Performance Analysis of Multirate Multiservice Optical CDMA Networks Adopting Overlapping PPM Signaling

Abstract

In this paper, an optical code-division multiple-access (OCDMA) system employing overlapping pulse-position modulation (OPPM) is proposed to support multimedia services with different bit-rate and quality-of-service (QoS) requirements in OCDMA networks. Both wrapped OPPM (WOPPM) and unwrapped OPPM (UOPPM) are considered. The proposed system achieves multirate and multi-QoS transmission by using multilength variable-weight optical orthogonal codes (MLVW-OOCs) as signature sequences and using different values of OPPM modulation parameters. Furthermore, numerical analysis is performed for two different receiver structures, namely, correlation receivers with and without hard-limiters. In our analysis, the multiple-access interference (MAI) is considered as the main performance limiting factor. In addition, the performance of the proposed system is evaluated and compared to that of traditional OOK-OCDMA system. Our results reveal that under both pulsewidth and throughput constraints, the performances of the proposed WOPPM-and UOPPM-OCDMA systems are significantly superior to that of OOK-OCDMA system. Index Terms-Bit-error-rate (BER), code division multiple access (CDMA), multiple-access interference (MAI), ON-OFF keying (OOK), overlapping pulse-position modulation (OPPM), quality of service (QoS). I. INTRODUCTIONO PTICAL code-division multiple-access (OCDMA) has gained much attention as one of the promising multipleaccess technique for future optical-access networks [1]-[4]. This is mainly due to the attractive OCDMA features, such as full asynchronous entire optical channel sharing among multiple users without any waiting time, which results in low latency access and less transmission delay. In addition to simplified and distributed network control, secure data transmission, soft capacity on demand, bursty traffic, and the ability to support multimedia services differentiation at the physical layer [5], [6].Both on-off keying (OOK) and pulse-position modulation (PPM) have been commonly used as modulation techniques in Manuscript

Analysis and Design of Adaptive OCDMA Passive Optical Networks

“…The system model considered in this paper is the common On-Off Keying (OOK) OCDMA with chip rate R c and N active users [25], [31]. Each user has a transmitter that consists of an OOK modulator and a 1D/2D optical delay line encoder.…”

Optical Code-Division Multiplexing (OCDM) Networks Adopting Code-Shift Keying/Overlapping PPM Signaling: Proposal and Performance Analysis

“…, N } is composed of one OPPM modulator and M c 2D OCDM encoders (or one tunable). OPPM modulator only involves time delaying of the optical pulses into one of the M p overlapping spreading intervals (called slots) that constitute an OPPM frame [17], [18]. In OPPM technique, a slot of duration τ = LT c , where L is the code length and T c is the chip duration, is divided into γ ∈ {1, 2, .…”

“…The average probability of self interference on a specific mark of an undesired slot is p I /w. For the case M p − 1 + γ < 2γ + 1, p I for 2D OCFHC/OOC OCDM can be calculated as [18]:…”