Recently, system-on-chip (SoC) solutions have been realized by integrating not only complex digital processing but also extensive analog and radio frequency (RF) circuits in a single chip. This paper presents a novel RF self test methodology suitable for complex radio SoC's. The proposed methodology employs the digital processor embedded in an SoC to enable self-testing using low-cost digital automatic test equipments (ATE). Moreover, to achieve increased RF test coverage achievable through internal loopback, the embedded processor also utilizes a compact assisted test board and interfaces to it through simple general purpose I/O's (GPIO). The proposed self-test methodology has been successfully applied in the mass production (MP) of a 65nm CMOS combo SoC that includes Wi-Fi, Bluetooth, GPS and FM. The final test (FT) and wafer probe test (PT) of the SoC have been accomplished with a 3X reduction in total test time compared to conventional test methodology using RF instruments.

A low-complexity blind frequency-dependent I/Q imbalance compensation scheme is proposed based on linear prediction (LP) method. It provides non-iterative processing which reduces computational complexity. No special training sequence is used and I/Q mismatch calibration is performed using any received sequence. Frequency-dependent (FD) I/Q imbalance can be compensated simply by matching the filter responses of the I and Q branches. This is achieved by estimating the inverse impulse responses of the I and Q branches using LP and then finding the `difference' filter that can be used in one of the branches to match the other branch. Using simulations, we show that the proposed method has at least 5-7 dB better image rejection ratio (IRR) performance compared to other blind FD I/Q estimation techniques in the literature, for a realistic mismatch scenarios. Moreover, the computational complexity of the proposed technique is shown to be 20x less than the least complex blind estimation scheme in the literature for an 8-tap compensation filter. Finally, we propose the use of a noise-generator for offline-calibration.

With the proliferation of multi-standard mobile devices, in-device coexistence (IDC) has become a key challenge in the design of modern radios. Typical IDC use cases involve radio transmitters (aggressors) that are interfering with radio receivers (victims) collocated on the same device. Isolation of the sensitive receiver from high power transmitters on the same device poses major difficulties due to insufficient frequency separation between the aggressors and their victims. In this paper, we present an adaptive approach to suppress unwanted out-of-band signal power (i.e. TX skirt)from the aggressor to minimize desensitization at the victim. The proposed method relaxes off-chip filtering requirements and reduces guard band spacing, leading to a low cost integrated solution for multi-standard radios. To highlight the effectiveness of the proposed algorithm, we have demonstrated greater than 30 dB improvement in signal-to-interference ratio (SIR) enabling the coexistence between Band-40 LTE and 2.4GHz Wi-Fi radios on the same device.

A novel highly-efficient multi-band multi-mode all digital quadrature transmitter is presented. The all digital transmitter uses in-phase (I) codeword and quadrature (Q) codeword to control a switching-mode power amplifier (PA) or digital PA (DPA) consisting of in-phase PA (I-PA) and quadrature PA (Q-PA), where each of the power cells inside I-PA or Q-PA is either on or off. Due to the load interaction between I-PA and Q-PA, a 2-dimensional digital pre-distortion is applied to linearize DPA. The total transmitter is implemented in 40nm CMOS LP process and occupies a die area of 0.7mm2. The digital quadrature transmitter can support 20MHz, 40MHz, and 80MHz WiFi signals, Band 38 and Band 40 LTE signals with class 3 output power, and Bluetooth BDR, EDR2, and EDR3 signals.

Modern radios use in-phase (I) and quadrature-phase (Q) channels for transmission and reception. However, IQ matching for high image rejection ratio is difficult and costly to realize by pure analog circuit techniques. Therefore, digital-assisted IQ compensation is required. This paper presents a novel joint TX/RX IQ compensation (JTRC) algorithm for low-IF feedback architecture. Conventional approaches are based on time-domain processing of test tones or frequency-domain processing of pilots in orthogonal frequency-division multiplexing (OFDM) systems. In contrast, JTRC employs time-domain blind source separation (BSS) for both OFDM and non-OFDM based systems without placing a specific requirement on the type of test signal. For example, JTRC supports both tones and modulated signals. Moreover, JTRC can be performed in the background during normal transmission mode using the actual transmitted signal. Unlike other BSS approaches that can only compensate for RX IQ mismatches while assuming a matched transmitter, JTRC can jointly compensate for both TX and RX IQ mismatches. We present an in-depth analysis that validates the JTRC algorithm and show simulation results that demonstrate its effectiveness.

An iterative receiver structure Is proposed for turbo-coded frequency-hop multiple access (FHMA) systems. In FHMA systems, the adjacent channel interference (ACI) is the major contributor of multiple access interference (MAI) if orthogonal hopping patterns are used. The ACI is a function of the tone spacings of the adjacent subchannels and the rolloff factor of the pulse-shaping filter. The calculation of the ACI for a square-root raised-cosine pulse-shaping filter in an FHMA system is presented in this paper. In addition, a low complexity iterative multiuser detector is developed to mitigate the degradation caused by ACI in the FHMA systems. The iterative receiver structure is based on a modified turbo decoding algorithm which makes use of the a posteriori log-likelihood ratio (LLR) information of the systematic bits to obtain the a posteriori information of the turbo-encoded parity bits. Iterations of the receiver/decoder are used as the mechanism to estimate and mitigate the MAI in the FHMA system. The properties of both soft and hard interference suppressors based on the modified turbo decoding algorithm are examined and an efficient recursive implementation is derived. Compared to maximum-likelihood multiuser detection, the proposed system is more practical and its complexity is only a linear function of the number of users. Simulation results show that the proposed iterative receiver structure offers significant performance gain in bandwidth efficiency and the required signal-to-noise ratio (SNR) for a target bit-error rate (BER) over the noniterative receiver structure. Moreover, the single user performance can be achieved when imperfect power control exists.

An iterative receiver structure is proposed for turbo-coded FHMA systems. In frequency-hop multiple access (FHMA) systems, the adjacent channel interference (ACI) is the major contributor of MAI if orthogonal hopping patterns are used. The ACI is a function of the tone spacings of the adjacent subchannels and the rolloff factor of the pulse-shaping filter. A low complexity iterative multiuser detector is developed to mitigate the degrading effect of ACI in the FHMA systems. Iterations of the demodulator and decoder are used as the mechanism to estimate and mitigate the MAI in the FHMA system. In addition, an iterative decoder structure based on a modified turbo decoding algorithm is proposed. Compared to maximum-likelihood multiuser detection, the proposed system is more practical and its complexity is only a linear function of the number of users. Simulation results show that the proposed iterative receiver structure offers significant performance gains in bandwidth efficiency and the required signal-to-noise ratio (SNR) for a target BER over a noniterative receiver structure.