General Construction Method of Multilength Optical Orthogonal Codes With Arbitrary Cross-Correlation Constraint for OCDMA Multimedia Network

Optical orthogonal codes (OOCs) have application in OCDMA system because of their good correlation properties. In this paper, two correlation-detection methods, difference method and distance method, were studied. Calculate amount of these correlation-detection methods was analyzed. Constraint condition of optimal optical orthogonal codes was discussed. Besides, a construction method of optimal (n,w,1) optical orthogonal code was presented based on difference set. Optimal (n,w,1) optical orthogonal code which has 2 code words each set was constructed by this construction method. Codewords relativity simulation proved the validity of the method. This construction method has practicability because of codewords' good correlation properties and large capacity.

A construction algorithm of multiple length optical orthogonal codes (ML OOCs) based on difference set is presented for multi-rate OCDMA passive optical networks (PON). Difference set is first defined. The fundamental of the algorithm is based on the relationship between OOCs and difference sets. Simulations based on the algorithm are done. The results show that the construction algorithm can encode arbitrary multiple length OOCs with arbitrary parameters. So, it can be used in OCDMA passive optical network to construct optical orthogonal codes to supporting multi-rate service.

A (v, k, /spl lambda//sub a/, /spl lambda//sub c/) optical orthogonal code (OOC) C is a family of (0, 1)-sequences of length v and weight k satisfying the following two correlation properties: (1) /spl Sigma//sub 0/spl les/t/spl les/v-1/x/sub t/x/sub t+i//spl les//spl lambda//sub a/ for any x=(x/sub 0/,x/sub 1/,/spl middot//spl middot//spl middot/,x/sub v-1/)/spl isin/C and any integer i not equivalent 0 mod v; and (2) /spl Sigma//sub 0/spl les/t/spl les/v-1/x/sub t/y/sub t+i//spl les//spl lambda//sub b/ for any x=(x/sub 0/,x/sub 1/,/spl middot//spl middot//spl middot/, x/sub v-1/) /spl isin/ C, y=(y/sub 0/,y/sub 1/,/spl middot//spl middot//spl middot/,y/sub v-1/) /spl isin/C with x/spl ne/y, and any integer i, where the subscripts are taken modulo v. The study of optical orthogonal codes is motivated by an application in optical code-division multiple-access communication systems. In this paper, upper bounds on the size of an optical orthogonal code are discussed. Several new constructions for optimal optical orthogonal codes with weight k/spl ges/4 and correlation constraints /spl lambda//sub a/=/spl lambda//sub c/=1 are described by means of optimal cyclic packings. Many new infinite series of such optimal optical orthogonal codes are thus produced.

Variable-weight optical orthogonal code (OOC) was introduced by Yang for multimedia optical CDMA systems with multiple quality of service (QoS) requirements. In this paper, four general constructions for optimal cyclic packings and optimal variable-weight OOCs are presented. Many new infinite classes of optimal (v, W,1,Q)-OOCs are obtained. New infinite classes of optimal (v, W,1,Q)-OOCs for |W| ≥ 4 are easily obtained by the constructions.

Orthogonal Frequency Division Multiplexing (OFDM) is the utmost widespread technology in wireless communications systems because of its orthogonality property, high spectral efficiency, and high data rates. It provides immunity to multipath fading and reduces Inter Symbol Interference (ISI). The tailback of OFDM is its high Peak to Average Power Ratio (PAPR), which distresses the dynamic range of HPA, introduces harmonics and large power back off required to minimize unsolicited harmonics. In this paper, an OFDM transceiver is implemented in LabVIEW with Universal Software Radio Peripheral (USRP), such that system complexity is less and BER performance is good. To reduce the PAPR, companding techniques are well-thought-out which include Square Root Companding (SQRT), Logarithmic Rooting (LogR) and Tangential Rooting Companding (TanhR). The performance of these techniques is analyzed and observed that TanhR reduces PAPR to 1.15 dB without degrading BER. OFDM is used in many wireless standards, including the 4G LTE downlink transmissions, DVB-T, WLAN. OFDM is also one of the prominent competing Multi Carrier Modulation (MCM) schemes for considering even for 5G wireless communications systems.

