Lifang Feng

Generalized Pairwise Z-Complementary Codes

An approach to generate generalized pairwise Z-complementary (GPZ) codes, which works in pairs in order to offer a zero correlation zone (ZCZ) in the vicinity of zero phase shift and fit extremely well in power efficient quadrature carrier modems, is introduced in this letter. Each GPZ code has MK sequences, each of length 4NK, where M is the number of Z-complementary mates, K is a factor to perform Walsh-Hadamard expansions, and N is the sequence length of the Z-complementary code. The proposed GPZ codes include the generalized pairwise complementary (GPC) codes as special cases.

Error-Resilient Scheme for Wavelet Video Codec Using Automatic ROI Detection and Wyner-Ziv Coding Over Packet Erasure Channel

The error-resilient for video transmission over the Internet in which regarded as the packet erasure channel is always a tough task and has gained lots of attentions. The main contradictory problem lies between error-resilient and bandwidth usage. Additional redundant data has to be added to achieve robust transmission which leads to huge bandwidth usage. In this paper, an error-resilient scheme called Wyner-Ziv Error-Resilient (WZER) based on a receiver driven layered Wyner-Ziv (WZ) coding framework is proposed. The WZER purposely emphasizes on the protection of the Region of Interest (ROI) area in the frame thus to achieve the better tradeoff between the bandwidth usage and error-resilience. WZER is designed to work for the scenario of wavelet based video coding over packet erasure channel, where several techniques including automatic ROI detection, ROI mask generation, Rate distortion optimization (RDO) quantization, WZ coding with layer design, and packet level Low Density Parity Check (LDPC) code are used. The performances of the proposed WZER are simulated based on average PSNR of luminance, perceptual reconstruction and bandwidth usage and compared with normal Forward Error Correction (FEC) full protection scheme and no protection scheme. The results show the advantages of the proposed WZER over traditional FEC protection, especially in the aspects of the recovery of the subject area and bandwidth efficiency.

A construction of inter-group complementary codes with flexible ZCZ length

A general construction of inter-group complementary (IGC) codes is proposed based on perfect complementary (PC) codes, interleaving operation, and the orthogonal matrix. The correlation properties of the newly constructed IGC codes can be described as follows: (1) the autocorrelation sidelobes of the codes are zeros in the zero correlation zone (ZCZ); (2) the cross-correlation functions (CCFs) between any two different codes of the same group are zeros in the ZCZ; (3) the CCFs between any two codes of different groups are zeros everywhere. The key point of this construction is that the ZCZ length of the generated IGC codes can be chosen flexibly. It is well known that there is a limitation between the ZCZ length and the number of mates; that is, the smaller is the length of ZCZ, the more are the IGC codes that can be generated. Therefore, if we can choose the ZCZ length of the IGC codes flexibly according to the requirement of the system, more users can be accommodated in the system.

A General Construction of Inter-Group Complementary Codes Based on Z-Complementary Codes and Perfect Periodic Cross-Correlation Codes

In this paper, a new construction of inter-group complementary (IGC) codes is proposed based on Z-complementary codes and perfect periodic cross-correlation (PPCC) codes. The correlation properties of the new generated IGC codes are as follows: (1) the autocorrelation sidelobe values of the codes are zeros in the zero correlation zone (ZCZ), (2) the cross-correlation values between different codes in the same group are zeros in the ZCZ, (3) the cross-correlation values between codes of different groups are zeros during the whole period. Comparing to the existed IGC codes, the ZCZ length of the generated IGC codes can be predefined flexibly; the number of groups and the number of codes in each group have more freedom according to the advantages of Z-complementary codes and PPCC codes.

Lower Bounds on Correlation of Z-Complementary Code Sets

A set of binary codes is called a Z-complementary code set if the sum of the autocorrelation functions of the codes involved is zero in the zero correlation zone (ZCZ) except at zero shift. Comparing to the traditional complementary code sets, the Z-complementary code sets not only have more freedom on the code length, but also have much more mates. In this paper, lower bounds on periodic/aperiodic correlation of Z-complementary binary code sets with respect to the number of mates, family size, sequence length, the length of ZCZ, maximum periodic/aperiodic autocorrelation sidelobe inside the ZCZ and maximum periodic/aperiodic crosscorrelation value inside the ZCZ, are derived. The proposed lower bounds provide theoretical criteria for designing, optimizing and choosing Z-complementary code set in applications.

