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Inter-symbol Interference in LTE and in any technology that uses symbols to transport the information.

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With the modulation techniques development the mobile communications is being affected so much through the symbols are carrying so huge information in it.

However with this increasing technique there is also a problem called Inter-symbol interference or ISI.

Particularly in telecom ISI is a form of distortion of a signal in which a symbol interferes with other symbols. There can be multiple cause to have this ISI. It can be caused by multipath propagation or the inherent non-linear frequency response of a channel causing successive symbols to "blur" together.

Theoretically a signal receives at receiver without any loss, noise and interference but in real scenarios it does not. It will have multiple delays, multipath propagation and Band Limited channels.

Delay Spread:

A transmitted symbol can be received multiple times at the receiver, more or less as an "echo" effect. This echo is what we call "Delay Spread".

Delay Spread in ISI

In the above figure, the transmitter transmits a single symbol. This symbol is propagated along different paths (A, B and C), and eventually reaching the receiver at multiple time instants, and therefore with multiple "replication."

The total elapsed time between the first and last is determined by the environment (including the structures, how close they are, etc..). For example, in an urban environment, where the reflection is high (many buildings, many vehicles parked and moving), this delay has a typical value of 5-10 microseconds.

Multipath Propagation:

Due to the signal propagation phenomena, like reflection or diffraction, a receiver can receive several delayed versions of the same signal. This creates Inter-Symbol Interference (ISI).

ISI in LTE

The multi-path impact is an overlapping of 2 symbols, called Inter-Symbol Interference (ISI). The modulation is based on the amplitude and on the phase, so in case of overlapping there are 2 different amplitudes and phases. The receiver is not able to decode the state of the symbol.

The guard time is called the Cyclic Prefix (CP). It permits to facilitate demodulation.

ISI in LTE

The cyclic prefix transforms the classical channel convolution into a cyclic convolution which permits easy demodulation after FFT.

ISI in LTE

Symbol Duration:

As can we easily conclude, a very important determining factor for the ISI is the time duration of the symbol.
If the symbol period (T) is very short compared to the "Delay Spread" (t) the impact is significant (T << t).

Symbol in ISI

But if we can extend the symbols length, most of them will not suffer the impact of ISI (T >> t).

Symbol

One small part of the symbol will continue to be impacted, but for most of its duration, the symbol will remain not affected by reflections propagated in "Multipath".

That is why the ISI is minimized when we use a higher symbol period (or Lower Symbol Rate).

Symbol in ISI LTE

posted May 20, 2014 by anonymous

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information, and service between devices. All cell phones are expected to incorporate some type of identity module eventually, in part because of this useful property. Basically, the ICC deployed for 2G networks was called a SIM and the UICC smart card running the universal subscriber identity module(USIM) application. The UICC card accepts only 3G universal mobile telecommunications service (UMTS) commands. USIMs are enhanced versions of present-day SIMs, containing backward-compatible information. A USIM has a unique feature in that it allows one phone to have multiple numbers. If the SIM and USIM application are running on the same UICC, then they cannot be working simultaneously.

What is a microsim card?
Simply put, a Micro SIM is really just the same as a standard SIM card, just a bit smaller in size. It was developed by the European Telecommunications Standards Institute who settled on the 12 x 15mm size. So, what is its purpose? When you want to use a mobile phone you need some way of communicating which mobile network you are subscribed to. Essentially, this is what the SIM card is for: to contain network specific info that enables you to be identified by whatever mobile phone network you are signed up to. If you don’t have a SIM your phone simply will not work. You can also save lots of mobile phone contacts and other information on a SIM.
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A regular SIM card is actually quite a large item when you consider how the current gadget world is focused on smaller and smaller scales, or more compact forms, for everything. Its size occupies a relatively large amount of internal space within the actual handset, which is often a frustration for the top designers. This is where the micro-SIM comes in. It actually made its appearance in the iPhone 4S and iPad, which are some of the thinnest gadgets seen so far in the industry. The iPhone 5 features a nano sim, what is even smaller.
What we consider today to be a conventional SIM, which we use today in normal phones, is in fact a more compact version of the credit card sized SIMs used in the old mobile bricks people carried around back in the 1990s. The micro-SIM is more like a micro micro-SIM in reality.
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File System in Sim:-
A SIM card contains a processor and operating system with between 16 and 256 KB of persistent, electronically erasable, programmable read-only memory (EEPROM). It also contains RAM (random access memory) and ROM (read-only memory). RAM controls the program execution flow and the ROM controls the operating system work flow, user authentication, data encryption algorithm, and other applications. The hierarchically organized file system of a SIM resides in persistent memory and stores data as names and phone number entries, text messages, and network service settings. Depending on the phone used, some information on the SIM may coexist in the memory of the phone. Alternatively, information may reside entirely in the memory of the phone instead of available memory on the SIM.

The hierarchical file system resides in EEPROM. The file system consists of three types of files: master file(MF), dedicated files, and elementary files. The master file is the root of the file system. Dedicated files are the subordinate directories of master files. Elementary files contain various types of data, structured as either a sequence of data bytes, a sequence of fixed-size records, or a fixed set of fixed-size records used cyclically.
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As can be seen in the above figure, dedicated files are subordinate directories under the MF, their contents and functions being defined by the GSM11.11 standards. Three are usually present: DF (DCS1800), DF (GSM), and DF (Telecom). Also present under the MF are EFs (ICCID). Subordinate to each of the DFs are supporting EFs, which contain the actual data. The EFs under DF (DCS1800) and DF (GSM) contain network-related information and the EFs under DF (Telecom) contain the service-related information.

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Exceptions:
The CAMEL protocol does not apply to Emergency Setup. If a mobile user dials 911 while roaming, the CAMEL protocol is disabled. This ensures that the caller is routed to the local emergency response system and not to services in his home calling area.

Applicability of CAMEL procedures:
1. The CAMEL feature is applicable to Mobile Originated and Mobile Terminated Call Related Activities.
2. CAMEL procedures are applicable to all circuit switched basic services without distinction (except Emergency calls).
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4. CAMEL procedures are applicable to GPRS sessions and PDP contexts
5. CAMEL procedures are applicable to Mobile Originating/Terminating short message service through both circuit switched and packet switched serving network entities
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9. CAMEL procedures are applicable to IP multimedia sessions addressed by either E.164 numbers or SIP URLs.

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