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In this paper, on-chip higher-order-mode dielectric-resonator antennas (DRAs), fed by a half-mode-backed cavity structure using standard CMOS technology, are presented. With the dominant cavity mode (half-TEz100), the half-mode cavity-feeding structure provided a high antenna radiation efficiency. The dielectric resonators (DRs) were designed to operate at higher-order modes (TEx?13, TEx?15) to enhance the antenna gain. At around 135 GHz, the proposed antennas demonstrated measured gains of 6.2 dBi and 7.5 dBi for the TEx?13 and TEx?15 modes, respectively, with corresponding simulated radiation efficiencies of 46% and 42%. Both antennas had a measured impedance bandwidth of 7%. The proposed antennas not only accomplished high gain without occupying a large chip area, but also maintained comparable or even improved cost performance and simplicity over other on-chip antennas.

This study describes a class of D-band hybrid couplers employing a structurally improved phase inverter in a standard CMOS technology. The proposed phase inverter, which consists of an inverter core and two quasi-parallel striplines along with two slots for impedance matching improvement, is characterised by an equivalent circuit model to facilitate the design procedure. A 180° coupler deploying the phase inverter features 38% size reduction and over 60% bandwidth improvement compared with its conventional counterparts. The proposed rat-race coupler achieves an insertion loss of around 1.1 and 30 dB isolation bandwidth of over 31 GHz, with a peak isolation of 41 dB at 118 GHz. A 90° coupler using the phase inverter demonstrates a return loss and isolation of 14 and 18 dB, respectively, in the whole D-band range. The measured amplitude and phase imbalances for the broadband coupler are, respectively, within 1 dB and 6° from 110 to 160 GHz. Both couplers can be inherently integrated with millimetre-wave circuits for on-chip system applications.

This brief proposes a guard ring using through-silicon vias (TSVs) to isolate thermal coupling in a 3-D integrated circuit (3-D IC). To verify this idea, simulation and measurement are carried out. A ring oscillator (RO) is implemented in a 65-nm CMOS and then measured in four different conditions. The results show that, without affecting the inherent electrical performance of the RO, the designed TSV ring shields the RO from high-temperature environments. The oscillation frequency shifting is mitigated from 5.96 MHz without TSV to 2.11 MHz with the proposed TSV ring. This TSV-based structure provides a good option to alleviate thermal coupling in a highly integrated 3-D IC.

In this paper, a six-port distributed model of on-chip single-turn transformers in silicon that can predict the features of the transformers up to 200 GHz is presented. Moreover, the proposed model is scalable with the diameter of the transformer. Based on the developed model, a transformer balun with improved differential-port balance is deployed in a D-band up-conversion mixer design in 0.13-μm SiGe BiCMOS technology. The mixer achieves a measured conversion gain (CG) of 4 ~ 7 dB and local-oscillator-to-RF isolation over 30 dB from 110 to 140 GHz. The results have one of the best CGs in the millimeter-wave range. A D-band two-stage transformer-coupled power amplifier (PA) integrated with a mixer is also reported here. Using the six-port transformer model, the performance of the PA can be conveniently optimized. At a 2-V supply, the gain and saturated output power of 20 dB and 8 dBm, respectively, are both experimentally achieved at 127 GHz. At 3 V, the measured output power rose to 11 dBm and this is the best power performance among the reported D-band silicon-based amplifiers to date.

This paper presents a terahertz (THz) transmitter (Tx) and receiver (Rx) chipset operating around 400 GHz in 0.13- μm SiGe BiCMOS technology. The Tx chip consists of a voltage-controlled oscillator, a buffer, a modulator, a power amplifier, a frequency tripler, and a substrate integrated waveguide (SIW) antenna. This antenna has an additional high-pass filtering characteristic to suppress the unwanted fundamental (f0) and second harmonic (2f0) signals by 50 and 30 dB, respectively. The Rx chip includes a proposed reconfigurable SIW antenna and a novel two-mode subharmonic mixer with ~ 5-dB reduction of conversion loss. The Rx chip consumes 50 nA from a 1.2-V supply. The measurement results of the Tx and Rx chips and a back-to-back test of the Tx/Rx chipset show the feasibility and pave the way of implementing a fully integrated THz system in silicon technology for mass production.

