Influence of WBAN standard on product design and development

June 23, 2010

WBAN standard is mostly focused on specifying a communication medium between two devices. It tries not to limit application in which it will be used. That means that it can only be a part of the idea for the product, a part stating that a product will have low-power wireless connectivity to other devices in its vicinity. This part limits a bit the rest of the product idea to devices which have some interesting information to exchange, some functionality to control etc.

With this idea, the product can be planned and its task can be clarified, conceptual and embodiment design done. A great advantage of this kind of technology is that during product design a choice of a given wireless technology is postponed in time, even up to the point of detail design. It comes from the WBAN standard’s property of commonality and modularity. To some extent all transceivers will have a very similar construction/interface. That means that even between this and a different technology it will be interfaced by SPI or UART. A change of wireless technology requires minor changes to the project of the device. Also design practices will stay the same as with previous wireless technologies, thus limiting unnecessary confusion. That means, in connection with previous post, that switching costs will be small not only for end users, but also for production companies.


Economic aspects of WBAN standard

June 22, 2010

Standard of body area network, as a description of network organization and interoperability of devices coming from different producers, can be considered as a compatibility/interface standard. This kind of standard has two very important concepts, which describe its influence on the market, as well as market’s influence on the standard. These two concepts are: network externalities and switching costs. They will be explained in this post, and also it will be shown how it works in practice, on the example of WBAN.

  • Network externalities

We can distinguish two types of this effect. Direct one is an effect of size of the network on its value that it presents to users. The bigger the network, the more useful it can be. Most famous examples of this kind of this connection is a phone. Usefulness of having a phone lays not really in the phone itself, but in the connections that a user can make to other people. That means that growth of this kind of popularity of such technology will speed up with each user joining the network. Other examples of this kind of effect is ex. social portals (Facebook, MySpace etc), email.

Second type is indirect one. It is based on the fact, that a user who already bought a product in one technology will try next time to buy a product, which is compatible with it. It can be strongly seen with computer market – after buying a hardware platform in one of technologies, software has to be chosen from compatible solutions. It is even more visible, but in a bit different fashion in the market of e-book readers: when a user decides to use a specific solution and buys a collection of books, there in most cases is no way to transfer them to a competitive reader.  But this will be actually discussed more in next point.

It has to be noted though that a solution allowing cooperation with larger group of different competitive technologies will be more appealing for users.

  • Switching costs

A different economical concept that concerns standardization is a concept of switching costs. This is based on the fact, that in real life nothing is for free. Each change of used technology is normally associated with a cost. Not only a cost of new purchase (transaction costs), but maybe also with some time and effort spent to get accustomed with this new technology (learning costs). As a third kind of costs (artificial costs) we can distinguish costs that are introduced by the companies to hold a user to their technology or service. It can be a cost described in a contract for breaking it before a specified time (as with GSM carriers), but also in a more positive aspect – loyalty programs in airlines/gas stations/ supermarkets. These switching costs can lead sometimes to a situation where the profit of changing a service of technology will be smaller than associated costs, thus limiting a choice of the user.

How WBAN standard is situated in all of this?

This question is not fully straight forward. Of course as an interface standard WBAN will be highly influenced by both of this phenomenon, but we have to take into account that this technology doesn’t have a direct predecessor. We can of course try to find some connection with wireless standards already available on the market, what will be discussed in later posts, but I believe it would be a bit farfetched. For example we could argue that Bluetooth technology could and does perform similar function – it ties several devices on the body area, with cooperation of product of different manufactures. Thus we could expect that switching cost would be high for users, who want to use it in personal manner, but we have to keep in mind that these two technologies do not rule out each other. It could be even an aspect giving advantage to this standard – with a proper set of interfacing devices available on the market, it could promote WBAN as a way to tie all these devices together in one network. Later on when WBAN will reach expected level of market penetration, interfacing devices will become obsolete.

Also in case of more professional applications, such as medical monitoring, there is no technology that currently takes place on the market. That of course doesn’t limit costs of purchase, or costs of learning new technology, but it’s not connected with a process of exchanging old to new, but more with a process of introducing new functionality.

Network externalities are another matter. This technology will take a full advantage, but also feel a full burden of this effect. At the beginning it will be possible to start slow introduction in hospitals, where all set of devices can be bought at once, thus allowing to obtain already a high initial gain of such change. For personal use that requires a good will of main manufactures in different fields. For example at the beginning it could be introduced as a communication between training equipment (step counters, bike meters etc) and a cell phone/mp3 player, and later on the usage could be broadened. Such approach could introduce this technology where network effect is not so important and later on basing on initial penetration bring it to more sensitive applications.

