OFDM发射机设计与FPGA实现

为使OFDM(正交频分复用)技术在宽带无线通信中得到实际运用,提出了基于IEEE 802.11a协议的OFDM发射机的设计方案及关键技术的实现方法。在设计中采用自顶向下的设计思想,通过数字锁相环、乒乓RAM(随机存储器)等方式提高系统运行的可靠性。并利用Altera公司的Cyclone IV E系列FPGA(现场可编程门阵列)器件的特点和灵活的IP Core(知识产权核)功能,实现了OFDM发射机的设计。在Modelsim环境下的仿真结果证明了该设计的有效性,且占用的资源少。     

基于IEEE 802．16d OFDM系统的FPGA设计

研究基于IEEE 802．16d OFDM系统的FPGA实现。首先探讨了基于802．16d的OFDM系统FPGA设计的构架。然后采用VHDL硬件描述语言实现了发送端和接收端各个模块。最后选用了Altera公司CycloneⅡ系列的EP2C35F484C6芯片,在QuartusⅡ软件环境下对VHDL代码进行了综合。     

基于IEEE 802.16a的OFDM基带调制系统的FPGA设计

本文研究了基于IEEE802.16a的OFDM基带调制系统的实时实现,提出了一种切实可行的IEEE802.16a的OFDM调制方式的FPGA实现方法与结构,并介绍了IFFT运算、QPSK映射和插入循环前缀的具体电路。最后给出了硬件性能分析。     

FPGA Implementation of FFT Algorithm for OFDM Based IEEE 802.16d （Fixed WiMAX） Communications

The IEEE 802.16d communication standard uses orthogonal frequency division multiplexing （OFDM）. In the widely used OFDM systems, the fast Fourier transform （FFT） and inverse fast Fourier transform pairs are used to modulate and demodulate the data constellation on the sub-carriers. In this paper, a high level implementation of a high performance FFT for OFDM modulator and demodulator is presented. The design has been coded in Verilog and targeted into Xilinx Spartan3 field programmable gate arrays. Radix-22 algorithm is proposed and used for the OFDM communication system. The design of the FFT is implemented and applied to fixed WiMAX--IEEE 802.16d communi- cation standard. The results are tabulated and the hardware parameters are compared. The proposed architecture is least in number of multipliers used and the memory size, and second to the least in number of adders used.     

Bandwidth-efficient wireless OFDM

Due to ever-increasing bandwidth demands in future wireless service, the radio frequency band becomes more and more invaluable. In this paper, we address channel equalization for bandwidth-efficient wireless orthogonal frequency-division multiplexing (OFDM). First, we show that in order to be free of both interchannel interference and interblock interference, wireless OFDM has to occupy a bandwidth wider than the Nyquist rate and use insufficient statistics in symbol demodulation. Thus, the conventional OFDM gains computational efficiency using the discrete Fourier transform (DFT) in demodulation at the cost of low efficiency of bandwidth usage and degradation in symbol error performance. Then we consider the OFDM that achieves high efficiency of bandwidth usage, allows interchannel interference and interblock interference to exist, and uses sufficient statistics in symbol demodulation. A one-tap decision feedback equalizer (DFE) is proposed for equalization of the bandwidth efficient OFDM system. Simulation and numerical evaluation for an indoor wireless asynchronous transfer mode network are carried out. It is demonstrated that though occupying a narrower bandwidth, the one-tap DFE-based bandwidth-efficient OFDM system achieves lower symbol error rate and higher mutual information than the conventional DFT-based OFDM system. The proposed OFDM system presents a monotonically increasing symbol error rate, and convex-down achieved mutual information with respect to increasing efficiency of bandwidth usage     

