Bit-error rate of TDMA links under cochannel interference inoverlaid cellular networks

This paper presents a series of numerical experiments conducted to investigate the error performance of a simulated digital time-division multiple-access (TDMA) radio link between a portable handset and the base station serving it, subject to interference coming from other portable handsets. The experiments take radio channel impairments such as fading, shadowing, and distance loss into account. Analytical expressions for the bit-error probability in uncoded digital radio transmission bursts under interference from nearby analog FM or digital minimum-shift keying (MSK) transmitters are reviewed. Numerical methods are used to extend analytical estimates of symbol error probability of a link with a single interferer, without channel impairments, to the case where the interference is due to a random distribution of transmitters whose signals are subject to fading, shadowing, and distance power loss. Specifically, three links, each based on one of three different modulation methods, MSK, quadrature phase-shift keying (QPSK) (proposed in the North American Digital Cellular Standard IS-54), and Gaussian MSK (GMSK) [used in the Global Standard for Mobile communications (GSM)] are simulated, and the bit-error rate (BER) results reported. The BER results generated thus indicate the sensitivity of the digital radio link to the user density for a given radio frequency (RF) bandwidth and, where applicable, to fading depth and postmodulation intersymbol interference (ISI) removal method. Possible extensions and applications of the simulation model to the problem of resource sharing between coexisting networks are suggested     

基于偏分复用技术的数字RoF系统研究

为有效缓解D-RoF系统高数字比特速率的不利影响,本文研究了偏振复用的D-RoF系 统,能有效 提高系统单波长的传输容量。分别在传统Stokes矢量检测和简化Stokes矢量检测下,采用一 路偏振态向量 追踪(OTV)与两路偏振态向量追踪(TTV)的DSP算法能够有效实现偏振解复用。仿真结果表明 ,两路偏振 态向量追踪方法能有效降低正交偏振复用D-RoF系统的功率预算,达到系统最终误码率时, TTV算法需要 的光功率要比OTV算法需要的光功率少2dBm。同时,可用TTV方法实现两路信号最小偏振复 用度为76° 的非正交偏振解复用,丰富了偏振复用的维度。该偏振复用D-RoF系统对其在未来5G无线传 输和有线数字电视传输具有重要意义。     

无线光DH-PIM与DPIM调制方式的性能研究

为了解决目前无线光通信采用的调制方式误包率大、传信率低等问题,研究了双头脉冲间隔调制(DH-PIM)和数字脉冲间隔调制(DPIM)的性能。分析了DPIM和DH-PIM两种调制方式的符号结构,比较了二者的传信率以及给定模型下的误包率。仿真与分析结果表明,DH-PIM的传信率较高,适合于实时性要求较高的传输系统,而DPIM的平均发射功率低,误包率较小,适合于要求低功率或高可靠性的系统。     

基于优化混频器的数字下变频系统的设计与实现

在利用频谱分析仪对信号进行实时频谱监测过程中,针对其数字下变频模块精度不高、逻辑资源耗费大、难以对数字中频信号进行实时处理的问题,本文对传统数字下变频系统的混频器模块进行优化并提出一种高效的数字下变频(DDC)系统。首先,设置模数转换器(ADC)的采样率为载波中心频率的4倍且采样率转换比率和子ADC的数量是4的正整数倍,此时混频器可以完全合并到多相CIC抽取滤波器中。接着,基于优化的混频器构建一套DDC系统,并为每个系统节点合理分配采样率转换倍数。最后,加入CIC补偿滤波器,提高数据传输过程中的精度。实验结果表明,与传统DDC相比,优化后的DDC资源消耗减少,数据精度误差从1.7%减小到0.8%。基本满足功耗低、精度高、稳定运行等要求。     

Waveform evaluations subject to hardware impairments for mm-wave mobile communications

