Tuesday, 27 October 2015

Planning & Optimization System-Bearer Efficiency

ncident Description (Incident Phenomena)
Bear Efficiency is an important parameter in LTE systemit directly effects the system throughput and the maximum data rate. What are the key factors of bear efficiency, we will give a research about this question.
 Networking Environment
 Problem Cause Analysis
In Atoll, the efficiency of bearers (modulation and coding schemes) are defined in the Radio Bearers table. The bearer effi­ciency is given in terms of bits/symbol. Remember that in Atoll symbol refers to one resource element, the data transmission unit which is 1 symbol duration long and 1 subcarrier width wide
Bearer efficiency is similar to spectral efficiency. The only difference is in the units used. Here is a simple example that compares spectral efficiency and bearer efficiency, and shows that the two are the same.
Where BLER is the Block Error Rate, r is the coding rate for the bearer, and M is the number of modulation states. For simpli­fication, we set BLER = 0, and use QPSK1/2, i.e., four modulation states and r = 0.5. With these values, we get a spectral effi­ciency of 1 bps/Hz for QPSK1/2. In other words, a communication channel using QPSK1/2 modulation and coding scheme can send 1 bps of useful data per unit bandwidth.
In order to compare the bearer efficiency and spectral efficiency of QPSK1/2, let’s say that QPSK1/2 has a bearer efficiency of 1 bits/symbol. Here as well, the number of bits refers to useful data bits. The width of a subcarrier in LTE is, from which we can calculate the useful symbol duration as well: . In one second, there can be symbol durations. If 15000 symbols are transmitted using QPSK1/2, this gives us a throughput of, which is the throughput achievable using one subcarrier of 15 kHz. We can find the spectral efficiency by normalizing the throughput to unit bandwidth.
 Summary and Notes
In order to compare equivalent quantities, we have ignored some system parameters, such as the cyclic prefix, and have considered that the entire frame is transmitted in one direction, uplink or downlink.

Budi Prasetyo

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