一种应用于OFDM系统中的符号精确定时算法的FPGA实现

OFDM技术是下一代移动通信的主流技术,在信息量大,功率受限的多媒体传感网的OFDM系统中,以突发模式传输数据,要求快速精确地完成定时同步。这里分析了一种应用于OFDM系统中基于长训练序列与本地序列互相关的精同步算法原理,同时给出了算法的FPGA设计方案,并在ISE中和FPGA测试板上进行验证。在实现的过程中,对传统实现方法进行了改进,对本地序列的位数进行截取符号位处理,并且对判决函数进行了近似处理。实现结果表明,该方法在不降低性能的前提下优化了系统资源损耗和运算速度,具有较好的工程实践价值。     

OFDM同步算法研究及实现

正交频分复用（Orthogonal Frequency Division Multiplexing,OFDM）技术具有很强的抗多径能力及较高的频谱利用率,能在无线信道中提供可靠的高速数据传输,是未来通信系统的主流技术之一,例如LTE、WiMax等新兴标准都利用OFDM调制技术进行下行数据传输.同时,OFDM技术对接收系统的同步精度要求严格,因此同步技术是实现OFDM通信系统的关键技术之一.文中对OFDM同步技术进行了深入研究,利用FPGA平台设计完成了基于Schmidl同步算法的OFDM通信接收系统,并利用真实仿真平台进行了仿真验证.     

一种OFDM调制解调器的FPGA实现

OFDM技术在高速数据传输中得到了广泛的应用，根据OFDM的特点，提出了一种基于IFFT/FFT的OFDM调制解调器的低成本FPGA实现方法，最后给出了FPGA上的15点FFT运算单元的计算结果。实践证明，该方法具有设计简单、快速、高效和实时性好等特点。     

802．16e系统变长可配置FFT的设计与实现

针对IEEE 802.16e OFDMA系统中变长子载波数目的特点,提出了一种高速变长可配置FFT/IFFT的整体结构,并创新性的提出了一种基于流水线的蝶型单元分支结构.该设计可以满足IEEE 802.16e OFDMA系统中所有FFT/IFFT变长点数的系统要求,并可方便的将其拓展到多种变长FFT/IFFT的具体应用场合.通过该结构设计出的FFT/IFFT模块已成功通过了Stratix II EP2S180 FPGA的实际验证并顺利应用于IEEE 802.16d OFDM系统的接收机原型中.     

Performance of BICM-OFDM systems in UWB interference

In this paper, we develop an analytical framework for performance analysis of generic bit-interleaved coded modulation orthogonal frequency-division multiplexing (BICMOFDM) systems impaired by ultra-wideband (UWB) interference. For practical relevance we consider multi-band OFDM (MB-OFDM), direct-sequence UWB (DS-UWB), and impulseradio UWB (IR-UWB) interference formats following recent IEEE/ECMA standards or standard proposals. Besides the exact analysis we calculate the bit error rate (BER) for the case when the UWB interference is modeled as additional Gaussian noise. Our results show that in general the BER of the BICM-OFDM system strongly depends on the UWB format and the OFDM sub-carrier spacing. While the Gaussian approximation is very accurate for DS-UWB, it may severely overor underestimate the true BER for MB-OFDM and IR-UWB interference. Our analysis is applicable to e.g. IEEE 802.11 wireless local area networks (WLANs), IEEE 802.16 wireless access systems (WiMAX), and 4th generation mobile communication systems. Furthermore, since the ECMA MB-OFDM standard is also based on the BICM-OFDM concept, our analysis can also be used to evaluate the impact of other UWB signals on ECMA MB-OFDM UWB systems.     

