Chapter 2 Literature Survey This chapter presents a brief report on literature reviewed in context to present work with an aim to identify current state of research in the domain. Literature review is presented in two sections, first related to review of remote access technologies both for short and long range and second related to study of current microcontroller technologies. General conclusions drawn on basis of literature reviewed are presented towards the end of the chapter. 2.1 Remote access technologies The concept of remote access of systems existed in different form since the era of automation and computers that well predates mobile communication technologies. It had been known by different names like telemetry, industrial automation, SCADA, etc. Mostly the technology solutions for remote access that existed at that time had been proprietary or custom-developed and highly expensive. This not only restricted its wide spread implementation but also constrained its implementation wherever used. Hence, presence of these technologies was limited to large sectors like process industries (eg. oil and gas industry), electricity transmission and distribution, railway networks etc. However, in 1990s the trends of globalization imposed the requirement of adhering to international and open standards for survival in the market. This in parallel was supported by remarkable growth in sector of programmable devices and communication technologies. This opened up opportunities of using various non-proprietary, open standard off-the-shelf technologies with embedded systems for the purpose of remote access. Literature is available discussing the use of various off-the-shelf technologies like public switched telephone network (PSTN), GSM, GPRS, Internet, Wi-Fi, power line carrier 10
communication (PLCC), Bluetooth, ZigBee, IrDA, etc, for remote access. Discussion on some of these technologies related to present work is discussed as follows. Global system for mobile communication (GSM) GSM represents the second generation (2G) cellular phone technology deployed in 1991 with proposed major use for voice communication. In 1995, Siemens launched first GSM based data module proposed to be used for machine-to-machine (M2M) industrial applications. However, there had not been substantial interest shown by the researchers in this area till the beginning of year 2000. Research paper by Peersman. C., et al., [4] can be considered to be one of the first in the line that explained the use of short message service (SMS) over GSM network for implementing telemetric services. In last one decade infrastructure of GSM network has considerably evolved with significant increase in geographical spread and number of users. This has also considerably reduced service charges. All these have resulted into growing interest in use of GSM network for remote access. In [5] feasibility of using GSM-SMS for remote data acquisition has been experimentally studied. Its performance has been tested in terms of transmission time, rate of delivery failure and correctness of data transmitted. The study shows that GSM-SMS technology with support of control system at backend can provide an efficient mechanism for remote data access in any system or a network and can satisfy real time operation needs of the system provided the rate of change of system parameters is relatively slow and system is present in good service coverage. Similar study on evaluating performance parameters has been presented in [6] using statistical approach on a sim and reflects similar conclusions. Literature [7]-[13] discusses various field and industrial applications based on use of SMS for remote data access. Basic system architecture discussed in all these papers is primarily same however researchers have made use of different platforms for implementation that varies from 8 bit programmable systems to digital signal processor and field programmable gate arrays (FPGA). Use of GSM-SMS technology for remote health monitoring and telemedicine has also been reported in number of literature [14]-[17]. Irrespective of the basic hardware of the system, 11
hardware related to SMS based remote access was based on use of low cost GSM modem. Thus, the study shows that SMS based remote access system proves to be a low-cost system with high-quality transmission characteristics on readily available network. General packet radio service (GPRS) GSM-SMS technology for remote access is not suitable for applications that require higher data rate, real time monitoring and/or connectivity through internet. For such applications the technology suitable is GPRS. As described in [18], [19] GPRS is often described as 2.5G cellular technology that lies between second (2G) and third (3G) generations. Compared to 3G, 2.5G (i.e. GPRS), has an easy migration path from 2G and hence has evolved relatively faster. GPRS is essentially the service operating on basic 2G network particularly to meet demands of data services. Unlike GSM that works on circuit switching data transfer, GPRS applies a packet radio principle to transfer data. This makes it compatible with the leading packet-based internet communication protocols like Internet protocol (IP). GPRS technology has been used effectively with number of diverse application domain. In [20], [21] onboard diagnosis system for an automobile linked to GPRS network for remotely monitored has been discussed. Literature [22] reports one of the most popular applications of GPRS that is vehicle tracking. Similar applications are reported related to health monitoring [23], [24], industrial monitoring [25], consumer applications [26], power systems [27], etc. Depending on the domain of application in each of the referred literature the design of the system being monitored, that is linked to GPRS as a communication link, changes. Depending on the application GPRS communication link has been used in different modes like dynamic IP based link, virtual static IP based link, virtual static IP based link with Virtual private network (VPN), etc. Data collected from the system being monitored is forwarded over GPRS link to internet and received on the web server. Performance of GPRS in term of data traffic throughput and transmission delay has been verified on simulation platform [28] as well as experimentally [29]. Studies indicate that nature of GPRS traffic has bursty characteristics and changes over different duration during day. Further the achieved data 12
rate has been relatively low compared to the theoretical maximum of 114 kbps. However, as applications related to remote monitoring and control mostly do not require high data rates the data rates achieved has been acceptable. Internet Internet has become a global medium for information exchange and has gone through explosive growth is past decade. Although the most visible growth has been within the world wide web, much of the real growth has been in the infrastructure and bandwidth. Further, the Web also has evolved from an entity providing static information to an infrastructure delivering dynamic information. Because of this universal interface available through internet it can be used as a technology for remote data access in embedded systems. For an embedded system to be connected to internet it requires TCP/IP capabilities. Systems with such capabilities then can be connected to any existing internet network in an ad-hoc manner and thus would become accessible over the internet globally. Literature [30]-[33] is available that discuss use of internet as technology for remote access with variety of embedded applications. Study of all these applications reveals that TCP/IP capabilities are added to the existing system using following possible alternatives. 1. Implement TCP/IP stack on the microcontroller of application system itself thus the system inherently provides Ethernet connectivity. To implement TCP/IP stack large capacity of program memory is needed, and microcontroller must operate very fast. Here, the designer must be familiar with TCP/IP protocol and correlative interface, so software program design is more complicated and workload is relatively serious. 2. Use ready-to-use Ethernet boards. These boards are microcontroller based boards and have open source TCP/IP stack and embedded web server ported on it. With minimum efforts in programming such boards can be easily interfaced with the application system providing Ethernet connectivity to the system. 13
