Orthogonal Codes-Based Dynamic Spectrum Access in Cognitive Radio Networks

Dynamic spectrum access(DSA) in cognitive radio(CR) networks became a challenging research area recently. In CR technology, the DSA between primary users(PUs) and secondary users(SUs) simultaneously can be achieved without degrading the performance of the PUs by SUs interference. This can be achieved by donating incentive power to the PUs in order to compensate the interference caused by the SUs. Consequently, PUs allow SUs to share the spectrum. In this paper, orthogonal codes-based dynamic spectrum access(OC-DSA) technique is proposed. OC-DSA technique employs orthogonality between PUs and SUs transmitted data symbols in addition to the incentive power donation. Compared to other techniques, the proposed technique uses a simple encoder at the SU network for the same PU network infrastructure. By applying orthogonal codes, the interference caused by SUs is canceled and hence the donated power to incentivize the PUs is reduced. Also, the SU packet rate is increased significantly. The simulation results show that the proposed technique provides effective improvements over other existing techniques in the signal strength and the bit error rate performance of both the PU network and the SU network at the receiver side. Moreover, the proposed technique requires less donated power to incentivize the PU and has higher packet rate.

Application of maximum rank distance codes in designing of STBC-OFDM system for next-generation wireless communications

Space-Time Block Coded(STBC)Orthogonal Frequency Division Multiplexing(OFDM)satisfies higher data-rate requirements while maintaining signal quality in a multipath fading channel.However,conventional STBCs,including Orthogonal STBCs(OSTBCs),Non-Orthogonal(NOSTBCs),and Quasi-Orthogonal STBCs(QOSTBCs),do not provide both maximal diversity order and unity code rate simultaneously for more than two transmit antennas.This paper targets this problem and applies Maximum Rank Distance(MRD)codes in designing STBCOFDM systems.By following the direct-matrix construction method,we can construct binary extended finite field MRD-STBCs for any number of transmitting antennas.Work uses MRD-STBCs built over Phase-Shift Keying(PSK)modulation to develop an MRD-based STBC-OFDM system.The MRD-based STBC-OFDM system sacrifices minor error performance compared to traditional OSTBC-OFDM but shows improved results against NOSTBC and QOSTBC-OFDM.It also provides 25%higher data-rates than OSTBC-OFDM in configurations that use more than two transmit antennas.The tradeoffs are minor increases in computational complexity and processing delays.

Linear Dispersion Orthogonal Space-Time Block Codes

A new architecture of space-time codes as a combination of orthogonal space-time block codes （OSTBC） and linear dispersion codes （LDC） is proposed in order to improve the bit error rate（BER） performance of OSTBC.The scheme proposed is named linear dispersion orthogonal space-time block codes （LDOSTBC）.In LDOSTBC scheme,firstly,the data is coded into LDC codewords.Then,the coded LDC substreams are coded into OSTBC codewords again.The decoding algorithm of LDOSTBC combines linear decoding of OSTBC and ML decoding or suboptimum detection algorithms of LDC.Compared with OSTBC scheme when the rate of LDC is MtR,the performance of LDOSTBC scheme can be improved without decreasing the data rate,where Mt is the number of transmit antennas and R is the spectral efficiency of the modulation constellation.If some rate penalty is allowed,when the rate of LDC is less than MtR the performance of LDOSTBC can be improved further.

Polar codes based OFDM-PLC systems in the presence of impulsive noise

Power line communication(PLC)has the potential to become the preferred technique for providing broadband communication to homes and offices with advantage of eliminating the need for new wiring infrastructure and reducing the cost.But it suffers from the impulsive noise because it introduces significant time variance into the power line channel.In this paper,a polar codes based orthogonal frequency division multiplexing(OFDM)PLC system is proposed to deal with the impulsive noise and thereby improve the transmission performance.Firstly,the impulsive noise is modelled with a multi-damped sine function by analyzing the time behavior of impulse events.Then the polar codes are used to combat the impulsive noise of PLC channel,and a low complexity bit-flipping decoding method based on CRC-aided successive cancellation list(CA-SCL)decoding algorithm is proposed.Simulations evaluate the proposed decoding algorithm and the results validate the suggested polar codes based OFDM-PLC scheme which can improve the BER performance of PLC with impulsive interference.

