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 coherent 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 3.6 times as large as 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.

In this paper, we briefly describe the proposed radio access scheme based on CDMA/FDD for next-generation mobile radio systems, and evaluate its performance through laboratory and field experiments on transmission power control (TPC) and diversity, which are the key technologies to achieve efficient CDMA systems. The design of the practical TPC method is discussed, and a robust method is presented for operation in low signal to interference power ratio (SIR). Laboratory experiments demonstrate that space and path diversity effectively improve the TPC performance in the Doppler frequency range of 40 to 80 Hz, and reduces the required Eb/N0 to achieve the BER of 10-3. The necessary diversity order for multipath fading mitigation in all the Doppler frequency range is also investigated. Through the field experiments in urban area of Tokyo using a developed system at 0. 96 Mcps, a low required Eb/N0 of 2. 8 dB can be obtained because of the effectiveness of the diversity.

This paper gives an overview of Turbo codes principles, performance, and design issues for practical application. As fundamentals of Turbo codes, encoder structure, interleaver, and iterative decoding are explained. The performance is analyzed through their weight distribution, and the analysis gives code design rules for component codes. Practical decoding algorithms are presented in addition to MAP algorithm. Design issues are discussed for mobile communications as an example of practical application. Finally, research trends are briefly mentioned.

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 (Eb/N0) 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 Eb/N0 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.

In this paper, we describe the implementation of the proposed single user type CDMA adaptive interference canceller (AIC) with RAKE structure in the developed testbed for the base station, and evaluate its performance in the multiuser and multipath fading environment. Laboratory experiment demonstrates that the AIC receiver is much more near-far resistant than the 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 the BER of 10-3 at C/PG = 33. 3 % in the 2-path fading channel, while the MF receiver cannot achieve the BER at C/PG of more than 20. 8%. Furthermore, we evaluate the effect of transmission power reduction in the transmitter with transmission power control (TPC). The experimental result shows 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 % and 33. 3%, respectively.

This paper presents an adaptive MLSE (Maximum Likelihood Sequence Estimator) suitable for TDMA cellular systems. The proposed MLSE has two special features such as handling wide dynamic range signals without analogue gain controls and fast channel tracking capability. In order to handle wide dynamic range signals without conventional AGCs (Automatic Gain Controller), the proposed MLSE uses envelope components of received signals obtained from a non-linear log-amplifier module which has wide log-linear gain characteristics. By using digital signal processing technique, the log-converted envelope components are normalized and converted to linear values which conventional adaptive MLSEs can handle. As a channel tracking algorithm of the channel estimator, the proposed MLSE adopts a QT-LMS (Quick-Tracking Least Mean Square) algorithm, which is obtained by modifying LMS algorithm to enable a faster tracking capability. The algorithm has a fast tracking capability with low complexity and is suitable for implementation in a fixed-point digital signal processor. The performances of the MLSE have been evaluated through experiments in TDMA cellular environments with π/4-shifted QPSK, 24.3k symbol/sec. It is shown that, under conditions of 65dB amplitude variations and 80Hz Doppler frequency, the MLSE successfully achieves less than 3% B.E.R., which is required for digital cellular systems.