TIDUD31B May 2017 – September 2019
For 2 Tx antenna TDM-MIMO, phase compensation needs to be done for the antenna samples received from the 2nd Tx antenna,
∆
φ
=
2
π
l
2
N
, where
l
=
[
-
N
2
,
.
.
.
,
N
2
-
1
]
is the Doppler index for the detected object, and N is the length of Doppler FFT.
In the case of velocity ambiguity, let v be the radial velocity of the detected object with Doppler index l from CFAR module. l’=l+i*N will represent radial velocity of v’=v+i*Vr,max, where i is an integer number, and l’ will be physically the same as l caused by velocity ambiguity. In turn, the phase compensation for 2nd for v’ will be
∆
φ
'
=
2
π
l
'
2
N
=
∆
φ
+
i
*
+
π
If we examine the formula above carefully, there are only 2 possible values of Doppler compensation for antenna samples from 2nd Tx antenna: H1=exp(-j*(Δφ+(2*k* π)) = exp(-j*Δφ), or H2=exp(-j*(Δφ+((2*k+1)* π)) = -exp(-j*Δφ).
In angular spectrum domain, as shown in Figure 16, when we apply Doppler compensation that correctly reflects the phase rotation from the true Doppler, we will see a spectrum shape in the blue curve, while the red curve represents the angular spectrum from compensation with a wrong hypothesis.
In the low level processing chain, we used a simple technique of just applying these two hypotheses of compensation factor to the antennas samples from 2nd Tx antenna, performing 2 angle estimations on 2 sets of data, and choosing the angle estimate corresponding to the larger peak from the angular spectrum. We call this angle correction for Vmax extension.