1,774 research outputs found
Power and Bandwidth Efficient Coded Modulation for Linear Gaussian Channels
A scheme for power- and bandwidth-efficient communication on the linear Gaussian channel is proposed. A scenario is assumed in which the channel is stationary in time and the channel characteristics are known at the transmitter. Using interleaving, the linear Gaussian channel with its intersymbol interference is decomposed into a set of memoryless subchannels. Each subchannel is further decomposed into parallel binary memoryless channels, to enable the use of binary codes. Code bits from these parallel binary channels are mapped to higher-order near-Gaussian distributed constellation symbols. At the receiver, the code bits are detected and decoded in a multistage fashion. The scheme is demonstrated on a simple instance of the linear Gaussian channel. Simulations show that the scheme achieves reliable communication at 1.2 dB away from the Shannon capacity using a moderate number of subchannels
Orthogonal Codes for Robust Low-Cost Communication
Orthogonal coding schemes, known to asymptotically achieve the capacity per
unit cost (CPUC) for single-user ergodic memoryless channels with a zero-cost
input symbol, are investigated for single-user compound memoryless channels,
which exhibit uncertainties in their input-output statistical relationships. A
minimax formulation is adopted to attain robustness. First, a class of
achievable rates per unit cost (ARPUC) is derived, and its utility is
demonstrated through several representative case studies. Second, when the
uncertainty set of channel transition statistics satisfies a convexity
property, optimization is performed over the class of ARPUC through utilizing
results of minimax robustness. The resulting CPUC lower bound indicates the
ultimate performance of the orthogonal coding scheme, and coincides with the
CPUC under certain restrictive conditions. Finally, still under the convexity
property, it is shown that the CPUC can generally be achieved, through
utilizing a so-called mixed strategy in which an orthogonal code contains an
appropriate composition of different nonzero-cost input symbols.Comment: 2nd revision, accepted for publicatio
Energy Optimal Transmission Scheduling in Wireless Sensor Networks
One of the main issues in the design of sensor networks is energy efficient
communication of time-critical data. Energy wastage can be caused by failed
packet transmission attempts at each node due to channel dynamics and
interference. Therefore transmission control techniques that are unaware of the
channel dynamics can lead to suboptimal channel use patterns. In this paper we
propose a transmission controller that utilizes different "grades" of channel
side information to schedule packet transmissions in an optimal way, while
meeting a deadline constraint for all packets waiting in the transmission
queue. The wireless channel is modeled as a finite-state Markov channel. We are
specifically interested in the case where the transmitter has low-grade channel
side information that can be obtained based solely on the ACK/NAK sequence for
the previous transmissions. Our scheduler is readily implementable and it is
based on the dynamic programming solution to the finite-horizon transmission
control problem. We also calculate the information theoretic capacity of the
finite state Markov channel with feedback containing different grades of
channel side information including that, obtained through the ACK/NAK sequence.
We illustrate that our scheduler achieves a given throughput at a power level
that is fairly close to the fundamental limit achievable over the channel.Comment: Accepted for publication in the IEEE Transactions on Wireless
Communication
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