Signaalinkäsittely- ja tietokonetekniikan laboratorio

Signaalinkäsittely- ja tietokonetekniikan laboratorio

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1999

# Conferences

16 R. Baghaie and P. Karttunen, "Implementation of mobile user tracking system," to appear in Proceedings Global Communications Conference, GLOBECOM'99, Rio de Janeiro, Brazil, December 1999.

15 V. Dimitrov and R. Baghaie, "Computing discrete Hartley transform using algebraic integers," to appear in Proceedings 33rd Asilomar Conference on Signals, Systems and Computers, Pacific Grove, CA, October 1999.

14 P. Karttunen, "An algorithm for Noise Subspace based Mobile User Tracking," in Proceedings IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC'99, Kyoto, Japan, September 1999.
ABSTRACT:
In this paper for the user tracking application we develop a step-by-step adaptation method for tracking the parameter vector in the noise subspace. Also, we develop the control strategy for the noise subspace roots eliminating the problems with the spurious roots. The performance comparison of the developed user tracking system will be investigated in terms of the tracking capability. As the performance criterion, the mean Direction-of-Arrival (DOA) error will be invoked in the stationary and non-stationary signal scenarios. The simulation results confirm that the proposed noise subspace approach can achieve similar tracking performance as the signal subspace approach in terms of the convergence speed and the final misadjustment level.

13 R. Baghaie, "Application of transformation techniques in CDMA receivers," in Proceedings IEEE Midwest Symposium on Circuits and Systems, MWSCAS'99, Las Cruces, New Mexico, August 1999.
ABSTRACT:
This paper discusses the application of different algorithm transformation techniques in Code Division Multiple Access receivers (CDMA). This is achieved by looking at some of the computational blocks that constitute the CDMA receivers. We focus on the Look-Ahead, Relaxed Look-ahead and Strength Reduction algorithm transformation techniques and demonstrate how CDMA receivers could benefit when utilizing these techniques during the course of implementation.

12 R. Baghaie and P. Karttunen, "VLSI implementation of CG based mobile user tracking system," in Proceedings IEEE Midwest Symposium on Circuits and Systems, MWSCAS'99, Las Cruces, New Mexico, August 1999.
ABSTRACT:
This paper considers the implementation of a signal subspace based mobile user tracking system that utilizes an efficient Conjugate Gradient (CG) based step-by-step adaptation scheme. First, we estimate the computational complexity of different units of the tracking system. Based on these estimations, we partition the implementation task into two parts: software and hardware. Finally, for the hardware implementation of the tracking unit a systolic architecture is proposed. With the aid of the proposed systolic array the time complexity of the tracking unit is reduced to O(M).

11 K. Kettunen, T. Laakso, "Iterative multiuser receiver utilizing soft decoding information," in Proceedings IEEE International Communications Conference, ICC'99, Vancouver, BC, Canada, pp. 942-946, June 1999.
ABSTRACT:
In this paper we propose a novel receiver structure that utilizes the soft information provided by the channel decoder in the multiuser detection. This receiver structure is based on a single-user version of the uncoded maximum a priori criterion. We derive the optimal multiuser likelihood calculation algorithm for this structure. In addition, suboptimal algorithms are proposed that are based on interference cancellation. Numerical simulations are reported which indicate that these suboptimal algorithms have a close-to-optimal coded BER performance even in the presence of high-power interferers.

10 P. Karttunen and R. Baghaie, "Conjugate Gradient Based Signal Subspace Mobile User Tracking," in Proceedings IEEE Vehicular Technology Conference, VTC'99, Houston, Texas, USA, vol. 2, pp. 1172-1176, May 1999.
ABSTRACT:
Adaptive antennas enable the increase in the system capacity through spatial interference suppression in the beamforming mode. All the spatial domain channel estimators must react fast to abrupt changes in the channel parameters. Additionally, they have to provide accurate enough tracking capabilities. In this paper, we construct the user tracking system by employing an efficient Conjugate Gradient (CG) method based on a step-by-step adaptation scheme. Furthermore, the paper investigates the tracking capability and the computational complexity issues of the proposed system. The simulation results confirm that the proposed CG method achieves better tracking performance than gradient methods both in the stationary and non-stationary signal scenario.

9 K. Kettunen, "Iterative multiuser receiver/decoders with enhanced variance estimation," in Proceedings IEEE 49th Vehicular Technology Conference, VTC'99, Houston, Texas, USA, pp. 2318-2322, May 1999.
ABSTRACT:
In this paper we study the impact of variance estimation on a receiver, where the soft information provided by the channel decoder is utilized in the multiuser detection. Specifically, we consider a receiver structure that resembles the structure of an iterative decoder for a serially concatenated code, but where the inner constituent decoder is replaced by an interference cancellation (IC) unit. The system performance with three different variance estimator methods is studied through numerical simulations. The results show that the variance estimation method has a great impact on the receiver performance especially in the case, where the different users are received with different powers.

8 S. Werner, J. Lilleberg, "Downlink channel decorrelation in CDMA systems with long codes," in Proceedings IEEE 49th Vehicular Technology Conference, VTC'99, Houston, Texas, USA, pp. ??-??, May 1999.
ABSTRACT:
In this paper we develop linear detectors suitable for a Code Division Multiple Access (CDMA) mobile receiver using long codes. The special signal structure in the downlink transmission is exploited to obtain a simple detection rule. A least-squares (LS) detector, a best linear unbiased estimator (BLUE) detector, and a linear minimum mean-square error (LMMSE) detector are derived. For the LMMSE detector we consider an adaptive implementation. The results show that improvement can be achieved using the proposed detectors compared with that of the conventional RAKE receiver.

7 R. Baghaie, "Systolic implementation of sample-by-sample conjugate gradient algorithm," in Proceedings IEEE Finnish Signal Processing Symposium, FINSIG'99, Oulu, Finland, pp. 252-256, May 1999.
ABSTRACT:
In this paper, we consider an efficient Conjugate Gradient (CG) algorithm that can be used when non-block processing or sample-by-sample update is of interest and compare its computational complexity with the conventional CG algorithm. We then review the VLSI implementation of the CG algorithms. Furthermore, for the hardware implementation of the sample-by-sample CG algorithm, a novel systolic array is proposed. With the aid of this systolic architecture, the time complexity of the algorithm will be reduced to O(N).

6 R. Insa Hernandez, R. Baghaie, and K. Kettunen, "Implementation of Gram-Schmidt conjugate direction and conjugate gradient algorithms," in Proceedings IEEE Finnish Signal Processing Symposium, FINSIG'99, Oulu, Finland, pp. 165-169, May 1999.
ABSTRACT:
In this paper, we consider the implementation of two iterative methods: the Gram-Schmidt Conjugate Direction (GSCD) and Conjugate Gradient (CG) algorithm. We first study the convergence properties of the algorithms. Furthermore, the fixed-point implementation of both CG and GSCD are presented. For the simulations purposes, the algorithms are applied to a multiuser detection scheme in a DS-CDMA system. Finally, for different number of users, wordlengths, and number of iterations, the MSE resulting from the quantization is estimated.

5 K. Kettunen, "Iterative multiuser receivers in coded CDMA systems," in Proceedings IEEE Finnish Signal Processing Symposium, FINSIG'99, Oulu, Finland, pp. 15-19, May 1999.
ABSTRACT:
In this paper, we consider the possibility of utilizing the channel decoder output in the cancellation of multiuser interference. The paper contains a summary of our earlier numerical results followed by a discussion about some observations based on these simulations.

4 R. Baghaie, "Transformation techniques in CDMA receivers," in Proceedings IEEE Finnish Signal Processing Symposium, FINSIG'99, Oulu, Finland, pp. 10-15, May 1999.

3 M. L. R. de Campos, S. Werner, J. A. Apolinario, "Householder-transform constrained LMS algorithm with reduced-rank updating," in proceedings Acoustics, Speech, and Signal Processing, ICASSP'99, Phoenix, Arizona, USA, Vol. 4, pp. 1857-1860, March 15-19, 1999.

