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Feedback reduction scheme for downlink multiuser diversity
Jaewoo So,Cioffi, J.M. IEEE 2009 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.8 No.2
<P>A group random access-based feedback scheme is proposed for multiuser diversity systems, where users are divided into several feedback groups according to their measured channel states. Different random access probabilities and number of feedback minislots are assigned to each feedback group. Each user competes to send a feedback message through random access if its scheduling metric exceeds a threshold. The base station jointly controls the random access probabilities, the thresholds, and the number of feedback minislots to adjust the feedback load. The proposed feedback scheme shows a good system capacity with limited feedback resources regardless of the number of users.</P>
Multiuser Diversity in a MIMO System With Opportunistic Feedback
Jaewoo So,Cioffi, J.M. IEEE 2009 IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY Vol.58 No.9
<P>An opportunistic feedback protocol with multiple thresholds and multiple access probabilities is proposed for multiuser diversity in multiple-input-multiple-output (MIMO) broadcast channels. Users compete to report the channel state information (CSI) via contention-based feedback channels if their scheduling metric exceeds a threshold. The users are divided into two classes according to their scheduling metric. For each class, the users have different random access probabilities and different chances to access feedback minislots. The performance of the proposed feedback protocol is evaluated in a MIMO system with zero-forcing (ZF) receivers in terms of the sum-rate capacity, the feedback load, and fairness. The simulation results show that the proposed feedback protocol significantly reduces the feedback load without sacrificing the sum-rate capacity too much. The proposed feedback protocol can be operated with existing scheduling algorithms without modification.</P>
Opportunistic Feedback With a Reservation Channel in a Wireless TDD System
Jae-Woo So,Cioffi, J.M. IEEE 2009 IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY Vol.58 No.3
<P>A random-access-based feedback protocol with a reservation-based (RB) channel is proposed for multiuser diversity in a wireless time-division-duplex system. The feedback channels consist of one RB channel and several contention-based (CB) channels. The users randomly access the CB channels if their channel states exceed a threshold, and a base station (BS) schedules a user who reports the highest signal-to-noise ratio from multiple users that successfully provide feedback. If there is no successful feedback in the CB channels, the BS uses the feedback information that a designated user reports through the RB channel. The proposed feedback protocol achieves an almost ideal sum-rate capacity with a fixed number of feedback channels regardless of the number of users.</P>
On the Use of Hexagonal Constellation for Peak-to-Average Power Ratio Reduction of an ODFM Signal
Seung Hee Han,Cioffi, J.M.,Jae Hong Lee IEEE 2008 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.7 No.3
<P>One of the main drawbacks of orthogonal frequency division multiplexing (OFDM) is the high peak-to-average power ratio (PAPR) of the OFDM signal. In this paper, we propose the use of hexagonal constellation for PAPR reduction of an OFDM signal. Because hexagonal constellation is the densest packing of regularly spaced points in two dimensions, we can have more signal points in a given area with hexagonal constellation than with quadrature amplitude modulation (QAM) constellation. We can exploit these extra degrees of freedom provided by the hexagonal constellation for PAPR reduction of an OFDM signal. We will apply the proposed technique to eliminate data rate loss due to the side information in partial transmit sequence (PTS) technique and selected mapping (SLM) technique.</P>
Gadolinium-doped ceria nanopowders synthesized by urea-based homogeneous co-precipitation (UBHP)
Accardo, G.,Spiridigliozzi, L.,Cioffi, R.,Ferone, C.,Di Bartolomeo, E.,Yoon, Sung Pil,Dell’Agli, G. Elsevier 2017 Materials chemistry and physics Vol.187 No.-
<P><B>Abstract</B></P> <P>Gadolinium (10%)-doped ceria was successfully synthesized by using an urea-based co-precipitation method (UBHP). A single fluorite phase was obtained after a low temperature (400 °C) calcination treatment. The resulting powders showed grains of nanometric size with some agglomerations and an overall good sinterability. Pellets were sintered at 1300 and 1500 °C for 3 h. The ionic conductivity was measured by electrochemical impedance spectroscopy measurements and a correlation between electrical properties and microstructure was revealed. The promising conductivity values showed that the synthesized powders are suitable for intermediate temperature solid oxide fuel cells (IT-SOFCs) applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Urea-based homogeneous co-precipitation is applied to synthesize nanocrystalline GDC. </LI> <LI> Dense GDC samples at different sintering temperatures were characterized. </LI> <LI> SEM and TEM revealed a well define microstructure and controlled composition. </LI> <LI> Correlation between electrochemical properties by EIS and microstructure was discussed. </LI> <LI> UBHP method can be used to prepare high performance GDC electrolytes. </LI> </UL> </P>
Tone injection with hexagonal constellation for peak-to-average power ratio reduction in OFDM
Seung Hee Han,Cioffi, J.M.,Jae Hong Lee IEEE 2006 IEEE COMMUNICATIONS LETTERS Vol.10 No.9
<P>One of the main drawbacks of orthogonal frequency division multiplexing (OFDM) is the high peak-to-average power ratio (PAPR) of the OFDM signal. Tone injection (TI) technique is a promising candidate for the reduction of the PAPR of an OFDM signal. But this technique requires the increase of the transmit signal power because of the injected signal. In this paper, we propose the use of hexagonal constellation as a method to achieve PAPR reduction without increasing signal power in the TI technique</P>
Coordinated Cognitive Tethering in Dense Wireless Areas
Haleh Tabrizi,Golnaz Farhadi,John Cioffi,Ghadah Aldabbagh 한국전자통신연구원 2016 ETRI Journal Vol.38 No.2
This paper examines the resource gain that can be obtained from the creation of clusters of nodes in densely populated areas. A single node within each such cluster is designated as a “hotspot”; all other nodes then communicate with a destination node, such as a base station, through such hotspots. We propose a semi-distributed algorithm, referred to as coordinated cognitive tethering (CCT), which clusters all nodes and coordinates hotspots to tether over locally available white spaces. CCT performs the following these steps: (a) groups nodes based on a modified k-means clustering algorithm; (b) assigns white-space spectrum to each cluster based on a distributed graph-coloring approach to maximize spectrum reuse, and (c) allocates physical-layer resources to individual users based on local channel information. Unlike small cells (for example, femtocells and WiFi), this approach does not require any additions to existing infrastructure. In addition to providing parallel service to more users than conventional direct communication in cellular networks, simulation results show that CCT can increase the average battery life of devices by 30%, on average.