1,655 research outputs found
SINR Analysis of Opportunistic MIMO-SDMA Downlink Systems with Linear Combining
Opportunistic scheduling (OS) schemes have been proposed previously by the
authors for multiuser MIMO-SDMA downlink systems with linear combining. In
particular, it has been demonstrated that significant performance improvement
can be achieved by incorporating low-complexity linear combining techniques
into the design of OS schemes for MIMO-SDMA. However, this previous analysis
was performed based on the effective signal-to-interference ratio (SIR),
assuming an interference-limited scenario, which is typically a valid
assumption in SDMA-based systems. It was shown that the limiting distribution
of the effective SIR is of the Frechet type. Surprisingly, the corresponding
scaling laws were found to follow with , rather
than the conventional form.
Inspired by this difference between the scaling law forms, in this paper a
systematic approach is developed to derive asymptotic throughput and scaling
laws based on signal-to-interference-noise ratio (SINR) by utilizing extreme
value theory. The convergence of the limiting distribution of the effective
SINR to the Gumbel type is established. The resulting scaling law is found to
be governed by the conventional form. These novel results are
validated by simulation results. The comparison of SIR and SINR-based analysis
suggests that the SIR-based analysis is more computationally efficient for
SDMA-based systems and it captures the asymptotic system performance with
higher fidelity.Comment: Proceedings of the 2008 IEEE International Conference on
Communications, Beijing, May 19-23, 200
Opportunistic Scheduling and Beamforming for MIMO-SDMA Downlink Systems with Linear Combining
Opportunistic scheduling and beamforming schemes are proposed for multiuser
MIMO-SDMA downlink systems with linear combining in this work. Signals received
from all antennas of each mobile terminal (MT) are linearly combined to improve
the {\em effective} signal-to-noise-interference ratios (SINRs). By exploiting
limited feedback on the effective SINRs, the base station (BS) schedules
simultaneous data transmission on multiple beams to the MTs with the largest
effective SINRs. Utilizing the extreme value theory, we derive the asymptotic
system throughputs and scaling laws for the proposed scheduling and beamforming
schemes with different linear combining techniques. Computer simulations
confirm that the proposed schemes can substantially improve the system
throughput.Comment: To appear in the Proceedings of the 18th Annual IEEE International
Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC),
Athens, Greece, September 3 - 7, 200
Opportunistic Scheduling and Beamforming for MIMO-OFDMA Downlink Systems with Reduced Feedback
Opportunistic scheduling and beamforming schemes with reduced feedback are
proposed for MIMO-OFDMA downlink systems. Unlike the conventional beamforming
schemes in which beamforming is implemented solely by the base station (BS) in
a per-subcarrier fashion, the proposed schemes take advantages of a novel
channel decomposition technique to perform beamforming jointly by the BS and
the mobile terminal (MT). The resulting beamforming schemes allow the BS to
employ only {\em one} beamforming matrix (BFM) to form beams for {\em all}
subcarriers while each MT completes the beamforming task for each subcarrier
locally. Consequently, for a MIMO-OFDMA system with subcarriers, the
proposed opportunistic scheduling and beamforming schemes require only one BFM
index and supportable throughputs to be returned from each MT to the BS, in
contrast to BFM indices and supportable throughputs required by the
conventional schemes. The advantage of the proposed schemes becomes more
evident when a further feedback reduction is achieved by grouping adjacent
subcarriers into exclusive clusters and returning only cluster information from
each MT. Theoretical analysis and computer simulation confirm the effectiveness
of the proposed reduced-feedback schemes.Comment: Proceedings of the 2008 IEEE International Conference on
Communications, Beijing, May 19-23, 200
Opportunistic Collaborative Beamforming with One-Bit Feedback
An energy-efficient opportunistic collaborative beamformer with one-bit
feedback is proposed for ad hoc sensor networks over Rayleigh fading channels.
In contrast to conventional collaborative beamforming schemes in which each
source node uses channel state information to correct its local carrier offset
and channel phase, the proposed beamforming scheme opportunistically selects a
subset of source nodes whose received signals combine in a quasi-coherent
manner at the intended receiver. No local phase-precompensation is performed by
the nodes in the opportunistic collaborative beamformer. As a result, each node
requires only one-bit of feedback from the destination in order to determine if
it should or shouldn't participate in the collaborative beamformer. Theoretical
analysis shows that the received signal power obtained with the proposed
beamforming scheme scales linearly with the number of available source nodes.
