![www.projectsatbangalore.com 09591912372
MIMO-OFDM PAPR Reduction by Residue Number
System
Yi Yao, Jianhao Hu
National Key Lab of Science and Technology on Communication, UESTC
Chengdu, Sichuan 611731, China
Abstract-Multi-input multi-output orthogonal frequency
division multiplexing (MIMO-OFDM) system has been widely
accepted a promising scheme for wireless communication systems.
However it still suffers the high peak-to-average power ratio
(PAPR), which is the main limitation of OFDM-based systems. In
this paper, we present a residue number system (RNS) based
PAPR reduction scheme in MIMO-OFDM systems. The proposed
scheme makes use of the properties of RNS to greatly reduce the
PAPR and the computational complexity as well. Compared with
the partial transmit sequence (PTS) scheme, the RNS-based
PAPR reduction scheme has not only much better PAPR
reduction performance without restriction to modulation format,
but also low computational complexity without side information.
Keywords-RNS, PAPR, PTS, MIMO
I. INTRODUCTION
One of the main challenges of OFDM-based systems is the
high peak-to-average power ratio (PAPR) of transmitted
signals, resulting in signal distortion. The combination of
multi-input multi-output (MIMO) and orthogonal frequency
division multiplexing (OFDM) could exploit the spatial
dimension capability to improve the system capacity by
employing spatially separated antennas. In MIMO-OFDM
systems, independent OFDM signals are transmitted from
multiple transmit antennas. Therefore, MIMO-OFDM systems
still suffer an inherent drawback of high PAPR.
There are some limitations for lossy PAPR reduction
technologies, such as clipping, peak windowing, companding
transform, etc [1], [2]. Nonlinear distortion and clipping of the
transmitted signals lead to system’s performance degradation.
Recently several lossless PAPR reduction technologies have
been proposed and investigated [3], [4], [5], [6], [7]; among
them, the partial transmit sequence (PTS) scheme is an
efficient approach and a lossless scheme for PAPR reduction
by optimally combining signal sub-blocks. Selective mapping
(SLM) is also a good approach, in which some statistically
independent sequences are generated from the same
information and the sequence with the lowest PAPR is
transmitted. Both schemes provide improved PAPR statistic at
the cost of additional complexity and loss of the data rate,
because they need to implement some extra IFFT and iterations
of phase optimization and transmit the side information. In
addition, SLM scheme leads to a higher computational
This work was supported by the National Natural Science Foundation of China
under Grants 61076096 and the National High Technology Project of China
under Grant 2012AA011702.
complexity at the same level of PAPR reduction, because it
operates on all carriers [8], [9].
Residue number system (RNS), a parallel number system, is
based on Chinese remainder theorem (CRT), which divides a
large integer into several independent and parallel smaller ones
with a specific modulus set. Due to the carry-free and parallel
properties, RNS further simplifies the computations by
decomposing a problem into a set of parallel, independent
residue computations [10]. Recently, more attention is also
paid to RNS in parallel communication field because of its
parallel and fault-tolerant properties [11], [12]. An RNS-based
OFDM transmission was proposed in [2], where we
concentrated on the RNS-based OFDM system’s description
and on the PAPR simulation results.
In MIMO-OFDM, a new kind of PAPR reduction scheme
by RNS will be presented in this paper. We utilize the parallel
property of RNS to convert input signals into smaller residue
signals, which are transmitted in a set of parallel, independent
residue sub-channels; and make use of the characteristic of
RNS modular operation to effectively reduce the PAPR. We
will evaluate its performance in comparison with conventional
MIMO-OFDM and PTS-MIMO-OFDM. It is demonstrated
that the proposed scheme improves PAPR performance and
greatly reduces computational complexity.
This paper is organized as follows: Section II gives an
overview of PAPR and PTS in MIMO-OFDM. The proposed
PAPR reduction scheme is described in Section III. Then we
evaluate the performance of PAPR reduction and
computational complexity in Section IV, while the conclusions
are offered in Section V.
II. SYSTEM MODEL
Throughout the paper we consider TN transmit antennas,
over which independent data streams should be communicated.
Space time coding as, e.g., in [7] is not considered here.
