Multicarrier channels with non-identical subcarrier fading distributions-analysis and adaptation

In this letter, the subcarrier fading distribution of multicarrier modulation (MCM) systems is derived based on channel-impulse response (CIR) information. Frequency-selective channels with arbitrary Rician-Rayleigh fading paths and inter-path correlations are considered. It is discovered that certain MCM channels experience different fading severity among the subcarriers. Motivated by this observation, a novel bit-loading cum power-control scheme that can achieve better spectral and power efficiency by adapting the subcarrier modulation parameters based on the long-term subcarrier fading statistics, instead of instantaneous channel state information, is proposed and studied.     

Performance analysis of multicarrier code selective CDMA system with frequency repetition

In this paper, we present a new Multi-Carrier Code-selective Code Division Multiple Access System (MC CS-CDMA) with frequency repetition. The code selection process enables the proposed scheme to decrease the number of subcarriers for the same transmission data rate and total bandwidth as conventional MC DS-CDMA. The remaining bandwidth can be used for frequency repetition in order to achieve frequency diversity gain. Our results show that by maintaining a constant data rate, total bandwidth and PAPR, the proposed MC CS-CDMA system achieves a much greater performance improvement than conventional MC DS-CDMA.     

Orthogonal multi-carrier CDMA system using a concatenatedorthogonal/PN spreading scheme

A new communication scheme combining both MC modulation and DS-CDMA with a concatenated orthogonal/PN spreading scheme is proposed. This scheme incorporates the advantages of both DS-CDMA with a concatenated scheme, and an MC modulation technique to combat the effect of a multipath fading channel. It is shown that the proposed system outperforms the MC-CDMA system with a conventional PN sequence     

Capacity analysis of an uplink synchronized multicarrier DS-CDMAsystem

An uplink synchronous transmission scheme has been proposed for DS-CDMA systems to increase the uplink capacity through transmission timing control and a proper code usage. Since the scheme suppresses the interference along the first paths of other users, it can achieve a significant capacity increase when combined with a multicarrier (MC) technique. This article mathematically compares the proposed uplink synchronized MC DS-CDMA system with conventional DS-CDMA and MC DS-CDMA systems in terms of the maximum number of users     

多小区5G认知无线电网络能量有效资源优化

为提高5G通信系统中能量利用效率,本文提出一种资源配置算法来解决多小区5G认知无线电网络中资源配置问题。针对需要优化的载波分配变量和功率变量,该算法采用交替优化的方式分别对上述变量进行优化。对于载波分配,所提算法依据最大化信噪比原则来分配载波;对于功率分配,本文将其转变为另外一个等效问题,然后利用连续凸近似方法求解。由于传统正交频分复用调制（OFDM）具有严重的频谱泄露,其他几种具有较低频谱泄露特性的5G候选调制方式,例如滤波器组多载波调制（FBMC）、通用滤波多载波调制（UFMC）、广义频分复用调制（GFDM）等,也被分析比较。仿真结果表明本文所提算法相比干扰受限算法具有更高的能量效率,并且证明具有较低频谱泄露的调制方式能取得更高的能量效率。      

An efficient radio resource management strategy for adaptive OFDM cellular systems

This paper presents an efficient Radio Resource Management （RRM） strategy for adaptive Orthogonal Frequency Division Multiplexing （OFDM） cellular systems. In the proposed strategy, only those users who have the same distance from their base stations can reuse a same subcarrier. This can guarantee the received Carrier-to-Interference ratio （C/I） of each subcarrier to be acceptable as required by system planning. Then by employing different modulation scheme on each subcarrier according to its received C/I, system spectral efficiency can be gracefully increased. Analytical and simulation results show that the spectral efficiency is improved by 40% without sacrificing the Bit Error Rate （BER） performance and call blocking probability and system capacity of the proposed strategy is better than conventional systems.     

Slow frequency-hopping multicarrier DS-CDMA for transmission overNakagami multipath fading channels

A novel multiple access scheme based on slow frequency hopping multicarrier direct-sequence code division multiple access (SFH/MC DS-CDMA) is proposed and investigated, which can be rendered compatible with the existing second-generation narrowband CDMA and third-generation wideband CDMA systems. The frequency hopping patterns are controlled by a set of constant-weight codes. Consequently, multirate communications can be implemented by selecting the corresponding sets of constant-weight codes having the required weights controlling the SFH patterns invoked. Two FH schemes, namely random and uniform FH, are considered and their advantages as well as disadvantages are investigated. We assume that the system operates in a multipath fading environment and a RAKE receiver structure with maximum ratio combining (MRC) is used for demodulation. The system's performance is evaluated over the range of multipath Nakagami (1960) fading channels, under the assumption that the receiver has all explicit knowledge of the associated frequency-hopping (FH) patterns invoked. Furthermore, the performance of the SFH/MC DS-CDMA system is compared to that of the conventional single-carrier (SC) DS-CDMA system and that of the conventional MC DS-CDMA system, under the assumptions of constant system bandwidth and of constant transmitted signal power     

