A Low-Power Baseband ASIC for an Energy-Collection IR-UWB Receiver

This paper reports on the realization and the characterization of an application-specific integrated circuit (ASIC) intended for the processing of impulse radio ultra-wideband (IR-UWB) baseband signals. The incoming baseband signals result from the direct down-conversion of IR-UWB radio-frequency pulses, which are modulated by a binary frequency-shift keying (BFSK) scheme. The realized mixed-signal integrated circuit features an analog demodulation based on the quadricorrelation method, a non-coherent pulse detector using an integrate-and-dump operation and a bit-level synchronization digital circuit. An novel acquisition algorithm intended for low duty-cycled IR-UWB signals enabling a signal-to-noise ratio (SNR) estimate is proposed. The baseband ASIC is able to demodulate, acquire and decode BFSK IR-UWB signals. It requires 13 mW of supply power during the initial acquisition and 6.5 mW during the signal tracking phase at a pulse repetition rate (PRR) of 5 MHz. The circuit is fabricated in a 0.18-$mu{hbox {m}}$ CMOS technology.      

A Low-Cost and Low-Power CMOS Receiver Front-End for MB-OFDM Ultra-Wideband Systems

This paper presents an RF receiver front-end for MB-OFDM-based ultra-wideband (UWB) systems. The receiver occupies only 0.35 mm² in a 0.18 mum CMOS process and consists of a low-noise amplifier, downconverter and a bandpass filter. There are no on-chip inductors and the receiver requires no off-chip matching components. The measured receiver gain is 21 dB, noise figure is less than 6.6 dB, input IIP₃ is -5.6 dBm, and the receiver consumes 19.5 mA from a 2.3 V supply. The receiver covers all the MB-OFDM bands from 3.1 to 8 GHz     

时空编码WCDMA下行链路MMSE接收机

ＷＣＤＭＡ下行链路的性能受到信道衰落和多址干扰的影响。本文提出一种带时空编码的ＷＣＤＭＡ下行链路ＭＭＳＥ接收机,可以在减小信道衰落的同时达到抑制多址干扰的目的。应用高斯近似法对接收机性能进行了分析。仿真结果表明,该接收机能使系统性能得以较大提高。     

Low-Power VLSI Implementation of the Inner Receiver for OFDM-Based WLAN Systems

In this paper, we propose low-power designs for the synchronizer and channel estimator units of the Inner Receiver in wireless local area network systems. The objective of the work is the optimization, with respect to power, area, and latency, of both the signal processing algorithms themselves and their implementation. Novel circuit design strategies have been employed to realize optimal hardware and power efficient architectures for the fast Fourier transform, arc tangent computation unit, numerically controlled oscillator, and the decimation filters. The use of multiple clock domains and clock gating reduces the power consumption further. These blocks have been integrated into an experimental digital baseband processor for the IEEE 802.11a standard implemented in the 0.25mum- 5-metal layer BiCMOS technology from Institute for High Performance Microelectronics.     

Downlink Specific Linear Equalization for Frequency Selective CDMA Cellular Systems

We derive and compare several linear equalizers for the CDMA downlink under frequency selective multipath conditions: minimum mean-square error (MMSE), zero-forcing (ZF), and RAKE. MMSE and ZF equalizers are designed based on perfect knowledge of the channel. The downlink specific structure involves first inverting the multipath channel to restore the synchronous multi-user signal transmitted from the base-station at the chip-rate, and then correlating with the product of the desired user's channel code times the base-station specific scrambling code once per symbol to decode the symbols. ZF equalization restores orthogonality of the Walsh-Hadamard channel codes on the downlink but often suffers from noise gain because certain channel conditions (no common zeros) are not met; MMSE restores orthogonality only approximately but avoids excessive noise gain. We compare MMSE and ZF to the traditional matched filter (also known as the RAKE receiver). Our formulation generalizes for the multi-channel case as might be derived from multiple antennas and/or over-sampling with respect to the chip-rate. The optimal symbol-level MMSE equalizer is derived and slightly out-performs the chip-level but at greater computational cost. An MMSE soft hand-off receiver is derived and simulated. Average BER for a class of multi-path channels is presented under varying operating conditions of single-cell and edge-of-cell, coded and un-coded BPSK data symbols, and uncoded 16-QAM. These simulations indicate large performance gains compared to the RAKE receiver, especially when the cell is fully loaded with users. Bit error rate (BER) performance for the chip-level equalizers is well predicted by approximate SINR expressions and a Gaussian interference assumption.     

