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Data Transfer for smart clothing: requirements and potential technologies

 

Jaana Rantanen and Marko Haennikainen

 

 

1. Introduction

Miniatuarisation of electronic components has made it possible to build small portable and handheld computer devices that can be carried almost anywhere and at any time. As a result, smaller and lighter devices having high processing capacity are available on the market. This equipment is becoming more wearable since components can be easily hidden inside clothing or embedded in a handbag, for example, and carried for long periods.

A wearable computer is a miniaturized version of a desktop computer that is carried during use. Consequently, a wearable computer is a mobile, fully functional, self-powered and self-contained computer. The basic difference from desktop computers is the type of user interface (UI), since mobility sets new requirements for usability. Wearable computers are intended for general data processing tasks, similar to their desktop counterparts. Basically, the use of the computer is moved to the actual surroundings of everyday life.

Another approach in wearable electronics is smart clothing. Smart clothes emphasize the importance of clothing while designing and implementing the wearable systems. Smart clothing applications are constructed using functional modules or intelligent fabric materials that are placed on or inside ordinary clothes. The functional modules can be non-electrical, e.g. an integrated first aid kit, but in our view they are considered to be electronics. Electronic functional modules for smart clothing applications are positioning, communication, and sensor systems, and different types of UI components, for example.

When constructing smart clothes, several functional modules are distributed to optional locations on clothing according to application design and user comfort. Therefore, the weight and size of the system are adapted. The system distribution results in data transfer requirements between the different modules. Since clothing has to maintain its profound properties, such as washability and wearing comfort, we have to consider carefully suitable solutions for data transfer.

For communications between the different components of smart clothing applications, both wires and wireless technologies are applicable. Wired connections are practical in many cases, but they can cause inflexibility and add to the weight of the system. Wireless connections increase flexibility but also the complexity of a system. Currently, data transfer issues are a true challenge in wearable systems. An applied solution is often a compromise based on application requirements, operational environment, available and known technologies, and costs.

This chapter evaluates the variety of technologies used to realize data transfer in smart clothing applications. Most potential technologies are considered for further analysis. Also, several smart clothing prototypes are introduced, concentrating on their data transfer solutions.

 

2. Smart clothing concept model

In introducing the architecture and functionality of smart clothing and its relation to the environment, a concept model has been used. An individual human user is the centre point of the model that is illustrated in Fig.1 . The concept model combines different clothing layers with additional components needed to integrate intelligence into clothing. The main layers concerned with smart clothing are the skin layer and two clothing layers.

Physically the closest clothing layer for the human user is an underwear layer, which transports perspiration away from the skin area. The function of this layer is to keep the interface between a user and the clothes comfortable and thus improve the overall wearing comfort. The second closest layer is an intermediate clothing layer, which consists of the clothes that are between the underclothes and outdoor clothing. The main purpose of this layer is considered to be an insulation layer for warming up the body. The outermost layer is an outerwear layer, which protects a human against hard weather conditions.

Additional equipment that is needed to construct smart clothing systems can also be divided into layers in a similar manner. In our division, the underwear layer with additional components corresponds to the skin layer of smart clothing systems. In the same way, the intermediate clothing layer is associated with an inner clothing layer and the outermost layer with an outer clothing layer.

 

2.1. Smart Clothing Layers

 

The skin layer is located in close proximity to the skin. In this layer we place components that need direct contact with skin or need to be very close to the skin. Therefore, the layer consists of different UI devices and physiological measurement sensors. The number of the additional components in underwear is limited owing to the light structure of the clothing.

An inner clothing layer contains intermediate clothing equipped with electronic devices that do not need direct contact with skin and , on the other hand, do not need to be close to the surrounding environment. These components may also be larger in size and heavier in weight compared to components associated with underclothes. It is often beneficial to fasten components to the inner clothing layer, as they can be easily hidden. Surrounding clothes also protect electronic modules against cold, dirt and hard knocks.

Generally, the majority of electronic components can be placed on the inner clothing layer. These components include various sensors, a central processing unit (CPU), and communication equipment. Analogous to ordinary clothing, additional heating to warming up a person in cold weather conditions is also associated with this layer. Thus, the inner layer is the most suitable for batteries and power regulating equipment, which are also sources of heat.

The outer clothing layer contains sensors needed for environment measurements, positioning equipment that may need information from the surrounding environment and numerous other accessories. In Fig.1, there are two different worlds (environments) presented that are in contact with the smart clothing. The term real world depicts the physical surroundings of smart clothing components that measure the environment. The term information networks represents the virtual environment accessed by communication technologies. The information networks can consist of communications with the external information systems, such as other network users and database servers.

 

2.2. Smart Clothing Implementation Model

 

Generally, smart clothes are intended for very specific applications. Therefore, the intelligence is usually implemented using only a few selected components. For reference, a generic implementation architecture for smart clothing systems is depicted in Fig.2. , showing a number of different types of component. The necessary components are CPU, various UI devices, power management equipment and data transfer components. The rest of the components vary according to the application requirements of the smart clothing system.