Journals

2 R. Baghaie and V. Dimitrov, "DHT algorithm based on encoding algebraic integers," IEE Electronics Letters, vol. 35, no. 16, pp. 1303-1305, August 1999.
ABSTRACT:
A novel algorithm for computing the discrete Hartley transform (DHT) is presented. The proposed algorithm is based on the algebraic integers encoding scheme. With the aid of this scheme, an error-free representation of the cas function becomes possible. Furthermore, for the implementation of the algorithm a fully pipelined systolic architecture with O(N) throughput is proposed.

1 Timo I. Laakso and Vesa Välimäki, "Energy-based effective length of the impulse response of a recursive filter," IEEE Trans. on Instrumentation and Measurement, Vol. 48, No. 1, pp. 7-17, Feb. 1999.
ABSTRACT:
A measure for the effective length of the impulse response of a stable recursive digital filter based on accumulated energy is proposed. The new measure finds applications in several fields of digital signal processing, including estimation of the extent of attack transients for filters with dynamically varying inputs, elimination of transients in variable recursive filters, and design and implementation of linear-phase IIR systems. A general definition and a simple algorithm to evaluate it are introduced, and closed-form expressions are derived for first and second-order all-pole filters. The effect of zeros on the effective length is analyzed. An upper bound for the effective length of higher-order filters is derived using results for low-order filters, which is illustrated for classical digital lowpass filters. The use of the measure is demonstrated with examples of implementation of linear-phase IIR systems and estimation of transients in variable IIR filters.

1998

# International Conferences

16 P. T. Karttunen, K. Kalliola, T. I. Laakso, and P. Vainikainen, "Measurement Analysis of Spatial and Temporal Correlation in Wideband Radio Channels with Adaptive Antenna Array," in Proceedings International Conference on Universal Personal Communications, ICUPC'98, Florence, Italy, pp. 671-675, October 1998.
ABSTRACT:
This paper investigates the spatial and temporal correlation by measurements of an 8-element adaptive antenna array. The channel measurement data is gathered at a 2.154 GHz range outdoor radio channel. The measurement analysis is divided into three different categories: Investigation of spatial correlation between antenna elements at the base station (BS), spatial correlation of different mobile station (MS) locations and temporal correlation of the different multipath components. Also the differences in the correlation coefficient functions by using the complex-valued taps instead of the magnitude-valued taps are studied at the BS. The measurement analysis reveals that signals strongly correlate in the nearby BS antenna elements. However, at the different MS locations uncorrelated signals can be received when the physical separation is larger than half a wavelength. The multipath components in the impulse response profile become temporally uncorrelated after the excess delay values of 50 ns.

15 J. A. Apolinario Jr., S. Werner, T. I. Laakso, and P. S. R. Diniz, "Constrained normalized adaptive filtering for CDMA mobile communications," in Proceedings IX European Signal Processing Conference EUSIPCO'98, Island of Rhodes, Greece, pp. 2053-2056, September 8-11, 1998.
ABSTRACT:
This work presents an extension of the classical LMS-based Frost algorithm to include both the Normalized LMS (NLMS) and the Binormalized Data-Reusing LMS (BNDR-LMS) algorithms. Two simple versions of these algorithms are derived for the Frost structure. These new algorithms were applied to a DS-CDMA mobile receiver. The results showed a considerable speed up of the convergence rate compared to the LMS Frost.

14 J. A. Apolinario Jr., P. S. R. Diniz, T. I. Laakso, and M. L. R. de Campos, "Step-size optimization of the BNDR-LMS algorithm," in Proceedings IX European Signal Processing Conference EUSIPCO'98, Island of Rhodes, Greece, pp. 1249-1252, September 8-11, 1998.
ABSTRACT:
The binormalized data-reusing least mean squares (BNDR-LMS) algorithm has been recently proposed and has been shown to have faster convergence than other LMS-like algorithms in cases where the input signal is strongly correlated. This superior performance in convergence speed is, however, followed by a higher misadjustment if the step-size is close to the value which allows the fastest convergence. An optimal step-size sequence for this algorithm is proposed after considering a number of simplifying assumptions. Moreover, this work brings insight in how to deal with these conflicting requirements of fast convergence and minimum steady-state mean square error (MSE).

13
R. Baghaie, S. Werner, and T. Laakso, "Relaxed look-ahead techniques for pipelined implementation of adaptive multiple-antenna CDMA mobile receivers," in Proceedings IX European Signal Processing Conference EUSIPCO'98, Island of Rhodes,Greece, pp. 877-880, September 1998.
ABSTRACT:
In this paper, Relaxed Look-Ahead technique for pipelined implementation of an adaptive Direct-Sequence Code Division Multiple Access receiver is proposed when multiple antennas are utilized for mobile communications. Adaptive multiple-antenna receivers can provide insensitivity to the interfering powers. They also provide room for more users or require smaller number of antennas than the matched filter solution. A number of approximation techniques are utilized to pipeline the adaptive algorithm used for the proposed multiple-antenna receiver. The resulting pipelined receiver achieves a higher throughput or requires lower power as compared to the receiver using the serial algorithm. With the aid of simulations, for different levels of pipelining and different number of antennas, the signal-to-interference ratio and the bit error rate versus the relative interfering power are illustrated.

12 M. L. R. de Campos, S. Werner, J. A. Apolinario., and Timo I. Laakso, "Constrained Quasi-Newton algorithm for CDMA mobile communications," in Proceedings SBT/IEEE International Telecommunications Symposium ITS'98, Sao Paulo, Brazil, pp. 371-376, August 9-13, 1998.
ABSTRACT:
This work presents the derivation of the constrained version of a Quasi-Newton (QN) algorithm. Application of such algorithm to the problem of direct-sequence code-division multiple access (DS-CDMA) is investigated through simulations. The algorithm is compared to other constrained adaptation algorithms known in the literature in terms of convergence rate for a similar misadjustment level. Two scenarios describing synchronous and asynchronous transmission are used in simulations of interference suppression in DS-CDMA communication, showing the great capability of the algorithm in such application.

11 S. Werner, J. A. Apolinário, "Multiple-Antenna CDMA Mobile Reception Using Constrained Normalized Adaptive Algorithms," in Proceedings SBT/IEEE International Telecommunications Symposium ITS'98, Sao Paulo, Brazil, pp. 354-358, August 9-13, 1998.
ABSTRACT:
In this paper we analyze adaptive algorithms for a multiple-antenna Code Division Multiple Access (CDMA) mobile receiver. We study the constrained versions of the Binormalized Data-Reusing LMS (BNDR-LMS) and the Normalized LMS (NLMS). Their performance is compared with that of the classical Frost algorithm. Time-varying step-sequences are used to further enhance the performance of the receiver. The results show that considerable improvement in the convergence speed can be achieved with the use of the normalized algorithms compared with the conventional Frost algorithm. Using an optimal step-sequence in the update provides a fast convergence and a near-optimum steady-state performance.

10 S. Werner, T. Laakso, J. Lilleberg, "Multiple-antenna receiver for CDMA mobile reception," in Proceedings IEEE International Conference on Communications ICC'98, Atlanta, Georgia, USA, June 7-11, 1998.
ABSTRACT:
This paper examines the utilization of multiple antennas for Direct-Sequence Code Division Multiple Access (DS-CDMA) mobile communications at the mobile receiver. A linear single-user multiple-antenna receiver is derived and its performance is compared with that of the conventional matched filter. An adaptive implementation of the receiver is also considered. The results show that the multiple-antenna receiver is insensitive to the interfering powers and can provide room for more users or a smaller number of antennas than the matched filter solution. Using the adaptive algorithm, the performance even with a single antenna is often much better than that of a matched filter with 4 antennas.

