Concatenated fibre-wireless channel identification in a multiuser CDMA environment

Abstract

Radio-over-fibre (ROF) has received increasing attention for its ability to enable broadband wireless access. This fibre-based wireless access scheme meets the demand for broadband service by integrating the high capacity of optical networks with the flexibility of radio networks (the optical and wireless channels are concatenated with one another). There are, however, impairments that come with this appealing technology. The nonlinear distortion of the optical link and the multipath dispersion of the wireless channel are two of the major factors. In order to limit the effects of these distortions, estimation, and subsequently equalisation, of the concatenated fibrewireless channel needs to be done. An estimation algorithm for the fibre-wireless uplink in a multiuser code division multiple access (CDMA) environment is presented using pseudonoise training sequences. It has already been shown by Fernando et al. (2001) that identification of the fibrewireless uplink is possible in a single user CDMA environment. However, the more difficult task of identification in a multiuser spread spectrum environment, which is more realistic, is shown. In the multiuser case, the cumulative effect of multiuser interference, multipath dispersion, nonlinear distortion and noise should all be handled together which makes it more challenging. Numerical evaluations of the developed algorithm show that a good estimation of both the linear and nonlinear systems is possible in the presence of 16 independent users and an signalto-noise ratio (SNR) of 22 dB. The estimation accuracy increases with the length of the PN sequence.

Tensor based receivers for nonlinear Radio Over Fiber uplinks in multiuser CDMA systems

“…The E/O conversion for each channel is modeled by the following polynomial CIX + c3lxl 2x, with Cl == -0.35 and C3 == 1 [1], [20]. Table II, where a short training sequence is used to obtain an initial estimate of the channel A (0) -Q matrix H .…”

Transmission of wired and wireless signals employing a hybrid radio-over-fibre passive-optical-network-based on dual quadrupling-frequency

“…However, 60 GHz wireless signals have high-path losses. In order to extend the wireless signal coverage, radio-over-fibre (ROF) technology was proposed [6][7][8][9]. ROF has been regarded as a key technique to meet bandwidth requirements for delivering multi-Gb/s data and video services to large number of users because it shows many advantages such as low-cost, decreasing power consumption, large bandwidth, high-transmission performance and so on [10].…”

Estimation of radio-over-fiber uplink in a multiuser CDMA environment using PN spreading codes

“…The least squares polynomial fit is then applied to the signalsq(n) and r(n). Refer to [1] and [6] for a detailed explanation.…”

“…The use of PN sequences is attractive because they are already widely used in spread spectrum communications. In [6], the fiber-wireless system was identified using a common wireless channel for each mobile user. This sort of environment may be encountered in a highly restricted indoor area and therefore has practical limitations.…”

“…This sort of environment may be encountered in a highly restricted indoor area and therefore has practical limitations. In this paper, by extending the work in [1] and [6], we propose the identification of a Wiener system in a multiuser CDMA discrete-time passband communication system where each user encounters a different wireless channel; we also include the effects of both wireless and optical channel noise. We then propose an algorithm to alleviate MAI which in turn improves identification accuracy.…”