Akihisa Ushirokawa

Likelihood Function for QRM-MLD Suitable for Soft-Decision Turbo Decoding and Its Performance for OFCDM MIMO Multiplexing in Multipath Fading Channel

This paper proposes likelihood function generation of complexity-reduced Maximum Likelihood Detection with QR Decomposition and M-algorithm (QRM-MLD) suitable for soft-decision Turbo decoding and investigates the throughput performance using QRM-MLD with the proposed likelihood function in multipath Rayleigh fading channels for Orthogonal Frequency and Code Division Multiplexing (OFCDM) multiple-input multiple-output (MIMO) multiplexing. Simulation results show that by using the proposed likelihood function generation scheme for soft-decision Turbo decoding following QRM-MLD in 4-by-4 MIMO multiplexing, the required average received signal energy per bit-to-noise power spectrum density ratio (E b /N 0 ) at the average block error rate (BLER) of 10 -2 at a 1-Gbps data rate is significantly reduced compared to that using hard-decision decoding in OFCDM access with 16 QAM modulation, the coding rate of 8/9, and 8-code multiplexing with a spreading factor of 8 assuming a 100-MHz bandwidth. Furthermore, we show that by employing QRM-MLD associated with soft-decision Turbo decoding for 4-by-4 MIMO multiplexing, the throughput values of 500 Mbps and 1 Gbps are achieved at the average received E b /N 0 of approximately 4.5 and 9.3 dB by QPSK with the coding rate of R= 8/9 and 16QAM with R = 8/9, respectively, for OFCDM access assuming a 100-MHz bandwidth in a twelve-path Rayleigh fading channel.

SSDT-site selection diversity transmission power control for CDMA forward link

This paper proposes site selection diversity transmission power control (SSDT), an advanced form of transmission power control (TPC) for CDMA forward link, SSDT realizes site selection transmission diversity instead of full site transmission diversity used in conventional TPC during soft hand over (SHO) mode. The major intention of the site selection is to mitigate interference caused by multiple site transmission done at conventional TPC. Simulation results indicated that the higher the capacity gain of SSDT is in comparison to conventional TPC, the lower the mobile station (MS) speed is. Capacity gain of about 55% for a pedestrian MS is achieved by SSDT in case of MS reception diversity and 6 finger RAKE reception. This paper also presents the benefits of SSDT in terms of its high path capturing efficiency and the mitigation of power imbalance among active BSs due to TPC command reception error.

Space-time iterative and multistage receiver structures for CDMA mobile communication systems

We propose novel space-time multistage and iterative receiver structures and examine their application in code division multiple access (CDMA) mobile communication systems. In particular we derive an expression for weighting coefficients in parallel interference cancellers (PICs) in a system with a large number of users, where decision statistics bias is pronounced. We further examine the parameters in this expression and show how to obtain a practical partial cancellation method that allows on-line estimation of the weighting coefficients. In the proposed multistage PIC, the coefficients are calculated by using only the variances of the detector outputs. We also examine an iterative PIC and observe that this receiver has similar limitations as the multistage PIC. The application of the novel parallel interference cancellation strategy in the iterative receiver structure results in a spectacular system capacity improvement with a negligible complexity increase relative to the standard iterative receiver. The performance of the proposed receivers is further enhanced by receiver adaptive array antennas and space-time processing.

Likelihood function for QRM-MLD suitable for soft-decision turbo decoding and its performance for OFCDM MIMO multiplexing in multipath fading channel

This paper proposes likelihood function generation of complexity-reduced maximum likelihood detection with QR decomposition and M-algorithm (QRM-MLD) suitable for soft-decision turbo decoding and investigates the throughput performance using QRM-MLD with the proposed likelihood function in multipath Rayleigh fading channels for orthogonal frequency and code division multiplexing (OFCDM) with multiple-input multiple-output (MIMO) multiplexing. Simulation results show that by using the proposed likelihood function generation scheme for soft-decision turbo decoding following QRM-MLD in 4-by-4 MIMO multiplexing, the required average received signal energy per bit-to-noise power spectrum density ratio (E/sub b//N/sub o/) at the average block error rate (BLER) of 10/sup -2/ at a 1-Gbps data rate is significantly reduced compared to that using hard-decision decoding in OFCDM access with 16 QAM modulation, the coding rate of 8/9, and 8-code multiplexing with a spreading factor of 8 assuming a 100-MHz bandwidth. Furthermore, we show that by employing QRM-MLD associated with soft-decision turbo decoding for 4-by-4 MIMO multiplexing, the throughput values of 500 Mbps and 1 Gbps are achieved at the average received E/sub b//N/sub o/ of approximately 4.5 and 9.3 dB by QPSK with the coding rate of R = 8/9 and 16 QAM with R = 8/9, respectively, for OFCDM access assuming a 100-MHz bandwidth in a twelve-path Rayleigh fading channel.

