WL1271 Skips data rates during a roam

Dear Sir

In general there are two algorithms in the s/w running in parallel that are related to this issue first is rate management and the other is rate fallback.

Rate management algorithm: The packet error rate and the effective throughput of every rate depend on the channel conditions (the air) between the STATION and the AP which are unknown to the STATION. Some important properties of the channel are signal power received at the AP, collision rate in the network, noise sources in the air such as neighboring networks creating co-channel or overlap channel. The algorithm is based on success/failure of packet transmission in each rate. It adjusts the rate dynamically to maximize throughput or to minimize PER or a combination of both.

Rate fallback algorithm: While the connection between the AP and STATION is satiable and the STATION detects low per (packet error rate) the STATION will transmit the packets in the highest available rate that is enabled at the ini file. But, when the STATION is not getting ACK respond packets from the AP, the STATION will re-transmit the packet. In case of the STATION doesn't get ACK respond to the retransmission, the STATION should reduce the rate to a different rate. (For example: if the STATION transmits on rate 54 and it is far from AP, the STATION will continue to transmit on rate 48). The STATION should continue fallback the rates and retransmit the packet, till it will receive an ACK packet for the last TX packet it sent, or it achieve 10 retries to this packet. When the connection is getting more satiable, it will return to the highest rate it can gradually. The rate fallback currently is an automatic feature, and we can’t configure it.

The only parameter we can configure at the STATION ini file currently is the number of retries. Default =10, can very between 1-255

 ( "RatePolicyUserShortRetryLimit" );

 ( "RatePolicyUserLongRetryLimit" );