U.S. patent application number 12/610546 was filed with the patent office on 2010-02-25 for method and an apparatus for a quick retransmission of signals in a communication system.
This patent application is currently assigned to QUALCOMM Incorporated. Invention is credited to Rashid A. Attar, Peter J. Black, Eduardo A.S. Esteves, Ahmad Jalali, Nagabhushanan T. Sindhushayana.
Application Number | 20100046497 12/610546 |
Document ID | / |
Family ID | 24191316 |
Filed Date | 2010-02-25 |
United States Patent
Application |
20100046497 |
Kind Code |
A1 |
Jalali; Ahmad ; et
al. |
February 25, 2010 |
METHOD AND AN APPARATUS FOR A QUICK RETRANSMISSION OF SIGNALS IN A
COMMUNICATION SYSTEM
Abstract
A method and an apparatus for quick retransmission of signals in
a communication system are disclosed. A transmitting terminal,
e.g., a base station, transmits signals in a form of packets to a
receiving terminal, e.g., a subscriber station. The receiving
terminal determines if the packet was intended for the receiving
terminal, and if so, the receiving terminal demodulates the packet.
The receiving terminal then computes a quality metric of the
packet, and compares the computed quality metric with a quality
metric contained in the packet. If the quality metrics match, the
packet is declared correctly received, and is forwarded for further
processing. If the quality metrics fail to match, the receiving
terminal sends a request for retransmission of the packet. The
transmitting terminal determines which packet needs to be
retransmitted based on the request for retransmission. The
transmitting terminal then schedules the packet for
retransmission.
Inventors: |
Jalali; Ahmad; (San Diego,
CA) ; Esteves; Eduardo A.S.; (San Diego, CA) ;
Sindhushayana; Nagabhushanan T.; (San Deigo, CA) ;
Black; Peter J.; (San Diego, CA) ; Attar; Rashid
A.; (San Diego, CA) |
Correspondence
Address: |
QUALCOMM INCORPORATED
5775 MOREHOUSE DR.
SAN DIEGO
CA
92121
US
|
Assignee: |
QUALCOMM Incorporated
San Diego
CA
|
Family ID: |
24191316 |
Appl. No.: |
12/610546 |
Filed: |
November 2, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11518329 |
Sep 7, 2006 |
7613978 |
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12610546 |
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|
10712582 |
Nov 12, 2003 |
7127654 |
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11518329 |
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09549017 |
Apr 14, 2000 |
6694469 |
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10712582 |
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Current U.S.
Class: |
370/345 |
Current CPC
Class: |
H04L 1/1877 20130101;
H04L 1/1848 20130101; H04L 1/1809 20130101; H04L 1/1692 20130101;
H04L 1/188 20130101; H04L 1/1887 20130101 |
Class at
Publication: |
370/345 |
International
Class: |
H04J 3/00 20060101
H04J003/00 |
Claims
1. A method for wireless communication, comprising: receiving a
request for data at a data rate; determining an amount of data
transmitted at the data rate; and transmitting the amount of data
in multiple forward link timeslots.
2. The method of claim 1, wherein: a preamble is transmitted in
each of the multiple forward link timeslots.
3. The method of claim 1, wherein: a preamble is transmitted in
only a first of the multiple forward link timeslots.
4. A method for wireless communication, comprising: decoding units
of signal transmitted in multiple forward link timeslots; if the
units of signal are incorrectly decoded, transmitting a short
acknowledgment; and setting a timer for the short acknowledgment to
await retransmission of the units of incorrectly decoded
signal.
5. The method of claim 4 further comprising: if the incorrectly
decoded units of signal are not retransmitted prior to expiration
of the timer, designating a radio link protocol (RLP) layer for
retransmission.
6. The method of claim 4, wherein: each unit of signal is assigned
a sequence number.
7. An apparatus for wireless communication, comprising: a receiver
operative to receive a request for data at a data rate; a processor
operative to determine an amount of data transmitted at the data
rate; and a transmitter operative to transmit the amount of data in
multiple forward link timeslots.
8. The apparatus of claim 7, wherein: the transmitter is further
operative to transmit a preamble in each of the multiple forward
link timeslots.
9. The apparatus of claim 7, wherein: the transmitter is further
operative to transmit a preamble in only a first of the multiple
forward link timeslots.
