Buffer allocation to repeated information blocks in data transmi

Details Buffer allocation to repeated information blocks in data transmi Buffer allocation to repeated information blocks in data transmi

1994-09-20

1996-07-16

Envall, Jr., Roy N.

Excavating

371 35, G06F 1110

Patent

active

055374166

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
This invention relates to apparatus for receiving information blocks, each of which includes a data block, from a further apparatus in a duplex communications system and in particular to such apparatus which is arranged to determine if a received information block has been corrupted by transmission and when it has, to request the further apparatus to repeat the transmission of the data block of that information block, the data blocks being stored in a receiver buffer.
2. Related Art
When exchanging information over a noisy channel information blocks can be corrupted so it becomes necessary to implement an Automatic Repeat request (ARQ) scheme if the lost data blocks are to be obtained. Of the known conventional ARQ schemes of stop-and-wait, go-back-N and selective repeat (SR), the last is the most efficient in terms of throughput as only those data blocks in corrupted information blocks are retransmitted. It is especially attractive to use such an SR scheme in communications systems with the noisiest channels, for example those using radio links, where many repeats may be needed.
The repeated data blocks when received in a later transmitted information block will generally need to be placed in a particular position relative to the data blocks already received. This is achieved in prior art systems by including as part of each data block a data block number which the apparatus can use to identify the data block and so position it appropriately.


SUMMARY OF THE INVENTION

According to the present invention, apparatus is arranged, on receiving a corrupted information block, to a) store a first receiver buffer address being the address at which the data block of the corrupted information block is to be stored if repeated in a later information block b) determine in which later information block the repeat transmission of the data block is expected to occur; and c) store the data block in the receiver buffer at the first receiver buffer address on receiving the later information block uncorrupted.
On receiving a corrupted information block, the apparatus stores nine address where the data block should have been stored if not corrupted. When the later information block containing the repeated data block is received by the apparatus, the data is (if not again corrupted) stored in the appropriate place in the buffer. Because the apparatus previously determined that this information block would contain the required repeated data block it can, when it arrives, store the data block at the required place in the buffer given by the stored first receiver buffer address. This can be without reference to any data block number which is now unnecessary and so can be omitted.
The present invention can therefore allocate received, repeated and non-repeated data blocks to their correct relative positions within the receiver buffer without the need for numbering of the data blocks and with a consequential reduction in the size of the data blocks being transmitted.
If the later information block is itself corrupted the original first receiver buffer address is retained and the apparatus again determines which later information block will have the next repeat of the required data block. If the later information block is not corrupted it will be stored in the receiver buffer at the stored first receiver buffer address.
This ARQ scheme can provide error free transmission on a noisy channel in one direction provided the return path is error free. Problems, however, occur when errors are introduced in both directions of the link. If an acknowledgement of a received information block is corrupted to become a non-acknowledgement, the contained data block would be repeated in a later information frame when neither required nor expected and so would be stored a second time but in an incorrect position in the receiver buffer if, on the other hand, a non-acknowledgement of a received information block is corrupted and is received as an acknowledgement, the data block in the later info

REFERENCES:
patent: 4774587 (1988-09-01), Schmitt
patent: 4887162 (1989-12-01), Arai
patent: 5036518 (1991-07-01), Tseung
patent: 5109384 (1992-04-01), Tseung
Carr, "New Video Coding Standard for the 1990s", Electronics and Communication Engineering Journal, vol. 2, No. 3, 1990, London GB, pp. 119-124.

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