Noboru Izuka

First-Ever Report on MBWA System Field Trial: Interference Issue in Sectored Cell Layout

This paper discusses results of a MBWA system field trial with fast low-latency access with seamless handoff orthogonal frequency division multiplexing (FLASH-OFDM). The results of the trial show that the downlink throughput performance is significantly impaired by inter-sector interference. To clarify the reasons of the impairment, we carry out a computer simulation on inter-sector interference reduction capability of frequency hopping orthogonal frequency division multiple access (FH-OFDMA), which is used as a multiple access scheme in FLASH-OFDM. The results are summarized as follows: (1) the interference reduction capability of FH-OFDMA is almost the same as that of direct sequence code division multiple access (DS-CDMA), which allocate the same frequency band to all sectors, and (2) in FH-OFDMA, a long hopping-pattern length yields no site diversity effect to reduce inter-sector interference. Additionally, a cumulative distribution of measured signal to noise and interference ratio (SNIR) shows that pilot signals in the neighboring sectors mainly impair the throughput performance. Since a sectored cell layout is mandatory for deployment of the MBWA systems in a high traffic area, inter-sector interference reduction is a key issue for these systems.

SCS-MC-CDMA system with best effort cell structure

This paper proposes SCS-MC-CDMA system with best effort cell structure. 4th generation mobile communication (4G) system is expected to offer 100 Mbps or higher data rate communication in the high-frequency microwave band. The system is characterized by relatively long delay paths, high maximum Doppler frequency, high power consumption at the mobile terminals and small cell coverage caused by the high data transmission rates and the high-frequency band. All of these are serious problems that must be solved. The proposed SCS-MC-CDMA system can realize high communication quality even under delay spreads as long as a few microseconds and maximum Doppler frequency as high as 1000 Hz. Channel estimation is accurate since code-multiplexed pilot symbols are used, and MMSEC is adopted to reduce inter-code interference. Concerning power consumption, the system can assign a number of sub-carriers, which may be narrower than the whole bandwidth of the system, to each user according to the users data rate requirements. This lowers the power consumption, especially for low data rate users such as voice users. Moreover, the best effort cell structure overcomes the small cell coverage issue by changing the maximum data rate for each user adoptively according to his distance from the base station or channel quality.

Measured downlink throughput performance of MBWA system in urban area

In this paper, we report on a mobile broadband wireless access(MBWA) system field trial with fast low-latency access with seamless handoff orthogonal frequency division multiplexing (FLASH-OFDM), which was carried out at Sendai city in Japan. This paper focuses on coverage and downlink throughput performance, which are the most important criteria for assessing wireless data communication systems. The field trial results show that the base-station can communicate to a subscriber at a cell edge with a throughput of 1.5 Mbit/s assuming circular cells of 0.4 km2, 0.6 km2, and 1.7 km2 when the sector antenna heights are 19 m, 58 m, and 84 m, respectively. Therefore, it is considered that the MBWA system is suitable to provide a broadband mobile data communication service to subscribers in an urban area.

Uplink throughput performance of FH-OFDMA improved by 16 QAM: Effect estimation and validation in MBWA system field trial

In this paper, we report on a mobile broadband wireless access (MBWA) system field trial with Fast Low-latency Access with Seamless Handoff Orthogonal Frequency Division Multiplexing (FLASH-OFDM), which was carried out at Sendai city in Japan. In this paper, the uplink throughput improvement effect of 16 quadrature amplitude modulation (QAM) is estimated by using the measured throughput and received signal level of quadrature phase shift keying (QPSK). The estimation results show that 16 QAM yields a higher uplink throughput than QPSK within coverage of 700 m when the base-station antenna height is 58 m. The results are validated by evaluating the uplink throughput performance of 16 QAM measured in the field trial. We consider that 16 QAM is useful to provide a mobile broadband data communication service to subscribers in uplink as well as downlink.

A proposal of sub-carrier selecting MC-CDMA system for 4G systems

Expectations are growing that the forthcoming 4th generation mobile communication systems will offer transmission data rates as high as 100Mbps or more. Because of the wide bandwidth transmission needed and the expected use of the high- frequency microwave band, the following issues are seen as barriers to the development of 4G systems; (1) high power consumption of mobile terminals, (2) small cell coverage area, and (3) high Doppler frequency. As a solution, we propose the Sub-Carrier Selecting MC-CDMA system. The proposed system is based on MC-CDMA, which is a combination of OFDM and CDMA. We add three features to MC-CDMA technology to resolve the above issues: (1) sub-carrier selection, (2) best-effort cell structure, and (3) MMSE combining. We detail the proposed system and demonstrate that it works well through computer simulations.

