g of impedance between these components. For example, maximum power will only be transmitted if the impedances of the transmitter, connecting cable and antenna are equal, otherwise power will be lost as a result of reflections at the connections between components. In the case of equipment with integrated antennas, this will be part of the design dealt with by the equipment manufacturer. However, this aspect will have to be considered when attaching an external antenna to a wireless network adapter or access point. Receiver Sensitivity As the strength of the signal reaching the receiver input drops, the decoding of data will be increasingly affected by noise and, as a result, will become increasingly error prone. The sensitivity limit of the receiver is determined by the allowable bit error rate and the receiver noise floor. Radio Communication Basics As these factors are discussed in the following sections, an example will be worked through, based on the following parameters: 802.11b DSSS system (2.4 GHz, 22 MHz spread bandwidth) DQPSK modulation 2 Mbps data rate or 2 MHz de-spread bandwidth required bit error rate of 1 in 105 receiver noise figure of 6 dB 20°C ambient temperature. Bit Error Rate The rate at which decoding errors occur is measured by the bit error rate (BER), with a BER of 1 in 105 being typical at the receiver sensitivity limit. Since data is transmitted in packets containing several hundreds or thousands of bits of data, even a 1 in 105 chance of an error in decoding any single bit will multiply up to a significant probability of an error in a large data packet, and the resulting packet error rate (PER) can be in the range of several percent. For example, with a BER of 1 in 105 the PER for a 100 bit data packet will be: -PER) = (1 - 10-5) 000 or PER = 0.1%, rising to 1% for a 1 kb data packet. The BER is a function of the signal-to-noise ratio in the receiver, and also depends on the specific type of modulation method being used. The signal-to-noise ratio of a communication channel is given by