Analysis of the efficiency of block frame transmission in IEEE 802.11 computer networks

Abstract

In infrastructure schemes of WLANs wireless computer networks, which are based on the use of the DSF (distributed coordination function) function and the CSMA/CA mechanism, the station STA (STAtion) sends a frame if the transmission channel is released after waiting for the end of the DIFS (distributed interframe space) interval and operation of the slot selec-tion mechanism for transmission (backoff mechanism). In case of collisions or damage to the frame by interference, the AP cannot decode the frame and does not send it back to the ACS station. The sending station STA waits for the re-ceipt of a potential ASK before the expiration of the corresponding timeout, and in case of receipt, starts the backoff procedure before transmission. The duration of the slot used in the backoff process depends on the speed of the physical layer technology. To reduce overhead, a transmission mechanism using frame blocks was proposed. This mechanism assumes that a block of frames intended for one recipient can be sent without con-firming the fact of correct reception by the AP access point of each frame separately. In this case, the sender (STA) competes for access to the channel for the first frame of the block. If it wins the access competition, the transmission of the first frame begins, and after receiving the ACK acknowledgment for it and a short SIFS separation interval, the STA transmits a whole block of frames, which is accompanied by a BAR service frame. The mechanism of frames block transmission in wireless computer networks IEEE 802.11 DCF with infrastructure topology has been analyzed. In protected mode, the depend-encies of network throughput on data transmission rate and the number of frames in a block are determined. It is shown that the mechanism of block transmission significantly increases the network throughput, especially in the range of higher transmission rates. With a marked increase in the intensity of interference the transmission of blocks becomes more complicated. Already with BER=10^-6 and the frames number of the order of 10 and more, in some cases there is a need to retransmit distorted in a block frames, and at BER=10^-5 there are many re-transmissions, so the resulting network throughput becomes small.