In modulation process two signals are used low frequency signal and high frequency signal

   The process of combining low frequency signal with high frequency signal in order transfer it through a large distances is known as modulation

   The advantages of modulation are:

    1.Reduces the height of antenna

    2.Avoid mixing of signals

    3.Increase the range of communication

    4.Improves the quality of reception

A yagi uda antenna contains one dtiven element ,one reflector and one or more directors

1.The input is supplied to the driven element so it is known as active element.

2.For reflectors and directors we are not applying any input.So the reflectors and directors are called as parasitic elements.

3.Driven element and the parasatic elements are placed parallel to each other and close to each other.

4.The reflector is placed back side of the driven element which is longer than driven element and compare to all elements.

5.The element infront of the driven element is director which is smaller than all elements.

6.The length of all elements will be calculated by relation.

      lambda=c/f

7.If the driven element is halfwave dipole the length is

    L=150/f(MHZ)

Approximate values

8.The length of driven element is L=143/f(MHZ).

9.The length of reflector is L=152/f(MHZ).

10.The length of director is L=137/f(MHZ).

11.Spacing between reflector and driven element is 75/f(MHZ).

12.Spacing between driven element and director is 40/f(MHZ).

13.Spacing between director 1 & director 2 is 38/f(MHZ).

example of yagi uda antenna:

Quality Attributes of embedded System:

These are the attributes that together form the deciding factor about quality of an embedded system.

There are two types of quality Attributes

1. Operational Quality Attributes :There are the attributes related to operation or functioning of an embedded system. The way an embedded system operates affects its overall quality.

2. Non-Operational Quality Attributes, :These are attributes not related to operation or functioning of an embedded system.

There are the attributes that are associated with the embedded system before it can be put into operation

OPERATIONAL ATTRIBUTES :-

1.Response: -

• It is a measure of quickness of the system.
• It gives you an idea about how fast your system is tracking the input variables
• most of the embedded system demand fast response which should be real-time.

2.Throughput :

• It deals with the efficiency of system
• It can be defined as rate of production or process over a static period of time. 

3. Reliability :

• It is the measure of how much percentage you rely upon the proper functioning of the system
• Mean Time b/w failures and Mean Time to repair are  terms used in defining system reliability.

4.Maintainability :

• maintainability deals with support and maintenance to the end user or a client in case of technical issues and product failures of routine system checkup

5. Security:

• Confidentiality, Integrity and Availability at three corner stones of information security
• Confidential data deals with protecting data from unauthorized disclosure.
• Integrity gives protection from unauthorized modification.
• Availability gives protection from unauthorized person.

6. Safety:

• Safety deals with the possible damage that can happen to the operating person and environment
• Due to breakdown of an embedded system or due to emission of hazardous materials from the embedded products.

NON - OPERATIONAL ATTRIBUTES :

a)Testability and Debug-ability:

• It deals with how easily one can test his/her design application by which means he/she can test it
• In hardware testing the peripherals and total hardware function in designer manner.
• Firmware testing is functioning in expected way

b)Evolvability:

• For embedded system, the quantitative attribute durability refer to ease with which the embedded product can be modified to tells advantage of  new firmware  (or) hardware technology

c) portability

• Portability is measured of %u201CSystem Independence%u201D
• An embedded product can be called portable if it is capable of performing its operations as it is intended to do in various environments irrespective of different processor and or controller and embedded operating systems.

d)Time to prototype and market:

• Time to Market is the time elapsed between the Conceptualization product and time at which product is ready for selling or use.
• Product prototyping help in reducing time to market.
• Prototyping is an informal kind of rapid product development in which important feature of the under consider are develop.
• In oden to shorten the time to prototype make use of all possible option like use of run, off the component etc..

e)Per unit and total cost:

•  Cost is important factor which needs to b carefully monitored. Proper market study and cost benefit analysis should be carried on before taking decisions on the per unit cost of the embedded product.
• When the product is introduced in the market for the initial period the sales and revenue will below.
• There won't be much compassion when the product sales and revenue increase
• During  the maturing phase, the growth will be steady and revenue reaches highest point and at retirement time there will be a drop in sales volume.

