Since space cooling accounts for some proportion of energy consumption in hot regions, including in the United States and Japan, energy-saving and demand response for space cooling are important, and interruption of air conditioner cooling may be one solution. In this paper, we propose a space-cooling scheduling control method using interruptions of an acceptable duration. The proposed method estimates the acceptable interruption duration based on survival analysis by treating air conditioner operations by occupants as an indicator of their thermal comfort. In the proposed method, use of the air conditioner is interrupted by turning it off (off mode) or switching it to fan mode. To evaluate the proposed method, we conducted a case study of an office in Japan during the summer. From the experimental results, we determined that acceptable interruption durations were 10 min for off mode and 20 min for fan mode. Use of fan mode in the proposed method may provide some energy-savings (9%), whereas use of off mode may increase the energy consumption compared with usual cooling because the interruption duration is so short that the energy consumed upon restarting cooling cannot be canceled out by the interruption.

We analyze decoupling structures of MIMO DS-CDMA channels with general multiuser detector front ends, using the replica method, in order to compare the space-time spreading (STS) and time spreading (TS) schemes. In the many- user limit, a MIMO DS-CDMA channel with the STS scheme is decoupled into a bank of single-user SIMO channels. On the other hand, a MIMO DS-CDMA channel with the TS scheme is decoupled into a bank of single-user MIMO channels. In view of performance, the STS scheme outperforms the TS scheme in the fast fading situation if transmit spatial correlations exist. In terms of complexity, the STS scheme does not require any space-time coding. On the other hand, the TS scheme does require space-time coding in order to achieve comparable performance to the STS scheme. The STS scheme improves the performance of communications and reduces the complexity of transmitter and receiver architectures.