Manual - EUSSO Technologies, Inc.

Manual - EUSSO Technologies, Inc.
802.11g Wireless LAN PCI Card
User Manual
Version: 1.0
(April, 2004)
COPYRIGHT
Copyright 2004/2005 by this company. All rights reserved. No part of this
publication may be reproduced, transmitted, transcribed, stored in a retrieval system,
or translated into any language or computer language, in any form or by any means,
electronic, mechanical, magnetic, optical, chemical, manual or otherwise, without the
prior written permission of this company
This company makes no representations or warranties, either expressed or implied,
with respect to the contents hereof and specifically disclaims any warranties,
merchantability or fitness for any particular purpose. Any software described in this
manual is sold or licensed "as is". Should the programs prove defective following their
purchase, the buyer (and not this company, its distributor, or its dealer) assumes the
entire cost of all necessary servicing, repair, and any incidental or consequential
damages resulting from any defect in the software. Further, this company reserves the
right to revise this publication and to make changes from time to time in the contents
hereof without obligation to notify any person of such revision or changes.
All brand and product names mentioned in this manual are trademarks and/or
registered trademarks of their respective holders.
Federal Communication Commission
Interference Statement
This equipment has been tested and found to comply with the limits for a Class B
digital device, pursuant to Part 15 of FCC Rules. These limits are designed to
provide reasonable protection against harmful interference in a residential installation.
This equipment generates, uses, and can radiate radio frequency energy and, if not
installed and used in accordance with the instructions, may cause harmful
interference to radio communications. However, there is no guarantee that
interference will not occur in a particular installation. If this equipment does cause
harmful interference to radio or television reception, which can be determined by
turning the equipment off and on, the user is encouraged to try to correct the
interference by one or more of the following measures:
1. Reorient or relocate the receiving antenna.
2. Increase the separation between the equipment and receiver.
3. Connect the equipment into an outlet on a circuit different from that to which the
receiver is connected.
4. Consult the dealer or an experienced radio technician for help.
FCC Caution
This equipment must be installed and operated in accordance with provided
instructions and a minimum 20 cm spacing must be provided between computer
mounted antenna and person’s body (excluding extremities of hands, wrist and feet)
during wireless modes of operation.
This device complies with Part 15 of the FCC Rules. Operation is subject to the
following two conditions: (1) this device may not cause harmful interference, and (2)
this device must accept any interference received, including interference that may
cause undesired operation.
Any changes or modifications not expressly approved by the party responsible for
compliance could void the authority to operate equipment.
Federal Communication Commission (FCC) Radiation Exposure Statement
This equipment complies with FCC radiation exposure set forth for an uncontrolled
environment. In order to avoid the possibility of exceeding the FCC radio frequency
exposure limits, human proximity to the antenna shall not be less than 20cm (8 inches)
during normal operation.
The antenna(s) used for this transmitter must not be co-located or operating in
conjunction with any other antenna or transmitter.
R&TTE Compliance Statement
This equipment complies with all the requirements of DIRECTIVE 1999/5/EC OF THE
EUROPEAN PARLIAMENT AND THE COUNCIL of March 9, 1999 on radio
equipment and telecommunication terminal Equipment and the mutual recognition of
their conformity (R&TTE)
The R&TTE Directive repeals and replaces in the directive 98/13/EEC
(Telecommunications Terminal Equipment and Satellite Earth Station Equipment) As
of April 8, 2000.
Safety
This equipment is designed with the utmost care for the safety of those who install and
use it. However, special attention must be paid to the dangers of electric shock and
static electricity when working with electrical equipment. All guidelines of this and of
the computer manufacture must therefore be allowed at all times to ensure the safe
use of the equipment.
EU Countries Intended for Use
The ETSI version of this device is intended for home and office use in Austria,
Belgium, Denmark, Finland, France, Germany, Greece, Ireland, Italy, Luxembourg,
the Netherlands, Portugal, Spain, Sweden, and the United Kingdom.
The ETSI version of this device is also authorized for use in EFTA member states:
Iceland, Liechtenstein, Norway, and Switzerland.
EU Countries Not intended for use
None.