Millimeter-wave bands are receiving great attention for mobile radio communications due to potential availability of enormous channel bandwidths. Larger channel bandwidths are very important to meet ever increasing data rate and capacity demands of future wireless networks. At high carrier frequencies, transmitted and received signals can suffer from severe hardware impairments. We evaluate the performance of several state-of-the-art waveforms, e.g., Cyclic-Prefix (CP)-OFDM, Windowed (W)-OFDM, Pulse-shaped (P)-OFDM, Universal-Filtered (UF)-OFDM, Filter-Bank Multi-Carrier with Offset Quadrature Amplitude Modulation, and DFT-spread (DFT-s)-OFDM, in the presence of hardware impairments. In particular, waveform comparisons have been evaluated in terms of bit error rate, error vector magnitude, and spectral confinement subject to oscillator phase noise and nonlinear power amplifier. It is observed that all waveforms perform similarly subject to hardware impairments—making CP-OFDM with low complexity filtering/windowing operations an attractive option to improve the spectral confinement. One major drawback of multi-carrier waveforms is the high peak-to-average power ratio (PAPR). Various low complexity PAPR reduction techniques for OFDM have been evaluated subject to hardware impairments. It is observed that in case of nonlinear PA and high power transmission, these simple PAPR reduction schemes can achieve similar performance as compared to DFT-s-OFDM, making OFDM also suitable for coverage limited scenarios where power efficiency is important.

     

Degradation in FH-MFSK mobile radio system capacity due to Rayleighfading and log-normal shadowing

A frequency-hopped multilevel frequency-shift-keying (FH-MFSK) system has been proposed for digital mobile radio communications. The performance of the system is evaluated by studying average probability of error caused by transmission impairments. The degradation in performance due to Rayleigh fading and log-normal shadowing environments is determined. With perfect transmission, where the degradation in the system performance is due to mutual interference between users only, the system can accommodate up to 209 simultaneous users at an average bit error rate of 10^-3. The system capacity decreases to 110 users as a result of additive white Gaussian noise (AWGN), mutual interference, frequency-selective Rayleigh fading, and log-normal shadowing with normalized area mean of 20 dB and standard deviation of 6 dB     

Design Technique for Multiplexing Asynchronous Digital Video and Audio Signals

To apply digital transmission to the distribution of television program material it is necessary to encode both sound and picture signals, protect them from the effects of transmission errors and multiplex them into a form suitable for the transmission link that is to be used. Coding, error protection and multiplexing have all received extensive study but their combined application in a system has received little discussion in the literature. This paper shows how a system was designed for a particular experimental application with a specified total bit rate. Particular emphasis is given to the multiplexing arrangements, including the necessary use of justification techniques. The equipment designed has been used in successful field trials of digital transmission by both cable and satellite.     

Design Philosophy and Hardware Implementation for Digital Subscriber Loops

This paper presents various requirements and configurations in the information network system (INS) NTT's version of the integrated services digital network (ISDN)- such as field trials, and technologies and equipment design of the digital subscriber loop using balanced wire pairs. The main aspects characterizing digital subscriber loops, are a customer access structure, a digital transmission system on existing subscriber loops, and customer interface. A configuration of two-wire digital subscriber loops with two customer access channels, which is adopted in the field trials, will be described. The time-shared two-wire digital transmission and power feeding methods on subscriber loops are discussed. The common mode rejection ratio (CMRR) is discussed in detail, since CMRR is one of the main factors which affects the transmission ability of balanced wire pairs. A proposed self-clocked four-wire customer interface utilizes time division multiplexing technique. The digital subscriber loop operates on a call-by-call basis for link establishment to avoid excessive power dissipations as well as to avoid impairments caused by crosstalk from other lines within a cable. Its design objectives and implementation are also discussed.     

Power-efficient schemes using directly modulated lasers for intensity modulation and direct detection OFDM-PONs

The intensity modulation and direct detection (IM/DD) passive optical network (PON) has been demonstrated as a cost-effective solution for a long-reach (\(>\!80\,\hbox {km}\)) access system because it can be easily installed and maintained with low cost and complexity. Meanwhile, orthogonal frequency division multiplexing (OFDM) has been widely used in PONs due to its high spectral efficiency and strong resistance to dispersion impairments. So, the IM/DD OFDM-PON emerged. The power efficiency has attracted great research interests in IM/DD OFDM-PONs. The previous works achieved power savings from the perspective of MAC-layer or hardware-level optimization, but they neglected designing appropriative algorithms, and the long-reach transmission performance cannot be guaranteed. In this paper, we propose an improved Hughes-Hartogs algorithm (IHHA) to adjust the number of bits and power level allocated for each subcarrier, with the objective to minimize the electrical transmitting power of all subcarriers. The OFDM signal is generated according to the bit/power allocation result of IHHA, and we conduct extensive simulations to verify the long-reach transmission performance of our system. Simulation results show that our system has high power efficiency by using IHHA, and bit error rate satisfies the forward error correction limitation after 100 km single-mode fiber transmission.     

