Nonparametric confidence bounds, using censored data, on the meanresidual life

An approach to inverting confidence bounds on the failure rate to obtain conservative nonparametric confidence statements about the mean residual life (MRL) for type I and II censoring and random right (left) censoring is described. A mild nonparametric condition of increasing (or decreasing) MRL is used. The condition of increasing (or decreasing) MRL is not required for the whole time axis. All example which uses type II censored data is included     

An information-theoretic framework for deriving canonical decision-feedback receivers in Gaussian channels

A framework is presented that allows a number of known results relating feedback equalization, linear prediction, and mutual information to be easily understood. A lossless, additive decomposition of mutual information in a general class of Gaussian channels is introduced and shown to produce an information-preserving canonical decision-feedback receiver. The approach is applied to intersymbol interference (ISI) channels to derive the well-known minimum mean-square error (MMSE) decision-feedback equalizer (DFE). When applied to the synchronous code-division multiple-access (CDMA) channel, the result is the MMSE (or signal-to-interference ratio (SIR) maximizing) decision-feedback detector, which is shown to achieve the channel sum-capacity at the vertices of the capacity region. Finally, in the case of the asynchronous CDMA channel we are able to give new connections between information theory, decision-feedback receivers, and structured factorizations of multivariate spectra.     

Bandwidth-efficient multiple access (BEMA): a new strategy based onsignal design under quality-of-service constraints forsuccessive-decoding-type multiuser receivers

This paper considers the design of signature waveforms for successive-decoding-type multiuser receivers (including the optimum successive decoder (OSD)) in a correlated-waveform multiple-access channel. The problem is to obtain signature waveforms that require as little bandwidth as possible while allowing the receiver to meet a given set of quality-of-service (QoS) objectives. The QoS objectives are specified for each user in terms of capacity, or equivalently, the signal-to-interference ratio. A (generally unachievable) lower bound is obtained on the minimum bandwidth required to achieve these QoS constraints. Moreover, a simple algorithm is proposed for obtaining signal sets that meet the QoS constraints when used with the OSD, and which, while not optimal, require a bandwidth that can be very close to the minimum required bandwidth. It is also shown that such signal sets allow for a significantly more efficient use of bandwidth than do orthogonal signals used in time- or frequency-division multiple access (TDMA/FDMA). Based on our signal design approach, we propose a new multiple-access strategy that we refer to as bandwidth-efficient multiple access (BEMA). While BEMA is more bandwidth efficient than TDMA or FDMA, it retains their desirable feature of needing only single-user coding (and decoding) for each user     

Signal design for bandwidth-efficient multiple-accesscommunications based on eigenvalue optimization

Bandwidth-efficient multiple access (BEMA) is a strategy where transmitter pulses are continually designed at the base station and are dynamically allocated to the transmitters via a feedback channel. Such pulses (or “signature waveforms”) are designed to conserve bandwidth while simultaneously enabling the receiver at the base station to meet a quality-of-service (QoS) specification for each transmitter. The key technical problem in BEMA communication is therefore the design of the transmitter pulses for the base station receiver. In an earlier paper, we presented solutions to this problem that were shown to be superior (in terms of strict bandwidth) to common signaling schemes such as time-, frequency-, and code-division multiple access (TDMA, FDMA, and CDMA). This paper uses the framework developed earlier, but considers strictly time-limited transmitter pulses and the root-mean squared (RMS) bandwidth measure. As in the earlier paper, significant bandwidth savings over the traditional multiple-access strategies are obtained. However, in contrast to the rank-conserving approach, the bandwidth gains of this paper are realized by tailoring the signature waveform design to conserve RMS bandwidth via eigenvalue optimization problems     

Optimal sequences for CDMA with decision-feedback receivers

We consider a symbol-synchronous code-division multiple-access (CDMA) system that is equipped with a multiuser decision-feedback receiver and for which power control is available. The users are each assigned a quality-of-service (QoS) threshold to be guaranteed by the system, and to cover scenarios for which there are multiple classes of users, these are not required to be equal to each other. For an ideal decision-feedback receiver, it is known that with enough power the system can always meet the users' QoS thresholds, so we instead minimize the sum of the users' received powers over system designs (i.e., signature sequences, power-control policy, and decision-feedback receiver) which guarantee the QoS requirements. It is found that the optimal design produces two classes of users, those whose sequences and powers satisfy with equality the generalized Welch bound inequality and those oversized users that are mutually orthogonal to each other and the rest of the users. In terms of power and bandwidth savings, the optimal sequences for the decision-feedback receiver are found to compare very favorably to optimal designs for linear receivers and to random sequences for the decision-feedback receiver.     

CDMA with power control and sequence design: the capacity region with and without multidimensional signaling

We consider the symbol-synchronous code-division multiple-access (CDMA) channel in which every user is assigned a rate at which arbitrarily reliable transmission in the Shannon sense is to be guaranteed. For an overloaded system in which the number of active users exceeds the available processing gain, we optimally design the users' signature sequences and a power-control policy to minimize the required sum-power (i.e., sum of the users' powers) while meeting the rate-tuple constraint with a (joint) maximum-likelihood receiver. This result is extended to find the power-constrained capacity region of the system; this is the set of all achievable rate-tuples over all signature sequences and power-control policies whose sum-power is constrained. Furthermore, it is shown that this capacity region may be substantially and maximally expanded in those regions where there are oversized users whose rate requirements are relatively large compared to those of the other users; this is accomplished by allowing for the flexibility of multidimensional signaling in the sense of a user simultaneously transmitting several different scalar symbols, each modulated by its own signature sequence. From the viewpoint of resource efficiency, this means that a multicarrier approach is essential in systems that support multiple classes of users. Finally, we also address the dual problem of determining the region of valid power-control policies subject to a sum-capacity constraint on the system.     

Near-barrier fusion of the ⁸B + ⁵⁸Ni proton-halo system

Fusion cross sections were measured for the exotic proton-halo nucleus ?B incident on a ??Ni target at several energies near the Coulomb barrier. This is the first experiment to report on the fusion of a proton-halo nucleus. The resulting excitation function shows a striking enhancement with respect to expectations for normal projectiles. Evidence is presented that the sum of the fusion and breakup yields saturates the total reaction cross section.