大气激光通信中垂直分层空时码的研究与实现

针对垂直分层空时(V-BLAST)码存在译码复杂度高、误码性能不理想等不足,本文将串行干扰消除(SIC)算法应用于V-BLAST码的译码中,提出了一种适合于大气激光通信的分层空时(LST)编码方案。采用仿真分析和硬件实验相结合的方法,验证了本文方案的正确性和合理性。实验结果证明了在大气激光通信中采用基于SIC算法的V-BLAST编码的可行性,为进一步提高通信的传输速率、改善系统性能提供了新方法和依据。     

网格编码调制与空时块码的级联和空时格码的比较

介绍了空时编码，阐述了正交空时分组编码的编解码过程及其与网格编码调制相结合的系统，并对空时分组编码、空时格栅编码、网格编码调制和空时分组编码级联这三者在相同的发送功率、相同的信息速率和相同的频带利用率的条件下的BER(误比特率)性能进行了比较，得出简单的网格编码调制和空时分组编码级联后的系统，可以比同复杂度甚至更高复杂度的空时格栅编码系统节省SNR(信噪比)。结论是针对两根发送天线和一根接收天线的，但对于更多天线的无线系统同样适用。     

空时网格码技术

介绍了空时信道模型,表述了空时网格码的设计准则,构造了最佳空时网格编码M-PSK方案,该方案适用于慢衰落和快衰落信道的各种发射天线数和频谱利用率;最后给出了空时网格码的译码方法。     

一种新的网格空时码

本文分析了空时码在平坦准静态衰落信道下的性能,指出分集增益和编码增益并不能准确衡量空时码的性能,提出一种设计网格空时码的新思路,即通过牺牲部分分集增益来降低调制阶数以提高系统性能.依据这一思想,本文给出一种传输速率为3bits/s/Hz,4-PSK调制,8状态的新的非满秩网格空时码.仿真结果表明,这种码虽然没有获得最大分集增益,但相比同速率的满秩网格空时码性能更好,实现更简单.     

空时网格码的正交构造法

空时编码是实现宽带无线数据通信的一种极有潜力的技术。然而，随着发射天线数目的增加，空时码的构造变得十分困难。本文提出了空时网格码的一种构造方法－正交构造法：这种方法可以根据已知的适用于M根发射天线的空时码来构造适用于KM（K≥2）根天线的空时码。仿真结果表明，对于相同的码率和和相近的译码复杂度，用正交构造法得到的空时码的差错性能甚至优于通过计算机搜索得到的空时卷积码。     

瑞利衰落信道下的网格酉空时调制的研究

酉空时是一种多天线系统信号调制方案,可以在不知道信道状态下进行解调。文中将网格编码与酉空时星座结合运用,性能仿真证明了网格酉空时调制系统非常适合无信道状态信息的无线通信系统,网格编码在一定程度上改进了系统的比特误码率性能。将网格编码下的酉空时调制与未编码的酉空时调制进行对比,结果显示在10^-4的比特误码率下可以得到10～15dB的编码增益。     

适用于串行级联结构的广义递归网格空时码设计

该文结合网格空时码(STTC)和分层空时码(BLAST)的优点,利用多个高码率卷积码,设计了一类适用于串行级联结构的广义递归STTC(G-RSTTC)。相比于传统以递归STTC为内码的串行级联空时码(SCSTC),其数据速率可随发送天线数增加而线性增加;相比于以BLAST为内码的SCSTC,基于G-RSTTC的SCSTC可获得更大的分集增益和编码增益。     

无线通信系统中的低码率空时网格码

空时网格编码能在频带利用率、分集增益、调制方式与编码网络图复杂度之间达到最佳的折衷。本文给出了几种低码率空时网格码的好码。理论分析和系统仿真表明,在相同的频带利用率下,该空时网格码可具有比空时块码级联卷积码具有更好的误码率性能,更适合于对频带利用率要求不高的功率受限无线通信系统。     

网格空时码在WCDMA中的解决方案

本文根据STTD向下兼容的特点,提出一种网格空时码在WCDMA中的解决方案,并给出一组适用于该方案的STTC编码.研究表明,在WCDMA系统中采用本文给出的编码方式,不仅能够具有与空时传输分集(STTD:Space-Time Transmit Diversity)相同的向下兼容特性,而且能够获得更好的抗衰落性能.     

Diversity coding scheme for wireless optical communication with direct detection

A new diversity coding scheme using four transmit apertures, one receive aperture and two detectors is proposed for wireless optical communication with direct detection. Pilot symbols are inserted to the encoding information sequence. Simulations show that the scheme can yield a signal-to-noise ratio gain of 6 dB at 10/sup -4/ error probability.     

Space-time coding scheme for the paired weak user in MIMO-NOMA systems

In view of the paired weak user’s poor outage performance in multiple-input multiple-output non-orthogonal multiple access (MIMO-NOMA) systems,Alamouti code was adopted to encode for the weak user in order to improve its outage performance by means of diversity,and the closed-form expression of the strong user’s ergodic capacity as well as the boundary-form expressions of the weak user’s ergodic capacity and outage probability was derived in the proposed model.Moreover,a power allocation algorithm for optimizing the system’s throughput was proposed.Finally,the numerical results show the accuracy of the derived expressions,the efficacy of the proposed algorithm,and that the weak user’s outage performance in the proposed coding scheme is far superior to that in the current coding scheme only adopting vertical Bell lab layered space-time (V-BLAST) code.     

