Large Families of Ternary Sequences with Aperiodic Zero Correlation Zone Sequences for a Multi-Carrier DS-CDMA System

A new method for generating families of ternary spreading sequences is presented. The sequences have aperiodic zero correlation zones and large families are created for a specific sequence length. The sequences are proposed as spreading sequences to provide high capacity and cancel multipath and multiple access interference (MAI) in a single carrier (SC) or multi-carrier (MC) direct-spread code division multiple access (DS-CDMA) system. A Multi-carrier DS-CDMA system is simulated that employs the new sequences as spreading sequences in a multipath channel. Bit error rates (BER) and frame error rates (FER) for a range of Eb/No values are presented and it is demonstrated that the proposed sequences improve the BER and FER performance when used in place of masked Walsh Codes for the frequency selective fading channel evaluated, when a single correlator receiver is used on each sub-carrier

Low-complexity medium access control protocols for QoS support in third-generation radio access networks

One approach to maximizing the efficiency of medium access control (MAC) on the uplink in a future wideband code-division multiple-access (WCDMA)-based third-generation radio access network, and hence maximize spectral efficiency, is to employ a low-complexity distributed scheduling control approach. The maximization of spectral efficiency in third-generation radio access networks is complicated by the need to provide bandwidth-on-demand to diverse services characterized by diverse quality of service (QoS) requirements in an interference limited environment. However, the ability to exploit the full potential of resource allocation algorithms in third-generation radio access networks has been limited by the absence of a metric that captures the two-dimensional radio resource requirement, in terms of power and bandwidth, in the third-generation radio access network environment, where different users may have different signal-to-interference ratio requirements. This paper presents a novel resource metric as a solution to this fundamental problem. Also, a novel deadline-driven backoff procedure has been presented as the backoff scheme of the proposed distributed scheduling MAC protocols to enable the efficient support of services with QoS imposed delay constraints without the need for centralized scheduling. The main conclusion is that low-complexity distributed scheduling control strategies using overload avoidance/overload detection can be designed using the proposed resource metric to give near optimal performance and thus maintain a high spectral efficiency in third-generation radio access networks and that importantly overload detection is superior to overload avoidance

Spread spectrum techniques for indoor wireless IR communications

Multipath dispersion and fluorescent light interference are two major problems in indoor wireless infrared communications systems. Multipath dispersion introduces intersymhol interference at data rates above 10 Mb/s, while fluorescent light induces severe narrowband interference to baseband modulation schemes commonly used such as OOK and PPM. This article reviews the research into the application of direct sequence spread spectrum techniques to ameliorate these key channel impairments without having to resort to complex signal processing techniques. The inherent properties of a spreading sequence are exploited in order to combat the ISI and narrowband interference. In addition, to reduce the impact of these impairments, the DSSS modulation schemes have strived to be bandwidth-efficient and simple to implement. Three main DSSS waveform techniques have been developed and investigated. These are sequence inverse keying, complementary sequence inverse keying, and M-ary biorthogonal keying (MBOK). The operations of the three systems are explained; their performances were evaluated through simulations and experiments for a number of system parameters, including spreading sequence type and length. By comparison with OOK, our results show that SIK, CSIK, and MBOK are effective against multipath dispersion and fluorescent light interference becausc the penalties incurred on the DSSS schemes are between 0-7 dB, while the penalty on OOK in the same environment is more than 17 dB. The DSSS solution for IR wireless transmission demonstrates that a transmission waveform can he designed to remove the key channel impairments in a wireless IR system

A low-loss reconfigurable frequency selective surface based antenna for direct antenna modulation

A directly modulating antenna incorporating a reconfigurable Frequency Selective Surface (FSS) for arbitrary phase modulation is designed and simulated. A 4-layer FSS is used to minimise constellation distortion, with only 1.5dB variation in transmitted magnitude for 360° phase change. Low loss substrates and Barium Strontium Titante (BST) variable capacitors are simulated to reduce the antenna loss to 1.3dB in the filter pass band and achieve an average total efficiency of 65% when producing an 8-PSK constellation

