Files for
Size:
585.37 Kb
Download

User Manual

AOI-812

IEEE 802.11g Wireless LAN PC Card

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 device and its antenna must not be co-located or operating in conjunction with any other antenna or transmitter.

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 Communications 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 2.5cm (1 inch) during normal operation.

Federal Communications Commission (FCC) RF Exposure Requirements

SAR compliance has been established in the laptop computer(s) configurations with PCMCIA slot on the side near the center, as tested in the application for Certification, and can be used in laptop computer(s) with substantially similar physical dimensions, construction, and electrical and RF characteristics. Use in other devices such a PDAs or lappads is not authorized. This transmitter is restricted for use with the specific antenna(s) tested in the application for Certification. 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 .........................................................

6

 

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 PC 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.

1.1Features

Works with both IEEE 802.11b and IEEE 802.11g products.

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 Cardbus interface.

1.2Specifications

Standard: IEEE 802.11b/g

Interface: 32-bit Cardbus

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

Security: 64/128-bit WEP Data Encryption, WPA, AES and IEEE 802.1x

1

Antenna: Printed Antenna with Diversity System

Drivers: Windows 98SE/Me/2000/XP

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: 8(H) x 118(W) x 54(D) mm

Temperature: 32~131°F (0 ~55°C)

Humidity: Max. 95% (NonCondensing)

Certification: FCC, CE

1.3Package Contents

Before you begin the installation, please check the items of your package. The package should include the following items:

One PC Card

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 the following descriptions.

Note1: Please do not install the card into your laptop computer before installing the software program from the CD.

Note2: The following installation was operated under Windows XP. (Procedures are similar for Windows 98SE/Me/2000.)

Note3: If you have installed the Wireless PC Card driver & utility before, please uninstall the old version first.

A. Insert the Installation CD to your CD-ROM Drive. Execute the “setup” program.

B. Click “Easy Install” or “Next” to continue.

C.The system starts to install the software of the card. Follow the instruction of the program to plug in the PC card into the Cardbus slot of your laptop computer.

3

D.The system will automatically detect the card and display “Hardware Installation” screen. Click “Continue Anyway” to continue.

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”.

F. Click “Finish” to complete the installation.

4

G. The “RaConfig” utility 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 PC 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-clicking the icon.

Right click the icon. There are some items for you to operate the configuration utility.

zLaunch Config Utilities

Select “Launch Config Utilities” to open the Configuration Utility tool.

zExit

Select “Exit” to close the Configuration Utility tool.

3.1Site 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.

 

 

3.2Profile

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 displays 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 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 laptop 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 as 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 connect to 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 include TKIP and AES. Note

 

that this option is only available to 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

The WEP keys are used to encrypt data transmitted in the

(Key1 ~ Key4)

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

 

selecting 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 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).

zNote: 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 advanced setting or check the link status and statistics from the “RaConfig” utility.

1.From here, right click the icon to select “View Available Wireless Networks”.

2.Press “Advanced” button from “Wireless Network Connection”.

12

3.Press “Configure” button to configure the WPA function for the current network.

Note: If “Use Windows to Configure my wireless network settings” is unchecked, 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 connect to 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.

3.3Link 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 received by the card. This

 

indicator helps to find the proper position of the wireless device for

 

quality network operation.

3.4Statistics

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

3.5Advanced

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 set 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

 

the accommodation to frame traffic for both 802.11b and 802.11g

 

wireless stations.

 

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

If you want to turn off the radio of the card temporarily, click this

 

button. To turn on the radio, click this button again.

3.6About

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 adapter.

1. What is the IEEE 802.11g standard?

802.11g is the 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 manufacturers to communicate.

3. What does IEEE 802.11 feature support

The product supports the following IEEE 802.11 functions:

zCSMA/CA plus Acknowledge Protocol

zMulti-Channel Roaming

zAutomatic Rate Selection

zRTS/CTS Feature

zFragmentation

zPower 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.

18

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.

19

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).

20