10. An apparatus for wireless communication, comprising: a decoder
operative to decode units of signal transmitted in multiple forward
link timeslots; a transmitter operative, if the units of signal are
incorrectly decoded, to transmit a short acknowledgment; and a
timer operative to be set for the short acknowledgment to await
retransmission of the units of incorrectly decoded signal.
11. The apparatus of claim 10 wherein: the apparatus is further
operative to designate a radio link protocol (RLP) layer for
retransmission if the incorrectly decoded units of signal are not
retransmitted prior to expiration of the timer.
12. The apparatus of claim 10, wherein: the apparatus is further
configured to assign a sequence number to each unit of signal.
13. An apparatus for wireless communication, comprising: receiver
means operative to receive a request for data at a data rate;
processor means operative to determine an amount of data
transmitted at the data rate; and transmitter means operative to
transmit the amount of data in multiple forward link timeslots.
14. The apparatus of claim 13, wherein: the transmitter means is
further operative to transmit a preamble in each of the multiple
forward link timeslots.
15. The apparatus of claim 13, wherein; the transmitter means is
further operative to transmit a preamble in only a first of the
multiple forward link timeslots.
16. An apparatus for wireless communication, comprising: decoder
means operative to decode units of signal transmitted in multiple
forward link timeslots; transmitter means operative, if the units
of signal are incorrectly decoded, to transmit a short
acknowledgment; and timer means operative to be set for the short
acknowledgment to await retransmission of the units of incorrectly
decoded signal.
17. The apparatus of claim 16 wherein: the apparatus is further
operative to designate a radio link protocol (RLP) layer for
retransmission if the incorrectly decoded units of signal are not
retransmitted prior to expiration of the timer.
18. The apparatus of claim 16, wherein: the apparatus is further
configured to assign a sequence number to each unit of signal.
Description
CLAIM OF PRIORITY UNDER 35 U.S.C. .sctn.120
[0001] The present Application for Patent is a divisional
application and claims priority to patent application Ser. No.
11/518,329 entitled "METHOD AND AN APPARATUS FOR A QUICK
RETRANSMISSION OF SIGNALS IN A COMMUNICATION SYSTEM" filed Sep. 7,
2006, U.S. Pat. No. 7,127,654, issued on Oct. 24, 2006, which is a
continuation application of U.S. Pat. No. 6,694,469, issued on Feb.
17, 2004, and assigned to the assignee hereof and hereby expressly
incorporated by reference herein.
BACKGROUND
[0002] 1. Field
[0003] The current invention relates to communication. More
particularly, the present invention relates to a novel method and
apparatus for quick retransmission of signals in a communication
system.
[0004] 2. Background
[0005] In a communication system, a communication channel through
which signals travel between transmitting and receiving terminals
is subject to various factors, changing characteristics of the
communication channel. In wireless communication systems these
factors comprise, but are not limited to: fading, noise,
interference from other terminals, and the like. Consequently,
despite extensive error control coding, certain packets are missed
or received erroneously at a receiving terminal. Unless defined
differently, a packet is a unit of a signal comprising a preamble,
a payload, and a quality metric. Therefore, Automatic
Retransmission reQuest (ARQ) schemes are often used at the link
layer of communication systems to detect missing or erroneously
received packets at the receiving terminal, and request
retransmission of these packets at the transmitting terminal. An
example of an ARQ is a Radio Link Protocol (RLP). RLP is a class of
error control protocols known as NAK-based ARQ protocols, which are
well known in the art. One such RLP is described in
TIA/EIA/IS-707-A.8, entitled "DATA SERVICE OPTIONS FOR SPREAD
SPECTRUM SYSTEMS: RADIO LINK PROTOCOL TYPE 2," hereinafter referred
to as RLP2, and incorporated herein by reference.
[0006] Existing ARQ schemes achieve retransmission of missing or
erroneously received packets by utilizing a sequence number unique
to each packet. When a receiving terminal detects a packet with a
sequence number higher than an expected sequence number, the
receiving terminal declares packet(s) with sequence number(s)
between the expected sequence number and the detected packet's
sequence number missing or erroneously received. The receiving
terminal then sends a control message requesting retransmission of
the missing packets to a transmitting terminal. Alternatively, the
transmitting terminal may resend the packet after a certain timeout
interval if the transmitting terminal has not received a positive
acknowledgement from the receiving terminal.
