SEMICON CHINA 2009部分参展产品展示

UltraFLEXTM测试系统提供了业界最领先的性能和精度,能够满足各种芯片的测试要求,包括微处理器、PC芯片组和视频处理器、硬盘驱动器、游戏机芯片、SOC和SIP、存储器、基带处理器和网络芯片。在提供广泛的测试覆盖率的同时,UltraFLEX也能通过无与伦比的高并行测试效率把芯片测试的吞吐率提到最高。     

基于PCAP的TD-LTE基站业务数据吞吐率测试技术

首先讲述了TD-LTE MIT环境及基站业务数据吞吐率测试需求,其次分析比较了几种常规数据吞吐率测试方法,最后分析了利用PCAP进行MIT环境下,基站在承载多小区、多用户时的最高业务数据吞吐率测试技术。     

变频芯片的吞吐率测试方法

吞吐率作为衡量网络系统性能的重要指标,其重要意义毋庸置疑,掌握其正确的测试方法及分析手段尤为重要。对于XN277(三网融合变频芯片)而言,其射频指标诸如通道增益、噪声系数、本振相位噪声等对吞吐率均有不同程度的影响。文章通过实际的测试工作,重点阐述了不同的通道增益对吞吐率的影响,同时结合IxChariot的应用,对吞吐率的测试方法进行了详细的验证与分析。     

近阈值低功耗8位微处理器的设计与实现

随着RFID、可穿戴设备和物联网等应用的兴起,低吞吐率、功耗和能耗敏感的芯片设计开始受到广泛的关注,基于阈值电压的低功耗电路设计成为新的发展方向。文中基于SMIC0.13μm1P6M混合信号工艺,通过设计面向近阈值电压的标准逻辑库,在采用标准Top-Down设计流程的基础上,完成了一款近阈值低功耗8位微处理器的设计。封装后芯片的测试结果表明,该微处理器的最低工作电压可达0.2V,工作频率1k Hz~25MHz。与基于传统逻辑库的微处理器比,在20MHz的工作频率下,功耗降低了36%。     

Design and implementation of an IEEE 802.11 baseband OFDM transceiver in 0.18 μm CMOS

An SISO IEEE 802.11 baseband OFDM transceiver ASIC is implemented.The chip can support all of the SISO IEEE 802.11 work modes by optimizing the key module and sharing the module between the transmitter and receiver.The area and power are decreased greatly compared with other designs.The baseband prototype has been verified under the WLAN baseband test equipment and through transferring the video.The 0.18μm 1P/6M CMOS technology layout is finished and the chip is fabricated in SMIC,which occupies a 2.6×2.6 mm~2 area and consumes 83 mW under typical work modes.     

瑞利信道下802．11DCF性能分析及仿真

文章对于Peter P.Pham提出的有限负载备件下二维马尔可夫链的分析模型进行了改进,推导出了IEEE802.11 DCF的吞吐率与饱和程度的关系。仿真了不同因素：节点数,传输速率、数据包长度对于IEEE802．11DCF性能的影响。仿真结果表明：在瑞利信道下,网络处于非饱和状态时,吞吐性能受到几种因素的综合作用。在大多数情况下,RTS／CTS接入方式的性能都优于基冬接入方式。     

适用于IEEE 802.11n的高速低功耗Viterbi译码器的设计

针对IEEE 802.11n SOC对信道编码的多码率、高吞吐率的要求,设计了适用于IEEE 802.11n卷积码的Viterbi译码器,具有高吞吐率,低功耗特点,可支持1/2,2/3,3/4,5/6码率.译码器采用全并行的加比选(ACS)单元,最高位清零防溢出处理,采用了一种可降低功耗的寄存器交换法,可有效减少寄存器翻转动态功耗.采用SMIC0.13tan CMOS工艺设计并实现了该译码器,时钟频率为240MHz时,最大数据吞吐率为480Mb/s,功耗为25mW.     