CONTENTS
1 INTRODUCTION ............................................................................. 1
1.1
Features ......................................................................................................................... 1
1.2
Specifications................................................................................................................ 1
1.3
Package Contents .......................................................................................................... 2
2 INSTALLATION PROCEDURE ..................................................... 3
3 CONFIGURATION UTILITY ......................................................... 3
3.1
Site Survey .................................................................................................................... 6
3.2
Profile............................................................................................................................ 7
3.2.1 Configure the Profile ................................................................................................ 8
3.2.2 Enable WPA in Windows XP ...................................................................................12
3.3
Link Status .................................................................................................................. 14
3.4
Statistics ...................................................................................................................... 15
3.5
Advance ...................................................................................................................... 16
3.6
About........................................................................................................................... 17
4 TROUBLESHOOTING .................................................................. 18
1 Introduction
Thank you for purchasing the 802.11g Wireless LAN PCI Card. This card complies with IEEE 802.11g
standard, which supports up to 54Mbps high-speed wireless network connections. It can also work with
IEEE 802.11b devices. When the card connects to 11b devices, the link speed will be up to 11Mbps.
For WLAN security issues, this card supports 64/128-bit WEP data encryption that protects your
wireless network from eavesdropping. It also supports WPA (Wi-Fi Protected Access) feature that
combines IEEE 802.1x and TKIP (Temporal Key Integrity Protocol) technologies. Client users are
required to authorize before accessing to APs or AP Routers, and the data transmitted in the network is
encrypted/decrypted by a dynamically changed secret key. This card has built-in AES engine which
ensure the highest degree of security and authenticity for digital information and it is the most advanced
solution defined by IEEE 802.11i for the security in the wireless network.
The power consumption of the card is also very low. Furthermore, this card provides several levels of
power saving modes allowing user customizes the way of saving the power from his/her portable or
handheld devices.
This card is cost-effective, together with the versatile features; it is the best solution for you to build your
wireless network.
1.1 Features
•
•
•
•
Works with both IEEE 802.11b and IEEE 802.11g products.
•
•
•
•
Detachable antenna with long length cable provides convenience to locate the antenna.
High-speed transfer data rate - up to 54Mbps.
High throughput supports multi-media data bandwidth requirement.
Supports 64/128-bit WEP, WPA (TKIP with IEEE 802.1x) and AES functions for high level of
security.
Automatic fallback increases data security and reliability.
Supports the most popular operating system: Windows 98SE/Me/2000/XP.
Supports 32-bit PCI interface.
1.2 Specifications
•
•
•
•
Standard: IEEE 802.11g/b
Interface: 32-bit PCI
Frequency Band: 2.4000 ~ 2.4835GHz (Industrial Scientific Medical Band)
Modulation: OFDM with BPSK, QPSK, 16QAM, 64QAM (11g)
BPSK, QPSK, CCK (11b)
•
Data Rate: 54/48/36/24/18/12/11/9/6/5.5/2/1Mbps auto fallback
1
•
•
Security: 64/128-bit WEP Data Encryption, WPA, AES and IEEE 802.1x
•
•
•
•
•
Drivers: Windows 98SE/Me/2000/XP
Antenna: External detachable dipole antenna (Connector: RP-SMA connector, Cable Length:
94 cm)
LEDs: TX/RX, Link
Transmit Power: 16dBm~18dBm
Power consumption: Tx: 350mA, Rx: 250mA
Receive Sensitivity: 54Mbps OFDM, 10% PER, -70dBm, 11Mbps CCK, 8% PER, -86dBm,
1Mbps BPSK, 8% PER, -92dBm
•
•
•
•
Dimension: 19(H) x 127(W) x 121(D) mm
Temperature: 32~131°F (0 ~55°C)
Humidity: Max. 95% (NonCondensing)
Certification: FCC, CE
1.3 Package Contents
Before you begin the installation, please check the items of your package. The package should include
the following items:
•
One PCI Card
•
One Extendable Antenna (94cm)
•
One CD (Driver/Utility/User’s Manual)
•
One Quick Guide
If any of the above items is missing, contact your supplier as soon as possible.
2
2 Installation Procedure
Before you proceed with the installation, please notice following descriptions.
Note1: The following installation was operated under Windows XP.
Windows 98SE/Me/2000.)
(Procedures are similar for
Note2: If you have installed the Wireless PCI Card driver & utility before, please uninstall the old
version first.