基于FPGA的OFDM调制解调系统设计与实现

正交频分复用(OFDM)是第四代移动通信的核心技术,该技术在高速数据传输中得到了广泛的应用。文章给出了正交频分复用系统的基本模型和该系统所采用的调制与解调方法;根据OFMD的特点,本设计提出了一种基于IFFT/FFT的OFDM调制解调器的低成本FPGA的实现方法。在ISE环境下完成对OFDM无线通信系统中快速傅里叶变换算法的仿真,仿真结果表明快速傅里叶变换在OFDM技术中具有一定的使用价值。实践证明,该方法具有设计简单、快速、高效和实时性等特点。     

FPGA Implementation of Carrier Synchronization for QAM Receivers

Software defined radios (SDR) are highly configurable hardware platforms that provide the technology for realizing the rapidly expanding third (and future) generation digital wireless communication infrastructure. While there are a number of silicon alternatives available for implementing the various functions in a SDR, field programmable gate arrays (FPGAs) are an attractive option for many of these tasks for reasons of performance, power consumption and flexibility. Amongst the more complex tasks performed in a high data rate wireless system is synchronization. This paper examines carrier synchronization in SDRs using FPGA based signal processors. We provide a tutorial style overview of carrier recovery techniques for QPSK and QAM modulation schemes and report on the design and FPGA implementation of a carrier recovery loop for a 16-QAM modern. Two design alternatives are presented to highlight the rich design space accessible using configurable logic. The FPGA device utilization and performance for a carrier recovery circuit using a look-up table approach and CORDIC arithmetic are presented. The simulation and FPGA implementation process using a recent system level design tool called System Generator for DSP described.     

用DSP实现基于802.16a的OFDM调制解调

正交频分复用(OFDM)技术是当今高速无线通信领域中的研究与应用热点,它具有抗多径衰落、频谱利用率高、采用自适应调制等优点,被普遍认为是宽带无线接入和第四代移动通信系统中的关键技术之一。研究了基于802.16a的OFDM技术,利用TMS320C6201实现了其基带调制解调,并对软件模块进行了优化,最高数据传输速率可达1.32Mbit/s。     

An elastic resource allocation algorithm enabling wireless network virtualization

Following the wired network virtualization, virtualization of wireless networks becomes the next step aiming to provide network or infrastructure providers with the ability to manage and control their networks in a more dynamic fashion. The benefit of the wireless mobile network virtualization is a more agile business model where virtual mobile network operators (MNOs) can request and thus pay physical MNOs in a more pay‐as‐you‐use manner. This paper presents some resource allocation algorithms for joint network virtualization and resource allocation of wireless networks. The overall algorithm involves the following two major processes: firstly, to virtualize a physical wireless network into multiple slices, each representing a virtual network, and secondly, to carry out physical resource allocation within each virtual network (or slice). In particular, the paper adopts orthogonal frequency division multiplexing (OFDM) as its physical layer to achieve more efficient resource utilization. Therefore, the resource allocation is conducted in terms of sub‐carriers. Although the motivation and algorithm design are based on IEEE 802.16 or WiMAX networks, the principle and algorithmic essence are also applicable to other OFDM access‐based wireless networks. The aim was to achieve the following design goals: virtual network isolation and resource efficiency. The latter is measured in terms of network throughput and packet delivery ratio. The simulation results show that the aforementioned goals have been achieved. Copyright © 2012 John Wiley & Sons, Ltd.     

Pilot Based Channel Estimation in IEEE 802 16a OFDM System

1　Introdution　IEEE 802 16[1] is a specification for fixed broadbandwireless Metropolitan Access Networks (MAN). The stan dard is expected to bring low cost and more bandwidth prod ucts for broadband wireless access in the next years. Thisstandard specifies the physical (PHY) and Medium AccessControl layer (MAC) of the air interface of interoperablepoint to multipoint and optional Mesh topology broadbandwireless access system. The specification enables access todata, …     

60 GHz broadband MAC system design for cable replacement in machine vision applications

In this paper, we present a wireless 60 GHz OFDM transceiver for a high-throughput GigE Vision standard compliant color CCD camera system used in machine vision applications. The OFDM transceiver provides net data rates up to 3.9 Gb/s. The medium access controller (MAC) offers the reliable GigE point-to-point cable replacement functionality with special support of an asymmetrical downlink scenario. The main focus is on the high throughput MAC design for frame based wireless transmissions and the integration onto a hardware platform. The OFDM baseband processor and the MAC were fully implemented in FPGA technology. The performance of the system was theoretically analyzed and measured in an indoor environment. The developed system fulfills the high throughput requirement as well as the low latency requirement of the used industrial HD video camera system.     