Central processing unit

The heart and brain of the smart clothing system is the CPU, where capacity varies according to the computing task. Often in smart clothing applications, small 8 to 16-bit microcontrollers are used. In comparison, wearable computing applications usually utilize more powerful processors with speeds up to 1Ghz. The CPU module itself may be a combination of several microcontroller units that are distributed at several locations in the clothing.

User interfaces

UI’s in smart clothing consist of several types of input and output devices for information feeding and selection. It is clear that devices suitable for desktop computing cannot be used with smart clothing applications. The ordinary keyboard and mouse have to be replaced by more suitable devices and new input/output concepts must be created. An example of a new innovative input device is the so-called Yo-Yo, which combines a display with a feeding and selecting system.

Alternative input methods are pen-based inputs, gestures, eye movement and speech recognition inputs. The last is a very promising method since it allows hands free operation. Output devices consist of components that give feedback from the function of the clothing or from external actions. These include, for example, displays, loudspeakers, lights and haptic feedback devices. Commonly displays are small liquid crystal displays embedded in a suitable place in the clothing. Obtrusive head mounted displays are suitable for special applications such as protective clothing incorporating a helmet.

Power management

The most important design rule for power management in smart clothing is to minimize the power consumption. Batteries are heavy and thus difficult to place inside smart clothes. A centralized power source is easier for recharging purposes, but leads to wiring requirements for power transfer. A currently available solution is to use Li-polymer batteries that are thin and have a good power capacity. Alternative methods are also used such as kinetic energy and piezoelectric materials.

 

3. Data Transfer in Smart Clothing

 

A number of different wired and wireless data transfer technologies are applicable for the requirements placed by smart clothing. The communication model for data transfer in smart clothing and the potential technologies are discussed in the following section.

 

3.1. Communication layers

Communications in smart clothing are divided into three different data transfer types. The communication model for smart clothing applications is illustrated in Fig.3. First, the internal communication refers to the data transfer between the separate components of a distributed smart clothing implementation. This includes, for example, the data collected from physiological sensors and input/output messages through the UI. As the name implies, this communication occurs inside clothes and between different smart clothing layers.

Second, external communication is needed for the data transfer between smart clothes and the external information networks. In a general communication model, there is only one access point at a time enabling the communication. For example, this access point can be a network interface for a cellular data network. The external communication is more easily manageable owing to this single access point.

The third type of communication is called personal space communication. Personal space data exchange takes place in situations when internal communication components initiate data transfer with an environment without a centralized access point, i.e. in an ad hoc manner. Personal space is the close proximity of the user, surrounding the human user while stationary or in motion. An example of such technology is a low range wireless link (Bluetooth) that can be utilized for both internal and external data transfer. The management of ad hoc external communications consisting of possible several parallel dynamic connections, is a challenge for the system design.

3.2. Data transfer requirements

The communication requirements for smart clothing are firmly application dependent. A summary of different potential smart clothing applications and services with estimated data transfer requirements is presented in Table 1. The estimates presented for possible applications are related to the experience of wearable computer applications. The transfer requirements cab be divided into internal and external. In addition and within the personal space coverage, the external data transfer can be implemented using internal technologies. The internal transfer services are divided into local health and security related measurements, different services provided through a display and audio input/output UIs, and control type of input interfaces. Many of the services require or result in external communications between the smart clothing and its environment. For example, external transfer requirements are placed by the reception of a video or audio stream and text messages.

3.3. Wired solutions for internal data transfer

Wired data transfer is in many cases a practical and straightforward solution. Thin wires routed through fabric are an inexpensive and high capacity medium for information and power transfer. However, the detaching and reconnecting of wires decrease user comfort and the usability of clothes. An advanced wired solution is the use of conductive fibres to replace ordinary plastic shielded wires. This makes smart clothing more like ordinary clothing. Also lightweight optical fibres are used in wearable applications, but their function has been closer to a sensor than a communication medium. Optical fibres are commonly used for health monitoring and also for lighting purposes, e.g. in shoes.

Cables

Wired communication implemented by plastic shielded cables is an inexpensive, high capacity and reliable data transfer method. Thin cables can be integrated or embedded inside clothing without affecting its appearance. However, wires form inflexible parts of clothing, thus decreasing the wearing comfort. …

The connections between the electrical components placed on different pieces of clothing are another challenge when using wires. During dressing and undressing, connectors should be attached or detached, decreasing the usability of clothing, Connectors should be easily fastened (or automatically fastened without special user attention), resulting in the need for new connector technologies.

Electrically conductive fibres

A potential alternative to plastic cables is to replace them with electrically conductive fibres. Conductive yarns twisted from fibres form a soft cable that naturally integrates in the clothing’s structure keeping the system as clothing-like as possible, Fibres yarns provide durable, flexible, and washable solutions. Electrically conductive yarns are either pure metal yarns or composites of metals with other materials. In composites other materials may, for example, provide strength or weight savings compared to pure metals. Metal clad aramid fibres are an example of strength solutions, which provide good electrical conductivity owing to copper, silver, and nickel coating. A sophisticated solution would be to knit electrically conductive fibre yarns directly into cloths to form natural communication channels. In this way it is possible to construct wearable platforms, which already contain internal communication; only application-specific electrical components need to be added. However, conductive yarns are often sued in the same way as plastic shielded cables.