[0007] Consequently, existing ARQ schemes cause a large delay
between the first transmission of a packet and a subsequent
retransmission. The ARQ does not declare a particular packet
missing or erroneously received until the next packet, containing a
sequence number higher then an expected sequence number is received
or until the timeout interval expires. This delay results in a
large variance in the end-to-end delay statistics, which has a
further detrimental effect on the network throughput. Transport
layer protocols, such as the transport control protocol (TCP),
implement a congestion control mechanism, which reduces the number
of outstanding packets in a network based on the variance of the
round-trip delay estimate. In effect, larger variance of delay
results in a reduction of the amount of traffic that is admitted
into the network and a subsequent reduction in throughput of a
communication system.
[0008] One approach to reducing the delay and the delay's variation
is to avoid retransmissions by ensuring that the first transmission
is received correctly with high probability. However, this approach
requires a large amount of power, which in turn reduces
throughput.
[0009] Based on the foregoing, there exists a need in the art for
an ARQ mechanism with low retransmission delay.
SUMMARY
[0010] The present invention is directed to a method and an
apparatus for quick retransmission (QARQ) of signals in a
communication system.
[0011] In accordance with one aspect of the invention, a receiving
terminal determines a quality metric of a packet of received
signal. The receiving terminal immediately sends a short
acknowledgement (SA) to a transmitting terminal in accordance with
the quality metric of the packet. If the quality metric indicates
that the packet was incorrectly received, then the SA is termed
negative acknowledgement (NAK); otherwise, the SA is termed
positive acknowledgement (ACK) or acknowledgement.
[0012] In another aspect of the invention, there exists a
determinable relationship between a particular packet and the SA;
therefore, there is no need for the SA to contain an explicit
indication as to which packet is to be retransmitted.
[0013] In accordance with another aspect of the invention, the SA
is a bit of energy.
[0014] In accordance with another aspect of the invention, the
transmitting terminal attempts retransmission of the packet a
predetermined number of times.
[0015] In accordance with yet another aspect of the invention, a
conventional, sequence-number-based ARQ is employed together with
the QARQ scheme.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] 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:
[0017] FIG. 1 is a block diagram of an exemplary communication
system;
[0018] FIG. 2 is an illustration of an exemplary forward link
signal structure;
[0019] FIG. 3 is a flowchart of an exemplary method of data
processing at the transmitting terminal;
[0020] FIG. 4 is a flowchart of an exemplary method of data
processing at a receiving terminal;
[0021] FIG. 5 is a detailed block diagram of the communication
system of FIG. 1; and
[0022] FIG. 6 is a diagram showing timing associated with packet
processing at a receiving terminal in accordance with an embodiment
of the invention.
DETAILED DESCRIPTION
[0023] FIG. 1 illustrates an exemplary communication system 100
capable of implementing embodiments of the invention. A first
terminal 104 transmits signals to a second terminal 106 over a
forward link 108A, and receives signals from the second terminal
106 over a reverse link 108B. The communication system 100 can be
operated bi-directionally, each of the terminals 104 and 106
operating as a transmitter unit or a receiver unit, or both
concurrently, depending on whether data is being transmitted from,
or received at, the terminal. In a wireless cellular communication
system embodiment, the first terminal 104 can be a base station
(BS), the second terminal 106 can be a mobile station (MS) such as
a phone, a laptop computer, a personal digital assistant and the
like. The forward link and reverse link can be electromagnetic
spectra.
[0024] In general, a link comprises a set of channels carrying
logically distinct types of information. These channels can be
transmitted according to a time division multiplex (TDM) scheme, a
code division scheme (CDM), or a combination of the two. In the TDM
scheme, the channels are distinguished in time domain. The forward
link consists of time slots in a periodic train of time intervals,
and the channels are transmitted in the time slots. Consequently,
the channels are transmitted one at a time. In the code division
scheme, the channels are distinguished by a pseudorandom orthogonal
sequence; consequently, the channels can be transmitted
simultaneously. A code division scheme is disclosed in U.S. Pat.
No. 5,103,459, entitled "SYSTEM AND METHOD FOR GENERATING SIGNAL
WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM" assigned to the
assignee of the present application and incorporated by reference
herein.
[0025] In one embodiment of the invention, a forward link comprises
a set of channels, e.g., a pilot channel, a medium access channel,
a traffic channel, and a control channel. The control channel is a
channel carrying signals to be received by all MSs monitoring the
forward link. In one embodiment of the invention, data being
carried on the traffic channel, including both first time
transmissions and quick retransmissions, can be demodulated without
information provided on a control channel. In another embodiment,
the control channel may carry information necessary for
demodulation of the data being carried on the traffic channel. For
a forward link signal structure of an exemplary embodiment of the
invention, refer to FIG. 2.
