Diagonal algebraic space-time block codes

We construct a new family of linear space-time (ST) block codes by the combination of rotated constellations and the Hadamard transform, and we prove them to achieve the full transmit diversity over a quasi-static or fast fading channels. The proposed codes transmit at a normalized rate of 1 symbol/s. When the number of transmit antennas n=1, 2, or n is a multiple of four, we spread a rotated version of the information symbol vector by the Hadamard transform and send it over n transmit antennas and n time periods; for other values of n, we construct the codes by sending the components of a rotated version of the information symbol vector over the diagonal of an n × n ST code matrix. The codes maintain their rate, diversity, and coding gains for all real and complex constellations carved from the complex integers ring Z [i], and they outperform the codes from orthogonal design when using complex constellations for n > 2. The maximum-likelihood (ML) decoding of the proposed codes can be implemented by the sphere decoder at a moderate complexity. It is shown that using the proposed codes in a multiantenna system yields good performances with high spectral efficiency and moderate decoding complexity     

DVB-T接收机中的CPE均衡技术

DVB—T是最近十年全球地面数字电视传输系统使用最广泛的一种标准，本文通过分析相位噪声对DVB—T传输系统的影响，提出了两种适用于该系统且易于硬件实现的CPE（公共相差）均衡方法，并比较了它们的实现复杂度。仿真表明，在多径衰落条件下，两种方法均提高了系统性能。     

Complexity analysis of software defined DVB-T2 physical layer

The second generation terrestrial TV broadcasting standard from the digital video broadcasting (DVB) project, DVB-T2, has recently been standardized. In this article we perform a complexity analysis of our software defined implementation of the modulator/demodulator parts of a DVB-T2 transmitter and receiver. First we describe the various stages of a DVB-T2 modulator and demodulator, as well as how they have been implemented in our system. We then perform an analysis of the computational complexity of each signal processing block. The complexity analysis is performed in order to identify the blocks that are not feasible to run in realtime on a general purpose processor. Furthermore, we discuss implementing these computationally heavy blocks on other architectures, such as GPUs (graphics processing units) and FPGAs (field-programmable gate arrays), that would still allow them to be implemented in software and thus be easily reconfigurable.     

Parameter optimization and simulated performance of a DVB-T digitaltelevision broadcasting system

A prototype of a digital television terrestrial broadcasting system has been implemented according to the European DVB-T standard. The first step in the construction of this prototype involved parameter optimization via simulation. This paper presents the optimization process of the system parameters and the final achieved BER performance. Important design aspects such as interleaving, convolutional puncturing codes, Viterbi decoding, pilot-based channel correction and optimal pilot power are considered. The DVB-T standard offers some suggested values of the C/N ratio needed to achieve the desired BER requirements in the receiver. However, they have been obtained assuming ideal channel correction and synchronization. Simulation results are provided here in non-ideal conditions     

An adaptive two-dimensional channel estimator for wireless OFDMwith application to mobile DVB-T

An adaptive channel estimator is proposed and investigated to improve the performance of the receiver for pilot aided wireless and mobile OFDM systems. The estimator consists of a two-dimensional Wiener filter which is implemented as a cascade of two one-dimensional filters. We propose an efficient algorithm for adaptation to time varying channels of the second filter. The method is applied to the Terrestrial Digital Video Broadcasting System (DVB-T), which was originally specified for fixed receivers and which is in the process of being extended for mobile reception. The results are shown after inner decoding. Depending on the channel conditions, the signal-to-noise ratio gain can be up to 1.6 dB. The method provides a compatible improvement to DVB-T receivers     

基于DVB-T2的旋转星座解映射算法及其改进

在广播和通信领域最新概念中,星座旋转作为一种分集技术被应用于DVB-T2标准。对于旋转星座采用基于硬判决的二维迭代LLR解映射算法进行了一些简化,但由于硬判决带来了误码传播,并且首次软信息计算仍较为复杂。提出了两种改进方案,分别从误码性能和运算复杂度方面对原算法进行了改进。仿真结果表明,信道条件较为恶劣时,改进方法在性能上优于原系统。     

