Adaptive reduced-rank interference suppression based on themultistage Wiener filter

A class of adaptive reduced-rank interference suppression algorithms is presented based on the multistage Wiener filter (MSWF). The performance is examined in the context of direct-sequence (DS) code division multiple access (CDMA). Unlike the principal components method for reduced-rank filtering, the algorithms presented can achieve near full-rank performance with a filter rank much less than the dimension of the signal subspace. We present batch and recursive algorithms for estimating the filter parameters, which do not require an eigen-decomposition. The algorithm performance in a heavily loaded DS-CDMA system is characterized via computer simulation. The results show that the reduced-rank algorithms require significantly fewer training samples than other reduced- and full-rank algorithms     

Signature sequence adaptation for DS-CDMA with multipath

Joint transmitter-receiver adaptation is studied for the reverse link of a direct sequence-code division multiple access system with short signature sequences. The signature for a particular user is computed at the receiver and transmitted back to the transmitter via a feedback channel. A reduced-rank transmitter adaptation scheme is presented in which the signature is constrained to lie in a lower dimensional subspace. This allows a tradeoff between system performance and the number of estimated parameters. Analytical and simulation results show that adaptation of relatively few transmitter coefficients can lead to significant performance improvements. Adaptive algorithms are derived for estimating the transmitter coefficients in the presence of multipath. We consider both collective optimization, in which the users adapt together to improve a global system performance criterion, and individual optimization, in which the signature for a particular user is adapted to optimize individual performance. Numerical results are presented, which show that both individual and collective joint transmitter-receiver adaptation can effectively preequalize the channel and avoid interference at high loads     

Simple Interpretation of the Verwey Transition in Magnetite

The Verwey transition in magnetite is rationalized in terms of an electronic model involving correlated electron occupancy of nearest-neighbor octahedral site pairs. This formalism can be restated in terms of order-disorder theory. The site pair representation of the lattice is analyzed in terms of possible occupation states that represent respectively the ground state of the system as a trapped electron, a first excited state in which an electron can resonate between the two constituents of a site pair, and a second excited state involving two electrons on neighboring sites. The free energy of this representative assembly is then minimized to obtain the equilibrium configuration. The Verwey transition is driven by the Coulomb repulsive interaction between electrons on neighboring sites. In certain limiting cases one obtains results equivalent to the phenomenological Strässler-Kittel model, which had been successfully used on an empirical basis to analyze both the first- and second-order Verwey transitions that have been experimentally encountered with increasing departures from the ideal 4/3 ratio of oxygen/iron in magnetite.     

IN rollout in the United States

Individual perspectives on advanced intelligent network (AIN) implementation are presented from four regional companies in the Unites States: Bell Atlantic, BellSouth, Ameritech, and US WEST. These perspectives range from trial to deployment activities and address a range of capabilities supported by the AIN architecture. AIN participation by all regional companies in the United States is summarized     

Asymptotic analysis of LMMSE multiuser receivers for multi-signature multicarrier CDMA in Rayleigh fading

This paper considers a multicarrier (MC) code-division multiple-access system where each user employs multiple signatures. The receiver is linear and minimizes the mean square error of the data estimate. Both multiple-user and single-user systems are considered, as well as single and multiple signatures per user. In each case, an asymptotic analysis is used to derive the output signal-to-interference-plus-noise ratio (SINR) as a function of the system loading, the noise power, and the fading properties of the channel. Asymptotic in this case means that the number of independent subcarriers and number of signatures per user each tends to infinity with fixed ratio. The associated bit-error rate (BER) is evaluated for binary phase-shift keying symbols. Simulations show that the asymptotic SINRs and BERs derived in each case are accurate for realistic finite systems.     

