A 90 nm CMOS 16 Gb/s Transceiver for Optical Interconnects

Interconnect architectures which leverage high-bandwidth optical channels offer a promising solution to address the increasing chip-to-chip I/O bandwidth demands. This paper describes a dense, high-speed, and low-power CMOS optical interconnect transceiver architecture. Vertical-cavity surface-emitting laser (VCSEL) data rate is extended for a given average current and corresponding reliability level with a four-tap current summing FIR transmitter. A low-voltage integrating and double-sampling optical receiver front-end provides adequate sensitivity in a power efficient manner by avoiding linear high-gain elements common in conventional transimpedance-amplifier (TIA) receivers. Clock recovery is performed with a dual-loop architecture which employs baud-rate phase detection and feedback interpolation to achieve reduced power consumption, while high-precision phase spacing is ensured at both the transmitter and receiver through adjustable delay clock buffers. A prototype chip fabricated in 1 V 90 nm CMOS achieves 16 Gb/s operation while consuming 129 mW and occupying 0.105 mm^2

The BLIXER, a Wideband Balun-LNA-I/Q-Mixer Topology

This paper proposes to merge an I/Q current-commutating mixer with a noise-canceling balun-LNA. To realize a high bandwidth, the real part of the impedance of all RF nodes is kept low, and the voltage gain is not created at RF but in baseband where capacitive loading is no problem. Thus a high RF bandwidth is achieved without using inductors for bandwidth extension. By using an I/Q mixer with 25% duty-cycle LO waveform the output IF currents have also 25% duty-cycle, causing 2 times smaller DC-voltage drop after IF filtering. This allows for a 2 times increase in the impedance level of the IF filter, rendering more voltage gain for the same supply headroom. The implemented balun-LNA-I/Q-mixer topology achieves > 18 dB conversion gain, a flat noise figure < 5.5 dB from 500 MHz to 7 GHz, IIP2 = +20 dBm and IIP3 = -3 dBm. The core circuit consumes only 16 mW from a 1.2 V supply voltage and occupies less than 0.01 mm2 in 65 nm CMOS

Cooperative Precoding with Limited Feedback for MIMO Interference Channels

Multi-antenna precoding effectively mitigates the interference in wireless networks. However, the resultant performance gains can be significantly compromised in practice if the precoder design fails to account for the inaccuracy in the channel state information (CSI) feedback. This paper addresses this issue by considering finite-rate CSI feedback from receivers to their interfering transmitters in the two-user multiple-input-multiple-output (MIMO) interference channel, called cooperative feedback, and proposing a systematic method for designing transceivers comprising linear precoders and equalizers. Specifically, each precoder/equalizer is decomposed into inner and outer components for nulling the cross-link interference and achieving array gain, respectively. The inner precoders/equalizers are further optimized to suppress the residual interference resulting from finite-rate cooperative feedback. Further- more, the residual interference is regulated by additional scalar cooperative feedback signals that are designed to control transmission power using different criteria including fixed interference margin and maximum sum throughput. Finally, the required number of cooperative precoder feedback bits is derived for limiting the throughput loss due to precoder quantization.Comment: 23 pages; 5 figures; this work was presented in part at Asilomar 2011 and will appear in IEEE Trans. on Wireless Com

Peak-to-Average Power Ratio Reduction of DOCSIS 3.1 Downstream Signals

Tone reservation (TR) is an attractive and widely used method for peak-to-average power ratio (PAPR) reduction of orthogonal frequency division multiplexing (OFDM) signals, where both transmitter and receiver agree upon a number of subcarriers or tones to be reserved to generate a peak canceling signal that can reduce the peak power of the transmitted signals. The tones are selected to be mutually exclusive with the tones used for data transmission, which allows the receiver to extract the data symbols without distortions. This thesis presents two novel PAPR reduction algorithms for OFDM signals based on the TR principle, which do not distort the transmitted signals. The first proposed algorithm is performed in the time domain, whereas the second algorithm is a new clipping-and-filtering method. Both algorithms consist of two stages. The first stage, which is done off-line, creates a set of canceling signals based on the settings of the OFDM system. In particular, these signals are constructed to cancel signals at different levels of maximum instantaneous power that are above a predefined threshold. The second stage, which is online and iterative, reduces the signal peaks by using the canceling signals constructed in the first stage. The precalculated canceling signals can be updated when different tone sets are selected for data transmission, accommodating many practical applications. Simulation results show that the proposed algorithms achieve slightly better PAPR reduction performance than the conventional algorithms. Moreover, such performance is achieved with much lower computational complexity in terms of numbers of multiplications and additions per iteration. Among the two proposed algorithms, the time-domain algorithm gives the best peak reduction performance but the clipping-and-filtering algorithm requires considerably less number of multiplications per iteration and can be efficiently implemented using the fast Fourier transform (FFT)/inverse fast Fourier transform (IFFT) structure

Designing Wireless Broadband Access for Energy Efficiency: Are Small Cells the Only Answer?