The challenge of deploying orthogonal frequency division multiplexing (OFDM) for high-speed railways (HSRs) is associated with its high mobility and delay spread. These two conditions introduce loss of orthogonality between the OFDM subcarriers, hence, degrades the system performance. Although OFDM can provide high spectrum efficiency, but due to its inherited rectangular pulse shape, the frequency spectrum produced is not very well localized, which blocks its coexistence with other systems in adjacent carriers. Compared to the conventional OFDM, filtered OFDM (f-OFDM) has a lower out-of-band (OOB) interference and spectrum leakage. Therefore, f-OFDM is attractive to be implemented in high mobility applications such as in HSR, as considered here. By using the Hann and root-raised cosine (RRC) filters, simulation results show that f-OFDM provides better bit error rate (BER) and reduced OOB emission compare to conventional OFDM.

The class of geometric orthogonal codes (GOCs) were introduced by Doty and Winslow (2016) for more robust macro-bonding in DNA origami. They observed that GOCs are closely related to optical orthogonal codes (OOCs). It is possible for GOCs to have size greater than OOCs of corresponding parameters due to slightly more relaxed constraints on correlations. However, the existence of GOCs exceeding the size of optimal OOCs of corresponding parameters have never been demonstrated. This paper gives the first infinite family of GOCs of size greater than optimal OOCs.

We consider multilength variable-weight time-and-frequency-hopping (TFH) codes for optical code-division multiple-access (CDMA) networks. To design a TFH code that can support differentiated requirements on transmission rates (TRs) and bit error rates (BERs), we propose a general construction method for two-dimensional optical CDMA code sequences with arbitrary code lengths and variable code weights. The cross-correlation peak and the autocorrelation sidelobe of the proposed code are made to be at most '1' and '0', respectively, for any pair of different-length and different-weight code sequences. We show that the ratio between signal-to-interference ratios (SIRs) of the codes with different weight and length can effectively be approximated by the ratio of the code weights, regardless of the code lengths for the proposed codes. Therefore, independent adjustment of code length and weight can differentiate TR and BER for multiple service classes, and it simplifies code design for the service differentiation. We also demonstrate BER performances under various conditions and corroborate that the proposed codes accomplish accurate and fine-tuned differentiation of TR and BER compared to the fixed-weight or fixed-length codes.

The peak-to-average raito (PAPR) in correlatively coded orthogonal frequency-division multiplexing (OFDM) system is studied. Correlative codes are proposed by large numbers of papers to significantly improve the spectral performance of OFDM with rectangular pulse. The large PAPR makes amplifier distort the signal before transmission and thus becomes one of the most serious drawbacks of OFDM. However, simulations illustrate that correlatively coded OFDM has much larger PAPR than uncoded OFDM. This makes its implementation very difficult. Selected mapping (SLM) is a promising PAPR reduction technique, which is distortionless and has good PAPR reducing performance. We use SLM to reduce the PAPR of correlatively coded OFDM, and prove that the very high spectral efficiency is not affected by the PAPR reduction. Simulations show that SLM can lower the PAPR of correlatively code OFDM efficiently without any loss of the spectral performance.

One of the most common methods used in modern communication systems is orthogonal frequency division multiplexing (OFDM) to reduce the resistance to selective frequency fading. Another important reason is the possibility of reducing interference between symbols. However, there are also drawbacks, including the high peak-to-average power ratio (PAPR), which affects the power loss, increasing the complexity of transmitters. In the proposed study, we reduce PAPR in OFDM-based systems by hiding information in the image to maintain data security. In this steganography method, we insert digital text into the image and hide it, thus providing greater reliability while simultaneously reducing the PAPR required in OFDM. Text steganography is a method for hiding a large amount of information, which is helpful in OFDM. This also helps keep the system free from noise. Therefore, sending hidden data over communication channels is a good way to avoid interference, as image transmission is less affected by interference, and upon receipt, the main structure can be reconstructed to extract the hidden data and the original image. This is a way to preserve communication channels, which is the main objective of this study. The proposed method was evaluated by comparing the results with other methods, and it was found that the amount of data loss is reduced to 50% compared to the conventional method, which is the most important part. Also, the transmitted signal power has improved PAPR to 5.9 dB compared to the conventional method, which helps improve the quality of wireless transmission of the OFDM signal

