Modulation and Coding for Noncoherent Communications

Until recently, the theory of noncoherent communications was premised on the use of orthogonal multi-pulse modulation such as frequency shift keying. The main drawback of this modulation scheme has been its poor spectral efficiency (rate/bandwidth). This paper considers instead the more general non-orthogonal multi-pulse modulation (NMM) technique. Optimal and suboptimal noncoherent detection strategies for NMM are reviewed and their asymptotic (high SNR) performances are characterized for the additive Gaussian as well as the Rayleigh fading channels. The resulting non-Euclidean distance measures are then used to design NMM signal sets that yield significantly higher bandwidth efficiencies than their orthogonal counterparts. NMM in conjunction with convolutional coding is also studied as a way to improve energy efficiency. Several optimal convolutional codes are examined together with our signal designs. An introduction to equalization on the noncoherent channel is also presented and illustrated by example. This paper thus contains several new results and attempts at the same time to give a tutorial exposition of the subject of noncoherent communications.     

On Trellis Coded Noncoherent Space-Time Modulation

Unitary space-time modulation (USTM) is well-tailored for noncoherent space-time modulation. Trellis coded USTM (TC-USTM) can obtain significant coding gains over uncoded USTM for the noncoherent block fading channel. Conventional TC-USTM schemes expand the signal set of uncoded USTM by a factor of two. In this letter, we propose a new TC-USTM scheme in which the size of USTM set is not limited to be just double for uncoded USTM. However, in TC-USTM schemes, because signals of the same trellis branch are transmitted over the same fading coefficients, one trellis branch can only obtain one temporal diversity. In this letter, we also propose a new trellis coded noncoherent space-time modulation scheme by interleaving space-time signals. The proposed scheme can enlarge temporal diversity at the price of increased complexity and delay. Simulation results demonstrate the excellent error performances of codes found by computer searches for both schemes.     

Noncoherent Detection of Tamed Frequency Modulation

Continuous-phase, constant-envelope digital modulation schemes are useful in various applications where a high spectrum utilization as well as immunity to nonlinear distortion is required. From this point of view, typical efficient schemes are digital partialresponse frequency modulation methods. The aim of this work is to investigate noncoherent detection in order to avoid the RF carrier recovery problem. In this paper we select for analysis tamed frequency modulation (TFM) as a particularly representative member of this class, but a similar analysis could be carried out for other partialresponse digital FM systems. After an evaluation of the optimal noncoherent detection and of differential phase detection of TFM, we propose a demodulation method based on a simple and efficient baseband processing of the output of a frequency demodulator. It turns out that the power loss with respect to coherent or optimal demodulation of TFM is on the order of 2 dB. The baseband processing here proposed is in some way equivalent to a partial recovery of the carrier phase and could be improved by using a more complex baseband processing such as a decoding scheme based on the Viterbi algorithm.     

Optimal Memoryless Relays With Noncoherent Modulation

We derive optimal memoryless relays for the case of noncoherent modulation over additive white Gaussian noise (AWGN) channels with or without fading. The derivation is flexible, as it can be applied to any binary hypothesis observed at the relay. We investigate several channels, including random phase and fading, and apply different modulation schemes, namely on-off-keying (OOK) and orthogonal frequency-shift-keying (FSK). We find that at low signal-to-noise ratios (SNR) the relay censors its observation, as it only transmits at nonzero energy if the observations seem reliable. Compared to the known results that optimal memoryless relays for the case of coherent binary-phase-shift-keying (BPSK) are combinations of soft-information and a hard-limiter, the noncoherent relays have considerably less emphasis on soft-information and converge much faster to the hard-limiter.      

