Elements of technology/standard

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.

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