[0026] In one embodiment of the invention, the reverse link
comprises a set of channels, e.g., a traffic channel and an access
channel. The reverse traffic channel is dedicated to transmission
from a single MS to the BSs comprising a network. The reverse
access channel is used by the MSs to communicate with the BSs in
the network when the MSs do not have traffic channel.
[0027] For simplicity, communication system 100 is shown to include
one BS 104 and one MS 106 only. However, other variations and
configurations of the communication system 100 are possible. For
example, in a multi-user, multiple access communication system, a
single BS may be used to concurrently transmit data to a number of
MSs. In addition, in a manner similar to soft-handoff, disclosed in
U.S. Pat. No. 5,101,501, entitled "METHOD AND SYSTEM FOR PROVIDING
A SOFT HANDOFF IN COMMUNICATIONS IN A CDMA CELLULAR TELEPHONE
SYSTEM," assigned to the assignee of the present application and
incorporated by reference herein, a MS may concurrently receive
transmissions from a number of BSs. The communication system of the
embodiments described herein may include any number of BSs and MSs.
Consequently, each of the multiple BSs is connected to a base
station controller (BSC) 102 through a backhaul similar to backhaul
110. The backhaul 110 can be implemented in a number of connection
types including, e.g., a microwave or wire-line E1 or T1, or
optical fiber. A connection 112 connects the wireless communication
system 100 to a public switched data network (PSDN), which is not
shown.
[0028] In an exemplary embodiment, each MS monitors signal quality
metric of signals received from BSs. A MS (for example MS 106)
receiving forward link signals from multiple BSs identifies the BS
associated with the highest quality forward link signal (for
example BS 104). The MS 106 then generates a prediction of a data
rate at which the packet error rate (PER) of packets received from
the selected BS 104 will not exceed a target PER. An exemplary
embodiment uses a target PER of approximately 2%. The MS 106 then
computes a rate at which a "tail probability" is greater than or
equal to the target PER. The tail probability is the probability
that the actual signal quality during the packet transmission
period is less than the signal quality required for successful
decoding of a packet correctly at a given rate. The MS 106 then
sends a message on the reverse link specifically to the selected BS
104, requesting data rate at which the specific selected base
station may transmit forward link data to the MS 106.
[0029] In one embodiment of the invention, the message is sent on a
data rate control channel (DRC). DRC is disclosed in application
Ser. No. 08/963,386 entitled: "A METHOD AND AN APPARATUS FOR HIGH
RATE DATA TRANSMISSION," now U.S. Pat. No. 6,574,211, issued Jun.
3, 2003, assigned to the assignee of the present invention, and
incorporated herein by reference.
[0030] In another embodiment of the invention, a dedicated reverse
link medium access channel (R-MACCH) is utilized. The R-MACCH
carries the DRC information, a reverse rate indicator (RRI) and SA
information.
[0031] In an exemplary embodiment, the BS 104 monitors the reverse
channel from one or more MSs and transmits data on forward link to
no more than one destination MS during each forward link transmit
time slot. The BS 104 selects a destination MS (for example MS 106)
based on a scheduling procedure designed to balance the grade of
service (GoS) requirements of each MS with the desire to maximize
throughput of the system 100. In an exemplary embodiment, the BS
104 transmits data to the destination MS 106 only at the rate
indicated by the most recent message received from the destination
MS. This restriction makes it unnecessary for the destination MS
106 to perform rate detection on the forward link signal. The MS
106 need only determine whether it is the intended destination MS
during a given time slot.
[0032] In an exemplary embodiment, BSs transmit a preamble within
the first time slot of each new forward link packet. The preamble
identifies the intended destination MS. Once a destination MS
establishes that it is the intended destination for data in a slot,
the MS begins decoding the data in the associated time slot. In an
exemplary embodiment, the destination MS 106 determines the data
rate of the data in the forward link based on the request message
the MS 106 sent. The number of forward link time slots used to
transmit a packet varies based on the data rate at which the packet
is sent. Packets sent at a lower rate are sent using a greater
number of time slots.
