Telecommunications – Transmitter – Diversity
Reexamination Certificate
2000-10-10
2004-06-22
Vuong, Quochien B. (Department: 2685)
Telecommunications
Transmitter
Diversity
C455S067110, C455S069000
Reexamination Certificate
active
06754473
ABSTRACT:
PRIORITY
This application claims priority to an application entitled “Apparatus and Method for Providing Closed-Loop Transmit Antenna Diversity in Mobile Communication System” filed in the Korean Industrial Property Office on Oct. 9, 1999 and assigned Serial No. 99-43679, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an apparatus and method for providing transmission antenna diversity on a downlink, and in particular, to an apparatus and method for providing closed-loop transmission antenna diversity by adaptively applying weights to closed-loop transmission diversity according to the channel environment in a mobile communication system.
2. Description of the Related Art
CDMA (Code Division Multiple Access) systems have evolved from the conventional voice transmission-based mobile communication systems to the new IMT-2000 standard, which provides such additional services as transmission of high quality voice, moving pictures, and Internet browsing.
For provision of these various services, the capacity of the downlink must have a higher gain for the increased traffic. For a mobile terminal that is moving at a low speed, it is known that a base station using antenna diversity can have gain about 1 to 7 dB higher than a base station which is not using antenna diversity in a CDMA mobile communication system. This implies that system capacity can be increased by two or three times and that a receiver of the terminal has a high enough gain.
The transmit antenna diversity is a scheme of transmitting a signal to a terminal through at least two transmission antennas from a base station. Two approaches may be taken when using transmission antenna diversity.
One of the approaches is a closed-loop scheme (feedback type transmission diversity). The mobile terminal estimates the strengths of signals received from the base station antennas and transmits weight information for each antenna to the base station. After changing weights for transmission power and phase based on the weight information, the base station transmits data.
The other approach is an open-loop scheme. The base station allocates equal transmission power to each antenna and transmits data through the antennas with different orthogonal codes.
The following description concerns the closed-loop transmit antenna diversity scheme.
A base station as described hereinbelow belongs to an UMTS (Universal Mobile Telecommunication System). While the base station may have more than two transmission antennas, two transmission antennas are assumed in the following description for greater clarity.
If the base station transmits signals through a plurality of antennas, i.e., with transmit antenna diversity, the reception BER (Bit Error Rate) is decreased at the terminal. For downlink transmission through the antennas, the base station allocates a unique weight to each antenna transmission signal. The antenna-specific weight should be set in such a way that the terminal can receive the next antenna signal with maximal power. If the terminal estimates the downlink channel environment and notifies the base station of the estimation, the base station can allocate an optimum weight to each antenna. To this end, the mobile terminal estimates the status of a channel on which a signal is received from the base station and transmits the estimated channel status (i.e., channel environment) to the base station.
FIG. 1
is a block diagram of a transmitting device with transmit antenna diversity in a general mobile communication system.
Referring to
FIG. 1
, reference numerals
101
and
111
denote a primary common pilot channel (P_CPICH) and a secondary common pilot channel (S_CPICH), respectively. The base station uses one P_CPICH
101
. It can also generate a plurality of S_CPICHs
111
to transmit on the downlink with feedback-mode transmit diversity. The P_CPICH
101
and S_CPICHs
111
are all 1 s and spread with one of orthogonal variable spreading factor (OVSF) code with Spreading Factor (SF)
256
. The P_CPICH
101
is scrambled with a primary scrambling code and the S_CPICH
111
is scrambled with a secondary scrambling code. Both the common pilot channels
101
and
111
are transmitted at 300 bits per 10-ms frame.
A spreader 103 spreads the P_CPICH
101
and a spreader
113
spreads the S_CPICH
111
. A multiplier
104
scrambles the spread P_CPICH
101
with a primary scrambling code. One primary scrambling code is assigned to each base station, in order to identify the base station. A multiplier
114
scrambles the spread S_CPICH
111
with the secondary scrambling code. An encoder
133
subjects a downlink dedicated physical data channel (DPDCH)
131
to encoding and rate matching. An interleaver
135
interleaves the downlink DPDCH received from the encoder
133
. A multiplexer (MUX)
137
multiplexes a TPC (transmit power control)
136
, a TFCI (Transmit Format Combination Indicator)
138
, and the interleaved DPDCH. The TPC
136
is used to control signal transmission power and the TFCI
138
provides information about the channel encoding method and transmission rate of the data. A MUX
141
multiplexes the multiplexed DPDCH, TFCI, and TPC received from the MUX
137
and a pilot signal
132
for antenna #
1
as indicated by reference numeral
180
. A MUX
151
multiplexes the multiplexed DPDCH, TFCI, and TPC received from the MUX
137
and a diversity pilot signal
134
for antenna #
2
as indicated by reference numeral
181
. The pilot signals
131
and
134
typically have the same pilot pattern but may have different pilot patterns.
A spreader
143
spreads the output of the MUX
141
with an assigned OVSF code. A multiplier
144
scrambles the output of the spreader
143
with the primary scrambling code or the secondary scrambling code. The secondary scrambling code is used instead of the primary scrambling code when there is lack of OVSF codes assigned to channels using the primary scrambling code. A multiplier
145
multiplies the output of the multiplier
144
with a weight
175
assigned to antenna #
1
180
. A summation device
160
sums the P_CPICH of antenna #
1
180
received from the multiplier
104
and the DPDCH received from he multiplier
145
. The sum is filtered by a filter
162
, modulated to a radio signal y an RF module
164
, and transmitted to the terminal through antenna #
1
180
.
A spreader
153
spreads the output of the MUX
151
. A multiplier
154
scrambles the output of the spreader
153
with the primary scrambling code or the secondary scrambling code. A multiplier
155
multiplies the output of the multiplier
154
with a weight
174
assigned to antenna #
2
181
. A summation device
161
sums the S_CPICH received from the multiplier
114
and the DPDCH received from the multiplier
155
. The sum is filtered by a filter
183
, modulated to a radio signal by an RF module
185
, and transmitted to the terminal through antenna #
2
181
.
A weight generator
171
generates weights
174
and
175
for antennas #
1
and #
2
based on downlink channel status information received from the mobile terminal and feeds them to the multipliers
155
and
145
, respectively. The weights
174
and
175
are expressed in complex vectors and one of them has a fixed value.
FIG. 2
is the format of a feedback signal message by which the terminal transmits the downlink channel status information to the base station.
Referring to
FIG. 2
, the feedback signal message is transmitted on an uplink dedicated physical control channel (UL_DPCCH), at a rate of ten bits per slot. Specifically, the feedback signal message includes a pilot field
201
, a TFCI field
202
, a FBI (Feedback Indicator) field
203
, and a TPC field
204
. These fields occupy a total of ten bits. The length of each field in the feedback signal message varies depending on the channel environment.
The channel environment is indicated by presence or absence of the TFCI field
202
and the FBI field
203
. Accordin
Choi Ho-Kyu
Choi Jin-Ho
Hwang Sung-Oh
Lee Hyun-Woo
Park Chang-Soo
Dilworth & Barrese LLP
Jackson Blane J.
Samsung Electronics Co,. Ltd.
Vuong Quochien B.
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