Patent Application
20070064832
A variety of modulation techniques exist that may be used in a communication system to encode information into a transmit signal. Examples of prior modulation techniques include amplitude modulation (AM) and frequency modulation (FM). Other prior modulation techniques include techniques that may combine amplitude and phase modulation, e.g. quadrature amplitude modulation (QAM), GPSK, etc.
It may be desirable in a communication system to employ a receiver having a relatively narrow receive band. For example, a narrow receive band may reduce the power consumption of a receiver. In addition, a narrow receive band may enable an increase in the sensitivity of a receiver.
Unfortunately, prior modulation techniques may have limited applicability to a communication system that includes a narrow band receiver. For example, the center frequency of the pass band of a narrow band receiver may drift with temperature. In addition, manufacturing variation in the components of a narrow band receiver may cause variation in the center frequency of its pass band. As a consequence, the pass band of a narrow band receiver may drift outside of the transmit band of a transmitter that employs a prior modulation technique, thereby breaking the communication link between the transmitter and the narrow band receiver.
A frequency ramp modulation technique is disclosed that encodes information using frequency ramps in a transmit signal. Frequency ramp modulation according to the present teachings may be employed in a communication system that includes a narrow band receiver to maintain communication even as the pass band of the narrow band receiver drifts with temperature or other factors.
Other features and advantages of the present invention will be apparent from the detailed description that follows.
The present invention is described with respect to particular exemplary embodiments thereof and reference is accordingly made to the drawings in which:
The frequency ramp in the transmit signal 20 may be an increase in a frequency of the transmit signal over time. The frequency ramp in the transmit signal 20 may be a decrease in a frequency of the transmit signal 20 over time. The frequency ramp in the transmit signal 20 may be a step-wise increase or decrease in a frequency of the transmit signal over time.
The ramp generator 30 generates a ramp signal 42 in response to an information signal 40. For example, the information signal 40 may carry digital information including a series of 0's and 1's to be carried via the transmit signal 20. In an embodiment corresponding to the information coding illustrated in
The voltage controlled oscillator 32 generates the transmit signal 20 at a frequency that is determined by a magnitude of the ramp signal 42. A rising ramp in the magnitude of the ramp signal 42 causes a rising ramp in the frequency of the transmit signal 20 and a falling ramp in the magnitude of the ramp signal 42 causes a falling ramp in the frequency of the transmit signal 20.
The band-pass filter 60 generates a filter output signal 70 by filtering out frequency components of the transmit signal 20 that do not fall within a pass band of the band-pass filter 60. The range of frequencies of the frequency ramps in the transmit signal 20, between f1 and f2, is selected in response to the pass band of the band-pass filter 60 and the likely drift in the center frequency of the pass band of the band-pass filter 60. The range between f1 and f2 is selected so that some part of the frequency ramps between f1 and f2 will overlap the pass band of the band-pass filter 60 even after variation in the center frequency of the band-pass filter 60, thereby maintaining communication between the transmitter 12 and the receiver 14.
The frequency ramp demodulator 62 recovers information from the filter output signal 70 by detecting rising and falling frequency ramps in the filter output signal 70. In an embodiment corresponding to the information coding illustrated in
The foregoing detailed description of the present invention is provided for the purposes of illustration and is not intended to be exhaustive or to limit the invention to the precise embodiment disclosed. Accordingly, the scope of the present invention is defined by the appended claims.
