WO2001022646A1

WO2001022646A1 - Cumulative acknowledgement transmission in an automatic repeat request

Info

Publication number: WO2001022646A1
Application number: PCT/IB2000/001263
Authority: WO
Inventors: Fujio Watanabe; Antti Lappetelainen
Original assignee: Nokia Corporation; Nokia Inc.
Priority date: 1999-09-20
Filing date: 2000-09-06
Publication date: 2001-03-29
Also published as: AU6719200A

Abstract

In the ETSI/BRAN HiperLAN2 protocol, timing is defined at which a receiver transmits an automatic repeat request control protocol data unit (ARQ C-PDU) data with cumulative acknowledgement (CumAck) data to a transmitter so that the transmitter does not transmit protocol data units (PDUs) having sequence numbers outside a designated sequence of PDUs. Also, the receiver transmits ARQ C-PDU data with CumAck to the transmitter if no PDUs within the designated sequence have been detected for a threshold amount of time or if such ARQ C-PDU data with CumAck has not been transmitted from the receiver to the transmitter for the threshold amount of time in order to update the bottom of the receiving window.

Description

CUMULATIVE ACKNOWLEDGMENT TRANSMISSION IN AN AUTOMATIC REPEAT REQUEST

TECHNICAL FIELD The present invention relates to a method and system for determining when to transmit a selective automatic repeat request (SR-ARQ) with cumulative acknowledgment information

(CumAck) from a receiving node to a transmitting node in a data packet network including,

but not limited to, an ETSI (European Telecommunications Standards Institute) BRAN

(broadband radio access network) Hiper LAN (local area network) -2.

Digital communication techniques have been provided to increase bandwidth efficiency in communication systems in order to more efficiently utilize the spectrum allocated to the

particular communication system.

Digital communication techniques obviously require that the data to be communicated be digitized. One such communication technique requires that the data be formatted into data

packets. These data packets can be communicated at discrete intervals and, once transmitted, concatenated together to recreate the information content contained therein.

Because data packets can be communicated at discrete intervals, a communication

channel need not be dedicated solely for the communication of packet data generated by a

transmitting station to receiving station as conventionally required in circuit-switched

communications. Instead, a single channel can be shared amongst a plurality of different transmitting and receiving station-pairs. Because a single channel can be utilized to effectuate communications by the plurality of pairs of communication stations, improved communication

capacity is possible.

In some digital communication systems, a random access channel is defined upon to

permit the communication of the packet of data. A transmitter which is to send a data packet is permitted random access to the random access channel. While such a scheme advantageously provides a simple manner by which to effectuate communication of data

packets, lack of coordination between separate sending stations might result in two sending stations attempting to transmit a packet of data simultaneously. In the event of such a collision, the data packets transmitted at the overlapping times by the separate communication

stations interface with one another, thus preventing successful communication of either data

packet.

A slotted ALOHA technique is an existing random access protocol for data packet communication on a random access channel. In such protocol, when a data packet is successfully transmitted to a receiver, the receiver returns a feedback acknowledgment to the

transmitter to inform the transmitter of the successful communication of the data packet. If,

also, a determination is made at the receiver of faulty transmission of the data packet or a

collision or other such errors resulting from transmission of the data packet on the random access channel, the feedback acknowledgment returned to the transmitter indicates an unsuccessful transmission.

Responsive to a feedback acknowledgment of an unsuccessful transmission, the data

packet is to be retransmitted by the transmitter.

Back-off schemes, such as a binary exponential back-off scheme, have been implemented to minimize the occurrence of collisions by exploiting the feedback acknowledgments returned by a receiver. Back-off schemes generally provide an improved

manner of effectuating retransmission of data packets from such transmitters. A transmitter,

also referred to as a terminal, is referred to as being backlogged if a prior transmission of the data packet is not successfully received at a receiver.

Data packet communications are effectuated, for instance, in conventional LAN's (local are networks). Wireless networks, operable in manners analogous to, wired LANs have also been developed and are utilized to communicate packets of data over a radio link upon which a random access channel is defined.

