STTD encoding for PCCPCH

Details STTD encoding for PCCPCH STTD encoding for PCCPCH

1999-08-13

2004-04-27

Bocure, Tesfaldet (Department: 2631)

Pulse or digital communications

Spread spectrum

Direct sequence

C375S347000, C455S137000

Reexamination Certificate

active

06728302

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to wideband code division multiple access (WCDMA) for a communication system and more particularly to space-time transmit diversity (STTD) detection for WCDMA signals.
BACKGROUND OF THE INVENTION
Present code division multiple access (CDMA) systems are characterized by simultaneous transmission of different data signals over a common channel by assigning each signal a unique code. This unique code is matched with a code of a selected receiver to determine the proper recipient of a data signal. These different data signals arrive at the receiver via multiple paths due to ground clutter and unpredictable signal reflection. Additive effects of these multiple data signals at the receiver may result in significant fading or variation in received signal strength. In general, this fading due to multiple data paths may be diminished by spreading the transmitted energy over a wide bandwidth. This wide bandwidth results in greatly reduced fading compared to narrow band transmission modes such as frequency division multiple access (FDMA) or time division multiple access (TDMA).
Previous studies have shown that multiple transmit antennas may improve reception by increasing transmit diversity for narrow band communication systems. In their paper
New Detection Schemes for Transmit Diversity with no Channel Estimation
, Tarokh et al. describe such a transmit diversity scheme for a TDMA system. The same concept is described in
A Simple Transmitter Diversity Technique for Wireless Communications
by Alamouti. Tarokh et al. and Alamouti, however, fail to teach such a transmit diversity scheme for a WCDMA communication system.
New standards are continually emerging for transmit diversity of next generation wideband code division multiple access (WCDMA) communication systems as described in Provisional U.S. Patent Application No. 60/116,268, filed Jan. 19, 1999, and incorporated herein by reference. These WCDMA systems are coherent communications systems with pilot symbol assisted channel estimation schemes. These pilot symbols are transmitted as quadrature phase shift keyed (QPSK) known data in predetermined time frames to any receivers within range. The frames may propagate in a discontinuous transmission (DTX) mode. For voice traffic, transmission of user data occurs when the user speaks, but no data symbol transmission occurs when the user is silent. Similarly for packet data, the user data may be transmitted only when packets are ready to be sent. The frames are subdivided into sixteen equal time slots of 0.625 milliseconds each. Each time slot is further subdivided into equal symbol times. At a data rate of 32 KSPS, for example, each time slot includes twenty symbol times. Each frame includes pilot symbols as well as other control symbols such as transmit power control (TPC) symbols and rate information (RI) symbols. These control symbols include multiple bits otherwise known as chips to distinguish them from data bits. The chip transmission time (T
C
), therefore, is equal to the symbol time rate (T) divided by the number of chips in the symbol (N).
A mobile unit must initially receive and synchronize with data frames transmitted by one or more remote base stations. Each base station continually transmits broadcast channel (BCH) data over the primary common control physical channel (PCCPCH) to identify itself to mobile units within the cell. Referring to
FIG. 1
, there is a simplified block diagram of a typical diversity transmitter of the prior art. The transmitter simultaneously transmits primary and secondary synchronization codes on respective primary (P-SCH)
150
and secondary (S-SCH)
160
channels to uniquely identify each base station signal received by the mobile unit. Circuits
156
and
166
modulate the gain of these synchronization codes in response to respective gain factors GP-SCH on lead