[0033] Once the MS 106 determines that the data are intended for
the MS 106, the MS 106 decodes the packet and evaluates a quality
metric of the received packet. Quality metric of a packet is
defined by a formula in accordance with a content of the packet,
e.g., a parity bit, a cyclic redundancy check (CRC), and the like.
In one embodiment of the invention, the quality metric is a CRC.
The evaluated quality metric and the quality metric contained in
the received packet are compared, and based on the comparison an
appropriate SA is generated. As discussed with reference to FIG. 5,
the SA in an exemplary embodiment can comprise only one bit.
[0034] In one embodiment, the SA is ACK based, i.e., an ACK message
is sent from a MS to a BS if a packet is correctly decoded and no
message is sent if the packet is incorrectly decoded.
[0035] In another embodiment the SA is NAK based, i.e., a NAK
message is sent from a MS to a BS if a packet is incorrectly
decoded, and no message is sent if the packet is correctly decoded.
An advantage of this approach is that high reliability and low
noise interference with other reverse links, as well as energy
saving at the MS, can be achieved. As discussed, because a BS is
transmitting a packet intended to only one MS, at most this MS
sends NAK, thus achieving a low interference on the reverse link.
In a well-designed system, the probability of the MS incorrectly
decoding the packet is low. Furthermore, if the NAK is a bit of
zero energy, the NAK contains low energy. Therefore, the MS can
allocate large amounts of power to the infrequent transmission of
the NAK bit.
[0036] In yet another embodiment, an ACK is a first value of energy
and a NAK is a second value of energy.
[0037] The SA is then sent to the BS 104 over a channel on the
reverse link 108b. In one embodiment of the invention, the reverse
link channel is a DRC.
[0038] In another embodiment of the invention, a code channel
orthogonal to the reverse link can be advantageously utilized.
Because a BS is transmitting a packet intended for only one MS, at
most this MS sends a SA, thus achieving a low interference on the
reverse link. In a well-designed system, the probability of the MS
incorrectly decoding the packet is low. Furthermore, if the SA is
an ACK as a bit of zero energy or a NAK as a bit of zero energy,
the orthogonal channel contains low energy. Therefore, the MS can
allocate a large amount of power to the infrequent transmission of
the SA bit, guaranteeing high reliability and low interference with
the reverse link.
[0039] In yet another embodiment of the invention, a dedicated
reverse link medium access channel (R-MACCH) is utilized. The
R-MACCH carries the DRC, the RRI and the ACK/NAK information.
[0040] The BS 104 detects the SA and determines whether a
retransmission of the packet is necessary. If the SA indicates that
a retransmission is necessary, the packet is scheduled for
retransmission, otherwise, the packet is discarded.
[0041] In an exemplary embodiment, the aforementioned QARQ scheme
cooperates with the RLP as will be disclosed in the following
description.
[0042] FIG. 2 shows the forward link signal structure transmitted
by each base station in an exemplary high data rate system. Forward
link signals are divided into fixed-duration time slots. In an
exemplary embodiment, each time slot is 1.67 milliseconds long.
Each slot 202 is divided into two half-slots 204, with a pilot
burst 208 transmitted within each half-slot 204. In an exemplary
embodiment, each slot is 2048 chips long, corresponding to a 1.67
millisecond slot duration. In an exemplary embodiment, each pilot
burst 208 is 96 chips long, and is centered at the mid-point of its
associated half-slot 204. A reverse link power control (RPC) signal
206 is transmitted to either side of the pilot burst in every
second half-slot 204b. In an exemplary embodiment, the RPC signal
is transmitted in the 64 chips immediately before and the 64 chips
immediately after the second pilot burst 208b of each slot 202, and
is used to regulate the power of the reverse link signals
transmitted by each subscriber station. In an exemplary embodiment,
forward link traffic channel data are sent in the remaining
portions of the first half-slot 210 and the remaining portions of
the second half-slot 212. In an exemplary embodiment, preamble 214
is 64 chips long and is transmitted with each packet. Because the
traffic channel stream is intended for a particular MS, the
preamble is MS specific.
[0043] In an exemplary embodiment, a control channel is transmitted
at a fixed rate of 76.8 kbps and the control channel is time
division multiplexed on the forward link. Because the control
channel messages are directed to all MSs, the control channel's
preamble is recognizable by all the MS.
[0044] FIG. 3 is an exemplary flowchart of a method for a BS using
QARQ to transmit or retransmit a packet to a MS. At step 300, the
BS receives a payload unit intended for transmission to a MS.