A General Construction of OVSF Codes With Zero Correlation Zone

In this letter, a general construction of orthogonal variable spreading factor (OVSF) codes with zero correlation zone (ZCZ) property is presented based on orthogonal sequence sets and -complementary sets. It is shown that the proposed general construction includes the conventional binary and ternary OVSF codes as special cases and can accommodate more flexible rate assignment in direct sequence code division multiple access (DS-CDMA) systems.

New Signature Waveforms for Multi-rate QS-CDMA System with QPSK Modulation

This paper presents a multi-rate quasi-synchronous CDMA (QS-CDMA) system with QPSK modulation based on the new signature waveforms, namely GPZ-chip waveforms which are constructed by the generalized pairwise Z-complementary (GPZ) codes and optimal chip waveforms. According to the properties of GPZ-chip waveforms, the multiple access interference of different users can be reduced or eliminated. The interferences among different streams of the same user are handled by an optimal (or suboptimal) multi-stream detector(s). The performance of the proposed system is simulated and analyzed in a cellular communication environment consisting of multipath fading. The result shows that the proposed system has similar performance as compared to the single-rate QS-CDMA system employing GPZ codes with one chip waveform due to the properties of multi-stream detection. Also, the proposed system can achieve a significant interference reduction as compared to the multi-rate system employing concatenated WH/m sequence sets with one chip waveform due to the zero correlation zone properties of the GPZ-chip waveforms, thus resulting better BER performance.

On the Spreading Sequences with Perfect Periodic Crosscorrelation Properties

To eliminate the multiple access interference of asynchronous direct sequence code division multiple access (DS-CDMA) system, a set of sequences with perfect crosscorrelation functions (CCFs) is desirable, although the corresponding autocorrelation function (ACF) cannot be simultaneously perfect based on the theoretical bounds. In this letter, a general construction of the spreading sequences with perfect periodic CCFs is presented, and the corresponding theoretical limit on the family size, the number of phases, and the sequence length is also investigated.

Generalized bounds on partial aperiodic correlation of complex roots of unity sequences

Partial correlation properties of sets of sequences are important in CDMA system as well as in ranging, channel estimation and synchronization applications. In general, it is desirable to have sequence sets with small absolute values of partial correlations. In this paper, generalized lower bounds on partial aperiodic correlation of complex roots of unity sequence sets with respect to family size, sequence length, subsequence length, maximum partial aperiodic autocorrelation sidelobe, maximum partial aperiodic crosscorrelation value and the zero or low correlation zone are derived. It is shown that the previous aperiodic sequence bounds such as Sarwate bounds, Welch bounds, Levenshtein bounds, Tang-Fan bounds and Peng-Fan bounds can be considered as special cases of the new partial aperiodic bounds derived.

The Construction of GOS Spreading Code Sets and Their Applications into Multi-Rate Multe-Cell QS-CDMA Systems

In this paper, a class of generalized orthogonal sequences (GOS) is presented with the the following characteristics, (1) the cross-correlations in the vicinity of zero shift (zero shift is excluded) between two arbitrary sequences from different GOS sets are zeros; (2) the cross-correlations in the vicinity of zero shift between two arbitrary sequences from different subsets of the same GOS set are zeros; and (3) two arbitrary different sequences from the same subset of the same GOS set are orthogonal. By applying the GOS sets to multi-rate multi-cell quasi-synchronous CDMA (QS-CDMA) system, the system interference is analyzed and compared with that of well-known concatenated orthogonal/PN sequence sets. It is shown that due to the zero correlation properties in the vicinity of zero shift, the interference of system employing GOS sets can achieve a bigger reduction than concatenated orthogonal/PN sequence sets, thus resulting better BER performance than that of latter under the same conditions.