This work discusses the design methodologies of 130-GHz high gain and high efficiency on-chip meander slot antennas in a standard CMOS technology. In the proposed structure, stacked dielectric resonators (DRs) are placed on the top of the on-chip feeding element to form series-fed antenna array for antenna gain and efficiency improvement. The integrated antenna with double stacked DRs achieved a measured gain of 4.7 dBi at 130 GHz with a bandwidth of 11%. The antenna size is 0.8 ×0.9 mm2 and the simulation results indicate a radiation efficiency of 43%. To the best of our knowledge, this is the first demonstration of an on-chip antenna gain and efficiency enhancement through stacked DRs.

We treat the problem of sum-rate maximization via scheduling and linear precoding in multiuser (MU) multiple-input-multiple-output (MIMO) systems with quantized feedback. We formulate the optimal quantized linear precoder design problem and provide the numerical procedure for finding the solution. We also provide a simple scheduling scheme that exploits the MU diversity gain. With the aim of sum-rate maximization, we further address the quantization codebook design based on the capacity measure by introducing a new distance metric. It is demonstrated that, with or without scheduling, the proposed optimal linear precoding scheme achieves significant gain over the conventional linear precoder designs with similar feedback overhead, such as the zero-forcing precoder. Moreover, although the proposed quantization codebook design improves the performance of other existing MU-MIMO precoding schemes, the performance gain offered by it is typically much higher when it is coupled with the proposed linear precoding design.

We treat the problem of outage minimization via power control in MIMO systems with quantized feedback. We formulate the optimal quantized power control design for a general MIMO system and provide the numerical procedure for finding the optimal solution. Our results not only extend but also show the deficiency of the existing quantized power control schemes for MISO systems. We further propose a design based on the pre-evaluation of the packet error rate performance of practical MIMO systems employing short-length LDPC codes and QAM modulations and with possibly unreliable feedback links. It is demonstrated that with only a few bits of feedback, the resulting quantized power control strategy achieves considerable gain over a system without power control.

We consider the sum-rate maximization via linear preceding in downlink MIMO-OFDM systems with quantized feedback. We address the preceding codebook design based on the capacity measure by introducing a new distance metric. We propose a codebook structure and its associated design algorithm that allows for significant reduction in the memory requirement and computational complexity in real-time system implementation. We then provide a system design approach comprising of four main ingredients: (i) a multi-rank beamforming (MRBF) scheme, (ii) an efficient CQI-based precoder selection algorithm, (iii) reduced feedback strategies, and (iv) novel channel quality indicator (CQI) combining. Our simulation results show that the proposed MRBF scheme can approach the precoding upper bounds with relatively few feedback bits. Moreover, with the same number of bits, the proposed scheme simultaneously achieves higher throughput and lower computational complexity in comparison to the other existing precoding schemes.

We consider coded multiple-input-multiple-output (MIMO) systems in block-fading channels employing iterative receivers, where the MIMO channels are scrambled by unitary matrices. We show that the unitary scrambling improves the outage performance with discrete input when the outer code rate is high, i.e., Ro > 0.5. We also demonstrate that the performance improvement from scrambling can be achieved by a small number of random unitary matrices. Moreover, with unitary scrambling, the signal model can be simplified, and the performance of the MIMO demodulator can be characterized by the singular values of the channel matrix. We then consider the design of irregular repeat-accumulate (IRA) codes for unitary scrambled MIMO block-fading channels. We propose a code design method by optimizing the IRA codes for extrinsic information transfer (EXIT) average with a given effective mutual information. We also propose a pessimistic code design for some system settings to improve the frame error rate performance.

We consider an optimal resource allocation strategy for cooperative relaying-enabled OFDMA multi-hop wireless networks. A cross-layer optimization problem is formulated that maximizes the balanced end-to-end throughput under the routing and the PHY/MAC constraints. A dual method is employed to solve the problem efficiently and optimally. A cooperative relaying technique is incorporated into the framework by introducing virtual links and nodes. Half-duplex operation of the radios is assumed, and mutual interference between the links is explicitly modeled to allow maximal spatial reuse of the spectral resources. Numerical results are provided to demonstrate how the bottleneck phenomenon typical in multi-hop networks can be alleviated by the proposed technique to yield significant improvement in the throughput.

We treat the problem of designing low-density parity-check (LDPC) codes to approach the capacity of relay channels. We consider an efficient analysis framework that decouples the factor graph (FG) of a B-block transmission into successive partial FGs, each of which denotes a two-block transmission. We develop design methods to find the optimum code ensemble for the partial FG. In particular, we formulate the relay operations and the destination operations as equivalent virtual MISO and MIMO systems, and employ a binary symmetric channel (BSC) model for the relay node output. For AWGN channels, we further develop a Gaussian approximation for the detector output at the destination node. Jointly treating the relay and the destination, we analyze the performance of the LDPC-coded relay system using the extrinsic mutual information transfer(EXIT) chart technique. Furthermore, differential evolution is employed to search for the optimum code ensemble. Our results show that the optimized codes always outperform the regular LDPC codes with a significant gain; in the AWGN case, when Protocol-II is employed and the relay is close to the source, the optimized code performs within 0.1dB to the capacity bound.

