Data Rate Effects & Wireless Reliability

For each data modulation method, the ability of the receiver to demodulate data from the recived radio signal ddecreases as the data rate increases - that is, BER increases as the transmitted data rate increases, due to reciver demodulation operation. However "demodulation BER" is not the only factor infulencing overall data reliability.

Because instantaneous noise closely follows a random probability function, any and every wireless message is vulnerable to random noise "attack" that can corrupt individual bits. Forward-error-correction (FEC) techniques can be used to recover the corrupted bits. For messages without FEC, the whole message becomes corrupt if one bit is corrupted. So the probability of a corrupted message relates to its "air-time" - the overall transmission time of the message. This depends on the length of the message (number of bits) and the transmitted data rate. The longer the message, the higher the probability of message corruption, but the higer the data rate, the lower the probability. So higher data rate has two effects; increasing demodulation BER but also reducing the risk of message corruption.

For reliable operation, all wireless messages need integral error-checking to check the integrity of the overall message. Message recovery is also required in the event of corruption. This is normally in the form of a message acknowledgement protocol with corrupted messages being re-transmitted, or messages being continuously transmitted such that occasional corrupted messages can be ignored.

In summary:

• BER increases with data rate because of reciver demodulation errors
• The probability of message corruption during transmission decreases with data rate increases.

   

• The probability of overall message corruption decreases with shorter messages.
• FEC functionality built-into the messages improves the rate of successful messages.

Wireless products with short messages such as Wireless I/O have a reliability advantage over Wireless Modems which transmit much larger amounts of data.