Error Performance of Rotated Phase Shift Keying Modulation over Fading Channels

In this paper, the modulation diversity is used to improve the performance of M-PSK modulation over fading channels. Modulation diversity can be achieved by rotating the signal constellation and using component interleaving. We derive symbol error probability expressions for rotated uncoded M-PSK over Ricean fading channels and obtain optimal rotation angles for M-PSK (M = 2, 4, 8). We show that rotated signal constellations with component interleaving improve the performance of M-PSK significantly as compared to the unrotated one over Rayleigh and Ricean fading channels. For example, when the ratio of the direct path power to the multipath signal power, K is 0 and 10, 8 and 1.5 dB gains are obtained, respectively, at a symbol error probability of 10⁻³ for 8PSK modulation. We also show that as K gets larger, the gain obtained by the rotation rapidly decreases. We develop a new asymmetric 8PSK signal constellation obtained from two QPSK signal constellations that are optimally rotated by different angles. This asymmetric 8PSK and also the rotated 8PSK signal constellation together with component interleaving are applied to four-state trellis-coded schemes. Simulation results show that these new schemes provide good performance improvements over the original TCM schemes and previous relevant works over Rayleigh and Ricean fading channels.     

Sphere Lower Bound for Rotated Lattice Constellations in Fading Channels

We study the error probability performance of rotated lattice constellations in frequency-flat Nakagami-m block-fading channels. In particular, we use the sphere lower bound on the underlying infinite lattice as a performance benchmark. We show that the sphere lower bound has full diversity. We observe that optimally rotated lattices with largest known minimum product distance perform very close to the lower bound, while the ensemble of random rotations is shown to lack diversity and perform far from it.     

一种M-QAM软判决解映射的简化算法研究

提出了一种适用于所有M-QAM软判决解映射的简化算法,并将其扩展到不对称的二维QAM解映射中,如DTMB中的32-QAM.并以32-QAM为例,用计算机仿真比较了不同算法的编码系统误码率和解码时间等性能.结果表明,在'降低M-QAM软判决解映射的判决复杂度时,该简化算法没有损失信噪比,性能良好,适用于DTMB系统.     

Coded Decision Directed Demodulation for Second Generation Digital Video Broadcasting Standard

Second generation terrestrial digital video broadcasting (DVB-T2) standard aims at providing high definition television and high rate services for the same spectrum allocation of current DVB-T standard. This goal is achieved by adopting new physical layer features that increase the spectrum efficiency. In this respect, the insertion of pilot tones in the orthogonal frequency division multiplexed (OFDM) signal, though allowing an efficient channel estimation, decreases the spectral efficiency. In this paper we evaluate performance of the coded decision directed demodulation (CD3) technique for channel estimation in DVB-T2. In fact, by iterating between decoding and channel estimation, with the latter obtained by using previously decoded symbols, CD3 is able to provide an accurate channel estimation with very few pilots, even in the presence of highly frequency dispersive and time-variant channels. Numerical results are provided for a comparison in terms of achievable throughput between DVB-T2 with CD3 and current DVB-T. Moreover, multiple antennas at the base station are also considered to provide spatial diversity and hence further improve system performance.      

一种8PSK、16APSK与32APSK软解映射的实现技术

8PSK、16APSK和32APSK是DVB-S2标准中常用的信号调制方式,采用这些高阶调制方式可以充分提高频谱利用率.而在与高效编译码结合时(如LDPC,TPC等),为了提高误码性能,接收端译码往往需要用到接收信号的软信息.以文献[2]为基础,根据信号模型提出了一种新颖实用的软解映射方法.计算机仿真结果表明:在高斯信...     