排列模式索引调制正交频分复用系统

多模索引调制正交频分复用系统(MM-OFDM-IM)在索引调制正交频分复用系统的基础上采用不同星座集对系统中的全部子载波进行索引调制,能有效地提高系统的子载波利用率和频谱效率。但全部子载波的利用影响了系统的子载波间抗干扰能力,导致误码率性能下降。针对这一问题,该文提出排列模式索引调制正交频分复用系统(PM-OFDM-IM)。该系统在MM-OFDM-IM的基础上重新引入静默子载波,既能保证系统较高的频谱效率,又能提高系统的误码率性能。同时该文提出一种基于幅值相移键控的分类映射模式,即按半径大小排列的星座集分类模式(PCC-R),该模式能够良好结合系统传输的额外信息。最后仿真结果验证,该系统能够更优地均衡系统的频谱效率和误码率性能,且所提分类映射方案可以达到更优的系统性能。     

MC-CDMA与DS-CDMA的性能比较研究

在分析传统DS-CDMA优缺点的基础上,介绍了一种新的具有高频谱效率和适合于高速数据传输的多载波CDMA(MC-CDMA)技术方案。阐明了MC-CDMA的结构和信号形式,进而对其优缺点作出了归纳。仿真结果显示,由于其内在的频率分集性能和克服多径时延的能力,MC-CDMA可以表现出比DS-CDMA更好的误码率性能。     

Asynchronous Layered Modulation for High Spectral Efficiency Transmission with Lower Sensitivity to Phase Errors

In this paper, an asynchronous double layered modulation scheme is proposed to achieve high spectral efficiency transmission but has lower sensitivity to phase errors. By intentionally introducing a delay offset to the transmitted signals at each layer, the asynchronous double layered format can use lower level quadrature amplitude modulation (QAM) to achieve the same spectral efficiency as the conventional high level QAM modulation. The error probability performance of the asynchronous double layered format is analyzed in the presence of phase errors and the symbol error rate and the bit error rate are derived in the closed-form expression. Both the theoretical analysis and the simulation results show that the asynchronous layered format can achieve the same spectral efficiency as the conventional high level QAM modulation while has lower sensitivity to the phase errors.     

Performance of broadband multicarrier DS-CDMA using space-time spreading-assisted transmit diversity

In this contribution multicarrier direct-sequence code-division multiple-access (MC DS-CDMA) using space-time spreading (STS)-assisted transmit diversity is investigated in the context of broadband communications over frequency-selective Rayleigh-fading channels. We consider the issue of parameter design for the sake of achieving high-efficiency communications in various dispersive environments. Furthermore, in contrast to conventional MC DS-CDMA schemes employing time (T)-domain spreading only, in this contribution we also investigate broadband MC DS-CDMA schemes employing both T-domain and frequency (F)-domain spreading, i.e., employing TF-domain spreading. The bit-error rate (BER) performance of STS-assisted broadband MC DS-CDMA is investigated for downlink transmissions associated with the correlation based single-user detector and the decorrelating multiuser detector. Our study demonstrated that when appropriately selecting the system parameters, broadband MC DS-CDMA using STS-assisted transmit diversity constitutes a promising downlink transmission scheme. This scheme is capable of supporting ubiquitous communications over diverse communication environments without BER performance degradation.     

新型副载波调制EDFA远程在线监控技术的原理论证

从理论和实验上论证了一种用于掺铒光纤放大器 (EDFA)远程在线监控和判断级连EDFA系统级间断点位置的技术方案。该方案利用频移键控 频分复用 (FSK FDM)技术进行声频副载波调制 ,通过光强度调制实现远程在线EDFA监控信息随主信号的传输。实验测得在副载波调制度为 3 %和 15 %时 ,10Gbit s波分复用 (WDM)光传输系统的功率代价分别为 0 16dB和 0 86dB。采用锁相技术 ,成功进行了 3 %调制度的监控信息解调。说明该方案可以实现对 5级EDFA系统的监控     

