A new reference voltage generator with ultralow standby current of less than 1 µA is proposed. The features are: 1) a merged scheme of threshold voltage difference generator and voltage-up converter with current mirror circuits, and 2) intermittent activation technique using self-refresh clock for the DRAM. This combination enables the average current to be reduced to 1/100 and the resistance of trimming resistor to be reduced to 1/10 compared to conventional reference voltage generators, while maintaining high accuracy and high stability. The proposed circuit was experimentally evaluated with a test device fabricated using 0.3-µm process. An initial error of less than 4% for 6 trimming steps of the trimming resistor, temperature dependence of less than 370 ppm/ from room temperature to 100, and output noise of less than 12 mV for 1 Vp-p Vcc bumping are achieved. These results are sufficient for achieving high-density battery operated DRAM's with low active and data-retention currents comparable to SRAM's.

This paper gives field experimental results on 16-ary quadrature amplitude modulation/time division multiple access (16QAM/TDMA) and trellis coded 16QAM/TDMA systems for land mobile communications in order to evaluate its capability of achieving large capacity and high quality data transmission. Pilot symbol aided space diversity and symbol timing synchronization based on maximum likelihood (ML) estimation are applied to both 16QAM/TDMA and trellis coded 16QAM/TDMA to improve transmission quality. For the trellis coded 16QAM/TDMA, trellis coding with Viterbi decoding and 2-frame symbol interleaving are further employed. The field experiments were conducted in the Tokyo metropolitan area of Japan. The results show that 16QAM/TDMA and trellis coded 16QAM/TDMA are practical modulation/access schemes for land mobile communication systems.

Delay Tolerant Network (DTN) has been emerged to support the network connectivity of the disruptive networks. A variety of routing methods have been proposed to reduce the latency for message delivery. PROPHET was proposed as a probabilistic routing that utilizes history of encounters and transitivity of nodes, which is computed as contact probability. While PROPHET improves the performance of DTN due to contact probability, contact probability is just one parameter reflecting the mobility pattern of nodes, and further study on utilizing contacting information of mobility pattern is still an important problem. Hence, in this paper, we try to improve routing for DTN by using a novel metric other than contact probability as mobility information. We propose the routing protocol to use mean residual contact time that describes the contact period for a given pair of nodes. The simulation results show that using the mean residual contact time can improve the performance of routing protocols for DTN. In addition, we also show in what situations the proposed method provides more efficient data delivery service. We characterize these situations using a parameter called Variation Metric.

Analysis of waiting time to deliver a message M from a source S to a destination D is deeply related to connectivity analysis, which is an important issue in fundamental studies of mobile multi-hop networks. In [1], we compared the mean waiting times of two methods to deliver M with the mean value of the minimum waiting time. The mean minimum waiting time was obtained by computer simulation because theoretical analysis of this mean is not easy, although another two methods were analyzed theoretically. In this paper, we propose an approximate method to theoretically analyze the mean minimum waiting time in a one-dimensional street network, and show that this method gives a good approximation of the mean minimum waiting time. Also, we consider shadowing and change of directions of mobile nodes at intersections as negative factors arising in two-dimensional street networks. We extend the above method to compute the mean minimum waiting time considering these factors, and discuss how the mean minimum waiting time is affected by these factors.

In multi-hop wireless networks, communication quality depends on the selection of a path between source and destination nodes from several candidate paths. Exploring how path selection affects communication quality is important to characterize the best path. To do this, in [1], we used expected transmission count (ETX) as a metric of communication quality and theoretically characterized minimum route ETX, which is the ETX of the best path, in a static one-dimensional random multi-hop network. In this paper, we characterize minimum route ETX in static two-dimensional multi-hop networks. We give the exact formula of minimum route ETX in a two-dimensional network, assuming that nodes are located with lattice structure and that the ETX function satisfies three conditions for simplifying analysis. This formula can be used as an upper bound of minimum route ETX without two of the three conditions. We show that this upper bound is close to minimum route ETX by comparing it with simulation results. Before deriving the formula, we also give the formula for a one-dimensional network where nodes are located at constant intervals. We also show that minimum route ETX in the lattice network is close to that in a two-dimensional random network if the node density is large, based on a comparison between the numerical and simulation results.

