PDA APPLICATIONS IN HEALTHCARE
Bo Henriksen, Viktor Candolin
Department of Computer Science
Åbo Akademi University, FIN-20520 Åbo, Finland
e-mail: ,
Abstract
Over recent years new technologies have come about that could change the way the healthcare industry works. It is only just now over the last year that technology advancement has made Personal Digital Assistants (PDAs) applications very efficient. Wireless communication, better PDAs and data acquisition devices (such as barcode and RFID scanners) have improved enough so that they can all be fitted in one portable device. First we will look into what technologies are available and their capabilities. Then we will look into what the demands are for PDA applications. In the last part we will look into what could be done with these tools.
The Technology
A typical healthcare application of the near future might be built as follows. Starting from the front end, we have the PDA. With this the end user interacts with the application. Information is entered in some way, using a barcode scanner, RFID tag reader, the keyboard or touch-screen. The input is then sent over some form of wireless link to the backend system. The backend system is similar to existing distributed application systems such as WAP systems or interactive web page server systems. Therefore we will not look closely at the backend system; a typical PDA application places no specific demands on the backend. We will look into the advancements in barcode technology, and briefly describe how it works. Likewise the RFID technology will be dissected and described. The wireless communication systems this essay will look into are 802.11b Wireless LAN, Blue Tooth and GPRS. We will describe each technology, discussing features such as range and power consumption. The PDA device itself will be described, in general terms. The demands that the PDA needs to fulfill will be investigated in the second part of the essay.
Barcode & RFID technology
Barcode technology
Conventional barcodes consists of single row of bars. The data is encoded in the horizontal width and that is why it is called ‘one dimensional’. Increasing the width of the barcode increases the amount of data content. Beyond a certain point the barcode becomes too wide to scan. Many different types of 1D barcodes exist. Some can only hold numeric (Interleaved 2 from 5) characters, where others like ‘Code 39’ and ‘Code 128’ can store both numeric and alpha characters. Each barcode is encoded in a unique way. Furthermore, a laser scanner can be programmed to scan only specified barcodes with specified lengths.
Conventional 1D barcode (Code 39)
2D barcodes is a new technology that can contain more information than the conventional 1D barcode. As more data is needed the size of the barcode can be increased in both horizontal and vertical directions.
2D Barcode (PDF417)
Barcode limitations
A conventional barcode can hold up to 21 characters, where the 2D barcode can hold up 249 characters. The 1D barcode has a high degree of redundancy. This means that a 1D barcode can be read with considerable degradation. Increasing the height increases its redundancy making it easier to scan. However, 1D barcodes can easily become too wide and unreadable, whereas the 2D barcode can be expanded in 2 directions.
1D barcodes has the advantage in low capacity applications with 15 characters or less like serial numbers etc. As soon as more data is needed the 2D barcode is a good replacement for the 1D barcode.
RFID technology
Radio Frequency Identification (RFID)is a highly powerful and cost productive technology that allows a wide range of objects to be identified, managed and tracked. A RFID tag is made of a small radio tags or transponders and readers/encoders that can be connected to an information system. Furthermore the tags contain a unique code that identifies them. A tag is activated by a radio signal with preset frequency and response with a signal in return. The reader/encoder can read and write data on the chip. Security issues can be addressed by an extensive number of user options.
RFID limitations
A typical radio tag is 12mm x 12mm. However, they can be produced in any size or shape that satisfies the application requirements. Tags are usually classified within two frequency ranges, namely 125 kHz (low frequency) and 13.56 MHz (high frequency). A tag can be either “passive” (no power is needed) or “active” (a small battery is placed on the chip to broaden the operating range). A tag comes in a wide range of materials and packages. Below we have mentioned a few of them:
- Small cylinders
- Plastic ear studs (for animals)
- Paper thin bags (for integration into paper brochures, books etc.
- ISO cards (similar to credit cards, used on busses in Finland)
A tag can hold from 64 bits to 1MB memory.
A tag can be used for identification, tracking, confirming of ownership, verification, storing and updating relating to objects or people. Furthermore it is resistant to dirt, high temperatures, vibration, moistness and shock. It can be read from any angle and location. Up to 10 tags can be read at the same time.
Connectivity
WLAN technology
Basically wireless LAN is a Local Area Network that has wireless capabilities. Although this sounds basic it is quite the opposite. The ability to transmit data through the air is quite complex and it is not the study of this paper.
