Chao-Chin Yang

Optical CDMA network codecs structured with M-sequence codes over waveguide-grating routers

A compact optical code-division multiple-access (OCDMA) network coder-decoder (codec) of a spectral-amplitude-coding (SAC) scheme is presented. The scheme utilizes M-sequence-coded OCDMA codecs structured on arrayed-waveguide-grating (AWG) routers. By using the cyclic properties of AWG routers and M-sequence codes, the codecs pair can encode-decode multiple code words simultaneously, thus, each user can share the same hardware for coding process. The configuration not only preserves the ability of multiple-access interference cancellation in SAC-OCDMA system, but also results in a cheap system with reduced system complexity.

Hybrid wavelength-division-multiplexing/spectral-amplitude-coding optical CDMA system

One spectral-amplitude-coding (SAC) scheme combined with wavelength-division-multiplexing (WDM) is proposed for optical code-division multiple-access systems. The supported code length is more flexible than the previous SAC codes and the corresponding encoder-decoder requires less fiber gratings, thus, the system becomes cheap and simple. As compared to the conventional SAC systems, this WDM/SAC system not only reserves the interference-cancellation property, but also has better performance against the effect of the phase-induced intensity noise arising in the photodetecting process. Thus, a larger number of active users can be supported under a given bit-error rate.

Two-dimensional M-matrices coding in spatial/frequency optical CDMA networks

A spatial/frequency encoder-decoder scheme is proposed for optical code-division multiple-access (OCDMA) communications. The coders adopt codewords with multiple-weight-per-row property and can be realized via compact hardware. With the proposed decoding scheme, an intended user will reject any interfering user and theoretically achieve quasiorthogonality between OCDMA users. The performance degradation due to various noise sources in previous discussed one-dimensional coding scheme can be improved.

Construction of quasi-cyclic LDPC codes from quadratic congruences

In this paper, we proposed a novel method for constructing quasi-cyclic low-density parity-check (QC-LDPC) codes based on circulant permutation matrices via a simple quadratic congruential equation. The main advantage is that QC-LDPC codes with a variety of block lengths and rates can be easily constructed with no cycles of length four or less. Simulation results show that the proposed QC-LDPC codes perform slight better than the random regular LDPC codes for short to moderate block lengths and have almost the same performance as Sridara-Fuja-Tanner codes.

Reductions of multiple-access interference in fiber-grating-based optical CDMA network

A fiber Bragg grating (FBG) encoder/decoder scheme based on correlation subtractions of nearly orthogonal M-sequence codes is presented. With proper coder design, a receiver can reject interfering users and obtain quasi-orthogonality between optical code-division multiple-access (CDMA) users in the network. However, optical CDMA networks may be degraded by multiple-access interference (MAI) due to nonflattened incoherent sources and nonideal FBG coders. A compensating module is therefore proposed to compensate for such MAI effects. As a result, the MAI effects induced by nonideal FBG coders can be perfectly eliminated by the compensating module. With spectral width reduction on the incoherent source, the scheme can partly compensate the MAI effects induced by nonflattened sources and further reduce the average error probability in the system performance.

Optical CDMA Passive Optical Network Using Prime Code With Interference Elimination

One novel decoding scheme of prime codes for interference elimination is proposed for optical code-division multiple-access network. This scheme uses the correlation property of prime codes for interference elimination without additional processing, and thus simplifies the coder implementation. By taking advantage of the cyclic property of the prime codes in the same code groups, the proposed compact encoder is low cost and suitable for the application of passive optical network (PON). In addition, the information encoding of each optical network unit (ONU) can adopt two-code keying using a simplified ONU decoder for performance enhancement. Thus, this is an economical solution for end users in the PON

Differentiated Service Provision in Optical CDMA Network Using Power Control

A simple scheme to use power control for differentiated service provision is proposed for the optical code-division multiple-access network. The main advantages of this scheme are: (1) Interference from other users can be eliminated theoretically. (2) The decoder with simple configuration can be used as compared to that in a previous power control scheme. (3) The design procedure of various service requirements in one network is simplified.

Modified legendre sequences for optical CDMA-based passive optical networks

One spectral-amplitude-coding optical code-division multiple access system is presented for passive optical networks. With the cyclic property of arrayed-waveguide grating (AWG) routers and the partially cyclic property of the proposed modified Legendre sequence, the central office needs two AWG routers and one fiber Bragg grating to generate each users normal and complementary codewords. Thus complementary encoding is accomplished with a cheap and simple configuration, allowing for low-power asynchronous transmission.

Code Space Enlargement for Hybrid Fiber Radio and Baseband OCDMA PONs

A hybrid analog and digital passive optical network based on optical code division multiple access is presented, and a code generation method is proposed to increase the number of codes for existing code families with fixed and ideal in-phase cross correlations. When code families with cyclic properties are used by this code generation method, compact encoders based on arrayed waveguide gratings can be used. The corresponding performance for this hybrid network is also analyzed.

Permuted M-matrices for the reduction of phase-induced intensity noise in optical CDMA network

Two codeword families and the corresponding encoder/decoder schemes are present for spatial/frequency optical code-division multiple-access communications. These 2-D codewords have multiple weights per row and can be encoded/decoded via compact hardware. With the proposed decoding mechanism, the intended user will reject interfering users and multiple-access interference is fully eliminated. In addition, the power of the same wavelength contributed by all interfering codewords is split and detected by distinct photodiodes in the decoder. Thus the performance degradation due to the beat noise arising in the photodetecting process is improved, as compared with the traditional 1-D coding scheme, and a larger number of active users is supported under a given bit-error rate.