[0045] At step 302 the BS determines whether the payload unit is a
payload unit to be transmitted or a payload unit to be
retransmitted. As discussed with reference to FIG. 1, the
retransmission request can be initiated only by the RLP at this
step.
[0046] If the payload unit is to be transmitted, the method
continues in step 304, in which the payload unit is provided to a
first time queue.
[0047] If the payload unit is to be retransmitted, the method
continues in step 306, in which the payload unit is provided to a
retransmission queue.
[0048] At step 308, the BS assembles payload units intended for a
particular MS to a packet a structure of which is determined in
accordance with a transmission data rate. The data rate at which
the packet is sent is based on a feedback signal received over the
reverse link from the destination MS. If the data rate is small,
then the packet (called a multiple-slot packet) of data is
transmitted in multiple forward link time slots. In an exemplary
embodiment, a preamble is transmitted within a new packet. The
preamble enables identification of the intended destination MS
during decoding. In an exemplary embodiment, only the first time
slot of the multiple-slot packet is transmitted with the preamble.
The preamble could alternatively be transmitted in every forward
link time slot.
[0049] At step 310, the BS transmits the packet in accordance with
a scheduler order as discussed with reference to FIG. 1.
[0050] After the packet has been transmitted, the BS tests at step
312 if a SA corresponding to the transmitted packet was received.
As disclosed with reference to FIG. 6, the BS knows when to expect
the SA.
[0051] If an ACK is received (or a NAK is not received) in the
expected time slot, the method continues at step 314. At step 314,
the packet is removed from the first time slot and the
retransmission queues, and the packet is discarded.
[0052] If a NAK is received (or an ACK is not received) in the
expected time slot, the method continues at step 316. At step 316,
parameters controlling retransmission are tested. The parameters
assure that a particular packet will not be retransmitted
repeatedly, thus increasing buffer requirements and decreasing
throughput of a communication system. In one embodiment, the
parameters comprise, e.g., the maximum number of times a packet can
be retransmitted and the maximum time for which a packet can remain
in the first-time queue after the packet has been transmitted. If
the parameters were exceeded, the packet is removed from the first
time and the retransmission queues, and the packet is discarded at
step 318. In this scenario, the QARQ retransmission processing
ends, and the packet may be retransmitted upon request from the RLP
processor as discussed with reference to FIG. 6. If the parameters
were not exceeded, the packet is rescheduled for retransmission at
step 320.
[0053] FIG. 4 is an exemplary flowchart of a method for a MS using
QARQ to generate a response to a BS. At step 400, the MS receives a
packet from the BS.
[0054] At step 402, the preamble of the packet is extracted. The
preamble is compared with a reference preamble at step 404. The
packet is discarded if the preamble indicates that the packet is
intended for another MS at step 406, and the flow returns to step
400 to wait for another packet. If the preamble indicates that the
packet is intended for the MS, the MS decodes the packet and
evaluates a quality metric of the received packet at step 408.
[0055] At step 410, the evaluated quality metric and the quality
metric contained in the received packet are compared. If the
evaluated quality metric and the quality metric contained in the
received packet do not match, an appropriate SA is sent at step
412. In the exemplary embodiment, the SA is a NAK, represented by a
bit of non-zero energy. A timer for the SA sent is started at step
414. The purpose of the timer is to limit a period for which the MS
waits for retransmission of the payload units of the incorrectly
decoded packet. In the exemplary embodiment, if the payload units
of the incorrectly decoded packet are not received within the timer
expiration period for the NAK associated with the incorrectly
decoded packet, the QARQ processing is aborted, and the RLP handles
the missing payload units. See steps 416-432 and accompanying
description.
[0056] If a packet was correctly decoded at step 410, an
appropriate SA is sent at step 416. In an exemplary embodiment, the
SA is a bit of no energy. The payload unit(s) contained in the
packet are then stored in a buffer at step 418.
[0057] At step 420, the RLP sequence number of the payload units is
tested against expected values of the RLP sequence number.
[0058] If the RLP sequence number indicates contiguity, it means
that all the payload units of the packet transmitted to the MS were
properly received. Consequently, all the payload units with
contiguous sequence numbers contained in the buffer are provided to
an RLP layer at step 420.
