LTE Emulator

LTE Emulator version 1.0 – technical report
The total signal to noise ratios are calculated for each user and for each OFDM sub-carrier,
finally generating a matrix G with a number of rows equal to the number of users, a number of
columns equal to the number of sub-carriers; this matrix stores the instantaneous signal to noise
ratios seen by each user in the entire bandwidth, which are applied to the radio resource
allocation (scheduler) block.
Note: considering that one chunk employs the same modulation, the number of
bits/QAM symbol allocation process uses an average signal to noise ratio on the
chunk sub-carriers.
The appendix presents some standardized multipath propagation channel profiles, for
various frequency bands.
5.2. The structure of the simulation program and the main processing performed
The simulation program is composed of two major components: an initialization and a
processing component; the latter performs the simulation processing involved by the
transmission processes of the main and secondary users.
The initialization component performs the following tasks:
o reads the parameters specified in the user interface;
o builds up the mapping and demapping tables necessary for QAM modulation and
demodulation;
o builds up the table required by the adaptive changing of the modulations employed;
o generates the control matrices of the error correcting codes and the auxiliary matrices
employed in the encoding process;
o computes the channel coherence time associated to different users;
o performs the initialization of different processing blocks;
The processing component performs, for each value of SNR0, the operations briefly
described bellow:
o simulation of the secondary users motion, by changing the values associated to the
attenuation parameter;
o generation of the radio channel affected by the multipath propagation and fast fading
both for the main user and the secondary users;
o allocation of the radio resources for all users, based on the characteristics of the
associated radio channels and on the characteristics of the provided services;
o generation of the test data for the main user;
o encoding of the main user’s data and generation of the appropriate transport frames;
o modulation of coded data on the OFDM sub-carrier and generation of the OFDMA
access data structures;
o generation of the noise signal, according to the value of instantaneous SNR characteristic
to each chunk associated to the main user transmission, and addition of the noise to the
transmitted signal;
o demodulation of data in each chunk associated to the main user transmission, and
reconstruction of the transport frames;
o decoding of the demodulated data;
o detection of post-decoding transmission error and implementation of the HARQ
retransmission process; it modifies the used coding rate (actually decreases it) and
resumes the transmission using the new coding rate;
Note: Since the simulator has only to generate some statistics, the simulation of the
retransmission process does not require the effective retransmission of the original
23