154
and GP-SCH on lead
164
. Circuit
170
adds the synchronization codes and applies them to time switch (TSW)
174
via lead
172
. Time switch
174
selectively applies the synchronization codes to switches SW
0
134
and SW
1
136
in response to the control signal at lead
140
as indicated by inset
190
. These P-SCH and S-SCH codes are transmitted as symbol
300
(
FIG. 3
) in time slot
1
.
Broadcast channel data (BCH) for the PCCPCH are applied to channel encoder
108
via lead
106
(FIG.
1
). Interleaver circuit
110
applies the BCH data to space-time transmit diversity (STTD) encoder circuit
112
. The STTD encoder produces encoded output data at lead
114
for the transmit antenna (Ant
1
) and at lead
116
for the diversity antenna (Ant
2
). Multiplex circuit
118
produces this STTD encoded BCH data on leads
120
and
122
at a time corresponding to data symbols
302
of time slot
1
(FIG.
3
). The BCH data are modulated by spreading and scrambling codes on lead
124
and applied to switches SW
0
134
and SW
1
136
. These switches SW
0
and SW
1
selectively multiplex SCH data with BCH data and pilot symbols in response to a control signal on lead
138
as shown at inset
190
. The BCH data at lead
180
are then applied to the transmit antenna (Ant
1
), and the data at lead
182
is applied to the diversity antenna (Ant
2
).
Pilot symbol data for the PCCPCH are applied to lead
100
. Diversity circuit
102
generates an open loop transmit diversity (OTD) symbol pattern at lead
104
for the diversity antenna. This OTD pattern together with the pilot symbol pattern for the transmit antenna is shown at TABLE I for each of the sixteen time slots in a frame. By way of comparison, the STTD pilot symbol pattern for diversity antenna (Ant
2
) transmission on the dedicated physical data channel (DPDCH) is also shown. The pilot symbols at leads
100
and
102
are applied to multiplex circuit
118
. Multiplex circuit
118
selectively applies the pilot symbols at leads
100
and
102
to leads
120
and
122
, respectively, at a time corresponding to pilot symbols
304
of time slot
1
(FIG.
3
). Thus, multiplex circuit
118
multiplexes STTD encoded data symbols
302
with OTD encoded pilot symbols
304
. The pilot symbols at leads
120
and
122
are then modulated with spreading and scrambling code. These modulated pilot symbols at leads
130
and
132
are further multiplexed with SCH data by switches
134
and
136
, respectively, in response to the control signal at lead
138
as shown at inset
190
. The resulting pilot symbols are applied to transmit and diversity antennas via leads
180
and
182
, respectively.
TABLE 1
TRANSMIT ANTENNA
STTD ANT 2
OTD ANT 2
SLOT
B
1
S
1
B
2
S
2
B
1
−S*
2
−B
2
S*
1
B
1
S
1
−B
2
−S
2
1
11
11
11
11
11
01
00
10
11
11
00
00
2
11
11
11
01
11
11
00
10
11
11
00
10
3
11
01
11
01
11
11
00
00
11
01
00
10
4
11
10
11
01
11
11
00
11
11
10
00
10
5
11
10
11
11
11
01
00
11
11
10
00
00
6
11
10
11
11
11
01
00
11
11
10
00
00
7
11
01
11
00
11
10
00
00
11
01
00
11
8
11
10
11
01
11
11
00
11
11
10
00
10
9
11
11
11
00
11
10
00
10
11
11
00
11
10
11
01
11
01
11
11
00
00
11
01
00
10
11
11
11
11
10
11
00
00
10
11
11
00
01
12
11
01
11
01
11
11
00
00
11
01
00
10
13
11
00
11
01
11
11
00
01
11
00
00
10
14
11
10
11
00
11
10
00
11
11
10
00
11
15
11
01
11
00
11
10
00
00
11
01
00
11
16
11
00
11
00
11
10
00
01
11
00
00
11
Turning now to
FIG. 2
, there is a block diagram showing signal flow in an OTD encoder
102
of the prior art for pilot symbol encoding of the transmitter of FIG.
1
. The pilot symbols are predetermined control signals that may be used for channel estimation and other functions as will be described in detail. The OTD encoder
102
receives pilot symbols B
1
, S
1
, B
2
and S
2
at symbol times T−4T, respectively, on lead
100
. These pilot symbols are applied to the transmit antenna (Ant
1
) via multiplex circuit
118
and switch SW
0
134
as previously described. The OTD encoder
102
simultaneously produces pilot symbols B
1
, S
1
, −B
2
and −S
2
at symbol times T−4T, respectively, at lead
104
for the OTD diversity antenna (Ant
2
). The pil

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