448 research outputs found
Explicit Space-Time Codes Achieving The Diversity-Multiplexing Gain Tradeoff
A recent result of Zheng and Tse states that over a quasi-static channel,
there exists a fundamental tradeoff, referred to as the diversity-multiplexing
gain (D-MG) tradeoff, between the spatial multiplexing gain and the diversity
gain that can be simultaneously achieved by a space-time (ST) block code. This
tradeoff is precisely known in the case of i.i.d. Rayleigh-fading, for T>=
n_t+n_r-1 where T is the number of time slots over which coding takes place and
n_t,n_r are the number of transmit and receive antennas respectively. For T <
n_t+n_r-1, only upper and lower bounds on the D-MG tradeoff are available.
In this paper, we present a complete solution to the problem of explicitly
constructing D-MG optimal ST codes, i.e., codes that achieve the D-MG tradeoff
for any number of receive antennas. We do this by showing that for the square
minimum-delay case when T=n_t=n, cyclic-division-algebra (CDA) based ST codes
having the non-vanishing determinant property are D-MG optimal. While
constructions of such codes were previously known for restricted values of n,
we provide here a construction for such codes that is valid for all n.
For the rectangular, T > n_t case, we present two general techniques for
building D-MG-optimal rectangular ST codes from their square counterparts. A
byproduct of our results establishes that the D-MG tradeoff for all T>= n_t is
the same as that previously known to hold for T >= n_t + n_r -1.Comment: Revised submission to IEEE Transactions on Information Theor
Attention-Enhanced Deep Learning for Device-Free Through-the-Wall Presence Detection Using Indoor WiFi System
Accurate detection of human presence in indoor environments is important for
various applications, such as energy management and security. In this paper, we
propose a novel system for human presence detection using the channel state
information (CSI) of WiFi signals. Our system named attention-enhanced deep
learning for presence detection (ALPD) employs an attention mechanism to
automatically select informative subcarriers from the CSI data and a
bidirectional long short-term memory (LSTM) network to capture temporal
dependencies in CSI. Additionally, we utilize a static feature to improve the
accuracy of human presence detection in static states. We evaluate the proposed
ALPD system by deploying a pair of WiFi access points (APs) for collecting CSI
dataset, which is further compared with several benchmarks. The results
demonstrate that our ALPD system outperforms the benchmarks in terms of
accuracy, especially in the presence of interference. Moreover, bidirectional
transmission data is beneficial to training improving stability and accuracy,
as well as reducing the costs of data collection for training. Overall, our
proposed ALPD system shows promising results for human presence detection using
WiFi CSI signals
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