The IEEE 802.11b standard operates in the 2.4-GHz band using uses Frequency Hopping Spread Spectrum (FHSS) modulation. Spread spectrum is the most widely used technology for WLAN. It is a wideband radio technology developed by the military for use in reliable and secure communication systems. There are two operating modes: Ad hoc mode and infrastructure mode. In Ad hoc mode wireless clients communicate directly with each other (peer-to-peer) without the use of an Access Point (AP see below). In infrastructure mode there are at least one AP and one wireless client. The client uses the AP to connect to a wired network, which can be an intranet or internet. Connected to the rest of the network via Ethernet cable, the AP translates wired network traffic to radio waves on the 2.4-GHz band (802.11b).
WLAN limitations
WLAN enables mobile computers to be in constant contact with servers and each other. Several devices can be connected to the network through an AP. An Access Point is a wireless local bridge that can connect remote wireless LAN users to a wired Ethernet. An AP can cover approximately 5,000 to 25,000 square meters depending on the structure of your building. A whole office or building can be covered with WLAN by setting up a number of APs. A throughput of 11 Mbps is advertised by vendors. However, testing reveals that cards like “Cisco 350 series” achieve a maximum of 4-6 Mbps.
As for power consumption WLAN card uses about 100-200 milli watt when in an active connection with an AP.
A typical WLAN would look like the following picture.
When a wireless adapter is turned on it begins to scan frequencies for wireless APs or adapters in ad hoc mode. Depending on the SSID the wireless adapter automatically chooses an AP with which to connect. However, in some cases where you have several APs working on different networks, it is possible to get a list of SSIDs and manually decide with which to connect.
Bluetooth technology
Bluetooth is a short-range wireless networking specification being developed by the Bluetooth Special Interest Group (SIG), a wide-reaching vendor alliance that includes the likes of 3Com , Ericsson , Lucent Technologies , Microsoft , Motorola , and Nokia , among others.
There are two main technologies within the Bluetooth specification, which is distributed freely to any SIG member company wishing to build compatible devices: the radio transmitter/receiver, which allows the devices to talk to each other, and the underlying networking logic, which allows that radio communication to be meaningful.
Bluetooth-based PCs and portables as well as peripherals, handhelds, smart telephones and other devices are able to communicate via radio waves. Seamless compatibility is one of the major advantages with Bluetooth. In contrast this means that you can place a printer near your computer and print to it. Place your mobile phone near your laptop and use PC software to update your phonebook, calendar etc.
A group of devices actively communicating within a ten-meter range of each other is called a piconet. Multiple piconets can operate in the same area because each piconet has its own frequency-hopping sequence.
Bluetooth limitations
Portable devices are limited to about 10 meters. Bluetooth specifies 79 different frequencies within the 2.4-GHz radio band -- the same band that high-end cordless telephones use. Because it's unlicensed, no special permits are required to build, sell, or operate Bluetooth radios.
The radios operate in a mode known as frequency hopping, which involves rapidly shifting between different radio channels within the band range to find the frequency with the least interference and noise. In especially noisy conditions, the radios switch frequencies up to 1,600 times per second and use spread spectrum technology, which means they simultaneously transmit on as many as five frequencies at a time.
As for power consumption, when not connected to a piconet, a 2.7-volt Bluetooth module will draw less than 30 micro amps of power. When serving as part of a piconet, but not transmitting data, the module draws about ten times that amount. Only when it is transmitting data does a Bluetooth system begin draining the battery, and even then, it draws only 33 milliamps for a fraction of a second.
GPRS technology
Generally speaking GPRS is packet data overlay onto an existing GSM network. It is a universal packet-switched data service in GSM based on IP. In order for GPRS to work the GSM network has been upgraded with 3 new devices.
- Gateway GPRS Support Node (GGSN)
- Serving GPRS Support Node (SGSN)
- Packet Control Unit (PCU) – an extension of Base Station Subsystem (BSS).
The GGSN and SGSN interact with the HLR (Home Location Register). They attain subscriber profile and authentication information. In contrast, the GGSN is a gateway to other external networks. These networks may include intranet, internet or X.25 networks. It provides different services such as security authentication of external network access, quality of service (QoS) and tunneling. The SGSN is connected directly to the BSS and it tracks user mobility, controls access and handles several user security mechanisms.