9
R. Baghaie and T. Laakso, "Implementation of low-power CDMA RAKE receivers using strength reduction transformation," in Proceedings IEEE Nordic Signal Processing Symposium, NORSIG'98, Vigsø, Denmark, pp. 169-172, June 1998.
ABSTRACT:
In a Code Division Multiple Access system operating in a multipath fading channel, a bank of RAKE receivers is needed for each active user at the base station. In this paper, low-power RAKE receivers are proposed that utilize the Strength Reduction (SR) transformation technique. The SR transformation can result in remarkable savings in consumed power and silicon area. A possible disadvantage of the SR transformation is that it increases the computation time of the critical path. However, this problem can be alleviated by different pipelining schemes.

8 R. Baghaie and S. Werner, "Pipelined adaptive CDMA mobile receivers," in Proceedings IEEE Nordic Signal Processing Symposium, NORSIG'98, Vigsø, Denmark, pp. 69-72, June 1998.
ABSTRACT:
Adaptive multiple-antenna receivers can provide insensitivity to the interfering powers and room for more users or they require smaller number of antennas compared to the matched filter solution. In this paper, pipelined implementation of an adaptive Direct-Sequence Code Division Multiple Access receiver is proposed when multiple antennas are utilized for mobile communications. A number of approximation techniques are utilized to pipeline the Recursive Least-Squares (RLS) algorithm used for the receiver. The resulting pipelined structure achieves a higher throughput or requires lower power as compared to the receiver using the conventional serial RLS algorithm. As a result of pipelining, the hardware overhead is only 2M extra latches. For different number of antennas and different levels of pipelining the signal-to-interference versus the relative interfering power are illustrated.

7 S. Werner, J. A. Apolinário, "Application of Constrained Normalized Algorithms for a Multiple-Antenna CDMA Mobile Receiver," in Proceedings IEEE Nordic Signal Processing Symposium NORSIG'98, Vigsø, Denmark, June 1998.
ABSTRACT:
Constrained adaptive receiver algorithms are considered in a multiple-antenna CDMA mobile receiver. We study the constrained versions of the Bi-normalized Data-Reusing LMS (BNDR-LMS) and the Normalized LMS (NLMS) and their performance are compared with the classical Frost algorithm. We make use of time-varying step-sequences to further enhance the performance of the receiver. The results show that considerable improvement in the convergence speed can be achieved with the use of the normalized algorithms compared with the conventional Frost algorithm. Using an optimal step-sequence in the update provides a fast convergence and a near optimum steady-state performance.

6 R. Baghaie, S. Werner, and T. Laakso, "Pipelined implementation of adaptive multiple-antenna CDMA receivers," in Proceedings IEEE International Conference on Acoustics, Speech, and Signal Processing, ICASSP'98, Seattle, Washington, vol. 6, pp. 3229-3232, May 1998.
ABSTRACT:
Pipelined implementation of an adaptive Direct-Sequence Code Division Multiple Access (DS-CDMA) receiver is proposed when multiple antennas are utilized for mobile communications. Adaptive multiple-antenna receivers can provide insensitivity to the interfering powers and room for more users or require smaller number of antennas than the matched filter solution. In this paper, a number of approximation techniques are utilized to pipeline the adaptive algorithm used for the proposed multiple-antenna receiver. The resulting pipelined receiver requires minimal hardware increase and achieves a higher throughput or requires lower power as compared to the receiver using the serial algorithm. Simulation results illustrate the signal-to-interference (SIR) versus the relative interfering power for different number of antennas and different levels of pipelining.

5 Timo I. Laakso and Vesa Välimäki, "Energy-based effective length of the impulse response of a recursive filter," in Proceedings IEEE Int. Conf. Acoustics, Speech, and Signal Processing, ICASSP'98, vol. 3, pp. 1253-1256, Seattle, Washington, May 12-16, 1998.
ABSTRACT:
A measure for the effective length of the impulse response of a stable recursive digital filter based on accumulated energy is proposed. A general definition and a simple algorithm for its evaluation are introduced, and closed-form expressions are derived for first-order IIR filters. The effect of zeros on the effective length is analyzed. An upper bound for the effective length of higher-order filters is derived using results for low-order filters. The new measure finds applications in several fields of digital signal processing, including estimation of the extent of attack transients for filters with dynamically varying inputs, elimination of transients in variable recursive filters, and design and implementation of linear-phase IIR systems.

4 Vesa Välimäki and Timo I. Laakso, "Suppression of transients in time-varying recursive filters for audio signals," in Proceedings IEEE Int. Conf. Acoustics, Speech, and Signal Processing, ICASSP'98, vol. 6, pp. 3569-3572, Seattle, Washington, May 12-16, 1998.
ABSTRACT:
A new method for suppressing transients in time-varying recur-sive filters is proposed. The technique is based on modifying the state variables when the filter coefficients are changed so that the filter enters a new state smoothly without transient attacks, as originally proposed by Zetterberg and Zhang. In this contribution we modify the Zetterberg-Zhang algorithm to render it feasible for efficient implementation. We explain how to determine an optimal transient suppresser to cancel the transients down to a desired level at the minimum complexity of implementation. The application of the method to time-varying all-pole and direct-form II filter structures is studied. The algorithm may be gener-alized for any recursive filter structure. The transient suppression technique finds applications in audio signal processing where the characteristics of a recursive filter needs to be changed in real time, such as in music synthesis, auralization, and equalization.

Journals

3 T. I. Laakso and A. Gyasi-Agyei, "Design of optimal symmetric FIR receive filters", Electronic Letters, Vol. 34, No. 25, pp. 2375-2377, 10th Dec. 1998.

2 Vesa Välimäki and Timo I. Laakso, "Suppression of transients in variable digital filters with a novel and efficient transient cancellation method," IEEE Trans. on Signal Processing, Vol. 46, No. 12, pp. 3408-3414, Dec. 1998.
ABSTRACT:
A new method for suppressing transients in recursive infinite impulse response (IIR) digital filters is proposed. The technique is based on modifying the state (delay) variables of the filter when coefficients are changed so that the filter enters a new state smoothly without transient attacks, as originally proposed by Zetterberg and Zhang. In this correspondence, we modify the Zetterberg-Zhang algorithm to render it feasible for efficient implementation. We define a mean square error (MSE) measure for transients and determine the optimal transient suppresser to cancel the transients down to a desired level at the minimum complexity of implementation. The application of the method to all-pole and direct-form II (DF II) IIR filter sections is studied in detail. Time-varying recursive filtering with transient elimination is illustrated for tunable fractional delay filters and variable-bandwidth lowpass filters.

1 Juha Kauraniemi, Timo I. Laakso, Iiro Hartimo, and Seppo J. Ovaska, "Delta operator realizations ofr direct-form IIR filters," IEEE Trans. on Circuits and Systems - II: Analog and Digital Signal Processing, Vol. 45, No. 1, pp. 41-52, January 1998.

1997

# Journals / Book Chapters

7 T. Laakso, L. P. Sabel, V. Rose, A. Yardim, and G. D. Cain, "A new delay Root-Nyquist filter design method for signals corrupted by ACI," In: T. Wysocki, H. Razavi and B. Honary (Eds.) Digital Signal Processing for Communication Systems, pp. 167-176, Kluwer Academic Publishers, London 1997.

6 Seppo J. Ovaska, Olli Vainio, and Timo I. Laakso, "Design of predictive IIR filters via feedback extension of FIR forward predictors," IEEE Trans. on Instrumentation and Measurement, Vol. 46. No. 5, pp. 1196-1201, Oct. 1997.

5 A. Yardim, T. I. Laakso, L. P. Sabel and G. D. Cain, "Frequency-sampling design of delay-root-Nyquist filters", Electronic Letters, Vol. 33, No. 1, pp. 35-37, 2nd Jan. 1997.