A. PAPR of MIMO-OFDM
The PAPR of output signals at each antenna is defined as the
ratio between the maximum peak power and the average power
2
,
2
,
max{ }
10log ( )
{ }
( 1,2, ; 0,1,2 , 1)
t
t
t
n k
n
n k
t T
s
PAPR dB
E s
n N k N
=
= = −K K
(1)
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MIMO-OFDM PAPR Reduction by Residue Number System
- 1. www.projectsatbangalore.com 09591912372 MIMO-OFDM PAPR Reduction by Residue Number System Yi Yao, Jianhao Hu National Key Lab of Science and Technology on Communication, UESTC Chengdu, Sichuan 611731, China Abstract-Multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) system has been widely accepted a promising scheme for wireless communication systems. However it still suffers the high peak-to-average power ratio (PAPR), which is the main limitation of OFDM-based systems. In this paper, we present a residue number system (RNS) based PAPR reduction scheme in MIMO-OFDM systems. The proposed scheme makes use of the properties of RNS to greatly reduce the PAPR and the computational complexity as well. Compared with the partial transmit sequence (PTS) scheme, the RNS-based PAPR reduction scheme has not only much better PAPR reduction performance without restriction to modulation format, but also low computational complexity without side information. Keywords-RNS, PAPR, PTS, MIMO I. INTRODUCTION One of the main challenges of OFDM-based systems is the high peak-to-average power ratio (PAPR) of transmitted signals, resulting in signal distortion. The combination of multi-input multi-output (MIMO) and orthogonal frequency division multiplexing (OFDM) could exploit the spatial dimension capability to improve the system capacity by employing spatially separated antennas. In MIMO-OFDM systems, independent OFDM signals are transmitted from multiple transmit antennas. Therefore, MIMO-OFDM systems still suffer an inherent drawback of high PAPR. There are some limitations for lossy PAPR reduction technologies, such as clipping, peak windowing, companding transform, etc [1], [2]. Nonlinear distortion and clipping of the transmitted signals lead to system’s performance degradation. Recently several lossless PAPR reduction technologies have been proposed and investigated [3], [4], [5], [6], [7]; among them, the partial transmit sequence (PTS) scheme is an efficient approach and a lossless scheme for PAPR reduction by optimally combining signal sub-blocks. Selective mapping (SLM) is also a good approach, in which some statistically independent sequences are generated from the same information and the sequence with the lowest PAPR is transmitted. Both schemes provide improved PAPR statistic at the cost of additional complexity and loss of the data rate, because they need to implement some extra IFFT and iterations of phase optimization and transmit the side information. In addition, SLM scheme leads to a higher computational This work was supported by the National Natural Science Foundation of China under Grants 61076096 and the National High Technology Project of China under Grant 2012AA011702. complexity at the same level of PAPR reduction, because it operates on all carriers [8], [9]. Residue number system (RNS), a parallel number system, is based on Chinese remainder theorem (CRT), which divides a large integer into several independent and parallel smaller ones with a specific modulus set. Due to the carry-free and parallel properties, RNS further simplifies the computations by decomposing a problem into a set of parallel, independent residue computations [10]. Recently, more attention is also paid to RNS in parallel communication field because of its parallel and fault-tolerant properties [11], [12]. An RNS-based OFDM transmission was proposed in [2], where we concentrated on the RNS-based OFDM system’s description and on the PAPR simulation results. In MIMO-OFDM, a new kind of PAPR reduction scheme by RNS will be presented in this paper. We utilize the parallel property of RNS to convert input signals into smaller residue signals, which are transmitted in a set of parallel, independent residue sub-channels; and make use of the characteristic of RNS modular operation to effectively reduce the PAPR. We will evaluate its performance in comparison with conventional MIMO-OFDM and PTS-MIMO-OFDM. It is demonstrated that the proposed scheme improves PAPR performance and greatly reduces computational complexity. This paper is organized as follows: Section II gives an overview of PAPR and PTS in MIMO-OFDM. The proposed PAPR reduction scheme is described in Section III. Then we evaluate the performance of PAPR reduction and computational complexity in Section IV, while the conclusions are offered in Section V. II. SYSTEM MODEL Throughout the paper we consider TN transmit antennas, over which independent data streams should be communicated. Space time coding as, e.g., in [7] is not considered here. A. PAPR of MIMO-OFDM The PAPR of output signals at each antenna is defined as the ratio between the maximum peak power and the average power 2 , 2 , max{ } 10log ( ) { } ( 1,2, ; 0,1,2 , 1) t t t n k n n k t T s PAPR dB E s n N k N = = = −K K (1) 441