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1.
The jamming robustness of frequency hopping (FH) systems with M-ary frequency shift keying (MFSK) modulation may be potentially neutralized by a follower partial-band jammer. In this paper, a maximum likelihood (ML)-based algorithm that uses a two-element array is proposed for joint follower jamming rejection and symbol detection in slow FH/MFSK systems over quasi-static flat Rayleigh fading channels. The algorithm is derived by treating both the received jamming components and the unknown data symbols as deterministic quantities to be jointly estimated in an integrated ML operation. In addition, an approximate expression for the symbol error rate (SER) of the proposed scheme is derived when BFSK signaling is employed in a jamming dominant scenario. Analytical and simulated results show that the proposed approach is able to remove jamming and outperform the conventional and sample matrix inversion (SMI)-based beam-formers in the presence of a follower partial-band jammer. 相似文献
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Both partial-band jamming and multi- tone jamming have severe effect on the acquisition of frequency-hopping (FH) signal in adverse environments. In this paper, an anti-jamming FH signal acquisition scheme based on cognitive correlation process is proposed to boost the robustness of acquisition. The main idea of this scheme is to utilize a priori knowledge of FH speed and FH pattern to distinguish jamming signal from received signal. Furthermore, theoretic analysis on detection probability and false probability is given to demonstrate the robust performance of the FH signal acquisition method compared with conventional acquisition scheme without any prior information on FH speed and pattern in adverse environments. 相似文献
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Miller L.E. Lee J.S. French R.H. Torrieri D.J. 《Communications, IEEE Transactions on》1992,40(1):160-170
An easily implemented matched filter scheme for acquiring hopping code synchronization of incoming frequency-hopping (FH) signals is analyzed, and its performance is evaluated for two types of jamming: partial-band noise jamming and partial-band multitone jamming. The system is designed to reduce jammer-induced false alarms. The system's matched filter output is compared to an adaptive threshold that is derived from a measurement of the number of acquisition channels being jammed. Example performance calculations are given for the frequency coverage of the jamming either fixed over the entire acquisition period or hopped, that is, changed for each acquisition pulse. It is shown that the jammer's optimum strategy (the worst case) is to maximize the false alarm probability without regard for the effect on detection probability, for both partial-band noise and multitone jamming. It is also shown that a significantly lower probability of false acquisition results from using an adaptive matched filter threshold, demonstrating that the strategy studied here is superior to conventional nonadaptive threshold schemes 相似文献
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The performance of a hybrid slow frequency hopped direct sequence multiple frequency shift keyed (SFH/DS MFSK) communication link in the presence of partial band multitone jamming is considered. The communication signal is characterized by a DS-spread MFSK signal bandwidth that may exceed the FH slot spacing, and the signal consists of multiple M-ary symbols per DS code period. An equation for the bit error rate (BER) is developed for the signal in the presence of multitone jamming. The equation is flexible enough to allow examination of optimization of jamming strategy. It is shown that the jamming strategy may be optimized by varying the number of tones, their placement, or both. It is shown that in the presence of optimized jamming, overlapping systems are more resistant to jamming than nonoverlapping systems with equal parameters (except for the number of FH slots). It is also demonstrated that, in some cases, the addition of DS spreading to an FH system, without increasing the total system bandwidth, can significantly improve the system's resistance to partial band multitone jamming 相似文献
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本文利用空时联合检测的方法,提出了在频率选择性信道下多天线发送的单载波频域均衡方案,它可以提供和一个发送天线多个接收天线单载波系统相同的分集增益,和单载波时域均衡相比具有低的复杂度。分析了信道估计误差对系统的影响,类似于基于迫零算法的线性均衡器的情形,在低信噪比下,信道估计误差对系统影响很大,给出了一种简单的克服方法。在不增加发射功率的情况下,使用信道编码可以进一步改善系统的性能。本方案的系统性能在6径典型城市信道模型下进行了评估,仿真的结果证明了本方案的有效性。 相似文献
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In this paper, MIMO OFDM–CDMA downlink scheme is proposed as a solution for improving performance of the OFDM–CDMA downlink system with pilot tone and threshold detection combining (optimum TDC). The new presented system with MIMO included uses space–time block coding applied to two, three and four transmit antennas and it has an arbitrary number of receive antennas. Bit error rate performance in the case of Ricean frequency selective fading is evaluated for the original system as well as for the one with MIMO included. For that reason an adequate simulation model is developed. The results show that the proposed system significantly outperforms the OFDM–CDMA downlink system with pilot tone and optimum TDC. 相似文献
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Athanasios D. Marousis Nikolaos D. Skentos Philip Constantinou 《Wireless Personal Communications》2011,59(4):713-739
In this work an enhanced semi-blind channel estimator is presented for multicarrier CDMA systems with multiple transmit and
receive antennas. The novel scheme is based on embedded pilots that are characterized as virtual users and their number is
determined in a dynamic fashion according to the propagation channel conditions. The superimposed code-multiplexed pilots
are used initially for channel estimation before the despreading operation, thus achieving per subcarrier estimation using
the known unique multi-layer pattern of the virtual users. Afterwards, the estimation is enhanced by using the despread pilots.
