Katsuhiko Hiramatsu

Performance Enhancement of E-UTRA Uplink Control Channel in Fast Fading Environments

Hybrid automatic repeat request (HARQ) is employed for the 3GPP Evolved Universal Terrestrial Radio Access (E-UTRA) downlink. Each user equipment (UE) sends its ACK/NACK corresponding to the downlink data reception to the base station via a physical uplink control channel (PUCCH). The ACK/NACK signals from the UE are first code spread by the cyclic shift sequences, and then spread by the orthogonal cover sequences. The ACK/NACK signals from each UE are multiplexed by means of code division multiple access (CDMA), however, it is difficult for the conventional PUCCH code design to satisfy the required bit error rate (BER) of 10 3 in fast- fading environments because of inter-code interferences among the orthogonal cover sequences. In this paper, we propose a novel PUCCH code design which can suppress the effect of inter-code interferences among the orthogonal cover sequences. And the simulation evaluations confirm that the proposed code design can significantly improve the performance of the ACK/NACK signals via PUCCH especially in fast-fading environments.

Technology evolutions in LTE/LTE-advanced and its applications

This paper presents key techniques in Long-Term Evolution (LTE) and LTE-Advanced as well as its potential applications. LTE supports peak rates up to 300 Mbps in downlink (DL) and 75 Mbps in uplink (UL), whereas LTE-Advanced would support 1.2 Gbps in DL and 600 Mbps in UL [1]. Since both peak and average throughput are dramatically improved compared to High-Speed Packet Access (HSPA) [2], LTE and LTE-Advanced would enable new applications such as real-time high-definition (HD) video sharing services, which provide new user experiences in wireless communications.

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.

A Study on Link Adaptation Scheme with Multiple Code Words for Spectral Efficiency Improvement on OFDM-MIMO Systems

In this paper, we propose the stream multiplexing scheme to achieve the high spectral efficiency on OFDM-MIMO system considering (a) the effects of the inter-stream interference suppression techniques, (b) the influence of the quality measurement in the receiver to select the modulation and coding scheme (MCS) and (c) the influence of the signaling overheads to the spectral efficiency. Two kinds of schemes for stream multiplexing, namely Multiple CodeWord (MCW) and Single CodeWord (SCW) are investigated and compared. In the simulations, we assume real channel estimation for SINR measurement for MCS selection and we compare the schemes with the spectral efficiency taking into account overheads. In consequence, it is presented that MCW can achieve the higher efficiency than SCW in the middle to high SINR region. Moreover, in 4 × 4 antenna configuration, a 2CW-MCW scheme where 2 codewords mapped onto 4 streams according to SINR of each streams is proposed. The scheme gives higher throughput by improving the MCS selection in the low SINR region due to increase of data length per a codeword and by reducing the signaling overhead due to the decrease of the number of codewords. As a result, the proposed scheme achieves spectral efficiency improvement in whole SINR region.

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.