328 |
International
Class: |
H04W 16/02 20060101
H04W016/02 |
Claims
1. A method for wireless communication, comprising: transmitting a
first slot of a first multi-slot packet; receiving an indicator
message indicating a reception status of the first slot of the
first multi-slot packet; and cancelling transmission of remaining
slots of the first multi-slot packet if the indicator message is an
acknowledgment.
2. The method as in claim 1, if the indicator message is negative,
the method further comprising: transmitting a next slot of the
first multi-slot packet; receiving an indicator message indicating
a reception status of the next slot of the first multi-slot packet;
and cancelling transmission of remaining slots of the first
multi-slot packet if the indicator message is an
acknowledgment.
3. The method as in claim 1, further comprising: encoding the first
multi-slot packet; and partitioning the first multi-slot packet
into multiple slots.
4. The method as in claim 1, wherein each slot of the first
multi-slot packet is transmitted at a predetermined time slot.
5. The method as in claim 1, further comprising: transmitting a
first slot of a second multi-slot packet in a time slot allocated
to one of the remaining slots of the first multi-slot packet.
6. The method as in claim 1, wherein the first multi-slot packet
has a target packet error rate corresponding to a normal end of the
first multi-slot packet, and wherein a packet error rate of the
first multi-slot packet is different from target packet error
rate.
7. The method as in claim 6, wherein the normal end of the first
multi-slot packet corresponds to transmission of all slots of the
multi-slot packet.
8. The method as in claim 1, wherein the first multi-slot packet
has a target data rate corresponding to transmission of all slots
of the first multi-slot packet, and wherein a data rate of the
transmitted first multi-slot packet is greater than the target data
rate.
9. The method as in claim 1, wherein the indicator message provides
closed loop rate adaptation for multi-slot packet data rates.
10. The method as in claim 9, further comprising: receiving a data
rate indicator; and determining a target data rate for the first
multi-slot packet as a function of the data rate indicator.
11. The method as in claim 1, wherein each slot of the first
multi-slot packet is transmitted at a predetermined time slot and
wherein the predetermined data slots are interlaced with
predetermined gap slots in an alternating pattern.
12. The method as in claim 1, further comprising: transmitting all
slots of the first multi-slot packets; receiving an extend
indicator; and transmitting at least one of the slots of the first
multi-slot packet in response to receiving the extended
indicator.
13. The method as in claim 1, further comprising: receiving,
periodically, information indicative of a quality measure of the
wireless channel, wherein cancelling transmission of remaining
slots of the first multi-slot packet if the decoding is successful
further comprises receiving a closed loop rate control message.
14. A wireless apparatus, comprising: means for transmitting a
first slot of a first multi-slot packet; means for receiving an
indicator message indicating a reception status of the first slot
of the first multi-slot packet; and means for cancelling
transmission of remaining slots of the first multi-slot packet if
the indicator message is an acknowledgment.
15. The wireless apparatus as in claim 14, further comprising:
means for transmitting a next slot of the first multi-slot packet
if the indicator message is negative; means for receiving an
indicator message indicating a reception status of the next slot of
the first multi-slot packet; and means for cancelling transmission
of remaining slots of the first multi-slot packet if the indicator
message is an acknowledgment.
16. The wireless apparatus as in claim 14, wherein the first
multi-slot packet has a target packet error rate corresponding to a
normal end of the first multi-slot packet, and wherein a packet
error rate of the first multi-slot packet is different from the
target packet error rate, and further comprising: means for
receiving a data rate indicator; and means for determining a target
data rate for the first multi-slot packet as a function of the data
rate indicator.
17. A computer program product, comprising: computer-readable
medium; and code for causing a computer to transmit a first slot of
a first multi-slot packet; code for causing a computer to receive
an indicator message indicating a reception status of the first
slot of the first multi-slot packet; and code for causing a
computer to cancel transmission of remaining slots of the first
multi-slot packet if the indicator message is an
acknowledgment.
18. The computer program product of claim 17, further comprising
code for causing a computer to calculate a number of slots for
transmission of a packet of data in a multi-slot packet.
19. The computer program product of claim 17, wherein the computer
program product further comprises: code for causing a computer to
transmit a next slot of the first multi-slot packet if the
indicator message is negative; code for causing a computer to
receive an indicator message indicating a reception status of the
next slot of the first multi-slot packet; and code for causing a
computer to cancel transmission of remaining slots of the first
multi-slot packet if the indicator message is an
acknowledgment.
20. The computer program product of claim 17, wherein the computer
program further comprises: code for causing a computer to encode
the first multi-slot packet; and code for causing a computer to
partition the first multi-slot packet into multiple slots.
21. A computer program which makes a computer execute: a first
procedure for transmitting a first slot of a first multi-slot
packet; a second procedure for receiving an indicator message
indicating a reception status of the first slot of the first
multi-slot packet; and a third procedure for canceling transmission
of remaining slots of the first multi-slot packet if the indicator
message is an acknowledgment.
Description
CLAIM OF PRIORITY UNDER 35 U.S.C. .sctn.120
[0001] The present application for patent is a Divisional and
claims priority to pending patent application Ser. No. 11/592,568
entitled "METHOD AND APPARATUS FOR FAST CLOSED-LOOP RATE ADAPTATION
IN A HIGH RATE PACKET DATA TRANSMISSION" filed Nov. 3, 2006; which
is a Continuation of patent application Ser. No. 09/570,210
entitled "METHOD AND APPARATUS FOR FAST CLOSED-LOOP RATE ADAPTATION
IN A HIGH RATE PACKET DATA TRANSMISSION" filed May 12, 2000, now
U.S. Pat. No. 7,245,594; all of which are assigned to the assignee
hereof and are hereby expressly incorporated by reference
herein.
