Technical overview G.hn

1 technical overview

1.1 optimization each medium
1.2 security
1.3 profiles

technical overview

g.hn specifies single physical layer based on fast fourier transform (fft) orthogonal frequency-division multiplexing (ofdm) modulation , low-density parity-check code (ldpc) forward error correction (fec) code. g.hn includes capability notch specific frequency bands avoid interference amateur radio bands , other licensed radio services. g.hn includes mechanisms avoid interference legacy home networking technologies , other wireline systems such vdsl2 or other types of dsl used access home.

ofdm systems split transmitted signal multiple orthogonal sub-carriers. in g.hn each 1 of sub-carriers modulated using qam. maximum qam constellation supported g.hn 4096-qam (12-bit qam).

the g.hn media access control based on time division multiple access (tdma) architecture, in domain master schedules transmission opportunities (txops) can used 1 or more devices in domain . there 2 types of txops:

contention-free transmission opportunities (cftxop), have fixed duration , allocated specific pair of transmitter , receiver. cftxop used implementing tdma channel access specific applications require quality of service (qos) guarantees.
shared transmission opportunities (stxop), shared among multiple devices in network. stxop divided time slots (ts). there 2 types of ts:

contention-free time slots (cfts), used implementing implicit token passing channel access. in g.hn, series of consecutive cfts allocated number of devices. allocation performed domain master , broadcast nodes in network. there pre-defined rules specify device can transmit after device has finished using channel. devices know next , there no need explicitly send token between devices. process of passing token implicit , ensures there no collisions during channel access.
contention-based time slots (cbts), used implementing csma/carp channel access. in general, csma systems cannot avoid collisions, cbts useful applications not have strict quality of service requirements.



optimization each medium

although elements of g.hn common 3 media supported standard (power lines, phone lines , coaxial cable), g.hn includes media-specific optimizations each media. of these media-specific parameters include:

ofdm carrier spacing: 195.31 khz in coaxial, 48.82 khz in phone lines, 24.41 khz in power lines.
fec rates: g.hn s fec can operate code rates 1/2, 2/3, 5/6, 16/18 , 20/21. although these rates not media specific, expected higher code rates used in cleaner media (such coaxial) while lower code rates used in noisy environments such power lines.
automatic repeat request (arq) mechanisms: g.hn supports operation both , without arq (re-transmission). although not media specific, expected arq-less operation appropriate cleaner media (such coaxial) while arq operation appropriate noisy environments such power lines.
power levels , frequency bands: g.hn defines different power masks each media.
mimo support: recommendation g.9963 includes provisions transmitting g.hn signals on multiple ac wires (phase, neutral, ground), if physically available.

security

g.hn uses advanced encryption standard (aes) encryption algorithm (with 128-bit key length) using ccmp protocol ensure confidentiality , message integrity. authentication , key exchange done following itu-t recommendation x.1035.

g.hn specifies point-to-point security inside domain, means each pair of transmitter , receiver uses unique encryption key not shared other devices in same domain. example, if node alice sends data node bob, node eve (in same domain alice , bob) not able eavesdrop communication.

g.hn supports concept of relays, in 1 device can receive message 1 node , deliver node farther away in same domain. relaying provides utilizability of multiple transport media , complex network topologies. while relay can read source , target addresses, cannot read message s content due body being end-to-end-encrypted.

profiles

the g.hn architecture includes concept of profiles. profiles intended address g.hn nodes different levels of complexity. in g.hn higher complexity profiles proper supersets of lower complexity profiles, devices based on different profiles can interoperate each other.

examples of g.hn devices based on high complexity profiles residential gateways or set-top boxes. examples of g.hn devices based on low complexity profiles home automation, home security , smart grid devices.