PN sequence identifying device in CDMA communication system

Details PN sequence identifying device in CDMA communication system PN sequence identifying device in CDMA communication system

1999-08-30

2003-08-05

Yao, Kwang Bin (Department: 2664)

Multiplex communications

Generalized orthogonal or special mathematical techniques

Particular set of orthogonal functions

C370S335000

Reexamination Certificate

active

06603735

ABSTRACT:

PRIORITY
This application claims priority to an application entitled “PN Sequence Identifying Device in CDMA Communication System” filed in the Korean Industrial Property Office on Aug. 29, 1998 and assigned Serial No. 98-35797, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a spread spectrum device in an asynchronous CDMA (Code Division Multiple Access) communication system, and in particular, to a device for identifying a PN sequence by assigning a null sign to a part of orthogonal codes used in the generation and identification of a hopping pattern.
2. Description of the Related Art
In a CDMA communication system, orthogonal codes provide channelization, and scrambling codes scramble data and improve spectral characteristics. In general, the scrambling codes are called a PN (Pseudorandom Noise) sequence. In CDMA systems, pseudorandom noise (PN) sequences spread the bandwidth of the modulated signal to a larger transmission bandwidth, and serve to distinguish among the different user signals by using the same transmission bandwidth in a multiple access scheme. M-sequence codes or Gold sequences codes are commonly used as a scrambling (PN) code.
FIG. 1A
illustrates PN sequences used by base stations within a plurality of cells in a typical CDMA communication system, and
FIG. 1B
illustrates an example of a PN sequence generator for generating the PN sequences.
FIG. 1A
shows seven (7) base stations, and each base station uses a different PN sequence to be distinguished from other base stations.
There are two methods of assigning the PN sequences to the base stations. In one method, the same PN sequence is assigned to all the base stations and a different sequence phase is given to each base station at a specific absolute time in the state where all the base stations use the same carrier and are synchronized by a reference time signal. In this case, the base stations have different PN sequence offsets. Specifically, a base station adds an in-phase signal spread by the same PN sequence with a quadrature-phase signal spread by a PN sequence having a different offset, for transmission. A corresponding addressed mobile station identifies the base station by the quadrature offset.
In the second method, different PN sequences are assigned to adjacent base stations which use the same carrier.
In accordance with the first base station identifying method, only one pair of PN sequences exists. Each base station has the same PN sequence pair and a unique pre-assigned corresponding PN offset. Each base station transmits an in-phase signal spread by the PN sequence and a quadrature-phase signal spread by a PN sequence delayed by the pre-assigned offset to a mobile station, to allow the mobile station to identify the base station. The PN sequence offsets for the base stations, illustrated at
FIG. 1
, BS#A to BS#G are listed in Table 1.
TABLE 1
base
station
PN sequence
offset value
remark
BS#A
PN_I, PN_Q
A
each base station uses the same
BS#B
PN_I, PN_Q
B
PN sequence and generates a
BS#C
PN_I, PN_Q
C
PN sequence according to its
BS#D
PN_I, PN_Q
D
corresponding offset at the
BS#E
PN_I, PN_Q
E
same time point.
BS#F
PN_I, PN_Q
F
BS#G
PN_I, PN_Q
G
In a conventional IS-95 system where the base stations are synchronized, an extended PN sequence of length 2
15
(=32768=64×512) evolved from a PN sequence of length 2
15-1
, in which 0s occur 14 (15—, 1) times and one more zero (0) is inserted, in order to distinguish a base station. Base stations can be identified by assigning them one of 512 starting points (offset #
0
to offset #
511
) resulting from dividing the length 32768 by 64 chip units. Therefore, in operating the base stations as shown in
FIG. 1A
, {A, B, C, D, E, F, G} ⊂ {0, 1, 2, . . . , 511} and #{A, B, C, D, E, F, G}=7. A base station BS#
1
outputs an extended PN sequence 64-chip-offset from an extended PN sequence of a base station BS#
0
and, base station BS#
2
outputs an extended PN sequence (2×64)-chip-offset from the extended PN sequence of base station BS#
0
, as shown in Table 2.
TABLE 2
base station
PN offset with t=0
BS #0
0
BS #1
64 chips
BS #2
2×64 chips
.
.
.
.
.
.
BS #(p−1)
(p−1)×64 chips
BS #p
p×64 chips
.
.
.
.
.
.
BS #510
510×64 chips
BS #511
511×64 chips
In the above method, since base stations transmit signals at the same time using timing information received from reference time source such as a GPS (Global Positioning System) satellite, it is possible to distinguish the base stations by the use of a pair of I and Q channel PN sequences having different offsets. That is, the conventional system can distinguish each base station since each base station uses the same PN sequence and spectrum-spreads a transmission signal using the same PN sequence with a corresponding offset value at the same time.
FIG. 1B
illustrates an example of a PN sequence generator according to the prior art. The PN sequence generator is a 2
18-1
length Gold sequence generator. It is used with a frame length of 10 msec which is a reduced frame length as compared with a conventional system. The chip rate is 4.096 Mcps corresponding to 40,960 chips per frame. The PN sequence generator generates a different PN sequence for each base station using an initial value corresponding to the number of the base station.
In the conventional method, since base stations transmit signals at the same time using timing information received from a reference time source such as the GPS satellite, it is possible to distinguish the base stations by the use of pairs of spread I and Q channel PN sequences having different offsets. However, if a base station is located within a building or in the subway and cannot receive a signal directly from the GPS satellite, a synchronous CDMA communication system receives a GPS signal in a receivable area and transmits the GPS signal to the base station via a wire link. Due to a delay involved receiving the GPS signal in via wire link, the base station lags behind the reference time of other base stations. Therefore, the base station performs a spreading operation for base station identification based on an incorrect (i.e., delayed) reference time and thus the base station cannot be identified using the reference time information. In addition, because the GPS satellite operates for military purposes, intentional misoperation or fatal damage will cause failures in a communication network.
Therefore, a CDMA system where base stations are asynchronous have been proposed in order to circumvent the problems inherent in a CDMA system where base stations are synchronized as described above in a conventional IS-95 system. However, asynchronous base stations cannot be distinguished only with pairs of spread PN sequence offsets as is true of synchronous systems. That is, it is impossible to distinguish base stations using auto-correlation in an asynchronous system. This is because there is a probability of contention between signals transmitted from two base stations since the base stations are not time-aligned and as a result, it cannot be determined at what time the two adjacent base station transmit. Even though the probability of a mobile station receiving a signal resulting from contention between the outputs of the two base stations is very low, the low probability can have a significant detrimental influence.
Therefore, an asynchronous CDMA communication system should be configured in such a way to overcome the aforestated problem. That is, a mobile station should identify a base station using cross-correlation by analyzing a spread spectrum signal received from an adjacent base station. In this method, all candidate PN sequences should be checked one by one to search for a corresponding base station when a mobile station is turned on or measures the signal stre

Affiliated with

Also associated with

Rating

PN sequence identifying device in CDMA communication system does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with PN sequence identifying device in CDMA communication system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and PN sequence identifying device in CDMA communication system will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3088196