As mentioned in the last section, mobility has become a factor determining the feasibility of telemedicine in various cases. Because many of these applications are based on the Internet, and mobility is required, wireless Internet appears as an attractive option. Modems for cellular data transmission were soon available in the 1990s after cellular phones hit the market. A study in 1995 presented the possibility of wireless teleradiology with some wireless modems commercially available at that time.  Files containing computer tomography (CT) and x-ray images that were scanned and stored in a PC were sent to a remote portable notebook via cellular modem. A Motorola Digital Personal Communicator cellular phone connected the portable wireless modem of the receiving side to the cellular communication system. They tested with Motorola's pocket modem, based on the CELLect protocol; AT&T's Keep-In-Touch cellular modem, utilizing the Extra Throughput Cellular (ETC) Protocol; and Megahertz's card-type modem, which used the Microcom Networking Protocol (MNP-10) for circuit-switched connection.
Cellular Digital Packet Data (CDPD), the first digital data application to use packet data for cellular phones, came out in 1992 to provide wireless data service. Based on TCP/IP protocols, it provides packet data communication at 19.2 kbps. Starting in 1999, Yamamoto's group attempted viewing CT images on a remote pocket computer equipped with a wireless digital modem that used the CDPD data network. ,  In one demonstration they downloaded five sets of CT images, saved in JPEG format, from a Web server to a Hewlett Packard 620LX and to a Sharp Mobilon 4500, using the Sierra Wireless Air Card 300. Device turn-on time plus download time ranged from 4 to 6 minutes, and the image quality was satisfactory. Then in 2001, the group performed similar tests with downloading 12-lead ECG recordings, which were saved as either JPEG or Internet fax, from the Web server to a Hewlett-Packard Jornada 680 pocket computer. 
Many GSM phones now have built-in traffic-channel modems. Via a local cable, infrared or Bluetooth™ link to the phone, a notebook computer or a personal digital assistant (PDA) can wirelessly connect to the Internet. A phone equipped with a browser application also can access the Internet itself. Numerous telemedicine applications have used GSM-based cellular data modems for data transmission. The following are just some examples.
In 1997, Giovas et al. in Greece investigated the feasibility of store-and-forward ECG transmission from a moving ambulance to a hospital-based station for prehospital diagnosis.  An ambulance was equipped with an ECG recorder connected to a notebook computer, which coupled to a GSM telephone via a PCMCIA data card. Data rate was 9.6 kbps. Curry and Harrop in the United Kingdom also had a similar idea of mobile telemedicine in the ambulance.  They tested a telemedicine ambulance installed with three cameras and a transmitting module, which also was based on GSM phone data connection at 9.6 kbps. A frame of the digitized video was sent to the hospital every 4 seconds. These pictures were received and displayed by a PC with modem at the A&E department.
The AMBULANCE project in 1998 went a step further.  Pavlopoulos' group developed a portable emergency telemedicine device that supported real-time transmission of critical biosignals as well as still images of the patient. The mobile station consisted of a notebook computer with CCD camera, a GSM modem from Siemens, and a biosignal monitor. Through TCP/IP over GSM and data rate of 9.6 kbps, three-lead ECG, blood pressure, oxygen saturation, heart rate, temperature, and still images were transmitted from the mobile station to the hospital consultation unit.
In the same year, Reponen et al. demonstrated CT examinations on a remote notebook computer that wirelessly connected to a computer network via a GSM cellular phone.  The notebook was equipped with a PCMCIA digital cellular data card that interfaced the computer to the phone. CT images, each 256 kb in JPEG format, were stored in a network directory in a Linux-based PPP server, which provided TCP/IP connections between the notebook and the LAN of the Department of Radiology of a hospital in Finland. After dialing into the PPP server, images were downloaded with an FTP program. At a nominal data rate of 9.6 kbps, average transfer time for a single CT slice was 55 seconds. Neuroradiologists' diagnoses from the images at the notebook were the same as that from original images in 66 cases and slightly different in two. Two years later, the group carried out similar tests with a GSM-based wireless PDA.  They downloaded the CT images using a Nokia 9000 Communicator equipped with FTP software. This time the PPP server was set up using Windows NT remote access service (RAS). The PDA was found to be suitable for the reading of most common emergency CT findings for consultation purposes.
Besides common cellular networks such as the GSM, other proprietary wireless networks also have been used in telemedicine. In 2000, Karlsten and Sj qvist described an information management system that utilized a network called Mobitex™, which was developed by Swedish Telecom.  The system was integrated into the emergency ambulance service in Uppsala County, Sweden, for in-ambulance and prehospital use. It consisted of stationary and mobile workstations that communicated via Mobitex™ on the 80 MHz channel at 1200 bps or via GSM. One function of the system was transmission of ECG and other data from mobile ambulance workstations to the stationary hospital workstations at predefined intervals.