A cross-layer design approach is considered for joint routing and resource allocation for the physical (PHY) and the medium access control (MAC) layers in multihop wireless backhaul networks. The access points (APs) are assumed to be equipped with multiple antennas capable of both transmit and receive beamforming. A nonlinear optimization problem is formulated, which maximizes the fair throughput of the APs in the network under the routing and the PHY/MAC constraints. Dual decomposition is employed to decouple the original problem into smaller subproblems in different layers, which are coordinated by the dual prices. The network layer subproblem can be solved in a distributed manner and the PHY layer subproblem in a semidistributed manner. To solve the PHY layer subproblem, an iterative minimum mean square error (IMMSE) algorithm is used with the target link signal-to-interference-and-noise-ratio (SINR) set dynamically based on the price generated from the upper layers. A scheduling heuristic is also developed, which improves the choice of the transmission sets over time. Simulation results illustrate the efficacy of the proposed cross-layer design.

A distributed joint routing and medium access control (MAC) algorithm is proposed for lifetime maximization of wireless sensor networks. By adopting the flow contention graph model and the resulting MAC constraints, the problem can be formulated into a linear programming problem, which can be solved distributively using dual decomposition. However, the message passing overhead of such a solution is high, since the information exchange must occur among the interfering links as well as the communicating links. In this work, the MAC layer constraints are relaxed in the form of a penalty function, which facilitates distributed optimization using only the collision statistic that each node can accumulate essentially at no extra cost. The resulting algorithm solves a convex optimization problem by a distributed primal-dual approach, where the network layer problem is solved in the dual domain, and the MAC layer problem is solved in the primal domain.

We consider the design of efficient rate-compatible (RC) irregular repeat accumulate (IRA) codes over a wide code rate range. The goal is to provide a family of RC codes to achieve high throughput in hybrid automatic repeat request (ARQ) scheme for high-speed data packet wireless systems. As a subclass of low-density parity-check codes, IRA codes have an extremely simple encoder and a low-complexity decoder while providing capacity approaching performance. We focus on a hybrid design method which employs both puncturing and extending. We propose a simple puncturing method based on minimizing the maximal recoverable step of the punctured nodes. We also propose a new extending scheme for IRA codes by introducing the degree-1 parity bits for the lower rate codes and obtaining the optimal proportions of extended nodes through density evolution analysis. The throughput performance of the designed RC-IRA codes in hybrid ARQ is evaluated for both AWGN and block fading channels. Simulation results demonstrate that our designed RC codes offer good error correction performance over a wide rate range and provide high throughput, especially in the high and low signal-to-noise ratio regions.

We propose a call (user) admission control (CAC) algorithm and a scheduling framework for real-time services in the enhanced third-generation (3G) cellular systems, e.g., WCDMA HSDPA or cdma2000 HDR systems, where multiple IP users share a time-slotted downlink packet channel in each cell. At the user or flow level, the CAC algorithm maximizes user accommodations under the QoS constraint, e.g., per-user expectation of profile rate, and the constraint of location-dependent resource availability. At the packet level, our scheduling framework, named maximum cost deduction (MCD), derives two algorithms - both are QoS-aware and channel-dependent: One is called real-time MCD (rt-MCD), which minimizes a delay-derived cost function of backlogged packets at the smallest timescale; the other is called non-real-time MCD (nrt-MCD), which balances between the real-time delay deduction and the non-real-time (i.e., large-timescale) per-user fairness. The cross-layer designed CAC and MCD algorithms exploit multi-user diversity based on online measured radio resource allocation. Together they provide high system efficiency and a balance between flow-level QoS (e.g. the aggregate goodput and the blocking rate of newly arrived users) and packet-level QoS (e.g., the packet queueing delay or loss). Extensive simulations and comparisons with the prior art show that our algorithms can deliver efficient real-time services and remain robust to different load scenarios that vary according to system dynamics and/or user mobility

