Pulse or digital communications – Spread spectrum – Frequency hopping
Reexamination Certificate
1998-02-25
2001-08-21
Chin, Stephen (Department: 2634)
Pulse or digital communications
Spread spectrum
Frequency hopping
C455S426100, C455S462000, C455S464000, C455S465000
Reexamination Certificate
active
06278722
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to portable telephones and more particularly to a portable telephone arranged for communicating in a frequency hopping system
2. Description of the Prior Art
The Federal Communications Commission (FCC) recently promulgated rulings in the utilization of spread spectrum systems, including a frequency hopping system. These rulings now allow for increased spectral utilization by portable telephones. Frequency hopping systems spread their energy by changing, or hopping the center frequency of the transmission many times a second in accordance with a pseudo-randomly generated list of communication channels. The result is a significantly higher signal to noise ratio than may be achieved by conventional techniques such as amplitude modulation that uses no bandwidth spreading.
Digital portable telephones are now being designed for use in spread spectrum systems, including frequency hopping systems. Examples of such digital portable telephones are described in U.S. Pat. No. 5,323,447 which issued to M. E. Gillis et al. on Jun. 21, 1994, U.S. Pat. No. 5,353,341 which issued to M. E. Gillis et al. on Oct. 4, 1994 and U.S. Pat. No. 5,463,659 which issued to W. J. Nealon et al. on Oct. 31, 1995. Each of these digital portable telephones utilizes time division duplexing for communicating between a base unit and its associated handset unit. In the operation of such a portable telephone, the base unit and the handset unit communicate with each other by alternately transmitting and receiving a signal on the same channel. Thus, while the base unit is transmitting on a channel, the handset unit is configured for receiving the signal from the base unit over that same channel. Similarly, while the handset unit is transmitting on the channel, the base unit is configured for receiving the signal from the handset unit. Due to the packetizing handling of voice data in these digital portable telephones, delays which result in echoes discernible by the user of the handset unit may be generated at certain packetizing rates of the voice data.
The effect of such echoes is minimized by employing an echo suppression arrangement such as is described in U.S. Pat. No. 5,381,475 which issued to M. C. Cavallo on Jan. 10, 1995. This suppression arrangement attenuates the reflected voice signal from the handset unit appearing in the base unit, and thereby prevents the sidetone echo from being coupled to and emanating at the handset unit. Although such arrangement effectively suppresses the echoes, it is desirable to design a simpler digital portable telephone which does not employ time division duplexing.
SUMMARY OF THE INVENTION
The prior art problem is solved in accordance with the present invention by a digital portable telephone which avoids the complex circuitry required to switch between transmit and receive states in the base unit and handset unit of the digital portable telephone while frequency hopping in a frequency hopping system.
In accordance with the invention, the architecture for this digital portable telephone provides improved performance over that of other digital portable telephones by combining the frequency hopping spread spectrum technique with other spread spectrum techniques in communications between the handset unit and the base unit of the portable telephone. Such other techniques are, in accordance with an aspect of the disclosure, delta modulation and signal redundancy in the transmission of the frequency hopped signal from the base unit to the handset unit and, similarly, from the handset unit to the base unit. These other forms of signal spreading are advantageously employed for providing additional processing gain and other benefits. Delta modulation, for example, spreads a transmitted signal in the manner of the rules promulgated by the FCC while not compromising voice quality. When the bit error rate in a signal increases, delta modulation is very forgiving of such bit errors and it is not necessary to blank the voice during reception of these errors. Signal redundancy in the transmission of the frequency hopped signal is achieved by configuring the circuit architecture of each unit in the portable telephone to transmit both sidebands of its frequency hopped signal. Such signal redundancy advantageously achieves a high level of immunity to interference from other portable telephones also operating in the same frequency hopping band. In addition, the circuit architecture is simplified and the cost for a portable telephone employing simplified circuits is less than a portable telephone employing circuitry for time division duplexing in a frequency hopping system.
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Chin Stephen
Ghayour Mohammad
Lucent Technologies - Inc.
Priest & Goldstein PLLC
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