Since the the optimal node selection rule requires an exhaustive search over
all possible subsets of source nodes, two low-complexity selection algorithms
are developed. Simulation results confirm the effectiveness of opportunistic
collaborative beamforming with the low-complexity selection algorithms.Comment: Proceedings of the Ninth IEEE Workshop on Signal Processing Advances
in Wireless Communications, Recife, Brazil, July 6-9, 200
Distributed Opportunistic Scheduling for MIMO Ad-Hoc Networks
Distributed opportunistic scheduling (DOS) protocols are proposed for
multiple-input multiple-output (MIMO) ad-hoc networks with contention-based
medium access. The proposed scheduling protocols distinguish themselves from
other existing works by their explicit design for system throughput improvement
through exploiting spatial multiplexing and diversity in a {\em distributed}
manner. As a result, multiple links can be scheduled to simultaneously transmit
over the spatial channels formed by transmit/receiver antennas. Taking into
account the tradeoff between feedback requirements and system throughput, we
propose and compare protocols with different levels of feedback information.
Furthermore, in contrast to the conventional random access protocols that
ignore the physical channel conditions of contending links, the proposed
protocols implement a pure threshold policy derived from optimal stopping
theory, i.e. only links with threshold-exceeding channel conditions are allowed
for data transmission. Simulation results confirm that the proposed protocols
can achieve impressive throughput performance by exploiting spatial
multiplexing and diversity.Comment: Proceedings of the 2008 IEEE International Conference on
Communications, Beijing, May 19-23, 200
Distributed Opportunistic Scheduling For Ad-Hoc Communications Under Noisy Channel Estimation
Distributed opportunistic scheduling is studied for wireless ad-hoc networks,
where many links contend for one channel using random access. In such networks,
distributed opportunistic scheduling (DOS) involves a process of joint channel
probing and distributed scheduling. It has been shown that under perfect
channel estimation, the optimal DOS for maximizing the network throughput is a
pure threshold policy. In this paper, this formalism is generalized to explore
DOS under noisy channel estimation, where the transmission rate needs to be
backed off from the estimated rate to reduce the outage. It is shown that the
optimal scheduling policy remains to be threshold-based, and that the rate
threshold turns out to be a function of the variance of the estimation error
and be a functional of the backoff rate function. Since the optimal backoff
rate is intractable, a suboptimal linear backoff scheme that backs off the
estimated signal-to-noise ratio (SNR) and hence the rate is proposed. The
corresponding optimal backoff ratio and rate threshold can be obtained via an
iterative algorithm. Finally, simulation results are provided to illustrate the
tradeoff caused by increasing training time to improve channel estimation at
the cost of probing efficiency.Comment: Proceedings of the 2008 IEEE International Conference on
Communications, Beijing, May 19-23, 200
Occupant satisfaction in post-refurbishment of historic buildings : baroque case studies in Valletta, Malta
This paper evaluates occupants’ subjective response to controlled architectural interventions in listed historic buildings, as part of a comprehensive plan to restore, rehabilitate and re-use the edifice. The overall strategy was to monitor a series of historic buildings, which typically represent the same period, namely 16th century architecture, depicting the Baroque period in Malta’s World Heritage Capital, Valletta. Such buildings often had discrete traditional physical features, such as ventilation stacks through their thick massive walls and an open courtyard, generating the typical introvert planning. These assisted the acclimatisation of their indoor spaces. Interventions were limited to exposing their thermal mass and re-activating the original features. The buildings were partially assessed for their thermal performance through a post-occupancy survey (POS), based on subjective evidence. Questionnaires and structured interviews were conducted with office staff, two years after entering the commissioned refurbished buildings. Results indicated that the revival of modest passive design solutions was effective in attaining comfort levels today, thus reducing the dependence on energy guzzling modern environmental control systems. This suggests that such featurerevealing interventions can be easily adapted to other similar historic buildings offered for refurbishment, thus achieving energy efficiency all round, also reducing their overall carbon footprint.peer-reviewe
A comparative study of the energetic performance of climate adaptive facades compared to static facade design in a Mediterranean climate
Energy-efficient design of building façades has so far predominantly been confined to static rigid forms. Recently however, attempts have been made to design environmentally responsive façades, hereby called Climate Adaptive Façades. These have the potential to better address the occupant's requirements, while also reducing energy demand. The present paper focuses on adaptable glazed façades, in a Mediterranean climate. It investigates the simulated energy performance of three types of climate-responsive façades that could be retrofitted to an existing glazed façade, in the process comparing the results to using comparable static façades solutions. Modelling dynamic façades is not an easy task and currently no single building performance simulation package appears to be capable of completely modelling the behaviour of these façades. For this reason a number of simulation packages had to be used to determine the energy demand required to achieve comfortable indoor thermal and lighting conditions. Through the results obtained, it was possible to compare energy demand of a dual-façade design approach, dynamic vs. static, thus identifying general trends. The results also highlight the fact that in order to improve over the predicted performance further studies using specialised tools capable of modelling such novel technologies are required.peer-reviewe
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