Kazuyuki Miya

CDMA/TDD cellular systems for the 3rd generation mobile communication

We propose CDMA/TDD cellular systems utilizing a base-station-based diversity scheme. A significant reduction in the required Eb/No resulting from the use of a hybrid diversity scheme combining the effects of space diversity and path diversity is shown. Because TDD uses only one radio frequency band and transmission diversity at the base station can be employed, space diversity is unnecessary at the mobile station and thus the mobile station can be made smaller. CDMA/TDD systems can also realize effective transmission power control with only the use of open-loop control. A single antenna and no duplexer are advantageous in CDMA/TDD for terminal size and battery life. This system is especially effective in an environment such as microcellular systems or indoor office systems where the spreading bandwidth is narrower than the coherent bandwidth, and path diversity gain by itself is small.

CDMA/TDD cellular systems utilizing a base-station-based diversity scheme

Presents a base-station-based transmission/reception diversity scheme for CDMA/TDD systems. In the paper, a significant reduction in the BER resulting from the use of a hybrid diversity scheme combining the effects of space diversity and path diversity is shown. By using transmission space diversity at the base station for the forward link, the transmission signal of a base station intended for a mobile station will always be transmitted in the best possible path, while the transmission signals from this same base station intended for other mobile stations will not always be transmitted in this same path. This scheme thus effectively improves the CIR at a mobile station. This scheme shows promise for applications in an environment when path diversity gain is not sufficient, for example, micro-cellular systems or indoor systems, without reception space diversity at a mobile station.

Design of error correction methods using redundancy of speech coder data

Error correction methods which provide higher speech quality on channels of poor quality in digital mobile communications are presented. Conventionally, to mitigate the degradation of speech quality, the parameters which are more sensitive to channel errors are protected by more powerful channel codes. In that respect, source coding and channel coding are integrated. To expedite the integration of source coding and channel coding, the method to improve the error correction performance of convolutional code for its middle position in the trellis and the method to use redundancy of speech coder data such as correlation of frame energy or pitch predictor lag between consecutive frames are presented and evaluated. The results obtained indicate that the presented error correction methods are efficient for redundant source information such as voice signals.<<ETX>>

Transmit diversity applied on the CDMA/TDD cellular systems

This paper shows that the result of cell search and open loop transmit divesty of CDMA/TDD. The TSTD type transmit diversity for the physical synchronisation channel (PSCH) can shorten the cell search time of user equipment (UE) at low Doppler frequency. The block STTD type transmit diversity for the primary common control channel (P-CCPCH) can improve the BER performance around 3 dB compared with a single antenna transmission. Furthermore the authors propose open loop type sector/cell selection handover. The improvement by using this scheme, as compared to hard handover, is almost 2 dB for between sectors and 1.1 dB to 1.6 dB for between cells, depending on the Doppler frequency. The change for the switching rate into 10 ms makes the gain of 0.8 dB at f/sub D/=53 Hz and 1.7 dB at f/sub D/=222 Hz, respectively.

Pilot signal generation scheme using frequency dependent cyclic shift sequence for inter-cell interference mitigation

Cyclic Shifted Zadoff-Chu (CS-ZC) sequences are adopted as a uplink pilot signal in Evolved Universal Terrestrial Radio Access (E-UTRA). In a Single Carrier Frequency Division Multiplexing Access (SC-FDMA) based cellular system, the Resource Blocks (RBs) are normally assigned independently among the cells. So, the assigned RBs to user equipment (UE) in different cells may partially overlap. These causes deteriorate the orthogonality between CS-ZC sequences. The deterioration of the orthogonality results in significant loss of channel estimation accuracy. The reason of the deterioration is that the different spectrum element of CS-ZC sequence is assigned at overlapped sub-carriers between cells. Therefore, we propose a frequency dependent cyclic shift sequence, which assigns the same spectrum element of CS-ZC sequence at overlapped sub-carriers between cells. Simulation results show that the proposed scheme can improve the BLER performance by 4dB with keeping the low Peak-to-Average power ratio (PAPR) property compared to the conventional scheme.