A Cross-Layering Design for IPv6 Fast Handover Support in an IEEE 802.16e Wireless MAN

Broadband wireless access networks, such as the IEEE 802.16 standard for wireless metropolitan area networks (WMANs), aim to provide high bandwidth, low-cost, scalable solutions that extend multimedia services from backbone networks to wireless users. Because of a larger coverage area, portability and mobility have become significant issues for providing high quality mobile services, as it is crucial to minimize handover latency and maintain IP session continuity. As a result, such issues were addressed by the IEEE 802.16e task group on the mobile WMAN. However, the scope of the IEEE 802.16e standard did not include cross-layering approaches for the enhancement of upper layer handover performance. This article proposes a new cross-layering design for fast IPv6 handover support over IEEE 802.16e. First, we describe the IEEE 802.16 deployment architectures, as well as the link layer, handover procedures in IEEE 802.16e. Next, we describe the operation of fast IPv6 handover and point out the need for interaction between the network layer and the link layer for proper performance. Then, we propose a new cross-layering design to achieve a proper behavior of the fast IPv6 handover over IEEE 802.16e. Finally, we present handover scenarios for the proposed techniques and discuss the major factors that contribute to the handover latency.     

Experiments on MIMO-OFDM system combined with adaptive beamforming based on IEEE 802.16e WMAN standard

This paper presents field experiments on a Multi-Input Multi-Output (MIMO) system that combines Adaptive Beamforming (ABF) and Spatial Multiplexing (SM) procedures. The combination of SM signal processing with ABF is applied to WiBro, the South Korean Orthogonal Frequency Division Multiplexing (OFDM) system that follows the IEEE 802.16e standard. The field experimental results show that ABF-MIMO OFDM system outperforms a simple MIMO OFDM system by 2 dB (1.5 dB) in the signal to noise ratio (SNR) for 16-QAM (64-QAM) under low correlated fading channel and 4 dB (2.5 dB) in the SNR for 16-QAM (64-QAM) under highly correlated fading channel, respectively, at the frame error rate (FER) of 1%. Details on the implementation of ABF-MIMO OFDM system is also presented in this paper. Through the system implementation and its field experimental results, we verify that the combination of MIMO OFDM system with ABF provides improved performance over a simple MIMO OFDM system in real propagation channel environment and, in particular, it is more effective in highly correlated fading channel.     

基于IEEE802.16e移动宽带无线接入网的切换过程分析与实现

随着WiMAX组织的发展壮大加快了IEEE802.16标准的发展,移动WiMAX ——IEEE802.16e标准的提出更加引人注目.该标准对IEEE802.16标准进行了补充和拓展,定义了一个结合固定和移动宽带无线接入的系统,填补了高速无线局域网和高移动性蜂窝系统之间的空白.对IEEE802.16e标准中规定的移动宽带无线接入系统的切换过程进行了分析,并提出了该过程的软件实现方案.     

Implementation of a Flexible LDPC Decoder

Low-density parity-check codes (LDPC) are among the most powerful error correcting tools today available. For this reason they became very popular in several applications such as the digital satellite broadcasting system (DVB-S2), wireless local area network (IEEE 802.11n) and metropolitan area network (802.16e). Whereas several code-specific decoders have been proposed in the literature, the implementation of a high performance yet flexible LDPC decoder still is a challenging topic. This work presents a novel formulation of the decoding algorithm that strongly simplifies internal communication requirements and enables the development of decoders supporting generally defined LDPC codes. The resulting architecture is tailored to decode both IEEE 802.11n and IEEE 802.16e LDPC codes, as well as any other code of comparable complexity. The implementation cost deriving from the full flexibility offered by the proposed approach is also evaluated.