Software Manual for the R&S ZVL-K1 - Rohde & Schwarz

R&S ZVL-K1 WiMAX, WiBro Measurements (Options K93)
with
r
l,
k
= g ⋅ a
l
l,
k
data symbol l k
channel transfer function H l,
k
⋅ H
l,
k
a , on subcarrier k at OFDM symbol l
⋅
j Φ l j 2π
⋅N
s N FFT ⋅ζ
⋅k
⋅l
j 2π
⋅N
s N FFT ⋅∆f
res ⋅T
⋅l
e { ⋅ e1
44 2443
⋅ e1
442 443 + nl
, k
CPE
SFO
res. CFO
number of Nyquist samples s N within the symbol time s T
useful symbol time s g T T T − =
independent and Gaussian distributed noise sample n l,
k
Within one OFDM symbol both the CPE and the residual CFO respectively cause the same phase
rotation for each subcarrier, while the rotation due to the SFO linearly depends on the subcarrier index.
A linear phase increase in symbol direction can be observed for the residual CFO as well as the SFO.
The results of the tracking estimation block are used to compensate the samples r l,
k . While a full
compensation is performed in the reference path, the signal impairments that are of interest to the user
are left uncompensated in the measurement path.
Channel Estimation / Equalization
According to Fig. 2-93, there are two coarse and one fine channel estimation blocks. Which of the two
coarse estimation blocks is used depends on the link direction. For DL subframes the coarse channel
estimation is based on the preamble and directly follows the coarse frequency compensation block. The
pilot–based estimation for UL subframes is tapped behind the full compensation block of the reference
path. Both of the coarse estimation blocks use available training symbols to determine initial estimates
ˆ of the channel transfer function at fixed positions in the subcarrier–symbol plane. Based on these
H l,
k
nodes, the missing CTF values are obtained by interpolation in both time and frequency direction. The
coarse estimation results are used for the above mentioned fine timing and to equalize the samples l k
of the reference path prior to symbol decision. Based on the decided data symbols, a fine channel
estimation is performed and then used to equalize the partially compensated samples of the
measurement path.
Analysis
The analysis block of the OFDMA measurement application allows to calculate a variety of
measurement variables.
EVM
The most important variable is the error vector magnitude (EVM).
EVM l,
k =
r ′′ ′ l,
k − aˆ
l,
k
aˆ
(37)
on subcarrier k at OFDM symbol l . The subsequent average values can be derived from (37).
1. EVM of subchannel n at OFDM symbol l :
1
2
EVM l,
subchannel n = ∑ EVM l,
k (38)
ch n
N
2. EVM of all pilot subcarriers:
3. EVM of all data subcarriers:
EVM
EVM
pilots
data
=
=
1
N
1
N
sc
sc
1303.6573.42 2.155 E-5
l,
k
sc kch
n
∑∑
l kp
∑∑
l kd
EVM
EVM
2
l,
kp
2
l,
kd
(39)
(40)
(36)
r , ′