Yoshihiko Asano

High-rate OFDM codes for peak envelope power reduction and error correction in MQAM systems

We describe a new coding technique that reduces the peak envelope power ratio (PEPR) and corrects errors in MQAM-OFDM systems. By introducing M-ary phase-shift-keying (MPSK) partitioning, we explain the design of hybrid codes having these two properties for MQAM-OFDM. Our technique is simply based on the phase difference between subset carriers and reduces, with very low redundancy, the PEPR of OFDM signals by means of the frequency-domain interleaving of code subsets. By using the MQAM-OFDM signal model, including the amplitude/phase error due to MPSK partitioning, our theoretical analysis of the PEPR performance gives tight upper bounds for any modulation scheme. We also discuss the trade-off between the PEPR reduction and the coding rate when the code length is expanded.

Performance analysis of simple transversal-filter-based multipath interference canceller with analytically derived tap coefficients for reverse link of multicarrier DS-CDMA systems

We analyze the performance of a simple multipath interference canceller consisting of a transversal filter connected in series with a RAKE receiver. We apply this receiver structure to the reverse link of multicarrier DS-CDMA systems and derive simultaneous equations that determine exact tap coefficients of the filter. The filter with the exact tap coefficients purifies the channel impulse response. The superior performance of the system is shown by numerical calculation. This MPI canceller will improve the bit error performance with small additions of circuitry and power consumption in single-and multiple-carrier DS-CDMA systems.

Simple retractable monopole antenna with small mismatch loss and high radiation efficiency for cellular portable phones

We studied a simple retractable monopole antenna for cellular portable phones using computational and experimental analysis. This antenna configuration uses an antenna element, consisting of a straight conducting wire in both the extended and retracted positions, by changing the feed point on the element. We found that the optimization of some parameters, such as the element length and the feed point, enable the input impedance of the retracted position to be adjusted to that of the extended position. This characteristic guarantees a low mismatch loss in both the extended and retracted positions. We also discuss the effect of the terminal height and the gap width between the element and the terminal. The numerical simulations and experiments using a simplified model prove that this antenna configuration has an excellent return loss characteristic above 20 dB, even in the retracted position, and that also it has a high efficiency of 85% in the extended position including the matching circuit loss. Since this antenna configuration also provides a spatially efficient and mechanically durable structure, we used it in a cellular portable phone.