A Neural Network-Based Blind Multiuser Receiver for DS-CDMA Communication Systems

The Universal Mobile Telecommunications System (UMTS) which is based on Wideband-Code Division Multiple Access (W-CDMA) techniques is one of the most important broadband wireless communication systems. Adaptive Blind Multiuser Detection was widely considered for mobile receivers. The main drawback of this approach is that it achieves the optimum solution after a certain number of bit times. This paper deals with a new neural network approach in order to reduce the convergence time in different application environments. In particular, a modified Kennedy-Chua neural network, based on the Hopfield model is proposed. The neural network stability was investigated by means of a suitable analytical approach, while the performance of the proposed receiver scheme was derived by means of computer simulations. The numerical results shown in this paper highlight a fast convergence behavior of the proposed scheme, in particular under multipath-fading conditions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Bit Error Probability for Baseband and Subcarrier Optical Communication Systems

Digital baseband and digital subcarrier noncoherent optical communication systems are considered in this paper. Expressions are developed for the bit error probability of optical subcarrier systems which use a nonliner polarization modulator and either a one-detector or a two-detector receiver, The expressions are evaluated numerically, and the results are used to compare the one- and two-detector subcarrier systems with the corresponding one- and two-detector baseband systems for a fLxed bit error probability.     

CSI-Based Resource Allocation for OFDM Downlink Broadband Multimedia Services in Cellular Systems

Using channel state information (CSI) in resource allocation in Orthogonal Frequency Division Multiplexing (OFDM) wireless cellular systems has been recently considered to improve the overall throughput. This paper presents an analytical framework to compare the performance of two resource allocation schemes, using CSI-based and random sub-carrier selection, in terms of their user outage probability and throughput in relation to the system load in frequency-selective fading and interference-limited environments. Analytical and simulation results are in good agreement and indicate that a proper use of CSI can achieve substantially better performance in interference limited cellular systems as compared to the blind approach and thus show the benefits of multi-user diversity.     

Differentiated TCP User Perception over Downlink Packet Data Cellular Systems

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     

未来移动通信系统中的小区间干扰协调技术

在未来移动通信系统中,小区间干扰成了主要干扰源,因此小区间干扰减少技术已成为人们的研究重点.本文结合3GPP相关提案,从静态和半静态两方面,对小区间干扰减少技术中的主流技术--小区间干扰协调技术进行了综述,并对该技术的未来研究方向进行了一些探讨.     

无源UHF RFID芯片中低功耗基带处理器的设计

对UHF RFID标签芯片的数字基带处理器结构及工作原理进行了分析。该基带处理器兼容ISO18000-6C协议。采用一系列先进的低功耗技术,如门控时钟技术、减小工作电压、降低时钟频率等,以降低无源射频识别标签的功耗。整个标签芯片采用TSMC 0.18μm 1P5M嵌入式EEPROM混合CMOS工艺实现。测试结果表明,该芯片正常工作的最低电压仅为1 V,平均电流为6.8μA,功耗为6.8μW,面积仅为150μm×690μm。     

小功率无线远程控制发射机和接收机

本文简述260～470MHz频段OOK(开关键控)发射机和接收机低成本方案。所设计的接收机用于跟踪和锁定SAW(表面声波)谐振器的载波或晶控PLL发射机。ASK(幅移键控)最简单形式是OOK，在OOK中由PCM(脉冲码调制)波形简单地开关载波。通常，低成本OOK发射机由SAW谐振器和用做Colpitts振荡器的晶体管组成。频率稳定性是令人满意的，可与晶控源相比。时间和温度会影响频率稳定性，300MHz SAW谐振器振荡器一般漂移为±150KHz。所设计的标准OOK接收机具有宽带响应，以便锁定位偏移的发射机，这是以灵敏度和选择性为代价的。本文所给出的…     

DS-CDMA系统下行盲多用户接收机

本文研究多径频率选择性衰落信道下，DS－CDMA系统下行盲多用户检测技术，提出了一种新的基于恒模算法的检测方法。利用下行信号的特征构造约束条件并采用投影梯度法求解优化问题，本文方法克服了常规恒模算法无法保证收敛到期望用户的缺点。仿真结果验证了本文方法具有良好的检测性能，可以在克服信道衰落的同时抑制多址干扰。     

Radio Resource Allocation Algorithms for the Downlink of Multiuser OFDM Communication Systems

