# High Performance Receiver Design for RX Carrier Aggregation
## 1 Introduction  
The ever increasing data crunch in wireless communication necessitates the means to increase the data rate with spectral efficiency. There are three main approaches to increasing the data rate in wireless communication: high-order modulation schemes (e.g., 64 QAM (Quadrature Amplitude Modulation), 128 QAM, and 256 QAM), high carrier frequency with large fractional bandwidth, and carrier aggregation (CA). The high-order modulation format is able to offer faster data rates and a higher level of spectral efficiency, but practically, modulation format is dictated by the link-budget, signal-to-noise ratio (SNR), and transceiver performance. High carrier frequency (e.g, millimeter-wave bands from 30 GHz to 300 GHz) is beneficial because signal bandwidth is a certain fraction of carrier frequency, and thus higher carrier frequency leads to large signal bandwidth. However, hostile channel characteristics at millimeter-wave bands reduce service coverage and impair communication performance [1].  
CA raises the bandwidth and capacity by combining two or more adjacent or non-adjacent RF channels [2]. CA is also the technical solution to overcome spectrum fragmentation, and can be applied to a wide variety of spectrum scenarios [3]. CA has been adopted by the Long-Term Evolution (LTE) standard for cellular systems, and is being extended to Licensed-Assisted Access (LAA) and LTE in Unlicensed spectrum (LTE-U). In addition, CA will be one of the key features to enable future 5 G wireless systems.  
A plethora of wireless standards exist in the radio frequency regime, and the number of wireless devices is increasing rapidly. Reception of wireless signals is becoming more challenging due to spectrum crowding and reduced channel capacity under the harsh wireless environment. Low noise performance is a must to improve the SNR of the reception signal at the sensitivity level. On the other hand, high linearity of the receiver is the capacity to handle large signal interferences and jammers with the simultaneous reception of small desired signals.  
These considerations call for new innovations on several fronts, from the circuit to the architectural level. In this paper, we propose a high-performance receiver architecture supporting legacy single-carrier operation, inter-band carrier aggregation, and intra-band carrier aggregation. The proposed architecture can be considered a single-input, and multi-output (SIMO) receiver, and two contrasting requirements--noise and linearity--which set the dynamic range performance of RFICs (Radio Frequency Integrated Circuits) are satisfied simultaneously. We demonstrate that the proposed architecture does not sacrifice performance in single-carrier operation, and no additional matching element is required. Comparative performance in different operation modes are elaborated.  
This paper is organized as follows. The system description of the proposed receiver architecture is discussed in Section 2. Several low noise amplifier (LNA) topologies suitable for receiver (RX) carrier aggregation are presented, and are evaluated with the proposed receiver architecture in Section 3. Concluding remarks are given in Section 4.