Hardware Installation
A. Turn off your computer and remove its cover.
B. Insert the PCI card to an available PCI slot firmly.
C. Secure this card to the rear of the computer chassis and put back the cover.
D. Secure the antenna to the antenna connector of the card.
E. Turn on the computer.
Software Installation
A. A “Found New Hardware Wizard” is displayed after the PCI card is installed and the computer is
restarted. Click “Cancel”.
B. Insert the Installation CD to your CD-ROM Drive. Execute the “setup” program.
3
C. Click “Easy Install” or “Next” to continue.
D. The system starts to install the software of the card. Please wait a moment.
E. The current setting of the “Country Channel” of the card is displayed for your reference. If you are in
different country, please change the “Country Channel” from the drop-down menu and click “Next”.
4
F. Click “Finish” to complete the installation.
G. The “RaConfig” is displayed and you can start to configure the card.
5
3 Configuration Utility
The Configuration Utility is a powerful application that helps you configure the PCI card and monitor the
link status and the statistics during the communication process.
The Configuration Utility appears as an icon on the system tray of Windows while the card is running.
You can open it by double-click on the icon.
Right click the icon, there are some items for you to operate the configuration utility.
Lauch Config Utilities
Select “Lauch Config Utilities” to open the Configuration Utility tool.
Exit
Select “Exit” to close the Configuration Utility tool.
3.1
Site Survey
When you open the Configuration Utility, the system will scan all the channels to find all the access
points/stations within the accessible range of your card and automatically connect to the wireless
device with the highest signal strength. From the “Site Survey” option, all the networks nearby will be
listed. You can change the connection to another networks or add one of the networks to your own
profile list.
6
Parameter
Description
Available Networks
This list shows all available wireless networks within range of your
card. It also displays the information of the networks including the
SSID, BSSID, Signal Strength, Channel, Encryption,
Authentication and Network Type. If you want to connect to any
networks on the list, double-click the item on the list, and the card
will automatically connect to the selected network.
Rescan Button
Click “Rescan” button to collect the information of all the wireless
networks nearby.
Connect Button
Click “Connect” to connect to the selected network.
Add to Profile Button
Add the selected network to Profiles list.
3.2
Profile
The “Profiles List” is for you to manage the networks you connect to frequently. You are able to
Add/Delete/Edit/Activate a profile.
Parameter
Description
Profiles List
The profiles list display all the profiles and the relative information
including Profile Name, SSID, Channel, etc.
Add/Delete/Edit Button
Click these buttons to add/delete/edit the selected profiles.
Activate Button
Click “Activate” to connect to the selected profile.
7
3.2.1 Configure the Profile
System Configuration
Parameter
Description
Profile Name
Define a recognizable profile name for you to identify the different
networks.
SSID
The SSID (up to 32 printable ASCII characters) is the unique
name identified in a WLAN. The ID prevents the unintentional
merging of two co-located WLANs.
You may specify a SSID for the card and then only the device with
the same SSID can interconnect to the card. If you want to add
one of the networks nearby to the profile list, pull down the menu,
all the networks nearby will be listed and you can add one of them
to the profile list.
Power Saving Mode
The power saving function is only available when the network type
is in Infrastructure.
CAM(Constantly Awake Mode) – The card will always set in
active mode.
Power Saving Mode – Enable the card in the power saving mode
when it is idle.
CAM When AC Power – Select this option to automatically switch
the card from power saving mode to CAM mode while the power
of your desktop computer is supplied by the AC power but not
battery.
8
Parameter
Description
Network Type
Infrastructure – This operation mode requires the presence of an
802.11 Access Point. All communication is done via the Access
Point or Router.
Ad-Hoc – Select this mode if you want to connect to another
wireless stations in the Wireless LAN network without through an
Access Point or Router.
Transmit Power
If you want to lower the transmit power of the card for saving the
power of the system, you can select the lower percentages from
the list.
11B Preamble Type
The preamble defines the length of the CRC block for
communication among wireless stations. This option is only active
in the Ad Hoc network.
There are two modes including Auto and Long Preamble. If
“Auto“ mode is selected, the card will auto switch the preamble
mode depending on the wireless stations which the card is
connecting to.
