A novel transmitter code optimisation technique based on adaptivecode-to-user allocation is presented for interference exploitation on the time division duplex downlink of binary phase shift keying-based multiple car...
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A novel transmitter code optimisation technique based on adaptivecode-to-user allocation is presented for interference exploitation on the time division duplex downlink of binary phase shift keying-based multiple carrier code division multiple access systems. The principle of the proposed technique is to exploit the dependency of multiple access interference on the instantaneous symbol values of the active users. The objective is to adaptively allocate the available spreading sequences to users on a symbol-by-symbol basis to enhance the ratio between constructive and destructive interference and thus optimise the decision variables at the downlink receivers. The resulting signal-to-interference plus noise improvement happens by making use of the energy inherent in the system so the performance benefit is attained with no additional power-per-user investment. It will be shown that when this optimisation technique is incorporated with common pre- and post-equalisation schemes, a significant bit error rate performance improvement is achieved while the associated adaptation overhead is kept less than 6% of the available bandwidth.
Optical code division multiple access (OCDMA) systems can support multiple classes of service by differentiating code parameters, power level, and diversity order. In this paper, we analyze bit error rate (BER) perfor...
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Optical code division multiple access (OCDMA) systems can support multiple classes of service by differentiating code parameters, power level, and diversity order. In this paper, we analyze bit error rate (BER) performance of a multiclass 1-D/2-D OCDMA system and propose a new approximation method that can be used to generate accurate estimation of system BER using a simple mathematical form. The proposed approximation provides insight into proper system level analysis, system level design and sensitivity of system performance to the factors such as code parameters, power level, and diversity order. Considering code design, code cardinality, and system performance constraints, two design problems are defined and their optimal solutions are provided. We, then, propose an adaptive OCDMA passive optical networks (OCDMA-PON) that adaptively shares unused resources of inactive users among active ones to improve upstream system performance. Using the approximated BER expression and defined design problems, two adaptive code allocation algorithms for the adaptive OCDMA-PON are presented and their performances are evaluated by simulation. Simulation results show that the adaptive code allocation algorithms can increase average transmission rate or decrease average transmitted optical power of optical network units for dynamic traffic patterns. According to the simulation results, for an adaptive OCDMA-PON with BER value of 10(-7) and user activity probability of 0.5, transmission rate (transmitted optical power) can be increased (decreased) by a factor of 2.53 (0.25) compared to fixed code assignment.
In this letter, we use stochastic optimization to schedule data transmissions in an adaptive optical code division multiple-access (OCDMA) system to maximize transmission rate. We employ Lyapunov drift theory to formu...
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In this letter, we use stochastic optimization to schedule data transmissions in an adaptive optical code division multiple-access (OCDMA) system to maximize transmission rate. We employ Lyapunov drift theory to formulate a general optimization problem for rate-maximized scheduling in which user codes are adaptively assigned such that time-averaged transmission rate is maximized and important system parameters such as stability and BER performance are maintained. Simulation results show that the overall transmission rate in a rate-maximized scheduled OCDMA system can be up to 3 (1.2) times better than the transmission rate in its counterpart OCDMA system with fixed code assignment scheme (with rate-efficient codeallocation algorithm).
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