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multicode-based WCDMA for reducing waste rate and reassignments in mobile cellular communications

COMPUTER COMMUNICATIONS 2006年第11期29卷 1948-1958页

作者： Chang, Ben-Jye Chang, Pei-Shang Chaoyang Univ Technol Dept Comp Sci & Informat Engn Taichung Taiwan

The third generation (3G) mobile communications are proposed to accomplish high data rate for personal multimedia communications. To achieve that, the UMTS standards adopt the orthogonal variable spreading factor (OVSF) code tree to assign a single channelization code for each accepted connection at the Wideband CDMA air interface. Nevertheless, there are two drawbacks within it, including code blocking and waste of the system bandwidth. One good solution for reducing waste rate is to adopt the mechanism of multiple codes assignment, in which each accepted connection can be assigned several codes for achieving that the summation rate of these codes is satisfied the required rate. Therefore, the waste rate can be reduced significantly;nevertheless, it brings some overhead, including large number of reassignments, long connection setup delay and computation complexity, and cost of using multiple rake combiners. Therefore, we propose herein an efficient multicode assignment algorithm to reduce the waste rate while reducing large number of reassignments. The motivation of this approach is to reserve high-rate codes for next arrival calls with concerning the current state of the OVSF code tree. Consequently, it makes the tree compact and thus obviously reduces the number of code reassignments. Since there is a trade-off between the waste rate and the number of rake combiners, the optimal number of rake combiners for multicode assignment is analyzed and thus minimizes the cost of rake combiner. Numerical results demonstrate that the proposed approach yield the least number of reassignments while reducing the waste rate significantly as compared to other approaches. (c) 2005 Elsevier B.V. All rights reserved.

关键词： WCDMA UMTS OVSF code multicode rake combiners waste rate reassignment

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multicode Sparse-Sequence CDMA: Approach to Optimum Performance by Linearly Complex WSLAS Detectors

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WIRELESS PERSONAL COMMUNICATIONS 2013年第2期71卷 1049-1056页

作者： Sun, Yi Xiao, Jizhong CUNY City Coll Dept Elect Engn New York NY 10031 USA

This paper investigates the performance-complexity tradeoff of the wide-sense likelihood ascent search (WSLAS) detectors in large multicode sparse-sequence CDMA. It is illustrated that when each sequence has sparsely only 16 nonzero chips, in a channel load up to 1.05 bits/s/Hz and a broad SNR region, the linearly complex WSLAS detectors can achieve the benchmark optimum BER while the complexity is significantly reduced from 0.5 times bit number to a constant less than 30 additions per bit by the sequence sparsity. The evaluation result of multiuse efficiency also shows that the sparse sequences of 16 nonzero chips can already provide a sufficient degree of freedom.

关键词： Sparsity CDMA Maximum likelihood Large system multicode

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multicode CDMA/CI for Multimedia Services over LEO Satellite Channel 3

Multicode CDMA/CI for Multimedia Services over LEO Satellite...

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3rd International Conference on Advances in Computing, Communications and Informatics (ICACCI)

作者： Kapoor, Rajan Kumar, Preetam Indian Inst Technol Patna Dept Elect Engn Patna 800013 Bihar India

ISBN: (纸本)9781479930807

multicode CDMA is a promising scheme to support multi rate services for multimedia communication. In this paper, a novel multicode CDMA scheme using Carrier Interferometry (CI) codes has been proposed to support multi rate services over LEO satellite channel. It is observed that use of CI codes not only help in mitigating multiple access interference but also reduces the Peak to Average Power Ratio (PAPR) compared to Walsh Hadamard (WH) codes. The percentage of symbols with PAPR greater than 9 dB is reduced from 80% to 10% by employing CI codes for data rate sixteen times the basic data rate. Also, at elevation angle of 30 degrees, high rate user observes as much as 8 dB SNR gain using CI codes. Additionally, orthogonal CI codes with arbitrary integer length can be generated.

关键词： Carrier Interferometry DS-CDMA Interference Mitigation LEO satellite land mobile satellite channel multicode Multirate PAPR Reduction

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multicode multicarrier interleave division multiple access communication

Multicode multicarrier interleave division multiple access c...

