Bell Labs Technical Journal 

About: Bell Labs Technical Journal is an academic journal. The journal publishes majorly in the area(s): Service provider & The Internet. It has an ISSN identifier of 1089-7089. Over the lifetime, 965 publications have been published receiving 23356 citations. The journal is also known as: Bell System Technical Journal.

Layered space-time architecture for wireless communication in a fading environment when using multi-element antennas

Abstract: This paper addresses digital communication in a Rayleigh fading environment when the channel characteristic is unknown at the transmitter but is known (tracked) at the receiver. Inventing a codec architecture that can realize a significant portion of the great capacity promised by information theory is essential to a standout long-term position in highly competitive arenas like fixed and indoor wireless. Use (n T , n R ) to express the number of antenna elements at the transmitter and receiver. An (n, n) analysis shows that despite the n received waves interfering randomly, capacity grows linearly with n and is enormous. With n = 8 at 1% outage and 21-dB average SNR at each receiving element, 42 b/s/Hz is achieved. The capacity is more than 40 times that of a (1, 1) system at the same total radiated transmitter power and bandwidth. Moreover, in some applications, n could be much larger than 8. In striving for significant fractions of such huge capacities, the question arises: Can one construct an (n, n) system whose capacity scales linearly with n, using as building blocks n separately coded one-dimensional (1-D) subsystems of equal capacity? With the aim of leveraging the already highly developed 1-D codec technology, this paper reports just such an invention. In this new architecture, signals are layered in space and time as suggested by a tight capacity bound.

WaveLAN®-II: A high-performance wireless LAN for the unlicensed band

Abstract: In July 1997 the Institute of Electrical and Electronics Engineers (IEEE) completed standard 802.11 for wireless local area networks (LANs). WaveLAN®-II, to be released early in 1998, offers compatibility with the IEEE 802.11 standard for operation in the 2.4-GHz band. It is the successor to WaveLAN-I, which has been in the market since 1991. As a next-generation wireless LAN product, WaveLAN-II has many enhancements to improve performance in various areas. An IEEE 802.11 direct sequence spread spectrum (DSSS) product, WaveLAN-II supports the basic bit rates of 1 and 2 Mb/s, but it can also provide enhanced bit rates as high as 10 Mb/s. This paper discusses various aspects of the system design of WaveLAN-II and characteristics of its antenna, radio-frequency (RF) front-end, digital signal processor (DSP) transceiver chip, and medium access controller (MAC) chip.

Massive MIMO: An Introduction

Abstract: Demand for wireless throughput, both mobile and fixed, will always increase. One can anticipate that, in five or ten years, millions of augmented reality users in a large city will want to transmit and receive 3D personal high-definition video more or less continuously, say 100 megabits per second per user in each direction. Massive MIMO-also called Large-Scale Antenna Systems-is a promising candidate technology for meeting this demand. Fifty-fold or greater spectral efficiency improvements over fourth generation (4G) technology are frequently mentioned. A multiplicity of physically small, individually controlled antennas performs aggressive multiplexing/demultiplexing for all active users, utilizing directly measured channel characteristics. Unlike today's Point-to-Point MIMO, by leveraging time-division duplexing (TDD), Massive MIMO is scalable to any desired degree with respect to the number of service antennas. Adding more antennas is always beneficial for increased throughput, reduced radiated power, uniformly great service everywhere in the cell, and greater simplicity in signal processing. Massive MIMO is a brand new technology that has yet to be reduced to practice. Notwithstanding, its principles of operation are well understood, and surprisingly simple to elucidate.

An overview of the femtocell concept

Abstract: The femtocell concept aims to combine fixed-line broadband access with cellular telephony using the deployment of ultra-low-cost, low-power third generation (3G) base stations in the subscribers' homes or premises. It enables operators to address new markets and introduce new high-speed services and disruptive pricing strategies to capture wireline voice minutes and to grow revenues. One of the main design challenges of the femtocell is that the hierarchical architecture and manual cell planning processes used in macrocell networks do not scale to support millions of femtocells. In this paper, a user-deployed femtocell solution based on the base station router (BSR) flat Internet Protocol (IP) cellular architecture is presented that addresses these problems, and several aspects of the proposed solution are discussed. The overall concept and key requirements are presented in detail. The auto-configuration and self-optimization process from purchase by the end user to the integration into an existing macrocellular network is described. Then the theoretical performance of a co-channel femtocell deployment is analyzed and its impact on the macrocell underlay is assessed. Finally, a financial analysis of a femtocellular home base station deployment in a macrocellular network is presented. It is shown that in urban areas, the deployment of publicly accessible home base stations with slightly increased coverage can significantly reduce the operator's annual network costs (up to 70 percent in the investigated scenario) compared to a pure macrocellular network.

Predicting risk of software changes

Abstract: Reducing the number of software failures is one of the most challenging problems of software production. We assume that software development proceeds as a series of changes and model the probability that a change to software will cause a failure. We use predictors based on the properties of a change itself. Such predictors include size in lines of code added, deleted, and unmodified; diffusion of the change and its component subchanges, as reflected in the number of files, modules, and subsystems touched, or changed; several measures of developer experience; and the type of change and its subchanges (fault fixes or new code). The model is built on historic information and is used to predict the risk of new changes. In this paper we apply the model to 5ESS® software updates and find that change diffusion and developer experience are essential to predicting failures. The predictive model is implemented as a Web-based tool to allow timely prediction of change quality. The ability to predict the quality of change enables us to make appropriate decisions regarding inspection, testing, and delivery. Historic information on software changes is recorded in many commercial software projects, suggesting that our results can be easily and widely applied in practice.