Pulse or digital communications – Transmitters
Reexamination Certificate
2001-01-10
2004-09-28
Tran, Khai (Department: 2631)
Pulse or digital communications
Transmitters
C370S469000
Reexamination Certificate
active
06798842
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to wireless communications. More specifically, the present invention discloses a method for determining a range of sequence number values for protocol data units that can be retransmitted to a receiver without causing confusion.
2. Description of the Prior Art
In current protocol standards for wireless communications, such as is found in the 3
rd
Generation Partnership Project (3GPP™), Technical Specification Group Radio Access Network, RLC Protocol Specification, layer two protocol data units (PDUs) are sent by a transmitter to a receiver. These PDUs have a format that is well defined by the communications protocol, and which includes a sequence number (SN) whose purpose is described below. PDUs are used to carry either layer two signaling information, or layer
3
data. Please refer to FIG.
1
.
FIG. 1
is a simplified block diagram of a layer
2
PDU
10
. The layer
2
PDU
10
includes a 12-bit SN entry
12
, and data
14
. The actual internal data structure of the PDU
10
can be quite complicated, but for the purposes of the present invention only the SN entry
12
is of importance. The data
14
may hold layer
2
signaling information, layer
3
data, or a combination of the two, and is not of direct relevance to the present invention.
Please refer to
FIG. 2
in conjunction with FIG.
1
.
FIG. 2
is a block diagram of a wireless communications system
20
. The wireless communications system
20
includes a receiver
24
and a transmitter
25
. The transmitter
25
sends the PDU
10
to the receiver
24
. The wireless environment can be quite noisy, and the receiver
24
may not properly receive the PDU
10
. The SN entry
12
within the PDU
10
is used by the receiver
24
to determine if all transmitted PDUs
10
have been properly received. For each PDU
10
holding successive data
14
, the transmitter
25
increments the value held within the SN entry
12
. By analyzing the SN entries
12
, the receiver
24
is able to determine which, if any, PDUs
10
were missed, and may subsequently request the transmitter
25
to retransmit the missed PDUs
10
. For example, the transmitter
25
may have a large block of data that the transmitter
25
breaks into 4 PDUs
10
, which are then successively transmitted to the receiver
24
. The first PDU
10
may have an SN entry
12
with a value of 92. The next PDU
10
would be transmitted with an SN entry
12
of
93
, followed by the third PDU
10
with an SN entry
12
of
94
, and the last with an SN entry
12
of
95
. By analyzing these successive values of the SN entries
12
, the receiver
24
is able to reconstruct the data sent by the transmitter
25
. If any PDUs
10
are found to be missing, the receiver
24
may explicitly inform the transmitter
25
of which PDUs
10
are to be retransmitted.
Both the receiver
24
and the transmitter
25
have windows within which they expect to receive the PDUs
10
and transmit the PDUs
10
, respectively. The receiver
24
has a receiving window
21
that is delimited by two state variables: VR(R)
22
, and VR(MR)
23
. VR(R)
22
marks the beginning of the receiving window
21
, and VR(MR)
23
marks the end of the receiving window
21
. The receiver
24
will only accept PDUs
10
that have SN entries
12
that are sequentially on or after VR(R)
22
and sequentially before VR(MR)
23
. The SN value held in VR(MR)
23
is not considered to be within the receiving window
21
. Similarly, the transmitter
25
has a transmitting window
26
that is delimited by two state variables: VT(A)
27
and VT(MS)
28
. VT(A)
27
marks the beginning of the transmitting window
26
, and VT(MS)
28
marks the end of the transmitting window
26
. The transmitter
25
will only transmit PDUs
10
that have SN entries
12
that are within the range of the transmitting window
26
, i.e., that are sequentially on or after VT(A)
27
, and sequentially before VT(MS)
28
.
