i think your question could be updated, or at least specify what you
mean by ad-hoc, i.e. do you mean ad-hoc as in 802.11a/b/g networks, or
in a general sense, i.e. all forms of arbitrary networking, e.g.
transient networking where people can come in and out of
communication, like radio and satellite devices such as cellular
phones, pagers, shortwave etc.
i'll break down the Data Comms terminology first, and try to answer
the question at the end.
you should be aware that propagation of signals is a major factor in
the efficiency of most communications - it's also inherent in most
digital devices that operate in logical operations, and it's
fundamental to the way digital technology works. there has to be a
synchronised operation of signals, and a synchronised delay in order
to discern between non-signals.
if you try to induce a shorter or arbitrary signal length, time,
intensity, wavelength or method, it will inevitably lead to a
comprimise in either reliability, speed or throughput.
creating a new transmission method, is probably the easiest way of
answering your question, without actually answering it. that's not
easy, and the existing Data Comms Methods are capable of transmitting
data in a situation where latency is necessarily important. especially
in UWB technology
http://en.wikipedia.org/wiki/Ultra_wideband
, since it's principally ad-hoc networking.
the series of buffers, protocols, and transmission mediums all present
stages in which the round-trip latency of information and signals has
to be factored to determine the round trip propagation delay (RTPD),
or latency. most communcations is two way, one-way broadcasting is
much easier to determine and plan for, since the receiver is where the
problems lie. http://en.wikipedia.org/wiki/Frequency_division_duplex
discusses some basics of Data Comms, duplexing or send/recieve signals
at the same time on the same medium.
any technology that deals with digital communication has it's own
propagation delay, since its mostly sending data in a linear, serial
fashion from one host to another. in a serial transmission, data is
sent in a regular fixed pattern.
the easiest methods to mitigate the delay, is by using Time Division
on a shared medium, to increase reliability.
http://en.wikipedia.org/wiki/Time_division_multiple_access
while it's not always the best choice, it is efficient and works in
conjunction with other methods to share data between hosts on the same
medium. ad-hoc networks usually share the same carrier, medium or
methods in order to switch in and out of the network, so they require
a network that shares data between hosts.
if you shorten the packets and buffers used to send out and receive,
it decreases the RTT, but loses data efficiency, as each small packet
cannot hold enough data to process checksums. any bad packet would
need to be deconstructed and/or tested at the other end using checksum
/ hamming / hashing functions that are heavily CPU/memory intensive,
and again, increase the mean propagation delay due to
re-transmission/verification.
for time-critical signals, shorter packets divided over time carry
less data, move faster, and provide data in a faster fashion at the
expense of reliability. larger packets hold more data, can hold better
checksums, requiring less retransmission, and can be verified in the
latency period between complete reception of new packets, increasing
the efficiency and throughput of the network.
The second method would be to use Frequency Division and send parallel
data streams, sending multiple channels of data in synchronous bursts
at a time, in order to maximise the data flow. this is the most common
method, and is the basis for the 16/32/64 bit bus paths in modern
CPU's, as well as radio, TV, and a lot of other transmission methods.
FDM is most common in broadcasting and analog transmission, it does
not allow for much reliability, but is designed to increase throughput
of data in a fixed time period.
Spread Spectrum technologies, such as OFDM, DSSS, FHSS, CDMA, etc, are
far more involving to descibe, but the effect is that reliability is
increased and so is throughput. OFDM is probably the easiest way of
mitigating propagation delays in transient network communication, as
long as the data protocols selected take advantage of the inherent
abilities of this type of signal modulation. |