Orthogonal frequency-division multiplexing (OFDM) with index modulation has been emerged as a promising technique for next-generation networks, where the specific activation pattern of the OFDM subcarriers is capable of conveying additional information implicitly without additional energy consumption, hence improving the system energy efficiency. In this paper, zero-padded tri-mode OFDM with index modulation (ZTM-OFDM-IM) is proposed, which is capable of achieving high spectral and energy efficiency. In ZTM-OFDM-IM, subcarriers are partitioned into subblocks. In each OFDM subblock, only a fraction of subcarriers are modulated by two distinguishable constellation alphabets, while the others remain empty, which reduces the energy consumption. With such an arrangement, extra information bits can be carried by the subcarrier activation pattern. At the receiver, a maximum-likelihood (ML) detector as well as a reduced-complexity two-stage log-likelihood ratio (LLR) detector are developed for signal demodulation. Theoretical performance analysis based on Euclidean distance metric and pairwise error probability are conducted. Besides, in order to attain better BER performance, the design strategies for the two distinguishable constellation alphabets are investigated, which is followed by brief discussions on generalization methods for the proposed ZTM-OFDM-IM. It is demonstrated via Monte Carlo simulations that ZTM-OFDM-IM is capable of enhancing the BER performance compared with the conventional OFDM and other conventional index-modulated OFDM benchmarks, which provides high-rate data transmission with low energy consumption. Moreover, the LLR detection of ZTM-OFDM-IM only suffers from slight performance loss in comparison with the ML detection and achieves significant complexity reduction.

Orthogonal frequency division multiplexing (OFDM) is widely used in wireless systems because of its high spectral efficiency, though it is known that it is highly vulnerable to frequency synchronization errors, which severely impede its performance. Such errors arise due to carrier frequency offset and Doppler frequency spread. They destroy the orthogonality among sub carriers and introduce inter carrier interference (ICI). The interference power is proportional to the received signal strength and amount of frequency offset. Several proposal to reduce the impact of ICI in OFDM use very complex signal processing and some have associated bandwidth efficiency loss. Since ICI is inversely proportional to the sub carrier bandwidth, it is interesting to investigate the gains in a system with adaptable sub carrier bandwidth. A system which can support variable sub carrier bandwidths simultaneously meeting the needs of different ICI conditions is compared against a normal OFDM system which uses fixed carrier bandwidth (FSB). Results show that the VSB schemes can be preferred over FSB OFDM system when users with different receive signal strength and Doppler condition have to be served simultaneously.

Orthogonal frequency division multiplexing (OFDM) has been adopted in various wireless communication standards to exploit its high spectral efficiency and robustness against multipath fading channels. Along with the potential benefits of OFDM transmissions, a stringent requirement on orthogonality among subcarriers makes OFDM highly susceptible to synchronization errors, i.e., time and frequency offsets. Addressing the carrier frequency offset (CFO) estimation problem, the paper proposes a pilot-aided CFO estimation scheme for both coarse and fine carrier frequency synchronization in single-input single-output (SISO) OFDM receivers. By exploiting the maximum likelihood (ML) principle, the proposed ML-based CFO estimation algorithm functions properly over a wide range of CFO values and outperforms existing correlation-based schemes.

OFDM is a multicarrier modulation technique which is used in communication systems like Wireless Personal Area Network (WPAN), Wireless Local Area Network (WLAN), Wireless Metropolitan Area Network (WMAN), Wi-Max, DVB-T etc for the high rate transmission over wireless radio channels. It is commonly known as a transmission technique of high spectral efficiency and robustness against frequency selective fading. The advantages of OFDM include simple digital realization, compatibility with multipath fading channel, less complex receivers and improve the bandwidth efficiency. At the same time, it also increases system capacity providing reliable transmission. But the main problem of OFDM systems is Peak to average power ratio due to its envelope fluctuation. The objective of this project this to provide a broader understanding in peak-to-average power ratio (PAPR) problem in orthogonal frequency division multiplexing (OFDM) systems. This paper showcases main three reduction techniques, precoding and SLM in combination with nonlinear companding in detail considering advantages and disadvantages of each technique.

OFDM (orthogonal frequency division multiplex) achieves high spectral efficiency in broadband wireless communications but has poor amplification efficiency due to its large peak-to-average power ratio. This paper presents achievable average power efficiency for the OFDM signal when the Doherty and extended Doherty transmitters are employed. By modelling the envelope of OFDM signal as a Rayleigh-distributed signal, average power efficiency for the OFDM signal is calculated as a function of clipping probability. Numerical calculation results assuming an ideal class-B amplifier and predistortion linearizer show that average drain efficiency of the two amplifiers for a clipping probability of 0.1% are 50.5 and 55.6%, respectively. It is concluded that the extended Doherty amplifier can improve power efficiency by several percents by optimizing the main amplifier contribution ratio alpha.