Description: This encyclopedia article gives an overview of the broad area of real-time systems. This task is daunting because real-time systems are everywhere, and yet no generally accepted definition differentiates real-time systems from non-real-time systems. The authors make an attempt at providing a general overview of the different classes of real-time systems, scheduling of tasks (or threads) in such systems, design tools and environments for real-time systems, real-time operating systems, and embedded systems. The authors conclude their discussion with research challenges that still remain.

Description: This paper discusses indoor propagation modeling. Abstract: The purpose of this study is to characterize the indoor channel for 802.11 wireless local area networks at 2.4 GHz frequency. This work presents a channel model based on measurements conducted in commonly found scenarios in buildings. These scenarios include closed corridor, open corridor, classroom, and computer lab. Path loss equations are determined using log-distance path loss model and log-normal shadowing. The Chi-square test statistic values for each access point are calculated to prove that the observed fading is a normal distribution at 5% significance level. A numerical analysis of measurements in each scenario was conducted and the study determined equations that describe path loss for each scenario.

Description: This paper discusses hybrid energy-aware synchronization algorithm in wireless sensor networks. Abstract: We present a time synchronization scheme for wireless sensor networks that aims to conserve sensor battery power while maintaining network connectivity for as long as possible. The proposed method creates a hierarchical tree by flooding the sensor network from a designated source point. It then uses a hybrid algorithm derived from the Timing-sync Protocol for Sensor Networks (TSPN) and the Reference Broadcast Synchronization Method (RBS) to periodically synchronize sensor clocks by minimizing the number of required transmissions. In multi-hop ad-hoc networks, a depleted sensor will drop information from all other sensors that route data through it, decreasing the physical area being monitored by the network. It is therefore imperative that time synchronization schemes are aware of the number of sensors being used at any given time. The proposed method uses several techniques and thresholds to maintain network connectivity. A new source point is chosen when the current one's battery power reaches a designated energy threshold. The network is also re-flooded whenever the number of used sensors drops below another threshold. We implement and show that their scheme can provide significant power savings over both TPSN and RBS; the ...

Description: This paper discusses an impact of interference model on capacity in CDMA cellular networks. Abstract: An overwhelming number of models in the literature use average interference for calculation of capacity of a CDMA network. In this paper, we calculate the actual per-user interference and analyze the effect of user-distribution on the capacity of a CDMA network. We show that even though the capacity obtained using average interference is a good approximation to the capacity calculated using actual interference for a uniform user distribution, the deviation can be tremendously large for non-uniform user distributions.

Description: Traditional design rules for cellular networks are not directly applicable to code division multiple access (CDMA) networks where intercell interference is not mitigated by cell placement and careful frequency planning. For transmission quality requirements, a minimum signal-to-interface ratio (SIR) must be achieved. The base-station location, its pilot-signal power (which determines the size of the cell), and the transmission power of the mobiles all affect the received SIR. In addition, because of the need for power control in CDMA networks, large cells can cause a lot of interference to adjacent small cells, posing another constraint to design. In order to maximize the network capacity associated with a design, the authors develop a methodology to calculate the sensitivity of capacity to base-station location, pilot-signal power, and transmission power of each mobile. To alleviate the problem caused by difference cell sizes, the authors introduce the power compensation factor, by which the nominal power of the mobiles in every cell is adjusted. The authors then use the calculated sensitivities in an iterative algorithm to determine the optimal locations of the base stations, pilot-signal powers, and power compensation factors in order to maximize capacity. The authors show examples of how networks using these design techniques ...