For example, a broadband radio access network (BRAN) standard promulgated by the ETSI (European Telecommunications Standards Institute) set forth a standard for operation of

a wireless LAN operable in the 5GHz range. In this standard, a medium access control

(MAC) frame structure is defined. The MAC frame structure includes a BCH (broadcast channel), a DLCH (down-link channel), a ULCH (up-link channel), and a RACH (random

access channel). An IBCH (inland control channel) is sometimes defined upon the BCH or

upon the DLCH. the IBCH is a logical channel. In the system defined by BRAN, as well as

other wireless LANs, mobile terminals are utilized by users of the network to effectuate

telephonic communications. The telephonic communications include, but are not limited to, voice and data communications.

In the system defined by the BRAN standard a mobile terminal transmits data packets

to an access point (AP) on the random access channel. The AP forms a portion of the

infrastructure of the LAN. If a determination is made that the data packet is successfully

transmitted to the infrastructure, the AP responds with a feedback acknowledgment indicating the successful delivery of the data packet. If, conversely, a collision or other error resulting in

unsuccessful transmission occurs, the AP returns a feedback acknowledgment indicating the

occurrence of the unsuccessful transmission,.

For example, in Fig. 1, communication system 100 provides for the communication of

packet data between a mobile terminal, or transmitter, 200 and a receiver, or access point, 300. The communication system 100 forms a multi-user communication system in which the

transmitter 200 is one of a plurality of transmitters capable of sending data packets upon a random access channel (RACH) 400. In communication system 100, RACH 400 is defined upon a radio link formed between the transmitter 200 and the receiver 300. In other

implementations, other types of communication systems can be similarly shown.

Again, the transmitter 200 is representative of a mobile terminal or sending station

which is able to send data packets, such a request packets, upon a RACH, and the receiver

300 is representative of an access point which is able to receive the packet data and return a feedback acknowledgment indicating whether the data packets have been successfully

communicated thereto.

The feedback acknowledgment returned by the receiver 300 is transmitted on a

broadcast channel (BCH) and/or inband control channel 500, and indicates whether or not the

data packets have been successfully communicated to the receiver 300 from the transmitter 200. Unsuccessful communication of the data packets is attributable, for instance, to

collisions during transmission of the packet data, as described above. Uplink (ULCH) and

Downlink (DLCH) channels 600 are defined in the system for communicating data between

the transmitter 200 and the receiver 300.

In the ETSI/BRAN HiperLAN-2 example of Fig. 1, the communication system is representative of a wireless LAN (local area network). The receiver 300 is installed at a

location in an interior of a building, for example, and is capable of communicating with

transmitters, including mobile units, such a transmitter 200, when positioned within the

coverage area defined by receiver 300. While no presently shown, other receivers are

disposed to define other coverage areas such as different floors of the building structure, for example. The receiver 300 is coupled to controller 700 which is able to control

communications in the communication system 100. Controller 700 may, in turn, be coupled to

other communication systems, including a macrocellular communication system, a public- switched telephonic network (PSTN), a TCP/IP network, as examples.

In the ETSI/BRAN HiρerLAN-2, each protocol data unit (PDU), which are data

packets, is identified by a sequence number (SN), having ten (10) bits therein, ranging from 0 to 1023 per packet. A transmitter will transmit PDUs in ascending SN order, from SN=0 to

SN=1023, as shown in 1 in Fig. 2. Accordingly, it does become necessary for SNs of respective PDUs to be repeated, that is there may be PDUs having the same SN but corresponding to a different packet. However, such repeating of SNs may result in

transmitters and/or receivers being unable to distinguish different PDUs having the sane SN.

Thus, to avoid such confusion of PDUs having the same SN, transmitting windows and

receiving windows are employed by the transmitter and receiver, respectively. Transmitting and receiving windows are specified ranges of PDUs which the transmitter can transmit and

the receiver can receive at a given time.

