This paper describes a 1-GHz portable digital delay-locked loop (DLL) with 0.15-µm CMOS technology. There are three factors contributing to jitter in digital DLLs. One is supply-noise induced jitter, another is jitter caused by delay time resolution and phase step in the delay line, and the third is jitter caused by the sensitivity of the phase detector. In order to achieve a low jitter digital DLL, we have developed a master-slave architecture that achieves infinite phase capture ranges and low latency, a delay line that improves the delay time resolution, a phase step suppression technique and a dynamic phase detector with increased sensitivity. These techniques were used to fabricate a digital DLL with improved jitter performance. Measured results showed that the DLL successfully achieves 29-ps peak-to-peak jitter with a quiet supply and 0.2-ps/ mV supply sensitivity.

The stability of slotted ALOHA systems with various types of capture phenomena and multiple packet reception capability is discussed in conjunction with the cusp catastrophe. The slotted ALOHA systems considered are classified into; 1) single packet reception with geometric capture, 2) independent multiple packet reception with geometric capture, 3) single packet reception with M-out-of-N capture (M N), 4) multiple packet reception with M-out-of-N capture, and 5) single packet reception with perfect capture. First, general expressions for the cusp points and the bifurcation sets are derived. Then, we present explicit formula for the stability of slotted ALOHA systems for the five types of capture and multi-packet reception capability and demonstrate how the bistable behavior is mitigated due to capture effect and multi-packet reception capability.

The channel throughput and packet delay of wireless medium access control (MAC) protocols with Rayleigh fading, shadowing and capture effect are analyzed. We consider CSMA/CA protocols as the wireless MAC protocols, since CSMA/CA protocols are based on the standard for wireless Local Area Networks (LANs) IEEE 802. 11. We analyze the channel throughput and packet delay for three types of CSMA/CA protocols; Basic CSMA/CA, Stop-and-Wait CSMA/CA and 4-Way Handshake CSMA/CA. We calculate the capture probability of an Access Point (AP) in a channel with Rayleigh fading, shadowing, and near-far effects, and we derive the throughput and packet delay for the various protocols. We have found that the performance of CSMA/CA in a radio channel model is 50 percent less than in an error free channel model in low traffic load, while the throughput and packet delay of CSMA/CA in a radio channel model show better performance than in an error free channel model in high traffic load. We also found that the 4-Way Handshake CSMA/CA protocol is superior to the other CSMA/CA protocols in high traffic load.

We have developed a Beam Space CMA (Constant Modulus Algorithm) Adaptive Array Antenna system (BSCMA adaptive array antenna) that may be suitable for mobile communications. In this paper, we present experimental results of interference cancellation characteristics using the developed system. The experiment was carried out in a large radio anechoic chamber, while desired and interference signals were transmitted to the system. We focused on the characteristics of capture, convergence and tracking in adaptive processing. The experimental results show excellent interference cancellation characteristics, and demonstrate that the BSCMA adaptive array antenna has a greater feasibility to be applied practically in mobile communications.

In a radio network, while deploying microcells enhances spectral efficiency, it increases handoff in number and puts restriction on mobility of a terminal. As a solution of this contradictory matter, we propose a random access micro-cellular system (RAMCS). In the system deployed microcells produce higher system capacity, and "handoff on a terminal" isn't required. Therefore flexible mobility is given to terminals, and a terminal becomes simple. The aspect of the air interface is as follows. On uplink, packets are transmitted by means of random access (e.g., slotted ALOHA) at the same channel in any cell. On downlink, packets are broadcast at the same carrier in any cell and they are picked out conforming to TDMA. In this paper, a model of RAMCS is proposed. In addition, characters of RAMCS (e.g., throughput, system capacity, and delay) are clarified comparing it with a primary cellular system, where a spectrum can be reused repeatedly in different cells.

Partial capture effect for multi-carrier radio packet communication network is evaluated in frequency selective fading channel. In multi-carrier modulation (MCM) network where each terminal uses several sub-carriers for transmission,the terminals have different instantaneous frequency responses because of its location, fading pattern, and other various factors. This generates the difference of received power in frequency domain, then partial capture effect can be considered at each sub-carrier. Moreover these partially captured packets are not damaged by inter symbol interference (ISI) caused by frequency selective fading, which seriously degrades single-carrier modulation (SCM) network. From this point of view we present the partial capture effect for the MCM network in the frequency selective fading environment. The results show that the MCM network with partial capture has more advantages than the MCM network without partial capture in terms of the throughput and the average number of transmissions.

In packet radio networks with TDMA, the throughput performance of network should be degraded due to the unequal traffic of each user. To overcome this problem, Mini-Slotted Alternating Priorities (MSAP) and TDMA with Parallel Transmission (TDMA/PT) were proposed. Especially, TDMA/PT can attain the thorughput performance more than one, even under unequal traffic. However, TDMA/PT cannot be used for mobile networks, because each terminal should know the location of every other terminal. In this paper, we propose an entirely new protocol named Slot Reservation TDMA with Parallel Transmissino: SR-TDMA/PT," which is suitable for mobile networks because a central station is able to locate every terminal easily. The central station also reserves time slots for each terminal so as to transmit packets in parallel as much as possible. Therefore, the throughput performance of SR-TDMA/PT is higher than TDMA/PT. We describe SR-TDMA/PT in detail and evaluate the performance of this protocol by simulation under various conditions.