Although this sounds easy, there are a few problems that slow down the usage of conductive fibres in clothing. The first problem is due to the lack of natural insulation material in conductive fibre yarns. Unshielded yarns can also conduct from their surface and this can cause unwanted short circuits when separate yarns are in touch with each other. Also conductive fibre yarns in close proximity, exposed to sweating or to other conductive material between the yarns may cause unwanted electrical conduction. A possible solution is to embed conductive fibre yarns inside waterproof tape. Tape shielding protects fibres against interferences from the outside world and acts as an insulator. […]

 

3.4. Wireless technologies for data transfer

For wireless communications, dedicated external technologies for a wide range and internal technologies within personal space can both be utilized. These are discussed in the following sections and summarized in Table 3. […]

Extended data transfer

Digital cellular data networks, such as global system for mobile telecommunications (GSM), are a current technology for wide area voice and data services for smart clothing applications. GSM represents the latest technological state of current second-generation mobile networks. The system has been developed mainly for voice services, but it also possesses capabilities for general data transfer. Future extensions, such as universal mobile telecommunications systems (UMTS) should bring more bandwidth and enable new, more demanding applications in mobile wide area data networks. […]

 

Wireless local area networks

Wireless local area networks (WLAN) can be utilized for high capacity communications within limited geographical areas, such as homes, offices, and public hot spot areas. Smart clothing applications are generally not expected to demand an office type of data communications, while WLAN is projected for a supplementary technology delivering third generation telecommunication services. Where WLAN infrastructure is available, WLAN provides reliable and low-cost data transfer, meeting most of the projected communication requirements for the external communication of smart clothing applications. Also, the miniaturization of WLAN technology has proceeded, as WLANs have already been integrated into palm top computers.

The Institute of Electrical and Electronics Engineers (IEEE) standard 802.11 is currently the most widely used WLAN technology. The system supports both direct and ad hoc networking between users and infrastructure-based topology where WLAN access points manage the data transfer between terminals and provide a connection to fixed networks. One of the original 802.11 physical layers uses infrared technology while two of them are spread spectrum radios of the 2.4. Ghz industrial, scientific, medical (ISM) band. All original physical layers provide up to 2 Mbit/s link rate. […]

 

3.5. Internal and personal space data transfer

 

Potential operational frequencies for internal and personal space wireless data transfer are radio bands that do not require a specific licence, special permission or carry licence fees, such as the 2.4 Ghz ISM band. In Europe, ISM bands are part of the frequencies allocated for short range devices (SRD)….

Generally, wireless personal area network (WPAN) technology can form a multipurpose link for extending and delivering services to smart clothing applications. WPAN differs from WLAN mainly by non-functional requirements, such as cost and power consumption that favor smart clothing types of application. Also, WPAN has a smaller operational area, lower data rate and fewer terminals per network compared to WLAN.

Bluetooth is the first available WPAN technology. The technology is a potential standard for low-range RF links, supporting both data and voice services. Bluetooth is a WPAN technology specified by an industry driven organization called the Bluetooth Special Interest Group (SIG). The main target of the technology is to replace a common serial cable with a wireless link…….[…]

A recent standardization approach in IEEE for low power RF systems has been taken in the P1451.5 working group for wireless sensor standards. The purpose for the group is to develop an open standard for wireless transducer communication that can accommodate various existing wireless technologies. The emerging work of the IEEE P1451.5 working group seems to be very promising for the smart clothing data transfer requirements. Several RF components (radio frequency) suppliers are providing modules with programmable transmission power and with several frequency alternatives. […] Radio frequency identification technology (RFID) is used in various tracking and identification applications, including smart cards, access control, logistics, sports events, electronic article surveillance, and animal identification. A large number of these RFID systems work using an inductive coupling principle in the data transmission. […]

 

4. Implementations for communication

 

4.1 Wearable computer vest

4.2 Reima survival suit (for arctic environments)

4.3. Heating jacket and sensor shirt

4.4. Personal position manager (fishing vest, used for fishermen)

 

5. Summary

 

A number of wired and wireless data transfer technologies are available for smart clothing applications. For wearability, conductive fibres are seen as the most suitable wired solution, while ordinary cables provide high reliability. Low-power wireless connections provide increased flexibility and also enable external data transfer within personal space. Different existing and emerging WLAN and WPAN types of technologies are general purpose solutions for the external communications, providing both high speed transfer and low costs. For wider area communications and full mobility, cellular data networks are currently the only practical possibility. Experiences with prototypes have shown the operability and potential of smart clothing, and also indicated the need for research on new technologies and usability.


From: Xiaoming Tao, Wearable Electronics and Photonics. Cambridge: Woodhead Publishing Ltd., 2005. Chapter 10.

Quoted with permisison. Copyright Woodhead Publishing Limited, ISBN 1 85573 605 5; no further copies allowed.