Showing papers by "Hiroshi Harada published in 2005"

Communicating system, communicating method, and base station

Abstract: A communication system, a communicating method and a base station are provided. When a base station generates an FCM, the base station detects the use rate of a transmission buffer and decides how slots of a frame of an uplink channel are structured. When the use rate of the transmission buffer is high, the base station designates the number of ACTSs to 0 so that the base station does not accept registration requests and so forth from mobile stations. When the use rate of the transmission buffer is low, the base station designates the number of ACTSs to 1. When the number of mobile stations is large as in a large convention hall, the base station generates TDMA frames each of which has only ACTSs. The base station can decide the number of ATCSs corresponding to the probability of which registration requests and so forth from mobile stations collide.

An OFDM Based Adaptive Modulation Scheme Employing Variable Coding Rate

Abstract: This paper proposes an OFDM based adaptive modulation scheme employing variable coding rate (VCR OFDM AMS), which selects optimum modulation and coding scheme (MCS) realized by combination of several modulation schemes and coding rates. The OFDM AMS with multilevel transmit power control (OFDM AMS/MTPC) can realize high data rate transmission in the dynamic parameter controlled-orthogonal frequency and time division multiple access (DPC-OF/TDMA). The employment of OFDM AMS/MTPC, however, makes transceiver design rather complex. To solve this problem, we propose to improve throughput performances of the OFDM AMS without employment of the MTPC. The simple OFDM AMS, however, does not fully utilize transmit power for throughput improvement because there is surplus transmit power which corresponds to power margin over required signal to interference plus noise power ratio (SINR). Thus, in order to improve transmit power efficiency for throughput increase, we reduce the required SINR gaps between adjacent MCSs by introducing many coding rates. Furthermore, this paper presents an effective bit loading algorithm when multiple coding rates as well as modulation schemes are used. Computer simulation confirms that the proposed VCR OFDM AMS gives sufficient throughput performances as an alternative to the OFDM AMS/MTPC.

A Channel Estimation Technique for Dynamic Parameter Controlled - OF/TDMA Systems

Abstract: This paper proposes a channel estimation technique for the dynamic parameter controlled - orthogonal frequency and time division multiple access (DPC-OF/TDMA) system. In the proposed scheme, channel impulse response that represents channel state information (CSI) is measured using a carrier interferometry (CI) which is equivalent to impulse transmission. Moreover, because the minimum unit (subchannel block) of subcarriers to be allocated to each terminal is 64 subcarriers, to achieve high accuracy of the estimated CSI with a spreading factor of 64, code-multiplexed pilot signal is applied to identify base station (BS) in the cell search process, and CSI between a terminal and each transmit antenna element in the BS is detected using a time-domain-multiplexed CI signal for ease of extension of the DPC-OF/TDMA to multi-input multi-output (MIMO) systems. Furthermore, we will also propose a CSI estimation scheme flexible to the plural subchannel block assignment cases. Computer simulation confirms that the proposed scheme can estimate the CSI regardless of the number of subchannel blocks assigned to each terminal

Enhancement of MLD for SDM/OFDM using power imbalance of polarization and pre-phase distortion scheme

Abstract: SDM/OFDM systems transmit different data using the same frequency, so it is necessary to reduce the co-channel interference for separating the simultaneously received signals. Previous studies have shown that the maximum likelihood detection (MLD) has the best BER performance. However, if the received powers of the desired symbols from different antennas are nearly the same, MLD shows poor detection property, since almost the same replicas may generate, even if the combination of the transmitted symbols are different. For enhancement of a MLD of SDM/OFDM, in this paper, we focus on a power imbalance of polarization and the pre-phase distortion scheme to diminish the same power and phase occurrence probability of the received signals.

Receiver, receiving method, program, and information recording medium

Abstract: When a receiver (200) receives a signal transmitted from a transmitter, an A/D converter (204) coverts the signal into a digital signal having two or more levels by A/D conversion. A zero level detector (207) converts the signal into a two-level digital signal of positive and negative levels. The converted signals are subjected to spectrum despreading by correlators (206, 208), and the signal having higher intensity is selected by absolute value detectors (209, 210), a comparator (211), and a switch (212). A decoder (213) decodes the selected signal. In a receiving state where the zero-level detector (207) is selected, the transmitter transmits the signal after the transmission signal is converted into a two-level one, and in a receiving state where the A/D converter (204) is selected, it transmits the signal after the transmission signal is converted into two-or-more-level one.

Effect of Delay Spread Enhancement in MIMO Eigenbeam Space Division Multiplexing Transmission

Abstract: MIMO (multiple-input multiple-output) transmission is a promising technology to improve the frequency usage efficiency in mobile radio communications. In this letter, MIMO transmission with eigenbeam space division multiplexing (E-SDM) is focused on and the site-dependent beamforming characteristics is examined to know the transmission characteristics. Site-dependent radiowave direction of arrival and impulse responses are obtained using ray tracing. Result shows that effect of radiowaves with longer delays is enhanced due to E-SDM beamforming, and rather more capability of treating a longer excess delay is necessary for time-domain multipath compensation.

