Gweon-Do Jo

A 2.14-GHz GaN MMIC Doherty Power Amplifier for Small-Cell Base Stations

A novel 2.14-GHz Doherty power amplifier (PA) was designed and fabricated using a 0.25- μm GaN on SiC monolithic microwave integrated circuit (MMIC), to build small-cell base stations. To reduce the size and loss, lumped passive elements were employed in a manner of minimizing the device count. The core components of the PA were integrated on the MMIC die to reduce the area, and low-loss chip inductors were mounted around the die to enhance the efficiency. An unconventional uneven power splitting was also used to enhance the performance. For a continuous wave, a 2-dB-gain-compression power of 40.5 dBm was obtained with a drain efficiency (DE) of 60.4%. At 7.3-dB backed-off power, a DE of 52.2% was obtained with a power gain of 15.7 dB. When a 10-MHz-bandwidth long-term evolution signal with 7.1-dB peak-to-average power ratio was applied, an adjacent channel leakage ratio (ACLR) of -34.7 dBc with a DE of 51.8% was achieved at an average power of 33.2 dBm. After a digital pre-distortion process, the ACLR and DE were improved to -49.6 dBc and 52.7%, respectively.

Performance evaluation of pilot channel acquisition system in CDMA forward link

The performance of window-based PN acquisition algorithm is fully analyzed by a Markov chain acquisition model on the assumption of direct sequence code division multiple access forward link. The algorithm with a moderate window size has shorter acquisition time than the immediate verification algorithm has-especially in low Ec/No. This results from the fact that the window-based algorithm, which verifies only one code phase that has maximum correlation output, consumes an additional penalty time in each window even in the condition of frequent false alarms. As the mean acquisition time varies with the window size, we may have the code acquisition fast with the proper window size according to Ec/No.

A Digitized IF-Over-Fiber Transmission Based on Low-Pass Delta-Sigma Modulation

In this letter, we propose and demonstrate a digitized intermediate frequency (IF)-over-fiber transmission system based on the delta-sigma modulation technique as a means of digitizing an analog IF signal. Using a realized 130-nm CMOS, two-level third-order low-pass delta-sigma modulator (DSM) chip operating at 622.08 MHz, a 64-Quadrature Amplitude Modulation long-term evolution (LTE) 10-MHz signal at a 10-MHz IF frequency was successfully digitized, transported over an emulated digital fiber-optic link, and analyzed in terms of signal spectra, error vector magnitude (EVM), and constellations. The difference between power levels of the received LTE IF signal and quantization noise due to the developed DSM was larger than 45 dB, and an EVM value of 2.48% for the received LTE signal was obtained.

A compact matched filter for rapid code acquisition

In this paper a compact digital matched filter acquisition system is proposed and investigated. The proposed digital matched filter (DMF) achieves a mean acquisition time comparable to that obtained by the conventional DMF but allows an unlimited period of integration and some advantages in terms of probabilities of detection and false alarm. Therefore the proposed DMF requires a short device length and still provides a fast acquisition. The probabilities for detection and false alarm in the AWGN channel are derived and the mean acquisition time is evaluated as a measure of performance. Its performance is compared to that of the conventional DMF and serial search acquisition system. The numerical results show the trade-off between the acquisition time and the number of stages of digital matched filter.

Real-time processing of a software defined W-CDMA modem

As the code division multiple access (CDMA) based third generation cellular infrastructure requires high performance signal processing in the baseband modem, a common approach of chip rate processing has been to use an application specific integrated circuit (ASIC) or field programmable gate array (FPGA) implementation. The use of digital signal processors (DSP) is explored for a wideband CDMA (W-CDMA) channel modem with the goal of increasing flexibility. Design concepts of a software defined radio (SDR) platform we implemented are presented, including its hardware-software architecture and test results. Practical issues for the optimization of DSP software are also discussed in detail.

Optimal detection considering AGC effects in multiple antenna systems

Most detection methods for multiple input multiple output (MIMO) systems are derived with an assumption that the noise from multiple receive paths is white. However, This assumption cannot be valid according to automatic gain control (AGC) schemes. If the independent AGC scheme which has difference gain for each receive path to minimize the quantization noise is employed, the AGC output noise is not white any more. Therefore, the colored noise effects due to AGC should be considered for the optimal detection. In detail, such colored noise effects should be included in the maximum likelihood (ML) detection criterion and the log likelihood ratio (LLR) calculation.

A single RF-chain load modulation transmitter of expansion structure for massive MIMO

The LM-MIMO system will be able to transmit a multiplex data stream which used the single RF-chain is one to in then technique. Because LM has a single RF-chain, LM hardware complexity and cost is low than a conventional MIMO. This paper presents a design of LM-MIMO basic element, is verified by EM-simulation and experiment. The proposed LM-MIMO is possible to massive MIMO system which use a large number of antennas and RF-chain.

Demodulation of 4×4 MIMO signal using single RF

Beam switching in the receiving antenna generates replicas in frequency domain, which enables MIMO decoding by using just single RF. It is fascinating to demodulate MIMO signals using single RF, which relieves the volume expansion by MIMO. However, this scheme has not been verified through a test-bed especially in 4×4 MIMO case. This paper presents test results of 4×4 MIMO receiver using single RF chain and beam switching antenna. Test results show the constellation and SNR of decoded 4×4 MIMO signal. When beam switching scheme applies, measured SNR was 12.95 dB on average and 17.85 dB at its maximum. This scheme can apply to massive MIMO system which requires quite a number of antennas and RF circuits.

Adaptive bit truncation and restoration for baseband signal compression

The distributed base station architecture is one of the good solutions to reduce the system complexity and manage the cellular mobile communication system more efficiently. Typical distributed base stations consist of base band units (BBUs) and remote radio heads (RRHs). RRHs are deployed apart from BBU and connected to it generally through a fiber optic cable. Compression of baseband signal is an efficient way to decrease the data rates on the fiber link between BBU and RRHs. This paper presents a compression and decompression scheme. It truncates least significant bits according to the largest absolute value in a block, thereby achieves lossy compression at each of I and Q data, respectively. It restores the signal by using proposed stuffing bits to suppress DC component in the signal and relieve signal to noise ratio degradation by compression and decompression. The simulation results suggest that the proposed scheme provides promising performance of error vector magnitude with low latency. It enables cost effective implementation since it does not require any multiply accumulate operation. Simple bit operations are needed in proposed scheme.

Jitter Effect on a Digital IF Transceiver for SDR-based Mobile communication Base Station

This paper outlines the time jitter effect of a sampling clock on a Software Defined Radio (SDR) technology- based-Digital Intermediate Frequency (IF) transceiver for a mobile communication base station. The implemented Digital IF transceiver is reconfigurable to three bandwidth profiles : 1.75 MHz, 3.5 MHz, and 7 MHz each incorporating the IEEE 802.16d Worldwide Interoperability for Microwave Access (WiMAX) standard and High-Speed Downlink Packet Access (HSDPA) standard. This transceiver can be reconfigured to other standard profiles through software downloaded onto identical hardware platforms, without changing any components or parts on board. This paper examines the relationship between the Signal-to- Noise Ratio (SNR) characteristics of a Digital IF transceiver with an under-sampling scheme and the sampling jitter effect on a multi-channel OFDM signal and a multi-code CDMA signal. The experimental results show that the SNR of the multi-channel OFDM system is more susceptible to sampling clock jitter compared to a multi-code HSDPA system.