Project Assignment

This project is an application type paper, in which we consider ourselves building a Wireless LAN system, with some fixed budget constraints. The assignment was originally to do a comparative survey on CDMA and TDMA Wireless LAN equipment to determine which will best fit our needs. During our vendor data collection we discovered that no vendors are using the TDMA technology so we altered the assignment to do a comparison study on CMDA – DIRECT SEQUENCE and CDMA – FREQUENCY HOPPING.

Definitions

 Wireless LAN (WLAN)

What is a wireless LAN?

 "A wireless LAN (WLAN) is a semi-mobile data communication system. Most often it’s used as an extension to a wired LAN within a building or give area. WLANs transmit and receive data using radio frequency (RF) technology, over the air, minimizing the need for wired connections. WLANs try to combine data connectivity with user mobility, and, through simplified configuration, enable movable LANs."

 The spreading techniques normally used in wireless LAN products can be divided into two families: Frequency Hopping Spread Spectrum (FHSS) and Direct Sequence Spread Spectrum (DSSS). The first approach resists interference by jumping rapidly from frequency to frequency in a pseudorandom way. The receiving system has the same pseudorandom algorithm as the sender, and jumps simultaneously. The second approach resists interference by mixing in a series of pseudorandom bits with the actual data. The receiver, using the same pseudorandom algorithms, strips out the extra bits.

 Some Applications for Wireless LANs

Wireless LANs frequently provide the final few meters of connectivity between a backbone network and the mobile user. The staff in hospitals use very small computers with wireless LAN capability receive patient information instantly. Audit teams or small workgroups increase productivity with quick network setup. In a dynamic environment with wireless LANs the overhead of moves, adds, and changes are minimized. Training sites at corporations and students at universities use wireless connectivity to facilitate access to information, information exchanges, and learning. When installing networked computers in older buildings it may be difficult to interconnect the computers without using wireless LANs as a network infrastructure solution. Trade show and branch office workers minimize setup requirements by installing preconfigured wireless LANs. Warehouse workers use wireless LANs to exchange information with central databases and increase their productivity. Network managers implement wireless LANs to provide backup for mission-critical applications running on wired networks.

Benefits of WLANs

"With wireless LANs, users can access shared information without looking for a place to plug in, and network managers can set up or augment networks without installing or moving wires."

How WLANs Work

"Wireless LANs use electromagnetic airwaves (radio and infrared) to communicate information from one point to another without relying on any physical connection. Radio waves are often referred to as radio carriers because they simply perform the function of delivering energy to a remote receiver. The data being transmitted is superimposed on the radio carrier so that it can be accurately extracted at the receiving end. This is generally referred to as modulation of the carrier by the information being transmitted. Once data is superimposed (modulated) onto the radio carrier, the radio signal occupies more than a single frequency, since the frequency or bit rate of the modulating information adds to the carrier. Multiple radio carriers can exist in the same space at the same time without interfering with each other if the radio waves are transmitted on different radio frequencies. To extract data, a radio receiver or augment networks without installing or moving wires. Wireless LANs tunes in (or selects) one radio frequency while rejecting all other radio signals on different frequencies.

In a typical WLAN configuration, a transmitter/receiver (transceiver) device, called an access point, connects to the wired network from a fixed location using standard Ethernet cable. At a minimum, the access point receives, buffers, and transmits data between the WLAN and the wired network infrastructure. A single access point can support a small group of users and can function within a range of less than one hundred to several hundred feet. The access point (or the antenna attached to the access point) is usually mounted high but may be mounted essentially anywhere that is practical as long as the desired radio coverage is obtained.

End users access the WLAN through wireless-LAN adapters, which are implemented as PC cards in notebook computers, ISA or PCI cards in desktop computers, or integrated within hand-held computers. WLAN adapters provide an interface between the client network operating system (NOS) and the airwaves (via an antenna). The nature of the wireless connection is transparent to the NOS."

The IEEE 802.x WLAN standard

"A set of specifications for Local Area Networks (LAN) from The Institute of Electrical and Electronic Engineers (IEEE). Most wired networks conform to 802.3, the specification for CSMA/CD based Ethernet networks or 802.5 the specification for token ring networks. There is an 802.11 committee working on a standard for 1 and 2 Mbps wireless LANs. The standard will have a single MAC layer for the following physical-layer technologies: Frequency Hopping Spread Spectrum, Direct Sequence Spread Spectrum, and Infrared. Draft versions of the specification are in process."

This standard covers both Ad-hoc systems and base-station systems. The standard specifies 3 different frequencies, 915 MHz, 2.4 GHz and 5.2 GHz. No licensing is required for these frequency bands. The standard also covers such things as multiple priorities, support for time critical and data traffic and power management.