Multicore CPUs:

Unlike multi processor systems that make use of multiple processors to carry out concurrent operations, multicore CPUs make use of multiple cores within a single processor. The idea here is to divide the processor into multiple cores such as dual, quad etc to carry out operations in parallel. The main advantage of these systems is that it improves potential performance of the overall system. One of the major examples of such systems in Intel processors whose speed of processing increased from 10 MHZ to 4 GHZ. This value is considered as limit for most (or) all of the chips that are based on CMOS because of the power constraints. These constraints can be removed by employing ILP mechanisms which are based on super scalar architecture and speculative execution.

Some systems use many-core GPU (Graphics Processing Units) that make use of thousands of processor cores. These GPUs are capable of managing instructions with varying magnitudes similar to that of multi core CPU.

Some of the processors that are based on multi-core and multithreaded processing are Intel i7. AMD opteron, IBM power 6 and many more. Multithreading: Multithreading is a feature which enables multiple threads to execute on a single processor in an overlapping manner. A thread is an atomic unit of a process and many threads usually make up a process. In a multithreading

environment, the resources of a processor are being shared by multiple threads, so each thread gets a separate copy of the functional unit or resource. Functional units generally include

a register file, a separate Program Counter (pc) or a separate page table to enable virtual memory access, which in turn enables multiple program to execute simultaneously by sharing the memory 

To enable multithreading, the hardware must be able to perform threads switching which is more efficient than switching the processes, as each process consists of threads and usually takes many clock cycles for its execution. As threads are lightweight they can execute and switch among themselves during the execution. Therefore they are considered more efficient and fast than processes.

Multithreading can be implemented in two ways

1. Fine-grained multithreading

2. Coarse-grained multithreading.

1. Fine Grained Multithreading: In this approach, the threads are switched on each instruction. The delay caused because of the switch operation of threads is very little. The threads are switched only if the current running thread encounters a stall. The subsequent thread is chosen from a pool of waiting threads in a round-robin fashion. The approach becomes effective if threads are switched at every clock cycle.

Advantage: The advantage of fine-grained multithreading is that it can efficiently recover the losses of throughput which come from short and long stalls of the thread.

Disadvantage: The execution of the stalled thread is delayed that in turn decreases the execution speed of that individual thread since another thread is being executed in its place.

2. Coarse-Grained Multithreading: Coarse-grained multithreading is another approach for implementing multithreading. In a coarse grained multithreading approach, the threads switch only when a costly stall is encountered. A costly stall can be defined as a stall where a thread requires resources which usually consumes more CPU clock cycles than required.

A level 2 cache miss is an example of a costly stall. If such a case is encountered in a coarse-grained approach, then another thread replaces it and executes till the stalled thread has recovered.

In contrast to a fine-grained approach, in a coarse-grained approach, the threads without stalls can be executed completely without any interruption until a costly stall is encountered.

The main disadvantage of coarse-grained multithreading is that, when a thread encounters a costly stall, its instruction pipeline which is carrying out the execution gets frozen. The new thread which replaces this frozen thread has to wait until the emptied pipeline is filled, prior to completion of instruction execution. The time delay is significant and appears to be an overhead. Coarse-grained multithreaded approach doesn't have the ability.

The key advantage of coarse grained multithreading is that it stops the execution of threads which encounter costly stall and replaces with a new thread. A costly stall consumes more clock cycles when compared to the time taken to remove a frozen thread and replace a new thread into the pipeline. Simultaneous Multithreading (SMT): In addition to the two multithreading approaches there is another approach which is implemented on a superscalar multiprocessor. A superscalar processor is a processor which issues multiple issues at the same time exploiting Instruction Level Parallelism (ILP) where multiple instructions are executed at the same time. A

Superscalar processors generally operate on more than one scalar. By scalar, we meant a single unit of data. This approach is a variation of fine-grained multithreading and is called

Simultaneous Multithreading (SMT). Simultaneous multithreading allows multiple threads to

execute at the same time and also let multiple instructions to get executed at the same time by a processor. 

By allowing multiple instructions to be executed on multiple independent threads, a higher degree of efficiency is achieved. Instructions are dynamically scheduled so that a processor can run multiple instructions on multiple threads without conflicts and dependencies. To maintain the execution of multiple threads on multiple instructions, the registers are renamed continuously so to avoid confusion between two threads.