This article surveys different resource allocation algorithms developed for the downlink of multiuser OFDM wireless communication systems. Dynamic resource allocation algorithms are categorized into two major classes: margin adaptive (MA) and rate adaptive (RA). The objective of the first class is to minimize the total transmit power with the constraint on users? data rates whereas in the second class, the objective is to maximize the total throughput with the constraints on the total transmit power as well as users? data rates. The overall performance of the algorithms are evaluated in terms of spectral efficiency and fairness. Considering the trade-off between these two features of the system, some algorithms attempt to reach the highest possible spectral efficiency while maintaining acceptable fairness in the system. Furthermore, a large number of RA algorithms considers rate proportionality among the users and hence, are categorized as RA with constrained-fairness. Following the problem formulation in each category, the discussed algorithms are described along with their simplifying assumptions that attempt to keep the performance close to optimum but significantly reduce the complexity of the problem. It is noted that no matter which optimization method is used, in both classes, the overall performance is improved with the increase in the number of users, due to multiuser diversity. Some on-going research areas are briefly discussed throughout the article.     

2.4GHz频段GFSK应用低功耗数字接收器

蓝牙、IEEE 802.11x和Zigbee等低功耗、近距离无线系统标准正在兴起.除低成本外,低功耗对于采用这些标准的便携式设备而言也是至关重要的.低成本是通过将收发器IC的外部元器件数量降至最少并采用标准基线IC工艺技术实现的.因此,CMOS的完全集成意义重大.此外,高度数字化的架构能低功耗地实现灵活性.     

Soft Linear Precoding for the Downlink of DS/CDMA Communication Systems

In this paper, we propose a transmitter-based linear-precoding scheme that outperforms conventional precoding by making use of a portion of the interference between the users in a code-division multiple-access (CDMA) system downlink. The utilization of part of the interference is achieved by selectively orthogonalizing the desired symbols to destructive interference by means of precoding while allowing interference that constructively contributes to the useful signal's energy. The existence and exploitation of constructive interference effectively spreads the signal constellation and enhances the signal-to-interference-plus-noise ratio (SINR) at the receiver. SINR improvement is attained with no need for additional power-per-user investment at the transmitter since energy that is inherent in the CDMA system is utilized. The scheme introduced in this paper applies to the downlink of cellular phase-shift keying (PSK)-based CDMA systems. Theoretical analysis and comparative simulations show that significant performance improvement can be attained with the proposed technique.      

Adaptive Receiver Structures for Fiber Communication Systems Employing Polarization-Division Multiplexing

Polarization-division multiplexing (PDM) is emerging as a promising technique for increasing data rates without increasing symbol rates. However, the distortion effects of the fiber transmission medium poses severe barriers for the implementation of this technological alternative. Especially, due to the fiber-induced polarization fluctuation orthogonally transmitted PDM signals are mixed at the receiver input. Therefore, a receiver compensation structure needs to be implemented to recover the original orthogonal transmitted components from their mixtures at the end of the fiber channel. This is in fact the focus of this article where a receiver algorithm is based on a recently proposed blind source separation scheme exploiting magnitude boundedness of digital communication signals. Through the use of this scheme, new receiver algorithms for recovering the original polarization signals in an adaptive manner are proposed. The key feature of these algorithms is that they can achieve high separation performance while maintaining the algorithmic complexity in a fairly low level that is suitable for implementation in optical fiber communication receivers. The performance of these algorithms are illustrated through some simulation examples.     

一种下行OFDM-SDMA系统资源分配算法

研究了OFDM-SDMA系统中的资源分配算法问题,针对已有算法的不足,提出了一种新的多用户调度指标,并在此基础上提出了次优多用户调度算法。针对整数比特约束,采用了两种合适的资源分配方案。由于新指标充分考虑了被调度用户之间的空间兼容性和信道质量,仿真结果证明所提算法可以获得较好的性能增益,且资源分配算法的收敛速度较快。     

用于低中频GPS接收机的CMOS闪烁型模数转换器

模数转换器引入的信噪比的降低会直接影响GPS接收机的灵敏度,需仔细设计以减小信噪比的降低。采用TSMC0.25μm CMOS单层多晶硅五层金属工艺设计了一个用于低中频GPS接收机的CMOS4bit16.368MHz闪烁型模数转换器。实现一个高性能闪烁型模数转换器的关键是得到一个低功耗、低回程噪声、低失调电压的前置放大器和比较器电路,因此重点放在了提出的新的前置放大器和比较器的设计和优化上。在时钟采样率16.368MHz和输入信号频率4.092MHz的条件下,转换器测试得到的信噪失真比为24.7dB,无杂散动态范围为32.1dB,积分非线性为 0.31/-0.46LSB,,差分非线性为 0.66/-0.46LSB,功耗为3.5mW。转换器占用芯片面积0.07mm2。测试结果表明了该模数转换器的有效性,并已成功应用于GPS接收机芯片中。