A multicode transmission (MC) system can transmit multiple data streams at one time. However, the amplitude of the transmission signal has sharp fluctuations. To avoid this problem, constant amplitude (CA) signaling schemes were studied, and some MC systems were developed such as the MC system with CA signaling (MC-CA) and the parallel combinatory MC system with CA signaling (PCMC-CA). In this paper, extension systems of PCMC-CA system are developed. In particular, two demodulation methods are discussed for the extension systems. Then, the bit error rate (BER) and data transmission rate are theoretically analyzed. The results shows that the extension systems has a better performance than the MC-CA system in both of the BER and data transmission rate.

Multicode CDMA systems convert a high-rate serial data stream into low-rate parallel data streams prior to transmission, but reducing the peak-to-average-power-ratio (PAPR) is a prerequisite. In this paper, we propose constant amplitude coding schemes with forward error correction (EC) capability. The proposed schemes overcome the adverse nonlinear effects of the high power amplifier (HPA) by using the transmitted signal of constant amplitude and parity channel. In the first scheme, we add the EC capability to the previously reported constant-amplitude rate 4/4 (Suil's) scheme, which can transmit data without energy loss. Next, we propose a rate 12/16 decoder with EC capability, which is slightly different from the previous work through the addition of EC capability. Lastly, we propose a new high-rate EC capable 16/16 scheme without energy loss, which makes it superior to the conventional 12/16 scheme which experiences excessive energy loss due to redundancy. Computer simulation results confirm that new 4/4 decoder along with 12/16 decoder and 16/16 encoder/decoder can effectively reduce the inherent problem of high PAPR in the multicode CDMA signal transmission. Our methods also yield better BER performance than other constant amplitude coding schemes.

The authors present an accurate analysis for multicode code division multiple access (CDMA) systems equipped with a multipath interference canceler (MPIC) over multipath fading channels. This letter verifies that the previous analysis has used the additional Gaussian approximation (AGA) for multipath interferences so that there is the performance mismatch between the previous analysis and simulations. Furthermore, it is confirmed that the proposed analysis, which does not use AGA, provides an analytical bound.

Frequency-domain equalization (FDE) based on the minimum mean square error (MMSE) criterion can significantly improve the BER performance of DS- and MC-CDMA systems in a severe frequency-selective fading channel. However, since the frequency-distorted signal cannot be completely equalized, the residual inter-code interference (ICI) limits the BER performance improvement. 4G systems must support much higher variable rate data services. Orthogonal multicode transmission technique has flexibility in offering variable rate services. However, the BER performance degrades as the number of parallel codes increases. In this paper, we propose an iterative frequency-domain soft interference cancellation (IFDSIC) scheme for multicode DS- and MC-CDMA systems and their achievable BER performances are evaluated by computer simulation.

In this paper, a parallel combinatory spread spectrum (PC/SS) system using a constant amplitude signaling scheme is proposed. The amplitude of the transmitted signal from multicode transmission systems such as PC/SS systems have a large dynamic range which requires that amplifiers have a wide linearity in the transmitter. From a view point of power efficiency, however, it is reasonable to use non-linear amplifiers rather than linear ones. In that case, the bit error rate performance must degrade because of non-linear distortion. The proposed system can avoid influence of the non-linear amplifiers by making the transmitted signal have a constant amplitude. The bit error rate performance and the data transmission rate performance are investigated. They prove that the proposed system is an attractive candidate among the constant amplitude signaling systems.

Multicode code-division multiple access (MC-CDMA) and variable processing gain CDMA (VPG-CDMA) are very appealing techniques for achieving high bit-rate data transmission and providing significant capacity gain in wireless channels. This letter provides the peak-to-average power ratio (PAPR) reduction scheme by using a code selective allocation (CSA) in a MC VPG-CDMA system. From simulation results, the MC VPG-CDMA system experiences a reduced PAPR thanks to the CSA algorithm and maintains an acceptable performance degradation even if encountered with nonlinear distortions introduced by a level clipper.

OFDM, MC-CDMA and DS-CDMA are being researched vigorously as the prospective signaling technique for the next generation mobile communications systems, which will be characterized by the broadband packet technology. With packet transmissions, hybrid ARQ (HARQ) will be inevitable for error control. HARQ with rate compatible punctured turbo (RCPT) codes is one of the promising techniques. Data rate equivalent to the OFDM system can be attained with MC-CDMA and DS-CDMA by assigning all the available codes to the same user resulting in what is commonly referred to as multicode MC-CDMA and multicode DS-CDMA. A rake receiver is used for receiving the DS-CDMA signals. However, recently minimum mean square error frequency-domain equalization (MMSE-FDE) has been proposed for the reception of DS-CDMA signals. In this paper, we introduce RCPT HARQ to DS-CDMA with MMSE-FDE and compare its throughput performance with OFDM, multicode MC-CDMA and multicode DS-CDMA with rake combining. MMSE weight for packet combining is introduced and the soft value generation for turbo coding in MC-CDMA and DS-CDMA with MMSE-FDE is presented. The throughput is theoretically evaluated for the uncoded case. For RCPT-HARQ, the comparison is done by computer simulations. It is found that the throughput of HARQ using DS-CDMA with MMSE-FDE is the same as or better than using MC-CDMA. However, with higher level modulation, type I HARQ using OFDM is better than using either MC-CDMA or DS-CDMA; for type II HARQ without redundancy in the first transmission, however, MC-CDMA and DS-CDMA gives a higher throughput.