On optimal signal sets for digital communications with finiteprecision and amplitude constraints

The maximum data rate that can be reliably communicated given a linear, time-invariant, dispersive channel, a receiver that samples the channel output to within an accuracy of ±d where d >0, and a transmitter with an output amplitude constraint is evaluated. For any dispersive channel the maximum rate depends on d and is finite. The transmitted waveforms must be designed so that two channel outputs associated with two distinct transmitted signals are separated in amplitude at a particular time by d. It is shown that given any channel impulse response with rational Laplace transform, there exists an optimal sets of inputs that are ±A everywhere where A is the maximum allowable amplitude. Furthermore, in any finite time interval, each input changes sign a finite number of times. If the channel impulse response is a single decaying exponential, it is shown that simple binary signaling, in which A or -A, depending on the current message bit, is transmitted during each symbol interval, maximizes the data rate     

Forward-link performance of satellite CDMA with linear interference suppression and one-step power control

Wideband direct-sequence (DS)-code-division multiple-access (CDMA) is a strong candidate for both terrestrial and satellite components of UMTS. The forward-link capacity of a satellite DS-CDMA system with a conventional matched filter (MF) receiver is limited by interference from adjacent beams and possibly overlapping beams from multiple satellites. In this paper, we study the performance of the linear minimum mean squared error (MMSE) receiver for the satellite forward link. System constraints are long propagation delay, which prevents accurate closed-loop power control, and low on-board power consumption, which implies a low received bit energy to noise density ratio at the mobile receiver. We consider a "one-step" power adjustment algorithm which attempts to compensate for random shadowing and path loss, and compare the associated performance of the MMSE and MF receivers. Dual-satellite diversity is also considered. The effect of code rate on performance is studied through the use of punctured convolutional codes and the evaluation of random coding bounds. Our results indicate that linear MMSE interference suppression can improve the quality of service and increase system capacity significantly.     

Performance and welfare of high-yielding dairy cows subjected to 5 or 8 cooling sessions daily under hot and humid climate

The objectives were to determine the effects of cooling of high-yielding dairy cows under a hot and humid climate on intake, milk yield, rumination time, and welfare parameters. Forty-two multiparous Israeli Holstein dairy cows were divided into 2 treatment groups and were housed in an open barn divided into 2 pens. The groups were subjected to different cooling schedules, in a crossover design as follows: cows were exposed to 5 or 8 cooling sessions per day (designated 5CS and 8CS, respectively) in the holding area of the milking parlor. Each period lasted 4 wk, and then treatments were switched for another 4-wk period. Each cooling session lasted 45 min, comprising cycles of 30s of showering and 4.5 min of ventilation without showering. Respiration rate and rectal temperature were recorded twice per week (Monday and Thursday) at 0630 and 1600 h. Rumination and lying times were recorded automatically. Rectal temperatures were 0.16 and 1.08°C lower in 8CS than in 5CS cows in the morning and afternoon, respectively. Respiration rate was lower in 8CS than in 5CS cows in the morning (49.1 and 54.6 breaths/min, respectively), and more so in the afternoon (50.0 and 83.0 breaths/min, respectively). Dry matter intake and milk yields were 9.3 and 9.6% higher in the 8CS than in the 5CS cows (27.0 vs. 24.7 and 40.1 vs. 36.6 kg/d, respectively), with no differences in milk fat and protein contents. Daily rumination time was 7.4% longer in the 8CS than in the 5CS (440.1 and 409.6 min/d, respectively); however, rumination time per unit of dry matter or neutral detergent fiber consumed was higher in the 5CS than in the 8CS cows. Although the 8CS cows moved 3 times more to the milking area for extra cooling sessions than the 5CS ones, they spent 9.9 min/d more than the 5CS ones in lying down (484.4 and 474.5 min/d, respectively), and used more of their free time (excluding milking and feeding time) in resting than the 5CS cows: 52.0 and 43.9%, respectively. It appears that increasing the cooling frequency from 5 to 8 times per day improved their feeling of welfare, so they could spend more time lying and ruminating. In conclusion, increasing the cooling frequency of high-yielding dairy cows under hot and humid conditions from 5 to 8 times a day increased their intake and milk yield, and lowered their respiration rate and rectal temperature. Moreover, the 8CS cows spent more time resting than 5CS cows, an indication that increasing cooling frequency improved animal welfare.