Multiplex communications – Generalized orthogonal or special mathematical techniques
Reexamination Certificate
1998-09-30
2001-01-30
Cangialosi, Salvatore (Department: 2732)
Multiplex communications
Generalized orthogonal or special mathematical techniques
C370S206000
Reexamination Certificate
active
06181674
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to wireless communication systems, and more particularly, to a method and apparatus for efficiently phase-shifting a plurality of signals and for sharing transmit shaping filters among the plurality of phase-shifted signals.
2. Description of Related Art
Transmit shaping filters are commonly used in communication systems in order to modify the baseband signal so that it is better suited for transmission over the intended channel.
FIG. 1
is a symbolic block diagram of a transmit signal processing portion
10
for a wireless CDMA communication system now being developed in the IS-95B Standard. As shown, the IS-95B Standard presently contemplates the transmission of up to “n+1” digital baseband signals A
0
-A
n
by directly sequencing the digital baseband signals A
0
-A
n
with I and Q spreading codes to form in-phase I
n
and quadrature Q
n
signals; delaying the quadrature signals Q
n
by ½ a PN chip relative to the in-phase signals I
n
; shaping the in-phase I
n
and quadrature Q
n
signals via “n+1” pairs of “baseband filters”
20
I,
20
Q to produce filtered signals I
n
′, Q
n
′; modulating the filtered signals I
n
′, Q
n
′ with variously phase-shifted I and Q carriers
cos
(
2
π
f
c
t
)
and
sin
(
2
π
f
c
t
)
cos
(
2
π
f
c
t
+
φ
1
)
and
sin
(
2
π
f
c
t
+
φ
1
)
⋮
⋮
cos
(
2
π
f
c
t
+
φ
n
)
,
and
sin
(
2
π
f
c
t
+
φ
n
)
to produce modulated components; combining the modulated components to form composite signals s
0
(t) to s
n
(t), and combining the composite signals s
0
(t) to s
n
(t)into a single transmit signal s(t).
The IS-95B Standard presently contemplates eight code channels (i.e. n=7), one fundamental channel transmitted without any phase offset and seven supplemental channels transmitted with the specific phase offsets shown in FIG.
2
. Only four phase offsets, 0, &pgr;/4, &pgr;n/2, and 3&pgr;/4 are needed for eight channels because each phase offset in the 0-to-&pgr; range has a 180° counterpart in the &pgr;-to-2&pgr; range. In other words, when transmitting information with in-phase and quadrature signals I, Q, transmitting I & Q with a phase offset of x is mathematically identical to transmitting −I & −Q with a phase offset of x±180°.
If separate shaping filters are implemented for each channel as suggested by
FIG. 1
, then the hardware is subject to a great deal of complexity and increased power consumption. Separate transmit shaping filters are normally required, however, if the filtering hardware may not be fast enough to support multi-channel filtering operation.
The different phase offsets of the different channels also add design complexity, either in the analog domain or digital domain. As it is known, the input of the shaping filter for each channel in IS-95B is either 1 or −1. The design of separate filters is relatively simple, therefore, since no multiplication is involved. Implementing phase rotation before the filter or grouping multiple signals together, however, produces multiple signal levels at the filter input. Consequently, multiplication may be required, and the complexity of the filter design may significantly increase.
There remains a need, therefore, for a method and apparatus in a wireless communication system for simply and efficiently phase shifting, shaping, and modulating a plurality of inphase and quadrature signals derived from a plurality of digital baseband signals.
SUMMARY OF THE INVENTION
In a first aspect, the invention may be regarded as a wireless communication system for transmitting eight digital baseband streams over eight code-channels in a wireless channel, the code-channels having predetermined phase offsets when modulated with a carrier, the code-channels being grouped into first and second groups of code-channels wherein the individual code-channels in each group have a phase offset of 0° or 90° and wherein the first and second groups as a whole have a phase offset of &Dgr;
GROUP
°, the system comprising: means for converting each digital baseband stream into inphase and quadrature signals I, Q,; means for grouping a first plurality of the code channels into a first orthogonal group of code channels comprising zero-degree channels which require a total phase rotation of 0° and ninety-degree channels which require a total phase rotation of 90°; means for grouping a second plurality of the code channels into a second orthogonal groups of code channels comprising zero-plus-delta degree channels which require a total phase rotation of 0°+&Dgr;
GROUP
° and ninety-plus-delta degree channels which require a total phase rotation of 90°+&Dgr;
GROUP
°; first and second pre-filter means for phase-rotating the inphase and quadrature signals I, Q of the ninety-degree channels by 90° to form phase rotated signals I
90
, Q
90
by setting I
90
=Q and Q
90
=−I; first and second pre-filter means for combining the signals I, Q of the zero-degree channels with the signals I
90
, Q
90
of the ninety-degree channels to form combined signals I
A
, Q
A
and I
B
, Q
B
, respectively; first means for filtering the combined signals I
A
, Q
A
to form filtered signals I
A
′, Q
A
′ that are better suited for transmission over the wireless channel; second means for filtering the combined signals I
B
, Q
B
to form filtered signals I
B
′, Q
B
′ that are better suited for transmission over the wireless channel, said second filtering means further comprising means for scaling the filtered signals I
B
′, Q
B
′ with phase-rotation coefficients K
I
, K
Q
to produce scaled and filtered signals K
I
I
B
′, K
Q
Q
B
′; post-filter means for phase-rotating the scaled and filtered signals K
I
I
B
′, K
Q
Q
B
′ by mathematically processing such signals to produce filtered and phase-rotated signals I
B
″, Q
B
″; and means for combining the phase-rotated and filtered signals I
A
′, Q
A
′ and the phase-rotated and filtered phase-rotated signals I
B
″, Q
B
″ to form final signals I
FINAL
, Q
FINAL
.
REFERENCES:
patent: 5600675 (1997-02-01), Engeler
patent: 5691974 (1997-11-01), Zehavi et al.
patent: 5748687 (1998-05-01), Ozluturk
Walley Kenneth S.
Xin Weizhuang
Yang Ganning
Akin Gump Strauss Hauer & Feld L.L.P.
Cangialosi Salvatore
Conexant Systems Inc.
Short Shane X.
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