Noncoherent iterative (turbo) decoding

Previously, noncoherent sequence detection schemes for coded linear and continuous phase modulations have been proposed, which deliver hard decisions by means of a Viterbi algorithm. The current trend in digital transmission systems toward iterative decoding algorithms motivates an extension of these schemes. In this paper, we propose two noncoherent soft-output decoding algorithms. The first solution has a structure similar to that of the well-known algorithm by Bahl et al. (1974), whereas the second is based on noncoherent sequence detection and a reduced-state soft-output Viterbi algorithm. Applications to the combined detection and decoding of differential or convolutional codes are considered. Further applications to noncoherent iterative decoding of turbo codes and serially concatenated interleaved codes are also considered. The proposed noncoherent detection schemes exhibit moderate performance loss with respect to corresponding coherent schemes and are very robust to phase and frequency instabilities     

一种非相干编码调制系统性能研究

研究了一种同时采用串行级联卷积码和独立观察时间非相干最大似然序列估计的算法的非相干编码调制系统的性能,给出了不同参数下的性能曲线,仿真结果表明,选择适当的观察间隔和观察长度可以在复杂度增加不大的条件下,达到接近于相干编码调制的性能。     

Kasami Code-Shift-Keying Modulation for Ultra-Wideband Communication Systems

Ultra-wideband (UWB) communication systems are generally applied to short-range wireless communications. In order to achieve higher rates or to support multiple access capabilities, direct sequence spread spectrum (DSSS) techniques have been introduced to UWB systems, and multiple pulses corresponding to a certain pseudo-noise (PN) code are transmitted to represent a symbol. In addition, the concept of M-ary code shift keying (M-CSK) was introduced into DSSS systems to achieve higher rates. In this work, we propose an M-CSK modulation technique based on the large set of Kasami sequences since it possesses good code properties, including a large code set size and low cross correlations. The modulation and demodulation schemes are developed, and the system performance in additive white Gaussian noise (AWGN) and UWB channels exposed to multiple user interference is investigated thoroughly. It was found that the Kasami M-CSK modulation is superior to other M-CSK modulation schemes in the bandwidth efficiency, and therefore a higher data rate can be achieved. Furthermore, based on our proposed demodulation scheme, the hardware complexity of receivers can be greatly reduced to O(M^1/3), and the implementation of receivers for a very large M becomes feasible.     

A Ultra-Wideband Amplitude Modulation (AM) Detector Using Schottky Barrier Diodes Fabricated in Foundry CMOS Technology

Utility of Schottky diodes fabricated in foundry digital 130-nm CMOS technology is demonstrated by implementing an ultra-wideband (UWB) amplitude modulation detector consisting of a low-noise amplifier (LNA), a Schottky diode rectifier, and a low-pass filter. The input and output matching of the detector is better than -10 dB from 0-10.3 GHz and 0-1.7 GHz, respectively, and almost covers the entire UWB frequency band (3.1-10.6 GHz). The measured peak conversion gain is -2.2dB. The sensitivity over the band for amplitude modulation with the minimum E _b/N_o of 6 dB is between -53 and -56 dBm. The power consumption is only 8.5 mW     

超宽带跳时扩频调制技术研究

简要介绍了超宽带无线通信中PPM、PAM、OOK及BPSK二进制跳时扩频调制技术的实现原理,给出了高斯信道环境下多用户系统的误码率性能,并对其发送信号的功率谱及在高斯信道下的误码率性能进行了仿真,最后指出,TH-BPSK易实现且具有较好的性能。     

PAC vs. MAC for Decentralized Detection Using Noncoherent Modulation

In decentralized detection, local sensor observations have to be communicated to a fusion center through the wireless medium, inherently a multiple-access channel (MAC). As communication is bandwidth- and energy-constrained, it has been suggested to use the properties of the MAC to combine the sensor observations directly on the channel. Although this leads to an array-processing gain if the sensors' transmissions combine coherently on the channel, it has been shown that this is not the case when they combine noncoherently. We review known results for the coherent case and then analyze the noncoherent case based on a simple on/off scheme combined with optimal sensor “censoring.” Since the optimal forwarding function is not available, we also bound the performance using an equivalent communication problem and a centralized estimator to verify trends. We find that for noncoherent modulation, there is no processing gain using the MAC for decentralized detection, but compared to parallel-access channels (PACs) the MAC avoids the noncoherent combining loss. Still the performance of the MAC approach is only of diversity one, as the output of the MAC is approximately a zero-mean complex Gaussian random variable for a large number of sensor. The MAC performance can be increased by using multiple independent channels, each used as a MAC by all sensors, which we term diversity-MAC. This approach always outperforms the PAC scheme on Rayleigh fading channels, where the output is exactly Gaussian, but has inferior performance across random phase channels when few sensors are used, as the PAC does not create “artificial” fading.      

