Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
1998-08-18
2002-05-28
Vo, Don N. (Department: 2631)
Pulse or digital communications
Spread spectrum
Direct sequence
C370S342000
Reexamination Certificate
active
06396868
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a transmitter and a transmitting method in a spread spectrum mobile communications system, and in particular, to a spread spectrum signal generating device and method for maintaining a minimal transmitted output peak-to-average power.
2. Description of the Related Art
With the advent of CDMA (Code Division Multiple Access) mobile communications systems, various DSS (Direct Spread Spectrum) transmission and reception schemes have been explored. Coherent demodulation is known to be an effective way of increasing the subscriber capacity of a DSS-CDMA mobile communications system. This is largely due to a small signal-to-noise ratio which is generally required to obtain a given frame error rate in a coherent system, as compared to an incoherent demodulation system.
To realize coherent demodulation in a mobile communications environment, the complex gain of a received multipath channel signal on each path should be obtained. Complex gains can be calculated using a decision directed method or a pilot assisted method. The latter is generally used as it exhibits excellent performance and easy realization. The article entitled “Performance of Adaptive Match Filter Receivers Over Fading Multipath Channels” by Pahlavan and Matthews, IEEE Transactions on Communications, Vol. 38, No. 12, December 1990, pp. 2106-2113 provides more detailed information regarding the pilot assisted gain calculation method.
The pilot assisted method is implemented either by a parallel probing technique or serial probing technique. In parallel probing, a transmitter spreads a spread user data signal which includes both information and data known to a receiver with different PN (Pseudo random Noise) sequences. On the other hand, in serial probing, data known to the receiver is periodically inserted in the spread user data signal which includes information and then these signals are spread with the same PN symbol.
For CDMA mobile radio communications, a user needs to transmit various forms of data such as voice data, control data, and packet data for high-speed data and multimedia service. Two conditions need to be considered for such data transmission systems. First, it is desirable to minimize a peak-to-average power ratio (PAR) at an output port of a communications terminal in order to decrease both power dissipation and manufacturing cost of the terminal. Second, intermittent output power from the terminal should be minimized as this may cause another device carried by a user, such as a hearing aid or a cardiac pacemaker, to malfunction. The serial probing method is inferior to the parallel probing in terms of moderating intermittent output power, but offers advantages over the parallel probing method in terms of PAR.
FIG. 1
is a block diagram of a transmitter for generating a transmission signal including a pilot signal on a reverse link in a point-to-point spread spectrum CDMA cellular communications system.
Referring to
FIG. 1
, a logical channel data generator
111
has a plurality of data generators for generating channel data, and a plurality of scramblers for scrambling the channel data. A channelizer
113
processes the data received from the logical channel data generator
111
in such a manner that both interference between channels and the PAR is minimized. An IQ signal mapper
115
maps the channelized signals received from the channelizer
113
into in-phase and quadrature-phase signals. A PN spreader
117
spreads the output of the IQ signal mapper
115
with PN codes. A baseband modulator
119
translates the spread signal received from the PN spreader
117
to a baseband signal and modulates the baseband signal. A frequency upconverter
121
upconverts the frequency of the modulated signal received from the baseband modulator
119
to a transmission frequency and outputs a radio transmission signal.
FIG. 2A
is a block diagram of the logical channel data generator
111
shown in
FIG. 1
, and
FIG. 2B
is a block diagram of the scramblers shown in FIG.
2
A.
Referring to
FIG. 2A
, the logical channel data generator
111
includes a pilot data generator
211
, a control data generator
213
, a voice data generator
215
, and a packet data generator
217
. The pilot data generator
211
outputs unmodulated consecutive bits
0
s. Control data generated from the control data generator
213
is composed of a power control command for power control on a forward link or other control information. The voice data generator
215
outputs data from a variable bit rate (VBR) vocoder. The voice data output from the vocoder can be, for example, a convolutionally encoded and interleaved bit sequence. The encoded voice data is output at a VBR of 1/2, 1/4, or 1/8, increasing the period of one bit time by two times, four times, or eight times, respectively. The packet data generator
217
has an output bit rate which is an integer multiple (from 1 to 8) of the highest bit rate of the voice data generator
215
.
Scramblers
219
,
221
, and
223
scramble the data received from the control data generator
213
, the voice data generator
215
, and the packet data generator
217
, respectively.
Referring to
FIG. 2B
, a switch
232
of the scramblers
219
,
221
, or
223
selectively outputs the output of a decimator
233
or data “0”, and an exclusive OR gate
231
exclusive-ORs the data received from the data generators
213
,
215
, or
217
with the output of the decimator
233
or the data “0” selected by the switch
232
. The decimator
233
decimates a second PN code sequence (i.e., long PN code sequence) P at the same bit rate as that of the control, voice, and packet data, which were all encoded and interleaved.
FIGS. 3A and 3B
are block diagrams of the channelizer
113
shown in
FIG. 1
, which are configured for the serial and parallel probe methods, respectively. Referring to
FIG. 3A
, rate adaptors
311
to
317
are connected to the respective data generators
211
to
217
and adjust the data rates at the data generators
211
to
217
. Signal mappers
321
to
327
, which are connected to the respective rate adaptors
311
to
317
, convert bits
0
s and
1
s of rate-adapted data to +1s and −1s, respectively. Multipliers
331
to
337
multiply the converted signals received from the signal mappers
321
to
327
by corresponding channel amplitude control signals A
0
to A
3
. A multiplexer
341
multiplexes the outputs of the multipliers
331
to
337
.
In the channelizer
113
using the serial probe scheme, the various data is time multiplexed to an output C
0
to occupy a different time slot therein and the time that the data occupies is adjusted by varying the number of repetitions on the outputs of the data generators
211
to
217
in the rate-adaptors
311
to
317
.
The rate-adapted data is converted from logical channel data
0
s and
1
s to +1s and −1s suitable for transmission by the signal converters
321
to
327
. The output signal from the signal converters
321
to
327
are applied to the multipliers
331
to
337
, which multiply the converted signals by channel amplitude control signals A
0
to A
3
, thereby determining the power levels.
Referring to
FIG. 3B
, rate adaptors
351
to
357
are connected to the data generators
211
to
217
of the logical channel data generator
111
and adjust data transmission rates at the corresponding data generators
211
to
217
. Signal mappers
361
to
367
are connected to the corresponding rate adaptors
351
to
357
, for converting bits
0
s and
1
s of rate-adapted data to +1s and −1s, respectively. Walsh code generators
371
to
377
generate Walsh codes W
0
to W
3
, respectively. Multipliers
381
to
387
multiply signals received from the signal mappers
321
to
327
by the Walsh codes W
0
to W
3
received from the Walsh code generators
371
to
377
, to remove both interference between channels and phase errors. Multipliers
391
to
397
multiply the outputs of the multipliers
381
to
Ahn Jae-Min
Chung Ha-Bong
Kang Hee-Won
Kim Je-Woo
Kim Young-Ky
Dilworth & Barrese LLP
Samsung Electronics Co,. Ltd.
Vo Don N.
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