Non-Coherent Code Acquisition in the Multiple Transmit/Multiple Receive Antenna Aided Single- and Multi-Carrier DS-CDMA Downlink

We analyse the characteristics of the Non-Coherent (NC) Multiple Transmit/Multiple Receive (MTMR) antenna aided Multi-Carrier (MC) DS-CDMA downlink employing a serial search based acquisition scheme, when communicating over spatially uncorrelated Rayleigh channels. The associated Mean Acquisition Time (MAT) performance trends are characterised as a function of both the number of antennas and that of the number of subcarriers. It is shown that the employment of both multiple transmit antennas and multiple subcarriers is typically detrimental in terms of the achievable NC acquisition performance, while that obtained by exploiting multiple receive antennas is always beneficial, regardless whether single-path or multi-path scenarios are considered. Based on our results justified by information theoretic considerations, our acquisition design guidelines are applicable to diverse NC MTMR antenna aided scenarios. Index Terms—MC-DS-CDMA, non-coherent, transmit/receive/ frequency diversity

Analysis of Serial Search Based Code Acquisition in Multiple Transmit Antenna Aided DS-CDMA Downlink

In this contribution we investigate the serial search based initial code acquisition performance of DSCDMA employing multiple transmit antennas both with and without Post-Detection Integration (PDI), when communicating over uncorrelated Rayleigh channels. We characterise the associated performance trends as a function of the number of transmit antennas. It is demonstrated that in contrast to our expectation, the achievable correct detection probability PD degrades at low c o E /I values, as the number of transmit antennas is increased. It is extremely undesirable to degrade the achievable acquisition performance, when the system is capable of attaining its target bit error rate performance at reduced SINR values, as a benefit of employing multiple transmit antennas. Our future research will focus on the study of designing iterative turbo-like acquisition schemes designed for MIMO systems

Differentially Coherent Code Acquisition in the MIMO-Aided Multi-Carrier DS-CDMA Downlink

Both differentially coherent and non-coherent code acquisition schemes designed for the multiple-input multiple-output (MIMO)-aided multi-carrier (MC)-DS-CDMA downlink are analysed, when communicating over uncorrelated Rayleigh channels. The attainable mean acquisition time (MAT) performance is studied as a function of both the number of multiple transmit/multiple receive antennas and that of the number of subcarriers. It is demonstrated that in contrast to the expectations, when the number of multiple transmit antennas and/or that of the subcarriers is increased in both the differentially coherent and the non-coherent code acquisition scenarios, the achievable MAT deteriorates over the entire signal-to-interference plus noise ratio (SINR) per chip (Ec/Io) range considered, except for the scenario of single-carrier (SC)-DS-CDMA using P ¼ 2 transmit antennas and R ¼ 1 receive antenna. As expected, the degree of performance degradation depends upon the specific scheme and the Ec/Io ratio considered, although paradoxically, the correctly synchronised MIMO-aided system is capable of attaining its target bit error ratio performance at reduced SINR values

MIMO CDMA-based Optical SATCOMs: A New Solution

A new scheme for MIMO CDMA-based optical satellite communications (OSATCOMs) is presented. Three independent problems are described for up-link and down- link in terms of two distinguished optimization problems. At first, in up-link, Pulse-width optimization is proposed to reduce dispersions over fibers as the terrestrial part. This is performed for return-to-zero (RZ) modulation that is supposed to be used as an example in here. This is carried out by solving the first optimization problem, while minimizing the probability of overlapping for the Gaussian pulses that are used to produce RZ. Some constraints are assumed such as a threshold for the peak-to-average power ratio (PAPR). In down-link, the second and the third problems are discussed as follows, jointly as a closed-form solution. Solving the second optimization problem, an objective function is obtained, namely the MIMO CDMA-based satellite weight-matrix as a conventional adaptive beam-former. The Satellite link is stablished over flat un-correlated Nakagami-m/Suzuki fading channels as the second problem. On the other hand, the mentioned optimization problem is robustly solved as the third important problem, while considering inter-cell interferences in the multi-cell scenario. Robust solution is performed due to the partial knowledge of each cell from the others in which the link capacity is maximized. Analytical results are conducted to investigate the merit of system.Comment: IEEE PCITC 2015 (15-17 Oct, India

