554 PIERS Proceedings, Moscow, Russia, August 19–23, 2012
Feng Gao 1 , Peng Gao 1 , Tong Wu 2 , and Runhong Shan 3
1 China Mobile Group Design Institute, Beijing 100080, China
2 China National Institute of Metrology, China
3 Copyright Protection Center of China, China
Abstract — This paper proposes a novel dual polarized omni-directional indoor antenna, which can be used as multi-input multi-output (MIMO) antenna in LTE system. The vertical dipole covers from 0 .
8 ∼ 3 GHz and the horizontal dipole covers GSM1800, TD-SCDMA, wireless local area network (WLAN) and long term evolution (LTE) systems. This indoor antenna has been experimented in MIMO systems for the WLAN system and LTE-TDD scale testing network separately. Based on the experiment, the cumulative distribution function (CDF) curve of Timing offset between uplink and downlink radio frames, reference signal received power (RSRP), signal to noise ratio (SNR) and throughput of downlink and uplink are studied, compared with singleinput single-output (SISO) system.
1. INTRODUCTION
In radio, multiple-input and multiple-output is the use of multiple antennas at both the transmitter and receiver to improve communication performance. The 3rd generation partnership project
(3GPP) has launched the study item of the long term evolution (LTE) system. MIMO technology has attracted attention in wireless communications, because it offers significant increases in data throughput and link range without additional bandwidth or increased transmit power. Because of these properties, MIMO is an important part of modern wireless communication standards such as
IEEE 802.11n (Wifi), 4G, 3GPP LTE, WiMAX and HSPA [1, 2].
China Mobile Communications Corporation (CMCC) have made progress for the TD-LTE system through LTE scale experimental network. This paper proposes a novel dual polarized omnidirectional indoor antenna, which can be used as multi-input multi-output (MIMO) antenna in LTE system. The vertical dipole covers from 0 .
8 ∼ 3 GHz and the horizontal dipole covers GSM1800,
TD-SCDMA, wireless local area network (WLAN) and LTE systems.
2. CONFIGURATION OF INDOOR MIMO ANTENNA MODEL
In MIMO systems, a transmitter sends multiple streams by multiple transmit antennas. The transmit streams go through a matrix channel which consists of all N transmit antennas at the transmitter and N r t
N r paths between the N t receive antennas at the receiver. Then, the receiver gets the received signal vectors by the multiple receive antennas and decodes the received signal vectors into the original information. A narrowband flat fading MIMO system is modelled as [3]
Y = Hx + n (1) where Y and x are the receive and transmit vectors, respectively, and H and n are the channel matrix and the noise vector, respectively. The system is shown in Figure 1.
The MIMO antenna is regarded as a multi-port microwave network. The incident wave and reflected wave relationship is given below [4]
·
¯ b
( N × 1)
( ∞× 1)
¸
= S ·
" b a +
( N × 1)
+
( ∞× N )
#
=
·
S
S aa ( N × N ) ba ( ∞× N )
S ab ( N ×∞ )
S bb ( ∞×∞ )
¸
·
" b a +
( N × 1)
+
( ∞× N
)
#
(2)
Referring to information theory, the ergodic channel capacity of MIMO systems where both the transmitter and the receiver have perfect instantaneous channel state information is [5]
C p − CSI
= E h max
Q ; tr ( Q ) ≤ 1 log
2 det
¡
1 + ρ HQH H
¢i
= E [log
2 det(1 + ρ DSD )] (3)

Progress In Electromagnetics Research Symposium Proceedings, Moscow, Russia, August 19–23, 2012 555
Figure 1: MIMO antenna channel model.
(a) vertical element (b) horizontal element
Figure 2: Structure of the dual-polarized antenna.
where () H denotes Hermitian transpose and ρ is the ratio between transmit power and noise power
(i.e., transmit SNR). The upper bound of SINR of the mobile receiver for a cell with K users is obtained as follows [6]
SINR k = det[ H − 1 k
σ 2 v k
1
+ σ
H
2 v k
2 k
]
(4)
Under the Gaussian approximation [7], the bit error rate (BER) can be written with the SINR as
BER k
= Q
³p
SINR k
´
(5) where Q ( · ) is Gaussian approximation function.
3. SIMULATION AND ANALYSIS OF DUAL-POLARIZED INDOOR ANTENNA
The Figure 2 shows the vertical polarized and the horizontal element of the antenna. The horizontal polarized element is formed with four folded dipoles which are rotating feed, and the vertical polarized element is formed with the inverted-cone monopole and the bottom board. Because the horizontal polarized element and vertical polarized element are coaxial, which can decrease the interplay, reduce the interference, and increase the isolation each other.
The frequency range of the dual-polarized antenna as shown in Figure 2 covered 824 ∼ 960 MHz,
1710 ∼ 3000 MHz by vertical polarized element and covered 1710 ∼ 2700 MHz by horizontal polarized element. The simulations of the antenna pattern are shown in Figure 3.
From the simulation and analysis, the non-circularity of the dual-polarized antenna is lower than
± 1 .
5 dB.
4. PERFORMANCE EVOLUTION OF INDOOR MIMO TESTED
4.1. Indoor LTE MIMO System Tested
In order to clarify the basic characteristics of our indoor MIMO tested, we have conducted measurements and indoor environment. Figure 4 shows the single and dual channel indoor distribution systems.
For the indoor LTE system tested, there are two environments respectively shown in Figure 4.
The Figure 4(a) shows the single channel indoor distribution system and the Figure 4(b) shows the dual channel indoor distribution system.

556 PIERS Proceedings, Moscow, Russia, August 19–23, 2012
(a) vertical polarization (b) horizontal polarization
Figure 3: Pattern of the dual-polarized antenna.
(a)
(b)
Figure 4: (a) Single channel indoor distribution system. (b) Dual channel indoor distribution system.
Figure 5: Dual polarized antenna CDF curve in middle section.
Antenna signal correlation can be used to solve pattern relationship. Figure 5 shows the dual polarized MIMO antenna NTA CDF distribution curve in midpoint region.
Figure 6 shows downlink throughput of six equipment manufacturers (EM) in LTE scale experimental network test. Several RRU should be integrated for same distribution system to save the network construction cost. Different frequency network could be recommended if several cells exist in same distribution system carrier bandwidth of 20 MHz.
4.2. Indoor WLAN MIMO System Tested
In order to verify the 802.11n WLAN performance based on MIMO systemthe wireless signal strength test, signal to noise ratio test, ping test, AP configuration check and interference test and
FTP test are implemented. Figure 7 and Figure 8 respectively show the dual polarization 2 × 2
MIMO 40 M mode uplink and downlink throughput.

Progress In Electromagnetics Research Symposium Proceedings, Moscow, Russia, August 19–23, 2012 557
Figure 6: Downlink throughput for same or different frequency network.
Figure 7: Uplink throughput in 40 M model 2 × 2
MIMO system in middle section.
Figure 8: Downlink throughput in 40 M model 2 × 2
MIMO system in middle section.
5. CONCLUSION
The system capacity and correlation of indoor WLAN system and LTE system are analyzed in this paper, comparation of SISO and MIMO system is tested. The test shows that transmitting power of terminal of dual channel MIMO antenna system can be reduced t using multipath effect, improve the downlink throughput, and SNR and anti-interference ability are improved obviously.
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