应用于超宽带系统中的低功耗、高速FFT/IFFT处理器设计

设计了一种应用于超宽带(UWB)无线通信系统中的FFT/IFFT处理器.采用8×8×2混合基算法进行FFT运算,实现了2路64点或者1路128点FFT功能,并为该算法提出了一种新型的8路并行反馈结构.该结构提高了处理器的数据吞吐率,降低了芯片功耗.为了减少处理器中的乘法数目,提高时序性能,提出了改进型移位加算法.设计的FFT/IFFT处理器采用SMIC 0.13μm CMOS工艺制造,芯片的核心面积为1.44mm2.测试结果表明,该芯片最高数据吞吐率到达1Gsample/s,在典型的工作频率500Msample/s下,芯片功耗为39.6mW.与现有同类型FFT芯片相比,该芯片面积缩小了40%,功耗减少了45%.     

基于新一代Wi-Fi的MAC层关键技术的仿真与分析

分析了新一代Wi-Fi(即IEEE 802.11ac)的MAC层技术,重点研究了IEEE 802.11ac的分布式协调功能和增强的分布式信道接入技术带来的系统增益,并对IEEE 802.11ac MAC层是否采用帧聚合和块应答机制时的数据吞吐效率、在不同信道接入技术下用户业务的公平性进行了仿真和分析。仿真和分析表明增强的分布式信道接入技术相对于传统的分布式协同功能可以显著提升系统吞吐量,并且MAC层通过采用帧聚合和块应答机制,提升了MAC层相对物理层的吞吐率,降低了MAC层协议固有的系统开销所带来的“短板效应”。     

安捷伦与GCT合作 加快WiMAX产品量产

安捷伦科技公司和GCT半导体公司日前宣布,双方将针对GCT的WiMAX芯片组开发一套WiMAX生产测试系统,用以提高生产吞吐率并推动产品的大规模部署。     

Throughput enhancement with a modified 802.11 MAC protocol with multi-user detection support

A modification to the traditional CSMA-based media access control protocol, named 802.11-MUD, is proposed in this paper which differs from the IEEE 802.11 in its support of simultaneous transmissions/receptions with multi-user detection (MUD). A joint information and renewal theoretic analysis framework is introduced to study the performance of 802.11-MUD. While the information theoretic part is useful for modeling the increase in sum capacity attributed to MUD, the renewal theoretic part is good for modeling the impact of MUD on alleviating the collision probability and increasing the network throughput. In addition, this analytical framework helps us finetune the 802.11-MUD system (called 802.11-MUD^* after the optimal tuning) and achieve significantly enhanced network throughput especially in busy networks.     

An area efficient and high throughput multi-rate quasi-cyclic LDPC decoder for IEEE 802.11n applications

In this paper, an area efficient and high throughput multi-rate quasi-cyclic low-density parity-check (QC-LDPC) decoder for IEEE 802.11n applications is proposed. An overlapped message passing scheme and the non-uniform quantization scheme are incorporated to reduce the overall area and power of the proposed QC-LDPC decoder. In order to enhance the decoding throughput and reduce the size of memories storing soft messages, an improved early termination (ET) scheme and base matrix reordering technique is employed. These techniques significantly reduce the total number of decoding iterations and memory accessing conflicts without mitigating the decoding performance. Equipped with these techniques an area efficient and high throughput multi-rate QC-LDPC decoder is designed, simulated and implemented with Xilinx Virtex6 (XC6VLX760-2FF1760) for an irregular LDPC code of length 1944 and code rates (1/2–5/6) specified in IEEE 802.11n standard. With a maximum clock frequency of 574.136–587.458 MHz the proposed QC-LDPC decoder can achieve throughput in the range of 1.27–2.17 Gb/s for 10 decoding iterations. Furthermore, by using Cadence RTL compiler with UMC 130 nm VLSI technology, the core area of the proposed QC-LDPC decoder is found to be 1.42 mm² with a power dissipation in the range of 101.25–140.42 mW at 1.2 V supply voltage.     