International Conferences

4 P. T. Karttunen, T. I. Laakso and J. Lilleberg, "Tracking of Mobile Users in Mobile Communication System Using Adaptive Convergence parameter", in Proceedings IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC'97, Vol. 3, pp. 989-993, Helsinki, Sept. 1-4, 1997.
ABSTRACT:
In future telecommunication systems, one of the most important ways to increase system capacity is to use adaptive antennas. They enable reception and transmission using narrow beams which drastically reduce interference for other users. The problem with the conventional adaptive tracking algorithms is that the adaptation performance is dictated by the choice of the convergence parameter or step size. In this paper we employ a multi-target tracking method and modify its tracking performance by adaptive step size. The simulation results show that the proposed adaptive control of convergence parameter gives fast convergence and small misadjustment errors, which cannot be combined by using fixed step size.

3 J. Kauraniemi and T. I. Laakso, "Roundoff noise analysis of modified delta operator direct form structures," in Proc. IEEE Int. Symp. on Circuits and Systems, ISCAS'97, Vol. 4, pp. 2365-2368, Hong Kong, June 1997.

Other Publications

2 P. Karttunen, Comparison of Direction of Arrival and Beamforming Methods, Master's thesis, Laboratory of Telecommunications Technology, TKK, Otaniemi, Jan. 1997.

1 Stefan Werner, Adaptive Multiple-Antenna Receiver for CDMA Mobile Reception, Internal Report, Laboratory of Telecommunications Technology, TKK, Otaniemi, October 1997.

1996

# Journals / Book Chapters

22 Timo I. Laakso, Lesley P. Sabel, Anush Yardim, and Gerald D. Cain, "Optimal receive filters for the suppression of ISI and adjacent channel interference", Electronic Letters, Vol. 32, No. 15, pp. 1346-1347, 18th July 1996.

21 I. Kale, J. P. Mackenzie and T. I. Laakso, "Motor car acoustic response modeling and order reduction via balanced model truncation", Electronic Letters, Vol. 32, No. 11, pp. 965-966, 23rd May 1996.

20 Timo I. Laakso and Seppo J. Ovaska, "A prefiltering approach for optimal polynomial prediction," IEEE Trans. on Signal Processing, Vol. 44, No. 1, pp. 701-705, March 1996.

19 P. T. Harju, T. I. Laakso, and S. J. Ovaska, "Applying IIR predictors on Rayleigh fading signal," Signal Processing, Vol. 48, No. 1, pp. 91-96, Jan. 1996.

18 Timo I. Laakso, Vesa Välimäki, Matti Karjalainen and Unto K. Laine, "Splitting the unit delay - tools for fractional delay filter design," IEEE Signal Processing Magazine, Vol. 13, No. 1, pp. 30-60, Jan. 1996.

International Conferences

17 Anush Yardim, Timo I. Laakso, Lesley P. Sabel, and Gerald D. Cain, "Design of efficient receive FIR filters for joint minimization of channel noise, ISI, and adjacent channel interference," in Proc. IEEE Global Communications Conference (GLOBECOM'96), pp. 948-952, London, UK, Nov. 18-22, 1996.

16 Aiping Huang, Timo I. Laakso, Seppo J. Ovaska, and Iiro O. Hartimo, "Optimal linear filtering for power estimation of slowly-varying complex-valued signals," in Proc. IEEE Int. Conf. on Signal Processing (ICSP?96), pp. 76-79, Beijing, China, Oct. 14-18, 1996.

15 Denise Bland, Timo Laakso and Andrzej Tarczynski, "Application of NUT-DFT for resampling of nonuniformly sampled signals", in Proc. the Third Int. Conf. on Electronics, Circuits, and Systems (ICECS'96), pp. 586-589, Rhodos, Greece, Oct. 13-16, 1996.

14 J. Kauraniemi and T. I. Laakso, "Elimination of limit cycles in a direct form delta operator filter," in Proc. VIII European Signal Processing Conference (EUSIPCO'96), Vol. 1, pp. 57-60, Trieste, Italy, Sept. 1996.

13 Timo I. Laakso, N. Paul Murphy and Andrzej Tarczynski, "Reconstruction of nonuniformly sampled signals using polynomial filtering", in Proc. IEEE Nordic Signal Processing Symposium (NORSIG'96), pp. 61-64, Espoo, Finland, Sept. 24-27, 1996.

12 Aiping Huang and Timo I. Laakso, "Power estimation approaches for complex-valued signals based on the Hammerstein model and the Wiener model," in Proc. IEEE Nordic Signal Processing Symposium (NORSIG'96), pp. 191-194, Espoo, Finland, Sept. 24-27, 1996.

11 Petri T. Karttunen, Seppo J. Ovaska, and Timo I. Laakso, "Comparison of direction of arrival estimation methods: a case study," in Proc. IEEE Nordic Signal Processing Symposium (NORSIG'96), pp. 223-227, Espoo, Finland, Sept. 24-27, 1996.

10 Denise M. Bland, Andrzej Tarczynski and Timo I. Laakso, "Spectrum analysis of nonuniformly sampled signals using the NUT-DFT", in Proc. IEEE Nordic Signal Processing Symposium (NORSIG'96), pp. 307-310, Espoo, Finland, Sept. 24-27, 1996.

9 N. P. Murphy, A. Tarczynski and T. I. Laakso, "Sampling-rate conversion using a wideband tuneable fractional delay element", in Proc. IEEE Nordic Signal Processing Symposium (NORSIG'96), pp. 423-426, Espoo, Finland, Sept. 24-27, 1996.

8 Izzet Kale, Jonathan P. Mackenzie, Timo I. Laakso and Gerald D. Cain, "Recursive filter approximation of long car audio impulse responses using balanced model truncation", in Proc. IEEE Nordic Signal Processing Symposium (NORSIG'96), pp. 435-438, Espoo, Finland, Sept. 24-27, 1996.

7 Jonathan P. Mackenzie, Izzet Kale, Timo I. Laakso and Gerald D. Cain, "Balanced model truncation: an alternative to linear prediction for speech coding", in Proc. IEEE Nordic Signal Processing Symposium (NORSIG'96), pp. 439-442, Espoo, Finland, Sept. 24-27, 1996.

6 Vesa Välimäki and Timo I. Laakso, "Splitting the unit delay - digital filter approximations for fractional delay", in Proc. IEEE Nordic Signal Processing Symposium (NORSIG'96), pp. 479-482, Espoo, Finland, Sept. 24-27, 1996.

5 Lesley P. Sabel, Timo I. Laakso, Anush Yardim, and Gerald D. Cain, "A new delay root-Nyquist filter design method for signals corrupted by ACI," in Proc. 4th UK/Australian International Symposium on DSP for Communication Systems, Perth, Western Australia, pp. 186-193, Sept. 23-27, 1996.

4 Aiping Huang and Timo I. Laakso, "Optimal design and adaptive implementation of power estimation using the Hammerstein model," in Proc. IEEE Midwest Symposium on Circuits and Systems, pp. 648-651, Ames, Iowa, USA, Aug. 18-21, 1996.

3 Andrzej Tarczynski, Denise Bland, and Timo Laakso, "Spectrum estimation of non-uniformly sampled signals", in Proc. IEEE International Symposium on Industrial Electronics (ISIE96), Warsaw, Poland, pp. 196-200, June 17-20, 1996.

2 Denise M. Bland, Timo I. Laakso, and Andrzej Tarczynski, "Analysis of algorithms for a non-uniform time discrete Fourier transform," in Proc. Int. Symp. on Circuits and Systems (ISCAS'96), Vol. 2, pp. 453-456, Atlanta, Georgia, May 12-15, 1996.

1 Juha Kauraniemi, Timo I. Laakso, Iiro Hartimo, and Seppo J. Ovaska, "Roundoff noise minimization in a direct form delta operator structure," in Proc. Int. Conf. on Acoustics, Speech, Signal Process. (ICASSP'96), Vol. 3, pp. 1371-1374, Atlanta, Georgia, May 7-10, 1996.

