Communication device with improved interference rejection and a method thereof

#The disclosed technology relates to a communication device, and in particular to a radio transmitter and a receiver that can operate with low power consumption and with improved interference rejection, therefore particularly suitable for use in low-power communication systems, such as wireless sensor networks and wireless body area networks.

#Realization of low power wireless transceiver is one of the key challenges in low power wireless sensor network (WSN) and wireless body area network (WBAN) applications. In such applications, only limited energy resources are available. However, it is necessary to maintain long or unlimited operation time for the radio nodes while maintaining a reasonable performance. As such, low power consumption becomes one of the most important requirements.

#With a stringent power consumption constraint, e.g. sub-mW, many radios have utilized amplitude modulation and envelope detection to eliminate the need for accurate, but power-hungry radio frequency (RF) generators and thus reducing the power consumption. FIG. 1 shows an architecture of a system 10, having a transmitter 12 and a receiver 14. The transmitter 12 has a baseband stage (BB) 20 for generating baseband signals, an up-conversion stage 22 for converting the baseband signals to a radio frequency (RF), and a transmit antenna 24. The receiver 14 has a receive antenna 40, a RF band-pass (BP) filter 42, a down-conversion stage 44 including an envelope detector, and a baseband processing stage 46 for handling the baseband output signal.

#For a better understanding of the present disclosure, reference will now be made, by way of example only, to the accompanying drawings in which:

#FIG. 1 is a schematic diagram of a conventional radio transmitter/receiver system.

#FIG. 2A and FIG. 2B illustrate schematic diagrams of a radio transmitter and a radio receiver system, respectively, in accordance with different embodiments.

#As mentioned above, front-end filters in a low power receiver design, using an envelope detector as the RF down-conversion stage, are typically only suitable for band selection. Within the selected frequency band, an additional interference rejection technique is needed to select the desired signal and to attenuate adjacent frequency interference.

#In certain embodiments illustrated here, it is proposed to use two frequency tones (commonly referred as carriers) to carry information from the transmitter, such that a RF signal comprising two radio frequency components (also referred as signals throughout the text) is produced and transmitted. In the receiver, an envelope detector is used to downconvert these two radio frequency components. At the output of the envelope detector an intermodulation component from the two frequency components is obtained, which is located at the frequency offset between the two frequency components. The intermodulation component contains relative frequency information between the two frequency components; amplitude, frequency and phase information of the two frequency components is preserved after the envelope detector. By making use of this relative information, the desired signal can be distinguished from unwanted interference, e.g. from nearby radio systems operating at similar or the same frequency band. Therefore, additional interference rejection is achieved.

#Compared to a conventional low power on-off keying (OOK) transceiver, the proposed method requires at least two signals—at least two carrier tones carrying the same information—to be sent by the transmitter. At the receiver side, an envelope detector is still the RF downconversion stage for the RF input, which means that no frequency synthesizer or oscillator at RF frequency is needed. The interference rejection of the disclosed envelope detector based receiver is improved as amplitude, frequency and phase information is extracted, with little impact on low power consumption. The extraction of amplitude, frequency and phase information is achieved as the relative frequency information between the two frequency components is preserved after the envelope detector.