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10th IEEE International Multitopic Conference

作者： Rehman, Habib ur Zaka, Imran Naeem, Muhammad Shah, Syed Ismail Ahmad, Jamil Ctr Adv Studies Engn Islamabad Pakistan Iqra Univ Islamabad Pakistan

ISBN: (纸本)9781424407941

A new Mulitcode Multicarrier Interleave Division Multiple Access (MC-MC-IDMA) system is proposed and analyzed in frequency selective channels. The system supports different modulation schemes for variables data rates. Each user transmits his message by choosing a sequence from an orthogonal code-set. An MC-MC-IDMA system achieves spreading gains both in time and frequency domains. Bit error rate of the system is derived and simulation results are presented.

关键词： multicode IDMA MC-IDMA

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Quaternary Constant-Amplitude Codes for multicode CDMA

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IEEE TRANSACTIONS ON INFORMATION THEORY 2009年第4期55卷 1824-1832页

作者： Schmidt, Kai-Uwe Tech Univ Dresden Commun Lab D-01062 Dresden Germany

A constant-amplitude code is a code that reduces the peak-to-average power ratio (PAPR) in multicode code-division multiple access (MC-CDMA) systems to the favorable value 1. In this paper, quaternary constant-amplitude codes (codes over Z(4)) of length 2(m) with error-correction capabilities are studied. These codes exist for every positive integer in, while binary constant-amplitude codes cannot exist if in is odd. Every word of such a code corresponds to a function from the binary m-tuples to Z(4) having 2 the bent property, i.e., its Fourier transform has magnitudes 2(m/2). Several constructions of such functions are presented, which are exploited in connection with algebraic codes over Z(4) (in particular quaternary Reed-Muller, Kerdock, and Delsarte-Goethals codes) to construct families of quaternary constant-amplitude codes. Mappings from binary to quaternary constant-amplitude codes are presented as well.

关键词： Bent function code code-division multiple access (CDMA) Delsarte-Goethals Kerdock multicode peak-to-average power ratio (PAPR) quaternary Reed-Muller

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Narrow-band interference suppression in wavelet packets based multicarrier multicode CDMA overlay system

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WIRELESS COMMUNICATIONS & MOBILE COMPUTING 2015年第2期15卷 203-214页

作者： Akho-Zahieh, Maryam M. Abdellatif, Nasser Appl Sci Private Univ Dept Elect & Comp Engn Amman 11931 Jordan

The wavelet packets based multicarrier (MC) multicode (MCD) code-division multiple-access (CDMA) transceiver consists of the MCD part, which ensures the transmission for high speed and flexible data rate;the MC part contributing to robustness to frequency-selective fading and flexibility for handling multiple data rates;and wavelet packets (WPs) modulation technique, which contributes to the mitigation of the interference problems. As WPs have lower sidelobes compared with sinusoidal carriers, this system is very effective in reducing the problem of inter-carrier interference. Of course, like any CDMA system, the system can suppress a given amount of interference. This paper considers an interference suppression scheme which will enhance the performance of the system. The receiver employs suppression filters to mitigate the effect of narrow-band jammer interference. The framework for the system and the performance evaluation are presented in terms of the bit error rate and the outage probability over a Nakagami fading channel. Also, we investigate how the performance is influenced by various parameters, such as the number of taps of the suppression filter and the ratio of narrow-band interference bandwidth to the spread-spectrum bandwidth. Finally, the performance of the system is compared with the performance of sinusoidal based MC/MCD-CDMA system denoted Sin-MC/MCD-CDMA. Copyright (c) 2012 John Wiley & Sons, Ltd.

关键词： suppression filter wavelet packet multicarrier multicode CDMA

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Frame time-hopping patterns in multirate optical CDMA networks using conventional and multicode schemes

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IEEE TRANSACTIONS ON COMMUNICATIONS 2005年第5期53卷 863-875页

作者： Forouzan, AR Nasiri-Kenari, M Rezaee, N Univ Canterbury Dept Elect & Comp Engn Christchurch 8005 New Zealand Univ Tehran Dept Elect & Comp Engn Tehran 14399 Iran Sharif Univ Technol Dept Elect Engn Tehran 113659363 Iran

A class of generalized optical orthogonal codes (OOCs), namely, frame time-hopping (FTH) patterns with an extremely large cardinality, are studied for implementing multirate and multiservice (MR/MS) optical CDMA (OCDMA) networks. Conventional MR/MS methods, namely variable spreading rate and parallel mapping,are considered. Using FTH patterns, the problem of low OOC code cardinality in conventional MR/MS schemes is removed. Moreover, several new multicode methods, using subcode concatenation scheme, are proposed for MR/MS OCDMA. The proposed multicode schemes present flexibility for supporting MR/MS applications such as lower implementation complexity and cost, less need for service synchronization, and finally lower link power budget. Multiple-access performances of the systems are evaluated using saddle-point approximation methods considering photodetector shot-noise, dark current, and circuit thermal noise. The results show that the conventional parallel mapping outperforms the other schemes in high received powers, and the proposed multicode method, using Walsh subcode along with difference modulation, presents the best performance in low received powers for the cases considered.