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#	*International Conferences*
16	P. T. Karttunen, K. Kalliola, T. I. Laakso, and P. Vainikainen, "Measurement Analysis of Spatial and Temporal Correlation in Wideband Radio Channels with Adaptive Antenna Array," in Proceedings International Conference on Universal Personal Communications, ICUPC'98, Florence, Italy, pp. 671-675, October 1998. ABSTRACT: This paper investigates the spatial and temporal correlation by measurements of an 8-element adaptive antenna array. The channel measurement data is gathered at a 2.154 GHz range outdoor radio channel. The measurement analysis is divided into three different categories: Investigation of spatial correlation between antenna elements at the base station (BS), spatial correlation of different mobile station (MS) locations and temporal correlation of the different multipath components. Also the differences in the correlation coefficient functions by using the complex-valued taps instead of the magnitude-valued taps are studied at the BS. The measurement analysis reveals that signals strongly correlate in the nearby BS antenna elements. However, at the different MS locations uncorrelated signals can be received when the physical separation is larger than half a wavelength. The multipath components in the impulse response profile become temporally uncorrelated after the excess delay values of 50 ns.
15	J. A. Apolinario Jr., S. Werner, T. I. Laakso, and P. S. R. Diniz, "Constrained normalized adaptive filtering for CDMA mobile communications," in Proceedings IX European Signal Processing Conference EUSIPCO'98, Island of Rhodes, Greece, pp. 2053-2056, September 8-11, 1998. ABSTRACT: This work presents an extension of the classical LMS-based Frost algorithm to include both the Normalized LMS (NLMS) and the Binormalized Data-Reusing LMS (BNDR-LMS) algorithms. Two simple versions of these algorithms are derived for the Frost structure. These new algorithms were applied to a DS-CDMA mobile receiver. The results showed a considerable speed up of the convergence rate compared to the LMS Frost.
14	J. A. Apolinario Jr., P. S. R. Diniz, T. I. Laakso, and M. L. R. de Campos, "Step-size optimization of the BNDR-LMS algorithm," in Proceedings IX European Signal Processing Conference EUSIPCO'98, Island of Rhodes, Greece, pp. 1249-1252, September 8-11, 1998. ABSTRACT: The binormalized data-reusing least mean squares (BNDR-LMS) algorithm has been recently proposed and has been shown to have faster convergence than other LMS-like algorithms in cases where the input signal is strongly correlated. This superior performance in convergence speed is, however, followed by a higher misadjustment if the step-size is close to the value which allows the fastest convergence. An optimal step-size sequence for this algorithm is proposed after considering a number of simplifying assumptions. Moreover, this work brings insight in how to deal with these conflicting requirements of fast convergence and minimum steady-state mean square error (MSE).
13	R. Baghaie, S. Werner, and T. Laakso, "Relaxed look-ahead techniques for pipelined implementation of adaptive multiple-antenna CDMA mobile receivers," in Proceedings IX European Signal Processing Conference EUSIPCO'98, Island of Rhodes,Greece, pp. 877-880, September 1998. ABSTRACT: In this paper, Relaxed Look-Ahead technique for pipelined implementation of an adaptive Direct-Sequence Code Division Multiple Access receiver is proposed when multiple antennas are utilized for mobile communications. Adaptive multiple-antenna receivers can provide insensitivity to the interfering powers. They also provide room for more users or require smaller number of antennas than the matched filter solution. A number of approximation techniques are utilized to pipeline the adaptive algorithm used for the proposed multiple-antenna receiver. The resulting pipelined receiver achieves a higher throughput or requires lower power as compared to the receiver using the serial algorithm. With the aid of simulations, for different levels of pipelining and different number of antennas, the signal-to-interference ratio and the bit error rate versus the relative interfering power are illustrated.
12	M. L. R. de Campos, S. Werner, J. A. Apolinario., and Timo I. Laakso, "Constrained Quasi-Newton algorithm for CDMA mobile communications," in Proceedings SBT/IEEE International Telecommunications Symposium ITS'98, Sao Paulo, Brazil, pp. 371-376, August 9-13, 1998. ABSTRACT: This work presents the derivation of the constrained version of a Quasi-Newton (QN) algorithm. Application of such algorithm to the problem of direct-sequence code-division multiple access (DS-CDMA) is investigated through simulations. The algorithm is compared to other constrained adaptation algorithms known in the literature in terms of convergence rate for a similar misadjustment level. Two scenarios describing synchronous and asynchronous transmission are used in simulations of interference suppression in DS-CDMA communication, showing the great capability of the algorithm in such application.
11	S. Werner, J. A. Apolinário, "Multiple-Antenna CDMA Mobile Reception Using Constrained Normalized Adaptive Algorithms," in Proceedings SBT/IEEE International Telecommunications Symposium ITS'98, Sao Paulo, Brazil, pp. 354-358, August 9-13, 1998. ABSTRACT: In this paper we analyze adaptive algorithms for a multiple-antenna Code Division Multiple Access (CDMA) mobile receiver. We study the constrained versions of the Binormalized Data-Reusing LMS (BNDR-LMS) and the Normalized LMS (NLMS). Their performance is compared with that of the classical Frost algorithm. Time-varying step-sequences are used to further enhance the performance of the receiver. The results show that considerable improvement in the convergence speed can be achieved with the use of the normalized algorithms compared with the conventional Frost algorithm. Using an optimal step-sequence in the update provides a fast convergence and a near-optimum steady-state performance.
10	S. Werner, T. Laakso, J. Lilleberg, "Multiple-antenna receiver for CDMA mobile reception," in Proceedings IEEE International Conference on Communications ICC'98, Atlanta, Georgia, USA, June 7-11, 1998. ABSTRACT: This paper examines the utilization of multiple antennas for Direct-Sequence Code Division Multiple Access (DS-CDMA) mobile communications at the mobile receiver. A linear single-user multiple-antenna receiver is derived and its performance is compared with that of the conventional matched filter. An adaptive implementation of the receiver is also considered. The results show that the multiple-antenna receiver is insensitive to the interfering powers and can provide room for more users or a smaller number of antennas than the matched filter solution. Using the adaptive algorithm, the performance even with a single antenna is often much better than that of a matched filter with 4 antennas.