Multihop wireless backhual networks are emerging as a cost-effective solution to provide ubiquitous and broadband access to meet the rapidly increasing demands of multimedia applications. In this paper, we consider the joint optimal design of routing, medium access control (MAC) scheduling and physical layer resource allocation for such networks, where beamforming antenna arrays are equipped at the physical layer. The notion of transmission set (TS) is introduced to separate the physical layer operations from those at the upper layers; and a column generation approach is employed to efficiently identify the TSs. We then apply the dual decomposition method to decouple the routing and scheduling subproblems, which are performed at different layers and are coordinated by a pricing mechanism to achieve the optimal overall system objective. To efficiently support multimedia traffic, an admission control criterion is considered for the system objective. The performance of the proposed scheme is verified by simulation results, and the impact of the physical layer capabilities on the network performance is evaluated. We also discuss the implementation issues of the cross-layer scheme based on the IEEE 802.16 mesh mode.

Current downlink scheduling algorithms in the (enhanced) third-generation (3G) cellular packet systems exploit instantaneous channel status of multiple users, but most of them are blind to traffic information. To improve TCP users' perception of quality-of-services (QoSs), characterized by response delay, goodput, and always-on connectivity, we propose a cross-layer hierarchical scheduler with traffic awareness and channel dependence to properly prioritize buffer and radio resource allocation among different TCP classes. The scheduler has two tiers: at the IP layer, an intrauser scheduler enhances a common practice, i.e., the DiffServ-based buffer management, by dequeuing same-user TCP packets according to per-class specified and measured responsiveness; at the MAC layer, an interuser scheduler transmits the dequeued packets by considering the opportunistic channel states, mean throughput, and class ID of all users. Both tiers consider the online measured throughput, a cross-layer metric, to achieve resource and performance fairness and TCP classification. Experiments show that, compared with (variations of) proportional fairness (PF) and other schemes, our scheduler can notably speed up time-critical interactive TCP services (HTTP and TELNET) or TCP slow-starts with minor cost to bulk file transfer (FTP) or long-lived flows. It offers scalable and low-cost TCP performance enhancement over the emerging cellular systems

We investigate a wireless system of multiple cells, each having a downlink shared channel in support of high-speed packet data services. In practice, such a system consists of hierarchically organized entities including a central server, Base Stations (BSs), and Mobile Stations (MSs). Our goal is to improve global resource utilization and reduce regional congestion given asymmetric arrivals and departures of mobile users, a goal requiring load balancing among multiple cells. For this purpose, we propose a scalable cross-layer framework to coordinate packet-level scheduling, call-level cell-site selection and handoff, and system-level cell coverage based on load, throughput, and channel measurements. In this framework, an opportunistic scheduling algorithm--the weighted Alpha-Rule--exploits the gain of multiuser diversity in each cell independently, trading aggregate (mean) down-link throughput for fairness and minimum rate guarantees among MSs. Each MS adapts to its channel dynamics and the load fluctuations in neighboring cells, in accordance with MSs' mobility or their arrival and departure, by initiating load-aware handoff and cell-site selection. The central server adjusts schedulers of all cells to coordinate their coverage by prompting cell breathing or distributed MS handoffs. Across the whole system, BSs and MSs constantly monitor their load, throughput, or channel quality in order to facilitate the overall system coordination. Our specific contributions in such a framework are highlighted by the minimum-rate guaranteed weighted Alpha-Rule scheduling, the load-aware MS handoff/cell-site selection, and the Media Access Control (MAC)-layer cell breathing. Our evaluations show that the proposed framework can improve global resource utilization and load balancing, resulting in a smaller blocking rate of MS arrivals without extra resources while the aggregate throughput remains roughly the same or improved at the hot-spots. Our simulation tests also show that the coordinated system is robust to dynamic load fluctuations and is scalable to both the system dimension and the size of MS population.

We propose the physical-layer (PHY) air interface solutions for downlink and uplink transmissions in broadband high-speed wireless cellular systems. A system based on low-density parity-check (LDPC) coded multiple-input-multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) time-division multiple-accessing (TDMA) (with scheduling) is proposed for downlink transmission; and a system based on orthogonal space-time block coded (STBC) multi-carrier code-division multiple-accessing (MC-CDMA) is proposed for uplink transmission. The proposed scheme can support ∼100 Mbps peak rate over 25 MHz bandwidth downlink channels and ∼30 Mbps sum rate of multiple users over 25 MHz uplink channels. Moreover, the proposed solutions provide excellent performance and reasonable complexity for mobile station and for base station.