As seen in Fig. 3, the transmitting window 2 is an interval k which is bounded by the

bottom of the transmitting window (BMtx) 3 and the top of the transmitting window (TPtx) 4,

and the boundaries of the transmitting window 2 are maintained by the transmitter. Similarly,

Fig. 4 shows a receiving window 5 which also is an interval k which is bounded by the bottom of the receiving window (BMrx) 6 and the top of the receiving window (TPrx) 7, and the

boundaries of the transmitting window 5 are maintained by the transmitter.

As described above, both the transmitting window 2 and the receiving window 5 are

defined in terms of interval k, and thus, the size of the transmitting window 2 and the receiving window 5 are the same. The size of the interval £ which defines the transmitting and receiving windows is set between the transmitter and receiver during an association phase, with the

smaller window size k requested by either the transmitter or the receiver being adopted as the

interval k which defines both the transmitting window 2 and the receiving window 5. The minimum and maximum window sizes are defined as 16 and 512 PDUs, respectively.

Description of selective automatic repeat request processing in accordance with the

ETSI/BRAN HiperLAN-2 protocol follows in the form of an example, corresponding to Fig.

5. First of all, in the association phase, the size of the transmitting and receiving windows

is set as interval k, which is cooperatively determined by the transmitter and receiver, in the

association phase, as being the smaller interval size requested by either the transmitter or

receiver. Accordingly, the transmitting window 2 and receiving window 5 are set as being the same size, that is the length of interval k=16, for example. Also, the bottom of the transmitting window (BMtx) 3 and the bottom of the receiving window (BMrx) 6 are set to be the same sequence number (SN), whereby BMtx=BMrx=SN=8 in the present example.

Similarly, the top of the transmitting window (TPtx) 4 and the top of the receiving window

(TPrx) 7 are set to be the same SN, whereby Tptx=TPrx=SN=23 in the present example.

Transmission of PDUs from the transmitter then begins with transmission of PDUs in the transmitting window 2, ranging from SN=8 to SN=23, in ascending order. Then, when the

receiver receives the PDUs from the transmitter, the receiver checks if all PDUs within the

receiving window 5 have been received.

In the present example of Fig. 5, the receiver determines that PDUs SN=10 and

SN=12 are missing, and is further unable to determine whether PDUs SN>15 are missing or have not been sent from the transmitter. Thus, according to standard SR-ARQ procedures, the receiver transmits ARQ C-PDU data to the transmitter, wherein the ARQ C-PDU may

selectively include cumulative acknowledgment (CumAck) data which indicates the lowest SN

in which is missing PDU has been detected. In the present example, the CumAck indicates

SN=10. That is, the receiver informs the transmitter that it has correctly received PDUs within the receiving window up until SN=9.

Fig. 6 shows an example of an uplink 10 in ETSI/BRAN HiperLAN 2 sent from a receiver/mobile terminal (MT) to a transmitter/access point (AP), in which one bit known as a cumulative acknowledgment indicator (CAI) 11 is provided to indicate that the ARQ C-PDU

includes CumAck.

The CumAck described in correspondence with HiperLAN2 indicates that all PDUs

below the specified SN have been correctly received within the receiving window. The

significance of CumAck is that, in wireless transmission, errors can frequently occur whereby the SN of PDUs sent within the transmitting window are not matched with the corresponding

SN of the receiving window.

However presently, when the transmitter transmits PDUs which are not within the

receiving window, the receiver merely discards such erroneous PDUs, and thus there is no

mechanism provided which immediately informs the transmitter of the asynchronous relationship between the transmitter and the receiver to thus enable the transmitting window

and receiving windows to be synchronized upon the detection of erroneous or missing PDUs

received within the receiving windows.

DISCLOSURE OF INVENTION

Therefore, it is an object of the present invention to improve the ETSI BRAN

HiperLAN 2 protocol, which is described above, by defining a time at which the receiver

transmits ARQ C-PDU data with CumAck to the transmitter so that the transmitter does not

transmit PDUs having sequence numbers outside the receiving windows.