Efficient GPU and CPU-based LDPC decoders for long codewords

The next generation DVB-T2, DVB-S2, and DVB-C2 standards for digital television broadcasting specify the use of low-density parity-check (LDPC) codes with codeword lengths of up to 64800 bits. The real-time decoding of these codes on general purpose computing hardware is useful for completely software defined receivers, as well as for testing and simulation purposes. Modern graphics processing units (GPUs) are capable of massively parallel computation, and can in some cases, given carefully designed algorithms, outperform general purpose CPUs (central processing units) by an order of magnitude or more. The main problem in decoding LDPC codes on GPU hardware is that LDPC decoding generates irregular memory accesses, which tend to carry heavy performance penalties (in terms of efficiency) on GPUs. Memory accesses can be efficiently parallelized by decoding several codewords in parallel, as well as by using appropriate data structures. In this article we present the algorithms and data structures used to make log-domain decoding of the long LDPC codes specified by the DVB-T2 standard??at the high data rates required for television broadcasting??possible on a modern GPU. Furthermore, we also describe a similar decoder implemented on a general purpose CPU, and show that high performance LDPC decoders are also possible on modern multi-core CPUs.     

Signal space diversity: a power- and bandwidth-efficient diversitytechnique for the Rayleigh fading channel

The increasing need for high data-rate transmissions over time- or frequency-selective fading channels has drawn attention to modulation schemes with high spectral efficiency such as QAM. With the aim of increasing the “diversity order” of the signal set we consider multidimensional rotated QAM constellations. Very high diversity orders can be achieved and this results in an almost Gaussian performance over the fading channel, This multidimensional modulation scheme is essentially uncoded and enables one to trade diversity for system complexity, at no power or bandwidth expense     

Terrestrial DVB (DVB-T): A Broadcast Technology for Stationary Portable and Mobile Use

Digital video broadcasting-terrestrial (DVB-T) is the name of the terrestrial transmission system which was developed by the DVB Project. DVB-T is in operation in many countries around the world. This paper analyzes the features of the system. It describes its capabilities with a special emphasis on mobile reception and looks at the introduction of DVB-T in Germany using the launch of DVB-T in this country as a case study. In order to analyze how an MPEG transport stream at the input of a DVB-T modulator is turned into a DVB-T signal, we consider the channel coding and modulation used. Then we look at various aspects of the system performance. The next section deals with mobile reception. Network planning issues, antenna diversity concepts for mobile receivers, and handover procedures will be considered. Finally, the introduction of DVB-T in Germany is presented as a case study. In contrast to various other countries Germany decided to offer DVB-T as a means of providing the "anywhere TV" experience. This implies that DVB-T signals can be received with mobile and portable receivers. In regions with DVB-T coverage analogue terrestrial TV services were discontinued just a few months after the launch of DVB-T.     

Real-Domain Decoder for Full-Rate Full-Diversity STBC with Multidimensional Constellations

In this letter, we present a new maximum likelihood (ML) decoding algorithm for space time block codes (STBCs) that employ multidimensional constellations. We start with a lattice representation for STBCs which transforms complex channel models into real matrix equations. Based on the lattice representation, we propose a new decoding algorithm for quasiorthogonal STBCs (QO-STBC) which allows simpleML decoding with performance identical to the conventional ML decoder. Multidimensional rotated constellations are constructed for the QO-STBCs to achieve full diversity. As a consequence, for quasi-orthogonal designs with an arbitrary number of transmit antennas N (N ? 4), the proposed decoding scheme achieves full rate and full diversity while reducing the decoding complexity from ∂(M_c^N/2) to ∂(M_c^N/4) in a M_c-QAM constellation.     

A 65 nm CMOS Multistandard, Multiband TV Tuner for Mobile and Multimedia Applications

This paper presents a direct conversion, multistandard TV tuner implemented on a 65 nm digital CMOS process occupying less than 7 . The tuner is compliant with several digital terrestrial, fixed and mobile TV standards, including DVB-T, DVB-H, T-DMB, and ISDB-T. It achieves a 3/3.2/3.5 dB noise figure at VHF, UHF, and L-band, respectively, while the measured sensitivity at UHF for the QPSK-frac12 DVB-T mode is at the PCB connector. The implemented RF front-ends support both single-ended and differential inputs. An integrated - fractional-N synthesizer operating from 1.2 to 1.8 GHz achieves less than 1 integrated phase error, thus enabling a maximum SNR in excess of 37 dB for VHF and UHF. Multistandard capability is also enabled by programmable channel-select filters. Power consumption is less than 140 mW in DVB-T mode for all three bands.     

