This paper gives field experimental results on 16-ary quadrature amplitude modulation/time division multiple access (16QAM/TDMA) and trellis coded 16QAM/TDMA systems for land mobile communications in order to evaluate its capability of achieving large capacity and high quality data transmission. Pilot symbol aided space diversity and symbol timing synchronization based on maximum likelihood (ML) estimation are applied to both 16QAM/TDMA and trellis coded 16QAM/TDMA to improve transmission quality. For the trellis coded 16QAM/TDMA, trellis coding with Viterbi decoding and 2-frame symbol interleaving are further employed. The field experiments were conducted in the Tokyo metropolitan area of Japan. The results show that 16QAM/TDMA and trellis coded 16QAM/TDMA are practical modulation/access schemes for land mobile communication systems.

Comparative performance evaluation between parallel combinatory CDMA (PC-CDMA) and Direct Sequence CDMA (DS-CDMA) has been conducted for high speed radio communication up to 2 Mbps under a multipath Rayleigh fading environment. For both DS-CDMA and PC-CDMA, user information rate per code of 128 kbps, convolutional code with 1/2 coding rate, the same bit interleaving and QPSK data modulation are applied to get transmission symbol rate of 128 ksps. The chip rate of 4. 096 Mcps is used to investigate the possibility of 2 Mbps transmission using only 5 MHz bandwidth. So the spreading factor of the spreading code is 32 for DS-CDMA. In PC-CDMA, 128 ksps data stream is divided into four 32 ksps data streams and according to the every four bits pattern, corresponding spreading code of spreading factor of 128 and its polarity are selected out of eight candidate spreading codes. In soft decision Viterbi decoding applied to PC-CDMA, branch metric is calculated for every bit by weighting the output levels of the PC-CDMA correlators for eight candidate spreading codes. By computer simulation under vehicular environment model with six multipaths, it has been shown that PC-CDMA can offer more capacity approximately by double than DS-CDMA for both downlink and uplink under the condition such as for vehicular for BER of 10-3, and 2 Mbps transmission per cell for downlink is possible not only in isolated cell condition but also in omni cell condition by PC-CDMA.

In this paper, we study and propose an inter-cell co-channel interference (CCI) mitigation method for pilot signals using cyclic shift Zadoff-Chu (CS-ZC) sequences for SC-FDMA-based uplink without tight scheduler coordination among cells. Firstly, we investigate the issue of severe detection performance degradation created by the lack of orthogonality among the pilot signals without alignment of the allocated frequency resource positions among cells when using the conventional CS-ZC sequences generation scheme. Secondly, we identify the primary factor causing the issue. Thirdly, we propose a frequency-dependent CS-ZC sequence generation scheme by allocating the same spectrum elements of the ZC sequence to the overlapped subcarriers among cells to mitigate the inter-cell CCI of the pilot signals without alignment of the frequency resource positions among cells. Finally, we confirm the validity of the proposal using uplink data BLER evaluation under a multipath fading condition by computer simulation compared to the conventional method, and show that the proposal achieves around 0.9 dB and 0.6 dB better performance at 10% BLER than the conventional method for 1 RB and 2 RBs frequency offsets in 3 RBs transmission bandwidth, respectively.

We previously proposed a next generation cellular system for IMT-2000 based on the Wideband DS-CDMA with TDD scheme (W-CDMA/TDD) and have evaluated its performance by computer simulation, laboratory and field experiment. With the W-CDMA/TDD, because of its correlation between the downlink and the uplink, transmission and reception space diversity (SD) at a base station and open-loop transmit power control (TPC) can be simply realized. This paper reports performance of laboratory and field experiments using a developed testbed. The results shows it has been confirmed that transmission and reception SD and open-loop TPC have sufficient performance under a field environment as well as laboratory environment.

