Fast Maximum-likelihood Decoding Research Articles

A Superimposed Pilot-Based Integrated Radar and Communication System

In this paper, a multiple-input multiple-output (MIMO) integrated radar and communication system based on orthogonal frequency division multiplexing (OFDM) signals is proposed. We consider a bistatic scenario. Exploiting superimposed pilots and orthogonal space-time block code (OSTBC) precoding, transmitted power can be effectively used in both information symbol sending and target sensing with little energy waste and performance degradation. The expectation maximization (EM) is employed to estimate unknown symbols and the channel jointly, which can take the place of matched filtering in traditional radar. In the EM algorithm, we propose to calculate the channel expectation by using Gaussian distribution of the symbol estimation, which can make full use of the OSTBC property of sensing spatial diversity with fast maximum likelihood decoding. The autocorrelation response, and the Doppler response of moving targets in slow time are verified by numerical experiments. Simulations also show superimposed pilot is suitable in the integrated radar and communication system, even when targets with large Doppler shift exist.

On the criteria for designing complex orthogonal space-time block codes

A complex orthogonal design (COD) used in space-time block codes is a kind of combinatorial design. It has been well studied because it has a fast maximum-likelihood decoding algorithm and achieves full diversity. When designing CODs, there are seven characteristics that should be considered, which include code rate, decoding delay, transceiver signal linearization, peak-to-average power ratio, etc. In this paper, we study the relationships among these design criteria. We prove that the maximum rate of generalized CODs (GCODs) that meet the last five criteria is 1/2. Moreover, we present a new method to construct GCODs based on CODs. Using this method on balanced complex orthogonal designs (BCODs), we obtain a novel class of GCODs that performs almost perfectly with respect to all the seven properties.

Signal Constellations of Quasi-Orthogonal Space–Time Codes for MIMO Systems

Orthogonal space---time codes (OSTCs) have recently captivated considerable attention due to their properties of full diversity and low implementation complexity. Quasi-orthogonal space---time codes (QOSTCs) provide full diversity and rate one, which enables simple pair wise decoding to be performed as well as better results to be obtained. In this paper, we derive effective OSTCs and QOSTCs for multi-input multi-output systems, which enable us to calculate coding gain of the OSTC. In addition, the fast maximum-likelihood (ML) decoding at the receiver can be performed separately. Since the QOSTC has a fast ML decoding, the symbol pairs can be decoded independently. With the constellation rotation of the symbol, rotated version of QOSTC is generated. OSTCs are designed to achieve the maximum diversity order for a given number of transmit and receive antennas subject to the constraint of having a simple decoding algorithm. This goal is achieved by properly choosing the signal constellations and comparing bit-error-rate (BER) to signal-to-noise ratio (SNR) for different quadrature pulse shift keying and quadrature-amplitude modulation techniques. The simulation results show that the QOSTC outperforms the OSTC at low SNR whereas it has higher complexity than the OSTC. From simulation result, we also compare the STC and space frequency code at BER versus SNR.

Study on Quasi-Orthogonal Space Time Block Code Based on Amplify-and-Forward Relay Networks

A kind of quasi-orthogonal space time block code for amplify-and-forward relay networks is analyzed in this paper. At the source, 4 single-antenna users transmit the quasi-orthogonal space time block code matrix. At the relay node, fast maximum-likelihood decoding algorithm is adopted and the decoded symbols are then encoded into quasi-orthogonal code which is transmitted through transmit antenna. At the destination, pair-wise decoding algorithm is utilized. Finally we compare the performance of the quasi-orthogonal space time block code in relay networks with that of the quasi-orthogonal space time block code in traditional communication system. Simulation results show that at the given BER of 10-3, the new code can provide about gain of 4dB and 1 dB comparing with that for the traditional quasi-orthogonal code, respectively. And at the given BER of 10-5, the new code can provide about gain of 4.6dB and 2.6dB comparing with that for the old quasi-orthogonal code, respectively.

Quasi Orthogonal Space Time Block Codes Using Various Sub-Block Matrices

Space-time block codes (STBCs) from Orthogonal designs have attracted attention due to their fast maximum likelihood decoding and full diversity, but the maximum symbol transmission rate for complex signals is only ¾ for four transmit antennas so quasi orthogonal STBC was proposed, in this paper the structure and characteristics of some new type of a Quasi-orthogonal space time block codes (QOSTBC)is analyzed, The error performance for these codes for four transmitted antennas over uncorrelated and spatially correlated MIMO channels is investigated. A maximum likelihood (ML) decoding algorithm for the suggested code is also provided.

