VLC系统中OIM-DCO-OFDM的新方案：提高频谱效率与性能

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本文探讨了一种创新的光索引调制辅助直流偏置光正交频分复用（OIM-DCO-OFDM）方案，旨在提升可见光通信（VLC）系统的性能。相比于传统的索引调制方法，这种新型方案利用索引位区分数据传输的两个通道：一个子载波承载原始信号，另一个子载波承载其共轭信号。这解决了传统相移键控（PSK）和正交幅度调制（QAM）技术中，由于星座图实轴对称导致无法区分原始信号与共轭信号的问题。在OIM-DCO-OFDM中，采用单极性脉冲幅度调制（PAM）来调制星座位，以增强接收端的索引位识别能力。此外，文中提出了一种基于零强迫（ZF）检测器的设计，旨在提高信号的检测精度。通过对比，与双模索引调制辅助DCO-OFDM（DM-DCO-OFDM）方案相比，当频谱效率达到1.21 bits/s/Hz时，OIM-DCO-OFDM在BER为10^-4时显示出1 dB和2 dB的性能提升，而在2.18 bits/s/Hz的效率下，优势更为显著。特别是在M=4的调制阶数下，OIM-DCO-OFDM方案能够实现高达80%的频谱效率提升，这在保证数据传输速率的同时，显著提高了系统效率。总体来说，这项研究对于 VLC 系统的信号处理和调制技术具有重要意义，不仅提高了频谱利用率，还通过解决共轭信号混淆问题，优化了系统的性能指标，为可见光通信系统的进一步发展提供了新的可能。

A Novel Optical IM Aided DCO-OFDM Scheme for VLC Systems 3

eﬃciency. Under the condition of same modulation order, the proposed scheme

has higher spectral eﬃciency improvement than DM-DCO-OFDM.

The rest of this paper is organized as follows. In Section 2, the system model

of DM-DCO-OFDM is reviewed. The OIM-DCO-OFDM system model is pre-

sented in Section 3. The simulation results and spectral eﬃciency analysis are

given in Section 4. Section 5 shows the conclusions.

2 Review of DM-DCO-OFDM

In DM-DCO-OFDM, N subcarriers are divided into G groups, each group con-

tains n subcarriers and p

bits, p

= p

+ p

. p

bits are fed into index selec-

tor to determine index pattern and p

bits are modulated by two diﬀerent constel-

lations, M

-ary A and M

-ary B. For each group, k subcarriers out of n subcar-

riers are selected to transmit the constellation A signals, and other n − k subcar-

riers transmit the constellation B signals. The transmitted bits in each group can

be calculated by p

= blog

(C (n, k))c + klog

) + (n − k)log

), where

bc is the ﬂoor function, C (n, l) is the binomial coeﬃcient. Noted that the symbol

of constellation A and constellation B should be diﬀerentiated with each other.

Otherwise, the index bits cannot be recovered at the receiver, which will lead to

bad BER performance. After index modulation and constellation mapping, Her-

mitian symmetry operation is used to obtain real signals before IFFT operation.

The Hermitian symmetry property can be represented by



= X

∗

N−i

, 0 < i < N/2

= X

N/2

= 0

(1)

where X

∈ X, X= [X

, . . . ,X

N−1

] is the frequency-domain complex signal-

s after constellation mapping. Then IFFT and parallel-to-serial operation are

employed to generate time-domain signal. Finally, a suitable DC-bias should be

added on the time-domain signals to create unipolar signals, i.e., only the time-

domain unipolar signals can be transmitted via LEDs. At the receiver side, the

reverse operations are used to obtain transmitted frequency-domain signals. The

maximum likelihood detector or the log-likelihood ratio detector can be selected

to recover index bits and constellation bits.

3 System Model of OIM-DCO-OFDM

Motivated by DM-DCO-OFDM, the proposed OIM-DCO-OFDM scheme also

uses all of subcarriers to transmit signals, which can achieve higher spectral

eﬃciency than O-OFDM-IM scheme. The block diagram of OIM-DCO-OFDM

transceiver is given in Fig. 1. For each OFDM block, m bits and N carriers

are divided into G groups, each group contains p bits and n subcarriers i.e.,

m = pG, N = nG. For each group, p bits are split into three parts, p

, p

and

, i.e., p = p

+ p

. The index bits p

are fed into index selector to choose

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VLC系统中OIM-DCO-OFDM的新方案：提高频谱效率与性能

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