Apparatus and method for synchronizing channels in a W-CDMA...

Details Apparatus and method for synchronizing channels in a W-CDMA... Apparatus and method for synchronizing channels in a W-CDMA...

2000-05-01

2004-05-25

Vanderpuye, Kenneth (Department: 2732)

Multiplex communications

Communication over free space

Having a plurality of contiguous regions served by...

C370S342000

Reexamination Certificate

active

06741578

ABSTRACT:

PRIORITY
This application claims priority to an application entitled “Apparatus and Method for Synchronizing Channels in W-CDMA Communication System” filed in the Korean Industrial Property Office on Apr. 29, 1999 and assigned Serial No. 99-15332, and an application filed in the Korean Industrial Property Office on May 25, 1999, and assigned Serial No. 99-18921, the contents of both of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a synchronizing device and method for a CDMA (Code Division Multiple Access) communication system, and in particular, to a device and method for synchronizing channels in a W-CDMA (Wideband-CDMA) communication system.
2. Description of the Related Art
Next generation W-CDMA mobile communication systems assign unique base station codes to each base station to perform asynchronous operation between the base stations. For 512 cells, 512 unique codes are assigned to identify 512 base stations. In such an asynchronous mode base station communication system, a mobile station detects the base station signal being currently received at the highest power, in order to successfully perform a call. However, in the asynchronous base station system, it takes quite a long time to examine the phases of all the possible codes in the cell search, so that it is difficult to apply a general cell search algorithm. Therefore, a multi-step cell search algorithm has been proposed. This method classifies 512 cells into 32 groups and each group includes 16 cells. To employ this method, sync channels are used which include a primary sync channel signal (code) and a secondary sync channel signal (code).
FIG. 1
shows a sync channel structure used for cell search in an asynchronous W-CDMA system. In
FIG. 1
, reference numeral
1
-
1
denotes a primary sync channel (PRIMARY SCH) signal, reference numeral
1
-
3
denotes a secondary sync channel (SECONDARY SCH) signal, and reference numeral
1
-
5
denotes a common pilot channel signal. One frame has 16 slots. The primary sync channel signal and the secondary sync channel signal are transmitted for a N-chip (256 chip) length at the starting point of every slot. Orthogonality between the two channel signals is maintained so that they can be transmitted at the same time. Further, the common pilot channel uses a unique PN (Pseudo Noise) code (spreading code) for each base station, and the period of the PN code is identical to one-frame length.
The W-CDMA system having the above channel structure uses Gold codes of period 2
18
−1 for the unique PN codes, and uses only M (=512) codes out of all possible Gold codes of that length. The common pilot channel signal is not transmitted simultaneously with the primary sync channel signal and the secondary sync channel signal, but only transmitted at other time periods.
The sync channels use sync codes, and the sync codes are generated by performing modulo operation between a Hadamard sequence and a hierarchical sequence. The hierarchical sequence y is generated using a sequence x
1
of length n
1
and a sequence x
2
of length n
2
, as follows:
 
y
(
i
)=
x
2
(
i
mod
n
2
)+
x
1
(
i÷n
1
) for
i=
0, . . . , (
n
1
*n
2
)−1
Further, the sequences x
i
and x
2
are select sequences of length 16 as follows.
X
1
=<0,0,1,1,0,1,0,1,1,1,1,1,0,0,0,1>
X
2
=<0,0,1,1,1,1,0,1,0,0,1,0,0,0,1,0>
The Hadamard sequences are obtained as the rows in a matrix H
8
constructed recursively by:
H
k
=
(
H
k
-
1
H
k
-
1
H
k
-
2
H
k
-
1
)
,
 
⁢
k
≥
1
The rows are numbered from top starting with row 0 (the all ones sequence). The nth Hadamard sequence is denoted as the nth row of H
8
numbered from the top, n=0,1,2, . . . ,255, in the sequel.
Therefore, let h
m
(i) and y(i) denote the ith symbol of the sequence h
n
and y, respectively where i=0, 1, 2 . . . , 255 and i=0 corresponds to the leftmost symbol.
By XOR-gating a 256-chip Hadamard sequence h
m
(i) and the hierarchical sequence y(i), a kth sync code is then defined as
C
sc, k
={h
m
(0)+
y
(0),
h
m
(1)+
y
(1),
h
m
(2)+
y
(2), . . . ,
h
m
(255)+
y
(255)},
Where m=8×k, k=0,1,2, . . . , 17, and the leftmost chip in the sequence corresponds to the chip transmitted first in time.
Then, synchronization code #0 generated in the above manner is assigned to the P-SCH signal, where
C
p
=C
sc, 0
The other synchronization codes, C
sc, 1
to C
sc, 17
are assigned in the respective slots of a secondary sync (S-SCH) signal.
The primary sync code c
p
is repeatedly transmitted only for 256 chips every slot, which is
{fraction (1/10)} of one slot. The sync code used for the primary sync channel signal is the same for every cell. The primary sync channel signal is used for detecting the slot timing of the received signal by the mobile station. The base station transmitter introduces a comma-free code when transmitting the secondary sync channel. The comma-free code is comprised of
32 code words, and each code word is comprised of 16 symbols and transmitted repeatedly in every frame. However, the 16 symbol values are not transmitted as they are, but each symbol value is mapped into a secondary sync code and is transmitted for frame synchronization and base station group information. The mobile stations have the comma free code table and know the mapping relation of the symbols and secondary sync codes. As shown in
FIG. 1
, an ith sync code, corresponding to a symbol value ‘i’, is transmitted every slot. C
s
i,k
indicates the ith secondary synchronization code inserted in the kth slot. The 32 code words of the comma-free code identify 32 groups, and the comma-free code has a unique cyclic shift feature for each code word. Therefore, it is possible to obtain information about the code groups and frame synchronization using the secondary sync channel signal (code). Here, “frame synchronization” refers to synchronization of timing or phase within one period of a PN spreading code in a spreading spectrum system. However, in the existing W-CDMA system, since both one period of the spreading code and the frame length are equal to 10 ms, this PN code synchronization will be referred to as frame synchronization.
In the mobile station, a correlation value is calculated for a spreading code of a base station in order to distinguish different base station codes used by different base stations. Forward common channels, such as a pilot channel and a broadcasting channel (BCH), can be used when calculating the correlation value for the spreading code of the base station. In the conventional W-CDMA system, the pilot symbol is transmitted on the broadcasting channel using Time Division Multiplexing (TDM). However, the recent harmonization group OHG (Organized Harmonization Group) recommends transmitting the forward common pilot.
FIG. 1
shows an example where the forward common pilot channel is transmitted by CDM (Code Division Multiplexing) and transmission of the pilot channel is discontinued when the sync code is transmitted.
FIG. 2
shows an example where the forward common pilot channel signal is transmitted by CDM and the pilot channel signal is continuously transmitted without discontinuation even when the sync channel signals are transmitted.
The common pilot channel signal can transmit the pilot symbol and data using time division multiplexing in every slot (the existing W-CDMA structure). Otherwise, there may be provided separate channels for transmitting the data. In this case, the channel frame for transmitting data should have the same boundary as the common pilot channel frame. Generally, the common pilot channel does not transmit data, but only transmits the pilot symbol, all +1 or −1.
In the synchronization process of the conventional W-CDMA system, the synchronization is acquired through three search steps. In the first step, synchronization of the 0.625 ms slot is acquired. In the sec

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