DigiCipher-all digital, channel compatible, HDTV broadcast system

DigiCipher, an all-digital HDTV (high-definition television) system, with transmission over a single 6 MHz VHF or UHF channel, is described. It provides full HDTV performance with virtually no visible transmission impairments due to noise, multipath, and interference. It offers high picture quality, while the complexity of the decoder is low. Furthermore, low transmitting power can be used, making it ideal for simulcast HDTV transmission using unused or prohibited channels. DigiCipher can also be used for cable and satellite transmission of HDTV. There is no satellite receive dish size penalty (compared to FM-NTSC) in the satellite delivery of DigiCipher HDTV. To achieve the full HDTV performance in a single 6 MHz bandwidth, a highly efficient unique compression algorithm based on DCT (discrete cosine transform) transform coding is used. Through the extensive use of computer simulation, the compression algorithm has been refined and optimized. Computer simulation results show excellent video quality for a variety of HDTV material. For error-free transmission of the digital data, power error correction coding combined with adaptive equalization is used. At a carrier-to-noise ratio of above 19 dB, essentially error-free reception can be achieved     

Wide-Band Digital Transmission over Analog Radio Relay Links

An experimental investigation has been performed to assess the feasibility of 8-phase phase-shift-keyed (PSK) signal transmission through a 6-GHz band microwave radio link with a 30-MHz nominal RF bandwidth. Only a portion of this bandwidth is currently being utilized to transmit one analog TV program or 1800channel frequency-division-multiplexed (FDM)/FM telephony. The link has been modified to have a 40-MHz bandwidth for this experiment. The digital modem is a 36-MHz bandwidth, 8-phase coherent PSK (CPSK), 36-Msymbol/s (108 Mbit/s) system. The work which has been performed includes the following: 1) study of the link bit error rate as a function of link carrier-carrier-to-noise ratio(C/N)with the transmitter TWT power output as a parameter; 2) study of the effects of an adjacent 1800-channel carrier (center-to-center separation of 36 MHz) on the error rate of the PSK carrier; and 3) perturbation of the 1800-channel FM carrier top channel noise power ratio (NPR) by an adjacent-channel 8-phase carrier (center-to-center separation of 36 MHz). In addition, experiments have been conducted through a four hop test simulator to examine the cumulative effect of transmission deviations such as group delay and TWT AM-PM transfer effect on the error rate performance for two different TWT power outputs, namely 2 and 4 W.     

Optimal coding rate of punctured convolutional codes inmultiservice wireless cellular systems

The microcellular link performance of future multimedia wireless systems could he improved by using error-correcting punctured convolutional codes in conjunction with slow-frequency hopping. However, the bandwidth expansion due to coding leads to a decrease in the signal-to-interference ratio (SIR) of a frequency-division time-division multiple-access (FD-TDMA) cellular radio link if the system capacity is to be maintained for a given bandwidth allocation. This work determines the best compromise between the power of error correction due to coding and the strength of the self-induced system interference in terms of numerous criteria for speech and data transmission. The aforementioned tradeoff is evaluated in terms of the average bit error rate (BER), the frame error rate, and the burst error distribution for voice transmission. For data transmission with a type 1 hybrid selective-repeat automatic repeat-request (ARQ) protocol, the criteria are average throughput and throughput distribution, the round-trip acknowledgment transmission delay distribution, and the buffering requirements at the transmitter and receiver. The study highlights that punctured codes can significantly improve performance for wireless data links in comparison with the rate 1/2 convolutional coding case or the no-coding case     

Error probability in optical fiber transmission systems

A method for evaluating the average error probability in digital fiber optic transmission systems is described. It takes into account the statistical properties of the main impairments that affect the information signal, i.e., shot noise (dark current included), thermal noise, and intersymbol interference. Unlike other methods, the analysis of shot-noise statistics does not entail the second-moment characterization alone, but uses a number of moments sufficient to evaluate the error probability with a high degree of accuracy. For this purpose it is shown how the cumulants of shot noise and intersymbol interference of any order can be computed. The baseband pulse response and the statistical distribution of the avalanche-photodetector gain are assumed to be available. Moreover, techniques for exploiting the cumulants are given; knowledge of the cumulants allows one to compute the probability of error by means of Gaussian numerical integration rules. Finally, some results and comparisons are reported.     