Fast downlink scheduling algorithms play a central role in determining the overall performance of high-speed cellular data systems, characterized by high throughput and fair resource allocation among multiple users. We propose a flexible channel-dependent downlink scheduling scheme, named the (weighted) alpha-rule, based on the system utility maximization that arises from the Internet economy of long-term bandwidth sharing among elastic-service users. We show that the utility as a function of per-user mean throughput naturally derives the alpha-rule scheme and a whole set of channel-dependent instantaneous scheduling schemes following different fairness criteria. We evaluate the alpha-rule in a multiuser CDMA high data rate (HDR) system with space-time block coding (STBC) or Bell Labs layered space-time (BLAST) multiple-input multiple-output (MIMO) channel. Our evaluation shows that it works efficiently by enabling flexible tradeoff between aggregate throughput, per-user throughput, and per-user resource allocation through a single control parameter. In other words the Alpha-rule effectively fills the performance gap between existing scheduling schemes, such as max-C/I and proportional fairness (PF), and provides an important control knob at the media-access-control (MAC) layer to balance between multiuser diversity gain and location-specific per-user performance.

In this paper, we propose to design linear-dispersion (LD) codes by minimizing the union bound based on the exact pairwise error probability (PEP). We find that the original programming is not convex, and we present a convex relaxation to the optimization problem. We employ the gradient descent methods to numerically search the optimum dispersion matrices. Simulation results show that codes optimized by the new criterion generally outperform the codes designed based on algebraic number theory. When the knowledge of spatial-fading correlation is available in advance for the design, significant gain relative to the codes designed without knowledge of channel correlation can be achieved by taking into account the correlation structure while performing the optimization. We demonstrate how to exploit knowledge of transmit and receive correlation in designing the LD codes. Numerical and simulation examples show that knowledge of transmit correlation has a large impact on the optimum performance of the LD codes. Furthermore, additional gain can be achieved from the knowledge of receive correlation.

The Cayley differential (CD) codes constitute a systematic way to construct differential unitary space-time modulations for noncoherent communication in multiple-antenna systems. The original CD codes are designed based on the criterion of maximizing the expected distance between codeword pairs. However, in practical systems, it is more sensible to design the codes according to the minimum error rate criterion. The main difficulty in such a design is that the error probability does not admit a closed-form expression and, thus, conventional optimization methods cannot be applied. In this paper, we formulate the minimum error-rate CD code design as an unconstrained stochastic optimization problem, and employ the stochastic approximation technique with gradient estimation to solve it. Simulation results show that codes generated by the proposed design procedure generally outperform the CD codes designed by maximizing the expected distance between codeword pairs and the Cayley threaded algebraic space-time codes that satisfy the full rank criterion. The new CD codes also enjoy better or comparable performance over other group based or nongroup designs.

We consider factor-graph-based soft self-iterative equalization in wireless multipath channels. Since factor graphs are able to characterize multipath channels to per-path level, the corresponding soft self-iterative equalizer possesses reduced computational complexity in sparse multipath channels. The performance of the considered self-iterative equalizer is analyzed in both single-antenna and multiple-antenna multipath channels. When factor graphs of multipath channels have no cycles or mild cycle conditions, the considered self-iterative equalizer can converge to optimum performance after a few iterations; but it may suffer local convergence in channels with severe cycle conditions.

We consider dynamic channel management (DCM), more specifically power control and channel allocation, in multi-carrier multi-antenna wireless cellular systems. A quasi-static channel model is assumed such that the channels remain approximately time-invariant within each packet. On a packet-by-packet basis, the mobile station (MS) receivers feed back the DCM parameters to the corresponding base station (BS) transmitters in order to minimize the transmission power and strive to satisfy every individual user's data-rate request. While optimum, centralized DCM for all active cells typically requires solution of a non-convex optimization problem (which is subject to local minima) and requires intense channel feedback to a central controller. We instead consider sub-optimal distributed DCM, where each individual cell locally optimizes its own performance based on the local channel information. In particular, we compare three distributed DCM schemes, namely the two-dimensional DCM, which jointly adjusts both spatial and frequency sub-channels of each BS–MS link, the one-dimensional DCM, which adjusts only the frequency sub-channels and the scalar DCM, which adjusts each BS–MS link by one scalar power coefficient. These DCM schemes are investigated in multi-cell environments with realistic parameters; and it is seen that due to the multiple antennas, the maximum supportable rate (i.e. the rate supported by practically finite transmission power) is significantly increased, for example by a factor of two for users using four antennas and close to cell boundary. Copyright © 2004 John Wiley & Sons, Ltd.