Furthermore, an iterative scheme is incorporated in channel estimation process minimizing the effect of multiuser interference
and operates either in interference cancellation, or in virtual user mode. The proposed architecture is evaluated for spatial
diversity systems (space- frequency block coded) with two transmit and up to four receive antennas operating in realistic
propagation channels for various modulation and coding schemes. The results demonstrate a significant performance improvement
especially as the channel is dominated by its time variant characteristics. The dynamic assignment of spreading codes in the
payload and the pilots offers to the system realistic flexibility and adaptivity in demanding channels achieving concurrently
maximization of the real overall system throughput, while maintaining low overhead and complexity burden. 相似文献
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Young Ju Kim Hwang Soo Lee 《Communications Letters, IEEE》2000,4(11):343-345
We present a generalized version of principal ratio combining (PRC), which is a near-optimum detection scheme for space-time codes in quasistatic flat fading environments. In Tarokh and Lo (1998), the performance penalty increases as the number of receive antennas increases. In the proposed scheme, receive antennas are optimally grouped by K, and the PRC detection method is applied to each group. This shows a flexible tradeoff between performance and decoding complexity by choosing the appropriate K 相似文献
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Belal A. Al-fuhaidi Hossam Eldin A. Hassan Moataz M. Salah 《Wireless Personal Communications》2014,74(2):439-456
Modern wireless communications require an efficient spectrum usage and high channel capacity and throughput. Multiple-input and multiple-output (MIMO), Linear equalizers, multi-user detection and multicarrier code-division multiple access (MC-CDMA) are possible solutions to achieve spectral efficiency, high channel capacity, eliminate multiple access interference (MAI), eliminate Inter symbol interference (ISI) and robustness against frequency selective fading. In this paper, we combine all these techniques and investigate BER performance. We propose a low complexity receiver structure for Single-input Multiple-output (SIMO) downlink MC-CDMA systems. It employs an interference cancellation scheme to suppress the interference caused by the multipath fading channel. Also, the proposed scheme is developed for MIMO MC-CDMA system. The performance analysis of Downlink MIMO MC-CDMA systems with V-BLAST over frequency selective fading channel is investigated under various number of transmit and receive antennas. The simulation results show proposed SIMO equalization with parallel interference cancellation scheme is effective in reducing the ISI and the MAI. It improves the performance significantly and the simulation results show that MIMO MC-CDMA with V-BLAST multi-user detection provides high data rate and the BER significant improvement. 相似文献
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分布式发射天线V-BLAST信号的排序干扰抵消检测 总被引:5,自引:1,他引:4
针对V-BLAST信号通过分布的发射天线进入信道,该文提出了一种由于发射天线地域上的分布性引起的各发射天线发射信号不同时到达接收天线的V-BLAST排序干扰抵消(Order Interference Cancellation, OIC)检测算法。计算机仿真显示,该算法适用于任意个数的接收天线,在较高信噪比(20dB)的条件下,性能优于直接迫零算法3dB以上。在相同信噪比条件下,分布发射天线V-BLAST的排序干扰抵消检测算法比集中发射天线V-BLAST的排序干扰抵消检测算法有着更好的性能。 相似文献
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In this paper, a transmit‐sense‐receive mode–based simultaneous transmit‐and‐receive cognitive antijamming (SCAJ) strategy is proposed to enhance spectrally efficient of airborne networks in congested electromagnetic spectrum environment. We explore the performance of spectrum sensing based on energy detection in SCAJ system. The tight close form expressions of jamming detection and false‐alarm probability are derived under different channels, the throughput of individual SCAJ system is analyzed, and SCAJ transceiver‐based airborne ad hoc network capacity is presented for air platform equipping with digital beamforming antennas. Simulation results show that proposed SCAJ technology can improve the antijamming capability and airborne ad hoc network capacity compared to the half‐duplex cognitive antijamming scheme. It is an effective approach to solve the problem of designing airborne networks arise from the limited availability of spectrum and the desire to provide much higher data rates. 相似文献
