
Advantages of A Novel Modulation technology Time
Shifted Non-orthogonal Frequency Division
Multiplexing
He Mingyan
Information Engineering College
Dalian University
Dalian, China
mingyan321@126.com
Abstract—Orthogonal frequency division multiplexing
(OFDM) is a high efficient multi-carrier modulation technique
for broadband communication applications with high peak to
average power ratio (PAPR). In order to reduce the adverse
effects of high PAPR on communication, a novel time shifted
non-orthogonal frequency division multiplexing (TS-NFDM)
technology is created by introducing the time-shift factor into
multi-carrier modulation in this paper, which brings distinct
advantages on bandwidth efficiency and PAPR. According to the
analysis of constellation diagram and experiment results, the
bandwidth efficiency of TS-NFDM is 4.29 times as higher as
OFDM approximately. PAPR of TS-NFDM also could be
reduced better than OFDM.
Keywords—OFDM; Time Shifted Non-orthogonal Frequency
Division Multiplexing (TS-NFDM); bandwidth efficiency; PAPR
I. INTRODUCTION
Orthogonal frequency-division multiplexing ( OFDM ) has
developed into a popular scheme for wideband digital
communication, used in applications such as digital television,
High Definition television, DSL Internet access, wireless
networks, and 4G mobile communications. MIMI-OFDM has
been the dominant air interface for 4G and 5G broadband
wireless communications. The symbol rate of OFDM is the
closest to the Nyquist rate[1]. There are some researches on
breaking Nyquist rate without consideration of ISI and the
change of minimum distance of signals in a signal space. Mazo
showed that for ideal sinc pulses the symbol time can be
reduced to 0.802T without suffering any loss in minimum
Euclidean distance [2], and the signaling rate can be increased
with as much as 25%. The subsequent researches [3], [4] have
shown the methods of computing the minimum distance of
faster-than-Nyquist (FTN) signaling. The time and frequency
compressions turns out that spectral savings of at least 50% are
possible in principle[5], the bandwidth per data symbol can be
further reduced. A non-orthogonal modulation method has a
much higher transmission rate than the traditional[6].
Time shifted non-orthogonal frequency division
multiplexing (TS-NFDM) is established in this paper. The new
modulation method which is improving [7], has much higher
bandwidth efficiency than OFDM. Just like the character FDM
of OFDM, TS-NFDM divides a radio channel into a large
number of closely spaced sub-channels, but the sub-channels
are non-orthogonal. TS-NFDM has the distinct advantages on
bandwidth efficiency and peak to average power ratio (PAPR),
which are brought by its time-shift character. The comparison
of TS-NFDM and OFDM on bandwidth efficiency and PAPR
is shown in this paper.
II. T
HE WAVEFORM STRUCTURE OF TS-NFDM
The signal of TS-NFDM can be described as following
11
() ( )
i
Q
F
ij ij
ij
gt g t
t
= =
= −
∑∑
(1)
where
is the sub-carrier i,
()(),
()
0,
ij ij ij ij ij
ij ij
ij
t go t t T
gt
tT
tt
t
Φ− − ∈
−=
∉
,
,
()
0,
ij ij
ij ij
ij
a tT
t
tT
t
∈
Φ− =
∉
is the amplitude of the sub-carrier ij,
denotes the valid period of the sub-carrier ij. The valid
periods are mostly the same, but there are time-shifts between
different valid periods.
0
2
()sin()
ij ij ij
ij
n
go t t
T
tt
π
−= −
is called the
base sub-carrier, where
. All of the sub-carriers
are divided into F groups.
is the period of base sub-carrier j
(
) in group i (
), where
is the number
of sub-carriers in group i . When
, there
could be
and
,
and
.
is the total number of base sub-carriers in one
symbol. In other words, the frequencies of the base sub-carriers
in one group are the same, the sub-carriers are included in the
same sub-channel, and
is the number of sub-channels.
denotes the time-shift of the sub-carrier
.
is the
interval between two adjacent sub-carriers, which is the same
2016 International Conference on Automatic Control and Information Engineering (ICACIE 2016)
© 2016. The authors – Published by Atlantis Press