Pulse or digital communications – Transceivers
Reexamination Certificate
1998-10-26
2002-08-13
Tse, Young T. (Department: 2634)
Pulse or digital communications
Transceivers
C375S239000, C375S297000, C375S306000, C375S326000, C332S128000, C455S086000
Reexamination Certificate
active
06434187
ABSTRACT:
BACKGROUND
This invention relates to wireless digital communication.
With ownership of home computers increasing, many households now have more than one computer. Purchasing separate peripherals (printers, scanners, modems, removable storage media) for each computer can be expensive and wasteful, when often only one of each peripheral may be needed. Also, households typically provide only one phone line for use by computer modems, requiring users of multiple computers to take turns accessing the on-line services. A home-based local area network (LAN) would allow the computers to share these peripherals, but most inexpensive networking hardware currently available requires cabling to physically connect the computers. As multiple-home-computer users often keep their computers in separate rooms, use of cable-based networking requires running cables through the house walls. This, in addition to the complications of administering network routers or hubs, has discouraged home use of current networking technology.
Some LAN technologies do not depend on re-wiring homes. Some use existing wiring, such as power lines or phone lines. To date, these technologies can experience interference and security problems (for example, power lines are typically shared with other nearby homes). In addition, existing wired LANs typically do not permit mobile access to the network by portable laptop computers. Wireless LANs (WLANs) have also been pursued for networking personal computers. For example, infrared-based networks have been developed, particularly in work-place environments for communication with mobile personal digital assistants (PDAs).
Digital radio communication has also been explored for WLANs. In 1985, the FCC established regulations to allow unlicensed use of certain bands if spread-spectrum (SS) techniques are used. In SS transmission, the energy radiated during transmission is spread across a wide spectrum of frequencies (or “channels”) and is therefore less likely to cause substantial interference with other radio communications. FCC SS regulations allow greater transmission of power to be used without special licensing, increasing the attainable range of communications for unlicensed systems.
Two principal SS transmission techniques include direct-sequence (DS) and frequency-hopping (FH). In DSSS, spreading is achieved through multiplication of the data by a binary pseudo-random sequence whose chipping rate is many times the data rate. In FHSS, the carrier frequency remains at a given channel for a duration of data transmission, and then “hops” to a new channel elsewhere within the spreading bandwidth.
DSSS allows for coherent demodulation, in which the receiver exploits knowledge of the carrier's phase reference to detect the encoded signals. With FHSS, however, phase coherence is difficult to maintain between hops. Non-coherent demodulation results in the advantage of reduced complexity, but at a cost of an increased probability of error. FHSS typically enables high data rates to be achieved without requiring the high-speed logic that an equivalent DSSS system would require. Also, a FHSS system can employ frequency diversity, which combats multipath fading by transmitting data at multiple frequencies, increasing the likelihood that data will be transmitted and received uncorrupted. The data requirements of digital communications equipment is increasing as the typical size of data files becomes larger. Complex modulation schemes have been used to handle higher bandwidth requirements and more efficiently use the bandwidth allocated to RF devices. However, existing modulation schemes can be either very logic-intensive or require very accurate and expensive clock references. An example of the former type of scheme is differential quadrature phase shift keying (DQPSK), in which complex (IQ) demodulation is required to recover the encoded data. An example of the latter type of scheme is frequency shift keying (FSK), in which small changes in frequency are used to represent the encoded data. The change in frequency in FSK is usually very small and the receiving system may have difficulty determining whether a particular shift in frequency it detects represents real data or an offset between transmitter and receiver reference clocks.
SUMMARY
In general, in one aspect, the invention features a method for radiofrequency (RF) transmission of digital information including generating an RF signal using a voltage-controlled oscillator (VCO), stabilizing the RF signal from the VCO by providing an error signal from a phase-locked loop (PLL) to an input of the VCO, and combining the digital information with the error signal of the PLL input to the VCO, thereby causing variations in frequency of the RF signal from the VCO that represent the digital information.
Embodiments of the invention may include one or more of the following features. The RF signal can be broadcast. The error signal of the PLL can be provided to the VCO by a loop filter. The rate of change of the digital information can be faster than a response time of the PLL. The digital information can be encoded such that it has a duty cycle which is substantially constant over the response time of the PLL. The digital information can be encoded according to the pulse position modulation (PPM) scheme defined by the IrDA 4PPM data encoding standard. A channel frequency of the RF signal can be changed according to a series of channel frequencies, wherein the series of channel frequencies is determined by generating a series of at least a first and a second channel-select signal, each channel-select signal comprising a frequency-valid indicator and a frequency-specification indicator, sending each channel-select signal in turn to the PLL, and changing the tuning frequency of the PLL according to the frequency specification of the first channel-select signal upon receiving the frequency-valid indicator of the second channel-select signal. The number of distinct channel frequencies in the series of channel frequencies can be a prime number. The series of channel frequencies can be repeated upon completion, and no channel can be used more than once in each repetition of the series of channel frequencies. The transmitted RF signal can be received, demodulated, a signal level threshold can be determined from the demodulated RF signal, and the demodulated RF signal can be compared to the signal level threshold to regenerate the digital information from the demodulated RF signal. The RF signal output of the VCO can be used as a local oscillator to demodulate the received RF signal.
In general, in another aspect, the invention features a method for RF transmission of digital information including generating an RF signal using a voltage-controlled oscillator (VCO), stabilizing the RF signal from the VCO by providing an error signal from a phase-locked loop (PLL) to an input of the VCO, encoding the digital information such that it has a duty cycle which is substantially constant over the response time of the PLL, forming a data packet containing the encoded digital information, and combining the data packet with the error signal of the PLL input to the VCO, thereby causing variations in frequency in the RF signal from the VCO that represent the data packets.
Embodiments of the invention may include one or more of the following features. The data packet can have a duty cycle which is substantially constant over the response time of the PLL. The digital information can be encoded and the packets can be formed according to the pulse position modulation (PPM) scheme defined by the IrDA 4PPM data encoding standard.
In general, in another aspect, the invention features a method for receiving digital information sent by an RF transmitter using the IrDA 4PPM data encoding standard including receiving a transmitted RF signal, demodulating the RF signal, determining a signal level threshold from the demodulated RF signal, comparing the demodulated RF signal to the determined signal level threshold to thereby regenerate IrDA-formatted data from the demo
Beard Paul F.
Harrington Drew M.
Moore Mark D.
Cypress Semiconductor Corp.
Maiorana P.C. Christopher P.
Tse Young T.
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