连续相位调制的非相干减少状态差分序列检测算法

该文提出了连续相位调制的一种非相干减少状态的差分序列检测(RSDSD)算法.该算法基于减少状态序列检测(RSSD)的思想,利用简化状态格状图进行一码元差分Viterbi检测.分析了全响应连续相位调制(CPM)信号和部分响应CPM信号简化状态格状图的最小平方欧氏距离.在AWGN信道下以八进制h=1/8的2RC信号为例给出RSSD和RSDSD算法的性能.对不同的简化方案以及存在多普勒频移时相干RSSD和非相干RSDSD的性能进行了比较.仿真结果表明:所提出的算法比相干最大似然序列检测在10-3误比特率时信噪比损失约为2dB,但它对于载波恢复困难的情形更为合适和稳健.     

Methods for Ultra-Wideband Pulse Generation Based on Optical Cross-Polarization Modulation

Optical methods for different type ultra-wideband (UWB) pulse generation based on cross-polarization modulation (CPM) are proposed and demonstrated in this paper. Two polarity-reverse pulses can be obtained by CPM and birefringence time delay to form a monocycle pulse. A semiconductor optical amplifier (SOA) is placed after the monocycle pulse process for doublet pulse generation. These two kinds of pulses can be employed in single-band impulse radio UWB (IR-UWB) systems. Two kinds of multi-band UWB pulses can be generated based on monocycle pulse train with proper apodization profiles, realized by hybrid photonic microwave filter and synchronous polarization modulation respectively. Experimental results show that these pulses can be used in multi-band UWB (MB-UWB) over fiber systems.      

Block Error Performance of Noncoherent FSK Modulation on Rayleigh Fading Channels

In this paper, the calculation of the probabilityP_{f}(M, N)of more thanMbit errors in a block ofNbits transmitted over a Rayleigh fading channel using noncoherent frequency shift keying is considered. Accurate approximations toP_{f}(M, N)are derived under the assumption of very slow fading. Approximations are also given when a selection diversity system is used. An application of the results to the calculation of the block error rate when the assumption of very slow fading is relaxed is then discussed.     

Slightly Frequency-Shifted Reference Ultra-Wideband (UWB) Radio

A promising ultra-wideband (UWB) radio technique being widely considered for low-data-rate applications, such as those often encountered in sensor networks, is the transmitted reference (TR) UWB scheme. However, the standard TR-UWB scheme, while often motivated by the simplicity of its receiver, is still dogged by implementation concerns. In particular, the receiver requires an extremely wideband delay element, which is difficult to incorporate into low-power integrated systems. In this paper, a TR scheme is proposed in which the separation between the data and reference signals, rather than being a time delay, is a slow rotation over the symbol interval. This provides a (slightly) frequency-shifted reference that, while orthogonal to the data-bearing pulse, still goes through a nearly equal channel. A detailed analysis of the proposed scheme is provided. Simulation results demonstrate the expected result that frequency shifting of the reference in the proposed manner is not effective for high-data-rate systems that experience appreciable intersymbol interference. However, for the targeted low-to-moderate data-rate applications, numerical results demonstrate that the proposed system not only achieves the primary goal of providing a much simpler receiver architecture, but also that it outperforms the standard TR-UWB system     

GMSK调制与非相干解调算法研究与仿真实现

高斯最小频移键控(Gaussian Filtered Minimum Shift Keying,GMSK)是一种连续相位非线性调制方式,具有包络恒定、相位平滑、频谱特性好和带外辐射功率小等多种优点,在移动通信和航天测控等领域得到广泛应用。介绍了GMSK的基本原理,并从频谱效率和包络特性两方面与其他调制方式进行对比分析。同时介绍了几种典型的非相干解调方式,并利用Matlab软件对不同解调方法的性能进行仿真。     

