Page 133 - ITU Journal Future and evolving technologies – Volume 2 (2021), Issue 2

ITU Journal on Future and Evolving Technologies, Volume 2 (2021), Issue 2

(a) Multi‑tap canceler, = = 1. (b) Multi‑tap canceler, = = 4.

(c) Multi‑AUX‑TX canceler, = = 1. (d) Multi‑AUX‑TX canceler, = = 4.
Fig. 4 – Probability of the residual SI power at each of the RX RF chains being less or equal to A = −60dBm versus the DL TX power P for = = 4.

6.1 Compared FD MIMO designs canceler results in 100(1 − / )% reduction in the re‑

quired number of AUX TXs. We have again used Section 5
We compare the presented FD MIMO designs versus the for the computation of TX/RX digital BF as well as the can‑
combined cancellation and spatial suppression design celer settings at the FD MIMO node . The G computation

presented in [4] as well as the digital BF design proposed was the same as for Design 1.
in [7]. We note that the designs presented in [20, 21] were Design 3: SotA with taps. This refers to a combina‑

not considered in the results that follow due to the fact tion of time domain analog cancellation with spatial sup‑
that they are only applicable to UpLink (UL) and Down‑ pression, as proposed in [4]. The TX beamformer is de‑
Link (DL) communications with = = 1, whereas signed to minimize SI caused from this operation by us‑

our proposed solutions hold for , ≥ 1. A detailed ing null space projection [4] for this communication side.

description of the FD MIMO designs that will be compared The RX BF was proposed to be an MMSE ilter in [4], we
is provided below.
however utilize the optimum combiner U obtained using

Design 1: Proposed with taps. This is the presented [29, Section 4.2], as explained in Section 5. Hence, we use
FD MIMO design with an ‑tap analog canceler. Com‑ the same combiner as in Designs 1 and 2. The time domain
paredwiththe SotAarchitectures[6, 15] requiringatleast cancellation is a canceler that requires in total taps

taps, our canceler results in 100(1− /( ))% (i.e., one tap per TX‑RX RF chain), as in the SotA schemes

reduction in the required taps’ numbers. The TX/RX dig‑ [6, 15]. We have made the same assumptions for the hard‑
ital BF as well as the settings for the canceler at the FD ware capabilities of the taps for this design as in Design 1.
MIMO node are computed as presented in Section 5. For Design 4: SotA with AUXTX. This design is similar to

H , Design 3 but uses AUX TXs in place of the analog taps. It
F being a MIMO channel, we have adoptedopen‑loop
MIMO precoding for the computation of G . particularly combines time domain cancellation with spa‑

Design 2: Proposed with AUXTX. This is the presented tial suppression [4]. The former is an analog canceler re‑
FD MIMO design for the case of multi‑AUX‑TX canceler quiring a total of AUX TX RF chains (i.e., one AUX TX

with AUX TX RF chains. Compared with the SotA archi‑ RF chain per RX RF chain), as in the SotA schemes [14, 16].
tectures [14, 16] which require at least AUX TXs, our In addition, the hardware capabilities of each AUX TX are

© International Telecommunication Union, 2021 119