An efficient modulation/coding scheme for MFSK systems on bandwidthconstrained channels

The performance of a bandwidth-efficient multiple-tone modulation scheme for M-ary frequency-shift keying (MFSK) is presented. The use of balanced incomplete block (BIB) designs is proposed to form the signaling frames. On each symbol interval the modulator selects a group of elements from a BIB design and divides its energy into the orthogonal waveforms corresponding to these elements. The multiple-tone FSK scheme based on these block designs is shown to increase greatly the bandwidth efficiency of a conventional M-ary FSK system. An implicit diversity is incorporated in the modulation scheme. Thus, a performance improvement comparable to that obtained by using time or frequency diversity is shown on a Rayleigh fading channel and also on an interference channel with partial-band Gaussian noise. The multiple-tone scheme based on this design is compared to a multiple-tone scheme based on Hadamard matrices suggested by J.F. Pieper et al. (1978). It is shown that similar performance is achieved on a fading channel, while an advantage close to 4 dB is obtained for the proposed scheme on an AWGN (additive white Gaussian noise) channel     

Signal processing scheme for reducing atmospheric modulation noise in optical communication

Intesity modulation of optical signals by the atmosphere limits exploitation of the negligible atmospheric depolarization effects as a means of transmitting information over the atmospheric channel. A simple signal processing technique is demonstrated that can be used to recover a demodulated polarization modulation audio signal from the atmospheric modulation noise.     

A new modulation scheme for IR-UWB communication systems

Since the poor performance of orthogonal binary Pulse Position Modulation (PPM) compared with binary Pulse Amplitude Modulation (PAM), this paper presents a new modulation scheme named Pulse Width Modulation (PWM) for Impulse Radio Ultra-WideBand (IR-UWB) communication systems. This modulation scheme uses pulses with equal amplitude and different widths to carry different information. The receiver employs differences between similarity coefficients among these pulses to distinguish different information. Bo...     

DS/SSMA communication system with trellis coding and CPM

A direct-sequence spread spectrum multiple access (DS/SSMA) communication system employing continuous phase modulation (CPM) and trellis coding is described and analyzed to obtain an estimate of the error probability. The trellis code provides significant coding gain while the CPM signal format gives desirable spectral properties. The analysis shows that significant improvement in error probability over the standard binary DS/SSMA system can be achieved with relatively simple codes     

适应超高速光通信系统的PM-MSK调制方案

先进的调制技术可以有效地改善光通信系统抵御色散、偏振模和非线性等损伤的能力,是超高速光通信系统中的重要技术。MSK(最小频移键控)是一种恒包络调制技术,具有色散容限较大和能量集中等优点,文章将MSK调制引入PM(偏振复用)系统,提出了一种适应于超高速光通信系统的PM-MSK调制方案。理论分析和数值仿真结果表明,该方案与RZ(归零)和QPSK(正交频移键控)方案相比,具有更好的误码率性能。     

大气激光通信系统偏振移位键控调制技术

为了实现自由空间高速激光通信,对基于偏振移位键控的激光通信调制和解调技术进行了研究。介绍了一种基于PolSK的调制与差分解调方法,对实现大气信道中高速激光通信的调制与解调方法进行了研究,并通过理论推导及计算机仿真验证了其可行性。仿真研究结果表明:虽然大气信道对激光的传输特性有一定的影响,但利用以左右旋圆偏振光调制为基础的偏振态移位键控方法实现数据调制传输,并采用差分探测解调技术,可以实现传输速率为2.5 Gb/s、传输距离为20 km的低误码率数据传输。基本满足了空间激光通信系统的稳定可靠性、简便易实现、抗干扰能力强等要求。     

Novel multi-band DFT-spread OFDM-PON systems based on intensity modulation and direct detection for cloud computing

Passive optical network (PON) has become a preferable access technique for cloud computing due to its elastic bandwidth capacity and transmission stability. In particular, the orthogonal frequency division multiplexing PON based on intensity modulation and direct detection (IM/DD OFDM-PON) has gained extensive attention since it is a cost- and spectral-efficient system, while for the traditional IM/DD OFDM-PON, the use of OFDM could lead to the high peak-to-average power ratio (PAPR), and it is impossible to satisfy the different QoS degrees required by ONUs under a cloud environment. Thus in this paper, we design a novel multi-band discrete Fourier transform (DFT)-spread IM/DD OFDM-PON. The DFT-spread is utilized to reduce the PAPR; meanwhile, a multi-band power allocation and bit loading are achieved to satisfy the different degrees of QoS requirement owned by ONUs. The simulation results show that our system has the better performance of PAPR reduction compared with the traditional IM/DD OFDM-PON; meanwhile, the different QoS degrees of all ONUs are guaranteed.     

Alamouti-type space-time coding for free-space optical communication with direct detection

A modification of the Alamouti code originally proposed for RF wireless applications is described that allows it to be applied in scenarios such as free-space optical communication with direct detection where unipolar modulations like pulse-position modulation and on-off keying are traditionally used to convey the information. The modification of the code and associated decision metric is such as to maintain all of the desirable properties of the original scheme.