It is a further object of the present invention to provide an ETSI/BRAN HiperLAN2 protocol in which the receiver transmits ARQ C-PDU data with CumAck to the transmitter if no PDUs within the receiving window have been detected for a threshold amount of time or if

such ARQ C-PDU data with CumAck has not been transmitted from the receiver to the transmitter for the threshold amount of time.

Thus, according to the present invention, the time at which a receiver must send an

automatic repeat request (ARQ) to a transmitter is determined as follows. First, a transmitter

and a receiver cooperatively define a uniform size for a transmitting window maintained by

said transmitter and said receiver, respectively. The transmitting and receiving windows are both predetermined intervals of specified packet data units (PDUs) in which PDUs can be transmitted and received at one time.

The transmitter then transmits the PDUs within said transmitting window. Next, the

receiver receives the PDUs from said transmitter, checks that the received PDUs are within

said receiving window, detects any missing or erroneous PDUs from said receiving window, and transmits an automatic repeat request control packet data unit (ARQ C-PDU) to said

transmitter at a predetermined time.

BRIEF DESCRIPTION OF THE DRAWINGS

The scope of the present invention will be apparent from the following detailed description, when taken in conjunction with the accompanying drawings, and such detailed

description, while indicating preferred embodiments of the invention, are given as illustrations

only, since various changes and modifications within the spirit and scope of the invention will

become apparent to those skilled in the art from this detailed description, in which:

Fig. 1 is an exemplary block diagram of a packet data communication system; Fig. 2 is an example of a continuous PDU stream in a HiperLAN2 protocol; Fig. 3 is an example of a transmitting window in a HiperLAN2 protocol; Fig. 4 is an example of a receiving window in a HiperLAN2 protocol;

Fig. 5 is an example of a transmission/receiving/ ARQ sequence in a HiperLAN2

protocol;

Fig. 6 is an example of an uplink ARQ C-PDU frame format transmitted from a receiver to a transmitter.

Fig. 7 shows an example of PDU reception from a transmitter at a receiver, according to the present invention;

Fig. 8 shows an example of an ARQ C-PDU with CumAck transmission from a

receiver in accordance with the present invention;

Fig. 9 shows a further example of an ARQ C-PDU with CumAck transmission within a

threshold amount of time from a receiver in accordance with the present invention; and

Fig. 10 shows an example of an ARQ C-PDU with CumAck transmission in response

to a discard message.

BEST MODE FOR CARRYING OUT THE INVENTION

According to current HiperLAN2 specifications, the time at which the receiver is to transmit ARQ C-PDU with CumAck to the transmitter is not defined. Thus, the present

invention defines the time at which the receiver transmits ARQ C-PDU with CumAck so that

the CumAck can help synchronize the transmitting and receiving windows.

The transmission of ARQ C-PDU with CumAck by a receiver to a transmitter,

according to the present invention, is described by way of example, as shown in Fig. 7.

Similar to the example shown in Fig. 5, the receiving window 5 in Fig. 7 has been defined as having an interval £=16, with BMrx SN=8 and TPrx SN=23. When the receiver

begins to receive PDUs from the transmitter, the receiver first detects PDU SN=6, which is beneath the BMrx of the receiving window, and further detects PDU SN=26 which is above

the TPrx of the receiving window 5. Accordingly, the receiver discards PDUs SN=6 and 26 since they are outside of the receiving window 5. Then the receiver transmits ARQ C-PDU with CumAck 12 to the transmitter, with the CumAck indicating SN=8 which is the BMrx. That is, the receiver is indicating that PDUs SN>7 which are outside of the receiving window

5 have been correctly received by the receiver.

Thus, if at least one of the PDUs within the receiving window 5 has not been correctly

received by the receiver, or in the case that the receiver has not transmitted an ARQ C-PDU

with CumAck for a threshold amount of time, the receiver must transmit the ARQ C-PDU

with CumAck before the threshold account of time has elapsed.