This letter describes a D-band 3-stage cascode amplifier developed using the IHP 0.13 μm SiGe BiCMOS technology. The amplifier is implemented with low-loss transformer for inter-stage matching and single-to-differential transformation. The large-signal characteristics of the cascode HBT configuration are used to optimize the bias condition for highest output power and gain performance. A measured amplifier achieves a peak power gain of 24.3 dB, with a 3 dB bandwidth of 20 GHz centered at 130 GHz. The amplifier exhibits a saturated output power of 7.7 dBm and an output 1 dB gain compression point of 6 dBm with a power consumption of 84 mW. The measured noise figure is 6.8 dB at 130 GHz and stays under 8 dB over the 3 dB bandwidth. To the best of our knowledge, the proposed amplifier exhibits the highest gain and output power among the silicon-based D-band amplifiers reported so far.

time-domain FDTD method and measurements. These pa- rameters were examined as functions of the distance of the monopole in front of the PBG slab and the location of the monopole relative to the structure of the unit cell of the PBG ! material whether the monopole is in front of a rod or a . hole . The previously introduced ''reflection plane concept'' for the PBG material was shown to be a useful design tool for this type of antenna. Measured results were used to demon- strate that radiation from an antenna is indeed reduced to a low level when it is placed within a finite volume of PBG material and excited at a frequency within the bandgap of the material. ABSTRACT:This letter presents a broadband corner reflector based on am onopole-type excitation structure. Using am oment method to opti- mize the different parameter structures, it is possible to use this structure from 1.8 to 6 GHz, with an a $erage gain of 9 dBi and a matching always better than 10 dB. The structure has been specially optimized for two frequencies of wireless communications, the 2.4 and 5 GHz bands. It has been used as a base station for indoor experimental communication systems in the abo$ eb ands.!1999 John Wiley & Sons, Inc. Mi- crowave Opt Technol Lett 21: 196#199, 1999.

This paper reports the first multifunctional 0.4-/spl mu/m BiCMOS-based transceiver chip developed for 5-GHz-band Gaussian minimum-shift keying modulation wireless systems. The chip integrates a low-noise radio-frequency amplifier, a down-mixer, and an intermediate-frequency (IF) amplifier in the down-converter path; an IF amplifier, a limiter, an up-mixer, and a buffer amplifier in the up-converter path; and a frequency doubler and a local oscillator amplifier in the local oscillator path. The chip featuring gain attenuation as well as standby mode operation uses a single 2.6-5.2-V bias voltage and dissipates 56 mW in receive mode and 66 mW in transmit mode. The transceiver chip size is 3.0/spl times/2.4 mm/sup 2/.

A quarter-wavelength diversity dipole configuration for a 2.4 GHz ISM band PC card application is reported. The structure is based on double-layer dipoles with a successive resonance. The dipoles are printed on a first layer and coupled to feeding lines on another layer to achieve the required space diversity with an easy matching to 50 Ω and high cross polarization within a given maximum space of 30 mm×50 mm. Classical measured antenna performances are shown, as well as a solution to cope with the implementation of the antenna in a PC card format. Measurement results are shown. This antenna system has been incorporated in a high-speed wireless LAN PC card system. © 1998 John Wiley & Sons, Inc. Microwave Opt Technol Lett 18: 351–354, 1998.

This paper deals with the design considerations, fabrication process, and performance of coplanar waveguide (CPW) heterojunction FET (HJFET) down- and up-converter monolithic microwave integrated circuits (MMIC's) for V-band wireless system applications. To realize a mixer featuring a simple structure with inherently isolated ports, and yet permitting independent port matching and low local oscillator (LO) power operation, a "source-injection" concept is utilized by treating the HJFET as a three-port device in which the LO signal is injected through the source terminal, the RF (or IF) signal through the gate terminal, and the IF (or RF) signal is extracted from the drain terminal. The down-converter chip incorporates an image-rejection filter and a source-injection mixer. The up-converter chip incorporates a source-injection mixer and an output RF filter. With an LO power and frequency of 7 dBm and 60.4 GHz, both converters can operate at any IF frequency within 0.5-2 GHz, with a corresponding conversion gain within -7 to -12 dB, primarily dominated by the related filter's insertion loss. Chip size is 3.3 mm/spl times/2 mm for the down-converter, and 3.5 mm/spl times/1.8 mm for the up-converter.

