Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction
Reexamination Certificate
1998-12-31
2003-06-17
Decady, Albert (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital data error correction
C370S320000, C370S474000
Reexamination Certificate
active
06581176
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for transmitting control frames and user data frames in a mobile radio communication system.
2. Discussion of Related Art
In a CDMA (Code Division Multiple Access) mobile radio communication system, it is prescribed in a Radio Link Protocol (RLP) of IS-707.2 of February 1998 a relay layer corresponding to a radio section between a terminal device and a base station, for the sake of a circuit data service or a packet data service.
RLP frames can be classified into two types, control frames and user data frames. The user data frames transport user traffic data while the control frames are used to send control information required for RLP initialization and error recovering. The control frames contain important information in RLP operation. As a result, if reliability were not ensured for these control frames, it would negatively impact the performance of an overall system. According to the RLP retransmission procedure, the NAK (Negative Acknowledgement) RLP control frame for a particular user data frame can be transmitted more than once at the same time to ensure the reliability and the missing user data frame will be retransmitted whenever it receives the NAK frame.
Currently, the transmission methods of the NAK control frames in RLP type
1
and RLP type
2
will be described hereinafter.
When an entity receiving RLP frames or an RLP destination transmits NAK control frames for incorrect or lost user data frames, an entity sending RLP or an RLP source retransmits RLP user data frames whenever it receives the NAK control frames. For example, if the RLP source receives two NAK control frames containing the same missing sequence number, it retransmits the missing user data frames twice. In other words, the total number of the retransmission of RLP user data frames matches exactly the total number of NAK frames transmitted containing the sequence number of that user frame.
The above method has a drawback in terms of flexibility. For example, in case of simultaneous voice and packet data service such as the service option VPI, it may occur that the NAK control frames can not be transmitted over a forward channel (FCH) due to a voice packet transmission. In this case, the NAK control frames could be transmitted over a supplemental channel (SCH) with a low frame error rate (FER).
Referring to
FIG. 2
showing a structure of the conventional RLP NAK control frame, it is constructed in the RLP NAK control frame by a data frame sequence number field SEQ with a length of 8 bits, a control field CTL with a length of 8 bits, a field FIRST with a length of 8 bits, a field LAST of a length of 8 bits, a frame check sequence field FCS with a length of 16 bits and a field, padding, with a variable length. The control field CTL is made up of a higher rank 4 bits and a lower rank 4 bits. If a value of the higher rank 4 bits is “1100”, it represents that the RLP control frame is the NAK frame and it requests to retransmit data frames. At this time, the lower rank 4 bits of the control field CTL is “0000”. A value “11010000” of the field CTL indicates a non-encrypted mode synchronization, a value “11010011” represents an encrypted mode synchronization, a value “11100000” provides a non-encrypted mode acknowledgement, a value “11100011” means an encrypted mode acknowledgement, a value “11110000” indicates a non-encrypted mode synchronization/acknowledgement, and a value “11110011” represents an encrypted mode synchronization/acknowledgement.
The field FIRST represents the 8 bit sequence number of a first data frame for which a retransmission is required. The field FIRST is used only in case of an NAK and its value is “00” except such case. The field LAST indicates the 8 bit sequence number of a last data frame for which the retransmission is required. The field LAST is also used only in case of the NAK and its value becomes “00” except such case.
The field FCS is a frame check sequence, the contents will be generated by 16 bits FCS polynomial specified in 3.1 of RFC 1662. The field FCS shall cover the fields SEQ, CTL, FIRST and LAST. The field, padding, is padding bits and it is required to fill the remainder of the frame. These bits shall be set to “0”.
In the conventional method for transmitting the RLP NAK control frames, in case that the number of sequence numbers of basically valid frames are more than the number of sequence numbers anticipated in the receiving station, NAK control frames for user data frames not received to the receiving station are required.
Referring to
FIG. 3
, when the receiving station receives user data frames with sequence numbers
1
,
2
,
3
, a sequence number V(N) necessary by the receiving station and a sequence number V(E) estimated by the receiving station become “4”. V(R) shown in
FIG. 3
indicates received sequence numbers. If a frame error rate (FER) becomes high owing to various causes of a radio section, the receiving station may receive a user data frame of a sequence number
14
instead of the user data frame of the sequence number
4
. The receiving station may actually receive user data frames having more sequence numbers than the sequence number
14
since there is much possibility for a burst occurrence of the FER on the radio section. Like this, in case the receiving station receives the user data frame having the sequence number
14
, the receiving station sends NAK control frames requiring for user data frames of missed sequence numbers
4
to
13
to the transmitting station. That is, the receiving station requests the transmitting station to retransmit the missed user data frames thereto. At this time, the receiving station operates of each retransmission counter for an NAK about the user data frames having the sequence number
4
to
14
. After that, the number of the retransmission counter increases whenever an effective idle frame or a new effective data frame is received.
In case the receiving station does not receive the missed user data frames even till the retransmission counter for the NAK reaches a given threshold, the receiving station requires the retransmission of the missed user data frames from the transmitting station. In other words, the receiving station transfers NAK control frames to the transmitting station A. If user data frames of sequences numbers
5
,
8
,
9
,
11
,
13
are received before the timer of the NAK retransmission counter is expired, the NAK timer does not operate for the frames of the sequence numbers
5
,
8
,
9
,
11
,
13
any more. Then, the receiving station B retransmits NAK control frames only for user data frames not received even by the retransmission of the transmitting station A, to the transmitting station A.
That is to say, an NAK control frame is sent for the user data frame of the sequence number
4
shown in
FIG. 3
, and after 20 ms, the NAK control frame is resent for the user data frame of the sequence number
4
. Also, NAK control frames are sent for the user data frames of sequence numbers
6
,
7
, and after 20 ms, the NAK control frames are resent for the user data frames of the sequence numbers
6
,
7
. And then, after 20 ms, an NAK control frame is transmitted for a user data frame of a sequence number
10
, and after 20 ms, the NAK control frame is retransmitted for the user data frame of the sequence number
10
. Also after 20 ms, an NAK control frame is transferred for a user data frame of a sequence number
12
, and after 20 ms, the NAK control frame is retransferred for the user data frame of the sequence number
12
to the transmitting station A.
Supposing that, after the transmission of all the NAK control frames, the receiving station B receives only the user data frame of the sequence number
7
till the NAK timer is expired, the receiving station B again sends the NAK control frames for the respective user data frames having the missed sequence numbers
4
,
6
,
10
,
12
each three times to the transmitting station A. In response to such operation, the transmitting station A transmits th
De'cady Albert
Fleshner & Kim LLP
Lamarre Guy
LG Information & Communications Ltd.
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