In a severe frequency-selective fading channel, the bit error rate (BER) performance of orthogonal multicode DS-CDMA is severely degraded since the orthogonality property of spreading codes is partially lost. The frequency-selectivity of a fading channel can be exploited by using frequency-domain equalization to improve the BER performance. Further performance improvement can be obtained by using transmit diversity. In this paper, joint transmit diversity and frequency-domain equalization is presented for the reception of orthogonal multicode DS-CDMA signals in a frequency-selective fading channel. As for transmit diversity, delay transmit diversity (DTD) and frequency-domain space-time transmit diversity (STTD) are considered. The achievable BER performance of multicode DS-CDMA in a frequency-selective Rayleigh fading channel is evaluated by computer simulation. It is shown that the frequency-domain STTD significantly improves the BER performance irrespective of the degree of the channel frequency-selectivity while DTD is useful only for a weak frequency-selective channel.

Orthogonal multicode direct sequence code division multiple access (DS-CDMA) has the flexibility in offering various data rate services. However, in a frequency-selective fading channel, the bit error rate (BER) performance is severely degraded since the othogonality among spreading codes is partially lost. In this paper, we apply frequency-domain equalization and antenna diversity combining, used in multi-carrier CDMA (MC-CDMA), to orthogonal multicode DS-CDMA in order to restore the code othogonality while achieving frequency and antenna diversity effect. It is found by computer simulations that the joint use of frequency-domain equalization and antenna diversity combining can significantly improve the BER performance of orthogonal multicode DS-CDMA in a frequency-selective fading channel.

This letter discusses the performance of online SNR estimation including fading parameter estimation for parallel combinatorial SS (PC/SS) systems. The PC/SS systems are partial-code-parallel multicode SS systems, which have high-rate data transmission capability. Nakagami-m distribution is assumed as fading channel model to cover a wide range of fading conditions. The SNR and fading parameter estimation considered in this letter is based on only a statistical ratio of correlator outputs at the receiver. Numerical results show that SNR estimation performance with fading parameter estimation is close to the one in the case of perfect fading parameter information, if the number of transmitting PN codes is less than a half of assigned PN codes.

This letter evaluates the peak-to-average power ratio (PAR) performance in a space-time block coded (STBC) multicode CDMA (MC-CDMA) system using a selected mapping (SLM) approach. The ordinary method is to apply the SLM scheme for each transmit antenna individually, while the investigated SLM-based STBC MC-CDMA system selects the transmitted sequence with the lowest average PAR over all transmit antennas concurrently. SLM-based STBC MC-CDMA system retrieves the side information very accurately at the expense of a slight degradation of the PAR performance, which can improve the overall detection performance of the STBC MC-CDMA system in the presence of erroneous side information compared to the ordinary SLM approach.

Direct sequence code division multiple access (DS-CDMA) provides flexible data transmission in wide range of data rates by the use of orthogonal multicode multiplexing. In a multipath fading environment, the transmission performance of multicode DS-CDMA degrades as that of single code DS-CDMA does. Chip interleaving is known to improve the bit error rate (BER) performance of the single code transmission by altering the fading channel into severely time selective fading channel. However, this partially destroys orthogonality property among spreading codes and thus, significantly degrades the BER performance of multicode DS-CDMA. In this paper, we propose the joint use of chip interleaving and time-domain minimum mean square error combining (MMSEC) equalization to improve the multicode DS-CDMA transmission performance. It is confirmed by computer simulations that the joint use of chip interleaving and MMSEC equalization significantly improves the BER performance of multicode DS-CDMA and achieves better BER performance compared to the single code DS-CDMA using chip interleaving and maximal ratio combining (MRC).

A novel scheme of subband adaptive array for multicode Direct Sequence Code Division Multiple Access (DS-CDMA) is proposed in this paper. The proposed scheme has a flexible configuration which allows basestation to be able to dynamically adapt to multirate transmission requests from subscribers. It is shown that the novel scheme can effectively suppress multiple access interferences (MAI) by appropriately forming main beam toward the desired user while pointing beampattern nulls toward MAI sources. Moreover, the combination of the subband adaptive array with the so-called cyclic prefix spreading code CDMA is also proposed to mitigate multipath fading and maximize diversity gain in multipath fading environment.