This paper presents a 60-GHz-band GaAs heterojunction FET (HJFET) low-noise amplifier (LNA) operating with a single bias supply. A diode-regulated self-bias circuit was incorporated for suppressing the FET drain-current variations due to threshold voltage nonuniformities. The effect of the bias circuit on the drain-current distribution is carefully discussed based on the FET dc characteristics. A developed three-stage monolithic microwave integrated circuit (MMIC) LNA exhibited an average noise figure of 3.3 dB with 18-dB gain from 58 to 62 GHz. The LNA could operate over 2-5 V with a constant noise figure. The LNA chip size is 1.85 mm/spl times/1.07 mm.

This paper Is concerned with the design considerations and performance results for low-voltage Si monolithic microwave integrated circuits (MMICs) developed for mobile and personal communications applications. A 0.4 /spl mu/m ECL-BiCMOS process technology was employed to develop bipolar-based RF amplifiers, MOS-based IF amplifiers, BiCMOS-based simplified Gilbert mixers, and monolithic down-converter as well as upconverter ICs incorporating these elements. These converters are designed to operate at a bias voltage of 2 V over 1.8-6.2 GHz exhibiting a conversion gain of 35-15 dB with a variable IF frequency of up to several 100 MHz. Chip size for both the downconverter and upconverter ICs is 1.0 mm/spl times/0.7 mm.

We report on a high power, high efficiency, and small-size monolithic coplanar waveguide oscillator incorporating a single-stage buffer amplifier on the same chip. For the oscillator design, by changing RF current level through the device, the optimum load line was chosen in order to have an oscillation frequency insensitive to the effect of the subsequently connected amplifier, based on a device-circuit interaction concept. The amplifier, on the other hand, which was driven directly by the oscillator, was designed to achieve an overall high power and high efficiency operation. At 21 GHz, the output power of the developed chip recorded 17 dBm with an overall DC-RF efficiency of 22%. By changing the length of a source feedback line, the oscillation frequency was varied from 21 GHz to 26 GHz. For all cases, the output power remained higher than 16 dBm.

In this paper, an ultra-low-energy biomedical signal processor (BSP) is proposed for wireless multi-channel physiological signal monitoring. This BSP integrates a RISC core and application-specific hardware accelerators (ASHAs) to achieve ultra low power consumption while meeting required performance. Various low power design techniques from system to circuit levels are applied, including event-driven signal processing, dynamic clock management, near-threshold operation, glitch-free clock generation, fine-grain clock gating, and ultra-low-voltage level shifting. The BSP can operate with supply from 1.8V down to 0.5V. With integrated ECG ASHAs based on the discrete wavelet transform, its overall energy consumption is 20.4pJ/cycle at 0.5V and 10MHz when performing a real-time wireless ECG monitoring.

In this paper, a D-band on-chip dielectric resonator antenna (DRA) fed by a half-mode backed cavity structure using a standard CMOS technology is presented. The half-mode cavity feeding structure in the proposed antenna permits easy excitation of both the dominant modes of the cavity (half-TEz110) and the dielectric resonator (TExe11). Based on this technology, a 135-GHz antenna is demonstrated, with a measured impedance bandwidth of 13% and a peak gain of up to 3.7 dBi at 132 GHz. Moreover, the radiation efficiency is simulated to be 62%. The chip size is 0.7 × 0.9 mm2 including the test pad. The proposed antenna is able to maintain comparable radiation performance of the off-chip antennas and has the advantage of easy integration with active circuits and also low cost.

This paper describes a D-band on-chip rat-race coupler using a novel phase inverter and developed in a standard CMOS process. The simple structural phase inverter which is based on the characteristic impedance and phase difference analysis has demonstrated its potential for wideband and compact millimeter-wave frequency range applications. The developed rat-race coupler using the proposed phase inverter, features a 40% size reduction and over 60% bandwidth improvement compared to conventional structures. In the complete D-band range, measured amplitude and phase imbalances for the coupler are within 0.5 dB and 15°, respectively. The port-to-port isolation is better than 25 dB in the D-band range with the highest value of 41 dB at 118 GHz. The insertion loss achieves 1.2 ± 0.3 dB and the coral size of the coupler is only 290 × 162 µm2. The proposed coupler has a huge potential for integration in single-chip systems over 100 GHz.

