Low Complexity Hybrid Precoding Algorithm
in Millimeter Wave MIMO Systems
Ye Wang
1
, Weixia Zou
1
1
Key Lab of Universal Wireless Communications, MOE, Beijing University of Posts and Telecommunications,
Beijing 100876, P. R. China
Email: yewautumn@live.com; zwx0218@bupt.edu.cn
Abstract—Millimeter wave (mmWave) communication
will become a key technology for 5G networks. To combat
the high path loss of mmWave, large antenna arrays and
directional beamforming are used by mmWave commu-
nication systems. However, with the increase of number
of antennas, the hardware and energy cost of traditional
digital precoder is very high. Hence, hybrid precoding
structure is introduced to overcome the difficulty. In
this paper, we will propose an iterative heuristic hybrid
precoding algorithm with full channel state information.
We show that the proposed algorithm achieves near-optimal
performance with low complexity. Therefore, the proposed
algorithm provides a competitive trade-off strategy between
performance and complexity for hybrid precoding design.
Moreover, we find that the proposed algorithm is also able
to achieve satisfactory spectral efficiency in quantization
scenarios.
Index Terms—Millimeter wave communication, hybrid
precoding, low complexity, alternating minimization.
I. INTRODUCTION
The demand of wireless networks has dramatically
increased in recent years. In the future, the preparing
5G networks plan to achieve the requirements of high
data rate, low latency and low cost [1]. To overcome
the lack of spectrum resource in low frequency band,
millimeter wave (mmWave) band is introduced for 5G
networks [1], [2]. The high frequency of mmWave leads
to high free space loss and less diffraction [2]. Due to
the short wavelength of mmWave, the antenna elements
of mmWave are very small. This characteristic makes
it feasible to package more antenna elements in an
antenna array. Therefore, massive MIMO can be used
to compensate the high path loss of mmWave.
For traditional MIMO system, the signal is processed
at the baseband, where both the amplitudes and phases of
signals can be modified [3]. Then, the baseband signals
are converted to analog signals by radio frequency (RF)
chains before being transmitted by antennas. Hence, it
is necessary to allocate an RF chain for each antenna
element. For mmWave communication system with large
antenna arrays, the energy consumption and hardware
cost of required RF chains is too high. Therefore,
hybrid precoding architecture [4] is proposed to solve
the problem. By splitting the precoding precess into
digital precoding and analog precoding, the number
of RF chains can be reduced substantially, while the
performance loss of the system is not obvious. In analog
RF domain, the key component is phase shifter (PS),
which can only adjust the phase of signal.
In the work of [3], the hybrid precoding problem was
converted to the problem whose target is to minimize
the Euclidean distance between hybrid precoder and the
optimal precoder. In addition, spatially sparse precoding
via orthogonal matching pursuit (OMP) algorithm was
proposed as a solution. Based on the characteristic of
spatially sparseness, [5]–[7] also provided some other
algorithms. Besides, by introducing an extra constraint
for digital matrix, [8] proposed precoding designs for
single-user massive MIMO system and multi-user mas-
sive multiple-input single-output (MISO) system, respec-
tively. In [9], the author used alternating minimization
(AltMin) method to solve hybrid precoding problem and
proposed three algorithms for mmWave communication
systems. [10] proposed several low complexity algo-
rithms with different trade-off strategies between perfor-
mance and complexity. The work in [11] used alternate
minimization and matrix decomposition in combination,
and provided a near-optimal design for hybrid precoder.
In this paper, based on manifold optimization method
[9], we propose low complexity manifold optimization
(LCMO) as our hybrid precoder design. Based on the
framework of alternating minimization, the proposed
algorithm can solve hybrid precoding problem without
introducing extra constraints. To simplify the process of
solving the analog precoding matrix, we decompose the
non-convex problem into a series of subproblems which
can be solved easily. Then we assemble the solutions
of all the subproblems together to obtain the result of
complete analog precoding matrix. Besides, we give a
feasible and general step adjustment strategy to make the
algorithm adaptive for precoders with different numbers
of RF chains and data streams. Through simulation and
complexity analysis, we find that LCMO achieves near-
optimal performance with much lower complexity.
The following notations are used in this paper: A is a
matrix; a is a column vector; a is a scalar; (A)
m,n
and
(A)
m,:
indicate the entry on the mth row and nth column
of A and the mth row of A respectively; A
∗
, A
T
and
A
H
represent the conjugate, transpose and conjugate
transpose of A respectively; abs(A), det(A) and kAk
F
are the elementwise absolute value, determinant and
Frobenius norm of A respectively; A
−1
and A
†
indicate
2018 IEEE/CIC International Conference on Communications in China (ICCC Workshops)
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