基于FPGA的高速误码插入技术分析

随机误码插入技术用于数字网传输损伤模拟系统,以模拟信号在信道中的误码损伤。提出了当前误码损伤模拟设备存在处理速度慢、效率不高的问题,针对此问题分析了基于FPGA的误码插入常规方法。在此基础上提出了一种新型的高速并行误码插入方案,该方案采用线性反馈移位寄存器构造多路随机数发生器,同时保证误码图案的等效性,实现了对信号的并行处理。进行了测试,结果符合指标要求,性能良好,便于实现。     

Performance analysis of APSK modulation for DVB‐S2 transmission over nonlinear channels

For increased bandwidth efficiency and receiver performance, standards for satellite broadcasting systems are evolving by utilizing efficient transmission techniques. The second‐generation digital video broadcasting for satellites (DVB‐S2) adopts the amplitude phase shift keying (APSK) modulation for enhanced performance over nonlinear channels. In this paper, we derive error rate bounds for APSK modulated symbols and generalize the bounds to the case of distorted constellation, which occurs when the maximum transmission amplitude is saturated by the soft‐limiter type channel. The derived bound is shown to significantly improve the previously known result, to accurately predict both the symbol error rate and bit error rate in the entire signal‐to‐noise ratio (SNR) region of interest. Using the derived formula, the optimal input power level for the soft‐limiter channel is determined, and the corresponding minimal error rates for 16‐ and 32‐APSK are quantified. The result is also interpreted in terms of optimal input back‐off (IBO) for nonlinear power amplifiers by evaluating the performance degradation as a function of IBO. Copyright © 2009 John Wiley & Sons, Ltd.     

BER Analysis of Equalized OFDM Systems in Nakagami, <Emphasis Type="Italic">m</Emphasis> < 1 Fading

The orthogonal frequency division multiplexing (OFDM) transmission scheme is currently experiencing increased popularity due to advances in very large scale integration technology. It is used for a variety of broadband systems such as asymmetric digital subscriber lines, very-high-speed digital subscriber lines, digital video, and audio broadcasting, and wide local area network standards such as IEEE 802.11a, IEEE 802.11 g, and ETSI Hiperlan/2. However, propagation impairments can cause severe degradation in bit error rates (BER) for coherent detection. We derive a semi-analytical method to evaluate BER of a quadrature phase shift keying (QPSK)-OFDM system in Nakagami, m < 1 fading and additive noise where pilot-assisted linear channel estimation and channel equalization are used. This allows modeling of more severe fading environments than can be depicted by a Rayleigh distribution. Numerical simulations are used to validate the proposed methods. The techniques developed can be applied to other channel estimation techniques, modulation schemes and the performance evaluation of equalized single carrier narrowband systems.     

Power minimization for delivering integrated multimedia servicesover digital subscriber line

We study the problem of designing an efficient resource allocation scheme in the application of providing integrated multimedia services over a digital subscriber line. For a predefined quality of service (QoS) requirement and data throughput, we show that the transmitted power consumption can be reduced by applying the parallel transmission framework previously proposed. Data streams are recognized as a set of layers with different data rate and bit error rate requirements. The characteristics of the telephone channel can be utilized to provide unequal error protection naturally and thus efficiently. Simulation results provide comparison of the proposed parallel transmission framework to the existing schemes designed for general data, and demonstrate significant performance improvement, such as a 0.5-2 dB power gain     

Error correction performance in digital subscriber looptransmission systems

The author describes an error correction system for digital subscriber loop transmission systems which use time compression multiplexing (TCM). An interleaved block code is used to correct the burst errors due to impulse noise from analog telephone circuits. This interleaving method requires no extra hardware and contributes no additional delay. To evaluate the transmission performance of this error correction system, the bit error rate after decoding is derived on the basis of a burst error model for 200 kb/s digital subscriber transmission using the alternate mark inversion (AMI) line code. The experimental results for a 200 kb/s TCM system show that burst errors are substantially reduced