Motorola (Canada)

This paper attempts to present a comprehensive tutorial survey of the development of efficient modulation techniques for bandlimited channels, such as telephone channels. After a history of advances in commercial high-speed modems and a discussion of theoretical limits, it reviews efforts to optimize two-dimensional signal constellations and presents further elaborations of uncoded modulation. Its principal emphasis, however, is on coded modulation techniques, in which there is an explosion of current interest, both for research and for practical application. Both block-coded and trellis-coded modulation are covered, in a common framework. A few new techniques are presented.

In this paper, a new empirical model for indoor propagation prediction is presented. The inspiration for our model is to enhance existing empirical models for indoor propagation prediction by incorporating additional phenomena suggested by electromagnetic techniques such as the uniform theory of diffraction (UTD), but still retain the straightforwardness of the empirical approach. The advantage is that computation time for indoor propagation prediction is low without greatly compromising prediction accuracy. Comparisons of our predicted results to measurements indicate that improvements in accuracy over conventional empirical models are achieved.

A 24-dimensional block code based on the Leech lattice is described for use in a 19200-b/s modem. Encoding (the process of converting binary data into message point coordinates) and detection (conversion of the received coordinates into the coordinates of the nearest code point of the lattice) are described. Decoding (the further conversion of these into binary data) is not described, since it consists of an easily achieved reversal of the encoding process. Block (1000-bit-length) error rates in the presence of white noise for baud rates of 2400 and 2743, the two baud rates at which the modem can operate, are presented. Encoding plus decoding was successfully programmed for an ADSP2100 signal processor requiring altogether slightly less than one half the processing capability.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

While the quality of service (QoS) profiles for a number of general packet radio service (GPRS) classes has been specified by ETSI, how QoS management is provided by means of traffic scheduling, traffic shaping, and connection admission control, in a GPRS network is an implementation issue that is attracting significant current research interest. This paper presents an evaluation of several traffic scheduling methods, including of FIFO, static priority scheduling (SPS) and earliest deadline first (EDF) by simulations, with the objective of meeting the delay profiles defined for a number of GPRS classes. Traffic sources representative of GPRS applications, including e-mail, fleet management and World Wide Web applications are employed. We focus on the forward link which represents the bottleneck of a typical GPRS data connection. Results show that EDF is able to meet the delay requirements at a much higher channel utilization compared to the other alternatives.

A novel neuro-fuzzy constructive cost model (COCOMO) for software estimation is proposed. The model carries some of the desirable features of the neuro-fuzzy approach, such as learning ability and good interpretability, while maintaining the merits of the COCOMO model. Unlike the standard neural network approach, this model is easily validated by experts and capable of generalization. In addition, it allows inputs to be continuous-rating values and linguistic values, therefore avoiding the problem of similar projects having different estimated costs. Also presented in this paper is a detailed learning algorithm. The validation, using industry project data, shows that the model greatly improves the estimation accuracy in comparison with the well-known COCOMO model.

One of the main design tradeoffs of pilot-based techniques of combating the effects of multipath fading is the pilot filter bandwidth. The approach presented is to store a precalculated bank of pilot filters and automatically select the best one as the signal-to-noise, (SNR) or vehicle speed change. The authors address the issue of adjusting the filter bandwidth as speed changes. They call this technique the filter switching algorithm. This technique can provide a 1.0 dB improvement for a normalized Doppler frequency of 2%; up to 2.0 dB can be gained when operating at a lower Doppler frequency. The algorithm is found to be very robust, in the sense that self-noise and decision direction have little effect on its operation and the resulting bit error rate.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Accurate software estimation such as cost estimation, quality estimation and risk analysis is a major issue in software project management. We present a soft computing framework to tackle this challenging problem. We first use a preprocessing neuro-fuzzy inference system to handle the dependencies among contributing factors and decouple the effects of the contributing factors into individuals. Then we use a neuro-fuzzy bank to calibrate the parameters of contributing factors. In order to extend our framework into fields that lack of an appropriate algorithmic model of their own, we propose a default algorithmic model that can be replaced when a better model is available. Validation using industry project data shows that the framework produces good results when used to predict software cost.

