Direct Sequence Spread Spectrum

Most commercial part 15.247 spread spectrum systems transmit an RF signal bandwidth as wide as 20 to 254 times the bandwidth of the information being sent. Various spread spectrum systems have employed RF bandwidths 1000 times their information bandwidth. Common spread spectrum systems are of the 'direct sequence' (Figure 2.1) or 'frequency hopping' type, or else some combination of these two types (called a 'hybrid'). DSSS is an Amplitude Modulation (AM) technique (Figure 2.3). AM has a...

OSI Model and Communication Between Systems

Information being transferred from a software application in one computer system to a software application in another computer is required to pass through the OSI layers. An example of this would be if a software application in System A has information to transmit to a software application in System B then the application program in System A will pass its information to the application layer (Layer 7) of System A. The application layer then passes the information to the presentation layer...

Wireless Data Technologies

IEEE, Massachusetts Health Data Consortium (MHDC), Mobile Healthcare Alliance (MOHCA) and The Council of Communications Advisors Copyright 2003 John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, Email (for orders and customer service enquiries) cs-books wiley.co.uk Visit our Home Page on www.wileyeurope.com or www.wiley.com All Rights Reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic,...

Wireless Data Networks

Almost all 'Wireless' specialists will agree that the lack of standards was one of the main factors that held up the progress of WLANs. In 1997 the IEEE adopted the first Wireless LAN (WLAN) standard, IEEE Std 802.11-1997. There are three wireless LAN (WLAN) types, each of which uses a different part of the electromagnetic spectrum Infrared, Microwave, and Spread Spectrum Technology (SST). Each solution has its unique advantages and disadvantages associated with the nature of its...

Frequency Hopping Spread Spectrum

FHSS is a Frequency Modulation (FM) technique. FM modulates the frequency of the carrier wave with a modulating wave (Figure 2.1). The data is carried on a signal that jumps from one frequency to another in a preprogrammed, pseudorandom sequence. For the signal to be received correctly, the sequence must be known by the devices at both ends in advance. FHSS is probably more secure than DSSS since both receiver and transmitter must be in exact sequence, but it is also more expensive and complex...

The Network Layer OSI Layer

The network layer defines the network address, which differs from the MAC address. Some network layer implementations, such as the Internet Protocol (IP), define network addresses in a way in which route selection can be determined systematically by comparing the source network address with the destination network address and applying the subnet mask. Since this layer defines the logical network layout, routers can use this layer to determine how to forward packets. Because of this, much of the...

Multipath Propagation Defined

Multipath propagation occurs when an RF signal takes different paths when propagating from a source (e.g. a radio NIC) to a destination node (e.g. access point). While the signal is en route, walls, chairs, desks, and other items get in the way and cause the signal to bounce in different directions. A portion of the signal may go directly to the destination, and another part may bounce from a chair to the ceiling, and then to the destination. As a result, some of the signal will encounter delay...

CdmaOne IS95

CdmaOne is based on IP standards, giving it an inherent advantage over GPRS. Today, all cdmaOne handsets and base stations are packet data capable, and the networks utilize Internet protocol IP -based equipment. This allows for a high degree of backward and forward hardware compatibility for network operators looking to implement new higher speed data services and evolve to 3G, which is an IP-based standard. These cdmaOne networks already incorporate an IP gateway referred to as the...

Animal Identification

Activity in this area seems to have started in the area of racehorse identification. The intention was to develop a very small transponder that could be hermetically sealed in a tiny glass capsule, and imbedded under the skin of the animal providing positive proof as to the identity of the animal. The transponders are about 10 mm long, 1.5 mm in diameter, and contain a coil inside the glass vial with 1000 turns of very fine wire around a ferrite former. It is this coil that makes the...