[0059] If the RLP sequence number indicates non-contiguity, the
timer, corresponding to the last NAK sent (which was started at
step 414), is checked at step 422. If the timer has not expired,
the MS waits for retransmission of the missing payload units or
expiration of the timer for the last NAK sent.
[0060] If the timer for a particular NAK, and, consequently a
particular set of missing payload unit expired, the QARQ scheme for
these payload units is aborted. All payload units stored in the
buffer with sequence number higher than the missing payload units
associated with the particular NAK and lower than the missing units
associated with the next NAK (if any) are provided to an RLP layer
at step 424.
[0061] At step 426, the RLP layer checks the sequence numbers of
the delivered payload units. If the sequence number indicates
contiguity, the RLP layer delivers data from the buffer to a data
sink at step 428. Otherwise, the RLP layer generates RLP messages
requesting retransmission of the missing units at step 430. In one
embodiment of the invention, the RLP message requests
retransmission of all of the missing units in the buffer. In
another embodiment, the message requests retransmission of only the
latest detected missing payload units.
[0062] At step 432, the message is transmitted over the reverse
link to the serving BS.
[0063] FIG. 5 shows a detailed block diagram of the communication
system 100 of FIG. 1. Data to be delivered to the MS 106 arrive at
the BSC 102 through the connection 112 from the PSDN (not shown).
The data are formatted into payload units under the control of a
RLP processor 504. Although an RLP processor is shown in the
embodiment, other protocols, allowing retransmission based on
sequence number methods can be utilized. In one embodiment of the
invention, the payload unit is 1024 bits long. The RLP processor
504 also supplies a distributor 502 with information as to which
packets have been requested for retransmission. The retransmission
request is delivered to the RLP processor 504 through the RLP
message. The distributor 502 distributes payload units through a
backhaul to the BS, which serves the MS for which the data are
intended. The distributor 502 receives information about location
of the MS from the BS which serves the MS through the backhaul.
[0064] The payload units that arrived at the BS 104 through the
backhaul 110 are provided to a distributor 506. The distributor 506
tests whether the payload units are new payload units or payload
units provided by the RLP processor 504 for retransmission. If the
payload units are to be retransmitted, the payload units are
provided to a retransmission queue 510. Otherwise, the payload
units are provided to a first time queue 508. The payload units are
then assembled into packets in accordance with a data rate
requested by the MS 106, as described with reference to FIG. 1.
[0065] Assembled packets are provided to a scheduler 512. The
scheduler 512 cooperates with a QARQ controller 518 on assigning
priority between the first time packets and the packets intended
for retransmission to the MS 106. The packet transmitted to the MS
106 remains in the queues 508 and 510, while the BS 104 waits for a
SA from the MS 106.
[0066] The packets arriving at the MS 106 over the forward link
108a are provided to a preamble detector 520, which detects and
decodes a preamble of the packets. The preamble is provided to a
processor 521, which compares the decoded preamble to a reference
preamble. The packet is discarded if the preamble indicates that
the packet is intended for another MS; otherwise, the packet is
provided to a decoder 522, which decodes the packet. The decoded
packet is provided to a processor 521, which evaluates a quality
metric of the packet. The evaluated quality metric and the quality
metric contained in the received packet are compared, and based on
the comparison, an SA generator 526 generates an appropriate SA.
Though the preamble detector 520, the decoder 522, and the
processor 521 are shown as separate elements, one skilled in the
art will appreciate that the physical distinction is made for
explanatory purposes only. The preamble detector 520, the decoder
522, and the processor 521 may be incorporated into, single
processor accomplishing the above-mentioned processing.
[0067] If a packet was incorrectly decoded, i.e., the evaluated
quality metric and the quality metric contained in the received
packet do not match, the SA is sent and a timer 530 for the SA is
started. In the exemplary embodiment, the SA is a NAK represented
by a bit of non-zero energy. The purpose of the timer 530 is to
limit a period, for which the MS 106 waits for retransmission of
the payload units of the incorrectly decoded packet. If the payload
units of the incorrectly decoded packet are not received within the
timer 530 expiration period for the NAK associated with the
incorrectly decoded packet, the QARQ processing is aborted. A
retransmission of the missing payload units is handled by an
RLP.
