This paper proposes transmit power control (TPC) for pilot-based channel quality indicator (CQI) reporting in OFDMA/TDD systems. In the proposed TPC scheme, the terminal controls transmit power of pilot signals for CQI reporting, such that the base station (BS) can receive the pilot signals with higher power than the BS's interference-plus-noise power. In the proposed TPC scheme, the terminal determines appropriate transmit power using downlink pilot signals. The numerical results show that uplink signalling for CQI reporting can be effectively reduced by updating transmit power level in longer period than period of pilot signal transmission. Using appropriate period of updating the transmit power, the terminal can report one unit of CQI using a small number of uplink symbols, e.g. 1.5 symbols, keeping accuracy of CQI reporting.

This paper proposes a new partial channel state information (CSI) reporting for spatial scheduling in TDD/MIMO systems. In the proposed method, a terminal transmits pilot signals using transmit beams which have large channel gains between the base station (BS) and the terminal. Then, the BS can obtain partial CSI through responses of the pilot signals. Furthermore, adaptive allocation of pilot signals is proposed, in which pilot signals for CSI reporting are adaptively allocated to terminals depending on the number of terminals. We evaluate system throughput of spatial scheduling under the partial CSI reporting from multiple terminals. Numerical results show that the proposed method reduces uplink radio resources for CSI reporting effectively, keeping high system throughput of spatial scheduling.

In this paper, we propose OFDMA/TDD/MIMO system with spatial scheduling, showing frame structure and control procedures to achieve the proposed system. The frame structure includes all functions required for spatial scheduling in a subband of 200 kHz and in a frame time of 2.5 ms. We show that the frame structure can be a realistic solution to achieve spatial scheduling on subband basis. From the presented frame structure, about 60% of total radio resources are expected to be available for data symbol transmission. Furthermore, we estimate that data rate up to 570 Mbps can be supported on MAC layer for both uplink and downlink, under total bandwidth of 100 MHz.

This paper presents uplink spatial scheduling with adaptive transmit beamforming, where terminals perform system-based transmit beamforming in multiuser multi-input multi-output (MIMO) systems. In the presented spatial scheduling, the base station (BS) selects appropriate combination of terminals and their transmit beamforming among possible terminals. In the selection process, a terminal and its transmit beamforming for a signal are successively selected, considering the effect of the other predetermined signals. In performance evaluation, we show that the spatial scheduling achieves much larger system throughput than the system without spatial scheduling. We also present a basic system configuration in which the BS reports the target transmit beamforming to the selected terminal efficiently in time-division duplex (TDD) system downlink

This paper presents downlink spatial scheduling which nullifies interference among multiplexed signals perfectly in multiuser MIMO systems. Under the base station's zero-forcing transmit beamforming, each terminal can receive packet of interest without interference from the other multiplexed packets. The scheduling algorithm successively selects appropriate terminals for packet transmission in the presence of already selected packets. We show that the downlink spatial scheduler is equivalent to the virtual uplink spatial scheduler in terms of received signal characteristics. Applying the uplink scheduling concept to downlink, the downlink spatial scheduler achieves much higher system throughput than the system without spatial scheduling. Also, it is shown that the spatial scheduler has similar system throughput in uplink and downlink

This paper propose a new control scheme that the base station (BS) controls the terminal's transmit beamforming in time-division duplex (TDD)/multi-input multi-output (MIMO) systems. In the proposed scheme, the BS transmits pilot signals using proper downlink beamforming to instruct target beamforming to the terminal. Using responses of the pilot signals, the terminal computes weight for transmit beamforming. We theoretically show that the BS can control not only a single terminal's transmit beamforming but also multiple terminals' transmit beamforming simultaneously. Furthermore, efficient weight computation at the terminal is investigated to yield accurate transmit beamforming in the presence of noise. Numerical results show that the terminal can yield transmit beamforming close to the target beamforming in noise environments

This paper proposes a pilot-based channel state information (CSI) feedback in time-division duplex (TDD) / multi-input multi-output (MIMO) system, which enables the transmitter to perform transmit beamforming considering the receiver's interference. In the proposed method, the receiver sends reverse-link pilot signals spatially prefiltered by linear precoder dependent on the receiver's interference characteristics. The transmitter exploits responses of the reverse-link pilot signals to perform transmit beamforming considering the receiver's interference. The transmitter also predicts the receiver's output signal-to-interference-plus-noise power ratio (SINR) for each data stream. From simulation results, it is found that the transmitter achieves efficient transmission performance maintaining small control errors based on the proposed CSI feedback.

This paper proposes a new uplink signalling to report the terminal's channel quality in multiple subbands to the base station (BS) using channel reciprocity in orthogonal frequency division multiple access / time division duplex (OFDMA/TDD) systems. In the proposed method, the terminal transmits uplink pilot signals in the subbands with different transmit power which is inversely proportional to the subband- based interference-plus-noise power. The BS can obtain knowledge of the terminal's received signal-to-interference-plus-noise power ratio (SINR) on subband basis, measuring the pilot signal power. In performance evaluation, accuracy of the channel quality reporting and amount of the control signalling are examined. From numerical results, it is found that the proposed method becomes effective as the number of subbands and terminals for channel quality reporting increases.

Many enterprise networks require flexible dynamic group communications on the Internet. When we develop these systems on multicast communication framework, various types of security threats will occur. As a result, construction of secure group communication that protects users from intrusion and eavesdropping are very important matters. We propose an efficient key distribution method for a secure group communication over multicast communication framework. In this method, we use IP multicast mechanism to shorten rekeying time to minimize adverse effect on communication. In addition, we introduce a proxy mechanism for replies from group members to the group manager to reduce traffic generated by rekeying. We define a multicast communication network model and evaluate the proposed method by computations using the model. From results of the evaluation, the proposed method shortens the rekeying time and reduces concentration of traffic to the group management server in large systems.

The shared-buffering architecture is promising to make a large-scale ATM switch with small buffer size. However, there are two important problems, namely, memory-access speed and complex-control implementation. Advanced 0.5 /spl mu/m CMOS technology now makes it possible to integrate a huge amount of memory, and enables us to apply more sophisticated architecture than ever before. We propose the funnel-structured expandable architecture with shared multibuffering and the advanced searchable-address queueing scheme for these two problems. The funnel structure gives a flexible capability to build various sizes of ATM switches which are proportional to the number of LSI chips. The searchable-address queue, in which all the addresses of the stored cells for different output ports are queued in a single-FIFO hardware and the earliest address is found by the search function provided inside the queue, can reduce the total memory capacity drastically, and enables the address queue to be contained inside the LSI chip. This technique also has a great advantage for implementing the multicast and multilevel priority-control functions. A 622 Mbit/s 32/spl times/8 ATM switch LSI chip set, which consists of a BX-LSI and a CX-LSI, is developed using 0.5 /spl mu/m pure CMOS technology. By using four chip sets, a 622 Mbit/s 32/spl times/32 switch can be installed on one board.

There are several schemes to provide multicast function in an ATM switch. The authors have proposed a new multicast scheme in a shared buffering ATM switch. They discuss the cell-loss performance of ATM switch to compare various schemes. Computer simulation shows that this scheme achieves the best cell-loss performance and has a great advantage in the buffer size. Implementation of an LSI chip set and a 622 Mb/s 8/spl times/8 ATM switch board is also explained.>