Increasing fairness and efficiency using the MadMac protocol in ad hoc networks

The IEEE 802.11 MAC layer is known for its unfairness behavior in ad hoc networks. Introducing fairness in the 802.11 MAC protocol may lead to a global throughput decrease. It is still a real challenge to design a fair MAC protocol for ad hoc networks that is distributed, topology independent, that relies on no explicit information exchanges and that is efficient, i.e. that achieves a good aggregate throughput. The MadMac protocol deals with fairness and throughput by maximizing aggregate throughput when unfairness is solved. Fairness provided by MadMac is only based on information provided by the 802.11 MAC layer. MadMac has been tested in many configurations that are known to be unfair and compared with three protocols (IEEE 802.11 and two fair MAC protocols). In these configurations, MadMac provides a good aggregate throughput while solving the fairness issues.     

The Jamming problem in IEEE 802.11‐based mobile ad hoc networks with hidden terminals: Performance analysis and enhancement

The hidden‐terminal problem significantly degrades the performance of IEEE 802.11 DCF. Many previous works have investigated its influence on the throughput of CSMA‐based medium access control (MAC) protocols, especially IEEE 802.11 DCF. In this paper, we introduce a new Jamming problem for IEEE 802.11‐based mobile ad hoc networks, which is caused by hidden terminals. An analytical model is established for this problem. Based on this model, an adaptive DCF (ADCF), is designed to solve the jamming problem through adaptively adjusting the minimum contention window of hidden terminals. Simulation results effectively demonstrate that the proposed A‐DCF can avoid the jamming and in turn greatly improve channel utilization and throughput. Copyright © 2009 John Wiley & Sons, Ltd.     

Performance of IEEE 802.11 under Jamming

We study the performance of the IEEE 802.11 MAC protocol under a range of jammers that covers both channel-oblivious and channel-aware jamming. We consider two channel-oblivious jammers: a periodic jammer that jams deterministically at a specified rate, and a memoryless jammer whose interfering signals arrive according to a Poisson process. We also develop new models for channel-aware jamming, including a reactive jammer that only jams non-colliding transmissions and an omniscient jammer that optimally adjusts its strategy according to current states of the participating nodes. Our study comprises of a theoretical analysis of the saturation throughput of 802.11 under jamming, an extensive simulation study, and a testbed to conduct real world experimentation of jamming IEEE 802.11 using a software defined radio (GNU Radio combined with USRP boards). In our theoretical analysis, we use a discrete-time Markov chain analysis to derive formula for the saturation throughput of 802.11 under memoryless, reactive and omniscient jamming. One of our key results is a characterization of optimal omniscient jamming that establishes a lower bound on the saturation throughput of 802.11 under arbitrary jammer attacks. We validate the theoretical analysis by means of Qualnet simulations. Finally, we measure the real-world performance of periodic, memoryless and reactive jammers using our GNURadio/ USRP aided experimentation testbed.     

通过自适应调整最小竞争窗口最大化IEEE 802.11 DCF的饱和吞吐量

最大化802.11 DCF的饱和吞吐量对充分利用无线局域网宝贵的带宽资源具有重要意义。该文在分析802.11 DCF的饱和吞吐量与最小竞争窗口、最大回退等级、网络中竞争信道的节点数的关系的基础上,推导了根据网络中竞争信道的节点数,计算最小竞争窗口的最佳值的简单公式。给出了估计竞争信道的节点数并据此动态调整最小竞争窗口的最佳值的自适应算法。同时,该文对估计竞争节点数的算法的准确性和计算最小竞争窗口最佳值的公式的准确性进行了仿真分析,并比较了改进后的802.11 DCF的饱和吞吐量与原802.11 DCF的饱和吞吐量的大小。仿真结果证明了上述公式、算法是准确和有效的。     