[0068] If a packet was correctly decoded, the payload unit(s)
contained in the packet are stored in a buffer 528. The RLP
sequence number of the payload unit(s) contained in the packet is
checked by the decoder 522 against an expected value of the RLP
sequence number. If the RLP sequence number indicates contiguity,
all the payload units with contiguous sequence numbers contained in
the buffer 528 are provided to a RLP processor 526. Otherwise, the
timer 530, corresponding to the last NAK sent, is checked. If the
time has not expired, the payload units are stored in the buffer
528, and the MS 106 waits for retransmission of the missing payload
units or expiration of the timer 530 for the last NAK sent. If the
timer 530 for a particular NAK, and, consequently a particular set
of missing payload unit expired, all payload units in the buffer
528 with sequence number higher than the missing units associated
with the particular NAK and lower than the missing units associated
with the next NAK--if any--are provided to a RLP processor 526.
[0069] The RLP processor 526 checks the sequence numbers of the
delivered payload units. If the sequence number indicates
contiguity, the RLP processor 524 delivers data from the buffer 528
to the data sink 534. Otherwise, the RLP processor 526 instructs
RLP message generator 532 to generate RLP message requesting
retransmission of the missing units. In one embodiment of the
invention, the RLP message requests retransmission of all of the
missing units in the buffer 528. In another embodiment, the message
requests retransmission of only the latest detected missing payload
units. The message is then transmitted over the reverse link 108b
to the BS 104.
[0070] The data containing a SA and arriving at the BS 104 over the
reverse link are provided to a SA detector 514 and an RLP message
detector 516.
[0071] If the received data contain an ACK, which is detected in a
SA detector 514, the QARQ controller 518 removes the packet
associated with the ACK from the queues 508 and 510.
[0072] If a NAK is received, the QARQ controller 518 checks whether
parameters controlling retransmission were exceeded. In the
exemplary embodiment, the parameters comprise a maximum number of
times a packet can be retransmitted and a maximum time for which a
packet can remain in the first-time queue 508 after the packet has
been transmitted. If the parameters were exceeded, the QARQ
controller 518 removes the packet form the queues 508 and 510.
Otherwise, the QARQ controller 518 instructs the scheduler 512 that
the packet be rescheduled for transmission with higher priority.
The packet is moved from the first-time queue 508 to the
retransmission queue 510 if the QARQ controller 518 determines that
the non-acknowledged packet resides in the first time queue
510.
[0073] If the received data contain an RLP retransmission request,
which is detected by an RLP message detector 516, the RLP message
detector 516 provides the RLP message to the RLP processor 504
through the backhaul 110. The RLP processor then initiates the
procedure for re-transmitting the packet in accordance with the RLP
implemented.
[0074] FIG. 6 illustrates a relationship between a packet received
at a MS 106 and a SA transmitted from the MS 106. In slots n-4,
n-3, a receiver at the MS 106 receives a packet over the forward
channel link 108A, and determines if the packet was intended for
the MS 106. The MS 106 discards the packet if the packet was not
intended for the MS 106. Otherwise, the MS 106 decodes the packet,
evaluates a quality metric of the packet, and compares the
evaluated quality metric with the quality metric contained in the
packet in slots n-2, n-1. In slot n, a transmitter at the MS 106
sends a SA back to the BS 104 over the reverse channel link 108B.
In slot n+1, the SA received at the BS 104 is decoded and provided
to a QARQ controller. In slots n+2, n+3 the BS 104 retransmits the
packet if so requested. The position of the slots on the received
forward link channel 108A and the reverse link channel 108B is
synchronized at the MS 106. Therefore, the relative position of
slots on the forward channel link 108a and the reverse channel link
108B is fixed. The BS 104 can measure a round trip delay between
the BS 104 and the MS 106. Consequently, the time slot in which the
SA must arrive at the BS 104 can be ascertained, provided that a
relation between the received packet processing and the SA is
determinable.
[0075] In one embodiment of the invention, the relation between the
received packet processing and the SA is determinable by fixing the
number of slots between receiving a packet and sending a SA back,
i.e., slots n-2, n-1. Consequently, the BS 104 can associate each
packet with each SA. One skilled in the art will understand that
FIG. 5 is meant only to illustrate the concept. Consequently, the
number of slots allocated for a particular event may change, e.g.,
decoding and evaluating of a packet's quality metric may occur in
more or less than two slots. Furthermore, certain events are
inherently variable, e.g., length of a packet, delay between the SA
reception and the packet retransmission.
[0076] In another embodiment of the invention, the relation between
the received packet processing and the SA is determinable by
including information as to which packet is to be retransmitted
into the SA.
[0077] 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.
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