Wireless LAN Meeting the Needs in Tough Industrial Applications

The most widely used wireless technologies are Wireless LAN (WLAN) and Bluetooth® technology. These technologies meet different needs, but are often used in combination within the same site and even in the same device making coexistence an important issue. This article expands on the different possibilities of WLAN and how it is best applied in industrial applications.

There are several key WLAN features for industrial applications. For instance, in order to reduce interference, there are Frequency-Hopping Spread Spectrum (FHSS) and Direct-Sequence Spread Spectrum (DSSS). FHSS uses a narrow band carrier signal that “hops” from frequency to frequency. Therefore, a signal will only get affected if another signal is transmitting at the same frequency at the same time. DSSS combines data signal with a higher data rate bit sequence, or chipping code. This chipping code is a redundant bit pattern for each bit transmitted, which increases the interference resistance.

In order to transmit large amounts of data, there is Orthogonal Frequency Division Multiplexing (OFDM). OFDM works by splitting the radio signal into multiple smaller sub signals transmitted simultaneously at different frequencies.

In addition to the Wired Equivalent Privacy (WEP) - originally designed to provide the same security level as wired LANs - Wi-Fi Protected Access (WPA) offers improved data encryption through the Temporal Key Integrity Protocol (TKIP) and user authentication through an Extensible Authentication Protocol (EAP).

 

 

Industrial WLAN Requirements

• Reliability and robustness for tough environments
• Security where data may not be manipulated
• Ease of use for installation done by industrial users
• Future proof since industrial installations are large investments requiring long term solutions
• Determinism, as there are varying requirements on latency and timing
• Large network support for several nodes in large scale industrial processes
• Temperature handling to satisfy the extended temperature ranges
• Range capability since distances are typically substantial

 

Implementation Options

When deciding to implement a chipset or a module solution, there are a several essential considerations to be made. Firstly, one needs to determine what RF expertise and experience exists in-house. Secondly, one needs to assess one’s product volumes, as for low volumes, the development costs have a larger impact on product cost. Then, as wireless chipsets are under constant development, one needs to consider one’s product life cycle. A product with a 10+ year life cycle will require several redesigns and as radio transmitting devices require extensive costly approvals, this cost has to be taken several times during a product life cycle.

 

 

Industrial Integration

connectBlue focuses on modules for industrial OEMs where implementation parameters are important. Therefore, connectBlue has developed two WLAN modules that include all necessary RF, antenna and certifications. These modules target the customer in need of integrating WLAN with short time-to-market. Since the modules have the same form factor and interface layout as the Bluetooth modules from connectBlue, the customer has the possibility to prepare its host system for both Bluetooth technology and/or WLAN.

 

SPI WLAN Module

The SPI WLAN module is typically used when integrating WLAN in a device already using IP wired communication. It requires a TCP/IP stack and integration of a module specific WLAN driver in the host. This WLAN driver is available for Linux on TI OMAP and may be modified and adapted for other operating systems and microcontrollers. The interface to the module is SPI.

 

 

Serial WLAN Module

The Serial WLAN Module is a complete WLAN implementation including a TCP/IP stack and WLAN driver. The module interface is UART. It enables the host to stream data over TCP or UDP without an external driver or a TCP/IP stack. It combines simplicity, easy of use, and state of the art low power features. Further, the module is radio type approved and EMC certified for quick adoption in existing devices, facilitating quick time to market.

AT commands are used to configure and control the module in a similar way as the Bluetooth modules. The module is configured via a PC tool or AT commands such as:

AT*AGSSID ESSID	Read/set SSID of access point
AT*AGEM	Read/set Encryption mode (None, WEP64, WEP128, TKIP, AES/CCMP)
AT*AGSM	Read/set Security mode (Shared-WEP64, Shared-WEP128, WPAPSK-TKIP, WPA2-PSK-TKIP)
AT*AGFP	Read/set Encryption/Authentication key
AT*ANIP	Read/set IP-address
AT*ANDHCP	Read/set DCHP activation mode
AT*ADDM	Enter Data Mode