BACKGROUND OF THE INVENTION
[0002] I. Field of the Invention
[0003] The present invention relates to data communication. More
particularly, the present invention relates to a novel and improved
method and apparatus for performing fast closed-loop rate
adaptation in a high rate packet data transmission.
[0004] II. Description of the Related Art
[0005] Mobile computing and data access is steadily becoming
available to an increasing number of users. The development and
introduction of new data services and technologies that will
provide continuous data connectivity and full access to information
is presently occurring. Users can now use a variety of electronic
devices to retrieve voice or data information stored on other
electronic devices or data networks. Some of these electronic
devices can connect to data resources through wires and some can
connect to data resources through wireless solutions. As used
herein, an access terminal is a device providing data connectivity
to a user. An access terminal may be coupled to a computing device,
such as a desktop computer, a laptop computer, or a personal data
assistant (PDA), or it may be physically incorporated into any such
devices. An access point is equipment that provides data
connectivity between a packet switched data network and access
terminals.
[0006] An example of an access terminal that can be used to provide
wireless connectivity is a mobile telephone that is part of a
communication system capable of supporting a variety of
applications. One such communication system is a code division
multiple access (CDMA) system which conforms to the "TIA/EIA/IS-95
Mobile Station-Base Station Compatibility Standard for Dual-Mode
Wideband Spread Spectrum Cellular System," hereinafter referred to
as the IS-95 standard. The CDMA system allows for voice and data
communications between users over a terrestrial link. The use of
CDMA techniques in a multiple access communication system is
disclosed in U.S. Pat. No. 4,901,307, entitled "SPREAD SPECTRUM
MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL
REPEATERS," and U.S. Pat. No. 5,103,459, entitled "SYSTEM AND
METHOD FOR GENERATING WAVEFORMS IN A CDMA CELLULAR TELEPHONE
SYSTEM," both assigned to the assignee of the present invention and
incorporated by reference herein. It should be understood that the
present invention is equally applicable to other types of
communication systems. Systems utilizing other well-known
transmission modulation schemes such as TDMA and FDMA as well as
other spread spectrum systems may employ the present invention.
[0007] Given the growing demand for wireless data applications, the
need for very efficient wireless data communication systems has
become increasingly significant. The IS-95 standard is capable of
transmitting traffic data and voice data over the forward and
reverse links. A method for transmitting traffic data in code
channel frames of fixed size is described in detail in U.S. Pat.
No. 5,504,773, entitled "METHOD AND APPARATUS FOR THE FORMATTING OF
DATA FOR TRANSMISSION," assigned to the assignee of the present
invention and incorporated by reference herein. In accordance with
the IS-95 standard, the traffic data or voice data is partitioned
into code channel frames which are 20 msec wide with data rates as
high as 14.4 Kbps.
[0008] A significant difference between voice services and data
services is the fact that the former imposes stringent and fixed
delay requirements. Typically, the overall one-way delay of speech
frames must be less than 100 msec. In contrast, the data delay can
become a variable parameter used to optimize the efficiency of the
data communication system. Specifically, more efficient error
correcting coding techniques which require significantly larger
delays than those that can be tolerated by voice services can be
utilized. An exemplary efficient coding scheme for data is
disclosed in U.S. Pat. No. 5,933,462 entitled "SOFT DECISION OUTPUT
DECODER FOR DECODING CONVOLUTIONALLY ENCODED CODEWORDS," filed Nov.
6, 1996, assigned to the assignee of the present invention and
incorporated by reference herein.
[0009] Another significant difference between voice services and
data services is that the former requires a fixed and common grade
of service (GoS) for all users. Typically, for digital systems
providing voice services, this translates into a fixed and equal
transmission rate for all users and a maximum tolerable value for
the error rates of the speech frames. In contrast, for data
services, the GoS can be different from user to user and can be a
parameter optimized to increase the overall efficiency of the data
communication system. The GoS of a data communication system is
typically defined as the total delay incurred in the transfer of a
predetermined amount of data, hereinafter referred to as a data
packet.
[0010] Yet another significant difference between voice services
and data services is that the former requires a reliable
communication link which, in the exemplary CDMA communication
system, is provided by soft handoff. Soft handoff results in
redundant transmissions from two or more base stations to improve
reliability. However, this additional reliability is not required
for data transmission because the data packets received in error
can be retransmitted. For data services, the transmit power used to
support soft handoff can be more efficiently used for transmitting
additional data.
[0011] The transmission delay required to transfer a data packet
and the average throughput rate of a communication system are
parameters that measure the quality and effectiveness of the data
communication system. Transmission delay does not have the same
impact in data communication as it does for voice communication,
but it is an important metric for measuring the quality of the data
communication system. The average throughput rate is a measure of
the efficiency of the data transmission capability of the
communication system.
[0012] It is well known that in cellular systems, the
signal-to-interference-and-noise ratio (SINR) of any given user is
a function of the location of the user within the coverage area. In
order to maintain a given level of service, time division multiple
access (TDMA) and frequency division multiple access (FDMA) systems
resort to frequency reuse techniques, i.e. not all frequency
channels and/or time slots are used in each base station. In a CDMA
system, the same frequency allocation is reused in every cell of
the system, thereby improving the overall efficiency. The SINR
measured at any given user's mobile station determines the
information rate that can be supported for this particular link
from the base station to the user's mobile station. Given the
specific modulation and error correction method used for the
transmission, a given level of performance is achieved at a
corresponding level of SINR. For an idealized cellular system with
hexagonal cell layouts and utilizing a common frequency in every
cell, the distribution of SINR achieved within the idealized cells
can be calculated.
