Szu-Lin Su

Grey-based power control for DS-CDMA cellular mobile systems

The propagation channel of a mobile radio system exhibits severe signal shadowing and multipath fading, which results in wide variation of signal-to-interference ratio (SIR) at the receiver. To tackle this problem, power control is used to maintain the desired link quality and thus achieve higher capacity. In order to mitigate the channel variation effect precisely, a new application of grey theory to the power control strategy in the direct-sequence code-division multiple-access cellular mobile systems is introduced. This scheme aims to predict the SIR affected by the channel variation at the receiver and issue an appropriate control signal to the transmitter. The simulation results indicate that the grey-based scheme can offer less outage probability than the previous mechanisms.

Reverse-link power control strategies for CDMA cellular network

Power control (PC) is an important issue in the DS-CDMA cellular mobile radio system. For the IS-95 standard, the reverse-link PC strategy is based on fixed-step power change and it needs only one command bit per update. We call this strategy DM-PC. From the point of view of digital communication, ADM will have better performance with the same number of control bits compared to DM. So it appears to be a good idea to improve the DM-PC and be compatible with the current system as IS-95. However, the pure ADM-PC is not better than DM-PC from our earlier simulation results. Hence, we propose another PC strategy called modified ADM-PC. The simulation results show that it has better performance than DM-PC.

Performance analysis of soft handoff in cellular networks

In this paper a tractable model is developed to analyze the soft handoff process. A Markovian conception is applied to describe the systems statistic behavior in steady state. Theoretical performances such as channel efficiency, blocking probability and handoff refused probability are also determined.

A Novel QoS Admission Control for Ad Hoc Networks

For real-time traffic requirements in mobile ad hoc networks a novel and effective QoS admission control routing protocol (QACRP) is proposed in this paper. With a limit amount of extra overhead, QACRP can avoid network congestion by a simple and precise admission control to block most of overloading flow-requests in route discovery process. System simulations show that this proposed scheme can increase the system throughput and reduce both the dropping rate and the end-to-end delay when compared with previous QoS routing schemes like QoS-aware routing protocol and CACP protocol. Hence, QACRP is surely an effective routing protocol to provide QoS guarantee for real-time traffic.

Two-stage ensemble paging strategy for cellular communication systems

Instead of per user basis, we propose a simple paging strategy based on the consideration of ensemble paging channel resource of each cell. Using only the information of the last known locations of mobile subscribers, the proposed paging scheme under a maximum delay constraint can improve the system performance (discovery rate, blocking rate, and average paging delay) significantly in the heavy load.

Performance analysis of digital delay lock loops in the presence of Doppler shift

This paper considers discrete time analyses of digital delay lock loops (DDLL), and presents the results of an investigation concerning the performance degradation due to Doppler. The performance measures evaluated include the steady-state timing error probability density function (PDF) and the mean time to lose lock. The linear approximations are also provided and compared to the numerical results and simulations. The delay lock loop is a well-known technique to track the pseudo-noise (PN) codes for spread spectrum systems. Under a severe Doppler environment, such as in the low Earth orbit (LEO) satellite communication, it will be difficult to track the PN code for the first-order loop. Since the digital systems are more compact, lower cost, and more stable than their analog counterparts, we focus our attention on the digital first and second order code tracking loops that suffer from severe Doppler.

Topology-transparent link activation scheduling schemes for multihop CDMA ad hoc networks

In this paper, we study topology-transparent node activation transmission scheduling protocols for multihop TDMA ad hoc networks. We focus on quality-of-service (QoS) provisioning for each node, particularly when node mobility is considered. A framework for topology-transparent node activation scheduling based on theory of block designs is proposed. The proposed framework guarantees conflict-free transmission slots for each node in each frame by mathematical properties of block designs. Based on two mapping methods, called mapping I and mapping II, the proposed framework can be categorized into two types. With the proposed framework, we study and evaluate some series of block constructions. We then propose several topology-transparent scheduling algorithms based on the results derived. The proposed schemes maximize the minimum system throughput. Numerical results show that the proposed algorithms can outperform existing algorithms in achieving a higher minimum system throughput.

Design and analysis of dynamic mobility tracking in wireless personal communication networks

In personal communication networks (PCN), mobility tracking provides the function of locating a mobile user within the service area. We propose an intersection-oriented dynamic location update (LU) strategy, which is designed to minimize the cost of mobility tracking by optimally partitioning the service area into location registration (LR) areas on a per-user basis. A realistic mobility model is proposed in which we consider not only the mobility behavior of the individual subscriber, but also the street layout. Based on this model, a transient Markov process is developed to analyze the tracking cost. To reduce the implementation cost and to make the proposed strategy feasible, the concept of mobile subscriber (MS) grouping, and equivalent quadrangular LR area are also adopted.

Performance of digital code tracking loops for direct-sequence spread-spectrum signals in mobile radio channels

The performance of first- and second-order non-coherent digital delay lock loops (DDLL) for direct-sequence spread-spectrum (DS-SS) signals is investigated in the mobile radio environment. The mobile radio channel is first characterized by Rayleigh fading and Doppler shift. A closed-form expression for the timing error transition probability density function of the Chapman-Kolmogorov (C-K) equation is proposed. The probability density function of the steady-state timing error for the first- and second-order DDLL is obtained by solving the C-K equation numerically, and the results are confirmed by computer simulations. Furthermore, the mean time to lose lock (MTLL) of the first-order loop is evaluated, and some numerical results and simulation results are reported. Finally, the steady-state timing error and MTLL of the first-order loop for DS-SS signals in the log-normal fading environment are also presented, and the results are compared with those of Rayleigh and AWGN channels.

Topology-Independent Link Activation Scheduling Schemes for Mobile CDMA Ad Hoc Networks

In this paper, we study medium access control (MAC) protocols with quality-of-service (QoS) support, that is, topology-independent link activation transmission scheduling, for mobile code-division multiple-access (CDMA) ad hoc networks. QoS provisioning for each communication link is guaranteed without the need to adopt transmission schedules in mobile environments. An interference model, which captures the difference between transmission and interference ranges, is considered. Under this interference model, an approach to guaranteeing conflict-free transmission slots in each frame (QoS provisioning) for each communication link is proposed. Compared with the previously known method, superior performance is obtained. We then present a topology-independent link activation scheduling framework based on the theory of group-divisible (GD) designs. By the mathematical properties of GD designs, the proposed framework guarantees conflict-free transmission slots in each frame for each communication link, without the overhead due to the recomputation of transmission schedules when the network topology changes. With the proposed framework, we study and evaluate one series of GD design constructions. Based on the results derived, topology-independent link activation scheduling algorithms are then presented. The proposed schemes are designed for different objectives: maximizing the minimum system throughput and/or minimizing the schedule frame length. Numerical results show that the proposed algorithms outperform previously known schemes. The average performance of the proposed schemes is also derived.