Dynamic tuning of the IEEE 802.11 protocol to achieve a theoreticalthroughput limit

In wireless LANs (WLANs), the medium access control (MAC) protocol is the main element that determines the efficiency in sharing the limited communication bandwidth of the wireless channel. In this paper we focus on the efficiency of the IEEE 802.11 standard for WLANs. Specifically, we analytically derive the average size of the contention window that maximizes the throughput, hereafter theoretical throughput limit, and we show that: 1) depending on the network configuration, the standard can operate very far from the theoretical throughput limit; and 2) an appropriate tuning of the backoff algorithm can drive the IEEE 802.11 protocol close to the theoretical throughput limit. Hence we propose a distributed algorithm that enables each station to tune its backoff algorithm at run-time. The performances of the IEEE 802.11 protocol, enhanced with our algorithm, are extensively investigated by simulation. Specifically, we investigate the sensitiveness of our algorithm to some network configuration parameters (number of active stations, presence of hidden terminals). Our results indicate that the capacity of the enhanced protocol is very close to the theoretical upper bound in all the configurations analyzed     

Defining and maximizing PPT—a novel performance parameter for IEEE 802.11 DCF

Much research has been conducted on saturation throughput of IEEE802.11 DCF, and has led to some improvement. But increasing the successful transmission probability of packet is also important for saving stations' battery energy and decreasing the packet delay. In this paper, we define a new performance parameter, named Product of successful transmission Probability and saturation Throughput (PPT), for 802.11 DCF, which binds successful transmission probability and saturation throughput together. An analysis is given to maximize PPT. An expression of optimal minimum contention windows (CW_min) is obtained analytically for maximizing PPT. For simplicity, we give a name DCF‐PPT to the 802.11 DCF that sets its CW_min according to this expression. The performance of DCF‐PPT is simulated with different stations in terms of saturation throughput, successful transmission probability and PPT. The simulation results indicate that, compared to 802.11 DCF, DCF‐PPT can significantly increase the PPT and successful transmission probability (about 0.95) on condition that the saturation throughput is not decreased. Copyright © 2006 John Wiley & Sons, Ltd.     

Saturation throughput analysis of IEEE 802.11e enhanced distributed coordination function

The IEEE 802.11 Task Group E will soon approve the 802.11e standard for medium access control (MAC) layer quality-of-service (QoS) enhancements to the 802.11 protocol, and it is widely believed that these enhancements will allow 802.11 technology to form the foundation of high-bandwidth vertically integrated networks. At the heart of 802.11e is a modified contention-based access mechanism, named the enhanced distributed coordination function (EDCF). In this paper, we propose and validate an analytical model for the saturation throughput of EDCF. Key to the accuracy of our model is a treatment of the postcollision period, which has been ignored by all previous 802.11 models. With results from the ns-2 simulator, we show that our model can accurately predict throughput over a wide range of scenarios, and thereby demonstrate its usefulness as a predictive tool for use in QoS provision. With context provided by our analytical model, we discuss the primary throughput differentiation mechanisms of EDCF.     

Evaluation of IEEE 802.11 coexistence in WLAN deployments

Wi-Fi has become a successful technology since the publication of its first WLAN standard due to continuous advances and updates while remaining always backwards compatible. Backwards compatibility among subsequent standards is an important feature in order to take advantage of previous equipment when publishing a new amendment. At present, IEEE 802.11b support is still mandatory to obtain the Wi-Fi certification. However, there are several harmful effects of allowing old legacy IEEE 802.11b transmissions in modern WLAN deployments. Lower throughput per device is obtained at slow rates, but also the effect known as performance anomaly, which nearly leads to starvation of fast stations, has to be taken into account. Finally, backwards compatibility mechanisms pose an important penalty in throughput performance for newer specifications. This paper presents a thorough analysis of the current state of IEEE 802.11, comparing coverage range and throughput performance among subsequent amendments, and focusing on the drawbacks and benefits of including protection mechanisms.