Baseband signal: This is a signal with a frequency spectrum from 0 to a band-limited value B. Typically, it's the range of frequencies generated by the original required information and is used to modulate (see: modulation) an RF carrier before transmission

Carrier signal: A high-frequency signal (sinusoid, typically) that is modulated by the baseband. A carrier is necessary to make transmission more efficient as an extremely large antenna would be needed to efficiently (with maximum gain) transmit the low-frequency baseband signal. The carrier's frequency is determined by the region of the spectrum the FCC has allotted to that application, i.e., 2.45 GHz and 5 GHz for wireless LANs. Various parameters of the carrier can be modified, including frequency, phase, amplitude etc.

Coding: Methods by which errors can be detected and corrected in a communications channel to bring the capacity of that channel as close as possible to the Shannon Limit (see Shannon's Law). Viterbi and turbo codes are examples.

Coherence bandwidth: One effect of multipath propagation is delay spread, which causes frequency-selective fading. The coherence bandwidth is a measure of the delay spread whereby the larger the delay spread, the smaller the coherence bandwidth.

Dynamic range: Most basically defined as the ratio of the maximum signal strength a circuit can handle to minimum input level at which it can generate an intelligible output.

Fractional bandwidth: Defined mathematically as 2(Fh - Fl)/(Fh + Fl), where Fh and Fl are the high- and low-end limits of a signal 10 dB below peak emission.

Modulation: The process of superimposing the information carried in the baseband signal onto a high-frequency carrier.

Multipath interference: As radio signals radiate out from the source, they bounce off objects in the environment. The multiple signals that arrive at the receiver can cause interference by way of variations in signal strength, frequency distortion and time-delay spreads.

Noise floor: A measure (usually in decibels) of the constant level of noise present in all communication channels and systems.

Part 15 rules: The set of FCC guidelines governing intentional, unintentional or incidental radiators operating without a license. Covers wireless LANs, many fixed wireless access schemes as well as medical and industrial applications. A copy can be found at http://ftp.fcc.gov/oet/info/rules/ part15/part15_dec18_01.pdf

Shannon's Law: Based on the work of information theory pioneer Claude Shannon (1916-2001), this statement defines the theoretical maximum rate at which error-free digits can be transmitted over a bandwidth-limited channel in the presence of noise. It's usually expressed in the form C = W log2(1 + S /N ), where C is the channel capacity in bits per second, W is the bandwidth in Hertz, and S /N is the signal-to-noise ratio. Note: Error-correction codes (see: coding) can improve the communications performance relative to uncoded transmission, but no practical error-correction coding system exists that can closely approach the theoretical performance limit given by Shannon's Law. For more on Shannon, see http:// www.eetimes.com/story/OEG20010227S0045 and http://www.home.gil.com.au/~bredshaw/shannon.htm

Spectral mask: A graphical representation, in terms of frequency (in Hertz) vs. power (in dB) that shows the boundaries of any given spectrum rules, as typically defined by the FCC.

Tsunami: A giant wave, initiated by a sudden change (usually in relative position of underwater tectonic plates). The sudden change is typically enough to propagate the wave; however, its power can be enhanced and fed by lunar positioning and boundaries that focus its energy.