Performance comparison of MF and MMSE combined iterative soft interference canceller and V-BLAST technique in MIMO/OFDM systems

This paper proposes a complexity reduced iterative soft interference canceller (ISIC) to realize broadband mobile transmission in MIMO/OFDM systems and compares its performance with the V-BLAST technique. In the proposed scheme, we apply a minimum mean square error (MMSE) filter only in the first iteration and utilize a matched filter (MF) in the second and later iterations to reduce computational complexity by suppressing residual interference in the first iteration. Computer simulation results confirm that the proposed ISIC can achieve almost equal performance to the MMSE-based ISIC with multiplications reduced by 85 % and outperforms the V-BLAST receiver by about 2 dB in four transmit and receive antennas systems under exponentially distributed twelve path conditions.

Forward-link power control utilizing neighboring-cell pilot power for DS-CDMA cellular systems

This paper proposes for DS-CDMA cellular systems a forward-link power control scheme utilizing neighboring-cell pilot power in order to improve the quality of forward traffic channels and to increase traffic capacity. In this scheme, each mobile station measures pilot powers received from neighboring cells. Transmission power of the forward traffic channel is then controlled by base stations according to the pilot powers measured at the respective mobile station, and uniform service quality is provided to all channels. Simulation results show that the proposed scheme reduces outage and forced termination probabilities with a pilot power error of 1.5 dB, and increases capacity for the forced termination probability of 1% by 5% and 60% in the case of soft handover and hard handover.

New MLSE receiver free from sample timing and input level controls

A new maximum likelihood sequence estimator (MLSE) receiver which is tolerant of both aberrations in sample timing and variations in amplitude is presented. In the proposed receiver, input signals are represented in polar coordinates, and fractionally sampled signals are fed to the MLSE. These two features make it possible to greatly reduce control mechanisms without performance degradation. The performance of the receiver is evaluated both in computer simulations and in experiments in US time division multiple access (TDMA) cellular environments, and it is shown that under conditions of 65-dB amplitude variations it successfully achieves less than 3% bit error rate (BER) without controlling either input level or sample timing.

Development of parallel type multi-stage interference canceller for W-CDMA

This paper describes a developed W-CDMA base station testbed with a practical multi-stage interference canceller, which is processed by high-speed digital signal processing cards. The multi-stage canceller features a parallel structure with a cancellation control factor, which can make the parallel cancelling operation stable. A laboratory experiment demonstrates that the developed interference canceller has a high cancelling capability and near-far resistance even when the interference (2 users) power is 9 dB higher than the desired user. The development and experiment proves that this multistage canceller is feasible and effective technology for W-CDMA performance enhancement.

Capacity evaluation of CDMA-AIC: CDMA cellular system with adaptive interference cancellation

Direct-sequence code-division multiple-access (DS/CDMA) systems have received considerable attention for future personal communication systems, because of their potential for large capacity, wide coverage and high quality services. This paper describes a CDMA cellular system based on adaptive interference cancellation (CDMA-AIC) with a large capacity. In the CDMA-AIC, each base station employs a single-user type adaptive interference canceller (AIC), which consists of a fractionally chip-spaced code-orthogonalizing filter (COF) and a differential detector. The AIC adaptively removes power dominant multiple access interferences (MAIs) in the cellular system, regardless of whether they are intra-cell interferences or inter-cell interferences, without any information about them, such as spreading codes, signal received timings and channel parameters. Evaluation under the multiple cell environment demonstrates that the reverse link capacity of the CDMA-AIC with QPSK modulation is fourfold or more, compared with the capacity of the CDMA without MAI cancellation. Further, the capacity is less sensitive to transmission power control errors than that of the conventional CDMA systems.

Multilevel codes for high-speed voiceband data modem

A novel class of multilevel codes is proposed for achieving high coding gain. Multilevel codes composed of two-level codes are investigated from the standpoint of the systematic design of codes. Two-level codes as component codes are shown to be preferable to a combination of conventional one-level codes in coding gain and decoder delay. For a 19.2 kb/s voiceband modem application, this scheme presents a class of coded modulation superior to trellis-coded modulation in simultaneous realization of high coding gain, low/moderate decoder complexity, and short decoding delay.<<ETX>>