WHT-based composite motion compensated NTSC interframe directcoding

The motion compensated interframe differential pulse code modulation (DPCM) and discrete cosine transform (DCT) hybrid (MC DCT) coding was nominated as a standard scheme for component TV signals by ISO and ITU-R. However, in cases where an NTSC composite TV signal is used such as the United States and Japan, applying the MC DCT scheme with its luminance/chrominance separating and composing process causes unavoidable quality degradation. The reason for this additional process required for MC DCT is that a composite TV signal presents a “color subcarrier phase shift problem” in which the color subcarrier phase varies between a coding block and reference block according to the motion vector. In this paper, we propose a Walsh Hadamard transform (WHT)-based composite motion compensated NTSC interframe direct coding scheme. In this scheme, phase shifts of a color subcarrier and modulated chrominance components between a coding block and reference block can be effectively compensated by a simple process of coefficient permutation and polarity changes of several pairs of WHT coefficients to which 100% of the subcarrier energy and most of the modulated chrominance component's energy are packed. In the motion compensated DCT scheme, however, the energy of the color subcarrier and modulated chrominance components are spread over too many coefficients and a pair-based coefficient handling rule is not given to solve this problem. This paper demonstrates that the proposed scheme provides higher coding performance for a composite NTSC signal than does the motion compensated DCT scheme with its luminance/chrominance separating and composing process     

A comparison of telemetry signals in the presence and absence of asubcarrier

The performance of deep-space telemetry signals that employ a residual carrier modulation technique is compared in the presence and absence of a subcarrier. When the subcarrier is present, the performance for the resulting pulse-coded modulation/phase-shift keyed/phase-modulated (PCM/PSK/PM) scheme is evaluated for both sine-wave and square-wave subcarriers and non-return-to zero (NRZ) data. When the subcarrier is absent, the performance for the resulting PCM/PM technique is evaluated for both the NRZ and the bi-phase data format. The comparison is based on telemetry performance as well as bandwidth efficiency. The first criterion is characterized in terms of the symbol error rate (SER) as a function of symbol SNR, loop bandwidth-to-data rate ratio, and modulation index. The bandwidth efficiency is characterized by the occupancy factor. The results of both the analysis and measurements show that when the interference-to-carrier ratio (ICR) is less than -20 dB, the performance degradation in the absence of a subcarrier is negligible. Various combinations of loop bandwidth-to-data rate ratios and modulation indices that achieve this performance are derived and listed. Bandwidth occupancy comparison indicates that PCM/PM/NRZ is the most efficient in this regard. Therefore, by eliminating the subcarrier and using the PCM/PM/NRZ scheme, many advantages can be realized without any sacrifice in performance     

Performance of generalized multicarrier DS-CDMA over Nakagami-mfading channels

A class of generalized multicarrier direct sequence code-division multiple-access (MC DS-CDMA) schemes is defined and its performance is considered over multipath Nakagami-m fading channels. The spacing between two adjacent subcarriers of the generalized MC DS-CDMA is a variable, allowing us to gain insight into the effects of the spacing on the bit error rate (BER) performance of MC DS-CDMA systems. This generalized MC DS-CDMA scheme includes the subclasses of multitone DS-CDMA and orthogonal MC DS-CDMA as special cases. We present a unified analytical framework for determining the exact average BER of the generalized MC DS-CDMA system over generalized multipath Nakagami-m (1960) fading channels. The optimum spacing of the MC DS-CDMA system required for achieving the minimum BER is investigated and the BER performance of the system having optimum spacing is evaluated. The resultant BER is compared with that of both multitone DS-CDMA and orthogonal MC DS-CDMA     

Joint Opportunistic Spectrum Sharing and Dynamic Full Frequency Reuse in OFDMA Cellular Relay Networks

This paper considers the problem of spectrum sharing in orthogonal frequency division multiple access cellular relay networks. Firstly, a novel dynamic full frequency reuse scheme is proposed to improve the spectral efficiency. Different from the conventional full frequency reuse scheme which only allows the base station (BS) reusing the subcarriers in the specific regions, an improved full frequency reuse scheme is proposed to allow the BS reusing all the subcarriers in the whole BS coverage region to exploit additional multiuser diversity gain. In order to dynamically reuse the frequency resource among the BS and relay stations (RSs) to further improve the spectral efficiency, the adaptive subcarrier scheduling is introduced into the improved full frequency reuse scheme to obtain more multi-user diversity gain, which forms the proposed novel dynamic full frequency reuse scheme. Secondly, in order to further increase the system throughput, the opportunistic spectrum sharing scheme is introduced to allow the RSs selectively reusing the subcarriers among each other, which joint with the proposed dynamic full frequency reuse scheme to intelligently allocates the subcarriers originally reused by the BS and a RS to another suitable RS which can best improve the system performance after considering the additional interference. Thirdly, in order to select The optimal reusing combination scheme of BS and RSs to exploit more potential system performance, a heuristic approach based on genetic algorithm is proposed to search the optimal BS and RSs combination to opportunistically share the frequency resource. Simulation results show that the proposed dynamic full frequency reuse scheme can obtain high spectral efficiency, fine fairness and low outage probability compared to the conventional full frequency reuse scheme. Furthermore, the system performance can be improved when considering the opportunistic spectrum sharing among RSs. Finally, after adopting the genetic algorithm, the system performance can be greatly improved by the frequency reusing among the optimal BS and RSs combination.     