A New Generalized Complex Orthogonal Space-Time Block Codes

Recent research challenges in the wireless communication include the usage of diversity and efficient coding to improve data transmission quality and spectral efficiency. Space diversity uses multiple transmitting and/or receiving antennas to create independent fading channels without penalty in bandwidth efficiency. Space-time block coding is an encoding scheme for communication over Rayleigh fading channels using multiple transmitting antennas. Space-time block codes from complex orthogonal designs exist only for two transmitting antennas. This paper generalizes a new complex orthogonal space-time block code for four transmitting antennas, whose decoding complexity is very low. Simulations show that the generalized complex orthogonal space-time block code has low bit error rate, full rate and possibly large diversity.

OCDMA/OCDMA Overloading Scheme for Cellular DS-CDMA Using Orthogonal Gold Codes and Complex Scrambling

Overloading is a method to extend capacity limitation of multiple access techniques. The system becomes overloaded, when the number of users exceeds the signal dimensions. One of the efficient schemes to overload a CDMA system is to use two sets of orthogonal signal waveforms (O/O). In this paper, the BER performance of a new overloading scheme using scrambled orthogonal Gold code (OG/OG) sets is evaluated with soft decision interference cancellation (SDIC) receiver. When complex scrambling is not used, it is shown that OG/OG scheme provides 25% (16 extra users) channel overloading for synchronous DS-CDMA system in an AWGN channel, with an SNR degradation of about 0.35 dB as compared to single user bound at a BER of 1e-5. We have evaluated the overloading performance, when two set are scrambled with set specific deterministic or random complex scrambling sequence. It is shown that the amount of overloading increases significantly from 25% to 63% (40 extra users) by using random complex scrambling for N=64. For deterministic (periodic) scrambling, the overloading percentage increases considerably to 78. On a Rayleigh fading channel, an overloading of 40% is obtained without scrambling at a BER of 5e-4 with near single user performance. With complex scrambling overloading % increases considerably to 100%.

A construction of authentication codes with arbitration based on orthogonal spaces

In this paper we give a new construction of authentication codes with arbitration using orthogonal spaces. Some parameters and the probabilities of successful attacks are computed.

Space-time Block Codes Based on Quasi-Orthogonal Designs

A new space-time block codes based on quasi-orthogonal designs are put forward. First the channel model is formulated. Then the connection between orthogonal /quasi-orthogonal designs and space-time block codes is explored. Finally we make simulations for the transmission of 4 bits/s/Hz and 6 bits/s/Hz using eight transmit antennas using the rate 3/4 quasi-orthogonal space-time block code and the rate 1/2 full-diversity orthogonal space-time block code. Simulation results show that full transmission rate is more important for very low signal noise ratio (SNR) and high bit error probability (BEP), while full diversity is more important for very high SNR and low BEP.

A NEW ML DETECTION ALGORITHM FOR ORTHOGONAL MULTICODE SYSTEM IN NAKAGAMI FADING CHANNEL

Based on the Maximum-Likelihood (ML) criterion, this paper proposes a novel noncoherent detection algorithm for Orthogonal Multicode (OM) system in Nakagami fading channel. Some theoretical analysis and simulation results are presented. It is shown that the proposed ML algorithm is at least 0.7 dB better than the conventional Matched-Filter (MF) algorithm for uncoded systems, in both non-fading and fading channels. For the consideration of practical application, it is further simplified in complexity. Compared with the original ML algorithm, the simplified ML algorithm can provide significant reduction in complexity with small degradation in performance.

EXACT ERROR PROBABILITY OF ORTHOGONAL SPACE-TIME BLOCK CODES OVER FLAT FADING CHANNELS

Space time block coding is a modulation scheme recently discovered for the transmit an- tenna diversity to combat the effects of wireless fading channels. Using the equivalent Single-Input Single-Output (SISO) model, this paper presents closed-form expressions for the exact Symbol Error Rate (SER) and Bit Error Rate (BER) of Orthogonal Space-Time Block Codes (OSTBCs) with M-ary Phase-Shift Keying (MPSK) and M-ary Quadrature Amplitude Modulation (MQAM) over flat un- correlated Nakagami-m and Ricean fading channels.