伪码时钟调频非相干解调器的研究

分析了伪码时钟调频中频非相干解调器，推导了解调器的数学模型，讨论了其稳定性及门限性能。理论分析与实验结果相符合。     

Transmission and Reception by Ultra-Wideband (UWB) Antennas

Broadband antennas are very useful in many applications because they operate over a wide range of frequencies. The objective of this paper is to study the transient responses of various well-known antennas over broad frequency ranges. As such, the phase responses of these antennas as a function of frequency are of great interest. In the ensuing analysis, each antenna is excited by a monocycle pulse. Many antennas show resonant properties, and numerous reflections exist in the antennas' outputs. The first part of this paper deals with ways of converting various resonating antennas to traveling-wave antennas by using resistive loading. Appropriate loading increases the bandwidth of operation of the antennas. However, the drawback is the additional loss in the load applied to the antenna structure, leading to a loss of efficiency to around fifty percent. However, some of the antennas are inherently broadband, up to a 100:1 bandwidth. Hence, the transient responses of these antennas can be used to determine their suitability for wideband applications with a low cutoff frequency. The second part of the paper illustrates the radiation and reception properties of various conventional ultra-wideband (UWB) antennas in the time domain. An antenna's transient response can be used to determine the suitability of the antenna in wideband applications     

物理层网络编码中连续相位调制信号的非相干多符号检测

基于连续相位调制(CPM)的物理层网络编码(PNC)由于其高效的吞吐率和频谱利用率特性引起了越来越多的关注。现有关于CPM-PNC检测的研究大多建立在到达中继端的两节点信号载波相位完全同步或相位差已知的基础上。实际应用中,这一载波相位差不可避免,也很难准确估计。针对这一问题,该文提出一种中继端存在未知载波相位差条件下的CPM-PNC非相干多符号检测算法。该算法根据最大似然检测原理,通过观察多个码元来实现中间码元的检测,充分利用了CPM信号的相位记忆特性。仿真结果表明,该文所提出的CPM-PNC非相干多符号检测算法性能优越。而且随着观察窗口长度的增大,其性能显著提高并逐渐趋近最优相干检测性能。在误码率(BER)为10-4 时,相比于非相干单符号检测,观察窗口长度为5个码元时的CPM-PNC非相干多符号检测有6.7 dB的性能增益。     

Ultra-Wideband Pulse Generation Based on Cross-Gain Modulation in Fiber Optical Parametric Amplifier

A novel approach to generate ultra-wideband (UWB) monocycle or doublet pulse using cross-gain modulation in fiber optical parametric amplifier is demonstrated in a single experimental setup. The high-speed optical parametric process realizes the signal amplification, idler generation, and pump depletion simultaneously within femtosecond response time in the highly nonlinear fiber. After the combination of the three lightwaves with a suitable time delay between them, UWB pulse is obtained. A selective generation of monocycle or doublet pulse can be made by altering the optical attenuators without changing the wavelengths or the powers of the pump and the signal. In our experiment, high-quality UWB monocycle and doublet pulses with a fractional bandwidth of 115% and 126% were generated.      

Small Ultra-Wideband (UWB) Bandpass Filter With Notched Band

A compact ultra-wideband (UWB) bandpass filter (BPF) with notched band has been proposed and implemented in this letter. H-shaped slot is studied and adopted to tighten the coupling of inter-digital capacitor in order to improve the BPF's performance. Three pairs of tapered defected ground structures (DGS) are formed to assign their transmission zeros towards the out of band signal, thereby suppressing the spurious passband. Combining these two structures we obtain a small sized UWB BPF. Meander line slot is developed to reject the undesired wireless local-area network (WLAN) radio signals. An experimental UWB filter with notched band was fabricated with 35% less length as compared to an embedded open-circuited stub. The measured BPF insertion loss is less than 1.0 dB throughout the pass band of 2.8 to 10.8 GHz, the variation of group delay less than 0.20 ns in this band except for the notched band, and a wide stopband bandwidth with 20 dB attenuation up to at least 20.0 GHz.