9	R. Baghaie and T. Laakso, "Implementation of low-power CDMA RAKE receivers using strength reduction transformation," in Proceedings IEEE Nordic Signal Processing Symposium, NORSIG'98, Vigsø, Denmark, pp. 169-172, June 1998. ABSTRACT: In a Code Division Multiple Access system operating in a multipath fading channel, a bank of RAKE receivers is needed for each active user at the base station. In this paper, low-power RAKE receivers are proposed that utilize the Strength Reduction (SR) transformation technique. The SR transformation can result in remarkable savings in consumed power and silicon area. A possible disadvantage of the SR transformation is that it increases the computation time of the critical path. However, this problem can be alleviated by different pipelining schemes.
8	*R. Baghaie and S. Werner, "Pipelined adaptive CDMA mobile receivers," in Proceedings IEEE Nordic Signal Processing Symposium,* NORSIG'98, Vigsø, Denmark, pp. 69-72, June 1998.** ABSTRACT: Adaptive multiple-antenna receivers can provide insensitivity to the interfering powers and room for more users or they require smaller number of antennas compared to the matched filter solution. In this paper, pipelined implementation of an adaptive Direct-Sequence Code Division Multiple Access receiver is proposed when multiple antennas are utilized for mobile communications. A number of approximation techniques are utilized to pipeline the Recursive Least-Squares (RLS) algorithm used for the receiver. The resulting pipelined structure achieves a higher throughput or requires lower power as compared to the receiver using the conventional serial RLS algorithm. As a result of pipelining, the hardware overhead is only 2M extra latches. For different number of antennas and different levels of pipelining the signal-to-interference versus the relative interfering power are illustrated.
7	S. Werner, J. A. Apolinário, "Application of Constrained Normalized Algorithms for a Multiple-Antenna CDMA Mobile Receiver," in Proceedings IEEE Nordic Signal Processing Symposium NORSIG'98, Vigsø, Denmark, June 1998. ABSTRACT: Constrained adaptive receiver algorithms are considered in a multiple-antenna CDMA mobile receiver. We study the constrained versions of the Bi-normalized Data-Reusing LMS (BNDR-LMS) and the Normalized LMS (NLMS) and their performance are compared with the classical Frost algorithm. We make use of time-varying step-sequences to further enhance the performance of the receiver. The results show that considerable improvement in the convergence speed can be achieved with the use of the normalized algorithms compared with the conventional Frost algorithm. Using an optimal step-sequence in the update provides a fast convergence and a near optimum steady-state performance.
6	R. Baghaie, S. Werner, and T. Laakso, "Pipelined implementation of adaptive multiple-antenna CDMA receivers," in Proceedings IEEE International Conference on Acoustics, Speech, and Signal Processing, ICASSP'98, Seattle, Washington, vol. 6, pp. 3229-3232, May 1998. ABSTRACT: Pipelined implementation of an adaptive Direct-Sequence Code Division Multiple Access (DS-CDMA) receiver is proposed when multiple antennas are utilized for mobile communications. Adaptive multiple-antenna receivers can provide insensitivity to the interfering powers and room for more users or require smaller number of antennas than the matched filter solution. In this paper, a number of approximation techniques are utilized to pipeline the adaptive algorithm used for the proposed multiple-antenna receiver. The resulting pipelined receiver requires minimal hardware increase and achieves a higher throughput or requires lower power as compared to the receiver using the serial algorithm. Simulation results illustrate the signal-to-interference (SIR) versus the relative interfering power for different number of antennas and different levels of pipelining.
5	Timo I. Laakso and Vesa Välimäki, "Energy-based effective length of the impulse response of a recursive filter," in Proceedings IEEE Int. Conf. Acoustics, Speech, and Signal Processing, ICASSP'98, vol. 3, pp. 1253-1256, Seattle, Washington, May 12-16, 1998. ABSTRACT: A measure for the effective length of the impulse response of a stable recursive digital filter based on accumulated energy is proposed. A general definition and a simple algorithm for its evaluation are introduced, and closed-form expressions are derived for first-order IIR filters. The effect of zeros on the effective length is analyzed. An upper bound for the effective length of higher-order filters is derived using results for low-order filters. The new measure finds applications in several fields of digital signal processing, including estimation of the extent of attack transients for filters with dynamically varying inputs, elimination of transients in variable recursive filters, and design and implementation of linear-phase IIR systems.
4	Vesa Välimäki and Timo I. Laakso, "Suppression of transients in time-varying recursive filters for audio signals," in Proceedings IEEE Int. Conf. Acoustics, Speech, and Signal Processing, ICASSP'98, vol. 6, pp. 3569-3572, Seattle, Washington, May 12-16, 1998. ABSTRACT: A new method for suppressing transients in time-varying recur-sive filters is proposed. The technique is based on modifying the state variables when the filter coefficients are changed so that the filter enters a new state smoothly without transient attacks, as originally proposed by Zetterberg and Zhang. In this contribution we modify the Zetterberg-Zhang algorithm to render it feasible for efficient implementation. We explain how to determine an optimal transient suppresser to cancel the transients down to a desired level at the minimum complexity of implementation. The application of the method to time-varying all-pole and direct-form II filter structures is studied. The algorithm may be gener-alized for any recursive filter structure. The transient suppression technique finds applications in audio signal processing where the characteristics of a recursive filter needs to be changed in real time, such as in music synthesis, auralization, and equalization.
	*Journals*
3	T. I. Laakso and A. Gyasi-Agyei, "Design of optimal symmetric FIR receive filters", Electronic Letters, Vol. 34, No. 25, pp. 2375-2377, 10th Dec. 1998.
2	Vesa Välimäki and Timo I. Laakso, "Suppression of transients in variable digital filters with a novel and efficient transient cancellation method," IEEE Trans. on Signal Processing, Vol. 46, No. 12, pp. 3408-3414, Dec. 1998. ABSTRACT: A new method for suppressing transients in recursive infinite impulse response (IIR) digital filters is proposed. The technique is based on modifying the state (delay) variables of the filter when coefficients are changed so that the filter enters a new state smoothly without transient attacks, as originally proposed by Zetterberg and Zhang. In this correspondence, we modify the Zetterberg-Zhang algorithm to render it feasible for efficient implementation. We define a mean square error (MSE) measure for transients and determine the optimal transient suppresser to cancel the transients down to a desired level at the minimum complexity of implementation. The application of the method to all-pole and direct-form II (DF II) IIR filter sections is studied in detail. Time-varying recursive filtering with transient elimination is illustrated for tunable fractional delay filters and variable-bandwidth lowpass filters.
1	Juha Kauraniemi, Timo I. Laakso, Iiro Hartimo, and Seppo J. Ovaska, "Delta operator realizations ofr direct-form IIR filters," IEEE Trans. on Circuits and Systems - II: Analog and Digital Signal Processing, Vol. 45, No. 1, pp. 41-52, January 1998.