CDMA

What is CDMA?

"CDMA stands for "Code Division Multiple Access." It is a form of spread-spectrum, an advanced digital wireless transmission technique. Instead of using frequencies or time slots, as do traditional technologies, it uses mathematical codes to transmit and distinguish between multiple wireless conversations. Its bandwidth is much wider than that required for simple point-to-point communications at the same data rate because it uses noise-like carrier waves to spread the information contained in a signal of interest over a much greater bandwidth. However, because the conversations taking place are distinguished by digital codes, many users can share the same bandwidth simultaneously. The advanced methods used in commercial CDMA technology improve capacity, coverage and voice quality, leading to a new generation of wireless networks.

Old-fashioned radio receivers separate stations and channels by filtering in the frequency domain. CDMA receivers, conversely, separate communication channels by a pseudo-random modulation that is applied and removed in the digital domain. Multiple users can therefore occupy the same frequency band. This universal frequency reuse is crucial to CDMA's distinguishing high spectral efficiency. CDMA has gained international acceptance by cellular radio system operators as an upgrade because of its universal frequency reuse and noise-like characteristics."

"In a spread spectrum system, there is a possibility to multiplex users by assigning them different spreading keys. Such a system is called a Code Division Multiple Access (CDMA) system. However, most wireless LAN products are not CDMA systems since users belonging to the same wireless LAN utilize the same spreading key. Instead users are multiplexed in time using nearly the same Carrier Sense Multiple Access (CSMA) protocol as in Ethernet."

In Wireless Lan systems, the CDMA system is used differently than it was in Cellular systems. Cellular systems used the technology for medium access, to allow more users to utilize the channel at a time. Wireless Lans, on the other hand, utilize the technology at the physical layer to combat the effects of noise on the channel.

Direct Sequence CDMA

In Direct Sequence spread spectrum transmission, the user data signal is multiplied by a code sequence. Mostly, binary sequences are used. The duration of an element in the code is called the "chip time". The ratio between the user symbol time and the chip time is called the spread factor. The transmit signal occupies a bandwidth that equals the spread factor times the bandwidth of the user data.

With this technique, wireless Lans use an 11 bit chipping code. Because of this, there are several drawbacks in the direct sequence CDMA system.

It requires the rate of the channel to be much higher than the desired effective data rate.

It causes a delay in the signal.

It causes the equipment to be expensive

It is difficult to allow multiple users to access the channel at the same time.

 Frequency Hopping CDMA

 In frequency hopping systems, the transmitter changes the carrier frequency according to a certain "hopping" pattern. The advantage is that the signal sees a different channel and a different set of interfering signals during each hop. This avoids the problem of failing communication at a particular frequency, because of a fade or interference.

 With this technique, wireless Lan systems utilize 79 different channels. The hopping is done using a random number generator, which can be controlled by setting the seed to a certain value. While hopping, the system uses a fixed dwell time at each channel. As well as controlling the effects of noise, this system can allow multiple users on the channel simply by setting the seeds to different values, so that the two aren’t accessing the same channels at the same time.

Vendor Information

 Direct Sequence CDMA Systems

Aironet Wireless Communications, Inc.

http://www.lantimes.com/buyers/company/194019/339033.html

ARLAN 2000 Wireless LAN

Used to connect mobile or stationary wireless users, typically within a building, to a wired LAN. Uses 2.4GHz direct sequence spread spectrum radio and supports speeds up to 2M bps. Wireless Access Points connect directly to the network backbone and create a "microcell" of coverage up to 1,000 feet in radius for wireless clients. Multiple Access Points can be used to cover a larger area, and mobile users can seamlessly roam between them using our patented ARLAN Microcellular architecture. Wireless Adapters replace standard network interface cards (NIC) in client computers, and come with NDIS, ODI, and packet drivers.

Price:

AP2000-E Ethernet Access Point: $1,995;

AP2000-T Token-Ring Access Point: $2,795;

PC2000 PC-Card Adapter: $795; IC2000 ISA

Adapter: $995; MC2000 Microchannel

Adapter: $1,295

http://www.lantimes.com/buyers/company/194019/339034.html

ARLAN 1000 Wireless LAN

Used to connect mobile or stationary wireless users, typically within a building, to a wired LAN. Uses 900MHz direct sequence spread spectrum radio and supports speeds up to 860K bps. Wireless Access Points connect directly to the network backbone and create a "microcell" of coverage up to 2,000 feet in radius for wireless clients. Multiple Access Points can be used to cover a larger area, and mobile users can seamlessly roam between them using our patented ARLAN Microcellular architecture. Wireless Adapters replace standard network interface cards (NIC) in client computers, and come with NDIS, ODI, and packet drivers.