[0013] In a system that is capable of transmitting data at high
rates, which will be referred to hereafter as a High Data Rate
(HDR) system, an open-loop rate adaptation algorithm is used to
adjust the data rate of the forward link. An exemplary HDR system
is described in U.S. Pat. No. 6,574,211 entitled "METHOD AND
APPARATUS FOR HIGH RATE PACKET DATA TRANSMISSION," assigned to the
assignee of the present invention and incorporated herein by
reference. The open-loop rate adaptation algorithm adjusts the data
rate in accordance with the varying channel conditions typically
found in a wireless environment. In general, an access terminal
measures the received SINR during periods of pilot signal
transmissions on the forward link. The access terminal uses the
measured SINR information to predict the future average SINR over
the next data packet duration. An exemplary prediction method is
discussed in U.S. Pat. No. 6,426,971 entitled, "SYSTEM AND METHOD
FOR ACCURATELY PREDICTING SIGNAL TO INTERFERENCE AND NOISE RATIO TO
IMPROVE COMMUNICATIONS SYSTEM PERFORMANCE assigned to the assignee
of the present invention and incorporated herein by reference. The
predicted SINR determines the maximum data rate that can be
supported on the forward link with a given probability of success.
Hence, the open-loop rate adaptation algorithm is the mechanism by
which the access terminal requests an access point to transmit the
next packet at the data rate determined by the predicted SINR. The
open-loop rate adaptation method has proven to be very effective in
providing a high throughput packet data system even in adverse
wireless channel conditions, such as a mobile environment.
[0014] However, the use of an open-loop rate adaptation method is
impaired by the implicit feedback delay associated with the
transmission of the rate request feedback to the access point. This
implicit delay problem is exacerbated when channel conditions
change rapidly, thus requiring the access terminal to update its
requested data rate several times per second. In a typical HDR
system, the access terminal would make approximately 600 updates
per second.
[0015] Other reasons exist for not implementing a pure open-loop
rate adaptation method. For example, the open-loop rate adaptation
method is highly dependent upon the accuracy of the SINR estimate.
Hence, imperfect SINR measurements would prevent the access
terminal from making a precise characterization of the underlying
channel statistics. One factor that would lead to imprecise channel
statistics is the feedback delay discussed above. Due to the
feedback delay, the access terminal must predict a supportable data
rate in the near future using past and present noisy SINR
estimates. Another factor that would lead to imprecise channel
statistics is the unpredictable, bursty nature of received data
packets. In a packet data cellular system, such bursts cause sudden
changes in the interference levels seen at the access terminal. The
unpredictability of the interference levels cannot be efficiently
accounted for by a pure open-loop rate adaptation scheme.
[0016] Another reason for not implementing a pure open-loop rate
adaptation method is an inability to minimize the effects of
errors. For example, when the prediction error for an estimated
SINR is large, as in the case of some mobile environments, the
access terminal will transmit a conservative data rate request in
order to ensure a low packet error probability. A low packet error
probability will provide low overall delays in the transmission.
However, it is probable that the access terminal could have
successfully received a higher data rate packet. There is no
mechanism in the open-loop rate adaptation method to update a data
rate request based on estimated channel statistics with a data rate
based on the actual channel statistics during the transmission of a
data packet. Hence, the open-loop rate adaptation method would not
provide a maximized throughput rate when the prediction error for
an estimated SINR is large.
[0017] Another example in which the open-loop rate adaptation
method fails to minimize the effects of an error is the instance
when the access terminal has incorrectly decoded a received packet.
The Radio Link Protocol (RLP) requires a retransmission request
when the access terminal incorrectly decodes a packet, but the
retransmission request is generated only after detecting a gap in
the received sequence number space. Therefore, the RLP protocol
requires the processing of a subsequent received packet after the
incorrectly decoded packet. This procedure increases the overall
transmission delay. Some mechanism is needed to implement a quick
retransmission of some or all of the code symbols contained in the
data packet, wherein the mechanism would enable the access terminal
to correctly decode the packet without incurring excessive
delays.
[0018] Hence, there exists a present need to modify the open-loop
rate adaptation method in order to minimize transmission delays and
to maximize the throughput rate as discussed above.
SUMMARY
[0019] The present invention is directed to a novel and improved
method and apparatus for modifying an open-loop rate adaptation
algorithm to produce a hybrid open loop/closed loop rate adaptation
scheme. An access point advantageously generates a time interleaved
structure for slots in data packets, allowing an access terminal to
transmit indicator messages to the access point during periods
associated with gaps inserted into the interleaved structure.
[0020] In one aspect of the invention, the periods associated with
the interleaved gaps are of sufficient duration to allow the access
terminal to decode the data carried in the slots and to send an
indicator message based on the decoded data. In an alternative
aspect of the invention, the indicator messages are based on an
estimated signal-to-interference-and-noise level.