Low-density parity-check (LDPC) coded ultra high-data-rate OFDM system in frequency-selective fading

Abstract: In this paper, we investigate the performance when low-density parity-check (LDPC) coding is deployed in DPC-OF/TDMA (dynamic parameter controlled orthogonal frequency and time division multiple access) system, which is actually an orthogonal frequency division multiplexing (OFDM) system aiming at providing ultra high-data-rate transmission capability beyond 100 Mbps. The new DPC-OF/TDMA system is most likely to encounter the severe frequency-selective fading due to the fact that the bandwidth is large even in each subchannel (subband), and the error probability performance could be jeopardized by the subcarriers in deep fading. LDPC coding has excellent error correction capability, and this feature motivates us to deploy LDPC in DPC-OFATOMA system. The log-domain sum-product algorithm is considered as the decoding method of LDPC codes due to its computational complexity is lower than its probability-domain counterpart. In order to support the decoding algorithm., we introduce how to generate the log-likelihood ratio (LLR) for the codeword bits which are transmitted through the spectral-efficient multi-level modulation modes such as 16QAM. The frequency-selective fading encountered by DPC-OF/TDMA system is modeled by using the statistical channel model instead of any tap-delayed model, because our intention is to investigate the performance from the statistical point of view.

A Timing Synchronization Method with Low-Volume DSP for OFDM Packet Transmission Systems

Abstract: This paper proposes a simple timing synchronization method in order to design a timing synchronization circuit with low-complex and low-volume digital signal processing (DSP) for orthogonal frequency division multiplexing (OFDM) packet transmission systems. The proposed method utilizes the subtraction process for acquirement of a timing metric of fast Fourier transform (FFT) window, whereas the conventional methods utilize the multiplication process. This paper adopts the proposed method to a standardized OFDM format, IEEE 802.11a, and elucidates that the proposed one shows good transmission performance as well as the conventional one in fast time-variant multi-path Rayleigh fading channels by computer simulation.

Decreasing transmit power by adaptive loading for ultra high-data-rate OFDM system

Abstract: In this paper, we focus on developing an adaptive bit and power loading algorithm for DPC-OF/TDMA (dynamic parameter controlled orthogonal frequency and time division multiple access) system, which is actually an OFDM system supporting data transmission beyond 100 Mbps. The proposed adaptive loading algorithm is used in each subband of DPC-OF/TDMA system and aims at minimizing the transmit power under the conditions that the stable data rate and error probability are maintained. This is in responding to the requirement of DPC-OF/TDMA which should avoid generating strong interferences to other subbands, users and systems. On the other hand, this feature helps to prolong the battery lifespan. Based on the iterative mechanism, the proposed adaptive loading algorithm loads the bits and power to the subcarrier at which there is a modulation mode demanding the minimum average incremental power per incremental bit to guarantee the pre-designated bit error rate (BER). The performance investigations show the proposed algorithm can greatly decrease the transmit power and its dynamic range under the conditions that the data rate and BER are maintained to the target values.

Data rate dependent control channel allocation

Abstract: When a base station generates an FCM, the base station detects the use rate of a transmission buffer and decides how slots of a frame of an uplink channel are structured. When the use rate of the transmission buffer is high, the base station designates the number of ACTSs to 0 so that the base station does not accept registration requests and so forth from mobile stations. When the use rate of the transmission buffer is low, the base station designates the number of ACTSs to 1. When the number of mobile stations is large as in a large convention hall, the base station generates TDMA frames each of which has only ACTSs. The base station can decide the number of ATCSs corresponding to the probability of which registration requests and so forth from mobile stations collide.

Performance Evaluation of Dynamic Parameter Controlled OF/TDMA Based on PR-DSMA

Abstract: The next-generation wireless access system named DPC-OF/TDMA, which is capable of achieving 100 Mbps carrier bit rate under high mobility environment, has been proposed and is being developed. For the realization of this system, large size of cellular zone is required in order to increase system capacity. However, propagation delays between an access point (AP) and mobile stations (MSs) managed by the AP increase as the cellular zone size is large. These increased propagation delays falls system throughput. In this paper, application of PR-DSMA, which is robust against large propagation delays, to the MAC layer protocol of DPC-OF/TDMA is proposed to solve this problem. This paper also conducts performance evaluation in terms of automatic request control (ARQ) and cell radius by computer simulation

Stochastic determination method of substream modulation levels for MIMO eigenbeam space division multiplexing

Abstract: Multiple-input multiple-output (MIMO) eigenbeam space division multiplexing is a promising configuration to improve the transmission capacity and it uses adaptive modulation for the substreams. The modulation levels determined from the carrier-to-noise ratios, however, are sometimes optimistic and the use of the modulation levels results in transmission errors and transmission performance degradation. A novel determination method of substream modulation levels is proposed to alleviate the degradation. The proposed method calculates the expected bit error rates for possible modulations by mean of the delay profile. The simulation results show that the proposed modulation level determination method improves the transmission capacity by 30% compared with the conventional method.

100Mbps and beyond hotspot communication prototypes for next generation mobile communication systems

Abstract: In this paper, we show the concept of a beyond 3G cellular and hotspot (B3GC&HS) communication system, based on the results of our research and development (R&D). In the proposal, we use a packet-reservation-based protocol: packet reservation dynamic time-slotted multiple access (PR-DSMA). Based on the protocol, we can select the physical layer (PHY) from OFDM based PHY and single carrier based PHY adaptively to suit the user environment. In this paper, we especially show our R&D results on hot-spot communication systems based on single carrier based PHY and PR-DSMA. In the presentation, we show some prototypes on the MAC layer and PHY layer.