Intel PXA27 Series Design Manual page 286

Glossary
OFDM. See Orthogonal Frequency Division Multiplexing.
Orthogonal Frequency Division Multiplexing. A special form of multi-carrier modulation. In a multi-path
channel, most conventional modulation techniques are sensitive to inter-symbol interference unless the channel
symbol rate is small compared to the delay spread of the channel. OFDM is significantly less sensitive to inter-
symbol interference, because a special set of signals is used to build the composite transmitted signal. The basic
idea is that each bit occupies a frequency-time window that ensures little or no distortion of the waveform. In
practice, it means that bits are transmitted in parallel over a number of frequency-nonselective channels.
OTG. See USB OTG.
Packet. A bundle of data organized in a group for transmission. Packets typically contain three elements: control
information (for example, source, destination, and length), the data to be transferred, and error detection and
correction bits. Packet data is the basis for packet-switched networks, which eliminate the need to dial-in to send or
receive information, because they are "always on."
Packet Buffer. The logical buffer used by a USB device for sending or receiving a single packet. This determines
the maximum packet size the device can send or receive.
Packet ID (PID). A field in a USB packet that indicates the type of packet, and by inference, the format of the
packet and the type of error detection applied to the packet.
Packet Switched Network. Networks that transfer packets of data.
PCMCIA. Personal Computer Memory Card Interface Association (PC Card)
PCD. Pixel Clock Divider
PCS. Personal Communications Services. An alternative to cellular, PCD works like cellular technology because it
sends calls from transmitter to transmitter as a caller moves. But PCS uses its own network, not a cellular network,
and offers fewer "blind spots" than cellular, where calls are not available. PCS transmitters are generally closer
together than their cellular counterparts.
PDA. Personal Digital Assistant. A mobile handheld device that gives users access to text-based information. Users
can synchronize their PDAs with a PC or network; some models support wireless communication to retrieve and
send e-mail and get information from the Internet.
Phase. A token, data, or handshake packet. A transaction has three phases.
Phase Locked Loop (PLL). A circuit that acts as a phase detector to keep an oscillator in phase with an incoming
frequency.
Physical Device. A device that has a physical implementation; for example, speakers, microphones, and CD
players.
PID. See Packet ID or Process ID.
PIO. Programmed Input/Output
Pipe. A logical abstraction representing the association between an endpoint on a device and software on the host.
A pipe has several attributes; for example, a pipe may transfer data as streams (stream pipe) or messages (message
pipe). See also Stream Pipe and Message Pipe.
PLL. See Phase Locked Loop.
PM. Phase Modulation
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Glossary-10 Intel PXA27x Processor Family Design Guide