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IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences 2005 E88-A(7):1889-1896; doi:10.1093/ietfec/e88-a.7.1889
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Copyright © 2005 The Institute of Electronics, Information and Communication Engineers

Special Section on Multi-dimensional Mobile Information Networks -- Papers -- Wireless Communication Technology

Adaptive Subcarrier Block Modulation with Differentially Modulated Pilot Symbol Assistance for Downlink OFDM Using Uplink Delay Spread

Chang-Jun AHN1, Satoshi TAKAHASHI1,3, Hiroshi HARADA1, Yukiyoshi KAMIO1 and Iwao SASASE2

1 The authors are with The National Institute of Information and Communication Technology (NICT), Incorporated Administrative Agency, Yokosuka-shi, 239-0847 Japan. E-mail: junny700{at}nict.go.jp, 2 The author is with the Department of Information and Computer Science, Keio University, Yokohama-shi, 223-8522 Japan., 3 Presently, with the Department of Computer Engineering, Hiroshima City University, Japan.

In AMS/OFDM systems, base station is in control of the modulation level of each subcarrier, and then, adaptive modulated packet is transmitted from the base station to the mobile station. In this case, the mobile station is required the modulation level information (MLI) to demodulate the received packet. The MLI is generally transmitted as a data symbol, therefore, the throughput is degraded. In an OFDM, the channel response at a particular subcarrier frequency is not supposed to be totally different from its neighboring frequencies, and hence, they must have correlation which depends on the coherence bandwidth of the channel Bc. If we could assign the same modulation level for coherently faded subcarrier block, MLI is required only one time for each subcarrier block. Moreover, we can assign the data on the empty space of pilot signals for increasing the total transmission. In this paper, we propose an adaptive subcarrier block modulation with differentially modulated pilot symbol assistance for downlink OFDM using uplink delay spread.

Key Words: DMPSA-ASMS/OFDM, MLI, coherence bandwidth, RMS delay spread

Manuscript received October 28, 2004. Manuscript revised January 20, 2005. Final manuscript received February 16, 2005.


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