RTS Threshold
Minimum packet size required for an RTS (Request To Send). For
packets smaller than this threshold, an RTS is not sent and the
packet is transmitted directly to the wireless network. Select a
setting within a range of 0 to 2312 bytes. Minor change is
recommended.
Fragment Threshold
The value defines the maximum size of packets; any packet size
larger than the value will be fragmented. If you have decreased
this value and experience high packet error rates, you can
increase it again, but it will likely decrease overall network
performance. Select a setting within a range of 256 to 2312 bytes.
Minor change is recommended.
Channel
This setting is only available for Ad Hoc mode. Select the number
of the radio channel used for the networking. The channel setting
should be the same with the network you are connecting to.
9
Authentication vs. Security
Parameter
Description
Authentication Type
This setting has to be consistent with the wireless networks that
the card intends to connect.
None – No authentication is needed among the wireless network.
Shared – Only wireless stations using a shared key (WEP Key
identified) are allowed to connecting each other.
WPA-PSK –It is a special mode designed for home and small
business users who do not have access to network authentication
servers. In this mode, known as Pre-Shared Key, the user
manually enters the starting password in their access point or
gateway, as well as in each wireless stations in the network. WPA
takes over automatically from that point, keeping unauthorized
users that don't have the matching password from joining the
network, while encrypting the data traveling between authorized
devices. The encryption methods are including TKIP and AES.
Note that this option is only available for Windows XP.
10
Parameter
Description
Encryption Mode
None – Disable the WEP Data Encryption.
WEP – Enable the WEP Data Encryption. When the item is
selected, you have to continue setting the WEP Encryption keys.
TKIP – TKIP (Temporal Key Integrity Protocol) changes the
temporal key every 10,000 packets (a packet is a kind of message
transmitted over a network.) This insures much greater security
than the standard WEP security.
AES – AES has been developed to ensure the highest degree of
security and authenticity for digital information and it is the most
advanced solution defined by IEEE 802.11i for the security in the
wireless network.
Note: All devices in the network should use the same encryption
method to ensure the communication.
WPA Pre-Shared Key
The WPA-PSK key can be from eight to 64 characters and can be
letters or numbers. This same key must be used on all of the
wireless stations in the network.
WEP Key
(Key1 ~ Key4)
The WEP keys are used to encrypt data transmitted in the
wireless network. There are two types of key length: 64-bit and
128-bit. Select the default encryption key from Key 1 to Key 4 by
selected the radio button.
Fill the text box by following the rules below.
64-bit – Input 10-digit Hex values (in the “A-F”, “a-f” and “0-9”
range) or 5-digit ASCII characters (including “a-z” and “0-9”) as
the encryption keys. For example: “0123456aef“ or “test1”.
128-bit – Input 26-digit Hex values (in the “A-F”, “a-f” and “0-9”
range) or 13-digit ASCII characters (including “a-z” and “0-9”) as
the encryption keys. For example:
“01234567890123456789abcdef“ or “administrator”.
11
3.2.2 Enable WPA in Windows XP
Wi-Fi Protected Access (WPA) is a specification of standards-based, interoperable security
enhancement that strongly increases the level of data protection (encryption) and access control
(authentication) for existing and future wireless LAN systems. The technical components of WPA
include Temporal Key Integrity Protocol (TKIP) for dynamic key exchange, and 802.1x for
authentication.
There are two types of WPA security: WPA-PSK (no server) and WPA (with server). WPA requires a
Radius Server to complete the authentication among wireless stations and Access Points. Typically,
this mode is used in an enterprise environment. WPA-PSK uses a so-called pre-shared key as the
security key. A pre-shared key is a password that each wireless station uses the same key to access
the network. Typically, this mode will be used in a home environment.
To enable the WPA function in Windows XP, the following software systems are required:
1. Windows XP Service Pack 1 with Windows XP Support Patch for Wi-Fi Protected Access program
in addition.
2. Configure the card by Wireless built-in utility (Wireless Zero Configuration).
Note: In that kind of system, there are two utility selections when you open the configuration
utility of the card. You can select to use the XP’s built-in utility with full WPA function. If “Use
XP Wireless Zero Configuration” is selected, you can only configure the advance setting or
check the link status and statistics from the “RaConfig” utility.
1.
2.
From here, right click the
icon to select “View
Available Wireless
Networks”.