New design of no-zero-entry single symbol ML decodable STBCs based on group precoding

In multiple-input multiple-output (MIMO) systems, space–time block codes (STBCs) from orthogonal designs (ODs) and coordinate interleaved orthogonal designs (CIOD) have been attracting wider attention due to their amenability for fast (single symbol) maximum-likelihood (ML) decoding, and full-rate with full-rank over quasi-static fading channels. However, most of these codes, for transmitting antennas more than 4, have large number of zero entries in their codeword matrix. Due to the zero entries in the design, the transmitting antennas need to be switched on and off imposing severe hardware constraints. To solve this problem, we propose a method to generate a new class of no-zero-entry single symbol maximum likelihood decodable STBCs (NZESSDCs), which is based on coordinate interleaving and group precoding technique. The ability of the proposed group precoding based NZESSDCs (called G-NZESSDCs) on single symbol ML Decoding and full diversity are analyzed and derived. The performance evaluation is accomplished by numerical simulation and is compared with recently reported NZESSDCs (called C-NZESSDCs). Compared with C-NZESSDCs, the proposed G-NZESSDCs have same bit-error-rate (BER) performance and better peak-to-average ratio (PAPR) performance.

Novel Rotated Quasi-Orthogonal Space-Time Block Codes With the Fixed Nearest Neighbor Number

In this letter, we consider a coherent communication system equipped with multiple transmitter antennas and a single receiver antenna, i.e., a MISO system. For such a system, quasi-orthogonal STBC designs with fast maximum likelihood (ML) decoding have been proposed. However, full diversity cannot be achieved by such codes. The rotated quasi-orthogonal STBC overcomes such shortcomings and enables full diversity and optimal coding gain. However, for large constellations, the performance of such codes deteriorates due to the increase of the number of the nearest neighbor per symbol. In this letter, we propose to add the number of nearest neighbor as a design criterion. We show that for the rotated quasi-orthogonal code proposed in, the number of nearest neighbor tends to infinity when the size of constellation becomes infinite. Furthermore, we propose to have a particular value of rotation and show that this value not only achieves full diversity and maximum coding gain, but also has only a small number of nearest neighbors even for very large constellations.

</title> </titles> <contributors> <person_name sequence='first' contributor_role='author'> <surname></surname> </person_name> <person_name sequence='additional' contributor_role='author'> <surname></surname> </person_name> <person_name sequence='additional' contributor_role='author'> <surname></surname> </person_name> </contributors> <publication_date> <year>0</year> </publication_date> <pages> <first_page></first_page> <last_page></last_page> </pages> <publisher_item> <item_number item_number_type='arNumber'></item_number> </publisher_item> <doi_data> <doi>10.1109/TWC.2007.360551</doi> <resource>http://ieeexplore.ieee.org/lpdocs/epic03/wrapper.htm?arnumber= </resource> </doi_data> </journal_article> <journal_article> <titles> <title><![CDATA[Full-Diversity and Fast ML Decoding Properties of General Orthogonal Space-Time Block Codes for MIMO-OFDM Systems

In this letter we apply the general orthogonal space-time block codes (OSTBC) to MIMO-OFDM systems over frequency-selective fading channels and aim to exploit the potential multipath diversity. By replacing the scalar entry of an OSTBC matrix with the vector of repeated symbols, we obtain a new OSTBC which can achieve both spatial diversity and multipath diversity. Moreover, a fast maximum likelihood (ML) decoding is admitted. Simulation results show that the proposed OSTBC, for two transmit antennas, can obtain a higher diversity gain than the Alamouti code at the same ML decoding complexity

Single-symbol maximum likelihood decodable linear STBCs

Space-time block codes (STBCs) from orthogonal designs (ODs) and coordinate interleaved orthogonal designs (CIOD) have been attracting wider attention due to their amenability for fast (single-symbol) maximum-likelihood (ML) decoding, and full-rate with full-rank over quasi-static fading channels. However, these codes are instances of single-symbol decodable codes and it is natural to ask, if there exist codes other than STBCs form ODs and CIODs that allow single-symbol decoding? In this paper, the above question is answered in the affirmative by characterizing all linear STBCs, that allow single-symbol ML decoding (not necessarily full-diversity) over quasi-static fading channels-calling them single-symbol decodable designs (SDD). The class SDD includes ODs and CIODs as proper subclasses. Further, among the SDD, a class of those that offer full-diversity, called Full-rank SDD (FSDD) are characterized and classified. We then concentrate on square designs and derive the maximal rate for square FSDDs using a constructional proof. It follows that 1) except for N=2, square complex ODs are not maximal rate and 2) a rate one square FSDD exist only for two and four transmit antennas. For nonsquare designs, generalized coordinate-interleaved orthogonal designs (a superset of CIODs) are presented and analyzed. Finally, for rapid-fading channels an equivalent matrix channel representation is developed, which allows the results of quasi-static fading channels to be applied to rapid-fading channels. Using this representation we show that for rapid-fading channels the rate of single-symbol decodable STBCs are independent of the number of transmit antennas and inversely proportional to the block-length of the code. Significantly, the CIOD for two transmit antennas is the only STBC that is single-symbol decodable over both quasi-static and rapid-fading channels.