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This paper proposes a new MIMO based CDMA code acquisition scheme. The pilot codes consist of a number of short Gold code sequences which are transmitted in parallel using a group of transmit antennas. Reception diversity is performed by multiple receive antennas at the receiver. Three different acquisition detection techniques are proposed and compared. Corresponding threshold optimizations are investigated as well. Detection and false alarm probabilities are derived in closed form based on the outputs of non-coherent matched filters. The acquisition performance is evaluated in terms of mean acquisition time (MAT) in Rayleigh fading environment. It is shown that the proposed MIMO acquisition scheme exhibits a much better MAT performance than the conventional single-antenna acquisition scheme. The results reveal that multiple receive antennas can be utilized to significantly reduce the MAT at the expense of receiver complexity increase. On the other hand, increasing the number of transmit antennas makes the MAT performance more robust in the presence of strong interference. 相似文献
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Kyung Soo Woo Kyu In Lee Jong Ho Paik Kyung Won Park Won Young Yang Yong Soo Cho 《Broadcasting, IEEE Transactions on》2007,53(2):539-546
In this paper, we propose a differential space-frequency block code-orthogonal frequency division multiplexing (DSFBC-OFDM) scheme as a multiple-input multiple-output (MIMO) transmission technique for next generation broadcasting system. A linear decoding method for DSFBC, which performs comparably to the ML decoding method, is derived for the cases of two or four transmit antennas. A simple table lookup method is proposed to improve the efficiency of the encoding/decoding process of DSFBC for the case of non-constant modulus constellations. This not only reduces the computational load, but also removes the necessity of channel estimation. Also, synchronization techniques with a DSFBC-encoded phase reference symbol (PRS) are discussed. Finally, an MIMO channel model for the next generation broadcasting system is developed by extending the 3GPP MIMO model to fit broadcasting environments. The MIMO channel model is then used to compare BER performances of differential space block code schemes for various channel environments. Simulation results show that the DSFBC-16QAM scheme using either four transmit antennas with one receive antenna or two transmit antennas with two receive antennas achieves a performance gain of 12 dB, with a data rate twice faster than that of the conventional DQPSK scheme 相似文献
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扩跳频通信技术以其良好的抗干扰能力广泛地应用于现代军事与民用通信中,但其频谱效率不够高。因此本文给出了一种信息驱动扩跳频(MD-DS/FH)通信系统模型,即在发射机中的跳频图案不再由传统的跳频码发生器驱动,而由所传输的部分信息数据来代替,并且接收机釆用包络检测器对载波频率进行盲检测。本文推导了AWGN与Rayleigh衰落信道下系统的误比特率公式,给出了闭合表达式,并通过仿真验证了理论推导的正确性。理论分析与仿真结果表明,所给通信系统在提高扩跳频通信系统频谱效率的同时,也提高了系统的误比特率和抗阻塞噪声干扰性能。 相似文献
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For pt.1 see ibid., vol.COM-35, p.1329-41 (1987). A performance evaluation is presented for selective diversity with feedback for frequency-hopping M -ary frequency-shift-keyed systems operating over Rayleigh faded channels in the presence of partial-band noise and partial-band tone jamming. The behavior of uncoded and coded systems is studied. For coded systems, the performance is evaluated for hard-decision receivers without channel state information and soft-decision receivers with perfect jammer state information. The results demonstrate that the performance of uncoded FH/MFSK with selective diversity is unacceptable. However, this diversity technique can offer definite improvements for coded FH/MFSK systems. Specifically, the effectiveness of selective diversity signaling depends on the provision of a feedback channel between the transmitter and receiver to provide the transmitter with the fading gains of the independently faded channels. To obtain an improvement from the selective diversity signaling scheme described here, there must be multiple independently faded channels between the transmitter and receiver. If not, the performance of the selective diversity signaling scheme will be identical to the performance of FH/MFSK without diversity 相似文献