We analytically evaluated the effects of the analog components on a high-speed downlink packet access (HSDPA) system standardized by 3GPP. We considered the phase noise of synthesizers, the imbalance of demodulators between in-phase and quadrature channels, and the filters. The components are represented by the appropriate equations. We applied adaptive modulation and coding methods for HSDPA systems and base station transmission of adequate data rate signals complying with quality estimated by mobile stations (MSs). The quality represents a data rate indicating that MSs can receive the signals. We estimated the quality using a conventional signal-to-interference measurement of the common pilot channel (CPICH) and found that the phase noise creates a mismatch relationship between the quality and the data rate, while the demodulator imbalance and filters create a suitable relationship. We confirmed this using analytic methods and computer simulation.

In this paper, we evaluate the performance of asymmetric Time Division Duplex (TDD) system that employs Adaptive Modulation and Coding (AMC) and Hybrid ARQ, with consideration of the effect of control delays in TDD. Channel reciprocity characteristic in TDD allows utilization of open loop channel estimation to choose appropriate modulation and coding scheme (MCS) level for AMC. However, control delay in AMC and HARQ depends on TDD time slot allocation formats. Large control delay in AMC will result in false MCS selection due to the poor channel correlation between measured channel state from the received signals and instantaneous channel state of actual transmission with the MCS selected based on the measured channel state. We present an analytical approach to calculate the probability of MCS level selection error in different channel conditions for different asymmetric time slot allocations. From the theoretical and simulation results, it is shown that the instantaneous throughput per slot depends not only on maximum Doppler frequency but also on asymmetric slot allocations. Average delay time that yields error free packet reception in the downlink increases as the number of continuous downlink slots increases.

In the adaptive modulation and coding (AMC)-based orthogonal frequency division multiple access (OFDMA) system for broadband wireless service, a large number of users with short packets cause a serious capacity mismatch problem, which incurs resource under-utilization when the data rate of subchannel increases with a better channel condition. To handle the capacity mismatch problem, we propose an AMC-based subchannel multiplexing (ASM) scheme, which allows for sharing the same subchannel among the different simultaneous flows of the same user. Along with the ASM scheme, we also consider multi-class scheduling scheme, which employs the different packet scheduling algorithm for the different service class, e.g., packet loss rate-based (PLR) scheduling algorithm for real-time (RT) service and modified minimum bit rate-based (MMBR) scheduling algorithm for non-real-time (NRT) service. In the typical integrated service scenario with voice, video, and data traffic, we have shown that the proposed schemes significantly improve the overall system capacity.

In this letter, we propose the reducing method of feedback information for transmitting adaptable data rate in multi-user OFDMA/FDD system. In order to transmit the downlink channel information to Base-Station (BS) by using the limited uplink control channel, the proposed algorithm uses the channel variation level which describes the similarity among the adjacent clusters and uses just one modulation and coding scheme (MCS) level which represents the channel information of all clusters. The performance was investigated in one-cellular environment. It has a similar overhead for feedback information with conventional algorithm and has better performance than the conventional algorithm.

In this letter, we propose an adaptive turbo coded modulation scheme for orthogonal frequency division multiplexing (OFDM), and three power allocation algorithms with transmit power variable over subcarriers, variable over subbands and constant over subcarriers. Our object is to improve the overall throughput under target bit-error-rate (BER). Simulation results show that our fixed power adaptation scheme exhibits a more than 7 dB signal-noise-ratio (SNR) gain relative to non-adaptive turbo coded modulation, and an about 2 dB additional gain can be achieved with our variable power algorithm employed. We also discuss the effect of the number of subbands on throughput performance in our adaptive scheme.

In this letter, we propose a packet scheduling algorithm to support both real-time voice and video traffic for wireless multimedia data service in orthogonal frequency division multiple access (OFDMA) system. Our design objective is to maximize the number of real-time service users that can be supported in the system subject to QoS requirement of packet loss rate (PLR). Both time slots and subcarriers are taken into account as the basic resource allocation unit in OFDMA/FDD system. The simulation results show that our proposed algorithm can dramatically increase the number of users satisfying the underlying QoS requirement for the real-time service, as compared to the existing algorithm.

In this letter, a fixed-power variable-rate turbo coded modulation scheme for orthogonal frequency division multiplexing (OFDM) is proposed and subband adaptation algorithm based on capacity evaluation is presented. Our object is to improve the overall throughput under target bit-error-rate (BER). Simulation results show that our adaptive OFDM scheme exhibits an about 2.5-5 dB signal-noise-ratio (SNR) gain with target BER of 10-4 and subband number of 16 relative to fixed threshold adaptive turbo coded modulation. Moreover, unlike fixed threshold adaptation, with the number of subband decreased, throughput performance is not degraded due to our capacity evaluation algorithm.

An ultra-high-sensitivity HDTV color camcorder (camera with VTR) has been developed featuring image intensifiers with GaAsP photocathodes, which provide very high quantum efficiency. To achieve superior performance and a compact camera body, we combined three 1-inch image intensifiers with a 2/3-inch taking lens and three 2/3-inch CCDs by means of a new optical system capable of enlarging and reducing images. The camcorder provides excellent color reproducibility even under low light level conditions (0.2 lx) at an iris setting of f/2, with a signal-to-noise ratio of 55 dB at pedestal level. Its sensitivity is about 400 times greater than that of current HDTV CCD camcorders, making it particularly well suited for capturing images of faint objects in space, aurora, etc., filming the nocturnal activities of animals in their natural settings, and reporting breaking news at night.

A random access micro-cellular system based on CSMA (RAMCS/CSMA) is proposed. On uplink in RAMCS/ CSMA, packets are transmitted by means of CSMA at the same carrier frequency in any cell. On downlink, packets are broadcast conforming to TDMA, also at the same carrier frequency in any cell. In RAMCS/CSMA, deployed microcells produce higher system capacity. Nevertheless, " handoff on a terminal " isn't required. In this paper, overview of the system, fundamental uplink performance, and two kinds of power control methods are presented. As for the control methods, one is control according to packet priority. The other is a way according to location of a mobile terminal. By means of CSMA, throughput performance on uplink becomes great and is saturated at 0. 39 per cell. And the performance strongly depends on the threshold level on carrier sense. Such a throughput performance is peculiar to RAMCS/CSMA and different from an ordinary CSMA system. The optimum threshold is also indicated here. Furthermore, it is clarified that both power control methods highly improve the throughput performance. As a result, it is found that RAMCS/CSMA is excellent for mobile communications.