| dc.description.abstract | Presented in this thesis are the following theoretical investigations carried out on Automatic Repeat Request (ARQ) error?control schemes.
A new type of modified generalized stop?and?wait ARQ scheme is proposed and worked out. It is shown that this scheme yields better throughput efficiency than the modified stop?and?wait ARQ schemes proposed earlier.
In the proposed scheme, the transmitter sends m identical copies of a data block to the receiver. If the first received copy of the block is accepted by the receiver, then it sends a positive acknowledgement (ACK) to the transmitter and discards the succeeding (m ? 1) received copies of that block. The transmitter, soon after receiving the ACK, sends m copies of the next block in the queue. If the first copy of the block is not accepted by the receiver, it sends a negative acknowledgement (NAK) to the transmitter and checks the second copy. If the second copy is found to be error?free, the receiver sends ACK to the transmitter and discards the next (m ? 2) succeeding copies. It is only when the transmitter receives NAKs for all the copies of a data block sent that it retransmits m� identical copies of the same block. The retransmission continues until the transmitter receives at least one ACK from the receiver.
The number of copies of a block to be sent is optimized for maximum throughput efficiency. It is also shown that the maximum value of the throughput occurs when the number of copies of a block to be sent, either for the first transmission or subsequent retransmissions, is equal to a common optimum value m. The optimum value m is evaluated for the proposed scheme. The optimum value for the proposed scheme is found to be infinity. Under these circumstances, the proposed scheme reduces to a type of continuous ARQ scheme, wherein copies of a data block are sent continuously until the ACK is received for that block. The throughput efficiency for the proposed scheme is derived.
The number of copies of a data block to be sent, for the proposed scheme, can be taken to be the same as or greater than that of the optimum generalized stop?and?wait ARQ scheme proposed recently. When it is the same, the proposed scheme yields better throughput performance. When it is greater, the performance is further improved and is almost insensitive to block?error probability. Thus, the proposed scheme is potentially better than the schemes of this kind proposed earlier. The study conducted, results obtained, and conclusions drawn are presented with a firm mathematical background in this thesis. | |
