IEEE Circuits and Systems Magazine - Q2 2019 - 38

multi-output (MU-MIMO) mmW system. We provide the
design specification of components in array architectures to meet the SE requirement for each use case.
A. System Model of mmW MU-MIMO
We consider a mmW system where a BS of interest transmits data to multiple UEs in mmW access or a hub in
mmW self-backhauling. Both transmitter and receiver
are equipped with antenna array. Linear precoding techniques over flat fading channel are considered. In case
of frequency selective channel, the precoding can be extended using orthogonal-frequency-division-multiplexing (OFDM) by considering per sub-carrier precoding.
In the baseband equivalent model, the received symbol
at the u th UE is denoted as
y u = w Hu H u R ( Bs + z t) + w uH z r.

(1)

In the above equation, vector s = [s 1 f, s U ] contains the
U symbols. Matrix H u is the MIMO channel between
transmitter and u th UE receiver. Vector w u represent
the combining beamforming at the u th receiver. B and
R denote the precoding scheme in the baseband and RF
domain on the transmitter side, respectively. The trans-

mit noise due to DAC quantization error is denoted as z t
and thermal noise at the receiver is z r . Operation a H is
the Hermitian transpose of a.
In DA architecture, the precoding occurs entirely in
digital baseband and therefore there is no analog processing, i.e., R DA = I. The digital precoder B DA has dimension N DA # U.
In SA architecture, the digital precoder B SA has dimension M SA # U due to M SA RF chains. The RF precoder R SA has dimension N SA # M SA . Due to the fact that
every K SA of phase shifters connect to one RF-chain, R SA
is a block diagonal matrix
R SA = diag ^rSA, 1, f, rSA,M h,

(2)

where column vector rSA,m with length K SA represents
K SA phase shifters that connect to the m th RF-chain.
Each element of rSA,m has unit magnitude2. We define the
set Sm = {(m - 1) K SA + 1, f, mK SA} that contains indices
of array elements in the m th group.

2
In fact, analog precoding can be designed with both phase and magnitude tuning capability, which relaxes this constraint. The hardware
aspect of phase shifter is discussed in Section V-C.

Table II .
Link budget estimation in typical 5G use cases.
Dense-Urban
MBB

Use Case

50+Mbps
Everywhere

SelfBackhauling

Channel

Umi-LOS

Umi-NLOS

Uma-LOS

Freq. [GHz]

28

28

28

BW [MHz]

850

850

850

Distance [m]

100

100

707

Tx Power [dBm]

46.0

46.0

46.0

Tx Antenna Gain [dBi]

3.0

3.0

3.0

Pathloss a [dB]

104.4

125.1

118.3

12.7

25.3

17.0

b

Other Loss [dB]
Rx Gain [dB]

12.0

Rx NF [dB]

10.0

c

12.0

c

27.1d

10.0

10.0

Rx Noise [dBm]

-74.7

-74.7

-74.7

SNR w/o Tx Array [dB]

18.7

-14.7

15.5

Target SE [bps/Hz]

58.8

4.7

11.8

Simultaneous
Streams (U)

8

16

32

2

4

8

1

Per-UE SINRe [dB]

22.1

10.7

4.1

6.2

1.0

-3.0

35.5

a. Based on 3GPP model for above-6 GHz band [51].
b. Includes 3-sigma of shadowing loss and 25 mm/h rain absorption [52].
c. Based on 8 receiver antennas and 3 dBi antenna gain.
d. Based on 256 receiver antennas and 3 dBi antenna gain.
e. Based on equation SE = U log2(1 + SINR).

38

ieee circuits AND sYstems mAGAziNe

secoND QuArter 2019
IEEE Circuits and Systems Magazine - Q2 2019

Table of Contents for the Digital Edition of IEEE Circuits and Systems Magazine - Q2 2019