Performance analysis and code recognition for dual N-ary orthogonal hybrid modulation systems

A dual N-ary orthogonal hybrid modulation system is introduced in this paper, which can increase the data rate greatly compared with conventional N-ary orthogonal spread spectrum system, so it can be used for high rate data communication. Then, three code recognition algorithms are presented for dual N-ary orthogonal hybrid modulation system and the analytic bit error rate （BER） performance of the system in additive white Gaussian noise （AWGN） and fiat Rayleigh fading channel is derived. Finally, the computer simulation of the system with three code recognition algorithms is performed, which shows that the simplified maximum a posteriori （MAP） algorithm is the best for the system with a compromise between the performance and the complexity.

Frameworks of Non-Orthogonal Multiple Access Techniques in Cognitive Radio Communication Systems

Recently,the increasing demand of radio spectrum for the next generation communication systems due to the explosive growth of applications appetite for bandwidths has led to the problem of spectrum scarcity.The potential approaches among the proposed solutions to resolve this issue are well explored cognitive radio(CR)technology and recently introduced non-orthogonal multiple access(NOMA)techniques.Both the techniques are employed for efficient spectrum utilization and assure the significant improvement in the spectral efficiency.Further,the significant improvement in spectral efficiency can be achieved by combining both the techniques.Since the CR is well-explored technique as compared to that of the NOMA in the field of communication,therefore it is worth and wise to implement this technique over the CR.In this article,we have presented the frameworks of NOMA implementation over CR as well as the feasibility of proposed frameworks.Further,the differences between proposed CR-NOMA and conventional CR frameworks are discussed.Finally,the potential issues regarding the implementation of CR-NOMA are explored.

Analysis of Rate One Quasi-Orthogonal Space-Time Block Coding over Rayleigh Fading Channel

Full-rate is very important in any data transmission coding. For transmitting data at low bit rate than full-rate code, higher modulation scheme is required. But it is impossible to design full rate orthogonal designs with complex constellation for more than two transmit antennas. Only Alamouti code provides full-rate for two transmit antennas. In this paper, Bit Error Rate (BER) is calculated for Quasi-Orthogonal Space-time Block Coding (QOSTBC). Here we work with Rayleigh fading channel. We consider the codes which decodes pairs of symbols instead of simple separate decoding like Orthogonal Space-Time Block Coding. In Quasi-Orthogonal Space-time Block Code full-rate is achieved but full-diversity is sacrificed. Diversity is the most important techniques for providing reliable communication over fading channels. One of the diversity techniques that uses multiple transmit and/or receive antennas is space diversity. Multiple antenna technique provides a space diversity to struggle with the fading without necessarily sacrificing bandwidth resources, so the excellent solutions of removing the fading of the channel for broadband wireless communications is using space diversity. Then, with the constellation rotation of the symbol, rotated version of Quasi-Orthogonal Space-Time Block Code is generated. It provides full diversity. We simulate BER for QOSTBC, rotated QOSTBC, orthogonal STBC and for uncoded system. The simulation result shows that QOSTBC and rotated QOSTBC perform better than other systems. It shows that QOSTBC provides a full transmission rate but that rotated QOSTBC provides the full rate with the full diversity.

An improved method of generating the self-balanced chaotic spread-spectrum code

An improved method of generating the self-balanced chaotic spread-spectrum code is presented. The chaotic-map pseudorandom sequence is used as the generated source. After a series of processing two-valued quantization, inversion, all upside down, radix-S block upside down and shift combination, the proposed code is achieved. Theory analysis and simulation performance of the improved code are illustrated. And the results indicate that the suggested method gains a better performance than the traditional one by reasonable choices of the initial value and the S parameter in the im- proved method. Meanwhile the chaotic sequence＇ s characteristic of large addresses is inherited when the chaotic-map is used as the source. This advantage makes this improved code very suitable for the multiple access application in communication system.

A Non-orthogonal STFC-OFDM on Frequency-Selective Fading Channels

A new non-orthogonal space-time-frequency code (STFC) was proposed. In conjunction with orthogonal frequency-division multiplexing (OFDM), it is appropriate for the application on frequency-selective fading channels. On the basis of the existing non-orthogonal STC, frequency diversity is studied and a new non-orthogonal STFC is further designed. Monte-Carlo simulations show that the non-orthogonal STFC-OFDM has the advantage of large diversity order, high bandwidth efficiency and better BER performance when compared with the orthogonal STC/STFC-OFDM and non-orthogonal STC-OFDM systems.