DVB-T/H and T-DMB: Physical Layer Performance Comparison in Fast Mobile Channels

Terrestrial or Handheld Digital Video Broadcasting (DVB-T/H) and Terrestrial Digital Multimedia Broadcasting (T-DMB) are two popular broadcasting standards that enable digital television transmissions to handheld receivers. This paper presents a comprehensive performance comparison between the physical layers of DVB-T/H and T-DMB when employed for mobile communications. By exploiting a recently proposed fast simulation model, we assess the BER of the two coded OFDM systems in several realistic scenarios, taking into account Rayleigh and Rice channels, different mobile speeds, inner and outer channel coding, channel estimation, and one or two receive antennas. Our comparison shows that the DVB-T/H physical layer performance highly depends on the delay spread of the channel, whereas T-DMB is less sensitive to the frequency selectivity of the channel. As a result, DVB-T/H yields better performance than T-DMB in typical Rayleigh channels with significant delay spread. On the contrary, at high SNR, T-DMB outperforms DVB-T/H in Rice channels with low delay spread. As a side result, we show the performance improvement of DVB-H produced by MPE-FEC at the data link layer.      

基于USRP的DVB-T接收机实现

为提高地面数字电视广播(DVB-T)接收机的实现灵活性,基于由通用软件无线电外设(Universal Software Radio Peripheral,USRP)和通用计算机组成的软件无线电平台,实现DVB-T接收机。接收机以USRP作为射频前端,在通用计算机中完成全部基带信号处理、视频解码与显示等。测试结果表明,接收机可实现对DVB-T信号的接收,为接收机算法开发、验证与评估提供了更为灵活的方法。     

利用Turbo码改善DVB-T纠错性能的仿真研究

分别介绍了Turbo码和DVB-T系统中纠错机制的基本原理,并把Turbo码技术引入到DVB-T系统的纠错机制中,利用仿真系统对改进后的纠错机制进行研究.仿真结果表明,与原系统相比,引入Turbo码的DVB-T系统能有效地改善系统的纠错性能,而且在BER=10-7时,新的纠错机制比原系统有1 dB的编码增益.     

DIFFS: A Low Power,Multi-Mode,Multi-Standard Flexible Digital Front-End for Sensing in Future Cognitive Radios

Cognitive Radios provide communication devices with the flexibility to adjust to varying network and channel conditions. For this to be fully realizable spectrum sensing and signal reception have to happen simultaneously and have to require as little power as necessary to function in handheld devices. This work argues for the need of flexible digital-front ends as indispensable building block, able to perform control operations over the analog front-end and to perform sensing and synchronization procedures without the need of power consuming baseband processors. A low power, reconfigurable digital front-end that supports concurrent synchronization and sensing of high-throughput wireless standards is presented. Multiple operating modes, useful for various communication standards, such as LTE, WLAN and DVB-T are introduced and analyzed. The digital front-end has been implemented in 65 nm CMOS technology resulting in a chip area of 6.4 mm2. Fine grain clock gating allows synchronization at 4 mW and sensing at 7 mW power consumption. Experiments in combination with a reconfigurable analog front-end show that a 1.7 GHz wide frequency band can be scanned based on energy detection in an exceptionally low time window of 10 ms while consuming 13 mW power and that coarse energy detection can speed-up the sensing process. Furthermore, advanced feature detection for DVB-T and LTE signals is implemented and measured. Low power sensing of DVB-T signals shows that a target false alarm rate of 10 % and a detection probability of 90 % at an input power level of?106 dBm while consuming 7 mW power are possible. Synchronization-aided FFT-based LTE sensing with leakage cancellation was experimentally validated for various bandwidths showing a power consumption of maximum 20 mW.