The fixed length of the SN entry
12
, being 12 bits wide, can lead to confusion as to how to treat sequentiality of the PDUs
10
. The SN values 12 of the PDUs
10
have a limited range from zero to 4095, after which the SN values 12 rollover back to zero. Because of this, a PDU
10
with an SN value 12 of four, as an example, may be sequentially after a PDU
10
with an SN value 12 of 4092. Care must be taken when considering the SN values 12 to determine their sequential significance.
The receiving window
21
has a fixed receiving window size. The receiving window size is simply the number of SN values spanned by the state variables VR(R)
22
and VR(MR)
23
. That is, VR(MR)
23
is always kept a fixed SN value distance away from VR(R)
22
, which may be represented mathematically as:
VR
(
MR
)=
VR
(
R
)+receiving window size (1)
Note that equation (1) is a true 12-bit addition, and will suffer from the rollover discussed above. Thus, VR(MR)
23
does not always contain a value that is numerically larger than VR(R)
22
. Similarly, the transmitting window
26
has a transmitting window size, VT(WS)
26
a
, which indicates the number of SN values spanned by the state variables VT(A)
27
and VT(MS)
28
. VT(WS)
26
a
has an initial value that is set to a configured transmitting window size, which is supplied by layer
3
. As above, this may be represented mathematically as:
VT
(
MS
)=
VT
(
A
)+
VT
(
WS
) (2)
And again, the result from equation (2) may suffer from rollover. The receiver
24
may explicitly request the transmitter
25
to change the value of VT(WS)
26
a
. The requested value of VT(WS)
26
a
cannot be greater than the configured transmitting window size.
As the receiver
24
receives PDUs
10
from the transmitter
25
, the receiver
24
will update that value of the state variable VR(R)
22
to reflect the sequentially earliest SN value 12 before which all preceding PDUs
10
have been successfully received. Put another way, VR(R)
22
always holds the SN value
12
of the sequentially earliest PDU
10
that the receiver
24
is waiting to receive. Upon the successful reception of this PDU
10
, the receiver
24
advances the state variable VR(R)
22
to the SN value 12 of the next PDU
10
that needs to be received, and the state variable VR(MR)
23
is updated using equation (1) accordingly . In this manner, the receiving window
21
is advanced by the receiver
24
as the PDUs
10
stream in from the transmitter
25
. It should also be noted that the transmitter
25
may explicitly request the receiver
24
to advance the receiving window
21
with a layer
2
signaling PDU, but this has no bearing on the present invention.
The transmitting window
26
is advanced when the transmitter
25
receives a layer
2
status PDU from the receiver
24
. The layer
2
status PDU holds the most current value of the state variable VR(R)
22
, and is sent at periodic intervals by the receiver
24
, or in response to an explicit request from the transmitter
25
. The transmitter
25
will then set the state variable VT(A)
27
equal to the value held in the status PDU, which in effect sets VT(A)
27
equal to VR(R)
22
. The transmitter
25
updates the state variable VT(MS) using equation (2) accordingly. In this manner, the transmitting window
26
and the receiving window
21
move forward with each other in lock step.
The transmitter
25
has an additional state variable VT(S)
29
. When the transmitter
25
begins transmitting the PDUs
10
that lie within the transmitting window
26
, the transmitter
25
begins with a PDU
10
having an SN value 12 given by the state variable VT(A)
27
, and works sequentially forward until it reaches a PDU
10
having an SN value 12 that is equal to one SN prior to VT(MS)
28
. That is, the transmitter
25
transmits the PDUs
10
in sequence, beginning at VT(A)
27
and ending at VT(MS)−1. The state variable VT(S)
29
holds the SN value of the next PDU
10
to be transmitted. Thus, the PDUs with SN values on or sequentially after VT
AsusTek Computer Inc.
Hsu Winston
Tran Khai
LandOfFree
Retransmission range for a communications protocol does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Retransmission range for a communications protocol, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Retransmission range for a communications protocol will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3241798