Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
1999-09-30
2003-11-18
Le, Thanh Cong (Department: 2684)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S442000
Reexamination Certificate
active
06650911
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a sectored antenna system, and more particularly to a sectored array antenna system used in CDMA mobile communication systems, which provides high success rate of softer handoff and high antenna gain.
BACKGROUND OF THE INVENTION
The growing interest in supporting voice and image services over wireless medium demands increased capacities of mobile communication systems. In current cellular mobile communication systems, the cell site receives and transmits signals in an omni-direction. Digital cellular mobile communication systems divide wide areas into a number of cells, and communications are accomplished between the cell station and a number of mobile stations. Information signals are transmitted and received in analog or digital form through wireless communication channels.
Generally speaking, the wireless communication channel from the cell station to the mobile station is called forward link, while the wireless communication channel from the mobile station to the cell station is called reverse link. The cell station transmits a number of multiplexed signals to mobile stations and receives signals transmitted from a number of mobile stations simultaneously. To accomplish these complex objectives, multiple access methods or multiplexing methods are required.
As multiple access methods, FDMA (frequency division multiple access), TDMA (Time Division Multiple Access), and CDMA (Code Division Multiple Access) are available. Furthermore, it is known that in the light of capacity, CDMA method is better than the other multiple access methods. One good reference is “On the capacity of a cellular CDMA system”, K. S. Gilhousen, I. M. Jacobs, R. Padovani, A. Viterbi, L. A. Weaver, C. Wheatly, IEEE Transaction of Vehicle Technology, vol.40, No.2.
CDMA systems allocate unique pseudo noise code (PN code) to each user and transmit band spread signals. Receivers use the same code as the PN code in order to despread band spread signals.
CDMA systems determine system capacity on the basis of the received amount of interference. The CDMA system manipulates the sectorization method to increase system capacity. As a result, received amount of interference is decreased. A sectorization method requires installing a sector antenna at a cell station that receives signals in a limited directional range. However, increasing the number of users and their expectation for high quality service demands new communication systems with better capacity than conventional systems. More recently, spatial and temporal signal processing using a smart antenna has been proposed as a good technique in increasing system capacity. An array antenna has been proposed as well.
The array antenna is composed of several antenna sensors and constitutes a narrow beam in the direction of signal- source to suppress signals of other users. A typical antenna array consists of a number of antenna sensors coupled together via some forms of amplitude and phase shifting network to generate a single output. Several shapes of the antenna sensors are common. For example, uniform linear, circular, and planar arrays are available.
FIG. 1
is a diagram illustrating the operation of a sector antenna system in CDMA communication systems with a cell divided into 3 sectors. As shown in the figure, an array antenna
10
is installed at each sector and a beam
11
is constituted for communication with each mobile station.
If the type of signal wave projected to the array antenna 10 is assumed as a plane wave, a steering vector is obtained by equation 1.
a
(
θ
)
=
[
1
Exp
(
-
j
2
π
d
λ
sin
θ
)
Exp
(
-
j
4
π
d
λ
sin
θ
)
.
.
.
Exp
(
-
j
2
(
M
-
1
)
π
d
λ
sin
θ
)
]
[
Equation
1
]
where d is the distance between adjacent antenna sensors (DBAAE); &lgr; is the wavelength of the transmitted signal; &thgr; is an incidence angle &thgr;.
The permissible value that the phase
2
π
d
λ
sin
θ
may assume lies inside the range −&pgr; to &pgr;. This means that we must choose the spacing
d
≤
λ
2
sin
θ
,
so that there is a one-to-one correspondence between the value of the incidence angle &thgr; and the phase
2
π
d
λ
sin
θ
without ambiguity.
FIG. 2
is a diagram illustrating the operational range of a sector array antenna. As shown in the figure, when incidence angle &thgr; lies inside the range between −&thgr;
m
and &thgr;
m
, the maximum value of d is
λ
2
sin
θ
m
.
Here, the incidence angle &thgr;
m
does not exceed
π
2
in maximum.
In mobile communication systems, when a mobile station escapes from the service area of a cell station and gets into another cell, the handoff function enables users to maintain communications. Two methods such as hard handoff and soft handoff are available.
For an analog cellular system, hard handoff is used. In hard handoff, before establishing a new communication channel, the existent link has to be disconnected. Therefore, signal quality gets degraded since communication is lost for a short amount of time when handoff occurs.
On the contrary, in digital cellular system, when a mobile station escapes from the service area of a cell station and moves into another cell area, an additional link is established with a new cell station without losing the existent link with the former cell station. In other words, the handoff process is composed of the following procedures in CDMA mobile communication systems. First, a communication channel with a cell station is established. Second, another communication channel is established with a new cell station without losing the existent communication channel. Third, the existent channel is disconnected. This handoff process is called soft handoff. Main advantages of soft handoff are that the probability of unwanted call termination is low and users don't even realize if handoff has happened because at least a communication link is kept during the communication.
In addition, when a mobile station is moving from one sector to another sector, similar process to the soft handoff process occurs. This process is called softer handoff. In softer handoff, the receiver at cell station diversity combines received signals and demodulates them.
FIG. 3
is a diagram illustrating a CDMA communication system in a case that one cell is divided into three sectors and a softer handoff occurs. The ranges of transmitted and received beams of each sector antenna are overlapped to perform softer handoff between adjacent sectors. In the figure, a reference numeral
30
is designated to the area where softer handoff occurs,
31
is to the area where beams are overlapped between sector
1
and sector
2
, and
32
is to the inside angle between the central axis of sector
1
and the distal side of the overlap area
31
for illustrating that sector
1
and sector
2
are overlapped with the angular degree of 10.
Under the assumption that system capacity is to be guaranteed, studies regarding how to arrange antenna sensors in an antenna array have been performed in order to expedite softer handoff process.
SUMMARY OF THE INVENTION
The present invention provides a sectored array antenna system for CDMA mobile communication systems, which has the optimal distance between antenna sensors.
Advantages of the present invention are that success rate of softer handoff and antenna gain is increased and power consumption of terminals may be evenly distributed. In CDMA mobile communication systems, a cell is divided into a number of sectors. The present invention provides a sector antenna system, which is composed o
Chang Kyung Hi
Kang Yang Gi
Kim Seong Rak
Kyeong Mun Geon
Park Youn Ok
Cong Le Thanh
Corsaro Nick
Electronics and Telecommunications Research Institute
Seed IP Law Group PLLC
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