Thus far we have highlighted telemedicine applications that used cellular devices and networks. However, another technology often used in forming a wireless Internet link is a local wireless network. Zahedi et al. described a mobile teleconsultation system for video communication between a ward within a hospital and a remote physician situated outside the hospital.  Video stream captured by a camera was converted into IP packets by a software and Web server running in a notebook computer at the patient module. The wireless spread spectrum link between this patient module and the ISDN modem in the relay module connecting at 128 kbps allowed connection from the outside. At the physician side was a multimedia desktop PC equipped with an ISDN modem and a Web browser.
The Georgia Tech Wearable Motherboard™ (GTWM), developed at the Georgia Institute of Technology, was a vest that could be used to monitor vital signs, such as ECG, body temperature, and respiration. In 2000 Firoozbakhsh et al. set up a prototype wireless link between the GTWM and a LAN.  Acquired ECG waveform was digitized at a notebook terminal, and transmitted across an IEEE 802.11 Wave-LAN wireless network. Besides being accessed by other terminals connected to the LAN, the system could also be expanded to enable remote access over the Internet. Wireless LANs also have been utilized in other medical informatics systems for storing and retrieving medical images. 
In cases where telemedicine is practiced at places that are beyond the reach of wireless networks or even wired telecommunications services, satellite communication becomes the only option for Internet access. Satellite-based telemedicine is commonly practiced worldwide. For example, Dr. Bernald Lown started SatelLife in 1989, and initiated a medical information-sharing network called HealthNet.  Utilizing relatively cheap, low earth orbit satellites, the service provides store-and-forward Internet access to health professionals around the world. Whenever the satellite comes in range of a ground station, it exchanges messages with it. Messages received by the satellite are stored and later delivered to SatelLife's headquarters in Boston, where they are forwarded to other HealthNet users or via Internet to other Internet users. If users want to surf the Internet, they use a special Web-browsing software to issue requests, which are later processed at headquarters. The desired information is then sent to the users in subsequent message exchanges between satellite and users' stations.
Another recent example is a Web-based PACS developed by Hwang et al. in 2000.  An asymmetric satellite data communication system (ASDCS) allowed a remote hospital to download medical information from the telemedicine center's server. The client side had a PC installed with equipment capable of Ku-band and C-band satellite links. The radiological images and patient information could be viewed on a typical Web browser with the help of a Web application written in Java.
Yamamoto, L.G., Wireless teleradiology and fax using cellular phones and notebook PCs for instant access to consultants, Am. J. Emerg. Med., 13 (2), 184, 1995.
Yamamoto, L.G., Instant pocket wireless telemedicine consultations, Pediatrics, 104 (3), 670, 1999.
Yamamoto, L.G. and Williams, D.R., A demonstration of instant pocket wireless CT teleradiology to facilitate stat neurosurgical consultation and future telemedicine implications, Am. J. Emerg. Med., 18 (4), 423, 2000.
Yamamoto, L.G. and Shirai, L.K., Instant telemedicine ECG consultation with cardiologists using pocket wireless computers, Am. J. Emerg. Med., 19 (3), 248, 2001.
Giovas, P. et al., Transmission of electrocardiograms from a moving ambulance, J. Telemed. Telecare, 4 (1), 5, 1998.
Curry, G.R. and Harrop, N., The Lancashire telemedicine ambulance, J. Telemed. Telecare, 4 (4), 231, 1998.
Pavlopoulos, S. et al., A novel emergency telemedicine system based on wireless communication technology — AMBULANCE, IEEE Trans. Inf. Technol. Biomed., 2 (4), 261, 1998.
Reponen, J. et al., Digital wireless radiology consultations with a portable computer, J. Telemed. Telecare, 4 (4), 201, 1998.
Reponen, J. et al., Initial experience with a wireless personal digital assistant as a teleradiology terminal for reporting emergency computerized tomography scans, J. Telemed. Telecare, 6 (1), 45, 2000.
Karlsten, R. and Sj qvist, B.A., Telemedicine and decision support in emergency ambulances in Uppsala, J. Telemed. Telecare, 6 (1), 2000.
Zahedi, E. et al., Design of a Web-based wireless mobile teleconsultation system with a remote control camera, in Proc. 22nd Ann. IEEE EMBS Int. Conf., Enderle, J.D., Ed., Chicago, 2000.
Firoozbakhsh, B. et al., Wireless communication of vital signs using the Georgia Tech Wearable Motherboard, in 2000 IEEE Int. Conf. on Multimedia and Expo, 3, 1253, 2000.
Pedersen, P.C. et al., Low cost wireless LAN based medical informatics system, in Proc. 1st Joint BMES/EMBS Conf., Blanchard, S.M. et al., Eds., Atlanta, 1225, 1999.
Groves, T., Sate1Life: getting relevant information to the developing world, Br. Med. J., 313 (7072), 1606, 1996.
Hwang, S. et al., Development of a Web-based picture archiving and communication system using satellite data communication, J. Telemed. Telecare, 6 (2), 91, 2000.