1999

1998

R. Baghaie, S. Werner, and T. Laakso, "Relaxed look-ahead techniques for pipelined implementation of adaptive multiple-antenna CDMA mobile receivers," in Proceedings IX European Signal Processing Conference EUSIPCO'98, Island of Rhodes,Greece, pp. 877-880, September 1998.

R. Baghaie and T. Laakso, "Implementation of low-power CDMA RAKE receivers using strength reduction transformation," in Proceedings IEEE Nordic Signal Processing Symposium, NORSIG'98, Vigsø, Denmark, pp. 169-172, June 1998.

1997

1996

#	*Conferences*
16	R. Baghaie and P. Karttunen, "Implementation of mobile user tracking system," to appear in Proceedings Global Communications Conference, GLOBECOM'99, Rio de Janeiro, Brazil, December 1999.
15	V. Dimitrov and R. Baghaie, "Computing discrete Hartley transform using algebraic integers," to appear in Proceedings 33rd Asilomar Conference on Signals, Systems and Computers, Pacific Grove, CA, October 1999.
14	P. Karttunen, "An algorithm for Noise Subspace based Mobile User Tracking," in Proceedings IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC'99, Kyoto, Japan, September 1999. ABSTRACT: In this paper for the user tracking application we develop a step-by-step adaptation method for tracking the parameter vector in the noise subspace. Also, we develop the control strategy for the noise subspace roots eliminating the problems with the spurious roots. The performance comparison of the developed user tracking system will be investigated in terms of the tracking capability. As the performance criterion, the mean Direction-of-Arrival (DOA) error will be invoked in the stationary and non-stationary signal scenarios. The simulation results confirm that the proposed noise subspace approach can achieve similar tracking performance as the signal subspace approach in terms of the convergence speed and the final misadjustment level.
13	*R. Baghaie, "Application of transformation techniques in CDMA receivers," in Proceedings IEEE Midwest Symposium on Circuits and Systems, MWSCAS'99, Las Cruces, New Mexico, August 1999.* ABSTRACT: This paper discusses the application of different algorithm transformation techniques in Code Division Multiple Access receivers (CDMA). This is achieved by looking at some of the computational blocks that constitute the CDMA receivers. We focus on the Look-Ahead, Relaxed Look-ahead and Strength Reduction algorithm transformation techniques and demonstrate how CDMA receivers could benefit when utilizing these techniques during the course of implementation.
12	R. Baghaie and P. Karttunen, "VLSI implementation of CG based mobile user tracking system," in Proceedings IEEE Midwest Symposium on Circuits and Systems, MWSCAS'99, Las Cruces, New Mexico, August 1999. ABSTRACT: This paper considers the implementation of a signal subspace based mobile user tracking system that utilizes an efficient Conjugate Gradient (CG) based step-by-step adaptation scheme. First, we estimate the computational complexity of different units of the tracking system. Based on these estimations, we partition the implementation task into two parts: software and hardware. Finally, for the hardware implementation of the tracking unit a systolic architecture is proposed. With the aid of the proposed systolic array the time complexity of the tracking unit is reduced to O(M).
11	K. Kettunen, T. Laakso, "Iterative multiuser receiver utilizing soft decoding information," in Proceedings IEEE International Communications Conference, ICC'99, Vancouver, BC, Canada, pp. 942-946, June 1999. ABSTRACT: In this paper we propose a novel receiver structure that utilizes the soft information provided by the channel decoder in the multiuser detection. This receiver structure is based on a single-user version of the uncoded maximum a priori criterion. We derive the optimal multiuser likelihood calculation algorithm for this structure. In addition, suboptimal algorithms are proposed that are based on interference cancellation. Numerical simulations are reported which indicate that these suboptimal algorithms have a close-to-optimal coded BER performance even in the presence of high-power interferers.
10	P. Karttunen and R. Baghaie, "Conjugate Gradient Based Signal Subspace Mobile User Tracking," in Proceedings IEEE Vehicular Technology Conference, VTC'99, Houston, Texas, USA, vol. 2, pp. 1172-1176, May 1999. ABSTRACT: Adaptive antennas enable the increase in the system capacity through spatial interference suppression in the beamforming mode. All the spatial domain channel estimators must react fast to abrupt changes in the channel parameters. Additionally, they have to provide accurate enough tracking capabilities. In this paper, we construct the user tracking system by employing an efficient Conjugate Gradient (CG) method based on a step-by-step adaptation scheme. Furthermore, the paper investigates the tracking capability and the computational complexity issues of the proposed system. The simulation results confirm that the proposed CG method achieves better tracking performance than gradient methods both in the stationary and non-stationary signal scenario.
9	K. Kettunen, "Iterative multiuser receiver/decoders with enhanced variance estimation," in Proceedings IEEE 49th Vehicular Technology Conference, VTC'99, Houston, Texas, USA, pp. 2318-2322, May 1999. ABSTRACT: In this paper we study the impact of variance estimation on a receiver, where the soft information provided by the channel decoder is utilized in the multiuser detection. Specifically, we consider a receiver structure that resembles the structure of an iterative decoder for a serially concatenated code, but where the inner constituent decoder is replaced by an interference cancellation (IC) unit. The system performance with three different variance estimator methods is studied through numerical simulations. The results show that the variance estimation method has a great impact on the receiver performance especially in the case, where the different users are received with different powers.
8	S. Werner, J. Lilleberg, "Downlink channel decorrelation in CDMA systems with long codes," in Proceedings IEEE 49th Vehicular Technology Conference, VTC'99, Houston, Texas, USA, pp. ??-??, May 1999. ABSTRACT: In this paper we develop linear detectors suitable for a Code Division Multiple Access (CDMA) mobile receiver using long codes. The special signal structure in the downlink transmission is exploited to obtain a simple detection rule. A least-squares (LS) detector, a best linear unbiased estimator (BLUE) detector, and a linear minimum mean-square error (LMMSE) detector are derived. For the LMMSE detector we consider an adaptive implementation. The results show that improvement can be achieved using the proposed detectors compared with that of the conventional RAKE receiver.
7	*R. Baghaie, "Systolic implementation of sample-by-sample conjugate gradient algorithm," in Proceedings IEEE Finnish Signal Processing Symposium, FINSIG'99, Oulu, Finland, pp. 252-256, May 1999.* ABSTRACT: In this paper, we consider an efficient Conjugate Gradient (CG) algorithm that can be used when non-block processing or sample-by-sample update is of interest and compare its computational complexity with the conventional CG algorithm. We then review the VLSI implementation of the CG algorithms. Furthermore, for the hardware implementation of the sample-by-sample CG algorithm, a novel systolic array is proposed. With the aid of this systolic architecture, the time complexity of the algorithm will be reduced to O(N).
6	R. Insa Hernandez, R. Baghaie, and K. Kettunen, "Implementation of Gram-Schmidt conjugate direction and conjugate gradient algorithms," in Proceedings IEEE Finnish Signal Processing Symposium, FINSIG'99, Oulu, Finland, pp. 165-169, May 1999. ABSTRACT: In this paper, we consider the implementation of two iterative methods: the Gram-Schmidt Conjugate Direction (GSCD) and Conjugate Gradient (CG) algorithm. We first study the convergence properties of the algorithms. Furthermore, the fixed-point implementation of both CG and GSCD are presented. For the simulations purposes, the algorithms are applied to a multiuser detection scheme in a DS-CDMA system. Finally, for different number of users, wordlengths, and number of iterations, the MSE resulting from the quantization is estimated.
5	*K. Kettunen, "Iterative multiuser receivers in coded CDMA systems," in Proceedings IEEE Finnish Signal Processing Symposium, FINSIG'99, Oulu, Finland, pp. 15-19, May 1999.* ABSTRACT: In this paper, we consider the possibility of utilizing the channel decoder output in the cancellation of multiuser interference. The paper contains a summary of our earlier numerical results followed by a discussion about some observations based on these simulations.
4	R. Baghaie, "Transformation techniques in CDMA receivers," in Proceedings IEEE Finnish Signal Processing Symposium, FINSIG'99, Oulu, Finland, pp. 10-15, May 1999.
3	M. L. R. de Campos, S. Werner, J. A. Apolinario, "Householder-transform constrained LMS algorithm with reduced-rank updating," in proceedings Acoustics, Speech, and Signal Processing, ICASSP'99, Phoenix, Arizona, USA, Vol. 4, pp. 1857-1860, March 15-19, 1999.
	*Journals*
2	*R. Baghaie and V. Dimitrov, "DHT algorithm based on encoding algebraic integers," IEE Electronics Letters, vol. 35, no. 16, pp. 1303-1305, August 1999.* ABSTRACT: A novel algorithm for computing the discrete Hartley transform (DHT) is presented. The proposed algorithm is based on the algebraic integers encoding scheme. With the aid of this scheme, an error-free representation of the cas function becomes possible. Furthermore, for the implementation of the algorithm a fully pipelined systolic architecture with O(N) throughput is proposed.
1	Timo I. Laakso and Vesa Välimäki, "Energy-based effective length of the impulse response of a recursive filter," IEEE Trans. on Instrumentation and Measurement, Vol. 48, No. 1, pp. 7-17, Feb. 1999. ABSTRACT: A measure for the effective length of the impulse response of a stable recursive digital filter based on accumulated energy is proposed. The new measure finds applications in several fields of digital signal processing, including estimation of the extent of attack transients for filters with dynamically varying inputs, elimination of transients in variable recursive filters, and design and implementation of linear-phase IIR systems. A general definition and a simple algorithm to evaluate it are introduced, and closed-form expressions are derived for first and second-order all-pole filters. The effect of zeros on the effective length is analyzed. An upper bound for the effective length of higher-order filters is derived using results for low-order filters, which is illustrated for classical digital lowpass filters. The use of the measure is demonstrated with examples of implementation of linear-phase IIR systems and estimation of transients in variable IIR filters.