Fig. 8 shows an example of an ARQ C-PDU with CumAck transmission from a

receiver in accordance with the present invention.

An independent rule for the an example of an ARQ C-PDU with CumAck transmission

from a receiver in accordance with the present invention transmission from the receiver to the transmitter is to transmit the ARQ C-PDU with CumAck when the time

{ ARQ_time_threshold} has passed from the most recent ARQ C-PDU with CumAck

transmission, and/or there is a possibility to shift the receiver bottom window by at least

{ ARQ_C-PDU_threshold} whereby { ARQ_time_threshold} is measured as the time in which

the receiver receives the threshold amount of PDUs from the transmitter. More specifically, if

the threshold amount of time {ARQ_time_threshold} passes without the receiver having received any PDUs within the receiving window 5, the receiver updates the bottom of the

receiving window and transmits ARQ C-PDU with CumAck to the transmitter indicating that

SN=BMrx.

Optimal values for parameters of {ARQ time threshold} and {ARQ C- PDU_threshold} vary, depending on the wireless system and the device capabilities of the

receiver. In the ETSI/BRAN HiperLAN2 wireless protocol, the values depend, for example, on the interval size k set by the transmitter and receiver during the association phase, an ARQ

processing delay class, and used link adaptation mode. Fig. 9 shows example of an ARQ C-PDU with CumAck transmission within a threshold amount of time from a receiver in accordance with the present invention. In the

example of Fig. 9, the interval k indicating the size of the transmitting window 2 and receiving

window 5 is set at k=512, with BMrx SN=0 and TPrx SN=511, and the threshold time in

which the receiver must transmit an ARQ C-PDU with CumAck to the transmitter is 16 PDUs. That is, the threshold amount of time is the time required for the receiver to receive 16

PDUs from the transmitter.

Since PDU SN=3 is shown as missing/erroneous in Fig. 8, the transmitter transmits

ARQ C-PDU with CumAck=3, indicating that all PDUs less than SN=2 have been received

correctly at the receiver. The transmitter then retransmits the missing PDUs based on the ARQ C-PDU with CumAck=3, and the receiver then transmits ARQ C-PDU with CumAck=7, indicating that all PDUs less than SN=6 have been received correctly at the receiver.

However, during the transmission of the next 16 PDUs, the receiver does not receive

any PDUs from the transmitter. If the connection between the transmitter and receiver is still

open, the receiver must transmit the ARQ C-PDU with CumAck to the transmitter so that the transmitter can update the transmitting window 2, in terms of BMtx and Tptx. That is, the threshold {ARQ_time_threshold} and {ARQ_C-PDU_threshold} is presently defined, as an

example, as the transmission time for 16 PDUs, by which time the receiver must transmit the ARQ C-PDU with CumAck to the transmitter.

Furthermore, in the event that the transmitter transmits discard data to the receiver, instructing that all PDUs below the specified SN be discarded, the receiver transmits the ARQ

C-PDU with CumAck to the transmitter indicating that all PDUs below the specified SN have

been discarded.

Fig. 10 shows an example of an ARQ-C-PDu with CumAck transmission in response to a discard message. In the example, the transmitter transmits a discard message 20

instructing the discard of all PDUs below SN=16, and thus PDUs SN<16 are to be discarded

from the transmitter and receiver. Thus, when the receiver receives the discard message 20,

the receiver discards all PDUs SN<16 and then transmits an ARQ C-PDU with CumAck SN=17, which indicates that subsequent to the discard of all PDUs with SN<16, SN=17 is the next erroneous or missing PDU. It is noted that the receiver discards the discard message if

the discard message itself includes an error.

While the present invention has been described in detail and pictorially in the

accompanying drawings, it is not limited to such details since many changes and modifications may be made thereto without departing from the spirit and scope of the present invention. It is intended that all such modifications fall within the scope of the following claims.