This paper reports the experimental results of the development of a novel capacitive divider for high-voltage pulse measurements. The low-voltage (LV) arm capacitor was prepared by thermally growing silicon oxide on commercially available silicon wafers to form capacitors of very large capacitance per unit area (>10 nF with 2 /spl mu/m oxide thickness on a 30 mm-diameter wafer). With the proposed design for LV arm capacitance, divider ratios of the order >10000 can easily be obtained.

Scheduling is an important aspect in the support of QoS in GPRS. Scheduling in GPRS is different from scheduling in ATM due to the existence of the MAC protocol, multi-slot capability restriction, and difference in QoS requirements. Two scheduling algorithms, the static priority scheduling (SPS) and modified earliest deadline (MED), have been analyzed. Both scheduling algorithms allow GPRS to attain high channel utilization, with MED performing slightly better than SPS. Queue lengths and normalized frame scheduling advance are two possible congestion metrics available from the scheduler, with the latter being more versatile across a variety of traffic statistics and system bandwidth.

We study the problem of managing handoffs (HOs) in user-centric cell-free massive MIMO (UC-mMIMO) networks. Motivated by the importance of controlling the number of HOs and by the correlation between efficient HO decisions and the temporal evolution of the channel conditions, we formulate a partially observable Markov decision process (POMDP) with the state space representing the discrete versions of the large-scale fading and the action space representing the association decisions of the user with the access points (APs). We develop a novel algorithm that employs this model to derive a HO policy for a mobile user based on current and future rewards. To alleviate the high complexity of our POMDP, we follow a divide-and-conquer approach by breaking down the POMDP formulation into sub-problems, each solved separately. Then, the policy and the candidate pool of APs for the sub-problem that produced the best total expected reward are used to perform HOs within a specific time horizon. We then introduce modifications to our algorithm to decrease the number of HOs. The results show that half of the number of HOs in the UC-mMIMO networks can be eliminated. Namely, our novel solution can control the number of HOs while maintaining a rate guarantee, where a 47%-70% reduction of the cumulative number of HOs is observed in networks with a density of 125 APs per km <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Most importantly, our results show that a POMDP-based HO scheme is promising to control HOs.

The Global System for Mobile Communications (GSM) already includes basic data services, but growing demand for higher bit rates and efficient bandwidth utilization has motivated a plan to introduce several new data services. These new high speed circuit switched data (HSCSD) and general packet radio service (GPRS) are described. An architectural vision has been created which introduces distributed packet data switching separated from the mobile switching center as a generation 2.5 network on the road to the third generation Universal Mobile Telecommunications System (UMTS).

The daily volatility is a crucial variable in the study of financial risks. Traditional financial engineering methods based on parametric models such as the GARCH family, have limited success in volatility forecasting due to their rigid and linear structure. In the current paper, the integrated volatility of the 1998-2002 S&P100 index has been calculated and wavelet transformed to find the time horizon(s) that suits the subsequent forecasting procedure. In a genetic algorithm (GA) process, a group of rules based on predetermined format is trained to extract patterns from the time series. Those rules are tested to predict the 2003 S&P100 series. With 100 simple 'IF/THEN' rules on a 4-lag recursive memory, the forecasting accuracy is shown to average 75%, matching the level achieved in other proprietary research and far superior to that of GARCH models.

This paper studies the performance of the three retransmission mechanisms (i.e., RLC/MAC, LLC and TCP) in a General Packet Radio Service (GPRS) network accessing the Internet. This assessment is done through the end-to-end performance evaluation of Internet applications such as HTTP and FTP over GPRS. A simulation platform including client mobile stations, base station subsystems, GPRS support nodes, servers and an Internet backbone was implemented in OPNET. The low transmission rate and high radio link error rate over the air interface of a GPRS network affect the overall system performance greatly. Simulation results show that whereas the RLC/MAC block retransmission mechanism is crucial to increase the link utilization efficiency, LLC layer user-data retransmission is not necessary for TCP traffic over GPRS.

