This paper proposes an active radio frequency (RF) cancellation solution to suppress the transmitter (TX) passband leakage signal in radio transceivers supporting simultaneous transmission and reception. The proposed technique is based on creating an opposite-phase baseband equivalent replica of the TX leakage signal in the transceiver digital front-end through adaptive nonlinear filtering of the known transmit data, to facilitate highly accurate cancellation under a nonlinear power amplifier (PA). The active RF cancellation is then accomplished by employing an auxiliary transmitter chain, to generate the actual RF cancellation signal, and combining it with the received signal at the receiver (RX) low noise amplifier (LNA) input. A closed-loop parameter learning approach, based on the decorrelation learning rule, is also developed to efficiently estimate the coefficients of the nonlinear cancellation filter in the presence of a nonlinear PA with memory, finite passive isolation, and a nonlinear LNA. The performance of the proposed cancellation technique is evaluated through comprehensive RF measurements adopting commercial LTE-Advanced transceiver hardware components. The results show that the proposed technique can provide an additional suppression of up to 54 dB for the TX passband leakage signal at the LNA input, even at very high transmit power levels and with wide transmission bandwidths. Such novel cancellation solution can therefore substantially improve the TX-RX isolation, hence reducing the requirements on passive isolation and RF component linearity, as well as increasing the efficiency and flexibility of the RF spectrum use in the emerging 5G radio networks.
Detecting the presence of primary users and ability to find white spaces in the spectrum are the key enablers of the opportunistic communication. This paper analyzes the trade-offs in cyclostationary-based spectrum sensing algorithm implementations in terms of performance, hardware complexity, and power consumption. The evaluation of the algorithm implementations is performed on field-programmable gate arrays. The analysis presented will provide the designer understanding of dependency between algorithm complexity and power consumption, which is inherently limiting factor of implementation feasibility for cognitive mobile devices.
Radio transmitters are evolving towards digitalintensive solutions to exploit reconfigurability and benefit from CMOS process scaling. Outphasing has been identified as a suitable candidate for digital wideband transmitters. However, with recent digital-intensive outphasing transmitters the achieved performance in terms of adjacent channel leakage ratio (ACLR) has been limited. This paper identifies the sampling images of the modulating phase signal as the main factor limiting the ACLR of digital outphasing transmitters. We present a new digital interpolating phase modulator architecture, capable of providing significantly better sampling image attenuation. When evaluated in outphasing configuration with a 100 MHz OFDM signal at the carrier frequency of 2.46 GHz, and 10-bit phase resolution, the proposed solution achieves an ACLR of-59 dBc, compared to-43 dBc achievable with the phase modulator architecture utilized in state-of-the-art digital outphasing transmitters. The proposed digital interpolating phase modulator is also capable of custom carrier generation, a straightforward method for generating an arbitrary carrier frequency up to 1.25 times the phase modulator sampling rate.
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