[0021] In another aspect of the invention, the indicator messages
are one bit long, which is interpreted by the access point in
accordance with the timing of the arrival of the bit.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The features, objects, and advantages of the present
invention will become more apparent from the detailed description
set forth below when taken in conjunction with the drawings in
which like reference characters identify correspondingly throughout
and wherein:
[0023] FIG. 1 is a diagram of an exemplary one-slot gap interlaced
structure for multi-slot packets;
[0024] FIG. 2 is a diagram of an exemplary uniform N-slot gap
interlaced structure for multi-slot packets;
[0025] FIG. 3 is a diagram of an exemplary non-uniform N-slot gap
interlaced structure for multi-slot packets;
[0026] FIG. 4 is a diagram of an exemplary STOP control indication
for a multi-slot packet;
[0027] FIG. 5 is a diagram of an exemplary EXTEND control
indication for a multi-slot packet; and
[0028] FIG. 6 is a block diagram of an exemplary embodiment of the
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] In an exemplary embodiment of a data communication system,
forward link data transmission occurs from one access point to one
or more access terminals at the data rate requested by the access
terminal(s). Reverse link data communication can occur from one
access terminal to one or more access points. Data is partitioned
into data packets, with each data packet being transmitted over one
or more time slots. At each time slot, the access point can direct
data transmission to any access terminal in communication with the
access point.
[0030] Initially, the access terminal establishes communication
with an access point using a predetermined access procedure. In
this connected state, the access terminal can receive data messages
and control messages from the access point, and is able to transmit
data messages and control messages to the access point. The access
terminal then monitors the forward link for transmissions from the
access points in the active set of the access terminal. The active
set contains a list of access points in communication with the
access terminal. Specifically, the access terminal measures the
signal-to-interference-and-noise ratio (SINR) of the forward link
pilot from the access points in the active set, as received at the
access terminal. If the received pilot signal is above a
predetermined add threshold or below a predetermined drop
threshold, the access terminal reports this to the access point.
Subsequent messages from the access point direct the access
terminal to add or delete the access point to or from its active
set, respectively.
[0031] If there is no data to send, the access terminal returns to
an idle state and discontinues transmission of data rate
information to the access point(s). While the access terminal is in
the idle state, the access terminal periodically monitors the
control channel from one or more access points in the active set
for paging messages.
[0032] If there is data to be transmitted to the access terminal,
the data is sent by a central controller to all access points in
the active set and stored in a queue at each access point. A paging
message is then sent by one or more access points to the access
terminal on the respective control channels. The access point may
transmit all such paging messages at the same time across several
access points in order to ensure reception even when the access
terminal is switching between access points. The access terminal
demodulates and decodes the signals on one or more control channels
to receive the paging messages.
[0033] Upon decoding the paging messages, and for each time slot
until the data transmission is completed, the access terminal
measures the SINR of the forward link signals from the access
points in the active set, as received at the access terminal. The
SINR of the forward link signals can be obtained by measuring the
respective pilot signals. The access terminal then selects the best
access point based on a set of parameters. The set of parameters
can comprise the present and previous SINR measurements and the
bit-error-rate or packet-error-rate. For example, the best access
point can be selected based on the largest SINR measurement. The
access terminal then identifies the best access point and transmits
to the selected access point a data rate control message
(hereinafter referred to as the DRC message) on the data rate
control channel (hereinafter referred to as the DRC channel). The
DRC message can contain the requested data rate, or alternatively,
the quality of the forward link channel (e.g., the SINR measurement
itself, the bit-error-rate, or the packet-error-rate). In the
exemplary embodiment, the access terminal can direct the
transmission of the DRC message to a specific access point by the
use of a Walsh code that uniquely identifies the access point. The
DRC message symbols are exclusively OR'ed (XOR) with the unique
Walsh code. Since each access point in the active set of the access
terminal is identified by a unique Walsh code, only the selected
access point which performs the identical XOR operation as that
performed by the access terminal, with the correct Walsh code, can
correctly decode the DRC message. The access point uses the rate
control information from each access terminal to efficiently
transmit forward link data at the highest possible rate.
[0034] At each time slot, the access point can select any of the
paged access terminals for data transmission. The access point then
determines the data rate at which to transmit the data to the
selected access terminal based on the most recent value of the DRC
message received from the access terminal. Additionally, the access
point uniquely identifies a transmission to a particular access
terminal by appending an identifying preamble to a data packet
directed to an access terminal. In the exemplary embodiment, the
preamble is spread using a Walsh code that uniquely identifies the
access terminal.
[0035] In the exemplary embodiment, the forward link capacity of
the data transmission system is determined by the data rate
requests of the access terminals. Additional gains in the forward
link capacity can be achieved by using directional antennas and/or
adaptive spatial filters. An exemplary method and apparatus for
providing directional transmissions are disclosed in U.S. Pat. No.
5,857,147, entitled "METHOD AND APPARATUS FOR DETERMINING THE
TRANSMISSION DATA RATE IN A MULTI-USER COMMUNICATION SYSTEM," filed
Dec. 20, 1995, and U.S. Pat. No. 6,285,655 entitled "METHOD AND
APPARATUS FOR PROVIDING ORTHOGONAL SPOT BEAMS, SECTORS, AND
PICOCELLS," filed Sep. 8, 1997, both assigned to the assignee of
the present invention and incorporated by reference herein.
Fast Closed-Loop (FCL) Rate Control Adaptation
[0036] In an HDR system, an open-loop rate adaptation scheme uses a
fast feedback channel to allow a transmission of a DRC message from
an access terminal to an access point while the access point
concurrently transmits a data packet to the access terminal on the
forward data link. Hence, the access terminal can command the
access point to either terminate or extend the current transmission
in accordance with actual SINR conditions at the receiving access
terminal. In an exemplary embodiment, the fast feedback channel is
used to carry extra information as described below.
[0037] The forward link data rates in an HDR system vary from 38.4
kbps to 2.456 Mbps. The duration of each packet transmission in
number of slots as well as other modulation parameters are
described in Table 1. In this embodiment, a slot corresponds to a
period of 1.666 ms, or equivalently, 2048 chips transmitted at the
chip rate 1.2288 Mcps.
