We describe a DS-CDMA adaptive modulation system in which high-rate-data for moving pictures and LANs is transmitted to a high-speed traveling mobile terminal in the down-link. The transmission data rate is constant by changing the data-modulation level and the number of multiplex channels. We use computer simulation to evaluate the performance of the system using a RAKE receiver in a multipath-channel environment. For fdTslot 0.08, which is fading maximum Doppler frequency fd normalized by slot time Tslot, the following results are obtained. The average bit error rate (BER) of BER 1 10-3 necessary to ensure quality of high-rate-data transmission for moving pictures and LANs without error correction is attainable at low symbol-to-noise power ratio of ES/N0 14 dB and channel-use rate lower than 65%. The cell capacity of 17.2% is about 1.4 times that of the conventional system. Also, fdTslot=0.08 corresponds to the traveling speed of about 250 km/h at a carrier frequency of 8 GHz. Thus, the system enables high-rate-data and high-quality transmission needed for the moving pictures and LANs at mobile terminals with a traveling speed higher than 100 km/h at high carrier frequencies of the microwave band.

This paper gives laboratory as well as the results of field experiment and describes the implementation of a system developed to evaluate and demonstrate multimedia multimode time division multiple access (MTDMA). The equipment has been developed with the radio transmission technology for future public land mobile telecommunication systems (FPLMTS/IMT-2000) in mind. To meet FPLMTS/IMT-2000 requirements the system employs the following techniques: a hybrid multiplex modulation system consisting of quadrature phase shift keying (QPSK) and 16-ary quadrature amplitude modulation (16QAM), a high data transmission bit rate of 2 Mbit/sec for QPSK, 4 Mbit/sec for 16QAM, and diversity combining and adaptive equalization technique. For the diversity adaptive equalization technique, we used a decision feedback equalizer (DFE) consisting of one feedback (FB) transversal filter and two feed-forward transversal (FF) filters. The output signals from two branches of space diversity reception antennas are then fed to the two FF filters of the DFE. For middle-speed mobile radio communication for a micro-cellular pedestrian environment, a QPSK modulation system is selected to obtain wide coverage, while for a pico-cellular indoor office environment, the delay spread is small, and a 16QAM modulation system is selected to achieve a high bit rate. The results given here of laboratory and field experiments show the technical feasibility of MTDMA for future public land mobile telecommunication systems.

A slow frequency-hopping/16-ary quadrature amplitude modulation (slow-FH/16QAM) system based on time-division-multiple-access (TDMA) is appropriate for third-generation land mobile cellular communications because of its high immunity to interference. The system uses 16QAM for high spectral efficiency and slow-FH and forward-error-correction (FEC) for high-quality transmission. To reduce sensitivity to interference, the system uses an improved decoding scheme based on a minimum Euclidean-distance which is effective when the interference level is dispersed by FH. The bit error rate (BER) of the system due to interference has been evaluated in a previous study, both theoretically and by computer simulation. Although computer-simulated results showed that the system improved the BER, the hardware feasibility was not considered. This paper presents a hardware implementation of the system and the results of experimental transmission using equipment we developed to verify the system and to confirm the BER performance. The laboratory experimental results indicated that the system could provide high-quality transmission over a channel that has frequency-selective fading and co-channel interference. This system provided an Eb/N0 of 9 dB with space diversity and one of 15 dB without it, when BER=10-3 and fd=120 Hz. Field experiments were also conducted in a suburban area of Tokyo to demonstrate the BER performance. The results meant that the system could lower sensitivity to vehicle velocity more than a system without FH and that the BER performance of the system was improved notably against that of a system without FH, especially at low vehicle velocity.