Press “Advanced” button
from “Wireless Network
Connection”.
12
3.
Press “Configure” button to configure the WPA
function for the current network.
Note: Uncheck “Use Windows to Configure my wireless network settings”, the “RaConfig” utility will be
enabled again.
Parameter
Description
Network Authentication
Open –No authentication is needed among the wireless network.
Shared – Only wireless stations using a shared key (WEP Key
identified) are allowed to connecting each other.
WPA – This mode is for enterprise with an authentication server
(Radius Server), WPA-enabled access point, and a WPA-enabled
client. Once WPA is enabled, all clients and access points on the
network must be WPA-enabled in order to access the network.
WPA-PSK – It is a special mode designed for home and small
business users who do not have access to network authentication
servers. In this mode, known as Pre-Shared Key, the user
manually enters the starting password in their access point or
gateway, as well as in each PC on the wireless network. WPA
takes over automatically from that point, keeping unauthorized
users that don't have the matching password from joining the
network, while encrypting the data traveling between authorized
devices.
13
Parameter
Description
Data Encryption
WEP – In WPA or WPA-PSK mode, WEP is also able to be the
encryption method for the transmission data.
TKIP – TKIP (Temporal Key Integrity Protocol) changes the
temporal key every 10,000 packets (a packet is a kind of message
transmitted over a network.) This insures much greater security
than the standard WEP security.
AES – AES has been developed to ensure the highest degree of
security and authenticity for digital information and it is the most
advanced solution defined by IEEE 802.11i for the security in the
wireless network.
Note: All devices in the network should use the same encryption
method to ensure the communication.
3.3
Link Status
From the “Link Status” option, you can view all the information of the network you are connecting to.
Parameter
Description
Status
Display the SSID and MAC ID of the network the card is
connecting to.
Current Channel
Display the number of the radio channel and the frequency used
for the networking.
14
Parameter
Description
Current Tx Rate
Display the transmission rate of the network. The maximum
transmission rate is 54Mbps.
Throughput (Kbits/sec)
Display the speed of data transmitted and received.
Link Quality
This bar indicates the quality of the link. The higher the
percentage, the better the quality.
dBm
If you want to know the signal strength in the unit of dBm, select
this check box.
Signal Strength
This bar shows the signal strength level. The higher percentage
shown in the bar, the more radio signal been received by the card.
This indicator helps to find the proper position of the wireless
device for quality network operation.
3.4
Statistics
This option enables you to view the available statistic information with its Tx counts (Tx success, Tx
error, RTS Success and RTS Failed), and its Rx counts (Rx success, Rx error). You may reset the
counters by clicking ”Reset Counter”.
15
3.5
Advance
This option enables you to configure more advanced settings, for example: wireless mode, protection
mode and etc.
Parameter
Description
Wireless Mode
802.11 B/G mix – If you have a mix of 802.11b and 802.11g
wireless stations in your network, it is recommended to setting the
card to this mode. This mode is also the default setting.
802.11 B only – This card can be compatible with both 802.11g
and 802.11b wireless stations. If there are only 802.11b wireless
stations in the network, you can set the card to this mode.
Tx BURST
Tx Burst enables the card to deliver the better throughput in the
same period and environment.
B/G Protection
If you have a mix of 802.11b and 802.11g wireless stations in the
network, it is recommended to enable the protection mechanism.
This mechanism can decrease the rate of data collision between
802.11b and 802.11g wireless stations. When the protection mode
is enabled, the throughput of the card will be a little lower due to
many of frame traffic should be transmitted.
Auto – Based on the status of the network and automatically
disable/enable protection mode.
On – Always enable the protection mode.
Off – Always disable the protection mode.
16
Parameter
Description
ADHOC_OFDM
When the network type is in Ad Hoc mode, that the card can only
work in 11b data rate. It is defined by Wi-Fi organization. If you
want to enable the data rate up to 54Mbps (11g), select
“ADHOC_OFDM”.
Tx Rate
There are several options including
Auto/1/2/5.5/11/6/9/12/18/24/36/48/54Mbps for you to select.
When the “Auto” is selected, the device will choose the most
suitable transmission rate automatically. The higher data rate you
designated in the network, the shorter distance is allowed
between the card and the wireless stations.