TABLE-US-00001 TABLE 1 Forward Link Modulation Parameters Data Rate
Data Rate Number of Bits per number (kbps) Slots Packet Code Rate
Modulation 1 38.4 16 1024 1/4 QPSK 2 76.8 8 1024 1/4 QPSK 3 102.4 6
1024 1/4 QPSK 4 153.6 4 1024 1/4 QPSK 5 204.8 3 1024 1/4 QPSK 6
307.2 2 1024 1/4 QPSK 7 614.4 1 1024 1/4 QPSK 8 921.6 2 3072 3/8
QPSK 9 1228.8 1 2048 1/2 QPSK 10 1843.2 1 3072 1/2 8PSK 11 2457.6 1
4096 1/2 16QAM
[0038] In an exemplary embodiment, the structure of the multi-slot
packets is modified to carry data in predetermined data slots, but
not in predetermined gap slots. When the multi-slot packets are
structured in accordance with the exemplary embodiment, the access
terminal that is receiving the multi-slot packet can utilize the
duration of the predetermined gap slots for other purposes. For
example, the access terminal can use the time between the data
slots to decide if the packet can be correctly decoded with the
soft code symbols accumulated thus far. The access terminal can use
various methods for determining whether the data slots have been
correctly decoded, these methods including, but not limited to,
checking the CRC bits associated with the data or estimating a
predicted SINR based on received SINR of pilot and traffic
symbols.
[0039] FIG. 1 is a diagram of an exemplary one-slot gap interlaced
structure for multi-slot packets, wherein the predetermined data
slots and the predetermined gap slots are interlaced in an
alternating pattern. This embodiment will be referred to hereafter
as a one-slot gap pattern. Multi-slot packet 100 is transmitted
from an access point to an access terminal with data contained in
alternating slots. For example, if the access terminal is
transmitting in accordance with Data Rate 2 from Table 1, then
there are 8 data slots in a multi-slot packet, and data would be
carried in slots 1, 3, 5, 7, 9, 11, 13, and 15. Slots 2, 4, 6, 8,
10, 12, 14, and 16 would not be used to transmit portions of the
multi-slot packet. A DRC message from the access terminal can be
transmitted to the access point during time periods associated with
the empty slots. In the above example, it should be clear that an
access point can transmit another data packet to the same or
different access terminal during the gap slots associated with the
transmission of the 8-slot packet example.
[0040] In addition to DRC messages, this embodiment permits the
transmission of indicator messages from the access terminal to the
access point, which indicates a reception status of the access
terminal, such indicator messages including, but not limited to
STOP indicator messages or EXTEND indicator messages. It should be
noted that the usage of indicator messages herein described for
this embodiment are applicable for other embodiments that
follow.
[0041] In an HDR system, code symbols that are transmitted in a
packet at data rates of 307.2 kbps and below are repeats of the
code symbols that are transmitted in a packet at 614.4 kbps. In
general, most of the code symbols transmitted in a given slot are
shifted repetitions of the code symbols transmitted in the first
slot of the packet. The lower data rates require a lower SINR for a
given low probability of packet error. Hence, if the access
terminal determines that channel conditions are not favorable, the
access terminal will transmit a DRC message requesting a data rate
below 614.4 kbps. The access point will then transmit multi-slot
packets in accordance with the structure described in FIG. 1.
However, if the actual channel conditions improve so that the
access terminal needs fewer repeated code symbols than originally
specified by the open-loop rate adaptation algorithm, the structure
described in FIG. 1 will allow the access terminal to transmit an
indicator message, such as a STOP indicator message, on the reverse
link feedback channel.
[0042] FIG. 2 is a diagram that illustrates the use of a STOP
indicator message. An access point transmits a data packet 200 in
accordance with the interleaved structure of FIG. 1. Slots n, n+2,
and n+4 are slots carrying data. A DRC message 210 is received
during slot period n-1, so that data in slots n, n+2, n+4, and n+6
are scheduled for transmission in accordance with the requested
data rate. A STOP indicator message 220 is transmitted by the
access terminal because the access terminal has received enough
repetitions of the code symbols in slots n, n+2, and n+4 to
determine the complete data without receiving any more repetitions
carried by n+6. Hence, the access terminal is ready to receive new
data. STOP indicator message 220 is received by the access point
during slot n+5. Upon receiving the STOP indicator message 220, the
access point will cease transmitting repetitions in the remaining
allocated data slot n+6 and begin the transmission of a new data
packet in slot n+6. Unused allocated slots can be reassigned to
another packet transmission directed toward any access terminal. In
this manner, a closed loop rate adaptation can be performed to
optimize resources when actual channel conditions allow for a
higher data rate than the one specified in the original DRC message
based on estimated channel conditions. In the example above, an
effective data rate 4/3 times higher than the original requested
data rate is achieved by sending the STOP indication.
[0043] In another aspect of this embodiment, an indicator message
can be sent from the access terminal to the access point to enable
more repetitions of the code symbols whenever the actual channel
conditions are worse than the estimated channel conditions. The
indicator message can be referred to as an EXTEND indicator
message. Another use for an EXTEND indicator message arises when a
one slot packet is incorrectly decoded by the access terminal. In
this case, the access terminal may transmit an EXTEND indicator
message requesting the retransmission of the data carried in a
specified slot. The structure of FIG. 1 allows the access point to
retransmit the data on the very next slot, referred to herein as an
extended data slot, following the decoding of the EXTEND indicator
message. FIG. 3 is an illustration of this use for an EXTEND
indicator message. Data packet 300 is constructed in accordance
with the structure of FIG. 1, so that alternating slots are
designated gap slots. A DRC message 310 is received by the access
point that provides the preferred rate for data transmitted in data
slot n. Data is also transmitted in slot n+2 in accordance with the
requested data rate. However, an EXTEND indicator message 320 is
received by the access point that orders data repetition at data
slot n+4 due to an error in decoding the data carried in slot
n+2.