In this paper, we study and propose an inter-cell co-channel interference (CCI) mitigation method for pilot signals using cyclic shift Zadoff-Chu (CS-ZC) sequences for SC-FDMA-based uplink without tight scheduler coordination among cells. Firstly, we investigate the issue of severe detection performance degradation created by the lack of orthogonality among the pilot signals without alignment of the allocated frequency resource positions among cells when using the conventional CS-ZC sequences generation scheme. Secondly, we identify the primary factor causing the issue. Thirdly, we propose a frequency-dependent CS-ZC sequence generation scheme by allocating the same spectrum elements of the ZC sequence to the overlapped subcarriers among cells to mitigate the inter-cell CCI of the pilot signals without alignment of the frequency resource positions among cells. Finally, we confirm the validity of the proposal using uplink data BLER evaluation under a multipath fading condition by computer simulation compared to the conventional method, and show that the proposal achieves around 0.9 dB and 0.6 dB better performance at 10% BLER than the conventional method for 1 RB and 2 RBs frequency offsets in 3 RBs transmission bandwidth, respectively.

We previously proposed a next generation cellular system for IMT-2000 based on the Wideband DS-CDMA with TDD scheme (W-CDMA/TDD) and have evaluated its performance by computer simulation, laboratory and field experiment. With the W-CDMA/TDD, because of its correlation between the downlink and the uplink, transmission and reception space diversity (SD) at a base station and open-loop transmit power control (TPC) can be simply realized. This paper reports performance of laboratory and field experiments using a developed testbed. The results shows it has been confirmed that transmission and reception SD and open-loop TPC have sufficient performance under a field environment as well as laboratory environment.

This 0.8 µm 4 Mbit BiCMOS DRAM achieves the world's fastest chip-enable access time of 17 ns. BiCMOS technology has been employed because of its ability to enhance DRAM performance. Some new circuits, such as a dynamic pull-down type address buffer, a noise immune cascode amplifier, and an offset-cross output circuit are introduced to reduce access time. This paper explains in more detail the noise immune cascode amplifier, and the offset-cross output circuit. A conventional cascode amplifier can operate very rapidly in spite of a heavy parasitic capacitance associated with the data read out line of the memory array. However, when noise, which is inevitably caused by operation, appears on the power supply, bipolar transistors in cascode amplifier cut off, and the cascode amplifier loses its speed advantage. In the noise immune cascode amplifier, a resistor and two capaciters are added to maitain a stable base level of the bipolar transistors. So the cascode amplifier can continue to operate normally, despite the power supply noise. A conventional output circuit is composed of two level converters, four inverters and output transistors. The input swing (the level gap between the data level and the refernce level which are input to the level converters) is 0.5 V, which is not sufficient for the level converter to drive the load capacitance connected with the output transistors. To increase the drivability of the level converter, two 2-stage inverters must be inserted between the level converters and output transistors. In the proposed offset-cross circuit however, the input swing is increased to 1.5 V, which is sufficient for the level converter to drive the load capacitance directly, so the four inverters can be eliminated. The access time is improved by 1.5 ns using the noise immune cascode amplifier, and by 1.7 ns using the offset-cross output circuit. This chip is constructed using a conventional 0.8 µm BiCMOS process. Therefore, it can be used to realize a high speed and low cost memory system.

Hybrid automatic repeat request (HARQ) is employed for the 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 (CS) sequences, and then code spread again by the orthogonal cover (OC) 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 [1] in fast-fading environments because of inter-code interference (ICI) among the OC sequences. Therefore, resource management of PUCCH is required depending on the mobility of the UEs to maximize the performance of the ACK/NACK signals and the capacity of PUCCH simultaneously. In this paper, we propose a novel code design for PUCCH, which can suppress the effects of ICI among the OC sequences, and thus can simplify the resource management of PUCCH. The simulation evaluations confirm that the proposed code design can significantly improve the performance of the ACK/NACK signals via PUCCH in fast-fading environments, and any complicated resource management based on the mobility of the UEs are not necessary.

Information floating (IF) permits mobile nodes to transmit information to other nodes by direct wireless communication only in transmittable areas (TAs), thus avoiding unneeded and inefficient information distribution to irrelevant areas, which is a problem with the so-called epidemic communication used in delay tolerant networks. In this paper, we propose applying IF to sensor networking to find and share available routes in disaster situations. In this proposal, IF gathers and shares information without any assistance from gateways, which is normally required for conventional wireless sensor networks. A performance evaluation based on computer simulation results is presented. Furthermore, we demonstrate that the proposed method is effective by highlighting its advantageous properties and directly comparing it with a method based on epidemic communication. Our findings suggest that the proposed method is a promising step toward more effective countermeasures against restricted access in disaster zones.

