Research Projects

This proposal is originated in response to the emerging challenges in wireless transmitter design due to increasing requirements of high data rate and seamless connectivity in 4G/ 5G. These challenges are in terms of handling high crest-factor spectral efficient signals, concurrent transmission for carrier aggregation (CA) and multiple input multiple output (MIMO) techniques for high channel capacity in a practical front-end. Among multi-channel communication issues, such as MIMO or multiband communication, most of the national-level research efforts are devoted to massive MIMO techniques with theoretical support in simulation environment. Such studies take bandwidth of the channel into account, however they rarely consider whether front-end will support the required bandwidth. Although these techniques promise advantages such as high throughput, very high spectrum efficiency and capability to transmit very high power, the total power consumed is rarely considered. Total power includes the cost of power consumed by power amplifier as well as baseband signal processing. Moreover, constraint related to low-cost hardware implementation are rarely considered. This proposal establishes that although high data rates are desirable, they should be not at the price of signal quality. Indeed, power amplifier nonlinearity has been known to significantly distort the signal even for single channel transmission. Multi-channel processing generates even higher distortion terms in the presence of power amplifier, therefore there is a need for investing the efforts toward implications of practical hardware limitations for multichannel processing. To address several small yet important practical limitations, this research proposal targets the power efficient digital/analog predistortion techniques which support CA and MIMO transmission along with mitigation of non-linearity, crosstalk between adjacent branches, nonlinearity, gain and phase imbalance, etc. For complete study of effects of incorporated solutions and proof-of-concept, the MIMO antenna along with suitable beam forming and diversity technique will also be incorporated. This project envisions a standalone power and spectrum efficient 32×32 MIMO communication system for high throughput data streaming application with the speed of 1 GBPS.

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1. The investigators proposed a less complicated, novel DPD model for linearizing large-scale MIMO transmitters along with its characterization procedure. The proposed DPD model is implemented in a 4 by 1 subarray of MIMO transmitters having nonlinearity of PA, nonlinear crosstalk, and linear crosstalk impairments. The results show that nonlinearity due to crosstalk can be modeled on half the order of nonlinearity compared to the main branch's nonlinearity order.

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Lekha Wireless Solutions Private Limited, Bangalore