[0044] In another aspect of this embodiment, single-slot packets
may be requested when the estimated SINR indicates a reduced
probability of packet success, for example, a probability of packet
success of 80-90%. Based on the received single-slot packet, the
access terminal can send an EXTEND indicator to the access point,
requesting retransmission of the packet, if the first single-slot
packet has not been decoded correctly. This aspect of the
embodiment has the advantage of an improved data throughput rate,
which is achieved by the initial transmission of a high data rate.
In accordance with this embodiment, the high data rate transmission
can be adjusted according to actual channel conditions. FIG. 3 also
illustrates this aspect of the invention. If the DRC message 310
carries a data request of 307.2 kbps, then data is transmitted in
slots n and n+2 at the requested rate. However, if the access
terminal detects an improvement in the channel conditions, the
access terminal can send a DRC message 330 carrying a data request
of 1.2 Mbps. The access point will then transmit a single-slot
packet at 1.2 Mbps in slot n+5. During the time associated with the
gap slot n+6, the access terminal detects a deterioration in the
channel conditions, which necessitates the retransmission of the
data in slot n+5. A EXTEND message 340 is transmitted and the
access point retransmits the data from slot n+5 in slot n+7.
[0045] In one exemplary embodiment, the access terminal may be
allowed to send up to N.sub.EXT(i) EXTEND indicator messages per
packet, where i=1, 2, . . . , 11 corresponds to one of the Data
Rates illustrated in Table 1.
[0046] The procedure described above for a closed loop rate
adaptation is exemplary in transmissions where the data packet
comprises one or two slots. It should be noted that the extended
data slot carries code symbols that are repetitions of previously
transmitted code symbols, and therefore, the code symbols in the
extended data slots may be advantageously soft-combined with the
previously received code symbols prior to the decoding step in
order to improve reliability. The identification of which code
symbols are to be transmitted in an extended data slot is an
implementation detail and does not affect the scope of this
invention.
[0047] The fast closed loop rate adaptation method described above
can be implemented to rely on the same fast feedback channel used
by the open loop rate adaptation scheme, but it should be noted
that another separate channel may also be used to implement the
closed loop rate adaptation method without altering the scope of
the invention.
[0048] Another aspect of implementation is the formulation of the
indicator messages. In an embodiment wherein only two indicator
messages, the STOP indicator message and the EXTEND indicator
message, are designated in the system, the system needs only use
one bit to carry the indicator message. DRC messages carry multiple
bits for rate selection and access point identification, but only
one bit is needed to indicate a STOP indicator message or an EXTEND
indicator message if the system discriminates the context of the
bit upon usage. For example, an indicator bit may be designated as
a FCL bit. If the access point detects the presence of the FCL bit
from an access terminal in slot n, then the access point will
interpret the FCL bit as a STOP indicator message if a data slot of
a multi-slot packet directed to this access terminal is scheduled
for transmission in slot n+1. However, the access point will
interpret the FCL bit as an EXTEND indicator message if a packet
scheduled to this access terminal and according to a requested data
rate ended exactly in slot n-1. Alternatively, the access point can
also interpret the FCL bit as an EXTEND indicator message if a
previous EXTEND indicator message caused the retransmission of a
slot of a specified packet exactly in slot n-1 and less than
N.sub.EXT EXTEND indicator messages have been processed for this
packet. If none of these situations are applicable, then the bit
can be discarded as a false alarm.
[0049] In another embodiment, the indicator messages can be
transmitted on the same feedback channel reserved for the open loop
DRC messages by using one of the reserved DRC codewords. However,
in this embodiment, the access terminal cannot simultaneously
transmit a DRC message and an indicator message such as a STOP
indicator message because only one message can be transmitted at a
time. Hence, the access terminal will be prevented from being
served another packet during the first slot released after the STOP
indication was sent. However, other access terminals may be served
in the first slot release. The efficiency of this embodiment is
then maximized if the access point serves many access terminals
since the probability that packets for a given access terminal
would be contiguously scheduled is reduced.
[0050] In another embodiment, the indicator messages can be
transmitted on a separate assigned channel, which can be created
using extra Walsh functions on the reverse link. This approach has
the extra advantage of allowing the access terminal to control the
reliability of the FCL channel to a desirable level. In the
embodiments described above, it should be observed that only one
access terminal should be transmitting at any given time.
Therefore, it is feasible to increase the power allocated to
transmit the indicator message without affecting reverse link
capacity.
[0051] As noted previously, the access point can maximize
efficiency by transmitting data to other access terminals during
the gap slots.
[0052] FIG. 4 is a diagram of an exemplary interlaced structure for
multi-slot packets, wherein the predetermined data slots and the
predetermined gap slots are interlaced in a uniform N-slot pattern.
This embodiment will be referred to hereafter as the uniform N-slot
gap pattern. Multi-slot packet 400 is transmitted from an access
point to an access terminal with the data contained in every
N.sup.th slot. N-1 slots are gap slots, wherein the access terminal
may use the delay associated with the gap slots to attempt decoding
the data received in the previous data slot. As is well known in
the art, blocks of data bits may be transmitted with coding to
enable the recipient of the data to determine the existence of any
errors in the data transmission. An example of such a coding
technique is the generation of cyclic redundancy check (CRC)
symbols. In one aspect of this embodiment, the delay caused by the
uniform insertion of gaps enables the access terminal to decode CRC
bits and to determine if the data slot was successfully decoded.
