1,992 research outputs found
Sensing Throughput Tradeoff for Cognitive Radio Networks with Noise Variance Uncertainty
This paper proposes novel spectrum sensing algorithm, and examines the
sensing throughput tradeoff for cognitive radio (CR) networks under noise
variance uncertainty. It is assumed that there are one white sub-band, and one
target sub-band which is either white or non-white. Under this assumption,
first we propose a novel generalized energy detector (GED) for examining the
target sub-band by exploiting the noise information of the white sub-band,
then, we study the tradeoff between the sensing time and achievable throughput
of the CR network. To study this tradeoff, we consider the sensing time
optimization for maximizing the throughput of the CR network while
appropriately protecting the primary network. The sensing time is optimized by
utilizing the derived detection and false alarm probabilities of the GED. The
proposed GED does not suffer from signal to noise ratio (SNR) wall (i.e.,
robust against noise variance uncertainty) and outperforms the existing signal
detectors. Moreover, the relationship between the proposed GED and conventional
energy detector (CED) is quantified analytically. We show that the optimal
sensing times with perfect and imperfect noise variances are not the same. In
particular, when the frame duration is 2s, and SNR is -20dB, and each of the
bandwidths of the white and target sub-bands is 6MHz, the optimal sensing times
are 28.5ms and 50.6ms with perfect and imperfect noise variances, respectively.Comment: Accepted in CROWNCOM, June 2014, Oulu, Finlan
On the Number of RF Chains and Phase Shifters, and Scheduling Design with Hybrid Analog-Digital Beamforming
This paper considers hybrid beamforming (HB) for downlink multiuser massive
multiple input multiple output (MIMO) systems with frequency selective
channels. For this system, first we determine the required number of radio
frequency (RF) chains and phase shifters (PSs) such that the proposed HB
achieves the same performance as that of the digital beamforming (DB) which
utilizes (number of transmitter antennas) RF chains. We show that the
performance of the DB can be achieved with our HB just by utilizing RF
chains and PSs, where is the rank of the
combined digital precoder matrices of all sub-carriers. Second, we provide a
simple and novel approach to reduce the number of PSs with only a negligible
performance degradation. Numerical results reveal that only PSs per RF
chain are sufficient for practically relevant parameter settings. Finally, for
the scenario where the deployed number of RF chains is less than ,
we propose a simple user scheduling algorithm to select the best set of users
in each sub-carrier. Simulation results validate theoretical expressions, and
demonstrate the superiority of the proposed HB design over the existing HB
designs in both flat fading and frequency selective channels.Comment: IEEE Transactions on Wireless Communications (Minor Revision
Multipath Multiplexing for Capacity Enhancement in SIMO Wireless Systems
This paper proposes a novel and simple orthogonal faster than Nyquist (OFTN)
data transmission and detection approach for a single input multiple output
(SIMO) system. It is assumed that the signal having a bandwidth is
transmitted through a wireless channel with multipath components. Under
this assumption, the current paper provides a novel and simple OFTN
transmission and symbol-by-symbol detection approach that exploits the
multiplexing gain obtained by the multipath characteristic of wideband wireless
channels. It is shown that the proposed design can achieve a higher
transmission rate than the existing one (i.e., orthogonal frequency division
multiplexing (OFDM)). Furthermore, the achievable rate gap between the proposed
approach and that of the OFDM increases as the number of receiver antennas
increases for a fixed value of . This implies that the performance gain of
the proposed approach can be very significant for a large-scale multi-antenna
wireless system. The superiority of the proposed approach is shown
theoretically and confirmed via numerical simulations. {Specifically, we have
found {upper-bound average} rates of 15 bps/Hz and 28 bps/Hz with the OFDM and
proposed approaches, respectively, in a Rayleigh fading channel with 32 receive
antennas and signal to noise ratio (SNR) of 15.3 dB. The extension of the
proposed approach for different system setups and associated research problems
is also discussed.Comment: IEEE Transactions on Wireless Communication
Au large des Saintes-Maries-de-la-Mer – Étude d’ensemble des épaves antiques chargées de barres et de lingots de fer (SM2, SM6, SM9, SM10)
L’ensemble des lingots et des barres de fer, mis au jour ces dernières années sur les épaves de Camargue, présente une telle homogénéité qu’il permet de dresser une première typologie des formes. Ce classement provisoire, basé sur des critères de longueur et de section, individualise actuellement six types (fig. 1).Fig. 1 – Table typologique des lingots de fer des épaves de CamargueDAO : G. Frommertz, L. Long (Drassm).Le type 1, attesté sur plusieurs épaves de Camargue, regroupe de longues b..
Au large des Saintes-Maries-de-la-Mer – Saintes-Maries-de-la-Mer 6
L’épave se situe à un mille en face de Port-Gardian (le port des Saintes-Maries-de-la-Mer), à 13,80 m de fond.Le corps principal du gisement, partiellement recouvert de filets, dépassait de 75 cm au-dessus du sable lors de notre expertise avec L’Archéonaute. Il se compose d’une très grande concrétion ferrocalcaire de 8,10 m de long pour 4,70 m de large. La hauteur de cette masse concrétionnaire dépasse 1,50 m. D’autres concrétions de taille plus modeste (entre 1 m et 3 m) s’amoncellent en dé..
Au large des Saintes-Maries-de-la-Mer – Saintes-Maries-de-la-Mer 2
L’épave se situe face au Petit Rhône par 10,5 m de fond. Longue de 15 m, elle se caractérise par un ensemble de concrétions métalliques à la surface desquelles apparaissent des fragments d’amphores Dr. 2/4 espagnoles, le tout recouvert de filets de chalut (fig. 1 et 2). Le corps principal du gisement est constitué par une masse concrétionnaire de près de 8 m de long pour 4,3 m de large au centre de laquelle l’agencement de lingots et de barres de fer laisse entrevoir la carlingue métallifiée..
Au large des Saintes-Maries-de-la-Mer – Saintes-Maries-de-la-Mer 10
L’épave, qui était très ensablée lors de sa découverte, se situe à l’ouest des Saintes-Maries-de-la-Mer, face à l’étang d’Icard, par 11 m à 12 m de fond. Elle est très exactement à 670 m au sud de l’épave SM2.De la masse concrétionnaire principale, recouverte de filets et mesurant entre 5 m et 8 m de long pour 3 m de large, nous avions prélevé, à l’origine, trois barres de fer. Ces premiers échantillons de forme 1, relativement aplatis, présentaient des estampilles illisibles (Long 1997, p. ..
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