Energy efficiency maximization for full duplex MIMO cloud radio access networks

Science & Technology Development Journal – Engineering and Technology, 3(3):488-499
Open Access Full Text Article Research Article
1Faculty of Electrical & Electronics
Engineering, Ho Chi Minh City
University of Technology (HCMUT), 268
Ly Thuong Kiet Street, District 10, Ho
Chi Minh City, Vietnam
2Vietnam National University Ho Chi
Minh City, Linh Trung Ward, Thu Duc
District, Ho Chi Minh City, Vietnam
Correspondence
Ha Hoang Kha, Faculty of Electrical &
Electronics Engineering, Ho Chi Minh
City University of Technology (HCMUT),
268 Ly Thuong Kiet Street, District 10,
Ho Chi Minh City, Vietnam
Vietnam National University Ho Chi Minh
City, Linh Trung Ward, Thu Duc District,
Ho Chi Minh City, Vietnam
Email: hhkha@hcmut.edu.vn
History
 Received: 17-3-2020 
 Accepted: 4-12-2020 
 Published: 20-12-2020
DOI :10.32508/stdjet.v3i3.685 
Energy efficiencymaximization for full duplexMIMO cloud radio
access networks
Tien Ngoc Ha1,2, Xuan-Xinh Nguyen1,2, Ha Hoang Kha1,2,*
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ABSTRACT
This paper studies the energy efficiency (EE) in full-duplex (FD) multiple-input multiple-output
(MIMO) cloud radio access networks (CRANs). A cloud control unit (CU) transfers information signals
with multiple downlink (DL) and uplink (UL) users through FD radio units (RUs) by limited capacity
FH links. In DL transmission, the signals intended to the DL users are centrally processed at the
CU and, then, compressed to transfer to the RUs before they are forwarded to the DL users. On
the other hand, the signals from the UL users to the RUs are compressed and forwarded to the
CU for signal detection processing. Thus, the precoding designs and compression strategies for
the UL and DL transmission are critical for the system performance. The conventional methods
commonly focus on maximizing the spectral efficiency (SE) in the networks. Although the SE max-
imization based methods can offer the superior SE performance, they can result in the inefficient
usage of the energy in the networks. Thus, this paper focuses on the joint design of the precoders
and quantization covariance matrices to maximize the EE. The EE maximization problem is formu-
lated as an optimization problem of the precoders and quantization covariancematrices subject to
the transmit power constraints at each RU, each user and the limited capacity of FH links. To deal
with the non-convexity of the formulated design problem, we exploit a successive convex approx-
imation (SCA) method to derive the concave lower bound function of the sum rate and a convex
upper bound of capacity functions of FH links. Then, the Dinkelbach approach is exploited to de-
rive an efficient iterative algorithm (IA) guaranteeing convergence. Numerical results are given to
demonstrate the EE performance of the proposed algorithm.
Key words: Full-duplex, CRAN, precoding design, energy efficiency
INTRODUCTION
Over the past years, the explosive surge in the amount
of mobile data has resulted in the challenging require-
ments of advanced wireless communication possess-
ing techniques to obtain not only higher achievable
data rates but also lower power consumption1. Cloud
radio access networks (CRANs) are a modern archi-
tecture for the next generation of mobile wireless sys-
tems. CRANs rely on the leverage of a baseband
processing with central unit (CU) that leads to not
only the effective joint transmission but also the re-
placement high-cost high-power base stations with
the low-cost low-power radio units (RUs). As such,
CRAN approaches can both enhance spectrum effi-
ciency and reduce power consumption. CRANs have
thus attracted significant investigations, see, e.g., 2
and references therein.
On the other hand, multi-antenna techniques have
also been recognized as the efficient transmission
methods because they provide more degrees of free-
dom enable to steer signal’s directions to the de-
sired users which are called beamforming or pre-
coding techniques. Hence, they are able to simul-
taneously transfer more than one data streams over
a specific resource, that can thus potentially achieve
greater data rates. On this view, CRAN systems with
multiple antennas have studied extensively as a po-
tential approach to improve spectral efficiency (SE).
There are studies on various implementation scenar-
ios for CRAN systems including either only multi-
antenna at RUs and single-antenna user equipments
(UEs) namely as multiple-input single-output CRAN
(MISO CRAN)3–7, or multi-antenna at both RUs
and UEs, referred as multiple-input multiple-output
CRAN (MIMO CRAN) 8–10. Reference3 addressed
the problemof concurrently optimizing both sum rate
(SR) and total transmit power (TP) by using a multi-
objective framework. They investigated on the algo-
rithm for jointly beamforming, turning RUs on/off,
and associating UEs to RU groups. Moreover, the au-
thors in4  ... limitations are investigated in this example. In this ex-
ample, the TP budgets of the RUs are set 25 dBm. The
average achievable EE is depicted in Figure 5while the
average achievable SR is shown in Figure 6. From the
two figures, we can see that both achievable EE and SR
are improved when the FH capacity increases. Noting
that when the FH capacity is low, it is a bottleneck to
restrict the system performance. In such cases, to re-
duce the FH traffic, the system will switch to a single
RU association19. Therefore, when the FH capacity
increases, the achievable EE and SR are increased. On
the other hand, the achievable EE and SR increase as
SI decreases.
CONCLUSION
In this paper, a joint design of FH compression and
precoding has been studied for a FD MIMO CRAN.
