Shousei Yoshida

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.

Multiuser space-time interference cancellation system for CDMA mobile communications

An efficient combination of a smart antenna and a multi-stage multiuser interference canceller is proposed for W-CDMA system enhancement. In the proposed advanced receiver, interference cancellation is carried out at the signal level before beamforming by regenerating a spread signal replica of each user signal with the inverse beamforming process. Computer simulation demonstrates that the proposed space-time processing enables one to achieve a joint capacity gain given by the smart antenna and multiuser detection.

QRM-MLD combined with MMSE-based multipath interference canceller for MIMO multiplexing in broadband DS-CDMA

This paper proposes maximum likelihood detection with QR decomposition and the M-algorithm (QRM-MLD) sophisticatedly combined with the multipath interference canceller (MPIC) based on multipath interference (MPI) replica generation exploiting two-dimensional minimum mean squared error (MMSE) for multiple-input multiple-output (MIMO) multiplexing in broadband DS-CDMA. Simulation results clarify that the proposed QRM-MLD coupled with MPIC exhibits excellent signal separation capability by sufficient MPI suppression effect through a three-stage MPIC comprising two-dimensional MMSE, followed by QRM-MLD associated with soft-decision Turbo decoding. We also show that the throughput values of 200,250, and 300 Mbps (corresponding frequency efficiency values are 5.0, 6.0, and 7.5 bits/sec/Hz, respectively) are achieved at the average received signal energy per bit-to-noise power spectrum density ratio (E/sub b// N/sub 0/) of approximately 6.0,9.5, and 13.0 dB by QPSK with the coding rate of R = 8/9, 8PSK with R = 3/4, and 8PSK with R = 8/9, respectively in 4-by-4 MIMO multiplexing, for broadband DS-CDMA assuming a 40-MHz bandwidth in a six-path Rayleigh fading channel with the maximum Doppler frequency of 20 Hz.

A digital coherent receiver suitable for land-mobile satellite communications

Describes an advanced coherent demodulation technique suitable for land-mobile satellite communications. The proposed technique features a combined narrow/wide band dual open loop (DOL) carrier phase estimator, which effectively enables the coherent receiver to track fast phase fluctuations caused by fading, without degradation in phase slip characteristics. Additionally, an open loop phase estimator has inherent quick recovery performance. Its bit error rate (BER) performance is shown to be superior to that for existing detection schemes, achieving a 10/sup -2/ BER at 6.3 dB E/sub b//N/sub 0/ (0.9 dB greater than the theoretical E/sub b//N/sub 0/ condition for perfect carrier phase tracking) for QPSK over a Rician fading channel with the 10 dB Rician factor and the 1/16 baud rate fading pitch. The paper also describes a quick bit timing recovery scheme, with interpolation, featuring an open loop structure. Further, it presents an experimental digital modem developed through the use of digital signal processors. >

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.

Performance evaluation of CDMA adaptive interference canceller with RAKE structure using developed testbed in multiuser and multipath fading environment

We describe the implementation of the proposed single user type CDMA adaptive interference canceller (AIC) with RAKE structure in a base station testbed, and evaluate its performance in the multiuser and multipath fading environment. Laboratory experiments demonstrate that the AIC receiver is much more near-far resistant than a conventional matched filter (MF) receiver in the multiuser case. When the power of the other users is 6 dB larger than that of the desired user, the AIC receiver can achieve a BER of 10/sup -3/ at C/PG=33.3% (eight users) in the 2-path fading channel, while the MF receiver cannot achieve the BER at C/PG of more than 20.8% (five users), it can achieve the BER at C/PG=33.3% in the equal power case. Furthermore, we evaluate the effect of transmission power reduction in a mobile station with transmission power control (TPC). Experimental results show that the required transmission power can be greatly reduced by 3.0 dB and 9.2 dB with the AIC receiver at C/PG=29.2% (seven users) and 33.3% (eight users), respectively.

A partial spectrum transmission method for dynamic spectrum access

This paper proposes a partial spectrum transmission (PST) method for dynamic spectrum access (DSA). For DSA, it is preferable to select modulation scheme which is appropriate for the low-priority users condition and radio environment by taking into account the required Eb/N0, frequency efficiency and PARR. When received SINR condition is better, QAM is selected for high-speed packet communication. However, QAM may cause link performance degradation due to the shorter Euclidean distance. On the other hand, PSK is capable of preventing such performance degradation. In this paper, we propose a PST method using PSK. It is shown by computer simulations that the required Eb/N0 at a BLER of 10-2 and the PAPR for the proposed PST (1/2) are approximately maximum 1dB better than those of 16QAM respectively.