#	*Journals / Book Chapters*
7	T. Laakso, L. P. Sabel, V. Rose, A. Yardim, and G. D. Cain, "A new delay Root-Nyquist filter design method for signals corrupted by ACI," In: T. Wysocki, H. Razavi and B. Honary (Eds.) Digital Signal Processing for Communication Systems, pp. 167-176, Kluwer Academic Publishers, London 1997.
6	Seppo J. Ovaska, Olli Vainio, and Timo I. Laakso, "Design of predictive IIR filters via feedback extension of FIR forward predictors," IEEE Trans. on Instrumentation and Measurement, Vol. 46. No. 5, pp. 1196-1201, Oct. 1997.
5	A. Yardim, T. I. Laakso, L. P. Sabel and G. D. Cain, "Frequency-sampling design of delay-root-Nyquist filters", Electronic Letters, Vol. 33, No. 1, pp. 35-37, 2nd Jan. 1997.
	*International Conferences*
4	P. T. Karttunen, T. I. Laakso and J. Lilleberg, "Tracking of Mobile Users in Mobile Communication System Using Adaptive Convergence parameter", in Proceedings IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC'97, Vol. 3, pp. 989-993, Helsinki, Sept. 1-4, 1997. ABSTRACT: In future telecommunication systems, one of the most important ways to increase system capacity is to use adaptive antennas. They enable reception and transmission using narrow beams which drastically reduce interference for other users. The problem with the conventional adaptive tracking algorithms is that the adaptation performance is dictated by the choice of the convergence parameter or step size. In this paper we employ a multi-target tracking method and modify its tracking performance by adaptive step size. The simulation results show that the proposed adaptive control of convergence parameter gives fast convergence and small misadjustment errors, which cannot be combined by using fixed step size.
3	J. Kauraniemi and T. I. Laakso, "Roundoff noise analysis of modified delta operator direct form structures," in Proc. IEEE Int. Symp. on Circuits and Systems, ISCAS'97, Vol. 4, pp. 2365-2368, Hong Kong, June 1997.
	*Other Publications*
2	P. Karttunen, Comparison of Direction of Arrival and Beamforming Methods, Master's thesis, Laboratory of Telecommunications Technology, TKK, Otaniemi, Jan. 1997.
1	Stefan Werner, Adaptive Multiple-Antenna Receiver for CDMA Mobile Reception, Internal Report, Laboratory of Telecommunications Technology, TKK, Otaniemi, October 1997.

#	*Journals / Book Chapters*
22	Timo I. Laakso, Lesley P. Sabel, Anush Yardim, and Gerald D. Cain, "Optimal receive filters for the suppression of ISI and adjacent channel interference", Electronic Letters, Vol. 32, No. 15, pp. 1346-1347, 18th July 1996.
21	I. Kale, J. P. Mackenzie and T. I. Laakso, "Motor car acoustic response modeling and order reduction via balanced model truncation", Electronic Letters, Vol. 32, No. 11, pp. 965-966, 23rd May 1996.
20	Timo I. Laakso and Seppo J. Ovaska, "A prefiltering approach for optimal polynomial prediction," IEEE Trans. on Signal Processing, Vol. 44, No. 1, pp. 701-705, March 1996.
19	P. T. Harju, T. I. Laakso, and S. J. Ovaska, "Applying IIR predictors on Rayleigh fading signal," Signal Processing, Vol. 48, No. 1, pp. 91-96, Jan. 1996.
18	Timo I. Laakso, Vesa Välimäki, Matti Karjalainen and Unto K. Laine, "Splitting the unit delay - tools for fractional delay filter design," IEEE Signal Processing Magazine, Vol. 13, No. 1, pp. 30-60, Jan. 1996.
	*International Conferences*
17	Anush Yardim, Timo I. Laakso, Lesley P. Sabel, and Gerald D. Cain, "Design of efficient receive FIR filters for joint minimization of channel noise, ISI, and adjacent channel interference," in Proc. IEEE Global Communications Conference (GLOBECOM'96), pp. 948-952, London, UK, Nov. 18-22, 1996.
16	Aiping Huang, Timo I. Laakso, Seppo J. Ovaska, and Iiro O. Hartimo, "Optimal linear filtering for power estimation of slowly-varying complex-valued signals," in Proc. IEEE Int. Conf. on Signal Processing (ICSP?96), pp. 76-79, Beijing, China, Oct. 14-18, 1996.
15	Denise Bland, Timo Laakso and Andrzej Tarczynski, "Application of NUT-DFT for resampling of nonuniformly sampled signals", in Proc. the Third Int. Conf. on Electronics, Circuits, and Systems (ICECS'96), pp. 586-589, Rhodos, Greece, Oct. 13-16, 1996.
14	J. Kauraniemi and T. I. Laakso, "Elimination of limit cycles in a direct form delta operator filter," in Proc. VIII European Signal Processing Conference (EUSIPCO'96), Vol. 1, pp. 57-60, Trieste, Italy, Sept. 1996.
13	Timo I. Laakso, N. Paul Murphy and Andrzej Tarczynski, "Reconstruction of nonuniformly sampled signals using polynomial filtering", in Proc. IEEE Nordic Signal Processing Symposium (NORSIG'96), pp. 61-64, Espoo, Finland, Sept. 24-27, 1996.
12	Aiping Huang and Timo I. Laakso, "Power estimation approaches for complex-valued signals based on the Hammerstein model and the Wiener model," in Proc. IEEE Nordic Signal Processing Symposium (NORSIG'96), pp. 191-194, Espoo, Finland, Sept. 24-27, 1996.
11	Petri T. Karttunen, Seppo J. Ovaska, and Timo I. Laakso, "Comparison of direction of arrival estimation methods: a case study," in Proc. IEEE Nordic Signal Processing Symposium (NORSIG'96), pp. 223-227, Espoo, Finland, Sept. 24-27, 1996.
10	Denise M. Bland, Andrzej Tarczynski and Timo I. Laakso, "Spectrum analysis of nonuniformly sampled signals using the NUT-DFT", in Proc. IEEE Nordic Signal Processing Symposium (NORSIG'96), pp. 307-310, Espoo, Finland, Sept. 24-27, 1996.
9	N. P. Murphy, A. Tarczynski and T. I. Laakso, "Sampling-rate conversion using a wideband tuneable fractional delay element", in Proc. IEEE Nordic Signal Processing Symposium (NORSIG'96), pp. 423-426, Espoo, Finland, Sept. 24-27, 1996.
8	Izzet Kale, Jonathan P. Mackenzie, Timo I. Laakso and Gerald D. Cain, "Recursive filter approximation of long car audio impulse responses using balanced model truncation", in Proc. IEEE Nordic Signal Processing Symposium (NORSIG'96), pp. 435-438, Espoo, Finland, Sept. 24-27, 1996.
7	Jonathan P. Mackenzie, Izzet Kale, Timo I. Laakso and Gerald D. Cain, "Balanced model truncation: an alternative to linear prediction for speech coding", in Proc. IEEE Nordic Signal Processing Symposium (NORSIG'96), pp. 439-442, Espoo, Finland, Sept. 24-27, 1996.
6	Vesa Välimäki and Timo I. Laakso, "Splitting the unit delay - digital filter approximations for fractional delay", in Proc. IEEE Nordic Signal Processing Symposium (NORSIG'96), pp. 479-482, Espoo, Finland, Sept. 24-27, 1996.
5	Lesley P. Sabel, Timo I. Laakso, Anush Yardim, and Gerald D. Cain, "A new delay root-Nyquist filter design method for signals corrupted by ACI," in Proc. 4th UK/Australian International Symposium on DSP for Communication Systems, Perth, Western Australia, pp. 186-193, Sept. 23-27, 1996.
4	Aiping Huang and Timo I. Laakso, "Optimal design and adaptive implementation of power estimation using the Hammerstein model," in Proc. IEEE Midwest Symposium on Circuits and Systems, pp. 648-651, Ames, Iowa, USA, Aug. 18-21, 1996.
3	Andrzej Tarczynski, Denise Bland, and Timo Laakso, "Spectrum estimation of non-uniformly sampled signals", in Proc. IEEE International Symposium on Industrial Electronics (ISIE96), Warsaw, Poland, pp. 196-200, June 17-20, 1996.
2	Denise M. Bland, Timo I. Laakso, and Andrzej Tarczynski, "Analysis of algorithms for a non-uniform time discrete Fourier transform," in Proc. Int. Symp. on Circuits and Systems (ISCAS'96), Vol. 2, pp. 453-456, Atlanta, Georgia, May 12-15, 1996.
1	Juha Kauraniemi, Timo I. Laakso, Iiro Hartimo, and Seppo J. Ovaska, "Roundoff noise minimization in a direct form delta operator structure," in Proc. Int. Conf. on Acoustics, Speech, Signal Process. (ICASSP'96), Vol. 3, pp. 1371-1374, Atlanta, Georgia, May 7-10, 1996.