Publication date: 24 April 2007
Imagine you are the manager of a cement company. Your job is to manufacture cement and deliver it to sites all over the country. Production of cement is one challenge but the distribution logistics of delivering thousands of tonnes of product to geographically dispersed customers makes the enterprise particularly challenging. Supply can suddenly become urgent, unforeseen increases in production can leave your customers desperate for cement to prevent their manufacturing process grinding to a halt.
The ability to forecast demand in this environment enables a far more efficient delivery scheduling process. It makes your fleet more cost-effective and keeps customer satisfaction levels high.
The only feasible way to gauge demand from customer sites is to know what they have in their silos in real-time and this can only be achieved if a direct connection from HQ to these remote sites (typically via the internet) can be established.
Given the often remote locations of such manufacturing sites with no land-lines in place for internet access, how can we provide the connection needed?
The solution for the situation described above and many similar applications is to use GPRS ‘cellular’ connectivity.
In the early 1980s, the ‘Groupe Special Mobile’ embarked on the study and development of a pan-European public land mobile system. This work culminated in a European digital standard for mobile (cellular) telephony known as GSM.
The first evolution of GSM occurred in 2001 when General Packet Radio Service (GPRS) was introduced. This IP based extension to GSM was designed solely for data transfer and allows mobile devices to send and receive information at higher data rates than was possible with GSM connections.
In simple terms, anywhere a mobile phone can obtain a signal a GPRS router can be used to provide internet connectivity to industrial equipment. Devices such as PCs, PLCs, serial to Ethernet gateways and data-loggers can then be accessed from a remote PC providing access to real-time data in ways never previously possible.
Image 1
A typical ‘cellular router’. Connects one or many Ethernet devices to the internet without wires.
Vehicle tracking – live data on the status and position of an entire vehicle fleet can be viewed at a central location. This facilitates more effective preventative maintenance and allows for better staff management.
Vehicle counting – by setting up car counting nodes around the UK, it has become possible to see the density and flow of traffic in real-time. This allows research into traffic movement trends and enables the highway authority to issue warnings and apply suitable diversions if accidents occur.
Environmental monitoring – data logging systems in the field normally have to be retrieved to a laboratory before data can be processed. With GPRS connections, wind speed, humidity, temperature variation and other environmental variables can be processed as they happen.
Remote diagnostics – Many companies sell equipment with a PLC fitted to control movement and processes. With a GPRS router installed, the equipment manufacturer can remotely diagnose faults without a costly site visit to rectify simple problems.
GPRS effectively provides a data cable the length and breadth of the globe, allowing PCs to connect to devices in hard to reach locations, on moving vehicles or on off-shore rigs (signal strength permitting). However, there are a number of pitfalls that can easily snare unsuspecting engineers who incorrectly believe implementation of GPRS to be trivial.
Image 2: GPRS in a typical security application
GPRS is the bottleneck of any IP based connection. Whilst a wired Ethernet connection will happily transfer raw data at 100Mbps, GPRS connections can offer as little as 20kbps. The theoretical limit of 171kbps is never realised on modern networks – 50kbps download and 25kbps upload is the typical data transfer rate available.
Bandwidth limitations can be a show-stopper for GPRS projects. However, if the application is considered as a whole and front-end processing can be applied, it is often possible to overcome bandwidth issues with intelligent system design.
Most software that is supplied with Ethernet devices operates as a client application. The Ethernet device acts as a server listening for an incoming connection. This means that the PC must have a route to the target IP address of the device. As standard, GPRS cannot provide this. Mobile devices lease a private DHCP IP address from the mobile network to enable communications. Because the IP address is private, the device is not visible on the public internet and end to end communications cannot take place from your PC to the device.
There are a number of workarounds to this problem and the most popular is to obtain a SIM card with a static public IP address. This effectively means that your Ethernet device is visible on the internet and can be accessed from anywhere in the world. Firewall and authentication measures provide network security.
Signal coverage provided by mobile networks is now well established all over the world. In the UK, operators claim up to 99% GSM/GPRS coverage. The figure quoted is always the ‘population’ coverage and not the ‘geographical’ coverage – clearly the marketing department had some influence in the figures we see.
This means that all populated areas, even rural ones will tend to have GPRS connectivity but many completely isolated locations will not. This is a classic problem for the environmental monitoring fraternity. They could benefit most from real-time connectivity but their equipment is often located in very remote areas - on mountains, in woodland, even off-shore. The problem can sometimes be solved by simply changing the SIM card to one from a different network operator – not all services are equal in all places! Coverage distribution charts are available from most network operators. Consult these before embarking on your GPRS installation.
It is easy to forget that every SIM card in a system will generate some degree of cost. In always-on applications, just keeping the network connection alive (idle TCP connections are terminated by network operators after a set period) will cost money. Specialist network operators can offer multiple SIMs on a single contract making system management easier and airtime subscriptions more cost-effective.
Many potential users of GPRS cellular routers have previously used GSM modems for remote connectivity. This easy to implement solution requires two GSM modems, one or two SIM cards and basic configuration, providing an end to end RS232 connection at 9600bps.
As an IP based service, GPRS is distinctly different. It is more accurate to describe it as a connection to the internet. This means the integrator must understand the concepts of internet connectivity and TCP/IP to maximise the benefits of a GPRS installation.
Despite the handful of stumbling-blocks associated with GPRS and other IP based cellular connectivity solutions, the M2M market is expected to enter a substantial growth phase between 2006 and 2011. This will be driven by the new generation of high-bandwidth cellular protocols such as 3G (UMTS) and HSDPA (Super 3G)
Whilst the 384kbps download of 3G is already a reality, the multi-megabit rates promised by HSDPA will create a whole new industry. At these speeds, HSDPA could offer a last-mile data delivery solution to compete with current broadband technologies and other wireless incarnations such as WiMax.
IP-based cellular routers follow the same basic principles regardless of which wireless technology is used. To invest time now understanding the principles of GPRS would not be wasted, as the concepts for remote cellular access are the same. Get your wireless scheme up and running now, gain the competitive advantage that it brings to your business and seamlessly upgrade to high-speed networks once the coverage is in place.
With several years of cellular integration experience, Amplicon’s application engineers can help with system design and hardware selection – no need for costly consultants!
For further information please contact sales@amplicon.co.uk
DHCP Software that automatically assigns IP addresses to devices logging onto a TCP/IP network. It eliminates having to manually assign permanent IP addresses
HSDPA High-Speed Downlink Packet Access is a mobile telephony protocol. Also called 3.5G or Super 3G. It is a packet-based data service in W-CDMA downlink with data transmission up to 8 to 10Mbps
M2M M2M is a term used to designate the concept of communications between a device containing some amount of data and another device that requires access to that data. M2M is commonly translated as Machine-to-Machine or Man-to-Machine. The most common implementation of M2M is through cellular telemetry systems.
SIM Subscriber Identification Module. The smart card necessary for the operation of GSM phones
UMTS Universal Mobile Telecommunications Service. A 3G mobile telecommunications standard supporting a theoretical data throughput of up to 2 Mbps
WiMax Worldwide Interoperability for Microwave Access. A certification mark for products that pass conformity and interoperability tests for the IEEE 802.16 standards. IEEE 802.16 is working group number 16 of IEEE 802 specialising in point-to-multipoint broadband wireless access
