Jimmy Nsenga

Mixed Analog/Digital Beamforming for 60 GHz MIMO Frequency Selective Channels

Multi-antenna architectures, where beamforming processing is shared between analog and digital, are of great interest for future multi-Gbps wireless systems operating at 60 GHz. In this spectrum band, wireless systems can integrate large antenna arrays in a very small volume thanks to a wavelength of about 5 mm and thus provide the required gain to meet the severe link budget. However, the cost and power consumption of an analog front-end (AFE) chain, that carries out translation between radio frequency (RF) and digital baseband, are too high at 60 GHz to afford one AFE for each antenna. In this paper, we consider low cost multi-antenna architectures with a lower number of AFE chains than antenna elements. We propose a joint design of transmit-receive mixed analog/digital beamformers that aim at maximizing the received average signal-to-noise-ratio (SNR). The proposed scheme shows better performance than state-of-art solutions, which combine antenna selection techniques and digital beamforming.

Impact of Phase Noise on OFDM and SC-CP

Single-carrier with cyclic prefix (SC-CP) is seen as an interesting air interface to replace orthogonal frequency- division multiplexing (OFDM) because it features a lower peak- to average power ratio (PAPR) while still allowing low complexity frequency domain equalization (FDE). Both air interfaces are highly sensitive to phase noise (PN) that degrades their system performances. In this paper, we study and compare analytically the PN impact on both air interfaces. Simulations are also carried out to validate the analytical results. PN causes the same common phase error (CPE) on both air interfaces, as well as it leads to Inter-Carrier Interference (ICI) in OFDM and inter-symbol interference (ISI) in SC-CP. However OFDM is found to be slightly less affected than SC-CP in both flat channels and frequency selective channels. It is shown also that CPE is the dominate impact if the PN cut-off frequency is smaller than the subcarrier spacing.

Air Interface and Physical Layer techniques for 60 GHz WPANs

Thanks to the unprecedented availability of huge bandwidth, the capacity offered by wireless systems in the 60 GHz band can exceed the mythical barrier of 1 Gbps wireless, enabling the deployment of new applications. However, the performance can be limited by the non-ideality of the analog front-ends, multipath fading and the difficulty to achieve a reasonable link budget at high data rates. The goal of this paper is to introduce high rate communications in the 60 GHz band and the associated challenges. We will first introduce WPANs in the 60 GHz band, describing the possible applications, the propagation channel and the standardization context. Furthermore, based on the characteristics of the propagation channel, we will show that beamforming is desirable to boost the link budget, reduce interference and, in some cases, reduce multipath. Next, we will introduce candidate PHY layer solutions that at the same time meet the throughput requirements and relax the analog front-end design. Our solutions rely on the combination of block transmission combined with (nearly) constant envelope modulation: this provides low peak-to-average power ratios, easy equalization, good spectral properties and modest front-end requirements in terms of phase noise and ADC resolution. The receiver signal processing associated with the modulation techniques will be described and link level simulation results will be provided, highlighting the front-end friendliness of the modulation technique

Supplementary Proof for "Equalization Algorithms in the Frequency Domain for Continuous Phase Modulations"

To enable frequency domain equalization of continuous phase modulations (CPM), a block construction that ensures cyclicity over each block without disrupting the phase continuity between them was proposed in . We formalize and prove the constraints that should be respected to enable the application of this technique to any CPM scheme.