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IEICE Transactions on Communications 2006 E89-B(2):500-508; doi:10.1093/ietcom/e89-b.2.500
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Copyright © 2006 The Institute of Electronics, Information and Communication Engineers

Regular Section -- Papers -- Wireless Communication Technologies

Superimposed Frequency Symbol Based Adaptive Downlink OFDM with Frequency Spreading and Equalization

Chang-Jun AHN1, Hiroshi HARADA1 and Yukiyoshi KAMIO1

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

In AMS/OFDM systems, a base station controls the modulation level of each subcarrier with feedback information (FBI), and then, adaptive modulated packets are transmitted from the base station to the mobile station. In this case, the mobile station requires modulation level information (MLI) to demodulate the received packet. The MLI is generally transmitted as a data symbol, so the throughput is degraded. To overcome this problem and increase the total throughput, in this paper, we propose superimposed frequency symbol based adaptive OFDM with frequency spreading and equalization. In the proposed system, each S/P transformed signal is spread by orthogonal spreading codes and combined. This means that each subcarrier holds several superimposed S/P transformed signals with the same power rate. In this case, the frequency-selective faded subcarriers obtain the same power rate for each S/P transformed signal. Therefore, the detected signals also obtain the same SINR, and as a result, we can assign the same modulation level for each frequency symbol spreading block. Hence, the proposed system requires only one piece of FBI and MLI for each frequency symbol spreading block, as compared with conventional adaptive OFDM.

Key Words: AMS/OFDM, frequency symbol spreading, frequency equalization, MMSEC, ORC

Manuscript received April 28, 2005. Manuscript revised August 17, 2005.


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N.-S. KIM, S. CHO, and C.-J. AHN
Subcarrier Block Power Control for Adaptive Downlink OFDM with Frequency Spreading and Equalization
IEICE Trans B: Communications, July 1, 2006; E89-B(7): 2102 - 2105.
[Abstract] [PDF]


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