Channel construction in SCS-MC-CDMA system

This paper promises a chip-by-chip channel estimation method for time domain spreading MC-CDMA systems to allow the use of MMSEC. MMSEC effectively compensates the loss of orthogonality among spreading codes, so that we can realize high communication quality even in very fast fading environments. Moreover, the chip-by-chip channel estimation method makes it possible to freely select the time domain or frequency domain as the spreading domain of data symbols.

Coverage Estimation of Uplink 16 QAM Signal up to 20 MHz Bandwidth Based on Field Trial Results of FH-OFDMA System

In this paper, we report on a mobile broadband wireless access (MBWA) system field trial with Fast Low-latency Access with Seamless Handoff Orthogonal Frequency Division Multiplexing (FLASH-OFDM), which was carried out at Sendai city in Japan. This paper describes coverage estimates of an uplink 16 quadrature amplitude modulation (QAM) signal under the condition of constant terminal output power when the bandwidths are from 2.56 MHz to 20.48 MHz. The estimates are based on the field trial results of 1.28 MHz bandwidth. The results show that wider bandwidth yields narrower coverage area. 16 QAM can be used within 55 %, 45 %, 35 %, and 25 % of the field trial area when the signal bandwidths are 2.56 MHz, 5.12 MHz, 10.24 MHz, and 20.48 MHz, respectively. We consider that 16 QAM is useful even if the signal bandwidth is wider than that 10 MHz.

Investigation on single-carrier and multi-carrier hybrid system for uplink

Multi-carrier (MC) transmission is attractive in next-generation mobile communication systems because of yielding high data rate and robustness against frequency-selective fading. An issue of the MC signal is high peak power. The MC signal is not effective for long distance transmission since longer distance requires higher output power. On the other hand, single-carrier (SC) transmission is effective for keeping a wide coverage area because of low peak power. To obtain both the merits of MC and SC, we consider a hybrid method that uses SC or MC. In this paper, an issue of the SC/MC hybrid system is discussed. We estimate an effect of carrier frequency offset on bit error rate (BER) performance by using computer simulation. The results show that SC is more sensitive to frequency offset than MC. To mitigate effects of the frequency offset, we propose an interference reduction method that removes head and tail symbols of block in the SC transmission. The simulated results show that the proposed method significantly improves the BER performance, and is effective to realize the SC/MC hybrid system.

Hybrid single-carrier and multi-carrier system: Improving uplink throughput with optimally switching modulation

We have already proposed a hybrid single-carrier (SC) and multi-carrier (MC) system for next-generation mobile communication system. A SC signal has low peak-to-average power ratio (PAPR), which yields high power output for wide coverage. A MC signal is robust against frequency-selective fading and has high data rate with quadrature amplitude modulation (QAM). By appropriately selecting SC and MC signals, both high data rate and wide coverage system were attained in the proposed hybrid system. In this paper, uplink throughput of the proposed hybrid system was calculated using a computer simulation. Simulation results showed that the proposed system attained 20% higher throughput than conventional SC frequency division multiple access (FDMA) systems when the distance between the base station and a mobile station was 100 m. The proposed hybrid system also attained 52% wider coverage than conventional orthogonal frequency division multiple access (OFDMA) systems when throughput was 0.5 bit/s/Hz.

Peak power reduction in SCS-MC-CDM system

The paper proposes a method that reduces the peak power in an SCS-MC-CDM (sub-carrier selecting multi-carrier code division multiplex) system with time domain spreading. In the proposed method, the transmitter can reduce its peak power by optimizing each sub-carriers phase. The method requires significantly fewer weighting factor multiplications to optimize the phase than the PTS (partial transmit sequences) method. The receiver requires no side information to regenerate the original signal. A computer simulation was carried out to estimate the proposed methods performance. The simulation results show that the proposed method reduces the number of weighting factor multiplications to 0.002% of that required in the PTS method when the proposed method yields almost the same peak power as the PTS method.