Lie-Liang Yang

Performance of generalized multicarrier DS-CDMA over Nakagami-m fading channels

A class of generalized multicarrier direct sequence code-division multiple-access (MC DS-CDMA) schemes is defined and its performance is considered over multipath Nakagami-m fading channels. The spacing between two adjacent subcarriers of the generalized MC DS-CDMA is a variable, allowing us to gain insight into the effects of the spacing on the bit error rate (BER) performance of MC DS-CDMA systems. This generalized MC DS-CDMA scheme includes the subclasses of multitone DS-CDMA and orthogonal MC DS-CDMA as special cases. We present a unified analytical framework for determining the exact average BER of the generalized MC DS-CDMA system over generalized multipath Nakagami-m (1960) fading channels. The optimum spacing of the MC DS-CDMA system required for achieving the minimum BER is investigated and the BER performance of the system having optimum spacing is evaluated. The resultant BER is compared with that of both multitone DS-CDMA and orthogonal MC DS-CDMA.

Multicarrier DS-CDMA: a multiple access scheme for ubiquitous broadband wireless communications

We identify some of the key problems that may be encountered when designing a broadband multiple access system with bandwidth on the order of tens or even hundreds of megahertz. We commence with a comparative discussion in terms of the characteristics of three typical code-division multiple access schemes: single-carrier direct-sequence CDMA (SC DS-CDMA), multicarrier CDMA (MC-CDMA), and multicarrier DS-CDMA (MC DS-CDMA). Specifically, their benefits and deficiencies are analyzed when aiming to support ubiquitous communications over a variety of channels encountered in indoor, open rural, suburban, and urban environments. It is shown that when communicating in such diverse environments, both SC DS-CDMA and MC-CDMA exhibit certain limitations that are hard to circumvent. By contrast, when appropriately selecting the system parameters and using transmit diversity, MC DS-CDMA becomes capable of adapting to such diverse propagation environments at a reasonable detection complexity.

A recursive algorithm for the error probability evaluation of M-QAM

A general recursive algorithm for the efficient and accurate computation of the bit error rate (BER) of square-shaped M-QAM constellations over additive white Gaussian noise (AWGN) channels is derived. We take advantage of the relationship amongst different square-shaped M-QAM constellations using Gray coded bit mapping.

Serial acquisition of DS-CDMA signals in multipath fading mobile channels

This paper compares the mean acquisition time (MAT) performance of two serial search acquisition schemes over frequency-selective multipath Rayleigh fading channels. Both the conventional cell-by-cell detection and the novel joint two-cell detection are characterized. In contrast to the majority of published results considering only one correct timing state (H/sub 1/ cell) in the uncertainty region of the pseudonoise (PN) sequence, this paper analyzes the MAT performance of the serial search acquisition schemes with multiple timing states in the uncertainty region. The MAT performance comparison between the conventional cell-by-cell detection and the joint two-cell detection shows that the latter can achieve an improved acquisition performance at almost the same complexity.

Redundant residue number system based error correction codes

In this paper residue number system (RNS) arithmetic and redundant residue number system (RRNS) based codes as well as their properties are reviewed. We propose a number of applications for RRNS codes and demonstrate how RRNS codes can be employed in global communication systems, in order to simplify the associated systems by unifying the entire encoding and decoding procedure across global communication systems.

Transmit-Diversity-Assisted Space-Shift Keying for Colocated and Distributed/Cooperative MIMO Elements

Space-shift keying (SSK) modulation is a recently proposed multiple-input-multiple-output (MIMO) technique, which activates only a single transmit antenna during each time slot and uses the specific index of the activated transmit antenna to implicitly convey information. Activating a single antenna is beneficial in terms of eliminating the interchannel interference and mitigates the peak-to-mean power ratio while avoiding the need for synchronization among transmit antennas. However, this benefit is achieved at a sacrifice, because the transmit diversity gain potential of the multiple transmit antennas is not fully exploited in existing SSK-assisted systems. Furthermore, a high-SSK throughput requires the transmitter to employ a high number of transmit antennas, which is not always practical. Hence, we propose four algorithms-open-loop space-time space-shift keying (ST-SSK), closed-loop feedback-aided phase rotation, feedback-aided power allocation, and cooperative ST-SSK-to achieve a diversity gain. The performance improvements of the proposed schemes are demonstrated by Monte Carlo simulations for spatially independent Rayleigh fading channels. Their robustness to channel estimation errors is also considered. We advocate the proposed ST-SSK techniques, which can achieve a transmit diversity gain of about 10 dB at a bit error rate (BER) of 10-5, at the cost of imposing a moderate throughput loss that is dedicated to a modest feedback overhead. Furthermore, our proposed ST-SSK scheme lends itself to efficient communication, because the deleterious effects of deep shadow fading no longer impose spatial correlation on the signals that are received by the antennas, which cannot readily be avoided by colocated antenna elements.

