Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1998-07-01
2001-07-24
Ngo, Ricky (Department: 2664)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S342000, C370S441000, C370S479000, C708S250000
Reexamination Certificate
active
06266331
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to high speed data transmission in a Code Division Multiple Access (CDMA) system. In particular, the invention relates to the generation of multiple spreading sequences applicable to the reverse channels of a mobile radio terminal device (hereinafter “mobile station”) which is effectively used in a mobile communication system employing CDMA operations such as a personal communication system (PCS), a digital cellular telephone, or the like.
BACKGROUND OF THE INVENTION
There are three major types of multiple access digital transmission systems, known as Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), and Code Division Multiple Access (CDMA). FDMA entails spreading the calls to be transmitted by assigning each call a specific frequency band which can be separated from the others by filtering at the receiving end. TDMA entails sending the multiple calls using the time sharing of the entire band of the transmission channel. That is to prevent information overlapping, only one station transmits data at a time and, when it does, it occupies all of the channel band width.
FDMA and TDMA are rarely used today because of their inherent problems. FDMA requires a receiver for each transmission channel, so that a considerable number of receivers are required in a central base station if it is to be possible to converse simultaneously with a large number of mobile stations. TDMA systems encounter difficult problems with equalization if the transmission channel is disrupted by echoes or by jamming.
CDMA uses spread spectrum techniques and is a preferred multiple access digital transmission system. In a CDMA communication system, a call between a base station and a mobile station is established by employing code channels. In other words, the mobile station selects an optimum base station for communication and the base station assigns to the mobile station code channels to be used for communication.
In CDMA, a digital data signal is multiplied by a spreading sequence before it is transmitted. A different spreading sequence is associated with each mobile station (i.e., each user) connected to a base station. A spreading sequence is usually in the form of a pseudo-random binary sequence characterized by its chip frequency, and by a repetition period of the pseudo-random sequence called the code period.
A digital data signal to be transmitted is in the form of a binary signal characterized by its bit frequency. The bit frequency is a multiple of the chip frequency, and the spreading factor of a spreading sequence is the ratio between the chip frequency and the bit frequency.
The digital data signal to be transmitted is combined with the spreading sequence, for example by modulo addition or by multiplication, depending upon the nature of the signals. The resulting signal is filtered and then transmitted over a code channel. The code channel is distinguished at the base station in accordance with the distinctions of the spreading sequences for the mobile station. The number of spreading sequences for a mobile station corresponds to the number of code channels.
At the receiving end, after further filtering, decoding is effected by combining the received signal with a local replica of the spreading sequence synchronized to the transmission. It results in the retrieval of the original digital data signal.
A CDMA communication method, one of the spread spectrum communication methods, has been disclosed, for example, in “Mobile Station—Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System” TIA/EIA/IS-95A, Jul. 1995 as a TIA/EIA standard. This IS-95A standard has been modified to incorporate the high speed data capacity that requires simultaneous transmission of up to eight code channels. Consequently, the transmission of high speed data requires simultaneous generation of eight spreading sequences to be incorporated within the eight code channels.
FIG. 1
is a block diagram of a prior art spreading sequence generator
100
used to generate multiple spreading sequences. The spreading sequence generator
100
comprises a long code generator
102
, a mask register
104
, an AND operator
110
, and a modulo-2 adder
114
.
The long code generator
102
generates a long code
108
, and the mask register
104
generates a masking stream
106
. In a typical embodiment, the long code
108
comprises forty two states and the masking stream
106
comprises forty two mask bits. The long code
108
and masking stream
106
are combined by an AND operator
110
and the product is then fed to the modulo-2 adder
114
. The resulting output
116
is a spreading sequence to be used for various mobile stations transmitting high speed data.
In the prior art, to generate eight different spreading sequences, the above process is repeated eight different times by loading the mask register with eight different masks during one chip interval. The output sequentially produces eight different spreading sequences, one for each code channel.
This sequential approach of generating eight different spreading sequences is very expensive and time consuming as it requires eight separate operations. Moreover, extra circuitry is required to handle the loading of the masks and the multiplexing of the output.
Therefore, there exists a need for a device which may generate multiple spreading sequences in parallel with reduced power and time requirements.
SUMMARY OF THE INVENTION
The present invention discloses a device for generating multiple spreading sequences efficiently. The preferred embodiment according to the principles of the invention is a spreading sequence generator which generates eight different spreading sequences in parallel.
The present invention uses the presently known forty two bit long code and forty two bit masking stream mechanism. In the preferred embodiment, there exists eight code channels differentiated by a three bit code channel index number. The long code states and mask bits comprise two subgroups. The first subgroup comprises thirty nine states and thirty nine masking bits which are common for all eight channels used in the high speed transmission. The second subgroup comprises three states and three masking bits. These three mask bits and states are unique for each code channel.
The thirty nine states and thirty nine bits belonging to the first subgroup are logically combined to generate a parity check sum output. The output from this group is termed the master output.
The three states and three masking bits belonging to the second subgroup are used to generate eight different secondary outputs, one for each code channel. First, the masking bits belonging to the second subgroup are logically combined with the corresponding code channel index number to generate eight different masks. The masks and states are then combined to generate the secondary outputs. Each of the eight masks is then combined with the corresponding states in the second group, thereby creating eight different secondary outputs.
These three bit wide secondary outputs from the second subgroup are combined with the master output from the first group through a modulo-2 adder. The output of the modulo-2 adder is the spreading sequence for the corresponding code channel. In total, eight spreading sequences are generated, one for each code channel.
In the preferred embodiment, the spreading sequence generator comprises a master sequence generator and eight secondary sequence generators. The spreading sequence generator also comprises eight different modulo-2 adders which are used for generating parity check sum outputs.
The master sequence generator is responsible for creating a master output from the first subgroup. The secondary sequence generators create eight different secondary outputs. Each of the secondary outputs is combined with the master output through one of the eight modulo-2 adders to create eight different spreading sequences. In a preferred embodiment, the eight different spreading sequences are generate
Baker Thomas W.
Cesari Richard A.
Wang Xiao-an
Lucent Technologies - Inc.
Ngo Ricky
Synnestvedt & Lechner LLP
LandOfFree
Device for generating multiple spreading sequences in... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Device for generating multiple spreading sequences in..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Device for generating multiple spreading sequences in... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2454386