Claims

WE CLAIM

1. A method for determining when a receiver must send a repeat request to a transmitter, said method comprising the steps of: defining a transmitting window at said transmitter and a receiving window at

said receiver; transmitting, from said transmitter, protocol data units within said transmitting

window; receiving the protocol data units from said transmitter at said receiver; checking, at said receiver, that the received protocol data units are within said

receiving window;

detecting, at said receiver, any missing or erroneous protocol data units from

said receiving window; and transmitting, from said receiver, control data of a repeat request to said transmitter at a predetermined time.

2. A method according to Claim 1, wherein the predetermined time at which said

receiver transmits said control data of a repeat request to said transmitter is defined as the amount of time necessary for a predetermined number of protocol data units to be transmitted from said transmitter.

3. A method according to Claim 1, wherein the size of said transmitting window

and said receiving window is determined as being an interval of sequential protocol data units to be transmitted and received at once, each of the sequential protocol data units being assigned as ascending sequential number.

4. A method according to Claim 3, wherein said control data of a repeat request includes cumulative acknowledgment data which indicates a sequential number of one of said

protocol data units received at said receiver, said control data of a repeat request indicating that all protocol data units received at said receiver having a sequential number less than the

indicated sequential number have been received without error.

5. A method according to Claim 4, wherein said receiver transmits said control

data of a repeat request with cumulative acknowledgment data to said transmitter when said receiver determines that one of said protocol data units received from said transmitter is

outside said receiving window.

6. A method according to Claim 4, wherein said receiver transmits said control

data of a repeat request with cumulative acknowledgment data to said transmitter when said

receiver determines that one of said protocol data units received from said transmitter is

missing from said receiving window.

7. A method according to Claim 4, wherein said receiver transmits said control

data of a repeat request to said transmitter continuously until said receiver receives said

protocol data units correctly.

8. A method according to Claim 4, wherein said receiver updates said receiving window when said receiver has not received any protocol data units from said transmitter for

the predetermined amount of time, and transmits said control data of a repeat request to said transmitter indicating the update of said receiving window.

9. A communication system for effectuating retransmission of protocol data units,

comprising: a transmitter; and a receiver; wherein:

said transmitter and said receiver cooperatively define a size for a transmitting window maintained by said transmitter and said receiver, respectively,

said transmitter transmits protocol data units within said transmitting

window, said receiver receives the protocol data units from said transmitter at

said receiver, checks that the received protocol data units are within said receiving window,

detects any missing or erroneous protocol data units from said receiving window, and

transmits control data of a repeat request to said transmitter at a predetermined time.

10. A system according to Claim 9, wherein the predetermined time at which said

receiver transmits said control data of a repeat request to said transmitter is defined as the

amount of time necessary for a predetermined number of protocol data units to be transmitted

from said transmitter.

11. A system according to Claim 9, wherein the size of said transmitting window

and said receiving window is determined as being an interval of sequential protocol data units

to be transmitted and received at once, each of the sequential protocol data units being assigned as ascending sequential number.

12. A system according to Claim 11, wherein said control data of a repeat request

includes cumulative acknowledgment data which indicates a sequential number of one of said protocol data units received at said receiver, said control data of a repeat request indicating that all protocol data units received at said receiver having a sequential number less than the

indicated sequential number have been received without error.

13. A system according to Claim 12, wherein said receiver transmits said control data of a repeat request with cumulative acknowledgment data to said transmitter when said receiver determines that one of said protocol data units received from said transmitter is

outside said receiving window.

14. A system according to Claim 12, wherein said receiver transmits said control data of a repeat request to said transmitter when said receiver determines that one of said protocol units is missing from said receiving window.

15. A system according to Claim 12, wherein said receiver transmits said control

data of a repeat request to said transmitter continuously until said receiver receives said protocol data units correctly.

16. A system according to Claim 12, wherein said receiver updates said receiving

window when said receiver has not received any protocol data units from said transmitter for