This paper presents an automatic gain control (AGC) amplifier with temperature compensation for high-speed applications. The proposed AGC consists of a folded Gilbert variable gain amplifier (VGA), a dc offset canceller, inductorless post amplifiers, a linear open-loop peak detector (PD), an integrator, a symmetrical exponential voltage generator, and a compensation block for temperature stability. The novel temperature compensation scheme ensures the AGC stability and accuracy over -20°C-200°C by predicting the integrator biasing voltage based on the crucial blocks duplication technique. The proposed linear open loop PD combined with the linear-in-dB VGA manages the dB-linear error of less than 0.3 dB for the received signal strength indication (RSSI). The AGC chip is fabricated using a 0.13-μm SiGe BiCMOS technology. Consuming a power of 72 mW from a 1.2-V supply voltage, the fabricated circuit exhibits a voltage gain of 40 dB and a 3-dB bandwidth of 7.5 GHz. With a 215 - 1 pseudo-random bit sequence at 5-Gb/s, the measured peak-to-peak jitter is less than 40pspp across the -20°C-200°C temperature range. The low linear-in-dB error and the wide operating temperature range achieving the high-speed data input signal indicate the suitability of the proposed techniques for high-speed AGC amplifiers.

In this chapter, we consider a cellular downlink packet data system employing the space-time block coded (STBC) multiple- input-multiple-output (MIMO) scheme. Taking the CDMA high data rate (HDR) system for example, we evaluate the cross-layer performance of typical scheduling algorithms and a point-to-point power control scheme over a time division multiplexing (TDM)-based shared MIMO channel. Our evaluation focuses on the role of those schemes in multi-user diversity gain, and their impacts on medium access control (MAC) and physical layer performance metrics for delay-tolerant data services, such as throughput, fairness, and bit or frame error rate. The cross-layer evaluation shows that the multi-user diversity gain, which comes from opportunistic scheduling schemes exploiting independent channel oscillations among multiple users, can increase the aggregate throughput and reduce the transmission error rate. It also shows that STBC/MIMO and one-bit and multi-bit power control can indeed help the physical and MAC layer performance but only at a risk of limiting the multiuser diversity gain or the potential throughput of schedulers for delay-tolerant bursty data services.

We treat the problem of sum-rate maximization via scheduling and linear precoding in multi-user (MU-) MIMO systems with quantized feedback. We formulate the optimal quantized linear precoder design problem and provide the numerical procedure for finding the solution. We also provide a simple scheduling scheme that exploits the multi-user diversity gain. It is demonstrated that, with or without scheduling, the proposed optimal linear precoding scheme achieves a significant gain over the conventional linear precoder designs with similar feedback overhead such as the zero-forcing precoder. Moreover, although the proposed quantization codebook design improves the performance of other existing MU-MIMO precoding schemes, the performance gain offered by it is typically much higher when it is coupled with the proposed linear precoding design.

We consider the sum-rate maximization via linear precoding in downlink MIMO systems with quantized feedback. We address the precoding codebook design based on the capacity measure by introducing a new distance metric. We propose a codebook structure and its associated design algorithm that allows for significant reduction in the memory requirement and computational complexity. We then provide a system design approach comprising of a multi-rank beamforming (MRBF) scheme, an efficient CQI-based precoder selection algorithm, reduced feedback strategies and novel channel quality indicator (CQI) combining. Our simulation results show that the proposed MRBF scheme can approach the precoding upper bounds with relatively small feedback bits. Moreover, with the same number of bits, the proposed scheme simultaneously achieves higher throughput and lower computational complexity in comparison to the other existing precoding schemes.

We consider the use of linear constellation preceding and linear equalization in a multicarrier system to obtain improved performance over multipath fading channels at a low complexity. We split the full set of subcarriers into smaller groups and spread the data symbols assigned to each group via precoding matrices. To obtain diversity order gains at a given data rate, we derive the optimal split of the subcarriers (optimal grouping) and the optimal number of symbols assigned to each group (optimal loading) using a diversity-multiplexing tradeoff analysis. We also derive the necessary and sufficient optimality conditions for the precoder design and provide examples of such optimal precoders.

We treat the problem of quantization codebook design for MIMO precoding schemes. We propose a design criterion based on the capacity measure which is different from the maximum mutual-minimum-distance conventionally used to design the codebook. The latter criterion is derived from SNR maximization which is not necessarily the capacity- optimal quantization strategy. While the capacity expression does not directly define a valid distance metric for the design, a bound on the capacity expression can be used to formulate the quantization codebook design. We introduce a new distance metric on the Grassmanian manifold which is used to design the optimal precoder codebook. While the original formulation can be used for the (space) correlated channel model, we propose a differential codebook design in order to track changes in the channel statistics when the channel is correlated in time (or in frequency, e.g., across different tones in OFDM systems). Simulation results has shown considerable improvement through the proposed codebook design both for single user (SU-) and multiple user (MU-) MIMO systems.