In this paper, we propose the stream multiplexing scheme to achieve the high spectral efficiency on OFDM-MIMO system considering (a) the effects of the inter-stream interference suppression techniques, (b) the influence of the quality measurement in the receiver to select the modulation and coding scheme (MCS) and (c) the influence of the signaling overheads to the spectral efficiency. Two kinds of schemes for stream multiplexing, namely Multiple CodeWord (MCW) and Single CodeWord (SCW) are investigated and compared. In the simulations, we assume real channel estimation for SINR measurement for MCS selection and we compare the schemes with the spectral efficiency taking into account overheads. In consequence, it is presented that MCW can achieve the higher efficiency than SCW in the middle to high SINR region. Moreover, in 44 antenna configuration, a 2CW-MCW scheme where 2 codewords mapped onto 4 streams according to SINR of each streams is proposed. The scheme gives higher throughput by improving the MCS selection in the low SINR region due to increase of data length per a codeword and by reducing the signaling overhead due to the decrease of the number of codewords. As a result, the proposed scheme achieves spectral efficiency improvement in whole SINR region.

We propose a soft decision Viterbi decoding scheme and a self-interference cancellation method applicable to a Parallel Combinatory CDMA (PC-CDMA) system. In this decoding scheme, branch metric is calculated for every bit by weighting the output levels of the PC-CDMA correlators so as to enable an effective soft decision capability to the system. The effectivity of this scheme is then further enhanced by the use of a simple pseudo-random bit interleaving scheme. Moreover, to increase the capacity of the PC-CDMA system, we propose a simple self-interference cancellation method for self-induced cross-correlation arising from the multipath environment. This further enhances the efficacy of the decoding scheme because the false contributions of the self-induced cross-correlation component are removed from the branch metric prior to soft decision Viterbi decoding. Finally, we simulated a possible PC-CDMA system with a user data rate of 1.92Mbps, transmitting it at a chip rate of 3.84Mcps and at 7.68Mcps under a multipath-Rayleigh fading interference environment. For a chip rate of 7.68Mcps, BER after Viterbi decoding is less than 3.2e-7 even without the use of interference cancellation. For a chip rate of 3.84Mcps, BER after Viterbi decoding with interference cancellation is 1.0e-4.

We previously proposed a next generation cellular system for IMT-2000 based on wideband DS-CDMA with TDD scheme and have evaluated its performance by computer simulation, laboratory and field experiments. This paper presents the design concept of TDD-mode operation on wideband DS-CDMA systems. These systems employ almost the same techniques with a little difference as FDD-mode. We also present the schemes of the TDD-mode specific techniques such as fast cell search, transmission diversity and transmitter power control and show the evaluation results of them are effective. Performance can be improved by use of enhanced techniques such as interference cancellation and adaptive antenna array diversity.

The Future Public Land Mobile Telecommunication Systems (FPLMTS) standards have made it quite clear that in the near future, the capability in doing wireless data transmission will become necessary in order to make the tether-free use of multimedia applications possible. CDMA is considered the most appropriate and probable radio access method of FPLMTS for its high capacity and flexibility in accommodation of multimedia and variable rate users. In order to further increase the capacity of CDMA system, several techniques have been studied and proposed such as an interference canceller and adaptive array antenna. We propose the novel multi-user detection type interference cancellation technique named SRIC (Symbol Ranking type IC) in this paper. SRIC is very feasible for its small amount of operation compared with other multi-user detection type ICs and can be added to a base station with slight alteration according to the requirement of higher capacity. The performance of SRIC depends on the method of calculating the likelihood. We studied three methods. In order to reduce the operations, we tried to propose two more methods. We confirmed that SRIC can make the system capacity about three times greater than that of a conventional RAKE receiver. We also confirmed that SRIC can be reduce its operations very much at some sacrifice of their performance. There are nine variants of SRIC, which have a trade off between performance and amount of operation. We can choose one of them which is most fit to our requirement. The first operation of SRIC is common with that of a conventional RAKE receiver. Therefore, SRIC can be introduced to conventional systems afterwards by inserting the interference canceller block which functions replica generation, removal, and ranking between output of a RAKE receiver and FEC decoder.