Multiplex communications – Generalized orthogonal or special mathematical techniques
Reexamination Certificate
1999-03-10
2002-04-09
Hsu, Alpus H. (Department: 2662)
Multiplex communications
Generalized orthogonal or special mathematical techniques
C370S335000, C370S342000, C375S146000, C375S297000, C455S115200, C455S450000, C455S522000
Reexamination Certificate
active
06370109
ABSTRACT:
BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention relates to Code Division Multiple Access (CDMA) systems. More particularly, the present invention includes, but is not limited to, a novel and improved CDMA base station that controls transmit power based on quadrature signal calculations.
II. Description of the Related Art
Code Division Multiple Access (CDMA) technology is commonly used in communications systems. In a typical CDMA system, a CDMA base station transmits a CDMA signal to numerous CDMA communications devices, such as wireless telephones. The CDMA signal is comprised of numerous individual user signals. The CDMA base station generates the CDMA signal by encoding each individual user signal with a unique spreading sequence, such as a pseudo random sequence. The CDMA base station then adds the encoded user signals together to form the CDMA signal.
In a CDMA system, individual user signals are not separated based on frequency or time, but are spread across the entire frequency band. Each CDMA communications device derives its particular user signal based on the unique spreading sequence. Due to this combination of multiple signals encoded with random sequences, the CDMA signal has special power concerns because each signal represents noise to the other signals that share the frequency band. Thus, CDMA transmission systems must carefully track the power of each signal.
Baseband CDMA signals are typically generated in a well-known quadrature format comprised of quadrature CDMA signals I and Q. Quadrature CDMA signals I and Q are transmitted using carriers of the same frequency, but in phase quadrature. In other words, an RF CDMA signal can be constructed by modulating I by cosine (2×pi×frequency×time) and by modulating Q by sine (2×pi×frequency×time). In IS-95A, quadrature signals carry the same data with different pseudo-random sequence codes.
FIG. 1
depicts a multi-sector base station
100
that is currently known in the art. The base station
100
is divided into geographic sectors with callers A-F in sector
1
and callers G-L in sector
2
. For the sake of illustration, caller F will move from sector
1
to sector
2
as indicated by the dashed lines, but the operation of the base station
100
is first discussed prior to the caller F move from sector
1
to sector
2
. Those skilled in the art will appreciate that the diagram of the base station
100
has been simplified for clarity.
The sector
1
portion of the base station
100
includes cell site modems
102
and
104
, gain control
106
, summing circuit
108
, CDMA signal processor
110
including gain
112
, and antenna
114
. The sector
2
portion of the base station
100
includes cell site modems
122
and
124
, gain control
126
, summing circuit
128
, CDMA signal processor
130
including gain
132
, and antenna
134
.
In operation, the cell site modem
102
receives signals for callers A, B, C and applies conventional CDMA processing to generate CDMA quadrature signals I and Q. The cell site modem
102
provides the CDMA quadrature signals I and Q to the summing circuit
108
. The cell site modem
104
receives signals for callers D, E, F and applies conventional CDMA processing to generate CDMA quadrature signals I and Q. The cell site modem
104
provides the CDMA quadrature signals I and Q to the summing circuit
108
. The summing circuit separately combines the I signals and the Q signals and transfers them to the CDMA signal processor
110
. The CDMA signal processor
110
performs analog conversion, filtering, up-conversion, and amplification to provide a Radio Frequency (RF) CDMA signal to the antenna
114
. The antenna
114
transmits the RF CDMA signal
116
over the air to the callers A-F in sector
1
.
The cell site modem
122
receives signals for callers G, H, I and applies conventional CDMA processing to generate CDMA quadrature signals I and Q. The cell site modem
122
provides the CDMA quadrature signals I and Q to the summing circuit
128
. The cell site modem
124
receives signals for callers J, K, L and applies conventional CDMA processing to generate CDMA quadrature signals I and Q. The cell site modem
124
provides the CDMA quadrature signals I and Q to the summing circuit
128
. The summing circuit separately combines the I signals and the Q signals and transfers them to the CDMA signal processor
130
. The CDMA signal processor
130
performs analog conversion, filtering, up-conversion, and amplification to provide an RF CDMA signal to the antenna
134
. The antenna
134
transmits the RF CDMA signal
136
over the air to the callers G-L in sector
2
.
Each cell cite modem
102
,
104
,
122
, and
124
provides gain information
118
to both the gain control
106
and the gain control
126
. The gain information
118
includes the squared gain for each call, pilot signal, and overhead. Gain control
106
and gain control
126
each maintain a database that incorporates the gain information
118
.
The CDMA signal processor
110
monitors the transmit power (Pout) of the CDMA signal
116
for sector
1
and provides a Pout value
119
for sector
1
to the gain control
106
. The gain control
106
compares the Pout value
119
for the CDMA signal
116
to a Gain Value (GV) equal to the sum of the squared gains for the CDMA signal
116
. The squared gains for the CDMA signal
116
are obtained from the gain information
118
. The gain control
106
transfers a control signal
117
to the gain
112
to adjust the Pout to maintain a ratio of GV to Pout at a pre-determined value.
FIG. 2
shows the desired relationship between Pout and the GV. The points X and Y represent operational measurements, and the arrows represent the control applied through the control signal
117
to the gain
112
to maintain the pre-determined value. Those skilled in the art are aware that the slope of the pre-determined value blossoms during start-up and wilts during shut-down.
The CDMA signal processor
130
monitors the Pout for sector
2
and provides the Pout value
139
for sector
2
to the gain control
126
. The gain control
126
compares the Pout value
139
for the CDMA signal
136
to a GV equal to the sum of the squared gains for the CDMA signal
136
. The squared gains for the CDMA signal
136
are obtained from the gain information
118
. The gain control
126
transfers a control signal
137
to the gain
132
to adjust Pout to maintain a ratio of GV to Pout at a predetermined value.
When caller F moves from sector
1
to sector
2
, the cell site modem
104
for sector
1
transfers the caller F quadrature signals
141
and
142
to the summing circuit
128
for sector
2
. Thus, the CDMA signal
136
now includes the caller F signal. As a result, the gain control
126
must now add the square of the caller F gain to its GV.
It should be appreciated that each cell site modem must transfer all gain information
118
to the gain control in each sector. This requires a data transfer arrangement across all sectors, and much of the transferred data is unnecessary. For example, gain control
126
does not need the gain for caller A unless caller A moves into sector
2
. The gain control for each sector must also track the calls in its sector and perform repeated calculations based on a changing database. The current power calculation technique for CDMA base stations should be improved to reduce data transfer and storage.
SUMMARY OF THE INVENTION
The above-described problem is solved with CDMA quadrature signal technology that controls the transmit power of a CDMA signal. The CDMA quadrature signal technology eliminates unnecessary data transfer and storage because gain control is accomplished without transferring or using per call gain information. The CDMA quadrature signal technology receives a CDMA signal, and in response, processes quadrature components of the CDMA signal to generate a power control signal. The CDMA quadrature signal technology adjusts the gain of the CDMA signal in response to the power control signal.
Harms Brian K.
Knight Robin D.
Pressley Todd A.
Schwartz Bruce S.
Soong Anthony C. K.
Edwards Christopher
Hsu Alpus H.
Miller R. Ben
Qualcomm Incorporated
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