Audrey M. Viterbi

Erlang capacity of a power controlled CDMA system

This work presents an approach to the evaluation of the reverse link capacity of a code-division multiple access (CDMA) cellular voice system which employs power control and a variable rate vocoder based on voice activity. It is shown that the Erlang capacity of CDMA is many times that of conventional analog systems and several times that of other digital multiple access systems. >

Soft handoff extends CDMA cell coverage and increases reverse link capacity

The effect of handoff techniques on cell coverage and reverse link capacity is investigated for a spread spectrum CDMA system. It is shown that soft handoff increases both parameters significantly relative to conventional hard handoff. >

Other-cell interference in cellular power-controlled CDMA

An improved series of bounds is presented for the other-cell interference in cellular power-controlled CDMA. The bounds are based on allowing control by one of a limited set of base stations. In particular, it is shown that the choice of cellular base station with least interference among the set of N/sub c/>1 nearest base stations yields much lower total mean interference from the mobile subscribers than the choice of only the single nearest base station. >

Performance of power-controlled wideband terrestrial digital communication

Performance of a wideband multipath-fading terrestrial digital coded communication system is treated. The analysis has applications to a cellular system using direct-sequence spread-spectrum code-division multiaccess (CDMA) with M-ary orthogonal modulation on the many-to-one reverse (user-to-base station) link. For these links, power control of each multiple-access user by the cell base station is a critically important feature. This feature is implemented by measuring the power received at the base station for each user and sending a command to either raise or lower reverse link transmitter power by a fixed amount. Assuming perfect interleaving, the effect of the power control accuracy on the system performance is assessed. >

Soft Handoff Extends CDMA Cell Coverage and Increase Reverse Link Capacity

We present a simple model for analyzing the soft handoff, and hard handoff performance as well as quantitative performance improvement measures for the capacity of the reverse links. The results will be based on a propagation model that represents the μth power of the distance (average path loss) and the log-normal component representing the shadowing losses.

Improved union bound on linear codes for the input-binary AWGN channel, with applications to turbo codes

While improved bounds have been central to proofs of the coding theorem and the tightness of the random coding bound for rates near capacity, most results for specific codes, both block and convolutional, have been based on the simple union bound. We present an improved bound for the input-binary AWGN channel in terms of the weights of the code-words of a linear block code.

Erlang Capacity of a Power Controlled Cdma System

A limited amount of bandwidth is allocated for wireless services. A wireless system is required to accommodate as many users as possible by effectively sharing the limited bandwidth. Therefore, in the field of communications, the term multiple access could be defined as a means of allowing multiple users to simultaneously share the finite bandwidth with least possible degradation in the performance of the system. There are several techniques how multiple accessing can be achieved. There are various basic schemes like Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA) , Code Division Multiple Access (CDMA), Space Division Multiple Access (SDMA), Random Access (Packet Radio).

New results on serial concatenated and accumulated-convolutional turbo code performance

Previous methods for analyzing serial concatenated turbo codes employing union error bounds are extended to determine the complete output weight enumeration function of the code; this provides the opportunity to employ a more refined bound due to Polytrev, with considerably improved results limited, however, to block lengths of about 256 bits by computational constraints. The method is then applied to a new class of “accumulated-convolutional” codes, which is a simple special subclass of serial concatenated codes inspired by the “repeat-accumulate” codes of Divsalar et al. Performance appears to be superior to that of conventional codes and results are obtained for much longer block lengths, with impressive results in regions approaching channel capacity.RésuméDes méthodes usuelles employant la borne de l’union pour analyser les turbo codes concaténés en série sont étendues pour déterminer la fonction compléte d’énumération de poids en sortie d’un code; on peut utiliser une borne plus fine proposée par Polytrev, borne qui amé-liore considérablement les résultats. Cette borne est cependant limitée, pour des raisons de complexité de calcul à des blocs de longueur de l’ordre de 256. La méthode est ici appliquée à une nouvelle classe de codes « convolutifs accumulés », qui est une simple classe particulière de codes concaténés en série, inspirés des codes à « répétition-accumulation » de Divsalar et al. Les performances obtenues sont supérieures à celles des codes classiques et les résultats, qui sont obtenus pour des blocs bien plus longs, sont impressionnants dans la région approchant la capacité du canal.

A tandem of discrete-time queues with arrivals and departures at each stage

A discrete-time system of a tandem of queues with exogenous arrivals and departures at each stage is considered. A customer leaving queuek−1 departs the system with probability 1−ρ[k] and continues to queuek with probabilityρ[k]. Exogenous arrivals to each stage are i.i.d. at each time slot. An approximate analysis of the occupancy and busy-period distributions of each stage based on a General Busy-period with batches and Memoryless (geometric) Idle period renewal Process (GBMIP) provides improved performance over two-state Markov approximations and gives exact results when there are no interstage departures.