An indirect effect is obvious – it makes only sense when a person buys devices incorporating this technology, as this is only way to form a true body area network. A direct effect depends on the final vision of adaptation of WBAN users will evolve. It becomes more and more apparent that world is connected in a network of size and shape previously unimaginable. At the moment each user’s computer is an end node of this network, but with use of WBAN technology, we can become a part of the network itself. In such a case direct effect would be very important, but as this idea may seem a bit scary it is possible that these two networks will be kept separate- limiting direct influence.


EFC PHY for Human Body Communication

June 21, 2010

As this is intriguing part of standard draft from engineering point of view, I decided to include a short description what it really is.

Transmitter is shown on the image bellow:

The description included in the standard is quite brief in this topic, but it gives a basic idea of what is included in this solution:

“The EFC specification is designed to provide robust performance for HBC.  EFC transmitter is implemented with only digital circuits and needs one electrode (instead of antenna), and EFC receiver can be implemented without any blocks related to RF carrier signals (mixer, VCO, ADC/DAC, etc.).  These allows EFC device to have very low implementation complexity and low power consumption.

There are two bands of operation centered at 16MHz and 27MHz with the bandwidth of 4MHz.  Both operating bands are for the United States, Japan, and Korea, and the operating band centered at 27MHz is for Europe.”

“The data to be transmitted is created by mapping 4 bits (a symbol) from FIFO to a 16-bit chip.  […] The 16-bit chip is then spread by applying FSC.  The spreading factor of FSC used determines the final data rate. “

Also what is interesting, with this kind of communication it’s hard to keep the spectrum in some normal shape, so a special care should be taken to limit interferences with a 400Mhz medical band:

“A transmit spectrum mask shall be used to remove harmonics and possible interference in other bands, especially with 400MHz medical band.  The transmit power spectrum shall be less than 0 dBr (dB relative to the maximum spectral density of the signal) for  , -3 dBr for  , -0.5 dBr/MHz for  as a function of the frequency, and -33 dBr for , where fc is channel center frequency and fBW is the channel bandwidth. The recommended transmit spectrum mask for fc=16MHz is shown in Figure [below]”


Elements of technology/standard

June 20, 2010

Draft of the standard created by task group 6 of IEEE specifies the scope of this standard as:

“This is a standard for short range, wireless communication in the vicinity of, or inside, a human body (but not limited to humans). It uses existing ISM bands as well as frequency bands approved by national medical and/or regulatory authorities. Support for Quality of Service (QoS), extremely low power, and data rates up to 10 Mbps is required while simultaneously complying with strict non-interference guidelines where needed. This standard considers effects on portable antennas due to the presence of a person (varying with male, female, skinny, heavy, etc.), radiation pattern shaping to minimize SAR* into the body, and changes in characteristics as a result of the user motions.

*SAR (Specific Absorption Rate) measured in (W/kg) = (J/kg/s). SAR is regulated, with limits for local exposure (Head) of: in US: 1.6 W/kg in 1 gram and in EU: 2 W/kg in 10 gram. This limits the transmit power in US < 1.6 mW and in EU < 20 mW.”

It can give us some idea what will be included in the standard description and where will be the emphasis (extremely low power, low or medium transfer speeds, safety for human body during long operation, no interferences especially in hospital environment). It means that except description of physical communication link we can expect also specification of MAC layer with mechanisms of decreasing power consumption and some higher layers to assure interoperability.

But let’s see what major sections are in current draft, with initial short description what each section includes:

General framework elements

The most interesting part for us, because we don’t plan to implement this standard. It gives the basis for all other elements of the document. Treats about “the network topology used for medium access, the reference model used for functional partitioning, the time base used for access scheduling, the state diagram used for frame exchange, and the security paradigm used for message protection”. It will be described in greater details in one of later posts.

MAC frame formats

This part describes in detail construction of MAC frames, transmit order that they have to obey, as well as fields they have to consist of depending on type of frame. Also fields that are used in these frames are defined.

MAC functions

Here we can find a specification access modes and structures to medium access with details of their operation, a description of setting up of the connection between hub and unconnected nodes. Also here is an extension about two-hop star topology. Power management, clock synchronization and coexistence are addressed as well at the end of this section. It is also important section the understanding of operation of this technology, but as it’s not direct scope of this blog, information from this part will be included to some extent in the description of first section.

