Wireless LAN PCMCIA Card

ü What is DSSS What is FHSS And what are their differences

Frequency-hopping spread-spectrum (FHSS) uses a narrowband carrier that changes frequency in a pattern that is known to both transmitter and receiver. Properly synchronized, the net effect is to maintain a single logical channel. To an unintended receiver, FHSS appears to be short-duration impulse noise. Direct-sequence spread- spectrum (DSSS) generates a redundant bit pattern for each bit to be transmitted. This bit pattern is called a chip (or chipping code). The longer the chip is, the greater the probability that the original data can be recovered. Even if one or more bits in the chip are damaged during transmission, statistical techniques embedded in the radio can recover the original data without-the need for retransmission. To an unintended receiver, DSSS appears as low power wideband noise and is rejected (ignored) by most narrowband receivers.

üWhat is Spread Spectrum

Spread Spectrum technology is a wideband radio frequency technique developed by the military for use in reliable, secure, mission-critical communication systems. It is designed to trade off bandwidth efficiency for reliability, integrity, and security. In other words, more bandwidth is consumed than in the case of narrowband transmission, but the trade off produces a signal that is, in effect, louder and thus easier to detect, provided that the receiver knows the parameters of the spread-spectrum signal being broadcast. If a receiver is not tuned to the right frequency, a spread – spectrum signal looks like background noise. There are two main alternatives, Direct Sequence Spread Spectrum (DSSS) and Frequency Hopping Spread Spectrum (FHSS).

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IBM PCMCIA Card user manual What is Dsss What is Fhss And what are their differences
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PCMCIA Card specifications

The IBM PCMCIA card, also known as the Personal Computer Memory Card International Association card, revolutionized the way portable computing expanded its capabilities. Introduced in the early 1990s, these cards allowed laptops to extend their functionality through modular hardware. With a focus on portability, the PCMCIA card architecture supported a range of device types, including network cards, modems, and storage devices, significantly enhancing the versatility of personal computers.

One of the primary features of the PCMCIA card is its compact size. Measuring just 85.6 mm x 54 mm, the standard Type I card is thin enough to fit seamlessly into a laptop's dedicated PCMCIA slot. The architecture supports several form factors, including Type I, Type II, and Type III cards, each varying in thickness and application. This versatility allows manufacturers to develop a variety of cards suited for specific functions like memory expansion, connectivity, and other peripheral interfaces.

Technologically, the IBM PCMCIA card operates on a 68-pin connector design, enabling both data transfer and device communication. One of the early major functionalities of these cards was to support local area network (LAN) communications, which paved the way for mobile computing and telecommuting. Additionally, with the introduction of CardBus technology, higher data transfer rates became possible, allowing for speeds up to 132 Mbps. This enhanced performance ensured that laptops could leverage the capabilities of powerful networking and multimedia devices.

Another key characteristic of IBM's PCMCIA cards is their Plug and Play functionality. As operating systems evolved, they began to support automatic detection of PCMCIA devices, minimizing user intervention for installation. This ease of use contributed to the widespread adoption of removable hardware, facilitating a more seamless computing experience for users on the go.

PCMCIA cards also laid the groundwork for several successor technologies, including the more modern ExpressCard interface. While newer interfaces have largely supplanted PCMCIA in many applications, its impact on computing standards and practices endures.

In conclusion, the IBM PCMCIA card exemplifies innovation in portable computing. Its compact design, support for a variety of devices, robust technologies, and ease of integration transformed laptops into multifunctional powerhouses, defining mobile computing for years to come. As technology continues to advance, the foundational principles exhibited by PCMCIA cards remain relevant in today's fast-paced digital landscape.
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