832 research outputs found
Turbo Packet Combining for Broadband Space-Time BICM Hybrid-ARQ Systems with Co-Channel Interference
In this paper, efficient turbo packet combining for single carrier (SC)
broadband multiple-input--multiple-output (MIMO) hybrid--automatic repeat
request (ARQ) transmission with unknown co-channel interference (CCI) is
studied. We propose a new frequency domain soft minimum mean square error
(MMSE)-based signal level combining technique where received signals and
channel frequency responses (CFR)s corresponding to all retransmissions are
used to decode the data packet. We provide a recursive implementation algorithm
for the introduced scheme, and show that both its computational complexity and
memory requirements are quite insensitive to the ARQ delay, i.e., maximum
number of ARQ rounds. Furthermore, we analyze the asymptotic performance, and
show that under a sum-rank condition on the CCI MIMO ARQ channel, the proposed
packet combining scheme is not interference-limited. Simulation results are
provided to demonstrate the gains offered by the proposed technique.Comment: 12 pages, 7 figures, and 2 table
Clearing the Rf Smog: Making 802.11 Robust to Cross-Technology Interference
Recent studies show that high-power cross-technology interference
is becoming a major problem in todayâs 802.11 networks. Devices
like baby monitors and cordless phones can cause a wireless
LAN to lose connectivity. The existing approach for dealing
with such high-power interferers makes the 802.11 network switch
to a different channel; yet the ISM band is becoming increasingly
crowded with diverse technologies, and hence many 802.11 access
points may not find an interference-free channel.
This paper presents TIMO, a MIMO design that enables 802.11n
to communicate in the presence of high-power cross-technology
interference. Unlike existing MIMO designs, however, which require
all concurrent transmissions to belong to the same technology,
TIMO can exploit MIMO capabilities to decode in the presence
of a signal from a different technology, hence enabling diverse
technologies to share the same frequency band. We implement a
prototype of TIMO in GNURadio-USRP2 and show that it enables
802.11n to communicate in the presence of interference from baby
monitors, cordless phones, and microwave ovens, transforming scenarios
with a complete loss of connectivity to operational networks.National Science Foundation (U.S.) (NSF grant CNS-0831660)National Science Foundation (U.S.) (NSF grant CNS- 0721857)United States. Defense Advanced Research Projects Agency (DARPA ITMANET
Performance evaluation of turbulence-accentuated interchannel crosstalk for hybrid fibre and free-space optical wavelength-division-multiplexing systems using digital pulse-position modulation
A hybrid fibre and free-space optical communication link using digital pulse-position modulation (DPPM) in a wavelength-division-multiplexing system is proposed. Such a system, which could provide a power efficient, robust and flexible solution to high-speed access networks, is a contender for a passive optical network solution and could readily be deployed in areas with restrictions in optical fibre installation, or alternatively as a disaster recovery network. Interchannel crosstalk and atmospheric turbulence are major impairments in such a system and could combine in some cases to degrade the system. Both impairments are investigated here and the results are presented in the form of bit error probability, required optical transmission power and power penalties. Depending on the position of the interferer relative to the desired user, power penalties of about 0.2â3.0 dB for weak turbulence and above 20 dB for strong turbulence regimes are reported for bit error rate of 10â6. DPPM scheme with a coding level of 2 show about 2 dB improvements over onâoff-keying scheme
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