Optimizing Multi-Antenna Systems with Partial Channel Knowledge
Institute of Electrical and Electronics Engineers (IEEE) 1 (2003) 217-220
Outage Capacity with two-bit channel feedback for a two-transmit and single receive antenna system
GLOBECOM - IEEE Global Telecommunications Conference 2 (2003) 844-848
Abstract:
Channel information at the transmitter is known to significantly increase information throughput. However, practical constraints in the opposite link limit the possible amount of feedback. In this paper we describe a way to calculate the capacity of a simple, yet relevant feedback scheme. In particular, we consider the case of a two-antenna transmitter and a single antenna receiver, and limit the amount of feedback to 2 bits. This case is of practical interest because it is included in the UMTS standards. We determine the transmission weights maximizing the outage mutual information, and find that they interpolate between beamforming and orthogonal coding. Further, the case of the feedback bits having finite and generally unequal probabilities of error is also considered. In the latter case, the optimal relative phase between the two transmitting antennas deviates from their symmetric ± π ± π/4 value. This effect is important, if the bits are fed back at different times and thus their reliability is not the same (one feedback bit being more stale than the other).Theory of surface-acoustic-wave propagation in the v = 5/2 fractional quantum Hall state
International Journal of Modern Physics B 16:20-22 (2002) 2959
Striped states in quantum Hall effect: Deriving a low-energy theory from Hartree-Fock
Physical Review B - Condensed Matter and Materials Physics 64:15 (2001) 1553011-15530114
Abstract:
There is growing experimental and theoretical evidence that very clean two-dimensional electron systems form unidirectional charge density waves (UCDW) or "striped" states at low temperatures and at Landau level filling fractions of the form v = M + x with 4 < M < 10 an integer and 0.4 ≳ x ≳ 0.6. Following previous work, we model the striped state using a Hartree-Fock approach. We construct the low-energy excitations of the system by making smooth deformations of the stripe edges analogous to the construction of edge state excitations of quantum Hall droplets. These low-energy excitations are described as a coupled Luttinger liquid theory, as discussed previously by MacDonald and Fisher [Phys. Rev. B 61, 5724 (2000)]. Here, we extend that work and explicitly derive all of the parameters of this low energy theory using a Hartree-Fock approach. We also make contact with the equivalent low-energy hydrodynamic approach of Fogler and Vinokur [Phys. Rev. Lett. 84, 5828 (2000)] and similarly derive the parameters of this theory. As examples of the use of these results, we explicitly calculate the low-energy excitation spectrum and study tunneling into the striped state.Communication in a disordered world
Physics Today 54:9 (2001) 38-43