Price:

AP1000-E Ethernet Access Point: $1,795;

AP1000-T Token-Ring Access Point: $2,595;

PC1000 PC-Card Adapter: $695; IC1000 ISA

Adapter: $895; M12000 Microchannel

Adapter: $1,095

 Digital Equipment Corp.

http://www.lantimes.com/buyers/company/192291/322224.html

RoamAbout

Digital offers a complete portfolio of mobile and wireless products. RoamAbout PC Cards -- wireless PC Cards that provide wireless LANs between portable devices, and a connection back to the wired LAN with the RoamAbout Access oint. RoamAbout ISA Adapters -- wireless ISA adapters that provide wireless LANs between desktop devices. RoamAbout Access Point -- a wireless bridge that allows users of wireless desktop and portable devices to communicate with the wired Ethernet network.

Price: $595 to $1,795

 http://www.europe.digital.com/info/LI01KW/LI01KWAH.HTM

http://www.europe.digital.com/info/LI01KW/LI01KWSC.TXT

RoamAbout Access Point -- provides the bridge between wireless and wired LANs

 RoamAbout 2.4 GHz Direct Sequence Wireless LAN adapters -- provide a secure, high-performance wireless 2.4 GHz LAN connection for portable computers with a PCMCIA slot and desktop PCs with an ISA bus slot

 RoamAbout 915 MHz Direct Sequence Wireless LAN adapters -- provide a secure, high-performance wireless 915 MHz LAN connection for portable computers with a PCMCIA slot and desktop PCs with an ISA bus slot

 Lucent's WaveLAN

http://www.lantimes.com/buyers/company/200320/366449.html

Lucent's WaveLAN products provide a flexible means of connecting computers within a facility and linking multiple facilities. They are designed for restaurant, hospital, and warehouse environments that require mobile data collection and wireless transmission. Available in 915MHz and 2.4GHz versions, the WaveLAN product line includes the WaveLAN/PCMCIA card for notebook and portable computers (both PC and Macintosh), WaveLAN/AT card for desktop computers, WavePOINT access point, WaveAROUND roaming software, WaveMANAGER installation/survey program,and WaveMODEM wireless modem for OEM products. WaveLAN products have been selected by major vendors worldwide including NEC, Hitachi, Toshiba, Digital Equipment, and Epson.

Price: $1,295-WavePOINT II; $545-WaveLAN/AT Card;

$495-WaveLAN PCMCIA Card

 http://www.wavelan.com/

ftp://ftp.wavelan.com/pub/pdf-file/wp/fs-wp1.pdf

Frequency Hopping Systems

 Aironet Wireless Communications, Inc.

http://www.lantimes.com/buyers/company/194019/339032.html

ARLAN 3000 Wireless LAN

Used to connect mobile or stationary wireless users, typically within a building, to a wired LAN. Uses 2.4GHz frequency hopping spread spectrum radio and supports speeds up to 2M bps. Wireless Access Points connect directly to the network backbone and create a "microcell" of coverage up to 1,000 feet in radius for wireless clients. Multiple Access Points can be used to cover a larger area, and mobile users can seamlessly roam between them using our patented ARLAN Microcellular architecture. Wireless PC-Card Adapters replace standard network interface cards (NIC) in client computers, and come with NDIS, ODI, and packet drivers.

Price:

AP3000-E Ethernet Access Point: $1,895;

AP3000-T Token-Ring Access Point: $2,695;

PC3000 PC-Card Adapter: $695

Breeznet http://www.breezecom.com/

http://www.lantimes.com/buyers/company/200065/361671.html

The BreezeNET AP-10 PRO Access Point is a 3M bps, wireless LAN device which creates a cell

of connectivity for BreezeNET wireless client devices, including the SA-PC PRO PCMCIA Adapter and SA-10 and SA-40 PRO station adapters. The AP-10 PRO is a networking infrastructure product which has been designed to deliver maximum performance and functionality. With its faster, more efficient processors and antenna diversity, the AP-10 PRO Access Point transmits data reliably at ranges up to 3,000 feet, requiring 25 percent less equipment.

Price: $1,495

Version: AP-10 PRO

Digital Equipment Corp.

http://www.lantimes.com/buyers/company/192291/322224.html

RoamAbout

Digital offers a complete portfolio of mobile and wireless products. RoamAbout PC Cards -- wireless PC Cards that provide wireless LANs between portable devices, and a connection back to the wired LAN with the RoamAbout Access oint. RoamAbout ISA Adapters -- wireless ISA adapters that provide wireless LANs between desktop devices. RoamAbout Access Point -- a wireless bridge that allows users of wireless desktop and portable devices to communicate with the wired Ethernet network.

