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The process behind the thermal design of telecommunications equipment used in central office environments is described. Methods used in system-level and board-level thermal design and the thermal testing of prototypes are discussed.

The need for accurate positioning has gained significant interest recently, especially in cluttered environments where signals from satellite navigation systems are not reliable. Positioning systems based on ultrawide bandwidth (UWB) technology have been considered for these environments because UWB signals are able to resolve multipath and penetrate obstacles. These systems usually obtain range measurements from time-of-arrival (TOA) estimation of the first path, which can be a challenge in dense multipath environments. In this paper, we analyze and compare the performance of matched filter (MF) and energy detector (ED) TOA estimators based on thresholding in UWB dense multipath channels. The main advantage of threshold-based estimators is that they have the potential for complete analog implementation and hence they are particularly attractive for applications that require low cost battery-powered devices. Closed-form expressions for the estimator bias and mean square error (MSE) are derived as a function of the signal-to-noise ratio. A comparison with results obtained from Monte Carlo simulation confirms the validity of our analytical approach. This analysis enables us to determine the threshold value that minimizes the MSE, a critical parameter for optimal estimator design. A simple criteria to determine the threshold value is also presented. It is shown that the estimation accuracy is mainly affected by the ambiguity in the selection of the correct peak at the output of the MF or ED, caused by the fading characteristics of the first path. We also evaluate the performance loss of ED estimators with respect to MF estimators. Finally, results based on experimental measurements in an indoor residential environment are presented in order to compare the performance of TOA estimators in realistic environments. Index Terms--Localization, multipath channel, ranging, time-of-arrival (TOA), ultra-wide bandwidth (UWB).

This paper presents a low-complexity interleaver design that facilitates the high throughput turbo decoding required for next generation wireless systems. Specifically, it addresses the interleaver design issues that arise when several Log-MAP processors are used in parallel to improve turbo decoding throughput. In such a parallel decoder, memory access contentions occur when more than one extrinsic value is to be written to or read from the same memory block at the same time. These contentions may be avoided by designing contention-free (CF) interleavers that incorporate hardware constraints into the interleaver description. The paper first derives bounds on the number of CF interleavers, demonstrating that the fraction of interleavers of a given size that are contention-free is quite small. In spite of this, a class of contention-free "inter-window shuffle" (IWS) interleavers are shown via simulation to achieve near-WCDMA performance. Further, the paper shows that the memory requirement of CF IWS interleavers is small compared to an alternate contention-resolving method that uses a modified memory addressing scheme. Finally, we note that the advantages of contention-free interleavers have led to the adoption of a CF quadratic permutation polynomial (QPP) interleaver in the 3GPP long term evolution (LTE) standard. Index Terms--High throughput turbo decoding, parallel turbo decoding, contention-free interleavers, memory access in interleaving.

The Euclidean norm of the instantaneous channel, when combined with long-term channel statistics has provided information for the transmitter to utilize multiuser diversity in time, frequency and space. An asymptotic analysis has shown that channel realizations with large channel norm have provided additional spatial channel state information (CSI) at the transmitter, thus making it ideal for multiuser diversity transmission schemes.

This paper presents Schottky barrier diode circuits fully integrated in a 0.13-[micro]m SiGe BiCMOS process technology. A subharmonically pumped upconverter and a frequency doubler are demonstrated that operate beyond 100 GHz without the need of external components. The upconverter has a size of 430 x 780 [micro][m.sub.2] including on-chip matching elements and bond pads. It has a conversion gain of -6 to -7 dB from 100 to 120 GHz. The upconverter achieves a high single-sideband saturated output power of -4 dBm from 100 to 120 GHz and a high linearity with a 1-dB compression point of -6 dBm. The frequency doubler has a size of 360 x 500 [micro][m.sub.2] and can deliver up to 2.5 dBm at 110 GHz. Index Terms--Frequency doubler, millimeter waves, power generation, Schottky barrier diodes (SBDs), silicon germanium (SiGe), subharmonic mixer (SHM), terahertz.

