Communications and Network, 2013, 5, 390-393

http://dx.doi.org/10.4236/cn.2013.53B2071 Published Online September 2013 (http://www.scirp.org/journal/cn)

Performance Comparison between OQAM and

N-continuous OFDM

Guobing Cheng, Huilei Li, Shaoqian Li, Lisha Gong, Binhong Dong, Peng Wei

National Key Laboratory of Science and Technology on Communications,

University of Electronic Science and Technology of China, Chengdu, China

Email: guobingcheng12@163.com

Received August, 2013

ABSTRACT

Orthogonal frequency division multiplex/offset QAM (OFDM/OQAM) and N-continuous OFDM are both improved

multi-carrier modulation (MCM) techniques for the transmission of signals over multipath fading channels. In this pa-

per, we aim to compare these two techniques with respect to out-of-band radiation , bit error ratio (BER) and calcu lation

complexity. Analysis and simulation results show that, compared to the N-continuous OFDM, the OFDM/OQAM has

lower out-of-band radiation, calculation consumption and similar BER performance.

Keywords: OFDM/OQAM; N-continuous OFDM; Out-of-band Radiation

1. Introduction

Orthogonal frequency division multiplexing (OFDM) is

an efficient scheme and it has been some practical appli-

cations. However, the trad itional OFDM has some intrin-

sic drawbacks that the discontinuous phase between ad-

jacent symbols leads to high out-of-band radiations and

its robustness to multi-path propagation effect is acquired

by the insertion of a cyclic prefix (CP). To alleviate these

drawbacks, another MCM schemes such as N-continuous

OFDM and OFDM/offset QAM (OFDM/OQAM) are

proposed in [1,2] respectively. Compared to traditional

CP-OFDM, OFDM/OQAM may provide a higher useful

bit rate since it operates without CP and N-continuous

OFDM has less out-of-band radiation since it has several

continuous order of derivatives at the edge of adjacent

OFDM symbols.

For OFDM/OQAM system, pulse shapes with good

time-frequency localization (TFL) can be introduced.

Among these, a pulse shape named extended Gaussian

functions (EGF) is widely used and its TFL can be ad-

justed by the time and frequency real parameters [3].

Through selecting a suitable parameter, an OFDM/

OQAM signal with very low out-of-band radiation can

be acquired [4]. On the other hand, in the traditional

OFDM system, each OFDM symbol is independently

and the transmitted signals are no t continuous, leading to

high out-of-band radiation. In order to overcome the dis-

continuities between consecutive OFDM symbols, N-

continuous OFDM scheme is proposed at the price of

increasing calculation complexity and/or system per-

formance. Therefore, we have to comprise between these

aspects for practical application.

In this paper, we compare the performance of OFDM/

OQAM and N-continuous OFDM. Firstly, the system

models of them are given in section II. And then we ana-

lyze the out-of-band radiation, bit error ratio (BER) and

calculation complexity of these two schemes in section

III. The simulation results are shown in section IV. Brief

conclusion is given in section V. The analysis and simu-

lation results show that, compared to the N-continuous

OFDM, the OFDM/OQAM system has similar system

performance, lower out-of-band radiation and less calcu-

lation consumption.

2. System Model

2.1. System Model of OFDM/OQAM System

The baseband version of a continuous-time OFDM/

OQAM transmitting signal can be written as [2]

,0

12

,0

0,

mn

Mjjmt

mn

nm

staeegt n

(1)

with M an even number of sub-carriers, ,mn the real-

valued symbol conveyed by the sub-carrier of index m

during the symbol time of index n0

a

the subcarrier

spacing and 0

the time offset between the adjacent real

part and imaginary part of an OFDM/OQAM symbol.

00 0

1 2T1

, with 0 the duration of the complex-

valued symbols. T

,mn

is an additional phase term given

by

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