In mobile multi-hop networks, a source node S and a destination node D sometimes encounter a situation where there is no multi-hop path between them when a message M, destined for D, arrives at S. In this situation, we cannot send M from S to D immediately; however, we can deliver M to D after waiting some time with the help of two capabilities of mobility. One of the capabilities is to construct a connected multi-hop path by changing the topology of the network during the waiting time (Capability 1), and the other is to move M closer to D during the waiting time (Capability 2). In this paper, we consider three methods to deliver M from S to D by using these capabilities in different ways. Method 1 uses Capability 1 and sends M from S to D after waiting until a connected multi-hop path appears between S and D. Method 2 uses Capability 2 and delivers M to D by allowing a mobile node to carry M from S to D. Method 3 is a combination of Methods 1 and 2 and minimizes the waiting time. We evaluate and compare these three methods in terms of the mean waiting time, from the time when M arrives at S to the time when D starts receiving M, as a new approach to connectivity evaluation. We consider a one-dimensional mobile multi-hop network consisting of mobile nodes flowing in opposite directions along a street. First, we derive some approximate equations and propose an estimation method to compute the mean waiting time of Method 1. Second, we theoretically analyze the mean waiting time of Method 2, and compute a lower bound of that of Method 3. By comparing the three methods under the same assumptions using results of the analyses and some simulation results, we show relations between the mean waiting times of these methods and show how Capabilities 1 and 2 differently affect the mean waiting time.

We previously proposed a next generation cellular system for IMT-2000 based on wideband DS-CDMA with TDD scheme and have evaluated its performance by computer simulation, laboratory and field experiments. This paper presents the design concept of TDD-mode operation on wideband DS-CDMA systems. These systems employ almost the same techniques with a little difference as FDD-mode. We also present the schemes of the TDD-mode specific techniques such as fast cell search, transmission diversity and transmitter power control and show the evaluation results of them are effective. Performance can be improved by use of enhanced techniques such as interference cancellation and adaptive antenna array diversity.

In multi-hop wireless networks, since source and destination nodes usually have some candidate paths between them, communication quality depends on the selection of a path from these candidates. For network design, characterizing the best path is important. To do this, in [1], [2] we used expected transmission count (ETX) as a metric of communication quality and showed that the best path for ETX is modeled by a path that consists of links whose lengths are close to each other in static one-dimensional multi-hop networks with a condition that the ETX function of a link is a convex monotonically increasing function. By using the results of this characterization, a minimum route ETX can be approximately computed in a one-dimensional random network. However, other metrics fail to satisfy the above condition, like medium time metric (MTM). In this paper, we use MTM as a metric of communication quality and show that we cannot directly apply the results of to the characterization of the best path for MTM and the computation of minimum route MTM. In this paper, we characterize the path that minimizes route MTM in a different manner from [1] [2] and propose a new approximate method suitable for the computation of minimum route MTM.

In multi-hop wireless networks, communication quality depends on the route from a source to a destination. In this paper, we consider a one-dimensional multi-hop wireless network where nodes are distributed randomly and theoretically analyze the relation between communication quality and routing policy using a measure called the Expected Transmission Count (ETX), which is the predicted number of data transmissions required to send a packet over that link, including retransmissions. First, we theoretically analyze the mean length of links, the mean number of hops, and the mean route ETX, which is the sum of the ETXs of all links in a route, of Longest Path Routing (LPR), and Shortest Path Routing (SPR). Second, we propose Adjustable Routing (AR), an approximation to Optimum Routing (OR), which minimizes route ETX. We theoretically compute the above characteristic values of AR. We also theoretically compute a lower bound of the mean route ETX of OR. We compare LPR, SPR, and OR using the results of analyses and show differences between these algorithms in the route ETX.

Information floating delivers information to mobile nodes in specific areas without meaningless spreading of information by permitting mobile nodes to directly transfer information to other nodes by wireless links in designated areas called transmittable areas. In this paper, we assume that mobile nodes change direction at intersections after receiving such information as warnings and local advertisements and that an information source remains in some place away from the transmittable area and continuously broadcasts information. We analyze performance of information floating under these assumptions to explore effects of the behavior changes of mobile nodes, decision deadline of the behavior change, and existence of a fixed source on information floating. We theoretically analyze the probability that a node cannot receive information and also derive the size of each transmittable area so that this probability is close to desired values.