In this paper, a frequency-division counterpart of joint power control and sequence design problem for code-division multiple-access (CDMA) systems is solved. Total transmit and receive power minimizations are considered for frequency-division multiplexing (FDM) and frequency-division multipleaccess (FDMA) communications over overloaded channels. After the definition of channel overloading for CDMA systems is extended to the frequency-division systems, the user admissibility is characterized by a necessary and sufficient condition for the existence of the optimal solution under unequal signal-to-interference-plus-noise ratio constraints at the output of linear receivers and asymmetric data transmission rate constraints among users. The optimal signal power, bandwidth, transmit waveform, and receive waveform are derived for each user as the decision parameters of the optimization problem. It is shown that, if this solution is applied for the uplink users to minimize the total receive power, the optimal FDMA system performs the same as the optimal CDMA system. It is also shown that, if this solution is applied for the downlink users to minimize the total transmit power, the optimal FDM system always outperforms the code-division system that minimizes the extended total squared correlation. Numerical results suggest that the optimal FDM system and the optimal downlink code-division system achieve the same performance when the total transmit power is minimized. Index Terms--Code-division multiple-access (CDMA), frequency-division multiplexing (FDM), frequency-division multiple-access (FDMA), power control.

An alternative technique based on chaotic encryption and conventional cryptography is presented for providing security in two levels.

In this paper, we analyze optimal (in space and time) adaptive power transmission policies for fading channels when the channel-state information (CSI) at the transmitter (CSIT) and the receiver (CSIR) is available. The transmitter has a long-term (time) average power constraint. There can be multiple antennas at the transmitter and at the receiver. The channel experiences Rayleigh fading. We consider beamforming and space-time coded systems with perfect/imperfect CSIT and CSIR. The performance measure is the bit error rate (BER). We show that in both coded and uncoded systems, our power allocation policy provides exponential diversity order if perfect CSIT is available. We also show that, if the quality of CSIT degrades then the exponential diversity is retained in the low SNR region but we get only polynomial diversity in the high SNR region. Another interesting conclusion is that in case of imperfect CSIT and CSIR, knowledge of CSIT at the receiver is very important. Finally, for the optimal power control policy of the uncoded system we find the error-exponents which provide the rate versus diversity-order tradeoff for this policy. This tradeoff is of an entirely different nature than the well-known Zheng-Tse tradeoff. Index Terms--Beamforming, channel-state information receiver (CSIR), channel-state information transmitter (CSIT), convolutional codes, error exponents, fading channels, power allocation, rate versus diversity order tradeoff, space-time codes.

A theory is given on maximizing the product of energy gain and bandwidth for broadband signal transmission in wireless links with dispersive antennas, which are properly terminated to the transmitter and receiver front-ends. For this, a cascaded network model of the two-antenna channel based on the link decomposition theory [1] is employed to indicate practical conditions on maximizing gain-bandwidth product through selections of: i) real, dispersive antenna geometries; ii) their port terminations; and iii) assigned operational passbands. As a result, the gain-bandwidth product can be optimized for any given antenna geometry by appropriately specified terminal loads and operational bandwidths and vice-versa. This paper is numerically illustrated for canonical flat and solid dipole antennas by inspecting the predicted values of link gain-bandwidth products and related deviations of group delay used to measure signal distortions. Index Terms--Antenna dispersion, energy gain, gain-bandwidth product, generator, group delay, load, receiver, transmitter.

A parallel architecture for high-bandwidth analog-to-digital conversion is presented. The proposed architecture uses frequency translation along with multi-rate signal processing to digitize a wide-band continuous-time analog signal through an array of identical narrowband analog-to-digital converters (ADCs). The basic idea behind this structure is to decompose the input signal into smaller frequency (channels). Each channel is composed of a two-path system that includes mixers, identical low-pass filters and identical baseband ADCs. The signal in each two-path channel is sampled and digitized into narrowband quadrature signals. After digitizing the signal in each channel, the low-rate subband samples are upconverted back to their respective center frequencies, then filtered and combined to reconstruct the digital representation of the original wide-band input signal. The digital filters are designed to minimize the reconstruction error. The effects of some major nonidealities are discussed. Several simulation results are also presented to demonstrate the performance of the system. Index Terms--Analog-to-digital conversion, multi-rate signal processing, parallel analog-to-digital converter (ADC) structure, wide-band.

The effects of altitude, increased ambient temperature, and increased relative humidity on the board level forced convection typical of telecommunications products were systematically examined through numerical simulation and analytical techniques. Altitude was found to have the most significant impact on component temperature rise above inlet air temperature. Depending on the proportion of upstream-heating to self-heating for a given component, the component temperature rise above inlet air temperature was found to increase by 40% to 88% at 5000 m when compared to the base line case at sea level. Inlet air temperature was found to translate linearly to component temperature increase. The second-order effects due to property changes with temperature were found to be less than 3% on the component temperature rise. The relative humidity was not found to significantly impact the component temperature rise at an inlet temperature of 25[degrees]C. However, the property changes at a 55[degrees]C inlet were more significant, and require further study. A temperature multiplier concept is introduced to aid practicing engineers in extrapolating data at standard conditions to the operating extremes.