Security services

As name suggests this section explains the implementation of security measures as encryption and key negotiation between a node and hub. It is one of the elements that show that a scope of this standard is not only about the medical applications, as the need for security in this field is limited.

PHY specification

This section is still empty, but specification of physical medium is provided in NB, UWB and HBC sections, depending on type of communication to be used.

PHY management

Same situation as above.

Narrowband (NB) PHY specification

Section contains a description of first out of three radio communication modes. It operates in one of several frequency bands in ranges between 400MHz to 2.4GHz with data rates of up to 970kbps

Ultra wideband (UWB) PHY specification

This part describes second of three physical mediums. It works on frequency of 6.4- 8.7 GHz with -15dBm output power and FSK modulation.

Human Body Communications (HBC) PHY specification

This section specifies an EFC PHY for Human Body Communication. It’s a way description of transmitter and receiver basically without use of any RF related elements (no mixer, VCO, ADC/DAC). All transmission is performed in digital form and it’s spread in frequency using proper spread codes. This part is very interesting from the point of RF design, as this solution has a great advantage of very low complexity and power consumption.


Wireless body area networks. What is it really? (part 3)

June 19, 2010

A full set of applications as specified by the task force (TG6) of IEEE, divided into two classes (class A: Medical, class B: Non-medical):

As you can see this technology can really be implemented in many different branches of life and can be next breakthrough in a way we perceive electronics.


Wireless body area networks. What is it really? (part 2)

June 16, 2010

Patients and doctors noticed that even if they don’t use all of the sensors, there are still a lot of connections that have to be made for data transfer. It would be much more comfortable for a patient to use a wireless technology. To make it even more complicated, a perfect situation would be if each of such sensors could be manufactured by a different company and still cooperate. This a ground reason for specifying a standard of Wireless Body Area network.

But the world doesn’t end on the topic of medical monitoring. Such system of wireless communication can be used in much broader range of applications especially that application of this technology is almost always connected with some kind of Broad Area Network. For example Jaff [1] in his thesis lists such applications:

  • medical domain: ex. sleep staging, for computer-assisted physical rehabilitation, for monitoring patient at home, at hospital
  • fitness and wellness: monitoring of workout, step meters (like one from NIKE embedded in a shoe)[2] , bike speed sensors and cadence sensors. What is interesting at the moment NIKE pedometer uses proprietary wireless technology, so it can’t be used with anything else than IPOD.
  • military domain: real-time information about the location and physiological status.
  • safety and security domain: biosensors used for monitoring firefighters or hazardous material workers (using hazmat sensors), for detecting chemical and biological attacks, for automatic identification and authorization (similar to RFID tags)
  • social networking and entertainments domain: exchanging digital profile or business cards, match making (hobby, interest, game, community member), creating groups with same preference and emotion

[1]http://uu.diva-portal.org/smash/get/diva2:231674/FULLTEXT01

[2]http://www.apple.com/ipod/nike/


Wireless body area networks. What is it really?

June 15, 2010

Modern technology changed our lives dramatically. Almost all of us in modern societies have a cell phone, mp3 player, a watch and sometimes some more gadgets in our pockets or other parts of our body. Even if they incorporate Bluetooth, which by the way is very power hungry, they are most of the time not connected together. The idea behind Wireless Body Area networks, which comes from the medical circles, states that there should be a network between all devices we have on us. Such a network should allow devices to communicate on short distances (2 meters is maximum due to the size of average human being), but what is even more important with ultra low power consumption.

As you could read a moment ago, the idea behind this technology comes from medical environment, specifically hospitals. During hospitalization period a patient has to be monitored by many different sensors. If you really think about it there exist many different monitoring systems, each having its most suitable place on human body and each collecting data that has to be sent to the central point. Such sensors are for example (Jaff, 2009):

  • An ECG sensor for monitoring heart activity
  • An EMG sensor for monitoring muscle activity
  • An EEG sensor for monitoring brain electrical activity
  • A SpO2 sensor for monitoring blood oxygen saturation
  • A cuff-based pressure sensor for monitoring blood pressure
  • A resistive or piezoelectric chest belt sensor for monitoring respiration
  • A blood glucose level sensor
  • A temperature sensor for monitoring body temperature
  • A location sensor (e.g., GPS) to track user’s location
  • Accelerometer-based motion sensors to estimate type and level of user’s activities