Price: $595 to $1,795

 http://www.europe.digital.com/info/LI01KW/LI01KWAH.HTM

http://www.europe.digital.com/info/LI01KW/LI01KWSC.TXT

RoamAbout Access Point -- provides the bridge between wireless and wired LANs

RoamAbout 2.4 GHz Frequency Hopping Wireless LAN adapters -- provide a secure, steady wireless 2.4 GHz LAN connection for portable computers with a PCMCIA slot and desktop PCs with an ISA bus slot

Radio Frequency band 2.4 -- 2.4835 GHz

Radio type Spread spectrum

Spread Frequency hopping spectrum technique

Independent 15 channels

Output power 100 mW

Power Approximately 10% -- 15% of typical consumption portable computer battery life

with PC card Standby mode: 5 mA

 IBM Wireless LAN

http://www.lantimes.com/buyers/company/191950/340124.html

A solution for small- to medium-sized businesses. The new IBM Wireless LAN Entry product family is a PCMCIA radio frequency adapter with an integrated radio and an IBM 8227 Wireless LAN Entry Access Point. The IBM WirelessLAN Entry uses advanced spread spectrum technology operating in the 2.4GHz band. The features of the IBM Wireless LAN Entry include a low-cost mobile Ethernet LAN connectivity for existing LAN Applications, simplified wireless solution, mobile computer support with fully integrated PCMCLA Type II extended adapter, automatic roaming for multicell coverage, new workgroup applications support with peer-to-peer networking, low-power consumption adapter which extends system battery life, and wireless transparent MAC bridge (8227) with Remote Program Load (RPL) and SNMP management.

Price: Wireless LAN Entry Credit Card Adapter $445;

Access Point/Integrated antenna $1,350

IBM http://www.raleigh.ibm.com

http://www.networking.ibm.com/wireles/wdprods/jb.htm

Advanced Spread Spectrum Frequency Hopping (SSFH) radio technology in the 2.4GHz frequency band plus Time Division Multiple Access (TDMA) provide excellent interference protection and high network capacity; standard features include data encryption.

Proxim

http://www.proxim.com/

RangeLAN2 7530 Token Ring Access Points (APs) provide standards-based connectivity from your Token Ring wired network to your wireless RangeLAN2 or WLI Forum- compatible product. With comprehensive management features, easy installation, exceptional durability and reliability, and outstanding performance, the RangeLAN2 Token Ring access point meets your requirements for industrial-strength wireless networking equipment.

The RangeLAN2 7530 AP uses Proxim’s patented frequency hopping spread-spectrum (FHSS) technology, winner of PC Magazine’s Editors’ Choice and LAN Magazine’s Product of the Year awards. More OEM solutions providers have standardized on RangeLAN2 technology than all other wireless LAN products combined.

 Radio Data Rate 1.6 Mbps

Channels Supports 15 independent, non-interfering "virtual channels" (hopping patterns)

Range (Standard Antenna)

Up to 500 feet radius (150 meters) indoors

1000+ feet radius (300+ meters) outdoors

(more with optional antennas)

Radio

Frequency Band 2.4 GHz frequency band, actual frequencies in use vary by country

Radio Type Frequency Hopping Spread Spectrum (FHSS)

Radio Power Output 100 mW

http://www.lantimes.com/buyers/company/192294/307408.html

RangeLAN2/Access Point is a wireless local bridge, operating at the Data-link level (layer 2) of the OSI model. As a layer 2 system, RangeLAN2/Access Point provides protocol-independent access for RangeLAN 2 mobile computer users into existing IEEE 802.3 wired Ethernet LANs. RangeLAN2/Access Point is designed to optimize the performance and reliability of hybrid wired/wireless LANs by filtering or discarding local packets and only forwarding packets meant for other network traffic. Once identified, the address information is stored and forwarded within the network if required, resulting in an overall reduction in network traffic.

Price: $1,895

http://www.lantimes.com/buyers/company/192294/307406.html

RangeLAN2/ISA is a long-range, high-performance wireless LAN adapter for AT-bus desktop PCs and servers. RangeLAN2/ISA's data rate of 1.6M bps exceeds the data rate requirements of most standard PC applications, making it an ideal wireless platform for high-speed LAN environments. The RangeLAN 2 family delivers a range of up to 500 feet in normal office locations and up to 1,000 feet in open-space environments. The RangeLAN2 family provides transparent access to standard-wired LAN environments. RangeLAN2/ISA provides an easy-to-install, wireless extension to existing wired client/server LANS for desktop locations that are difficult or expensive to wire.

