Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-10-05
2003-04-08
Bost, Dwayne (Department: 2681)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C375S142000, C375S150000
Reexamination Certificate
active
06546245
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to digital cordless telephones, and more particularly to a digital cordless telephone that implements an inverted code sequence cordless signaling.
2. Background of Related Art
Cordless telephones are popular consumer devices that allow a user in a home or office the freedom to stray hundreds of feet from a base station. The typical cordless telephone includes a base station that is physically connected to the user's telephone company lines and a hand-held handset unit. The physical hard wire connection between a corded handset and a conventional telephone set is replaced by a radio frequency (RF) link.
Initially, the remote handsets of cordless telephones communicated with their base station using analog signals. In more recent years, advancements have been made with respect to cordless telephones allowing digital communications between the remote handset and its base station. The entry of cordless telephones into digital communications generally provides better voice quality because of increased noise rejection, and a somewhat higher range. However, the increased voice quality and higher range involves using many more components and an increasing complexity in the digital cordless telephones. Consequently, the increased components and increased complexity may result in a higher cost for the digital cordless telephone for the average consumer.
FIG. 6A
shows relevant features of a conventional frequency hopping digital remote handset
600
of a digital cordless telephone. In
FIG. 6A
, the remote handset
600
includes a controller
605
, a radio frequency (RF) transceiver
610
, a coder-decoder (CODEC)
615
, a microphone
620
, a speaker
625
and a spread spectrum module
630
.
The controller
605
may be a digital signal processor (DSP), microprocessor, or microcontroller. The controller
605
provides an execution platform for a software program that operates the remote handset
600
.
The RF transceiver
610
provides a RF interface between the remote handset
600
and a base station. The remote handset
610
relays voice signals between a base station via RF link. The RF transceiver
610
provides a conversion between RF signals and the digitized voice signals.
The CODEC
615
provides a way to convert between the analog voice signals and the digital voice signals. The CODEC
615
is typically an electronic device that converts analog voice signals to digital voice signals via an analog-to-digital converter (not shown). Also, the CODEC
615
converts received digital voice signals to analog voice signals via a digital-to-analog converter (not shown).
The microphone
620
provides a way for the user to input voice signals into the remote handset
600
.
The speaker
625
provides a way for the user to hear the output voice signals from the remote handset
600
.
The spread spectrum module
630
provides a way for the remote handset
600
to convert between digital voice signals into a spread spectrum digital voice signal.
The spread spectrum module
630
includes an error-correcting module
635
, a digital frequency synthesizer
640
, a transmitting frequency multiplier
650
, a pseudo-noise (PN) code generator
645
, a clock
655
, a receiving frequency multiplier
660
, a mixer
662
, a message demodulator
670
, a early-late gate module
665
, a code loop module
675
, and an error correction module
680
.
In the transmit direction, a microphone
620
outputs an analog signal to the CODEC
615
which converts the microphone input signal to a digital microphone signal. The digital microphone signal is inputted to the spread spectrum module
630
for encoding into a spread spectrum digital signal.
The digital microphone signal is initially passed to the error correcting module
635
of the spread spectrum module
630
to provide a way to reconstruct the digital microphone signal if there are any errors during transmission to a base station.
After the error-correcting module
635
, the digital microphone signal is passed to the digital frequency synthesizer
640
. The digital frequency synthesizer
640
provides a way to produce another frequency from a reference signal based on an input control word. In this particular embodiment, the input control word may be m bits long. In the input control word, one of the m bits is part of the digital microphone signal and the PN generator
645
supplies the rest of the (m−1) bits. The PN generator
645
supplies the (m−1) bits in a PN sequence, which is passed to the digital frequency synthesizer
640
. The digital frequency synthesizer
640
then generates a new signal in one of the M frequencies, where M=2
m
. Thus, the digital microphone signal is mapped into one of M=2
m
frequencies.
The mapped digital microphone signal is then passed to the transmitting frequency multiplier
650
. The transmitting frequency multiplier
650
processes the mapped digital microphone signal into yet another frequency. The frequency multiplication is used to increase the processing gain and bandwidth of the mapped digital microphone signal. The output of the transmitting frequency multiplier
650
is then a spread spectrum digital signal ready for transmission.
The spread spectrum digital signal is transmitted by a RF transceiver
610
to a complementary base station
600
′ shown in FIG.
6
B.
Referring back to
FIG. 6A
, in the receive direction, the RF transceiver
610
receives a RF digital spread spectrum signal from the complementary base station
600
′. The RF transceiver
610
translates the RF digital spread spectrum signal to a digital spread spectrum signal. The RF transceiver
610
then passes the spread spectrum digital signal to the spread spectrum module
630
for further processing.
The digital spread spectrum signal is multiplied by an identical signal from the PN generator
645
used during the transmission of the digital spread spectrum signal at the mixer
662
. The PN generator
645
supplies (m−1) bits in a PN sequence to the receiving frequency multiplier
660
. The receiving frequency multiplier
660
generates the identical signal used during the transmission of the digital spread spectrum signal which is then sent to the mixer
662
to be processed with the incoming digital spread spectrum signal.
The resulting digital signal from the mixer
662
is a binary frequency shift keyed (FSK) signal. The message demodulator
670
demodulates the resulting digital signal. The message demodulator
670
is typically an FSK-type demodulator.
The demodulated digital signal is then passed to the error correction module
680
to recover the original digital signal. The timing synchronization in the receive path is controlled by the early-late gates
665
which controls the clock frequency.
The decoded digital signal is driven to the CODEC
615
as input. The CODEC
615
converts the digital signal to an analog signal to drive the speaker
625
.
The base station
600
′, shown in
FIG. 6B
, contains circuitry which is complementary to that contained in the remote handset
100
, i.e., a complementary RF transceiver
610
′, a controller
605
′, a CODEC
615
′, and a spread spectrum module
630
′. The base station
600
′ also includes a telephone line interface
690
to interface with a public switched telephone network.
Although digital spread spectrum cordless telephones operate adequately; a limiting factor in their popularity is their cost. In implementing spread spectrum techniques, there may be a larger number of components used in the digital cordless telephones. With the increased the number of components, there is a corresponding increase in the cost of the telephone.
Another cost factor, which may push the price of the digital spread spectrum cordless telephone, is the implementation of a cordless signaling protocol. The cordless signaling protocol is used to implement typical commands such as ‘Talk’, ‘Ring’, ‘Flash’, and etc. The command generation and processing may intr
Agere Systems Inc.
Bollman William H.
Bost Dwayne
Contee Joy K.
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