Full-duplex transmission of IEEE 802.11ac-compliant
MIMO WLAN signals over a 2-km 7-core fiber
Yuting Fan (樊宇婷)
1
, Jianqiang Li (李建强)
1,
*, Yi Lei (雷 艺)
1
, Ming Tang (唐 明)
2
,
Feifei Yin (尹飞飞)
1
, Yitang Dai (戴一堂)
1
, and Kun Xu (徐 坤)
1
1
State Key Laboratory of Information Photonics and Optical Communications,
Beijing University of Posts and Telecommunications, Beijing 100876, China
2
Wuhan National lab for Optoelectronics (WNLO) & National Engineering Laboratory for
Next Generation Internet Access System, School of Optical and Electronic Information,
Huazhong University of Science and Technology, (HUST), Wuhan 430074, China
*Corresponding author: jianqiangli@bupt.edu.cn
Received September 7, 2016; accepted October 28, 2016; posted online December 8, 2016
In this Letter, we experimentally demonstrate a full-duplex transmission system of IEEE 802.11ac-compliant
multiple-input multiple-output (MIMO) signals over a 2-km 7-core fiber for in-building wireless local-area net-
work (WLAN) distributed antenna systems. For full-duplex 3 × 3 MIMO demonstration, the crosstalk impacts
of both fiber-transmission-only and optic-wireless transmission situation are evaluated. The results indicate that
the impact of crosstalk on radio-over-fiber (ROF) link performance is not significant and the quality of the cas-
caded multi-core fiber and wireless channel is mainly determined by the wireless part. To further improve the
system capacity, polarization multiplexing (PolMux) technology is employed to achieve a full-duplex 6 × 6
MIMO over a single 7-core fiber. Although employing the PolMux method will slightly decrease the EVM
and condition number performance as opposed to a non-PolMux MCF system, it is still a competitive solution
in large optical connection demand scenarios that require a low cost.
OCIS codes: 350.3950, 060.4230, 060.2360.
doi: 10.3788/COL201715.010011.
Distributed antenna systems (DASs) using radio-over-
fiber (RoF) techniques have been recognized as a promising
solution for in-building and hotspot wireless coverage
[1–3]
.
With a shared RoF-DAS infrastructure, it is preferable
to simultaneously distribute wireless local-area network
(WLAN) signals as an important complement to cellular
signals. Recently, several commercial WLAN products
compliant with IEEE 802.11ac standards have become
available. In the physical layer, 802.11ac further enhance s
the RF channel bandwidth up to 160 MHz, the modulation
level up to 256-ary quadrat ure amplitude modulation
(256-QAM), and the spatial-stream number up to 8
for multi-user multiple-input multiple-output (MIMO)
[4]
.
With these features, 802.11ac can achieve at least 1 Gb/s
rates for the multiple user case and at least 500 Mb/s rates
for the single user case, which represents an increase of
five times the maximum achievable rates compared to
802.11n. To distribute scalable 802.11ac signals using an
RoF DAS architecture, up to 8 weakly correlated channels
are required for MIMO transmission. Obviously, several
parallel single-mode fiber (SMF) links are not an efficient
solution for scalable RF signal distribution use.
Space-division multiplexing (SDM) over a multi-core
fiber (MCF) has been under intensive research to increase
the capacity per cross-sectional area of the fiber
[5,6]
.MCF
has been acknowledged because of its high space efficiency,
especially in large optical connection demand scenarios.
More recently, the suitability of SDM in MCF was
evaluated for long term evolution (LTE)-advanced optical
fronthaul systems in 4-core MCF
[7,8]
. The work demon-
strated a full-duplex 2 × 2 LTE-MIMO system and dis-
cussed the crosstalk penalty caused by the bending
radius and the impact of same or counter-propagations
in fiber-transmission-only environments. As the RoF
DAS architecture is significant in providing wireless cover-
age, the optic-wireless link joint impact is an important is-
sue to be evaluated for wireless use. On the other hand, the
polarization multiplexing (PolMux) method can effectively
double the spectral efficiency and could carry more chan-
nels on a signal fiber. Researchers have employed PolMux
methods for 2 × 2 MIMO-fiber transmission systems
[9,10]
.In
this Letter, the optic-wireless link impact of the crosstalk
and the performance of using PolMux in MCF to further
improve the capacity will be herein evaluated.
Due to power and cost considerations in real implemen-
tations, most of commercially available 802.11a c products
support 3 or 6 spatial streams. Hence, two scenarios
are considered in this Letter: full-duplex 802.11ac-
compliant 3-spatial stream with wireless transmission
(Scenario1), and 6-spatial stream with PolMux transmis-
sion (Scenario2) over a 2 km 7-core MCF. Note that the
medium-access control protocol of the IEEE 802.11 stan-
dards defines the maxi mum time delay in the physical
layer, thus commonly limiting fiber reaches lower than
2 km. The inner core is reserved as a dedicated control
channel for the remote antenna unit (RAU)
[11]
. The
impacts of the crosstalk on the link dynamic range and
optical power sensitivity were also evaluated.
COL 15(1), 010011(2017) CHINESE OPTICS LETTERS January 10, 2017
1671-7694/2016/010011(5) 010011-1 © 2016 Chinese Optics Letters