We have addressed the EE maximization problem for
this considered system model by developing the IA
using successive convex approximation and Dinkel-
bach approaches to deal with the non-convex prob-
lem. Finally, by numerical simulation results, we
have shown that the considered FDCRAN system can
bring significant EE gains over the HD scheme when
SI is low. In addition, the results have unveiled the
interesting influence of FH rate levels on the system
EE performance. Particularly, the bottleneck situa-
tion caused by the limited FH capacity leads to the
degradation in the EE system performance.
ACKNOWLEDGMENT
This research is funded by Vietnam National Foun-
dation for Science and Technology Development
(NAFOSTED) under grant number 102.04-2017.308.
LIST OF ABBREVIATIONS
CRAN: xloud radio access network
CU: control unit
D.C.: difference of convex
DL: downlink
EE: energy efficiency
FD: full-duplex
FH: fronthaul
HD: half-duplex
IA: iterative algorithm
MIMO: multiple-input multiple-output
MISO: multiple-input single-output
OP: optimization problem
QoS: quality-of-service
RA: receive antenna
RU: radio unit
494
Science & Technology Development Journal – Engineering and Technology, 3(3):488-499
Figure 2: Convergence behaviors of our IA for different levels of residual SI.
SE: spectral efficiency
SI: self-interference
SR: sum-rate
TA: transmit antenna
TP: transmit power
UE: user equipment
UL: uplink
CONFLICT OF INTEREST
The authors declare that there is no conflict of interest
regarding the publication of this article.
AUTHORS’ CONTRIBUTIONS
All the authors contribute equally to the paper includ-
ing the research idea and written manuscript.
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Figure 5: The average achievable EE versus different levels ofCFH .
498
Figure 6: The average achievable SR versus different levels ofCFH .
Tạp chí Phát triển Khoa học và Công nghệ – Kĩ thuật và Công nghệ, 3(3):488-499
Open Access Full Text Article Bài Nghiên cứu
1Khoa Điện-Điện tử, Trường Đại học
Bách Khoa TP.HCM, Việt Nam
2Đại học Quốc gia Thành phố Hồ Chí
Minh
Liên hệ
Hà Hoàng Kha, Khoa Điện-Điện tử, Trường
Đại học Bách Khoa TP.HCM, Việt Nam
Đại học Quốc gia Thành phố Hồ Chí Minh
Email: hhkha@hcmut.edu.vn
Lịch sử
 Ngày nhận: 17-3-2020
 Ngày chấp nhận: 4-12-2020 
 Ngày đăng: 20-12-2020
DOI :10.32508/stdjet.v3i3.685 
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Cực đại hóa hiệu suất năng lượng trong hệ thốngMIMO CRAN
song công
Hà Ngọc Tiến1,2, Nguyễn Xuân Xinh1,2, Hà Hoàng Kha1,2,*
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TÓM TẮT
Bài báo này nghiên cứu hiệu quả năng lượng của hệ thốngMIMO CRAN song công. Một trạm điều
khiển trung tâm (CU) truyền tín hiệu thông tin với các thiết bị người dùng đường lên và đường
xuống thông qua các trạm vô tuyến RU song công bằng các đường liên kết FH có dung lượng
giới hạn. Trong kênh truyền đường xuống, các tín hiệu mong muốn phát cho người dùng đường
xuống được xử lý tập trung ở trạm điều khiển trung tâm và sau đó được nén để truyền đến các
trạm vô tuyến RU trước khi chúng được chuyển tiếp đến người dùng đường xuống. Mặc khác, các
tín hiệu từ người dung đường lên đến các trạm vô tuyến được nén và chuyển đến trạm điều khiển
trung tâm cho việc xử lý giải mã tín hiệu. Do đó, việc thiết kế tiền mã hóa và chiến lược nén cho
truyền đường lên và đường xuống là quan trọng đối với hiệu năng hệ thống. Các phương pháp
phổ biến là tập trung tối đa hóa hiệu suất phổ trong mạng. Mặc dù các phương pháp dựa trên
cực đại hóa hiệu suất phổ có thể cung cấp hiệu suất phổ tốt, chúng có thể dẫn đến việc sử dụng
năng lượng không hiệu quả. Do đó, bài báo này tập trung thiết kế đồng thời bộ tiền mã hóa và
các ma trận hiệp phương sai lượng tử để tối đa hóa hiệu suất năng lượng. Vấn đề tối đa hóa hiệu
suất năng lượng được biểu diễn như một bài toán tối ưu của các ma trận tiền mã hóa và ma trân
hiệu phương sai lượng tử phụ thuộc vào điều kiện ràng buộc công suất phát ở mỗi trạm vô tuyến,
mỗi người dùng và dung lượng giới hạn của các liên kết FH. Để giải quyết vấn đề không lồi của bài
toán thiết kế, chúng tôi khai thác phương pháp xấp xỉ lồi tuần tự để rút ra hàm biên dưới lõm của
tổng tốc độ kênh và biên trên lồi của dung lượng đường liên kế FH. Sau đó, giải thuật Dinkelbach
được khai thác để phát triển giải thuật lặp hiệu quả đảm bảo tính hội tụ. Các kết quả mô phỏng
số được thực hiện để minh họa hiệu suất năng lượng EE của giải thuật.
Từ khoá: Song công, CRAN, thiết kế tiền mã hóa, hiệu suất năng lượng
Trích dẫn bài báo này: Tiến H N, Xinh N X, Kha H H. Cực đại hóa hiệu suất năng lượng trong hệ thống 
MIMO CRAN song công. Sci. Tech. Dev. J. - Eng. Tech.; 3(3):488-499.
499