Mahmoud Taherzadeh

Bio: Mahmoud Taherzadeh is an academic researcher from Huawei. The author has contributed to research in topics: Decoding methods & Codebook. The author has an hindex of 5, co-authored 6 publications receiving 653 citations.

SCMA Codebook Design

Abstract: Multicarrier CDMA is a multiple access scheme in which modulated QAM symbols are spread over OFDMA tones by using a generally complex spreading sequence. Effectively, a QAM symbol is repeated over multiple tones. Low density signature (LDS) is a version of CDMA with low density spreading sequences allowing us to take advantage of a near optimal message passing algorithm (MPA) receiver with practically feasible complexity. Sparse code multiple access (SCMA) is a multi-dimensional codebook-based non-orthogonal spreading technique. In SCMA, the procedure of bit to QAM symbol mapping and spreading are combined together and incoming bits are directly mapped to multi-dimensional codewords of SCMA codebook sets. Each layer has its dedicated codebook. Shaping gain of a multi-dimensional constellation is one of the main sources of the performance improvement in comparison to the simple repetition of QAM symbols in LDS. Meanwhile, like LDS, SCMA enjoys the low complexity reception techniques due to the sparsity of SCMA codewords. In this paper a systematic approach is proposed to design SCMA codebooks mainly based on the design principles of lattice constellations. Simulation results are presented to show the performance gain of SCMA compared to LDS and OFDMA.

Low Complexity Techniques for SCMA Detection

Abstract: Sparse code multiple access (SCMA) is a codebook- based non-orthogonal multiplexing technique. In SCMA, the procedure of bit to QAM symbol mapping and spreading of CDMA are combined together and incoming bits are directly mapped to multi-dimensional codewords of SCMA codebook sets. Due to the sparse nature of codewords, SCMA enjoys the low complexity reception, taking advantage of a near optimal message passing algorithm (MPA). This makes SCMA a candidate for supporting massive connectivity in future 5G networks, where the number of users can potentially be higher than the codeword length (spreading factor). To this end, more efficient reception techniques are needed on top of what MPA delivers. In this paper, some complexity reduction techniques are presented to further reduce the SCMA decoding complexity. These techniques are considered from two perspectives: i) transmitter-side technique, by designing SCMA codebooks with a specific structure providing low complexity of detections, and ii) low complexity decoding techniques taking advantage of the SCMA codebook structure. The proposed techniques are evaluated in terms of both complexity and performance. It is shown that significant amount of complexity reduction is possible using the proposed techniques with negligible performance penalty, which paves the way of supporting various applications in future 5G systems using SCMA.

SCMA: A Promising Non-Orthogonal Multiple Access Technology for 5G Networks

Abstract: Sparse code multiple access (SCMA) is a code domain non-orthogonal multiple-access technique introduced for future 5G wireless networks. This paper describes the basic ideas of SCMA, the SCMA codebook design, the encoder and decoder, as well as the SCMA enabled transmission schemes for different application scenarios, including uplink grant-free contention-based transmission, downlink multi-user superposition, and downlink open-loop CoMP for ultra-dense networks even with moving users. We shall show from design principles and application examples that SCMA can resolve some major issues of current wireless systems and establish itself as a strong candidate for 5G networks.

An Ecien t Quasi-Maximum Likelihood Decoding for Finite Constellations

Abstract: In Multi-Input Multi-Output (MIMO) systems, maximum-likelihood (ML) decoding is equivalent to nding the closest lattice point in an N- dimensional complex space. In general, this algorithm is shown to be NP hard. In this paper, we propose a quasi-maximum likelihood algorithm based on Semi- Denite Programming (SDP). We introduce several SDP relaxation models for MIMO systems, with in- creasing complexity. The general algorithm built on these models has a near-ML performance with poly- nomial computational complexity. models has a near-ML performance with polynomial compu- tational complexity. This general algorithm can be employed for any arbitrary constellation for the input constellation. Bit Error Rate (BER) performance in the proposed algorithm is near opti- mal for any M-ary QAM or PSK constellation. Simulation results show that Bit Error Rate (BER) performance of the proposed algorithm is near optimal for M-ary QAM or PSK constellation (with an arbitrary binary labeling, say Gray la- beling). The rest of the paper is organized as follows. In Section II, the MIMO system model is introduced. The distance mini- mization in Euclidean space is formulated in terms of a binary quadratic minimization problem in Section III. Section IV is devoted to the semi-denite relaxation of this problem. Sec- tion V presents the extension of the proposed algorithm for PSK constellation and any other constellation. The simula- tion results is presented in Section VI. Finally, Section VII conclude our paper.

A randomization method for quasi maximum likelihood decoding

Abstract: In Multiple-Input Multiple-Output (MIMO) systems, Maximum-Likelihood (ML) decoding is equivalent to £nding the closest lattice point in an N dimensional complex space. In (1), we have proposed several quasi- maximum likelihood relaxation models for decoding in MIMO systems based on semi-de£nite programming. In this paper, we propose randomization algorithms that £nd a near-optimum solution of the decoding problem by exploring the solution of the corresponding semi-de£nite relaxations.