Generalised Pre-Coding Aided Spatial Modulation

A new Multiple Input Multiple Output (MIMO) transmission scheme termed as Generalised Pre-coding aided Spatial Modulation (GPSM) is proposed, where the key idea is that a particular subset of receive antennas is activated and the activation pattern itself conveys useful information. This is in contrast to the previously proposed Spatial Modulation (SM) schemes, which operated by activating a specific subset of transmit antennas. We provide both analytical and numerical results characterizing the GPSM scheme proposed for both conventional as well as for large-dimensional MIMO configurations subject to both realistic imperfect Channel State Information at the Transmitter (CSIT) and to the low-rank approximation invoked for large-dimensional MIMO configurations. We also design a so-called reinforcement matrix for attaining substantial performance improvements for our proposed GPSM scheme. Our investigations show that the GPSM scheme constitutes a flexible alternative to the state-of-the-art MIMO transmission schemes, especially because it is capable of achieving a high throughput. Moreover, the benefits of mapping information to the spatial domain rather than relying on conventional modulation has substantial benefits in the medium to high Signal to Noise Ratio (SNR) region. Quantitatively, GPSM is capable of supporting the same throughput as the conventional full-multiplexing gain based MIMO arrangements at an SNR gain of about 1dB at the same receiver complexity. Furthermore, the reinforcement matrix aided GPSM scheme attains a further 3-4dB performance improvement as compared to the conventional GPSM scheme.

Software-defined-radio-assisted adaptive broadband frequency hopping multicarrier DS-CDMA

Against the backdrop of the explosive expansion of the Internet and the continued dramatic increase in demand for high-speed multimedia wireless services, there is an urgent demand for flexible, bandwidth-efficient transceivers. Multistandard operation is also an important requirement for the future generations of wireless systems. This article presents a versatile broadband multiple access scheme, combining frequency hopping with multicarrier DS-CDMA (FH/MC DS-CDMA). In the short term, the proposed FH/MC DS-CDMA scheme could be employed in the existing second- and third-generation CDMA system bands. Hence, it has the potential of supporting compatibility with these existing systems. This article also shows that FH/MC DS-CDMA exhibits a high grade of flexibility in the context of system design and parameter reconfiguration. Therefore, in the long term, the proposed FH/MC DS-CDMA scheme is capable of meeting the requirements of future broadband mobile wireless systems, with the aid of introducing more advanced techniques facilitated by the employment of software-defined radios (SDR) and with the advent of efficient adaptive baseband algorithms.

SVD-Assisted Multiuser Transmitter and Multiuser Detector Design for MIMO Systems

A novel singular value decomposition (SVD)-based joint multiuser transmitter (MUT) and multiuser detector (MUD) aided multiple-input-multiple-output (MIMO) system is proposed, which takes advantage of the channel state information (CSI) of all users at the base station (BS), but only of the mobile station (MS)s own CSI, to decompose the multiuser (MU) MIMO channels into parallel single-input-single-output (SISO) channels, where each SISO channel corresponds to the singular values of a particular MSs channel matrix. Based on the proposed scheme, the SVD-based transmission carried out in the context of a single user can readily be extended to the MU case for both the uplink (UL) and downlink (DL). As a beneficial application of the proposed scheme, we improve the systems achievable throughput and highlight its future applications.

Transmitter Preprocessing Aided Spatial Modulation for Multiple-Input Multiple-Output Systems

This paper proposes and studies a transmitter preprocessing aided spatial modulation (PSM) scheme, which conveys information jointly by a conventional amplitude-phase modulation (APM) and a preprocessing aided space shift keying (pre-SSK) modulation. In contrast to the existing SSK modulation, which carries information using the indexes of transmitter antennas and assumes channel state information at receiver (CSIR), the pre-SSK modulation extracts the transmitted information using the indexes of receive antennas and assumes channel state information at transmitter (CSIT). This paper addresses the issues of preprocessing optimization and detection of PSM signals. Furthermore, the bit-error-rate (BER) performance of the PSM is investigated, when assuming that the channel from any transmit antenna to any receive antenna experiences independent Rayleigh fading. Our studies show that, when appropriately designed, the pre-SSK and APM invoked can enhance each other, resulting in that the PSM is capable of attaining a better BER performance than the corresponding pure pre-SSK and pure APM.