Initial synchronisation of wideband and UWB direct sequence systems: single- and multiple-antenna aided solutions

This survey guides the reader through the open literature on the principle of initial synchronisation in single-antenna-assisted single- and multi-carrier Code Division Multiple Access (CDMA) as well as Direct Sequence-Ultra WideBand (DS-UWB) systems, with special emphasis on the DownLink (DL). There is a paucity of up-to-date surveys and review articles on initial synchronization solutions for MIMO-aided and cooperative systems - even though there is a plethora of papers on both MIMOs and on cooperative systems, which assume perfect synchronization. Hence this paper aims to ?ll the related gap in the literature

Differential Coherent Code Acquisition in the Multiple Transmit/Receive Antenna Aided DS-CDMA Downlink

In this contribution we investigate both differentially coherent and noncoherent code acquisition schemes in the multiple transmit/receive antenna aided DS-CDMA downlink, when communicating over uncorrelated Rayleigh channels. It is demonstrated that in contrast to our expectations, the achievable Mean Acquisition Time (MAT) degrades at low Ec/Io values, as the number of transmit antennas is increased in both differentially coherent and noncoherent code acquisition system scenarios, even though the degree of performance degradation depends upon the specific scheme considered. Ironically, our findings suggest that increasing the number of transmit antennas in a MIMO-aided CDMA system results in combining the low-energy, noise-contaminated signals of the transmit antennas, which ultimately increases the MAT by an order of magnitude, when the SINR is relatively low. Therefore our future research will be aimed at specifically designing acquisition schemes for MIMO systems

Scaling up MIMO: Opportunities and Challenges with Very Large Arrays

This paper surveys recent advances in the area of very large MIMO systems. With very large MIMO, we think of systems that use antenna arrays with an order of magnitude more elements than in systems being built today, say a hundred antennas or more. Very large MIMO entails an unprecedented number of antennas simultaneously serving a much smaller number of terminals. The disparity in number emerges as a desirable operating condition and a practical one as well. The number of terminals that can be simultaneously served is limited, not by the number of antennas, but rather by our inability to acquire channel-state information for an unlimited number of terminals. Larger numbers of terminals can always be accommodated by combining very large MIMO technology with conventional time- and frequency-division multiplexing via OFDM. Very large MIMO arrays is a new research field both in communication theory, propagation, and electronics and represents a paradigm shift in the way of thinking both with regards to theory, systems and implementation. The ultimate vision of very large MIMO systems is that the antenna array would consist of small active antenna units, plugged into an (optical) fieldbus.Comment: Accepted for publication in the IEEE Signal Processing Magazine, October 201

Analysis and optimization of pilot symbol-assisted Rake receivers for DS-CDMA systems

The effect of imperfect channel estimation (CE) on the performance of pilot-symbol-assisted modulation (PSAM) and MRC Rake reception over time- or frequency-selective fading channels with either a uniform power delay profile (UPDP) or a nonuniform power delay profile (NPDP) is investigated. For time-selective channels, a Wiener filter or linear minimum mean square error (LMMSE) filter for CE is considered, and a closed-form asymptotic expression for the mean square error (MSE) when the number of pilots used for CE approaches infinity is derived. In high signal-to-noise ratio (SNR), the MSE becomes independent of the channel Doppler spectrum. A characteristic function method is used to derive new closed-form expressions for the bit error rate (BER) of Rake receivers in UPDP and NPDP channels. The results are extended to two-dimensional (2-D) Rake receivers. The pilot-symbol spacing and pilot-to-data power ratio are optimized by minimizing the BER. For UPDP channels, elegant results are obtained in the asymptotic case. Furthermore, robust spacing design criteria are derived for the maximum Doppler frequency