Upper bounds on the bit error rate (BER) for maximum likelihood (ML) decoding are derived in convolutional coded parallel combinatorial spread spectrum (PC/SS) systems over additive white Gaussian noise (AWGN) channels. PC/SS systems can achieve higher data transmission than conventional multicode SS systems. To make the derivation tractable, we put a uniform interleaver between a convolutional encoder and a PC/SS transmitter. Since the PC/SS transmitter is employed as the "inner encoder," the bounds are obtained in a similar manner of the derivation in serially concatenated codes through a uniform interleaver. Two different error patterns in the PC/SS system are considered in the performance analysis. Numerical results show that the derived BER bounds are sufficiently accurate. It is found that the coded PC/SS systems outperform coded all-code-parallel DS/SS systems under the same data rate conditions if the number of pre-assigned PN codes increases.

Existing MultiCode-CDMA MAC protocols perform only single dimensional access control either in the code or time domain. In this paper, we propose a MAC protocol, called SCTAC which can perform simultaneous code-time access control to achieve better system utilization. Also, SCTAC intends to provide service differentiation among different traffic classes. In order to simultaneously control access in both the code and time domain, SCTAC decouples the function of transmission ordering from the function of packing the scheduled transmissions in the resource space. As such, different transmission scheduling algorithms can be adopted without altering the MAC protocol. A water filling approach is used for efficient transmission packing where each of the scheduled transmissions is treated as a rectangular capsule with an arbitrary size and the resource space is viewed as a water container. In addition, SCTAC uses different request sending probabilities with an improved probability update algorithm to achieve service differentiation. Simulation results indicate that SCTAC is capable of providing different performances to different traffic classes. The results also confirm that SCTAC can achieve higher throughput compared to single dimensional access control protocols. Therefore, SCTAC is a better MAC protocol.

The implementation of conventional Multi-Code Code Division Multiple Access (MC-CDMA) system needs many orthogonal codes (OCs) compared to traditional Direct Sequence-CDMA (DS-CDMA) systems. To reduce the number of OCs in MC-CDMA for multi-media services, we propose a new scheme in which a sub-orthogonal code (SOC) technique is adopted. To clarify the validity of our proposed system, the computational simulations have performed.

In this paper, multiuser detector (MUD) based on radial basis function (RBF) is proposed and simulated for a multicode DS/CDMA system in an AWGN and a multipath fading channels. The performance of RBF-based MUD is compared with that of many suboptimal multiuser detectors in terms of bit error probability. To obtain simulation results, importance sampling technique is employed. From the simulation results, it is confirmed that the RBF-based MUD outperforms decorrelating detector, and achieves near-optimum performance under various environments. The results in this paper can be applied to design of MUD for a multicode DS/CDMA system.

The Direct-Sequence Code Division Multiple Access (DS-CDMA) is one of the most likely candidates for the 3rd generation mobile communication systems. On the other hand, a network supporting integrated data transfer and providing predictable qualities of service (QoS) to such application is an attractive issue. This paper proposes several schemes based on the majority rule concerned with resource reservation to investigate the performance of a CDMA cellular system. The admission control is based on the residue capacity and required signal-to-noise ratio (SNR) for multimedia traffic including voice, data and video. The system performance is explored with variable spreading gain and multi-code CDMA systems under the proposed schemes. Moreover, several system parameters including the handoff probability (lifetime in a cell) and the traffic load are investigated to study the impact to system performance. The results show the trade-off between the blocking probability of new calls and dropping probability of handoff calls under diversified situations. However, it is inefficient under resource reservation due to unused capacity. In this paper, we also propose a resource-borrowing scheme to improve system performance. Simulation results show that our proposed algorithm really improves the system performance in a multimedia CDMA cellular system with resource reservation.

In this letter, we present a method to generate sets of sequences suitable for multicode transmission in quasi-synchronous (QS) CDMA systems. We focus on Gold code but extension to orthogonal Gold code is straightforward. We show that by appropriate classification of sequences, it is possible to have sets whose cross correlation is small in QS situations.

In this letter, the constant amplitude transmission for orthogonal multicode systems is discussed. In order to obtain the high power efficiency, we require the high power amplifier which has non-linear characteristic. The nonlinear distortion, however, may occur because of the multicode signals having large amplitude fluctuations. If we can achieve the constant amplitude transmission, the nonlinear distortion can be neglected. In this letter, I investigate the property of the information bit streams that can achieve the constant amplitude transmission and show that the bent sequences can achieve the constant amplitude transmission.