The existing GSM radio network is upgraded with a BSS. Normally this includes a software upgrade to the radio transceivers and base station control nodes. Typically the BSS contains a PCU that manages the packet data transfer between user devices and the GPRS core network. The PCU supports data frame retransmission and many other GPRS protocol functions.
GPRS limitations
GPRS provides fast data transfers and “always on” connections. GPRS currently supports bandwidths up to 115 kbps. However, this bandwidth is divided up into 8 timeslots. Carriers and terminal devices decide how much is allocated for downstream, upstream. Typically this means an average of 50 kbps for downstream and 20 kbps for upstream depending on the service provider. “Always on” connections remove long delays reconnecting to the network. Information can also be forwarded to the subscriber in real-time. Furthermore this allows the providers to bill subscribers per packet rather than by the minute, thus enabling cost-effective connections.
The Requirements
In this chapter we will take a look at what components make a modern PDA, and how these components enable or restrict certain applications. PDAs are different from desktop PCs in that the more capable and feature rich a PDA is, the bigger and heavier it is. Desktop PCs use a casing that enables installing hardware without increasing the size of the unit, and weight is irrelevant. Laptop computers have the same problems as PDAs regarding space and weight but they are not as evident.
The Battery
Because every other electronic feature added impacts the battery performance we will start with looking at it. Physically there are two kinds of batteries used for PDA devices, Lithium Ion and Polymer. Both are small and hold a lot of power compared to older technologies like Ni-Cd or Ni-Mh batteries. The Polymer battery is the newer battery type and more expensive. While it can store about the same energy per volume as Li-Ion batteries it is more formable. The material that stores the energy is pulverized in a plastic bag so it can be bent into odd shapes and made as thin as 1 millimeter.
Regardless of the battery type used the calculations remain the same. An application being planned will assert some amount of time as the required continuous time that the PDA has to be able to operate. For example a PDA being used for stocktaking by workers with eight-hour working days will need a device that can support at least that. Many manufacturers seem to report their devices operating time as 1½ times the continuous power on time. Whether or not this value can be trusted depends on the application, if the user takes a lot of breaks allowing the device to power down temporarily, the value can be quite accurate. But if any kind of wireless communication is used, the manufacturers specified mean operating time is useless. An imaginary example:
Battery capacity:
2300 mAh(milliAmpere Hours)
Measured average power consumption by a PDA:
170 mA
Measured average power consumption by 803.11b WLAN card:
200 mA
Resulting PDA continuous on time with WLAN operating:
2300 / (170+200) = 6,2 hours.
The values above are not actual measurements, but are not misrepresenting. They are in the region the authors have seen in their daily work with many manufacturers PDA devices. These values can be replaced with real measurements to give a worst case operating time for a certain device in a certain configuration. Please note that the value above, about 6 hours, is good for today’s PDA devices. A typical consumer market PDA using a WLAN card continuously would achieve somewhere between 1½ and 3 hours of continuous on time. There are two options when a manufacturer adds features to a PDA device, they can increase the battery size to retain longevity or they can sacrifice longevity to retain size and weight.
Shelf life might also be something to take into account in some applications. It is important to note that virtually no PDA on the market today is completely powered off when in sleep mode. At the very least the PDA has to keep the RAM memory with power and update the real-time clock. This means that if the PDA is left in sleep mode, at some point it will run out of power and loose the contents of the RAM memory. While this will not break the device, it will only contain what was pre-loaded into it in ROM or FLASH memory in the factory. The maximum sleep time a device can sustain can be calculated as above. Take for instance a device with a sleep current consumption of 4 mA. This would yield a maximum sleep time of 575 hours, or about 24 days.
In most PDA, the battery will be the heaviest single component, and increasing battery capacity increases weight and volume in the same proportion. In the following sections we will give some typical power consumption values for components, and with this section the reader should be able to see how this affects battery life. It should be noted that active battery research does not predict a substantial increase in the energy capacity of today's batteries. Battery technology improves very slowly compared to other areas of PDA development.
Processing Power
On desktop and laptop systems processing power is often seen as pure positive, the more the better. We cannot afford this luxury on a PDA system since the modern microprocessors consume exponentially more electrical power the more processing power they give. For any given microprocessor, an increase in performance demands a bigger increase in power consumption. This is because the amount of power lost as heat increases with performance. Processors typically become less efficient electrically the more processing power they give. For these reasons we should seek to choose a PDA that has only sufficient processing power, as this will give the best battery life possible.