Spectral efficiency of direct-sequence code-division multiple-access in cellular mobile radio

In this paper, the spectral efficiency achieved by a direct-sequence code-division multiple-access (DS-CDMA) system operating in a cellular mobile radio environment is discussed. In contrast to previous works, here, spectral efficiency is examined in terms of channel capacity per user, estimated in an average sense, and the system's inherent diversity potential is considered. The analysis covers only the forward link, assuming a static model of operation for the considered DS-CDMA system. In addition, it is shown that the application of a power control scheme leads to spectral efficiency enhancement due to cochannel interference reduction. Hence, the derived expressions provide a means for quantitative evaluation of cellular DS-CDMA spectral efficiency with respect to multiple-access and cochannel interference. © 1997 John Wiley & Sons, Ltd.     

Quality of Service Aware Inter Carrier Interference Mitigation and Antenna Selection Schemes for Beyond 4G Systems

Future broadband wireless communication systems demand high quality of service (QoS) for anytime anywhere multimedia applications. The standards which use orthogonal frequency division multiplexing (OFDM) coupled with multi input multi output (MIMO) are expected to rule the future wireless world. Time selective nature of the channel introduces inter carrier interference (ICI), which is the major performance limiting parameter in OFDM based systems. ICI causes loss in spectral efficiency and results in poor bit error rate (BER) performance, affecting the QoS of MIMO-OFDM systems. The conventional single input single output (SISO)-OFDM-flexible subcarrier spacing (FSS) system offers better performance than the fixed subcarrier spacing systems in terms of ICI mitigation. But BER and spectral efficiency performance of SISO-OFDM-FSS is not good enough to satisfy the requirements of future wireless broadband services. To improve the BER performance, SISO-OFDM system is replaced by space frequency block coded (SFBC)-OFDM system, which adds spatial and frequency diversity benefits to the conventional system. More number of antennas in the MIMO scheme increases the hardware cost, computational complexity and percentage of overhead. In the present study, to improve the spectral efficiency and to reduce the complexity and cost, optimal transmit antenna selection (OTAS) is combined with the SFBC-OFDM-FSS scheme. The simulation results prove that the proposed SFBC-OFDM-FSS-OTAS scheme offers better QoS than the conventional SISO-OFDM-FSS scheme.     

采用自适应调制的空间复用系统研究

针对采用V-BLAST检测算法的空间复用系统,提出新的自适应调制方案.传统自适应调制依据的是接收天线处检测到的信噪比,而提出的自适应调制根据的是V-BLAST检测算法中多次串行迭代检测后检测该数据流时的实际比特信噪比,由于多次迭代后未检信号的信噪比会升高,可以在满足目标误比特率要求的前提下尽可能采用较高的调制制式来提高频谱效率.仿真结果表明,改进型自适应调制算法对应的频谱效率明显优于传统自适应调制算法.     

Spectrally shaped generalized multitone direct sequence spread spectrum

In this paper, a new modulation scheme that is called spectrally shaped generalized multitone direct sequence spread spectrum (SSG-MT-DS-SS) is proposed. This scheme enables moderate shaping of the transmitted spectrum without the use of spectral-shaping filters; instead, the spectrum is shaped by appropriate selection of the parameters of each subcarrier. These parameters are amplitude, data rate, processing gain, and the frequency separation between adjacent subcarriers. Since these parameters are selectable, this scheme is a completely generalized MT-DS-SS approach. Analysis and simulation results show that by properly choosing these parameters, the level of the spectral sidelobes can be reduced, while slightly changing the width of the mainlobe and simultaneously obtaining a good error-probability performance, on both additive white Gaussian noise and dispersive fading channels. For even a small number of subcarriers (e.g., 3-5), spectral sidelobes can be reduced by 3-6 dB from those of the conventional MT-DS-SS spectrum, with little or no degradation in error-probability performance. For larger numbers of subcarriers, additional sidelobe reductions are attainable. In addition, the SSG-MT-DS-SS system has a smaller peak-to-average power ratio than the conventional MT-DS-SS when the amplitudes of each subcarrier are not identical.