3. Use special network chips, commonly called Ethernet controllers, to connect the application system to Internet. These chips are designed to serve as an Ethernet network interface for any controller, thus helps to realizes TCP/IP protocol by hardware. Application system interprets and executes the data or instructions transmitted from network chip for actualizing Internet connection. Use of network chip can economize microcontroller resource and design and realization becomes relative simple. Literature [34], [35] is also available that discuss other off-the-shelf and/or open standard technologies for remote access giving their advantages and disadvantages. Short range remote access technologies Bluetooth, ZigBee, IrDA and Wi-Fi are some off-the-shelf technologies popular for short range wireless data access. Literature [36]-[39] is available that discusses the characteristics of these technologies. Cost, size, performance and power are common design metrics considered for selection of the technology. IrDA [37] is a simple technology to implement in comparison to others and also consumes less power; however the preferred communication mode is line of sight. Further, mechanism of data security is absent in IrDA. Similarly, Wi-Fi consumes high power and is mainly for higher bit rates [38]. Due to these reasons Bluetooth and ZigBee are more adopted technologies in embedded system compared to them. In [40] a point to point network has been implemented using Bluetooth for the purpose of health monitoring. In contrast to this in [41] it is used to set up a sensor network for remote monitoring of patient s physiological signals. As Bluetooth supports relatively short range communication their use is found to be abundant in indoor applications like health monitoring and home security. In applications that involve monitoring a multi-node network spread over relatively longer distance and one that are constrained in power, ZigBee is more preferred technology compared to Bluetooth. In [42] ZigBee technology has been elaborately evaluated in terms of its energy efficiency, networking and data management capabilities and security for wireless sensor networks. Number 14
of applications in domain of wireless sensor networks [43], health monitoring [44], industrial monitoring and control, etc, are reported in literature. In many instances depending on the application ZigBee technology is also used in combination with other wireless technologies like WLAN [45], GPRS [46], Ethernet [47], etc. 2.2 Microcontroller technologies Microcontrollers are the engine of embedded domain and selection of proper microcontroller critically decides the success or failure of the design. As microcontroller technology is improving at a very fast rate and with large number of leading manufacturers in the field regular review of market becomes essential. Literature [48], [49] highlights methods and criterions for selecting appropriate microcontroller for an embedded system. These criterions cover both technical as well as non-technical issues associated with design process. Some of the important technical issues that play part in selection of microcontroller are its architecture, computational power, memory support, on-chip peripherals, options for connectivity with external hardware, in-built special function hardware, power consumption, speed of operation, development tools, etc. Similarly some of the non-technical issues are project budget, size and weight restrictions or aesthetic considerations, operating environment, availability in market, support from manufacturer, expertise of development team, etc. The trends in microcontroller technology few years back was towards smaller, faster and cheaper microcontrollers; however the paradigm in today s market has shifted towards technology that demands low power, provides easy in handling complex software development and have greater integration of intelligent peripherals [50]. Increase in number of battery operated application has compelled microcontroller technology to come up with ultra low power designs. One such example is 16-bit microcontroller MSP430 from Texas Instruments [51]. Similarly demand of better software development support has brought programmable system-on-chip (PSoC) type of devices in the market. For example, PSoC4 from Cypress [52] is an ARM based device 15
that supports programmable mixed-signal hardware IP. Using this platform it is possible to build own custom mixed-signal system-on-chip with programmable analog and digital blocks combined with flexible routing and interconnects. Such devices help to shorten development schedule and accelerate time-to-market. Though the microcontroller technology is becoming more featurful and complex by time, still as per the research [50], around 80 percent of embedded applications are still based on 8-bit or 16-bit microcontroller. However, as 32-bit microcontrollers like ARM, are becoming competitive in pricing, it is expected that in next few years market share of such processor is going to increase. 2.3 General observations on basis of literature survey General observations on basis of literature survey are listed as follows. 1. Use of off-the-shelf technologies for remote access is efficient as well as economic solution for remote monitoring and control of system. 2. Number of off-the-shelf technologies both for long range and short range data communication are available in market to be used for remote access 3. Much work has been done in using GSM-SMS and GPRS technology for remote data access. However, most of the designed systems required higher operational cost and hence are justified only for industrial and biomedical application in developed and developing countries. 4. Most of the applications designed around GSM-SMS technology involved one way communication. Systems can be made more effective and meaningful if two way communication is established. 5. Internet technology is one of the feasible and effective solutions for remote data access; however making embedded system compatible to internet technology is little more demanding. 16
6. There exist still wide scopes of using all these technologies in number of sectors other than industrial, e.g. education, health care, agriculture and other sectors of social welfare. Further efforts are required to provide low cost solutions using these technologies. 7. Number of technical and non-technical issues should be considered while selecting a microcontroller for embedded system. 8. Though 8-bit and 16-bit microcontrollers are dominating embedded market currently, 32-bit microcontrollers are push hard through better features and reduced price. 17