This paper discusses the suitability of using a multiport amplifier (MPA) for a power section of space telecommunication payloads with power flexibility requirements. The performances of an MPA-based architecture are compared to those of a classical amplification architecture having one power amplifier per beam. This study is based on a 4 x 4 K a-band MPA composed of four paralleled traveling-wave tube amplifiers (TWTAs). First, a static model of the MPA has been extracted from conventional characterizations. Second, the MPA has been characterized in a realistic environment for telecommunication operation. The good agreement between measured and simulated data serves to validate the MPA model. Once the model has been validated, exhaustive simulations are performed to compare the performances of the MPA-based and classical architectures in terms of power consumption and the TWTA's saturation power. As a result, the MPA approach proves to be an interesting solution because of its greater flexibility, lower power consumption, and lower saturation power required by the TWTAs. Index Terms--Communication systems, multiport circuits, power amplifiers (PAs), satellite communication, traveling-wave amplifiers, traveling-wave tubes (TWTs).

A comprehensive technology computer-aided design (TCAS) framework is developed that can predict the phase noise spectrum of an oscillator using nonlinear perturbation analysis based on the device-circuit mixed-mode simulation technique. The framework is used to show that simulations of the period jitter and the phase noise spectrum of a CMOS LC voltage controlled oscillator (VCO) can be done through a physics-based approach, making it very useful for the design of low-noise communication systems.

In this paper, we address the issue of perturbed information at the transmitter in a multiple-input multiple-output (MIMO) system. Two schemes, correlation matrix feedback and channel information feedback, are proposed to convey information necessary for achieving capacity to the transmitter. This information is perturbed due to various impairments. A perturbation analysis is carried out to study the variations in mutual information for each of the proposed schemes. For ergodic channels, this analysis is used to design a MIMO system with a limited rate feedback. Using a codebook-based approach, vector quantizers are designed to minimize the loss in ergodic capacity for each of the proposed schemes, and their performance is studied. A non-codebook method, parameter-based feedback, is also presented, and the underlying rate-performance tradeoff is highlighted. Index Terms--Channel state information (CSI), ergodic capacity, limited-rate feedback, multiple-input multiple-output (MIMO) system, perturbation analysis, perturbed information, vector quantization.

In this note, we study several issues in the design of localized quality-of-service (QoS) routing schemes that make routing decisions based on locally collected QoS state information (i.e., there is no network-wide information exchange among routers). In particular, we investigate the granularity of local QoS state information and its impact on the design of localized QoS routing schemes from a theoretical perspective. We develop two theoretical models for studying localized proportional routing: one using the link-level information and the other using path-level information. We compare the performance of these localized proportional routing models with that of a global optimal proportional model that has knowledge of the global network QoS state. We demonstrate that using only coarser-grain path-level information it is possible to obtain near-optimal proportions. We then discuss the issues involved in implementation of localized proportional routing and present some practical schemes that are simple and easy to implement. Index Terms--Localized proportional routing, quality-of-service (QoS) routing.

An overview is presented of the challenges and design issues in the system-level design of mixed analog-digital telecom front-ends. The progress in very large scale integration technology allows the integration of complex systems on a chip, containing both analog and digital parts. In order to boost the design productivity and guarantee the optimality of such systems while meeting the time-to-market constraints, a systematic top-down design approach has to be followed with sufficient time and attention paid to system-level architectural design before proceeding to the detailed block or circuit design. This paper will present high-level system exploration tools that allow to analyze architectural alternatives for the telecom front-end and to explore system tradeoffs such as finding the optimal analog-digital partitioning. This will be illustrated with results from experimental tools. Finally, the crucial underlying technology for such high-level design will be described in detail: analog behavioral modeling, efficient high-level simulation methods, and analog power/area estimation. Index Terms--RF modeling and simulation, telecom system exploration and architectual design.

This paper deals with communication optimization which is a crucial issue in automatic parallelization. From a system of parameterized affine recurrence equations we propose a heuristic that determines a set of efficient space-time transformations. It focuses on distant communications removal using broadcast - including anticipated broadcast, and locality enforcement. KEY WORDS: Automatic parallelization techniques; communication optimization; broadcast; system of recurrence equations.