Bit Error Rate Performance of Quadrature Modulation Transmission Using Reconfigurable Frequency Selective Surfaces

A low-complexity radio transmitter is implemented and evaluated using a novel direct antenna modulation (DAM) technique incorporating a reconfigurable antenna. The antenna uses reconfigurable frequency selective surfaces (FSS) to directly phase modulate a radio frequency carrier wave with a quadrature phase shift keying (QPSK) modulation. A hardware-in-the-loop demonstration of the transmitter in a single in single out (SISO) communications system has been developed. To achieve a BER of 10−4 the proposed system required only 4dBm extra transmit power compared with instrument grade transmission

Frequency Selective Surface Loaded Antenna for Direct Antenna Modulation

A reconfigurable antenna loaded with Frequency Selective Surfaces (FSS) to achieve direct antenna phase modulation is presented and simulated. Placing FSS with integrated varactor diodes into a monopole-fed cavity allows control of the transmitted phase of a carrier signal with a bias voltage. As such, Direct Antenna Modulation (DAM) can be achieved, producing a phase modulator that can be included in a low complexity transmitter. Simulation shows such an antenna can achieve QPSK modulation with between 3.5dB and 4.5dB magnitude variation between constellation points with acceptable phase stability with radiation angle in the antenna 3dB beamwidth

Non-iterative downlink training sequence design based on sum rate maximization in FDD massive MIMO systems

This paper considers the problem of downlink (DL) training sequence design with limited coherence time for frequency division duplex (FDD) massive MIMO systems in a general scenario of single-stage precoding and distinct spatial correlations between users. To this end, a computationally feasible solution for designing the DL training sequences is proposed using the principle of linear superposition of sequences constructed from the users' channel covariance matrices. Based on the non-iterative superposition training structure and the P-degrees of freedom (P-DoF) channel model, a novel closed-form solution for the optimum training sequence length that maximizes the DL achievable sum rate is provided for the eigenbeamforming (BF) precoder. Additionally, a simplified analysis that characterizes the sum rate performance of the BF and regularized zero forcing (RZF) precoders in closed-form is developed based on the method of random matrix theory and the P-DoF channel model. The results show that the superposition training sequences achieve almost the same rate performances as state-of-the-art training sequence designs. The analysis of the complexity results demonstrates that more than four orders-of-magnitude reduction in the computational complexity is achieved using the superposition training design, which signifies the feasibility of this approach for practical implementations compared with state-of-the-art iterative algorithms for DL training designs. Importantly, the results indicate that the analytical solution for the optimum training sequence length with the P-DoF channel model can be effectively used with high accuracy to predict the sum rate performance in the more realistic one ring (OR) channel model, and thus, near optimal solutions can be readily obtained without resorting to computationally intensive optimization techniques

Optical energy-constrained slot-amplitude modulation for dimmable VLC. Suboptimal detection and performance evaluation

Energy-constrained slot-amplitude modulation (ECSAM) enables light dimming, eliminates light flicker and constrains the peak optical power while providing robust communication links. However, the complexity of the maximum-likelihood (ML) based ECSAM receiver increases exponentially with required spectral efficiency. This paper provides a comprehensive performance evaluation of ECSAM for the indoor visible light communication (VLC) channel with multipath propagation under realistic illumination constraints and imperfect channel estimation. A sub-optimal receiver that employs a slot-by-slot detection algorithm followed by a slot-correction mechanism for reducing the receiver complexity is proposed. Additionally, the method for optimal selection of parameters when designing the signal waveform is presented. The analytical upper bound on the symbol error rate of ECSAM is derived using the union-bound technique. The results show that the error performance of the sub-optimal receiver are comparable to that of the optimal ML receiver. Compared with conventional power or bandwidth efficient VLC modulation techniques such as multiple pulse position modulation (MPPM) and pulse amplitude modulation (PAM), ECSAM provides complete flexibility in modifying the signal constellation for a desired dimming level to maximise the spectral efficiency and provide a robust bit error rate performance especially in the multipath propagation channel induced intersymbol interference