The authors describe a parallel processing architecture for real-time digital signal processing that has demonstrated virtually 100% data processing efficiency in a number of areas. The Teamed-Architecture Signal Processor (T-ASP) is a field-proven, commercially available optimal system solution to the extremely high computational and I/O rates encountered in modern digital-signal-processing environments. The design of T-ASP involves the consideration and implementation of many architectural concepts used to enhance the performance of a computer, including programmability, parallel processing, vector processing and pipelining, memory interleaving, double cache memories, multiple high-speed I/O interfaces, and segmentation of the processors for elimination of both CPU and data-handling overhead. The authors discuss hardware architecture design and implementation; hardware management; and software architecture design and implementation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Two estimators for the carrier frequency of different classes of signals are proposed. These estimators are based on modeling the signal with either an autoregressive AR (2) model, or a mixed autoregressive, moving-average, ARMA (2, 2) model. In addition, an equation is derived to obtain the spectrum peak frequencies directly from the model parameters, thus eliminating the step of calculating the spectrum across the whole band. This equation enables us to obtain a closed form for the estimation error.

The convergence of voice, data, and video networks is creating a new environment for telecommunications. In response to the changes, telecommunications equipment manufacturers and service providers are competing fiercely to bring an optimum solution to customers. The evolution of GSM to GPRS and to UMTS is a cellular wireless industry endeavour to meet this demand. This evolution will see the core wireless network infrastructure change from circuit-switched to packet-switched where voice and data are transported using IP as the common protocol. However, this poses a number of challenges, one of which is how to run the key mobile application part signaling protocols over IP. MAP defines the application protocols between switches and databases (e.g., MSC, VLR, SGSN, HLR) for supporting mobility management, security management, radio resource management, and mobile equipment management. UMTS supports both circuit-switched and packet-switched services.

The ambiguity problem in direction-of-arrival (DOA) estimation using a sensor array, manifests itself as spurious peaks in the DOA spectrum, making the true targets indistinguishable from the false alarms. A criterion that determines the presence of certain ambiguities inherent to a symmetric linear array has been proposed in the literature (Manikas, A. and Proukakis, C., IEEE Trans. Sig. Processing, vol.46, no.8, p.2166-79, 1998). The criterion is a useful tool to design reliable sensor arrays. A generalization of this ambiguity criterion is presented. The new ambiguity criterion encompasses more ambiguous DOAs and therefore gives a more accurate measurement of the reliability of an array design.

I/Q modulators have been widely used to perform digital modulation such as QPSK, QAM, GMSK and MCM. In practice, there exists a small non-90/spl deg/ phase error between the I and Q channels of an I/Q modulator. Also, the I and Q channels may not always have the same gain. The phase error and gain imbalance cause unwanted image signals that are generated in-band and consequently, degrades the system performance. This paper presents an I/Q modulator image rejection algorithm through modulation signal pre-distortion. The presented algorithm is simple and lends itself well towards a digital signal processor (DSP) implementation. Due to its simplicity, the implementation results in almost no increase in modulator complexity. Experimental results shows that for an MCM modulation system, this algorithm can reduce the image by at least 10 dB. For portable products like modems and handhelds, this feature is specially attractive because low complexity implies low cost, small product size and/or long battery life.

With the explosion of the Web, focused Web crawlers are gaining attention. Focused Web crawlers aim at finding Web pages related to the pre-defined topic. CINDI Robot is a focused Web crawler devoted to finding computer science and software engineering academic documents. We propose a multi-level inspection scheme to discover relevant Web pages. Through this multi-level inspection scheme, the text feature of the content contributes to the classification; furthermore other Web characteristics, such as URL pattern, anchor text and so on, assist the decision process. The experiment result demonstrates this multi-level inspection method outperforms other traditional methods.

Traditional parametric methods have limited success in estimating and forecasting the volatility of financial securities. Recent advance in evolutionary computation has provided additional tools to conduct data mining effectively. The current work applies the genetic programming in a Time Series Data Mining framework to characterize the S&P100 high frequency data in order to Forecast the one step ahead integrated volatility. Results of the experiment have shown to be superior to those derived by the traditional methods.