A Survey on Non-Orthogonal Multiple Access for 5G Networks: Research Challenges and Future Trends

Abstract: Non-orthogonal multiple access (NOMA) is an essential enabling technology for the fifth-generation (5G) wireless networks to meet the heterogeneous demands on low latency, high reliability, massive connectivity, improved fairness, and high throughput. The key idea behind NOMA is to serve multiple users in the same resource block, such as a time slot, subcarrier, or spreading code. The NOMA principle is a general framework, and several recently proposed 5G multiple access schemes can be viewed as special cases. This survey provides an overview of the latest NOMA research and innovations as well as their applications. Thereby, the papers published in this special issue are put into the context of the existing literature. Future research challenges regarding NOMA in 5G and beyond are also discussed.

A Survey on Non-Orthogonal Multiple Access for 5G Networks: Research Challenges and Future Trends

Abstract: Non-orthogonal multiple access (NOMA) is an essential enabling technology for the fifth generation (5G) wireless networks to meet the heterogeneous demands on low latency, high reliability, massive connectivity, improved fairness, and high throughput. The key idea behind NOMA is to serve multiple users in the same resource block, such as a time slot, subcarrier, or spreading code. The NOMA principle is a general framework, and several recently proposed 5G multiple access schemes can be viewed as special cases. This survey provides an overview of the latest NOMA research and innovations as well as their applications. Thereby, the papers published in this special issue are put into the content of the existing literature. Future research challenges regarding NOMA in 5G and beyond are also discussed.

Nonorthogonal Multiple Access for 5G and Beyond

Abstract: Driven by the rapid escalation of the wireless capacity requirements imposed by advanced multimedia applications (e.g., ultrahigh-definition video, virtual reality, etc.), as well as the dramatically increasing demand for user access required for the Internet of Things (IoT), the fifth-generation (5G) networks face challenges in terms of supporting large-scale heterogeneous data traffic. Nonorthogonal multiple access (NOMA), which has been recently proposed for the third-generation partnership projects long-term evolution advanced (3GPP-LTE-A), constitutes a promising technology of addressing the aforementioned challenges in 5G networks by accommodating several users within the same orthogonal resource block. By doing so, significant bandwidth efficiency enhancement can be attained over conventional orthogonal multiple-access (OMA) techniques. This motivated numerous researchers to dedicate substantial research contributions to this field. In this context, we provide a comprehensive overview of the state of the art in power-domain multiplexing-aided NOMA, with a focus on the theoretical NOMA principles, multiple-antenna-aided NOMA design, on the interplay between NOMA and cooperative transmission, on the resource control of NOMA, on the coexistence of NOMA with other emerging potential 5G techniques and on the comparison with other NOMA variants. We highlight the main advantages of power-domain multiplexing NOMA compared to other existing NOMA techniques. We summarize the challenges of existing research contributions of NOMA and provide potential solutions. Finally, we offer some design guidelines for NOMA systems and identify promising research opportunities for the future.

A Survey of Non-Orthogonal Multiple Access for 5G

Abstract: In the fifth generation (5G) of wireless communication systems, hitherto unprecedented requirements are expected to be satisfied. As one of the promising techniques of addressing these challenges, non-orthogonal multiple access (NOMA) has been actively investigated in recent years. In contrast to the family of conventional orthogonal multiple access (OMA) schemes, the key distinguishing feature of NOMA is to support a higher number of users than the number of orthogonal resource slots with the aid of non-orthogonal resource allocation. This may be realized by the sophisticated inter-user interference cancellation at the cost of an increased receiver complexity. In this paper, we provide a comprehensive survey of the original birth, the most recent development, and the future research directions of NOMA. Specifically, the basic principle of NOMA will be introduced at first, with the comparison between NOMA and OMA especially from the perspective of information theory. Then, the prominent NOMA schemes are discussed by dividing them into two categories, namely, power-domain and code-domain NOMA. Their design principles and key features will be discussed in detail, and a systematic comparison of these NOMA schemes will be summarized in terms of their spectral efficiency, system performance, receiver complexity, etc. Finally, we will highlight a range of challenging open problems that should be solved for NOMA, along with corresponding opportunities and future research trends to address these challenges.

Massive machine-type communications in 5g: physical and MAC-layer solutions

Abstract: MTC are expected to play an essential role within future 5G systems. In the FP7 project METIS, MTC has been further classified into mMTC and uMTC. While mMTC is about wireless connectivity to tens of billions of machinetype terminals, uMTC is about availability, low latency, and high reliability. The main challenge in mMTC is scalable and efficient connectivity for a massive number of devices sending very short packets, which is not done adequately in cellular systems designed for human-type communications. Furthermore, mMTC solutions need to enable wide area coverage and deep indoor penetration while having low cost and being energy-efficient. In this article, we introduce the PHY and MAC layer solutions developed within METIS to address this challenge.