Rather than sending indicator messages based on SINR estimation,
the access terminal may send indicator messages based on the actual
success or failure of decoding a data slot. It should be noted that
the time needed to decode data is usually proportional to the
number of information bits contained in the packet. Thus, as seen
in Table 1, the higher data rate packets require more time for
decoding. When determining an optimal value for N, the worst case
delay must be taken into account when selecting the interlacing
period.
[0053] In another aspect of this embodiment, the delay caused by
the uniform insertion of gaps enables the access terminal to
determine the estimated SINR during the reception of the data slots
and transmit a DRC message advantageously.
[0054] In addition, extra slots of delay can be inserted in the
multi-slot packet to enable the access terminal to transmit
additional messages to the access point.
[0055] In a manner similar to the transmission of indicator
messages for the one-slot gap pattern embodiment, STOP indicator
messages and EXTEND indicator messages can be used in the uniform
N-slot gap pattern. In addition, the formulation of the indicator
messages can be accomplished using only one bit, if the system
discriminates the context of the bit upon usage. For example, an
indicator bit may be designated as a FCL bit. If the access point
detects the presence of the FCL bit from an access terminal in slot
n, then the access point will interpret the FCL bit as a STOP
indicator message if a data slot of a multi-slot packet directed to
this access terminal is scheduled for transmission in slot n+1.
However, the access point will interpret the FCL bit as an EXTEND
indicator message if a packet scheduled to this access terminal,
according to a requested data rate, ended exactly in slot n-p+1,
wherein p is the period of the assigned data slots to an access
terminal. Alternatively, the access point can also interpret the
FCL bit as an EXTEND indicator message if a previous EXTEND
indicator message caused the retransmission of a slot of a
specified packet exactly in slot n-p+1, and less than N.sub.EXT
EXTEND indicator messages have been processed for this packet. If
none of these situations are applicable, then the bit can be
discarded as a false alarm.
[0056] FIG. 5 is a diagram of another exemplary interlaced
structure for multi-slot packets, wherein the predetermined data
slots and the predetermined gap slots are interlaced in a
non-uniform slot pattern. This embodiment of the invention will be
referred to hereafter as the non-uniform N-slot gap pattern.
Multi-slot packet 500 is structured so that delays interlaced
between data slots are a function of the data rate. The number of
gap slots required between data slots of a packet at rate i, say
N(i), is fixed and known by all access terminals and access point.
Although this embodiment allows for the latency of each data rate
packet to be minimized, there are a certain number of constraints
that the access point must satisfy when scheduling the packets for
transmission. One such constraint is the prevention of overlapping
data slots.
[0057] As an example of the non-uniform slot pattern, the DRC
messages of FIG. 5 can be used to transmit data in staggered
patterns. In this example, DRC message 510 requests that data
transmitted in slots n-2, n+2, and n+6 be transmitted at 204.8
kbps. DRC message 520 requests that data is transmitted in slots
n+1 and n+3 at 921.6 kbps. DRC message 530 requests that data is
transmitted in slot n+8 at 1.2 Mbps. Although the individual DRC
messages are for periodic transmissions, the periodic transmissions
are combined to create an aperiodic, non-uniform pattern. It should
be noted that there is a constraint as to the data pattern
initiated by DRC message 520. A two-slot data packet with a one
slot gap in between the pair of data slots could have been
scheduled to begin transmission at n+1 or n-1, but not at n. If the
pattern had begun at n, then the current slot n+3 data would have
been transmitted at slot n+2, which would have overlapped the data
slot pattern scheduled with DRC message 510.
[0058] In a manner similar to the transmission of indicator
messages for the one-slot gap pattern embodiment, STOP indicator
messages and EXTEND indicator messages can be used in the
non-uniform N-slot gap pattern. In addition, the formulation of the
indicator messages can be accomplished using only one bit, if the
system discriminates the context of the bit upon usage. For
example, an indicator bit may be designated as a FCL bit. If the
access point detects the presence of the FCL bit from an access
terminal in slot n, then the access point will interpret the FCL
bit as a STOP indicator message if a data slot of a multi-slot
packet directed to this access terminal is scheduled for
transmission in slot n+1. However, the access point will interpret
the FCL bit as an EXTEND indicator message if a packet scheduled to
this access terminal, according to a requested data rate, ended
exactly in slot n-N(i), wherein N(i) is the number of gap slots
required between data slots and i indicates a data rate index
number. Alternatively, the access point can also interpret the FCL
bit as an EXTEND indicator message if a previous EXTEND indicator
message caused the retransmission of a slot of a specified packet
exactly in slot n-N(i) and less than N.sub.EXT EXTEND indicator
messages have been processed for this packet. If none of these
situations are applicable, then the bit can be discarded as a false
alarm.
[0059] Various advantages are achieved when using the uniform slot
gap pattern over the non-uniform slot gap pattern and vice versa. A
system using the uniform slot gap pattern could achieve maximum
slot efficiency by staggering periodic patterns across all slots.