OPTIMAL ANTENNA SUBSET SELECTION AND BLIND DETECTION APPROACH APPLIED TO ORTHOGONAL SPACE-TIME BLOCK CODING

An approach combining optimal antenna subset selection with blind detection scheme for Orthogonal Space-Time Block Coding (OSTBC) is proposed in this paper. The optimal antenna sub- set selection is taken into account at transmitter and/or receiver sides, which chooses the optimal an- tennas to increase the diversity order of OSTBC and improve further its performance. In order to en- hance the robustness of the detection used in the conventional OSTBC scheme, a blind detection scheme based on Independent Component Analysis (ICA) is exploited which can directly extract transmitted signals without channel estimation. Performance analysis shows that the proposed ap- proach can achieve the full diversity and the flexibility of system design by using the antenna selec-tion and the ICA based blind detection schemes.

Security in Multicast Over α-μ Fading Channels with Orthogonal Frequency Division Multiplexing

The orthogonal space-frequency block coding (OSFBC) with orthogonal frequency division multiplexing (OFDM) system reduces complexity in the receiver which improves the system performance significantly. Motivated by these advantages of OSFBC-OFDM system, this paper considers a secure wireless multicasting scenario through multiple-input multiple-output (MIMO) OFDM system employing OSFBC over frequency selective α-μ fading channels. The authors are interested to protect the desired signals from eavesdropping considering the impact of the number of multicast users and eavesdroppers, and the fading parameters α and μ. A mathematical model has been developed based on the closed-form analytical expressions of the probability of non-zero secrecy multicast capacity (PNSMC) and the secure outage probability for multi-casting (SOPM) to ensure the security in the presence of multiple eaves-droppers. The results show that the security in MIMO OSFBC OFDM system over α-μ fading is more sensitive to the magnitude of α and μ and this effect increases in the high signal-to-noise ratio (SNR) region of the main channel.

多基站无线非正交多址接入的平滑视频流传输算法

视频服务需求的快速增长对于视频流畅播放提出了巨大挑战,从用户体验角度分析,视频播放中的卡顿时间可能是最重要指标之一。随着5G网络技术的发展,非正交多址接入(NOMA)技术被重点关注,NOMA技术具有叠加编码和连续干扰消除2个特点,根据这2个特点实现数据的并行传输。利用NOMA技术的并行传输能力来提高基站为用户提供视频的实时性。在用户需求视频名称和视频分辨率给定的情况下,通过联合基站-用户配对方式和基站功率分配来降低视频播放时的卡顿时间。通过对问题进行建模,并提出1个两步启发式算法对问题进行求解,第1步为确定基站与用户的配对方式,第2步为分配基站的发射功率。实验结果表明,基于NOMA的传输调度方案与传统的传输调度方案相比,用户需求的平均卡顿时间有明显的下降,相对于在不采用NOMA机制时,在2-SIC接收机情况下,用户平均卡顿时间减少了55.56%。

烟标二维码等级影响因素及其质量控制研究

目的解决烟草包装上二维码质量控制的问题,为二维码的质量控制提供技术支持。方法设计正交实验,利用方差分析法确定影响二维码质量等级的关键生产参数,并使用多元线性回归算法建模二维码质量。结果发现在生产中二维码的符号反差、固有图形污损、调制比的评级最不稳定,是质量控制的关键;不同基底表面能对墨滴扩散产生影响,建立了调制比和固有图形污损的质量预测模型。结论强调评级参数及其影响因素对质量控制的重要性,利用建模算法实现二维码质量控制,并指出质量预测模型对支持二维码的质量控制具有重要意义。

多接收子阵下特征波束的角度空间调制方法

基于波束赋形的波束切换空间调制算法,不仅可以提高频谱效率,还可以利用天线阵列增益提高能量效率。该文利用信道响应构造统计平均的协方差矩阵,构造正交特征向量作为阵列的加权矢量,形成相互独立的多个等效传输信道,利用波束赋形增益和分集增益提高无线通信的传输可靠性和传输能力。进一步采用天线子阵分组方法,克服信道相关性带来的不利影响。性能分析和仿真结果表明,特征波束角度空间调制方案可获得更多的波束组合数目,会明显改善译码性能和频谱效率。