Unitary space-time codes from Alamouti's scheme with APSK signals

Unitary space-time codes have been used in differential space-time modulation, when neither the transmitter nor the receiver of a multiple antenna system knows the channel state information in Rayleigh fading channels. Among the codes in literature, unitary orthogonal space-time codes, constructed from Alamouti's scheme, have the advantage of fast maximum likelihood (ML) decoding but they require signal constellations to be phase-shift keying (PSK). In this paper, unitary space-time codes are constructed from Alamouti's scheme with amplitude/phase-shift keying (APSK) constellations. We show that the unitary space-time codes from Alamouti's scheme with APSK signals have larger diversity products than those with PSK signals while the complexity of their ML decoding algorithm is comparable. Our newly proposed 4 b/s/Hz code has about 2 dB gain over the same rate code with PSK signals at bit-error rate (BER) of 10/sup -3/ with one receive antenna. We also propose a noncoherent scheme of rate 5 b/s/Hz, which has the same BER performance as the 4 b/s/Hz unitary orthogonal space-time code in DSTM while having comparable decoding complexity.

Signal constellations for quasi-orthogonal space-time block codes with full diversity

Space-time block codes (STBCs) from orthogonal designs proposed by Alamouti, and Tarokh-Jafarkhani-Calderbank have attracted considerable attention lately due to their fast maximum-likelihood (ML) decoding and full diversity. However, the maximum symbol transmission rate of an STBC from complex orthogonal designs for complex signals is only 3/4 for three and four transmit antennas, and it is difficult to construct complex orthogonal designs with rate higher than 1/2 for more than four transmit antennas. Recently, Jafarkhani, Tirkkonen-Boariu-Hottinen, and Papadias-Foschini proposed STBCs from quasi-orthogonal designs, where the orthogonality is relaxed to provide higher symbol transmission rates. With the quasi-orthogonal structure, the quasi-orthogonal STBCs still have a fast ML decoding, but do not have the full diversity. The performance of these codes is better than that of the codes from orthogonal designs at low signal-to-noise ratio (SNR), but worse at high SNR. This is due to the fact that the slope of the performance curve depends on the diversity. It is desired to have the quasi-orthogonal STBCs with full diversity to ensure good performance at high SNR. In this paper, we achieve this goal by properly choosing the signal constellations. Specifically, we propose that half of the symbols in a quasi-orthogonal design are chosen from a signal constellation set A and the other half of them are chosen from a rotated constellation e/sup j/spl phi// A. The resulting STBCs can guarantee both full diversity and fast ML decoding. Moreover, we obtain the optimum selections of the rotation angles /spl phi/ for some commonly used signal constellations. Simulation results show that the proposed codes outperform the codes from orthogonal designs at both low and high SNRs.

On Space-Time Block Codes from Complex Orthogonal Designs

Space-time block codes from orthogonal designs recently proposed by Alamouti, and Tarokh-Jafarkhani-Calderbank have attracted considerable attention due to the fast maximum-likelihood (ML) decoding and the full diversity. There are two classes of space-time block codes from orthogonal designs. One class consists of those from real orthogonal designs for real signal constellations which have been well developed in the mathematics literature. The other class consists of those from complex orthogonal designs for complex constellations for high data rates, which are not well developed as the real orthogonal designs. Since orthogonal designs can be traced back to decades, if not centuries, ago and have recently invoked considerable interests in multi-antenna wireless communications, one of the goals of this paper is to provide a tutorial on both historical and most recent results on complex orthogonal designs. For space-time block codes from both real and (generalized) complex orthogonal designs (GCODs) with or without linear processing, Tarokh, Jafarkhani and Calderbank showed that their rates cannot be greater than 1. While the maximum rate 1 can be reached for real orthogonal designs for any number of transmit antennas from the Hurwitz–Radon constructive theory, Liang and Xia recently showed that rate 1 for the GCODs (square or non-square size) with linear processing is not reachable for more than two transmit antennas. For GCODs of square size, the designs with the maximum rates have been known, which are related to the Hurwitz theorem. In this paper, We briefly review these results and give a simple and intuitive interpretation of the realization. For GCODs without linear processing (square or non-square size), we prove that the rates cannot be greater than 3/4 for more than two transmit antennas.

Two generalized complex orthogonal space-time block codes of rates 7/11 and 3/5 for 5 and 6 transmit antennas

Space-time block codes from orthogonal designs have two advantages, namely, fast maximum-likelihood (ML) decoding and full diversity. Rate 1 real (pulse amplitude modulation-PAM) space-time codes (real orthogonal designs) for multiple transmit antennas have been constructed from the real Hurwitz-Radon families, which also provides the rate 1/2 complex (quadrature amplitude modulation-QAM) space-time codes (complex orthogonal designs) for any number of transmit antennas. Rate 3/4 complex orthogonal designs (space-time codes) for three and four transmit antennas have existed in the literature but no high rate (>1/2) complex orthogonal designs for other numbers of transmit antennas exist. We present rate 7/11 and rate 3/5 generalized complex orthogonal designs for five and six transmit antennas, respectively.