In conventional full-duplex radio communication systems, the transmitter (Tx) is active at the same time as the receiver (Rx). The isolation between the Tx and the Rx is ensured by duplex filters. However, an increasing number of long-term evolution (LTE) bands crave multiband operation. Therefore, a new front-end architecture, addressing the increasing number of LTE bands, as well as multiple standards, is presented. In such an architecture, the Tx and Rx chains are separated throughout the front-end. Addition of bands is solved by making the antennas and filters tunable. Banks of duplex filters are replaced by tunable filters and antennas, providing a duplexer function over the air between the Tx and the Rx. A hardware system has been designed and fabricated to demonstrate the performance of this front-end architecture. Measurements demonstrate how the architecture addresses inter-modulation and Rx desensitization due to the Tx signal. The filters and antennas demonstrate tunability across multiple bands. System validation is detailed for LTE band I. Frequency response, as well as linearity measurements of the complete Tx and Rx front-end chains, show that the system requirements are fulfilled.Index Terms-Low-noise amplifier (LNA), power amplifier (PA), tunable filters, tunable front-end, tunable microelectromechanical systems (MEMS) capacitors, tunable narrowband antennas.

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The branch correlation coefficient (BCC), the branch power ratio (BPR), and the total mean power (TMP) are often used to characterize the mobile multiple-input multiple-output (MIMO) channel. This work investigates to which degree these parameters are useful for maximizing the channel capacity of multiple-input multiple-output (MIMO) handheld devices used in data mode. A statistical point of view is applied, using about 2800 outdoor to indoor channel sounder measurements obtained with combinations of ten different handsets, four to eight test users, and a variety of different use cases (UCs). All measurements were made in an urban environment in a setup with two different base stations (BSs) and with the users inside a single building. For each measurement combination, the mean capacity (MC) and associated values of BCC, BPR, and TMP are obtained. From the data it is found that the MC is only weakly correlated with both the BCC and the BPR, while the MC is highly correlated with the TMP.Index Terms-Branch correlation, branch power ratio, channel capacity, dual-band propagation, mean effective gain, multiple-input multiple-output (MIMO) channels, optical link, propagation measurements, user-interaction.

The evolution of modern mobile terminals has been driven by two key factors, the user interface and broadband connectivity. However, while the peak performance near the base station may be state-of-the-art, real world performance (in building, in suburbs and rural areas, in-car and on-person) has substantially fallen over the years. This has not only impacted achievable data rates and reduced battery life but, in many cases, actually prevented useful connections for voice or data. The key factor driving this degradation has been changing antenna location and reduced antenna volume driven by the race for thinner and display-dominated platforms. Reduced antenna volume leads to a tradeoff between bandwidth and efficiency. To maintain acceptable efficiency, tunable and reconfigurable antennas are being deployed to enable effective use of reduced instantaneous bandwidths. This capability brings new challenges as well as new opportunities to the handset designer.

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