Modern wireless communication equipment such as outphasing power amplifiers or systems like massive-MIMO rely heavily on transmission of complex wideband modulated radio frequency signals on parallel signal paths. As these signal bandwidths increase, wireless transmitters are more susceptible to amplitude and phase distortions across frequency. We propose a novel method to quantify the complex signal distortions in each transmit path and a technique to pre-compensate the transmitter over a wide bandwidth of interest. This work has been experimentally validated with measured results on two separate RF test benches using signal bandwidths up to 100 MHz. An outphasing power amplifier bench for WCDMA at S band requiring 4 signal paths and a satellite uplink modulator using 8-PSK at Ku band requiring two signal paths were tested in the experimental validation. Further, it is also validated that this method requires only one iteration to calibrate a set of parallel RF signal paths.

Next generation wireless communications such as 5G are expected to feature wide channel bandwidths on the order of hundreds of MHz. As bandwidths increase, circuit impairments caused by frequency dependent behaviour such as ripple and tilt in gain and group delay become more significant. PAPR of OFDM signals also increase with increasing number of subcarriers. Transmitter circuit characterisation for the wide-band frequency response is needed to pre-compensate the signal to be transmitted. In this article, we propose a novel scheme which uses the circuit characteristics combined with the channel response to generate the keys for encrypting signals to provide an additional tier of security at the physical layer. The modulated constellation of the signal of interest is encrypted by dispersing its phases in addition to encrypting the bits using Diffie Hellman scheme. It is also shown that the method is able to reduce the PAPR of OFDM signals. This scheme is experimentally validated from end-to-end on a millimetre wave wireless link at 28.9 GHz demonstrating security against a well-positioned eavesdropper and a reduction of PAPR by 3.5 dB in a 2048 point OFDM signal with 1664 active QPSK modulated sub-carriers. Index Terms-Encryption, wireless communication, physical layer security, peak to average power ratio. I. INTRODUCTION M ODERN wireless communications involve transmission of digital data over vector modulated radio frequency (RF) carriers. Unlike, wired communication schemes, wireless data transmission is of broadcast nature where the occurrence of transmission is sensed and can be received by multiple

Modern wireless communication systems employ wideband modulated RF carriers to communicate the data of interest between the nodes in the network. The security of communications has been conventionally addressed in the data link layers through scrambling and data encryption schemes. These schemes however do not secure the air interface parameters such as modulation scheme and leave them susceptible to eavesdropping and interception by man-in-the-middle platforms. Physical layer security schemes such as directional modulation, DFT S OFDM and RF fingerprinting have been proposed. In this paper, we propose a novel physical layer encryption scheme based on the spectral profile of the intended modulated signal through deliberately introduced constellation distortion to conceal the modulation scheme. The scheme uses a dispersive filter in the modulator with unique group delay profiles unknown to the eavesdropper. The appropriate inverse filter is employed in the authorized receivers to recover the original modulated basebands for demodulation.

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Next generation wireless communication systems such as fifth generation mobile communications and high throughput satellites have promised a step increase in the rate at which digital data can be transmitted. This requires wideband modulators consisting of high speed digital to analogue converters and RF upconverters to generate the wideband signal of interest. In this paper we demonstrate a scheme to generate a wide bandwidth modulated signal by bandwidth interleaving multiple modulators of narrower bandwidths. The proposed scheme is experimentally validated with measured results on an 8PSK signals of symbol rate 80 MSPS with modulation characteristics in accordance with DVB-S2 standard.