Price: $595

Version: ISA

RangeLAN2/PCMCIA is a high-performance, wireless LAN adapter for portable computers equipped with a PCMCIA Type II slot. RangeLAN2/PCMCIA is based on frequency hopping spread spectrum technology in the 2.4GHz to 2.4835GHz band. With a data rate requirement of most standard PC LAN applications, it is an ideal wireless platform for mobile computer users in high-speed LAN environments. It is operable at a distance of up to 500 feet in normal office environments and up to 1,000 feet in open spaces. Through a multichannel approach, RangeLAN2/PCMCIA enables 15 independent wireless LANs to operate within the same physical space, effectively increasing the aggregate capacity of RangeLAN2/PCMCIA networks by 15 times.

Price: $695

Version: PCMCIA

RDC Networks

http://www.lantimes.com/buyers/company/196323/307604.html

PortLAN

PortLAN is a high-performance wireless LAN solutions designed for mobile users and to avoid wiring problems. The product consist of an access point bridged to Ethernet and a user unit with a PCMCIA or ISA interface, plus a small radio. Expandable configuration cover multiple cells, supporting roaming. PortLAN supports major NOS's. RDC's implementation of Spread Spectrum Frequency Hopping radio technology yields breakthrough in distances and robustness against interferences, meaning higher network availability. PortLAN uses the 2.4GHz ISM band. (no license needed, FCC in the USA, ETSI in Europe). The product is available through a network of resellers and system integrators.

Price: $695 user unit

$2,195 access point (hub)

Wave Wireless Networking

http://www.lantimes.com/buyers/company/196160/365833.html

SPEEDLAN 3i is a high-performance, indoor, wireless LAN that operates at data rates of up to 3M bps. 2.5M bps throughput can be achieved by using a multicell, wireless roaming configuration. SPEEDLAN 3i single-piece, wireless LAN adapter for portable computers is equipped with a PCMCIA Type II card slot. 2.4GHz ISM band, optional data encryption. License-free.

Price: $1,700-base

$700-PCMCIA card

$3,100-both

http://www.speedlan.com/

SPEEDLAN 3i Specifications

Model: SPEEDLAN 3i

Description: 2.4 GHz Wireless LAN Access Point

Wireless Medium: Frequency Hopping Spread Spectrum Radio

Operating Frequency: 2.4000-2.4835 GHz (in US and Canada)

2.4000-2.5000 GHz (in Europe)

2.4710-2.4970 GHz (in Japan)

Performance:

Data Rate (DR) per Channel: 3 Mbps with fallback to 1.65 Mbps

Typical Number of Channels: 15 (US, Canada, and Europe), 4 (Japan)

Channel Throughput: 2.5 Mbps @ 3.Mbps DR, 1 Mbps @ 1.6 Mbps DR

Access Point

Users per Access Point: 60

Output Power: 50 mW

Maximum Channels/Hopping Patterns: 75

Hopping Speed: 20 ms

Adapter PC Card Type II

Output Power: 50 mW

Maximum Channels/Hopping Patterns: 75

Hopping Speed: 20 ms

Current Draw*: Max Peak-400 mA, Sleep Mode

Current-15 mA, Transmit-350 mA

Other Support: PCMCIA Card and Socket Services ver. 2.1, Hot swapping,

Suspend and resume, Speedlan Power Saving Protocol,

IEEE 802.11 compliant

Deciding between the Direct Sequence and Frequency Hopping technologies is really not difficult. Frequency Hopping will be used. The difference in price between the two technologies is insignificant, so this decision is based on the features and drawbacks of the technologies themselves. Direct Sequence does not have all of the features that Frequency Hopping has and it has more drawbacks.

• The use of the 11 bit chipping code in the Direct Sequence system causes the required data rate of the channel to be much greater.
• Direct Sequence causes a delay in the signal.
• It is difficult for multiple users to access the channel in Direct Sequence due to the fact that very few codes can be used. However, by using different seeds with Frequency Hopping, multiple users can access the channel.

Since we are limited by a fixed budget, we must decide on what type of architecture we should pick for our system.

If the requirements deem that only a small local Wireless Lan is needed, we would stick with an Ad-hoc system. This solution would be the least expensive. Here we will only require the adapter cards for each node in the network. These nodes would be set up in a point-to-point network, eliminating the need for an access point. If however, the requirements are such that a point-to-point network is not suitable, we must go with a Basic Service Set, which includes an access point. Since the access point is the most expensive portion, this will drive our price up.