Multiplexing is not only a primary mechanism in communication systems but also in normal life. Multiplication describes how many users can share a medium with minimum are no interference. One example from your everyday life is Highways with several lanes. Several users use the same medium with probably no interference.
Space division multiplexing
For wireless communication, multiplexing can be carried out in four dimensions: space, time, frequency, and code. In this field, the task of multiplexing is to assign space, time, frequency, and code to each communication channel with a point of interference and a peak of medium utilization. The word communication channel here only indicates an Association of senders and receivers that need to exchange data.
In wireless transmission, space division multiplexing separate standard for each communication from with a far enough gap between senders. Using space-division multiplexing, obvious obstacles arise if two or more channels were established within the same space, for example, many radio stations want to broadcast in the same city. Then, one of the multiplexing systems must be applied (frequency, time, or code division multiplexing).
Frequency division multiplexing
Frequency division multiplexing (FDM) describes schemes to subdivide the frequency dimension into several non-overlapping frequency bands. Each channel k1 is now allotted its own frequency band as indicated. Senders using a certain frequency band can use this band continuously. Again, Guard spaces are needed to avoid frequency band overlapping also called adjacent channel interference.
This scheme is applied for radio stations within the same religion, radio station has its one frequency. This really simple multiplication scheme does not require Complex coordination between sender and receiver, the receiver only has to tune into the particular sender.
However, this scheme also exhibits disadvantages. While radio stations broadcast 24 hours a day, mobile communication typically takes place for only a few minutes a day. Specifying a separate frequency for each possible communication scenario would thus be a large waste of frequency sources. Additionally, the fixed assignment of a frequency to a sender executes this came very inflexible and restricts the number of senders.
A more flexible multiplexing scheme for typical Mobile Communications is time-division multiplexing. Here a channel k1 is given the whole bandwidth for a certain amount of time, that is, All senders use the same frequency but at different points in time. Again, guard spaces, which now represent time gaps, how to separate the different periods when the sender uses the medium.
Additionally, for a receiver tunning into a sender now does not involve adjusting the frequency but listening to accurately the right point in time. However, this scheme is very flexible as one can specify more sending time to send us a huge load and only less sending time to send us a light load.
A disadvantage of this scheme is again necessary coordination between different senders. No one has to control the sequence of frequencies and the time of changing to another frequency. Two senders will interfere as soon as they select the same frequency at the same time. However, if the frequency change is fast enough, the periods of interference may be so small that, depending on the coding of data into signals, a receiver can still recover the original data.
Code division multiplexing
While SDM and FDM are well known from the early days of radio transmission and TDM is used in connection with many applications, code division multiplexing (CDM) is a new scheme in commercial communication systems. First used in military applications due to its inherent security features, it is now also introduced in many civil wireless transmission scenarios. Separation is now achieved by assigning the channel its own code, guard faces are realized by using codes with the necessary distance in code space, e.g., orthogonal codes.
The main Advantage of CDM for wireless transmission is the protection against interference and tapping. Different codes have to be assigned, but code space is huge compared to the frequency space and, thus, assigning individual codes to each sender typically does not cause problems.
The main disadvantage of this scheme is the relatively high complexity of the receiver. A receiver has to know the code and must separate the channel with user data from the background noise composed of other signals and environmental noise.
Software quality assurance Software quality is described as conformance to explicitly state functional and performance requirements, explicitly documented standards and implicit features that are anticipated of all professionally developer software ... Read More
A tunnel establishes a virtual pipe for data packets between a tunnel entry and a tunnel endpoint. Packets entering a tunnel are forwarded inside the tunnel leave the tunnel unchanged. Tunneling, that is, sending a packet through a tunnel, is achieved by using encapsulation ... Read More
The overall structure of the software components and how the success provides a conceptual integrated file system. In other words, architecture is the hierarchical structure of program components, how these components interact, and the structure of data that are used by the components ... Read More
Real-time and distributed system design The real-time system is a software system the correct functioning of the system depends on the results produced by the system the time at which these results are produced ... Read More
Waterfall Model The waterfall model also called classic life cycle requirements is well defined and stable. It suggests a systematic, sequential approach to software development. It begins with customer specification of requirements and processes through planning, modeling, instruction, and deployment ... Read More
Software Design A software design is an essential engineering description of some software product that is to be established. A design can be determined to the customer's requirements and can be assessed for quality against predefined patterns ... Read More