Multi-Gigabit Radio System Demonstrators for Next Generation Mobile Networks

Licentiate thesis, 2015

Driven by the exponential growth in mobile broadband subscriptions and mobile data traffic, transport capacity of mobile networks has to be enhanced accordingly, including wireless backhaul and the emerging fronthaul networks. Utilizing wide bandwidth is the most straightforward way to capacity upgrade. Millimeter-wave frequency bands with large available bandwidth offer the opportunities to realize high capacity wireless links. However, there are challenges associated with the radio link implementation. For example, wide bandwidth is required for components like low noise amplifiers, power amplifiers, modulators and demodulators (modems). Another challenge is the signal quality degradation due to high frequency impairments. The solutions presented in the thesis are applicable to implementations based on commercially available hardware. Multi-gigabit modems are proposed using simple modulation differential quadrature phase shift keying (DQPSK), which do not need carrier recovery and power hungry mixed signal devices. To improve spectral efficiency, a 16-QAM modem is designed with optimized hardware efficiency. This in turn relaxes the demand on the sampling rate of analog to digital converters (ADC) and the resource requirement on digital signal processing. As proof-of-concept demonstration, DQPSK modems are implemented and verified at 2.5 and 5 Gbps. A 5 Gbps radio system based on the hardware efficient 16-QAM modem is also demonstrated at 70/80 GHz (E-band). The presented modems and systems address challenges in applying wide bandwidth/high symbol rate to realizing high capacity. Moreover, it defines the baseline for further capacity enhancement when combined with high spectral efficiency techniques. Besides the mobile backhaul application, high capacity wireless links are required to support the mobile fronthaul as a new network segment, which connects a centralized baseband pool to distributed remote radio units. A data-rate adaptable DQPSK modem solution is proposed for digital wireless fronthaul to transmit multi-gigabit CPRI (common public radio interface). An E-band digital fronthaul link is implemented using this modem at 5 Gbps. To overcome the low bandwidth efficiency of the digital fronthaul, an analog fronthaul technology is introduced as an enabler for cost efficient and scalable fronthaul networks. An analog fronthaul link is demonstrated at E-band complemented with phase noise mitigation for 64-QAM LTE transmission.