For example, in a uniform pattern wherein slots n, n+4, n+8, . . .
are assigned to one access terminal, a second access terminal can
be assigned slots n+1, n+5, n+9, . . . , a third access terminal
can be assigned slots n+2, n+6, n+10, . . . , and a fourth access
terminal can be assigned slots n+3, n+7, n+11, . . . . In this
manner, all slots are fully utilized to increase the efficiency of
the network. However, in certain circumstances, it may be more
desirable to implement a non-uniform slot gap pattern. For example,
during high speed data transmissions, only one slot of data is
transmitted with large amounts of code symbols. In such cases, the
access terminal would require a relatively long duration to decode
the received code symbols. Hence, the implementation of a uniform
slot pattern would require correspondingly large periods with large
amounts of gap slots, which would not be efficient. Under this
circumstance, a non-uniform gap slot pattern may be preferable.
[0060] FIG. 6 is a block diagram of an apparatus for performing FCL
rate control in an HDR system. Access terminal 701 performs SINR
estimation and prediction at SINR estimation element 722 based on
the strength of the received forward link signal from access point
700. The results from SINR estimation element 722 are sent to open
loop rate control element 723, which implements the open loop rate
control algorithm in order to select a data rate in accordance with
the results from SINR estimation element 722. The open loop rate
control element 723 generates a DRC message to be sent over the
reverse link to the access point 700. The DRC message is decoded at
the DRC decoder 713 and the results are sent to the scheduler 712
so that the access point 700 can schedule data transmission at the
specified requested rate in the slot following the decoding of the
DRC message. It should be noted that the elements so far described
are performing the open loop rate adaptation algorithm described
above. The FCL rate control process is implemented by the scheduler
712 with the generation of interlaced packets as described above
and the closed loop rate control element 725, which optionally
allows the access terminal 701 to implement an FCL rate
adaptation.
[0061] In FIG. 6, a one-slot gap pattern is implemented by
scheduler 712 to serve two access terminals simultaneously. Thus,
the access point 700 maintains two independent buffers, transmit
buffer A 710 and transmit buffer B 711, in order to maintain the
code symbols needed to generate a new slot repetition or slot
extension. It should be noted that more transmit buffers may be
utilized in accordance with the embodiments described herein.
[0062] Access point 700 transmits a data packet to access terminal
701. While receiving the data packet, the access terminal 701 may
feed the results from the SINR estimation element 722 to the closed
loop rate control element 725 or alternatively, the access terminal
701 may feed the results from the decoder 720 to the closed loop
rate control element 725. Buffer 721 may be inserted to aid in the
ordered delivery of decoded information from the decoder 720 to the
upper layer protocols, which will not be described herein. The
closed loop rate control element 725 can use results from either
the decoder 720 or the SINR estimation element 722 to determine
whether to generate an indication message. The indication message
is transmitted on the reverse link to the access point 700, wherein
an FCL indicator decoder 714 decodes the indicator message and
feeds the decoded indicator message to the scheduler 712. The
scheduler 712, DRC decoder 713, and the FCL indicator decoder 714
at access point 700 can be implemented as separate components or
can be implemented using a single processor and memory. Likewise,
the decoder 720, buffer 721, SINR estimation element 722, open loop
rate control element 723, and the closed loop rate control element
725 at the access terminal 701 can be implemented as separate
elements or can be combined on a single processor with memory.
[0063] Outer loop rate control element 724 may be inserted to
compute long term error statistics. The results of such statistical
computations can be used to determine a set of parameters that can
be used adjust both the open loop rate control element 723 and the
closed loop rate control element 725.
[0064] As discussed herein, the FCL rate adaptation method may
decide to send an indicator message, such as a STOP indicator
message or an EXTEND indicator message, to an access point. This
method provides a fast correction mechanism to compensate for
inaccuracies of the open loop rate control scheme. A multi-slot
packet transmission can be stopped when there is sufficient
information to decode the packet. Alternatively, a slot of an
on-going multi-slot packet transmission can be repeated when
successful decoding is not guaranteed.
[0065] The FCL rate adaptation method also improves the throughput
rate by allowing the open loop rate control scheme to be aggressive
in requesting one-slot packets at higher rates, since the FCL rate
adaptation method allows for the transmission of an extended slot
of data if a high rate packet cannot be decoded successfully.
Throughput is also improved when the FCL rate adaptation method
stops a multi-slot packet earlier than expected by the open loop
rate control algorithm.
[0066] For example, an open loop rate control scheme can be
designed so that the open loop rate control selects high rates
using one-slot packets with a packet error rate (PER) of
approximately 15% after the end of the first slot and a PER of at
most 1% at the end of the extended slot. An extended slot would add
at least 3 dB of average SINR in addition to any time diversity
gain and puncturing loss reduction. For multi-slot packets, the
open loop rate control algorithm can target a PER of 1% at the
normal end of the packet. Hence, there would be a large probability
of packet success with a reduced number of slots, which corresponds
to a higher than expected rate. In addition, an extended slot would
provide an extra margin for successful decoding if necessary, thus
reducing the requirement of a delayed retransmission. It should be
noted that SINR values for optimal efficiency will vary according
to the various modulation techniques implemented in the network, so
that the possible implementation of various SINR values as
threshold values are not intended to limit the scope of the
embodiments described herein.
[0067] In addition, the decision on whether to generate a STOP,
EXTEND, or no FCL indication based upon SINR calculations should
not be very aggressive, otherwise the probability of packet errors
would be dominated by the probability that the closed loop rate
control algorithm will erroneously assume that a packet can be
correctly decoded.
[0068] The previous description of the preferred embodiments is
provided to enable any person skilled in the art to make or use the
present invention. The various modifications to these embodiments
will be readily apparent to those skilled in the art, and the
generic principles defined herein may be applied to other
embodiments without the use of the inventive faculty. Thus, the
present invention is not intended to be limited to the embodiments
shown herein but is to be accorded the widest scope consistent with
the principles and novel features disclosed herein.
* * * * *