17,727 research outputs found
Embedded Rank Distance Codes for ISI channels
Designs for transmit alphabet constrained space-time codes naturally lead to
questions about the design of rank distance codes. Recently, diversity embedded
multi-level space-time codes for flat fading channels have been designed from
sets of binary matrices with rank distance guarantees over the binary field by
mapping them onto QAM and PSK constellations. In this paper we demonstrate that
diversity embedded space-time codes for fading Inter-Symbol Interference (ISI)
channels can be designed with provable rank distance guarantees. As a corollary
we obtain an asymptotic characterization of the fixed transmit alphabet
rate-diversity trade-off for multiple antenna fading ISI channels. The key idea
is to construct and analyze properties of binary matrices with a particular
structure induced by ISI channels.Comment: Submitted to IEEE Transactions on Information Theor
Maximum-rate Transmission with Improved Diversity Gain for Interference Networks
Interference alignment (IA) was shown effective for interference management
to improve transmission rate in terms of the degree of freedom (DoF) gain. On
the other hand, orthogonal space-time block codes (STBCs) were widely used in
point-to-point multi-antenna channels to enhance transmission reliability in
terms of the diversity gain. In this paper, we connect these two ideas, i.e.,
IA and space-time block coding, to improve the designs of alignment precoders
for multi-user networks. Specifically, we consider the use of Alamouti codes
for IA because of its rate-one transmission and achievability of full diversity
in point-to-point systems. The Alamouti codes protect the desired link by
introducing orthogonality between the two symbols in one Alamouti codeword, and
create alignment at the interfering receiver. We show that the proposed
alignment methods can maintain the maximum DoF gain and improve the ergodic
mutual information in the long-term regime, while increasing the diversity gain
to 2 in the short-term regime. The presented examples of interference networks
have two antennas at each node and include the two-user X channel, the
interferring multi-access channel (IMAC), and the interferring broadcast
channel (IBC).Comment: submitted to IEEE Transactions on Information Theor
Pulse Shaping Diversity to Enhance Throughput in Ultra-Dense Small Cell Networks
Spatial multiplexing (SM) gains in multiple input multiple output (MIMO)
cellular networks are limited when used in combination with ultra-dense small
cell networks. This limitation is due to large spatial correlation among
channel pairs. More specifically, it is due to i) line-of-sight (LOS)
communication between user equipment (UE) and base station (BS) and ii)
in-sufficient spacing between antenna elements. We propose to shape transmit
signals at adjacent antennas with distinct interpolating filters which
introduces pulse shaping diversity eventually leading to improved SINR and
throughput at the UEs. In this technique, each antenna transmits its own data
stream with a relative offset with respect to adjacent antenna. The delay which
must be a fraction of symbol period is interpolated with the pulse shaped
signal and generates a virtual MIMO channel that leads to improved diversity
and SINR at the receiver. Note that non-integral sampling periods with
inter-symbol interference (ISI) should be mitigated at the receiver. For this,
we propose to use a fractionally spaced equalizer (FSE) designed based on the
minimum mean squared error (MMSE) criterion. Simulation results show that for a
2x2 MIMO and with inter-site-distance (ISD) of 50 m, the median received SINR
and throughput at the UE improves by a factor of 11 dB and 2x, respectively,
which verifies that pulse shaping can overcome poor SM gains in ultra-dense
small cell networks.Comment: Accepted to 17th IEEE International Workshop on Signal Processing
Advances in Wireless Communication
Near-Instantaneously Adaptive HSDPA-Style OFDM Versus MC-CDMA Transceivers for WIFI, WIMAX, and Next-Generation Cellular Systems
Burts-by-burst (BbB) adaptive high-speed downlink packet access (HSDPA) style multicarrier systems are reviewed, identifying their most critical design aspects. These systems exhibit numerous attractive features, rendering them eminently eligible for employment in next-generation wireless systems. It is argued that BbB-adaptive or symbol-by-symbol adaptive orthogonal frequency division multiplex (OFDM) modems counteract the near instantaneous channel quality variations and hence attain an increased throughput or robustness in comparison to their fixed-mode counterparts. Although they act quite differently, various diversity techniques, such as Rake receivers and space-time block coding (STBC) are also capable of mitigating the channel quality variations in their effort to reduce the bit error ratio (BER), provided that the individual antenna elements experience independent fading. By contrast, in the presence of correlated fading imposed by shadowing or time-variant multiuser interference, the benefits of space-time coding erode and it is unrealistic to expect that a fixed-mode space-time coded system remains capable of maintaining a near-constant BER
Multi-Source Cooperative Communication with Opportunistic Interference Cancelling Relays
In this paper we present a multi-user cooperative protocol for wireless
networks. Two sources transmit simultaneously their information blocks and
relays employ opportunistically successive interference cancellation (SIC) in
an effort to decode them. An adaptive decode/amplify-and-forward scheme is
applied at the relays to the decoded blocks or their sufficient statistic if
decoding fails. The main feature of the protocol is that SIC is exploited in a
network since more opportunities arise for each block to be decoded as the
number of used relays NRU is increased. This feature leads to benefits in terms
of diversity and multiplexing gains that are proven with the help of an
analytical outage model and a diversity-multiplexing tradeoff (DMT) analysis.
The performance improvements are achieved without any network synchronization
and coordination. In the final part of this work the closed-form outage
probability model is used by a novel approach for offline pre-selection of the
NRU relays, that have the best SIC performance, from a larger number of NR
nodes. The analytical results are corroborated with extensive simulations,
while the protocol is compared with orthogonal and multi-user protocols
reported in the literature.Comment: in IEEE Transactions on Communications, 201
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