Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via time channels
Reexamination Certificate
2000-12-14
2004-02-17
Pham, Chi (Department: 2667)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via time channels
C370S508000
Reexamination Certificate
active
06693920
ABSTRACT:
BACKGROUND OF THE INVENTION
I. Field of the Invention
The current invention relates to quality assurance. More particularly, the present invention relates to method and apparatus for waveform quality measurement.
II. Description of the Related Art
Recently, communication systems have been developed to allow transmission of signals from an origination station to a physically distinct destination station. In transmitting signal from the origination station over a communication link, the signal is first converted into a form suitable for efficient transmission over the communication link. As used herein, the communication link comprises a media, over which a signal is transmitted. Conversion, or modulation, of the signal involves varying a parameter of a carrier wave in accordance with the signal in such a way that the spectrum of the resulting modulated carrier is confined within the communication link bandwidth. At the destination station the original signal is replicated from a version of the modulated carrier received over the communication link. Such a replication is generally achieved by using an inverse of the modulation process employed by the origination station.
Modulation also facilitates multiple-access, i.e., simultaneous transmission and/or reception, of several signals over a common communication link. Multiple-access communication systems often include a plurality of remote subscriber units requiring intermittent service of relatively short duration rather than continuous access to the common communication link. Several multiple-access techniques are known in the art, such as time division multiple-access (TDMA), frequency division multiple-access (FDMA), and amplitude modulation (AM). Another type of a multiple-access technique is a code division multiple-access (CDMA) spread spectrum system that conforms to the “TIA/EIA/IS-95 Mobile Station-Base Station Compatibility Standard for Dual-Mode Wide-Band Spread Spectrum Cellular System,” hereinafter referred to as the IS-95 standard. The use of CDMA techniques in a multiple-access communication system is disclosed in U.S. Pat. No. 4,901,307, entitled “SPREAD SPECTRUM MULTIPLE-ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS,” and U.S. Pat. No. 5,103,459, entitled “SYSTEM AND METHOD FOR GENERATING WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM,” both assigned to the assignee of the present invention and incorporated herein by reference.
FIG. 1
illustrates an ideal waveform
100
of an embodiment of a code division communication system in accordance with the IS-95 standard. For the purposes of this document, a waveform is a manifestation, representation or visualization of a wave, pulse or transition. The idealized waveform
100
comprises parallel channels
102
distinguished from one another by a cover code. The cover code in a communication system according to the IS-95 standard comprises Walsh codes. The ideal waveform
100
is then quadrature spreaded, baseband filtered and upconverted on a carrier frequency. The resulting modulated waveform
100
, is expressed as:
s
(
t
)
=
∑
i
R
i
(
t
)
ⅇ
-
jω
c
t
(
1
)
where:
&ohgr;
c
is the nominal carrier frequency of the waveform;
i is the index of the code channels summation; and
R
i
(t) is the complex envelope of the ideal i-th code channel. Equipment, e.g., a transmitter of the code division communication system, generates actual waveform x(t) that is different from the ideal waveform. Such an actual waveform x(t) is expressed as:
x
(
t
)
=
∑
i
b
i
[
R
i
(
t
+
τ
i
)
+
E
i
(
t
)
]
·
ⅇ
-
j
[
(
ω
c
+
Δω
)
(
t
+
τ
i
)
+
θ
i
]
(
2
)
where:
b
i
is the amplitude of the ideal waveform relative to the ideal waveform for the i
th
code channel;
&tgr;
i
is the time offset of the ideal waveform relative to the ideal waveform for the i
th
code channel;
&Dgr;&ohgr; is the radian frequency offset of the signal;
&thgr;
i
is the phase offset of the ideal waveform relative to the ideal waveform for the i
th
code channel; and
E
i
(t) is the complex envelope of the error (deviation from ideal) of the actual transmit signal for the i-th code channel.
The difference between the ideal waveform s(t) and the actual waveform x(t) is measured in terms of frequency tolerance, pilot time tolerance, and waveform compatibility. One method to perform such a measurement, is to determine modulation accuracy defined as a fraction of power of the actual waveform x(t) that correlates with the ideal waveform s(t), when the transmitter is modulated by the code channels. The modulation accuracy is expressed as:
ρ
overall
=
∫
T
1
T
2
&LeftBracketingBar;
s
(
t
)
·
x
(
t
)
*
&RightBracketingBar;
·
ⅆ
t
{
∫
T
1
T
2
&LeftBracketingBar;
s
(
t
)
&RightBracketingBar;
2
·
ⅆ
t
}
·
{
∫
T
1
T
2
&LeftBracketingBar;
x
(
t
)
&RightBracketingBar;
2
·
ⅆ
t
}
(
3
)
where:
T
1
is beginning of the integration period; and
T
2
is the end of the integration period.
For discrete time systems, where s(t) and x(t) are sampled at ideal sampling points t
k
, Equation 3 can be written as:
ρ
overall
=
∑
k
=
1
N
|
S
k
·
X
k
*
|
2
{
∑
k
=
1
N
|
S
k
|
2
}
·
{
∑
k
=
1
N
|
X
k
|
2
}
(
4
)
where:
X
k
=x[k]=x(t
k
) is k
th
sample of the actual waveform; and
S
k
=s[k]=s(t
k
) is the corresponding k
th
sample of the ideal waveform.
A multiple-access communication system may carry voice and/or data. An example of a communication system carrying both voice and data is a system in accordance with the IS-95 standard, which specifies transmitting voice and data over the communication link. A method for transmitting data in code channel frames of fixed size is described in detail in U.S. Pat. No. 5,504,773, entitled “METHOD AND APPARATUS FOR THE FORMATTING OF DATA FOR TRANSMISSION”, assigned to the assignee of the present invention and incorporated by reference herein. In accordance with the IS-95 standard, the data or voice is partitioned into code channel frames that are 20 milliseconds wide with data rates as high as 14.4 Kbps. Additional examples of a communication systems carrying both voice and data comprise communication systems conforming to the “3rd Generation Partnership Project” (3GPP), embodied in a set of documents including Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214 (the W-CDMA standard), or “TR-45.5 Physical Layer Standard for cdma2000 Spread Spectrum Systems” (the IS-2000 standard). Such communication systems use a waveform similar to the one discussed above.
Recently, a data only communication system for a high data rate (HDR) transmission has been developed. Such a communication system has been disclosed in co-pending application Ser. No. 08/963,386, entitled “METHOD AND APPARATUS FOR HIGH RATE PACKET DATA TRANSMISSION,” filed Nov. 3, 1997, assigned to the assignee of the present invention and incorporated by reference herein. The HDR communication system defines a set of data rates, ranging from 38.4 kbps to 2.4 Mbps, at which an origination terminal (access point, AP) may send data packets to a receiving terminal (access terminal, AT). The HDR system utilizes a waveform with channels distinguished both in time domain and code domain.
FIG. 2
illustrates such a waveform
200
, modeled after a forward link waveform of the above-mentioned HDR system. The waveform
200
is defined in terms of frames
202
. (Only frames
202
a,
202
b,
202
c
are shown in
FIG. 2.
) In an exemplary embodiment, a frame comprises 16 time slots
204
, each time slot
204
being 2048 chips long, corresponding to a 1.67 millisecond slot duration, and, consequently, a 26.67 ms frame duration. Each slot
204
is divided into two half-slots
204
a,
204
b,
with pilot bursts
206
a,
206
b
transmitted with in ea
Black Peter
Montojo Juan
Sindhushayana Nagabhushana
Baker Kent
Jones Prenell
Kalousek Pavel
Pham Chi
Qualcomm Incorporated
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