Optical Power Reduction for Multiple-Subcarrier Modulated Indoor Wireless Optical Channels

Abstract

Multiple-subcarrier modulated (MSM) indoor wireless optical systems provide high speed bandwidth-efficient communication as well as multi-access capability at low cost. A major drawback of such systems is the high average optical power requirement.To address this problem, trellis codes are designed for data transmission realizing an average optical power reduction as high as 0.95 dB. A simultaneous peak optical power reduction up to 0.44 dB is also possible by employing this technique.Moreover, the unregulated bandwidth available in wireless optical channels is ex ploited to reduce the average optical power in MSM wireless optical systems. Data transmission is confined in a bandwidth located near DC, while reserved carrier sig nals are designed outside the data bandwidth to reduce the average optical power.Distorted out-of-band signals at higher frequency are removed at the receiver by low-pass filtering and not used for detection. To design the out-of-band carrier am plitudes, both a standard optimization algorithm over the set of real numbers and an exhaustive search over discrete constellation are proposed. It is shown that significant average optical power reduction as high as 2.56 dB is achieved.It is assumed that a symbol-by-symbol bias is used in MSM wireless optical sys tems since it offers significant optical power reduction. The received DC bias level provides a degree of diversity and is used at the receiver to improve detection. It is also used to design trellis codes with better distance properties. In this manner, an additional average optical power reduction up to 0.50 dB is achieved with a simulta neous peak power reduction of 0.46 dB for MSM wireless optical systems.lV

Optimizing Constellations for Single-Subcarrier Intensity-Modulated Optical Systems

“…2 depicts a two-dimensional contour plot of the three objective functions together with the admissible region Υ. The constraint in (21) guarantees that the signals belong to the admissible region Υ, therefore satisfying the nonnegativity criterion of the channel. The minimum distance d min in (22) serves as a good measure of error probability performance in the presence of AWGN at high SNR.…”

“…In [20], DMT was shown to suffer considerably in peak-power limited systems. Kang and Hranilovic [21] and You and Kahn [22] proposed techniques to reduce the MSM power penalty.…”

Power Efficient Subcarrier Modulation for Intensity Modulated Channels

“…The main drawback of the MSM family is the poor optical average power efficiency due to the high peak-to-average power ratio (PAPR) in the MSM electrical signal, which requires an increased DC bias to make the signal nonnegative. [15,19] investigated power reduction techniques for MSM, [20] investigated PAPR reduction for OFDM, and [4,21] studied the light emitting diode (LED) nonlinearity effects on OFDM and DMT, respectively.…”

Optical Impulse Modulation for Diffuse Indoor Wireless Optical Channels

“…An insight of this work is that since the optical spectrum is unregulated, the extra degrees of freedom available at the transmitter due to highspeed modulators can be exploited to mitigate the channel amplitude constraints. One way of doing this is by using a set of reserved high-frequency carriers in a multiple-subcarrier modulated wireless optical system [9]. In this section, OIM is presented as an alternative approach of achieving the same goal for optical intensity PAM and PPM systems.…”