Sharif Digital Repository

With improving of technology, using of Wireless Sensor Networks (WSN) is rapidly increasing. In some application, wireless sensor network do need to supply realtimeness. In the other hand, in many cases, sensor networks are in risky environments distributed. Therefore, security is a key factor in sensor networks to performing their works properly optimized and maximum. Hence, both security and realtimeness features are important features of sensor networks. But because of common resource use, increasing efficiency of a feature will result in decreasing efficiency of other feature. In this thesis, we indicated to study mutual effect of security and realtimeness in Wireless Sensor Networks in... 

Hard real-time embedded systems often operate in harsh environmental conditions that necessitate fault tolerant computing techniques. These embedded systems are also energy-constrained, since energy consumption is one of the key objectives. Examples include satellites, surveillance systems, autonomous seaborne and airborne systems. Generally, fault tolerance is obtained by hardware or time redundancy in these systems. Checkpointing with rollback recovery which employs time redundancy is one of the common techniques for tolerating transient faults in real-time embedded systems. Using checkpointing in energy constrained hard real-time systems should be carefully employed. In this thesis, we... 

VLSI technology scaling has resulted in the integration of a larger number of cores in a single chip in successive technology nodes, offering a great potential to realize task-level redundancy for reliability enhancement in safety-critical applications. However, since battery technology no longer advances commensurately with integration density, multi-core platforms may have limited utility in battery-powered embedded systems. In this thesis, we propose an energy-budget-aware reliability management (enBudRM) method for multi-core embedded systems featuring hybrid energy source (with renewable and non-renewable energy sources). Our method is composed of two phases. In the offline phase, we... 

Providing low-power fault tolerance is usually an important requirement in real-time embedded systems. A faulty result in safety-critical systems and a failure to meet a deadline in hard real-time systems can cause catastrophic consequences for the system or environment. Therefore, these systems must be highly reliable and meet real-time constraints. Slack time in time redundancy techniques (e.g. roll-back recovery) can be used to increase system reliability and to save energy. Time redundancy techniques are suitable from an energy consumption point of view but may not be sufficiently reliable for tight real-time constraints. In the condition of tight timing constraints, the hardware... 

Temporary or permanent overload commonly occurs in soft real-time systems. In such situations,the scheduler cannot guarantee the completion of all tasks prior to their deadlines.Hence, some tasks are usually aborted before or during the execution with the aim of maximizing system utility. For this purpose, time-utility function (TUF) of tasks is used to determine how to maximize the accrual utility of the system. Tasks which can provide more utility are more preferable for execution. Previous works on utility accrual maximizing algorithms have not considered memory allocation in accruing utility of soft real time systems. In this thesis, we present an online scheme for multicore embedded... 

One of the most important characteristics of real-time systems is executing tasks before their specified deadlines. The tasks’ execution may require several resources like processor, I/O ports, and data structures. Some of these resources may be shared between several tasks and their availability is important in executing tasks before the deadlines. Allocating shared resources which are used in mutually exclusive manner often encounteres some problems such as priority inversion and deadlock. Resource access protocols are used to minimize or eliminate these problems. The effect of using these protocols issupporting tasks’ execution before their deadlines. To meet deadlines is of decisive... 

Recent advances in miniaturization and low power design have led to a flurry of activity in wireless sensor networks (WSNs). Sensor networks have different constraints than traditional wired networks. A wireless sensor network is a special network with large numbers of nodes equipped with embedded processors, sensors, and radios. These nodes collaborate to accomplish a common task such as environment monitoring or asset tracking. Many of these applications interface with real world environments and delivery of data is subject to certain constraints. So It is often necessary for communication to meet real-time constraints. Most existing real-time protocols don’t use packet scheduling schemes... 

Scheduling of real-time processes is often one of the greatest challenges in designing distributed embedded systems. Low energy consumption and fault tolerance are key objectives in the design of embedded systems. However, these objectives are at odds, and there is a trade-off between them. A large part of this thesis includes a comprehensive study on previous researches on energy consumption and fault tolerance in hard real-time embedded systems. Real-time systems usually use system level energy management methods, i.e., dynamic voltage scaling (DVS) and dynamic power management (DPM). Also hard real-time systems often use replication to achieve fault tolerance. In this thesis, we...