When the wireless mode is “802.11 B only”, the maximum data
rate is 11Mbps (11b) so that there are only “Auto/1/2/5.5/11Mbps”
options you can select.
Turn Off RF Button
3.6
If you want to turn off the radio of the card temporarily, click this
button. To turn on the radio, click this button again.
About
By choosing this option, you can click the hyperlink to connect the website for the information of the
wireless chipset vendor and review basic information about the Utility such as the Driver, Utility and
EEPROM Version. The MAC Address of the card is displayed in the screen as well.
17
4 Troubleshooting
This chapter provides solutions to problems usually encountered during the installation and operation
of the card.
1. What is the IEEE 802.11g standard?
802.11g is the new IEEE standard for high-speed wireless LAN communications that provides for
up to 54 Mbps data rate in the 2.4 GHz band. 802.11g is quickly becoming the next mainstream
wireless LAN technology for the home, office and public networks.
802.11g defines the use of the same OFDM modulation technique specified in IEEE 802.11a for
the 5 GHz frequency band and applies it in the same 2.4 GHz frequency band as IEEE 802.11b.
The 802.11g standard requires backward compatibility with 802.11b.
The standard specifically calls for:
A. A new physical layer for the 802.11 Medium Access Control (MAC) in the 2.4 GHz frequency
band, known as the extended rate PHY (ERP). The ERP adds OFDM as a mandatory new
coding scheme for 6, 12 and 24 Mbps (mandatory speeds), and 18, 36, 48 and 54 Mbps
(optional speeds). The ERP includes the modulation schemes found in 802.11b including
CCK for 11 and 5.5 Mbps and Barker code modulation for 2 and 1 Mbps.
B. A protection mechanism called RTS/CTS that governs how 802.11g devices and 802.11b
devices interoperate.
2. What is the IEEE 802.11b standard?
The IEEE 802.11b Wireless LAN standard subcommittee, which formulates the standard for the
industry. The objective is to enable wireless LAN hardware from different manufactures to
communicate.
3. What does IEEE 802.11 feature support?
The product supports the following IEEE 802.11 functions:
CSMA/CA plus Acknowledge Protocol
Multi-Channel Roaming
Automatic Rate Selection
RTS/CTS Feature
Fragmentation
Power Management
4. What is Ad-hoc?
An Ad-hoc integrated wireless LAN is a group of computers, each has a Wireless LAN adapter,
Connected as an independent wireless LAN. Ad hoc wireless LAN is applicable at a
departmental scale for a branch or SOHO operation.
5. What is Infrastructure?
An integrated wireless and wireless and wired LAN is called an Infrastructure configuration.
Infrastructure is applicable to enterprise scale for wireless access to central database, or
wireless application for mobile workers.
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6. What is BSS ID?
A specific Ad hoc LAN is called a Basic Service Set (BSS). Computers in a BSS must be
configured with the same BSS ID.
7. What is WEP?
WEP is Wired Equivalent Privacy, a data privacy mechanism based on a 40 bit shared key
algorithm, as described in the IEEE 802 .11 standard.
8. What is TKIP?
TKIP is a quick-fix method to quickly overcome the inherent weaknesses in WEP security,
especially the reuse of encryption keys. TKIP is involved in the IEEE 802.11i WLAN security
standard, and the specification might be officially released by early 2003.
9. What is AES?
AES (Advanced Encryption Standard), a chip-based security, has been developed to ensure the
highest degree of security and authenticity for digital information, wherever and however
communicated or stored, while making more efficient use of hardware and/or software than
previous encryption standards. It is also included in IEEE 802.11i standard. Compare with AES,
TKIP is a temporary protocol for replacing WEP security until manufacturers implement AES at
the hardware level.
10. Can Wireless products support printer sharing?
Wireless products perform the same function as LAN products. Therefore, Wireless products can
work with Netware, Windows 2000, or other LAN operating systems to support printer or file
sharing.
11. Would the information be intercepted while transmitting on air?
WLAN features two-fold protection in security. On the hardware side, as with Direct Sequence
Spread Spectrum technology, it has the inherent security feature of scrambling. On the software
side, WLAN series offer the encryption function (WEP) to enhance security and Access Control.
Users can set it up depending upon their needs.
12. 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.
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13. What 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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