1,920 research outputs found
Time Localization and Capacity of Faster-Than-Nyquist Signaling
In this paper, we consider communication over the bandwidth limited analog
white Gaussian noise channel using non-orthogonal pulses. In particular, we
consider non-orthogonal transmission by signaling samples at a rate higher than
the Nyquist rate. Using the faster-than-Nyquist (FTN) framework, Mazo showed
that one may transmit symbols carried by sinc pulses at a higher rate than that
dictated by Nyquist without loosing bit error rate. However, as we will show in
this paper, such pulses are not necessarily well localized in time. In fact,
assuming that signals in the FTN framework are well localized in time, one can
construct a signaling scheme that violates the Shannon capacity bound. We also
show directly that FTN signals are in general not well localized in time.
Therefore, the results of Mazo do not imply that one can transmit more data per
time unit without degrading performance in terms of error probability.
We also consider FTN signaling in the case of pulses that are different from
the sinc pulses. We show that one can use a precoding scheme of low complexity
to remove the inter-symbol interference. This leads to the possibility of
increasing the number of transmitted samples per time unit and compensate for
spectral inefficiency due to signaling at the Nyquist rate of the non sinc
pulses. We demonstrate the power of the precoding scheme by simulations
Approaching Gaussian Relay Network Capacity in the High SNR Regime: End-to-End Lattice Codes
We present a natural and low-complexity technique for achieving the capacity
of the Gaussian relay network in the high SNR regime. Specifically, we propose
the use of end-to-end structured lattice codes with the amplify-and-forward
strategy, where the source uses a nested lattice code to encode the messages
and the destination decodes the messages by lattice decoding. All intermediate
relays simply amplify and forward the received signals over the network to the
destination. We show that the end-to-end lattice-coded amplify-and-forward
scheme approaches the capacity of the layered Gaussian relay network in the
high SNR regime. Next, we extend our scheme to non-layered Gaussian relay
networks under the amplify-and-forward scheme, which can be viewed as a
Gaussian intersymbol interference (ISI) channel. Compared with other schemes,
our approach is significantly simpler and requires only the end-to-end design
of the lattice precoding and decoding. It does not require any knowledge of the
network topology or the individual channel gains
Massive MU-MIMO-OFDM Downlink with One-Bit DACs and Linear Precoding
Massive multiuser (MU) multiple-input multiple- output (MIMO) is foreseen to
be a key technology in future wireless communication systems. In this paper, we
analyze the downlink performance of an orthogonal frequency division
multiplexing (OFDM)-based massive MU-MIMO system in which the base station (BS)
is equipped with 1-bit digital-to-analog converters (DACs). Using Bussgang's
theorem, we characterize the performance achievable with linear precoders (such
as maximal-ratio transmission and zero forcing) in terms of bit error rate
(BER). Our analysis accounts for the possibility of oversampling the
time-domain transmit signal before the DACs. We further develop a lower bound
on the information-theoretic sum-rate throughput achievable with Gaussian
inputs.
Our results suggest that the performance achievable with 1-bit DACs in a
massive MU-MIMO-OFDM downlink are satisfactory provided that the number of BS
antennas is sufficiently large
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