The main usage of cellular networks has changed from voice to data traffic, mostly requested by static users. In this paper, we analyze how a cellular network should be designed to provide such wireless broadband access with maximal energy efficiency (EE). Using stochastic geometry and a detailed power consumption model, we optimize the density of access points (APs), number of antennas and users per AP, and transmission power for maximal EE. Small cells are of course a key technology in this direction, but the analysis shows that the EE improvement of a small-cell network saturates quickly with the AP density and then "massive MIMO" techniques can further improve the EE.Comment: Published at Small Cell and 5G Networks (SmallNets) Workshop, IEEE International Conference on Communications (ICC), 6 pages, 5 figures, 1 tabl

RF system model for In-band full duplex communications

Abstract. In recent years by increasing the demands for communication services various technologies are examined in order to improve the throughput and spectrum efficiency of the wireless communication systems. For improving the performance a communication network, system deficiencies such as transmitter and receiver impairments need to be removed or compensated. One way to improve the network efficiency is to employ full duplex technology. Full duplex technology doubles the network capacity compared to the case when typical frequency division duplexing (FDD) or time division duplexing (TDD) are employed in a transceiver design. Although full duplex (FD) technology has enhanced the performance of the radio communication devices, the main challenge in full duplex communication is the leaking self-interference signal from the transmitter to the receiver. Different methods are employed to suppress the self-interference signal in digital and analog domains which are categorized as passive or active cancellations. These techniques are discussed in this thesis in order to understand from which point in the propagation path, the required signal for cancellation can be taken and how those techniques are employed in digital and analog domains. For having a good self-interference cancellation (SIC) both analog and digital cancellation techniques are needed since typical digital suppression method is low complex and somewhat limited. In this thesis, first we start with discussing about the full duplex technology and the reason why it has become popular in recent years and later full duplex deficiencies are examined. In the following chapters different cancellation methods are introduced and some results are provided in Chapter 5

Four-element phased-array beamformers and a self-interference canceling full-duplex transciver in 130-nm SiGe for 5G applications at 26 GHz

This thesis is on the design of radio-frequency (RF) integrated front-end circuits for next generation 5G communication systems. The demand for higher data rates and lower latency in 5G networks can only be met using several new technologies including, but not limited to, mm-waves, massive-MIMO, and full-duplex. Use of mm-waves provides more bandwidth that is necessary for high data rates at the cost of increased attenuation in air. Massive-MIMO arrays are required to compensate for this increased path loss by providing beam steering and array gain. Furthermore, full duplex operation is desirable for improved spectrum efficiency and reduced latency. The difficulty of full duplex operation is the self-interference (SI) between transmit (TX) and receive (RX) paths. Conventional methods to suppress this interference utilize either bulky circulators, isolators, couplers or two separate antennas. These methods are not suitable for fully-integrated full-duplex massive-MIMO arrays. This thesis presents circuit and system level solutions to the issues summarized above, in the form of SiGe integrated circuits for 5G applications at 26 GHz. First, a full-duplex RF front-end architecture is proposed that is scalable to massive-MIMO arrays. It is based on blind, RF self-interference cancellation that is applicable to single/shared antenna front-ends. A high resolution RF vector modulator is developed, which is the key building block that empowers the full-duplex frontend architecture by achieving better than state-of-the-art 10-b monotonic phase control. This vector modulator is combined with linear-in-dB variable gain amplifiers and attenuators to realize a precision self-interference cancellation circuitry. Further, adaptive control of this SI canceler is made possible by including an on-chip low-power IQ downconverter. It correlates copies of transmitted and received signals and provides baseband/dc outputs that can be used to adaptively control the SI canceler. The solution comes at the cost of minimal additional circuitry, yet significantly eases linearity requirements of critical receiver blocks at RF/IF such as mixers and ADCs. Second, to complement the proposed full-duplex front-end architecture and to provide a more complete solution, high-performance beamformer ICs with 5-/6- b phase and 3-/4-b amplitude control capabilities are designed. Single-channel, separate transmitter and receiver beamformers are implemented targeting massive- MIMO mode of operation, and their four-channel versions are developed for phasedarray communication systems. Better than state-of-the-art noise performance is obtained in the RX beamformer channel, with a full-channel noise figure of 3.3 d