关键词： frame time-hopping (FTH) multicode multirate (MR) multiservice (MS) optical CDMA optical orthogonal codes (OOCs) parallel mapping subcode concatenation variable spreading rate Walsh code

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Analytical framework for simultaneous MAC packet transmission (SMPT) in a multicode QDMA wireless system

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IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY 2004年第1期53卷 223-242页

作者： Krishnam, M Reisslein, M Fitzek, F Arizona State Univ Dept Elect Engn Tempe AZ 85287 USA Acticom GMBH D-13507 Berlin Germany

Stabilizing the throughput over wireless links is one of the key challenges in providing high-quality wireless multimedia services. Wireless links are typically stabilized by a combination of link-layer automatic repeat request (ARQ) mechanisms in conjunction with forward error correction and other physical layer techniques. In this paper, we focus on the ARQ component and study a novel class of ARQ mechanisms, referred to as simultaneous MAC packet transmission (SMPT). In contrast to the conventional ARQ mechanisms that transmit one packet at a time over the wireless air interface, SMPT exploits the parallel code channels provided by multicode code-division multiple access. SMPT stabilizes the wireless link by transmitting multiple packets in parallel in response to packet drops due to wireless link errors.' While these parallel packet transmissions stabilize the link layer throughput, they also increase the interference level in a given cell of a cellular network or cluster of an ad hoc network. This increased interference reduces the number of traffic flows that can be simultaneously. supported in a cell/cluster. We develop an analytical framework for the class of SMPT mechanisms and analyze the link-layer buffer occupancy and the code usage in a wireless system running some form of SMPT. Our analysis quantifies the tradeoff between increased link-layer quality of service and reduced number of supported flows in SMPT with good accuracy, as verified by simulations. In A typical scenario, SMPT reduces the probability of link-layer buffer overflow by over two orders of magnitude (thus enabling high-quality multimedia services, such as real-time video streaming) while supporting roughly 20% fewer flows than conventional ARQ. Our analytical framework provides a basis for resource management in wireless systems running some form of SMPT and optimizing SMPT mechanisms.

关键词： automatic repeat request (ARQ) buffer occupancy capacity code-division multiple access (CDMA) link-layer quality of service (QoS) multicode packet-loss probability throughput

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Iterative frequency-domain soft interference cancellation for multicode DS- and MC-CDMA transmissions and performance comparison

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IEICE TRANSACTIONS ON COMMUNICATIONS 2006年第12期E89B卷 3344-3355页

作者： Ishihara, Koichi Takeda, Kazuaki Adachi, Fumiyuki Tohoku Univ Grad Sch Engn Dept Elect & Commun Engn Sendai Miyagi 9808579 Japan

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.

关键词： DS-CDMA MC-CDMA frequency-domain equalization (FDE) multicode interference cancelation

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Blind channel estimation in multicode CDMA using multiantenna receiver

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WIRELESS PERSONAL COMMUNICATIONS 2004年第3期28卷 163-178页

作者： Melvasalo, M Koivunen, V Aalto Univ SMARAD CoE Signal Proc Lab FIN-02015 Helsinki Finland

In this paper blind channel estimation methods for long code CDMA system with multicode transmission are proposed. By allocating multiple codes, higher data rates may be provided to a user. Blind channel estimation allows reducing pilot signaling. Hence, higher effective data rates may be achieved and larger sample support may be obtained by using both the information symbols and known pilot symbols for channel estimation. Algorithms are extended to multi-antenna receiver which further improves the performance. The performance of the algorithms is studied in extensive simulations using WCDMA system model. The effects of code selection, interference and noise, number of antennas, antenna correlation are considered using frequency selective channel models. The proposed methods are more robust in the face of interference and code selection than the well-known subspace method in [7]. The computational complexity is lower as well.

关键词： WCDMA multicode antenna array blind channel estimation subspace methods

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