ncident Description (Incident Phenomena)  
Bear Efficiency is an important parameter in LTE system，it 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  
Solution  
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. 
Tuesday, 27 October 2015
Planning & Optimization SystemBearer Efficiency
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